Evaluation of the enzyme manganese peroxidase in an industrial sequence for the lignin oxidation and bleaching of eucalyptus kraft pulp

Methylene blue as a lignin surrogate in manganese peroxidase reaction systems

Manganese peroxidase (MnP) is associated with lignin degradation and is thus relevant to lignocellulosic-utilization technologies. Technological applications require reaction mixture optimization. A surrogate substrate can facilitate this if its susceptibility to degradation is easily monitored and mirrors that of lignin. The dye methylene blue (MB) was evaluated in these respects as a surrogate substrate by testing its reactivity in reaction mixtures containing relevant redox mediators (dicarboxylic acids, fatty acids). Relative rates of MB degradation were compared to available literature reports of lignin degradation under similar conditions, and suggest that MB can be a useful lignin surrogate in MnP systems.

PCDD/F formation from chlorophenols by lignin and manganese peroxidases

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F) formation was studied, in vitro, with two different chlorophenol mixtures (group "di+tri" 2,4-dichlorophenol; 2,3,4-, 2,3,5-, and 3,4,5-trichlorophenols and group "tri+tetra+penta" with 2,4,5-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol) and two different lignolytic enzymes, lignin and manganese peroxidase (LiP and MnP respectively), which can be found during the composting process of sewage sludge. The concentrations of PCDD/F in final samples are compared to the PCDD/F content of the control samples containing the chlorophenols. High increases were observed for experiments with MnP and phosphate buffer. Experiments that contained tri-, tetra- and pentachlorophenol with MnP resulted in more than 8·10(8)ng of OCDD kg(-1) chlorophenol which was much higher than the initial amount (1·10(7)ng OCDD kg(-1) chlorophenol). In relation to LiP experiments, only those at 37°C showed a moderate increase (from 1.3·10(7) to 2.6·10(7)ng of OCDD kg(-1) chlorophenol). The results agree with the literature in which high amounts of HpCDD and OCDD were found after a composting process and could explain the biogenic formation suggested by others, but the incidence on the total toxicity is less than that expected.

An overview of key pretreatment processes employed for bioconversion of lignocellulosic biomass into biofuels and value added products

The hunt for alternative sources of energy generation that are inexpensive, ecofriendly, renewable and can replace fossil fuels is on, owing to the increasing demands of energy. One approach in this direction is the conversion of plant residues into biofuels wherein lignocellulose, which forms the structural framework of plants consisting of cellulose, hemicellulose and lignin, is first broken down and hydrolyzed into simple fermentable sugars, which upon fermentation form biofuels such as ethanol. A major bottleneck is to disarray lignin which is present as a protective covering and makes cellulose and hemicellulose recalcitrant to enzymatic hydrolysis. A number of biomass deconstruction or pretreatment processes (physical, chemical and biological) have been used to break the structural framework of plants and depolymerize lignin. This review surveys and discusses some major pretreatment processes pertaining to the pretreatment of plant biomass, which are used for the production of biofuels and other value added products. The emphasis is given on processes that provide maximum amount of sugars, which are subsequently used for the production of biofuels.