WO1992008363A1

WO1992008363A1 - Lipid fractionation and products so obtained

Info

Publication number: WO1992008363A1
Application number: PCT/AU1991/000105
Authority: WO
Inventors: Corran Norman Stuart Mclachlan; Gary Norris Kerkin; Peter Vines; Christopher John Malcolm
Original assignee: Portwall Pty. Limited
Priority date: 1990-11-13
Filing date: 1991-03-21
Publication date: 1992-05-29
Also published as: CS81091A3; AU7468291A

Abstract

There is described a process for extracting part of the lipids from a lipid or lipid containing mixture comprising contacting the lipid or mixture with a subcritical fluid at a suitable temperature and pressure and of a type such that part of the lipid is more soluble therein than the remainder of the lipid or other components of the mixture, under conditions so that a part of the lipid component is taken up by the fluid, and then recovering the lipid from that fluid, and optionally recovering the remainder of the lipid which is not taken up by the fluid. The process for example can be used to fractionate the triglycerides in butter or milk fat using subcritical carbon dioxide.

Description

LIPID FRACTIONATIOI _WD PRODUCTS SO OBTAINED

This invention relates to the processing of lipids and more particularly the processing of lipids to produce a mixture of lipid fractions.

Milk-fat is a complex mixture of fatty acids and triglycerides with a range of molecular weights and degree of unsaturation and exhibiting a broad and variable melting range. In additio it contains many minor components- the major of which are cholesterol, mono- and di-glycerides and phospholipids. Their relative composition varies from animal to animal, seasonally, and on nutrient quality and type. In addition milk-fat contains vitamins A,D and carotene.

The unique physical characteristics, especially the melting properties and plastic range of milk fat do not suit it to a number of food-fat applications. However, fractionation of the milk fat into fractions and blending those fractions in combinations to give the desired properties will facilitate an increased utilisation of milk fat in many food applications. Examples of these applications are spreadable butters, confectionary and baking products, dietetic and cholesterol reduced butters and fats.

A convenient measure of the distribution of triglycerides is by reference to the carbon number distribution. Short chain triglycerides are recognised as having carbon numbers ranging from 28 to 40; and the longer chain triglycerides having carbon numbers 42 and up to 54.

The fractionation of milk-fat has been the subject of considerable investigation. The techniques used and the procedures developed have included: Melt Crystallisation

Fjaervoll [Fjaervoll, A; Dairy Industries, 35 (1970), 502-505], Riel et al [Riel, R R & Pacquet, R; Canadian Institute of Food Science and Technology Journal, 5 (1972), 210-213] Jebson [Jebson, R S; New Zealand Journal of Dairy Science and Technology, 11 (1976), 206-210] and Makhlouf et al [Makhlouf J, Arul, J, Boudreau, A, Verret, P & Sahasrabuhde, M, Canadian Institute of Food Science and Technology Journal, 20 (1987), 236-245] among others have described this process in which milk-fat is melted and then slowly cooled to allow selective crystallisation of lipid material. Processes of this type suffer the disadvantage of difficult temperature control associated with the effects of seasonal changes in milk-fat composition.

Molecular Distillation

Bracco [Bracco, U; British Patent No. 1559064 (1980)]; Arul et al [Arul, J, Boudreau, A, Tardif, R Makhlouf, J & Bellavia, T; Journal of the American Oil Chemists Chemists' Society, 65 (10, 1988), 1642], and others describe a process in which milk-fat is heated to 200-300°C and then distilled in a wiped-film evaporator at reduced pressure, typically 0.2-0.05 bar. This process suffers from the disadvantages of thermal degradation of flavours and vitamins which occur at high temperatures, and the production of a low-melting point product which has an inferior oxidative stability.

Solvent Extraction

R Norris [United States Patent No. 4,005,228, (1977)] describes a solvent extraction/crystallisation process in which milk-fat is either partially crystalised and slurried with an organic solvent, or heated and mixed with cold organic solvent to form a slurry of partially crystalised milk-fat, or is completely dissolved in a solvent and then fractionally crystalised out of the solution by cooling it. The solid component of the slurry is separated mechanically. The preferred solvents are propan- 2-ol, acetone, ethyl acetate, hexane or other petroleum derivatives, or mixtures thereof.

