Stability and Physical Properties of Emulsions Prepared with and without Soy Proteins

The ability of emulsifiers (gum arabic, starch and soy protein isolate (SPI)) and texture modifiers (gum tragacanth and carrageenan) alone and as a mixture with SPI to stabilize oil-in-water emulsions at high oil concentrations was studied. Parameters investigated included droplet size distribution, color (DE), viscosity and creaming stability. At 10% (w/v) emulsifier to oil ratio, emulsions stabilized with gum arabic, starch and SPI had average oil droplet sizes lower than 1µm. Increasing the oil content by two-fold (emulsifier/oil ratio of 10:20), increased the average droplet size of the gum arabic and SPI emulsions to 1.5 and 4.2 mm, respectively, while that of the starch emulsion remained unchanged. At 5% oil concentration, gum tragacanth and carrageenan stabilized emulsions yielded two average droplet sizes of 0.5 µm (52.7%) and 1.8 µm (46.5%), and 0.5 µm (48.8%) and 1.7 µm (46.6%), respectively. Increasing the oil concentration to 10% increased the particle size with fairly similar proportions. Gum arabic stabilized emulsions had lower DE than starch and SPI (except at 20% oil content). DE of carrageenan and tragacanth emulsion decreased significantly when used as a mixture with SPI. Droplet size strongly affected color. All concentrated emulsions exhibited shear-thinning behavior irrespective of oil, emulsifier type and concentration. SPI, followed by starch and gum arabic emulsions showed good stabilities over the 15 days storage period. Gum tragacanth and carrageenan emulsion stabilities were only improved when combined with SPI, particularly at 5% oil concentration.