Reuse of Cornus officinalis nutlet for bioenergy

Yue, X., Li, Z., Lam, S., Peng, W., and He, Y. (2022). "Reuse of Cornus officinalis nutlet for bioenergy," BioResources 17(4), 6411-6444.

Abstract

As a traditional nourishing Chinese herbal medicine, Cornus officinalis Sieb. et Zucc. has a long history of application. At present, only the flesh of the fruit of Cornus officinalis is used as a medicine, which wastes a large quantity of ingredients in the nutlet. To improve the comprehensive utilization efficiency of the fruit’s nutlet, which could be used when there is a shortage of the plant’s fruit in the market, this study used Fourier transform-infrared spectroscopy (FT-IR), gas chromatography-mass spectrometry (GC-MS), thermogravimetric (TG) analysis, pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS), and nuclear magnetic resonance (NMR) techniques to analyze the Cornus officinalis nutlet. The results showed that the active ingredients of Cornus officinalis nutlet have great medicinal value and could become a substitute for the fruit. After extracting the active ingredients, the residue can be used as a good biomass liquid fuel, providing reference for the future to replace fossil fuels. This study provides the scientific basis for the comprehensive utilization of high-quality resources for Cornus officinalis.

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Reuse of Cornus officinalis Nutlet for Bioenergy

Xiaochen Yue,^a,# Zhaolin Li,^a,# Su Shiung Lam,^b Wan-Xi Peng,^a,* and Yifeng He ^a,*

DOI: 10.15376/biores.17.4.6411-6444

Keywords: Cornus officinalis nutlet; NMR analysis; Py-GC-MS; TGA-DTG; Biofuel

Contact information: a: School of Forestry, Henan Agricultural University, Zhengzhou 450002, China; b: Pyrolysis Technology Research Group, Institute of Tropical Aquaculture and Fisheries (AKUATROP), Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia;

*Corresponding authors: heyifeng310@163.com; pengwanxi@163.com; ^#These authors equally contributed to this work as co-first authors.

INTRODUCTION

Wood is an organic substance formed by natural growth. In addition to cellulose, hemicellulose, and lignin, it contains other minor components. Wood extract can be obtained with the use of ethanol, benzene, ethyl ether, acetone, dichloromethane, and other organic solvents. Wood extract contains more than 700 types of compounds, some of which can be used directly in dyes, preservatives, spices, activators, pesticides, and pharmaceuticals. However, few studies have researched the composition, content, and nature of wood extracts as biomass, which has not been given sufficient attention in the wood processing industry.

As a clean energy in the 21^st century, there has been great interest in biomass energy because fossil resources are being depleted. Analyzing the composition of wood extracts increases the comprehensive understanding of the role and benefits that bioenergy can play. Tannins from bark can strengthen phenolic resin or urea-formaldehyde resin (Zhang et al. 2015). Wani et al. (1963) found that paclitaxel from mushroom extracts has an anti-cancer effect on leukemia, breast cancer, ovarian cancer, lung cancer, melanoma and colon cancer (Peng et al. 2017a; Ge et al. 2018). However, few studies have been conducted on the composition of the nutlet of Cornus officinalis using a variety of extraction methods.

