Aroma Characterization and Key Volatile Identification in Wuyi Rock Tea Prepared from Wuyi Mingcong Tea Plant Varieties

Abstract

Wuyi Mingcong (WYMC) is a distinctive tea germplasm resource from Wuyi Mountain, known for its unique aroma and quality characteristics. However, the aroma quality of WYMC has been insufficiently studied. In this study, the aroma profiles of seven characteristic tea plant resources WYMC tea samples were characterized using sensory evaluation combined with headspace solid-phase microextraction and gas chromatography–mass spectrometry (HS-SPME-GC-MS). The results revealed that “floral,” “fruity,” “clean and refreshing,” “woody,” and “sweet” were the main aroma characteristics. A total of 37 volatile compounds were found to contribute significantly to the aroma profiles of the seven WYMC tea samples, with dihydrolinalool and (E)-β-ionone likely being the key contributors to their floral and fruity notes. Ten key volatile markers were identified as responsible for aroma differences between the Fujian Shuixian (SX) and seven WYMC tea samples. Phenylethyl alcohol, cis-3-hexenyl benzoate, δ-cadinene, nerol, and β-myrcene may be critical for the formation of WYMC’s characteristic aroma. cis-3-hexenyl benzoate and nerol may act as “broad-spectrum” aroma contributors, enhancing the overall intensity or layered nature of WYMC’s scent. The results of this study enrich the understanding of the aroma characteristics of WYMC and provide a theoretical foundation for the development and utilization of tea germplasm resources in the Wuyi Mountain.

1. Introduction

Tea is one of the most popular beverages globally, including black tea, green tea and oolong tea, etc. [1]. In China, Wuyi Mountain is one of the major producing areas of oolong tea, and the oolong tea produced here is often referred to as ‘Wuyi rock tea (WRT)’. The common tea plant varieties used for ‘Wuyi rock tea’ processing include the ‘Fujian Shuixian (SX)’ tea plant and ‘Rougui (RG)’ tea plant, which are currently the two largest tea plant germplasms in terms of planting area at the Wuyi Mountain [2,3]. Wuyi Mountain is also an important treasure trove of tea plant germplasm resources. According to incomplete statistics, Wuyi Mountain has over a hundred natural tea plant germplasm resources [2,4]. Some elite varieties, selected from these Wuyi Mountain local germplasm resources, were called ‘Wuyi Mingcong (WYMC)’ such as, ‘Dahongpao (DHP)’, RG, and ‘Shuijingui (SJG)’ [2].

The flavor characteristics of WRT are shaped by multiple factors [5,6,7]. Extensive studies have used transcriptomic and metabolomic approaches to investigate how different regions and processing techniques influence the formation of its quality traits, exploring changes in both volatile and nonvolatile compounds [8,9,10,11]. Additionally, WRT produced from different tea plant varieties typically exhibits distinct flavor qualities and, especially, aroma characteristics. For example, RG-WRT is noted for a cinnamon-like aroma, while SX-WRT features a floral aroma with woody notes [12]. Previous research analyzed 16 WRT samples from different oolong tea plant varieties to explore their aroma profiles [13]. However, most of these varieties were not ‘WYMC’ types; WYMC is a characteristic tea plant resource of Wuyi Mountain, and the aroma characteristics of WRT derived from different ‘WYMC’ tea plant varieties remain unclear.

In this study, the aroma components of eight WRT samples of seven characteristic ‘WYMC‘ tea varieties within a certain planting area of Wuyi Mountain and one national-level cultivar ‘SX‘ were compared and analyzed. The sensory evaluation, in combination with quantitative descriptive analysis (QDA), headspace solid-phase microextraction gas chromatography-mass spectrometry (HS–SPME–GC–MS), and molecular docking experiments, was used to investigate the contribution of different aroma volatiles to the aroma profiles of WYMC-WRT samples and the aromatic distinctions between WYMC and SX. The findings are expected to offer a theoretical basis for future efforts aimed at promoting and breeding WYMC varieties.

2. Materials and Methods

2.1. Tea Sample Collection

The test samples were collected in the spring of 2023 from tea cultivars (Camellia sinensis var. sinensis) grown on the tea germplasm plantation of Wuyi University (Wuyishan City, Fujian Province, China, 27° 73′ N, 118° 00′ E). Their planting land is flat, and the altitude (213 m), soil type (yellow loam), climate (annual average temperature of about 18.0 °C, annual average rainfall of about 2000 mm, and annual average relative humidity of about 80%), irrigation, and fertilization management measures are consistent. After preliminary investigation, the growth potential of the selected seven WYMC tea varieties was excellent, and the quality of WRT was good. Therefore, we selected seven tea varieties as the experimental group, including “Rogui (RG)”, “Hongdujuan (HDJ)”, “Honghaitang (HHT)”, “Mujinluohan (MJLH)”, “Zuiguifei (ZGF)”, “Zhengtaiyin (ZTY)”, and “Guoshanlong (GSL)”. “Fujian Shuixian (SX)” was selected as the control group.

