Biosynthesis of Jasmine Lactone in Tea ( Camellia sinensis) Leaves and Its Formation in Response to Multiple Stresses

Effect of Mechanical Damage in Green-Making Process on Aroma of Rougui Tea

Rougui Tea (RGT) is a typical Wuyi Rock Tea (WRT) that is favored by consumers for its rich taste and varied aroma. The aroma of RGT is greatly affected by the process of green-making, but its mechanism is not clear. Therefore, in this study, fresh leaves of RGT in spring were picked, and green-making (including shaking and spreading) and spreading (unshaken) were, respectively, applied after sun withering. Then, they were analyzed by GC-TOF-MS, which showed that the abundance of volatile compounds with flowery and fruity aromas, such as nerolidol, jasmine lactone, jasmone, indole, hexyl hexanoate, (E)-3-hexenyl butyrate and 1-hexyl acetate, in green-making leaves, was significantly higher than that in spreading leaves. Transcriptomic and proteomic studies showed that long-term mechanical injury and dehydration could activate the upregulated expression of genes related to the formation pathways of the aroma, but the regulation of protein expression was not completely consistent. Mechanical injury in the process of green-making was more conducive to the positive regulation of the allene oxide synthase (AOS) branch of the α-linolenic acid metabolism pathway, followed by the mevalonate (MVA) pathway of terpenoid backbone biosynthesis, thus promoting the synthesis of jasmonic acid derivatives and sesquiterpene products. Protein interaction analysis revealed that the key proteins of the synthesis pathway of jasmonic acid derivatives were acyl-CoA oxidase (ACX), enoyl-CoA hydratase (MFP2), OPC-8:0 CoA ligase 1 (OPCL1) and so on. This study provides a theoretical basis for the further explanation of the formation mechanism of the aroma substances in WRT during the manufacturing process.

Analysis of aroma precursors in Jinmudan fresh tea leaves and dynamic change of fatty acid volatile during black tea processing

Aroma is an important factor affecting the quality of tea. Fatty acids are one of precursors and their derived contributes to tea aroma considerably. In this study, we analyzed the fatty acids of Jinmudan fresh tea leaves in different stalk position. It was found that with shoot maturity increased, the content of PUFAs (Polyunsaturated fatty acids) was increased while the content of SFAs (Saturated fatty acids) and MUFAs (Monounsaturated fatty acids) gradually decreased. During the processing period, totally 704 kinds of compounds were identified, among them, 27 kinds of fatty acid-derived volatile compounds were selected including 6 kinds of aldehydes, 8 kinds of alcohols, 13 kinds of esters and their dynamic change were revealed. Finally, the character of aroma during main processing stages and processed tea was concluded by using a flavor wheel. This study results provide a theoretical basis for the improvement of processing and quality in Jinmudan black tea.

One-pot process for the biotransformation of vegetable oils into natural deca- and dodecalactones

Deca- and dodecalactones are highly desired natural compounds that are essential for creating flavor formulations with fruity, peachy, creamy, and floral notes. Although natural ingredients are preferred by consumers, these lactones cannot be extracted from natural sources. Therefore, the biotechnological processes that produce these compounds in their natural form are crucial for the flavor industry. Here, we report a study on the biotransformation of vegetable oils into natural deca- and dodecalactones. The proposed process is performed one-pot, through the sequential use of three different biotransformation steps, namely the lipase-mediated hydrolysis of the triglycerides, the use of probiotic bacteria for the hydration of the unsaturated fatty acids and the transformation of the obtained hydroxy-fatty acids into lactones derivatives employing Yarrowia lipolytica. By using a specific vegetable oil in combination with a selected bacterial strain, it is possible to obtain a preferred lactone derivative such as γ-dodecalactone, dairy lactone, tuberose lactone, or δ-decalactone in a concentration ranging from 0.9 to 1.5 g/L. Overall, our method is suitable for the industrial production of these lactones as it is easily scalable, it can be performed in only one bioreactor and it makes use of generally recognized as safe (GRAS) microorganisms.

Lipids: A noteworthy role in better tea quality

New shoots from tea plants (Camellia sinensis) are changed into finished tea after the process, which endows the products with a characteristic flavor. Tea quality is reflected in all aspects, from new shoots to the finished tea that are affected by cultivar, cultivation condition, harvest season, manufacturing methods, and quality of fresh tea leaves. Lipids are hydrophobic metabolites connected with tea flavor quality formation. Herein, we emphasize that the lipids composition in preharvest tea leaves is crucial for materials quality and hence tea flavor. The characterization of lipids in preharvest tea leaves provides a reference to obtain better tea quality. Lipids transformation in postharvest stages of tea leaves differs from varieties of tea types, and lipid oxidations functions in the tea flavor formation. A comprehensive overview of the lipids in tea leaves of preharvest and postharvest stages is necessary to improve tea quality.

Effect of shaking manners on floral aroma quality and identification of key floral-aroma-active compounds in Hunan black tea

Shaking is a key process effecting the floral aroma of Hunan black tea (HBT). In this study, the aroma composition of HBTs shaken in the early withering stage (ES1, ES1 + LS1, and ES2), shaken in the late withering stage (LS1), and not shaken (NS), and the identification of main floral aroma compounds were analyzed using sensory evaluation combined with gas chromatography-mass spectrometry (GC-MS), gas chromatography-olfactometry (GC-O), and aroma recombination experiments. Sensory evaluation results showed that the floral aroma of HBT shaken in the early withering stage was with high intensity, whereas HBT shaken in the late withering stage had low-intensity floral aroma. GC-MS identified a total number of 81 differential volatile compounds in HBT, including 30 esters, 18 aldehydes, 15 alcohols, 12 terpenes, 4 ketones, and 2 nitrogen-containing compounds. Further screening of important floral aroma differential compounds was performed using sensory-guided, odor activity value (OAV), and GC-O analysis, which identified three critical floral aroma differential compounds. Eventually, absolute quantification analysis and aroma recombination experiments confirmed that indole and methyl jasmonate were the most critical compounds of HBT determining floral aroma intensity. The findings of this study provide valuable guidance for the production of HBT with rich floral aroma attributes.

