Characterization Of The Molecular Mechanism For Biomass Enzymatic Saccharification Under Steam Explosion And Surfactant Supply In Miscanthus

Miscanthus is a desired bioenergy crop with enormous lignocellulose residues for biofuels and other chemical products.Due to lignocellulose recalcitrance,however,it becomes essential to optimize pretreatment conditions for enhanced biomass enzymatic saccharification and bioethanol production.In this study,we initially selected ten representative Miscanthus accessions that exhibited diverse cell wall compositions.Then we performed the steam explosion pretreatment and supplied three surfactants into sequential enzymatic hydrolysis reactions to enhance biomass saccharification in ten Miscanthus accessions.Based on the correlation analysis,we identified major wall polymer features that determined steam-exploded biomass saccharification,leading to a mechanistic model about lignocellulose enzymatic hydrolysis.In addition,we detected three surfactant enhancements to biomass saccharification and bioethanol production,and compared their distinct roles.The main results of this study are described as follows:(1)Steam explosion pretreatment enhanced biomass enzymatic saccharification by 1.3-5.97 folds in ten Miscanthus accessions,which might be due to either increased cellulose contents and relatively reduced hemicellulose and lignin levels or altered wall polymer features in the steam-exploded biomass residues.The altered wall polymer features included cellulose crystallinity(Cr I)and cellulose DP(degree of polymerization),hemicellulosic Ara and Xyl and Xyl/Ara,and three monomers of lignin.(2)Based on correlation analysis,H-monomer was determined to be only negative factor on direct biomass enzymatic hydrolysis without any pretreatment.However,three major wall polymer features were the factors negatively affecting biomass enzymatic saccharification in the steam-exploded residues including cellulose DP,hemicellulosic Ara,Xyl level and S-monomer level.Although Xyl and S-monomer levels of steam-exploded residues were the negative factors on DY values,three factors negatively affected DY/DB ratios including cellulose DP,Xyl or Ara and S-monomer,in supporting the findings about DY/DB as the key positive factor on biomass enzymatic hydrolysis of the steam-exploded residues.(3)By measuring porosity of steam-exploded residues,this study demonstrated the ratio of DY(large pore size)to DB(small pore size)was the key positive factor on biomass enzymatic saccharification.(4)The optimal concentrations of three surfactants(2%Tween-80,0.5%PEG4000 and 1% Silwet L-77)were determined for enhancing biomass enzymatic saccharification.Notably,1% Silwet L-77 treatment was more effective than other two surfactants for enhancing enzymatic hydrolysis of raw biomass materials.However,2%Tween-80 led to the highest biomass saccharification of the steam-exploded residues.(5)After pretreatment with 1% Na OH,the 2% Tween-80 treatment led to a complete enzymatic hydrolysis of the steam-exploded residues.The steam-exploded residues pretreated with 1% Na OH also exhibited largely destructed lignocellulose surfaces under scanning electron microscopy,which was consistent with their complete enzymatic hydrolysis.(6)The three surfactants all significantly enhanced sequential bioethanol productivity.In particular,both 1%Na OH+2%Tween-80 and 1%Na OH+0.5%PEG4000 pretreatments could led to the highest ethanol yield at 16.2%(dry matter),which was 2.2 folds higher than that of the control.Protein analysis further indicated that the 1%Na OH+2%Tween-80 pretreatment increased the enzyme concentration in supernatants of the enzymatic hydrolysis reaction comparing with other pretreatments,suggesting that the pretreatment may enhance the use of enzymes for biomass digestion.