Method for evaluating the risk of spontaneous oxidation odor in raw milk

Abstract

To provide a method of quickly evaluating the risk of spontaneous oxidation odor generation in raw milk to obtain milk and other dairy products of good quality with reduced off-flavors.SOLUTION: The above object is attained by the following method, etc., the method including: a step of generating hexanal in raw milk by subjecting the raw milk to an oxidation treatment for at least 30 minutes at a temperature of less than 10°C in the presence of an oxidation catalyst; a step of stopping the generation of hexanal in the raw milk by subjecting the raw milk in which hexanal has been generated to oxidation termination treatment in the presence of an antioxidant; a step of measuring the concentration of hexanal in the raw milk; and a step of evaluating the risk of spontaneous oxidation odor occurring in the raw milk on the basis of the measured concentration of hexanal in the raw milk.SELECTED DRAWING: Figure 9A

Description

[Technical Field]

[0001] The present invention relates to a method for early evaluation of the possibility of spontaneous oxidation odor occurring due to storage of raw milk. [Background technology]

[0002] Raw milk obtained by milking dairy cows is usually transported to a dairy factory and stored (stored) at a low temperature of around 5°C. The stored raw milk then undergoes processing such as homogenization and sterilization before being filled, packaged, and shipped to the market as milk.

[0003] Stored raw milk may have a spontaneously oxidized odor. This is believed to be due to the oxidation of unsaturated fatty acids such as linoleic acid contained in the raw milk, resulting in the production of aroma compounds such as hexanal. The spontaneously oxidized odor is an unpleasant odor such as a papery or cardboard smell. If raw milk with such a spontaneously oxidized odor is used, the resulting milk will also have an unpleasant odor, significantly reducing the product value.

[0004] The occurrence of spontaneous oxidative odor is said to be determined by the balance between unsaturated fatty acids contained in raw milk and antioxidants such as beta-carotene and vitamin E. For example, raw milk obtained from dairy cows raised on large amounts of concentrated feed is said to have an increased amount of unsaturated fatty acids, making it more susceptible to the occurrence of spontaneous oxidative odor.

[0005] The spontaneous oxidation odor increases over time. As a result, even if raw milk does not have an unpleasant odor when it is received at a dairy factory, it may develop an unpleasant odor due to the spontaneous oxidation odor after being stored for 2 to 3 days after receipt. On the other hand, it is known that the generation of the spontaneous oxidation odor can be suppressed by subjecting raw milk to processing such as homogenization and sterilization (for example, Non-Patent Document 1).

[0006] Several methods for suppressing the generation of spontaneous oxidation odor in raw milk are known. Many of them are methods of changing the feed and feeding method for dairy cows to reduce the amount of unsaturated fatty acids contained in raw milk. As a method of treating raw milk, a method of suppressing abnormal flavor in raw milk by performing a treatment to reduce the dissolved oxygen concentration using nitrogen gas on the raw milk after milking is known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Non-Patent Documents

[0008]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] Among the methods for suppressing the generation of spontaneous oxidation odor in raw milk, the method of changing the feed and feeding method for dairy cows is difficult to uniformly require feed conditions for all dairy farmers who collect milk, and is not realistic. Also, in the feeding form with a high concentrate ratio, unsaturated fatty acids in raw milk tend to increase and the amount of antioxidants tends to decrease, making it difficult to eliminate the risk of spontaneous oxidation odor generation in raw milk.

[0010] The method described in Patent Document 1 is a method of aerating raw milk with nitrogen gas to reduce the dissolved oxygen concentration in raw milk. In order to apply this method, it is necessary to provide an inlet hole for nitrogen gas in the cooling tank and the milk storage tank, and to flow nitrogen gas into the raw milk while adjusting the pressure, which has the problem that the equipment design and process become complicated.

[0011] On the other hand, as described in Non-Patent Document 1, spontaneous oxidized odor can be suppressed by subjecting raw milk to processing such as homogenization and sterilization. Therefore, if raw milk is promptly subjected to processing without being stored, high-quality milk can be produced without waiting for the generation of spontaneous oxidized odor in the raw milk. However, in actual milk production, it is difficult to process all raw milk immediately after receipt, and a certain amount of raw milk is stored at low temperatures.

[0012] Furthermore, if it were possible to determine at the time of receipt whether raw milk would develop a spontaneous oxidized odor during storage, it would be possible to separate raw milk that can be immediately processed from raw milk that can be stored. However, because raw milk can develop a spontaneous oxidized odor during storage, it is desirable that this determination be made in a shorter time. However, few methods have been known to date for quickly assessing the risk of developing a spontaneous oxidized odor in raw milk.

[0013] Therefore, the problem that the present invention aims to solve is to provide a method for quickly evaluating the risk of spontaneous oxidized odor development in raw milk in order to obtain high-quality dairy products such as milk with reduced off-flavors. [Means for solving the problem]

[0014] The inventors conducted extensive research to solve the above problems, and by combining various conditions selected from a large number of options, they designed a process to generate hexanal in raw milk, and succeeded in generating hexanal in raw milk immediately after receipt at a concentration equal to or higher than that on the third day after storage in a shorter period of time.

[0015] However, the inventors discovered that with such hexanal-generating treatment, hexanal generation continues even during the waiting time for measuring the hexanal concentration, and that even in raw milk after the same treatment, the hexanal concentration varies from measurement sample to measurement sample, making it impossible to measure the hexanal concentration stably.

[0016] Therefore, the inventors repeated trial and error to design a process for stopping hexanal generation. When the raw milk after the hexanal generation process was subjected to the hexanal generation stop process, it was possible to stop the generation of hexanal in the raw milk, and they succeeded in stably measuring the hexanal concentration.

[0017] Furthermore, the inventors measured the hexanal concentration on the third day after storage of various raw milks, and from the trend of the measured hexanal concentrations, they found criteria for determining raw milk with a high risk of spontaneous oxidation odor and raw milk with a low risk of spontaneous oxidation odor. Based on such findings, the inventors finally succeeded in creating a method for evaluating the risk of spontaneous oxidation odor occurring in raw milk, etc., as a solution to the problems of the present invention. The present invention has been completed based on the findings and successful examples first discovered by the inventors.

