Milk Protein Concentrates and Dairy Products

Abstract

An object of the present invention is to provide a milk protein concentrate that ensures heat stability while not impairing the milk flavor. The milk protein concentrate of the present invention contains, per 20% by mass of total solids, 9.0 to 15.5% by mass of protein, 0.20 to 1.30% by mass of ash, 0.01 to 0.08% by mass of Na, 0.03 to 0.36% by mass of K, 0.08 to 0.34% by mass of Ca, more than 0.00 to 0.02% by mass of Mg, 0.08 to 0.20% by mass of P, and more than 0.00 to 0.25% by mass of Cl, and has a thermal coagulation time of 8 minutes or longer at 130°C and a pH of 6.4 to 6.7. A variety of dairy products rich in milk flavor can be produced using this milk protein concentrate as a raw material.

Description

[Technical field]

[0001] The present invention relates to a milk protein concentrate and also to a dairy product produced using the milk protein concentrate as a raw material. [Background technology]

[0002] In the past, it has been proposed to "decalcify skim milk using a cation exchange resin to produce a milk protein concentrate" (see, for example, JP2010-502182A and JP2011-024589A). Such milk protein concentrates (milk concentrates) have high thermal stability and are used as useful raw materials for various dairy products such as infant formula, beverages, fermented milk, and ice cream. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2010-502182 [Patent Document 2] JP 2011-024589 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when a dairy product is prepared using the milk concentrate obtained as described above, although the saltiness and bitterness of the dairy product are reduced, the dairy flavor tends to be insufficient.

[0005] An object of the present invention is to provide a milk concentrate that ensures heat stability while not impairing the milk flavor, and a method for producing the same. [Means for solving the problem]

[0006] The method for producing a milk concentrate according to the first aspect of the present invention is a method for producing a thermally stable (excellent thermal stability) milk concentrate, and includes a pH adjustment step, a first milk concentrate preparation step, a first water addition step, a second milk concentrate preparation step, a second water addition step, and a third milk concentrate preparation step. In the pH adjustment step, the pH of the raw milk is adjusted to a range of 5.5 or more and less than 6.5 to prepare a pH-adjusted raw milk. In the first milk concentrate preparation step, the pH-adjusted raw milk is ultrafiltered to prepare a first milk concentrate. It is preferable to leave the pH-adjusted raw milk at rest or stir it for a predetermined time before proceeding from the pH adjustment step to the first milk concentrate preparation step. This is to allow ions such as calcium to be sufficiently dissociated (liberated) from proteins (i.e., casein, etc.). In the first water addition step, water of a mass of 0.6 times or more the mass of the first milk concentrate is added to the first milk concentrate to prepare a diluted first milk concentrate. The water is preferably adjusted to a temperature in the range of more than 0°C and not more than 10°C. In the second milk concentrate preparation step, the diluted first milk concentrate is ultrafiltered to prepare a second milk concentrate. In the second water addition step, water is added to the second milk concentrate in an amount of at least 0.6 times the mass of the second milk concentrate to prepare a diluted second milk concentrate. In this case, similarly to the first water addition step, the water is preferably adjusted to a temperature in the range of more than 0°C and not more than 10°C. In the third milk concentrate preparation step, the diluted second milk concentrate is ultrafiltered to prepare a third milk concentrate.

[0007] In this method for producing a milk concentrate, the pH of the raw milk is adjusted to a range of 5.5 or more and less than 6.5, and then the raw material (i.e., pH-adjusted raw milk) is subjected to ultrafiltration. Here, in the pH-adjusted raw milk, calcium ions, magnesium ions, etc. that are electrostatically bound to proteins are in a partially dissociated state (normally, when the pH of the pH-adjusted raw milk is 5.2 or less, all calcium ions, magnesium ions, etc. are dissociated). When the pH-adjusted raw milk is ultrafiltered three times, the partially dissociated calcium ions, magnesium ions, etc. are discharged together with the water content of the permeate. As a result, a milk concentrate is prepared in which calcium ions, magnesium ions, etc. remain in a moderate amount. Therefore, the heat stability of this milk concentrate is improved, and the milk flavor of the dairy products produced using it is not impaired. Furthermore, in this method for producing a milk concentrate, no ion exchange treatment is performed. Therefore, the number of work steps is reduced in the overall flow of the method for producing a milk concentrate, and the production cost can be kept low. In addition, since the milk concentrate produced by this method has excellent heat stability as described above, when dairy products, etc. are produced using this milk concentrate as a raw material, there is no need to complicate the operation in the heat sterilization process. Therefore, the milk concentrate produced by this method can, in some cases, keep the production cost of dairy products, etc. low.

[0008] In addition, it has been revealed that the milk concentrate produced by this production method has a longer heat coagulation time in the pH range of about 6.4 to about 6.7 compared to conventional milk concentrates, and has the same heat coagulation time in the pH range of about 6.7 to about 7.0. In other words, this milk concentrate exhibits excellent heat stability over a wide pH range.

[0009] The above-mentioned method for producing a milk concentrate preferably further comprises a pH readjustment step. In the pH readjustment step, the pH of the third milk concentrate is adjusted to a range of 6.5 to 7.0. This makes it possible to suppress the sourness of the third milk concentrate. In addition, in the pH readjustment step, the quantitative balance of sodium ions and potassium ions in the third milk concentrate can be adjusted by using sodium hydroxide and potassium hydroxide.

