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11 (
6
); 802-814
doi:
10.1016/j.arabjc.2017.12.031

Systematic characterization of volatile organic components and pyrolyzates from Camellia oleifera seed cake for developing high value-added products

, , , , , , ,
a College of Forestry, Henan Agricultural University, Zhengzhou 450002, Henan, China
b Key Laboratory of Cultivation and Protection for Non-Wood Forest Trees (Ministry of Education), Central South University of Forestry and Technology, Changsha 410117, Hunan, China

⁎Corresponding authors at: College of Forestry, Henan Agricultural University, Zhengzhou 450002, Henan, China (D. Zhang). zhangdangquan@163.com (Dangquan Zhang)

Received: , Accepted: ,
© The Author(s) 2018
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
1 These authors contributed equally to this work.

Abstract

Camellia oleifera seed cake (COSC), a byproduct during oil production of C. oleifera seeds, has been extremely abundant. However, due to the lack of systematic and in-depth analysis about the chemical composition of COSC, it is difficult to develop high value-added products, resulting in low processing efficiency or even directly abandoned. In this paper, the VOCs (Volatile organic components) characteristics of COSC and the variation rule of COSC groups before/after extraction were revealed, and the thermal loss law of COSC and the pyrolyzates characteristics at different temperatures were also explained. The main VOCs of ethanol extractive of COSC are alcohols, those of petroleum ether extractive are alkanes and organic acids, and those of benzene/ethanol extractive are esters. It is first reported here that rich 1,6,10-Dodecatrien-3-ol,3,7,11-trimethyl-, (E)-, namely nerolidol with wide use in cosmetics and biomedicine, exists in COSC extractives. In addition, bioactive VOCs such as β-caryophyllene, humulene and (E)-Atlantone were observed in three COSC extractives. The total content trend from high to low is petroleum ether extractive, ethanol extractive, benzene/ethanol extractive, indicating that petroleum ether extractive has the best developing prospects. The analytic results of FTIR further confirm that: (1) the COSC contains components including Si compounds, ethers, organic acids, esters and alcohols, (2) the four kinds of organic silicon detected are naturally occurring components in COSC, and (3) organic solvent extraction does not make compound groups of COSC significantly changed. There are four obvious stages in thermogravimetry treatment of COSC: the first (30–100 °C), the second (180–240 °C), the third (240–400 °C), and the fourth (400–567 °C), and the order of the mass loss is the third, the second, the fourth and the first. During thermogravimetry treatment, three critical turning points of temperature (240 °C, 400 °C and 567 °C) were observed, accompanied by significantly chemical changes such as macromolecule pyrolyzed into small volatile molecules. The four COSC extractive pyrolyzates at 300 °C, 450 °C, 600 °C and 750 °C have different content variation in the components, such as heterocyclic type with a high-low-high-low change, hydrocarbons and acids shown by the high-low-low-high process, and ketone and the alcohol with a low-high-low-high change. The 450 °C pyrolyzates of COSC residue after extraction are heterocyclic, ketone, phenolic more than esters, hydrocarbons, phosphide, acids, aldehydes, alcohols and acyl; the 600 °C pyrolyzates are heterocyclic, ketone, phenolic more than esters, ammonium, phosphide, acid, aldehydes and alcohols. Here, a large number of new components are produced in the pyrolysis treatment for COSC extractive and residue, providing a new approach for the high-grade application of COSC.

Keywords

Camellia oleifera seed cake (COSC)
Volatile organic component (VOC)
Pyrolyzates
Organic solvent extractive
Component characteristic
1

1 Introduction

Camellia oleifera, an evergreen arbor of Theaceae, is one of important tree-bearing oil plants with a long history of cultivation in China. C. oleifera grows in tropical and subtropical regions of Asia, especially in south-west China (Chen et al., 2010; Sukor et al., 2017). Japan, Myanmar, Vietnam and other countries also have a small amount of distribution. It is regarded as one of the world’s most important tree-bearing edible oil crops, along with oil palm, olive and coconut, and has a quite high value of comprehensive utilization. It is also known as the ‘Oriental olive oil’ because of extremely similar composition to olive oil, with high nutritional value and uses in hygiene applications (Zong et al., 2015; Razali and Said, 2017).

According to the statistics, the cultivation area of C. oleifera is about 5 million hectares in China, and the annual output of C. oleifera seeds is about 202 million tons (Fu, et al., 2015; Ismail and Hanafiah, 2017). At present, China is the largest country producing C. oleifera seed in the world. After pressing of C. oleifera seed, the cake-like residue becomes C. oleifera seed cake (COSC), also known as tea cake, tea meal, etc. COSC is the key by-product of oil production, and the average annual output is about 162 million tons (Fu et al., 2015; Halim et al., 2017). COSC contains tea saponin, protein, polysaccharide and other components, which can be extensively applied to chemical industry, building materials, agriculture, aquaculture, pharmaceutical and healthcare industries, and so forth (Sulaiman et al., 2015; Kijprayoon et al., 2014; Chen et al., 2010). In addition, tea saponin can be extracted from COSC (Liu et al., 2016; Shamsudin et al., 2017), or polishing powder and compound feed are produced using COSC. The comprehensive benefits of COSC processing can also be greatly improved through comprehensive utilization. In some studies, it has been shown that COSC has the total energy of 19,600 kJ/kg, contains crude protein 15.94%, mineral 3.37%, crude fat 6.64%, soluble sugar 4.3%, polysaccharide 26.09%, saponin 12.8%. Therefore, COSC is worthy of development and utilization of protein feed. At present, the researches on COSC have been mainly focused on the antibacterial, antioxidant and antitumor activities of the biologically active components such tea saponin, polysaccharide, conjugated linoleic acids (CLAs), etc. (Sulaiman et al., 2015; Zong et al., 2016; Guo et al., 2016; Chen et al., 2013; Li et al., 2014; Zhang et al., 2014).

