聖露西亞產兩種馬尾藻. Sargassum fluitans和 S. natans的生物活性和化學成分分析

Abstract

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Abstract: From 2011, an influx of free-floating seaweed has severely affected the Caribbean region. Sargassum fluitans and S. natans were identified as the two species responsible for the influx. These two species were found to naturally coexist. Currently, the only use for them is as fertilizer; however, this approach may be insufficient to effectively utilize the large amount of seaweeds. It was found that seaweeds possess a variety of phytochemicals exhibiting many bioactive properties including antioxidant, insecticidal, mosquito larvicidal, and antimicrobial activities. Therefore, the objective of this study is to investigate potential biological activities of Sargassum fluitans and S. natans, and isolate and identify the bioactive compounds responsible for such activities. The two species were separated and underwent methanolic extraction to obtain crude extracts, which were partitioned into n-hexane, ethyl acetate, n-butanol and water layers. All four layers were then subjected to tests for insecticidal activity, larvicidal activity, antimicrobial activity, and DPPH scavenging activity. Preliminary results showed that 24 hours post treatment, S. natans and S. fluitans extracts exhibited slight larvicidal properties, and no significant insecticidal and antimicrobial activities were observed. DPPH scavenging assay showed that the n-hexane and ethyl acetate layers of both species possessed antioxidant properties at the concentration of 1000 ppm. Both n-hexane and ethyl acetate layers were further separated, and the collected fractions were combined according to DPPH antioxidant activity assay. Results showed that S. fluitans’ fractions had higher antioxidant activity than those of S. natans with the most bioactive fractions having scavenging activities of 49.2 ± 2.3%, 58.4 ± 1.7% and 76.5 ±6.4% at a concentration of 500 ppm. Bioactive compounds responsible for the antioxidant activity were isolated and identified. Seven compounds were purified by HPLC, and further identified to be kjellmanianone (1), palmitic acid (2), methyl palmitate (3), dodecanoic acid (4), palmitoleic acid (5), lauroleic acid (6), and ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate (7) based on spectroscopic analysis. From HPLC analysis, the carotenoid fucoxanthin (8) was identified by comparison with the authentic standards. Upon further analysis it was seen that ethyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate (7) possessed antioxidant activity with free radical scavenging activity (%) of 37.1 ± 0.2% at 1000 ppm.