In this study, the effect of various household food-processing methods (washing, peeling, processing into jam and fruit juice, freezing, storage) on pesticide residues (abamectin, buprofezin, ethoxazole, imazalil, and thiophanate-methyl) in oranges was investigated. Residue analyses were performed by quick-easy-cheap-efficient-rugged-safe (QuEChERS) extraction and liquid chromatography coupled with triple quadrupole mass spectrometry (LC-MS/MS) analysis. The limit of quantification of the method for each pesticide was 10 µg/kg. Physicochemical properties of the pesticides and the type of the food process had a considerable effect on the fate of pesticide residue. Pesticide residues were mostly dispersed on orange peels and washing with tap water decreased the residue levels by 26–84%. The amount of residue in oranges was reduced by 63–100% during fruit juice processing, while residues were removed by 90–100% after jam processing. Pesticides with a high octanol–water coefficient were absorbed by the wax of the orange peel, therefore they remained on the peel and could not easily be removed by washing. Moreover, pesticides with lower water solubility did not diffuse easily through the fruit juices from the pulp section of the fruit. The processing factor was greater than 1 for the separation of the orange peel and less than 1 for the washing step and jam and fruit juice productions.

The effect of different drying conditions (based on hot air convective drying and vacuum drying with or without microwave pretreatment) on residual behavior of abamectin, buprofezin, imazalil, and thiophanate-methyl in orange slices was investigated. Processing factors ranged between 1.55 and 3.41, indicating concentration of the residue levels in dried orange slices due to the moisture losses. However, based on the normalized residue concentration with dry matter content of the slices, pesticide residue levels in fresh orange slices reduced by 40.8%–73.2% after drying processes. Hot air drying caused more reduction in residue levels compared to vacuum drying. It was observed that decrease in absolute pressure of vacuum drying from 30 kPa to 15 kPa, increase in drying temperature from 60 °C to 80 °C, and application of microwave pretreatment increased the degradation rate. Moreover, the Pearson analysis revealed that degradation rate in the residue levels during drying was negatively proportional to the octanol-water coefficient of pesticides. Therefore, the highest degradation rate was obtained for buprofezin and thiophanate-methyl during hot air drying (at 80 °C) with application of microwave pretreatment and the lowest degradation rate was obtained for abamectin during vacuum drying (at 60 °C and 30 kPa).