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. 2022 Dec 21;12(1):27. doi: 10.3390/foods12010027

Characterization of the Key Aroma Compounds in Different Aroma Types of Chinese Yellow Tea

Xin Hong 1,2,†, Chao Wang 1,3,†, Ronggang Jiang 1,3, Tengfei Hu 1, Xuexue Zheng 1, Jianan Huang 1,3, Zhonghua Liu 1,2,3, Qin Li 1,2,3,*
Editors: Antonio Cilla, Emily D Niemeyer
PMCID: PMC9818532  PMID: 36613243

Abstract

Yellow tea is one of the six major tea categories in China. The floral fragrance type, high-fired fragrance type, fresh fragrance type, and corn-like fragrance type were the main aroma types of yellow tea screened by QDA. A total of 103 volatiles were identified in yellow teas by HS-SPME/GC-MS analysis. Using multivariate analysis and OAVs, forty-seven aroma compounds were identified as key aroma compounds for the formation of different aroma types of yellow teas. Among them, 8, 14, 7, and 18 key aroma compounds played an important role in the formation of aroma characteristics of floral fragrance, high-fired fragrance, fresh fragrance, and corn-like fragrance types of yellow teas, respectively. Furthermore, PLS analysis revealed that 12 aroma compounds were the key contributors to the ‘floral and fruity’ and ‘sweet’ attributes, five aroma compounds contributed to the ‘roasted’ attribute, and four aroma compounds related to the ‘fresh’ and ‘grassy’ attributes. This study provides new insights into the aroma characteristics formation of different aroma types of yellow teas and will provide a valuable theoretical basis for improving the flavor quality of yellow tea during the manufacturing process.

Keywords: yellow tea, aroma types, key aroma compounds, sensory attributes, multivariate analysis

1. Introduction

Tea is a kind of widely consumed beverage ranking second only to water around the world [1]. Yellow tea is one of the six major tea categories in China, which is famous for its unique appearance and flavors, such as yellow dry tea, yellow infusion, and yellow brewed leaves that have an elegant fragrance and smooth taste. Meanwhile, yellow tea also possesses several healthy benefits for humans, such as anti-cancer, anti-bacterial, antioxidant, and gastrointestinal protecting effects [2,3,4]. The main manufacturing process of yellow tea are fixing, rolling, sealed yellowing, and drying. Among them, sealed yellowing is the key processing stage that contributes to the typical flavor characteristic formation of yellow tea [2]. Although yellow tea is increasingly deeply loved by consumers, its key aroma compounds that responsible for the special aroma formation are still unknown. It is difficult to establish flavor directed processing technology for yellow tea. Therefore, the study of yellow tea, particularly, research on its key aroma compounds for this special aroma, has important value for improving the flavor quality of yellow tea during the manufacturing process.

Tea aroma is a critical criterion to evaluate the overall quality of yellow tea [4]. Many aroma components were identified in yellow tea by previous studies, but different yellow tea possesses a wide range of key aroma compounds. This might result from the different raw materials, processes, and parameters of different yellow teas. The detailed information is summarized in Table S1. Our previous study indicated that different levels of tenderness of tea leaves will form the different characteristic aromas and key aroma compounds in yellow tea. Phenylacetaldehyde was identified as the key aroma compound in the bud-type yellow tea, due to its special fresh aroma; Ethyl hexanoate, benzyl alcohol, geraniol, phenethyl alcohol, citral, neral, and myrcene were identified as major contributors in bud-leaf yellow tea due to their flowery, fruity and sweet aroma notes; 2-pyrrole formaldehyde, 3-ethyl-2,5-dimethylpyrazine, 2-ethyl-5-methylpyrazine, and 2,3-diethyl-5-methylpyrazine are the key aroma compounds in multi-leaf yellow tea due to their roasted aroma notes [5]. Another study also revealed that key aroma compounds, including (E,E)-3,5-octadien-2-one, (Z)-linalool oxide (furanoid), (E)-2-heptenal, naphthalene, geraniol, (E)-linalool oxide (furanoid), styrene, linalool, α-ionone, 1-octen-3-ol, (E)-β-ionone, and (E,Z)-3,5-octadien-2-one, presented great differences in the different tenderness levels of yellow tea [6]. In addition, the different manufacturing processes can significantly affect the aroma profile of yellow tea and lead to the different characteristics of aroma in yellow tea. A previous study revealed that the high temperature roasting process was essential for special flavor formation of yellow teas with strong ‘roasted’, ‘nutty’, and ‘woody’ odors, as well as weak ‘fatty’ and ‘fruity’ odors [7]. This was also the key process for unique ‘crispy-rice-like’ odor formation in yellow tea [8]. In addition, different temperatures of roasting processes could result in different aroma characteristics of yellow tea, causing odors such as ‘fresh’, ‘tender corn’, ‘ripe corn’, and so on [9]. The degree of yellowing process significantly affects the composition of the aroma profile in yellow tea [10].

In summary, it is reasonable to hypothesize that different raw materials and processing technologies will lead to different compositions of the aroma profile, as well as cause different types of characteristic aromas in yellow tea. However, up to now, there are scarcely any systematic comparative study focused on the composition of key aroma compounds in different aroma types of yellow tea. Therefore, in this study, our goals are to (a) screen out the main aroma types of yellow tea by sensory-directed flavor analysis; (b) identify the key aroma compounds responsible for characteristic aroma formation in the different aroma types of yellow tea; (c) illuminate the correlation the aroma compounds and sensory attributes. Our findings will provide important information for the key aroma compounds that contribute to the different characteristic aroma formation of yellow tea, and also provide valuable information for improving the aroma quality of yellow tea during the manufacturing process.

2. Materials and Methods

2.1. Sample Collection and Chemicals

Ninety-seven yellow tea samples were collected from the tea market all over China in 2021 (Table S2). The C7-C40 n-alkanes and ethyl decanoate (99.99%) were obtained from Sigma-Aldrich (St. Louis, MO, USA). Fifty authentic standards were purchased from J&K Chemical Ltd. (Beijing, China) (Table S3). All the solvents were of chromatography grade, and all the chemicals were of analytical reagent grade, unless otherwise stated.

2.2. Sensory Analysis

Sensory analysis was approved by the Hunan Agricultural University Institutional Review Board Committee (TSF-780-2021). Twelve panelists (six males and six females, aged from 25 to 55 years) were selected from the Tea Science Department in Hunan Agricultural University. All participants received written information about the study and signed informed consent forms to participate. The yellow tea samples with representative aroma characteristics were selected by sensory evaluation according to the Chinese standards ‘Methodology of Sensory Evaluation of Tea’ (GB/T 23776-2018) and submitted to the quantitative descriptive analysis (QDA) [11]. Each sample was evaluated three times. The detailed information about sensory evaluation is described in Supplement Material S1.

2.3. Qualitative and Quantitative Analysis

The volatile compounds were analyzed by the HS-SPME/GC-MS method according to our previous study [12]. Briefly, each sample was initially ground and homogenized. The tea powder (1 g), NaCl (0.5 g), and ethyl decanoate (10 μL, 8.64 mg/L) were introduced into a 20 mL headspace bottle and infused with 5 mL of boiling water. The vial was immediately sealed and kept at 80 °C for 10 min. A 65-μm polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber (Supelco, Bellefonte, PA, USA) was exposed to the sample for 40 min. Next, the SPME fiber was inserted into GC injection port (230 °C for 5.0 min) and subsequently analyzed. Each sample was analyzed three times.

GC conditions: An Agilent 7890B GC system coupled with an Agilent 5977A MSD mass spectrometer (Agilent, Santa Clara, CA, USA) was used. An Agilent HP-5MS capillary column (30 m × 0.25 mm i.d. × 0.25 μm film thickness) was used for separation; the carrier gas was helium (purity > 99.999%) with a constant flow rate of 1 mL/min. The injection mode was set to splitless. The oven temperature was initially held at 50 °C for 3 min, raised to 170 °C at a rate of 3 °C/min, raised to 190 °C at a rate of 5 °C/min, then raised to 250 °C at a rate of 15 °C/min, and finally held at temperature for 2 min. MS conditions: EI ionization energy, ion source temperature, quadrupole temperature, and mass scanning range were set to 70 eV, 230 °C, 150 °C, and 35–400 atomic mass units (amu), respectively. Retention indices (RIs), authentic standards, and mass spectra matching in the standard NIST17 library were used for identification. RIs were calculated after analyzing C7-C40 n-alkane series under the same chromatographic conditions. Moreover, some commercially available standards were applied to verify the analysis results under the same conditions. The volatile compounds with available standards were quantitated according to our previous study. For the volatile compounds without the available standards, the quantitation was carried out using the standard that had the same carbon atom or a similar functional structure [12].

