Étude du pouvoir antioxydant et antimicrobien des extraits d'algues marines du littoral de Mostaganem.

Abstract

In the context of the growing search for new natural sources of bioactive compounds, this study focuses on the antioxidant and antimicrobial potential of six marine algae species (Ulva rigida, Ulva compressa, Cystoseira compressa, Jania rubens, Caulerpa racemosa, and Dictyota spiralis), collected along the Mostaganem coast line in Algeria. The methanolic extracts, obtained by maceration, were first subjected to a quantification of their total polyphenol and flavonoid contents. Their antioxidant activity was then evaluated using the DPPH method, while their antimicrobial activity was studied using the disk diffusion technique and by determining the minimum inhibitory concentration (MIC) and minimum bactericidal or fungicidal concentration (MBC/MFC). The results showed variable yields, Cystoseira compressa exhibiting the highest yield (16%), indicating a richness in polar compounds. Phytochemical analysis revealed that this species had the highest polyphenol content (7.056 mg GAE/g), while Caulerpa racemosa was distinguished by its high flavonoid content (9.93 mg QE/g). Cystoseira compressa showed the highest antioxidant activity (IC₅₀ = 254.98 μg/mL), although lower than that of ascorbic acid. On the other hand, Dilophus spiralis displayed relatively low antioxidant activity. The antimicrobial activity, revealed that Gram-positive strains (Staphylococcus aureus, Bacillus cereus) and the yeast Candida albicans were more sensitive to the tested extracts than Gram-negative bacteria. Caulerpa racemosa and Ulva lactuca showed the best results, with the lowest MIC values of 0.3 and 12.5 mg/mL, respectively. The MBC/MIC ratio confirmed bactericidal or fungicidal activity for certain extracts, particularly Ulva rigida and Cystoseira compressa. These results confirm that the marine macroalgae from the Mostaganem coast represent a promising source of antioxidant and antimicrobial compounds, with potential applications in the pharmaceutical and agri-food sectors.