Cornus officinalis Sieb. et Zucc. is a deciduous shrub or small tree of Cornaceae that produces clusters of fruits known as Asiatic cornelian cherries (Corni Fructus or Shu Zhu Yu). It is used as a food plant, and its mature fruit is also used in traditional Chinese medicine. The fruit is sour, astringent, tepid, and is used as a liver and kidney tonic. The active ingredient has antibacterial and diuretic properties, lowers blood pressure, decreases postprandial hyperglycemia, and stimulates the immune system and other physiological activity resin (Zhang et al. 2013; He et al. 2019). Immuno-pharmacological activity analysis of the various components isolated from the seed or nutlet of Cornus officinalis revealed some differences in their immunocompetence. Among them, both polysaccharides and glycosides have immunosuppressive effects. The effect of the monoterpenoid iridoid on the content of sICAM-1 and TNF-α in the model of vascular complications in diabetic rats may be related to its inhibitory effect on non-enzymatic glycation reaction (Gang et al. 2013). The nutlet extract of Cornus officinalis increases superoxide dismutase (SOD) blood activity in rats, inhibits free radical generation, and reduces malondialdehyde (MDA) levels (Tan et al. 2006). The annual output of Cornus officinalis fruit (COF) in China is more than 6000 tons every year, and in recent years, the inventory of COF is 3000 tons every year (Chen et al. 2012). The situation that the output of COF exceeds the sales is becoming increasingly obvious. In addition, the increase of manual picking costs has led to no one willing to manage the COF after it has become mature and abandoned, resulting in waste of C. officinalis resources. However, in view of the solution to this situation, the current research focuses on the use of Cornus officinalis nutlet as medicine instead of flesh to increase the application of COF. Little research on the application of Cornus officinalis nutlet as biofuel has been conducted. Therefore, it is more urgent to find ways to expand the application of C. officinalis and realize the maximum resource utilization of C. officinalis.

In this study, the components of C. officinalis nutlet (CON) from COF and its extracts were analyzed by Fourier transform-infrared spectroscopy (FT-IR), gas chromatography-mass spectrometry (GC-MS), thermogravimetric (TG) analysis, pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS), and nuclear magnetic resonance (NMR) techniques, providing reference for the medical and industrial use of C. officinalis as a bioenergy source.

EXPERIMENTAL

Materials

The nutlets of Cornus officinalis were obtained from Xixia County Forest Farm, Nanyang City, Henan Province, China. The nutlets were dried, and it was confirmed that the pulp residues in the nutlets had been removed. The nutlets were extracted using four solvents (ethanol, methanol, ethanol/benzene (1:1), and ethanol/methanol (1:1)) and were named B1, B2, B3, and B4, as shown in Table 1. Then 20 g of CON powder was weighed for each, and organic solvent extraction was used to obtain the extracts. The amount of organic solvent was 300 mL, the extraction time was 4 hours, and the extraction temperature was 78 ℃ (B1), 64 ℃ (B2), 80 ℃ (B3), and 70 ℃ (B4). Finally, a rotary evaporator was used to concentrate the solution to 30 mL to obtain the extracts. The experimental process is shown in Fig. 1.

Table 1. Optimization of Experimental Program

Fig. 1. Experimental flow chart

FT-IR

The samples were analyzed with a Fourier transform infrared (FT-IR) spectrophotometer (Shimadzu, Kyoto, Japan) using KBr discs containing 1.00% finely ground sample (Jiang et al. 2017; Peng et al. 2017a).

TGA-DTG

The CON powder was examined with a thermogravimetric analyzer (TGA Q50 V20.8 Build 34; TA Instruments, New Castle, DE, USA). The nitrogen release rate was 60 mL/min. The TG temperature program began at 30 ℃ temperature and increased to 300 ℃ at a rate of 5 ℃/min.

PY-GC-MS

The powder of CON was analyzed by thermal cracking-gas chromatography-mass spectrometry (CDS5000-Agilent7890B-5977A; Agilent Technologies, Santa Clara, CA, USA). The carrier gas used high purity helium, the pyrolysis temperature was 500 ℃, the heating rate was 20 ℃/ms, and the pyrolysis time was 15 s. The pyrolysis product transfer line and the injection valve temperature were set to 300 ℃. A capillary column HP-5MS was used (30 m × 0.25 mm × 0.25 μm), and shunt mode was used with a split ratio of 1:60 and shunt rate of 50 mL/min. The temperature of the GC program began at 40 ℃ for 2 min, increased to 120 ℃ at a rate of 5 ℃/min, and then increased to 200 ℃ at a rate of 10 ℃/min for 15 min.

