Impact of Pressing Conditions on the Phenolic Composition,Radical Scavenging Activity and Glutathione Content of Brazilian Vitis vinifera White Wines and Evolution During Bottle Ageing

The pre-fermentation techniques applied during the production of white wine, such as skin maceration or grape pressing, can directly affect the quality of the final product. There is a constant search for methods that can enhance the sensorial characteristics, such as varietal aromas, and phenolic composition of white wines. The aim of this study was to investigate the effect of different pressing conditions on the phenolic composition, antioxidant activity and glutathione content of white musts and wines produced in southern Brazil and to evaluate these characteristics during bottle ageing. By applying different pressures, three fractions of musts were obtained: free-run must, light pressed must and heavy pressed must. The musts and their corresponding wines were analysed by spectrophotometric and chromatographic assays. Pressing positively affected the chemical composition of the musts and wines, and the wines produced with pressed fractions of the musts presented higher polyphenol content and radical scavenging power. The main phenolic compounds affected by the pressing conditions were caftaric acid, catechin and epicatechin. During bottle ageing, an increase in certain individual phenolic compounds could be observed by liquid chromatography. Samples produced with heavy pressed musts presented a higher browning index. Furthermore, the application of pressure to the grape musts during winemaking increased the contents of total glutathione by factors of up to 22 and 15 for light pressed and heavy pressed musts, respectively. After 8 months of bottle ageing, the glutathione content decreased in all samples.