Method for measuring lipid oxidation level, sheet for measuring lipid oxidation level, reagent for measuring lipid oxidation level

Abstract

To provide a method of measuring a lipid oxidation degree, which allows sample preparation by a simple method.SOLUTION: Provided is a lipid oxidation degree measurement method for measuring the degree of lipid oxidation of oil in a specimen, the method including: an adsorption step of adsorbing an oil content in a specimen to an oil content adsorption sheet having a thickness of 100 μm or less; and a reaction step of performing a color reaction between a lipid peroxide in the oil content and a color reagent, with the oil content adsorbed to the oil content adsorption sheet. According to the lipid oxidation degree measurement method of the present invention, the degree of lipid oxidation can be measured by a simple operation because the color reaction is carried out in a state in which the oil is adsorbed to the oil adsorption sheet after the oil in the specimen is adsorbed to the oil adsorption sheet having a thickness of 100 μm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for measuring the degree of lipid oxidation of oil in a subject. The present invention also relates to a sheet for measuring the degree of lipid oxidation and a reagent for measuring the degree of lipid oxidation used in the method for measuring the degree of lipid oxidation.

Background Art

[0002] In oil-containing foods such as meat processed foods and oil processed foods, when the oil oxidizes, the flavor deteriorates. Therefore, the degree of oxidation of the lipids in the products and raw materials is measured to control the quality. As a method for measuring the degree of lipid oxidation, a method of measuring the content of lipid peroxides by a color reaction is known. For example, Patent Document 1 discloses a TBA test paper composed of a dried fiber piece or cloth piece impregnated with a 2-thiobarbituric acid (TBA) reagent containing a non-volatile acid and a divalent iron salt. In this TBA test paper, the oil of the subject is placed, water is dropped thereon, and then heated with an infrared lamp for 10 minutes to perform a color reaction between TBA and lipid peroxides. In addition, Non-Patent Document 1 discloses a method for measuring the degree of lipid oxidation of meat using a TBA test paper. In this method, an aqueous potassium chloride solution is added to a minced sample to prepare a homogenate, and the TBA test paper is impregnated with this homogenate sample. In the discussion of this document, it is described that it is possible to measure the degree of lipid oxidation using a TBA test paper by preparing a solid sample such as meat in a liquid state.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Non-Patent Documents

[0004]

Non-Patent Document 1

[0005] In the invention described in Patent Document 1, liquid oils and fats are used as the sample applied to the TBA test paper. In the invention described in Non-Patent Document 1, a liquid sample is prepared by mincing the material and then homogenizing it with an extraction solvent. Therefore, when measuring the lipid oxidation degree of oils contained in a solid sample, there is a problem in that sample preparation is complicated. Therefore, the object of the present invention is to provide a method for measuring lipid oxidation levels that allows for the preparation of samples in a simple manner. [Means for solving the problem]

[0006] The inventors of the present invention, after diligently investigating the above problem, focused on the fact that when oil (fat) contained in a solid sample is applied to TBA test paper, uneven color development occurs, resulting in unstable test results. They then discovered that by attaching an oil-absorbing sheet with a thickness of 100 μm or less, the oil is evenly absorbed by the oil-absorbing sheet, resulting in uniform color development and enabling measurement of lipid oxidation degree. Based on this finding, the inventors completed the present invention. In other words, the present invention relates to the following lipid oxidation degree measurement sheet, lipid oxidation degree measurement reagent, and lipid oxidation degree measurement method.

[0007] The lipid oxidation degree measuring sheet of the present invention, which solves the above problems, is a lipid oxidation degree measuring sheet comprising an oil adsorption sheet for adsorbing oil, characterized in that the thickness of the oil adsorption sheet is 100 μm or less. The lipid oxidation degree measurement sheet of the present invention has a thickness of 100 μm or less, so when the oil-adsorbing sheet is attached to a solid sample, the oil is evenly adsorbed onto the sheet. As a result of the even adsorption of oil onto the sheet, uniform color development is observed, and the test results are stable. Furthermore, since it is possible to measure the lipid oxidation degree without preparing solid lipids into liquid samples, a lipid oxidation degree measurement method that allows for simple sample preparation can be provided. Moreover, the measurement time can be significantly reduced.

