Peptides surviving the simulated gastrointestinal digestion of milk proteins: biological and toxicological implications

Resistance to proteases throughout the gastrointestinal (GI) tract is a prerequisite for milk-derived
peptides to exert biological activities. In this work an in vitro multi-step static model to simulate complete
digestion of the bovine milk proteins has been developed. The experimental set-up involved the
sequential use of: (i) pepsin, (ii) pancreatic proteases, and (iii) extracts of human intestinal brush border
membranes, in simulated gastric, duodenal and jejuneal environments, respectively. Enzymatic concentrations
and reaction times were selected in order to closely reproduce the in vivo conditions. The aim
was to identify the peptide candidates able to exhibit significant bioactive effects. Casein and whey protein
peptides which survived the in vitro GI digestion have been identified by the combined application
of HPLC and mass spectrometry techniques. While the permanence of the main potentially bioactive
peptides from both casein and whey proteins was found of limited physiological relevance, the high
resistance to proteolysis of specific regions of b-lactoglobulin (b-Lg), and especially that of the peptide
b-Lg f125-135, could have implications for the immunogenic action of b-Lg in the insurgence of cow's
milk allergy.