Production method of highly unsaturated fatty acid ethyl ester

Abstract

The present invention provides a method of producing/purifying highly unsaturated fatty acids and/or derivatives thereof while suppressing deterioration of a silver salt aqueous solution, in production/purification of highly unsaturated fatty acids and/or derivatives thereof using the aqueous solution of silver salt. The present invention also contacts or mixes a mixture having a peroxide value (POV) of 10 or smaller with an aqueous solution of silver salt, in a method of purifying highly unsaturated fatty acids and/or derivatives thereof from a mixture comprising highly unsaturated fatty acids and/or derivatives thereof.

Claims

1. A method of purifying highly unsaturated fatty acid derivatives from a mixture comprising highly unsaturated fatty acid derivatives, comprising a step selected from the group consisting of the following (1) to (4): (1) (a) providing the mixture having a peroxide value (POV) of 1 or smaller, wherein the peroxide value of the mixture is adjusted by a POV reducing agent, and (b) contacting the mixture with an aqueous solution of silver salt; (2) (a) providing the mixture having a peroxide value of 1 or smaller, wherein the peroxide value of the mixture is adjusted by a POV reducing agent, and (b) mixing the mixture with an aqueous solution of silver salt; (3) (a) decreasing a peroxide value of the mixture to 1 or smaller by contacting the mixture with a POV reducing agent, and (b) contacting the mixture with an aqueous solution of silver salt; and (4) (a) decreasing a peroxide value of the mixture to 1 or smaller by contacting the mixture with a POV reducing agent, and (b) mixing the mixture with an aqueous solution of silver salt, wherein the derivatives comprise at least one of a methyl ester, ethyl ester, amide, methyl amide, triglyceride, diglyceride or monoglyceride derivative.

2. The method according to claim 1, wherein the highly unsaturated fatty acid derivatives are highly unsaturated fatty acid ethyl esters.

3. The method according to claim 2, wherein the highly unsaturated fatty acid ethyl esters are selected from the group consisting of 18:3?3, 18:3?6, 18:4?3, 20:4?6, 20:5?3, 22:5?3, and 22:6?3.

4. The method according to claim 1, wherein the aqueous solution of silver salt is a silver nitrate aqueous solution.

5. The method of claim 1, wherein the POV reducing agent is selected from the group consisting of acid clay, activated clay, activated carbon, and silicic acid.

6. The method according to claim 1, further comprising (c) adding an antioxidant to the mixture.

7. The method according to claim 6, wherein the step (c) is performed before the step (b).

8. The method according to claim 1, wherein the step (b) is performed under a condition selected from the group consisting of under a nitrogen gas environment and under a light-blocking environment.

Description

DESCRIPTION OF EMBODIMENTS

(1) Hereinafter, the present invention will be described. Throughout the present specification, it should be understood that unless particularly stated otherwise, an expression in its singular form also includes the conception of plurality. It should be also understood that unless particularly stated otherwise, the terms used in the present specification have the meanings that are conventionally used in the art. Therefore, unless defined otherwise, all technical and scientific terms used in the present specification have the same meanings as commonly understood by those having ordinary skill in the art to which the present invention pertains. In the case of conflict, the present specification, including the definitions, will control. In addition, in the present specification, wt % and percent concentration of mass can be interchangeably used. Furthermore, in the present specification, unless particularly stated otherwise, % means wt %.

Definition of Terms

(2) Hereinafter, the definitions of the terms that are particularly used in the present specification will be listed.

(3) The term raw material oils and fats as used herein refers to oils and fats that are used as the raw materials in the purification of the present invention. Deacidification treatment may or may not be performed on the raw material oils and fats. Preferably, the raw material oils and fats of the present invention are raw material oils and fats on which deacidification treatment is performed.

(4) The term purification as used herein refers to any operation that increases the concentration of substances to be the target of purification.