In this study, a total of 90 tea plants were randomly selected from each tea cultivar, and every 30th plant was a replicate, so each cultivar had three replicates of tea samples. The fresh leaves of the three and four leaves of each cultivar were picked as raw materials for the traditional production process of Wuyi rock tea, which involves withering, shaking (six times), fixing, twisting, drying, and roasting. The post-harvested tea leaves were spread under sunlight and withered (24–26 °C, 65–70% relative humidity, 2–3 cm thickness, withering to soft leaves, leaf edge slightly curled, green gas decreased, fragrance revealed as moderate, and time of 30 min)→green-making (hand-made green, the first shaking 10–15 turns, spread for 30 min, the second shaking 20–30 turns, spread for 60 min, the third shaking 30–40 turns, spread for 80 min, the fourth 40–50 turns, spread for 90 min, the fifth shaking 50–60 turns, spread for 120 min, the sixth shaking 52–60 turns, and spread for 120 min; the thickness of the spread leaves was thickened step by step, until the leaves achieved a bright-yellow surface, a “tortoise-back” curl, the signature “three-red-seven-green” coloration with cinnabar-red edges, and a balanced floral-fruity aroma, time of 8 h)→fixing (manual fixing, pot temperature 220~240 °C, and the amount of leaves per pot is about 0.75 kg; the appropriate standard for fixing was that the leaves became soft and sticky, turned dark, developed a fragrance, and had no green odor; process lasted 6~8 min)→rolling (the leaves were rolled for 7–10 min until tea juice exuded and they formed tight strips)→drying (baking machine drying, gross fire temperature 120 °C, time of 30 min, airing for 2 h and then full fire, full fire temperature 80 °C, time of 120 min)→picking→redrying (baking machine drying, temperature 110~120 °C, time of 40 min). After the eight tea samples were prepared, the impurities were removed, and the samples were sealed for future use.

2.2. Sensory Evaluation

The sensory evaluation team consisted of thirteen trained evaluators (seven females and six males, aged 25–40 years; all had the qualification of senior tea evaluator). The sensory quality (appearance, liquor color, aroma, taste, and infused leaves) of Wuyi rock tea (WRT) was evaluated according to the standards of China in GB/T 23776-2018 [14]. Before the sensory evaluation, each tea sample was labeled with codes and randomly arranged in the process of sensory evaluation and quantitative descriptive analysis to improve the accuracy of the sensory quality evaluation of the tea samples. During the evaluation process, 5 g of each uniformly mixed WRT sample was placed in an independent lidded teacup. Then 110 mL of boiling water was added to the cup. The tea samples were brewed three times, and the first bubble (2 min), the second bubble (3 min), the third bubble (5 min), and each tea soup was subjected to sensory evaluation. The aroma characteristics and intensity of the tea leaves were recorded by evaluators, with the aroma descriptors referencing Guo et al. [15]. The evaluators agreed that the aroma of the tea samples could be described in terms of five attributes: namely, “floral”, “fruity”, “sweet”, “woody”, and “clean and refreshing”.

The quantitative descriptive analysis (QDA) method [13,16,17,18] was used to quantitatively evaluate the aroma intensity of the samples. Before quantitative evaluation, 13 evaluators were tested for WRT aroma recognition, evaluation, description and perception, and flavor analysis ability. The scores were all >80%, indicating that the 13 evaluators had the ability to perform QDA quantitative analysis. The scores of each attribute in QDA quantitative analysis ranged from 0 to 10. The higher the score, the stronger the intensity; 0 = no intensity or no perceived intensity, 3 = weak intensity, 5 = moderate intensity, 7 = high intensity, and 10 = extremely high intensity. The first cup was used to assess the type of aroma; the second cup was used to determine the intensity of the aroma; and the third cup was used to reassess the aroma and aroma persistence. Each evaluator evaluated each sample three times and all data are expressed as averages.

2.3. Electronic Nose Detection

The aroma characteristics of Wuyi rock tea were assessed using the PEN3 electronic nose from AIRSENSE, which is equipped with ten sensors (all sensors are sensitive to a large class of substances, rather than a single substance). These sensors include the following: W1C for aromatic ingredients and benzene; W5S for nitrogen oxide; W3C for ammonia and aromatic components; W6S for hydrogen; W5C for short-chain alkanes and aromatic components; W1S for methyl groups; W1W for inorganic sulfides and terpenes; W2S for alcohols, ethers, aldehydes, and ketones; W2W for aromatic components and organic sulfides; and W3S for long-chain alkanes (the performance descriptions of sensors were provided by the electronic nose manufacturer, and the specific description is shown in Table S1). Prior to the experiment, the electronic nose system was preheated for 30 min to achieve stability. The system was then flushed, and the sensor array was continuously purged until all sensor signals reached stable baseline values. For each measurement, 1.0 g of a tea sample was placed in a 100 mL beaker, which was sealed with double layers of cling film and equilibrated at 80 °C for 5 min after standing for 30 min at room temperature. The detection time for each sample was 120 s, with the sample injecting speed of 400 mL/min; after each experiment, the flush time was selected as 120 s to ensure the accuracy and reliability of the results. Each sample was tested three times.

