Magnetic immobilization of Rhodotorula toruloides for biomass reuse in fermentation cycles and biocatalytic processes...

The goal of the present study was to define better conditions for the invertase production from the yeast Rhodotorula toruloides in the surface adhesion fermentation (SAF) in the presence of magnetic chitosan-coated (MnFe₂O₄-Ch) manganese ferrite nanoparticles and to evaluate their reuse in different fermentation cycles. The synthesis of MnFe₂O₄-Ch was performed using the one-step chemical coprecipitation method, which was assisted with hydrothermal treatment. Box-Behnken design was applied to establish the relationship between the selected parameters. The reuse of the immobilized biomass was evaluated with and without the MnFe₂O₄-Ch addition in several fermentation cycles. According to X-ray diffraction results, the MnFe₂O₄-Ch exhibited a spinel structure with a crystallite size of 20.73 nm. The mean particle hydrodynamic size was 181.7 nm, the magnetic saturation was measured to be 39.6 emu/g at 20 kOe and 300 K. The growth of R. toruloides microorganism was stimulated with MnFe₂O₄-Ch, and a more significant effect was observed at the concentration of 2 mg/mL. The microorganism produced an invertase enzyme, and higher enzyme activity (1.88 IU/mL) was detected with the MnFe₂O₄-Ch at 1 mg/mL. The enzymatic activity increased by 69% in surface adhesion fermentation compared to submerged fermentation. In the third cycle of SAF with reused immobilized yeast and MnFe₂O₄-Ch addition, the enzymatic activity increased compared to the first two cycles of reuse, reaching values without significant difference compared to the enzymatic activity in the initial SAF. Surface adhesion fermentation may be an appropriate method to improve invertase production from R. toruloides.