Dynamic Changes of Volatile Compounds during the Xinyang Maojian Green Tea Manufacturing at an Industrial Scale

Dynamic changes and the effects of key procedures on the characteristic aroma compounds of Lu'an Guapian green tea during the manufacturing process

As a kind of green tea with unique multiple baking processes, the flavor code of Lu'an Guapian (LAGP) has recently been revealed. To improve and stabilize the quality of LAGP, further insight into the dynamic changes in odorants during the whole processing is required. In this study, 50 odorants were identified in processing tea leaves, 14 of which were selected for absolute quantification to profile the effect of processes. The results showed that spreading is crucial for key aroma generation and accumulation, while these odorants undergo significant changes at the deep baking stage. By adjusting the conditions of the spreading and deep baking, it was found that low-temperature (4 °C) spreading for 6 h and low-temperature with long-time baking (final leaf temperature: 102 °C, 45 min) could improve the overall aroma quality. These results provide a new direction for enhancing the quality of LAGP green tea.

Combined multi-omics approach to analyze the flavor characteristics and formation mechanism of gabaron green tea

Gabaron green tea (GAGT) has unique flavor and health benefits through the special anaerobic treatment. However, how this composite processing affects the aroma formation of GAGT and the regulatory mechanism was rarely reported. This study used nontargeted metabolomics and molecular sensory science to overlay screen differential metabolites and key aroma contributors. The potential regulatory mechanism of anaerobic treatment on the aroma formation of GAGT was investigated by transcriptomics and correlation analyses. Five volatiles: benzeneacetaldehyde, nonanal, geraniol, linalool, and linalool oxide III, were screened as target metabolites. Through the transcriptional-level differential genes screening and analysis, some CsERF transcription factors in the ethylene signaling pathway were proposed might participate the response to the anaerobic treatment. They might regulate the expression of related genes in the metabolic pathway of the target metabolites thus affecting the GAGT flavor. The findings of this study provide novel information on the flavor and its formation of GAGT.

The Effects of Nitrogen Fertilizer on the Aroma of Fresh Tea Leaves from Camellia sinensis cv. Jin Xuan in Summer and Autumn

Nitrogen fertilization level and harvesting season significantly impact tea aroma quality. In this study, we analyzed the volatile organic compounds of fresh Jin Xuan (JX) tea leaves under different nitrogen application levels (N0, N150, N300, N450) during summer and autumn. A total of 49 volatile components were identified by gas chromatography-mass spectrometry (GC-MS). Notably, (E)-2-hexenal, linalool, and geraniol were the main contributors to the aroma of fresh JX leaves. The no-nitrogen treatment (N0) presented the greatest quantity and variety of volatiles in both seasons. A greater difference in volatile compounds was observed between nitrogen treatments in summer vs. autumn. The N0 treatment had a greater total volatile concentration in summer, while the opposite was observed in the nitrogen application treatments (N150, N300, N450). Summer treatments appeared best suited to black tea production. The concentration of herbaceous aroma-type volatiles was higher in summer, while the concentration of floral volatiles was higher in autumn. Volatile concentrations were highest in the N0 and N450 treatments in autumn and appeared suitable for making black tea and oolong tea. Overall, this research provides valuable insights into how variations in N application rates across different harvesting seasons impact the aroma characteristics of tea leaves.

Changes in profiles of volatile compounds and prediction of the storage year of organic green tea during the long-term storage

In the present study, the volatile compounds in organic green tea with a continuous storage period (ranging from 1 to 16 years) were comprehensively analyzed and compared through SDE-GC-MS and chemometrics. The results revealed that the total of 124 volatiles were identified, and their total amount was increased with the prolongation of the storage years. Ketones, alcohols, esters, and aromatic hydrocarbons were the main types of volatiles in organic green tea, among which 26 volatile compounds were significantly correlated with storage years, and six volatile compounds that were most seriously affected by the storage years. The results of the support vector machine classification combined with multiple linear regression analysis showed that the content-period prediction model for the six volatile compounds can accurately predict the storage years of organic green tea. Therefore, this study offers novel insights into volatile compounds changes during the storage of green tea.

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.