[0008] Furthermore, the lipid oxidation degree measuring reagent of the present invention is characterized by containing 2-thiobarbituric acid and urea. The lipid oxidation degree measuring reagent of the present invention contains urea, which enhances the color development in the color reaction between TBA and lipid peroxides. This enhancement of color development improves analytical accuracy. Furthermore, when performing the color reaction between TBA and lipid peroxides with oil adsorbed onto an oil adsorption sheet, there is a problem of weak color development, so the effect of enhancing color development is even more pronounced.

[0009] One embodiment of the lipid oxidation degree measuring reagent of the present invention is characterized by containing trehalose and being in a solid state. A problem with colorimetric reagents containing TBA is that sodium sulfite and ferrous sulfate react and turn green when stored as a solution. However, by making the lipid oxidation level measuring reagent a solid, discoloration is suppressed, resulting in excellent storage stability. Furthermore, by including trehalose, moisture absorption of the solid lipid oxidation level measuring reagent is suppressed, making it possible to provide a lipid oxidation level measuring reagent with particularly excellent storage stability.

[0010] The present invention relates to a lipid oxidation degree measurement method for measuring the lipid oxidation degree of oil in a sample, and is characterized by comprising: an adsorption step of adsorbing oil in the sample onto an oil adsorption sheet with a thickness of 100 μm or less; and a reaction step of performing a color reaction between lipid peroxides in the oil and a color-developing reagent while the oil is adsorbed onto the oil adsorption sheet. According to the lipid oxidation degree measurement method of the present invention, the oil in the sample is adsorbed onto an oil adsorption sheet with a thickness of 100 μm or less, and then a color reaction is performed while the oil is adsorbed onto the oil adsorption sheet. Therefore, the lipid oxidation degree can be measured with a simple procedure.

[0011] The present invention relates to a method for measuring the degree of lipid oxidation of oil in a subject, and is characterized by comprising a step of preparing a colorimetric reagent for measuring lipid oxidation containing 2-thiobarbituric acid and urea. According to the lipid oxidation degree measurement method of the present invention, a reagent for measuring lipid oxidation degree containing TBA and urea can be prepared, thereby enhancing the color development of the color reaction between TBA and lipid peroxides. Furthermore, enhancing the color development of the color reaction has the effect of improving analytical accuracy.

[0012] The present invention relates to a method for enhancing color development in a color reaction between lipid peroxide and 2-thiobarbituric acid, characterized by the addition of urea. According to the color enhancement method of the present invention, the color development of the color reaction between TBA and lipid peroxides is enhanced by adding urea, thereby improving analytical accuracy. [Effects of the Invention]

[0013] According to the present invention, a method for measuring lipid oxidation levels that allows for the preparation of samples in a simple manner can be provided. [Brief explanation of the drawing]

[0014] [Figure 1]It is a schematic explanatory diagram showing a method for measuring the degree of lipid oxidation according to an embodiment of the present invention. Figure 1(A) shows a sheet preparation step of preparing an oil-absorbing sheet. Figure 1(B) shows an adsorption step of adsorbing the oil contained in the meat raw material onto the oil-absorbing sheet. [Figure 2] It is a schematic explanatory diagram showing a method for measuring the degree of lipid oxidation according to an embodiment of the present invention. Figure 2(C) shows a reaction step of performing a color reaction between the hydroperoxide lipid in the oil and the coloring reagent in a state where the oil is adsorbed on the oil-absorbing sheet. Figure 2(D) shows a heating step of heating the oil-absorbing sheet on which the oil and the coloring reagent are adsorbed. Figure 2(E) shows an evaluation step of evaluating the degree of coloration by the color reaction between the hydroperoxide lipid in the oil and the coloring reagent. [Figure 3] It is a graph showing the relationship between the "method for measuring the degree of lipid oxidation using a sheet for measuring the degree of lipid oxidation" of the present invention and sensory evaluation. [Figure 4] It is a graph showing the color development enhancing effect of urea in the "method for measuring the degree of lipid oxidation using a reagent for measuring the degree of lipid oxidation containing urea" of the present invention. [Figure 5] It is a graph showing a calibration curve created by the "method for measuring the degree of lipid oxidation using a reagent for measuring the degree of lipid oxidation containing urea" of the present invention.

