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The changes of five pesticides including imidacloprid, triadimefon, fenitrothion, chlorpyrifos-methyl, and chlorpyrifos in wheat flour during Chinese steamed bun and bread processing were systematically investigated. The pesticide residues were determined by high performance liquid chromatography coupled with diode array detector. Dough mixing step in both Chinese steamed bun and bread processing reduced the concentration of five pesticide residues significantly by 33 to 46%. It was mainly attributed to the increase of moisture content in mixed dough during this step. The reduction of pesticides in fermenting step varied from 2 to 22% in Chinese steamed bun and bread processing. Resting step in both Chinese steamed bun and bread processing has little effect on the pesticide residues with the reduction from 2 to 8%. The five pesticides have different behaviours in steaming step of Chinese steamed bun processing and in baking step of bread processing. During the steaming step, only the concentrations of triadimefon and imidacloprid residues in crust were increased by 52 and 1%, the others in crust and in crumb of Chinese steamed bun were decreased by 4 to 38%. After the baking step, the concentrations of triadimefon and imidacloprid residues in crust, and the triadimefon residue in crumb of bread were increased by 65, 83, and 14%, respectively, the others were all reduced. The processing factors (PFs) for triadimefon and imidacloprid in crust in the steaming and baking steps, for triadimefon in crumb in the baking steps were greater than 1, and the others were all less than 1. Overall, this study provides important references for monitoring pesticide residues in the processing of wheat flour products. The PFs obtained could be helpful for the risk assessment of pesticides in wheat flour products.

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