Technical Field
[0001] The field of the invention is the refining of fat, particularly but non-exclusively
the refining of vegetable butters.
[0002] From whatever source they are obtained, fats require purification in a refining process,
to remove impurities and improve both the appearance and performance of the fat. In
the edible context with which the invention is concerned, taste also is improved by
refining. The invention is particularly concerned with a class of fats known generally
as vegetable butters from their relatively high melting characteristics, compared
with the majority of fats from vegetable sources which are generally liquid at ambient
temperatures and are usually described as vegetable oils.
[0003] Oils and fats may be classified into two distinct groups differing markedly both
in their properties and stability and require very different approaches in detail
to refining processes applied to them. Those high in polyunsaturation, including linoleic
and more highly unsaturated fatty acids, and prized accordingly for their dietetic
value, may contain 40% or more of these acids in their glycerides, they are liquid
at ambient temperature and are susceptible to the development of reversionary flavours
after refining, owing to their susceptibility to oxidation arising from their high
degree of unsaturation. Examples of these high PUFA vegetable oils include soyabean
containing 52% polyunsaturated fatty acids, cottonseed (53%), groundnut (32%), linseed
(65% including no less than 53% of triunsaturated fatty acid), safflower (77%) and
sunflower (64%). Marine oils are also notable for their high PUPA content.
[0004] In contrast, most animal fats are substantially less unsaturated. They are accordingly,
high-melting and less prone to flavour reversion as are vegetable butters. Like most
other vegetable fats, vegetable butters consist principally of triglycerides of predominantly
Cl6 and C
18 fatty acids, but vegetable butters contain more saturated fatty acids. These are
distributed principally in the alpha- or 1- and 3-positions of the triglycerides which
constitute the principal component of fats and in this vegetable butters closely resemble
cocobutter and in their refined form are therefore used as cocoabutter substitutes
since the close similarity of their structure is matched by similar melting performance
including most importantly, organoleptic response. Examples of vegetable butters include
cocobutter itself with only 4% linoleic acid, shea (10%), sal (2.8%) mango kernel
(5%) and mowrah (up to 18%), with palm oil (10%).
[0005] The application of selective adsorption methods for the removal on an industrial
scale of impurities from glyceride oils and fats is a relatively recent event in refinery
practice. A miscella is made of the fat or oil in a suitable organic solvent, usually
a hydrocarbon such as hexane, and the solution brought into contact with an appropriate
adsorbent material of suitable particle size. The process necessitates removal of
the solvent from the raffinate solution and is therefore expensive to operate. The
cost of the process may also be prohibitively high if the effective life of the adsorbent
is short. Nevertheless, the removal of the small quantities of polar compounds present
may have a dramatic effect, particularly on the melting characteristics of vegetable
butters and is not readily achieved by alternative methods. The invention is particularly
useful therefore in reducing the cost of achieving high quality fats for edible purposes
such as chocolate manufacture and also for pharmaceutical application by enhancing
the effective life of adsorbents used for producing such fats.
Background art
[0006] USP 2,976,156 discloses a method of refining liquid vegetable oils by contact with
alumina adsorbent in which it is recommended that bleaching treatment can be omitted.
[0007] USP 3,955,004 discloses a similar process to that of USP 2,976,156 and in addition
discloses as adsorbent mixtures of silica and alumina. The oils, which include coconut,
palm kernel and palm oil, are dissolved in a suitable solvent. After contact with
the adsorbent, the refined oil is separated from the solvent and bleached.
[0008] French Patent 990704 discloses bleaching a solution of glyceride oil and subjecting
the solution to silica treatment. None of these references reveals the necessity for
combining the application of adsorption and bleaching steps with regeneration as provided
for by the present invention and applied to vegetable butters to be fractionated.
\
[0009] USP 4,284,580 describes the fractionation of triglyceride mixtures by selective adsorption
on surface- aluminated silica gel adsorbent. The process disclosed in this reference
relies upon differential adsorption characteristics exhibited by different degrees
of unsaturation between the many triglycerides of glyceride oils and fats in order
to obtain fractions of different Iodine Values.
