Abstract
The edible brown seaweed, Sargassum polycystum C. Agardh was harvested from the coastal region of Malaysia. In this study, analysis of the nutrition and metal content in the methanol extract showed positive for sodium, potassium, magnesium, vitamins A and E and arsenic contamination. The brine shrimp lethality assay (BSLA) revealed the extract to be non-toxic with LC(50) value of 15.60 mg mL(-1) (LC(50) > 1). The antioxidant and antibacterial activities of the methanol extract were measured through various bioassays. The structural and physicochemical characterisation of the NaAlg, analysed through the (1)H-NMR analysis revealed the M:G ratio of NaAlg at 0.733 with mannuronic (M) and guluronic (G) fractions at F (M) = 0.423 and F (G) = 0.577, respectively. The degraded NaAlg through methods of ultraviolet irradiation and sonication showed an increment in the in vivo antioxidant activities at intervals of 15 min, 30 min, 60 min, 90 min and 120 min. The Fourier transform infrared spectroscopy (FTIR) spectra of polysaccharides taken before and after UV irradiation showed breakage of covalent bonds and thus, increase in the intensity of both O-H and C-O stretching vibrations. Therefore, the increment in antioxidant activities observed in the treated samples were related to changes seen in their molecular structures.