2.4. Odor Activity Value

Odor activity values (OAVs) are frequently applied to evaluate the contributions of aroma compounds. The compound with OAV > 1 was considered as key a aroma-active compound, which significantly contributed to the formation of aroma characteristics. The OAV was calculated as the ratio of the dividing the calculated concentration of each aroma compound to its odor threshold (OT) in water. The aroma characteristics and OTs were taken from previous literature [6,7,13,14,15,16,17,18,19,20,21] and online databases (FEMA, https://www.femaflavor.org/ and TGSC, http://www.thegoodscentscompany.com/search2.html (accessed on 1 March 2022)).

2.5. Multivariate Analysis

The data were preprocessed by mean centering and scaling prior to analysis. Principal component analysis (PCA), hierarchical cluster analysis (HCA), supervised orthonormal partial least-squares discriminant analysis (OPLS-DA), and partial least-squares analysis (PLS) were performed with SIMCA-P+ (Version 14.0, Umetrics, Umea, Sweden). The aroma compounds were used as the X variables and the aroma sensory attributes as the Y variables for PLS analysis. All data were presented as the mean values ± SD. Significant differences between groups were declared significant at p < 0.05.

3. Results and Discussion

3.1. Different Aroma Type of Yellow Tea

In this study, 26 yellow tea samples with typical aroma characteristics were selected from 97 yellow tea samples for QDA (Table S2). As shown in Figure 1A, a flavor wheel was established by sensory evaluation. The flavor wheel consisted of three tiers, one first-tier descriptor, five s-tier descriptors, and forty-six third-tier descriptors. The five s-tier descriptors have been widely used to describe the aroma characteristics of yellow tea in previous studies, including ‘floral and fruity’, ‘roasted’, ‘sweet’, ‘fresh’, and ‘green’ [7,8].

Figure 1.

Figure 1

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Flavor wheel of yellow tea (A) and radar of sensory aroma notes profile among the four aroma types of yellow tea: (B) ‘floral fragrance’ type. (C): ‘high-fired fragrance’ type. (D): ‘fresh fragrance’ type. (E): ‘corn-like fragrance’ type.

According to the second-tier descriptors and their sensory intensities, the aroma characteristics of 26 yellow tea samples could be divided into four aroma types, namely floral fragrance (H1-H7), high-fired fragrance (HG1-HG4), fresh fragrance (Q1-Q6), and corn-like fragrance (Y1-Y9). The floral fragrance type of yellow tea had a predominantly ‘floral and fruity’ attribute, whereas the other attributes were only weakly present (Figure 1B). The high-fired fragrance type of yellow tea mainly featured high intensity in the ‘roasted’ attribute, while the ‘floral and fruity’ attribute was moderate (Figure 1C). The fresh fragrance type of yellow tea had a strong ‘fresh’ attribute, while the ‘green’ and ‘sweet’ attributes were moderate (Figure 1D). The corn-like fragrance type of yellow tea was marked by strong ‘sweet’ and ‘floral and fruity’ attributes, while the ‘roasted’ attribute was moderate (Figure 1E).

3.2. Volatile Profile in Different Aroma Types of Yellow Tea

The volatile profiles of different aroma types of yellow teas were analyzed by HS-SPME/GC-MS with external standard method (Table S3). A total of 103 volatile compounds were identified and quantified in the different aroma types of yellow teas (Table 1), and 101, 91, 90, and 97 volatile compounds were identified in the floral fragrance, high-fired fragrance, fresh fragrance, and corn-like fragrance types of yellow teas, respectively. These identified volatile compounds belong to seven categories, including 16 alcohols, 2 phenols, 13 nitrogenous compounds, 10 aldehydes, 33 hydrocarbons, 13 ketones, and 16 esters. As shown in Figure S1A, alcohols (33.48%) and aldehydes (21.90%) were the predominant categories in the floral fragrance type of yellow tea, and (Z)-linalool oxide (furanoid), (E)-linalool oxide (furanoid), linalool oxide (pyranoid), hotrienol, (Z)-citral, and citral were the most abundant volatiles compared with the other aroma types of yellow tea (Figure S1B). Indeed, the alcohols and aldehydes have been reported to provide ‘floral’ and ‘fruity’ attributes, which have a good coordinating effect on the aroma profiles of tea products [6,22]. Nitrogenous compounds (60.10%) and hydrocarbons (17.27%) were the main categories in the high-fired fragrance type of yellow teas (Figure S1A). Among them, 1-ethyl-1H-pyrrole, 2,4-dimethyl-3-ethylpyrrole, 2,5-dimethyl-3-ethylpyrazine, 2-methyl-5-ethylpyrazine, methyl anthranilate, and p-xylene were the most abundant volatile compounds compared with the other aroma types of yellow teas (Figure S1B). These pyrroles, pyrazines, and their derivatives are usually generated from the Maillard reaction during roasting and baking treatments, which are thought to contribute to the formation of the ‘roasted’ aroma [1,7]. Esters (45.06%) and alcohols (28.03%) were the dominant categories in the fresh fragrance type of yellow tea (Figure S1A). Among them, ethyl hexanoate, ethyl nonanoate, and (E)-3-hexen-1-ol were the most abundant chemical structures, compared with the other aroma types of yellow tea (Figure S1B). Esters have been reported to play an important role in the fresh aroma characteristics formation of yellow tea [6]. Hydrocarbons (21.68%) and ketones (11.62%) were the dominant categories in the corn-like fragrance type of yellow tea (Figure S1A). Compared with the other aroma types, styrene, (E)-β-ocimene, β-cedrene, toluene, mesityl oxide, 2,3-octanedione, and β-ionone were the most abundant in the corn-like fragrance type (Figure S1B). Hydrocarbons and ketones with ‘sweet’, ‘floral’, and ‘fruity’ aroma notes, which are found to dominate the volatile compounds of black tea and are considered to provide a unique aroma for black tea [23,24]. The results showed that there were significant differences in the composition of volatile compounds of yellow teas with different aroma types.

Table 1.

Identification of the volatiles in different aroma types of yellow tea.

