Abstract:

The major flavor components in milk fermented by lactic acid bacteria alone or together with yeast isolated from
Sayram Ketteki were analyzed by solid-phase micro-extraction (SPME)-gas chromatography-mass spectrometry (GC-MS). Results
showed that volatile fatty acids were mainly produced in milk fermented by Lactobacillus helveticus MB 2-1 alone, of which acetic
acid was the major component. In milk fermented by Lactobacillus helveticus MB 2-1 and Streptococcus hermophilus MB 5-1
together, the content of acids showed an obvious decrease while ketones indicated a significant increase; meanwhile, 3-hydroxy-2-
butanone was the major flavor compound. Totally 11 kinds of volatile components were detected in milk fermented by L. helveticus
MB 2-1, S. thermophilus MB 5-1 and Kluyveromyces. marxianus Y51-1, including acids, alcohols, esters and ketones, of which
the major flavor components were ethanol, acetic acid, ethyl ester and 3-hydroxy-2-butanone. Only 9 volatile components were
detected in yogurt from the market, of which 2,3-butanedione was the major flavor compound. This study further illustrated that
Sayram Ketteki is a unique local fermented dairy product in China. There was a significant difference in fermentation microflora,
sensory characteristics and major flavor components between Sayram Ketteki and common yogurt.

Key words: Sayram Ketteki, Lactobacillus helveticus, Streptococcus thermophilus, Kluyveromyces marxianus, flavor components, solid-phase micro-extraction (SPME)-gas chromatography-mass spectrometry (GC-MS)