Applications of natural plant extracts in soft drinks - Natural Food Additives, Ingredients and Flavourings - page 336

materials and during the processing of citrus fruit it is usual for the oil to be
removed prior to the fruit being pressed for juice extraction. Various processes
may be employed during the processing of oranges and lemons for the removal of
oil. One method is to allow fruit to be lightly compressed by rollers with needles
in their surfaces before the fruit is sliced and compressed for juice removal. A
water spray removes the oil which may be later separated, usually by means of a
centrifuge.
An alternative technique, as used in the FMC Corporation process, where
removal of oil takes place at the same time as the fruit is compressed for juice
removal. A water spray removes the oils and separation of water and oil is again
effected by the use of a centrifuge. Removal of oil from limes may be carried out
by the above processes although traditionally, when limes are processed, the
whole fruit is crushed in a tapering screw press. By use of appropriate screens
much of the juice and oil mixture can be separated leaving a residue of peel, pulp
and some juice. Oil may be separated from the juice/oil mixture again by
centrifugation. The residue is frequently allowed to stand in a vertical cylindrical
vessel to allow natural pectolytic enzymes to break down the structure and release
more oil. An oil layer fl oats to the top of the vessel and may be easily separated
and removed. Alternatively, the mass of peel and pulp after initial pressing may
also be subjected to steam distillation (see Section 15.3). Essential oil of lime
readily distils in steam and is easily separated from the condensate.
It is important to distinguish between so-called 'cold pressed' citrus oils that
are produced by entirely mechanical techniques and citrus essential oils,
particularly lime, that are removed by steam distillation. The chemical composition
of a cold pressed oil and its distilled counterpart varies considerably, with many
of the more volatile and labile components being absent in the latter. Additionally,
some components may undergo thermal transformation during steam distillation
giving the resulting oil a signifi cantly different organoleptic character. As an
example, the principal components of both cold pressed and distilled lime oil are
shown in Table 15.1. The presence of more volatile components such as geranial
and neral give the expressed oil a fresher characteristic aroma. Most oils from
orange and lemon are expressed rather than distilled.
Expressed citrus oils are important items of commerce, although present in
fruit in much smaller proportion (typically around 0.2-0.4% w/w) than juices

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Table 15.1 Comparison of principal components of cold pressed and distilled lime oils

Distilled lime oil % Cold pressed lime oil %

Limonene 52 Limonene 45

Gamma terpinene 8 Beta-pinene 14

Alpha-terpineol 7 Gamma-terpinene 8

Terpinolene 5 Geranial 3

p -Cymene 5 Neral 2

1,4-cineol 3

1,8-cineol 2

Beta-pinene 2