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Residual gas effects on heat transfer in overpressure processing of flexible packages Weintraub, Sara Elisabeth 1986

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RESIDUAL GAS EFFECTS ON HEAT TRANSFER IN OVERPRESSURE PROCESSING OF FLEXIBLE PACKAGES  by  SARA ELISABETH WEINTRAUB B . S c , University of Alberta, 1982  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Food Science)  We accept t h i s paper as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1986 © S a r a Weintraub, 1986  In p r e s e n t i n g  this thesis  r e q u i r e m e n t s f o r an of  British  it  freely available  agree that  in partial  advanced degree a t  Columbia,  understood that for  Library  s h a l l make  for reference  and  study.  I  for extensive copying of  h i s or  be  her  g r a n t e d by  s h a l l not  be  Food  Science  The U n i v e r s i t y o f B r i t i s h 1956 Main Mall V a n c o u v e r , Canada V6T 1Y3  Date  April  9,  19 86  of  further this  Columbia  thesis  head o f  this  my  It is thesis  a l l o w e d w i t h o u t my  permission.  Department o f  the  representatives.  copying or p u b l i c a t i o n  f i n a n c i a l gain  University  the  f o r s c h o l a r l y p u r p o s e s may by  the  the  I agree that  permission  department o r  f u l f i l m e n t of  written  ii  ABSTRACT  Experiments have been performed to t e s t e f f e c t s heating  rate  indices  (f )  of  ditions  i n overpressure r e t o r t  h  test  pouches  processes.  l o c a t e d thermocouples were employed as within water  the  pouch  activity  syringe which  of  a  from 0  provide  a  through a  formed  varied  to  food.  Air  silicone  septum.  to  vapor  rubber With  35 mL.  subjected  droplet  repeated  on  which by  would  the  a  steam/air  industrial-scale vertical  mixture.  injections,  horizontal  positive  flow  retorts  air  were  retort  and  the  pouch were  120  and  125°C  75 and  85%  steam  (2)  the  the  hypodermic  employed:  (3)  added  volumes  115,  Lagarde s t e a m / a i r r e t o r t ,  steam/air  a  s u r f a c e of  temperatures of  Three  centrally  simulate  means of  on  con-  Water was  were s t u d i e d under p r e s s u r e l e v e l s c o r r e s p o n d i n g to 65, in  variable with  a test material.  injected  Processing  to  Teflon bricks  pressure  was  o f entrapped a i r  (1)  an  a  pilot-scale  same  pilot-scale  r e t o r t u s i n g superheated water w i t h a i r o v e r p r e s s u r e . The  heating  were a l s o of  studied at  variance  conditions  of  the  revealed  of  significant bricks  rates  teflon different  no  tested  in  the  retort  temperatures and  among  the  retort  forced  packaging analysis  (p>0.05)  among  There were, however,  systems  used.  circulation  h e a t i n g than i n the  pouch  pressures;  differences  overpressure l e v e l .  Lagarde  demonstrated more r a p i d  without  significant  temperature and  differences  bricks  In  steam/air  general, retort  p i l o t - s c a l e r e t o r t w i t h both  media t y p e s . R e l a t i o n s h i p s of volume c o n s i s t e d  of  heating rate indices  either  one  or  two  as  f u n c t i o n s of  essentially  segment formed a p l a t e a u r e g i o n i n which t h e r e was  linear no  included  segments.  air One  change i n f ^ w i t h  increasing some  volumes of i n c l u d e d a i r .  conditions  increasing  only,  exhibited  a i r volumes.  consecutive analysis.  A  p o i n t s was  Critical  above which the  moving  increase  of  against  the  heating  of  the  rate  remaining  rates.  of  experiments  for  a i r to  with  creasing mental types larger  imply  second  of  steam/air  entrapped  demonstrated  that  amounts of  a i r to  of  no  temperature  linear  section. were  Steeper  showed  ten  volumes  different  performed  to com-  functions  an  with  increase i n  media  processing  heat  over-  i n the pouch with  was  shown  Critical  heat  allowed  up  on  heating  to  display  a i r volumes  substantially  higher  s l o p e s were e v i d e n t on  than  the i n -  indicating  a more severe  detri-  transfer.  S t u d i e s with  retort  i n the  Lagarde  i n c l u d e d without  c o n d i t i o n s were made by d e t e r m i n i n g  function  to be those  detrimental e f f e c t  volumes of non-condensible  gas r e l a t i o n s h i p s .  of  covariance  significantly  be entrapped  and  a i r on  be  consisting  volume  with  f u n c t i o n of  b a s e l i n e by  t h a t with  processes  mixtures.  with  air  a  A i r o v e r p r e s s u r e above 80 kPa  overpressure  steam/air  effect  a  as  n  a n a l y s i s was  vs.  i n c l u d e d with  overpressure  section  Predictions retort  be  s l o p e s i n the  water/air  those  unchanged.  Increasing  decreasing  f  apparent  section.  p r e s s u r e , l a r g e r amounts of a i r may  35 mL  in  r e g r e s s i o n frame  Covariance  a p p r e c i a b l e data i n the second  to  section,  f ^ v s . a i r volume f u n c t i o n was  pare  transfer  second  volumes of a i r were c o n s i d e r e d  the b a s e l i n e .  Results  an  compared  (p<0.05) from slopes  The  retort  affecting  allowed  heat  gases which would expansion  for  transfer. prevail  f a c t o r s from  at  ideal  Comparisons of s l o p e s of the l o g f ^ vs. a d j u s t e d a i r  significant  p o s i t i v e f l o w r e t o r t had steam/air p r o c e s s e s had  differences.  the l e a s t  Water/air  processes  s l o p e , the Lagarde and  increasing slopes, r e s p e c t i v e l y ^  in  positive  the flow  iv  TABLE OF CONTENTS Page  ABSTRACT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES NOMENCLATURE ACKNOWLEDGEMENTS  i i iv v i i ix x x i i  INTRODUCTION  1  LITERATURE REVIEW  5  I  Retort Pouch  5  1. 2.  Development o f Pouch M a t e r i a l E v a c u a t i o n Techniques  5 6  3.  Pouch S e a l s  9  II  C r i t i c a l Factors Affecting Processing  12  1.  R e s i d u a l Gases  13  a.  Pressure-Volume S t u d i e s  13  b. c. d.  E f f e c t on Heating Rate Methods o f Measurement Other E f f e c t s o f R e s i d u a l Gases  17 21 23  2.  P r o c e s s i n g Media  25  3.  Processing Conditions  29  A.  Package T h i c k n e s s  31  EXPERIMENTAL  33  I  Sample Preparation  33  1.  Test Bricks  33  2.  Packaging  35  II  III  Air Measurement  37  1.  Non-destructive  Measurement o f A i r  2. 3.  D e s t r u c t i v e Measurement o f A i r Combining D e s t r u c t i v e and N o n - d e s t r u c t i v e of A i r  Processing Conditions  37 40 Measurements 42  43  V  Page IV  V  Retorts  43  1. 2.  Lagarde Steam/Air V e r t i c a l Positive Flow - Steam/Air  45 46  3.  V e r t i c a l P o s i t i v e Flow - Water/Air  48  Data Acquisition  50  1. 2.  Temperature P r o f i l e Measurement Analysis of Heating Rate Index ( f ^ )  50 51  3.  Data Treatment  52  RESULTS AND DISCUSSION  54  I  Air Measurement  54  II  Unpackaged Bricks  56  III  Packaged Bricks:  IV  Break-point Values  64  1.  Determination of Break-point  64  2.  Factors Affecting Break-point Volumes  72  a. b. c. d. e.  72 74 75 76 77  3. V  VI  VII  Included Air  Steam Percentage or Pressure Level Temperature Brick Thickness Media Type: Steam/Air and Water/Air Retorts: Lagarde and Positive Flow Steam/Air  Importance of Plateau Region  61  79  Air Volumes Above the Break-point  80  1.  81  Factors Affecting the Second Section  a. Brick Thickness b. Steam Percentage/Pressure Level c. Temperature d. Media Type: Steam/Air and Water/Air e. Retorts: Lagarde and Positive Flow Steam/Air Prediction of Pouch Expansion 1. Expansion Factors 2. Comparison of Adjusted Volume Relationships  81 83 86 89 92 95 96 100  Other Process Parameters  106  vi  Page  CONCLUSIONS  107  LITERATURE CITED  109  APPENDICES  116  I  N o n - d e s t r u c t i v e a i r measurements  116  II  Back c a l c u l a t i o n s f o r combination n o n - d e s t r u c t i v e a i r measurements  o f d e s t r u c t i v e and 118  I l i a H e a t i n g r a t e index v s . i n c l u d e d a i r r e l a t i o n s h i p f o r t h i n b r i c k s i n p o s i t i v e f l o w steam/air r e t o r t (a, 115°C; b, 120°C; c, 125°C)  119  I l l b H e a t i n g r a t e index v s . i n c l u d e d a i r r e l a t i o n s h i p f o r t h i c k b r i c k s i n p o s i t i v e f l o w steam/air r e t o r t (a, 115°C; b, 120°C; c, 125°C)  120  I I I c H e a t i n g r a t e index v s . i n c l u d e d a i r r e l a t i o n s h i p f o r t h i n b r i c k s i n p o s i t i v e flow water/air r e t o r t (a, 115°C; b, 120°C; c , 125°C)  121  Hid  H e a t i n g r a t e index v s . i n c l u d e d a i r r e l a t i o n s h i p f o r t h i c k b r i c k s i n p o s i t i v e flow water/air r e t o r t (a, 115°C; b, 120°C; c, 125°C)  122  vii  LIST OF TABLES Page T a b l e 1.  Thermophysical  T a b l e 2.  Summary of p r o c e s s i n g temperatures studied.  T a b l e 3.  T a b l e 4.  T a b l e 5.  T a b l e 6.  p r o p e r t i e s of t e f l o n . and  34 pressures 44  A n a l y s i s of v a r i a n c e f o r h e a t i n g r a t e i n d i c e s of unpackaged t e f l o n b r i c k s .  57  Duncan's m u l t i p l e range t e s t f o r h e a t i n g r a t e s of unpackaged b r i c k s i n d i f f e r e n t r e t o r t s .  58  C o e f f i c i e n t s of v a r i a t i o n of h e a t i n g r a t e i n d i c e s of unpackaged b r i c k s .  60  T e s t f o r s i g n i f i c a n c e of s l o p e of the b a s e l i n e 125°C-65% steam with S t u d e n t - t t e s t . H : s l o p e = 0.  66  S t u d e n t - t t e s t on f ^ of unpackaged b r i c k s compared to f-^ v a l u e s of b a s e l i n e . H : =  67  B r e a k - p o i n t v a l u e of t h i n b r i c k s determined by c o v a r i a n c e a n a l y s i s on a moving r e g r e s s i o n frame.  70  B r e a k - p o i n t v a l u e of t h i c k b r i c k s determined by c o v a r i a n c e a n a l y s i s on a moving r e g r e s s i o n frame.  71  0  T a b l e 7.  Q  T a b l e 8.  T a b l e 9.  T a b l e 10. C o v a r i a n c e a n a l y s i s r e s u l t s comparing b a s e l i n e s between r e t o r t systems t e s t e d .  78  T a b l e 11. C o v a r i a n c e a n a l y s i s on f ^ vs. i n c l u d e d a i r , v a l u e s above b r e a k - p o i n t ; comparison of b r i c k t h i c k n e s s , 115°C-85% steam ( p r e s s u r e l e v e l 3 ) .  82  T a b l e 12. C o v a r i a n c e a n a l y s i s on f ^ v s . i n c l u d e d a i r , v a l u e s above b r e a k - p o i n t ; comparison of p r e s s u r e l e v e l , a t 115°C.  84  T a b l e 13. C o v a r i a n c e a n a l y s i s on vs. included a i r , values above b r e a k - p o i n t ; comparison of temperature a t 85% steam p r e s s u r e l e v e l 3 ) .  87  Table  14. C o v a r i a n c e a n a l y s i s on f ^ v s . i n c l u d e d a i r , v a l u e s above b r e a k - p o i n t ; comparison of media type.  T a b l e 15. C o v a r i a n c e a n a l y s i s on f ^ v s . i n c l u d e d a i r , v a l u e s above b r e a k - p o i n t ; comparison of steam/air r e t o r t s .  90  93  viii  Page  T a b l e 16.  T h e o r e t i c a l expansion f a c t o r s f o r c o n d i t i o n s  T a b l e 17. C o v a r i a n c e a n a l y s i s on l o g f ^ v s . a d j u s t e d a l l d a t a ; comparison of systems t e s t e d .  studied.  99  air, 104  ix  LIST OF FIGURES Page Figure  1.  Apparatus  f o r n o n - d e s t r u c t i v e measurement o f a i r .  38  Figure  2.  Apparatus  f o r d e s t r u c t i v e measurement o f a i r .  41  Figure  3.  H e a t i n g r a t e index as a f u n c t i o n o f i n c l u d e d a i r ; Lagarde r e t o r t , t h i n b r i c k s . ( a , 115°C; b, 120°C; c, 125°C).  62  H e a t i n g r a t e index as a f u n c t i o n of i n c l u d e d a i r ; Lagarde r e t o r t t h i c k b r i c k s . (a, 115°C; b, 120°C; c, 125°C).  63  Moving r e g r e s s i o n frame performed w i t h c o v a r i a n c e a n a l y s i s t o determine b r e a k - p o i n t s .  69  H e a t i n g r a t e index v s . i n c l u d e d a i r f o r comparison of p r e s s u r e l e v e l ; t h i c k b r i c k s processed a t 115°C i n the Lagarde r e t o r t .  85  H e a t i n g r a t e index vs. i n c l u d e d a i r f o r comparison of temperature; t h i c k b r i c k s processed a t 85% steam i n p o s i t i v e flow r e t o r t .  t 88  H e a t i n g r a t e index v s . i n c l u d e d a i r f o r comparison of media t y p e ; t h i c k b r i c k s processed a t 115°C and 85% steam ( 3 ) .  91  H e a t i n g r a t e index v s . i n c l u d e d a i r f o r comparison of steam/air r e t o r t s ; t h i c k b r i c k s p r o c e s s e d a t 115°C and 85% steam.  94  F i g u r e 4.  Figure  5.  F i g u r e 6.  Figure  7.  F i g u r e 8.  F i g u r e 9.  Figure  Figure  10.  11.  H e a t i n g r a t e index f u n c t i o n s of a d j u s t e d a i r volumes for a l l conditions; thin bricks. ( a , Lagarde; b, P o s i t i v e Flow Steam/Air; c, P o s i t i v e Flow W a t e r / A i r ) .  101  H e a t i n g r a t e index f u n c t i o n s of a d j u s t e d a i r volumes for a l l conditions; thick bricks. ( a , Lagarde; b, P o s i t i v e Flow Steam/Air; c, P o s i t i v e Flow W a t e r / A i r ) .  102  X  NOMENCLATURE a  h a l f - l e n g t h of t e f l o n b r i c k  A  t h i r d non-destructive a i r reading, a f t e r processing  a  w  (cm) (g)  water a c t i v i t y  b  h a l f - w i d t h of t e f l o n b r i c k  B  buoyant f o r c e (N); p r o c e s s i n g (g)  c  h a l f - t h i c k n e s s of t e f l o n b r i c k  Cp  s p e c i f i c heat c a p a c i t y ( c a l / g  EF  expansion  f^  h e a t i n g r a t e index  Fo  process l e t h a l i t y  g  gravitational f o r c e (N/kg); d i f f e r e n c e i n degrees r e t o r t temperature and product temperature (C°)  H ^  h e i g h t of water of each mL  H  h e i g h t of water volume  w  (cm)  second n o n - d e s t r u c t i v e a i r r e a d i n g ,  (cm) C°)  factor (min) (min)  i n the buret  between  (cm)  (cm)  I  first  j  lag factor  k  thermal  Mg  weight of o b j e c t  Pj  atmospheric  P2  p a r t i a l p r e s s u r e of water at p r e s s u r e of e n c l o s e d a i r (kPa)  P  p a r t i a l p r e s s u r e of a i r e n c l o s e d  a  before  non-destructive a i r reading, i n i t i a l  c o n d u c t i v i t y ( c a l / s cm  reading  (g)  C°)  (mg)  pressure  (kPa) t e m p e r a t u r e T2  plus  partial  (kPa)  p r e s s u r e when package i s i n a s t a t e of n e u t r a l buoyancy Pj^  p r e s s u r e of r e t o r t d u r i n g p r o c e s s i n g  STP  standard  c o n d i t i o n s of temperature and  (kPa) pressure  (kPa)  the  xi  initial  temperature (K)  T  l  T  2  V  l  V  2  volume of a i r i n pouch a t p r o c e s s i n g c o n d i t i o n s  m  measured volume of a i r (mL)  V  maximum volume to f i l l  V  temperature of p r o c e s s (K) volume of a i r i n pouch a t atmospheric c o n d i t i o n s  the pouch  (mL) (mL)  (mL)  max V  o  V  pch  V  volume o f o b j e c t a t STP  (mL)  volume o c c u p i e d by empty pouch  (mL)  volume of sample ( b r i c k and pouch) e x c l u d i n g a i r (mL) s  V  volume of sample ( b r i c k and pouch) i n c l u d i n g a i r (mL) sa  V  t  volume of o b j e c t a t r e t o r t c o n d i t i o n s  W  h  p r e s s u r e of water l e v e l i n graduate (kPa)  W  pch  W  W  s ws  (mL)  weight of an empty pouch (g) weight of sample (g) weight of package suspended i n water (g)  W ws+a j.  weight o f package and added a i r suspended i n water (g)  a  thermal d i f f u s i v i t y  B  volume  Am  d i f f e r e n c e i n mass (g)  At  d i f f e r e n c e i n temperature (°C)  Po  d e n s i t y of o b j e c t  P  p  pr  w  2 (m / s ) ;  l i n e a r thermal expansion  expansion  (g/mL)  d e n s i t y of product (g/mL) d e n s i t y of water (g/mL)  factor  xii  ACKNOWLEDGEMENTS  The  author  knowledgeable  i s sincerely advice  grateful  to Dr. M a r v i n  and e n c o u r a g e m e n t  during  A. Tung  the course  for of  his  this  r e s e a r c h p r o j e c t and review of the t h e s i s . She Dr. W.D. Science for  also  wishes  Powrie,  t o thank  the members o f the r e s e a r c h  Dr. J . Vanderstoep,  both  and Dr. K. V. Lo o f the Department  their  contribution  t o the p r o j e c t  committee,  o f the Department  of  Food  of Bio-Resource E n g i n e e r i n g  and c o n s t r u c t i v e  review  o f the  thesis. Much a p p r e c i a t i o n i s extended  t o H.S. Ramaswamy and T r u d i Smith f o r  t h e i r v a l u a b l e e x p e r t i s e and a s s i s t a n c e . The author i s g r a t e f u l t o her p a r e n t s , Jerome gnd Ann Weintraub f o r their  support  Benoit Girard  and u n d e r s t a n d i n g .  A  special  thank  f o r h i s p a t i e n c e and encouragement.  you i s extended  to  -1-  INTRODUCTION  I n n o v a t i v e food packaging has p l a y e d an important r o l e i n p r o v i d i n g consumers w i t h the wide v a r i e t y o f food p r o d u c t s t h a t e x i s t s today. research tinual  and development  process.  flexible sales  recent  package or r e t o r t  by  1980 ( P e t e r s ,  Industrial ity  One  of a l t e r n a t e  and  traditional  development,  a shelf-stable  1975) and e a r n e d  is a  thin  t h e 1978 Food  (Mermelstein, 1978).  requirements  canned  technology  con-  profile  pouch, was p r o j e c t e d t o reach $2 b i l l i o n i n  Achievement Award  energy  packaging  The  place  and f r o z e n  retort  foods.  Technology  Comparisons of q u a l -  pouch  Products  products  i n between  i n pouches  may  have  s u p e r i o r q u a l i t y as compared t o canned goods and p r o c e s s i n g was r e p o r t e d to be l e s s e n e r g y - i n t e n s i v e than f r e e z i n g Since canning,  (Davis  taste,  color,  little  uses  and  processors i s cost. requirement lower  reported reduced  an a l t e r n a t i v e  between  by M e r m e l s t e i n and  to  p o u c h e s and c a n s .  r e p o r t e d by many  authors  1980; M e r m e l s t e i n ,  1976).  profile  packages r e s u l t i n  the b o i l - i n - b a g  technique i s  The package i s e a s i l y  space.  A major  opened and  concern  to food  S t e f f e e t a l . (1980) r e p o r t e d t h a t t h e t o t a l  requirement  material  for thin  clean-up.  disposal  for retorting  energy  made  P r e p a r a t i o n by  simple and r e q u i r e s storage  considered  package have been  required  1980).  t e x t u r e and r e t e n t i o n o f h e a t - s e n s i t i v e v i t a m i n s  e t a l . , 1972).  less  been  1982; Cage and C l a r k ,  p r o c e s s i n g times  improved  have  are t y p i c a l l y  o f the f l e x i b l e  and Young,  Shorter  pouches  comparisons  Advantages (Tuomy  retort  (Heintz,  pouches was 75% l e s s  than  f o r cans.  when p r o c e s s i n g i n f l e x i b l e (1978).  storage  energy A 60%  p a c k a g e s was  W i l l i a m s e t a l . (1983) d e s c r i b e d  costs  associated  with  retort  pouch  -2-  packaging.  However, i n i t i a l equipment c o s t s were r e p o r t e d  Although of  retort  had  p r o j e c t i o n s have been made and  pouches has  reasonable  America has  been l i m i t e d .  success  in  been l i m i t e d  their  to be  high.  advantages c i t e d ,  European c o u n t r i e s and  introduction.  the  Japan have  Production  to s m a l l i n d i v i d u a l companies.  use  in  North  Presently,  the  i n d u s t r y t a r g e t s f o r s p e c i a l t y goods or foods f o r a p a r t i c u l a r f u n c t i o n . Peters Frost  (1985) d e s c r i b e d a l i n e of Smoky Canyon foods produced by Land (Lansing,  iasts.  IL)  Adams  processing  of  aimed  (1984) seafood  directly  indicated products  ducts such as red snapper and competitive spread  with  frozen  consumer  exposure  to  that  campers and  there  in retort  was  a  pouches.  outdoor  bright Higher  enthus-  future priced  blue crab meat f o r r e s t a u r a n t use  counterparts  acceptance  products,  toward  of  (Adams e t  the  perhaps  by  technology,  popular  there  national  For  must  brands  in pro-  could  a l . , 1983).  o'  wide-  be  in  be  more retort  pouches. Adoption of the technology introduced  an  "A  l a Carte"  having  a relatively  pended  in  1985.  Anon.  companies  have  shown an  investment may speeds  and  the  be  low  due  lack  line  capacity  which  was  interest.  been slow.  manufactured  (Anon. 1982), but  (1982) r e p o r t e d  that  in  production  Nestle  and  of  regulations  of thermal p r o c e s s i n g .  aspects  have made the  technology  Kraft  facilities was  sus-  Campbell  Soup  H e s i t a t i o n towards l a r g e - s c a l e  to some t e c h n o l o g i c a l problems such as  aspects  critical  by l a r g e companies has  or  concrete  information  slow  line  regarding  I n t r o d u c t i o n of m a t e r i a l s and t e c h n i c a l a reality,  but a d d i t i o n a l knowledge of  f a c t o r s a f f e c t i n g r e t o r t pouch p r o c e s s i n g i s e s s e n t i a l .  Beverly  (1980) d e s c r i b e d c r i t i c a l  f a c t o r s as those which a f f e c t  the  -3-  adequacy of the s t e r i l i z a t i o n of  the system.  flexible film, to  p r o c e s s , product  Some of the c r i t i c a l  nature  of  retort  t h e r e i s a tendency  equal the r e t o r t p r e s s u r e .  maintained. pressure degree, early  T h e r e f o r e , as  may the  of  the  When  burst.  to overcome t h i s  temperature  This i s a process.  problem.  of  factor  retort  rises,  heating.  particular  of  the  the  pouch a l l o w s  problem  effect  on  of  of utmost importance  heating  forecasted  volume  behavior.  success,  technical  of  residual  these  increases For  to  retort  aspects  be  internal a  large  problem d u r i n g processes  the have the  composition.  i n thermal gases from  a certain  pouch when i t i s s e a l e d .  f o r expansion  pouch  flexible  More i n f o r m a t i o n i s needed on  Moreover, t h e r e i s i n e v i t a b l y  which remains w i t h i n the  the  pressure  A i r overpressure  pouches i s the r e l e a s e of entrapped  during  a  p r e s s u r e w i t h i n the package  performance of these media types i n r e l a t i o n to t h e i r Another c r i t i c a l  with  Only a s m a l l p r e s s u r e d i f f e r e n t i a l can  i f i t exceeds  cooling  processing  internal  the product  and  pouch may  stages  been used  increase  or the economics  parameters are a consequence of the  pouches. f o r the  quality  The  processing the  product  amount of a i r  flexible  nature  gases which c o n t r i b u t e s to  which  may  have  a  pouch technology must  be  detrimental to reach i t s  advanced  and  critical  parameters i n thermal p r o c e s s i n g must be i d e n t i f i e d and c h a r a c t e r i z e d . Heat p e n e t r a t i o n s t u d i e s and to  d e s i g n adequate heat  process parameters d e r i v e d may  processes.  They a l s o  a heat p e n e t r a t i o n t e s t , a time-temperature  the food  product are  i s recorded.  produced  by  of  energy  factors.  curve a t a g i v e n p o i n t i n  Changes i n the amount of thermal  transmission  used  p r o v i d e a means to e v a l -  uate h e a t i n g behavior of products s u b j e c t e d t o v a r i o u s c r i t i c a l In  be  from  the  energy  heating  in a media  -4-  surrounding the object ( B a l l and Olson, 1957). tiometric  devices are used  to sense  Thermocouples and poten-  changes i n heat  energy.  Pflug  (1975) and Bee and Park (1978) described many types of equipment a v a i l able and techniques used to perform heat penetration t e s t s . Data collected are organized by plotting the temperature difference between  the retort  function  and centerpoint (g) on a logarithmic  of time on an a r i t h m e t i c  different  procedures  parameters.  for plotting  scale.  scale  as a  Stumbo (1973) d i s c u s s e d  and evaluating  thermal processing  Computer programs have allowed f o r analysis of heat pene-  t r a t i o n data i n a minimal time (Tung and Garland, 1978). process parameter,  An important  the heating rate index ( f ^ ) i s the time required f o r  the straight l i n e portion of the heat penetration curve to traverse one log cycle. 1977;  Heating rate indices have been used by many authors (Evans,  Berry and Kohnhorst,  1983; Ramaswamy, 1983) to evaluate c r i t i c a l  factors by comparing heating behavior of foods i n various package forms. Because of the need to understand  the effects  of noncondensible  gases within a f i l l e d retort pouch on the thermal s t e r i l i z a t i o n process, a  study was i n i t i a t e d  using a model system.  The objectives of this  investigation were to: 1.  Study  the influence  of noncondensible  gases  within  a pouch on  heating rate indices of materials contained by those pouches, 2.  Characterize and compare  this  influence  under  different  over-  pressure processing conditions and retort systems, and 3.  Determine  l i m i t s at which residual gases would interfere with ex-  pected heating behavior, as indicated indices.  by changes i n the heating rate  -5-  LITERATURE REVIEW I  Retort Pouch  1.  Development of Pouch M a t e r i a l Development  began the  with  late  IL)  Reynolds and  capable  of w i t h s t a n d i n g  i n t o adequate m a t e r i a l s  Inc.  and  (Richmond,  the  U.S.  VA),  and  retort  or  in  evaluate  pouches  individual"  or  pouches and  conjunction  R&D  Flexible  C  with  hopes  to  with  a  ration  and  75  um)  foods.  They concluded  closure  s e a l s made w i t h  and  Steinberg  impulse  ages t e s t e d were c l e a r l a m i n a t e s , c r e a t e d a problem w i t h  gas  U.S.  the  have work-  Laboratories  production  of  Army has a vested replace  Both  the  to  shelf  interest  "meal-combatusing  retort  1978). (1956) t e s t e d the s u i t a b i l i t y  Trithene  that general an  for  Natick  "meal-ready-to-eat"  f a m i l i a r foods (Mermelstein,  (50  the  completely new  Packaging  Command ( N a t i c k , MA).  with  The  in  p r o j e c t s l i e i n work done by  suitable materials  E a r l y work by Nelson and polyester  processing  s e a l i n g techniques  Continental  Army N a t i c k  s t a b l e foods i n r e t o r t a b l e pouches. in  and  thermal  C o n t i n e n t a l manufactured packaging m a t e r i a l s and  independently  develop  pouch  O r i g i n s of many r e s e a r c h  Metals  (Chicago,  a  research  1950's.  Reynolds  ed  of  (50  and  strength  100  of  um)  the  for  which c o n t r i b u t e d  permeability  (Hu  retorting  f i l m s was  s e a l e r must be improved. to eye  e t a l . , 1955;  of  good The  but  pack-  appeal,  but  Ayoub e t a l . ,  1974). Keller great  (1959)  reported  that  laminates  containing  aluminum  promise because of e x c e l l e n t b a r r i e r p r o p e r t i e s as was  polyester/aluminum packaging carried  foil/vinyl  materials,  out  and  i t was  laminate.  