Effects of Electron Irradiation on the Preservation of Citrus Unshiu:Part III. Storage and browning of peel by irradiation

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The fruits of Citrus Unshiu which were almost ripened were harvested at November and were stored for 15 or 18 days at 20, 10and 4°C, and were irradiated from both of the stem-end and another end by the electron beam of a Cockcroft-Walton type accelerator at the 300 KeV with dose of 150 Krad (± 25%).The situation of fruits stored was observed at the storage temperature of 20, 10 and 4°C before and after irradiation. Figures 1 and 2 show the appearance of browning of peel. The appearance of browning of peel are slight for Citrus Unshiu(late variety) which were stored at 20°C before or after irradiation and which lost the weight hastily (Fig. 1). For the others, the browning of peel appeared more strongly and more early at the higher temperature of storage before or after irradiation. For the early variety of Citrus Unshiu (Fig. 2), the browning of peel are observed to be stronger at the higher temperature of storage before irradiation, and to be slighter at the smaller difference of temperature between before and after irradiation. It seems likely that the browning of peel appears more early at the higher temperature after irradiation. Beside these experiments, it was observed that the browning of peel appeared on all fruits irradiated at 1 or 7 days after harvest. It has been reported for potato bulbs irradiated that the increase of respiration was related to the browning of fibro-vascular regions. It is considered similarly that the appearance of browning of peel is related to the respiration of fruits under the several temperature conditions after irradiation. The results for the effect of electron irradiation on the browning of fruits wrapped with the film of cellulose acetate or dampproof cellophane are shown in Fig. 3. For the late variety, the browning of peel wrapped with film is not remarkable and appears for more number of fruits comparingwith non wrapped ones. It was observed generally that the degree of browning of peel was strongest on about 30 days after irradiation under 4°C and faded slightly with storage time. Figure 4 shows the results of the rate of browning by the different electron accelerating voltage. The difference of the rate of browning is slight between 300 and 500 KeV, and it would be said that the rate of browning is smaller for 500 KeV than 300 KeV. Beside these, in the preliminary test that an alminium plate was set at the front of irradiation window and the irradiation was done with the dose of 150 Krad at 114 KeV, the browning of peel did not appeared so strongly. The situation of storage at 29th, March (4 months after irradiation) are shown in Table 1. It is not good for the fruits stored under the temperature of 10°C before irradiationand 20°C after irradiation. This ones are larger in the loss of weight and wilted. The fruits wrapped with cellulose acetate film are not good and the numbers of rotted fruits are more comparatively with the results in last year. In the tests, No. 2 and 3, of Table 1, the numbers of fruits deteriorated or infected with fungi are less for the irradiated than for the non-irradiated fruits. From these results, it was recommended for the storage of fruits of Citrus Unshiu that the fruits harvested were immediatedly cured at 4°C until the weight loss of 3%, and stored at 4°C in a basket which was piled up to ten baskets and was surrounded with a corrugated cardboard sheet to prevent from being exposed directly to cool wind.
日本食品照射研究協議会の論文

Effects of Electron Irradiation on the Preservation of Citrus Unshiu:Part III. Storage and browning of peel by irradiation

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日本食品照射研究協議会 | 論文

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