Identification of Key Odor Compounds from Three Kinds of Wood Species

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Qi-Fan Wang, Ya-Li Shao, Tian-Yu Cao and Jun Shen* Identification of Key Odor Compounds from Three Kinds of Wood Species

Identification and analysis of key odor compounds from three kinds of wood species by Gas Chromatography-Mass spectroscopy-Olfactometry

Abstract: In order to solve the problem of indoor odor and better understand the chemical composition and sources of odor from solid wood, we collected the volatile substances from Populus ussuriensis Kom, Pinus sylvestris var, mongolica Litv, and Tilia amurensis Rupr, using the Micro-Chamber/Thermal Extractor and Gas Chroma- tography-Mass spectroscopy-Olfactometry. Results showed that: The main odor compounds of Populus ussuriensis Kom were aromatics (1 kind), aldehydes (1 kind), the main odor compounds of Pinus sylvestris var, mongolica Litv, were aromatic (2 kinds), alkenes (8 kinds), alcohols (4 kinds) and aldehydes (1 kind). The main odor compounds of Tilia amurensis Rupr, were alkenes (2 kinds), alcohols (1 kind), aldehydes (1 kind). At the same time, 7 kinds unknown compounds were detected from Populus ussuriensis Kom., which appeared at 9.02, 9.7, 20.6, 25.03, 28.82, 32.88, and 34.58 minutes, with the odor of sweet, plastic&spicy, special, stimulat- ing&burning&plastic&spicy, stinky, plastic&spicy and plastic, respectively. 6 kinds unknown compounds were detected from and Tilia amurensis Rupr., which appeared at 5.70, 9.73, 9.92, 30.27, 30.9, and 32.38 minutes and presented as stinky, plastic&stinky, earthy, stinky, delightful, and aromatic. The emergence times of odor compounds focused around 5 to 12 minutes and 18 to 36 minutes. The volatile substances of Populus ussuriensis Kom, Pinus sylvestris var, mongolica Litv, and Tilia amurensis Rupr, were 25, 27 and 40 kinds corresponding, with the key odor compounds of alkenes, aldehydes, and alcohols. The odor intensity of VOCs from the three wood species did not show a positive correlation with the concentrations. The aroma of three kinds of wood species are composed of several aroma-active volatile

|| Qi-Fan Wang, Northeast Forestry University, 26 Hexing Road, Harbin 150040, China. Email: [email protected] Ya-Li Shao, Northeast Forestry University, 26 Hexing Road, Harbin 150040, China. Email: [email protected] Tian-Yu Cao, Northeast Forestry University, 26 Hexing Road, Harbin 150040, China. Email: [email protected] Jun Shen, Northeast Forestry University, 26 Hexing Road, Harbin 150040, China. Email: [email protected]

DOI 10.1515/9783110540048-011, © 2017 Jun Shen et al, published by De Gruyter. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License. 102 | Wang, Shao, Cao, Shen components which can affect the overall flavor for their low threshold.

Keywords: Chromatography-Mass spectroscopy-Olfactometry; Populus ussuriensis Kom; Pinus sylvestris var, mongolica Litv; Tilia amurensis Rupr; Key odor compounds

