Ultrafiltration is an attractive downstream processing technique for concentrating enzymes and could be considered the Primary step of purification. However, the efficiency of this process is often limited by protein fouling and shear-induced enzyme inactivation, which decreases permeate flux and results in the loss of enzyme activity. Although the rejection of phytase was higher than 99%, the loss of the enzyme activity was 14% during operation, indicating that the shear forces generated in the filter have significant influences on the enzyme activity. Two preparations using glycerol (25% and 35%, v/v) as a cryo-protecting agent at different temperatures were studied. The preparation containing 35% glycerol retained 70% of the initial enzyme activity at 70 degrees C after I h and had more than 3 and 6 months storage half-life at 29 degrees C and 4 degrees C, respectively. (C) 2013 Elsevier Ltd. All rights reserved.