Bacteriocins producing lactic acid bacteria: Isolation, optimization of growth condition for bacteriocins production and application in foods.

Lactic acid bacteria (LAB) produce a variety of compounds with antimicrobial activity. Among them are bacteriocins, which have attracted great interests due to their antimicrobial effects on spoilage and pathogenic microorganisms and potential applications in food to enhance microbial safety. The objectives of our studies were to isolate and characterize bacteriocins producing LAB strains, determine the optimal growth conditions including pH, culture media and temperature for LAB and bacteriocins production by measuring optical density (OD), bacteriocin activity and viability of LAB, and further explore their application in foods.
LAB strains were isolated from horticultural commodities and dairy products. The antimicrobial properties of LAB isolates were determined using the agar diffusion bioassay. Bacteriocins producing LAB were identified using 16S rRNA gene sequencing and molecular weight of bacteriocins was determined using SDS-PAGE technique. Antimicrobial effectiveness of LAB and bacteriocins were investigated against a range of spoilage and pathogenic bacteria and fungi. Growth curves of bacteriocinogenic LAB grown under various growth conditions were investigated using a Bioscreen C. For the selected growth conditions, the relationship of pH, OD, bacteriocin activity (AU) and viability of LAB (CFU/ml) were determined. These research findings provided useful information on application of LAB and bacteriocins efficiently in foods to improve food safety and quality.
Challenge tests were also conducted on lettuce or cantaloupe juice culture medium as well as on fresh-cut vegetables inoculated with L. innocua at 104 CFU/ml. Results showed that bacteriocinogenic LAB such as Lactococcus lactis (7.17) and Enterococcus faecium (13.2) significantly reduced Listeria spp. (p=0.005) during storage at 4 or 20°C. These results suggest that bacteriocins producing LAB would be used for food protection when applied as protective cultures in food system.