[0010] In the above-mentioned method for producing a milk concentrate, it is preferable that the raw milk is skim milk and the milk concentrate is a milk protein concentrate (hereinafter, also referred to as "Milk Protein Concentrate" (MPC)). This ensures thermal stability and, when used as a raw material for dairy products, etc., a milk protein concentrate that does not lose its milk flavor can be obtained.

[0011] The milk concentrate according to the second aspect of the present invention is a milk concentrate produced by the above-mentioned method for producing a milk concentrate. The composition of this milk concentrate is such that, per 20% by mass of the total solid content, the protein content is in the range of 9.0% by mass to 15.5% by mass, the ash content is in the range of 0.20% by mass to 1.30% by mass, the sodium content is in the range of 0.01% by mass to 0.08% by mass, the potassium content is in the range of 0.03% by mass to 0.36% by mass, the calcium content is in the range of 0.08% by mass to 0.34% by mass, the magnesium content is in the range of more than 0.00% by mass to 0.02% by mass, the phosphorus content is in the range of 0.08% by mass to 0.20% by mass, and the chlorine content is in the range of more than 0.00% by mass to 0.25% by mass. This milk concentrate can be used as a raw material to produce various dairy products rich in milk flavor. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a plot diagram showing the effect of pH on the thermal coagulation time of the milk concentrate of Example 1, together with a plot diagram showing the effect of pH on the thermal coagulation time of the milk concentrate of Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The milk concentrate according to the embodiment of the present invention is produced through a pH adjustment step, a first milk concentrate preparation step, a first water addition step, a second milk concentrate preparation step, a second water addition step and a third milk concentrate preparation step. The milk concentrate will be described in detail below, followed by a detailed description of its production method and its uses.

[0014] <Milk concentrate> The milk concentrate according to the embodiment of the present invention is a concentrate of raw milk, cow's milk, special cow's milk, skim milk (raw milk, cow's milk, or special cow's milk from which milk fat has been removed) or partially skim milk (raw milk, cow's milk, or special cow's milk from which milk fat has been partially removed), and is, for example, concentrated milk (raw milk, cow's milk, or special cow's milk from which milk solids have been concentrated and milk fat has been removed from 25.5% or more and 7.0% or more) as specified in the "Ministry of Health, Labour and Welfare Ordinance on the Compositional Standards of Milk and Dairy Products" and skim milk (raw milk, cow's milk, or special cow's milk from which milk fat has been removed) or skim milk (raw milk, cow's milk, or special cow's milk from which milk fat has been removed). It may be "concentrated raw milk, cow's milk or special cow's milk with less than 25.5% milk solids (hereinafter referred to as "concentrated milk outside the Ministerial Ordinance")," "concentrated raw milk, cow's milk or special cow's milk with less than 18.5% non-fat milk solids after removing milk fat (hereinafter referred to as "skimmed concentrated milk outside the Ministerial Ordinance")," etc., but is preferably a milk protein concentrate (also referred to as Milk Protein Concentrate (hereinafter abbreviated as MPC)). For the sake of convenience, raw milk, cow's milk, special cow's milk, skimmed milk and partially skimmed milk may be collectively referred to as "raw milk".

[0015] In addition, the milk concentrate according to the embodiment of the present invention contains, per 20% by mass of the total solid content, protein in the range of 9.0% by mass to 15.5% by mass, ash in the range of 0.20% by mass to 1.30% by mass, sodium (Na) in the range of 0.01% by mass to 0.08% by mass, potassium (K) in the range of 0.03% by mass to 0.36% by mass, calcium (Ca) in the range of 0.08% by mass to 0.34% by mass, magnesium (Mg) in the range of more than 0.00% by mass to 0.02% by mass, phosphorus (P) in the range of 0.08% by mass to 0.20% by mass, and chlorine (Cl) in the range of more than 0.00% by mass to 0.25% by mass.

[0016] The protein content of the milk concentrate according to an embodiment of the present invention is preferably in the range of 10.0% by mass or more and 15.5% by mass or less, more preferably in the range of 10.5% by mass or more and 15.0% by mass or less, even more preferably in the range of 11.0% by mass or more and 15.0% by mass or less, even more preferably in the range of 11.5% by mass or more and 14.5% by mass or less, even more preferably in the range of 12.0% by mass or more and 14.0% by mass or less, and particularly preferably in the range of 12.5% ​​by mass or more and 13.5% by mass or less, per 20% by mass of the total solids.

[0017] Furthermore, the ash content of the milk concentrate according to an embodiment of the present invention is preferably in the range of 0.30% by mass or more and 1.30% by mass or less, more preferably in the range of 0.35% by mass or more and 1.25% by mass or less, even more preferably in the range of 0.40% by mass or more and 1.20% by mass or less, even more preferably in the range of 0.45% by mass or more and 1.20% by mass or less, and particularly preferably in the range of 0.50% by mass or more and 1.15% by mass or less, per 20% by mass of the total solids content.

[0018] Furthermore, the sodium (Na) content of the milk concentrate according to the embodiment of the present invention is preferably in the range of 0.01% by mass or more and 0.07% by mass or less, more preferably in the range of 0.01% by mass or more and 0.06% by mass or less, even more preferably in the range of 0.02% by mass or more and 0.06% by mass or less, and particularly preferably in the range of 0.02% by mass or more and 0.05% by mass or less, per 20% by mass of the total solids content.

