Wine chemical, sensory, aroma compound and protein analysis of wines produced from chemical and biological fungicide treated Chenin blanc grapes

Abstract

Fungal diseases in vineyards are one of the main causes leading to economic losses within the viticulture sector and are continuously increasing with time. The most common of these fungal diseases are powdery mildew, downy mildew and grey mould which are controlled by the use of fungicides. However, fungicide residues can alter the fermentation process and prevent some biochemical pathways of yeast metabolism involved in phenolic and/or aroma compound production that are critical for sensory quality. In this study, Chenin blanc grapes treated with chemical and natural fungicides were used to produce small-scale wines and laboratory-scale fermentations. Treatments consisted of a control (an approved chemical used in industry), a 1x and 2x treatment (new formulations). Laboratory-scale fermentations were conducted in duplicate using the commercial Saccharomyces cerevisiae (S. cerevisiae) Active Dry Wine Yeast (ADWY) strains VIN 13 and VIN 7. The fermentations were monitored by weighing frequently until they stabilised (CO2 weight loss). Small-scale wines were made according to the standard Nietvoorbij experimental wine making procedure. At the end of fermentation, lees samples were subjected to CHEF gel electrophoreses to confirm that the inoculated yeast strain completed the fermentations. Moreover, fermenting wine samples, collected at the start and end of the fermentation, were subjected to protein extraction, quantification and characterisation the yeast proteins expressed at the various stages of fermentation. Resultant wines were subject to chemical and sensory evaluations five months after bottling. From the results obtained in the above study, it was concluded that the inoculated yeast strains used for wine making completed the fermentations at a similar rate to their respective controls (registered fungicide). In addition, small-scale cellar fermentations showed that the fungicide treatments (1x the recommended dosage [Treatment 1] and 2x the recommended dosage [Treatment 2]) compared to the controls had no notable negative effects on wine aroma and sensory profiles although differences were observed in the proteins expressed after the fermentation. The chemical and biological fungicides had no notable effects on the wine making procedure and quality of resulting wines compared to the registered fungicide.