Abstract
In the previous report we studied the effects of gamma-ray irradiation on red beans. In this paper authors tried to prevent the mold growing and the vermin damage on rice which has been the most important food in Japan from very early ages. For the prevention of the vermin damage some cereals were irradiated by radial rays, but for the preservation of rice, any systematic research had not been published.
Rice was irradiated by cobalt-60 gamma-rays at the dose of from 0.5×104r to 400.0×104r in about 1/7 mm thick polyethylene film bags. Atmosphere was air or nitrogen. After irradiation samples were storaged at room temperature for 18 months. Outward appearances, tastes, changes in nutrient components were estimated. Relations between irradiation doses and these factors were investigated and the optimum dose was determined.
Results obtained were as follows:
1) Irradiation at the dose of more than 40.0×104r caused the coloration of yellowish brown and its density increased with irradiation dose.
2) Vermin did not grow when irradiated at the dose of more than 4.0×104r. Irradiataion at the dose of more than 40.0×104r could keep the rice from getting moldy and prevent the vermin damage. In nitrogen atmosphere results were better in some degree.
3) When irradiated at the dose of less than 4.0×104r, taste of the boiled rice was good, but over 40.0×104r, the boiled rice was not fit for eating and after 6 months' storage this difference became quite remarkable.
4) Effects of irradiation on the contents of water and fats were not recognized. Acid value was most changeable by irradiation and much increased in the polished rice than in the unpolished one. The specific gravity, refractive index, saponification value and iodine number were almost unchanged until 6 months later, but after 18 months' storage, the acid value increased and both the refractive index and the iodine number decreased with the irradiation dose. These changes were also more remarkable in the polished rice than in the unpolished one.
5) Therefore, for the preservation of rice, it was preferable to irradiate at the dose of 10.0 ×104r on unhulled rice and polish it before cooking.
