Abstract
Propionibacterium freudenreichii has been successfully applied to industrial anaerobic production of vitamin B12. In the traditional fed-batch fermentation process, 5,6-dimethylbenzimidazole (DMB) is used as a precursor. However, DMB can inhibit the synthesis of vitamin B12 metabolic intermediates, which is not conducive to semi-continuous fermentation of P. freudenreichii. To improve the fermentation efficiency, vitamin B12ex-situ biosynthesis was proposed and a membrane separation coupling fermentation technology was designed with adenosylcobinamide (Ado-cbi) as the indicator signal. The results showed that P. freudenreichii cells should be partly separated online at 84 h with 0.22-μm spiral membrane. The fourfold concentrated suspension was suitable for ex-situ biosynthesis of vitamin B12 with the addition of 3.60 mg L−1 DMB at 30 ℃ and pH 7.0. In the semi-continuous coupling fermentation process, vitamin B12 concentration reached 56.76 ± 3.86 mg L−1, an improvement of 161.6 %, while reutilizing fermentation wastewater and improving the anaerobic fermentation efficiency of P. freudenreichii.
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