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Changes in the Digestibility of Dried Casein and Glucose Mixtures Occurring During Storage at Different Temperatures and Water Activities¹

Department of Food Science, Southeast Dairy Foods Research Center, North Carolina State University, Raleigh 27695-7624

² Corresponding author.

ABSTRACT

The digestibility of a dried, stored casein and glucose mixture was determined as a function of storage temperature, water activity, and carbohydrate:protein ratio by using the immobilized digestive enzyme assay. The sample contained either a 3:1 or 10:1 molar ratio of glucose:casein -amino groups and was stored for 30 d at either 30 or 60°C and at a water activity of .2 or .5. The extent of digestion was measured using two biodigesters, one containing immobilized pepsin and the other, immobilized trypsin, -chymotrypsin, and intestinal mucosal peptidases. The biodigesters were operated in a fluidized-bed mode that permitted analysis of samples containing insoluble material. Losses in digestibility compared with unstored dried casein:glucose mixtures ranged from 18 to 88%. The largest changes in digestibility were observed upon changes in the water activity or temperature of storage. As would be expected from the extent of Maillard reactions, the greatest loss of digestibility occurred during storage of the high carbohydrate sample at the highest temperature and water activity.

¹ Paper Number 12069 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh 27695-7601. The use of trade names in this publication does not imply endorsement by the North Carolina Research Service of the products named nor criticism of similar ones not mentioned. This research was supported in part by US Army Natick RD & E Center, subcontracted through USDA, Beltsville, MD.