ANTIMICROBIAL ACTIVITY AND PRELIMINARY CHARACTERIZATION OF PEPTIDES PRODUCED BY LACTIC ACID BACTERIA ISOLATED FROM SOME VIETNAMESE FERMENTED FOODS

Abstract

     In this study, 170 strains isolated from 22 samples of fermented foods were identified as lactic acid bacteria by biochemical and morphological methods. Of which, fifty two isolated strains had antibacterial activity when tested using the agar well-diffusion method. Two strains, CS3.7 and FME1.7, expressed high antimicrobial activity against all of the four indicator bacteria: E. coli, Bacillus cereus, Listeria monocytogenes, and Salmonella spp., and were selected for further studies. The results showed that both strains had antimicrobial activity against the indicator strains 2 hours before the bacteria reached the stationary phase. The antimicrobial activity of the cell free supernatants was completely lost when incubated with papain enzyme for 2 hours at room temperature. This result led us to conclude that antimicrobial substances of the free cell supernatants were peptides. Characterization of the peptides demonstrated that they were highly stable at 68^oC, in which residual activity of FME1.7 and CS3.7 was above 90% and 75% for 20 min, respectively. At 100^oC for 10 min, the antimicrobial activity of the two strains remained around 40%. The study also indicated that the peptides were stable at pH 5. However, antimicrobial activity was significantly reduced when incubated in other pHs. The results showed that peptides of CS3.7 and FME1.7 are quite promising to be used as biopreservatives because of their high range of antimicrobial activity and thermostability.