However, few studies exist with regard to the composition analysis of volatile organic components (VOCs) from COSC extractives by different organic solvents and from COSC residues after extraction. Here, the VOCs of COSC extractives by solvents (ethanol, benzene/ethanol and petroleum ether) were detected by gas chromatography/mass spectrometry (GC/MS), and their residues were analyzed by Fourier transform infrared spectroscopy (FTIR), moreover, COSC was analyzed by thermogravimetry (TG), its extractives and residues were further determined using pyrolysis-GC/MS (Py-GC/MS) at different temperatures. The systematic characterization of VOCs and pyrolyzates may lay a foundation for the high value-added application of COSC.

2

2 Materials and methods

2.1

2.1 Materials and reagents

COSC samples were provided by Hunan Institute of Food Quality Supervision and Research, China. After dried at 40 °C, COSC samples were smashed into powder using FZ102 Disintegrator suitable for plant (TanjingTaisite Ins. Corp., China), in succession, 200 mesh powders were sieved out via AS200 Sieving Instrument (USA). All reagents were purchased from the Sigma Chemical Company (USA) unless noted otherwise.

2.2

2.2 Methods

2.2.1

2.2.1 COSC extraction by three solvents

COSC samples were extracted with solvents (ethanol, benzene/ethanol (2:1) and petroleum ether) under reflux for 5 h, respectively, and then filtrated fast with filter paper immersed in the same solvents for 24 h. The filtrated extractives were evaporated at 45 °C under a vacuum of 0.01 MPa then concentrated to 20 mL, finally transferred to a sealed reagent bottle. The extracted residues were dried at 50 °C. Both the concentrated extractives and the residues were kept at 4 °C for the following determination.

2.2.2

2.2.2 VOCs analysis by GC/MS

1.0 mL concentrated extractives were aspirated into a 1.5 mL centrifuge tube, mixed with an appropriate amount of anhydrous sodium sulfate at room temperature for 2 h, then centrifuged at 1200 rpm for 2 min, and 700 μL of supernatant was removed into the reagent bottle to be detected by GC/MS. GC temperature program consisted of start temperature at 50 °C held for 1 min, followed by a temperature ramp of 5 °C min−1 to 150 °C held for 10 min, then 8 °C min−1 to 250 °C held for 2 min, while the volatiles of the extractive (1 μL) were released in a split mode (ratio of 1:10) to a capillary column (30 m × 250 μm × 0.25 μm); the carrier gas was high purity He (99.999%), with a column pressure 57.4 kPa; vaporization chamber temperature was 280 °C. The program of MS was scanned over the 35–600 AMU (m/z), with an ionizing voltage of 70 eV and an ionization current of 150 µA of electron ionization (EI). The flow velocity of helium was 1.2 mL/min. Ion source temperature was 230 °C, and quadropole temperature was 200 °C (Liu et al., 2017a,b; Prasadani et al., 2017; Rahman et al., 2017).

2.2.3

2.2.3 COSC and extracted residue analysis by FTIR

Fourier transform infrared spectroscopy (FTIR) is widely applied in the identification of chemical bond and functional groups of various compounds (Suksuwan et al., 2015; Savchenko et al., 2017; Khan et al., 2017). COSC samples and its three kinds of extracted residues were dried at 100 °C for 4 h, in succession, put them in the dry container with desiccant to prevent moisture absorption, which will reduce adverse influence on posterior FTIR. A certain amount of potassium bromide was ground and sieved out using AS200 Sieving Instrument (USA), put in the dry pot, then kept in the muffle furnace (with SX-2.5-10 box-type control resistance furnace control box) at 150 °C for 5 h, finally, covered by a heating lamp. 0.5–2 mg of the sample was mixed with 200 mg potassium bromide fast and completely in the mortar with a smooth surface, and then tableted in the tablet press. The pressed sample was tested in a FTIR (SHIMADZU, IRAffinity-1) from 4000 cm−1 to 400 cm−1.

2.2.4

2.2.4 COSC thermostability by TG

Thermogravimetric analysis (TGA) was conducted using a thermogravimetric analyzer (TGA Q50 V20.8 Build 34, USA) with a sensitivity of 0.01 μg, using empty crucible clamp as a reference. Furnace temperature ranges from 30 °C to 600 °C. An accurate mass of COSC sample (6606.00 μg) was placed in a TG crucible. The temperature program of TGA started at 30 °C, and increased to 600 °C at 10 °C/min. The carrier gas was high purity nitrogen, with a flow rate of 40 mL/min.

2.2.5

2.2.5 Extractives and residues analysis by Py-GC/MS

Using pyrolysis apparatus PY-2020iS (Frontier Co., Ltd, Japan), 0.2μL extractives were separately pyrolyzed at 300 °C, 450 °C, 600 °C and 750 °C in helium atmosphere, and 0.1 mg residues were separately pyrolyzed at 450 °C and 750 °C, then the pyrolyzed products (pyrolyzates) were analyzed by online linked GC/MS. The GC/MS analysis was carried out on the Agilent5975C/6890N (Agilent Corp., USA), which was linked to a mass selective detector. An elastic quartz capillary column DB-5MS (30 m × 0.25 mm × 0.25 µm) coated with a neutral phase (Agilent Corp., USA) was used. The carrier gas was helium and the injection port temperature was 250 °C. The temperature program of GC began at 50 °C and increased at 10 °C/min until 300 °C, followed by a split injection at ratio of 30:1. The program of MS was scanned over the 35–550 AMU (m/z), with an ionizing voltage of 70 eV and an ionization current of 150 µA of electron ionization (EI). The flow velocity of helium was 1.0 mL/min (He et al., 2011; Ghafar et al., 2017; Aziz and Hanafiah, 2017).

3

3 Results and analysis

3.1

3.1 VOCs characteristics of COSC extractives

It can be observed that 24, 21 and 20 VOCs were detected from three COSC extractives by solvents (ethanol, petroleum ether, benzene/ethanol (2:1)) (Fig. 1, Table 1), respectively. The main VOCs of ethanol extractive are alcohols, and those of petroleum ether extractive are alkanes and organic acids, however, the esters were mainly detected in VOCs of benzene/ethanol extractive.

