In order to investigate the differences in the aroma composition of black tea samples made from different tea cultivars in the region of Huangshan, fresh leaves of nine tea cultivars widely planted in that region were selected to process black tea, including ‘Keemun Zhuyezhong’, the major cultivar for Keemun black tea processing, and eight clones, namely ‘Cuilv No.1’, ‘Fuzao No.2’, ‘Wancha No.4’, ‘Shuchazao’, ‘Wancha 91’, ‘Zhongcha 108’, ‘Zhenong 117’, and ‘Zhenong 139’. The sensory evaluation results showed that all nine black tea samples had a sweet aroma, and ‘Keemun Zhuyezhong’ black tea also possessed a strong floral scent. ‘Wancha No.4’ black tea also had a lightly floral aroma. The floral aroma of ‘Keemun Zhuyezhong’ and ‘Wancha No.4’ black tea was significantly stronger than that of the other cultivars. Forty-six major volatile compounds were identified by headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS), and 21 volatile components with OAVs greater than one were found. Principal component analysis (PCA) showed that the aroma composition of ‘Zhuyezhong’ and ‘Wancha No.4’ black tea was clearly different from that of the others. Subsequently, seven differential components including (E)-β-ionone, linalool, β-myrcene, geraniol, hexanal, nonanal, and heptanal were identified by orthogonal partial least squares-discriminant analysis (OPLS-DA), with variable importance projection (VIP) values greater than one among all samples. These volatile components may be the dominant factors causing the aroma difference among the nine black tea samples. These results provide insights into the differential aroma compounds among black tea samples manufactured from different cultivars and the ‘Keemun aroma’.

Herein, we used an ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) system to investigate changes in the profile of non-volatile metabolites in green tea after different periods (15, 40, 80 and 120 days) of storage at 37 ℃. The color of green tea and tea infusion changed after 40 days of storage at 37 ℃ when compared with the control (stored at −80 ℃). During 40 days of storage, the content of catechins did not significantly change, but the content of free amino acids significantly decreased. A total of 684 non-volatile components were identified, 77 of which were found to be characteristic differential metabolites, the major ones being polyphenols, lipids and organic acids. The content of octadecadien-6-ynoic acid, an umami-related compound, significantly decreased after 40 days and was undetected after 80 days. The content of theaflavine-3-catechin, related to the color and taste of tea infusion, significantly increased with storage time. Similarly, the content of flavone glycoside increased with storage time. Moreover, the content of lipids such as triacylglycerols (TAGs) and diacylglycerol (DAGs) changed significantly after 15 days, and the content of free fatty acids increased with storage time. The findings from this study showed that the contents of lipids and flavonoids in green tea significantly changed during storage, which played an important role in the quality deterioration of green tea.

Taiping Houkui green tea is mainly made from the young shoots of the sextual tea line ‘Shidacha’. In the present study, the differences in the quality and genetic evolution of green tea made from the young shoots of five ‘Shidacha’ varieties (Gaojiazao, Huangzhong, Shidacha No.2, Shidacha No.6, and Guangyangzao) and two non-‘Shidacha’ tea varieties (Fuzao No.2 and Shuchazao) were explored. The volatile and non-volatile metabolites of the seven tea samples were analyzed, and the differences in genome-wide transcriptional levels and genetic background among the seven tea varieties were analyzed using RNA sequencing (RNA-seq). No significant differences in catechin content or the total content of free amino acids were found among all tea samples except Shuchazao, whereas caffeine content differed significantly among all samples. The contents of floral aroma compounds such as linalool, linalool oxide, geraniol and jasmone were relatively high in the infusion of ‘Shidacha’ green tea. RNA sequencing results showed that the genome-wide transcriptional level of Guangyangzao was close to that of the non-‘Shidacha’ tea varieties. In principal component analysis (PCA), Guangyangzao and the other ‘Shidacha’ varieties were distributed in different quadrants. Phylogenetic analysis showed that the non-‘Shidacha’ tea varieties had a close genetic relationship with each other as well as Gaojiazao and Huangzhong, but was far away from the other ‘Shidacha’ varieties. The transcriptional levels of most of the key enzyme genes involved in the biosynthesis of linalool, indole, nerolidol and jasmone lactone were higher in the ‘Shidacha’ tea varieties than in the non-‘Shidacha’ ones. This study provides important theoretical support for the breeding of excellent ‘Shidacha’ varieties and provides a theoretical basis for follow-up research on the formation mechanism of floral aroma compounds in tea leaves.

