Butanol-acetone-riboflavin fermentation

Fermentative Manufacture. Throughout the years, riboflavin yields obtained by fermentation have been improved to the point of commercial feasibiUty. Most of the riboflavin thus produced is consumed in the form of cmde concentrates for the enrichment of animal feeds. Riboflavin was first produced by fermentation in 1940 from the residue of butanol—acetone fermentation. Several methods were developed for large-scale production (41). A suitable carbohydrate-containing mash is prepared and sterilised, and the pH adjusted to 6—7. The mash is buffered with calcium carbonate, inoculated with Clostridium acetohutylicum and incubated at 37—40°C for 2—3 d. The yield is ca 70 mg riboflavin/L (42) (see Fermentation). 

The physiological state of the organism influences the yield of riboflavin, as well as that of volatile solvents, and consequently requires control (Leviton 1946). Transfer of inocula when approximately 25% of the gaseous products of fermentation have envolved is conducive to high yields. Butanol-acetone fermentation was of considerable importance during and shortly after World War II. For years it was of little or no importance, but recently it has again become of commercial interest. 

The Clostridia, particularly C. acetobutylicum, were the first microorganisms to attract interest for the production of riboflavin, initially as a by-product of the butanol-acetone fermentation process. More recently, however, Candida and especially the ascomycetes E. ashbyii and A. gossypii which yield much more flavin per imit of fermentation volume and are less sensitive to metal ion contamination in the medium, have replaced the... 

The first organism employed primarily for riboflavin production was Clostridium aceto-butylicum, the anaerobic bacterium used for the microbial production of acetone and butanol. Riboflavin was purely a byproduct and was found in the dried stillage residues in amounts ranging from 40 to 70 xg/g of dried fermentation solids. Later investigations disclosed that riboflavin could be produced by yeast such as Candida flareri or C. guillier-mondi, and the yield was as high as 200 mg/L. 

Over the years the butanol or the other minor solvents became more important than the acetone, and the process continued to develop. Different species of clostridia were used to produce these other solvents (e.g. C. butylicum for butanol and isopropanol, and C. butyricum for butyric and acetic acids). Strains were isolated which made a very efficient use of molasses rather than starch. The pH of the medium was controlled by aqueous ammonia rather than by chalk, giving a completely soluble medium suitable for in-line sterilisation. The spent cells recovered at the end of the fermentation were found to be a good source of riboflavin (Vitamin B2), and, after drying, were used as a supplement to animal feeds. The carbon dioxide and hydrogen were collected and sold, and continuous distillation was developed for the solvent recovery. 

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