What Is The Chemical Makeup Of A Tree

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Chemical composition of barks from Quercus faginea copse and label of their lipophilic and polar extracts

• Joana P. A. Ferreira,
• Isabel Miranda,
• Vicelina B. Sousa,
• Helena Pereira

x

• Published: May 15, 2018
• https://doi.org/10.1371/journal.pone.0197135

Figures

Abstract

The bark from Quercus faginea mature trees from 2 sites was chemically characterized for the first fourth dimension. The barks showed the post-obit limerick: ash 14.6%, total extractives thirteen.ii%, suberin 2.9% and lignin 28.2%. The polysaccharides were equanimous mainly of glucose and xylose (50.three% and 35.1% of all monosaccharides respectively) with iv.viii% of uronic acids. The suberin composition was: ω-hydroxyacids 46.three% of total compounds, ɑ,ω-alkanoic diacids 22.3%, alkanoic acids five.9%, alkanols 6.7% and aromatics 6.nine% (ferulic acid four.0%). Polar extracts (ethanol-water) had a high phenolic content of 630.3 mg of gallic acrid equivalents (GAE)/one thousand of excerpt, condensed tannins 220.7 mg of catechin equivalents (CE)/g extract, and flavonoids 207.seven mg CE/g of extract. The antioxidant activity was very loftier respective to 1567 mg Trolox equivalents/one thousand of extract, and an IC50 of 2.63 μg extract/ml. The lipophilic extracts were constituted mainly by glycerol and its derivatives (12.three% of all compounds), alkanoic acids (27.eight%), sterols (xi.5%) and triterpenes (17.eight%). In view of an integrated valorization, Quercus faginea barks are interesting sources of polar compounds including phenols and polyphenols with possible interesting bioactivities, while the sterols and triterpenes contained in the lipophilic extracts are also valuable bioactive compounds or chemical intermediates for specific loftier-value market niches, such as cosmetics, pharmaceuticals and biomedicine.

Commendation: Ferreira JPA, Miranda I, Sousa VB, Pereira H (2018) Chemical limerick of barks from Quercus faginea trees and characterization of their lipophilic and polar extracts. PLoS ONE 13(five): e0197135. https://doi.org/10.1371/journal.pone.0197135

Editor: Ing-Feng Chang, National Taiwan University, TAIWAN

Received: September 24, 2017; Accustomed: April 26, 2018; Published: May 15, 2018

Copyright: © 2018 Ferreira et al. This is an open access commodity distributed under the terms of the Creative Eatables Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Information Availability: All the relevant data are within the newspaper.

Funding: The sampling was supported by the project OAKWOODS (PTDC/AGR-AAM/69077/2006) funded by Fundação para a Ciência e a Tecnologia (FCT). Nosotros thank José L. Louzada for providing the samples from Site 1 and Sofia Knapic for project management. We as well give thanks Joaquina Silva and Lidia Silva for help with the chemical assay. This piece of work was supported past the Strategic Project (UID/AGR/00239/2013) of Centro de Estudos Florestais, past the national funding from FCT. The tertiary author acknowledges a post-doctor scholarship by FCT (SFRH /BPD/ 97970/2013).

Competing interests: The authors have declared that no competing interests be.

Introduction

The Quercus faginea Lam. (Portuguese oak) species is native to the Western Iberian Peninsula, and the North African countries of Morocco, Tunisia and People's democratic republic of algeria, where it coexists with other oaks such equally Q. ilex L., Q. suber L., Q. pyrenaica Willd., and Q. robur L. Its distribution has get fragmented in the terminal centuries [1], and there are concerns on a hereafter area reduction with warming and reduced rainfall trends, since drought is the main limiting factor of sub-Mediterranean oaks [2], and specifically of Q. faginea [3–iv].

Although the forest from this species was valued and intensively exploited for naval construction in the XV-XVI centuries [5], nowadays it is non used in a significant extent, fifty-fifty if its potential and environmental and cultural importance are acknowledged. Full general descriptions of Q. faginea wood refer good artful advent, high density, and considerable mechanical strength [6–eight].

Recent inquiry efforts take been made to increase knowledge on the growth and forest characteristics of Q. faginea with the objective to contribute towards its valorization for high-quality end-uses [nine–11].

Little is known virtually the bark of Q. faginea. One detailed written report of bawl anatomy and biometric features was made recently: it showed a persistent rhytidome including iii–v sequential periderms with thin cork layers with a discontinuous development [12]. Noesis on the bark complex structure and chemical composition allows a more efficient sampling, fractioning and processing towards specific end-uses.

Bark is an of import protection component of trees due east.g. confronting fire, frost, fungal diseases or animate being injuries, depending on thickness and structure, and therefore a contributor to sustainability [13, 14]. Barks from different tree species are currently left in the forest or burnt in mills of wood, pulp and paper industries [15,16]. In improver to their fuel value, barks are now viewed also as potential resource for biorefineries given their chemical complication and diversity and several studies are increasing the otherwise rather scarce information on barks [17–24]. They tin can be a source of high-value chemicals for a diversity of areas, from pharmaceutical and bioactive natural compounds to green polymers and bio-based materials [16,17].

In this study, the bark from Q. faginea mature trees growing in two locations in Portugal in the species distribution area was chemically analyzed regarding the summative chemical composition and the composition of suberin, lipophilic and polar extractives. The antioxidant properties of the bark extracts were besides evaluated. It is our goal to contribute to the valorization of Q. faginea nether a full resource approach, and thereby to the strengthening of the species distribution.

Materials and methods

The samples from the Quercus faginea trees were collected in two locations: one stand up in the northeast of Portugal (site 1), near Macedo de Cavaleiros and the other stand up in the centre of Portugal (site two), well-nigh Vimeiro. For the showtime site, the authority who issued the permission was Instituto da Conservação da Natureza e das Florestas ICNF, and for site two the private owner was asked and gave permission. These report does not involve endangered or protected species.

Sampling

The bark samples were obtained from Quercus faginea trees selected from two stands located in the region of the species natural distribution in Portugal. One stand was located almost Macedo de Cavaleiros (northeast of Portugal, 41° thirty′ N, 07° 01′ W; 554 m altitude; site ane) and the other near Vimeiro (centre of Portugal, 39° 29′ N, 09° 01′ Westward; 100 k altitude; site two). The stands resulted from natural regeneration and were unmanaged, mixed and uneven-aged with an average tree age of twoscore years (site one) and 125 years (site ii) [11].

Three trees from each stand were randomly selected for this report. A cross-sectional disc at breast height (1.3 1000 above ground) was taken and the bark manually removed. The bark samples were air-dried in a well ventilated indoor room, protected from low-cal. The samples were ground individually in a cutting factory (Retsch SM 2000) using an output sieve of 10 mm 10 10 mm, followed past one of 2 mm x 2 mm and fractionated with a vibratory system (Retsch AS 200basic) with standard sieves. Afterwards sieving, the xl–60 mesh (0.425 mm—0.250 mm) fractions were nerveless for chemic assay.

