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Article

Differences in Chemical Constituents between Dalbergia oliveri Heartwood and Sapwood and Their Effect on Wood Color

by
Liuming Wei
,
Ruoke Ma
and
Yunlin Fu
*
College of Forestry, Guangxi University, Nanning 530004, China
*
Author to whom correspondence should be addressed.
Molecules 2022, 27(22), 7978; https://doi.org/10.3390/molecules27227978
Submission received: 14 October 2022 / Revised: 13 November 2022 / Accepted: 15 November 2022 / Published: 17 November 2022
(This article belongs to the Special Issue Advances on Natural Products: Isolation, Identification and Biological Activity)
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Versions Notes

Abstract

:
The purpose of this study was to characterize and quantify the chemical constituents of heartwood and sapwood of Dalbergia oliveri extract in order to investigate the chemical components that determine the formation of heartwood’s color. In this work, the types of pigments in heartwood and sapwood extract were analyzed using UV-Visible (UV) Spectrophotometer, and the main pigment components of heartwood and sapwood extract were identified and quantified using ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS). The results showed that the difference in content of the main components between heartwood and sapwood of Dalbergia oliveri was slight, and the lignin structure between heartwood and sapwood is basically identical; flavonoid pigments were found to be the primary chromophoric components of heartwood and sapwood extract. However, a total of 21 flavonoids were identified in heartwood and sapwood, of which the unique substances to heartwood were vitexin, isorhamnetin, and pelargonidin, and the content of isoliquiritigenin, formononetin, and biochanin A were 253, 37, and 583 times higher in the heartwood than in the sapwood, respectively, which could be the main pigment components affecting the significant color difference between heartwood and sapwood of Dalbergia oliveri. These results will provide a foundation for revealing the underlying mechanism of color difference between heartwood and sapwood and provide a theoretical basis for wood coloring.

1. Introduction

Dalbergia oliveri Gamble ex Prain (D. oliveri) belongs to the genera of Dalbergia, a family of Fabaceae, and is commercially known as Burmese tulipwood, which is mainly distributed in Myanmar, Thailand, Vietnam, Laos, etc. It was included in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species in 1998 [1]. Sapwood and heartwood are yellow and light red or reddish brown, respectively. Compared to sapwood, heartwood has texture, strong natural durability, fragrance, and potential medicinal value [2,3,4]. Therefore, it has always been used as a material for high-class furniture, which has been loved by people. As market demand increased, many of the original sources of rosewoods have been indiscriminately harvested and drastically reduced. As a result, the price of rosewood increased rapidly. As an example, Dalbergia bariensis timber originating from Vietnam is 3478.3–3913.0 USD/m3, while imported Dalbergia bariensis timber is 1787.0 USD/m3 [5]. To cater for changing market needs, fast-growing and abundant plantation timber (eucalyptus, poplar) has become an alternative in China because of its short rotation period and low price, but the drawbacks are poor decay resistance effect and monotone color of the wood [6,7]. Color affects the visual aesthetics and decorative qualities of wood and wood products, which is an important indicator to evaluate the ornamental and commercial value. Natural dyes are used in textile dyeing and food coloration due to their fewer toxins, UV resistance, and antibacterial properties [8,9]. It is worth noting that natural dyes can be an effective solution to the problem of monotonous wood color, but their few sources, high cost, and poor water fastness have restricted the development of natural dyes in wood dyeing, which is still in the experimental research stage [10,11]. Zhu et al. [12,13,14] reported that natural dyes extracted from residues of Dalbergia cochinchinensis using ethanol exhibited desirable color appearance, water fastness, and permeability, as well as having some anti-UV properties and mold-inhibition properties in wood staining, and natural dyes from other plants have been repeatedly discussed in the literature [11,15]. A large number of residues (shavings, trimmings) are left over in the production and processing of rosewood. It is often used as fuel, resulting in a large number of wasted resources. Thus, natural dyes extracted from rosewood residues are applied to fast-growing woods. It not only improves the utilization rate of rare rosewood resources, but also increases the added value of fast-growing wood.
The difference in heartwood and sapwood color and natural durability is mainly due to the changes in chemical composition and contents during the formation of heartwood [8,16]. Previous studies have shown that wood color is closely related to the chemical composition, which mainly included flavonoids, anthraquinones, and phenolic compounds [16,17,18]. Therefore, it is important to explore the chemical composition that determines the formation of wood color for the preparation technology of wood dyeing. Including affluent chemical components, the extractives of D. oliveri have the potential value of providing natural dyes. Liu et al. [19] probed D. oliveri extractives by using gas chromatography-mass spectrometry (GC-MS) and finally detected a total of 32 compound components, with relative contents of more than 1% and high alcohol and ketone levels. However, the relationship between the chemical composition of D. oliveri extractives and wood color has not been clarified.
Based on the above issues, this study aimed to investigate the correlation between the chemical composition of D. oliveri extracts and wood color and to reveal the cause for the formation of color in D. oliveri wood. For this purpose, we processed the waste of D. oliveri wood as the research material, and ultraviolet-visible (UV) spectroscopy was used to analyze the main types of chromophores. They were identified and quantified by ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS).

