Process Integration Of Propionic Acid /Vitamin B₁₂ Coupling Fermentation And Metabolic Component Control

Fermentation process of propionibacterium strains will not only produce propionic acid based of organic acids,but also produce vitamin B₁₂,the traditional fermentation process is often only harvest a product.In order to improve the economics of fermentation,a new bioreactor characterized by membrane separation and in situ adsorption of ion exchange resin was established to realize the two-product coupling fermentation of propionic acid/vitamin B₁₂.The carbon source components in the base regulate the heterogeneous acid components in the metabolites and improve the substrate conversion efficiency of propionic acid.The main research results of this paper are as follows:In order to solve the adverse effect of DMB on fermentation and the feedback inhibition of propionic acid in semi-continuous fermentation of Propionibacterium freudenreichii,a semi-continuous coupling fermentation process of "edge fermentation,edge separation and side transformation" was established,to achieve the production of propionic acid/vitamin B₁₂.（1）Based on the membrane separation of bacteria,the anion chromatography technique was used to separate the propionic acid from the fermentation broth in situ to remove the feedback inhibition of propionic acid.The results showed that the yield of propionic acid reached 57.55g/L,the yield of propionic acid was 0.34g/（L.h）and the conversion of glycolic acid was 0.61g/g after the adsorption of ZGD630 with weakly basic anion exchange resin,compared with batch fermentation were increased by 24.54%,21.43%,19.61%.（2）A 10 L scale propionic acid/vitamin B₁₂ bi-product coupled fermentation system was established by considering the volume of fermentation tank,the adsorption capacity of ZGD630 resin and the membrane flux.The cell transformation process of vitamin B₁₂ was established.The results showed that when the fermentation was carried out for 84 h,the fresh seed liquid was added to the fermentation broth for removing propionic acid on the basis of the on-line separation of the cells at 84 hours,and 0.9 mg/L DMB was added for vitamin B₁₂.The yield of vitamin B₁₂ was 28.36mg/L at the end of fermentation,which was 18.26 %higher than that of batch fermentation.The yield of propionic acid was 59.75g/L,which increased by 33.73%.（3）The yield of propionic acid was 122.47g/L after the five-cycle continuous fermentation system,and the yield of vitamin B₁₂ was 54.81mg/L.The process was only 504 h,which was equivalent to 3 batches of fermentation time.The equipment utilization efficiency has been significantly improved,reflecting the good application prospects.In order to effectively control the ratio of mixed acid（succinic acid,lactic acid and so on）in the fermentation broth,the conversion efficiency of the carbon source to propionic acid was improved.Propionibacterium acidipropionici was used as the experimental strain to optimize the carbon source components in the culture medium and concentration,pH adjustment,increased propionic acid production.（1）The content and proportion of propionic acid,succinic acid,lactic acid and acetic acid in the fermentation broth were analyzed when the glucose and glycerol were used as the single carbon source and the two were mixed（different proportions）.The results showed that the yield of propionic acid was 45.58g/L and 48.52g/L respectively when the glucose and glycerol were single carbon source,and the yield of succinic acid was 26.08g/L and 10.29g/L,respectively.When the fed-batch fermentation was carried out,the yield of lactic acid increased first and then decreased,indicating that the different concentration of carbon source affected the production of mix acid.Thus,the proportion of the acid in the fermentation broth can be controlled by adjusting the ratio of glycerol to glucose.（2）Optimize the ratio of glycerol to glucose in the culture medium and increase the yield of propionic acid.The results showed that when the concentration of glycerol and glucose was20g/L and 80g/L（1:4）,the yield of propionic acid was 54.75g/L,which was increased by20.12%;the yield of succinic acid was 8.49g/L,67.45%,sugar and acid conversion rate of0.57g/g,increased by 18.75%.（3）The glycerol concentration in the fermentation broth was maintained at below 5g/L by the way of subsection supplement.The results showed that the yield of propionic acid was56.29g/L and the yield was 0.24g/（L.h）,and the conversion of glycolic acid was 0.61g/g.（4）The effects of NH3H₂ O,Ca（OH）₂,KOH and NaOH on the metabolism of propionic acid were analyzed.The results showed that when Ca（OH）₂ was used to adjust the pH value,the yield of propionic acid was the highest,also conducive to the production of calcium propionate products.