# Analysis of Volatile Components inTremella fuciformis by Electronic Nose Combined with GC-MS

Authors: Lijun Fu; Jing Tian; Li Liu; Yongzheng Ma; Xiumin Zhang; Changyang Ma; Wenyi Kang; Yong Sun
Journal: Journal of Food Quality
 (2022)

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## Abstract

In order to quickly evaluate the quality ofTremella fuciformis, the volatile components of T. fuciformis from 4 provinces in China, including Hebei, Henan, Fujian, and Sichuan, were analyzed by electronic nose combined with gas chromatography-mass spectrometry (GC-MS), and the key aroma compounds were determined by relative odor activity value (ROAV). The results showed that the electronic nose combined with the principal component analysis method could distinguish the samples from four regions with good discrimination. At least 117 volatile components were detected in T. fuciformis by GC-MS and a total of 58, 59, 62, and 55 volatile components were identified from Hebei, Henan, Fujian, and Sichuan, respectively, of which there were 18 common components. The volatile components in T. fuciformis were mainly hydrocarbons, followed by aldehydes, acids, and esters, while acetic acid and hexanal were relatively rich in T. fuciformis. Based on the ROAV, 8 key components affecting the aroma of T. fuciformis strongly were found. Among them, hexanal, nonanal, and pentanal were the common components of T. fuciformis, while butyrolactone, 1-octen-3-ol, and 2-carene were the unique key aroma components of T. fuciformis in Hebei Province. Besides, octanal and butyrolactone were the special key components absent in the Sichuan and Henan samples, respectively.


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## Body

## 1. Introduction

Edible fungi are rich in species and contain more nutrients, which have broad research prospects and potential application value in healthy food and medicine [1–3]. Tremella fuciformis, known as white fungus or snow fungus, mainly grows in the subtropical zone, as well as the tropical zone, temperate zone, and frigid zone [4]. As recording about a traditional and valuable edible fungus in China, T. fuciformis is rich in protein, amino acids, crude fiber, trace elements, and other nutrients and has the functions of nourishing body fluid and lungs, tonifying the brain and heart, moisturizing skin, antitumor, treating chronic bronchitis, and postpartum weakness [5–12].Usually, consumers mainly use their own olfactory systems with less reliability and more subjectivity to evaluate the sensory quality ofT. fuciformis. At present, GC-MS and other methods are often used to detect its volatile components [13], but the sensory evaluation is not subjective, with individual differences, abstraction, and other shortcomings. An electronic nose is often used to simulate the human olfactory system, with the characteristics of high automation, low operating cost, short detection time, and good repeatability. And, it can be directly applied to the rapid odor determination of most substances and has been widely applied in the field of internal quality detection of agricultural products [14]. The combined application of the electronic nose and GC-MS can well realize the comprehensive analysis of volatile components in samples [15–17]. In this paper, electronic nose and GC-MS were used to detect and analyze the volatile components of T. fuciformis collected from four different regions, and the differences among the regions would be analyzed based on the compound content and ROAV value. The research on the volatile components of T. fuciformis could provide scientific and theoretical guidance for inspectors to analyze the quality and a reference for consumers to choose suitable products, benefiting the market of T. fuciformis.


## 2. Materials and Methods

### 2.1. Materials

#### 2.1.1. Instruments and Equipment

Instruments and equipment used were as follows: SuperNose-14 electronic nose (ISENSO Inc., USA), HH-S4 digital thermostatic water bath (Kunlun Ultrasonic Instruments Co., Ltd, China), multifunction grinder (Yongkang Bo'ou Hardware Products Co., Ltd., China), GCMS-QP2010UL GC-MS (Shimadzu Inc., Japan), and AB135-S electronic balance (Sartorius Scientific Instruments (Beijing) Co., Ltd., China). The Unscrambler X 10.4 statistical analysis software (CAMO Inc., Norway).


#### 2.1.2. Samples

TheT. fuciformis was commercially available from Fujian, Henan, Sichuan, and Hubei provinces of China, the specific origin information of different batches of T. fuciformis is shown in Table 1. The research group only selected the samples from Hebei, Henan, Fujian, and Sichuan provinces because the output of T. fuciformis in these four provinces has a large yield and high quality. In the same province, we selected samples from different urban areas and different brands, which are representative. Among them, T. fuciformis from Gutian in Fujian is the most famous.Table 1
Origin regions ofT. fuciformis.
No.City, province1Ningde, Fujian2Ningde, Fujian3Datian, Fujian4Ningde, Fujian5Ningde, Fujian6Gutian, Fujian7Ningde, Fujian8Ningde, Fujian9Datian, Fujian10Gutian, Fujian11Gutian, Fujian12Ningde, Fujian13Ningde, Fujian14Gutian, Fujian15Ningde, Fujian16Zhangzhou, Fujian17Ningde, Fujian18Ningde, Fujian19Putian, Fujian20Gutian, Fujian21Gutian, Fujian22Ningde, Fujian23Gutian, Fujian24Xiamen, Fujian25Ningde, Fujian26Putian, Fujian27Sanmenxia, Henan28Zhengzhou, Henan29Shangqiu, Henan30Xinxiang, Henan31Xinxiang, Henan32Luoyang, Henan33Longfeng, Henan34Longfeng, Henan35Xinxiang, Henan36Guangyuan, Sichuan37Guangyuan, Sichuan38Tongjiang, Sichuan39Qingchuan, Sichuan40Jianyang, Sichuan41Bazhong, Sichuan42Tongjiang, Sichuan43Cangzhou, Hebei44Hebei45Cangzhou, Hebei46Langfang, Hebei47Langfang, Hebei48Cangzhou, Hebei49Langfang, Hebei50Cangzhou, Hebei


### 2.2. Experimental Methods

#### 2.2.1. Electronic Nose Detection

The odor ofT. fuciformis was determined by the modified method [18–21]. The powder of T. fuciformis (5.0 g) was put in the headspace bottle, and the injection needle was inserted into the headspace vial at room temperature.


#### 2.2.2. GC-MS Testing

The volatile components ofT. fuciformis [22–24] were determined by the GC-MS. The GC-MS condition was a DB-5MS capillary column (0.1 μm × 30.0 m × 250 μm). The temperature of the program was as follows: the initial column temperature was 50°C and the temperature was raised to 180°C at the rate of 5°C/min, kept for 2 minutes, then was raised to 120°C at the rate of 8°C/min, kept for 2 minutes, and raised to 220°C at 5°C/min for 3 minutes. The total flow is 7.0 mL/min while the column flow is 1.00 mL/min. The temperature of the ion source of the mass spectrometer was set at 230°C and the interface temperature was 250°C. The MS scan range was 20∼450 m/z.


#### 2.2.3. Identification of Compounds

For the qualitative and quantitative analysis of volatile compounds, the National Institute of Standards and Technology (TNIST) mass spectral library was used for compound identification (similarity between the peaks ≥85%), and the peak area normalization method was adopted to calculate the relative content of each volatile component. The retention time and MS were used for qualitative analysis of volatile components in the samples.


#### 2.2.4. Evaluation of Volatile Aroma Substances

The relative odor activity value (ROAV) was used to evaluate the contribution of volatile components to the total aroma of samples [25]. The ROAV calculation formula was as follows:(1)ROAVi=CriCrstan×TstanTi×100.CriTi were relative contents of volatile components/% and odor threshold/(μg/kg); Crstan and Tstan were the relative content/% and odor threshold/(μg/kg) of the components contributing most to the overall aroma of the sample, respectively.


## 2.1. Materials

### 2.1.1. Instruments and Equipment

Instruments and equipment used were as follows: SuperNose-14 electronic nose (ISENSO Inc., USA), HH-S4 digital thermostatic water bath (Kunlun Ultrasonic Instruments Co., Ltd, China), multifunction grinder (Yongkang Bo'ou Hardware Products Co., Ltd., China), GCMS-QP2010UL GC-MS (Shimadzu Inc., Japan), and AB135-S electronic balance (Sartorius Scientific Instruments (Beijing) Co., Ltd., China). The Unscrambler X 10.4 statistical analysis software (CAMO Inc., Norway).


