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
2008
Simova, E. | Beshkova, D. | Dimitrov, Z. | Simov, Z.
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.
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