THERMAL INACTIVATION OF SALMONELLA ENTERITIDIS PT 30 AND ENTEROCOCCUS FAECIUM IN EGG POWDERS AT DIFFERENT WATER ACTIVITIES
Pérez Reyes, Marco Esteban
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Egg powders have seen an increasing demand in the food market, because their functional properties, and less storage space requirements. However, industrial egg powders processing consists of several unit operations, where they can be contaminated with Salmonella. The objectives of this research were to: study the impact of the temperature and composition on the aw of the egg powders; develop a prediction model of aw at elevated temperatures; obtain the D80°C-values of Salmonella Enteritidis PT30 and E. faecium in the egg powders; assess the impact of aw on the quality of egg white powder after thermal treatment. The changes of aw in the egg powders with temperatures between 20 and 80°C were measured using a Vapor Sorption Analyzer and a High-Temperature Cell (HTC). A model-based on Cassius Clapeyron equation was developed, which allows getting the moisture sorption isotherms of egg powders at different temperatures. The D80°C-value of S. Enteritidis PT30 and E. faecium inoculated in the egg powders preconditioned to three aw levels (0.3, 0.45, 0.6) at 20°C were determined using aluminum thermal death test cells. The results showed a significant increase (P<0.05) in the aw values in all three egg powders when the sample temperature was raised from room temperature to 80°C. The D80°C-values ranged from 5.3±0.1 to 25.9±0.2 min for S. Enteritidis while for E. faecium the D80°C-values varied between 10.4±0.4 and 43.8±0.4 in samples of the three different aw levels. This study validates a log-linear relationship between the thermal resistance of Salmonella and the aw of food products at high temperatures in egg powders. With the increase of the aw and thermal treatment time, the egg white powder samples became lighter. The loose and tap bulk densities of the egg white powder decreased when aw increased. In conclusion, the aw of egg powders increases at 80°C. An increase in aw of egg powder sharply reduces the D80°C-value of Salmonella. E. faecium is an ideal surrogate for egg powder. This study should serve as a good reference for the food industry to select appropriate processing e.g. aw and time, for thermal control of Salmonella in egg white powder.