Studies On The Isolation And Selection Of Protease Producing Strains From Traditional Fermented Soy Product And The Properties Of Protease

A protease producting strain was isolated from a traditional fermented soy product. The characteristic of the protease and the change of fermented tofu by the strain were studied in this research.The results of the experiments showed that the highest protease activity is M2 strain and the lowest protease activity is M1. M2 strain showed a good heredity stability by stability study. M2 strain is belonged to Fungi, Phycomycetes,Mucorales,Mucoraceae,Mucor Micheli ex Fries by lab identify according to colony form, micro observation and scanning electron microscope.The results showed that M2 strain can produce protease well at 28℃,initial pH 5.0,liquid volume 100 mL and on a rotary shaker with a speed of 150 r/min. The protease of M2 strain producted is maybe protease compound, basis is acidic protease, the ideal conditions for the protease activity were pH 4,55℃. and had good stability in pH 5~6 and 4℃. Some metal ions had influence on protease activity. Mn2+, Ca2+ and Mg2+ could activate protease activity but Zn2+, Fe2+, and Fe3+ could inhibit protease activity at level of 5.0 mmol/L. Meanwhile NaCl showed an activation effect at low level but an inhibitory effect at high level. The protease MWs were above 30KD.The texture and microstructure of fermented tofu by Mucor were studied by texture analyer and scanning electronmicroscopy (SEM). Proteolysis of tofu was analyzed by SDS-PEGA electrophoresis with unfermented tofu as a control. The TPA profiles showed that hardness and adhesiveness of fermented tofu were increased while the cohesiveness and springiness were reduced. The microstructure of fermented tofu was homogeneous. Results from SDS-PEGA analysis and microstructure analysis all indicated that proteins were degraded during tofu fermentation.