A, B and C are GC/MS ion chromatograms of VOCs from COSC extractives by ethanol, Petroleum ether and benzene/ethanol, respectively.
Fig. 1 A, B and C are GC/MS ion chromatograms of VOCs from COSC extractives by ethanol, Petroleum ether and benzene/ethanol, respectively.
Table 1 VOCs of three COSC extractives.
No. Component names Relative content (%)
Ethanol Petroleum ether Phenyl/ethanol
1 2-Ethylhexyl chloroformate – 1.08 –
2 2-Decene, 6-methyl-, (Z)- – 4.73 –
3 Cyclopropane, octyl- – 1.2 –
4 2,3-Butanediol 0.18 – –
5 1-Undecene, 5-methyl- – 0.6 –
6 1-Dodecene – 0.35 –
7 Hexanoic acid – 0.37 –
8 2,4-Hexadiyne – – 0.26
9 Cyclohexane, 1-(1,1-dimethylethyl)-4-methyl- – 0.29 –
10 Tetraethyl silicate 0.55 – –
11 2,4,6-Cycloheptatrien-1-one, 4-methyl- 0.43 – 0.80
12 1,7-Octadien-3-ol, 2,6-dimethyl- – 0.43 –
13 Linalool 0.18 – –
14 Nonanal 0.31 – –
15 Octanoic acid – 0.37 –
16 Pyridine, 2-nitro- – – 0.28
17 Nonanoic acid – 0.48 –
18 Benzene, cyclohexyl- – – 0.31
19 2,6-Dimethoxyphenol 0.45 – 0.48
20 Cyclohexane, 1,1′-methylenebis- – 0.4 –
21 (1,4-Dimethylpent-2-enyl) benzene – – 0.54
22 β-Caryophyllene 0.89 1.16 1.10
23 Humulene 0.29 0.36 0.35
24 d-Glycero-d-ido-heptose 0.26
25 Decane, 5-ethyl-5-methyl- – – 0.24
26 1,6,10-Dodecatrien-3-ol, 3,7,11-trimethyl-, (E)- 7.54 13.53 8.12
27 Caryophyllene oxide – 0.32 –
28 d-Glycero-d-ido-heptose 0.30 – –
29 Cyclooctasiloxane, hexadecamethyl- 4.15 – 3.82
30 Spiro [2.2] pentane-1-carboxylic acid, 2-cyclopropyl-2-methyl- – – 0.26
31 Methoxyacetic acid, 2-tridecyl ester 0.26
32 Heptadecane – – 0.36
33 (E)-Atlantone 1.39 1.61 0.92
34 Octadecane, 6-methyl- 0.35 – 0.37
35 Methoxyacetic acid, 4-tridecyl ester 0.33 – –
36 Cyclononasiloxane,octadecamethyl- 5.09 0.81 3.95
37 1,2-Benzenedicarboxylic acid, bis(2-methylpropyl) ester – – 0.60
38 Dibutyl phthalate – – 1.63
39 Phthalic acid, butyl dodecyl ester 2.81 – –
40 n-Hexadecanoic acid – 2.64 –
41 Cyclodecasiloxane, eicosamethyl- 4.53 – 3.35
42 Hexadecanoic acid, ethyl ester 0.21 – –
43 1-Hexadecanol, 2-methyl- 0.41 – –
44 tert-Hexadecanethiol 0.38 – –
45 cis-Vaccenic acid – 5.66 –
46 Oleic Acid 0.41 – –
47 Naphthalene, 2,7-bis(1,1-dimethylethyl)- – 0.56 –
48 Octasiloxane, 1,1,3,3,5,5,7,7,9,9,11,11, 13,13,15,15-Hexadecamethyl- 3.27 0.61 2.95

All the three extractives have the same peak with large relative area in GC/MS chromatograms of VOCs from COSC extractives (Fig. 1). The rich component is 1,6,10-Dodecatrien-3-ol,3,7,11-trimethyl-, (E)- (formula C15H26O), namely nerolidol, with the relative contents 7.54%, 13.53% and 8.12% (Table 1), respectively. Compared with extractions by ethanol and benzene/ethanol, the nerolidol is also inclined to petroleum ether extraction. The usage of nerolidol is widespread across different industries, such as in cosmetics (e.g. shampoos and perfumes) and in non-cosmetic products (e.g. detergents and cleansers). In fact, US Food and Drug Administration (FDA) has also permitted the use of nerolidol as a food flavoring agent (Chan et al., 2016). Moreover, the trans-nerolidol can improve the anti-proliferative effect of doxorubicin in intestinal cancer cell lines (Hanusova et al., 2017; Basheer et al., 2017). It is suggested that the rich nerolidol in the three COSC extractives could be developed into high value-added products such as cosmetic ingredient, food flavoring agent and anticancer adjuvant.

Several Si compounds were detected in three COSC extractives. Cyclononasiloxane, octadecamethyl- and Octasiloxane, 1,1,3,3,5,5,7,7,9,9,11,11,13,13,15,15-hexadecamethyl- are both present in VOCs of the three COSC extractives. The former content in extractives by ethanol, petroleum ester and benzene/ethanolis 5.09%, 0.81% and 3.95%, and the latter is 3.27%, 0.61% and 2.95%. While Cyclooctasiloxane, hexadecamethyl- (4.15%, 3.82%) and Cyclodecasiloxane, eicosamethyl- (4.53%, 3.35%) were only detected in the COSC extractives by ethanol and benzene/ethanol. Some reports showed that Cyclononasiloxane, octadecamethyl- has antibacterial activity (Ahsan et al., 2017; Musthafa et al., 2013; Hassan et al., 2017).

In addition, β-Caryophyllene (0.89%, 1.16% and 1.10%), Humulene (0.29%, 0.36% and 0.35%) and (E)-Atlantone (1.39%, 1.61% and 0.92%) were present in COSC extractives by ethanol, petroleum ether and benzene/ethanol. β-Caryophyllene has moderate antibacterial activity and strong antifungal activity from data prepared by Rungquet al. (2016). According to Darshanee et al. (2017), β-Caryophyllene is isomer with Humulene, which can attract some whiteflies. Humulene also has a significant antiproliferative effect on various cancer cell lines (Ambroz et al., 2017). (E)-Atlantone has antioxidant potentials (Chaudhary et al., 2015), anticonvulsant properties (Orellana-Paucar et al., 2013) and antifungal activity (Chaudhary et al., 2012; Halim et al., 2017).

