Radiation sensitivity of 3-strain cocktail pathogens inoculated into seasoned and fermented squid and enhancement of microbial quality by irradiation

Abstract

Commercial squid Jeotkal was purchased, radiation-sterilized, and inoculated with a 3-strain cocktail of each Listeria monocytogenes (ATCC 19114, 19115, and 19111), Staphylococcus aureus (ATCC 6538, 25923, and 29213), and Vibrio parahaemolyticus (ATCC 17802, 33844, and 27969). The inoculated samples were then irradiated again at 0, 0.5, 1, 2, and 5 kGy. The D-10 values of the cocktail of each L. monocytogenes, S. aureus, and V. parahaemolyticus were 0.85, 0.83, and 0.25 kGy, respectively. No viable cells were detected at 5 kGy of irradiation. Commercial squid Jeotkal was also irradiated without sterilization and showed that irradiation significantly reduced the initial microbial level not only immediately after irradiation but also during storage at 10C for 4 weeks (P < 0.05). The total aerobic bacterial number of red pepper powder was 6.31 log cfu/g level and showed to be the most responsible for the microbial contamination of squid Jeotkal among the tested ingredients used for manufacturing. Sensory quality was not affected by the irradiation treatment. Results suggest that low-dose (1 kGy or above) irradiation can improve the microbial quality and reduce the risk by the foodborne pathogens in squid Jeotkal, which has limited alternative sterilization methods because of the temperature characteristics of the products.