稀酸预处理可打破木质纤维原料天然抗降解屏障, 提高后续酶解和发酵效率, 从而使其更高效地转化为生物燃料, 然而在亚细胞水平上纤维细胞壁的解构机理仍有待深入研究。 采用共聚焦显微拉曼光谱技术与主成分聚类分析法结合, 研究了稀酸预处理前后马尾松细胞壁区域化学变化特点。 结果表明, 累计贡献率高达94.61%的第一与第二主成分空间中光谱样本散点呈现规律性分布; 聚类分析可准确提取细胞壁不同形态区域平均拉曼光谱。 结合拉曼成像分析发现, 细胞角隅木质化程度高, 含有较多木质素, 次生壁木质化程度低, 含有较多碳水化合物。 稀酸预处理导致马尾松细胞壁发生了不均一解构, 其致密空间结构被破坏, 次生壁中碳水化合物典型特征峰2 890 cm-1处信号强度降低了26.9%, 表明碳水化合物从该区域大量脱除; 碳水化合物在复合胞间层少量脱除, 而细胞角隅则出现了其轻微富集。 木素在稀酸预处理后发生了重新分布, 细胞角隅区拉曼信号显著增强。 碳水化合物(主要为半纤维素)的溶出及木质素的重新分布削弱了生物质原料的抗降解性, 有利于后续酶解糖化。 该研究不仅提供了一种快速、 高效的纤维细胞壁区域化学分析方法, 还为林木生物质高值转化的研究奠定了重要的理论基础。

Dilute acid pretreatment (DAP) is an attractive method to overcome the natural recalcitrance of lignocellulosic materials, the enzymatic conversion of which can be improved significantly. Therefore, lignocellulosic biomass can be converted to biofuels with a higher efficiency. However, the mechanism of cell wall deconstruction during DAP on sub-cell level is still unclear. In this study, the topochemical changes of Pinus massonianafiber cell walls after DAP was investigated using confocal Raman microscopy combined with principal component analysis and cluster analysis. The samples were presented with specific distribution in the first and second principal component space, which were with cumulative contribution of 94.61%. The accurate average Raman spectra from different lamellas of cell walls were obtained by cluster analysis. With Raman imaging combined, it was observed that the high-lignified cell corner (CC) was with a high concentration of lignin and the low-lignified secondary wall (SW) was with a high concentration of carbohydrates. The heterogeneity of cell wall deconstruction in Pinus Massoniana during DAP was alsovisualized; the compact structure of raw materials was disrupted. The Raman intensity of typical carbohydrates bans at 2890 cm-1 in the SW decreased 26.9% when compared with that for untreated samples, which indicated thatvast carbohydrates were removed from the SW. A certain amount of carbohydrates was also removed from the compound middle lamella (CML), but slight carbohydrates enrichment was observed in the cell corner. Lignin redistributed during DAP and therefore the Raman intensity of lignin in cell corner was enhanced. The removal of carbohydrates (mainly hemicelluloses) and the lignin redistribution can improve the enzymatic hydrolysis by increasing the cellulose accessibility. The present study not only provides a convenient and efficient method for investigating topochemistry of fiber cell walls, but also brings new insights into studying the high-value conversion of lignocellulosic biomass.