2.4. Analysis of Volatile Aroma Components in Tea Samples

Volatile aroma components extraction: 1.0 g of tea sample was weighed into a 20 mL headspace vial with 2.5 mL saturated NaCl solution and 10 μL (50 μg/mL) methyl 2-hydroxybenzoate-d4 (dissolved in n-hexane) as isotope labeled internal standard. Each sample was mixed in equal amounts to make quality control (QC) samples, and a QC sample was added every eight times to detect the stability of the experiment. The ion flow diagrams of different QC quality control samples are shown in the attached Figure S1. Each sample was subsequently heated to static equilibrium at 80 °C for 20 min [19]. Then, the 120 μm DVB/CWR/PDMS fibrehead (Agilent Technologies, Santa Clara, CA, USA) was inserted into a headspace vial for 40 min, followed by desorption at 250 °C for 5 min.

GC-MS analysis: The identification and quantification of volatile components were carried out using an Agilent Model 8890 GC and a 7000D mass spectrometer (Agilent) equipped with a 30 m × 0.25 mm × 0.25 μm DB-5MS (Agilent J&W Scientific, Folsom, CA, USA). The injector temperature was set at 250 °C, and the sample was fed without a shunt. The initial temperature was held at 40 °C for 1 min, then increased to 280 °C at a rate of 5 °C/min and held for 5 min. High-purity helium (purity > 99.999%) was used as carrier gas at constant flow rate of 1 mL/min. Then, 50~500 m/z mass spectra were recorded in electron impact (EI) ionization mode at 70 eV with an ion source, and with interface temperatures set at 230 °C, and 250 °C, respectively. Biology determination was repeated three times for each rock tea sample (Metware Biotechnology Co., Ltd., Wuhan, China).

The metabolites in the samples were identified by comparing the mass spectrum with the data system library (MWGC and NIST 20, MWGGG is a self-built database of volatile metabolome of Metware Biotechnology Co., Ltd., Wuhan, China), the linear retention index (RI, calculated from n-alkanes C₇–C₄₀), and using match score > 75% [20] (Metware Biotechnology Co., Ltd., Wuhan, China). The quantification process included a comparison of the peak areas of the internal standard (IS) to calculate the contents of the aroma components (μg/g). The concentrations of volatile compounds were estimated by using a semi-quantitative method, through normalizing the peak area of each identified volatile compound to the internal standard [21].

2.5. Characterization and OAV Calculation of Volatile Compounds

The odor activity values (OAVs) were determined as the ratios of the relative contents to their odor thresholds in water for each volatile compound to assess the impacts of volatile compounds [22]. The formula for calculating the OAV is as follows:

$$\mathrm{OAV} ={\displaystyle \frac{{\mathrm{C}}_{\mathrm{i}}}{\mathrm{O}{\mathrm{T}}_{\mathrm{i}}}}$$

(1)

where C_i (µg/g) is the relative content of volatile component and OT_i (µg/g) is the aroma threshold of the volatile components in water. The thresholds were taken from the previous literature [13,23,24,25,26,27,28].

2.6. Molecular Docking of the Binding Interactions Between the Aroma Active Compounds and the Olfactory Receptors

Five-dimensional structural models of the compounds were obtained from PubChem (https://pubchem.ncbi.nlm.nih.gov, accessed on 10 September 2025). Three-dimensional structural models of the olfactory receptors were obtained from UniProt (https://www.uniprot.org, accessed on 10 September 2025). Proteins (receptors) and aroma compounds (ligands) were then hydrogenated and charged using CB-Dock2 (https://cadd.labshare.cn/cb-dock2/php/index.php, accessed on 11 September 2025) [29].

2.7. Statistical Analysis

A radar map was generated using Origin 2021. Unsupervised principal component analysis (PCA) was performed using the statistics function prcomp within the R package stats 3.5.1. A heatmap was generated using the R package complexheatmap 2.12.0. Flavor wheel plots were drawn using the R package ggplot2. OPLS-DA was performed using the R package MetaboAnalystR. Bar charts were drawn using GraphPad Prism9. The one-way analysis of variance (ANOVA) was performed using IBM SPSS Statistics 25 to assess differences in volatile content among different tea plant varieties. When ANOVA results were significant (p < 0.05), Duncan’s multiple range test (DMRT) was used for post-hoc multiple comparisons.

3. Results and Discussion

3.1. Sensory Evaluation of SX and WYMC Teas

The flavor characteristics of WRT vary depending on the tea plant germplasm. To assess quality differences, SX and seven WYMC tea samples (RG, ZGF, MJLH, ZTY, HDJ, HHT, and GSL) underwent sensory evaluation by an expert panel. The results of the sensory evaluation showed that most samples had a sturdy, tight shape with a greenish-auburn and black bloom appearance (Figure 1 and Table S2). Tea broths of these samples were predominantly orange and bright (Figure 1 and Table S2). All the samples presented significant floral, fruity, or clean and refreshing aromas, with HDJ tea and SX tea also displaying woody notes. In terms of taste, these teas were characterized by a strong, thick, mellow, brisk, and sweet aftertaste, with a distinctive “Yan” flavor (Table S2). The infused leaves were yellow-green, soft, bright, and even, with a distinctive red edge, which is typical of WRT (Figure 1 and Table S2). Overall, sensory results indicated that all selected teas possessed typical WRT characteristics.

