Submitted to: Journal of Food Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/27/2006
Publication Date: 5/1/2007
Citation: Alvarez, I., Niemira, B.A., Fan, X., Sommers, C.H. 2007. Modeling the irradiation-followed-by-heat inactivation of salmonella inoculated in liquid whole egg. Journal of Food Science. 72(5):M145-M152. Interpretive Summary: Salmonella contamination of egg and liquid whole egg products is a frequent cause of foodborne illness in the U.S. Both thermal treatment and ionizing radiation may be used to improve the miocrobiological safety of eggs in the U.S. Ionizing radiation and heat treatments can both inactivate Salmonella in liquid whole egg, however, excessive use of either damages the quality of the egg product. When irradiation is followed by heat treatment, a synergistic inactivation of Salmonella in liquid whole egg is obtained, with minimal impact of the combination treatment on the liquid whole egg quality. In this study mathematical models were developed to describe the injury and inactivation of Salmonella species, suspended in liquid whole egg, by irradiation and heat. These mathematical models will assist egg processors to provide safer egg products to consumers and assist regulatory agencies in the formulation of science based food safety policies.
Technical Abstract: This study presents mathematical models which describe the inactivation of Salmonella Enteritidis, Salmonella Typhimurium, and Salmonella Senftenberg suspended in liquid whole egg (LWE) by irradiation followed by heat treatments (IR-H treatments). These models also enable prediction of cell injury in Salmonella after exposure to IR-H. Salmonella viability decreased exponentially (primary model) with heat treating time for all the radiation doses (0, 0.1, 0.3, 0.5, 1.0, and 1.5 kGy) and temperatures investigated (55, 57, and 60 degrees C). Two secondary models that related the thermal DT values with radiation dose, heating temperature, and recovery medium after treatments were also developed. Quadratic polynomial models best fitted thermal DT values at any of the conditions investigated. The developed tertiary models enabled to establish the process criterion (combinations of irradiation doses, temperature and heat treatment times) required to achieve a given reduction (performance criterion) in Salmonella spp. suspended in LWE or the cell damage caused by the treatments, while simultaneously minimizing the impact of the process on LWE quality. Process criteria to obtain the established performance criteria (a 5-log10 reduction) on any of the investigated Salmonella serovars were determined to be 58.8 degrees C/3.5 min following 1.0 kGy, 57.7 degrees C/3.5 min following 1.5 kGy when treated cells were recovered in tryptic soy agar and 59.3 degrees C/3.5 min following 0.5 kGy, 58.4 degrees C/3.5 min following 1.0 kGy or 57.4 degrees C/3.5 min following 1.5 kGy when cells were recovered in tryptic soy agar amended with 3 percent NaCl. Based on our results, current industrial LWE heat treatments (60 degrees C/3.5 min) would inactivate 3 log10 cycles of the Salmonella population. The results of this study can be applied for engineering design, evaluation and optimization of IR-H process as a new technique to obtain Salmonella-free LWE.