Rheology of Swiss Cheese Fondue

Protein-protein interactions explain the temperature-dependent viscoelastic changes occurring in colloidal protein gels

Denaturation of protein solutions can be induced by higher temperatures and the presence of non-polar organic solutions. The denatured proteins form aggregates and gels through protein interactions occurring between their amino acid side chains. Depending on the involved side chains, the denaturation conditions lead to different gel properties. As model systems, a variety of food proteins were gelled through different mechanisms to cover a whole range of protein-protein interactions. Especially the temperature dependence of the viscoelastic properties in a simple rheometer method was found to be very different. These differences could be explained by the different thermodynamic properties of the involved protein-protein interactions. Electrostatic interactions were shown to weaken the resulting gel upon temperature increase whereas entropically driven interactions such as hydrophobic or covalent links were strengthened with increased temperatures. A proposed model explaining these results can be used to assess protein interactions in hydrogels in a non-invasive way and could also have applications to describe the temperature behavior of other hydrogels.

Viscoelastic Behavior and Constitutive Relation of Heavy Crude Oils

Heavy crude oil exhibits very complex viscoelastic behaviors due to its complex composition of resins, asphaltenes, saturates, and aromatics. It has a great influence on oil production and transportation. In this work, the viscoelastic behaviors of three different heavy crude oils were measured using a rotational rheometer. In conclusion, all of these heavy crude oils display linear viscoelastic behaviors in the experimental range. The loss modulus (E″) of the three crude oils decreased as the experimental temperature increased, and the variation trends of the three crude oils were basically the same. However, the experimental temperature has almost no effect on the storage modulus (E'), which always retained a constant value of 0.4 Pa. Furthermore, the storage modulus (E') and loss modulus (E″) increase as the angular frequency increases. To describe the physical deformation characteristics of viscoelastic materials, the generalized Maxwell model and the fractional derivative Maxwell model are used to establish the constitutive relation of heavy crude oil. In conclusion, the generalized Maxwell model and the fractional derivative Maxwell model can predict the experimental results very well. All of the square of the correlation coefficient (R ²) values are greater than 0.95. However, the number of fitting parameters for the fractional derivative Maxwell model is less than that for the fourth-order generalized Maxwell model which can save the calculating time. Therefore, the fractional derivative Maxwell model is suggested to describe the viscoelastic behavior of heavy crude oil in industrial applications.

The effect of milk fat substitution on the rheological properties of Edam-type cheese

In cheese-like products, milk components (in particular fat) are partially or completely replaced with non-dairy substitutes. An attempt was made in this study to determine whether Edam-type cheese can be distinguished from its substitute, where milk fat was replaced with palm oil, based on rheological properties. The rheological properties of Edam cheese and its substitute were analyzed during a 16-week ripening period, based on the results of a stress-relaxation test. The values of the rheological parameters were estimated with the use of the generalized Maxwell model and a non-linear model proposed by the authors, which accounted for the plastic deformation of the analyzed samples. The study revealed that both methods were equally effective in describing the stress relaxation process; therefore, they can be regarded as equivalent. Excluding the initial stage of ripening (which is not important from the consumers’ point of view), the replacement of milk fat with palm oil did not influence the rheological properties of Edam-type cheese and the cheese-like product. In subsequent stages of ripening, no significant differences were found in the rheological properties of both products, which could only be used to evaluate their ripeness.