The disadvantages of this process is the loss of desirable characteristics such as flavours and vitamins into the solvent phase, and the contamination of the product with a solvent which may be unacceptable physiologically. Norris does not address all these problems but suggests the necessity to strip the solvent with steam or other gas. A recent patent application by Keen et al [Keen, AR, Ward, DD & Hobman, PG; European Patent Application No. 89301304.8, Publication No. 0 329 347 A2] which deals with the extraction of cholesterol from milk-fat using solvents such as methanol describe the necessity to subject the fat phase to steam distillation to remove all traces of the solvent. A further disadvantage of the process therefore, is potential thermal damage to fragile components such as flavours, enzymes and phospholipids.

Bradley, RL, J. Dairy Sci. 72,2834-2840 (1989) has reported lipid extraction from butter and its subsequent fractionation by distillation.

Supercritical Carbon Dioxide Fractionation

Kaufmann et al [Kaufmann, VW, Biernoth, G, Frede, E, Merk, W, Precht, D & Timmen, H; Milchwissenschaft, 37 (1982), 92], Arul et al [Arul, J, Boudreau, A, Makhlouf, J, Tardiff, R & Sahasrabudhe, M R; Journal of Food Science, 52 (5, 1987), 1231- 1236, and Kankare et al [Kankare, V, Antila, V, Harvala T, and Komppa, V; Milchwissenschaft, 44 (7, 1989, 407-411)] among others describe processes whereby milk-fat fractions are selectively extracted into the supercritical carbon dioxide. In US Patent 4,504,503 (1985) Bie oth et al teach that butter may be fractionated with supercritical carbon dioxide at 60^βC- 100 "C and 150 bar-260 bar (15 MPa to 26 MPa) and report that anhydrous butter should be used to avoid hydrolysis. Shishikura et al [Shishikura, Al, Fujimoto, K, Kaneda, T, Aral, Kl, and Salto S, Agric. Biol. Chem. 50 (5), 1209-1215, 1986] also reported a deleterious effect of moisture on milk-fat solubility and concentrated their work on anhydrous butter oil obtained from n-hexane extraction of butter.

Novak, R A, Robey, R J and Scott A D, AICHE 1988 Summer Meeting, Denver, Colorado, Aug 21-24 also reported fractionation studies of anhydrous butter-fat using supercritical carbon dioxide.

In all instances the milk-fat is fractionally dissolved in supercritical carbon dioxide at pressures typically ranging from 100-400 bar and at temperatures between 33-80^βC. The triglycerides so dissolved are subsequently recovered by reducing the temperature and pressure to subcritical conditions under which they are no longer soluble, generally with the carbon dioxide in a gaseous state. One of the disadvantages of this procedure is all the triglyceride fractions produced, including the undissolved residue, contain significant quantities of cholesterol. For example in a typical case Kankare et al reported 3.22 mg/g cholesterol in their lightest fractions through to 1.61 mg/g in the undissolved residue.

We have been unable to locate any reports of dissolution and fractionation of milk-fats, or other lipids at sub-critical conditions. The only work in this area is that of Haring [Haring, PGM, European Patent Application No. 88202673.8, Publication No. 0 321 055 Al (1988)] in which a process for the extraction of lactones from lipid materials is described. The process is claimed to provide low yield with high selectivity resulting in a relatively small extracted fraction substantially enriched in lactones. _>

In accordance with this invention there is provided a process for separating at least part of the lipids from a lipid/water mixture comprising bringing a subcritical fluid at a suitable temperature and pressure and of a type such that at least part of the lipid is more soluble therein than water, into contact with the lipid-water mixture, in an extractor under conditions so that at least a part of the lipid component in the mixture is taken up by the fluid and then recovering the lipid from that fluid.

Alternatively the mixture containing lipids may be essentially anhydrous being comprised of a range of lipid materials with minor concentrations of other dairy materials and water.

Alternatively the mixture containing lipids may be essentially comprised of oils derived from vegetable matter, other plant matter, or other animal matter with minor concentrations of other materials and water.