[0019] The content of potassium (K) in the milk concentrate according to the embodiment of the present invention depends on the content of sodium (Na), but is preferably in the range of 0.03% by mass to 0.34% by mass, more preferably in the range of 0.03% by mass to 0.32% by mass, even more preferably in the range of 0.04% by mass to 0.30% by mass, and particularly preferably in the range of 0.04% by mass to 0.28% by mass. The content of potassium (K) is preferably 3 times to 4 times the content of sodium (Na), more preferably 3.2 times to 3.9 times the content of sodium (Na), even more preferably 3.4 times to 3.8 times the content of sodium (Na), and particularly preferably 3.6 times to 3.7 times the content of sodium (Na).

[0020] Furthermore, the calcium (Ca) content of the milk concentrate according to the embodiment of the present invention is preferably in the range of 0.08% by mass or more and 0.32% by mass or less, more preferably in the range of 0.09% by mass or more and 0.30% by mass or less, even more preferably in the range of 0.10% by mass or more and 0.28% by mass or less, and particularly preferably in the range of 0.12% by mass or more and 0.26% by mass or less, per 20% by mass of the total solids content.

[0021] Furthermore, the magnesium (Mg) content of the milk concentrate according to the embodiment of the present invention is preferably in the range of more than 0.00% by mass to not more than 0.02% by mass, and more preferably in the range of more than 0.00% by mass to not more than 0.01% by mass, per 20% by mass of the total solids.

[0022] Furthermore, the phosphorus (P) content of the milk concentrate according to an embodiment of the present invention is preferably in the range of 0.08% by mass or more and 0.19% by mass or less, more preferably in the range of 0.09% by mass or more and 0.19% by mass or less, even more preferably in the range of 0.10% by mass or more and 0.18% by mass or less, and particularly preferably in the range of 0.11% by mass or more and 0.18% by mass or less, per 20% by mass of the total solids content.

[0023] Furthermore, the chlorine (Cl) content of the milk concentrate according to the embodiment of the present invention is preferably in the range of 0.01% by mass to 0.20% by mass, more preferably in the range of 0.02% by mass to 0.20% by mass, even more preferably in the range of 0.03% by mass to 0.18% by mass, and particularly preferably in the range of 0.05% by mass to 0.18% by mass, per 20% by mass of the total solids.

[0024] Furthermore, the total solids content of the milk concentrate according to the embodiment of the present invention is typically in the range of 14% by weight to 22% by weight, preferably in the range of 16% by weight to 22% by weight, more preferably in the range of 18% by weight to 22% by weight, and even more preferably in the range of 20% by weight to 22% by weight.

[0025] Furthermore, the thermal coagulation time at 130°C of the milk concentrate according to the embodiment of the present invention (the time until a coagulation occurs in the milk concentrate or the time until the viscosity of the milk concentrate increases) is preferably 2 minutes or more, more preferably 4 minutes or more, even more preferably 6 minutes or more, and particularly preferably 8 minutes or more.

[0026] <Method of manufacturing milk concentrate> As described above, the milk concentrate according to the embodiment of the present invention is produced through a pH adjustment step, a first milk concentrate preparation step, a first water addition step, a second milk concentrate preparation step, a second water addition step, and a third milk concentrate preparation step. In addition, when the milk concentrate according to the embodiment of the present invention is skim milk concentrate, non-Ministry Ordinance skim milk concentrate, or milk protein concentrate, it is preferable to provide a skim milk preparation step before the pH adjustment step. In addition, it is preferable to provide a pH readjustment step after the third milk concentrate preparation step. These steps are described in detail below.

[0027] (1) Skim milk preparation process In the skim milk preparation process, skim milk or partially skim milk is prepared from raw milk, cow's milk, or special milk. The term "skim milk" as used herein means raw milk, cow's milk, or special milk from which milk fat has been removed, for example, "raw milk, cow's milk, or special milk with milk fat content of less than 0.5%". The term "partially skim milk" as used herein means raw milk, cow's milk, or special milk from which milk fat has been partially removed, for example, "raw milk, cow's milk, or special milk with milk fat content of 0.5% or more and less than 3.0%". As described above, the skim milk preparation process does not necessarily have to be carried out. Commercially available skim concentrated milk or non-Ministry Ordinance skim concentrated milk may be purchased and used as raw milk (starting material) in the pH adjustment process.

[0028] Methods for preparing skim milk or partially skim milk from raw milk, cow's milk, or special milk include, for example, a method of subjecting milk fat from raw milk, cow's milk, or special milk to centrifugation (hereinafter also referred to as "centrifugation method"), and a method of subjecting milk fat from raw milk, cow's milk, or special milk to membrane separation (hereinafter also referred to as "membrane separation method", for example, microfiltration). When using the centrifugation method, it is preferable to centrifuge the milk fat while keeping the temperature of the raw milk, cow's milk, or special milk within a range of 45°C to 55°C. In such a case, it is preferable to cool the obtained skim milk or partially skim milk before the pH adjustment step. In such a case, the cooling temperature is preferably within a range of from a temperature at which the skim milk or partial skim milk remains liquid to 10°C, and more preferably within a range of from 1°C to 5°C.

