Development of a Magnetically Separable Co-immobilized Laccase and Versatile Peroxidase System for the Conversion of Lignocellulosic Biomass to Vanillin

Abstract

Lignin obtained from renewable biomass is a potential feedstock for the synthesis of variousvalue-added chemicals through efficient biocatalytic routes. The ligninolytic enzymes-assisteddepolymerization of lignin to vanillin constitutes the most commercially attractive and promisingapproach in green chemistry as vanillin constitutes the second most prevalent flavoring agent.Thus, in the present work, immobilized laccase and versatile peroxidase, and further, a co-immobilized laccase and versatile peroxidase system on magnetic silica microspheres (MSMS)were developed to generate a robust biocatalytic system that mediates the depolymerization oflignin obtained fromCasuarina equisetifoliabiomass. The depolymerization of lignin by free andimmobilized laccase showed a vanillin yield of 24.8% and 23%, respectively, at pH 4.0 in 6 h at 30°C against a vanillin yield of 20% and 21.7% with the free and immobilized versatile peroxidase,respectively, at pH 5.0°C and 50°C. Comparatively, the system with the co-immobilized laccase andversatile peroxidase exhibited a 1-fold and 1.2-fold higher vanillin yield than the free andimmobilized laccase system, respectively. On comparing with the versatile peroxidase system,the co-immobilized biocatalytic system displayed 1.3-fold and 1.2-fold increased vanillin yield thanthe free and immobilized versatile peroxidase system, respectively, at a pH of 6.0 in 6 h at 30°Cwith an enzyme concentration of 1 U/ml. The reusability studies of the co-immobilized biocatalyticsystem exhibited that both the enzymes retained up to 40% of its activity till sixth cycle.Implications: The waste biomass ofCasuarina equisetifoliais widely available around the coastalregions of India which does not have any agricultural or industrial applications. The present workexploits the lignocellulosic content of theCasuarinabiomass to extract the lignin, which providesa renewable alternative for the production of the commercially high-valued compound, vanillin.This work also integrates a co-immobilized biocatalytic process comprising of laccase and versatileperoxidase leading to an environmentally benign enzymatic process for the depolymerization oflignin to vanillin.