EXTRACTION TECHNOLOGIES: SOME ADVANTAGES AND DISADVANTAGES
Recently, natural food additives consumers posed a question: why earlier well-known
sub critical CO2 spices and herbs extracts are trying to be replaced by supercritical?
What is their difference?
The difference is in the following:
- In much higher temperature and pressure during the supercritical extraction,
this destroys extremely valuable unstable volatile elements;
- In obtaining extracts with various chemical composition from the same plant;
- In properties of the obtained extract and its applicability to an end-product,
where the extract is used;
- In economic feasibility, when choosing the type of a used extract.
Let's consider the existing extraction ways.
Isolation of aromatic components from a cellulose matrix is usually conducted
with the help of the water vapor distillation method or with the help of extraction
methods (fig. 1).
Water vapor distillation of volatile components is conducted at the temperature
of about 100 ?С and allows extracting substances from vegetative raw materials
at rather low boiling temperatures (150 - 250 ?С). To the advantages of the steam
distillation method could be added such benefits as its feasibility in field conditions
and low cost of essential oils. However, at high distillation temperatures volatile
substances undergo danaturation and some valuable components get modified, aromas
get distorted. Besides, some essential oils require fining due to the formation
of undesirable decomposition products. Storage periods of such oils are limited,
already in 6-9 months periods, the polymerization process begins and smell gets
even more deformed. Vacuum distillation is a more progressive method in comparison
with the usual atmospheric ones, however it is used, mainly, for crude oils fining.
It is also widely known the extraction of valuable components from vegetative
raw materials with the help of organic solvents: acetone, gasoline, hexane, dichlorethane,
diethyl ether, isopropanol, petroleum-ether, ethyl chloride, ethanol, and et.
Extraction oils, in most cases, have a higher quality than steam distillation
oils, as the structure of extracts includes natural fixing agents and flavoring
substances, which are usually absent in essential oils. The structure of extracts
significantly depends on the used solvent. For example, when using hydrophilic
solvents (acetone, glycerin, ethanol) there are extracts obtained, which are soluble
in the water and contain significant amounts of painting and other undesirable
substances. Waterproof solvents (hexane, dichlorethane, tetrachloride carbon,
etc.) better extract fatty substances; however they do not isolate carbohydrates,
pitches, gum. World practice shows, that extract oils have their consumers and
are widely used in the food, perfumery - cosmetic industry, household chemical
goods and light industry. However, the majority of used solvents are flammable
and explosive, some of them are toxic. High-temperature solvent distillation from
miscella (as well as in case of steam distillation) results in undesirable qualitative
structure changes of extracts.
Better quality extracts are obtained due to the use of liquefied gases as solvents.
The method of valuable substances extraction from raw materials with the help
of the liquid food carbon dioxide, CO2 in the subcritical condition (critical
point Р=7,4 МPa, t=31,10 ?С) got practical application. Its main advantage, that
CO2 - participates in the metabolism of all living substances on the planet and
exists in a human body. Certainly the following conditions are attractive, when
choosing the liquefied CO2, as an extracting agent: environmentally safety and
cleanliness, selectivity in relation to a number of biologically active substances,
absence of residual solvents in the product, fire-and explosion safety, chemical
inertness in the absence of a catalyst, high molecular diffusion coefficient,
low viscosity and superficial tension. To the important advantages, except for
the listed above, availability and low cost of carbon dioxide, as well as the
multi-variant approach and durability of equipment operation could be attributed.
A parametrical line of extraction equipment has been developed, technological
modes of valuable components extraction from more than 100 kinds of vegetative
raw materials are mastered and constantly improved, and various ways of technological
processes intensification are approved and used in manufacture.
On fig. 2 there is the scheme of one of the installations, successfully used at
this enterprise. A distinctive feature of such installation is the possibility
of solvent supply in the shop from a stationary large-tonnage tank; the advanced
evaporator design, allowing conducting fast solvent distillation from miscella
in a thin layer. In order to reduce the extraction process duration, ultrasonic
fields of various intensity are used. Also the removal of air remains from an
extractor with the loaded raw material is provided, which enables to conduct the
components extraction process in strictly adjustable conditions. The condenser-cooling
scheme has been modified and the technological defects of a draft tube (vapor
tube) have been eliminated.
