Method for storing liquid milk concentrate, liquid milk concentrate, and method for producing same

Abstract

The present invention addresses the problem of providing a method for storing a liquid milk concentrate for a long period of time while maintaining the viscosity of the liquid milk concentrate at a low level. In the method of the present invention, a sterilized liquid milk concentrate is refrigerated and preserved by adjusting the pH of the liquid milk concentrate to fall within the range of more than 4.6 and less than 6.5. It is required to be specified that various acids, such as lactic acid, acetic acid, hydrochloric acid, citric acid, carbon dioxide, etc., which can be added to food products, for example, can be used as pH regulators. In addition, the raw milk is preferably skimmed milk, and the milk concentrate is preferably a milk protein concentrate.

Description

Technical Field

[0001] The present invention relates to a method for preserving a liquid milk concentrate. In addition, the present invention relates to a liquid milk concentrate and a method for producing the same. Background Art

[0002] Conventionally, there has been proposed "a method for producing a liquid milk concentrate, which comprises adding an acid to raw milk such as skim milk to prepare acidic raw milk, then ultrafiltering the acidic raw milk to prepare a milk concentrate, and finally adding sodium hydroxide, potassium hydroxide, potassium carbonate, etc. to the milk concentrate to neutralize the milk concentrate" (for example, refer to the following Patent Documents 1 to 5).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-038359

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2018-038360

[0007] Patent Document 3: Japanese Patent Application Laid-Open No. 2018-038361

[0008] Patent Document 4: Japanese Patent Application Laid-Open No. 2018-064481

[0009] Patent Document 5: Japanese Patent Application Laid-Open No. 2018-064482

[0010] Patent Document 6: Japanese Patent Application Laid-Open No. 2018-074915 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] However, the viscosity of the liquid milk concentrate produced in this way rises relatively quickly, and it cannot be transported by a tanker truck or the like. Therefore, when the producer of the liquid milk concentrate has to transport the liquid milk concentrate, it must be transported quickly after its production, and the arrangement status of transportation equipment such as tanker trucks must be taken into account during its production. Therefore, producers of liquid milk concentrates seek a technology that can preserve liquid milk concentrates for a long time (about 20 to about 30 days) while maintaining a relatively low viscosity.

[0013] An object of the present invention is to provide a method for preserving a liquid milk concentrate for a long time (about 20 to about 30 days) while maintaining a relatively low viscosity. Another object of the present invention is to provide a liquid milk concentrate that can be preserved for a long time (about 20 to 30 days) while maintaining a relatively low viscosity and a method for producing the same.

[0014] Solution for solving problems

[0015] The method of the first solution of the present invention is a method of adjusting the pH of a sterilized liquid milk concentrate to fall within a range of more than 4.6 and less than 6.5 and refrigerating and storing the liquid milk concentrate.

[0016] The inventors of the present application conducted in-depth research and found that when using the preservation method of the liquid milk concentrate of the present invention, it is possible to store the liquid milk concentrate for a long time (about 20 to about 30 days) while maintaining the viscosity of the liquid milk concentrate at a low level. It should be noted that this is also the case when the protein content is high.

[0017] It should be noted that in the method of the first solution, it is preferred to adjust the pH such that the intrinsic viscosity of the heat-sterilized liquid milk concentrate at 5°C falls within a range of 0.01 dL / g or more and 0.8 dL / g or less, and the pH of the heat-sterilized liquid milk concentrate falls within a range of more than 4.6 and less than 6.5. It should be noted that the upper limit value of the intrinsic viscosity is preferably 0.5 dL / g, more preferably 0.35 dL / g, and further preferably 0.33 dL / g. In addition, the lower limit value of the intrinsic viscosity is preferably 0.1 dL / g, more preferably 0.2 dL / g, further preferably 0.25 dL / g, and particularly preferably 0.3 dL / g. Furthermore, the range of the intrinsic viscosity is preferably a range of 0.2 dL / g or more and 0.5 dL / g or less, more preferably a range of 0.3 dL / g or more and 0.33 dL / g or less. In addition, in the relationship between the intrinsic viscosity and the pH at 5°C, it is preferred that the intrinsic viscosity falls within a range of 0.1 dL / g or more and 0.5 dL / g or less, and the pH falls within a range of more than 5.2 and less than 6.5, more preferably the intrinsic viscosity falls within a range of 0.2 dL / g or more and 0.35 dL / g or less, and the pH falls within a range of more than 5.6 and less than 6.5, further preferably the intrinsic viscosity falls within a range of 0.3 dL / g or more and 0.33 dL / g or less, and the pH falls within a range of more than 5.8 and less than 6.5.

[0018] The manufacturing method of the liquid milk concentrate of the second aspect of the present invention is a method for manufacturing a liquid milk concentrate suitable for refrigerated storage, which includes an acidification step, a concentration step, a heat sterilization step, and a pH adjustment step. In the acidification step, the liquid raw milk is acidified to prepare a liquid acidified raw milk. It should be noted that before entering the concentration step from the acidification step, it is preferable to let the acidified raw milk stand or stir for a specified time. This is to allow calcium ions and the like to dissociate (free) sufficiently from proteins (i.e., casein, etc.). In the concentration step, the acidified raw milk is subjected to ultrafiltration treatment to prepare a liquid milk concentrate. In the heat sterilization step, the liquid milk concentrate is heat sterilized to prepare a sterilized liquid milk concentrate. In the pH adjustment step, the pH of the sterilized liquid milk concentrate is adjusted to fall within a range exceeding 4.6 and less than 6.5.

[0019] The inventors of the present application conducted in-depth research and found that: if the manufacturing method of the liquid milk concentrate of the present invention is used, a liquid milk concentrate that can be refrigerated and stored for a long time (about 30 days) while maintaining a relatively low viscosity can be obtained. It should be noted that this is also the case when the protein content is high.

[0020] It should be noted that in the above manufacturing method of the liquid milk concentrate, in the acidification step, it is preferable to acidify the liquid raw milk in such a way that the pH of the liquid milk concentrate obtained in the concentration step falls within a range of 6.4 or more and 7.0 or less.

[0021] The in-depth research results of the inventors of the present application have shown that: if the pH of the liquid milk concentrate is within the above range, the thermal stability of the liquid milk concentrate is good. Therefore, if this manufacturing method of the liquid milk concentrate is used, it is possible to transfer from the concentration step to the heat sterilization step without further pH adjustment steps.

[0022] In addition, in the above manufacturing method of the liquid milk concentrate, the raw milk is skim milk, and the milk concentrate is preferably a milk protein concentrate (also referred to as "Milk Protein Concentrate" (hereinafter simply referred to as "MPC").).

[0023] In addition, in the above manufacturing method of the liquid milk concentrate, it is preferable that in the pH adjustment step, the intrinsic viscosity of the sterilized liquid milk concentrate at 5°C falls within a range of 0.01 dL / g or more and 0.8 dL / g or less, and the pH of the sterilized liquid milk concentrate falls within a range exceeding 4.6 and less than 6.5, and its pH is adjusted accordingly. It should be noted that the upper limit value, lower limit value, range of this intrinsic viscosity, and the relationship between the range of the intrinsic viscosity and the range of the pH are the same as those described in the method of the first aspect.

[0024] The liquid milk concentrate of the third aspect of the present invention is produced by the method for producing the liquid milk concentrate of the second aspect.

