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Studies on intermediate moisture beef meat patties Fierheller, Murray Gordon 1974

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STUDIES ON INTERMEDIATE MOISTURE BEEF MEAT PATTIES by MURRAY GORDON FIERHELLER B.Sc, Un i v e r s i t y of B r i t i s h Columbia, 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of Food Science We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA October, 1974 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e fo r reference and study. I f u r t h e r agree t h a t permiss ion for e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . It i s understood that copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be a l lowed without my w r i t t e n p e r m i s s i o n . Department of /tk*t^ } c it'll(:' C-The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada / i ABSTRACT Recent studies have shown that intermediate moisture foods, while stable to microbia l growth, are susceptible to chemical changes resu l t ing i n loss of qua l i t y . This study observed the effects of different water a c t i v i t i e s , c i t r i c acid contents, fat contents, and pH on l i p i d oxidat ion and non-enzymatic browning of a meat product. An intermediate moisture beef patty was produced by equi-l i b r a t i n g and cooking the raw meat i n various g l y c e r o l , water, c i t r i c acid and sodium chlor ide solu t ions . Experimental resul ts showed that peroxide values increase with increasing water a c t i v i t i e s between Aw 0.655 and 0.818. C i t r i c acid d id not affect the formation of peroxides but prevented peroxide breakdown. There was a loss of the brown colour of the cooked meat patty and an increase i n yellowness possibly due to oxida t ion . The loss of colouring and yellowing was greatest at low pH and high water a c t i v i t i e s . Non-enzymatic browning was not apparent. L i p i d oxidat ion was the primary cause of the product de ter iora t ion . The shelf l i f e was l imi ted to three to four months by the development of rancid odours. i i TABLE OF CONTENTS Page Introduction . . 1 Literature Review 4 Methods and Materials 9 Results and Discussion 16 Bibliography 43 i i i LIST OF TABLES Table Page I Sample Combinations for L i p i d Oxidation Analysis Showing Fat, C i t r a t e , G l y c e r o l , Moisture Contents and Water A c t i v i t i e s . 10 II Sample Combinations for Non-enzymatic Browning Analysis Showing Fat, C i t r a t e , Moisture, Glycerol Contents and Water A c t i v i t i e s . . . . 12 III Analysis of Variance - Peroxide Values . . . . . . . . 19 IV Duncans Mult i p l e Range Test - E f f e c t s of D i f f e r e n t Water A c t i v i t i e s on Peroxide Values 19 V Monomolecular Rate Constants Showing C o r r e l a t i o n Constant to Equation 1 20 VI Duncans M u l t i p l e Range Test - E f f e c t s of D i f f e r e n t C i t r a t e Levels and Aw on Peroxide Values 23 VII Duncans Mult i p l e Range Test - E f f e c t s of Fat Levels and Aw on Peroxide Values 29 VIII Duncans M u l t i p l e Range Test - Change i n pH with Time . 29 IX Analysis of Variance - Hunter L and b Values 32 X Duncans M u l t i p l e Range Test -. Changes i n Hunter L and b Values with Time . 32 XI Duncans Mult i p l e Range Test - I n i t i a l Hunter L and b Values at D i f f e r e n t Water A c t i v i t i e s 35 XII Duncans M u l t i p l e Range Test - I n i t i a l Hunter L and b Values at D i f f e r e n t pH 39 XIII Analysis of Variance - Block Differences 40 i v LIST OF FIGURES Figure Page 1 Change i n Peroxide Value at D i f f e r e n t Water A c t i v i t i e s (0% C i t r a t e ) . 17 2 Rate of L i p i d O x i dation at D i f f e r e n t Water A c t i v i t i e s 22 3 Change i n Peroxide Value at D i f f e r e n t C i t r a t e Levels (Aw 0.818) 24 4 Change i n Peroxide Value a t D i f f e r e n t C i t r a t e L evels (Aw 0.707) 26 5 Rate of L i p i d O x i dation at D i f f e r e n t C i t r a t e Concentrations 27 • 6 Change i n pH w i t h Time at D i f f e r e n t Water A c t i v i t i e s 30 7 Change i n Hunter L and b Values at D i f f e r e n t Water A c t i v i t i e s 34 8 • D i f f e r e n c e s i n Hunter Colourmeter Values Between the I n i t i a l Observation at 10 Days and Each Subsequent Observation at D i f f e r e n t 'Water A c t i v i t i e s 36 9 D i f f e r e n c e s i n Hunter Colourmeter Values Between the I n i t i a l Observation and Each Subsequent Observation at D i f f e r e n t pH Levels . . 38 ACKNOWLEDGEMENT I wish to thank the members of my committee, Professor E.L. Watson, Department of A g r i c u l t u r a l Engineering and my thesis supervisor; Dr. W.D. Powrie, Head of Department of Food Science; Dr. J.F. Richards and Dr. M.A. Tung, professors i n the Department of Food Science, for t h e i r help i n preparing t h i s t h e s i s . I also wish to give a s p e c i a l note of thanks to my wife, Susan, f o r her dedicated support and much appreciated assistance. 1 INTRODUCTION Intermediate moisture foods (IMF) do not have a r i g i d d e f i n i t i o n . C h a r a c t e r i s t i c a l l y they have reduced moisture contents to prevent microbial spoilage but r e t a i n enough moisture to present a s o f t moist texture. T y p i c a l examples are dried f r u i t s , honey, maple.syrup, some dried sausages, and f r u i t cake. Intermediate moisture foods are therefore a t t r a c t i v e because of several properties: 1. They do not require r e f r i g e r a t i o n or thermal processing. With a water a c t i v i t y (Aw) below 0.80 they are stable to b a c t e r i a l , yeast and most mold growth. (29) 2. They do not require rehydration before consumption, as i s the case with freeze-dried products. Their moisture content i s i n the range of 20% to 50%, but they s t i l l r e t a i n a soft moist texture. 3. The packaging requirements are n o t ^ s t r i c t ; cheap, f l e x i b l e materials are s u f f i c i e n t . If the package i s broken IMF are not susceptible to spoilage. (31) If an IMF was manufactured by dehydration.to the desired moisture content, most products would have a dry, b r i t t l e texture, even at an Aw of 0.85. The only products capable of r e t a i n i n g a s o f t , moist texture are those with a high natural soluble s o l i d s content: f o r example, f r u i t s . The soluble s o l i d s l e v e l would have to be increased fo r products high i n protein or starch. Bone (3) outlines the c r i t e r i a 2 fo r choosing such solutes. At present, g l y c e r o l , sodium chloride, sugars and combinations of these seem to be the most useful solutes. (4) A major problem i n choosing a humectant i s the flavour i t imparts to the product. Commercially, IMF technology has gained i t s greatest s t r i d e s i n the pet food industry. The main humectant used i s sucrose, i n amounts ranging from 20-30%. Dogs do not