Screening and Identification of a Strain Capable of Producing Acid Phytase and Optimization of Its Fermentation Conditions

A strain with higher acid phytase activity isolated from soil was identified as Aspergillus niger.The optimal fermentation conditions for improved production of phytase by the strain were incubation in a medium composed of 3 g/100mL wheat bran and 0.5 g/100mL(NH4)2SO4,at an initial pH of 5.5 for 84 h.Under the optimal fermentation conditions,the phytase activity was up to 12.06 U/mL.The optimal reaction pH and temperature of this enzyme were 5 and 45 ℃,respectively.The relative enzyme activity remained to be 60% after heating treatment at 55 ℃ for 30 min.In addition,the enzyme was stable in acidic and neutral media.The phytase activity was inhibited by Ca2+,Fe2+,Na+,K+,Zn2+ and Cu2+,while activated by Mg2+ and Ba2+.