Unraveling the self-regulation mechanism of molecular weight in cross-flow enzymatic membrane reactors for stable oligodextran production.

The enzymatic membrane reactor (EMR) offers a sustainable approach to biomanufacturing, yet maintaining stable performance over prolonged periods remains a significant challenge due to membrane fouling and enzyme activity decline. To tackle these issues, we innovatively utilized a loose ultrafiltration membrane in a cross-flow EMR that completely retains enzymes while lacking the capability to separate intermediate and target products, thereby preventing the excessive retention of target products by the fouled membrane. By optimizing the dextran/dextranase ratio and substrate residence time, we achieved flexible control over the molecular weight (Mw) of products in the permeate. Our findings indicate that decreased enzyme activity exacerbates concentration polarization, leading to reduced permeate flux and prolonged residence time. This dynamic facilitates a re-matching of the substrate/enzyme ratio with residence time, effectively addressing the instability of the EMR caused by declining enzyme activity. Notably, this study reveals the intrinsic relationships between enzyme activity, permeate flux, and membrane fouling dynamics, alongside their self-regulation mechanisms for product Mw. Leveraging the ability of dextranase to preferentially degrade higher Mw dextran, a continuous feeding mode was employed under optimal conditions, allowing the EMR to sustain steady-state operation for 28 h while consistently producing oligodextran within the target Mw range of 3–6 kDa. Furthermore, the successful application of industrial-grade dextran substrate highlights the scalability and industrial relevance of EMRs for continuous oligodextran production. [Display omitted] • A loose UF membrane is used in EMR to avoid excessive retention of target products caused by fouling. • Product molecular weight is well controlled by optimizing dextran/dextranase ratio and residence time. • Self-regulation effect among enzyme activity, permeate flux, and residence time in the EMR is clarified. • It exhibits unique fouling behavior in a mixed molecular weight dextran and enzymatic reaction system. • Industrial-grade dextran is used in the EMR for the first time and shows similar results as pure dextran. [ABSTRACT FROM AUTHOR]