Isolation and identification of some antibacterial peptides in the plasmin-digest of β-casein

• Plasmin-digest of β-casein may use as a source of antibacterial agent in food chain.
• Antibacterial peptides were active against probiotic bacteria, so the effect of these compounds in probiotic products should be considered.
• In this study eight antibacterial peptides (βC1, βC3, βC5, βC6, βC8, βC11, βC12, and βC14) were identified.
• Antibacterial peptides βC1, βC12, and βC14, which corresponded to the residues 100–105, 100–107 and 170–183 of bovine β-casein, are novel antibacterial domain not previously reported.
• Antibacterial peptides were almost hydrophobic, with a basic amino acid, in their C-terminal residue and some had a net positive charge.

This study was an attempt to explore the antibacterial properties of plasmin and plasmin generated peptides from bovine β-casein, and then to identify active peptides using RP-HPLC. The target bacteria were Escherichia coli, Staphylococcus aureus (both pathogenic), Lactobacillus casei, and Lactobacillus acidophilus (both probiotic). Eight of the peptides (βC1, βC3, βC5, βC6, βC8, βC11, βC12, and βC14) exhibited antibacterial activity, with βC8, βC12, and βC14 being the most active. The plasmin digest of bovine β-casein was found to be one of the best compounds in terms of antibacterial potential. Measurement of the minimum inhibitory concentration (MIC) revealed the Gram-positive bacteria to be generally more sensitive to antibacterial activity than the Gram-negative bacteria. The eight antibacterial peptides were identified using LC-Mass. The molecular masses of βC1, βC3, βC5, βC6, βC8, βC11, βC12, and βC14 were corresponded to the f(100–105), f(108–113), f(177–183), f(170–176), f(98–105), f(106–113), f(100–107), and f(170–183) regions of bovine β-casein, respectively. It was also found that the hydrophobicity of a peptide greatly contributes to its antibacterial activity, but positive charge does not. This study showed that the plasmin digest of β-casein can be regarded as a natural antibacterial agent in the food chain.