共聚焦显微拉曼光谱在木质纤维细胞壁预处理中的应用进展

在能源紧缺和环境恶化的双重压力下，利用农林生物质替代化石资源生产生物燃料、生物基化学品和材料逐步发展成为世界范围内的研究热点，而细胞壁中纤维素、半纤维素、木质素以及其他少量组分的空间分布不均一性和化学结构复杂性构成了天然抗降解屏障，严重阻碍生物质的转化效率，因此需要对木质纤维原料进行预处理，以期破坏细胞壁的宏观壁垒，实现生物质的低成本高效转化。在此过程中，全面了解木质纤维细胞壁的化学组成、结构特性及其在生物质转化过程中的解构机理是高效利用农林生物质的重要前提。由于拉曼光谱具有样品制备要求低、灵敏度高、且能在原位状态下对样品进行定性、定量分析等特点，使得拉曼光谱成为研究木质细胞壁结构的有力工具。尤其与显微技术相结合时，可以同时获得木质纤维细胞壁主要组分的微区分布与超分子结构信息，实现生物质转化过程中化学组分动态变化的可视化研究。首先介绍了拉曼光谱成像的工作原理，并对纤维素、半纤维素和木质素的拉曼特征信号进行了归属。其次，总结了近几年拉曼光谱在生物质转化领域内的应用与研究进展，综述了拉曼光谱在未处理状态下以及稀酸、水热、稀碱等不同预处理过程中的分析方法，对细胞壁主要组分的分布进行表征，以揭示预处理过程中各组分的溶出过程及迁移规律，为在细胞及亚细胞水平探究预处理诱导细胞壁主要组分动态溶解机制提供了有效路径。此外，针对检测中收集的光谱数量过多、分析难等问题，文章重点介绍了主成分聚类分析法和顶点成分分析法两种拉曼数据分析方法，用于提取特征信息并对光谱进行分类研究，以深入探究特定组分的空间分布和分子结构。最后，根据上述分析展望了拉曼光谱在生物质转化领域的研究趋势，为相关研究提供技术参考。

Advances in the Application of Confocal Raman Spectroscopy in Lignocellulosic Cell Walls Pretreatment

In light of the gradual depletion of fossil fuels and emerging environmental concerns,there is a hot topic to make use of lignocellulosic biomass to produce biobased value-added fuels,chemicals,and materials worldwide.However,bioconversion is normally hindered by the complex structure and heterogeneous components(cellulose,hemicelluloses,lignin and pectin)distribution in the cell wall assembly.Therefore,to overcome the recalcitrance,biomass pretreatment became an essential step towards low-cost biomass conversion.In this process,it is greatly importance to have a comprehensive understanding of the chemical composition,structural characteristics of cell walls and their deconstruction mechanism in biomass conversion for efficient utilization of agroforestry biomass.Raman spectroscopy has been used to investigate the structure of cell walls at a multi-scale due to its simple sample preparation,high sensitivity,and quantitative and qualitative analysis of the characteristics of samples in situ.Moreover,the chemical structure of the main components of cell walls and micro-zone distribution information can be provided by Raman spectroscopy combined with microtechnique to realize the dynamic change of composition of visualization research.Firstly,it introduces the working principle of Raman spectroscopy.On account that cellulose,hemicellulose and lignin have different Raman characteristic signals.The concentration and distribution of different components in a certain region can be calculated by integrating the characteristic Raman bands.Secondly,the research progress of Raman spectroscopy application in the field of biomass conversion was summarized.It is especially reviewed that the analysis methods for revealing the spatial distribution pattern and migration regularity of main components within cell walls during dilute acid,hydrothermal and alkali pretreatment processes.It provides an effective way to explore the dynamic dissolution mechanism of cell wall components induced by biomass pretreatments at cellular and subcellular levels.In addition,to solve the problems of excessive number of collected spectra and difficult analysis,this work mainly introduces two Raman data analysis methods,namely principal component clustering analysis and vertex component analysis,which are used to extract characteristic information and perform spectral classification,so as to further explore the spatial distribution and molecular structure of specific components.Finally,based on the above analysis,we also discuss the future challenges and prospects of Raman spectroscopy in the field of biomass conversion,which will provide technical reference for related research.