Influence of storage temperature on the stability of heat treated phycocyanin--carrageenan complexes in liquid formulations

The protein chromophore complex present in cyanobacteria like Arthrospira platensis can be utilized as a natural food colorant, but the appearance is prone to changes under environmental conditions that alter the protein-chromophore interactions. The study investigates the color stability of phycocyanin stabilized by λ-carrageenan during storage at 4 and 25 °C under different heating and pH conditions. Phycocyanin solutions and combinations with -carrageenan (1: 4) were prepared at a pH of 2.5-6.0, with and without thermal treatment at 70 C and 90 C. Visual appearance, absorption spectra, zeta potential, and the diameter of the structures formed were observed over a period of 28 days. Considerable color losses were determined for pure phycocyanin at a pH of 2.5 to 4.5 when the samples were stored at 25 C, which was improved by the formation of soluble complexes with -carrageenan in associative conditions. Interestingly, soluble complexes at a pH < pI were found to be more resistant at high treatment temperatures with a higher storage stability than co-soluble polymers at a pH > pI, but soluble structures formed at a pH of 2.5 had a significantly larger diameter (871 185 nm) that increased in size during storage (2025 1012 nm after 14 d at 25 C) than at a pH of 3.0 (200 ± 5 nm) when heated to 90 C. These results were related to changes in protein structure and mass transport phenomena and might be of high importance for low-viscous food formulations. The protein-chromophore interactions of phycocyanin are prone to changes in environmental conditions. Loss of these interactions leads to disappearance of the color. After stabilization with λ-carrageenan, phycocyanin can be stabilized over 28 days.