Method of evaluating spontaneous oxidation risk of 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 are known for suppressing the spontaneous generation of oxidized odors in raw milk. Most of these involve changing the feed and feeding method given to dairy cows to reduce the amount of unsaturated fatty acids contained in raw milk. As a method for processing raw milk, a method is known in which the raw milk after milking is treated with nitrogen gas to reduce the dissolved oxygen concentration, thereby suppressing abnormal flavors in raw milk (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5259850 [Non-patent literature]

[0008] [Non-Patent Document 1] Milk Science Vol. 57, No.3 125-129, 2008 Summary of the Invention [Problem to be solved by the invention]

[0009] Among the methods for suppressing the spontaneous oxidative odor generation in raw milk, changing the feed and feeding method given to dairy cows is not realistic because it is difficult to require uniform feed conditions for all dairy farmers who collect milk. Furthermore, in feeding patterns that involve a high amount of concentrated feed, the amount of unsaturated fatty acids in raw milk tends to increase and the amount of antioxidants tends to decrease, making it difficult to eliminate the risk of spontaneous oxidative odor generation in raw milk.

[0010] The method described in Patent Document 1 involves aerating raw milk with nitrogen gas in order to reduce the dissolved oxygen concentration in the raw milk. To apply this method, nitrogen gas inlet holes must be provided in the cooling tank and the milk storage tank, and the nitrogen gas must be introduced into the raw milk while adjusting the pressure, which poses a problem of complex facility design and processes.

[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 further repeated trial and error to design a process to stop the generation of hexanal, and when they subjected raw milk after the hexanal generation process to the hexanal generation stopping process, they were able to stop the generation of hexanal in the raw milk and succeeded in stably measuring the hexanal concentration.

[0017] Furthermore, the inventors measured the hexanal concentration of various raw milks on the third day after storage, and from the trends in 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 these findings, the inventors have finally succeeded in creating a method for evaluating the risk of spontaneous oxidation odor in raw milk, which can solve the problem of the present invention. The present invention was completed based on the findings and successful examples first discovered by the inventors.

[0018] Therefore, according to the present invention, there are provided methods of the following aspects. [1] A step of generating hexanal in raw milk by subjecting the raw milk to an oxidation treatment in the presence of an oxidation catalyst at a temperature of less than 10°C for at least 30 minutes; 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 stopping treatment in the presence of an antioxidant; Measuring the concentration of hexanal in raw milk; determining the risk of spontaneous oxidation odor occurring in raw milk based on the measured hexanal concentration in the raw milk; A method for assessing the risk of spontaneous oxidation flavor development in raw milk, comprising: [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 equal to or higher than 0°C 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 standard hexanal concentration is 24 μg / l. [7] The method according to any one of [1] to [4], wherein 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. [8] A method for producing milk or dairy products in which the generation of spontaneous oxidized odor is suppressed, comprising a step of processing raw milk determined to be at risk of generating spontaneous oxidized odor by the method described in any one of [1] to [4] on the same day to obtain milk or dairy products in which the generation of spontaneous oxidized odor is suppressed. [Effects of the Invention]