The fluid is preferably carbon dioxide but ₂0, SF_g, CFgCl, CF₂C1, CH₂CF₂, C,F„, CHF.-, ethane, propane, butane, ethylene or acetone, which are considered unobjectionable from a health point of view can also be used. Mixtures of these fluids can also be used. This invention will be further described with reference to the use of carbon dioxide alone.

When cream is contacted with carbon dioxide at a high pressure, the amount of the lipid fraction that is extracted into the carbon dioxide fluid varies with the temperature of the extraction. When the temperature is below the critical temperature, it is found that the solubility of high molecular weight lipids, such as those above carbc number 40 in the lipi_~ fraction is low while the relative / low molecular weight lipids, namely those below about carbon number 40 are dissolved into the high pressure fluid. In this case where subcritical conditions are employed, the high molecular weight lipids will remain in the water phase if present, namely those lipids having a carbon number greater than about 40. The fraction is itself a product of ttie invention. One of its uses will be to add it to the butter-fat which has been extracted into the carbon dioxide stream. Butter produced from butter-fat with a carbon number below 40, has a low softening point which is a desirable property in certain situations. The softening point of that butter can be raised by adding the lipids of carbon number greater than 40. By varying the amount of added high molecular weight lipids, the softening point can be tailored to suit any desired situation.

A further surprising property of the high molecular weight fraction is that it is cholesterol free. This is contrary to the results of Bradley et al, for example, who found that when supercritical carbon dioxide is used to fractionate, substantial quantities of cholesterol were present in all fractions of the lipid.

The conditions of temperature and pressure under which the extraction is effected may vary for reasons mentioned above depending upon the desired product. The temperature at a minimum will be sufficient under the conditions of pressure employed to achieve sufficient dissolution of a desired fraction of the lipids. This will normally be above -10°C. The maximum temperatures will be mainly determined by cost constraints and the desire to avoid damage to heat sensitive ingredients in the butter-fat or other desired product. The temperature will thus be between -10^βC and 80°C. Where a fractionation of the lipids is desired, the temperature will preferably be between 0°C and 31°C. The pressure is generally between 75 and 350 bar and more preferably between 150 and 280 bar. The minimum pressure will be again dictated by the need to achieve a satisfactory dissolution of the desired lipid fraction(s) in the carbon dioxide stream. Water has a relatively limited solubility in sub- or supercritical carbon dioxide which increases with temperature at constant pressure whereas carbon dioxide solubility for lipids decreases with temperature at constant pressure.

To achieve the optimum separation of the lipids from the liquor the carbon dioxide must intimately contact the surface of a thin film of the fat-in-water emulsion in a continuous co- current or counter-current manner. The emulsion may be converted into the form of a thin film in any known manner as, for example, by passing the fat-in-water emulsion over a surface in the form of a thin film covering the same; by passing the emulsion through a cascade or packed bed, containing rings or other distribution systems known to the art, or a device which corresponds to a thin film surface evaporator or the like, or by spray nozzle or other droplet generating device. Alternatively the extraction may take place in a liquid-fluid extraction involving plate mixer-settler units. It is not intended that the separation process be limited but is to follow process steps well recognised in the art of chemical engineers.

We prefer the use of a spray nozzle or other mist or droplet generating device to finely disperse milk-fat into the carbon dioxide stream in a chamber of suitable geometry. This method has been found to ensure a sterol-free residue.

The amount of carbon dioxide will be sufficient to dissolve the milk-fat and hence will be preferably 30-150 times the weight of milk-fat to be dissolved.

An important feature of the invention is to then reduce the cholesterol content in the lipid fraction in the high pressure fluid stream to produce a low cholesterol product, preferably a cholesterol free product. The cholesterol can be removed by methods known in the art, such as using an adsorbent. The adsorbent can be an inorganic compound or organic compound, which preferentially adsorbs cholesterol. There are many such adsorbents described in the literature. It is preferred within the scope of this invention, to use an adsorbent which selectively removes cholesterol and at the same time removes only a small amount, if any, of the lipid. The preferred materials are those described in our New Zealand Patent Application No. 221,503. The methods described in that specification may be incorporated in the processes of this invention.

The cholesterol-free or low-cholesterol product can be then recovered by changing the fluid to the supercritical state through an increase in temperature at constant pressure or by lowering the pressure at constant temperature. When the fluid is in a subcritical state the product can be recovered by reducing the pressure and/or increasing the temperature.

