Structural and functional characterization of ovalbumin-proanthocyanidin-sodium alginate conjugates and their application in sunflower oil emulsion systems

This study aimed to investigate the structural and functional properties of the ovalbumin (OVA)-proanthocyanidin (PC)-sodium alginate (SA) conjugates, and evaluate the physicochemical stability of the conjugate-based sunflower oil emulsions. The formation of the OVA-PC-SA covalent conjugates was confirmed through glycosylation degree, SDS-PAGE and multispectral methods including fluorescence, fourier-transform infrared and circular dichroism spectroscopy. The results showed that the conformation of OVA was changed after grafting with SA, leading to a decrease in α-helix content and a notable increase in β-sheet content. As the mass ratio of OVA-PC conjugate to SA decreased from 8:1 to 1:4 (w/w), the grafting degree of OVA-PC-SA conjugates increased [from (18.10 ± 1.10)% to (55.14 ± 5.05)%], indicating a deeper level of glycosylation. The covalent binding of SA made the surface microstructure of OVA smoother and more uniform. Moreover, the OVA-PC-SA conjugates exhibited better emulsifying properties and thermal stability compared to pure OVA and OVA-PC conjugate. The interfacial tension of OVA-PC-SA conjugates was time-dependent, and the interfacial adsorption of the conjugates was related to the added amount of SA. Additionally, the OVA-PC-SA conjugate acted as a novel emulsifier to stabilize the sunflower oil emulsions, with the improvement of the emulsions’ physicochemical stability as the mass ratio of OVA-PC conjugate to SA decreased from 8:1 to 1:4 (w/w). This study may offer new insights into enhancing the functional properties of OVA and suggest the application of OVA-PC-SA conjugate as a novel emulsifier in food emulsification systems.