Thermal Injury and Recovery of Salmonella enterica Serovar Enteritidis in Ground Chicken with Temperature, pH, and Sodium Chloride as Controlling Factors†

Abstract

Cells of Salmonella enterica serovar Enteritidis were grown at 25 and 35°C, heat injured (55, 60, and 62.5°C), and recovered in tryptic soy broth (TSB) at various NaCl concentrations (2.0 and 3.5%) and pH levels (5.5 and 6.5). To assess the interactions of growth temperature, heating temperature, NaCl concentration and pH on the thermal injury and recovery of Salmonella Enteritidis in ground chicken, a randomized design with each experimental combination was used. When a logistic equation for nonlinear survival curves was used, D-values of cells of Salmonella Enteritidis grown at 25°C were 7.60, 5.73, and 4.81 min at 55, 60, and 62.5°C, respectively. For cells grown at 35°C, the D-values were 12.38, 7.45, and 5.70 min at 55, 60, and 62.5°C. The influence of tryptic soy agar and double modified lysine agar (DMLIA) on the recovery of heat-injured cells was determined. Recovery was significantly reduced on DMLIA at increased pH levels and NaCl concentrations. Higher numbers of cells were recovered in TSB with 2.0% NaCl than in TSB with 3.5% NaCl. It was observed that the rate of recovery of heat-injured cells was similar at each pH. Therefore, a pH range of 5.5 to 6.5 does not have a major inhibitory effect on the recovery of Salmonella Enteritidis.