Surface texture of particle gels - A feature in two dimensions or three dimensions?

摘要

This work uses heat-set whey protein gels as model particle gels and investigates characteristic features at the surface as well as of the network. Whey protein is a milk protein widely used in the food industry for gelation and texture formation. The aggregation and network formation of this globular protein have been previously well investigated in the bulk phase. Surface properties of heat-set whey protein gels (14 wt%) are investigated here using surface friction measurement and confocal laser scanning microscope (Leica, Germany).Surface properties of protein gels have been assessed in terms of surfaces roughness, surface glossiness, and surface wetness. A simple mechanical device has been developed based on the Texture Analyser (Stable Micro Systems, Surrey, UK) for accurate measurements of surface friction forces. Surface friction forces of whey protein gels were investigated as a function of surface sliding speed and normal load. It was found that the surface friction of whey protein gels containing a small amount of NaCl became much less sliding-speed dependent but much more normal-load dependent. Thicker layers of surface water and much rougher surfaces of salt-containing gels are possible explanations. Confocal microscopy observations revealed that the protein gel without salt addition has a smooth and flat surface, while the gel with added salt has a much rougher surface.