The storage properties of edible oils are improved by first contacting
the oil, in solution in a non-polar solvent, with a metal or metalloid
oxide adsorbent in a column, and subsequently treating the oil with
a bleaching earth after the solvent has been removed.
What is claimed is:
1. A process for treating edible glyceride oil to improve its colour
and its storage properties, in which the edible glyceride oil, in
solution in a nonpolar solvent, said solution containing from 10-95%
by weight of the solvent, is first contacted at a temperature between
0-60.degree.C with a metal oxide or metalloid oxide adsorbent with
an average pore size of between 30-2000 A selected from the group
consisting of silicas and aluminas and mixtures thereof in a column
containing the adsorbent, in a ratio of oil to adsorbent of 0.3:1
to 20:1 and the oil is subsequently treated with a bleaching earth
after removal of the solvent from the oil.
2. A process according to claim 1 in which the oil is further
subjected to a deodorizing treatment.
3. A process according to claim 1 in which the oil is subjected
to an alkali refining before treatment with the adsorbent.
4. A process according to claim 1 in which the oil is an untreated
crude oil and the adsorbent is silica gel.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for treating edible
glyceride oils. More particularly, this invention relates to a process
for treating edible glyceride oils to improve their storage properties,
comprising treating edible glyceride oils with particular adsorbents
and a bleaching earth in a determined sequence.
2. Description of the Prior Art
It is well-known that edible glyceride oils tend to develop "off-flavours"
during storage, causing said oils to become less and less acceptable
for edible purposes. To reduce the formation of off-flavours and
to improve generally the storage properties of edible glyceride
oil, it has therefore been common practice to subject the edible
glyceridic oil to a refining treatment. However, even such edible
oils may still show a tendency to form off-flavours, especially
under prolonged storage conditions.
Various refining treatments are known in the art, the most common
method being desliming, neutralisation, earth bleaching and steam
deodorisation. However, particularly with glyceride oils which have
already a strong unacceptable flavour of their own, such processes
do not always yield an edible glyceride oil with satisfactory storage
properties. It has now been found that by subjecting an edible glyceride
oil first to a treatment with a suitable adsorbent, and subsequently
to a treatment with a bleaching earth, significant improvements
are achieved in the storage properties of the edible glyceride oil.
It has already been proposed in the art to treat edible glyceride
oils with an adsorbent. Thus, British Patent Specification No. 865807
describes a process for treating edible oils with activated alumina,
in which process the oil is in solution in a non-polar solvent.
The oil, preferably in unbleached condition, is passed through a
column which contains the alumina, and subsequently deodorised with
steam. Another proposal is given in French Patent Specification
No. 990704 according to which the oil, dissolved in a solvent,
is passed through a column containing a silica gel. The oil may
be a crude oil, or an oil which has undergone a bleaching treatment.
SUMMARY OF THE INVENTION
It has now been found that a significant and unexpected improvement
is obtained in the storage stability of edible glyceride oils, treated
in solution in a column containing an adsorbent such as silica gel
or alumina, if the edible glyceride oil is subsequently bleached
with a bleaching earth. Whereas the prior art teaches that the oil
is treated with the adsorbent instead of the bleaching treatment
with a bleaching earth, or bleached before said treatment with the
adsorbent, it has now been found that a subsequent bleaching step
gives unexpected advantages which are not obtained if the two treatments
are carried out in reverse order, i.e. first bleaching and then
treating the oil with an adsorbent.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention therefore relates to a process for treating
edible glyceride oil to improve its storage properties, in which
the edible glyceride oil, in solution in a non-polar solvent, is
contacted with an adsorbent in a column containing the adsorbent,
and is characterized in that the oil, after said treatment with
the adsorbent, is treated with a bleaching earth.
The edible glyceride oils which can be treated according to the
present invention are all the edible glyceride oils well-known in
the oil and fat industry. Examples thereof are coconut, palm, palmkernel,
marine, soyabean, linseed, rapeseed, sunflowerseed, safflower, cottonseed,
grapeseed oil and so on.
The benefit of the present invention is particularly obtained with
palm oil, soyabean oil and grapeseed oil. The edible glyceride oils
can be treated in a crude form, i.e. in the form of a solution in
a non-polar solvent, e.g. in the miscella, or they may already have
undergone some pre-refining treatment. It is of advantage if the
edible glyceride oils have been subjected to an alkai pre-refining
step, in which the free fatty acids are neutralized.
It is essential that the edible glyceride oil should be in solution
in a non-polar solvent when being treated with the adsorbent. Suitable
non-polar solvents are petroleum fractions, pentane, hexane, cyclohexane,
heptane and the like, including mixtures of various non-polar solvents.
Particularly suitable is a petroleum fraction with a boiling point
in the range of 63.degree. - 71.degree.C. The amount of solvent
may vary from 10 - 95% by weight of the solution, and generally
varies from 50 - 80% by weight of the solution.
