Inactivation and sublethal injury of Salmonella Typhimurium on beef and in aqueous solution treated with lactic acid

Salmonella Typhimurium, a common foodborne pathogen, is widespread in foods. Lactic acid (LA) has been employed to control bacteria in food, while it can induce the formation of sublethally injured bacteria. The sublethal injury of LA against S. Typhimurium on beef was determined in this study, meanwhile the inactivation and sublethal injury kinetics of S. Typhimurium in aqueous solution treated with LA at different temperatures (4, 25, and 37 °C) and concentrations (1, 2, 4, and 6 mM) were also investigated and fitted. The sublethal injury was also validated by flow cytometry (FCM) and high content imaging system (HCS). LA could induce sublethally injured S. Typhimurium on beef and in aqueous solution, the injury ratios in both the cytoplasmic and outer membrane increased with increasing exposure time (0-180 min), concentration (1-6 mM) and temperature (4-37 °C). Modified Logistic and modified Weibull models fitted the inactivation kinetics well, and the parameters indicated that LA caused accumulated damage to S. Typhimurium. The inactivation and sublethal injury effects of LA on S. Typhimurium were verified by FCM and HCS analysis.