Studies on Starter Metabolism. IV. Effect of Various Substrates on the Formation of Acetoin by a Mixed Strain Starter Culture

The mechanism and the source of carbon for the formation of acetoin by a mixed culture consisting predominantly of Streptococcus eremoris and Leuconostoc species have been studied, using both a reconstituted milk and a dialyzed milk medium.Of the various metabolites added to the dialyzed medium, only citric, oxalacetic, pyruvic, and alpha-keto butyric acids stimulated the formation of ketol; the alpha-keto butyric acid gave rise to a ketol tentatively identified as 3-hydroxy-2-pentanone.Acetaldehyde, isobutyraldehyde, and crotonic acid inhibited acetoin formation.The tricarboxylic acid cycle intermediates, malic, succinic, cis-aconitic, and alpha-keto glutaric '-)54 w.O.MIZUNO AND J. J. JEZESKI