Composition and Antioxidant Activity of the Essential Oil from Aerial Parts of Sibiraea laevigata

Abstract

The genus Sibiraea (Rosaceae), which are large deciduous shrubs, comprises only four species distributed mainly in southeast Europe, Siberia of Russia, and Western China [1]. Tibetan herdsmen living in pasture areas of Qinghai-Tibet Plateau in China often collect the leaves and twigs of S. laevigata (L.) Maxim. and S. angustata (Render) Hand.-Mazz. to consume as a kind of tea, named “Liucha.” Although there is no formal record in any pharmacopeia, these two plants are usually employed by Tibetan herdsmen to cure hyperlipidemia, hypopepsia, and upset stomach [2]. The aerial parts of S. laevigata and S. angustata can release an extraordinary smell, which prompted us to investigate their volatile constituents in order to discover therapeutic agents. Previously, Tao and his co-workers had identified 43 compounds from the essential oils of the aerial part of S. angustata, and E-ocimenone and linalool were found to be the principal components [3]. Herein we report for the first time the chemical composition of essential oils from the leaves and twigs of S. laevigata and evaluate its antioxidant activity by the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. The fresh leaves and small twigs were collected from the meadow near the suburbs of Hezuo, Gansu Province of China, and identified by Mr. Pin Du from Gansu Normal University For Nationalities. A voucher specimen is deposited at the herbarium in the Laboratory of Botany, College of Marine Science, Shandong University. The collected materials were crumbled to fragments, and mixtures of 100 g of leaves and twigs were hydrodistilled for 3 h using a Clevenger apparatus to give the essential oils. The oil was dried over anhydrous sodium sulfate and stored at 4 C until analysis. GC-MS analysis was carried out using a Hewlett Packard 6890 gas chromatograph (Agilent Technologies, Palo Alto, CA, USA) with the HP GC ChemStation Rev. A.05.04 data handling system. Detailed analytical conditions and procedures were analogous to those of our previous research [4]. From the essential oil of aerial parts of S. laevigata, 55 ingredients were detected. The aliphatic esters dominate the constituents, with more than 45% of the compounds identified as ethyl palmitate (15.8%), mandenol (9.3%), ethyl laurate (4.2%), 2-ethylnon-1-en-3-ol (3.3%), ethyl linolenate (3.2%), etc. (Table 1). The main cyclic terpenoid constituents are 4,4-dimethyl-2-propenylcyclopentanone (7.0%), nerol (5.9%), pulegone (2.4%), and verbenone (1.5%), which are different from those in S. angustata [3]. Nerol, pulegone, and verbenone can be found naturally in a variety of plants and are common ingredients of perfume and essential oils [5–7]. Verbenone is an insect pheromone and can be used to control the population of Southern pine beetle [7]. The antioxidant activity of the essential oil was tested by the DPPH method. At a concentration of 10 g/mL, 22.4% of the radicals can be scavenged, but the radical scavenging activity was not raised at a higher concentration. The antioxidant activity of the essential oil from S. laevigata was not potent. The presence of abundant verbenone suggests its potential as a household repellent.