Pile-fermentation is the key process for the formation of dark tea quality. Quick and accurate assessment of the degree of pile-fermentation is key to this processing. Color is an important indicator of quality evaluation. The significant color changes can be used to judge the pile-fermentation degree, which constitutes a basis for the exploration and establishment of a fast method for the assessment of pile-fermentation degree. The color change of pile-fermentation leaves and tea liquor were observed in the experiments. The results showed that: (1) The overall leaf color changed from green to yellow during the pile-fermentation process. And it's mainly due to the significant increase in the values of a and b. Besides, the color change rate of leaf veins was significantly faster than that of leaves. Temperature and water content had significant effects on the color change of pile-fermentation leaves. The former mainly affected the value of a, and the latter mainly affected the L, a and b value. (2) The color of tea liquor changed from light green and bright to yellow during pile-fermentation, which was mostly due to the significant increase of b value. The change of tea liquor color was positively correlated with temperature, but had no significant effect on water content. (3) The a value of leaves and veins showed a linear trend with image changes and sensory quality formation in the process of pile-fermentation, which can be used to establish a color discrimination model for the degree of pile-fermentation. Conclusion: The leaf color and soup color showed a significant change to yellow during the piling process, and the a value of leaves and veins shows a certain linear trend with the piling process. On this basis, an evaluation model corresponding to the sensory evaluation results of leaves and veins has been established: (1) y = -0.0872x² + 0.4086x + 96.345 (R² = 0.721); (2) y = -0.0247x² + 0.4996x + 96.323 (R² = 0.8577). Through the rapid determination of a value of leaves and veins in the pile, the sensory results of the pile can be predicted, which can quickly assist the tea maker to judge the degree of pile-fermentation, and is of great significance to improve the processing quality of black tea.

Keemun black tea samples which made from one bud and one fresh leaf of ‘Fuzao No.2' tea tree were baked at 60 ℃ for 30 min, 60 min, 90 min. Unbaked samples were used as a control. The effect of baking on the quality of premium Keemun black tea was studied by sensory evaluation and analysis of volatile compounds. The results showed that the contents of volatile compounds increased after baking. Baking for 30 min could better maintain the unique aroma characteristics of Keemun black tea and improve the taste quality. As the baking time increased, the quality of aroma and taste gradually decreased. Linalool and its oxides, benzyl alcohol, geraniol, phenylacetaldehyde and methyl salicylate were the main compounds to distinguish the aroma changes of Keemun black tea at different baking treatments. The results of this study provide a theoretical guidance for optimizing the baking process in the production of Keemun black tea.

Guangde Huangjinya tea is a key regional public brand of Guangde City. In recent years, Guangde Huangjinya tea industry has developed rapidly, which produced good economic and social benefits. Guangde City has become the distribution center of Huangjinya tea, forming its own advantages. This paper introduces the quality characteristics and processing technology of Guangde Huangjinya tea, summarizes the practical experience in its development. Proposals have been put forward to strengthen policy guidance and consolidate the industrial foundation for promoting the high-quality development of Guangde Huangjinya tea industry. Particularly, it aims to promote the diversified value of tea products through the integrated development of the primary, secondary and tertiary industries.

In order to understand the contribution of stems and leaves to the quality of Keemun black tea, this study analyzed the differences in aroma, taste quality and metabolites among black tea manufactured from tender leaves, tender stems, single buds and intact buds with leaves (mainly one bud with two leaves) from the tea variety ‘Fuzao 2’ by gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), sensory evaluation, and preference evaluation. The results showed that all four black teas were sweet aroma type, and the bud-leaf tea had a strong sweet aroma. The single-bud tea had a fresh and brisk taste. The tender-stem tea scored highest in preference evaluation. Metabolite analysis showed the content of catechins was the highest in the single-bud black tea and the lowest in the tender-stem black tea, while free amino acids were significantly enriched in the tender-stem black tea, reaching up to 80 mg/g. The contents of quercetin and rutin were higher in the stem black tea, while the contents of kaempferol-3-O-glucoside and kaempferol-3-O-rutinoside were the highest in the leaf black tea. The ratio of thearubigins to theaflavins was 11.6, 9.4, 14.6, and 8.2 in black tea made from intact buds with leaves, buds, leaves, and tender stems, respectively. The total amount of volatile compounds in the tender-stem black tea (32.37 μg/g) was significantly lower than that in the bud (100.01 μg/g), leaf (95.67 μg/g), and bud-leaf black tea (92.42 μg/g). The contents of benzaldehyde, benzeneacetaldehyde and indole were higher in the tender stem black tea, while the contents of β-ionone, α-ionone and linalool oxide in the leaf black tea were higher than those in the other three black teas. This study shows that high contents of theanine in tender stems and glycoside aroma precursors in tea leaves contribute primarily to the formation of the quality of Keemun black tea.