Abstract
Tea processing plays an important role in the formation of tea aroma. In order to explore the composition and variation in aroma during Rizhao green tea processing, gas chromatography-ion mobility spectrometry was employed to investigate the formation and changes of tea aroma in four processing stages. A total of 62 volatile compounds were identified, including alcohols, aldehydes, ketones, esters, terpenes, and oxygen compounds. Relative odor activity value was used to identify 17 characteristic aroma compounds. The main aromatic compounds of chestnut-like aroma were linalool, pentanal, hexanal, heptanal, octanal, nonanal, 2-methylbutanal, 3-methylbutanal, 3-methylthiopropanal, and methyl 2-methylbutanoate. There were significant changes in the volatile components at different processing stages. Samples of tea leaves and green tea had special aroma characteristics, while samples of fixated and rolled leaves had similar aroma compounds. The results are beneficial for the improvement of the flavor and quality of Rizhao green tea. Practical Application. Tea is the world’s most consumed nonalcoholic beverage, with a multitude of health-promoting benefits, such as antioxidant, antiobesity, and antiallergic activities. At present, the research on the aroma compounds of Rizhao green tea mainly focuses on the aroma characteristics of finished tea and the aroma differences of different kinds of commercial tea. This study explored the effects of the processes on aroma compounds, and the results provide a theoretical reference for the improvement of tea processing technology, tea quality control, and evaluation methods.
1. Introduction
According to the fermentation degree, tea can be classified as green, white, yellow, oolong, black, or dark tea [1]. Rizhao green tea is a type of green tea produced in Rizhao in the Shandong Province of China. Fresh leaves, buds, and tender stems of the tea plants (Camellia sinensis (L.) O. Kuntze) are processed, without fermentation, through high-temperature fixation, rolling, and drying techniques [2]. The city of Rizhao has a warm, temperate, and humid monsoon climate, adequate light, large temperature differences between day and night, weakly acidic soil, and high organic matter content. These unique climatic and geographical conditions are conducive to the growth of tea trees and the accumulation of metabolites. Therefore, Rizhao green tea has unique and excellent qualities, such as strong buds and leaves, which can endure repeated brewing, yellow-green soup, chestnut-like aroma, and is gaining increasing worldwide popularity that is known as “the first tea in the northern region of the Yangtze river” [3].
Flavor substances are important quality characteristics of tea. There are great differences in the composition and content of flavor substances in tea with different fermentation degrees [4]. In addition, these tea flavor substances differ due to chemical changes in processing [5]. Tea aroma is one of the important factors that determine the quality of tea and is detected by human olfactory organs [6]. Previous studies have shown that the volatile components of Rizhao green tea include hydrocarbons, alcohols, and esters with special floral and fruity aromas, indoles, and furans with roasted aromas. Among them, cis-3-hexenol, linalool, hexanal, 3-methylbutanal, and 2-pentylfuran provide the chestnut-like aroma of Rizhao green tea [7].
Tea aroma quality is determined via sensory evaluation, electronic nose, gas chromatography-olfactometry, and odor activity values. Sensory evaluation relies on human sensory organs and has uncertainty and instability caused by human error [8]. Instrumental analysis methods, such as chromatography and mass spectrometry, require complex sample pretreatment and cannot achieve rapid detection in the field [9]. Relative odor activity value (ROAV) is a new method of evaluating the contribution of different threshold compounds to the overall aroma, and it can be used to determine the contribution of volatile substances to the aroma characteristics of samples [10]. It has been used to identify key aroma compounds in foods [11, 12].
Gas chromatography-ion mobility spectroscopy (GC-IMS) is a new gas chromatography separation and detection technology that has emerged recently. It does not require sample pretreatment and achieves nondestructive and rapid detection [13], making it suitable for trace detection of volatile components [14]. GC-IMS first separates the complex volatile components of green tea by gas phase. The components flowing out at different retention times collide with the reverse drift gas molecules, and the secondary separation is carried out [15]. By obtaining the ion drift time and ion peak intensity, each component can be qualitatively and quantitatively analyzed. At present, GC-IMS is applied in traditional Chinese medicine [16], clinical examination [17], food [18] and environmental analysis [19].