[0019] According to the present invention, it is possible to quickly evaluate the possibility of spontaneous oxidized odor occurring after storage of raw milk before storage at low temperatures. As a result, according to the present invention, it is expected that the time to use the raw milk can be determined shortly after receipt, such that raw milk that is likely to generate spontaneous oxidized odor can be processed early, and raw milk that is unlikely to generate spontaneous oxidized odor can be processed after storage at low temperatures, and further, high-quality dairy products such as milk in which the generation of spontaneous oxidized odor is suppressed can be stably produced. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 shows the hexanal concentrations (peak areas) of DO and D3 of raw milk 1A and DO and D3 of raw milk 1B, as described in Example 1 of the Examples below. [Figure 2] FIG. 2 shows the hexanal concentrations (peak areas) of the control (D0 raw milk) and test samples 3-1 to 3-5, as described in Example 3 of the Examples described below. [Figure 3]FIG. 3 shows the hexanal concentrations (peak areas) of control (D0 raw milk) test samples 4-1 to 4-3, as described in Example 4 of the Examples described below. [Figure 4] FIG. 4 shows the hexanal concentrations (peak areas) of test samples 5-1-1 to 5-1-6 related to raw milk 5A and test samples 5-2-1 to 5-2-6 related to raw milk 5B, as described in Example 5 of the Examples described later. [Figure 5A] FIG. 5A shows the hexanal concentrations (peak areas) of test samples 6-1-1 to 6-1-4 related to raw milk 6A and test samples 6-2-1 to 6-2-4 related to raw milk 6B, as described in Example 6 of the Examples described later. [Figure 5B] FIG. 5B shows the hexanal concentrations (peak areas) of test samples 6-3-1 to 6-3-5 related to raw milk 6C, as described in Example 6 of the Examples described later. [Figure 6A] FIG. 6A shows the hexanal concentrations (peak areas) of test samples 7-1-1 to 7-1-8 related to raw milk 7A and test samples 7-2-1 to 7-2-8 related to raw milk 7B, as described in Example 7 of the Examples described later. [Figure 6B] FIG. 6B shows the hexanal concentrations (peak areas) of test samples 7-3-1 to 7-3-8 related to raw milk 7C, as described in Example 7 of the Examples described below. [Figure 7] FIG. 7 shows the hexanal concentrations (peak areas) of test samples 8-1 to 8-7 relating to raw milk 8, as described in Example 8 of the Examples described below. [Figure 8] FIG. 8 shows the hexanal concentrations (peak areas) of test samples 9-1 to 9-3, as described in Example 9 of the Examples described below. [Figure 9A] FIG. 9A is a graph showing the relationship between the sensory evaluation results and the measurement results of hexanal concentration by the rapid method, as described in Example 10 of the Examples below. [Figure 9B] FIG. 9B is a graph showing the relationship between the sensory evaluation results and the measurement results of the hexanal concentration of D3 raw milk, as described in Example 10 of the Examples below. DETAILED DESCRIPTION OF THE INVENTION

[0021] Each aspect of the present invention will be described in detail below, but the present invention can take various forms as long as it achieves its object.

[0022] Unless otherwise specified, the terms used in this specification are used in the sense commonly used by those skilled in the food industry and should not be construed as having an unduly restrictive meaning. Furthermore, the speculations and theories made in this specification are based on the inventors' knowledge and experience to date, and therefore the present invention is not limited solely to such speculations and theories.

[0023] "And / or" means any one or any or all combinations of two or more of the associated listed items. "About" means an amount within ±10% of the quantity that follows the term. For example, "about 100" means 100±10%, i.e., 90 to 110. The "to" in a numerical range includes the preceding and following numerical values; for example, "0% to 100%" means a range greater than or equal to 0% and less than or equal to 100%. "More than" and "less than" mean the lower and upper limits, respectively, excluding the preceding numerical value; for example, "more than 1" means a numerical value greater than 1, and "less than 100" means a numerical value less than 100. "Comprising" means that elements other than those explicitly stated as being included can be added (same meaning as "comprising at least"), but also encompasses "consisting of" and "consisting essentially of." That is, "comprising" can mean including the explicitly stated elements and any one or more elements, consisting of the explicitly stated elements, or consisting essentially of the explicitly stated elements. Elements include limitations such as ingredients, steps, conditions, and parameters. The number of digits in an integer value matches the number of significant digits. For example, 1 has one significant digit, and 10 has two significant digits. Also, the number of digits after the decimal point in a decimal value matches the number of significant digits. For example, 0.1 has one significant digit, and 0.10 has two significant digits.

[0024] The meanings of terms used in this specification that are set forth in the "Ministerial Ordinance on Milk and Dairy Products Compositional Standards, etc." (Ministry of Health, Labour and Welfare Ordinance No. 106 of 2018; hereinafter referred to as the Milk Ordinance) shall be interpreted as set forth in the Milk Ordinance.

[0025] One aspect of the present invention relates to a method for evaluating the risk of spontaneous oxidized odor generation in raw milk, which evaluates whether or not raw milk is likely to generate spontaneous oxidized odor when stored in a refrigerator for a predetermined period of time.

[0026] A method according to one embodiment of the present invention aims to detect spontaneous oxidized odors that may occur during refrigerated storage of raw milk at an early stage. The present inventors have previously confirmed that when raw milk received at a dairy factory is stored at 5°C for 3 days, some raw milk generates spontaneous oxidized odors. In one embodiment of the present invention, hexanal, a component of spontaneous oxidized odors, is used as an indicator to forcibly generate hexanal in raw milk at an early stage at a concentration equal to or higher than the concentration of hexanal generated after refrigerated storage. The concentration of hexanal generated after refrigerated storage is estimated from the concentration of hexanal generated, and the possibility of spontaneous oxidized odors occurring in raw milk after refrigerated storage is evaluated.

