No abstract

"Thickness" is one of the descriptors of texture in liquid and semisolid foods. In this study, friction in thickener aqueous solutions was evaluated, using a biomimetic friction evaluation system, to show the correlation between friction data and sensory thickness and the recognition mechanism of this sensation during the process of eating. This system can measure friction forces under sinusoidal movement on fractal agar gel, which mimics the morphology and physical properties of the tongue. We found that an increase in the viscosity of the thickener aqueous solution was responsible for both the sensory score of thickness and the asymmetric profile of the friction coefficient in a reciprocating motion. In the case of low viscosity liquids such as water, many of the subjects did not feel thickness, and the friction profile "stable pattern I," that is, a static friction coefficient larger than kinetic friction and a similar profile in the outward and inward processes were observed. However, in the case of solutions containing 3 or 5 wt% of food thickener, the friction profile "unstable pattern I," that is, different friction behaviors in the outward and inward processes, was observed, and many of the subjects experienced strong thickness. In addition, the static friction coefficient at the first cycle was small, and the changes of friction coefficient by the reciprocating motion being repeated was large. These friction phenomena can occur in the mouth and are expected to induce sensory thickness.

The self-diffusion coefficient in Lennard–Jones fluid was studied by molecular dynamics simulation. Simulations were done at 414 states in the temperature–volume plane. An equation of state for the self-diffusion coefficient was derived by the least-square fitting. The calculated equation of state was in agreement with the experimental results on CO2. Its pressure dependence was also consistent with that in liquid hexane. The liquid structure was analyzed by the excess coordination number, the distributions of the cluster size and the hole volume. The volume dependence of the self-diffusion coefficient in the two-phase region was discussed in terms of the coordination number in the first shell.