Structural features and antioxidant activity of tannin from persimmon pulp

Phenolic compounds from persimmon pulp were extracted with methanol acidified with 1% HCl, and then purified on AB-8 macroporous resin. The tannic extracts obtained were fractionated by polysulfone ultrafiltration membrane with molecular weight cutoff of 10,000 Da into two fractions: low molecular weight tannin (LMWT) and high molecular weight tannin (HMWT). HPLC–MS analysis showed that gallic acid was one of the main components of LMWT fraction. The molecular weight distribution of HMWT was determined to be in the range of 1.16 × 104 Da to 1.54 × 104 Da, with the molecular weight of 1.28 × 104 Da in Mn¯ and 1.39 × 104 Da in Mw¯ by GPC method. HPLC–MS showed that the thiolysis degradation products of HMWT consist of (epi) gallocatechin, epigallocatechin-3-O-gallate, epicatechin-3-O-gallate and an unknown monomer with the ratio of 1:7:3:1 by estimation of the peak area on HPLC. The antioxidant properties of persimmon tannins were evaluated using the hydroxyl radical scavenging activities by 2-deoxyribose oxidation system and salicylic acid system, superoxide anion scavenging activity, and linoleic acid lipid peroxidation inhibition activity, respectively. HMWT exhibited excellent antioxidant activities in all tested systems in a dose-dependent manner. The antioxidant activity of HMWT was significantly stronger than that of LMWT and grape seeds proanthocyanidins (GSP), suggesting that high molecular weight condensed tannins are the major antioxidant composition in persimmon pulp.