Interaction of enzymes with lignocellulosic materials: causes, mechanism and influencing factors

Abstract

For the production of biofuel (bioethanol), enzymatic adsorption onto a lignocellulosic biomass surface is a prior condition for the enzymatic hydrolysis process to occur. Lignocellulosic substances are mainly composed of cellulose, hemicellulose and lignin. The polysaccharide matrix (cellulose and hemicellulose) is capable of producing bioethanol. Therefore, lignin is removed or its concentration is reduced from the adsorption substrates by pretreatments. Selected enzymes are used for the production of reducing sugars from cellulosic materials, which in turn are converted to bioethanol. Adsorption of enzymes onto the substrate surface is a complicated process. A large number of research have been performed on the adsorption process, but little has been done to understand the mechanism of adsorption process. This article reviews the mechanisms of adsorption of enzymes onto the biomass surfaces. A conceptual adsorption mechanism is presented which will fill the gaps in literature and help researchers and industry to use adsorption more efficiently. The process of enzymatic adsorption starts with the reciprocal interplay of enzymes and substrates and ends with the establishment of molecular and cellular binding. The kinetics of an enzymatic reaction is almost the same as that of a characteristic chemical catalytic reaction. The influencing factors discussed in detail are: surface characteristics of the participating materials, the environmental factors, such as the associated flow conditions, temperature, concentration, etc. Pretreatment of lignocellulosic materials and optimum range of shear force and temperature for getting better results of adsorption are recommended.

Evaluating polymer interplay after hot water pretreatment to investigate maize stem internode recalcitrance

“…HWP increased the porosity of the cell wall, as indicated by the increase in the proportion of the water pool associated with pore diameter in the range 5–15 nm, which includes the average diameter of enzymes involved in hydrolysis. The increase in this pore size range was significantly correlated with higher saccharification yield ( R 2 = 0.97), in agreement with the fact that 90% of the hydrolytic enzyme accessibility depends on the internal wall pores [ 9 ]. The increase in cell wall porosity was also supported by Simons’ staining as shown by the increased adsorption of DY11 probe, which has a r H close to that of cellulase.…”

“…Biomass accessibility is considered to be the main factor responsible for recalcitrance; it is influenced by various factors specific to LB which are difficult to apprehend due to their strong interconnections [ 7 – 9 ]. Among the factors which contribute to recalcitrance, those linked to the composition of the LB, such as hemicellulose or lignin content, can be distinguished from structural factors, including porosity, specific surface area of the cellulose, and ultrastructural factors related to cellulose (crystallinity, degree of polymerisation) [ 7 ].…”

Bioethanol Production from Cellulose-Rich Corncob Residue by the Thermotolerant Saccharomyces cerevisiae TC-5

“…One of the major limitations of SSF is the operation temperature. The optimal temperature for enzymatic hydrolysis is around 40–55 °C [ 14 ], whereas that for fermentation is around 20–35 °C [ 15 ]. Thus, screening of thermotolerant ethanolic microorganisms, which can grow at 37–50 °C, is required to overcome these limiting factors [ 5 ].…”

Saccharification and Fermentation of Cellulolytic Agricultural Biomass to Bioethanol using Locally Isolated Aspergillus niger S48 and Kluyveromyces sp. Y2, respectively

“…Pretreatment is usually done to remove lignin or reduce its concentration. This will enhance the hydrolysis of cellulose and hemicellulose either by chemical or enzymes to yield fermentable sugars that are converted to bioethanol during fermentation [9,10]. The fermentation of the sugars obtained from the hydrolysis to ethanol is the final step of the process [7,8] For efficient bioethanol production using lignocellulosic plant biomass, the enzymes engaged for hydrolysis must adsorb to the biomass surface before the breaking down of the biomass will take place [8].…”