Heat treatment and homogenization influence the gastric digestion of bovine milk protein in growing pigs as an adult human model

Background Bovine milk processing influences the structure of the curd formed during gastric digestion, which may alter gastric protein hydrolysis and impact amino acid (AA) release into the small intestine. Objective This study aimed to determine the influence of heat treatment and homogenization on the gastric protein digestion and amino acid emptying of bovine milk. Methods Nine-week-old pigs (n=144) consumed either raw, pasteurized non-homogenized (PNH), pasteurized-homogenized (PH), or ultra-high-temperature homogenized (UHT) bovine milk for ten days. On day 11, fasted pigs received the milk treatment (500 mL) before gastric contents were collected at 0, 20, 60, 120, 180, and 300 min postprandially. The apparent degree of gastric protein hydrolysis (based on the release of free amino groups), apparent gastric disappearance of individual proteins (based on SDS-PAGE gel band intensity), and the gastric emptying of digested protein and AA were determined. Results During the first 60 min, the rate of apparent gastric protein hydrolysis was fastest for pigs fed UHT milk (0.29%/min vs on average 0.07%/min for pigs fed raw, PNH, and PH milk). Differences in the apparent degree of gastric protein hydrolysis and emptying were reflected in the rate of digested protein entering the small intestine. The AA gastric emptying half-time was generally shorter for pigs fed PH and UHT milk than pigs fed raw and PNH milk. For example, the gastric release of total essential AA was more than twofold faster (P<0.01) for pigs fed PH or UHT milk compared to pigs fed raw or PNH milk (i.e., homogenized vs non-homogenized milk). Conclusions Heat treatment and homogenization increased the apparent gastric degree of protein hydrolysis and the release of digested protein into the small intestine. However, the rate of AA entering the small intestine was mainly increased by homogenization.