### 2.1.2. Samples

TheT. fuciformis was commercially available from Fujian, Henan, Sichuan, and Hubei provinces of China, the specific origin information of different batches of T. fuciformis is shown in Table 1. The research group only selected the samples from Hebei, Henan, Fujian, and Sichuan provinces because the output of T. fuciformis in these four provinces has a large yield and high quality. In the same province, we selected samples from different urban areas and different brands, which are representative. Among them, T. fuciformis from Gutian in Fujian is the most famous.Table 1
Origin regions ofT. fuciformis.
No.City, province1Ningde, Fujian2Ningde, Fujian3Datian, Fujian4Ningde, Fujian5Ningde, Fujian6Gutian, Fujian7Ningde, Fujian8Ningde, Fujian9Datian, Fujian10Gutian, Fujian11Gutian, Fujian12Ningde, Fujian13Ningde, Fujian14Gutian, Fujian15Ningde, Fujian16Zhangzhou, Fujian17Ningde, Fujian18Ningde, Fujian19Putian, Fujian20Gutian, Fujian21Gutian, Fujian22Ningde, Fujian23Gutian, Fujian24Xiamen, Fujian25Ningde, Fujian26Putian, Fujian27Sanmenxia, Henan28Zhengzhou, Henan29Shangqiu, Henan30Xinxiang, Henan31Xinxiang, Henan32Luoyang, Henan33Longfeng, Henan34Longfeng, Henan35Xinxiang, Henan36Guangyuan, Sichuan37Guangyuan, Sichuan38Tongjiang, Sichuan39Qingchuan, Sichuan40Jianyang, Sichuan41Bazhong, Sichuan42Tongjiang, Sichuan43Cangzhou, Hebei44Hebei45Cangzhou, Hebei46Langfang, Hebei47Langfang, Hebei48Cangzhou, Hebei49Langfang, Hebei50Cangzhou, Hebei


## 2.1.1. Instruments and Equipment

Instruments and equipment used were as follows: SuperNose-14 electronic nose (ISENSO Inc., USA), HH-S4 digital thermostatic water bath (Kunlun Ultrasonic Instruments Co., Ltd, China), multifunction grinder (Yongkang Bo'ou Hardware Products Co., Ltd., China), GCMS-QP2010UL GC-MS (Shimadzu Inc., Japan), and AB135-S electronic balance (Sartorius Scientific Instruments (Beijing) Co., Ltd., China). The Unscrambler X 10.4 statistical analysis software (CAMO Inc., Norway).


## 2.1.2. Samples

TheT. fuciformis was commercially available from Fujian, Henan, Sichuan, and Hubei provinces of China, the specific origin information of different batches of T. fuciformis is shown in Table 1. The research group only selected the samples from Hebei, Henan, Fujian, and Sichuan provinces because the output of T. fuciformis in these four provinces has a large yield and high quality. In the same province, we selected samples from different urban areas and different brands, which are representative. Among them, T. fuciformis from Gutian in Fujian is the most famous.Table 1
Origin regions ofT. fuciformis.
No.City, province1Ningde, Fujian2Ningde, Fujian3Datian, Fujian4Ningde, Fujian5Ningde, Fujian6Gutian, Fujian7Ningde, Fujian8Ningde, Fujian9Datian, Fujian10Gutian, Fujian11Gutian, Fujian12Ningde, Fujian13Ningde, Fujian14Gutian, Fujian15Ningde, Fujian16Zhangzhou, Fujian17Ningde, Fujian18Ningde, Fujian19Putian, Fujian20Gutian, Fujian21Gutian, Fujian22Ningde, Fujian23Gutian, Fujian24Xiamen, Fujian25Ningde, Fujian26Putian, Fujian27Sanmenxia, Henan28Zhengzhou, Henan29Shangqiu, Henan30Xinxiang, Henan31Xinxiang, Henan32Luoyang, Henan33Longfeng, Henan34Longfeng, Henan35Xinxiang, Henan36Guangyuan, Sichuan37Guangyuan, Sichuan38Tongjiang, Sichuan39Qingchuan, Sichuan40Jianyang, Sichuan41Bazhong, Sichuan42Tongjiang, Sichuan43Cangzhou, Hebei44Hebei45Cangzhou, Hebei46Langfang, Hebei47Langfang, Hebei48Cangzhou, Hebei49Langfang, Hebei50Cangzhou, Hebei


## 2.2. Experimental Methods

### 2.2.1. Electronic Nose Detection

The odor ofT. fuciformis was determined by the modified method [18–21]. The powder of T. fuciformis (5.0 g) was put in the headspace bottle, and the injection needle was inserted into the headspace vial at room temperature.


### 2.2.2. GC-MS Testing

The volatile components ofT. fuciformis [22–24] were determined by the GC-MS. The GC-MS condition was a DB-5MS capillary column (0.1 μm × 30.0 m × 250 μm). The temperature of the program was as follows: the initial column temperature was 50°C and the temperature was raised to 180°C at the rate of 5°C/min, kept for 2 minutes, then was raised to 120°C at the rate of 8°C/min, kept for 2 minutes, and raised to 220°C at 5°C/min for 3 minutes. The total flow is 7.0 mL/min while the column flow is 1.00 mL/min. The temperature of the ion source of the mass spectrometer was set at 230°C and the interface temperature was 250°C. The MS scan range was 20∼450 m/z.


### 2.2.3. Identification of Compounds

For the qualitative and quantitative analysis of volatile compounds, the National Institute of Standards and Technology (TNIST) mass spectral library was used for compound identification (similarity between the peaks ≥85%), and the peak area normalization method was adopted to calculate the relative content of each volatile component. The retention time and MS were used for qualitative analysis of volatile components in the samples.


### 2.2.4. Evaluation of Volatile Aroma Substances

The relative odor activity value (ROAV) was used to evaluate the contribution of volatile components to the total aroma of samples [25]. The ROAV calculation formula was as follows:(1)ROAVi=CriCrstan×TstanTi×100.CriTi were relative contents of volatile components/% and odor threshold/(μg/kg); Crstan and Tstan were the relative content/% and odor threshold/(μg/kg) of the components contributing most to the overall aroma of the sample, respectively.


## 2.2.1. Electronic Nose Detection

The odor ofT. fuciformis was determined by the modified method [18–21]. The powder of T. fuciformis (5.0 g) was put in the headspace bottle, and the injection needle was inserted into the headspace vial at room temperature.


## 2.2.2. GC-MS Testing

The volatile components ofT. fuciformis [22–24] were determined by the GC-MS. The GC-MS condition was a DB-5MS capillary column (0.1 μm × 30.0 m × 250 μm). The temperature of the program was as follows: the initial column temperature was 50°C and the temperature was raised to 180°C at the rate of 5°C/min, kept for 2 minutes, then was raised to 120°C at the rate of 8°C/min, kept for 2 minutes, and raised to 220°C at 5°C/min for 3 minutes. The total flow is 7.0 mL/min while the column flow is 1.00 mL/min. The temperature of the ion source of the mass spectrometer was set at 230°C and the interface temperature was 250°C. The MS scan range was 20∼450 m/z.


## 2.2.3. Identification of Compounds

For the qualitative and quantitative analysis of volatile compounds, the National Institute of Standards and Technology (TNIST) mass spectral library was used for compound identification (similarity between the peaks ≥85%), and the peak area normalization method was adopted to calculate the relative content of each volatile component. The retention time and MS were used for qualitative analysis of volatile components in the samples.


## 2.2.4. Evaluation of Volatile Aroma Substances

The relative odor activity value (ROAV) was used to evaluate the contribution of volatile components to the total aroma of samples [25]. The ROAV calculation formula was as follows:(1)ROAVi=CriCrstan×TstanTi×100.CriTi were relative contents of volatile components/% and odor threshold/(μg/kg); Crstan and Tstan were the relative content/% and odor threshold/(μg/kg) of the components contributing most to the overall aroma of the sample, respectively.


## 3. Results and Discussion

### 3.1. The Results ofT. fuciformis from Different Regions Based on Electronic Nose

#### 3.1.1. PCA Analysis ofT. fuciformis

Principal component analysis (PCA) is a common method which could extract the characteristic information of samples from complicated information through reducing dimensions and data transformation without loss of original information. The factors with the large and leading contribution rates extracted from the electronic nose sensor data ofT. fuciformis originating from four different regions (Figure 1) could inhibit the differences in the samples among different regions in the PCA distribution map [26, 27].Figure 1
PCA result ofT. fuciformis from different regions.Note: “Fu, Si, Yu and Ji” represent “Fujian, Sichuan, Henan and Hebei,” respectively, and the numbers represent different sample batches.In Figure1, the cumulative variance contribution rate of PC-1 (80%) and PC-2 (9%) reached 89%, which indicated the two principal components could retain most of the information of these samples and was sufficient to analyze the similarity relationship between samples [28]. It could be seen that the spatial distribution of principal components of T. fuciformis samples was relatively scattered, and those from each origin region were relatively concentrated and separated. Therefore, the two principal components could distinguish the samples from the four regions well. The samples from Hebei and Henan Province were located in the upper right and lower right of Figure 1, respectively, while those from Fujian Province and Sichuan Province were located in the upper left and lower left, respectively. These results also confirmed the differences of T. fuciformis from different regions.Note: “C” represents the gas sensor and numbers indicate the different sensor types.


#### 3.1.2. Loading Analysis ofT. fuciformis

Loading analysis is a similar method with PCA to extract the principal components from the origin data. However, the PCA algorithm is special for sample analysis, while loading analysis is for sensors of electronic noses. In this part, loading analysis was used to analyze the contribution of each sensor to the distinguishment ofT. fuciformis (Figure 2) [26, 29]. It could be seen that C1, C3, C4, C5, C6, C8, and C9 sensors contributed a large proportion to the 1st principal component for the T. fuciformis.Figure 2
Loadings analysis ofT. fuciformis from different regions.


