Physicochemical and Rheological Properties of Commercial Kefir Drinks

Kefir is one of the most preferred fermented beverages, and its production constitutes a significant portion of the dairy industry. In this study, the physicochemical and rheological properties of commercial plain kefir drinks were compared. Kefir drinks of dominant brands in the Turkish kefir market (n=6) were obtained from national markets, and samples with different production dates for each brand were used as replications. The ranges for the dry matter, protein and fat contents (%) of kefir drinks were 9.49-11.97, 2.30-3.44 and 2.50-3.00%, respectively. Moreover, the pH values of samples were in a range between 3.86 and 4.06 while their total titratable acidity (%, lactic acid) values ranged from 0.71 to 0.93%. Significant differences were found among the physicochemical properties of commercial kefir drinks (p<0.05). Rheological analyses were conducted at three different temperatures (4.0, 10.0 and 25.0±0.3°C), and the power law model was used to interpret the rheological characteristics of kefir drinks, which resulted in high coefficient of determination (R2) values. Besides, the apparent viscosity values of samples (at a shear rate of 111.6 s-1) were inversely related to temperature and varied between 0.48 and 1.76 mPa.s (p<0.05). Activation energy values of samples were between 21.51 and 36.18 kJ/mol. Significant differences in physicochemical and rheological properties were found among the commercial kefir samples of different brands, indicating the compositional variations of raw materials and kefir cultures used in their production.