Friction Measurements with Yoghurt in a Simulated Tongue-palate Contact

The perception of many food attributes is related to mechanical stimulation and friction experienced in the tongue-palate contact duringmastication. Friction in the tongue-palate is determined by the changing film properties (composition, component distribution, thickness) in the conjunction. We suggest this evolution is essentially determined by tongue-palate film loss rather than shear flow entrainment which predominates in conventional bearing lubrication. The paper reports friction measurements in a simulated tongue-palate contact for a range of high and lowfat dairy foods. A reciprocating, sliding contactwith restricted stroke length (bcontact width) was used; under these conditions there is negligible shear-entrainment of fluid from outside the contact area. The tongue-palate contact was simulated by a PDMS ball and glass surface. The effect of hydrophobic and hydrophilic surfaces on friction was investigated for different fat contents (0, 4.2, 9.5% wt fat). Friction was measured over 60 s of rubbing. Significant differenceswere observed in the friction changewith time for different fat contents (μ 9.5 b μ 4.2 b μ 0 wt%) and for different surface energy conditions (μ hydrophilic b μ hydrophobic). Post-test visualisation of the rubbed films showed that lowfriction coefficientwas associatedwith the formation of a thin oil film on deposited particulate solids.