破解吸附型灰分对木质纤维水热预处理和酶水解影响的策略与机理

According to the composition characteristics of waste wheat straw containing higher content of adsorbed ash, a comprehensive study will be carried out to break the buffering system derived from adsorbed ash during hydrothermal pretreatment, and thus improving the yields of xylo-oligosaccharides as well as enzymatic saccharification. Specifically, the formation mechanism and influential factors of buffering system derived from adsorbed ash in the process of hydrothermal pretreatment will be investigated, as well as the corresponding breaking buffering system strategy and its potential mechanism, and the effects of the stronger weakly acidic condition during hydrothermal pretreatment on lignin structure and the influential factors of cellulose saccharification. Based on a series of research, the project will reveal the formation mechanism of buffering system derived from adsorbed ash during hydrothermal pretreatment, lignin structure changes, lignin migration pattern, and the changes on characteristics of pretreated substrates correlated with enzymatic saccharification under the stronger weakly acidic condition during the pretreatment. The result can provide basis for design of the co-production technology of bio-sugars and xylo-oligosaccharides from the waste cellulosic residues containing high adsorbed ash content.

本项目针对麦糠纤维素废弃物吸附型灰分含量高的组成特点，围绕破解吸附型灰分在水热预处理过程中形成的缓冲体系，提高水热预处理过程中低聚木糖溶出率和预处理物料酶水解性能，开展吸附型灰分水热预处理中缓冲体系形成机制及影响因素、破坏吸附型灰分形成缓冲体系的技术方法与机理、水热预处理弱酸性反应环境增强对木质素的作用以及对与纤维素糖化相关的底物因子的影响作用等研究。阐明吸附型灰分在水热预处理过程中形成缓冲体系的机制，解析原料中木质素在水热预处理弱酸性反应环境增强条件下的结构变化和迁移规律，揭示弱酸性反应环境增强对与纤维素糖化相关的底物因子的影响机制。研究结果可为设计吸附型灰分含量高的纤维素废弃物高效生产生物质糖并联产低聚木糖的技术方法提供理论依据。

项目研究了麦糠水热预处理中吸附型灰分缓冲体系形成机理及影响因素、破坏缓冲体系的技术方法及机理、水热预处理弱酸性反应环境增强对木质素结构和纤维素糖化相关底物因子的影响和麦糠高效生产生物质糖并联产低聚木糖集成技术的建立。主要结论如下：.（1）麦糠吸附型灰分中不溶性矿物和有机质均使预处理体系弱酸性反应环境减弱，其中不溶性矿物负面影响最大。不溶性矿物与H+的阳离子交换反应是吸附型灰分在麦糠水热预处理过程中形成缓冲体系的主要原因，水热预处理体系弱酸性反应环境产生的H+因其阳离子交换能力高于K+、Na+、Ca2+、Mg2+等离子，致使H+与吸附型灰分中不溶性矿物所吸附的上述金属离子发生交换作用，原先与不溶性矿物结合的K+、Na+、Ca2+、Mg2+等离子被置换进入液相，导致水热预处理的弱酸性反应环境减弱。.（2）麦糠水热预处理过程中添加Fe3+，可消除麦糠水热预处理形成的缓冲体系，使水热预处理弱酸性反应环境增强。交换性金属盐Fe3+的引入可使麦糠水热预处理液pH值下降，麦糠水热预处理的弱酸性环境得到增强。当添加20 mmol/L FeCl3至麦糠水热预处理中，预处理液中低聚木糖浓度可从2.8 g/L提高至6.2 g/L，预处理麦糠的纤维素酶水解得率从49.7%增加至66.6%。.（3）水热预处理过程中Fe3+的引入降低了残留木质素与纤维素酶的非生产性结合，麦糠（WWS）中木质素（MWL）对蛋白质的吸附量从MWLRaw中的11.9 mg/g下降到4.3 mg/g。预处理后的WWS的MWL表面电荷分别从-19.5 mV (MWLRaw)下降到-16.2 mV (MWLFe-100)，疏水性分别从1.1 L/g (MWLRaw)降低到0.5 L/g (MWLFe-100) 。此外，Fe3+的引入使麦糠中木质素发生解聚，β-O-4键、β-β和β-5键的含量降低，而木质素的总酚缩合型羟基和非缩合型羟基含量增加。Fe3+的引入使预处理麦糠中木质素疏水性和电负性降低、官能团变化，削弱了纤维素酶与木质素的结合力，提高了预处理麦糠的酶解效率。.（4）通过破解麦糠中灰分缓冲体系对酶水解的影响，建立了基于FeCl3辅助的麦糠水热预处理方法，1.0 kg麦糠生产低聚木糖和葡萄糖的含量从27.7 g和137.9 g分别提高至62.0 g和160.6 g。