Djajadi Demi T, Jensen Mads M, Oliveira Marlene, Jensen Anders, Thygesen Lisbeth G, Pinelo Manuel, Glasius Marianne, Jørgensen Henning, Meyer Anne S
1Department of Chemical and Biochemical Engineering, Technical University of Denmark, Søltofts Plads Building 229, 2800 Kongens Lyngby, Denmark.
2Department of Chemistry, Aarhus University, Langelandsgade 140, 8000 Aarhus C, Denmark.
Biotechnol Biofuels. 2018 Apr 2;11:85. doi: 10.1186/s13068-018-1085-0. eCollection 2018.
Lignin is known to hinder efficient enzymatic conversion of lignocellulose in biorefining processes. In particular, nonproductive adsorption of cellulases onto lignin is considered a key mechanism to explain how lignin retards enzymatic cellulose conversion in extended reactions.
Lignin-rich residues (LRRs) were prepared via extensive enzymatic cellulose degradation of corn stover ( subsp. L.), × stalks (MS) and wheat straw ( L.) (WS) samples that each had been hydrothermally pretreated at three severity factors (log ) of 3.65, 3.83 and 3.97. The LRRs had different residual carbohydrate levels-the highest in MS; the lowest in WS. The residual carbohydrate was not traceable at the surface of the LRRs particles by ATR-FTIR analysis. The chemical properties of the lignin in the LRRs varied across the three types of biomass, but monolignols composition was not affected by the severity factor. When pure cellulose was added to a mixture of LRRs and a commercial cellulolytic enzyme preparation, the rate and extent of glucose release were unaffected by the presence of LRRs regardless of biomass type and severity factor, despite adsorption of the enzymes to the LRRs. Since the surface of the LRRs particles were covered by lignin, the data suggest that the retardation of enzymatic cellulose degradation during extended reaction on lignocellulosic substrates is due to physical blockage of the access of enzymes to the cellulose caused by the gradual accumulation of lignin at the surface of the biomass particles rather than by nonproductive enzyme adsorption.
The study suggests that lignin from hydrothermally pretreated grass biomass retards enzymatic cellulose degradation by acting as a physical barrier blocking the access of enzymes to cellulose rather than by inducing retardation through nonproductive adsorption of enzymes.
众所周知，木质素会阻碍生物精炼过程中木质纤维素的高效酶促转化。特别是，纤维素酶在木质素上的非生产性吸附被认为是解释木质素如何在延长反应中阻碍酶促纤维素转化的关键机制。
通过对玉米秸秆（亚种 ）、×茎（MS）和小麦秸秆（ ）（WS）样品进行广泛的酶促纤维素降解制备了富含木质素的残渣（LRR），每个样品都在3.65、3.83和3.97的三个严重程度因子（log ）下进行了水热预处理。LRR具有不同的残余碳水化合物水平——MS中最高；WS中最低。通过ATR-FTIR分析，在LRR颗粒表面无法检测到残余碳水化合物。LRR中木质素的化学性质因三种生物质类型而异，但单木质醇组成不受严重程度因子的影响。当将纯纤维素添加到LRR和商业纤维素分解酶制剂的混合物中时，无论生物质类型和严重程度因子如何，葡萄糖释放的速率和程度都不受LRR存在的影响，尽管酶吸附到了LRR上。由于LRR颗粒表面被木质素覆盖，数据表明在木质纤维素底物上延长反应期间酶促纤维素降解的延迟是由于木质素在生物质颗粒表面逐渐积累导致酶无法接触到纤维素的物理阻碍，而不是由于非生产性酶吸附。
该研究表明，水热预处理草类生物质中的木质素通过作为物理屏障阻止酶接触纤维素来延迟酶促纤维素降解，而不是通过酶的非生产性吸附诱导延迟。