[0018] Therefore, according to the present invention, the following methods of each aspect are provided. [1] A step of generating hexanal in raw milk by subjecting the raw milk to an oxidation treatment at a temperature of less than 10°C for at least 30 minutes in the presence of an oxidation catalyst; A step of stopping the generation of hexanal in the raw milk by subjecting the raw milk in which hexanal has been generated to an oxidation stop treatment in the presence of an antioxidant; A step of measuring the concentration of hexanal in the raw milk; A step of determining the risk of spontaneous oxidation odor occurring in the raw milk based on the measured concentration of hexanal in the raw milk and including a method for evaluating the risk of spontaneous oxidation odor occurring in raw milk. [2] The method according to [1], wherein the antioxidant is ascorbic acid or a salt thereof. [3] The method according to [1], wherein the oxidation catalyst is at least one metal oxidation catalyst selected from the group consisting of copper wire and copper sulfate. [4] The method according to [3], wherein the copper sulfate has a final concentration of 50 ppm to 300 ppm. [5] The method according to any one of [1] to [4], wherein the temperature is 0°C or higher and lower than 5°C, and / or the time is 50 minutes to 100 minutes. [6] The method according to any one of [1] to [4], wherein the concentration of the reference hexanal is 24 μg / l. [7] The step of measuring the concentration of hexanal in the raw milk is a step of measuring the concentration of hexanal in the raw milk using a capillary gas chromatography device equipped with a flame ionization detector, according to any one of [1] to [4]. [8] A method for producing milk or dairy products with suppressed generation of spontaneous oxidation odor, including a step of obtaining milk or dairy products with suppressed generation of spontaneous oxidation odor by processing, on the same day, the raw milk determined to have a risk of generating spontaneous oxidation odor by the method according to any one of [1] to [4].

Advantages of the Invention

[0019] According to the present invention, it is possible to quickly evaluate the possibility of spontaneous oxidation odor occurring after storage of raw milk before storage at low temperature. Thus, according to the present invention, raw milk with a high possibility of generating spontaneous oxidation odor can be processed early, and raw milk with a low possibility of generating spontaneous oxidation odor can be processed after storage at low temperature. It is expected to determine the usage time of raw milk within a short time after acceptance, and further stably produce high-quality dairy products such as milk with suppressed generation of spontaneous oxidation odor.

Brief Description of the Drawings

[0020]

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Figure 9A

Figure 9B

Best Mode for Carrying Out the Invention

[0021] Hereinafter, each aspect of the present invention will be described in detail, but the present invention can take various aspects as long as its object is achieved.

[0022] Unless otherwise specified, each term in this specification is used in the meaning commonly used by those skilled in the food field and should not be construed as having an unduly restrictive meaning. Also, the assumptions and theories made in this specification are based on the inventors' knowledge and experience so far, and the present invention is not limited only by such assumptions and theories.

[0023] “And / or” means any one of the plurality of listed related items, or any combination or all combinations of two or more of them. “About” means an amount within ±10% of the quantity following that term. For example, “about 100” means 100 ± 10%, that is, 90 to 110. “~” in a numerical range means a range including the numerical values before and after it. For example, “0% ~ 100%” means a range that is 0% or more and 100% or less. “Exceeding” and “less than” mean the lower limit and the upper limit respectively without including the numerical value before them. For example, “exceeding 1” means a numerical value greater than 1, and “less than 100” means a numerical value less than 100. “Including” means that elements other than the elements explicitly stated as being included can be added (synonymous with “including at least”), and includes “consisting of” and “essentially consisting of”. That is, “including” can mean including the explicitly stated elements and any one or two or more elements, consisting of the explicitly stated elements, or essentially consisting of the explicitly stated elements. Examples of elements include limitations such as components, steps, conditions, parameters, etc. The number of digits of an integer value coincides with the number of significant figures. For example, the significant figure of 1 is 1 digit, and the significant figure of 10 is 2 digits. Also, for a decimal value, the number of digits after the decimal point coincides with the number of significant figures. For example, the significant figure of 0.1 is 1 digit, and the significant figure of 0.10 is 2 digits.

[0024] Among the meanings of the terms in this specification, those described in the "Cabinet Order Concerning Component Standards, etc. of Milk and Dairy Products" (Ministry of Health, Labour and Welfare Ordinance No. 106 of 2018; hereinafter also referred to as the "Milk etc. Cabinet Order") shall be interpreted as having the meanings as described in the Milk etc. Cabinet Order.

[0025] A method according to one aspect of the present invention relates to a method for evaluating the risk of spontaneous oxidation odor generation in raw milk, which evaluates whether there is a possibility of generating a spontaneous oxidation odor when the raw milk is refrigerated and stored for a predetermined period.

[0026] A method according to one aspect of the present invention is a method for early detection of a possible spontaneous oxidation odor generated when raw milk is refrigerated and stored. The present inventors have hitherto confirmed that when the raw milk received at a dairy factory is stored at 5°C for 3 days, a spontaneous oxidation odor is generated depending on the raw milk. In a method according to one aspect of the present invention, hexanal, which is one component of the spontaneous oxidation odor, is used as an index, and hexanal is forcibly generated in the raw milk at an early stage at a concentration equal to or higher than the concentration of hexanal generated after refrigerated storage, and the concentration of hexanal after refrigerated storage is estimated from the concentration of the generated hexanal, and it is evaluated whether there is a possibility of generating a spontaneous oxidation odor in the raw milk after refrigerated storage.

[0027] A method according to one aspect of the present invention includes the following steps: A step of generating hexanal in raw milk by subjecting the raw milk to an oxidation treatment at a temperature of less than 10°C for at least 30 minutes in the presence of an oxidation catalyst. A step of stopping the generation of hexanal in the raw milk by subjecting the raw milk in which hexanal has been generated to an oxidation stop treatment in the presence of an antioxidant. A step of measuring the concentration of hexanal in the raw milk, and A step of determining the risk of spontaneous oxidation odor generation in raw milk based on the measured concentration of hexanal in the raw milk.

[0028] (1) Hexanal generation step The method of one embodiment of the present invention includes a step of subjecting raw milk to an oxidation treatment in order to generate hexanal in the raw milk. In the present specification, this step is also referred to as the "hexanal generation step".

[0029] The raw milk may be any milk that is a raw material for milk and dairy products, and may be freshly milked cow's milk (raw milk), or raw milk that has been subjected to some treatment, either is fine. When the raw milk is subjected to the method of one embodiment of the present invention, it is preferable to homogenize it by inversion mixing or the like so that there is no bias in the components contained in the raw milk.

[0030] In the hexanal generation step, the raw milk is subjected to an oxidation treatment in the presence of an oxidation catalyst. The oxidation catalyst is not particularly limited as long as it is a catalyst used for oxidizing the components in the solution. For example, metal oxidation catalysts such as copper, iron, silver, platinum, rhodium, and palladium, which are commonly used in liquid-phase oxidation, can be mentioned. Considering the oxidation activity and economy, copper is preferable. Copper is not particularly limited as long as it has an oxidation activity. For example, it can be used as copper wire, copper sulfate, etc. From the viewpoint of handling, copper sulfate is preferable.

