Volatile Components of the Fruits of Vangueria madagascariensis J. F. Gmel. from Cuba

Journal of Essential Oil Research: JEOR, Jul/Aug 2004 by Pino, Jorge, Marbot, Rolando, Vazquez, Carlos

Abstract

The volatile constituents of the fruits of Vangueria madagascariensis J. F. Gmel. growing in Cuba were isolated by simultaneous distillation/solvent extraction and analyzed by GC and GC/MS. Seventy-four compounds were identified in the aroma concentrate, of which 2-furfural and hexadecanoic acid were found to be the major constituents.

Key Word Index

Vangueria madagascariensis, Rubiaceae, Spanish tamarind, fruit volatiles, 2-furfural, hexadecanoic acid.

Introduction

The tamarind of Indies or Spanish tamarind is the species Vangueria madagascariensis J. F. GmeL, probably native to Madagascar. This fruit belongs to the botanical family Rubiaceae. It is an evergreen shrub growing to a height of about 5 m. The fruits are globose, 2 to 4 cm in diameter, with greenish yellow color inside and out. The soft flesh of the ripe fruit has a pleasant slightly acid flavor. It is usually eaten fresh, in preserves and beverages (1).

The aromatic properties led us to investigate its composition in order to determine the respective influence of the volatile components. To date, the aroma of V madagascariensis fruit has not been the subject of a previous study.

Experimental

Materials and isolation of the volatile constituents: Samples of ripe fruits (500 g) were collected from the National Botanic Garden in Havana, in May 2001, from a unique specimen at the same time. A voucher specimen of the plant has been deposited in the Herbarium of the National Botanic Garden.

After addition of an internal standard (methyl undecanoate, 2 mg), pulp (100 g) was blended with distilled water (600 mL), adjusted to pH 7 with IN sodium hydroxyde solution, and simultaneously distilled and extracted for 90 min in a LikensNickerson microapparatus with 25 mL of diethyl ether (previously redistilled and checked as to purity). The volatile concentrate was dried over anhydrous sodium sulfate and concentrated to 0.6 mL on a Kuderna-Danish evaporator with a 12-cm Vigreux column and then, to 0.2 mL with a gentle nitrogen stream.

GC analysis: The extract was analyzed using a Hewlett-Packard 6890 gas Chromatograph equipped with a flame ionization detector (FID). The analysis was performed using a SPB-5 column (30 m � 0.25 mm, 0.25 �m) with an oven temperature program of 60�C (2 min), 4�C/min to 250�C (20 min). The carrier gas was helium with a flow-rate of 1 mL/min. The temperature of the injector and detector was 250�C. The injection was made in the split mode (1:10 ratio). Linear retention indices were calculated against those of n-paraffins (2). These conditions were used for quantitative analysis, by the internal standard method. The recovery of the method was determined by the standard addition technique applied to a sample. The analytes (Iimonene, methyl hexanoate, 1-hexanol, (Z)-S-hexenol, 2-phenylacetaldehyde, benzaldehyde and [alpha]-terpineol) were added at two different concentrations. The average recoveries were about 88-102% and their relative standard deviations were lower than 10%.

GC/MS analysis: The sample was analyzed with a HewlettPackard 6890 (series II) gas Chromatograph equipped with an HP-5973 mass-selective detector. The Chromatographie conditions were the same as those described for GC-FID. The detector operated in impact electron mode (70 eV) at 230�C. Detection was performed in the scan mode between 30 and 400 amu.

Compounds were identified by comparing their spectra to those of the Wiley library or our IDENT library, and also by comparison of their retention indices to those of standard compounds and data from literature (3,4).

Results and Discussion

The volatile constituents of Spanish tamarind fruit were obtained by simultaneous steam distillation-solvent extraction and analyzed by GC and GC/MS using fused silica capillary columns. Table I summarizes the analyses of the fruit volatiles according to order of elution on the SPB-5 column. The yield of total volatiles, estimated by the addition of a measured amount of internal standard to the pulp, was approximately 65 mg/kg of fruit pulp.

Seventy-four constituents were identified, all of them reported for the first time as volatile components of Spanish tamarind. A rough survey of the chemical classes represented in this fruit flavor was as follows: Furanoids comprise the largest class of volatiles (29.0%). The composition of the other classes of compounds was as follows: fatty acids, 28.4%; aldehydes and ketones, 21.1%; esters 11.7%; alcohols, 5.3%; terpenoids, 4.4%; and others, 0.1%. Major constituents found in Spanish tamarind flavor were 2-furfural (11.93 mg/kg) and hexadecanoic acid (5.19 mg/kg).

Some compounds present, e.g. furfural, and some furan derivatives could probably be degradation products of ascorbic acid and sugars (5,6). Nevertheless, the concentrate was found, on appropriate redilution with water, to possess the characteristic Spanish tamarind aroma. Odor descriptors provided by an informal sensory panel included caramel-like, green, fatty and waxy. The odor of the 2-unsaturated aldehydes, the authors believe, is a detectable attribute of Spanish tamarind. The presence of higher amounts of fatty acids could be responsible for the acidic and pungent notes observed in Spanish tamarind.