New flavanol derivatives from grape (Vitis vinifera) byproducts. Antioxidant aminoethylthio-flavan-3-ol conjugates from a polymeric waste fraction used as a source of flavanols

A new family of antioxidants has been obtained from a residual fraction of polymeric polyphenols of grape origin. The integral exploitation of resourc es is important in any sustainable production scheme. Many byproducts and r esidues generated by the agroindustries. contain polyphenols with potential application as preventative agents against cancer and cardiovascular disea ses. Among these polyphenols. oligomeric proanthocyanidins. are particularl y significant. The polymeric forms, considered of less interest because of their astringent properties, constitute the largest portion of the biologic ally active plant proanthocyanidins. The new compounds described here resul t from the breakdown of polymeric flavanols in the presence of cysteamine a nd bear an amino function, which facilitates their isolation from complex m ixtures by cation-exchange gels or resins. In this way, valuable antioxidan t molecules can be efficiently obtained from otherwise wasted polymers. The new molecules appear to be as effective as their underivatized counterpart s (flavan-3-ols) as antioxidants.