3.2. Aroma Characterization of SX and WYMC Teas

The electronic nose is mainly used to identify and compare the overall volatile odor of tea [30]. In order to further explore the aroma characteristics of WYMC and reveal its aroma profile, the aroma attributes of the eight WRT samples were analyzed using an electronic nose, and the results are displayed in a radar diagram (Figure 1b). The radargrams showed significant similarity in aroma attributes across the samples, with variations only in response values. All the samples presented relatively high response values for the sensor W5S and showed fluctuations in the sensor W2. W2W is mainly sensitive to aromatic components with floral and fruity aroma, and W5S is mainly sensitive to nitrogen oxides. This result was also consistent with the WYMC sensory evaluation of the overall flower and fruit aroma. Although there are some similarities in the overall profile of aroma, there are also significant differences between different samples from the fluctuation of response values of sensors W5S and W2W.

Oolong teas produced by different varieties usually exhibit different flavors, known as “varieties flavor” [12]. As shown in Figure 2a, the odor types of SX and seven WYMC teas were described as “floral”, “fruity”, “clean and refreshing”, “woody”, and “sweet”, with varying intensities among the eight tea plant varieties. SX tea has high-intensity sweet and floral odors, RG tea has a high-intensity floral odor, ZGF tea has high-intensity clean and refreshing and floral odors, ZTY tea has a high-intensity clean and refreshing odor, HDJ tea has a high-intensity fruity odor, HHT tea has high-intensity clean and refreshing and floral odors, GSL tea has a high-intensity fruity odor (scores ≥ 7), MLJH tea has moderate intensity clean and refreshing and sweet odors, and SX tea and HDJ tea also have woody odors.

The results of the electronic nose and QDA revealed that the eight samples overall exhibited characteristic floral and fruity aromas. While their general aroma profiles were similar, differences were observed, allowing each sample to demonstrate unique aromatic characteristics. However, aroma perception is a complex outcome, likely influenced by the composition, concentration, and proportional balance of aromatic substances in the samples. Therefore, it is necessary to further identify the key aroma-active compounds that contribute to these specific aroma profiles and their differences.

3.3. Analysis of the Aroma Components of SX and WYMC Teas Using HS-SPME-GC-MS

As shown in Figure S1, the total ion chromatogram (TIC) profiles of volatile compounds detected in QC samples exhibited highly overlapping curves, with consistent retention times and peak intensities, demonstrating stable instrument performance and the reliability of the HS-SPME-GC-MS analytical methodology employed in this study. A total of 192 aroma volatile compounds were identified, including 10 alcohols (2.44–5.02 μg/g), 19 ketones (2.90–5.63 μg/g), 55 terpenoids (23.30–46.60 μg/g), 38 esters (14.83–29.31 μg/g), 14 heterocyclic compounds (8.67–22.05 μg/g), 27 hydrocarbons (4.10–7.74 μg/g), 11 aromatics (0.47–1.85 μg/g), 12 aldehydes (0.44–0.89 μg/g), 3 phenols (0.89–2.46 μg/g), 2 nitrogen compounds (0.22–4.98 μg/g), and 1 acid (0.00–0.01 μg/g); the classification results of the 192 aroma volatile compounds are shown in Table S3. The contents of terpenoids and esters ranked first and second, respectively, among the eight tea samples, indicating that these two types of compounds are the primary contributors to the aroma of the eight tea samples. The classifications, abundances, and percentages of the different volatile compounds in the eight tea samples were illustrated in Figure 2b–d.

Among these tea samples, aromas’ volatile concentrations varied significantly: HDJ tea, SX tea, and HHT tea showed the highest levels at 118.90 μg/g, 108.96 μg/g, and 104.89 μg/g, respectively. The total aroma volatile contents of the other five samples were lower, with values as follows: MJLH tea (79.08 μg/g), RG tea (77.87 μg/g), GSL tea (73.05 μg/g), ZTY tea (66.77 μg/g), and ZGF tea (65.98 μg/g). Notably, HDJ tea had the highest total aroma volatile content across all samples. Specifically, its terpenoid and ester contents were 45.80 μg/g and 30.67 μg/g, respectively. These two components made up more than half of its total volatile content and were significantly higher than those in SX tea. These results thus suggest that HDJ tea plant could be a suitable variety for producing WRT with high aroma quality.

