Effect of ι-Carrageenan on Flocculation, Creaming, and Rheology of a Protein-Stabilized Emulsion

The influence of ι-carrageenan on the surface activity of bovine serum albumin (BSA) and on the properties of BSA-stabilized oil-in-water emulsions is reported. Surface tension data at low ionic strength indicate a weak electrostatic protein−polysaccharide interaction at neutral pH, which becomes much stronger at pH 6 but disappears in 0.1 M NaCl. The effect of the attractive BSA−ι-carrageenan interaction on the droplet-size distribution and creaming stability of protein-stabilized emulsions (20 vol % n -tetradecane, 1.7 wt % BSA, 5 mM) has been investigated over a range of pH values. At pH 6 the system behavior is interpreted in terms of bridging flocculation leading to a gel-like emulsion network over a certain limited polysaccharide concentration range. This was confirmed by small-deformation oscillatory rheological measurements on equivalent concentrated emulsions (40 vol %). There is a good correlation with the rheology of the dextran sulfate plus BSA emulsions studied previously, suggesting that the flocculation mechanism is similar for the two sets of systems. Keywords: Protein−polysaccharide interaction; ι-carrageenan; bovine serum albumin; emulsion stability; creaming; bridging flocculation; rheology