Method for fractionating a triglyceride oil

Description

[0001] The present invention relates to a method for fractionating a triglyceride oil.

[0002] Triglyceride oils are usually derived from natural sources and comprise a mixture of triglycerides of varying compositions and structures. The variety of components in a triglyceride oil produces a mixture in which different fractions crystallise from the liquid phase at different temperatures. Where the triglyceride oil is used as an edible oil for example by the consumer, it is desirable that the oil remains in a fully liquid state. It can, however, be the practice to store oil in a refrigerator, at which temperature (5°C) higher melting fractions of the oil may crystallise. Such a problem is particularly severe in the case of for example groundnut oil. Groundnut oil not only crystallises very quickly, but crystallises in the form of very small crystals. The crystals are of the order of 1 micrometre and are so small that, although they only comprise about 1 to 2 wt% of the groundnut oil at domestic refrigerator temperature, they render the oil unpourable. The oil cannot therefore be readily employed.

[0003] Removal of the crystals by filtration is not possible. The crystals are so small that they pass through and/or block conventional filter cloths having a pore size of 10 to 100 micrometre. Fractionation of e.g. groundnut oil is thus not practised prior to sale. The consumer has had to accustom himself to e.g. groundnut oil looking unsightly and being unpourable on being kept in a refrigerator.

[0004] According to the present invention there is provided a method for fractionating a triglyceride oil into a stearin fraction and an olein fraction including admixing with the oil a second triglyceride oil containing tripalmitn, the admixture being such to provide a ratio of tripalmitin to stearin fraction of not less than 1 part by weight tripalmitin to 5 parts by weight stearin fraction, and lowering the temperature of the admixture from a temperature at which it is fully molten to a temperature at which the stearin fraction crystallises. Throughout this specification "stearin fraction" indicates a solid triglyceride fraction of the triglyceride starting oil to be fractionated.

[0005] By means of the present method we have found that the crystal phase previously encountered no longer forms on cooling. Although we do not wish to be bound by any theory, we believe that the high meting components in the first triglyceride oil form, on cooling, mixed crystals with the tripalmitin of the second oil. The size of these mixed crystals can be of the order of 50 micrometre and large enough to allow, if desired, a separation to be effected of the crystalline phase from the remaining liquid phase. Preferably the present method includes separating the stearin fraction from at least some of the olein fraction. Suitable means of separation include filtration, settling and cen- trtfugation. If desired, however, the admixture can be sold to the consumer. On storage in a domestic refrigerator, a crystalline phase will form but its larger size crystals need not render the product unpourable.

[0006] For the appropriate mixed crystals to occur, the admixture must be fully molten prior to cooling to a temperature at or below which the stearin fraction crystallises. The second triglyceride oil may be added at a temperature at which it is fully liquid to the first triglyceride oil which is also at a temperature at which it is fully liquid. Alternatively, the first and/or the second triglyceride oil may contain at least some crystalline fraction on admixture and the resulting mixture is heated to a temperature at which it is fully liquid prior to lowering the temperature to a temperature at or below that at which stearin fraction crystallises. Preferably the molten admixture is cooled with stirring.

[0007] The admixture is preferably such to provide a ratio of tripalmitin to stearin fraction of up to 15 parts by weight tripalmitin to 1 part by weight stearin fraction, more preferably of up to 5 parts by weight tripalmitin to 1 part by weght stearin fraction.

[0008] Examples of suitable second triglyceride oil include refined palm oil, a fraction of palm oil and commercially available additives. Examples of appropriate palm oil fractions include dry fractionated palm oil stearin containing about 20 to 25 wt% tripalmitin, wet fractionated palm oil stearin containing about 50 wt% tripalmitin and fractions obtained on further fractionation of palm oil stearin to increase the tripalmitin content yet further. Suitably the second triglyceride oil contains at least 20 wt% tripatmitin, preferably at least 50 wt%, even more preferably at least 80 wt% tripalmitin. Provided, however, the required amount of tripalmitin is present in the admixture with respect to the stearin fraction it is desired to remove from the first triglyceride oil, the overall composition of the second triglyceride oil may be any appropriate form. For example palm oil can be employed as the second triglyceride oil and usually contains between 5 and 10 wt% tripalmitin.

[0009] The present invention is particularly applicable where the first triglyceride oil is selected from the group comprising groundnut oil and fractions thereof. Where the first triglyceride oil is groundnut oil, the stearin fraction suitably comprises between 0.5 wt% and 4.0 wt%, more particularly between wt% and 3 wt% of the groundnut oil. The separation is suitably carried out at a temperature between 0 and 5°C.

