Changes in pesticide residues in field-treated fresh grapes during raisin production by different methods of drying

Drying is one of the best food preservation methods, especially for grapes. This study aimed to determine the fate of pesticides after grapes are being subjected to different drying methods, namely, sun-, oven-, shade-, and alkaline-drying, which are employed in raisin production. Pesticide residues were determined by gas chromatography–tandem mass spectrometry (GC–MS/MS). Washing before drying decreased the diazinon, ethion, phosalone, penconazole, and hexaconazole levels in the grape samples by 52.04%, 6.75%, 9.99%, 56.54%, and 20.97%, respectively. In the raisins, the concentration of all the pesticide residues increased based on wet weight, and this result was due to dehydration; by contrast, the concentrations of the pesticides decreased based on dry weight. The sun-drying method demonstrated the greatest efficiency in residue removal wherein it decreased the diazinon, ethion, phosalone, penconazole, and hexaconazole levels by 76.65%, 68.40%, 69.55%, 72.74%, and 82.19% (dry weight), respectively. On the contrary, the shade-drying method demonstrated the least efficiency in reducing the residue levels (19.57%–42.55%). The evaluation of the processing results showed pesticide residue level in the raisins prepared using the investigated drying methods was higher than the maximum residual limits (MRL). This finding indicates that it is necessary to consider the pre-harvest interval in pesticide application in grape.