### 3.2. GC-MS Results ofT. fuciformis

#### 3.2.1. Components Analysis ofT. fuciformis

The volatile components ofT. fuciformis from four regions were analyzed by GC-MS in Table 2.Table 2
Composition of volatile components ofT. fuciformis.
NumberCompound nameMolecular formulaRelative content/%RI valueLiteratureHebeiHenanSichuanFujianAlcohols1Pentyl alcoholC5H12O1.221.12—0.95761[30]22-Ethyl-1-decanolC12H26O0.02———139331-HexanolC6H14O0.57——0.02860[20]41-Octen-3-olC8H16O0.38———969[20]5EucalyptolC10H18O5.00———10596LinalolC10H18O0.05———1082[31]7Isotridecyl alcoholC13H28O0.01———149282-TetradecyloxyethanolC16H34O2—0.010.03—193092-Butyl-1-octanolC12H26O—0.03—0.03139310Isopentyl alcoholC5H12O———0.21697[20]Aldehyde11HexanalC6H12O27.3525.2123.6021.60806[20]12FurfuralC5H4O20.010.17—0.0283113HeptanalC7H14O0.431.04——905[20]142-Furancarboxaldehyde, 5-methyl-C6H6O2—0.08——92015OctanalC8H16O1.030.04—0.041005[30]16BenzeneacetaldehydeC8H8O0.820.01——1081[20]17NonanalC9H18O2.580.190.071.061104[20]18BenzaldehydeC7H6O0.230.02—0.08982[20]19PentanalC5H10O5.050.380.010.23707[20]202-Ethyl-1-pentanolC7H16O———0.03896Acids21Acetic acidCH3COOH35.3649.4239.9240.85576[31]224-Methylvaleric acidC6H12O21.73———91023Nonanoic acidC9H18O20.40———127224Octanoic acidC8H16O2—1.521.52—2069[32]25Pentanoic acidC5H10O2—0.21——116126Heptanoic acidC7H14O2—2.011.33—1078[30]27Hexanoic acidC6H12O2—0.69—3.721856[32]Esters28ButyrolactoneC4H6O26.08—1.060.1182529gamma-ButyrolactoneC5H8O22.79———88630Heptadecyl trifluoroacetateC19H35F3O20.52———181231Hydrazinecarboxylic acid, ethyl esterC3H8N2O20.14———92832Sulfurous acid, hexyl pentadecyl esterC21H44O3S—0.42—0.18273233n-Hexyl formateC7H14O2—0.65—0.01981[20]34Docosyl pentafluoropropionateC25H45F5O2—0.01——236935Sulfurous acid, 2-ethylhexyl isobutyl esterC12H26O3S——0.02—1709362-Ethylhexyl acrylateC11H20O2——0.01—120837Hexatriacontyl pentafluoropropionateC39H73F5O2——0.02—376138Formic acid, ethenyl esterC3H4O2——25.12—574391-Methyl-2-oxocyclohex-3-enecarboxylic acid, methyl esterC9H12O3———0.011274Hydrocarbons402, 10-TrimethyldodecaneC15H32—0.010.010.02132041Bute hydrocarbonC19H40—0.72—0.031653423-MethylheptadecaneC18H38—0.02——1746433-MethylundecaneC12H260.030.020.040.031150[33]44DodecaneC12H260.150.090.100.301214[30]45TetradecaneC14H300.150.06—0.541413[20]464,6-DimethyldodecaneC14H300.190.050.02—128547DodecamethylcyclohexasiloxaneC12H36O6Si60.040.03—0.10124048HeptadecaneC17H360.071.160.040.211711492,5-DimethyltridecaneC15H32—0.010.020.021384506-MethyltridecaneC14H30—0.010.010.01134951OctadecaneC18H380.020.290.030.0718105210-MethylnonadecaneC20H42—0.01——194553OctacosaneC28H580.130.140.010.052804543,8-DimethyldecaneC12H260.020.020.030.02108655CampheneC10H160.940.250.030.1194356HexadecaneC16H340.370.290.090.331612[20]575-MethyltetradecaneC15H32—0.06—0.051448584-MethyltetradecaneC15H32—0.01—0.021448593-MethyltetradecaneC15H320.410.02—0.06144860EicosaneC20H420.550.140.060.19200961TetratriacontaneC34H700.120.03—0.013401624-MethylpentadecaneC16H340.020.36—0.081548632,6,10,15-TetramethylheptadecanC21H440.010.02——185264NonadecaneC19H400.010.080.040.071910658-HexylpentadecaneC21H44—0.010.010.072045662,2,4,6,6-PentamethylheptaneC12H260.870.631.480.83981[20]672,3-DimethylundecaneC13H28—0.01——1185682-Bromo dodecaneC12H25Br0.030.120.050.15144669(9E)-9-octadeceneC18H36—0.01——181870HeptacosaneC27H56—0.01——2705712,6,10,14-TetramethylhexadecaneC20H420.451.130.020.531753722,2,4,4,6,8,8-HeptamethylnonaneC16H34—0.02——129473PentadecaneC15H32—0.320.01—1512[30]74HMNC16H340.04—0.03—129475UndecaneC11H240.02—0.04—1115[20]762,6,11-TrimethyldodecaneC15H320.02—0.01—13207711-MethyldodecaneC13H280.01———124978HeneicosaneC21H440.02—0.010.062109792-CareneC10H160.01———94880gamma-TerpinenC10H160.21———998811-TrideceneC13H261.01—0.02—1304825-Methyl-5-propylnonaneC13H280.02—0.01—1229832,5-DimethyldecaneC12H260.03—0.01—1086842,4-DimethyldecaneC12H260.01———108685DocosaneC22H460.01—0.03—220886Benzene, 1-methyl-2-(phenylmethyl)-C14H14——0.02—1580871-Benzyl-3-methylbenzeneC14H14——0.02—158088DotriacontaneC32H66——0.01—3202892,3,7-TrimethyldecaneC13H28——0.01—1121902,5-DimethylundecaneC13H28——0.03—1185911-Sec-butyl-1-(2-methylbutyl)cyclopropaneC12H24——0.02—1062922,6,11,15-TetramethylhexadecaneC20H42——0.010.021753934-EthylundecaneC13H28——0.01—124994(5E)-5-octadeceneC18H36——0.010.011818953-Ethyl-3-methyldecaneC13H28——0.01—1229965-IsobutylnonaneC13H28——0.020.041185975-ButylnonaneC13H28——0.010.041249982,2-DimethyldecaneC12H26———0.041130992-MethyltetradecaneC15H32———0.0114481002-MethylhexadecaneC17H36———0.0116471019-MethylnonadecaneC20H42———0.0119451022-Methyl-6-propyldodecaneC16H34———0.011483103DecamethylcyclopentasiloxaneC10H30O5Si5———0.011034104TetratetracontaneC44H90———0.0243951052,2-DimethylundecaneC13H28———0.2712291064-MethyldodecaneC13H28———0.021249107UndecylcyclohexaneC17H34———0.011775Categories108Nickel tetracarbonylC4NiO40.092.200.160.29—1094,7-DimethylbenzofuranC10H10O0.02———1244110HydroxylamineH3NO2.424.883.51——1114-Hexen-3-oneC6H10O5.66———7621122-UndecanoneC11H22O—0.16——1251113Didecyl etherC20H42O—0.07—0.032085114OxygenO2—3.57—25.26—115Carbon monoxideCO——0.060.10—116p-(1-Propenyl)anisoleC10H12O——0.01—1190[30]1172-Cyclohexen-1-oneC6H8O———0.01873Note. “—”means not detected. In Table 2, the constituents marked red were first detected from T. fuciformis.A total of 117 volatile components, including 68 hydrocarbons, 12 esters, 10 alcohols, 10 aldehydes, 7 acids, and 10 other compounds, were detected fromT. fuciformis. However, the relative contents of acids and aldehydes were the highest, which was consistent with Li Xiang’s research on T. fuciformis and bag cultivated T. fuciformis [13]. Moreover, 58, 59, 62, and 55 volatile components were detected from Hebei, Henan, Fujian, and Sichuan Provinces, respectively. Within them, there were a total number of 18 common components. However, a variety of volatile components were detected in T. fuciformis for the first time, such as eucalyptol, 2-butyl-1-octanol, 2-ethyl-1-pentanol, benzeneacetaldehyde, 4-methylvaleric acid, gamma-butyrolactone, n-hexyl formate, bute hydrocarbon, hydroxylamine, 2-carene have not been reported.Among the 68 hydrocarbon compounds ofT. fuciformis, most of them belonged to the saturated hydrocarbons, such as 5-methyltetradecane, bute hydrocarbon, 2, 6, 10, 14-tetramethylhexadecane, 4, 6-dimethyldodecane, and 2, 6, 10-trimethyldodecane. However, these compounds had generally low relative content in the samples with high threshold values, which contributed less to the overall odor of T. fuciformis. In contrast, unsaturated hydrocarbons such as (5E)-5-octadecene, camphene, and 2-carenecontribute more for its relatively low thresholds [34]. Besides, no unique compounds with high relative content (≥1) were found for the samples from different regions.Esters are usually one type of compound with a fruit aroma and contribute to the overall aroma ofT. fuciformis [35]. A total of 12 ester compounds were detected from T. fuciformis. Of them, butyrolactone (6.08%) and γ-butyrolactone (2.79%) were the top 2 esters of Hebei samples, while γ-butyrolactone, heptadecyl trifluoroacetate, and hydrazinecarboxylic acid, ethyl ester were the unique volatile constituents. For the Sichuan samples, the unique ester components included sulfurous acid, 2-ethylhexyl isobutyl ester, 2-ethylhexyl acrylate, hexatriacontyl pentafluoropropionate and formic acid, and ethenyl ester, of which the relative content of formic acid, ethenyl ester was as high as 25.12%. These unique components identified for corresponding regions would be used to distinguish the samples from this region from other regions.Volatile acids are usually derived from the oxidation or biosynthesis of fatty acids [36, 37]. In this research, 7 kinds of acid compounds were detected in T. fuciformis. Acetic acid is a common acid with a fishy smell of oil [38] and exists in T. fuciformis at a high relative content (35.36%∼49.42%). However, due to its high aroma threshold, it has little contribution to the overall odor of T. fuciformis.Volatile alcohols in plants mainly come from the decomposition of secondary hydroperoxides of fatty acids and the reduction of sugars and amino acids [36]. Most alcohols are generally floral and fruity aromas [39]. According to the above GC-MS analysis results, 10 kinds of alcohol were detected, including 7 kinds in Hebei, 3 kinds in Henan, 4 kinds in Fujian, and 1 kind in Sichuan. Not only that, the relative content of volatile alcohols was also high in the Hebei region. 2-ethyl-1-decanol, 1-octen-3-ol, eucalyptol, linalol, and isotridecyl alcohol were special to the samples of the Hebei region, while isopentyl alcohol to the samples in Fujian. These unique volatile components of different samples might be taken as a mark for the distinguishment of different regions.Aldehyde compounds are mainly derived from fatty acid oxidation and amino acid metabolism [40], and their aroma thresholds are usually low. Therefore, it usually plays an important role in the overall aroma, although the content of aldehyde compounds is low [41]. There were 10 kinds of aldehydes in T. fuciformis, and 8 species were detected in Hebei province, nine in Henan province, seven in Fujian province, and three in Sichuan province. Among them, hexanal, nonanal, and pentanal were the common aldehyde volatile components of T. fuciformis, while 5-methyl-2-furancarboxaldehyde and 2-ethyl-1-pentanol were the unique aldehyde volatile components of Henan and Fujian provinces, respectively.Besides,T. fuciformis also included phenols, ketones, furans, and so on. In addition, gases were detected in T. fuciformis. Because the whole detection environment was gaseous, the components in the air may have been detected in the sample, such as oxygen and carbon monoxide. But these gases are colorless and tasteless and did not affect the aroma quality of T. fuciformis. Among them, the detected ketones included 4-hexen-3-one, 2-undecanone, and 2-cyclohexen-1-one, and the relative content of 4-hexen-3-one, a unique component in Hebei samples, was relatively high. Nickel tetracarbonyl was the common component detected in all the 4 regions, while hydroxylamine was also detected in the samples from considerate regions except Fujian.


