Bioactive metabolites from algae: occurrence, extraction techniques, functional properties, food applications and therapeutic prospects

This review critically summarizes the major algal-derived bioactive compounds, including phenolics compounds (e.g., phlorotannins, bromophenols, phenolic acids), sterols (e.g., fucosterol, β-sitosterol), and polysaccharides (e.g., carrageenan, fucoidan, ulvan), as well as key pigments such as astaxanthin, β-carotene, lutein, violaxanthin, zeaxanthin, and chlorophylls. In addition, state-of-the-art extraction technologies including supercritical fluid extraction, pressurized liquid extraction, ultrasound assisted, microwave assisted, surfactant assisted, and enzyme assisted extractions, and carbon dioxide-expanded liquids) were systematically compared considering key parameters such as yield, versatility, compound selectivity, extract quality, cost-effectiveness, technical complexity, operational conditions, and sustainability principles. Based on this comparative evaluation, ultrasound assisted extraction emerged as the most versatile among advanced technologies, same as enzyme assisted extraction within ulterior techniques. The potential incorporation of these bioactive compounds into novel algae-based food systems, either as functional ingredients or texturizing agents, was also discussed. Moreover, their relevance in alternative therapeutic applications was also highlighted, with a proof-of-concept focused on the antiviral potential of sulfated polysaccharides (carrageenan, fucoidan, and ulvan). Overall, algae-based ingredients were found to be promising biofunctional agents for innovative food products, nutraceutical formulations, and therapeutic alternatives.