Food entering the oral cavity undergoes a series of complex processing behaviors. It is subjected to compression and shearing by the teeth, tongue, and palate to reduce its size and mix with saliva until it is swallowed. The oral processing behaviors are thought to be closely related to both food and oral frictional properties. Much effort has been made in recent decades about food oral tribology to explore this complicated lubrication behavior. Understanding the lubrication mechanism of food in the mouth is important for improving the consumption experience and developing the novel food. This paper provides a new perspective on the effects of composition, texture, structure, and saliva-food component interactions on lubrication properties of different foods, the relationship between sensory perception and oral frictional behavior, and the mechanism and pattern of lubrication categorized by common food types. The roles of tribology in the improvement of food taste, the search for healthier ingredient substitutes, functional foods, and the development of green foods are analyzed. Conceptual and numerical prediction models among physical properties, sensory perception, and frictional behavior of food are discussed. Studies of simulating oral processing, such as the selection of friction pair materials, physical modification of contact surfaces, addition of saliva, different modes of motion, and contact forms are concluded and classified. The progress of commercial friction apparatus as well as customized friction devices applied to the food sector in recent years are described. The characteristics, performances, and applications of these tribological instruments are analyzed and compared. In addition, the results achieved by oral tribology in identifying adulterated foods and ensuring food safety are presented. Finally, some suggestions are put forward for the current challenges and future development of food oral tribology.

Real oral processing is the squeezing and shearing between two soft surfaces. The importance of soft palate surface cannot be ignored while focusing on tongue substitutes. Thus the effects of viscoelasticity, roughness of upper jaw substitutes, and fluid rheological properties on lubrication properties were explored by in vitro oral tribology experiments. Different palate substitutes significantly changed the friction curves of pure water, milk, and yogurt. The boundary friction coefficients of pure water and milk are higher under softer or smooth palate substitutes due to stronger viscoelastic responses of friction pairs. Their boundary friction coefficients are lowest at rigid upper jaw substitutes owing to smaller contact angles and deformation. However, the boundary friction coefficient of yogurt is lower owing to its high viscosity, low loss factor, and large particle size under soft friction pairs. In addition, it is highest at rigid palate friction pair because a smaller contact area reduces the entrainment of yogurt, resulting in poor lubricating performance.