Comparative Studies on Antioxidant, Angiotensin-Converting Enzyme Inhibitory and Anticoagulant Activities of the Methanol Extracts from Two Brown Algae (Sargassum horneri and Sargassum thunbergii)

Two important brown algae, Sargassum horneri and Sargassum thunbergii are widely distributed along the coastal line of China. In this study, antioxidant, angiotensin-converting enzyme (ACE) inhibitory effects, and anticoagulant activities of the methanol extracts of S. horneri and S. thunbergii were investigated and compared. Total phenolic compounds and the fucoxanthin content were determined by the spectrophotometric and HPLC analyses, respectively, to relate phytochemical content to bioactivities of two Sargassum species. The phenolic compounds of S. horneri and S. thunbergii were also analyzed by LC-MS/MS. The results showed that S. horneri displayed higher antioxidant activities compared to S. thunbergii in all antioxidant bioassays evaluated, except the DPPH radical scavenging assay. Moreover, S. horneri showed a stronger ACE inhibitory effect (IC50 = 0.44 mg/mL) compared to S. thunbergii (IC50 = 1.81 mg/mL). Both S. horneri and S. thunbergii significantly prolonged the activated partial thromboplastin time (APTT) in blood plasma, and the APTT-prolonging effect of S. horneri was stronger than that of S. thunbergii. Salicylic acid was identified as the main phenolic compound in S. horneri, followed by m-coumaric acid, ferulic acid, and p-coumaric acid. Furthermore, S. thunbergii contained carnosic acid and salicylic acid. The total phenolic and fucoxanthin contents are positively correlated with antioxidant, ACE inhibitory and anticoagulant activities. These results indicated that S. horneri and S. thunbergii can be used as natural sources of functional foods because of their abundant bioactive compounds.