Approaches for improving the rheological characterization of fermented dairy products

Sammanfattning: Fermented dairy products are wildly consumable products in today societies, and these products are known for their unique rheological properties due to the complex structural systems they possess. The simplest rheological model for describing yogurt behavior is the Power Law model, but this model parameters are not sufficient for describing the complex behavior during flow and filling. Therefore, it is important to utilize more sophisticated models that can capture other properties of the products such as the yield stress and the time dependency. Another challenge is to define a standard measuring protocol that can produce reliable and repeatable results, and at the same time can overcome the challenges associated with the thixotropic and viscoelastic behavior of the samples. This investigation includes a review of the possible regression methods that can be utilized using EXCEL sheets, and recommend the more suitable method for analyzing rheological measurements. This study also compares the behavior of several yogurt products (Vanilla, Naturell and Långfil) using different models with and without including the yield stress. The investigation includes an attempt to measure the zero- shear viscosity and infinite- shear viscosity which are important parameters for further CFD simulations. The thixotropic behavior of the three products was also described qualitatively and improved the understanding of the break down and build- up of the studied samples, and to what extent thixotropy can affect the rheological measurements. The study also recommends several methods for eliminating the time effect to improve the measurements of the studied products, which can also be applied to other types of samples. Elongation tests were performed using two different methods, and even though the results are difficult to interrupt, it was possible to qualitatively estimate the elasticity difference between the studied samples.