(5) The term peroxide value as used herein is interchangeably used with POV, and it represents an amount of peroxides, which are the primary products generated in the early stage of autoxidation of oils and fats. While not wishing to be bound by theory, it is considered that deterioration of silver salt (e.g., silver nitrate) is caused due to the lipid peroxide included in the mixture (raw material oils and fats). In other words, it appears that silver salt such as silver nitrate is denatured due to the reaction of silver salt such as silver nitrate with lipid peroxide. In addition, when a peroxide exists in the mixture (raw material oils and fats), since the peroxide is unstable, it is degraded and generates aldehyde. Since aldehyde generally has toxicity, it is also important to suppress the generation of aldehyde. The POV of the mixture (e.g., raw material oils and fats) used in the purification method of the present invention is 14 or smaller, 13 or smaller, 12 or smaller, 11 or smaller, 10 or smaller, 9 or smaller, 8 or smaller, 7 or smaller, 6 or smaller, 5 or smaller, 4 or smaller, 3 or smaller, 2 or smaller, 1 or smaller, or 0.5 or smaller. The peroxide value (POV) can be measured by reacting potassium iodide with the sample, and titrating the free iodine from potassium iodide by hydroperoxide in the oils and fats. In more details, it is as described in The JOCS Standard Methods for the Analysis of Fats, Oils and Related Materials, 2003 Edition (edited by Japan Oil Chemists' Society).

(6) The term acid value as used herein is an index of carboxylic acids included in fatty acids, and it refers to the number of mg of potassium hydroxide that is required to neutralize the free fatty acids included in 1 g of the sample. The measurement method of the acid value is as described in The JOCS Standard Methods for the Analysis of Fats, Oils and Related Materials 2003 Edition (edited by Japan Oil Chemists' Society).

(7) The peroxide value does not have a direct relationship with the acid value. The value of the peroxide value gets higher as the oxidation advances, and peroxides are generated. However, since peroxides are unstable, they are degraded over time. In addition, even if the acid value of a mixture is low, the peroxide value (POV) might be high. For example, when a sample is contacted with a POV reducing agent the POV does not necessarily becomes 10 or smaller. Thus, in order to confirm that the POV is 10 or smaller, measurement of POV is necessary. Even if the acid value is 5 or smaller, the POV is not necessarily 10 or smaller, and rather, the POV often exceeds 10. In addition, in Patent Literature 5, sufficient results could not be obtained in prevention of deterioration of a silver salt aqueous solution by only setting the acid value to 5 or smaller. Thus, it was essential to set the free fatty acid content per 1 g of silver to 0.2 meq or smaller.

(8) While not wishing to be bound by theory, in an aspect of the present invention, decrease of the processing ability of a silver salt aqueous solution is suppressed by removing a lipid peroxide and/or an oxidation product of the lipid peroxide and/or a degradation product of the lipid peroxide in the raw materials. The method of removing such lipid peroxide and/or an oxidation product of the lipid peroxide and/or a degradation product of the lipid peroxide in the raw materials representatively can be decrease of the peroxide value due to processing by a POV reducing agent, but is not limited thereto. As long as such lipid peroxide and/or oxidation product of the lipid peroxide and/or degradation product of the lipid peroxide are removed from the raw materials, even if the peroxide value is not decreased, reduction in the processing ability of the silver salt aqueous solution can be suppressed, and it is possible to exert the desired effect of the present invention.

(9) The term POV reducing agent as used herein refers to an agent that has action of decreasing the peroxide value (POV). For example, the POV reducing agent can be, but is not limited to, acid clay, activated clay, activated carbon, and silicic acid. As silicic acid (also referred to as silica), for example, silica gel, which is gelated silicic acid, can be utilized. In the present invention, for example, the method of allowing the peroxide value of a mixture comprising highly unsaturated fatty acid derivatives to be 10 or smaller can be, but is not limited to, contacting of the mixture with the POV reducing agent, mixing of the mixture with the POV reducing agent, input of the POV reducing agent into the mixture for stirring, or liquid-passing of the mixture through a column filled with the POV reducing agent.