[0027] The method of one aspect of the present invention comprises the steps of: generating hexanal in the raw milk by subjecting the raw milk to an oxidation treatment in the presence of an oxidation catalyst at a temperature of less than 10°C for a period of at least 30 minutes; 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 stopping treatment in the presence of an antioxidant; Measuring the concentration of hexanal in raw milk; and A process for determining the risk of spontaneous oxidation odor occurring in raw milk based on the measured concentration of hexanal in the raw milk.

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

[0029] The raw milk may be any milk that can be used as a raw material for cow's milk and dairy products, and may be either milk from a milked cow (raw milk) or raw milk that has been subjected to some kind of processing. When raw milk is subjected to the method of one aspect of the present invention, it is preferable to homogenize it by inversion mixing or the like to prevent bias in the components contained in the raw milk.

[0030] In the hexanal generation process, raw milk is subjected to oxidation treatment in the presence of an oxidation catalyst. The oxidation catalyst is not particularly limited as long as it is a catalyst used to oxidize components in a solution, and examples thereof include metal oxidation catalysts such as copper, iron, silver, platinum, rhodium, and palladium, which are commonly used in liquid-phase oxidation. However, copper is preferred in terms of oxidation activity and economic efficiency. The copper is not particularly limited as long as it has oxidation activity, and can be used in the form of, for example, copper wire or copper sulfate, but copper sulfate is preferred from the viewpoint of handling.

[0031] The amount of the oxidation catalyst used may be an amount sufficient to generate hexanal in the raw milk, and can be appropriately set depending on the type of 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 copper sulfate is used as an 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 generated in raw milk after oxidation treatment tends to be lower than the concentration of hexanal generated in raw milk after storage at 5 ° C for 3 days. Furthermore, when the final concentration of copper sulfate exceeds 300 ppm, the concentration of hexanal generated in raw milk after oxidation treatment tends to be significantly higher than the concentration of hexanal generated in raw milk after storage at 5 ° C for 3 days. Note that, as described in the examples below, 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 within the range of 300 ppm to 1,000 ppm, this tendency does not occur. Furthermore, in this specification, copper sulfate refers to copper sulfate pentahydrate. Therefore, a copper sulfate usage amount (final concentration) of "50 ppm to 300 ppm" indicates that the amount of copper sulfate pentahydrate used is "50 ppm to 300 ppm." When a hydrate or anhydrous copper sulfate other than copper sulfate pentahydrate is used as copper sulfate, the usage amount can be determined by converting the amount of copper sulfate pentahydrate used into its respective molecular weight. For example, usage amounts of copper sulfate pentahydrate of 50 ppm to 300 ppm, 80 ppm to 150 ppm, and 100 ppm correspond to usage amounts of anhydrous copper sulfate of 32 ppm to 192 ppm, 51 ppm to 96 ppm, and 64 ppm, respectively. The copper sulfate may be copper sulfate pentahydrate or any other hydrate or anhydrous copper sulfate.

[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 generated in raw milk after oxidation treatment tends to be significantly lower than the concentration of hexanal generated in raw milk after storage at 5°C for 3 days. On the other hand, the lower the temperature of the oxidation treatment, the greater the amount of hexanal generated. Therefore, the temperature of the oxidation treatment is preferably 5°C or lower, more preferably -5°C or higher but less than 5°C, and even more preferably about 0°C. The temperature of the oxidation treatment may be either the temperature of the raw milk itself or the temperature of the ambient environment of the raw milk (for example, the temperature of a refrigerator or ice water used to cool a container containing raw milk).

[0034] The oxidation treatment of raw milk is carried out for at least 30 minutes. If the oxidation treatment time is less than 30 minutes, the amount of hexanal generated will be insufficient, and the risk of spontaneous oxidation odor in raw milk may not be evaluated. On the other hand, the longer the oxidation treatment time, the greater the amount of hexanal generated tends to be, but the evaluation time will be unnecessarily long. Therefore, the oxidation treatment time is preferably 30 to 150 minutes, more preferably 40 to 120 minutes, and even more preferably 50 to 100 minutes. Note that the start time (0 hours) of the oxidation treatment is the time when a container containing raw milk containing an oxidation catalyst is placed in an ambient environment set at a predetermined temperature.

