Cellulase adsorption and relationship to features of corn stover solids produced by leading pretreatments

Abstract

Although essential to enzymatic hydrolysis of cellulosic biomass to sugars for fermentation to ethanol or other products, enzyme adsorption and its relationship to substrate features has received limited attention, and little data and insight have been developed on cellulase adsorption for promising pretreatment options, with almost no data available to facilitate comparisons. Therefore, adsorption of cellulase on Avicel, and of cellulase and xylanase on corn stover solids resulting from ammonia fiber expansion (AFEX), ammonia recycled percolation (ARP), controlled pH, dilute acid, lime, and sulfur dioxide (SO(2)) pretreatments were measured at 4 degrees C. Langmuir adsorption parameters were then estimated by non-linear regression using Polymath software, and cellulase accessibility to cellulose was estimated based on adsorption data for pretreated solids and lignin left after carbohydrate digestion. To determine the impact of delignification and deacetylation on cellulose accessibility, purified CBHI (Cel7A) adsorption at 4 degrees C and hydrolysis with whole cellulase were followed for untreated (UT) corn stover. In all cases, cellulase attained equilibrium in less than 2 h, and upon dilution, solids pretreated by controlled pH technology showed the greatest desorption followed by solids from dilute acid and SO(2) pretreatments. Surprisingly, the lowest desorption was measured for Avicel glucan followed by solids from AFEX pretreatment. The higher cellulose accessibility for AFEX and lime pretreated solids could account for the good digestion reported in the literature for these approaches. Lime pretreated solids had the greatest xylanase capacity and AFEX solids the least, showing pretreatment pH did not seem to be controlling. The 24 h glucan hydrolysis rate data had a strong relationship to cellulase adsorption capacities, while 24 h xylan hydrolysis rate data showed no relationship to xylanase adsorption capacities. Furthermore, delignification greatly enhanced enzyme effectiveness but had a limited effect on cellulose accessibility. And because delignification enhanced release of xylose more than glucose, it appears that lignin did not directly control cellulose accessibility but restricted xylan accessibility which in turn controlled access to cellulose. Reducing the acetyl content in corn stover solids significantly improved both cellulose accessibility and enzyme effectiveness.

Chemical Pretreatment Methods for the Production of Cellulosic Ethanol: Technologies and Innovations

“…A loading of 0.1 gram of slake lime per gram of biogas is common and process time varies from hours to weeks [26]. Lime improves hydrolysis rates of biomass by removing acetyl groups and a considerable portion of the lignin fraction [120], reducing counter-productive cellulase adsorption [14] and formation of degradation byproducts [121], and promoting cellulose accessibility [122].…”

Adsorption, immobilization and activity of cellulase in soil: the impacts of maize straw and its humification

“…In addition to that, light fraction of SOM (here fresh maize straw) plays an important role in retaining of cellulase molecule from washing out. Kumar and Wyman (2009) studied cellulase adsorption and desorption kinetics upon dilution with an equal amount of fresh buffer at 4 o C and at a loading of 400 mg cellulase/g solids for Avicel glucan and for corn stover solids pretreated by different materials. They reported that although pure Avicel cellulose contained no lignin, it desorbed the least amount of protein, while the highest percentage release was from the controlled pH pretreated solids (30%).…”

“…The sorption and binding of cellulase molecules to insoluble microcrystalline cellulose (Avicel) have been investigated by a number researchers and the Langmuir isotherm have been used for expressing cellulase adsorption on cellulose (Boussaid and Saddler 1999;Lynd et al 2002;Daset al 2012). The adsorption and activity of cellulase on raw and pretreated agricultural wastes and residues have been considered (Azevedo et al 2000;Lu et al 2002;Hu et al 2008;Kumar and Wyman 2009;Boonme 2012;Liu and Hu 2012;Du et al 2012) due to its applications in different industries. Despite the importance of cellulases in the C-cycle in aquatic and terrestrial environments, most studies on these enzymes deal with their production, purification, characterization, and immobilization on natural, or synthetic adsorbent instead of with their reaction in natural environments.…”

Simultaneous Saccharification and Fermentation of Ground Corn Stover for the Production of Fuel Ethanol Using Phanerochaete chrysosporium, Gloeophyllum trabeum, Saccharomyces cerevisiae, and Escherichia coli K011

“…1. Unlike the SSF process in previous works, ours does not use pretreated corn stover samples [13,19,25,42] or the addition of expensive commercial enzymes [12,26,53]. Instead, cellulases and hemicellulases are produced by G. trabeum and P. chrysosporium in situ upon corn stover enzyme induction performed via solid substrate fermentation in a pH range of 4.5-4.8 at 37 o C for 4 days, conditions that are suitable not only for the growth of the fungi but also for production of cellulolytic enzymes [38,43,44].…”

“…These enzyme consortia are usually a mixture of several enzymes that may include endoglucanases, exoglucanases or cellobiohydrolases, glucosidases or cellobiases, endoxylanases, xylosidases and galactosidases, among others [1,31,50,54]. The conventional method for the breakdown of lignocellulosics to fermentable sugars requires the use of expensive commercial enzymes [12,26,53]. However, these enzymes are not only substrate specific, they are largely susceptible to inhibition from compounds usually associated with lignin.…”