object to t h i s excessive sweetness, but most humans would not f i n d many dishes palatable. (16) This problem w i l l of course have to be solved before IMF are acceptable for human consumption. IMF were thought to be remarkably stable during t h e i r i n i t i a l development. Labuza (18) states that both l i p i d oxidation and non-enzymatic browning reach a maximum between Aw 0.50 and 0.85. Enzymatic a c t i v i t y also increases with increasing Aw but i s e a s i l y c o n t r o l l e d by blanching or cooking. Both browning and autoxidation cause o f f - f l a v o u r and odors, t e x t u r a l changes such as increased toughness, loss of water binding capacity, loss of colour or darkening of colour, and decreased n u t r i t i o n a l q u a l i t y . L i p i d oxidation i s e s p e c i a l l y serious because of the low threshold l e v e l s of the obnoxious products. The C 0-C 1 0 aldehydes are a l l detectable by smell at l e v e l s as lowaas .001 to .01 ppm. (23) This research w i l l i nvestigate the development of non-enzymatic browning and l i p i d oxidation i n an intermediate moisture meat product. This study w i l l also investigate the e f f e c t s of high concentrations bf c i t r i c acid ( 1 % to 2%) which reduce the pH and thus possibly retard non-enzymatic browning. As a sequestering agent, c i t r i c acid binds trace metals and possibly retards l i p i d oxida t ion . C i t r i c acid imparts a pleasant sour taste sensation that can be used to mask the harsh b i t t e r -sweet f lavour of g l y c e r o l , or the excessive sweetness of glucose and sa l t iness of sodium chlor ide . 4 LITERATURE REVIEW Intermediate moisture foods were o r i g i n a l l y thought to be stable to oxidative r a n c i d i t y . Brockman (4) observed no s i g n i f i c a n t chemical, ph y s i c a l or sensory changes i n m i l i t a r y experimental IMF a f t e r four months storage at 38°C. Loncin e_t a l . (25) observed no d i f f e r e n c e i n the oxidation rate between Aw 0.11 and 0.75. They did observe a marked increase i n the peroxide value at Aw below 0.18.• Their work was done on ,spray dried milk powder. L i p i d oxidation has long been known to be a problem at the low water a c t i v i t i e s of dehydrated foods. An increase i n the moisture from Aw 0 was observed to decrease oxidation. Salwin (33) found the moisture content, with optimum protective e f f e c t , to be near the monolayer value for most foods. In a review, Labuza (18) states the main protective mechanisms are: 1) Water hydrogen bonds with the hydroperoxides, protecting them from decomposing and i n i t i a t i n g more free r a d i c a l s . 2) Water hydrates the metal c a t a l y s t s of l i p i d oxidation. Water can also form inso l u b l e metal hydroxides, removing the c a t a l y s t s completely. 3) Water decreases the s t a b i l i t y of free r a d i c a l s , reducing the t o t a l number a v a i l a b l e for i n i t i a t i n g l i p i d oxidation. Heidelbaugh and Karel (12) concluded from t h e i r studies that an increase i n Aw from 0.51 to 0.75 increased l i p i d oxidation. In addition, they found that g l y c e r o l added to the model system reduced the antioxidant 5 e f f e c t of water at low water a c t i v i t i e s . Without g l y c e r o l , the optimum Aw at which l i p i d oxidation was at a minimum, was 0.51 and with g l y c e r o l the Aw was 0.20. Labuza (18) presents a " s t a b i l i t y map" showing increased autoxidation i n the intermediate moisture range. He and h i s co-workers have v e r i f i e d t h e i r e a r l i e r findings of increased oxidation rate with increased moisture content. (21), (20), (5), (6) I t i s i n t e r e s t i n g that Heiss and Eichner (14) also presented a " s t a b i l i t y map" about the same time as Labuza, showing no increase i n oxidation with increasing moisture content at high water a c t i v i t i e s . The pro-oxidant e f f e c t of water i n the IM range of Aw 0.6 to 0.8 i s probably due to an increased s o l u b i l i t y of metal c a t a l y s t s to reaction s i t e s . (18), (12) Labuza (18) found that the rate of l i p i d oxidation reached a maximum at high water a c t i v i t i e s . A decrease i n oxidation was observed by increasing Aw from 0.6 to 0.75. In t h e i r model system t h i s increase i n Aw more than doubled the moisture content suggesting a decrease i n rate due to a d i l u t i o n e f f e c t . In l a t e r work, Choii et a l . (5) observed increased l i p i d oxidation up to Aw 0.89. I t i s doubtful whether a decrease i n oxidation does occur i n the high moisture foods except at very high water a c t i v i t i e s . Non-enzymatic browning has been observed to reach a maximum rate between Aw 0.3 and 0.7, depending on the type of food product. (13), (18), (25) Labuza (18) accounts for the maximum as follows: 1) increased d i f f u s i o n and s o l u b i l i t y of reactants with increased moisture content contributes to the increased browning rate at low water 6 a c t i v i t i e s ; 2 ) further increasing the moisture content r e s u l t s i n mass d i l u t i o n causing the observed maximum browning rate, followed by a decrease, at high water a c t i v i t i e s . Loncin et a l . ( 2 5 ) f e e l that the decrease i n browning at the high water a c t i v i t i e s i s due to an i n h i b i t i o n by water, which i s one of the f i r s t products of browning. Eichner and Karel ( 8 ) found that both mass d i l u t i o n and product i n h i b i t i o n reduce browning but that the i n h i b i t i o n by water was f a r greater. Their r e s u l t s also show that i n systems of high v i s c o s i t y , as at low water a c t i v i t i e s ( 0 . 3 2 ) , browning i s decreased. The addition of g l y c e r o l to t h i s low water a c t i v i t y system had a p l a s t i c i z i n g e f f e c t , increasing the rate of browning. From the above l i t e r a t u r e i t would appear that the rate of autoxidation and non-enzymatic browning could determine the shelf l i f e of an IMF. A means for i n h i b i t i n g or reducing these reactions would have to be used i n order to make such a.product successful f o r human consumption. Much work has been done on the use of antioxidants. For commer-c i a l l y rendered f a t s , the best all-round method i s a combination of butylated hydroxyanisol (BHA), propyl g a l l a t e , and c i t r i c a c i d . ( 1 0 ) BHA appears to be the most useful phenolic antioxidant, with low t o x i c i t y CLD,-Q 5 0 0 0 mg/kg body weight of r a t s ) . Butylated hydroxytoluene (BHT) has been observed to i n -crease l i v e r weight and cause abnormal c e l l u l a r behavior. Propyl g a l l a t e i s more e f f e c t i v e i n dried meats than i n products with more moisture, such as sausage. ( 9 ) Chou and Labuza ( 6 ) i n t h e i r study of antioxidants i n IMF found ethylenediaminetetracetic