The aromatic-ring substitution patterns of p-hydroxyphenyl (N), guaiacyl (G
) and syringyl (S) lignin-units are conserved after pyrolytic breakdown ena
bling analysis of the composition of lignins with different origins. Analyt
ical pyrolysis has been used to investigate lignin degradation by several w
hite-rot fungi including Pleurotus eryngii, a species characterised by the
ability to degrade lignin selectively. Using Py-GC/MS it was found that the
composition of wheat lignin was modified by P. eryngii causing a decrease
of S/G ratio in the residual lignin. Simultaneously, degradation pro ducts
were incorporated into lignin-polysaccharide complexes. In order to get add
itional insight on wheat lignin modification by these fungi, the biodegrade
d samples were permethylated before Py-GC/MS. In this way it was shown that
the free phenolic lignin-units (around 50% of the total H and G units and
only 6% of S units) were preferentially removed as compared with the etheri
fied ones. Moreover, it was possible to demonstrate that the lignin side-ch
ains were attacked in situ resulting in the increased amounts of ether-link
ed vanillic and syringic acids, identified as the corresponding methyl este
rs by Py-GC/MS of permethylated samples. When 50% of wheat lignin was degra
ded by P. eryngii, the relative abundance of aromatic acids was over 15% of
the total lignin derived products. These results validate some of the mech
anisms postulated for lignin degradation by white-rot fungi, which were bas
ed on simple model compounds. (C) 2001 Elsevier Science B.V. All rights res
erved.