Nutritional composition, bioactive metabolites, and functional properties of red seaweed ( <i>Gelidium spinosum</i> )

Abstract This study characterised the Gelidium spinosum extracts obtained with solvents of different polarities (methanol, ethyl acetate, and n-hexane) through proximate and mineral analyses, GC–MS profiling, secondary metabolite screening, and in vitro assays. The seaweed exhibited a carbohydrate- and protein-rich profile with notable mineral content, particularly calcium (3.69% dry weight; equivalent to 3,690 mg/100 g) and iron. Clear solvent selectivity was observed: The methanolic extract showed the broadest secondary metabolite profile and the highest phenolic-, alkaloid-, and saponin-associated responses, whereas ethyl acetate exhibited the highest steroid-associated response. Consistent with these trends, methanol displayed the strongest 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity among the extracts (IC5₀ = 229.13 μg/ml), while α-glucosidase inhibition by the crude extracts remained modest compared with the positive control (acarbose). GC–MS tentatively identified volatile and semi-volatile constituents across the fractions (e.g., fatty acids and hydrocarbons), supporting the observed solvent-dependent chemical profiles. Overall, G. spinosum is nutritionally relevant and shows assay-specific bioactivity in crude extracts, supporting further work using targeted fractionation and broader functional assays beyond DPPH.