Antioxidant and antibacterial potentials of some Thai native plant extracts

Eight native Thai plant rarely studied were extracted by using distilled water and 95% ethanol then were investigated for their total phenolics, free radical scavenging, metal chelating and five antibacterial capacities. Five bacteria consisted of one gram-negative (Esherichia coli) and four gram-positive (Stapphylococcus aureus, Stapphylococcus epidermidis, Bacillus cereus and Bacillus subtilis). Significant difference was observed among solvent extractions used and the plant species. The aqueous extracts gave higher antioxidant abilities but lower antibacterial capacities than the ethanol ones. Principle component analysis (PCA) revealed that the free radical scavenging was correlated to the total phenolics. Among the eight species, S. gratum extracts showed the strongest free radical scavenging ability, while, C. harmandiana showed the strongest chelating capacity. The G. cowa extracts were exception in antibacterial capacities because their activities against all the test bacteria. Some native Thai plant rarely studied could be used as alternative natural sources for antibacterial and antioxidant substances.