Comprehensive applications of metabolomics on tea science and technology: Opportunities, hurdles, and perspectives

With the development of metabolomics analytical techniques, relevant studies have increased in recent decades. The procedures of metabolomics analysis mainly include sample preparation, data acquisition and pre-processing, multivariate statistical analysis, as well as maker compounds' identification. In the present review, we summarized the published articles of tea metabolomics regarding different analytical tools, such as mass spectrometry, nuclear magnetic resonance, ultraviolet-visible spectrometry, and Fourier transform infrared spectrometry. The metabolite variation of fresh tea leaves with different treatments, such as biotic/abiotic stress, horticultural measures, and nutritional supplies was reviewed. Furthermore, the changes of chemical composition of processed tea samples under different processing technologies were also profiled. Since the identification of critical or marker metabolites is a complicated task, we also discussed the procedure of metabolite identification to clarify the importance of omics data analysis. The present review provides a workflow diagram for tea metabolomics research and also the perspectives of related studies in the future.

Identification of key volatile and odor-active compounds in 10 main fragrance types of Fenghuang Dancong tea using HS-SPME/GC-MS combined with multivariate analysis

Fenghuang Dancong tea (FHDC), a famous oolong tea originating from Guangdong Province in China, is known for its rich and unique fragrance. Nevertheless, the identification of the key aroma compounds with the difference fragrance types of FHDC remains uncertain. In order to characteristic the volatile components in different fragrance types of FHDC, 10 well-known fragrance types of FHDC and Tieguanyin (TGY) as a control were analyzed by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography mass spectrometry (GC-MS). Results indicated that 172 volatile compounds were identified as common volatile compounds among all the tea samples. A total of 16 compounds were identified as key compounds that could be used to distinguish between FHDC and TGY. Among the 10 FHDC fragrance types, indole, hotrienol, benzyl nitrile, and jasmine lactone were found to be the most abundant compounds. Despite the presence of certain similarities in aroma components, each type exhibits unique fragrance characteristics as a result of variation in compound composition content and proportion. Furthermore, using statistical and odor activity value analysis, 20 aroma-active compounds were recognized as potential characteristic markers accountable for the diverse fragrance types of FHDC. This research enhances our comprehension of the various fragrance types of FHDC and provides reference values for their rapid identification in the market.

5mC DNA methylation modification-mediated regulation in tissue functional differentiation and important flavor substance synthesis of tea plant (Camellia sinensis L.)

In plants, 5mC DNA methylation is an important and conserved epistatic mark involving genomic stability, gene transcriptional regulation, developmental regulation, abiotic stress response, metabolite synthesis, etc. However, the roles of 5mC DNA methylation modification (5mC methylation) in tea plant growth and development (in pre-harvest processing) and flavor substance synthesis in pre- and post-harvest processing are unknown. We therefore conducted a comprehensive methylation analysis of four key pre-harvest tissues (root, leaf, flower, and fruit) and two processed leaves during oolong tea post-harvest processing. We found that differential 5mC methylation among four key tissues is closely related to tissue functional differentiation and that genes expressed tissue-specifically, responsible for tissue-specific functions, maintain relatively low 5mC methylation levels relative to non-tissue-specifically expressed genes. Importantly, hypomethylation modifications of CsAlaDC and TS/GS genes in roots provided the molecular basis for the dominant synthesis of theanine in roots. In addition, integration of 5mC DNA methylationomics, metabolomics, and transcriptomics of post-harvest leaves revealed that content changes in flavor metabolites during oolong tea processing were closely associated with transcription level changes in corresponding metabolite synthesis genes, and changes in transcript levels of these important synthesis genes were strictly regulated by 5mC methylation. We further report that some key genes during processing are regulated by 5mC methylation, which can effectively explain the content changes of important aroma metabolites, including α-farnesene, nerolidol, lipids, and taste substances such as catechins. Our results not only highlight the key roles of 5mC methylation in important flavor substance synthesis in pre- and post-harvest processing, but also provide epimutation-related gene targets for future improvement of tea quality or breeding of whole-tissue high-theanine varieties.

Aroma Profile Development in Beer Fermented with Azacca, Idaho-7, and Sultana Hops

Hops are among the most costly and environmentally impactful raw materials used in brewing, yet they play a crucial role in the aroma of beer. However, predicting beer aroma based on hop variety or hopping method remains arduous. This is partly because hop oils are unique for each hop variety, and they may be biotransformed by yeast enzymes during fermentation. Even slight molecular structure modifications can dramatically affect the organoleptic properties of beer. Through combined chemical and sensory analysis of dry-hopped beers prepared with different hop varieties (Azacca, Idaho-7, and Sultana), this work aimed to profile the aromas and the overall biotransformation processes taking place during fermentation. A total of 51 volatile organic compounds (VOCs) were semi-quantified and monitored: 19 esters, 13 sesquiterpenes, 7 ketones, 7 alcohols, 4 monoterpenes, and 1 volatile acid. There were significant similarities in the measured analytes and perceived aromas of these beers, but one hop variety (Sultana) delivered an increased quantity of unique aromas and an increased concentration of volatiles in the headspace for the same quantity of hop pellets added. This work provides practical information to brewers who utilize hops in beer production.

Formation of 8-hydroxylinalool in tea plant Camellia sinensis var. Assamica 'Hainan dayezhong'

Linalool and its derivatives contribute greatly to tea aroma. Here, 8-hydroxylinalool was found to be one of the major linalool-derived aroma compounds in Camellia sinensis var. assamica 'Hainan dayezhong', a tea plant grown in Hainan Province, China. Both (Z)-8-hydroxylinalool and (E)-8-hydroxylinalool were detected, and the E type was the main compound. Its content fluctuated in different months and was the highest in the buds compared with other tissues. CsCYP76B1 and CsCYP76T1, located in the endoplasmic reticulum, were identified to catalyze the formation of 8-hydroxylinalool from linalool in the tea plant. During withering of black tea manufacturing, the content of both (Z)-8-hydroxylinalool and (E)-8-hydroxylinalool significantly increased. Further study suggested that jasmonate induced gene expression of CsCYP76B1 and CsCYP76T1, and the accumulated precursor linalool may also contribute to 8-hydroxylinalool accumulation. Thus, this study not only reveals 8-hydroxylinalool biosynthesis in tea plants but also sheds light on aroma formation in black tea.

