It has previously been reported that γ-irradiation of rice causes development of a characteristic off-odor in the cooked rice flavor and it was detected as significant in the sensory test with the doses of 200 Krads or above (Table 1). The present investigation was undertaken to see the component of off-odor in the cooked rice flavor by means of GLC analysis.
The unpolished rice samples (Koshihikari) were packed in polyethylene bags and exposed to γ-rays of cobalt-60 with the doses from 10 to 5000 Krads. These samples were then polished and cooked with water 3:4 in weight. Sampling of the head space gas by microsyringe was done at 30 minutes after the cooking, and GLC analysis was made on a Shimazu gas chromatograph GC-4 equipped with FID and a glass column of Carbowax 20M.
As shown in Fig. 4 the head space gas of unirradiated rice gas about 22 peaks in the gaschromatogram, and most of the main peaks were identified by comparing their retention times with those of the authentic carbonyl compounds and their 2.4-DNP derivatives (Tables 2 and 3), and in addition by the pretreatment of the head gas with the C.P. resin (selectively adsorbing resin for carbonyl compound) to remove carbonyl components of the gas. (Fig. 4) The gas chromatograms of the irradiated ones are shown in Fig. 5. It is to say that the volatile components were increased in general with increase in the irradiation dose. However, there is no marked differences in the chromatographic pattern and each peak height between the rice samples exposed to 20 and 200 Krads as compared with a significant difference in the off-odor development between these two samples. The increase in the volatile components became to remarkable especially with the doses of 2000 Krads or above and in the low boiling fractions such as propionaldehyde, n-butylaldehyde, n-valeraldehyde, methyl iso-propyl ketone, n-caproaldehyde, and etc. The increase of these carbonyl compounds may be attributed to direct effect of radiation on amino acids or fatty acids and/or to enhanced strecker degradation of amino acids with increased amount of carbonyl compounds by irradiation.

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Satsuma oranges were irradiated with the doses of 50-200 Krad of ⁶⁰Co γ-rays and with a dose of 150 Krad ofcathode rays (4 MeV). The browning of calyx was causedby irradiation and the browning of peel at high doses.
The occurring of browning in the peel of Satsuma orangesirradiated was prevented in the storage at 6°C, but notof calyx. The carbon dioxide and ethylene production of Satsuma oranges increased temporarily with irradiation (Fig. 2 and 4) and those increasing rates lowered, trans-fering to 6°C after irradiation (Fig. 3 and 5). Ascorbicacid in Satsuma oranges was oxidized to dehydroascorbicacid by gamma radiation immediately after irradiation, but not by cathode rays irradiation (Table 2 and 3).
Titratable acidity in irradiated Satsuma oranges tendedto decrease after irradiation (Table 4). Sugar contentsin irradiated samples slightly decreased more than thatin control (Table 5). Acceptance of Satsuma orangeslowered with the doses above 100 Krad.

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In correlation with the radiation killing of bacterial cells, DNA-strand scissions and their repair during postirradiation incubation were investigated by the sedimentation analysis using neutral (for doublestrand scissions) and alkaline (for single-strand scissions)sucrose gradients.Radioresistant strains, Micrococcus radiodurans and Escherichia coli B/r, were employed as the test organisms. Double-strand scissions in DNA were estimated to occur at the rate of one double cut per 800 eV. This rate is in a good agreement of the values reported for other types of bacterial and mammaliancells. The rejoining of these double-strand scissions was observed during the repair process of the postirradiation incubation (Fig. 1) and the mean rejoiningtime was found to be about 50 minutes. This rejoining repair was inhibited by adding chloramphenicol, tetracycline or actinomycin D to the postirradiation incubation medium (Fig. 1). M. radiodurans cells were also found to loss their colony forming ability when the postirradiation incubation was carried out in the presenceof these inhibitors of protein or RNA synthesis(Fig. 2). Thus, it is suggested that the high resistance character of M. radiodurans to gamma rays may be due to the efficient capacity of this rejoining repair. Although the similar results were obtained with E. coli B/r, the radiation lethal effect could not be fully explained by the result of the sedimentation analysis. The sedimentation patterns of DNA from irradiated E. coli B/r(Fig. 3) indicated that there might be a possibility of the repair of double-strand scissions in DNA detectedby the current technique. Studies on these problems should be done to establish the relationship between radiation-induced DNA-strand breaks and the radiation lethal effects.

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