As stated above, the edible glyceride oil, in solution in a non-polar
solvent, is contacted with an adsorbent. Although this contacting
could be carried out in a simple stirring or percolating process,
sufficient contact time being the governing factor, advantageously
and hence preferably the contacting is carried out in a column which
contains the adsorbent, as e.g. described in British Patent Specification
No. 865807 and French Patent Specification No. 990704.
The temperature at which the contacting may be carried out may
vary widely. For most practical purposes the temperature will lie
between 0.degree. and 60.degree.C, and preferably between 10.degree.
The amount of adsorbent to be used is dependent upon a number of
factors, e.g. pore size of the adsorbent, type of adsorbent, thickness
of the layer in the column, throughput in the column, and so on.
In general the ratio of oil to adsorbent varies between 0.3 : 1
and about 20 : 1. The adsorbent to be used in the present invention
are metal oxides and metalloid oxides, particularly alumina and
silica. Particularly silicas in the form of silica gels are especially
suitable in the present invention. Mixtures of silicas and aluminas
may also be used, as well as mixtures of silicas or aluminas with
other adsorbents, provided the amount of silica or alumina is predominant.
The silica or alumina must neither be too fine nor too coarse.
In general such silicas or aluminas are used which have an average
pore size above 30 A, preferably between 50 and 2000 A. Suitable
examples of aluminas and silicas to be used in the present invention
are aluminas such as gibbsite or bayerite, and silicas such as silica
gels known under the trade names Sorbsil (Joseph Crosfield and Sons,
Warrington, UK) and Kieselgel M (Fa. Herrman, Cologne, Germany).
Other examples of suitable aluminas or silicas are Aluminiumoxid
504C (Fluka AG, Buchs, Switzerland), Kieselgel No. 7734 (E. Merck,
Darmstadt, Germany) and Silica Gel Type 62 (Grace GmbH., Bad Homburg
After contacting with the adsorbent, the edible glyceride oil is
subjected to a treatment with bleaching earth. This treatment is
carried out under the conditions for a bleaching treatment with
a bleaching earth. Such conditions are: temperature generally from
50.degree. to 120.degree.C, pressure generally from 1 to 760 mm
Hg, amount of bleaching earth generally from 0.05 to 5%.
Various usual types of bleaching earths may be used, mostly activated
fuller's earth. Suitable examples are commercial products like Tonsil
ACCFF, Tonsil 60 C (Fa. Sudchemie, Munich, Germany), furthermore
Fulmont C300 (Laporte Industries Ltd., Redhill, U.K.).
It has been found that in the process of the invention less bleaching
earth is required than in conventional bleaching processes. Preferably
the amount of bleaching earth is from 0.05 to 0.5%. The bleaching
earth treatment may be carried out directly after the oil has been
contacted with the adsorbent, or may be carried out after the oil
has undergone further refining treatments such as desliming, neutralization
and the like. The latter will take place e.g. when a crude oil is
contacted with the adsorbent. In this respect it has been found
that if silica gel is used as the adsorbent material, a pre-neutralization
step is superfluous, as the silica gel adsorbs practically all free
fatty acids present in the crude oil.
Silica gel has, moreover, the further advantage over e.g. alumina
that it hardly adsorbs the tocopherols which are useful as antioxidants
and vitamins in the edible glyceride oils.
It is essential that the treatment with bleaching earth is carried
out when the solvent has been removed from the oil, e.g. by distillation.
In carrying out the process of the invention clear edible glyceride
oils are obtained with improved storage properties, particularly
with regard to a significantly reduced tendency to form off-flavours
on prolonged standing. In comparison with conventional refining
treatments, the fatty acid composition of the glyceride oil remains
practically unaltered and particularly the amount of essential fatty
acids remains unchanged.
After the bleaching step the oil may further be subjected to all
usual treatments to obtain edible oils suitable for particular purposes.
It has been found that a subsequent deodorizing treatment, e.g.
with steam, may further improve the colour and the storage properties
of the oil. Hence a preferred embodiment of the present invention
is a three-step process comprising treatment with adsorbent, treatment
with bleaching earth and steam deodorization.
The present invention will further be illustrated by way of Example.
Four samples of soyabean oil were used. Samples I - III had been
subjected to an alkali neutralization and were used as a 25% hexane
solution, Sample IV was a crude oil in miscella (abt. 30% oil in
70% hexane). These solutions were contacted with Kieselgel M (ex
Fa. Herrmann, Cologne, Germany) which had an average pore size of
50 - 200 A, in a column. The column had a diameter of 12 cm, a height
of 100 cm and a volume of 11.3 liters.
