Changes in grape seed polyphenols during fruit ripening

The quantity and characterization of extracted flavan-3-ol monomers and pro cyanidins was determined in seeds from Vitis vinifera cv. Cabernet Sauvigno n berries, over the course of ripening and at different levels of vine wate r status. The per berry extractive yield of all polyphenols decreased with maturity, and followed second-order kinetics. The flavan-3-ol monomers decr eased most rapidly, followed by the procyanidin extension units and finally , the terminal units. The relative proportion of procyanidin extension unit s did not vary with maturity. During fruit ripening, the mean degree of pol ymerization of extracted procyanidins is unchanged when analyzed intact by HPLC, but decreases by thiolytic degradation. The proportion of extracted p rocyanidins resistant to acid catalyzed thiolysis increased with maturity. Changes in vine water status affected polyphenol amounts, indicating that c ultural practices can. be used to influence composition. Oxidation of the s eed polyphenols during fruit ripening, could explain these observations. (C ) 2000 Published by Elsevier Science Ltd.