Structural changes of residual lignin in softwood kraft pulp treated with manganese peroxidase |
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| Authors: | Katsunobu Ehara Yuji Tsutsumi Tomoaki Nishida |
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| Institution: | (1) Department of Forest Resources Science, Faculty of Agriculture, Shizuoka University, 422-8529 Shizuoka, Japan |
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| Abstract: | Structural changes of residual lignin in unbleached softwood kraft pulp (SWKP) during manganese peroxidase (MnP) treatment were investigated to obtain some understanding of the biobleaching action of SWKP with MnP treatment. Alkaline-extracted lignin from darkened SWKP by MnP showed more intense color and contained moreo-quinone than that from control SWKP. However, no difference in the conjugated -carbonyl was observed between the lignins from MnP-treated and control SWKP. The nitrobenzene oxidation analysis revealed that oxidative condensation of non-condensed lignin in SWKP occurs during an early stage of MnP treatment. These observations were supported by the model experiment in which the lignin prepared from control SWKP was subjected to MnP treatments three times, and the changes of color and functional groups in the lignin were determined after each treatment. These results suggested that an increase ino-quinone and the condensation reaction of non-condensed lignin in SWKP are responsible for the characteristic darkening of SWKP during MnP treatment. It was also ascertained that darkened lignin was degraded and brightened by repeated MnP treatments. |
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| Keywords: | Kraft pulp Residual lignin Manganese peroxidase Functional group Alkaline nitrobenzene oxidation |
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