Stabilizing enzymatic membrane reactor for precise production of oligodextran with tailored molecular weight

Enzyme membrane reactor (EMR) provides an effective strategy for controlling molecular weight (Mw) of oligodextrans. However, the synergistic effect between dextran hydrolysis and product separation as well as continuous operation stability remains still unclear. We observed that covalently immobilized dextranase exhibited more obvious exo-hydrolysis behavior compared to free enzymes probably due to enzyme conformational alterations. Using non-covalently immobilized enzyme, suitable ultrafiltration membrane, optimal substrate/enzyme ratio and matched permeate flux, the yield of the target product reached 62.8%. However, the non-covalently immobilized dextranase exhibited reduced hydrolytic activity and more obvious membrane fouling (caused by high-Mw dextran). When free dextranase with high activity was used together with suitable permeate flux and high shear rate, the yield increased to 72.0%. The obtained EMR maintained stable for 8 h with slight fouling formation because enzymatic hydrolysis and membrane separation were well matched. The polydispersity index of the target product reached 1.3 (analytical grade) following diafiltration purification.