2-Decene, 6-methyl-, (Z)- (4.73%), Caryophyllene oxide (0.32%), n-Hexadecanoic acid (2.64%), cis-Vaccenic acid (5.66%) and Naphthalene,2,7-bis(1,1-dimethylethyl)- (0.56%) were detected only in COSC extractive by petroleum ether. Caryophyllene oxide has a significant antiproliferative effect on various cancer cell lines (Ambroz et al., 2017), and also has antinociceptive activity, which is probably related to central and peripheral analgesia, along with anti-inflammatory activity (Chavan et al., 2010). In addition, Caryophyllene oxide presents a strong antinociceptive effect (de Oliveira et al., 2017). Hexadecanoic acid is also a bioactive compound (Anisha and Radhakrishnan, 2017). Djousse et al. (2014) reported cis-vaccenic acid may be associated with a lower risk of HF with antecedent CHD, and can reduce unsaturated fatty acids toxicity in certain situation according to Sec (2015).

1,2-Benzenedicarboxylic acid, bis(2-methylpropyl) ester (0.60%) and Dibutyl phthalate (1.63%) were only detected in COSC extractive by benzene/ethanol. They are the isomers, while researches most focused on Dibutyl phthalate (DBP), a kind of plasticizer, which is often present in consumer products and the coating of some oral medications, but has some negative effects (Rasmussen et al., 2017; Lara et al., 2017). It can be suggested that COSC may be contaminated by DBP-containing packing during Camellia oil production, therefore, pollution-free production should be adopted to achieve DBP-free Camellia oil and COSC.

Hexadecanoic acid, ethyl ester (0.21%), tert-Hexadecanethiol (0.38%) and Oleic Acid (0.41%) were only detected in ethanol extractive from COSC. Hexadecanoic acid, ethyl ester is either a nature compound in the COSC or n-Hexadecanoic acid of COSC reacted with ethanol, because of n-Hexadecanoic acid (2.64%) only found in COSC extractive by petroleum ether. De Assis Lage (2015) and Musa (2015) discovered that hexadecanoic acid, ethyl ester has also antimicrobial activity. The last beneficial component was Oleic acid which is correlated with the prevention and therapy for many diseases (Trevisan et al., 1990; Kris-Etherton et al., 1999).

The beneficial VOCs such as β-Caryophyllene, Humulene, Caryophyllene oxide, Hexadecanoic acid ethyl ester were detected in COSC extractives, while their contents are relatively less. Especially, Caryophyllene can be used as raw material of natural antibacterial agents, food spices.

3.2

3.2 Chemical group changes of COSC and residues

The FTIR absorption peaks mainly occurred between 1800 cm−1 and 800 cm−1 in the range from 4000 cm−1 to 400 cm−1, while minor trend changes of the FTIR absorption peaks were observed between COSC and the extracted residues (Fig. 2). There is a strong absorption peak near 600 cm−1 (Fig. 2A), indicating that there is the C—Cl or C—Br bond. Thisis consistent with the GC/MS compound: 2-Ethylhexyl chloroformate.

A, B, C and D are Infrared spectra of COSC and its three extractives by ethanol, petroleum ether and benzene/ethanol, respectively.
Fig. 2 A, B, C and D are Infrared spectra of COSC and its three extractives by ethanol, petroleum ether and benzene/ethanol, respectively.

The peak at 1742 cm−1 corresponds to the C⚌O bond of the aldehyde compounds. Two other peaks are two elementary contributions attributed to the —COO− compounds and R—NO2, RN⚌O bonds (at 1549 cm−1 and 1518 cm−1, respectively). Two peaks at 1660 cm−1 (C⚌C bonds) and 1602 cm−1 (O—H bending bands) are overlapped (Prasadani et al., 2017; Cruz et al., 2015; Savchenko et al., 2017).

The absorption peak at 1255 cm−1 indicates that Si—CH3 bonds are present. There are overlapped peaks of Si—O—Si at 1154 cm−1 and 1058 cm−1(Liu et al., 2017). There are three absorption peaks at 3336 cm−1, 2390 cm−1 and 2846 cm−1, the first two absorption peaks are caused by O—H stretching, and the peak at 2846 cm−1 also corresponds to C⚌O stretching vibration of the aldehyde compounds, and the latter two are overlapped peaks. The peak at 778 cm−1 is of nitrogen heterocyclic compounds.

In contrast to COSC, the absorption peak at 1742 cm−1 disappears in ethanol extractive and benzene/ethanol extractive, and the peaks at 1518 cm−1 and 1380 cm−1 can’t also been observed obviously in ethanol extractive except for the overlap peaks at 2864 cm−1 not found in three extractives by ethanol, petroleum ether and benzene/ethanol, and the peak at 1154 cm−1 also disappears in petroleum ether extractive and benzene/ethanol extractive, indicating that some aldehydes and nitrogen compounds have been extracted by the three organic solvents.

The groups in the chemical structure of VOCs detected by GC/MS are consistent with the result of FTIR, further indicating that the COSC contains organic silicon, ethers, organic acids, esters and alcohols, etc. In addition, it can be concluded that organic solvent extraction does not make compound groups of COSC significantly changed.

3.3

3.3 Volatility characteristics of COSC

There are four obvious stages of mass loss for COSC during 30–600 °C TG analysis (Fig. 3). The loss of the first stage is from the initial temperature of 30 °C to 100 °C, with the quality of 6341.61 μg at 100 °C, and this part of the mass loss should be the evaporation of water and a small amount of volatile matter freed. The second stage starts at 180 °C until the mass reduces to 5902.15 μg at 240 °C, with a slight mass loss (6.92%), which should be caused by further shrinkage between the molecules or by pyrolysis of some macromolecules into small molecules with better volatility. The mass in the third stage from 240 °C to 400 °C reduces significantly to 2640.99 μg, with the loss of 55.25%. During 30–600 °CTG treatment, there is an obvious peak observed in the corresponding DTG curve, and reaches its maximum at 342 °C, showing that the rate of COSC mass loss is the fastest in this temperature range. The fourth stage begins with a gentle mass loss period from 400 °C until the pyrolysis of COSC finishes basically at 567 °C, and the mass reduces to 2048.74 μg, with the loss of 22.43%. According to DTG curve, the rate of mass loss is ranged: third stage, second stage, fourth stage and first stage, moreover, there are three critical temperature turning points during TG treatment. At the three temperature points, the COSC mass changes significantly, which may be caused by significant chemical changes, such as pyrolysis of macromolecules into small molecules. Therefore, these temperature points can provide a theoretical basis for heating treatment of COSC.

