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At present, several novel pile-fermentation styles have been developed for ripened Pu-erh tea (RPT) processing. In this study, tea pigments, phenolic compounds, purine alkaloids and amino acids in six RPTs produced through three various fermentation styles were determined by using HPLC and amino acid analyzer to reveal chemical differences caused by fermentation style, respectively. Additionally, dynamic changes of phenolic compounds and purine alkaloids were explored during a whole new-type fermentation. Despite three various fermentation styles, these RPTs demonstrated consistent sensory and major quality components including three tea pigments, two flavonoids and three purine alkaloids. However, RPTs of the new-type fermentation had relatively higher contents of seven catechins, gallic acid, two flavonols (i.e. quercetin and kaempferol), two other flavonoids (i.e. rutin and luteolin) and 10 amino acids such as l -theanine and l -arginine. The new-type fermentation decelerated the degradation of four galloylated catechins, rutin, amino acids and soluble sugars, but contributed to the accumulations of three non-galloylated catechins, two flavonols, luteolin and gallic acid. Therefore, the new-type fermentation could be a potential style for RPT processing with a shorter fermentation cycle. • Sensory, quality constituents exhibit consistency among various fermentation styles. • Fermentation style affect phenolic compounds, amino acids in ripened Pu-erh teas. • New-type fermented tea contain higher catechins, flavonols, gallic acid, amino acids. • New-type fermentation accumulated 3 catechins,2 flavonols, luteolin and gallic acid. [ABSTRACT FROM AUTHOR]

To explore the impact of harvest season in white tea, high-performance liquid chromatography (HPLC) and amino acid analyzer were developed for the determinations of 17 phenolic compounds, 3 purine alkaloids, 19 amino acids, γ-aminobutyric acid (GABA) and 4 main quality components in 18 Bai mudan sub-type of Xinyang white teas harvested in spring, summer and autumn seasons, respectively. Additionally, the in vitro antioxidant capacity was evaluated by 5 various assays. Principal component analysis (PCA), hierarchical cluster analysis (HCA) and partial least squares-discriminant analysis (PLS-DA) could completely classify these white teas by the harvest season, and indicated its profound impact on chemical composition in white tea. 14 Characteristic compounds (VIP ≥1.0), such as (−)-epigallocatechin (EGC), gallic acid, caffeine, l -theanine, conduced to identify the harvest season of white tea. Through comparison, the spring tea was observed to possess the highest amino acids, catechins contents and in vitro antioxidant capacity. (−)-Epicatechin (EC), EGC, (−)-epicatechin gallate (ECG) and (−)-epigallocatechin gallate (EGCG) were considered as the major antioxidants in white tea due to their highly significantly (p < 0.01) positive correlations. Overall, the research results provided support for the identification of harvest season in white tea. • Xinyang white teas were classified by harvest season through multivariate statistical analysis. • Spring and autumn teas possessed relatively higher amino acids, catechins and gallic acid. • 14 Characteristic compounds (VIP ≥1.0) conduced to identify the harvest season of white tea. • Spring tea had the highest antioxidant capacity of FRAP, ABTS, HSA and SSA. • EC, EGC, ECG and EGCG were confirmed as major antioxidants in the white tea. [ABSTRACT FROM AUTHOR]

This study investigated the changes of main quality components and the effect of bioactivities of black tea during a manufacturing process that adds to enzymatic treatment. It used black tea harvests in summer and autumn for manufacturing and analyzed the number of main quality components and bioactivities of the black tea produced by treating cellulase during rolling and polyphenol oxidase (PPO) and peroxidase (POD) during fermentation. The results found that the contents of total catechins (TC), total polyphenols (TP), reducing sugars (ReS), and individual catechins in the tea infusions of summer and autumn black tea that were obtained during enzymatic treatments decreased significantly (p < 0.05). However, the content of free amino acid (FAA), the tea quality parameter such as the total liquor color (TLC), the briskness index (BI), and the tea pigments including total theaflavin (TF), thearubigens (TR), TRSI, and TRSII all increased significantly (p < 0.05). Moreover, the biological activity enhanced black tea's antioxidant and metabolic capacity with enzymatic treatments were proved by in vitro experiments. The results of this study contribute to gaining further knowledge on how black tea's quality and potential health benefits are maximized by using exogenous enzyme addition methods in the manufacturing process preparation. • The quality is significantly enhanced by enzymatic treatment in the manufacturing process of black tea. • TF and TR improved bioactivities more than total polyphenol, free amino acids, and catechin. • Enzymatic treatment of black tea may effectively increase TLC levels in tea liquor and improve the quality of black tea brew. [ABSTRACT FROM AUTHOR]

