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Deamination of Glutamic and Aspartic Acids by Geotrichum candidum

Department of Food Science, Cornell University, Ithaca, NY 14853

ABSTRACT

Strains of Geotrichum candidum were isolated from the surface of a commercial sample of Limburger cheese and from raw milk. Growth of the isolates in an acidified tryptone-yeast extract medium was accompanied by a rise in the pH of the medium from 3.5 to above 7.0. Ammonia production, as indicated by Nessleriza-tion, was associated with the deamination of glutamic and aspartic acids. The first reaction in the production of ammonia from glutamic acid, isomerization to (ß-methylaspartic acid, required vitamin B₁₂ and the second reaction, the deamination of ß-methylaspartic acid to mesaconic acid and ammonia, was dependent on magnesium and potassium. The conversion of aspartic acid to fumaric acid and ammonia required magnesium. These minerals were in sufficient amounts in the Limburger cheese for optimum deaminase activity.