Insight into pH-induced oat β-glucan/whey protein phase behavior and phase transformation mechanism

The interactions between whey protein isolate (WPI) and oat β-glucan (Glu) were studied under varying pH conditions to explore their phase behavior. The phase diagram of the WPI/Glu system, when subjected to pH adjustments, revealed three distinct regions: a co-soluble region at pH 2.0-3.4 and pH 6.1-7.0, a soluble complex region between pH 5.5 and 6.0, and an insoluble complex region from pH 3.5 to 5.4. Moreover, the presence of low concentrations of NaCl (15 mM and 30 mM) was found to enhance complex formation within these regions, while higher concentrations (50 mM) inhibited complexation. Additionally, when the mass ratio of WPI to Glu was 1:2, the binding sites between the two molecules became fully saturated. Any deviation from this ratio, resulted in a reduction in the number of complexes formed within the defined phase regions. Finally, the composition of the upper and bottom phases in the insoluble complex region (phase separation region) was studied. At pH 4.5, when the ratio of WPI to Glu was 1:4, it was found that 77 % of β-Lg and 76 % of α-La were partitioned into the bottom and upper phases, respectively. This phase behavior study offers a novel approach for separating specific protein components.