Rheological Quality Control Tests of Commercial Strawberry Stirred Yogurt: Pseudo-chewing Process

Background: The rheological behavior of yogurt plays a crucial role in determining the quality of the product. This study aimed to develop a rheological quality control test replicating pseudo-chewing using experimental rheological protocols. Methods: The strawberry stirred yogurt sample was produced, in a 90 g pot, and commercialized in April 2023 by SOUMMAM dairy products, Bejaia, Akbou, Algeria. Rheological properties of a 0.6 ml yogurt sample were evaluated for each test measurement using a rheometer with a cone/plate geometry at a constant temperature of 25±0.1 °C. The shear flow experimental protocol involved three steps: a shear rate ramp, followed by a plateau at the maximum shear rate for 15 min, and afterward the ramp was reversed to measure the downward flow curve. The viscoelastic properties were evaluated by two experimental protocols in the Linear Viscoelastic Region. These properties were studied under oscillatory frequencies (0.1-100 Hz) with and without pre-shearing at 400 1/s for 15 min to simulate the pseudo-chewing process. All experimental data were analyzed and fitted using MS Excel and MS Excel Solver. Results: The stirred yogurt samples showed a non-Newtonian viscoelastic flow behavior with thixotropy. Both upward and downward shear rate flow curves of the sample exhibited shear-thinning behavior described by the Herschel-Bulkley model with high regression coefficient of R2=0.98 and 0.99, respectively. Dynamic measurements showed that pseudo-chewing causes considerable changes in rheological parameters such as complex modulus, complex viscosity, and loss tangent. The pre-shearing altered complex modulus and complex viscosity, corresponding to an alteration in the yogurt’s firmness and flow properties. Conclusions: The rheological procedures suggested in the present study can be used as rheological quality control tests of commercial strawberry stirred yogurt. This procedure can successfully simulate pseudo-chewing by offering information on the flow and viscoelastic characteristics of yogurt in the mouth during mastication.