Mangrove plants are the source of various secondary bioactive metabolite and had been used in traditional medicine for any diseases. This study aimed to investigate phytochemical bioactive components of two mangrove plants, Rhizophora mucronata and Rhizophora apiculata in Rhizophoraceae family. Eight extracts of four parts (pod, leaf, twig, bark) of each plant were prepared by maceration with methanolic solvent. Phytochemical analysis was conducted through the aid of a standard test, and was confirmed by quantitative analysis based on the determination of the total saponin, phenolic and flavonoid contents. Free radical scavenging activity was studied in vitro by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2/-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) methods. Antibacterial activity was performed by hole-plate diffusion method and determination of Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC). The pod of R. mucronata predominantly showed the highest total saponin content (8.05±0.50 mg EE/ g CE) and the bark presented a great amount of phenolic and total flavonoid contents (2.12±0.11 mg GAE/ g CE and 6.73±0.25 mg RU/ g CE). R. mucronata showed greater free radical scavenging activity than R. apiculata at a concentration of 100 g/mL supported by DPPH and ABTS assays. Antibacterial screening showed that the maximum zone of inhibition was noted for R. mucronata extracts against Streptococcus agalactiae, Aeromonas hydrophila, Vibrio harveyi and Vibrio parahemolyticus (8.50–13.56 nm). The R. mucronata pod extract had the lowest MIC to only in A. Hydrophila. Meanwhile, R. mucronata bark extract had the lowest MIC to S. agalactiae and A. hydrophila. The higher antibacterial activity of R. mucronata extracts was consistent with the greater saponin, phenolic and flavonoid contents and antioxidant activity of extracts of these species with significant value p < 0.05. The present study highlighted that R. mucronata could be used as a potential source of bioactive compounds against aquatic pathogenic bacteria.
Key words: Antioxidant, aquatic pathogens, mangrove plant, phytochemical, secondary metabolite
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