The silica gel was slurried in hexane and was allowed to stand
for 1 hour. The column was half filled with hexane and the silica
gel slurry was brought into the column. After closing the top of
the column the oil in solution was pumped into the column at the
bottom. The oil solution was kept at a temperature of 20.degree.C
and 50.degree.C respectively, before feeding into the column by
means of a heat exchanger. The jacket of the column was kept at
the same temperatures. The residence time was 0.25 h., the through-flow
At each column treatment various fractions were collected, which
are characterized as follows:
oil/silica gel ratio (in kg/kg) Sample I 1.2 - 1.6 Sample II 1.3
14 1.6 Sample III 0.54 - 1.2 Sample IV 0.47 - 2.1
In all fractions no epoxytriglycerides could be determined. Complete
adsorption of the epoxytriglycerides at the silica gel is an indication
for the proper performance of the column treatment. After evaporation
of the hexane the oils were bleached with 2% bleaching earth (Tonsil
ACCFF ex Fa. Sudchemie, Munich, Germany) for 20 minutes at 105.degree.C/1
mm Hg. Thereafter the oils were deodorized for 5 hours at 180.degree.C/1
mm Hg with 60% water. In the case of the crude oil (Sample IV) the
column treatment was followed by a desliming process prior to the
earth bleaching. The results of these experiments were as follows:
Appearance: all oils were colourless after the treatment.
Storage properties: 50 g samples of the treated oils were stored
in the dark in 100 ml bottles with air head space.
The taste of the oils was assessed at regular intervals over a
period of 14 weeks by a test panel consisting of 12 - 15 persons
familiar with soyabean oil taste. A comparison was made between
the oils treated according to the present invention, oils which
had been conventionally refined and oils which had been treated
with silica gel but without subsequent bleaching. The results are
shown in FIGS. 1-4. These results clearly show a significant improvement
of the oils treated according to the present invention.
A sample of grapeseed oil was used. The oil had been subjected
to a desliming treatment with water, an alkali neutralization and
a soda-waterglass boiling. After filtration 560 g oil were dissolved
in 1120 ml hexane. This solution was contacted with Kieselgel M
(ex Fa. Herrmann, Cologne, Germany) which had an average pore size
of 50 - 200 A, in a column. The column had a diameter of 6 cm, a
height of 50 cm and a volume of 1.4 liters.
140 g silica gel were slurried in hexane and allowed to stand for
1 hour. The column was half filled with hexane and the silica gel
slurry was brought into the column. After the level of the hexane
was lowered to the level of the silica gel, the grapeseed oil solution
was brought into the column. It passed through the silica gel within
4 hours. The process was kept at a temperature of 20.degree. C.
The yield of the silica gel treated oil was increased up to 93%
by washing the silica gel with fresh hexane. After evaporation of
the solvent the oil was subsequently bleached with 2% bleaching
earth (Tonsil ACCFF ex Fa. Sudchemie, Munich, Germany) for 20 minutes
at 105.degree.C/1 Hg. Thereafter the oil was deodorized for 5 hours
at 210.degree.C/1 mm Hg with 60% water.
Appearance: the oil was almost colourless
Lovibond colour in a 2 inch cell: 2 yellow
Storage properties: 50 g samples of the treated oils were stored
in the dark in 100 ml bottles with air head space.
The taste of the oil was assessed at regular intervals over a period
of 14 weeks by a test panel consisting of 12 - 15 persons.
A comparison was made between the oil treated according to the
present invention and the oil which had been conventionally refined,
i.e. without silica gel treatment. The taste of the fresh deodorized
oil treated according to the present invention was excellent. The
keeping quality of the silica gel refined grapeseed oil was satisfactory
for more than 8 weeks.
The appearance of the conventionally refined grapeseed oil was
an intensive green. The Lovibond colour in a 2 inch cell was 40
yellow, 0.3 red, 9 blue. The taste of this oil was objectionable
already after deodorization. These results clearly show a significant
improvement of the oil treated according to the present invention.
Four experiments were carried out with soyabean oil, in which the
order of the treatment with the adsorbent and the bleaching earth
The treatment with the adsorbent in the column was carried out
both in the presence as well as in the absence of a solvent, as
was the bleaching treatment.
The conditions for the treatment with the adsorbent in the column
adsorbent: silicagel as in Example I
ratio oil/silicagel: 100:25 parts by weight in the case of the
treatment in miscella, 500 g oil were dissolved in 1166 g hexane.
The conditions for the treatment with bleaching earth were:
bleaching earth: Tonsil ACCFF as in Example I
pressure: 1 mm Hg
time: 30 min.
ratio oil/bleaching earth: 100:2 parts by weight.
In the case of the treatment in miscella, the miscella was stirred
under reflux conditions for 30 minutes at 65.degree.C. The miscella
consisted of 1166 g hexane and 500 g oil.
The order of the treatments was as follows:
A: miscella silicagel treatment, then bleaching
B: miscella silicagel treatment, then miscella bleaching
C: bleaching treatment, then miscella silicagel treatment
D: miscella bleaching treatment, then miscella silicagel treatment
The thus treated oils were stored and assessed as to their taste
in the manner as described in Example I. An oil with acceptable
properties should have an initial assessment of >6 and should
have an assessment after 10 weeks' storage of not significantly
less than 5.
In FIG. 5 the results of the assessments are shown. It is clear
from these results that process A gives the best results, and that
process B is better than processes C and D, which are not according
to the present invention.