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Master's Dissertation
DOI
10.11606/D.97.2017.tde-06022017-101817
Document
Author
Full name
Daniele Sporck Gonçalves da Silva
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
Lorena, 2016
Supervisor
Committee
Milagres, Adriane Maria Ferreira (President)
Lacerda, Talita Martins
Mulinari, Daniela Regina
Title in Portuguese
Isolamento de xilanas do bagaço de cana-de-açúcar integrado à hidrólise enzimática da celulose residual
Keywords in Portuguese
bagaço de cana-de-açúcar
extração alcalina
Xilana
xilanase
Abstract in Portuguese
A intensa busca por fontes renováveis de energia traz como alternativa a utilização da biomassa lignocelulósica para produção de biocombustíveis e biopolímeros a partir de seus componentes, celulose, hemicelulose e lignina. Nesse estudo, a partir do bagaço de cana-de-açúcar obteve-se uma polpa enriquecida em glucana e xilana utilizando-se o pré-tratamento quimio-termomecânico em solução sulfito alcalino (10% Na2SO3 e 5% NaOH). O pré-tratamento removeu 43% de lignina e 8% de xilana do bagaço e após uma etapa de lavagem do material, ocorreu maior dissolução da lignina (53%), xilana (17,4%) e também uma pequena solubilização de glucana (5%). O objetivo foi isolar e caracterizar as xilanas do bagaço pré-tratado e aquelas solubilizadas no licor e também avaliar a degradabilidade enzimática da celulose residual. A extração de xilanas foi realizada em condição alcalina, assistida ou não por xilanases, a partir do bagaço pré-tratado lavado (BLA) e não lavado (BNL). A extração enzimática das xilanas foi feita com 8 UI de xilanase comercial (Luminase) por grama de material, em tampão fosfato 50 mM, 50º C, pH 8 por 24 horas. Os métodos químicos para a extração das xilanas empregaram 40% NaOH (m/m), com variações nas condições de incubação entre os métodos de Lopez (L) (60º C, 2h) e Hoije (H) (25º C, 16h). Os rendimentos de sólidos e de xilana obtidos por Hoije foram próximos a 60%, diferente do observado para as xilanas extraídas pelo método de Lopez e enzimático. No método de Hoije utilizou-se o bagaço pré-tratado com sulfito alcalino, parcialmente deslignificado com clorito de sódio em meio ácido, e obteve-se xilanas mais puras. O menor rendimento de xilanas foi obtido através do método enzimático (22 a 30%). Todas as xilanas apresentaram composição majoritária de xilose (60-80%), seguido de grupos arabinosil (7-12%), ácidos urônicos (4-13%), ácidos hidroxicinâmicos (0,3-1,2%) e lignina (3-10%). A relação xilose/arabinose das xilanas variou de 7 a 10, enquanto que a relação xilose/ácidos urônicos apresentou uma faixa mais ampla (9-28). Este grau de substituição refletiu na maior solubilidade das xilanas. As xilanas isoladas com xilanases apresentaram duas frações com massas molares ponderais médias (Mw) de 3.700 g/mol e 800 g/mol, inferiores às das xilanas isoladas pelo método de Hoije (24.300 g/mol) e de Lopez (24.450 g/mol). As xilanas recuperadas do licor sulfito apresentaram um rendimento de 34% e massa molar ponderal média de 28.660 g/mol. As xilanas isoladas pelos métodos químicos foram caracterizadas por FT-IR e mostraram absorções em números de ondas característicos, com perfil semelhante. A conversão enzimática de glucana dos resíduos, após extração de xilanas com o método de Hoije, foi maior que dos bagaços pré-tratados. Quando a extração de xilanas foi realizada através dos métodos de Lopez ou enzimático essa melhoria não foi observada.
Title in English
Isolation of xylan from sugarcane bagasse integrated with enzymatic hydrolysis of residual cellulose
Keywords in English
alkaline-extraction
sugarcane bagasse
Xylan
xylanases
Abstract in English
The intensive search for renewable energy sources is often ssociated with the use of lignocellulosic biomass for biofuel production as well for the extraction of biopolymers from their components: cellulose, hemicellulose and lignin. In the present study, a pulp enriched in glucan and xylan was obtained from sugarcane bagasse using chemi-thermomechanical alkaline sulfite solution (10% Na2SO3 and 5% NaOH) pretreatment. The pretreatment removed 43% of lignin and 8% of xylan from the pulp, and a greater dissolution of lignin (53%) and xylan (17.4%) and also an additional dissolution of glucan (5%) was reached after a washing step of the material. The aim was to isolate and characterize xylans from the pretreated bagasse as well as those solubilized in the liquor, and also to evaluate the enzymatic degradability of the residual pulp. The xylan extraction was performed in alkaline conditions, being assisted or not by xylanases from the washed pretreated bagasse (WB) and unwashed pretreated bagasse (UWB). Enzymatic extraction of xylan was performed with 8 IU commercial xylanase (Luminase) per gram of material in 50 mM phosphate buffer, 50° C, pH 8, for 24 hours. The chemical methods for xylan extraction employed 40% NaOH (w/w), with varying in the incubation conditions using the Lopez (L) (60 ° C, 2h) and Hoije (H) (25 ° C, 16h) methods. The solids and xylan yields obtained through the Hoije method were near 60%, which were different from those observed for the xylan extracted by Lopez and enzymatic methods. In the Hoije method (H), sugarcane bagasse was pretreated with alkali sulfite and was partially delignificated with sodium chlorite in an acid medium, resulting in even more pure xylans. The lowest xylan yield was obtained by the enzymatic method (22 to 30%). All xylans presented xylose as major component (60-80%), followed by arabinosyl groups (7-12%), uronic acids (4-13%), hydroxycinnamic acids (0.3-1.2%), and lignin (3-10%). The xylose/arabinose ratio of xylan ranged from 7 to 10, while the xylose/uronic acids ratio showed a greater range (9-28). This degree of substitution reflected in an increasing in the xylan solubility. Xylans isolated by xylanases exhibited two fractions with an weight average molecular weight (Mw) of 3.700 g/mol and 800 g/mol, which were lower than those xylans isolated through the Hoije (24.300 g/mol) and Lopez (24.450 g/mol) methods. The xylan recovered from sulfite liquor had a yield of 34% and an weight average molar weight of 28.660 g/mol. The xylans isolated by chemical methods were characterized by FT-IR, and showed absorptions at characteristic wavenumbers with similar profile. After the extraction of xylans with Hoije method, the enzymatic conversion of glucan residues was higher than the one for the pretreated bagasse. When the xylan extraction was performed wiht the Lopez or enzymatic methods, such improvement was not observed.
 
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Publishing Date
2017-02-06
 
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