Identity of Esters Produced in Milk Cultures of Pseudomonas Fragi

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Abstract
Isovalerate and acetate esters were the principal esters detected in the steam distillate of a milk culture of P. fragi which possessed a fruity aroma after 14 days incubation at 8[degree] C. Free isovaleric acid was the most prominent acid detected in culture distillates. Ethanol was the only volatile alcohol detected in cultured milk. Supplementation of sterile milk with ethanol prior to culturing stimulated rapid production of esters by the organism. In such cultures isovalerate ester was most prominent. Addition of as little as 0.01 ppm of ethyl isovalerate to milk closely simulated the fruity aroma produced in P. fragi milk cultures. Evidence is presented which indicates that ester production in milk culture may be markedly affected by the previous nutrition and/or incubation temperature of P. fragi cells used as inoculum. The role of leucine as a probable substrate in the production of isovalerate ester is discussed.