Characterization of commercial green tea leaves by the analysis of low molecular weight carbohydrates and other quality indicators

Promiscuity in Polyphenol-Protein Interactions-Monitoring Protein Conformational Change upon Polyphenol-Protein Binding by Nano-Differential Fluorimetry (Nano-DSF)

In this article, we introduce nano-differential fluorimetry (nano-DSF) as an analytical technique that is suitable for investigating polyphenol-protein interactions in solution. Nano-DSF monitors conformational changes in proteins induced by external agents upon interaction at the molecular level. We demonstrate the suitability of this technique to qualitatively monitor an interaction between selected dietary polyphenols and selected proteins including BSA, ovalbumin, amylase, pepsin, trypsin, mucin and ACE-1. Protein conformational changes induced by dietary polyphenols can be investigated. As a major advantage, measurements are carried out at a high dilution, avoiding the precipitation of polyphenol-protein complexes, allowing the rapid and efficient acquisition of quantitative and qualitative binding data. From this concentration, quantitative binding data could be obtained from the fluorescence response curve in line with published values for the association constants. We demonstrate that qualitative interactions can also be established for real food extracts such as cocoa, tea or coffee containing mixtures of dietary polyphenols. Most importantly, we demonstrate that polyphenols of very different structural classes interact with the same protein target. Conversely, multiple protein targets show an affinity to a series of structurally diverse polyphenols, therefore suggesting a dual level of promiscuity with respect to the protein target and polyphenol structure.

The Release of Organic Acids and Low Molecular Weight Carbohydrates from Matcha Tea After In Vitro Digestion

BACKGROUND/OBJECTIVES

This study tested the influence of in vitro digestion on the release of organic acids and low molecular weight saccharides of matcha.

METHODS

The concentrations of analytes in the raw and undigested portion of matcha were measured using HPLC with spectrometric and refractometric detection to establish their residual values after a two-step enzymatic digestion that was finally presented as a retention factor.

RESULTS

It was established that dry matter digestibility values after simulated gastric and both gastric and intestinal phases were 67.3 and 85.9%, respectively. Native matcha, citric acid (44.8 mg/g), malic acid (32.2 mg/g), trehalose (36.1 mg/g), and L-arabinose (8.20 mg/g) reached the highest values and were predominant, whereas D-fructose, xylose, maltose, and saccharose were not detected. Regarding gastric phase digestion, succinic and malic acids, trehalose and D-glucose were the worst-releasing compounds and their remaining factors reached 34, 19, 18, and 50%, respectively, whereas L-arabinose was completely released. Focusing on gastric and small intestinal digestion, the least-releasing compounds of matcha tea leaves were succinic acid and trehalose, with their retention factors at 7 and 13%, which can proceed with the leaf matrix to the large intestine.

CONCLUSIONS

Malic, oxalic, and citric acids, the carbohydrates D-glucose, L-arabinose, and L-rhamnose, are almost entirely released from matcha tea during digestion in the stomach and small intestine and can be available for absorption in the small intestine. In the measurement of oxalic acid, considering that the process of shading tea leaves increases the concentration of this acid and its retention factor value is too small, it would be appropriate in the future to evaluate the recommended maximum daily intake of matcha tea for people sensitive to the formation of urinal stones.

Comprehensive analysis of pigment alterations and associated flavor development in strip and needle green teas

Strip/needle green teas (SGT/NGT) processed using innovative technologies are in high demand; however, mechanisms behind their color and flavor have not been comprehensively studied. We aimed to reveal the dynamics of major pigmented components (carotenoids, lipids, flavonoids, and Maillard products) and their contributions to the flavor of green teas. The total content of flavonoids in SGT and NGT were 255 ± 4.51 and 201 ± 3.91 mg·g-1, respectively; these values are slightly lower than that in fresh leaves (FLs), resulting in a fresh and sweet aftertaste. In average, carotene content in SGT/NGT (24.8 μg·g-1) was higher than in FL (17.4 μg·g-1), whilst xanthophyll content (603 μg·g-1) decreased to one-half of that in FL (310 μg·g-1). Among the 218 primary metabolites, glutamine, glutamic acid, and arginine were found to accumulate and were dominate contributors for the umami and sweet taste. Notably, more than 96 volatiles were screened and revealed their correlations with carotenoids, lipids, and amino acids. Overall, the synergism between pigments and their non-enzymatic derivates' contribution to GT characterized flavor was illustrated.