[0025] The inventors of the present application conducted in-depth research and found that the liquid milk concentrate of the present invention can be refrigerated for a long time (about 30 days) while maintaining a relatively low viscosity. It should be noted that this also applies to the case of a high protein content.

[0026] The milk concentrate of the fourth aspect of the present invention is a heat-sterilized milk concentrate, the intrinsic viscosity at 5 °C falls within the range of 0.01 dL / g or more and 0.8 dL / g or less, and the pH falls within the range of more than 4.6 and less than 6.5. It should be noted that the upper limit value, lower limit value, range of the intrinsic viscosity, and the relationship between the range of the intrinsic viscosity and the range of the pH are the same as those described in the method of the first aspect.

[0027] The inventors of the present application conducted in-depth research and found that the liquid milk concentrate of the present invention can be refrigerated for a long time (about 30 days) while maintaining a relatively low viscosity. It should be noted that this also applies to the case of a high protein content.

[0028] Effects of the Invention

[0029] According to the present invention, it is possible to store the liquid milk concentrate for a long time (about 30 days) while maintaining a relatively low viscosity of the liquid milk concentrate. Detailed Description of the Embodiment

[0030] The liquid milk concentrate of the embodiment of the present invention is a liquid milk concentrate suitable for refrigerated storage, and is produced through an acidification step, a concentration step, a heat sterilization step, and a pH adjustment step. It should be noted that the liquid milk concentrate produced in this way can also be neutralized as needed at the end of refrigerated storage. Hereinafter, after the liquid milk concentrate is described in detail, its production method and uses will be described in detail.

[0031] <Liquid milk concentrate>

[0032] The liquid milk concentrate according to an embodiment of the present invention is obtained by concentrating raw milk, whole milk, special milk, or skim milk (obtained by removing the milk fat component from raw milk, whole milk, or special milk) or partially skimmed milk (obtained by partially removing the milk fat component from raw milk, whole milk, or special milk). For example, it is not only concentrated milk (obtained by concentrating raw milk, whole milk, or special milk, with milk solids content of 25.5% or more and milk fat content of 7.0% or more) and skimmed concentrated milk (a substance obtained by concentrating the one obtained by removing the milk fat component from raw milk, whole milk, or special milk, with non-fat milk solids content of 18.5% or more and bacterial count (per 1 g by standard plate culture method) of 100,000 or less) as specified in the "Ordinance of the Ministry of Health, Labour and Welfare Concerning Standards for Ingredients of Milk and Dairy Products, etc.", but also can be "a substance obtained by concentrating raw milk, whole milk, or special milk, with milk solids content less than 25.5% (hereinafter referred to as 'concentrated milk outside the ordinance')", "a substance obtained by concentrating the one obtained by removing the milk fat component from raw milk, whole milk, or special milk, with non-fat milk solids content less than 18.5% (hereinafter referred to as'skimmed concentrated milk outside the ordinance')", etc. However, it is preferably a liquid milk protein concentrate (also called Milk Protein Concentrate (hereinafter simply referred to as "MPC")). It should be noted that hereinafter, for the sake of convenience of explanation, raw milk, whole milk, special milk, skim milk, and partially skimmed milk are sometimes collectively referred to as "raw material milk".

[0033] In addition, with respect to 20% by mass of the total solid component, the milk concentrate according to an embodiment of the present invention contains protein in the range of 7.0% by mass or more and 20.0% by mass or less, calcium (Ca) in the range of 0.20% by mass or more and 0.70% by mass or less, and magnesium (Mg) in the range of more than 0.00% by mass and 0.10% by mass or less.

[0034] It should be noted that the protein content in the liquid milk concentrate according to an embodiment of the present invention is preferably in the range of 7.0% by mass or more and 20.0% by mass or less, more preferably in the range of 10.0% by mass or more and 20.0% by mass or less, further preferably in the range of 12.0% by mass or more and 20.0% by mass or less, further preferably in the range of 14.0% by mass or more and 20.0% by mass or less, and further preferably in the range of 16.0% by mass or more and 20.0% by mass or less with respect to 20% by mass of the total solid component.

[0035] In addition, the content of calcium (Ca) in the milk concentrate according to the embodiment of the present invention is preferably in the range of 0.2% by mass or more and 0.7% by mass or less, more preferably in the range of 0.2% by mass or more and 0.6% by mass or less, still more preferably in the range of 0.2% by mass or more and 0.5% by mass or less, and particularly preferably in the range of 0.2% by mass or more and 0.3% by mass or less, based on 20% by mass of the total solid content.

[0036] In addition, the content of magnesium (Mg) in the milk concentrate according to the embodiment of the present invention is preferably in the range of more than 0.00% by mass and 0.10% by mass or less, more preferably in the range of more than 0.00% by mass and 0.05% by mass or less, based on 20% by mass of the total solid content.

[0037] Furthermore, the content of the total solid content of the liquid milk concentrate according to the embodiment of the present invention is generally in the range of 14% by mass or more and 22% by mass or less, preferably in the range of 16% by mass or more and 22% by mass or less, more preferably in the range of 18% by mass or more and 22% by mass or less, and still more preferably in the range of 19% by mass or more and 22% by mass or less.

[0038] In addition, the viscosity of the liquid milk concentrate according to the embodiment of the present invention, immediately after being stored for 20 days in a temperature environment of 2 to 4°C, is preferably 50,000 mPa·s or less, more preferably 30,000 mPa·s or less, still more preferably 10,000 mPa·s or less, still more preferably 7,000 mPa·s or less, still more preferably 5,000 mPa·s or less, still more preferably 3,000 mPa·s or less, still more preferably 2,000 mPa·s or less, and particularly preferably 1,000 mPa·s or less.

[0039] In addition, the viscosity of the liquid milk concentrate according to the embodiment of the present invention, immediately after being stored for 30 days in a temperature environment of 2 to 4°C, is preferably 50,000 mPa·s or less, more preferably 30,000 mPa·s or less, still more preferably 10,000 mPa·s or less, still more preferably 7,000 mPa·s or less, still more preferably 5,000 mPa·s or less, still more preferably 3,000 mPa·s or less, and particularly preferably 2,000 mPa·s or less.

[0040] <Method for manufacturing liquid milk concentrate>

[0041] The liquid milk concentrate according to the embodiment of the present invention is manufactured through an acidification step, a concentration step, a heat sterilization step, and a pH adjustment step as described above. In addition, when the liquid milk concentrate according to the embodiment of the present invention is skimmed concentrated milk, skimmed concentrated milk outside the ordinance, or liquid milk protein concentrate, it is preferable to provide a skim milk preparation step before the acidification step. In addition, as described above, the liquid milk concentrate thus manufactured can be neutralized as needed at the end of cold storage. Hereinafter, these steps will be described in detail.

[0042] (1) Skim milk preparation step

[0043] In the skim milk preparation step, skim milk or partially skimmed milk is prepared from raw milk, cow milk, or special milk. It should be noted that the "skim milk" mentioned here is obtained by removing the milk fat component from raw milk, cow milk, or special milk. For example, it is a "substance with a milk fat component of less than 0.5% in raw milk, cow milk, or special milk", etc. In addition, the "partially skimmed milk" mentioned here is obtained by partially removing the milk fat component from raw milk, cow milk, or special milk. For example, it is a "substance with a milk fat component in the range of 0.5% or more and less than 3.0% in raw milk, cow milk, or special milk", etc. It should be noted that the skim milk preparation step is not necessarily carried out as described above. It is also possible to purchase commercially available skimmed concentrated milk or skimmed concentrated milk outside the ordinance and use it as raw milk (starting material) in the acidification step.

