BINDING CAPACITY OF INSOLUBLE BERRY CELL WALL MATERIAL FOR TANNIN AND LARGE POLYMERIC PIGMENTS

Tannins and polymeric pigments are some of the most abundant and important phenolics found in grapes and wine. They are known to interact with proteins and polysaccharides, but their behavior with the insoluble cell wall matrix of grape berries has received little attention. We developed a convenient assay to measure the tannin-binding capacity of cell walls from berry skins and mesocarp tissue and used this assay to study the binding capacity of fruit during ripening. The ability of cell walls to bind tannins generally increased during ripening. We found that mesocarp cell walls had about twice the capacity to bind tannins compared with skin cell walls. We also examined the binding capacity in several varieties and across growing regions. We studied adjacent Cabernet Sauvignon vineyards in Napa Valley giving wines with drastically different levels of tannin in finished wine even though the fruit contained almost identical levels of tannin at harvest. Berry cell walls from a vineyard giving low tannin wines had a higher tannin-binding capacity per berry than another vineyard giving wines with higher tannin levels. This suggests that the tannin-binding capacity of cell walls may influence extractability of tannins from fruit during fermentation. Chemical fractionation of the insoluble cell wall matrix indicated that cellulose and hemicellulose play a role in tannin binding whereas the chelator-soluble pectins do not. This work suggests that the tannin-binding capacity of berry cell walls may be an unrecognized factor that can influence tannin extraction and retention in finished wines. We advise you to read the entire article. Original title: BINDING CAPACITY OF INSOLUBLE BERRY CELL WALL MATERIAL FOR TANNIN AND LARGE POLYMERIC PIGMENTS