Green, white and black teas showed different degrees in enzymatic fermentation through relevant processing procedures. To reveal the impact of enzymatic fermentation in tea-leaves, 44 chemical components including 17 phenolic compounds, 3 purine alkaloids, 19 free amino acids and γ-aminobutyric acid (GABA) in 27 various tea samples were determined by HPLC and amino acid analyzer, respectively. Additionally, E-tongue and 5 various assays were developed for taste evaluation and in vitro antioxidant activities analysis. Multivariate statistical analyses, such as PCA, HCA and PLS-DA (R2X = 1.000, R2Y = 0.932, Q2 = 0.908, respectively) divided theses teas into green, white and black tea categories, indicating the profound impact of enzymatic fermentation on tastes and chemical compositions. The enzymatic fermentation highly significantly (p < 0.001) promoted the decreases of 5 catechins (i.e. C, EC, GC, ECG and EGCG), gallic acid, rutin and 6 free amino acids, and the accumulations of 4 flavonoids (i.e. taxifolin, myricetin, queretin and luteolin), ellagic acid and 4 free amino acids in tea-leaves. The bivariate correlation analysis confirmed that 7 catechins, GG and 7 free amino acids might impress bitterness, umami and astringency, which also contributed to the antioxidant activities in tea-leaves. This study advanced the knowledge about enzymatic fermentation in tea-leaves processing. • Enzymatic fermentation caused the chemical differences among green, white and black teas. • Enzymatic fermentation significantly impact 5 catechins,5 flavonoids, 6 free amino acids. • Slight enzymatic fermentation might improve the in vitro antioxidant activities in tea-leaves. • Catechins, free amino acids contributed to antioxidant activities, bitterness, umami, astringency. [ABSTRACT FROM AUTHOR]

Shaken black tea (SBT) is a new type of black tea that combines the traditional black tea processing technology with the shaking process of oolong tea. In this study, non-targeted metabolomics analysis based on ultra-high-pressure liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS) was applied to comprehensively analyze the non-volatile metabolites of SBT during the manufacturing process. Using multivariate statistical analysis, 93 compounds were screened as differential compounds. During the whole process of SBT, amino acids, dipeptides, theaflavins and lipids contents showed significant increases, while that of catechins and procyanidin C1 significantly decreased. Compared with fresh leaves, the content of proteinaceous amino acids (PAAs) in the dried black tea increased 1.61-fold, and total catechins decreased to 7.25%. The results of hierarchical clustering analysis (HCA) showed that fermentation is the key process that causes the variations of these metabolites, followed by drying and shaking. The biosynthesis metabolism of amino acids, flavonoids and linoleic acid are abundant, mainly due to the stress response of fresh tea leaves to dehydration and mechanical damage during shaking processing. It is beneficial to explore the quality formation during the production of SBT through comprehensive analysis of the changes in metabolites. • Fermentation led to significant changes in metabolites, followed by drying, shaking. • Shaking process promoted the accumulation of amino acids, dipeptides and theaflavins. • Remarkable increase of dipeptides is mainly in the fermentation and drying process. • Variation of taste compounds, amino acids, flavonoids, and dipeptides, were studied. • Metabolic pathway of key compounds like amino acids, flavonoids, lipids, were revealed. [ABSTRACT FROM AUTHOR]

