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

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 D₁₀ 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. Jeotkal, a representative Korean salted and fermented fish product, has an important role in the diet and nutrition of Koreans. However, high amounts of salt are added to Jeotkal to extend its shelf life, and this has been brought to the consumer's concern. Thus, a low-salted Jeotkal (usually using only 8% of salt) is being produced but companies are faced with problems on microbial safety and the reduction of the product's shelf life. Many attempts including the addition of natural preservatives or using high hydrostatic pressure have been carried out to solve these problems; however, most of these attempts were proven to have some drawbacks such as poor flavor and texture. Irradiation is an effective tool to control foodborne pathogens and to avoid cross contamination for this kind of products which has limited alternative sterilization methods because of the temperature characteristics. Therefore, the result of this study may provide an evidence for the industry and the legal authority to use irradiation technology properly in the production of squid Jeotkal.