acid (EDTA) to be most e f f e c t i v e , reducing 7 oxidation ten to twenty times over a control. BHA was found to be more effective at the lowest moisture contents studied, a -tocopherol was found to be a f a i r l y poor antioxidant. C i t r i c acid has an advantage in being a natural constituent of many fruits and vegetables and would find approval from the general populus as a food additive. It i s being used in combination with other anti-oxidants. (9) In low levels i t has a synergistic effect. For example, i t prevents discolouration caused by the reaction of propyl gallate with iron, and i t increases the st a b i l i t y of a-tocopherol. (9) There is some doubt of the effectiveness of c i t r i c acid alone as an antioxidant. Labuza et a l . (21) found that c i t r i c acid (100 ppm fat basis) was more effective.at intermediate moisture levels. Their reason was that chelating agents most l i k e l y become bound to protein, reducing their effectiveness. Later, Chou and Labuza (6) found that adding 0.5 moles of sodium citrate per mole of metal reduced l i p i d oxidation in a model system two times. Lemon et a l . (24) found in systems that are free of trace metals or primary antioxidants, c i t r i c acid does not prevent autoxidation. It appears to have only a minor protective effect on animal fats unless there is a high proportion of heavy metals present, causing a low natural s t a b i l i t y . (9) Further work is required to determine i f c i t r i c acid would be more effective in high concentrations. There are various methods of inhibiting non-enzymatic browning. Moisture control as mentioned above is only practical in very low moisture systems. Browning is negligible at temperatures below -20°C. Fermentation to remove sugars has been used with spray-dried egg whites. Chemical food 8 additives are the simplest method. Of the various ad d i t i v e s , s u l f i t e s i n the form of sulphur dioxide or sodium b i s u l f i t e are the most e f f e c t i v e . The sulphite reacts with the sugar moiety, thus i n h i b i t i n g the reaction. (35) S u l f i t e s are l i m i t e d by a.corrosive taste apparent at l e v e l s above 500 ppm. (10) I t i s v o l a t i l e and tends to disappear from open systems. I t also destroys thiamine. Non-enzymatic browning i s base catalyzed. Reynolds (32) observed an increase i n reaction rate of 1.6 to 1.7 times going from pH 3.5 to 4.7, and 2.1 to 2.4 times from pH 4.7 to 5.6. Song and Chichester (34) observed i n a model system that the rate increased considerably as pH approached the pKa value of the re a c t i v e amino ac i d . They also found thata -methyl-D-glucoside i s far le s s r e a c t i v e than glucose and that D-arabinose, which forms l e s s stable hemiacitals, i s more r e a c t i v e , a l l suggesting that the free aldehydic form i s necessary for r e a c t i o n . 9 METHODS AND MATERIALS Materials One boneless beef hip from two d i f f e r e n t animals was used to represent two blocks. Each hip, having the surface adipose f a t removed, was ground once i n a Hobart meat grinder with a V 1 hole p l a t e . The ground meat was mixed w e l l by hand for a more homogeneous sample. The above procedure was followed with the adipose t i s s u e . C i t r i c acid, sodium c i t r a t e , sodium chl o r i d e and potassium sorbate used i n formulating the i n f u s i o n solutions were a l l "Fisher" reagent grade. U.S.P. grade g l y c e r o l was obtained from a l o c a l chemical supplier. G e l a t i n and potato starch used i n formulating the raw meat p a t t i e s were "Fisher" reagent grade. 1. Preparation of samples f o r l i p i d oxidation experiments The ground beef was divided into three l o t s and ground adipose f a t was added to each l o t estimated to give 10%, 15% and 20% f a t contents r e s p e c t i v e l y . 5% g e l a t i n and 5% starch ( t o t a l wet weight basis) were added to each l o t so that these s t a b i l i z e r s would increase the firmness of the cooked product. Twelve i n f u s i o n solutions were formulated with 4 d i f f e r e n t g l y c e r o l contents and 3 d i f f e r e n t c i t r a t e contents. Table I summarizes the 36 sample combinations and shows the f i n a l f a t , c i t r a t e and moisture contents. 0.75% potassium sorbate was added to a l l the i n f u s i o n solutions < P c CD CO o o o ?r fD 03 > < < < ro ro ro M M i-i P 03 03 00 (W oo ro ro ro Q o 03 H - r t CO ro ro r t i-i n C o H > h-1 ro o r t o n • o o 0 3 r t r t • * * •P- t o O V O • • • O N V O Ln v l -P- L n 1+ 1+ 1+ M O O • • • LO v l O O o O N OJ LO o O N v l • • • v l O N o L n v l 1+ 1+ 1+ h- 1 o o • • • tO -p- o 00 00 L n LO -> O o Ln • • • v l o O O N LO v l LO 1+ 1+ 1+ O O o • / • • V O •P- o o v i -P-IV3 L n o 1—' LO • • • 00 O N M o r o oo 1+ i+ 1+ o o o • • • L n •P- o LO O N o 1+ O LO • • l - 1 t o V O O N N> O 5-s i— 1 o Ln O O O • • • O N O N O N L n O N L n -P- LO 00 LO Lo t o O I-1 00 O H 00 t o V O -P* O O O • • • v l v i v l O O I—' I—1 O N v l LO LO LO v l CO v l 00 LO -P-M O O N O O O v l v l v l O N L n v i ro v i M -P- .p- -P--P- tv3 tv3 LO v l O N O -P- LO O O O 00 00 00 H N H H L n j s Ln L n L n -P- -P* LO -P- -P- M O M M L n 1+ O L n t o ' l - * t-i vo S-9 t o M O •. • 5-9 t o O 5 ^ 5-5 Lo M O • • 3-9 LO L n 5-S 5-9 O O O O N O N O N -P - v l 00 00 L n O LO LO LO V O Iv3 L n 00 v l L n O O O v l v l v l O I— i - 1 O vo i—• LO LO LO 00 00 v l O N V O L n -P- 00 L n O O O v l v l v l O N O N v l O N v l t o -P- -P-Ul Ul *• O N -P- v l v i L n O N O O O 00 00 00 N3 tvJ v l O N LO Ln L n L n -P- 4>- tv) I—* O N v l i—1 L n L n t o O 5-8 1+ O O N • • t o L n O N L n 5-3 t o M O • • 5-3 t o O 5-3 5-S LO M O • • 5-9 LO L n 5-3 5-9 O O O O N O N O N -P- -P- L n N 00 ^ t o t o t o O N oo si t o LO O 00 L n LO O O O O N O N v l V O V O o 00 V O 00 LO LO LO O N -P- L n L n OO .p-v l O N v l O O O • • • V l V l VI L n L n O N L n V O O -P- -P- -P--P- -P- t o O N t - 1 V O Ln V D L n O O O 00 00 00 O N H U H H L n L n L n -P- I—1 h-1 -P* O N V D H Di v l Fat Content raw patty Fat Content cooked patty Ci t ra te Content cooked patty Ci t ra te Content Infusion s o l . oo E l o 03 r t 1—• ro o n O > M o v<! r t o ro < <-t o r t i— 1 •• t, 03 03 0 - O N r t Cu L n ro • • I-i s t o o Ln Pd H - P CO r t r t H -C O n ro o H"i o o H 0 r t Hi ro c 0 Ln CO r t o H -o o -P- 0 l-h O n o o I- 1 o C ?r r t ro H-Cu O 0 hi 03 r t r t i *<! LO Ln O N Ln H 03 CT Ui o 03 H- 3 CO X! r t C ro I-i ro n o o Q o CT 0 H « r t 0 ro P 0 r t r t H -CO o 0 03 CO 0 Cu i-h o s i i-i 03 r t f ro H-i-i - 0 H -> Cu o r t O H- X <! H-H- Cu r t P H* r t ro H-CO O 0 > 0 P h- 1 v<! CO H-CO cn 0 * o Z H* 0 OQ P r t o H-r t i-i P r t ro O V ! O ro »-( o 01 11 to inhibit mold contamination. 