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-derivedpeptides to exert biological activities. In this work an in vitro multi-step static model to simulate completedigestion of the bovine milk proteins has been developed. The experimental set-up involved thesequential use of: (i) pepsin, (ii) pancreatic proteases, and (iii) extracts of human intestinal brush bordermembranes, in simulated gastric, duodenal and jejuneal environments, respectively. Enzymatic concentrationsand reaction times were selected in order to closely reproduce the in vivo conditions. The aimwas to identify the peptide candidates able to exhibit significant bioactive effects. Casein and whey proteinpeptides which survived the in vitro GI digestion have been identified by the combined applicationof HPLC and mass spectrometry techniques. While the permanence of the main potentially bioactivepeptides from both casein and whey proteins was found of limited physiological relevance, the highresistance to proteolysis of specific regions of b-lactoglobulin (b-Lg), and especially that of the peptideb-Lg f125-135, could have implications for the immunogenic action of b-Lg in the insurgence of cow'smilk allergy.