Study On Process Of Propionic Acid Fermentation

The propionic acid which is mainly produced by chemical methods is an important industrial product. With the lack of fossils, the bio-manufacture of chemical products is becoming more and more important. The process of propionic acid fermentation has been the hot research areas.The Propionibacterium shermanii W125 is an excellent strain used in industrial for VB₁₂ production. It can accumulate propionic acid and acetic acid when it accumulate VB₁₂ intracellular. Because the content of propionic acid is less than 2 % and without any extraction value, it is released with waste water. This paper focused on improving the propionic acid yield and with the VB₁₂ yield unreduced. The main research results are as follows:A simple effective chromatography method is established to detect propionic acid, acetic acid and VB₁₂.The metabolic characteristics of Propionibacterium shermanii W125 is studited. The standardized operating procedures is established. The Propionibacterium W125 strain induced by ultraviolet light, a mutant strain W321 was selected with fast-growing, high yield of acid and the vitamin B₁₂ output unreduced.The batch fermentation of P. shermanii W321 was studied. The results showed that the fermentation cycle was 66 h, the yields of propionic acid and Vitamin B₁₂ was 2.87 % and 42μg/mL respectively, under the condition of 6 %glucose; 2.5 %corn slurry (dry matter); 0.2 %KH₂PO₄; 10 mg/L CoCl₂; 20 %inoculation; culture temperature, 30°C; pH 6.5. The yields of propionic acid and vitamin B₁₂ were 36,7 % and 5.2 % higher respectively, and the fermentation cycle was shortened by 30 h, compared with the W125 fermentation.The impact of sugar-fed-batch fermentation technology on the acid yield by P. shermanii W321 was studied. The initial glucose concentration was 6 %, then added 3 % glucose since the fermentation time at 48 h, 72 h and 108 h. The production of propionic acid reached to 4.5 % and transformation sugar into propionic acid was 30 %, the cell wet weight was 7.82 % and the vitamin B₁₂ production was 44μg/mL, the fermentation cycle was 168 h. Although the fermentation cycle longer 102 h than traditional batch fermentation, the final concentration of propionic acid, cell wet weight and vitamin B₁₂ productions increased. The KS impermeability impact on acid yield by P. shermanii W321 was studied. The results showed that KS accelerate obviously the cell-growth and the rate of acid yield. Associated with sugar-fed fermentation technology, at the condition of 0.3 %KS, the initial glucose concentration was increased to 9 %, then added 3 % glucose since the fermentation time at 60 h and 84 h. The fermentation cycle was 114 h. At the end of fermentation, the production of acid was reached to 5.35 % and transformation sugar into propionic acid was 36.1 %, the cell wet weight was 9.9 %, the vitamin B₁₂ production was 51μg/mL, the fermentation cycle was 114 h. Compared with the fed-batch fermentation technology whose initial sugar was 6%, the final propionic acid concentration, and transformation sugar into propionic acid, the cell wet weight and vitamin B₁₂ were increased, and the fermentation cycle were shortened. After fermentation broth filtered, the cell was for vitamin B₁₂ extraction. The colorless fermentation liquid was obtain after bleached.The changes of fermentation kinetics of P. shermanii W321 under the condition of decompression was firstly reported. The result indicated that the cell-growth and fermentation product decreased. From the metabolic cycle ways, the CO₂ was involved in the Wood-Werkman cycle by methlmalonyl CoA carboxylase catalyzed carboxy group tranferring reaction. Decompression might reduce the concentration of CO₂ in fermentation broth, and impact CO₂ carboxylating reaction.In conclusion, the P. shermanii W125 was induced and the mutant strain(W321) fermentation technology was studied. The level of propionic acid fermentation was improved from 2 % to 5.35 %, and increased by 268 %; the VB12 production was improved from 40μg/mL to 51μg/mL, and increased by 20.7 %.