Concentration of carrageenan determined the degree of phase
separation and if protein or polysaccharide formed the continuous
network. When k-carrageenan concentration was 0.1 and 0.2%,
the k-carrageenan phase appeared as separate, spherical droplets
dispersed in a continuous protein-rich gel network. The size of the
carrageenan-rich droplets became larger as carrageenan concentration
increased. At 0.3 and 0.4% k-carrageenan, the continuous
protein network was disrupted by the enlarging volume fraction of
the carrageenan phase. Isolated, dispersed spheres of carrageenan
turned into continuous channels through the WPI phase, forming
what appeared to be a bicontinuous microstructure similar to that
observed by Norton and Norton (2010) for gelatin and maltodextrin.
For the confirmation of bicontinuous microstructure, 3D
images were taken as described by van den Berg et al. (2007a). An
interconnected pore structure was observed in all three planes
(images not shown), confirming a bicontinuous structure. At 0.5
and 0.6% carrageenan, the continuity of the protein phase disappeared
and the network inverted into a carrageenan continuous
structure. In this type of network, spherical micro domains of whey
protein were embedded in a carrageenan continuous phase. It
appeared that phase separation occurred prior to protein gelation
and the non-equilibrium situation was “frozen” into the structure
when protein gelation occurred. The depletion interactions
increased with increasing carrageenan concentration resulting in
denser micro domains with smaller volume fraction.