IJRES 1 (2014) 17-25
Chemical composition of Algerian cork according the origin and the quality
Dehane B.*, Benrahou A., Bouhraoua R., Hamani F. Z. and Belhoucine L.
Département des Ressources Forestières, Faculté SNVTU, Laboratoire Gestion Conservatoire de l’Eau, Sol et Forêts (LGCESF), Rocade1, Université Abou Bekr Belkaid de Tlemcen-Algérie.
Article History ABSTRACT Received 14 September, 2014 This research deepens knowledge on the properties of Algerian cork, by Received in revised form 17 reporting the relationship between two main characteristics in terms of physical October, 2014 Accepted 23 October, 2014 appearance (porosity and density); and of the chemical composition of the material. Samples in natural cork belonging to three quality classes used by the Key words: cork industry were selected from planks, extracted from representative trees of Algerian cork, six origins of the Algerian North [Jijel, Guelma, Tizi-Ouzou, M'Sila (Oran), Tennes Chemical composition, (Chlef) and Hafir (Tlemcen)]. For every provenance the porosity, the density of Quality, the cork and the chemical composition were determined. Results obtained show Interaction. that the chemical composition of the cork (Suberin, lignin and extractives) is relatively homogeneous about the geographical position (p>0.05). This situation changes by adopting the concept of the geographical area of the cork oak and the quality. Indeed, suberin which is the main contents of the suber (34.45 %), Article Type: was linked to the good quality classes and tends to yield every time the porosity Full Length Research Article and density, as well as raised the extractives. ©2014 BluePen Journals Ltd. All rights reserved
INTRODUCTION
The cellular structure and the chemical composition of texture, density and the frequency of its porosity all the cork of Quercus suber L. are the basis for its low changes. These changes can limit the applications of the density, impermeability in liquids, its elasticity and impact product because they are considered as defects (Molinas strength. These remarkable set of properties are the and Oliva, 1990). Cork is found predominantly in the central reason for its use as a barrier against liquids, Mediterranean region (2 275 000 ha). The major cork heat, sound, chemicals, vibration and the dumping producing nations are Portugal, Spain, Algeria, Morocco, (Natividade, 1956; Gibson et al., 1981; Pereira, 1987). Tunisia, Italy and France. Cork production has shown These unique properties drew very early the attention of significant expansion in recent years with 340 000 tons researchers. The cellular structure of this plant material annually. Cork is used in a variety of products - from was observed for the first time under the microscope, by construction materials to gaskets and most importantly - Robert Hooke in 1664, and the first chemical experiences as a stopper for premium wines. The cork industry with the cork dates back to the 18th century. However, employs an estimated 30 000 workers in a variety of jobs cork is a natural product produced annually by the plant, (Apcor, 2004). Quercus suber, which by its nature and the The properties of the cork and its afterward quality heterogeneousness of factors affecting its production; divert widely the specificities of its chemical composition has a strong variability and this makes the quality and the chemical structure of its components. The concept difficult to define (Carrasquinho, 1987). During suberin, the lignin and the polysaccharides (cellulose and the process of its formation, its growth, color, hemicellulose), and extractives are the main compounds quoted in the bibliography bound to the chemistry of the cork (Silva et al., 2005). The suberin is a very complex polymer, responsible for elastic properties and for *Corresponding author: E-mail: [email protected]. impermeability of the cork. Its relative proportion lines up
Int. J. Res. Environ. Stud. 18
Figure 1. Geographical distribution of the 60 provenances in the North of Algeria.