Mode for Carrying Out the Invention

[0015] Hereinafter, the method for measuring the degree of lipid oxidation, the sheet for measuring the degree of lipid oxidation, the reagent for measuring the degree of lipid oxidation, and the color development enhancing method of the present invention will be described in detail. Note that the matters described in the embodiments are merely examples for explaining the present invention and are not limited thereto. Also, the description of the configuration of each invention shall be replaced with the description of the configuration of other inventions that can be regarded as substantially the same.

[0016] [Method for Measuring Degree of Lipid Oxidation] The method for measuring the degree of lipid oxidation of the present invention is a method for measuring the degree of lipid oxidation of the oil content in a test sample. The degree of lipid oxidation represents the degree of lipid oxidation based on the content of lipid peroxides generated when lipids are oxidized. Examples include measured values of the content of peroxides and aldehydes, which are lipid peroxides, and the degree of color development in the color reaction of lipid peroxides.

[0017] The test sample is not particularly limited as long as it contains an oil content. Examples include oil-containing foods such as processed meat products, processed dairy products, and processed oil products, or their raw materials. Processed meat products include, for example, processed livestock meat products such as ham, fresh ham, bacon, and salami, and processed fish meat products such as fish sausage, chikuwa, and hanpen. Examples of their raw materials include meat raw materials and fish meat raw materials. Processed dairy products include, for example, cheese and butter. Processed oil products include, for example, margarine and shortening. Examples of their raw materials include edible oils and fats. It is preferably used in quality confirmation tests of products and raw materials in the food industry or feed industry. In addition, it can also be used in research and development in the cosmetics industry, research and development in the pharmaceutical industry, and research and development in the field of biochemistry. For example, in research and development in the cosmetics industry, it can be applied to humans as a test sample and used as a method for measuring the degree of lipid oxidation of sebum.

[0018] The shape of the test sample is not particularly limited and may be solid or liquid. In view of the effect of the present invention that the preparation of a sample applied to the method for measuring the degree of lipid oxidation can be performed by a simple method, it is preferably solid.

[0019] The oil content in the test sample is not particularly limited as long as it is a lipid adsorbed on an oil adsorption sheet with a thickness of 100 μm or less. For example, it may be a liquid oil or a solid fat.

[0020] The lipid oxidation degree measurement method of the present invention will be described with reference to the drawings. Figures 1 and 2 are schematic diagrams showing an embodiment of the lipid oxidation degree measurement method of the present invention. Figure 1(A) shows a sheet preparation step in which an oil adsorption sheet is prepared, Figure 1(B) shows an adsorption step in which oil contained in meat raw materials is adsorbed onto the oil adsorption sheet, Figure 2(C) shows a reaction step in which a color reaction is carried out between lipid peroxides in the oil and a color-developing reagent while the oil has been adsorbed onto the oil adsorption sheet, Figure 2(D) shows a heating step in which the oil adsorption sheet with the adsorbed oil and color-developing reagent is heated, and Figure 2(E) shows an evaluation step in which the degree of color development due to the color reaction between lipid peroxides in the oil and the color-developing reagent is evaluated. In addition, although not shown, a color-developing reagent preparation step is provided prior to the reaction step in Figure 2(C).

