Variation of boscalid residues in Welsh onion during cooking processes

The residue levels of the fungicide, boscalid on Welsh onions after cooking via different methods, were investigated. After boscalid treatment, Welsh onions of varying sizes were cooked via stir-frying, baking, and boiling under different heating times, and residue quantification was realized via LC-MS/MS (limit of quantification, 0.01 mg/kg; recovery rate, 84.6-102.7%). Residues levels after stir-frying and baking were 1.81-2.28 (processing factor (PF), 0.70-0.88) and 0.57-1.16 (0.22-0.45) mg/kg, respectively. Boiling 0.8 and 5 cm slices resulted in residue levels of 0.49-0.88 (0.19-0.34) and 0.23-0.58 (0.09-0.22) mg/kg, respectively, and the PF for baking and boiling decreased with increasing heating time, indicating an effective reduction of residue level by heat. However, stir-frying showed increased residue levels with extended heating owing to water loss. Thus, boiling was the most effective method in reducing pesticide residue levels in Welsh onions.