Aroma Identification and Classification in 18 Kinds of Teas (Camellia sinensis) by Sensory Evaluation, HS-SPME-GC-IMS/GC × GC-MS, and Chemometrics

Tea (Camellia sinensis) is one of the most popular beverages worldwide. Many types of tea products continuously emerge in an endless stream; so, the classification of tea becomes more difficult. Aroma is a vital indicator of tea quality. The present study deals with the identification of aroma compounds in 18 different kinds of tea belonging to three typical tea varieties, including green tea, oolong tea, and black tea, using GC-IMS and GC × GC-O-MS. Moreover, the clustering of all 18 tea samples and the in depth correlation analysis between sensory evaluation and instrumental data were performed using the PCA and OPLS-DA. The results revealed that in all 18 kinds of tea, a total of 85 aroma compounds were detected by GC-IMS, whereas 318 were detected by GC × GC-O-MS. The PCA result revealed that green tea, oolong tea, and black tea could be clearly separated based on their peak areas. The OPLS-DA result showed that a total of 49 aroma compounds with VIP value > 1.0 could be considered as the potential indicators to quickly classify or verify tea types. This study not only compared the aroma differences across different types of teas, but also provided ideas for the rapid monitoring of tea quality and variety.

Microbial Transformations of Halolactones and Evaluation of Their Antiproliferative Activity

The microbial transformations of lactones with a halogenoethylocyclohexane moiety were performed in a filamentous fungi culture. The selected, effective biocatalyst for this process was the Absidia glauca AM177 strain. The lactones were transformed into the hydroxy derivative, regardless of the type of halogen atom in the substrate structure. For all lactones, the antiproliferative activity was determined toward several cancer cell lines. The antiproliferative potential of halolactones was much broader than that observed for the hydroxyderivative. According to the presented results, the most potent was chlorolactone, which exhibited significant activity toward the T-cell lymphoma line (CL-1) cell line. The hydroxyderivative obtained through biotransformation was not previously described in the literature.

Aroma formation and transformation during sealed yellowing process of Pingyang yellow tea

Yellow tea, a unique type of tea in China which is characterized with yellow color, has gained increasing popularity due to its pleasant taste. However, transformation of aroma compounds during sealed yellowing has been poorly understood. Results of sensory evaluation exhibited that yellowing time was the key factor for flavor and fragrance formation. A total of 52 volatile components during sealed yellowing process of Pingyang yellow soup were further collected and analyzed. The results demonstrated that the sealed yellowing process significantly increased the ratio of alcohol and aldehyde compounds in the aroma volatiles of yellow tea, which were primarily composed of geraniol, linalool, phenylacetaldehyde, linalool oxide and cis-3-hexenol, and their proportion increased with the prolongation of sealed yellowing. Mechanistic speculation revealed that the sealed yellowing process promoted release of alcoholic aroma compounds from their glycoside precursors and enhanced Strecker and oxidative degradation. This study revealed the transformation mechanism of aroma profile during the sealed yellowing process, which would facilitate processing of yellow tea.

Aroma characteristics of Wuyi rock tea prepared from 16 different tea plant varieties

Wuyi rock tea (WRT) is famous for its long history and unique characteristic of floral, fruity and nutty flavors. This study investigated the aroma characteristics of WRTs prepared from 16 different oolong tea plant varieties. The sensory evaluation results showed that all WRTs had an 'Yan flavor' taste, and the odor was strong and lasting. Roasted, floral and fruity odors were the prime aroma profiles for WRTs. Furthermore, a total of 368 volatile compounds were detected using HS-SPME-GC-MS and analyzed with OPLS-DA and HCA methods. The volatile compounds heterocyclic compounds, esters, hydrocarbons, terpenoids and ketones were the major aromatic components of the WRTs. Specifically, the volatile profiles among newly selected cultivars were comparatively analyzed, and 205 differential volatile compounds were found with variable importance in the projection (VIP) values above 1.0. These results indicated that the aroma profiles of WRTs were mainly dependent on the cultivar specificities of volatile compounds.

Comparative study of the volatile fingerprints of roasted and unroasted oolong tea by sensory profiling and HS-SPME-GC-MS

Roasting plays important roles in shaping the volatile profile of oolong tea. In this study, the sensory attributes and volatile compositions of 153 roasted or unroasted oolong tea samples, belonging to four typical types, namely, High Mountain oolong tea (HMT), Tieguanyin tea (TGYT), Dongding oolong tea (DDT) and Wuyi rock tea (WRT), were studied in detail. Based on the sensory evaluation by tea evaluation experts, their respective sensory profiles were established and compared. Unroasted teas had more pronounced fresh and green flavors, while roasted teas had higher scores in pungent and caramel flavors. In particular, WRT demonstrated a unique fragrance of floral fruity flavors. By using HS-SPME-GC-MS analysis, a total of 128 compounds were identified across all samples. Notably, it was found that roasting largely increased the variety of volatile compounds in oolong tea. Furthermore, the characteristic volatile compounds of each type of tea were identified by PLS-DA modeling. Linalool and geraniol were the characteristic volatiles of HMT. Four volatiles, including (E)-nerolidol, jasmin lactone, benzeneacetaldehyde, and 4-methyl benzaldehyde oxime were identified as the characteristic volatiles of TGYT. Seven volatiles, including N-ethyl pyrrole, 3-(hydroxy methyl) pyridine, 4-pyridylcarbinol, 1-methyl pyrrole-2-carboxaldehyde, 2-ethyl-3,5-dimethyl pyrazine, 4-amino-2,3-xylenol, and 4,6-dimethyl pyrimidine were the characteristic volatiles of DDT. For WRT, 2,2,6-trimethyl cyclohexan-1-one, hexanoic acid, benzaldehyde, benzyl alcohol, β-cyclocitral, (E)-β-ionone, α-ionone, and octanoic acid were the characteristic volatiles. These findings expand our knowledge of the volatile fingerprints of oolong tea.