[0010] It is to be understood that the present invention extends to fractions of triglyceride oil obtained by the present method.

[0011] Embodiments of the present invention will now be described by way of example only with reference to the following Examples.

Example 1

[0012] To a sample of refined and neutralised groundnut oil was added 2 wt% tripaimitin in the form of a triglyceride oil comprising a fraction obtained from palm oil stearin and containing at least 90 wt% tripalmitin. Both the groundnut oil and the tripalmitin were at 70°C and were thus fully liquid. The two triglycerides were stirred together. The temperature of the mixture was lowered with stirring in 20 minutes to 17°C, at which temperature crystals started to appear. Cooling was continued but at a slower rate, the mixture being cooled with stirring to 1°C in a further 3 hours.

[0013] The crystalline phase formed comprised compact spherulites about 50 micrometre in size and was readily separated by filtration at a rate of 0.4 cubic metre/ square metre per hour. 4.1 wt% with respect to the total triglycerides present of crystalline phase was separated. At least therefore 2.05 wt% stearin fraction was separated from the groundnut oil. The separation efficiency was 0.21. The yield of liquid olein phase was 82.5% with respect to the original total groundnut oil.

Example 2

[0014] The procedure of Example 1 was repeated employing, in place of the 90 wt% tripalmitin fraction, 2 wt% of a palm oil stearin containing 52% tripalmitin. A crystalline phase comprising compact spherulites (50 micrometre) with attached agglomerates of smaller crystals was filtered. Similar results were obtained as in Example 1.

[0015] The olein product of both Examples 1 and 2 was stored at 5°C for 6 days. In each case the oil remained dear.

Comparative Examples

[0016] The procedure of Example 1 was followed employing in place of the tripalmrtin, tristearin (SSS) obtained from the hydrogenation of groundnut oil. On cooling to 0°C about 3.2% crystalline phase formed. The crystals, however, consisted of open, more or less spherulitic crystals (10 to 20 micrometre) which included a large amount of extremely small crystals (much smaller than 1 micrometre) and were so small that filtration was not possible.

[0017] In a further comparative Example following the procedure of Example 1, 4 wt% palm mid-fraction consisting primarily of POP and containing less than 7 wt% PPP was employed as the second triglyceride oil. On cooling very small crystals were formed which could not be filtered by conventional means.

Claims

1. Method for fractionating a triglyceride oil into a stearin fraction and an olein fraction including admixing with the oil a second triglyceride oil containing tripaimitin, the admixture being such to provide a ratio of tripalmitin to stearin fraction of not less than 1 part by weight of tripalmitin to 5 parts by weight stearin fraction, and lowering the temperature of the admixture from a temperature at which it is fully molten to a temperature at which the stearin fraction crystallises.

2. Method according to Claim 1, wherein the second triglyceride oil is refined palm oil.

3. Method according to Claim 1, wherein the second triglyceride oil is a fraction of palm oil.

4. Method according to Claim 1 or Claim 3, wherein the second triglyceride oil comprises at least 80 wt% tripaimitin.

5. Method according to any one of the preceding Claims, wherein the admixture is such to provide a ratio of tripalmitin to stearin fraction of up to 15 parts by weight tripalmitin to 1 part by weight stearin fraction.

6. Method according to Claim 5, wherein the admixture is such to provide a ratio of tripalmitin to stearin fraction of up to 5 parts by weight tripalmitin to 1 part by weight stearin fraction.

7. Method according to any one of the preceding Claims, wherein the first and second triglyceride oils are admixed at a temperature at which the admixture is fully liquid.

8. Method according to any one of Claims 1 to 6, wherein the first and/or the second triglyceride oil contains at least some crystalline fraction on admixture.

9. Method according to Claim 8, wherein the admixture is heated to a temperature at which the admixture is fully liquid.

10. Method according to any one of the preceding Claims including separating the stearin fraction from at least some of the olein fraction.

11. Method according to Claim 10, wherein the stearin fraction is separated by filtration, settling and/or centrifuging.

12. Method according to any one of the preceding Claims, wherein the first triglyceride oil is selected from the group comprising groundnut oil and fractions thereof.

13. Method according to Claim 12, wherein the first triglyceride oil is groundnut oil and the stearin fraction comprises between 0.5 wt% and 4.0 wt% of the groundnut oil.