Thermogravimetric curve of COSC.
Fig. 3 Thermogravimetric curve of COSC.

3.4

3.4 Component characteristics of pyrolyzates from extractives and residues

3.4.1

3.4.1 Component characteristics of extractive pyrolyzates

There were 31, 42, 47 and 85 peaks detected in the pyrolyzates of COSC extractives at 300 °C, 450 °C, 600 °C and 750 °C (Tables 2 and 3). 28 compounds (99.64% of the total peak area), 34 compounds (99.17% of the total peak area), 37 compounds (99.31% of the total peak area) and 80 compounds (97.88% of the total peak area) were identified, respectively.

Table 2 Component types of four pyrolyzates from COSC extractives.
No. Components Relative content (%)
300 °C 450 °C 600 °C 750 °C
1 Heterocycles 17.89 3.7 31.48 18.43
2 Hydrocarbons 16.62 10.33 6.55 20.34
3 Ketones 12.46 32.56 16.14 21.83
4 Alcohols 13.69 20.49 13.51 16.53
5 Acid 12.22 4.09 6.13 8.56
6 Esters 15.77 16.61 11.01 6.89
7 Aldehydes 9.27 4.21 12.34 –
8 Phenols 2.03 – – 2
9 Acyl – 4.89 – 1.5
10 Ammonium – 3.03 1.41 –
11 Ether – – – 3.09
12 Nitrile – – 1.41 –

The component content is quite different in the pyrolyzates of the COSC extractives at 300 °C, 450 °C, 600 °C and 750 °C (Tables 2 and 3). At 300 °C, the contents of ester, hydrocarbon, ketone, acid and heterocyclic are more than those of aldehydes and phenols; at 450 °C, the contents of ester, ketone and alcohol are more than those of heterocyclic, acid, aldehydes, acyls and ammonium; at 600 °C, the contents of heterocyclic, ketone, alcohol, aldehydes and ester are more than those of hydrocarbon, acid, ammonium and nitrile; at 750 °C, the contents of heterocyclic, hydrocarbon, ketone and alcohol are more than those of acid, ester, phenol, acyl and ether.

