Variability in the chemical composition and antioxidant properties of sapwood and heartwood extracts of some tropical woods from Côte d’Ivoire
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Appolinaire B. Bley-Atse
,
Florence B. Niamké
Abstract
In Africa, the forestry industry generates significant waste that remains underexploited. Studies have highlighted the presence of active biomolecules in durable wood species. This study characterised the extracts of three durable tropical woods: Nauclea diderrichii, Mansonia altissima, and Milicia excelsa. Moreover, we estimated their insecticidal potential. Once the wood powders samples were prepared, the extractions were carried out by cold maceration for 2 h in a hydroethanolic solvent in a 50/50 (v/v) ratio of ethanol and water. The yields for aqueous extractions (0.9 ± 1.2 % to 1.3 ± 0.1 %) were lower than those for hydroethanolic extractions (4.3 ± 0.7 % to 5.2 ± 0.8 %). Aqueous extracts contained alkaloids, tannins, quinones, polyterpenes, sterols, polyphenols, flavonoids, anthocyanins, and saponins, while hydroethanolic extracts contained the same compounds but in higher proportions. Total polyphenol and flavonoid contents of the aqueous extracts were 2.2 mg GA Eq/g and 0.6 mg QEq/g, respectively, compared to the hydroethanolic extracts with contents of 93.4 ± 0.1a mg GA Eq/g and 97.0 ± 1.1a mg QEq/g (p = 0.005). The antioxidant activity of the aqueous extracts was 8.2 ± 0c µmol Trolox Eq/L, while that of the hydroethanolic extracts was 60.6 ± 0.3a µmol Trolox Eq/L (p = 0.005). These results suggest that the wood extracts studied contain bioactive molecules with potential applications in sustainable control of crop pests.
1 Introduction
Chemical control is the most widely used method of pest management. This method combines traditional practices, such as spraying and fumigation, with innovative practices, including endotherapy (Moura et al. 2023). Therefore, chemical control offers several advantages, including effectiveness, rapidity, and duration of action. However, this method has certain drawbacks, such as persistence, environmental pollution, and toxicity to humans, animals, and beneficial organisms (Mariau and Philippe 1983). Several studies have proposed alternative solutions. Integrated pest management, which combines several techniques simultaneously, appears to be an effective solution to this problem (Vasileiadis et al. 2011). These techniques include the use of resistant plant varieties, crop rotation, and physical control using insect-proof nets (Gogo et al. 2014). Some selected insecticide plants, such as Ocimum gratissimum L., and essential oils derived from Citrus limon L., Mentha piperita L. have been used to control pests (Picard et al. 2012). Repellent or attractive pheromones can also be used to control pests (Smart et al. 2014). Biological control using parasitoids, predators, and entomopathogenic fungi is also used to control several pests (Murali-Baskaran et al. 2018). Many studies have also been conducted on plant extracts (Manh and Tuyet 2020). Botanical pesticides are effective against crop pests, cost-efficient, easily biodegradable, and non-toxic to non-target organisms. They are naturally available in the environment and have several effects. These effects are due to the phytochemical compositions of the plants. Therefore, they can be integrated into pest management systems and contribute to sustainable agriculture (Lengai et al. 2020). However, the forestry industry generates a significant amount of waste globally. Many wood-producing countries generate more than 2 million m3 of sawdust annually (Mwango and Kambole 2019). In Africa, logging produces large quantities of waste, estimated at over 30,000 m3/year (De Meeûs 2019). Sawmills alone generate 40–60 % of the solid waste produced during log processing (Souza et al. 2018). Poor waste management results in health and environmental issues, such as air pollution, greenhouse gas emissions, and the destruction of plant and aquatic life (Mwango and Kambole 2019). Nevertheless, waste is mainly valorised in the treatment of industrial water and the elimination of organic and inorganic pollutants (Adegoke et al. 2022). It can also be used as woody biomass in the manufacture of compost, biochar, and sawdust-based biofuel composite briquettes for domestic use (Zanli et al. 2022). Despite these uses, much of the waste remains underexploited (De Meeûs 2019). These underexploited wastes can be valorised by improving waste management, contributing to better natural resource conservation. In addition, several studies have shown that sustainable tropical tree species synthesise biomolecules in their wood that are responsible for their natural resistance, including total phenols, tannins, and flavonoids (Niamké et al. 2021). Phenolic compounds are known for their ability to neutralise free radicals and slow the fungal biodegradation process (Anouhe et al. 2018). The isolated chemicals could serve as an additional source of revenue for the forestry industry and be used for wood preservation, cosmetics, dermatology, and nutraceuticals (Ansel et al. 2016). In addition, several studies have confirmed that terpenes have insecticidal properties against a variety of insect pests (Smith et al. 2018). However, a large number of bioactive compounds (lignans, gallic acid, stilbenes, flavonoids, and terpenes) in certain tree branches, such as knots, are often left behind. Knots are particularly rich in bioactive substances compared to the heartwood and sapwood of softwoods (Kebbi-Benkeder et al. 2015). Although these biomolecules have been chemically characterised, their application as biopesticides against crop pests remains limited. Given the functional properties of biomolecules, the extractives in the waste products of forest tree species could serve as alternatives to chemical pesticides (De Meeûs 2019). Hassan et al. (2018) primarily on evaluating heartwood extractives against wood insects, such as termites. However, sapwood, along with tree nodes and other shoots, could also represent a valuable asset in the fight against insect pests, highlighting the interest of this study. Sapwood may also contain non-structural carbohydrates, gums, resins, silicates, and extractive precursors. The synthesis of bioactive extractives in the sapwood and extractive precursors stored in the heartwood during the duraminisation process shows the importance of sapwood in terms of molecules of interest (Hillis 2012; Taylor et al. 2002). It is also a fact that trees originating from forests are now more disturbed than those previously studied. New defence and bioactive molecules are likely to be synthesised in these trees. Therefore, this study aimed to characterise extracts from three tropical woods, Nauclea diderrichii (Badi), Mansonia altissima (Bete), and Milicia excelsa (Iroko), to assess their potential as biopesticides. More specifically, this study aimed to produce aqueous and hydroethanolic sapwood and heartwood extracts from these species and to perform phytochemical characterisation to evaluate their suitability for use as biopesticides.
