Sesquiterpenoids with free-radical-scavenging properties from marine macroalga Ulva fasciata Delile

Free-radical-scavenging activities of various solvent extracts of Ulva fasciata, a chlorophytan marine macroalga with significance as a food ingredient, from the southwestern coast of the Indian peninsula, were evaluated using in vitro tests, including 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) scavenging assays. Ethyl acetate (EtOAc) extract of Ulva fasciata displayed markedly stronger DPPH (89.8 ± 4.2%) and ABTS+ scavenging (82.6 ± 3.7%) activities at 0.1 mg/ml than dichloromethane and n-hexane extracts. Radical scavenging assay-guided chromatographic separation of the EtOAc extract, using a step gradient of petroleum ether/EtOAc yielded five major sesquiterpenoids. After 8 min of incubation the ABTS+ scavenging activity of one of these sesquiterpenoids was higher (71.4 ± 1.5%) than that of Trolox (44.1 ± 1.5%), and therefore may have potential as a natural antioxidant in the food industry.