Mechanism Of Pretreatments For Efficient Biomass Saccharification And Ethanol Production In Rapeseed Stalks

Rapeseeds is an important oil crop over the world,and its stalk provides enormous biomass resource convertible for bioethanol and bioproducts.In principle,bioethanol conversion involves in three major steps:initial physical and chemical pretreatment to disrupt wall polymers,sequential enzymatic hydrolysis to release soluble sugars and final yeast fermentation to produce bioethanol.However,lignocellulose recalcitrance decides an unacceptably costly biomass process for bioethanol production at large scale,with potential secondary pollution from chemical and wastes release into the environment.Hence,it becomes essential not only to find out the optimal biomass process technology,but also to understand how rapeseed stalk could be completely digested for maximum bioethanol production.Based on our previously-achieved data,this work selected three representative rapeseed stalks that showed distinct cell wall compositions and wall polymers features,and then performed steam explosion?SE?followed with chemical?acid,alkali?pretreatments to reduce lignocellulose recalcitrance for enhanced biomass enzymatic saccharification and bioethanol production.Meanwhile,this study determined cell wall compositions,major wall polymer features,biomass porosity and cellulose accessibility of the pretreated biomass residues in three rapeseed stalks.Furthermore,it also examined how Tween-80 could block lignin adsorption with mixed-cellulases applied in biomass enzymatic hydrolysis.Here are major results below:1.The steam explosion?SE?pretreatments with three rapeseed stalks could extract about 62%hemicelluloses and all pectin,leading to the degree polymerization?DP?of ?-1,4-glucans reduced by 18%-29%,the biomass porosity increased by 34%-43%and the cellulose accessibility raised by 1.4-1.7 folds.2.The steam explosion followed with the 6%H₂SO₄ pretreatment?two-step pretreatments:SE+6%H₂SO₄?extracted more than 80%hemicelluloses,which led to the lowest values of both cellulose DP and surface accessibility among all pretreatments performed in this study.3.The two-steps?SE+5%Ca O?pretreatments could remove 33%-42%of lignin,resulting in the biomass porosity increased by 32%-53%and cellulose accessibility raised by 1.2-1.4 fold in three rapeseed stalks.4.Supplement of 1%Tween-80 into enzymatic hydrolysis effectively blocked lignin adsorption with mixed-cellulases in the pretreated biomass residues of three rapeseed stalks.5.Even though three pretreatments performed above led to distinct biomass enzymatic hydrolysis and bioethanol production in three rapeseed stalks,the SE+5%Ca O two-step pretreatments with the stalk of desirable rapeseed cultivar?Bn13? could cause almost complete enzymatic saccharification to maximize bioethanol yield of 20.5%?%dry matter?with relatively high hexose-ethanol conversion rate at 93%,compared to the previously-reported bioethanol yields achieved in rapeseed stalks.Taken all together,this study finally proposed a hypothetic model of effective biomass enzymatic saccharification for high bioethanol production in rapeseed stalks under three distinct pretreatments by largely extracting hemicelluloses and lignin,characteristically reducing cellulose DP and Cr I,much increasing biomass porosity and cellulose surface accessibility,coupled with the Tween-80 blocking lignin adsorption with the mixed-cellulases.Hence,this model has not only interpreted why the desirable rapeseed stalk could be completely digested for maximum bioethanol yield,but it has also provided a cost-effective and green-like strategy for high bioethanol production in rapeseed stalks and other crops.