[0021] <Sheet preparation steps> The sheet preparation step shown in Figure 1(A) is the step of preparing the oil-absorbing sheet 4. The oil-absorbing sheet 4 is a sheet with a thickness of 100 μm or less and is a component for absorbing oil in the sample. The material of the oil-absorbing sheet 4 is not particularly limited, but examples include pulp fibers, glass fibers, and polypropylene.

[0022] The thickness of the oil-absorbing sheet 4 is 100 μm or less, preferably 80 μm or less, more preferably 50 μm or less, even more preferably 40 μm or less, and particularly preferably 30 μm or less. The thickness of the oil-absorbing sheet 4 can be measured in accordance with Japanese Industrial Standard (JIS) P8118:2014 "Paper and cardboard - Test methods for thickness, density and specific volume". Note that the thickness of the oil-absorbing sheet 4 refers to the actual thickness of the oil-absorbing layer; for example, in the case of a laminate, it refers to the thickness of the outermost layer on the side used.

[0023] The sheet preparation step may involve processing materials such as pulp to a thickness of 100 μm or less by known means, or using commonly available oil-blotting paper.

[0024] <Adsorption Step> The adsorption step shown in Figure 1(B) is a step in which oil from the subject is adsorbed onto an oil-adsorbing sheet with a thickness of 100 μm or less. As shown in Figure 1(B), the subject in this embodiment is a meat raw material 1 (pork) having fat 3 on a part of the surface of lean meat 2. In the adsorption step, the oil-adsorbing sheet, which is oil-blotting paper 4, is pressed and attached to the fat 3 of the meat raw material 1, which is the subject. This allows the oil from the subject to be adsorbed onto the oil-blotting paper 4.

[0025] <Steps for preparing the color-developing reagent> The step of preparing the colorimetric reagent is the step of preparing the lipid oxidation degree measurement reagent 6 shown in Figure 2(C). The lipid oxidation degree measurement reagent 6 contains a colorimetric reagent that reacts with lipid peroxides to produce a color reaction. Examples of colorimetric reagents include 2-thiobarbituric acid (TBA), potassium iodide, and starch.

[0026] Reagents for measuring lipid oxidation levels that contain TBA may also contain, in addition to TBA, organic acids such as citric acid as pH adjusters, sulfites (sodium salts, potassium salts, etc.) as reagents to suppress false reactions, ferrous ions such as ferrous sulfate, or color enhancers such as urea.

[0027] Reagents for measuring lipid oxidation levels are prepared by dissolving various materials such as colorimetric reagents and pH adjusters in a solvent such as water to create a colorimetric reagent solution. It is preferable to prepare and store the lipid oxidation level measuring reagents in advance so that they can be easily prepared when needed. When preparing lipid oxidation level measuring reagents in advance, they should be stored in a form and under storage conditions that provide excellent storage stability. For example, they may be stored frozen as a colorimetric reagent solution (liquid lipid oxidation level measuring reagent) or as a solid lipid oxidation level measuring reagent. From the viewpoint of particularly excellent storage stability, it is preferable to use a solid lipid oxidation level measuring reagent.

[0028] When the reagent for measuring lipid oxidation is in solid form, it is preferable that it contains trehalose. The inclusion of trehalose suppresses moisture absorption of the solid reagent for measuring lipid oxidation, thereby improving its storage stability. The trehalose content relative to the solid content of the reagent for measuring lipid oxidation is not particularly limited, but for example, it is 10 to 90% by mass as pure trehalose. The lower limit is preferably 20% by mass or more, and more preferably 30% by mass or more. The upper limit is preferably 70% by mass or less, and more preferably 50% by mass or less.

[0029] The method for preparing a solid lipid oxidation level measuring reagent is not particularly limited, but examples include mixing various solid materials or drying a color-developing reagent solution to obtain a solid lipid oxidation level measuring reagent. The drying method is not particularly limited, but freeze-drying is preferred. The solid lipid oxidation level measuring reagent obtained by freeze-drying is easily soluble in water, which has the effect of making it easy to re-prepare the color-developing reagent solution.

