ABSTRACT
Different solvent extracts of a red algae, Hypnea flagelliformis,and two brown algae, Cystoseira myrica and Sargassum boveanum, collected from the Persian Gulf coast were subjected to different bioassays including: 1,1-diphenyl-2-picrylhydrazyl [DPPH] free radical scavenging assay, antibacterial and antifungal activity by thin layer chromatography [TLC]-bioautography, agar disc diffusion [ADD] and nutrient-broth micro-dilution [NBMD] bioassays. The water extracts were found to have the most antioxidant activity.The antibacterial minimum inhibitory concentrations [MIC] of the active extracts were determined for the susceptible organisms, Staphylococcus aurous and Bacillus subtilis, using NBMD bioassays.The active substances were identified as free fatty acids [FFA] using gas chromatography-mass spectrometry [GC-MS] and after derivatization to their methyl esters, their concentrations were measured using GC- flame ionization detection [GC-FID]. In addition to the fatty acids, fucosterol, cholesterol and 22-dehydroxychlosterol were detected as the major sterols in S. boveanum extract using GC-MS analyses