Use of gamma radiation to inactivate stressed Salmonella spp., Escherichia coli O157:H7 and Listeria monocytogenes in tahini halva

Tahini halva or its major ingredient, tahini, have been implicated in several foodborne outbreaks in Europe and USA. The aim of the study was to i) assess the effect of desiccation and heat stresses on the sensitivity of Salmonella spp., Listeria monocytogenes and Escherichia coli O157:H7 in tahini halva to gamma radiation, and ii) evaluate effect of irradiation on chemical (acid, peroxide, and p-anisidine values) and physical (color) characteristics of the product. Tahini halva samples were inoculated with fresh, desiccation stressed or heat stressed cocktail cultures of the tested microorganisms separately then exposed to gamma radiation at doses of 0-4 KGy to determine D10-value. Desiccation stress decreased the resistance ratio of Salmonella and L. monocytogenes toward gamma radiation to 0.85 and 0.73; respectively, compared to unstressed cells, while it did not affect the resistance of E. coli O157:H7. On the other hand, heat stress increased the resistance ratio of E. coli O157:H7 and L. monocytogenes to 1.14 and 1.18, respectively. However, the resistance ratio of heat stressed Salmonella was significantly reduced to 0.9. Irradiation dose of 4.0 KGy did not affect significantly the color and acid value whereas, peroxide and p-anisidine values increased significantly as the irradiation doses increased.