including  many  determined  Evaluations  plastics  that  and  aluminum  of  shown by  more than  combinations,  foil  was  showed a 100 were  an e s s e n t i a l  -6-  component  of  the  packaging  material  (Rubinate,  pouches used i n North America have aluminum f o i l in  the  laminate.  by  Ebben  Foil-free  (1979) and  transparent  shelf  life  of  p o l y e s t e r , which p r o v i d e d proved  to be  costly  1970).  The  inner  layer  was  polyolefin  Strength  as  a  heat  in  printability and  was  and  Typical strength.  s e n s i t i v e to water  commonly  polypropylene  s e a l a b l e l a y e r and  an  the  flexible  military  m a t e r i a l has  service.  Agarwal  been  and  tested  studies  of  enclosing  the  performed  rough  comparison between  the  handling.  rough  handling  pouch i n a  of  or  a  inert  Kumta  p r i m a r i l y as  (1974)  studied  puncture r e s i s t a n c e of f l e x i b l e packages w i t h d i f f e r e n t probes. inary  these  contact.  of  for  serving  Products  reported  s i x to e i g h t weeks.  but  s u r f a c e f o r food  package  a  i n Japan as  i n England.  suggested  (Goldfarb, modified  Packaging  A l l retort  as the middle m a t e r i a l  pouches were produced  DRG  packages had  o u t e r m a t e r i a l was Nylon was  by  1964).  paperboard  handling  pouches  treatment  and  containers  evolved  cans.  in  their  the  conventional  folder.  Burke and  by  vibration  Their  results  capabilities  and  of  the  Prelim-  p r a c t i c e of  Schultz drop  showed  a  no  (1972)  tests  for  difference  withstanding  However, cans r e s u l t e d i n more damage to the outer  rough  shipping  container.  2.  Evacuation Removal  practice.  of  The  Techniques noncondensible significance  d e t a i l i n a forthcoming as  much gas  function  as  of  gas  section.  possible.  operation;  gases  in  retort  removal  will  pouches be  is  discussed  standard i n more  E s s e n t i a l l y , i t i s d e s i r a b l e to remove  Evacuation  usually  from  i s performed  conjunction  with  as  p a r t of a m u l t i filling  and/or  a  -7-  closure-sealing ers  used  operation  preformed  (Larapi, 1977).  pouches.  An  First  g e n e r a t i o n vacuum  elementary  attempt  employed  " s n o r k e l " t e c h n i q u e , where a tube w i t h a t a p e r e d end was short  unsealed  removal  with  applied. air  section  this  of  the  technique.  pouch. The  Goldfarb  pouch  was  and  described a i r a  vacuum  When the pouch c o l l a p s e d , the s n o r k e l was withdrawn.  c o n t e n t s were r e p o r t e d  t o be  less  than 5 mL  the  inserted into a  (1971)  purged  seal-  per pouch.  was  Residual This  tech-  nique p r e s e n t e d problems by p o s s i b l e c o n t a m i n a t i o n o f the s e a l a r e a w i t h tube w i t h d r a w a l . and  similar  1973).  Use  o f mechanical vacuum chambers was  t o systems  Two  Piscataway, Horizontal  i n use  systems  commonly  NJ)  a  and  conveyors  f o r luncheon meats (Lampi and Rubinate, used  d e s i g n by  which  moved  were S w i s s - V a c Koch  Multivac  under  a  hood  use  itions  o f a Swiss-Vac resulting  system.  i n slow  Pouches  production  (Hamac-Hansella,  (Kansas  and  vacuum chamber, were c h a r a c t e r i s t i c o f t h i s t y p e . ed  more widespread  closed  City, to  MO).  form  M o r r i s (1981) r e p o r t -  were p l a c e d manually onto  speeds,  but  a  a  better  pos-  vacuum  was  created. Systems  are a v a i l a b l e  the headspace. min  An improvement i n pouch  f o r mechanical  reported vacuum  by  implementing  Przybyla  Mitsubishi  Steam was  injected  cooling.  Fill  vacuum  t o 60  (1984).  machine  by  steam filling  pouches/min  Morris Magic  A development  by FMC  speeds from 30 w i t h steam  P a n t r y Foods  immediately p r i o r t o s e a l i n g  speeds were f a s t e r  to remove a i r from  (1981) d e s c r i b e d  (rated  Inc.  pouches/  flush  use o f a  were steam-  (Hamilton,  ON).  t o c r e a t e a vacuum upon  a t 50 pouches  a l t h o u g h poorer a i r removal o c c u r r e d , i t was products.  flush  well suited  per minute)  and  t o more l i q u i d  (Santa C l a r a , CA), t h e Steam Flow  Pouch  -8-  Filler  and  Sealer,  was  r e p o r t e d by  Strasser  (1979).  This operation  i n v o l v e d use of both mechanical vacuum and steam f l u s h i n g . first  flushed  filled.  with  steam,  An a d d i t i o n a l  duced  just  prior  to  then moved  was  environment  sealing.  to  gas was  B e v e r l y (1979) demonstrated  be  intro-  the a i r  Removal of 40-50% o f the o r i g i n a l  found w i t h steam f l u s h a l o n e ; f u r t h e r m o r e , w i t h the steam t u n n e l  system,  93-95% o f a i r was  Removal ipulation for  air-free  j e t steaming or a d d i t i o n of i n e r t  removal e f f i c i e n c y o f t h i s equipment. air  t o an  Pouches were  of  a i r i n other  of the pouch.  packaging  removed. systems  Tsutsumi  viscous l i q u i d s .  minimum by s t r e t c h i n g  was  ensured  physical  man-  (1979b) d e s c r i b e d a non-vacuum method A i r within  the pouch was  both s i d e s of the pouch p r i o r  o p e r a t i o n s of opening, f i l l i n g  by  and  reduced  to s e a l i n g .  sealing occurred.  to a  Normal  A m o d i f i c a t i o n to  t h i s type o f e v a c u a t i o n i n v o l v e d a p p l y i n g p r e s s u r e w i t h p l a t e s from both sides,  creating  Narrow  bars  area.  Heid (1970) d e s c r i b e d a unique system designed w i t h the i n t e n t of  reducing in  a  squeezing  prevented  residual  the  headspace  the U n i t e d S t a t e s by FMC  other  processes  pouch was  i n that  pouch s t r e t c h e d  The  pouch  cook.  A  product  gases.  was  submerged  level  from  The  gases  being  out of the  pushed  system,  up  into  developed  and  package. the  seal  patented from  e v a c u a t i o n o c c u r r e d d u r i n g p r o c e s s i n g and Two  clamps  the  h e l d the unsealed p o r t i o n of  t o a c t as a one-way v a l v e a l l o w i n g gases t o escape.  of r e s i d u a l low  to force  C o r p o r a t i o n (Santa C l a r a , CA), d i f f e r e d  sealed a f t e r cooking.  the  exhaustion  action  of  i n water  gases.  f o r heat  Sealing  residual  was  a i r (1 mL)  p r o c e s s i n g and performed was  i n d u s t r i a l a p p l i c a t i o n has been r e p o r t e d t o d a t e .  after  concomitant the  desired  r e p o r t e d , however,  no  -9-  A  second  generation  remove a i r and machinery pouches  Additional  Div.  two  savings  system, City,  pouch.  by  could  pouches.  result  would  systems  of  FL)  be  this  I t was 90  form, this  type  with  capable  packages  use  per  of r o l l  lower  developed.  a  speed  higher  introduced  120  efficiency.  equipment  than costs  machine  (Anon., 1980).  Another  Koch M u l t i v a c  (Kansas  packages per minute, a l t h o u g h  minute  were  typical  of r e t o r t  At  Rexham's B a r t e l t  form/fill/seal  by  of 250  operational costs.  a microprocessor  of  type  stock rather  that although  have been  was  fill,  (Anon.,  real-  1983).  More  pouch p r o c e s s i n g may  result  more f a v o r a b l e .  Pouch S e a l s Seal  integrity  has  long  food c o n t a i n e r s .  Thermally  pose a p a r t i c u l a r  problem due  A statement by Nelson stand  pressure  this  With  the  type  similar  of  and  development  pouches  new  as  a  vital  criterion  foods packaged i n f l e x i b l e  to s t r e s s e s which develop  during  be  pouches heating.  s u r f a c e , a major stumbling  removed" i l l u s t r a t e d  materials  and  modes of  this  was  due  to  the  block  problem.  s e a l i n g , advances  by Roop e t a l . (1983) r e p o r t e d t h a t  testing  for  (1956) t h a t " i f the s e a l a r e a c o u l d  general  could  A r e c e n t study during  considered  Steinberg  to the  of  been  processed  of p r o c e s s i n g  have o c c u r r e d . ure  to  speeds of  lower p r o d u c t i o n c o s t s , making the technology  3.  to  developed  (1980) to be approaching  substantially  introduced  electronically  MO).  from the  advances i n the t e c h n i c a l a s p e c t s in  Clark  (1981) claimed  h o r i z o n t a l i n design,  istically  was  Production  Cage and  Lopez  there  (Sarasota,  operating  equipment  minute which would g r e a t l y i n c r e a s e p r o d u c t i o n  were h i g h e r least  the  were r e p o r t e d  per  preformed  seal  of  material  fail-  strength  -10-  l i m i t a t i o n s r a t h e r than the s e a l formed. Closure roll  seals  stock  were  for  preformed  formed  on  f o r m / f i l l / s e a l equipment. Keegan  (1973) d e s c r i b e d  pouches and  the  previously  a l l peripheral  or  A review of heat s e a l i n g methods by Brown  and  f o r many package t y p e s .  f o r r e t o r t pouches, e i t h e r the  hot  jaw  sealer  or p l a t e w i t h an  and  a silicone-rubber r e s i l i e n t  forces  consists  down  utilizes clamps  a  the  created  a  for  considered tested  by  ination  a bar  jaw  a  to  current  to  create  flow  at  seal.  by  the  seal.  that  (1975) to  the  Pressurization-hold  strength during no  was  of  defect-free (1.6  seconds.  reduced  processing  signs  mm)  testing  to  visible band  for  an  at  be  point  7  resistance  et  of  the  impulse  and  seal rupture.  seal  the  with hot  bar  sealed. report-  (12.3  withstand  recommended  N/cm). 138  kPa seal  restrainment there  must  required  a  minimum  width  1/16  seal  1/8  of  be  Signs of delam-  In a d d i t i o n ,  a  was  formed c o u l d  processors that  M i l i t a r y standards  and  layers  were f u s i o n  to  which  summarized  inner  l i n e a r inch  ability  the  were covered w i t h  a weld was  pounds per  closure,  to  by the U.S.D.A. were  temperature  aberrations.  sealer  wire  a l . (1976)  Rubinate (1964) cautioned high  impulse  Voltage applied  surfaces  the  An  of f a i l u r e .  required  used.  A p r e s s u r e source  surfaces  Fusion  film  required  prevent  across  top  high  Assurance t h a t  s e a l to the  indicate  Shenkenberg  (gauge) f o r 30  the  Lampi  essential.  assembled h e a t e r on  seal.  fibreglass cloth. performance  hot  each end.  through  S p e c i f i c a t i o n s of t e n s i l e s t r e n g t h ed  the  Typically, A  f i x e d underneath.  contact  tensioning would  jaw  or impulse s e a l was  The  high be  jaw  wire supported  to form the  t e f l o n coated  criteria  upper  tension  caused h e a t i n g a  of  from  filler/sealer  techniques  described  seals  of  in  (3.2  be  clean in mm)  -11-  according mainly  to M i l l e v i l l e  from  contamination  material.  A  guards  which  protect  the  ision  fold-over  to d e t e c t  of  area  or  by  filler  wrinkling  Lampi  package  et  opening  nozzle  prior  has  to  pouch  filling  and  high  (Tsutsumi,  another  s e a l i n g has  the  a l . (1976) used  design  posed  of  during  reduce c o n t a m i n a t i o n  wrinkling  c l o s u r e area  these  them. was  improvements,  recommended  (Milleville  conditions  rather  and  that  are  75%  rejection  were s e t , based  Lampi  a l . (1976).  acceptable,  defects  V i s u a l examination  (1977) s t a t e d  et  the  Improved  occurrence the  seal  illustrated  into  as  to  prec1972).  challenge.  helped  to  minimize  on  however, methods  i s a common p r a c t i c e .  than  sampling  operation  with  the  Tsutsumi  system  or  or  of  100%  reported  inspection.  criteria  d e f e c t s , was would  large  of  i n s p e c t i o n s under  whereby  blisters  particles  (1974)  complete v i s u a l  s e v e r i t y of  wrinkles  occluded  A  Use  exist  a random p r o p o r t i o n  a r u l e of thumb, v i s u a l  effective.  Small  however,  occur;  Badenhop, 1980).  d e f e c t s from a f i l l i n g  ideal  the  result  wrinkles.  pouches  Lampi  V i s i b l e d e f e c t s were thought to  pumps have helped  of  inspection  0.02%  lowered  upper a r e a s .  Despite  the  were  the  Stretching  in  s p e c i a l design  filling  Reducing  (1981).  for  described be  by  considered  wrinkles  must  be  rejected. There for  on-line  described The  i s a need  i n s p e c t i o n of  flux.  sealed  pouches.  as an e f f e c t i v e d e f e c t d e t e c t o r  instrument  seal w i l l  f o r development of n o n - d e s t r u c t i v e  works  show s u r f a c e  D e t a i l s of  the  on  transient-heat  Infra-red (Goldfarb,  detection  temperature v a r i a t i o n s by design  were r e p o r t e d  test  equipment  scanning  1971;  where a  has  been  Lampi, 1977). contaminated  impedance of  by Lampi (1977).  the A  heat  caliper  -12-  measurement was ness due aided  inspection  acquisition  merit  module  the  the  system  for  an  irregularities  isolate  quality control  image  of  defects  the  and  ming on c r i t e r i a f o r d e f e c t s and inspection  and  This  occur,  threshold  weak spots  may  assurance  form  then  a  An  computer  extensive  or  program-  that  proper  i n the  seals  are  formed  of r e t o r t pouches.  pouch m a t e r i a l  If  resulting in  processing.  C r i t i c a l Factors A f f e c t i n g Processing  increasing  ations.  towards  need  of  pouch  has  Identification recently  densate  from  established retorts. acids  In  foods  crucial.  not  work  seals  identifying  processing  just  f o r e s t a b l i s h i n g processing  Considerable  evaluation  are  pouch s e a l s .  l e v e l s of r e j e c t i o n .  As the technology f o r r e t o r t pouches c o n t i n u e s an  thick-  decision rejected  system r e q u i r e d  f a i l u r e from s t r e s s e s imposed by thermal  II  i n seal  determine whether they would  f r e e of c o n t a m i n a t i o n or d e f e c t s , a i d s p r o c e s s i n g defects  of  product,  M e c h a n i c a l implementation of the  package o n - l i n e .  Stringent  detected  G a g l i a r d i et a l . (1984) designed a computer-  stored  image to  rejection.  accepted  which  to contaminants.  video  analyzed  developed  and  and  has  been  material  controlling  been  of c r i t i c a l  apparent  done  tradition order in  to  retort  r e t o r t s as of  processing  set regulations pouches,  and  the  canned  similar  effort  during  thermal  Milleville, For  for  1980). example,  r o l e of removal of  con-  parameter  well  foods  governing  specific-  standards  ongoing p r o c e s s .  critical  studies  A  factors  (Badenhop  a  packaging  setting  integrity.  Smith et a l . (1985) r e p o r t e d vertical  and  critical  f a c t o r s i s an  to' develop, t h e r e i s  the  evaluating  in  i n the  vertical  processing critical  of  steam low-  parameters  -13-  F a c t o r s are  generally considered  adequacy of the s t e r i l i z a t i o n of the system. nature for  of  pouch,  for retort  product  are: gas  product  Berry  pouch  heating  (1979)  and,  identified  processing.  Those  characteristics,  entrapment.  Factors  i f they  due  that a  are  time  and  factors w i l l 1.  of  pouch  Although  many c r i t i c a l  i n metal  considerably.  pouch,  size, by  of  In  thermal  the  of  predictable  the  weight  and  retort  design  are  cool cycle.  However,  change  solid,  in  liquids  due  to  circulation,  Many of  and,  are  entrapped  cans only  the  volume  flexible may  these  gases as  similar  differ  a small  change  nature  of  from  entrapped  stability.  the  thermal gases.  primarily providing  r e t o r t i n g , assurance of uniform  product  to  gases  result  particularly,  reasons f o r removal of  t r a n s f e r and  of  of r i g i d  total  pouch b u r s t i n g d u r i n g  heat  effects  processing  occurs.  (1977) c i t e d  preclusion  the  fill  f a c t o r s i n pouch p r o c e s s i n g  processing,  significant  expansion Lampi  can  volume  a  critical  be d e a l t w i t h i n more d e t a i l . Gases  total  the  present  f a c t o r s p e r t a i n i n g to  contributed  e f f e c t i v e n e s s of  Residual  those  in  the  flexible  not  number  the  economics  to the  r a c k i n g c o n f i g u r a t i o n s , the h e a t i n g media employed, mode of come-up  affect  q u a l i t y or the  a d d i t i o n a l parameters e x i s t  containers.  factors  residual  process,  critical  Many f a c t o r s must be c o n s i d e r e d  the  rigid  to be  and  A d d i t i o n a l advantages  of removal of a i r a r e e a s i e r d e t e c t i o n of s p o i l a g e and  easier cartoning  or c a s i n g . a.  Pressure-Volume One  packages was  of  the  Studies  first  studies  regarding  performed by Wallenberg and  a i r entrapped  J a r n h a l l (1957).  in  Their  flexible results  -14-  showed t h a t a maximum r a t i o between e n c l o s e d package must not be exceeded i n order level  differed  subjected  depending  on  to dry a i r there  t o prevent  the c o n d i t i o n s  was no apparent  volume t o s u r f a c e o f 2:1 ( c o r r e s p o n d i n g pouch) compared in  bursting  suggestion  to a r a t i o  when that  studies  autoclaved  microscopic  moisture  that  content  a  sealed  package  feasibility and  Results it  steam.  leaks  occurred  without  cook  i n d i c a t e d that  Keller  (1959),  residual  When  a r a t i o of  was  Rubinate flexible  a i r overpressure  trials,  I t was a l s o e v i d e n t dependent  i n the o r d e r  volume. using  was, however, t h e  i n the dry a i r  as used  from  on the  Relative  o f 80.3 kPa w i t h  (1964) s t u d i e d t h e  packages i n 100% steam f o r glass  containers.  f o r use o f pure steam as a heat t r a n s f e r medium  was e s s e n t i a l t o remove as much a i r as p o s s i b l e .  environment without  with  i n the package.  of r e s i d u a l gas i n a 155 g pouch p e r m i t t e d  was  bursting  to bursting  high p r e s s u r e s  of constant  with  of s t e r i l i z a t i o n .  There  bursting.  of the a i r enclosed  o f thermal p r o c e s s i n g  a water  The maximum  t o 75% o f maximum volume o f the  with  the r e s i s t a n c e  h u m i d i t i e s o f 100% c r e a t e d  bursting.  o f 3:1 ( o r 40% o f maximum volume) r e s u l t i n g  r e l i e v i n g i n t e r n a l pressures their  a i r and s u r f a c e a r e a o f the  b u r s t i n g the pouch.  but a l t h o u g h  use o f pure  gas was removed, a water  A maximum o f 10 mL  processing with  a pure steam  S i m i l a r r e s u l t s were found by steam was p o s s i b l e i f enough  cook w i t h  superimposed  a i r pressure  preferred. The  gases  flexibility  during  of the f i l m s and r e s u l t i n g expansion from entrapped  heating  prompted  studies  by D a v i s  e t a l . ( 1 9 6 0 ) on  pressure/volume r e l a t i o n s which e x i s t i n f l e x i b l e c o n t a i n e r s . apparatus was designed  t o measure  the expansion  A special  i n volume o f packages  -15-  containing  water  and a i r w i t h  p r e s s u r e s were found of  t h e water,  expansion  increasing internal  t o develop  an i n c r e a s e  of the food  pressure.  Internal  due t o an i n c r e a s e i n t h e vapor  i n pressure  product  with  pressure  o f a i r i n t h e h e a d s p a c e and  i n c r e a s i n g temperature.  These  i n t e r n a l p r e s s u r e s were q u a n t i f i e d u s i n g t h e i d e a l gas law, as f o l l o w s :  (1)  where P^V^ and T^ a r e p r e s s u r e , volume and temperature ( a b s o l u t e ) o f t h e air V  m a x  before ,  processing,  T2  i s temperature  t h e maximum volume o f the pouch.  P2 i s the p a r t i a l  water a t temperature T2, p l u s the p a r t i a l In  the experiment,  105 mL. gas  the maximum  volume  Good agreement was found  laws and t h e a c t u a l p r e s s u r e  volumes of entrapped developed  air.  pressure  process and pressure of  o f the e n c l o s e d a i r .  o f the bag was assumed  t o be  between the p r e s s u r e c a l c u l a t e d by t h e created inside  the pouch w i t h  various  A maximum p r e s s u r e d i f f e r e n t i a l o f 2.7-23 kPa  i n a pouch c o o l e d with  f a i l u r e s were found.  o f the h e a t i n g  superimposed  Data from i n t e r n a l  a i r pressure,  and y e t no  p r e s s u r e s t h a t e x i s t and know-  ledge o f s t r e n g t h o f the pouch a l l o w the c a l c u l a t i o n o f optimum  filling  l e v e l s of containers. The  use o f o v e r r i d i n g a i r p r e s s u r e  pouches was d e s c r i b e d by Whitaker thermal  expansion  of s o l i d  t o prevent  (1971).  and l i q u i d  expansion  of r e t o r t  I d e a l gas r e l a t i o n s h i p s and  components  i n a food  system o f  peas and b r i n e were used t o c a l c u l a t e p r e s s u r e s i n the system.  When no  air  11.3 mL  when  was p r e s e n t , processed  227 g o f product  a t 126°C  with  pure  would  expand  steam.  an a d d i t i o n a l  A maximum  allowable  pouch  -16-  expansion  of 35 mL  was  predetermined.  Therefore,  the volume a t  retort  c o n d i t i o n s d i d not exceed the a l l o w a b l e expansion.  C o n s i d e r a t i o n of the  same  If  system  essentially pressure  with dry,  5 mL the  of  a i r was  volume  of  described.  water i n the product  product  due  to  increased  However, when water was  contained  a i r would  of steam w i t h i n the r e t o r t .  i n the system, D a l t o n ' s  the  decrease  law of p a r t i a l p r e s s u r e s must be c o n s i d e r e d .  reached  r e t o r t temperature, the same as r e t o r t  pressure.  ure  can  assuming  a i r i n the  volume  of  35 mL  Calculated  system  and  partial  taking pressures  be  calculated  As  the p a r t i a l p r e s s u r e of  vapor w i t h i n the pouch was of  was  into  account  expansion  of  included  a i r were  P a r t i a l pressa  of  maximum the  pouch  contents.  equivalent  to  the  r e q u i r e d o v e r r i d i n g a i r p r e s s u r e s f o r p r e v e n t i o n of pouch b u r s t i n g . Yamano pressure  (1976) p r e d i c t e d pouch expansion  needed  to  prevent  pouch  s t a t e of e q u i l i b r i u m , the r e t o r t internal  pouch p r e s s u r e .  internal  pressure  pressure.  was  bursting.  at  considered gas  steam/air  eratures.  A  retort  plotted  was  relationship  to  laws,  ratios.  a  size  165  volume  x 200 mm of  headspace  50 mL  was  could  be  ratios between  against  space expansion  to determine pouch  was  be  due  r a t i o of the headspace  Expansion determined pressure  temperature  r a t i o s of headspace at  containing  assumed.  From  c a l c u l a t e d , and  250 mL this,  of an  different  of  food  the  head-  r a t i o of two f o r and  expansion  consequently  temp-  a i r within  for different  A maximum a l l o w a b l e expansion  pouch  the  to both water vapor and a i r  partial  processing  a  assumed to be equal to the  an expansion  were  the in  As w i t h p r e v i o u s l y d e s c r i b e d experiments,  From the i d e a l  various  When the  p r e s s u r e was  and a t o t a l pouch volume were determined. gases  i n order  a  headspace  ratio  of  the  a safe o v e r r i d i n g  -17-  p r e s s u r e of 20-30 kPa was b.  determined,  E f f e c t on H e a t i n g Rate B e s i d e s the problem  in  pouches a r e of concern  transfer  i s required.  p o t e n t i a l problem flexible  of pouch b u r s t i n g , r e s i d u a l gases  for safety  Nelson  and  reasons  since a predictable  Expansion  of  gases  to expansion of gases i n  would  result  i n an  e f f e c t from poor heat c o n d u c t i v i t y of entrapped gases. that  superimposed  a i r p r e s s u r e ( a t 220  p r o c e s s would improve allowed to expand.  retortable  of  entrapped  180 g of a f^,  or  heating were  the  penetration  Results  of  required  the  caused  The  pouches  that  line  f  n  effect  containing  heating rate  selected  index,  portion  process  increasing  to a t o t a l  Higher  Longer  on  headspace  o f 20 mL,  an  f  required  a  n  for  gas  6 to  7.2  value o f  values r e p r e s e n t slower  p r o c e s s i n g times  of  lethality  an i n c r e a s e i n f ^ v a l u e s from  5 mL  reported.  the i n s u l a t i n g  straight  for a  demonstrated  an a d d i t i o n a l  rates.  described  were performed  slope  time  0 t o 15 mL  was  the  quantified.  processed a t 120°C.  reciprocal  and  With  minutes  Experiments  product  evaluated.  minutes. 9.4  gases.  curve  throughout  a t Toyo S e i k a n K a i s h a L t d . (1973), a producer  pouch p r o d u c t s i n Japan,  negative  They recommended  gauge) h e l d  R e s u l t s , however, were not  curry  volumes from  kPa,  insulating  heat t r a n s f e r because entrapped gases would not be  A study performed of  heat  S t e i n b e r g (1956) r e c o g n i z e d the  of reduced heat t r a n s f e r due  pouches.  included  heat  adequate  s t e r i l i z a t i o n were r e p o r t e d w i t h l a r g e r amounts o f a i r entrapped i n the package.  A  institutional Increases  similar size  result pouches  i n process  time  was were up  to  r e p o r t e d by processed 35%  had  Kopetz  et a l . (1979) when  i n horizontal been  noticed  orientation.  when  150 mL  of  -18-  r e s i d u a l gas remained w i t h i n the pouch. an i n s u l a t i n g l a y e r accounted  S t r a t i f i c a t i o n and  f o r the i n c r e a s e s seen.  P r e d i c t i o n s by Badenhop and M i l l e v i l l e al  size  retort  Significant file  of  the  h e a t i n g was holding  capacity  F  (76  buyers  on in  the  restrained et  x 38.1  cm)  can  s i d e s and  prompting  heat  of  5 15%  pouches. or  size  for  from  can  the pouch  with  ends.  the same  I t was  the p r o d u c t . problem w i t h  effects  also  However, regard  to  green  racking  each  100  mL  and  green  were  increase  n  o r  found in  diced to  air  beans  using  methods. ^  air  experiments  orientation  restraining  beans  entrapped  Processing  m  for  of  pears  pouches.  retort and  of  to reach an F 2 0 0 F ° ^ ^ ^-  both  Required pears  and  increase content  by for  I n c r e a s e s were l a r g e r when pouches were placed i n  unconstrained  al.  retort  sandwiched)  min  the  characteristics  horizontal  (firmly  severe  be e a s i e r to d e a l w i t h s i n c e  a particular  investigated  penetration  with  less  pro-  research i n t h i s area.  (1981)  institutional  low  pouch capable of  i n (19 mm)  i n v o l v e d i n choosing  pouches present  p r o c e s s i n g times  constrained  cm  from  would be  size  approximately  43.2  cm)  t h a t the i n s t i t u t i o n a l market may  value  Beverly  In a 12 x 15 i n (30.5  interest.  The  because  i n a number 10  performed  Q  quality  spot  constraining  an  product  In c o n t r a s t , the c o l d  Huerta-Espinosa  thermal  improve  i s 0.75  r e s i d u a l gases,  were  c o s t advantages were r e p o r t e d .  