Compositional changes of wheat lignin by a fungal peroxidase analyzed by pyrolysis-GC-MS

Wheat-straw treatment with a Mn2+-oxidizing peroxidase from the ligninolytic fungus Pleurotus eryngii was investigated using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). Changes in the ratio between p-hydroxyphenyl (H), guaiacyl (G) and syringyl (S) lignin units were found, consistent with a degradation of S units and increase of the H content after enzymatic treatment. However, the most noticeable modification was the significant decrease of lignin phenolic content as revealed by Py-GC-MS of methylated straw. It was shown that 10 U of peroxidase per mg of straw decreased the amount of phenolic H units from 31% in the control to 3% in the treated straw, that of G units from 40 to 4%, and completely removed the small amount of phenolic S units present in wheat straw. The same tendency to decrease lignin phenolic content was observed when lower enzyme doses were used. These results provide conclusive evidence for modification of lignin during in vitro treatment of a natural lignocellulosic substrate with a ligninolytic peroxidase. (C) 2001 Elsevier Science B.V. All rights reserved.