Compounds CAS RI a/ RI b Identification c Floral Fragrance Type High-Fired Fragrance Type Fresh Fragrance Type Corn-Like Fragrance Type
Concentration μg/L d
Alcohol compounds
α-Terpineol 98-55-5 1188/1187 MS, RI, STD 225.15 ± 233.04 a 5.83 ± 2.92 b 12.9 ± 27.31 b 2.9 ± 3.76 b
(E)-3-Hexen-1-ol 928-97-2 852/845 MS, RI, STD 4780.39 ± 2834.72 a 95.09 ± 37.48 b 465.72 ± 172.67 b 220.41 ± 299.25 b
Linalool 78-70-6 1098/1098 MS, RI, STD 516.47 ± 267.65 a 21.68 ± 2.7 b 31.02 ± 9.65 b 25.35 ± 22.21 b
Cedrol 77-53-2 1598/1598 MS, RI, STD 90.87 ± 57.19 a 0 ± 0 b 10.44 ± 21.85 b 14.92 ± 29.72 b
Nerolidol 7212-44-4 1559/1560 MS, RI, STD 54.22 ± 82.44 a 1.35 ± 0.89 b 1.36 ± 2.03 b 0.72 ± 0.73 b
Phenethyl alcohol 60-12-8 1110/1109 MS, RI, STD 261.77 ± 202.52 a 4.77 ± 0.95 b 12.93 ± 8.27 b 7.16 ± 11.47 b
(Z)-Linalool oxide (Furanoid) 5989-33-3 1072/1069 MS, RI 4366.05 ± 5485.02 a 167.36 ± 39.01 b 52.29 ± 21.05 b 103.34 ± 191.67 b
4-Terpinenol 562-74-3 1179/1174 MS, RI, STD 33.63 ± 32.84 a 1.45 ± 0.48 b 1.02 ± 1.03 b 0.75 ± 0.83 b
Olivetol 500-66-3 1528/1523 MS, RI, STD 331.77 ± 180.81 a 12.28 ± 7.09 b 4.57 ± 3.69 b 5.11 ± 4.6 b
(E)-Linalool oxide (Furanoid) 34995-77-2 1085/1085 MS, RI 5055.04 ± 5418.54 a 153.71 ± 52.51 b 65.77 ± 32.59 b 111.81 ± 215.29 b
1-Octen-3-ol 3391-86-4 974/974 MS, RI, STD 190.28 ± 150.79 a 10.94 ± 4.92 b 8.26 ± 3.52 b 16.1 ± 14.42 b
Hotrienol 29957-43-5 1101/1102 MS, RI 2385.59 ± 2896.62 a 167.73 ± 90.58 b 23.79 ± 13.41 b 23.42 ± 24.67 b
(E)-2-Octen-1-ol 18409-17-1 1068/1065 MS, RI 67.6 ± 58.93 a 2.8 ± 1.33 b 0.12 ± 0.17 b 2.61 ± 3.19 b
Linalool oxide (Pyranoid) 14049-11-7 1174/1171 MS, RI 1214.45 ± 1380.18 a 10.03 ± 5.67 b 17.92 ± 14.76 b 20.89 ± 25.25 b
Geraniol 106-24-1 1251/1252 MS, RI, STD 256.28 ± 271.23 a 1.47 ± 0.2 b 2.15 ± 1.78 b 3.15 ± 6.99 b
Benzyl alcohol 100-51-6 1031/1030 MS, RI, STD 163.51 ± 217.15 a 61.32 ± 61.29 b 1.66 ± 1.81 b 1.29 ± 2.12 b
Phenols
2,4-Di-tert-butyl phenol 96-76-4 1503/1509 MS, RI 35.76 ± 24.47 a 15.81 ± 16.34 b 2.45 ± 1.85 b 2.13 ± 2.33 b
Butylated hydroxytoluene 128-37-0 1513/1511 MS, RI, STD 23.26 ± 22.93 a 5.38 ± 6.54 b 0.44 ± 0.53 b 2.11 ± 2.46 b
Nitrogenous compounds
1-Ethyl-1H-pyrrole 617-92-5 808/806 MS, RI, STD 748.12 ± 1175.84 a 1045.09 ± 332.94 a 64.02 ± 64.02 b 64.49 ± 74.35 b
1-Butyl-1H-pyrrole 589-33-3 937/941 MS, RI 5.4 ± 13.24 ab 11.68 ± 6.23 a 0 ± 0 b 0 ± 0 b
Caffeine 58-08-2 1842/1842 MS, RI 0.22 ± 0.54 a 0 ± 0 a 0 ± 0 a 0 ± 0 a
o-Tolunitrile 529-19-1 1134/1135 MS, RI 210.18 ± 237.22 a 34.17 ± 4.65 b 2.26 ± 0.92 b 9.08 ± 11.2 b
2,4-Dimethyl-3-ethylpyrrole 517-22-6 -/1045 MS, STD 234.35 ± 290.74 a 315.59 ± 131.86 a 14.26 ± 10.24 b 15.35 ± 15.94 b
2-Amino-5-methylbenzoic acid 2941-78-8 -/901 MS 261.44 ± 36.42 a 231.53 ± 263.98 a 68.5 ± 44.28 b 47.11 ± 25.43 b
3,5-Diethyl-2-methyl pyrazine 18138-05-1 1150/1156 MS, RI 24.69 ± 60.16 b 80.73 ± 20.4 a 0.45 ± 0.52 b 1.16 ± 0.63 b
2,3-Diethyl-5-methylpyrazine 18138-04-0 -/1153 MS, STD 6.25 ± 15.19 b 22.31 ± 5.18 a 0.09 ± 0.1 b 0.19 ± 0.16 b
Methyl anthranilate 134-20-3 1336/1337 MS, RI, STD 1015.82 ± 2037.28 ab 1452.42 ± 617.44 a 36.23 ± 33.71 b 65.21 ± 99.75 b
2,5-Dimethyl-3-ethylpyrazine 13360-65-1 1079/1076 MS, RI 76.98 ± 164.5 a 311.45 ± 93.86 b 2.48 ± 2.74 b 4.3 ± 3.51 b
2-Methyl-5-ethylpyrazine 13360-64-0 998/994 MS, RI 301.75 ± 623.85 ab 599.82 ± 340.49 a 14.73 ± 5.12 b 19.63 ± 11.57 b
Indole 120-72-9 1289/1288 MS, RI, STD 239.83 ± 297.89 a 11.05 ± 4.94 b 8.71 ± 8.86 b 1.67 ± 2.12 b
1-Methyl-1H-pyrrole-2-carboxaldehyde 1192-58-1 913/921 MS, RI, STD 1.16 ± 1.02 a 0 ± 0 b 0.24 ± 0.39 b 0.22 ± 0.32 b
Aldehyde compounds
Citral 5392-40-5 1268/1268 MS, RI 7389.23 ± 8424.4 a 3.94 ± 0.44 b 48.97 ± 69.74 b 81.71 ± 202.4 b
β-Homocyclocitral 472-66-2 1254/1255 MS, RI 18.32 ± 21.23 a 0.02 ± 0.03 b 0 ± 0 b 0 ± 0 b
β-Cyclocitral 432-25-7 1216/1217 MS, RI, STD 102.02 ± 63.97 a 16.47 ± 7.26 b 3.44 ± 1.94 b 9.66 ± 6.03 b
(E,E)-2,4-Heptadienal 4313-03-5 1009/1007 MS, RI, STD 170.56 ± 134.43 a 43.77 ± 30.61 b 0.81 ± 1.8 b 32.8 ± 38.91 b
Phenyl acetaldehyde 122-78-1 1040/1039 MS, RI, STD 294.92 ± 264.44 a 74.67 ± 23.37 b 16.46 ± 15.74 b 50.55 ± 103.14 b
Safranal 116-26-7 1196/1196 MS, RI 87.81 ± 88.74 a 6.42 ± 3.98 b 0.87 ± 1.2 b 4.3 ± 5.08 b
Decanal 112-31-2 1203/1203 MS, RI, STD 93.75 ± 48.22 a 9.24 ± 5.22 b 0.39 ± 0.53 b 2.87 ± 2.22 b
Heptanal 111-71-7 899/896 MS, RI, STD 61.56 ± 31.9 a 1.95 ± 1.97 b 0 ± 0 b 4.17 ± 3.54 b
(Z)-Citral 106-26-3 1240/1238 MS, RI 7507.57 ± 8322.52 a 3.5 ± 0.94 b 64.23 ± 67.01 b 82.84 ± 186.8 b
Benzaldehyde 100-52-7 957/954 MS, RI, STD 454.84 ± 168.82 a 90.09 ± 11.45 b 27.68 ± 15.45 b 49.95 ± 42.31 b
Hydrocarbon compounds
2-Methylnaphthalene 91-57-6 1287/1288 MS, RI, STD 8.32 ± 4.51 a 0.64 ± 0.24 b 0.03 ± 0.05 b 0.93 ± 1.61 b
Naphthalene 91-20-3 1178/1177 MS, RI, STD 209.91 ± 181.88 a 11.48 ± 8.91 b 0 ± 0 b 12.47 ± 9.96 b
1-Methylnaphthalene 90-12-0 1302/1304 MS, RI, STD 3.18 ± 1.63 a 0.27 ± 0.11 b 0.02 ± 0.02 b 0.33 ± 0.47 b
Fluorene 86-73-7 1572/1573 MS, RI 0.08 ± 0.14 a 0 ± 0 b 0 ± 0 b 0 ± 0 b
Acenaphthene 83-32-9 /1476 MS 0.22 ± 0.44 a 0 ± 0 b 0 ± 0 b 0.03 ± 0.08 ab
2-Vinyl-naphthalene 827-54-3 1381/1374 MS, RI 1.45 ± 0.88 a 0 ± 0 b 0 ± 0 b 0 ± 0 b
Alloocimene 673-84-7 1128/1127 MS, RI 153.04 ± 112.83 a 23.62 ± 3.2 b 11.79 ± 0.99 b 11.97 ± 2.65 b
Geraniolene 6709-39-3 879/877 MS, RI 11.09 ± 9.92 a 12.99 ± 6.91 a 0.62 ± 0.84 b 0.84 ± 0.76 b
Tridecane 629-50-5 1299/1297 MS, RI 13.31 ± 12.22 a 6.67 ± 5.54 b 1.2 ± 1.39 b 1.89 ± 2.37 b
D-Limonene 5989-27-5 1024/1025 MS, RI, STD 258.27 ± 231.56 a 36.42 ± 6.57 b 4.85 ± 7.01 b 7.96 ± 8.09 b
