Peciulyte Ausra, Karlström Katarina, Larsson Per Tomas, Olsson Lisbeth
Department of Biology and Biological Engineering, Division of Industrial Biotechnology, Chalmers University of Technology, Kemivägen 10, Gothenburg, SE-412 96 Sweden.
Innventia AB, Drottning Kristinas väg 61, Stockholm, SE-114 86 Sweden.
Biotechnol Biofuels. 2015 Apr 1;8:56. doi: 10.1186/s13068-015-0236-9. eCollection 2015.
The efficiency of enzymatic hydrolysis is reduced by the structural properties of cellulose. Although efforts have been made to explain the mechanism of enzymatic hydrolysis of cellulose by considering the interaction of cellulolytic enzymes with cellulose or the changes in the structure of cellulose during enzymatic hydrolysis, the process of cellulose hydrolysis is not yet fully understood. We have analysed the characteristics of the complex supramolecular structure of cellulose on the nanometre scale in terms of the spatial distribution of fibrils and fibril aggregates, the accessible surface area and the crystallinity during enzymatic hydrolysis. Influence of the porosity of the substrates and the hydrolysability was also investigated. All cellulosic substrates used in this study contained more than 96% cellulose.
Conversion yields of six cellulosic substrates were as follows, in descending order: nano-crystalline cellulose produced from never-dried soda pulp (NCC-OPHS-ND) > never-dried soda pulp (OPHS-ND) > dried soda pulp (OPHS-D) > Avicel > cotton treated with sodium hydroxide (cotton + NaOH) > cotton.
No significant correlations were observed between the yield of conversion and supramolecular characteristics, such as specific surface area (SSA) and lateral fibril dimensions (LFD). A strong correlation was found between the average pore size of the starting material and the enzymatic conversion yield. The degree of crystallinity was maintained during enzymatic hydrolysis of the cellulosic substrates, contradicting previous explanations of the increasing crystallinity of cellulose during enzymatic hydrolysis. Both acid and enzymatic hydrolysis can increase the LFD, but no plausible mechanisms could be identified. The sample with the highest initial degree of crystallinity, NCC-OPHS-ND, exhibited the highest conversion yield, but this was not accompanied by any change in LFD, indicating that the hydrolysis mechanism is not based on lateral erosion.
纤维素的结构特性会降低酶促水解的效率。尽管人们已努力通过考虑纤维素分解酶与纤维素的相互作用或酶促水解过程中纤维素结构的变化来解释纤维素酶促水解的机制，但纤维素水解过程仍未被完全理解。我们已从纳米尺度分析了纤维素复杂超分子结构的特征，包括原纤维和原纤维聚集体的空间分布、可及表面积以及酶促水解过程中的结晶度。还研究了底物孔隙率和可水解性的影响。本研究中使用的所有纤维素底物均含有超过96%的纤维素。
六种纤维素底物的转化率如下，从高到低依次为：从未干燥的苏打浆制得的纳米晶纤维素（NCC - OPHS - ND）＞从未干燥的苏打浆（OPHS - ND）＞干燥的苏打浆（OPHS - D）＞微晶纤维素＞经氢氧化钠处理的棉花（棉花 + NaOH）＞棉花。
在转化率与超分子特征（如比表面积（SSA）和横向原纤维尺寸（LFD））之间未观察到显著相关性。发现起始材料的平均孔径与酶促转化率之间存在强相关性。在纤维素底物的酶促水解过程中，结晶度得以保持，这与先前关于纤维素在酶促水解过程中结晶度增加的解释相矛盾。酸水解和酶促水解均可增加LFD，但未发现合理的机制。初始结晶度最高的样品NCC - OPHS - ND表现出最高的转化率，但LFD没有任何变化，这表明水解机制并非基于横向侵蚀。
