Fractionation of triglyceride oils

Process for separating solid fatty material from a triglyceride oil, which comprises the steps PA1 a. heating the oil or a solution of the oil in an inert solvent until no longer a substantial amount of solid material is present, PA1 b. adding a crystallisation modifying substance to the oil or to the solution of the oil, PA1 c. cooling the oil resulting in crystallising a solid stearin phase besides a liquid olein phase and PA1 d. recovering the stearin phase by separating it from the olein phase, characterized in that the crystallisation modifying substance is a polysaccharide being an inulin or phlein with a molecular weight of 500-3990 Da, preferably 1300-2500 Da, of which at least 50% of the hydroxyl groups on the saccharide subunits are connected to (C8-C24) unbranched alkyl chains and the remaining hydroxyl groups, optionally, are connected with a (C1-C7)-alkyl chain, preferably in the form of an acetic ester.

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. 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 olein 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 olein fraction 
in the separated stearin fraction. The olein fraction is thereby entrained 
in the inter- and 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 the 
yield of the olein. 
For the related solvent fractionation process, where the fat to be 
fractionated is crystallised from a e.g. 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 of 
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. sucrose fatty acid esters, described in U.S. Pat. No. 
3,059,010 and fatty acid esters of glucose and derivatives, described in 
U.S. Pat. No. 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 U.S. Pat. No. 
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. U.S. Pat. No. 
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 olein phase. Not pre-published patent 
application WO 95/04122 deals with dry fractionation using esterified 
inulins and phleins as crystal habit modifiers. Publications describing 
such habit modifiers are e.g. GB 1 015 354 or U.S. Pat. No. 2,610,915 
where such effect is accomplished by the addition of a small amounts of a 
polymerisation product of esters of vinyl alcohol or of a substituted 
vinyl alcohol. U.S. Pat. No. 3,059,008 describes the use of dextrin 
derivatives for the same purpose. However, these crystallisation modifying 
substances are still far from ideal. In the former case after three days 
of crystallization an increase in olein yield from 71% to only 82% was 
reported. 
Although such improvement may seem fair, a need exists for more powerful 
crystallisation modifying substances which act faster and in a dry 
fractionation environment and which deliver still better improvements in 
olein yield. The selection of such habit modifiers is a problem, because 
it is not possible to predict which substances will succesfully comply 
with these requirements. 
STATEMENT OF INVENTION 
Polysaccharide esters have been found which are suited as crystallisation 
modifying substances. In contrast to many modifiers of the prior art, the 
present ones greatly increase the separation efficiency. 
Accordingly the invention relates to a process employing such modifiers for 
separating solid fatty material from a triglyceride oil, which comprises 
the steps 
A. heating the oil or a solution of the oil in an inert solvent until no 
longer a substantial amount of solid material is present, 
B. adding a crystallisation modifying substance to the oil or to the 
solution of the oil, 
C. cooling the oil resulting in crystallising a solid stearin phase besides 
a liquid olein phase and 
D. recovering the stearin phase by separating it from the olein phase, 
characterized in that the crystallisation modifying substance is a 
polysaccharide being an inulin or phlein with a molecular weight of 
500-3990 Da, preferably 1300-2500 Da, of which at least 50% of the 
hydroxyl groups on the saccharide subunits are connected to (C8-C24) 
unbranched alkyl chains and the remaining hydroxyl groups, optionally, are 
connected with a (C1-C7)-alkyl chain. 
At microscopic inspection the effect of the presence of such 
crystallisation modifying substance is that in the oil crystals and 
crystal aggregates are formed which are conspicuously different from the 
crystals obtained without crystallisation modifying substance. These 
crystals and aggregates can be filtered more effectively since the stearin 
fraction retains less of the olein fraction even at low or moderate 
filtration pressure. The altered crystallisation results therefore in a 
considerable increase of the separation efficiency. 
DETAILS OF THE INVENTION 
The oil to be fractionated is mixed with the crystallisation modifying 
substance before crystallisation starts, preferably before the oil is 
heated so that all solid triglyceride fat and preferably also the 
modifying substance is liquified. 
Then the oil is cooled to the chosen crystallisation temperature. A 
suitable crystallisation temperature for e.g. palm oil is 
15.degree.-35.degree. C. By choosing a different temperature the 
composition of the olein and stearin phases may change. Crystallisation 
proceeds at the chosen temperature until a constant solid phase content is 
reached. The crystallisation time varies depending on the desired solid 
phase content. Usual times are in the range of 4-16 hours, but sometimes 
the crystallizing fat needs more time for reaching equilibrium. During 
crystallisation the oil may be stirred, e.g. with a gate stirrer. But 
stagnant crystallisation sometimes gives the best separation efficiency. 
For the separation of the solid phase from the liquid phase generally a 
membrane filter press is used, because it allows rather high pressures. 
Suitable pressures are 3-50 bar, to be exerted for about 20-200 minutes. 
However, even with a low or moderate pressure the stearin phase obtained 
according to the present invention is easily separated from the olein 
phase. As a rule it takes about 30-60 minutes to have both phases properly 
separated. 
The solids content of the crystal slurry before separation and of the 
separated stearin phase is measured according to the known pulse NMR 
method (ref. Fette, Seifen, Anstrichmittel 1978, 80, nr. 5, pp. 180-186). 
The characteristic alkyl chains of crystallisation modifying substances of 
the present invention are preferably attached to the polysaccharide 
backbone via an ester bridge, e.g. by reacting a suitable fatty acid or 
mixture of fatty acids, optionally in the form an active derivative, with 
the hydroxyl groups of the polysaccharide. 
A method which is particularly suitable because it may qualify as 
food-grade comprises the use of the methyl ester of the fatty acid(s) and 
the peracetate ester of the polysaccharide. Applying common process 
conditions such as an appropriate solvent and the presence of a usual 
basic substance the reaction of the reactants deliver the desired 
polysaccharide esters which may be recovered from the mixture. 
The condition that at least 50% of the hydroxyl groups should be esterified 
is to be understood as the minimum esterification degree of the overall 
amount of hydroxyl groups and not necessarily of the hydroxyl groups of 
each individual subunit. 
The alkyl chains attached to the polysaccharide backbone may be the same or 
different. 
The best results have been obtained when the size of the alkyl chains 
attached to the saccharide subunits matches the size of the fatty acid 
alkyl chains of the desired stearin phase. Matching occurs when a 
substantial part of the chains have the same or about the same number of 
carbon atoms. Substantial in this respect has to be understood as being 
valid for 60-100% of the chains. Therefore, when palm oil is fractionated, 
preferred alkyl chains are cetyl (C16) and stearyl (C18) alkyl chains. 
Inulin is a polyfructose comprising a terminal glucose subunit where the 
subunits are mutually connected via a .beta.-1,2 glycosidic linkage. 
Phlein is a polyfructose comprising a terminal glucose subunit where the 
subunits are mutually connected via a .beta.-2,6 glycosidic linkage. The 
inulin or phlein molecular weight, being 500-3990 Da, preferably 1300-2500 
Da, corresponds with a chain length (denoted as GF.sub.n) of the inulin or 
phlein being n=2-23, preferably n=7-14. 
At least 50% of the hydroxyl groups have been esterified with a 
(C8-C24)-alkyl containing fatty acid, preferably chosen from the group 
comprising lauric acid, myristic acid, palmitic acid and stearic acid and 
the remaining hydroxyl groups have been esterified with a (C1-C7)-alkyl 
containing fatty acid, preferably acetic acid. The molecular weight of 
inulin fully esterified with three palmitic acid residues is 5.5 * the 
molecular weight of non-esterified inulin. 
A particularly preferred group of inulin esters has been esterified for at 
least 50% with a mixture of lauric and palmitic acid in a ratio of 9:1 to 
1:9. This crystallisation modifying substance is particularly succesful in 
stirred crystallisation. 
The process of the invention preferably is carried out as a dry 
fractionation process, although the invention is useful too for solvent 
fractionation or detergent fractionation. 
The process can be applied on triglyceride oils containing relatively high 
melting fat such as palm oil, palm kernel oil, shea oil, coconut oil, 
cottonseed oil, butter oil, hydrogenated rapeseed oil, hydrogenated 
soybean oil or fractions of these oils or oils obtained from the previous 
oils by interesterification. 
The process is particularly useful for fractionating palm oil. The palm oil 
might be crude, but generally a refined quality is used. 
The crystallisation modifying substance is suitably applied in an amount of 
0.005-2 wt.%, preferably 0.01-1 wt.% on the total amount of oil. 
A particular advantage of the crystallisation modifying esters of the 
present invention is that they are composed of polysaccharides and fatty 
acids, both of which are natural, physiologically acceptable substances 
and for which a method of preparation is available which may qualify as 
food-grade. 
The invention comprises in particular the use as a triglyceride oil 
crystallisation modifying substance of all esters of inulin and phlein as 
defined hereinbefore.