[0035] The oxidation treatment is carried out at the temperature and time described above by bringing the raw milk into intimate contact with the oxidation catalyst. To bring the raw milk and the oxidation catalyst into intimate contact with each other, it is preferable to stir and mix the container containing the raw milk and the oxidation catalyst. It is also preferable to seal the container containing the raw milk and the oxidation catalyst so that the raw milk does not volatilize during the reaction. Any container may be used as long as it is made of a material that is resistant to denaturation or adsorption of the components in the raw milk and the oxidation catalyst.

[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 ascorbic acid is used as the 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 the ascorbic acid antioxidant is preferably 500 ppm to 1,500 ppm, and more preferably about 1,000 ppm.

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

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

[0043] (3) Hexanal concentration measurement process The method of one embodiment 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 a "hexanal concentration measurement step."

[0044] The method for measuring hexanal concentration is not particularly limited as long as it can measure the hexanal concentration in raw milk. For example, since hexanal is an organic compound with a relatively low boiling point, methods using chromatography such as gas chromatography and liquid chromatography are included. In order to measure hexanal concentration more quickly, a method using gas chromatography is preferred, and a method using a capillary gas chromatography device equipped with a flame ionization detector is more preferred. In addition, as a capillary gas chromatography device equipped with a flame ionization detector, it is preferable that the device has a rapid heating and concentration function built into the main body, a short analysis time (e.g., about 10 minutes per cycle), high sensitivity analysis, and the ability to process many samples in a short time. Such devices include, but are not limited to, the "Flash GC Nose Heracles Neo" (manufactured by Alpha Moss Japan).

[0045] In the hexanal concentration measurement step, depending on the method and apparatus used, the raw milk after the hexanal generation stopping step may be subjected to pretreatment such as dilution or concentration.

[0046] When the concentration of hexanal is measured by a chromatographic method, the concentration of hexanal may be determined from the peak area, or may be determined from a calibration curve prepared 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 after the hexanal generation stopping step using capillary GC measurement and conditions described in Example 1 below.

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

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

[0050] The hexanal concentration used as an index for judgment can be set from the hexanal concentrations in raw milk that has developed a spontaneously oxidized odor due to refrigerated storage and raw milk that has not been detected as having a spontaneously oxidized odor. For example, the index can be the hexanal concentration in raw milk that has not been detected as having an off-odor after being stored at 5°C for 3 days.

[0051] The hexanal concentration used as an index for judgment may be set from the hexanal concentration in raw milk judged to have a poor sensory evaluation after refrigerated storage by sensory evaluation. For example, according to the inventors' investigations, when raw milk was stored at 5 ° C. for 3 days, the hexanal concentration in raw milk that passed the sensory evaluation was less than 24 μg / l. Therefore, if the hexanal concentration obtained in the hexanal concentration measurement step is less than 24 μg / l, it is determined that the raw milk to be measured is unlikely to generate spontaneous oxidized odor by refrigerating it (raw milk with a low risk of spontaneous oxidized odor generation), or if the hexanal concentration obtained in the hexanal concentration measurement step is 24 μg / l or more, it is preferably determined that the raw milk to be measured is likely to generate spontaneous oxidized odor by refrigerating it (raw milk with a high risk of spontaneous oxidized odor generation).

[0052] It is preferable to subject raw milk determined to have a high risk of generating spontaneous oxidized odor in the spontaneous oxidized odor risk determination step to processing for milk and dairy products as soon as possible in order to obtain high-quality milk and dairy products with reduced off-flavors. It is preferable to subject raw milk determined to have a low risk of generating spontaneous oxidized odor in the spontaneous oxidized odor risk determination step to processing for milk and dairy products after refrigerated storage, or, if necessary, without refrigerated storage.

[0053] In a method according to one embodiment of the present invention, the hexanal generation process, the hexanal generation stopping process, the hexanal concentration measurement process, and the spontaneous oxidized odor risk assessment process can be performed in a total of about 2 to 3 hours. Furthermore, by applying the method according to one embodiment of the present invention, even in such a short time, it is possible to select raw milk that may exhibit an unpleasant odor when stored at 5°C for 3 days. Therefore, the method according to one embodiment of the present invention allows the time to use raw milk to be determined in a short time after receipt, and enables the stable production of high-quality milk and dairy products with reduced unpleasant odors.

