Modeling the effect of protein and fat on the thermal resistance of Salmonella enterica Enteritidis PT 30 in egg powders.

Microorganisms in low-moisture foods (LMFs) exhibit prolonged survivability and high heat resistance. Various external factors (water, food texture, nutritional compounds, etc.) influence the microbial heat resistance in LMFs; yet, the influential degree of each factor is not fully understood. In this study, the thermal resistance parameters (D and z values) of Salmonella enterica Enteritidis PT 30 (S. Enteritidis) at 80, 85, and 90 °C at the room-temperature water activity (aw, 25°C) of 0.32 ± 0.02 were measured. A series of egg powders with different fat and protein ratios (obtained by mixing egg white and yolk powders) were chosen as the model foods. Primary and secondary models were built from the isothermal inactivation kinetics of S. Enteritidis in the tested samples. The importance of fat and protein was then confirmed by controlling the water activity at the treatment temperature (aw, treatment temperature) via thermal water activity cells. The survivor curves of S. Enteritidis fitted well with the Weibull-type and log-linear models. The D values of S. Enteritidis increased with increasing fat (0-56.7%, w.b.) and decreasing protein contents (83.59-31.81%, w.b.). Incorporating the modified Bigelow model into the log-linear model yielded the zfat and zprotein of 58.96 and 57.14, respectively. At the controlled aw, 90°C of 0.32 ± 0.02, the D90°C values of S. Enteritidis increased remarkably (P < 0.05), but the values in egg white, whole egg, and egg yolk powders (11.73 ± 1.24, 23.82 ± 2.0, and 60.0 ± 2.4 min) were remarkably different. Our study identified that the influential degrees of fat, protein (zfat and zprotein values), and aw on the thermal resistance of S. Enteritidis in egg powders is in the order: aw,treatment temperature > fat > protein. Fat considerably increased the thermal resistance of S. Enteritidis even at the same aw,treatment temperature. This study quantified the effect of fat and protein on the thermal resistance of S. Enteritidis and emphasized the non-negligible effects of food components in LMFs' microbial safety.

Influence of low water activity on the thermal resistance of Salmonella Enteritidis PT30 and Enterococcus faecium as its surrogate in egg powders.

Egg powders are increasingly popular ingredients, due to their functionality and compactness, in industrial food production and preparation at homes. However, there is a lack of studies that evaluate the thermal resistance of Salmonella Enteritidis PT30 and its potential surrogate Enterococcus faecium NRRL B-2354 in egg powders. This study examined the log-linear relationship between the thermal resistance of Salmonella Enteritidis (D-value) and the water activity (aw) of egg powders. The changes of aw in the egg powders with temperature were measured using a Vapor Sorption Analyzer and a high-temperature cell. The D80 ℃-value of S. Enteritidis PT30 and E. faecium inoculated in the egg powders preconditioned to three aw levels (0.3, 0.45, and 0.6) at 20 ℃ were determined using aluminum thermal death test cells. The aw values increased (P < 0.05) in all three egg powders when the temperature of the samples was raised from room temperature to 80 ℃. The D80 ℃-values ranged from 5.3 ± 0.1 to 25.9 ± 0.2 min for S. Enteritidis while 10.4 ± 0.4 to 43.8 ± 0.4 for E. faecium in samples of the three different aw levels. S. Enteritidis PT30 showed a log-linear relationship between D80 ℃-values and aw80 ℃ for the egg powders. This study contributes to our understanding of the impact of aw on the development of thermal treatments for low-moisture foods.