Antimicrobial and antioxidant activities and phenolic contents in the water extract of medicinal plants

The objective of this study was to determine the radical scavenging activity, total phenolic index, antimicrobial activity, and minimum inhibitory concentration (MIC) of water extracts of 32 medicinal plant species that have been commonly used in medical herbs. The freeze dried weight per dried materials was above 30% for 4 extracts: Terminalia chebula, Pueraria thunbergiana, Cinnamomum cassia and Cornus officinalis. Total phenolic index and radical scavenging activity of T chebula extract presented the highest value (585.87 mg/g, 38.15%), followed by S. officinalis (429.21 mg/g, 29.33%), P thunbergiana (377.31 mg/g) and R. coreanus miquel (316.23 mg/g, 26.77%). The extracts from T chebula, R. coreanus miquel, C. sappan, L aromaticum, S. officinalis and C. japonica possessed outstanding antimicrobial activity against Escherichia coli, Salmonella typhimurium, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis and Lactobacillus plantarum. MIC was determined on those extracts that showed high efficacy against the test organisms. The efficiency of MIC value of T chebula extract against B. subtilis, L coli, P aeruginosa and S. aureus was 7.8, 31.2, 15.6 and 7.8 mg/mL, respectively. In addition, the total phenolic content and radical scavenging activity were very closely correlated for the set of all samples (p<0.01, r=0.85). The correlation coefficient between total phenolic index and antimicrobial activity was 0.89 (E. coli), 0.79 (B. subtilis), 0.78 (S. aureus), 0.85 (L. plantarum), 0.85 (P. aeruginosa) and 0.25 (S. typhimurium) (all p<0.05).