Lignin valorisation via enzymes: A sustainable approach

Lignin is the 3rd most abundant biopolymer surpassed by cellulose and hemicellulose and is the most abundant aromatics resource available on earth for utilization by mankind. It was considered undesirable historically which was usually burned as inefficient fuel. Lignin’s 3D recalcitrant nature caused hinderance to feasible biorefinery of holocellulosic fraction of biomass; however, with the rise of lignin biorefinery the concept has changed completely. Now modern biorefinery of biomass insists on making complete value of all the streams including lignin by valorising into variety of phenolics, biopolymers and other high value-added chemicals. Biological depolymerisation of lignin via enzymes is environmentally benign and preferred approach by virtue of low chemical requirement and disposal and energy demand; however, economic challenges are ahead. Robust enzymes are available in nature which can either modify or depolymerise lignin to add further value. Lignin modifying as well as lignin degrading auxiliary enzymes are instrumental and pave the way to a green process for lignin valorisation. This review article is focussed on various lignin degrading as well as lignin modifying enzymes produced by microorganisms especially fungi for degradation or modification of lignin, and its mechanisms, along with the strength and challenges for sustainable bio-based economy development.