1 Introduction

In recent years, people are increasingly using wood materials in their interior deco- rating because of its natural affinity and visual sense of harmony. The release of volatile organic compounds (VOCs) in indoor air is therefore increasing. Organic compounds can release either pleasant or irritating odors into the surrounding envi- ronments. These odors are composed of a variety of single compounds, and some of those compounds may be harmful to human’s health. Gas chromatography–mass spectroscopy olfactometry (GC-MS-O) is improved from the GC-MS by detecting VOCs emissions from wood and combining the separation ability of GC-MS with the sensitive olfactory ability of humans. GC-MS-O separates the various VOCs components and uses our noses as detectors [1] to evaluate each compound, separately. Based on the sensitivity of the human sense of smell, which can exceed that of other chemical detectors, GC-MS-O was used to select and evaluate active odor substances from complex mixtures of VOCs [2]. This method is helpful in identifying key odor compounds and determining the intensity of those compounds. GC-MS-O was first proposed in 1964 [3, 4]. It was performed by smelling the outflow components of GC-MS directly. This method combined not only the GC-MS advantages of high separation efficiency, strong qualitative ability, high sensitivity, and quantitative accuracy but also the sensory evaluation of humans. In 1976, Acree et al. improved the original GC-MS-O technology by adding humid air and by smelling the GC outflow after film chromatography processing. In the mid-1980s, Acree and Ullrich [5, 6] used dilution-analysis methods to analyze the intensity of the various odors at the same time, which made GC-MS-O technology widely applicable in many situations. Currently, there are four major GC-MS-O detection methods [7], the dilution analysis, time–intensity analysis, detection frequency methods, and poste- rior intensity evaluation. With the development of extraction and separation technology, GC-MS-O has been widely used in the research of fruits [8], vegetables [9], dairy products [10], paint [11], gypsum [12], and other fields such as tobaccos, flavoring agents and wines. In total, there are many researches on odor emissions, but there is few researches about the odor emission from wood materials, especially solid woods. The odor problem of interior decoration has impacted people’s life a lot. Usually, we can only smell the overall odor but cannot know the single key odor components that make up the overall odor. This study isolated and indentified the key odor compounds Identification of Key Odor Compounds from Three Kinds | 103

from Populus ussuriensis Kom, Pinus sylvestris var. mongolica Litv. and Tilia amurensis Rupr. And at the same time, the characteristics and intensities of the key odor compounds were showed and chemical composition and source of overall odor were found to provide basic data of interior decoration materials.

2 Materials and Methods

2.1 Experimental Materials

The essential parameters of the three wood species are presented in Table 1. The samples were cut into round pieces (60 mm diameter) for the microcham- ber/thermal extractor apparatus. The exposed area was 5.65 × 10−3 m2. After the edg- es of specimen were sealed with aluminum foil to prevent the release of compounds. The samples were stored in Teflon bags and placed in a refrigerator until needed.

2.2 Experimental Equipments

2.2.1 Sampling Devices

Two sampling devices were used. The Micro-Chamber/Thermal Extractor µ-CTE 250 (Markes International Inc., UK) consists of four cylindrical micropools (each with a microcell diameter of 64 mm by a depth of 36 mm). The sampling temperature can be adjusted up to 250 °C. It can test four samples at the same time. The other sampling device was a Tenax TA tube (Markes International Inc., UK). In this device, the material of the pipe body is stainless steel, and the sampling tube contains 200 mg of 2, 6-dibenzofurans porous polymer, which can efficiently adsorp or desorp the volatile organic gases.

2.2.2 Detection and Analysis Devices

Three detection and analysis devices were used. (i) The Unity thermal analysis desorption unit (Markes International Inc., UK). Nitrogen was used as the carrier gas. The related parameters include: thermal desorption temperature, 280 °C, cold-trap adsorption temperature, −15 °C, and thermal analysis time, 10 minutes; and injection time, 1 minute. (ii) DSQ II series GC-MS (Thermo Scientific, Germany). Chromatography was performed with a DB-5 quartz capillary column (3,000 mm by 0.26 mm by 0.25 μm). Helium was used as the carrier gas with a constant velocity of 1.0 mL/min by splitless injection. The chromatographic column was initially kept at 40 °C for 2 104 | Wang, Shao, Cao, Shen

minutes; then, the temperature was increased to 50°C (in 2 °C/min increments) and was held for 4 minutes. Finally, the temperature was elevated to 250 °C (in 10 °C/min increments) and held for 8 minutes. The injection port temperature was 250 °C. The following GC-MS conditions were applied: ionization mode, electron ionization (EI); ion energy, 70 eV; transmission line temperature, 270 °C; ion source temperature, 230 °C; and mass scan range, 50 to 650 atomic mass units. (iii) Sniffer 9000 Olfactory Detector (Brechbühler, Switzerland). Combined with GC or GC-MS, the quantitative and qualitative analyses can be made, and the compound’s odor intensity can be reflected directly and recorded. The effluent of the GC capillary is divided into two parts, one part enters the mass spectrometer, and the other part is used for sensory evaluation (ratio 1:1). The transmission line temperature was 150 °C, and nitrogen was used as the carrier gas through a purge valve. Humid air was added to prevent dehydration of the nasal mucosa.

