Analysis of Young Shoots of 'Anji Baicha' (Camellia sinensis) at Three Developmental Stages Using Nontargeted LC-MS-Based Metabolomics

Dynamic changes of key metabolites in Longjing green tea during processing revealed by widely targeted metabolomic profiling and sensory experiments

In this study, widely targeted metabolomics and chemometrics were utilized to comprehensively analyse the formation of taste compounds in Longjing green tea. A total of 580 non-volatile metabolites were identified by using ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry, and alterations in three metabolic pathways were investigated. Notably, the fixation process reduced phosphatidic acid levels, resulting in the formation of lyso-phosphatidylcholine and lyso-phosphatidylethanolamine, as well as the release of esterified polyunsaturated fatty acids. Baiye No.1 had high levels of L-glutamic acid and l-glutamine, while Longjing 43 showed elevated levels of flavones. Correlation analysis and sensory verification indicated that the specific concentration of L-leucine could decrease the umami of the tea. These findings advance our understanding of Longjing green tea quality improvement and cultivar development.

Multi-Omics Research Accelerates the Clarification of the Formation Mechanism and the Influence of Leaf Color Variation in Tea (Camellia sinensis) Plants

Tea is a popular beverage with characteristic functional and flavor qualities, known to be rich in bioactive metabolites such as tea polyphenols and theanine. Recently, tea varieties with variations in leaf color have been widely used in agriculture production due to their potential advantages in terms of tea quality. Numerous studies have used genome, transcriptome, metabolome, proteome, and lipidome methods to uncover the causes of leaf color variations and investigate their impacts on the accumulation of crucial bioactive metabolites in tea plants. Through a comprehensive review of various omics investigations, we note that decreased expression levels of critical genes in the biosynthesis of chlorophyll and carotenoids, activated chlorophyll degradation, and an impaired photosynthetic chain function are related to the chlorina phenotype in tea plants. For purple-leaf tea, increased expression levels of late biosynthetic genes in the flavonoid synthesis pathway and anthocyanin transport genes are the major and common causes of purple coloration. We have also summarized the influence of leaf color variation on amino acid, polyphenol, and lipid contents and put forward possible causes of these metabolic changes. Finally, this review further proposes the research demands in this field in the future.

Integrative transcriptome and whole-genome bisulfite sequencing analyses of a temperature-sensitive albino tea plant cultivar

Green tea made from albino buds and leaves has a strong umami taste and aroma. The cultivar 'Zhonghuang 2' (ZH2, Camellia sinensis) is a natural mutant with young shoots that are yellow in spring and green or yellow-green in summer. However, the mechanism of leaf color change remains unclear. Here, we found that young shoots of ZH2 were yellow at low temperature (LT) and green at high temperature (HT), indicating that ZH2 is a temperature-sensitive cultivar. Transmission electron microscopy analysis showed that the grana in the chloroplasts of young shoots grown at LT were poorly stacked, which caused a lack of photoreactions and chlorophyll. RNA-seq results showed 1279 genes differentially expressed in the young shoots grown at LT compared with those at HT, including genes related to cytochrome synthesis, chloroplast development, photosynthesis, and DNA methylation. A whole-genome bisulfite sequencing assay revealed that the dynamics of DNA methylation levels in the CG, CHG, and CHH contexts decreased under LT, and the change was most obvious in the CHH context. Furthermore, 72 genes showed significant changes in both expression and DNA methylation levels, and most of them were related to cytochrome synthesis, chloroplast development, photosynthesis, transcription factors, and signaling pathways. These results demonstrate that DNA methylation is involved in the LT-regulated albino processes of ZH2. Changes in DNA methylation levels were associated with changes in gene expression levels, affecting the structure and function of chloroplasts, which may have a phenotypic impact on shoot and leaf color.

Characterization of the Sensory Properties and Quality Components of Huangjin Green Tea Based on Molecular Sensory-Omics

Huangjin green tea (HJC) is one of the most famous regional green teas in China, and has gained attention for its unique flavor. Research on HJC has focused mainly on the synthesis of L-theanine, with fewer studies concentrating on sensory characteristics. In this study, molecular sensory science techniques, including color analysis, gas chromatography-ion mobility spectrometry, and E-tongue, were used to characterize the sensory properties of HJC, with Fuding Dabai and Anji Baicha teas used as conventional and high amino acid controls, respectively. The sensory characteristics and main quality components of HJC lie somewhere between these two other teas, and somewhat closer to the conventional control. They were difficult to distinguish by color, but significant differences exist in terms of volatile organic compounds (VOCs), E-tongue values on bitterness and astringency, and their contents of major taste components. VOCs such as (E)-2-octenal, linalool, ethyl acrylate, ethyl acetate, and 2-methyl-3-furanethiol were found to be the main differential components that contributed to aroma, significantly influencing the tender chestnut aroma of HJC. Free amino acids, tea polyphenols, and ester catechins were the main differential components responsible for taste, and its harmonious phenol-to-ammonia ratio was found to affect the fresh, mellow, heavy, and brisk taste of HJC.

