Scalable two-stage recovery of C-phycocyanin from Synechocystis salina via tangential ultrafiltration for sustainable textile dyeing

C-phycocyanin (C-PC) is a high-value phycobiliprotein extensively used as a natural blue colourant, whose commercial deployment is primarily constrained by downstream purity, stability, and scalability. In this work, a simple, robust, and scalable two-stage process is developed for the recovery of C-PC from Synechocystis salina , combining mild clarification by osmotic shock with tangential-flow ultrafiltration. Phosphate-buffer extraction (0.1 M, pH 7.0) enabled the recovery of 85% of the intracellular C-PC, albeit with low initial purity (A₆₁₅/A₂₈₀ < 0.38). Subsequent ultrafiltration using membranes with molecular weight cut-offs (MWCO) of 10, 50, and 100 kDa allowed simultaneous concentration and purification. The 100 kDa membrane showed the best overall performance, achieving a purity ratio of 1.09, C-PC recovery of 92%, a global yield of 78.1%, and a final concentration of 1.01 mg·mL −1 (14-fold concentration), while maintaining stable permeate flux and low filtration resistance, indicative of favourable scale-up potential. To overcome the intrinsic instability of C-PC, the effect of food-grade stabilizing additives (2.5 mM) was assessed, extending shelf life at 25 °C from 77 days (no additive) to 127 and 208 days with benzoic and citric acid, respectively. Finally, the purified and stabilized C-PC extracts were successfully applied as natural dyes on different textile materials (cotton, cotton/viscose-rayon/polyester, and cotton/polyester) using conventional mordants, yielding homogeneous colouration with acceptable colour stability. Overall, this integrated clarification–ultrafiltration and stabilization strategy provides an industrially viable route for producing commercial-grade C-PC with enhanced shelf life, enabling its use in food formulations and sustainable textile dyeing.