2.3 Experimental Method

2.3.1 Sampling Method

The experiment used the Tenax TA sampling tubes tubes to adsorb VOCs from different wood species under constant experimental conditions (sampling temperature, 40 °C; ratio of air exchange rate to loading factor, 0.5; air flow rates, 47 mL/min). Four samples were collected under these conditions, with a sampling cycle of 8 hours. Each sample’s contents were 3 liters. After sampling, the Tenax TA sampling tubes were wrapped in teflon plastic bags until needed.

2.3.2 Analytical Method

Two analytical methods were used. GC-MS and its built-in software were used to analyze the VOCs. The MS detection peak used the 2008 spectral library of the Na- tional Institute of Standards and Technology (NIST) (matching degrees up to 800 °C or above). An internal-standard method was used in this experiment, with deuteri- um substituted for toluene at a concentration of 200 ng/μL, which added 2 μL. The internal-standard quantitative-analysis method used the following equation (1):

/ (1)

Where Ai and as are the peak area of the products tested and the internal standard substance, respectively; and ms is the amount of the internal standard. After detected by GC-MS, the compounds were identified using the NIST (2008 standard spec-

Identification of Key Odor Compounds from Three Kinds | 105

trum) and Wiley libraries. The primary odor compounds were identified by mass spectrometry, retention index, and odor characterization. The refractive index value was calculated through the retention time of n-alkane under the same conditions [13]. The second analytical method used was GC-O. The time-intensity method was chos en for analysis of the compounds. As the sample was injected and the chromatogram yielded peaks, the sensory evaluation assessors perceived and described the column outflow from the odor port simultaneously. The time of the odor, the odor type, and the intensity of the odor were recorded. After specific training, four assessors (with ages between 20 and 30 years, no history of smoking, and no olfactory organ disease) formed a GC-O odor-analysis evaluation group. The experimental environment was well ventilated, and there were no peculiar smells in the room. The temperature was kept between 17 and 25 °C during the entire experimental process. Activities, such as eating, which could pos- sibly have an effect on indoor odors, were forbidden for 5 hours before the experiment. Experimental results were recorded when the same odor characteristics were described by at least two assessors at the same time. The intensity value was based on the average value of the different assessors. The grade division of the substance’s odor concentration was mainly based on the human sense of smell. The experiment’s discrimination of odor intensity was made according to the Japanese standard [14] (see Table 2).

3 Results and Discussion

3.1 Odorous VOCs from Populus Ussuriensis Kom.

GC-MS-O was used to detect the VOCs odors from three wood species qualitatively and quantitatively. Figures 1 shows the total ion current of Populus ussuriensis Kom.. The corresponding analytical results are shown in Table 3 and Table 4. From table 3, we can note that there were more components in the alkanes categories than in the others. Components were also found in these categories: aromatics, alkenes, aldehydes and ethers (small amounts). The totally species of volatile substances from Populus ussuriensis Kom. were 25. Table 4 shows the relevant in- formation of odor compounds, including retention time, retention index (RI), mass concentration, odor character and odor intensity. We can see that the key odor compounds from Populus ussuriensis Kom. mainly appear in aromatics and aldehydes.The odor compounds listed in order of intensity from the largest to the smallest were: hexanal (grass; odor intensity 3), 2-ethyl-furan (special; odor intensity 1), and seven unknown compounds that weren’t detected by GC-MS but were detected by the human olfactory system. The odors from these seven unknown compounds 106 | Wang, Shao, Cao, Shen appeared at 9.02, 9.7, 20.6, 25.03, 28.82, 32.88, and 34.58 minutes were sweet (odor intensity 2); plastic, spicy; (odor intensity 2.5); special (odor intensity 2); stimulat- ing, burning-plastic, spicy (odor intensity 4); stinky (odor intensity 3); plastic, spicy (odor intensity 2.5); and plastic (odor intensity 3), respectively. These compounds could not be detected by mass spectrometry because their concentration was below the GC-MS detection limit, but they could be detected by the human olfactory system at low thresholds.

