Analysis of Lignin Isolated from Spruce with Secondary Cell Wall Removed

Wood from white spruce, Picea glauca, that has been preserved by rapid burial in lake sediments 10000 years ago was investigated and compared to fresh white spruce wood. The old sample has an intact outer cell wall and middle lamella but most of the secondary cell wall has been selectively removed by bacteria. Klason lignin content was found to be 60% in the old sample, more than twice as high as that found in normal wood. This was rather expected since the middle lamella and primary wall has a higher content of lignin than the secondary wall. After thioacidolysis of the samples the lignin monomer content in the old spruce was 9% lower than that of the reference wood, possibly due to more condensed lignin. This finding was supported by SEC analysis of the thioacidolysed samples. A small amount of coumaryl monomers, 3%, was found in the old spruce and none in the reference wood. The carbohydrate monomer distribution showed that galactose and arabinose and xylose content is higher in old spruce than in white spruce reference, and glucose content is 20% lower in old spruce as compared to reference white spruce. This confirms microscopical evidence that secondary wall was at least partially removed. No new oligomeric lignin structures could be identified with GC-MS analysis of the thioacidolysis products. Millwood lignin from samples were subjected to quantitative NMR analysis by combining {13} C and HSQC techniques, which showed that the lignin structures in mill wood lignin from the old spruce sample was almost identical to those of the reference wood.