Celluclast and Cellic® CTec2: Saccharification/fermentation of wheat straw, solid–liquid partition and potential of enzyme recycling by alkaline washing

Abstract

The hydrolysis/fermentation of wheat straw and the adsorption/desorption/deactivation of cellulases were studied using Cellic(®) CTec2 (Cellic) and Celluclast mixed with Novozyme 188. The distribution of enzymes - cellobiohydrolase I (Cel7A), endoglucanase I (Cel7B) and β-glucosidase - of the two formulations between the residual substrate and supernatant during the course of enzymatic hydrolysis and fermentation was investigated. The potential of recyclability using alkaline wash was also studied. The efficiency of hydrolysis with an enzyme load of 10 FPU/g cellulose reached >98% using Cellic(®) CTec2, while for Celluclast a conversion of 52% and 81%, was observed without and with β-glucosidase supplementation, respectively. The decrease of Cellic(®) CTec2 activity observed along the process was related to deactivation of Cel7A rather than of Cel7B and β-glucosidase. The adsorption/desorption profiles during hydrolysis/fermentation revealed that a large fraction of active enzymes remained adsorbed to the solid residue throughout the process. Surprisingly, this was the case of Cel7A and β-glucosidase from Cellic, which remained adsorbed to the solid fraction along the entire process. Alkaline washing was used to recover the enzymes from the solid residue. This method allowed efficient recovery of Celluclast enzymes; however, this may be achieved only when minor amounts of cellulose remain present. Regarding the Cellic formulation, neither the presence of cellulose nor lignin restricted an efficient desorption of the enzymes at alkaline pH. This work shows that the recycling strategy must be customized for each particular formulation, since the enzymes found e.g. in Cellic and Celluclast bear quite different behaviour regarding the solid-liquid distribution, stability and cellulose and lignin affinity.

Enzymatic Activity of Some Industrially-Applied Cellulolytic Enzyme Preparations

“…As it was reported earlier in the literature, e.g. [17,20], cellulolytic enzyme cocktails which were used in our experiments have distinct ability to adsorption on lignin molecules. Despite of significantly higher hydrolytic efficiency of CTec2 than C1.5L enzyme cocktail, CTec2 shows higher affinity towards lignin and therefore significant number of active enzyme molecules remained unproductively adsorbed to the solid residues during hydrolysis, what finally resulted in lower yield of enzyme-catalysed degradation of feedstocks containing more lignins.…”

“…20 hours the significant slowdown in monosaccharide release from ray straw biomass can be observed. It can be hypothesized as being a negative effect caused by the hindered access of enzyme molecules to the substrate, or by adsorption of enzymes molecules on lignin chains, as well as it can also be associated with inhibition of enzymes by products or instability of enzyme molecules in reaction conditions [17,18].…”

Characterization of three plant biomass-degrading microbial consortia by metagenomics- and metasecretomics-based approaches

“…In industry, it is recommended to dose the Cellic CTec2 in accordance with the level of cellulose in the substrate. If (pretreated) plant biomass contains an appreciable amount of hemicellulose, it is advised to combine Cellic CTec2 with HTec2 (endoxylanases) to boost cellulose hydrolysis (Cannella and Jørgensen 2014; Rodrigues et al 2015). …”

Some critical aspects of the enzymatic hydrolysis at high dry‐matter content: a review

“…Bailey and Ollis found a significant loss of activity over 50 °C because of changes to the structure of proteins. However, more recent commercial cellulase preparations are less stable even at normal process conditions of 40–50 °C and pH 5.0 . The effect of pH is also important.…”

“…However, more recent commercial cellulase preparations are less stable even at normal process conditions of 40-50 °C and pH 5.0. 39,40 The effect of pH is also important. Normally, the optimal pH for commercial cellulase preparation is 4.5-5.5, which is compatible with the common yeast fermentation employed.…”