between 22, 1-51% and 7% (Gil, 1997). The lignin, component and the area of distribution of the cork oak. responsible for the structural rigidity of cells and for the This contradiction infers subdivisions of the species in compression resistance is situated between 16.6-27.6% sub-species or in varieties often mor-phologically and of the total weight. Polysaccharides (cellulose: 10% and genetically different (corky tissue, dimensions of acorns, hemicellulose: 12 %) results from the exclusively linear wood and phellem) (Lacaze and Touzet 1986). In this condensation of units glucose united between them by study, two levels of originality specificity to the ecological linked ß (1-4) and of a polysaccharide heteropolymers and geographical situation of cork oak in Algeria we (Gibson and Ashby, 1988). The main constituents are examined: xylane, mainly 4-0-methyglucoronoxylane isolated, using alkaline solution (Pereira, 2007). Finally, the extractive The origin 1 that is related to the geographical position. material- Friedelin- is the major constituent (1% of the The origin 2 which includes the geographical area cork) obtained after extraction of the cork in the (coast and mountain). dichloromethane. Betulin (0.5 %) as well as several fatty acids (arachidic, cerotic, oleic and linoleic) are also The study which focused on the chemical composition of present in the extracts (Riboulet and Alegoet, 1986; cork compared with its origin and quality (quality classes) Castola et al., 2002; Pereira, 2007). The ecological and has never been conduct in Algeria. The purpose of this environmental diversity of Algeria make the cork oak work was to deepen knowledge on the properties of cork, irregularly distributed. From a dense and continuous by emphasizing the link between the physical charac- formations of more than 150 000 ha east towards the teristics (density and porosity) and the relative proportion center of the country, it forms only scattered population of the main structural elements (suberin, lignin and and it is less important in the west. This situation has extractives). being strongly shaped by man over the centuries. The productive surface have passed 450 000 in 220 000 ha, because it is about a monoecious species whose MATERIALS AND METHODS allogamy are aggravated by the frequent of occurrence of the inter-specific phenomena of hybridization, the Sampling ecological requirements of cork oak make the species adopts different adaptations according to the climatic and Samples of cork (calas) which served as basis for the edaphic characteristics which reign in every type of study were collected from six origins, representing all environment. The concept of origin is vital for the species, varieties of cork oak forest of the North of Algeria (Figure it integrates several variants: the ecological component 1). The choice of trees for each origin was made based (ground, humidity and exposure), the geographical on the outside aspect of the trunk: Righteousness of the
Dehane et al. 19
trunk, absence of pathogenic fungus, cracks and blaze. functional phloem (sedimenting material). The resulting The extraction sample was made without hurting the fractions were dried at 60°C during two days before phellogen. Circular plots of 20 m radius (with number of chemical analysis was carried out. The summative trees per plot ranging between 25 and 30) were marked chemical analyses included only the determination of in each forest. Three trees were sampled at random for extractives, suberin and lignin. The extraction method each plot, extracting from each tree at 1.30 m high and was based on a well-defined method in literature and a facing the center of the plot a rectangular sample of cork conventional approach (Conde et al., 1998; Pereira, with dimensions of 10×10 cm (100 cm2). The rotation age 1988, 2007; Sen et al., 2010). All the experiments were to obtain the sample was 9 years. In total, 60 samples performed in duplicate. were obtained from the six forests. Extractives were determined by successive Soxhlet The samples were taken to the laboratory and were extractions with dichloromethane (6 h), ethanol (8 h) and stabilized at room temperature (20°C) until constant hot water (20 h). After each extraction step and the weight was achieved. An industrial treatment was carried solution allowed to evaporate, the solid residue was out to preserve the natural characteristics of cork. weighed with an analytical balance. Total thickness was determined for each sample from Suberin content was determined in extractive-free belly to back according International Organization for material by the use of methanolysis for depolymerisation. Standardization (ISO 1216:1998) standard. To determine A 1.5 g of extractive-free material was refluxed with 100 3 the volumetric density (kg/m ) of each sample, their ml of a 3% methanolic solution of