This work consists of the evaluation of the phytochemical compositions and the study of the antioxidant and antimicrobial activities of three algae (green algae: Ulva lactuca, brown algae: Cystoseira amentacea var. stricta, and red algae: Corallina elongata) collected from the Algerian west coast.
For the extraction we used the maceration method and the antioxidant activity was determined using the scavenging activity of DPPH free radical and ferric-reducing antioxidant power assay for the antimicrobial activity of the extracts of the three algae, we used the diffusion method. The results of the dosages of polyphenols and flavonoids indicate the richness of the species C. elongata in polyphenols with a value of (219.43 mg EAG/g) and of Ulva lactuca in flavonoids with (65.17 mg EQ/g). As for the measurement of anti-radical activity, we note that the best antioxidant activity is that of the red algae extract C. elongata with an IC50 value of 275.70 μg/ml. For the antibacterial activity, the results obtained show that the crude extracts of Ulva and Cystoseira act in the same way on Bacillus cereus, Bacillus subtilus, and Methicillin-resistant Staphylococcus aureus (SARM) with diameters of (8 mm), (10 mm) and (22 mm) respectively for Ulva and (20 mm), (14 mm) and (21 mm) respectively for Cystoseira. As for Corallina extract, the inhibition zones vary from (16 mm) against B. subtilus, to 8mm for Klebsiella and Staphylococcus, passing through an inhibition zone of (12 mm) for E. coli.