Catechins In Tea Samples Research Articles

Indicator displacement assay for freshness monitoring of green tea during storage

Aging of green tea leads to reductions in its flavor and health value, yet in situ testing methods for green tea freshness are lacking. A novel sensitive indicator displacement assay (IDA) sensor was constructed and applied for monitoring of green tea freshness during storage. Low-cost pH dyes and metal ions were used as indicators and receptors, respectively, for the targeted detection of catechins in tea samples. The feasibility of the IDA reaction was verified using images and UV–vis spectroscopy, respectively. IDA combined with supervised algorithms achieved accurate identification of green tea freshness with an accuracy of 86.67%, and acceptable accuracies in the prediction of catechin monomers and total catechins with ratio of prediction to deviation values over 1.5. Thus, the developed IDA sensor is capable of qualitative and quantitative monitoring of the green tea freshness during storage, providing a new option for quality evaluation and control of green teas.

Quantification of tea-derived catechins without the requirement for respective calibration curves by single reference liquid chromatography based on relative molar sensitivity.

Many studies report the monitoring of catechins in tea samples by chromatographic techniques. Unfortunately, only a small number of screening assays for catechins exist as a result of the complexity of authentic standards for the respective calibration curves. In the present study, a single reference (SR) exhaustive assay for the simultaneous quantification of tea-derived catechins by liquid chromatography (LC) with photodiode array and fluorescence detectors based on relative molar sensitivity (RMS) was developed as a screening assay of common tea samples without respective calibration curves using authentic standards. Three original SR standards were proposed based on flavonoid structures, evaluated by quantitative 1 H-NMR based on an indirect standard (1,4-bis(trimethylsilyl) benzene-d4 ) and successfully separated in a LC chromatogram. In tea samples with these added SR calculated based on RMS, the concentrations of eight tea-derived catechins could be measured with a relative SD of < 8.5% by a single LC run. This LC screening assay based on RMS allows reliable quantification without the requirement for respective calibration curves using authentic standards. © 2020 Society of Chemical Industry.

Separation and determination of six catechins in tea by pressurized capillary electrochromatography

An efficient pressurized capillary electrochromatography (pCEC) method has been successfully developed for the determination of six catechins in tea. The separation was performed on a reversed-phase EP-100-20/45-3-C18 capillary column (total length of 45 cm, effective length of 20 cm, diameter of 100 μm, ODS packing inside for 3 μm). The mobile phase ratio of organic phase, the concentration of phosphate buffer and sodium heptanesulfonate, separation voltage, and other experimental conditions were investigated and optimized. The mobile phase was 15 mM NaH2PO4 and 12 mM sodium heptanesulfonate (pH 3.0)/methanol (64:36) at a flow rate of 0.04 mL/min. Under optimal conditions including applied voltage of −4 kV and a UV detection wavelength of 230 nm, the six catechins in the tea were well separated. The calibration curves for the analytes had good linearity in the range of 8.02 μg/mL–202.13 μg/mL with a correlation coefficient of 0.9928–0.9997. The limits of detection (LOD) for the six catechins were 4.62 μg/mL–11.63 μg/mL (S/N = 3). The recoveries of the six catechins were 96.2%–108.4% with a relative standard deviation (RSD) between 0.78% and 4.51%. The method has been used for the determination of six catechins in tea samples with good results.

Preparation and application of magnetic graphene oxide coated with a modified chitosan pH-sensitive hydrogel: an efficient biocompatible adsorbent for catechin

A MSPE method using a pH-sensitive green chitosan-based adsorbent coupled with GC-MS was developed for determination of catechin in tea samples.

