Study On Proanthocyanidins From Sea Buckthorn Seed

Sea buckthorn (Hippophae Linn) has been recognized as a versatile nutraceutical crop with great economic and environmental potential in China in recent years, which has led to development of over 1.3×106 hectares of sea buckthorn orchards. The main application of the sea buckthorn seeds, estimated to be about 26.3×104 tones per annum, is to extract oil. Proanthocyanidins from sea buckthorn seed have attracted increasing attention recently. Plant proanthocyanidin displays various types of physiological function including antioxidant activity, anti-tumor activity and anti-hypertensive activity. In this work, systematic experiments were carried out on characterization of proanthocyanidins from sea buckthorn seeds. The methods for measurement of sea buckthorn seed proanthocyanidins were studied. The antioxidant activity of sea buckthorn seed proanthocyanidins was evaluated using different model systems. Furthermore, the proanthocyanidin compounds were purified and their structures were elucidated.Antioxidant-rich fractions were extracted from the seeds of sea buckthorn using various solvents and analyzed for their phenolic components. The antioxidant activity of the extracts was evaluated using a copper-catalyzed lecithin liposome oxidation assay, DPPH assay and reducing power assay. The results showed that proanthocyanidins were the predominating polyphenols while flavonols represented minor components in all extracts. 70% acetone was found to be the most effective for the extraction of proanthocyanidins. 70% acetone extract gave the highest antioxidant activity in a copper-catalyzed lecithin liposome oxidation assay, which also showed good reducing power and DPPH radical scavenging capacity. Positive correlations were found between proanthocyanidin content and antioxidant activity of sea buckthorn seed extracts.The proanthocyanidin compounds were isolated and purified by column chromatography with polyamide, Toyopearl HW-40F, Sephadex LH-20 and ODS. Their structures were elucidated on the basis of spectral data (MS, 1H-NMR and 13C-NMR). Four monomeric flavan-3-ols and two dimeric procyanidins were identified as catechin (Ⅰ), epicatechin (Ⅱ), gallocatechin (Ⅲ), epigallocatechin (Ⅳ), catechin-(4α-8)-catechin (procyandin B3,Ⅴ)and gallocatechin-(4α-8)-epicatechin (Ⅵ). CompoundⅤandⅥwere obtained from Hippophae for the first time.Depolymerization of procyandin B3 in the presence of benzyl mercaptan was studied to develop a method for proanthocyanidin determination. Degradation products were separated and identified by HPLC in combination with electrospray ionization mass spectrometric detection (HPLC/ESI-MASS) and different reaction conditions were compared. The results showed the heterocyclic ring cleavage product of the extension unit was the main product in the side reaction of thiolysis. The highest deploymerization yield (88.7%) and lowest extent of epimerization (2.2%) obtained with 40℃30 min treatment made it suitable for the structural analysis and quantitative determination of proanthocyanidins.The monomeric flavan-3-ols, oligomeric and polymeric proanthocyanidins were isolated...