Bark extractives and suberin monomers from Arbutus andrachne and Platanus orientalis

Abstract

Arbutus andrachne and Platanus orientalis grow naturally in Turkey. They do not occur in stands but can be seen as solitary trees. A. andrachne is seen in coastal parts of Anatolia, whereas P. orientalis can be found from west to the east of Turkey, mostly in river banks. Lipophilic extractives, hydrophilic extractives, and suberin monomers from Arbutus andrachne and Platanus orientalis bark was analyzed by chromatography. The total amount of lipophilic extractives was higher in P. orientalis (8.55 mg/g). However, the total amount of hydrophilic extractives had a bigger proportion, 100.86 mg/g, in A. andrachne bark. Dioic and hydroxy acids were the dominant group in the suberin monomers of both species of bark. Acid 1,18-dioic-18:0 and acid 18-hydroxy-18:1 were determined as the main compounds of suberin monomers in both samples. In addition, total amount of suberin monomers was determined to be 11.36 mg/g in A. andrachne and 15.95 mg/g in P. orientalis bark.

Full Article

Bark Extractives and Suberin Monomers from andrachne and Platanus orientalis

İlhami Emrah Dönmez,^a,* Jarl Hemming,^b and Stefan Willför ^b

Arbutus andrachne and Platanus orientalis grow naturally in Turkey. They do not occur in stands but can be seen as solitary trees. A. andrachne is seen in coastal parts of Anatolia, whereas P. orientalis can be found from west to the east of Turkey, mostly in river banks. Lipophilic extractives, hydrophilic extractives, and suberin monomers from Arbutus andrachne and Platanus orientalis bark was analyzed by chromatography. The total amount of lipophilic extractives was higher in P. orientalis (8.55 mg/g). However, the total amount of hydrophilic extractives had a bigger proportion, 100.86 mg/g, in A. andrachne bark. Dioic and hydroxy acids were the dominant group in the suberin monomers of both species of bark. Acid 1,18-dioic-18:0 and acid 18-hydroxy-18:1 were determined as the main compounds of suberin monomers in both samples. In addition, total amount of suberin monomers was determined to be 11.36 mg/g in A. andrachneand 15.95 mg/g in P. orientalis bark.

Keywords: Arbutus andrachne; Platanus orientalis; Lipophilics; Hydrophillics; Suberin monomers

Contact information: a: Süleyman Demirel University Faculty of Forestry Department of Forest Industrial Engineering, East Campus, 32100-Çünür, Isparta, Turkey; b: Laboratory of Wood and Paper Chemistry Åbo Akademi University, Porthansgatan 3–5, FI-20500 Åbo/Turku, Finland;

* Corresponding author: emrahdonmez@sdu.edu.tr

INTRODUCTION

Wood and tree bark contain lignocellulosic materials—cellulose, hemicelluloses (polyoses), and lignin—as well as extractives. Because extractives can be utilized in the medicinal, pharmaceutical, and cosmetic fields, they have the potential to affect how trees are used. Extractives are lipophilic and hydrophilic components that can be recovered with neutral solvents (Fengel and Wegener 1989; Sjöström 1993; Holmbom 1999). They are a wide variety of non-structural, low molecular weight organic compounds. Extractives can protect wood from decay, add color and odor to wood, and enhance the strength properties of the wood. Extractives may also inhibit setting of concrete, glues, and finishes and cause problems in papermaking (Hillis 1987; Amusant et al. 2007; Hashemi et al. 2009). Extractives can be seen in both kraft and sulfite pulping as polyphenols in polymer fraction and fatty acids, terpenoids, steroids, lignans, and other compounds in monomer fractions (Holmbom 1999). Some of the extractives are unsaponifiable (hydrocarbons, sterols, various alcohols, aldehydes, etc.), and some are saponifiable (fats, sterols, esters). Phenols, one of the most important extractive substances group, are very interesting as antioxidants because of their natural origin and the ability to act as efficient free radical scavengers (Hertog et al. 1993, 1995; Langley-Evans 2000). There are a number of publications on the potential health benefits of polyphenols (Dreosti 1991; Friedman and Kimball 1986; Pietta 2000; Tiwari 2001; Lee et al. 2003; Modun et al. 2003). The current studies focus on natural antioxidants, especially plant polyphenolics (Skerget et al. 2005; Miranda et al. 2016). Utilization of polyphenolics in traditional folk medicine are gaining interest because of antioxidant properties of plants. Trees are an abundant source of phenolic compounds. These compounds can easily be isolated from wood by hydrophilic extraction after removing the lipophilic extractives by hexane extraction (Holmbom et. al. 2003; Willför et al. 2003). Polyphenolic compounds are ubiquitous in foods of plant origin, and thus they constitute an integral part of the human diet. Recent interest in polyphenols has greatly increased, since these phytochemicals have been implicated in suppressed rates of degenerative processes, such as cardiovascular disorders and cancer (Bravo 1998; Duthie et al. 2000). The amount of extractives and their composition vary with respect to the botanical families, tree species, growth region, tissue, and extraction methods. The tree species is probably the most important factor that affects the extractive content and component. Usually a higher extractive content is found in hardwoods than in softwoods (Hillis 1987).