2. Results and Discussion

2.1. Main Chemical Components Analysis of D. oliveri Sapwood and Heartwood

2.1.1. Main Chemical Component Contents and PH Value of Sapwood and Heartwood

The main component contents and PH value of heartwood and sapwood of D. oliveri are shown in Table 1. It can be seen that the content of holocellulose in heartwood of D. oliveri was 8.54% lower than that in sapwood. The content of α-cellulose in heartwood was 3.18% higher than that in sapwood, and the Klason lignin content in heartwood was slightly higher than that in sapwood, by 0.34%. The acid-insoluble lignin was slightly higher in heartwood. The acid-soluble lignin was just lower than sapwood. The results for holocellulose and α-cellulose in sapwood and heartwood are consistent with those reported in the literature for Eucalyptus globulus (21.1–24.1% and 43.4–46.1%), but Dalbergia oliver has a higher content than that of Eucalyptus globulus [20]. The results were similar to those of other studies, including the Klason lignin content in sapwood and heartwood of Quercus faginea (28.1% and 28.6%, respectively), Quercus Laurina (25.1% and 25.5%, respectively), and Quercus crassifolia (24.9% and 25.2%, respectively) reported in the literature [21,22]. Lignin macromolecules contain chromophoric groups such as benzene rings, carbonyl vinyl groups, and auxochrome groups such as hydroxyl, carboxyl, and ether bonds, which can give wood its color. Therefore, the difference in the functional group structure between heartwood and sapwood requires further characterization and analysis to explore its effect on color.

2.1.2. Characterization of Klason Structure

As shown in Figure 1, the peak positions of the infrared spectra of Klason lignin in heartwood and sapwood of D. oliveri were basically identical. It showed that the chemical functional groups of Klason lignin in heartwood and sapwood were basically the same. The absorption peaks at wavelengths 1606, 1504, 1456, and 1419 cm−1 belong to the vibrational absorption of the aromatic skeleton. The absorption peaks at 1268, 1026, and 868 cm−1 were assigned to guaiacyl units. The absorption peaks at 1314, 1216, and 1112 cm−1 were from the syringyl unit. This shows that the heartwood lignin of D. oliveri is mainly composed of guaiac-based units and syring-based units, which is the same type of lignin reported in Dalbergia odorifera [23].
The main factors affecting the color of wood are lignin and wood extracts [24]. The difference in lignin content and functional group structure between heartwood and sapwood was not obvious. Therefore, it is speculated that lignin may not be the main reason for the obvious color difference of D. oliveri. Previous studies had found that in several larch species, a* (reddish) and L* (brightness) parameters were highly correlated with wood extractive content, while b* (yellowish) parameters were closely related to cell wall chemical composition (cellulose, hemicellulose, and lignin) [25]. This indicated that the extract may be the main reason for the obvious color difference between heartwood and sapwood when the heartwood is red in color.