(10) The term highly unsaturated fatty acids as used herein means unsaturated fatty acids having 16 or higher carbon number, which also have two or more double bonds within the molecule. For example, they can be, but are not limited to, docosahexaenoic acid (C22:6, DHA), eicosapentaenoic acid (C20:5, EPA), arachidonic acid (C20:4, AA), docosapentaenoic acid (C22:5, DPA), stearidonic acid (C18:4), linolenic acid (C18:3), and linoleic acid (C18:2). The derivatives of the highly unsaturated fatty acids that can be obtained with the acquisition method of the present invention refer to derivatives where fatty acids may or may not be the free type. For example, they can be, but are not limited to, highly unsaturated fatty acids, and ester-type derivatives such as methyl ester and ethyl ester, amide-type derivatives such as amide and methyl amide, fatty alcohol-type derivatives, triglyceride, diglyceride, and monoglyceride, of highly unsaturated fatty acids.

(11) The term silver salt as used herein refers to silver salt that may form a complex with unsaturated bonds in unsaturated fatty acids. For example, it can be, but is not limited to, silver nitrate, silver perchlorate, silver acetate, silver trichloroacetate, and silver trifluoroacetate. The silver salt is dissolved into water such that the concentration becomes, preferably 15% or higher, more preferably 20% or higher, and even more preferably 40% or higher, to achieve a silver salt aqueous solution, and this is used for purification of highly unsaturated fatty acid derivatives. In addition, the silver salt concentration in the silver salt aqueous solution is not particularly limited, but preferably the saturating concentration is the upper limit.

(12) The term antioxidant as used herein refers to a substance that reduces or removes harmful reactions involved with oxygen in living organisms, foods, daily necessities, and industrial raw materials. Representatively, the antioxidant can be, but is not limited to, butylhydroxytoluene, tocopherol, and a tocopherol derivative. For example, the tocopherol derivative can be, but is not limited to, d-?-tocopherol, d-?-tocopherol, d-?-tocopherol, d-?-tocopherol, 1-?-tocopherol, l-?-tocopherol, 1-?-tocopherol, and 1-?-tocopherol; dl-?-tocopherol, dl-?-tocopherol, dl-?-tocopherol, and dl-?-tocopherol, which are mixtures thereof; and tocopherol acetate, tocopherol succinate, tocopherol phosphate, tocopherol aspartate, tocopherol glutamate, tocopherol palmitate, tocopherol nicotinate, tocopherol linoleate, and polyethoxylated tocopherol, which are derivatives thereof.

(13) In the purification method of the present invention, the method of selectively separating highly unsaturated fatty acid derivatives from a mixture of derivatives of fatty acids is representatively performed by, but is not limited to: adding an aqueous solution of silver salt that may forma complex with unsaturated bonds into the above-described mixture of derivatives of fatty acids containing the highly unsaturated fatty acid derivatives; stirring preferably for 5 minutes to 4 hours, more preferably for 10 minutes to 2 hours to form the complex of water-soluble silver salt-highly unsaturated fatty acid derivatives; and selectively dissolving only the highly unsaturated fatty acid derivatives into a silver salt aqueous solution.

(14) In addition, with regard to the reaction temperature of the above-described highly unsaturated fatty acid derivatives and the silver salt aqueous solution, the lower limit can be any temperature as long as the silver salt aqueous solution is a liquid, and the upper limit is 100? C. However, in consideration of the oxidative stability of the highly unsaturated fatty acid derivatives, the solubility of silver salt to water, the generation speed of the complex, and the like, the reaction temperature is preferably 10 to 30? C.

