Effects of pretreatment on morphology, chemical composition and enzymatic digestibility of eucalyptus bark: a potentially valuable source of fermentable sugars for biofuel production - part 1

Author(s):Show less -

Lima, Marisa A. ^[1] ; Lavorente, Gabriela B. ^[2] ; da Silva, Hana K. P. ^[2] ; Bragatto, Juliano ^[2] ; Rezende, Camila A. ^[1] ; Bernardinelli, Oigres D. ^[1] ; deAzevedo, Eduardo R. ^[1] ; Gomez, Leonardo D. ^[3] ; McQueen-Mason, Simon J. ^[3] ; Labate, Carlos A. ^[2] ; Polikarpov, Igor ^[1]

Affiliation

^[1] Univ Sao Paulo, Inst Fis Sao Carlos, BR-13560970 Sao Carlos, SP - Brazil

^[2] Univ Sao Paulo, Dept Genet ESALQ, Lab Max Feffer Genet Plantas, BR-13418900 Piracicaba, SP - Brazil

^[3] Univ York, Dept Biol, CNAP, York YO10 5YW, N Yorkshire - England

• Document type: Journal article
• Source: BIOTECHNOLOGY FOR BIOFUELS; v. 6, MAY 9 2013.
• Web of Science Citations: 58

Abstract

Background: In recent years, the growing demand for biofuels has encouraged the search for different sources of underutilized lignocellulosic feedstocks that are available in sufficient abundance to be used for sustainable biofuel production. Much attention has been focused on biomass from grass. However, large amounts of timber residues such as eucalyptus bark are available and represent a potential source for conversion to bioethanol. In the present paper, we investigate the effects of a delignification process with increasing sodium hydroxide concentrations, preceded or not by diluted acid, on the bark of two eucalyptus clones: Eucalyptus grandis (EG) and the hybrid, E. grandis x urophylla (HGU). The enzymatic digestibility and total cellulose conversion were measured, along with the effect on the composition of the solid and the liquor fractions. Barks were also assessed using Fourier-transform infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (NMR), X-Ray diffraction, and scanning electron microscopy (SEM). Results: Compositional analysis revealed an increase in the cellulose content, reaching around 81% and 76% of glucose for HGU and EG, respectively, using a two-step treatment with HCl 1%, followed by 4% NaOH. Lignin removal was 84% (HGU) and 79% (EG), while the hemicellulose removal was 95% and 97% for HGU and EG, respectively. However, when we applied a one-step treatment, with 4% NaOH, higher hydrolysis efficiencies were found after 48 h for both clones, reaching almost 100% for HGU and 80% for EG, in spite of the lower lignin and hemicellulose removal. Total cellulose conversion increased from 5% and 7% to around 65% for HGU and 59% for EG. NMR and FTIR provided important insight into the lignin and hemicellulose removal and SEM studies shed light on the cell-wall unstructuring after pretreatment and lignin migration and precipitation on the fibers surface, which explain the different hydrolysis rates found for the clones. Conclusion: Our results show that the single step alkaline pretreatment improves the enzymatic digestibility of Eucalyptus bark. Furthermore, the chemical and physical methods combined in this study provide a better comprehension of the pretreatment effects on cell-wall and the factors that influence enzymatic digestibility of this forest residue. (AU)

• FAPESP's process: 09/18354-8 - Dynamics and structure of polymer systems as studied by nuclear magnetic resonance
• Grantee: Eduardo Ribeiro de Azevedo
• Support type: Regular Research Grants
• FAPESP's process: 10/52362-5 - Targeted analysis of microbial lignocellulolytic secretomes: a new approach to enzyme discovery
• Grantee: Igor Polikarpov
• Support type: Regular Research Grants
• FAPESP's process: 08/56255-9 - Structure and function of enzymes and auxiliary proteins from Trichoderma, active in cell-wall hydrolysis
• Grantee: Igor Polikarpov
• Support type: Program for Research on Bioenergy (BIOEN) - Thematic Grants
• FAPESP's process: 10/08370-3 - Biophysical and biochemical studies of exoglucanases from Trichoderma harzianum involved in the biodegradation of cellulose
• Grantee: Wanius José Garcia da Silva
• Support type: Regular Research Grants
• FAPESP's process: 10/11135-6 - Structural and morphological aspects of the cell-wall degradation and its biopolymers
• Grantee: Camila Alves de Rezende
• Support type: Scholarships in Brazil - Post-Doctorate