[0031] The amount of the oxidation catalyst used may be an amount sufficient for hexanal to be generated in the raw milk, and can be appropriately set according to the type of the oxidation catalyst. The amount of the oxidation catalyst used is preferably an amount that generates hexanal in the raw milk before storage at a concentration equal to or higher than the concentration of hexanal generated in the raw milk after storage at 5°C for 3 days.

[0032] Specifically, when using copper sulfate as the oxidation catalyst, the amount of copper sulfate used is preferably such that the final concentration when mixed with raw milk is 50 ppm to 300 ppm, more preferably 80 ppm to 150 ppm, and even more preferably about 100 ppm. When the final concentration of copper sulfate is less than 50 ppm, the concentration of hexanal in the raw milk generated by subjecting it to the oxidation treatment tends to be lower than the concentration of hexanal generated in the raw milk after storage at 5°C for 3 days. Also, when the final concentration of copper sulfate exceeds 300 ppm, the concentration of hexanal in the raw milk generated by subjecting it to the oxidation treatment tends to be much higher than the concentration of hexanal generated in the raw milk after storage at 5°C for 3 days. As described in the examples to be mentioned later, within the range of 50 ppm to 300 ppm, the concentration of hexanal tends to increase depending on the final concentration of copper sulfate, but this tendency does not exist within the range of 300 ppm to 1,000 ppm. Further, in this specification, copper sulfate refers to copper sulfate pentahydrate. Therefore, when the amount of copper sulfate used (final concentration) is "50 ppm to 300 ppm", it means that the amount of copper sulfate pentahydrate used is "50 ppm to 300 ppm". When using a hydrate or anhydride other than copper sulfate pentahydrate as copper sulfate, the amount used may be determined by converting based on the molecular weight of each with reference to the amount of copper sulfate pentahydrate used. For example, 50 ppm to 300 ppm, 80 ppm to 150 ppm, and 100 ppm as the amount of copper sulfate pentahydrate used correspond to 32 ppm to 192 ppm, 51 ppm to 96 ppm, and 64 ppm, respectively, as the amount of anhydrous copper sulfate used. Copper sulfate may be copper sulfate pentahydrate, or any other hydrate or anhydride.

[0033] The oxidation treatment of raw milk is carried out at a temperature below 10°C. When the temperature of the oxidation treatment is 10°C or higher, the concentration of hexanal in the raw milk generated by subjecting it to the oxidation treatment tends to be much lower than the concentration of hexanal generated in the raw milk after storage at 5°C for 3 days. On the other hand, since the lower the temperature of the oxidation treatment, the greater the amount of hexanal generated, the temperature of the oxidation treatment is preferably 5°C or lower, more preferably -5°C or higher and lower than 5°C, and even more preferably about 0°C. Note that the temperature of the oxidation treatment may be either the temperature of the raw milk itself or the temperature of the surrounding environment of the raw milk (for example, the temperature of a refrigerator that cools the container containing the raw milk, ice water, etc.).

[0034] The oxidation treatment of raw milk is carried out for at least 30 minutes. When the time of the oxidation treatment is less than 30 minutes, the amount of hexanal generated is insufficient, and there is a possibility that the risk of the spontaneous oxidation odor of the raw milk cannot be evaluated. On the other hand, although the longer the time of the oxidation treatment, the greater the amount of hexanal generated, the evaluation time becomes unnecessarily long accordingly. Therefore, the time of the oxidation treatment is preferably 30 minutes to 150 minutes, more preferably 40 minutes to 120 minutes, and even more preferably 50 minutes to 100 minutes. Note that for the time of the oxidation treatment, the time when the container containing the raw milk added with the oxidation catalyst is placed in the surrounding environment set at a predetermined temperature is taken as the start time (0 hour).

[0035] The oxidation treatment is carried out by bringing the raw milk and the oxidation catalyst into good contact at the above-mentioned temperature and time. In order to bring the raw milk and the oxidation catalyst into good contact, it is preferable to subject the container containing the raw milk and the oxidation catalyst to stirring and mixing. Also, in order to prevent the raw milk from volatilizing during the reaction, it is preferable to seal the container containing the raw milk and the oxidation catalyst. The container to be used may be a container made of a material in which the components in the raw milk and the oxidation catalyst are less likely to denature or adsorb.

[0036] Non-limiting specific embodiments of the hexanal generation process include a process in which raw milk collected from dairy cows is inverted and mixed, then the raw milk after inversion and the oxidation catalyst are added to a polypropylene centrifuge tube, the centrifuge tube is then sealed with a lid and stirred and mixed for several seconds using a vortex mixer, and then the centrifuge tube after stirring and mixing is placed in a refrigerator or ice water and subjected to oxidation treatment for at least 30 minutes.

[0037] (2) Hexanal generation stopping process The method of one embodiment of the present invention includes a step of subjecting raw milk to an oxidation stopping treatment to stop the generation of hexanal in the raw milk. In this specification, this step is also referred to as a "hexanal generation stopping step."

[0038] To prevent the generation of hexanal, the raw milk is subjected to an oxidation-stopping treatment in the presence of an antioxidant. The antioxidant is not particularly limited as long as it is a substance used to prevent the oxidation of components in a solution, and examples thereof include water-soluble antioxidants such as ascorbic acid and its salts, cysteine hydrochloride, sodium bisulfate, sodium metabisulfite, sodium sulfite, sodium hydrogensulfite, and glutathione; and metal chelating agents such as citric acid, ethylenediaminetetraacetic acid (EDTA), sorbitol, tartaric acid, and phosphoric acid. However, from the viewpoints of antioxidant properties and ease of handling, ascorbic acid and its salts are preferred.

[0039] The amount of antioxidant used may be sufficient to stop the generation of hexanal in raw milk by the oxidation catalyst, and can be appropriately set depending on the type of antioxidant. The amount of antioxidant used is preferably an amount that causes almost no change in the concentration of hexanal in raw milk before and after the addition of the antioxidant, more preferably an amount greater than the amount of the oxidation catalyst, and even more preferably an amount sufficiently greater than the amount of the oxidation catalyst.

