Oxidative enzymes in lignin biorefinery

Today the rising energy consumption and the depletion of fossil fuel feedstocks have focused the attention \ud on the use of alternative renewable materials and on the development of environmentally friendly processes \ud that operate in mild reaction conditions. \ud Lignin is the second most abundant organic polymer in plant kingdom and constitutes up to 30% of wood. It \ud constitutes to date the bottleneck to the development of integrated biorefinery processes since it is the residue of modern saccharification processes. Current processes of bioethanol production from wood originate \ud about 500g of lignin each liter of bioethanol. From this viewpoint the development of processes of lignin \ud upgrade through oxidative depolymerization or functionalisation is mandatory.\ud In Nature the selective oxidation of lignin is carried out by white rot basidiomycetes fungi that produce a \ud pool of extracellular ligninolytic enzymes such as laccases and peroxidases. In particular laccases can easily \ud oxidise phenolic groups and in presence of radical mediator, such as 1-Hydroxybenzotriazole, their reactivity can be extended towards other functional groups as phenyl-aryl ethers. Mnperoxidase and lignin peroxidases are able to oxidize lignin at the phenolic and non–phenolic aryl-ether positions respectively. \ud Laccases and peroxidases constitute an interesting tool for the development of alternative oxidative processes due to their low substrate specificity and relatively wide pH of action. In the last years both laccases and \ud peroxidases have been used in several biotechnological applications such as oxidation of organic pollutants, \ud pulp delignification, bleaching and development of biosensors or biofuel cells. Unfortunatly, the exploitation \ud of their potentiality is prevented, specially in the case of peroxidases, by their low stability.\ud The basic requirement for the development of economically sustainable enzymatic processes are the possible recycle of the catalyst and a high stability of the enzyme. As such a number of different immobilization \ud techniques have been developed. \ud Recently, significant efforts have been made to develop organo-catalytic cascade reactions with the objective to mimic the biosynthetic strategy, but to date the innovative potential of biocatalysis by promoting the \ud multistep catalytic concept by multienzyme systems has not been fully explored.\ud The use of oxidative enzymes in lignin upgrade, the design and development of oxidative multienzyme biocatalysts for lignin selective oxidation will be reported