Control of wood thermal treatment and its effects on decay resistance: a review

Kévin Candelier1, Marie-France Thévenon1, Anélie Petrissans2, Stéphane Dumarçay2, Philippe Gérardin2, Mathieu Pétrissans2
1CIRAD-Unité de Recherches BioWooEB, TA-B 114/16, Montpellier, France
2LERMAB, EA 4370, Faculté des Sciences et Technologies, Université de Lorraine, F-54506, Vandoeuvre-Lès-Nancy, France

Tóm tắt

AbstractKey messageAn efficient use of thermal treatment of wood requires a depth understanding of the chemical modifications induced. This is a prerequisite to avoid problems of process control, and to provide high quality treated wood with accurately assessed properties to the market. Properties and structural anatomy of thermally modified woods are slightly different than un-processed woods from a same wood species. So it is necessary to create or adapt new analytical methods to control their quality.ContextHeat treatment as a wood modification process is based on chemical degradation of wood polymer by heat transfer. It improves mainly the resistance of wood to decay and provides dimensional stability. These improvements, which come at the expense of a weakening of mechanical properties, have been extensively studied. Since a decade, researches focused mainly on the understanding of wood thermal degradation, on modelling, on quality prediction and quality control.AimsWe aimed at reviewing the recent advances about (i) the analytical methods used to control thermal treatment; (ii) the effects on wood decay resistance and (iii) the advantages and drawbacks of a potential industrial use of wood heating.MethodsWe carried out a literature review of the main industrial methods used to evaluate the conferred wood properties, by thermal treatment. We used papers and reports published between 1970 and 2015, identified in the web of science data base..ResultsApproximately 100 papers mostly published after 2000 were retrieved. They concentrated on: (i) wood mass loss due to thermal degradation determination, (ii) spectroscopic analyses of wood properties, (iii) colour measurements, (iv) chemical composition, (v) non-destructive mechanical assessments and (vi) use of industrial data.ConclusionsOne of most interesting property of heat-treated wood remains its decay resistance. Durability test with modified wood in laboratory are expensive and time-consuming. This review displays data from different analytical methods, such as spectroscopy, thermogravimetry, chemical analyses or mechanical tests that have the potential to be valuable indicators to assess the durability of heat treated wood at industrial scale. However, each method has its limits and drawbacks, such as the required investment for the equipment, reliability and accuracy of the results and ease of use at industrial scale.

Từ khóa


Tài liệu tham khảo

Allegretti O, Brunetti M, Cuccui I, Ferrari S, Nocetti M, Terziev N (2012) Thermovacuum modification of spruce (Picea abies karst.) and fir (Abies albamill.) wood. Bioresources 7:3656–3669

Altgen M, Welzbacher C, Humar M, Militz H (2012) ESR-spectroscopy as a potential method for the quality control of thermally modified wood. Proceedings of the 2nd Workshop Cost Action FP0904, Nancy, pp 132–133

Andersons B, Chirkova J, Andersone I, Irbe I (2012) Prediction of the properties of soft deciduous wood in thermal modification. Proceedings of the 2nd Workshop Cost Action FP0904, Nancy, pp 96–97

Bächle H, Zimmer B, Wegener G (2012) Classification of thermally treated wood by FT-NIR spectroscopy and SIMCA. Wood Sci Technol 46:1181–1192

Bal BC (2014) Some physical and mechanical properties of thermally modified juvenile and mature black pine wood. Eur J Wood Prod 72:61–66

Bekhta P, Niemz P (2003) Effect of high temperature on the change in color, dimensional stability and mechanical properties of spruce wood. Holzforschung 57:539–546

Boonstra M (2008) A two-stage thermal modification of wood, PhD Thesis in A plied Biological Sciences: Soil and Forest management. Henry Poincaré University, Nancy

Boonstra MJ, Tjeerdsma B, Pizzi A, Tekely P, Pendlebury J (1996) Chemical modification of Norway spruce and Scots pine: a 13C NMR CP-MAS study of the reactivity and reactions of polymeric wood components. Holzforschung 50:215–220

Boonstra MJ, Tjeerdsma B (2006) Chemical analysis of heat treated softwoods. Holz Roh Werkst 64:204–211

Boonstra MJ, Pizzi A, Zomers F, Ohlmeyer M, Paul W (2006) The effects of a two stage heat treatment process on the properties of particleboard. Holz Roh Werkst 64:157–164

Borgeais A (2012). The high temperature treatment of wood. The network timber professionals in Brittany [in French], Book (Abibois), 11 pages. Available at http://abibois.com/category/4-preservation-et-entretien?download=14.

