Adsorption of Cellulose Enzymes on Lignocellulosic Materials and Influencing Factors: A Review

Abstract

Adsorption of enzymes onto lignocellulosic substrates and their integration is a major concern in the production of bioethanol. Information of the adsorption of enzymes, adsorption characteristics and practical viewpoints are necessary for understanding of an adsorption system. Adsorption of enzymes depends on so many factors, instead of examining the role of all these, this study deals with the factors affecting the key adsorption process such as accessibility of enzymes to lignocellulosic substrate or substrate components and adsorption isotherms. Extensive analysis of the published literature on enzymatic adsorption onto lignocellulosic materials from 1994 to 2016 has consolidated in this review. The observations have enlightened some of the conflicting results in literature, especially increase or decrease to enzymatic adsorption under the influence of temperature, pH, presence or removal of lignin and hemicellulose for adsorption, enzyme to substrate ratio, inhibition by end-product and synergy of the components of cellulases mixture. It was concluded that an optimum removal of lignin is more important for creating accessibility of enzymes to substrates than non-removal. Effect of pH along with varying temperature on natural substrates has more room to work. End-product inhibition may be controlled by pretreatment and optimum enzyme to substrate ratio. The synergic actions of cellulases are obstructed by high enzyme concentration or high substrate concentration. This review will help in design of enzymatic adsorption step for bioethanol production from lignocellulosic materials.