高效协同酶解中性汽爆玉米秸秆的工艺优化

Optimization of enzymatic saccharification process forneutral steam exploded corn stover

玉米秸秆是我国主要的农业废弃物之一,在木质纤维素乙醇领域具有广阔的应用前景。而玉米秸秆预处理和酶法糖化成本过高是目前工艺中的重点和难点之一。从4种纤维素降解酶制剂中优选出对中性汽爆玉米秸秆有最佳协同效果的木霉和黑曲霉纤维素酶制剂(6∶4体积比混合)。在此基础上,评估了木聚糖酶、β-葡萄糖苷酶、β-葡聚糖酶、漆酶、锰过氧化物酶等酶制剂,聚乙二醇-4000、吐温-80、牛血清白蛋白等非酶因子对糖化效率的影响,得到了一组高效协同降解汽爆玉米秸秆的复合酶体系,并获得了适宜的糖化工艺。结果表明,以每克中性汽爆预处理的玉米秸秆为底物,加入10FPU木霉/曲霉混合酶液,并添加1000IU的木聚糖酶和0.05 gPEG4000,于50℃/150 r.min-1条件下水解144 h,糖化液中纤维二糖、葡萄糖和木糖的浓度分别达到8.4、25.1、15.5 g.L-1,总转化率、纤维素、半纤维素的转化率分别可以达到71.1%、81.5%和55.3%。糖化产物中六碳糖和五碳糖总浓度达到49 g.L-1。

Corn stover is one of the major agricultural residues in China and could be potential source for ethanol production by saccharification process. But the problem in current process is higher cost for pretreatment and enzymatic saccharification of corn stover. In this paper, four kinds of cellulase candidates （ volume ratio 6 ： 4） were optimized based on the best synergistic effect for the degradation of neutral steam exploded corn stover, and Trichoderma L8 and Aspergillus niger were filtered. Then, the effect of enzymes （xylanase, p-glucosidase, j？-glucanase, laccase, manganese peroxidase） and non-enzyme factors （polyethylenegtycol （PEG） -4000, Tween-80, bovine serum albumin） on saccharification efficiency was evaluated to get a mixed enzyme system which could make steam exploded corn stove high efficient synergistic degradation, and to obtain suitable conditions of saccharification process. The results showed that only xylanase in selected enzymes had positive effects on the saccharification, while for non-enzyme factors polyethylenegiycol （PEG） -4000 and Tween 80 could enhance the saccharification rates. The optimized enzyme was a mixture of Trichoderma L8 cellulase, fl-glucosidase from Aspergillus niger andxylase, and the optimized conditions of enzymatic degradation condition for one gram neutral steam exploded corn stover （10%, W/V） as follows： 10FPU cellulase, plus 1000IU xylanase and 0.05 g PEG- 4000. After incubation at 50°C and 150 r ·min ^1 for 144 h, the final concentration of cellobiose, glucose, and xylose were 8.4 g · L^1, 25. 1 g · L ^1 , and 15.5 g · L 1, and the final conversion of total biomass, cellulose and hemicellulose were 71.1%, 81.5% and 55.3%, respectively. Observation of scanning electron microscope indicated that most the free fiber disappeared within 24 h. Some of the partially destroyed structures in the pretreatment process were also degested slowly with time prolonged.