Evolution of proanthocyanidins in bunch stems during berry development (Vitis vinifera L

Proanthocyanidins from bunch stems of two red varie-ties (Castelão Francês and Touriga Francesa) and one white variety (Viosinho) (Vitis vinifera L.) harvested in 1998, were separated into monomers (catechins), oligomers (degree of polymerization ranging from 2 to 12-15) and polymers (de-gree of polymerization>12-15), and then quantified during grape development (40 d before veraison until ripening). In addition, low molecular weight catechins [(+)-catechin and (-)-epicatechin], dimeric procyanidins (B1, B2, B3, B4), galloylated dimeric procyanidins (B1-3-0-gallate, B2-3-0-gallate, B2-3-0-gallate), and trimeric procyanidins (C1, T2) from grape stems were quantified by HPLC. At harvest the polymeric fraction was the most abun-dant (28.0- 35.8 mg·g-1 stem). For the three grape varie-ties, the content of catechins, oligomeric and polymeric fractions decreased during berry development mainly after veraison. Grape stems are also an important source of pro-anthocyanidins in the grape cluster when compared to the flavanol content in seeds. From an industrial point of view, stems seem to be an important source of proanthocyanidins for potential use as nutriceutical, enological products, chemical standards or even in winemaking to regulate flavanol composition in wine. K e y w o r d s: grapevine cluster stem, maturation, proanthocyanidins, polymerization degree