Another important benefit of the invention is the fact that high pressure carbon dioxide is a highly effective bacteriocide, particularly when moist. It is therefore possible in accordance with the invention to obtain sterile butter without the need for other micro-organism control methods such as pasteurisation.

This procedure therefore offers a process for making cholesterol-free lipid fractions, in which the melting point is varied to suit any desired conditions by first dissolving the milk-fat in high pressure carbon dioxide at a temperature belo its critical temperature so that high molecular weight lipids remain; passing lipid-laden carbon dioxide fluid to an adsorbent which is designed to remove substantially all the cholesterol; recovering the lipid from the carbon dioxide stream; and if desired, adding to that lipid fraction, high molecular weight lipid from the dissolution step. Lipid fractions so obtained may be blended in suitable quantities with or without additional moisture and salt to produce cholesterol free butter as described in our New Zealand Patent Specification No. 233031 (1990).

The invention therefore provides a process for fractionating a lipid containing material into a high-molecular weight fraction and a low-molecular weight fraction, comprising treating the lipid containing material with a high pressure fluid at a temperature below its critical temperature, the temperature being chosen so that lipids of a molecular weight below a desired level are dissolved in the high pressure fluid, while the higher molecular weight lipids remain, and then recovering the low-molecular weight lipids from the high-pressure fluid stream and, if desired, recovering any high-molecular weight lipids from the residue.

In a further aspect of the invention, there is provided a process for modifying the sterol and lipid content in a lipid material containing sterols, comprising a subjecting the lipid material to a high-pressure fluid at a temperature below its critical temperature, so that low-molecular weight lipids containing substantially all the sterols are dissolved in the fluid and the high-molecular weight lipids substantially free of the sterols remain; contacting the sterol/lipid laden fluid with an adsorbent which is designed to selectively adsorb substantially all the sterols from the lipids, while leaving all the lipids substantially in the fluid; recovering the lipid from the high-pressure fluid and if desired recovering the high-molecular weight lipid from the dissolution step; and further, if desired, modifying the properties of the low- molecular weight lipid fraction by adding at least a part of the high-molecular weight fraction to the low-molecular weight material; and still further, if desired, recovering the sterols from the adsorbent. The invention also includes a process in which the fluid is in a supercritical state and hence substantially all the lipids will be extracted into the fluid. The temperature of the fluid is then lowered to a subcritical temperature at which 'time those high molecular weight lipids which are insoluble will precipitate and can be recovered whilst the lipid and cholesterol laden fluid can be further processed as described above.

While this invention has been described with reference to preferred embodiments, it is not to be construed as being limited thereto and moreover where specific steps or materials are mentioned, and equivalents are known to exist thereto, such equivalents are incorporated herein as if specifically set forth.

Example

Anhydrous milk-fat in liquid form containing 99.5% fat, 0.5% moisture by weight, was introduced into subcritical carbon dioxide at- a rate of 3.4 kg/hr. The carbon dioxide flow rate was 250 kg/hr. The two fluids were contacted at a temperature of 15°C, and a pressure of 250 bar. After contact the fat-rich carbon dioxide was passed to a separator in which the dissolved fat was recovered. The C0₂ was recirculated.

The residue not dissolved in the CO., was recovered and found to contain 99.9% fat and 0.1% moisture. The triglyceride profile in Figure 1 shows that this residue was essentially comprised of carbon number C40 and above. This residue was free of cholesterol.

Figure 2 indicates the variation of softening point of the extracted fraction with extraction temperature.

The attached drawing shows in schematic form the process of the inventio . Lipid containing material is fed into the extractor and subcritical carbon dioxide contacts that material. The heavy fractions of the lipid are not solubilised in the carbon dioxide stream and hence are recovered from the extractor. The remaining lipid rich stream then is fed to the adsorber where cholesterol is removed and then to a separator where the light lipid fractions are recovered. The carbon dioxide is then recycled back to the extractor.

