Monitoring bacterial metabolites in cultured buttermilk by high performance liquid chromatography and headspace gas chromatography.

A commercial buttermilk culture was added to Grade a skim milk. Samples were analyzed hourly for a total of eighteen hours. Headspace gas chromatography measured changes in acetaldehyde, acetone, ethanol, and diacetyl concentrations. High performance liquid chromatography measured changes in orotic, citric, pyruvic, lactic, uric, acetic, and propionic acid concentrations. Consumption of orotic acid and citric acid substrates was noted. Production of diacetyl, ethanol, pyruvic, lactic, acetic, and propionic acids was observed. Acetaldehyde concentration increased initially and then decreased as ethanol was formed. Acetone and uric acid concentrations remained constant during fermentation. In addition, chemical changes occurring during refrigeration were measured after seven days. Acetaldehyde, ethanol, and acetic acid increased in concentration; diacetyl, orotic, citric, pyruvic, lactic, and propionic acids decreased in concentration. Also, a headspace gas chromatographic test was done for the quantitation of acetoin.