title: Improved sugar yields from biomass sorghum feedstocks: comparing low-lignin mutants and pretreatment chemistries.
abstract: BACKGROUND
  For biofuel production processes to be economically efficient, it is essential to maximize the production of monomeric carbohydrates from the structural carbohydrates of feedstocks. One strategy for maximizing carbohydrate production is to identify less recalcitrant feedstock cultivars by performing some type of experimental screening on a large and diverse set of candidate materials, or by identifying genetic modifications (random or directed mutations or transgenic plants) that provide decreased recalcitrance. Economic efficiency can also be increased using additional pretreatment processes such as deacetylation, which uses dilute NaOH to remove the acetyl groups of hemicellulose prior to dilute acid pretreatment. In this work, we used a laboratory-scale screening tool that mimics relevant thermochemical pretreatment conditions to compare the total sugar yield of three near-isogenicbrown midrib(bmr) mutant lines and the wild-type (WT) sorghum cultivar. We then compared results obtained from the laboratory-scale screening pretreatment assay to a large-scale pretreatment system.
  
  
  RESULTS
  After pretreatment and enzymatic hydrolysis, thebmrmutants had higher total sugar yields than the WT sorghum cultivar. Increased pretreatment temperatures increased reactivity for all sorghum samples reducing the differences observed at lower reaction temperatures. Deacetylation prior to dilute acid pretreatment increased the total sugar yield for all four sorghum samples, and reduced the differences in total sugar yields among them, but solubilized a sizable fraction of the non-structural carbohydrates. The general trends of increased total sugar yield in thebmrmutant compared to the WT seen at the laboratory scale were observed at the large-scale system. However, in the larger reactor system, the measured total sugar yields were lower and the difference in total sugar yield between the WT andbmrsorghum was larger.
  
  
  CONCLUSIONS
  Sorghumbmrmutants, which have a reduced lignin content showed higher total sugar yields than the WT cultivar after dilute acid pretreatment and enzymatic hydrolysis. Deacetylation prior to dilute acid pretreatment increased the total sugar yield for all four sorghum samples. However, since deacetylation also solubilizes a large fraction of the non-structural carbohydrates, the ability to derive value from these solubilized sugars will depend greatly on the proposed conversion process.
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory (NREL), 15013 Denver West Parkway, Golden, CO 80401 USA ; Valorization of Agricultural Products Department-Biomass, Bioproducts and Energy Unit, Walloon Agricultural Research Center (CRA-W), Chaussée de Namur, 146, 5030 Gembloux, Belgium.
authors.forename: Bruno
authors.initials: B
authors.lastname: Godin
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory (NREL), 15013 Denver West Parkway, Golden, CO 80401 USA.
authors.forename: Nick
authors.initials: N
authors.lastname: Nagle
authors.affiliation: Agricultural Research Service (ARS)-Grain, Forage, and Bioenergy Research Unit, United States Department of Agriculture (USDA), University of Nebraska, 251 Filley Hall/Food Industries Complex, East Campus, Lincoln, NE 68583-0937 USA.
authors.forename: Scott
authors.initials: S
authors.lastname: Sattler
authors.affiliation: Valorization of Agricultural Products Department-Biomass, Bioproducts and Energy Unit, Walloon Agricultural Research Center (CRA-W), Chaussée de Namur, 146, 5030 Gembloux, Belgium.
authors.forename: Richard
authors.initials: R
authors.lastname: Agneessens
authors.affiliation: Valorization of Agricultural Products Department-Biomass, Bioproducts and Energy Unit, Walloon Agricultural Research Center (CRA-W), Chaussée de Namur, 146, 5030 Gembloux, Belgium.
authors.forename: Jérôme
authors.initials: J
authors.lastname: Delcarte
authors.affiliation: National Bioenergy Center, National Renewable Energy Laboratory (NREL), 15013 Denver West Parkway, Golden, CO 80401 USA.
authors.forename: Edward
authors.identifier: 0000-0002-7361-8931
authors.initials: E
authors.lastname: Wolfrum
keywords: Biofuels; Brown midrib; Pretreatment; Sorghum bicolor; Total sugar yield