Metabolomics Provides A Novel Interpretation of the Changes in Main Compounds during Black Tea Processing through Different Drying Methods

Unraveling the effects of drying techniques on chaya leaves: Metabolomics analysis of nonvolatile and volatile metabolites, umami taste, and antioxidant capacity

Chaya (Cnidoscolus chayamansa) leaves are known for their strong umami taste and widespread use as a dried seasoning. This study aimed to assess the impact of different drying methods [freeze drying (FD), vacuum drying, oven drying at 50 °C and 120 °C (OD120) and pan roasting (PR)] on the metabolome using mass spectrometry, umami intensity, and antioxidant properties of chaya leaves. The predominant volatile compound among all samples, 3-methylbutanal, exhibited the highest relative odor activity value (rOAV), imparting a malt-like odor, while hexanal (green grass-like odor) and 2-methylbutanal (coffee-like odor) are the second highest rOAV in the FD and PR samples, respectively. OD120 and PR samples possessed the highest levels of umami-tasting amino acids and 5'-ribonucleotides as well as the most intense umami taste, whereas FD samples exhibited the highest antioxidant capacity. These findings enhance our understanding of the aroma characteristics, umami taste, and antioxidant potential of processed chaya leaves.

Effects of processing technology on tea quality analyzed using high-resolution mass spectrometry-based metabolomics

Fixation is a crucial step in green tea processing that can impact quality. In this study, we explored the differences in the chemical components of steamed and fried green teas made from the same batch of fresh tea leaves using different fixing methods. Results showed that concentrations of sucrose and free amino acids were significantly higher in steamed green tea. Abundances of 12 compounds including purine nucleoside, pyrimidine nucleoside derivatives, and catechins were higher in fried green tea, while 34 compounds such as amino acids and their derivatives, benzofurans and flavonoids were higher in steamed green tea. Thus, steaming retained more compounds associated with sweet and fresh tastes, such as free amino acids, while frying produced more compounds with bitter tastes, such as catechin. This might explain why steamed green tea is mellower than fried tea.

The influence of rolling pressure on the changes in non-volatile compounds and sensory quality of congou black tea: The combination of metabolomics, E-tongue, and chromatic differences analyses

Rolling represents an essential stage in congou black tea processing. However, the influence of rolling pressure on tea flavor and non-volatile compounds remains unclear. Herein, a combination of untargeted metabolomics, tea pigments quantification, E-tongue, colorimeter and sensory evaluation was used to evaluate the effect of rolling pressure on black tea quality. As the rolling pressure increased, theaflavins (TFs), thearubigins (TRs), and theabrownins (TBs) significantly elevated. The tea metabolic profiles fluctuated and 47 metabolites were identified as key differential metabolites including flavan-3-ols, flavonol/flavone glycosides, phenolic acids, amino acids. These substances altered possibly due to the variations in enzymatic oxidation of tea phenolics and amino acids. Overall, black tea with moderate rolling pressure presented higher sweetness, lower bitterness, and higher quality index (10 TFs + TRs)/TBs. The results were verified by a validation batch. This study provided new insights into the regulation of rolling pressure and a guidance for black tea processing.

Tea Harvesting and Processing Techniques and Its Effect on Phytochemical Profile and Final Quality of Black Tea: A Review

Tea (Camellia sinensis) has grown for over 300 years and is recognized worldwide as among other well-renowned crops. The quality of black tea depends on plucking (method, standard, season, and intervals), withering and rolling (time and temperature), fermentation (time, temperature, and RH), drying (temperature and method), and storage conditions, which have a high influence on the final quality of black tea. At the rolling stage, the oxidation process is initiated and ends at the early drying stage until the enzymes that transform tea polyphenols into thearubigins (TRs) and theaflavins (TFs) are denatured by heat. By increasing fermentation time, TRs increased, and TF decreased. Each is liable for black tea's brightness, taste, and color. The amino acids and essential oils also grant a distinctive taste and aroma to black tea. Throughout withering, rolling, and fermentation, increases were found in essential oil content, but during drying, a decrease was observed. However, the Maillard reaction, which occurs when amino acids react with sugar during drying, reimburses for this decrease and enhances the flavor and color of black tea. As compared to normal conditions, accelerated storage showed a slight decrease in the total color, TF, and TRs. It is concluded that including plucking, each processing step (adopted technique) and storage system has a remarkable impact on black tea's final quality. To maintain the quality, an advanced mechanism is needed to optimize such factors to produce high-quality black tea, and an objective setting technique should be devised to attain the desirable quality characteristics.

