Method for inhibiting oxiation of oils and fats or fatty acids

Abstract: A method for inhibiting the oxidation of oils and fats or fatty acids which comprises adding an antioxidant and an oxyacid having an average particle size of 200 µm or less to said oils and fats or fatty acids. According to this method, the oxyacid is easily dispersed or dissolved in said oils and fats or fatty acids, and the oxidation inhibiting effect is remarkably improved without deteriorating the quality of the oils and fats or fatty acids.

Description: FIELD OF THE INVENTION This invention relates to a method for inhibiting the oxidation of fatty acids, and more particularly to a method for inhibiting oxidation which comprises adding an antioxidant together with a hydroxy carboxylic acid (hereinafter referred to as an oxyacid) as a synergist to fatty acids, wherein the oxyacid is added in the form of finely divided grains. BACKGROUND OF THE INVENTION Fatty acids and their derivatives obtained from animal or plant sources are used in many industrial fields because of their surface-modifying functions, lubrication functions and physiological activities. However, fatty acids, especially unsaturated fatty acids, tend to undergo oxidation which causes coloring of fatty acids and the formation of peroxides that generate unpleasant odors. Fatty acids and their derivatives changed in quality by degradation of such peroxides are not desirable as materials for food, cosmetics, pharmaceutical drugs and the like. Antioxidants are generally used to prevent oxidation of fatty acids. In an oxygen-contacting system, however, the oxidation inhibiting effect does not last long because of rapid consumption of the antioxidant. Addition of an antioxidant in a large quantity (500 ppm or more) to strengthen its oxidation inhibiting effect is not desirable because it causes side reactions. For example, in the process of soap production, soap often develops an undesirable color when prepared by saponification. Consequently, in order to minimize the amount of antioxidant while simultaneously improving the oxidation inhibiting effect, concurrent use of a synergist is generally practiced. Examples of synergists having an oxidation inhibition function include oxyacids, phosphoric acid and derivatives thereof, various amino acids and derivatives thereof, flavone derivatives, sulfur compounds and the like, of which oxyacids are most widely used. German Patent Publication No. 2,038,468 discloses a process for the purification of fatty acids in which oxyacids are added to fatty acids and then distilled. This process, however, is insufficient to inhibit the oxidation of fatty acids. Also, because they have a low solubility in fatty acids, oxyacids are generally added in the form of aqueous or alcohol solution to fatty acids, water or alcohol is sufficiently removed by distillation under reduced pressure and then excess crystalized oxyacids are removed. This method, however, is not advantageous from an industrial point of view due to the reduction in quality of fatty acids caused by the solvent remaining after distillation, as well as the considerable time and labor required for carrying out these operation steps. In addition, the use of ester derivatives of oxyacids with monoglycerides has been proposed and practiced with the aim of increasing their solubilities in oils and fats or fatty acids. However, the effects of such ester derivatives are insufficient and they are expensive as compared to oxyacids. Techniques for dispersing oxyacid solutions making use of surface active agents and the like have also been practiced. However, such surface active agents, solvents and the like become impurities in the oils and fats or fatty acids and reduce the quality of the resulting products. WO 93/00015 discloses suspensions of micron-sized ascorbic acid particles and their use as antioxidants for substrates in which ascorbic acid is insoluble such as animal and vegetable oils and other oily substances. Further disclosed is the inclusion of a natural antioxidant, such as tocopherol, in such compositions. SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a method for inhibiting the oxidation of fatty acids which comprises adding both an antioxidant and an oxyacid to said fatty acids. In this method, the oxyacid is dispersed or dissolved by a simple operation without reducing the qualities of the fatty acids, to thereby remarkably improve the oxidation inhibiting effect. With the aim of achieving the above object, the present inventors have conducted extensive studies and found that the dispersibility or solubility of oxyacids in fatty acids is remarkably increased when the oxyacid in the form of finely divided particles is added concurrently with an antioxidant. The present invention has been accomplished on the basis of this finding. Accordingly, the present invention relates to a method for inhibiting