Bourgeois J, Bartholin MC, Guyonnet R (1989) Thermal treatment of wood: analysis of obtained product. Wood Sci Technol 23:303–310

Brischke C, Welzbacher C, Brandt K, Rapp A (2007) Quality control of thermally modified timber: interrelationship between heat treatment intensities and CIE L*a*b* color data on homogenized wood samples. Holzforschung 61:19–22

Burmester A (1970) Formbeständigkeit von Holz gegenüber Feuchtigkeit Grundlagen und Vergütungsverfahren. BAM Berichte Nr. 4.

Burmester A (1973) Investigation on the dimensionnal stabilization of woood. Bundesanstalt fûr Materialprûfung, Berlin-Dahlem, 50–56. Holz Roh Werkst 33:333–335

Burmester A (1975) Zur Dimensionsstabilisierung von holz. Holz Roh Werkst 33:333–335

Candelier K, Chaouch M, Dumarçay S, Petrissans A, Petrissans M, Gérardin P (2011a) Utilization of thermodesorption coupled to GC-MS to study stability of different wood species to thermodegradation. J Anal App Pyrol 92:376–383

Candelier K, Dumarçay S, Pétrissans A, Gérardin P, Pétrissans M (2011b) Mechanical properties of heat treated wood after thermodegradation under different treatment intensity. International Conference “Mechano-chemical transformations of wood during thermo-hydro-mechanical processes”, 16–18 February 2011, Biel (Switzerland).

Candelier K, Dumarçay S, Petrissans A, Desharnais L, Petrissans M, Gérardin P (2013a) Comparison of chemical composition and decay durability of heat treated wood cured under different inert atmospheres: Nitrogen or vacuum. Polym Degrad Stab 98:677–681

Candelier K, Treu A, Dibdiakova J, Larnoy E, Dumarçay S, Pétrissans A, Gérardin P, Pétrissans M (2013b) Utilization of TG-DSC to study thermal stability of beech and silver fir. Document No. IRG/WP 13–40628. The International Research Group on Wood Preservation, Sweden

Candelier K, Dumarçay S, Pétrissans A, Pétrissans M, Kamdem P, Gérardin P (2013c) Thermodesorption coupled to GC-MS to characterize volatiles formation kinetic during wood thermodegradation. J Anal App Pyrol 101:96–102

Candelier K, Dumarçay S, Pétrissans A, Gérardin P, Pétrissans M (2013d) Comparison of mechanical properties of heat treated beech woods cured under nitrogen or vacuum. Polym Degrad Stab 98:1762–1765

Candelier K, Dumarçay S, Pétrissans A, Gérardin P, Pétrissans M (2014) Advantage of vacuum versus nitrogen to achieve inert atmosphere during softwood thermal modification. Pro Ligno 10:10–17

Candelier K, Hannouz S, Elaieb MT, Collet R, Dumarçay S, Pétrissans A, Gérardin P, Pétrissans M (2015) Utilization of temperature kinetic as a method to predict treatment intensity and corresponding treated wood quality: durability and mechanical properties of thermally modified wood. Maderas-Ciencia Tecnologia 17:253–262

Chaouch M (2011) Effect of treatment intensity on the elemental composition and durability of heat-treated wood: development of a predictive marker of resistance to basidiomycete fungi [in French]. PhD Thesis. Université de lorraine, Nancy

Chaouch M, Pétrissans M, Pétrissans A, Gérardin P (2010) Use of wood elemental composition to predict heat treatment intensity and decay resistance of different softwood and hardwood species. Polym Degrad Stab 95:2255–2259

Chaouch M, Dumarçay S, Pétrissans A, Pétrissans M, Gérardin P (2013) Effect of heat treatment intensity on some conferred properties of different European softwood and hardwood species. Wood Sci Technol 47:663–673

Chen Y, Fan Y, Gao J, Stark NM (2012) The effect of heat treatment on the chemical and color change of black locust (Robinia pseudoacacia) wood flour. Bioresources 7:1157–1170

CRIQ (2003) Forest products issued from 2nd transformation processes – Wood heat treatment [in French]. Report to the ministère des Ressources naturelles, de la Faune et des Parcs (MRNFP) by the Centre de recherche industrielle du Québec (CRIQ).

