Abstract: The aggregation process of alkaline protease in aqueous solution was investigated by the change of particle size and Zeta potential with time and mass fraction.The dynamic surface tension of protease at air-water interface and its rheological properties were studied.Also,the changes of the enzyme activity of alkaline protease with time were determined.The relationship between protease activity and surface properties as well as aggregation behavior was examined.The results showed that particle size of protease aggregates increases with time and mass fraction while the value of Zeta potential declines,which results in the phase separation of the alkaline protease and water;as well as increase of particle size of the protease aggregates,it will results in change of kinetic process for diffusion of alkaline protease onto the interface,and thereby affects surface tension and visco-elasticity of the interface;the enzyme activity of alkaline protease decreases with its aggregation in solution.

Key words: detergent additive, protease, dynamic surface tension, dilatational rheology, enzyme activity