[0030] Solid lipid oxidation level reagents are preferably stored in smaller portions. When dispensing, it is easy to do so by aliquoting the color-developing reagent solution into vials or other containers before freeze-drying.

[0031] Furthermore, the lipid oxidation level reagent may be adsorbed onto an oil-adsorbing sheet in advance. By adsorbing the lipid oxidation level reagent onto the oil-adsorbing sheet, the color reaction can be performed simply by adsorbing the oil from the sample onto the oil-adsorbing sheet and then dropping the solvent necessary for the reaction. Therefore, the step of preparing the color-developing reagent solution can be omitted, and the lipid oxidation level can be measured in an extremely simple manner.

[0032] <Reaction Steps> The reaction step shown in Figure 2(C) is a step in which, with oil adsorbed onto the oil adsorption sheet, a color reaction is carried out between the lipid peroxides in the oil and a color-developing reagent. As shown in Figure 2(C), the lipid oxidation level measuring reagent 6 is added dropwise to the oil adsorption sheet, mixing the oil adsorbed onto the oil adsorption sheet with the lipid oxidation level measuring reagent 6.

[0033] When TBA is used as a colorimetric reagent, it reacts with malondialdehyde, a lipid oxidation product, to produce a red condensate (red pigment). In addition to producing the red pigment, TBA also reacts with linoleic acid oxide to produce a yellow pigment. Adding sulfites (sodium salt, potassium salt, etc.) to the lipid oxidation level measuring reagent suppresses the reaction that produces the yellow pigment and increases the production of the red pigment.

[0034] Furthermore, adding urea to the lipid oxidation level measuring reagent enhances the red color development and suppresses the precipitation of the reagent in the color development reagent solution. The urea content in the color development reagent solution is not particularly limited, but for example, it is 0.05 to 1.0 g / 10 mL. Within this range, a sufficient effect of enhancing the red color development is observed. The lower limit is preferably 0.1 g / 10 mL or more, more preferably 0.2 g / 10 mL or more, and even more preferably 0.3 g / 10 mL or more. The upper limit is preferably 0.8 g / 10 mL or less, and more preferably 0.5 g / 10 mL or less. Furthermore, from the viewpoint of suppressing the precipitation of the reagent in the color-developing reagent solution, the lower limit of the urea content is preferably 0.1 g / 10 mL or more, more preferably 0.2 g / 10 mL or more, and even more preferably 0.3 g / 10 mL or more.

[0035] <Heating step> The heating step shown in Figure 2(D) involves heating an oil adsorption sheet on which the oil content in the sample and the lipid oxidation level measurement reagent have been adsorbed. Heating promotes the color reaction between the lipid peroxides in the oil and the color-developing reagent, allowing for rapid measurement of the lipid oxidation level.

[0036] The heating method is not particularly limited, as long as it can heat the oil-absorbing sheet without it burning. For example, as shown in Figure 2(D), the oil-absorbing sheet 4 can be heated by placing it on an electric heater such as a hot plate 7. Other methods include boiling water in a container covered with aluminum foil and heating the oil-absorbing sheet by placing it on top of the aluminum foil. From the viewpoint of suppressing the occurrence of uneven coloring during color development, an electric heater is preferred.

[0037] The heating temperature is, for example, 60 to 150°C. The lower limit of the heating temperature is preferably 70°C or higher, more preferably 80°C or higher, and even more preferably 90°C or higher. The upper limit of the heating temperature is preferably 130°C or lower, more preferably 120°C or lower, and even more preferably 110°C or lower.

[0038] <Evaluation Steps> The evaluation step shown in Figure 2(E) is a step to evaluate the degree of color development of the color reaction that occurs on the oil adsorption sheet. Since the evaluation step provides information on the content of lipid peroxides contained in the oil in the sample, the degree of lipid oxidation of the oil in the sample can be measured.

