Low-sodium high-calcium high-protein milk and preparation method thereof

Abstract

The invention provides low-sodium high-calcium high-protein milk and a preparation method thereof, and the preparation method comprises the following steps: 1) separating raw milk to obtain skimmed milk and single cream; 2) performing nanofiltration concentration and sterilization treatment on the skimmed milk, and performing sterilization treatment on the single cream; and (3) mixing the concentrated and degermed skimmed milk with the sterilized single cream as required, homogenizing and pasteurizing to obtain the low-sodium high-calcium high-protein milk. According to the invention, through nanofiltration concentration, a part of sodium is filtered out while protein and calcium are concentrated, so that the sodium content in the milk is lower than that of other high-protein milk products with the same concentration degree; meanwhile, through centrifugal sterilization, microfiltration sterilization and pasteurization processes, the quality guarantee period of the milk can be prolonged to 20 days or above while high-content active protein in the milk is guaranteed.

Description

Technical Field

[0001] The invention relates to the field of dairy product processing, in particular to a low-sodium, high-calcium, high-protein milk and a preparation method thereof. Background Art

[0002] As consumers' demand for nutrition and health increases, high-protein milk has gradually become a market trend. Various companies use various concentration methods to increase the content of nutrients such as protein and calcium in milk. Common milk concentration methods in the prior art include evaporation concentration, falling film concentration, and reverse osmosis (RO) concentration, which has gradually become popular in recent years. When using these concentration processes, when the milk is concentrated to a protein content of ≥4.5% or higher, it begins to show a distinct salty taste. Although the nutrition is improved, the overly salty taste makes it easily unacceptable to consumers. The reason is that while concentrating the protein, the content of sodium, potassium and other ions in the milk is increased, and the increase in salt content will have a certain negative impact on the taste and consumer health.

[0003] Sodium is one of the essential minerals for the human body. It helps maintain functions such as fluid balance, nerve conduction and muscle contraction. However, excessive sodium intake may have adverse effects on health, such as increasing the risk of high blood pressure and cardiovascular disease. Therefore, sodium intake needs to be controlled in moderation.

[0004] Nanofiltration membrane technology can achieve the concentration of dairy products while allowing salt ions to pass through the membrane, thereby reducing the salt ion content in the concentrated milk. For example, patent CN115500388A discloses a method for preparing concentrated milk, in which fresh milk is directly subjected to nanofiltration, and then concentrated milk is obtained through degassing, homogenization and sterilization. However, the sodium content in the milk is still high (>50mg / 100g), and the calcium content in the prepared milk varies. Therefore, it is currently necessary to develop a high-protein milk that can reduce the sodium ion content in the milk as much as possible to ensure taste and health while ensuring that the milk has high protein and calcium content.

[0005] In addition, although fresh milk that has not been ultra-high temperature sterilized retains the content and activity of various active proteins in milk, including α-lactalbumin, β-lactoglobulin, lactoferrin, and immunoglobulin, its storage conditions are relatively strict and its shelf life is short. For example, most fresh milk needs to be stored at 0-4°C, and the shelf life is generally no more than 20 days. Therefore, how to extend the shelf life of milk while ensuring the content of active proteins in milk is also a major problem faced by those skilled in the art. Summary of the invention

[0006] In view of the shortcomings of the prior art described above, the object of the present invention is to provide a low-sodium, high-calcium, high-protein milk and a preparation method thereof, so as to solve the problems in the prior art of the salty taste of milk and potential health problems caused by the increase of sodium ion concentration during the milk concentration process, as well as the problems of harsh storage conditions and short shelf life of existing fresh milk with high active protein content.

[0007] The first aspect of the present invention provides a method for preparing low-sodium, high-calcium, high-protein milk, comprising the following steps:

[0008] 1) Separating the raw milk to obtain skimmed milk and cream;

[0009] 2) Nanofiltration concentration and sterilization of skimmed milk and sterilization of cream;

[0010] 3) The concentrated and sterilized skimmed milk is mixed with the sterilized cream as required, and then homogenized and pasteurized to obtain a high-protein milk with low sodium and high calcium.

[0011] Preferably, the raw milk is raw cow's milk, and the raw milk is separated by centrifugation at a temperature of 40 to 60° C. and a rotation speed of 4000 to 5000 rpm.