[0029] (2) pH adjustment process In the pH adjustment step, the pH of raw milk (e.g., cooled raw milk) is adjusted to a range of 5.5 or more and less than 6.5 to prepare pH-adjusted raw milk. In addition, from the viewpoint of ease of adjusting the amount of alkali added and ease of maintaining low viscosity, it is preferable that the pH is a predetermined value. That is, in such a case, in the pH adjustment step, the pH of the pH-adjusted raw milk is preferably in the range of 5.5 or more and 6.2 or less, more preferably in the range of 5.5 or more and 6.0 or less, and even more preferably in the range of 5.5 or more and 5.8 or less. In addition, since the pH of raw milk is usually in the range of 6.4 or more and 7.2 or less, an acid is used in this pH adjustment step. And, as this acid, an acid that can be added to food, that is, an acid that is harmless to the human body, such as hydrochloric acid, lactic acid, acetic acid, etc., is used. In this way, when the pH of the raw milk is adjusted to the acidic side, calcium ions, magnesium ions, etc. electrostatically attached to proteins in the pH-adjusted raw milk are dissociated from the proteins. By appropriately adjusting the pH of the raw material milk within the above range, the content (number) of calcium ions, magnesium ions, etc. that dissociate in the raw material milk can be adjusted.

[0030] In this pH adjustment step, it is preferable to leave the pH-adjusted raw milk to stand or stir for a predetermined time after adding the above-mentioned acid to the raw milk. Here, the predetermined time is preferably 0.5 hours or more, more preferably 1 hour or more, even more preferably 1.5 hours or more, and particularly preferably 2 hours or more. There is no particular upper limit to this predetermined time, but the predetermined time is, for example, preferably 10 hours or less, more preferably 8 hours or less, even more preferably 6 hours or less, and particularly preferably 4 hours or less. In addition, in this pH adjustment step, it is preferable to leave the pH-adjusted raw milk to stand or stir at a predetermined temperature. Here, the predetermined temperature is preferably within a range of from a temperature at which the pH-adjusted raw milk remains liquid to 25°C or less, more preferably within a range of from 1°C to 20°C, even more preferably within a range of from 2°C to 15°C, and particularly preferably within a range of from 3°C to 10°C.

[0031] (3) First milk concentrate preparation process In the first milk concentrate preparation step, after the pH adjustment step, the pH-adjusted raw milk is ultrafiltered to prepare a first milk concentrate (first milk protein concentrate). At this time, calcium ions, magnesium ions, etc. dissociated in the pH adjustment step are separated as permeate from the pH-adjusted raw milk (or the first milk concentrate). In addition, flat membranes, hollow fiber membranes, spiral membranes, ceramic membranes, rotating membranes, vibrating membranes, etc. are used as ultrafiltration membranes used in ultrafiltration treatment, and the molecular weight cutoff of the ultrafiltration membrane is preferably in the range of 8000 Da to 12000 Da, more preferably in the range of 9000 Da to 11000 Da, and even more preferably in the range of 9500 Da to 10500 Da. Incidentally, the lower limit of this concentration ratio may vary depending on the type of raw milk, etc., but 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, and when the raw milk is raw milk, the concentration ratio is preferably 1.5 times or more, more preferably 2 times or more. The upper limit of this concentration ratio can be determined by the degree of pressure resistance of the ultrafiltration membrane and the ultrafiltration device, but for example, when the raw milk is skim milk, the concentration ratio is preferably 4 times or less, more preferably 3.5 times or less, and when the raw milk is raw milk, the concentration ratio is preferably 3 times or less, more preferably 2.5 times or less. In addition, the inventor's intensive research has revealed that the higher the concentration ratio, the higher the thermal stability of the third milk concentrate (described below), the smaller the amount of alkali required to be added in the pH readjustment (neutralization) step, and the lower the viscosity of the third milk concentrate after the pH readjustment step.

[0032] (4) First water addition step In the first water addition step, water having a mass of 0.6 times or more of the mass of the first milk concentrate is added to the first milk concentrate to prepare a first milk concentrate dilution. This water may be a buffer solution or the like. The amount of water added can be determined by the capacity of the ultrafiltration membrane device and the tank, and is preferably in the range of 0.6 times or more and 2 times or less, more preferably in the range of 0.7 times or more and 1.5 times or less, and even more preferably in the range of 0.8 times or more and 1 times or less. In addition, from the viewpoint of suppressing the growth of general bacteria, the temperature of this water is preferably in the range of more than 0 ° C. and 20 ° C. or less, more preferably in the range of 1 ° C. or more and 20 ° C. or less, more preferably in the range of 2 ° C. or more and 15 ° C. or less, and particularly preferably in the range of 3 ° C. or more and 10 ° C. or less.

[0033] In addition, in this first water addition step, after adding the above-mentioned water to the first milk concentrate, it is preferable to leave the first milk concentrate diluted product still or stir it for a predetermined time. Here, this predetermined time is preferably 0.1 hours or more, more preferably 0.3 hours or more, even more preferably 0.5 hours or more, and particularly preferably 1 hour or more. And, there is no particular upper limit to this predetermined time, but, for example, the predetermined time is preferably 10 hours or less, more preferably 8 hours or less, even more preferably 6 hours or less, and particularly preferably 4 hours or less. Also, in this first water addition step, it is preferable to leave the first milk concentrate diluted product still or stir it at a predetermined temperature. Here, this predetermined temperature is preferably in the range of from the temperature at which the first milk concentrate diluted product remains liquid to 25°C or less, more preferably in the range of from 1°C to 20°C, even more preferably in the range of from 2°C to 15°C, and particularly preferably in the range of from 3°C to 10°C.

