Optimization of conditions for generation of antimicrobial peptides from milk proteins by Lactobacillus spp.

The batch growth conditions for the generation of antimicrobial peptides from skim milk were optimized by using Lactobacillus spp. Proteolysis being important factor for peptide production, 4 Lactobacillus strains were screened for proteolytic activity, two strains each from Lactobacillus acidophilus and Lactobacillus delbrueckii. L. acidophilus NCDC 14 and L. delbrueckii NCDC 09 with higher activity were selected to produce antimicrobial peptides. Incubation period (12-72 h), inoculum level (1-3%) and incubation temperature (37 and42°C) had an individual effect on antimicrobial activity of 10KDa Ultrafiltered skim milk hydrolysates checked against pathogenic E. coli ATCC 25922. Optimal conditions for generation of antimicrobial peptides include incubation period of 48 and 12-24 h, inoculums level of 2 and 1% and incubation temperature of 37°C for L. acidophilus NCDC 14 and L. delbrueckii NCDC 09 with proteolysis in range of 7.34-8.51 and 20-27.2 mMLeucine, respectively. Antimicrobial activity increased with proteolysis (>8.51 and >11 mMLeucine) but upto a certain extent after which it decreased for both strains. Maximum antimicrobial zone diameter obtained was 20 and 16.5 mm for L. acidophilus NCDC 14 and L. delbrueckii NCDC 09, respectively. The variables studied were very relevant due to their significance in improving the peptide production from both microorganisms and likely economic optimum conditions.