Soluble complexes of ovalbumin with fucoidan: Energetics of binding, protein stability and functional properties

Abstract

The interaction between ovalbumin (OVA) and fucoidan (FVF), a branched sulfated polysaccharide of seaweeds, was studied by turbidimetry, velocity sedimentation, and high-sensitivity differential scanning calorimetry (HS-DSC). The boundary conditions of the existence of soluble OVA−FVF complexes were determined as a function of pH and/or OVA−FVF mixture composition. The yield of soluble OVA−FVF complexes was determined from the velocity sedimentation data at pH 4.0 and 5.0 in 5 mM NaCl. It achieved a maximal value of ∼90% at pH 5.0 and the OVA/FVF weight ratio of about 6. According to HS-DSC data, the denaturation behavior of OVA bound to FVF changed significantly as compared with that of the free protein. Depending on pH and OVA−FVF mixture composition, one or two heat capacity peaks were observed on the thermograms assigned either to the free or to bound protein. The denaturation temperature of the bound OVA was about 20 °C lower than that of the free OVA. Based on the HS-DSC results, the OVA to FVF binding curves were derived at pH 5.0 and 5.5. Both were well approximated by the Langmuir equation with n=66±3 and Kb=105.2±0.1 M−1 at pH 5.0, and n=1.1±0.2 and Kb=104.6±0.2 M−1 at pH 5.5. Some emulsifying and foaming properties of the OVA−FCD complexes were characterized and compared with those of OVA alone. The complexes showed a significantly lower emulsifying threshold. The foaming ability of the complexes could exceed that of OVA by more than twice. These results imply a high potential of the OVA−FCD complexes as emulsion and foam stabilizers.