Composition of essential oils of four Hedychium species from Vietnam

Background Vietnam is a country blessed with many medicinal plants widely used as food and for medicinal purposes, and they contain a host of active substances that contribute to health. However, the analysis of chemical constituents of these plant species has not been subject of literature discussion. Results In this study, the chemical compositions of essential oils of four Hedychium species, obtained by hydrodistillation, were determined by means of gas chromatography-flame ionization detector (GC-FID) and gas chromatography–mass spectrometry (GC-MS) techniques. Individually, α-pinene (52.5%) and β-pinene (31.8%) were present in the leaf oil of Hedychium stenopetalum Lodd., while linalool (45.2%), (E)-nerolidol (8.7%) and α-pinene (5.0%) were identified in the root. The leaf of Hedychium coronarium J. König was characterized by β-pinene (20.0%), linalool (15.8%), 1,8-cineole (10.7%), α-pinene (10.1%) and α-terpineol (8.6%); while β-pinene (23.6%), α-humulene (17.1%) and β-caryophyllene (13.0%) were identified in the root. Hedychium flavum Roxb., gave oil whose major compounds were β-pinene (22.5%), α-humulene (15.7%) and β-caryophyllene (10.4%) in the leaf; α-humulene (18.9%), β-caryophyllene (11.8%) and β-pinene (11.2%) in the stem, as well as β-pinene (21.8%), linalool (17.5%) and 1,8-cineole (13.5%) in the root. The main constituents of Hedychium ellipticum Buch.-Ham. ex Smith were (E)-nerolidol (15.9%), β-pinene (11.8%) and bornyl acetate (9.2%) in the leaf with 1,8-cineole (40.8%), α-pinene (18.3%) and β-pinene (11.0%) occurring in the root. Conclusions Ubiquitous monoterpenes and sesquiterpenes were identified as characteristic markers for Hedychium species. This work is of great importance for the evaluation of Hedychium essential oils grown in Vietnam. Electronic supplementary material The online version of this article (doi:10.1186/s13065-014-0054-3) contains supplementary material, which is available to authorized users.


Background
In continuation of our research aimed at the isolation and characterization of volatile constituents of Vietnamese flora [1], we report herein compounds identified in four Hedychium species. The genus Hedychium consists of about 50 species and is one of the most popular genera of Zingiberaceae because of its attractive foliage, diverse and showy flowers, and sweet fragrance [2]. Hedychium stenopetalum C. Lodd., is a potentially one of the tallest of all Hedychium species growing anything up to 3 to 4 m tall with big, bold oblong hairy leaves 8-10 cm long. This herbaceous plant has spikes of ghost white flowers with faint greenish-yellow tint to the base of the labellum. The stamens are white. The stems are about 30-40 cm long. The seeds are pale brown squarish shape 3-4 mm while the root is a thick pinky coloured spreading rhizome. Hedychium stenopetalum has a large natural range from north-eastern India to Guangxi province in China and down into northern Vietnam and Laos [3]. A glycoside, syringetin 3-rhamnoside was isolated from H. stenopetalum [4]. The major compounds in the rhizome essential oils of H. stenopetalum were β-pinene, linalool and 1,8-cineole [5].

Results and discussion
Additional file 1: Table S1 indicates the identities and the percentage compositions of compounds present in the Hedychium species. The identified compounds represent 95.3%-99.1% of the total oils content. α-Pinene (52.5% and 5.0% respectively) and β-pinene (31.8% and 12.3% respectively) were common to the leaf and root oils of H. stenopetalum. The root oil contained quantitative amount of linalool (45.2%) and (E)-nerolidol (8.7%) which were present in the leaf in much lower amounts (0.5% and 1.3% respectively). 1,8-Cineole, the main compound of a previous study [5] was not identified in the leaf oil but present in much lower quantity (1%) in the root oil. Though linalool and β-pinene as seen in the present study were of significant quantity in the precious work [5], the high content of α-pinene in our oil samples confer some quantitative and qualitative variations between results from Vietnam and elsewhere.

Analysis of the oils
Gas chromatography (GC) analysis was performed on an Agilent Technologies HP 6890 Plus Gas chromatograph equipped with a FID and fitted with HP-5MS column (30 m × 0.25 mm, film thickness 0.25 μm, Agilent Technology). The analytical conditions were: carrier gas H 2 (1 mL/min), injector temperature (PTV) 250°C, detector temperature 260°C, column temperature programmed from 60°C (2 min hold) to 220°C (10 min hold) at 4°C/min. Samples were injected by splitting and the split ratio was 10:1. The volume injected was 1.0 μL. Inlet pressure was 6.1 kPa. Each sample was analyzed thrice. The relative amounts of individual components were calculated based on the GC peak area (FID response) without using correction factors.
An Agilent Technologies HP 6890 N Plus Chromatograph fitted with a fused silica capillary HP-5 MS column (30 m × 0.25 mm, film thickness 0.25 μm) and interfaced with a mass spectrometer HP 5973 MSD was used for the GC/MS analysis, under the same conditions as those used for GC analysis. The conditions were the same as described above with He (1 mL/min) as carrier gas. The MS conditions were as follows: ionization voltage 70 eV; emission current 40 mA; acquisitions scan mass range of 35-350 amu at a sampling rate of 1.0 scan/s.

Identification of constituents
The identification of constituents was performed on the basis of retention indices (RI) determined with reference to a homologous series of n-alkanes, under identical experimental conditions, co-injection with standards (Sigma-Aldrich, St. Louis, MO, USA) or known essential oil constituents, MS library search (NIST 08 and Wiley 9 th Version), and by comparing with MS literature data [40,41].

Conclusion
For the first time, the compositions of the leaf and root essential oil of the Vietnamese grown Hedychium stenopetalum, Hedychium coronarium and Hedychium ellipticum as well as the leaf, stem and root of Hedychium flavum were elucidated. Although, ubiquitous terpenes were identified in the sample, the composition pattern was found to be different from the same species previously studied from other parts of the world. The quantitative composition and the relative proportions of the oil components are widely influenced by the factors such as nature and age of the plant genotype, ontogenic development, environmental and growing conditions, handling procedures e.t.c. These may largely be responsible for the observed compositional variations between the studied oil samples and previous results elsewhere.