Alireza Goodarzi - Young Researches and Elite Club, Borujerd Branch, Islamic Azad University, Borujerd, Iran
Vahid Goodarzi - Department of microbiology, Islamic Azad University, Arak branch

The objective of this study was to determine formation of antibacterial substances in supernatants of L. delbrueckii during cold storage and evaluate whether the application of this bacteria to raw ground beef would result in significant reductions of E. coli O157:H7 during refrigerated storage. Antibacterial activity of a newly isolated Lactobacillus delbrueckii MDC 9617 at refrigeration temperatures against food-borne pathogen Escherichia coli O157: H7 was studied. The size of inhibition zone depends on concentration of LAB cells. The cells 1×109 CFU/ml of L. delbrueckii produced significant amount of antibacterial substances mainly hydrogen peroxide 35 μg/ml in sodium phosphate buffer (0.2 M, pH 6.5) and 40 μg/ml in beef broth at 5 °C during submerged cultivation without of growth. Submerged cocultivation of E. coli O157: H7 with lactobacilli in NB broth at 5°C reducing the total number of the pathogen more than 3 log for 5 days. The cell suspension intendent for treatment must contain 108-9 CFU/ ml of LAB. L. delbrueckii reduced initial amount 2×105 of E. coli O157: H7 in ground beef cocultivation up to 3 log for 3 days and become undetectable after 7 days. The application of L. delbrueckii bacteria does not cause any changes in sensory characteristics of ground beef by itself; moreover promote expanding of shelf-life due to inhibition of psychrophilic spoilage microorganisms.

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