Determination of catechins in green tea infusions by reduced flow micellar electrokinetic chromatography

Electronic Sensor Technologies in Monitoring Quality of Tea: A Review

Tea, after water, is the most frequently consumed beverage in the world. The fermentation of tea leaves has a pivotal role in its quality and is usually monitored using the laboratory analytical instruments and olfactory perception of tea tasters. Developing electronic sensing platforms (ESPs), in terms of an electronic nose (e-nose), electronic tongue (e-tongue), and electronic eye (e-eye) equipped with progressive data processing algorithms, not only can accurately accelerate the consumer-based sensory quality assessment of tea, but also can define new standards for this bioactive product, to meet worldwide market demand. Using the complex data sets from electronic signals integrated with multivariate statistics can, thus, contribute to quality prediction and discrimination. The latest achievements and available solutions, to solve future problems and for easy and accurate real-time analysis of the sensory-chemical properties of tea and its products, are reviewed using bio-mimicking ESPs. These advanced sensing technologies, which measure the aroma, taste, and color profiles and input the data into mathematical classification algorithms, can discriminate different teas based on their price, geographical origins, harvest, fermentation, storage times, quality grades, and adulteration ratio. Although voltammetric and fluorescent sensor arrays are emerging for designing e-tongue systems, potentiometric electrodes are more often employed to monitor the taste profiles of tea. The use of a feature-level fusion strategy can significantly improve the efficiency and accuracy of prediction models, accompanied by the pattern recognition associations between the sensory properties and biochemical profiles of tea.

Quality assessment of instant green tea using portable NIR spectrometer

Caffeine and catechin are two main components of instant green tea, and are essential components of tea quality. This paper mainly focuses on the feasibility of rapidly determining instant green tea components by using a portable near infrared (NIR) spectrometer. The two main components (caffeine and catechin) were studied. In addition, the instrument performance levels of portable and benchtop NIR spectrometers were studied and compared. Quantitative models developed using portable and benchtop spectrometers for measuring caffeine, total catechins, and four individual catechins were established and compared. After preprocessing using standard normal variate (SNV), the Rp values of the caffeine, total catechins, (-)-epigallocatechin, (-)-epigallocatechin 3-gallate, (-)-epicatechin, and (-)-epicatechin gallate in the partial least squares models for a portable NIR spectrometer were 0.974, 0.962, 0.669, 0.945, 0.942 and 0.905, respectively. For a benchtop NIR spectrometer, Rp values were 0.993, 0.958, 0.883, 0.955, 0.966 and 0.936, respectively. Passing-Bablok regression method results indicated no significant differences between the two instruments. A genetic algorithm (GA) and the successive projections algorithm (SPA) were used to screen the wavelength of the NIR spectrum and establish the model. The GA obtained more robust modeling results. This study concludes that the developed portable spectroscopy system combined with appropriate variable selection methods can be effectively used for rapid determination of caffeine, total catechins, and four individual catechins in instant green tea.

Composition Analysis by UPLC-PDA-ESI (-)-HRMS and Antioxidant Activity Using Saccharomyces cerevisiae Model of Herbal Teas and Green Teas from Hainan

Different teas from everywhere are very useful and have been extensively studied. We studied the antioxidant activity of herbal teas and green teas from Hainan, Mallotus oblongifolius Muell. Arg. (MO), Ilex kudingcha C.J. Tseng (KD), Camellia sinensis var. assamica (J. W. Mast.) Kitam. Hainan Dayezhong (DY), and Camellia sinensis (L.) O. Ktze. (produced from Hainan Baisha (BS)). The total phenol content and total flavonoid content from water extracts, resin extracts and fractions of herbal teas and green teas were compared. Later, eight fractions of herbal teas and green teas were subjected to UPLC-PDA-ESI-(-)-HRMS. We determined 1-diphenyl -2-picryl-hydrazyl radical and hydroxyl free radical scavenging activity by electron paramagnetic resonance spectroscopy. We subjected Saccharomyces cerevisiae to hydrogen peroxide, stress and evaluated antioxidant activity of herbal teas and green teas in cellulo. The experiment identified more than 14 potential antioxidant compounds from herbal teas and green teas. The herbal teas and green teas had a clearance rate higher than ferulic acid at the same concentrations. MO best reduced intracellular oxidation levels and increased catalase, glutathione reductase activities, glutathione reduced and glutathione oxidized content. KD had the highest cell survival rate and reduced cell lipid peroxidation. DY best improved superoxide dismutase activity and BS was the most active in the halo test. Therefore, we concluded that MO had stronger antioxidant activity than other herbal teas and green teas from Hainan, especially, which reduce S. cerevisiae oxidative stress under H₂O₂ stress.

