In Vitro and in Situ Bacteriocin Activity of Lactic Acid Bacteria from Bulgarian Dairy Products and Methods for Making of Lactobacillus Protective Fermented Milks with Bacteriocin Inhibitory Substances

SIMOVA, E. D., D. M. BESHKOVA, Z. P. DIMITROV and Z. I. SIMOV, 2008. In vitro and in situ Bacteriocin activity of lactic acid bacteria from Bulgarian dairy products and methods for making of Lactobacillus protective fermented milks with Bacteriocin inhibitory substances. Bulg. J. Agric. Sci., 14: 28-42 The studies are based on two theses: 1) Fermented milks are the shortest route and the most appropriate way to assimilate the biologically active substances of lactic acid bacteria (LAB); 2) The most efficient way to introduce bacteriocins in a milk product is by using bacteriocin-producing starter cultures. For the purpose of proving and evaluating the potential application of bacteriocin-producing probiotic LAB as protective cultures two natural milk strains (Lactobacillus bulgaricus BB18 and Lactococcus lactis BCM5) with the highest and widest spectrum of antimicrobial activity against Gram-positive and Gram-negative pathogenic bacteria selected from 1428 LAB strains isolated from authentic home-made Bulgarian fermented milk products and kefir grains were investigated for bacteriocinogenesis in milk. The strains exhibited highly efficient bacteriocinogenesis (1600 – 2000 BU ml-1) and growth activity (1011 – 1012 CFU ml-1) in milk. Lb. bulgaricus BB18 strain with the widest spectrum of bacteriocin activity against Gram (-) pathogenic bacteria (including Helicobacter pylori) was used for protective yogurt starter formation, in which bacteriocin yield was increased by 32% and bacteriocinogenesis was shortened by 3 h through stimulated bacteriocinogenic and growth activities. Temperature stress and Lb. bulgaricus BB18 growth at a lower than the optimal growth temperature (30°C) induced an increase in bacteriocin yield (3600 BU ml-1) in the starter. Methods for making protective yogurt and ultrafiltrate (UF) fermentate with high concentration of the bacteriocin-inhibitory substances and viable probiotic cells were developed.