NaOCH3 in CH3OH length and width were measured using a flexible rule of 1 during 3 h. The sample was filtrated and washed with mm accuracy. While to calculate the density, the mass methanol. The filtrate and the residue were refluxed with was determined with a precision balance of 0.001 g. 100 ml CH3OH for 15 min and filtered again. The The analyses of corky appearance (defects and combined filtrates were acidified to pH 6 with 2 M H2SO4 porosity visual) (Quality visual: Q1) was realized by the and evaporated to dryness. The residues were mean of Calcor program (2008) (Garcia de Ceca, 2001). suspended in 50 ml of water and the alcoholysis products Each sample is assigned to its respective class 1:1st-3rd recovered with dichloromethane in three successive (good quality), 2: 4th-5th (medium quality), 3(6th) (poor extractions, each with 50 ml dichloromethane. The com- quality) based on the identification of defects. bined extracts were dried over anhydrous sodium Numerical analysis (Q2) of the samples was possible sulphate (Na2SO4) and the solvent was evaporated to by the acquisition of the image of the tangential section of dryness. Suberin extracts were quantified gravimetrically the 60 samples with a scanner. The belly of each sample and the results were expressed in percentage of cork dry was sanded on the entire section and then cleaned with weight. compressed air. The porosity of the tangential section The lignin contents were determined on the extracted was studied by image analysis (González Adrados et al., and desuberinised materials. Sulphuric acid (72%, 3.0 2005), using the Olympus software cell^D. CP (%): the ml) was added to 0.35 g of extracted and desuberinised coefficient of porosity represents the percentage of the sample and the mixture was placed in a water bath at total area of the pores in the total area of cork. The 30°C for 1 h after which the sample was diluted to a porosity calculated for all samples were ordered concentration of 3% H2SO4 and hydrolysed for 1 h at according to the classification of Natividade (1956): good 120°C. The residue was washed with hot water, dried quality (1.5
Int. J. Res. Environ. Stud. 20
Figure 2. Chemical composition according to Origin1.
μ = a constant matrix of the overall mean. On its part, the average density was 254.18 kg/m3 and α·j = a matrix whose columns are the deviations of each the porosity averaged 5.96%. The average values of the class of quality (A,B,C). contents in suberin present important differences βi· = a matrix whose rows are the deviations of each according to the quality and the origin, ranging between provenance. 39.29 (Mountain, A) and 30.79% (Coast, C). On the other γij = a matrix of interactions. hand, the variations were small for the contents (lignin), εijk = a matrix of random disturbances. which was 15.01% (Mountain, A) and 17.95% (Coast, B), respectively. The average values of extractives varied between 12.77% (Mountain, A) and 14.20% (Coast, C). RESULTS AND DISCUSSION
Chemical composition according to the geographical Chemical composition of cork versus origin 2-quality position (Origin 1) The chemical composition of cork cannot be limited to a Generally, all studies that investigated the chemical simple presentation of the rates of the main contents composition of cork did not highlight the influence of the found. In reality, this composition is very close in geographical origin (Jové et al., 2011; Pereira, 2007) structure of the cork both physically and anatomically (Figure 2). (Pereira, 2007). To substantiate our results, a statistical analysis was done which included the visual aspect (quality) and the origin 2. The results obtained are Chemical composition according to the geographical presented in Tables 2-4 while Figure 3 includes the area (Origin 2) distribution of the three classes according to the variables considered. On the other hand, if the chemical compounds are stacked in the quality (industrial process) and in the origin 2 (the geographical area which includes the cork oak of The chemical components the coast and the mountain), the results changes significantly. The results of Table 2 confirmed that the quality Table 1 shows that the average chemical composition (p<0.001) and the provenance 2 (p<0.01) hold a of the studied samples contained 34.45% of suberin, significant influence on the content of suberin. Contrarily, 16.15% of the lignin and 13.53 % of extractives. The rest lignin was strongly influenced by the origin 2 (p<0.001) (approximately 36% of constituents) were the than the quality of the cork (p>0.05). The extractives components not analyzed, mainly carbohydrates appeared to be influenced only by the quality (p<0.001). (cellulose and hemicelluloses) and compound minerals. The interaction between origin 2 and quality was without
Dehane et al. 21
Table 1. Measures for each measured variable.
