Irradiation preservation of foods I. Prolongation of the keeping quality of fresh fish by radiation pasteurization

Abstract

The prolonging of refrigeration shelf life (at 0° C) of pike and saithe was studied by radiation pasteurizing the fish with cobalt-60 gamma rays. The fish were packed whole in polyethylene bags. The radiation doses varied for pike between 150—1200 krad and for saithe between 150—250 krad. Organoleptic evaluations showed burnt off-flavour and off-odour in irradiated pike, which in fish that had been subject to small doses of 150 and 250 krad disappeared only after about one week of storing under refrigeration. For saithe no off-flavour was noticed when it was irradiated with a dose below 250 krad. After radiation at only 150 krad for saithe and 300 krad for pike the total bacterial counts in the muscle were reduced by nearly 100 per cent. With radiation doses of 150, 250 and 300 krad, the shelf life of pike under refrigeration increased 2.5, 3.5 and 5.2 times, respectively, compared with non-irradiated fish. The shelf-life times listed in the same order were 10, 14 and 21 days, but for non-irradiated fish only 4 days. For saithe the shelf life increased from 23 days (of non-irradiated fish) to 40 days when irradiated with a dose of only 150 krad. When whole fish were irradiated with large doses of 600 and 1200 krad, spoilage caused by bacteria was prevented for a long time while enzymatic spoilage caused by intestines was detected after 38 days as the contents of the intestines became decomposed and the flesh at the side of the abdominal cavity turned soft