[0044] Examples of the method for preparing skim milk or partially skimmed milk from raw milk, cow milk, or special milk include a method of centrifugally separating the milk fat of raw milk, cow milk, or special milk (hereinafter also referred to as the "centrifugal separation method"); a method of membrane-separating the milk fat of raw milk, cow milk, or special milk (hereinafter also referred to as the "membrane separation method". For example, there is microfiltration treatment.) and the like. It should be noted that when using the centrifugal separation method, it is preferable to centrifugally separate the milk fat while maintaining the temperature of raw milk, cow milk, or special milk in the range of 45°C or more and 55°C or less. In addition, in the above case, it is preferable to cool the obtained skim milk or partially skimmed milk before the acidification step. It should be noted that in the above case, the cooling temperature is preferably in the range above the temperature at which the skim milk or partially skimmed milk remains liquid and 10°C or less, more preferably in the range of 1°C or more and 5°C or less.

[0045] (2) Acidification step

[0046] In the acidification process, an acid is added to raw milk (e.g., cooled raw milk) to acidify the raw milk and prepare liquid acidified raw milk. It should be noted that at this time, the pH of the liquid acidified raw milk is preferably determined such that the pH of the liquid milk concentrate finally obtained in the concentration process is in the range of 6.4 or more and 7.0 or less. Additionally, this pH is, for example, more preferably in the range of 5.8 or more and less than 6.8, further preferably in the range of 6.0 or more and 6.5 or less, and particularly preferably in the range of 6.1 or more and 6.3 or less. As the acid used in this acidification process, for example, acids that are solids or liquids at normal temperature and pressure such as hydrochloric acid, lactic acid, acetic acid, citric acid, etc., and acids that are gases at normal temperature and pressure such as carbon dioxide can be used. It should be noted that as a method of blowing carbon dioxide into raw milk, for example, methods using ordinary nozzles, in-line nozzles, sintered metal porous filters, etc. can be cited. Moreover, when the pH of the raw milk is adjusted to the acidic side, calcium ions, magnesium ions, etc. that are electrostatically attached to proteins dissociate from the proteins in the acidified raw milk. And by appropriately adjusting the pH of the raw milk within the above range, the content (concentration (mass%)) of calcium ions, magnesium ions, etc. dissociated in the raw milk can be adjusted.

[0047] It should be noted that in this acidification process, after adding the acid to the raw milk, it is preferred to let the acidified raw milk stand or stir for a specified time. Here, this specified time is preferably 0.5 hours or more, more preferably 1 hour or more, further preferably 1.5 hours or more, and particularly preferably 2 hours or more. Moreover, there is no particular upper limit for this specified time. The specified time is, for example, preferably 10 hours or less, more preferably 8 hours or less, further preferably 6 hours or less, and particularly preferably 4 hours or less. Additionally, in this acidification process, it is preferred to let the acidified raw milk stand or stir at a specified temperature. Here, this specified temperature is preferably in the range above the temperature at which the acidified raw milk remains liquid and 15°C or less, more preferably in the range of 1°C or more and 10°C or less, further preferably in the range of 1°C or more and 5°C or less.

[0048] (3) Concentration process

[0049] In the concentration process, after the acidification process, ultrafiltration treatment is performed on the acidified raw milk to prepare a milk concentrate (milk protein concentrate). At this time, calcium ions, magnesium ions, etc. dissociated in the acidification process are separated from the acidified raw milk (or milk concentrate) as permeate components. As a result, a "milk concentrate with reduced calcium and magnesium content (concentration)" is obtained. It should be noted that, as described above, the pH of the milk concentrate obtained in this process is preferably in the range of 6.4 or more and 7.0 or less. This is because if the pH of the milk concentrate is within this range, the thermal stability of the milk concentrate is excellent, and even if heat sterilization is performed in a subsequent process, the milk concentrate is extremely difficult to deteriorate. The ultrafiltration membrane used for the ultrafiltration treatment is a flat membrane, a hollow fiber membrane, a spiral membrane, a ceramic membrane, a rotary membrane, a vibrating membrane, etc. The cut-off molecular weight of the ultrafiltration membrane is preferably in the range of 8000 Da or more and 12000 Da or less, more preferably in the range of 9000 Da or more and 11000 Da or less, and further preferably in the range of 9500 Da or more and 10500 Da or less. The lower limit value of the concentration ratio can be changed according to the type of raw milk, etc. For example, when the raw milk is skim milk, the concentration ratio is preferably 2.5 times or more, more preferably 3 times or more. When the raw milk is raw milk, the concentration ratio is preferably 1.5 times or more, more preferably 2 times or more. In addition, the upper limit value of the concentration ratio can be determined according to the pressure resistance of the ultrafiltration membrane and the ultrafiltration device. For example, when the raw milk is skim milk, the concentration ratio is preferably 6 times or less, more preferably 5.5 times or less. When the raw milk is raw milk, the concentration ratio is preferably 5 times or less, more preferably 4.5 times or less.

[0050] This concentration process can also be repeated. In this case, the concentration process can be continuously repeated, or the concentration process can be intermittently repeated with other processes interposed. It should be noted that the other processes in the latter case are, for example, a diafiltration process. Diafiltration refers to the process of adding a pure solvent (such as ion-exchanged water, etc.) to the milk concentrate during ultrafiltration treatment and continuously discharging low-molecular-weight substances, ions, etc. In addition, this diafiltration process can also be repeated.

[0051] (4) Heat sterilization process

[0052] In the heat sterilization step, the obtained liquid milk concentrate is heat sterilized to prepare a sterilized liquid milk concentrate. It should be noted that when implementing this step, from the perspective of thermal stability, the pH of the liquid milk concentrate is preferably set within the range of 6.4 or more and 7.0 or less. In addition, as the method of "heat sterilization" mentioned here, for example, low-temperature holding sterilization method, continuous low-temperature sterilization method, high-temperature holding sterilization method, high-temperature short-time sterilization method, ultra-high temperature instantaneous sterilization method, etc. can be cited. It should be noted that among these heat sterilization methods, the ultra-high temperature instantaneous sterilization method is most preferred. In the low-temperature holding sterilization method, the liquid milk concentrate is heat sterilized at a temperature of 63°C to 65°C for about 30 minutes in a holding manner. In addition, in the continuous low-temperature sterilization method, the liquid milk concentrate is continuously heat sterilized at a temperature of 65°C to 68°C for 30 minutes or more. In addition, in the high-temperature holding sterilization method, the liquid milk concentrate is heat sterilized at a temperature of 75°C or more for 15 minutes or more in a holding manner. In addition, in the high-temperature short-time sterilization method, the liquid milk concentrate is continuously heat sterilized at a temperature of 72°C or more for 15 seconds or more. In addition, in the ultra-high temperature instantaneous sterilization method, the liquid milk concentrate is heat sterilized at a temperature of 120 to 150°C for 2 to 3 seconds. It should be noted that the heat sterilization conditions at this time can be set to the same protein denaturation rate as the above heat sterilization conditions, for example, it can be set to 100°C × 50 seconds.

