Studies on fermentative, microbiological and biochemical properties of kefir and kefir grains.

摘要

Kefir is a self-carbonated refreshing fermented milk drink, which has an exotic taste due to a mixture of lactic acid, slight alcohol, carbon dioxide and other flavor products. It is produced by fermentative activity of “kefir grains” which have a relatively stable and specific balance of microorganisms that exists in a complex symbiotic relationship. In this study, fermentative, microbial, and biochemical properties of kefir and kefir grains were examined. In the first study, the changes in organic acids (orotic, citric, pyruvic, lactic, uric, acetic, propionic, butyric and hippuric) and volatile flavor substances (acetaldehyde, acetoin, diacetyl, ethanol) as a result of microbial growth through kefir fermentation and 21 day of cold storage were determined. Also, microbial growth during kefir fermentation and cold storage was determined. Kefir cultures produced 7739μg/g lactic acid on day 21. Acetic, propionic and butyric acids were not detected during kefir fermentation and storage. The average final concentration of acetaldehyde was 11 μg/g at the end of the storage. Ethanol concentration reached 0.08% by day 21. Lactic acid bacteria, lactococci, lactobacilli and yeast populations increased during fermentation and slightly increased during cold storage. Kefir grains had lactic acid bacteria: yeast ratio of 109:106. Scanning electron microscopy indicated that yeast colonized especially on the surface towards middle part, however, short, long and curved lactobacilli were noted throughout the grain. The antimutagenic power of kefir was determined and compared to yogurt and milk using different mutagens in the Ames Salmonella microsomal test. Acetone extracted fermented milk samples were significantly inhibited mutagenicity at different percentages for MMS, SA, AFB1 and 2-AA. After antimutagenicity was determined, the quantities of anticarcinogenic components of milk, yogurt and kefir were determined along with the fatty acid and amino acid profiles of milk, yogurt and kefir. Fatty acid results indicated that kefir had higher concentrations of fatty acids than milk and yogurt. Butyric, palmitic, palmitoleic, oleic acids and three isomers of CLA (c9, t11; t10, c12; t9, t11), which have been proven as anticarcinogenic components of milk fat, were in higher concentrations in kefir. Results indicated that only very slight differences in amino acid profiles occurred among the three different products. Kefir had higher amounts of threonine (P 0.05), serine (P > 0,05), alanine (P > 0.05), lysine (P > 0.05), and ammonia (P > 0.05) than milk or yogurt.