Influence of κ-carrageenan on the properties of a protein-stabilized emulsion

We report on the influence of kappa-carrageenan (kappa-CAR) on the surface activity of bovine serum albumin (BSA) and on the properties of BSA-stabilized oil-in-water emulsions. Surface tension data at low ionic strength indicate an electrostatic interaction at neutral pH which becomes much stronger at pH 6. The effect of the attractive BSA-kappa-CAR interaction on the state of aggregation and creaming stability of protein-stabilized emulsions (20 vol% n-tetradecane, 1.7 wt% BSA, 5 mM) has been investigated at three pH values. At pH 6 the system behaviour is interpreted in terms of bridging flocculation leading to an emulsion droplet gel network over a certain limited polysaccharide concentration range. While the trend of behaviour is qualitatively similar to that reported recently for equivalent BSA + iota-carrageenan (iota-CAR) solutions and emulsions, the BSA-kappa-CAR interaction is clearly weaker than the BSA-iota-CAR interaction under similar pH and ionic strength conditions. This means that a higher polysaccharide content is required to induce flocculation in systems containing kappa-CAR, and also that the resulting emulsion gel network is weaker. The behaviour is consistent with the lower density of charged sulfate groups on the kappa-CAR as compared with the iota-CAR. (C) 1998 Elsevier Science Ltd. All rights reserved.