Extractives in bark vary more than those from wood of the same tree. Moreover bark contains suberin. Suberin is a natural aliphatic-aromatic cross-linked polyester. It is found in the cell walls of all normal and wounded external tissues. Its main purpose is to protect the plant from environmental conditions (Kolattukudy and Espelie 1989; Kolattukudy 2001; Bernards 2002; Pollard et al. 2008). Its amount and composition in bark varies depending on the species and the isolation method (Gandini et al. 2006). Most of the studies have been focused on Quercus suberand Betula pendula because cork of Q. suber and outer bark of B. pendula include almost 50% suberin by weight (Pereira 1988; Lopes et al. 2000; Pinto et al. 2009). However, the composition of suberin studied in some tree bark such as Pseudotsuga menziesii (22 %), Eucalyptus globulus(less than 1%), and Pinus sylvestris (1.75 to 4.72 %) was presented previously (Dönmez et al.2012; Miranda et al. 2013; Ferreira et al. 2015).

In many industries, bark is considered waste that is burned for energy production (Hemingway 1981). However, bark is a rich source of chemicals, for instance lipophilics, phytosterols, and other phenolic compounds (Kähkönen et al. 1999; Freire et al. 2002 a,b; Pietarinen et al. 2006; Ferreira et al. 2013). This makes the bark a possible raw material for new pharmaceutical and bioactive compounds, green polymers, and bio-based materials (Miranda et al. 2013; Baptista et al. 2013).

Arbutus andrachne is a woody plant that grows as a bush or a small tree. It is an evergreen tree with thick branches. A. andrachne has light-colored and bright bark that is peeled off as sheets like oriental plane (Anşin and Özkan 1993), and it has red-colored fruits that are harvested from the wild and consumed (Serçe et al. 2010). There is limited research on A. andrachne; most of the existing papers have been focused on the sugar composition, protein, ash content, and antioxidant activity of its fruits (Alarcao-E-Silva et al. 2001; Şeker and Toplu 2010; Serçe et al. 2010).

Platanus orientalis is a large deciduous tree known for its longevity and spreading crown. It is seen in the parks and landscapes as an ornamental plant (Khan et al. 2013). The phenolic composition of its leaves and buds and the effects of environmental stress have been studied, but there is limited knowledge of the chemical composition of P. orientalis bark. Most studies on its chemical composition have focused on anticancer or antiseptic properties and activity against urinary infections (Mitrocotsa et al. 1993; Mitrocotsa et al. 1999; Dimas et al. 2000; El-Alfy et al. 2008). To the best of our knowledge, there has been no research about extractive and suberin composition of A. andrachne and P. orientalis bark. It was aimed to determine the amount and the composition of lipophilic, hydrophilic extractives and suberin monomers of A. andrachne and P. orientalis bark.

MATERIALS AND METHODS

Materials

Arbutus andrachne (L.) and Platanus orientalis (L.) were harvested from Isparta, Eğirdir, Aşağıgökdere, Turkey, where the altitude is 375 m. Cross-sections of the trees were taken according to the TAPPI T 257 cm-85 standard (1985). Bark was then separated from wood. All samples were stored at -24 °C. Bark was broken into small pieces, which were freeze-dried and ground by a Wiley mill to 1 mm (Ekman 1983). To remove volatile compounds, a second drying procedure was treated to the ground samples.

Extraction

Approximately 5 g of ground bark from each sample was sequentially extracted with an accelerated solvent extractor (ASE) apparatus (model ASE 200, Dionex Inc., Sunnyvale, CA, USA). Samples were successively extracted with n-hexane, acetone:water (95:5, v:v), and finally distilled water. After extraction, 100-mL aliquots of extractives were prepared with the same solvent used in extraction. For gravimetric analyses, 10 mL of the aliquot was evaporated completely, leaving a film of extractives in the solvent container. The containers were weighed before and after extraction to determine the extractive yield in mg/g. An internal standard (heneicosanoic acid and betulinol) was added to the hexane and acetone:water (95:5, v:v) extracts. The mixture was evaporated under nitrogen prior to silylation. Hexane and acetone:water (95:5, v:v) extracts were used for chromatography analysis.