[0010] Indian Oil Soap Journal (1969), 34 (7), pages-147-150. Laboratory scale purification
of sal oil is described in which crude sal oil is purified by chromatography in benzene
solution over an alumina column. No column regeneration is described, nor was the
solution pre-bleached.
[0011] USP 2,589,097 describes the removal of reversionary flavours from soyabean and similar
highly unsaturated oils, which may first be bleached, using column adsorption treatment.
[0012] European Patent Application 53016 published 2nd June 1982 describes refining sal
fat by contact with a specially prepared particulate adsorbent in a column.
General description of the invention
[0013] This invention relates to fat refining, particularly but not exclusively to refining
vegetable butters.
[0014] Fats may be refined by contact, in a solution or miscella of a non-polar solvent,
with an adsorption agent, usually packed in a column and based on silica and/or alumina
activated by heat treatment. The adsorption agent selectively retains polar impurities,
for example partial glycerides and colouring matter, and oxidised compounds which
are highly polar, whereas the triglycerides constituting the principal components
of the fats remain unabsorbed in a raffinate from which the purified fat is recovered
by removing the solvent.
[0015] The absorption agents become less effective with prolonged and/or repeated use, as
polar compounds accumulate on them. Desorption of these polar compounds by treatment
with polar solvents is incompletely effective with the more tenacious polar compounds
absorbed from vegetable butters such as shea, sal and others. We have now found that
regeneration is facilitated by subjecting the fat or the fat miscella to pretreatment
by contact with bleaching earth and/or active carbon, to adsorb the more highly polar
compounds before treatment with the adsorption agent, preferably packed in a column
through which the miscella is percolated. The less highly polar compounds, e.g. diglycerides,
adsorbed by the adsorption agent may then be readily removed in a subsequent desorption
step, e.g. by percolation with a polar solvent. The refined fat may be separated from
the raffinate, for example by distilling off the non-polar solvent, or by fractional
crystallisation, preferably to recover a fat fraction having a slip melting point
of at least 35°C.
[0016] Excepting the lauric fats, e.g. palm kernel and -coconut oil, about
1/3 of the triglycerides of the fats with which the invention is chiefly concerned
are symmetrical, disaturated C
16/C
18 triglycerides.
[0017] Generally they contain less than 20% linoleic acid and, for the most part, not more
than 10% and are low in polyunsaturated fatty acids generally.
[0018] Such fats are usually expelled or extracted from tropical or sub-tropical fruit,
either the fruit seeds or whole fruit. Although sometimes cultivated in plantations,
as for palm oil, usually the fruit grows wild and is collected at irregular intervals
in the forests after having fallen. Due to the prevailing elevated temperature and
the moisture content of the earth, extensive enzymic reaction can occur, converting
the natural triglycerides of the fats contained in the fruit seeds or in the pericarp
by hydrolysis to mono- and diglycerides and free fatty acids. Other common reactions
encountered in the fruit are hydroperoxidation, epoxidation and hydroxylation of the
unsaturated fatty acid radicals contained in the triglycerides of the fat. These enzymic
reactions produce a host of highly polar compounds which adhere tenaciously onto adsorbents,
both on their surface and in their pores, which makes their desorption very difficult
and which consequently result in the failure to regenerate the adsorbents for re-use.
[0019] The solvent in the fat miscella is preferably hexane or other inert aliphatic hydrocarbon
compositions, preferably with a boiling point below 100°C to facilitate evaporation
from the miscella without exposing the fat to excessively high temperatures. The fat
in the miscella may be in crude form or undergo some preliminary refining beforehand,
preferably neutralisation.
[0020] Regeneration comprises desorption and reactivation, preferably effected in two steps.
