Characterization of a thermo-tolerant mycelial β-fructofuranosidase from Aspergillus phoenicis under submerged fermentation using wheat bran as carbon source

• High levels of mycelial fructofuranosidase were obtained using wheat bran.
• The homodimeric enzyme was purified until the electrophoretic homogeneity.
• The thermo-tolerant mycelial fructofuranosidase was activated by Mn2+ and Ag+.
• The enzyme hydrolyzes sucrose, raffinose and inulin with high affinity for sucrose.
• The enzyme has potential for future biotechnological application.

The filamentous fungus Aspergillus phoenicis (Aspergillus saitoi) produced high levels of mycelial β-D-fructofuranosidase (invertase) when cultivated under submerged fermentation using Khanna medium with wheat bran as the carbon source for 72 h at 40 °C, under orbital agitation (100 rpm). The mycelial invertase was purified 20-fold with 24% recovery through two chromatographic steps (DEAE-cellulose and Sephacryl S-200). The enzyme was characterized as a monomeric glycoprotein with 2% carbohydrate content and a native molecular mass of 131 kDa comprising two 70-kDa subunits. The optimal temperature and pH for activity were 65 °C and 4.5, respectively. The enzyme was resistant to temperatures of 50 °C and 60 °C and stable at pH 4.0–7.0. Activity increased in the presence of different ions, especially Mn2+ (+177 %), and Ag+ increased the invertase activity by 91%. The mycelial invertase hydrolyzed sucrose, raffinose, and inulin, with greater specificity for the former. The K1/2 and Vmax values for sucrose were 22.5 mM and 124.9 U mg−1, respectively.