2,7-Dimethyl naphthalene 582-16-1 1415/1412 MS, RI 1.39 ± 0.92 a 0 ± 0 b 0 ± 0 b 0.03 ± 0.09 b
2-Carene 554-61-0 1012/1012 MS, RI 115.94 ± 129.63 a 30.49 ± 6.73 b 12.35 ± 2.02 b 12.23 ± 1.99 b
β-Cedrene 546-28-1 1420/1417 MS, RI 166.66 ± 130.48 a 3.77 ± 1.66 b 10.61 ± 13.71 b 31.25 ± 49.55 b
Hexadecane 544-76-3 1599/1596 MS, RI 39.41 ± 35.07 a 3.88 ± 1.26 b 2.24 ± 0.97 b 1.57 ± 0.76 b
meta-Cymene 535-77-3 1024/1020 MS, RI, STD 51.45 ± 50.12 a 7.26 ± 1.73 b 0.61 ± 1.05 b 0.91 ± 1.41 b
α-Farnesene 502-61-4 1506/1506 MS, RI 2.8 ± 0.69 a 2.31 ± 0.05 b 2.49 ± 0.51 ab 2.3 ± 0.04 b
δ-Cadinene 483-76-1 1521/1522 MS, RI 55.66 ± 55.14 a 0.94 ± 0.55 b 3.79 ± 5.03 b 6.05 ± 3.88 b
Longifolene 475-20-7 1402/1402 MS, RI 150.2 ± 132.38 a 4.36 ± 2.91 b 10.93 ± 8.07 b 31.22 ± 55.36 b
α-Ionene 475-03-6 1352/1354 MS, RI 3.69 ± 4.61 a 2.52 ± 1.88 a 0 ± 0 b 0.13 ± 0.23 b
α-Cedrene 469-61-4 1409/1409 MS, RI 0.66 ± 1.44 a 0 ± 0 a 0 ± 0 a 0.09 ± 0.25 a
2,6,10-Trimethyltridecane 3891-99-4 1462/1459 MS, RI 5.12 ± 2.18 a 2.25 ± 0.75 b 0.58 ± 0.34 c 0.95 ± 0.57 c
(E)-β-Ocimene 3779-61-1 1036/1035 MS, RI 1003.92 ± 1027.43 a 112.7 ± 46.49 b 39.78 ± 23.51 b 49.26 ± 28.06 b
1,2-Dihydro-1,1,6-trimethylnaphthalene 30364-38-6 1349/1350 MS, RI 14.96 ± 25.32 a 15.81 ± 6.64 a 0.03 ± 0.03 b 0.44 ± 0.69 b
γ-Muurolene 30021-74-0 1484/1471 MS, RI 1.87 ± 2.75 a 0 ± 0 b 0.03 ± 0.07 b 0.02 ± 0.04 b
α-Calacorene 21391-99-1 1542/1541 MS, RI 11.41 ± 13.42 a 0.03 ± 0.05 b 0.14 ± 0.32 b 0.22 ± 0.22 b
Pristane 1921-70-6 1706/1702 MS, RI 3.38 ± 3.29 a 0.4 ± 0.54 b 0 ± 0 b 0 ± 0 b
α-Ylangene 14912-44-8 1346/1348 MS, RI 4.59 ± 6.03 a 0.01 ± 0.01 b 0.17 ± 0.31 b 0.35 ± 0.32 b
δ-3-Carene 13466-78-9 1011/1017 MS, RI, STD 140.93 ± 109.31 a 66.79 ± 25.09 b 2.46 ± 1.75 c 9.89 ± 4.89 c
Myrcene 123-35-3 991/988 MS, RI, STD 339.1 ± 225.54 a 31.77 ± 4.51 b 12.1 ± 2.95 b 15.92 ± 15.12 b
Toluene 108-88-3 758/751 MS, RI 1163.56 ± 401.83 a 462.85 ± 176.27 b 32.08 ± 8.09 c 229.08 ± 114.89 c
para-Xylene 106-42-3 861/859 MS, RI 514.7 ± 393.68 a 240.56 ± 178.25 b 6.41 ± 4.22 c 54.49 ± 21.34 bc
α-Muurolene 10208-80-7 1500/1498 MS, RI 98.24 ± 107.26 a 3.49 ± 0.78 b 7.54 ± 7.46 b 8.19 ± 3.72 b
Styrene 100-42-5 888/885 MS, RI 147.58 ± 98.38 a 45.48 ± 27.68 b 2.28 ± 1.56 b 25.3 ± 15.74 b
Ketone compounds
Acetophenone 98-86-2 1062/1063 MS, RI, STD 199.32 ± 155.19 a 36.59 ± 3.09 b 2.23 ± 4.3 b 11.06 ± 7.62 b
β-Ionone 79-77-6 1483/1484 MS, RI 267.17 ± 184.23 a 45.6 ± 10.27 b 15.4 ± 2.67 b 21.95 ± 6.9 b
Dl-Camphor 76-22-2 1143/1141 MS, RI, STD 7.28 ± 5.5 a 0.37 ± 0.41 b 0.07 ± 0.15 b 4.26 ± 9.72 b
2,3-Octanedione 585-25-1 982/980 MS, RI 206.87 ± 136.13 a 67.59 ± 38.12 b 13.75 ± 3.26 b 35.11 ± 25.95 b
Hexahydrofarnesyl acetone 502-69-2 1846/1846 MS, RI 0.77 ± 1.89 a 0 ± 0 a 0 ± 0 a 0 ± 0 a
Jasmone 488-10-8 1396/1396 MS, RI, STD 176.27 ± 294.1 a 0.26 ± 0.37 b 1.99 ± 1.59 b 0.56 ± 0.59 b
Geranyl Acetone 3796-70-1 1452/1451 MS, RI, STD 145.64 ± 87.28 a 10.34 ± 1.14 b 2.49 ± 1.06 b 5.8 ± 2.5 b
Dihydro-β-ionone 17283-81-7 1438/1436 MS, RI 11.72 ± 1.58 a 10.08 ± 0.04 b 9.78 ± 0.05 b 9.84 ± 0.08 b
Mesityl oxide 141-79-7 775/788 MS, RI 793.17 ± 378.67 a 51 ± 35.76 b 79.28 ± 35.32 b 138.28 ± 126.65 b
L-Menthone 14073-97-3 1154/1144 MS, RI, STD 142.74 ± 68.72 a 6.53 ± 10.09 b 1.52 ± 3.18 b 24.54 ± 22.6 b
α-ionone 127-41-3 1425/1425 MS, RI, STD 34.35 ± 28.45 a 15.54 ± 1.9 b 10.4 ± 0.28 b 10.91 ± 0.52 b
Dehydro-β-ionone 1203-08-3 1482/1481 MS, RI 21.66 ± 25.06 a 10.74 ± 0.83 ab 9.75 ± 0.05 b 9.79 ± 0.1 b
Methyl heptenone 110-93-0 981/983 MS, RI, STD 161.19 ± 131.58 a 22.09 ± 6.33 b 3.25 ± 2.87 b 13.33 ± 5.92 b
Ester compounds
Ethyl benzoate 93-89-0 1170/1168 MS, RI, STD 1.11 ± 0.85 a 0.1 ± 0.09 b 0.03 ± 0.02 b 0.05 ± 0.05 b
Methyl benzoate 93-58-3 1091/1091 MS, RI, STD 4.74 ± 4.39 a 2.07 ± 0.96 b 0.11 ± 0.07 b 0.4 ± 0.43 b
Diisobutyl phthalate 84-69-5 1869/1870 MS, RI 14.81 ± 10.96 a 0.8 ± 0.52 b 0.31 ± 0.11 b 0.18 ± 0.07 b
Ethyl Palmitate 628-97-7 1992/1992 MS, RI, STD 0 ± 0 b 0 ± 0 b 0.74 ± 0.9 a 0.44 ± 0.74 ab
(Z)-3-Hexen-1-yl isovalerate 35154-45-1 1184/1235 MS, RI, STD 13.78 ± 14.81 a 0.31 ± 0.24 b 1.13 ± 1.79 b 0.98 ± 1.84 b
(Z)-3-Hexen-1-yl hexanoate 31501-11-8 1382/1380 MS, RI, STD 70.01 ± 72.93 a 2.23 ± 3.09 b 8.22 ± 14.2 b 1.58 ± 2.98 b
δ-Tetradecalactone 2721-22-4 / MS 3.68 ± 2.25 a 0.76 ± 0.32 b 0.12 ± 0.05 b 0.14 ± 0.08 b
(Z)-3-Hexen-1-yl benzoate 25152-85-6 1566/1568 MS, RI, STD 11.31 ± 9.15 a 1.86 ± 0.79 b 1.51 ± 0.14 b 1.65 ± 0.22 b
(Z)-3-Hexen-1-yl butyrate 16491-36-4 1186/1185 MS, RI, STD 17.35 ± 18.12 a 0.2 ± 0.1 b 2.16 ± 3.52 b 0.35 ± 0.45 b
Benzyl acetate 140-11-4 1160/1162 MS, RI, STD 16.96 ± 11.29 a 2.86 ± 0.6 b 0.48 ± 0.31 b 0.98 ± 0.87 b
Ethyl hexanoate 123-66-0 996/997 MS, RI 17380.43 ± 16045.79 a 66.66 ± 13.46 b 1184.3 ± 814.84 b 963.44 ± 761.99 b
Ethyl nonanoate 123-29-5 1294/1295 MS, RI 622.07 ± 347.71 a 7.03 ± 5.22 b 49.43 ± 14.46 b 32.48 ± 41.07 b
Methyl salicylate 119-36-8 1191/1191 MS, RI, STD 158.34 ± 84.82 a 45.37 ± 14.95 b 2.32 ± 1.02 c 4.6 ± 6.96 bc
Linalyl acetate 115-95-7 1257/1226 MS, RI, STD 193.27 ± 272.59 a 11.07 ± 4.4 b 1.2 ± 0.61 b 1.9 ± 1.37 b
Methyl palmitate 112-39-0 1926/1926 MS, RI, STD 0 ± 0 c 8.04 ± 6.78 a 3.98 ± 1 b 3.06 ± 1.78 b
Ethyl octanoate 106-32-1 1196/1196 MS, RI, STD 11.84 ± 9.17 a 0 ± 0 b 0.57 ± 0.17 b 0.57 ± 0.45 b
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a Retention index of compounds in reference. b Retention index of compounds on HP-5MS. c “MS” mass spetrum comparison using NIST17 library. “RI” retention index in agreement with literature value. “STD” confirmed by authenic standards. d Different letters indicated significant difference.

