Abstract
N-Ethyl-2-pyrrolidinone-substituted flavanols (EPSF) are marker compounds for long-term stored white teas. However, due to their low contents and diasteromeric configuration, EPSF compounds are challenging to isolate. In this study, two representative epimeric EPSF compounds, 5′′′R- and 5′′′S-epigallocatechin gallate-8-C N-ethyl-2-pyrrolidinone (R-EGCG-cThea and S-EGCG-cThea), were isolated from white tea using centrifugal partition chromatography (CPC). Two different biphasic solvent systems composed of 1. N-hexane-ethyl acetate-methanol-water (1:5:1:5, v/v/v/v) and 2. N-hexane-ethyl acetate-acetonitrile-water (0.7:3.0:1.3:5.0, v/v/v/v) were used for independent pre-fractionation experiments; 500 mg in each separation of white tea ethyl acetate partition were fractionated. The suitability of the two solvent systems was pre-evaluated by electrospray mass-spectrometry (ESI-MS/MS) analysis for metabolite distribution and compared to the results of the CPC experimental data using specific metabolite partition ratio KD values, selectivity factors α, and resolution factors RS. After size-exclusion and semi-preparative reversed-phase liquid chromatography, 6.4 mg of R-EGCG-cThea and 2.9 mg of S-EGCG-cThea were recovered with purities over 95%. Further bioactivity evaluation showed that R- and S-EGCG-cThea possessed in vitro inhibition effects on α-glucosidase with IC50 of 70.3 and 161.7 μM, respectively.
Highlights
Tea (Camellia sinensis, Theaceae) is one of the most consumed beverages in the world due to its health benefits and pleasant flavor [1,2]
Zhu et al investigated the enantiomeric distributions of 23 volatile lactones and terpenoids in white teas and found that S-linalool content and S/R-dihydro-actinidiolide ratio significantly decreased and increased, respectively with the change of storage time, serving as potential markers for the reliable differentiation of white teas stored over different time periods [6]
For non-volatile compounds, Ning et al found that the contents of flavanols and amino acids decreased with increasing storage duration, while gallic acid increased [7]
Summary
Tea (Camellia sinensis, Theaceae) is one of the most consumed beverages in the world due to its health benefits and pleasant flavor [1,2]. Besides long-term stored white teas [8,9], EPSF compounds were discovered in fresh. The contents of EGCG, R- and S-EGCG-cThea were approximately 47.1, 0.8, and 0.4 mg/g in stored white teas, respectively [8,18]. Due to their low contents, the occurrence of epimeric compounds, and the interference of high-content. EGCG, the isolation procedures of R- and S-EGCG-cThea from white teas are extremely challenging and require various processing steps, which limit further investigation into the health benefits of epimeric EPSF compounds.
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