by Blaine Friedlander
The food colorant derived from cyanobacteria — phycocyanin — provides a vivid blue pigment that food companies crave, is natural, and contains nutritional protein. But…it can be unstable when placed in soft drinks and sport beverages, and then lose its hues under fluorescent light on grocery shelves.
With the help of physics and the intense X-ray beams from Cornell University’s synchrotron, food scientists have found the recipe for phycocyanin’s unique behavior, and they now have a chance to stabilize it. The new research was published Nov. 12 in the American Chemical Society’s journal BioMacromolecules.
“If you want to put phycocyanin into acidified beverages, the blue color fades quickly due to thermal treatment,” said Alireza Abbaspourrad, the Youngkeun Joh Assistant Professor of Food Chemistry and Ingredient Technology in the Department of Food Science in the College of Agriculture and Life Sciences. “So, most food companies seeking blues in their food use synthetic food dye.”
The food scientists wanted to understand phycocyanin’s color properties and how it worked. So, they partnered with the Macromolecular Diffraction Facility of the Cornell High Energy Synchrotron Source (MacCHESS) and used Size-Exclusion Chromatography coupled to Small-Angle X-ray Scattering (SEC−SAXS) on a beamline.
The research, “Tuning C-Phycocyanin Photoactivity via pH-Mediated Assembly–Disassembly,” was authored by Ying Li, a doctoral student in food science; Richard Gillilan, staff scientist at the Macromolecular X-ray science at the Cornell High Energy Synchrotron Source, or MacCHESS; and Dr. Abbaspourrad.
Phycocyanin was placed into a biological fluid and brought to the MacCHESS laboratory. There, intense beamline X-rays were channeled into tiny drops of the fluid. The small-angle X-ray scattering showed that as pH levels, the molecular strands changed into different shapes, folds and assemblies.
“So as pH changes, the phycocyanin molecules form in different ways,” Ms. Li said. “If the pH goes up, the molecules come together and if the pH level goes down, the molecules disassemble. As we changed the environmental stimulus for the phycocyanin, the molecules modulated their behavior in terms of how they interact with light. It’s a relationship of the protein structure and the color stability.”
The acidity of the environment can essentially mediate an assembly-disassembly pathway, Dr. Abbaspourrad said. “Through the X-ray scattering we could see the proteins and see how their monomers are assembled together and how the oligomers disassemble,” he said. “That’s the root cause for how the blue color fades.”
This research was funded by U.S. Department of Agriculture (National Institute of Food and Agriculture), and CHESS is supported by the National Science Foundation, New York state, and the National Institutes of Health and its National Institute of General Medical Sciences.
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