Grape enzymes

The acid medium ruptures the proteophospho-lipid membrane, breaking the protein bonds and, consequently, releasing the contents of the vacuoles. All of the anthocyanins are then extractable and solubilized in the solution at pH 1. At pH 3.2, extraction is approximately comparable to that occurring in fermentation vats. If the membrane is not porous, anthocyanins circulate very little, but if it is broken down by grape enzymes, the pigments... 

In red winemaking, these preparations are used in particular for press wines and heat-treated grapes and must. In the latter case, the must is very rich in pectic compounds and devoid of endogenous grape enzymes. These are destroyed by heat (Martiniere and Ribereau-Gayon, 1973). Pectolytic enzymes can also be used at the time of running off after a traditional maceration. 

Enzymatic reactions, activated by grape enzymes, are involved in cell wall degradation. They favor the dissolution of their vacnolar contents (Section 11.7.3). Commercial enzymatic preparations have recently been developed to activate these phenomena they have pectinase, cellulase, hemi-cellulase and protease activities of diverse origins (Amrani-Joutei, 1993). These enzymes seem to favor the extraction of skin tannins over skin anthocyanins. They act on the tannins linked to the polysaccharides of the cell wall, giving the enzymatic wine a more full-bodied character than the control wine. 

Since a few years, new activities have been discovered in relation with fruit cell wall architecture, like new pectinases [1] (i.e. rhamnogalacturonase for the apple) new glycosidases [2](i.e. apiosidase for the grape). The improvement of the knowledge of fruit composition, cell wall chemistry, enzymology of endogenous and exogenous enzymes allow to supply the juice producers with preparations more and more purified and specific, blended in optimal combinations. 

Mathieu, S., F. Bigey et al. (2007). Production of a recombinant carotenoid cleavage dioxygenase from grape and enzyme assay in water-miscible organic solvents. Biotechnol. Lett. 29(5) 837-841. 

The mash that ferments to form wine sometimes includes grape skins which are rich in enzymes. 

Major enzymes catalyzing flavonoid reactions are oxidative enzymes (i.e., polyphenoloxi-dases and peroxidases) arising from grape but also from molds contaminating them. Various hydrolytic enzymes (glycosidases, esterases), excreted by the fermentation yeasts or fungi or present in preparations added for technological purposes (e.g., pectinases), are also encountered in wine. 

Pectinases and (3-glucanases are the only enzymes allowed in wine-making by European legislation. They are used as clarification and filtration agents and also to release aroma compounds that are mostly present in grape as nonvolatile glycosidic precursors. Pectolytic enzymes are also reported to increase extraction of phenolic compounds and wine color... 

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