GC-MS

The components of CON were analyzed by a gas chromatography-mass spectrometry (GC-MS) instrument (Agilent Technologies, Santa Clara, CA, USA). A quartz capillary column was used (30 mm×0.25 mm×0.25 μm) with the starting temperature at 50 ℃, and then the temperature was increased at a rate of 8 ℃/min up to 250 ℃ without retention, with a subsequent rate of 5 ℃/min to 300 ℃ without retention. The temperature of the inlet was 250 ℃, the column flow was 1.0 mL/min, the split ratio was 20:1, and the carrier gas used was high purity helium. For MS, the ionization mode was EI, the electron energy was 70 eV, the temperature of the ion source was 230 ℃, the temperature of the quadrupole was 150 ℃, and the starting point of the scan was 30 to 600 amu.

NMR

A Nuclear Magnetic Resonance Polarimeter (Agilent-400 MR; Agilent Technologies, Santa Clara, CA, USA) was used, and the solvent was Methanol-d4. One NMR probe was used to determine ¹H-NMR, ¹³C-NMR, and 2D-NMR. The conditions were as follows: ¹H-NMR: duration 1.000 s, pulse 45 degrees, sample-and-hold time 2.556 s, pulse width 6410.3 Hz, and ¹H-NMR frequency 399.79 MHz. ¹³C-NMR: duration 1.000 s, pulse 45 degrees, sample and hold time 1.311 s, pulse width 25000.0 Hz, ¹³C-NMR frequency 100.53 MHz, hydrogen decoupling frequency 399.79 MHz, and power 38 dB. 2D-HSQC: duration 1.000 s, sample and hold time 0.150 s, two pulse widths 4807.7 Hz and 20105.6 Hz, frequency of 2D-HSQC 399.79 MHz, frequency of carbon decoupling 100.54 MHz, and power 38 dB (Lu et al. 2011; Albrecht-Schmitt 2012; Chow et al. 2014; Zabow et al. 2015; Wu et al. 2017).

RESULTS AND DISCUSSION

Chemical Composition of CON extracts

FT-IR analysis

Figure 2 shows the infrared contrast spectra of CON from the four extracts (Shenderova et al. 2011; Kaznowska et al. 2017; Koo et al. 2018). The absorption peaks in the infrared spectrum of 3400 cm^-1 or more may be stretching vibrations or anti-telescopic vibrations of free hydroxyl groups in liquid water. The absorption peak is due to the intermolecular association near the broad peak at 3420 to 3300 cm^-1. Absorption peaks at 3030 cm^-1are formed by the stretching vibration of saturated C-H bonds. The absorption peak at 2925 cm^-1 may be formed by antisymmetric stretching of the CH₂ group. The absorption peak at 2380 to 2300 cm^-1 is formed by the antisymmetric expansion of CO₂. The absorption peak at 1750 to 1650 cm^-1 is due to the C=O double bond stretching vibration. The absorption peak at 1450 cm^-1 is due to the CH₃ asymmetric corner vibration formation. The absorption peak at 1200 cm^-1 is the C-O-C antiscathetic stretching of the ester species. The absorption peak at 1100 cm^-1 is due to the symmetric and antisymmetric C-O-C stretching of esters and ethers, respectively. The absorption peak at 940 cm^-1 may be formed by out-of-plane bending of COH. The absorption peaks of cellulose (at 2950 cm^-1), hemicellulose (1730 cm^-1), and lignin (1739 cm^-1, 1630 cm^-1, and 878 cm^-1) were slightly decreased in the chemical composition tested, indicating that hydrolysis occurred in part of it (Xu et al. 2013, Hu et al. 2014; Ge et al. 2018). The absorption peaks of the extracts are mainly concentrated in the bands of 3700 to 3000 cm^-1, 3000 to 2850 cm^-1, and 1690 to 870 cm^-1. The main chemical components were esters, aldehydes, ethers, fatty acids, hydrocarbons, and aromatics. In addition, the characteristic absorption peaks decreased, indicating partial extraction of esters, alcohols, ethers, fatty acids, hydrocarbons, and aromatics (Bassilakis et al. 2001; Peng et al. 2017b; Jiang et al. 2018).

