Screening Of High Yield Strain Of Phytase And Optimizating Of Its Fermentation Conditions

Phytase is the general term for a class of enzymes that catalysis phytic acid and its saltsto inositol and phosphoric acid （salt）, and it is a phosphate monoester hydrolases. So far,phytase has been successfully applied in many fields, such as the medicine and the feedstuff.But there are also some problems on the applications.According to the enzyme production capacity of producing strains is low, it is necessarilyto select new strains and tobtain phytase which is imperative.Aspergillus niger QM-10is mutated with the mutagens of UV, MW, EMS and⁶⁰Co γ ray,and a high-yield mutant E-15was got. The strain has a titer of4920U/mL, which is as2times compared with Aspergillus niger QM-10. Its heredity is stable.The method of single factor optimization was used to optimize the medium compositionof phytase fermentation. The fermentation condition in a flask and10L fermentor ofsubmerged fermentation with Aspergillus niger Co-79were determined. After optimization,the medium composition was as follows: glucose3%,（NH₄）₂SO₄2%, MgSO₄·7H₂O0.05%,KCl0.05%, FeSO₄·7H₂O0.0005%, MnSO₄·7H₂O0.0005%，K₂HPO₄0.06%，Tween-800.2%，and initial pH value5.5. The fermentation conditions was as follows: With thevolume of liquid80mL/500mL, inoculum size2%, culture time120h, culture temperature30℃. Pack fluid amount to6.5L, the initial agitation speed was200r/min and the aerationrate is1.5vvm, after about22h the aeration rate and agitation speed should be adjustedaccording to the dissolved oxygen which should be above20%, after120h’s fermentation, theyield of phytase is5320u/mL.Enzymological properties was:55℃was the best reaction temperature, the best reactiontime was10min, optimum reaction pH was5.5and the enzymatic property is stable.