Characterization of different grades of Jiuqu hongmei tea based on flavor profiles using HS-SPME-GC-MS combined with E-nose and E-tongue

In order to distinguish different grades of Jiuqu hongmei tea (black tea), four different grades of Jiuqu hongmei tea were used as materials in this study: Super Grade (SuG), First Grade (FG), Second Grade (SG), and Third Grade (TG). HS-SPME-GC-MS combined with electronic nose (E-nose) and electronic tongue (E-tongue) technology was used to detect and analyze tea samples. The results showed that 162 volatile substances were identified, mainly alcohols, followed by hydrocarbons, aldehydes, ketones and esters. Twenty-nine volatile compounds were found in all grades of tea samples. The results of heat map analysis showed that the relative contents of five volatile compounds in different grades of Jiuqu hongmei tea were positively correlated with the grades of Jiuqu hongmei tea. By orthogonal partial least squares discriminant analysis (OPLS-DA), 35 different compounds of SuG and FG, 30 different compounds of SG and TG, 34 different compounds of FG and SG were found. Overall, the results indicated that there were significant differences in volatile compounds among different grades of Jiuqu hongmei tea, and the use of HS-SPME-GC-MS combined with E-nose and E-tongue could provide a scientific reference method as an effective tool for detecting flavor characteristics of other types of black tea grades.

Integrated metabolomics and transcriptomics analysis reveals that the change of apoplast metabolites contributes to adaptation to winter freezing stress in Euonymus japonicus

Euonymus japonicus, a common urban street tree, can withstand winter freezing stress in temperate regions. The apoplast is the space outside the plasma membrane, and the changes of metabolites in apoplast may be involved in plant adaptation to adverse environments. To reveal the molecular mechanism underlying the winter freezing stress tolerance in E. japonicus, the changes in physiological and biochemical indexes, apoplast metabolites, and gene expression in the leaves of E. japonicus in early autumn and winter were analyzed. A total of 300 differentially accumulated metabolites were identified in apoplast fluids in E. japonicus, which were mainly related to flavone and flavonol biosynthesis, and galactose metabolism, amino acid synthesis, and unsaturated fatty acid synthesis. Integrated metabolomics and transcriptomics analysis revealed that E. japonicus adjust apoplast metabolites including flavonoids such as quercetin and kaempferol, and oligosaccharides such as raffinose and stachyose, to adapt to winter freezing stress through gene expression regulation. In addition, the regulation of ABA and SA biosynthesis and signal transduction pathways, as well as the activation of the antioxidant enzymes, also played important roles in the adaptation to winter freezing stress in E. japonicus. The present study provided essential data for understanding the molecular mechanism underlying the adaptation to winter freezing stress in E. japonicus.

Theaflavin Ameliorates Streptococcus suis-Induced Infection In Vitro and In Vivo

Streptococcus suis (S. suis) is one of the most important zoonotic pathogens that threaten the lives of pigs and humans. Even worse, the increasingly severe antimicrobial resistance in S. suis is becoming a global issue. Therefore, there is an urgent need to discover novel antibacterial alternatives for the treatment of S. suis infection. In this study, we investigated theaflavin (TF1), a benzoaphenone compound extracted from black tea, as a potential phytochemical compound against S. suis. TF1 at MIC showed significant inhibitory effects on S. suis growth, hemolytic activity, and biofilm formation, and caused damage to S. suis cells in vitro. TF1 had no cytotoxicity and decreased adherent activity of S. suis to the epithelial cell Nptr. Furthermore, TF1 not only improved the survival rate of S. suis-infected mice but also reduced the bacterial load and the production of IL-6 and TNF-α. A hemolysis test revealed the direct interaction between TF1 and Sly, while molecular docking showed TF1 had a good binding activity with the Glu198, Lys190, Asp111, and Ser374 of Sly. Moreover, virulence-related genes were downregulated in the TF1-treated group. Collectively, our findings suggested that TF1 can be used as a potential inhibitor for treating S. suis infection in view of its antibacterial and antihemolytic activity.

Effects of hot-air drying on the bioactive compounds, quality attributes, and drying and color change kinetics of coffee leaves

Drying is a key step that affects the chemical composition and quality of tea. In the present study, we reported the impacts of drying temperature and time on drying and color change kinetics, phytochemical composition, antioxidant activity, and surface microstructure of coffee leaves during hot-air drying. The results showed that drying temperature was positively (p < 0.05) correlated with the drying rate (DR), color index a* and total color change ΔE, and total soluble sugar (TSS), while negatively correlated with color indexes b* and L*, soluble protein content, and the DPPH scavenging capacity. Drying time has similar impacts on the color indexes and soluble protein as drying temperature. The content of total free amino acid and TSS increased by 62.5% and 47.4%, respectively, when coffee leaves were dried at 160°C for 24 min, under which the total phenolic content and DPPH and ABTS scavenging capacities reached the maximum of 108.04 mg GAE/g, 515.07 µmol Trolox/g, and 606.70 µmol Trolox/g, respectively. Drying significantly decreased the contents of chlorogenic acids and mangiferin and antioxidant activity, while high-temperature short-time drying helped retain phenolic compounds in coffee leaves. The DR fitted Page kinetic model. The color changes fitted the first-order kinetic models and the activation energies ranged from 16.00 to 31.06 kJ·mol^-1 . Prolonged drying time caused serious wrinkles on the surface of coffee leaves and the stomata closed. PRACTICAL APPLICATION: Drying decreased soluble protein while increasing free amino acid and soluble sugar. High-temperature short-time drying helps retain phenolics in the coffee leaves. The color change of coffee leaves during drying follows first-order kinetic. Prolonged drying time resulted in loosened texture of coffee leaves. Our study suggested that drying coffee leaves at 160°C for 24 min results in the coffee leaf tea being of better quality.

