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The present invention relates to the treatment of microbial oils, in particular
those containing one or more polyunsaturated fatty acids (PUFAs). The treatment
comprises adding a solvent to the oil, and cooling the oil until a precipitate forms,
and then removing the precipitate. The resulting oil may be enriched in PUFAs.
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Although microbial oils, for example containing PUFAs, are known, there is
a need to improve the quality of the oil, and in particular to increase the amount of
PUFAs in the oil. The oil can thus be made more concentrated, and so less oil may
be required in order to deliver a desired quantity of a PUFA. There is also a need to
be able to purify microbial and PUFA-containing oils sufficiently in order that they
can be incorporated into foodstuffs such as infant formula or other edible
compositions, such as pharmaceuticals. This purification process is desirably
efficient and cost-effective.
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WO-A-97/43362 (Gist-Brocades B.V.) describes the extraction of sterols
from microbial oils with a polar solvent. However, unlike the present invention, it
does not include the cooling of the oil (winterisation) or the formation of precipitate,
which is then removed.
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A first aspect of the present invention thus relates to a process for treating a
microbial oil or an oil comprising an (e.g. Ω3 or Ω6) PUFA. This process may
comprise adding a precipitate inducer (or enhancer) to the oil. Cooling (of the oil
and precipitate inducer mixture) can then take place until a precipitate forms or at
least part of the oil solidifies. The precipitate (solid or solidified matter) may then
be removed (from the e.g. residual oil).
PUFAs and oils
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Preferably the oil is a microbial oil or it comprises one or more PUFAs. It is
usually a liquid. Preferred PUFAs are C18, C20 or C22 (e.g. Ω6 or Ω3) PUFAs.
Preferred Ω3 and Ω6 PUFAs include:
- (Ω3) docosahexaenoic acid (DHA), suitably from algae or fungi, such as the
dinoflagellate Crypthecodinium or the fungus Thraustochytrium;
- (Ω6) γ-linolenic acid (GLA);
- (Ω3) α-linolenic acid (ALA);
- (Ω6) dihomo-γ-linolenic acid (DGLA);
- (Ω6) arachidonic acid (ARA); and
- (Ω3) eicosapentaenoic acid (EPA).
-
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The microbial oil may thus comprise an Ω3 or an Ω6 PUFA. The Ω3 PUFA
(e.g. DHA)-containing oil may be a marine, e.g. fish (such as tuna) oil. The Ω6
and/or Ω3 PUFA (e.g. ARA, DHA or EPA)-containing oil can be a microbial or
single cell oil.
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An Ω6 and/or Ω3 PUFA-containing microbial oil (e.g. GLA, ARA and EPA)
can be obtained from fungi, such as Mortierella, Pythium or Entomophthora. Ω3
PUFAs (e.g. EPA) can be produced from algae such as Porphyridium or Nitzschia.
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Preferably the microbial (or Ω6 or Ω3 (e.g. ARA, DHA or EPA)) oil can be
produced by a single cell or a microorganism. This may be a bacteria, yeast, algae or
fungi. Preferred fungi are of the order Mucorales. The fungus may be of the genus
Mortierella, Phycomyces, Blakeslea or Aspergillus. Preferred fungi are of the
species Mortierella alpina, Blakeslea trispora and Aspergillus terreus.
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Preferred yeasts are of the genus Pichia or Saccharomyces, for example
Pichia ciferrii. Bacteria can be of the genus Propionibacterium. Preferred algae are
dinoflagellate and/or belong to the genus Crypthecodinium, for example are of the
species Crypthecodinium cohnii.
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The Ω6 and/or Ω3 PUFA-containing oil may be an edible oil or a vegetable
oil. These include blackcurrant, borage and primrose oils, and often contain an Ω6
PUFA, e.g. GLA. They also include olive, sunflower and soybean, soy flower oils,
for example cooking and/or salad oils.
Production of crude oils
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The starting (e.g. crude) oil may be a microbial (e.g. single cell) oil, or it may
be a marine (e.g. fish) oil or vegetable oil (either crude or partially treated). In
particular, crude oils containing Ω3 PUFAs (DHA and/or EPA) can be marine oils.
If the PUFA oil is to contain GLA, then the crude oil may be a vegetable oil, for
example blackcurrant, borage, sunflower, soybean or primrose oil.
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A number of documents describe the production of crude PUFA oils.
Microbial oils containing ARA are disclosed in WO-A-92/13086 (Martek), EPA in
WO-A-91/14427 (Martek) and DHA in WO-A-91/11918 (Martek). The present
Applicant has already described various methods for extracting PUFA oils from
microbial sources, and these can be found in WO-A-97/36996 and WO-A-97/37032
(both Gist-Brocades). Preparation of ARA, DHA and EPA-containing oils is also
described in WO-A-92/12711 (Martek).