#### 3.2.2. Analysis of Volatile Components ofT. fuciformis among Different Regions

In Figure3, there was no obvious difference in the types of volatile substances contained in Tremella among the 4 regions. The most abundant volatile component type was hydrocarbons, which were about 3 times as many as the other types. By comparing these substances among the samples from the 4 regions, it could be found that more types of hydrocarbons were detected in the T. fuciformis from Fujian, while more aldehyde types and acid types were detected in the Henan samples, more alcohol types from Hebei samples, and more ester from Sichuan samples.Figure 3
Volatile components types ofT. fuciformis from different producing areas.In general, the relative contents of acid in the 4 regions (in Figure4) were the highest of the detected volatile components, followed by aldehydes. However, the proportion varied from region to region. Also, it can be seen that the T. fuciformis from Henan owned more contents of acids while the Hebei samples had more aldehyde and Sichuan had more esters.Figure 4
Relative contents of volatile compounds inT. fuciformis.


### 3.3. ROAV Analysis of Key Aroma Compounds

ROAV is used as one common index, which may range from 0 to 100 and reflects the aroma contribution degree of each volatile component. The higher the ROAV value of the compound, the greater the contribution of the compound to the overall odor of the sample [42–44]. By referring to the researched 29 compounds with the given aroma threshold values from relevant literature and combining, the corresponding ROAV analysis results were calculated and are shown in Table 3.Table 3
ROAV value of 29 components inT. fuciformis from different regions.
NumberCompound nameAroma thresholdROAV(μG/L) [31, 45–50]HebeiHenanSichuanFujianAlcohols11-Hexanol250<0.1——<0.121-Octen-3-ol15.5———3Eucalyptol1.30.22———4Linalol1.50.48———5Pentyl alcohol4000<0.1<0.1—<0.16Isopentyl alcohol120———<0.1Aldehydes7Hexanal4.587.971001001008Furfural3000<0.1<0.1——9Heptanal32.076.19——10Octanal0.721.31.02—1.1911Benzeneacetaldehyde4<0.1<0.1——12Nonanal137.343.391.3322.0813Benzaldehyde350<0.1<0.1—<0.114Pentanal203.650.34<0.10.24Acids15Acetic acid22000<0.1<0.1<0.1<0.116Nonanoic acid3000<0.1———17Octanoic acid500——<0.1—18Pentanoic acid3000————19Heptanoic acid100——0.25—20Hexanoic acid3000———<0.1Esters21Butyrolactone0.88100—22.972.622gamma-Butyrolactone1000.81———23n-Hexyl formate19800—<0.1—<0.1Hydrocarbons24Dodecane2040<0.1<0.1<0.1<0.125Tetradecane1000<0.1<0.1—<0.126Hexadecane300<0.1<0.1<0.1<0.1272-Carene0.0114.47———Others282-Undecanone255—<0.1——29p-(1-Propenyl)anisole15——<0.1—Note. “—”means not detected.Overall, there were 8 compounds (ROAV ≥1) including 1-octen-3-ol, heptanal, octanal, nonanal, pentanal, hexanal, butyrolactone, and 2-carene, which were taken as the key aroma compounds ofT. fuciformis. Among them, hexanal and nonanal were the common key aroma compounds and could be used as the characteristic identification components of T. fuciformis. As a basic product of the oxidative decomposition of linoleic acid, hexanal is a common volatile oil with the fragrance of green, grass, and fruit [51], contributing greater than the others to the overall aroma of T. fuciformis. Nonanal is also a common aroma compound with the fragrance of flowers, fat, and wax, and a low threshold value, and it offers people a pleasant feeling [52]. 1-Octene-3-ol, also known as agaritol with the aroma of fresh mushroom, licorice, and rose, was the unique key aroma compound of Hebei samples. This compound was mainly used as pharmaceutical raw materials and in aromatics [53]. Besides, butyrolactone generally has the fragrance characteristics of coconut or peach [40, 42], while heptanal has the odor of fat or fish [36]. These substances play an important role in the overall fragrance of T. fuciformis.In HebeiT. fuciformis, all the 8 key aroma compounds were discovered, of which butyrolactone (ROAV = 100) is the compound with the highest ROAV, and it can be used as the aroma base of T. fuciformis, followed by hexanal, nonanal, octanal, 2-carene, 1-octen-3-ol, pentanal, and heptanal. But on the other hand, 1-octen-3-ol and 2-carene were the special compounds of these samples and could be used to distinguish the Hebei samples from the other 3 regions. The modified aroma compounds were eucalyptol, linalool, and γ-butyrolactone, which were also unique for Hebei samples. The potential aroma compound, nonanoic acid, was unique for the Hebei sample, while the other 3 compounds, acetic acid, dodecane, and hexadecane, were common for all the collected T. fuciformis.The ROAV value of hexanal in the samples from Sichuan, Henan, and Hebei was 100, indicating that this component contributed the most to the aroma of tremella from these three regions. For theT. fuciformis of Henan province, there were 4 key aroma compounds, and hexanal was the highest, followed by heptanal, nonanal, and octanal. However, the samples from Henan province lacked butyrolactone, compared with the other three regions, so the compound could be used to distinguish other samples from Henan province. Pentanal and 2-undecanone were the modified and potential aroma compound in Henan province.Three key volatile aroma compounds with threshold values were identified in Sichuan samples, which were hexanal, butyrolactone, and nonanal from high to low. Heptanoic acid was the modified aroma compound ofT. fuciformis, while octanoic acid and p-(1-propenyl) anisole were the potential aroma compounds unique to Sichuan samples. On the other hand, octanal was a key aroma compound for the samples from Hebei, Henan, and Fujian, but not for the Sichuan samples.Four kinds of key volatile aroma compounds detected in Fujian samples with the ROAV from high to low were hexanal, nonanal, octanal, and butyrolactone. The modified aroma compound was pentanal as well as Henan samples, and the potential aroma compounds special to Fujian samples were isopentyl alcohol and hexanoic acid.