7.5% sodium chloride was added as a, seasoning and to help reduce the water activity. The infusion solution was adjusted to pH 6.0 using a c i t r i c acid:sodium citrate ratio of 1:10.39. Patties were formed by hand from 50g of the above raw meat mixtures. The dimensions were approximately 8 cm in diameter by 1 cm in thickness, Each 50g patty was placed in a 600 ml glass beaker with 100 g of infusion solution and equilibrated at 40°C. After 18 to 24 hours of. equilibration, the pat£y-infusion solution combination in each beaker was heated in a hot water bath (95°-100°C) for 20 minutes, then cooled and stored at 40°C for approximately another 20 to 24 hours. The beakers were slightly heated in hot water to liquefy the excess gelled infusion solution. The patties were then drained of excess solution and packaged in sealable pouches. The pouches were produced by Seaforth Plastics Ltd., Burnaby, British Columbia (code name LDS2). They are a laminate of nylon (1 mil thickness) on the outside surface and polyethylene (3 mil thickness) on the 2 inside surface. Oxygen permeability i s 1.2 cc/100 in per day at 1 atm pressure and 72°F. Water permeability i s 0.4g/100 in^ per day at 100°F and 92% relative humidity. The patties were stored in the pouches for various times at 22°-24°C prior to analysis. The maximum storage time was 6 months. 2. Preparation of samples for non-enzymatic browning experiments The raw patty mixture was prepared in the same manner as above, except that no extra fat was added. • The infusion solution contained 4 different glycerol contents, 2 different citrate contents and 3 different c i t r i c acid:sodium citrate $ % % S3 rt fl) H O O co 1+ o o o OS OS VO OS 1+ o OS o ~ J o oo h-' I—1 I—1 *• H1 to O • • • Ui LO •p- -J 00 •^J •P-1+ 1+ 1+ o OS O Ul o •P-o o O LO o VO •P- 1—1 -^J 00 o OS 00 Ul 1—1 Ul I—1 Ul M o Ul o Ul o Ui ^9 S--9 CO I—1 LO 1—1 LO M LO O LO o LO O ^9 ^ 9 S-9 O O O o O o OS Ul OS OS OS OS Ul Ul Ul •P- Ui Ul O to Ui -P- --4 (—' ro LO N3 LO LO CO VO to VO 1—> to o Ul ~-J 00 00 -P- Ul H* to -P- o O o O O O o OS OS ~ J OS OS OS VO VO o VO 00 VO VO •^1 o VO oo -P-LO LO LO 00 •P- to LO VO LO LO Ui VO OS to O OS LO LO -P- 00 -J O VO -~J LO -P- o o o o o o o O 1—" • • • —J o OS .p- 1—1 OS LO ~J I-1 Ul LO O .(-> OS -P- •p- to VO Ul 1+ 1+ 1+ Co -p- . CO -P- CO •p-O o o 00 00 -P- 00 Lo VO o Os to Ui VO Ul O OS o 00 OS OS to VO Ul VO to Ul o o o o O o o 1—1 • • • 00 oo 00 00 00 00 00 CO (-> to to o l-> • to M o o OS 1—' 1—• Ui to VO 1+ 1+ 1+ Ul Ui •P- Ul -p- Ul o o o o LO 00 CO 00 to Ul Ul o VO -p- ~~J to .p-LO Ul o VO VO Ul -P-A c i d : S a l t Ratio Infusion Solut ion pH Cooked Patty-Ci t ra te Content Infusion Solut ion Ci t ra te Content Cooked Patty oo o OS Ul to Ul Ul o -p-o CO Ul OS Ul o O ID H o (D t-i PS B) rt H-O O Hi 3 Hi c 03 H-O 3 o O 13 r a t i o s . The 24 sample combinations are outlined i n Table II showing f i n a l c i t r a t e contents, g l y c e r o l contents, moisture contents and pH. P a t t i e s used for water soluble pigment extraction were the same size as those used i n the l i p i d oxidation experiments. P a t t i e s used for Hunter colour parameter determinations were formed by hand from 200g of raw meat mixture and to a s i z e of approximately 14 cm i n diameter and 2 cm thick. These large p a t t i e s were necessary to cover.the o p t i c a l port of the Hunter Colour Meter. The 200g p a t t i e s were placed i n 4000 ml beakers with 400 g of i n f u s i o n s o l u t i o n . The e q u i l i b r a t i o n , cooking and packaging procedure i s the same as f o r the l i p i d oxidation experiments. Peroxide Value Determination Whole p a t t i e s were removed from t h e i r pouches, comminuted i n a Waring Blendor for 10-30 sec and placed i n screw cap j a r s . Duplicates of approximately 15g of each sample were freeze-dried i n c e l l u l o s e extraction thimble's for 30 hours, then extracted with petroleum ether using a Goldfisch Extractor for 12 hours. The peroxide value was determined by the A0AC method (2) on the l-2g of f a t extracted. Moisture contents were calculated from the w e i g h t l o s s during drying. Water Soluble Pigment Determination Whole p a t t i e s were removed from t h e i r pouches and cut i n h a l f . One h a l f of each patty was comminuted i n a Waring Blendor and then placed i n i n d i v i d u a l screw cap j a r s . The remaining h a l f p a t t i e s were replaced i n t h e i r pouches which were then resealed and stored for a future determination. 14 Duplicates of approximately lOg of each sample were freeze-dried i n aluminum drying dishes of 50 mm diameter and 15 mm deep. The dried samples were steeped i n d i s t i l l e d water and f i l t e r e d through a Mil i p o r e f i l t e r system (1.2^, pore size) by the method of Karel and Nickerson (17). The O.D. of the f i l t r a t e was measured on a Beckman DB Spectrophotometer. Grinding of the dry sample to pass through a 2 mm screen was omitted because g l y c e r o l caused the dry p a r t i c l e s to s t i c k together and plug the 2 mm screen of a Wiley M i l l . Wet samples were pureed i n a Waring Blendor to compensate f o r t h i s omission. Hunter Lab Value Determinations Colour parameters of whole p a t t i e s i n t h e i r pouches were determined using a Hunter Lab Colour Difference Meter (Model D25). Values were determined twice on each side of the pouch. The instrument was standardized against the white colour standard. Water A c t i v i t y Determinations Water a c t i v i t y was determined on the 10 to 20g of samples remain-ing i n the screw cap j a r s a f t e r some of the sample had been removed f o r peroxide determinations or water soluble pigment determinations. A two-holed rubber stopper was f i t t e d to the top of the j a r s and a i r was r e c i r c u -l a t e d over the sample and through a sensor of an EG&G Dew Point Hydrometer (Model 880) f o r lh hours at 20°C. 1% hours was found to be long enough to e q u i l i b r a t e the highest moisture content samples. One determination was made on each sample. 