2 Materials and methods
2.1 Materials
Samples were collected in the Akoupe forest, classified as Besso, located in the Me region of southeastern Côte d’Ivoire (06°14′–06°30′ N and 003°37’ −003°48′ W). The selection criteria were the potential of bioactive substances and resource availability. These three trees have one thing in common: they are all durable woods (Thomas et al. 2023). In addition, there is the availability of resources. Large trees are found in forest areas, and their wood is widely used and appreciated by the forestry industry. A bibliographical approach was followed by a survey, via questionnaire forms, of forestry research and management structures, SODEFOR (“Forests Development Society”); CNRA (“National Center for Agronomic Research”), and the Ministry of Water and Forests. Three trees per species were harvested: N. diderrichii (Badi), M. altissima (Bete), and M. excelsa (Iroko). To minimise variability, trees with straight trunks, high forks, and no visible signs of disease were selected and collected. In terms of dendrometric characteristics, the trees collected had diameters ranging from 50 to 80 cm and heights between 13 and 19 m. Once felled in the field, each tree was sampled by cutting a 1.3 m long log. The samples were then transported to a sawmill. At the sawmill, each log was cut into two central planks, labelled A and B, each 4 cm thick (Figure 11). The sawn boards were stored in a warehouse well protected from rain and sun at the National Polytechnic Institute Felix Houphouët-Boigny (INP-HB) in Yamoussoukro, where they were kept at a temperature of 27 ± 2 °C.
Sapwood and heartwood powder process. Sw: sapwood, Hw: heartwood.
2.2 Methods
2.2.1 Plant material processing
Once dried, the logs were separated into sapwood and heartwood sections. These different parts were then reduced to test specimens, which were dried and ground into small pieces before being further reduced to a fine powder (2.5 mm in diameter) using an electric grinder. The dried powders were stored in jars and sealed for the planned experiments (Figure 1).
2.2.2 Preparation of extracts
Two solvents were used. First, distilled water was used to create aqueous extracts. Second, a mixture of water and alcohol (50/50 (v/v)) was used to prepare the hydroethanolic extracts. Wood (sapwood and heartwood) was ground into a 2 mm diameter powder using an electric grinder. Aqueous extracts were obtained by mixing 300 mL of distilled water with 30 g of shredded wood for 2 h hydroethanolic extracts were prepared separately by mixing and macerating 30 g of shredded wood in 300 mL of a 50/50 (v/v) hydroethanolic solution for 2 h. After filtration, the solvent was recovered using a rotary evaporator at 40 °C. To evaporate the remaining solvent and allow drying, the extracts were placed in an oven at 40 °C for 24 h. The extractions were conducted under laboratory conditions at 27 ± 2 °C with a relative humidity of 60 ± 10 %. Extraction was repeated three times following the same procedure, and the extraction yield was calculated (Figure 2).
Extracts process. Nauclea diderrichii (Badi); Mansonia altissima (Bete); Milicia excelsa (Iroko).
2.2.3 Phytochemical screening
Screening was performed on both types of extracts using standard characterisation methods (Rojas et al. 1992; Ronchetti et al. 1971; Vlietinck et al. 1995; Zuharah et al. 2021). These tests were used to target specific chemical families, particularly alkaloids, flavonoids, polyphenols, terpenes, sterols, saponins, and tannins.
2.2.4 Data collection
2.2.4.1 Determination of the extraction yield
The extraction rate was determined using the following equation:
The Initial mass is the mass of the wood powder obtained after shredding (g).
The Final mass was that of the dry extract obtained after evaporation (g).
2.2.4.2 Wood extracts characterisation
Chemical groups known for their biological activities were identified using colourimetric tests. Role tests were used to detect specific colourations or precipitates of the major chemical families, in accordance with the methods described by Clemen-Pascual et al. (2022) and Harborne (1998). Each test was repeated thrice, and the results were interpreted as follows: the positive sign “+” indicated the presence of the chemical groups and the negative sign “−” indicated the absence of the groups (Dah-Nouvlessounon et al. 2015).
