Shallow Irradiation of Citrus Unshiu by Cathode Ray

Part I. Effective pasteurizing dose of radiation to Pen. digitatum and the effects of irradiation on the fruit quality

Abstract

Citrus Unshiu (Japanese mandarin orange "Satsuma") is particulary susceptible to gamma ray irradiation and the adverse effects on flesh flavor and peel appearance were found when fruit was subjected to 50 Krad or more. The work has conducted on shallow irradiation (surface radurization) of Citrus Unshiu by cathode ray to prevent the off-flavor.
Pasteurizing effect on Pen. digitatum inoculated to lower shoulder of fruit was decreased with the time from inoculation to irradiation even the inoculated fruits were stored at 5°C before irradiation. With higher dose softening of peel and the destruction of oil-gland developed during the postirradiation storage and finally the browning of peel appeared. These phenomena depended on the storage time from the harvest to the radiation treatment; deterioration was more severe with the shorter storage after harvest. The browning was accelerated at room temperature but repressed at 5°C storage. The browning was not affected by curing treatment (RH: 75-80%, 5-7°C for 3 weeks) immediately after harvest.
There was same pasteurizing effect by the cathode ray of 1.0 and 0.5 Mev. Pannel test detected the deteriorated flavor change with gamma ray irradiation over 50 Krad and the acceptability was lost over 100 Krad, but the shallow irradiation with 1.0 Mev of cathode ray did not change the flavor acceptability up to 250 Krad.
Analytical data of fruit flesh and juice showed no significant differences between irradiated and non-irradiated spmples after the long term storage. Shallow irradiation of 100-300 Krad appeared to cause some advantages in score of acceptability after the long term storage.