Claims

WHAT WE CLAIM IS:

1. A process for extracting part of the lipids from a lipid or lipid containing mixture comprising contacting the lipid or mixture with a subcritical fluid at a suitable temperature and pressure and of a type such that part of the lipid is more soluble therein than the remainder of the lipid or other components of the mixture, under conditions so that a part of the lipid component is taken up by the fluid, and then recovering the lipid from that fluid, and optionally recovering the remainder of the lipid which is not taken up by the fluid.

2. A process according to claim 1 in which the fluid in a subcritical state is selected from C0₂, N_? ⁰' ^SF ₆ ^{f CF} ₃ ^C^ CF₂C1₂, CH₂CF₂, ₃F„, CHF-, ethane, propane, butane, ethylene or acetone and mixtures thereof.

3. A process according to claim 2 in which the fluid is carbon dioxide.

4. A process according to claims 1, 2, or 3 in which the lipid/water mixture is cream or other animal derived lipid containing mixture.

5. A process according to claims 1, 2, or 3 in which the lipid mixture is anhydrous milk-fat.

6. A process according to claims 1, 2 or 3 in which the lipid mixture is derived from vegetable or other plant matter.

7. A process according to claims 1 to 6 in which the carbon dioxide is at a temperature between -10°C and 31^βC and at a pressure between 75 bar and 350 bar.

8. A process according to any of the above claims wherein the fraction of the lipid extracted into the subcritical carbon dioxide stream is lipids containing cholesterol and having carbon numbers below about C40 and, if present, water.

9. A process according to claim 8 wherein the fraction not dissolved in the subcritical carbon dioxide stream is largely free of cholesterol.

10. A process according to any one of the preceding claims in which the lipid laden fluid is contacted with a suitable adsorbent capable of removing cholesterol if present.

11. A process according to claim 10 wherein the cholesterol adsorbed onto the adsorbent is recovered by eluting the adsorbent with a fluid in a subcritical or supercritical state in the presence or otherwise of a suitable cosolvent.

12. A process according to claim 11 wherein the elution takes place in situ or otherwise.

13. A process according to claims 1 to 12 in which lipid and, if present, water are recovered from the fluid by suitable changes in temperature and pressure such that the dissolved lipid fraction and any water becomes essentially insoluble in the fluid.

14. A process according to claim 13 wherein the lipids and, if present, water so recovered exist in two separate phases.

15. A process according to claim 14 wherein the lipid phase so recovered is substantially anhydrous and the water phase, if present, is substantially free of fat.

16. A process according to claim 13 wherein the lipids and, if present, the water so recovered are essentially homogeneous.

17. A process according to claim 8 wherein following extraction the lipid laden fluid is subjected to step wise reductions in temperature to successively further fractionate the higher molecular weight fraction of the lipid.

18. A process according to claim 17 in which the successively insoluble and essentially cholesterol free fractions are separated and recovered from the fluid.

19. A process according to claim 13, 14, 15, 16 and 17 in which the lipid and water or lipid/water fractions and the fraction of greater than C40 undissolved in the extractors, thus produced are blended in any desired combination and optionally worked to produce butters or spreads with or without the addition of salt and water.

20. A process according to any of the above claims in which residual dissolved carbon dioxide is removed from the lipid by a vacuum degassing system, or a nitrogen flushing system with or without vacuum assistance, or some other suitable removal system, and preferably in which the carbon dioxide so removed is recovered.

21. A process according to any of the above claims wherein the supercritical or subcritical fluid, after removal of the extracted materials, is recycled for contacting with the anhydrous milk-fat, cream, or other oil.

22. A process for fractionation of a lipid or lipid containing mixture comprising contacting the lipid or mixture with a supercritical fluid at a suitable temperature and pressure and of a type so that substantially all lipids are taken up by the fluid, and then reducing the temperature so that the fluid is in a subcritical state so that some of the lipids become insoluble therein, and recovering the lipids remaining in the fluid.

- 23. A process for extracting at least part of the lipids from a lipid or lipid/water mixture contacting the mixture with a subcritical fluid at a suitable temperature and pressure and of a type such that at least part of the lipid is more soluble therein than the water, into co- current, counter-current or other suitable contact with the lipid or lipid/water mixture, in an extractor under conditions so that at least a part of the lipid component in the mixture is taken up by the fluid during its passage through the extractor, and then recovering the lipid from that fluid.