The effects of Steviol Glycosides on Listeria monocytogenes and Salmonella typhimurium Growth Dynamics

Sugar is commonly substituted by stevia-based products in the food industry and in our daily lives. This substitution results in a change in the food product characteristic formula and properties that may affect the growth dynamics of food pathogenic and spoilage bacteria. This work studies the effect of table sugar (TS), laboratory sucrose (LS), commercial stevia (St) and steviol glycosides (SVGly) on the growth dynamics of Salmonella typhimurium and Listeria monocytogenes. Experiments were carried out in general and minimal culture media at 3 equivalent concentrations, in terms of sweetness intensity (TS and LS at 3, 9 and 15 % (w/v); St at 0.3, 0.9 and 1.5 % (w/v); and SVGly at 0.01, 0.03 and 0.05 % (w/v)). Incubation temperatures were: 4, 8 and 20 °C for general media, and for minimal media 20 °C. To establish the role of these sweeteners, their concentration evolution in minimal media was determined via HPLC analysis. The results revealed slow maximum specific growth rates (µmax) of S. typhimurium in general media with increasing concentrations of TS and LS at 20 °C; and reduced maximum cell population (Nmax) at 8 °C. The growth of L. monocytogenes in general culture media remains invariable, independently of the sweetener added, except at 4 °C. At this critical temperature, the presence of TS, LS and St seems to facilitate the growth of L. monocytogenes, presenting higher µmax values in comparison to SVGly and the control. Varying bacterial response to changes in media formulation suggests that further research is required, focusing on revealing the microbial dynamics in structured media, as well as in real food products.status: publishe