[0053] (5) pH adjustment step

[0054] In the pH adjustment step, the pH of the sterilized liquid milk concentrate is adjusted to a range exceeding 4.6 and less than 6.5. This is because if the pH of the sterilized liquid milk concentrate is within this range, the liquid milk concentrate is not likely to thicken during cold storage, and the time constraints from manufacturing to transportation are alleviated. And pH 4.6 is the isoelectric point of casein, which is the main protein type of the milk protein concentrate. Therefore, by making the pH of the sterilized liquid milk concentrate exceed 4.6, isoelectric point precipitation can be prevented. It should be noted that the above pH is preferably in the range of 5.0 or more and less than 6.5, more preferably in the range of 5.2 or more and less than 6.5, further preferably in the range of 5.5 or more and less than 6.5, further preferably in the range of 5.8 or more and less than 6.5, and particularly preferably in the range of 6.0 or more and less than 6.5. In addition, the cold storage temperature during cold storage is preferably in the range above the temperature at which the sterilized liquid milk concentrate remains liquid and 15°C or less, more preferably in the range of 1°C or more and 10°C or less, further preferably in the range of 1°C or more and 5°C or less. And in this pH adjustment step, an acid is used as the pH adjuster. As such an acid, for example, acids that are solids or liquids under normal temperature and pressure such as hydrochloric acid, lactic acid, acetic acid, citric acid, etc., and acids that are gases under normal temperature and pressure such as carbon dioxide can be used. It should be noted that as a method of blowing carbon dioxide into the raw milk, for example, methods using ordinary nozzles, in-line nozzles, sintered metal porous filters, etc. can be cited.

[0055] It should be noted that in this pH adjustment step, after adding an acid to the sterilized liquid milk concentrate, it is preferred to let the sterilized liquid milk concentrate stand or stir for a specified time. Here, the specified time is preferably 0.5 hours or more, more preferably 1 hour or more, further preferably 1.5 hours or more, and particularly preferably 2 hours or more. Moreover, there is no particular upper limit for the specified time. The specified time is, for example, preferably 10 hours or less, more preferably 8 hours or less, further preferably 6 hours or less, and particularly preferably 4 hours or less. In addition, in this pH adjustment step, it is preferred to let the sterilized liquid milk concentrate stand or stir at a specified temperature. Here, the specified temperature is preferably in the range above the temperature at which the sterilized liquid milk concentrate remains liquid and 15°C or less, more preferably in the range of 1°C or more and 10°C or less, further preferably in the range of 1°C or more and 5°C or less.

[0056] In addition, in this pH adjustment step, it is preferable to adjust the pH such that the intrinsic viscosity of the sterilized liquid milk concentrate at 5°C falls within the range of 0.01 dL / g or more and 0.8 dL / g or less, and the pH of the sterilized liquid milk concentrate falls within the range of more than 4.6 and less than 6.5. It should be noted that the upper limit value of this intrinsic viscosity is preferably 0.5 dL / g, more preferably 0.35 dL / g, and further preferably 0.33 dL / g. In addition, the lower limit value of this intrinsic viscosity is preferably 0.1 dL / g, more preferably 0.2 dL / g, further preferably 0.25 dL / g, and particularly preferably 0.3 dL / g. Furthermore, the range of this intrinsic viscosity is preferably 0.2 dL / g or more and 0.5 dL / g or less, and more preferably 0.3 dL / g or more and 0.33 dL / g or less. In addition, in the relationship between the intrinsic viscosity and pH at 5°C, it is preferable that the intrinsic viscosity falls within the range of 0.1 dL / g or more and 0.5 dL / g or less, and the pH falls within the range of more than 5.2 and less than 6.5. More preferably, the intrinsic viscosity falls within the range of 0.2 dL / g or more and 0.35 dL / g or less, and the pH falls within the range of more than 5.6 and less than 6.5. Further preferably, the intrinsic viscosity falls within the range of 0.3 dL / g or more and 0.33 dL / g or less, and the pH falls within the range of more than 5.8 and less than 6.5.

[0057] <Neutralization treatment>

[0058] In the neutralization treatment, the pH of the liquid milk concentrate (such as the cooled milk concentrate, the milk concentrate at room temperature) is adjusted to a range of more than 6.5 and 7.0 or less to prepare a neutralized liquid milk concentrate. It should be noted that in the neutralization treatment, the pH of the neutralized liquid milk concentrate is preferably set within the range of more than 6.5 and 6.9 or less, more preferably set within the range of 6.6 or more and 6.9 or less, and further preferably set within the range of 6.7 or more and 6.9 or less. In this neutralization treatment, at least one of the following treatments is carried out: a) an alkali addition treatment of adding an alkali to the liquid milk concentrate and b) a separation treatment of separating carbon dioxide from the liquid milk concentrate. It should be noted that when both the separation treatment and the alkali addition treatment are carried out, it is preferable to carry out the alkali addition treatment after the separation treatment. Hereinafter, the separation treatment and the alkali addition treatment will be described in detail.

[0059] (1) Alkali addition treatment

[0060] In the alkali addition treatment, an alkali that can be added to food, i.e., an alkali harmless to the human body, such as sodium hydroxide, potassium hydroxide, potassium carbonate, etc. is used. At this time, the alkali is preferably used in the form of a diluted aqueous solution. Specifically, it is more preferably used in the form of an aqueous alkali solution of 0.5 to 3N, and further preferably used in the form of an aqueous alkali solution of 2N. In addition, at this time, it is preferable to use a mixed aqueous solution of sodium hydroxide and potassium hydroxide such that the ratio of sodium ions / potassium ions in the liquid milk concentrate becomes the ratio of sodium ions / potassium ions in the raw milk, or a ratio close to this ratio. Specifically, it is more preferable to use a mixed aqueous solution of sodium hydroxide:potassium hydroxide of 2 to 4:8 to 6, and further preferably use a mixed aqueous solution of sodium hydroxide:potassium hydroxide of 3:7.

[0061] It should be noted that in this alkali addition treatment, after adding the above alkali to the liquid milk concentrate, it is preferable to leave it to stand or stir and neutralize the liquid milk concentrate for a specified time. Here, the specified time is preferably 0.1 hour or more, more preferably 0.3 hour or more, further preferably 0.5 hour or more, and particularly preferably 1 hour or more. Moreover, the upper limit of this specified time is not particularly limited. The specified time is, for example, preferably 10 hours or less, more preferably 8 hours or less, further preferably 6 hours or less, and particularly preferably 4 hours or less. In addition, in this neutralization treatment, it is preferable to leave it to stand or stir the neutralized liquid milk concentrate at a specified temperature. Here, the specified temperature is preferably in the range above the temperature at which the neutralized liquid milk concentrate remains liquid and 25°C or lower, more preferably in the range of 1°C or higher and 20°C or lower, further preferably in the range of 2°C or higher and 15°C or lower, and particularly preferably in the range of 3°C or higher and 10°C or lower.

[0062] (2) Separation treatment

[0063] In the separation treatment, at least any one of the following treatments is carried out: i) a blowing treatment of blowing an inert gas into the liquid milk concentrate; ii) a decompression treatment of placing the liquid milk concentrate in a reduced-pressure environment; and iii) a holding treatment of applying heat, physical stimulation, and holding while stirring the milk concentrate in a tank. It should be noted that when both the blowing treatment and the decompression treatment are carried out, it is preferable to carry out these treatments simultaneously. In addition, the blowing treatment and the holding treatment, or the decompression treatment and the holding treatment can also be carried out simultaneously. Examples of the inert gas used in the blowing treatment include nitrogen, helium, argon, etc. In addition, examples of the blowing method include a method using a normal nozzle, an in-line nozzle, etc.