Metabolic and Transcriptomic Profiling Reveals Etiolated Mechanism in Huangyu Tea (Camellia sinensis) Leaves

Leaf color is one of the key factors involved in determining the processing suitability of tea. It relates to differential accumulation of flavor compounds due to the different metabolic mechanisms. In recent years, photosensitive etiolation or albefaction is an interesting direction in tea research field. However, the molecular mechanism of color formation remains unclear since albino or etiolated mutants have different genetic backgrounds. In this study, wide-target metabolomic and transcriptomic analyses were used to reveal the biological mechanism of leaf etiolation for 'Huangyu', a bud mutant of 'Yinghong 9'. The results indicated that the reduction in the content of chlorophyll and the ratio of chlorophyll to carotenoids might be the biochemical reasons for the etiolation of 'Huangyu' tea leaves, while the content of zeaxanthin was significantly higher. The differentially expressed genes (DEGs) involved in chlorophyll and chloroplast biogenesis were the biomolecular reasons for the formation of green or yellow color in tea leaves. In addition, our results also revealed that the changes of DEGs involved in light-induced proteins and circadian rhythm promoted the adaptation of etiolated tea leaves to light stress. Variant colors of tea leaves indicated different directions in metabolic flux and accumulation of flavor compounds.

Integrated transcriptome and amino acid profile analyses reveal novel insights into differential accumulation of theanine in green and yellow tea cultivars

Tea cultivars with yellow- or white-leaf variations have a high economic value due to their high amino acid (especially theanine) concentration. However, the dynamic changes of amino acid components (especially theanine) and related gene expression during new shoot development in these cultivars are still unclear. In this study, 264 tea samples from four representative varieties picked during the harvest period in spring were analyzed for their amino acid profiles. The dynamic change rules of ethylamine and 19 amino acids were summarized in normal green and yellow cultivars during new shoot development. Interestingly, the theanine concentration in the yellow cultivar was significantly higher than that in the green cultivar, and increased gradually as the leaves matured until they reached a maximum in the one bud and three leaves stage. The amino acid concentration in the leaves of the yellow cultivar increased significantly with leaf position, which was generally in contrast to the normal green cultivar. Transcriptome and correlation analyses revealed that CsGS1, CsPDX2, CsGGP5, CsHEMA3 and CsCLH4 might be the key genes potentially responsible for the differential accumulation of theanine in green and yellow tea cultivars. These results provide further information for the utilization and improvement of tea plants.

Effects of different tea tree varieties on the color, aroma, and taste of Chinese Enshi green tea

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Chinese Enshi green tea quality varies with tea tree varieties.

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Chlorophyll and chlorophyllide determine the green tea color.

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Echa 10 endows Enshi green tea with fresh and mellow taste.

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Echa 10 endows Enshi green tea with clear flavor and honeysuckle fragrance.

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Phenethyl alcohol, jasmine, dodecane and octadecane contribute to honeysuckle scent.

Green tea processed by Echa 10 was shown to have a fresh and mellow taste as well as clean aroma with a clear honeysuckle fragrance. The colors of different Enshi green teas are closely related with the content of chlorophyll and chlorophyllide. The five green teas also vary in their aroma style. Echa 10 imparts a special honeysuckle fragrance, which was further analyzed by molecular sensory analysis and the formation of this honeysuckle fragrance was attributed to the key components of dodecane, octadecane, phenethyl alcohol, and jasmonone. In aroma evaluation, Echa 10 green tea showed the best performance, which is mainly related with the content of geraniol, linalool, phenethyl alcohol, and benzyl alcohol. Additionally, Echa 10 scored the highest in taste evaluation, which is mainly determined by the contents and ratios of tea polyphenols, amino acids, caffeine, and soluble sugars.

