Low Dose Gamma Irradiation to Reduce Pathogenic Vibrios in Live Oysters (Crassostrea virginica)

Pathogenic strains of Vibrio (Vibrio vulnificus and V. parahaemolyticus), natural inhabitants of estuarine and ocean environments, can cause serious illness and death in susceptible persons from consumption of raw half-shell oysters. Objectives of this study were (1) to establish the irradiation dose needed to reduce pathogenic vibrios to nondetectable levels and (2) to determine consumer's ability to differentiate between irradiated and control oysters. Live oysters, Crassostrea virginica, with naturally incurred and artificially inoculated pathogenic vibrios, were exposed to 0-3 kGy dose Cobalt-60 gamma radiation. Vibrio vulnificus (MO-624) was reduced from 10 ⁶ cfu/g oyster meat to nondetectable levels (< 3 mpn/g oyster meat) with 0.75-1.0 kGy irradiation exposure. Vibrio parahaemolyticus, 03:K6 (TX-2103), required 1.0-1.5 kGy for reduction to nondetectable levels. Using triangle difference testing, sensory panelists were asked to identify differences between treated (1 kGy) and untreated oysters. Sensory difference tests, triangle method, by 146 volunteers confirmed that panelists, many of whom worked in the seafood industry, were unable to distinguish non-irradiated from irradiated oysters (p < 0.001).