## 3.1. The Results ofT. fuciformis from Different Regions Based on Electronic Nose

### 3.1.1. PCA Analysis ofT. fuciformis

Principal component analysis (PCA) is a common method which could extract the characteristic information of samples from complicated information through reducing dimensions and data transformation without loss of original information. The factors with the large and leading contribution rates extracted from the electronic nose sensor data ofT. fuciformis originating from four different regions (Figure 1) could inhibit the differences in the samples among different regions in the PCA distribution map [26, 27].Figure 1
PCA result ofT. fuciformis from different regions.Note: “Fu, Si, Yu and Ji” represent “Fujian, Sichuan, Henan and Hebei,” respectively, and the numbers represent different sample batches.In Figure1, the cumulative variance contribution rate of PC-1 (80%) and PC-2 (9%) reached 89%, which indicated the two principal components could retain most of the information of these samples and was sufficient to analyze the similarity relationship between samples [28]. It could be seen that the spatial distribution of principal components of T. fuciformis samples was relatively scattered, and those from each origin region were relatively concentrated and separated. Therefore, the two principal components could distinguish the samples from the four regions well. The samples from Hebei and Henan Province were located in the upper right and lower right of Figure 1, respectively, while those from Fujian Province and Sichuan Province were located in the upper left and lower left, respectively. These results also confirmed the differences of T. fuciformis from different regions.Note: “C” represents the gas sensor and numbers indicate the different sensor types.


### 3.1.2. Loading Analysis ofT. fuciformis

Loading analysis is a similar method with PCA to extract the principal components from the origin data. However, the PCA algorithm is special for sample analysis, while loading analysis is for sensors of electronic noses. In this part, loading analysis was used to analyze the contribution of each sensor to the distinguishment ofT. fuciformis (Figure 2) [26, 29]. It could be seen that C1, C3, C4, C5, C6, C8, and C9 sensors contributed a large proportion to the 1st principal component for the T. fuciformis.Figure 2
Loadings analysis ofT. fuciformis from different regions.


## 3.1.1. PCA Analysis ofT. fuciformis

Principal component analysis (PCA) is a common method which could extract the characteristic information of samples from complicated information through reducing dimensions and data transformation without loss of original information. The factors with the large and leading contribution rates extracted from the electronic nose sensor data ofT. fuciformis originating from four different regions (Figure 1) could inhibit the differences in the samples among different regions in the PCA distribution map [26, 27].Figure 1
PCA result ofT. fuciformis from different regions.Note: “Fu, Si, Yu and Ji” represent “Fujian, Sichuan, Henan and Hebei,” respectively, and the numbers represent different sample batches.In Figure1, the cumulative variance contribution rate of PC-1 (80%) and PC-2 (9%) reached 89%, which indicated the two principal components could retain most of the information of these samples and was sufficient to analyze the similarity relationship between samples [28]. It could be seen that the spatial distribution of principal components of T. fuciformis samples was relatively scattered, and those from each origin region were relatively concentrated and separated. Therefore, the two principal components could distinguish the samples from the four regions well. The samples from Hebei and Henan Province were located in the upper right and lower right of Figure 1, respectively, while those from Fujian Province and Sichuan Province were located in the upper left and lower left, respectively. These results also confirmed the differences of T. fuciformis from different regions.Note: “C” represents the gas sensor and numbers indicate the different sensor types.


## 3.1.2. Loading Analysis ofT. fuciformis

Loading analysis is a similar method with PCA to extract the principal components from the origin data. However, the PCA algorithm is special for sample analysis, while loading analysis is for sensors of electronic noses. In this part, loading analysis was used to analyze the contribution of each sensor to the distinguishment ofT. fuciformis (Figure 2) [26, 29]. It could be seen that C1, C3, C4, C5, C6, C8, and C9 sensors contributed a large proportion to the 1st principal component for the T. fuciformis.Figure 2
Loadings analysis ofT. fuciformis from different regions.


