Degradation of pesticides in wheat flour during noodle production and storage.

The fate of five pesticides comprising triadimefon, imidacloprid, fenitrothion, chlorpyrifos-methyl, and chlorpyrifos in wheat flour during noodle production and accelerated storage was systematically investigated. Pesticide residues were determined by high-performance liquid chromatography with diode array detection (HPLC-DAD) after each processing step and accelerated storage. The results indicated that dough mixing reduced the concentration of five pesticide residues by 23-42%, mainly owing to the increase of moisture content. Dough resting had little effect on the residues of triadimefon, imidacloprid, and fenitrothion, but decreased chlorpyrifos-methyl and chlorpyrifos significantly by 24% and 15%, respectively. The pesticide residues increased by 3% to 69% during the drying step, attributed to the different role played by thermal evaporation or thermal degradation and concentration of the different pesticides. Boiling lowered the pesticide residues significantly by 56% to 74% in both fresh noodles and dried noodles. All the pesticide residues decreased during accelerated storage, especially for fenitrothion, chlorpyrifos-methyl, and chlorpyrifos. The processing factors (PFs) of the five pesticides in the drying step were greater than 1, while the others were all less than 1. The whole process for noodle production was beneficial to reduce the pesticide residues with PFs ranging from 0.15 to 0.35. The PFs of five pesticides in accelerated storage were all below 1.

Residue changes of five pesticides during the production and storage of rice flour.

The residue changes of five pesticides in samples from different steps of rice flour production and accelerated storage were systematically investigated. Rice flour was produced both by the extrusion process and the drying on roller process. The change of pesticide residues varied in different processing steps and storage time. The water adjusting step had little influence on the pesticide residues. The pesticide residues were decreased significantly in the extruding, soaking, and grinding steps with reduction from 21% to 76%. The drying step increased or decreased the pesticide residues in varying degrees through concentration due to water evaporation and thermal evaporation or thermal degradation. All the pesticide residues decreased during the accelerated storage, especially for methidathion and chlorpyrifos, neither was detected after accelerated stored for 14 days. The processing factors (PFs) for imidacloprid and isocarbophos in the drying step were greater than 1, and the others were all less than 1. The whole drying on roller process had lower PFs than the whole extrusion process, indicated that the drying on roller process had a greater effect on pesticide residues. The PFs of accelerated storage for five pesticides were all below 1. Overall, this study provides important references for monitoring pesticide residues in the processing and storage of rice flour. Moreover, the PFs obtained in this study could be useful in the dietary exposure and risk assessment of pesticides in rice flour.