would  kg),  institution-  become of  spot  institutional  packed  can has  the c o l d  a few  content  and  required.  is 3 in  suggested only  pouch  5 l b (2.3  surface.  (1980) t h a t the  pouch would r e p l a c e the #10  cook time  f o r m a t i o n of  (1980)  from  conditions. studies  Similar  with  r e s u l t s were found  institutional  (12 x 17 i n ) r e t o r t pouches processed  size,  i n c o n f i n e d and  30.5  by x  unconfined  -19-  horizontal  orientation.  volumes  ranging  achieve  an F  Q  from  value  Water was c o n t a i n e d  0  t o 250 mL  i n the package w i t h a i r  and t h e r e q u i r e d  o f 6 min were determined.  when pouches were u n c o n f i n e d  process  times  to  Results revealed that  t h e r e was a 20% i n c r e a s e i n r e q u i r e d p r o -  cess time with 250 mL o f a i r ; whereas, c o n f i n e d pouches d i s p l a y e d a 10% increase. ivity  The n e g a t i v e  impact  o f entrapped  and economics o f the system.  gases a f f e c t s  I t appeared  the p r o d u c t -  t o be more d r a s t i c i f  pouches were processed w h i l e u n c o n f i n e d on s u p p o r t i n g r a c k s . Another  study  by B e r r y  and Kohnhorst  gases i n i n s t i t u t i o n a l s i z e r e t o r t pouches. of  celery  soup were processed  on  entrapped  Whole k e r n e l c o r n and cream  f o r 40 and 50 minutes,  pouches c o n t a i n i n g up t o 250 mL o f r e s i d u a l of  (1983) focused  air.  respectively, i n  Heating  rate indices  the cream of c e l e r y soup were found t o i n c r e a s e from 33.5 min w i t h no  air  present  t o a v a l u e o f 57.3 min when 250 mL o f a i r was i n c l u d e d i n  the  pouch.  Broken h e a t i n g c u r v e s  whole  kernel  corn  i n brine.  were d i s p l a y e d i n pouches c o n t a i n i n g  The f ^ remained  i n c r e a s i n g a i r c o n t e n t s but f 2 from  t h e second  about  t h e same  straight  with  l i n e p o r t i o n of  the h e a t i n g curve demonstrated an i n c r e a s e o f 67% when 250 mL o f a i r was entrapped. Racking effects 0,  design  o f entrapped  20 and 50 mL  bentonite  shown t o be a c o n t r i b u t i n g  gases i n s t u d i e s by Evans (1977).  were  suspension.  (unconfined) 69 kPa.  was a l s o  tested  in retail  size  pouches  factor  t o the  A i r volumes o f containing  Pouches were t e s t e d when processed  a 7%  i n restrained  or c o n s t r a i n e d p o s i t i o n s a t a i r o v e r p r e s s u r e s  o f 34.5 and  R e s u l t s showed t h a t both a i r c o n t e n t and the method o f r a c k i n g  were s i g n i f i c a n t .  Increased  f ^ v a l u e s of 11% were found when 50 mL o f  -20-  air  was  included  i n c r e a s e s o f 19% Air  rubber  vertical  (15-30 mL)  the  vertical  were  found  has  thermally  under  processing  insulating  of  regulations,  foods. good  prevented  or  Entrapped  heating rates i n  up  to  260%  higher  orientation  MRE  in a single  program  residual  a u t h o r s and American  gas  and  level.  (Milleville of  Reviewers this  serving  retail  f o r adequate  have  not  imposed  specifications  In a r e p o r t  sealing  i n England.  transfer  exist.  of entrapped a i r should be g e n e r a l -  Association  after  65%.  regarding allowable  agencies  practice  pouch b u r s t i n g .  comments, s u g g e s t i n g t h a t  current  horizontal  unconstrained  gave r e a s o n a b l e assurance  a i r content  specification  allowable  government  manufacturing  This level  recommended f o r use  The  f ^ values  to provide g u i d e l i n e s  Although  Food P r e s e r v a t i o n Research maximum  in  on  b e h a v i o r and u l t i m a t e decrease i n heat  (197A) suggested t h a t 10 mL  t r a n s f e r and  10 mL  either  packaging  P r e d i c t a b l e heat t r a n s f e r must be ensured  some  accepted.  of  mL.  levels  r a n g i n g from 105-120°C and s t e a m / a i r r a t i o s above  made i t n e c e s s a r y  additional  effects  to i n f l u e n c e  but  showed  f a c t o r i n the  processing conditions.  constrained orientation  volumes o f a i r .  a  the  processed  different  pouches  of a i r compared to 0  when p r o c e s s i n g i n the h o r i z o n t a l  The  Tsutsumi  bricks  investigated  i n pouches d i d not appear  a t temperatures  rates  (1983)  orientation  air  Restrained  found not t o be a s i g n i f i c a n t  Ramaswaray  silicone  c o n s t r a i n e d pouch.  f o r pouches c o n t a i n i n g 50 mL  o v e r p r e s s u r e was  tested.  ly  in a  2%  of  heat  prepared by Carapden and Badenhop, product  1980),  volume  was  from the U n i t e d S t a t e s added level  size  was  too low  pouch was  processors  I t was  of p r e d i c t a b l e  suggested  have by  and  more  realistic.  adopted both  that a  the  a  10  mL  English  r e v i e w e r s t h a t measurement of r e s i d u a l gases s h o u l d  -21-  be a r o u t i n e i n p r o c e s s q u a l i t y c o n t r o l c.  Methods o f Measurement The  trapped that  most  gases  commonly  Shappee  and  apparatus  i n water  level  (1972)  An opening  a measuring  water  t o execute  Werkowski  used.  immersed  used  i s a destructive  i t i s simple  into  procedure.  procedure  test.  to evaluate  Advantages o f t h i s  and equipment described  below  used  technique a r e  i s readily  i n detail  available.  the technique  by d i s p l a c i n g  the c o l l e c t e d  t o escape  and be c o l l e c t e d  t h e water p r e s e n t .  gas w i t h i n  the c y l i n d e r  Since the was  above t h a t o f t h e s u r r o u n d i n g tank, a c o r r e c t i o n was a p p l i e d volume  using Boyles  law.  Although  this  the d e s t r u c t i v e n a t u r e was a disadvantage be  evaluated.  and  i n t h e package was made when i t was t o t a l l y  and the a i r was a l l o w e d cylinder,  amounts o f en-  test  usually  t o the gas  was simple and s t a n d a r d ,  when m u l t i p l e samples were t o  N o n - d e s t r u c t i v e a i r measurement would  be u s e f u l  i n this  r e s p e c t and some procedures have been i n v e s t i g a t e d . A n o n - d e s t r u c t i v e a i r measurement proposed (1972) was d e r i v e d from ology  Archimedes' p r i n c i p l e  i n v o l v e d weighing  a  package  while  by Shappee and Werkowski and B o y l e s  suspended  law.  i n water  Methodand  then  r e d u c i n g the p r e s s u r e i n a s u r r o u n d i n g vacuum chamber u n t i l  the entrap-  ped  of neutral  gases  buoyancy.  expanded,  rendering  t h e pouch  into  At t h i s s t a t e , t h e pouch n e i t h e r f l o a t e d  to the bottom.  The f o l l o w i n g e q u a t i o n was used  of a i r i n t h e pouch a t atmospheric  P  V  P  state  t o the t o p nor sank  t o c a l c u l a t e the volume  pressure:  W  N( WS>  w  =  a  w  P  s  1" N  ... (2)  -22-  where P j was  the atmospheric  p r e s s u r e a t the time of t e s t i n g , P^j was  the  i n a s t a t e of n e u t r a l buoyancy and W  was  p r e s s u r e when the package was  the weight i n water of the package a t atmospheric between d e s t r u c t i v e and and of  a linear 0.996.  found  with a c o e f f i c i e n t  However, a c t u a l a i r volumes were s l i g h t l y  and  Comparisons  n o n - d e s t r u c t i v e a i r measurements were performed  r e l a t i o n s h i p was  u l a t e d volumes. pressure  pressure.  wg  T h i s was  of  determination  h i g h e r than  a t t r i b u t e d to d i f f e r e n c e s i n d a i l y  additional  pressure  d e s t r u c t i v e method apparatus  due  having  to  the  water  a compressive  head  calc-  atmospheric in  a c t i o n on  the  non-  the package  volume. Research by Yaraaguchi  e t a l . (1972) determined  between the same n o n - d e s t r u c t i v e measurement and methods. affect  a close correlation  traditional destructive  However, v a p o r i z a t i o n of d i s s o l v e d gases i n foods appeared  vacuumization  at n e u t r a l buoyancy.  operations  f o r accurate  Ghosh and R i z v i  determination  of  (1982) r e p o r t e d r e s u l t s  pressure  suggesting  t h a t n o n - d e s t r u c t i v e a i r measurements were e s s e n t i a l l y h i g h e r than w i t h d e s t r u c t i v e methodology. ies  i n measuring  buoyancy. ure  may  true  not  be  equivalent  a n a l y s i s was  factors  were  pressure  not i d e a l l y  to  the  used  to  pouch p r e s s u r e and  Correction  They a t t r i b u t e d d i f f e r e n c e s to  internal  S i n c e the pouch was  regression internal  a  the  point  of n e u t r a l  f l e x i b l e , the i n t e r n a l pressure.  describe  relationship  the  found  difficult-  environmental  pressure  determined  at  to  press-  A multiple between  of the system a t n e u t r a l buoyancy. to  obtain  an  improved  estimate  of  residual a i r . Application of  of  non-destructive  n e u t r a l buoyancy, i s l i m i t e d  techniques,  based  on  the  principle  t o packages which s i n k i n water.  Con-  -23-  sidering  the p o s s i b i l i t y  t e c h n i q u e was measure  and  a  in a  in a  vacuum  chamber.  (1985) f u r t h e r  pressures within  Two  i n water  the pouch.  levels  corrected  that  changes  f o r expansion  was  described  air. ped  a  pouch w h i l e  Archimedes'  a  buret  were r e c o r d e d .  registered  R i z v i and  suspended  p r i n c i p l e was  (1981).  required. i n water,  used  was  on  Klemaszewski  Knowledge  the  They a l s o  Another  then weighing  to c a l c u l a t e  internal  t h e b u r e t must  The t e s t was  was  of  be  tech-  product  performed  by  the pouch i n  the volume o f e n t r a p -  gases. d.  Other E f f e c t s of R e s i d u a l Gases Entrapped  gases, i n a d d i t i o n t o c a u s i n g d e l e t e r i o u s e f f e c t s  heat t r a n s f e r , w i l l a f f e c t product s t a b i l i t y and q u a l i t y . must  top.  to c a l c u l a t e  a i r i n the water.  Huerta-Espinosa  on  B o y l e s law  t o atmospheric p r e s s u r e .  i n volume  method  vacuum l e v e l s were a p p l i e d  E q u a t i o n s were developed  d e n s i t y and volume of the pouch was weighing  with  The  t h i s t e c h n i q u e and measured a c t u a l  of d i s s o l v e d  by  i n water.  Then the e n t i r e apparatus  entrapped.  amount of a i r i n c l u d e d as c o r r e c t e d determined  float  different  the amount of gas  investigated  (1983) t o n o n - d e s t r u c t i v e l y  container f i t t e d  added t o a l e v e l i n the b u r e t .  to c a l c u l a t e  nique  Rizvi  i n p r o d u c t s which  pouch  volume d i f f e r e n c e s  used  by G y l y s and  gases  placing  Water was placed  developed  residual  involved  of p r o c e s s i n g p r o d u c t s such as bakery goods, a  be  taken  into  quality  control.  hushed  tomato  account Analysis  gravy  was  when d e c i d i n g of  headspace  performed  G e n e r a l l y , gases i n the headspace 10% CO2,  0.6%  O2 and 0.2%  R^.  after  by  upon r e s i d u a l gases  in a  Yamaguchi  These  factors  gas  levels for  pouch  containing  et  al.  processing consisted  Oxygen i n the headspace  on  was  of  (1972). 89%  of p a r t i c u l a r  -24-  concern  because many  Tsutsumi  oxidative  (1974) s t a t e d  accepted w i t h regard  that  about  leading  material phere. finite  to o x i d a t i v e  provides  a i r was  generally  occurring  i n foods i s the p e r o x i d a t i o n of  rancidity.  Aluminum  i n the r e t o r t  pouch  a good b a r r i e r t o i n t r u s i o n of oxygen from the atmos-  Therefore,  i t may be assumed t h a t the t o t a l amount o f oxygen i s  and the extent  1974).  10 mL of remaining  e x i s t i n foods.  to o x i d a t i o n .  One of the r e a c t i o n s lipids  deteriorative reactions  Other food  o f the r e a c t i o n cannot exceed  components such as v i t a m i n s ,  exhaustion  (Karel,  pigments and some amino  a c i d s a r e a l s o oxygen s e n s i t i v e . Studies  by Toyo Seikan K a i s h a L t d . (1973) r e v e a l e d  C retention just after s t e r i l i z a t i o n the of  package. vitamin  0 mL  C, compared t o 83.7, 92.8 and 95.5% respectively.  i n cherry  packaged under h i g h residual  gases  created  cated  higher  but  significant  pie f i l l i n g  Espinosa  increasing  a i r content i n  thermally  i t may  r e t a i n e d with 10, 5 and investigated  processed  i n vitamin  be assumed  Ascorbic  C retention acid  in institutional  amounts of entrapped  that  high  vacuum  Results  of French  pouches were e v a l u a t e d ascorbic  a i r were c o n t r a r y  s t u d i e s and t o the a u t h o r ' s s u g g e s t i o n  pouches  indi-  i n a small  (measurements taken one  contents  Observations of increased  C  Although measurement o f  i n t e r n a l vacuum p r i o r t o s e a l i n g r e s u l t e d  increase  vitamin  i n retort  an environment with lower a i r l e v e l s .  processed (1981).  (1980)  and low vacuum c o n d i t i o n s .  week a f t e r p r o c e s s i n g ) . thermally  Pereira  was not performed,  conditions that  vitamin  Occluded a i r volumes o f 20 mL r e s u l t e d i n 75.7% r e t e n t i o n  of a i r ,  retention  depended on i n i t i a l  that  green  beans  by Huerta-  a c i d content  with  t o f i n d i n g s i n other  t h a t r e s i d u a l gases be minimized.  -25-  The  same author  air.  s t u d i e d o t h e r i n d i c e s of q u a l i t y  C o l o r measurements were performed  processed w i t h v a r i a b l e a i r c o n t e n t s . to  have a  values  significant  were  detected. olics,  reduced Darker  implying  browning.  effect  and  a  colors  the  on  color  of  diced pears;  were e x p l a i n e d by  formation  of  and  green  beans  I n c r e a s e d a i r c o n t e n t s were shown  d r a m a t i c a l l y darker  greenness.  Loss  of  a  polymeric  color  the l o s s o f magnesium i o n s from pheophytin  reported  d i c e d pears  entrapped  Hunter  overall  L  and  appearance  reduction i n t o t a l compounds  which  i s pale  pigment i n green  phen-  responsible for  beans was  the c h l o r o p h y l l molecule, olive  o x i d a t i o n which occured  i n color.  Beverly  i n peaches a f t e r  b was  Hunter r e s u l t s f o r green beans showed i n c r e a s e d l i g h t n e s s  decreased  ing  on  s e n s i t i v e to  due  thereby et  and to  form-  a l . (1980)  8 months of  storage.  Samples w i t h i n s u f f i c i e n t a i r removal showed severe browning. S t u d i e s have been performed u t e s of foods  processed  i n pouches compared t o cans.  p r o c e s s i n g a luncheon-type 26%  more thiamine  flavor  and  comparing n u t r i e n t and  ham  of  attrib-  Young (198A) found  product i n r e t o r t pouches r e t a i n e d 16  than canned c o u n t e r p a r t s .  texture  quality  peaches  thermally  Research processed  evaluating color, demonstrated  that  quality  d e t e r i o r a t i o n d u r i n g s t o r a g e c o u l d be minimized  by u s i n g  pouches  compared  recognizing  advantages  of  to  cans  retort  ( P o t t e r et  pouches,  the  a l . , 1982).  problem  of  air  and  In  inclusion  retort  and  the its  d e t r i m e n t a l e f f e c t s must be c o n s i d e r e d .  2.  P r o c e s s i n g Media In the development of r e t o r t  prevent  problems  during processing.  associated with  pouch p r o c e s s e s , e f f o r t s were made t o high  internal  pressures  which  occur  Of p a r t i c u l a r concern were l a t t e r s t a g e s of the cook  -26-  c y c l e and may  during cooling  exceed  retort  environment  because  pressure.  a t these s t a g e s the i n t e r n a l p r e s s u r e  Typically,  a i r overpressure i n a  or o v e r p r e s s u r e w i t h water may  ure d i f f e r e n t i a l s .  steam  be employed t o reduce p r e s s -  Pure steam p r o c e s s e s have been employed f o r h e a t i n g ,  however, a i r o v e r p r e s s u r e must be i n t r o d u c e d d u r i n g the c o o l . Fundamental  studies  (1964) and  Pflug  recognized  potential  presented and  fewer  and  (UHT)  internal  concluded  i n terms  systems  t y p e s were performed S t u d i e s on  that  100%  The  possibility  Air  of  cook  of p h y s i c a l  Refrigeration  in  the  the  superior  and  distribution,  remained  overpressure  times  substantially was  essential  processes include to  ensure  desired  changes o f some foods a f t e r  marketplace  Tung e t a l . (1984a) s t u d i e d h  v a l u e 8.3%  were found  and  future  work  processed a t 130  and  during  5.4% and  cooling.  and  i n combining  135°C compared t o of the t e s t  v a l u e a t h i g h temperatures.  pouches i n c o n v e n t i o n a l canning r e t o r t s was  of the  temp-  problem.  higher f o r s i l i c o n e  expansion  the  prolonged s t o r a g e .  reduced  diffusivity  than  lethality  to e i t h e r  retort  135  the requirement  D i f f e r e n c e s were a t t r i b u t e d thermal  of  high  h e a t i n g r a t e s a t h i g h temperatures.  h i g h e r f o r n y l o n and  i n bricks  ultra  lower  e r a t u r e and water a c t i v i t y were suggested as remedies t o the  mean f  r e p o r t e d by  (HTST) and  temperatures  come-up  S i n c e s h o r t cook times were a s s o c i a t e d w i t h these  of h i g h temperature  monitoring  Pflug of  use of pure steam was  i n which  by  efficiencies  steam was  of temperature  i n Japan,  temperatures  temperature.  Disadvantages close  (1967).  of c o n t a i n e r s .  150°C were employed.  retort  media  media  (1979a) f o r h i g h t e m p e r a t u r e - s h o r t time  temperature  systems,  Borrero  problems  heating rate  Tsutsumi  comparing  A  rubber  105-120°C. b r i c k or a  P r o c e s s i n g of  r e p o r t e d by Roop and  -27-  Nelson  (1981).  S u c c e s s f u l p r o c e s s i n g o f c o n f i n e d pouches a t 115.6  pure steam was Pflug  be  achieved.  (1964) r e p o r t e d  potentially  that  more troublesome  implemented  for  although  than  provision  have been performed can  be  of  overpressure North  with  provided cook  made b e c a u s e  sufficient  each  260 kPa  were c i t e d i n g s and  great  by a r e t o r t  water  deal  of  potentially change  was  surface  circulation,  total  u n i f o r m heat  described  steam/air  These  Europe.  two  Studies  distribution  of  engineer as  (Anon, 1983).  processes  as  energy.  Surface  heat  transfer  been shown t o  ratios  Advantages  company c h i e f  w i t h water  has  of  75%  or g r e a t e r  steam/air  Tung and  requiring  Smith  h i g h water  transfer  was  with  transfer.  In steam/air  when steam  processes  p r o v i d i n g energy  cooks than  exists  have  d i s t r i b u t i o n than an e q u i v a l e n t water  pressure.  i n v o l v e d i n heat  heat  and  may  P f l u g and B o r r e r o (1967) r e p o r t e d  immersion  lower  America  were  steam, they  conditions.  medium t y p e  more u n i f o r m temperature  with  steam/air  comparing media t y p e s , yet no c o n c l u s i v e recommend-  c e r t a i n advantages and d i s a d v a n t a g e s . that,  w a t e r / a i r and  p r o c e s s i n g w i t h pure  types of media a r e common i n Japan,  ation  C in  condenses  (1980)  use  and  thought  steam/air  on  to  s i n c e no  processes the  sav-  a be  phase a  high  package  and  r e l e a s e s the l a t e n t heat of v a p o r i z a t i o n . A  comparison  (1976). were  Heating  of  r a t e s of  evaluated.  associated erature, steam/air  with  steam/air  It  was  water  f ^ values exhibited  of a  and  30 g  pouches  apparent  processes. 8.2  min  heating  w a t e r / a i r was  that  c o n t a i n i n g 25% very  long  When the water  were rate  performed  observed. index  of  Samples 10.2  min.  Yamano  bentonite  come-up retort  by  times  reached  were temp-  processed The  cake  with  results  -28-  indicated  t h a t water may  be an e f f e c t i v e medium, however, come-up times  were" much  faster  when employing  steam/air  determined  t h a t use of s t e a m / a i r was  mixtures.  the  higher  use  heat  transfer (1979)  of  hot  transfer  water  (1964).  Lopez  overriding  coefficients  coefficients and  with  of  and  heating  (1981)  based  ease  coefficients  595,  on  and 497 W/m  dropped  was  B e v e r l y (1979) advo-  a i r pressure  of  media were  control.  as  both  calculations  of heat  Beverly by  Pflug  75% steam/ a i r m i x t u r e s were  C respectively.  significantly  because  Overall  r e p o r t e d by  theoretical  C o e f f i c i e n t s f o r steam, water and  found to be 965,  it  f e a s i b l e , and perhaps cheaper, many  r e s e a r c h e r s have recommended w a t e r / a i r p r o c e s s e s . cated  Although  the  O v e r a l l heat  percentage  of  transfer  air in  the  mixture i n c r e a s e d . In  terms  Beverly water  for a  r e p o r t e d by  mixing.  heat  Research  of  Kopetz  time  they  pouches rapid  steam/air  to  with  et  to  with d i f f e r e n t  target  (1980) as and  that water  even heat which  the  h e a t i n g media,  are  F  of  Q  being  pressure  6 min.  Steam/air  difficult control,  to  compared  water/air  to was  a  15-16%  water more  of  penetration. to  He  suggested  better.  For  efficient.  entrapped  this  Tsutsumi  particularly  air, in  order  a v o i d i n g the  p r o v i d e adequate  was  increase in  systems.  p r o c e s s e s were commonly used,  necessary  with  a l t h o u g h the r e t o r t response  indicated  amounts  employ  along  c o n t a i n e r were g e n e r a l l y  a l . (1979)  containing large  ratios  a  temperature  steam/air  concluded  and  reach  Wilson  rates  (1979b) r e p o r t e d t h a t  attain  required  In w a t e r / a i r systems,  transfer  by  processing  for  times  product  necessity  adequate  reason,  280 g  were  the  slow,  process  (1980) r e p o r t e d a l o n g e r p r o c e s s i n g time i n s t e a m / a i r than w i t h  mixtures with  of  to low  overpressure  -29-  for  preventing  pouches  from  i n t e r f e r e n c e by a i r w i t h heat  3.  bursting  because  of  the  potential  transfer.  Processing Conditions Optimum s t e a m / a i r r a t i o s  concern  have been a f o c u s of i n t e r e s t .  t h a t p r o c e s s i n g w i t h h i g h a i r percentages w i l l  cause  There i s deviations  i n heat t r a n s f e r c o n d i t i o n s due t o the low s p e c i f i c heat c a p a c i t y o f a i r and  the  absence  example,  the  of  overall  compared to 965 W/m 75  to  95%  were  temperature air  was  a  condensation heat  reported  from  f^  same t e m p e r a t u r e .  after  temperature  by  coefficient  little  of  with  steam.  air is  Pflug  come-up. n  16.8 W/m  and  Borrero  (1967)  to  An  investigation  70%  distribution  Yamano and  were p r a c t i c a l were  c o m p o s i t i o n above 70%.  effect  on  by  C  from  improve  drops when  Pflug  et a l .  of pouches heated a t 240°F i n 90% steam d i d  R e s u l t s by  steam/air  For  Increasing steam/air r a t i o s  found  ratios  heating  from  rates.  Komatsu f o r use.  to  be  (1969)  suggested  Heating rates  and  independent  of  almost  These f i n d i n g s were f u r t h e r  work of Toyo S e i k a n K a i s h a L t d . (1973).  decreasing  as  v a l u e s f o r pouches processed w i t h 75% steam a t the  s t e a m / a i r m i x t u r e s over  steam/air  by  change  u n i f o r m i t y and reduce the d u r a t i o n of temperature  introduced  differ  transfer  C f o r pure steam.  (1963) r e v e a l e d t h a t the f not  phase  100  to  Their  results  approximately  However,  supported  showed  60  r e d u c t i o n below  or  that  70%  60%  had  steam  i n c r e a s e d v a l u e s o f the h e a t i n g r a t e index d r a m a t i c a l l y . Heat  penetration studies  v a l u e s i n c r e a s e d up  t o 11% by  by  Tung  et  a l . (1984a)  showed  that  d e c r e a s i n g the steam content from  50% i n a p i l o t s c a l e p o s i t i v e f l o w r e t o r t .  Conversely, i n a p i l o t  100  f  h  to  scale  -30-  commercial  retort  significant  over  (Lagarde)  that  range  steam  content  was  of composition.  found  t o be  Properties of  media were c h a r a c t e r i z e d by comparing s u r f a c e heat t r a n s f e r in  studies  Ramaswamy pilot  by Tung  e t a l . (1983).  scale  retorts  with increasing 12,000 W/m al. a  e t a l . (1984b) u s i n g Surface  were  found  transfer  transfer  estimate  f o r 50 and 100% steam,  and  heat  o f media rate  coefficients d e s c r i b e d by  coefficients  i n both fashion  C o e f f i c i e n t s i n the o r d e r of 2,000 and  (1984b) p o i n t e d out t h a t the s u r f a c e heat  valuable  steam/air  t o i n c r e a s e i n an e x p o n e n t i a l  steam c o n t e n t s .  C were found  heat  methodology  non-  heating  indices  respectively.  transfer  potential,  would  provide  Tung e t  coefficient  gave  but the o v e r a l l  heat  practical  information  regarding heating of foodstuffs. Limited variable et  s t u d i e s have examined e f f i c i e n c i e s o f w a t e r / a i r cooks with  overpressure  conditions.  a l . (1979) i n d i c a t e d  systems helped  that  to maintain  heat  P r e l i m i n a r y i n v e s t i g a t i o n s by Kopetz  overriding  penetration rates.  showed a 6-12% r e d u c t i o n i n p r o c e s s was i n c r e a s e d from effects required  of water  to reduce  experimentally  superimposed  peroxidase  derived  P r e s s u r e was found  time  69 t o 172 kPa (gauge). with  z-value  a i r pressure  a i r pressure  activity. were  factor.  data  a i r pressure  (1980) s t u d i e d t h e on  processing  A 2.85 D p r o c e s s  evaluated  t o be a s i g n i f i c a n t  Their limited  when o v e r r i d i n g Pereira  i n water/air  f o r cherry  time  w i t h an  pie f i l l i n g .  G e n e r a l l y , pouches p r o -  cessed under 103 kPa o f superimposed a i r p r e s s u r e r e q u i r e d l e s s time f o r s t e r i l i z a t i o n than when processed w i t h no o v e r r i d i n g p r e s s u r e , w i t h some exceptions.  Water c i r c u l a t i o n v e l o c i t y was found  (1983) t o be an important  f a c t o r when employing  by P e t e r s o n and Adams  water/air processes.  An  -31-  increase  i n process  (0.6 L / s ) f l o w  time  o f 9.6% was found  from  high  r a t e s f o r 10% b e n t o n i t e suspensions  (6.9 L / s ) t o low  i n institution  size  r e t o r t pouches processed a t 250°F w i t h 69 kPa o v e r p r e s s u r e . Variable  temperature  Ramaswamy (1983). for  of the p r o c e s s i n g  Temperature was found  the h e a t i n g r a t e o f s i l i c o n e  flow  retort  significant higher  with  steam/air  difference  mean  media.  when  processing  s t u d i e d by  processed  factor  i n a positive  bricks  showed a  rate indices.  (23.48 m i n ) compared  differences  r a t e s a t v a r i a b l e temperatures bricks  bricks  However, n y l o n  a t 120°C  No s i g n i f i c a n t  was  not t o be a s i g n i f i c a n t  (p<0.05) i n t h e h e a t i n g  f ^ was f o u n d  (22.25 min).  rubber  media  A 5.5%  t o a 105°C  (p>0.05) were found  i n heating  w i t h e i t h e r s i l i c o n e rubber or n y l o n t e s t  in a  forced  circulation  Lagarde  pilot  scale  retort.  4.  Package T h i c k n e s s Retort  because  products  o f the t h i n  benefits. As  pouch  profile  derive  cross section  One f a c t o r a f f e c t i n g  previously discussed,  their  rapid  heating  contributing  characteristics towards  overall  pouch t h i c k n e s s i s r a c k i n g c o n s t r a i n t s .  confined  racks  will  not permit  expansion  of  r e s i d u a l gases and i t was p o s s i b l e t o use 100% steam f o r pouch p r o c e s s ing  (Roop  and Nelson,  establishes processing.  a  maximum  1981). thickness  Improper confinement  In confined that  pouches,  the package  due t o inadequate  the rack  will  attain  spacing during  c i r c u l a t i o n of pro-  c e s s media between l a y e r s may be d e t r i m e n t a l t o the h e a t i n g r a t e o f t h e product. The fill  expansion  weights  o f pouch c o n t e n t s  a r e important  factors  (particularly when  utilizing  residual  gases) and  unconfined  racking  -32-  designs. Fill  Expansion  weights  thickness.  are Berry  of entrapped  critical and  gases has been discussed previously.  because  Kornhorst  of  ultimate differences i n pouch  (1983) found  decreased  heating rates  (higher f ^ values) with an increase i n f i l l weight when processing cream of celery soup and kernel corn i n brine.  Effects were more pronounced  for the soup, since natural convection currents were enhanced with large fill  weights of corn i n b r i n e .  B e v e r l y et a l . (1980) developed  a  relationship i n order to determine f ^ values for several pouch thicknesses. 0.62,  For  and 0.75  respectively. nesses  by  the  product  tested, f ^ values for thicknesses of  inches were calculated to be 8.A,  0.59,  9.3 and 13.6 minutes,  Heating rate indices can be compared for various thick-  multiplying the  f ^ value  r a t i o of thickness (Ramaswamy, 1983).  by  the square  of the appropriate  -33-  EXPERIMENTAL  I  Sample P r e p a r a t i o n  1.  Test Bricks Experiments  u t i l i z i n g model systems have proved  ing  factors affecting  of  m a t e r i a l s has been  (Pflug,  thermal  (Ramaswamy, (Cadillac  1983).  bricks  Montreal,  placement  couple  with  of a  a fused  bentonite  1983) and b r i c k s were  slabs.  teflon-insulated  fabricated  24 AWG  the  m a t e r i a l t o prevent  entering.  ensure  warped  that  location.  15.0  The groove was f i l l e d  teflon  phases.  The  thermo-  Each p a i r o f  coating  (Plastidip,  in sufficiently  thermocouple movement and steam  or water  with from  slightly  A d d i t i o n a l screws were r e q u i r e d around o u t e r edges  the b r i c k with  s t u d i e d and w i l l Final  virgin  Four machine screws a t 5.5 cm away from t h e c e n t e r p o i n t h e l d  the b r i c k t o g e t h e r . to  or n y l o n  copper/constantan  s l a b s was cemented t o g e t h e r w i t h a f l e x i b l e p l a s t i c I n c . , Northwood, CA).  suspensions  o f metal from  variety  One s l a b was c h a n n e l l e d t o a l l o w  end p l a c e d a t t h e c e n t r a l  PDI  A wide  PQ) f o r use i n e x p e r i m e n t a l  b r i c k s c o n s i s t e d o f two t e f l o n for  f o r example,  and Adams,  Test  Plastics,  processing of f o o d s t u f f s .  implemented,  1964; P e t e r s o n  v a l u a b l e i n compar-  dimensions  remained  repeated  be r e f e r r e d were:  sandwiched  processing.  together,  Two b r i c k  since  teflon  t h i c k n e s s e s were  t o i n f u t u r e d i s c u s s i o n s as t h i c k o r t h i n .  thick  bricks,  2.1 cm t h i c k ,  11.1 cm w i d e ,  cm l o n g ; t h i n b r i c k s , 1.3 cm t h i c k , 12.1 cm wide and 15.0 cm l o n g . Using  teflon  bricks  has many advantages.  I t heats  w i t h a thermal d i f f u s i v i t y s i m i l a r t o many food p r o d u c t s . physical  p r o p e r t i e s as  described  by M a n t e l l  (1958)  by  conduction  Table 1 l i s t s  and a  calculated  thermal d i f f u s i v i t y which i s comparable t o l i t e r a t u r e v a l u e s as c i t e d by  -34-  TABLE 1 Thermophysical p r o p e r t i e s  Properties  of t e f l o n ( M a n t e l l ,  S p e c i f i c Gravity  2.1  - 2.3  S p e c i f i c Volume ( s . v . )  475.9 cm  Thermal C o n d u c t i v i t y  6 x 10"  (k)  _ 5  Thermal Expansion (TE)  Water A b s o r p t i o n  Calculation  a  (Cp)  0.25  (WA)  6 x 10~  4  10 /C°  g/cm /kg c a l / s cm (linear)  cal/g  4  ( L o n c i n and  c a l / s cm  C°  = p Cp  2.2 =  1.09  C°  C°  0  of thermal d i f f u s i v i t y  k  teflon.  1958)  (p)  S p e c i f i c Heat C a p a c i t y  of  g cm x 10~  • 0-25 7  2  m /s  cal/g  C°  Merson,  1979)  -35-  Tung e t a l . (1984a). are no thermal  Another  trials.  used  with r e t o r t  This provided  Importantly,  teflon  consistent  and  r e p e a t a b l e measurements,  thereby  characteristics.  Packaging Retort  Al  processing.  be f a b r i c a t e d i n an i d e n t i c a l manner and be used f o r numerous  r e d u c i n g v a r i a t i o n s due t o sample  2.  be assumed t h e r e  d e g r a d a t i o n s or permanent m o d i f i c a t i o n s o f p r o p e r t i e s a t  the h i g h temperatures b r i c k s may  advantage i s t h a t i t may  pouches (American  f o i l / 7 6 ym  14.4  x 20.5  droplet  Polypropylene)  cm  inside  cure  f o r at  was least  which a i r was tight seal  injected  FL).  an  x  23.1  into  hours.  cm  s e a l a n t (Dow  and  used.  Corning  A  Corp.,  c o r n e r o f the pouch and allowed to  This  with removal  f u n c t i o n e d as  a  septum  through  of the s y r i n g e n e e d l e , an  were Use  fitted of  airtight  with  packaging  e x t r a gaskets  glands  sealing  from e s c a p i n g through  seal,  tightening  was  r e q u i r e d on  25  cm  of  thermocouple  with connectors  occasionally  repackaging  box  air-  extending  the  was  r e q u i r e d due  to  pouches.  nec-  In order to  screw  fittings  Pouches were prepared from  the  leakage  of  pouch  the  immediate  A c o t t o n b a l l was  i n s i d e the pouch, d i r e c t l y below the septum t o a i d i n j e c t i o n .  and  CT), s i n c e  a i r into  of the b r i c k and f a c i l i t a t e d  i n t o p r e v i o u s l y prepared  Cape  were  (Omega E n g i n e e r i n g , Inc., Stamford,  T h i s allowed easy removal  repackaging  wire  Ecklund,  the f i x t u r e .  with  about  (O.F.  the s t u f f i n g  s i g n s o f gasket d e f o r m a t i o n appeared.  pouch.  P o l y e s t e r / 9 ym  o u t s i d e dimensions  until first  equipped  12 ym  c o n s i d e r a t i o n ) were  silicone  i n a lower  and  e s s a r y to prevent gases ensure  of  Neenah, WI;  reformed.  Pouches Coral,  eight  16.0  seal  2.5 mL)  applied  Co.,  of  (taking  (approximately  Midland, MI))  Can  placed  -36-  Each  brick  thermocouple. pressure  was  placed  Water  in a  pouch  and  was  added  to  (10 mL)  s i m u l a t i n g a food m a t e r i a l .  connected the  pouch  free  and  exhibiting  a c t i v i t y approaching Samples For  some t r i a l s ,  with  a  narrow  setting. al  were  vacuum a  corresponding  to a  at  model  extension  provide  vapor  no a b s o r p t i o n of  assumed t o be  total-  t o foods w i t h a water  sealer  remove as AG-5,  was  much a i r as  Algau,  employed  W. at  possible.  Germany) the  equipped  maximum  an adequate s e a l f o r r e t o r t p r o c e s s i n g , an  jaw  pressure  fill  275 kPa  after  a mechanical  Foods I n c .  for solid  of  (Hamilton, foods  addition-  a i r l i n e p r e s s u r e 375  and  temperature  vacuum packaging  kPa  setting  were l e s s  of  than  vacuum Swiss-Vac machine l o c a t e d ON.)  with  vacuum  (Packages I n d u s t r i e s Group,  at operating c o n d i t i o n s o f :  In o t h e r t r i a l s ,  Magic P a n t r y  tion  impulse  to  (Model  Volumes of a i r remaining  mL.  similar  formed u s i n g a S e n t i n e l s e a l e r MA)  5.0  pressure  packaged  Multivac  bar  I n c . , Hyannis,  227°C.  vapor  an  1.0.  To ensure  s e a l was  a  to  S i n c e t h e r e was  water by t e f l o n , as i n d i c a t e d i n T a b l e 1, water was ly  to  was  speeds  used.  I t was  a  rated  at  30  3-8  to  elapse  produc-  pouches  per  minute ( M o r r i s , 1981). Pouch  integrity  was  tested  by  appearance of a i r w i t h i n the pouch. since  the  pouch  was  packaged  tightly  leakage were n o t i c e d , repackaging was  ensured.  was  allowing  h  Leakage c o u l d be d e t e c t e d a g a i n s t the  brick.  with  no  visually  I f s i g n s of  necessary u n t i l an a i r t i g h t  sample  -37-  II  Air Measurement  1.  Non-destructive Measurement of A i r A non-destructive measurement was  useful  i n these experiments to  determine a i r volumes within the pouch prior to processing. Shappee and Werkowski (1972), and R i z v i and Gylys (1983) described a method of nondestructive  measurement  as  discussed  earlier.  determining  the vacuum pressure within  a bell  pouch to achieve neutral buoyancy i n water.  Procedures j a r necessary  This method was  involved for the attempted  with results showing inconsistencies and lack of r e p r o d u c i b i l i t y .  That  approach was abandoned and a modified technique was employed to monitor addition of a i r and possible leakage of gases, into or out of the pouch. It was performed by weighing a vacuum packaged pouch while suspended i n water.  Figure 1 i l l u s t r a t e s  the apparatus used  for t h i s purpose.  A  scale equipped with a hook on the underside for weighing, mounted on a wooden base with a c i r c u l a r depicted.  basin i s  There was clearance between the wooden base and water basin.  Pouches were suspended immersed  hole and placed over a water  i n water.  from the hook by use of a c l i p  Water l e v e l was  kept constant and  and  totally  the scale  was  zeroed with the c l i p on. Once each package was fully  injected  weighed, desired volumes of a i r were care-  through the s i l i c o n e  target a i r volumes were administered.  septum.  In each set of t r i a l s ,  For 14 bricks of each thickness,  Figure 1 .  Apparatus f o r n o n - d e s t r u c t i v e  measurement of a i r .  -39-  two  bricks  volumes  were  of 0,  left  unpackaged  10, 20 and 30 mL  and  three  of a i r .  bricks  were  Each b r i c k was  number, and the b r i c k s were randomly a s s i g n e d  injected  with  identified  by a  t o the v a r i o u s t e s t con-  ditions. A f t e r a i r a d d i t i o n , samples were weighed Archimedes' p r i n c i p l e ,  i n water a g a i n .  the d i f f e r e n c e i n weight was  equal  Based on  to the volume  of a i r added from the e q u a t i o n :  W  ws  W  V  A  where W sample  v  ~ ws+a = P w s § + P w l 8 - P m  =  and  added  V g  ...(4)  s  p V! w  i s weight of the sample  wg  w  a i r i n water;  i n water and W  p  the  w  density  w g + a  i s weight of the  of water;  V  i s the  s  volume of the sample; V j i s the volume of a i r ; and g i s the g r a v i t a t i o n al force. the mass  D e r i v a t i o n of t h i s e q u a t i o n  density of  the  assumption, technique  2.  sample  addition  was  measurements 1.  of water equal  used  and of only  t o 1.0  g/mL,  air will a i r and as  a  i s shown i n Appendix I .  any  be  reduced  measure  of a i r added, the  by  leakage may  relative  were performed i n t h r e e  f o r each mL  1.0 be  of  Assuming  g.  With  this  monitored.  This  a i r volumes.  The  stages:  a f t e r vacuum packaging, after  injecting  d e s i r e d volumes o f a i r , j u s t  prior  to p r o c e s s i n g ,  and 3.  a f t e r p r o c e s s i n g , j u s t p r i o r to d e s t r u c t i v e a i r measurement.  The d i f f e r e n c e between measurement two and one, r e p r e s e n t s the amount of air  added  by i n j e c t i o n .  P o s s i b l e a i r leakage d u r i n g  c a l c u l a t e d by the d i f f e r e n c e of measurements  p r o c e s s i n g may  t h r e e and two.  Any  be  pouches  -40-  with leakage g r e a t e r than 5 mL were o m i t t e d .  2.  D e s t r u c t i v e Measurement of A i r Conventional  opened  under  a i r measurement  water  and  S i n c e pouch i n t e g r i t y such  gases  i s lost  are and  equipment assembled  collected  in  illustrated, filled  buret  the buret was  to the 50 mL  constant  column  whereby a  in this  pouch i s vessel.  from the pouch,  Shappee and  experiment. air.  the  volumetric  the a i r i s d i s c h a r g e d  to measure entrapped  the mouth of a 50 mL  A  procedure  methods are g e n e r a l l y termed " d e s t r u c t i v e " .  (1972) d e s c r i b e d the method used  was  is a  Werkowski  Figure 2 depicts  A f u n n e l was  attached to  to i n c r e a s e the area f o r e n t r y of gases. i n v e r t e d and  p l a c e d i n a water b a s i n .  measure by s u c t i o n w i t h an a t t a c h e d rubber  height  above  the  water  level  As  Water tube.  was  ensured  by  con-  the  pouch p r e v e n t i n g  s i s t e n t l y immersing to a marking on the f u n n e l . Testing  was  any accumulation  performed  by  of a i r bubbles  carefully  immersing  on o u t s i d e s u r f a c e s , then an opening  was  cut i n a c o r n e r of the pouch w h i l e d i r e c t l y under the f u n n e l .  Entrapped  gases  taken  were a l l o w e d  to  escape  and  be  collected.  prevent gases from e s c a p i n g beyond the f u n n e l a r e a . measured  by  displacement  d i f f e r e n t i a l due  of  water.  t o water h e i g h t was  A  p  W  P  V  to  Volumes of gas were  correction  necessary u s i n g the  ( l- h>  for  pressure  relationship:  ,m  l  where V j i s the volume of a i r a t atmospheric due  C a r e was  to the water l e v e l i n the buret (W^)  was  p r e s s u r e P^. calculated  The  from:  pressure  Figure 2.  Apparatus f o r destructive measurement of a i r .  -42-  W  IL^ i s the  height  of  measured volume and H  3.  water  V  - \  from  " <m  ' H^)  water  (6)  level  to  final  amount  yielded  third  standpoint, ence  air  from  of  after  air  volume  processing.  valuable.  on  non-destructive  shown i n Appendix  II.  water of the  pouch p o s t - p r o c e s s i n g  puts  same r e f e r e n c e  the vacuum packaged b r i c k ) may Similarly,  present  can  be  found  a  provided  the  measurements from  measurement.  Equations  From  mL/g  this  differ-  d e s c r i b i n g back  A measurement of the weight i n non-destructive  point.  Initial  and  destructive  volumes of a i r ( i n  be determined by d i f f e r e n c e s i n these  p r o j e c t e d weight  by  the  buret.  Combining i n f o r m a t i o n  measurements.  are  values.  i t s own,  performed, assuming a 1.0  calculations  the  i n the  Non-destructive  non-destructive  back c a l c u l a t i o n was  measurements a t  is  m  For example, d e s t r u c t i v e r e s u l t s were r e l a t e d  (post-processing)  the  mark; V  Measurements of A i r  r e l a t i v e volumes a t v a r i o u s s t a g e s .  these t e s t s was the  measurement  of  50 mL  i s the h e i g h t of water of each mL  mT|  Combining D e s t r u c t i v e and N o n - d e s t r u c t i v e Destructive  to  h  of  pouch i n water w i t h  c o r r e c t i n g non-destructive  a i r volume by  no  two air  calc-  ulated d i f f e r e n c e s . Each each run  processing  set  c o n s i s t e d of  were determined.  For  the  three  first  runs.  run,  Volumes of a i r f o r  the a i r volume was  as t h a t p r i o r t o p r o c e s s i n g , back c a l c u l a t e d from the f i n a l A i r measurements by  run  two  were  a i r volume.  the d e s t r u c t i v e method were used f o r volumes of a i r  i n pouches of the t h i r d run. of  taken  An e s t i m a t i o n of volumes of a i r i n pouches  c a l c u l a t e d by  from measurements b e f o r e and  one  after  half  the  processing.  d i f f e r e n c e between  values  -43-  III  Processing Conditions Overpressure  pressure.  processes  Operations  a r e c h a r a c t e r i z e d by r e t o r t  employing  c o n d i t i o n s as t h e f r a c t i o n temperatures. saturated  Fractional  steam  retort  pressure  retort  pressures  ventional  pressure from at  citation  steam and a i r mixtures  o f steam ( o r percentage steam  content  (absolute)  steam  and a i r .  specific  f o r water  temperature  retort  From  temperatures  t o these  steam) a t d e s i g n a t e d  i s calculated  at  refer  as t h e r a t i o o f  temperature  to  this  relationship,  can  be  and a i r p r o c e s s e s  and  total  desired  determined.  Con-  s t a t e s temperature  and  amount o f o v e r p r e s s u r e . In t h i s experiment water/air  processes  s i m i l a r r e t o r t c o n d i t i o n s f o r both steam/air and  were  studied.  V a r i a b l e s consisted of three  temp-  e r a t u r e s : 115, 120 and 125°C, and t h r e e p r e s s u r e l e v e l s c o r r e s p o n d i n g t o 65,  75  and  referred and  85%  steam.  Pressure  f o r water/air  t o as 1, 2 and 3 f o r each temperature,  85% steam, r e s p e c t i v e l y .  pressures. dition  levels  A  full  (a t o t a l  of  Table 2 l i s t s  factorial  design  18  was  runs)  with  Consequently,  three runs.  IV  experiments  temperatures  d u p l i c a t e runs  performed.  I t was at least  were performed  are  c o r r e s p o n d i n g t o 65, 75  a l l retort  pouches packaged w i t h b r i c k s c o u l d w i t h s t a n d runs.  processes  o f each  determined  and conthat  three consecutive  i n s i x sets,  each  with  A l l runs were c a r r i e d out i n random o r d e r .  Retorts Experiments  steam/air  were c a r r i e d out on t h r e e r e t o r t systems.  mixtures  overpressure.  and  the t h i r d  employed  superheated  Two  water  utilized with a i r  -44-  TABLE 2 Summary o f p r o c e s s i n g temperatures and p r e s s u r e s  Temperature, °C  % Steam ( P r e s s u r e L e v e l )  studied.  R e t o r t P r e s s u r e , kPa  115  65 (1)  259.9  115  75 (2)  225.2  115  85 (3)  198.8  120  65 (1)  305.2  120  75 (2)  264.5  120  85 (3)  233.4  125  65 (1)  356.8  125  75 (2)  309.2  125  85 (3)  272.8  as r e f e r r e d t o f o r w a t e r / a i r  processes  -45-  1.  Lagarde Steam/Air Phase one o f the experiments i n v o l v e d  scale  Lagarde  Pantry  retort  processing  i n an  industrial  ( J . Lagarde, Montelimar, F r a n c e ) l o c a t e d a t Magic  Foods I n c . , Hamilton, ON.  The p r o c e s s i n g p l a n t was equipped  4-car h o r i z o n t a l r e t o r t s of 1.1 m diameter and 4.6 m l e n g t h . retort this  was  used  system.  retort  for a l l trials.  A 9.3 kW  The same  Steam/air m i x t u r e s were employed i n  (12.5 hp) turbo  f o r c e d the h e a t i n g medium  f a n l o c a t e d a t the r e a r o f the  toward the door through two s i d e p l e n -  ums, r e t u r n i n g to the f a n a f t e r p a s s i n g through the r e t o r t l o a d , producing  a h o r i z o n t a l media  characteristic an  o f the r e t o r t  with  flow  design  pattern.  Media  flow  thereby  rates  were  and t h e r e f o r e were not v a r i a b l e by  operator. Desired  through  steam  steam/air  ratios  a d d i t i o n and t o t a l  pneumatic a c t i o n v a l v e s . although  were  Automatic  Process  temperatures  pressure  Automatic  manual c o n t r o l was  panel.  c o n t r o l was and  operation  programmed  pressures  and c o n t r o l l e d i n p u t s  by  temperature  control  by a i r i n t r o d u c t i o n through  p o s s i b l e with  ramping were i n p u t onto the c a r d . levels  achieved  of the system  a switchboard  on  was  the f r o n t  by use o f an aluminum  f o r time  profiles  An e l e c t r i c  and any  eye d e t e c t e d  o f steam and a i r .  used,  card.  desired  the d e s i r e d  In automatic  operation  t h e r e was a s h o r t v e n t i n g p e r i o d a f t e r "steam on" when the turbo f a n was not  i n operation.  during ulation  Following  c o o l i n g when c o l d o f water  during  the h e a t i n g  water was  added  c o o l i n g was  c y c l e , the f a n was turned o f f to f l o o d  ensured  the r e t o r t .  by c u r r e n t s  Circ-  created  with  pumps. A filled  retort  holds  four  cars  of racks  c o n t a i n i n g pouches.  In  -46-  all  cases  c a r number  pouches.  Ballast  orientation  four  cars  Although  r a c k s was a p p r o x i m a t e l y metal  were  o f t h e sample  "unconstrained".  t o improve  (closest  t o the door) was used  placed  i n a l l other  considered  3.8 cm.  circulation,  unconstrained,  ballast  determined  2.  pouches.  however, no spacer  levels  Flow  -  positive  flow  retort  between expanded  were  present.  Other l e v e l s were f i l l e d  Each sample pouch was randomly p l a c e d  Positive  were  p o s i t i o n s from the top were used  (position runs.  Steam/Air  A second phase o f experiments was c a r r i e d vertical  clearance  by random number g e n e r a t i o n ) f o r each s e t o f t h r e e  Vertical  Racking  T r a y s were made o f c o n v o l u t e d  f i f t e e n pouches were p l a c e d on each l e v e l .  with  positions.  c a r was h o r i z o n t a l and t h e p o u c h e s  Sample r a c k s i n the f o u r t h and seventh and  f o r sample  designed  out u s i n g a p i l o t  f o r steam/air  D e t a i l s o f c o n s t r u c t i o n and o p e r a t i o n employing s t e a m / a i r  scale  processing. i n t h i s system  have been r e p o r t e d elsewhere (Tung e t a l . , 1984a; Young, 1984).  A homo-  geneous steam and a i r environment was c r e a t e d by c o n t i n u a l f l o w o f media through tion; were  the system.  I t i s c a p a b l e o f f l o w i n upward and downward d i r e c -  however, upward introduced  through  a ring  a t t h e bottom  shaped m a n i f o l d  f o l d was connected Control  f l o w was used  i n this  through  with  experiment.  Steam and a i r  a cross spreader  and v e n t e d  h o l e s on the u n d e r s i d e .  The mani-  t o a vent l i n e a t the t o p o f the r e t o r t .  o f t h e system  was a t t a i n e d  e r a t u r e and p r e s s u r e c o n t r o l l e r Previously  described  conditions  were a d j u s t e d .  by a T a y l o r  ( T a y l o r Instruments  set points  of desired  temp-  L t d . , Toronto, ON).  temperature  and  pressure  regulated  through  the s e t p o i n t s .  A prop-  Proportional valves,  pneumatic a c t i o n by t h e c o n t r o l l e r , maintained  fullscope  -47-  ortional while  valve  on  the  p r e s s u r e was  steam  line  controlled  by  maintained  the  target  temperature,  a p r o p o r t i o n a l v a l v e on  the vent  line  (from the m a n i f o l d ) . Air were  was  mixed  added before  at  a constant  entering  adjusted  through  a  Limited,  Downsview, ON)  the  calibrated with  d e s i r e d medium f l o w r a t e was  r a t e to the cross  spreader.  Flowrator a head  steam l i n e  A i r flow  flowmeter  pressure  and  of  kPa  and  Porter  (gauge).  The  40 s t a n d a r d c u b i c f e e t per minute (scfm) or  68  nrVh a t standard c o n d i t i o n s of temperature and p r e s s u r e .  at  this  r a t e was  r a t e s were  (Fischer 414  the media  approximately  equivalent to f i v e  Medium f l o w  complete  changes  of  the r e t o r t environment per minute (Ramaswamy, 1983).  To a c h i e v e d e s i r e d  media  on  flow  rates,  rotameter  settings  were  based  the f o l l o w i n g  relationship:  Rotameter S e t t i n g  =  medium f l o w r a t e (scfm) (100% steam) ... calibration  A calibration Using 25.4  the  f a c t o r of  equation,  .394  settings  f o r 75% steam and  15.2  Samples were p r e s s u r e introduced air.  near  the  s c f m / u n i t x 100  retort  cooled bottom  was  previously 35.5  70-80°C.  Retort  pressure  steam,  steam. i n a l l experiments. while  maintaining  Cold  then  slowly  water  overpressure  an i n t e r n a l temperature  was  determined.  f o r 65%  E l e v a t e d p r e s s u r e l e v e l s were s u s t a i n e d f o r the f i r s t  c o o l c y c l e u n t i l samples reached ly  factor  f o r c o n d i t i o n s were  f o r 85%  (7)  reduced  of to  was with  p a r t of the approximateatmospheric  pressure.  ance  A rack  was  above  each  constructed to provide h o r i z o n t a l level  was  adjusted  to  3.2  cm  by  positioning. supports  to  Clearprovide  -48-  " u n c o n s t r a i n e d " p o s i t i o n i n g o f pouches. spacer  levels  package. levels the  between  sample  t o ensure  circulation  around t h e  Each l a y e r was hexagonal i n shape and h e l d f i v e pouches. S i x  were assembled  assembly  to hold  reached  a l l sample b r i c k s .  approximately  samples were a d e q u a t e l y  3.  layers  Racks were made w i t h a d d i t i o n a l  The f i n a l  15 cm b e l o w  height of  the manifold. A l l  immersed d u r i n g c o o l i n g .  V e r t i c a l P o s i t i v e Flow - Water/Air The  pilot  implement  scale v e r t i c a l  p o s i t i v e f l o w r e t o r t was a l s o m o d i f i e d t o  water/air processing.  w i t h i n t h e same v e s s e l .  C o n t r o l o f temperature  to t h a t d e s c r i b e d f o r s t e a m / a i r tained  water heated  steam  spreader  T h i s would enable  comparison  and p r e s s u r e was s i m i l a r  o p e r a t i o n , except  that the r e t o r t  by steam and a g i t a t e d by a i r a d d i t i o n  a t t h e bottom.  Although  o f media  the a i r f l o w  con-  through t h e  r a t e s were not  n e c e s s a r i l y e q u i v a l e n t t o f i v e changes o f r e t o r t environment per minute, they  were  Variations  c o n s i s t e n t with  flow  i n operation occurred  rates during  used  with  steam/air  t h e "steam  processes.  on" and " s t a r t o f  c o o l " o p e r a t i o n s and w i l l be e l u c i d a t e d . P f l u g and B o r r e r o (1967) d e s c r i b e d use o f water p r o c e s s i n g w i t h a i r overpressure involved water. This  i n a retort  filling  of similar  design.  Their operation  procedure  t h e r e t o r t w i t h water, then a p p l y i n g steam t o heat t h e  U s i n g t h i s t e c h n i q u e , come-up times o f 17 minutes were r e p o r t e d .  was  therefore,  considered a  method  unacceptable was  developed  f o r comparison whereby  with  preheated  other water  systems; could  be  introduced to the r e t o r t . The h o t water r e s e r v o i r on an FMC 500W U n i v e r s a l S t e r i l i z e r  (F.M.C.  -49-  Corporation,  Santa  Clara,  d e s i r e d temperatures. a  steam  injection  CA)  The  port,  was  then  back i n t o  connected  from  the  storage  the  A 3.8  reservoir  cm  determined  that  vessel.  Only  ( o u t s i d e diameter)  t o the  p o s i t i v e f l o w r e t o r t f o r t r a n s f e r of preheated trials  p r o c e s s i n g water t o  the  employed, so v a l v e s e n t e r i n g the p r o c e s s i n g  v e s s e l were c l o s e d a t a l l t i m e s . was  t o pre-heat  r e t o r t used a pump t o c i r c u l a t e c o l d water t o  r e s e r v o i r of t h i s system was  pipe  used  water  should  be  bottom vent water.  preheated  flexible  line  of  the  A few p r e l i m i n a r y  to  10C°  higher  than  that desired f o r processing. A driving ential  f o r c e f o r the t r a n s f e r was  between  additional  vessels.  a i r pressure  Since  the  c r e a t e d by a p r e s s u r e  difference  (approximately  i n height  70 kPa)  was  differ-  was  minimal,  introduced  to  r e s e r v o i r j u s t p r i o r t o "steam on" e n s u r i n g r a p i d t r a n s f e r o f the water.  The  elevated vessels  water  pressure was  receiving  temperature  and  by  the  Cooling  was  set  Differential  pressure  the vent  line  to maintain  pressure  controller  proportional valve  an  between  s e t p o i n t on  the water t r a n s f e r v a l v e s were opened and was  simultaneously  processing vessel.  a l l pouches were immersed  a i r was  valve  heated  the  remained  transfer.  v a l v e s were c l o s e d . and  keeping  controller  the  control  transfer.  v e s s e l a t z e r o , so  At "steam on"  to  during  upheld  open d u r i n g the  steam  reservoir  the  Operating  set to i n i t i a t e  Once water  (as i n d i c a t e d p r e s s u r e was  reached  the  the i n p u t of  the d e s i r e d  on a s i g h t g l a s s ) , then  retort  s e t by the  level  transfer  controller  introduced. o p e r a t i o n s were s i m i l a r  t o s t e p s performed  s t e a m / a i r media w i t h a few d i s t i n c t d i f f e r e n c e s .  when  employing  A f t e r steam was  turned  -50-  off,  hot water  that  almost  was  drained  a l l hot  water  from the r e t o r t . was  removed  Care was  taken t o ensure  w i t h o u t a decrease i n p r e s s u r e  which was m a i n t a i n e d by a d d i t i o n o f a i r .  C o l d water was  then i n t r o d u c e d  through the bottom water l i n e and c o o l i n g proceeded as d e s c r i b e d  earlier  f o l l o w i n g steam/air processes.  V  Data A c q u i s i t i o n  1.  Temperature Samples  P r o f i l e Measurement  prepared as  previously  described  were  randomly  placed i n  r a c k p o s i t i o n s determined by random number t a b l e s (Khazanie, 1979). e x t e n s i o n thermocouple w i r e from the sample was ing  24 AWG  mental  copper c o n s t a n t a n wire f i t t e d  temperatures  wire) with fused of  the two  were  tips.  monitored  by  connected t o c o r r e s p o n d -  through the r e t o r t . s i x thermocouples  In the Lagarde r e t o r t ,  sample t r a y s were m o n i t o r e d .  The  Environ-  (of  similar  t h r e e l o c a t i o n s on each  In the v e r t i c a l p o s i t i v e f l o w  systems, two thermocouples were s e c u r e d on a l t e r n a t e sample l a y e r s . thermocouples  with  c o n n e c t i o n s were  thermometer u s i n g a steam A  precalibrated  Columbus, OH) was was  fitted  calibrated  pressure  transducer  (Model  A-5/1148,  of  retort  Sensotec,  used t o monitor r e t o r t p r e s s u r e d u r i n g p r o c e s s i n g .  t o a b l e e d e r p o r t on top o f the Lagarde r e t o r t  voltage  the  environment.  the upper s i d e o f the v e r t i c a l p o s i t i v e ation  against  All  10 V  (DC)  was  provided  flow r e t o r t . using  It  or a p o r t  on  A constant e x c i t -  a Hewlett-Packard power  s u p p l y (Model #62148, Hewlett-Packard Co., Rockaway, N J ) . A Doric for  logging  Digitrend data  235  (Doric  f o r experiments  Scientific, performed  San  Diego,  a t Magic  CA)  was  used  P a n t r y Foods.  Kaye Ramp I I S c a n n e r / P r o c e s s o r (Kaye Instruments I n c . , B e d f o r d , MA)  A was  -51-  used  f o r experiments  Channels channel  from  from  performed  thermocouples  i n the v e r t i c a l were  Readings were taken a t one minute  through a 35 minute 6-7  minutes  minutes  were  period  typical  (including  were c h a r a c t e r i s t i c  come-up  f o r each  Channel subsequent  i n t e r v a l s from steam on  time).  Come-up times of  whereas 4-6  times i n the p i l o t  and w a t e r / a i r systems, r e s p e c t i v e l y .  2.  come-up  i n the Lagarde,  systems.  read i n m i l l i v o l t s .  numbers and thermocouple c o n n e c t i o n s were i d e n t i c a l set of runs.  flow  t o r e a d i n °C and t h e  programmed  the p r e s s u r e t r a n s d u c e r was  positive  minutes  and  3-5  s c a l e steam/air  C o o l i n g data were not c o l l e c t e d .  A n a l y s i s of H e a t i n g Rate Index ( f ^ ) Data were r e c o r d e d on both a paper s t r i p from the data l o g g e r and a  magnetic  tape.  A  Columbia  300D D i g i t a l  Data P r o d u c t s I n c . , Columbia,  MD)  Cartridge  Recorder  (Columbia  connected t o the a u x i l i a r y  I/O board  of the data l o g g e r through an RS232 c a b l e was used f o r r e c o r d i n g on the magnetic  tape.  microcomputer  Data (Apple  on the tape were t r a n s f e r r e d Computer  t o an Apple I I P l u s  I n c . , C u p e r t i n o , CA)  u s i n g programs developed f o r t h i s  for  computations  purpose.  One s t e p i n v o l v e d e x t r a c t i o n of e n v i r o n m e n t a l temperatures f o r each run.  O v e r a l l mean temperature from time o f s t a b i l i z a t i o n t o end of cook  was c a l c u l a t e d  as r e t o r t  the s t r i p tape p r i n t o u t . 30 was c a l c u l a t e d .  temperature.  R e t o r t p r e s s u r e s were taken from  An average mV r e a d i n g from minute 15 t o minute  R e t o r t p r e s s u r e (Pp i n p s i g ) of each run was d e t e r -  mined by:  (mV, mean  11.395) (8)  0.834  -52-  T h i s r e l a t i o n s h i p was The  v a r i a b l e used as a b a s i s f o r comparison of h e a t i n g  the h e a t i n g over  time  using  p r e v i o u s l y determined by c a l i b r a t i o n t e c h n i q u e s .  r a t e index ( f ) , as d e s c r i b e d n  for  each  a program on  difference  b r i c k were e x t r a c t e d the  microcomputer.  between r e t o r t and  logarithmic  ordinate  as  a  evaluated  as the n e g a t i v e  this  determined  line  index  by  ( f ) represented h  t i o n i n g value.  function  the  behavior. samples, these  as  the  well,  Slightly  particularly  samples,  limits  f ^ values  In t h i s point  of  (g  v a l u e ) was Heating  time  ( i n minutes) r e q u i r e d  broken h e a t i n g  those  and  p l o t t e d on index  heating with  chosen  The  curves  large  to  of  rate  f o r a log reducrates.  (1983) found were  amounts of  represent  heating  the  a  apparent included  of  similar  for  some  air.  For  "straight-line" on the  a was  c u r v e s i n some samples  Kohnhorst  portion  ordinate.  Data Treatment For each s e t of c o n d i t i o n s , h e a t i n g  f u n c t i o n of i n c l u d e d a i r volumes. after ing,  temperature  rate  indicated f a s t e r heating  Berry  broken  l e a s t squares.  were taken from a c o n s i s t e n t i n t e r v a l of g v a l u e  3.  profiles  were determined  program the  time.  method of  Lower f ^ v a l u e s  bricks;  and  Temperature  was  r e c i p r o c a l s l o p e of a s t r a i g h t - l i n e p o r t i o n  Ramaswamy (1983) r e p o r t e d packaged  center  earlier.  behavior  vacuum packaging and a  exactly  continuum as  of  targeted  small  Due but  each  of  a  to v a r i a t i o n i n the amount of a i r measurable leakage d u r i n g  a i r measurements for  r a t e i n d i c e s were measured as  the  resulted. duplicate  process-  A i r volumes were runs.  Therefore,  not to  ensure a homogeneous continuum, d u p l i c a t e runs were combined. Regression  analysis  was  used  to  describe  the  e f f e c t of  residual  -53-  gases  on  heating  rate  between f a c t o r s s t u d i e d covariance conditions  (Snedecor,  indices.  Comparisons  of  these  i n the experiment were performed by a n a l y s i s of 1965).  Analysis  on bare b r i c k s i n c l u d e d  of v a r i a n c e  was  by UBC MFAV  ( L e , 1978).  on the UBC Amdahl 470 V/8  computer.  done  for  a l l  i n each r u n .  Computations were performed f o r a n a l y s i s o f v a r i a n c e analysis  relationships  Both program  and c o v a r i a n c e  packages were a v a i l a b l e  -54-  RESULTS AND DISCUSSION I  Air  Measurement  The n o n - d e s t r u c t i v e measurement o f a i r u t i l i z e d  p r o v i d e d a f a s t and  r e l i a b l e method o f m o n i t o r i n g r e s i d u a l gas entrapped  i n a package.  weight o f pouches i n water were measured t o w i t h i n 0.1 g. volume  changes  previously  t o 0.1 mL  described  destructive  were  measurements  measurement.  based  and  The r e s u l t a n t  w i t h subsequent  c a n be  detected. on c o u p l i n g  volumes  Back  Consequently,  calculations  information  quantified  by  from  non-  destructive a i r  "no a i r weight" was v a l u a b l e  industry  i n comparison  performs d e s t r u c t i v e measurements as a r o u t i n e  q u a l i t y c o n t r o l t e s t f o r r e s i d u a l a i r i n pouches.  S i n c e the a n a l y s i s i s  d e s t r u c t i v e i n n a t u r e , o n l y a s m a l l r e p r e s e n t a t i v e sample i s t e s t e d . opening  a pouch immersed  i n water r e n d e r s  u s a b l e f o r other q u a l i t y c o n t r o l purposes. ments as d i s c u s s e d  results  may  N o n - d e s t r u c t i v e a i r measure-  by Shappee and Werkowski (1972) c o u l d  be u n r e l i a b l e .  non-destructive specific f i l l air  a i r measurement  weights.  measurements  density  be a c c e p t a b l e .  on Archimedes'  f o r an " o n - l i n e "  principle.  with  such a method f o r  I t required  a known  t o be packaged and a v a l u e of weight and volume  contributed  by an empty  homogeneous  product.  package i n a i r ,  t o employ  t o automated packaging  H u e r t a - E p i n o s a (1981) u t i l i z e d  based  o f the product  There i s a p o t e n t i a l applicable  In  the c o n t e n t s un-  However, as found i n t h i s study, some methods can be d i f f i c u l t and  as  readings.  Presently,  addition,  The  pouch.  These would be c o n s t a n t  Consequently,  from  the f o l l o w i n g r e l a t i o n s h i p  fill  weight  applies:  values  for a  o r weighing the  -55-  V  W 5  s-  ""  P C h  +  Vh  •••(«  ^pr where V of  i s volume  g  the sample  o f the sample e x c l u d i n g a i r ,  and  weight of an  volume of the pouch and  ^  p  i  s  t  h  empty  pouch  W  g  a r e weight  respectively,  product d e n s i t y .  e  and  Vp ^ c  i s the  The package volume  excluding a i r could  be determined.  If f i l l  weights were c o n s t a n t ,  may  value  require  an  be  a  constant  Next, the package would as  and  not  be weighed w h i l e  additional  this  measurement.  suspended i n water.  A volume  c o n t r i b u t e d by the package, c o n t e n t s and a i r i s c a l c u l a t e d from: W V sa v  ~  - W s  ws P  where V when  i s volume  g a  suspended  volume  w  of sample and a i r ,  i n water  and  of a i r entrapped  p  ^  within  . . ... (10)  i  st  h  W e  wg  i s the weight of the sample  density  a pouch  of water.  Therefore,  c a n be c a l c u l a t e d  from the  d i f f e r e n c e between the two v a l u e s found i n e q u a t i o n s (9) and ( 1 0 ) . If  fill  performed  weights were  by o n l y  adequately  obtaining  immerse  the vacuum s e a l e r .  the pouches i n a s h a l l o w  be suspended and weighed.  this  analysis  may  be  the weight of the pouch i n water. I t c o u l d  be performed j u s t as the pouch l e f t would  consistent  A conveyor b e l t  trough and random  samples would  Other i n d u s t r i e s have implemented the buoyant  e f f e c t as a c r i t e r i o n f o r g r a d i n g p r o d u c t s ; f o r example, peas a r e p l a c e d in  a flotation  tank c o n t a i n i n g b r i n e t o s e p a r a t e mature from green p r o -  d u c t s (Cruess, 1958).  -56-  II  Unpackaged Bricks Unpackaged b r i c k s were i n c l u d e d i n each r u n .  by  which  factors  may  be  studied  independently  r e s i d u a l gases.  An a n a l y s i s of v a r i a n c e was  experiment  thin  for  a n a l y s i s are was  found  centage  thick  bricks  tabulated i n Table  3.  No  Ramaswamy  level).  (1983) where  (p>0.05) f o r n y l o n  temperatures  is  similar  bricks  This finding  This  performed  significant  the  difference  vertical  and the  found  reported  i n Table retort  evident  with  retorts  difference  4.  were  either were  retort from  flow r e t o r t  yielded  In  was  regard  w a t e r / a i r or to  be  bricks. employing  slightly  lower  seen test  to  significantly  found  when p r o c e s s i n g t h i c k positive  (p>0.05) per-  findings  of  non-significant  positive  flow  and  Lagarde  demonstrates t h a t a l l t h r e e p r e s s u r e l e v e l s  Duncan's m u l t i p l e range  Lagarde  All  the  and  have the same e f f i c i e n c y of h e a t i n g on an unpackaged sample  significant  retorts.  of  steam  which e x c l u d e s the p o t e n t i a l e f f e c t s of the pouch and r e s i d u a l A  of  factorial  Results  c o n s i s t e n t with were  effects  on the  of temperature  factors  i n both  without  separately.  i n heating rates for variables (pressure  retorts.  and  They p r o v i d e a means  i n the was  data  performed  thin  bricks,  faster  (low  steam/air  are  heating rates i n  the  f^  and  different results  i n the  significantly  from  gases.  values) pilot  different  than  scale  from  retort.  each  H i g h e s t mean f ^ v a l u e s were found steam/air. heating  Water/air  rate  indices,  p r o c e s s i n g i n the Lagarde system were lowest.  were  other i n the  media i n the same and  values  I t i s evident  found from  these r e s u l t s t h a t p r o c e s s i n g of unpackaged b r i c k s i n the Lagarde system may  p r o v i d e more e f f i c i e n t  heat  v e r t i c a l p o s i t i v e f l o w systems.  t r a n s f e r than w a t e r / a i r or steam/air i n  -57-  TABLE 3. A n a l y s i s of v a r i a n c e f o r h e a t i n g r a t e i n d i c e s of unpackaged t e f l o n b r i c k s .  df  Thin F-Ratio  df  Thick F-ratio  Retorts  2  6.46**  2  20.94**  Temperature  2  1.57  ns  2  0.15  ns  level  2  1.55  ns  2  0.47  ns  R e t o r t s - Temperature  4  1.11  ns  4  0.07  ns  R e t o r t s - Steam  4  0.38  ns  4  0.71  ns  Temperature - Steam  4  0.71  ns  4  1.04  ns  Source of V a r i a t i o n  Steam % - P r e s s u r e  Interactions  81  Error  ns not s i g n i f i c a n t  (p>0.05)  ** s i g n i f i c a n t a t p<0.01  81  -58-  TABLE 4 Duncan's m u l t i p l e range t e s t f o r h e a t i n g r a t e s o f unpackaged b r i c k s in different retorts.  Thin Bricks  Thick  Bricks  Retort f ^ (min)  Duncan Test'''  f ^ (min)  mean ( s t d . dev.)  mean ( s t d . dev.)  Lagarde  6.08 (0.31)  17.78  (0.80)  Steam/Air  6.42 (0.51)  19.24  (1.09)  Water/Air  6.46 (0.65)  18.32  (0.83)  V a l u e s w i t h the same d i f f e r e n t (p>0.05)  Duncan Test''  letter  within  a  column  a r e not s i g n i f i c a n t l y  -59-  Previous Ramaswamy indices for  studies  (1983) found  of unpackaged  s i l i c o n e rubber.  kernel  found  large  coefficients  bricks  ranging  Heating  indicated  variability  of v a r i a t i o n from  f o r heating  A.5-5.1% f o r n y l o n  no r e s i d u a l  (1983) w i t h c o e f f i c i e n t s  bricks.  vary from  potatoes  and 6.A%  of v a r i a t i o n  o f 9.9%.  As  i n s e t s o f data  5-10% f o r t h i n b r i c k s and A.5-5.7% f o r t h i c k  I n c o n t r a s t , experiments  penetration with  rate  a i r were r e p o r t e d by  i n T a b l e 5, s i m i l a r c o e f f i c i e n t s o f v a r i a t i o n  each r e t o r t  i n f ^ values.  r a t e i n d i c e s f o r pouches c o n t a i n i n g whole  corn i n brine with e s s e n t i a l l y  B e r r y and Kohnhorst  from  have  by P a t i n o  and H e i l  (1985) on heat  i n b r i n e (no volumes o f a i r r e p o r t e d ) showed  c o e f f i c i e n t s o f v a r i a t i o n i n the order o f 15.9-25.5%. A v a l u e o f thermal  diffusivity  ( a ) may be c a l c u l a t e d  from  measured  h e a t i n g r a t e i n d i c e s and b r i c k geometry by the r e l a t i o n s h i p r e p o r t e d by Olson and Jackson  .933  a=  whereby  The average  m /s f o r t h i c k —7  1.09  x 10  T a b l e 1.  (11)  a , b and c a r e o n e - h a l f  respectively. 10  (19A2):  brick  calculated  and 1.02 x 10  t h i c k n e s s , l e n g t h and w i d t h  thermal  d i f f u s i v i t i e s were 8.82 x  m /s f o r t h i n  bricks  9 m /s c a l c u l a t e d  from t h e r m o p h y s i c a l  p r o p e r t i e s of t e f l o n i n  D i f f e r e n c e s may be due t o the composition o f t e f l o n from which  the b r i c k s were made or p o s s i b l e e f f e c t s o f the p l a s t i c used  compared t o  t o secure thermocouples a t b r i c k c e n t e r .  rubber  compound  -60-  TABLE 5. C o e f f i c i e n t s of v a r i a t i o n f o r h e a t i n g r a t e of unpackaged b r i c k s .  Brick Thickness  Thin  Retort  P o s i t i v e flow steam/air Positive  C o e f f i c i e n t of V a r i a t i o n , % ( s t d . dev./mean) x 100  8.0  flow  water/air  Thick  indices  10.0  Lagarde  5.2  P o s i t i v e flow steam/air  5.7  Positive  flow  water/air  A.5  Lagarde  4.5  -61-  III  Packaged Bricks: Heating  rate  Included Air  indices  containing  a i r processed  Figures  and 4  bricks  3  i n retort  a r e examples  processed  illustrated  ( f ^ , min) were  i n Appendix  f i g u r e s , a general  conditions  o f data  i n the Lagarde  found  as p r e v i o u s l y  collected  retort.  i n the data  conditions, particularly  from  A l l other  I I I ( a , b, c and d ) .  trend  for a l l test  was e v i d e n t .  level  ships  line.  conditions two  ( u s u a l l y 75% steam, p r e s s u r e  sections;  described  horizontal  one being  level  a horizontal line  and t h i c k  o f these  I t appears t h a t some  rate indices.  a  thin  By o b s e r v a t i o n  those o f 65% steam ( p r e s s u r e  essentially  described.  relationships are  e f f e c t o f i n c l u d e d a i r volumes on h e a t i n g form  packages  Data  1) showed no  These r e l a t i o n f o r some  other  2) appeared t o c o n s i s t o f  s i m i l a r t o the r e l a t i o n s h i p  above and a second p a r t demonstrating an i n c r e a s e i n f ^ as a i r  volumes i n c r e a s e .  T h i s trend  was apparent i n many c o n d i t i o n s .  Another  type of r e l a t i o n s h i p was observed f o r c o n d i t i o n s o f 115°C and 85% steam (pressure plateau  level  3) w i t h  and f ^ v a l u e s  Therefore,  thick bricks. increased  There i s no apparent s e c t i o n of  a t very  low l e v e l s  of included  the r e l a t i o n s h i p o f f ^ as a f u n c t i o n o f a i r content  air.  can be  described  as c o n t a i n i n g e i t h e r one or both s e c t i o n s of a two p a r t model.  One  exists  part  effect umes  by i n c r e a s i n g  system  plateau  on f ^ ; the other  distinct  behavior used.  periphery brick  as a  A  f ^ values  patterns plateau  are f i l l e d  surface  part  with  so heat  demonstrating describes with  exist  a i r volumes  the changing e f f e c t  increased  may be e x p l a i n e d may  that  when  of a i r v o l -  a i r contents.  These two  by the nature o f t h e model  void  areas  around  the b r i c k  a i r , but an a i r l a y e r has not formed  transfer  have no  i s maintained.  Heating  rate  on the indices  -6216 15-  Legend  14-  A  13-  6 5 % steom  X 755! steom •  12-  8 5 % steom  1110-  »H *x  8-  X Xn  7-  x  Ai x »  X  •  D A D  •  4<A  x  x  6-  1615-  Legend  14-  A  6 5 % steom  13-  x  75% tliom  12-  D  8 5 % steam  • x  v  •d  c  11-  o cc  10-  ct> _c  9H  o  8-  01  x  X 7-  D X  ;  to 6-  ^  A  B  x x  4  X •  •  x  A  *  A ^  A  A A  A  X  1615-  Legend  14A  65% stiam  13-  X 75% itiom  12-  •  8 5 % steam  1110-  s87-  A X  A  A A  A  X  A x  A  4  6510  IS  20  25  — i — 30  35  Included A i r (mL)  Figure 3.  Heating rate index as a function of included a i r ; Lagarde r e t o r t , thin bricks, (a, 115°C; b, 120°C; c, 125°C)  -633 4 3 3 3 2  Legend  31  /} 653  3 0 2 9 2 8  •  steom  x  75X sleom  •  853  O  D •  sleom  27 2 6  X  2 5  x  24  D  X  2 3 2 2  A  x x  * x  x  O  V  21 2 0  A  x  19 18  31 3 0  Legend  29  I " x  0)  "D  C  £  "5  2E  steom  x  753  steom  D  85%  iltom  2 5 24 2 3  C  2 2  S  21  1  A 653  0D  A  x  2 0 19 18  31  3 0 -  Legend  2 9 2 8 -  £  653  steom  2 7 -  X  753  steom  2 6  •  853  steam  2 5  2 4 2 3  2 2 21 2 0  D  8  X  A  1918 17  i K>  15  2 0  2 5  3 0  35  Included A i r (mL)  Figure A.  Heating rate index as a function of included a i r ; Lagarde r e t o r t , thick bricks, (a, 115°C; b, 120°C; c, 125°C)  -64-  begin  t o i n c r e a s e once the o u t e r v o i d  layer  o f a i r begins  t o form  over  l o c a t i o n s have been f i l l e d  the brick  face.  and a  D i f f e r e n c e s between  c o n d i t i o n s may be due t o the volumes o f a i r a t which a t r a n s i t i o n one  p a r t to the o t h e r o c c u r s .  line,  I n c o n d i t i o n s d e s c r i b e d as a h o r i z o n t a l  the t r a n s i t i o n or b r e a k - p o i n t would occur a t volumes o f a i r l a r g e r  than the maximum t e s t e d . umes demonstrate a very break-point Due  Cases where f  i n two ways.  i n c r e a s e s a t very low a i r v o l -  s m a l l o r i m p e r c e p t i b l e p l a t e a u , so no  apparent  o f t h e data, comparisons between v a r i a b l e s were First,  volumes of a i r a t which a t r a n s i t i o n  p l a t e a u r e g i o n t o an upward  Secondly,  n  exists.  t o the nature  performed the  from  comparisons  were  made  trend  ( i f i t e x i s t s ) were  between  c o n d i t i o n s where  from  determined. appreciable  data e x i s t e d i n the upward s e c t i o n or p a r t two o f the model.  IV  Break-point  1.  Determination In  65%  Values of Break-point  a l l retorts,  the f ^ v s . i n c l u d e d a i r r e l a t i o n s h i p s a t 125°C and  steam or p r e s s u r e l e v e l  expected  s i n c e these  tested.  Due t o f l e x i b i l i t y  1 exhibited a horizontal line.  conditions represent  the h i g h e s t  retort  pressure  o f the pouch, i t has been shown t o respond  to  t h e o r e t i c a l p r e s s u r e volume r e l a t i o n s h i p s  is  c l e a r from  level  T h i s may be  (Nelson e t a l . , 1956).  It  the data t h a t c o n d i t i o n s o f 125°C and 65% steam ( p r e s s u r e  1) l i m i t  pouch  expansion  so no r e s t r i c t i o n  on h e a t  transfer  o f the r e g r e s s i o n was performed  to s t a t -  o c c u r r e d i n the range o f a i r volumes t e s t e d . A  test  istically hypothesis  on s i g n i f i c a n c e  determine  i f a horizontal  o f s l o p e equal  line  exists  (Zar,  1974).  t o zero was t e s t e d u s i n g a Student's  A  null  t-test.  -65-  Results for  of  this analysis  each  Based  thickness  on  this  all  Student's  exists  between  exists  Results of  t-test  f  as  n  these  i n Table  six  1 was  packaged  between  relationship  lines  finding,  steam/pressure l e v e l A  i n Table  cases.  horizontal  and  also  used  to  unpackaged  function  of  the  two  line  i t i v e flow r e t o r t w i t h t h i n b r i c k s .  of  establish  against  bare  means d i f f e r was  no  a i r for  attributed  and  10  edges  mL  to  of  an  water  extended  added  added.  outward  the  possible  caused  reduced  baseline f  values.  n  (p<0.05) i n f i v e  demonstrated  to heat  Another  and  relationship  i n the  In a l l cases the mean f  resistance  65%  difference  brick  f o r packaged b r i c k s than t h e i r unpackaged c o u n t e r p a r t s . be  and  comparison.  if a  Since  and  (p>0.05).  125°C  f o r means of  included  significant difference  in a l l retorts  horizontal  bricks.  were compared  7 show t h a t  that  essentially  used as a b a s e l i n e  values  No  were  the  was  a  6 indicated  media  was  pos-  larger  Differences  transfer  reason  h  out  from the  may  be  may  pouch  that  pouch  c i r c u l a t i o n between  samples. Comparisons variance  analysis  respective because which  with  baseline.  they  had  displayed  slope,  level no  between  or  a l l conditions  Thick  no  and  thin  in  bricks  significant difference  overall  (p>0.05) were  evidence  d i f f e r e n c e was  were c o n s i d e r e d  lines  d i f f e r e n t magnitudes of  statistical  significant  for  regression  of  a  determined  were  performed  using  co-  each  retort  against  the  were a n a l y z e d  baselines. from  Those  the  considered  break-point.  separately conditions  baseline as  horizontal  Conditions  i n e i t h e r slope  in  or l e v e l  either lines  where  (p<0.05)  to have an upward s e c t i o n ( i n a l l c a s e s , e i t h e r s l o p e  l e v e l were h i g h e r ) .  a  or  -66-  TABLE 6. T e s t f o r s i g n i f i c a n c e o f s l o p e of the b a s e l i n e 125°C-65% steam w i t h Student t - t e s t . H : slope = 0 . Q  Brick  Retort  Slope (min/mL)  0.012  Lagarde  Thin  Thick  ns  Thickness  t  calc  0.0319 ns  P o s i t i v e flow steam/air  -0.0032  -0.0055 ns  P o s i t i v e flow water/air  0.0089  0.0515 ns  Lagarde  0.0041  0.0055 ns  P o s i t i v e flow steam/air  0.0056  0.0046 ns  P o s i t i v e flow water/air  0.0009  0.0015 ns  not s i g n i f i c a n t (p>0.05): a c c e p t  H  0  -67-  TABLE 7. Student t - t e s t on f o f unpackaged b r i c k s compared t o f v a l u e s o f b a s e l i n e . H : vi = y h  h  Q  2  mean f ^ , min Brick  Thin  Thick  Retort  unpackaged  packaged  t  calc.  Lagarde  6.08  6.83  6.24**  P o s i t i v e flow steam/air  6.42  6.71  1.91 ns  P o s i t i v e flow water/air  6.46  6.95  3.97**  Lagarde  17.78  19.74  7.58**  P o s i t i v e flow steam/air  19.24  19.49  2.56*  P o s i t i v e flow water/air  18.32  20.12  6.18**  ns  not s i g n i f i c a n t (p>0.05)  *  s i g n i f i c a n t a t p <0.05: r e j e c t  H  Q  **  s i g n i f i c a n t a t p <0.01: r e j e c t  H  Q  -68-  The  procedure  p o i n t s may frame. use  be  used  f o r determining  d e s c r i b e d as  T h i s concept was  covariance  p o i n t s of t r a n s i t i o n analysis  in a different application.  