ARTÍCULO

Valorization of Moroccan olive stones by using it in particleboard panels

M. Elbir¹, A. Moubarik^2♠, E.M. Rakib³, N. Grimi⁴, A. Amhoud¹, G. Miguel⁵, H. Hanine⁶, J. Artaud⁷, P. Vanloot⁷, M. Mbarki^1
1Equipe Systèmes Chimiques Complexes, Faculty of Science and Technology, University Sultan Moulay Slimane. PB 523, Beni Mellal, Morocco.
²MAScIR-NANOTECH, ENSET, Avenue de l'Armée Royale, Madinat El Irfane, 10100 Rabat, Morocco.
³ Laboratory of Organic and Analytical Chemistry, Faculty of Sciences and Technology, University Sultan Moulay Slimane., B.P 523, Beni-Mellal, Morocco.
⁴ Université de Technologie de Compiègne EA 4297 TIMR, UTC/ESCOM, Centre de Recherche de Royallieu, B.P. 20529, 60205 Compiègne, France. ]]> ⁵Department of Biotechnology, University of Algarve, Faro, Portugal.
⁶Laboratoire de Valorisation et Sécurité des Produits Agro-alimentaires, Faculté des Sciences et Techniques, Université Sultan Moulay Slimane, B.P 523, Beni-Mellal, Morocco
⁷ISM2, UMR 6263, Equipe AD2EM, Université Paul Cézanne, case 451, 13397 Marseille Cedex 20, France.

Corresponding author

The main objective of this work was to find new applications to valorize olive stones (endocarp and seed). In order to improve knowledge on olive stones, the phenolic compounds concentration of three varieties of Moroccan olive trees: Moroccan Picholine, Menara and Haouzian were studied. Olive stones of three varieties were characterized by Fourier Transform Mid Infrared Spectroscopy (FT-MIR). Total phenolic compounds are quantified after solid-liquid extraction by an assay of Folin-Ciocalteu. Moroccan Picholine stones (11.32 mg GAE/g DM) have a higher content of total phenolic compounds than Haouzia stones (4.55 mg GAE/g DM) and Menara stones (3.56 mg GAE/g DM). Thermogravimetric analysis indicates that up to 195°C; there is no degradation of the stones. The biocide performance on agar-agar was tested with decay fungi. Biodegradation studies show that the most interesting results are obtained with Moroccan Picholine stones. The presence of Moroccan Picholine in a particleboard panels improves the total resistance of the particleboard panels against both Coriolus versicolor and Coniophora puteana rot fungi.

Keywords: Decay resistance, olive stone, particleboard, phenolic compounds 

Oleaceae is a family comprising 600 species in 25 genera. Many of the genera are economically important such as the olive (Olea europaea) which is cultivated for its fruit and oil (Wallander and Albert 2000). The olive tree is among the oldest woody crops and is particularly widespread throughout the Mediterranean region and plays an important role in its rural economy, local heritage, and environment protection. The largest producing countries are located in the Mediterranean and Middle East regions providing 98% of the total cultivated surface area, and 99% of the total olive fruit production (Niaounakis and Halvadakis 2006, Besnard et al. 2011).

Olea europaea dried fruit has pharmacological properties, such as anti-bacterial, anti-viral, anti-inflammatory activities and detoxification (Ding 1999). Such properties have been attributed to the presence of many compounds including phenols. Olive fruits are rich in phenolic compounds that represent 1 to 14% weight of dry pulp. The phenolic composition in the various parts of the fruit is complex depending on the variety, collection season, growing conditions, and time of ripening (Solinas et al. 1975, Vlahov 1992, Esti et al. 1998, Romani et al. 1999). Very few studies have focused upon the phenolic composition of olive seeds, nevertheless some phenolic compounds have been identified including salidroside, nuzhenide, hydroxytyrosol, nuzhenide 11-methyl oleoside, oleuropein, tyrosol, and demethyloleuropein (Figure 1) at all stages of maturation (Maestro-Durán et al. 1994, Servili et al.1999, Silva et al. 2010).

The main objectives of this work are the extraction of phenolic compounds, the characterization (chemical, thermal and biological) and the valorization of Moroccan olive stones in particleboard panels.

EXPERIMENTAL METHODS

Plant materials

Mature olive fruits were obtained from the Moroccan Picholine variety, which grows widely in the province of Beni Mellal and from Menara and Haouzia varieties growing in the province of Marrakech of Middle Atlas and Marrakech-Tensift-Al Haouz (Morocco), respectively. Olive fruits were boiled (between 70 and 80°C) in water for 8 minutes, and pulped by crushing them manually. Olive stones were then air dried on paper towels (2-4 days). After drying, the olive stones were ground (particle less than 0.5 mm) in a knife mill "Retsch SK1".