Table 3 Components of four COSC extractive pyrolyzates.
No. Component names Area (%)
300 °C 450 °C 600 °C 750 °C
1 1,4-Dimethyl-1,2,3,4-tetrahydronaphthalene 1.65 1.02 2.67 –
2 Benzene, ethyl-1,2,4-trimethyl- 3.96 – – –
3 Naphthalene, 1,2,3,4-tetrahydro-2,5,8-trimethyl- 2.57 – – –
4 Naphthalene, 1,2,3,5,6,7,8,8a-octahydro-1,8a-dimethyl-7-(1-methyletheny) 2.76 – – –
5 Bicyclo 7.2.0 undec-4-ene, 4,11,11-trimethyl-8-methylene- 2.27 – – –
6 Tridecane, 2,2,4,10,12,12-hexamethyl-7-(3,5,5-trimethylhexyl)- 1.79 – – –
7 3′,5′-Dimethoxyacetophenone 7.87 – – –
8 Benzothiazole, 2-(methylthio)- 2.53 1.11 2.91 –
9 2,8-Dimethyl-2,3,4,5,6,7-hexahydro-1 h-2-benzazonine 2.15 – 1.94 –
10 1-Dotriacontanol 1.92 1.27 3.01 10.27
11 Methyl 8-3-oxo-2-(pent-2-en-1- yl)cyclopent-1-enyl oct-6-ynoate 2.29 – – –
12 Tetradecanoic acid, 12-methyl-, (s)- 2.3 – – –
13 Bis(2-methoxyethyl) phthalate 6.60 – 4.11 –
14 Cholest-4-en-3-one, 26-hydroxy- 2.41 – – –
15 Hexadecanoic acid 6.35 4.09 4.84 5.12
16 13-Docosenoic acid, methyl ester, (z)- 2.43 1.86 – –
17 9-Octadecenal, (z)- 9.27 4.21 9.64 –
18 (z)14-Tricosenyl formate 3.57 – – –
19 Dodecane, 1-fluoro- 2.03 – 4.49 5.66
20 9-Hexadecenoic acid, eicosyl ester, (z)- 2.17 – – –
21 2-Pyrrolidinone, 1-(9-octadecenyl)- 2.18 – – –
22 Bis(2-ethylhexyl) phthalate 2.31 – – –
23 Squalene 12.8 3.31 2.06 –
24 .gamma.-tocopherol 2.03 – – –
25 Cholesterol 2.31 – – –
26 Ergosta-5,22-dien-3-ol, (3.beta.,22e)- 2.67 3.35 1.99 –
27 Ergost-5-en-3-ol, (3. beta.)- 2.87 2.43 2.31 –
28 .gamma.-sitosterol 3.92 3.6 4.81 –
29 Propanamide, n-methyl- – 1.02 – –
30 2-Cyclohexen-1-one, 4,4,6-trimethyl- – 1.00 – 0.7
31 3′,5′-Dimethoxyacetophenone – 2.85 10.61 2.73
32 3,7,11,15-Tetramethyl-2-hexadecen-1-ol – 1.25 – 0.83
33 2(1h)-Benzocyclooctenone, decahydro-10a-methyl-, trans- – 2.00 – 4.4
34 10,13-Octadecadienoic acid, methyl ester – 1.55 – –
35 9-Octadecenoic acid (z)-, methyl ester – 2.45 – 3.63
36 Z, z-6,28-heptatriactontadien-2-one – 17.28 2.48 11.48
37 Undecane 3-cyclohexyl-, 3-cyclohexyl- – 2.58 1.67 1.39
38 Z-25-Tetratriaconten-2-one – 2.14 – –
39 (z)-6-Pentadecen-1-ol – 7.31 – 2.09
40 Methanone, dicyclohexyl- – 3.45 – –
41 Tetracontane, 3,5,24-trimethyl- – 2.87 – –
42 2-Nonenoic acid, methyl ester – 1.87 – –
43 7-Decen-2-one – 2.4 – –
44 Cetrimonium bromide – 3.03 – –
45 Didodecyl phthalate – 1.72 1.84 –
46 9-Octadecenoic acid (z)-, 2-hydroxy-1-(hydroxymethyl)ethyl ester – 1.86 – –
47 Z-28-Heptatriaconten-2-one – 1.44 – –
48 Tritetracontane – 1.57 – 2.26
49 Ergosta-4,6,22-triene – 1.57 – –
50 Stigmastan-3-ol, 5-chloro-, acetate, (3. beta, 5 alpha) – 5.30 – 1.54
51 Cholest-5-en-3-ol (3. beta.)-, carbonochloridate – 3.87 – 0.81
52 Vitamin e – 1.28 – –
53 3-Furaldehyde – – 1.29 –
54 Valproic acid – – 1.29 –
55 Cyclohexanone, 4-ethoxy- – – 1.45 –
56 Benzenepropanenitrile – – 1.41 –
57 5-Methyl-2-thiophenecarboxaldehyde – – 1.41 –
58 Benzaldehyde, 2-hydroxy-, oxime – – 2.35 –
59 Benzene, bis(1-methylethyl)- – – 1.34 –
60 Oxiranecarboxylic acid, 3-ethyl-3-phenyl-, ethyl ester,trans – – 1.5 –
61 Benzene, 1-ethyl-3-(1-methylethyl)- – – 2.57 –
62 Naphthalene, 1,2,3,4-tetrahydro-1,4,6-trimethyl- – – 2.8 –
63 Naphthalene, 1,2,3,5,6,7,8,8a-octahydro-1,8a-dimethyl-7-(1-methyletheny) – – 3.02 –
64 Bicyclo 7.2.0 undec-4-ene, 4,11,11-trimethyl-8-methylene- – – 2.05 –
65 2,4,5-Trimethoxyamphetamine – – 1.41 –
66 24-Noroleana-4(23),12-diene, 3-methyl-, (3 alepha)- – – 3.22 –
67 1,2,3,3a,4a,5,6,7,8,9,9a,9b-Dodecahydrocyclopenta def phenanthrene – – 2.03 –
68 2-Phenanthrenol, 4b,5,6,7,8,8a,9,10-octahydro-4b,8,8-Trimethyl-1- (methy) – – 1.39 –
69 Bicyclohexyl, 4-phenyl- – – 1.3 –
70 Tetradecanoic acid, 10,13-dimethyl-, methyl ester – – 1.31 –
71 1,3,6,10-Cyclotetradecatetraene, 3,7,11-trimethyl-14-(1-methylethyl) -, s – – 1.61 –
72 4-Octadecenoic acid, methyl ester – – 2.25 –
73 Z-24-Tritriaconten-2-one – – 1.6 1.28
74 Cycloheptene – – – 1.02
75 Cycloheptene, 5-bromo- – – – 0.86
76 4,5-Nonadiene – – – 0.85
77 Benzene, 1,1′- oxybis(methylene) bis- – – – 3.09
78 Cyclopentane, 1,2,3-trimethyl- – – – 1.76
79 Cyclopentane, 1-ethyl-3-methyl- – – – 0.7
80 Bicyclo 4.1.0 heptan-2-one – – – 0.75
81 P-xylene – – – 2.01
82 Cyclopentane, 2-ethyl-1,1-dimethyl- – – – 1.26
83 2-Norcaranone, 3-methyl- – – – 1.24
84 Benzene, propyl- – – – 0.7
85 1,5-Cyclododecadiene, (e,z)- – – – 0.69
86 1 h-Indene, 1-chloro-2,3-dihydro- – – – 0.75
87 Benzene, butyl- – – – 0.62
88 Cyclopropane, 1-butyl-1-methyl-2-propyl- – – – 5.68
89 Bicyclo 4.1.0 heptane, 2-methyl- – – – 1.38
90 Cyclopentylphenylmethanol – – – 0.64
91 Phenol, 2-methoxy-4-methyl- – – – 0.61
92 1,3,5,8-Undecatetraene – – – 0.91
93 2,4-Dodecadiene, (e,z)- – – – 1.44
94 Naphthalene – – – 0.62
95 Cyclododecene, (e)- – – – 1.6
96 Ethinamate – – – 0.69
97 Phenol, 2,6-dimethoxy- – – – 0.69
98 10,13-Octadecadiynoic acid, methyl ester – – – 0.7
99 Benzene, 1-cyclohexyl-3-methyl- – – – 0.67
100 Oleic acid – – – 1.65
101 5-Heptadecene, 1-bromo- – – – 0.63
102 (r)-(-)-(z)-14-Methyl-8-hexadecen-1-ol – – – 1.62
103 Cyclopropane, 1-methyl-1-(2-methylpropyl)-2-nonyl – – – 0.69
104 Cyclohexane, undecyl- – – – 0.85
105 7-Tetradecyne – – – 1.39
106 Cyclopropanenonanoic acid, 2- (2-butylcyclopropyl) methyl-,methyl- – – – 1.02
107 2-Naphthalenol, decahydro- – – – 0.7
108 Octadecanoic acid, 2-propenyl ester – – – 1.79
109 Cyclopentane, 1,1′- 3-(2-cyclopentylethylidene)-1,5-pentanediyl bis- – – – 1.55
110 1,3-Dioxolane, 4-ethyl-5-octyl-2,2-bis(trifluoromethyl)-,trans- – – – 0.83
111 2,6,10-Dodecatrien-1-ol, 3,7,11-trimethyl,(e,e)- – – – 1.08