To investigate the similarities and differences of volatile compounds among the four aroma types of yellow teas, PCA and HCA were performed based on the quantitative results of the identified volatile compounds. The results of PCA (the total variance of model was 89%) (Figure 2A) and HCA (Figure 2B) showed that the yellow teas could be divided into four groups according to their aroma types, which indicated that there were significant differences in the volatile profile among the four aroma types of yellow teas. Based on these results, six OPLS-DA models were established to investigate the discriminatory volatile compounds (Figure S2). Among the four types of yellow tea, 75 discriminative volatile compounds, which might play an important role in the formation of different aroma characteristics and contribute to the distinction of these four aroma types of yellow teas (Figure S3), were identified.

Figure 2.

Figure 2

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PCA (A) and HCA (B) of the different aroma types of yellow teas.

3.3. Key Aroma Compounds in Different Aroma Types of Yellow Tea

It is well known that the characteristic aroma of yellow tea is formed by a series of volatile compounds with a certain composition and proportion. The characteristic aroma mainly depends on the concentrations of aroma compounds and their OAVs. OAV is usually used to evaluate the contribution of the aroma compound to the odor of tea [13]. Therefore, the aroma attributes and OAVs of all the identified volatile compounds were calculated and listed in Table S4. Sixty-one volatile compounds were identified with OAV > 1 in at least one aroma type of yellow tea. Twenty-four volatile compounds with OAVs > 1 were common in all yellow tea samples, and 12 (linalool, phenethyl alcohol, 1-octen-3-ol, α-ionone, β-ionone, dehydro-β-ionone, (E,E)-2,4-heptadienal, phenyl acetaldehyde, methyl anthranilate, ethyl hexanoate, myrcene, and α-muurolene) had OAVs > 10. Most of aroma compounds with high OAVs (OAV > 10) possess ‘floral’, ‘fruity’, ‘citrus’, ‘green’, and ‘fatty’ odors, which endow yellow tea with clean and pure scents and play a major role in the formation of a variety of aroma types of yellow teas [6].

Combined with the results of OPLS-DA, a total of 47 discriminative aroma compounds were identified in the four aroma types of yellow tea based on the three conditions: the values of predictive component variable importance in the projection (VIP) ≥ 1.0, p ≤ 0.05 and OAV > 1 (Figure 3). Among these discriminative aroma compounds, eight, fourteen, seven, and eighteen aroma compounds with the highest levels in the floral fragrance, high-fired fragrance, fresh fragrance, and corn-like fragrance types of yellow teas, respectively. High contents of these discriminative aroma compounds might play an important role in the formation of different aroma characteristics of yellow tea. Therefore, these discriminative aroma compounds were recognized as key aroma compounds in different aroma types of yellow tea.

Figure 3.

Figure 3

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Heatmap of the discriminatory aroma compounds in the different aroma types of yellow teas.

In the floral fragrance types of yellow tea, (Z)-citral, citral, jasmone, (E)-linalool oxide (furanoid), decanal, geraniol, (E)-2-octen-1-ol, and safranal were identified as the key aroma compounds. Among them, (Z)-citral and citral with ‘citrus’ odor have been reported to be responsible for the formation of strongly fruity fragrance in lemon basil and hops [25,26]. €-Linalool oxide (furanoid) possesses a ‘floral’ odor and has been widely detected in yellow tea, green tea, black tea, and oolong tea. It has been considered as the important compound that contributes to ‘floral’ aroma formation in tea products [1,6,8,27,28]. In addition, as a vital odoriferous compound of honey, safranal has been regarded as an important aroma-active compound because of its ‘ripe fruit’ and ‘honey’ odor [6,14,16,29]. (E)-2-Octen-1-ol emits a ‘grassy’ odor and has been considered as an aroma-active compound responsible for the ‘green’ aroma characteristics formation of asam sunti [30].

In high-fired fragrance type of yellow tea, 3,5-diethyl-2-methylpyrazine, 2-methyl-5-ethylpyrazine, 2,3-diethyl-5-methylpyrazine, 2,5-dimethyl-3-ethylpyrazine, o-tolunitrile, dextro-limonene, α-ionene, acetophenone, methyl anthranilate, benzyl alcohol, methyl benzoate, 1,2-dihydro-1,1,6-trimethylnaphthalene, methyl salicylate, and para-xylene were identified as the key aroma compounds. Pyrazines, usually possess a ‘roasted’ attribute generated by heat treatment and exist abundantly in a large number of cooked, roasted, and toasted foods. For example, 3,5-diethyl-2-methylpyrazine, 2,3-diethyl-5-methylpyrazine, 2-methyl-5-ethylpyrazine, and 2,5-dimethyl-3-ethylpyrazine produce a ‘roasted hazelnut’ note, and have are considered as important contributors for the ‘roasted’ odor formation of yellow tea, green tea, coffee, and coco [7,8,9,31]. In addition, para-xylene with a ‘roasted’ attribute was identified as an aroma compound in yellow tea. This has long been considered to be a key characteristic aroma marker for the roasting process of oolong tea [7,32]. In addition, methyl anthranilate has a typical ‘grape juice’ odor that can improve the ‘floral and fruity’ aroma characteristics in many kinds of tea [6,8,12,33].

In the fresh fragrance type of yellow tea, indole, phenethyl alcohol, (E)-3-hexen-1-ol, α-terpineol, ethyl hexanoate, ethyl nonanoate, and ethyl octanoate were identified as the key aroma compounds. Esters are well-known aroma compounds that play an important role in the properties of beverages. Ethyl nonanoate, ethyl hexanoate, and ethyl octanoate are the representative ester compounds that can provide ‘floral’, ‘fruity’, and ‘waxy’ odors [6,34]. For example, ethyl hexanoate has been identified as an important aroma compound in oolong tea with a ‘pineapple’ odor, which contributes to the ‘sweet fruit’ aroma formation of special aroma characteristics of black tea [23,35]. Ethyl nonanoate has been considered as a potential aroma-active compound in fruits, and it also contributes to the formation of ‘rose-like’ aroma in black tea [35,36]. In addition, (E)-3-Hexen-1-ol has a ‘green’ note and has been reported to contribute to the formation of ‘green’, ‘grass’, and ‘fresh’ odors of black tea and oolong tea [16,23].

