Antioxidant and antibacterial activities and identification of bioactive compounds of various extracts of Caulerpa racemosa from Algerian coast

Objective: To evaluate the antibacterial and antioxidant activities and to identify the volatile bioactive compounds present in different crude extracts of the seaweed Caulerpa racemosa var. cylindracea. Methods: Caulerpa racemosa harvested from the intertidal zone of Mostaganem coast (N 35°54’37.94”, E 0°3’17.37”) was subjected to Soxhlet extraction using methanol, chloroform, and hexane solvents. Antioxidant properties were assessed by using 2,2’-diphenyl-1- picrylhydrazyl (DPPH), 2,2’-azino-bis(3-ethylbenzothiazoline- 6-sulfonic acid) (ABTS) and β-carotene bleaching assays. The antibacterial activity was evaluated on six standard bacterial strains using the agar disc diffusion method. The GC-MS analysis was performed using non-polar and polar capillary columns. Results: The chloroform extract of Caulerpa racemosa exhibited higher contents of polyphenols [(123.91±1.46) mg gallic acid equivalent/ g dry extract] and tannins [(59.28±5.43) mg catechin equivalent/ g dry extract] (P<0.001) and was the most effective in scavenging DPPH [(1.98±0.08) mg/mL] and ABTS [(1.66±0.05) mg/mL] radicals. The hexane extract displayed the best antibacterial activity against Staphylococcus aureus, Bacillus cereus, and Pseudomonas aeruginosa, producing inhibition zones of (11.16±0.76), (9.00±0.00) and (9.33±1.15) mm, respectively. The l-(+)-ascorbic acid 2,6- dihexadecanoate and 4-hydroxy-2methylproline were among the most abundant volatile compounds. Besides conventional fatty acids, cis-10-heptadecenoic acid, nonahexacontanoic acid, and dodecanoic acid, 3-hydroxy- were identified. Two phytosterols were identified: stigmast-5-en-3-ol- (12.9%) and stigmast-5-en-3.beta.-ol, (24S)- (4.57%). Conclusions: The preliminary identification of the volatile compounds reveals the presence of some new bioactive components not reported previously in Caulerpa racemosa from other geographical areas. Some of these compounds possess an interesting potential for pharmaceutical/nutraceutical applications.