I t was  cluded  for  fluctuation  line  the  last  a i r volumes.  allowed  stage  with  as  in  the  the  significant  data.  i n each  c o n d i t i o n were  difference  significant The  determined  still  no  by  the  significant  line  A i r volumes up t o the determined  larger  a i r volume  different ditions  from  with  consistently  As was  for  (p>0.05)  against  a  are  represents listed  represented performed  normal at  each  the  the  the  the  base-  performed.  baseline  from  frame e x h i b i t transition  or  8 and  An  i n Tables  9.  on a l l data up t o the b r e a k - p o i n t as  (p>0.05) from  In a l l c a s e s ,  there  was  the r e s p e c t i v e b a s e l i n e s .  b r e a k - p o i n t s were then c o n s i d e r e d to be  included,  of  t h a t amount  the a n a l y s i s was  i n F i g u r e 5.  determined  the b a s e l i n e .  evidence  was  because  i n a l l r e s p e c t s , from  compared  values  difference  the p l a t e a u r e g i o n .  yet  analysis  performed  of d e c r e a s i n g a i r c o n t e n t s u n t i l  performed  dashed  (p>0.05) i n  p o i n t s of h i g h e s t i n -  h i g h e s t a i r volume of the f i r s t  a d d i t i o n a l comparison was illustrated  test,  s c h e m a t i c a l l y d e p i c t s how  ing  breakpoint.  the  difference,  The  no  of  Covariance  respective retorts.  data  p o i n t s were chosen  sensitivity  significant  F i g u r e 5.  Frames  data  difference  the h i g h -  The moving frame was  ten c o n s e c u t i v e  frame moved i n order  showed no  line.  Ten  desired  a moving r e g r e s s i o n  employed to determine  e i t h e r s l o p e or l e v e l from the b a s e l i n e . beginning  break-  p r e v i o u s l y d e s c r i b e d by Tung e t a l . (1984a) f o r  e s t a i r volume a t which d a t a show no  by  on  or  by the moving r e g r e s s i o n frame, i f a the  relationship  became  These a n a l y s e s were performed break-point.  a l l retorts,  The  processing  significntly on a l l con-  same method was conditions  and  repeated brick  Positive  Baseline  Air  (mL)  Flow Steam/Air - T h i n  115  Condition  Air  f. (min) n  C - 7 5 1 Steam (mL)  f, ( m i n ) n  3.5  7.82  0.5  6.53  5.1  7.06  1.6  5-3  7-26  2.0  7.15 6.68  5.3  6.61  2.9  7.00  5.6  6.11  3.6  6.63  6.0  7.6  6.81  9.2  5-98 7.44  8.6  6.81  9-A  6.96  8.8  9.9 10.8  6.22  9.  7.15 7.28  7.51  9.6  10.9  10.2  18.3  6.3A 6.28  7.75 6.88  15-0  8.87  18.4  6.43  16.3  8.69  18.5 18.8  6.50  16.5  o.Sk  6.07  17.3  7.35  19-3  6.13  20.5  9.37  20.7 20.8  6.13  21.1  9.31  6.79  22.0  21 .1  6.09  28.6  7.23  27.1 30.2  9.9^ 10.86  29.1  7.33  32.3  29.2  7.24  h  ns  11.5^ 10.02  order  ns  not s i g n i f i c a n t  *  significant  Figure  5-  at  Bricks  of  performance  (p>0.05) p<0.05.  Moving r e g r e s s i o n frame performed w i t h to determine b r e a k - p o i n t s .  covariance  analysis  -70-  TABLE 8. B r e a k - p o i n t v a l u e s o f t h i n b r i c k s determined by c o v a r i a n c e a n a l y s i s on a moving r e g r e s s i o n frame.  B r e a k - p o i n t V a l u e s (mL) Retort  Positive flow steam/air  Positive flow water/air  Lagarde  Temperature °C  65% steam (1)  115  17.0  10.2  9.0  120  29.5  18.5  13.6  125  29.2  28.8  9.1  115  29.2  1  24.8  15.9  120  30.8  1  28.2  24.6  125  30.4  115  29.8  1  20.3  11.6  120  28.7  1  26.0  14.4  125  31.7  1  31.8  <5.0  ns t o maximum a i r volume. sd t o minimum a i r volume.  75% steam (2)  34.3  1  85% steam (3)  20.2  2  -71-  TABLE 9. B r e a k - p o i n t v a l u e s o f t h i c k b r i c k s determined by c o v a r i a n c e a n a l y s i s on a moving r e g r e s s i o n frame.  B r e a k - p o i n t V a l u e s (mL) Retort  Positive flow steam/air  Positive flow water/air  Lagarde  Temperature °C  65% steam (1)  115  15.3  120  31.8  125  34.5  115  32.3  120  29.8  125  31.8  115  31.6  1  16.4  <5.0  120  28.8  1  19.4  9.7  125  30.3  ns t o maximum a i r volume. sd t o minimum a i r volume.  75% steam (2)  85% steam (3)  2  11.0  <5.0  28.9  9.3  27.3  <5.0  2  1  13.2  <5.0  2  1  25.0  9.3  1  35.0  30.7  1  1  13.3  <5.0  2  2  -72-  thicknesses.  Since  differences  only  one  value  between v a l u e s may  of  break-point  not be s t a t i s t i c a l l y  may  be  determined,  tested.  Therefore,  comparisons are made by d i f f e r e n c e s i n magnitude of each b r e a k - p o i n t .  2.  F a c t o r s A f f e c t i n g Break-Point a.  Steam Percentage  Volumes  or P r e s s u r e L e v e l  R e s u l t s shown i n T a b l e s 8 and point  of  differences  examination be  of  f o r each  overpressure  air  percentages  variable  of  In a l l c a s e s , b r e a k - p o i n t  study.  be s t u d i e d from the s t a n d or  pressure  increased  I t i s apparent  volumes  may  be  up  temperature,  overpressures  tested.  and  brick  As  to  65%  with  steam/pressure degrees  no  Therefore,  first air  previously explained,  bricks  packaged  in flat  may  thick-  level  in  of o v e r p r e s s u r e ,  interference in  the  1  heat  the  transfer.  (p>0.05) i n degree  differences  test  pouches.  this  larger  observed  may  a t t r i b u t e d t o the i n f l u e n c e of p r o c e s s i n g c o n d i t i o n s on entrapped  angular  By  volumes of a i r i n c r e a s e d as the degree  that at higher  entrapped  retort  R e s u l t s from bare b r i c k s demonstrated no s i g n i f i c a n c e of  level.  of v a l u e s a c c o r d i n g t o rows, the degree of o v e r p r e s s u r e  compared  ness.  i n steam  9 may  samples c o n s i s t e d of  be  gases. rect-  A i r e n t e r i n g the pouch c o u l d  accumulate around the t h i n edges of the b r i c k s , then as volumes of  increase layers  Tables  8  and  9  pressure ( l e v e l  indicate  only  form  over  that  almost  1) l i m i t expansion  i n v o i d a r e a s near allowed  could  because expansion  volumes  of  larger  s u r f a c e s of the  a l l conditions with  so t h a t entrapped  the b r i c k edges.  small  the  exist  during processing occurred  the b r e a k - p o i n t , a c u s h i o n of a i r may  steam/  gases remained o n l y  C o n d i t i o n s of reduced  a i r to  65%  brick.  overpressure  i n peripheral brick to a l a r g e r degree.  have accumulated  areas Above  between the l a r g e  -73-  f a c e s of the b r i c k and fer  to  thin  the  l o c a t e d thermocouple.  An  example  processed  i n the  at  115°C  bricks  mL  mL  f o r 85%  (level  impeding  centrally  p o i n t s of 29.8 11.6  the pouch m a t e r i a l , thereby  i n Table  steam.  Thick  evidence  Consequently,  sufficient  heat  at  bricks  processed  at  8  displayed  (maximum a i r volume) a t 65% steam, 20.3  3) showed no  transfer  Lagarde r e t o r t  heat t r a n s -  mL  115°C  break-  f o r 75%  and  of  85%  and  steam  of a p l a t e a u s e c t i o n i n a l l t h r e e r e t o r t s .  expansion  s m a l l occluded  may  have o c c u r r e d  a i r volumes  (<5.0  to i n t e r f e r e  mL)  with  when p r o c e s s i n g  with 30 kPa a i r o v e r p r e s s u r e . R e s u l t s of t h i s study i n d i c a t e t h a t when p r o c e s s i n g with  lower  steam r a t i o s (65% steam), heat t r a n s f e r i n pouches w i t h l a r g e amounts of a i r w i l l be m a i n t a i n e d .  S t u d i e s by P f l u g and B o r r e r o (1967) e s t a b l i s h e d  t h a t h i g h e r steam/air r a t i o s p r o v i d e d a more e f f e c t i v e medium because of increased  enthalpy  experiments  and  suggest  heating e f f i c i e n c y .  that  a  higher  degree  However, f i n d i n g s i n these of o v e r p r e s s u r e  will  e f f e c t i v e n e s s of h e a t i n g when l a r g e amounts of a i r are entrapped package. limit  improve i n the  T h i s study makes no p r e d i c t i o n s below 65% steam ( l e v e l 1) as a  exists  where  excessive  a i r overpressure  will  reduce  heating  e f f i c i e n c y i n the media. Most on  either  p r e v i o u s s t u d i e s d e a l i n g w i t h r e s i d u a l gas have f o c u s s e d  pressure-volume  volumes to by entrapped  prevent  relations  to determine  pouch b u r s t i n g (Whitaker,  a i r on heat  maximum a l l o w a b l e  1971)  gas  or the i n t e r f e r e n c e  t r a n s f e r at a s i n g l e processing c o n d i t i o n .  In  a study by Evans (1977), h e a t i n g r a t e i n d i c e s were e v a l u a t e d f o r pouches of  variable  results  a i r content  showed an  processed  at  two  levels  of o v e r p r e s s u r e .  i n c r e a s e i n f ^ w i t h h i g h a i r volumes (50 mL),  yet  His no  -74-  e f f e c t was c o n t r i b u t e d by o v e r p r e s s u r e even when pouches were r e s t r a i n e d (as compared t o c o n s t r a i n e d ) . and  125°C  at pressures  D i f f e r e n c e s from representative evaluated.  this  t o 75% s t e a m  and 8 5 % s t e a m .  o f 65% steam was not t e s t e d and h i g h e r a i r volumes were  A  study  were i n c o n s i s t e n t ; vacuum  corresponding  study may be due t o the f a c t t h a t an o v e r p r e s s u r e  by  vacuum on pouches w i t h  low  C o n d i t i o n s s t u d i e d were s i m i l a r t o 120°C  Pereira  (1980)  two o v e r p r e s s u r e  evaluated levels.  various  degrees  The r e p o r t e d  setting  i s similar  (may assume h i g h  to r e s u l t s  i n this  p r o c e s s i n g l i m i t e d gas expansion b.  a i r ) a shorter s t e r i l i z a t i o n  levels  I n some  t h e maximum  increased.  This  pressures  at high  setting  principle (Tsutsumi, saturated  heat  This f i n d -  overpressure  transfer,  may be compared by s t u d y i n g t h e t a b l e s  At c o n d i t i o n s o f 65 and 75% steam ( p r e s s -  1 and 2 ) , p e r m i s s i b l e a i r volumes i n c r e a s e w i t h  temperature.  pressure  where h i g h e r  and maintained  o f temperature  i n columns f o r each s e c t i o n .  reached  study  time  Temperature Effects  ure  results  however, f o r one t h i c k n e s s ( t h i n n e s t package) with a  was r e q u i r e d when a h i g h e r degree o f o v e r p r e s s u r e was used. ing  of  may  be  tested  employing f o r UHT  Superheated  pressure  This  a t 65% steam  and r e m a i n e d  explained  temperatures.  when  1979a).  f o r example  a i r level  trend  i s employed  vapor  cases,  by  larger  results  t h e same steam  as  1),  i t  temperature  saturation  percentage.  vapor retort  The same  pouches i n Japan  steam a t h i g h temperatures process  (level  i n a higher  processing of f l e x i b l e  t o adequately  increasing  pouches  provide high i n pure  steam  ( f o r h e a t i n g o n l y ) w h i l e p r e v e n t i n g pouch b u r s t i n g . At  c o n d i t i o n s o f 85% steam ( p r e s s u r e l e v e l  3) volumes d e v i a t e  -75-  from  the p a t t e r n d i s p l a y i n g lower  ible  explanation  scale  retort  of t h i s  b r e a k - p o i n t v a l u e s a t 125 C.  occurrence  in trials  may be due t o low rotameter  steam ( p r e s s u r e l e v e l  3).  Although  performed  have  similar  been  insufficient  situation,  i n the p i l o t  s e t t i n g s a t c o n d i t i o n s o f 85%  media f l o w r a t e s were c o n s t a n t , t h e  amounts o f a i r p a s s i n g through t h e system were lower. may  A poss-  and r e s u l t e d  however, was found  Media c i r c u l a t i o n  i n poor heat  i n the Lagarde.  transfer.  A  Media f l o w r a t e s  are very h i g h i n t h i s system due t o t h e turbo f a n c i r c u l a t i o n mechanism, c.  B r i c k Thickness Although  tudes  the two b r i c k t h i c k n e s s e s have much d i f f e r e n t  of b a s e l i n e f ^ values,  significant  difference  from  thin  t h e maximum  than  f o r thick  of a i r which  the b a s e l i n e may  v a l u e s i n T a b l e 8 and T a b l e 9. exists,  volumes  I n almost  a  10-15 mL  by s t u d y i n g  section  i s higher f o r  F o r example, w i t h w a t e r / a i r p r o c e s s i n g a t  difference  r e g i o n between t h i c k n e s s e s .  no  a l l cases where a b r e a k - p o i n t  p r e s s u r e l e v e l s 2 and 3 a t 115°C and l e v e l 3 a t 120°C, imately  demonstrate  be compared  a i r volume o f the h o r i z o n t a l bricks.  magni-  i n volume  t h e r e i s approx-  o f a i r forming  the plateau  T h i s magnitude o f d i f f e r e n c e o c c u r s i n some  other c o n d i t i o n s , but not every  case.  V a r i a t i o n s i n the volume o f a i r a t which no i n f l u e n c e on h e a t i n g r a t e o c c u r s may be a r e f l e c t i o n o f the pouch s i z e i n r e l a t i o n t o the brick sizes,  volume. there  Since would  similar  be a  available  around  accumulate  i n surrounding  when  bricks  thin  difference  the brick  were  pouches were  edges.  spaces  packaged  used  t o package both  i n the p o t e n t i a l Consequently,  before compared  residing  over  to pouches  volume more  of  brick space  a i r could  the b r i c k containing  face thick  -76-  bricks. d.  Media Type: Steam/Air and Water/Air Modification  itate  w a t e r / a i r p r o c e s s i n g enabled  within  the same r e t o r t .  ditions the  o f the v e r t i c a l  using  No  studying  flow  retort  different  to f a c i l -  p r o c e s s i n g media  I n o r d e r t o compare b r e a k - p o i n t v a l u e s o f con-  the media  baselines.  positive  types,  a covariance  significant  difference  analysis  was performed  (p>0.05) was  found  between  b a s e l i n e s o f w a t e r / a i r media and s t e a m / a i r i n the v e r t i c a l p o s i t i v e retort  (see T a b l e  10) f o r e i t h e r  thick  or t h i n  bricks.  on  flow  Although  a  s i g n i f i c a n t d i f f e r e n c e (p<0.05) was found between r e t o r t s f o r unpackaged thick  bricks,  attributable  i t i s not apparent  when comparing b a s e l i n e s .  to l a r g e r v a r i a b i l i t y  T h i s may be  i n data when a i r was i n c l u d e d i n the  package. Break-point studied. provided cluded thin  I t was apparent  systems i n T a b l e s 8 and 9 may be  t h a t superheated  p r o c e s s i n g media which allowed  i n t h e sample  bricks reflected  pressure  v a l u e s f o r these  level,  pouches with  f o r water/air  h i g h e r than f o r s t e a m / a i r .  l a r g e r volumes o f a i r t o be i n -  no i n c r e a s e i n f ^ v a l u e s .  t h i s occurrence  values  water w i t h a i r o v e r p r e s s u r e  Data f o r  s t r o n g l y ; a t 115°C f o r each processing  ranged  from  over-  7-14 mL  A d i f f e r e n c e between media types was demon-  s t r a t e d by both b r i c k t h i c k n e s s e s a t 115°C and 65% steam ( p r e s s u r e l e v e l 1). 15.3 no  When mL  with  ( t h i n ) and 17.0 mL  evidence  employing  processing  of a  steam/air  a  break-point  was  exhibited at  ( t h i c k ) o f i n c l u d e d a i r , however, t h e r e was  break-point  with  similar  processing  c o n d i t i o n s when  w a t e r / a i r media. These  studies indicated  t h a t when u s i n g w a t e r / a i r  processes,  -77-  heating than  rate  when s t e a m / a i r  superheated pressure meter  water  were a f f e c t e d mixtures  with  would  be more e f f e c t i v e  heating  head.  bricks  rates  o f pouches  using  of approximately 1  10 kPa p r e s s u r e .  results.  Bare  brick  t h a t w a t e r / a i r media  of a i r volumes.  i n steam/air  transfer  be due t o an i n c r e a s e o f  demonstrated  media types w i t h s i m i l a r  by i n c l u d e d a i r  heat  A water depth  contribute  independent  degree  Improved  a i r o v e r p r e s s u r e may  i n t h e case o f t h i c k  have s t u d i e d  to a lesser  were used.  due t o a h y d r o s t a t i c  i n the v e s s e l  analysis may  indices  Other  researchers  Yamano (1976) compared  and w a t e r / a i r media.  Although  long come-up times were a s s o c i a t e d w i t h water p r o c e s s e s , when the media reached d e s i r e d temperatures, air over  mixtures.  Pflug  steam/air  associated  media  with  h e a t i n g r a t e s were f a s t e r than w i t h steam/  and B o r r e r o based  (1967) recommended  on s i m p l i c i t y  water/air mixtures  use o f w a t e r / a i r  o f use and h i g h e r e n t h a l p i e s  per u n i t  volume.  Tsutsumi  (1979b)  s t a t e d t h a t w a t e r / a i r p r o c e s s e s were commonly used i n Japan when pouches c o n t a i n e d l a r g e r amounts o f i n c l u d e d a i r . e.  Retorts: Steam/air  utilized Analysis  i n both  Lagarde media  and P o s i t i v e Flow with  the Lagarde  similar  steam) o f each  retort.  p r o c e s s i n g c o n d i t i o n s were  and v e r t i c a l  o f c o v a r i a n c e was performed  Steam/Air  positive  flow  systems.  on b a s e l i n e c o n d i t i o n s (125°C, 65%  No s i g n i f i c a n t  difference  (p >0.05) was found  between the r e l a t i o n s h i p s i n each b r i c k t h i c k n e s s ( T a b l e 10). a significant  d i f f e r e n c e was found  packaged, t h i s was not apparent attributable the  to larger  packages.  Values  between r e t o r t s  when comparing  variabilities i n Tables  Although  f o r both b r i c k s un-  baselines.  T h i s may be  i n data when a i r was i n c l u d e d i n  8 and 9 may be compared  f o r these  TABLE 10 C o v a r i a n c e a n a l y s i s r e s u l t s comparing b a s e l i n e s between r e t o r t systems t e s t e d .  Brick Thickness  Thin  Thick  Comparison  T e s t of Slope  F Ratio T e s t o f Slope  Overall  Pos. flow s/a v s . Pos. flow w/a  0.69 ns  3.51 ns  2.10 ns  Pos. flow s/a v s . Lagarde  0.44 ns  0.37 ns  0.40 ns  Pos. f l o w w/a v s . Lagarde  0.08 ns  0.21 ns  1.08 ns  Pos. f l o w s/a v s . Pos. flow w/a  3.51 ns  2.91 ns  3.30 ns  Pos. f l o w s/a v s . Lagarde  1.57 ns  0.59 ns  1.08 ns  Pos. flow w/a v s . Lagarde  0.31 ns  1.09 ns  0.54 ns  ns - not s i g n i f i c a n t  (p>0.05)  -79-  systems.  Larger  volumes  o f a i r comprise  Lagarde compared t o the v e r t i c a l  the p l a t e a u  p o s i t i v e f l o w system.  was demonstrated i n both b r i c k t h i c k n e s s e s . 115°C  and 65% steam  exist  i n the Lagarde  apparent was  exemplify retort  a t the maximum  detected  processing with s i m i l a r retort.  (thin retort  demonstrate idual  i n t e r f e r e n c e i n heating However, a  b r i c k s ) or 15.3 mL  (thick  rate  was  break-point  b r i c k s ) when  c o n d i t i o n s i n the v e r t i c a l p o s i t i v e  results  an e f f e c t  gases.  Since  indicate  that  on the h e a t i n g similar  systems  used  f o r processing  r a t e of products  flow  media  compositions  retorts  a h o r i z o n t a l a i r f l o w p a t t e r n i s ensured  fan  causing  media  Media f l o w i n t h e v e r t i c a l perpendicular  t o flow  parallel  positive  were  t o the b r i c k  plane.  utilized, In Lagarde  by c i r c u l a t i o n w i t h a  across  flow r e t o r t  may  containing res-  d i f f e r e n c e s may be due t o the e f f e c t i v e n e s s o f c i r c u l a t i o n .  tion,  conditions  Other c o n d i t i o n s e x h i b i t the same t r e n d s . These  turbo  occurrence  Sufficient  volumes o f a i r added.  a t 17.0 mL  This  f o r the  R e s u l t s from c o n d i t i o n s o f  the d i f f e r e n c e . so no  region  the b r i c k  surface.  i s i n an upward  Therefore,  circulation  direcmay be  h i n d e r e d by b r i c k s on t h e bottom l a y e r s .  3.  Importance o f P l a t e a u Region Study o f t h e data  showed h e a t i n g r a t e i n d i c e s as a f u n c t i o n o f a i r  entrapped  i n packaged b r i c k s t o c o n s i s t  One  was  part  increase i n f  essentially h  brick  horizontal line,  with increasing a i r contents.  be e x p l a i n e d by t h e r i g i d the  a  of either  periphery.  nature  one o r two s e c t i o n s .  the other  T h i s two p a r t behavior may  o f t e f l o n b r i c k s forming  Care must be taken  e x h i b i t e d an  v o i d areas i n  i n extrapolating r e s u l t s to a  -80-  food out  system. to  the  A food product  edges and  from T a b l e s 8 and quality  control  results  levels  and  do not  more p l i a b l e form would  a i r would accumulate on  9 may  not d i r e c t l y  specifications  knowledge c o n c e r n i n g The  of s o f t e r and  (on  the b e h a v i o r  suggest  top.  Consequently,  quality  the  b a s i s of heat  that included a i r l i m i t s  levels  deteriorative  implications  in  specific  85%  regard steam  10 mL  V  factor  (level  3)  t r a n s f e r ) without  may  be  to p r o c e s s  t e s t e d on a food  of entrapped  quality  may  be  set at  be  control  a concern  levels,  A i r Volumes Above the  Any  p r e s e n t ) from  which  a horizontal  changes  and  other  evaluated.  Also  c o n d i t i o n s of  115°C  because a i r volumes of l e s s  and than  transfer.  Break-Point  p r e v i o u s l y d e s c r i b e d moving r e g r e s s i o n frame determined  i n c l u d e d a i r at  higher  times when h i g h  product,  gases must be  d i s p l a y e d an i n t e r f e r e n c e w i t h heat  The of  to  must  as  of a i r with pouches c o n t a i n i n g foods.  contribute a limiting  control  data  be e x t r a c t e d f o r implementation  o v e r p r e s s u r e s are used and adequate c i r c u l a t i o n i s ensured. in  fill  a  transition  line,  t o one  or b r e a k - p o i n t  values  occurred ( i f  p o r t r a y i n g an i n c r e a s e i n h e a t -  i n g r a t e i n d i c e s with h i g h e r a i r volumes.  Work by p r e v i o u s r e s e a r c h e r s  have shown a r e l a t i o n s h i p of t h i s nature where i n c l u d e d a i r r e s u l t e d i n an  insulating  in  f ^ values, Huerta-Espinosa  increased  times  (1983) found v a l u e s or  effect  a  required similar  data  transfer.  Evans (1977) r e p o r t e d i n c r e a s e s  (1981) d e s c r i b e d the i n s u l a t i n g  for  behavior  sterilization evaluated  and  by  Berry  and  decreasing  effect  by  Kohnhorst  sterilization  F . Q  Experimental the  on heat  existing  variables beyond  may the  be  compared  break-point  by  covariance a n a l y s i s  describing  the  on  increasing  -81-  trend.  A  simple a r i t h m e t i c A large  standard  r e l a t i o n s h i p was  cribe  the  large  variations e x i s t i n f ^ values.  pared  since  others  data.  linear  e r r o r of e s t i m a t e may Only  many r e l a t i o n s h i p s e x h i b i t e d  showed  information  increases  was  a t high  available  d a t a i n the  for a  sections  were parameters of used and  1.  some c o n d i t i o n s may  only  reliable  above the  i n t e r e s t since  on  des-  be expected  regression  as  be com-  horizontal sections  a i r volumes, beyond which  comparisons of e q u a t i o n s were f o c u s s e d iable  found t o best  and  insufficient  line.  Therefore,  those c o n d i t i o n s with a p p r e c -  break-point.  differing  S l o p e s of the  lines  ranges of a i r volumes were  i n t e r c e p t s were i n e v i t a b l y d i f f e r e n t .  F a c t o r s A f f e c t i n g the Second a.  Brick In  Section  Thickness  the  previous  section  i t was  determined  that  thin  bricks  c o u l d accommodate l a r g e r volumes of a i r than t h i c k b r i c k s without impeding  heat t r a n s f e r .  compared. provided ships  Retort  The  degree of i n c r e a s e  conditions  were  used  for  comparison.  difference  r e l a t i o n s h i p of h e a t i n g thick bricks.  reached added  and  to  the  thicknesses. formed  115°C  and  85%  steam  heating  (p>0.05)  was  indicated found  so the in  between  level  was 3)  relation-  Table  11,  slopes  in  no the  r a t e index as a f u n c t i o n of a i r volume f o r t h i n  I t may rates  be assumed t h a t once a c r i t i c a l a i r volume began t o be  pouch i n c r e a s e d Consequently,  (past c r i t i c a l  As  region  (pressure  a l a r g e amount of data beyond the b r e a k - p o i n t ,  significant  and  of  beyond the p l a t e a u  a f f e c t e d , a d d i t i o n a l a i r volumes  f ^ w i t h the a  cushion  was  of  same s e v e r i t y f o r both a i r of  s i m i l a r thickness  brick was  volumes) f o r each a d d i t i o n a l volume o f a i r added.  -82-  TABLE 11 Covariance a n a l y s i s on v s . i n c l u d e d a i r , v a l u e s above b r e a k - p o i n t ; comparison o f b r i c k t h i c k n e s s , 115°C-85% steam ( p r e s s u r e l e v e l 3)  Retort  Brick Thickness  Slope (mL/min)  Comparison  T e s t o f Slope F Ratio  Lagarde  Thin Thick  0.396 0.254  Thin vs. Thick  2.24 ns  P o s i t i v e flow steam/air  Thin Thick  0.091 0.104  Thin vs. Thick  1.33 ns  P o s i t i v e flow water/air  Thin Thick  0.192 0.261  Thin vs. Thick  0.21 ns  ns  not s i g n i f i c a n t  (p>0.05)  -83-  It  was  for  apparent  thin  compared  were performed b.  i n Tables to  thick  of  115°C was  with  used  Table  12.  steam  were not  In one  line  i n F i g u r e 6.  1).  I f no  used  break-points  f o r comparison.  found  This finding expansion  processing with  overpressure  i n s u l a t i o n e f f e c t was Comparisons findings  of  The  supports  resulting  from  o n l y was  were  of  allowing  may  displayed  evidence  expansion  be  of  The  steam percentages  i n other  s i n c e no  This  gases.  have l i m i t e d  expansion  that  reflect  degrees  of  vertical  employing  water  processing  with  The  a i r overpresure  positive also  flow  65%  over-  t o a l a r g e r degree t o r e s u l t  was  difference.  found.  f o r 75 and  However, i t must be noted  significant  the  included.  more g r a d u a l i n c r e a s e of h e a t i n g r a t e . no  lower  Therefore,  (p>0.05) were  higher  of  slope  to a  systems d i d not  differences  indicated  illustrat-  larger  attributed  in  former  t h a t h i g h e r degrees  gases.  steam may  the  differ-  75% steam, the  more severe as a d d i t i o n a l a i r was  statistically  respectively.  pressure  Although  reported  r e l a t i o n s h i p s are  residual  85%  and  However, s l o p e s were l a r g e s t f o r 85% steam then decreased steam,  levels)  apparent,  Results are  between s l o p e s of 85  limit  these  (pressure  of the t h r e e systems ( L a g a r d e ) , a s i g n i f i c a n t  overpressure  of  percentages  or p l a t e a u s e c t i o n  having a l a r g e r s l o p e than the l a t t e r .  degree  variables  f o r t h i c k b r i c k s i n a l l t h r e e systems.  (level  ence (p<0.05) was  ed  of  s i n c e i t c o n t a i n e d the lowest b r e a k - p o i n t volumes of a i r ,  steam  relationships  comparisons  Level  variable  systems a h o r i z o n t a l 65%  Further  bricks.  Steam P e r c e n t a g e / P r e s s u r e  were compared a t 115°C  two  9 t h a t b r e a k - p o i n t volumes were l a r g e r  bricks.  