Standard assays do not predict the efficiency of commercial cellulase preparations towards plant materials

Abstract

Commercial cellulase preparations are potentially effective for processing biomass feedstocks in order to obtain bioethanol. In plant cell walls, cellulose fibrils occur in close association with xylans (monocotyls) or xyloglucans (dicotyls). The enzymatic conversion of cellulose/xylans is a complex process involving the concerted action of exo/endocellulases and cellobiases yielding glucose and xylanases yielding xylooligomers and xylose. An overview of commonly measured cellulase-, cellobiase-, and xylanase-activity, using respectively filter paper, cellobiose, and AZCL-dyed xylan as a substrate of 14 commercially available enzyme preparations from several suppliers is presented. In addition to these standardized tests, the enzyme-efficiency of degrading native substrates was studied. Grass and wheat bran were fractionated into a water unsoluble fraction (WUS), which was free of oligosaccharides and starch. Additionally, cellulose- and xylan-rich fractions were prepared by alkaline extraction of the WUS and were enzymatically digested. Hereby, the capability of cellulose and xylan conversion of the commercial enzyme preparations tested was measured. The results obtained showed that there was a large difference in the performance of the fourteen enzyme samples. Comparing all results, it was concluded that the choice of an enzyme preparation is more dependent on the characteristics of the substrate rather than on standard enzyme-activities measured.

An optimized microplate assay system for quantitative evaluation of plant cell wall–degrading enzyme activity of fungal culture extracts

“…The most effective means of lignocellulosic hydrolysis uses a cocktail of different cellulolytic enzymes, but conversion is still not optimal (Berlin et al, 2007;Cherry and Fidantsef, 2003;Irwin et al, 1993;Jeoh et al, 2002;Kabel et al, 2006). There is a need to develop more effective cocktails with a range of properties complementary to current cellulase systems, at a significantly reduced cost.…”

“…Complete hydrolysis requires relatively large quantities of the enzyme product and often must incorporate additional enzymes with different catalytic behaviors in order to better degrade lignocellulosic biomass (Rosgaard et al, 2006). A comparison of enzyme activities of 14 commercial products on filter paper, cellobiose, AZCL-dyed xylan and grass and wheat bran fractions found large differences in performance dependent on the substrate (Kabel et al, 2006). Due to the heterogeneous composition of plant biomass, the enzymatic components needed for hydrolysis do not fall neatly into any catalytic activity category.…”

Latest Frontiers in the Biotechnologies for Ethanol Production from Lignocellulosic Biomass

“…FPU, filter paper units). However the complexity of the lignocellulosic substrates does not make easy the prediction of the enzymes dosage on the base of the standard activities (Kabel et al, 2006). As consequence, the process must be tailored to the specific biomass used.…”

High‐throughput microplate technique for enzymatic hydrolysis of lignocellulosic biomass

“…Other cellulolytic enzyme activities (e.g., xylanolytic, cellobiase) estimated using conventional substrate assays (e.g., filter paper, cellobiose, oat spelt, and birch wood xylan) are not representative of their true hydrolytic efficiency on a realistic biorefinery feedstock, that is, lignocellulosic substrates. It has been recently shown that the enzyme combination that produces the best hydrolytic yields depends on the characteristics of the substrate rather than on standard enzyme-activities measured (Kabel et al, 2005). The standard activity assays for enzymes do not correlate well with their true hydrolytic potential for different lignocellulosic substrates.…”