Enzyme Technology in Bioethanol Production from Lignocellulosic Biomass: Recent Trends with a Focus on Immobilized Enzymes

Abstract

Enzyme immobilization is a useful tool to produce biocatalysts with improved performance, such as high activity, high stability at operational conditions, and easy recovery and reuse.  In this context, the production of second-generation ethanol using immobilized enzymes was reviewed. Emphasis was placed on the pre-treatment and/or hydrolysis steps to increase efficiency and reduce the cost of the process. In addition, the process design of bioethanol using immobilized enzymes was critically reviewed. In the enzymatic pre-treatment, laccases, manganese peroxidases, lignin peroxidases, and lytic polysaccharide monooxygenases are the main enzymes involved. When considering processes with heterogeneous biocatalysts, laccases are the most explored enzyme. In the hydrolysis step, cellulases and hemicellulases or a mixture of them are the main enzymes explored in the literature frequently using magnetic nanoparticles as support for enzyme immobilization.  Although enzyme immobilization is a mature technology, the use of these biocatalysts is frequently limited to only one step of the bioethanol production process, such as pre-treatment or hydrolysis performed using Benchmark Technology. However, some recent papers have explored innovative design processes using a mixture of immobilized enzymes or co-immobilized enzymes to join some process steps, thereby decreasing the cost of enzymes and equipment.