[0064] <Use of milk concentrate>

[0065] The milk concentrate of the embodiments of the present invention, particularly the neutralized milk concentrate, can be used as a component of the raw material for dairy products. That is, the milk concentrate can be used alone as the raw material for dairy products (raw milk), or can be mixed with other raw materials such as water, raw milk, pasteurized milk, skim milk, whole milk powder, skim milk powder, whole milk concentrate, skim milk concentrate, buttermilk, butter, cream, cheese, etc., and used as the raw material for dairy products (such as a part of the raw milk).

[0066] It should be noted that the above-mentioned dairy products include, for example, milk beverages (including processed milk), yogurt, lactic acid bacteria beverages, fermented milk, ice cream, cream, cheese, etc. It should be noted that any components can be added to the dairy products as needed. There is no particular limitation, and such arbitrary components may include: components blended in general dairy products, namely sweeteners, acidulants, vegetables, fruits, fruit, vegetable juices, fruit juices, fruit extracts, vitamins, minerals, peptides, amino acids and other nutritional raw materials, useful microorganisms such as lactic acid bacteria, bifidobacteria, propionic acid bacteria, cultures of useful microorganisms, fermented products of useful microorganisms, existing functional raw materials such as royal jelly, glucosamine, astaxanthin, polyphenols, flavors, pH regulators, excipients, acidulants, colorants, emulsifiers, preservatives, etc. At this time, the sweeteners include, for example: glucose, fructose, maltose, sucrose, oligosaccharides, granulated sugar, honey, maple syrup, agave syrup, coconut sugar, molasses, starch syrup, glucose-fructose liquid sugar, trehalose, maltitol, palatinose, xylitol, sorbitol, licorice extract, stevia-processed sweeteners, momordica grosvenori extract, thaumatin, glycerol, curculin, monellin, miraculin, erythritol, etc. These sweeteners not only provide sweetness to dairy products, but also can inhibit sourness and "astringency", so they are preferably added actively when manufacturing dairy products.

[0067] When the above-mentioned dairy product is fermented milk, the milk concentrate can be used as a component of the raw material mixture for fermented milk. It should be noted that in the preparation of the fermented milk raw material mixture, for example, raw materials such as milk concentrate and other arbitrary components (such as sweeteners, acidulants, minerals, vitamins, flavors, etc.) are added (blended), heated, mixed, and dissolved. Then, in addition to the milk concentrate, water, raw milk, pasteurized milk, whole milk powder, whole milk concentrate, buttermilk, butter, cream, cheese, etc. can also be added, heated, mixed, and dissolved in the raw material mixture. In addition, whey protein concentrate (WPC), whey protein isolate (WPI), α-lactalbumin (α-La), β-lactoglobulin (β-Lg), etc. can be added, heated, mixed, and dissolved in the raw material mixture.

[0068] It should be noted that when the above dairy product is fermented milk, the fermented milk is manufactured through processes such as the preparation process of the raw material mixture, the (heating) sterilization process of the raw material mixture, the cooling process of the raw material mixture, the addition process of the starter, the fermentation process, and the cooling process of the fermented milk, in the same way as the manufacturing method of the existing fermented milk. At this time, in the preparation process of the raw material mixture, as described above, the raw materials are added, heated, mixed, dissolved (prepared), etc. It should be noted that in the above-mentioned respective processes, the treatment conditions in the general manufacture of fermented milk can be appropriately adopted. In addition, it is preferable to sequentially carry out the (heating) sterilization process of the raw material mixture, the cooling process of the raw material mixture, the addition process of the starter, the fermentation process, and the cooling process of the fermented milk.

[0069] <Characteristics of the liquid milk concentrate of the embodiment of the present invention>

[0070] Compared with the conventional liquid milk concentrate, the increase in viscosity of the liquid milk concentrate obtained as described above is suppressed for a longer time.

[0071] Examples

[0072] Hereinafter, examples and comparative examples are shown to explain the present invention in more detail. It should be noted that the present invention is not limited to this example.

[0073] (Example 1)

[0074] Using a microbubble nozzle developed by Sakamoto Kogyo Co., Ltd., carbon dioxide was blown into 985 kg of skim milk (solid component concentration: 9.4% by mass, protein content: 3.4% by mass, calcium concentration: 119 mg%), and the pH of the skim milk was reduced from 6.78 to 6.15 to prepare acidified skim milk. Then, an ultrafiltration membrane manufactured by KOCH Co., Ltd. (cut-off molecular weight: 10,000 Da, membrane area: 6.1 m 2)The acidified skim milk is concentrated. It should be noted that during the concentration process, ion-exchanged water is added to the acidified skim milk for percolation, and then the acidified skim milk is further concentrated. As a result, 135 kg of a liquid milk protein concentrate (MPC) with a total solid content of 20.9% by mass, a protein content of 16.9% by mass, a calcium concentration of 408 mg%, and a pH of 6.53 is obtained. Then, a part of the milk protein concentrate is taken out and divided into two parts. One part is diluted with water. As a result, the total solid content of the milk protein concentrate is 19.9% by mass, the protein content is 16.1% by mass, and the pH is 6.60. In addition, the other part is diluted with different amounts of water. As a result, the total solid content of the milk protein concentrate is 18.2% by mass, the protein content is 14.7% by mass, and the pH is 6.61. Hereinafter, the milk protein concentrate with a total solid content of 20.9% by mass is referred to as the first milk protein concentrate, the milk protein concentrate with a total solid content of 19.9% by mass is referred to as the second milk protein concentrate, and the milk protein concentrate with a total solid content of 18.2% by mass is referred to as the third milk protein concentrate. Then, the heat coagulation times of the first milk protein concentrate, the second milk protein concentrate, and the third milk protein concentrate at 130 °C are confirmed, and the results are all more than 12 minutes, showing sufficient thermal stability.

[0075] Next, the first milk protein concentrate, the second milk protein concentrate, and the third milk protein concentrate are respectively heat-sterilized at 130 °C for 4 seconds to obtain the sterilized first milk protein concentrate, the sterilized second milk protein concentrate, and the sterilized third milk protein concentrate. It should be noted that the total solid content of the sterilized first milk protein concentrate is 20.4% by mass, the protein content is 16.6% by mass, and the pH is 6.68. In addition, the total solid content of the sterilized second milk protein concentrate is 19.4% by mass, the protein content is 15.9% by mass, and the pH is 6.69. In addition, the total solid content of the sterilized third milk protein concentrate is 18.2% by mass, the protein content is 14.9% by mass, and the pH is 6.70.

[0076] Subsequently, the sterilized first milk protein concentrate was divided into two parts. Carbon dioxide was blown into one part until the pH of that part reached 6.37, and the other part was left as it was. Hereinafter, the sterilized first milk protein concentrate of the former is referred to as the 11th milk protein concentrate (pH 6.37), and the sterilized first milk protein concentrate of the latter is referred to as the 12th milk protein concentrate (pH 6.68). It should be noted that here, the 11th milk protein concentrate corresponds to the example, and the 12th milk protein concentrate corresponds to the comparative example. In addition, the sterilized second milk protein concentrate was divided into two parts. Carbon dioxide was blown into one part until the pH of that part reached 6.35, and the other part was left as it was. Hereinafter, the sterilized second milk protein concentrate of the former is referred to as the 21st milk protein concentrate (pH 6.35), and the sterilized second milk protein concentrate of the latter is referred to as the 22nd milk protein concentrate (pH 6.69). It should be noted that here, the 21st milk protein concentrate corresponds to the example, and the 22nd milk protein concentrate corresponds to the comparative example. In addition, the sterilized third milk protein concentrate was divided into three parts. Carbon dioxide was blown into one part until the pH of that part reached 6.16, carbon dioxide was blown into another part until the pH of that part reached 6.49, and the remaining part was left as it was. Hereinafter, the original sterilized third milk protein concentrate is referred to as the 31st milk protein concentrate (pH 6.16), the next sterilized third milk protein concentrate is referred to as the 32nd milk protein concentrate (pH 6.49), and the last sterilized third milk protein concentrate is referred to as the 33rd milk protein concentrate (pH 6.70). It should be noted that here, the 31st milk protein concentrate corresponds to the example, the 32nd milk protein concentrate corresponds to the example, and the 33rd milk protein concentrate corresponds to the comparative example. The physical properties of the above milk protein concentrates are summarized in Table 1 below.