[0039] Methods for evaluating the degree of color development include, as shown in Figure 2(E), evaluating it using a colorimeter 8A based on the values ​​of chromaticity (a*, b*) and lightness (L*), and visually evaluating it using a color sample 8B in which lipid peroxides of known concentrations have developed color. For example, in a color reaction using TBA as a color-developing reagent, when evaluating the degree of color development using a colorimeter, the a* value can be used as an indicator to measure the degree of lipid oxidation because it turns red.

[0040] [Sheet for measuring lipid oxidation levels] The lipid oxidation degree measuring sheet of the present invention is a lipid oxidation degree measuring sheet comprising an oil-adsorbing sheet for adsorbing oil, characterized in that the thickness of the oil-adsorbing sheet is 100 μm or less. The characteristics and usage method of the oil-adsorbing sheet are as described in the "Lipid Oxidation Degree Measurement Method" above. The lipid oxidation degree measurement sheet of the present invention provides a lipid oxidation degree measurement kit for easily measuring the degree of lipid oxidation.

[0041] The lipid oxidation level measuring sheet of the present invention may have a lipid oxidation level measuring reagent adsorbed onto it. By adsorbing the lipid oxidation level measuring reagent onto the sheet, a color reaction can be performed simply by adsorbing the oil from the sample, thus enabling the measurement of lipid oxidation level in an extremely simple manner.

[0042] [Reagents for measuring lipid oxidation levels] The lipid oxidation degree measuring reagent of the present invention is characterized by containing 2-thiobarbituric acid and urea. Furthermore, the lipid oxidation degree measuring reagent of the present invention preferably contains trehalose and is in solid form. The characteristics, preparation method, and usage method of the reagent for measuring lipid oxidation are as described in the "Method for Measuring Lipid Oxidation" section above. The lipid oxidation degree measurement reagent of the present invention enhances the color development of TBA and provides a lipid oxidation degree measurement kit with improved analytical accuracy.

[0043] [Methods to enhance color development] The present invention relates to a method for enhancing color development in a color reaction between lipid peroxide and 2-thiobarbituric acid, characterized by the addition of urea. The color reaction between lipid peroxides and 2-thiobarbituric acid, as well as the amount of urea added, are as described in the "Method for Measuring Lipid Oxidation" section above. [Examples]

[0044] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. [Test 1: Method for measuring lipid oxidation using a lipid oxidation level measurement sheet] <Preparation of reagents for measuring lipid oxidation levels> 0.7 g of 2-thiobarbituric acid was added to 100 g of warm ultrapure water to prepare a thiobarbituric acid solution, which was then allowed to return to room temperature. 2.0 g of citric acid, 0.2 g of sodium sulfite, 0.1 g of ferrous sulfate, 3.0 g of urea, and 5.0 g of trehalose dihydrate were weighed and added to the thiobarbituric acid solution to prepare a colorimetric reagent solution. Next, the colorimetric reagent solution was dispensed in 1 mL portions, freeze-dried, and solid lipid oxidation level reagents were obtained. When using the solid lipid oxidation level reagent, 1 mL of ultrapure water was added to prepare a new colorimetric reagent solution.

[0045] <Measurement of lipid oxidation levels> The lipid oxidation level was measured using the lipid oxidation level reagent described above, as shown in Figures 1 and 2. Shiseido's "Oil-blotting paper that removes sebum that causes dullness" was used. 1 mL of the lipid oxidation level reagent was dropped onto the oil-absorbing sheet that had absorbed the oil. The heating conditions using a hot plate were 100°C for 2 minutes. The lipid oxidation level was evaluated using a colorimeter, "Spectrophotometer CM-700d" (manufactured by Konica Minolta), and evaluated using the a* value.