In the first step adsorbed polar compounds are desorbed from the adsorbents by contact
with a polar organic solvent which preferably comprises a monohydric fatty alcohol
containing up to 6 carbon atoms and particularly methanol, ethanol and isopropanol,
and alcohol-hydrocarbon mixtures, preferably aliphatic, which may be miscible or immiscible,
preferably azeotropic mixtures to facilitate removal from the regenerated adsorbent
by evaporation. In the second step, residual polar solvent (e.g. methanol) used for
the desorption operation is driven out of the column by heating and preferably a volatile
aliphatic hydrocarbon, e.g. hexane either in the vapour phase or as a superheated
liquid. The formation of azeotropic mixtures is also helpful in this case. Herein
the first step is called "desorption" and the second step "reactivation".
[0021] Pretreatment, adsorption and desorption are preferably carried out at temperatures
from 15 to 75°C, more preferably not in excess of 60°C, but pretreatment in particular
may be carried out at temperatures from 30 to 110°C and adsorption and desorption
at 40 to 80°C. Adsorption is preferably effected in particular at 30 to 60°C, particularly
approximately between 20 and 50%.
[0022] Reactivation is preferably carried out between 50 to 170°C. Substantially less bleaching
aid or active carbon is used in the pre-treatment step than adsorption agent, from
0.5 to 5% by weight of the fat being adequate for the former, but with preferably
a fat:adsorbent ratio from 10:1 to 1:1 by weight of the fat. Preferably both the pre-
treatment and adsorption steps are applied to the same solution of fat.
[0023] Suitable bleaching earths for use in the invention include activated Fuller's earth,
for example Tonsil and Fulmont, Lucilite, Kieselsaure of Degussa. Granulated or non-granulated
active carbon, e.g. Norit, may alternatively or in addition be used. Bleaching earths
are usually acid-activated natural earths of structures typified by Montmorillonit
and Bentonit. Acid treatment increases their propensity for adsorption of highly polar
organic compounds including highly polar pigments, e.g. chlorophyll. These earths
are not suitable for the adsorption of bulk amounts of diglycerides etc, but very
useful in the preliminary treatment step for the removal of small amounts of highly
polar organic compounds prior to the treatment of the fat with adsorbents like silica
gel or A1
20
3. These highly polar compounds otherwise prevent the regeneration of the adsorbents
like silica gel and make their reuse difficult, if not impossible.
[0024] Active carbon also adsorbs highly polar compounds both by surface adsorption (e.g.
pigments etc) and also by π-electron interaction (e.g. aromatic compounds, polyene
compounds, etc). All active carbons, both granulated and non-granulated, are suitable
for this purpose and may be used in conjunction with bleaching earths.
[0025] The adsorption agent may comprise silica gel, alumina or mixtures thereof including
co-precipitates. Examples of aluminas include gibbsite and bayerite and among proprietary
examples include Aluminiumoxid 504C. Suitable silica gels include Sorbsil of Messrs
J Crosfield & Sons Limited, Warrington, England and Kieselgel-M of Messrs Herrmann,
Cologne, Germany.
[0026] Preferably adsorption is effected by percolating the miscella through a column packed
with the adsorbent and with a length:diameter ratio of 5:1 to 1:2, particularly approximately
equal diameter and length, with a residence time in the column of 5 to 30 minutes,
especially 15 minutes.
[0027] Adsorbents suitable for use in the process of the invention preferably exhibit a
specific surface area of 300 to 500 m2/g, a pore volume of 0.7 to 1.5 mls/g, an -
average pore diameter of 30 to 2000 A, preferably 60 to . 180 A, a weight:volume ratio
of 0.2:0.5 g/ml and pH of 6.5 to 7.5. Preferably silica gel adsorbent used in this
invention contains more than 95% Si0
2 with not more than approximately 4 to 8% of volatiles removed at 140°C after 4 hours.
Particle size by sieve analysis should preferably include not more than approximately
5% of 0.3 mm and not more than 25% of 0.2 mm.