Summative chemical analysis

Chemic summative analyses included determination of ash, extractives soluble in dichloromethane, ethanol and water, suberin, Klason and acid soluble lignin and the monomeric limerick of polysaccharides. All determinations were fabricated with duplicate samples.

Ash was adamant by measuring the residue remaining afterwards incinerating the sample overnight in a conceal furnace at 525°C (TAPPI T 211 om-02).

The extractives were determined with procedures adjusted from Tappi 204 cm-97, in a soxhlet organisation successively with dichloromethane, ethanol and water (all supplied by Sigma-Aldrich, ≥99.8% purity, St. Louis, MO, United states of america), under reflux, during 6h, 16h and again 16h, respectively. The extractives solubilized by each solvent were adamant by mass difference of the solid residue subsequently drying at 105 °C and reported as percent of the original sample.

The suberin content was determined in the extractive-free material past use of methanolysis for depolymerization [25]. A 1.5 chiliad sample of extractive-free material was refluxed with a 3% (one thousand/v) solution of NaOCH₃ in CH_threeOH (100 ml) during three h (both supplied past Sigma-Aldrich, 95% and ≥99.8% purity respectively, St. Louis, MO, United states of america). The sample was filtrated and washed with methanol, and the filtrated residuum was refluxed again with 100 ml CH₃OH for 15 min and filtrated. The combined filtrates were acidified to pH 6 with ii M H_iiSO₄ (Merck KGaA, 98% purity, Darmstadt, Germany) and evaporated to dryness. The residues were suspended in water (50 ml) and the products recovered with dichloromethane in three successive extractions (of l ml each). The combined extracts were dried over anhydrous Na_twoThen₄ (ACS Sigma-Aldrich, ≥99% purity, St. Louis, MO, United states of america), and the solvent evaporated to dryness. The suberin extracts were quantified and the results expressed in percent of the initial dry mass.

Klason and acrid-soluble lignin, and carbohydrates contents were adamant on the extracted and desuberinized materials. Sulphuric acid (72%, iii.0 ml) was added to 0.35 g of the sample and the mixture was placed in a h2o bath at xxx°C for 1 h, after which it was diluted to iii% H₂SO₄ and hydrolyzed for one h at 120°C. The sample was vacuum-filtered through a crucible and washed with boiling purified water. Klason lignin was determined as the mass of the solid balance after drying at 105°C (TAPPI T 222 om-02). The acid-soluble lignin was adamant on the combined filtrate by measuring the absorbance at 206 nm using a UV/VIS spectrophotometer (TAPPI Useful Method UM 250). The remaining acid solution was kept for sugar analysis.

The composition of polysaccharides was evaluated after hydrolysis by determining the content in neutral monossacharides (rhamnose, arabinose, xylose, galactose, mannose and glucose), uronic acids (galacturonic and glucuronic acids) in the hydrolysate from the lignin assay using High Pressure Ion-exchange Chromatography with a pulsed amperometric detector (HPIC-PAD). The compounds were separated in a Dionex ICS-3000 organisation, with an Aminotrap plus Carbopac PA10 column (250 x four mm). The content of acetic acid was also determined in the hydrolysate using a Loftier-Pressure Ion-exclusion Chromatography with a UV/Visible detector (HIPCE-UV). The compounds were separated in a Thermo Finnigan Surveyor installed with a Biorad Aminex 87H column (300 ten 7.eight mm).

Ethanol-h2o extracts composition

Extracts were prepared using approximately 1 g of the bark samples and a solution of ethanol/water (50/fifty, 5/v), with a 1:x (thousand/v) solid-liquid ratio for 60 min at 50°C in an ultrasonic bathroom (Branson 2200 Scientific Back up, Inc., Hayward, CA, The states). The sample was filtrated and the supernatant extract was used to determine the contents in full phenolics, flavonoids and condensed tannins. Each analysis was performed at least 3 times and at least three independent replicates were prepared for each standard and sample.

The antioxidant activity of these extracts was also determined using DPPH and FRAP methodologies.

Total phenolics.

The total phenolic content was determined using a modified Folin-Ciocalteu method [26]. Gallic acid (GA) was used as standard, the experiment was conducted in triplicate.

An aliquot of each bark extract (100 μl) was mixed with 4 ml of Folin-Ciocalteau (1:ten v/v) reagent (Sigma-Aldrich, ≥99.8% purity, St. Louis, MO, U.s.) and vortexed. Afterward 3–8 min at room temperature, 4 ml of Na_iiCO₃ (Sigma-Aldrich, ≥99.9% purity, St. Louis, MO, USA) solution (vii.5% m/v) were added, vortexed and incubated in a thermostatized water-bathroom at 45°C for ane min. The absorbance of the resulting blueish colored mixtures was recorded with a spectrophotometer (UV-160A Recording Spectrophotometer, Shimadzu) at 765 nm against a blank containing only water. The same process was followed for preparation of the gallic acid (Sigma-Aldrich, ≥99% purity, St. Louis, MO, USA) scale curve, using seven previously prepared stock standard solutions in the range of 0.014 to 0.762 thou/l; the calibration curve of gallic acrid was y = 0.0076x+0.0108 (r^two = one.000). The total phenolic content was expressed as milligrams of gallic acid equivalents (GAE) per k of excerpt.

Total flavonoids.

Full flavonoid content was determined using a modified aluminum chloride methodology with catechin (CA) as standard [24]. Aliquots (1 ml) of the excerpt solutions, or catechin standard solution, were taken to iv ml water and 0.3 ml NaNO₂ (Sigma-Aldrich, ≥99% purity, St. Louis, MO, Usa) solution (5% m/5) and kept during 5 min in the dark. And then 0.iii ml AlCl_three (Sigma-Aldrich, ≥99% purity, St. Louis, MO, USA) solution (10% g/v) was added, and after 6 min 2 ml NaOH (Sigma-Aldrich, ≥98.0% purity, St. Louis, MO, U.s.a.) solution (4%, m/five) and 2.4 ml water were added sequentially and vigorously shaken. Absorbance was recorded at 510 nm after 30 min incubation, against water (UV-160A Recording Spectrophotometer, Shimadzu). A standard calibration plot was generated using six sequentially and independently prepared stock standard solutions of catechin (Sigma-Aldrich, ≥99.0% purity, St. Louis, MO, USA) with concentration from 0.10 to ane.0 mg/ml. The concentrations of flavonoid in the exam samples were calculated from the calibration plot (y = 0.9268x, r^two = 0.950) and expressed as mg catechin (CA) equivalent/m of extract.

