ARS | Publication request: The effect of cryogenic freezing and gamma irradiation on the survival of Salmonella on frozen shrimp

Submitted to: Journal of Food Processing and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 26, 2011
Publication Date: December 1, 2011
Citation: Sommers, C.H., Rajkowski, K.T., Sheen, S., Samer, C., Bender, E. 2011. The effect of cryogenic freezing and gamma irradiation on the survival of Salmonella on frozen shrimp. Journal of Food Processing and Technology. DOI: 10.4172/2157-7110 S8-001.

Interpretive Summary: Consumption of shrimp contaminated with Salmonella has been shown to cause occasional foodborne illness outbreaks. Most shrimp sold in the U.S. is frozen, or has been previously frozen. Ionizing (gamma) radiation for decontamination of shrimp is allowed in many countries, but is not currently allowed in the U.S. The U.S. Food and Drug Administration is evaluating a petition which would allow irradiation of crustaceans, including shrimp, in the U.S. We evaluated the effect of cryogenic freezing on the survival of Salmonella in shrimp and found that freezing reduced Salmonella populations by 90%. Cryogenic freezing, followed by treatment with ionizing radiation (2.25 kGy), reduced 99.999% of the Salmonella on shrimp. This information will assist regulatory agencies in their petition review process, and assist seafood processors provide safer seafood to consumers.

Technical Abstract: Unfortunately, contraction of foodborne 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 (-115C, 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 3 months of frozen storage (-20C). 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 evaluating the effects of cryogenic freezing on Salmonella spp. survival. Radiation D-10 values for Salmonella spp. on frozen shrimp were approximately 0.56 kGy. Cryogenic freezing (-115C), followed by gamma irradiation (2.25 kGy) produced a >5 log reduction of Salmonella spp., and that reduction was maintained during 3 months frozen storage (-20C). These results indicate that both cryogenic freezing and gamma irradiation contribute to inactivation of Salmonella spp. on frozen shrimp.