In current study, the effects of Iranian rice cooking method (Kateh) on residue levels of 41 pesticides were investigated. The pesticides were selected according to Iranian National Standards Organization (INSO) regulations and covered 18 permitted and 23 banned pesticides belonging to different chemical classes such as organophosphate, triazole, and carbamate. A 250 g portion of rice sample was soaked in 2.5 L spiked tap water containing studied pesticides at final concentration 2 μg/mL and then, the effects of washing and cooking were investigated. The pesticides were analyzed simultaneously in a single run using positive electrospray ionisation with multiple reaction monitoring (MRM) after extraction with QuEChERS method. The results showed that washing removed different portions of pesticide residues in the range between 12.0-88.1%. Washing effect was not associated with the water solubility of the pesticides but amount of residue binding to rice matrix was a major factor for residue reduction. In Iranian method of rice preparation, cooking process includes boiling and steam cooking. In this study, the amount of the pesticide residues was decreased in the range of 20.7-100%. Under these conditions, volatilization, hydrolysis, and thermal degradation caused the reduction of the pesticide residues.
Keywords: Cooking process; LC–MS/MS; Multi-residue analysis; Pesticide residues; Rice.