Elution of Radioactive Cesium from Tofu by Water Soaking

摘要

Elution of cesium-137 (~(137)Cs) from tofu into water was investigated to know the behavior of ~(137)Cs during preservation and cooking. The food processing retention factor (Fr ) reached 0.55 when tofu was soaked in water at a ratio of 1:2 w /w for 24 h at 4°C. Doubling the amount of water did not further significantly decrease Fr . When tofu was held in water at a ration of 1:2 w/w at a temperature of 80°C for 50 min, Fr was 0.72. Increasing the amount of water to 10 times the tofu weight did not further reduce Fr significantly. Cesium-137 is mostly bound to tofu and does not freely diffuse into water. Tofu was then soaked in water at a ratio of 1:2 w/w at 4°C for 24 h, placed in new water at a ratio of 1:2 w/w, and held at 80°C for 50 min, resulting in an Fr 0.33. This value is close to an estimated Fr calculated by multiplying the Fr of 0.55 from soaking at 4°C by the Fr of 0.72 from the hot water treatment. The calculated Fr from soybeans sequentially processing into tofu, soaking tofu at 4°C for 24 h and in hot water at 80°C for 50 min was about 0.1, indicating 90% removal of ~(137)Cs. Degree of decrease in ~(137)Cs during preservation and cooking of tofu demonstrated in this study will be useful for exposure assessment of ~(137)Cs through oral intake of contaminated soybeans after processing and cooking.