The part of the wood cell (parenchyma cells) that is physiologically inactive and filled with a non-organic structure (extractives) which contributes to its colorations and natural durability is the heartwood. This natural durability is related to the extractive content in the heartwood, in particular phenolic extractives, which are dominant and contain antioxidant activities (Rababah
The extractives are responsible for the odor, wood color, and protection from microbe and insect attacks (Umezawa, 2000). Furthermore, they are chemical constituents located in the lignocellulosic tissue that contains a higher diversity of organic compounds, such as triglycerides, neutral compounds, and phenolic compounds (Nascimento
Studies related to extractives in mahogany were extensively conducted on the bark (Falah
Because the presence of heartwood is very important as it is related to natural durability and its quality, research is necessary to investigate the extractive changes that occur during the heartwood formation process. The formation process transforms sapwood into heartwood (Niamké
Five species of
Wood sampling scheme for extractive analysis.
By visual inspection, trees within the age of 1 and 2 years contained sapwood only. Meanwhile, in the case of 4–5-year-old tree samples which possessed a heartwood area, each disc was divided into sapwood and heartwood. The heartwood had a distinctive salmon pink to red color compared with the light sapwood color. Lemmens (2005) stated that the
Furthermore, the disc samples were stored at room temperature and air-dried after measuring the area of heartwood. Afterwards, air-dried wood specimens were collected by drilling in a disc from sapwood (0.5 cm from bark-sapwood border) and heartwood (1.0 cm from the sapwood-heartwood border). The drilled wood was then separately milled to a powder and sieve-screened (to pass a 1 mm sieve) for chemical analysis. Table 1 shows more detailed information on wood specimens.
Description of tree samples from young
No | Age (year) | Average of DBH (cm) | Average of total merchantable height (m) |
---|---|---|---|
1 | 1 | 1.08 ± 0.28 a | 0.54 ± 0.10 |
2 | 2 | 1.99 ± 0.32 | 1.72 ± 0.16 |
3 | 3 | 4.46 ± 0.10 | 4.25 ± 0.10 |
4 | 4 | 6.13 ± 1.12 | 4.80 ± 0.77 |
5 | 5 | 8.05 ± 1.17 | 6.60 ± 1.20 |
Note: a = Diameter is taken at the level height 10%
Sodium carbonate, sodium hydroxide, aluminum chloride, and Folin-Ciocalteu’s phenol reagent were purchased from Merck (Darmstadt, Germany), while standard components of gallic acid and D-glucose were purchased from Sigma-Aldrich (Chemie GmbH, USA).
The powder (0.8 to 1.5 g) was successively extracted by
The total phenolic content (TPC) was determined by the Folin-Ciocalteu method (Singleton
Total soluble polysaccharides (TSP) were measured according to DuBois
The data were statistically handled using the SPSS program (version 16 IBM, New York, USA). Analysis of variance (ANOVA) was conducted and the significant differences were set at a 95% confidence level. Also, two-way ANOVA was applied to determine the effect of tree age and axial position (bottom and top) on the extractive content, TPC, and TSP. All the obtained data were normally distributed after analysis, and Duncan’s test was performed to evaluate groups that differ.
The average value of n-hexane, methanol, and hot water extractive content from bottom to top parts were 2.39 to 0.71%, 7.81 to 1.61%, and 5.21 to 1.01%, respectively (Table 3). In addition, Figure 2a showed that the total extractive content ranged from 3.93 to 13.7% of dried wood. Methanol solution has the highest contribution of total extractives, it ranged from 25 to 70.2% based on extractive weight (Figure 2b). Meanwhile, the value for hot water and n-hexane ranged from 13.6 to 50.3% and 10 to 29%, respectively.
Total extractive content of
Figure 3 showed that the TPC in the methanol extracts ranged from 107.3 to 480.2 mg GAE/g dried extract. Furthermore, the amount of TSP ranged from 160 to 688 mg GE/g dried extract with the mean values of 440.3 mg GE/g dried extract (Figure 4).
Total phenolic content based on mg GAE/g dried extract from
Total soluble polysaccharide content based on mg GE/g dried extract from
The ANOVA of extractive contents showed significant tree age and axial position interactions (Table 2). Prior to heartwood formation (1 to 3 years) (Table 3) generally the extractive content increased with the increasing tree age at the bottom of the tree, where the content of hexane and hot water extract increased significantly from the age of 1 to 2 and 1 to 3 years. Meanwhile, the methanol extract slightly decreased from the age of 2 to 3 years, after slightly increasing from the age of 1 to 2 years. Furthermore, the total extractive content increased significantly from the age of 1 to 3 years. At the top of the tree, hexane and hot water extract decreased significantly (hot water extract) at the age of 3 years, although slightly increased previously at the age of 1 to 2 years. Meanwhile, a significant decrease was found in the methanol extract (from tree age of 1 to 2 and 1 to 3 years) and in the total extractive content (from tree age of 1 to 3 years and 2 to 3 years).