Hydrolysis of Suberin

As an internal standard, 0.5 g of cholesterol was dissolved in 50 mL acetone, and 1 mL of this solution was transferred to a 50-mL test tube. The solvent was evaporated in a water-bath under nitrogen. Extractive-free, ground bark (100 mg) and 10 mL of 0.5 M KOH in 90% ethanol were added to the same tube. Hydrolysis was performed at 70 °C for 1.5 h with continuous stirring. After hydrolysis, 1 mL of the solution was taken from liquid phase and placed in a 15-mL test tube, and 1 mL of distilled water and 2 to 3 drops of bromocresol green were added. The pH was adjusted to 3.5 with 2 to 3 drops of 0.25 M H₂SO₄, and 2 mL of MTBE (methyl tert-buthyl ether) was added. The tubes were shaken vigorously. The MTBE phase was moved to a new test tube and evaporated in a water bath under nitrogen prior to silylation (Ekman 1983).

Chromatography

Quantitative analyses (peak areas vs. internal standards) of both extractives and suberin monomers from the bark of A. andrachne and P. orientalis were performed with a Pelkin Elmer Autosystem XL gas chromatograph (GC; PerkinElmer Inc., Waltham, MA, USA) equipped with an HP-1 25 m × 0.2 mm (0.11 μm film thickness) column and flame ionization detector (FID). The carrier gas was H₂ at 0.8 mL/min, constant flow. The initial oven temperature was 120 °C (1 min hold), and was increased at a rate of 6 °C/min to 320 °C (15 min hold). The split-splitless injector was used in split mode (split ratio: 1:24). The injector temperature was 260 °C, and the FID temperature was 320 °C. One μL of each sample was injected. Individual compounds were identified with an HP 6890-5973 gas chromatography/mass spectrometry (GC-MS) instrument (Agilent Technologies Inc., Santa Clara, CA, USA) equipped with an identical HP-1 column and using the same temperature program, but using helium as carrier gas.

RESULTS AND DISCUSSION

Extractives

The lipophilic and hydrophilic extractives of A. andrachne and P. orientalis bark were studied by gravimetric measurements (Table 1) and by GC and GC-MS (Table 2). Although the hexane extracts of P. orientalis bark were more concentrated than in A. andrachne, the total amount of identified lipophilics were higher in A. andrachne bark (1.03 mg/g).

Similar to the gravimetric results, the total amount of identified hydrophilics (acetone:water 95:5, v:v extracts) were twofold higher in A. andrachne bark (61.17 mg/g) than in P. orientalis bark (38.42 mg/g).

Table 1. Gravimetric Amounts of Extractives from A. andrachne and P. orientalis Bark (mg/g to Dry Weight)

Fatty acids and sterols were the main groups in both lipophilic extractives samples. Fatty acids composed 32.03% and 50.51% of the total lipophilic extractives in A. andrachne and P. orientalisbark, respectively. Palmitic acid was the most abundant fatty acid in both species. While it was determined as 0.22 mg/g in A. andrachne and 0.20 mg/g in P. orientalis bark, it was found 21.21% in Robinia pseudoacacia bark and 0.6 to 0.7 mg/kg in Pseudotsuga menziesii bark (Hosseinihashemi et al. 2016; Ferreira et al. 2015). Sitosterol was the only phytosterol detected in both samples, and it was observed to be within the range of 0.12 to 0.32 mg/g in both samples. Ferreira et al. (2015) studied the dichloromethane extracts of bark fractions of Pseudotsuga menziesii. β-sitosterol had the highest amount (43.3 to 78.8 mg/kg) in the sterols group.

Two phenolic compounds (3,4-dihydroxybenzoic acid and catechin) were found in both species. Catechin was the major component, with 1.35 mg/g in A. andrachne and 1.64 mg/g in P. orientalis bark. Catechin was also detected in other species barks and in medicinal and aromatic plats. It was detected as 5.5 mg/g in Pinus pinaster bark (Curkovic-Perica et al. 2015). Catechin is also a major constituent of black and green tea extract supplement that comprises 14.1 to 42.1 mg per dose (Henning et al. 2004). Catechin, derived from plant sources, is an important component to prevent heart diseases (Arts et al. 2001; Garbisa et al. 2001).

