Probing the stability of the food colourant R-phycoerythrin from dried Nori flakes

This study aimed to characterise the stability of R-phycoerythrin (R-PE), a vivid natural colourant with emerging potential for application in the food industry. High-quality (A560/A280 >= 5), native (alpha-helix content 75%) R-PE was purified from commercial dried Nori (Porphyra sp.) flakes. Thermal unfolding revealed two transitions (at 56 and 72 degrees C), ascribed to different protein subunits. Contrary to elevated temperature, high-pressure (HP) treatment showed significant advantages: The R-PE unfolding was partly reversible and the colour bleaching was minimal. Binding of Cu2+ (6.3 x 105 M-1) and Zn2+ (1.7 x 103 M-1) influenced conformational changes in the protein tetrapyrrole chromophore without affecting R-PE structure and stability (colour). The results give new insights into the stability of R-PE suggesting its usefulness for the replacement of toxic synthetic dyes. Preservation of the red colour of R-PE could be considered in fortified food and beverages by HP processing. R-PE may act as a biosensor for Cu2+ in aquatic systems.