Differences in the occurence and efficiency of antimicrobial compounds produced by lactic acid bacteria

To provide consumers with new, attractive, and healthy food products, chemical additives could be replaced by lactic acid bacteria (LAB). Twelve highly antagonistic LAB strains were screened to find the best manufacturers of antimicrobial agents and key components that ensure greater effectiveness of their antagonistic activity. The tested LAB strains appeared to produce and excrete natural antimicrobial compounds such as ethanol (0.27–0.87%), lactic (5.6–19.9 g/L), citric (0.3–3.3 g/L), benzoic (0.2–1.8 mg/L), and sorbic (0.1–1.2 mg/L) acids. The individual LAB strain showed strain-specific abilities to produce individual compounds: citric acid was observed for Streptococcus thermophilus 43, sorbic acid for Lactococcus lactis 140/2, and diacetyl for other L. lactis strains. Lactobacillus helveticus R reached the highest antimicrobial activity by the production of the largest amount of lactic acid, while L. lactis 140/2 achieved that by the complex of produced organic acids. Enterococcus faecium 41-2B was mostly effective protein producing strain (1.2 g/100 g); moreover, enterocins A and P coding genes with antimicrobial activity against Listeria monocytogenes were found in these Enterococcus strains. Five LAB strains were characterized by containing 1–2 plasmids. The study demonstrated a delicate balance of natural antimicrobial synthesis; meanwhile, the insertion of some preservatives in the medium could not significantly decrease their antagonistic activity.