[0012] More preferably, the centrifugal separation temperature is 50-55° C., and the centrifugal separation speed is 4500-5000 rpm.

[0013] Preferably, the fat content of the skimmed milk obtained after the centrifugal separation is ≤0.05wt%.

[0014] The nanofiltration concentration described in the present invention is a kind of membrane filtration process, and its material is a polyamide film composite material.

[0015] Preferably, the pore size of the nanofiltration membrane used in the nanofiltration concentration is 0.5-2 nm.

[0016] Preferably, the temperature of the nanofiltration concentration is 4-10°C.

[0017] Preferably, the feed pressure during the nanofiltration concentration is 15 to 20 bar.

[0018] Further preferably, the feed pressure during the nanofiltration concentration is 15 to 17 bar; for example, the feed pressure may be 15 bar, 16 bar or 17 bar.

[0019] In some specific embodiments, the feed pressure during the nanofiltration concentration is 15 bar.

[0020] Preferably, the feed flow rate during the nanofiltration concentration is 300 to 500 kg / h, preferably 300 to 400 kg / h.

[0021] Preferably, the sterilization includes one or both of centrifugal sterilization and microfiltration sterilization.

[0022] Further preferably, the sterilization includes centrifugal sterilization and microfiltration sterilization.

[0023] The sterilization step in the present invention may be performed before or after nanofiltration and concentration.

[0024] Preferably, the centrifugal sterilization step is prior to nanofiltration concentration.

[0025] Since the temperature of raw milk separation is 40-60°C, and the temperature required for centrifugal sterilization is also 40-60°C, the centrifugal sterilization step is designed to be after the raw milk separation and before the nanofiltration concentration. This can save heat sources and use centrifugal force to separate high-density microorganisms (such as spores) from milk, thereby reducing the number of microorganisms in dairy products and improving product quality.

[0026] Preferably, the microfiltration sterilization step is performed after the nanofiltration concentration.

[0027] Designing the microfiltration sterilization step after nanofiltration concentration can further remove bacteria and spores that still exist in the milk after centrifugal sterilization and concentration, ensuring that the content of microorganisms in the concentrated milk is within an extremely low range. Microfiltration sterilization technology can achieve long-term preservation of the product and extend the shelf life while avoiding high-temperature treatment.

[0028] Since nanofiltration membrane concentration requires the skim milk to be in a low temperature state, a plate heat exchanger or a tubular heat exchanger can be used to cool the skim milk after centrifugal sterilization to 4-8°C for use.

[0029] Preferably, the temperature of the centrifugal sterilization is 40-60°C, and the rotation speed is 5000-6000rpm.

[0030] Further preferably, the microfiltration sterilization uses a microfiltration ceramic membrane, the pore size of the microfiltration ceramic membrane is 0.8-1.4 μm, and the temperature of the microfiltration sterilization is 50-60°C.

[0031] Most preferably, the pore size of the microfiltration ceramic membrane used in the present invention is 1.2-1.4 μm.

[0032] The present invention preferably uses a microfiltration ceramic membrane with a larger pore size, which can avoid excessive waste of raw milk during the sterilization process.

[0033] Most preferably, the temperature of the microfiltration sterilization used in the present invention is 50-55°C.

[0034] Preferably, the cream sterilization temperature is 115-125° C., and the sterilization time is 15-25 seconds.

[0035] More preferably, the cream is sterilized at a temperature of 120-125°C.

[0036] More preferably, the sterilization time is 15 to 20 seconds.

[0037] Preferably, after sterilization, the cream is cooled to 50-60°C.

[0038] Preferably, the cream is cooled and mixed with concentrated and sterilized skimmed milk as required.

[0039] Further preferably, the on-demand mixing is to determine the amount of cream to be added according to the required fat content in the milk to be prepared.

[0040] Preferably, the mixing of the concentrated and sterilized skim milk and the sterilized cream is an online mixing in a pipeline.

[0041] Preferably, the homogenization temperature of the concentrated and sterilized skimmed milk and the sterilized cream after mixing is 55-65°C.

[0042] More preferably, the homogenization temperature is 60-65°C.

[0043] Preferably, the homogenization pressure is 150-400 bar.

[0044] More preferably, the homogenization pressure is 200-300 bar.

