Renewable bio ionic liquids-water mixtures-mediated selective removal of lignin from rice straw: Visualization of changes in composition and cell wall structure

• Published in: Biotechnology and bioengineering 2013-07, Vol.110 (7), p.1895-1902
• Main Authors: Hou, Xue-Dan, Li, Ning, Zong, Min-Hua
• Format: Article
• Language: English
• Subjects: Amino acids; Biomass; Carbohydrates; Cell Wall - ultrastructure; Cells; Cellulose - metabolism; cholinium amino acids ionic liquids; delignification; enzymatic hydrolysis; Enzymes; Glucose - metabolism; Ionic Liquids - chemistry; Lignin - isolation & purification; lignin distribution; lignocellulosic biomass; Microscopy, Confocal; Microscopy, Electron, Transmission; Oryza - chemistry; Oryza - cytology; Oryza sativa; Plant Stems - chemistry; pretreatment; Solvents - chemistry; Water - chemistry; Xylose - metabolism
• ISSN: 0006-3592; 1097-0290
• DOI: 10.1002/bit.24862

Pretreatment of rice straw by using renewable cholinium amino acids ionic liquids ([Ch][AA] ILs)‐water mixtures and the subsequent enzymatic hydrolysis of the residues were conducted in the present work. Of the eight mixtures composed of ILs and water, most were found to be effective for rice straw pretreatment. After pretreatment with 50% ILs‐water mixtures, the enzymatic digestion of the lignocellulosic biomass was enhanced significantly, thus leading to satisfactory sugar yields of >80% for glucose and approximately 50% for xylose. To better understand the ILs pretreatment mechanism, confocal laser scanning microscopy combined with immunolabeling and transmission electron microscopy were used to visualize changes in the contents and distribution of two major components—lignin and xylan. The results coupled with changes in chemical structures (infrared spectra) of the substrates indicated occurrence of extensive delignification, especially in cell corner and compound middle lumen of cell walls, which made polysaccharides more accessible to enzymes. This pretreatment process is promising for large‐scale application because of the high sugar yields, easy handling, being environmentally benign and highly tolerant to moisture, and significantly reduced cost and energy consumption. Biotechnol. Bioeng. 2013; 110: 1895–1902. © 2013 Wiley Periodicals, Inc. [Ch][AA] ILs‐water mixtures proved to be highly promising solvents for lignocellulosic biomass pretreatment under mild conditions. Good sugar yields were obtained in the enzymatic hydrolysis of rice straw after pretreatment using these mixtures at 90°C. The changes in the contents and distribution of the main components in cell walls were visualized by microscopic techniques.