Condensed tannins.

Condensed tannins content was determined by the vannilin-sulphuric acrid assay using catechin every bit standard [27]. An aliquot (ane ml) of the extract sample was dried and dissolved in ten ml of methanol. An aliquot of ane ml was added to 2.5 ml of vanillin (Sigma-Aldrich, ≥99.0% purity, St. Louis, MO, USA) solution (1% m/five in methanol) and 2.5 ml of sulphuric acid 25% (m/5 in methanol), and the book of 10 ml completed with methanol. The extract samples and blanks (with one ml of methanol) were incubated for exactly 15 min. Subsequently, the absorbance was measured at 500 nm using a UV–Vis spectrophotometer (UV-160A Recording Spectrophotometer, Shimadzu). The aforementioned procedure was followed for preparation of the catechin calibration plot from standards with concentrations of 10, xx, twoscore, sixty, 80 and 100 mg/fifty (y = 0.0738x+0.0054, r² = 0.996). The results were expressed every bit mg catechin (CA) equivalents/thousand of extract (mg CA/g).

Antioxidant activeness.

The antioxidant activity of the ethanol-h2o extracts was determined past 2 methods to embrace the various mechanisms of antioxidant action [28,29]: two,two-diphenyl-1-picryhydrazyl (DPPH), which measures the free radical scavenging chapters, and ferric reducing/antioxidant power (FRAP), which measures the sample'south ferric reducing power.

The DPPH assay was performed using 2,two-diphenyl-1-picrylhydrazyl hydrate (DPPH, Sigma-Aldrich, ≥99.0% purity, St. Louis, MO, United states), a nitrogen centered gratuitous radical having an odd electron that changes from majestic to yellow when the odd electron is paired in the presence of a radical scavenger to class the reduced DPPH-H [28,29]. The DPPH results are expressed either every bit IC₅₀ value or every bit Trolox equivalents on a dry extract base of operations.

Different dilutions of the initial extract and of a stock Trolox (Sigma-Aldrich, ≥97.0% purity, St. Louis, MO, USA) solution (0.2 mg/ml) in methanol were prepared. An aliquot of 100 μL of each methanolic solution were added to 3.ix ml of a DPPH methanolic solution (24 μg/ml). The blank sample consisted of 100 μl of methanol added to 3.ix ml of DPPH solution. After thirty min incubation at room temperature in the dark, the absorbance was measured at 515 nm.

The radical scavenging activeness of each sample was calculated past the DPPH inhibition percent as follows: I % = [(Abs₀-Abs_i)/Abs₀]×100, where Abs₀ was the absorbance of the blank and Abs₁ was the absorbance in the presence of the extract at different concentrations. The IC_fifty inhibiting concentration represents the concentration of a sample necessary to sequester 50% of the DPPH radicals and was obtained by plotting the inhibition percentage against the extract concentration. The scavenging event was besides expressed as the Trolox equivalent antioxidant capacity (TEAC) determined from the scale curve with Trolox solution of different concentrations and the per centum of scavenging effect on the DPPH radical.

The ferric reducing antioxidant power (FRAP) assay depends on the reduction of ferric ion into ferrous ion [30]. The FRAP reagent was obtained by mixing 300 mM sodium acetate buffer (pH three.6), 10 mM TPTZ (tripyridyl triazine, Sigma-Aldrich, ≥98.0% purity, St. Louis, MO, USA) solution and xx.0 mM FeCl_three.6H2O solution in a ratio of x:1:1 (volume). An aliquot (100 μl) of extract or standard was then added to 3 ml of the FRAP reagent and the reaction mixture was incubated at 37°C for thirty min. The absorbance was measured at 593 nm in comparison with a blank. Aqueous solutions of known Trolox concentrations in the range of 0–0.v Mmol/L were used for the calibration, and the results were expressed as Mmol Trolox equivalents/g dry mass.

Lipophilic extracts composition

The lipophilic extracts that were solubilized from the bark samples with dichloromethane were recovered as a solid residue afterward solvent evaporation and dried overnight under vacuum at room temperature. Aliquots (2 mg) of each sample were taken and derivatized in 100 μL of pyridine (Sigma-Aldrich, ≥99.eight% purity, St. Louis, MO, USA); the compounds with hydroxyl and carboxyl groups were trimethylsilylated into trimethylsilyl (TMS) ethers and esters, respectively, by calculation 100 μl of bis(trimethylsily)-trifluoroacetamide (BSTFA, Sigma-Aldrich, ≥99.0% purity, St. Louis, MO, U.s.). The reaction mixture was heated at 60°C for 30 min in an oven.

The derivatized extracts were immediately analyzed by injection in a GC–MS Agilent 5973 MSD with the following GC conditions: Zebron 7HG-G015-02 cavalcade (30 m, 0.25 mm; ID, 0.1 μm film thickness), flow ane ml/min, injector 280 °C, oven temperature programme, 100 °C (one min), rate of 10 °C/min up to 150 °C, rate of 4 °C/min upward to 300 °C, rate of 5 °C/min up to 370 °C, rate of viii °C/min upwards to 380 °C (5 min). The MS source was kept at 220 °C and the electron impact mass spectra (EIMS) taken at lxx eV of free energy.

The compounds were identified as TMS derivatives past comparison their mass spectra with a GC–MS spectral library (Wiley, NIST), and past comparing their fragmentation profiles with published data [31,32]. For semi-quantitative analysis the area of peaks in the full ion chromatograms of the GC–MS analysis was integrated and their relative proportions expressed every bit surface area proportion of the full chromatogram area. Each aliquot was injected in triplicate and results presented past mean (only standard divergence inferior to 5% was considered).

Suberin composition

Aliquots of the dichloromethane extracts (5 ml) from the suberin depolymerization reaction were taken, evaporated under North₂ menstruum and dried at room temperature (r.t.) nether vacuum overnight. The samples were derivatized as described above and immediately analyzed past injection in a GC–MS Agilent 5973 MSD with the following GC weather condition: Zebron 7HG-G015-02 column (30 m, 0.25 mm; ID, 0.one μm film thickness), menstruum 1 ml/min, injector 280°C, oven temperature program, 100°C (i min), charge per unit of 8°C/min upwards to 250°C, rate of 5°C/min up to 300°C (5 min), rate of 5°C/min up to 350°C (5 min), rate of x°C/min upwardly to 380°C (5 min). The MS source was kept at 220°C and the electron impact mass spectra (EIMS) taken at 70 eV of energy.

The compounds were identified and quantified as described higher up. Each aliquot was injected in triplicate and results presented past hateful (merely standard difference inferior to v% was considered).

