GROWTH SUPPRESSION OF LISTERIA-MONOCYTOGENES BY LACTATES IN BROTH, CHICKEN, AND BEEF

Sodium or potassium lactate is available commercially as a neutral aqueous solution (60%), approved for use as a flavoring agent in meat and poultry products. While recommended also for extending shelf life, little work on its antimicrobial effects has been published and none in relation to Listeria monocytogenes. Studies in tryptic soy broth showed that concentrations higher than 5% delayed growth of three strains of L. monocytogenes. Experiments in sterile comminuted chicken and beef at 35, 20, and 5-degrees showed growth suppression by 4% lactate, which increased with decrease in storage temperature. The organism was consistently more sensitive to lactate in beef than in chicken, displaying an extended lag phase of 1-2 weeks at 5-degrees-C. Combinations of lactate (4%) with NaCl (3%) or nitrate (140 ppm) did not enhance the effect. Lactate did not alter the beef or chicken pH, and no difference was observed between the effect of the two salts, inferring that the lactate ion is responsible for the delay in listerial growth.