Clustering of instrumental methods to characterize the texture and the rheology of slimy okra (Abelmoschus esculentus) suspensions

Flow structure of okra mucilage in rotating wall vessel system

The rotating-wall vessel (RWV) bioreactor, a 3D suspension culture system, faces challenges related to non-uniform tissue growth during the incubation of bone and heart tissues. Okra mucilage, an extract from okra pods with non-Newtonian rheological properties, has shown potential as a plasma replacement agent and has no induced cytotoxic effects. In this study, we investigated the flow structure of okra mucilage in rotating wall vessel system. By modifying the RWV and adding okra mucilage, we analyzed the flow structure using a high-speed camera and particle image velocimetry (PIV). Our results showed that okra mucilage creates a concentric circle-shaped rigid-like rotation at all rotation speeds (1-50 rpm). The high viscosity of okra mucilage resulted in a low terminal velocity for microparticles and quick response to rotational movements. These findings suggest that okra mucilage has the potential to enhance the uniformity of tissue growth in RWV systems by stabilizing the flow structure and reducing microparticle sedimentation.

Brittle and ductile yielding in soft materials

Many soft materials yield under mechanical loading, but how this transition from solid-like behavior to liquid-like behavior occurs can vary significantly. Understanding the physics of yielding is of great interest for the behavior of biological, environmental, and industrial materials, including those used as inks in additive manufacturing and muds and soils. For some materials, the yielding transition is gradual, while others yield abruptly. We refer to these behaviors as being ductile and brittle. The key rheological signatures of brittle yielding include a stress overshoot in steady-shear-startup tests and a steep increase in the loss modulus during oscillatory amplitude sweeps. In this work, we show how this spectrum of yielding behaviors may be accounted for in a continuum model for yield stress materials by introducing a parameter we call the brittility factor. Physically, an increased brittility decreases the contribution of recoverable deformation to plastic deformation, which impacts the rate at which yielding occurs. The model predictions are successfully compared to results of different rheological protocols from a number of real yield stress fluids with different microstructures, indicating the general applicability of the phenomenon of brittility. Our study shows that the brittility of soft materials plays a critical role in determining the rate of the yielding transition and provides a simple tool for understanding its effects under various loading conditions.

Contact forces and motion behavior of non-Newtonian fluid-solid food by coupled SPH-FEM method

The non-Newtonian fluid-solid interaction food has complex physical properties and complicated contact force, which brings the greater technical challenge to improving the food fetching rate. In this work, we used the smooth particle hydrodynamics and finite element coupling method for a node-to-surface penalty function contact to characterize the contact forces between non-Newtonian fluid food and solid foods. The shear rheological properties and density of non-Newtonian fluid food, including xanthan gum (XG) and guar gum (GG), were investigated by a viscometer and densitometer, respectively. The results showed that the shear viscosity of non-Newtonian fluid food depends to some extent on the mass ratio of the thickening gums. We investigated the effects of the end-effector with different fetching velocities and different inclination angles, and the nut root powder paste (NRPP) food with different ratios of XG and GG, on the fetching rate, stress-strain, and motion behavior. The results showed that the stress increased with increasing v₁ and w; however, the v₂ had less effect on the stress. The sparseness of the distribution of solid food was related to the v₁ and w, whereas it was less influenced by the v₂ . The distribution of solid food became denser in the X-Z plane and sparser in the X-Y plane with increasing inclination angle. The motion behavior of viscoelastic solid foods depended on the mass ratio of XG to GG dissolved in NRPP. The present work can provide a theoretical foundation for meal-assisting robots and robots in the field of food engineering with the task of improving the food fetching rate.

Sensory quantitative descriptive analysis of African slimy okra (Abelmoschus esculentus) preparations and its correlation with instrumental parameters

Okra (Abelmoschus esculentus) is one of the ingredients used in traditional West and Central African gastronomy because of the slimy texture it gives to sauces, soups and stews. However, in the literature, the definition of "sliminess" is unclear, the textural perception of these slimy preparations has not been described, and the possibility of measuring the textural quality of these sauces instrumentally has not been established. This study therefore aims (a) to identify the sensory attributes adapted to describe the texture of these slimy sauces and (b) to verify that the instrumental measurements adapted to characterize the rheology and texture of these sauces are well correlated to these attributes. Nine okra sauces were prepared by varying their formulation and the preparation process. A quantitative descriptive sensory analysis and a ranking test were carried out with a trained panel of 16 panelists. The texture of the okra-based slimy sauces prepared can be described using 11 attributes referring to their consistency and to their adhesive, elastic, elongation and functional properties. Results showed that sliminess is a complex textural property resulting from the combined perception of stringiness and viscosity of semi-solid matrices. Therefore, it is not possible to correctly predict the sensory perception of sliminess with a single instrumental measurement. However, measuring their consistency index K and their stringiness is necessary and sufficient to characterize the texture of these sauces and to predict the sensory perception of their consistency and elongational properties.