Aggregate status determining the foaming behavior of phycocyanin: insights from bulk phase and air-water interface...

C-phycocyanin (C-PC) exhibits diverse foaming properties under acidic pH conditions (5.6-2.0), but the relationship between pH-induced structural changes and air-water interfacial properties is unclear. At pH 5.6 and 5.0, C-PC proteins remained segregated, forming a relatively denser interfacial layer with typical strain hardening during the compression of the interface. At pH 4.0 and 3.0, C-PC proteins formed large aggregates (100-500 nm) and exhibited Pickering-like characteristics. As surface hydrophobicity increased, the foaming capacity increased to ∼100%. At pH 2.0, a mixture of segregated proteins and smaller aggregates (30-50 nm) showed the highest adsorption rate and the highest interfacial modulus, which resulted in a foaming capacity of 147%. This study theoretically understands the pH-induced changes in protein structure and aggregate states, and illustrates how these changes result in the excellent foaming properties. It also expands the application of C-PC as a functional alternative protein in high-efficiency foaming agents.