STRUCTURAL VARIABILITY OF LIGNINS AND ASSOCIATED PHENOLIC-ACIDS IN WHEAT-STRAW

Contents and structure of lignins and associated phenolic acids have b een comparatively studied in the different anatomic components of whea t straw (internodes, nodes and leaves). Lignin contents were estimated by two gravimetric methods (Klason lignin and Acido-insoluble lignin) . Monomeric structure of lignins was characterised by thioacidolysis a nd alkaline nitobenzene oxidation. Contents in p-coumaric and ferulic acids associated to cell walls through eater and/or ether bonds were d etermined by alkaline hydrolysis at 35 degrees and acidolysis, respect ively. Alkaline hydrolysis at 170 degrees was also applied for the cha racterisation of the ester and ether structures involving p-hydroxycin namic acids. The results obtained clearly show a variability of the co ntents in lignins and cell wall linked p-hydroxycinnamic acids. This v ariability is also observed on the level of the monomeric composition and the degree of condensation of the in situ lignins. Esterified and etherified phenolic acids represent and additional level of variabilit y.