CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of priority under 35 U.S.C. Â§ 119(e) of U.S. Provisional Application No. 60/947,284, filed Jun. 29, 2007, the disclosure of which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to methods for producing and purifying esters of polyunsaturated fatty acids from triglyceride containing compositions. The invention also relates to compositions comprising polyunsaturated fatty acids.

BACKGROUND OF THE INVENTION

It is desirable to increase the dietary intake of many beneficial nutrients. Particularly beneficial nutrients include fatty acids such as omega-3 and omega-6 long chain polyunsaturated fatty acids (LC-PUFAs) and esters thereof. Omega-3 PUFAs are recognized as important dietary compounds for preventing arteriosclerosis and coronary heart disease, for alleviating inflammatory conditions and for retarding the growth of tumor cells. Omega-6 PUFAs serve not only as structural lipids in the human body, but also as precursors for a number of factors in inflammation, such as prostaglandins and leukotrienes. Long chain omega-3 and the omega-6 PUFAs represent important classes of PUFAs.

There are two main series or families of LC-PUFAs, depending on the position of the double bond closest to the methyl end of the fatty acid: the omega-3 series contains a double bond at the third carbon, while the omega-6 series has no double bond until the sixth carbon. Thus, docosahexaenoic acid (â€œDHAâ€ ) has a chain length of 22 carbons with 6 double bonds beginning with the third carbon from the methyl end and is designated â€œ22:6 n-3â€ . Other important omega-3 LC-PUFAs include eicosapentaenoic acid (â€œEPAâ€ ), which is designated â€œ20:5 n-3,â€ and omega-3 docosapentaenoic acid (â€œDPA n-3â€ ), which is designated â€œ22:5 n-3.â€ Important omega-6 LC-PUFAs include arachidonic acid (â€œARAâ€ ), which is designated â€œ20:4 n-6,â€ and omega-6 docosapentaenoic acid (â€œDPA n-6â€ ), which is designated â€œ22:5 n-6.â€

Because humans and many other animals cannot directly synthesize omega-3 and omega-6 essential fatty acids, they must be obtained in the diet. Traditional dietary sources of PUFAs include vegetable oils, marine animal oils, fish oils and oilseeds. In addition, oils produced by certain microorganisms have been found to be rich in LC-PUFAs. The oils derived from each of these sources, however, also contain substantial levels of saturated fatty acids and other undesirable impurities.

Numerous methods have been used to isolate or purify PUFAs and derivatives thereof from crude oils. Among these processes are fractional crystallization at low temperatures, urea adduct crystallization, extraction with metal salt solutions, super critical fluid fractionation on countercurrent columns and high performance liquid chromatography.

The increased use of PUFAs and esters thereof in the fields of medicine and nutrition has created a commensurate need for PUFAs that are concentrated and free of impurities. Previous efforts directed to purifying PUFAs, however, have suffered from problems such as high costs and decreased yields due, in part, to the use of harsh reagents. Accordingly, there is a need for improved methods of isolating and purifying PUFAs in a form that can be consumed and utilized by humans and other animals.

SUMMARY OF THE INVENTION

The present invention provides a method for purifying a composition comprising triglycerides having polyunsaturated fatty acid residues comprising reacting the composition in the presence of an alcohol and a base to produce an ester of a polyunsaturated fatty acid from the triglycerides and distilling the composition to recover a fraction comprising the ester of the polyunsaturated fatty acid.

In some embodiments, the step of reacting the composition in the presence of an alcohol and a base is performed at a temperature from about 60Â° C. to about 120Â° C.

In some embodiments, the step of reacting the composition in the presence of an alcohol and a base is performed for a time from about 2 hours to about 12 hours.

In some embodiments, the composition comprising triglycerides having polyunsaturated fatty acid residues has not been subjected to one or more treatments selected from the group consisting of refining, desolventization, deodorization, winterization, chill filtration, and bleaching.

In some embodiments, the composition comprising triglycerides having polyunsaturated fatty acid residues has not been subjected to refining, desolventization, deodorization, winterization, chill filtration, and bleaching.

In some embodiments, the composition comprising triglycerides having polyunsaturated fatty acid residues is from a source selected from the group consisting of a plant, a microorganism, an animal, and mixtures of the foregoing.

In some embodiments, the source is a microorganism selected from the group consisting of algae, bacteria, fungi and protists.

In some embodiments, the source is selected from the group consisting of plants selected from the group consisting of soybean, corn, rice, safflower, sunflower, canola, flax, peanut, mustard, rapeseed, chickpea, cotton, lentil, white clover, olive, palm, borage, evening primrose, linseed and tobacco and mixtures thereof.

