Irradiation and postirradiation storage at 2+/-2 degrees C of tilapia (Tilapia nilotica x T-aurea) and Spanish mackerel (Scomberomorus commerson): Sensory and microbial assessment

Tilapia (low-fat farm fish, Tilapia nilotica x T. aurea) and Spanish mackerel (high-fat seawater fish, Scomberomorus commerson) were subjected to gamma irradiation doses of 1.5, 3.0, 4.5, 6.0, and 10.0 kGy by using a semicommercial gamma irradiator. The irradiated and unirradiated (controls) fish were stored at 2 +/- 2 degrees C and samples were drawn at day 0, 4, 8, 12, 16, and 20 for sensory evaluation and microbiological analysis. Doses of 3.0 and/or 4.5 kGy extended the sensory acceptability (appearance, odor, texture, taste) and the microbial quality (total count and coliforms) by 8 days compared to the unirradiated controls. Hydrogen sulfide-producing bacteria were low in both types of fish and a dose of 1.5 kGy kept this flora at low levels throughout the storage period. Moreover, this dose level was also sufficient to eliminate Salmonella spp. from both fish. Yersinia and Campylobacter species were effectively eliminated by doses of 1.5 and 3.0 kGy. Doses of 6.0 and 10.0 kGy caused a reduction in psychrotrophic counts but were detrimental to the quality of both species of fish.