Résumé:
This work focuses on the seasonal variation of antibacterial and antioxidant activity of the green alga Caulerpa racemosa var. cylindrcea extracts. This species was harvested on the Mostaganem coast at the beaches of Salamandre, Sablette and Stidia between December-February (winter) and March-May 2017 (spring).Four solvents were used for soxhlet extraction: methanol, hexane, chloroform and acetone.Phytochemical screening and evaluation of antioxidant and antibacterial activities were carried out. The yield of the crude extract during the two seasons showed that the highest values are those obtained for the methanol extract (19.22% and 8.82% for the spring and winter season, respectively). On the other hand,the hexane extract reached only 1.69% and 0.27% during the spring and winter season. It is the "spring" extracts of the alga that have demonstrated the best antibacterial activity on the strain Bacillus cereus, Pseudomonas aeruginosa et staphylococcus aureus and this for the all testedconcentrations (100 mg/ml, 200mg/ml et 500mg/ml).However, this activity remains lower than that exerted by antibiotics Cefazolin, gentamicin and chloramphenicol. Neverthless, these extracts had no inhibitory effect against Escherichia coli,Enterococcus faecalis & Proteus mirabilis. Phytochemical screening revealed the presence of polyphenols, including flavonoids, in all extracts, especially those of Caulerpa collected during the winter. The chloroform extract was the richest one in metabolites (polyphenols, alkaloids, saponins, sterols, amino acids and reducing sugars). The best antioxydant capacity against the free radical DPPH is that of the chloroform extract (IC50 of 5.22 mg / ml and 1.98 mg / ml for the winter and spring season, respectively) .On the other hand, the methanolic extract of the spring season has the lowest DPPH radicaltrapping ability (IC50 of 14.64 mg / ml and 42.06 mg / ml during the winter and spring season, respectively). Finally, Caulerpa racemosa collected on the Mostaganem coast is an potentially interesting alga for its antibacterial and especially antioxidant activity.
