Degradation of whey from caprine milk by human proteolytic enzymes, and the resulting antibacterial effect against Listeria monocytogenes

Abstract

Protein degradation of caprine whey by human proteolytic enzymes was studied with regard to antibacterial effect on Listeria monocytogenes. The digestion was performed by a two-step degradation-assay, using human gastric juice (HGJ) at pH 2.5, and human duodenal juice (HDJ) at pH 8. Protein profiles were studied by SDS-PAGE after each step and compared with degradation performed by commercial enzymes. Both types of enzymes, both human and commercial, left most of β-LG intact. However, proteins like serum albumin, laktoferrin and immunoglobulins were rapidly degraded. Only minor parts of α-lactalbumin (α-LA) was degraded by human enzymes, while treatment with commercial enzymes gave full degradation of α-LA. The two types of enzymes resulted in different peptide profiles, where the commercial enzymes degraded whey into smaller peptides much more efficiently. The protein digests produced by HGJ and HDJ were screened for antibacterial effects against L. monocytogenes, a food born bacteria responsible for fatal and sometimes deadly infections. Cells of L. monocytogenes were strongly inhibited by caprine whey obtained after reaction with both HGJ and HDJ. Undigested caprine whey and the products from the first step of digestion with HGJ demonstrated no significant effect. This indicates that during digestion the antibacterial effect of caprine whey hydrolysates are most effective in the duodenum. This gives a promising opportunity to inhibit listeriosis in humans, and results are also useful for development of dietary supplement, nutraceuticals and functional foods.