In this study, terpenoids were the most abundant aroma components across all eight tea samples, with concentrations exceeding 20 μg/g in all samples (Figure 2c). This result corroborates findings by Yue et al. [13], suggesting that terpenoids play a crucial role in the aroma quality and are closely related to tea aroma intensity. Terpenoids are mainly synthesized via the methylerythritol phosphate (MEP) pathway or the mevalonate (MVA) pathway [31]. Key terpenoids such as linalool, geraniol, (E)-β-ionone, and trans-nerolidol were present in high concentrations in eight tea samples, contributing floral and woody aromas. Geraniol and linalool are monoterpenes formed by the hydrolysis of glycosides, which play a role in the floral and fruity aroma of tea [23,32]. At the same time, short-term sunlight-induced withering significantly upregulated key genes involved in terpenoid metabolic pathways, increasing aroma formation during oolong tea manufacturing [33]. Esters are the primary source of sweet, floral, and fruity tea aromas, and extracellular lipids can be broken down and converted into aromatic compounds during the production process, which is an important factor affecting the aroma of oolong tea [34,35]. In this study, esters accounted for the second largest pro-portion of the aroma substance content of these eight tea samples. cis-3-hexenyl hexanoate, a key aroma compound formed during rolling, contributes floral and fruity notes [36], and was highly concentrated in all eight tea samples. Previous studies have shown that ester content gradually increases during SX processing, playing a key role in shaping its aroma intensity and odor characteristics [37]. Notably, cis-jasminalactone showed the highest relative content in SX tea, highlighting its significance in the aroma profile of this variety. Heterocyclic compounds also play an important role in the aroma formation of oolong tea. The heterocyclic compound indole has the highest concentration in eight tea samples, which is an important substance affecting the floral aroma of oolong tea [38], and indole is also a key substance constituting the basic aroma characteristics of jasmine tea and the chestnut aroma of green tea [8,39]. The results of volatile component analysis showed that abundant terpenoids and esters were the main material basis for the characteristic aroma of the flower and fruit aromas of the eight Wuyi rock tea varieties. This is also consistent with the results of the previous sensory evaluation, identifying floral and fruity odors.

3.4. Identification of Key Aroma Volatile Compounds in the WYMC Tea Samples

In tea, among the many aroma components, only a few play a dominant role in determining the characteristic aroma of the tea [40]. Notably, the concentration of aroma components does not directly reflect the tea’s characteristic aroma. For this reason, previous studies have employed the odor activity value (OAV) to assess the contribution of individual aroma components to the overall aroma of tea. Specifically, an OAV > 1 indicates that the compound exerts some influence on the tea’s aroma, while an OAV > 10 means the compound is regarded as making a significant contribution to the aroma [41,42,43]. By calculating the OAV based on the reported thresholds of volatile substances, this study screened 37 important volatile compounds that contribute to the aroma of seven WYMC samples. The aroma wheel for the seven WYMC samples was constructed based on OAV > 1, as shown in Figure 3 and

Table 1. The 37 aroma volatile compounds with OAV > 1 in eight samples.

Compounds	Odor Description	CAS	Threshold (μg/g)	SX	RG	ZGF	MJLH	ZTY	HDJ	HHT	GSL
Alcohols
1-Octen-3-ol	mushroom, floral, and hay	3391-86-4	0.001	349.56	240.04	182.00	332.89	282.25	329.18	213.32	242.11
Phenylethyl alcohol	soft, and lasting rose	60-12-8	0.14	7.80	22.19	18.22	18.38	9.18	22.46	26.51	18.80
(E)-3-Hexen-1-ol	clean, and fresh	928-97-2	0.11	1.60	1.12	2.63	4.53	2.43	6.03	2.27	1.94
Ketones
6-Methyl-5-hepten-2-one	fruity, and fresh	110-93-0	0.05	33.25	20.27	8.33	15.15	17.05	15.42	18.27	10.05
2,2,6-Trimethyl-cyclohexanone	pungent, honey, and herbal	2408-37-9	0.0001	1263.25	1314.71	1143.29	1780.44	1516.46	1197.04	1144.50	1311.46
Jasmone	elegant jasmine	488-10-8	0.007	90.46	41.04	52.83	37.11	74.12	294.82	137.83	97.33
Geranylacetone	fresh rose	3796-70-1	0.06	10.28	8.99	8.81	10.22	9.71	7.84	7.71	6.85
Terpenoids
Nerol	rose	106-25-2	0.049	1.31	1.68	3.23	2.26	1.37	4.69	1.25	2.05
β-Myrcene	sweet orange, and balsamic	123-35-3	0.015	28.86	28.09	57.76	57.23	36.29	77.47	24.86	42.97
γ-Terpinene	citrus, and lemon	99-85-4	0.002	42.82	65.68	21.99	28.56	24.45	43.35	35.03	29.48
β-Ocimene	citrus, and green	13877-91-3	0.0067	92.90	47.44	73.64	81.59	63.21	196.67	68.98	70.11
Linalool	sweet, and floral	78-70-6	0.006	253.85	166.52	141.70	199.61	176.34	596.10	200.51	264.00
2,6-Dimethyl-2,4,6-octatriene	floral	673-84-7	0.034	0.64	0.50	0.66	0.81	0.56	1.01	0.38	0.58
Safranal	woody, and herbal	116-26-7	0.003	22.91	31.90	21.76	27.77	23.39	24.01	18.65	22.95
β-Cyclocitral	saffron, herbal, sweet, and fruity	432-25-7	0.003	48.74	43.77	34.21	50.11	53.94	32.45	34.90	31.49
Geraniol	mild, and sweet rose	106-24-1	0.0066	268.98	173.30	808.52	530.10	337.00	916.28	219.13	515.91
(+)-α-Pinene	herbaceous	7785-70-8	0.0053	12.09	7.68	96.13	5.06	74.63	26.79	22.29	3.15
α-Ionone	warm, woody, and violet	127-41-3	0.0004	813.18	698.14	299.13	542.75	872.44	359.90	829.71	359.11
cis-β-Farnesene	green	28973-97-9	0.087	37.64	38.34	17.42	33.10	33.13	41.38	76.01	30.82
(E)-β-Ionone	violet	79-77-6	0.0002	8718.50	7529.17	6229.88	8498.84	10269.65	6375.36	5939.87	6096.80
δ-Cadinene	thyme, and woody	483-76-1	0.0015	24.53	23.29	57.97	64.21	37.04	64.16	73.56	183.90
trans-Nerolidol	woody, floral, and fruity	40716-66-3	0.25	34.83	32.86	18.97	29.29	27.70	43.16	60.83	33.04
trans-Linalool oxide (furanoid)	floral	34995-77-2	0.19	3.41	1.82	4.79	6.04	1.81	10.96	7.88	6.59
Dihydrolinalool	floral, and fruity	29957-43-5	0.00065	6425.26	8288.17	2624.28	2426.63	2376.62	4362.25	5333.76	4057.73
Esters
Methyl salicylate	strong wintergreen	119-36-8	0.04	15.22	5.77	21.45	23.62	8.46	28.83	16.53	17.09
cis-3-Hexenyl valerate	green apple	35852-46-1	0.06	11.93	8.16	7.64	9.37	4.91	12.52	11.10	8.17
Hexyl 2-methylbutyrate	fruity	10032-15-2	0.022	28.78	25.22	12.79	11.58	5.63	16.67	19.25	16.59
cis-3-Hexenyl hexanoate	sweet, and apple-pear	31501-11-8	0.781	7.39	7.24	7.85	9.52	5.96	11.90	7.35	6.40
Dihydroactinidiolide	woody, and floral	17092-92-1	0.0021	244.68	187.02	127.09	204.60	281.29	122.27	183.30	128.53
cis-3-Hexenyl benzoate	green, floral, and balsamic	25152-85-6	0.5	0.72	1.38	1.60	1.33	0.77	1.52	1.42	1.13
Hexyl benzoate	woody, balsamic, and fruity	6789-88-4	0.073	2.94	7.30	3.28	2.20	1.41	2.86	3.75	4.00
Methyl jasmonate	strong floral, and green	1211-29-6	0.07	4.62	1.45	1.91	1.99	2.54	10.30	3.85	3.03
cis-Jasminlactone	coconut, fruity, and jasmine	25524-95-2	2	4.10	1.06	1.20	1.56	1.31	2.12	2.46	0.57
Heterocyclic compounds
2-Pentyl-furan	fruity, and vegetal	3777-69-3	0.006	150.84	134.56	64.97	163.67	128.00	205.32	108.34	104.65
Indole	light floral, orange, and jasmine	120-72-9	0.04	509.19	110.42	191.14	218.06	236.70	328.48	318.96	185.46
Aldehydes
Decanal	green, spicy, citrus, and rose	112-31-2	0.0001	323.24	443.87	179.50	316.67	241.98	290.09	222.78	189.48
Benzaldehyde	bitter almond	100-52-7	0.35	0.67	1.07	0.38	0.66	0.41	0.57	0.67	0.31