oxidation of fatty acids which comprises adding an antioxidant selected from t-butylhydroxyanisole and 2,6-di-t-butyl-p-cresol and hydroxy carboxylic acid selected from tartaric acid, citric acid and malic acid having an average particle size of 200 µm or less to said fatty acids. According to this method, oxyacids are easily added and the oxidation inhibition effect is remarkably improved without degrading the quality of fatty acids. Other objects and advantages of the present invention will be apparent from the following detailed description. DETAILED DESCRIPTION OF THE INVENTION Examples of fatty acids for use in the present invention include those which are obtained by hydrolyzing animal and plant oils, such as tallow fatty acid, lard fatty acid, milk fat fatty acid, palm oil fatty acid, palm kernel oil fatty acid, soybean oil fatty acid, rapeseed oil fatty acid, coconut oil fatty acid, cotton seed oil fatty acid, safflower oil fatty acid, linseed oil fatty acid, sunflower oil fatty acid, olive oil fatty acid, rice oil fatty acid, corn oil fatty acid, tung oil fatty acid, camellia oil fatty acid, fish oil fatty acid, jojoba oil fatty acid, and hydrogenation-refined, bleached, dried and deodorized fatty acids thereof, as well as free fatty acids obtained by solid-liquid separation or fractional distillation of the above fatty acids, such as oleic acid, linoleic acid, erucic acid, linolenic acid, lauric acid, myristic acid, palmitic acid and stearic acid. The antioxidant for use in the present invention is 2,6-di-t-butyl-p-cresol or t-butylhydroxyanisole. These antioxidants may be used in an amount of preferably from 1 to 500 ppm based on the weight of the fatty acids, more preferably from 10 to 300 ppm based on the weight of the fatty acids or from 10 to 200 ppm based on the weight of the fatty acids. The oxyacid used in the present invention is tartaric acid, citric acid or malic acid. According to the present invention, these oxyacids are formed into finely divided particles having an average particle size of 200 µm or less, preferably 100 µm or less, which may be effected either by wet grinding or dry grinding. Wet grinding is desirable for the purpose of preventing secondary aggregation after grinding. When dry grinding is employed, it is desirable to disperse the finely divided oxyacid in an appropriate dispersion medium using a disoersion machine, and then adding the dispersion to the oils and fats or fatty acids. When wet grinding is employed, it is desirable to use fatty acids, especially those to which the oxyacid is added, as the dispersion medium. The grinding machine is not particularly limited, and includes a sand mill, a bead mill and a media mill. Illustrative examples of the grinding machine include the Pearl Mill and Super Mill manufactured by Ashizawa Ltd., the Sand Mill, Media Mill and Super Mill manufactured by Inoue Seisakusho K.K. and Attritor and the Bead Mill and My Mill manufactured by Mitsui miike Machine Co., Ltd. With regard to the construction material of the grinding mill, ceramic or ceramic-coated materials are preferred. The concentration of the oxyacid in the dispersion medium at the time of grinding may be in the range of from 1 to 40% by weight, preferably from 10 to 30% by weight. According to the present invention, when the thus finely divided oxyacid is added together with the aforementioned antioxidant to fatty acids, the oxyacid is easily dispersed or dissolved in the fatty acids. As a result, the oxidation inhibition effect is improved while avoiding the problems of the prior art such as coloring due to the use of a large amount of antioxidant and quality reduction due to contamination by impurities. The thus finely divided oxyacid may be added to fatty acids in an amount of preferably from 50 to 1,000 ppm, more preferably from 200 to 800 ppm based on the weight of the fatty acids. Thus, according to the present invention, a finely divided oxyacid and an antioxidant are both added to fatty acids. As a result, the oxyacid is easily added to fatty acids and a remarkable increase in the oxidation inhibition effect is obtained without causing coloring, quality reduction and the like problems. EXAMPLES The following Examples are provided to further illustrate the present invention. It is to be understood, however, that these Examples are for the purpose of illustration only, and are not to be construed as limiting the invention. In the following Examples, each oxyacid was used in the form of a dry-ground powder (dry-ground into a predetermined particle size using a Jet Mill manufactured by Nippon Pneumatic Mfg. Co., Ltd. as a dry grinding machine) or wet-ground powder (wet-ground into a predetermined particle size in an amount of 20% by weight in a dispersion medium using a Pearl Mill manufactured by Ashizawa Ltd. as a wet grinding machine and palm oil fatty acid as the dispersing medium), and the