[0034] (5) Second milk concentrate preparation process In the second milk concentrate preparation step, the first milk concentrate diluted with water in the first water addition step, i.e., the diluted first milk concentrate, is subjected to ultrafiltration to prepare a second milk concentrate (second milk protein concentrate). At this time, calcium ions, magnesium ions, etc. dissociated in the pH adjustment step are separated as permeate from the diluted first milk concentrate (or the second milk concentrate). In addition, flat membranes, hollow fiber membranes, spiral membranes, ceramic membranes, rotating membranes, vibrating membranes, etc. are used as ultrafiltration membranes used in ultrafiltration treatment, and the molecular weight cutoff of the ultrafiltration membrane is preferably in the range of 8000 Da to 12000 Da, more preferably in the range of 9000 Da to 11000 Da, and even more preferably in the range of 9500 Da to 10500 Da. In addition, the ultrafiltration membrane used in the first milk concentrate preparation process may be used as it is, or a new ultrafiltration membrane may be used as the ultrafiltration membrane. In the latter case, the same type of ultrafiltration membrane as that used in the first milk concentrate preparation process may be used, or a different type of ultrafiltration membrane from that used in the first milk concentrate preparation process may be used. The lower limit of this concentration ratio may vary depending on the type of raw milk, etc., but for example, when the raw milk is skim milk, this concentration ratio is preferably 1.5 times or more, more preferably 1.8 times or more, and when the raw milk is raw milk, this concentration ratio is preferably 1.3 times or more, more preferably 1.6 times or more. The upper limit of the concentration ratio can be determined by the pressure resistance of the ultrafiltration membrane and the ultrafiltration device, but for example, when the raw milk is skim milk, the concentration ratio is preferably 3.5 times or less, more preferably 3 times or less, and when the raw milk is raw milk, the concentration ratio is preferably 2.8 times or less, more preferably 2.3 times or less. This concentration ratio is set to be lower than the concentration ratio in the first milk concentrate preparation step.

[0035] (6)Second water addition step In the second water addition step, water of a mass of 0.6 times or more of the mass of the second milk concentrate is added to the second milk concentrate to prepare a diluted second milk concentrate. This water may be a buffer solution or the like. The amount of water added can be determined by the capacity of the ultrafiltration membrane device and the tank, and is preferably in the range of 0.6 times or more and 2 times or less, more preferably in the range of 0.7 times or more and 1.5 times or less, and even more preferably in the range of 0.8 times or more and 1 times or less. In addition, from the viewpoint of suppressing the growth of general bacteria, the temperature of this water is preferably in the range of more than 0 ° C. and 20 ° C. or less, more preferably in the range of 1 ° C. or more and 20 ° C. or less, more preferably in the range of 2 ° C. or more and 15 ° C. or less, and particularly preferably in the range of 3 ° C. or more and 10 ° C. or less.

[0036] In addition, in the second water addition step, after adding the above-mentioned water to the second milk concentrate, it is preferable to leave the second milk concentrate diluted product still or stir it for a predetermined time. Here, the predetermined time is preferably 0.1 hours or more, more preferably 0.3 hours or more, even more preferably 0.5 hours or more, and particularly preferably 1 hour or more. And, there is no particular upper limit to this predetermined time, but the predetermined time is, for example, preferably 10 hours or less, more preferably 8 hours or less, even more preferably 6 hours or less, and particularly preferably 4 hours or less. Also, in the second water addition step, it is preferable to leave the second milk concentrate diluted product still or stir it at a predetermined temperature. Here, this predetermined temperature is preferably in the range of the temperature at which the second milk concentrate diluted product remains liquid to 25°C or less, more preferably in the range of 1°C to 20°C or less, even more preferably in the range of 2°C to 15°C or less, and particularly preferably in the range of 3°C to 10°C or less.

[0037] (7) Third milk concentrate preparation process In the third milk concentrate preparation step, the second milk concentrate diluted with water in the second water addition step, i.e., the diluted second milk concentrate, is subjected to ultrafiltration to prepare a third milk concentrate (third milk protein concentrate). At this time, calcium ions, magnesium ions, etc. dissociated in the pH adjustment step are separated as permeate from the diluted second milk concentrate (or the third milk concentrate). As a result, the desired "milk concentrate with reduced calcium and magnesium content (concentration)" is obtained. In addition, flat membranes, hollow fiber membranes, spiral membranes, ceramic membranes, rotating membranes, vibrating membranes, etc. are used as ultrafiltration membranes used in the ultrafiltration process, and the molecular weight cutoff of the ultrafiltration membrane is preferably in the range of 8000 Da to 12000 Da, more preferably in the range of 9000 Da to 11000 Da, and even more preferably in the range of 9500 Da to 10500 Da. In addition, as the ultrafiltration membrane, the ultrafiltration membrane used in the second milk concentrate preparation process may be used as it is, or a new ultrafiltration membrane may be used. In the latter case, the same type of ultrafiltration membrane as that used in the second milk concentrate preparation process may be used, or a different type of ultrafiltration membrane from that used in the second milk concentrate preparation process may be used. Meanwhile, the lower limit of this concentration ratio may vary depending on the type of raw milk, etc., but for example, when the raw milk is skim milk, this concentration ratio is preferably 1.5 times or more, more preferably 1.8 times or more, and when the raw milk is raw milk, this concentration ratio is preferably 1.3 times or more, more preferably 1.6 times or more. The upper limit of the concentration ratio can be determined by the pressure resistance of the ultrafiltration membrane and the ultrafiltration device, but for example, when the raw milk is skim milk, the concentration ratio is preferably 3.5 times or less, more preferably 3 times or less, and when the raw milk is raw milk, the concentration ratio is preferably 2.8 times or less, more preferably 2.3 times or less. This concentration ratio is set to be lower than the concentration ratio in the first milk concentrate preparation step.

