Volatile Constituents of Rhizomes and Leaves of Alpinia allughas Roscoe

Abstract

The GC and GC/MS analyses of the oils from the rhizome and leaves of Alpinia allughas led to identification of 22 and 42 constituents, respectively. The major constituents of the rhizome oil were β-pinene (55.3%) and α-pinene (9.7%) whereas in the leaf oil β-pinene (25.5%), 1,8-cineole(23.3%) and α-humulene (9.7%) were major. The unique feature is the dominant presence of two pinenes (rhizome (65%) and leaf (30.9%)) unlike other species of Alpinia.

Key Word Index

Alpinia allughas, Zingiberaceae, essential oil composition, 1,8-cineole, β-pinene.

Introduction

The members of family Zingiberaceae have been subjected to extensive chemical and pharmaceutical investigations because of their use in Indian and oriental medicines and as spices and food-flavoring agents (1). Although plants of family Zingiberaceae grow throughout India, the North-Eastern Indian region is rich in of Zingiber floral diversity comprising about 75% of the total taxa found all over the country (2). As part of chemical screening of the Zingiberaceae of Himalayan region (3-6), we have investigated the chemistry of essential oils from rhizomes and leaves of Alpinia allughas. The literature search revealed no reports on the oil composition, except for a preliminary report (7). We now report the comparative chemical composition of aerial and underground part of A. allughas.

Alpinia allughas Roscoe. (Zingiberaceae) is an herb with an elongate leafy stem and horizontal root stocks, with oblong or lanceolate leaves. The flowers are found in terminal, racemes or panicles, braceolate, large, sometimes enveloping the buds. It also possesses a loosely tubular calyx, three toothed, cylindric corolla tube, rarely longer than the calyx, oblong or linear oblong, corolla lobes upper usually broader and more convex than tghe lateral, one perfect, stamen, a flattened filament, anther cells diversing at the top, occasionally with an orbicular crest, lateral stamenoides minute or obsolete. A spreading lip, often orbicular with incurved margins, sometimes with two subulate processes at the base of the claw. A three celled ovary, few ovules or many on each placenta, a filiform style, a subglobose stigma, globose fruit, dry or fleshy, usually indehiscent, with globose or angled seeds (8).

Experimental

Plant material: Fresh rhizomes and leaves were collected from tarai region of Kumaon hills. The specimen has been deposited in Department of Chemistry, G. B. Pant University of Agrie. & Tech., Pantnagar. The identity of the plant was confirmed by Sumer Chandra, Systematic Botany Division of Forest Research Institute, Dehradun, where herbarium specimens Herbarium nos.: 9747 & 72265 dated 12 Jan., 2004 have been deposited.

Oil isolation: Fresh rhizomes (1 kg) and leaves (1 kg) were separately hydrodistilled using a Clevenger-type apparatus for 5 h to yield 0.1% v/w and 0.08% v/w oil from the rhizomes and leaves, respectively. The oils were extracted with diethyl ether and dried over anhydrous Na^sub 2^SO^sub 4^ and stored under N^sub 2^ at low temperature until analyzed.

Chemical Analysis: The oil samples were analyzed by gas chromatography (GC) and by gas chromatography-mass spectrometry (GC/MS). The oils were analyzed by using Nucon 5765 gas Chromatograph (RTX-5MS column, 30m x 0.32 mm; 0.25pm film thickness, FID), split ratio 1: 48, N2 flow of 4 kg/cm2 and Thermoquest Trace GC 2000 interfaced with Finnigan MAT Polaris Q Ion trap Mass spectrometer fitted with RTX-5 MS (Restek Corp.) fused silica capillary column (30 m x 0.25 mm; 0.25 µm film coating). The column temperature 60°-210°C was programmed at 3°C/ min using He as carrier gas at 1.0 ml/ min. The injector temperature was 210°C, injection size 0.1 µL prepared in hexane, split ratio 1:40. MS were taken at 70 eV with mass range of m/z 40-450. Characterization was done on the basis of Retention Index, Library MS Search (NIST & WILEY), by comparing with the mass spectral literature data (9). The relative amounts of individual components were calculated based on FID response in GC without using correction factors.

Results and Discussion

GC and GC/MS of the each oil showed the presence of over 50 constituents in the rhizome, out of which 22 compounds contributing 85.2% of the oil were identified. The oil is mainly consisted of monoterpene hydrocarbons (68.5%), β-pinene (55.3%) and α-pinene (9.7%) beingthetwomajorcomponents. Among the oxygenated monoterpenes which constitute 5.1% of the oil are 1,8-cineole (2.1%), terpinen-4-ol (2.2%), bornyl acetate (0.3%) and linalool (0.5%). Among sesquiterpenoids (11.6%), the main constituents were α-humulene (1.5%), β-selinene (3.2%), β-caryophyllene (1.1%), α-selinene (1.7%), 7-epi-α-eudesmol (4.1%) and trace of patchouli alcohol which adds to the characteristic aroma of the oil.

Forty-two compounds (88.0%) were identified in the leaf oil. Identified compounds include 10 monoterpene hydrocarbons (31.3%) and were dominated by β-pinene (25.5%) and α-pinene (5.4%). Among 8 oxygenated monoterpenes (27.7%), the major compounds were 1,8-cineole (23.3%), α-terpineol (1.5%) and myrtenol (1.1%). Fifteen sesquiterpene hydrocarbons contribute 16.5% of the oil. β-Caryophyllene (3.7%), α-humulene (9.7%) and α-guaiene (1.0%) were the major constituents identified. Among the eight oxygenated sesquiterpenes (12.4%), the major constituents identified were humulene epoxide II (4.4%), caryophyllene oxide (3.0%), patchouli alcohol (1.9%) and (Z)-β-elemone (1.4%). Aditerpenes was also noticed in the oil.