particle size of each oxyacid was measured using a Microtrack manufactured by Nikkisou Co., Ltd. Inventive Example 1 A 50 ppm portion of t-butylhydroxyanisole and 500 ppm of tartaric acid finely wet-ground to have an average particle size of 50 µm were added to palm oil fatty acid (neutralization value: 207.5, iodine value: 53.2) which had been obtained by distilling palm oil-hydrolyzed fatty acid. The mixture was stored at 80°C in the presence of air and its peroxide value was measured periodically in accordance with Standard Oil and Fat Analytical Method JOCS (Official and Tentative Methods of the Japan Oil Chemist's Society) 2.4.12-86. After an 8-day storage period, the fatty acid was made into soap in the manner described below, to conduct a soap color measurement and a DEA coloring test (Diethanolamine heat color stability test). The results are shown in Tables 1 (Peroxide value) and 2 (Color of soap and DEA coloring test). 〈Soap color measurement〉 The fatty acid sample was mixed with an equimolar amount of sodium hydroxide aqueous solution (28% by weight), kneaded using a double arm mill, dried to a water content of about 15% by weight, compressed with a plodder and then molded using a soap press. Whiteness (W) and yellowness (b) of the thus obtained soap were measured using a SM color computer manufactured by Suga Test Instruments Co., Ltd. 〈DEA coloring test〉 The fatty acid sample was mixed with an equimolar amount of diethanolamine and ethanol, the mixture was allowed to react for 20 minutes in a boiling water bath, and then the hue of the resulting sample was measured in accordance with the APHA method (Standard Oil and Fat Analytical Method JOCS 2.3.2.5-71). When the hue exceeded APHA 500, it was measured in accordance with the Gardner method (Standard Oil and Fat Analytical Method JOCS 2.3.1.3-71). Comparative Example 1 Palm oil-hydrolyzed fatty acid (neutralization value: 207.5, iodine value: 53.2) was distilled in the same manner as described in Inventive Example 1, and 50 ppm of t-butylhydroxyanisole was added to the resulting palm oil fatty acid. The mixture was stored at 80°C in the presence of air and its peroxide value was measured in the same manner as described in Inventive Example 1. After an 8-day storage period, the fatty acid was made into soap to conduct a soap color measurement and DEA coloring test in the same manner as described in Inventive Example 1. The results are shown in Tables 1 and 2. Comparative Example 2 Palm oil-hydrolyzed fatty acid was distilled in the same manner as described in Inventive Example 1, and t-butylhydroxyanisole was added in an amount of as much as 500 ppm to the resulting palm oil fatty acid (neutral value: 207.5, iodine value: 53.2). The mixture was stored at 80°C in the presence of air, and its peroxide value was measured in the same manner as described in Inventive Example 1. After an 8-day storage period, the fatty acid was made into soap to conduct a soap color measurement and DEA coloring test in the same manner as described in Inventive Example 1. The results of these tests are shown in Tables 1 and 2. Inventive Example 2 Beef tallow-hydrolyzed fatty acid was distilled to obtain tallow fatty acid, (neutralization value: 205.4, iodine value: 52.7) to which was subsequently added 50 ppm of 2,6-di-t-butyl-p-cresol and 500 ppm of tartaric acid. The tartaric acid had been finely divided to have an average particle size of 100 µm by dry grinding. The resulting mixture was stored at 80°C in the presence of air, and its peroxide value was measured in the same manner as described in Inventive Example 1. After an 8-day storage period, the fatty acid sample was made into soap to conduct a soap color measurement and DEA coloring test in the same manner as described in Inventive Example 1. The results are shown in Tables 1 and 2. Inventive Example 3 Palm oil-hydrolyzed fatty acid (neutralization value: 206.8, iodine value: 52.5) was subjected to hydrogenation at 160-200°C under a hydrogen pressure of 3 atmospheric pressures in the presence of a nickel catalyst to reduce the iodine value by 10 and then distilled. The resulting palm oil fatty acid was mixed with 50 ppm of 2,6-di-t-butyl-p-cresol and 500 ppm of citric acid which had been finely divided by dry grinding to have an average particle size of 50 µm. The mixture was stored at 80°C in the presence of air, and its peroxide value was measured in the same manner as described in Inventive Example 1. The results are shown in Table 1 below. After an 8-day storage period, the fatty acid sample was made into soap to conduct a soap color measurement and the DEA coloring test in the same manner as described in Inventive Example 1. The results are shown in Table 2 below. In order to evaluate the stability of soap, the fatty acid sample just after preparation was made into a soap in the same manner as described in Inventive Example 1. The thus