15 pH Determination The sample pH was determined on lOg of sample after the water a c t i v i t y determinations. The lOg sample was blended with 100 ml of d i s t i l l e d water for 30 seconds i n a Waring Blendor. (7) One determination was made on each sample. Glycerol Determinations Glycerol content was determined on 5g of random sample for peroxide determinations or water soluble pigment determinations. The test procedure used i s an AOAC (1) tentat ive method. Wet samples were extracted with acetone for 18 hours to remove the g l y c e r o l . The dried extract was dissolved i n water and oxidized with an excess of potassium dichromate. The excess dichromate was determined by t i t r a t i n g the oxidized mixture wi th ferrous ammonium sul fa te , wi th diphenylamine as the ind ica to r . A l l determinations were made at the end of the test per iod. Crude Fat Determinations The fat content was determined from 5g of random samples for peroxide value or water soluble pigment determinations, The standard method of the AOAC (2) was applied using petroleum ether for extract ing the l i p i d mate r ia l . Anhydrous ether was found to p a r t i a l l y extract g lycero l as w e l l as fa t ; therefore, i t was not used. A l l determinations were made at the end of the test per iod. 16 RESULTS AND DISCUSSION The peroxide value (P.V.) increased i n a l l samples during the f i r s t months of observations. Samples with an Aw of 0.765 reach a maximum peroxide value between 120-160 days, and samples with an Aw of 0.818 reach a maximum P.V. i n 60-120 days, as shown i n Figure 1. Peroxides are un-stable intermediates of oxidation. The P.V. at any one time i s a function of the rate of formation minus the rate of decomposition. A maximum P.V. i s reached when the rate of decomposition equals the rate of formation; and when the peroxides decompose f a s t e r than they are formed, the P.V. decreases with time. (28) The peroxide value has been widely used for studying l i p i d oxidation. A peroxide value of 20 meq. peroxide/Kg f a t has been associated with the threshold detection of r a n c i d i t y . (37) A problem of using the P.V. for i n d i c a t i n g the actual degree of r a n c i d i t y i s that peroxides do not have a flavour or odour. Some f i s h products have very high peroxide values without an apparent off-odour. (23) Detailed odour analysis was not used i n t h i s study, but rancid odours were apparent i n the meat samples during the t h i r d and fourth month of storage, when samples reached peroxide values of 30 to 50 meq. peroxide/Kg f a t . The odour was very objectionable i n most samples but p a r t i c u l a r l y i n samples with water a c t i v i t i e s of 0.818. Labuza e_t a l . (21) reported s i m i l a r findings where rancid odours were detectable i n intermediate moisture chicken samples at a P.V. of 40-50 meq. peroxide/Kg f a t . A l l the three variables tested, f a t , c i t r a t e and moisture B a LO CO LO o o O K K o d d * £ * * < < < < CO CO d -+-o K O O o o CO o C N i D f 6>i/-bain a-npA apixojaj Figure 1 . Change i n Peroxide Value at D i f f e r e n t Water A c t i v i t i e s (0% C i t r a t e ) 18 content, had a significant effect on the peroxide value (Table III). Changes in water activity had the greatest effect. Increasing Aw from 0.655 to 0.763 significantly increased the average P.V. (Table IV). In samples with water activities of 0.818, a decrease in the average P.V. was observed a^fter approximately 110 days. Reaction rates were calculated using the kinetic equation derived by Labuza et_ a l . (19) for a methyl linoleate model system. d ROOH „ „„„„ h !• —TZ— = Km ROOH dt Km = monomolecular rate constant ROOH = peroxide value. They state the equation is valid i f the substrate concentration does not change significantly. Observations past the maximum P.V. were excluded from the calculations for Km. The maximum P.V. occurs when the amount of available oxidizable fat is so depleted that the rate of peroxide decomposition equals, then exceeds the rate of formation. (28) The coefficient of determination to the rate equation was variable, ranging from 2 r = 0.66 to 0.99 (Table V). There was a better correlation of the data to equation 1 by eliminating peroxide values that appeared to level off with time. A second reason that some correlations were low is that the two blocks were assumed to oxidize at the same rate, so that the composite data could be used in the calculating of Km. This assumption was not true, as w i l l be explained later. It was, of course, assumed that the rate equation 1 does apply to the meat system under study so the experimental results could be compared more easily than by comparing P.V. alone. 19 Table I I I A n a l y s i s of Variance-Peroxide Values Source of Variance d.f. F value R e p l i c a t e 1 54.9 Time 4 182.1 Fat 2 13.8 C i t r a t e 2 20.4 Moisture 3 12.9 A l l F values s i g n i f i c a n t at a = 0.01. Table IV Duncans M u l t i p l e Range Test E f f e c t s of D i f f e r e n t Water A c t i v i t i e s on Peroxide Values Aw mean P.V.^ 2 mean P.V. 0.655 ': 14.21 a 22.43 a 0.707 18.31 b 27.70 b 0.763 27.50 c 36.90 c 0.818 30.46 c 27.46 b Means w i t h i n each column w i t h d i f f e r e n t s u b s c r i p t s a r e . s i g n i f i c a n t l a t a = 0.05. 1. F i r s t three observations. 2. T o t a l observations. 20 Table V Monomolecular Rate Constants (Showing C o e f f i c i e n t of Determination) to Equation 1 Water A c t i v i t y C i t r a t e Content Fat Content 3.26% 5.19% 6.55% Km* N** x 10" 2 Km* N** r x 10" 2 Km* N** r x 10 0.655 0% 2.83 18 0.669 3.93 18 0.795 3.43 18 0.922 , 1.0% 2.00 20 0.665 2.65 17 0.729 2.66 17 0.911 2.2% 2.00 20 0.742 2.32 15 0.713 1.94 19 0.720 0.707 0% 2.97 • 19 0.762 3.30 18 0.789 2.14 17 0.765 1.0% 4.69 9 0.749 3.09 18 0.793 1.95 19 0.747 2.2% 3.44 11 0.945 3.14 17 0.851 2.10 20 0.710 0.763 0% 4.24 14 0.823 4.49 18. 0.899 2.56 18 0.870 1.0% 3.76 17 0.909 3.07 13 0.972 3.21 13 0.884 •2.2% . • 3.93 7 0.939 3.79 17 0.800 3.66 8 0.820 0.818 0% 4.17 8 0.902 10.11 6 0.854 1.0% 8.80 6 0.987 8.96 5 0.924 5.36 10 0.956 2;i2% 5.01 15 0.944 3.87 12 0.870 • 4.13 14 0.805 * monomolecular rate constant (meq. perox./Kg f a t ) 2 / d a y ** number of observations used i n c a l c u l a t i o n 2 flr r = c o e f f i c i e n t of determination The l i p i d oxidation rate was observed to increase with increasing water activity and a sharp increase in rate was noticed between Aw;<0.763 and 0.818 (Figure 2). There was no apparent decrease in the rate over the water activity range studied, as found by Labuza (18) in model systems. Cooked meats have been noted to deteriorate rapidly due to l i p i d oxidation, with off-flavours detected as early as two hours after cooking. (36) Most cooked meats have a water activity in the range of 0.70 to 0.80. (20) Lipid oxidation also occurs in fresh meats (Aw = 0.99) at refrigerated temperatures. (11) Using these high water activities would not be a practical approach for controlling l i p i d oxidation because of resultant increases in yeast and bacterial growth. The effects of c i t r i c acid-sodium citrate on the average P.V. at different water activities was not consistent. There was definitely no effect at Aw 0.707 and 0.763 (Table VI). Increasing citrate levels in the infusate slightly reduced the six month average P.V. at Aw 0.655, but marked-ly increased the P.V. at Aw 0.818. It was observed that samples at Aw 0.818 and 0% citrate did not reach very high maximum peroxide values compared to the samples with citrate (Figure 3). It would appear that c i t r i c acid has some effect on the breakdown of peroxides. It would be d i f f i c u l t from this study to predict how c i t r i c acid produces a high P.V. C i t r i c acid could be.increasing the stability of the hydrogen peroxide or i t s free radical. It could also reduce the rate of peroxide decomposition by sequestering the trace metal catalysts involved in. the reaction or by some other method. This protective effect has also been observed for milk 22 i o V e r t i c a l b a r s i n d i c a t e 95% c o n f i d e n c e l i m i t s .70 .80 Water Activity F i g u r e 2. Rate o f L i p i d O x i d a t i o n a t D i f f e r e n t Water A c t i v i t i e s 23 Table VI Duncans M u l t i p l e Range Test E f f e c t s of D i f f e r e n t C i t r a t e L e v e l s and Aw on Perox ide Va lues Mean Peroxide Value C i t r a t e Level Water A c t i v i t y % 0.655 0.707. 