Microalgae have emerged as a sustainable and efficient source of protein, offering a promising alternative to conventional animal and plant-based proteins. Species such as Arthrospira platensis and Chlorella vulgaris contain protein levels ranging from 50% to 70% of their dry weight, along with a well-balanced amino acid profile rich in essential amino acids such as lysine and leucine. Their cultivation avoids competition for arable land, aligning with global sustainability goals. However, the efficient extraction of proteins is challenged by their rigid cell walls, necessitating the development of optimized methods such as bead milling, ultrasonication, enzymatic treatments, and pulsed electric fields. These techniques preserve functionality while achieving yields of up to 96%. Nutritional analyses reveal species-dependent digestibility, ranging from 70 to 90%, with Spirulina platensis achieving the highest rates due to low cellulose content. Functionally, microalgal proteins exhibit emulsifying, water-holding, and gel-forming properties, enabling applications in baking, dairy, and meat analogs. Bioactive peptides derived from these proteins exhibit antioxidant, antimicrobial (inhibiting E. coli and S. aureus), anti-inflammatory (reducing TNF-α and IL-6), and antiviral activities (e.g., Dengue virus inhibition). Despite their potential, commercialization faces challenges, including regulatory heterogeneity, high production costs, and consumer acceptance barriers linked to eating habits or sensory attributes. Current market products like Spirulina-enriched snacks and Chlorella tablets highlight progress, but food safety standards and scalable cost-effective extraction technologies remain critical for broader adoption. This review underscores microalgae’s dual role as a nutritional powerhouse and a source of multifunctional bioactives, positioning them at the forefront of sustainable food and pharmaceutical innovation.

Marine stromal proteins represent a promising but underexplored source of natural emulsifiers for developing functional emulsions. This study investigated the effects of high-intensity ultrasound (HIU) on the physicochemical characteristics, interfacial properties, and antioxidant performance of emulsions formulated with stromal protein extracted from Dosidicus gigas mantle and cinnamon essential oil. Sonication time (0, 3, 5, and 10 min) and amplitude (40, 70, and 100%) were evaluated. The physicochemical and colloidal properties of the emulsions were evaluated through oil-holding capacity (OHC), particle size, polydispersity index (PDI), zeta potential, and rheological behavior. At the same time, antioxidant performance was determined using DPPH, ABTS, FRAP, and erythrocyte hemolysis inhibition assays. HIU markedly improved the physicochemical properties of the emulsions. The Z-average droplet diameter of the emulsions ranged from 195.3 ± 1.5 to 368.7 ± 4.0 nm. The treatment at 5 min and 70% amplitude produced the smallest droplets (195.3 ± 1.5 nm), corresponding to an approximately 27% reduction compared with the untreated emulsion (268.7 ± 4.6 nm), as well as the lowest PDI (0.215 ± 0.026) and a zeta potential of −15.8 ± 0.4 mV. Ultrasound also improved oil retention and enhanced antioxidant performance, although the magnitude of the response depended on the assay employed. The emulsions inhibited AAPH-induced erythrocyte hemolysis by approximately 77–95%, with the highest inhibition observed after treatment for 10 min at 40% amplitude. Overall, HIU enhanced the interfacial functionality of squid stromal proteins, supporting their potential application as natural emulsifiers in protein-based antioxidant delivery systems.