Evaluation of the ability of lysozyme and nisin to control meat spoilage bacteria

The antimicrobials lysozyme, nisin, and mixtures of the two were studied to ascertain their abilities to control the growth of the meat-borne spoilage bacteria, Brochothrix thermosphacta B2 and Carnobacterium sp. 845. The goal was to optimize an antimicrobial for potential use in preservation of fresh meats. Their efficacies were evaluated in APT broth, in a meat juice extract and on cores of lean and fat pork tissue. Both lysozyme and nisin alone as well as mixtures of the two effectively inhibited B. thermosphacta B2 at 250 μg/ml in APT broth, the lowest concentration evaluated, for 10 days at 2°C. In the presence of 500 μg/ml lysozyme, B. thermosphacta B2 grew after 12 days incubation. Only 125 μg of antimicrobial/ml was required to inhibit B. thermosphacta B2 for 27 days at 2°C in pork juice. An estimated surface concentration of 130 μg/cm2 of each of the antimicrobials effectively inhibited B. thermosphacta B2 on inoculated cores of fat and lean pork tissue when the cores were incubated in vacuum packages for 6 weeks at 2°C. In APT broth and in pork juice, lysozyme showed no antimicrobial activity against Carnobacterium sp. 845 at concentrations of 500 and 1000 μg/ml, respectively. Nisin and mixtures of the two antimicrobials inhibited Carnobacterium sp. 845 so that its numbers were at least 3 log units lower than untreated samples after 26 and 27 days incubation for APT and pork juice, respectively. The antimicrobial effect was concentration dependent. On lean pork tissue, numbers of Carnobacterium sp. 845 were significantly lower than untreated samples or samples treated with 195 μg/cm2 lysozyme when 260 μg/cm2 of a 1:3 (w/w) ratio of nisin to lysozyme was introduced to the cores. The inhibitory effect lasted for 14 of 42 days incubation in vacuum at 2°C. On fat tissue, both lysozyme alone and the 1:3 nisin/lysozyme mixture inhibited Carnobacterium sp. 845 for 21 days storage in vacuum at 2°C. On fat and lean tissue, mixtures of nisin and lysozyme would be more effective antimicrobials than either nisin or lysozyme alone.