[0040] Specifically, when using ascorbic acid as an antioxidant, the amount of ascorbic acid used is preferably such that the final concentration when mixed with raw milk is several to several tens of times the final concentration of the oxidation catalyst, more preferably 2 to 20 times, and even more preferably 5 to 15 times. For example, when the final concentration of copper sulfate used as the oxidation catalyst is 100 ppm, the final concentration of ascorbic acid as the antioxidant is preferably 500 ppm to 1,500 ppm, and more preferably about 1,000 ppm.

[0041] The oxidation stopping treatment may be carried out by bringing the raw milk and the antioxidant into good contact. For example, it can be carried out by adding an antioxidant to the raw milk after the hexanal generation step and stirring and mixing at room temperature for several seconds to several tens of seconds.

[0042] Non-limiting specific embodiments of the hexanal generation stopping step include a step of subjecting to an oxidation stopping treatment in which an antioxidant is added to a polypropylene centrifuge tube containing raw milk and an oxidation catalyst after the hexanal generation step, and then the centrifuge tube is sealed with a lid and stirred and mixed at room temperature for several seconds using a vortex mixer.

[0043] (3) Hexanal concentration measurement step The method according to one aspect of the present invention includes a step of measuring the concentration of hexanal in raw milk. In this specification, this step is also referred to as the "hexanal concentration measurement step".

[0044] The method for measuring the hexanal concentration is not particularly limited as long as the hexanal concentration in raw milk can be measured. For example, since hexanal is an organic compound with a relatively low boiling point, methods using chromatographic methods such as gas chromatography and liquid chromatography can be mentioned. In order to measure the hexanal concentration more quickly, it is preferably a method using gas chromatography, and more preferably a method using a capillary gas chromatography device equipped with a flame ionization detector. Further, as the capillary gas chromatography device equipped with a flame ionization detector, it is preferable that a device realizes functions such as incorporating a high-speed temperature increase and concentration function into the main body, having a short analysis time (for example, about 10 minutes per cycle), being able to analyze with high sensitivity, and being able to process many samples in a short time. Examples of such a device include, but are not limited to, "Flash GC Nose Heracles Neo" (manufactured by Alpha MOS Japan).

[0045] In the hexanal concentration measurement step, depending on the method and device used, etc., pretreatment such as dilution and concentration may be performed on the raw milk after the hexanal generation stop step.

[0046] When measuring the concentration of hexanal by a chromatographic method, the concentration of hexanal may be determined by the peak area, or may be determined by a calibration curve created from the concentration and peak area of a hexanal standard substance.

[0047] Non-limiting specific embodiments of the hexanal concentration measurement step include a step of measuring the hexanal concentration in raw milk according to the capillary GC measurement and conditions described in Example 1 below for the raw milk after the hexanal generation stop step.

[0048] (4) Spontaneous oxidation odor risk determination step The method of one aspect of the present invention includes a step of determining the risk of spontaneous oxidation odor occurring in raw milk based on the concentration of hexanal in the raw milk. In this specification, this step is also referred to as the "spontaneous oxidation odor risk determination step".

[0049] In the spontaneous oxidation odor risk determination step, by checking whether the concentration of hexanal in the raw milk obtained in the hexanal concentration measurement step is greater than or less than an index (threshold value), the risk (possibility) of spontaneous oxidation odor occurring when the raw milk is stored refrigerated is evaluated. That is, when the concentration of the above hexanal is greater than the index, there is a high possibility that spontaneous oxidation odor will occur when the raw milk subjected to the method of one aspect of the present invention is stored refrigerated, and / or it is determined that such raw milk is raw milk with a high risk of spontaneous oxidation odor occurrence; when the concentration of the above hexanal is less than the index, it is determined that there is a low possibility that spontaneous oxidation odor will occur when the raw milk subjected to the method of one aspect of the present invention is stored refrigerated, and / or it is determined that such raw milk is raw milk with a low risk of spontaneous oxidation odor occurrence.

[0050] The hexanal concentration serving as the determination index can be set from the hexanal concentrations in the raw milk in which spontaneous oxidation odor has occurred and the raw milk in which no spontaneous oxidation odor has been felt by refrigerated storage. For example, the index can be the concentration of hexanal in the raw milk in which no off-odor has been felt among the raw milk stored at 5°C for 3 days.

[0051] The hexanal concentration serving as the determination index may also be set from the hexanal concentration in the raw milk that has been sensory evaluated after refrigerated storage and is determined to have a poor sensory evaluation. For example, according to the investigation by the present inventors, when the raw milk is stored at 5°C for 3 days, the hexanal concentration in the raw milk that passed the sensory evaluation was less than 24 μg / l. Therefore, when the hexanal concentration obtained in the hexanal concentration measurement step is less than 24 μg / l, it is determined that there is a low possibility that spontaneous oxidation odor will occur by refrigerated storage of the measured raw milk (raw milk with a low risk of spontaneous oxidation odor occurrence), or when the hexanal concentration obtained in the hexanal concentration measurement step is 24 μg / l or more, it is preferably determined that there is a high possibility that spontaneous oxidation odor will occur by refrigerated storage of the measured raw milk (raw milk with a high risk of spontaneous oxidation odor occurrence).

[0052] For raw milk determined to have a high risk of spontaneous oxidation odor by the spontaneous oxidation odor risk determination step, it is preferable to subject it to the processing of milk and dairy products at an early stage in order to obtain high-quality milk and dairy products with reduced off-odor. For raw milk determined to have a low risk of spontaneous oxidation odor by the spontaneous oxidation odor risk determination step, it is preferable to subject it to the processing of milk and dairy products after refrigerated storage or, if necessary, without refrigerated storage.

[0053] The method according to one aspect of the present invention can carry out the hexanal generation step, the hexanal generation stop step, the hexanal concentration measurement step, and the spontaneous oxidation odor risk determination step in about 2 to 3 hours in total. And if the method according to one aspect of the present invention is applied, even though it is carried out in such a short time, for example, raw milk that may have an off-odor when stored at 5°C for 3 days can be selected. Therefore, by the method according to one aspect of the present invention, the use time of raw milk can be determined in a short time after acceptance, and high-quality milk and dairy products with reduced off-odor can be stably produced.

[0054] (5) Another aspect of the present invention By applying the method according to one aspect of the present invention, it is possible to obtain milk and dairy products in which the generation of spontaneous oxidation odor is suppressed by using raw milk determined to have a risk of generating spontaneous oxidation odor. Therefore, as another aspect of the present invention, there is provided a method for producing milk or dairy products in which the generation of spontaneous oxidation odor is suppressed, including the step of subjecting raw milk determined to have a risk of generating spontaneous oxidation odor to processing on the same day by the method according to one aspect of the present invention to obtain milk or dairy products in which the generation of spontaneous oxidation odor is suppressed.

