Structure and composition of sweet sorghum stalk components

Stem bark and pith of sweet sorghum were analyzed with reference to their sucrose, simple reducing sugars, cellulose, hemicelluloses, lignin and associated phenolic acids contents. Moreover, lignin monomeric units (guaiacyl and syringyl) engaged in non-condensed structures were characterized by thioacidolysis, whereas cell wall associated phenolic acids (p-coumaric and ferulic acids) were estimated by alkaline hydrolysis at 170 degrees C. The results obtained showed that bark and pith are heterogeneous as far as their chemical composition and the structure of their-chemical components are concerned. In particular, the pith content in water soluble sugars is twice as high compared with the one in the bark, whereas bark is enriched in lignocellulosic fibres. Bark lignin is twice as important in content and less condensed in structure compared to pith lignin. p-Coumaric acid is the predominant p-hydroxycinnamic acid associated to the cell walls, whereas ferulic acid is present in significant quantities. (C) 1997 Elsevier Science B.V.