bacteria are more resistant than gram-negative ones. Coc-coid forms are more radioresistant than rod-shaped cells. Bacterial spores exhibit the most resistance to radiation with the exception of some gram-positive cocci. Compared to bacterial spores, viruses are more or equally resistant to irradiation. Although the amount of radiation needed to inactivate microbial toxins is similar to that for bacterial spores, the radiation level for inactivation of botulinum toxin is much higher than that needed to kill the bacterial cells (98) (Table 3).

In general, Z)10-values for bacterial vegetable cells (excluding cocci), bacterial spores, M. radiodurans, viruses, and bacterial toxins are 20-100, 150-450, 200-600, 400800, and 200-2,000 krad, respectively (99-104).

Low-dose irradiation treatment of seafoods usually does not induce detectable changes in flavor, texture, and appearance with the exception of a slight loss of flavor in a few products (105,106). The level of irradiation is one factor in determining the type of microorganisms remaining that cause spoilage of irradiated seafood. The spoilage microflora of irradiated fish after a low dose of s 100-150 krad treatment consists mainly of pseudomonads. At dose levels higher than 100 krad, Maraxella-Acinetobacter represented the dominant group of organisms in fish spoilage. Irradiation of packaged fish favors the growth of lactic acid bacteria that will be the major spoilers. In general, non-irradiated fish spoils at an aerobic plate count (APC) of 106/g whereas low-dose irradiated fish spoils at about 108/g (94).

Under the optimum dose of 100-300 krad, fish and shellfish can be maintained three to seven weeks at refrig eration without altering the fresh-product characteristics (Table 4). Compared with the regular 10- to 14-day shelf life of the unirradiated products, low-dose irradiated products have a shelf life two to three times longer (94,109). To insure efficiency and successful processing, the seafood should initially be of high quality and irradiated products should be maintained as near 0°C as possible without freezing.

The safety of irradiated seafood must be evaluated based on the absence of microorganisms and microbial toxins harmful to man, the nutritional contribution of the product, and the absence of any significant amount of toxic compounds formed in the irradiated products (101). Low-dose irradiated seafood, particularly lean fish species, have been found to pose no potential health hazards (94,110). Despite the approval of over 35 countries irradiation in foods and the USDA clearance of low-dose application for poultry irradiation, seafood irradiation has not been permitted. This process can become a successful technique for seafood preservation once it is approved in the United States.

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