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In order to investigate the changes in the characteristic aroma components of sun-dried green tea during processing, the volatile substances in fresh, fixated, rolled and sun-dried leaves of Yunnan large leaf tea were determined using solvent flavor-assisted evaporation extraction (SAFE) combined with gas chromatography-mass spectrometry (GC-MS), and the aroma active components of sun-dried green tea were identified by odor activity value (OAV). The results showed that totally 67 volatile compounds were detected, the major ones being alcohols, esters and aldehydes, and the total amount of volatile substances increased from fresh leaves to the end of fixation. The total amount of volatile substances slightly decreased in sun-dried leaves compared to fresh leaves, but the number of volatile substances increased. A total of 23 aroma active compounds with OAV > 1 were found in sun-dried green tea, with the major ones being those contributing to floral and green aromas such as linalool, geraniol and nonanal. Aldehydes were the most prominent component in each processing stage. Using gas chromatography-flame ionization detector (GC-FID) and high performance liquid chromatography-photo-diode array (HPLC-PDA), a total of 7 fatty acids were detected, with saturated fatty acids being the major components; 13 carotenoids were detected, including lutein, whose content was the highest in all processing stages. During the processing of sun-dried green tea, the total amounts of fatty acids and carotenoids decreased continuously, especially linoleic acid and linolenic acid, and the content of hexanal as their major degradation product showed the opposite trend. The contents of terpene ketones, ionone and its oxidized derivatives such as β-ionone and 5,6-epoxy-β-ionone significantly increased as a result of the degradation and transformation of carotenoids. The trends of fatty acids and carotenoid precursors during the processing of sun-dried green tea were correlated with their associated aroma products. In conclusion, the results of this study may provide theoretical guidance for the targeted aroma improvement of sun-dried green tea.

According to the results of sensory evaluation performed by experts, 14 black tea samples were divided into two groups based on their aroma quality: high-quality and quality-deficient black tea. Using fast gas chromatography-electronic-nose (GC-E-Nose) and gas chromatography-mass spectrometry (GC-MS) combined with multivariate statistical analysis, discriminant analysis of the two groups were carried out, and the key differential components between these groups were selected. The results showed that 117-dimensional dataset was obtained by the fusion of the GC-E-Nose (44-dimensional) and GC-MS (73-dimensional) data and used to establish a model for accurate classification of the two types of black tea employing orthogonal partial least squares-discriminant analysis (OPLS-DA). The model’s explanatory and predictive capacity (R2Y = 0.976, Q2 = 0.959) were better than those of the model established based on the GC-E-Nose or GC-MS data. Based on variable important in projection (VIP) scores > 1.6 and P < 0.05, eight key aroma components including dimethyl sulfide (B3 and B25), β-ionone (A59), (3E)-4,8-dimethylnon-1,3,7-triene (A20), dihydroactinidiolide (A64), linalool (A17), phenylethyl alcohol (A19), δ-octyl lactone (A41) and γ-nonalatone (A45) were selected, which played an important role in the classification. These results showed that GC-E-Nose combined with GC-MS allows rapid and accurate discrimination between quality-deficient and high-quality black tea, which can be used as a supplement to traditional sensory evaluation, providing technical support for quality control and improvement of black tea.

As one of the most popular beverages in the world, tea is highly susceptible to mold contamination during its planting, processing, and distribution. Toxigenic fungi produce mycotoxins under suitable conditions, and humans drinking tea may be at risk of ingesting mycotoxins. In this review, we briefly describe the sources, types, and hazards of mycotoxins in tea, summarize the current status of mycotoxin contamination in tea, discuss the advantages and disadvantages of mycotoxin detection technologies, and outline the prevention and control measures for mycotoxins in tea. This article is expected to provide a reference for the quality control of tea.

Fresh leaves of Fuding Dabai tea (Camellia sinensis (L.)) consisting of one bud and two leaves were used to manufacture Congou black tea, and the changes in the physicochemical properties and microstructure of the bud and the two leaves were explored during the manufacturing process. It was found that during the rolling process, the color of the bud and the leaves gradually turn from green to red, but the degree of color change of the lower leaf was lower than that of the bud and the upper leaf. Besides, optical microscopic (OM) and transmission electron microscopic (TEM) analysis showed the structures of mesophyll cells and chloroplasts in both leaves were destroyed in the rolling process, indicating the beginning of fermentation. The chemical composition analysis showed that during the Congou black tea manufacturing process, the contents of tea polyphenols and catechins decreased, the contents of theaflavins and thearubigins increased at first, then decreased and finally leveled off, and the content of theabrownins kept increasing; the contents of all these compounds changed most during rolling. There was no significant difference in the oxidation degree of total catechins, epigallocatechin, epigallocatechin gallate, epicatechin gallate and theaflavins between the two leaves (P > 0.05), indicating that their fermentation degrees were similar. During the entire process, the contents of chlorophyll a, chlorophyll b and total chlorophyll decreased and the contents of pheophytin and pheophorbide increased for the bud and the leaves. The content of chlorophylls in the lower leaf was always much higher than that in the upper leaf (P < 0.05). This study provides a theoretical basis for processing high-quality congou black tea by improving the utilization rate of fresh tea leaves.