3.2 Odorous VOCs from Pinus Sylvestris var. Mongolica Litv.

The total ion current of Pinus sylvestris var. mongolica Litv. was showed in Figures 2. The corresponding analytical results are shown in Table 5 and Table 6. From table 5, we can note that there were more components in the aromatics and alkenes categories than in the others. Components were also found in these categories: alkanes, aldehydes, alcohols and ethers (small amounts). The totally species of volatile substances from Pinus sylvestris var. mongolica Litv. were 27. Ta- ble 6 shows the key odor compounds from Pinus sylvestris var. mongolica Litv.. The compounds, ordered by odor intensity from largest to smallest were as following: α- pinene (turpentine; odor intensity3), 3-carene (pine; odor intensity3), toluene (spicy, plastic, stinky; odor intensity2), 1-methyl-5-1-methylethenyl-cyclohexene (turpentine; odor intensity 1.5), d-limonene (lemon; odor intensity 2), copaene (burning-plastic; odor intensity 2), α,α,4-trimethyl-3-cyclohexene-1-methanol (flow- ers; odor intensity 2), 1-methyl-2-1-methylethyl-benzene (aromatic; odor intensity 1), camphene (camphor; odor intensity 1), α-myrcene (lipids; odor intensity 1), 1- methyl-4-1-methylethyl-1,4-cyclohexadiene (special; odor intensity 1), benzaldehyde (almond bitterness; odor intensity 1), exo-fenchol (small fennel; odor intensity 1), borneol (camphor; odor intensity 1), and 4-methyl-1-1-methylethyl-3-cyclohexen- 1-ol (stinky; odor intensity 1).

3.3 Odorous VOCs from Tilia Amurensis Rupr.

The total ion current of Tilia amurensis Rupr. was showed in Figures 3. The corresponding analytical results are shown in Table 7 and Table 8. From table 7, we can note that there were more components in the aromatics, alkanes and alkenes categories than in the others. Components were also found in these categories: aldehydes, alcohols and ethers. Aldehydes have the fewest species, only two species were found in it. The totally species of volatile substances from Tilia amurensis Rupr. were 40. Table 8 shows the key odor compounds from Tilia amurensis Rupr. The compounds, by odor intensity from largest to smallest were 1-methyl-5-1-methylethenyl-cyclohexene (turpentine; odor intensity 3), 3- Identification of Key Odor Compounds from Three Kinds | 107

carene (pine; odor intensity 1), α,α,4-trimethyl-(s)-3-cyclohexene-1-methanol (flower; odor intensity 1), hexanal (grass; odor intensity 1), and 6 unknown compounds that were not detected by GC-MS but were detectable by the human olfactory system. They unknown compounds appeared at 5.70, 9.73, 9.92, 30.27, 30.9, and 32.38 minutes and presented as stinky (odor intensity 3); plastic, stinky (odor intensity 2.5); earthy (odor intensity 2); stinky (odor intensity 2); delightful (odor intensity 1); and aromatic (odor intensity 2).

3.4 The Analysis of Percentage, Odor Intensities and Emerging Times of Different Components

Figure 4 shows the percentage of different components in three kinds of wood species. The percentages of aromatics in Populus ussuriensis Kom, Pinus sylvestris var. mongolica Litv. and Tilia amurensis Rupr. Were 36, 9, and 28 percent, respectively compared with the percentages of odor aromatics, which were 1, 3, and 0 percent, respectively. The percentages of alkenes were 1, 84, and 41 percent, compared with the percentages of odor alkenes, which were 0, 80, and 30 percent, respectively. The percentages of alkanes were 21, <1, and 11 percent, compared with the percentages of key odor alkanes, which were all 0. The percentages of aldehydes were 17, <1, and 4 percent, respectively, compared with the percentages of odor aldehydes, which were 15, close to 0, and 4 percent, respectively, and there 25, <1, and 10 percent in the “other” category, respectively. Meanwhile, the alcohols were about 6 percent in both Pinus sylvestris var. mongolica Litv. and Tilia amurensis Rupr., compared with the percentages of odor alcohols, which were 6 % and 4 % (Fig. 4). In these three wood species, the key odor compounds were alkenes, aldehydes, and alcohols, and the alkanes always had no odor. The percentages of the various odor compounds showed significant differences from the percentages for the total compounds in these three wood species because most compounds in solid wood had no odor or contributed little to the odor. The contribution of a substance to the overall atmos- phere is related to the threshold of the species [15]. Just as in food industry, the compounds which contribute to the overall flavor are <5 percent [16]. Figure 5 shows the times of emergence (the time it takes before the odor be- comes apparent) and the intensities of the various odor compounds in the three wood species. Results showed emergence times focusing around 5 to 12 minutes and 18 to 36 minutes. The odor intensity of VOCs from the wood species did not show a positive correlation with the concentrations, because some compounds (such as butylated hydroxytoluene and 2,2,7,7-tetramethyloctane) found in high concentrations had no characteristic odor or odor intensity. Tables 3 through 5 also show that when concentration decreased, the odor for some key odor compounds disappeared, such as benzene, 1-methyl-21-methylethyl- benzene, α-pinene, copaene, and undecanol. When the concentration from the 108 | Wang, Shao, Cao, Shen compounds fell below certain limits, they were too diluted to smell them. Different woods release compounds with different mass concentrations, so some key odor compounds detected in one wood species may not have key odor characteristics in another tree species.