[0055] Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples, and the present invention can take various aspects as long as the problems of the present invention can be solved. In the examples, copper sulfate pentahydrate was used as copper sulfate.

Examples

[0056] [Example 1. Temporal change in hexanal concentration in raw milk] Raw milk 1A and raw milk 1B collected from different dairy farmers were each inversely mixed to make them uniform. For the raw milk after inverse mixing, it was used as raw milk 1A (test sample 1-1-1) and raw milk 1B (test sample 1-2-1) immediately after storage for 0 days, that is, immediately after acceptance (D0). Also, for the raw milk after inverse mixing that was stored at 5°C for 3 days, it was used as raw milk 1A (test sample 1-1-2) and raw milk 1B (test sample 1-2-2) after storage for 3 days (D3).

[0057] For each test sample, the hexanal concentration (peak area) was measured using a capillary gas chromatography (GC) device "Flash GC Nose Heracles Neo" (manufactured by Alpha MOS Japan Co., Ltd.). The conditions for capillary GC measurement are as follows.

[0058] Sample amount: 5 g Headspace vial: 20 ml Incubation: 80°C (15 minutes) Headspace injection volume: 5,000 μl FID temperature: 260°C Injector temperature: 220°C Trap temperature 70°C Column: MXT-5, 10 m, 180 μm ID Oven temperature: 40°C (10 seconds), 1.5°C / second to 250 °C (90 seconds) Retention time of hexanal: 50 seconds Sample cooling tray temperature: 15°C

[0059] The measurement results of the hexanal concentration (peak area) of each test sample are shown in Figure 1. As shown in Figure 1, there was almost no difference in hexanal concentration between raw milk 1A and raw milk 1B at D0. However, a large difference in hexanal concentration was observed between raw milk 1A and raw milk 1B at D3.

[0060] As shown by the above results, by using hexanal as an indicator, it was found that raw milk 1A has a relatively high risk of spontaneous oxidation odor, and raw milk 1B has a relatively low risk of spontaneous oxidation odor. Also, it was found that in the case of raw milk at D0, the level of the risk of spontaneous oxidation odor cannot be determined using the concentration of hexanal as an indicator. Therefore, in order to be able to evaluate the risk of spontaneous oxidation odor even in raw milk at D0, a method for forcibly generating hexanal in raw milk was investigated.

[0061] [Example 2. Method for generating hexanal in raw milk] Raw milk 2 was inversely mixed uniformly. 20 g of the inversely mixed raw milk was weighed into a 50-ml polypropylene centrifuge tube.

[0062] Next, 10 g of coiled copper wire (diameter 0.35 mm) was added to the centrifuge tube containing the raw milk. The centrifuge tube containing the raw milk and the copper wire was subjected to a reaction treatment of standing still in a thermostat set at 10°C for 1 hour.

[0063] Regarding the raw milk (test sample 2) remaining after taking out the copper wire from the centrifuge tube after the reaction treatment, the hexanal concentration was measured in the same manner as in Example 1. As a control, the inversely mixed raw milk before adding the copper wire was used. Note that the test sample was allowed to stand on a cooling tray (15°C) for 120 minutes until the hexanal concentration was measured.

[0064] As a result, from the comparison of the peak areas of hexanal in the measured chromatogram, it was found that the hexanal concentration of test sample 2 was three times or more that of the control.

[0065] From the above results, it was found that hexanal can be forcibly generated in raw milk by subjecting the raw milk added with copper wire to a reaction treatment at 10°C for 1 hour.

[0066] [[ID=2s]] [Example 3. Method for stopping the hexanal generation reaction] Capillary GC measurement took more than 10 minutes. As a result, even when using the same sample, there were variations in the peak area of hexanal in the obtained chromatograms for each measurement. Therefore, a method for stopping the hexanal generation reaction was investigated.

[0067] Using raw milk 3, 2.5 g of coiled copper wire (diameter 1.2 mm), and a 30-ml glass container, 400 μl of a 5% (w / v) ascorbic acid aqueous solution was added to the 30-ml glass container subjected to reaction treatment in the same manner as in Example 2 except for these (the final concentration of ascorbic acid was 0.1% (w / v) (1,000 ppm)).

[0068] The lid of the centrifuge tube to which ascorbic acid was added was tightly closed, and it was subjected to a reaction stop treatment of stirring and mixing for 5 seconds using a vortex mixer. For raw milk (test sample 3-1) left standing on a cooling tray (15°C) for 45 minutes after the reaction treatment, raw milk (test sample 3-2) left standing on a cooling tray (15°C) for 145 minutes after the reaction treatment, raw milk (test sample 3-3) left standing in a cooling tray (15°C) for 85 minutes after the reaction stop treatment, raw milk (test sample 3-4) left standing in a cooling tray (15°C) for 185 minutes after the reaction stop treatment, and raw milk (test sample 3-5) left standing in a cooling tray (15°C) for 225 minutes after the reaction stop treatment, the hexanal concentration (peak area) was measured in the same manner as in Example 1. As a control, raw milk 3 of D0 was used. The results are shown in Figure 2.

[0069] As shown in Figure 2, the hexanal concentration of test sample 3-2 was about 2.7 times that of the control, indicating that the oxidation reaction proceeded even after the reaction treatment when it was not subjected to the reaction stop treatment. On the other hand, the hexanal concentrations of test samples 3-3 to 3-5 subjected to the reaction stop treatment were 1.3 times or less that of the control, and no significant difference was observed among them.

[0070] From the above results, it was found that the hexanal concentration can be stably measured by subjecting the raw milk subjected to the reaction treatment to further reaction stop treatment.

[0071] [Example 4. Catalyst for hexanal generation reaction] The copper wire used as a catalyst for the oxidation reaction is a hard metal body and may be limited in handling. Therefore, the use of copper sulfate as a catalyst to be used was examined as follows.

[0072] Raw milk 4 was inversely mixed to be uniform. 20 g of the raw milk after inverse mixing was weighed into a 50 ml polypropylene centrifuge tube.

[0073] Next, 100 μl of a 2% (w / v) copper sulfate aqueous solution was added to the centrifuge tube containing the raw milk so that the final concentration of copper sulfate was 100 ppm (0.01% (w / v)). After tightly closing the lid of the centrifuge tube containing the raw milk and copper sulfate, it was stirred and mixed for 5 seconds using a vortex mixer. The centrifuge tube after stirring and mixing was immersed in ice water confirmed to be at 0 °C and subjected to a reaction treatment of standing still for 1 hour.

