Comparison of physiochemical, rheological and sensory properties of yoghurt made from fresh cow's milk and powdered milk

Two types of yoghurt including fresh cow's milk and powdered milk were produced according to typical production methods. Physiochemical, rheological and organoleptic properties of yoghurts were analyzed during 21 days of storage. Rheological measurements revealed an obvious shear thinning profile for both samples. Power law was shown to be useful for description of flow behaviour of samples and it was found that flow index behaviour was less than unity. Yoghurt from fresh milk had a larger consistency index than powdered milk yoghurt, but flow index behaviour was lower indicating higher shear thinning property. Viscosity of both samples showed significant variations during 21 days of storage. Flow index behaviour for samples decreased during storage which indicates more shear thinning behaviour of the samples and this is due to a decrease in Total Dry Solids of the samples. During storage time pH decreased while acidity increased. Fat variations were significant at 5% level from the first day until the th day and such variations showed a decrease trend. Yoghurts from powdered milk showed a more stiff texture than yoghurts from fresh milk. Yoghurts from powdered milk have a higher acceptability between panelists than yoghurts from fresh milk and this is because of the similarity in exture, lavor and odor of the final product.