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Indulin AT biodegradation by basidiomycetous fungi, actinobacteria and commercial laccases was evaluated using a suite of chemical analysis methods. The extent of microbial degradation was confirmed by novel thermal carbon analysis (TCA), as the treatments altered the carbon desorption and pyrolysis temperature profiles in supernatants. Laccase treatments caused only minor changes, though with increases occurring in the 850°C and char precursor fractions. After fungal treatments, lignin showed a similar change in the TCA profile, along with a gradual decrease of the total carbon, signifying lignin mineralization (combined with polymerization). By contrast, bacteria produced phenolic monomers without their further catabolism. After 54days of cultivation, a 20wt% weight loss was observed only for fungi, Coriolus versicolor, corroborating the near-80% carbon mass balance closure obtained by TCA. Compositional changes in lignin as a result of biodegradation were confirmed by thermal desorption (TD)-pyrolysis-GC-MS validating the carbon fractionation obtained by TCA.

Low substrate solubility and slow decomposition/biotransformation rate are among the main impediments for industrial scale lignin biotreatment. The outcome and dynamics of kraft lignin biomodification by basidiomycetous fungi, Coriolus versicolor, were investigated in the presence of dimethyl sulfoxide (DMSO). The addition of 2 vol % DMSO to aqueous media increased the lignin solubility up to 70%, while the quasi-immobilized fungi (pregrown on agar containing kenaf biomass) maintained their ability to produce lignolytic enzymes. Basidiomycetous fungi were able to grow on solid media containing both 5–25 g/L lignin and up to 5 vol % DMSO, in contrast to no growth in liquid media as a free suspended culture. When a fungal culture pregrown on agar was used for lignin treatment in an aqueous medium containing 2–5% DMSO with up to 25 g/L lignin, significant lignin modification was observed in 1–6 days. The product analysis suggests that lignin was biotransformed, rather than biodegraded, into an oxygenated and cross-linked phenolic polymer. The resulting product showed the removal of phenolic monomers and/or their immediate precursors based on gas chromatography and thermal desorption–pyrolysis–gas chromatography–mass spectrometry analyses. Significant intramolecular cross-linking among the reaction products was shown by thermal carbon analysis and 1H NMR spectroscopy. An increase in polarity, presumably due to oxygenation, and a decrease in polydispersity of the lignin treatment product compared to untreated lignin were observed while using liquid chromatography.

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Unlike previous lignin biodegradation studies, white rot fungi were used to produce functional biopolymers from Kraft lignin. Lignin-based polymers (hydrogel precursors) partially soluble in both aqueous and organic solvents were produced employing a relatively fast (6 days) enzymation of Kraft lignin with basidiomycetes, primarily Coriolus versicolor, pre-grown on kenaf/lignin agar followed by either vacuum evaporation or acid precipitation. After drying followed by a treatment with alkaline water, this intermediate polymer became a pH-sensitive anionic hydrogel insoluble in either aqueous or organic solvents. The yield of this polymer increased from 20 to 72 wt% with the addition of 2% dimethylsulfoxide to distilled water used as a medium. The mechanical stability and buffering capacity of this hydrogel can be adjusted by washing the intermediate polymer/hydrogel precursor prior to drying with solvents of different polarity (water, methanol or ethanol). Any of these polymers featured a significant thermal resilience assessed as a high thermostable “coked” fraction in thermal carbon analysis, apparently resulting from significant covalent cross-linking that occurs during the treatment of their intermediate precursors.