Testing matrix, inoculum size, and incubation temperature affect monolaurin activity against Listeria monocytogenes

Abstract

Current literature reports conflicting minimal inhibitory concentrations (MIC) (range 10–96 g ml −1) of glycerol monolaurate (monolaurin) against Listeria monocytogenes. To resolve these disagreements, the individual MIC of monolaurin against eight L. monocytogenesstrains was determined using the standard agar dilution technique on three commercial media (trypticase soy agar, plate count agar, and Oxford modified medium), and a catfish-based medium using three inocula sizes and three incubation temperatures. Mean MIC was 16 g ml −1on commercial media at 25 and 35°C. Endpoints at 15°C were twofold lower (8 g ml −1) than at 25 and 35°C. On catfish-based medium, MIC values were four- to eightfold higher (64–128 g ml −1) compared with commercial media and depended on incubation temperature and size of inoculum tested. Poor solubility of monolaurin (85 g ml −1) in aqueous solutions and its reduced activity in the presence of food components limits its application as an antimicrobial agent in foods.