Section VI - Composition and constituents of nutmeg and mace

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1. Fixed oil
2. Essential oil

The principal constituents of the spices nutmeg and mace are steam volatile oil (essential oil), fixed (fatty) oil, proteins, cellulose, pentosans, starch, resin and mineral elements.

Percentages of constituents differ between the spices and this is a consequence of geographical origin, quality and duration of storage and even growing locations. Thus the fixed oil content of sound nutmegs varies from 25 40% while that of mace is 20- 30%. Worm eaten nutmegs have a higher content of volatile oils than sound nutmegs since in the former the starches and fixed oil have been selectively eaten by insects.

1. Fixed oil

There are two general methods by which the fixed oil of nutmeg is extracted. In one method, sound, ground nutmeg is subjected to intense hydraulic pressure and heat (heated plates in the presence of steam) while, in the other the ground nutmeg is extracted by refluxing with a solvent like diethyl ether. Both processes will result in the crude fixed oil containing significant quantities of essential oil in the average of 10-12%. Prior steam distillation will lead to a significant reduction of essential oil in the prepared fixed oil.

The extracted or expressed fixed oil is a semi-solid aromatic (smell and taste of nutmeg), orange coloured fat, known as concrete, expressed oil or nutmeg butter which melts at 4S-51°C and has a density of 0-990 -0.995. It is completely soluble in hot alcohol, but sparingly so in cold. However, it is freely soluble in ether and chloroform.

The major component of the fixed oil is Trimyristin and Power and Salways (1908) gave the following components and their relative abundance for the analysis of a fixed oil for which there was not prior distillation to remove essential oil from the nutmeg raw material:

If essential oil is previously extracted, then the relative abundance of trimyristin in the fixed oil will increase.

2. Essential oil

The essential oil is usually obtained by steam distillation of dried kernels. It is a colourless or yellow liquid with the characteristic odour and taste of nutmeg. The oil is insoluble in water but soluble in alcohol and has a density at 25°C of 0.859 - 0.924, refractive index at 20°C, 1.470 - 1.488 and optical rotation at 20°C of + 10° - +45°. This oil keeps best in the cool in tightly closed containers protected from light.

Extensive analyses have been carried out on the volatile oil of nutmeg and these have provided the major classes of compounds constituting the oil as: monoterpene hydrocarbons, 61 - 88%; oxygenated monoterpenes (simple and others) ie. monoterpene alcohols, monoterpene esters; aromatic ethers; sesquiterpenes, aromatic monoterpenes, alkenes, organic acids and some miscellaneous.

Table 10 lists and updates most of the compounds identified in the volatile oils of nutmeg and mace with the appropriate references. A-and b-pinene and sabinene constitutes the major components of the monoterpene hydrocarbon fraction where as myristicin is the major constituent of the aromatic-ether fraction.

It must be noted that the composition of distilled volatile oil is not identical to the natural oil in the kernel or oleoresin extract. Thus about 30 55% of the kernel consist of oil and 45 - 60% of solid matter. The essential or volatile oil accounts for 5 - 15% of the nutmeg kernel while the fixed oil accounts for 24 40% of the nutmeg kernel. Fixed oils are virtually absent from mace and volatile oil accounts for 4 - 17% of the composition of mace. There is always in the distilled volatile oil a higher percentage of monoterpenes, especially a and b-pinene and sabinene since there is incomplete distillation of the oxygenated components which possess higher boiling points.

On organoleptic grounds it has been stated that West Indian oils are weaker in odour and less spicy than East Indian oils. From studying and comparing East and West Indian oil, Baldry et al. (1976) have suggested that the composition differences are more a reflection of the proportion and the constituting compounds more so than absence of constituents. The major quantitative differences were lower proportions of a-pinene, safrole and myristicin and higher proportions of sabinene in the West Indian oils.

In the literature reference is often made to West Indian nutmeg and mace oils with no clear distinction being made as to the actual West Indian source. Dann et al. (1977) reported on a detailed study of the comparison of essential oil yields and compositions of nutmeg and mace collected on Grenada from individual trees growing on the island. Investigations were carried out on dried kernels and cured mace. Analysis revealed that quality of the constituents in the oil of nutmeg and mace from individual trees was very similar. However, there was variation in the quantity of components of the two oils. Thus where as the nutmeg oils showed 8593 % monoterpene hydrocarbons, 6.6 - 12% oxygenated monoterpenes and sesquiterpenes and 3.5% aromatic ethers, the values for the mace oils were 75-94, 4.7 - 17.6 and 05.9% respectively.

The monoterpene hydrocarbons and oxygenated monoterpenes compositions of both oils from the same tree were very similar in quantity and quality except for lower concentration of a-pinene in the nutmeg oil. Elemicin was the major component of the aromatic-ether fraction in both the nutmeg and mace oils with contributions form smaller quantities of safrole and myristicin. The proportion of aromatic-ethers was always higher in the mace than in the nutmeg oil. Dann e, al. (1977) also reported that taste panels were able to detect differences in the organoleptic properties of mace and nutmeg oils from the same tree thus suggesting that aromatic ether may play a key role in the organoleptic character for essential oils of nutmeg and mace. This points to the fact that it may be very important to have characteristics for comparison of the oils from Nutmeg and Mace of the introduced Malayan plants.

TABLE 10. CONSTITUENTS IDENTIFIED IN NUTMEG AND MACE ESSENTIAL OILS

REFERENCES FOR CONSTITUENTS IDENTIFIED IN TABLE 10

1. Wallach (1885,1889)
2. Semmler (1890,1891)
3. Thomas (1903)
4. Schimmel & Co. (1910)
5. Power and Salway (1907)
6. Lee et al. (1961)
7. Jaureguiberry and Wolf (1962)
8. Ikeda et al (1962)
9. Bejnarowicz and kirch (1963)
10. Shulgin et al. (1963, 1964)
11. Itty and Nigam (1966)
12. Shulgin et al (1967)
13. Sammy and Nawar (1968)
14. Sandford and Heinz (1971)
15. Forrest and Heacock (1972)
16. Salzer (1975a)
17. Baldry et al. (1976)
18. Dann et al. (l 917)
19. Power & Salway (1908)
20. Forrest et al. (1972)
21. Guo and Yu (1985)
22. Schenk and Lamparsky (1981)
23. Janssens et al. (1990)
24. Rasheed et al. (1984)
25. Rasheed (1985)
26. Carr (1973)
27. Sarath - Kumara et al. (1985)

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