Effect of low-dose radiation of γ-rays on the storage life of Satsuma oranges

This paper presents the results of experiments on the effect of low-dose radiation of γ-rays on the storage life of early (November 16th) and late (December 16th) harvest Satsuma oranges.1. The irradiations were carried out with a Co-60 source at the Radiation Center of Osaka Prefecture. Satsuma oranges were irradiated at the doses of 50, 100 and 200 Krad at the rate of 1×105rad/hr. Subsequent to irradiation, they were stored at room temperature (2°-17°C) and at low temperature (2°-6°C).2. Irradiation above the dose of 100 Krad caused the partial browning of peel of both early and late harvest fruits. In the fruits irradiated at the dose of 50 Krad, the browning was not observed. The 50 Krad-fruits stored at low temperature were favorable in appearance, showing little shrinkage of peel, and they had less microbial growth. The rotting of the fruits irradiated at the doses of 100 and 200 Krad was caused by the infection of Alternaria citri PIERCE et ELLIS. However, no symptom of Alternaria citri was observed in the control fruits and the 50 Krad-fruits, and their rotting was caused by the infection of Penicillium.3. The titratable acidity decreased with high doses immediately after irradiation, and this tendency was greater immediately after irradiation than during the storage. The organic acids were fractionated the stepwise elution chromatography on silica gel (100 mesh). It was found that the concentrations of citric acid and malic acid were lower in irradiated fruits than in unirradiated ones and that in irradiated samples succinic acid accumulated.4. The content of ascorbic acid in irradiated fruits decreased with high doses, and while that of dehyroascorbic acid in irradiated ones increased with high doses, immediately after irradiation. The rates of decreasing of ascorbic acid and of increasing of dehydroascorbic acid during storage were slightly higher in the fruits of 100 and 200 Krad than in unirradiated fruits. The content of ascorbic acid in the 50 Krad-fruits was more than in other lots at the end of the experiment. No change in sugar content by gamma irradiation was noted.