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UBC Theses and Dissertations

Lactulose preparation using food-safe reagents Layton, Anne Alexandra


Lactulose is efficiently synthesized from lactose using catalysts such as boric acid and triethylamine . However, since neither catalyst is food-safe, both must be removed after processing. Lactulose is also produced inadvertently during heat treatment of dairy products, although in small quantity. Studies have indicated that altering the heat processing conditions can improve lactulose yield . A high lactulose , mixed carbohydrate preparation was produced without the use of toxic catalysts . Using two Taguchi's fractional factorial designs, eight factors were tested as to their influence on lactulose yield : pH, lactose, NaOH, citrate and phosphate concentrations, heating temperature and duration , and purification of the lactose substrate. In the first design, lactose concentration (at levels of 40, 79, and 155 mg/mL) , pH (9.0, 10.5, and 12.0), heating temperature (90, 110, and 130°C), citric acid concentration (40, 70, 100 mM) and in the second design, NaOH concentration (18, 50, and 100 mM) , was shown to significantly influence lactulose yield . All other factors did not significantly influence lactulose yield at the selected levels . The interactions of lactose, citrate , and phosphate concentrations of the first design also significantly influenced lactulose yield . The conditions selected for the conversion of lactose to lactulose was decalcified whey permeate at > 70 mg/mL lactose , a pH of 10.5-11.0, with an added 50 mM sodium citrate , was heat treated at 110°C for 10 minutes. Approximately 30% of initial lactose was converted to lactulose via primarily the Lobry de Bruyn and Alberda van Ekenstein transformation. Again using a Taguchi design, four factors were tested to if they significantly influenced the preferential precipitation of lactose over lactulose in a cooled aqueous solution : pH, sugar concentration, temperature decrease, and final temperature. The pH of the mixed carbohydrate solution (at levels of 7.0, 9.0, and 10.7) and sugar concentration (29, 39, and 52%) both significantly influenced either the lactulose yield of precipitation or the sugar ratio in the decant. For further study, the lactulose preparation was concentrated to approximately 50% solids and pH 10.5, cooled from 65° C to 20° C at 5C°/hour, and held for 24 hours, preferentially precipitating lactose over lactulose. After one cooling cycle, there was a lactose yield of approximetly 82% and a 1:1 lactose: lactose ratio . After a second precipitation of the decanted portion , there was a 78% lactulose yield and a 3.4:1 lactulose : lactose ratio . There was a total loss of about 40% of lactulose through the two precipitation cycles. Ion-exchange columns removed the majority of the natural and added salts from the lactulose preparations. Activated charcoal removed most of the brown colour of the preparation but also 30% of the solids . The final syrup contained 59% lactulose , 26% lactose, 5.0% galactose, 1.0% glucose, and 0.81% fructose, based on total solids . Carbohydrates were assayed using an enzymatic spectro-photometric method. An unidentified substance was detected using thin - layer chromatography of carbohydrates.

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