Production of useful modified lignin polymers by bioconversion of lignocellulose with Streptomyces

Lignin degrading strains of Streptomyces were grown on lignocelluloses from a variety of plant sources. These actinomycetes readily degraded the lignin present in the residues and released a major portion of the lignin into the growth medium as a water soluble, modified polymer. The polymer, an acid precipitable polyphenolic lignin (APPL), was recovered from spent culture media by acid precipitation or dialysis/lyophilization. APPL's were shown to be mostly free of nonlignin components. As compared to native lignin they were more oxidized, were especially enriched in phenolic hydroxyl groups, and were significantly reduced in methoxyl groups. The yield of APPL from different lignocelluloses correlated with their biodegradability. Grasses such as corn stover were the optimal lignocellulose type for APPL production by Streptomyces. In contrast white-rot fungi produced only small amounts of APPL as they decomposed lignin. A solid state bioconversion process was developed using Streptomyces viridosporus T7A to produce APPL from corn stover lignocellulose in yields >or= 30% of the initial lignin present in the substrate. APPL produced by S. viridosporus was examined for its properties and possible use as an antioxidant. The APPL was shown to have good antioxidant properties after mild chemical treatment to reduce the alpha-carbonyl groups present in the APPL. Oxidation of the APPL with hydroxyl radical (OH(*)) further improved its antioxidant properties probably as the result of aromatic ring hydroxylation reactions. As compared with currently used commercial antioxidants, the modified APPL was thought to be competitive when economics of production was considered. Native lignin on the other hand was shown to exhibit no antioxidant properties, even after reduction and/or oxidation.