0.763 0.818 0.0 25.84 a 28.07 c 36.81 d 10.16 e 1.0 22.80 ab 28.28c 36.52 d 24.63 ac 2.2 18.72 b 26.73 ac 37.37 d 47.10 f means with d i f f e r e n t subscripts are s i g n i f i c a n t at 01 = 0.05 24 6 - " 0 0 0) O O O J_ 1 - l _ - » — • * — -I— U U U o 00 o o o • CN 2 2. o -a o £ 00 c o . o o " C N o o o o o ro o C N JDJ 6>j/-b8LU 9 n p y \ a p j x o j s j Figure 3. Change i n Peroxide Value at Different C i t r a t e Levels (Aw 0.818) 25 peroxides. (15) The mode of action was not explained. G i t r a t e had no apparent e f f e c t s on the peroxide value at the lower water a c t i v i t i e s studied (Figure 4). Sodium c i t r a t e c r y s t a l i z e s out of solutions at water a c t i v i t i e s below Aw 0.75. (6) I t i s probable that c i t r a t e s would not be mobile to reach reaction s i t e s to protect peroxides at lower water a c t i v i t i e s than Aw 0.763 studied. It i s doubtful that c i t r i c a c i d has any e f f e c t on the rate of peroxide formation. There was l i t t l e change i n the rate constant (Km) at Aw 0.707 and 0.763, and a s l i g h t decrease at Aw 0.655 (Figure 5). There appeared to be a s l i g h t increase i n Km at Aw 0.818 by increasing the c i t r a t e l e v e l i n the infusate. Samples at t h i s water a c t i v i t y reached . maximum P.V. very r a p i d l y , l i m i t i n g the number of observations u s e f u l f o r c a l c u l a t i n g rate constants (Table V). As a r e s u l t , the confidence l i m i t s (a= 0.05) are very large. In summary, c i t r i c acid was not e f f e c t i v e at preventing peroxide formation i n the water a c t i v i t y range studied, but i t did protect peroxides from decomposing. In cooked meats, f e r r i c hemochrpmogen produced from heat-denatured myoglobin and hemoglobin i s possibly the major c a t a l y s t i n peroxide formation and decomposition. (27) If c i t r i c a c i d i s not an e f f e c t i v e sequesterant f o r t h i s hemo-bound i r o n , c i t r a t e would have no e f f e c t on peroxide formation. I f t h i s theory i s v a l i d , c i t r a t e would have to protect peroxides from decomposing by increasing the s t a b i l i t y of the peroxide r a d i c a l rather than by decreasing the c a t a l y t i c e f f e c t of the ferrous hemochromogen. Varying the f a t content had the l e a s t e f f e c t on peroxidejvalues 26 o.v m o • < I i i i o • < cu cu cu • D "o o U U u O O ^ 6 - CN » < D O o O - 4 -O 4- 4 - 4-o 00 o NO o o C N o o o 00 o o o C N co o CD E o o o CN | D i 6>j/'bauj anjDA a p i x o j a j Figure 4. Change i n Peroxide Value at Different. C i t r a t e Levels (Aw 0.707) V e r t i c a l bars indicate 95% confidence U n i t s 0.0 1.0 2.0 Citrate Concentration % Figure 5. Rate of L i p i d Oxidation at Different Ci t ra te Concentrations 28 (Table III). A higher average P.V. was observed at 5.2% fat than at 3.3% or at 6.6% (Table VII). There appeared to be l i t t l e consistency as to whether increased fat content increased or decreased oxidation. It i s possible that the amount of fat is not an important factor in l i p i d oxidation. Watts (38) found no relation between the amount of fat in cooked beef to TBA values, For some unknown reason, samples with 5.2% fat also had a significantly higher moisture content than 3.3% and 6.6% fat contents. The higher moisture content could explain the higher P.V. at 5.2% fat. A significant decrease in pH was.observed through the time period (Table VIII). The pH change in samples at Aw 0.657, 0.707, 0.763 was small, but samples at Aw 0.818 decreased by about .0.3 pH units over the test period (Figure 6) . The pH appeared to decrease at a steady rate between 30 and 190 days, suggesting peroxide decomposition i s at a steady rate in this period. Aldehydes formed from the scission of peroxides are oxidized to the corresponding carboxylic acids. (30) It has also been postulated that aldehydes can be decarboxylated to produce formic acid and it s esters. (26) Formic acid has a lower dissociation constant than other carboxylic acids, and therefore, decreases the pH more. Samples for non-enzymatic browning analysis developed very low absorbencies in water extracts over the test period. The optical density (O.D.) increased from an average of 0.004 to 0.007 units in 185 days ( \ = 420 m/j) . This suggests that a very l i t t l e amount. of water soluble melanoidens were formed. If non-enzymatic browning was occurring to any extent in the test samples the increase in O.D. would be much higher. (17) 29 Table VII Duncans Multiple Range Test Effects of Fat Levels and Aw on Peroxide Values Fat Level Peroxide Value Water Activity % 0.655 0.707 0.763 0.818 Av.P.V. 3.3 18.79 a 23.59 ab 37.73 de 32.92 c 28.30 f 5.2 25.88 b 35.66 cdc 39.36 e 26.09 b 31.75 g 6.6 22.57 ab 23.84 b 33.62 cd 23.36 ab 25.85 h Means with different subscripts are significant at a = 0.05. Table VIII Duncans Multiple Range Test  Change in pH with Time Time Day pH 30 6.12 a 97 6.03 b 150 6.01 be 180 5.99 c 193 5.95 d Means with different subscripts are significant at a = 0.05. o • 30 i n t o o K O CO 00 O r-K CO O •OO o o o o CN o o o CO < < < < o o o o C N 0 <D e - 4 -O <> -t— C N OC Hd Figure 6. Change i n pH with Time at D i f f e r e n t Hater A c t i v i t i e s 31 The t e s t v a r i a b l e s did not a f f e c t the O.D. i n a way i n d i c a t i v e of browning. For example, the pH had no s i g n i f i c a n t e f f e c t on the O.D. Increasing pH should increase the O.D. (32) Decreasing water a c t i v i t y appeared to reduce s l i g h t l y the O.D. This i s the opposite to r e s u l t s expected from non-enzymatic browning. (18) Samples at Aw 0.657 showed the highest O.D., but did not always produce clear f i l t r a t e s (1.2^. f i l t e r pore s i z e ) . Hunter L and b values increased s i g n i f i c a n t l y with time (Table X). Hunter a values did not change appreciably. An increase i n L values i s i n d i c a t i v e of increasing l i g h t n e s s , and i n t h i s case, a fading of the brown "meat" colour. This l o s s of colour suggests that the cooked meat pigments are being oxidized. Watts (37) found that myoglobin, as w e l l as being a c a t a l y s t for l i p i d oxidation, i s also oxidized, r e s u l t i n g i n colour fading. Heat denatured myoglobin would be the primary meat pigment i n t h i s study. There would be very l i t t l e melanoiden formation because of the low cooking temperatures used. Mela-noidens and the heme group of myoglobin are very unsaturated molecules, therefore, would be susceptible to oxidation. Loss of colour would r e s u l t from the destruction of the molecule. The l o s s of the brown "meat" colour was v i s u a l l y apparent during the test period. Increasing b values i n d i c a t e that the i n t e n s i t y of the yellow colour of the samples i s increasing. One of the products of l i p i d oxidation i s the formation of polymers. They are brown i n colour and i n low concen-t r a t i o n s could account for increasing Hunter b values. The increase i n i yellowness was not noticeable v i s u a l l y . 