Exploring the therapeutic potential of marine macroalgae: antioxidant, in vitro antidiabetic, and antibacterial activities of Stoechospermum polypodioides (J.V. Lamouroux) J.Agardh

Seaweeds, or macroalgae, are recognized for their medicinal and edible properties and are commonly utilized in the pharmaceutical and food industries. This study aimed to investigate the phytochemical components, antioxidant properties, in vitro antidiabetic effects, and antibacterial activities of Stoechospermum polypodioides, a macroalga from the southern coast of India. The phenolic composition was quantified using the Folin-Ciocalteu assay, while the total flavonoid content was measured using the aluminium chloride method. Antioxidant activity was evaluated through DPPH radical and ABTS cation scavenging assays, total antioxidant capacity (TAC), and ferric reducing ability. Inhibition assays for α-amylase and α-glucosidase were conducted to explore the antidiabetic potential. Antibacterial activity was tested against four bacterial pathogens. The phenolic content of the methanol extract of S. polypodioides was found to be 350 ± 10.14 mg GAE/g, and the flavonoid content was 206.8 ± 7.43 mg QE/g. The methanol extract demonstrated scavenging activity against DPPH and ABTS, with IC50 values of 29.22 µg/ml and 31.20 µg/ml, respectively. An effective reduction of Mo(VI) to Mo(V) was also noted, with an IC50 of 44.2 µg/ml. Additionally, the extract showed strong reducing ability, evidenced by an absorbance of 0.987 ± 0.012 at 700 nm at the highest concentration tested (1000 µg/ml). Furthermore, the methanol extract effectively inhibited α-amylase (IC50 = 21.6 µg/mL) and α-glucosidase (IC50 = 22.6 µg/mL). The S. polypodioides extract also exhibited significant antibacterial activity, particularly against Staphylococcus aureus. Based on these bioactivities, S. polypodioides may be considered a potential source of bioactive agents.