Effect of gamma-irradiation on the microflora of freshwater fish. I. Microbial load, lag period, and rate of growth on yellow perch (Perca flavescens) fillets.

Microbial flora were compared in irradiated and nonirradiated yellow perch fillets. These studies included effects of irradiation on the total microbial population, the lag phase, and rate of growth in this freshwater fishery product. The work was conducted concurrently with sensory and chemical evaluation, and constituted part of an investigation designed to evaluate the effect of substerilization doses (0.3 and 0.6 Mrad) of Co(60) gamma rays on the storage life of yellow perch fillets at 1.0 or 6.0 C. In five storage tests, total plate counts prior to irradiation did not exceed 8.7 x 10(5) per gram of sample; this count was reduced nearly 100% by irradiation with either 0.3 or 0.6 Mrad. Progressively lower maximal bacterial populations and lengthened lag phases were obtained as more radiation was used. The growth rate of the population did not appear to decrease significantly. Microbial data obtained in these studies confirmed the sensory and chemical studies, by indicating that irradiation can significantly extend the refrigerated shelf life of freshwater fish.