[0038] (8) pH readjustment process In the pH readjustment step, the pH of the third milk concentrate (e.g., the cooled third milk concentrate, the room temperature third milk concentrate) is adjusted to a range of 6.5 to 7.0 to prepare a milk concentrate with a readjusted pH (hereinafter also referred to as a "pH-adjusted milk concentrate" or "pH-adjusted third milk concentrate"). From the viewpoint of easiness in improving thermal stability and easiness in maintaining low viscosity, it is preferable that the pH is a predetermined value. That is, in the pH readjustment step, the pH of the pH-adjusted milk concentrate is preferably set to a range of 6.5 to 6.9, more preferably set to a range of 6.5 to 6.8, and even more preferably set to a range of 6.5 to 6.7. Since the pH of the third milk concentrate is usually set to a range of 5.5 to less than 6.5, an alkali is used in this pH readjustment step. As this alkali, an alkali that can be added to food, that is, an alkali that is harmless to the human body, such as sodium hydroxide, potassium hydroxide, potassium carbonate, etc., is used. In this case, the alkali is preferably used in the form of a dilute aqueous solution, more preferably in the form of a 1 to 3 N aqueous alkali solution, and even more preferably in the form of a 2 N aqueous alkali solution. In addition, in this case, it is preferable to use a mixed aqueous solution of sodium hydroxide and potassium hydroxide so that the ratio of sodium ions to potassium ions in the third milk concentrate is the same as or close to the ratio of sodium ions to potassium ions in the raw milk, and more preferably to use a mixed aqueous solution of sodium hydroxide:potassium hydroxide in a ratio of 2 to 4:8 to 6, and even more preferably to use a mixed aqueous solution of sodium hydroxide:potassium hydroxide in a ratio of 3:7.

[0039] In addition, in this pH readjustment step, after adding the above-mentioned alkali to the third milk concentrate, it is preferable to leave the pH-adjusted milk concentrate to stand or stir for a predetermined time. Here, the predetermined time is preferably 0.1 hours or more, more preferably 0.3 hours or more, even more preferably 0.5 hours or more, and particularly preferably 1 hour or more. And, there is no particular upper limit to this predetermined time, but the predetermined time is, for example, preferably 10 hours or less, more preferably 8 hours or less, even more preferably 6 hours or less, and particularly preferably 4 hours or less. Also, in this pH readjustment step, it is preferable to leave the pH-adjusted milk concentrate to stand or stir at a predetermined temperature. Here, this predetermined temperature is preferably in the range of a temperature at which the pH-adjusted milk concentrate remains liquid to 25°C or less, more preferably in the range of 1°C to 20°C or less, even more preferably in the range of 2°C to 15°C or less, and particularly preferably in the range of 3°C to 10°C or less.

[0040] <Uses of milk concentrate> The milk concentrate (third milk concentrate) according to the embodiment of the present invention can be used as one component of the raw material of dairy products. That is, this milk concentrate may be used alone as the raw material (raw milk) of dairy products, or may be mixed with other raw materials such as water, raw milk, pasteurized milk, skim milk, whole milk powder, skim milk powder, whole fat concentrated milk, skim milk concentrated milk, buttermilk, butter, cream, cheese, etc., and used as the raw material of dairy products (part of raw milk, etc.).

[0041] The above-mentioned dairy products include, for example, milk drinks (including processed milk), yogurts, lactobacillus drinks, fermented milk, ice creams, creams, cheeses, etc. Any ingredient can be added to the dairy product as needed. Such optional ingredients are not particularly limited, but include ingredients that are generally blended into dairy products, such as sweeteners, acidulants, vegetables, fruits, seeds, vegetable juices, fruit juices, seed juices, vegetable, fruit, seed extracts, vitamins, minerals, peptides, amino acids, and other nutritional materials, useful microorganisms such as lactobacilli, bifidobacteria, and propionic acid bacteria, cultures of useful microorganisms, fermented products of useful microorganisms, royal jelly, glucosamine, astaxanthin, polyphenols, and other existing functional ingredients, flavors, pH adjusters, excipients, acidulants, colorants, emulsifiers, preservatives, etc. In this case, examples of sweeteners include glucose, fructose, maltose, sucrose, oligosaccharides, sugar, honey, maple syrup, agave syrup, baum sugar, molasses, starch syrup, glucose-fructose liquid sugar, trehalose, maltose, palatinose, xylitol, sorbitol, licorice extract, stevia-processed sweetener, Monk fruit extract, thaumatin, glycerin, curculin, monellin, miraculin, erythritol, etc. These sweeteners not only impart sweetness to dairy products but also suppress sourness and "bitterness," so it is preferable to actively add them during the production of dairy products.