Dilik T, Hiziroglu S (2012) Bonding strength of heat treated compressed Eastern red cedar wood. Mater Des 42:317–320

Elaieb MT, Candelier K, Pétrissans A, Dumarçay S, Gérardin P, Pétrissans M (2015) Heat treatment of Tunisian soft wood species: Effect on the durability, chemical modifications and mechanical properties. Maderas Ciencia Tecnologia 17:699–710

EN 113 (1996) Wood preservation products. Wood preservatives – Test method for determining the protective effectiveness against wood destroying basidiomycetes – Determination of the toxic values.

EN 335 (2013) Durability of wood and wood-based products - Use classes: definitions, application to solid wood and wood-based products.

EN 350–1 (1994) Durability of wood and wood based products – Natural durability of solid wood – Part 1: Guide to principles of testing and classification of the natural durability of wood.

Esteves B, Pereira H (2008) Quality assessment of heat treated wood by NIR spectroscopy. Holz Roh Werkst 66:323–332

Esteves BM, Domingos IJ, Pereira HM (2007) Improvement of technological quality of eucalyptus wood by heat treatment in air at 170°C-200°C. For Prod J57:47–52

Esteves B, Velez Marques A, Domingos I, Pereira H (2008) Heat-induced color changes of pine (Pinus pinaster) and eucalypt (Eucalyptus globulus) wood. Wood Sci Technol 42:369–384

Fengel D, Wegener G (1989) Wood chemistry ultrastructure relation. Walter de Gruyter.

Gieleber (1983) Dimensionsstabilierung von holz durch eine Feuchte/Wârme/Druck-Behandlung. Holz Roh Werkst 41:87–94

Gonzáles Peňa M, Hale M (2008) Colour in thermally modified wood of beech, norway spruce and scots pine, Part 2: Properties predictions from colour changes. Holzforschung 63:394–401

Gunduz G, Aydemir D, Karakas G (2009) The effects of thermal treatment on the mechanical properties of wild Pear (Pyrus elaeagnifolia Pall.) wood and changes in physical properties. Mater Des 30:4391–4395

Hakkou M, Pétrissans M, Zoulalian A, Gérardin P (2005) Investigation of wood wettability changes during heat treatment on the basis of chemical analysis. Polym Degrad Stab 89:1–5

Hakkou M, Pétrissans M, Gérardin P, Zoulalian A (2006) Investigation of the reasons for fungal durability of heat-treated beech wood. Polym Degrad Stab 91:393–397

Hamada J, Petrissans A, Mothe F, Petrissans M, Gerardin P (2013) Analysis of the effects of the European oak natural variability on the modification of the density distribution and chemical composition during the heat treatment. Proceedings of the Joint focus workshop of COST Action FP1006 & FP0904, 16–18 October, 2013 Rogla, Slovenia

Hannouz S, Collet R, Bléron L, Marchal R, Gérardin P (2012) Mechanical properties of heat treated French species wood. Proceedings of the 2nd Workshop Cost Action FP0904, Nancy, pp 940, 72–74

Hannouz S, Collet R, Buteaud JC, Bléron L, Candelier K (2015) Mechanical characterization of heat treated ash wood in relation with structural timber standards. Pro Ligno 11:3–10

Hietala S, Maunu S, Sundholm F, Jämsa S, Viitaniemi P (2002) Structure of thermally modified wood studied by liquid state NMR measurements. Holzforschung. 56:522–528

Hill CAS (2006) Wood modification: Chemical. Thermal and other processes, Wiley, Chichester

Hillis W (1984) High temperature and chemical effects on wood stability. Part 1. General consideration. Wood Sci Technol 18:281–293

Inari G, Pétrissans M, Lambert JL, Erhardt JJ, Gérardin P (2006) XPS characterization of wood chemical composition after heat treatment. Surf Interf Anal 38:1336–1342

Inari G, Petrissans M, Lambert J, Ehrhardt JJ, Gerardin P (2007) Chemical reactivity of heat-treated wood. Wood Sci Technol 41:157–168