Fig. 2. FT-IR spectra of samples B1, B2, B3, and B4

GC-MS analysis

The total ion chromatograms of four types of extractives analyzed by GC-MS are shown in Figs. 3 through 6. The spectrum of each peak was retrieved using a computer and the wiley7n.1 standard spectrum. The peak area normalization method was used to calculate the content of each component, and specific results are shown in Tables S1 through S4.

Fig. 3. Total ion chromatograms of ethanol extract from CON

Fig. 4. Total ion chromatograms of a methanol extract of CON

Fig. 5. Total ion chromatograms of ethanol/benzene extract from CON

Fig. 6. Total ion chromatograms of ethanol/methanol extract from CON

Fig. 7. Distribution of samples B1, B2, B3, and B4 after GC-MS analysis

According to the results of GC-MS analysis, 93 peaks were detected in B1, and 93 chemical constituents were identified. The results show that the content of more substances were as follows: 3-Furaldehyde (9.21%), Maleic anhydride (4.44%), 4H-Pyran-4-one,2,3-dihydro-3,5-dihydroxy-6-methyl- (1.46%), 5-Hydroxymethylfurfural (16.48%), Malic acid (7.08%), 4-Ethylbiphenyl (2.93%), 1,2,3-Benzenetriol (16.61%), Vanillin (1.82%), Spiro[4.5]decan-7-one, 1,8-dimethyl-8,9-epoxy-4-isopropyl- (2.58%), 9,12-Octadecadienoic acid (Z,Z)- (2.30 %), Ethylamine, N,N-diheptyl-2-(2-thiophenyl)- (1.88 %), octamethyl-Cyclotetrasiloxane, (1.37 %), and 4-butoxy-1,1′-Biphenyl (1.53 %).

According to the results of the GC-MS analysis, 65 peaks were detected in B2, and 65 chemical constituents were identified. The results show that the content of more substances were as follows: 3-Furaldehyde(7.29%), Maleic anhydride(5.25%), 4H-Pyran-4-one, 2,3-dihydro-3,5-dihydroxy-6-methyl-(1.95%), 5-Hydroxymethylfurfural(17.34%), Malic acid(4.29%), 4-Ethylbiphenyl(5.25%), 1,2,3-Benzenetriol(23.46%), Vanillin (1.25%),Spiro[4.5]decan-7-one, 1,8-dimethyl-8,9-epoxy-4-isopropyl- (1.58%), 1H-Benzo[d,E]phthalazine, 6-methoxy-1,3-dimethyl- (2.48%), 9,12-Octadecadienoic acid (Z,Z)- (2.21%), 6H-Dibenzo[b,d]pyran-6-one, 7,9-dihydroxy-3-methoxy-1-methyl- (1.16%), 4-Methyl-2,4-bis(p-hydroxyphenyl)pent-1-ene, 2TMS derivative (1.77%), 4-Methyl-2,4-bis(p-hydroxyphenyl)pent-1-ene and 2TMS derivative(1.54%).

According to the results of GC-MS analysis, 66 peaks were detected in B3, and 59 chemical constituents were identified. The results show that the content of more substances were as follows: Furfural (6.88%), 1H-Imidazole, 1,2-dimethyl- (2.37%), Levoglucosenone (2%), 5-Hydroxymethylfurfural (18%), Malic acid (3.92%), 1,2-Cyclobutanedicarboxylic acid, trans- (2.16%), 1,2,3-Benzenetriol (10.13%), Benzaldehyde, 3-hydroxy-4-methoxy- (3.31%), 2-(4′-Methoxymethylbiphenyl-4-yl)propan-2-ol (1.97%), 2-Acetoxy-3,3-dimethyl-2-(3-oxo-but-1-enyl)-cyclobutanecarboxylic acid, methyl ester (5.34%), N-2,4-Dnp-L-arginine (2.30%), 9,12-Octadecadienoic acid (Z,Z)-(11.92%) and Heptasiloxane, 1,1,3,3,5,5,7,7,9,9,11,11,13,13-tetradecamethyl- (3.76%).

