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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., (© 2023 The Authors. Journal of Food Science published by Wiley Periodicals LLC on behalf of Institute of Food Technologists.)

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., (© 2019 Society of Chemical Industry.)

Jinmudan (JM) tea, produced using Camellia sinensis, cultivar JM, is popular among consumers because of its strong floral and fruity aroma. Aroma profiles of white, green, black, and oolong teas, which were obtained from JM and Tanyangcaicha (TY, control and indigenous variety), were investigated. Sensory evaluation was used to describe the quality characteristics of the tea samples. A combination of headspace solid-phase microextraction, gas chromatography–mass spectrometry (HS-SPME/GC–MS), and chemometrics was used to extract and analyze the volatiles in the samples; 162 volatiles were identified and categorized on the basis of their chemical structures. The proportions of chemical categories differed among the teas. The same type of tea obtained from JM and TY differed significantly in concentrations and categories of volatiles. This study will improve our understanding of the profile of volatile compounds in JM teas and create a basis for investigating the biological characteristics of JM teas. [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]

Ancient tea plants black tea (ATBT) has outstanding sweet-mellow taste, but what contributes to its quality remains unclear. We tested 36 freeze and 9 finished tea sampled from five processing stages for ATBT by electronic tongue (ET), high performance liquid chromatography, and gas chromatography-tandem mass spectrometry. ET and chromatographic data revealed variation of sensory characteristics and chemical compounds among the five processing steps of ATBT. Through the correlation analysis and principal component analysis, it was concluded that ester-catechins and soluble sugars content in tea leaves had significant effect with the bitterness and sweetness in tea infusions (p < 0.05). Catechins, theaflavins, soluble sugars, and ET signals was considered an important information for determining the processing steps, and it had an impact on the taste of the tea infusions. These findings indicated that accurate processing control is effective approach to maintaining chemical constituents of contributes to taste quality in ATBT. [Display omitted] • The changes of taste metabolites during ATBT processing were firstly revealed. • Monosaccharides contribute to the sweet taste of ATBT. • Theaflavins contribute to the mellow taste of ATBT. • Ester-catechin was negatively correlated with the sweetness of the tea infusion. [ABSTRACT FROM AUTHOR]

To identify the microorganisms responsible for the formation of the main quality components of Qingzhuan brick tea (QZBT) during solid-state fermentation (SSF), predominant thermoduric strains were isolated from the tea leaves collected during SSF. According to their capability of releasing cellulase, pectase, protease, and polyphenol oxidase, four strains were selected as starter cultures to ferment sun-dried tea leaves during artificially inoculated SSF. According to the major enzymatic activities and quality components content (tea polyphenols, catechins, amino acids, soluble sugar, and theabrownin), it was found that Aspergillus fumigatus M1 had a significant effect on the transformation of polyphenols and Bacillus subtilis X4 could enhance the ability of bioconversion of strain M1. Strain X4 and M1 may be the core microbes responsible for developing these biochemical components of QZBT, as the values of quality components of tea leaves fermented by these two strains for 6 days was very close to that of the sample naturally fermented for 35 days in the tea factory. The results could be significant in developing industrial starters for the manufacture of QZBT and stabilizing the product quality of different batches. [ABSTRACT FROM AUTHOR]

Withering leads to the formation of high-quality flavor in black tea. This study investigated the effects of natural withering (NW), sun withering (SW), and warm-air withering (WW) on the flavor compounds of withered leaves by using target metabolomic and transcriptomic approaches. The results revealed that 4282, 4770, and 1246 differentially expressed genes (DEGs) were identified in the NW, SW, and WW samples, respectively. The expression of DEGs involved in volatile compound and flavonoid biosynthesis was the highest in the WW sample, which may be the main reason for the significant increase in volatile compound and catechin contents in the WW sample. The withering methods mainly affected the contents of non-proteinaceous amino acids, such as theanine. Withering methods significantly affect the expression levels of DEGs involved in metabolic pathways; this provides a systematic explanation for flavor formation in black tea. • Different withering methods affect the flavor formation of black tea. • The essence of the withering method is the type of stress. • Warm-air withering increased the content of flavor compounds. • Comprehensive explanation of the mechanism of action of withering method of black tea. [ABSTRACT FROM AUTHOR]

• Different withering methods affect the aroma quality of Keemun black tea. • Sun withering significantly enhanced the floral and fruity of Keemun black tea. • Methional, geraniol and linalool are the most active-aroma in Keemum black tea. • A more comprehensive profile of Keemun aroma was obtained. Withering is a key process that affects the aroma of Keemun black tea (KBT). In this study, the aroma composition of KBT through natural withering, sun withering, and warm-air withering was analysed using gas chromatography–mass spectrometry. The results revealed significant differences in the three samples. Gas chromatography–olfactometry and aroma extract dilution analysis were performed with screening through a relative odour activity value (rOAV) > 1. In total, 11 aroma-active compounds (geraniol, (Z)-4-heptenal, 1-octen-3-ol, (E)- β -ionone, 3-methylbutanal, linalool, β -damascenone, (E , E)-2,4-decadienal, methional, (E , E)-2,4-nonadienal, and (E)-2-nonenal) were found to be responsible for the differences in aroma caused by different withering methods. Linalool (rOAV, 161) and geraniol (rOAV, 785) were responsible for the higher flowery and fruity aromas when sun withering was applied, whereas methional (rOAV, 124) contributed to the intense roasty aroma when warm-air withering was employed. Moreover, our results were verified by quantitative descriptive analysis and addition experiments. [ABSTRACT FROM AUTHOR]