The COSC extractive pyrolyzates at 300 °C, 450 °C, 600 °C and 750 °C shows a distinct difference between the relative contents of the main components, such as heterocyclic type with a high-low-high-low change, hydrocarbons and acids shown by the high-low-low-high change, and ketone and alcohol with a low-high-low-high change. There are also some types of components that are not included the existing types. There are quite differences among properties and functions of the components such as hydrocarbons, ethers, esters, acids, alcohols and phenols, aldehydes and heterocycles. Therefore, it is also significantly different among the pyrolyzates’ function of four COSC extractives. A number of beneficial substances, such as squalene with hypocholesterolemic effect (Hien et al., 2017), gamma-tocopherol reducing sputum eosinophilia according to Burbank et al. (2017), and Gamma.-sitosterol (Balamurugan et al., 2015), are detected in four pyrolyzates. It is suggested that the gradient temperature pyrolysis can broaden application range of COSC extractives, providing a scientific basis for developing of high value-added products.

3.4.2

3.4.2 Component characteristics of residue pyrolyzates

There are 48 and 45 peaks in the COSC residue pyrolyzates at 450 °C and 600 °C, then 44 compounds (96.84% of the total peak area) and 41 compounds (97.12% of the total peak area) are identified.

The contents are quite different among component types in COSC residue pyrolyzates at 450 °C and 600 °C (Tables 4 and 5). At 450 °C, the contents of heterocyclic, ketone, phenolic are more than those of esters, hydrocarbons, phosphide, acids, aldehydes, alcohols and acyl; at 600 °C, the contents of heterocyclic, ketone, phenolic are more than those of esters, ammonium, phosphide, acid, aldehydes and alcohols. The content changes in types of components of extractive pyrolyzates at 300 °C and 450 °C are distinctly different. Some types of components decrease in content, such as ester, ketone, aldehyde and acyl; some keep the similar content, such as heterocyclic, phosphide; some show an increased trend, such as phenol, acid, alcohol.

Table 4 Types comparison of components of two COSC residue pyrolyzates.
No. Components Relative content/%
450 °C 600 °C
1 Eester 8.69 6.04
2 Heterocycles 39.03 38.73
3 Ketones 24.93 12.22
4 Hydrocarbons 1.26 –
5 Phenols 12.05 15.67
6 Ammonium – 3.96
7 Phosphide 2.07 2.04
8 Acid 2.6 5.67
9 Aldehydes 3.41 1.8
10 Alcohols 3.04 6.77
11 Acyl 2.87 1.28
12 Ethers – 5.81
Table 5 Components of COSC extractive pyrolyzates at 450 °C and 600 °C.
No. Component names Area (%)
450 °C 600 °C
1 2-Propenoic acid, phenyl ester 1.61 2.14
2 Pyridine 2.42 2.52
3 Cyclopentene, 3-ethyl- 3.67 –
4 Toluene 6.63 –
5 2-Pyrrolidinone, 5-(cyclohexylmethyl)- 1.35 –
6 Pyrimidine, 5-methyl- 1.34 –
7 2-Cyclohexen-1-one, 4,4,6-trimethyl- 2.42 –
8 1 h-Pyrrole, 3-methyl- 6.06 7.78
9 1,1′-Bicyclohexyl -2-one 1.84 –
10 1,3,5,7-Cyclooctatetraene 1.53 –
11 Cyclopropane, 2-(1,1-dimethyl-2-pentenyl)-1,1-dimethyl- 1.26 –
12 4-Hydroxybut-2-enoic acid lactone 1.45 –
13 1 h-Pyrrole, 2,3-dimethyl- 1.44 –
14 Piracetam 1.32 –
15 2-(2-Oxopropyl)furan-3-carboxaldehyde 1.7 1.39
16 Bicyclo 4.1.0 heptan-2-one 1.15 –
17 Carbonic acid, butyl phenyl ester 1.34 –
18 Propanoic acid, 2,2-dimethyl-, phenyl ester 1.61 –
19 1,3-Cyclopentanedione, 2-methyl- 1.41 –
20 Phenol, 4-methyl- 3.47 –
21 Benzoic acid, 3,5-dimethyl-, (2,4-dimethyl)methyl ester 1.43 –
22 Benzene, 1-isocyano-4-methyl- 1.44 –
23 4,5-Dihydropyrrole-5-one-2-propionamide 1.52 –
24 2-Propanone, o- (phenylamino)carbonyl oxme 1.7 –
25 1-Naphthalenol, 1,2,3,4-tetrahydro- 2.05 –
26 Phenol, 4-ethyl-2-methoxy- 1.7 –
27 3,6-bis(Benzyl)-tetrazine 3.76 1.82
28 Ethanone, 1-(2-hydroxy-5-methylphenyl)- 1.96 –
29 Phenol, 3,4-dimethoxy- 2.76 –
30 1 h-Indole, 4-methyl- 2.43 2.89
31 Phenol, 2-methoxy-4-(1-propenyl)- 2.07 –
32 2 h-Pyrido 1,2-f 1,6 diazacyclooctadecin-11(6h)-one,10-(3-aminopropyl)o 1.77 –
33 Benzene, 1,2,3-trimethoxy-5-methyl- 2.34 2.03
34 3′,5′-Dimethoxyacetophenone 8.68 6.74
35 Diphosphine, tetramethyl-, 1,2-disulfide 2.07 2.04
36 Cyclohexanone, 5-methyl-2-(1-methylethyl)-,cis- 1.78 –
37 Cyclobuta 1,2-d:4,3-d' dipyrimidine-2,4,5,7(3h,6h)-tetrone,hexahydro-1,3,4 2.47 –
38 Oleic acid 2.6 1.91
39 9-Octadecenal, (z)- 3.41 –
40 Cyclohexane, 1,2-diethyl-1-methyl- 1.35 –
41 3-Hexadecanol 1.43 –
42 1-Dotriacontanol 1.61 1.39
43 9-Octadecenoic acid (z)-, 9-octadecenyl ester,(z)- 1.25 –
44 Cholest-5-en-3-ol (3.beta.)-, carbonochloridate 1.35 –
45 Silacyclopentane – 5.55
46 Benzene, 1,1′- oxybis(methylene) bis- – 3.02
47 Phenol, 2-(phenylmethoxy)- – 10.37
48 1,1′-Bicyclopentyl -2-one – 1.07
49 2-Pyridinecarboxylic acid, 6-methyl- – 1.29
50 12-Heptadecyn-1-ol – 2.16
51 Ethylbenzene – 1.87
52 2-Octynoic acid, methyl ester – 1.58
53 Benzeneethanamine, n- (4-hydroxy)hydrocinnamoyl- – 2.57
54 Ethinamate --- 1.28
55 Bornyl methyl ether – 1.27
56 2 h-Pyran, 2-(tert-butylthio)tetrahydro- – 1.28
57 1,3-Isobenzofurandione, hexahydro-4,7-dimethyl- – 1.83
58 1-Propanol, 2-methyl-2- (2-methyl-2-propenyl)oxy- – 1.28
59 Bicyclo 2.2.1 heptan-2-ol, endo- – 1.63
60 (7r,8r)-Ethyl 8-hydroxy-trans-bicyclo 4.3.03-3-nonene-7-carboxylate- – 1.29
61 4-Hexen-1-ol, 5-methyl-2-(1-methyletheny – 1.59
62 Phenol, 2-methyl- – 3.08
63 P-tolylethanamine, n- 4-hydroxyhydrocinn – 1.39
64 Bicyclo 2.2.1 heptane, 2-ethylidene-1,7,7-trimethyl-,(e)- – 1.29
65 1-(2-Benzyloxyethyl)cyclohexene – 1.51
66 (e)-3-Chloro-2-methyl-2-pentenal – 1.8
67 3- (.beta.-benzylamino)ethyl indole – 2.14
68 Indole – 4.31
69 3,9-Epoxy-p-mentha-1,8(10)-diene – 2.03
70 Phenol, 2,6-dimethoxy- – 2.22
71 4(1h)-Isobenzofuranone, hexahydro-3a,7a—imethyl-,cis-(+/−)- – 1.83
72 Z, z-6,28-Heptatriactontadien-2-one – 2.58
73 1-Heneicosyl formate – 1.18
74 Stigmastan-3-ol, 5-chloro-, acetate, (3. beta,5 alpha)- – 1.05