[0074] 400 μl of a 5% (w / v) ascorbic acid aqueous solution was added to the centrifuge tube subjected to the reaction treatment (the final concentration of ascorbic acid was 0.1% (w / v)). The lid of the centrifuge tube to which ascorbic acid was added was tightly closed and subjected to a reaction stop treatment of stirring and mixing for 5 seconds using a vortex mixer. For the raw milk (test sample 4-1) left standing for 150 minutes in a cooling tray (15 °C) after the reaction stop treatment, the raw milk (test sample 4-2) left standing for 250 minutes in a cooling tray (15 °C) after the reaction stop treatment, and the raw milk (test sample 4-3) left standing for 300 minutes on a cooling tray (15 °C) after the reaction stop treatment, the hexanal concentration (peak area) was measured in the same manner as in Example 1. As a control, raw milk 4 of D0 was used. The results are shown in Figure 3.

[0075] As shown in Figure 3, it was found that hexanal was generated in test samples 4-1 to 4-3 using copper sulfate as a catalyst, and the concentration of hexanal hardly changed among them. The hexanal concentration of test sample 4-1 was about 5.5 times that of the control (D0).

[0076] From the above results, it was found that even when copper sulfate was used as the catalyst, hexanal could be forcibly generated in raw milk, and by subjecting it to the reaction termination treatment, the hexanal concentration could be stably measured.

[0077] [Example 5. Time of hexanal generation reaction] Regarding the time of the hexanal generation reaction, it was examined as follows.

[0078] Raw milk 5A and raw milk 5B collected from different dairy farmers were each inversely mixed uniformly. 20 g of the raw milk after inverse mixing was weighed into a 50 ml polypropylene centrifuge tube.

[0079] Next, 60 μl of a 10% (w / v) copper sulfate aqueous solution was added to the centrifuge tube containing the raw milk so that the final concentration of copper sulfate was 300 ppm. After tightly closing the lid of the centrifuge tube containing the raw milk and copper sulfate, it was stirred and mixed for 5 seconds using a vortex mixer. The centrifuge tube after stirring and mixing was immersed in ice water confirmed to be at 0°C and subjected to a reaction treatment of standing for 30 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, or 180 minutes.

[0080] 400 μl of a 5% (w / v) ascorbic acid aqueous solution was added to the centrifuge tube subjected to the reaction treatment. The lid of the centrifuge tube to which ascorbic acid was added was tightly closed, and it was subjected to a reaction termination treatment of stirring and mixing for 5 seconds using a vortex mixer. Regarding raw milk 5A (test samples 5-1-1 to 5-1-6 for each reaction time) and raw milk 5B (test samples 5-2-1 to 5-2-6 for each reaction time) after the reaction termination treatment, the hexanal concentration (peak area) was measured in the same manner as in Example 1. The results are shown in Figure 4.

[0081] As shown in Figure 4, it was found that in both raw milk 5A and raw milk 5B, by setting the time of the hexanal generation reaction to 30 minutes or more, the amount of hexanal increased over time. Also, in raw milk 5A and raw milk 5B, it was found that a difference occurred even at 30 minutes after the reaction, and a clear difference occurred at 60 minutes or more after the reaction.

[0082] From the above results, it was found that the hexanal generating reaction can be carried out for 30 minutes or more.

[0083] [Example 6. Amount of copper sulfate used in the hexanal generation reaction] The amount of copper sulfate used in the hexanal generation reaction was examined as follows.

[0084] Raw milk 6A and raw milk 6B collected from different dairy farms were mixed by inversion until they were homogeneous. 20 g of the raw milk after inversion mixing was weighed into a 50 ml polypropylene centrifuge tube.

[0085] Next, 100 μl of 1% (w / v), 2% (w / v), or 4% (w / v) copper sulfate aqueous solution was added to the centrifuge tube containing the raw milk so that the final copper sulfate concentration was 50 ppm, 100 ppm, or 200 ppm. The centrifuge tube containing the raw milk and copper sulfate was tightly capped and then stirred and mixed for 5 seconds using a vortex mixer. After stirring and mixing, the centrifuge tube was immersed in ice water that had been confirmed to be at 0°C and left to stand for 60 minutes for reaction treatment.

[0086] To the centrifuge tubes used for the reaction, 400 μl of 5% (w / v) ascorbic acid solution was added. The centrifuge tubes containing ascorbic acid were tightly capped and subjected to reaction termination by stirring and mixing for 5 seconds using a vortex mixer. After the reaction termination, the hexanal concentration (peak area) was measured for raw milk 6A (test samples 6-1-1 to 6-1-3 for each amount of copper sulfate) and raw milk 6B (test samples 6-2-1 to 6-2-3 for each amount of copper sulfate) in the same manner as in 1 above. Furthermore, the hexanal concentration (peak area) was also measured for raw milk 6A (test sample 6-1-4) and raw milk 6B (test sample 6-2-4) after inversion mixing and storage at 5°C for 3 days (D3). The results are shown in Figure 5A.

[0087] As shown in Fig. 5A, it was found that by setting the final concentration of copper sulfate to 50 ppm, the concentration of hexanal can be made comparable to that of the raw milk of D3. Also, when the final concentration of copper sulfate was set to 200 ppm, it was found that the hexanal concentration increased with respect to the raw milk of D3.

[0088] Similarly, for the raw milk 6C, 200 μl (1,000 ppm) or 100 μl (500 ppm) of 10% (w / v) copper sulfate, or 150 μl (300 ppm) or 100 μl (200 ppm) of 4% (w / v) copper sulfate was added, and the hexanal generation reaction was carried out so that the final concentration of copper sulfate became 200 ppm, 300 ppm, 500 ppm or 1,000 ppm. The measurement results of the hexanal concentration (peak area) of the test samples 6-3-1 to 6-3-4 and the test sample 6-3-5 which is the raw milk 6C of D3 are shown in Fig. 5B.

[0089] As shown in Fig. 5B, it was found that as the final concentration of copper sulfate increased, it deviated greatly from the hexanal concentration in the raw milk of D3. Also, when the amount was too large, such as 1,000 ppm, it was found that the generation amount of hexanal decreased and a stable hexanal generation reaction might not occur.

[0090] From the above results, it was found that the amount of copper sulfate used in the hexanal generation reaction can be an amount such that the final concentration becomes 50 ppm or more. Also, it was found that by setting the amount of copper sulfate used in the hexanal generation reaction to an amount such that the final concentration becomes 300 ppm or less, hexanal comparable to that of the raw milk of D3 can be generated.