Inari G, Pétrissans M, Pétrissans A, Gérardin P (2009) Elemental composition of wood as a potential marker to evaluate heat treatment intensity. Polym Degrad Stab 94:365–368

Jimenez JP, Acda MN, Razal RA, Madamba PS (2011) Physico-Mechanical Properties and Durability of Thermally Modified Malapapaya [Polyscias nodosa (Blume) Seem.] Wood. Philipp J Sci 140:13–23

Johansson D, Moren T (2006) The potential of color measurement for strength prediction of thermally treated wood. Holz Roh Werkst 64:104–110

Junga U, Militz H (2005) Particularities in agar block tests of some modified woods caused by different protection and decay resistance. Proceedings of the 2nd European Conference on Wood Modification, Göttignen

Kačíková D, Kačíkb F, Čabalováb I, Ďurkovičc J (2013) Effects of thermal treatment on chemical, mechanical and colour traits in Norway spruce wood. Bioresour Technol 144:669–674

Kamdem DP, Pizzi A, Guyonnet R, Jermannaud A (1999) Durability of heat treated wood. Document No. IRG/WP 99–40145. The International Research Group on Wood Preservation, Rosenheim

Kamdem DP, Pizzi A, Jermannaud A (2002) Durability of heat-treated wood. Holz Roh Werkst 60:1–6

Kim G, Yun K, Kim J (1998) Effect of heat treatment on the decay resistance and the bending properties of radiate pine sapwood. Mater und Organismen 32:101–108

Kocaefe D, Poncsak S, Boluk Y (2008) Effect of thermal treatment on the chemical composition and mechanical properties of birch and aspen. Bioresources 3:517–537

Kollman A, Fengel D (1965) Changes in chemical composiyion of wood by heat treatment. Holz Roh Werkst 12:461–468

Kollman A, Schneider A (1963) On the sorption behavior of heat stabilized wood. Holz Roh Werkst 21:77–85

Korkut S, Korkut DS, Kocaefe D, Elustondo D, Bajraktari A, Çakıcıer N (2012) Effect of thermal modification on the properties of narrow-leaved ash and chestnut. Ind CropProd 35:287–294

Kotilanen R (2000) Chemical changes in wood during heating at 150-260°C. Department of Chemistry. Finland, University of Jyväskylä, pp. 51

Li MY, Shi-Chao Cheng SC, Li D, Wang SN, Huang AM, Sun SQ (2015) Structural characterization of steam-heat treated Tectona grandis wood analyzed by FT-IR and 2D-IR correlation spectroscopy. Chin Chem Lett 26:221–225

Matsuo M, Yokoyama M, Umemura K, Gril J, Yano H, Kawai S (2010) Color changes in wood during heating: kinetic analysis by applying time-temperature superposition method. Appl Phys A 99:47–52

Matsuo M, Yokoyama M, Umemura K, Sugiyama J, Kawai S, Gril J, Kubodera S, Mitsutani T, Ozaki H, Sakamoto M, Imamura M (2011) Aging of wood: Analysis of color changes during natural aging and heat treatment. Holzforschung 65:361–368

Mazela B, Zakrzewski R, Grzeskowiak W, Cofta G, Bartkowiak M (2003) Preliminary research on the biological resistance of thermally modified wood. Proceedings of the 1st European Conference on Wood Modification, Ghent

Mazela B, Zakrzewski R, Grzeskowiak W, Cofta G, Bartkowiak M (2004) Resistance of thermally modified wood to basidiomycetes. ; EJPAU, Wood Technology, 7(1). Avaible at http://www.ejpau.media.pl.

McDonald A, Fernandez M, Kreber B (1997) Chemical and UV–VIS spectroscopic study on kiln brown stain formation in Radiata pine. Proceedings of the 9th international symposium of wood and pulping chemistry, Montreal, 70, 1–5.

