Determination of some physicochemical, rheological and sensory properties of commercial kefir samples

In this study, the physical, chemical, and microbiological properties, as well as the rheological properties and 5-hydroxymethylfurfural (5-HMF) content of kefir samples sold nationally in Turkey, were determined. In this context, water holding capacity, total dry matter, pH, titratable acidity, fatty acid and color contents of kefir samples, microbiological lactobacilli count, total mesophilic aerobic bacteria count and total yeast mold count, as well as shear rate versus shear stress values obtained from rheological measurements of the samples, of the samples were determined. Using these experimental data, the conformity of kefir samples with some known rheological models was determined. In addition, a sensory evaluation was carried out with 35 panelists to examine the consumer appreciation of kefir samples. The dry matter content of kefir samples was found to be between 8.93 and 11.11. When the water-holding capacity of kefir samples was analyzed, the highest value was found to be 39.44%. When the 5-HMF values of kefir samples were analyzed, the highest value was 6.673 mg/L. Microbiologically, 7.90-8.81 log cfu/mL total mesophilic aerobic bacteria, 7.52-8.40 log cfu/mL of lactobacilli and 3.41-5.59 log cfu/mL of total yeast and mold were counted. The mean values of L*, a* and b* of the samples were 85.94, -3.62 and 5.62, respectively. When the kefir samples were examined for their suitability to rheological models such as Bingham, Exponential and Herschel-Bulkley, it was determined that Herschel-Bulkley was the most suitable model in terms of the highest R2 and the lowest error squares in statistical evaluation criteria. It was determined that all of the samples showed non-Newtonian pseudoplastic flow behavior at different temperatures. When the sensory evaluation was examined, it was seen that the taste and odor were at low values. It was observed that the kefirs examined were in compliance with the fermented milk communique in terms of fat content and titration acidity, as well as in terms of the number of total mesophilic aerobic bacreria, lactobacilli and yeast mold number determined as microbiological criteria in the final product.