(15) At the time of contacting the above-described highly unsaturated fatty acid derivatives with the silver salt aqueous solution, said contact is preferably performed under inert gas, e.g., nitrogen atmosphere, while blocking out light by considering the oxidative stability of the highly unsaturated fatty acid derivatives and the stability of silver salt. For example, by setting nitrogen atmosphere during production, incorporation of oxygen, which is the cause of oxidation, can be blocked, and it is also possible to suppress the increase of peroxides due to oxidation of raw materials. In addition, by blocking out the light, which promotes oxidation, it is possible to further suppress oxidation and suppress the increase of peroxides.

(16) The method of dissociating the highly unsaturated fatty acid derivatives from the complex of the above-described highly unsaturated fatty acid derivatives and silver salt is not particularly limited, but it is for example, extraction by organic solvents and a method of adding water to insolubilize the highly unsaturated fatty acid derivatives for separation.

(17) In the purification method/production method of highly unsaturated fatty acid derivatives using a mixture (raw materials) having a low peroxide value, which is the characteristic of the present invention, for example, it is possible to combine (1) management of the free fatty acid content in the mixture (raw materials) and/or (2) management of the acid value in the mixture (raw materials). For example, in an aspect of the present invention, the free fatty acid content in the silver salt aqueous solution is managed to 0.5 meq or smaller, 0.4 meq or smaller, 0.3 meq or smaller, 0.25 meq or smaller, 0.2 meq or smaller, 0.15 meq or smaller, 0.1 meq or smaller, or 0.07 meq or smaller. For example, in another aspect of the present invention, the acid value in the mixture (raw materials) can be managed to 10 or smaller, 9 or smaller, 8 or smaller, 7 or smaller, 6 or smaller, 5 or smaller, 4 or smaller, 3 or smaller, 2 or smaller, or 1 or smaller.

(18) Hereinafter, the purification method of highly unsaturated fatty acid derivatives of the present invention will be explained more specifically based on the Examples and the like. However, the present invention is not limited thereto.

EXAMPLES

Example 1

(19) A highly unsaturated fatty acid ethyl ester was purified from a fatty acid ethyl ester mixture by the following method.

(20) Firstly, 50 g of distilled water was added to 50 g of silver nitrate to be stirred/dissolved. 20 g of a mixture of fatty acid ethyl esters (acid value 0.7; POV 6; EPA ethyl ester purity 44.9% (fatty acid composition area %); DHA ethyl ester purity 7.4%) was mixed with 100 g of this silver nitrate aqueous solution, and stirring was performed for 30 minutes at 20? C. Subsequently, the solution was left to stand for 30 minutes, and was separated into two layers. This upper layer was disposed, and only the lower layer was separately collected for addition of 100 g of cyclohexane to be stirred for 30 minutes at 60? C. Subsequently, the solution was left to stand for 30 minutes, and was separated into two layers. This upper layer was separately collected to obtain a concentrate of highly unsaturated fatty acid ethyl esters. In addition, the lower layer containing silver nitrate was separately taken to measure the free fatty acid content. This lower layer containing silver nitrate was used for purification of highly unsaturated fatty acid ethyl esters again. The above-described reactions were carried out under nitrogen atmosphere. These operations were repeated.

(21) TABLE-US-00001 TABLE 1 (Summary of results of Example 1) Fatty acid derivative Purified highly unsaturated fatty acid derivative Batch peroxide EPA ethyl DHA ethyl peroxide EPA ethyl DHA ethyl number value acid value ester (%) ester (%) value acid value yield (%) ester (%) ester (%) 1 6.0 0.7 44.9 7.4 5.6 0.7 46.5 76.8 13.5 2 5.9 0.7 47.0 77.0 13.4 3 6.4 0.6 46.9 77.2 13.1 4 5.5 0.8 46.5 76.9 13.3 5 5.8 0.8 46.7 76.5 13.6 6 6.1 0.8 46.9 77.1 13.1 7 6.3 0.8 46.7 76.9 13.6 8 5.9 0.8 47.2 77.2 13.0 9 5.7 0.8 46.9 76.7 13.4 10 6.0 0.8 47.1 77.0 13.1

(22) The results of treating 10 batches of the above-described mixture are shown in the above-described Table 1.