4 Conclusion

Three wood species were analyzed with GC-MS-O in this experiment. The results showed that the volatile substances of Populus ussuriensis Kom, Pinus sylvestris var. mongolica Litv. And Tilia amurensis Rupr. were 25, 27 and 40 kinds corresponding, with the key odor compounds of alkenes, aldehydes, and alcohols. The key odor compounds from Populus ussuriensis Kom. were hexanal, 2-ethyl-furan. The primary odor compounds from Pinus sylvestris var. mongolica Litv. were α-pinene, 3-carene, toluene, d-limonene, copaene, α4-trimethyl-3-cyclohexene-1-methanol, 1-methyl-5- 1-methylethenyl-cyclohexene, 1-methyl-2-1-methylethyl-benzene, camphene, α- myrcene, 1-methyl-4-1-methylethyl-1,4-cyclohexadiene, benzaldehyde, exo-fenchol, borneol, and 4-methyl-1-1-methylethyl-3-cyclohexen-1-ol. The key odor compounds from Tilia amurensis Rupr. were 1-methyl-5-1-methylethenyl-cyclohexene, 3-carene, hexanal, α,α,4-trimethyl-(s)-3-cyclohexene-1-methanol. At the same time, 7 unknown compounds in Populus ussuriensis Kom. and 6 unknown compounds in Pinus sylvestris var. mongolica Litv.were found, which had clear odor characteristics. The emergence times of odor compounds focused around 5 to 12 minutes and 18 to 36 minutes. The odor intensity of VOCs from the three wood species did not show a positive correlation with the concentrations for most compounds in solid wood had no odor or contributed little to the odor. The aroma of three kinds of wood species are composed of several aroma-active volatile components which can affect the overall flavor for their low threshold.

Identification of Key Odor Compounds from Three Kinds | 109

5 Tables

Tab. 1: Essential parameters of experimental wood species

Number Wood Province Production Size Thickness Density Moisture DBH1/ cm date /mm /mm /g cm-3 content

1 Populus Xiao Hinggan 2015 D=60 14 0.38 11% 42 ussuriensis Mountains, Kom. China 2 Pinus syl- Russia 2015 D=60 14 0.43 10% 38 vestris var. mongolica Litv. 3 Tilia amuren- Russia 2015 D=60 14 0.52 10% 40 sis Rupr. 1DBH: diameter at breast height

Tab. 2: Odor intensity criterion (Japan)

Odor intensity 01 23 45 (grade)

Representation Odorless Barely A little Significant Strong Very strong method detectable sense smell smell smell of smell

Tab. 3: The main components of VOCs emitted from Populus ussuriensis Kom

Category Main components

Aromatics Benzene, Toluene, Butylated Hydroxytoluene, 2-ethyl-Furan Alkenes Dimethyl-Diazene, 2-Butenal, 1-Ethylcyclopropanol, Alkanes Hexamethyl-Cyclotrisiloxane, 2,2,7,7-Tetramethyloctane, Decane, Octamethyl- Cyclotetrasiloxane, 2,2,4,4-Tetramethyloctane, 3,3-dimethyl-Heptane, 4,6- dimethyl-Undecane Aldehydes Pentanal, Hexanal Others 1-Penten-3-one, Dibutyl phthalate