.

Analysis of the 37 key volatile compounds revealed that dihydrolinalool and (E)-β-ionone had OAVs > 2000, making these the top two compounds in terms of OAV ranking among the important volatile components. Previous studies have shown that dihydrolinalool is a key compound in forming the aroma of beauty tea [24], and (E)-β-ionone is a key factor in enhancing the floral aroma of green tea [10,44]. According to our results and these previous studies, dihydrolinalool and (E)-β-ionone may be the main contributors to the floral and fruity aromas of these seven WYMC tea samples. This is also consistent with our sensory evaluation results.

A comparison revealed that in HDJ, the OAV of linalool (sweet, fresh, and floral) [45], 2-pentyl-furan (fruity) [46], β-ocimene (citrus, and green) [44], and jasmone (jasmine) [25] were significantly higher than those of the other six WYMC samples. This could contribute to the more pronounced floral and fruity aroma characteristics of HDJ. In ZGF, (+)-α-pinene (herbaceous) [9] had an OAV > 90, indicating that it might significantly contribute to ZGF’s fresh aroma. In ZTY, the OAV of (E)-β-ionone (violet) [25] was greater than 10,000, the highest among all compounds, indicating its important contribution to ZTY’s aroma characteristics. δ-Cadinene (thyme, herbal, woody, and dry) [47] is an active ingredient in the volatile oils of some herbaceous plants. In GSL, its OAV > 180, significantly higher than in other WYMC samples, which may contribute to GSL’s aroma characteristics.

In summary, the aroma characteristics of tea are the result of the synergistic effect of multiple compounds. Notably, key compounds with high OAVs were identified as major contributors to the shared aroma profile of the eight WRT samples. Dihydrolinalool and (E)-β-ionone contribute to the floral and fruity notes, and δ-cadinene to the woody character. This result was also consistent with the previous sensory evaluation results of floral, fruity, and woody fragrances. However, the ‘varietal flavor’ exhibited by SX and WYMC depends on a few key aroma components and can be used as a marker for the chemical differentiation of the seven WYMCs. Therefore, it is necessary to find the key aroma markers to distinguish the seven WYMCs.

