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Soluble sugar is one of the important characteristic metabolites contributing to the flavor quality of tea. However, little is known about the changes and metabolic pathways of sugar in summer–autumn black tea varieties during the solid-state fermentation of Ganoderma lucidum. Therefore, this study is aimed at investigating the effects of the solid-state fermentation of Ganoderma lucidum on soluble sugar metabolism in three summer–autumn black tea varieties. In this study, we combined targeted metabolomics technology, gas chromatography-mass spectrometry, and multivariate statistical analysis to reveal the metabolic rules of 13 different sugars in three varieties of summer–autumn black tea under the action of Ganoderma lucidum. Using multivariate statistical analysis, 8 common key sugar differential metabolites were selected from the three groups of samples: D-fructose, trehalose, lactose, maltose, D-galactose, glucose, L-rhamnose, and xylitol. The eight different sugars contributed to the quality difference between Ganoderma lucidum tea and black tea in this study. To better explore the patterns of sugar changes, the metabolic pathways of 13 different sugars were screened and analyzed. The result revealed that the solid-state fermentation of Ganoderma lucidum increased the sweet characteristics and decreased the bitter characteristics of the three summer–autumn black tea varieties. In addition, these results showed that the solid-state fermentation of Ganoderma lucidum could produce lactose in tea, reduce glucose and fructose contents, and increase xylitol content. The solid-state fermentation of Ganoderma lucidum can regulate soluble sugar metabolism in three summer–autumn black tea varieties, leading to an improvement in their quality. This study has potential practical significance for regulating the flavor quality of summer–autumn tea. [ABSTRACT FROM AUTHOR]

Our previous study showed that COPPER-CONTAINING AMINE OXIDASE (CuAO) and AMINOALDEHYDE DEHYDROGENASE (AMADH) could regulate the accumulation of γ-aminobutyric acid (GABA) in tea through the polyamine degradation pathway. However, their biological function in drought tolerance has not been determined. In this study, Camellia sinensis (Cs) CsCuAO1 associated with CsAMADH1 conferred drought tolerance, which modulated GABA levels in tea plants. The results showed that exogenous GABA spraying effectively alleviated the drought-induced physical damage. Arabidopsis lines overexpressing CsCuAO1 and CsAMADH1 exhibited enhanced resistance to drought, which promoted the synthesis of GABA and putrescine by stimulating reactive oxygen species' scavenging capacity and stomatal movement. However, the suppression of CsCuAO1 or CsAMADH1 in tea plants resulted in increased sensitivity to drought treatment. Moreover, co-overexpressing plants increased GABA accumulation both in an Agrobacterium-mediated Nicotiana benthamiana transient assay and transgenic Arabidopsis plants. In addition, a GABA transporter gene, CsGAT1, was identified, whose expression was strongly correlated with GABA accumulation levels in different tissues under drought stress. Taken together, CsCuAO1 and CsAMADH1 were involved in the response to drought stress through a dynamic GABA-putrescine balance. Our data will contribute to the characterization of GABA's biological functions in response to environmental stresses in plants. [ABSTRACT FROM AUTHOR]

Umami amino acids inhibit the bitter and astringent taste presentation of catechins, which is essential for the taste regulation of green tea. In this study, the concentration–intensity trends and taste threshold properties of major catechin monomers were investigated using an electronic tongue. The taste and chemical structure interactions between the ester‐type catechins and theanine, glutamic acid (Glu), and aspartic acid (Asp) were further analyzed by in vitro simulation and analysis of their reciprocal chemical structures. The results showed that the bitterness and astringency of the major catechin monomers increased with increasing concentration, and their bitterness thresholds and their electron tongue response values were higher than those of the astringent values, while the bitterness and astringency of the ester‐type catechins were higher than those of the nonester type. The three amino acids inhibited the bitterness intensity of ester catechins (epigallocatechin gallate, epicatechin gallate, and gallocatechin gallate) at different concentrations, and the effects on the astringency intensity of ester catechins were complicated. Ester catechins significantly enhanced the umami intensity of theanine, Glu, and Asp at different concentrations. Their reciprocal chemical structures showed that hydrogen bonding was the main interaction force between the three ester‐type catechins and the umami amino acids, with theanine and Glu interacting more strongly with ester‐type catechins than Asp, and Glu having a lower binding energy to ester‐type catechins, which bonded more easily. [ABSTRACT FROM AUTHOR]

