Abstract: Cellulose acetate (CA) was used to modify a microporous polytetrafluoroethylene (PTFE) membrane, and papain was immobilized on the CA-PTFE composite membrane. The final aim of this study was to investigate the deactivation of lipase in fresh rice bran using the immobilized enzyme membrane. The conditions for deactivating lipase in fresh rice bran were optimized using a combination of one-factor-at-a-time method and response surface methodology. The relative lipase activity was taken as the response. The results showed that the optimal conditions for deactivation of rice bran lipase were determined as follows: ambient air relative humidity 72%, deactivation temperature 71 ℃, and time 113 min. Under these conditions, the relative lipase activity of rice bran decreased to 35.2% indicating good deactivation efficiency. After storage for two months, the relative lipase activity of rice bran remained below 36.0%, and the immobilized enzyme membrane still retained 73.0% of its initial activity after sixth repeated use. Thus, this study concluded that the immobilized enzyme membrane could be repeatedly applied to stabilize rice bran by effectively inactivating lipase.

Key words: composite membrane, immobilization, papain, deactivation, lipase activity, repeated use