Isolation and characterisation of a novel antibacterial peptide from bovine αS1-casein

Bovine casein was hydrolysed with a range of proteolytic enzymes including pepsin, trypsin, α-chymotrypsin and β-chymotrypsin, and assessed for antibacterial activity. The pepsin digest of bovine casein, which showed antibacterial activity, was fractionated using reverse phase high performance liquid chromatography and the antibacterial peptides isolated were characterised using electrospray ionisation mass spectrometry. Two antibacterial peptides were identified, a novel peptide (Cp1) which corresponded to residues 99–109 of bovine αS1-casein and a previously reported peptide (Cp2) which corresponded to residues 183–207 of bovine αS2-casein. The minimum inhibitory concentration (MIC) of Cp1 and Cp2 were determined against a range of bacterial cultures. Cp1 exhibited an MIC of 125 μg mL−1 against all Gram-positive bacteria tested, and MIC ranging between 125 and >1000 μg mL−1 against the Gram-negative bacteria tested. Cp2 was generally far more potent against the Gram-positive bacteria, exhibiting an MIC of 21 μg mL−1, compared to MICs ranging from 332 to >664 μg mL−1 against most of the Gram-negative bacteria tested.