In the oil, it is preferred that most of the PUFA is in the form of triglycerides. Thus,
preferably at least 50%, such as at least 60%, or optimally at least 70%, of the PUFA
is in triglyceride form. Of these triglycerides, preferably at least 40%, such as at
least 50%, and optimally at least 60% of the PUFA is present at the α-position of the
glycerol (present in the triglyceride backbone), also known as the 1 or 3 position. It
may be preferred that at least 20%, such as at least 30%, optimally at least 40% of
the PUFA is at the β(2) position.
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Preferably the original microbial oil is a crude oil. It may have been
extracted from microbes or single cells, for example by using a solvent, such as
supercritical carbon dioxide, hexane or isopropanol. The oil may have been
processed and/or treated before the process of the present invention is performed.
Precipitate inducer
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The inducer which is added to the microbial oil is preferably one that elevates
or increases the temperature at which the precipitate forms, for example the
temperature at which crystallisation starts. It may thus increase the crystallisation
temperature of the oil. The inducer may facilitate precipitation: without the inducer
it has not been found possible to form a precipitate (at least at temperatures down to
about -20°C, such as those found in freezers). With no inducer added, no precipitate
formed in a control experiment (see Comparative Example 5).
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The inducer is preferably an (organic) liquid, although it may be polar or nonpolar.
Preferably the inducer will have a melting point of below the precipate, that
is to say a temperature bow that at which the precipitate forms. Thus the inducer
preferably has an m.p. below -70°C, such as below -80°C optimally below -90°C.
The inducer is suitably a clear liquid.
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Suitably the inducer will be a solvent for (or miscible with) fats or oils, in
particular a solvent for (or miscible with) saturated triglycerides (that is to say,
triglycerides from saturated fatty acids) or a PUFA. Particularly preferred inducers
are hexane and/or acetone.
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The inducer is preferably a liquid that is miscible with the oil, and hence a
preferred inducer is one that can dissolve or is miscible with a PUFA. Inducers that
may thus not be suitable are those that are immiscible with the oils, in particular
alcohols (e.g. methanol, isopropanol).
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The precipitate inducer can therefore be regarded as a solvent for the oil to
which it is added. However, the inducer is preferably a non-solvent for at least one
component of the oil that is present in the precipitate, that is to say it does not
dissolve or it is immiscible with this component. This component which may be a single
compound) is one that is desired to be removed, and this is achieved by removing the
precipitate (or solidified matter) from the remaining oil. Although not wishing to be
bound by theory, it is thought that the precipitate inducer may bind to or surround the
component that is to be removed.
The inducer may thus in same way
face the component out of solution (ie. out of the oil).
However, whatever the mechanism, the precipitate
inducer clearly seems to play an important role in being able to facilitate the
formation of the precipitate. It appears to assist or induce precipitate formation, and
such a precipitate can contain at least one component that the inducer is not a solvent
for.
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In the same way as one can describe compounds as hydrophilic and
hydrophobic, one can think of various components in the oil as being either
inducer-liking (the inducer is a solvent for that component) or inducer-hating (the
inducer is a non-solvent for that component). Once the precipitate performs, the
precipitate may contain more inducer-hating component(s) than the remaining oil.
Thus, when the oil separates into two phases, namely the remaining oil (usually on
top) and the precipitate (usually on the bottom), the oil will be enriched in an
inducer-loving component (or depleted in an inducer-hating component) while the
precipitate will be enriched in an inducer-hating component (but depleted in an
inducer-loving component).
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The ratio of oil:inducer is preferably from 1:1 to 1:10, such as from 1:2 to
1:9. These ratios are particularly applicable if the solvent comprises acetone or
hexane.
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The inducer may be added to the oil when one or both of the oil and inducer
are liquids, such as at room temperature. However, addition can take place at any
suitable temperature of from 0-20°C, preferably from 0°C to 20°C, optimally 2°C to
30°C.
Cooling
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The oil and inducer are mixed and then the mixture is allowed to cool. The
mixture is suitably homogeneous, i.e. a one-phase mixture. Cooling may take place
naturally or passively (for example by placing the mixture outside in a cool
environment). However, the oil can be actively cooled, for example using a heat
exchanger.
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Preferably however the oil is cooled by using a refrigerator or freezer.
Cooling may take place slowly. Preferably the oil and inducer mixture is placed in
an environment that is at a temperature below which a precipitate forms. This
temperature is preferably below 0°C or -5°C, such as below -10°C, suitably below -
20°C, and optimally at or below -25°C. The time taken to cool the oil (and solvent
mixture) may be from 1 to 30 hours, such as from 16 to 24 hours, optimally from 18
to 22 hours.
