Bioactive peptides and/or bacteriocins are important antimicrobial
metabolites produced by LAB, which are proteinaceous in
nature. Such compounds inhibit specific microorganisms, particularly
Gram-positive bacteria.8 In order to investigate whether the
antimicrobial compounds that inhibited the growth of S. aureus
were proteinaceous, the CFS of selected LAB was neutralized to
eliminate the effects of acids and treated with protease. Proteolytic
enzymes that degrade proteins present in the CFS would therefore
render the proteinaceous antimicrobial compounds ineffective in
exerting their bactericidal effect.22 Among the selected strains, the
CFS of two strains, W. cibaria BD 1514h (B7) and L. fermentum BD
8913f (D10), showed a significant reduction (p < 0.05) in the
inhibitive action compared to the neutralized CFS (Figure 1). The
presence of proteinaceous antimicrobial compounds in these two
strains was confirmed. In addition, the inhibitive action of the
precipitated protein fractions of all selected strains was postulated
to be a result of the concentration of bioactive peptide-like compounds
through the salting out method. Many bioactive peptides of
LAB were produced in small amounts; therefore, to effectively
evaluate the antimicrobial activities of such peptides, one crucial
step was to concentrate the CCFS with the ammonium sulfate
precipitation method, which was employed in this study.25 Bioactive
peptides including bacteriocins can easily form pores on the
cytoplasmic membrane of sensitive cells and disrupt nucleic acids,
subsequently leading to ion leakage, loss of proton motive force,
and ultimately cell death.