Inactivation of stressed Escherichia coli O157:H7 in tahini (sesame seeds paste) by gamma irradiation

Tahini, sesame seeds paste, is of great concern to both regulatory agencies and food processors as it may be exposed to microbial contamination through processing. This study aimed to evaluate the effect of gamma irradiation on inactivation of stressed Escherichia coli O157:H7 and microbiota in tahini, and on the color and peroxide, p-anisidine, and acid values of tahini. Tahini samples were inoculated with a cocktail of 4 strains of unstressed or stressed (heat, cold, starvation, salt, acid, alkaline or ethanol stress) E. coli O157:H7 and exposed to gamma irradiation for up to 1.0 kGy. The D10-values of unstressed and stressed cells ranged from 0.31 to 0.39 kGy. Stresses (except for starvation) reduced the irradiation resistance of E. coli O157:H7 significantly (P < 0.05) in tahini. Irradiation dose of 1 kGy reduced inoculated E. coli O157:H7 and microbiota in tahini by 2.6-3.2 log10 CFU/g and 1.6 log10 CFU/g, respectively, and did not affect (P > 0.05) tahini quality (color and oxidative rancidity). Irradiation might be used as an effective means of eliminating E. coli O157:H7 and other foodborne pathogens with similar irradiation resistance, if present, in tahini in post-packaging situation without compromising the quality.