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Organic Acid Production of Propionibacteria. II. Effect of Growth Accessory Substances on Propionic and Acetic Acid Production in Milk¹

Department of Dairy Technology, The Ohio State University, Columbus

ABSTRACT

Cultures of propionibacteria for Swiss cheese are usually grown in broth and added to the milk at the beginning of the cheese-making operation. It would be advantageous to grow these organisms in milk for economic reasons and, also, because of the possibility of developing adaptive enzymes which may be important in the enzymatic activity of these organisms during the cheese-ripening process. However, attempts to grow propionibacteria in milk have been unsatisfactory, probably because their nutritional requirements have not been satistied.

In the previous paper of this series (4), results revealed that the propionic and acetic acid production of Propionibacterium shermanii, grown in broth media, could be increased by the addition of various metabolic intermediates. These findings encouraged further work to determine if the activity of these organisms in milk could be stimulated in a similar manner.

Wood et al. (11) obtained an ether-soluble factor from yeast extract which was indispensable for the growth of all cultures or propionic acid bacteria, tested on a synthetic medium that contained ammonium sulfate as the nitrogen source.

¹ Technical Article 11–56, Department of Dairy Technology, The Ohio State University. Supported in part by funds from the Ohio Dairy Products Research Fund.