Militz H (2002) Heat treatment of wood: European Processes and their background. Document No. IRG/WP 02–40241. The International Research Group on Wood Preservation, Cardiff, Wales

Mitsui K, Takada H, Sugiyama M, Hasegawa R (2001) Changes in the properties of light-irradiated wood with heat treatment: Part 1 Effect of treatment conditions on the change in colour. Holzforschung 55:601–605

Mitsui K, Murata A, Kohara M, Tsuchikawa S (2003) Color modification of wood by light-irradiation and heat treatment. Proceedings of the 1st European conference on wood modification, Ghent

Mohareb A, Sirmah P, Pétrissans M, Gérardin P (2012) Effect of heat treatment intensity on wood chemical composition and decay durability of Pinus patula. Eur J Wood Prod 70:519–524

Nguila Inari G, Pétrissans M, Pétrissans A, Gérardin P. (2009). Elemental composition of wood as a potential marker to evaluate heat treatment intensity. Polym Degrad Stab 94:365–368

Nuopponen M., Vuorinen T., Jamsa S., Viitaniemi P (2004) Thermal modifications in softwood studied by FT-IR and UV resonance raman spectroscopie. J Wood Chem Technol 24(1):13–26

Olarescu MC, Campean M, Ispas M, Cosereanu C (2014) Effect of thermal treatment on some properties of lime wood. Eur J Wood Prod 72:559–562

Patzelt M, Emsenhuber G, Stingl R (2003) Color measurement as means of quality control of thermally treated wood. Procedings of the 1st European Conference on Wood Modification, Ghent

Paul W, Ohlmeyer M, Leithoff H (2006) Thermal modification of OSB-strands by a one-step heat pretreatment - Influence of temperature on weight loss, hygroscopicity and improved resistance. Holz Roh Werkst 65:57–63

Pétrissans M, Pétrissans A, Gérardin P (2007) Check the durability of heat-treated beech wood [in French]. Tracés, Bulletin technique Technologie du bois de la Suisse Romande 17:12–16

Pétrissans M, Pétrissans A, Gérardin P (2013) Pore size diameter, shrinkage and specific gravity evolution during the heat treatment of wood. Journal of Innovation In Forest Industry And Engineering Design.

Pétrissans A, Younsi R, Chaouch M, Gérardin P, Pétrissans M (2014) Wood, thermodegradation: experimental analysis and modeling of mass loss kinetics. Maderas Ciencia Tecnologia 16:133–148

Popescu CM, Popescu MC (2013) A near infrared spectroscopic study of the structural modifications of lime (Tilia cordata Mill.) wood during hydro-thermal treatment. Spectrochim Acta Mol Biomol Spectrosc 115:227–233

Popescu MC, Froidevaux J, Navi P, Popescu CM (2013) Structural modifications of Tilia cordata wood during heat treatment investigated by FT-IR and 2D IR correlation spectroscopy. J Mol Struct 1033:176–186

Prinks MJ, Ptasinski KJ, Jansen FJJG (2006) Torrefection of wood, part 2. Analysis of products J Anal App Pyrol 77:35–40

Rapp A (2001) Review on heat treatments of wood, COST ACTION E22- Environmental optimisation of wood protection. Proceedings of Special Seminar in Antibes, França

Rep G, Pohleven F, Bucar B (2004) Charateristics of thermally modified wood in vacuum. Document No. IRG/WP 04–40287. The International Research Group on Wood Preservation, Ljubljana

Rusche H (1973a) Thermal degradation of wood at temperature up to 200°C: Part I. Holz Roh Werkst 31:273–281

Rusche H (1973b) Thermal degradation of wood at temperature up to 200°C: Part II. Holz Roh Werkst 31:307–312

Sandak A, Sandak J, Allegrtti O (2015) Quality control of vacuum thermally modified wood with near infrared spectroscopy. Vacuum 114:44–48

Seborg R, Tarkow H, Stamm A (1953) Effect of heat upon the dimensional stabilization of wood. J For Prod Soc 3(9): 59–67.Sehistedt-Persson (2003) Colour responses to heat treatment of extractives and sap from pine and spruce. Proceedings of the 8th International IUFRO wood drying conference, Brasov, pp 459–464

Sehistedt-Persson M (2003) Colour responses to heat treatment of extractives and sap from pine and spruce. Proceedings of the 8th IUFRO Wood Drying Conference European, Brasov

Senesi N and Senesi GS (2005) Electron-spin resonance spectroscopy. Encyclopedia of soils in the environment. Daniel, H. Oxford, Elsevier, 426–437.

