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

⿢A fast delignification phase and a following slow one were shown in Ps and Ps-Ct.⿢Pseudo-first-order reactions were revealed for both the two phases.⿢Ps biodelignification in the fast phase was extended by Ct.⿢Uncondensed G unit and E β-O-4 structures were biodegraded by Ps.⿢Ps biodegradation of condensed lignin and T β-O-4 structures was enhanced by Ct.

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, β-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, Cα-Cβ, β-O-4, and the cleavage and polymerization of 5-5⿲. Compared with Ps fermentation, Ps-Ct fermentation enhanced the biodegradation of condensed, β-O-4 structures and threo β-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.

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