Design of a Novel Multi-Layer Enzyme Membrane Reactor for Low-Fouling, Tailored Production of Oligodextran

Abstract

Controlling the molecular weight (Mw) of oligosaccharides in an enzymatic conversion process is a challenge in the production of intermediate-sized oligosaccharides. The enzymatic membrane reactor (EMR) with immobilized enzymes is proposed as a strategy to improve production of the intermediate-sized oligosaccharides. The immobilized enzymes catalyze reactions near the membrane surface, and the target molecules can be immediately separated from the enzymes once they reach the desired size. Hence, EMRs with immobilized enzymes enable better control on the product quality. However, immobilizing enzymes directly on the membrane surface usually causes inevitable membrane fouling and reduces the membrane separation performance. In this study, we proposed a novel configuration of EMR that contains a porous 3-D fibrous layer, that was produced via electrospinning, a porous mechanical support layer on top and a commercial separation membrane on the bottom. Polydopamine (PDA), tannic acid (TA) and (3-Aminopropyl) triethoxysilane (APTES) were firstly used to modify electrospun fibers to offer binding sites for enzyme immobilization. Then the enzymes were filtrated through the 3-layer structure for the immobilization. In comparison to the incubation-immobilized enzymes (produced 0.075 𝜇mol-isomaltose/min), the ‘fouling-induced’ enzyme immobilization proposed here significantly increased the immobilized enzyme activity up to 11.5 𝜇mol-isomaltose/min. Moreover, the extra layer on the membrane surface preserved the desired catalytic pattern of the enzymes, and reduced membrane fouling caused by the enzymes, and thus the membrane preserved high selectivity towards the oligosaccharides products. In the production of low Mw oligosaccharides, due to the high enzyme activity (up to 11.3 𝜇mol-isomaltose per minute) on the catalytic layer and excellent selectivity of the membrane, stable Mw of oligosaccharides were obtained, which indicates a successful high-performance EMR. Different separation membrane materials were compared in this work. Due to its good hydrophilicity and small pore size, RC10 membrane showed an excellent antifouling ability in the 3-layer EMR, and had the high oligodextran productivity.

Keywords: Enzyme Membrane Reactor, Oligodextran, Antifouling, Electrospun fibers.