Fate of quinoxyfen residues in grapes, wine, and their processing products

Quinoxyfen is a new fungicide that belongs to the family of the quinolines, recently introduced to control powdery mildew (Uncinula necator). In this paper the fate of quinoxyfen residues from vine to wine and in their proces sing products was studied. After the last of four applications at the recom mended rate, 0.38 mg/kg of residue was found on the grapes, which is under the legal limit fixed in Italy (0.5 mg/kg). The degradation rate was accord ing to a pseudo-first-order kinetics (r = 0.964) and the half-life was 7.24 days. Vinification was carried out with and without maceration. During the vinifications without maceration < 50% of the residues passed from the gra pes to the musts. Separation of the lees (8%) from the must by centrifugati on caused no detectable residues in centrifuged must. At the end of ferment ation with and without maceration no quinoxyfen residues were determinable in the wine. No effect on the alcoholic or malolactic fermentation was obse rved even in the presence of higher quinoxyfen concentrations than those fo und in the grapes at harvest time. During fermentation, the yeasts partiall y degraded the pesticides and completly adsorbed them. Bacteria, on the oth er hand, do not have any degradative effect on the pesticides. The raisins obtained by sun-drying did not contain any residues, whereas those obtained by oven-drying show the same amount of residues as in the fresh grapes. Du ring the sun-drying process the fruit weight decreased by a factor of 4; th e decrease in the oven-drying was equivalent. Samples of dregs and liquid l ees, fortified with high levels of quinoxyfen, were double-distilled. The f irst dregs distillate, with an alcohol content of 32.1%, did not show any r esidues, whereas the first lees distillate, with an alcohol content of 34.5 %, showed 7% of the initial residues. After the second lees distillation, t he obtained product showed an alcoholic content of 81.2% and no residues of quinoxyfen (< 0.01 mg/kg).