Chemical composition and enzymatic digestibility of sugarcane clones selected for varied lignin content

Abstract

BackgroundThe recalcitrance of lignocellulosic materials is a major limitation for their conversion into fermentable sugars. Lignin depletion in new cultivars or transgenic plants has been identified as a way to diminish this recalcitrance. In this study, we assessed the success of a sugarcane breeding program in selecting sugarcane plants with low lignin content, and report the chemical composition and agronomic characteristics of eleven experimental hybrids and two reference samples. The enzymatic digestion of untreated and chemically delignified samples was evaluated to advance the performance of the sugarcane residue (bagasse) in cellulosic-ethanol production processes.ResultsThe ranges for the percentages of glucan, hemicellulose, lignin, and extractive (based on oven-dry biomass) of the experimental hybrids and reference samples were 38% to 43%, 25% to 32%, 17% to 24%, and 1.6% to 7.5%, respectively. The samples with the smallest amounts of lignin did not produce the largest amounts of total polysaccharides. Instead, a variable increase in the mass of a number of components, including extractives, seemed to compensate for the reduction in lignin content. Hydroxycinnamic acids accounted for a significant part of the aromatic compounds in the samples, with p-coumaric acid predominating, whereas ferulic acid was present only in low amounts. Hydroxycinnamic acids with ester linkage to the hemicelluloses varied from 2.3% to 3.6%. The percentage of total hydroxycinnamic acids (including the fraction linked to lignin through ether linkages) varied from 5.0% to 9.2%, and correlated to some extent with the lignin content. These clones released up to 31% of glucose after 72 hours of digestion with commercial cellulases, whereas chemically delignified samples led to cellulose conversion values of more than 80%. However, plants with lower lignin content required less delignification to reach higher efficiencies of cellulose conversion during the enzymatic treatment.ConclusionSome of the experimental sugarcane hybrids did have the combined characteristics of high biomass and high sucrose production with low lignin content. Conversion of glucan to glucose by commercial cellulases was increased in the samples with low lignin content. Chemical delignification further increased the cellulose conversion to values of more than 80%. Thus, plants with lower lignin content required less delignification to reach higher efficiencies of cellulose conversion during the enzymatic treatment.

Lignification in Sugarcane: Biochemical Characterization, Gene Discovery, and Expression Analysis in Two Genotypes Contrasting for Lignin Content

“…The values for lignin content presented in our study are significantly lower than those previously reported for sugarcane bagasse (Lopes et al, 2011;Masarin et al, 2011;Rezende et al, 2011). Sugarcane bagasse is the residue produced after Suc extraction and is composed of 39% cellulose, 25% hemicelluloses, and 23% lignin, among other minor components (Carroll and Somerville, 2009).…”

Pré-Tratamento Sob Pressão Atmosférica Visando Ao Aumento Da Digestibilidade Enzimática De Bagaço De Cana-De-Açúcar Usando Glicerol Em Meio Ácido

“…O bagaço in natura foi também caracterizado com realção à quantidade de extrativos, conforme descrito por Masarin et al (2011).…”

Bioprocesses for biofuels: an overview of the Brazilian case

“…Pretreatment can break down lignin and hemicellulose bonds, disrupt the crystalline arrangement of cellulose, increase digestibility and cell wall porosity, and improve accessibility to enzymes during hydrolysis [24].…”