A review on matcha: Chemical composition, health benefits, with insights on its quality control by applying chemometrics and multi-omics

This review discussed the origin, manufacturing process, chemical composition, factors affecting quality and health benefits of matcha (Camellia sinensis), and the application of chemometrics and multi-omics in the science of matcha. The discussion primarily distinguishes between matcha and regular green tea with processing and compositional factors, and demonstrates beneficial health effects of consuming matcha. Preferred Reporting Items for Systematic Reviews and Meta-Analyses was adopted to search for relevant information in this review. Boolean operators were incorporated to explore related sources in various databases. Notably, climate, cultivar, maturity of tea leaves, grinding process and brewing temperature impact on the overall quality of matcha. Besides, sufficient shading prior to harvesting significantly increases the contents of theanine and chlorophyll in the tea leaves. Furthermore, the ground whole tea leaf powder delivers matcha with the greatest benefits to the consumers. The health promoting benefits of matcha are mainly contributed by its micro-nutrients and the antioxidative phytochemicals, specifically epigallocatechin-gallate, theanine and caffeine. Collectively, the chemical composition of matcha affected its quality and health benefits significantly. To this end, more studies are required to elucidate the biological mechanisms of these compounds for human health. Chemometrics and multi-omics technologies are useful to fill up the research gaps identified in this review.

The Effects of Fixation Methods on the Composition and Activity of Sea Buckthorn (Hippophae rhamnoides L.) Leaf Tea

Fixation is the key step to improve the quality of sea buckthorn leaf tea. Composition and activity are important indexes to evaluate the quality of sea buckthorn leaf tea. Comparing the effects of fixation methods on components and activities provides a theoretical basis for the contemporary, controllable, and continuous production of sea buckthorn leaf tea. The effects of six different fixed methods, pan-firing fixed (PF), steaming fixed (SF), boiling water fixed (BF), hot air fixed (HF), microwave fixed (MWF), and infrared fixed (IRF) for sea buckthorn leaf tea in terms of α-glucosidase inhibitory activity, lipase inhibitory ability, and the antioxidant capacity were studied. The total flavonoids (TF) content, total soluble phenolics (TP) content, water-soluble carbohydrate (WSC) content, the inhibitory activity of α-glucosidase, lipase inhibitory ability, and the antioxidant capacity of fixed sea buckthorn leaf tea were significantly higher ( $p\le 0.05$ ) compared with sea buckthorn leaf. IRF and MWF samples had higher ( $p\le 0.05$ ) contents of TF (92.48 mg RE/g and 79.20 mg RE/g), TP (115.37 mg GA/g and 135.18 mg GA/g) and WSC (4.24% and 4.39%). The DPPH radical scavenging activity of the SF sample was the strongest one, followed by the MWF sample and IRF sample ( $p\le 0.05$ ). The hydroxyl radical scavenging ability and reducing power of IRF were the strongest one, followed by the MWF sample ( $p\le 0.05$ ). The IRF sample had the strongest α-glucosidase inhibitory activity ( $p\le 0.05$ ), and the MWF sample had the strongest lipase inhibitory ability while samples contained the same amount of total polyphenols ( $p\le 0.05$ ). Principal component analysis results showed that the IRF sample, MWF sample, and SF sample had higher comprehensive principal component values. MWF takes less time than IRF, which operated at 2,450 MHz (full power of 700 W) for 2 min. Therefore, MWF was the most suitable fixation method for sea buckthorn leaf tea. Practical Applications. Leaf tea is the main product of sea buckthorn leaf. However, at present, the quality of sea buckthorn leaf tea in the market is uneven, the processing methods are diverse, and there is no certain quality standard. This paper provides some data support and theoretical support for the production, processing, and purchase of sea buckthorn leaf tea.