Two-way ANOVA analysis for extractive, TPC, and TSP contents of
Source of variation | df | Parameters | |||||
---|---|---|---|---|---|---|---|
Methanol | Hot water | Total Extractive | TPC | TSP | |||
Tree age (T) | 10 | *** | *** | ** | *** | *** | ** |
Axial (A) | 1 | *** | n.s | *** | *** | *** | *** |
T × A | 10 | *** | ** | *** | *** | ** | *** |
Error | 46 | ||||||
Total | 67 |
df degrees of freedom;
n.s. not significant at 5% level,
P<0.05,
P<0.01,
P<0.001.
The interaction of tree age with an axial position on the extractive content of
Solvent | 1 year | 2 years | 3 years | |||
---|---|---|---|---|---|---|
Bottom | Top | Bottom | Top | Bottom | Top | |
Sapwood | Sapwood | Sapwood | Sapwood | Sapwood | Sapwood | |
0.71 ± 0.14 a | 1.09 ± 0.24 bc | 1.26 ± 0.08 bc | 1.28 ± 0.20 bcd | 1.41 ± 0.41 cd | 0.96 ± 0.13 ab | |
Methanol | 4.30 ± 0.85 bcde | 7.48 ± 2.34 f | 4.48 ± 0.48 abcde | 4.36 ± 1.04 cde | 3.72 ± 1.09 abcd | 2.57 ± 0.98 abc |
Hot water | 2.09 ± 0.70 bc | 2.09 ± 0.50 bc | 3.57 ± 1.19 e | 2.22 ± 0.36 bc | 5.21 ± 0.65 f | 1.01 ± 0.20 a |
Total | 7.10 ± 1.23 bc | 10.7 ± 2.27 de | 9.31 ± 1.25 cde | 7.86 ± 0.69 cd | 10.3 ± 1.59 de | 4.54 ± 0.95 ab |
Solvent | 4 years | |||
---|---|---|---|---|
Bottom | Top | |||
Sapwood | Heartwood | Sapwood | Heartwood | |
1.64 ± 0.28 de | 1.90 ± 0.42 e | 1.14 ± 0.10 bc | 1.22 ± 0.06 bc | |
Metanol | 4.16 ± 1.34 bcde | 4.74 ± 1.32 cde | 1.66 ± 0.33 a | 1.93 ± 0.27 ab |
Hot water | 3.19 ± 0.47 de | 3.40 ± 0.54 e | 1.13 ± 0.18 a | 1.50 ± 0.43 ab |
Total | 8.98 ± 1.57 cde | 10.0 ± 1.16 de | 3.93 ± 0.52 a | 4.65 ± 0.56 ab |
Solvent | 5 years | |||
---|---|---|---|---|
Bottom | Top | |||
Sapwood | Heartwood | Sapwood | Heartwood | |
1.31 ± 0.47 bcd | 2.39 ± 0.16 f | 1.29 ± 0.11 bcd | 1.42 ± 0.13 cd | |
Metanol | 6.42 ± 0.51 ef | 7.81 ± 1.33 f | 5.19 ± 2.38 cde | 7.55 ± 3.96 f |
Hot water | 3.20 ± 0.35 de | 3.52 ± 0.62 e | 2.42 ± 0.86 bcd | 2.69 ± 1.26 cde |
Total | 10.9 ± 0.41 e | 13.7 ± 1.80 f | 8.90 ± 2.29 cde | 11.7 ± 4.16 ef |
Note: Average of five trees ± the standard deviation; The same letters in the same row are not significantly different at
From the age of 3 to 4 years in sapwood, the levels of hexane and methanol increased with tree age at the base of the tree, while the reverse pattern was found in the amount of hot water extract and total extractives, where the hot water content decreased significantly. At the top part, a slight increase in the extractive content was found in the amount of hexane and hot water extract, while the content of methanol and total extractives were found to decrease. After the formation of heartwood (4 to 5 years), the content of methanol and hot water extract increased (except for hexane) with tree age in the bottom sapwood. The same pattern was shown in heartwood, except for the hot water extract which slightly increased. Further at the top of the tree, both in sapwood and heartwood, the extractive content of methanol and hot water increased significantly from the age of 4 to 5 years. A similar trend was shown by the total extractive content, where its level drastically increased with increasing tree age.
In the axial position, the extractive content generally descends from the bottom to the top of the tree before heartwood formation (Table 3, Figure 2). A significant reduction was found in the amount of hexane extract at the age of 3 years and hot water at the age of 2 and 3 years. The reverse trend was found at the age of 1 year, where the extractive content increased significantly in hexane and methanol extracts. Furthermore, a similar pattern was also shown in the total extractive content, where the levels decreased significantly at the age of 3 years and increased significantly at the age of 1 year.
In addition, from the age of 3 to 4 years, the content of extractive patterns was similar to before heartwood formation (except for methanol extract at the age of 3 years and hexane extract at the age of 4 years, which slightly decreased). After the formation of heartwood, at the age of 4 years both in sapwood and heartwood, the extractive content decreased significantly from the bottom to the top of the tree. The same trend was also shown at the age of 5 years, although the decrease was not significant (except for methanol extract). Furthermore, in the radial profiles, extractive content in the heartwood both at the base and at the upper part of the tree was higher than in the sapwood at the age of 4 years. The same pattern was also shown at the age of 5 years, where the content of hexane extract in heartwood was significantly larger compared to sapwood at the bottom and a similar trend was shown by the methanol extract at the top of the tree.
