EFFECTS OF THE PROCESSING STEPS IN TOFU PRODUCTION ON PESTICIDE-RESIDUES

Tofu is a traditional Japanese food that has become an international food. Soybeans are sprayed with pesticides to prevent damage by pests during storage and shipment. To test the effect of each stage of soybean processing on these pesticides, soybeans were spiked with four pesticides. The soybeans were subjected to tofu production conditions in the laboratory. The concentrations of the pesticides in the washed soybeans, soybean milk, okara, and tofu were determined immediately after each process. Conclusions from these experiments are as follows: (1) The persistence of each of the tested pesticides after tofu production is negligible (<0.5%). (2) With the exception of captan, the concentrations of pesticides in the soybean milk were essentially the same as in the raw soybeans and were not decreased with further cooking. Captan levels dropped to less than 10% of the original values at 2.5 min. (3) The washing of soybeans caused the concentrations of dichlorvos, malathion, chlorpyrifos, and captan in or on the soybeans to decrease markedly. The residues in the soybeans decrease with the first two washings; however, there is no further reduction with subsequent washings.