Alkaloids
For alkaloid detection, 4 mL of each extract solution, “5 mg/mL ethanol/water,” was evaporated in a water bath. The residue was dissolved in 4 mL of alcohol at 60 °C. The alcoholic solution was dispensed into two test tubes for analysis. Two drops of Bourchardat reagent, an iodine-iodide reagent, were added to one of the test tubes. A reddish-brown precipitate was observed, indicating the presence of alkaloids in the sample. Two drops of Dragendorff reagent, an “aqueous solution of potassium iodide-bismuth”, were added to the other tube. The appearance of a precipitate or orange colouration also indicates the presence of alkaloids.
Polyphenols
Polyphenols were detected using the method described by Clemen-Pascual et al. (2022). A 2 % alcoholic ferric chloride solution was added to 2 mL of extract (5 mg/mL) for each wood species studied. The appearance of a dark blue-black or green colour indicates the presence of phenolic compounds in the extract.
Tannins
Catechic tannins were detected using the method described by Longanga Otshudi et al. (2000) and Tona et al. (1998). To 5 mL of extract, “5 mg/mL”, 15 mL of Stiasny’s reagent, 10 mL of 30 % formalin, and 5 mL of concentrated HCl were added. The resulting mixture was kept in a water bath at 80 °C for 30 min and then cooled. Precipitates were observed, indicating the presence of catechic tannins. The solution containing catechic tannins was filtered through a Whatman filter (grade 4 CHR), and the collected filtrate was saturated with sodium acetate. Three drops of 2 % ferric chloride were then added to the mixture. The appearance of an intense blue-black colour indicated the presence of gallic tannins (Longanga Otshudi et al. 2000; Tona et al. 1998).
Flavonoids
A few drops of 10 % NaOH solution were added to 3 mL of the extract solution (5 mg/mL). A yellow-orange colour indicated the presence of flavonoids.
Saponins
Wood extract (5 mg/mL) was dissolved in 10 mL of distilled water and shaken for 30–45 s. After standing for 15 min, the height of the foam was measured. The persistence of foam over 1 cm indicates the presence of saponins.
Sterols and polyterpenes
A dry extract (0.1 g) was dissolved separately in hot 1 mL of acetic anhydride in a capsule and poured into a test tube containing 0.5 mL of concentrated sulphuric acid (H2SO4). The appearance of violet colour, turning blue and then green, indicated the presence of sterols and triterpenes (Dah-Nouvlessounon et al. 2015).
Quinones
The Borntraeger “double ammonia dilution” reagent was used for quinone detection in the samples. A 2 mL aliquot of the plant extract was obtained from each capsule. The residue was added to 5 mL of 5-fold diluted HCl. The mixture was then placed in a test tube and heated in a boiling water bath for half an hour. The mixture was then cooled under a stream of cold water, and the hydrolysate was extracted with 20 mL of chloroform in a test tube. Finally, the chloroform phase was collected in a test tube, and 0.5 mL of twice-diluted ammonia was added. The appearance of a red-to-violet colouration indicates the presence of quinones (Longanga Otshudi et al. 2000; Rojas et al. 1992).
Anthocyanin
Anthocyanin content was determined using the method described by Lee et al. (2005). Each sample was diluted in 1.5 mL buffer (pH 1.0) and 1.5 mL buffer (pH 4.5). The absorbance (A) of the two solutions was recorded at 520 and 700 nm, respectively, using a spectrophotometre. The total anthocyanin concentration (TAC), expressed in mg per mL cyanidin 3-glycoside equivalent, was calculated using the following formula:
A = (A520 nm − A700 nm) pH 1.0 − (A520 nm − A700 nm) pH 4.5.
WM: Molecular weight of cyanidin-3-glucoside (cyd-3-glu) = 449.2 g/mol.
F: Dilution factor = 1.5.
L: Tank length = 1 cm.
ɛ: molar extinction coefficient = 26,900 L mol−1 cm−1
103: conversion factor from g to mg.
2.2.4.3 Determination of phytochemical content
Polyphenols
The total polyphenol content of the extracts was determined using the Folin-Ciocalteu method described by Wood et al. (2002). To this end, 2.5 mL of diluted Folin-Ciocalteu reagent (1/10) was added to 30 μL of the hydroethanolic extract (5 mg/mL). The resulting mixture was placed in the dark for 2 min, and 2 mL of sodium carbonate solution (75 g/L) was added. The mixture was heated in a water bath (50 °C) for 15 min and then rapidly cooled. The analyses were repeated three times, and the average polyphenol content was expressed in milligrams of gallic acid equivalent per gram of dry extract weight (mg GA Eq/g).
Flavonoids
The method described by Wood et al. (2002) was used to determine the total flavonoid content. In a 25 mL flask, 0.75 mL of 5 % (m/v) sodium nitrite (NaNO2) was added to 2.5 mL of the extract. Then, 0.75 mL of 10 % (m/v) aluminium chloride (AlCl3) was added to the mixture and incubated in the dark for 6 min. After incubation, 5 mL of sodium hydroxide (NaOH 1 N) was added, and the volume was increased to 25 mL. The mixture was shaken before being assayed using a UV-visible spectrophotometer, and the absorbance was recorded at 510 nm. The trials were performed in triplicate. Flavonoid content was quantified in grams per litre of quercetin equivalent extract (µg quercetin equivalent/g).