Characterization of key volatile compounds in jasmine tea infusion with different amount of flowers

The quality of jasmine tea is related to the volatiles of its infusion. In this study, the volatiles of jasmine tea infusion were extracted under the optimal conditions with a 50/30 μm DVB/CAR/PDMS fiber, tea/water ratio of 1:25 and extraction time of 5 min. A total of 204 volatiles were analyzed by comprehensive two-dimensional gas chromatography-quadrupole time-of-flight mass spectrometry (GC × GC-Q-TOF-MS). Twenty-five compounds were identified as the key volatile compounds by fold change (FC), orthogonal partial least squares discriminant analysis (OPLS-DA), and two-way orthogonal partial least squares analysis (O2PLS). Then optimal amount of flowers (80%-120%) was obtained by the equation describing key volatiles and quality of jasmine tea infusion. And 80% amount of flowers was more appropriate considering the production cost and more pleasant taste. This study laid a foundation for the extraction and research of volatiles of tea infusion and guided the reasonable amount of flowers to produce jasmine tea.

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.

The Cultivar Effect on the Taste and Aroma Substances of Hakka Stir-Fried Green Tea from Guangdong

The flavor and quality of tea largely depends on the cultivar from which it is processed; however, the cultivar effect on the taste and aroma characteristics of Hakka stir-fried green tea (HSGT) has received little attention. High-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), and sensory evaluations were used to detect and predict the essential taste and aroma-contributing substances of HSGTs made from Huangdan (HD), Meizhan (MZ) and Qingliang Mountain (QL) cultivars. Orthogonal partial least squares data analysis (OPLS-DA) ranked four substances that putatively distinguished the tastes of the HSGTs, epigallocatechin gallate (EGCG) > theanine > epigallocatechin (EGC) > epicatechin gallate (ECG). Ten substances with variable importance in projections (VIPs) ≥ 1 and odor activation values (OAVs) ≥ 1 contributed to their overall aromas, with geranylacetone having the most significant effect on HD (OAV 1841), MZ (OAV 4402), and QL (OAV 1211). Additionally, sensory evaluations found that HD was relatively equivalent to QL in quality, and both were superior to MZ. HD had a distinct floral aroma, MZ had a distinct fried rice aroma, and QL had a balance of fried rice and fresh aromas. The results provide a theoretical framework for evaluating the cultivar effect on the quality of HSGT and put forward ideas for future HSGT cultivar development.

Sensomics-Assisted Characterization of Key Flowery Aroma Compounds in Lu'an Guapian Green Tea Infusion (Camellia sinensis)

The volatile fraction was isolated from the premium and common grade of Lu'an Guapian green tea infusion by solvent-assisted flavor evaporation distillation. With the application of aroma extract dilution analysis, a total of 52 aroma-active compounds were revealed in the flavor dilution (FD) factor area of 32-8192. Besides, five additional odorants with higher volatility were identified using solid-phase microextraction. The aroma profiles, FD factors, and quantitative data of premium Guapian (PGP) and common Guapian (CGP) showed apparent differences. The intensity of the flowery attribute was significantly higher in PGP than in CGP, while cooked vegetable-like was the most outstanding odor note in CGP. The recombination experiment and the omission test of PGP clarified that dimethyl sulfide, (E,E)-2,4-heptadienal, (E)-β-ionone, (E,Z)-2,6-nonadienal, 2-methylbutanal, indole, 6-methyl-5-hepten-2-one, hexanal, 3-methylbutanal, γ-hexalactone, methyl epijasmonate, linalool, geraniol, and (Z)-3-hexen-1-ol were the key odorants of PGP tea infusion. The omission and addition tests of flowery odorants manifested that (E)-β-ionone, geraniol, and (E,E)-2,4-heptadienal, with higher odor activity values in PGP than in CGP, contributed to the flowery attribute most. The difference in the concentration of the abovementioned odorants with flowery odor notes could be one of the main factors which led to the difference in aroma quality between the two grades of Lu'an Guapian.

Understanding of formation and change of chiral aroma compounds from tea leaf to tea cup provides essential information for tea quality improvement

Abundant secondary metabolites endow tea with unique quality characteristics, among which aroma is the core component of tea quality. The ratio of chiral isomers of aroma compounds greatly affects the flavor of tea leaves. In this paper, we review the progress of research on chiral aroma compounds in tea. With the well-established GC-MS methods, the formation of, and changes in, the chiral configuration of tea aroma compounds during the whole cycle of tea leaves from the plant to the tea cup has been studied in detail. The ratio of aroma chiral isomers varies among different tea varieties and finished teas. Enzymatic reactions involving tea aroma synthases and glycoside hydrolases participate the formation of aroma compound chiral isomers during tea tree growth and tea processing. Non-enzymatic reactions including environmental factors such as high temperature and microbial fermentation involve in the change of aroma compound chiral isomers during tea processing and storage. In the future, it will be interesting to determine how changes in the proportions of chiral isomers of aroma compounds affect the environmental adaptability of tea trees; and to determine how to improve tea flavor by modifying processing methods or targeting specific genes to alter the ratio of chiral isomers of aroma compounds.