Stability and Antioxidant Activity of Food-Grade Phycocyanin Isolated from Spirulina platensis

Food-grade phycocyanin was obtained from Spirulina platensis cultured in seawater-based medium and purified by ammonium sulfate precipitation. The stability of phycocyanin under different conditions, including different pH, temperature, light, and edible stabilizing agents, was systematically investigated by spectroscopy methods. The optimum pH range for phycocyanin was found to be 5.0–6.0. Phycocyanin was kept stable at temperatures up to 45ºC over short time periods (i.e., no significant changes were observed in the relative concentration of phycocyanin, CR). In contrast, incubation at a relatively high temperature resulted in a decrease in the CR and half-life in a temperature-dependent manner. Constant exposure to light at 100 μmol m–2 s–1 for 36 h, decreased the CR value of phycocyanin (pH5.0) to 78.4%. Sodium chloride was an effective stabilizing agent for phycocyanin, and its efficacy increased in a concentration-dependent manner for all concentration ranges assessed in this study. Moreover, phycocyanin exhibited concentration-dependent antioxidant activities in 2,2′-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid) and α,α-Diphenyl-β-pricrylhydrazyl assays. Taken together, our results suggest that the optimal conditions for preserving the stability of food-grade phycocyanin isolated from S. platensis are a pH of 5.0–6.0, low temperature, darkness, and the addition of edible stabilizing agents.