EXAMPLE 1
[0028] 40 g of the neutralised solid fraction (0.1% free fatty acids) remaining from dry
fractionating crude sal fat obtained by solvent extraction of the seeds of sal fruits
(Shorea robusta) were dissolved to form a 20% solution in hexane which was pretreated
with 2% bleaching earth Tonsil
ACCFF and 0.4% active carbon Norit FND at 25 to 40°C with agitation for 45 minutes before
the bleaching earth and the carbon was filtered off and the pretreated hexane solution
passed at 40°C down a column 3 cm in diameter and 21 cm long, packed with silica gel
(Kieselgel M of Messrs Herrmann, Cologne), using a residence time of 12 minutes and
a fat:gel ratio of 2:1. After collecting the eluate raffinate the silica was regenerated
by washing in the column with isopropanol/hexane 20/80 mixture, removed from the column
and dried at 160°C for 16 hours and reused as before, adopting the same quantity of
fat each cycle. Particulars of the gel are as follows:- Specific surface area 450
m
2/g, pore volume 0.73 mls/g, average pore diameter 60A weight:volume ratio 0.43 g/ml,
pH 7.2, SiO
2 99.0%, volatiles as above 2.4%, sieve analysis 2% of 0.2 mm, 75% of 0.1 mm, 18% of
0.063 mm and 4.5% of 0.05 mm and 0.5% of 0.04 mm.
[0029] 5 cycles were completed and the fat recovered from the eluate raffinate and examined
after each upon removing the solvent.
[0030] The same fat and the same gel was used for a similar series of experiments in which
the miscella pretreatment with bleaching earth and active carbon was omitted. After
5 regeneration cycles the eluate fats and the used silica gels were compared with
each other.
[0031] Results appear in the accompanying Table 1, in which the Lovibond measurements were
made in a 1" cell for the crude fat and a 2" cell for the treated samples.
[0032] The results show that the silica-treated raffinates which are miscella-bleached prior
to silica treatment, remain consistently high in quality, even after several recycles,
whereas those without previous miscella-bleaching show progressive deterioration in
properties with increasing recycling of the silica. This is also reflected in the
colour measurement of the silicas after the 6th regeneration. The sample used for
treating the miscella-bleached samples showed a lighter colour (yellow index 27.3
as measured by Zeiss Elrepho instrument) than the corresponding sample used for treating
the fat without previous miscella-bleaching (yellow index 42.6).
EXAMPLE 2
[0033] A solution in hexane of neutral illipe fat was pre- treated with bleaching earth
and carbon as described in Example 1 and passed down a column 0.85 m in diameter,
packed to a depth of 0.85 m with silica gel of the type "Sorbsil" from Messrs J Crosfield
& Sons Ltd, Warrington, England, the weight of silica gel being the same weight as
the fat. The gel characteristics were as follows:
Total surface = 331 m2/g, pore volume = 1.16 ml/g, pore diameter = 140 A, pH = 7.6, weight:volume ratio
= 0.35 g/ ml, SiO2 content = 99.1%, particle size = 85.5% between 0.05 and 0.2 mm, 5.5% above 0.3 mm
and 9% below 0.05 mm.
[0034] After distilling off the hexane a light-coloured refined fat practically free of
diglycerides was obtained from the refined solution.
[0035] The spent silica column was then washed down at 80°C under pressure with an azeotrope
mixture of isopropanol and hexane in a weight ratio of 22:78, to desorb and remove
the material adsorbed on the silica. The column was then reactivated for reuse by
passing down hexane at 180°C and 13-bar. The reactivated silica column was used again
to refine a fresh batch of neutralised illipe, pre-treated as described, the whole
cycle of refining, desorption and reactivation being repeated 15 times.
[0036] Neutralised illipe from the same batch was similarly refined by treatment with silica
but without the pre-treatment. The silica progressively lost its adsorptive capacity
with repeated reuse. This was shown by the increasing diglyceride content of the refined
fat and its increasing colour and also by the considerable drop in stabilised dilatation
values D of the fat at 32.5°C. These results are shown in Table 2 and clearly demonstrate
that the miscella pre-treatment purifies the neutralised fat to such an extent that
after subsequent silica treatment the spent silica can be regenerated successfully
by desorbing with a mixture of isopropanol and hexane and reactivated by superheated
hexane. Such a regenerated silica gel can be reused for satisfactory diglyceride removal
from the illipe fat. Omission of the pre-treatment eventually renders the spent silica
non-regenerable, as evidenced by total failure to adsorb diglycerides after limited
reuse.
