Antibacterial peptides derived from caprine whey proteins, by digestion with human gastrointestinal juice

Abstract

Peptides in caprine whey were identified afterin vitrodigestion with human gastrointestinal enzymes in order to determine their antibacterial effect. The digestion was performed in two continuing steps using human gastric juice (pH 2·5) and human duodenal juice (pH 8) at 37°C. After digestion the hydrolysate was fractionated and 106 peptides were identified. From these results, twenty-two peptides, located in the protein molecules, were synthesised and antibacterial activity examined. Strong activity of the hydrolysates was detected againstEscherichia coliK12,Bacillus cereusRT INF01 andListeria monocytogenes, less activity againstStaphylococcus aureusATCC 25 923 and no effect onLactobacillus rhamnosusGG. The pure peptides showed less antibacterial effect than the hydrolysates. When comparing the peptide sequences from human gastrointestinal enzymes with previously identified peptides from non-human enzymes, only two peptides, β-lactoglobulin f(92–100) and β-casein f(191–205) matched. No peptides corresponded to the antibacterial caprine lactoferricin f(14–42) or lactoferrampin C f(268–284). Human gastrointestinal enzymes seem to be more complex and have different cleavage points in their protein chains compared with purified non-human enzymes. Multiple sequence alignment of nineteen peptides showed proline-rich sequences, neighbouring leucines, resulting in a consensus sequence LTPVPELK. In such a way proline and leucine may restrict further proteolytic processing. The present study showed that human gastrointestinal enzymes generated different peptides from caprine whey compared with non-human enzymes and a stronger antibacterial effect of the hydrolysates than the pure peptides was shown. Antimicrobial activity against pathogens but not against probiotics indicate a possible host-protective activity of whey.