Effect of processing on herbicide residues and metabolite formation during traditional Chinese tofu production

Abstract

The fates of clomazone, fomesafen, and quizalofop-p-ethyl and its metabolite quizalofop (acid) in soybean samples during tofu processing were systematically assessed. Residues were determined using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS) after each processing step, including washing, soaking, grinding and filtering, cooking, coagulating, and squeezing. The pesticide distribution at each step of the process was studied, and pesticide processing factors were calculated. Differences in the pesticide residue levels were found at each processing step. Changes in pesticide residues in the tofu products was closely related to their physicochemical properties such as octanol-water partition coefficient (Kow), water solubility, and vapor pressure. The results showed that soaking prominently decreased fomesafen residues by 72.0%, as indicated by its high water-solubility and low log Kow. Grinding and filtering reduced pesticide residues by 88.8%–94.8%, mainly due to dilution or okara separation. The processing factors were generally <1 for each step and for the entire process, except those for cooking, coagulating, and squeezing. These results demonstrated that the overall process could significantly reduce clomazone, fomesafen, quizalofop-p-ethyl, quizalofop (acid) residues during tofu processing.