110 | Wang, Shao, Cao, Shen

Tab. 4: Odor compounds of Populus ussuriensis Kom. determined by GC-MS-O

Compounds Retention Time Retention Mass concen- Odor Odor (RT) index(RI) tration/μg·m-3 charac- inten- Identification ter sity method

Aromatics 6.87 2-ethyl-Furan 7.51 687 6.87 Special 1 MS, odor, RI Aldehydes 134.56 Hexanal 11.31 774 134.56 Grass 3 MS, odor, RI Others – Unknown 9.02 726 – Sweet 2 RI, odor Unknown 9.7 740 – Plastic, 2.5 RI, odor Spicy Unknown 20.6 959 – Special 2 RI, odor Unknown 25.03 1068 – Stimulat- 4 RI, odor ing,Burnni ng,plastic, Spicy Unknown 28.82 1178 – Stink 3 RI, odor Unknown 32.88 1305 – Plastic, 2.5 RI, odor Spicy Unknown 34.58 1352 – Plastic 3 RI, odor

Tab. 5: The main components of VOCs emitted from Pinus sylvestris var. mongolica Litv

Category Main components

Aromatics Benzene, Toluene, 1-methyl-2-1-methylethyl-Benzene, 1-methyl-4-1-methylethenyl- Benzene, Decahydro-4,8,8-trimethyl-9-methylene--1,4-Methanoazulene, Octahydro-7- methyl-4-methylene-1-1-methylethyl-Naphthalene, Butylated Hydroxytoluene Alkenes Dimethyl-Diazene, à-Pinene, Camphene, á-Myrcene, 3-Carene, 1-methyl-5-1- methylethenyl-Cyclohexene, D-Limonene, 1-methyl-4-1-methylethyl-1,4- Cyclohexadiene, 1-methyl-4-1-methylethylidene-Cyclohexene, Copaene Alkanes Dimethoxy-Methane, Hexamethyl-Cyclotrisiloxane Aldehydes Benzaldehyde, Furfura Alcohols Exo-Fenchol, Borneol, 4-methyl-1-1-methylethyl-3-Cyclohexen-1-ol, à,à4-trimethyl-3- Cyclohexene-1-methanol, à,à,4-trimethyl-(S)-3-Cyclohexene-1-methanol Others Acetic acid

Identification of Key Odor Compounds from Three Kinds | 111

Tab. 6: Odor compounds of Pinus sylvestris var. mongolica Litv. determined by GC-MS-O

Compounds Retention Time Retention Mass Odor Odor Identification (RT) index(RI) concentra charac- intensi- method tra- ter ty tion/μg·m- 3

Aromatics 397.19 Toluene 10.06 747 40.49 Spicy, 2MS, odor, RI Plastic, Stink 1-methyl-2-1-methylethyl- 22.96 1014 356.70 Aromatic 1 MS, odor, RI Benzene Alkenes 9930.95 à-Pinene 19.41 933 924.94 Turpen- 3MS, odor, RI tine Camphene 19.97 945 47.17 Camphor 1 MS, odor, RI á-Myrcene 21.76 985 75.31 Lipids 1 MS, odor, RI 3-Carene 22.78 1009 6119.43 Pine 3 MS, odor, RI 1-methyl-5-1-methylethenyl- 23.20 1020 8.13 Turpen- 1.5 MS, odor, RI Cyclohexene tine D-Limonene 23.39 1025 2676.50 Lemon 2 MS, odor, RI 1-methyl-4-1-methylethyl- 24.40 1052 43.60 Special 1MS, odor, RI 1,4-Cyclohexadiene stimulat- ing Copaene 35.68 1383 35.87 Burn- 2MS, odor, RI ning, plastic Aldehydes 14.06 Benzaldehyde 19.25 929 14.06 Almond 1MS, odor, RI bitterness Alcohols 708.62 Exo-Fenchol 26.24 1100 121.67 Small 1MS, odor, RI fennel Borneol 27.99 1153 80.85 Camphor 1 MS, odor, RI 4-methyl-1-1-methylethyl-3- 28.40 1165 32.68 Stink 1MS, odor, RI Cyclohexen-1-ol à,à4-trimethyl-3- 28.77 1177 473.42 Flower 2 MS, odor, RI Cyclohexene-1-methanol