Histone deacetylase CsHDA6 mediates the regulated formation of the anti-insect metabolite α-farnesene in tea (Camellia sinensis)

α-Farnesene accumulated in tea plants following infestations by most insects, and mechanical wounding is the common factor. However, the specific mechanism underlying the wounding-regulated accumulation of α-farnesene in tea plants remains unclear. In this study, we observed that histone deacetylase inhibitor treatment induced the accumulation of α-farnesene. The histone deacetylase CsHDA6 interacted directly with CsMYC2, which was an important transcription factor in the jasmonic acid (JA) pathway, and co-regulated the expression of the key α-farnesene synthesis gene CsAFS. Wounding caused by insect infestation affected CsHDA6 production at the transcript and protein levels, while also inhibited the binding of CsHDA6 to the CsAFS promoter. The resulting increased acetylation of histones H3/H4 in CsAFS enhanced the expression of CsAFS and the accumulation of α-farnesene. In conclusion, our study demonstrated the effect of histone acetylation on the production of tea plant HIPVs and revealed the importance of the CsHDA6-CsMYC2 transcriptional regulatory module.

The Impact of Different Withering Approaches on the Metabolism of Flavor Compounds in Oolong Tea Leaves

In this study, complementary metabolomic and proteomic analyses were conducted on the solar- and indoor-withered oolong tea leaves, and freshly plucked leaves as the control, for the purpose to reveal the mechanisms underlying the initial formation of some flavor determinants during the early stage of oolong tea processing. As a result, a total of 978 non-volatile compounds and 152 volatile compounds were identified, the flavonoids and several esters were differently accumulated in various tea samples. In total, 7048 proteins were qualitatively and quantitatively determined, the analysis on pathway enrichment showed that phenylpropanoid, flavonoid metabolisms, and protein processing in endoplasmic reticulum were the major pathways discriminating the different tea samples. The joint protein-metabolite analysis showed that the multiple stresses such as dehydration, heat, and ultra-violet irradiation occurred during the withering step induced the dynamic and distinct changes in the biochemical network in the treated leaves compared to fresh leaves. The significant decreases in flavonoids, xanthine alkaloids, and several amino acids contributed to the alleviation of bitter or astringent taste of withered leaves, although the decomposition of L-theanine resulted in the loss of umami flavor over the solar-withering step. Moreover, the fruity or floral aromas, especially volatile terpenoids and phenylpropanoids/benzenoids, were retained or accumulated in the solar withered leaves, potentially aiding the formation of a better characteristic flavor of oolong tea made by indoor withered tea leaves. Distinct effects of solar- and indoor-withering methods on the flavor determinant formation provide a novel insight into the relationship between the metabolite accumulation and flavor formation during the withering step of oolong tea production.

The stress-induced metabolites changes in the flavor formation of oolong tea during enzymatic-catalyzed process: A case study of Zhangping Shuixian tea

To interpret the environmental stresses induced dynamic changes of volatile and non-volatile constitutes in oolong tea leaves during enzymatic-catalyzed processes (ECP), metabolomic and proteomic studies were carried out using the processed leaf samples collected at the different stages of ECP for Zhangping Shuixian tea manufacture. Non-processed leaves were applied as control. Out of identified 980 non-volatiles and 157 volatiles, 40 non-volatiles and 8 volatiles were screened out as biomarkers, respectively. The integrated analysis on metabolites-proteins showed that phenylpropanoid biosynthesis, flavonoid biosynthesis, and phenylalanine metabolism were significantly enriched and highly correlated to the dynamic changes of key metabolites during ECP stage. A biological pathway network was constructed to illuminate the enzymatic-catalyzed production of critical flavoring compounds, including carbohydrates, amino acids, flavonoids, and volatile phenylpropanoids/benzenoids. The electronic-sensory analyses indicated leaf dehydration and mechanical wounding occurred over the sun-withering and turning-over steps are indispensable to form characteristic flavor of Shuixian tea.

Exogenous stimulation-induced biosynthesis of volatile compounds: Aroma formation of oolong tea at postharvest stage

Volatile organic compounds (VOCs) are produced by plants responding to biotic and abiotic stresses. According to their biosynthetic sources, induced VOCs are divided into three major classes: terpenoids, phenylpropanoid/benzenoid, and fatty acid derivatives. These compounds with specific aroma characteristics importantly contribute to the aroma quality of oolong tea. Shaking and rocking is the crucial procedure for the aroma formation of oolong tea by exerting mechanical damage to fresh tea leaves. Abundant studies have been carried out to investigate the formation mechanisms of VOCs during oolong tea processing in recent years. This review systematically introduces the biosynthesis of VOCs in plants, and the volatile changes due to biotic and abiotic stresses are summarized and expatiated, using oolong tea as an example.

Lipidomics analysis unravels changes from flavor precursors in different processing treatments of purple-leaf tea

BACKGROUND

Lipids are one of the most important bioactive compounds, affecting the character and quality of tea. However, the contribution of lipids to tea productions is still elusive. Here, we systematically identified the lipid profiles of green, oolong, and black teas in purple-leaf tea (Jinmingzao, JMZ) and green-leaf tea (Huangdan, HD), respectively.

RESULTS

The lipids analysis showed regular accumulation in tea products with different manufacturing processes, among which the fatty acids, glycerolipids, glycerophospholipids, and sphingolipids contribute to the quality characteristics of tea products, including typical fatty acyl (FA), monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerols (DGDG), and phosphatidylcholine (PC). Compared tea materials with products, levels of fatty acids were up-regulated, while glycerolipids and glycerophospholipids were down-regulated in tea products. FA 18:3, FA 16:0, MGDG 36:6, DGDG 36:6, PC 34:3, and PC 36:6 were the negative contributors to green tea flavor formation of purple-leaf tea. The pathway analysis of significant lipids in materials and products of purple-leaf tea were enriched linolenic acid metabolism pathway and glycerolipid metabolism.

CONCLUSION

This study provides insights into the lipid metabolism profiles of different tea leaf colors, and found that fatty acids are essential precursors of black tea flavor formation. © 2021 Society of Chemical Industry.

