Investigation of adsorption kinetics and isotherm of cellulase and β-glucosidase on lignocellulosic substrates

Clear understanding of enzyme adsorption during enzymatic hydrolysis of lignocellulosic biomass is essential to enhance the cost-efficiency of hydrolysis. However, conclusions from literature often contradicted each other because enzyme adsorption is enzyme, biomass/pretreatment and experimental condition specific, which makes descriptions and modeling of enzyme-substrate interaction difficult and inconsistent from case to case. This study investigated adsorption kinetics and isotherm under actual hydrolysis conditions with commercial cellulase and β-glucosidase on Avicel, dilute acid pretreated Creeping Wild Ryegrass (pCWR) and lignin residue of pCWR after enzymatic hydrolysis. It was found that β-glucosidase has little affinity to Avicel, but significant affinity to dilute acid pCWR and lignin with maximum adsorption capacity (Emax) of 161.57 and 173.50 mg protein/g-substrate, respectively. During hydrolysis, adsorption of cellulase on Avicel was productive and reversible (Emax = 22.86 mg protein/g-substrate); however, nonproductive and irreversible adsorption of cellulase on pCWR (Emax = 42.55 mg protein/g-substrate) and lignin (Emax = 86.07 mg protein/g-substrate) became significant and resulted in cellulase deactivation. Lignin is a key issue causing high cost of enzymatic hydrolysis of lignocellulosic biomass. The nonionic surfactant, Tween 20 was found to significantly overcome nonproductive adsorption of cellulase and β-glucosidase on lignin by reducing the adsorption affinity. All adsorption data including with and without Tween 20 were fit well to Langmuir isotherm. The results from this research will provide useful data for model development of enzymatic hydrolysis.