Tribological properties of microparticulated whey protein as a fat replacer in liquid and semi-liquid model foods

The current understanding of the mechanisms underlying the fat mimicking properties of fat replacers such as microparticulated whey protein (MWP) is limited. MWP is known to provide fat-related mouth-feel in a limited range of foods, such as yoghurts and cheeses. Rheological and tribological properties are well known to contribute to the perception of fat related attributes. The aim of
this study was to investigate the tribological and rheological properties of MWP in liquid and semi-solid model foods to reveal the mechanism underlying the fat mimicking properties of MWP. A mouth-mimicking tribometer was used to determine the tribological properties of MWP in four matrices: liquid (MWP in water; MWP in o/w emulsions) and semi-solid model foods (MWP in gelatin
gels; MWP in emulsion-filled gels). In liquids, increasing the concentration of MWP from 0.1 to 8 % significantly reduced the friction coefficient. The reduction in friction coefficient with increasing MWP concentration was accompanied by an increase of viscosity. After considering the impact of viscosity on lubrication, a significant reduction of friction coefficient with increasing MWP remained. This suggests that the decrease of friction coefficient is not only caused by the
increase of viscosity but probably by a ball-bearing lubricating effect of MWP due to its spherical shape and small size. In semi-solid gelatin gels, the addition of MWP reduced the friction coefficient of broken-down gels, but to a smaller extent compared to liquid foods, probably due to the presence of semi-solid gel particles. In emulsion-filled gels, addition of MWP reduced the friction coefficient. The binding properties of fat droplets to the gel matrix bound /unbound) also influenced the frictional properties, which lead to very complex relationships between composition and frictional behavior. We conclude that the addition of MWP decreased the friction coefficient of liquid and semi-solid foods probably due to a ball-bearing mechanism. Bulk properties of the foods, especially the oral breakdown behavior of gels, additionally influence the frictional properties of MWP containing gels.