[0046] <Evaluation of pork> Seventeen pork samples with slightly yellowed fat were used as test subjects. The degree of lipid oxidation was confirmed by sensory evaluation (one panelist), and the samples were divided into three categories: 6 samples with "no or slight oxidative odor," 3 samples with "weak oxidative odor," and 8 samples with "strong oxidative odor." Furthermore, 17 pork samples were evaluated using the lipid oxidation level measurement method described above. The results are shown in Figure 3.

[0047] As shown in Figure 3, all samples evaluated by sensory evaluation as having "no or slight oxidative odor" had low a* values. Samples evaluated by sensory evaluation as having "a weak oxidative odor" or "a strong oxidative odor" showed some variation in a* values, but many samples had high a* values. From these results, it was found that the degree of oxidative odor can be generally understood by the evaluation results of the lipid oxidation degree measurement method of the present invention.

[0048] [Test 2: Method for measuring lipid oxidation using a reagent containing urea] <Preparation of reagents for measuring lipid oxidation levels> Lipid oxidation level measuring reagents were prepared in the same manner as in Test 1, except that the amount of urea added was 0 g / 10 mL, 0.1 g / 10 mL, 0.3 g / 10 mL, and 0.4 g / 10 mL, and ferrous sulfate was omitted.

[0049] <Measurement of lipid oxidation levels> In the "Evaluation of Pork" section of Test 1, one sample was evaluated as having "no oxidative odor" and another as having "a strong oxidative odor." Lipid oxidation levels were measured using various lipid oxidation reagents with varying amounts of urea added. The lipid oxidation levels were measured in the same manner as in Test 1, except that ferrous sulfate was omitted from the lipid oxidation reagents. The results are shown in Figure 4. The results represent the average of three measurements taken for each sample, and the error bars in the graph indicate the standard deviation.

[0050] Referring to Figure 4, it was observed that adding urea to a lipid oxidation level measuring reagent using TBA as a colorimetric reagent enhanced the color development.

[0051] <Creating a calibration curve> A calibration curve was created using a lipid oxidation level measuring reagent prepared with urea added at a concentration of 0.3 g / mL, and an aqueous solution of tetraethoxypropane at a known concentration. For aqueous solutions of known concentrations of tetraethoxypropane, seven samples were prepared by diluting tetraethoxypropane to 0.02% by mass in ultrapure water by half. For lipid oxidation degree measurement, 1 mL of ultrapure water was added to the freeze-dried lipid oxidation degree reagent, followed by the addition of 100 μL of tetraethoxypropane aqueous solution of known concentration, and then mixed using a vortex mixer. 1 mL of this mixture was dropped onto the entire surface of filter paper "GA-200" (manufactured by ADVANTEC). The filter paper was then heated by steam for 2 minutes. For steam heating, a conical flask containing water was sealed with aluminum foil, heated to a boil, and the filter paper was placed on top of the aluminum foil and heated. Lipid oxidation levels were evaluated by measuring the a* value using a colorimeter. The results are shown in Figure 5. Measurements were taken three times, and the average of the three measurements was used. The error bars in the graph indicate the standard deviation.

[0052] Referring to Figure 5, it was confirmed that a linear calibration curve can be created by measuring lipid oxidation using a lipid oxidation level reagent containing urea.

[0053] [Test 3: Urea Precipitation Prevention Test] <Preparation of reagents for measuring lipid oxidation levels> A lipid oxidation level measuring reagent was prepared in the same manner as in Test 1 (referred to as "lipid oxidation level measuring reagent (urea+)"; urea concentration: 0.3 g / 10 mL). In addition, a lipid oxidation level measuring reagent was prepared as a control reagent, in the same manner as in Test 1 except that urea was not added (the control reagent is referred to as "lipid oxidation level measuring reagent (urea-)").

[0054] <Preservation Test> After storage at room temperature (25°C) for 24 hours, no precipitation was observed with the lipid oxidation level measuring reagent (urea+), but precipitation was observed with the lipid oxidation level measuring reagent (urea-). It was found that the addition of urea suppresses the precipitation of the lipid oxidation level measuring reagent.