Extraction and estimation of total phenolic compounds

The solid-liquid extraction of total phenolic compounds was performed with a Soxhlet apparatus. Olive stone powder (60 g) was extracted in a Soxhlet apparatus, first with hexane (500 ml) for 5 hours to remove lipids, then with acetone (500 ml) for 5 hours and finally with ethanol (500 ml) for 5 hours to remove total phenolic compounds (Rakib et al. 2010).

Total phenols are estimated by Folin-Ciocalteu method (Singleton and Rossi 1965, Scalbert et al. 1989). A 2.5 ml portion of Folin-Ciocalteu reagent and 2 ml of a sodium carbonate solution (75 g/l) are added to 0.5 ml of the diluted extract. The assay tubes are kept 15 min in a water bath at 50°C and then transferred to cold water. The absorbance read was 760 nm. A calibration curve with equation: y = 0.0021x + 0.0015 (r² = 0.99) was constructed using gallic acid solutions within the range 10–100 mg/l. Contents of total phenolic compound in olive stones were expressed as gallic acid equivalents in milligrams per gram dry matter (mg GAE/g, DM). The results were averages of triplicate analyses.

Fourier Transform Middle-Infrared Spectroscopy (FT-MIR)

Analyses were performed with FT-MIR. The spectra of the samples were recorded with a Perkin Elmer's FTIR (Spectrum One). Samples were deposited without preparation on attenuated total reflection (ATR) cell that is equipped by a diamond crystal. The crystal was cleaned between measurements by deionized water and dried by lint-free tissue. Spectra were recorded between 4000 and 600 cm^-1, at 0.5 cm^-1 nominal resolution.

Thermogravimetric analysis (TGA)

Particleboard preparation

Single layer laboratory particleboards of dimension 350 mm x 310 mm x 14 mm were prepared from maritime pine (Pinus pinaster). The addition of the commercial Urea Formaldehyde (UF) resins to the particles was 7.5 % based on solid mass; press time was 7.5 min at 195°C press platen temperature with a maximum specific pressure of 25 kg/cm². The UF resin had a density of 1280–1290 kg/m³, a pH of about 8.5–9, and a viscosity of 350–600 mPa.s, all measured at 20 ± 2°C; the gel time was 40-50 seconds at 100°C. The content of free formaldehyde is maximum 0.15 % based on the liquid resin. The particles with size between 1 to 4 mm were dried to approx 2 ± 0.5 % moisture content prior to application of the resin. Each olive stone powder was ground and mixed at different concentrations (from 0 to 15%, w/w) in particles. The target board density was 710 kg/m³. The particleboards were pre-conditioned at 25°C and 65 % relative humidity in a Vötsch climate room for one week before testing.

Biological properties

Decay test of the particleboard composites

Particleboards composites measuring 20 × 20 × 14 mm³ were prepared for decay test, from Maritime pine (Pinus pinaster). A fungal decay test was done according to an adaptation of the standard EN 113 (AFNOR 1996) using a brown rot fungus, Coniophora puteana (BAM Ebw.15) and the white rot fungus, Coriolus versicolor (CTB 863A). A culture medium was prepared in Roux flasks. In each one, a nutritive medium, made up of a malt-agar mixture was placed (40 g of malt and 20 g of agar dissolved in 1000 ml distilled water). After sterilization (121°C for 20 min at 1 bar), the Coriolus versicolor and Coniophora puteana were inoculated on culture medium in Petri dishes under sterile conditions. Then they were placed in constant conditions at 25°C and 65% relative humidity for 3 weeks to favour fungal development. After being conditioned at 25°C and 65% air moisture content, the particleboard composite samples were put into Petri dishes and exposed to Coriolus versicolor and Coniophora puteana for 16 weeks in darkness. Finally, test results were expressed as percentage of weight loss of composite panels due to fungal attacks after decay test using equation (1) (the measurement was done after drying of each sample). Ten replicates were used for each decay fungus. Weight loss was calculated as follows:

Where m_i and m_f are the oven-dry weights of the sample before and after the decay test.

Decay test of olive stone powders

In order to confirm the fungicidal effect, olive stone powder was added to the culture medium. Each olive stone powder was ground and mixed at different concentrations (from 0 to 7%, p/v) in malt-agar culture medium. After sterilization, the Coriolus versicolor and Coniophora puteana fungi were inoculated in the centre of the culture medium under sterile conditions. Then they were placed in constant conditions at 25°C and 65% relative humidity for 15 days to favour fungal development. The mean radius of the fungal development was measured. Test results were expressed as percentage of fungal development using equation (2). Ten replicates were used for each fungal development.

Where

R_o: is the mean radius of the fungal development after 15 days (control: without presence of olive stone powder). 

