Hemicellulose hydrolysis lignin removal

Schwald, W., Brownell, H. H., and Saddler, J. N. 1988. Enzymatic hydrolysis of steam treated aspen wood influence of partial hemicellulose and lignin removal prior to pretreatment. J. Wood Chem. Technol, 5(4), 543-560. 

Ohgren K, Bura R, Saddler J, Zacchi G. (2007). Effect of hemicellulose and lignin removal on enzymatic hydrolysis of steam prelreated com stover. Bioresour Technol, 98, 2503-2510. 

Lignin is a high-energy content biopolymer rich in phenolic components. It provides structural integrity to plants. The combination of hemicellulose and lignin provide a protective sheath around the cellulose and this sheath must be modified or removed before efficient hydrolysis of cellulose can occur. 

Sugars in ARP liquid exist only in oligomer form, i.e., xylo-oligosaccharides (XOS). After acid hydrolysis of the ARP liquor, large amount of xylose monomer appears. It proves that hemicellulose sugars in the ARP liquor is either in the form of XOS or lignin carbohydrate complex. Hemicellulose removal in ARP is proportional to the extent of lignin removal. The reason for this is unclear at this time. 

Figure 6. Effect ofxylan removal (a) and lignin removal (b) on enzymatic digestibility of cellulose produced by hemicellulose hydrolysis of com stover at the conditions noted.

Cellulose nanowhiskers (CNWs), also known as cellulose nanocrystals (CNCs) or nanocrystalline cellulose, are usually produced by the acid hydrolysis of natural cellulosic material after removing nonceUulosic substances such as dewaxing, hemicelluloses, and lignin. Most CNWs show a high crystallinity index and a lower aspect ratio. Thus it is expected that CNWs extracted from tunicates exhibit a high... 

Processes need to be developed to expose LHC for effective penetration of chemicals that promote separation of LHC or which render cellulose accessible by swelling. These processes can have many objectives (1) to get at cellulose (2) to remove hemicellulose from the reaction site before cellulose hydrolysis (3) to remove lignin from the site and (4) to bring penetrating or hydrolysis agents into effective contact with cellulose. 

Lignin is a complex phenolic cell wall polymer that is chemically cross-linked with hemicellulose and cell wall proteins. Most of the methods to determine lignin content are based on the removal of all other cell wall constituents, typically through acid hydrolysis, which will readily remove hemicellulose under mild conditions, and non-crystalline cellulose under more severe conditions. Several different methods will be discussed below. The different methods have also been extensively reviewed and compared by Hatfield et al. (1994), Brinkmann et al. (2002), Fukushima and Hatfield (2004), and Hatfield and Fukushima (2005). 

The production of fuel ethanol from renewable lignocellulosic material ("bioethanol") has the potential to reduce world dependence on petroleum and to decrease net emissions of carbon dioxide. The lignin-hemicellulose network of biomass retards cellulose biodegradationby cellulolytic enzymes. To remove the protecting shield of lignin-hemicellulose and make the cellulose more readily available for enzymatic hydrolysis, biomass must be pretreated (1). 

---