32 Table IX Analysis of Variance - Hunter L and b Values Source of Variance d.f. Hunter L Values F score Hunter b Values F score Blocks 1 25.9 14.1 Time 4 52.1 210.9 pH 2 140.5 151.6 Citrate cont. 1 52.3 12.1 Water activity 3 213.8 309.0 A l l F scores are significant at a = 0 . 0 1 . Table X Duncans Multiple Range Test Changes in Hunter L a b Values with Time Time Day L Values a Values b Values 10 68 111 170 213 29.7 a 32.6 b 33.9 c 34.6 cd 35.3 d 2.7 a 2.1 b 2.4 b 2.2 b 2.2 b 5.1 a 7.0 b 8.0 c 9.1 d 10.0 c Means within each column with different subscripts are significant at a = 0.05. 33 Changes in water activity had the greatest effect on Hunter L and b values (Table IX). The Hunter colour values increased rapidly at the beginning of the test period (Figure 7). The rate of change decreased with time to a possible maximum value or a slow constant rate of increase. Hunter L values would be expected to reach a maximum because the total amount of denatured myoglobin that can be oxidized i s constant. Samples at Aw 0.653 were visib l y much darker in colour than the samples at higher water a c t i v i t i e s . The dark brown colour of the lowest moisture samples closely resembled that of a meat patty i f i t had been cooked by frying. I n i t i a l Hunter L and b values were increased by water activity (Table XI). It i s probable that the rapid change in colour in the f i r s t ten days accounts for some but not all.of this i n i t i a l difference between the water act i v i t i e s . Increasing the glycerol content affected the colour of the cooked meat patties. Although texture was not assessed experimentally, i t was observed that patties at low water activities were much harder to break up than were those with higher water a c t i v i t i e s . The higher glycerol concentrations also increased the stiffness of the gelled infusate after cooking. It i s possible that glycerol, by removing "free" water surrounding the meat proteins, gelatin and starch, allows.closer intermolecular contact and interaction upon cooking, causing increased toughness and the darker colours. Figure 8 shows the difference between Hunter colour values at the f i r s t observation and each subsequent observation. There was a slight difference in the amount of Hunter L, and b increased in"value at different water activities (Figure 8). Higher water activities tended to show a greater increase in yellowness and colour fading than a lower o • © B 9 O U X \ B • , • O •A \ i • w \ w \ a © • O \ \ \ \ o • • • CO o — o IO t> r -O O K 00 £ £ £ £ < < < < 3 4 o o CN o - in cn - X D T5 o • o v - E o CN oo o CN Figure 7. Change i n Hunter L and B Values at Different Water A c t i v i t i e s 35 Table XI Duncans Multiple Range Test I n i t i a l Hunter L and b Values at Different Water Activities Water Activity L Values b Values 0.653 26.1 a 3.3 a 0.696 27.8 a 4.7 b 0.741 31.2 b 5.4 b 0.816 33.8 c 6.8 c Means within each column with different subscripts are significant at 0t = 0.05. o a • I c o o r- «o IT) O T f r --O ~0 K oo • • • • * • * • * i < < <••< o o CN o IT) to o o "3 2 CD o o ts: o <> o L O o O ro O CN Figure 8 . Differences i n Hunter Colourmeter Values Between the I n i t i a l Observation at 10 Days and.Each Subsequent Observation at D i f f e r e n t Water A c t i v i t i e s 37 water activity. This is consistent with the observation that increases in peroxide values are greater at high water act i v i t i e s . Colour changes were not as dependent on changes in water activity as was the P.V. The greatest significant difference was between samples at Aw 0.696 and 0.741. The sample pH had very l i t t l e significant effect on i n i t i a l Hunter L and b values,• (Table XII). The greatest difference was the effect the pH had on the change in values with time (Figure 9). Samples at pH 4.96 and at 5.38 increased in yellowness and the colour faded more than in samples at pH 6.01. A pH dependency was found in fresh meats where low pH increased peroxide values greater than did high pH. (37) This dependency disappeared in cooked meats where the P.V. did not increase appreciably. Later Tims and Watts (36) found that cooked meats increased TBA values faster than fresh meats, but the effect of pH was not documented. Green (11) found that i f fresh meat was kept at high pH (6.2) i t remained red under aerobic conditions and rancid odours did not occur. The results of this study suggest that the oxidation of cooked meat pigments is dependent on pH. Block 2 was observed to fade more and develop higher peroxide values than block 1 (Table XIII). The greatest significant difference between these blocks was the pH. The average pH of block 2 was lower than that of block 1 in both l i p i d oxidation test samples and water soluble pigment extraction samples. This is a further indication that low pH increases l i p i d oxidation in intermediate moisture cooked meats. Time days Time days 39 Table XII Duncans Multiple.Range Test I n i t i a l Hunter L and b Values at Different pH pH L Values b Values 4.96 30.9 a 5.2 a 5.40 30.8 a 5.3a 6.01 27.6 b 4.7 a Means within each column with different subscripts are significant at a = 0.05. 