Determination of cell wall ferulic and p-coumaric acids in sugarcane bagasse

To completely determine ferulic and p-coumaric acids and related phenolic compounds in the cell walls of sugarcane bagasse (SCB), a second mild alkaline hydrolysis of the alkali-soluble lignin preparations and acid hydrolysis of the 90% acidic dioxane-soluble lignin fractions were performed, which released 48.8% of the total ester-linked p-CA and 43.8% of the total esterified FA from the alkali-soluble lignin fractions, and 38.8% of the total ether-linked p-CA and 38.5% of the total ether-linked FA from the 90% acidic dioxane-soluble lignin preparations, respectively. Based on the dry weight, it has been found that the SCB contained 1.76% p-CA and 1.29% FA as well as minor quantities of related phenols. Further study of the solubilized lignin samples by combining with UV and FT-IR spectroscopy, and 1H and 13C NMR spectroscopy confirmed that a predominant amount of p-CA (69.5-76.4%) is ester-linked to the cell wall components, mainly to lignin. On the other hand, about half of the FA (44.0-55.0%) is esterified to the cell wall hemicelluloses, and the remaining half of the FA is also be etherified through the phenolic oxygen to lignin component in the cell walls of SCB.