UPLC-QQQ-MS/MS-based widely targeted metabolomic analysis reveals the effect of solid-state fermentation with Eurotium cristatum on the dynamic changes in the metabolite profile of dark tea

Eurotium cristatum is the predominant fungus and key contributor to the characteristics of post-fermented Fu brick tea (FBT) during manufacturing. In this study, the influence of solid-state fermentation (SSF) with E. cristatum on the chemical profile dynamic changes of dark tea was investigated. Results indicated that total phenolics, flavonoids, theaflavins, thearubigins, and galloyl catechins consistently decreased, degalloyl catechins and gallic acid increased in the initial stage of fermentation and decreased after long-term fermentation, and theabrownins continually increased. UPLC-QQQ-MS/MS-based widely targeted metabolomic analysis revealed that the metabolites of dark tea processed by SSF with E. cristatum were drastically different from the raw material. A total of 574 differential metabolites covering 11 subclasses were detected in the whole SSF of dark tea, and the most drastic changes occurred in the middle stage. Phenolic acids and flavonoids were the two major classes of differential metabolites. A series of reactions such as degradation, glycosylation, deglycosylation, methylation, and oxidative polymerization occurred during SSF. Overall, SSF with E. cristatum greatly influenced the metabolites of dark tea, which provided valuable insights that E. cristatum is critical in forming the chemical constituents of FBT.

Identifying key genes involved in yellow leaf variation in 'Menghai Huangye' based on biochemical and transcriptomic analysis

Albino tea plants generally have higher theanine, which causes their tea leaves to taste fresher, and they are an important mutant for the breeding of tea plant varieties. Earlier, we reported an albino germplasm, 'Menghai Huangye' (MHHY), from Yunnan Province and found that it has a lower chlorophyll content during the yellowing stage, but the mechanism underlying low chlorophyll and the yellowing phenotype is still unclear. In this study, the pigment contents of MHHY_May (yellowing, low chlorophyll), MHHY_July (regreening, normal chlorophyll), and YK10_May (green leaves, normal chlorophyll) were determined, and the results showed that the lower chlorophyll content might be an important reason for the formation of the yellowing phenotype of MHHY. Through transcriptome sequencing, we obtained 654 candidates for differentially expressed genes (DEGs), among which 4 genes were related to chlorophyll synthesis, 10 were photosynthesis-related, 34 were HSP family genes, and 19 were transcription factor genes. In addition, we analysed the transcription levels of the key candidate genes in MHHY_May and MHHY_July and found that they are consistent with the expression trends in MHHY_May and YK10_May, which further indicates that the candidate differential genes we identified are likely to be key candidate factors involved in the low chlorophyll content and yellowing of MHHY. In summary, our findings will assist in revealing the low chlorophyll content of MHHY and the formation mechanism of yellowing tea plants and will be applied to the selection and breeding of albino tea cultivars in the future.

Jintiange Capsule Alleviates Rheumatoid Arthritis and Reverses Changes of Serum Metabolic Profile in Collagen-Induced Arthritic Rats

Purpose

Jintiange capsule (JTG), an approved drug developed as a substitute for tiger bone (TB), has been clinically applied for osteoporosis therapy since 2003. The drug is composed of bionic TB powder, in which peptides and proteins are primarily enriched from other bone extracts. However, as a precious material of traditional Chinese medicine (TCM), TB has been mainly understood and used in TCM to relieve osteoporosis, rheumatoid arthritis and bone injury. Inspired by those, the purpose of this study was to investigate whether JTG also had an effect on relieving rheumatoid arthritis in collagen-induced arthritic (CIA) rats and explore potential mechanism from the perspective of serum metabolic profile changes.

Methods

JTG was analyzed using Nano LC-MS/MS and orally administered in CIA rats for 6 weeks. After administration, intervention effects of JTG on synovial inflammation, bone micro-architecture and bone metabolism were studied, and the impact of JTG on serum metabolic profiles in CIA rats was investigated by metabolomics.

Results

Nine bioactive peptides were identified in JTG. In animal treatments, JTG alleviated paw swelling (P < 0.01), arthritic severity (P < 0.01) and synovial tissue proliferation, as well as inflammatory cell infiltration of ankle joint, decreased bone loss, improved microstructure of bone in CIA rats by regulating bone absorption and formation, specifically increasing bone mineral density (BMD) (P < 0.05), bone volume fraction (BVF) (P < 0.05), trabecular number (Tb.N) (P < 0.05) and decreasing trabecular separation (Tb.Sp) (P < 0.05). Besides, serum IL-6 was down-regulated remarkably in CIA rats (P < 0.05). Furthermore, metabolomics analysis revealed that 32 metabolites were regulated significantly (P < 0.05) by comparison between CIA model and JTG in 360 mg/kg dose. The pathway analysis implied that JTG was involved in regulation of biosynthesis of phenylalanine.

Conclusion

JTG alleviates rheumatoid arthritis and reverses changes in serum metabolic profile in CIA rats.

