Surface activation of hierarchically porous diatomite modified with polyethyleneimine for immobilizing d-allulose 3-epimerase

Abstract

d-Allulose, a low-calorie functional sweetener popular among the obese population, can be biosynthesized using d-allulose 3-epimerase (DAE). However, there are currently no commercially viable immobilized DAE enzymes on the market for the large-scale production of d-Allulose. In this study, immobilizing the DAE enzyme was developed based on polymer-activated diatomite with surface enhancement using crosslinkers. Specifically, the amino groups of polyethyleneimine were successfully carried on the porous diatomite and then activated by glutaraldehyde to form a biopolymer coating. The obtained carrier was firmly covalently linked to the DAE enzyme via the Schiff-base reaction. The constructed immobilized DAE with a “core-shell” structure showed a high specific activity of 2088.93 ± 9.85 U/g and an excellent conversion rate of 34.4%. This biocatalyst was stable within a wide temperature and pH range. It also showed outstanding thermal stability, the half-lives of the immobilized DAE were 109 and 124 times that of the free DAE at 55 °C and 60 °C, respectively. Moreover, the immobilized DAE remained at about 81.33% of the initial enzyme activity after 8 recycles. The results of this study may contribute to the cost reduction of d-Allulose industrial production and provide a potential immobilized enzyme strategy for future large-scale manufacturing of d-Allulose.