Comparative Sustainability Assessment of Alkali and Deep Eutectic Solvent-Based Protein Recovery from Spirulina ( <i>Arthrospira platensis</i> ): Influence on Physicochemical and Functional Properties

As the demand for sustainable proteins rises, alternative protein sources like microalgae, particularly Spirulina, have gained attention for their high protein content and low resource requirements. However, there is a lack of studies on efficient extraction methods that consider both functional performance and sustainability. To bridge this, this study explores protein extraction from Spirulina using conventional alkali extraction and deep eutectic solvents (DES), with and without ultrasound treatment, focusing on physicochemical, functional, and environmental performance. Results revealed significantly higher recovery (∼30%) by alkali extractions (A, A-US) compared to DES extractions (∼5%) (DES, DES-US). However, DES systems yielded higher purity proteins (∼80%) relative to alkali extracts (∼60%). Ultrasound treatment enhanced protein recovery in alkali systems but showed nominal influence on DES systems. Functional characterization indicated variations in different parameters, depending on the extraction route. A and A-US showed better near-neutral pH solubility compared to DES and DES-US. On the other hand, DES extracts showed higher antioxidant activity and performed better in functional properties like oil and water-holding capacities and emulsifying capacities. Additionally, life cycle assessment (LCA) revealed higher environmental impacts across most categories by DES extractions, including global warming potential (∼70 kg CO 2 eq) compared to alkali extraction (∼46 kg CO 2 eq). Ultrasound’s environmental burdens were only marginal on both routes. Thus, this study provides a comprehensive guide integrating process efficiency, product functionality, and sustainability, offering critical insights for the selection of solvents for practical and scalable extraction technologies.