Note: Descriptions are shown in the official language in which they were submitted.
WO 95/26391 PG"T/EP95/01038
1
~i~~767
Fractionation of triglyceride oils
The present invention is concerned with a process for
fractionating triglyceride oils. The fractionation
(fractional crystallisation) of triglyceride oils is
described by Gunstone, Harwood and Padley in The Lipid
Handbook, 1986 edition, pages 213-215. Generally
triglyceride oils are mixtures of various triglycerides
having different melting points. The composition of
triglyceride oils may be modified e.g. by separating from
them by crystallisation a fraction having a different
melting point or solubility.
One fractionation method is the so-called dry fractionation
process which comprises cooling the oil until a solid phase
crystallises and separating the crystallised phase from the
liquid phase. The liquid phase is denoted as olefin
fraction, while the solid phase is denoted as stearin
fraction.
The separation of the phases is usually carried out by
filtration, optionally applying some kind of pressure.
The major problem encountered with phase separation in the
dry fractionation process is the inclusion of a lot of
liquid olefin fraction in the separated stearin fraction.
The olefin fraction is thereby entrained in the inter- and
7214 (V) Cpl
21 ~ ~'~ ~'~ 2
intracrystal spaces of the crystal mass of the stearin
fraction. Therefore the separation of the solid from the
liquid fraction is only partial.
The solids content of the stearin fraction is denoted as
the separation efficiency. For the dry fractionation of
palm oil it seldom surpasses 50 wt.% . This is detrimental
to the quality of the stearin as well as to the yield of
the olefin.
For the related solvent fractionation process, where the
fat to be fractionated is crystallised from e.g. a hexane
or acetone solution, separation efficiencies may be up to
95%.
Dry fractionation is a process which is cheaper and more
environmentally friendly than solvent fractionation. For
dry fractionation an increase of separation efficiency is
therefore much desired.
It is known to interfere with the crystallisation by adding
to a crystallising oil a substance which will be generally
indicated as crystallisation modifying substance. The
presence of small quantities o.f such a substance in the
cooling oil may accelerate, retard or inhibit
crystallisation. In certain situations the above substances
are more precisely indicated as crystal habit modifiers.
Known crystallisation modifiers are e.g. fatty acid esters
of glucose and derivatives which are described in
US 3,059,011. These crystallisation modifiers are effective
in speeding up the crystallisation rate but are not
reported to increase the separation efficiency. They do not
even allude to such an effect.
Other crystallisation modifiers, e.g. as described in US
3,158,490 when added to kitchen oils have the effect that
solid fat crystallisation is prevented or at least
retarded. Other types of crystallisation modifiers,
particularly referred to as crystal habit modifiers, are
widely used as an ingredient for mineral fuel oils in which
waxes are prone to crystallize at low temperatures. US
AINENDED SHEEP
r~ 7214 (V) cpl
3
3,536,461 teaches the addition of a crystal habit modifier
to fuel oil with the effect that the cloud point (or pour
point) temperature is lowered far enough to prevent crystal
precipitation. Or, alternatively, the solids are induced to
crystallize in a different habit so that the crystals when
formed can pass fuel filters without clogging them.
Other crystal habit modifiers are actually able to change
the habit of the crystallized triglyceride fat crystals in
a way such that after crystallization the crystals, the
stearin phase, can be more effectively separated from the
liquid phase, the olefin phase. Publications describing such
crystal habit modifiers are e.g. US 3,059,010 describing
sucrose fatty acid esters for that purpose, further
GB 1 015 354 or US 2,610,915 where such effect is
accomplished by the addition of small amounts of a
polymerisation product of esters of vinyl alcohol or of a
substituted vinyl alcohol and finally co-pending PCT
application WO 95/04122 with the addition of esterified
copolymers of malefic anhydride and styrene. US 3,059,008
describes the use of dextrin derivatives for the same
purpose. None of them has appeared to be ideal with respect
to high separation efficiency and fitness to be used for
the preparation of food ingredients.
SU 1722377 (DERWENT 93-074294) discloses that fatty acid
monoglycerides influence the crystallisation of milk fat.
Chemical Abstracts 84, (1976) 42219 deals specifically with
monoglycerides of unsaturated fatty acids which accelerate
the crystallization of hardened vegetable oils.
Fatty acid monoglycerides which have been esterified with
citric acid and which are marketed under the name Acidan~
have shown to modify the crystallization rate of
triglyceride fat, particularly glycerol tristearin (J. Am.
Oil. Chem. Soc. 59, (1982) p. 181-185).
