title: Multi-scale structural and chemical analysis of sugarcane bagasse in the process of sequential acid-base pretreatment and ethanol production by Scheffersomyces shehatae and Saccharomyces cerevisiae.
abstract: BACKGROUND
  Heavy usage of gasoline, burgeoning fuel prices, and environmental issues have paved the way for the exploration of cellulosic ethanol. Cellulosic ethanol production technologies are emerging and require continued technological advancements. One of the most challenging issues is the pretreatment of lignocellulosic biomass for the desired sugars yields after enzymatic hydrolysis. We hypothesized that consecutive dilute sulfuric acid-dilute sodium hydroxide pretreatment would overcome the native recalcitrance of sugarcane bagasse (SB) by enhancing cellulase accessibility of the embedded cellulosic microfibrils.
  
  
  RESULTS
  SB hemicellulosic hydrolysate after concentration by vacuum evaporation and detoxification showed 30.89 g/l xylose along with other products (0.32 g/l glucose, 2.31 g/l arabinose, and 1.26 g/l acetic acid). The recovered cellulignin was subsequently delignified by sodium hydroxide mediated pretreatment. The acid-base pretreated material released 48.50 g/l total reducing sugars (0.91 g sugars/g cellulose amount in SB) after enzymatic hydrolysis. Ultra-structural mapping of acid-base pretreated and enzyme hydrolyzed SB by microscopic analysis (scanning electron microcopy (SEM), transmitted light microscopy (TLM), and spectroscopic analysis (X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Fourier transform near-infrared (FT-NIR) spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy) elucidated the molecular changes in hemicellulose, cellulose, and lignin components of bagasse. The detoxified hemicellulosic hydrolysate was fermented by Scheffersomyces shehatae (syn. Candida shehatae UFMG HM 52.2) and resulted in 9.11 g/l ethanol production (yield 0.38 g/g) after 48 hours of fermentation. Enzymatic hydrolysate when fermented by Saccharomyces cerevisiae 174 revealed 8.13 g/l ethanol (yield 0.22 g/g) after 72 hours of fermentation.
  
  
  CONCLUSIONS
  Multi-scale structural studies of SB after sequential acid-base pretreatment and enzymatic hydrolysis showed marked changes in hemicellulose and lignin removal at molecular level. The cellulosic material showed high saccharification efficiency after enzymatic hydrolysis. Hemicellulosic and cellulosic hydrolysates revealed moderate ethanol production by S. shehatae and S. cerevisiae under batch fermentation conditions.
authors.affiliation: Department of Biotechnology, School of Engineering of Lorena, Estrada Municipal do Campinho, University of São Paulo, Caixa Postal 116 12.602.810, Lorena, São Paulo, Brazil.
authors.forename: Anuj K
authors.initials: AK
authors.lastname: Chandel
authors.affiliation: Department of Biotechnology, School of Engineering of Lorena, Estrada Municipal do Campinho, University of São Paulo, Caixa Postal 116 12.602.810, Lorena, São Paulo, Brazil.
authors.forename: Felipe Af
authors.initials: FA
authors.lastname: Antunes
authors.affiliation: Materials Spectroscopy Laboratory, Department of Physics, Federal University of Juiz de Fora, Juiz de Fora 36036-330 Minas Gerais, Brazil.
authors.forename: Virgilio
authors.initials: V
authors.lastname: Anjos
authors.affiliation: Materials Spectroscopy Laboratory, Department of Physics, Federal University of Juiz de Fora, Juiz de Fora 36036-330 Minas Gerais, Brazil.
authors.forename: Maria Jv
authors.initials: MJ
authors.lastname: Bell
authors.affiliation: Materials Spectroscopy Laboratory, Department of Physics, Federal University of Juiz de Fora, Juiz de Fora 36036-330 Minas Gerais, Brazil.
authors.forename: Leonarde N
authors.initials: LN
authors.lastname: Rodrigues
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, São Carlos, São Paulo CEP 13560-970, Brazil.
authors.forename: Igor
authors.initials: I
authors.lastname: Polikarpov
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, São Carlos, São Paulo CEP 13560-970, Brazil.
authors.forename: Eduardo R
authors.initials: ER
authors.lastname: de Azevedo
authors.affiliation: Instituto de Física de São Carlos, Universidade de São Paulo, Caixa Postal 369, São Carlos, São Paulo CEP 13560-970, Brazil.
authors.forename: Oigres D
authors.initials: OD
authors.lastname: Bernardinelli
authors.affiliation: Departmento de Microbiologia, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Rosa
authors.affiliation: Department of Biochemistry and Microbiology, Institute of Biosciences, CIES/UNESP, Rio Claro, São Paulo, Brazil.
authors.forename: Fernando C
authors.initials: FC
authors.lastname: Pagnocca
authors.affiliation: Department of Biotechnology, School of Engineering of Lorena, Estrada Municipal do Campinho, University of São Paulo, Caixa Postal 116 12.602.810, Lorena, São Paulo, Brazil.
authors.forename: Silvio S
authors.initials: SS
authors.lastname: da Silva
keywords: Bioethanol; Enzymatic hydrolysis; Sequential acid–base pretreatment; Structural analysis; Sugarcane bagasse; Yeasts
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