40 Table XIII Analysis of Variance Block Differences L i p i d Oxidation Test Samples Mean Values Block 1 Block 2 F score peroxide value 25.22 32.05 182.1* -pH 6.24 5.82 1530.8* moisture cont. 41.66 40.59 12.9* water a c t i v i t y 0.735 0.735 0.2 N.S Non-enzymatic Browning Test Samples Mean Values Block 1 Block 2 F score Hunter L 32.5 33.9 52.1* Hunter b 7.6 8.1 14.1* pH 5.54 5.37 142,.'0* moisture cont. 29.22 40.91 33.1* water a c t i v i t y 0.733 0.722 16.5* * s i g n i f i c a n t at d= 0.01 4 1 The pH was observed to decrease during l i p i d oxidation (Figure 6) and low pH was found to catalyse pigment oxidation (Figure 9) . It i s interesting that the acid by-products of l i p i d oxidation accelerate further oxidation. In Figure 9 and Figure 8 increases in Hunter L values corres-pond to the increases in Hunter b values. The reaction profiles are quite similar. The increase in Hunter b values would not necessarily be expected to follow the same shape of curve as increases in Hunter L values i f the b values were the result of polymer formation. Colour development (Hunter b values) from polymerization would be expected to have a longer lag phase in relation to myoglobin oxidation (Hunter L values), polymerization being an end product of l i p i d oxidation. Figure 9 suggests that a loss in the brown "meat" colour.corresponds to an increase in yellow by-products. Lawric (22) reports that during high temperature storage (35°C) of dehydrated meat, myoglobin is converted to bi l e pigments causing the meat to pale and yellow. It i s possible that the increase in Hunter b values i s due to bile pigments and not i n i t i a l polymerization products as previously mentioned. This study suggests that l i p i d oxidation i s a problem to be considered when formulating an intermediate moisture meat product. Samples prepared for this study were limited to three or four months' shelf l i f e by rancid odours. C i t r i c acid, the only antioxidant tested, did not control the development of peroxides. Much investigation w i l l have to be done to prolong the shelf l i f e of these meat products to meet public approval. 42 Conclusion 1. L i p i d oxidat ion was the prominent deter iora t ing factor of the intermediate moisture meat pat t ies produced, l i m i t i n g the i r shelf l i f e to three or four months. 2. This study confirms that as water a c t i v i t y increases between Aw 0.65 and 0.82, l i p i d oxidation increases. 3. C i t r i c acid has possibly very l i t t l e effect on the rate of peroxide formation but does protect peroxide breakdown. 4. The pH decreased during l i p i d oxidat ion. 5. Pigment oxidation i n the meat pat t ies resulted i n the i r colour fading and yel lowing. 6. Low pH increased the rate of pigment oxidat ion. . 43 BIBLIOGRAPHY 1. AOAC. 1945. " O f f i c i a l Methods of, Analysis". 6th ed., p. 434. Association of O f f i c i a l A g r i c u l t u r a l Chemists, Washington, D.C. 2. AOAC. 1965. " O f f i c i a l Methods of Analysis". 10th ed., p. 331. Association of O f f i c i a l A g r i c u l t u r a l Chemists, Washington, D.C. 3. Bone, D. 1973. Water a c t i v i t y i n I.M.F. Food Tech. 27:41. 4. Brockman, M.C. 1970.. Development of IMF for m i l i t a r y use. Food Tech. 24:896. 5. Chou, H-E., Acott, K.M. and Labuza, T.P. 1973. Sorption h y s t e r i s i s and chemical r e a c t i v i t y : L i p i d Oxidation. J . Food S c i . 38:316. 6. Chou, H-E. and Labuza, T.P.' 1974. Antioxidant effectiveness i n IM content model systems. J . Food S c i . 39:479. 7. C o l l i n s , J.L., Chen, C C , Park, J.R., Mundt, J.O., McCarty, I.E. and Johnstone, M.R. 1972. Preliminary studies on some properties of intermediate moisture, deep-fried f i s h f l e s h . J . Food S c i . 37:189. 8. Eichner, K. and Karel, M. 1972. The influence of water a c t i v i t y on the sugar-amino .browning re a c t i o n i n model systems under various conditions. J . Agr. Food Chem. 20:218. 9. FAO N u t r i t i o n Meetings Report Series No. 50C 1972. A review of the technological e f f i c a c y of some antioxidants and synergists. 10. F u r i a , T.E. ed. 1968. "Handbook of Food Additives". Chemical Rubber Co., Cleveland, Ohio. . 11. Green, B.E. 1969. L i p i d oxidation and pigment changes i n raw beef. J . Food S c i . 34:110. 12. Heidelbaugh, N.D. and Karel, M. 1970, E f f e c t of water-binding agents on the catalyzed oxidation of methyl l i n o l e a t e . J . AOCS 47:539. 13. Heiss, R. and Eichner, K. 1971. Moisture content and shelf l i f e . ' Part I. Food Manufacture 46(5):53. 14. Heiss, R. and Eichner, K. 1971. Moisture content and shelf l i f e . Part I I . Food Manufacture 46(6):37. 44 15. H i l l , L.M., Hammond, E.G. and. Seal, R.G. 1969. E f f e c t of a n t i o x i -dants and synergists on peroxide decomposition i n milk f a t . J . Dairy S c i . 52:1914. 16. Kaplow, M. 1970. Commercial development of intermediate moisture foods. Food Tech. 24:889. 17. Karel, M. and Nickerson, J.T. 1964. E f f e c t s of r e l a t i v e humidity, a i r and vacuum on browning of dehydrated orange j u i c e . Food Tech. 18:1214. 18. Labuza, T.P. 1971. Properties of water and the keeping q u a l i t y of foods. Proceedings of the 3rd Int. Congress of Food S c i . and Technology, SOS/70. 19. Labuza, T.P., Tsyuki, H. and Karel, M. 1969. K i n e t i c s of oxidation of methyl l i n o l e a t e v J . AOCS 46:409. 20. ."• Labuza, T.P., Heidelbaugh, N.D., S i l v e r , M. and Karel, M. 1971. Oxidation at intermediate moisture content. J . AOCS 48:86. 21. Labuza, T.P., McNally, L., Gallagher, D., Hawkes, J . and Hurtado, F. 1972. S t a b i l i t y of intermediate moisture foods. 1. L i p i d oxidation. J . Food S c i . 37:154. 22. Lawrie, R.A. • 1966. "Meat Science", p. 220. Pergamon Press, Oxford, England. 23. Lea, C H . 1961. "L i p i d s and Their Oxidation", p. 11. Schultz, H.W., Day, E.A. and Sinnhuber, R.O., eds. A v i , Westport, Conn. 24. Lemon, H.W., Knapp, R.M. and Allman, A. 1950. The e f f e c t of c i t r i c a c i d upon the oxidation of peanut o i l and of the methyl esters derived from peanut o i l . Can. J . Res., Sec. F. 28:453. 25. Loncin, M., Bimbenet, J . J . and Lenges, J . 1968. Influence of the a c t i v i t y of water on the spoilage of foo d s t u f f s . Food Tech. 3:131. 26. Loury, M. 1972. Possible mechanisms of autoxidative r a n c i d i t y . L i p i d s 7:671. 27. Love, J.D. and Pearson, A.M. 1971. L i p i d oxidation i n meat and meat products. A Review. J . AOCS 48:547. 28. Lundberg, W.O. 1961. "L i p i d s and Their Oxidation", p. 45. Schultz, H.W., Day, E.A. and Sinnhuber, R.O., eds. Avi, Westport, Conn.. 29 Mossel, D.A. and Ingram, M. 1955. Physiology of microbial food spoilage. J . Appl. Bact. 18:322. -45 30. Nawar, W.W. 1969. Thermal degradation of l i p i d s . A Review. J . Agr. Food Chem. 17:18. 31. Potter, N.N. 1970. Intermediate moisture foods: P r i n c i p l e s and technology. Food Prod. Devel. 4:38. 32. Reynolds, T.M. 1965. Chemistry of non-enzymatic browning I I . Adv. Food Res. 14:167. 33. Salwin, H. 1959. Defining minimum moisture contents f o r dehydrated foods. Food Tech. 13:594. 34. Song, P. and Chichester, CO. 1966. K i n e t i c behaviour and mechanism?of i n h i b i t i o n i n the M a i l l a r d reaction I I . J . Food S c i . 31:914. 35. Song, P. and Chichester, CO. 1967. K i n e t i c behaviour and mechanism of i n h i b i t i o n i n the M a i l l a r d r e a c t i o n IV. J . Food S c i . 32:107. 36. Tims, M.J. and Watts, B.M. 1958. Protection of cooked meats with phosphates. Food Tech. 12:240. 37. Watts, B.M. 1954. Oxidative r a n c i d i t y and d i s c o l o r a t i o n i n meat. Adv. Food Res. 5 :1. 38. . Watts, B.M. 1961. " L i p i d s and Their Oxidation", p. 202. Schultz, H.W., Day, E.A.,and Sinnhuber, R.O., eds. Avi, Westport, Conn. 

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