Lignin and Associated Phenolic Acids in Cell Walls

Abstract

Abstract Many types of phenolic compounds are found in cell wall preparations or as insoluble residues remaining after the extraction of metabolites soluble in organic solvents. This chapter describes procedures for the isolation and analysis of lignin and other phenolic compounds from plant material. Since most analytical methods for phenolic compounds are specific for phenolic hydroxy-groups, it is essential that all soluble phenolic compounds are extracted from the tissue during the preparation of the insoluble residue or cell wall fraction. Many simple phenolic compounds may not be completely extracted by nonaqueous organic solvents. Indeed, the removal of water by acetone or methanol may cause hydrogen-bonding of phenolic compounds, such as chlorogenic acid, to the insoluble residue leading to spurious results. Moreover, it is possible for phenolic compounds to be oxidized by endogenous phenolases, during the extraction procedure. The oxidation products of compounds, such as chlorogenic acid, can then chemically react with freeNH2 or -SH groups on amino acid side chains to yield complex oxidation products bound to protein. This may be cell wall protein itself, or protein which is hydrogen bonded to the cell wall during the extraction procedure.