Characterization of antimicrobial peptides produced by Lactobacillus acidophilus LA-5 and Bifidobacterium lactis BB-12 and their inhibitory effect against foodborne pathogens

This study aimed to optimize the production of antimicrobial peptides (AMPs) by pure and mixed cultures of Lactobacillus acidophilus LA-5 and Bifidobacterium lactis BB-12 in milk model media and then characterize the properties of produced AMPs. The optimal conditions for AMPs bio-production by L. acidophilus LA-5, B. lactis BB-12, and their mixed culture were temperatures of 38.71, 42.00, and 39.00 degrees C, fermentation times of 26.15 h, 60.00 h, and 36.00 h, and yeast extract concentrations of 4.45%, 6.00%, and 5.00% in cheese whey. At optimal conditions, the inhibition activities of AMPs against L. monocytogenes were 14.03 +/- 0.68 mm, 13.33 +/- 0.81 mm, and 11.02 +/- 1.04 mm by L. acidophilus LA-5, B. lactis BB-12, and their mixed culture, respectively. The SDS-page analysis indicated that L. acidophilus LA-5 and B. lactis BB-12 produced AMPs with two and three fractions, respectively. The Fourier-transform infrared spectroscopy and nuclear magnetic resonance tests showed the typical characteristics of a peptide for produced AMPs. The DSC test indicated that produced AMPs had high-temperature stability. These AMPs were bioactive in a wide range of pH (3-9) and temperature (40-100 degrees C for 30 min). The results of minimum inhibitory concentration and minimum bactericidal concentration showed that the AMPs had antimicrobial effects against important food-borne pathogens.