Phycocyanin, a light-harvesting protein from algae, has recently gained attention as both a natural blue colorant and a potential bio-based emulsifier. While its intact polymeric form exhibits strong color, controlled disassembly and partial denaturation can tune its balance of hydrophilic and hydrophobic regions, thereby enhancing interfacial activity at the expense of some color intensity.

To investigate this structure–function relationship, phycocyanin was dissolved in urea solutions with a concentration gradient to induce stepwise dissociation. Structural transitions were monitored using transmission electron microscopy (TEM), polyacrylamide gel electrophoresis (PAGE), and size-exclusion chromatography (SEC) coupled with small-angle X-ray scattering (SAXS). SAXS-based modeling with DAMMIN, GASBOR, and DENSS provided three-dimensional insights into the conformational changes, which were benchmarked against known crystal structures. Tensiometry and measurements of emulsifying and foaming capacities further evaluated interfacial properties.

With the increase of urea concentration, phycocyanin transformed from uneven to small and uniform particles under the TEM. This shift was verified by PAGE and SEC. The chromatographic eluent was continuously irradiated with X-rays, producing integrated scattering intensity profiles. Phycocyanin converged to a smaller and more homogeneous structure, and the structure changed from intact globular to denatured non-globular, contributing to the boosted emulsifying capacity. Three modeling algorithms were applied to compare and align with the already-solved crystal structures, achieving good fitting scores. These conformational changes increased specific surface area and promoted a more balanced hydrophilic–lipophilic character, resulting in lower air–water and oil–water interfacial tensions and improved dynamic adsorption kinetics. Consequently, both emulsification and foaming performance were significantly enhanced.

This work clarifies how chemical denaturation modulates the structural hierarchy of phycocyanin and links these changes to functional improvements at interfaces. It supports the use of dissociated phycocyanin in juices, low-temperature dairy products, and functional beverages, after the removal of urea by the urea-shifting method, as a clean-labeled blue colorant, a natural emulsifier, and an excellent antioxidant.

Alireza Abbaspourrad

Cornell University College of Agriculture and Life Sciences

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