Chemical Composition and Antioxidant Activity of the Leaf Essential Oil of Schefflera venulosa

Published in Khimiya Prirodnykh Soedinenii, No. 6, November–December, 2021, pp. 981–982.

The genus Schefflera J. R. Forst. & G. Forst. (Araliaceae) is comprised of about 550–600 species, with greater species diversity in the tropical and subtropical regions of the world [[1]]. Schefflera venulosa (Wight & Arn.) Harms is an evergreen shrub occurring in forests along streams, rivers, and in mangrove swamps, which often tend to be scandent and epiphytic in nature. The species is distributed in India, Myanmar, Indo-China, W. S. China, Bangladesh, and some parts of the Malay Peninsula. The stems and leaves of the plant are used in Chinese folk medicine for the treatment of arthritis and headache [[3]]. In India, different parts of the plant are used in traditional medicine for treatment of rheumatism [[4]], dropsy and paralysis [[5]], and foot and mouth diseases of livestock [[6]]. The extract of the plant has a variety of biological activities, including spermicidal, antioxidant, and anticancer properties [[7]]. Though several triterpenes, sesquiterpenes, glycosides, and steroids from the leaf extract of the species have been isolated and identified [[9]], no report is yet available on the presence of essential oil in the leaves. Therefore, this is the first report on the chemical composition and antioxidant activity of the leaf essential oil of Schefflera venulosa.

The leaves of Schefflera venulosa were collected from Tamana Reserve Forest of Khurda Forest Division, Odisha (N 19°52′53.9′′, E 085°03′26.2′′), and the identity of the species was ascertained in consultation with the literature on flora of Odisha [[11]] and by matching with authentic specimens in the Herbarium of Regional Plant Resource Centre (RPRC), Bhubaneswar, India, where the voucher specimen (No. 11395 Dt.26.6.2020) was also deposited. The fresh leaf samples (500 g) were subjected to hydrodistillation in a Clevenger apparatus for a period of 6 h. The essential oil obtained was pale yellow in color, and the oil yield was 0.05% (v/w). The extracted oil was dried over anhydrous sodium sulfate to remove moisture and was kept in an airtight vial at 4°C.

Qualitative analysis of the essential oil was carried out on a Clarus 580 gas chromatograph equipped with an SQ8S MS detector. Quantitative analysis of the essential oil was done on a Clarus 580 gas chromatograph (GC) equipped with a flame ionization detector (FID), keeping the programming and column condition the same as that of GC-MS. Area percentages were obtained from the GC-FID response without the use of an internal standard or correction factors. Identification of components was done by matching the compound′s mass spectra with the in-built NIST library, co-injection of authentic compounds, and by comparing retention indices (RI) with published literature [[12]]. Retention indices (RI) relative to a series of homologous n-alkanes (C8–C20) was calculated according to [[13]].

GC-MS analysis of the essential oil leaf of S. venulosa resulted in the identification of a total of 42 constituents, accounting to 99.72% of the total oil content, where germacrene D (38.79%) was the predominant constituent followed by β-caryophyllene (13.64%), α-humulene (9.29%), germacrene B (7.91%), and β-selinene (7.90%) (Table 1). The major compounds in the oil were sesquiterpene hydrocarbons (94.63%), followed by oxygenated sesquiterpenes (4.00%). Nerol acetate was the only oxygenated monoterpene detected in the leaf essential oil. These results are in agreement with studies involving other species of Schefflera. While germacrene D was the major constituent of the essential oil of Schefflera rodrigueziana from Costa Rica [[14]], β-caryophyllene was the major compound of Schefflera stellata from India [[15]] and Schefflera arboricola from Vietnam [[2]]. β-Pinene and α-humulene were the predominant components in the leaf essential oil of Schefflera heptaphylla [[16]], and limonene in Schefflera myriocarpa [[18]].

TABLE 1. Chemical Composition of Leaf Essential Oil of Schefflera venulosa

aCompounds listed in order of elution from Elite-5 MS column; RI: retention indices calculated from homologous series of (C8–C20) n-alkanes on Elite-5 MS column; Method of identification: RI, MS, and *RI, MS, CI (co-injection with authentic compounds).

The antioxidant activity of the essential oil was assessed following the protocol of Jena et al. [[19]]. In the DPPH assay, the IC50 value of Schefflera venulosa leaf essential oil had lower antioxidant activity (49.61 ±0.85 μg/mL) compared to ascorbic acid (6.89 ± 0.11 μg/mL) and BHT (22.78 ± 0.31 μg/mL). Among the samples tested, the leaf essential oil exhibited the highest radical scavenging ability with ABTS (5.21 ± 0.07 μg/mL) as compared to BHT (14.03 ± 0.18 μg/mL) but less in comparison to ascorbic acid (2.62 ± 0.03 μg/mL). The antioxidant property of the essential oil might be due to the additive or synergistic effect of the main constituents with minor constituents [[20]].

Germacrene D acts as a precursor for the synthesis of sesquiterpenes like cadinenes and selinenes [[21]] and possesses insect repellent activities [[22]]. The leaf essential oil of Schefflera venulosa showed strong antioxidant activity and can be used as natural antioxidants in phytotherapy. However, more research needs to be done in order to exploit the species for other pharmaceutical applications.

The authors are grateful to Dr. S. C. Si, Dean, Centre for Biotechnology, and Dr. M. R. Nayak, President, Siksha 'O' Anusandhan University, for providing necessary facilities and encouragements.