Pretreatment of microcrystalline cellulose flakes with CaCl2 increases the surface area, and thus improves enzymatic saccharification

Glucose production from cellulose flakes with cellulases was improved after pretreatment with saturated CaCl2 at room temperature. When pretreated microcrystalline cellulose flakes (Funacel II, Funakoshi Co., Ltd, Tokyo, Japan) were saccharified with the cellulases, 76.8% of the substrate was converted into glucose within 5 h, whereas the corresponding conversion rate of water-pretreated cellulose flakes was 33.8%. To clarify the mechanism of the promotion, cellobiohydrolase I purified from Trichoderma longibrachiatum was used as the model cellulase, which degraded CaCl2-pretreated cellulose more quickly than the water-pretreated cellulose under tested conditions. The maximum amount of the enzyme bound to CaCl2-pretreated cellulose at 37 degrees C was estimated as 1.14 nmol/mg of cellulose, whereas that to water-pretreated cellulose was 0.527 nmol/mg of cellulose. The specific activity of the bound enzyme greatly decreased with the increase of the surface density (rho) of the bound enzyme, and no significant positive effects of the CaCl2-pretreatment on the specific activity could be observed at the same rho value, suggesting that the promotion was attributed mainly to the increase of the surface area of cellulose. The effect was also observed with dewaxed cotton or filter paper, but not with nata de coco cellulose or bagasse cellulose as the substrates. This suggests that the CaCl2-pretreatment serves to increase the surface area of cellulose flakes via liberation of cellulose particles which were artificially aggregated during harsh drying processes of the flakes.