Effects of turning over intensity on fatty acid metabolites in postharvest leaves of Tieguanyin oolong tea (Camellia sinensis)

Fatty acid derived volatiles (FADVs) are major contributors to the aroma quality of oolong tea (Camellia sinensis). Most of the processing time for oolong tea is taken up by turning over treatments, but the full profile of fatty acid metabolic changes during this process remains unclear. In this study, we detected fatty acids, their derived volatiles, and related genes of Tieguanyin oolong tea using biochemical and molecular biology methods. The results showed that with an increase in turning over intensities, the content of total unsaturated fatty acids continuously dropped and the content of characteristic FADVs, such as hexanoic acid (Z)-3-Hexenly ester and 2-exenal, continued to increase. Lipoxygenase (LOX), a key gene family in the fatty acid metabolic pathway, showed different patterns, and CsLOX1 (TEA025499.1) was considered to be a key gene during the turning over processes. We found that fruit-like aroma (Z)-3-Hexen-1-ol acetate had a strong correlation with the expression levels of eight Camelia sinensis LOX family genes. Tieguanyin had relatively rich pleasant volatile compounds with moderate turning over intensity (five times turning over treatments). This study provides an overall view of how fatty acid metabolites change and affect the quality of oolong tea with different turning over intensities during processing.

Variations in Fatty Acids Affected Their Derivative Volatiles during Tieguanyin Tea Processing

Fatty acids (FAs) are important precursors of oolong tea volatile substances, and their famous derivatives have been shown to be the key aroma components. However, the relationship between fatty acids and their derivatives during oolong tea production remains unclear. In this study, fresh Tieguanyin leaves were manufactured into oolong tea and green tea (control), and fatty acids and fatty acid-derived volatiles (FADV) were extracted from processed samples by the sulfuric acid–methanol method and solvent-assisted flavor evaporation (SAFE), respectively. The results showed that unsaturated fatty acids were more abundant than saturated fatty acids in fresh leaves and decreased significantly during tea making. Relative to that in green tea, fatty acids showed larger variations in oolong tea, especially at the green-making stage. Unlike fatty acids, the FADV content first increased and then decreased. During oolong tea manufacture, FADV contents were significantly and negatively correlated with total fatty acids; during the green-making stage, methyl jasmonate (MeJA) content was significantly and negatively correlated with abundant fatty acids except steric acid. Our data suggest that the aroma quality of oolong tea can be improved by manipulating fatty acid transformation.

Regulation of biosynthesis of the main flavor-contributing metabolites in tea plant (Camellia sinensis): A review

In the process of adapting to the environment, tea plants (Camellia sinensis) endow tea with unique flavor and health functions, which should be attributed to secondary metabolites, including catechins, L-theanine, caffeine and terpene volatiles. Since the content of these flavor-contributing metabolites are mainly determined by the growth of tea plant, it is very important to understand their alteration and regulation mechanisms. In the present work, we first summarize the distribution, change characteristics of the main flavor-contributing metabolites in different cultivars, organs and under environmental stresses of tea plant. Subsequently, we discuss the regulating mechanisms involved in the biosynthesis of these metabolites based on the existing evidence. Finally, we propose the remarks and perspectives on the future study relating flavor-contributing metabolites. This review would contribute to the acceleration of research on the characteristic secondary metabolites and the breeding programs in tea plants.

Feasible strategies for studying the involvement of DNA methylation and histone acetylation in the stress-induced formation of quality-related metabolites in tea (Camellia sinensis)

Tea plants are subjected to multiple stresses during growth, development, and postharvest processing, which affects levels of secondary metabolites in leaves and influences tea functional properties and quality. Most studies on secondary metabolism in tea have focused on gene, protein, and metabolite levels, whereas upstream regulatory mechanisms remain unclear. In this review, we exemplify DNA methylation and histone acetylation, summarize the important regulatory effects that epigenetic modifications have on plant secondary metabolism, and discuss feasible research strategies to elucidate the underlying specific epigenetic mechanisms of secondary metabolism regulation in tea. This information will help researchers investigate the epigenetic regulation of secondary metabolism in tea, providing key epigenetic data that can be used for future tea genetic breeding.

New Insights into Stress-Induced β-Ocimene Biosynthesis in Tea (Camellia sinensis) Leaves during Oolong Tea Processing

As the major contributors to the floral odors of tea products, terpenoid volatiles play critical roles in the defense response of plants to multiple stresses. Until now, only a few TPS genes in tea plants (Camellia sinensis) have been functionally validated. In this study, by comparative studies conducted at gene, protein, and metabolite levels during oolong tea processing, we isolated an ocimene synthase gene, CsOCS, which displays a low similarity to previously characterized tea ocimene synthases. Further prokaryotic expression and subcellular localization analysis showed that it is plastid-located and could produce (E)-β-ocimene and (Z)-β-ocimene using GPP as the substrate. The optimum temperature and pH of the enzyme were 30 °C and 7.5, respectively. Treatment with exogenous methyl jasmonate elevated the transcript level of CsOCS and enhanced the emission of ocimene from tea leaves. Collectively, CsOCS is implicated as a key enzyme for β-ocimene synthesis during oolong tea processing.

Involvement of DNA methylation in regulating the accumulation of the aroma compound indole in tea (Camellia sinensis) leaves during postharvest processing

The manufacturing process of tea (Camellia sinensis), especially oolong tea, involves multiple postharvest stresses. These stresses can induce the formation and accumulation of many important aroma compounds, such as indole-a key floral aroma contributor of oolong tea. However, little is known about the regulation mechanisms of aroma compound formation, especially epigenetic regulation. DNA methylation is an important epigenetic modification. Changes in the DNA methylation levels of promoter sequences can regulate gene expression under stress conditions. In this study, the differences in DNA methylation levels and histone 3 lysine 9 dimethylation levels of indole key biosynthetic gene (tryptophan synthase β-subunit 2, CsTSB2) were detected between untreated and continuous wounding treatment tea leaves. The results show that the DNA methylation levels affect the ability of the basic helix-loop-helix family transcription factor CsMYC2a to bind to the promoter of CsTSB2. Analyses of the transcript levels of DNA methyltransferases during oolong tea processing screened out candidate genes involved in the regulation of secondary metabolite product biosynthesis/accumulation. The results suggest that the domains rearranged methyltransferase 3, a DNA methyltransferase, is involved in the DNA methylation regulation of indole formation during the oolong tea manufacturing process. This is the first report on the involvement of DNA methylation in the regulation of aroma compound formation in tea leaves exposed to postharvest stresses.