The current method for processing bud yellow tea usually results in astringent taste that is not sufficiently yellowing. Therefore, two factors in the production phase that affect tea quality were studied: number of times the tea leaves undergo the yellowing process and predrying of leaves to reduce their water content before a second yellowing process. We then evaluated the colour and nonvolatile compounds of the produced tea. Results revealed that gallated catechins and the polyphenol–amino acid ratio decreased significantly, and the colour of the tea changed from green to yellow after two yellowing processes. Predrying leaves to a lower water content resulted in the accumulation of free amino acids and soluble sugars, and an increase in the brightness and yellow colour of tea infusion. Bud yellow tea with the highest taste evaluation score and yellowness was obtained when the leave samples underwent two yellowing processes and the water content in the leaves was 40%. [ABSTRACT FROM AUTHOR]

BACKGROUND: Non‐volatile compounds play a key role in the quality and price of Keemun black tea (KBT). The non‐volatile compounds in KBT samples from different producing areas normally vary greatly. The development of rapid methods for tracing the geographical origin of KBT is useful. In this study, we develop models for the discrimination of KBT's geographical origin based on non‐volatile compounds. RESULTS: Seventy‐two KBT samples were collected from five towns in Anhui province to determine 13 KBT compounds by high‐performance liquid chromatography (HPLC). Analysis of variance showed that the content of 13 compounds in KBT indicated significant differences (P < 0.05) among five towns. Three multivariate statistical models including principal component analysis (PCA), soft independent modeling of class analogy (SIMCA), and linear discriminant analysis (LDA) were built to discriminate origin. Principal component analysis effectively extracted three principal components, namely theaflavins, galloylated catechins, and simple catechins. The high sensitivity (64.5%–99.2%) was achieved of SIMCA model. To establish the discriminant functions, six variables (gallic acid, (+)‐catechin, (−)‐epigallocatechin gallate, theaflavin‐3‐gallate, theaflavin‐3,3′‐di‐gallate, and total theaflavins) were chosen from 13 variables, and LDA was applied. This gave a satisfactory overall correct classification rate (94.4%) and cross‐validation rate (88.9%) for KBT samples. CONCLUSION: The results showed that HPLC analysis together with chemometrics is a reliable approach for tracing KBT and guaranteeing its authenticity. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

BACKGROUND Keemun black tea (KBT) is one of the most popular tea beverages in China as a result of its unique flavor and potential health benefits. The geographical origin of KBT influences its quality and price. The present study aimed to apply a head‐space solid phase microextraction approach and gas chromatography–mass spectrometry combined with chemometric analysis to profile the volatile compounds of KBT collected from five production areas. RESULTS: Thirty‐one peaks were detected in 61 KBT samples. Hierarchical cluster analysis, principal component analysis (PCA), k‐nearest neighbor (k‐NN) and stepwise linear discriminant analysis (SLDA) were employed to visualize the volatile fractions. The results of unsupervised statistical tools were compared using a test for similarities and distinctions, which showed that different sources may be associated. A satisfying combination of average recognition (91.7%) and cross‐validation prediction abilities (84.6%) was obtained for the PCA–k‐NN. Among all of the statistical tools, SLDA provided promising results, with 100% recognition and 96.4% prediction ability. CONCLUSION: The results obtained in the present study indicate that the volatile compounds can be used as indicators to identify the geographical origin of KBT. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Summary: The effects of roasting treatment on sensory quality and related compounds in green tea were investigated. The combined application of roasting temperature and time 100 °C for 90 min, 120 °C for 60 min and 140 °C for 30 min achieved the most satisfying sensory quality. The HPLC analysis showed that the contents of cis‐catechins, bitter and umami amino acids reduced with increase in temperature, while the contents of trans‐catechins and soluble sugar increased with the temperature rise. The content of caffeine and sweet amino acids did not change significantly compared with untreated tea sample. The decrease in cis‐catechins, total polyphenols and bitter amino acids reduced the bitterness and astringency of the green tea, while the increase in total soluble sugars improved the sweetness and mellow taste. The sensory evaluation results showed that the sensory quality of the tea was significantly enhanced through roasting treatment. Roasting treatment significantly improved the sensory quality of green tea. [ABSTRACT FROM AUTHOR]