The Effect of Salmonella Enteritidis on the Thermal Properties of Egg Albumen and Yolk

Salmonella-inoculated and uninoculated fresh eggs were microwave processed to achieve pasteurization. However, quality degradation was observed in the albumen of inoculated eggs but not in the uninoculated eggs although the processing was the same. Previous work showed that dielectric properties of egg albumen and yolk do not change in the presence of the bacteria. A new hypothesis was therefore proposed that heat capacity is affected by its presence. If an egg has a lowered heat capacity it will become hotter for a given amount of microwave energy input than eggs having normal heat capacities. The goal of the experiments was to determine whether Salmonella at varying concentrations and different incubation times affects the temperature-dependent thermal properties of egg albumen and yolk during in-shell growth. Although the main concern was Salmonella’s effect on the heat capacity of albumen, the equipment used could measure thermal conductivity as well and measurements on yolk were included for completeness. The thermal properties of both egg albumen and yolk were measured by the KD2 Pro thermal properties analyzer (Decagon Instruments, Pullman, WA) via the supplied 30 mm dual-needle sensor. Variables were temperature (7oC, 30oC, 40oC, 50oC, 55oC and 60oC), bacterial inoculum (0, 103, 106, 108 cfu/ml) and incubation time (0 or 30 hours). The measurements showed no significant difference in thermal properties between inoculated and uninoculated samples of egg albumen and yolk regardless of change in temperature, bacterial concentration and incubation period. The absence of an effect on either the dielectric (previous study) or thermal (present study) parameters by the presence of Salmonella leaves unexplained the quality differences between similarly processed inoculated and uninoculated eggs. A biochemical explanation based on the interaction between metabolic byproducts and egg proteins, affecting how they denature, is a topic for future research.M.S. in Food Safety and Technology, December 201