Tribo-rheology and sensory analysis of a dairy semi-solid

Tribology science is devoted on explaining the friction behavior of interacting surfaces in relative motion. Several tribological systems have been used to measure coefficient of friction (CoF) vs sliding speed of entrained food layer between two rubbing surfaces. These results can be correlated with fat-related attributes perceived during oral processing. This study aims to investigate the effect of starch, carrageenan and fat on the friction profile; flow behavior and particle size distribution. Friction curves were obtained for custards using a tribo-rheometer with a rotating metallic geometry rubbing the surface of 3 M tape with roughness similar to that depicted by human tongue. Confocal Laser Scanning Microscopy (CLSM) images of custard collected during friction experiment helped to explain the characteristics of tribological regimes. As expected, fat-containing samples depicted remarkably lower CoF than skim compositions (fat: 0.2 < CoF < 0.08 and skim: 0.6 < CoF<0.3). The presence of fat not only influenced CoF magnitude but the establishment of tribological regimes (TRs). Fat-custards depicted three TRs, assigned as: (1) fluid entrainment (decreasing-CoF), (2) gel particle entrainment (increasing-CoF) and (3) accumulation of multi-layers of material at high speeds (decreasing or sometimes constant-CoF). Skim-samples, however, presented a prolonged decreasing CoF over the sliding speed range tested. Conversely to tribo-rheological results, sensory analysis revealed lack of hydrocolloid effect on the perception of fat-related attributes. This was assigned to the presence of saliva facilitating the food microstructure breakdown. We emphasize that our tribological study focused on the friction trend; future experiments will involve the use of saliva to explain the mechanisms of food oral processing.