[0054] (5) Another aspect of the present invention By applying the method of one aspect of the present invention, it is possible to obtain milk and dairy products in which the generation of spontaneous oxidized odor is suppressed by using raw milk that has been determined to be at risk of generating spontaneous oxidized 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 oxidized odor is suppressed, which includes a step of processing raw milk that has been determined to be at risk of generating spontaneous oxidized odor by the method of one aspect of the present invention on the same day to obtain milk or dairy products in which the generation of spontaneous oxidized odor is suppressed.

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples and can take various forms as long as the object of the present invention can be achieved. In the examples, copper sulfate pentahydrate was used as the copper sulfate. [Example]

[0056] [Example 1. Changes in hexanal concentration in raw milk over time] Raw milk 1A and raw milk 1B collected from different dairy farmers were inverted and mixed to make them uniform. The raw milk after inversion and mixing was designated as raw milk 1A (test sample 1-1-1) and raw milk 1B (test sample 1-2-1) after 0 days of storage, i.e., immediately after receipt (D0). Furthermore, the raw milk after inversion and mixing was stored at 5°C for 3 days, and designated as raw milk 1A (test sample 1-1-2) and raw milk 1B (test sample 1-2-2) after 3 days of storage (D3).

[0057] The hexanal concentration (peak area) of each test sample was measured using a capillary gas chromatography (GC) device "Flash GC Nose Heracles Neo" (manufactured by Alpha Moss Japan Co., Ltd.) under the following capillary GC measurement conditions:

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

[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 on D0. However, there was a large difference in hexanal concentration between raw milk 1A and raw milk 1B on D3.

[0060] As the above results show, by using hexanal as an indicator, it was found that raw milk 1A is raw milk with a relatively high risk of spontaneous oxidized odor, and raw milk 1B is raw milk with a relatively low risk of spontaneous oxidized odor. Furthermore, it was found that the risk of spontaneous oxidized odor cannot be determined using the hexanal concentration as an indicator for D0 raw milk. Therefore, we investigated a method for forcibly generating hexanal in raw milk so that the risk of spontaneous oxidized odor can also be evaluated in D0 raw milk.

[0061] [Example 2. How hexanal is produced in raw milk] Raw milk 2 was mixed by inversion to make it uniform. 20 g of the raw milk after inversion mixing was weighed into a 50 ml polypropylene centrifuge tube.

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

[0063] The copper wire was removed from the centrifuge tube after the reaction treatment, and the remaining raw milk (test sample 2) was measured for hexanal concentration in the same manner as in Example 1. As a control, raw milk after inversion mixing before adding the copper wire was used. The test sample was left to stand on a cooling tray (15°C) for 120 minutes before measuring the hexanal concentration.

[0064] As a result, a comparison of the peak areas of hexanal in the chromatograms obtained by measurement revealed that the hexanal concentration in test sample 2 was three times higher than that of the control.

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

[0066] [Example 3. How to stop the hexanal generation reaction] Capillary GC measurements take more than 10 minutes, which results in variations in the peak area of ​​hexanal in the chromatograms obtained from each measurement, even when the same sample is used. Therefore, we investigated a method for terminating the hexanal-generating reaction.

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

[0068] The centrifuge tubes containing ascorbic acid were tightly capped and subjected to a reaction termination treatment by stirring and mixing for 5 seconds using a vortex mixer. The hexanal concentration (peak area) was measured in the same manner as in Example 1 for raw milk that had been left to stand on a cooling tray (15°C) for 45 minutes after the reaction (Test Sample 3-1), raw milk that had been left to stand on a cooling tray (15°C) for 145 minutes after the reaction (Test Sample 3-2), raw milk that had been left to stand on a cooling tray (15°C) for 85 minutes after the reaction termination (Test Sample 3-3), raw milk that had been left to stand on a cooling tray (15°C) for 185 minutes after the reaction termination (Test Sample 3-4), and raw milk that had been left to stand on a cooling tray (15°C) for 225 minutes after the reaction termination (Test Sample 3-5). Raw milk 3 on D0 was used as a control. The results are shown in Figure 2.

