Antioxidant gallocatechins, dimeric and trimeric proanthocyanidins from sea buckthorn (Hippopha� rhamnoides) pomace

Abstract

Residues such as peels and seeds that result from fruit juice production may contain substantial amounts of valuable natural antioxidants. In order to isolate the potential antioxidants gallocatechins and proanthocyanidins, pomace from sea buckthorn (Hippophae rhamnoides) berries was extracted by acetone-water (75:25, v/v) and fractionated by Sephadex LH-20 gel chromatography and semipreparative HPLC. The structures of the monomeric flavan-3-ols isolated, (+)-gallocatechin and (−)-epigallocatechin, were elucidated by electrospray mass spectrometry (ESI-MS) and 1H and 13C NMR spectroscopy. Five dimeric proanthocyanidins were identified by HPLC-ESI-MS(-MS) and by acid-catalyzed cleavage in the presence of phloroglucinol. Moreover, nine trimeric proanthocyanidins were tentatively identified by HPLC-ESI-MS(-MS) in the Sephadex fractions of sea buckthorn pomace. The isolated flavan-3-ols and proanthocyanidins were potent in scavenging Fremy’s salt, a synthetic free radical. They possessed antioxidant capacities that were higher or comparable to that of ascorbic acid or Trolox. On comparing the antioxidant capacities of monomeric flavan-3-ols and dimeric proanthocyanidins, no significant influence from the degree of polymerization (DP) was observed.