Invertase production by Rhodotorula toruloides in submerged and surface adhesion on magnetic nanoparticles fermentations

The invertase production by Rhodotorula toruloides was evaluated in the submerged fermentation and surface adhesion fermentation on the chitosan-coated magnetic manganese ferrite nanoparticles (MnFe2O4-Ch). The synthesis of chitosan-coated manganese ferrite was carried out by coprecipitation in a one-step method. According to X-ray diffractograms, the manganese ferrite magnetic nanoparticles had a spinel structure, and the crystal size calculated by the Scherrer equation was 20.12 nm. FTIR verified the presence of chitosan amino groups, which were quantified spectrophotometrically in reaction with ninhydrin, obtaining 7.53 mmol/g of nanoparticles. The hydrodynamic size of MnFe2O4-Ch was analyzed by DLS and revealed the presence of agglomerates. The mean particle size, obtained through Gaussian fitting of the histogram, was 239 nm. The MnFe2O4-Ch magnetic saturation was 36.7 emu/g at 20 kOe and 300 K. In the kinetic assay, by counting free cells in the Neubauer chamber after applying an external magnetic field, it was demonstrated that equilibrium in the absorption of yeast in MnFe2O4-Ch was achieved after 2 h of incubation. Adsorption isotherm at 30 degrees C was fitted to the Freundlich model. The fermentation was performed in the presence and absence of MnFe2O4-Ch. Results on the gravimetric assay and cell count with and without trypan blue assay indicated that the presence of magnetic nanoparticles in the fermentation had no adverse effect on the growth and viability of R. toruloides. The highest enzymatic activity (0.86 +/- 0.03 UI/mL) was observed in the presence of MnFe2O4-Ch at 1 mg/mL. Fermentation by adhesion to the surface of magnetic nanoparticles may have advantages in enzyme production by yeast.