UV-C light-activated gallic acid and non-thermal technologies for inactivating Salmonella Typhimurium inoculated in aqueous solution and whole cow milk

This study aimed to evaluate the effect of UV-C light-activated gallic acid (GA) alone and combined with ultrasound (US) or ultraviolet-C light (UV-C, 254 nm) on the inactivation of Salmonella Typhimurium in aqueous solution for being later applied to whole cow milk. First-order, Weibull, and Beta models were used to describe the inactivation kinetics of S. Typhimurium by GA alone and combined with non-thermal technologies. Results indicated that GA concentration, the UV-C light activation process, and the combination of US and UV-C light significantly affected (p < 0.05) the inactivation of S. Typhimurium in aqueous solution, which was properly described by the first order (R² > 0.84), Weibull (R² > 0.96), and Beta (R² > 0.83) models. The activation process of GA increased its antimicrobial activity in the range of 40.87–101.44 %. Moreover, with the highest concentration of GA and the application of US or UV-C light, >5 log reductions were achieved. Nevertheless, although these combinations were applied to whole cow milk, a low reduction (2.0-log cycles) was obtained, regardless of the GA activation and non-thermal technologies. Therefore, the effect of GA, whether UV-C light activated or not, on S. Typhimurium depends on the food matrix. This highlights that in whole cow milk, this treatment was insufficient to ensure safety, even when combined with non-thermal technologies.

Industrial relevance

UV-C light and US are non-thermal technologies used as alternatives to thermal treatments. These technologies can be used on their own or in combination; however, in many cases, the necessary microbial reduction is not attained, thus the use of complementary techniques or processes is required. GA is a phenolic compound with low antimicrobial activity; however, UV-C light may activate its antimicrobial activity. In this sense, this study shows the potential application of GA and non-thermal technologies for inactivating S. Typhimurium in an aqueous solution and the first approach of this methodology in whole cow milk as a liquid food product.