Epigenetic Regulation of the Phytohormone Abscisic Acid Accumulation under Dehydration Stress during Postharvest Processing of Tea (Camellia sinensis)

The plant hormone abscisic acid (ABA) accumulates in tea leaves under dehydration stress during the withering process. However, the mechanism underlying ABA biosynthesis regulation remains largely unclear. In the present study, we found increased expression of ABA biosynthesis genes under dehydration stress during postharvest processing of tea. Furthermore, dehydration stress promoted ABA accumulation by increasing histone acetylation of ABA anabolism genes but by decreasing the levels of histone H3 lysine 9 dimethylation and DNA methylation of ABA biosynthesis genes. We screened candidate regulators of histone deacetylation and DNA methylation under dehydration stress. Taken together, our results indicate a role for epigenetic modifications during postharvest processing of tea.

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.

Absolute Quantitative Volatile Measurement from Fresh Tea Leaves and the Derived Teas Revealed Contributions of Postharvest Synthesis of Endogenous Volatiles for the Aroma Quality of Made Teas

Characteristic aroma is a well-appreciated feature contributing to tea quality. Although extensive studies have been made to investigate aroma biosynthesis and gene expressions during tea making processes, it remains unclear whether the endogenous volatile biosynthesis during postharvest tea processing contributes to the aroma quality of made tea. To critically evaluate this question, we used the same batch of fresh tea leaves and produced three different types of tea with different degrees of fermentation (green tea, oolong tea, and black tea). Total volatiles were extracted by solvent-assisted-flavor evaporation, then quantified by gas chromatography-flame ionization detector combined with response factor correction for quantitative measurement. Compared with fresh tea leaves, the volatile profiles of the made teas were dramatically altered, with significant loss for the majority of endogenous volatiles and simultaneous gain for non-endogenous volatiles. By calculation of odor-activity values, the potential volatiles contributing to the aroma characteristics of each tea type were identified. Our data suggest that postharvest synthesis of endogenous volatiles did not contribute to the aroma quality of made tea.

How does tea (Camellia sinensis) produce specialized metabolites which determine its unique quality and function: a review

Tea (Camellia sinensis) is both a plant and a foodstuff. Many bioactive compounds, which are present in the final tea product and related to its quality or functional properties, are produced during the tea manufacturing process. However, the characteristic secondary metabolites, which give tea its unique qualities and are beneficial to human health, are produced mainly in the leaves during the process of plant growth. Therefore, it is important to understand how tea leaves produce these specialized metabolites. In this review, we first compare the common metabolites and specialized metabolites in tea, coffee, cocoa, and grape and discuss the occurrence of characteristic secondary metabolites in tea. Progress in research into the formation of these characteristic secondary metabolites in tea is summarized, including establishing a biological database and genetic transformation system, and the biosynthesis of characteristic secondary metabolites. Finally, speculation on future research into the characteristic secondary metabolites of tea is provided from the viewpoints of the origin, resources, cultivation, and processing of tea. This review provides an important reference for future research on the specialized metabolites of tea in terms of its characteristics.

Architecture and Dynamics of the Wounding-Induced Gene Regulatory Network During the Oolong Tea Manufacturing Process (Camellia sinensis)

Understanding extensive transcriptional reprogramming events mediated by wounding during the oolong tea manufacturing process is essential for improving oolong tea quality. To improve our comprehension of the architecture of the wounding-induced gene regulatory network, we systematically analyzed the high-resolution transcriptomic and metabolomic data from wounding-treated (after turnover stage) tea leaves at 11 time points over a 220-min period. The results indicated that wounding activates a burst of transcriptional activity within 10 min and that the temporal expression patterns over time could be partitioned into 18 specific clusters with distinct biological processes. The transcription factor (TF) activity linked to the TF binding motif participated in specific biological processes within different clusters. A chronological model of the wounding-induced gene regulatory network provides insight into the dynamic transcriptional regulation event after wounding treatment (the turnover stage). Time series data of wounding-induced volatiles reveal the scientific significance of resting for a while after wounding treatment during the actual manufacturing process of oolong tea. Integrating information-rich expression data with information on volatiles allowed us to identify many high-confidence TFs participating in aroma formation regulation after wounding treatment by using weighted gene co-expression network analysis (WGCNA). Collectively, our research revealed the complexity of the wounding-induced gene regulatory network and described wounding-mediated dynamic transcriptional reprogramming events, serving as a valuable theoretical basis for the quality formation of oolong tea during the post-harvest manufacturing process.

Jasminum grandiflorum: Influence of Flower Processing and Geographic Origin on Flower Absolute Composition

Five Jasminum grandiflorum flower absolutes harvested as flower buds and processed in the “ J. sambac-way” in different locations in the southern Indian state of Tamil Nadu were analyzed using gas chromatography (GC) and GC-mass spectrometry. These absolutes were compared with 5 commercial Indian J. grandiflorum flower absolutes manufactured in the traditional “ J. grandiflorum-way” from open flowers. Focus was placed on 42 key ingredients to investigate the influence of such a flower processing on the absolute composition. Our study established olfactive and composition differences of such absolutes produced via the “ J. sambac-way.” In addition, geographic variations in this species were analyzed by comparing 5 commercial Indian J. grandiflorum flower absolutes with absolutes from Egypt and Morocco, respectively. A composition range of the absolutes was established for the 3 main J. grandiflorum flower grower countries using a total of 14 commercial samples. The 12 main ingredients in the absolutes showed variations between 4.3% and 89.7%.

Analytical strategy coupled to chemometrics to differentiate Camellia sinensis tea types based on phenolic composition, alkaloids, and amino acids

Catechins, amino acids, and alkaloids are primary chemical components of tea and play a crucial role in determining tea quality. Their composition and content largely vary among different types of tea. In this study, a convenient chemical classification method was developed for six Camellia sinensis tea types (white, green, oolong, black, dark, and yellow) based on the quantification of their major components. Twenty-one free amino acids, 6 catechins, 2 alkaloids, and gallic acid in 24 teas were quantified using ultra-high-performance liquid chromatography (UHPLC). The total catechin contents in these tea samples ranged from 10.96 to 95.67 mg/g, while total free amino acid content ranged from 2.63 to 25.89 mg/g. Theanine (Thea) was the most abundant amino acid in all tea varieties. Catechin and amino acid levels in tea were markedly reduced upon fermentation of tea. Furthermore, high-temperature processing (roasting) during tea production induced degradation and epimerization of catechins, yielding epimerized catechins, simple catechins, and gallic acid. Principal component analysis revealed that major ester-catechins (EGCG and ECG), major amino acids (Thea), and major alkaloids (caffeine) are potential factors for distinguishing different types of tea. Linear discriminant analysis showed that 100% of teas were correctly classified in which (+)-catechin, ECG, EGC, gallic acid, GABA, cysteine, lysine, and threonine were the most discriminating compounds. This study shows that quantification of the major tea components combined with chemometric analysis, can serve as a simple, convenient, and reliable approach for classifying tea according to fermentation level. PRACTICAL APPLICATION: Different Camellia sinensis tea types can be produced worldwide but it is still challenging to know which chemical markers can be used to trace their production. in this paper we used a targeted methodology to classify six tea types (white, green, oolong, black, dark, and yellow) based on phenolic composition, alkaloids, and amino acids. The main chemical markers responsible for the discrimination were pinpointed with the use of chemometric tools.

