Advances in ultrasound-enhanced recovery of marine algal polysaccharides: toward sustainable bioprocessing

The growing emphasis on environmental sustainability has intensified interest in the extraction and valorization of polysaccharides from marine algal species due to their non-toxic nature and notable bioactivities. Although various conventional extraction techniques have been employed, these often involve high energy consumption, prolonged processing times, limited selectivity, and the potential degradation of polysaccharide bioactivity. To address these limitations, a range of sustainable and cost-effective extraction methods has been developed, including enzyme-assisted extraction (EAE), supercritical fluid extraction (SFE), subcritical water extraction (SWE), microwave-assisted extraction (MAE), and ultrasound-assisted extraction (UAE). Among these, the UAE, either as a standalone method or integrated within a biorefinery framework, has emerged as a promising and green technology. It offers higher extraction efficiency with reduced time, energy, and cost requirements. Polysaccharides extracted via ultrasound (US) have demonstrated enhanced anticancer, bioactive, and rheological properties. Furthermore, integrating the UAE with green solvents, such as natural deep eutectic solvents (NaDESs), or complementary techniques, including MAE, hot water extraction (HWE), and EAE, has been shown to further improve yields by 2-6 % and enhance functional quality. This review highlights the potential of the UAE, both individually and in combination with other methods for the efficient recovery of algal polysaccharides. It also evaluates the influence of the UAE on the biofunctional properties of the extracted compounds, underscoring their applicability across diverse industrial sectors. Nonetheless, further research is warranted to optimize process parameters, ensure safety, enhance antioxidant activity (AOA), and improve purification and characterization, as well as better understand the structure-activity relationships of these valuable biopolymers.