Some mono- and disaccharide sugars and their alcohol derivatives were also detected. Arbutusspecies fruits have large amounts of sugars (Serçe et al. 2010), and similar results were observed in bark. Maltitol was determined as the largest amount in the sugar group in A. andrachne bark (16.56 mg/g) whereas it was seen as the smallest (0.01 mg/g) in P. orientalis bark. Pinitol+d-glucose composed 12.8% of total sugar group of A. andrachne and 59.35% of total sugar group of P. orientalis. It was previously reported that the dominance of glucose, xylose, arabinose, and galactose were determined as the monomeric composition of polysaccharides of some tree species’ bark (Miranda et al. 2016; Miranda et al. 2013; Ruiz-Aquinon et al. 2015). However in the present study, the dominant monosaccharides were pinitol+d-glucose (with 7.12 mg/g in A. andrachne, 6.60 mg/g in P. orientalis bark), sorbopyranose (5.68 mg/g in A. andrachne, 1.89 mg/g in P. orientalis bark), and d-fructose (4.45 mg/g in A. andrachne and 0.04 in P. orientalisbark).

In addition, betulinic acid and sinapyl alcohol were observed only in acetone:water (95:5, v:v) extracts, but lupeol was determined in both extracts of the species. Betulinic acid, a triterpenoid component, is found in the bark of several trees, especially birch.

Table 2. Extractives of A. andrachne and P. orientalis Bark (mg/g)

*: Overlapped

Suberin Monomers

This report is the first to characterize the total amount and composition of suberin monomers from A. andrachne and P. orientalis bark. The total amount of suberin monomers was 11.36 mg/g in A. andrachne and 15.95 mg/g in P. orientalis bark. The composition and the amount of suberin monomers are shown in in Table 3. The amount of suberin was previously reported to be present in small amounts in bark of Teak (1.9 %), Eucalypt (0.98 %), and larger amount in Birch bark (5.9 %) (Miranda et al. 2013; Baptista et al. 2013).

Alcohols 18:0 and 20:0 were detected in both samples. Alcohol 18:0 was the most abundant fatty alcohol; it was present at 0.11 mg/g and 0.09 mg/g in A. andrachne and P. orientalis bark, respectively.

Seven different fatty acids were found in the samples, comprising 15.15% of A. andrachnesuberin monomers and 12.92% of P. orientalis bark. Acid 20:0 and acid 16:0 were the major constituents of saturated fatty acids in A. andrachne (0.51 mg/g) and P. orientalis (0.49 mg/g) bark. However, acid 18:2 was the most abundant unsaturated fatty acid in A. andrachne (0.46 mg/g) and in P. orientalis (0.33 mg/g).

Table 3. Suberin Monomers in A. andrachne and P. orientalis Bark

Dioic and hydroxy acids were the predominant groups in bark of both species. Dioic and hydroxy acids represent 81 to 84% of the total suberin monomers in both A. andrachne and P. orientalis bark. This is in agreement with the literature that dioic and hydroxy acids have the biggest proportion in cork of Q. suber and birch outer bark suberin (Ferreira et al. 2013). The most abundant compounds in both samples were 18-hydroxy-18:1 acid and 1,18-dioic-18:1 acid, which were also detected as the major constituents of suberin monomers in the bark of pines growing in Turkey (Hafızoğlu 1989; Dönmez et al. 2012).

CONCLUSIONS

1. Lipophilic and hydrophilic extractives as well as suberin monomers from the bark of A. andrachne and P. orientalis were analyzed by GC and GC-MS. The total amount of lipophilic extractives in A. andrachne bark (3.00 mg/g) was smaller than in P. orientalis(8.55 mg/g). However, twice the amount of hydrophilic extractives was found in A. andrachne (100.86 mg/g).
2. Sugars were the highest group in A. andrachne bark. Sugars were detected almost five-times more than in P. orientalis bark.
3. The dioic and hydroxy acids most prominent in both A. andrachne and P. orientalis bark were acid 1,18-dioic-18:0 and acid 18-hydroxy-18:1.
4. The largest amounts of fatty acids as suberin monomers in A. andrachne were acid 20:0, acid 18:2, and acid 16:0. The bark of P. orientalis exhibited the following main fatty acid compounds as suberin monomers: acid 16:0, acid 18:2, and acid 18:0.
5. Catechin was the most predominant constituents of phenolics detected in both samples. Because of catechin amount of the extracts, antioxidant properties of the barks can be studied.

ACKNOWLEDGEMENTS

The authors thank Dr. Annika Smeds, Laboratory of Wood and Paper Chemistry, Åbo Akademi University, Turku, Finland, for her help with chromatographic analyses.

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Article submitted: September 28, 2015; Peer review completed: December 18, 2015; Revised version received and accepted; December 31, 2015; Published: February 2, 2016.

DOI: 10.15376/biores.11.1.2809-2819