[0091] [Example 7. Temperature of the hexanal generation reaction] The temperature of the hexanal generation reaction was examined as follows.

[0092] Raw milk 7A and raw milk 7B collected from different dairy farms were mixed by inversion until they were homogeneous. 20 g of the raw milk after inversion mixing was weighed into a 50 ml polypropylene centrifuge tube.

[0093] Next, 100 μl of 1% (w / v), 2% (w / v), or 4% (w / v) copper sulfate aqueous solution was added to the centrifuge tube containing the raw milk so that the final copper sulfate concentration was 50 ppm, 100 ppm, or 200 ppm. The centrifuge tube containing the raw milk and copper sulfate was tightly capped and then stirred and mixed for 5 seconds using a vortex mixer. After stirring and mixing, the centrifuge tube was immersed in ice water confirmed to be at 0°C or left to stand in an incubator set at 5°C for 60 minutes for reaction treatment.

[0094] To the centrifuge tubes used for the reaction, 400 μl of 5% (w / v) ascorbic acid solution was added. The centrifuge tubes containing ascorbic acid were tightly capped and subjected to reaction termination by stirring and mixing for 5 seconds using a vortex mixer. After the reaction termination, the hexanal concentration (peak area) was measured for raw milk 7A (test samples 7-1-1 to 7-1-6 for each temperature and amount of copper sulfate) and raw milk 7B (test samples 7-2-1 to 7-2-6 for each temperature and amount of copper sulfate) in the same manner as in Example 1. Furthermore, the hexanal concentration (peak area) was also measured for raw milk 7A (test samples 7-1-7 to 7-1-8) and raw milk 7B (test samples 7-2-7 to 7-2-8) after inversion mixing and storage at 5°C for 2 days (D2) or 3 days (D3). The results are shown in Figure 6A.

[0095] As shown in Figure 6A, for raw milk 7A, it was found that by setting the hexanal reaction temperature to 5 ° C or less, the hexanal concentration was the same or higher than that of D3 raw milk. However, for raw milk 7B, it was found that when the hexanal reaction temperature was 5 ° C, the hexanal concentration tended to be lower than that of D3 raw milk. In contrast, for both raw milks, it was found that when the hexanal reaction temperature was 0 ° C, the hexanal concentration was the same or higher than that of D3 raw milk. In addition, when the hexanal reaction temperature was set to -1.4 ° C by adding salt to ice water, the reaction proceeded to the same extent as when the hexanal reaction temperature was set to 0 ° C.

[0096] Similarly, for raw milk 7C, the hexanal generation reaction was carried out so that the final copper sulfate concentration was 50 ppm or 100 ppm and the temperature was 10°C, 25°C, or 50°C.The measurement results of the hexanal concentration for test samples 7-3-1 to 7-3-6 and test samples 7-3-7 to 7-3-8, which are raw milk M of D2 or D3, are shown in Figure 6B.

[0097] As shown in Figure 6B, when the temperature of the hexanal reaction is between 10°C and 50°C, the concentration of hexanal produced by the hexanal generation reaction is lower than the hexanal concentration in raw milk D3, indicating that the amount of hexanal generated is insufficient.

[0098] From the above results, it was found that the temperature in the hexanal generation reaction can be set to less than 10°C.

[0099] [Example 8. Parallel processing of hexanal generation treatment and generation stop treatment] The following investigation was carried out to determine whether the risk of spontaneous oxidation odor in raw milk can be evaluated on a chromatogram by carrying out a hexanal-generating reaction in the presence of a predetermined amount of ascorbic acid.

[0100] Each of the raw milks 8 was mixed by inversion until it was homogeneous. After inversion mixing, 20 g of the raw milk was weighed and placed in a 50 ml polypropylene centrifuge tube.

[0101] Next, 100 μl (25 ppm) or 200 μl (50 ppm) of a 0.5% (w / v) aqueous ascorbic acid solution or 400 μl (1,000 ppm) of a 5% (w / v) aqueous ascorbic acid solution was added to a centrifuge tube containing raw milk so that the final concentration of ascorbic acid was 25 ppm, 50 ppm, or 1,000 ppm. The lid of the centrifuge tube to which ascorbic acid was added was tightened firmly, and the mixture was stirred and mixed for 5 seconds using a vortex mixer. Further, 100 μl of a 2% (w / v) aqueous copper sulfate solution was added to the centrifuge tube to which ascorbic acid was added so that the final concentration of copper sulfate was 100 ppm. After firmly tightening the lid of the centrifuge tube containing raw milk, ascorbic acid, and copper sulfate, the mixture was stirred and mixed for 5 seconds using a vortex mixer. The centrifuge tube after stirring and mixing was immersed in ice water confirmed to be at 0°C and subjected to a reaction treatment of standing for 60 minutes.

[0102] For the raw milk 8 after the reaction treatment (test samples 8-1 to 8-3 for each concentration of ascorbic acid), the hexanal concentration (peak area) was measured in the same manner as in Example 1. Also, for the raw milk after inversion mixing, the hexanal concentration (peak area) was similarly measured for the raw milk 8 (test samples 8-4 to 8-6) stored for 0 days (D0), 2 days (D2) at 5°C, or 3 days (D3). Further, for the raw milk 8 (test sample 8-7) in which the reaction stop treatment was carried out after the reaction treatment in the same manner as in Example 6 with the final concentration of copper sulfate being 100 ppm and the reaction time being 60 minutes for the raw milk after inversion mixing, the hexanal concentration (peak area) was similarly measured. The tests for test samples 8-1 to 8-3 and 8-7 were carried out with a repetition number of 2. The results are shown in FIG. 7.

[0103] As shown in Figure 7, the results of test sample 8-7 show that when the reaction was stopped after the hexanal generation reaction, the hexanal concentration was equal to or greater than that of the D3 raw milk. In contrast, when the hexanal generation reaction was carried out in the presence of ascorbic acid, the hexanal concentration was lower than that of the D3 raw milk, or the reaction stopping effect was insufficient, and there was a large variation depending on the time until measurement, making it difficult to obtain stable data.

[0104] These results indicate that when the hexanal-generating reaction is carried out in the presence of ascorbic acid, it is not appropriate to evaluate the risk of spontaneous oxidation odor of raw milk on a chromatogram.