Biochemical Pathway of Benzyl Nitrile Derived from l-Phenylalanine in Tea (Camellia sinensis) and Its Formation in Response to Postharvest Stresses

Volatiles affect tea (Camellia sinensis) aroma quality and have roles in tea plant defense against stresses. Some volatiles defend against stresses through their toxicity, which might affect tea safety. Benzyl nitrile is a defense-related toxic volatile compound that accumulates in tea under stresses, but its formation mechanism in tea remains unknown. In this study, l-[²H₈]phenylalanine feeding experiments and enzyme reactions showed that benzyl nitrile was generated from l-phenylalanine via phenylacetaldoxime in tea. CsCYP79D73 showed activity for converting l-phenylalanine into phenylacetaldoxime, while CsCYP71AT96s showed activity for converting phenylacetaldoxime into benzyl nitrile. Continuous wounding in the oolong tea process significantly enhanced the CsCYP79D73 expression level and phenylacetaldoxime and benzyl nitrile contents. Benzyl nitrile accumulation under continuous wounding stress was attributed to an increase in jasmonic acid, which activated CsCYP79D73 expression. This represents the first elucidation of the formation mechanism of benzyl nitrile in tea.

Alternative Splicing of Key Genes in LOX Pathway Involves Biosynthesis of Volatile Fatty Acid Derivatives in Tea Plant (Camellia sinensis)

Volatile fatty acid derivatives (VFADs) produced in tea plants (Camellia sinensis) not only have been shown to function as defense compounds but also impart a "fresh green" odor to green tea products; however, little is known about alternative splicing (AS) of genes in regulating the production of VFADs in plants. In this study, the contents of VFADs and corresponding transcriptome profiles were obtained in five different months (April, June, August, September, and October). Correlation analysis identified seven unique transcripts of enzyme-coding genes (CsLOX2, CsLOX4, CsADH4, CsADH8, and CsADH10), which are responsible for regulating VFAD biosynthesis; four AS transcripts of these genes (CsLOX2, CsLOX4, CsADH4, and CsADH8) were validated by RT-PCR. By employing the gene-specific antisense oligodeoxynucleotide-mediated reduction method, we found the expression levels of alternatively spliced transcripts of CsLOX4-iso1, CsLOX4-iso2, and CsADH4-iso3 were lower, and the contents of cis-3-hexenol were correspondingly reduced in the leaves of tea plant; this result suggested that the AS play important roles in regulating biosynthesis of VFADs in C. sinensis. Our results provide new insights into the important contribution of AS events in regulating the VFAD biosynthesis in tea plant.

Increasing Temperature Changes Flux into Multiple Biosynthetic Pathways for 2-Phenylethanol in Model Systems of Tea (Camellia sinensis) and Other Plants

2-Phenylethanol (2PE) is a representative aromatic aroma compound in tea (Camellia sinensis) leaves. However, its formation in tea remains unexplored. In our study, feeding experiments of [²H₈]L-phenylalanine (Phe), [²H₅]phenylpyruvic acid (PPA), or (E/Z)-phenylacetaldoxime (PAOx) showed that three biosynthesis pathways for 2PE derived from L-Phe occurred in tea leaves, namely, pathway I (via phenylacetaldehyde (PAld)), pathway II (via PPA and PAld), and pathway III (via (E/Z)-PAOx and PAld). Furthermore, increasing temperature resulted in increased flux into the pathway for 2PE from L-Phe via PPA and PAld. In addition, tomato fruits and petunia flowers also contained the 2PE biosynthetic pathway from L-Phe via PPA and PAld and increasing temperatures led to increased flux into this pathway, suggesting that such a phenomenon might be common among most plants containing 2PE. This represents a characteristic example of changes in flux into the biosynthesis pathways of volatile compounds in plants in response to stresses.

Formation of α-Farnesene in Tea (Camellia sinensis) Leaves Induced by Herbivore-Derived Wounding and Its Effect on Neighboring Tea Plants

Herbivore-induced plant volatiles (HIPVs) play important ecological roles in defense against stresses. In contrast to model plants, reports on HIPV formation and function in crops are limited. Tea (Camellia sinensis) is an important crop in China. α-Farnesene is a common HIPV produced in tea plants in response to different herbivore attacks. In this study, a C. sinensis α-farnesene synthase (CsAFS) was isolated, cloned, sequenced, and functionally characterized. The CsAFS recombinant protein produced in Escherichia coli was able to transform farnesyl diphosphate (FPP) into α-farnesene and also convert geranyl diphosphate (GPP) to β-ocimene in vitro. Furthermore, transient expression analysis in Nicotiana benthamiana plants indicated that CsAFS was located in the cytoplasm and could convert FPP to α-farnesene in plants. Wounding, to simulate herbivore damage, activated jasmonic acid (JA) formation, which significantly enhanced the CsAFS expression level and α-farnesene content. This suggested that herbivore-derived wounding induced α-farnesene formation in tea leaves. Furthermore, the emitted α-farnesene might act as a signal to activate antibacterial-related factors in neighboring undamaged tea leaves. This research advances our understanding of the formation and signaling roles of common HIPVs in crops such as tea plants.