2.2.4.4 Determination of antioxidant activity using the ABTS+ method
The ABTS+ method is based on the ability of compounds to reduce the ABTS+ radical cation (2.2′-azinobis-3-ethylbenzothiazoline-6-sulphonic acid). The ABTS+ radical cation was produced by reacting 8 mM ABTS (87.7 mg in 20 mL distilled water) and 3 mM potassium persulphate (0.0162 g in 20 mL distilled water) in a 1:1 (v/v) ratio. The mixture was then incubated in the dark at room temperature for 12–16 h. The ABTS+ solution was diluted with methanol to obtain a solution with an absorbance of 0.7 ± 0.02 at 734 nm. A 3.9 mL test portion of the diluted ABTS+ solution was added to 100 µL of the test compound. After shaking, the mixture was incubated in the dark (T = 30 ± 2 °C) for 6 min. The residual ABTS+ radical absorbance was measured at 734 nm using a UV-visible spectrophotometer. This value should be between 20 % and 80 % of the absorbance of the blank sample (Choong et al. 2007; Wood et al. 2002). The tests were repeated three times, and the results were expressed in µmol Trolox equivalent per litre of extract (µmol Trolox Eq/L). Antioxidant activity was expressed as the percentage of inhibition. A calibration line was generated using the following Trolox concentrations: 0.375, 0.5, 0.625, 1, 1.125, 1.375, and 1.5 µmol. The inhibition rate (%I) of ABTS+ was calculated as follows:
A0 = ABTS absorbance diluted,
Equations (1) and (2) were used to express the antioxidant activities (Equation (3)) of the different extracts:
Antioxidant activity or concentration.
Extract concentration before dilution = 0.1 g/20 mL; df: dilution factor.
2.2.5 Data analysis
Data were collected using Excel 365 Office and analysed using XLSTAT 2023 1.2. (1406) for Analysis of Variance (ANOVA). The results were statistically analysed using the non-parametric Kruskal-Wallis test. Multiple comparison analysis using Dunn’s test was performed to compare the total polyphenol content, total flavonoid content, and antioxidant activity. Statistical tests were performed at a 5 % significance level.
3 Results and discussion
3.1 Results
3.1.1 Wood chip extraction yield
The yields of aqueous extracts ranged from 0.9 ± 1.2 % to 1.3 ± 0.1 %, which were significantly lower (p < 0.05) than those of hydroethanolic extracts, which ranged from 4.3 ± 0.7 % to 5.2 ± 0.8 %. No significant differences (p > 0.05) were observed between the yields of heartwood hydroethanolic extracts (4.3 ± 0.7 % to 5.2 ± 0.8 %), and those of sapwood (3.6 ± 0.1 % to 4.7 ± 0.9 %) (Figure 2). Similarly, aqueous extracts yields from heartwood (1.0 ± 1.2 % to 1.3 ± 0.1 %) and sapwood (0.9 ± 1.2 % to 0.9 ± 0.1 %) were not significantly different (p > 0.05) (Figure 3).
Aqueous and hydroethanolic extract yields: (a) aqueous extract yields; (b) hydroethanolic extract yields.
3.1.2 Characterisation of various aqueous and hydroethanolic wood extracts
The aqueous extracts contained alkaloids, tannins, quinones, polyterpenes, sterols, polyphenols, flavonoids, anthocyanins, and saponins (Tables 1 and 2). Tannins, anthocyanins, and saponins were present in all the wood extracts. Polyphenols and flavonoids were specifically found in M. altissima and M. excelsa extracts. Polyterpenes and sterols were exclusively detected in all three sapwood types. The hydroethanolic extracts contained alkaloids, catechic tannins, polyphenols, flavonoids, anthocyanins, and saponins (Table 1). Alkaloids (Dragendorff’s test), tannins (catechic), polyphenols, and flavonoids were present in all wood extracts. Saponins were only found in the M. altissima sapwood extracts. Statistical analyses were also performed on the quantitative composition of polyphenols, flavonoids, and antioxidant activity of these extracts (Tables 3 and 4). In aqueous extracts, total polyphenol content ranged from 0.5 ± 0 to 2.2 ± 0 mg GA Eq/g (Table 3). Similarly, the total flavonoid content varied from 0.3 ± 0 to 0.6 ± 0 mg quercetin Eq/g. The antioxidant activity ranged from 1.9 ± 0 to 8.2 ± 0 µmol Trolox. Comparing the averages of these three parameters revealed no significant differences (Table 3). For the hydroethanolic extracts, significant differences were observed for the three parameters. The total polyphenol content ranged from 0.1 ± 0.1 to 93.4 ± 0.1 mg GA Eq/g, with N. diderrichii heartwood showing the highest concentration, significantly exceeding that of N. diderrichii sapwood, which in turn had a higher polyphenol content than M. altissima and M. excelsa wood extracts (Table 4). Total flavonoid content varied from 0.2 ± 0.3 to 197 ± 1.1 mg quercetin Eq/g, with M. altissima heartwood containing significantly higher flavonoid content than M. altissima and N. diderrichii sapwood. The hydroethanolic extract of M. altissima heartwood had the highest antioxidant activity, surpassing that of N. diderrichii heartwood and M. excelsa sapwood (p > 0.05). These extracts had similar antioxidant activities, which were significantly higher than those of M. altissima and N. diderrichii sapwood and M. excelsa heartwood (Table 4).
