Improved oxidative stability of fish oil emulsion by grafted ovalbumin-catechin conjugates

Conjugates of ovalbumin (OVA) with (+)-catechin (C), (-)-epigallocatechin (EGC) or (-)-epigallocatechin gallate (EGCG) were synthesized through a free-radical grafting approach. The covalent binding between OVA and catechins was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). OVA-catechin conjugates were further characterized by a combination of steady-state fluorescence spectroscopy, differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and circular dichroism (CD) analyses. Results suggested that the conjugates contained less alpha-helix but more beta-sheet secondary structure than OVA. The catechin-grafting reaction led to improved surface hydrophobicity and decreased tertiary conformation stability of OVA. Compared with that emulsified by OVA, fish oil emulsion coated by conjugates demonstrated smaller droplet size, better storage stability and less viscosity. Besides, conjugates inhibited the lipid oxidation in fish oil emulsion more effectively than OVA because of their higher antioxidant activity and interfacial accumulation.