Composition of cell wall phenolics and polysaccharides of the potential bioenergy crop - Miscanthus.

The composition and concentrations of cell wall polysaccharides and phenolic compounds were analyzed in mature stems of several Miscanthus genotypes, in comparison with switchgrass and reed ( Arundo donax), and biomass characteristics were correlated with cell wall saccharification efficiency. The highest cellulose content was found in cell walls of M. sinensis'Grosse Fontaine' (55%) and in A. donax (47%) and lowest (about 32%) in M. sinensis'Adagio'. There was little variation in lignin contents across M. sinensis samples (all about 22-24% of cell wall), however, Miscanthus× giganteus (M × g) cell walls contained about 28% lignin, reed - 23% and switchgrass - 26%. The highest ratios of cellulose/lignin and cellulose/xylan were in M. sinensis'Grosse Fontaine' across all samples tested. About the same total content of ester-bound phenolics was found in different Miscanthus genotypes (23-27 μg/mg cell wall), while reed cell walls contained 17 μg/mg cell wall and switchgrass contained a lower amount of ester-bound phenolics, about 15 μg/mg cell wall. Coumaric acid was a major phenolic compound ester-bound to cell walls in plants analyzed and the ratio of coumaric acid/ferulic acid varied from 2.1 to 4.3, with the highest ratio being in M × g samples. Concentration of ether-bound hydroxycinnamic acids varied greatly (about two-three-fold) within Miscanthus genotypes and was also the highest in M × g cell walls, but at a concentration lower than ester-bound hydroxycinnamic acids. We identified four different forms of diferulic acid esters bound to Miscanthus cell walls and their concentration and proportion varied in genotypes analyzed with the 5-5-coupled dimer being the predominant type of diferulate in most samples tested. The contents of lignin and ether-bound phenolics in the cell wall were the major determinants of the biomass degradation caused by enzymatic hydrolysis. [ABSTRACT FROM AUTHOR]