Process-intensified continuous biomanufacturing of mannitol via fiber-bed immobilized Lactobacillus buchneri and membrane-coupled separation

Abstract

D-Mannitol is a high-value functional sugar alcohol used in food, pharmaceutical, and chemical applications, but biological production requires improved productivity and operational stability to better compete with catalytic hydrogenation. Lactic acid bacteria are promising whole-cell catalysts for mannitol production because they reduce fructose to mannitol via mannitol dehydrogenase (MDH). In this study, a wild-type food-associated Lactobacillus buchneri CGMCC 7300 isolated from fermented vegetables was used to construct a continuous biotransformation system integrating cotton fiber-bed immobilization and membrane separation. This strain enabled stable whole-cell fructose-to-mannitol conversion without genetic modification, and process performance was improved through engineering integration rather than microbial strain engineering. The process combined fructose-glucose redox balancing, 0.1 μm microfiltration-mediated cell retention and product withdrawal, cotton fiber-bed immobilization, and weak-base anion-exchange deacidification. The optimized fructose-to-glucose ratio of 1.25 balanced reducing-power supply and demand and enabled 95% fructose conversion in shake-flask transformation. In the 7 L system, microfiltration-assisted cell retention and medium renewal increased biomass to OD₆₀₀ = 8.3 and supported stable free-cell continuous operation with 51.50 g/L mannitol. Further integration with a cotton fiber-bed reactor enabled operation at a higher dilution rate (0.06 h⁻¹), maintaining 52.05 g/L mannitol, > 90% fructose conversion, and a volumetric productivity of 3.12 g/(L·h), approximately twofold higher than the free-cell continuous process. The system retained stable conversion during the 120 h continuous operating window and used an inexpensive reusable carrier. These results demonstrate that coupling immobilized-cell engineering with membrane-assisted operation improves productivity and operational stability in continuous mannitol biotransformation.

Graphical abstract

Keywords

Mannitol / Lactobacillus buchneri / Cotton fiber-bed immobilized reactor / Membrane-coupled separation / Continuous biotransformation / Sugar alcohol biomanufacturing.

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Funding

National Natural Science Foundation of China(31871740)

National Key R&D Program of China(2024YFA0917900)

Rights & permissions

Jiangnan University