FOOD IRRADIATION, JAPAN

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Gamma-ray sterilization by ⁶⁰Co source has been already popular in Japan. Many Kinds of medical plastic devices such as catheters, disposable syringes, dializers etc, has been irradiated at ⁶⁰Co irradiation facilities instead of the conventional ethylene oxide fumigation method. On the other hand, improvement of the quality of electron accelerators has made it easier to take advantage of relatively high energy electrons which are profitable for radiation sterilization because of their high dose rate saving process hours and easiness of source handling and radiation control. So electron-beam sterilization is now under investigation in Japan and, partly, it will be practiced in the near future. Yet few data are available in the present situation. Especially for high energy electron beams near 10MeV, more data are necessary for practical application of electron-beam sterilization. Therefore, in this study, sensitivity of Bacillus pumilus E601, the biological standard of radiation sterilization, was examined using 10MeV electron beams from linear accelerator and sterility of the beams was also checked at each depth of plastic boards in order to get basic information for determination of sterility dose. Endospores from B. pumilus were dried on filter papers (ToyoNo.1) and irradiated by 10MeV electron beams or ⁶⁰Co gamma-rays. The survival curves were shown in Fig. 1. The D values were obtained as 1.9 kGy ±0.2 for electron beams and 1.7 kGy ±0.1 for ⁶⁰Co gamma-rays, both of which were similar. Electron beams could sterilize the endospores nearly uniformly till 3cm depth of plastic boards at 10MeV (Fig. 2, 3). This indicates a possibility to sterilize relatively bulky products such as dializers etc.

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