INFLUENCE OF DIFFERENT FACTORS ON DESICCATION SURVIVAL AND THERMAL RESISTANCE OF SALMONELLA AND RADIOFREQUENCY PASTEURIZATION OF LOW-MOISTURE FOODS

Abstract

Salmonella outbreaks associated with low-moisture food have become a food safety concern for the industry, government and public. Current sanitary practices have proven inefficient, intervention technologies need to be studied. Developing effective intervening treatments is challenging due to the limited information and understanding on Salmonella’s survival and inactivation kinetics in dry foods. The objective of this research was to better understand some extrinsic and intrinsic parameters affecting Salmonella’s thermal resistance in low-moisture foods, assess the effectiveness of Radiofrequency (RF) pasteurization for Salmonella in wheat flour, and evaluate Enterococcus faecium as a surrogate for RF inactivation of Salmonella. Five inoculation methodologies were evaluated on their effects over Salmonella’s population counts after inoculation, survival after equilibration to a low-water activity (aw) environment, and changes in thermal resistance in wheat flour. Water activity and food composition were explored with respect to their influence on the thermal resistance of Salmonella in almond meal (oil rich food) and organic wheat flour (carbohydrate rich food) using two types of cells. One cell had a Relative Humidity (R. H.) controlling solution to keep the food aw at 0.45 (TAC cells). The other cell allowed the foods’ aw to naturally elevate with temperature (TDT cells). Biofilm effects on short desiccation and thermal resistance of Salmonella, were studied by comparing the thermal resistance in wheat flour of 4 biofilm non-former strains, and 3 former strains after equilibration to 0.45 aw. Potential and effectiveness or RF as a pasteurization technology for low-moisture foods was also evaluated. Measurements of temperature uniformity during RF treatment of 3 low-moisture foods were made using an infrared camera. Finally, the effectiveness of RF treatments to pasteurize (achieve a 5 log reduction) of S. Enteritidis PT 30 and its surrogate E. faecium in wheat flour at different aw (0.25, 0.45, 0.65) was evaluated. Overall conclusions were that inoculation methodology, biofilm formation, food composition and aw can profoundly affect the thermal resistance of Salmonella and should be taken into account when designing new pasteurization treatments. And that RF can effectively pasteurize some low-moisture products like wheat flour.