Chemical Compounds And Bioactivities Of Essential Oil And Ethanol Extract From Rhododendron Tomentosum

The essential oil (EO) and ethanol extract of Rhododendron tomentosum from Da Hinggan Mountains, Northeastern China were prepared by simultaneous distillation extraction method (SDE) and refluxing method, respectively. EO and ethanol extract of R. tomentosum contained a large number of active compounds, and both of them showed antioxidant activities in the experiments of DPPH and ABTS radical-scavenging activities and reducing power on Fe3+. The results of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) indicated that EO and ethanol extract had broad-spectrum antimicrobial activities. The specific results were as follows:(1) The chemical profile of EO was determined through GC/MS qualitatively and GC quantitatively. Fifty-one components were identified, and 4-thujene (27.05%), a-thujenal (12.24%) and (-)-4-terpineol (9.78%) were the major components. The contents of p-cymene, y-terpinene, borneol, (-)-4-terpineol and trans-?-ionone were detected to be 1.65,3.53,1.26,6.74 and 0.09 mg/mL, respectively.(2). The volatile components of ethanol extract of R. tomentosum was mainly composed of a-farnesene (8.35%), n-tetradecane (6.37%), hexadecanoic acid (6.14%), oblivon C (5.89%) and lilac aldehyde (4.85%). The total flavonoid content was 208 mg rutin equivalent/g dry weight (DW), and the total phenol content was 23.3 mg gallic acid equivalent/g DW. HPLC analysis showed that the contents of hyperoside, quercetin and kaempferol in the extract were 1.29,0.32 and 0.03 mg/g, respectively.(3). Experiments of DPPH radical-scavenging activities, ABTS radical-scavenging activities and reducing power on Fe3+ were carried out to evaluate the antioxidant activities of R. tomentosum EO and ethanol extract.IC5O (half maximal inhibition concentration) of ethanol extract for DPPH and ABTS radical-scavenging capacities were 0.3 and 0.084 mg/mL, respectively. At the maximum experimental concentration, the radical-scavenging capacities of EO to DPPH and ABTS were 9.34% and 10.50%, respectively. In addition, the reducing power of ethanol extract on Fe3+ was higher than that of the EO. The results indicated that both of R. tomentosum EO and ethanol extract had antioxidant activities, and the antioxidant activity of ethanol extract was higher than that of EO.(4). The antimicrobial activities of R. tomentosum EO and ethanol extract were determined by measuring MIC and MBC values against 3 bacterial and 2 fungus strains. The MIC of EO and ethanol extract towards Escherichia coli, Staphylococcus aureus, Bacillus subtilis, Cryphonectria parasitica and Canidia albicans were in the range of 5-10 mg/mL and 1.25-5 mg/mL, respectively. MBC of EO and ethanol extract were both?5 mg/mL. The results indicated that R. tomentosum EO and ethanol extract had broad-spectrum antimicrobial activities, and the antimicrobial activity of ethanol extract was higher than that of EO.