Els H.A. de Hoog

Fat retention at the tongue and the role of saliva : Adhesion and spreading of 'protein-poor' versus 'protein-rich' emulsions

Fat perception of food emulsions has been found to relate to in-mouth friction. Previously, we have shown that friction under mouth-like conditions strongly depends on the sensitivity of protein-stabilized emulsion droplets to coalescence. Here, we investigated whether this also implies that oral fat retention depends in a similar manner on the stability of the emulsion droplets against coalescence. We investigate the separate contributions of droplet adhesion and droplet spreading to fat retention at the tongue, as well as the role of saliva. We perform ex vivo (Confocal Raman Spectroscopy; Confocal Scanning Laser Microscopy) experiments using pigs tongue surfaces in combination with human in vivo experiments. These reveal that protein-poor (unstable) emulsions are retained more at the tongue than protein-rich (stable) emulsions. Furthermore, the layer formed by adhering protein-poor droplets is more stable against rinsing. Saliva is found to be very efficient in removing fat and emulsion droplets from the oral surface but its role in fat retention needs further research. We relate our results to the colloidal forces governing droplet adhesion and spreading.

Protein-Polysaccharide Interactions to Alter Texture

The sensory perception of texture is an important contributor of our general appreciation of foods. Food texture is mainly described in terms of mouthfeel and afterfeel attributes. The role of oral processing in the perception of texture and the role of microstructure therein have been reviewed regularly over recent years (Chen & Engelen 2012, Foegeding et al. 2011, Stieger & van de Velde 2013) and are not, therefore, addressed in this review. The scope of this review relates to the molecules that underlay the texture of foods. Protein, carbohydrate, and fat are the major structuring components in foods. In this review we focus on the physical interactions between proteins and polysaccharides that form the basis for the microstructure and texture of these foods. In general, food products are classified in four categories by their sensory and rheological properties: liquids, semisolids, soft solids, and hard solids (van Vliet et al. 2009). These four categories provide a useful classification framework, although they are not precisely defined by specific rheological properties. The current review focuses on semisolid and soft-solid foods.

Self-diffusion of charged colloidal tracer spheres in transparent porous glass media: Effect of ionic strength and pore size

The influence of charge on diffusion in porous media was studied for fluorescent colloidal silica spheres diffusing in a porous glass medium. The bicontinuous porous silica glasses were optically matched with an organic solvent mixture in which both glass and tracers are negatively charged. Using fluorescence recovery after photobleaching, the long-time self-diffusion coefficient DSL of the confined silica particles was monitored in situ as a function of the ionic strength and particle to pore size ratio. At high salt concentration DSL reaches a relatively high plateau value, which depends on the particle to pore size ratio. This plateau value is unexpectedly higher than the value found for uncharged silica spheres in these porous glasses, but still significantly smaller than the free particle bulk diffusion coefficient of the silica spheres. At low salt concentration DSL reduces markedly, up to the point where colloids are nearly immobilized. This peculiar retardation probably originates from potential t...