Influence of storage temperature on the stability of heat treated phycocyanin-λ-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 λ-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 λ-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.