Portulaca oleracea gum and casein interactions and emulsion stability

It is well documented that weak or strong interactions between macromolecules such as proteins or polysaccharides can synergistically improve the emulsifying capabilities of each of the biopolymers. The present study explores the nature of the adsorbed layer in emulsions formed in the presence of casein and a new anionic hydrocolloid extracted from Portulaca oleracea L. (POG). in several emulsification protocols. Electrophoretic mobility of medium chain triglyceride oil emulsion droplets and the corresponding adsorbing creamed phases were measured. The zeta potential magnitudes were calculated in view of the possible pH dependent ionic-hydrogen bonding interactions between casein and a new ionic gum at the oil-water interfaces. Emulsions stability were determined from the emulsification stability indices (ESI) and emulsification activity index (EAI). It was found that FOG can adsorb by itself or together with casein onto the oil-water interface. Displacement of the FOG, from the interface, by the casein will take place at pH values that will enhance repulsion forces between the biopolymers. However, complementary adsorption of a possible casein-POG complex will occur if the pH is enhancing strong attraction interaction between the two biopolymers. The attraction forces between the two biopolymers will enhance the stability of oil-in-water emulsions formed in the presence of the two macromolecular amphiphiles. (C) 1999 Elsevier Science Ltd. All rights reserved.