Yellowing is the key process used to produce the unique yellow tea, but the effect of the yellowing process on tea quality and chemical composition remains unclear. Here, electronic eye and tongue and metabolomics were applied to investigate dynamic changes in tea leaves during the yellowing process for the first time. During the first 18 h of yellowing, the colour of tea leaves was observed becoming yellowish. Compounds related to umami and sweetness (amino acids, catechins, sucrose, phenolic acids, etc.) are at high levels. However, after 24 h of yellowing, the colour of tea becomes darker, with richness of tea infusion decreasing significantly. The levels of most catechins, amino acids, phenolic acids, and glycosidically bound volatiles (GBVs) decreased significantly, whereas betaine, piperidine, theasinensin B, and lysophosphatidylcholines (LPCs) increased significantly. Meanwhile, according to partial least-squares (PLS) analysis, most amino acids and sucrose were positively correlated with umami and sweetness; most catechins and phenolic acids had positively correlated with bitterness and astringency; phaeophorbides were positively correlated with red value (+a*) of tea leaves' colour. This work provides a comprehensive, novel knowledge on the quality and chemical changes of yellow tea during the yellowing process. • Metabolomics and electronic multi-sensors were used for yellow tea study. • A dynamic view was acquired by the determination of quality and metabolites. • Yellow tea quality is optimal after 18 h under 40 °C. • The decline in amino acids and catechins is responsible for taste deterioration. [ABSTRACT FROM AUTHOR]

Tea is processed from the postharvest tender leaves from tea plants (Camellia sinensis). Leaves containing more trichomes are considered to produce higher quality tea, but no evidence is available to support this opinion. In the present study, morphological and metabolic analyses of trichomes showed that tea trichomes were unicellular, simple, and rich in many water-soluble metabolites, including free catechins, caffeine, and amino acids. Furthermore, the analysis of known quality-related and non-targeted metabolites in fresh tea leaves and tea products showed that the presence of trichomes did not change the overall metabolite profiles of fresh tea leaves, white tea, and black tea, but might affect the non-targeted metabolites in green tea. Overall, more trichomes might only indicate higher quality tea leaves, while metabolites in the leaf might be the key factor. This study provides the first determination of the contribution of trichomes to tea quality. • The morphology and metabolite of trichomes were observed and analyzed. • Tea trichomes were unicellular, simple, and rich in many water-soluble metabolites. • Trichome affected non-targeted metabolites of green tea. • Trichomes may only serve as an indicator of higher tea quality. • Contribution of trichomes to tea metabolites was uncovered firstly. [ABSTRACT FROM AUTHOR]

Fuzhuan brick tea is a distinctive Chinese dark tea for its significant health benefits and unique quality characteristics by a unique fungal fermentation stage, in which Eurotium cristatum strains play a crucial role in the post-fermentation process. In this study, the biochemical characteristics and lipid-lowing activity of E. cristatum (MF800948)-fermented loose tea (FT) were investigated. The results showed that total phenolics, flavonoids, catechins and free amino acids were decreased after fermentation, while three purine alkaloids, soluble carbohydrates and theabrownins were significantly increased compared to green tea. In addition, d -limonene (27.71%) and β-myrcene (11.55%) were the predominant volatiles in FT, giving the characteristic fruity and balsamic scent to the fermented loose tea. Correspondingly, the aqueous extract of FT showed potent lipid-lowering activity in a high-fat zebrafish model and the optimum effective concentration was 500 μg/mL, at which the lipid level declined to 51.49% compared to control group. Hence, it was suggested that loose tea fermented by E. cristatum (MF800948) could provide valuable insights for developing a high-quality and hypolipidemic dark tea. • A novel fermented loose tea by Eurotium cristatum (MF800948) is firstly prepared. • Chemical components in the fermented loose tea dramatically alter in relative to green tea. • Theabrownins in Eurotium cristatum (MF800948)-fermented loose tea are significantly increased. • Aqueous extract of the fermented loose tea is efficient in lowering lipid level in vivo. [ABSTRACT FROM AUTHOR]