蒸汽预处理玉米秸秆酶水解速率下降的因素分析

为评价导致纤维素酶水解速率下降的因素，以底物质量浓度为50 g/L葡聚糖及酶用量为20 FPIU/g滤纸酶活和10 IU/g β-葡萄糖苷酶活的蒸汽预处理玉米秸秆酶水解为研究对象，探讨了影响酶水解速率的潜在因素，包括物料反应性能、纤维素酶非特异性吸附、酶失活及终产物抑制。结果表明：酶用量40 FPIU/g条件下酶水解6 h及12 h后，蒸汽预处理玉米秸秆的物料反应性能分别下降了16.0%及23.7%，然而，在酶用量为20 FPIU/g时，物料反应性能的下降对酶水解速率的影响极其有限；酶解木质素的添加使得1 h酶解上清液中酶蛋白浓度降低了20.8%，但初始酶水解速率并未显著降低，即木质素对纤维素酶的非特异性吸附对酶水解速率影响不大；两段酶水解中纤维素酶的更新使得7h酶水解速率由一段酶水解中的1.30 g/(L·h)提高至1.83 g/(L·h)；两段酶水解中终产物的去除则使得7 h酶水解速率提高至4.76 g/(L·h)，是一段酶水解中7 h酶水解速率的3.66倍。综合而言，酶失活及终产物抑制对酶水解速率影响较大，其中终产物抑制是导致蒸汽预处理玉米秸秆酶水解速率降低的关键因素。

Evaluation of the Factors Contributing to Declining Enzymatic Hydrolysis Rates of Steam Pretreated Corn Stover

To evaluate the factors contributing to the decreasing enzymatic hydrolysis rates, the potential factors, including substrate reactivity, enzyme non-productive binding, enzyme deactivation and end-product inhibition, were investigated in enzymatic hydrolysis of steam pretreated corn stover (SPCS), with solid concentration of 50 g/L glucan and enzyme loading including 20 FPIU/g glucan of filter paper activity and 10 IU/g glucan of β-glucosidase activity. The results showed that the substrate reactivity of SPCS decreased 16. 0% and 23. 7%, respectively, after hydrolysis for 6 h and 12 h. But the effects of the decline in substrate reactivity on enzymatic hydrolysis rates were limited, with enzyme loading including 20 FPIU/g glucan of filter paper activity and 10 IU/g glucan ofβ-glucosidase activity. The enzymatic residual lignin addition reduced the enzyme concentration in supernatant by 20. 8% at 1 h, but this did not reduce the initial hydrolysis rates. This indicated that enzyme non-productive binding on lignin did not influence the enzymatic hydrolysis rates obviously. Enzyme renewal in two-stage hydrolysis increased hydrolysis rate for 7 h from 1. 30 g/( L ·h) in one-stage hydrolysis to 1. 83 g/(L·h). While the end-product removal in two-stage hydrolysis raised hydrolysis rate for 7 h to 4. 76 g/(L·h), which was 3. 66 folds higher than that in one-stage hydrolysis. Generally, the results revealed that the enzyme deactivation and the end-product inhibition showed the obvious effects on enzymatic hydrolysis rates. Moreover, the end-product inhibition was the dominating factors for the declining hydrolysis rates of SPCS.