[0077] It should be noted that the quantitative analysis methods of the above various components are as described below.

[0078] · Protein content: Modified Dumas method (combustion method)

[0079] · Calcium concentration: ICP emission spectrometry (high-frequency inductively coupled plasma emission spectrometry)

[0080] [Table 1]

[0081]

[0082] The above 7 kinds of milk protein concentrates (refer to Table 1) were stored at 2 - 4 °C, and the change in viscosity of these milk protein concentrates was measured using a B-type viscometer TVB-10M manufactured by Toki Sangyo Co., Ltd., and the results shown in Tables 2 - 8 were obtained. It should be noted that in order to prevent the milk protein concentrates from spoiling during refrigerated storage, 2-bromo-2-nitropropane-1,3-diol was added to each milk protein concentrate before refrigerated storage so that the final concentration became 0.02% by mass. Here, the results of the 11th milk protein concentrate are shown in Table 2, the results of the 12th milk protein concentrate are shown in Table 3, the results of the 21st milk protein concentrate are shown in Table 4, the results of the 22nd milk protein concentrate are shown in Table 5, the results of the 31st milk protein concentrate are shown in Table 6, the results of the 32nd milk protein concentrate are shown in Table 7, and the results of the 33rd milk protein concentrate are shown in Table 8. The measurement conditions during viscosity measurement are also shown in each table. From these results, it can be seen that when the pH is adjusted to less than 6.5, the viscosity is maintained lower during refrigerated storage compared to the case where it is not adjusted (pH is 6.5 or higher).

[0083] [Table 2]

[0084]

[0085] [Table 3]

[0086]

[0087] [Table 4]

[0088]

[0089] [Table 5]

[0090]

[0091] [Table 6]

[0092]

[0093] [Table 7]

[0094]

[0095] [Table 8]

[0096]

[0097] (Example 2)

[0098] 916 kg of skim milk (solid component concentration: 9.2% by mass, protein content: 3.3% by mass, calcium concentration: 122 mg%, pH 6.82) was not acidified and concentrated using the same ultrafiltration membrane as that shown in Example 1. It should be noted that during the process, ion-exchanged water was added to the concentrated skim milk for diafiltration, and then the skim milk was further concentrated. As a result, 132 kg of a liquid milk protein concentrate (MPC) with a total solid component of 19.7% by mass, a protein content of 15.9% by mass, a calcium concentration of 431 mg%, and a pH of 6.95 was obtained. It should be noted that the heat coagulation time of this milk protein concentrate at 130 °C was 12 minutes, maintaining sufficient thermal stability. Next, the milk protein concentrate was heat-sterilized at 130 °C for 4 seconds to obtain the sterilized fourth milk protein concentrate. The sterilized fourth milk protein concentrate was divided into two parts. Carbon dioxide was blown into one part until the pH of one part reached 6.26 to obtain the sterilized 41st milk protein concentrate. The other part was left as it was to prepare the sterilized 42nd milk protein concentrate (the sterilized 42nd milk protein concentrate was treated as a comparative example).

[0099] Similar to Example 1, the sterilized 41st milk protein concentrate and the sterilized 42nd milk protein concentrate were stored at 2 - 4 °C, and the change in the viscosity of these milk protein concentrates was measured using a B-type viscometer TVB-10M manufactured by Toki Sangyo Co., Ltd. As a result, the results shown in Table 9 and Table 10 were obtained. It should be noted that in order to prevent the milk protein concentrate from spoiling during refrigerated storage, 2-bromo-2-nitropropane-1,3-diol was added to each milk protein concentrate before refrigerated storage so that the final concentration became 0.02% by mass. Here, the results of the 41st milk protein concentrate are shown in Table 9, and the results of the 42nd milk protein concentrate are shown in Table 10. The measurement conditions during viscosity measurement are also shown in each table. From these results, it can be seen that even without acidifying the skim milk, compared with the case where the pH adjustment process is not performed after sterilization, the viscosity is maintained at a lower level during refrigerated storage when the pH adjustment process is performed after sterilization.

[0100] [Table 9]

[0101]

[0102] [Table 10]

[0103]

[0104] (Example 3)

[0105] Using a microbubble nozzle developed by Sakamoto Giken Co., Ltd., carbon dioxide was blown into 840 kg of skim milk (solid component concentration: 9.2% by mass, protein content: 3.5% by mass, calcium concentration: 123 mg%), and the pH of the skim milk was reduced from 6.75 to 6.16 to prepare acidified skim milk. Then, an ultrafiltration membrane manufactured by KOCH Co., Ltd. (cut-off molecular weight: 10,000 Da, membrane area: 6.1 m 2 ) was used to concentrate the acidified skim milk. It should be noted that during the concentration process, ion-exchanged water was added to the acidified skim milk for diafiltration, and then the acidified skim milk was further concentrated. As a result, 116 kg of a liquid milk protein concentrate (MPC) with a total solid component of 21.0% by mass, a protein content of 17.0% by mass, a calcium concentration of 395 mg%, and a pH of 6.49 was obtained. Then, the milk protein concentrate was diluted with water. As a result, the total solid component of the milk protein concentrate was 19.2% by mass, the protein content was 15.5% by mass, and the pH was 6.53. The heat coagulation time of the milk protein concentrate at 130 °C was 12 minutes, maintaining sufficient thermal stability. Then, the milk protein concentrate was heat-sterilized at 130 °C for 4 seconds to obtain the sterilized fifth milk protein concentrate. The sterilized fifth milk protein concentrate was divided into two parts, and 0.5 N hydrochloric acid was added until the pH of one part reached 5.20 to obtain the sterilized 51st milk protein concentrate. The other part was added with water in the same manner as the solid component concentration of the sterilized 51st milk protein to prepare the sterilized 52nd milk protein concentrate (the sterilized 52nd milk protein concentrate was treated as a comparative example).

[0106] In the same manner as in Example 1, the sterilized 51st milk protein concentrate and the sterilized 52nd milk protein concentrate were stored at 2 - 4 °C, and the change in the viscosity of these milk protein concentrates was measured using a B-type viscometer TVB-10M manufactured by Toki Sangyo Co., Ltd. As a result, the results shown in Tables 11 and 12 were obtained. It should be noted that in order to prevent the milk protein concentrate from spoiling during refrigerated storage, 2-bromo-2-nitropropane-1,3-diol was added to each milk protein concentrate before refrigerated storage so that the final concentration became 0.02% by mass. Here, the results of the 51st milk protein concentrate are shown in Table 11, and the results of the 52nd milk protein concentrate are shown in Table 12. The measurement conditions during viscosity measurement are also shown in each table. From these results, it can be seen that regardless of the type of acid, when a pH adjustment step was performed after sterilization compared to when no pH adjustment step was performed after sterilization, the viscosity was maintained lower during refrigerated storage..

