Design of a novel test cell to study the influence of water activity on the thermal resistance of Salmonella in low-moisture foods

A novel test cell was developed to study the influence of water activity (a(w)) on thermal inactivation of food pathogens in low-moisture foods (LMF). The cell consisted of multiple wells with a shared head space; aw of the inoculated food sample was controlled by lithium chloride (LiCI) solution of selected molality during heating. The performance of the test cell was evaluated by studying sample heating uniformity using finite element simulation and by comparing measured headspace relative humidities (RH) with predicted RH provided by LiCI solutions. The new cells were used to determine thermal resistance (D-value) of Salmonella at 80 degrees C in organic wheat flour (OWF) maintained at a(w) of 0.45. The D-value of Salmonella was also determined in conventional thermal death time test cells in which a(w) of OWF samples increased from 0.45 at room temperature to 0.73 at 80 degrees C according to the measured isotherm. The results demonstrated that aw significantly influenced the D-values of Salmonella, and the new test cells can be used to directly relate thermal resistance of food pathogens to water activities of LMF at processing temperatures. (C) 2017 Elsevier Ltd. All rights reserved.