066: Elucidating Structure-Functionality Relationships of Phycocyanin Through Size-Exclusion Chromatography With Small-Angle X-Ray Scattering

Introduction

Phycocyanin, an antenna-like light-harvesting protein from algae, has been proven to be a competitive blue colorant and emulsifier through the denaturation process. Controlled disassembly and denaturation allow converting phycocyanin from intact polymers to unfolded subunits, and balancing the hydrophilic-to-hydrophobic character, thus sacrificing part of its blue color feature to earn enhanced emulsifying capacity.

Methods

A series of urea solutions were prepared with a concentration gradient to dissolve phycocyanin. The dissociation process of phycocyanin was observed under a transmission electron microscope (TEM) and the polyacrylamide gel electrophoresis (PAGE). Besides, the solutions were sent to a size-exclusion chromatographic (SEC) system coupled with small-angle X-ray scattering (SAXS). Thus, phycocyanin in different advanced structures in solutions was modeled based on the scattering profiles, with DAMMIN, GASBOR, and DENSS algorithms. Furthermore, interfacial properties were assessed by tensiometries and emulsifying-to-foaming capacity evaluations.

Results

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, in which disassembled and denatured phycocyanin in different tertiary structures were further analyzed for structure. 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. Thanks to phycocyanin’s smaller size, partially denatured structure (brings balanced hydrophilic-lipophilic character), and increased unit surface area, elevated interfacial capacities were anticipated and verified. These results yielded lowered air-water and oil-water interfacial energy needed and improved dynamic interfacial adsorbing parameters with promoted emulsifying and foaming properties.

Significance

The feasibility of disassembling and denaturing phycocyanin was proved, to make it a better emulsifier. This study elucidated how phycocyanin reacted in environments of increasing urea concentrations and how the structural changes enhanced phycocyanin’s functionalities. 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.

Authors: Qike Li, Alireza Abbaspourrad