Detection of Metabolites Produced by Psychrotrophic Bacteria Growing in Milk

Abstract

The objective of this investigation was to evaluate the use of gas-liquid chromatography for the detection of metabolites produced by psychrotrophic bacteria in milk. Alcaligenes viscolactis, Pseudomonas fragi, Pseudomonas perolens, and Bacillus pumilus were inoculated into pasteurized milk or raw milk which had been “cold sterilized” with hydrogen peroxide. The milk samples were incubated at 7 C, and plate counts were determined at intervals. Samples of the headspace vapors were analyzed by gas-liquid chromatography. Chromosorb W coated with 10% Carbowax 20M gave clearer separation of the volatiles than Gas Chrom Z coated with 4% Apiezon L. In general, chromatograms contained peaks representing acetaldehyde, acetic acid, acetone, ethanol, and an unidentified compound. Acetaldehyde was the best indicator of high numbers of psychrotrophic bacteria in milk. Direct analysis of headspace vapors of milk by gas-liquid chromatography appears to have the potential for providing a rapid means of detecting metabolites produced by bacteria in milk. © 1976, American Dairy Science Association. All rights reserved.