Statistical analysis

All results were expressed as mean and standard deviation (SD). The significance of differences (p ≤ 0.05) amongst the corresponding mean values was determined using one-manner analysis of variance (ANOVA) using the Sigmaplot ^® statistical software (version 11.0).

Results and give-and-take

Chemical limerick

The summative chemical composition of the Q. faginea bawl samples, from the two sites, is summarized on Table 1. No significant differences were found between the trees of site 1 and the trees of site ii. The mean composition was (in % of the oven dry bark): xiv.vi% ash, xiii.2% extractives, 2.nine% suberin, 28.2% lignin and 41.1% polysaccharides. Apropos the extractives, the ethanol and water-soluble compounds showed college proportion (representing 85.6% of the full extractives and eleven.3% of the bark) than the dichloromethane extractives (14.iv% of the extractives and i.ix% of the bark).

The humidity in the Q. faginea bark samples from the two sites was determined subsequently 24 h oven-drying at threescore °C and 2 h at 100 °C, corresponding to thirteen.4–14.2% of bark.

The extractives content of Q. faginea bark is very similar to that of the sapwood and heartwood of the trees in these two sites [11]. The results are, however, much college than those found in the bark of other Quercus species: 4.6% in Q. robur [33], 2.i% in Q. petraea [34], 5–vi% in Q. vulcanica [35], 5.iv% in Q. alba, half-dozen.6% in chestnut oak and v.viii% in Q. stellata [36]. In a few cases of other species, the bark was separated in phloem and cork: in Q. cerris rhytidom, the extractives corresponded to 6.five% and sixteen.7% in the phloem and cork respectively [37], and in Q. suber to 6.2% and 10.iv% respectively [38], and in Pseudotsuga menziesii to 28.four% and 29.ii% [22].

The suberin content was low, which is consistent with the cellular characteristics of Q. faginea bark that contains periderms that produce merely thin cork layers; therefore, the bark is mostly constituted by the lignocellulosic phloem tissues [12]. In fact, suberin content is in straight relation with the proportion of cork in the bark i.e. barks with more than cork will take more suberin. This is the instance for instance of species such equally Q. suber [39, twoscore], Q. cerris [18, 37], Pseudotsuga menziesii [22] or Q. variabilis barks [24]. In species with a small proportion of cork, the content in suberin is correspondingly depression e.one thousand. in the bark of Pinus pinea [41] or Tectona grandis [42].

Lignin content is relatively loftier (28.ii%). This is justified by the substantial lignification of bawl fibers and sclereids [12]. Lignin content is similar to the observed for sapwood and heartwood (28–29%) of copse from the same species [11]. The comparison with barks of other Quercus species shows similar range of values to those reported for Q. robur (25–35%) [33, 43], Q. petraea (17–30%) [34, 43], Q. alba and Q. stellata (14–26%) [36], and Q. vulcanica (25%) [35].

The carbohydrate composition based on the monosaccharides found in the acid hydrolysates is summarized in Tabular array ii. The major monosaccharide was glucose (over 50% of the total) and xylose (35.1%); rhamnose and arabinose be in very small amounts and, together with galactose and mannose deemed for only ix% of total monosaccharides) while uronic acids represented iv.6%; no acetylation of the polysaccharides was detected. Comparison to the carbohydrate composition of Q. faginea wood, glucose and xylose also represented the major monosaccharides (approximately 90% of the full neutral monosaccharides).

Similar composition was reported for the Q. cerris rythidome [37] where glucose and xylose also constituted the major monosaccharides identified (48.4% glucose and 27.9–40.3% xylose). Other barks showed a similar pattern e.g. 47.0% and 33.8% of glucose and xylose respectively in Betula pendula [21].

Ash content was particularly high. Information technology is known that bawl accumulates inorganic materials and their content is ordinarily much college than in wood which in this species was well-nigh 19 times over [xi]. Previously, was already observed that crystals and druses occurred profusely in chambered axial parenchyma in Q. faginea bark likewise as big prismatic crystals in sclereids that might may explain these findings [12]. The ash content of Q. faginea bark was higher than that of other Quercus species, namely in the co-occurring cork oaks (0.7%) [19], the American oak, Q. alba (0.ii–1%) [36] and the and then-chosen European oaks (0.3%) [33] and 9–10% [43]. Still, the content was similar to that of Q. vulcanica that reached thirteen.5% [35].

Ethanol-h2o extracts composition

Tabular array 3 shows the yield and composition of the ethanol-water (ane:1) extracts concerning full phenolics, flavonoids and condensed tannins content.

The extraction yield under the conditions used was lower than the total polar extractives determined by soxhlet extraction (6.4% vs. 11.iii%). This yield departure between extraction processes was also obtained when analysing sapwood and heartwood of Q. faginea trees [11]. This indicates that the extraction procedure may be optimized to improve extraction yield e.g. past increasing extraction time or temperature.

Phenolic substances are the major constituents of extractives (Table 3), representing 54% to 72% of the Q. faginea bawl ethanol-water extracts (respective to 40.5 and 38.0 mg GAE/g of bawl). This is similar to the value found for methanol-h2o extracts of cork from Algerian Q. suber (787.0 mg GAE/ grand extract) [44] likewise as for phenolic contents determined in the heartwood of Q. robur, Q. petraea and Q. pyrenaica [12]. The bark of Q. faginea contains more phenolics than its sapwood (nineteen.5 mg GAE/yard of woods) merely lower than heartwood (81.8 mg GAE/chiliad of woods) [11].

The extracts were rich in flavonoids and condensed tannins (204.7 and 220.vii mg CE/g of excerpt respectively) with some differences between sites: the bark extracts from site 1 were richer in condensed tannins than those from site ii and the opposite was observed concerning flavonoid content. The natural betwixt-tree variability and the tree age difference between site one and ii may contribute to this departure [45] for wood phenolic composition. Overall the Q. faginea bark content in flavonoids and tannins was much above the values found for sapwood and heartwood [11].

The phenolic richness of the Q. faginea bark extracts let to consider a valorization of this material. Plant polyphenols are important complimentary radical scavenging antioxidants because they are able to capture free radicals and chelate metals that could exist responsible for promoting lipid peroxidation, while flavonoids may act against several human diseases and as potent antioxidants depending on the molecular construction, the position of the hydroxyl group and other chemical features [46].

Antioxidant action of ethanol-water extracts.

The antioxidant capacity of the ethanol-water extracts from Q. faginea bark was evaluated by measuring the scavenging chapters confronting the radical DPPH· and past the ferric reducing antioxidant ability (Tabular array 3). The bark extracts exhibited loftier antioxidant activity (IC₅₀ of 3.01 μg excerpt/ml and ii.25 μg extract/ml for site ane and 2, respectively), when compared to the antioxidant standard Trolox (3.81 μg Trolox/ml).

