Sustainable shrimp-shell-derived chitosan as an integrated bioflocculant and complex-forming stabilizer for Spirulina...

The instability of C-phycocyanin (C-PC) during processing and the labor-intensive harvesting of Spirulina platensis are major challenges in microalgal pigment production. To address these issues, this study aimed to valorize shrimp waste into chitosan (Cs) as a bioflocculant and stabilizer. Through demineralization with a yield of 63.15% followed by deproteinization with a yield of 35.50%, chitin was recovered with an overall yield of 22.41%. Subsequent deacetylation with 83.55% efficiency produced 18.73% Cs with a degree of deacetylation (DD) of 80.99%, medium molecular weight (251 kDa), and superior crystallinity (98.16%) compared to commercial chitosan. Application of shrimp-derived chitosan enabled rapid and efficient microalgal harvesting, achieving 99.9% recovery at 125 mg L^-1 within 60 min, while maintaining stable C-PC yields (∼70 mg g^-1 biomass). Increasing chitosan concentrations enhanced pigment purity and promoted chitosan/C-phycocyanin (Cs/C-PC) complex formation, confirmed by FTIR shifts indicating new hydrogen bonding and structural reorganization. The Cs/C-PC complex exhibited markedly higher thermal stability and antioxidant activity than native C-PC. During thermal exposure, the complex retained 50.3% residual concentration after 120 min, extending the half-life from 21.5 min for C-PC to 121 min for the complex (>5-fold improvement). Antioxidant performance was also enhanced, with a reduced IC₅₀ (128.45 μg mL^-1 vs. 166.39 μg mL^-1 for C-PC), and near-neutral pH (6-7) preserved stability. These results highlight the dual functionality of shrimp-derived chitosan in overcoming harvesting and C-PC stability limitations through bioflocculation and Cs/C-PC complex formation, improving pigment quality and antioxidant retention, thereby offering a sustainable strategy for bioproduct production.