STATEMENT OF INVENTION
AMp
WO 95/26391 PCT/EP95/01038
2186764
It has been found that in triglyceride fat fractionation
monoglycerides or diglycerides of fatty acids are suited to
enhance the separation efficiency. Accordingly the
invention relates to a process for separating solid fatty
material crystallised from a triglyceride oil, which
comprises the steps:
a. heating the oil until no longer a substantial
amount of solid triglyceride is present in the oil,
b. cooling and crystallising the triglyceride oil
resulting in a solid stearin phase besides a liquid olefin
phase and
c. recovering the stearin phase by separating it
from the olefin phase,
where before crystallisation starts a crystallisation
modifying substance is added to said triglyceride oil or to
a solution of said triglyceride oil in an inert solvent,
characterized in that the crystallisation modifying
substance is a monoglyceride or diglyceride of fatty acids
optionally esterified with citric acid.
DETAILS OF THE INVENTION
The oil to be fractionated is mixed with the
crystallisation modifying substance (the additive) before
crystallisation starts, preferably before the oil is heated
or dissolved in the solvent so that all solid triglyceride
fat and preferably also the modifying substance is
liquefied.
Then the oil or solution is cooled to the chosen
crystallisation temperature. A suitable temperature range
for e.g. palm oil is 15-35°C. To each temperature belongs a
specific composition of the olefin and stearin phases.
Crystallisation proceeds at the chosen temperature until
the crystallised oil stabilises to a constant solid phase
content. The crystallisation time increases when more solid
phase is desired and the temperature is lowered. Usual
WO 95/26391 7 ~ PCT/EP95101038
7 5
times are in the range of 4-16 hours. During
crystallisation the oil may remain quiescent or is stirred,
e.g. with a gate stirrer. The improvement in separation
efficiency may depend on the mode of crystallisation,
either stagnant or stirred. Often good results are obtained
with stagnant crystallisation rather than with stirred
crystallisation. From the point of view of process economy,
however, stirred crystallization is preferred.
The stearin and olefin phases may be separated by filtration
but for an effective.separation of the solid from the
liquid phase generally a membrane filter press is used,
which allows higher pressures. Suitable pressures are 3-50
bar, exerted for about 20-200 minutes. However, already
with a low or moderate pressure the stearin phase obtained
according to the present invention is easily and with a
high efficiency separated from the olefin. As a rule it
takes about 30-60 minutes to get a proper separation of
both phases.
The solids content of the crystal slurry before separation
and of the stearin phase obtained after separation is
measured according to the known pulse NMR method (ref.
Fette, Seifen, Anstrichmittel 1978, 80, nr. 5, pp. 180-
186).
The effect of the invention is believed to be caused by
alteration of the crystal structure or crystal habit of the
stearin under the influence of the additives. These might
interfere in different ways with the growth of the various
crystal faces.
At microscopic inspection the effect of the presence of the
mono- or diglyceride additives is that the crystals and
crystal aggregates formed in the oil are conspicuously
different from the crystals obtained without those
crystallisation modifying substances. These crystals and
aggregates can be filtered more effectively in that the
stearin fraction retains less of the olefin fraction even at
low or moderate filtration pressure. The altered
WO 95/26391 PCT/EP95/01038
6
crystallisation results therefore in a considerable
increase of the separation efficiency.
The present process for obtaining stearin with increased
solid levels is characterised by the use of crystallisation
modifying substances which are mono- or diglycerides of
fatty acids. The ester group preferably is situated at
either or both of the terminal carbon atoms of the glyceryl
moiety. Optionally the remaining hydroxyl groups) have
been esterified with citric acid, preferably 0.5 - 2 mol
equivalents, so that a part or all the hydroxyl groups have
been esterified.
Generally, the best results are obtained when the length of
the fatty acid side-chains match the length of the fatty
acid chains of the desired stearin phase. Matching chains
should have the same or about the same number of carbon
atoms. Therefore, when palm oil is fractionated, preferred
fatty acids are C14, C16 and C18 fatty acids.
The mono- or diglycerides used in the invention may be
derived from a single fatty acid, such as glycerol
monopalmitate, mono-oleate or dipalmitate, but usually
these are derived from various fatty acids with a
distribution which reflects the fatty acid distribution of
the edible fat used for the preparation of the mono- or
diglyceride.
Although the invention is useful for solvent fractionation
or detergent fractionation, the process preferably is
carried out as a dry fractionation process.
The process can be applied on triglyceride oils containing
relatively high melting fat, for which fractionation is
desired such as palm oil, palm kernel oil, shea oil,
coconut oil, cottonseed oil, butter oil, hardened rapeseed
oil, hardened soybean oil or fractions of these oils.
The process is particularly useful for fractionating palm
oil. The palm oil might be crude, but generally a refined
W0 95/26391 PCT/EP95101038
~igs~ s~ 7
quality is used.
Palm oil contains fully saturated triglycerides SSS. The
palm oil to be fractionated preferably has a SSS content
< 8.5 wt.%, more preferably 7-8.5 wt.% and the palmitic
acid : oleic acid ratio preferably is less than 1.17, more
preferably 1.08-1.16.
