Abstract: The kinetic behaviors of casein hydrolysis by Aspergillus oryzae protease were studied under different substrate concentrations, temperatures and pHs. The optimal temperature and pH for 10 min-reactions are: 50 ℃ and pH 9 respectively. The experiment results showed that at 40 ℃, the kinetics of casein hydrolysis by the protease fit the Mchaelis-Menton equation which can be written as r=0.243CS/0.0282+CS and the relation between hydrolysis rate and hydrogen ion concentration is: r=lgCH++3.14013/0.19759+0.05484(lgCH++3.14013)+(lgCH++3.14013)2. The protease relative deactivity at 50 ℃ follows a= 0.82531e(-0.02169t)+0.17469e(-0.41914t). The energy of activation (Ea) under 50℃ is 30.67 kJ. The effects of different chemicals on protease activity were observed under the same condition as protease activity assay. The protease activity is enhanced by 10 mmol/L H3BO3 or Mg2+ and inhibited by EDTA, SDS, Zn2+, Mn2+ or Sn2+ obviously, however it is not affected by 10 mmol/L H2O2.

Key words: Aspergillus oryzae, protease, kinetic