Out of all vitamins now available commercially, vitamin B12 and vitamin B2 (riboflavin) are the main that are produced by microbial fermentations.
Vitamin B12 (Cyanocobalamine; Cobalbumin)
This vitamin is recovered as a by-product of streptomycin and aureomycin antibiotic fermentations. A soluble cobalt salt is added to the fermentation reaction as a precursor to vitamin B12. Relatively high amounts of this vitamin accumulate in the fermentation medium at concentrations that are not toxic to Streptomyces species.
Vitamin B12 (Cyanocobalamine) is also produced on large scale by direct fermentation. Propionibacterium shermanii or Pseudomonas denitrificans are the bacteria which are used now-a-days for fermentation processes. P. shermanii is grown in anaerobic culture for 3 days at 30°C and in aerobic culture of 4 days; the fermentation medium (growth medium) contains glucose, corn steep liquor (a waste product of starch manufacture), ammonia and cobalt chloride. Ammonia is used in the form of ammonia hydroxide that maintains the pH of the medium at 7. Pseudomonas denitrificans is grown for 2 days in aerobic culture medium containing sucrose, betaine, glutamic acid, cobalt chloride, 5, 6 dimethylbenzimidazol, and salts.
The vitamin resulted in the fermentation are retained within the cells. The cells are, therefore, collected by high-speed centrifugation and the vitamin B12 is recovered by releasing the vitamin from the cells by treating with acid, heating, cyanide, etc. The vitamin thus released from the cell is absorbed on ion-exchange resin IRC-50 or charcoal. It is then purified further by phenol and water. The vitamin is finally crystallized from aqueous-acetone solutions. The normal yield is 23 mg/litre when Propionibacterium is used.
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