## 3.2. GC-MS Results ofT. fuciformis

### 3.2.1. Components Analysis ofT. fuciformis

The volatile components ofT. fuciformis from four regions were analyzed by GC-MS in Table 2.Table 2
Composition of volatile components ofT. fuciformis.
NumberCompound nameMolecular formulaRelative content/%RI valueLiteratureHebeiHenanSichuanFujianAlcohols1Pentyl alcoholC5H12O1.221.12—0.95761[30]22-Ethyl-1-decanolC12H26O0.02———139331-HexanolC6H14O0.57——0.02860[20]41-Octen-3-olC8H16O0.38———969[20]5EucalyptolC10H18O5.00———10596LinalolC10H18O0.05———1082[31]7Isotridecyl alcoholC13H28O0.01———149282-TetradecyloxyethanolC16H34O2—0.010.03—193092-Butyl-1-octanolC12H26O—0.03—0.03139310Isopentyl alcoholC5H12O———0.21697[20]Aldehyde11HexanalC6H12O27.3525.2123.6021.60806[20]12FurfuralC5H4O20.010.17—0.0283113HeptanalC7H14O0.431.04——905[20]142-Furancarboxaldehyde, 5-methyl-C6H6O2—0.08——92015OctanalC8H16O1.030.04—0.041005[30]16BenzeneacetaldehydeC8H8O0.820.01——1081[20]17NonanalC9H18O2.580.190.071.061104[20]18BenzaldehydeC7H6O0.230.02—0.08982[20]19PentanalC5H10O5.050.380.010.23707[20]202-Ethyl-1-pentanolC7H16O———0.03896Acids21Acetic acidCH3COOH35.3649.4239.9240.85576[31]224-Methylvaleric acidC6H12O21.73———91023Nonanoic acidC9H18O20.40———127224Octanoic acidC8H16O2—1.521.52—2069[32]25Pentanoic acidC5H10O2—0.21——116126Heptanoic acidC7H14O2—2.011.33—1078[30]27Hexanoic acidC6H12O2—0.69—3.721856[32]Esters28ButyrolactoneC4H6O26.08—1.060.1182529gamma-ButyrolactoneC5H8O22.79———88630Heptadecyl trifluoroacetateC19H35F3O20.52———181231Hydrazinecarboxylic acid, ethyl esterC3H8N2O20.14———92832Sulfurous acid, hexyl pentadecyl esterC21H44O3S—0.42—0.18273233n-Hexyl formateC7H14O2—0.65—0.01981[20]34Docosyl pentafluoropropionateC25H45F5O2—0.01——236935Sulfurous acid, 2-ethylhexyl isobutyl esterC12H26O3S——0.02—1709362-Ethylhexyl acrylateC11H20O2——0.01—120837Hexatriacontyl pentafluoropropionateC39H73F5O2——0.02—376138Formic acid, ethenyl esterC3H4O2——25.12—574391-Methyl-2-oxocyclohex-3-enecarboxylic acid, methyl esterC9H12O3———0.011274Hydrocarbons402, 10-TrimethyldodecaneC15H32—0.010.010.02132041Bute hydrocarbonC19H40—0.72—0.031653423-MethylheptadecaneC18H38—0.02——1746433-MethylundecaneC12H260.030.020.040.031150[33]44DodecaneC12H260.150.090.100.301214[30]45TetradecaneC14H300.150.06—0.541413[20]464,6-DimethyldodecaneC14H300.190.050.02—128547DodecamethylcyclohexasiloxaneC12H36O6Si60.040.03—0.10124048HeptadecaneC17H360.071.160.040.211711492,5-DimethyltridecaneC15H32—0.010.020.021384506-MethyltridecaneC14H30—0.010.010.01134951OctadecaneC18H380.020.290.030.0718105210-MethylnonadecaneC20H42—0.01——194553OctacosaneC28H580.130.140.010.052804543,8-DimethyldecaneC12H260.020.020.030.02108655CampheneC10H160.940.250.030.1194356HexadecaneC16H340.370.290.090.331612[20]575-MethyltetradecaneC15H32—0.06—0.051448584-MethyltetradecaneC15H32—0.01—0.021448593-MethyltetradecaneC15H320.410.02—0.06144860EicosaneC20H420.550.140.060.19200961TetratriacontaneC34H700.120.03—0.013401624-MethylpentadecaneC16H340.020.36—0.081548632,6,10,15-TetramethylheptadecanC21H440.010.02——185264NonadecaneC19H400.010.080.040.071910658-HexylpentadecaneC21H44—0.010.010.072045662,2,4,6,6-PentamethylheptaneC12H260.870.631.480.83981[20]672,3-DimethylundecaneC13H28—0.01——1185682-Bromo dodecaneC12H25Br0.030.120.050.15144669(9E)-9-octadeceneC18H36—0.01——181870HeptacosaneC27H56—0.01——2705712,6,10,14-TetramethylhexadecaneC20H420.451.130.020.531753722,2,4,4,6,8,8-HeptamethylnonaneC16H34—0.02——129473PentadecaneC15H32—0.320.01—1512[30]74HMNC16H340.04—0.03—129475UndecaneC11H240.02—0.04—1115[20]762,6,11-TrimethyldodecaneC15H320.02—0.01—13207711-MethyldodecaneC13H280.01———124978HeneicosaneC21H440.02—0.010.062109792-CareneC10H160.01———94880gamma-TerpinenC10H160.21———998811-TrideceneC13H261.01—0.02—1304825-Methyl-5-propylnonaneC13H280.02—0.01—1229832,5-DimethyldecaneC12H260.03—0.01—1086842,4-DimethyldecaneC12H260.01———108685DocosaneC22H460.01—0.03—220886Benzene, 1-methyl-2-(phenylmethyl)-C14H14——0.02—1580871-Benzyl-3-methylbenzeneC14H14——0.02—158088DotriacontaneC32H66——0.01—3202892,3,7-TrimethyldecaneC13H28——0.01—1121902,5-DimethylundecaneC13H28——0.03—1185911-Sec-butyl-1-(2-methylbutyl)cyclopropaneC12H24——0.02—1062922,6,11,15-TetramethylhexadecaneC20H42——0.010.021753934-EthylundecaneC13H28——0.01—124994(5E)-5-octadeceneC18H36——0.010.011818953-Ethyl-3-methyldecaneC13H28——0.01—1229965-IsobutylnonaneC13H28——0.020.041185975-ButylnonaneC13H28——0.010.041249982,2-DimethyldecaneC12H26———0.041130992-MethyltetradecaneC15H32———0.0114481002-MethylhexadecaneC17H36———0.0116471019-MethylnonadecaneC20H42———0.0119451022-Methyl-6-propyldodecaneC16H34———0.011483103DecamethylcyclopentasiloxaneC10H30O5Si5———0.011034104TetratetracontaneC44H90———0.0243951052,2-DimethylundecaneC13H28———0.2712291064-MethyldodecaneC13H28———0.021249107UndecylcyclohexaneC17H34———0.011775Categories108Nickel tetracarbonylC4NiO40.092.200.160.29—1094,7-DimethylbenzofuranC10H10O0.02———1244110HydroxylamineH3NO2.424.883.51——1114-Hexen-3-oneC6H10O5.66———7621122-UndecanoneC11H22O—0.16——1251113Didecyl etherC20H42O—0.07—0.032085114OxygenO2—3.57—25.26—115Carbon monoxideCO——0.060.10—116p-(1-Propenyl)anisoleC10H12O——0.01—1190[30]1172-Cyclohexen-1-oneC6H8O———0.01873Note. “—”means not detected. In Table 2, the constituents marked red were first detected from T. fuciformis.A total of 117 volatile components, including 68 hydrocarbons, 12 esters, 10 alcohols, 10 aldehydes, 7 acids, and 10 other compounds, were detected fromT. fuciformis. However, the relative contents of acids and aldehydes were the highest, which was consistent with Li Xiang’s research on T. fuciformis and bag cultivated T. fuciformis [13]. Moreover, 58, 59, 62, and 55 volatile components were detected from Hebei, Henan, Fujian, and Sichuan Provinces, respectively. Within them, there were a total number of 18 common components. However, a variety of volatile components were detected in T. fuciformis for the first time, such as eucalyptol, 2-butyl-1-octanol, 2-ethyl-1-pentanol, benzeneacetaldehyde, 4-methylvaleric acid, gamma-butyrolactone, n-hexyl formate, bute hydrocarbon, hydroxylamine, 2-carene have not been reported.Among the 68 hydrocarbon compounds ofT. fuciformis, most of them belonged to the saturated hydrocarbons, such as 5-methyltetradecane, bute hydrocarbon, 2, 6, 10, 14-tetramethylhexadecane, 4, 6-dimethyldodecane, and 2, 6, 10-trimethyldodecane. However, these compounds had generally low relative content in the samples with high threshold values, which contributed less to the overall odor of T. fuciformis. In contrast, unsaturated hydrocarbons such as (5E)-5-octadecene, camphene, and 2-carenecontribute more for its relatively low thresholds [34]. Besides, no unique compounds with high relative content (≥1) were found for the samples from different regions.Esters are usually one type of compound with a fruit aroma and contribute to the overall aroma ofT. fuciformis [35]. A total of 12 ester compounds were detected from T. fuciformis. Of them, butyrolactone (6.08%) and γ-butyrolactone (2.79%) were the top 2 esters of Hebei samples, while γ-butyrolactone, heptadecyl trifluoroacetate, and hydrazinecarboxylic acid, ethyl ester were the unique volatile constituents. For the Sichuan samples, the unique ester components included sulfurous acid, 2-ethylhexyl isobutyl ester, 2-ethylhexyl acrylate, hexatriacontyl pentafluoropropionate and formic acid, and ethenyl ester, of which the relative content of formic acid, ethenyl ester was as high as 25.12%. These unique components identified for corresponding regions would be used to distinguish the samples from this region from other regions.Volatile acids are usually derived from the oxidation or biosynthesis of fatty acids [36, 37]. In this research, 7 kinds of acid compounds were detected in T. fuciformis. Acetic acid is a common acid with a fishy smell of oil [38] and exists in T. fuciformis at a high relative content (35.36%∼49.42%). However, due to its high aroma threshold, it has little contribution to the overall odor of T. fuciformis.Volatile alcohols in plants mainly come from the decomposition of secondary hydroperoxides of fatty acids and the reduction of sugars and amino acids [36]. Most alcohols are generally floral and fruity aromas [39]. According to the above GC-MS analysis results, 10 kinds of alcohol were detected, including 7 kinds in Hebei, 3 kinds in Henan, 4 kinds in Fujian, and 1 kind in Sichuan. Not only that, the relative content of volatile alcohols was also high in the Hebei region. 2-ethyl-1-decanol, 1-octen-3-ol, eucalyptol, linalol, and isotridecyl alcohol were special to the samples of the Hebei region, while isopentyl alcohol to the samples in Fujian. These unique volatile components of different samples might be taken as a mark for the distinguishment of different regions.Aldehyde compounds are mainly derived from fatty acid oxidation and amino acid metabolism [40], and their aroma thresholds are usually low. Therefore, it usually plays an important role in the overall aroma, although the content of aldehyde compounds is low [41]. There were 10 kinds of aldehydes in T. fuciformis, and 8 species were detected in Hebei province, nine in Henan province, seven in Fujian province, and three in Sichuan province. Among them, hexanal, nonanal, and pentanal were the common aldehyde volatile components of T. fuciformis, while 5-methyl-2-furancarboxaldehyde and 2-ethyl-1-pentanol were the unique aldehyde volatile components of Henan and Fujian provinces, respectively.Besides,T. fuciformis also included phenols, ketones, furans, and so on. In addition, gases were detected in T. fuciformis. Because the whole detection environment was gaseous, the components in the air may have been detected in the sample, such as oxygen and carbon monoxide. But these gases are colorless and tasteless and did not affect the aroma quality of T. fuciformis. Among them, the detected ketones included 4-hexen-3-one, 2-undecanone, and 2-cyclohexen-1-one, and the relative content of 4-hexen-3-one, a unique component in Hebei samples, was relatively high. Nickel tetracarbonyl was the common component detected in all the 4 regions, while hydroxylamine was also detected in the samples from considerate regions except Fujian.


### 3.2.2. Analysis of Volatile Components ofT. fuciformis among Different Regions

In Figure3, there was no obvious difference in the types of volatile substances contained in Tremella among the 4 regions. The most abundant volatile component type was hydrocarbons, which were about 3 times as many as the other types. By comparing these substances among the samples from the 4 regions, it could be found that more types of hydrocarbons were detected in the T. fuciformis from Fujian, while more aldehyde types and acid types were detected in the Henan samples, more alcohol types from Hebei samples, and more ester from Sichuan samples.Figure 3
Volatile components types ofT. fuciformis from different producing areas.In general, the relative contents of acid in the 4 regions (in Figure4) were the highest of the detected volatile components, followed by aldehydes. However, the proportion varied from region to region. Also, it can be seen that the T. fuciformis from Henan owned more contents of acids while the Hebei samples had more aldehyde and Sichuan had more esters.Figure 4
Relative contents of volatile compounds inT. fuciformis.


