Description
Evergreen tree (shrub) native to the Far East; actual growing site
questionable. It was introduced into the Mediterranean region at
the time of the Crusades. The plant grows to 6 m (20 ft.) high. It
has strong, branched roots and an erect trunk with several
branches; the lower limbs are sometimes covered with thorns. The
tree has alternate oval leaves, white flowers (from February to
October), and oval fruits that are yellow when ripe. The rind of
the fruits is thin, and the epicarp is rough; the segmented endocarp contains a sour juice and oval seeds. The leaves (and terminal
twigs), fruits, and rind are the parts used. Lemon has a character istic lemon-leaf odor and a sour, bitter taste.
Lemon petitgrain is obtained by steam distillation of the leaves.
It has small, terminal twigs and small, unripe fruits with yields
varying between 0.16 to 0.23%. It is a clear, mobile, pale-yellow
or amber liquid exhibiting the characteristic odor of the leaves.
For flavoring use, lemon petitgrain oil must be terpeneless. Its
main constituents include d-α-pinene, camphene, d-limonene,
dipentene, l-linalool, geraniol, nerol, and the corresponding ace tates, esterified cineol, and citral.
Lemon essential oil is obtained by cold expression (mechanical or
manual) of the peel in yields of approximately 4% based on the
weight of the fruit. (A less valuable quality of oil is obtained by
steam distillation of the peel.) The expressed oil is a mobile, clear
liquid that may become turbid on cooling; it is pale yellow or
greenish-yellow. The physical-chemical constants of lemon essen tial oil vary, depending on the source of the fruit-Spain, California,
Florida, Israel, Italy.
To date more than forty constituents have been identified in the
oil, which contains approximately 90% limonene (by weight).
Other important terpenes include α- and β-pinene, myrcene, citral,
and γ-terpinene. The non-volatile residue contains citropten (or
limettin). From the normal essential oil, the terpeneless and ses quiterpeneless oils are obtained by vacuum rectification, washing
with dilute alcohol or by column chromatography. Rectification is
important to achieve a product with good solubility. Terpeneless
oils are also more stable, as they are less sensitive to oxidation.
Soluble essences are prepared by using low-strength ethanol with
yields of 1/50, 1/100, 1/200, and 1/400 with reference to formu lated syrups.
Using typical extraction techniques, the derivatives are a fluid
extract and a tincture (20% in 70% ethanol) obtained from the
dried peel. By properly compounding the essential oil (raw or
terpeneless), juice, pectins, and sugars, it is possible to prepare
pastes suitable for flavoring carbonated beverages.
The preparation of lemon juice is similar to that of orange.
