The effect of home processing on postharvest fungicide residues in citrus fruit: residues of imazalil, 2-phenylphenol and thiabendazole in 'home-made' marmalade, prepared from late Valencia oranges.

The effects of domestic marmalade-making procedures on residues of imazalil, 2-phenylphenol and thiabendazole in 'sweet' oranges were investigated by comparing residue levels in raw fruit and in marmalades, prepared by heating the oranges with water and sugar for about 4 h in a preserving pan on a gas ring or for about 1 h in a microwave oven. Determination of residues in raw oranges and in marmalades was carried out by extraction with dichloromethane, followed by clean-up and reversed phase HPLC with UV detection for imazalil and fluorescence detection for 2-phenylphenol and thiabendazole. Residue analysis showed that the extent of carry-through of imazalil, 2-phenylphenol and thiabendazole residues into the marmalades depended on the method of marmalade-making and the nature of the fungicide. Persistence of fungicides was higher in the marmalade prepared in the microwave oven than in that prepared in the preserving pan. An increase (about 50%) in levels of imazalil in the fruit portions of marmalades compared with raw fruit residue levels indicated that imazalil was more readily extracted from oranges after processing. Comparison of 2-phenylphenol levels in raw fruit and fruit portions of marmalades showed that the longer exposure to heat, needed for marmalade-making in a preserving pan, reduced residue levels more severely (48%) than cooking in the microwave oven (13%). Thiabendazole levels in the fruit portion of marmalade prepared in the microwave oven stayed the same as in the raw fruit, but cooking in the preserving pan decreased residue levels by about 22%.