Farklı yağ oranlarının ve farklı starter kültürlerin kefirin nitelikleri üzerine etkisi
Özet
In this study, the effect of different levels of fat and starter cultures on some properties of kefir was examined. For this purpose, kefir samples were made from cows? milk with different fat levels, by adding kefir grains for the first stage fermentation to a pH value of 5.0-5.5, then by using starter cultures for the second stage. Properties of kefir samples obtained by this two-stage fermentation were investigated comparatively with those of the samples made by traditional method and the possibilities for improving the aroma and flavour characteristics by using different starter cultures tried to reveal. Thermophilic, probiotic, mesophilic-aromatic cultures of bacteria and yeast cultures were used to stimulate the formation of acidity, carbondioxide and aroma?flavour compounds. Fifteen samples of kefir, totally (5 different starter cultures x 3 different fat level), were analyzed for sensorial, chemical and microbiological properties on days 1, 5, 10, 16 and 23 during the storage for over 3 weeks. Free fatty acids and aroma compounds were also determined in the samples.According to the results, titratable acidity, carbondioxide content, tyrosine value and lactic acid content increased during the storage in all the samples, while the number of microorganisms decreased especially from days 5 and 10. Concentration of acetaldehyde and ethanol increased gradually, whereas acetone and diacetyl concentrations decreased during the storage in the samples with 3 different fat levels. Contents of free fatty acids also showed a gradual increase during the storage depending on the fat levels in the samples. From the sensorial point of view, whole fat kefir samples were preferred to the non-fat and half-fat samples. Furthermore, the samples made by second stage fermentation had an overall points higher than those of the samples made by traditionally. Kefir samples made by using probiotic, mesophilic-aromatic culture of bacteria and yeast culture were preferred more by the panel members.