evaluation of flavor and aroma compounds present in kefir

abstract: kefir is fermented milk that has a unique flavor because of acetaldehyde, diacetyl, acetoin and ethanol. the aim of this study was to evaluate flavor and aroma compounds present in kefir. two types of starter (christian hansen and sacco) and three levels of temperatures (30, 33 and 35oc) were used for the preparation of kefir samples. the samples were analyzed for acetaldehyde, diacetyl, acetoin and ethanol by gc equipped with fid detector. levels of acetaldehyde, diacetyl, acetoin and ethanol were increased with raising the temperature and decreased during cold storage from the first day until the 14th day. ph was decreased and acidity was increased in all samples during cold storage. after organoleptic evaluation, the prepared sample by sacco at 35oc was known as the best sample and then the prepared samples by sacco at 33 and 30oc were recognized as the favorable samples.   keywords: aroma and flavor compounds, fermentation, kefir, starter.