Lactose monolaurate (LML) was previously found to be an antimicrobial against Listeria monocytogenes in culture medium at concentrations between 3 and 5 mg ml−1. In this study, the microbial inhibitory activity of LML in dairy products inoculated with a 5-strain cocktail of clinical isolates of L. monocytogenes was investigated. Addition of LML at a concentration of 5 mg ml−1 resulted in 4·4, 4·0 and 4·2 log reductions in 0·5% fat, 1% fat and 3·25% fat milks, respectively; 4·1, 4·4, and 3·5 log reductions in nonfat, 1% fat, and 1·5% fat yogurts, respectively; and 4·0 log reductions in both nonfat and 2% fat cottage cheese. The inhibitory effect of LML was only observed at 37°C and not 5°C. Experiments suggest that both the lauric acid and the esterified lactose moiety of LML play roles in the growth inhibition.
Significance and Impact of the Study
A novel sugar ester, lactose monolaurate, inhibited the growth of a five-strain cocktail of Listeria monocytogenes in milk, yogurt and cottage cheese. This is the first report of the use of a sugar ester to inhibit the growth of Listeria in food systems.