Preventive Effect of Sodium L-Ascorbate for Decomposition of Thiophanate-methyl in Homogenized Crops

Abstract

Effect of sodium L-ascorbate (SL-A) on the residue analysis of thiophanate-methyl (TM) is described. TM in homogenized samples of grape, apple, tomato, and so on, was considerably unstable in storage, and the recoveries from samples such as unpolished rice, cooked polished rice and soil were low (24-61%).Addition of SL-A to homogenized samples increased the stability of TM during storage and analytical procedure, and resulted consequently in good recoveries (78-97%) and also improved precision of data. It was suggested that oxidative decomposition was responsible for the instability of TM, because several antioxidants made TM stable in homogenized grape. The decomposition of TM in homogenized grapes was dependent on incubation temperature and pH, and it required heat-labile component in the grape. Either catalase or sodium azide prevented the decomposition of TM in homogenized grapes. These results evidenced that oxidative decomposition of TM occurred enzymatically in the homogenized preparation of the grape and this decomposition was inhibited by SL-A.