[0107] [Table 11]

[0108]

[0109] [Table 12]

[0110]

[0111] (Example 4)

[0112] For 1020 kg of milk protein concentrate obtained by concentrating skim milk using an ultrafiltration membrane manufactured by Koch Corporation (cut-off molecular weight: 10,000 Da, membrane area: 20.0 m 2 ), carbon dioxide was blown in through a sintered metal porous filter to lower the pH of the milk protein concentrate from 6.7 to 6.5, and an acidified milk protein concentrate was prepared. Next, using an ultrafiltration membrane manufactured by Koch Corporation (cut-off molecular weight: 10,000 Da, membrane area: 6.1 m 2 ), ion-exchanged water was added to the acidified milk protein concentrate for diafiltration, and then the acidified milk protein concentrate was further concentrated. As a result, 642 kg of a liquid milk protein concentrate (MPC) with a total solid content of 19.8% by mass, a protein content of 15.7% by mass, a calcium concentration of 456 mg%, and a pH of 6.6 was obtained. Next, the milk protein concentrate was diluted with water. As a result, the total solid content of the milk protein concentrate was 19.5% by mass, the protein content was 15.6% by mass, and the pH was 6.6. The heat coagulation time of the milk protein concentrate at 130 °C was 11 minutes, maintaining sufficient thermal stability. Next, the milk protein concentrate was heat-sterilized at 100 °C for 50 seconds to obtain the sterilized sixth milk protein concentrate. The sterilized sixth milk protein concentrate was divided into five parts, and one part was used as the sterilized sixth 1 milk protein concentrate (the sterilized sixth 1 milk protein concentrate was treated as a comparative example). In addition, hydrochloric acid (HCl) was added to the second part until its pH reached 6.4 to obtain the sterilized sixth 2 milk protein concentrate (the sterilized sixth 2 milk protein concentrate was treated as an example). In addition, hydrochloric acid (HCl) was added to the third part until its pH reached 5.9 to obtain the sterilized sixth 3 milk protein concentrate (the sterilized sixth 3 milk protein concentrate was treated as an example). In addition, hydrochloric acid (HCl) was added to the fourth part until its pH reached 5.6 to obtain the sterilized sixth 4 milk protein concentrate (the sterilized sixth 4 milk protein concentrate was treated as an example). In addition, hydrochloric acid (HCl) was added to the last part until its pH reached 5.2 to obtain the sterilized sixth 5 milk protein concentrate (the sterilized sixth 5 milk protein concentrate was treated as an example).

[0113] Next, the intrinsic viscosities (dL / g) of the above five sterilized milk protein concentrates were determined, and the results are as follows. It should be noted that the intrinsic viscosity is a characteristic value representing the expansion of the molecular chains of macromolecules (proteins in this case) in a solution. Here, the total solid content contained in the protein concentrate was taken as the measurement object, and the measured value corresponding to the overall intrinsic viscosity was used.

[0114] · Sterilized milk protein concentrate No. 61: 0.349 dL / g

[0115] · Sterilized milk protein concentrate No. 62: 0.330 dL / g

[0116] · Sterilized milk protein concentrate No. 63: 0.314 dL / g

[0117] · Sterilized milk protein concentrate No. 64: 0.291 dL / g

[0118] · Sterilized milk protein concentrate No. 65: 0.772 dL / g

[0119] As factors that increase the intrinsic viscosity of milk protein concentrates, for example, heat sterilization treatment and an increase in calcium ions in milk protein concentrates can be cited. During heat sterilization treatment, a part of the denatured whey protein binds to the surface of the micelles, and another part forms a complex with κ-casein. The denatured whey protein binds to the micelles, thereby increasing the micelle size and the intrinsic viscosity.

[0120] On the other hand, as factors that reduce the intrinsic viscosity of milk protein concentrates, for example, sterilization treatments such as pulsed electrolytic sterilization treatment with less denatured whey protein and an increase in sucrose can be cited.

[0121] In the relationship with pH, the intrinsic viscosity of the sterilized milk protein concentrate No. 64 is the minimum value. Therefore, it is considered that the closer the pH of the milk protein concentrate is to 5.6, the more the intrinsic viscosity decreases, and the farther the pH of the milk protein concentrate is from 5.6, the more the intrinsic viscosity increases.

[0122] It should be noted that the intrinsic viscosity of the milk protein concentrate was determined by the method shown below.

[0123] First, each milk protein concentrate was diluted with ion-exchanged water so that the solid component concentration became 0.2, 0.4, 0.6, 0.8, and 1.0 mass%. It should be noted that for the sake of convenience, the milk protein concentrate diluted with ion-exchanged water will be hereinafter referred to as "diluted milk protein concentrate solution".

[0124] Next, a coaxial twin-cylinder system was installed in a modular compact rheometer MCR302 manufactured by Anton Paar GmbH, and the rheometer was subjected to a measurement at a temperature of 5° C. and a shear rate of 2 to 200 s. -1 The viscosity of the milk protein concentrate dilution was measured under the conditions of . It should be noted that the zero shear viscosity of the milk protein concentrate dilution was obtained from the measurement data of the area showing Newtonianity in the measurement range, and was used as the viscosity of the milk protein concentrate dilution of each concentration. In addition, when calculating the zero shear viscosity, the density of the milk protein concentrate dilution was set to 1 for calculation. Similarly, the zero shear viscosity of ion exchange water was obtained as the viscosity of the solvent.

[0125] Next, the viscosities of the milk protein concentrate dilution and ion-exchanged water obtained as described above were substituted into the following formula (1) to obtain the specific viscosity of each milk protein concentrate dilution.

[0126] η sp =(η-η s ) / η s (1)

[0127] It should be noted that, in the above formula (1), sp is the specific viscosity of the diluent of the milk protein concentrate, η is the viscosity of the diluent of the milk protein concentrate, η s is the viscosity of ion exchange water.

[0128] Next, the specific viscosity and protein concentration of the milk protein concentrate dilution were substituted into the formula (2) below to determine the reduced viscosity of each milk protein concentrate dilution.

[0129] η red =η sp / c (2)

[0130] It should be noted that in the above formula (2), η red is the concentrated viscosity of the milk protein concentrate diluent, η sp is the specific viscosity of the diluent of the milk protein concentrate, and c is the solid content concentration of the diluent of the milk protein concentrate.

[0131] Finally, for each milk protein concentrate, a linear function ((reduced viscosity) = a × (solid content concentration) + b) was derived from the data pair of the solid content concentration in the milk protein concentrate dilution and the reduced viscosity of the milk protein concentrate dilution by the least square method, and the reduced viscosity b at a solid content concentration of 0 (g / dL) was obtained from the linear function, and this b was taken as the intrinsic viscosity. That is, the intrinsic viscosity was expressed by the following formula (3).

[0132]

[0133] The intrinsic viscosity obtained from the relative viscosity is consistent with the intrinsic viscosity obtained from the logarithmic viscosity. In this example, this was verified, and it was confirmed that the above-mentioned intrinsic viscosity obtained from the relative viscosity is accurate.

