Investigation of ovotransferrin conformation and its complexation with sugar beet pectin

Small-angle X-ray scattering (SAXS) has been used to investigate the conformation of ovotransferrin (OVT) in solutions of different pH values. OVT was found to be a spherical molecule at native state in aqueous solutions. Radius of gyration (Rg) of OVT increased by 19.6% upon transition from native to molten globular state, and Rg increased by 9.7% as OVT further unfolded to an extended conformation. Besides, OVT showed concentration scaling behaviors at molten globule state. The information about size and shape was expected to facilitate the understanding of interactions between OVT and sugar beet pectin (SBP). Increasing OVT/SBP mixing ratios altered critical pH transition points in phase diagram, and the ratio of 5:1 was close to the saturated complexation ratio between OVT and SBP. Turbidities of OVT–SBP mixtures decreased significantly in the presence of sodium chloride, indicating the domination of electrostatic interaction in OVT–SBP complexation. Atomic force microscopy data illustrated the formation, association and dissociation processes of OVT–SBP complexes. Fluorescence spectroscopy results revealed that binding constant between OVT and SBP decreased with increasing temperature. The negative ΔH and positive ΔS further indicated the strong attractive interaction between OVT and SBP, which overcame the entropy contribution. Emulsions stabilized by OVT–SBP complexes had smaller droplet sizes and better physical stability than those stabilized by either pure OVT or SBP.