Further, we analyzed the extraction ability of carbon dioxide in sub- and supercritical
conditions, using our own researches' results, the published data, and the data
gathered from the Internet. In tab. 1 there are shown the extraction results of
the basic organic compounds from vegetative raw material as a result of various
Essentially there is a question: whether it is necessary to extract completely
all components from vegetative raw materials, or prefer a selective way and extract
only those groups of substances, which are able to improve qualitative characteristics
of a ready product. A unique extraction agent - carbon dioxide in the sub- critical
conditions, meets these requirements.
It is particularly interesting, that at room temperature (+18 … +22 ?С) liquid
CO2 during the first extraction stage isolates volatile compounds, and in the
process of their accumulation miscella obtains properties of a less selective
solvent and its usage, as an extraction agent, allows to enrich the extract with
other valuable components in the constant, natural conditions.
The best confirmation of the sub-critical СО2-exctraction development prospects
can be the 12- year successful working experience of an extraction factory. Application
of СО2-extracts in foodstuff is already not simply a part of technology, however
the ideology of those, who aspire to conduct a good business in the manufacture
of a quality and healthy product.
The method of supercritical extraction (desorption) of valuable components from
vegetative raw material started to be mastered rather recently, but not always
for those kinds of raw material, where such method is justified.
The main advantage of the supercritical extraction is an opportunity to conduct
a graduated, preparative extraction of certain valuable components from raw material.
As for the disadvantages, such factors as the complexity of equipment, working
under the pressure of up to 1000 atmospheres (100 МPа), necessity to maintain
rather high processing temperatures: from 40 up to 90 ?С.
It is not necessary to completely deny the advantages of the sub- and supercritical
extraction methods. Each technology occupies its own consumer niche. For example,
the supercritical extraction is successfully used abroad for caffeine extraction
from coffee, nicotine from tobacco, oils from soybeans, etc. However, there is
no point in applying supercritical extraction, for example, with regards to:
- Clove buds or laurel leaves (except for bitter fractions extractions, which
are bad for a human being)
- Seeds of coriander, anise, fennel, caraway, anise tree, nutmeg and other aromatic
raw materials with the high contents of fat oils (up to 20-40 %) for exception
of less valuable fat oil extractions, reducing an extract storage period and decreasing
the concentration of target aromatic and flavoring substances.
- Specific aromatic plants, which are valuable only because of essential oils
presence, and that the deep extraction products don't have to be present in their
Supercritical extracts have lower cost in comparison to sub-critical CO2 extracts,
however the contents of aromatic and flavoring substances in these extracts is
lower. It is possible to conceder the processing of amaranth seeds, as an example.
If the output of CO2 extracts is 4 %, when using the sub-critical extraction method
of isolating biologically active substances from amaranth seeds with liquid CO2,
and the contents of the most valuable main substance squalene in such an extract
is 23 % (out of the sum of extraction substances), the output of the supercritical
extract can be as high as 8 %, due to the fat oil, available in the seeds, however
the squalene contents in this extract will be 12 %. In this case, the supercritical
extracts should have the price twice below the amaranth CO2 extract price, which,
probably, would be unprofitable to supercritical extracts manufacturers.
Scientific forecasts have shown that the extraction of valuable components by
the sub-and supercritical carbon dioxide is going to remain the most perspective
technological process for at least 10 years. These technologies are economically
justified in case of valuable raw materials processing with the high contents
of biologically active substances. Reduction in quality of dry spices also improves
the prospects of using sub-critical CO2 extracts, as quality of such extracts
is always stable. Creation of original recuperation and regeneration systems of
solvents will make these technologies economic and environmentally friendly. We
would like to invite all interested firms to cooperate with us.
DDF Australia Pty. Ltd.
Unit 105 1 Rosebery av. Rosebery NSW 2018 Australia
Tel +61 2 9662 0677 fax +61 2 9662 0633