Example 2 (Using Raw Materials Having Various POVs and Acid Values)

(23) A highly unsaturated fatty acid ethyl ester was obtained from a fatty acid ethyl ester mixture by the following method.

(24) Firstly, 50 g of distilled water was added to 50 g of silver nitrate to be stirred/dissolved. 20 g of a mixture of fatty acid ethyl esters (acid value 0.2 to 1.5; POV 1.0 to 9.5; EPA ethyl ester purity 40-48% (fatty acid composition area %); DHA ethyl ester purity 5-10%) was mixed with 100 g of this silver nitrate aqueous solution, and stirring was performed for 30 minutes at 20? C. Subsequently, the solution was left to stand for 30 minutes, and was separated into two layers. This upper layer was disposed, and only the lower layer was separately collected for addition of 100 g of cyclohexane to be stirred for 30 minutes at 60? C. Subsequently, the solution was left to stand for 30 minutes, and was separated into two layers. This upper layer was separately collected to obtain a concentrate of highly unsaturated fatty acid ethyl esters. In addition, the lower layer containing silver nitrate was separately taken to measure the free fatty acid content. This lower layer containing silver nitrate was used for purification of highly unsaturated fatty acid ethyl esters again. The above-described reactions were carried out under nitrogen atmosphere. These operations were repeated.

(25) TABLE-US-00002 TABLE 2 (Summary of results of Example 2) Using raw materials having various POVs and acid values Fatty acid derivative Purified highly unsaturated fatty acid derivative Batch peroxide EPA ethyl DHA ethyl peroxide EPA ethyl DHA ethyl number value acid value ester (%) ester (%) value acid value yield (%) ester (%) ester (%) 1 1.5 0.2 40.5 9.5 1.6 0.2 43.0 72.5 18.4 2 2.0 0.2 43.8 71.9 18.9 3 1.9 0.2 43.2 72.1 18.6 4 9.5 0.9 43.8 7.6 8.6 0.9 46.2 76.9 13.3 5 9.3 0.9 46.5 76.5 13.6 6 9.8 0.9 46.3 77.1 13.1 7 5.2 1.5 47.8 6.8 5.1 1.4 46.7 76.9 13.6 8 5.8 1.6 47.2 77.2 13.0 9 4.9 1.5 46.9 76.7 13.4 10 5.5 1.3 47.1 77.0 13.1

(26) The results of treating 10 batches of the above-described mixture are shown in the above-described Table 2. These results show that the peroxide values do not correlate with the acid values, and that remarkable purity and yield could be obtained by setting the peroxide value to 10 or smaller.

Example 3 (Using Raw Materials where POV 15 of Raw Materials is Decreased to POV 1 with Activated Clay)

(27) A highly unsaturated fatty acid ethyl ester was obtained from a fatty acid ethyl ester mixture by the following method.

(28) Firstly, 10 g of activated clay was added to 1 kg of a mixture of fatty acid ethyl esters (acid value 0.5; POV 15; EPA ethyl ester purity 45.3% (fatty acid composition area %); DHA ethyl ester purity 6.8%) to be stirred for 30 minutes at 50? C. under nitrogen atmosphere. Subsequently, the activated clay was removed by filtering, and when POV was measured, it was 1.0. 20 g of this mixture of fatty acid ethyl esters (acid value 0.6; POV 1.0) was mixed with 100 g of a silver nitrate aqueous solution, where 50 g of distilled water was added to 50 g of silver nitrate to be stirred/dissolved, and stirring was performed for 30 minutes at 10? C. Subsequently, the solution was left to stand for 30 minutes, and was separated into two layers. This upper layer was disposed, and only the lower layer was separately collected for addition of 200 g of cyclohexane to be stirred for 30 minutes at 40? C. Subsequently, the solution was left to stand for 30 minutes, and was separated into two layers. This upper layer was separately collected to obtain a concentrate of highly unsaturated fatty acid ethyl esters. In addition, the lower layer containing silver nitrate was separately taken to measure the free fatty acid content. This lower layer containing silver nitrate was used for purification of highly unsaturated fatty acid ethyl esters again. The above-described reactions were carried out under nitrogen atmosphere. These operations were repeated.

