Lubrication of oral surfaces by food emulsions: the importance of surface characteristics

The friction between surfaces in relative motion lubricated by food emulsions has been measured. Different types of surfaces were tested, including metal, glass, rubber, and mucosal surfaces (pig tongue and pig esophagus). We demonstrate that the load-dependent behavior of the coefficient of kinetic friction was different for various types of surfaces used; it decreased with increasing load for the mucosal surfaces, but that was constant for glass metal surfaces. We show that this difference is an effect of the roughness and the deformability of the surfaces. For mucosal surfaces, the friction force did not depend on the oil fraction in the measured range of 10% to 40% (w/w). Further more, 3 commercial dairy products were tested between these surfaces. The lubrication properties of low fat (1.5% fat content) and high-fat (3.5% fat content) milk were comparable to those of the model emulsions. However, the friction force of the commercial cream (3.5% fat content) was found to be much lower.