According to the results of GC-MS analysis, 43 peaks were detected in B4, and 39 chemical constituents were identified. The results show that the content of more substances were as follows:3-Furaldehyde (6.16%), Maleic anhydride (7.45%), 4H-Pyran-4-one, 2,3-dihydro-3,5-dihydroxy-6-methyl- (1.44%), 5-Hydroxymethylfurfural (18.87%), Thiophene, 2-propyl-(1.66%),1,2,3-Benzenetriol (32.63%), 2-Acetoxy-3,3-dimethyl-2-(3-oxo-but-1-enyl)-cyclobutanecarboxylic acid, methyl ester (2.39%),2,5-dimethoxy-4-ethylthio-benzaldehyde (6.42%), 9,12-Octadecadienoic acid (Z,Z)- (3.06%) and Octasiloxane, 1,1,3,3,5,5,7,7,9,9,11,11,13,13,15,15-hexadecamethyl- (1.54%).

Figure 7 shows that there were different distributions of the retention time of different components from the hawthorn kernel. For B1 sample, 18%, 55%, 19%, and 8% sample retention times were less than 10, 20, and 30 min, and greater than 30 min, respectively. For B2 sample, 18%, 60%, 10%, and 12% of the sample components had retention times less than 10, 20, and 30 min, and retention times greater than 30 min, respectively. For B3 sample, 16%, 51%, 26%, and 7% sample components retained retention times of less than 10, 20, and 30 min and greater than 30 min, respectively. For B4 sample, the 20%, 63%, 12%, and 5% sample retention times were less than 10, 20, and 30 min, and greater than 30 min, respectively (de Jong et al. 2018; Wan-Ibrahim et al. 2018; Wang et al. 2018).

Analysis of NMR spectra

The ¹H-NMR spectrum is the most widely used nuclear magnetic resonance spectrum. As the hydrogen core has a large magnetic spin ratio γ, its magnetic properties are strong, the detection sensitivity is high, and the signal is easy to observe (Lanza et al. 2010). There are a large number of hydrogen atoms in different chemical environments of organic compounds, and therefore, the ¹H-NMR spectrum can provide important structural information for many organic compounds (Fig. 8) (Feigenson and Meers 1980; Martin et al. 2008; Maulidiani et al. 2018; Pinto et al. 2018). The chemical shifts of protons are mainly distributed in the alkane compounds saturated at δ 0.6 to δ 1.6. At other locations, the peak of δ 3.34 should be the CD₃OD solvent peak. The first proton occurs at a δ value of approximately 1.15 pm, and the chemical shift value at this position should be the alkane proton(-C-C-H). The first proton moves slightly to the right and appears at a delta value of approximately 1.3 ppm. Near the delta value of 3.3 to 3.6 ppm, the solvent peak of CH₃OH is predominant. Proton chemical shifts on carbon atoms directly attached to the halogen also occur at this position. The chemical shifts of the protons on α-C in the vicinity of the carbonyl or cyanide groups are 2 to 3 μm with an anisotropic effect on C=C and the sp2 hybridization of olefinic carbons. The chemical shift of olefinic compounds is within 4.5-6 μm. When change occurs, coupled with aryl, the value of δ will increase; the peak is most obvious at δ5.3 and δ7.0. The chemical shift of α-H in the hydrogen atom of the ether molecule is approximately 3.5 ppm. The δ value of the hydroxyl proton is approximately 4 to 8 ppm. The chemical shift of the aromatic compound is in the range of 6.3 to 8.5, and the value of the heterocyclic aromatic proton is within the range of 6.0 to 9.0. Based on the peaks of the specific chemical shifts shown by the ¹H-NMR spectrum, additional compounds from CON can be roughly determined.