prepared soap, packaged with a polyethylene bag (Unipack manufactured by Seisannihonsha Co., Ltd.) and aged at 40°C to measure the change with time of the whiteness (W) and yellowness (b) using an SM color computer (manufactured by Suga Test Instruments Co., Ltd.) The results are shown in Table 3 below. Comparative Example 3 The same palm oil-hydrolyzed fatty acid (neutralization value: 206.8, iodine value: 52.5) as used in Inventive Example 3 was treated and mixed with 2,6-di-t-butyl-p-cresol and citric acid in the same manner as described in Inventive Example 3 except that the citric acid used was an unground one having an average particle size of 350µm. The mixture was stored at 80°C in the presence of air and its peroxide value was measured in the same manner as described in Inventive Example 1. The results are shown in Table 1 below. After an 8-day storage period, the fatty acid sample was made into soap to conduct a soap color measurement and the DEA coloring test in the same manner as described in Inventive Example 1. The results are shown in Table 2 below. In order to evaluate the stability of soap, the fatty acid sample just after preparation was made into a soap in the same manner as described in Invention Example 1. The thus prepared soap was packaged and aged to measure the change with time of the whiteness (W) and yellowness (b) in the same manner as described in Inventive Example 1. The results are shown in Table 3 below. Peroxide value (milliequivalent/kg) After storage for: just after preparation 2 days 4 days 6 days 8 days 10 days 12 days Inventive Example 1 0.1 0.2 0.2 0.5 0.8 1.0 1.8 Comparative Example 1 0.1 2.1 4.8 7.0 9.1 13.5 28.0 Comparative Example 2 0.1 0.2 0.2 0.4 0.6 0.9 1.3 Inventive Example 2 0.1 0.2 0.3 0.5 0.8 1.5 2.9 Inventive Example 3 0.1 0.2 0.3 0.3 0.7 1.0 1.6 Comparative Example 3 0.1 1.2 2.5 3.1 5.2 8.8 11.2 Color of soap DEA coloring test Whiteness (W) Yellowness (b) APHA method Gardner method Inventive Example 1 88 4 180 - Comparative Example 1 75 8 500+ G5 Comparative Example 2 75 9 500+ G5 Inventive Example 2 88 4 180 - Inventive Example 3 92 3 150 - Comparative Example 3 80 8 500+ G4 Color of soap After storage for: just after preparation 4 days 8 days 12 days 16 days Inventive Example 3 Whiteness(W) 95 94 92 88 84 Yellowness(b) 3 3 4 5 6 Comparative Example 3 Whiteness(W) 95 87 79 74 67 Yellowness(b) 3 7 11 14 18 Thus, the results of the fatty acid oxidation stability tests conducted in Inventive Examples 1 to 3 and Comparative Examples 1 to 3 (the peroxide value, color of soap and DEA coloring test of Tables 1 and 2) show that the method of the present invention is excellent in inhibiting oxidation of fatty acids, and does not cause problems such as coloring at the time of formation of derivatives such as soap. Therefore, the present invention provides an industrially useful method for inhibiting oxidation. The excellent oxidation inhibiting effect obtained by the method of the present invention is mainly based on the good dispersibility of finely divided oxyacids in fatty acids. This is confirmed by the following dispersibility test in which ascorbic acid was used as the oxyacid and palm oil fatty acid was used as the dispersion medium. 〈Dispersibility test〉 Samples of ascorbic acid used in the test were of unground commercially available ascorbic acid having an average particle size of 350 µm. The following 4 ground samples having particle sizes of 100 µm or less were prepared by subjecting the above commercial product to dry or wet grinding. Dry grinding sample 1: average particle size 70 µm Dry grinding sample 2: average particle size 40 µm Wet grinding sample 1: average particle size 20 µm Wet grinding sample 2: average particle size 5 µm A 500 ppm portion of each of the above unground sample and 4 ground samples was added to palm oil fatty acid, and its dispersing or dissolving state was observed under a gently stirred condition (adjusted to 300 rpm using a turbine blade having a diameter of about 1/2 that of the vessel) to evaluate its dispersibility or solubility based on the following criterion. The results are shown in Table 4. o: Perfectly clear liquid showing sufficient dissolution ▵: Cloudy liquid showing dispersion but insufficient dissolution X: Precipitation in the bottom showing almost no dispersion Inventive Samples Comparative Sample Dry 1 Dry 2 Wet 1 Wet 2 unground Average particle size (µm) about 70 about 40 about 20 about 5 about 350 Dispersibility after: 0 hr ▵ ▵ ▵ ▵ X 0.5 hr ▵ ▵ o o X 1 hr ▵ o o o X 3 hrs o o o o X 6 hrs o o o o X 24 hrs o o o o X The results of Table 4 show that the ground oxyacid has excellent dispersibility or solubility as compared to the unground sample. Additionally, dispersibility or solubility is further improved as the average particle size of the oxyacid is decreased by wet-grinding. While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof.

