Due to the small amounts of essential oils in the plant and the
significant importance of them, many methods have been developed to
determine the amount of these compounds. Two common and important
techniques for the analysis of essential oils are chromatography and
mass spectrometry. gas chromatography with mass spectrometry (GC-MS) and
high performance liquid chromatography (HPLC) and are the most widely
used [7, 15, 16]. Gas chromatography-mass spectrometry (GC-MS) has
added to the development and improvement in the analysis of essential
oils which could be distinguished compounds with very similar chemical
structures of each other [17]. In general, Gas chromatography (GC)
for the analysis of volatile compounds and liquid chromatography (LC)
for Analysis of non-volatile compounds in essential oils used [18].
In addition to essential oils, other aromatic compounds extracted from
plants include: concrete (obtained by extraction with non-polar
solvents), absolute (obtained by washing concretes in ethanol or
methanol and vacuum distilling alcohol away ), pomade (obtained
by a process known as enfleurage (described in later sections),
resinoids (resinoids are extracted from the natural resin material by
hydrocarbon solvent. Resinoids are usually derived from dry matter)
[17, 19].
Essential oils can be extracted from different plants by various
extraction methods. The manufacturing of essential oils, and essential
oil extraction method are dependent on botanical material used. The
another factor for extraction essential oil is state and form of
material. One of the important factors that have a great impact on the
quality of essential oil is the extraction method. Inappropriate
extraction procedure can lead damage the chemical structure of the
essential oil, which in turn changes the quality and natural properties
of the essential oil [4]. In generally, extraction methods can be
divided into two groups: conventional methods (distillation, cold
pressing and etc.) and novel methods (supercritical fluid, microwave and
etc.). Investigation in novel technologies, in the last decades has led
to more efficient extraction processes for example reduction of energy
consumption and extraction time, high yield and improvement of essential
oils quality. Recently, due to the limitations and disadvantages of
methods of extraction from intact plants, large companies are trying to
move their way to biotechnology methods and make a variety of plant
compounds by microorganisms. By doing this, they have no stress about
problems such as climate conditions, supply shortages, natural
disasters, plant diseases etc., and a product with very high efficiency
and quality is obtained. Production of natural products and volatile
through biotechnology can be an appropriate response to consumer demand
in relation to the consumption of natural products and move towards
”green processes” and environmentally friendly.
In this review, we have tried to explain the production methods of
essential oils, including conventional, novel and biotechnology methods,
and make a general comparison between them.