2.2. UV-Visible Spectroscopy of D. oliveri Extracts

As shown in Figure 2, there were two peaks between 200–290 nm for the alcoholic extracts of heartwood and sapwood petroleum ether layer, and the peaks were near 210 and 285 nm, respectively. It indicated that the characteristic peaks of aromatic compounds exist in heartwood and sapwood of the petroleum ether layer extract, and the content of heartwood was higher than that of sapwood. Heartwood and sapwood water layer alcohol extracts had absorption peaks near 230, 265, and 330 nm in the ultraviolet region, but heartwood had a stronger absorption peak near 330 nm, while it was a shoulder peak in the sapwood. It shows that the chromophoric system between heartwood and sapwood in the water layer extract is roughly the same. It all contains chromophoric groups, such as benzene rings and conjugated double bonds, while the content of chromophoric groups in heartwood was higher. Heartwood and sapwood of the alcoholic extract of the ethyl acetate layer had absorption peaks near 225 and 270 nm. In addition, the heartwood had a weak and broad absorption peak at 400–600 nm, while sapwood had no absorption peak in the visible region. This indicates that chromogenic groups such as benzene rings exist in both heartwood and sapwood, while there was a long conjugate chain or polycyclic aromatic hydrocarbons at 400-600 nm in heartwood [26]. Therefore, heartwood had different chromogenic groups from sapwood.
The difference in wood color is associated with filled or deposited extracts in the cell wall [27]. Fen et al. [28] conducted an extensive targeted metabolic analysis of Taxus L heartwood and sapwood extracts and found significant differences in flavonoid substances, and 71 flavonoid compounds related to wood color were identified in heartwood using liquid chromatography-electrospray ionization-mass spectrometry (LC-EI-MS) technology. Flavonoids usually have obvious absorption peaks around 230–290 nm or 300–350 nm, and anthocyanins have two peaks between 200 and 700 nm, one at 500–600 nm in the visible light region, and the other is around 275 nm in the UV region. But most phenols have no absorption at 500 nm [29]. Thus, it is preliminarily determined that the main chromophoric substances in heartwood and sapwood of D. oliveri are flavonoid pigments. However, there are anthocyanins in heartwood, but not in sapwood, and the content of chromophoric groups in heartwood is also higher than that in sapwood. It may be the main reason for the obvious difference in color between heartwood and sapwood, and will be further identified by UHPLC-MS.

2.3. Identification of Pigment Components in D. oliveri Heartwood and Sapwood Extract

The chemical constituents of heartwood and sapwood for D. oliveri were explored by UHPLC-MS, and a total of 21 (details of MS/MS spectra and structural identification are given in Supplemental Figure) flavonoids were identified (Table 2). These include: seven flavonoids (orientin, vitexin, hispidulin, scrophulein, chrysin, 5-hydroxy-6,7-dimethoxy-2-phenyl-4H-chromen-4-one, diosmetin), eight isoflavones (daidzin, ononin, daidzein, glycitin, genistein, glycidein, formononetin, biochanin A), one flavonol (isorhamnetin), 3 flavanones (liquiritigenin, 2-(3,4-dihydroxyphenyl)-7-hydroxy-3,4-dihydro-2H-1-benzopyran-4-one, naringenin), one chalcone (isoliquiritigenin), and one anthocyanin (pelargonidin). The unique ingredients of sapwood of D. oliveri are daidzin, ononin, and glycitin. The unique components of heartwood are vitexin, isorhamnetin, and pelargonidin.

2.3.1. Flavonoids

Compounds 1 (tR = 4.68) and 2 (tR = 5.38) were identified as orientin and vitexin, both flavonoid monosaccharide carbon glycosides, which were relatively stable between the A, B, and C rings and undergo cleavage mainly through the breaking of their glycosidic bonds. Taking orientin as an example, its excimer ion peak was m/z 449 ([M+H]+), with a possible molecular formula of C21H20O11. The MS2 characteristic fragment ions at m/z 431, m/z 413, m/z 353, m/z 329, and m/z 299 are consistent with the data reported in the literature for this compound [30], and its possible cleavage pathway was shown in Figure 3.
Compounds 5 (tR = 7.46), 10 (tR = 9.29), 11 (tR = 9.47), 17 (tR = 10.51), and 18 (tR = 10.52) were identified as hispidulin, scrophulein, chrysin, 5-hydroxy-6,7-dimethoxy-2-phenyl-4H-chromen-4-one, and diosmetin, all of which were flavonoids, and the main cleavage mode was the easy loss of neutral small molecules such as H2O, CO2, CO, etc. The C ring is prone to generate characteristic fragment ions by the Retro Diels–Alder (RDA) cleavage. Taking scrophulein and diosmetin as examples, the scrophulein’s molecular formula was probably C17H14O6, and the excimer ion peak in positive ion mode was m/z 315 ([M+H]+), which upon fragmentation yields the product ions at m/z 300, m/z 283, m/z 255, and m/z 168, as reported in the literature [31], and its possible cleavage pathway was shown in Figure 3. Diosmetin had an excimer ion peak at m/z 301 ([M+H]+), and its molecular formula was probably C16H12O6. The MS2 characteristic fragment ions at m/z 286, m/z 269, m/z 241, m/z 153, and m/z 134, which are consistent with the data reported in the literature for this compound [32], and its possible cleavage pathway was shown in Figure 3.