## 3.2.1. Components Analysis ofT. fuciformis

The volatile components ofT. fuciformis from four regions were analyzed by GC-MS in Table 2.Table 2
Composition of volatile components ofT. fuciformis.
NumberCompound nameMolecular formulaRelative content/%RI valueLiteratureHebeiHenanSichuanFujianAlcohols1Pentyl alcoholC5H12O1.221.12—0.95761[30]22-Ethyl-1-decanolC12H26O0.02———139331-HexanolC6H14O0.57——0.02860[20]41-Octen-3-olC8H16O0.38———969[20]5EucalyptolC10H18O5.00———10596LinalolC10H18O0.05———1082[31]7Isotridecyl alcoholC13H28O0.01———149282-TetradecyloxyethanolC16H34O2—0.010.03—193092-Butyl-1-octanolC12H26O—0.03—0.03139310Isopentyl alcoholC5H12O———0.21697[20]Aldehyde11HexanalC6H12O27.3525.2123.6021.60806[20]12FurfuralC5H4O20.010.17—0.0283113HeptanalC7H14O0.431.04——905[20]142-Furancarboxaldehyde, 5-methyl-C6H6O2—0.08——92015OctanalC8H16O1.030.04—0.041005[30]16BenzeneacetaldehydeC8H8O0.820.01——1081[20]17NonanalC9H18O2.580.190.071.061104[20]18BenzaldehydeC7H6O0.230.02—0.08982[20]19PentanalC5H10O5.050.380.010.23707[20]202-Ethyl-1-pentanolC7H16O———0.03896Acids21Acetic acidCH3COOH35.3649.4239.9240.85576[31]224-Methylvaleric acidC6H12O21.73———91023Nonanoic acidC9H18O20.40———127224Octanoic acidC8H16O2—1.521.52—2069[32]25Pentanoic acidC5H10O2—0.21——116126Heptanoic acidC7H14O2—2.011.33—1078[30]27Hexanoic acidC6H12O2—0.69—3.721856[32]Esters28ButyrolactoneC4H6O26.08—1.060.1182529gamma-ButyrolactoneC5H8O22.79———88630Heptadecyl trifluoroacetateC19H35F3O20.52———181231Hydrazinecarboxylic acid, ethyl esterC3H8N2O20.14———92832Sulfurous acid, hexyl pentadecyl esterC21H44O3S—0.42—0.18273233n-Hexyl formateC7H14O2—0.65—0.01981[20]34Docosyl pentafluoropropionateC25H45F5O2—0.01——236935Sulfurous acid, 2-ethylhexyl isobutyl esterC12H26O3S——0.02—1709362-Ethylhexyl acrylateC11H20O2——0.01—120837Hexatriacontyl pentafluoropropionateC39H73F5O2——0.02—376138Formic acid, ethenyl esterC3H4O2——25.12—574391-Methyl-2-oxocyclohex-3-enecarboxylic acid, methyl esterC9H12O3———0.011274Hydrocarbons402, 10-TrimethyldodecaneC15H32—0.010.010.02132041Bute hydrocarbonC19H40—0.72—0.031653423-MethylheptadecaneC18H38—0.02——1746433-MethylundecaneC12H260.030.020.040.031150[33]44DodecaneC12H260.150.090.100.301214[30]45TetradecaneC14H300.150.06—0.541413[20]464,6-DimethyldodecaneC14H300.190.050.02—128547DodecamethylcyclohexasiloxaneC12H36O6Si60.040.03—0.10124048HeptadecaneC17H360.071.160.040.211711492,5-DimethyltridecaneC15H32—0.010.020.021384506-MethyltridecaneC14H30—0.010.010.01134951OctadecaneC18H380.020.290.030.0718105210-MethylnonadecaneC20H42—0.01——194553OctacosaneC28H580.130.140.010.052804543,8-DimethyldecaneC12H260.020.020.030.02108655CampheneC10H160.940.250.030.1194356HexadecaneC16H340.370.290.090.331612[20]575-MethyltetradecaneC15H32—0.06—0.051448584-MethyltetradecaneC15H32—0.01—0.021448593-MethyltetradecaneC15H320.410.02—0.06144860EicosaneC20H420.550.140.060.19200961TetratriacontaneC34H700.120.03—0.013401624-MethylpentadecaneC16H340.020.36—0.081548632,6,10,15-TetramethylheptadecanC21H440.010.02——185264NonadecaneC19H400.010.080.040.071910658-HexylpentadecaneC21H44—0.010.010.072045662,2,4,6,6-PentamethylheptaneC12H260.870.631.480.83981[20]672,3-DimethylundecaneC13H28—0.01——1185682-Bromo dodecaneC12H25Br0.030.120.050.15144669(9E)-9-octadeceneC18H36—0.01——181870HeptacosaneC27H56—0.01——2705712,6,10,14-TetramethylhexadecaneC20H420.451.130.020.531753722,2,4,4,6,8,8-HeptamethylnonaneC16H34—0.02——129473PentadecaneC15H32—0.320.01—1512[30]74HMNC16H340.04—0.03—129475UndecaneC11H240.02—0.04—1115[20]762,6,11-TrimethyldodecaneC15H320.02—0.01—13207711-MethyldodecaneC13H280.01———124978HeneicosaneC21H440.02—0.010.062109792-CareneC10H160.01———94880gamma-TerpinenC10H160.21———998811-TrideceneC13H261.01—0.02—1304825-Methyl-5-propylnonaneC13H280.02—0.01—1229832,5-DimethyldecaneC12H260.03—0.01—1086842,4-DimethyldecaneC12H260.01———108685DocosaneC22H460.01—0.03—220886Benzene, 1-methyl-2-(phenylmethyl)-C14H14——0.02—1580871-Benzyl-3-methylbenzeneC14H14——0.02—158088DotriacontaneC32H66——0.01—3202892,3,7-TrimethyldecaneC13H28——0.01—1121902,5-DimethylundecaneC13H28——0.03—1185911-Sec-butyl-1-(2-methylbutyl)cyclopropaneC12H24——0.02—1062922,6,11,15-TetramethylhexadecaneC20H42——0.010.021753934-EthylundecaneC13H28——0.01—124994(5E)-5-octadeceneC18H36——0.010.011818953-Ethyl-3-methyldecaneC13H28——0.01—1229965-IsobutylnonaneC13H28——0.020.041185975-ButylnonaneC13H28——0.010.041249982,2-DimethyldecaneC12H26———0.041130992-MethyltetradecaneC15H32———0.0114481002-MethylhexadecaneC17H36———0.0116471019-MethylnonadecaneC20H42———0.0119451022-Methyl-6-propyldodecaneC16H34———0.011483103DecamethylcyclopentasiloxaneC10H30O5Si5———0.011034104TetratetracontaneC44H90———0.0243951052,2-DimethylundecaneC13H28———0.2712291064-MethyldodecaneC13H28———0.021249107UndecylcyclohexaneC17H34———0.011775Categories108Nickel tetracarbonylC4NiO40.092.200.160.29—1094,7-DimethylbenzofuranC10H10O0.02———1244110HydroxylamineH3NO2.424.883.51——1114-Hexen-3-oneC6H10O5.66———7621122-UndecanoneC11H22O—0.16——1251113Didecyl etherC20H42O—0.07—0.032085114OxygenO2—3.57—25.26—115Carbon monoxideCO——0.060.10—116p-(1-Propenyl)anisoleC10H12O——0.01—1190[30]1172-Cyclohexen-1-oneC6H8O———0.01873Note. “—”means not detected. In Table 2, the constituents marked red were first detected from T. fuciformis.A total of 117 volatile components, including 68 hydrocarbons, 12 esters, 10 alcohols, 10 aldehydes, 7 acids, and 10 other compounds, were detected fromT. fuciformis. However, the relative contents of acids and aldehydes were the highest, which was consistent with Li Xiang’s research on T. fuciformis and bag cultivated T. fuciformis [13]. Moreover, 58, 59, 62, and 55 volatile components were detected from Hebei, Henan, Fujian, and Sichuan Provinces, respectively. Within them, there were a total number of 18 common components. However, a variety of volatile components were detected in T. fuciformis for the first time, such as eucalyptol, 2-butyl-1-octanol, 2-ethyl-1-pentanol, benzeneacetaldehyde, 4-methylvaleric acid, gamma-butyrolactone, n-hexyl formate, bute hydrocarbon, hydroxylamine, 2-carene have not been reported.Among the 68 hydrocarbon compounds ofT. fuciformis, most of them belonged to the saturated hydrocarbons, such as 5-methyltetradecane, bute hydrocarbon, 2, 6, 10, 14-tetramethylhexadecane, 4, 6-dimethyldodecane, and 2, 6, 10-trimethyldodecane. However, these compounds had generally low relative content in the samples with high threshold values, which contributed less to the overall odor of T. fuciformis. In contrast, unsaturated hydrocarbons such as (5E)-5-octadecene, camphene, and 2-carenecontribute more for its relatively low thresholds [34]. Besides, no unique compounds with high relative content (≥1) were found for the samples from different regions.Esters are usually one type of compound with a fruit aroma and contribute to the overall aroma ofT. fuciformis [35]. A total of 12 ester compounds were detected from T. fuciformis. Of them, butyrolactone (6.08%) and γ-butyrolactone (2.79%) were the top 2 esters of Hebei samples, while γ-butyrolactone, heptadecyl trifluoroacetate, and hydrazinecarboxylic acid, ethyl ester were the unique volatile constituents. For the Sichuan samples, the unique ester components included sulfurous acid, 2-ethylhexyl isobutyl ester, 2-ethylhexyl acrylate, hexatriacontyl pentafluoropropionate and formic acid, and ethenyl ester, of which the relative content of formic acid, ethenyl ester was as high as 25.12%. These unique components identified for corresponding regions would be used to distinguish the samples from this region from other regions.Volatile acids are usually derived from the oxidation or biosynthesis of fatty acids [36, 37]. In this research, 7 kinds of acid compounds were detected in T. fuciformis. Acetic acid is a common acid with a fishy smell of oil [38] and exists in T. fuciformis at a high relative content (35.36%∼49.42%). However, due to its high aroma threshold, it has little contribution to the overall odor of T. fuciformis.Volatile alcohols in plants mainly come from the decomposition of secondary hydroperoxides of fatty acids and the reduction of sugars and amino acids [36]. Most alcohols are generally floral and fruity aromas [39]. According to the above GC-MS analysis results, 10 kinds of alcohol were detected, including 7 kinds in Hebei, 3 kinds in Henan, 4 kinds in Fujian, and 1 kind in Sichuan. Not only that, the relative content of volatile alcohols was also high in the Hebei region. 2-ethyl-1-decanol, 1-octen-3-ol, eucalyptol, linalol, and isotridecyl alcohol were special to the samples of the Hebei region, while isopentyl alcohol to the samples in Fujian. These unique volatile components of different samples might be taken as a mark for the distinguishment of different regions.Aldehyde compounds are mainly derived from fatty acid oxidation and amino acid metabolism [40], and their aroma thresholds are usually low. Therefore, it usually plays an important role in the overall aroma, although the content of aldehyde compounds is low [41]. There were 10 kinds of aldehydes in T. fuciformis, and 8 species were detected in Hebei province, nine in Henan province, seven in Fujian province, and three in Sichuan province. Among them, hexanal, nonanal, and pentanal were the common aldehyde volatile components of T. fuciformis, while 5-methyl-2-furancarboxaldehyde and 2-ethyl-1-pentanol were the unique aldehyde volatile components of Henan and Fujian provinces, respectively.Besides,T. fuciformis also included phenols, ketones, furans, and so on. In addition, gases were detected in T. fuciformis. Because the whole detection environment was gaseous, the components in the air may have been detected in the sample, such as oxygen and carbon monoxide. But these gases are colorless and tasteless and did not affect the aroma quality of T. fuciformis. Among them, the detected ketones included 4-hexen-3-one, 2-undecanone, and 2-cyclohexen-1-one, and the relative content of 4-hexen-3-one, a unique component in Hebei samples, was relatively high. Nickel tetracarbonyl was the common component detected in all the 4 regions, while hydroxylamine was also detected in the samples from considerate regions except Fujian.