Origin 2 Quality Number Suberin (%) Lignin (%) Extractives (%) Porosity (%) Density (kg/m3) A 9 36.41 (1.77) 17. 32 (2.63) 12.92 (0.76) 3.63 (1.55) 222.10 (25.79) B 11 33.14 (0.69) 17. 95 (2.94) 13.74 (0.63) 5.90 (2.56) 218.59 (20.79) Coast C 10 30.79 (1.01) 16.15 (2.29) 14.20 (0.77) 11.30 (2.35) 256.13 (26.29) Total 30 33. 34 (2.55) 17.162 (2.63) 13.65 (0.87) 7.02 (3.87) 232.15 (29.09)
A 12 39. 29 (2.69) 15. 01 (0.30) 12.77 (0.89) 2.98 (1.22) 257.11 (26.00) B 10 33. 56 (3.04) 15. 23 (2.63) 14.25 (0.99) 5.00 (2.37) 275.94 (47.02) Mountain C 8 32. 52 (3.28) 17. 32 (0.44) 14.62 (0.57) 7.68 (2.91) 305.19 (62.64) Total 30 35. 57 (4.23) 15. 15 (0.63) 13.42 (1.13) 4.91 (2.83) 276.21 (47.67)
A 21 38.05 (2.69) 16. 00 (2.04) 12.83 (0.82) 3.26 (1.37) 242.11 (30.87) B 21 33. 34 (2.11) 16.66 (2.52) 13.51 (0.84) 5.45 (2.45) 245.90 (45.52) Total C 18 31. 56 (2.40) 15.75 (1.86) 14.38 (0.70) 9.69 (3.14) 277.93 (51.10) Total 60 34. 45 (3.64) 16.15 (2.17) 13.53 (1.00) 5.96 (3.52) 254.18 (45.01)
Values in parenthesis are standard deviations.
Table 2. Chemical components.
Variable Origin 2 Quality Origin 2* quality F 8.042 38.968 1.534 Suberin (%) p 0.006 0.000 0.225 F 15.504 1.030 1.137 Lignin (%) p 0.000 0.364 0.328 F 0.124 18.388 1.621 Extractives (%) p 0.726 0.000 0.207
Significance level: p<0.001; p<0.01; p<0.05.
Table 3. Physicals aspects of Algerian cork.
Porosity (%) Density (kg/m3) Parameters F p F p Origin 2 9.04 0.004 25.03 0.000 Quality 38.29 0.000 6.80 0.002 Origin 2* Quality 2.61 0.083 0.50 0.60
Significance level: p<0.001; p<0.01; p<0.05.
Table 4. Correlation matrix between variables measured (Spearman non-parametric test).
Porosity Suberin Lignin Extractives Density Porosity significance 1 Suberin significance -0.58**, 0.000 1 Lignin significance 0.06, 0.640 -0.22, 0.090 1 Extractives significance 0.55**, 0.000 -0.41**, 0.001 0.01; 0.923 1 Density significance 0.32*, 0.012 -0.07 ; 0.610 -0.31*, 0.016 0.34**, 0.009 1
**Correlation is significant at 0.01 level (2-tailed); *, correlation is significant at 0.05 level (2-tailed).
Int. J. Res. Environ. Stud. 22
Quality QualityQuality Quality Quality Quality A A 22,0022,00 A A A 222,002.00 A B B B B B B C C C C C C
40,0040.00 20,0020,00
40,00 40,00 20,0020.00
18.00 18,0018,00
(%) 18,00
35,00 35,00335,005.00
Lignin
Lignin (%) Lignin
Lignin (%) Lignin
Lignin (%) Lignin
Suberin (%) Suberin
Suberin (%) Suberin Suberin (%) Suberin Suberin (%) Suberin 116,006.00 16,0016,00
114,004.00 14,0014,00 30,00 30,00330,000.00
1212,00.00 12,0012,00
Coast CoastCoast Mountain MountainMountain Coast CoastCoast MountainMountainMountain
Origin 2OriginOrigin 2 2 Origin Origin2 Origin 2 2
Quality Quality 1616,00.00 Quality A A 22,00 A B B B C C C 1515,00.00
40,00 20,00
14,00
(%) 14.00
18,00
35,00 113,003.00
Lignin (%) Lignin
Extractives (%) Extractives Extractives Suberin (%) Suberin 16,00
112,002.00
14,00 30,00 111,001.00
Coast Mountain 12,00 Origin 2 Coast Mountain Coast Mountain Origin 2 Origin 2 Figure 3. Distribution of the chemical components according to the quality and origin 2.
