Creamy mouthfeel of emulsion-filled gels with different fat contents: Correlating tribo–rheology with sensory measurements

The aim of the study was to better understand the relationships between tribological, rheological and creamy mouthfeel properties of emulsion-filled gels. Micellar casein dispersions differing in fat content (0–10.5% w/w) were acidified with glucono-δ-lactone to prepare the emulsion-filled gels. Tribological and rheological properties of emulsion-filled gel bolus were determined after in vitro oral processing. A three-zone tribological profile is proposed to describe the friction behavior of gel bolus over a broad range of sliding speeds. The results showed that with increasing fat content of gel bolus, apparent viscosities at low shear rates (≤10 s−1) and friction coefficients decreased, while sliding speed at the transition point between Zone 2 and Zone 3 (v2) increased. To reveal the microstructural basis of friction behavior, confocal images of gel bolus differing in fat content were obtained after shear treatment in the tribometer. With increasing sliding speed, the gel bolus gradually disintegrated and released oil droplets from the gel matrix which oil droplet subsequently coalesced. This structure evolution accelerated with increasing fat content of gel bolus. Descriptive sensory analysis showed that with increasing fat content creaminess, smoothness, thickness and mouth-coating intensities increased. Partial least squares regression analysis revealed that the apparent viscosity of gel bolus at a shear rate of 0.1s−1 and 10s−1, as well as the sliding speed v2 were strongly correlated with creaminess for all emulsion-filled gels (correlation coefficients were 0.933, 0.939 and 0.897, respectively), and the correlation between viscosity and creamy mouthfeel was stronger than friction coefficient.