The Effect of Single and Double Doses of Gamma Radiation on Pre-rigor Mortis Filleted Saithe
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Saithe, caught on the western coast of Norway, was filleted immediately after killing, packed in plastic bags and irradiated using a cobalt- 60 source at the Institute of Atomic Energy, Kjeller. The doses were 50, 100, 150, 50 + 50 and 50 + 100 krad. All samples were analysed for their total bacterial count, proteolytic activity, ammonia, total volatile acids, trimethylamine oxide, tri- and dimethylamine and formaldehyde. The organoleptic quality was evaluated by a panel of tasters. Double doses were more effective in reducing the total bacterial count than an equivalent single dose. A close relation was found between the bacterial count and the proteolytic activity. The trimethylamine oxide concentration was found to vary between 33 and 44 mg/100 g muscle, decreasing rapidly in non-irradiated fillets to 3 mg/100 g. In non-irradiated fillets trimethylamine oxide was mainly reduced to trimethylamine and in irradiated fillets to dimethylamine and formaldehyde. A split dose of 50 + 50 krad may have a favourable effect on the total bacterial number, but the analyses of proteolytic activity, the volatile acids and the trimethylamine indicated that a higher proportion of spoilage bacteria survive. The low proteolytic activity and the high content of DMA/FA prove that split doses of 50 + 100 krad as compared with single dose of 150 krad, are particularly favourable in the case of saithe.