effect on the three variables (suberin. lignin and distribution of the three classes of quality. extractives) (p>0.05). ANOVA 2 showed a highly significant difference in In Figure 3, we observed that increase in the suberin porosity and density of the entire sample. It clearly correlated with improvement in the quality of the cork. indicate that the coefficient of porosity and density are This observation concerned both origins and samples influenced by the quality (p<0.001; p<0.000) and the from mountain and from the coast. The rate of lignin was origin 2 (p<0.000; p< 0.001). The interaction between the more important in the samples from the coast (17.16 %) two parameters was not significant (p>0.05) (Figure 4). than those from mountain (15.15 %). On the other hand, the difference between the quality classes of every origin was not significant between coast (A: 17.32%; B: Relationship between chemical and physical aspects 16.15%; C: 17.95%) and mountain (A: 15.01%; B: 15. 23%; C: 17.32%). In order to identify possible relation between the five variables (suberin, lignin, extractives, porosity and density), a correlation matrix was performed (Table 4). Physical aspects Table 4 shows a negative relationship between porosity and suberin (r=-0.58). Conversely, the rate of porosity Figure 4 includes the variables according to the correlates well with the rates of extractables (r= 0.55).
Dehane et al. 23
QualityQuality Quality Quality A A 45450,000.0022,00 A 1515,00.00 A B B B B C C C 40400,000.00 C
40,00 20,00
)
3 350,00
1010,00.00 350.00
(%)
kg/m 18,00
(
300300,00.00
35,00
Porosity
Lignin (%) Lignin
Porosity (%) Porosity Suberin (%) Suberin 5.00 Density 250,0016,00 5,00 25(Kg/m3) Density 0.00
200200,00.00 14,00 30,00 0.00 0,00 150150,00.00
12,00 Coast Mountain Coast Mountain Coast Mountain Coast Mountain Origin 2 Origin 2 Origin 2 Origin 2 Figure 4. Distribution of porosity and density according to the quality and origin 2.
Lignin seems a neutral element in the correlation matrix gases where from a better elasticity and plasticity. except with the density(r=-0.31). According to Amorim (2000), the more the rate of suberin Through the obtained results, it seems clear that the increases, the more important is the quality of the cork. content in suberin is the main contents of the chemical Therefore, the rate of suberin increases every time the composition of the studied cork, that is, a global average cork is healthy of pores of big sizes. of 34.45%. This rate is distributed between 33.34% for The good correlation between porosity and extractives the samples of the coast (Jijel, M'Sila and Tennes) and is explained by the fact that the presence of these 35.57% for those of mountain (Tizi Ouzou, Guelma and phenolics in the cork is due to the existence in the Hafir). These intervals (33.34‒35.57%) are close to those periphery of lenticels least suberized cells that facilitate obtained by Pereira (1987, 2007) and Jové et al. (2011) the embedding of these extractives. According to (34.4 %), compared with the results of Cáceres Esteban Caceres Esteban et al. (2009), the coefficient of porosity et al. (2009), who fixed the rate of the suberin to 47.91%, increases with plenty of phenolic substances in the our corks were far from this standard. channels and having lenticular cells suberized partially, According to several authors, the contents in suberin of oxidized and cured in contact with air. the cork oak are more important than in other species: According to Pereira (2007), lignin acts as a liaison 33% in Pseudotsuga menziesii (Graça and Pereira, between other compounds. It is a majority component 2000), 28% in Quercus cerris (Sen et al., 2010) and 5% with suberin acting on the structure of the cork, in in Calotropis procera (Pereira, 1988). particular, the cell walls. According to Marques et al. As regards the rate of lignin (17.16‒15.15%), our (1994), its role is to provide mechanical support and results became integrated into the limits obtained for the rigidity to the cell walls. High density corresponds to thick cork of six regions of the Iberian Peninsula and heavy walls and small cell height (15 μm) (Gibson et (13.40‒23.12%) (Jové et al., 2011). On the other hand, al., 1981). our