The occurrence of p-hydroxyphenylpropane units in the middle-lamella lignin of spruce (Picea abies)

Summary A sieving technique has been developed for the separation of middle-lamella fragments. The middle-lamella fraction as well as the whole wood and compression wood from Picea abies have been analysed by nitrobenzene oxidation and acidolysis in order to determine the content of p-hydroxyphenylpropane units in the middle-lamella lignin. These analyses revealed only traces of p-hydroxyphenylpropane units in the whole wood and in the middle-lamella fraction but considerable amounts were found in compression-wood lignin. This points to the fact that middle-lamella lignin is of guaiacyl nature and that earlier results reporting high proportions of p-hydroxyphenylpropane units in the middle lamella-lignin may be due to the inclusion of compression wood in the fraction studied. The acidolysis experiments further indicate that the middle-lamella lignin has fewer uncondensed -0-4 aryl ether structures than the whole wood lignin.The skilful technical assistance of Mrs. Britta Samuelsson and Mr. Johan Lindberg is highly appreciated. The author also thanks Dr. Knut Lundquist for supplying some of the reference compounds, and Dr. Hanne-Lise Hardell for help with the microscopic pictures