乙酸⁃亚硫酸盐两步预处理对杨木木质素吸附纤维素酶的影响

Effect of acetic acid-sulfite two-step pretreatment on the adsorption of poplar lignin toward cellulase

以杨木为原料,采用乙酸预处理制备低聚木糖后,对固体残渣进行亚硫酸盐预处理移除木质素,以提高杨木纤维素的酶解效率,但该两步预处理对杨木木质素结构及其非生产性吸附酶的影响仍不明确。笔者考察了乙酸-亚硫酸盐两步预处理对杨木酶水解率、木质素结构和木质素理化性质的影响,探讨了该两步预处理对杨木木质素吸附及脱附纤维素酶的特性。结果表明,两步预处理后杨木残渣中木质素含量减少,当酶添加量为20 FPU/g干物质量时,纤维素水解得率从32.4%增加到67.1%。乙酸-亚硫酸盐预处理后木质素(AA-AS-lignin)的Zeta电位、疏水性及分子量减小,而其紫丁香基与愈创木基结构单元数量比值S/G、酚羟基及硫元素的含量增加。相比未预处理的木质素(BM-lignin),AA-AS-lignin对纤维素酶水解的抑制率从1.0%增加到16.5%。AA-AS-lignin对纤维素酶的吸附增强,结合强度从24.7 mL/g(BM-lignin)增大到72.1 mL/g。乙酸-亚硫酸盐预处理降低了木质素对纤维素酶的脱附能力,纤维素酶的脱附回收率从61.1%降低到28.8%,且相较于BM-lignin,结合在AA-AS-lignin上的纤维素酶的水解活力较低。研究结果可指导乙酸-亚硫酸盐预处理后杨木的高效纤维素酶水解,为实现杨木的多组分转化利用提供了新思路。

Recently,efficient production of xylo-oligosaccharides from poplar by acetic acid(AA)pretreatment was developed,but the content of residual lignin in poplar after the AA pretreatment could be risen to 30%,which had adverse impact on subsequent cellulase hydrolysis of poplar.In this work,poplar was pretreated by AA to produce xylo-oligosaccharides firstly,and then the AA-pretreated poplar residues were pretreated with sulfite to remove lignin for achieving efficient enzymatic hydrolysis of cellulose in poplar.Effects of acetic acid-sulfite two-step(AA-AS)pretreatment on chemical components and enzymatic hydrolysis yield of poplar,and on the adsorption properties of residual lignin with cellulase after the AA-AS pretreatment were investigated.The results showed that the lignin content in the residue decreased after the AA-AS pretreatment.When the cellulase dosage was 20 FPU/g dry matter,the hydrolysis yield of poplar after the AA-AS pretreatment increased from 32.4%to 67.1%.After the AA-AS pretreatment,the zeta potentials,hydrophobicity,and molecular weights of lignin decreased,while the S/G ratio,phenolic hydroxyl,and sulfur content increased.After the AA-AS pretreatment,compared with the untreated lignin(BM-lignin),the inhibition degree of lignin(AA-AS-lignin)to cellulase hydrolysis increased from 1.0%to 16.5%.The AA-AS pretreatment intensified the binding of lignin with cellulase,and the binding strength increased from 24.7 mL/g(BM-lignin)to 72.1 mL/g(AA-AS-lignin).The AA-AS pretreatment reduced the desorption capacity of cellulase from lignin,the recovery of cellulase from lignin decreased from 61.1%to 28.8%after the pretreatment,and the activity of cellulase bound on the AA-AS-lignin was lower than that on the BM-lignin.The stronger cellulase adsorption capacity of residual lignin after the AA-AS pretreatment might be responsible for its intensified inhibition to cellulose hydrolysis.It was speculated that the increase of phenolic hydroxyl content of lignin after the AA-AS pretreatment might be the main reason for the strong adsorption capacity of the AA-AS-lignin to cellulase.The rigid fiber structure of native poplar materials and the formation of condensed lignin structures in poplar residues during the acetic acid pretreatment at 170℃both might be the reasons for the low removal ratio of lignin by the second step of sulfite pretreatment.The residual lignin in poplar after the AA-AS pretreatment could reduce the hydrolysis efficiency of cellulose in poplar by means of blocking cellulase access and non-productively binding cellulase.Therefore,the conditions(such as temperature and reagent concentration)of the sulfite pretreatment in the second step need to be further optimized to realize the efficient conversion and utilization of hemicellulose and cellulose in poplar.