High temperature water activity as a key factor influencing survival of Salmonella Enteritidis PT30 in thermal processing

Abstract

Salmonella in low-moisture foods has enhanced thermal tolerance and is difficult to control. The objective of this research was to study relationship between thermal tolerance of Salmonella Enteritidis PT30 and water activity (aw) of food matrices measured at elevated temperatures during thermal processing. Three different foods were selected for this study. They were wheat flour (WF), almond flour (AF) and whey protein (WP), representing carbohydrate-, fat-, and protein-rich food systems, respectively. Pre-equilibrated powders were inoculated independently with S. Enteritidis PT30 and conditioned to aw of 0.25, 0.45, 0.60, and 0.80 at room temperature (∼20 °C). Aluminum thermal death time test cells (TDT cells) and newly designed thermal aw cells (TAC, with controlled aw) were heated at 80 °C to determine D-values (the time needed to active 90% of target bacteria) of S. Enteritidis PT30 in the three powders. Water activities of powders in the TDT cells at 80 °C were calculated to be between 0.41 and 0.89, while in the TAC were controlled to 0.32, 0.50, 0.63, and 0.81, respectively. Results showed that D80°C-values of S. Enteritidis PT30 decreased exponentially with increasing aw of foods at the treatment temperature 80 °C regardless of the food matrices and the testing methods. Thus, it is critical to understand how aw of a food matrix changes with temperature when selecting appropriate treatment conditions for thermal control of Salmonella in low-moisture foods.