Discriminated release of phenolic substances from red wine grape skins (Vitis vinifera L.) by multicomponent enzymes treatment

Detailed insight into the effects of enzymatic treatments on grape phenolics is of significant importance for grape processing for wine making. This study examined the release of phenols during enzymatic (pectinolytic and cellulolytic) degradation of the cell wall polysaccharides in skins of Merlot and Cabernet Sauvignon wine grapes (Vitis vinifera L.). Anthocyanins were released from skins during the early phases of the enzymatic treatments, but were then degraded during further enzymatic treatment; flavonols underwent transformation from glycosylated (rutin) to deglycosylated (quercetin) during the enzymatic treatment; phenolic acids, including hydroxybenzoic acids and hydroxycinnamic acids, were released as a function of monosaccharides liberation, i.e. as a function of the enzyme catalyzed cell wall degradation of the skins, and with some of the phenolic acids perhaps released from the lignin. The data moreover suggest that p-coumaric acid was also released during enzyme catalyzed degradation of acylated anthocyanins, probably as a result of cinnamate esterase activity. The data thus provided unexpected new clues as to how the enzymatic treatment with multicomponent pectinolytic enzymes may promote (a) discriminated release of phenols from grape skins, and (b) molecular changes in the phenols.