Characterization of Effects of Different Tea Harvesting Seasons on Quality Components, Color and Sensory Quality of "Yinghong 9" and "Huangyu" Large-Leaf-Variety Black Tea

Harvesting seasons are crucial for the physicochemical qualities of large-leaf-variety black tea. To investigate the effect of harvesting seasons on physicochemical qualities, the color and sensory characteristics of black tea produced from "Yinghong 9" (Yh) and its mutant "Huangyu" (Hy) leaves were analyzed. The results demonstrated that Hy had better chemical qualities and sensory characteristics, on average, such as a higher content of tea polyphenols, free amino acids, caffeine, galloylated catechins (GaCs) and non-galloylated catechins (NGaCs), while the hue of the tea brew (ΔE*ab and Δb*) increased, which meant that the tea brew was yellower and redder. Moreover, the data showed that the physicochemical qualities of SpHy (Hy processed in spring) were superior to those of SuHy (Hy processed in summer) and AuHy (Hy processed in autumn), and 92.6% of the total variance in PCA score plots effectively explained the separation of the physicochemical qualities of Yh and Hy processed in different harvesting seasons. In summary, Hy processed in spring was superior in its physicochemical qualities. The current results will provide scientific guidance for the production of high-quality large-leaf-variety black tea in South China.

Characterization of Roasting Time on Sensory Quality, Color, Taste, and Nonvolatile Compounds of Yuan An Yellow Tea

Roasting is crucial for producing Yuan An yellow tea (YAYT) as it substantially affects sensory quality. However, the effect of roasting time on YAYT flavor quality is not clear. To investigate the effect of roasting time on the sensory qualities, chemical components, odor profiles, and metabolic profile of YAYTs produced with 13 min roasting, 16 min roasting, 19 min roasting, 22 min roasting, and 25 min roasting were determined. The YAYTs roasted for 22 min got higher sensory scores and better chemical qualities, such as the content of gallocatechin (GC), gallocatechin gallate (GCG), free amino acids, solutable sugar, meanwhile the lightness decreased, the hue of tea brew color (b) increased, which meant the tea brew got darker and yellower. YAYTs roasted for 22 min also increased the contents of key odorants, such as benzaldehyde, nonanal, β-cyclocitral, linalool, nerol, α-cedrol, β-ionone, limonene, 2-methylfuran, indole, and longiborneol. Moreover, non-targeted metabolomics identified up to 14 differentially expressed metabolites through pair-wise comparisons, such as flavonoids, phenolic acids, sucrose, and critical metabolites, which were the main components corresponding to YAYT roasted for 22 min. In summary, the current results provide scientific guidance for the production of high quality YAYT.

Long-term tea consumption reduces the risk of frailty in older Chinese people: Result from a 6-year longitudinal study

Background

Vast accumulative evidence suggests that the consumption of tea and its components have various potential health benefits. This study used a longitudinal study to examine the causality between tea consumption and frailty in older Chinese people.

Methods

This study employed the longitudinal data from 2008 to 2014 of the Chinese Longitudinal Healthy Longevity Survey (CLHLS), which were systematically collected through face-to-face interviews. Two thousand four hundred and seventy three participants completed six-follow-up surveys in 2014 and were analyzed in this study. The frailty index recommended by Searle and co-authors, including 44 health deficits, was used. A Generalized Estimating Equation (GEE) was applied to determine the risk ratio (RR) with a 95% confidence interval (CI) for frailty, and further subgroup analyses were conducted to investigate whether the risk differed stratified by age, sex, and socioeconomic status. Additionally, the interaction between tea consumption with sex and frailty was tested.

Results

Of the 2,473 participants, 14.1% were consistent daily tea drinkers, and 22.6% reported frailty at the 6-year follow-up. Compared to non-tea drinkers, consistent daily tea drinkers reported a significantly lower ratio of having frailty [risk ratio (RR) = 0.54, 95% confidence interval (CI): 0.38-0.78], adjusting for sociodemographic characteristics, health behavior, socioeconomic status, and chronic illnesses. In further subgroup analyses, consistent daily tea consumption significantly reduced the risk of frailty for males (RR = 0.53, 95% CI: 0.32-0.87) but not females (RR = 0.65, 95% CI: 0.37-1.12); in the young (RR = 0.40, 95% CI: 0.22-0.74) but not in the oldest (aged ≥ 80) (RR = 0.66, 95% CI: 0.40-1.06); informal education (RR = 0.48, 95% CI: 0.28-0.84) but not formal education (RR = 0.62, 95% CI: 0.37-1.03); financial dependence (RR = 0.42, 95% CI: 0.25-0.71) but not financial independence (RR = 0.71, 95% CI: 0.41-1.23). Additionally, females showed a lower tea-mediated risk of frailty in occasional tea consumers (RR = 0.51, 95% CI: 0.29-0.89) and inconsistent tea drinkers (RR = 0.58, 95% CI: 0.37-0.93).

Conclusions

Habitual tea consumption can reduce the risk of frailty in older Chinese, and the benefit varied by age, sex, education, and financial support.