Phytochemical screening of aqueous extracts of wood studied.
| Extracts Species Common name Radial parts |
Aqueous extracts | ||||||
|---|---|---|---|---|---|---|---|
|
Nauclea diderrichii
Badi |
Mansonia altissima
Bete |
Milicia excelsa
Iroko |
|||||
| Sapwood | Heartwood | Sapwood | Heartwood | Sapwood | Heartwood | ||
| Alkaloïdes | Dragendorf | + | + | + | + | − | − |
| Mayer | + | + | + | + | − | − | |
| Catechic Gallic |
Tannins | + | + | + | + | + | + |
| Tannins | + | + | + | + | + | − | |
| Quinones | − | + | − | − | − | + | |
| Polyterpenes & sterols | + | − | + | − | + | − | |
| Polyphenols | − | − | + | + | − | − | |
| Flavonoids | − | − | − | − | − | + | |
| Anthocyanins | + | + | + | + | + | + | |
| Saponins | + | + | + | + | − | + | |
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(+) Presence of secondary metabolites; (−) absence of secondary metabolites.
Phytochemical screening of hydroethanolic extracts wood studied.
| Extracts Species Common name Radial parts |
Hydroethanolic extracts | ||||||
|---|---|---|---|---|---|---|---|
|
Nauclea diderrichii
Badi |
Mansonia altissima
Bete |
Milicia excelsa
Iroko |
|||||
| Sapwood | Heartwood | Sapwood | Heartwood | Sapwood | Heartwood | ||
| Alkaloïdes | Dragendorf | + | + | + | + | + | + |
| Mayer | + | + | + | + | − | − | |
| Catechic Gallic |
Tannins | + | + | + | + | + | + |
| Tannins | − | − | − | − | − | − | |
| Quinones | − | − | − | − | − | − | |
| Polyterpenes & sterols | − | − | − | − | − | − | |
| Polyphenols | + | + | + | + | + | + | |
| Flavonoids | + | + | + | + | + | + | |
| Anthocyanins | + | + | − | + | − | − | |
| Saponins | − | − | + | − | − | − | |
-
(+) Presence of secondary metabolites; (−) absence of secondary metabolites.
Antioxidant profile of aqueous extracts wood studied.
| Extracts | Aqueous extracts | p-Value | |||||
|---|---|---|---|---|---|---|---|
| Species Common name |
Nauclea diderrichii Badi |
Mansonia altissima Bete |
Milicia excelsa Iroko |
||||
| Radial parts | Sapwood | Heartwood | Sapwood | Heartwood | Sapwood | Heartwood | |
| Total polyphenolics (mg GA Eq/g) | 0.9 ± 0c | 1.4 ± 0c | 0.5 ± 0c | 0.8 ± 0c | 2.2 ± 0c | 1 ± 0c | 0.221 |
| Total flavonoids (mg quercetin Eq/g) | 0.3 ± 0c | 0.3 ± 0c | 0.4 ± 0c | 0.6 ± 0c | 0.3 ± 0c | 0.6 ± 0c | 0.221 |
| Anti-oxidant activity (µmol Trolox Eq/L) | 4.8 ± 0.09ab | 4.0 ± 0.25b | 5.6 ± 0ab | 8.2 ± 0c | 1.9 ± 0a | 2.7 ± 0a | 0.005 |
-
aHighly significant; bsignificant; cmoderately significant and dweakly significant.
Antioxidant profile of hydroethanolic extracts wood studied.
| Extract | Hydroethanolic extracts | p-Value | |||||
|---|---|---|---|---|---|---|---|
| Species Common name |
Nauclea diderrichii Badi |
Mansonia altissima Bete |
Milicia excelsa Iroko |
||||
| Radial parts | Sapwood | Heartwood | Sapwood | Heartwood | Sapwood | Heartwood | |
| Total poly-phenolics (mg GA Eq/g) | 72.5 ± 2.8b | 93.4 ± 0.1a | 0.1 ± 0c | 1.6 ± 0c | 0.1 ± 0c | 0.1 ± 0c | 0.006 |
| Total flavonoids (mg quercetin Eq/g) | 111.0 ± 0.1b | 96.8 ± 0.1 ab | 116.4 ± 0b | 197 ± 1.1a | 0.2 ± 0c | 0.2 ± 0c | 0.006 |
| Anti-oxidant activity (µmol Trolox Eq/L) | 7.7 ± 0.1c | 24.9 ± 0.5b | 13.4 ± 0ab | 60.1 ± 0.3a | 2.1 ± 0d | 5.0 ± 0c | 0.005 |
-
Means followed by the same letters on the same line of the table are not significantly different (p < 0.05). Mean ± S.E.M = mean values ± standard error of mean. aHighly significant; bsignificant; cmoderately significant and dweakly significant.
