Abstract Description

South Africa's diverse seaweed species, mainly brown seaweeds, are vital to marine ecosystems and are a rich source of undiscovered bioactive compounds. These seaweeds contain substances such as the carotenoid fucoxanthin and phenolic compounds, which offer antioxidant properties and show potential in combating diabetes, obesity, and cancer. With diabetes and obesity being widespread and often fatal, existing starch and lipid enzyme-inhibiting treatments frequently result in adverse side effects, highlighting the need for safer alternatives. This study therefore sought to optimise the sequential extraction of fucoxanthin and phenolics from four brown seaweeds (Ecklonia radiata, Ecklonia maxima, Sargassum elegans and Sargassum incisifolium) in order to investigate their inhibitory activities against α-amylase, α-glucosidase and pancreatic lipase, as well as their antioxidant properties. Extractions for fucoxanthin were optimised using solvent-based methods. The compounds were quantified and identified using HPLC and LC/MS. The yields obtained for the phenolic compounds were much higher than those obtained for fucoxanthin. The highest yield of phenolic compounds was obtained from the seaweed S. incisifolium - 10 mg/g dry weight (DW) of gallic acid equivalents (GAE). In contrast, the highest yield of fucoxanthin was obtained from E. radiata, at 0.082 mg/g DW. Phenolic compounds were powerful inhibitors of the enzyme α-glucosidase, with the phenolics from S. incisifolium exhibiting an IC50 of 2.502 µg/ml. Data collection for the inhibition of pancreatic lipase is currently underway, and we anticipate that the results will reveal a similar pattern. No inhibition of α-amylase was observed. Antioxidant activities (as assessed by the ferric reducing activity assay) were the highest in the extracts obtained from S. incisifolium, with IC50 values of 430.2 and 336.2 µg/ml for the fucoxanthin and phenolic fractions, respectively, while for the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, the IC50 values for this species were 84.48 and 53.87 µg/ml for the fucoxanthin and phenolic fractions, respectively. The findings of this study are shedding new light on maximising the therapeutic potential of brown seaweeds, particularly with regards to the use of phenolic compounds and fucoxanthin as supplements for treating diabetes and obesity.