Minced Meat Shelf Life Prolongation Cause of Antimicrobial Substances Produced by Lactobacillus Delbrueckii in The Cold Condition

Nowadays biopreservation is an alternative method for protective foods and extend their shelf life during the storage. The aim of this research was to determine formation of antibacterial substances supernatants of L. del-brueckii 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. MRS agar, Nutrient broth (NB), Tryptose agar (T-agar) and Beef broth (BB) prepared by dissolving of 20 g powder in 1 L distilled water, Sodium phosphate buffer (PBS) (pH 6.5), Physiological saline - 0.9% NaCl, Peroxide Test strips were used. Antibacterial activity was evaluated by agar disk diffusion method. H2O2 amount was determined by Merckoquant Peroxide test strips.Microbiological analysis of the ground beef infected by Escherichia coli O157: H7 and treated by Lactobacillus delbrueckii MDC 9617 was done by plating of serial dilution in physiological saline on Tryptose agar. 150 g of fresh minced meat was inoculated with 1×105 CFU/g pathogen and divided into three equal portions. Were pre-pared L. delbrueckii cultures 1×107 CFU/ml and added into 3 samples of infected minced meat, mixed and pack-aged in vacuum polyethylene bags. All samples were kept at 5°C. The cells 1×109 CFU/ml of L. delbrueckii MDC 9617 produced significant amount of antibacterial substances mainly hydrogen peroxide 35 μg/ml in sodium phosphate buffer 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 MDC 9617 reduced initial amount 2x105 of E. coli O157: H7 in ground beef cocultivation up to 3 log for 3 days and become undetectable after 7 days. L. delbrueckii MDC 9617 strain exerts inhibitory action against E. coli O157:H7 and dramatically (more than 95 %) reduced number of pathogen bacteria in both submerged and solid-state cocultivation trials at refrigeration temperatures

Keywords:

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