In vitro studies of the digestion of caprine whey proteins by human gastric and duodenal juice and the effects on selected microorganisms.

The in vitro digestion of caprine whey proteins was investigated by a two-step degradation assay, using human gastric juice (HGJ) at pH 2.5 and human duodenal juice (HDJ) at pH 7.5. Different protein and peptide profiles were observed after the first (HGJ) and second (HDJ) enzymatic degradation. The minor whey proteins serum albumin, lactoferrin and Ig were rapidly degraded by HGJ, while alpha-lactalbumin (alpha-LA) and beta-lactoglobulin (beta-LG) were more resistant and survived both 30 and 45 min of the enzymatic treatment. Further digestion with HDJ still showed intact beta-LG, and the main part of alpha-LA also remained unchanged. The protein degradation by HGJ and HDJ was also compared with treatment by commercial enzymes, by using pepsin at pH 2.5, and a mixture of trypsin and chymotrypsin at pH 7.5. The two methods resulted in different caprine protein and peptide profiles. The digests after treatment with HGJ and HDJ were screened for antibacterial effects on some selected microorganisms, Escherichia coli, Bacillus cereus, Lactobacillus rhamnosus GG and Streptococcus mutans. Active growing cells of E. coli were inhibited by the digestion products from caprine whey obtained after treatment with HGJ and HDJ. Cells of B. cereus were inhibited only by whey proteins obtained after reaction with HGJ, while the products after further degradation with HDJ demonstrated no significant effect. Screenings performed on cells of Lb. rhamnosus GG and S. mutans all showed no signs of inhibition.