The texture of foods, including the properties that determine how consumers bite and swallow, is an important part of developing foods that are more fun. To fully understand these characteristics, better testing methods and devices are needed to detect the movement in liquid materials, especially foods that are complex liquids, such as jellied desserts.
Test equipment has been improved using different geometries in the test chamber, and more recently, better results have been obtained by using information from rheological tests together with results from other tests, such as testing. As inner visualization techniques and ultrasound imaging were used. However, information about time-dependent properties could not be obtained using conventional methods.
In a study published this week in Physics of Fluids, Taiki Yoshida, Yuji Tasaka, and Peter Fischer present an updated method that can simultaneously measure linear viscoelasticity and phase retardation in an opaque liquid. The ultrasound spinning rheometry method they have developed uses food speed profiles in the equation of motion to capture information about complex rheological properties.
The researchers used a popular Japanese dessert called Fruiche, which contains pulp and whole milk and turns into a gelled form with an egg-shaped structure. The complexity of this fluid includes properties that are difficult to measure with conventional rheometry methods due to the influence of shear, shear banding, shear localization, wall slippage, and elastic instability.
"Judging food rheology as a function of time is a challenging goal," Yoshida said. "Based on the equation of motion, the ultrasonic spin rheometry method can evaluate the instantaneous rheological properties from the measured velocity profiles so that it can represent real rheological properties and their time dependence from the perspective of the physics of fluids."
The updated process has applications in the chemical art for understanding the polymerisation and dispersion densities as well as in complex liquids such as clay with applications in construction and cosmetics. The researchers want to further develop the method to get more information about the invisible properties of complex fluids. They also plan to develop the industrial aspects of the technology, including inline rheometry for test samples flowing in a tube.
Taiki Yoshida et al, Ultrasonic spinning rheometry test on the rheology of gelled food for making better tasting desserts, Physics of Fluids (2019). DOI: 10.1063/1.5122874