The Effect of Cryogenic Freezing Followed by Gamma Radiation on the Survival of Salmonella spp. on Frozen Shrimp

Abstract

Unfortunately, contraction of food borne illness due to consumption of contaminated seafood, including shrimp, is an occasional occurrence. Cryogenic freezing and gamma irradiation are safe and effective technologies that can be used to control and inactivate pathogenic bacteria in foods. In this study, the effect of cryogenic freezing and gamma irradiation for inactivation of Salmonella spp. on shrimp was investigated. We found that cryogenic freezing of raw shrimp (-82oC, 3 min), using a pilot scale industrial liquid nitrogen freezer, resulted in a 1.27 log reduction of Salmonella spp. on whole shrimp, which was maintained during 12 weeks of frozen storage (-20oC). During our evaluation of selective microbiological media for recovery and enumeration of Salmonella spp. we found that Brilliant Green Sulfur Agar produced results indistinguishable from that of non-selective Tryptic Soy Agar when determining the effect of cryogenic freezing on Salmonella spp. survival. Radiation D10 values for Salmonella spp. on frozen shrimp were approximately 0.56 kGy. Cryogenic freezing (-82oC), followed by gamma irradiation (2.25 kGy) produced a >5 log reduction of Salmonella spp., and that reduction was maintained during 12 weeks frozen storage (-20oC). These results indicate that both cryogenic freezing and gamma irradiation contribute to inactivation of Salmonella spp. on frozen shrimp.