There was a significant interaction between age and axial position in TPC in the ANOVA test (Table 2). Before heartwood formation (Figure 3), TPC increased with tree age. It increased significantly from the age of 1 to 2 years at the bottom of the tree. A similar trend was also found in the TPC at the age of 3 to 4 years at the bottom sap-wood part, although TPC decreased at the top of the tree. However, a reverse pattern was found from the age of 4 to 5 years after heartwood formation, where the TPC increased significantly at the top sapwood part.
Axially, before heartwood formation (1 to 3 years), the TPC content decreased from the bottom to top part except for 1-year-old trees, which slightly increased from the base to the upper part of the trees. The same pattern was shown during heartwood formation. A significant decrease was found at the age of 4 years in sapwood. In addition, a similar trend was also shown after the formation of heartwood, where both in sapwood and heartwood (4 and 5 years old), the TPC content significantly decreased from the bottom to the top of the tree. Furthermore, in the radial variation, both at the age of 4 and 5 years, the difference in TPC between sap-wood and heartwood was more visible at the bottom than at the top, where the TPC of heartwood was higher than that in the sapwood samples.
The ANOVA of TSP showed significant tree age and axial position interactions (Table 2). Generally, the TSP level increased with the increasing tree age before the formation of heartwood (Figure 4), where both at the bottom and top of the tree, a significant increase was found from the age of 1 to 2 years. Meanwhile, at the top part, the amount of TSP from the age of 2 to 3 years decreased significantly. Furthermore, the TSP content slightly increased again from the age of 3 to 4 years both at the bottom and top of the tree in sapwood. Then, TSP at the bottom both in sapwood and heartwood decreased significantly from the age of 4 to 5 years after the formation of heartwood. In contrast, the amount of TSP increased significantly at the top heartwood of the tree.
In axial position, the TSP increased from the bottom to the top of the tree (except for the age of 3 years) before heartwood formation. TSP from the age of 3 to 4 years, with the axial pattern being the same as that of TPC, decreased drastically from the base sapwood to the upper sapwood. Furthermore, the TSP trend at the age of 4 and 5 years was the same as that of TCP at the same age where the TSP level dropped from the bottom to the top of the tree. Meanwhile in the radial variation, TSP in sapwood was higher than in heartwood. A significant difference was found at the age of 4 years at the top, and at 5 years at the base of the tree.
Theoretically, the non-polar solution (
In contrast, extractive levels of this study were higher compared to the content of petrol ether (0.8%), acetone (3.2%), methanol (3.4%), hot water (1.1%), and cold water (2.1%) (Rutiaga Quiñones
TPC of this study was lower compared to previous research. Batubara
In general, the extractive content increased with increasing tree age. The same pattern has been reported in previous studies in
However, in this study it was also found that the extractive content decreased from a certain tree age, namely in the hot water extract at the bottom and in the methanol extract at the top part from the age of 3 to 4 years. In addition, especially at the top of the tree from 1 to 3 years, the extractive content decreased significantly. This may be influenced by the certain proportion of sugar components which decreases with age at the top of the tree. Berrocal
In axial variation, the extractive content at the bottom part was greater compared to the top of the tree (except for 1-year-old trees). A similar trend was reported in previous work in other species, such as superior teakwood,
In the radial profiles, the extractive content in heartwood was higher than in the sapwood part. A similar trend has been reported in other species, such as
The high levels of extractives in heartwood are related to the heartwood formation process, where the accumulation of extractives is a key feature in the formation of heartwood (Hillis, 1971). Umezawa (2000) reported that heartwood is richer in polyphenols and resin acids (diterpenes). In heartwood (with a lower pH condition), the most abundant of the soluble sugars (xylose, mannose, and arabinose) were derived from hydrolyses. This is supported by the decreasing TSP content from sap-wood to heartwood as well as a reverse pattern found in TPC. Thus, the decline in TSP from sapwood to heartwood indicates that the content of certain TSP compounds is metabolized at the sapwood-heartwood boundary (Niamké
In the transition zone, the amount of starch can be hydrolyzed to glucose by hydrolyzing enzymes (amyloglycosidases) (Magel
Based on the ANOVA analysis, there was a significant interaction between tree age and axial position in all parameters. The distribution of the extractive content, TPC, and TSP increased with increasing tree age, except for a certain age before heartwood formation (3 years) at the top of the tree (for methanol and TSP content). The highest increase was found after heartwood formation (4 to 5 years) in hexane, methanol, and the total extractive fractions. On the other hand, the three parameters generally have a similar pattern both in axial and radial variation (except TSP and TPC), where in axial position, its distribution decreased from the bottom to top of the tree, particularly after the age of 2 years. This might be one of the characteristics of