Nature of precipitate (or sediment) and its removal
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The precipitate is usually a solid that forms due to cooling and for
convenience this term (including its use in "precipitate inducer") refers to the
solidified matter resulting from the lowering in temperature. Preferably the
precipitate comprises crystals. If so, then the inducer may increase the
crystallisation temperature of the oil (or one or more component(s) in the oil). The
crystals may comprise only one component or compound. The precipitate may thus
comprise one or more impurities and/or unwanted compounds, for example a
saturated triglyceride. Solidification occurs at (or, to put another way, the melting
point of the solidified matter or precipitate is) preferably from -1°C to -25°C, such as
from -3°C to -20°C, preferably from -5°C to -17°C. Solidification occurs at about -
15°C if the solvent is acetone and about -5°C if the solvent is hexane.
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Suitably the melting point of the precipitate is increased by the addition of the
inducer. With no inducer present, no precipitate was formed even when the oil was
cooled to -20°C (see Comparative Example 5).
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Preferably the precipitate will not contain much PUFA, or at least only a
small amount. The amount of PUFA (e.g. ARA) in the precipitate is preferably less
than 40%, such as less than 35%, optimally less than 30% (by weight: 1% here is
equivalent to 10g PUFA/kg oil).
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The precipitate is preferably denser than the oil. If this is so, then the
precipitate may fall or migrate to the bottom of the oil. It may thus be or form a
sediment. In this case the precipitate may be removed by centrifugation. This can
take place in a closed system, and so may minimise exposure of the oil to degrading
substances, such as oxygen in the atmosphere. Preferred centrifuges are laboratory
or industrial centrifuges. Centrifugation may take place at from 2000 rpm to 8000
rpm, such as from 3000 to 7000 rpm, optimally from 4000 to 6000 rpm. Put another
way, centrifugation may occur at from 2,000-8,000g, such as from 3,000-7,000g,
optimally from 4,000-6,000g. This may take place at from 1 to 4 minutes, such as
from 12 to 3 minutes, preferably for about 2 minutes.
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Preferably the precipitate (or crystals) is removed by filtration. Here any
crystals formed may be sufficiently large enough to be removed by filtration. One
can use a plate and frame filter press or vacuum filtration. If using a filter press, the
pressure used is suitably from 0.2 to 0.5 bar. Removal may be by centrifugation or
filtration or both.
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The cooling may thus result in a 2-phase system. A top layer may be liquid,
such as a residual oil. The bottom layer may be solid, and is thus the solidified
matter (or precipitate/sediment). Preferably the top layer is enriched in a PUFA
while the bottom layer is depleted in the PUFA. Thus, the residual oil may have a
concentration of the PUFA greater than the original oil and the solidified matter a
reduced concentration of the PUFA. This was unexpected as PUFAs often have a
low m.p. and would be expected to solidify first.
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The residual oil may have a concentration of a PUFA (e.g. ARA) of at least
35%, such as at least 37%, preferably at least 40%, optimally at least 42%.
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Preferably, after the precipitate has been removed, the inducer is removed.
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The inducer may be allowed to evaporate, for example at room temperature
or above. A suitable temperature is from 20 to 80 or 100°C, such as from 25 to
60°C, optimally from 30-50°C. Removal of the inducer may take place with the aid
of a vacuum.
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As will be realised, since solidification usually takes place below 0°C, then
warming to room temperature may cause the solidified matter to melt and once again
to become liquid. Thus removal of the solidified matter preferably occurs while that
matter is still solid (or at a temperature below the melting point of that matter). Thus
removal preferably occurs at below 0°C, preferably below -5°C, optimally below
-10°C.
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Steps (b) - cooling - and (c) - removal of the solidified matter - can be
repeated at least twice, for example to enrich the oil further each time. Of course all
the steps (a) to (c) can be repeated, for example with the same or different inducer.
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The (treated) oil resulting from the process of the invention, which forms the
second aspect of the invention, can be used for various purposes without further
processing, or can be additionally subjected to one or more purifying and/or refining
steps. The oil may thus be subjected to the purifying process described in European
patent application no. 00306606.5 filed on 2 August 2000.
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The oil can be used as an additive or a supplement, for example in food
compositions, such as in infant formula. It may however also be used in cosmetic or
pharmaceutical compositions. The invention in a third aspect therefore relates to an
edible composition, such as a foodstuff, feed, pharmaceutical or cosmetic
composition which comprises, or to which has been added, the oil of the second
aspect of the invention. Preferred compositions are foods such as infant formula
and nutritional supplements.
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The oil of the invention can therefore have a relatively high PUFA content.
This may be at least 38%, preferably at least 40%, optimally at least 42% (by
weight).
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The oil is particularly suitable for nutritional purposes, and so can be used as
or in a nutritional supplement. The oil may be supplied as an oil, or it may be
encapsulated, for example, in a gelatin capsule. The oil can thus be incorporated
into foods, feeds or foodstuffs, suitable for animal or human consumption. Suitable
examples are health drinks and bread.
