Optimisation of Extraction Methods, Antioxidant Potential, and Molecular Docking Studies of <em>Dunaliella salina</em> and <em>Spirulina platensis</em> Extracts for Cosmetic Applications

Microalgae are valuable marine resources with bioactive compounds that can be used for health and industrial applications. This study investigated the optimisation of extraction methods and antioxidant properties of Dunaliella salina and Spirulina platensis to explore their potential as sources of natural compounds for cosmetic use. Extraction was performed using aqueous, methanol, and ethanol solvents, with methanol yielding the highest recovery in D. salina (21.67% ± 0.58) and aqueous extraction being most effective for S. platensis (24.00% ± 0.50). Phytochemical analysis revealed solvent-dependent variation, as methanolic D. salina extracts showed maximum phenolic content (32.15 ± 2.05 mg GAE/g DW), while aqueous extracts contained the highest flavonoids (94.90 ± 0.90 mg QE/g DW). In S. platensis, aqueous extracts exhibited superior phenolic (70.99 ± 1.03 mg GAE/g DW) and flavonoid content (65.39 ± 2.68 mg QE/g DW). Antioxidant capacity assessed by ABTS, DPPH, and FRAP assays confirmed strong radical scavenging and reducing activities, with methanolic S. platensis showing the highest ABTS activity (IC50 = 113.44 µg/mL) and aqueous extracts demonstrating the strongest reducing power (FRAPIC50 = 138.08 µg/mL). Molecular docking revealed strong binding of key phytochemicals with Keap1 protein, suggesting a role in oxidative stress modulation. These findings highlight the potential of D. salina and S. platensis as marine-derived sources of natural antioxidants for biotechnological and cosmetic applications.