There is no systematic report on the changes and formation mechanism of aroma compounds in Rizhao green tea during processing. In this study, GC-IMS technology was used to collect and analyze the volatile components of Rizhao green tea during processing, and the key odorants were screened by the ROAV method to explore the influence of processing on the aromatic substances in Rizhao green tea. The analysis of volatile components during tea processing is important to study the effects of the processes on aroma compounds in Rizhao green tea and the improvement of Rizhao tea flavor and quality.
2. Materials and Methods
2.1. Experimental Materials and Instruments
Rizhao green tea samples were collected on the first week of May in 2021 at Shenggushan Tea Farm Co., Ltd. (Rizhao, Shandong, China). The fresh tea leaves with one or two leaves and one bud were repeatedly collected and screened by tea makers to ensure the samples are more representative in appearance, colour, shape, and other aspects, and then converted into commercial premium green tea of first grade, according to the standard process of withering, fixation, rolling, and drying. Postharvested samples were spread out from 4 h to 6 h. Following this step, tea samples were fixed at 230°C for 1 min to reach a relative humidity of 60%, rolled at room temperature for 35 min, and dried at 90°C for 20 min to produce Rizhao green tea. Tea samples () from four key processing stages were named as tea leaves (TL), fixated leaves (FL), rolled leaves (RL), and green tea (GT) and were placed in centrifuge tubes, packed with sealing film, and transported to the laboratory at low temperature. The tea samples from each processing step were crushed with a household blender for 7–8 s and stored at −20°C.
The volatile metabolites of Rizhao green tea were analyzed using the FlavourSpec® GC-IMS system (G.A.S. Department of Shandong Haineng Science Instrument Co., Ltd., Shandong, China) equipped with an autosampler unit (CTC Analysis AG, Zwingen, Switzerland), Laboratory Analytical Viewer analysis software, GC × IMS Library Search software, and the NIST and IMS built-in databases.
2.2. GC-IMS Analysis
Samples (1.5 g) from different processing stages were weighed into 20-mL head space bottles and incubated at 50°C for 15 min with rotation at 500 rpm. Then, 500 μL of the headspace sample was injected into the heated injector (85°C). After injection, the samples were detected by GC-IMS instrument. Each sample was analyzed at least in triplicate.
The GC-IMS conditions were as follows: an MXT-5 capillary column (, 1 m) was used at a column temperature of 60°C. The carrier gas was pure helium (99.999%) for 0–20 min. and with the following linear gradient: the initial carrying flow rate of carrying was 2 mL/min, held for 2 min and then increased to 100 mL/min for 18 min. The IMS drift tube was 110°C, and the drift gas was pure helium (99.999%) at 150 mL/min for 20 min.
2.3. Data Analysis
The GC-IMS data analysis software included VOCal and three plug-ins, which were used to analyze the samples from different perspectives. The reporter and Gallery Plot plug-ins were used to obtain the differences in the spectra of the tea samples and generate fingerprints of the volatile compounds. The dynamic principal component analysis (PCA) plug-in and K-fingerprint analysis were used to perform dynamic PCA for clustering analysis and similarity analysis of samples. VOCal was mainly used to analyze spectrograms and to obtain qualitative and quantitative information. The NIST and IMS databases were built into the software for qualitative analysis of the materials. Volatile compound content is the normalized relative peak volume (%), and the results are presented as the mean of triplicate measurements.
2.4. Statistical Analysis
The processed data were then exported to SIMCA 14.1 (Umetrics AB, Umea, Sweden) software for multivariate statistical analysis, including PCA, partial least-squares discriminant analysis (PLS-DA), and orthogonal partial least-squares discriminant analysis (OPLS-DA). A cross-validation plot of the OPLS-DA model was generated with 200 permutation tests. After multivariate statistical analysis, the differences between groups were tested with the Student t-test (), and univariate statistical analysis was performed by one-way ANOVA using SPSS Statistics 26.0 (IBM Corp., Armonk, NY).
2.5. ROAV Calculation
The ROAV was used to evaluate the contribution of volatile compounds to the overall aroma and was calculated according to the formula [12]:
Where represents the odor activity value of , represents the odor activity value for the compounds that contribute the most to the overall flavor. (%) and (mg/kg) represent the relative content and the sensory threshold of each volatile component, respectively, represents the relative content of the compound that contributes the most to the overall flavor (%), and represents the sensory threshold for the compounds that contributes the most to the overall flavor (mg/kg).
