Antimicrobial effect of donkeys’ milk digested in vitro with human gastrointestinal enzymes

Individual donkey milk samples were digested in vitro by a two-step model, using human gastric juice at two different pH values (2 and 4) and further continuous intestinal digestion by human duodenal juice at pH 7.5. The degradation of proteins was assessed after each step. Caseins and β-lactoglobulins were digested rapidly in the gastric juice at pH 2 compared with pH 4 while whey proteins such as lysozyme and α-lactalbumin were very resistant during the total digestion. The identified peptides were mainly derived from β- and αs1-casein and the two β-lactoglobulins. The antimicrobial effect of milk and digested milk samples was tested on selected pathogenic bacteria. No significant inhibition of Bacillus cereus RT INF01 was observed, while a significant growth reduction was shown on Escherichia coli 10208355 during its stationary phase. Digested and undigested donkeys’ milk also significantly inhibited Listeria monocytogenes 2230/92 in a dose dependent way.