[0055] [Test 4: Examination of the effect of urea in preventing precipitation] In the same manner as in Experiment 1, reagents for measuring lipid oxidation were prepared with urea addition amounts of 0 g / 10 mL, 0.05 g / 10 mL, 0.1 g / 10 mL, 0.3 g / 10 mL, 0.5 g / 10 mL, and 0.8 g / 10 mL. These reagents were stored at room temperature (25°C) for 24 hours. Precipitation was observed at 0 g / 10 mL and 0.05 g / 10 mL, and slight precipitation was observed at 0.1 g / 10 mL. No precipitation occurred at 0.3 g / 10 mL, 0.5 g / 10 mL, and 0.8 g / 10 mL. [Industrial applicability]

[0056] The lipid oxidation degree measuring sheet, lipid oxidation degree measuring reagent, and lipid oxidation degree measuring method of the present invention can be suitably used in methods for measuring the degree of lipid oxidation by a color reaction between lipid peroxides and a color-developing reagent. For example, it can be particularly suitably used in methods for measuring the lipid oxidation degree of oil-containing foods such as processed meat products and processed oil-and-fat products, or their raw materials. Furthermore, it can be used in fields such as the development of cosmetics and pharmaceuticals, and research and development in the biochemistry field. For example, it can be suitably used in methods for measuring the lipid oxidation level of sebum.

[0057] Furthermore, the lipid oxidation degree measurement sheet and the lipid oxidation degree measurement reagent of the present invention can be used independently or in combination as a lipid oxidation degree measurement kit. Since the lipid oxidation degree measurement kit can measure lipid oxidation degree in a simple manner, it can be suitably used in food quality confirmation tests and in measuring the content of lipid peroxides in research fields. [Explanation of Symbols]

[0058] 1: Meat raw material (subject), 2: Lean meat, 3: Fatty meat, 4: Oil-blotting paper (oil-absorbing sheet), 5: Oil, 6: Reagent for measuring lipid oxidation level, 7: Hot plate (heater), 8A: Colorimeter, 8B: Color sample

Claims

1. A lipid oxidation degree measuring kit for measuring the degree of lipid oxidation of oils in oil-containing foods or their raw materials, The system includes an oil-absorbing sheet for adsorbing the aforementioned oil, The thickness of the oil-absorbing sheet is 100 μm or less. Furthermore, a kit for measuring lipid oxidation levels is characterized by comprising a colorimetric reagent containing 2-thiobarbituric acid and urea.

2. In the lipid oxidation degree measurement kit according to claim 1, A kit for measuring lipid oxidation levels, characterized in that the color-developing reagent contains trehalose and is in a solid state.

3. In a method for measuring the degree of lipid oxidation of oils in oil-containing foods or their raw materials, An adsorption step of adsorbing the oil onto an oil adsorption sheet with a thickness of 100 μm or less, A method for measuring the degree of lipid oxidation, characterized by comprising a reaction step in which, with the oil adsorbed onto the oil adsorbent sheet, a color reaction is carried out between the lipid peroxides in the oil and a color-developing reagent.

4. In the lipid oxidation degree measurement method described in claim 3, A method for measuring the degree of lipid oxidation, characterized in that the color-developing reagent used in the aforementioned color reaction contains 2-thiobarbituric acid and urea.

5. In the lipid oxidation degree measurement method according to claim 3 or 4, A method for measuring the degree of lipid oxidation, characterized in that the color-developing reagent contains trehalose and is in a solid state.

6. In a method for measuring the degree of lipid oxidation of oils in oil-containing foods or their raw materials, An adsorption step of adsorbing the oil onto an oil adsorption sheet with a thickness of 100 μm or less, With the oil adsorbed onto the oil adsorbent sheet, The system comprises a reaction step of carrying out a color reaction between lipid peroxides in the oil and 2-thiobarbituric acid, A method for enhancing color development, characterized by enhancing color development by adding urea in the aforementioned color reaction.

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