Determination of Organic Acids and Volatile Flavor Substances in Kefir during Fermentation

The production of organic acids and volatile flavor components was measured during kefir starter culture fermentation. Samples were collected at 0, 5, 10, 15, and 22 h of fermentation (final pH=4.6). Samples were analyzed for orotic, citric, pyruvic, uric, lactic, acetic, butyric, propionic and hippuric acids by HPLC. Acetaldehyde, ethanol, acetoin and diacetyl production were monitored using GC equipped with headspace autosampler. Levels of orotic, citric, and pyruvic acids slightly decreased during fermentation. Hippuric acid was totally consumed by 15 h of incubation. Acetic, propionic, and butyric acids and diacetyl were not detected. Production of ethanol began only after 5 h of incubation whereas acetaldehyde and acetoin increased during fermentation.