Improving design of thermal water activity cell to study thermal resistance of Salmonella in low-moisture foods

Water activity (aw) influences the thermal resistance (D-value) of pathogens in low-moisture foods (LMF). However, the influence of food matrices on aw at elevated temperatures is complicated. A recent study reported that a novel thermal water activity cell (TAC) could be used to control aw of LMF using LiCl solution (select molality) during the isothermal determination of D-values of Salmonella. This research proposed a new version of TAC (TAC II) that could significantly reduce the time to establish the moisture-equilibrium between LMF and LiCl solutions during D-value measurements. Wheat flour (WF) samples inoculated with Salmonella (aw at room temperature = 0.45) were treated in TAC II at 80 °C under controlled relative humidity (RH) (50%) provided by LiCl solution (9.37 mol kg−1). Results showed that the moisture-equilibrium was established to the controlled RH condition at 80 °C in <4 min for tests with TAC II, as opposed to >14 min for TAC. The D-value of Salmonella PT30 in WF (80 °C, RH 50%) tested with TAC II (20.7 ± 1.1 min) was significantly higher (p < 0.05) than the reported result obtained from TAC. TAC II provides more accurate estimation of D value for giving relative humidity at high temeprature, and it offers to improve our understanding of the isolated effect of aw (corresponding RH) at high temperatures on the D-values of Salmonella in LMF.