(29) TABLE-US-00003 TABLE 3 (Summary of Results of Example 3) (Using raw materials where POV 15 of raw materials is decreased to POV 1 with activated clay) Fatty acid derivative Purified highly unsaturated fatty acid derivative Batch peroxide EPA ethyl DHA ethyl peroxide EPA ethyl DHA ethyl number value acid value ester (%) ester (%) value acid value yield (%) ester (%) ester (%) 1 1.0 0.6 45.3 6.8 1.1 0.6 47.1 77.0 12.9 2 0.9 0.6 46.9 77.2 12.6 3 1.3 0.7 46.8 77.1 12.9 4 1.0 0.6 47.0 76.9 13.1 5 1.6 0.7 47.2 77.1 13.0 6 1.3 0.6 46.9 77.3 12.6 7 1.1 0.7 47.3 77.5 12.4 8 1.2 0.7 46.8 77.1 12.8 9 1.3 0.6 46.9 76.9 13.1 10 0.9 0.6 47.2 77.2 12.8

(30) The results of treating 10 batches of the above-described mixture are shown in the above-described Table 3. These results demonstrate that a remarkable effect was exerted by decreasing the peroxide value from 15 to 1.0.

Comparative Example 1 (Using Raw Materials with POV 15 Before the Decrease of POV in Example 3)

(31) A highly unsaturated fatty acid ethyl ester was obtained from a fatty acid ethyl ester mixture by the following method.

(32) 20 g of a mixture of fatty acid ethyl esters (acid value 0.5; POV 15; EPA ethyl ester purity 45.3% (fatty acid composition area %); DHA ethyl ester purity 6.8%) was mixed with 100 g of a silver nitrate aqueous solution, where 50 g of distilled water was added to 50 g of silver nitrate to be stirred/dissolved, and stirring was performed for 60 minutes at 10? C. Subsequently, the solution was left to stand for 30 minutes, and was separated into two layers. This upper layer was disposed, and only the lower layer was separately collected for addition of 200 g of cyclohexane to be stirred for 30 minutes at 40? C. Subsequently, the solution was left to stand for 30 minutes, and was separated into two layers. This upper layer was separately collected to obtain a concentrate of highly unsaturated fatty acid ethyl esters. In addition, the lower layer containing silver nitrate was separately taken to measure the free fatty acid content. This lower layer containing silver nitrate was used for purification of highly unsaturated fatty acid ethyl esters again. The above-described reactions were carried out under nitrogen atmosphere. These operations were repeated.

(33) TABLE-US-00004 TABLE 4 (Summary of results of Comparative Example 1) Using raw materials before the decrease of POV in Example 3 Fatty acid derivative Purified highly unsaturated fatty acid derivative Batch peroxide EPA ethyl DHA ethyl peroxide EPA ethyl DHA ethyl number value acid value ester (%) ester (%) value acid value yield (%) ester (%) ester (%) 1 15.0 0.5 45.3 6.8 15.2 0.6 46.5 76.8 13.5 2 14.6 0.7 46.2 77.1 13.2 3 15.3 0.8 45.8 76.9 13.7 4 15.0 0.8 45.4 77.2 13.2 5 15.5 0.9 45.2 77.3 13.1 6 14.9 0.8 44.6 76.9 13.8 7 15.2 0.8 44.2 76.5 13.9 8 15.4 0.9 43.7 76.2 14.1 9 14.7 0.9 43.1 76.1 14.3 10 15.2 0.9 42.3 76.3 14.1

(34) The results of treating 10 batches of the above-described mixture are shown in the above-described Table 4. When compared to the results of Table 3 (the case where the peroxide value is decreased from 15 to 1.0), the results of Table 4 demonstrate that a remarkable effect of the present invention was confirmed by decreasing the peroxide value from 15 to 1.0.

