[Study on Weight Change Rate after Rehydration of Dried Kotake Mushroom]

The level of radioactive cesium in food that is generally consumed in the rehydrated state can be calculated from measurements taken in the dried state using the specific weight change rate set by the Ministry of Health, Labour and Welfare. However, only a few dried foods have a specified weight change rate. Accurate specific weight change rates are critical in determining the compliance of a dried food item with Japanese maximum limits (JMLs) for radioactivity. We investigated the weight change rate of dried to rehydrated kotake mushrooms, which may contain relatively high concentrations of radioactive cesium and whose weight change rate has a large effect on the judgment of JML compliance. The average weight change rate of dried kotake mushrooms was 5.7 (range: 4.2 to 6.9), which was 1.4 times larger than the currently applied weight change rate of 4.0. Since the minimum weight change rate was 4.2 in this study, it was considered that the weight change rate currently applied to dried kotake mushrooms was a reasonable value. Further data is required in order to set specified weight change rates and to evaluate the validity of currently applied weight change rates in dried kotake mushroom.