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.