[0042] When the dairy product is fermented milk, the milk concentrate may be used as one component of the raw material mix of the fermented milk. In addition, in the preparation of the raw material mix of the fermented milk, for example, raw materials such as the milk concentrate and other optional ingredients (for example, sweeteners, acidulants, minerals, vitamins, flavors, etc.) are added (blended), heated, mixed, and dissolved. In addition to the milk concentrate, water, raw milk, pasteurized milk, whole milk powder, whole fat concentrated milk, buttermilk, butter, cream, cheese, etc. may be added, heated, mixed, and dissolved in the raw material mix. In addition, whey protein concentrate (WPC), whey protein isolate (WPI), α-lactalbumin (α-La), β-lactoglobulin (β-Lg), etc. may be added, heated, mixed, and dissolved in the raw material mix.

[0043] When the dairy product is fermented milk, the fermented milk is produced through steps such as a step of blending a raw material mix, a step of (heating) sterilizing the raw material mix, a step of cooling the raw material mix, a step of adding a starter, a fermentation step, and a step of cooling the fermented milk, in the same manner as in conventional methods for producing fermented milk. In this case, in the step of blending the raw material mix, the raw materials are added, heated, mixed, dissolved (blended), etc., as described above. In each of the steps described above, the processing conditions used in the production of general fermented milk may be appropriately adopted. In addition, it is preferable that the step of (heating) sterilizing the raw material mix, the step of cooling the raw material mix, the step of adding a starter, the fermentation step, and the step of cooling the fermented milk are carried out in this order.

[0044] <Characteristics of Milk Concentrate> The milk concentrate obtained as described above has relatively high concentrations of calcium, magnesium, etc., compared to conventional milk concentrates, but has well improved or maintained heat stability. And dairy products prepared using this milk concentrate as a raw material have relatively high concentrations of calcium, magnesium, etc., compared to conventional dairy products prepared using milk concentrates as a raw material, but have well improved or maintained milk flavor and other physical properties.

[0045] In addition, it has been revealed that the heat coagulation time of the milk concentrate thus obtained is longer in the pH range of about 6.4 to about 6.7 compared to conventional milk concentrates, and the heat coagulation time is equivalent in the pH range of about 6.7 to about 7.0. In other words, this milk concentrate exhibits excellent heat stability over a wide pH range. EXAMPLES

[0046] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0047] Example 1 1. Preparation of Milk Concentrate (Third Milk Concentrate) First, using a cream separator (Separator F-3, manufactured by Elecream, volume: 0.37 L), raw milk was centrifuged at 50°C (rotation speed: 7000-8000 rpm, processing flow rate: 315 L / h, processing time: 4.2 seconds, gravitational acceleration: 1500-4400 G) to prepare skim milk, which was then cooled to 5°C (skim milk preparation step). Next, a 2N aqueous hydrochloric acid solution was added to the cooled skim milk to adjust the pH of the skim milk to 5.7, and the skim milk was left at 5-10°C for 2 hours (pH adjustment step). Next, a hollow fiber membrane module (Romicon Hollow fiber CTG3" HF25-43 PM-10, manufactured by Koch, molecular weight cutoff: 10,000 Da, membrane area: 2.3 m) was used. 2 ) was used to ultrafilter (UF) the left skim milk at a concentration ratio of 3.2 times to produce a first milk concentrate (first milk protein concentrate) (first milk concentrate preparation step). Next, cold water (5°C) of 0.8 times the mass of the first milk concentrate was added to the first milk concentrate, and they were mixed to prepare a first milk concentrate dilution (first water addition step). Then, using the above hollow fiber membrane module, the first milk concentrate dilution was ultrafiltered (UF) at a concentration ratio of 1.8 times to produce a second milk concentrate (second milk protein concentrate) (second milk concentrate preparation step). Next, cold water (5°C) of 0.8 times the mass of the second milk concentrate was added to the second milk concentrate, and they were mixed to prepare a second milk concentrate dilution (second water addition step). Then, using the above-mentioned hollow fiber membrane module, the diluted second milk concentrate was subjected to ultrafiltration (UF) at a concentration ratio of 1.8 times to produce a third milk concentrate (third milk protein concentrate) (third milk concentrate preparation process).

[0048] Before ultrafiltration of skim milk using the hollow fiber membrane module, the hollow fiber membrane was washed with an alkaline aqueous solution to which chlorine was added at 200 ppm. Then, after cooling the hollow fiber membrane while circulating cold water (3 to 5°C) through the hollow fiber membrane module, the cooling water was discharged from the hollow fiber membrane module. Then, the above-mentioned left skim milk (5 to 10°C) was put into a 20L jacketed tank. When ultrafiltration of skim milk using the hollow fiber membrane module, the hollow fiber membrane module was connected to the tank by piping or the like, and the tank was indirectly cooled, and a cooling pipe was provided in the middle of the piping to indirectly cool the piping. The concentration ratio for ultrafiltration of skim milk was determined from the amount of skim milk charged (treatment amount), the processing flow rate of the permeate (permeation flow rate), the total solid concentration of the retentate (concentrate), and the protein concentration.

[0049] Then, this third milk concentrate was divided into five, and a 2N aqueous solution of sodium hydroxide / potassium hydroxide containing sodium hydroxide and potassium hydroxide in a molar ratio of 3:7 was added so that the sodium (ion) / potassium (ion) ratio of each third milk concentrate was equivalent to that in cow's milk (approximately 4 / 15), and the pH of each third milk concentrate was adjusted to 6.40, 6.45, 6.50, 6.60, or 6.75 in a constant temperature environment of 20°C, thereby preparing milk concentrates with readjusted pH (pH readjusted milk concentrates) (pH readjustment process).

