Fucoidan improves the structural integrity and the molecular stability of β-lactoglobulin.

β-lactoglobulin (β-lg) was covalently bonded with fucoidan through Maillard reaction at 60 °C for 96 h under 79% RH condition. The molecular characters of the conjugate were investigated using fourier transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), and circular dichroism (CD) spectroscopy. And, its thermal properties, surface activity, and zeta-potential were compared with intact β-lg, β-lg-fucoidan mixture, and fucoidan under different pH conditions. AFM indicated that the conjugate was nano-structured, regular spherical-shaped and generally large sized compared to β-lg-fucoidan mixture. CD spectra and FT-IR showed that tertiary structure of β-lg slightly unfolded, but little change in secondary structure occurred. This explained that glycation under Maillard condition resulted in a molten globule state of β-lg. Differential scanning calorimetry (DSC) data exhibited that fucoidan shifted the temperature of phase transition and improved thermal stability of β-lg molecule. In addition, the conjugate prominently decreased the surface tension with pH-dependency.