2.3.2. Isoflavones

Compounds 3 (tR = 5.52), 7 (tR = 8.46), and 14 (tR = 9.96) were identified as daidzin, ononin, and glycitin, all of which were isoflavone monosaccharide glucoside compounds, and the main cleavage mode is the loss of one molecule of glucoside followed by the loss of neutral molecules such as H2O, CO2, and CO, etc. Taking ononin as an example, the excimer ion peak at m/z 431 ([M+H]+), which upon fragmentation yields the product ions at m/z 269, m/z 237, m/z 181, and m/z 137, which are inferred from the literature [33] and the database, and its possible cleavage pathway was shown in Figure 4.
Compounds 9 (tR = 9.04), 15 (tR = 10.12), 16 (tR = 10.41), 20 (tR = 11.52), 21 (tR = 12.78) were identified as daidzein, genistein, glycidein, formononetin, and biochanin A, all of which are isoflavones. The main cracking method was easily lost neutral molecules such as H2O, CO2, CO, etc. When there was a methoxy group substitution, it was easy to lose a molecule of CH3. The RDA cleavage of the C ring was mainly affected by the substitution positions on the A and B rings. Taking daidzein and biochanin A as examples, the excimer ion peak of daidzein in positive ion mode was m/z 255 ([M+H]+), the molecular formula was probably C15H10O4, and the MS2 characteristic fragment ions at m/z 227, m/z 199, m/z 181, m/z 137, and m/z 119. Combined with the retention time of the reference substance and the database, the compound was identified as daidzein, and its possible cleavage pathway is shown in Figure 4. In the positive ion mode, the excimer ion peak of biochanin A is m/z 285 ([M+H]+), the molecular formula is probably C16H12O5, and the MS2 characteristic fragment ions at m/z 257, m/z 229, m/z 197, and m/z 137, and its possible cleavage pathway is shown in Figure 4. Furthermore, the retention time of this compound matches well with that of biochanin A standard.

2.3.3. Flavonol

Compound 6 (tR = 8.14) had an excimer ion peak of m/z 317 ([M+H]+), and its molecular formula is presumably C16H12O7. The MS2 fragment at the m/z values of 285, 257, 229, and 153 were inferred from the literature [34], and the database identified the compound as isorhamnetin, and its possible cleavage pathway is shown in Figure 5.

2.3.4. Flavanones

Compounds 4 (tR = 7.34), 8 (tR = 8.51), and 13 (tR = 9.73) are 2-(3,4-dihydroxyphenyl)-7-hydroxy-3,4-dihydro-2H-1-benzopyran-4-one, liquiritigenin, and naringenin, all of which are dihydroflavonoids. The main cleavage method is RDA cleavage; the C ring 1 and 3 bonds are broken, and neutral molecules H2O, CO2, CO, etc. are also lost. Taking liquiritigenin as an example, the excimer ion peak in positive ion mode is m/z 257 ([M+H]+), the molecular formula was inferred to be C15H12O4, and the MS2 characteristic fragment ions at m/z 239, m/z 211, and m/z 137. The compound was identified as liquiritigenin based on the retention time of the reference substance and the database, and its possible cleavage pathway is shown in Figure 6.

2.3.5. Chalcone

Compound 19 (tR = 11.13) had an excimer ion peak of m/z 257 ([M+H]+), and its molecular formula is presumably C15H12O4. The MS2 characteristic fragment ions of m/z 239, m/z 211, m/z 137, and m/z 119, which are inferred from the retention time of the reference substance and the database. The compound was identified as isoliquiritigenin, and its possible cleavage pathway is shown in Figure 7.

