Changes in polyphenol and polysaccharide content of grape seed extract and grape pomace after enzymatic treatment

► Tannase cleaved the galloylated form of catechin releasing gallic acid. ► Tannase increased the antioxidant activity of grape by-products. ► Carbohydrases degraded the cell wall polysaccharides of grape pomace increasing the content of monosaccharides. ► Pectinase facilitated the release of gallic acid from grape pomace increasing the antioxidant activity. ► Cellulase was not efficient for phenolic release and antioxidant activity improvement.