Effect of Chinese traditional cooking on eight pesticides residue during cowpea processing

• Log Kow was the key factor influencing final residues after processing.
• Oil after frying cowpea could gather residues from cowpea.
• Increasing frying time and frequency increased residues transferred to oil.
• Oil after frying was not recommended to reuse.
• Blanching (5 min) + stir-frying (3 min) could eliminate all the residues.

Thermal processing can concentrate residues or convert residues to more toxic metabolites in food. Chinese traditional cooking pays more attention to thermal processing and more vegetables were eaten after thermal processing. In this study, the effect of Chinese traditional cooking (washing, blanching, stir-frying, frying and combined operations) on eight pesticides residues (pyridaben, procymidone, chlorothalonil, difenoconazole, α-cypermethrin, bifenthrin, S-fenvalerate and λ-cyhalothrin) in cowpea which was one of the most important legume crops in China was examined. Result showed washing and blanching could reduce residues with low Kow while stir-frying and frying were more effective to residues with high Kow; stir-frying and frying could concentrate residues with low Kow; the residue levels in oil increased following increasing frying time and frequency especially the residues with high Kow; one metabolite studied in this paper was not detected. Blanching (5 min) followed by stir-frying (3 min) was the most effective combined operation.