Gamma irradiation processing to reduce the risk of Vibrio infections from raw oysters
L. S. ANDREWS, Experimental Seafood Processing Laboratory, CREC, Mississippi State University, 2710 Beach Blvd, Suite 1E, Biloxi, MS 39531, M. L. Jahncke, Virginia Seafood Agricultural Research and Extension Center, Virginia Polytechnical Institute, 102 S. King Street, Hampton, VA 23669, and P. Mallikarjunan, Department of Biological Systems Engineering, Virginia Polytechnical Institute, Virginia Tech, Blacksburg, VA 24061.
Vibrio vulnificus and V. parahaemolyticus are natural inhabitants of estuarine and ocean environments. As such they are naturally concentrated in filter feeding molluscan shellfish, oysters, clams, etc. These Vibrio pathogens cause serious illness and death in susceptible persons when consumed along with raw half-shell oysters. Environmental strains of various Vibrio spp have proven to be relatively sensitive to irradiation exposure compared with other food borne pathogens like Salmonella and Listeria. Pathogenic strains of V. vulnificus and V. parahaemolyticus are more resistant to thermal processing and have not been tested for their sensitivity to gamma irradiation. The objective of this study was to investigate irradiation processing as an alternative post harvest treatment (PHT) for raw shell stock oysters to reduce pathogenic strains V.v. and V.p. to nondetectable levels and still maintain the raw half-shell qualities consumers expect in raw oysters. Live oysters, with naturally incurred and artificially inoculated Vibrios, were exposed to 0-3 kGy dose Cobalt-60 gamma radiation. Vibrio vulnificus was effectively reduced from 106 cfu/g oyster meat to nondetectable levels (<3 mpn/g oyster meat) with an exposure dose of 0.75 kGy. Vibrio parahaemolyticus, TX03:K6, proved to be more resistant and required 1.0 kGy for its reduction to nondetectable levels. Sensory quality was maintained with irradiation exposure up to 1.5 kGy. Higher irradiation doses increased the mortality rate and reduced shelf life. At > 2 kGy, the oysters produced an unpleasant yellow exudate. In summary, a 1 kGy dose reduced the Vibrios to nondetectable levels and at the same time maintained good sensory quality, a normal shelf life of 15 days, and minimum mortality. Upon approval by the USFDA, irradiation processing of live oysters will provide an effective post harvest treatment for reducing the risk of Vibrio illnesses.
Session 44, Seafood Technology: Safety