[0045] The invention homogenizes before pasteurization, and can effectively prevent the phenomenon of fat and protein aggregation in the process of preheating milk.

[0046] Preferably, the pasteurization temperature is 72-75°C.

[0047] Preferably, the pasteurization time is 15 to 18 seconds.

[0048] The pasteurization in the present invention adopts a relatively low temperature, which can kill the pathogens in the milk and at the same time better preserve the nutrients and natural flavor in the milk.

[0049] The second aspect of the present invention protects a low-sodium, high-calcium, high-protein milk obtained by the preparation method as described above.

[0050] Preferably, based on the total mass of the milk, the protein content of the high-protein milk is ≥4.5g / 100g.

[0051] Further preferably, based on the total mass of milk, the protein content of the high-protein milk is 4.5-7.0 g / 100 g, for example, 4.5-5.0 g / 100 g, 5.0-5.5 g / 100 g, 5.5-6.0 g / 100 g, 6.0-6.5 g / 100 g or 6.5-7.0 g / 100 g.

[0052] In some specific embodiments, based on the total mass of the milk, the protein content of the high-protein milk is 4.5-5.0 g / 100 g.

[0053] Preferably, based on the total mass of the milk, the calcium content of the high-protein milk is ≥175 mg / 100 g.

[0054] Further preferably, based on the total mass of milk, the calcium content of the high-protein milk is 175-200 mg / 100g, for example, 175-180 mg / 100g, 180-185 mg / 100g, 185-190 mg / 100g, 190-195 mg / 100g or 195-200 mg / 100g.

[0055] In some specific embodiments, based on the total mass of the milk, the calcium content of the high-protein milk is 175-185 mg / 100 g.

[0056] Preferably, based on the total mass of milk, the sodium content of the high-protein milk is ≤56 mg / 100 g.

[0057] In some preferred embodiments of the present invention, based on the total mass of milk, the sodium content of the high-protein milk is ≤60 mg / 100 g. In some further preferred embodiments of the present invention where the nanofiltration feed pressure is 15-17 bar, based on the total mass of milk, the sodium content of the high-protein milk is ≤50 mg / 100 g.

[0058] Further preferably, based on the total mass of milk, the sodium content of the high-protein milk is 20-50 mg / 100 g, for example, 20-30 mg / 100 g, 30-40 mg / 100 g or 40-50 mg / 100 g.

[0059] In some specific embodiments, based on the total mass of milk, the sodium content of the high-protein milk is 40-50 mg / 100 g.

[0060] Preferably, based on the total volume of the milk, the α-lactalbumin content in the high-protein milk is ≥1800 mg / L.

[0061] Further preferably, based on the total volume of the milk, the α-lactalbumin content in the high-protein milk is 1800-2500 mg / L, for example, 1800-2000 mg / L, 2000-2200 mg / L or 2200-2500 mg / L.

[0062] In some specific embodiments, based on the total volume of the milk, the α-lactalbumin content in the high-protein milk is 1800-2100 mg / L.

[0063] Preferably, based on the total volume of the milk, the β-lactoglobulin content in the high-protein milk is ≥4000 mg / L.

[0064] Further preferably, based on the total volume of the milk, the β-lactoglobulin content in the high-protein milk is 4000-5000 mg / L, for example, 4000-4300 mg / L, 4300-4600 mg / L or 4600-5000 mg / L.

[0065] In some specific embodiments, based on the total volume of the milk, the β-lactoglobulin content in the high-protein milk is 4000-4300 mg / L.

[0066] Preferably, based on the total volume of the milk, the lactoferrin content in the high-protein milk is ≥65 mg / L.

[0067] Further preferably, based on the total volume of the milk, the lactoferrin content in the high-protein milk is 65-100 mg / L, for example, 65-70 mg / L, 70-80 mg / L, 80-90 mg / L or 90-100 mg / L.

[0068] In some specific embodiments, based on the total volume of the milk, the lactoferrin content in the high-protein milk is 65-80 mg / L.

[0069] Preferably, based on the total volume of the milk, the immunoglobulin content in the high-protein milk is ≥250 mg / L.

[0070] Further preferably, based on the total volume of the milk, the immunoglobulin content in the high-protein milk is 250-350 mg / L, for example, 250-270 mg / L, 270-290 mg / L, 290-310 mg / L, 310-330 mg / L or 330-350 mg / L.

