Efficient One Pot Extraction and Depolymerization of Grape (Vitis vinifera) Pomace Procyanidins for the Preparation of Antioxidant Thio-Conjugates

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Abstract
Antioxidant thio-conjugates were obtained from white grape pomace by a clean and efficient one pot extraction and depolymerization method using water and cysteamine hydrochloride. To evaluate the potential of grape pomaces of different origins as sources of proanthocyanidins and conjugates, we conducted varietal comparative studies of polyphenol content, antioxidant power, and procyanidin composition. Xarel·lo proved to be the richest source of polyphenols. The total conversion into the conjugates was as high as 8 g/kg of Xarel·lo grape pomace, with a 50-fold excess of cysteamine, and 3 g/kg, with a 5-fold excess of cysteamine. After purification by preparative cation exchange and reversed phase high-performance liquid chromatography, 17 g of 63% pure 4β-(2-aminoethylthio)epicatechin (acetate salt) was obtained from 35 kg of moist pomace. The procedure described here will make the antioxidant thio-derivatives efficiently available directly from raw plant byproducts such as grape pomace. Keywords: Grape; Vitis vinifera; polyphenols; procyanidins; catechins; flavanols; antioxidants; free radical scavenging