Claims: A method for inhibiting oxidation of fatty acids which comprises adding an antioxidant selected from t-butylhydroxyanisole and 2,6-di-t-butyl-p-cresol and hydroxy carboxylic acid selected from tartaric acid, citric acid and malic acid having an average particle size of 200 µm or less to said fatty acids. A method according to Claim 1, wherein the hydroxy carboxylic acid is prepared by wet grinding in a dispersion medium formed from fatty acids. A method according to Claim 1 or Claim 2, wherein 1-500 ppm of the antioxidant is added to the fatty acids. A method according to Claim 3, wherein 10-300 ppm of the antioxidant is added to the fatty acids. A method according to Claim 4, wherein 10-200 ppm of the antioxidant is added to the fatty acids. A method according to any preceding Claim, wherein 50-2000 ppm of the hydroxy carboxylic acid is added to the fatty acids. The method according to Claim 6, wherein 100 to 1000 ppm of the hydroxy carboxylic acid is added to the fatty acids. A method according to any preceding Claim, wherein said hydroxy carboxylic acid has an average particle size of 100 µm or less. A method according to Claim 8, wherein said hydroxy carboxylic acid has an average particle size of 70 µm or less. A method according to Claim 9, wherein said hydroxy carboxylic acid has an average particle size of 40 µm or less. A method according to Claim 10, wherein said hydroxy carboxylic acid has an average particle size of 20 µm or less. A method according to Claim 8, wherein said hydroxy carboxylic acid has an average particle size of from 5 to 100 µm. A method according to Claim 12, wherein said hydroxy carboxylic acid has an average particle size of from 5 to 40 µm. A method according to Claim 13, wherein said hydroxy carboxylic acid has an average particle size of from 5 to 20 µm. A method according to Claim 1, wherein said hydroxy carboxylic acid having an average particle size of 200 µm or less is prepared by dry grinding. A mixture that is stable to oxidation comprising fatty acids, an antioxidant and hydroxy carboxylic acid, wherein said hydroxy carboxylic acid has an average particle size of 200 µm or less and is dispersed in said fatty acids. A mixture according to Claim 16, wherein said hydroxy carboxylic acid has an average particle size of 100 µm or less. A mixture according to Claim 16, wherein said hydroxy carboxylic acid has an average particle size of 40 µm or less. The use of a mixture according to any of Claims 16-18 in foods, cosmetics or medicaments.

Inventors: MATSUO TAKESHI, OHHATA YOSHIHIRO, SUGINO MASAAKI, TAKAYANAGI ISAO, TAKEO HIROYUKI, YAMAMOTO HIDETO, MATSUO, TAKESHI, OHHATA, YOSHIHIRO, SUGINO, MASAAKI, TAKAYANAGI, ISAO, TAKEO, HIROYUKI, YAMAMOTO, HIDETO, OHHATA, YOSHIHIRO, C/O SHISEIDO KUKI FACTORY, TAKAYANAGI, ISAO, C/O SHISEIDO KUKI FACTORY
Applicants: NOF CORP, SHISEIDO CO LTD, NOF CORPORATION, SHISEIDO COMPANY LIMITED
Application year: 1995
Main classification: C11B5
IPC codes: C11B5