Studies On The Extraction And Activities Of Proanthocyanidins From Iongan Pericarps

Proanthocyanidins, also known as condensed tannins, are a class of oligomeric and polymeric flavan-3-ols, with kinds of biological activities. Longan pericarps, as a byproduct in the process of longan processing, was a potential source of proanthocyanidins. Therefore, in order to alleviate environment pollution pressure and enhance the added value of longan, this article analysized the antioxidant activity in vitro of extract and fractions from longan pericarps. The extraction of proanthocyanidins from longan pericarps was optimized. The extraction was then separated by Sephadex LH-20 column and were structurally characterized. Antioxidant activities in vitro and a-amylase inhibitory activity of proanthocyanidins were investigated in present work. The results were showed as below:1. Antioxidant activities in vitro were evaluated, and LPEF (ethyl acetate fraction from longan pericarps) showed the highest scavenging activities against DPPH (1,1-diphenyl-2-picrylhydrazyl) radical, ABTS [2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt] radical cation and reducing power with IC50 values of 0.506 mg/mL,0.228 mg/mL 0.253 mg/mL, respectively. LPEF possessed the highest total phenolic content of 230.816 mg GAE/g extract, expressed as gallic acid equivalents, followed by LPDF (diethyl ether fraction from longan pericarps), LPBF (n-butyl alcohol fraction from longan pericarps), LPCE (methanol crude extract from longan pericarps) and LPR (residue fraction from longan pericarps).2. The effects of extraction time (X1), solvent-to-solid ratio (X2), ethanol concentration (X3) and temperature (X4) on the yield of proanthocyanidins were investigated using response surface methodology in view of single factor experiment. An extraction time of 25 min, a solvent-to-solid ratio of 17:1 (mL/g), an ethanol concentration of 51% and a temperature of 50 ℃ were found to be optimal for extracting of proanthocyanidins from longan pericarps. Under these conditions, the yield of proanthocyanidins was 1.21%. Analysis of variance showed that the regression equation was significant fit, and the sequence of the factors was X2>X3>X4>X1.3. Proanthocyanidins from longan pericarps were separated with Sephadex LH-20 column, and then structurally characterized by UV-vis, infrared spectra (IR), nuclear magnetic resonance (NMR) and mass spectrometry (MS) methods. The mean degree of polymerization of proanthocyanidins from longan pericarps was determined to be 3.3 according to 1H NMR. I3C NMR signals showed the presence of predominantly procyanidins together with a few prodelphinidin units. MS results indicated that proanthocyanidins from longan pericarps, which were A type oligomers with degree of polymerization from 2 to 8, were predominantly composed of catechin/epicatechin.4. Antioxidant activities of proanthocyanidins were evaluated in vitro, and the results showed that proanthocyanidins have high DPPH radical scavenging activity, ABTS radical cation scavenging activity and reducing power, with IC50 values of 0.083 mg/mL,0.054 mg/mL and 0.061 mg/mL, which were comparable to Vc.5. α-Amylase inhibitory activity of proanthocyanidins from longan pericarps was evaluated. The results showed that proanthocyanidins were potent a-amylase inhibitors as evidenced by IC50 value at 0.075 mg/mL. The inhibitory type was uncompetitive inhibiton.