2.3.6. Anthocyanin

Compound 12 (tR = 9.61) had an excimer ion peak of m/z 271 ([M+H]+), and the molecular formula was presumed to be C15H10O5, with MS2 characteristic fragment ions at the m/z values of 239, 211, 151, and 137, which are inferred from the literature [35] and the database. The compound was identified as pelargonidin, and its possible cleavage pathway is shown in Figure 8.

2.4. Analysis of the Causes of Color Difference between D. oliveri Heartwood and Sapwood

2.4.1. Different Pigment Components between Heartwood and Sapwood of D. oliveri

The unique pigment components of sapwood of D. oliveri were daidzin, ononin, and glycitin, all of which were isoflavone glycosides, and their color state was white, while the unique pigment component of heartwood was vitexin (flavonoid carbon glycosides) and isorhamnetin (flavonol). Its color state was yellow. Pelargonidin (anthocyanin) was red, and sapwood has no anthocyanin pigment, which is consistent with the results of UV spectroscopy (see Table 3).
This research confirmed that the main factor affecting plant color was the content and type of pigment molecules [36]. Wang et al. [37] reported that anthocyanins are the main coloring substances in the magnolia of purplish red and purple, while white and yellow-green magnolias contain no anthocyanins. In addition, anthocyanins have been reported to be the main pigments in red fruits [38,39]. Flavonoids and flavonols can form stable and complex pigment complexes with anthocyanins as copigments [40]. The color of pelargonidin was red, which was consistent with the color of D. oliveri. As flavonoid carbon glycosides and flavonols, vitexin and isorhamnetin have carbonyl auxochrome groups located at the 7 and 4 positions in their own structures, which can promote electron transfer and rearrangement, deepening the color of the compound. In addition, it can also combine with anthocyanins to form stable pigments [41]. In conclusion, pelargonidin, vitexin, and isorhamnetin can be used as potential markers for the color difference between heartwood and sapwood of D. oliveri.

2.4.2. Differences in the content of main chemical components between heartwood and sapwood of D. oliveri

It can be seen from Table 4 that the content of heartwood pigment components liquiritigenin, genistein, isoliquiritigenin, formononetin, and biochanin A were 293.6505 ug/g, 161.8764 ug/g, 4787.8213 ug/g, 2133.5930 ug/g, and 2000.0880 ug/g. The content in sapwood was 31.7227 ug/g, 58.3365 ug/g, 18.9532 ug/g, 57.3800 ug/g, and 3.43030 ug/g, and the content of pigment in heartwood was 9, 3, 253, 37, and 583 times higher than that in sapwood, respectively. The results showed that the content of the pigment components isoliquiritigenin, formononetin, and biochanin A in heartwood was significantly higher than that in sapwood.
In another study conducted by Qiu et al., the content of compounds in heartwood and sapwood of teak (Tectona grandis) was significantly different, which was consistent with the results obtained in this paper that the content of chemical components in heartwood was greater than that in sapwood [42]. Isoliquiritigenin belongs to the chalcone, and its color state was yellow. It is an important substrate for the synthesis of other flavonoids and can form anthocyanins through a series of transformations by chalcone isomerase [43]. Formononetin and biochanin A are isoflavones, and their color state is yellow. There are carbonyl, methoxy, and other auxochromic groups related to wood color in the structure. Therefore, isoliquiritigenin, formononetin, and biochanin A may be the main pigment components to cause the color difference between heartwood and sapwood.

3. Materials and Methods

3.1. Materials and Preparation of Extracts

Dalbergia oliver shavings were taken from Laoyongchun Hongmu Furniture Factory, Nanning, China. It was identified by the Guangxi University Testing Centre as Dalbergia oliver heartwood and sapwood. They were then ground and passed through a 0.3 mm sieve, and these samples were used for the determination of the main chemical composition.
First, 1 g of dried wood powder was accurately weighed into a conical flask, and 30 mL 70% (v/v) of ethanol was added to it. Then, ultrasonic extraction was performed for 30 min; this process was repeated one more time. Subsequently, the extract was filtered and evaporated until dry by rotary evaporation under a vacuum to obtain the concentrated solution. The suspension solution was prepared by adding distilled water to the concentrate. After that, extraction was performed using petroleum ether and ethyl acetate, in that order. Three solutions were collected, concentrated, and evaporated to obtain the extract of the sample. These samples were used for extract analysis.
The dried sample (0.05 g) was precisely weighed and added to an 80% (v/v) methanol solution (5 mL), following which the extraction was performed by sonication for 40 min (40 kHz). The extraction solution (0.1 mL) was diluted 10 times with methanol and passed through a 0.22 µm microporous filter membrane, and then placed in a chromatography sample bottle. These samples were used to extract UHPLC-MS analysis.