3. Results and Discussion
3.1. Qualitative and Multivariate Statistical Analysis of Rizhao Green Tea Processing
The volatile compounds in the Rizhao green tea samples from four key processing stages, namely, tea leaves (TL), fixated leaves (FL), rolled leaves (RL), and green tea (GT), were analyzed by GC-IMS technology. As shown in Figure 1, the qualitative and quantitative analyses of Rizhao green tea at different processing stages were carried out by VOCal software, which is built in to the GC-IMS. A total of 85 volatile substances were detected (Table S1, list of the 85 volatile compounds in the process of Rizhao green tea). Sixty-two volatile substances, including monomers and dimers, were identified through the NIST database and IMS database built into the software. The compounds include 15 alcohols, 20 aldehydes, 13 ketones, 10 esters, 2 terpenes, and 2 oxygen compounds.
Rizhao green tea samples from four processing stages were analyzed by multivariate statistical analysis. The results are shown in Figure 2. In the score scatter plot of PCA (Figure 2(a)), the cumulative contribution rate of the two principal components was 79%, which could distinguish TL and GT successfully, and a close aggregation was seen between the FL and RL samples, indicating the differences between and similarities of their volatile component compositions. The results of PLS-DA (Figure 2(b)) and OPLS-DA (Figure 2(c)) are consistent with those of PCA. The cross-validation with 200 permutation verifications (Figure 2(d)) indicate that the OPLS-DA model is reliable.
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Figure 2(e)shows the Euclidean distance between samples. It can be seen from the figure that the distance between FL and RL was the closest, and the distance between TL and GT was the farthest, indicating that the volatile substances in Rizhao green tea at different processing stages were quite different, and some substances showed certain regularity, that is, the volatile components of TL and GT were relatively special, while the volatile components of FL and RL were highly similar.
3.2. Spectral Analysis and Fingerprint of Volatile Compounds
The GC-IMS instrument-supported reporter plug-in could directly compare the differences in the spectra between samples. Figure 3(a) is a three-dimensional spectrum of volatile substances in samples, in which the ordinate is the retention time of gas chromatography, and the abscissa is the ion migration time. Figure 3(b) shows the comparison plots of volatile components in the samples. With the TL sample as the reference, the different volatile substances were evaluated by comparing the spectrum colors of the other three types of samples. The darker the red was, the more the corresponding substance concentration was higher than that in TL. The darker the blue, the reverse was true. It could be seen that there are great differences in volatile substances between the four groups, and the most volatile substances in TL are significantly higher than those in the other three groups. The contents of volatile organic compounds in FL and RL were similar in the abscissa of 1.2–1.75 and the ordinate of 250–420 s.
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Figure 4 shows the fingerprints of volatile compounds in Rizhao tea at different processing stages. Comparing the composition and changes of aroma in different processing stages, the results are consistent with the results of the difference comparison plots and multivariate statistical analysis. The volatile compounds in the red frame included (E)-ocimene, linalool, linalool oxide monomer, and its dimer, benzene acetaldehyde monomer and its dimer, alpha-phellandrene, methyl salicylate, 2-pentyl furan, and benzaldehyde monomer and its dimer, 3-methylthiopropanal monomer and its dimer, n-hexanol monomer and its dimer, (E)-2-hexenyl, (E)-2-pentenal, heptan-2-ol, and methyl hexanoate monomer and its dimer, 3-methyl-1-pentanol, 2-butanol, ethyl acetate, isoamyl acetate, 3-pentanone, methyl acetate, butanal, and (E)-2-hexen-1-ol monomer and its dimer, 2-heptanone monomer and its dimer, 2-methylbutanal, 3-methylbutanal, and unknown substances that were not identified numbered 1, 10, 20, 21, 22. Their relative contents in tea samples were significantly higher than that in other processing stages, and they were identified as special volatile substances in TL.
The volatile substances in the yellow frame included methyl-5-hepten-2-one, oct-1-en-3-ol, 2-butoxyethanol, 3-hydroxybutan-2-one, methyl isobutyl ketone, 2-butanone, acetone, ethyl formate, methyl 2-methylbutanoate, 2-pentanone, and 1-pentanol monomer and its dimer, and unknown substances 11, 13, 14, 15, 17, 18. Their relative contents were significantly higher than those of the samples in other processing stages, and they were identified as unique volatile substances in the FL and RL samples.
