Characteristics and oxidative stability of soy protein-stabilized oil-in-water emulsions: Influence of ionic strength and heat pretreatment

Some physicochemical characteristics, microstructure and stability of native and preheated (95 °C, 15 min) soy protein isolate (SPI)-stabilized emulsions, formed at varying protein concentrations (c; 0.5–4.0%, w/v) in the absence or presence of 300 mM NaCl, were characterized. The emulsifying ability, flocculated state of droplets, microstructure, interfacial protein concentration (Γ) of the fresh emulsions, as well as stability of these emulsions against coalescence, flocculation, creaming and even lipid oxidation upon storage up to 2 weeks were evaluated. In general, increasing c was favorable for the emulsification efficiency, but the flocculated state of oil droplets or size of the flocs in the fresh emulsions was more affected by the presence of salt, and/or the heat pretreatment. Increasing ionic strength or application of a heat pretreatment resulted in remarkable increases in extents of droplet flocculation in the fresh emulsions, as well as amount and concentrat,ion of adsorbed proteins at the interface. All the emulsions exhibited an extraordinary stability against coalescence and/or flocculation. Increasing c led to a progressive increase in stability against creaming, especially for the preheated SPI emulsions with 300 mM NaCl. All the emulsions at c = 1% or above exhibited a similarly high oxidative stability upon storage up to 9 days. Even at c = 0.5%, the oxidative stability of the formed emulsions could be greatly improved by increasing ionic strength, and/or application of a heat pretreatment. The findings have important implications for the development of an important kind of protein-stabilized emulsions with industrial relevance.