Phytochemical Characterization, In Vitro Antioxidant Activity, and Quantitative Analysis by Micellar Electrokinetic Chromatography of Hawthorn (Crataegus pubescens) Fruit

Due to their antioxidant properties, polyphenolic compounds are considered beneficial for human health. In this work, we investigated the polyphenol profile and antioxidant activity of edible tejocote (Crataegus pubescens) fruit extracts by micellar electrokinetic chromatography (MEKC) and HPLC/UV. The major phenolic compounds in the pulp extracts were (+)-catechin (9.17 ± 0.20 mg/100 mg dry fruit), (−)-epicatechin (4.32 ± 0.11 mg/100 mg dry fruit), and chlorogenic acid (5.60 ± 0.24 mg/100 mg dry fruit). The total phenolic content was 168.6 ± 0.9 mg gallic acid equivalent/g dry fruit; the total proanthocyanidin content was 84.6 ± 1.4 mg cyanidin/100 g dry fruit; and the total flavonoid content was 55.89 ± 1.43 mg quercetin/g dry fruit. Interestingly, procyanidins (dimers, trimers, and tetramers of (−)-epicatechin and (+)-catechin) were detected in the extract. This is the first study reporting the presence of polymeric polyphenols in Crataegus pubescens fruit. Accordingly, these fruits demonstrate great potential as a natural source of antioxidant phenolic compounds and could therefore be used as a nutraceutical and functional food.

Quantitative separation of hesperidin, chrysin, epicatechin, epigallocatechin gallate, and morin using ionic liquid as a buffer additive in capillary electrophoresis

Recently, an increasing interest has been observed in ionic liquids (ILs) due to their potentialities in various chemical processes. ILs have some unique properties making them excellent additives in CE. In this work a simple, rapid, and reliable CZE method has been developed and validated using 1-butyl-3-methyl imidazolium hexafluorophosphate (BMIM-PF₆ ) ionic liquid as a buffer additive for the determination/separation of five flavonoids including hesperedin, epicatechin (EC), epigallocatechin gallate (EGCG), and morin using photodiode array (PDA) detector. The effect of several parameters such as concentration and pH of the running buffer, applied voltage, and concentration of ionic liquid were optimized. CZE at 25°C with 25 mM borate buffer of pH 9.0 at an applied voltage of 17 kV by adding 17.5 mM of IL was found to be suitable for the separation/determination of all five analytes within 08 min. Validation of the method was performed in terms of linearity, accuracy, precision, and limit of detection and quantification. The calibration curves were plotted in the concentration range of 1-200 μg/mL for all five analytes. The response was linear with R²  = 0.990 for EC, chrysin, and hesperidin, 0.992 for morin, and 0.988 for EGCG. LOD and LOQ were obtained within the range of 0.4-0.5 and 1.4-1.7 μg/mL, respectively. The proposed method showed good reproducibility with RSD of less than 3% for both migration time and peak height. The method was successfully applied for the determination of flavonoids from citrus fruits and tea samples.

Modelling Extraction of White Tea Polyphenols: The Influence of Temperature and Ethanol Concentration

The optimization of the extraction of natural antioxidants from white tea has fostered intensive research. This study has investigated the effects of ethanol-water mixtures, temperature and time on the extraction of polyphenols and antioxidant components from white tea. The response surface methodology was applied to identify the best extraction conditions. The best conditions to maximize the extraction of total polyphenols were: ethanol, 50%, for 47.5 min. Although the yield of polyphenols was optimal at 65 °C, the maximum antioxidant capacity was achieved with an extraction temperature of 90 °C. This study has identified the optimal conditions for the extraction of tea liquor with the best antioxidant properties. Epigallocatechin gallate, epicatechin gallate, epigallocatechin and epicatechin were extracted from white tea at concentrations up to 29.6 ± 10.6, 5.40 ± 2.09, 5.04 ± 0.20 and 2.48 ± 1.10 mg/100 g.

Advance of CE and CEC in phytochemical analysis (2012–2013)

This article presents an overview of the advance of CE and CEC in phytochemical analysis, based on the literature not mentioned in our previous review papers [Chen, X. J., Zhao, J., Wang, Y. T., Huang, L. Q., Li, S. P., Electrophoresis 2012, 33, 168–179], mainly covering the years 2012–2013. In this article, attention is paid to online preconcentration, rapid separation, and sensitive detection. Selected examples illustrate the applicability of CE and CEC in biomedical, pharmaceutical, environmental, and food analysis. Finally, some general conclusions and future perspectives are given.