[0050] 2. Physical property confirmation test (1) Thermal stability test First, 4 mL of each pH-readjusted milk concentrate was weighed into a 14 mL round-bottom vial and sealed. Next, the round-bottom vial was immersed in an oil bath at 130° C. and shaken while visually checking each pH-readjusted milk concentrate, and the time until coagulation occurred and the time until the viscosity increased in the pH-readjusted milk concentrate were measured, and this measured time was taken as the "thermal coagulation time". Finally, 2 hours after the pH readjustment, the pH of each pH-readjusted milk concentrate at 10° C. was measured, and this pH was taken as the pH of each pH-readjusted milk concentrate.

[0051] The results of this confirmation test are shown in Table 1. The data shown in Table 1 is shown in a graph in Figure 1.

[0052] (2) Sensory testing (2-1) The pH-readjusted milk concentrate was used as the raw milk to prepare fermented milk, which was then subjected to a sensory test. The method for preparing the fermented milk will be described below, followed by a detailed description of the sensory test.

[0053] Each pH-readjusted milk concentrate was heat-sterilized and stored in a sterilized tray (a 5 L stainless steel container). In this heat sterilization, the pH-readjusted milk concentrate was heated to a temperature of 95° C. in a batchwise manner using a tray.

[0054] Next, each heat-sterilized, pH-readjusted milk concentrate was placed in a tray and the temperature was adjusted to 43°C. Then, a lactic acid bacteria starter (a mixed starter of Lactobacillus bulgaricus and Lactobacillus thermophilus isolated from Meiji Bulgaria Yogurt LB81) was added to each pH-readjusted milk concentrate at 2% by mass, and the mixture was stirred and held for 10 minutes.

[0055] Next, 70 g of each of the pH-readjusted milk concentrates to which the lactic acid bacteria starter had been added was filled into a cup of about 100 mL volume. Meanwhile, the remaining pH-readjusted milk concentrates were left in the vat. Then, the cups and the vat were placed in an incubator at 43°C to ferment each pH-readjusted milk concentrate. Then, when the pH of each pH-readjusted milk concentrate reached 4.6, the fermented milk in the cup was placed in a refrigerator (3 to 5°C) and kept overnight (about 12 hours) to produce hard-type fermented milk. Meanwhile, when the pH of each pH-readjusted milk concentrate reached 4.6, the fermented milk in the vat was cooled in a cold water bath (3 to 5°C) while stirring to produce soft-type fermented milk.

[0056] (2-2) A panel of five experts tasted the hard and soft fermented milks chilled (5°C) and rated them on a five-point scale for sweetness, saltiness, sourness, bitterness, milky flavor, smoothness, and the strength (degree) of unpleasant odor. At this time, the majority of the expert panelists evaluated that "the fermented milk of Example 1 (described above) is less bitter and has a richer milky flavor and smoothness than the fermented milk of Comparative Example 1 (described below)."

[0057] Comparative Example 1 In the preparation of the milk concentrate, the pH adjustment step was omitted, and the skim milk cooled was subjected to ultrafiltration only the first time (first time) without adjusting the pH of the skim milk. A pH readjusted milk concentrate was prepared in the same manner as in Example 1. Then, a confirmation test of thermal stability was carried out on the pH readjusted milk concentrate in the same manner as in Example 1. Note that in Comparative Example 1, the pH readjustment step was carried out only for the purpose of comparison with Examples 1 and 2, and does not negate the patentability of the pH readjustment in the present invention.

[0058] The results of this confirmation test are shown in Table 1. The data shown in Table 1 is shown in a graph in Figure 1.

[0059] [Table 1]

[0060] <Considerations on Examples and Comparative Examples> As is clear from Figure 1, it was revealed that within the pH range of 6.4 to 6.7, the pH readjusted milk concentrate prepared in Example 1 had superior heat stability compared to the pH readjusted milk concentrate prepared in Comparative Example 1, and within the pH range of 6.75 to 7.0, the pH readjusted milk concentrate prepared in Example 1 exhibited heat stability equivalent to that of the pH readjusted milk concentrate prepared in Comparative Example 1. Furthermore, within the pH range of 6.4 to 7.0, the pH readjusted milk concentrate prepared in Example 1 should be evaluated as having a remarkable level of heat stability.

Claims

1. per 20 mass% of the total solid content, the protein content is within the range of 9.0 mass% or more and 15.5 mass% or less, the ash content is within the range of 0.20 mass% or more and 1.30 mass% or less, the sodium content is within the range of 0.01 mass% or more and 0.08 mass% or less, the potassium content is within the range of 0.03 mass% or more and 0.36 mass% or less, the calcium content is within the range of 0.08 mass% or more and 0.34 mass% or less, the magnesium content is within the range of more than 0.00 mass% and 0.02 mass% or less, the phosphorus content is within the range of 0.08 mass% or more and 0.20 mass% or less, and the chlorine content is within the range of more than 0.00 mass% and 0.25 mass% or less, The thermal coagulation time at 130°C is 8 minutes or longer within the pH range of 6.4 to 6.

7. Milk protein concentrate.

2. 2. The milk protein concentrate of claim 1, which is in liquid form.

3. A dairy product produced using the milk protein concentrate according to claim 1 or 2 as a raw material.

4. The dairy product is fermented milk.

4. The dairy product of claim 3.

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