The reducing ability of the extracts past the FRAP analysis was three.85 mM Trolox/ g extract (0.29 mM Trolox/ m bark) and 5.03 mM Trolox/ chiliad extract (0.26 mM Trolox/ g extract). As expected the reducing power was college in the extracts with college polyphenolic content given their redox properties and and so their power to act every bit reducing agents, hydrogen donor, singlet oxygen quenchers or metal chelators.

The comparison of the results with literature data must be done cautiously due to differences in methods and calculations. However, it is clear that the extracts of Q. faginea bawl show a very high antioxidant capacity when compared to other extracts: reported by that the IC_l value for Q. suber cork is 2.79 (water extract), three.58 (methanol extract) and 5.84 (methanol-water extract) (compared with ii.12 μg/ml for ascorbic acid in methanol and 2.46 μg/ml for ascorbic acid in water [47]. This antioxidant action is similar than that reported for Eucalyptus sideroxylon bark ethanol:H_twoO excerpt in which the IC₅₀ value was 2.25 μg/ml, equally compared to Trolox (IC₅₀ of two.xc μg/ml) [48]. The scanvenging activity of the hydroalcoholic excerpt of Eastward. grandis, East. urograndis and E. maidenii barks was also determined and showed comparatively less antioxidant activity, with an IC₅₀ values of, respectively, vi.26 μg/ml, 6.fourteen μg/ml and viii.24 μg/ml compared with ii.17 μg/ml for ascorbic acid [49].

In general, the chemical characteristics of the ethanol-water extracts of bark from Q. faginea permit considering its employ a source of antioxidants in food or cosmetics industries.

Lipophilic extracts composition

The results of the GC-MS analysis of the non-polar dichloromethane bawl extracts of Q. faginea are summarized in Table 4.

Triterpenes constitute one of the most abundant class of compounds (xvi.i% and 19.5% of all compounds, respectively for site ane and site two). Amidst triterpenes, friedelin (5.ane–6.4% of all compounds), olean-18-ene (2.1–ii.three%) and betulinic acrid (1.9–3.0%) constitute ninety.one% of all the identified triterpenes/triterpenoids. β-Amyrin, ɑ-amyrin, betulin and ursolic acid) were also identified in smaller amounts.

Several authors have reported the presence of betulin, betulinic acid, lupeol and oleanolic acrid in birch bawl species [fifty, 51] and of friedelin, cerin, lupeol, ursolic acids in oak barks [49–54]. Barks from Eucalyptus species are likewise very rich in triterpenic compounds equally ɑ-amyrin, β-amyrin, betulonic and betulinic acids, oleanolic and ursolic acids [55, 15].

Saturated alkanoic acids institute also i abundant grouping of compounds (30.4% and xvi.3% of all compounds for site 1 and site 2 respectively). They are the major compounds identified in the lipophilic bark extracts from the trees from site ane, namely hexadecanoic, octadecanoc and docosanoic acids, respective to nineteen.5%, ii.6% and two.nine%, respectively. In site 2, saturated alkanoic acids were likewise found in considerable amounts, with hexadecanoic, octadecanoic and docosanoic acids also as the virtually representative (seven.4%, ane.ix% and 1.vii%, respectively). Substituted alkanoic acids, saturated ω-hydroxyacids and ɑ,ω-diacids were also constitute in the lipophilic extracts from trees from both sites, but in smaller amounts (5.1%, 0.six% and 1.i% for site 1, respectively, and 3.ix%, 0.8% and 0.2% for site 2, respectively). Alkanols comprise but 1.vii–i.8% of all compounds, with eicosanol and tricosanol as major compounds. Concatenation lengths vary from C9 to C26, but C16 is the most arable, corresponding to 53.6% and 45.1% of the total fatty acids, in the lipophilic extracts from sites 1 and ii, respectively.

The same blueprint of composition was found for other lipophilic hardwood bark extracts like birch trees [23, 56] or Populus balsamifera [57].

Glycerol and glycerol derivatives constituted 16.0% of all compounds in the bark lipophilic extracts from site ane, with glycerol representing 11.iii%. In site 2, the amount of glycerol and its derivatives was considerably lower (viii.half dozen%).

Sterols were identified in high amounts only only in trees from site 2, constituting 20.three% of all compounds, almost tenfold the amount found in site 1 (two.8%). β-sitosterol was the major sterol (16.8% of all compounds); stigmasterol, stigmastanol and campesterol were too identified in smaller amounts.

Aromatics were nowadays (1.5–1.1% of all compounds) including ferulic acrid although in small amounts (<1%).

There are some articulate differences in the composition of the bawl lipophilic extracts from both sites: in extracts from site ane, the saturated alkanoic acids are conspicuously the near abundant group (xxx.ix% vs. sixteen.3%), while for site 2, the major grouping is the sterols (twenty.3% vs. ii.8%).

Lipophilic bark extracts from Q. faginea copse are different from those reported for the wood of the same trees [xi]. The composition was not influenced past the geographical location. Aromatics are the major class of compounds in sapwood (22.8%) and as well saturated alkanoic acids (15.7%) and sterols (ten.6%); in heartwood, saturated alkanoic acids correspond the major class of identified compounds (25.8%), accompanied by triterpenes (13.0%), sterols (12.8%) and substituted alkanoic acids (ten.4%).

Suberin composition

The results for the suberin composition obtained past GC-MS assay are summarized in Tabular array 5, given in mg of compound per kg of dry out mass. This is the nearly commonly used quantification of suberin monomers in the depolymerized mixtures [58]. The mixtures contain the compounds that are soluble in the depression polarity organic solvent used for the recovery of the suberin monomers after depolymerization by partition between h2o and an organic phase after acidification of the reaction mixture; h2o soluble monomers, namely glycerol are removed in the aqueous stage [25].

The main constituents institute in suberin from Q. faginea bawl are fatty acids (70.7–88.3% of all compounds): substituted ω-hydroxyacids (15.three% in site i and 40.2% in site ii), saturated ω-hydroxyacids (26.8% in site 1 and x.8% in site 2), and substituted ɑ,ω-alkanoic diacids (thirteen.three%in site one and 27.3%in site two). The differences between the barks from both sites are evident: in site i the ω-hydroxyacids correspond to 60.5% of total fatty acids and in site 2 substituted ω-hydroxyacids and ɑ,ω-diacids institute 80.one% of total fatty acids.

Factors such every bit the local geoclimate, seasonal changes, external conditions such as low-cal, temperature and humidity may bear on the composition of secondary metabolites [59] and contribute to the differences on the chemical composition of the barks from the two sites.

