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

Peptides in caprine whey were identified after in vitro digestion 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 degrees 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 against Escherichia coli K12, Bacillus cereus RT INF01 and Listeria monocytogenes, less activity against Staphylococcus aureus ATCC 25 923 and no effect on Lactobacillus rhamnosus GG. 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, beta-lactoglobulin f(92-100) and beta-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.