Sublethal injury effects of lactic acid against Salmonella Typhimurium biofilm on foods and food contact surfaces.

Lactic acid (LA) is broadly utilized as a disinfectant in the food industry, but its sublethal injury effects against Salmonella Typhimurium biofilm on different food matrices and food contact surfaces remain poorly understood. The sublethal injury effects of LA against S. Typhimurium biofilm inoculated on foods (eggshells, pork skin, and Chinese cabbage leaves) and food contact surfaces (rubber, polypropylene, stainless steel, and glass) were investigated in this study. Meanwhile, the changes of morphological characteristic, swimming motility, metabolic activity, and adhesion ability were also determined during the formation of sublethally injured biofilm cells. The results showed that LA effectively inactivated biofilm cells and induced sublethal injury on all tested foods and food contact surfaces, with injury ratios varying significantly depending on the surface types. The highest injury ratios on eggshells and Chinese cabbage leaves reached 58.18% and 66.76%, respectively, while on stainless steel and glass, the injury ratios exceeded 90%. Morphological analysis revealed cell deformation, membrane damage, and loosened biofilm structure after LA treatment. Swimming motility, metabolic activity, and adhesion ability of the biofilm cells were all significantly decreased, with more pronounced effects on food contact surfaces than on foods. These findings highlight that food matrices provide protective effects against LA-induced sublethal injury, whereas smooth, nonporous food contact surfaces enhance LA efficacy. This study provides a theoretical basis for optimizing disinfection strategies and controlling sublethally injured biofilm cells in the food industry.