INVESTIGATION OF LIGNINS STRUCTURE IN CEREAL CROPS BY CHEMICAL DEGRADATION METHODS

The monomeric composition of in situ lignins in sorghum, maize and whe at straw stems is investigated by two chemical degradation methods: th ioacidolysis and alkaline nitrobenzene oxidation. It is shown that the structural information obtained in the case of lignin characterisatio n by alkaline nitrobenzene oxidation is strongly dependent on the reac tion conditions, namely the temperature and the reaction time, as indi cated by the significant variations in the yields of aromatic aldehyde s that correspond to the three main constitutive lignin units, p-hydro xyphenyl (H), guaiacyl (G) and syringyl (S), Moreover, the complementa ry character of the two methods that stems from their different specif icities is discussed in view of the molecular heterogeneity of lignins . Finally, the results obtained indicate a significant structural vari ability of the lignins of the three crops examined. (C) 1998 Elsevier Science Limited. All rights reserved.