Abstract
Proanthocyanidins in Chinese bayberry leaves (PCBLs) were qualitatively analyzed. NMR data suggest that PCBLs are mostly composed of (epi)gallocatechin gallate units. Matrix-assisted laser desorption time-of-flight MS data indicate 95 possible prodelphinidin structures, ranging from dimers to tridecamers. Preparative normal-phase HPLC and further analysis by reverse-phase HPLC together with electrospray ionization MS enabled detection of 20 compounds, including seven newly identified compounds in Chinese bayberry leaves. The antioxidant capacity of PCBLs was evaluated by (1,1-diphenyl-2-picryl-hydrazyl), ferric-reducing antioxidant power, and oxygen radical absorption capacity assays. The EC50 of DPPH radical scavenging activities (as 50% decrease in the initial DPPH concentration) were 7.60 µg. The FRAP and ORAC values were 8859.33±978.39 and 12991.61±1553.34 µmol Trolox equivalents per gram, respectively. The results indicate the high antioxidant potency of PCBLs.
Highlights
Proanthocyanidins (PAs), called condensed tannins, are a class of colorless phenolics characterized by an oligomeric or polymeric structure based on flavan-3-ol units [1]
All other reagents and solvents used were of analytical grade, unless stated otherwise. 2,5-Dihydroxybenzoic acid (DHB), trifluoroacetic acid (TFA), 6-hydroxy-2,5,7,8-tetramethyl-choman-2-carboxylic acid (Trolox), 2,29-azobis(2-methylpropionamidine)dihydrochloride (AAPH), (1,1-diphenyl-2-picrylhydrazyl) (DPPH), 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ), 29,79dichlorofluorescin diacetate, and fluorescein disodium salt were purchased from Sigma-Aldrich
This study demonstrated by NMR spectroscopy that Chinese bayberry leaves PAs are mostly composed of (E)gallocatechin gallate (GCG) units
Summary
Proanthocyanidins (PAs), called condensed tannins, are a class of colorless phenolics characterized by an oligomeric or polymeric structure based on flavan-3-ol units [1]. PAs can be divided into several classes on the basis of the hydroxylation patterns of their constitutive units and the linkages between them (Figure 1). Flavan-3-ol units are most frequently linked via B-type bonds, namely, C4RC8 or C4RC6 linkages [2]. An additional C2RO7 or C2RO5 linkage may exist, leading to doubly bonded A-type PAs [3]. The most common constitutive units of propelargonidin, procyanidin, and prodelphinidin are (epi)afzelechin [(E)AF], (epi)catechin [(E)CA], and (epi)gallocatechin [(E)GC], respectively [3]. Some of these units could be esterified with other moleculars such as glucose or gallic acid[5]. The chromatographic separation of PAs is complicated because of the enormous variety of similar isomeric oligomers in plant or food sources [6]
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