In vitro and in silico assessment of antioxidant potential of crude sulfated polysaccharide and phenolic extracts from Gracilaria gracilis macroalgae harvested from Atlantic and Mediterranean coasts: A comparative study

Over the past decades, the exploration of bioactive compounds from seaweed has garnered considerable interest among scientists owing to their manifold health benefits. These compounds display diverse biological activities, holding promising potential for applications in the nutraceutical, pharmaceutical, and cosmetic industries. This study aims to compare and evaluate the in vitro antioxidant properties of sulfated polysaccharide and phenolic fractions of the red seaweed Gracilaria gracilis sourced from both the Moroccan Atlantic coast and the Tunisian Mediterranean coast. Additionally, molecular docking was employed to explore the virtual antioxidant impact of various phytochemicals identified in prior research. Sulfated polysaccharide extracts (PSGM and PSGT) were obtained via hot water extraction, while phenolic fractions were procured using successive polarity solvents, namely dichloromethane (DCGM and DCGT), ethyl acetate (AEGM and AEGT), and n-butanol (BTGM and BTGT). The in vitro antioxidant activity was assessed using DPPH, ABTS, TAC, and FRAP assays. Moreover, the Autodock Vina software was used for molecular docking. The in vitro findings indicate that BTGM and PSGM exhibited the highest DPPH and ABTS scavenging activity, albeit displaying lower TAC and FRAP antioxidant potential. Conversely, PSGT and AEGT showcased superior antioxidant power in TAC and FRAP assays, albeit with lower scavenging effects in DPPH and ABTS assays, while BTGT exhibited lower activity across all four assays. Certain extracts demonstrated a correlation between their phytochemical composition and antioxidant activity, a relationship corroborated by in silico studies revealing eleven phytochemicals from G. gracilis (carbohydrates, phenolic compounds, and pigments) with significantly stronger negative binding energies with antioxidant target proteins. Consequently, G. gracilis emerges as a sustainable source of natural antioxidants offering protection against free radicals and oxidative stress, warranting further exploration in food and clinical medicine. • Gracilaria gracilis is a sustainable source of antioxidants for nutraceutical, pharma, and cosmetic use. • Sulfated polysaccharides and polyphenols were extracted via heat and solvents, revealing efficient bioactive strategies. • BTGM & PSGM excel in DPPH/ABTS, while PSGT & AEGT show stronger TAC/FRAP antioxidant effects, per assay results. • Docking studies found 11 G. gracilis phytochemicals with strong antioxidant protein binding, confirming in-silico relevance. • G. gracilis shows promise for food and medical use by helping reduce oxidative stress and guard against free radical damage.