Thermal and acidic denaturation of phycocyanin from Arthrospira platensis: Effects of complexation with λ-carrageenan on blue color stability

The pH and temperature sensitivity of the natural blue pigment phycocyanin from Arthrospira platensis limits its application as food colorant. This study examines the effect of protein stabilization by the anionic polysaccharide λ-carrageenan on phycocyanins color appearance at pH 2.5-6.0, unheated and after heat treatments (70/90 °C). Electrostatic interactions, hydrophobic interactions, hydrogen bonds and disulfide-bridges were assessed by adding NaCl, urea and dithiothreitol (DTT) to the samples. Measurements of the zeta potential, transmittance and two-dimensional gel electrophoresis coupled to mass spectrometry confirmed electrostatic interactions around the zero surface charge of phycocyanin over a broad pH range (∼4.1-6.4). Despite a color shift towards turquoise, the color remained stable during heating, especially below of pH 3.5. Precipitation was inhibited over the entire pH range. Overall, electrostatic complexation of phycocyanin and λ-carrageenan is a promising technique to stabilize proteinaceous colorants, helping to reduce food waste and foster a shift to renewable materials.