Ji Zhe, Ma Jianfeng, Xu Feng
Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing 100083, China.
Microsc Microanal. 2014 Apr;20(2):566-76. doi: 10.1017/S1431927614000063. Epub 2014 Feb 19.
Alkali pretreatment is a promising pretreatment technology that can effectively deconstruct plant cell walls to enhance sugar release performance. In this study, multi-scale visualization of dynamic changes in poplar cell walls during sodium hydroxide pretreatment (2% w/v, 121°C) was carried out by light microscopy (LM), confocal Raman microscopy (CRM) and atomic force microscopy (AFM). LM observations indicated that swelling occurred primarily in the secondary wall (S) but alkali had little effect on the cell corner middle lamella (CCML). Correspondingly, there was a preferential delignification in the S at the beginning of pretreatment, while the level of delignification in CCML (88%) was higher than that in the S (83%) for the whole process revealed by Raman spectra. It also suggested that prolonging residence time to 180 min would not remove lignin completely but cause rapid loss of carbohydrates, which was further visualized by Raman spectroscopy images. Furthermore, AFM measurements illustrated that pretreatment with alkali exposed the embedded microfibrils from noncellulosic polymers clearly, enlarged the diameter of microfibrils, and decreased the surface porosity. These results suggested that there was a synergistic mechanism of lignocellulose deconstruction regarding cell wall swelling, main components dissolution, and microfibril morphological changes that occurred during alkali pretreatment.
碱预处理是一种很有前景的预处理技术，它可以有效地解构植物细胞壁，提高糖释放性能。在本研究中，通过光学显微镜（LM）、共聚焦拉曼显微镜（CRM）和原子力显微镜（AFM）对氢氧化钠预处理（2% w/v，121°C）过程中杨树细胞壁的动态变化进行了多尺度可视化。光学显微镜观察表明，肿胀主要发生在次生壁（S）中，但碱对细胞角中间层（CCML）几乎没有影响。相应地，预处理开始时次生壁中优先发生脱木质素，而拉曼光谱显示，整个过程中细胞角中间层的脱木质素水平（约88%）高于次生壁（约83%）。这也表明，将停留时间延长至180分钟不会完全去除木质素，但会导致碳水化合物快速损失，拉曼光谱图像进一步证实了这一点。此外，原子力显微镜测量表明，碱预处理清楚地暴露了非纤维素聚合物中嵌入的微纤丝，增大了微纤丝的直径，并降低了表面孔隙率。这些结果表明，在碱预处理过程中，细胞壁肿胀、主要成分溶解和微纤丝形态变化存在木质纤维素解构的协同机制。