Sivonen H, Maunu SL, Sundholm F, Jämsä S, Viitaniemi P (2002) Magnetic resonance studies of thermally modified wood. Holzforschung 56:648–654

Sjöström E (1981) Wood polysaccharides, in Wood chemistry. Fundamentals and applications. Academic press. Chapter 3:49–67

Stamm A, Hansen L (1937) Minimizing wood shrinkage and swelling: effect of heating in various gases. Ind Eng Chem 29:831–833

Stamm A, Burr H, Kline A (1946) Stayb-wood-A heat stabilized wood. Ind Eng Chem 38:630–634

Sundqvist B (2004) Color changes and acid formation in wood during heating. PhD Thesis. Lulea, University of Technology, Sweden

Sundqvist B, Morén T (2002) The influence of wood polymers and extractives on wood colour induced by hydrothermal treatment. Holz Roh Werkst 60:375–376

Surini T, Charrier F, Malvestio J, Charrier B, Moubarik A, Castéra P (2012) Physical properties and termite durability of maritime pine Pinus pinaster Ait., heat-treated under vacuum pressure. Wood Sci Technol 46: 487–501.

Šušteršic Ž, Mohareb A, Chaouch M, Pétrissans M, Petrič M, Gérardin P (2010) Prediction of decay resistance of heat treated wood on the basis of its elemental composition. Polym Degrad Stab 95:94–97

Tenorio C, Moya R (2013) Thermogravimetric characteristics, its relation with extractives and chemical properties and combustion characteristics of ten fast-growth species in Costa Rica. Thermochim Acta 563:12–21

Tiemann H (1920) Effects of different methods of drying on the strength and hygroscopicity of wood. 3er Ed. “The Kiln drying of lumber”, Chap 11, J.P.Lippincott Co.

Tjeerdsma BF, Militz H (2005) Chemical changes in hydrothermal treated wood: FTIR analysis of combined hydrothermal and dry heat treated wood. Holz Roh Werkst 63:102–111

Tjeerdsma BF, Boonstra M, Pizzi A, Tekely P, Militz H (1998) Characterisation of the thermally modified wood: molecular reasons for wood performance improvement. Holz Roh Werkst 56:149–153

Tjeerdsma BF, Stevens M, Militz H (2000) Durability aspects of hydrothermal treated wood. Document No. IRG/WP00-40160. The International Research Group on Wood Preservation, Kona Surf, Hawaii

Tudorović N, Popović Z, Milić G, Popadić R (2012) Estimation of heat treated wood properties by color change. Bioressources 7:799–815

Viitaniemi P, Jämsä S, Viitanen H (1997) Method for improving biodegradation resistance and dimensional stability of cellulosic products. United States Patent No. 5678324 (US005678324).

Viitaniemi P, Jämsä S, Sundholm F (2001) Method of determining the degree of modification of heat modified wood products. WO/2001/053812, Search International and National Patent Collections.

Welzbacher CR, Rapp OA (2002) Comparison of thermally modified wood originating from four industrial scale process – durability. Document No. IRG/WP 02–40229. The International Research Group on Wood Preservation, Cardiff, Wales

Welzbacher CR, Brischke C, Rapp OA (2007) Influence of treatment temperature and duration on selected biological, mechanical, physical and optical properties of thermally modified timber. Wood Mater Sci Eng 2:66–76

Welzbacher CR, Jazayeri L, Brischke C, Rapp AO (2008) Increased resistance of thermally modified Norway spruce timber (TMT) against brown rot decay by Oligoporus placenta – Study on the mode of protective action. Wood Research 53:13–26

Willems W (2013) Methods of TMT quality control. Proceedings of the Cost Action FP 0904 :“Potential of THM Wood in Industrial Production”, May 16–17 2013, Dresden

Willems W, Tausch A, Militz H (2010) Direct estimation of the durability of high-pressure steam modified wood by esr-spectroscopy. Document No. IRG/WP 10–40508. The International Research Group on Wood Preservation, Biarritz

Willems W, Gérardin P, Militz H (2013) The average carbon oxidation state of thermally modified wood as a marker for its decay resistance against Basidiomycetes. Polym Degrad Stab 98:2140–2145

Yildiz S, Gezer D, Yildiz U (2006) Mechanical and chemical behaviour of spruce wood modified by heat. Build Environ 41:1762–1766

Zanuncio AJV, Motta JP, Silveira TA, De Sa FE, Trugilho PF (2014) Physical and colorimetric changes in Eucalyptus grandis wood after heat treatment. Bioresources 9:293–302