3.2. Reagents and Standard

Chromatographically pure methanol, formic acid; standard products: formononetin, daidzein, isoliquiritigenin, liquiritigenin, genistein, chickpea A; all purity > 97%.

3.3. Determination of Chemical Composition

Determination of α-cellulose and hemicellulose content was measured by reference to the Chinese national standards according to GBT 2677.10-1995, “Fibrous raw material-Determination of Holocellulose” and GBT 744-1989, “Pulps-Determination of α-cellulose”, respectively.
The determination of lignin was carried out in accordance with the National Renewable Energy Laboratory (NREL) NREL/TP-510-42618, Determination of structural carbohydrates and lignin in biomass.

3.4. Fourier Infrared Spectroscopy (FTIR) Analysis of Lignin

The spectral characteristics of the lignin were determined using Fourier infrared spectroscopy (Thermo Fisher Scientific, Waltham, MA, USA). The sample was carefully ground, and 1–2 mg of the sample was ground with 0.1 g potassium bromide. The mixture was crushed into a preform. The analysis was performed in the measurement range of 400–4000 cm−1 with 32 cumulative scans.

3.5. UV Spectroscopic Analysis

The extract was measured using a UV spectrophotometer (Shimadzu Corporation, Shanghai, China). The analysis was ensured in the measurement range of 190–1100 cm−1. The resolution and sampling time of the instrument was set to 3.3 nm and 1 ms, respectively. Spectral data for the sample was collected and analyzed.

3.6. Ultra-High Performance Liquid Chromatography-Mass Spectrometry (UHPLC-MS) Analysis

The chemical composition of the samples was identified by UHPLC-MS (Thermo Fisher Scientific, Waltham, MA, USA). The chromatographic column was ACQUITY UPLC BEH C18 (2.1 mm × 50 mm × 1.7 μm). The ratio of formic acid and water was 1:1000 in mobile phase A. Methanol was chosen as mobile phase B. Gradient elution conditions were as follows: 0–15.0 min, 5% B; 15.0–18.0 min, 5–80% B; 18.0–18.1 min,100–5% B; 18.1–21 min, 5% B. The flow rate was 0.3 mL·min−1. The column temperature was 30 °C. The injection volume was 1 μL. The electrospray ionization was 300 °C. The transfer capillary temperature was 320 °C. The spray voltage in positive ion mode was 3.0 kV. The scan modes were selected as Full MS and Full MS/dd-MS2, respectively. The primary and secondary scan resolutions were 70,000 and 17,500. The flow rates of sheath gas and auxiliary gas were 206 and 69 kPa. The mass range was 100–1000 Da.
The content of the characteristic flavonoid component was determined by the external standard method. The standard working curve of flavonoids was established by the ratio of peak area and sample concentration.

3.7. Data Analysis

A t-test for the parameters of the chemical composition of the wood was run in SPSS package ver.24.0.0.0. The identification of chemical components uses the XIC Manager module in the Compound Discoverer 3.1 software (Thermo Fisher Scientific, Waltham, MA, USA). for automatic screening and analysis of accurate relative molecular masses, combined with relevant literature, mzCloud Mass Spectral Library database, compound secondary mass spectrometry fragmentation rules, and retention times of chemical standards to infer their possible chemical structures.

4. Conclusions

The content of the main components in the heartwood and sapwood of D. oliveri was not obvious, and heartwood and sapwood were weakly acidic. The lignin content was similar between heartwood and sapwood, and the functional group structure was basically identical. The main color-emitting components of heartwood of D. oliveri are flavonoids and anthocyanins, and for sapwood they are flavonoids. The pigment components in heartwood and sapwood of D. oliveri were identified, and their main components were quantified. A total of 21 flavonoid compounds were identified from heartwood and sapwood, among which vitexin, isorhamnetin, pelargonidin, isoliquiritigenin, formononetin, and biochanin A may be the main pigment components affecting the color difference between heartwood and sapwood.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules27227978/s1, Supplemental Figure: Structural identification of flavonoid components in D. oliveri.