on data of t h i c k  Conditions  in  8 and  in a there  retort  demonstrated  no  -84-  TABLE 12 C o v a r i a n c e a n a l y s i s on v s . i n c l u d e d a i r , v a l u e s above b r e a k - p o i n t ; comparison o f p r e s s u r e l e v e l , a t 115°C.  Retort  % Steam/ Pressure Level  Slope (mL/min)  Comparison  T e s t o f Slope F Ratio  4.84*  85 75  0.271 0.540  85 v s . 75  P o s i t i v e flow water/air  3 2  0.145 0.104  3 vs. 2  0.54 ns  P o s i t i v e flow steam/air  85 75 65  0.260 0.178 0.088  85 v s . 75 75 v s . 65 85 v s . 65  1.14 ns 0.83 ns 4.02 ns  Lagarde  ns  not s i g n i f i c a n t  *  significant  (p>0.05)  (p<0.05)  32-T 31-  Legend  30 29  c  28 27  X  0) TJ  •  65% steom  A  75% steam  X  8 5 % steam  X  x  26  x  25  A  24 °  A -'A'  A  ,A-""A  ox  ,---A - A'  A  i  00  cn c.  Q) X  Ul  I  •  22 21  •  20 19  -a  • •  •  18 17  T  5  10  15  20  25  30  35  Included Air (mL)  Figure  6.  Heating r a t e index v s . i n c l u d e d a i r f o r comparison of p r e s s u r e t h i c k b r i c k s processed at 115°C i n the Lagarde r e t o r t .  level;  -86-  significant levels.  d i f f e r e n c e (p>0.05)  A s i m i l a r t r e n d was  was  slightly  steeper  75%  steam, r e s p e c t i v e l y ) .  w i t h no evidence c.  than  between  slopes  at  different  pressure  e v i d e n t s i n c e the s l o p e a t p r e s s u r e l e v e l  at pressure  level  Pressure l e v e l  2 (corresponding  t o 85  1 exhibited a horizontal line  of an upward t r e n d ,  e f f e c t s of temperature on the f ^ v s . i n c l u d e d a i r f u n c t i o n  were compared a t a c o n s t a n t  degree of o v e r p r e s s u r e .  Conditions at  steam ( p r e s s u r e l e v e l 3) were t e s t e d because more i n f o r m a t i o n was f o r the  second  equation  i n the model.  of the c o v a r i a n c e a n a l y s i s . retorts  t h e r e was  no  each temperature may  significant  allow  demonstrating  an  Table  In the Lagarde and  c r e a s e s above the c r i t i c a l  value  for of  d i f f e r e n c e (p<0.05) was 115 and  on  heat  transfer,  showed no  intermediate  (p>0.05) from exhibited  a  either  supported  break-point  values.  temperatures  degree,  resulting  could  the  and  found  significant  125°C  A  i n the p r e v i o u s  acute  of  of i n -  difference.  no  a  slope  relationships The  slope  significance  interference i n  at  which  a  lower  section describing  pressures  entrapped  In  signif-  relationships  larger  s a t u r a t i o n vapor  more  showing  7 d e p i c t s the  expansion  although  severity  between s l o p e s o f the  difference.  cause a  115°C Figure  results Lower  in  to  value.  significant  temperature  low  found  of  volumes of a i r to be i n c l u d e d  125°C, the former being g r e a t e r than the l a t t e r .  120°C was  results  p o s i t i v e flow w a t e r / a i r  the v e r t i c a l p o s i t i v e f l o w system employing steam/air mixtures icant  avail-  13 shows the  T h i s would i n d i c a t e t h a t  for differing  effect  85%  d i f f e r e n c e (p>0.05) between s l o p e s  the l i n e s f o r a l l t h r e e temperatures.  without  and  Temperature The  able  3  associated  gases to a heat  with  larger  transfer  as  -87-  TABLE 13  C o v a r i a n c e a n a l y s i s on v s . i n c l u d e d a i r , v a l u e s above b r e a k - p o i n t ; comparison o f temperature a t 85% steam ( p r e s s u r e l e v e l 3 ) .  Retort  Temperature (°C)  Slope (min/mL)  Comparison  T e s t o f Slope F Ratio  Lagarde  115 120 125  0.271 0.209 0.236  115 v s . 120 120 vs. 125 115 v s . 125  0.71 ns 0.09 ns 0.16 ns  P o s i t i v e flow water/air  115 120 125  0.145 0.140 0.056  115 vs. 120 120 v s . 125 115 v s . 125  0.07 ns 3.15 ns 3.37 ns  P o s i t i v e flow water/air  115 120 125  0.260 0.198 0.174  115 v s . 120 120 vs. 125 115 vs. 125  0.86 ns 0.27 ns 5.40 *  ns  not s i g n i f i c a n t  *  significant  (p>0.05)  a t p<0.05  33 32-  •  31-  •  30 29-  c  28-  E.  27-  Legend •  •  •  115 C  i 00 00 I  10  15  20  35  Included Air (mL)  Figure 7.  Heating rate indices vs. included a i r for comparison of temperature; thick bricks processed at 85% steam i n positive flow r e t o r t .  -89-  d i s p l a y e d by the l a r g e r s l o p e .  d.  Media Type: Steam/Air and  Water/Air  Comparisons between steam/air ical  p o s i t i v e flow r e t o r t  beyond c r i t i c a l 85%  cases  no  a  plateau  slopes  Other may  by  expected  pressure.  best  lines  slope  slope  evidence  found  with  115°C  from  no  and  In  was  found  found  when  steam/air  processing  in  these  115°C  test  and  85%  types.  d i f f e r e n c e (p>0.05).  level  It  3 would show d i f f e r e n c e s  retort  higher  comparing  steam  between media  c o n d i t i o n s of the low-  r e l a t i o n s h i p s (Figure  significantly  65%  processing;  condition,  significant  represented  of  14 a r e r e s u l t s from the one  pressure  these  and  provided  apparent p l a t e a u s .  than  break-point  reflects  8)  for water/air values.  A  t h a t steam/air  the The  which larger  mixtures  p r o v i d e a l e s s e f f i c i e n t h e a t i n g medium r e s u l t i n g i n g r e a t e r degrad-  a t i o n of heat possible to  In T a b l e  f o r comparisons s i n c e t h e r e were no  f o r steam/air  supports  may  that  Data  Conditions  d i f f e r e n c e (p<0.05) was  demonstrated  2)  120°C were s t u d i e d s i n c e t h e r e  f o r water/air  analysis.  a l a r g e r degree s i n c e they  est  and  d e s c r i b i n g data  steam ( p r e s s u r e l e v e l  comparison.  s e c t i o n only  covariance  conditions  be  for  comparisons were made.  steam, a s i g n i f i c a n t  to  C o n d i t i o n s o f 75%  substantial information  demonstrated  w a t e r / a i r media i n the v e r t -  system were made on e q u a t i o n s  steam ( p r e s s u r e l e v e l 3) a t 115°C  was  of  values.  and  t r a n s f e r w i t h a d d i t i o n a l amounts i n c l u d e d a i r .  that h y d r o s t a t i c pressure  l i m i t i n g the expansion  i n the w a t e r / a i r  of non-condensible  I t may  be  system c o n t r i b u t e d  gases, thereby  resulting in  a lower s l o p e . Other  conditions  (p>0.05); however,  tested  demonstrated  i n a l l cases  slopes  no  significant  difference  were l a r g e r f o r steam/air  pro-  -90-  TABLE 14 C o v a r i a n c e a n a l y s i s on f v s . i n c l u d e d a i r , v a l u e s above b r e a k - p o i n t ; comparison o f media t y p e . h  Processing Conditions  Media Type  115°C-75% steam (2)  Steam/air Water/air  0.189 0.151  s/a vs.  w/a  0.12 ns  115°C-85% steam (3)  Steam/air Water/air  0.260 0.104  s/a vs.  w/a  13.8  120°C-75% steam (2)  Steam/air Water/air  0.179 0.050  s/a vs.  w/a  0.15 ns  120°C-85% steam (3)  Steam/air Water/air  0.198 0.140  s/a v s .  w/a  1.07 ns  ns  not s i g n i f i c a n t  *  significant  (p>0.05)  a t p<0.05  Slope (min/mL)  Comparison  T e s t of Slope F Ratio  *  33 32  •  31  •  30  •  c F  E  0)  TJ C  Legend  28  •  • Steam/air  D  A Water/air  26  • ft  • A  9S  •  "5  cn  •  A  A,.  23  I  A A  A A  "o  X  A  20  A A  17-  0  10  15  20  25  30  Included Air (mL)  Figure 8.  Heating rate index vs. included a i r for comparison of media type; thick bricks processed at 115°C and 85% steam (3).  35  -92-  cesses.  Although  different.  a t r e n d was e v i d e n t , the s l o p e s were n o t  Combining  this  information with  results  statistically  from c r i t i c a l  vol-  umes which d i s p l a y e d no s i g n i f i c a n t  d i f f e r e n c e from a b a s e l i n e , i t may  be  show an improvement  assumed  processes  that water/air with  regard  processes  t o the e f f e c t s  o f entrapped  over  steam/air  gases on heat  trans-  fer. e.  Retort Design: Similar  to previous  beyond t h e c r i t i c a l cant  difference  Values the  Lagarde and P o s i t i v e Flow Steam/Air  volume.  comparisons,  there  R e s u l t s from T a b l e  (p>0.05) between  slopes  were a p p r e c i a b l e  15 i n d i c a t e d no  data  signifi-  of the r e l a t i o n s h i p s t e s t e d .  o f s l o p e s r e v e a l e d no c o n s i s t e n c i e s as some v a l u e s were l a r g e r i n  Lagarde  illustrates  and some  i n the v e r t i c a l  an example of these  point values  positive  flow  relationships.  retort.  From r e s u l t s  o f the p l a t e a u r e g i o n s , i t was e v i d e n t  Figure  9  on break-  t h a t l a r g e r volumes  of  a i r c o u l d be i n c l u d e d without  a f f e c t i n g heat t r a n s f e r when p r o c e s s i n g  in  the Lagarde  circulation  flow  parallel  retort.  Forced  I t may  would  be l a r g e r  be expected (more  that  severe)  however, t h i s was n o t the case. processing  additional ical  slopes  o f the i n c r e a s i n g  f o r the v e r t i c a l In some cases  positive  differ-  relationship flow  system;  l a r g e r s l o p e s were found  i n t h e Lagarde, which may be due t o t h e absence o f an  spacer  l a y e r t h a t was i n h e r e n t  p o s i t i v e flow r e t o r t .  i n r a c k s used w i t h  r e t o r t an adequate c l e a r a n c e was necessary i n the p o s i t i v e  flow  the v e r t -  As a i r volumes i n c r e a s e d beyond t h e c r i t i c a l  p o i n t , r a c k c l e a r a n c e above t h e pouch would be reduced.  as  f a n and media  t o the b r i c k s u r f a c e may be r e s p o n s i b l e f o r t h i s  ence.  when  by the turbo  retort  a spacer  I n the Lagarde  t o ensure c i r c u l a t i o n , wherel a y e r ensured  circulation  even  -93-  TABLE 15 Covariance  a n a l y s i s on v s . i n c l u d e d a i r , v a l u e s above b r e a k - p o i n t ; comparison o f steam/air r e t o r t s .  Processing Conditions  Retort  115°C--75% steam  Lagarde  0.053  Pos. f l o w  0.189  Lagarde  0.271  Pos.  0.261  115°C--85% steam  120°C--75% steam  120°C--85% steam  ns  not s i g n i f i c a n t  flow  Slope (min/mL)  Lagarde  0.138  Pos.  0.180  flow  Lagarde  0.209  Pos.  0.198  (p>0.05)  flow  Comparison  T e s t o f Slope F Ratio  Lag. v s . Pos.  1.45 ns  Lag. v s . Pos.  0.04 ns  Lag. v s . Pos.  .007 ns  Lag. v s . Pos. .024 ns  35  i  i  i  i  l  0  5  10  15  20  l 25  l  30  i  35  Included Air (mL)  Figure 9 .  Heating r a t e index vs. i n c l u d e d a i r f o r comparison of steam/air r e t o r t s ; t h i c k b r i c k s processed a t 115°C and 8 5 % steam.  -95-  if  clearance  racking  space  was d i m i n i s h e d .  configurations  Other  t o be an important  rate  heat  penetration.  orientation showed  with  that  orientation dent  that  Ramaswamy constrained  processing reduced  with  heat  Evans  r e s i d u a l gases.  Constrain-  o f i n t e r f e r e n c e by entrapped gases on  (1983)  studied  vertical  and u n c o n s t r a i n e d unconstrained  transfer rates.  types.  Results  racking  i n the h o r i z o n t a l  From t h i s  study, i t was e v i above t h e  pouch may be reduced when l a r g e volumes o f a i r a r e entrapped.  To ensure  circulation,  racking  rack  and h o r i z o n t a l  was employed, c l e a r a n c e  proper  i f "unconstrained"  determined  r a c k i n g d e s i g n s by e v a l u a t i n g  i n d i c e s o f pouches c o n t a i n i n g  ment o f pouches reduced t h e extent  have  factor i n processing.  (1977) compared r e s t r a i n e d and c o n s t r a i n e d heating  researchers  adequate  flow  channels  should  be provided  between  sample l a y e r s .  VI  P r e d i c t i o n o f Pouch Expansion Previous  tion and  s e c t i o n s have d e a l t w i t h the r e l a t i o n s h i p o f f ^ as a f u n c -  of residual pressure  sense  gases measured  (STP).  t o determine  at conditions  o f standard  These r e l a t i o n s h i p s were v a l u a b l e heating  rates  o f products  since  temperature  i n a practical  s i m i l a r a i r volume  measurements a r e performed i n q u a l i t y c o n t r o l programs.  However,  vari-  a b l e s may be s t u d i e d by p r e d i c t i n g t h e volume o f a i r which would p r e v a i l at  retort conditions.  showed pressure  no s i g n i f i c a n t level.  When  Analysis  of variance  differences  performed  i n variables  a i r was i n c l u d e d  on bare  bricks  o f t e m p e r a t u r e and  i n a pouch,  differences  were  a t t r i b u t e d t o an i n t e r a c t i o n between entrapped a i r and r e t o r t c o n d i t i o n s of  temperature and p r e s s u r e .  Predicted  volumes o f a i r may account f o r  -96-  any  i n t e r a c t i o n so a l l p r o c e s s i n g c o n d i t i o n s i n each system  may be com-  bined. A major study on pressure-volume revealed  that,  applied. in  due t o f l e x i b l e  relations  by Davis e t a l . (1960)  n a t u r e o f the pouch, i d e a l gas t h e o r i e s  P r e s s u r e s w i t h i n the pouch a r o s e from vapor p r e s s u r e o f water  food, a i r p r e s s u r e i n the headspace o r r e l e a s e d  thermal expansion o f the food i t s e l f . based  Whitaker  (1977) d e r i v e d e q u a t i o n s  on B o y l e ' s law and D a l t o n ' s law o f p a r t i a l  find  a total  maximum cited  overriding  volume  p r e s s u r e s i n order t o  pressure necessary to l i m i t  (determined  where volume expansion  when no a i r was entrapped (1976) u t i l i z e d  from t h e product and  by  confinement).  o f packaged  A  specific  peas i n b r i n e  and when a i r was i n c l u d e d .  the same c o n c e p t s .  With  expansion  beyond a  example  was  was  calculated  S t u d i e s by Yamano  water and a i r c o n t a i n e d i n a  pouch, expansion was p r i m a r i l y caused by a i r p r e s s u r e changes w i t h i n the headspace.  Expansion  sion)  determined  were  maximum  expansion  ratios  (expansion headspace equal t o pouch expan-  for different  ratio  retort  conditions.  t o p r e c l u d e pouch b u r s t i n g ,  a safe  Assuming  a  overriding  a i r p r e s s u r e o f 20-30 kPa was determined.  1.  Expansion F a c t o r s Pressure  existing  volume r e l a t i o n s h i p s were used  at retort  conditions.  In a system  to predict of brick,  expansion o f a l l components must be q u a n t i f i e d . considered  negligible  characteristics  factor  (a of  water and a i r ,  Expansion o f water was  o r d e c r e a s i n g , and s i n c e o n l y 10 mL o f water was  added, any changes were s m a l l . the  volumes o f a i r  of  10~~Vc°)  teflon  as l i s t e d  Brick which  expansion has a  i n T a b l e 1.  may be e s t i m a t e d  linear  thermal  Volume expansion  from  expansion (B) was  -97-  calculated  by  the  V  where V  t  following  = V  relationship:  (1 + 6At)  Q  i s o r i g i n a l volume, V  Q  ...  i s volume a t r e t o r t c o n d i t i o n s ,  t  denotes temperature d i f f e r e n c e .  C o n s i d e r i n g even the  temperature change of 100C°, volume expansion was sion  due  to  entrapped  when c o n s i d e r i n g describing  the  air  was  expansion r a t i o s volumes i s as  and  retort  T^  are  temperature  a i r within  the  equal  to  Since  10 mL  tribute  to  pressures system, P ,  of the was  2  V  l  P  important  water  was  total applied  because added  to  the  ( i n absolute),  T2  is  pressure exhibited  by  pouch was  f l e x i b l e nature  Dalton's  pressure  due  expansion f a c t o r of ^2^1  of a i r a t r e t o r t c o n d i t i o n s  assumed to of  law  to  of  follows:  con-  partial the  p r e s s u r e of water (  t n e  for a l l r e t o r t conditions  example c a l c u l a t i o n a t 115°C-75% steam i s as  be  film.  a i r within  r a t i o of  t o volume of a i r measured) may  Expansion f a c t o r s were c a l c u l a t e d  the  pouch, vapor p r e s s u r e w i l l  pressure.  calculate  (13)  p  l a  r e t o r t p r e s s u r e minus s a t u r a t i o n An  relationship  T  indicates  the  the  component  1 2  temperature a  a  Expan-  ... T  P  of  to  internal  The  =  T o t a l pressure within  pressure  from the  insignificant.  most  At  follows:  =  ( i n a b s o l u t e ) and  at r e t o r t temperature. ume  V  room p r e s s u r e and  pouch.  retort  a  the  and  l a r g e b r i c k and  p o t e n t i a l e f f e c t on h e a t i n g r a t e .  Expansion F a c t o r (EF)  where  therefore  (12)  be  vol-  found.  tested.  An  -98-  atmospheric p r e s s u r e r e t o r t pressure = 56.3 kPa.  100 kPa.  - s a t u r a t i o n vapor p r e s s u r e  a t 115°C  r e t o r t temperature = 388°K. room temperature = 298°K.  Expansion  This  expansion  pouch i t w i l l values  factor,  factor expand  o f expansion  2.31  indicates  that  (14)  f o r each mL o f a i r added  2.31 times when r e a c h i n g  t o the  retort conditions.  factors f o r r e t o r t conditions  studied  Other  are i n Table  16. Factors explanation  tabulated  f o r each  condition  of f i n d i n g s i n previous  provide  sections.  s i o n f a c t o r s r e f l e c t s volumes o f a i r i n c l u d e d apparent 85%  i n Table  a decrease  steam r e s u l t s i n an i n c r e a s e  decrease (with  i n expansion  a  constant  baseline  degree  was  As p r e v i o u s l y  displaying  same  Results  calculated  discussed,  no s i g n i f i c a n t  overpressure  was  regions.  It i s  i n o v e r p r e s s u r e from 65% steam t o Additionally, a  as temperatures  of overpressure).  degree o f o v e r p r e s s u r e i n c r e a s e d . the  i n plateau  i n expansion f a c t o r s .  t o determine the b r e a k p o i n t  (1.07).  volumes  factor  aiding  The magnitude o f expan-  I t may  r e l a t i o n s h i p o f 125°C and 65% steam  parisons one  16 t h a t  information  be noted  t h a t the  1) used  f o r com-  (level  has an expansion there  increase  factor close to  was an i n c r e a s e  of maximum  d i f f e r e n c e from the b a s e l i n e ,  as the  S i m i l a r l y , i n c r e a s i n g temperature a t  characterized  by  larger  showed t h a t when expansion f a c t o r s were s m a l l ,  plateau  regions.  l a r g e volumes o f  -99-  TABLE 16 T h e o r e t i c a l expansion f a c t o r s f o r c o n d i t i o n s  studied.  Steam (%) Temperature, °C  65  75  85  115  1.43  2.31  4.36  120  1.25  1.99  3.76  125  1.07  1.73  3.26  -100-  air  could  be  included  within  the  pouch without  interfering  with  heat  transfer. Measured volumes of a i r ive  expansion  factors  to  may  determine  p r e v a i l i n g during processing. by  control  mechanisms  be a d j u s t e d by m u l t i p l y i n g by  as  the  corresponding  R e t o r t temperature and previously  i n s t a n c e s a c t u a l c o n d i t i o n s may  described;  have s l i g h t  respect-  volumes  of  p r e s s u r e were s e t however,  in  many  d e v i a t i o n s from the t a r g e t .  To c o r r e c t f o r these d i f f e r e n c e s , a l l volumes of a i r were a d j u s t e d on  expansion  10  and  f a c t o r s c a l c u l a t e d from a c t u a l r e t o r t c o n d i t i o n s .  11  illustrate  i n d i c e s and metic to  (level  115°C;  75%  adjusted  3.26  (pressure  volumes.  the  log  (125°C)  to  from  1.73 level  out  (125°C) to 2)  with  were r e p r e s e n t e d  4.36  2.31 data  (115°C)  so  by  data  rate arith-  the a b s c i s s a was  for  1.07 over  heating  conditions  for  125°C  lower  to  adjusted  due  of  65%  1.43  at  volumes.  (115°C) were determined ranging  expansion were  from  low  to  with  pressure  medium level  f a c t o r s ranging  spread  across  the  for  from  entire  to h i g h a d j u s t e d a i r c o n t e n t s .  A semi-logarithmic  Volume R e l a t i o n s h i p s  r e l a t i o n s h i p c l e a r l y i n d i c a t e d an i n c r e a s e i n f ^  with, i n c r e a s i n g a d j u s t e d with  Factors  approximately  were spread  Comparison of A d j u s t e d  demonstrated  of data p o i n t s a l o n g factors.  of  based  Figures  f a c t o r s (on an  C o n d i t i o n s of lower o v e r p r e s s u r e  equivalent)  a b s c i s s a from low  2.  varied  f a c t o r s of  steam  (85%  1)  expansion  therefore, values  Expansion  3  Uneven s p a c i n g  differences i n  steam  r e l a t i o n s h i p s between  volume of a i r a d j u s t e d w i t h expansion  scale).  air  volumes  of  air.  i n c l u d e d a i r volumes were no  The  plateau  longer  section  apparent  as  because  -101-  1.1  -10  10  30  50 Adjusted Air  Figure 10.  70  90  i  110  130  (mL)  Heating rate index functions of adjusted a i r volumes for a l l c o n d i t i o n s ; t h i n b r i c k s , (a, Lagarde; b, P o s i t i v e Flow Steam/Air; c, Positive Flow Water/Air).  -10216-,  F i g u r e 11.  :  H e a t i n g r a t e index f u n c t i o n s of a d j u s t e d a i r volumes f o r a l l conditions; thick bricks. (a, Lagarde; b, P o s i t i v e Flow Steam/Air; c, P o s i t i v e f l o w W a t e r / A i r ) .  -103-  those  values  Covariance employed and  remained a t lower ranges of the a d j u s t e d  a n a l y s i s was  i n these  slopes  performed  experiments.  describing  (p<0.01) was  found  each  that  Table  and  17 shows r e s u l t s  relationship.  A  media  systems  o f the a n a l y s i s  significant  difference  between a l l t h r e e systems f o r both t h i c k n e s s e s .  v a l u e s of the s l o p e s and cate  to compare r e t o r t  volume a b s c i s s a .  processing  o b s e r v a t i o n of F i g u r e s 10 and with  steam/air  media  From  11, r e s u l t s  utilizing  the  indi-  vertical  p o s i t i v e f l o w r e t o r t , d i s p l a y s a more severe e f f e c t of r e s i d u a l gases on h e a t i n g r a t e than demonstrated by p r o c e s s i n g i n the Lagarde. water  with a i r overpressure  compared lower  to  both  slope.  steam/air  The  results  media was  air  systems  may  c i r c u l a t i o n and  be  demonstrated  similar  concur with f i n d i n g s from unadjusted attributable  all,  l e s s s e n s i t i v e to i n c r e a s i n g a i r  systems, as were  Above  f o r each  a i r volumes. to  the  by  a  significantly  brick thickness  and  D i f f e r e n c e s i n steam/  turbo  fan  driven  media  flow p a t t e r n s p a r a l l e l to pouch p o s i t i o n i n the Lagarde.  T h i s system p r o v i d e s more r a p i d h e a t i n g than the v e r t i c a l p o s i t i v e retort.  Higher  steam/air  may  function  heat  account  of a d j u s t e d  due  to an  The  results  transfer coefficients  increase were  for  a  more g r a d u a l  a i r volume. i n pressure  contrary  to  for water/air increase  compared  in log  from  h y d r o s t a t i c f o r c e s i n the  findings  by  Milleville  (1980)  of the r e s i d u a l a i r bubble w i t h i n the pouch was  t o reduce heat  transfer.  heating  rate  a i r volume  indices  of  approach  pouches  may  prove  containing  to a be  system. where  a  expected  However, o b s e r v a t i o n s of the buoyant e f f e c t  a i r i n s i d e the pouch were performed a t atmospheric adjusted  f ^ as  Another p l a u s i b l e e x p l a n a t i o n may  buoyant e f f e c t  The  flow  of  pressure. useful residual  in predicting gases  when  -104-  TABLE 17 Covariance  a n a l y s i s on l o g v s . a d j u s t e d a i r , a l l data; comparison o f systems t e s t e d .  Brick Thickness  R e t o r t System  Thin  Lagarde  T e s t o f Slope F Ratio  2.32  Lag. v s . s/a  10.6 **  (s/a)  2.89  L a g . v s . w/a  99.2 **  P o s i t i v e flow w a t e r / a i r (w/a)  0.84  s/a  203  Lagarde  1.18  L a g . v s . s/a  8.13  steam/air  1.46  L a g . v s . w/a  22.5 **  P o s i t i v e flow water/air  0.77  s/a  70.4 **  steam/air  Positive  **  Comparison  3  Positive  Thick  Slope (mL~^) x (10~ )  significant  flow  v s . w/a  **  flow  a t p<0.01  v s . w/a  -105-  processing  within  the range  of c o n d i t i o n s studied.  An  estimate  of  expanded a i r volumes t h a t w i l l p r e v a i l a t r e t o r t c o n d i t i o n s can be c a l c ulated  and h e a t i n g  r a t e s may  be determined.  s i m u l a t i n g a food w i t h water a c t i v i t y most  extreme  lower  water  water  vapor.  case  activity  food  Many products a lower  may  be  F o r example, an expansion  85% steam  i s 4.36; compared  of a, = .95 a t i d e n t i c a l w  difference exists,  so water a c t i v i t y  have a  partial  calculated  p r e s s u r e due t o  w  these  = 1.0 f o r 115°C  factor  conditions.  slightly  to r e f l e c t  f a c t o r when a  to a calculated  retort  used,  w  exhibit  factors  system  ( a ) equal t o one, r e p r e s e n t s the  expansion.  and w i l l  Expansion  differences. and  o f pouch  The model  Quite ^  of 3.40 f o r a a  substantial  o f t h e food processed must be con-  s i d e r e d an important f a c t o r when e v a l u a t i n g e f f e c t s o f r e s i d u a l gases on heating behavior. Another cessing These  products  goods  ditions  such  require  CO2)  (usually  structure  application as bakery  leavening  i s essential  i s important  to r i s e ,  Andres  practical  of t h i s foods  approach  or b a t t e r s i n r e t o r t  and i n c l u s i o n  f o r texture.  t o a c h i e v e a balance  and Duxbury  C o n t r o l of processing  gases con-  between a l l o w i n g the product Leavening,  are the three c r i t i c a l  (1972) developed  pro-  pouches.  o f non-condensible  but p r e v e n t i n g the pouch from b u r s t i n g . and s t e r i l i z a t i o n  may a i d when  differential  s e t t i n g of  f a c t o r s o f concern. pressure  s e n s i n g and  c o n t r o l l i n g methods t o a c h i e v e proper product t e x t u r e and m a i n t a i n pouch seal i n t e g r i t y during r e t o r t processing. d e t a i l s of t h e i r  developments.  They d i d n o t , however, p r o v i d e  -106-  VII  Other P r o c e s s Parameters As p r e v i o u s l y d e s c r i b e d ,  in  the  brick.  surface,  the  sensor  (1985).  Their  position  of  itions  error  mentation.  value  Berry  allowed  the  point must  50 mL  steam  not  a  also  h  was  of  Adams  show  range  evident  of  t h i s was  large  2/3  of for  then be or  pouches c o n t a i n i n g  highly  not  a great  sensitive  amounts of  samples  required  air.  to  that  the  greater  for  heating  I t was  i n order  location.  locations  found  air in this  a  desired  l a r g e amounts of r e s i d u a l gases.  within  t h a t w i t h more slowest  heating  A similar testing experiment.  to compare s t e r i l i z a t i o n  achieve  value  curve to a c t u a l  thermocouple  s i z e pouch, the  containing  to  pos-  concern i n e x p e r i -  maximum pouch t h i c k n e s s .  evaluated  time  coldest  institutional  the  that  not h i g h l y s e n s i t i v e to thermocouple  (1983) d e s c r i b e d  a i r i n an  performed  processes  is  the  b r i c k midplane.  