Differentiation of green tea samples by chiral CD‐MEKC analysis of catechins content

Abstract

A chiral CD-MEKC method, enantioselective for catechin and gallocatechin, was developed, validated and applied to the analysis of tea samples. The method was addressed to the fast and simultaneous quantitation of the most represented and biologically important green tea catechins and methylxanthines. The CD-MEKC was based on SDS as surfactant (90 mM) and hydroxypropyl-beta-CD (25 mM) as chiral selector, under acidic conditions (25 mM borate-phosphate buffer, pH 2.5). The method was first applied to study the thermal epimerisation of epi-structured catechins, (-)-epicatechin and (-)-epigallocatechin, to non-epi-structured (-)-catechin and (-)-gallocatechin. The latter compounds, being non-native molecules, were for the first time regarded as useful phytomarkers of tea samples subjected to thermal treatment. The proposed method was applied to the analysis of more than twenty tea samples of different geographical origins (China, Japan, Ceylon), having undergone different storage conditions and manufacturing processes. Finally, factor analysis was used to visualise the useful information contained in the data set, showing that it was possible to distinguish tea samples on the basis of their different contents of native and non-native catechins.

At the interface of antioxidant signalling and cellular function: Key polyphenol effects

“…The naturally occurring form of epicatechin is (–)‐epicatechin (and derivatives) and of catechin is (+)‐catechin, and these are indicated when it is clear which form was used. However, some processing and extraction techniques can cause formation of (+)‐epicatechin and of (–)‐catechin , which are not resolved on a reverse phase HPLC column, and therefore not readily observed . Therefore some of the effects ascribed to (epi)catechins in this report may be due to enantiomeric mixtures, if not explicitly stated.…”

Enantioseparation of hydroxyeicosatetraenoic acids by hydroxypropyl‐γ‐cyclodextrin‐modified micellar electrokinetic chromatography

“…That is, the distribution coefficient of the solute between the pseudostationary phase and the surrounding aqueous phase determines the relative migration order. Chiral compounds have been successfully separated by MEKC when CDs have been added to the buffer solution . CDs and their derivatives have been widely used in CE for the separation of several mixtures of enantiomeric compounds.…”

Simultaneous determination of seven hydrophilic bioactive compounds in water extract of Polygonum multiflorumusing pressurized liquid extraction and short-end injection micellar electrokinetic chromatography

“…Due to the poor stability of several investigated components in alkaline condition [25-28], low pH was used in this study. Since the EOF and dissociation of the analytes were strongly suppressed in this acidic condition, the migration time mainly depended on the negative SDS micelles carrying the analytes to the detection windows.…”