Carbon makes up the skeleton of organic molecules. The importance of ¹³C NMR analysis to chemical research is clearly recognized. The chemical shift of ¹H NMR is usually in the range of 0 to 15 ppm, while the usual range of ¹³C NMR is 0 to 300 ppm, which is approximately 20 times that of ¹H (De Feyter et al. 2018; Lusk and Gullion 2018; Tang et al. 2018). In the ¹H NMR, it is not directly observed that the absorption signal of hydrogen groups such as C=O, C=C, and C=N can be clear, given their characteristic absorption peak by ¹³C NMR. Figure 9 is a study of the structural change of a sample using ¹³C-NMR spectroscopy. Between 10 and 50 ppm, mainly chemical bond shifts of saturated alkanes occur. As can be seen from the figure, the first proton appears at a δ value of approximately 18 ppm. The chemical shift value at this position should be the alkane proton-(CH₂)-CH₃. The second proton shifts back, showing a δ value of 40 ppm. Where possible, the chemical bond at this location should be an alkane containing the N element. For carbohydrate polymer carbon, all important signals are generally distributed in the 50-110 ppm region (Xue et al. 2014). The chemical shift value of the alkyne alkynyl carbon should be near 69 ppm and 78 ppm, and the chemical bonds present are predominantly -C=C-bonds. The chemical shift value of the olefinic carbon is between 100 and 120 ppm. The chemical bonds at the peaks of 98 ppm and 110 ppm are -HC-CH-. The chemical shift values of the aromatic ring carbons and heteroaromatic ring carbons are generally in the range of 120 to 160 ppm, and peaks tend to appear in lower fields. A peak appeared at 145 ppm, which may be the chemical shift values of benzene and its derivatives. Among the hydroxy compounds, because the electron density of the π-bonds in C=O is small, the chemical shift value tends to be lower in the field, and the δ value generally appears between 160 and 220 ppm. The peak appears at 172 ppm and 176 ppm and is probably a hydroxycarbon compound (Sharma and Rajarathnam 2000; Cimino et al. 2004; Xie et al. 2017; Gurjar and Kaur 2018).

2D-HSQC is one of the most common two-dimensional NMR spectra. It provides information on ¹H nucleus and ¹³C nucleus single bonds and is of great significance for structural analysis (Moniz et al. 2018; Xiao et al. 2018; Yao et al. 2018). It is also available in ¹H and ¹³C-NMR spectra. The resolution of overlapping signals reveals the link between these two aromatic units (Shupe et al. 2012; Fu et al. 2017; Fakeeha et al. 2018; Khan et al. 2018). To obtain further information on the structural characterization of methanol/ethanol samples, 2D-HSQC NMR analysis was performed. The aliphatic region (δC/δH 10–40/0.5–2.5), side chain (δC/δH 50–95/2.5–6.0), and the aromatic (δC/δH 95–150/5.5–8.0) region of the HSQC spectra of the sample are shown in Figure 10. Additionally, δC/δH 110/6.97, δC/δH 120/6.8, δC /δH 114/6.7, δC/δH 104/6.68, δC/δH 72/4.82, and δC/δH 86/4.19 illustrate the interconnected hydrogen and carbon. As shown by 2D-HSQC NMR, δC/δH 15-45/0.2–1.5 are a hydrocarbon-saturated hydrocarbon connection. δC/δH 55-75/4.5–6.5,1.7-3.5 are mainly the carbon spectra of some alkynes and some of the olefins. δC/δH 110-140/6.3–8.3, 4.5–6.5 are predominantly aromatic and olefinic carbons. δC/δH 60-80/3.1–4 are alcohols, ethers, phenols, and other oxygen-containing compounds.