In vitro antioxidant capacity of tea of Echinodorus grandiforus, “leather hat,” in Wistar rat liver

Oxidative stress has been considered as one of the factors responsible for hepatic diseases, which sometimes require new ways of treatment. The present study aimed to evaluate the in vitro antioxidant capacity of the tea of Echinodorus grandiforus (“leather hat” plant) in rat liver. Different preparations of tea were evaluated for phenolic composition, antioxidant activity by DPPH assay and ability to inhibit lipid peroxidation induced by copper sulfate. The antioxidant activity was assessed in liver tissue treated with sodium azide in the presence or absence of tea by assays for lipid peroxidation (TBARS), protein oxidation (carbonyl) and the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD). The results show that different preparations of tea are important sources of polyphenols and contain theobromine, catechin and vitexin. Furthermore, the results indicate that this tea exhibits an antioxidant activity by its ability to scavenge DPPH radical. Different preparations of tea prevented damage to lipids and proteins induced by sodium azide, as well as assisting in restoring CAT and SOD activities. Thus, it can be seen that E. grandiforus tea had antioxidant activity in serum and liver being able to prevent oxidative damages generated by sodium azide.

Radical scavenging of white tea and its flavonoid constituents by electron paramagnetic resonance (EPR) spectroscopy

White tea (WT) presents high levels of catechins, which are known to reduce oxidative stress. WT is the least processed tea, unfermented and prepared only from very young tea leaves. The subject of this paper is the use of the spin trap method and electron paramagnetic resonance (EPR) spectroscopy as the analytical tool to measure, for the first time, the radical scavenging activity of WT and its major catechin components, epicatechin (EC), epicatechin-3-gallate (ECG), epigallocatechin (EGC), and epigallocatechin-3-gallate (EGCG), against the methoxy radical, using ferulic acid as antioxidant pattern. The antioxidant activity has been measured by the decrease of the intensity of the spectral bands of the adduct DMPO-OCH3 in the EPR with the amount of antioxidant in the reactive mixture. Tea leaves and buds were extracted with waterless methanol. It has been proved that tea compounds with more antiradical activity against methoxy radical are those with the gallate group, EGCG and ECG.

Estimation of tea catechin levels using micellar electrokinetic chromatography: a quantitative approach

A simple, inexpensive micellar electrokinetic chromatography (MEKC) method with UV detection was used to determine seven catechins and one xanthine (caffeine) in tea. All the compounds were successfully separated (15kV) within a 15-min migration period with a high number of theoretical plates (>8.0×10(4)) in a running buffer (pH 7) containing 10mmoll(-1) sodium tetraborate, 4mmoll(-1) sodium phosphate, and 25mmoll(-1) SDS. The regression lines of all standard catechins were linear within the range of 0.03-4μgml(-1). Green tea infused at 95°C for 10min showed higher levels of catechins (especially epigallocatechin galate, epicatechin gallate, and epicatechin) than tea infused at 80°C. In addition, major differences were observed in the levels of catechins in the first and second infusions (both brewed at 95°C for 10min). Finally, green tea leaves were infused separately with tap water, deionised water, spring water, reverse osmosis water, and distilled water at 95°C, and the catechin content of the infusions was investigated by the proposed method. In the infusion brewed with tap water, catechins appeared to be epimerisation from the epistructure to the nonepistructure. This epimerisation may take place more readily in tap water than in distilled water owing to the complexity of the ions present in tap water.

Analysis of some selected catechins and caffeine in green tea by high performance liquid chromatography

Green tea seems to have a positive impact on health due to the catechins-found as flavanols. Thus, the present study was aimed to develop a low cost reversed phase high performance liquid chromatographic (HPLC) method for simultaneous determination of flavanol contents, namely catechin (C), epicatechin (EC), epigallocatechin (EGC), epicatechin 3-gallate (ECG) and epigallocatechin 3-gallate (EGCG) and caffeine in 29 commercial green tea samples available in a Saudi Arabian local market. A C-18 reversed-phase column, acetonitrile-trifluoroacetic acid as a mobile phase, coupled with UV detector at 205 nm, was successfully used for precise analysis of the tested analytes in boiled water of digested tea leaves. The average values of N (No. of theoretical plates), HETP (height equivalent of theoretical plates) and R(s) (separation factor) (at 10 μg ml(-1) of the catechins EC, EGC, EGCG and ECG) were 2.6×10(3)±1.2×10(3), 1.7×10(-3)±4.7×10(-4) cm and 1.7±5.53×10(-2), respectively. The developed HPLC method demonstrated excellent performance, with low limits of detection (LOD) and quantification (LOQ) of the tested catechins of 0.004-0.05 μg ml(-1) and 0.01-0.17 μg ml(-1), respectively, and recovery percentages of 96-101%. The influence of infusion time (5-30 min) and temperature on the content of the flavanols was investigated by HPLC. After a 5 min infusion of the tea leaves, the average concentrations of caffeine, catechin, EC, EGC, ECG and EGCG were found to be in the ranges 0.086-2.23, 0.113-2.94, 0.58-10.22, 0.19-24.9, 0.22-13.9 and 1.01-43.3 mg g(-1), respectively. The contents of caffeine and catechins followed the sequence: EGCG>EGC>ECG>EC>C>caffeine. The method was applied satisfactorily for the analysis of (+)-catechin, even at trace and ultra trace concentrations of catechins. The method was rapid, accurate, reproducible and ideal for routine analysis.