EFFECT OF GAMMA-IRRADIATION ON FROZEN SHRIMPS FOR DECONTAMINATION OF PATHOGENIC BACTERIA

Twelve samples of imported frozen shrimps were used in this study. The total aerobic bacteria were at 2 x 10(4) to 6 X 10(6) per gram. A few of Vibrio parahaemolyticus, V. mimicus, V. alginolyticus, V. vulnific us, V. fluvialis and Listeria monocytogenes were isolated from many sa mples. However, Salmonella was not detected in any of the samples. Aft er exposure to 4 - 5 kGy of gamma-rays, the total aerobic bacteria in frozen shrimps were reduced by approximately 2 - 3 log cycles. The dos e necessary to reduce the vibrio isolates and Aeromonas hydrophila at a level of below 10(-4) per gram was about 3 kGy in frozen shrimps, wh ereas about 3.5 kGy was required for L. monocytogenes and Salmonella t yphimurium. In this study, unpleasant off-odor was clearly detected in the non-frozen shrimps irradiated at 2.5 kGy. On the other hand, off- odor was negligible in the frozen product below 5 kGy irradiation. No remarkable changes of peroxide values were also obtained up to 9 kGy o f irradiation in the frozen shrimps. However peroxide values of non-fr ozen shrimps were clearly increased even irradiated at 4 kGy. Trimethy lamine content was not changed at doses below 10 kGy in both of frozen and non-frozen shrimps. Shelf-life of defrosted shrimps were extended ca. 2 times under non-frozen market conditions.