Effect of Alkaline pH on the Heat Resistance of Salmonella Enteritidis

Introduction: Egg white is widely used in food formulation for its emulsifying properties; however, this ingredient may be contaminated by Salmonella Enteritidis. To ensure food safety, heat treatment should be applied with a temperature no more than 62°C. Moreover egg white also presents the particularity to have an alkaline pH close to 9.2 which could be taken into account to optimize pasteurization process.

Purpose: The aim of this study was to quantify the effect of alkaline pH on the heat resistance and the revivification of Salmonella Enteritidis.

Methods: Thermal inactivation kinetics of Salmonella Enteritidis NCTC 13349 were performed using capillary method. Different conditions for treatment and incubation media were studied from pH 7 to 10. Inactivation kinetics were fitted using the Weibull model and the effects of the heating and recovery pHs on the bacterial resistance were quantified using a modular model approach.

Results: Concave shaped inactivation kinetics (log CFU vs heating time) were fitted by the Weibull model in which parameter "δ" (first decimal reduction time) quantifies bacterial heat resistance. A large effect of alkaline pH of treatment and recovery media was observed on heat resistance. An increase of treatment medium from pH7 to pH9.5 leads to a fivefold reduction the Salmonella Enteritidis NCTC 13349 heat resistance. Whereas an increase from pH 7 to pH 9.5 of the recovery medium leads to a two-fold reduction of heat treatment time for the same efficiency. Thus, heat treatment at 56°C for both treatment and incubation media at pH7 presents similar bacterial reduction than a heat treatment at 52.3°C at pH 9.2.

Significance: Taking into account the alkaline pH of egg white during pasteurization and storage allows minimizing heat treatment intensity. These results ensure a risk/benefit approach yielding destruction of Salmonella Enteritidis and functional properties of egg white.