Author Contributions

Conceptualization and study design, L.W.; sample preparation, data acquisition, and targeted method development and validation, L.W. and R.M.; data processing and analysis, interpretation of results, compound identification, and original draft preparation, L.W. and R.M.; supervision and manuscript revision, R.M. and Y.F.; resources, Y.F.; project administration and funding acquisition, Y.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported financially by the National Natural Science Foundation of China (No. 31870540).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are available from the corresponding author on request.

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability

Not applicable.

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Molecules 27 07978 g001 550
Figure 1. Infrared spectrum of Klason lignin of D. oliveri.
Figure 1. Infrared spectrum of Klason lignin of D. oliveri.
Molecules 27 07978 g001
Molecules 27 07978 g002 550
Figure 2. UV spectrum of D. oliveri heartwood and sapwood extract. (a) petroleum ether layer, (b) water layer, (c) ethyl acetate layer.
Figure 2. UV spectrum of D. oliveri heartwood and sapwood extract. (a) petroleum ether layer, (b) water layer, (c) ethyl acetate layer.
Molecules 27 07978 g002
Molecules 27 07978 g003 550
Figure 3. Chemical structure and fragmentation pathways of (a) orientin, (b) scrophulein, and (c) diosmetin.
Figure 3. Chemical structure and fragmentation pathways of (a) orientin, (b) scrophulein, and (c) diosmetin.
Molecules 27 07978 g003
Molecules 27 07978 g004 550
Figure 4. Chemical structure and fragmentation pathways of (a) ononin, (b) daidzin, and (c) biochanin A.
Figure 4. Chemical structure and fragmentation pathways of (a) ononin, (b) daidzin, and (c) biochanin A.
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Molecules 27 07978 g005 550
Figure 5. Chemical structure and fragmentation pathways of isorhamnetin.
Figure 5. Chemical structure and fragmentation pathways of isorhamnetin.
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Molecules 27 07978 g006 550
Figure 6. Chemical structure and fragmentation pathways of liquiritigenin.
Figure 6. Chemical structure and fragmentation pathways of liquiritigenin.
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Molecules 27 07978 g007 550
Figure 7. Chemical structure and fragmentation pathways of isoliquiritigenin.
Figure 7. Chemical structure and fragmentation pathways of isoliquiritigenin.
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Molecules 27 07978 g008 550
Figure 8. Chemical structure and fragmentation pathways of pelargonidin.
Figure 8. Chemical structure and fragmentation pathways of pelargonidin.
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Table
Table 1. Main chemical components of sapwood and heartwood of D. oliveri.
Table 1. Main chemical components of sapwood and heartwood of D. oliveri.
PH ValueHolocellulose (%)α-Cellulose (%)Klason Lignin (%)
Acid-Insoluble LigninAcid-Soluble LigninTotal
sapwood6.2880.35 ± 1.0 a63.63 ± 0.3 a25.96 ± 0.6 a1.94 ± 0.1 a27.90 ± 0.6 a
heartwood5.9271.81 ± 2.2 b66.81 ± 0.8 b26.79 ± 0.4 a1.45 ± 0.1 b28.24 ± 0.3 a
Different letters mean significant differences at the 0.05 level.
Table
Table 2. Pigment components of D. oliveri extract analyzed by UHPLC-MS.
Table 2. Pigment components of D. oliveri extract analyzed by UHPLC-MS.
No.Structure TypeTRMolecular FormulaMolecular Mass [M+H]+MS2Identification
TheoreticalMeasured
1Flavonoids4.68C21H20O11449.1078449.1091431.0955, 413.0857, 353.0653, 329.0649, 299.0543Orientin
2Flavonoids5.38C21H20O10433.1129433.1124415.1023, 397.0915, 313.0700, 283.0597, 255.0652Vitexin