There are quite differences among properties of the components such as hydrocarbons, ethers, esters, carboxylic acids, alcohols and phenols, aldehydes, heterocycles. Therefore, it is also significantly different for the constituent function of the COSC extractive pyrolyzates at 450 °C and 600 °C, and thus the application prospects would be also significantly different. Similarly, the findings will provide scientific basis for broadening application range of COSC residues by pyrolysis.

4

4 Discussion

The main VOCs of ethanol extractive from COSC are alcohols, those of petroleum ether extractive are alkanes and organic acids, and those of benzene/ethanol extractive are esters. The three extractives are all rich in the VOC: 1,6,10-Dodecatrien-3-ol,3,7,11-trimethyl-, (E)-,namely nerolidol, which has been widely used in cosmetics, food and biomedicine. In addition, many beneficial VOCs such as nonanal, β-caryophyllene, humulene and caryophylleneoxidearefound in COSC extractives. Generally, the relative content from high to low is petroleum ether extractive, ethanol extractive, benzene/ethanol extractive. In the actual processing and utilization, it is quite necessary to select an appropriate solvent for extraction and preparation according to the different demands for VOCs. Here, it can be seen that COSC extractive by petroleum ether will be a nicely developing prospects.

The results of FTIR further confirm: (1) the COSC contains components including organic silicon, ethers, organic acids, esters and alcohols, (2) the four kinds of organic silicon detected are naturally occurring components in the COSC, and (3) organic solvent extraction does not make compound groups of COSC changed significantly.

There are four obvious stages in thermogravimetry treatment of COSC: the first stage 30–100 °C, the second stage 180–240 °C, the third stage 240–400 °C, and the fourth stage 400–567 °C. The order of the mass loss is the third, the second, the fourth and the first stage. During thermogravimetry treatment, three critical turning points of temperature (240 °C, 400 °C and 567 °C) are observed, accompanied by significantly chemical changes such as pyrolysis of macromolecules into small volatile molecules.

Further researches were performed on the intrinsic cause of COSC mass loss and the characteristics of components in pyrolysis at high temperature. It is found that many volatile substances have been produced. Firstly, for COSC extractive pyrolyzates at 300 °C, 450 °C, 600 °C and 750 °C, it is obvious different in the relative content of their components, such as heterocyclic type with a high-low-high-low change, hydrocarbons and acids shown by the high-low-low-high change, and ketone and alcohol with a low-high-low-high change. Secondly, for the pyrolyzates of COSC residue at 450 °C, heterocyclic, ketone, phenolic are more than esters, hydrocarbons, phosphide, acids, aldehydes, alcohols and acyl, however, heterocyclic, ketone, phenolic are more than esters, ammonium, phosphide, acid, aldehydes and alcohols at 600 °C. The pyrolysis of the extractive and the residue produces a large number of VOCs at high temperatures differently, which also confirms our inference for mass loss during thermogravimetry treatment. Additionally, there are significant differences in the pyrolyzates of COSC extractives and residues at different temperatures, and a large amount of new other components are produced in the pyrolysis treatment. Therefore, pyrolysis treatments at high temperatures will provide a new approach for the high-grade application of COSC.

5

5 Conclusion

It is first reported here that rich 1,6,10-Dodecatrien-3-ol,3,7,11-trimethyl-, (E)-, namely nerolidol, exists in COSC extractives. In addition, bioactive VOCs such as β-caryophyllene, humulene and (E)-Atlantone were observed in three COSC extractives. The total content trend from high to low is petroleum ether extractive, ethanol extractive, benzene/ethanol extractive. COSC extractive by petroleum ether will be a nicely developing prospect.

Pyrolysis treatments at high temperatures will provide a new approach for the high-grade application of COSC.

Acknowledgements

This project is supported by the Science and Technology project of Hunan Province, China (2016NK2154), and the National Natural Science Foundation of China (31172257).

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