Development of a thermo-stable and recyclable magnetic nanobiocatalyst for bioprocessing of fruit processing residues and D-allulose synthesis

•Smt3-D-psicose 3-epimerase was immobilized onto functionalized magnetic nanoparticles.•Immobilization remarkably improved the thermal stability of enzyme.•The immobilized enzyme showed reusability potential for multiple duty-cycles.•The nanobiocatalyst was employed for bioprocessing of fruit processing residues and biosynthesis of D-allulose production.

The aim of the study was to covalently immobilize Smt3-D-psicose 3-epimerase onto functionalized iron oxide magnetic nanoparticles. After immobilization, Km of the immobilized enzyme increased, however, Vmax was nearly the same as that of its free form, indicating that immobilization has no detrimental effects on its catalytic output. The covalent immobilization caused a reduction in the deactivation rate constant (kd) values leading to 4-5 fold enhancement in its half-life at 50-65 °C, indicating significant thermal stability of the iron-enzyme nanobioconjugate. The immobilized enzyme showed excellent storage stability by losing only 20% activity even after 60 days of storage at 4 °C. The immobilized enzyme retained up to 90% of its initial activity even after 10 consecutive cycles of catalyzing D-fructose epimerization reactions. Thus, after immobilization the enzyme exhibited remarkable improvements in thermal tolerance, storage stability and recycling efficiency, useful for development of industrially exploitable process for D-allulose production.