PHENOLIC-ACID BRIDGES BETWEEN POLYSACCHARIDES AND LIGNIN IN WHEAT INTERNODES

Saponification at room temperature and alkaline treatment at 170° was used to release cinnamic acids in ester and α-aryl ether linkages, respectively, from polymeric components of mature and maturing wheat internodes. The wall components contain similar amounts of esterified and etherified cinnamic acids. Ferulic acid (FA) was the predominant etherified cinnamic acid. The results confirm those obtained using room temperature saponification and alkaline nitrobenzene oxidation. The content and type of linkage of p-coumaric (PCA) and FA in Björkman lignins and fractions obtained during their purification were compared in extract-free, ball-milled wheat internode walls, with and without, prior saponification with 0.5 M sodium hydroxide at room temperature. The small amounts of Björkman lignin from untreated wheat internodes contained chiefly esterified PCA. However, in the corresponding lignin fraction from pre-saponified internodes, which was obtained in high yield, the cinnamic acids were mainly in the etherified form and FA predominated. These results are interpreted in terms of a structure with polysaccharide-ester-FA-ether-lignin bridges which on saponification release large amounts of a Björkman lignin equivalent beariing esterified FA. © 1990.