Growth, survival and heat resistance of Salmonella Typhimurium and Escherichia coli in regular and omega-3 hen's egg products

Abstract

Omega-3 enriched eggs are currently produced by hens fed a flax diet. Since omega-3 polyunsaturated fatty acids are prone to oxidation, the addition of vitamin E is supplemented into the hen's diet as an antioxidant. Typically these eggs contain about 2 and 4 times more omega-3 fatty acids and vitamin E, respectively compared to regular eggs. Since table eggs have a long history of association with foodborne salmonellosis, it was of interest to compare the growth and/or survival of several bacterial pathogens in omega-3 and regular eggs. In this respect nalidixic-resistant Escherichia coli and Salmonella Typhimurium were inoculated into regular and omega-3 hen's egg products (whole eggs, albumen, yolk) and incubated at 22, 8 and -20C. Time-course studies indicated that by 72 h both Salmonella and E. coli levels increased by 7 logs at 22C in both types of whole egg. At 8C population levels for these bacteria both increased by approximately 3 logs at 6 weeks. In regular and omega-3 yolks, salmonellae maintained at 22 and 8C for 48 h and 6 weeks increased by approximately 6 and 1.5 logs, respectively. E. coli levels were higher in egg yolk compared to Salmonella at both temperatures. Regardless of the yolk source, however, no significant (P>0.05) differences in population levels were observed. Survival patterns of E. coli at -20C were not significantly (P>0.05) different between whole egg sources. This trend was also observed in the yolks. For Salmonella no significant (P>0.05) differences in survival were observed between yolk preparations maintained at -20C. Increasing the level of α-tocopherol from c. 63 to 240 ppm in regular egg yolk, resulted in no significant (P>0.05) differences in the growth of Salmonella at 22C. In addition, when the bacterium was heated in regular egg yolk amended with vitamin E at 56.5C, no significant (P>0.05) difference was observed in resistance regardless of α-tocopherol (55-713 ppm) or total tochopherol (92-1238 ppm) level.