GB2079773A - Process for the recovery of triglycerides - Google Patents

Abstract

A process for the recovery of triglycerides, or mixtures of triglycerides, of higher fatty acids in crystalline form from naturally occurring fats or oils which comprises heating the naturally occurring fats or oils to the nucleus-forming temperature (TK) of the required triglyceride or mixture of triglycerides, maintaining resulting melt at the nucleus-forming temperature until crystal nuclei form, rapidly raising the temperature to the selection and transformation temperature (TS), lowering the temperature of the melt at a few degrees above the solidification point (TE), obtained in dependence upon the selected cooling rate, and the crystals are filtered off at the filtration temperature (TF) typical of these crystals which is at least 2 to 4 DEG C below the solidification point (TE), is disclosed.

Description

SPECIFICATION Process for the recovery of triglycerides This invention relates to a process for the recovery of triglycerides; more particularly, it relates to a process for the recovery of one or more triglycerides of higher fatty acids in crystalline form from naturally occurring fats or oils.

The recovery of naturally occurring fats and oils in highly pure form has been gaining in significance for some time. This is primarily attributable to the fact that certain triglycerides of higher fatty acids or certain mixtures of these triglycerides which occur in natural fats and oils having selected properties, such as clearly defined melting points or ranges, degrees of unsaturation and rheological behaviour, are desirable for a variety of purposes. In general, naturally occurring fats and oils are mixtures of various triglycerides, glycerol being differently esterified with a variety of fatty acids. Normally, all these triglycerides have fairly closely related properties so that separation, for example by distillation, is very difficult.In addition, these triglycerides, particularly when they contain unsaturated fatty acids in the molecule, are highly sensitive to oxygen, particularly at elevated temperatures such as those required for distillation.

For this reason, efforts have been made to find other separation techniques in order to separate the various triglycerides in the naturally occurring fats and oils or to isolate particular mixtures of individual triglycerides from the naturally occurring fats and oils.

It is known that various naturally occurring fats and oils and individual triglycerides of higher fatty acids exhibit polymorphism, i.e. they occur or are capable of occurring in various crystal forms. Thus, numerous fats are known to occur in a-, ss- and ss'-forms. These various crystal forms have different properties which are not confined solely to the relative position of the molecules. It is also known that the individual crystal forms may be transformed at certain temperatures, the so-called "transformation temperatures", and thereafter exhibit another crystal form.

It is this knowledge which forms the basis of the present invention. An object of the present invenion is to provide a process for the recovery of pure triglycerides of higher fatty acids or particular fractions of triglycerides of higher fatty acids in crystalline form.

Accordingly, the present invention relates to a process for the recovery of triglycerides, or mixtures of triglycerides of higher fatty acids in crystalline form from naturally occurring fats and oils which comprises heating the naturally occurring fats or oils to the nucleus forming temperature (TK) of the required triglyceride or mixture of triglycerides, maintaining the resulting melt at the nucleus forming temperature until crystal nuclei form, rapidly raising the temperature to the selection and transformation temperature (TS), lowering the temperature of the melt to a few degrees above the solidification point (TE), obtained in dependence upon the selected cooling rate, and the crystals are filtered off at the filtration temperature (TF) typical of these crystals which is at least 2 to 4"C below the solidification point (TE).

The filtrate obtained after filtration may then be subjected to another crystallisation process of the type described above, the appropriate temperatures required for the other triglycerides or triglyceride mixture required being selected for nucleus formation, selection and transformation, solidification and filtration.

The effect of the process according to the present invention is that the triglycerides crystallise in pure form, i.e. they are formed without the inclusion of parts of the melt and without the incorporation of other molecules. In addition, the crystals may be grown to a very large size. The larger the crystals, the smaller the specific surface thereof and hence the lower the risk of impurities being entrained by wetting of the surface during separation of the crystals. In addition, if the crystals are fairly large, they are easier to separate from the melt, for example, by filtration.

