Thermal and pH Stability of the B-Phycoerythrin from the Red Algae Porphyridium cruentum

Phycoerythrin is the major light-harvesting pigment-protein of the red algae Porphyridium cruentum and is widely used as fluorescent probe and analytical reagent. Additionally this protein has a potential application as natural dye in food industry. Nevertheless the knowledge of the functional properties of this alga protein is limited, hindering its application as food additive. In this article we report a biophysical characterization of B-phycoerythrin from Porphyridium cruentum (B-PE) in order to study its stability and spectral properties in a broad range of pHs. This information can help in its potential application as colorant in the food industry. Spectroscopic data obtained in this work show that B-PE has a stronger functional stability in the pH range 4.0–10.0, and Size Exclusion Chromatography suggests that the protein maintains a (αβ)6-γ oligomeric structure in that range of pHs. At pH 7.0, an apparent Tm value of 77.5 ± 0.5 °C was calculated. At this pH, the protein is highly stable with a loss of only 20 % of its spectral properties (absorbance and fluorescence) after 25 days at room temperature. These results indicate that B-PE is more stable in a broad range of pHs than other phycoerythrin proteins, which would facilitate its use in the food industry.