3.5. Differential Analysis of Volatile Compounds Between SX and WYMC Teas

In this study, we employed principal component analysis (PCA) to examine the relative contents of aroma components in SX and seven WYMC tea samples. As shown in Figure 4a, the eight tea samples clustered into distinct regions; among them, MJLH, RG, ZGF, ZTY, and GSL are clustered closer together, while HHT, HDJ, and SX form separate clusters. The first two principal components accounted for over 60% of the variance. In general, good separation is indicated when the cumulative contribution of the PCA model reaches 60% [48]. The results of PCA suggested that the eight tea samples exhibited significant differences in terms of their volatile compounds. The clustering heatmap (Figure 4b) reveals that HDJ formed an isolated cluster, while SX, MJLH, and RG were grouped together, and the remaining WYMC samples formed another group, suggesting that HDJ differs from the other samples in terms of its aromas’ volatile contents.

To further explore the differences between SX and the seven WYMC samples, an OPLS-DA model was constructed to screen for key metabolites that differed significantly. The OPLS-DA score plot (Figure 4c) and the 200 random permutation tests (Figure 4d) showed a model fit of R²Y = 0.989 and a predictive ability of Q² = 0.97, indicating that the model was reliable. The OPLS-DA score plot clearly distinguished SX from the seven WYMC samples, and 65 key differential volatile compounds (DVCs) were identified based on VIP > 1. The classification results of the 65 DVCs are shown in Table S4 and Figure 5.

3.6. Potential Key Volatile Markers Responsible for the Different Fragrances of SX and WYMC Teas

The above studies found that the aroma characteristics, volatile compound concentration, and odor intensity of SX and 7 WYMC were significantly different. In order to better understand the differences in key characteristic compounds and aroma-active compounds between SX and WYMC aroma types, we screened ten key volatile markers leading to aroma differences based on VIP > 1, OAV > 1, and FC > 1.5, and the results are shown in

Table 2. Ten key marker volatiles distinguish SX and WYMC.

Compounds	Odor Description	VIP	OAV	Precursor	Structural Formula
6-Methyl-5-hepten-2-one	fruity, and fresh	2.11	8.33~33.25	Carotenoids
Phenylethyl alcohol	soft, and lasting rose	2.06	7.8~26.51	Amino acids
Indole	light floral, orange, and jasmine	2.05	110.42~509.19	Amino acids/ Carbohydrates
cis-Jasminlactone	coconut, fruity, and jasmine	2.02	1.06~4.1	Fatty Acids
cis-3-hexenyl benzoate	green, floral, and balsamic	1.96	0.5~1.6	Fatty Acids
Hexyl 2-methylbutyrate	fruity	1.49	5.63~28.78	Fatty Acids
δ-Cadinene	thyme, and woody	1.35	23.29~183.9	Carotenoids
Dihydrolinalool	floral, and fruity	1.16	2376.62~8288.17	Carotenoids
Nerol	rose	1.13	1.25~4.69	Carotenoids
β-Myrcene	sweet orange, and balsamic	1.01	24.86~77.47	Carotenoids

and Figure 6. The ten key volatile markers are produced from three main precursors: carotenoids, lipids, and amino acids/carbohydrates [49]. The relative contents of indole, cis-Jasminlactone, 6-methyl-5-hepten-2-one, hexyl 2-methylbutyrate, and dihydrolinalool in SX were all significantly (p < 0.05) higher than the average relative contents of the seven WYMC tea samples. In contrast, the average relative contents of phenylethyl alcohol, cis-3-hexenyl benzoate, δ-cadinene, nerol, and β-myrcene in the seven WYMC samples were significantly (p < 0.05) higher than those in SX, so they were hypothesized to be the key volatiles for the aroma characteristics of the seven WYMC samples. The content of β-myrcene in HDJ exceeded 1 μg/g, significantly higher than that in SX, suggesting it may be an important substance in shaping the aroma characteristics of HDJ. Additionally, although nerol, δ-cadinene, and cis-3-hexenyl benzoate accounted for relatively small proportions in the seven WYMC samples, their contents were significantly higher than those in SX. Notably, the relative content of phenylethyl alcohol was significantly higher in all seven WYMC samples compared to SX. It is speculated that phenylethyl alcohol may play an important role in the formation of WYMC aroma characteristics.

Indole has been confirmed as a characteristic volatile compound in oolong tea, mainly formed during processing [50]. cis-Jasminlactone, providing fruity and sweet floral aromas, is primarily produced by lipid degradation during the “turning-over” process [51]. In addition, 6-methyl-5-hepten-2-one has been identified as a key characteristic aroma compound in DHP [52], and these compounds may explain the unique floral aroma of SX. Dihydrolinalool has a fresh floral and fruity aroma, which has previously been shown to have an important relationship with the aroma quality of beauty tea [53]. Some studies have shown that β-myrcene is an important substance affecting the floral and fruity aroma of tea [54], and that cis-3-hexenyl benzoate exhibits sweet floral and fruity aroma, which affects the aroma characteristics of black tea [36], and that nerol and δ-cadinene are mainly expressed as a floral, woody fragrance, and these compounds further influence the formation of the aroma characteristics of WYMC. Phenylethyl alcohol imparts a pleasant floral aroma and has three main synthetic pathways in tea: the phenylacetaldehyde (PAld) pathway, the phenylpyruvic acid (PPA) plus PAld pathway, and the (E/Z)-phenylacetaldoxime ((E/Z)-PAOx) plus PAld pathway [55,56]. Previous studies indicate that phenylethyl alcohol is associated with the aroma quality of white tea, Guangdong black tea, and Weishan yellow tea [25,35,57]. The higher content of phenylethyl alcohol in WYMC compared to SX suggests that this compound may be a key contributor to the characteristic aroma of WYMC germplasm resources. To further investigate the mechanisms behind the aroma formation of WYMC, subsequent analysis can be conducted based on the transformation of precursor substances during the processing.

