Distribution of Radioactive Cesium during Rice Cooking

The dynamics of radioactive cesium (Cs-134 plus Cs-137) during rice cooking were investigated to examine the effect of rice bran removal ratio on the distribution of radioactive cesium in the cooked rice fraction. The removal ratios of bran used in this study were 0, 30, 50, 70, and 100 %. The radioactive cesium in brown rice, pre-cooked rice, cooked rice and washing water were measured with a germanium semiconductor detector. Processing factor (Pf, ratio of radioactive cesium concentration in processed materials to raw materials) and food processing retention factor (Fr, ratio of radioactive cesium content in processed materials to raw materials) were calculated. The Pf values for cooked brown rice and cooked polished rice were 0.43 and 0.25-0.26, respectively; and the Fr values for cooked brown rice and cooked polished rice were 0.95 and 0.62-0.64, respectively. Both Pf and Fr values for cooked brown rice showed significantly higher levels than those of polished rice; however, the increase of removal ratio from 30 % to 100 % had no significant effect (p<0.05) on Pf and Fr values for cooked rice. From these results, rice polishing contributes to the removal of radioactive cesium during rice cooking; however, differences of bran removal ratio, even from 30 % to 100 %, had little effect on the dynamics of radioactive cesium during rice cooking.