Expression patterns of alpha-amylase and beta-amylase genes provide insights into the molecular mechanisms underlying the responses of tea plants (Camellia sinensis) to stress and postharvest processing treatments

The alpha-amylase and beta-amylase genes have been identified from tea plants, and their bioinformatic characteristics and expression patterns provide a foundation for further studies to elucidate their biological functions. Alpha-amylase (AMY)- and beta-amylase (BAM)-mediated starch degradation plays central roles in carbohydrate metabolism and participates extensively in the regulation of a wide range of biological processes, including growth, development and stress response. However, the AMY and BAM genes in tea plants (Camellia sinensis) are poorly understood, and the biological functions of these genes remain to be elucidated. In this study, three CsAMY and nine CsBAM genes from tea plants were identified based on genomic and transcriptomic database analyses, and the genes were subjected to comprehensive bioinformatic characterization. Phylogenetic analysis showed that the CsAMY proteins could be clustered into three different subfamilies, and nine CsBAM proteins could be classified into four groups. Putative catalytically active proteins were identified based on multiple sequence alignments, and the tertiary structures of these proteins were analyzed. Cis-element analysis indicated that CsAMY and CsBAM were extensively involved in tea plant growth, development and stress response. In addition, the CsAMY and CsBAM genes were differentially expressed in various tissues and were regulated by stress treatments (e.g., ABA, cold, drought and salt stress), and the expression patterns of these genes were associated with the postharvest withering and rotation processes. Taken together, our results will enhance the understanding of the roles of the CsAMY and CsBAM gene families in the growth, development and stress response of tea plants and of the potential functions of these genes in determining tea quality during the postharvest processing of tea leaves.

Elucidation of ( Z)-3-Hexenyl-β-glucopyranoside Enhancement Mechanism under Stresses from the Oolong Tea Manufacturing Process

The enzymatic hydrolysis of glycosidically bound volatiles (GBVs) plays an important role in tea aroma formation during the tea manufacturing process. However, during the enzyme-active manufacturing process of oolong tea, most GBVs showed no reduction, while ( Z)-3-hexenyl-β-glucopyranoside significantly enhanced at the turnover stage. This study aimed to determine the reason for this increase in ( Z)-3-hexenyl-β-glucopyranoside. Continuous wounding stress in the turnover stage did not enhance the expression level of glycosyltransferase 1 ( CsGT1), while it induced a significant increase in the ( Z)-3-hexenol content ( p ≤ 0.05). Furthermore, observing the cell structures of tea leaves exposed to continuous wounding and subcellular localizations of CsGTs suggested that the interaction of ( Z)-3-hexenol (substrate) and CsGT1 (enzyme) was available. In conclusion, both continuous wounding and subcellular localizations led to a ( Z)-3-hexenyl-β-glucopyranoside enhancement mechanism during the oolong tea's turnover stage. These results advance our understanding of GBV formation during the tea manufacturing process and their relationship with the stress from the tea manufacturing process. In addition, the information will help us further evaluate contribution of GBVs to enzymatic formation of oolong tea aroma compounds.

Influence of Chloroplast Defects on Formation of Jasmonic Acid and Characteristic Aroma Compounds in Tea (Camellia sinensis) Leaves Exposed to Postharvest Stresses

Characteristic aroma formation in tea (Camellia sinensis) leaves during the oolong tea manufacturing process might result from the defense responses of tea leaves against these various stresses, which involves upregulation of the upstream signal phytohormones related to leaf chloroplasts, such as jasmonic acid (JA). Whether chloroplast changes affect the formation of JA and characteristic aroma compounds in tea leaves exposed to stresses is unknown. In tea germplasms, albino-induced yellow tea leaves have defects in chloroplast ultrastructure and composition. Herein, we have compared the differential responses of phytohormone and characteristic aroma compound formation in normal green and albino-induced yellow tea leaves exposed to continuous wounding stress, which is the main stress in oolong tea manufacture. In contrast to single wounding stress (from picking, as a control), continuous wounding stress can upregulate the expression of CsMYC2, a key transcription factor of JA signaling, and activate the synthesis of JA and characteristic aroma compounds in both normal tea leaves (normal chloroplasts) and albino tea leaves (chloroplast defects). Chloroplast defects had no significant effect on the expression levels of CsMYC2 and JA synthesis-related genes in response to continuous wounding stress, but reduced the increase in JA content in response to continuous wounding stress. Furthermore, chloroplast defects reduced the increase in volatile fatty acid derivatives, including jasmine lactone and green leaf volatile contents, in response to continuous wounding stress. Overall, the formation of metabolites derived from fatty acids, such as JA, jasmine lactone, and green leaf volatiles in tea leaves, in response to continuous wounding stress, was affected by chloroplast defects. This information will improve understanding of the relationship of the stress responses of JA and aroma compound formation with chloroplast changes in tea.

Validation of reference genes for gene expression studies in post-harvest leaves of tea plant (Camellia sinensis)

Tea is one of three major non-alcoholic beverages that are popular all around the world. The economic value of tea product largely depends on the post-harvest physiology of tea leaves. The utilization of quantitative reverse transcription polymerase chain reaction is a widely accepted and precise approach to determine the target gene expression of tea plants, and the reliability of results hinges on the selection of suitable reference genes. A few reliable reference genes have been documented using various treatments and different tissues of tea plants, but none has been done on post-harvest leaves during the tea manufacturing process. The present study selected and analyzed 15 candidate reference genes: Cs18SrRNA, CsGADPH, CsACT, CsEF-1α, CsUbi, CsTUA, Cs26SrRNA, CsRuBP, CsCYP, CselF-4α, CsMON1, CsPCS1, CsSAND, CsPPA2, CsTBP. This study made an assessment on the expression stability under two kinds of post-harvest treatment, turn over and withering, using three algorithms-GeNorm, Normfinder, and Bestkeeper. The results indicated that the three commonly used reference genes, CsTUA, Cs18SrRNA, CsRuBP, together with Cs26SrRNA, were the most unstable genes in both the turn over and withering treatments. CsACT, CsEF-1α, CsPPA2, and CsTBP were the top four reference genes in the turn over treatment, while CsTBP, CsPCS1, CsPPA2, CselF-4α, and CsACT were the five best reference genes in the withering group. The expression level of lipoxygenase genes, which were involved in a number of diverse aspects of plant physiology, including wounding, was evaluated to validate the findings. To conclude, we found a basis for the selection of reference genes for accurate transcription normalization in post-harvest leaves of tea plants.