[0134] In addition, in the same manner as in Example 1, the sterilized 61st milk protein concentrate, the sterilized 62nd milk protein concentrate, the sterilized 63rd milk protein concentrate, the sterilized 64th milk protein concentrate, and the sterilized 65th milk protein concentrate were stored at 2 to 4°C, and the change in the viscosity of these milk protein concentrates was measured using a B-type viscometer TVB-10M manufactured by Toki Sangyo Co., Ltd. As a result, the results shown in Tables 13 to 17 were obtained. It should be noted that in order to prevent the milk protein concentrate from spoiling during refrigerated storage, 2-bromo-2-nitropropane-1,3-diol was added to each milk protein concentrate before refrigerated storage so that the final concentration became 0.02% by mass. Here, the results of the 61st milk protein concentrate are shown in Table 13, the results of the 62nd milk protein concentrate are shown in Table 14, the results of the 63rd milk protein concentrate are shown in Table 15, the results of the 64th milk protein concentrate are shown in Table 16, and the results of the 65th milk protein concentrate are shown in Table 17. The measurement conditions at the time of viscosity measurement are also shown in each table. From this result, it can be seen that regardless of the type of acid, the viscosity is maintained lower during refrigerated storage when the pH is adjusted to less than 6.5 after sterilization compared to when the pH is not adjusted to less than 6.5 after sterilization.

[0135] [Table 13]

[0136]

[0137] [Table 14]

[0138]

[0139] [Table 15]

[0140]

[0141] [Table 16]

[0142]

[0143] [Table 17]

[0144]

[0145] The intrinsic viscosity (dL / g) of the 61st to 65th milk protein concentrates after refrigerated storage was determined, and the following results were obtained.

[0146] · Sterilized 61st milk protein concentrate: 0.396 dL / g

[0147] · Sterilized 62nd milk protein concentrate: 0.324 dL / g

[0148] · Sterilized 63rd milk protein concentrate: 0.313 dL / g

[0149] · Sterilized 64th milk protein concentrate: 1.425 dL / g

[0150] · Sterilized 65th milk protein concentrate: 2.491 dL / g

[0151] Furthermore, the results of measuring the thermal coagulation time at 130 °C of the 61st to 65th milk protein concentrates after cold storage, and the thermal coagulation time at 130 °C of the substances obtained by adjusting the 62nd to 65th milk protein concentrates to pH 6.5 with 1N aqueous sodium hydroxide solution are shown in Table 18.

[0152] [Table 18]

[0153]

[0154] It can be confirmed from Table 18 that the 62nd milk protein concentrate and the 63rd milk protein concentrate adjusted to pH 6.5 have a thermal stability of more than 0.5 minutes, and thus can be used as a component of the raw material for dairy products that require heat sterilization.

[0155] From the above results, it is considered that in order to maintain a low viscosity, it is sufficient to store in the range where the pH exceeds 4.6 and is less than 6.5. However, in order to maintain a low viscosity and further ensure thermal stability after storage, it is necessary to adjust the intrinsic viscosity to the range of 0.30 dL / g or more and less than 0.35 dL / g.

[0156] (Comparative Example 1)

[0157] Using a microbubble nozzle developed by Sakamoto Technology, carbon dioxide was blown into 664 kg of skim milk (solid component concentration 9.3 mass%, protein content 3.3 mass%, calcium concentration 124 mg%) to lower the pH of the skim milk from 6.70 to 5.79, and acidified skim milk was prepared. Then, the acidified skim milk was concentrated using an ultrafiltration membrane (cut-off molecular weight: 10,000 Da, membrane area: 6.1 m 2 ) manufactured by KOCH Co., Ltd. It should be noted that during the process, ion-exchanged water was added to the acidified skim milk during concentration for diafiltration, and then the acidified skim milk was further concentrated. As a result, 87 kg of a liquid milk protein concentrate (MPC) with a total solid component of 21.1 mass%, a protein content of 16.7 mass%, a calcium concentration of 358 mg%, and a pH of 6.29 was obtained. It should be noted that hereinafter, this milk protein concentrate will be referred to as the primary milk protein concentrate. The thermal coagulation time of this primary milk protein concentrate at 130 °C was 0.5 minutes, and the thermal stability was insufficient.

[0158] Next, an aqueous potassium hydroxide solution was added to the above-mentioned primary milk protein concentrate to obtain a liquid milk protein concentrate (MPC) with a total solid content of 20.6% by mass, a protein content of 16.4% by mass, and a pH of 6.53. It should be noted that hereinafter, this milk protein concentrate will be referred to as the secondary milk protein concentrate. The heat coagulation time of this secondary milk protein concentrate at 130 °C was 12 minutes or more, and its thermal stability was sufficient.

[0159] Next, the above-mentioned secondary milk protein concentrate was heat-sterilized at 130 °C for 4 seconds to obtain a sterilized milk protein concentrate with a total solid content of 20.5% by mass, a protein content of 16.5% by mass, a calcium concentration of 351 mg%, and a pH of 6.53. Then, this sterilized milk protein concentrate was stored at 2 to 4 °C, and the change in the viscosity of these milk protein concentrates was measured using a B-type viscometer TVB-10M manufactured by Toki Sangyo Co., Ltd. As a result, the results shown in Table 19 were obtained. From Table 19, it can be seen that the viscosity of this milk protein concentrate exceeded 30,000 mPa·s at the time 4 days after the start of cold storage at 2 to 4 °C, and it was unable to maintain a low viscosity.

[0160] [Table 19]

[0161]

Claims

1. A method for adjusting the pH of a heat - sterilized liquid milk concentrate to fall within a range exceeding 4.6 and less than 6.5 and refrigerating the liquid milk concentrate.

2. The method according to claim 1, wherein, the pH is adjusted in such a manner that the intrinsic viscosity of the heat - sterilized liquid milk concentrate at 5°C falls within a range of 0.01 dL / g or more and 0.8 dL / g or less, and the pH of the heat - sterilized liquid milk concentrate falls within a range exceeding 4.6 and less than 6.

5.

3. A method for manufacturing a liquid milk concentrate, comprising: an acidification step of acidifying a liquid raw milk to prepare a liquid acidified raw milk; a concentration step of subjecting the acidified raw milk to ultrafiltration to prepare a liquid milk concentrate; a heat - sterilization step of heat - sterilizing the liquid milk concentrate to prepare a sterilized liquid milk concentrate; and a pH - adjustment step of adjusting the pH of the sterilized liquid milk concentrate to fall within a range exceeding 4.6 and less than 6.

5.

4. The method for manufacturing a liquid milk concentrate according to claim 3, wherein, in the acidification step, the liquid raw milk is acidified in such a manner that the pH of the liquid milk concentrate obtained in the concentration step falls within a range of 6.4 or more and 7.0 or less.

5. The method for manufacturing a liquid milk concentrate according to claim 3, wherein, the raw milk is skim milk, and the milk concentrate is a milk protein concentrate.

6. The method for manufacturing a liquid milk concentrate according to claim 3, wherein, in the pH - adjustment step, the pH is adjusted in such a manner that the intrinsic viscosity of the sterilized liquid milk concentrate at 5°C falls within a range of 0.01 dL / g or more and 0.8 dL / g or less, and the pH of the sterilized liquid milk concentrate falls within a range exceeding 4.6 and less than 6.

5.

7. A liquid milk concentrate produced by the method for manufacturing a liquid milk concentrate according to any one of claims 3 to 6.

8. A heat - sterilized milk concentrate having an intrinsic viscosity at 5°C falling within a range of 0.01 dL / g or more and 0.8 dL / g or less, and a pH falling within a range exceeding 4.6 and less than 6.5.

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