3.2 Discussion
3.2.1 Characterisation of the various aqueous and hydroethanolic extracts
Analysis of the yields of the three hydroethanolic wood extracts showed that the yields were similar. The aqueous extraction rates were also close but lower than the hydroethanolic yields. Analysis of the sapwood extraction yields showed no significant differences. However, there was a significant difference between the sapwood and heartwood yields. The extract rate of M. excelsa heartwood was the highest, followed by those of M. altissima and N. diderrichii. However, M. excelsa had the highest sapwood yield (4.7 ± 0.9 %). A recent study of heartwood extracts from three species by Thomas et al. (2023), carried out under the same laboratory, extraction, and handling conditions, showed that N. diderrichii had the highest yield (7.8 ± 0.6 %), followed by M. altissima (6.8 ± 1.1 %) and M. excelsa (6.5 ± 0.9 %). Admittedly, the yields obtained by these authors were generally higher, but the only difference was that in this study, M. excelsa had the highest yield. Maceration is one of the most appropriate conventional extraction techniques, balancing product quality, process efficiency, and production costs. The method used in the current study, which combines green solvents, namely water and ethanol, is environmentally friendly and should be encouraged for the extraction of bioactive compounds from plant tissues. The use of environmentally friendly, sustainable, and non-toxic extraction methods should be encouraged to meet the growing expectations of consumers, as they offer ecological alternatives to dangerous synthetic chemicals. The authors showed that it produces fewer impurities in the final extract, preserves heat-sensitive compounds, uses different inorganic solvents, and consumes little energy (Jha and Sit 2022). It is also a low-energy cost technique. This technique can be applied in a controlled environment and almost any other type of environment. Some authors studying the extractive content of heartwood from 22 tropical species obtained slightly higher extractive contents, except for N. diderrichii extract. The yields obtained were 12.7 %, 8.2 %, and 6.6 % for M. excelsa, M. altissima, and N. diderrichii, respectively (Huang et al. 2009; Mounguengui et al. 2016; Thomas et al. 2023). The dissimilarities observed between the results of these authors and those of this study could be due to the nature of the extraction solvents. Indeed, in their work, they used methanol, a solvent reputed to extract extractives efficiently. These facts were stated by Mounguengui et al. (2016), where the toluene/ethanol mixture resulted in a higher extraction (5.8 ± 0.1 %) than ethanol alone (1.6 ± 0.1 %). Huang et al. also reported that the contents of extractable compounds of M. excelsa were 10 % for methanol, 7.6 % for acetone, and 2.1 % for dichloromethane (Huang et al. 2009). These differences could be linked to the affinity of the molecules for the extraction solvents. In addition to the nature of the extraction solvent, the extraction yield can be explained by the particle size in the grinding and drying conditions. The diversity of the geographical site, edaphic influence of the soil, plant species, and part of the plant used for extraction could also affect the extraction yield (Bilgin and Şahin 2013; Bopenga et al. 2023; Nagawa et al. 2015). The age of the trees sampled, solvent, extraction technique, extraction time, and storage time of the samples after collection could also lead to differences in the results (Bopenga et al. 2023; Fernández-Agulló et al. 2015).
3.2.2 Phytochemical screening
Analysis of the 12 extracts (six aqueous and six hydroethanolic) of sapwood and heartwood revealed the presence of alkaloids, catechic tannins, polyphenols, flavonoids, and saponins in all three species studied. The content of secondary metabolites in sapwood was relatively low compared to that found in heartwood. Polyphenols and flavonoids were found in sapwood and heartwood extracts from M. altissima and M. excelsa, respectively. Moreover, these metabolites were absent in N. diderrichii. However, quinones were only found in the aqueous extracts of M. excelsa heartwood. Saponins and polyterpenes were primarily identified in the aqueous extracts of all three species. In contrast, quinones were absent from the hydroethanolic extracts of all three woods. Various authors such as Lamidi et al. (1995) and Rodrigues et al. (2011) have highlighted the chemical families that are most prevalent during their work. However, the results varied according to the authors. This dissimilarity may be due to the solvents used, such as chloroform, hexane, acetone, or methanol, the part of the plant studied, and the season (dry or rainy) during which the plant samples were collected. Some convincing results obtained from N. diderrichii leaves and M. altissima bark confirms these ideas (Aderibigbe and Anowai 2020; Murray et al. 1972). The results showed that the aqueous extract of N. diderrichii stem bark contains flavonoids, polyphenols, triterpenoids, tannins, saponins, glycosides, cardiac glycosides, and alkaloids. However, this extract is devoid of anthraquinones and sterols (Mbiantcha et al. 2020). In addition, Huang et al. (2009) showed the presence of tannins and saponins in the same wood ethanolic extract. Nevertheless, the absence of alkaloids in the ethanolic extracts has been noted (Huang et al. 2009). Furthermore, screening of the aqueous extract of M. excelsa trunk bark revealed the presence of alkaloids, polyphenols, saponosides, and anthocyanins, whereas the presence of secondary metabolites was not observed in the organic extract (Ibibia et al. 2016). The presence of phytoingredients in N. diderrichii leaves has been observed by certain authors such us Kuete and Seukep (2023) and Murray et al. (1972). A recent study on the phytochemistry and antibacterial potential of the Nauclea genus, pure ethanol used by the authors, revealed a chemical similarity with the current study (Kuete and Seukep 2023). Other studies have also shown that most of the identified chemical groups have medicinal and antifungal properties (Anouhe et al. 2018; Murray et al. 1972). In summary, the hydroalcoholic solvent, ethanol and water (V/V) appears to be suitable for the optimal extraction of chemical substances.
