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

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Abstract
A new family of antioxidants has been obtained from a residual fraction of polymeric polyphenols of grape origin. The integral exploitation of resources is important in any sustainable production scheme. Many byproducts and residues generated by the agroindustries contain polyphenols with potential application as preventative agents against cancer and cardiovascular diseases. Among these polyphenols oligomeric proanthocyanidins are particularly significant. The polymeric forms, considered of less interest because of their astringent properties, constitute the largest portion of the biologically active plant proanthocyanidins. The new compounds described here result from the breakdown of polymeric flavanols in the presence of cysteamine and bear an amino function, which facilitates their isolation from complex mixtures by cation-exchange gels or resins. In this way, valuable antioxidant molecules can be efficiently obtained from otherwise wasted polymers. The new molecules appear to be as effective as their underivatized counterparts (flavan-3-ols) as antioxidants. Keywords: Grape; Vitis vinifera; polyphenols; proanthocyanidins; catechins; flavan-3-ols; cysteamine; amines; cation exchange; isolation; antioxidants; antiradical activity