The bitter taste is generally considered an undesirable sensory attribute. However, bitter‐tasting compounds can significantly affect the overall flavor of many foods and beverages and endow them with various beneficial effects on human health. To better understand the relationship between chemical structure and bitterness, this paper has summarized the bitter compounds in foodstuffs and classified them based on the basic skeletons. Only those bitter compounds that are confirmed by human sensory evaluation have been included in this paper. To develop food products that satisfy consumer preferences, correctly ranking the key bitter compounds in foodstuffs according to their contributions to the overall bitterness intensity is the precondition. Generally, three methods were applied to screen out the key bitter compounds in foods and beverages and evaluate their sensory contributions, including dose‐over‐threshold factors, taste dilution analysis, and spectrum descriptive analysis method. This paper has discussed in detail the mechanisms and applications of these three methods. Typical procedures for separating and identifying the main bitter compounds in foodstuffs have also been summarized. Additionally, the activation of human bitter taste receptors (TAS2Rs) and the mechanisms of bitter taste transduction are outlined. Ultimately, a conclusion has been drawn to highlight the current problems and propose potential directions for further research. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: A new method for post‐assembly modification of peptides via the Pd‐catalyzed endogenous group‐directed sp3 C—H arylation with aryl iodides is developed. The sulfide side chain of methionine (Met) residue can facilitate the arylation of both β and γ methyl C—H bonds of N‐terminal aliphatic amino acids of peptides via formation of 5 or 6‐membered palladacycle intermediates. The reactions can proceed in moderate to good yield and with excellent diastereoselectivity. [ABSTRACT FROM AUTHOR]

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To explore the relationship between the moisture content of withered tea leaves and their physical properties (i.e., elasticity, plasticity, flexibility, and texture) during withering, texture analyzer was employed to test the elasticity and flexibility of withered tea leaves with different moisture contents. The texture was evaluated by computer vision technology. The withered tea leaves with different moisture contents were used to process congou black tea, which was then subjected to sensory evaluation. Results showed that good elasticity, optimal flexibility, and plasticity were achieved when the moisture content of the withered tea leaves of Fudingdabai comprising two leaves and one bud varied arranging from 65.51 to 61.48%. The sensory evaluation of congou black tea revealed that moderate withering was better than long‐term withering and that both moderate and long‐term withering were better than no withering during processing. The moisture content was significantly correlated with the flexibility and plasticity of the withered tea leaves. Fresh tea leaves undergoing moderate withering with moisture content of 65.51–61.48% to process congou black tea, good tea shape and liquor color were achieved. This study provided new evidence that the moisture content of withered tea leaves significantly affected the quality of black tea. [ABSTRACT FROM AUTHOR]

Summary: Theaflavin‐3,3′‐digallate (TFDG) is the main product formed by oxidative condensation between (−)‐Epigallocatechin‐3‐gallate (EGCG) and (−)‐Epicatechin‐3‐gallate (ECG). Some sub‐products, such as homo‐ and hetero‐oligomers of EGCG and ECG, are also produced simultaneously, which significantly decreases the yield of TFDG. In general, the optimum temperature for TFDG synthesis is 20 °C below which can reduce its generation resulting in the coexistence of a large amount of unreacted substrates (ECG and EGCG). Therefore, a higher possibility of increasing the formation of TFDG could be achieved if a suitable synthetic method can be developed at a low temperature. Our results showed that simultaneous dropwise addition of both EGCG and ECG could markedly enhance the content of TFDG at ice bath. Using such technique, the production of TFDG increased by 47.60% as compared to the group synthesised under the optimum temperature. The absorbance of TFDG at 278 nm is 2.36 times higher than that of ECG with equimolar concentration. Therefore, a rapid, simple and accurate calculation method of TFDG yield was developed via the spectral correlation. Based on the counting method, the yield of TFDG was 30.58% by using the novel synthetic method of TFDG. [ABSTRACT FROM AUTHOR]