Guangzhou Institute of Energy Conversion, Key Laboratory of Renewable Energy and Gas Hydrate, Chinese Academy of Sciences, Guangzhou 510640, China.
Appl Biochem Biotechnol. 2012 Sep;168(1):206-18. doi: 10.1007/s12010-011-9468-8. Epub 2012 Jan 22.
Hemicellulose and lignin are the main factors limiting accessibility of hydrolytic enzymes besides the crystallinity of cellulose. The decomposition behavior of hemicellulose and lignin in the step-change flow rate hot water system was investigated. Xylan removal increased from 64.53% for batch system (solid concentration 4.25% w/v, 18 min, 184°C) to 83.78% at high flow rates of 30 ml/min for 8 min, and then 10 ml/min for 10 min. Most of them (80-90%) were recovered as oligosaccharide. It was hypothesized that the flowing water could enhance the mass transfer to improve the sugars recovery. In addition, the solubilization mechanism of lignin in the liquid hot water was proposed according to the results of Fourier transform-infrared spectroscopy and scanning electron microscopy of the water-insoluble fraction and gas chromatography-mass spectrometry of the water-soluble fraction. It was proposed that lignin in the liquid hot water first migrated out of the cell wall in the form of molten bodies, and then flushed out of the reactor. A small quantity of them was further degraded into monomeric products such as vanillin, syringe aldehyde, coniferyl aldehyde, ferulic acid, and p-hydroxy-cinnamic acid. All of these observations would provide important information for the downstream processing, such as purification and concentration of sugars and the enzymatic digestion of residual solid.
除了纤维素的结晶度外，半纤维素和木质素也是限制水解酶可及性的主要因素。研究了在阶跃流速热水系统中半纤维素和木质素的分解行为。与分批系统（固含量 4.25%w/v，18 min，184°C）相比，在 30 ml/min 的高流速下 8 min 后，木聚糖去除率从 64.53%增加到 83.78%，然后在 10 ml/min 下 10 min 后，大部分（80-90%）被回收为低聚糖。据推测，流动水可以增强传质，从而提高糖的回收率。此外，根据水不溶性部分的傅里叶变换红外光谱和扫描电子显微镜以及水溶性部分的气相色谱-质谱的结果，提出了木质素在液态热水中的溶解机制。提出木质素在液态热水中首先以熔融体的形式从细胞壁中迁移出来，然后从反应器中冲洗出来。一小部分木质素进一步降解为单体产物，如香草醛、苯甲醛、松柏醛、阿魏酸和对羟基肉桂酸。所有这些观察结果都将为下游处理（如糖的纯化和浓缩以及残余固体的酶解）提供重要信息。
