title: Evaluation of lime and hydrothermal pretreatments for efficient enzymatic hydrolysis of raw sugarcane bagasse.
abstract: BACKGROUND
  Ethanol production from sugarcane bagasse requires a pretreatment step to disrupt the cellulose-hemicellulose-lignin complex and to increase biomass digestibility, thus allowing the obtaining of high yields of fermentable sugars for the subsequent fermentation. Hydrothermal and lime pretreatments have emerged as effective methods in preparing the lignocellulosic biomass for bioconversion. These pretreatments are advantageous because they can be performed under mild temperature and pressure conditions, resulting in less sugar degradation compared with other pretreatments, and also are cost-effective and environmentally sustainable. In this study, we evaluated the effect of these pretreatments on the efficiency of enzymatic hydrolysis of raw sugarcane bagasse obtained directly from mill without prior screening. In addition, we evaluated the structure and composition modifications of this bagasse after lime and hydrothermal pretreatments.
  
  
  RESULTS
  The highest cellulose hydrolysis rate (70 % digestion) was obtained for raw sugarcane bagasse pretreated with lime [0.1 g Ca(OH)2/g raw] for 60 min at 120 °C compared with hydrothermally pretreated bagasse (21 % digestion) under the same time and temperature conditions. Chemical composition analyses showed that the lime pretreatment of bagasse promoted high solubilization of lignin (30 %) and hemicellulose (5 %) accompanied by a cellulose accumulation (11 %). Analysis of pretreated bagasse structure revealed that lime pretreatment caused considerable damage to the bagasse fibers, including rupture of the cell wall, exposing the cellulose-rich areas to enzymatic action.
  
  
  CONCLUSIONS
  We showed that lime pretreatment is effective in improving enzymatic digestibility of raw sugarcane bagasse, even at low lime loading and over a short pretreatment period. It was also demonstrated that this pretreatment caused alterations in the structure and composition of raw bagasse, which had a pronounced effect on the enzymes accessibility to the substrate, resulting in an increase of cellulose hydrolysis rate. These results indicate that the use of raw sugarcane bagasse (without prior screening) pretreated with lime (cheaper and environmentally friendly reagent) may represent a cost reduction in the cellulosic ethanol production.
authors.affiliation: Department of Biochemistry and Technology Chemistry, Institute of Chemistry, São Paulo State University-UNESP, R. Prof. Francisco Degni 55, Araraquara, SP CEP 14800-060 Brazil.
authors.forename: Maira Prearo
authors.initials: MP
authors.lastname: Grimaldi
authors.affiliation: Department of Biochemistry and Technology Chemistry, Institute of Chemistry, São Paulo State University-UNESP, R. Prof. Francisco Degni 55, Araraquara, SP CEP 14800-060 Brazil.
authors.forename: Marina Paganini
authors.initials: MP
authors.lastname: Marques
authors.affiliation: Department of Biochemistry and Technology Chemistry, Institute of Chemistry, São Paulo State University-UNESP, R. Prof. Francisco Degni 55, Araraquara, SP CEP 14800-060 Brazil.
authors.forename: Cecília
authors.initials: C
authors.lastname: Laluce
authors.affiliation: Department of Biochemistry and Technology Chemistry, Institute of Chemistry, São Paulo State University-UNESP, R. Prof. Francisco Degni 55, Araraquara, SP CEP 14800-060 Brazil.
authors.forename: Eduardo Maffud
authors.initials: EM
authors.lastname: Cilli
authors.affiliation: Department of Biochemistry and Technology Chemistry, Institute of Chemistry, São Paulo State University-UNESP, R. Prof. Francisco Degni 55, Araraquara, SP CEP 14800-060 Brazil.
authors.forename: Sandra Regina Pombeiro
authors.initials: SR
authors.lastname: Sponchiado
keywords: Chemical composition; Enzymatic hydrolysis; Hydrothermal pretreatment; Lime pretreatment; Scanning electron microscopy; Sugarcane bagasse; Thermogravimetric analysis; X-Ray diffraction