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Metabolic Profiles of Brassica juncea Roots in Response to Cadmium Stress

Brassica juncea has great application potential in phytoremediation of cadmium (Cd)-contaminated soil because of its excellent Cd accumulating and high biomass. In this study, we compared the effects of Cd under 48 h and 7 d stress in roots of Brassica juncea using metabolite profiling. The results showed that many metabolic pathways and metabolites in Brassica juncea roots were altered significantly in response to Cd stress. We found that significant differences in levels of amino acids, organic acids, carbohydrates, lipids, flavonoids, alkaloids, and indoles were induced by Cd stress at different times, which played a pivotal role in the adaptation of Brassica juncea roots to Cd stress. Meanwhile, Brassica juncea roots could resist 48 h Cd stress by regulating the biosynthesis of amino acids, linoleic acid metabolism, aminoacyl-tRNA biosynthesis, glycerophospholipid metabolism, ABC transporters, arginine biosynthesis, valine, leucine and isoleucine biosynthesis, and alpha-linolenic acid metabolism; however, they regulated alpha-linolenic acid metabolism, glycerophospholipid metabolism, ABC transporters, and linoleic acid metabolism to resist 7 d Cd stress. A metabolomic expedition to the response of Brassica juncea to Cd stress will help to comprehend its tolerance and accumulation mechanisms of Cd.

Analysis of Differentiated Chemical Components between Zijuan Purple Tea and Yunkang Green Tea by UHPLC-Orbitrap-MS/MS Combined with Chemometrics

Zijuan tea (Camellia sinensis var. assamica cv. Zijuan) is a unique purple tea. Recently, purple tea has drawn much attention for its special flavor and health benefits. However, the characteristic compounds of purple tea compared with green tea have not been reported yet. The present study employed a non-targeted metabolomics approach based on ultra-high performance liquid chromatography (UHPLC)-Orbitrap-tandem mass spectrometry (MS/MS) for comprehensive analysis of characteristic metabolites between Zijuan purple tea (ZJT) and Yunkang green tea (YKT). Partial least squares-discriminant analysis (PLS-DA) indicated that there are significant differences in chemical profiles between ZJT and YKT. A total of 66 major differential metabolites included catechins, proanthocyanins, flavonol and flavone glycosides, phenolic acids, amino acids and alkaloids were identified in ZJT. Among them, anthocyanins are the most characteristic metabolites. Nine glycosides of anthocyanins and six glycosides of proanthocyanins were found to be significantly higher in ZJT than that in YKT. Subsequently, pathway analysis revealed that ZJT might generate anthocyanins and proanthocyanins through the flavonol and flavone glycosides. Furthermore, quantitative analysis showed absolutely higher concentrations of total anthocyanins in ZJT, which correlated with the metabolomics results. This study presented the comprehensive chemical profiling and the characterized metabolites of ZJT. These results also provided chemical evidence for potential health functions of ZJT.

Non-targeted and targeted metabolomics profiling of tea plants (Camellia sinensis) in response to its intercropping with Chinese chestnut

BACKGROUND

Intercropping is often used in the tea producing areas where land resources are not so abundant, and the produced green tea is tasted more delicious through a tea-Chinese chestnut intercropping system according to the experience of indigenous farmers. The length and weight of tea leaf increase under this intercropping system and their root systems are stratified vertically and coordinate symbiosis. However, the delicacy mechanism under the intercropping is not fully understood.

RESULTS

Green tea from the Chinese chestnut-tea intercropping system established in the 1980s ranked highest compared with a pure tea plantation from the same region. Based on the non-targeted metabolomics, 100 differential metabolites were upregulated in the tea leaves from intercropping system relative to monoculture system. Twenty-one amino acids were upregulated and three downregulated in response to the intercropping based on the targeted metabolomics; half of the upregulated amino acids had positive effects on the tea taste. Levels of allantoic acid, sugars, sugar alcohols, and oleic acid were higher and less bitter flavonoids in the intercropping system than those in monoculture system. The upregulated metabolites could promote the quality of tea and its health-beneficial health effects. Flavone and flavonol biosynthesis and phenylalanine metabolism showed the greatest difference. Numerous pathways associated with amino acid metabolism altered, suggesting that the intercropping of Chinese chestnut-tea could greatly influence amino acid metabolism in tea plants.

CONCLUSIONS

These results enhance our understanding of the metabolic mechanisms by which tea quality is improved in the Chinese chestnut-tea intercropping system and demonstrate that there is great potential to improve tea quality at the metabolomic level by adopting such an intercropping system.