Alireza Goodarzi - Armbiotechnology Scientific and Production Center NAS RA, Yerevan, Armenia
Vahid Goodarzi - Department of microbiology, Islamic Azad University, Arak branch.

The strains of Lactobacillus delbrueckii subsp. lactis widely used in food preservation due to ability produce high amount of hydrogen peroxide at refrigerator temperatures to inhibit food-borne pathogens and psychrophilic spoilage microorganisms. In order to improve of bio-preservation efficacy of L. delbrueckii MDC 9617 mutations causing resistance to streptomycin (str) were used. Among UV-mutagenized population of L. delbrueckii three str mutants producing high amounts of H2O2 were selected. Str mutants produced significant amounts of hydrogen peroxide 50-60 μg/ml in sodium phosphate buffer (0.2 M, pH 6.5) and in beef broth (BB) at 5 °C for 5 days submerged cultivation without of growth. Evaluation mutants antibacterial activity at refrigeration temperatures against food-borne pathogen Escherichia coli O157: H7 revealed elimination of pathogen total number up to practically undetectable amount for 3 days. In case of solid-state cultivation on agar-based medium, disks soaked by mutant cells suspensions formed2larger inhibitory zones on E. coli O157: H7 lawn for one-day cold exposition. The size of inhibition zone depends on concentration of LAB cells. Str mutants L. delbrueckii reduced initial amount 2×105 of E. coli O157: H7 in ground beef up to 3 log for 3 days of solid-state cocultivation when the wild strain reduced only 2 log. The application of L. delbrueckii mutants did not cause any changes in sensory characteristics of ground beef, moreover promotes expanding of shelf-life due to inhibition of psychrophilic spoilage microorganisms.

Biopreservation, Lactobacillus delbrueckii, Str mutations, refrigerated temperatures, hydrogen peroxide, E. coli O157: H7