The present work aimed to study the fate of field-applied pesticides during malting and mashing processes. Twenty-four field-collected barley samples were subject to micromalting followed by lab-scale mashing to investigate the carryover of residual pesticides from barley to malt and then from malt to sweet wort. The citrate-buffered QuEChERS sample preparation method was adapted for simultaneous determination of 57 pesticide residues in grain, malt, spent grains, and sweet wort samples using ultra-performance liquid chromatography coupled with tandem mass spectroscopy (UPLC-MS/MS). Residues of four fungicides (fenpropimorph, pyraclostrobin, tebuconazole, and trifloxystrobin) and two insecticides (chlorpyrifos and pirimiphos-methyl), frequently found in the barley samples, were investigated in detail in this study. The carryover percentages of these pesticides to malt, against the concentration of residues in barley grain, ranged from 22% for pirimiphos-methyl up to 78% for fenpropimorph. The results confirm a general rule that residues of pesticides with log P values >2 remain on the malt, but it was found that their transfer potential is more related to its individual physical-chemical properties but does not much correlate to their log P values. In the second part of the study, a noticeable carryover from malt to sweet wort was observed for pyraclostrobin, fenpropimorph, and tebuconazole residues, and these values ranged from 2 to 15%. Moreover, the analysis of pesticide residues in spent grain after mashing revealed that the spent grain samples contain on average once as much pyraclostrobin and tebuconazole residues as the original malt. It was concluded that (1) pyraclostrobin and tebuconazole residues could be incorporated into or associated with macromolecules in barley grain to form "hidden" (bound) forms, and (2) the parent compounds are subsequently released from their hidden forms during mashing.
Keywords: hidden forms; malt; malting; mashing; pesticide residues; sweet wort.