Abstract: The perception of fat-related sensory attributes in food emulsions during oral processing mainly depends on the complex interactions between the emulsion droplets and the oral soft surface as well as saliva. A range of surface behaviors including adhesion, wetting, and spreading of emulsion droplets on the tongue surface influence the frictional and lubricative properties of emulsions. In this study, the effect of oil droplet size, applied normal load, and saliva addition on the tribological properties of an oil-in-water (O/W) emulsion prepared using microfluidized pea protein isolate (PPI) as an emulsifier. The results showed that with increasing applied normal load (0.5-2.0 N), the friction coefficient of the emulsion decreased obviously. With the decrease in droplet size, the number of droplets available for entrainment increased, resulting in a decrease in friction coefficient (10%-30%) and a decrease in boundary regime range of 15%-20% and thus enabling lubrication at lower entrainment speeds. During simulated oral processing, addition of saliva induced the flocculation of droplets, increasing droplet size, preventing droplets from being entrained into the oral surface, and ultimately resulting in a higher friction coefficient for the emulsion. This study can provide technical support for regulating the oral texture sensory properties of pea protein-based emulsion and the development of plant-based products.

Key words: pea protein; emulsions; oral processing; friction coefficient; saliva