Evaluation of carbohydrates and quality parameters in six types of commercial teas by targeted statistical analysis

The content of low molecular weight carbohydrates (LMWC) of six types of tea produced from the leaves of Camellia sinensis were analyzed by hydrophilic interaction chromatography (HILIC) coupled to mass spectrometry. Quantities of sucrose, glucose, fructose, myo-inositol, maltose, mannitol, raffinose, galactinol, and stachyose were determined in samples of white, yellow, green, black, oolong, and dark tea. Sucrose was the most abundant carbohydrate in all types of tea. The concentration of all measured carbohydrates except mannitol was lowest in dark tea samples. Correlation analyses using quantitative data of LMWCs, antioxidant activity, and color parameters were performed on black tea samples to evaluate the interaction of different quality parameters. Carbohydrates depletion was observed during tea processing with formation of Amadori compounds with theanine.

Design of Experiments Assessment for the Determination of Moisture Content in Five Herbal Raw Materials Contained in Tea Products

Research interest in natural raw materials is rapidly growing due to the high demand for natural products like herbal teas. Their quality control has a direct impact on safety and efficacy. The aim of this study was to evaluate the impact of sample�s mass and temperature on moisture content in Camellia sinensis (Black tea), Cassia fistula (Senna), Chamaemelum nobile (Chamomille), Lippia alba (Juanilama) and Tilia platyphyllos (Linden) with a gravimetric method developed through a full factorial 32 DoE. A response optimizer was executed in order to establish the test conditions that allow obtaining a response according to a target value from a certified method. DoE�s ANOVA shows reproducibility for Camellia sinensis, Cassia fistula, and Lippia alba. Also, the method�s model is able to explain the response variability for all samples based on the R2 (adj). The composite desirability for the proposed conditions of analysis for the five herbal materials is satisfactory according to each target value. However, the lack of reproducibility in Chamaemelum nobile and Tilia platyphyllos and also, the response prediction problems according to the R2 (pred) for Cassia fistula and Chamaemelum nobile, suggest the execution of further studies for them. Therefore, the present method is considered to be adequate for the analysis of moisture content in Camellia sinensis and Lippia alba raw herbs.

Changes in low molecular weight carbohydrates in kale during development and acclimation to cold temperatures determined by chromatographic techniques coupled to mass spectrometry

Kale (Brassica oleracea) is a cool-season vegetable widely employed in the elaboration of diverse products such as tea and smoothies in USA or in the Northern German cuisine in wintertime. Besides, kale is gaining attention due to the diverse health benefits reported in the literature for its consumption, e.g. antigenotoxic and anticarcinogenic effect, protection of cardiovascular system and gastrointestinal tract. Low molecular weight carbohydrates (LMWC) are compounds directly related with kale flavour and nutritional quality. Despite different studies focusing on the chemical composition of kale, few information on LMWC is available. Thus, in this work a multianalytical approach was conducted in order to perform a comprehensive study of kale LMWC; their evolution during plant development and acclimation to cool temperatures was also evaluated. Gas chromatography coupled to mass spectrometry allowed the identification of 13 LMWC, being myo-inositol, galactinol, maltose and melibiose described for the first time in kale. Eight major LMWC were quantified in three different commercial kale cultivars using hydrophilic interaction liquid chromatography coupled to mass spectrometry to monitor possible differences in their content during plant development and as consequence of plant acclimation to cold temperatures. Overall, for all types of kales under study, the content of maltose and sucrose decreased during the plant development while the concentration of fructose, melibiose, maltose, raffinose and galactinol was increased in all kale types exposed to low temperatures. These results underline the importance of controlling the temperature during kale cultivation in order to obtain products with a high nutritional value.