3.2.3 Total polyphenols, total flavonoids and antioxidant activity
The total polyphenol and flavonoid contents varied among the extracts. The total polyphenol and flavonoid contents were low in the aqueous extracts. Similarly, the antioxidant activity was low. In contrast, hydroethanolic extracts showed high levels of total polyphenols and flavonoid content. The total polyphenol content of the N. diderrichii heartwood and sapwood extracts was the highest. The total polyphenol content of M. altissima and M. excelsa extracts was the lowest. In a similar study conducted on the methanolic extract of 22 tropical species, the authors such as Huang et al. (2009), obtained polyphenol contents of 71 mg GA Eq/g and 320 mg GA Eq/g for N. diderrichii and M. excelsa, respectively. This is in agreement with De Meeûs (2019), who showed the richness of biomolecules, mainly phenolic compounds, in the latex and sapwood of M. excelsa. The authors Mounguengui et al. (2016) studied the polyphenol content of ten Congolese essences and obtained a polyphenol content of 164 mg GA Eq/g in the N. diderrichii extract. The extract was obtained using a mixture of toluene and ethanol 1/2 (v/v). Therefore, the observed differences could be explained by the nature of the extraction solvent and sample. The work carried out on acetone extracts of fresh and dried M. excelsa sapwood, heartwood, and bark showed significant differences between polyphenol and flavonoid values. Phenolic concentrations in fresh samples were higher in heartwood and sapwood than in bark, whereas concentrations in dry samples were higher in heartwood and bark than in sapwood. In contrast, the total flavonoid content of the bark was the highest, followed by that of the sapwood and heartwood (De Meeûs 2019). Thus, the total flavonoid content of M. altissima heartwood was high, whereas those of M. altissima sapwood, N. diderrichii sapwood, and N. diderrichii heartwood were average. The lowest total flavonoid levels were found in M. excelsa. According to some authors, such as Thomas et al. (2023), species with a total polyphenol content above 90 mg GA Eq/g are potentially rich in phenolic biocompounds. Thus, N. diderrichii heartwood and M. excelsa are important sources of phenolic compounds. However, studies on heartwood from the same species have revealed higher levels of total polyphenols and flavonoids than those observed in the present study. The polyphenol contents were 130.7 ± 16.8 mg GA Eq/g for M. excelsa, 93.5 ± 23.3 mg GA Eq/g for N. diderrichii, and 66.7 ± 13 mg GA Eq/g for M. altissima (Thomas et al. 2023). Flavonoids were found at 120 ± 17.2 mg Eq/g in M. excelsa, 108.8 ± 22.5 mg Eq/g in N. diderrichii, and 63.3 ± 12.7 mg Eq/g in M. altissima. Very little research has been conducted on the determination of total flavonoid content in heartwood, particularly in sapwood. The composition of the extractives from 12 different tropical wood species was determined by sequential extraction followed by silylation and GC, GC/MS analysis. Hexane and an acetone/water mixture (5/1) were used as the extraction solvents. Phenolic acids, flavonoids, sterols, stilbenes, and lignan extractives were obtained. The highest quantity was found in Afzelia (36.1 mg/g), whereas the lowest quantity (0.3 mg/g) was observed in Wenge and Opepe (Pekgözlü and Niemz 2012). The hydroethanolic extract of M. altissima heartwood presented a high antioxidant activity, while N. diderrichii heartwood and M. excelsa sapwood showed average antioxidant activities. The antioxidant activities of M. altissima sapwood, N. diderrichii sapwood, and M. excelsa heartwood were the lowest. The high total polyphenol content is thought to be responsible for the antioxidant activity observed in these species (Huang et al. 2009). Similar results on the genotoxic and clastogenic activities of Nauclea bark saponins, assessed on Chinese hamster ovary cells by Liu et al. showed similarities with the results of this study (Liu et al. 2011). Mounguengui et al. (2016) and Huang et al. (2009) also showed that the antioxidant activity (AOA) of N. diderrichii varied according to the solvent used: 22 % for toluene/ethanol and 18 % for ethanol. These values were higher than those obtained from N. diderrichii in this study but close to the AOA of the hydroethanolic extract of M. altissima heartwood (20.1 %). Phenolic extracts of heartwood are excellent antioxidants because they contain phenolic or aromatic amino groups (Schultz and Nicholas 2000). In addition, various studies have been conducted on the chemical composition of the leaves, bark, trunk, and roots of the species studied. Most of these studies have focused on the total polyphenol, tannin, saponin, and lignin contents (Adebayo et al. 2019; Liu et al. 2011). In light of the above results, durable wood extracts could be a potential means of controlling crop pests. The originality of this study lies in the fact that it focuses on green chemistry through ecological extraction using environmentally friendly solvents, in this case, water and ethanol. Characterisation of the wood extracts showed that the waste and rejects left behind by forestry industries and sawmills are rich reservoirs of biomolecules that should be exploited sustainably. In Africa, many botanical extracts used as biopesticides are derived from plants. Moreover, the extraction process generally uses harmful solvents, such as ketones, chloroform, and chlorobenzene. Therefore, few eco-extraction studies have been conducted on trees. Moreover, the literature often states that only the heartwood of trees can be valorised, as it is rich in natural bioactive substances. Overall, this study showed that sapwood contains interesting substances that could be exploited and potentially used as biopesticides. Although the quantities were slightly lower than those found in the heartwood, these substances were equally biologically active. In the interest of preserving the environment and health, this ecological approach should be encouraged, as it has produced good results. The combination of sapwood and heartwood, or even whole wood, could be a crucial element in the formulation of bioinsecticides against insect crop pests. This formulation could encourage the gradual replacement of chemical pesticides, which are responsible for serious health and environmental problems.
