Abstract: The free glucoamylase in the 0.05 mol/L acetate-sodium acetate buffer(pH 4:6) was precipitated by ammonium sulfate and then cross-linked by glutaraldehyde to prepare glucoanylase aggregate,which is a carrier-free immobilized enzyme.The preparation process and the enzymatic characters of cross-linked glucoamylase aggregate were studied.Results showed that the final activity of the cross-linked glucoamylase aggregate is 3.15×104 U/g(dry).The optimum pH and reaction temperature as well as Km of the cross-linked glucoamylase aggregate are 4.6,50 ℃ and 1.75% respectively.As the content of xanthan gum is 5.0 mg/g(free glucoamylase),the residual activity and thermostability of the cross-linked glucoamylase aggregate are both higher than the free glucoamylase.

Key words: glucoamylase, cross-linked glucoamylase aggregate, immobilization