Identification Of Cell Wall Bound Phenolics For Biomass Degradation In Energy Plants

Biofuels produced from lignocellulose are energetic, economic and environmental advantages in comparison with fossil fuels. However, the recalcitrant structures of lignocellulose need a pretreatment step to break up barriers caused by complex cross-linking of cell walls. The purpose of pretreatment is to alter the lignocellulose macroscopic and microscopic structure as well as its sub-microscopic chemical composition, and to improve the rate of enzyme hydrolysis for increasing yields of fermentable sugars. Nowadays, various strategies have been developed for effective utilization of lignocellulosic biomass. Thus, understanding of cell walls composition, polymerization, and regulation will give insight into manipulating rationally cell walls of bioenergy crops.This research included identification of the cell wall bound phenolics and determination of biomass degradation in Miscanthus and rice in order for finding out the key factors that determine lignocellulose degradability.The composition of cell wall polysaccharides and phenolics were analyzed in mature stems of several Miscanthus genotypes and rice T-DNA insertion mutants. There was little content of amorphous cellulose (3.37-6.14%), pectic polysaccharides (0.7-7.39%), acid soluble lignin (1.83-5.01%) in Miscanthus and rice straw. The highest content of hemicelluloses (31.6%) and acid-insoluble lignin (29.4%) were in Miscanthus, with the lowest content of crystalline cellulose (31.96%). The main monosaccharides of 4M KOH extraction fraction from Miscanthus and rice straw were xylose and arabinose. More coniferyl (G) and sinapyl (S) monolignins were detected by HPLC in Miscanthus straw than rice, with a similar content of p-coumaryl (H). The ratios of (G+S)/H is 2.6-2.9 in Miscanthus, and the ratios of (G+S)/H is 1.39-2.08 in rice, which indicates that the lignification of Miscanthus cell walls is stronger than one in rice. We identified eight main phenolics bound in Miscanthus and rice cell walls, and found varied concentration and proportion. Total content of ester-bound phenolics was 1.87-4.59mg/g in different Miscanthus genotypes, whereas rice was 1.97±0.14 mg/g. Ferulic acid was 48.1-62.5%, indicating an association with cell wall polymers by ether bonds mostly. P-coumaric acid was 51.9-76.6%, suggesting an association with cell wall polymers to most degree by ester bonds. There was a little variation in degree of polymerization of residues from different cell wall isolation procedures in all samples. Finally, the pretreatment by alkaline at room temperature is very promising in increasing effectiveness and reducing the cost in terms of the degradation of Miscanthus and rice.