Kim Youngmi, Kreke Thomas, Mosier Nathan S, Ladisch Michael R
Laboratory of Renewable Resources Engineering, Purdue University, West Lafayette, Indiana, 47907-2022; Department of Agricultural and Biological Engineering, West Lafayette, Indiana, 47907-2022.
Biotechnol Bioeng. 2014 Feb;111(2):254-63. doi: 10.1002/bit.25009. Epub 2013 Aug 22.
Single stage and multi-stage liquid hot water pretreatments of mixed hardwood pinchips were investigated at various severities (log R0 = 3.65-4.81) to assess the efficiencies of the pretreatments with respect to achieving high pentose sugar yields and improved enzymatic digestibility of pretreated cellulose. We investigate the effect of pretreatment parameters that is, temperature, and time, as expressed in the severity factor, on the recovery of sugars and hydrolyzability of pretreated cellulose. We find the severity factor, in its widely used form, is an incomplete measure for evaluating the pretreatment efficiencies and predicting overall sugar yields when pretreatment temperatures above 200°C are used. Corrections to the severity factor and its correlation to the measured pretreatment responses (% xylan solubilization, xylan recovery as fermentable sugars, cellulose enzymatic digestibility) indicate a greater influence of temperature on the pretreatment efficiencies than predicted by the commonly used severity factor. A low temperature, long residence time is preferred for hemicellulose dissolution during the pretreatment since the condition favors oligosaccharide and monomeric sugar formation over sugar degradation. On the contrary, high cellulose hydrolyzability is achieved with a high temperature (>200°C), high severity pretreatment when pretreatment is followed by enzyme hydrolysis. In multi-stage pretreatment, the first low-severity pretreatment is optimized for solubilizing fast-hydrolyzing hemicellulose while minimizing formation of furans. The subsequent pretreatment is carried out at over 200°C to recover the difficult-to-hydrolyze hemicellulose fraction as well as to increase susceptibility of pretreated cellulose to enzymes. High recovery (>92%) of hemicellulose-derived pentose sugars and enhanced enzymatic hydrolysis of pretreated cellulose (where >80% glucose yield results with 20 FPU = 32 mg protein/g glucan or 10-13 mg/g initial hardwood) are achieved by applying a multi-stage pretreatment. This work shows how the severity equation may be used to obtain a single characteristic curve that correlate xylan solubilization and enzymatic cellulose hydrolysis as a function of severity at pretreatment temperatures up to 230°C.
研究了混合硬木片的单级和多级液态热水预处理在不同反应程度下（对数R0 = 3.65 - 4.81）的情况，以评估预处理在实现高戊糖产率和提高预处理纤维素酶解性方面的效率。我们研究了预处理参数（即温度和时间，以反应程度因子表示）对糖回收率和预处理纤维素水解性的影响。我们发现，当使用高于200°C的预处理温度时，广泛使用形式的反应程度因子是评估预处理效率和预测总糖产率的不完整指标。对反应程度因子的修正及其与实测预处理响应（木聚糖溶解百分比、作为可发酵糖的木聚糖回收率、纤维素酶解性）的相关性表明，温度对预处理效率的影响比常用反应程度因子预测的更大。预处理期间，低温、长停留时间有利于半纤维素溶解，因为这种条件有利于寡糖和单糖形成而非糖降解。相反，当预处理后进行酶水解时，高温（>200°C）、高反应程度的预处理可实现高纤维素水解性。在多级预处理中，第一次低反应程度预处理针对快速水解的半纤维素溶解进行优化，同时尽量减少呋喃的形成。随后的预处理在200°C以上进行，以回收难水解的半纤维素部分，并提高预处理纤维素对酶的敏感性。通过应用多级预处理，可实现半纤维素衍生戊糖的高回收率（>92%）和预处理纤维素的增强酶解（其中20 FPU = 32 mg蛋白质/克葡聚糖或10 - 13 mg/克初始硬木时葡萄糖产率>80%）。这项工作展示了如何使用反应程度方程获得一条单一特征曲线，该曲线将木聚糖溶解和酶解纤维素水解与高达230°C预处理温度下的反应程度关联起来。