times,  within  I t was  on  P e t e r s o n and  process  critical  slab.  by  layer  without a f f e c t i n g p r o c e s s times was  on),  Kornhorst  f a c t o r s can of  from the  from a s t r a i g h t l i n e p o r t i o n of the h e a t i n g  measured be  the  sample, so  pouches c o n t a i n i n g than  of  determined  a  with-  However, the l a g f a c t o r j (a measure of the r a t i o of g  at  and  center  was  Measurement of f  as e s t i m a t e d g  a i r form  p o i n t would s h i f t  thermocouple  location within  entrapped  placement e r r o r s were s t u d i e d  the  thick slabs.  of  r e s u l t s , based' on  the  around  position  When v o l u m e s  coldest heating  Temperature  thermocouples were c e n t r a l l y l o c a t e d  Lag values  sterilization  of  -107-  OONCLUSIONS  The air  may  relationship  of  be  as  described  l i n e a r segments. change i n f  One  with  n  heating  rate  index  c o n s i s t i n g of  as  a  either  f u n c t i o n of  one  or  two  included  essentially  segment formed a p l a t e a u r e g i o n where t h e r e was  i n c r e a s i n g volumes of  included a i r .  The  second  no  sec-  t i o n , apparent i n some c o n d i t i o n s o n l y , e x h i b i t e d an i n c r e a s e i n f ^ as a f u n c t i o n of i n c r e a s i n g a i r volumes. Increased of 125°C and in  the  35 mL  overpressure  85%  plateau  to be  versely,  l e v e l s and  steam) allowed region.  Air  i n c l u d e d with no  even  small  overpressure  the  above  detrimental effect  amounts  exception  f o r l a r g e r volumes of a i r to be i n c l u d e d  of  entrapped  t r a n s f e r when p r o c e s s i n g w i t h 30 kPa p r e s s u r e and  temperatures ( w i t h the  80 kPa  allowed  on h e a t i n g  air  to  rates.  Con-  degraded  heat  Increasing  over-  (<5 mL)  a i r overpressure.  up  temperature were a l s o shown to d i s p l a y d e c r e a s i n g s l o p e s i n  second l i n e a r  s e c t i o n where an  i n c r e a s e i n f ^ i s seen as a f u n c t i o n  of i n c r e a s i n g a i r volumes. P r o c e s s i n g w i t h w a t e r / a i r media allowed included evaluated  i n the  plateau  in a  positive  r e g i o n compared flow  retort.  second  segment were demonstrated w i t h  severe  detrimental  with  retort  retort, transfer  types  effect  of  that  l a r g e r volumes of a i r c o u l d be than  with  the  positive  flow  to s t e a m / a i r .  . As  w e l l , steeper  steam/air  entrapped  demonstrated  l a r g e r volumes of a i r to be  heat  transfer.  processing  entrapped retort.  slopes  of  the  media i n d i c a t i n g a more  a i r on when  Both media were  No  without  in  the  Studies Lagarde  affecting  heat  s i g n i f i c a n c e was  seen  i n s l o p e s of the second s e c t i o n . Expansion  factors for  processing  c o n d i t i o n s were  determined  from  -108-  i d e a l gas laws.  The f a c t o r s were used  sion that occurs a t r e t o r t  t o a d j u s t a i r volumes f o r expan-  conditions.  A l i n e a r r e l a t i o n s h i p was  found  between the l o g a r i t h m of h e a t i n g r a t e index and a d j u s t e d a i r volumes on an  arithmetic axis.  ences; least  water/air slope,  the  Comparisons  processes Lagarde  of s l o p e s showed  i n the p o s i t i v e and  increasing slopes, respectively.  positive  flow  flow  significant retort  steam/air  being  differof the  processes  had  -109-  LITERATDRE CITED Adams, J.P. 1984. R e t o r t Foods 153 ( 3 ) : 90.  pouch  uses  f o r seafood  Adams, J . P . , P e t e r s o n , W.R. and O t w e l l , seafood i n i n s t i t u t i o n a l - s i z e d retort ( 4 ) : 123. Agarwal, S.R. and Kumta, U.S. 1974. Modern Packaging 47 ( 1 0 ) : 43.  products.  Prepared  W.S. 1983. P r o c e s s i n g of pouches. Food T e c h n o l . 37  Puncture r e s i s t a n c e  of  flexibles,  Andres, C. and Duxbury, D.D. 1972. Automatic l i n e produces t h e r m a l l y processed foods i n f l e x i b l e packages. Food P r o c e s s i n g 33 ( 1 1 ) : 58. Anon.  1980. Research and development a s s o c i a t e s f i n d a l l - o u t commitment t o r e t o r t a b l e pouch. Package Eng. 25 ( 5 ) .  Anon. 1982. 97. Anon. 1983.  What's happening w i t h  The r e t o r t  pouch:  how  the r e t o r t  military  pouch? Food Eng. 54 ( 4 ) :  c l o s e ? Food Eng. 55 ( 1 ) : 83.  Ayoub, J.A., B e r k o w i t z , D., Kenyon, E.M. and Wadsworth, C K . 1974. Continuous microwave s t e r i l i z a t i o n of meat i n f l e x i b l e pouches. J . of Food S c i . 39 ( 2 ) : 309. Badenhop, A.F. and M i l l e v i l l e , H.P. 1980. Special report: a l s i z e r e t o r t pouches. Food P r o c e s s . 41 ( 1 ) : 82.  Institution  Ball,  C O . and O l s o n , F.C.W. 1957. S t e r i l i z a t i o n i n Food Technology, 1st Ed., McGraw-Hill Book Company, I n c . , New York, NY.  Bee,  G.R. and P a r k , D.K. 1978. H e a t p e n e t r a t i o n measurement f o r thermal p r o c e s s d e s i g n . Food T e c h n o l . , 32 ( 6 ) : 56.  B e r r y , M.R., J r . 1979. The s t e r i l i z a t i o n of food i n pouches - c r i t i c a l parameters f o r s t i l l p r o c e s s i n g . P r o c e e d i n g s o f the c o n f e r e n c e h e l d i n I n d i a n a p o l i s , IN: Using R e t o r t Pouches Worldwide - Focus on the Present w i t h a Look t o the F u t u r e . Sponsored by Food S c i e n c e s I n s t . Purdue U n i v . , March 14-15, p.7. B e r r y , M.R., J r . and K o h n h o r s t , A.L. thermal p r o c e s s i n g o f i n s t i t u t i o n a l ( 6 ) : 487.  1983. C r i t i c a l factors for pouches. J . of Food P r o t . 46  B e v e r l y , R.G. 1979. S t e r i l i z a t i o n methodology a p p l i e d t o pouches and trays. P r o c e e d i n g s of the c o n f e r e n c e h e l d i n I n d i a n a p o l i s , IN: U s i n g R e t o r t Pouches Worldwide - Focus on the P r e s e n t w i t h a Look to the F u t u r e . Sponsored by Food S c i e n c e s I n s t . Purdue U n i v . , March 14-15, p.102.  -110-  B e v e r l y , R.G. (3):100.  1980.  Retort  pouch  i n the  '80's.  Food  Eng.  52  B e v e r l y , R.G., S t r a s s e r , J . and Wright, B. 1980. C r i t i c a l f a c t o r s i n f i l l i n g and s t e r i l i z i n g o f i n s t i t u t i o n a l pouches. Food T e c h n o l . 34 (9): 44. Brown, F. and Keegan, P.B. Packaging 46 ( 1 2 ) : 314.  1973.  Heat  sealing  methods.  Modern  Burke, P.T. and S c h u l t z , G.L. 1972. The comparative performance o f f l e x i b l e packages and metal cans. T e c h n i c a l Report, Army N a t i c k L a b o r a t o r i e s , N a t i c k , MA. Cage,  J.K. and C l a r k , W.L. 1980. O p p o r t u n i t i e s and c o n s t r a i n t s f o r f l e x i b l e packaging o f f o o d s . Food T e c h n o l . 34 ( 9 ) : 28.  Cruess, W.V. 1958. Commercial F r u i t and V e g e t a b l e P r o d u c t s , McGraw-Hill Book Company, I n c . , New York, NY.  4 t h Ed.,  D a v i s , E.G., K a r e l , M. and P r o c t o r , B.E. 1960. The pressure-volume r e l a t i o n i n f i l m packages d u r i n g heat p r o c e s s i n g . Food T e c h n o l . 14 ( 3 ) : 165. D a v i s , R.B., L o n g , F . E . and R o b e r t s o n , W.F. 1972. Engineering c o n s i d e r a t i o n s i n r e t o r t p r o c e s s i n g o f f l e x i b l e packages. Food T e c h n o l . 26(8): 65. Ebben, K.M. 1979. P r o d u c i n g p o u c h e s and t r a y s t o s u i t p a r t i c u l a r needs. P r o c e e d i n g s o f the c o n f e r e n c e h e l d i n I n d i a n a p o l i s , IN: U s i n g R e t o r t Pouches Worldwide - Focus on t h e P r e s e n t w i t h a Look to the F u t u r e . Sponsored by Food S c i e n c e s I n s t . Purdue Univ., March 14-15, p. 27. Evans, K.W. 1977. The e f f e c t o f entrapped a i r on the r a t e of heat p e n e t r a t i o n i n s t e r i l i z e d f l e x i b l e pouches. T e c h n i c a l Memo No. 164, The Campden Food P r e s e r v a t i o n Research Assn., p.16. G a g l i a r d i , G.R., S u l l i v a n , D. and Smith, N.F. 1984. video i n s p e c t i o n . Food T e c h n o l . 38 ( 4 ) : 53. Ghosh, A. and R i z v i , S.S.H. 1982. Correction d e s t r u c t i v e measurement o f r e s i d u a l volume pouches. J . o f Food S c i . 47 ( 3 ) : 969. G o l d f a r b , P.L. 1970. Pouch f o r l o w - a c i d i n g 43 ( 1 2 ) : 70. G o l d f a r b , P.L. 1971. Pouch Packaging 44 ( 1 ) : 70.  foods.  f o r low-acid  Computer-aided  f a c t o r s f o r nonof a i r i n r e t o r t  P a r t I , Modern Packag-  foods.  Part  I I , Modern  -111-  G y l y s , R.B. and R i z v i , S.S.H. 1983. f o r d e t e r m i n a t i o n of a i r content S c i . 48 ( 3 ) : 1560.  A simple n o n - d e s t r u c t i v e method i n polymeric packages. J . Food  Heid, J . L . 1970. R e t o r t p r o c e s s minimizes r e s i d u a l headspace w i t h ' b r e a t h a b l e ' pouch. Food Product Develop. 4 ( 6 ) : 82. H e i n t z , D.A. 1980. Marketing T e c h n o l . 34 ( 9 ) : 32. Hu,  o p p o r t u n i t i e s f o r the r e t o r t  gases  pouch.  Food  R.H., L e g a u l t , Nelson R. and S t e i n b e r g , M.P. 1955. F e a s i b i l i t y of u s i n g p l a s t i c f i l m packages f o r heat processed f o o d s . Food Techn o l . 19 ( 9 ) : 236.  H u e r t a - E s p i n o s a , V.M. 1981. S i g n i f i c a n c e of A i r Removal i n I n s t i t u t i o n a l S i z e R e t o r t a b l e Pouches, M.Sc. T h e s i s , Oregon S t a t e U n i v e r s i t y , C o r v a l l i s , OR. K a r e l , M. 1974. Packaging protection for Food T e c h n o l . 28 ( 8 ) : 50. K e l l e r , R.G. 1959. Flexible Packaging 33 ( 1 ) : 145.  packages  for  oxygen-sensitive  processed  Khazanie, R. 1979. Elementary S t a t i s t i c s i n a World Goodyear P u b l i s h i n g Co., I n c . , Santa Monica, CA.  products.  foods.  of  Modern  Applications,  Kopetz, A.A., Prange, C A . and F l e s s n e r , R.J. 1979. The f u t u r e i n our hands: c r i t i c a l f a c t o r s i n r e t o r t pouch thermal p r o c e s s assurance. A c t i v i t i e s Report of the R&D A s s o c i a t e s 31 ( 2 ) : 49. Lampi, R.A. 1977. Food Res. 23:  Flexible 305.  packaging  f o r thermoprocessed  Lampi, R.A. and Rubinate, F . J . 1973. Performance r e t o r t pouch s e a l s . Food T e c h n o l . 30 ( 2 ) : 38.  and  foods.  integrity  Adv.  of  Lampi, R.A., S c h u l z , G.L., C i a v a r i n i , T. and Burke, P.T. 1976. Thermoprocessed foods i n f l e x i b l e packages: t r a n s i t i o n to p r o d u c t i o n . Package D e v e l . 3 ( 4 ) : 12. Le,  CP 1978. UBC MFAV A n a l y s i s of V a r i a n c e / c o v a r i a n c e . C e n t r e , U n i v e r s i t y of B r i t i s h Columbia, Vancouver, BC.  L o n c i n , M. and Merson, R.L. 1979. Food E n g i n e e r i n g Selected Applications. Academic P r e s s , New York,  Computing  - Principles NY.  and  Lopez, A. 1981. A Complete Course i n Canning. Book I . B a s i c Inform a t i o n on Canning, 11th Ed., The Canning Trade Inc., B a l t i m o r e , MD. M a n t e l l , C.L. (Ed.) 1958. E n g i n e e r i n g M a t e r i a l s Handbook, McGraw-Hill Book Co., New York, NY.  1st  Ed.,  -112-  M e r m e l s t e i n , N.H. 1976, An overview Food T e c h n o l . 30 ( 2 ) : 28.  of the r e t o r t  pouch  i n the U.S.  M e r m e l s t e i n , N.H. 1978. R e t o r t pouch earns 1978 IFT food technology i n d u s t r i a l achievement award. Food T e c h n o l . 32 ( 6 ) : 22. M i l l e v i l l e , H.P. 1980. Steam/air r e t o r t i n g o f pouches: problems, utions. A c t i v i t i e s Report o f t h e R&D A s s o c i a t e s 32 ( 2 ) : 45. Milleville, H.P. 1 9 8 1 . Retort P r o c e s s i n g 42 ( 1 ) : 92.  pouch  processing  advances.  sol-  Food  M i l l e v i l l e , H.P. and Badenhop, A.F. 1980. G u i d e l i n e s on good manuf a c t u r i n g p r a c t i c e f o r s t e r i l i z a b l e f l e x i b l e packaging o p e r a t i o n s for low-acid foods. From T e c h n i c a l Manual No. 4, Campden Food P r e s e r v a t i o n R e s e a r c h A s s o c i a t i o n , D e p t . o f Food S c i e n c e and T e c h n o l . , Oregon S t a t e Univ., C o r v a l l i s , OR. M o r r i s , C.E. 1981. I n s i d e North America's new r e t o r t pouch p l a n t . Eng. 53 ( 6 ) : 56. Nelson, A . I . , Hu, K.H. and S t e i n b e r g , M.P. 1956. films. Modern Packaging 29 ( 1 0 ) : 173. Nelson, A . I . and S t e i n b e r g , M.P. bags. Food Eng. 28 ( 1 ) : 92.  1956.  Food  Heat p r o c e s s i b l e food  Retorting  foods  i n plastic  O l s o n , F.C.W. and J a c k s o n , J.M. 1942. H e a t i n g c u r v e s , practical application. I n d . Eng. Chem. 34: 337.  t h e o r y and  P a t i n o , H. and H e i l , J.R. 1985. A s t a t i s t i c a l a p p r o a c h t o e r r o r a n a l y s i s i n thermal p r o c e s s c a l c u l a t i o n s . J . of Food S c i . 50 ( 4 ) : 1110. P e r e i r a , V i n c e n t e de P a u l a 1980. P r o c e s s i n g of Cherry P i e F i l l i n g i n R e t o r t a b l e Pouches. Ph.D. T h e s i s , Michigan S t a t e Univ. Dept. o f Food S c i e n c e and Human N u t r i t i o n , E a s t L a n s i n g , MI. P e t e r s , J.W., 1975. R e t a i l debut o f r e t o r t pouch earns consumer a c c e p t ance. Food Product D e v e l . 9 ( 2 ) : 22. P e t e r s , J.W. 1985. 'Niche Packaging 30 ( 3 ) : 31.  marketing'  targets retort  pouch  a t campers.  P e t e r s o n , W.R. and Adams, J.P. 1983. Water v e l o c i t y e f f e c t on heat p e n e t r a t i o n parameters d u r i n g i n s t i t u t i o n a l s i z e r e t o r t pouch p r o cessing. J . o f Food S c i . 48 ( 2 ) : 457. P e t e r s o n , W.R. and Adams, J . P . 1985. T e m p e r a t u r e s e n s o r p l a c e m e n t e r r o r s i n i n s t i t u t i o n a l s i z e r e t o r t pouches. J . o f Food S c i . 50 ( 1 ) : 192.  -113-  P f l u g , I . J . 1964. E v a l u a t i o n o f H e a t i n g M e d i a f o r P r o d u c i n g S h e l f S t a b l e Food i n F l e x i b l e Packages. Phase I . F i n a l Report, C o n t r a c t DA19-AMC-145(N). US Army N a t i c k L a b o r a t o r i e s , N a t i c k , MA. P f l u g , I . J . 1975. P r o c e d u r e s f o r C a r r y i n g Out a Heat P e n e t r a t i o n T e s t and A n a l y s i s o f t h e R e s u l t i n g Data. U n i v e r s i t y o f Minnesota P r e s s , M i n n e a p o l i s , MN. P f l u g , I . J . , Boch, J.H. and Long, F.E. 1963. S t e r i l i z a t i o n f l e x i b l e packages. Food T e c h n o l . 17 ( 9 ) : 87.  o f foods i n  P f l u g , I . J . and B o r r e r o , C. 1967. H e a t i n g Media f o r P r o c e s s i n g Foods i n F l e x i b l e Packages. Phase I I . Tech. Rep. 67-47-GP. U.S. Army N a t i c k L a b o r a t o r i e s , N a t i c k , MA. P o t t e r , K.M., Tung, M.A. and K i t s o n , peach s l i c e s s t o r e d i n f l e x i b l e T e c h n o l . J . 15 ( 2 ) : 96.  J.A. 1982. Q u a l i t y o f processed pouches. Can. I n s t . Food. S c i .  P r z y b y l a , A. 1984. S h e l f s t a b l e foods e x p e r t i s e p r o d u c t i o n . P r e p a r e d Foods 153 ( 5 ) : 90.  lies  i n retort  pouch  Ramaswamy, H.S., 1983. Heat T r a n s f e r S t u d i e s of Steam/air M i x t u r e s f o r Food P r o c e s s i n g i n R e t o r t Pouches. Ph.D. T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia, Vancouver, BC. Ramaswamy, H.S., Tung, M.A. and S t a r k , R. 1983. A method t o measure s u r f a c e heat t r a n s f e r from steam/air m i x t u r e s i n batch r e t o r t s . J . o f Food S c i . 48 ( 3 ) : 900. Rees, J . A . 1979. S t e r i l i z a t i o n m e t h o d o l o g y a p p l i e d t o p o u c h e s and trays. P r o c e e d i n g s o f t h e c o n f e r e n c e h e l d i n I n d i a n a p o l i s , IN: U s i n g R e t o r t Pouches Worldwide - Focus on t h e P r e s e n t w i t h a Look to the F u t u r e . Sponsored by Food S c i e n c e s I n s t . Purdue Univ., March 14-15., p.88. R i z v i , S.S.H. and G y l y s , R.B. 1983. N o n - d e s t r u c t i v e a i r i n pouches. Packaging 28 ( 9 ) : 65.  method  R i z v i , S.S.H. and Klemaszewski, J . L. 1985. S i m p l i f i e d amount o f a i r i n packages. Packaging 30 ( 3 ) : 72.  test  measures  measures  Roop, R.A., Marks, J . S . and N e l s o n , P.E. 1983. E f f e c t o f thermal p r o c e s s i n g and a g i t a t i o n i n 100% steam on t h e s e a l s t r e n g t h o f r e t o r t a b l e pouches. J . o f Food S c i . 48 ( 1 ) : 250-252. Roop, R.A. and Nelson, P.E. 1981. P r o c e s s i n g r e t o r t pouches ventional s t e r i l i z e r s . J . o f Food S c i . 47 ( 1 ) : 303. Rubinate, F . J . 1964. 71.  A new l o o k i n p a c k a g i n g .  i n con-  Food T e c h n o l . 18 ( 1 1 ) :  -114-  Shappee, J . and Werkowski, S . J . 1972. Study o f a N o n - d e s t r u c t i v e T e s t f o r D e t e r m i n i n g the Volume o f A i r i n F l e x i b l e Food Packages. Techn i c a l Report, Army N a t i c k L a b o r a t o r i e s , N a t i c k , MA. Shenkenberg, D. 1975. USDA s t a t u s on f l e x i b l e r e t o r t a b l e pouches f o r meat p r o d u c t s . A c t i v i t i e s Report o f t h e R&D A s s o c i a t e s 27 ( 1 ) : 157. Smith, T., Tung, M.A., Bennett, L. and Cumming, D.B. 1985. Importance of removing condensate from v e r t i c a l r e t o r t s . Food T e c h n o l . , 39 ( 6 ) : 53. Snedecor, G.W. 1965. Statistical U n i v e r s i t y P r e s s , Ames, IA.  Methods,  5th ed., The Iowa  State  S t e f f e , J . F . , W i l l i a m s , J.R., C h i n n a n , M.S. and B l a c k , J.R. 1980. Energy requirements and c o s t s o f r e t o r t pouch v s . can packaging systems. Food T e c h n o l . 3 4 ( 9 ) : 39. S t r a s s e r , J.H. 1979. Update on r e t o r t pouch f i l l e r s and A c t i v i t i e s Report o f the R&D A s s o c i a t e s 31 ( 2 ) : 54. Stumbo, C.R. 1973. Therraobacteriology Academic P r e s s , New York, NY. Toyo Seikan K a i s h a L t d . 1973. Opening Guide, Tokyo, Japan.  i n Food  up  Processing.  tomorrow's  sterilizers.  2nd. Ed.,  markets.  RP-F  Tsutsumi Y. 1972. R e t o r t pouch - i t ' s development and a p p l i c a t i o n t o f o o d s t u f f s i n Japan. Japan P l a s t i c s 1:24. Tsutsumi Y. 1974. The growth o f r e t o r t a b l e pouch food packaging i n Japan. The 36th Annual N a t i o n a l Packaging Forum o f the Packaging I n s t i t u t e , C h i c a g o , I L , October 7-9. T s u t s u m i , Y. 1979a. New t e c h n o l o g y a p p l i e d t o p o u c h e s and f u t u r e trends. P r o c e e d i n g s o f the c o n f e r e n c e h e l d i n I n d i a n a p o l i s , IN: U s i n g R e t o r t Pouches Worldwide - Focus on the P r e s e n t w i t h a Look to the F u t u r e . Sponsored by Food S c i e n c e s I n s t . Purdue Univ., March 14-15, p.67-68. Tsutsumi, Y. 1979b. S t e r i l i z a t i o n methodology a p p l i e d t o pouches and trays. P r o c e e d i n g s o f the c o n f e r e n c e h e l d i n I n d i a n a p o l i s , IN: U s i n g R e t o r t Pouches Worldwide - Focus on t h e P r e s e n t w i t h a Look to the F u t u r e . Sponsored by Food S c i e n c e s I n s t . Purdue U n i v . , March 14-15, p.86-87. Tung, M.A. and G a r l a n d , T.D. 1978. Computer p r o c e s s e s . J . Food S c i . 43 ( 2 ) : 365.  calculation  o f thermal  -115-  Tung, M.A., Ramaswamy, H.S. and Papke, A.M. 1984a. T h e r m o p h y s i c a l S t u d i e s f o r Improved Food P r o c e s s e s . F i n a l Report. DSS F i l e No. 35SZ.01804-9-0001, prepared f o r t h e A g r i c u l t u r e Canada PDR Program, Ottawa, ON. Tung, M.A., Ramaswamy, H.S., Smith, T. and S t a r k , R. 1984b. Surface heat t r a n s f e r c o e f f i c i e n t s f o r steam/air m i x t u r e s i n two p i l o t scale r e t o r t s . J . Food S c i . , 49 ( 3 ) : 939. Tung, M.A. and Smith, T. 1980. I n n o v a t i o n s i n thermal p r o c e s s i n g , i n Processing 2000 Symposium, p.103, MacDonald College of M c G i l l U n i v e r s i t y , M o n t r e a l , PQ. Tuomy, J.M. and Young, R. 1982. R e t o r t - p o u c h packaging o f muscle foods f o r t h e armed f o r c e s . Food T e c h n o l . 36 ( 2 ) : 68. Wallenberg, E. and J a r n h a l l , B. 1957. Modern Packaging 31 ( 7 ) : 165. Whitaker, W.C. 1971. 44 ( 2 ) : 83.  Processing  Heat s t e r i l i z a t i o n  flexible  pouches.  i n plastics.  Modern Packaging  W i l l i a m s , J.R., S t e f f e , J . F . and B l a c k , J.R. 1983. S e n s i t i v i t y of s e l e c t e d f a c t o r s on c o s t s o f r e t o r t pouch packaging systems. Food T e c h n o l . 37 ( 4 ) : 92. W i l s o n , D.C. 1980. T h e o r e t i c a l problems i n pouch p r o c e s s i n g . Proceedi n g s of winter meeting o f American S o c i e t y of A g r i c u l t u r a l E n g i n e e r s , Chicago, I L . December 2-5. Yamaguchi, K., Komatsu, Y. and K i s h i m o t o , A. 1972. S t e r i l i z a t i o n of foods i n f l e x i b l e packages, P a r t V I , N o n - d e s t r u c t i v e method f o r d e t e r m i n i n g r e s i d u a l a i r i n pouches. J . Food S c i . T e c h n o l . (Japan) 19 ( 7 ) : 316. Yamano, Y. 1976. S t u d i e s o f Thermal P r o c e s s i n g o f F l e x i b l e Food Packages by Steam and A i r R e t o r t . Ph.D. T h e s i s , Kyoto U n i v e r s i t y , Kyoto, Japan. Yamano, Y. and Komatsu, Y. 1969. S t e r i l i z a t i o n o f foods i n f l e x i b l e p a c k a g e s , P a r t I , Heat c h a r a c t e r i s t i c s o f a p i l o t r e t o r t f o r s t e r i l i z a t i o n o f f l e x i b l e packages. J . Food S c i . T e c h n o l . (Japan) 16 ( 3 ) : 113. Young, K.E. 1984. Thiamine D e g r a d a t i o n i n a Luncheon-type Ham Product T h e r m a l l y Processed i n R e t o r t Pouches and Cans. M.Sc. T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia, Vancouver, BC. Zar,  J . H . 1974. Biostatistical Englewood C l i f f s , NJ.  Analysis.  Prenctice  Hall Inc.,  -116-  APPENDIX I N o n - d e s t r u c t i v e A i r Measurement  Archimedes P r i n c i p l e :  B - Mg = pV g - p V g = (p - p ) V g Q  where  B Mg p p V g  = = = = = =  Q  Q  Applied  o  Q  Q  buoyant f o r c e (upward) weight o f o b j e c t ( f o r c e downward) density of surrounding f l u i d density of object volume o f o b j e c t gravitational field  to non-destructive  Mg - B = p  1.  Q  Q  a i r measurement  V g - p V g = (p -p) Q  Q  V g  Q  Q  Before a i r a d d i t i o n  W  M  B  b§ -  l = (Pb-Pw)  V  wb  =  W^ M^ Bj  = = =  weight o f b r i c k i n water mass of b r i c k buoyant f o r c e ( b e f o r e a i r added)  P^  = =  density of b r i c k volume o f b r i c k  where w  2.  After a i r addition  W  w b a " b a " 2 - (Pb+a " P > < V a > g M  +  B  +  V  W  where  ^wb+a M^ B2 +a  P^ V„ a  + a  =  = = = =  weight o f b r i c k and a i r i n water mass of b r i c k and a i r buoyant f o r c e ( a f t e r a i r added) d e n s i t y o f b r i c k and a i r volume o f a i r  -117-  Expand these e q u a t i o n s .  From E q u a t i o n  1: W  wb = Pb V  - PwV  = M g -  p V g  b  M  W  b § = wb  +  w  b  V  Pw b§  From E q u a t i o n 2: W  wb a - Pb a +  M  - b a +  M  (  +  W  b + a § = wb+a  W  V  S  " Pw ( V a > 8  8 " Pw < V a > 8 V  +  Pw  (  W  Assuming mass of a i r n e g l i g i b l e , then M W  V  W  +  wb + Pw b § = wb+a  b + a  S  = M V  b  + V  Pw ( b a > 8  Rearrange t o : W  W  V  wb - wb+a = P ( b  + V  W  a)8 - P V g w  b  = P V g + P V g - p V g w  b  Amg  = p V g  Am  = pwVa  w  w  a  w  b  a  Assuming d e n s i t y o f water a t 25°C = 1.0 g/mL, f o r each mL o f a i r added, the mass of the b r i c k and a i r w i l l be reduced by 1.0 g.  -118-  APPENDIX I I Back C a l c u l a t i o n s f o r Combination o f D e s t r u c t i v e and A i r Measurements  1.  Leakage o f a i r d u r i n g p r o c e s s i n g ,  Non-destructive  mL:  = (B-A) 1.0 mL/g 2.  Non-destructive  volume, post p r o c e s s i n g ,  = (I-A) 1.0 3.  mL/g  I n i t i a l volume of a i r ( b e f o r e a i r a d d i t i o n ) , = V - (I-A) 1.0  4.  mL:  mL:  mL/g  P r o j e c t e d weight of pouch c o n t a i n i n g no a i r , g: = A + V 1.0  where:  g/mL  V =  c o r r e c t e d d e s t r u c t i v e a i r measurement  I =  f i r s t n o n - d e s t r u c t i v e a i r r e a d i n g (g) ( p r i o r to a i r addition)  B =  second n o n - d e s t r u c t i v e a i r r e a d i n g (g) (before processing)  A =  t h i r d n o n - d e s t r u c t i v e a i r r e a d i n g (g) ( a f t e r processing)  (mL)  -119-  APPENDIX I l i a H e a t i n g r a t e index v s . i n c l u d e d a i r relationship f o r thin bricks i n p o s i t i v e f l o w steam/air r e t o r t ( a , 115°C; b, 120°C; c, 125°C).  Legend A 65% lltom  X 75% sttom • X  • 8 5 % steom • X  EL  O  x  X  D  *  A  *  8  A  4X  I  gA  Legend A 6 5 % steom X 75% steom D D  • 8 5 % steam  0)  c o  ca  u> x  "5  *x£>  A*  A A  X  IX*£°  u 1312-  O•  *  X  Legend A 6 5 % steom X 7 5 % steom • 8 5 % steam  fi  11-  1  • o o  10 9  • •  8-  a 7-  X  D £  *X  A 6-  A  A  *AA X  A  'AA A i  5 IS  20  Included A i r ( m L )  25  i 30  35  -120-  APPENDIX I l l b i n g r a t e index v s . i n c l u d e d a i r r e l a t i o n s h i p f o r t h i c k bricks p o s i t i v e flow steam/air r e t o r t ( a , 115°C; b, 120°C; c, 125°C).  32  TT •  30-|  Legend  29 28  26-|  •  A  653 steom  X  753 steom  •  8 5 3 steom  O  ° oft  25  O  •  D  24  x  •  A  2322-  x  x  D  D  A *  x° *  2120 *  19 18  A x A  A A  H  3130-  Legend  29c  x V  28-  A  27-  x 753 steom  TJ  25-  oo r  23  Ol _c  22  c  •  26-  653 steom  8 5 3 steom  24  "5 x«  D  D  • A • X  21  (  A  19  A  A  A  A A  a  20  A ,  A X  •  18  31 30  Legend  29  A 6 5 3 steom  28 27 26  X  753 steom  •  6 5 3 steom  u  oo o o  25 24 23  X  22  • X  X  x 21 X X  20 19  *  A  4  X X  A  A *A  18 17  x x x x x  4  - i — 15  20  Included A i r (mL)  25  30  35  -121-  APPENDIX I I I c ;ating r a t e index v s . i n c l u d e d a i r relationship for thin bricks p o s i t i v e f l o w w a t e r / a i r r e t o r t ( a , 115°C; b, 120°C; c, 125°C).  Legend A  Pr. lev. 1  X  Pr. lav. 2  •  Pr. lav. 3  o  • •  o o  Q  Q<d& x  • A'  A ^  A D  A  X  *  AXA  6H  Legend  9H  A  Pr. lav. 1  X  Pr. lav. 2  D  Pr. lev. 3  x  t?  •o  x "  x  •  "5  X x  cc .c  7H  fl  "5  I  D  X  A  x  6H  Legend ro H  7 ^ °>b A A  A  Pr. lav. 1  x  Pr. lav. 2  D  Pr. lav. 3  A  A "  X  A  6H  10  15  20  Included Air (mL)  25  30  35  -122-  APPENDIX H i d H e a t i n g r a t e index v s . i n c l u d e d a i r r e l a t i o n s h i p f o r t h i c k b r i c k s p o s i t i v e flow w a t e r / a i r r e t o r t ( a , 115°C; b, 120°C; c, 125°C).  2827-  Legend  26-  A  Pr. l a v . 1  25-  x  Pr. l e v . 2  24-  •  Pr. l e v . 3  O'  X  23-  •  ®  O  D D X  2221-  O  •  X .  X  A X  A  20A  •  x x  A  A  K  A  A ,  19-  18-  27-  Legend  26A  Pr. l e v . 1  25-  X  Pr. l e v . 2  24-  •  Pr. l e v . 3  • • O  •8 »H  "5  20-  _c  <c I  D  22-  2H 19-  X  X  c £ O OC CT,  • o  aP °  * AA  D  D  A  0  •a  X  *  0  D  • x  *  A  P  h  27-  Legend  26-  A Pr. l e v . 1  25-  X  Pr. l e v . 2  24-  Q  Pr. l e v . 3  • •  •  23-  •  D  2221-  X  o  A  A  19-  X*  A#  20A*  D  *  A  A  A  XX  A  A  *A  **•  X  18-  n-  —T— K>  15  20  Included A i r ( m L )  -i— 25  —r— 30  35  

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