Stabilisation of cellulases by cross-linking with glutaraldehyde and soil humates

β-Glucosidase and carboxymethyl cellulase were induced in and extracted from Aspergillus niger and Trichoderma reesei cultures and cross-linked with glutaraldehyde or complexed with a soil polyphenolic structure (humates). The concentration of the bifunctional reagent (2•5 or 5•0%) determined the activity of the immobilised β-glucosidase while the time and temperature of reaction had no significant influence. Although the catalytic activity of the cross-linked cellulases was 85% smaller than that of the free counterparts, they resisted thermal inactivation to a greater extent. When cellulases were bound to soil humates, their activity was much higher than that of the free enzymes. Furthermore, their thermal stability was enhanced by their complexation to the colloids. In contrast, when cellulases were bound to humates in the presence of glutaraldehyde, the cross-linked humate-enzyme complexes obtained showed a partial deactivation (β-glucosidase 10•4% and CMCase 37•1%). The thermostability of the immobilised CMCase was reduced (9•1%) but the thermostability of the β-glucosidase was increased (36•9%) with respect to its soluble counterpart at 60°C.