Chun Mee green tea (CMGT), one of the major export teas from China, has a comprehensive classification (grading) system. However, the chemical constituents underlying grade differentiation, as well as their associations with astringency and bioactivity, remain unclear. In this study, we integrated quantitative descriptive analysis (QDA), tea-mucin complex analysis, in vitro bioactivity evaluations, and metabolomics, supported by Random Forest (RF) modeling and correlation analysis. QDA demonstrated that higher-grade samples exhibited superior overall sensory quality and stronger astringency. Tea-mucin complex analysis (turbidity, particle size, SEM) confirmed reduced aggregation in lower grades, consistent with weaker astringency. Quantitative analysis revealed a significant decrease in major flavor compounds (EGCG, caffeine, and amino acids) as the grade declined. Liquid chromatography-mass spectrometry (LC-MS)-based metabolomics further classified samples into high-grade (T1, T2, T3) and low-grade (T4, T5, T6, 1, 2) clusters, identifying 68 grade-differentiating markers. High-grade teas exhibited stronger antioxidant activity and inhibition effects on α-amylase and α-glucosidase. RF and correlation analysis revealed that catechins, phenolic acids, hydrolysable tannins, and acylated quercetin glycosides were critical for grading, with trans-p-coumaroylquinic acid and its derivatives contributing significantly to both astringency and antioxidant capacity. In addition, a grade estimation model based on four compounds (5-galloylquinic acid, EGCG, ECG, GCG) was constructed using elastic net and ridge regression, achieving high accuracy (R² = 0.995, RMSE = 0.168). Commercial samples verification confirmed the model’s reliability for ranking CMGT grades from the same factory. These findings provide an objective approach for grade evaluation and may facilitate the refinement of CMGT grading standards.

The taste of tea infusion is one of the important indicators to evaluate the tea quality. The main taste characteristics include bitterness, astringency, umami, sweetness, and sweet after taste. The flavor of tea is the comprehensive effect of various flavor substances in tea, such as catechins, flavonol glycosides, amino acids, purine alkaloids, etc. With the development of molecular sensory science, an increasing number of flavor substances in tea and their corresponding taste properties have been clarified. The present study focuses on the typical taste characteristics of tea to primarily review the material basis of tea taste formation, the significant impact of processing technology on the formation of taste of different tea types, and analyze the interaction effect between some taste substances. The goal of this paper is to provide a reference for the study of tea taste.

Aroma is one of the key factors in evaluating tea quality. Tea aroma substances can be divided into four major categories according to their formation pathways: amino acid-derived volatiles, glycosidically bound volatiles,fatty acid-derived volatiles, and carotenoid-derived volatiles. The presence of diverse volatile aroma compounds in tea,with varying concentrations and composition ratios, results in distinct aroma characteristics. Numerous studies have used analytical chemistry methods to investigate the composition of tea aroma compounds, and further applied molecular sensory science to explore the content and profiles of key aroma compounds. Recombinant and omission experiments have been conducted to identify the key aroma compounds responsible for typical tea aroma profiles. Based on the application of molecular sensory science in the study of tea aroma compounds, the present study discusses the major aroma compounds in tea, summarizes the key components of distinct aroma types, and examines the synergistic and masking effects among these aroma substances. Furthermore, the formation mechanisms (pathways) of tea aroma compounds are summarized, providing a reference for future research of tea flavor chemistry.

This work aims to compare the chemical composition and anti-inflammatory effects on RAW264.7 macrophages of Keemun black tea stems and leaves. A total of 50 volatile compounds were identified in tea stems and leaves, and aldehydes, alcohols, and esters were the main volatile compound categories. There were 11 key volatile compounds, including geraniol, benzeneacetaldehyde, methyl salicylate, linalool, etc. contributed to distinguishing the tea stems from the tea leaves. In the quantitative and liquid chromatography-mass spectrometry (LC-MS)-based metabolomics analysis, higher contents of amino acids, monosaccharides, and quinic acids were found in stems than those in leaves. Inversely, higher contents of tea pigments, flavan-3-ols, gallic acid, purine alkaloids, and flavonol glycosides were present in tea leaves than in stems. LC-MS-based metabolomics also revealed that organic acids were the most critical non-volatile compounds responsible for the differences between tea stems and leaves. Furthermore, tea stems had better inhibiting effects of pro-inflammatory cytokines (interleukin (IL)-1β and IL-6) in lipopolysaccharide-challenged RAW264.7 macrophages than tea leaves, while no significant differences exist between leaves and stems for inhibiting the secretion of tumor necrosis factor α (TNF-α) and NO. In conclusion, our results support using Keemun black tea stems as a novel source of anti-inflammatory compounds.

Larger-leaf yellow tea (LYT) is a characteristic type of Chinese tea produced in Huoshan County, Anhui Province, which is made by mature leaves with stems. According to recent report, LYT showed competitive effects in anti-hyperglycemia in comparison to other teas such as green or black tea. However, the bioactive compounds of LYT are still undiscovered so far. For this purpose, 5 fractions of LYT were prepared by sequential extraction. The in vitro bioassay results indicated that the ethyl acetate fraction of LYT had the strongest inhibitory effects on α-glucosidase and α-amylase. Fluorescence-quenching analysis and protein-binding test revealed that the compounds of ethyl acetate fraction could inhibit α-glucosidase and α-amylase activities through binding to enzymes or other mechanisms. All chromatographic peaks of high-performance liquid chromatography (HPLC) of ethyl acetate fraction were separated and collected. The purified compounds were identified by liquid chromatography-mass spectrometry (LC-MS), and subsequently screened by calculating their inhibition ratio on α-glucosidase at the real concentration in LYT infusion. The results showed that (–)-epigallocatechin gallate, (–)-gallocatechin gallate, caffeine, N-ethyl-2-pyrrolidone-substituted flavan-3-ols were effective inhibitors for α-glucosidase.

Roasting is a common manufacture technology for processing various teas. It is not only used in decreasing the water content of finished tea, but also improving the flavor of teas. In the present study, the roasted and non-roasted teas were compared by liquid-chromatography mass spectrometry and sensory evaluation. The roasted tea tasted less bitter and astringent. The content of main galloylated and simple catechins, caffeine and theobromine in roasted were significantly lower than non-roasted teas. Targeted taste-compounds metabolomics revealed that (–)-epigallocatechin gallate, kaempferol-glucose-rhamnose-glucose and (–)-epicatechin gallate were main contributors tightly correlated to astringent intensity. Flavonol glycosides including kaempferol-glucose, quercetin-glucose, kaempferol-glucose-rhamnose-glucose, and quercetin-glucose-rhamnose-glucose in roasted teas were also significantly less than non-roasted teas. To study the chemical changes during roasting, tea with a strong astringency was roasted under 80, 100, 120, 140, and 160 ℃. With the increase of roasting temperature, the bitter and astringent intensity of tea was gradually decreased, but the main astringent compounds including (–)-epigallocatechin, (–)-epigallocatechin gallate and kaempferol/quercetin glycosides were irregularly varied with temperature. The Pearson correlation coefficient analysis suggested procyanidin B2, coumaroylquinic acids and gallotannins were tightly correlated to the astringent and bitter perceptions, while N-ethyl-2-pyrrolidone-substituted flavan-3-ols were negatively correlated.