Abstract
The chemical components, as well as the antibacterial and antioxidant activities of the essential oil (EO) and crude extracts prepared from Rhodiola crenulata were investigated. The essential oil was separated by hydrodistillation, and gas chromatography-mass spectrometry (GC-MS) was used to identify its constituents. A total of twenty-seven compounds was identified from the EO, and its major components were 1-octanol (42.217%), geraniol (19.914%), and 6-methyl-5-hepten-2-ol (13.151%). Solvent extraction and fractionation were applied for preparing the ethanol extract (crude extract, CE), petroleum ether extract (PE), ethyl acetate extract (EE), n-butanol extract (BE), and water extract (WE). The CE, EE and BE were abundant in phenols and flavonoids, and EE had the highest total phenol and total flavonoid contents. Gallic acid, ethyl gallate, rosavin and herbacetin were identified in the EE. The antibacterial activity results showed that the EO exhibited moderate inhibitory activity to the typical clinic bacteria, and EE exhibited the strongest antibacterial activity among the five extracts. For the compounds, ethyl gallate showed the strongest inhibitory activity to the test bacteria, and its minimum inhibitory concentration (MIC) value and minimum bactericidal concentration (MBC) value for all the tested bacteria was 0.24 mg/mL and 0.48 mg/mL, respectively. The results of antioxidant activity showed that both CE and EE exhibited strong antioxidant activities in the DPPH radical scavenging and Fe2+ reducing power tests, however, EO showed relatively weaker antioxidant ability. Ethyl gallate and rosavin exhibited excellent activity in the DPPH radical scavenging assay, and their IC50 value was 5.3 µg/mL and 5.9 µg/mL, respectively. Rosavin showed better reduction power activity than the other three compounds. These results could provide more evidence for the traditional use of R. crenulata, and would be helpful for improving its application further.
Highlights
Rhodiola L., which belongs to the Crassulaceae, includes plenty of valuable medicinal alpine plant resources
The crude extracts with different polarity, the essential oil, and the compounds identified from the extract were screened for their antibacterial and antioxidant activities, which would help to reveal the material basis of the traditional use of R. crenulata in the Chinese Pharmacopoeia
It could be concluded that ethyl gallate, gallic acid and herbacetin were three important components which could inhibit the growth of the five clinical pathogenic bacteria, and they might contribute to the antibacterial activity of ethyl acetate extract (EE)
Summary
Rhodiola L., which belongs to the Crassulaceae, includes plenty of valuable medicinal alpine plant resources. Many high-value or well known herbal medicinal products of Rhodiola are commercially available, such as Rhodiola capsule, Rhodiola tablets and Rhodiola oral liquid These Rhodiola preparations are mainly made from the rhizomes of Rhodiola, and they usually have significant effects on relieving stress-induced fatigue, exhaustion, anxiety, etc. Over 100 compounds, such as salidroside, arbutin, gallic acid, ethyl gallate, tyrolsol, kaempferol, herbacetin, rhodiolinin and rosavin, have been successfully separated and characterized from this plant [20,21,22,23,24]. The crude extracts with different polarity, the essential oil, and the compounds identified from the extract were screened for their antibacterial and antioxidant activities, which would help to reveal the material basis of the traditional use of R. crenulata in the Chinese Pharmacopoeia. The rhizomes (A) and the ethanol extract (B) prepared from R. crenulata
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