Influences of sulfhydryl oxidase isolated from Aspergillus niger on physicochemical properties of starch and rheological properties of wheat dough

The sulfhydryl oxidase (SHOxase; EC. 1.8.3.2) which catalyzes the oxidation of sulfhydryl groups to disulfides was purified from Aspergillus niger using a combination of chromatographies. The influence of SHOxase on starch properties was tested by rheometer, farinographand scanning electron microscopy (SEM). Moreover, the gelatinization and retrogradation were studied by differential scanning calorimetry (DSC). The data showed that the SHOxase blended on dough formula increased the stability time of dough in a farinograph and all parameters of viscoelastic properties compared to the control. Furthermore, SEM image of SHOxase on dough showed that the gluten matrix was distinctly developed. The peak temperature (Tp) of the starch gelatinization and enthalpy value (∆Hg) of control during mixing were compared with the SHOxase blended wheat flour. Mixing increased the Tp of the starch gelatinization and the ∆Hg. The addition of SHOxase in the blend increased the Tp and decreased the ∆Hg of the starch gelatinization. According to the Avrami equation, the retrogradation rate of starch during storage was slower than that of the control. The abilities of SHOxase to strengthen, decrease of ∆Hg and retard of retrogradation of wheat dough are likely attributable to its ability to catalyze formation of disulfide bonds in the systems.