Studies On Production And Properties Of Sulfhydryl Oxidase From Aspergillus Sojae In Shake Flask Culture

Sulfhydryl oxidase is a kind of flavoprotein, which is comprised by a peptide chain and prothetic group. The prothetic group can be a FAD or FMN, they are derived from vitamin B2. Microbial SOX can improve the strength of bread dough.The strain of this study is Aspergillus sojae ATCC20235 purchased from ATCC. The fermentation conditions and medium components had been optimized, showed that using the composition of the following medium: cane sugar 30 g/L,fish meal,peptone 6.8 g/L,K₂HPO₄·3H₂O 2 g/L,MnCl₂·4H₂O 2 mg/L,BaCl₂ 500μg/L,H₃BO₃ 1 mg/L,pH 8.5,and culturing at 30℃with shaking speed of 220 r/min for 72 h could make the SOX activity reach 250 U/L.After removing the Mycelium pellet, the supernatant was precipitated by ammonium sulfate, purified by ion-exchange column chromatography and gel filtration chromatography sequently, the final enzyme activity reached 75 U/mg and was 187.5 times than that of the initial.The major properties of SOX had also been studied, the optimal reaction temperature of SOX is 30℃, the optimal pH is 7.5, SOX is stable when the temperature below 50℃, pH between 5-6. the enzyme activity and thermal stability of SOX can inhibited by Fe³⁺. the other metal ions, K⁺,Ba²⁺,Mn²⁺,Ca²⁺,Na+,Mg²⁺,show little influence on SOX. In addition, the reaction kinetic constant Km is 2.16 mmol/mL, Vm is 526 mmol/min.mL.In farinograph and extensograph, the results showed that the addition of sulhydryl oxidase could enhance the stability time , tensile resistance and decrease weaken degree significantly. In the addition of 100-150 U/kg flour, the dough has better fermentation and baking features.