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Preferred features and characteristics of one aspect of the invention are
equally applicable to another aspect mutatis mutandis.
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The invention will now be described, by way of example, with reference to
the following Examples. These are provided merely for means of illustration, and
are not to be construed being limiting on the invention.
EXAMPLE 1
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Crude arachidonic acid (ARA) oil (100 ml) was obtained from
Mortierella
alpina using hexane as the extracting solvent. The protocol for preparing such an oil
is described in Example 16 of WO-A-97/36996 (Gist-Brocades B.V.). This crude oil
was mixed with 400 ml of n-hexane. The resulting homogeneous mixture was
placed in a freezer held at a temperature of from -18°C to -25°C for 20 hours. A
precipitate of crystals formed at about -15°C. Hence a 2-phase system formed, with a
top (liquid) layer (the remaining oil) and a bottom layer (solid, precipitate). The
precipitate was separated using a laboratory centrifuge (type Sigma 4-10) at 5000
rpm for 2 minutes. The hexane was removed from each of the remaining oil and the
precipitate by evaporation overnight at 30°C in a vacuum. The ARA content of the
precipitate and residual oil was analyzed by means of gas chromatography (GC) and
the results are shown below in Table 1.
| Substance | ARA (g/kg) |
| Original oil | 345 |
| Oil:precipitate | 317 |
| Oil:residual oil | 406 |
EXAMPLE 2
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Crude ARA oil (20 ml), from the same source as that in Example 1, was
mixed with 80 ml of acetone. The resulting homogeneous mixture was placed in a
freezer held at a temperature of from -18°C to -25°C for 20 hours. A precipitate of
crystals formed at about -15°C to give a 2-phase system consisting of a top liquid
layer and a bottom solid layer. The precipitate was separated using a laboratory
centrifuge (type Sigma 4-10) at 5000 rpm for 2 minutes. The hexane was removed
separately from both the residual oil and precipitate by evaporation overnight at 30°C
in a vacuum. The ARA content of both layers was analyzed by means of gas
chromatography (GC) and the results are shown below in Table 2.
| Substance | ARA (g/kg) |
| Original oil | 345 |
| Oil:precipitate | 240 |
| Oil:residual oil | 433 |
EXAMPLE 3
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Different amounts of solvent (acetone) were added to the crude arachidonic
oil used in Example 1. The resulting homogeneous mixtures were placed in a freezer
held at a temperature of from -18°C to -25°C for 20 hours. A precipitate of crystals
formed at about -15°C to give a 2-phase system of a top layer (liquid) and a bottom
layer (solid, precipitate). The precipitate was separated using a laboratory centrifuge
(type Sigma 4-10) at 5000 rpm for 2 minutes. The hexane from both layers was
removed by evaporation overnight at 30°C in a vacuum and their ARA content was
analyzed by means of gas chromatography (GC) The results are shown below in
Table 3.
| Ratio of Oil:acetone | ARA (g/kg) |
| | Oil:top layer (residual oil) | Oil:bottom layer (precipitate) |
| Original oil | 358 |
| 1:1 | 364 | 351 |
| 1:2 | 399 | 326 |
| 1:3 | 394 | 296 |
| 1:4 | 421 | 261 |
EXAMPLE 4
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Different amounts of solvent (acetone) were added to the crude arachidonic
oil used in Example 1. The resulting homogeneous mixtures were placed in a freezer
held at a temperature of from -18°C to -25°C for 20 hours. A precipitate of crystals
formed at about -15°C to give a 2-phase system consisting of a top layer (liquid,
residual oil) and a bottom layer (solid, precipitate). The precipitate was separated
using a laboratory centrifuge (type Sigma 4-10) at 5000 rpm for 2 minutes. The
acetone was removed from both layers separately by evaporation overnight at 30°C
in a vacuum. The ARA content of both layers was analyzed by means of gas
chromatography (GC) and the results are shown below in Table 4.
| Ratio of Oil:acetone | ARA (g/kg) | Yield |
| | Oil : top layer (residual oil) | Oil: bottom layer (precipitate) | (% of oil recovered from top layer) |
| Original oil | 341 | - |
| 1:3 | 374 | 265 | 59 |
| 1:4 | 382 | 224 | 72 |
| 1:5 | 383 | 204 | 76 |
| 1:6 | 371 | 191 | 77 |
| 1:7 | 372 | 185 | 77 |
| 1:8 | 368 | 183 | 77 |
| 1:9 | 368 | 178 | 78 |
Comparative Example 5
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Arachidonic oil, from the same source as used in Example 1, was placed in a
freezer held at a temperature of from -18°C to-25°C for 20 hours (i.e. with no
precipitate inducer added). The oil was cooled to below -20°C. Surprisingly, even
at -20°C, with no inducer, no precipitate formed.