[0069] As shown in Figure 2, the hexanal concentration in test sample 3-2 was approximately 2.7 times that of the control, indicating that the oxidation reaction continued even after the reaction treatment if the reaction was not stopped. In contrast, the hexanal concentrations in test samples 3-3 to 3-5, which were subjected to the reaction stopping treatment, were 1.3 times or less that of the control, and no significant difference was observed between them.

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

[0071] [Example 4. Catalyst for hexanal generation reaction] The copper wire used as a catalyst for the oxidation reaction is a hard metal, and handling it can be limited. Therefore, we investigated the use of copper sulfate as a catalyst as follows.

[0072] The raw milk 4 was mixed by inversion to make it uniform. 20 g of the raw milk after inversion 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 copper sulfate concentration was 100 ppm (0.01% (w / v)). 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 1 hour for reaction treatment.

[0074] To the centrifuge tubes used for the reaction, 400 μl of a 5% (w / v) aqueous solution of ascorbic acid was added (final concentration of ascorbic acid: 0.1% (w / v)). 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. The hexanal concentration (peak area) was measured in the same manner as in Example 1 for raw milk (Test Sample 4-1) left to stand on a cooling tray (15°C) for 150 minutes after reaction termination, raw milk (Test Sample 4-2) left to stand on a cooling tray (15°C) for 250 minutes after reaction termination, and raw milk (Test Sample 4-3) left to stand on a cooling tray (15°C) for 300 minutes after reaction termination. Raw milk 4 on D0 was used as a control. 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, which used copper sulfate as a catalyst, and that the hexanal concentration was almost the same among them. The hexanal concentration in 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 is used as a catalyst, hexanal can be forcibly generated in raw milk, and that by subjecting the raw milk to a reaction stopping treatment, the hexanal concentration can be measured stably.

[0077] [Example 5. Hexanal generation reaction time] The reaction time for hexanal generation was examined as follows.

[0078] Raw milk 5A and raw milk 5B 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.

[0079] Next, 60 μl of a 10% (w / v) copper sulfate solution was added to the centrifuge tube containing the raw milk so that the final copper sulfate concentration was 300 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 30, 60, 90, 120, 150, or 180 minutes for reaction treatment.

[0080] To the centrifuge tubes used for the reaction, 400 μl of a 5% (w / v) aqueous solution of ascorbic acid was added. The centrifuge tubes containing ascorbic acid were tightly capped and subjected to reaction termination treatment by stirring and mixing for 5 seconds using a vortex mixer. After reaction termination treatment, the hexanal concentration (peak area) was measured for 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) 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, the amount of hexanal increased over time by extending the hexanal-generating reaction time to 30 minutes or more. It was also found that differences occurred between raw milk 5A and raw milk 5B even after 30 minutes of reaction, and that clear differences occurred after 60 minutes or more of 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 Figure 5A, it was found that the hexanal concentration could be made similar to that of D3 raw milk by increasing the final copper sulfate concentration to 50 ppm. Furthermore, it was found that the hexanal concentration was higher than that of D3 raw milk when the final copper sulfate concentration was increased to 200 ppm.

[0088] Similarly, 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 to raw milk 6C, and a hexanal-generating reaction was performed so that the final copper sulfate concentration was 200 ppm, 300 ppm, 500 ppm, or 1,000 ppm.The measurement results of the hexanal concentration (peak area) of test samples 6-3-1 to 6-3-4 and test sample 6-3-5, which is raw milk 6C of D3, are shown in Figure 5B.

[0089] As shown in Figure 5B, as the final copper sulfate concentration increases, the hexanal concentration in the raw milk obtained in D3 becomes significantly different from that in D3. Furthermore, when the final concentration is too high, such as 1,000 ppm, the amount of hexanal generated becomes small, and it is possible that a stable hexanal generation reaction may not occur.

[0090] From the above results, it was found that the amount of copper sulfate used in the hexanal generation reaction can be set to an amount that results in a final concentration of 50 ppm or more. Furthermore, it was found that by using an amount of copper sulfate used in the hexanal generation reaction that results in a final concentration of 300 ppm or less, it is possible to generate hexanal at the same level as D3 raw milk.

[0091] [Example 7. Temperature of 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 uniform. 20 g of the raw milk after inversion mixing was weighed into a 50 ml polypropylene centrifuge tube.

