Phenolics and Ripening in Grape Berries

This hypothetical condensed tannin is made up of four subunits: catechin, epicatechin, epigallocatechin, epicatechin gallate. The first subunit (catechin) is bound to the second (epicatechin) by an interflavan bond between carbon 4 of catechin and carbon 8 of epicatechin. The first three subunits are referred to as “extension” subunits and only the epicatechin gallate has a free 4 position and is thus referred to as a “terminal” unit.

The anthocyanins found in grape berries.

The hydroxycinnamates found in grape berries.

Structure of catechin and epicatechin, the most abundant monomeric flavan-3-ols in grape.

The flavonols of grape: found in the berry as glucosides, galactosides, and glucuronides where R3 is glucose, galactose, or glucuronic acid, respectively.

The biochemical pathway that leads to the major soluble phenolic classes found in the grape berry. Compounds or classes that accumulate in the fruit are outlined by rectangles and intermediates (not outlined) are usually present at very low levels. Caftaric, coutaric, and fertaric acids are the tartrate esters of the respective cinnamic acid.

The biochemical pathway to the major flavonoids found in grape berries. Compounds that accumulate in the fruit are outlined by rectangles and the intermediates are present at very low levels.

Biosynthesis of the flavan-3,4-diol from caffeoyl-CoA and malonyl-CoA. CHS, chalcone synthase; CHI, chalcone isomerase; F3H, flavanone-3-hydroxylase; DFR, dihydroflavonol-4-reductase.

Formation of catechin, epicatechin, anthocyanidin (cyanidin), cyanidin-3-glucoside. LAR, leucoanthocyanidin reductase; ANS, anthocyanidin synthase; ANR, anthocyanidin reductase; UFGT, UDP glucose-flavonoid 3-O-glucosyl transferase.

Changes in skin and seed tannin in Cabernet Sauvignon berries during ripening. Tannin is expressed in catechin equivalents (CE) on a per berry basis, 1998 and 1999 (Harbertson et al. 2002).