Effect of gamma and electron beam irradiation on the survival of pathogens inoculated into salted, seasoned, and fermented oyster

The objective of this study was to identify the efficacy of gamma and electron beam irradiation of the food-borne pathogens including 3-strain cocktail of Listeria monocytogenes (ATCC 19114, 19115, and 19111), Staphylococcus aureus (ATCC 6538, 25923, and 29213), and Vibrio parahaemolyticus (ATCC 17802, 33844, and 27969) in salted, seasoned, and fermented oyster (oyster Jeotkal, 8% salt), commercially available in the market. Irradiation (0, 0.5, 1, 2, and 5 kGy) significantly reduced the initial microbial level not only immediately after irradiation but also during storage at 10 °C for 4 weeks (P ≤ 0.05). No viable cell was detected at 5 kGy of irradiation at a detection limit of 101 CFU/g. Gamma irradiation was more effective than electron beam irradiation, and yielded D10 values of 0.60, 0.71, and 0.29 kGy for L. monocytogenes, S. aureus, and V. parahaemolyticus, and those of electron beam irradiation were 0.69, 0.94, and 0.29 kGy, respectively. V. parahaemolyticus was most sensitive to irradiation and storage among all pathogens tested. Sensory quality was not affected by irradiation treatment. Results suggest that a low dose irradiation can improve the microbial quality and reduce the risk by the food-borne pathogens of oyster Jeotkal, which has limited alternative sterilization methods due to the temperature sensitivity of food products.