Characterization of Lipophilized Monomeric and Oligomeric Grape Seed Flavan-3-ol Derivatives

Grape seed proanthocyanidins, composed of flavan-3-ols of different degrees of polymerization, are natural food antioxidants. Flavan-3-ols in grape seed are usually polyhydroxy derivatives which exhibit hydrophilic character. Monomeric and oligomeric flavan-3-ols were modified structurally to improve their lipophilicity, expand their application in lipophilic media, and enhance their cellular absorption in the body. The esterification of the water-soluble flavan-3-ols was prepared by Lipozyme TL IM with lauric acid, and their enhanced lipophilicity was confirmed by a 1-octanol/water partition coefficient. The chemical structures of monomeric and oligomeric flavan-3-ol derivatives, identified by HPLC-MS-MS and ¹H and ¹³C NMR, were 3'-O-lauroyl catechin, 3'-O-lauroyl epicatechin, 3',5'-2-O-lauroyl epigallocatechin, 3',3″,5″-3-O-lauroyl epicatechin gallate, 3',3″-2-O-lauroyl procyanidin A2, 3',3″-2-O-lauroyl procyanidin B1, and 3',3″,3‴-3-O-lauroyl procyanidin C1. Flavan-3-ol derivatives exhibited the highest 1,1-diphenyl-2-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activities compared to that of parent flavan-3-ols, butylated hydroxytoluene and tert-butyl hydroquinone. The results suggest that flavan-3-ol derivatives may be used as potential lipophilic antioxidants in the food industry.