Characterization of coacervation behavior between whey protein isolate and propylene glycol alginate: A morphology, spectroscopy, and thermodynamics study

The interactions between whey protein isolate (WPI) and propylene glycol alginate (PGA) were investigated as a function of pH and the mass ratio. The results showed that WPI and PGA formed a soluble and uniform complex at a mass ratio of 2:1 and pH 4.0 through forces such as electrostatic attraction and hydrogen bonding. Isothermal titration calorimetry confirmed that the contribution of positive enthalpy (ΔH) and entropy (ΔS) were the beneficial indicator in the process of combining WPI and PGA under the same mass ratio but different pH. Fourier transform infrared spectroscopy, fluorescence spectroscopy and circular dichroism confirmed that hydrogen bonding was also one of the interaction forces in addition to electrostatic interactions between WPI-PGA complex. The freeze-dried WPI-PGA complex showed the same amorphous structure as WPI. These formed WPI-PGA complexes provided insights for interaction mechanism of proteins and polysaccharides as well as a theoretical basis for the food industry.