Comparative Example 2 (Conducted by Changing the Condition of Example 1, which is Under Nitrogen Atmosphere, to an Open Air System)

(35) A highly unsaturated fatty acid ethyl ester was obtained from a fatty acid ethyl ester mixture by the following method.

(36) Firstly, 50 g of distilled water was added to 50 g of silver nitrate to be stirred/dissolved. 20 g of a mixture of fatty acid ethyl esters (acid value 0.7; POV 6; EPA ethyl ester purity 44.9% (fatty acid composition area %); DHA ethyl ester purity 7.4%) was mixed with 100 g of this silver nitrate aqueous solution, and stirring was performed for 60 minutes at 20? C. Subsequently, the solution was left to stand for 60 minutes, and was separated into two layers. This upper layer was disposed, and only the lower layer was separately collected for addition of 100 g of cyclohexane to be stirred for 60 minutes at 60? C. Subsequently, the solution was left to stand for 30 minutes, and was separated into two layers. This upper layer was separately collected to obtain a concentrate of highly unsaturated fatty acid ethyl esters. In addition, the lower layer containing silver nitrate was separately taken to measure the free fatty acid content. This lower layer containing silver nitrate was used for purification of highly unsaturated fatty acid ethyl esters again. The above-described reactions were carried out in an open air system. These operations were repeated.

(37) TABLE-US-00005 TABLE 5 (Summary of results of Comparative example 2) Conducted by changing the condition of Example 1, which is under nitrogen atmosphere, to an open air system Fatty acid derivative Purified highly unsaturated fatty acid derivative Batch peroxide EPA ethyl DHA ethyl peroxide EPA ethyl DHA ethyl number value acid value ester (%) ester (%) value acid value yield (%) ester (%) ester (%) 1 6.0 0.7 44.9 7.4 12.3 0.6 46.5 77.0 12.9 2 19.5 0.7 46.0 77.2 12.6 3 20.1 0.6 45.7 77.1 12.9 4 22.3 0.7 45.2 76.9 13.1 5 16.4 0.8 44.9 77.1 13.0 6 20.1 0.7 44.2 77.3 12.6 7 19.6 0.7 43.9 77.5 12.4 8 22.1 0.7 43.1 77.1 12.8 9 20.3 0.8 42.7 76.9 13.1 10 18.5 0.8 42.1 77.2 12.8

(38) The results of treating 10 batches of the above-described mixture are shown in the above-described Table 5. When these results are compared to the results of Example 1, it is demonstrated that the results under nitrogen atmosphere exert a more remarkable effect than the case of the open air system.

(39) As described above, the present invention is exemplified by the use of its preferred Embodiments of the present invention. However, the present invention should not be interpreted solely based on the Embodiments. It is understood that the scope of the present invention should be interpreted solely based on the scope of the claims. It is also understood that those skilled in the art can implement equivalent scope of technology, based on the description of the present invention and common knowledge from the description of the detailed preferred Embodiments of the present invention. Furthermore, it is understood that any patent, any patent application and any references cited in the present specification should be incorporated by reference in the present specification in the same manner as the contents are specifically described therein.

INDUSTRIAL APPLICABILITY

(40) According to the present invention, a method of producing/purifying highly unsaturated fatty acids and/or derivatives thereof while suppressing deterioration of a silver salt aqueous solution is provided in production/purification of highly unsaturated fatty acids and/or derivatives thereof using the aqueous solution of silver salt.