Effect of gamma irradiation on commercial eggs experimentally inoculated with Salmonella enteritidis

Abstract

Using intact, fresh shell eggs, inoculated with 10 8 colony-forming units (cfu) of S. enteritidis, the effect of three doses of gamma irradiation on bacteriologic population and physical characteristics (Haugh units and yolk color) of the eggs was determinated. Penetration test area was picked at random just off the air cell of each egg. Aluminum cylinders were attached to the egg surface with a rim of molten paraffin, and 10 8 S. enteritidis was then applied to inoculate the egg. Eggs were then irradiated within 2 hours using a Cobalt-60 gamma source at either 1, 2, or 3 kGy. A second set of inoculated, non-irradiated was used as controls. Following irradiation, eggs were maintained at 4°C for 42 hours prior culture. Irradiation with 1 kGy resulted in a significant (P < .05), 3.9 log reduction in detectable S. enteritidis in the shell and a higly significant (P < .025) 95% reduction in detectable S. enteritidis in the internal shell membranes. Irradiation of eggs with either 2 or 3 kGy reduced bacterial contamination to non-detectable levels in both the shell and internal membranes. However, irradiation at either 1, 2 or 3 kGy resulted in a significant (P <- .05) decrease (approximately 50%) in Haugh units. Additionally, irradiation of intact shell eggs at 2 or 3 Kgy significantly (P ≤ .05) reduced yolk color regardless of the level of irradiation exposure implemented. This data indicates that gamma irradiation of intact raw eggs is effective in reducing (1 kGy) or eliminating (2 or more kGy) S. enteritidis contamination. However, each of the levels of irradiation used in the present experiments caused marked reduction of selected measures of egg quality.