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

Biotechnology for Biofuels

Marisa A Lima³  Gabriela B Lavorente¹  Hana KP da Silva¹  Juliano Bragatto¹  Camila A Rezende³  Oigres D Bernardinelli³  Eduardo R deAzevedo³  Leonardo D Gomez²  Simon J McQueen-Mason²  Carlos A Labate¹  Igor Polikarpov³ 

[1] Laboratório Max Feffer de Genética de Plantas, Departamento de Genética - ESALQ, Universidade de São Paulo, Caixa Postal 83, 13418-900, Piracicaba, SP, Brazil

[2] CNAP, Department of Biology, University of York, Heslington, York YO10 5YW, UK

[3] Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, 13560-970, São Carlos, SP, Brazil

关键词: Enzymatic hydrolysis;    Scanning electron microscopy;    FTIR;    Solid-state NMR;    Chemical composition;    Alkali pretreatment;    Acid pretreatment;    Bioethanol;    Bark;    Eucalyptus grandis x urophylla;    Eucalyptus grandis;   

Others  :  798037
DOI  :  10.1186/1754-6834-6-75

 received in 2012-12-04, accepted in 2013-04-26,  发布年份 2013

【 摘 要 】

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.

【 授权许可】

   
2013 Lima et al.; licensee BioMed Central Ltd.

【 图 表 】

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