Interfacial compositions, microstuctures and properties of oil-in-water emulsions formed with mixtures of milk proteins and κ-carrageenan: 1. Sodium caseinate

Abstract

Studies have been carried out on the changes in droplet size, surface coverage and composition, and stability of emulsions formed with 30% (w/w) soya oil, and aqueous solution containing 0.5 and 3.0% sodium caseinate and varying concentration of κ-carrageenan. In all emulsions, except those made using 3.0% sodium caseinate, addition of κ-carrageenan up to 0.4% (w/w), before homogenisation, slightly increased the average droplet size, but had no significant effect on protein surface coverage and composition. Addition of low levels of κ-carrageenan (<0.2%) caused extensive flocculation of oil droplets, which resulted in very low creaming stability. At higher κ-carrageenan concentrations, the creaming stability increased, apparently due to the formation of a network of flocculated droplets. Emulsions formed with 3% sodium caseinate without added κ-carrageenan showed extensive flocculation, due to the presence of excess unadsorbed casein molecules in the emulsion. Addition of κ-carrageenan into these emulsions resulted in gradual improvement in creaming stability. All emulsions formed without κ-carrageenan showed Newtonian behaviour (except those made with 3% sodium caseinate), as expected for unflocculated systems. The viscosity of the emulsions increased with an increase in κ-carrageenan concentration; the emulsions containing κ-carrageenan showed a clear pseudoplastic behaviour, indicating reversible flocculation of oil droplets. The creaming stability of emulsions made with mixtures of milk proteins and κ-carrageenan closely appears to be related to the structure and rheology of emulsions.