Degradation of alkali lignin by two ascomycetes and free radical scavenging activity of the products

Biodegradation and bioconversion of extracted alkali lignin was performed under varying concentrations of carbon and nitrogen sources, by two potential Ascomycetes ligninolytic fungus isolated from soil. Fungus, F10 was identified as Aspergillus flavus, while APF4 as Emericella nidulans based upon closed similarity with their morphology and high homology in 18S rRNA gene sequences. The alkali lignin degradation was checked in term of disappearance of lignin content and colority. Selected fungus, degraded 19–41.6% of alkali lignin (0.25%, w/v) within 21 days of incubation and reduced the colority up to 14.4–21%. The activity of ligninolytic enzymes was periodically checked. During alkali lignin degradation manganese peroxidase (13.31 U/ml), lignin peroxidase (13.73 U/ml) and laccase (0.05 U/ml) activities were observed (at highest level). The alkali lignin degradation products and functional group changes in degraded lignin were analysed through gas chromatography-mass spectroscopy (GC-MS) and solid state ¹³C-NMR spectroscopy, respectively. The functional group modifications in alkali lignin moiety, alter its biochemical property, thus fungal mediated modified alkali lignin was further tested for reactive free radical scavenging potential with respect to hydroxyl, nitric oxide and superoxide radicals. Results demonstrate that the alkali lignin undergo degradation in studied nutritional conditions (high-carbon low nitrogen) and consequently increase its free radical scavenging activity up to 1–18%.