In corn-like fragrance of yellow tea, styrene, α-ionone, dehydro-β-ionone, dihydro-β-ionone, methyl heptenone, geranyl acetone, toluene, β-cyclocitral, mesityl oxide, naphthalene, 1-methylnaphthalene, 2-methylnaphthalene, δ-cadinene, cedrol, α-muurolene, heptanal, (E,E)-2,4-heptadienal, and l-menthone were identified as the key aroma compounds. Among them, styrene and toluene possessed ‘sweet balsam’ and ‘floral’ odors, which were also detected in yellow tea, black tea and are considered to play an important role in the formation of their aroma characteristics [6,8,24]. In addition, mesityl oxide presents a ‘honey’ odor and has been found in green tea and yellow tea, which contributes to the formation of a characteristic ‘sweet’ aroma [5,37]. As an unsaturated aldehyde, (E,E)-2,4-heptadienal is derived from the oxidation of polyunsaturated fatty acids and has ‘fatty’, ‘green’, and ‘nutty’ notes, and has been identified as a key aroma compound to form the special aroma of melons and green tea [37,38].

In addition, characteristic aromas were also impacted by the interactions among volatile compounds or volatile and non-volatile compounds [39]. Zhu et al. revealed that mixed aroma compounds with similar structures mainly present a synergistic effect and additive action, and a masking effect was found among aroma compounds with different structures in oolong tea [39]. Vicente Ferreira et al. also reported that the non-volatile higher alcohol content had an important impact on the characteristic aroma formation of wine [40,41,42].

3.4. Relationship between Aroma-Active Compounds and Sensory Attributes

To explore the relationships between the aroma-active compounds (OAV > 1) and sensory attributes, a PLS model was established. Two latent variables were included in the PLS model, which represented 86.90% of X-matrix variance (aroma-active compounds) and explained 99.30% of Y-matrix variance (sensory attributes). As shown in Figure 4, the positions of the sensory attributes and aroma-active compounds of yellow tea between the two ellipses indicated that they were well explained by the PLS model. Among these samples, the floral fragrance (H1–H7) and corn-like fragrance types of yellow teas (Y1–Y9) are mainly located on the upper part of PC2. The fresh fragrance type of yellow tea samples (Q1–Q6) are mainly located in the negative region of PC1 and PC2. The high-fired fragrance type yellow tea samples (HG1–HG4) are mainly located in the positive region of PC1 and negative region of PC2. This clearly indicates that tea samples can be divided into four groups according to their aroma types.

Figure 4.

Figure 4

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PLS plots for the tea samples, the sensory analysis, and active-aroma volatiles (OAV > 1). VC1: acetophenone; VC6: (E)-3-hexen-1-ol; VC7: 2-methylnaphthalene; VC8: naphthalene; VC9: 1-methylnaphthalene; VC66: 3,5-diethyl-2-methyl pyrazine; VC67: 2,3-diethyl-5-methylpyrazine; VC72: l-menthone; VC76: methyl anthranilate; VC77: 2,5-dimethyl-3-ethylpyrazine; VC78: 2-methyl-5-ethylpyrazine; VC81: ethyl hexanoate; VC83: ethyl nonanoate; VC89: safranal; VC92: decanal; VC93: heptanal; VC94: methyl heptanone; VC95: toluene; VC96: para-xylene; VC97: ethyl octanoate; VC103: styrene.

The five attributes (‘floral and fruity’, ‘roasted’, ‘fresh’, ‘grassy’, and ‘sweet’) that significantly correlated with some aroma-active compounds were located between the inner and outer ellipses. The ‘floral and fruity’, ‘sweet’, and ‘roasted’ attributes were located on the positive dimension, and the ‘fresh’ and ‘green’ attributes were located on the negative dimension of the first PC1. The floral fragrance and corn-like fragrance types of yellow tea samples were strongly associated with ‘floral and fruity’ and ‘sweet’ attributes, the high-fired fragrance type of yellow tea was strongly associated with ‘roasted’ attribute, and the fresh fragrance type of yellow tea was strongly associated with ‘fresh’ and ‘green’ attributes. Furthermore, the ‘floral and fruity’ and ‘sweet’ attributes were positively correlated to l-menthone, heptanal, naphthalene, 2-methylnaphthalene, 1-methylnaphthalene, methyl heptenone, decanal, styrene, safranal, toluene, para-xylene, and acetophenone. A previous study suggested that the ‘floral and fruity’ attribute was related to the ‘sweet’ attribute in tea [43]. The ‘roasted’ attribute was positively correlated to methyl anthranilate, 2,3-diethyl-5-methylpyrazine, 2-methyl-5-ethylpyrazine, 2,5-dimethyl-3-ethylpyrazine, and 3,5-diethyl-2-methyl pyrazine. It is well known that the intensity of the ‘roasted’ attribute mainly depends on the content of pyrazine compounds, which has been confirmed by a previous study [1]. The ‘fresh’ and ‘green’ attributes were positively correlated with (E)-3-hexen-1-ol, ethyl hexanoate, ethyl nonanoate, and ethyl octanoate. Previous studies have shown that ethyl esters with low detection thresholds usually exist in large amounts in wine and play a vital role in the formation of fruity aroma characteristics [44]. Meanwhile, it has also been reported that these esters make an important contribution to the fresh aroma characteristics of yellow tea, which differs from green and black teas [6].

4. Conclusions

According to the difference of aroma characteristics, yellow teas were divided into four main aroma types by QDA, including the floral fragrance, high-fired fragrance, fresh fragrance, and corn-like fragrance. Among them, floral fragrance yellow tea had a predominant ‘floral and fruity’ attribute, high-fired fragrance yellow tea was mainly featured with high intensity in the ‘roasted’ attribute, fresh fragrance yellow tea had a strong ‘fresh’ attribute, and corn-like fragrance yellow tea was marked by strong ‘sweet’ and ‘floral and fruity’ attributes. In addition, a total of 103 volatile compounds were identified and quantified in yellow teas by HS-SPME/GC-MS. According to multivariate statistical analysis and OAVs, 47 volatile compounds were identified as the key aroma compounds for the formation of different aroma types of yellow tea. Among them, eight aroma compounds dominated with ‘floral and fruity’ attribute in the floral fragrance type, fourteen aroma compounds dominated with ‘roasted’ attribute in the high-fired fragrance type, seven aroma compounds dominated with ‘floral and fruity’ and ‘grassy’ attributes in the fresh fragrance type, and eighteen aroma compounds dominated with ‘floral and fruity’ and ‘sweet’ attributes in the corn-like fragrance type. Furthermore, PLS analysis revealed that the ‘floral and fruity’ and sweet attributes were positively correlated to l-menthone, heptanal, naphthalene, 2-methylnaphthalene, 1-methylnaphthalene, methyl heptenone, decanal, styrene, safranal, toluene, para-xylene, and acetophenone. The ‘roasted’ attribute was positively correlated to methyl anthranilate, 2,3-diethyl-5-methylpyrazine, 2-methyl-5-ethylpyrazine, 2,5-dimethyl-3-ethylpyrazine, and 3,5-diethyl-2-methyl pyrazine. The ‘fresh’ and ‘grassy’ attributes were positively correlated to (E)-3-hexen-1-ol, ethyl hexanoate, ethyl nonanoate, and ethyl octanoate. Overall, this study provides new insights into the key aroma compounds that are responsible for the characteristic aroma in different aroma types of yellow tea, and will provide an important theoretical basis for establishing flavor directed processing of yellow tea.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/foods12010027/s1, Supplement Material S1: The detail information of sensory evaluation; Figure S1: Differences of the volatile categories (A) and discriminatory volatiles (B) among the four aroma types of yellow tea; Figure S2: Score plot of OPLS-DA 1 for floral fragrance type versus high-fired fragrance type with R2X (cum): 0.565, R2Y (cum): 0.989, Q2 (cum): 0.984 (A) and permutation testing of the OPLS-DA 1 (B); Score plot of OPLS-DA 2 for floral fragrance type versus fresh fragrance type with R2X (cum): 0.557, R2Y (cum): 0.99, Q2 (cum): 0.985 (C) and permutation testing of the OPLS-DA 2 (D); Score plot of OPLS-DA 3 floral fragrance type versus corn-like fragrance type with R2X (cum): 0.504, R2Y (cum): 0.993, Q2 (cum): 0.989 (E) and Permutation testing of the OPLS-DA 3 (F); Score plot of OPLS-DA 4 for floral fragrance type versus fresh fragrance type with R2X (cum): 0.595, R2Y (cum): 0.989, Q2 (cum): 0.985 (G) and permutation testing of the OPLS-DA 4 (H); Score plot of OPLS-DA 5 for floral fragrance type versus fresh fragrance type with R2X (cum): 0.511, R2Y (cum): 0.994, Q2 (cum): 0.99 (I) and permutation testing of the OPLS-DA 5 (J); Score plot of OPLS-DA 6 for floral fragrance type versus fresh fragrance type with R2X (cum): 0.479, R2Y (cum): 0.991, Q2 (cum): 0.98 (K) and permutation testing of the OPLS-DA 6 (L); Figure S3: Heatmap of the 47 discriminatory aroma compounds in the different aroma types of yellow tea; Table S1: The main volatile compounds in different raw material or processing parameters of yellow tea; Table S2: Yellow tea samples information; Table S3: The standard curve of identified volatile compounds in yellow tea; Table S4: The OAV values of the volatile compounds identified in Yellow tea.