The volatile compounds in the green box are 2-hexanone monomer and its dimer, nonanal, (E)-hept-2-enal monomer and its dimer, octanal monomer and its dimer, cyclohexanone monomer and its dimer, heptanal monomer and its dimer, (E)-3-hexen-1-ol, butyl acetate, 2-furanmethanol, hexanal monomer and its dimer, pentanal, and unknown substances 2, 3, 4, 5, 6, 7, 8, 16, 19, 23. Their relative contents were significantly higher than those of the samples in other processing points, and they are specific to the GT sample.
In summary, linalool, phellandrene, methyl salicylate, methyl hexanoate, benzaldehyde, benzene acetaldehyde, 2-heptanone, hexanol, 2-pentylfuran, and other substances had the highest relative content in the TL. The relative contents of pentanal, hexanal, heptanal, octanal, nonanal, and other substances in the GT samples were the highest; the contents of acetone, butanone, and pentanone were the highest in the FL or RL samples.
3.3. Changes in Volatile Compounds in Rizhao Green Tea during Processing
There are two sources of tea aroma compounds: one is inherent in fresh leaves and the other is generated from precursors during manufacturing through enzymatic and thermophysical activities [20]. The original free aroma compounds in fresh leaves are not only few in species but are also very small in retention after processing. Therefore, processing is the main reason for tea aroma production [21]. As shown in Figure 5, the volatile organic compounds in Rizhao green tea vary greatly at different processing stages. Alcohols accounted for 44.00% of the total aroma in the TL. However, the content gradually reduced after processing. In the GT stage, they accounted for less than 10.00%. Aldehydes were relatively stable and increased significantly only at the final stage of green tea processing. This is due to the Strecker reaction and phospholipid-induced lipid degradation [22]. The proportion of ketones increased gradually with the advance of the processing stage, especially from the TL stage to the FL stage. Compared with other stages, esters accounted for a higher proportion in TL. Ester content decreased significantly from TL to FL and then stabilized. The proportion of terpenes and oxygen compounds was always less than 1.00%.
Fresh leaves contain a variety of esters, such as (E)-2-hexenyl acetate and methyl salicylate. After high-temperature fixation, the aroma compounds in fresh tea leaves changed fundamentally. Most of the low-boiling grass aroma substances were lost, and the contents of high-boiling aldehydes, alkenes, and aromatic hydrocarbons increased significantly, such as 2-methylbutanal, 3-methylbutanal, and nonanal. With the increase in temperature and the decrease in water content, a variety of enzymatic reactions occur, which greatly increase the types of aroma compounds in tea. At the same time, a large number of volatile compounds were produced in the dehydration reaction of sugar, amino acids, and pectin, forming roasted and fresh aromas [23]. Tea fixation led to the dissipation of volatile metabolites with low boiling point as well as green flavor. Fixation also promoted the formation of ketones, aldehydes, and other metabolites with chestnut, floral, and fruity aromas.
Rolling can damage the cells of fresh leaves, causing the overflow of tea juice and increasing the leaching rate of tea. This leads to the further transformation and degradation of biochemical components within the tea. However, most aroma compounds show a decreasing trend during shaping after rolling. Unrolled tea is often floral. Most of the rolled tea is green, and the aroma concentration and freshness are lower than unrolled tea. Catechins inhibited the formation of terpenic alcohols, such as geraniol and linalool, at the subcellular level, catechins are mainly located in the chloroplasts and vacuoles [24]. When the cells were distorted and the outer membrane of the chloroplast was broken due to rolling, polyphenols were mixed with various inclusions located in the cytoplasm, which may affect the formation and transformation of aromatic substances in rolling tea [25].
The thermophysical and chemical effects of the drying process are important for the development of green tea aroma. After the drying process, the content of aromatic substances in the products changed significantly, compared with fresh leaves and fixated leaves. The contents of aliphatic alcohols and aldehydes, with green flavors and low boiling points, continued to decrease. Esters, aroma compounds, terpenes with clean or floral aromas, and furfural are the products of the Maillard reactions and impart a pleasant and roasted burnt flavor. The contents of these compounds greatly increased. Some original components of lower content in fixated leaves increased significantly during the drying stage, such as pentanal, heptanal, nonanal, and cyclohexanone, which greatly enriched the aroma compounds in tea.
The aroma compounds in Rizhao green tea underwent tremendous changes through three key processes, including fixation, rolling, and drying. These changes are related to the enzymatic reactions and chemical reactions during processing.
