Effect of casein to whey protein ratio of skim milk on the physical properties of a yoghurt drink, Ayran

This study investigated the physical properties of Ayran, a traditional Turkish salt-containing yoghurt drink, made at 8% total solids with various casein (CN)-to-whey protein (WP) ratios. The Ayran samples were made at the CN-to-WP ratios of 4:1, 3:1, 2:1 and 1.5:1. Graininess, visual roughness, serum separation, particle size and rheological properties of the Ayran samples were evaluated. The experimental data obtained from rheological measurements were described by the power law model. As the CN-to-WP ratio increased, the number of grains, the perimeter of grains and the visual roughness decreased, however the serum separation of the Ayran samples increased. The particle size of Ayran made with a CN-to-WP of 4:1 was higher than those with other ratios of CN-to-WP. The high ratio of CN-to-WP caused a significant decrease in apparent viscosity of the Ayran samples, as well as in consistency index and thixotropy value. On the other hand, flow behavior index of the Ayran samples increased with an increase in the ratio of CN-to-WP.