Click here for additional data file. (1.3MB, zip)

Author Contributions

Conceptualization, Z.L., J.H. and Q.L.; methodology, X.H. and C.W.; validation, R.J., T.H. and X.Z.; investigation, R.J. and X.Z.; resources, R.J. and X.Z.; data curation, X.H. and R.J.; writing—original draft preparation, X.H. and C.W.; writing—review and editing, Q.L. and J.H.; supervision, Z.L.; project administration, Z.L. and Q.L.; funding acquisition, Q.L., J.H. and Z.L. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

The study was conducted in accordance with the Declaration of Helsinki, and approved by the Hunan Agricultural University Institutional Review Board Committee (TSF-780-2021).

Data Availability Statement

The data are available from the corresponding author.

Conflicts of Interest

The authors declare no conflict of interest.

Funding Statement

This research was funded by the National Natural Science Foundation of China, grant number 32272773, 31871764; and the National Key Research and Development Program of China (2022YFD1600805); and the China Tea Research System Project, grant number CARS-23; and the Project funded by China Postdoctoral Science Foundation, grant number 2022T150206; and the Natural Science Foundation of Hunan Province, grant number 2022JJ30023; and the Open Project Fund of College of Horticulture of Hunan Agricultural University, grant number 2021YYXK003; and the “1515 Talent Project” of Hunan Agricultural University.

