Improved design of aluminum test cell to study the thermal resistance of Salmonella enterica and Enterococcus faecium in low-water activity foods

Abstract

Salmonella enterica is a major cause of foodborne pathogen contamination in the United States. The heat resistance of Salmonella increases as aw decreases, leading to a significant challenge in the design of thermal processes. The aluminum thermal death time (TDT) cell is a common experimental tool to study the isothermal resistance of Salmonella and other pathogenic bacteria in foods. However, the TDT cell has the problem of a relatively long come-up time, and it is difficult to seal. This research improved the previous design of aluminum TDT cells and evaluated the performance of the improved design by using the thermal inactivation data of Salmonella enterica cocktail and Enterococcus faecium in brown rice flour. The come-up time of brown rice flour was reduced significantly, from 2.33 min in the previous design to 0.67 min (40 s) in the improved design of test cells when immersed in an 85 °C glycol bath. With the increase of the cavity diameter of the cell, it was easy to load and unload food samples. Additional new features of the improved design included the wrench flats on the outer surface of cell wall. The D-values for Salmonella in the aw 0.45 (measured at 25 °C) brown rice flour were 42.70, 17.51, 8.11, and 2.27 min at 70, 75, 80, and 85 °C, respectively. The D-values for Enterococcus faecium were 65.82, 22.28, 6.05, and 1.86 min at 70, 75, 80, and 85 °C, respectively. This research shows that the improved design of test cells is a reliable experimental tool to study the thermal resistance of microorganisms in low-aw foods. Accurate detection of microbial survival under isothermal conditions will provide reliable data for modeling and pathogen control during thermal processing to help ensure food safety and quality.