112 | Wang, Shao, Cao, Shen

Tab. 7: The main components of VOCs emitted from Tilia amurensis Rupr

Category Main components

Aromatics Benzene, Toluene, 1,3-dimethyl-Benzene, 1-methyl-2-1-methylethyl-Benzene, octahydro-1,7a-dimethyl-5-1-methylethyl-1,2,4-Metheno-1H-indene, 1,2,3,5,6,7,8,8a- octahydro-1,8a-dimethyl-7-1-methylethenyl-Naphthalene, 1,2,3,4,4a,5,6,8a- octahydro-7-methyl-4-methylene-1-(1-methylethyl)- Naphthalene, Butylated Hydroxy- toluene, 1,2,3,5,6,8a-hexahydro-4,7-dimethyl-1-1-methylethyl(1S-cis)-Naphthalene Alkenes Dimethyl-Diazene, 3,6,6-trimethyl-Bicyclo[3.1.1]hept-2-ene, á-Pinene, 3-Carene, 1- methyl-5-1-methylethenyl-Cyclohexene, 1-methyl-4-1-methylethylidene-Cyclohexene, Copaene, à-Calacorene Alkanes Hexamethyl-Cyclotrisiloxane, 2,2-dimethyl-3-methylene-Bicyclo[2.2.1]heptane, 2,2,4,6,6-pentamethyl-Heptane, Decane, Octamethyl-Cyclotetrasiloxane, 2,2,4,4- Tetramethyloctane, 5-Ethyldecane Aldehydes Pentanal, Hexanal Alcohols Undecanol, Z-2-Dodecenol, 1,3,3-trimethyl-(1R-endo)-Bicyclo[2.2.1]heptan-2-ol, à,à,4- trimethyl-(S)-3-Cyclohexene-1-methanol Others Acetic acid, Decyne, 1,2,3,4,4a,7,8,8a-octahydro-1,6-dimethyl-4-(1-methylethyl)-1- Naphthalenol

Tab. 8: Volatile compounds of Tilia amurensis Rupr. determined by GC-MS-O

Compounds Retention Time Retention Mass Odor Odor (RT) index(RI) concen- character inten- Identification tra- sity method tion/μg· m-3

Alkenes 319.18 3-Carene 22.65 1006 271.97 Pine 1 MS, odor, RI 1-methyl-5-1-methylethenyl- 23.32 1023 47.21 Turpen- 3MS, odor, RI Cyclohexene tine Aldehydes 39.79 Hexanal 11.39 775 39.79 Grass 1 MS, odor, RI Alcohols 42.97 à,à,4-trimethyl-(S)-3- 28.75 1176 42.97 Flower 1 MS, odor, RI Cyclohexene-1-methanol Others – Unknown 5.7 607 – Stink 3 RI, odor Unknown 9.73 740 – Plas- 2.5 RI, odor tic,Stink Unknown 9.92 744 – Earthy 2 RI, odor Identification of Key Odor Compounds from Three Kinds | 113

Compounds Retention Time Retention Mass Odor Odor (RT) index(RI) concen- character inten- Identification tra- sity method tion/μg· m-3

Unknown 30.27 1223 – Stink 2 RI, odor Unknown 30.9 1243 – Delightful 1 RI, odor Unknown 32.38 1290 – Aro- 2 RI, odor matic

6 Figures

Fig. 1: GC total ion chromatogram on the volatile components of Populus ussuriensis Kom.

Fig. 2: GC total ion chromatogram on the volatile components of Pinus sylvestris var. mongolica Litv. 114 | Wang, Shao, Cao, Shen

Fig. 3: GC total ion chromatogram on the volatile components of Tilia amurensis Rupr.

Fig. 4: The percentage of different components in three kinds of wood species Identification of Key Odor Compounds from Three Kinds | 115

5.0 Populus ussuriensis Kom. Pinus sylvestris var. mongolica Litv. 4.5 Tilia amurensis Rupr. 4.0

3.5

3.0

2.5

2.0 Indensity

1.5

1.0

0.5

0.0 0 5 10 15 20 25 30 35 40 45 50 Time(min)

Fig. 5: The odor intensities and emerging times of different odor compounds in three kinds of wood species

Acknowledgement: This study was supported by The National Key Research and Development Program of China (2016YFD0600706–2).

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