Antimicrobial, antidiabetic, antiviral, and antioxidant activities of fucoidan extracted from the brown seaweed Padina pavonica.

Macroalgae are considered a promising biological source of active substances, and sulfated polysaccharides are among the most important compounds with potential applications. Here, fucoidan from Padina pavonica collected from the Rocky Bay of Abu Qir in Alexandria was analyzed for its ash, water, protein, sulfated groups, elemental content, total sugars, and uronic acid levels. Additionally, its monosaccharides were qualitatively and quantitatively determined using high-performance liquid chromatography for fucose detection, which is the main fingerprint of fucoidans. The isolated fucoidan was characterized using FTIR, scanning electron microscopy, EDX, and thermogravimetric analysis (TGA). Its biological activities, including antiviral, antioxidant, antimicrobial, and antidiabetic effects, were then evaluated. The yields of fucoidan, fucose, and sulfate were found to be 17.8 ± 0.23%, 34.45%, and 9.52 ± 0.19%, respectively. It inhibited HSV-1 with an inhibition percentage of 30.89 ± 0.84. The maximum Ferric Reducing Antioxidant Power (FRAP) value reached 81.82 ± 1.44% at 1000 µg/ml. Padina fucoidan (PF) showed the largest inhibition zone of 18 mm against Methicillin-Resistant Staphylococcus aureus (MARSA) (ATCC 4330) with an MIC of 1.25 mg/L. It also demonstrated a promising inhibitory effect on α-Amylase enzyme, reaching 75.69 ± 1.05 at a concentration of 1000 µg/ml. We conclude that Padina pavonica is an excellent producer of fucoidan, with a significant sulfate content that enhances its biological activities, especially its antidiabetic properties.