Effect of gamma-irradiation on frozen shrimps for inactivation of microorganisms and shelf-life extension under defrosted

The effect of gamma-irradiation on inactivation of microorganisms in frozen shrimps was investigated for improving the hygienic quality and shelf-life after defrosted. Count of total aerobic bacteria in three different kinds of frozen shrimps were decreased below 104 per gram at 4 kGy of irradiation, and showed the similar pattern of inactivation curves under the same frozen condition . Coliforms were eliminated below 4 kGy of irradiation. Radiation-resistance of aerobic bacteria in frozen condition was larger than defrosted condition, and the necessary dose for inactivation of aerobic bacteria below the count of 104 per gram was required 3 kGy at defrosted condition, and 4 kGy at frozen condition. However, freezing could remarkably reduce the production of radiation induced off-odor from shrimps. Trimethylamine content in frozen shrimps did not get effect up to 50 kGy irradiation. Vibrio parahaemolyticus was isolated from 1 to 3 numbers in 100g of frozen shrimps, and necessary dose for elimination was decided as 1.5 to 2.0 kGy in frozen shrimps. Shelf-life of irradiated shrimps at 3 and 5 kGy was found to be 6 days at the storage condition of 5degC, whereas the unirradiated samples were putrefied below 3 days of storage. (author)