In the barks of site 1, suberin is mainly constituted by saturated ω-hydroxyacids including namely 24-hydroxytetracosanoic acid and its methyl ester (x.3%), 22-hydroxydocosanoic acid (half dozen.ii%) and the methyl ester of 18-hydroxyoctadecanoic acrid (5.0%). saturated and substituted alkanoic acids represented half-dozen.5% and ii.ane% of identified compounds (namely docosanoic acrid and the methyl esters of hexadecanoic, tetracosanoic and 9,12-octadecanedioic acids). Substituted ω-hydroxyacids and substituted ɑ,ω-diacids were also institute in high amounts (15,3% and 13.3%, respectively) where the major chemical compound identified was the methyl esters of 18-hydroxy-9,10-dihydroxyoctadecanoic (7.nine%) and 18-hydroxy-nine,10-epoxyoctadecanoic acid (5.three%). Alkanols represented 6.8% of all compounds, Saturated ɑ,ω-diacids corresponded to 3.8% (where the methyl ester of octadecanedioic acrid exist in 1.iv%), Aromatics represent 9.8% (mainly ferulic acrid and its methyl ester). Sterols and triterpenes were present in minor amounts.

In the barks of site two, suberin is richer in substituted ω-hydroxyacids (39.8%) and substituted ɑ,ω-diacids (27.iii%), mainly the methyl esters of 18-hydroxy-9,10-dihydroxyoctadecanoic acid (30.8%), xviii-hydroxy-nine-octadecanoic acrid (8.9%), 2-hydroxydecanedioic acid (12.0%) and the methyl esters of 9,10-dihydroxyoctadecanedioic (9.2%) and viii,9,xviii-trihydroxyoctadecanedioic acids (6.ane%). Saturated ω-hydroxyacids were also found in considerable amounts (ten.8%), and the methyl ester of 18-hydroxyoctadecanoic acid and 22-hydroxydocosanoic acrid are the major identified compounds. Alkanols represented 6.6% of all compounds (namely 1-octadecanol with 2.eight%), saturated alkanoic acids 3.2% (mainly hexadecanoic and octadecanoic acids). The methyl ester of ferulic acid was the only aromatic found representing iv.0% of the compounds. Concatenation lengths ranged from C14 to C26, but C18 was the most relevant, representing 52.2% and 73.ane% of the total fatty acids identified in site one and two, respectively.

This is the offset report of suberin composition from Q. faginea bark showing that information technology is characterized past the major presence of ω-hydroxyacids (46.3% of total compounds) and of ɑ,ω-alkanoic diacids (22.3%). This composition is quite different from that of cork from Q. suber in which the about important monomers are substituted ɑ,ω- diacids with mid-chain epoxy or diol substitutions [56]. Differences also occur with the suberin of Q. cerris cork where the ω-hydroxyacids represent 90% of the long chain monomers [37]. A more similar compositional blueprint is found with the suberins of Pseudotsuga menziesii cork [22] or Plathymenia coriacea [60].

It is worth noticing that the contents in saturated fatty acids such equally ω-hydroxyacids and alkanoic acids amounts are over twofold in site ane (younger copse) than in site ii (older trees), while ɑ,ω-alkanoic diacids and ω-hydroxyacids are the most representative in site 2.

Triterpenes and sterols are absent-minded in site 2. Although the number of samples used in these studies is small and general conclusions have to be made charily, the results suggest a possible relation between tree age and suberin chemic limerick: in older trees suberin is constituted past higher content of mid-chain substituted fatty acids, leading to a spatially less-compact macromolecular construction [61].

Conclusions

The barks from Quercus faginea mature trees from two sites were chemically characterized for the offset time, showing a loftier content of extractives, constituted mainly past polar compounds extractable with ethanol and water that include high contents of phenolics and polyphenolics, including of flavonoids. The ethanol-water extracts showed a very high antioxidant capacity, well to a higher place about reports on other materials.

The bark of Q. faginea contains a loftier amount of inorganic material and of lignin. In accord with its structural limerick the bark has a small amount of suberin. Suberin composition is dominated by ω–hydroxyacids (saturated and substituted) and to a bottom extent extent by ɑ,ω-diacids.

In an integrated valorization strategy, Quercus faginea barks are interesting sources of polar compounds including phenols and polyphenols with possible interesting bioactivities. The lipophilic extracts independent sterols and triterpenes that are as well valuable bioactive compounds or chemical intermediates for the synthesis of new valuable compounds with specific properties.

Acknowledgments

The sampling was supported by the project OAKWOODS (PTDC/AGR-AAM/69077/2006) funded by Fundação para a Ciência e a Tecnologia (FCT). We thank José Fifty. Louzada for providing the samples from Site 1 and Sofia Knapic for project management. We besides thank Joaquina Silva and Lidia Silva for help with the chemical analysis. This piece of work was supported past the Strategic Project (UID/AGR/00239/2013) of Centro de Estudos Florestais, by the national funding from FCT. The third author acknowledges a mail-doc scholarship by FCT (SFRH /BPD/ 97970/2013).