values move away from those of Condé et al. (1998) The density and extractives seem correlated to the (21.50‒24.30%). In the same context, the average porosity; this could be explained by the variation of contents of extractives (13.65‒13.42%) are not far from porosity of these provenances. According to Amorim those found by Pereira (2007) (10.70‒29.70 %) and they (2000), the more the surfaces of pores are superior, the fit well within the limits of Jové et al. (2011) more the gaseous exchanges with the outside (11.10‒17.80 %). The suberin is in reality only a fat acid environment are important, creating a partial suberization mixture and of heavy organic alcohols which return the of the cells of cork; thus a difference of permeability and cork impervious to liquids and very weakly permeable to consequently an accumulation of ethanolic solutions, and
Int. J. Res. Environ. Stud. 24
an increase of a part of the density of the cork. Suberin decreased from good to poor quality. It’s in Othmer (1979) showed that the diversity of the origins contrast with the porosity and consequently the density. and the conditions of culture of cork oak is often the It is the main constituent responsible for elastic causes of variations observed in the chemical com- properties and the impermeability of the cork. position of the cork. In Algeria, in cork oak forest of coast, Lignin is responsible for the structural rigidity of cells of the humidity of the air is important all the year (60%). the cork. It is not influenced by the quality. The content This maritime atmosphere is favorable to a good growth is more important in the origins of the coast than those of the cork. Corks stemming from this origin are of the mountain that has a more important density characterized by annual increases of fast type (>3 because of the reduced size of cells. mm/year) favoring an average exploitation all 7 in 9 years Extractives are strongly linked to the porosity and in maximum (Zenagui, 2014). This type of cork (of the consequently to the quality because of the importance coast) is frequently strewed with pores of various of the gaseous exchanges between the phloem and the surfaces favouring important gaseous exchanges with the outside environment. There is no significant difference outside environment. Cells produced mainly in spring between the origins of the coast and the mountain. appear in big sizes and to the thin walls where from the Density is also a fact limiting the quality by reducing density of the cellular walls is evicted by the density of suberized cells of the origins of the coast and by the circumferences of pores (Natividade, 1956; Dehane, amplifying the density of the cellular walls of those of 2006). the mountain. The cork oak of mountain is under the influence of the In spite of the correlations between the various continental character and the cold winters. The growth of compounds, the suberin stands out as the best the cork is very slow and late compared to that of the indicator to a good quality cork whether it is from the coast. The average exploitation exceeds 12 years, even coast or from the mountain. 15 years (Dehane, 2012). The suber production is mainly made in summer and in autumn, and includes small-sized assizes and thick walls. The porosity which results from it REFERENCES is dominated by pores with reduced surfaces (Dehane et al., 2011). Consequently, in this type of cork, the density Amorim (2000). Investissement et participation, S.G.P.S., S.A., site Internet développé par Proxima Créative APCOR, 2009: APCOR is more influenced by the weight of the cellular walls than year book. Guide. 83p. the circumferences of pores. This type of suber is denser APCOR (2004). http://www.corkqc.com. than that of the coast as it is in the case of our origins. Cáceres Esteban M. J., Garcia de Ceca J. L. & González-Adrados J. R. The variations of the physical and physiological (2009). Relación entre el aspecto visual, la densidad y la composición química del corcho.5e Congresso Forestral Espagnol. properties of the cork are also interpreted in the industrial 8p. process mainly during the operations of classification; this Carrasquinho M. I. (1987). 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