Functional Application of Thermo- Alkali- Stable Lignocellulolytic Enzymes in Kraft-Pulp Industry and Development of Fermentation Process for Production: A Review

For many years, microbial enzymes are commercially used as biocatalysts and efficiently catalyze various processes in industries. Biocatalysts are less corrosive to industrial processing equipment and due to their substrate specificity, they produced less toxic wastes which promotes environmental sustainability. At present, thermostable and alkali tolerant lignocellulolytic enzymes have gain enormous attention to be used as biocatalyst due their stability and robustness at high temperature and alkaline milieu. In this review, the characteristic of the several thermo–alkali-stable lignocellulolytic enzymes such as thermo–alkali-stable cellulases, thermo–alkali-stable xylanases and thermo–alkali-stable laccases as biobleaching agents in Kraft-pulp industry are described. This article discusses the characteristics of these enzymes such as their molecular weight, thermo-stability, pH tolerance, solvents compatibility and their stability towards the presence of metal ions and other chemicals. This review also discusses the development of fermentation process for the production of thermo–alkali-stable lignocellulolytic enzymes focusing on microorganisms (i.e. strain selection and strains improvement via mutation and recombinant techniques), culture medium optimization (i.e carbon, nitrogen and minerals) and other fermentation parameters (i.e. inoculums size, temperature, pH, agitation rate, aeration rate, and dissolved oxygen tension). The performances of strain producers in bioreactors and different mode of operation (i.e submerged and solid state fermentation) are also compared and discussed in this paper.