References

1. ane. Fabião A, Silva I. Consequence of individual tree shelters on early survival and growth of a Quercus faginea plantation. Ann. Ist. Sper. Selvic. 1996;27: 77–82. http://hdl.handle.net/10400.five/1334
   • View Article
   • Google Scholar
2. 2. Cotillas One thousand, Sabate South, Gracia C, Espelta JM. Growth response of mixed Mediterranean oak coppices to rainfall reduction. Could selective thinning have any influence on it? For. Ecol. Manage. 2009;258: 1677–1683.
   • View Article
   • Google Scholar
3. iii. Corcuera L, Camarero JJ, Gil-Pelegrí E. Furnishings of a severe drought on growth and wood anatomical properties of Quercus faginea. IAWA J. 2004;25: 185–204.
   • View Commodity
   • Google Scholar
4. 4. Montserrat-Marti G, Camarero JJ, Palacio S, Pérez-Rontome C, Milla R, Albuixech J, Maestro Chiliad. Summer-drought constrains the phenology and growth of two coexisting mediterranean oaks with contrasting leafage habit: implications for their persistence and reproduction. Trees. 2009;23: 787–799.
   • View Article
   • Google Scholar
5. 5. Reboredo F, Pais J. Evolution of forest comprehend in Portugal: A review of the 12th –20th centuries. J. Wood. Res. 2014;25: 249–256.
   • View Commodity
   • Google Scholar
6. vi. Knapic S, Louzada JL., Leal S, Pereira H. Radial variation of wood density components and ring width in cork oak trees. Ann. For Sci. 2007;64: 211–218.
   • View Article
   • Google Scholar
7. vii. Knapic Southward, Louzada JL, Pereira H. Variation of wood density components within and between Quercus faginea copse. Can. J. For. Res. 2011;41: 1212–1219.
   • View Article
   • Google Scholar
8. viii. Sousa VB, Louzada JL, Pereira H. Age trends and within-site effects in wood density and radial growth in Quercus faginea mature trees. Woods Systems 2016;25: e053, 9 pages.
   • View Article
   • Google Scholar
9. 9. Sousa VB, Cardoso S, Pereira H. Ring width variation and heartwood development in Quercus faginea. Wood Fiber Sci. 2013;45: 405–414.
   • View Article
   • Google Scholar
10. 10. Sousa VB, Cardoso South, Pereira H. Age trends in the woods anatomy of Quercus faginea. IAWA J. 2014;35: 293–306.
    • View Article
    • Google Scholar
11. 11. Miranda I, Sousa V, Ferreira J, Pereira H. Chemical characterization and extractives limerick of heartwood and sapwood from Quercus faginea. PLoS ONE. 2017;12: 1–14. pmid:28614371
    • View Article
    • PubMed/NCBI
    • Google Scholar
12. 12. Quilhó T, Sousa V, Tavares F, Pereira H. Bark anatomy and cell size variation in Quercus faginea. Turk. J. Bot. 2013;37: 561–570.
    • View Article
    • Google Scholar
13. xiii. Barij N, Cermak J, Stokes A. Azimuthal variations in xylem structure and water relations in cork oak (Quercus suber). IAWA J. 2011;32: 25–xl.
    • View Article
    • Google Scholar
14. 14. Dickison WC. Integrative Plant Anatomy. 2000. The states. Academic Press, Elsevier Publishers. ISBN: 978-0-12-215170-5
15. fifteen. Sartori C, Mota GS, Ferreira J, Miranda I, Mori FA, Pereira H. Chemic characterization of the bark of Eucalyptus urophylla hybrids in view of their valorization in biorefineries. Holzforschung 2016;70: 819–828.
    • View Article
    • Google Scholar
16. 16. Menon V, Rao One thousand. Trends in bioconversion of lignocellulose: Biofuels, platform chemicals & biorefinery concept. Prog. Energy Combust. Sci. 2012;38: 522–550.
    • View Article
    • Google Scholar
17. 17. Villaverde JJ, Sandín-Espana P, Sevilla-Morán B, López-Goti C, Alonso-Prados JL. Biospesticides from Natural Products: Current Development, Legislative Framework, and Future Trends. 2016;xi: 5618–5640.
    • View Article
    • Google Scholar
18. xviii. Şen A, Quilhó T, Pereira H. The cellular structure of cork from Quercus cerris var. cerris bark in a materials' perspective. Ind. Crops Prod. 2011;34: 929–936.
    • View Article
    • Google Scholar
19. nineteen. Miranda I, Gominho J, Pereira H. Cellular structure and chemical composition of cork from the Chinese cork oak (Quercus variabilis). J. Woods Sci. 2012a;59: 1–9.
    • View Article
    • Google Scholar
20. 20. Miranda I, Gominho J, Mirra I, Pereira H. Chemical characterization of barks from Picea abies and Pinus sylvestris after fractioning into different particle sizes. Ind. Crops Prod. 2012b;36: 395–400.
    • View Article
    • Google Scholar
21. 21. Miranda I, Gominho J, Mirra I, Pereira H. Fractioning and chemic characterization of barks of Betula pendula and Eucalyptus globulus. Ind. Crops Prod. 2013;41: 299–305.
    • View Article
    • Google Scholar
22. 22. Ferreira J, Miranda I, Gominho J, Pereira H. Selective fractioning of Pseudotsuga menziesii bawl and chemical characterization in view of an integrated valorization. Ind. Crops Prod. 2015;74: 998–1007.
    • View Article
    • Google Scholar
23. 23. Ferreira J, Quilhó T, Pereira H. Characterization of Betula pendula Outer Bark Regarding Cork and Phloem Components at Chemic and Structural Levels in View of Biorefinery Integration. J. Wood Chem. Technol. 2016a;0: 1–xvi.
    • View Article
    • Google Scholar
24. 24. Ferreira J, Miranda I, Şen U, Pereira H. Chemical and cellular features of virgin and reproduction cork from Quercus variabilis. Ind. Crops Prod. 2016b;94: 638–648.
    • View Article
    • Google Scholar
25. 25. Pereira H. Chemical limerick and variability of cork form Quercus suber L. Woods Sci. Technol. 1988;22: 211–218.
    • View Article
    • Google Scholar
26. 26. Singleton VL, Rossi JA. Colorimetry of total phenolics with phosphomolybdic phosphotungstic acid reagents. Am. J. Enol. Vitic. 1965;xvi: 144–158.
    • View Article
    • Google Scholar
27. 27. Abdalla S, Pizzi A, Ayed North, Bouthoury FC, Charrier B, Bahabri F, Ganash A. MALDI-TOF analysis of Aleppo pino (Pinus halepensis) bawl tannin. BioResource. 2014;9: 3396–3406.
    • View Article
    • Google Scholar
28. 28. Sharma OP, Bhat TK. DPPH antioxidant assay revisited. Nutrient Chem. 2009;113: 1202–442.
    • View Article
    • Google Scholar
29. 29. Benzie IF, Strain J. The Ferric Reducing Ability of Plasma (FRAP) as a measure of ''Antioxidant ability": the FRAP assay. Anal. Biochem. 1996;239: 70–76. pmid:8660627
    • View Article
    • PubMed/NCBI
    • Google Scholar
30. 30. Gan RY, Xu XR, Song FL, Kuang L, Li HB. Antioxidant action and full phenolic content of medicinal plants associated with prevention and treatment of cardiovascular and cerebrovascular diseases. J. Med. Plants Res. 2010;four: 2438–2444.
    • View Article
    • Google Scholar
31. 31. Eglinton M, Hunneman D. Gas chromatographic-mass spectrometric studies of long-chain hydroxy acids-I. Phytochemistry 1968;seven: 313–322.
