On the chemical aspects of the biodelignification of wheat straw with Pycnoporus sanguineus and its combined effects with the presence of Candida tropicalis

Pycnoporus sanguineus (Ps) and Candida tropicalis (Ct) can selectively degrade the lignin and hemicellulose in lignocellulosic cells respectively; Ps-Ct mixed fermentation may improve the multiphase reaction performance of lignin in the cell walls. Alkaline nitrobenzene oxidation, ozonation and infrared spectroscopy, which are the in-situ analytical techniques of lignin in the cells, were used to characterize the delignification kinetics, the reactions of the non-condensed, beta-O-4 structures and their stereochemistry of lignin in wheat straw in Ps and Ps-Ct fermentations. Results indicated that the biodelignification processes in Ps and Ps-Ct fermentations of wheat straw, being divided into a fast phase and a following slow phase, had the characteristics of a pseudo-first-order reaction in both the phases. The lignin reaction pathways in Ps and Ps-Ct mainly included the cleavage of ring, C alpha-C beta, beta-O-4, and the cleavage and polymerization of 5-5'. Compared with Ps fermentation, Ps-Ct fermentation enhanced the biodegradation of condensed, beta-O-4 structures and threo beta-O-4 structures in the lignin in the fast phase. A proposal scheme of biodelignification by Ps and Ps-Ct is outlined for the first time. These results will be helpful for the understanding and application of lignocellulosic biomass by mixed fermentations. (C) 2016 Elsevier B.V. All rights reserved.