Characterisation of Sargassum elegans fucoidans extracted using different technologies: Linking their structure to α-glucosidase inhibition

Fucoidan, a sulphated polysaccharide found in brown seaweeds, has gained attention for its potential as an α-glucosidase inhibitor (AGI), which is significant for managing type 2 diabetes mellitus (T2DM). Although the use of brown algae for fucoidan extraction is becoming more popular, a few challenges remain, such as low extraction yields and a lack of understanding of the structure-activity relationship of fucoidan as an AGI. This study compared fucoidan extraction yields from S. elegans using three novel extraction methods (citrate buffer, EDTA, and enzyme-assisted extraction) and two well-established extraction protocols (hot water and mineral acid extraction). The structure-activity relationships of the fucoidan extracts as potential AGIs were then investigated. The fucoidan extraction yields for enzyme-assisted, citrate buffer, EDTA, hot water extraction and mineral acid extraction were 28 %, 20 %, 15 %, and 2.5 % and 3 %, respectively. Distinct structural features were noted from the fucoidan extracted by different techniques, according to their chemical profiles confirmed by their carbohydrate content, FTIR and NMR, and physical characteristics. Each extract exhibited unique chemical and structural properties. With IC 50 values of 25 and 88 μg/ml, respectively, the fucoidans extracted by water and citrate buffer demonstrated the highest potency as AGIs, whereas the fucoidans extracted with the assistance of enzymes and EDTA showed IC 50 values of 186 and 273 μg/ml. In summary, the extraction technology affected the fucoidans' structural and chemical compositions, impacting their biological activity as AGIs. Fucoidan's potent activity as an AGI represents a promising strategy for mitigating the burden of diabetes by reducing or preventing hyperglycaemia. Leveraging fucoidan could contribute meaningfully to developing alternative, natural therapeutic interventions for managing T2DM. • The different extraction protocols yielded structurally unique fucoidans. • Degree of fucoidan sulphation influenced its α-glucosidase inhibitory potential. • Fucoidan extracts show potential as Type 2 diabetes mellitus biotherapeutics.