Coagulation behaviour of milk under gastric digestion: Effect of pasteurization and ultra-high temperature treatment

The digestion behaviours of pasteurized and UHT homogenized milks were investigated in in vivo rat stomach and in an in vitro dynamic human gastric simulator. The formation of coagulum under gastric conditions and the protein digestion profiles were similar in both systems. UHT milk formed curds with fragmented and crumbled structures, compared with the more cohesive curds formed from unheated or pasteurized milk. UHT milk had faster rates of protein hydrolysis and of the release of fat globules during digestion. These results are attributed to the differences in the structures of the curds formed from the samples with different treatments. The fragmented and crumbled structure of the curds obtained from UHT milk was probably the result of beta-lactoglobulin binding with casein micelles during processing, which sterically hindered aggregation of the casein micelles under gastric conditions. This study provides knowledge for understanding the gastric emptying and digestion of processed consumer milk.