4 Conclusions
This study aimed to perform a green extraction followed by a chemical characterisation of aqueous and hydroethanolic extracts from the sapwood and heartwood of three tropical woods from the Ivorian forest flora (N. diderrichii, M. altissima and M. excelsa), assessing the potential of forest waste as a source of biomolecule compounds. The yield of aqueous extraction was significantly lower (p < 0.05) than that of hydroethanolic extraction. Aqueous extracts contained alkaloids, tannins, quinones, polyterpenes, sterols, polyphenols, flavonoids, anthocyanins, and saponins, although in significantly lower proportions (p < 0.05) than their hydroethanolic counterparts. N. diderrichii heartwood extracts exhibited the highest total polyphenol content (93.4 ± 0.1 mg GA Eq/g) followed by N. diderrichii sapwood (72.5 ± 2.8 mg GA Eq/g). The hydroethanolic extract of M. altissima heartwood showed the highest antioxidant activity (60.1 ± 0.1 µmol Trolox Eq/L), while M. excelsa sapwood (2.1 ± 0 µmol Trolox Eq/L) had moderate antioxidant activity. These findings highlight the potential for valorising waste from forestry and wood industries. The studied extracts hold promise for applications in cosmetics, nutraceuticals, agriculture (biopesticides), and wood preservation industries. Given the hazardous nature of synthetic chemical pesticides and the abundance of bioactive molecules in wood extracts, the formulation of bioinsecticides from these extracts could contribute to sustainable crop pest management. Further studies, including chemical profiling using high-performance liquid chromatography (HPLC), mass spectrometry (MS), and nuclear magnetic resonance spectroscopy (NMR), are essential to identify the active compounds in the extracts and explore their potential applications as biopesticides derived from forest industry waste.
Funding source: Institut de Recherche pour le Développement
Award Identifier / Grant number: Reference N/Réf: D17.332/JMH/kf
Acknowledgments
This work stems from the “Bioactive for Agriculture and Wood Preservatives (B4AP)” project, Reference N/Réf: D17.332/JMH/kf whilst aim is to research and develop bioactive ingredients derived from ligneous resources for agriculture and wood preservation. It is one of 10 projects selected by PReSeD-CI 2 (Renewed partnership for research to serve development in Ivory Coast) as part of the C2D (debt reduction and development contract), co-funded by France and Ivory Coast and implemented by IRD (Institute for Development Research). A.B. Bley-Atse was awarded a travel scholarship to Madagascar by the French Embassy (French Government Scholarship). The authors would like to express their gratitude to Mr. Dina Rabe, Institutional Support Program ARES, University of Antananarivo, for his assistance in reviewing the article.
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Research ethics: Not applicable.
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Informed consent: Informed consent was obtained from all individuals included in this study, or their legal guardians or wards.
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Author contributions: Appolinaire B. Bley-Atse: investigation, data analysis, methodology, chemical analysis, drafting of final version, revision, and editing. Florence B. Niamké: supervision, revision, fund acquisition and project coordinator. Armand N. Adja: supervision, visualization and revision. T. Ramananantoandro: supervision, recommendation and revision. T. Digbe: assistance for sample collection and preparation. Jean-Claude N. Yao: chemical analysis assistance. Augustin A. Adima: supervision.
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Use of Large Language Models, AI and Machine Learning Tools: None declared.
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Conflict of interest: The authors state that there are no conflicts of interest regarding the publication of this article.
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Research funding: The research was funded by C2D (debt reduction and development contract), co-funded by France and Côte d’Ivoire and implemented by IRD (Institute for Development Research) through the project B4AP (Bioactive for Agriculture and wood preservatives), Reference N/Réf: D17.332/JMH/kf.
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Data availability: The data that support the findings of this study are available from the corresponding author, A. B. Bley-Atse, upon reasonable request.
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Articles in the same Issue
- Frontmatter
- Wood Chemistry
- Variability in the chemical composition and antioxidant properties of sapwood and heartwood extracts of some tropical woods from Côte d’Ivoire
- Valorisation the bark of forest species as a source of natural products within the framework of a sustainable bioeconomy in the Amazon
- Wood Physics/Mechanical Properties
- Mechanism of changes in the mechanical properties of wood due to water adsorption and desorption described by rheological considerations
- Investigating sapwood and heartwood density changes of short rotation teak wood after chemical and thermal modification using X-ray computed tomography
- Wood Technology/Products
- Fire behavior of thermally modified pine (Pinus sylvestris) treated with DMDHEU and flame retardants: from small scale to SBI tests
Articles in the same Issue
- Frontmatter
- Wood Chemistry
- Variability in the chemical composition and antioxidant properties of sapwood and heartwood extracts of some tropical woods from Côte d’Ivoire
- Valorisation the bark of forest species as a source of natural products within the framework of a sustainable bioeconomy in the Amazon
- Wood Physics/Mechanical Properties
- Mechanism of changes in the mechanical properties of wood due to water adsorption and desorption described by rheological considerations
- Investigating sapwood and heartwood density changes of short rotation teak wood after chemical and thermal modification using X-ray computed tomography
- Wood Technology/Products
- Fire behavior of thermally modified pine (Pinus sylvestris) treated with DMDHEU and flame retardants: from small scale to SBI tests
