Effect of aggregation and sodium salt on emulsifying properties of egg yolk phosvitin

Phosvitin (PVT) is one of the most relevant proteins of hen egg yolk as it could bind multivalent cations in a high quantity. In addition it is capable to stabilise emulsions. Generally, studies about emulsifying properties of protein deal with soluble proteins at a molecular state. However, technological processes and ionic strength conditions can affect the aggregated and charged states of proteins, altering thus their emulsifying properties. In this work, emulsifying properties of PVT at pH 6 in aggregated and non-aggregated states, at two different ionic strengths (0.05 and 0.15 M) have been studied. The emulsifying activity of PVT was inferred from the size of emulsion droplets measured by laser light diffraction. The stability of PVT emulsions under quiescent conditions was estimated by the changes in apparent droplet-size distribution. Light microscopy was used to visualise the aspect of emulsions under different states. To obtain complementary information about PVT solution before emulsion, the particle size and structural characteristics were measured. Non-aggregated PVT has better emulsifying activity than aggregated PVT. Nonetheless, aggregated PVT better stabilises emulsions against coalescence. To make fine emulsions, 0.05 M was a better condition than 0.15 M. Flocculation was highly influenced by NaCl concentration, and the combination of aggregated PVT and 0.15 M ionic strength showed the highest flocculated emulsion. The influence of hydrophobic interactions on aggregate stabilisation of PVT was also observed. The results imply that, by regulating the initial conditions of protein solution, it is possible to control the different mechanisms of PVT emulsion destabilisation.