Fig. 8. ¹H-NMR spectra of the sample

Fig. 9. ¹³C-NMRspectra of the sample

Fig. 10. 2D-HSQC NMR spectra of CON

Medicinal properties

The compounds identified in Tables S2 to S5 in the Appendix are also classified as esters, acids, phenols, tannins, iridoids, soaps, ketones, and glycosides. Among them, CON exhibits immunostimulant activity, and glycosides exhibit immunosuppressive and immunomodulatory effects. The iridoid glycosidesin from CON can reduce the serum levels of ICAM-1 and TNF-α in the vascular complication model of diabetic rats, thus resulting in the hypoglycemic effect of total terpenes in CON (Hong et al. 2003; Han et al. 2006; Hu et al. 2009). In addition, iridoid glycosides may inhibit thrombosis by changing the state of hypercoagulability of the blood and provide a good experimental basis for the prevention and treatment of thrombotic diseases. CON contains polyphenolic compounds, one of which is an ortho-phenolic hydroxyl that can be easily oxidized, and the active oxygen and other free radicals have a strong ability to be captured, making it a strong antioxidant and scavenger of free radicals. Maleic anhydride is an important basic raw material for unsaturated organic acid anhydride. It is used in pesticide production to synthesize organic phosphorus pesticides. Maleic anhydride is also used to produce unsaturated polyester resin, papermaking auxiliary, coatings, and pharmaceutical industry (Popadyuk et al. 2013). 5-Hydroxymethylfural (5-HMF) is an important furan compound. Because of its excellent chemical properties, it is widely used in medicine, chemistry, energy and other fields. Its derivatives have significant application prospects in fine chemicals, medicine, degradable plastics and other fields (Atanda et al. 2016). These active ingredients from CON are the same or similar to those reported in the COF (Gang et al. 2013; Zhang et al. 2013; He et al. 2019).

Behavior during Combustion of CONs

TGA and DTG analysis

The thermal stability of CON is largely responsible for its excellent flame-retardant properties, but it also determines the broad application prospects (Salasinska et al. 2020). Thermal stability analysis is an effective method to evaluate the flame retardancy and industrial applications of CON (Xie et al. 2011; Renneckar et al. 2004). Figure 11 shows the TGA curve and DTG curves of CON. According to Fig. 11, T5wt.% and T10wt.% are at 157 ℃ and 234 ℃, respectively. There are three stages in the process of weight loss. The first stage is 20 to 106 ℃, when small molecules with low moisture content and boiling point undergo evaporation. The weight loss during this stage is 4.6%. The second stage is 106 to 200 ℃. As long as the material component is slightly cracked, the weight loss is only 3%. The third stage is 200 to 300 ℃. At this decomposition stage, the organic matter of the components has undergone severe cracking with increasing temperature and the burning of other components. The content of the material has been reduced from 93.5% to 73.9%. The DTG curve at this stage is constantly increasing, indicating that the rate of material weight loss is also increasing (Dochia et al. 2018; Guo et al. 2019).

The three phases showed different properties and phenomena, with different kinetic parameters and reaction mechanisms, with a final residual mass of 73.9% (Rukthong et al. 2015; Liu et al. 2018; Lou et al. 2018). Between 20 and 250 ℃, CON showed a thermal weight of approximately 13 wt.%, and the weight loss was low, especially before 200 ℃. The weight loss was only 6.5%, indicating that CON had good thermal stability. Throughout the TG experimental tests, CON demonstrated good thermal stability within 200 ℃, indicating that it has excellent processing properties, and good prospects for research and industrial use.

Fig. 11. TGA and DTG thermal curves for CON

Py-GC-MS analysis

The total ion chromatograms of CON by Py-GC-MS are shown in Fig. 12 and the relative content of each component has been counted by area normalization (Lan and Peng 2012; Peng et al. 2012). The MS data was analyzed using the NIST standard MS map and publicly published books and articles, and then identifying each component. The analytical results are listed in Table S5.

According to the results of the Py-GC-MS analysis, 241 peaks were detected in Table 6, and 241 chemical constituents were identified. The results show that the content of more substances are as follows: 4-methyl-2-Hexanamine (2.82%), Glycidol (1.33%), Formic acid (1.13%), Acetic acid (8.72%), Furfural (2.78%), 1,2-Cyclopentanedione (1.06%), 2,2-diethyl-3-methyl-Oxazolidine (1.02%), 2-Methyliminoperhydro-1,3-oxazine (1.07%), 2-methoxy-Phenol (2.21%), Creosol (1.95%), Catechol (1.67%), 5-Hydroxymethylfurfural (2.07%), 2-Methoxy-4-vinylphenol (2.55%), 2,6-dimethoxy-Phenol (1.87%), 1,2,3-Benzenetriol (1.29%), Vanillin (1.81%), 3,5-Dimethoxy-4-hydroxytoluene (1.55%), trans-Isoeugenol (1.52%), 1-(4-hydroxy-3-methoxyphenyl)-2-Propanone (1.11%), (E)-Stilbene (3.27%), D-Allose (1.95%), 1,6-anhydro-.beta.-D-Glucopyranose (1.67%), (E)-2,6-Dimethoxy-4-(prop-1-en-1-yl)phenol (1.12%), and n-Hexadecanoic acid (1.31%).

