Isolation and characterisation of antibacterial peptides derived from the f(164-207) region of bovine alphaS2-casein

A chymosin digest of sodium caseinate, which showed antibacterial activity against Listeria innocua, was fractionated using reverse phase high performance liquid chromatography and the purified antibacterial peptides were characterised by mass spectrometry, N-terminal amino acid sequencing and comparison to peptide masses of theoretical enzymic digests of milk proteins. Five antibacterial peptides, Cr1, Cr3, Cr4, Cr5 and Cr7 corresponding to amino acid residues 181-207, 180-207, 175-207, 164-207 and 172-207 of bovine alpha(S2)-casein, respectively, were isolated. The minimal inhibitory concentration of peptides Cr1, Cr4 and Cr5 was determined against a range of Gram-positive and Gram-negative bacteria and showed similar activities to those of the bacteriocin peptide, nisin and the antibacterial peptide, lactoferricin B against certain Gram-positive bacteria. A partially purified chymosin digest of sodium caseinate (Cr(MIX)) was prepared and observed to be heat stable for up to 15 min on exposure to 121 degrees C. Although Cr(MIX) showed bactericidal activity against Salmonella Typhimurium in 0.1% (w/v) peptone medium, no antibacterial activity was observed when tested in skim milk at the same concentration.