[0101] Next, 100 μL (25 ppm) or 200 μL (50 ppm) of 0.5% (w / v) ascorbic acid solution or 400 μL (1,000 ppm) of 5% (w / v) ascorbic acid solution was added to the centrifuge tube containing the raw milk to achieve a final ascorbic acid concentration of 25 ppm, 50 ppm, or 1,000 ppm. The centrifuge tube containing the ascorbic acid was tightly capped and mixed using a vortex mixer for 5 seconds. Furthermore, 100 μL of 2% (w / v) copper sulfate solution was added to the centrifuge tube containing the ascorbic acid to achieve a final copper sulfate concentration of 100 ppm. The centrifuge tube containing the raw milk, ascorbic acid, and copper sulfate was tightly capped and mixed using a vortex mixer for 5 seconds. After 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 the reaction treatment.

[0102] The hexanal concentration (peak area) of raw milk 8 after the reaction treatment (test samples 8-1 to 8-3 for each ascorbic acid concentration) was measured in the same manner as in Example 1. Furthermore, the hexanal concentration (peak area) of raw milk 8 (test samples 8-4 to 8-6) after inversion mixing and storage for 0 days (D0), 2 days (D2), or 3 days (D3) at 5°C was also measured in the same manner. Furthermore, the hexanal concentration (peak area) of raw milk 8 (test sample 8-7) after inversion mixing was measured in the same manner as in Example 6, except that the final copper sulfate concentration was 100 ppm and the reaction time was 60 minutes. Test samples 8-1 to 8-3 and 8-7 were repeated twice. The results are shown in Figure 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 at various concentrations (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. A calibration curve was created by subtracting the peak area when nothing was added (0 μg / L) from the peak area obtained for each concentration. The resulting calibration curve was expressed as y = 316.06x (y: peak area, x: hexanal concentration (μg / L); R 2 =0.9991).

[0109] Meanwhile, 25 kinds of raw milk 10-1 to 10-25 were subjected to a hexanal generating reaction treatment and a reaction stop treatment, and then the hexanal concentration was measured. The same 25 kinds of raw milk were stored at 5 ° C for 2 days (D2 raw milk) and 5 ° C for 3 days (D3 raw milk). The hexanal concentration was measured. The rapid method was carried out by subjecting the raw milk after inversion mixing to a final copper sulfate concentration of 100 ppm, a reaction time of 60 minutes, and then carrying out a reaction stop treatment after the reaction treatment in the same manner as in Example 6, and measuring the hexanal concentration in the same manner as in Example 1.

[0110] Furthermore, a sensory evaluation was conducted on the 25 types of D3 raw milk. The sensory evaluation was conducted by multiple panelists (2-8 people, usually 3-6 people) who heated 100g of raw milk in a 200ml Erlenmeyer flask in a microwave oven, cooled it to about 40°C, smelled it, and then put it in their mouths but did not swallow it. The flavor was evaluated using a 5-point scale based on the following criteria. In accordance with ISO22935-3 and IDF99-3, a panel average score of less than 3.6 points was considered unacceptable.

[0111] <Judgment criteria> 5 points: No difference is felt from normal raw milk, and there is no problem at all as normal raw milk 4 points: Slightly different from normal raw milk levels, but no problem as normal raw milk 3 points: It is out of the normal raw milk level and cannot be considered normal raw milk. 2 points: Deviates significantly from normal raw milk levels 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 utilizing the method of one embodiment of the present invention, the time to use raw milk can be determined within a short time after receipt, making it possible to stably produce high-quality dairy products such as milk with reduced generation of spontaneous oxidized odor on an industrial scale, and further reducing unnecessary waste of raw milk.

Claims

1. A step of generating hexanal in raw milk by subjecting it 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 process to stop the generation of hexanal in raw milk by subjecting the raw milk, which has generated hexanal, to an oxidation-stopping treatment in the presence of an antioxidant, A process for measuring the concentration of hexanal in raw milk, A process to determine the risk of spontaneous oxidation odor occurring in 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, including [specific factors].

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 oxidation catalyst is a metal oxidation catalyst.

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

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

6. The method according to any one of claims 1 to 3, wherein 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.

7. A method for producing milk or dairy products in which the generation of spontaneous oxidative odor is suppressed, comprising the step of processing raw milk that has been determined to be at risk of generating spontaneous oxidative odor by any one of claims 1 to 3 on the same day, thereby obtaining milk or dairy products in which the generation of spontaneous oxidative odor is suppressed.

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