EXAMPLE 1 
Two samples were prepared each containing 1200 g of palm oil (neutralised, 
bleached, deodorised). The process is carried out as a common dry 
fractionation process, but to the first sample (A), 1.2 g (0.1 wt.%) of a 
crystallisation modifying substance was added. To the second sample (B), 
no crystallisation modifying substance was added. The crystallisation 
modifying substance is an inulin with an average molecular weight of about 
1700 Da. It is fully esterified (DS=3) with a 1:2 mixture of lauric and 
palmitic acid. 
Both samples were heated at 65.degree. C. until completely liquefied (no 
solid fat content) and then cooled in order to crystallize. 
Crystallisation proceeded under stagnant conditions at the chosen 
temperature of 23.degree. C. until a constant solid phase content was 
reached. The samples were pressed in a membrane filter for half an hour. 
After filtration the fractions were weighed. The olein yield is the weight 
of the filtrate. The stearin yield is the weight of the crystal mass 
(cake) remaining on the filter. The yields of the measured stearin and 
olein fractions are given in table 1. 
TABLE 1 
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sample A sample B 
0.1 wt. % modifier 
no modifier 
______________________________________ 
temperature / .degree.C. 
23 23 
stabilisation time / h 
188 16 
solid phase content 
15 12 
slurry / wt. % 
solid phase content 
71 34 
cake / wt. % 
olein yield / wt. % 
79 57 
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Before filtration, the two samples contained the same amount of solid fat. 
The comparison shows that the stearin fraction of the crystallisation 
modifying substance containing sample (A) has retained considerably less 
olein fraction than sample (B) without a crystallisation modifying 
substance. The separation efficiency showed a relative increase of 110%. 
EXAMPLE 2 
Example 1 was repeated while allowing the oil to crystallize under stirred 
conditions. The fractionation results are given in table 2. 
TABLE 2 
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sample A sample B 
0.1 wt. % modifier 
no modifier 
______________________________________ 
temperature / .degree.C. 
23 23 
stabilisation time / h 
7 5 
solid phase content 
15.5 13.7 
slurry / wt. % 
solid phase content 
58 53 
cake / wt. % 
olein yield / wt. % 
72 65 
______________________________________ 
The separation efficiency showed a relative increase of 10%.