The crystallisation modifying substance is suitably applied
in an amount of 0.005 - 5 wt.%, preferably 0.01-2 wt.% on
the total amount of oil.
The mono- or diglycerides to be used according to the
invention can be prepared using common methods for
preparing such well known products. The crystallisation
modifying substances of the present invention are generally
known and marketed as emulsifiers under various trade names
such as DimodanTM.
The citric esters are obtained using standard methods e.g.
by treating the monoglycerides under proper esterifying
conditions with 0.5 - 2 mol equivalents citric acid. The
obtained citric ester is neutralised. Such product is
marketed as an emulsifier by e.g. GRINDSTED under the trade
name AcidanTM.
A major advantage of the present crystallisation modifying
substances is that they have acquired the status of
permitted food ingredients and therefore may be used for
the fractionation of edible oils.
Example 1
Dry fractionation of palm oil
A sample was prepared containing 1000 g of palm oil
(neutralised, bleached, deodorised, having a SSS content of
8 wt.% and a palmitic acid : oleic acid ratio of 1.12) and
WO 95126391 ~ PCT/EP95101038
1 g (0.1%) of Acidan CNTM * . The sample was heated and
stirred at 65°C until completely liquefied (no solid phase
content) and then slowly cooled. Crystallisation proceeded
in a thermostated cabin in a stagnant mode at the chosen
temperature of 23°C until a constant solid phase content
was reached. The sample was filtered and pressed at 12 bar
in a membrane filter press for 30 minutes. After filtration
and pressing, the solid phase content of the cake was
measured and also the weight of the filtrate (the olefin
phase). The stearin yield is the weight of the crystal mass
remaining on the filter expressed as a percentage of the
feed. Table I shows the measured solid phase content of the
slurry, the increase of the solid phase content of the
stearin-cake and the olefin yield.
r Acidan CNT~ is a neutralised citric acid ester of monoglyceride
made from edible, refined, hydrogenated fat as marketed by GRINDSTED,
Brabrand, Denmark.
Examples 2-6
Dry fractionation of palm oil and palm kernel oil
The dry fractionation process of example 1 is repeated with
different additives and two oils (palm kernel oil and palm
oil). The palm kernel oil samples have been pressed at 6
bar, the palm oil ones at 12 bar. The ingredients and the
results are summarized in Table I.
Before filtration samples contained the same amount of
solid fat ((12% for palm oil, 25% for palm kernel oil). The
results of Table I show that the stearin fractions of the
crystallisation modifying substance containing samples 1-6
have retained considerably less olefin than the stearin
fractions of comparison samples A-D.
WO 95/26391 PCT/EP95/01038
9
TABLE I
Ex. Additive Add. Fat Slurry Incre Olefin
wt.% (1) SPC 2) ase % yield
wt.% (3) wt.%
1 AcidanTM (8) 0.16 PO 12 80 80
2 AcidanTM (8) 0.16 PK 25 10 50
3 Glycerol 0.1 PO 12 29 70
monopalmitate
4 Glycerol 0.1 PK 25 20 48
monopalmitate
Glycerol mono- 0.1 PO 12 29 70
oleate
6 Glycerol 0.1 PO 12 20 68
dipalmitate
Comparison
examples
A No additive - PO 12 0 (9) 60
B No additive - PK 25 0 (10 45
C Admul GLPTM 4) 3.0 PO 12 0 40
D Admul 0.05 PO 12 n.d. n.d.
DatemTM (6)
E Admul ACTM (7) 0.16 PO 12 n.d. n.d.
F Tween 60TM (5) 1.0 PO 12 -3 58
n.d. not determined: separation of stearin and olefin
phases not possible
(1) PK = palm kernel oil
PO = palm oil (neutralised, bleached, deodorised,
having a SSS content of 8 wt.% and a palmitic
acid . oleic acid ratio of 1.12)
(2) SPC = solid phase content before stearin/olein
WO 95126391 ~ ~ PCT/EP95/01038
separation
(3) increase of solid phase content, of stearin phase
(SE) compared with crystallization without
additive (comparison examples A and B)
(4) Admul GLPTM = monoacylglyceride esterified with
lactic acid (ex Quest)
(5) Tween 60TM = a sorbitan ester (ex Quest)
(6) Admul DatemTM = monoacylglyceride esterified with
diacetyltartaric acid (ex Quest)
(7) Admul ACTM = monoacylglyceride esterified with
acetic acid (ex Quest)
(8) Acidan TM is a neutralised citric acid ester of a
fatty acid monoglyceride made from edible fat (ex
GRINDSTED)
(9) Separation efficiency of palm oil without
additive ..... ??
(10) Separation efficiency of palmkernel oil without
additive ..... ??
When the additive is a mono- or diglyceride esterified with
another acid than citric acid, as in comparison examples C,
D and E, no increase of the solid phase content during dry
fractionation is achieved.
When using another well known emulsifier as additive as in
example F even a negative effect is observed.
