Thermostable invertases from Paecylomyces variotii produced under submerged and solid-state fermentation using agroindustrial residues

Abstract

The filamentous fungus Paecylomices variotii was able to produce high levels of cell extract and extracellular invertases when grown under submerged fermentation (SbmF) and solid-state fermentation, using agroindustrial products or residues as substrates, mainly soy bran and wheat bran, at 40°C for 72 h and 96 h, respectively. Addition of glucose or fructose (≥1%; w/v) in SbmF inhibited enzyme production, while the addition of 1% (w/v) peptone as organic nitrogen source enhanced the production by 3.7-fold. However, 1% (w/v) (NH₄)₂HPO₄ inhibited enzyme production around 80%. The extracellular form was purified until electrophoretic homogeneity (10.5-fold with 33% recovery) by DEAE-Fractogel and Sephacryl S-200 chromatography. The enzyme is a monomer with molecular mass of 102 kDa estimated by SDS–PAGE with carbohydrate content of 53.6%. Optima of temperature and pH for both, extracellular and cell extract invertases, were 60°C and 4.0–4.5, respectively. Both invertases were stable for 1 h at 60°C with half-lives of 10 min at 70°C. Mg²⁺, Ba²⁺ and Mn²⁺ activated both extracellular and cell extract invertases from P. variotii. The kinetic parameters K_m and V_max for the purified extracellular enzyme corresponded to 2.5 mM and 481 U/mg prot⁻¹, respectively.