3.4. Identification of Key Odorants Responsible for Rizhao Green Tea during Processing
The variations in the content of volatile organic compounds, the aroma sensory threshold [26] and the ROAV of the samples are shown in Table 1.
The common aroma types of green tea include pekoe-flavor, tender-flavor, delicate-flavor, chestnut-flavor, and high fired-flavor [27]. Rizhao green tea’s chestnut-like aroma is determined by the relative content of volatile components and sensory threshold. Only some compounds contributed significantly to the overall flavor of Rizhao green tea. By calculating the ROAV of the finished green tea, namely the GT sample, the main aromatic substances were determined. It is generally believed that the volatile substances with are key flavor substances in the sample, and the volatile substances with play a role in modifying the overall flavor of the sample. We selected the ROAV of octanal, which contributed the most to the flavor of the sample, as 100, and calculated the relative ROAV of each component. The key odorants compounds in Rizhao green tea included linalool (ROAV:6.5), pentanal (ROAV:7.7), hexanal-M (ROAV:5.6), hexanal-D (ROAV:12), heptanal-M (ROAV:2.4), heptanal-D (ROAV:1.5), octanal-M (ROAV:100), octanal-D (ROAV:16), nonanal (ROAV:1.1), 2-methylbutanal (ROAV:54), 3-methylbutanal (ROAV:13), 3-methylthiopropanal-M (ROAV:27), 3-methylthiopropanal-D (ROAV:40), and methyl 2-methylbutanoate (ROAV:6.7). Some volatile compounds also had an effect on the aroma characteristics of Rizhao green tea, such as oct-1-en-3-ol (ROAV:0.2), benzeneacetaldehyde-M (ROAV:0.6), 2-pentanone (ROAV:0.4), 2-hexanone-M (ROAV:0.2), 2-hexanone-D (ROAV:0.3), methyl-5-hepten-2-one (ROAV:0.2), isoamyl acetate (ROAV:0.2), and 2-pentyl furan (ROAV:0.7).
According to the flavor wheel classification method [28], 14 kinds of aroma compounds with a ROAV value greater than 1 were classified into five categories according to their flavor characteristics: green, fruity ester-like, citrus-like, floral, and caramel nutty flavors. Figure 6 shows the change trend of the key odorant compounds of different aroma types in each processing stage. It can be seen that the processing procedure has a great influence on the aroma compounds. The content of linalool, a floral aromatic substance, was significantly reduced in the fixation and drying stages. The contents of aromatic substances with green, fruity ester-like, and citrus-like flavors increased with processing, contributing to the strong and clean flavor of green tea. The increase in aromatic substances with caramel nutty flavor presents a cocoa, nutty flavor as well as a chestnut-like aroma with a roasted burnt flavor.
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3.5. Discussion
In Rizhao green tea products, ketones and aldehydes accounted for the largest proportion, followed by alcohols and esters. This was similar to previous research results. Li et al. [3] found that the aroma compounds in Rizhao green tea were mainly alcohols, aldehydes, acids, and phenols. Aldehydes, esters, and olefins also played a role. Liu [7] speculated that the aroma compounds in Rizhao curly green tea and Rizhao pelleted green tea were mainly hydrocarbons, esters, and alcohols, followed by ketones and aldehydes. The authors showed that the tea contains a large number of volatiles from saturated and unsaturated fatty acids, including alcohols and aldehydes. Saturated and unsaturated aldehydes and alcohols (especially C6, C9) are important contributors to the characteristic aroma of clean flavor [29].
