Development of recyclable magnetic cross-linked enzyme aggregates for the synthesis of high value rare sugar d-tagatose in aqueous phase catalysis

Abstract

In this study, a high value rare sugar D-tagatose was synthesized using recyclable magnetic catalysts. A magnetic cross-linked enzyme aggregate (mCLEA) of L-arabinose isomerase (L-AI) was developed for the transformation of D-galactose into D-tagatose. Similarly, a combined magnetic cross-linked enzyme aggregate (Combi-mCLEA) of dual enzyme L-AI and β-galactosidase (β-Gal) was also prepared for the synthesis of D-tagatose from lactose in a cascade reaction. To accomplish this, L-AI alone and together with β-Gal was stabilized in magnetic nanoparticles (MNPs) and precipitated by an appropriate precipitating agent and then cross-linked by glutaraldehyde under optimal conditions. Immobilized catalysts were characterized by scanning electron microscopy, confocal laser scanning microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. Results suggested that the immobilized catalysts retained a maximum initial activity and achieved equilibrium level conversion in 24 h of enzyme catalysis. The main advantage of the developed magnetic catalysts was their recovery using an external magnet after completion of the reaction. Additionally, mCLEA and Combi-mCLEA showed reusability potential for more than 10 consecutive batch cycles of rare sugar D-tagatose synthesis from D-galactose and lactose, respectively. Thus, these immobilized magnetic catalysts have shown promising catalytic potential for the synthesis of D-tagatose.