Extraction of phenolic-carbohydrate complexes from graminaceous cell walls

Barley straw and a preparation of perennial ryegrass were sequentially extracted with oxalic acid, dimethyl sulphoxide (DMSO) and a “cellulolytic” enzyme preparation Driselase and the fractions studied by methylation analysis, 13C NMR and other methods. Oxalic acid, as expected, solubilised the bulk of the arabinose and ferulic acid in both samples, although appreciable amounts of xylose were also solubilised. DMSO yielded polymeric lignin-carbohydrate complexes (LCC), both of which consisted predominantly of a β(1 → 4) xylan. From the results of methylation analysis, sensitivity to oxalic acid hydrolysis and size-exclusion chromatography after alkaline hydrolysis, it was evident that lignin polymers were attached to arabinosyl and xylosyl residues by both ester and aryl-ether linkages. After cellulolytic hydrolysis of the residues, thioacidolysis analysis of the lignin component in the DMSO-soluble and Driselase-insoluble fractions from ryegrass revealed differences in every measurable aspect. The DMSO-soluble lignin was found to be more highly condensed, have a higher S/G ratio and have a higher terminal G/internal G ratio.