Source, Etc

The bitter or Seville orange is the fruit of Citrus Aurantium, var. Bigaradia, Hooker filius (G. Aurantium, Linne; C. vulgaris, Risso, N.O. Rutaceoe), a small tree, probably a native of north-eastern India, but cultivated in most warm countries. In Europe it is grown in the countries bordering on the Mediterranean, whither it was probably brought by the Arabs, as it was unknown to the Greeks and Romans. The fruit is collected before it is quite ripe, packed in boxes and exported, the ripening being completed during the voyage. Bitter oranges are shipped chiefly from southern Spain (Seville and Malaga) and from Sicily (Messina and Palermo), Seville oranges being considered to be the best for medicinal use.

In addition to the fresh fruit the dried peel is also largely imported from Malta, Spain, and Morocco.

Indian orange peel (Cortex Aurantii Indicus) is obtained from varieties of Citrus Aurantium, Linne, grown in India and Ceylon; it closely resembles bitter-orange peel and may be employed in its place in India and the Eastern divisions of the Empire.

Description

The ovary of the orange tree is superior and poly-carpellary; it is composed of eight (or sometimes more) carpels, each containing two rows of seeds with axile placentation. During the growth of the ovary the loculi increase in size, and the outer wall (pericarp) in thickness. Into the loculi there grow from the inner epidermis of the pericarp numerous hair-like processes which fill with juice and completely occupy the loculi; they form the pulp contained in the ' quarters ' of the orange, the thin membrane enclosing each quarter being the endocarp. The fruit is a variety of berry sometimes termed ' hesperidium.'

Fig. 53.   Orange peel. D, transverse section, enlarged 100 diam.; l, oil glands. (Berg.)

Fig. 53. - Orange peel. D, transverse section, enlarged 100 diam.; l, oil-glands. (Berg).

The bitter orange may be distinguished from the sweet orange by its rougher and usually darker rind and sour, bitter pulp. The rind, which is agreeably aromatic and has also a bitter taste, shows, when cut transversely, a narrow yellow outer part corresponding to the epicarp, in which large oil-glands are discernible with the naked eye, and an inner white portion corresponding to the mesocarp.

The peel is used both fresh and dried. In cutting it from the fruit care should be taken not to rupture the oil-glands more than is necessary, for it is to the volatile oil they contain that the pleasant aroma of the peel is due; at the same time too much of the white ' zest' should not be removed, as that is lacking in bitterness. It may readily be dried in a warm room but large quantities of the dried peel are imported, especially from Malta; in the latter case it is generally in the form of very narrow strips cut by machinery (' gelatin cut'), or in wider spiral strips or in four ' quarters.' English cut peel is generally rather thick, but has a fine colour and aroma. The transverse section assumes a dark green colour when moistened with strong hydrochloric acid, a reaction that is occasionally useful in identifying the peel.

Constituents

Bitter orange peel contains volatile oil, aurantiamarin (an amorphous bitter principle), hesperidin, isohesperidin, hesperic acid (colourless, tasteless crystals), a bitter resin and bitter auranti-amaric acid The peel yields from 3.5 to 6. per cent, of ash.

The seeds contain about 40 per cent, of fixed oil, pectin and a crystalline bitter principle, limonin.

Hesperidin, C22H16012, is a colourless, tasteless, crystalline glucoside that occurs in all species of Citrus and in many other Rutaceous plants; by hydrolysis it yields hesperetin together with dextrose and rhamnose; hesperetin may be split up into isoferulic acid and phloroglucin.

Substitutes

The peel of the sweet orange is said to be frequently mixed with that of the bitter orange; it may be distinguished by being thinner, paler, and more yellow in colour and much less bitter in taste. Lemon peel (dried) scarcely changes colour with strong hydrochloric acid.

Uses

Bitter orange peel possesses both aromatic and bitter properties, and is used as a tonic and as an agreeable flavouring agent.

Oil of Neroli is the volatile oil distilled from fresh orange flowers; chief constituents linalol, geraniol (and their esters), limonene and methyl anthranilate (ortho-amidobenzoate).

Orange Flower Water is a saturated aqueous solution of the volatile oil obtained during the distillation; the residue contains the bitter principle limonin (naringin).

Oil of Orange is the volatile oil obtained from the rind of the bitter orange; chief constituents d-limonene, citral, citronellal, decyl alcohol, methyl anthranilate.

Oil of Portugal, the volatile oil from the rind of the sweet orange, has similar constituents.

Oil of Petit Grain, the volatile oil obtained originally from the immature fruits but now from the leaves and twigs, has also a very similar composition.