Ultra-small magnetic Candida antarctica lipase B nanoreactors for enzyme synthesis of bixin-maltitol ester.

Abstract

Bixin has desirable bioactivities but poor water solubility, which limits its practical applications. Enzymatic transesterification of methyl to alditol groups in bixin by Candida antarctica lipase B (CALB) improves bixin water solubility. Herein, magnetic CALB nanoreactors with diameter of 11.7nm and CALB layer thickness of 3.5nm were developed by covalently linking CALB onto silicon covered Fe3O4 nanoparticles. The CALB loading capacity in nanoreactors achieved 30%. The Michaelis constant (Km) and maximum reaction rate of magnetic CALB nanoreactors were 56.1mmol/L and 0.2mmol/(L·min). Magnetic CALB nanoreactors could circularly catalyze bixin-maltitol ester synthesis and keep catalytic efficiency of 62.6% after eight repetitive enzymatic reactions. Additionally, the optimal bixin-maltitol ester synthesis procedure was heating bixin-maltitol mixture at molar ratio of 1:7 in anhydrous 2-methyl-2-butanol-dimethylsulfoxide (8:2, v/v) at 50°C for 24h. Bixin-maltitol ester showed improved water solubility at pH 5.5 and 7.0.