3Isoflavones5.52C21H20O9417.1180417.1177255.0634, 177.1118, 133.0858Daidzin
4Flavanones7.34C15H12O5273.0758273.0755255.0649, 227.0703, 209.0584, 163.0387, 137.0232, 135.04382-(3,4-dihydroxyphenyl)-7-hydroxy-3,4-dihydro-2H-1-benzopyran-4-one
5Flavonoids7.46C16H12O6301.0707301.0705286.0469, 269.0439, 241.0491, 213.0544Hispidulin
6Flavonols8.14C16H12O7317.0656317.0654285.0390, 257.0437, 229.0490, 153.0181Isorhamnetin
7Isoflavones8.46C22H22O9431.1337431.1334269.0802, 237.0541, 237.0541
181.0645, 137.0231		Ononin
8 *Flavanones8.51C15H12O4257.0808257.0807239.0697, 211.0750, 137.0232Liquiritigenin
9 *Isoflavones9.04C15H10O4255.0652255.0651227.0700, 199.0750, 181.0644, 137.0231, 119.0490Daidzein
10Flavonoids9.29C17H14O6315.0863315.0860300.0621, 283.0595, 255.0645, 168.0567Scrophulein
11Flavonoids9.47C15H10O4255.0652255.0649137.0231, 119.0492Chrysin
12Anthocyanin9.61C15H10O5271.0601271.0599239.0700, 211.0755, 151.0389, 137.0232Pelargonidin
13Flavanones9.73C15H12O5273.0758273.0756255.0655, 153.0181, 119.0493Naringenin
14Isoflavones9.96C22H22O10447.1286447.1285285.0751, 241.0488, 213.0543Glycitin
15 *Isoflavones10.12C15H10O5271.0601271.0600225.0542, 197.0590, 169.0645, 137.0232Genistein
16Isoflavones10.41C16H12O5285.0758285.0758253.0488, 225.0542, 197.0595, 137.0231Glycitein
17Flavonoids10.51C17H14O5299.0914299.0916285.0711, 283.0599, 167.0339, 119.04905-hydroxy-6,7-dimethoxy-2-phenyl-4H-chromen-4-one
18Flavonoids10.52C16H12O6301.0707301.0707286.0466, 269.0438, 241.0488, 153.0179, 134.0360Diosmetin
19Chalcone11.13C15H12O4257.0808257.0807239.0699, 211.0752, 137.0232, 119.0492Isoliquiritigenin
20 *Isoflavones11.52C16H12O4269.0808269.0806254.0565, 237.0544, 137.0234, 118.0414Formononetin
21 *Isoflavones12.78C16H12O5285.0758285.0757257.0803, 229.0856, 197.0595, 137.0231Biochanin A
Note: * Confirmed by comparison with the reference substance.
Table
Table 3. Different chemical constituents between D. oliveri heartwood and sapwood.
Table 3. Different chemical constituents between D. oliveri heartwood and sapwood.
StructureCompoundColor
sapwoodisoflavonedaidzinwhite
isoflavoneononinwhite
isoflavoneglycitinwhite
heartwoodflavonoidvitexinyellow
flavonolisorhamnetinyellow
anthocyaninpelargonidinred
Table
Table 4. Content of main chemical components between heartwood and sapwood of D. oliveri.
Table 4. Content of main chemical components between heartwood and sapwood of D. oliveri.
CompoundCalibration CavesR2Heartwood (ug/g)Sapwood (ug/g)
Liquiritigeniny = 1,779,112.4834x + 16,661,916.14970.996293.650531.7227
Genisteiny = 1,371,988.0761x + 14,319,545.45880.995161.876458.3365
Isoliquiritigeniny = 1,779,112.4834x + 16,661,916.14970.9994787.821318.9532
Formononetiny = 3,740,086.0193x + 16,632,919.11630.9992133.593057.3800
Biochanin Ay = 2,293,814.2766x + 19,031,906.65420.9972000.08803.4303
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Wei, L.; Ma, R.; Fu, Y. Differences in Chemical Constituents between Dalbergia oliveri Heartwood and Sapwood and Their Effect on Wood Color. Molecules 2022, 27, 7978. https://doi.org/10.3390/molecules27227978

AMA Style

Wei L, Ma R, Fu Y. Differences in Chemical Constituents between Dalbergia oliveri Heartwood and Sapwood and Their Effect on Wood Color. Molecules. 2022; 27(22):7978. https://doi.org/10.3390/molecules27227978

Chicago/Turabian Style

Wei, Liuming, Ruoke Ma, and Yunlin Fu. 2022. "Differences in Chemical Constituents between Dalbergia oliveri Heartwood and Sapwood and Their Effect on Wood Color" Molecules 27, no. 22: 7978. https://doi.org/10.3390/molecules27227978

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