[0105] [Example 9. Confirmation of hexanal generation during short-term storage] For the raw milk after inversion mixing, a final copper sulfate concentration of 100 ppm, a reaction time of 60 minutes, and then a reaction termination treatment similar to Example 6 were performed, resulting in raw milk 9 (test sample 9-1), which was then subjected to a reaction treatment similar to Example 6. The hexanal concentration (peak area) was measured for raw milk 9 (test samples 9-2 to 9-3) similarly as in Example 1. Furthermore, for the raw milk after inversion mixing, the hexanal concentration (peak area) was also measured for raw milk 9 stored for 0 days (D0 0 h) and for 3 hours (D0 3 h) at 5°C. The results are shown in Figure 8.

[0106] As shown in Figure 8, the raw milk subjected to the reaction termination treatment after the hexanal generation reaction had a higher hexanal concentration compared to the raw milk at D0 0h. In contrast, there was almost no change in hexanal concentration between the raw milk at D0 3h and the raw milk at D0 0h.

[0107] From the above results, it was found that the hexanal concentration in raw milk did not increase even when stored at 5°C for a time similar to that of the hexanal generation reaction, whereas the hexanal generation reaction clearly increased the hexanal concentration.

[0108] [Example 10. Assessment of the risk of spontaneous oxidation of raw milk] For raw milk 10 to which hexanal was added while changing the concentration (0 μg / l, 8.1 μg / l, 20.25 μg / l, 40.5 μg / l, and 81 μg / l), the hexanal concentration (peak area) was measured by the method described in Example 1. From the peak areas at each obtained concentration, the peak area when nothing was added (0 μg / l) was subtracted to create a calibration curve. The obtained calibration curve was y = 316.06x (y: peak area, x: hexanal concentration (μg / l); R 2 = 0.9991).

[0109] On the other hand, after subjecting 25 types of raw milk 10-1 to 10-25 to hexanal generation reaction treatment and reaction stop treatment in sequence, the hexanal concentration was measured. Also, the hexanal concentrations of D2 raw milk stored at 5°C for 2 days and D3 raw milk stored at 5°C for 3 days of the same 25 types of raw milk were measured. The rapid method was carried out by, for the raw milk after inversion mixing, setting the final concentration of copper sulfate to 100 ppm and the reaction time to 60 minutes, performing reaction stop treatment in the same manner as in Example 6 after reaction treatment, and measuring the hexanal concentration in the same manner as in Example 1.

[0110] Furthermore, sensory evaluation was carried out on the above 25 types of D3 raw milk. For the sensory evaluation, multiple panelists (2 to 8 people, in principle 3 to 6 people) were used. 100 g of raw milk placed in a 200 ml Erlenmeyer flask was heated in a microwave oven and then cooled to about 40°C, smelled, and then the flavor when it was held in the mouth but not swallowed was judged by a 5-point scoring method according to the following criteria. In accordance with ISO22935-3 and IDF99-3, when the average score of the panel was less than 3.6 points, it was judged as unqualified.

[0111] <Judgment Criteria> 5 points: No difference from normal raw milk is felt, and there is no problem as normal raw milk 4 points: Slightly deviated from the normal raw milk level, but there is no problem as normal raw milk 3 points: Deviated from the normal raw milk level, and it is difficult to be considered normal raw milk 2 points: Greatly deviated from the normal raw milk level 1 point: Very large deviation from normal raw milk levels

[0112] The sensory evaluation results, the hexanal concentration of the rapid method, and the hexanal concentration of D2 / D3 raw milk are summarized in Table 1. Figure 9A shows a graph illustrating the relationship between the sensory evaluation results and the measurement results of the hexanal concentration of the rapid method, and Figure 9B shows a graph illustrating the relationship between the sensory evaluation results and the measurement results of the hexanal concentration of D2 / D3 raw milk. For Figure 9B, the hexanal concentrations of D2 raw milk and D3 raw milk were compared, and the higher concentration was used.

[0113] [Table 1]

[0114] As shown in Table 1, Figures 9A and 9B, one type of raw milk failed the sensory evaluation (raw milk 10-1, indicated by the arrow in Figures 9A and 9B). The hexanal concentrations of this raw milk by the rapid method and the D3 raw milk were 25.3 μg / L and 25.1 μg / L, respectively.

[0115] These results indicate that raw milk with a hexanal concentration of more than 24.0 μg / L at D0 measured by the rapid method may have a higher hexanal concentration at D3 and may fail the sensory evaluation at D3. Taken together, the rapid method can be used to evaluate the risk of spontaneous oxidation odor in raw milk, using a hexanal concentration of 24 μg / L as the standard.

[0116] In addition, when the relationship between the hexanal concentration measured by the rapid method and the hexanal concentration of D3 raw milk was investigated for the above 25 types of raw milk, a correlation (R 2 =0.7035). [Industrial Applicability]

[0117] By using the method of one aspect of the present invention, since the use time of raw milk can be determined in a short time after acceptance, it is possible to stably manufacture dairy products such as milk with good quality in which the generation of spontaneous oxidation odor is suppressed on an industrial scale, and further it is possible to reduce unnecessary waste of raw milk.

Claims

1. A step of generating hexanal in raw milk by subjecting the raw milk to an oxidation treatment at a temperature of less than 10°C for at least 30 minutes in the presence of at least one metal oxidation catalyst selected from the group consisting of a copper wire and copper sulfate; A step of stopping the generation of hexanal in the raw milk by subjecting the raw milk in which hexanal has been generated to an oxidation stop treatment in the presence of an antioxidant; A step of measuring the concentration of hexanal in the raw milk; A step of determining the risk of spontaneous oxidation odor occurring in the raw milk based on the measured concentration of hexanal in the raw milk A method for evaluating the risk of spontaneous oxidation odor occurring in raw milk, comprising the above steps.

2. The method according to claim 1, wherein the antioxidant is ascorbic acid or a salt thereof.

3. The method according to claim 1, wherein the copper sulfate is copper sulfate with a final concentration of 50 ppm to 300 ppm.

4. The method according to any one of claims 1 to 3, wherein the temperature is a temperature of 0°C or higher and less than 5°C, and / or the time is a time of 50 minutes to 100 minutes.

5. The method according to any one of claims 1 to 3, wherein the concentration of hexanal as the reference is 24 μg / l.

6. The step of measuring the concentration of hexanal in the raw milk is a step of measuring the concentration of hexanal in the raw milk using a capillary gas chromatography apparatus equipped with a flame ionization detector, according to any one of claims 1 to 3.

7. A method for producing milk or dairy products with suppressed generation of spontaneous oxidation odor, comprising a step of obtaining milk or dairy products with suppressed generation of spontaneous oxidation odor by subjecting the raw milk determined to have a risk of generating spontaneous oxidation odor by the method according to any one of claims 1 to 3 to processing treatment on the same day.

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