## 3.2.2. Analysis of Volatile Components ofT. fuciformis among Different Regions

In Figure3, there was no obvious difference in the types of volatile substances contained in Tremella among the 4 regions. The most abundant volatile component type was hydrocarbons, which were about 3 times as many as the other types. By comparing these substances among the samples from the 4 regions, it could be found that more types of hydrocarbons were detected in the T. fuciformis from Fujian, while more aldehyde types and acid types were detected in the Henan samples, more alcohol types from Hebei samples, and more ester from Sichuan samples.Figure 3
Volatile components types ofT. fuciformis from different producing areas.In general, the relative contents of acid in the 4 regions (in Figure4) were the highest of the detected volatile components, followed by aldehydes. However, the proportion varied from region to region. Also, it can be seen that the T. fuciformis from Henan owned more contents of acids while the Hebei samples had more aldehyde and Sichuan had more esters.Figure 4
Relative contents of volatile compounds inT. fuciformis.


## 3.3. ROAV Analysis of Key Aroma Compounds

ROAV is used as one common index, which may range from 0 to 100 and reflects the aroma contribution degree of each volatile component. The higher the ROAV value of the compound, the greater the contribution of the compound to the overall odor of the sample [42–44]. By referring to the researched 29 compounds with the given aroma threshold values from relevant literature and combining, the corresponding ROAV analysis results were calculated and are shown in Table 3.Table 3
ROAV value of 29 components inT. fuciformis from different regions.
NumberCompound nameAroma thresholdROAV(μG/L) [31, 45–50]HebeiHenanSichuanFujianAlcohols11-Hexanol250<0.1——<0.121-Octen-3-ol15.5———3Eucalyptol1.30.22———4Linalol1.50.48———5Pentyl alcohol4000<0.1<0.1—<0.16Isopentyl alcohol120———<0.1Aldehydes7Hexanal4.587.971001001008Furfural3000<0.1<0.1——9Heptanal32.076.19——10Octanal0.721.31.02—1.1911Benzeneacetaldehyde4<0.1<0.1——12Nonanal137.343.391.3322.0813Benzaldehyde350<0.1<0.1—<0.114Pentanal203.650.34<0.10.24Acids15Acetic acid22000<0.1<0.1<0.1<0.116Nonanoic acid3000<0.1———17Octanoic acid500——<0.1—18Pentanoic acid3000————19Heptanoic acid100——0.25—20Hexanoic acid3000———<0.1Esters21Butyrolactone0.88100—22.972.622gamma-Butyrolactone1000.81———23n-Hexyl formate19800—<0.1—<0.1Hydrocarbons24Dodecane2040<0.1<0.1<0.1<0.125Tetradecane1000<0.1<0.1—<0.126Hexadecane300<0.1<0.1<0.1<0.1272-Carene0.0114.47———Others282-Undecanone255—<0.1——29p-(1-Propenyl)anisole15——<0.1—Note. “—”means not detected.Overall, there were 8 compounds (ROAV ≥1) including 1-octen-3-ol, heptanal, octanal, nonanal, pentanal, hexanal, butyrolactone, and 2-carene, which were taken as the key aroma compounds ofT. fuciformis. Among them, hexanal and nonanal were the common key aroma compounds and could be used as the characteristic identification components of T. fuciformis. As a basic product of the oxidative decomposition of linoleic acid, hexanal is a common volatile oil with the fragrance of green, grass, and fruit [51], contributing greater than the others to the overall aroma of T. fuciformis. Nonanal is also a common aroma compound with the fragrance of flowers, fat, and wax, and a low threshold value, and it offers people a pleasant feeling [52]. 1-Octene-3-ol, also known as agaritol with the aroma of fresh mushroom, licorice, and rose, was the unique key aroma compound of Hebei samples. This compound was mainly used as pharmaceutical raw materials and in aromatics [53]. Besides, butyrolactone generally has the fragrance characteristics of coconut or peach [40, 42], while heptanal has the odor of fat or fish [36]. These substances play an important role in the overall fragrance of T. fuciformis.In HebeiT. fuciformis, all the 8 key aroma compounds were discovered, of which butyrolactone (ROAV = 100) is the compound with the highest ROAV, and it can be used as the aroma base of T. fuciformis, followed by hexanal, nonanal, octanal, 2-carene, 1-octen-3-ol, pentanal, and heptanal. But on the other hand, 1-octen-3-ol and 2-carene were the special compounds of these samples and could be used to distinguish the Hebei samples from the other 3 regions. The modified aroma compounds were eucalyptol, linalool, and γ-butyrolactone, which were also unique for Hebei samples. The potential aroma compound, nonanoic acid, was unique for the Hebei sample, while the other 3 compounds, acetic acid, dodecane, and hexadecane, were common for all the collected T. fuciformis.The ROAV value of hexanal in the samples from Sichuan, Henan, and Hebei was 100, indicating that this component contributed the most to the aroma of tremella from these three regions. For theT. fuciformis of Henan province, there were 4 key aroma compounds, and hexanal was the highest, followed by heptanal, nonanal, and octanal. However, the samples from Henan province lacked butyrolactone, compared with the other three regions, so the compound could be used to distinguish other samples from Henan province. Pentanal and 2-undecanone were the modified and potential aroma compound in Henan province.Three key volatile aroma compounds with threshold values were identified in Sichuan samples, which were hexanal, butyrolactone, and nonanal from high to low. Heptanoic acid was the modified aroma compound ofT. fuciformis, while octanoic acid and p-(1-propenyl) anisole were the potential aroma compounds unique to Sichuan samples. On the other hand, octanal was a key aroma compound for the samples from Hebei, Henan, and Fujian, but not for the Sichuan samples.Four kinds of key volatile aroma compounds detected in Fujian samples with the ROAV from high to low were hexanal, nonanal, octanal, and butyrolactone. The modified aroma compound was pentanal as well as Henan samples, and the potential aroma compounds special to Fujian samples were isopentyl alcohol and hexanoic acid.


## 4. Conclusion

The difference betweenT. fuciformis from different regions existed, and the electronic nose is a good technology to distinguish T. fuciformis from different regions. During the determination, the sensors of C1, C3, C4, C5, C6, C8, and C9 contributed much more to distinguish the overall odor of T. fuciformis. Electronic nose (PCA) combined with GC-MS (ROAV) suggested that the types and contents of volatile aldehydes might contribute significantly to the aroma degree of T. fuciformis from different regions. In the PCA results, the samples from Hebei and Henan were distributed on the right of the origin of coordinates. On the contrary, the samples from Sichuan and Fujian were and distributed on the left. In ROAV, aldehydes from Hebei and Henan provinces had more kinds of aroma components, higher content, and higher aroma activity. 1-Octen-3-ol, heptanal, octanal, nonanal, pentanal, hexanal, butyrolactone, and 2-carene were the key aroma compounds contributing to the aroma of T. fuciformis. 1-Octen-3-ol, 2-carene, eucalyptol, linalool, γ-butyrolactone, and nonanoic acid were special to the Hebei samples, while octanoic acid and p-(1-propenyl) anisole were special to the Sichuan samples, as well as isopentyl alcohol and hexanoic acid were special to the Fujian samples. On the other hand, butyrolactone was the missing aroma compound for the Henan samples, while octanal was for the Sichuan samples [54].



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*Source: 9904213-2022-04-27.xml*