Abstract
The temperature and pH stability of proteases have been extensively investigated. A neutral protease produced by Aspergillus oryzae was thermodynamically characterized at high-salt environment. When the protease was tested at 24% NaCl and 60 o C, its half-life was increased to 30.0 min, 111% longer than that of control. Its Gibbs free energy and activation energy for denaturation in high NaCl concentration solutions were higher than in low salt solutions and increased by 2.1 and 4.75 kJ/mol, respectively. The protease exhibited higher thermal stability in higher salt conditions. This feature is beneficial to soybean sauce fermentation by enhancing the protease performance and taste of the product. Analysis by far- ultraviolet circular dichroism (far-UV CD) spectroscopy revealed that α-helix conformation in the protease increased from 3.2 to 31.7%, respectively, when the NaCl concentration increased from 0 to 18%, in agreement with the results deduced by thermodynamic calculations.
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