In vivo Detection of Folpet and Its Metabolite Phthalimide in Grape Must and Wine

¹ Swiss Federal Research Station for Fruit-Growing, Viticulture and Horticulture, 8820 Wädenswil, Switzerland.

Folpet, N-(trichloromethylthio)-phthalimide and its metabolite phthalimide were determined using an HPLC technique in fresh and fermented must and wine of Léon Millot grapes treated with fungicides. In the freshly pressed turbid must, we detected high concentrations of folpet and limited amounts of phthalimide. After 24 hours no folpet was found since it had been adsorbed by the yeast cells. In contrast, the phthalimide concentration increased daily and reached a maximum of 1.36 mg phthalimide/L which corresponds to 2.72 mg folpet/L. Phthalimide was present in all the analyzed, unprocessed, turbid wines. On the other hand, no fungicide residue was found in the filtered wines, and only traces of phthalimide were detected. To study the influence of folpet on the fermentation, the musts from grapes treated with fungicide and from untreated grapes were spontaneously fermented. All treated samples began to ferment one to five days later than the untreated samples. In two unprocessed, turbid wines of two different grape varieties that received no fungicide treatment, a substance was co-eluted with folpet but could not be chemically attributed to folpet in multicomponent analysis (MCA). GC-MS analysis showed an ester of a C₁₈-fatty acid. The most reliable values were obtained in the analyses of unfiltered wines, as all folpet was available as phthalimide.

Key words: fungicide, folpet degradation, phthalimide, grape must, wine, alcoholic fermentation, HPLC-analysis

Submitted on January 2, 1996