3.7. Molecular Docking Analysis of the Interaction Between the Potential Key Volatile Markers of WYMC and Human Olfactory Receptors

The results demonstrated that ten key volatile markers were effectively able to discriminate the aroma profiles between SX and the seven WYMC teas. Among these, five compounds were significantly more abundant in WYMC than in SX. To elucidate their roles in shaping the characteristic WYMC aroma, molecular docking was employed to simulate the binding interactions between these five key aroma compounds and human olfactory receptor proteins, thereby evaluating their potential contribution to aroma perception. In molecular docking studies, the binding energy between a ligand and its receptor protein is inversely correlated with the likelihood of their interaction; a lower binding energy indicates a higher probability of stable interaction and a binding energy threshold of ≤−5.0 kcal/mol is generally recognized as indicative of strong binding affinity [58,59,60,61,62,63]. To investigate the role of five potential key volatile markers in shaping the aroma characteristics of Wuyi Mingcong (WYMC) tea, we performed molecular docking analyses between these volatiles and four common human olfactory receptors (ORs), specifically OR1G1, OR5M3, OR7D4, and OR8D1 [17,59]. The docking results (Figure 7) revealed distinct binding patterns: cis-3-hexenyl benzoate and nerol exhibited spontaneous binding to all four olfactory receptors, with binding energies consistently ≤−5.0 kcal/mol, indicating robust affinity across multiple ORs. Phenylethyl alcohol and β-myrcene showed selective yet strong binding to OR1G1, OR5M3, and OR7D4, also meeting the ≤−5.0 kcal/mol threshold. Notably, δ-cadinene displayed high specificity for OR5M3 and OR8D1, with exceptionally low binding energies of −7.7 kcal/mol and −7.0 kcal/mol, respectively, suggesting particularly stable interactions with these receptors.

These molecular docking results provide critical insights into the potential sensory mechanisms underlying WYMC tea’s unique aroma. The strong binding affinities (≤−5.0 kcal/mol) observed for all five volatiles with at least one olfactory receptor support their role as key contributors to WYMC’s aroma profile—their ability to stably interact with human ORs suggests they are likely perceived as integral components of the tea’s sensory characteristics.

The differential binding specificities further illuminate the complexity of WYMC’s aroma. For instance, cis-3-hexenyl benzoate and nerol, which bound to all four ORs, may act as “broad-spectrum” aroma contributors, enhancing the overall intensity or layered nature of WYMC’s scent. In contrast, δ-cadinene’s high selectivity for OR5M3 and OR8D1—coupled with its exceptionally low binding energies—implies it may play a specialized role in shaping a distinct note within WYMC’s aroma bouquet, potentially contributing to woody or earthy undertones often associated with Wuyi rock teas. Moreover, these findings bridge chemical composition and sensory perception: phenylethyl alcohol (linked to floral and sweet notes) and nerol (a known floral volatile) exhibited strong interactions with multiple ORs, aligning with the sensory evaluation results highlighting “floral” and “sweet” as dominant aroma descriptors of WYMC. This consistency between chemical binding affinity and sensory attributes strengthens the argument that these volatiles are indeed critical to WYMC’s aroma quality.

In summary, the perceived aroma of tea arises from the synergistic interaction of multiple volatile compounds acting on the human olfactory system. Molecular docking results aligned with the sensory evaluation—particularly floral, fruity, and woody notes—observed in the tea samples. These findings were further supported by GC-MS analysis, which showed the presence of five characteristic compounds associated with WYMC. The convergence of molecular docking and GC-MS results lends additional support to the role of these compounds as fundamental contributors to the aroma of WYMC.

4. Conclusions

This study primarily analyzed the aroma characteristics and their volatiles of seven WYMC tea samples and the national variety SX, using QDA combined with electronic nose and HS-SPME-GC-MS. The results revealed typical floral and fruity notes with terpenoids and esters as the dominant volatile compounds. Dihydrolinalool and (E)-β-ionone ranked in the top two for OAV, suggesting that these two compounds may be the primary contributors to the floral and fruity aroma of the seven WYMC samples. Ten key volatile markers were identified that distinguish seven WYMC teas from SX. Among these, phenylethyl alcohol, cis-3-hexenyl benzoate, δ-cadinene, nerol, and β-myrcene may be the key volatiles in the formation of WYMC aroma characteristics. The results of molecular docking experiments showed that the five potential key volatile markers affecting the aroma characteristics of WYMC had strong binding affinity with four common human olfactory proteins. Future work will explore the quality characteristics of these cultivars across different years, seasons, and geographical conditions. This systematic investigation aims to elucidate the varietal effects more comprehensively, thereby providing a robust foundation for expanding the cultivation and utilization of WYMC.