Abstract: The soil sample was collected from the organic-rich environment, and phytase production strains were obtained by preliminary screening with calcium phytate plate transparent ring method. Then phytase activity was determined by two different methods vanadium-ammonium molybdate method and acetone-ammonium phosphomolybdate method, and then compared. The results showed that the method of vanadium-ammonium molybdate was accurate and available. The orthogonal fermentation test determines that pH is 5, the yield of soluble enzyme is 1.25 g/100 mL, the optimum dosage of yeast powder is 1.80 g/100 mL, and the amount of calcium phytate is 1.0 g/100 mL.

Key words: phytase, enzyme activity, measure, vanadium-ammonium molybdate method, acetone-ammonium phosphomolybdate method