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 -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 -glucosidase supplementation, respectively. The decrease of Cellic® CTec2 activity observed along the process was related to deactivation of Cel7A rather than of Cel7B and -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 -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.