Research paper Investigation of adsorption kinetics and isotherm of cellulase and b- glucosidase on lignocellulosic substrates Yi Zheng a, * , Ruihong Zhang b , Zhongli Pan b, c a Department of Environmental Engineering and Earth Sciences, Clemson University, 342 Computer Court, Anderson, SC 29625, USA b Biological and Agricultural Engineering Department, University of California, Davis One Shields Avenue, Davis, CA 95616, USA c Processed Foods Research Unit, USDA-ARS-WRRC, 800 Buchanan St., Albany, CA 94710, USA article info Article history: Received 11 March 2015 Received in revised form 23 January 2016 Accepted 25 April 2016 Keywords: Adsorption kinetics Adsorption isotherm Cellulase b-glucosidase Creeping wild ryegrass Tween 20 abstract 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 con- tradicted 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 b-glucosidase on Avicel, dilute acid pretreated Creeping Wild Ryegrass (pCWR) and lignin residue of pCWR after enzymatic hydrolysis. It was found that b-glucosidase has little affinity to Avicel, but significant affinity to dilute acid pCWR and lignin with maximum adsorption capacity (E max ) of 161.57 and 173.50 mg protein/g-substrate, respectively. During hydrolysis, adsorption of cellulase on Avicel was productive and reversible (E max ¼ 22.86 mg protein/g- substrate); however, nonproductive and irreversible adsorption of cellulase on pCWR (E max ¼ 42.55 mg protein/g-substrate) and lignin (E max ¼ 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 b-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. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Lignocellulosic biomass is an excellent renewable feedstock for biofuel and chemical production via sugar platform. Sugar pro- duction from lignocellulosic biomass on a commercial scale is, however, still hindered by technical and economic obstacles. Enzymatic cellulose hydrolysis for sugar production offers advan- tages over chemical conversion routes such as milder conditions, higher yields and minimal byproducts generation. While a lot of research has been done on enzymatic hydrolysis, the high cost rendered cellulosic ethanol economically unfit primarily because enzyme is costly along with high enzyme dosages required to achieve desired sugar yield. Cost-efficient pretreatment technolo- gies and enzymatic hydrolysis (such as using better enzyme and process optimization) are the most commonly addressed ap- proaches to make biomass amenable to enzyme attack. Hence, obtaining better understanding of interaction between enzyme and biomass substrate is important to enhance the cost-efficiency of enzymatic hydrolysis, which is a key factor to achieve economically feasible cellulosic ethanol. Enzymatic hydrolysis of lignocellulosic biomass is a heterogeneous biocatalytic process in which enzyme adsorption on substrates and the formation of enzyme-substrate complexes are prerequisites for cellulose hydrolysis, and such complexes are a central feature of most conceptual and quantitative models of enzymatic hydrolysis. As a result, it is essential to accu- rately describe enzyme adsorption behavior. Although adsorption of commercial enzyme preparations (e.g. cellulase and b-glucosidase) and purified monocomponent en- zymes (e.g. TrCel 5A and TrCel 7A) has been studied on various lignocellulosic substrates for decades, no universal conclusion has been drawn on the mechanism of enzyme actions. In some cases, the reported results were contradictory. The main reasons could be * Corresponding author. E-mail address: zheng9@clemson.edu (Y. Zheng). Contents lists available at ScienceDirect Biomass and Bioenergy journal homepage: http://www.elsevier.com/locate/biombioe http://dx.doi.org/10.1016/j.biombioe.2016.04.014 0961-9534/© 2016 Elsevier Ltd. All rights reserved. Biomass and Bioenergy 91 (2016) 1e9