Interactions between hydrophobically modified starch and egg yolk proteins in solution and at oil/water interfaces

• Main Author: Magnusson, Emma
• Format: Others
• Language: English
• Published: Högskolan i Kalmar, Naturvetenskapliga institutionen 2009
• Subjects: egg yolk; OSA starch; interactions
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:hik:diva-2006

A common modification of starch is esterfication with anhydrous octenyl succinic acid (OSA).  The modification makes the polymer surface active and it also incorporates a carboxyl group to the starch, which can be negatively charged. The characteristics of OSA starch make it interesting for usage in combination with egg yolk proteins in food emulsions. It is not only the individual ingredients that affect the product; interactions between ingredients and ingredient-dispersion medium have a great impact on factors such as structure and stability. Knowledge about how the interactions affect emulsion properties would make it possible to predict the behavior of an emulsion, which would be a great advantage in the formulation of food emulsions. Therefore, this is a subject of interest. The purpose of this master thesis was to further investigate the interactions between OSA starch and α – β-livetin in solutions and in emulsions. First, the charges of the macromolecules were studied by titration. Interactions in solution were then analyzed through turbidity and solubility measurements. The adsorption of OSA starch onto livetin and the interfacial rheology were also studied. Finally, an emulsion stability experiment was made. Strong interactions between the two macromolecules were observed in solutions at pH 4.0. This was probably due to hydrophobic interaction; however it could also be explained by electrostatic interaction. In the emulsions the adsorption of starch onto livetin was highest at pH 4.5, and then decreased with increasing pH values. The absence of OSA starch adsorption at pH 4.0, despite the strong interaction in solution, could be explained by complex formation immediately in solution. Less starch would then be able to reach the interface and adsorb. In the interfacial rheology experiments, an indication of decreased complex dilational modulus of the interfacial layer, caused by OSA starch addition was seen at low pH values. This could be due to aggregation of the proteins and formation of an uneven interfacial layer. OSA starch would then be able to adsorb and disturb the elasticity. Some differences in the stability of an emulsion only containing livetin, and an emulsion with both livetin and OSA starch could be observed. However, more investigations are needed to be made to understand the underlying mechanisms.