EXAMPLE 3
[0037] A solution of neutralised shea nut fat in twice its weight of hexane, was bleached
at 80'C with 2% bleaching earth "Tonsil ACCFF" from Messrs Sudchemie, Munich, Germany.
The filtered solution was passed through a column as before, but packed with silica
"Kieselgel M" from Messrs Herrmann, Cologne, Germany, using half as much gel as fat
by weight and a refined fat recovered by evaporating the solvent from the treated
solutions.
[0038] The spent silica was desorbed in the column by washing with a mixture of 85 vol %
hexane and 15 vol % methanol at 50°C and reactivated by passing hexane vapour under
pressure at 90°C inlet temperature through the column, until methanol was completely
driven out. The column was reactivated and reused 5 times, the diglyceride content
being determined of the fat recovered after each use.
[0039] In a control test the unbleached neutralised fat was similarly refined and the diglyceride
content of the refined fat compared as shown in Table 3, from which it is evident
that bleaching prior to silica treatment exercises a beneficial effect on regeneration
and reuse of the silica.
1. Process for refining glyceride fats by contact with adsorbent material to remove
polar impurities by selective adsorption, wherein the fat is first contacted with
bleaching earth or active carbon and then in organic solution with a particulate adsorbent
and refined fat recovered from the raffinate solution and separated therefrom.
2. Process according to Claim 1, in which the fat comprises a vegetable fat low in
polyunsaturated fatty acids.
3. Process according to Claim 2, in which the fat is shea, sal, illipe, mango kernel,
aceituno, palm, olive oil or fractions or mixtures thereof.
4. Process according to any of the preceding claims, wherein the refined fat is fractionated
by fractional crystallisation to recover a fraction having a slip melting point of
at least 35°C.
5. Process according to any of the preceding claims, wherein the solvent is an aliphatic
hydrocarbon.
6. Process according to Claim 5, wherein the solvent comprises hexane.
7. Process according to any of the preceding claims, wherein the adsorbent is periodically
regenerated.
8. Process according to Claim 7, wherein the regeneration comprises desorption and
reactivation steps, wherein the adsorbent is first contacted with a polar organic
solvent and subsequently heated to remove residual solvent.
9. Process according to Claim 8, in which adsorption and desorption are effected at
40 to 80°C.
10. Process according to Claim 8 or 9, in which reactivation is effected at 60 to
170°C.
11. Process according to any of the preceding claims, in which the fat:adsorbent ratio
is 1:1 to 10:1 by weight of the fat.
12. Process according to any of the preceding claims, in which from 0.5 to 5% of bleach
or active carbon is used by weight of fat.
13. Process according to any of the preceding claims, wherein the bleach comprises
Fullers' Earth.
14. Process according to any of the preceding claims, wherein the adsorbent comprises
silica gel, alumina, or their mixtures or coprecipitates.
15. Process according to any of the preceding claims, wherein the adsorbent is packed
in a column with a length: diameter ratio of 5:1 to 1:2.
16. Process according to any of the preceding claims, wherein the residence time of
the adsorbent is from 5 to 30 minutes.
17. Process according to any of the preceding claims, wherein the adsorbent exhibits
a specific surface area of 300 to 500 m2/g, a pore volume of 0.7 to 1.5 mls/g, an average pore diameter of 30 to 2,000A and
a weight:volume ratio of 0.3:0.5 gms/ml.
18. Process according to any of the preceding claims, wherein the particle size of
the adsorbent includes not more than about 5% of 0.3 mls and not more than 25% of
0.2 mls.
19. Process according to any of the preceding Claims 7 to 18, wherein the adsorbent
is regenerated by contact with an azeotrope.
20. Process according to Claim 1 substantially as hereinbefore described with reference
to the accompanying Examples.
21. Fats whenever refined by a process as claimed in any of the preceding claims.