Ultra-high Performance Liquid Chromatography-Tandem Mass Spectrometry Analysis of Dynamic Changes in Non-volatile Compounds in Green Tea during Storage at Ambient Temperature

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

Identification of Volatile and Non-Volatile Components in Taiping Houkui Tea Made from ‘Shidacha’ and Non-‘Shidacha’ Tea Varieties and Phylogenetic Analysis

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

Contribution of Stems and Leaves to the Quality of Keemun Black Tea

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

Manufacturing process differences give Keemun black teas their distinctive aromas

Traditional Keemun black tea is also known as Congou black tea (CF). Over the last three decades, three other types of Keemun black tea (Jinzhen, JZ; Maofeng, MF; Xiangluo, XL) made by different processing have been introduced into the tea market. Total CF volatile concentrations ranged from 1666.3 to 2185.7 μg/L, followed by XL (1193.5–1916.1 μg/L), JZ (1058.9–1811.0 μg/L), and MF (987.5–1518.0 μg/L) tea infusions. A total of 79 volatiles in tea infusions was identified by two methods, among which fourteen with OAVs > 1 were identified and OAVs proportion of volatiles with flowery, fruity, or sweet notes to those with other notes differed in four Keemun black teas (CF = 6.58:1, MF = 5.16:1, JZ = 4.04:1, XL = 5.11:1). Phenylethyl alcohol oxidation resulted in phenylacetaldehyde formation which is the characteristic odorant in Keemun black tea. We clearly show that changes in tea processing gives the distinctive aroma to different Keemun black teas