The ROAV results showed that 17 kinds of volatile compounds had an effect on the aroma characteristics of Rizhao green tea products. Among them, linalool, pentanal, hexanal, heptanal, octanal, nonanal, 2-methylbutanal, 3-methylbutanal, 3-methylthiopropanal, and methyl 2-methylbutanoate were the key flavor compounds. Zhang [27] have reported that the contribution of linalool, hexanal, heptanal, nonanal, and other key aroma components to the characteristic aroma of chestnut-like green tea was preliminarily confirmed. In our study, the main flavor substances of Rizhao green tea are aldehydes and alcohols. Nevertheless, this is different from the results reached by He et al. [21], who reported that esters with floral or fruity flavors were more beneficial to the formation of aroma in fragrant green tea. Aldehydes are closely related to the formation of tea aroma. Low molecular aliphatic aldehydes have a strong pungent odor. With the increase in the relative molecular mass, the irritation degree of the odor decreases, and a pleasant aroma gradually appears. Among them, hexanal and heptanal with grassy aroma have low boiling point and high threshold [30], which is perceived to be one of the important reasons for the slight grassy aroma in green teas with chestnut-like aroma. Nonanal has rose and waxy aromas, and 2-methylbutanal has malty and cocoa aromas [31]. The threshold of saturated alcohols was higher than that of unsaturated alcohols, and it contributes to the flavor of tea at high concentrations. Unsaturated alcohols have a relatively low threshold and contribute greatly to tea flavor. For example, 1-octen-3-ol has a mushroom-like aroma [30]. Terpene alcohols have a high boiling point, which play an important role in the formation of tea aroma. Linalool belongs to monoterpene alcohols, with a floral and fruity flavor [32]. In addition, benzene acetaldehyde has honey and fruity flavors, and 2-pentylfuran has a bean aroma and a strong burned flavor, which may be the main contributor to the aroma of green tea with a heavy flavor [33]. The interaction between these volatile compounds constitutes the unique flavor characteristics of Rizhao green tea, which is consistent with previous studies [34].
The GC-IMS results show that the composition and content of volatile compounds in Rizhao green tea from the four key processing stages were significantly different. The results of the difference comparison plots show that the characteristic aromatic substances in tea leaves, fixated leaves, and rolled leaves were quite different from those in green tea, which was related to the treatment temperature at different processing stages and various enzymatic and biochemical reactions in tea processing. Tea aroma compounds are generated from four main pathways: carotenoid degradation, the oxidation of tea lipids, glycosides as precursors, and the Maillard reaction or the Stecker degradation reaction pathways [35]. Linalool is a monoterpene alcohol, with a boiling point of 199–200°C, which mainly exists in the tea plants in the form of glucosides. After tea leaves are picked, the glycosides are hydrolyzed by glucosidase into free linalool. β-D-Glucoside is the precursor of linalool and its oxidation products [36]. 2-Methylbutanal, methylthiopropanal, and benzene acetaldehyde were degraded by the Strecker reaction, and the corresponding precursors were isoleucine, methionine, and phenylalanine, respectively. Hexanal, heptanal, octanal, nonanal, and 1-octene-3-ol are the key aroma compounds derived from fatty acids in Rizhao green tea. The C9–C12 saturated aldehydes have good aroma at high dilution.
The above results revealed the change trend of volatile organic compounds in Rizhao green tea at different processing stages. We explored the formation mechanism of aromatic substances during processing, and the results provided a theoretical reference for the improvement of tea processing, tea quality control, and evaluation methods. Due to the incomplete data in the current GC-IMS spectral library, twenty-three volatile substances remain undetermined. In the future, further analysis will be carried out, in combination with gas chromatography-mass spectrometry and electronic nose. In addition, in order to retain the original components of tea leaves and other samples to the maximum extent, relatively mild temperature (50°C) was used for incubation. In the future, an incubation temperature (80°C–90°C) closer to the usually water temperature of tea infusion can be used for research.
4. Conclusion
In this paper, we employed GC-IMS technology to explore the evolution of volatile metabolites during Rizhao green tea processing. A total of 62 volatile components were detected, including alcohols, aldehydes, ketones, esters, terpenes, and oxygen compounds. The drying processes had the greatest influence on the evolution of the volatile metabolites, followed by fixation. Further analysis clarified the contribution of volatile substances to the aroma characteristics of samples. Ten compounds including linalool, pentanal, hexanal, heptanal, octanal, nonanal, methyl 2-methylbutanoate, 2-methylbutanal, 3-methylbutanal, and 3-methylthiopropanal were ultimately identified as the key odorants of the chestnut-like aroma of Rizhao green tea by the ROAV method. The result of the flavor wheel classification method showed that the contents of aromatic substances with green, fruity ester-like, caramel nutty, and citrus-like flavors exhibited a significant increasing trend from fresh leaves to the finished teas, whereas aromatic substances with floral flavors exhibited the opposite trend. This initial progress provides a theoretical basis for further research on the directional adjustment and control of tea aroma.
Data Availability
The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials.
Conflicts of Interest
The authors declare no potential conflicts of interest regarding the research, authorship, and publication of this article.
Supplementary Materials
Table S1 Qualitative analysis result of volatile substances. (Supplementary Materials)