A new design of soft texture analyzer tribometer (STAT) for in vitro oral lubrication study

Abstract

The relative movement between food particles as well as between food particles and oral surface is considered as critically important in influencing food oral processing and sensory perception. Precise characterization of oral lubrication/friction has recently attracted a lot of attention among food researchers for insight information about the controlling mechanisms of oral sensation and sensory perception. This study is a continuation of our effort in trying to establish a feasible in vitro soft tribology technique for food oral processing and sensory studies. Specific purpose of this study is to further improve the reliability and feasibility of a TA-tribometer developed previously by the group. A lighter and soft probe was produced to make it more consistent with that of oral conditions and a new connecting mechanism between the probe and the load cell was introduced with the help of 3D printing technique. A set of near-Newtonian fluids (water, syrup solutions and glycerol) with different shear viscosity were used as testing samples to assess the reliability at a wide range of sliding speeds and load pressures. Friction coefficients obtained at various experimental conditions were integrated and plotted as Stribeck curves. Viscosity/load ratio was introduced to understand and predicate the lubrication behavior of test fluids. The calculated Viscosity/load ratio not only influenced friction coefficient magnitude but the establishment of tribological regimes. A boundary regime can be clearly seen at a low range of viscosity/load ratio (0.00569–0.0327). For viscosity/load ratios between 0.211 and 5.097, lubrication would be most likely in mixed regime. Once viscosity/load ratio goes beyond 6.627, a hydrodynamic regime becomes dominant. Results verify the feasibility of the new modification and the improved device suggests a promising application for assessment the lubrication behavior of various near-Newtonian fluids. Future experiments will involve the use of beverages and semi-solids, explore the application potential for in vitro oral lubrication studies.