Interactions between hydrophobically modified starch and egg yolk proteins in solution and emulsions

In this paper we study the interaction between starch which has been hydrophobically modified, with octenyl succinic anhydride (OSA), and α-β-livetin, which is the water soluble fraction of egg yolk. The modification of the starch renders it surface active and also incorporates a carboxyl group to the starch, which can be negatively charged. The interaction was studied both in solution and emulsions, and at different pH (4.0–8.0). Solutions with different ratios between starch and protein was mixed and studied with turbidity measurements over time. Emulsions were formed with α-β-livetin after which the OSA-starch was added. The emulsions were separated by centrifugation and the surface load of α-β-livetin and OSA-starch was determined through serum depletion. Furthermore, the impact of the observed interaction on emulsion stability was investigated. The results show a strong interaction between the two biomacromolecules in solution at pH 4.0. In the emulsions the adsorption of starch onto livetin was highest at pH 4.5 followed by pH 6.0, while low at pH 4.0 and 8.0. The low adsorption of OSA-starch at pH 4.0, despite the strong interaction in solution, can be explained by complex formation immediately in solution. Less starch would, thus, be able to reach the interface and adsorb. Some differences in the stability of an emulsion only containing α-β-livetin, and an emulsion with both α-β-livetin and OSA-starch could be observed. However, the differences were not statistically significant.