In the process according to the present invention, it is essential that the melt should not be super-cooled. On the contrary, crystallisation must take place slowly because it is only in this way that the required crystals are selectively formed without unwanted molecules being incorporated into the crystal lattice.

If the naturally occurring fat or oil is heated to the nucleus-forming temperature (TK), the resulting melt contains a certain, albeit small, number of crystal nuclei of the triglyceride or mixture of a few triglycerides having the highest nucleus forming temperature. The presence of only this one form of crystal nuclei is necessary to allow selection and transformation to take place. Should no crystal nuclei be present at the particular nucleus-forming temperature, it is, of course, possible to add seeds to the melt.

When further crystal nuclei of the triglyceride or triglyceride mixture in question have formed in the melt due to the crystal seeds present, the temperature is rapidly increased to the selection and transformation temperature (TS), resulting in transformation of the crystal structure. The melt is then cooled to a few degrees above the maximum of the solidification curve (TE) to allow the crystals to grow in the crystal form now present. The crystals are then filtered off at the filtration temperature or filtration temperature range (TF).

Large crystals of the required triglyceride or triglyceride mixture in question characterised by high-purity are obtained in this way.

In view of the fact that naturally occurring fats and oils crystallise very slowly, it was surprising to find that the crystallisation times may be shortened by virtue of the fact that it is only at those temperatures at which appreciable quantities of crystals are formed that the temperature has to be reduced very slowly to the point at which crystallisation virtually ceases while the rest of the process steps may be carried out relatively quickly. As a result, the overall time which normally required for the crystallisation of fats and oils is considerably shortened and the triglycerides are kept largely intact.

Control of the temperature at which significant quantities of crystals are formed is particularly important and has to be carefully monitored. In this connection, it has proved to be particularly advantageous to follow the melt temperature by means of a temperature recorder.

The various temperatures determined in the practical application of the process according to the present invention are shown for some fats and oils in the following Table.

TK TS TE TF C C C C Palm Oii 47 72 37 35-15 Beef tallow 49 71 42 40-20 Lard 48 73 40 38-15 Shea butter 46 71 38 35-15 Butter 44 68 34 30-0 EXAMPLE 1 5 kg of de-acidified and bleached palm oil are heated to 72"C and maintained at that temperature for from 2 to 3 minutes. The oil is then cooled to 42"C in from 2 to 3 minutes and subsequently poured into a crystalliser having a cooling surface and stirrer, the temperature of the cooling liquid being maintained at 32"C. After about 3 hours, crystals consisting almost exclusively of tristearate have formed. The crystals are filtered off and dried under suction. Yield: 2.7 kg iodine number: 35; M.p. 53"C.

The olein as filtrate is returned to the crystalliser, the temperature of the cooling liquid being maintained at 15"C. After about 4 hours, more crystals have formed and are filtered off and dried under suction. Yield: 6.5 kg; iodine number: 33; M.p. 30"C.

The olein as filtrate has an iodine number of 61 and a turbidity point of 4"C.

Claims (4)

1. A process for the recovery of a triglyceride of a higher fatty acid or a mixture of such triglycerides in crystalline form from a naturally occuring fat or oil which comprises heating the naturally occurring fat or oil to the nucleus-forming temperature of the required triglyceride or mixture of triglycerides, maintaining the resulting melt at the nucleus-forming temperature until crystal nuclei form, rapidly raising the temperature to the selection and transformation temperature lowering the temperature of the melt to slightly above the solidification point and recovering the crystals at a temperature slightly below the solidification point.

2. A process as claimed in claim 1 in which the steps are repeated using the filtrate obtained after the first crystal fraction has been removed by filtration.

3. A process as claimed in claim 1 substantially as herein described.

4. A triglyceride of a higher fatty acid or a mixture of such triglycerides when recovered by a process as claimed in any of claims 1 to 3.