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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.

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This research analyzed the influence of fat content (1%, 3%, 5%, and 10%, w.b.) and of water activity (0.85, 0.90, 0.95, and 0.99) on the effectiveness of microwave heating within model systems (agar gel). Findings indicate that an increased fat content promotes more uniform heating in the model systems and results in longer heating times to reach the target temperature of 50°C. In the model systems with different aw values, the warming of the central model zone was slower while in the corners, heating was accelerated. Additionally, in these models, heating times increased as the aw was decreased. Practical Application The study of model systems allows for a detailed assessment of food when subjected to microwaves; and how heating is influenced by food properties such as aw and fat content. Findings indicate that changes in product formulation could improve the heating of ready‐to‐eat foods, either by increasing the fat content (better uniformity) or having high aw (shorter heating time).

This study aimed to investigate water activity (aw) changes in different egg powders (egg white, egg yolk, and whole egg) as influenced by temperature between 20°C and 80°C. A high‐temperature test cell was used to measure the aw in egg powders of different moisture contents (2 to 30% wet basis) during heating in a closed environment. Then, the net isosteric heat of sorption (qst) of the egg powders was calculated. The qst values were used in the Clausius–Clapeyron equation to generate the isotherms of the egg powders at 40°C and 80°C. The results showed that at fixed moisture content and temperature, egg yolk powder had higher aw than whole egg and egg white powders. In addition, aw of the three egg powders in closed containers all increased with temperature. Egg white powder had stronger binding capacity to water, as reflected by the higher qst, compared to the other two egg powders. Practical applications An important determinant for the survival of microorganisms during thermal treatments is food water activity (aw), which changes with temperature. Currently, there is no scientific data regarding aw changes in egg powders at elevated temperatures. Therefore, this study aimed to determine the aw changes in egg powders as a function of temperature and composition. Data produced by this study regarding aw changes provide useful information for designing effective heat treatments to control pathogens in egg powders. The isosteric data should also help estimate the energy efficiency of egg powder drying operations.