Phase behavior and complex coacervation of whey protein isolate-Tremella fuciformis polysaccharide solution

Different methods were used to monitor transformations and protein-polysaccharide complexes formation resulting from the interaction of whey protein isolate (WPI) and Tremella fuciformis polysaccharide (TPS) over the pH range of 2.0–7.0. WPI:TPS in the range of ratios from 16:1 to 2:1 were used along with the biopolymer concentrations of 0.1%–1% by mass. The binding properties of WPI to TPS and thermodynamic parameters for this interaction were analysed and calculated. WPI:TPS complex coacervates properties including viscoelasticity, secondary structure, and microstructure were studied. Results showed that both the WPI:TPS ratio and biopolymer concentration altered phase boundaries and critical pH values. For the 0.1% solution, the optimum for WPI:TPS coacervate formation occurred at pH 3.2 and WPI:TPS ratio of 2:1. When the maximum coacervate precipitation formed, the solution presented the least pronounced shear-thinning behavior and the lowest apparent viscosity value. By WPI:TPS interaction, the secondary structure of WPI was altered. Compared to gum Arabic (GA), TPS showed a stronger affinity towards WPI with higher binding sites (1.93–3.65) and binding constant 1.95 × 1010–5.25 × 1019 over temperatures from 288 K (14.85 °C) to 310 K (36.85 °C). Negative values of Gibbs free energy of WPI:TPS (−65.12 to −122.66 kJ/mol) and WPI:GA (−14.38 to −10.18 kJ/mol) combinations suggested binding occurred spontaneously. The WPI:TPS coacervates formed were given a stronger gel-like structure and higher density than the WPI:GA coacervate. Thus, the WPI:TPS coacervates have more potential to be the new alternatives for nutrient microencapsulation.