As shown in Fig. 13, there was a different distribution of retention times for the different components of CON. The retention times of 22%, 18%, 48%, and 12% for the sample component content were less than 10, 20, and 30 min and greater than 30 min, respectively. The molecular weight increases occurred in sample retention times greater than 30 min, 10-20 min, less than 10 min, and 20-30 min, with a higher molecular weight content than the other retention times in the 20-30 min retention period (Toraman et al. 2017; Dziwiński et al. 2018; Fang et al. 2018; Yu et al. 2018).

Glycidol obtained by pyrolysis contains epoxy group and hydroxyl group. It has active chemical properties and can carry out many ring opening reactions. Glycidol is hydrolyzed to generate glycerol, and propylene glycol is generated through catalytic hydrogenation, which is condensed with alcohols to generate glycerol ether (Bakhiya et al. 2011). It is often used in surface coatings, chemical synthesis, production of fungicides and so on. Another pyrolysis product, Vanillin, is the first essence synthesized by human beings. As an important edible flavor, Vanillin is used in almost all flavor types and is widely used in the food industry. In addition, the application of Vanillin in the medical field has been continuously expanded in recent years and has become the most potential field for Vanillin application (Abraham et al. 1991; Fitzgerald et al. 2004). The content of organic and inorganic substances in biomass combustion process determines whether it can be used as a good biofuel. The higher the inorganic content in the combustion process, the more unfavorable the element occurrence mode (chloride, sulfate, carbonate, oxalate, nitrate and some hydroxide, phosphate) (Vassilev and Vassileva 2016). The application and processing of these biofuels will lead to environmentally challenging thermochemical conversion. However, the main components of the detected from CON were esters, acids, phenols, anthraquinones and ketones, and the content of inorganic salts was relatively low (Table S5). By analyzing the main functions and functions of different compounds, CON can be more effectively and fully utilized.

Fig. 12. Total ion chromatograms of CON by Py-GC-MS

Fig. 13. Distribution characteristic of CON by Py-GC-MS

CONCLUSIONS

The absorbance peaks of the extract of Cornus officinalis nutshells (CONs) were concentrated in the 3700 to 3000 cm^-1, 3000 to 2850 cm^-1, and 1690 to 870 cm^-1 bands. The decrease in the characteristic absorption peak indicates that the esters, alcohols, ethers, fatty acids, hydrocarbons, and aromatic compounds had been partially extracted. By the identification using gas chromatography-mass spectrometry (GC-MS) tests, more than 60 kinds of chemical active ingredients were detected, which can play a certain role in immune regulation, hypoglycemia, inhibition of thrombosis formation, and anti-oxidation.
Through the research and analysis of the extract of CON, it was determined that the seed also has the same important medical value as the pulp, and has great application prospects in medicine and food.
In addition, in the CON extracts, many organic substances were the same or homologous to biomass oil, and the residue after the active ingredient is extracted can be used as a biomass liquid fuel. It may be possible to use it in place of fossil energy sources. After the above analysis, we want to provide the scientific basis for CON to become a high-quality resource.

Acknowledgments

This study was supported by the Program for Innovative Research Team (in Science and Technology) in University of Henan Province (No. 21IRTSTHN020), and Central Plain Scholar Funding Project of Henan Province (No. 212101510005).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships.

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Article submitted: June 9, 2022; Peer review completed: July 30, 2022; Revisions accepted: September 23, 2022; Published: September 29, 2022.

DOI: 10.15376/biores.17.4.6411-6444