RESULTS AND DISCUSSION

Impact of olive stones varieties on polyphenols extraction

Table 1 shows the polyphenols concentration in acetone and ethanol extracts. The results showed that Moroccan Picholine variety growing in the province of Beni Mellal had the higher contents of total phenolic compounds (11.32 mg/g DM), followed by Haouzia (4.55 mg/g DM) and Menara (3.56 mg/g DM) variety. The relative amounts of phenols found in our experiment are in agreement with those already reported by some authors which described the lower levels of phenols in stones and seeds in comparison to the remaining tissues (pulp, leaves) of olives (Ryan et al. 2003). Nevertheless, compared with some other berries, the total phenolics contents in olive stones (3.56-11.32 mg/g DM) are higher than those of Oregon canberries (4.95–9.80 mg/g DM) berries (Wada and Ou 2002) and bayberries (3.60-4.46 mg/g DM) (Zhongxiang et al. 2007). 

Thermal study of different olive stones

Thermogravimetric analysis can check the thermal decomposition and thermal stability of the olive stones. Figure 3 shows the TGA curve of the Moroccan Picholine, Menara and Haouzia varieties in air atmosphere at a heating rate of 5°C/min, result that matches to typical findings for the decomposition of other lignocellulosic materials. Two steps can be differentiated in the TGA curves: I- Up to 200 °C, the weight loss corresponds to moisture release; II- The main weight loss takes place between 200 and 400°C. In this temperature range, two decomposition processes are well defined, with maximum weight loss rates appearing at 245 and 330°C. The first step can be attributed to the group of reactions involved in hemicellulose degradation (Órfão et al. 1999, Williams and Besler 1993), and the second one to those related to the thermal decomposition of cellulose (Órfão et al. 1999, Williams and Besler 1993).

The curve also shows that thermal degradation began to occur only after the materials have absorbed certain amounts of heat energy. Heat initiated the degradation processes and the breakdown of the structure by causing molecular chain ruptures. The results obtained with thermogravimetric analysis confirm that at 195 °C they risk no degradation of the olive stones.

Weight losses of the particleboard composites caused by fungal decay after 16 weeks are shown in table 2. We can see that the control particleboard was attacked by both decay fungi (Coriolus versicolor and Coniophora puteana) with weight losses near 40%. This proves that the fungus was virulent and the test of durability was valid according to the relevant European Norm 113 (EN 113, 1996). The values of weight losses for all other particleboard panels decreased. Laboratory tests have shown that the addition of olive stones (5, 10 and 15%) is very effective in preventing attack by both decay fungi. We also observed that particleboard with Moroccan Picholine (5, 10 or 15%) showed considerable resistance to both the decay fungi compared with particleboard with Haouzia (5, 10 or 15%) and Menara (5, 10 or 15%).

Results in table 2 seem to indicate that Coniophora puteana could be more efficient in wood degradation than Coriolus versicolor. This may be due to the differences between their decay mechanisms. This tendency has been previously observed by Nemli et al. (2006) and Moubarik et al. (2009). 

Table 2. Weight loss of composite in presence of olive stones after exposure to both decay fungi (Coriolus versicolor and Coniophora puteana).

Ten replicates of each decay fungus. S.D: standard deviation.

Fungicide effect of olive stones

Hart and Hillis (1972) have demonstrated that the presence of phenolic compounds improves the durability of wood. Further studies evaluating the fungicide effect of phenolic compounds (tannins) also confirmed this activity (Pizzi and Conradie 1986, Charrier et al. 1995, Aloui et al. 2004, Cornelius et al. 2004, Moubarik et al. 2009).

Table 3. Effect of olive stone concentrations on fungus development.

Ten replicates of each fungal development. S.D: standard deviation.

CONCLUSION

The present work proposes an innovative valorization of olive stones for particleboard production. The result of polyphenols extraction from Moroccan Picholine variety growing in the province of Beni Mellal had the higher contents of total phenolic compounds (11.32 mg/g DM), followed by Haouzia (4.55 mg/g DM) and Menara (3.56 mg/g DM) variety. The thermogravimetric analysis shows no significant degradation of the three olive stones varieties at temperature less than 195 °C. A good correlation was observed between the resistance to fungi and the concentration of olive stones. A decrease in fungal development for both decay fungi Coriolus versicolor and Coniophora puteana is observed after olive stones incorporation into the culture medium. The results of the present work contribute to the valorization of olive stones in the Mediterranean countries and especially in Morocco that has an ambitious agricultural strategy called "Green Morocco".

ACKNOWLEDGMENT

The authors would like to thank the INRA (Beni Mellal and Marrakech) for their olives collection.

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Corresponding author:^♠amine.moubarik@yahoo.fr