Effect of pepsin-treated bovine and goat caseinomacropeptide on Escherichia coli and Lactobacillus rhamnosus in acidic conditions

Caseinomacropeptide (CMP) is a 7-kDa phospho-glycopolypeptide released from kappa-casein during milk digestion and in the cheesemaking process. The objective of the study was to analyze the effect of pepsin-treated CMP from cow and goat milk on the resistance of Escherichia coli and Lactobacillus rhamnosus during acid stress. Bacterial cells in the exponential growth phase were suspended in acidified phosphate buffered saline with or without pepsin-treated CMP. Viability was determined during a 90-min incubation period. Pepsin-treated CMP exhibited bactericidal activity at pH 3.5 when added in a dose-dependent manner to E. coli, decreasing survival by more than 90% within 15 min at 0.25 mg/mL. At pH >4.5, the bactericidal activity disappeared, indicating that pepsin-treated CMP was efficient at low pH only. The effectiveness of pepsin-treated CMP at pH 3.5 was not affected by the presence of glycoconjugates linked to CMP or by the bovine or caprine origin of milk. In contrast, L. rhamnosus, a probiotic, was more resistant to acid stress when pepsin-treated bovine or caprine CMP was added to the media. Viability reached 50% after 60 min of incubation at pH 3 compared with 5% survival in the media without added pepsin-treated CMP. Neither glycosylation extent nor sequence variations between CMP from bovine milk and caprine milk affected the protective activity of hydrolyzed CMP toward L. rhamnosus. This suggests that encrypted bioactive peptides released by the pepsin treatment of CMP had an antibacterial effect on E. coli in acidic media, but improved the resistance of L. rhamnosus to acid stress. The peptide fragment accountable for bactericidal activity is the N-terminal region kappa-casein f(106-124).