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

Wheat-straw treatment with a Mn2+-oxidizing peroxidase from the ligninolyti c fungus Pleurotus eryngii was investigated using pyrolysis-gas chromatogra phy-mass spectrometry (Py-GC-MS). Changes in the ratio between p-hydroxyphe nyl (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 d ecrease of lignin phenolic content as revealed by Py-GC-MS of methylated st raw. It was shown that 10 U of peroxidase per mg of straw decreased the amo unt 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 lign in phenolic content was observed when lower enzyme doses were used. These r esults provide conclusive evidence for modification of lignin during in vit ro treatment of a natural lignocellulosic substrate with a ligninolytic per oxidase. (C) 2001 Elsevier Science B.V. All rights reserved.