Sustainable Valorization of Alginate, a Review of Green Extraction, Structure–Function Relationships, and Next-Generation Food Applications

Alginate, a multifunctional polysaccharide derived from brown seaweeds, has gained increasing attention as a sustainable biopolymer for food and allied industries. Its structural composition, determined by the ratio and sequence of mannuronic and guluronic acid residues, governs its physicochemical and functional properties such as gelling, thickening, stabilizing, and film-forming abilities. However, conventional acid–alkali extraction methods remain resource-intensive and environmentally unsustainable, highlighting the need for greener, more efficient alternatives. This review systematically synthesizes recent advances in alginate valorization through a structured analysis of peer-reviewed studies on extraction technologies, structure–function relationships, and emerging food applications. Emphasis was placed on evaluating the efficiency, selectivity, and environmental impact of various green extraction methods. Findings reveal that sustainable technologies can significantly enhance yield and purity while reducing chemical and energy inputs. Parallel progress in structural and functional characterization has deepened our understanding of alginate’s molecular weight distribution, rheological behavior, and functional performance, linking extraction parameters to product quality. Beyond conventional uses, alginate is now being valorized into advanced food applications, including edible active films and coatings, encapsulation systems for bioactives, fat replacers in low-calorie formulations, and as emulsion stabilizers and foaming agents. Overall, this review underscores the promise of green extraction technologies in promoting environmentally responsible alginate production. It also highlights the need for standardized methodologies, species-specific optimization, and scalable processing to bridge the gap between laboratory innovation and industrial application.