Footnotes

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References

  • 1.Ho C.T., Zheng X., Li S.M. Tea aroma formation. Food Sci. Hum. Well. 2015;4:9–27. doi: 10.1016/j.fshw.2015.04.001. [DOI] [Google Scholar]
  • 2.Xu J.Y., Wang M., Zhao J.P., Wang Y.H., Tang Q., Khan I.A. Yellow tea (Camellia sinensis L.), a promising Chinese tea: Processing, chemical constituents and health benefits. Food Res. Int. 2018;107:567–577. doi: 10.1016/j.foodres.2018.01.063. [DOI] [PubMed] [Google Scholar]
  • 3.Wang Q., Zhao X., Qian Y., Wang R. In vitro antioxidative activity of yellow tea and its in vivo preventive effect on gastric injury. Exp. Ther. Med. 2013;6:423–426. doi: 10.3892/etm.2013.1117. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Zhai X.T., Zhang L., Granvogl M., Ho C.T., Wan X.C. Flavor of tea (Camellia sinensis): A review on odorants and analytical techniques. Compr. Rev. Food Sci. 2022;21:3867–3909. doi: 10.1111/1541-4337.12999. [DOI] [PubMed] [Google Scholar]
  • 5.Jiang R.G., Huang Y., Jin Y.L., Huang F.F., Liu Z.H., Huang J.A., Li Q. Analysis of Characteristic Aroma Components of Different Grades of Yellow Tea. Food Sci. 2021;42:89–98. [Google Scholar]
  • 6.Shi Y.L., Wang M.Q., Dong Z.B., Zhu Y., Shi J., Ma W.J., Lin Z., Lv H.P. Volatile components and key odorants of Chinese yellow tea (Camellia sinensis) LWT-Food Sci. Technol. 2021;146:111512. doi: 10.1016/j.lwt.2021.111512. [DOI] [Google Scholar]
  • 7.Guo X., Ho C.T., Schwab W., Wan X. Effect of the roasting degree on flavor quality of large-leaf yellow tea. Food Chem. 2021;347:129016. doi: 10.1016/j.foodchem.2021.129016. [DOI] [PubMed] [Google Scholar]
  • 8.Guo X., Ho C.T., Schwab W., Song C., Wan X. Aroma compositions of large-leaf yellow tea and potential effect of theanine on volatile formation in tea. Food Chem. 2019;280:73–82. doi: 10.1016/j.foodchem.2018.12.066. [DOI] [PubMed] [Google Scholar]
  • 9.Mao J.Y., Zhang L.X., Liu W.M., Xiang Q.Z. Effects of aroma-improving methods and temperatures on aroma of yellow tea. Tea Process. China. 2018;1:13–20. [Google Scholar]
  • 10.Gong S.Y., Zhou S.J., Xie Y.X., Fan F.Y., Qian H., Wang C.Y. Sensory demarcation of yellowing processing and the volatile components in Moganhuangya tea with different yellowing degrees. J. Tea. 2021;47:138–146. [Google Scholar]
  • 11.Wang Z.H., Yue C.N., Tong H.R. Analysis of taste characteristics and identification of key chemical components of fifteen Chinese yellow tea samples. J. Food Sci. Tech. 2021;58:1378–1388. doi: 10.1007/s13197-020-04649-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 12.Li Q., Li Y.D., Luo Y., Xiao L.Z., Wang K.B., Huang J.A., Liu Z.H. Characterization of the key aroma compounds and microorganisms during the manufacturing process of Fu brick tea. LWT-Food Sci. Technol. 2020;127:109355. doi: 10.1016/j.lwt.2020.109355. [DOI] [Google Scholar]
  • 13.Deng X., Huang G., Tu Q., Zhou H., Li Y., Shi H., Wu X., Ren H., Huang K., He X., et al. Evolution analysis of flavor-active compounds during artificial fermentation of Pu-erh tea. Food Chem. 2021;357:129783. doi: 10.1016/j.foodchem.2021.129783. [DOI] [PubMed] [Google Scholar]
  • 14.Flaig M., Qi S., Wei G., Yang X., Schieberle P. Characterization of the Key Odorants in a High-Grade Chinese Green Tea Beverage (Camellia sinensis; Jingshan cha) by Means of the Sensomics Approach and Elucidation of Odorant Changes in Tea Leaves Caused by the Tea Manufacturing Process. J. Agric. Food Chem. 2020;68:5168–5179. doi: 10.1021/acs.jafc.0c01300. [DOI] [PubMed] [Google Scholar]
  • 15.Giri A., Osako K., Okamoto A., Ohshima T. Olfactometric characterization of aroma active compounds in fermented fish paste in comparison with fish sauce, fermented soy paste and sauce products. Food Res. Int. 2010;43:1027–1040. doi: 10.1016/j.foodres.2010.01.012. [DOI] [Google Scholar]
  • 16.Guo X., Ho C.T., Wan X., Zhu H., Liu Q., Wen Z. Changes of volatile compounds and odor profiles in Wuyi rock tea during processing. Food Chem. 2021;341:128230. doi: 10.1016/j.foodchem.2020.128230. [DOI] [PubMed] [Google Scholar]
  • 17.Joshi R., Gulati A. Fractionation and identification of minor and aroma-active constituents in Kangra orthodox black tea. Food Chem. 2015;167:290–298. doi: 10.1016/j.foodchem.2014.06.112. [DOI] [PubMed] [Google Scholar]
  • 18.van Gemert L.J. Compilations of Flavour Threshold Values in Water and Other Media (Second Enlarged and Revised Edition) Oliemans Punter & Partners BV; Zeist, The Netherlands: 2015. [Google Scholar]
  • 19.Pang X., Yu W., Cao C., Yuan X., Qiu J., Kong F., Wu J. Comparison of Potent Odorants in Raw and Ripened Pu-Erh Tea Infusions Based on Odor Activity Value Calculation and Multivariate Analysis: Understanding the Role of Pile Fermentation. J. Agric. Food Chem. 2019;67:13139–13149. doi: 10.1021/acs.jafc.9b05321. [DOI] [PubMed] [Google Scholar]
  • 20.Wang M.Q., Ma W.J., Shi J., Zhu Y., Lin Z., Lv H.P. Characterization of the key aroma compounds in Longjing tea using stir bar sorptive extraction (SBSE) combined with gas chromatography-mass spectrometry (GC-MS), gas chromatography-olfactometry (GC-O), odor activity value (OAV), and aroma recombination. Food Res. Int. 2020;130:108908. doi: 10.1016/j.foodres.2019.108908. [DOI] [PubMed] [Google Scholar]
  • 21.Welke J.E., Zanus M., Lazzarotto M., Alcaraz Z.C. Quantitative analysis of headspace volatile compounds using comprehensive two-dimensional gas chromatography and their contribution to the aroma of Chardonnay wine. Food Res. Int. 2014;59:85–99. doi: 10.1016/j.foodres.2014.02.002. [DOI] [Google Scholar]
  • 22.Xu Y.Q., Wang C., Li C.W., Liu S.H., Zhang C.X., Li L.W., Jiang D.H. Characterization of Aroma-Active Compounds of Pu-erh Tea by Headspace Solid-Phase Microextraction (HS-SPME) and Simultaneous Distillation-Extraction (SDE) Coupled with GC-Olfactometry and GC-MS. Food Anal. Method. 2015;9:1188–1198. [Google Scholar]
  • 23.Liu H.C., Xu Y.J., Wen J., An K.J., Wu J.J., Yu Y.S., Zou B., Guo M.H. A comparative study of aromatic characterization of Yingde Black Tea infusions in different steeping temperatures. LWT-Food Sci. Technol. 2021;143:110860. [Google Scholar]
  • 24.Yun J., Cui C., Zhang S.H., Zhu J.J., Peng C.Y., Cai H.M., Yang X.G., Hou R.Y. Use of headspace GC/MS combined with chemometric analysis to identify the geographic origins of black tea. Food Chem. 2021;360:130033. doi: 10.1016/j.foodchem.2021.130033. [DOI] [PubMed] [Google Scholar]
  • 25.Al-Kateb H., Mottram D.S. The relationship between growth stages and aroma composition of lemon basil Ocimum citriodorum Vis. Food Chem. 2014;152:440–446. doi: 10.1016/j.foodchem.2013.12.001. [DOI] [PubMed] [Google Scholar]
  • 26.Inui T., Matsui H., Hosoya T., Kumazawa S., Fukui N., Oka K. Effect of Harvest Time and Pruning Date on Aroma Characteristics of Hop Teas and Related Compounds of Saaz Hops. J. Am. Soc. Brew. Chem. 2018;74:231–241. doi: 10.1094/ASBCJ-2016-4628-01. [DOI] [Google Scholar]
  • 27.Wang D.M., Takako Y., Kikue K., Akio K. Analysis of glycosidically bound aroma precursors in tea leaves. 1. Qualitative and quantitative analyses of glycosides with aglycons as aroma compounds. J Agric. Food Chem. 2000;48:5411–5418. doi: 10.1021/jf000443m. [DOI] [PubMed] [Google Scholar]
  • 28.Zhu Y.B., Zhang Z.Z., Yang Y.F., Du X.P., Chen F., Ni H. Analysis of the aroma change of instant green tea induced by the treatment with enzymes from Aspergillus niger prepared by using tea stalk and potato dextrose medium. Flavour Fragr. J. 2017;32:451–460. doi: 10.1002/ffj.3402. [DOI] [Google Scholar]
  • 29.Costa A.C., Garruti D.S., Madruga M.S. The power of odour volatiles from unifloral melipona honey evaluated by gas chromatography-olfactometry Osme techniques. J. Sci. Food Agric. 2019;99:4493–4497. doi: 10.1002/jsfa.9647. [DOI] [PubMed] [Google Scholar]
  • 30.Eren X., Christofora H.W., Didah N.F. Characterization of aroma compounds in Indonesian traditional seasoning (asam sunti) made from Averrhoa bilimbi L. Emir. J. Food Agric. 2017;29:378–386. [Google Scholar]
  • 31.Korhonova M., Hron K., Klimcikova D., Muller L., Bednar P., Bartak P. Coffee aroma-statistical analysis of compositional data. Talanta. 2009;80:710–715. doi: 10.1016/j.talanta.2009.07.054. [DOI] [PubMed] [Google Scholar]
  • 32.Liu X.B., Liu Y.W., Li P., Yang J.F., Wang F., Kim E.Y., Wu Y.Y., He P.M., Li B., Tu Y.Y. Chemical characterization of Wuyi rock tea with different roasting degrees and their discrimination based on volatile profiles. RSC Adv. 2021;11:12074–12085. doi: 10.1039/D0RA09703A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 33.Chen M.C., Zhu Y.J., Liu B., Chen Z., Zheng J.M., Guan M.D., Shi H., Wang Y.N., Yang W.W. Changes in the volatiles, chemical components, and antioxidant activities of Chinese jasmine tea during the scenting processes. Int. J. Food Prop. 2016;20:681–693. doi: 10.1080/10942912.2016.1177542. [DOI] [Google Scholar]
  • 34.Nascimento E.S.P., Cardoso D.R., Franco D.W. Quantitative Ester Analysis in Cachaça and Distilled Spirits by Gas Chromatography−Mass Spectrometry (GC−MS) J. Agric. Food Chem. 2008;56:5488–5493. doi: 10.1021/jf800551d. [DOI] [PubMed] [Google Scholar]
  • 35.Chen J.Y., Yang Y.Q., Deng Y.L., Liu Z.Q., Xie J.L., Shen S., Yuan H.B., Jiang Y.W. Aroma quality evaluation of Dianhong black tea infusions by the combination of rapid gas phase electronic nose and multivariate statistical analysis. LWT-Food Sci. Technol. 2022;153:112496. doi: 10.1016/j.lwt.2021.112496. [DOI] [Google Scholar]
  • 36.Choi J.Y., Lee S.M., Lee H.J., Kim Y.S. Characterization of aroma-active compounds in Chinese quince (Pseudocydonia sinensis Schneid) by aroma dilution analyses. Food Res. Int. 2018;105:828–835. doi: 10.1016/j.foodres.2017.12.015. [DOI] [PubMed] [Google Scholar]
  • 37.Zhu J., Niu Y., Xiao Z. Characterization of the key aroma compounds in Laoshan green teas by application of odour activity value (OAV), gas chromatography-mass spectrometry-olfactometry (GC-MS-O) and comprehensive two-dimensional gas chromatography mass spectrometry (GC × GC-qMS) Food Chem. 2021;339:128136. doi: 10.1016/j.foodchem.2020.128136. [DOI] [PubMed] [Google Scholar]
  • 38.Yang X., Yang F., Liu Y., Jian L., Song H.L. Identification of Key Off-Flavor Compounds in Thermally Treated Watermelon Juice via Gas Chromatography-Olfactometry-Mass Spectrometry, Aroma Recombination, and Omission Experiments. Foods. 2020;9:227. doi: 10.3390/foods9020227. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 39.Zhu J., Chen F., Wang L., Niu Y., Xiao Z. Evaluation of the synergism among volatile compounds in Oolong tea infusion by odour threshold with sensory analysis and E-nose. Food Chem. 2017;221:1484–1490. doi: 10.1016/j.foodchem.2016.11.002. [DOI] [PubMed] [Google Scholar]
  • 40.Arancha F.B., Maria-Pilar S.N., Vicente F. On the effects of higher alcohols on red swine aroma. Food Chem. 2016;210:107–114. doi: 10.1016/j.foodchem.2016.04.021. [DOI] [PubMed] [Google Scholar]
  • 41.Maria-Pilar S.N., Ignacio A., Sara F.T., Purificacion F.Z., Ana E., Vicente F. Chemo-sensory approach for the identification of chemical compounds driving green character in red wines. Food Res. Int. 2018;109:138–148. doi: 10.1016/j.foodres.2018.04.037. [DOI] [PubMed] [Google Scholar]
  • 42.Maria-Pilar S.N., Eva C., Laura C., Purificacion F.Z., Dominique V., Vicente F. Effects of the Nonvolatile Matrix on the Aroma Perception of Wine. J. Agric. Food Chem. 2010;58:5574–5585. doi: 10.1021/jf904377p. [DOI] [PubMed] [Google Scholar]
  • 43.Mao S.H., Lu C.Q., Li M.F., Ye Y.L., Wei X., Tong H.R. Identification of key aromatic compounds in Congou black tea by partial least-square regression with variable importance of projection scores and gas chromatography-mass spectrometry/gas chromatography-olfactometry. J. Sci. Food Agric. 2018;98:5278–5286. doi: 10.1002/jsfa.9066. [DOI] [PubMed] [Google Scholar]
  • 44.Ayestaran B., Martinez-Lapuente L., Guadalupe Z., Canals C., Adell E., Vilanova M. Effect of the winemaking process on the volatile composition and aromatic profile of Tempranillo Blanco wines. Food Chem. 2019;276:187–194. doi: 10.1016/j.foodchem.2018.10.013. [DOI] [PubMed] [Google Scholar]

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