    • View Article
    • Google Scholar
32. 32. Kolattukudy P, Agrawal Five. Structure and composition of aliphatic constituents of potato tuber skin. Lipids. 1974;ix: 682–691.
    • View Article
    • Google Scholar
33. 33. Wagenfuhr R, Schreiber C. Holzatlas, 5.E.B. 1974.Fachbuchverlag, Leipzig.ok
34. 34. Puech J-Fifty Vieillissement des eaux-de-vie en fûts de chêne. Extraction de la lignine et de ses produits de degradation. PhD Thesis, 1978, University of Paul Sabatier, Tolouse, France.
35. 35. Balaban M, Uçar G. Extractives and structural components in wood and bark of endemic oak Quercus vulcanica Boiss. Holzforschung 2001;55: 478–486.
    • View Commodity
    • Google Scholar
36. 36. Pettersen RC. The chemical composition of forest. In: The Chemistry of Solid Forest. Rowell R. (ed.). Am. Chem. Soc. 1984; Washington D.C., pp. 57–127.
37. 37. Şen A, Miranda I, Santos S, Graça J, Pereira H. The chemical composition of cork and phloem in the rhytidome of Quercus cerris bawl. Ind. Crop. Prod. 2010;31: 417–422.
    • View Commodity
    • Google Scholar
38. 38. Lourenço A, Rencoret J, Chemetova C, Gominho J, Gutierrez A, del Rio JC, Pereira H. Lignin composition and structure differs between xylem, phloem and phellem in Quercus suber. Front. Plant Sci. 2016;vii: 1612. pmid:27833631
    • View Commodity
    • PubMed/NCBI
    • Google Scholar
39. 39. Pereira H, Graça J, Baptista C. The effect of growth charge per unit on the structure and compressive properties of cork from Quercus suber L. IAWA Bull. 1992;13: 389–396.
    • View Commodity
    • Google Scholar
40. twoscore. Graça J, Pereira H. The periderm development in Quercus suber. IAWA Bull. 2004;25: 325–335.
    • View Commodity
    • Google Scholar
41. 41. Nunes E, Quilhó T, Pereira H. Anatomy and chemical limerick of Pinus pinea 50. bark. Ann. Forest Sci. 1999;56: 479–484.
    • View Article
    • Google Scholar
42. 42. Baptista I, Miranda I, Quilhó T, Gominho J, Pereira H. Characterisation and fractioning of Tectona grandis bark in view of its valorisation as a biorefinery raw-cloth. Ind. Crops Prod. 2013;l: 166–175.
    • View Commodity
    • Google Scholar
43. 43. Dedrie 1000, Jacquet Due north, Bombecka P-L, Héberta J, Richel A. Oak barks every bit raw materials for the extraction of polyphenols for the chemic and pharmaceutical sectors: A regional case study. Ind. Crop Prod. 2015;70: 316–321.
    • View Article
    • Google Scholar
44. 44. Touati R, Santos SAO, Rocha SM, Belhamel One thousand, Silvestre AJD. The potential of cork from Quercus suber L. grown in Algeria as a source of bioactive lipophilic and polar compounds. Ind. Crops Prod. 2015;76: 936–945.
    • View Article
    • Google Scholar
45. 45. Miller DP, Howell GS, Michaelis CS, Dickmann DL. The content of phenolic acids and aldehyde flavor components of white oak as afflicted by site and species. Am. J. Enol. Vitic. 1992;43: 333–338.
    • View Article
    • Google Scholar
46. 46. Iqbal Due east, Salim KA, Lim LB. Phytochemical screening, total phenolics and antioxidant activities of bark and leaf extracts of Goniothalamus velutinus (Airy Shaw) from Brunei Darussalam. J. King Saud Univ. Sci. 2015;27: 224–232.
    • View Article
    • Google Scholar
47. 47. Santos SAO, Pinto PCRO, Silvestre AJD, Neto CP. Chemic composition and antioxidant activity of phenolic extracts of cork from Quercus suber L. Ind. Crops Prod. 2010;31: 521–526.
    • View Article
    • Google Scholar
48. 48. Miranda I, Lima 50, Quilhó T, Knapic S, Pereira H. The bark of Eucalyptus sideroxylon as a source of phenolic extracts with anti-oxidant backdrop. Ind. Crops Prod. 2016;82: 81–87.
    • View Article
    • Google Scholar
49. 49. Santos SAO, Villaverde JJ, Freire CSR, Domingues MR, Neto CP, Silvestre AJD. Phenolic composition and antioxidant activity of Eucalyptus grandis, East. urograndis (E. grandis×E. urophylla) and Eastward. maidenii bark extracts. Ind. Crops Prod. 2012;39:120–127.
    • View Article
    • Google Scholar
50. 50. Seshadri TR, Vedantham TNC. Chemic examination of the barks and heartwoods of Betula species of American origin. Phytochemistry 1971;10: 897–898.
    • View Article
    • Google Scholar
51. 51. Pazhe A, Zandersons J, Rizhikovs J, Dobele M, Spince B, Jurkjane Five, Tardenaka A. Obtaining Pentacyclic Triterpenes from Outer Birch Bark. Latvian Journal of Chemical science. The Journal of Riga Technical University. 2012;51: 415–420.
    • View Article
    • Google Scholar
52. 52. Chu J-H, Hung Due south-H, Wang Y-H. Glucosides of the Chinese drug, Chen-Pi-Ying (lIex). Hua Hsueh Hsueh Pao 1958;22: 128–132.
    • View Commodity
    • Google Scholar
53. 53. Guenther Due east. The essential oils. D. Van Nostrand Company, Inc. 1952; New York 5: 254.
54. 54. Şen A, Melo MMR, Silvestre AJD, Silva CM. Prospective pathway for a greenish and enhanced friedelin product through supercritical fluid extraction of Quercus cerris cork. J. Supercrit. Fluids 2015;97: 247–255.
    • View Article
    • Google Scholar
55. 55. Domingues RMA, Sousa GDA, Silva CM, Freire CSR, Silvestre AJD, Neto CP. High value triterpenic compounds from the outer barks of several Eucalyptus species cultivated in Brazil and in Portugal. Ind. Crops Prod. 2011;33: 158–164.
    • View Article
    • Google Scholar
56. 56. Clermont LP. The fatty acids of aspen, poplar, basswood, yellow birch, and white birch. Pulp Paper Mag. Can. 1961;62: 511–514.
    • View Article
    • Google Scholar
57. 57. Kull U, Jeremias K. Fatty acid composition of saponifiable lipids from barks of Populus balsamifera during the course of a yr. Z. Pflanzenphysiol. 1972;68: 55–62.
    • View Article
    • Google Scholar
58. 58. Graça J, Pereira H. Suberin structure in potato periderm: glycerol, long-chain monomers, and glyceryl and feruloyl dimers. J. Agric. Food Chem. 2000;48: 5476–5483. pmid:11087505
    • View Article
    • PubMed/NCBI
    • Google Scholar
59. 59. Morison JIL, Lawlor DW. Interactions betwixt increasing CO₂ concentration and temperature on plant growth. Plant Cell. Environ. 1999;22: 659–682.
    • View Article
    • Google Scholar
60. lx. Mota GS, Sartori C, Ferreira J, Miranda I, Mori FA, Pereira H. Cellular structure and chemical composition of cork from Plathymenia reticulata occurring in the Brazilian Cerrado. Ind. Crops Prod. 2016;ninety: 65–75.
    • View Article
    • Google Scholar
61. 61. Pereira H. The rationale backside cork backdrop: a review of the construction and chemical science. BioRes. 2015;x: 6207–6229.
    • View Commodity
    • Google Scholar

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