Study On Lubrication Mechanism Of Fluid Food In Oral Environment

The texture properties of foods have a close relationship with the combination of their rheological properties and oral tissue surface characteristics,and it is difficult to assess the oral perception of fluid foods from rheological perspective only.The lubrication properties of fluid foods in the oral environment are significant since their contribution to insight of the action mechanism between tribology and perception of sensory attributes.In order to meet the increasingly diversified demand for beverages,the research on the lubrication mechanism of fluid food is extremely important.Therefore,this paper focuses on the experimental study of the lubrication properties of sucrose and soymilk powder solutions based on simulated oral environment,and the establishment of an oral soft contact slide model that encompasses both Newtonian and non-Newtonian fluid foods.The research results will provide technical support for the development of diversified beverages suitable for different populations.Firstly,a study of the lubrication properties of Newtonian fluid foods was carried out.The rheological properties of sucrose solution with different mass fractions and the mixture of artificial saliva were characterized,and the lubrication properties of sucrose solution in different simulated oral friction pairs were studied,and the effects of surface properties and artificial saliva on their lubrication properties were considered.The results showed that the sucrose solution with different mass fractions and its mixtures with artificial saliva are approximately Newtonian fluids,with the increase of uη,the average coefficient of friction undergoes a transition from stable,then decreasing,then increasing,indicating that the lubrication state transits from boundary lubrication to mixed lubrication,and finally reaches the fluid lubrication state.When uη is in the vicinity of the inflection point of the transition from the mixed lubrication state to the fluid lubrication state,the sucrose solution has a low average coefficient of friction.The lubrication properties of the sucrose solution mixed with artificial saliva at a mass ratio of 1:1 are not significantly improved.Since the difference in lubrication performance of sucrose solution between polydimethylsiloxane(PDMS)ball-disk friction pair and steel ballPDMS disk friction pair mainly stems from their wettability,the better wettability of sucrose solution in steel ball-PDMS disk friction pair leads to its lower average coefficient of friction in boundary and mixed lubrication states,indicating that the better wettability contributes to the improvement in lubrication performance of sucrose solution.Secondly,the research on the lubrication performance of non-Newtonian fluid food was carried out.The soymilk powder solutions with different mass ratios were prepared to investigate their rheological properties and the effects of sucrose and artificial saliva on their rheological properties.The lubricating properties of soymilk powder solutions in soft friction pairs constructed by PDMS ball-disk were studied,and the effects of adding sucrose and artificial saliva on the lubricating properties of different soymilk powder solutions were considered.The results showed that the viscosity of soymilk powder solution is positively correlated with the mass fraction of soymilk powder,and the addition of sucrose and artificial saliva contribute to the decrease of its viscosity.Sucrose can both improve the lubrication properties of the soymilk powder solution and its mixture with artificial saliva.Compared with other brewing ratios,the samples with a brewing ratio of 1:5(soy milk powder: water)has a lower average coefficient of friction,and from the perspective of smoothness,a brewing ratio of 1:5 is preferred recommended.Finally,in order to investigate the lubricating mechanism of fluid food under different working conditions,the simulated oral friction pair composed of PDMS balls and disks was applied to establish an oral soft contact slide model and to verify its reliability according to the theory of elastohydrodynamic lubrication.The results showed that under the fluid lubrication state,with the increase of uη,the pressure of Newtonian fluid food has little changes,but the film thickness and friction coefficient increase accordingly.The amplitude of roughness will affect the pressure and film thickness of Newtonian fluid food,but the effect on the coefficient of friction is negligible.As the load increases,the increases of contact area and pressure will lead the increases of film thickness of the non-Newtonian fluid food.But the film thickness of the Newtonian fluid food is almost constant and its friction coefficient decreases.The film thickness of non-Newtonian fluid food increases with the increase of rheological parameters,consistency coefficient and slip velocity.The above research results will provide a better technical reference for the development of beverages.