Preparation of phycocyanin-rich powder from Spirulina platensis algae using freeze/thaw/osmotic treatment coupled with Refractance Window drying and its application as a colorant in set-type yoghurt.

This study developed an integrated process combining green NaCl-assisted freeze/thaw extraction with Refractance Window (RW) drying technology to produce phycocyanin-rich powder from Spirulina platensis for application as a natural colorant in set-type yoghurt. NaCl-assisted extraction gave higher phycocyanin yield and purity than water, with 12 cycles identified as optimal. The extract was dried using RW drying at 70, 80, and 90 °C to produce phycocyanin-rich powders. Powders dried at 70 °C retained the highest phycocyanin content and most intense blue color, while higher temperatures degraded phycocyanin more than allophycocyanin and phycoerythrin, though all powders showed acceptable solubility and flowability. When incorporated into set-type yoghurt, the powders imparted distinct blue-green coloration, with the 70 °C powder producing the strongest color but also highest syneresis. These findings demonstrate that NaCl-assisted freeze/thaw extraction combined with RW drying effectively produces phycocyanin-rich powder, with drying temperature critically governing pigment retention as a natural food colorant.