PRODUCTION OF PROPIONIC-ACID

Propionic acid and its salts are widely used in industry and especiall y in the food industry as antifungal agents. The estimated world produ ction in 1992 was about 100 000 tonnes. A large part of this productio n is by petrochemical routes. Nevertheless, fermentation processes hav e been described since 1923. The increasing consumer demand for biolog ical products and the more efficient performance of new fermentation p rocesses have revived researcher and industrial interest for a new inv estigation of biological propionic acid production. From the low produ ctivity of batch processes (0.03 gl(-1) h(-1)), performance has rapidl y increased to 2 to 14 gl(-1) h(-1). This increase results from the em ergence of high density cell bioreactor technology. These bioreactors make it possible to concentrate large amounts of cells within the syst em during continuous fermentation and to reduce the cell inhibition ef fect of organic acid accumulation in the medium. Moreover, the use of glycerol as the principal carbon source enables propionic acid to be p roduced without acetic acid. The increased efficiency of membrane proc esses, such as electro-electrodialysis and electrodialysis with bipola r membrane, has considerably facilitated the recovery and purification steps from fermented media. The increased fermentation volumetric pro ductivity and downstream processing performance has led to an economic industrial biological propionic acid production.