Controlled electrochemical synthesis of yttrium (III) hexacyanoferrate micro flowers and their composite with multiwalled carbon nanotubes, and its application for sensing catechin in tea samples

We report the hierarchical growth of yttrium (III) hexacyanoferrate (YHCF), having a shape that resembles that of rose flower petals on a glassy carbon electrode (GCE) modified with functionalized multiwalled carbon nanotubes. The modified GCE displays excellent electrocatalytic activity toward catechin (CA) oxidation. The morphology and impedimetric response of YHCF were optimized by controlling the number of depositing cycles. As-synthesized YHCF micro flower was characterized by thin film X-ray diffraction (XRD) and infrared (IR) spectroscopic methods, respectively. By taking the advantage of a template-free, surfactant-less, and simple procedure, YHCF micro flowers have been prepared. The sensitivity and low detection limit of functionalized multiwalled carbon nanotube (fMWCNT)/YHCF/GCE toward CA are 1.311 μA μM−1 cm−2 and 0.28 μM, respectively. Moreover, the fabricated GCE exhibits sufficient recovery for CA determination in green tea and oolong tea samples.

Electrochemical Characterization of Epigallocatechin Gallate Using Square‐Wave Voltammetry

AbstractElectrochemical oxidation of (−)‐epigallocatechin gallate (EGCG), the main monomer flavanol found in green tea, has been investigated over a wide pH range at a glassy‐carbon electrode using square‐wave voltammetry (SWV). Square‐wave voltammograms of (−)‐epigallocatechin (EGC) and gallic acid have been studied as well. The I–E profile of EGCG, i.e. the oxidation potentials and the current responses of the first and the second peak, is pH dependent. The oxidation of EGCG is a quasireversible process over the studied pH range, which was also confirmed by the non‐linear relationship between the peak currents and squre root of frequency. The best SWV responses for EGCG were obtained at pH 2.0, frequency of 100 Hz, step of 2 mV and amplitude of 50 mV. Under these conditions, linear responses for EGCG were obtained for concentrations from 1×10−7 M to 1×10−6 M, and calculated LOD and LOQ for the first oxidation peak were 6.59×10−8 M and 2.19×10−7 M, respectively. The proposed electroanalytical procedure was applied for the determination of EGCG content in green tea. Developed SWV methodology represents a potential analytical tool in determination of catechins in tea samples.

Determining enediol compounds in tea using surface‐assisted laser desorption/ionization mass spectrometry with titanium dioxide nanoparticle matrices

We describe the use of titanium dioxide nanoparticles (TiO2 NPs) as selective probes and matrices for the determination of catechins using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). The interactions between the enediol compounds and TiO2 NPs were evident by the change in color of the TiO2 NP solution from milky white to orange. Through these interactions, the TiO2 NPs could be used to concentrate enediol compounds, including catechins and ascorbic acid. The limits of detection (LODs) for three catechins--catechin, (-)-epigallocatechin, and (-)-epigallocatechin gallate--at a signal-to-noise ratio of 3 were 0.45, 1.85 and 0.65 microM, respectively. The TiO2 NP matrices provide a number of advantages over conventional organic matrices (e.g. 2',4',6'-trihydroxyacetophenone), including ease of sample preparation, less background noise in the low-mass region, and high repeatability. The applicability of this method was confirmed through the high reproducibility of the determination of the two catechins in tea samples that had not been subjected to any sample preparation procedures (shot-to-shot variation: <10%).

Simultaneous analysis of theanine, chlorogenic acid, purine alkaloids and catechins in tea samples with the help of multi-dimension information of on-line high performance liquid chromatography/electrospray–mass spectrometry

A reverse phase high performance liquid chromatography (RP-HPLC) separation coupled with photo diode array detection (DAD) and electrospray ionization mass spectrometry (ESI–MS) detection was established for the analyzing of multiple bioactive compounds in tea and tea extracts. Theanine, chlorogenic acid, purine alkaloids and catechins were identified with authentic standard compounds and with MS-spectra. The content of theanine and catechins was measured by employing DAD and caffeine, chlorogenic acid, theobromine and theopylline by protonated molecular ion on selective ion recording (SIR) mode. The unity of LC/ESI–MS provides more qualitative and quantitative information comparing with general HPLC in the analysis of multi-components in tea, and complex extraction or sample pretreatment is unnecessary. The chromatogram acquired by using this method can be used as a bioactive components fingerprint for the quality control of tea and its extracts. With the help of multi-dimension information of HPLC–DAD–ESIMS, the compounds owning different chemical structure such as amino acid, catechins, etc. in tea and its extracts could be identified and determined in one run successfully.