Isolation and characterization of an activator-dependent protease from Aspergillus ochraceus screened from low denatured defatted soybean meal and the proteolysis of soy proteins

A strain of Aspergillus ochraceus was isolated from the stored low denatured soybean meals (LDSMs) and an extracellular protease was purified from the fungus grown culture to electrophoretical homogeneity. The protease had a molecular weight of approximately 70 kDa and showed proteolytic activities only in the presence of activators. The maximum activity was obtained in 1.4% sodium dodecyl sulfate (SDS) solution but similar activity could also be achieved in the presence of linoleic acid at the concentration as low as 0.05%. The protease was stable at pH 9.0-12.0 and remained active in the presence of methanol, ethanol, acetone and trichloromethane and was classified as serine protease. The thermal stability of the protease located in the temperature range of 4-40 degrees C and an activator independent autolysis was observed above 60 degrees C. Soy proteins was hydrolyzed by the purified protease in a model system using residual lipids from stored LDSMs as the activator and a degree of hydrolysis (DH) of 6.01% +/- 0.27 was obtained after reaction for 60 min at pH 9.0 and 40 degrees C. This study gives new insights into the quality control of the soy protein production and the use of fungal proteases in the modification of soy proteins.

Automated summary

A strain of Aspergillus ochraceus was isolated from stored low denatured soybean meals, and an extracellular protease was purified from the fungus culture. The protease showed high activity under specific conditions and has potential applications in the hydrolysis of soy proteins.