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Open Access Research

Ultra-structural mapping of sugarcane bagasse after oxalic acid fiber expansion (OAFEX) and ethanol production by Candida shehatae and Saccharomyces cerevisiae

Anuj K Chandel1*, Felipe F A Antunes1, Virgilio Anjos2, Maria J V Bell2, Leonarde N Rodrigues2, Om V Singh3, Carlos A Rosa4, Fernando C Pagnocca5 and Silvio S da Silva1*

Author Affiliations

1 Department of Biotechnology, University of São Paulo, School of Engineering of Lorena, Estrada Municipal do Campinho- Caixa,, Postal 116 12.602.810, Lorena/SP, Brazil

2 Material Spectroscopy Laboratory, Department of Physics, Federal University of Juiz de Fora,, 36036-330, Juiz de Fora, MG, Brazil

3 Division of Biological and Health Sciences, University of Pittsburgh, 16701, Bradford, PA, USA

4 Department of Microbiology, Federal University of Minas Gerais,, Belo Horizonte, MG, Brazil

5 Department of Biochemistry and Microbiology, Institute of Biosciences CEIS/UNESP – Rio, Claro/ SP, Brazil

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Biotechnology for Biofuels 2013, 6:4  doi:10.1186/1754-6834-6-4

Published: 16 January 2013

Abstract

Background

Diminishing supplies of fossil fuels and oil spills are rousing to explore the alternative sources of energy that can be produced from non-food/feed-based substrates. Due to its abundance, sugarcane bagasse (SB) could be a model substrate for the second-generation biofuel cellulosic ethanol. However, the efficient bioconversion of SB remains a challenge for the commercial production of cellulosic ethanol. We hypothesized that oxalic-acid-mediated thermochemical pretreatment (OAFEX) would overcome the native recalcitrance of SB by enhancing the cellulase amenability toward the embedded cellulosic microfibrils.

Results

OAFEX treatment revealed the solubilization of hemicellulose releasing sugars (12.56 g/l xylose and 1.85 g/l glucose), leaving cellulignin in an accessible form for enzymatic hydrolysis. The highest hydrolytic efficiency (66.51%) of cellulignin was achieved by enzymatic hydrolysis (Celluclast 1.5 L and Novozym 188). The ultrastructure characterization of SB using scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, Fourier transform–near infrared spectroscopy (FT-NIR), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) revealed structural differences before and after OAFEX treatment with enzymatic hydrolysis. Furthermore, fermentation mediated by C. shehatae UFMG HM52.2 and S. cerevisiae 174 showed fuel ethanol production from detoxified acid (3.2 g/l, yield 0.353 g/g; 0.52 g/l, yield, 0.246 g/g) and enzymatic hydrolysates (4.83 g/l, yield, 0.28 g/g; 6.6 g/l, yield 0.46 g/g).

Conclusions

OAFEX treatment revealed marked hemicellulose degradation, improving the cellulases’ ability to access the cellulignin and release fermentable sugars from the pretreated substrate. The ultrastructure of SB after OAFEX and enzymatic hydrolysis of cellulignin established thorough insights at the molecular level.