In some embodiments, the source is selected from the group consisting of a genetically modified plant and a genetically modified microorganism, wherein the genetic modification comprises the introduction of polyketide synthase genes.

In some embodiments, the source is a microorganism selected from the group consisting of Thraustochytriales, dinoflagellates, and Mortierella.

In some embodiments, the microorganism is Thraustochytriales, Schizochytrium or Thraustochytrium.

In some embodiments, the microorganism is a dinoflagellate of the genus Crypthecodinium.

In some embodiments, the source is an animal selected from aquatic animals.

In some embodiments, the polyunsaturated fatty acid is a polyunsaturated fatty acid having a chain length of at least 18 carbons.

In some embodiments, the polyunsaturated fatty acid is a polyunsaturated fatty acid selected from the group consisting of docosahexaenoic acid, docosapentaenoic acid, arachidonic acid, eicosapentaenoic acid, stearidonic acid, linolenic acid, alpha linolenic acid, gamma linolenic acid, conjugated linolenic acid and mixtures thereof.

In some embodiments, the polyunsaturated fatty acid is docosahexaenoic acid.

In some embodiments, the polyunsaturated fatty acid is arachadonic acid.

In some embodiments, the base is a base of the formula RO-M, wherein M is a monovalent cation and RO is an alkoxide of a C_1-6alkyl alcohol.

In some embodiments, the base is sodium ethoxide.

In some embodiments, the alcohol is a C_1-6alkyl alcohol.

In some embodiments, the alcohol is ethanol and the ester is an ethyl ester of the polyunsaturated fatty acid.

In some embodiments, the step of distilling the composition to recover a fraction comprising the ester of the polyunsaturated fatty acid is performed under vacuum.

In some embodiments, the step of distilling the composition to recover a fraction comprising the ester of the polyunsaturated fatty acid is performed at a temperature of less than about 170Â° C.

In some embodiments, the fraction recovered comprises at least about 50 wt. %, 75 wt. %, 90 wt. %, or 95 wt. % ester of the polyunsaturated fatty acid.

In some embodiments, the step of reacting the composition in the presence of an alcohol and a base produces an ester of a polyunsaturated fatty acid from the triglycerides by direct transesterification.

In some embodiments, the method further comprises a) combining the fraction comprising the ester of the polyunsaturated fatty acid with urea in a medium; b) cooling or concentrating the medium to form a urea-containing precipitate and a liquid fraction; and c) separating the precipitate from the liquid fraction.

In some embodiments, the medium further comprises an organic solvent that can solubilize the ester of the polyunsaturated fatty acid.

In some embodiments, the organic solvent comprises an alkyl alcohol comprising from 1 to 4 carbon atoms.

In some embodiments, the organic solvent comprises ethanol.

In some embodiments, the medium is cooled to a temperature of from about 0Â° C. to about 25Â° C. to form the urea-containing precipitate.

In some embodiments, at least a portion of the urea-containing precipitate is formed under a non-oxidizing atmosphere.

The present invention also provides a method for producing an ester of a polyunsaturated fatty acid from a composition comprising triglycerides having polyunsaturated fatty acid residues comprising transesterifying the composition in the presence of an alcohol and a base to produce an ester of the polyunsaturated fatty acid from the triglycerides and distilling the composition to recover a fraction comprising the ester of the polyunsaturated fatty acid.

The present invention further provides a method for purifying a composition comprising triglycerides having polyunsaturated fatty acid residues comprising reacting the composition in the presence of an alcohol and a base to produce an ester of the polyunsaturated fatty acid from the triglycerides and separating a fraction comprising at least about 75% ester of the polyunsaturated fatty acid.

In some embodiments, the step of separating comprises distilling.

The present invention also provides a method for preparing a composition comprising an ester of a polyunsaturated fatty acid comprising reacting a composition comprising triglycerides having polyunsaturated fatty acid residues in the presence of an alcohol and a base to produce an ester of a polyunsaturated fatty acid from the triglycerides, wherein the composition comprising triglycerides having polyunsaturated fatty acid residues has not been subjected to one or more treatments selected from the group consisting of refining, desolventization, deodorization, winterization, chill filtration, and bleaching.

In some embodiments, the step of reacting the composition in the presence of an alcohol and a base is performed at a temperature from about 60Â° C. to about 120Â° C.

In some embodiments, the step of reacting the composition in the presence of an alcohol and a base is performed for a time from about 2 hours to about 12 hours.

In some embodiments, the method further comprises a step of distilling the composition to recover a fraction comprising the ester of the polyunsaturated fatty acid.