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Journal of Dairy Science Vol. 48 No. 9 1174-1178
© 1965 by American Dairy Science Association ®
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Methyl Sulfide Production by Aerobacter aerogenes in Milk1

Tran T. Toan2, R. Bassette and T. J. Claydon

Department of Dairy and Poultry Science, Kansas State University, Manhattan

ABSTRACT

Aerobacter aerogenes was isolated as the causative organism in samples of commercial milk having defects described as cowy or feedy, or both. The fact that aqueous solutions of trace amounts of methyl sulfide (Me2S) give similar flavors led to a study of its production by A. aerogenes in milk. Inoculation of the organism into vacuum heat-treated, homogenized milk was followed by measuring bacterial development, titratable acidity, Me2S concentration, and flavor characteristics. In three separate trials, inoculated milk incubated at 5 C developed from 500–800 ppb Me2S when bacterial counts were between 1 and 100 million/milliliter. This occurred between the third and fifth day. Levels of Me2S were determined by gas chromatographic analysis from standard curves prepared in homogenized milk. The concentrations of Me2S produced greatly exceeded its threshold level of 115 ppb in homogenized milk. Flavors characterized as Me2S-like, molasses-like, or cowy were observed after three days when the Me2S peaks appeared. The Me2S concentration decreased rapidly from the fifth to the seventh day, during which time the odor characteristics of the milk also changed.

FOOTNOTES

1 Contribution no. 623, Department of Dairy and Poultry Science, Kansas Agricultural Experiment Station, Manhattan.

2 Present address: Saigon, Vietnam.






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Copyright © 1965 by the American Dairy Science Association ®.