[0071] In some specific embodiments, based on the total volume of the milk, the immunoglobulin content in the high-protein milk is 250-300 mg / L.

[0072] Preferably, the milk is fresh milk, and the shelf life of the milk at 10° C. is greater than 20 days.

[0073] In some specific embodiments, the shelf life of the milk at 10°C is ≥ 25 days.

[0074] As mentioned above, the full invention title of the present invention has the following beneficial effects:

[0075] 1. The preparation method of the present invention uses a nanofiltration membrane to concentrate skim milk, and uses microfiltration sterilization to remove most of the spores in the milk, and then sterilizes the cream at high temperature to kill the microorganisms in the cream. Finally, a pasteurization process is used to prepare low-sodium, high-calcium, and high-protein milk with a long shelf life and retained protein activity nutrition.

[0076] 2. Compared with ordinary high-protein and high-calcium milk, the sodium content of the milk of the present invention is ≤56 mg / 100 g. Compared with milk with the same high protein concentration, the sodium content is 25% or more lower, and the calcium content can reach more than 175 mg / 100 g.

[0077] 3. Compared with fresh milk with a high content of active protein, the milk of the present invention does not require strict refrigeration conditions of 0 to 6°C while ensuring that it has a high content of active protein, and greatly extends the shelf life of fresh milk. The shelf life of the milk of the present invention can reach more than 20 days at 10°C.

[0078] 4. The present invention separates raw milk into skim milk and cream, and sterilizes them respectively. Subsequently, the cream can be backfilled as needed according to the required fat content in the product to prepare milk with different fat contents. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 Shown is a process flow chart for preparing the low-sodium, high-calcium, high-protein milk of the present invention. DETAILED DESCRIPTION

[0080] After a lot of exploratory experiments, the inventors of the present invention found that skimmed milk and cream can be obtained by separating raw milk, sterilizing the skimmed milk by centrifugation, concentrating by nanofiltration, and sterilizing by microfiltration, and the cream is sterilized by high temperature, mixed with the sterilized concentrated skimmed milk, and then homogenized and pasteurized to obtain high-protein milk with low sodium and high calcium, wherein the sodium content is lower than that of other high-protein milk products with the same degree of concentration, and the contents of α-lactalbumin, β-lactoglobulin, lactoferrin and immunoglobulin are higher than those of milk products with the same shelf life that are directly sterilized by high temperature.

[0081] The present invention adopts the concentration and sterilization technology of membrane filtration, uses nanofiltration technology to filter out a part of sodium while concentrating protein and calcium, and uses microfiltration technology to remove most of the spores and microorganisms and retain the activity of milk protein, thus solving the problem that high-protein milk tastes salty after concentration, which is unfavorable to the health of consumers, and the problem that the activity of fresh milk protein is lost during the long shelf life. On this basis, the present invention is completed.

[0082] As a preferred technical solution, the preparation process flow chart of the low sodium and high calcium high protein milk of the present invention is as follows: Figure 1 The specific steps include:

[0083] 1) Centrifuging the raw milk to obtain skimmed milk and cream;

[0084] 2) the skimmed milk is sterilized by centrifugation to obtain pre-sterilized skimmed milk;

[0085] 3) The pre-sterilized skim milk is concentrated by nanofiltration to a protein level of ≥4.5% to obtain concentrated skim milk;

[0086] 4) sterilizing the concentrated skim milk through a microfiltration membrane to obtain sterilized concentrated skim milk;

[0087] 5) sterilizing the cream at high temperature to obtain sterilized cream;

[0088] 6) The concentrated skimmed milk and sterilized cream are mixed as required, homogenized and pasteurized to obtain a high-protein milk with low sodium and high calcium.

[0089] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0090] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified; it should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before or after the combination device / apparatus or the insertion of other devices / apparatuses between these explicitly mentioned two devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0091] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are for describing the specific embodiments rather than for limiting the scope of protection of the present invention; in the present specification and claims, unless otherwise expressly stated herein, the singular forms "a", "an" and "the" include plural forms.

[0092] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the grasp of the prior art by those skilled in the art and the record of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to realize the present invention.

[0093] In the following embodiments of the present application, the nanofiltration membrane material is a polyamide film composite material, and the microfiltration sterilization membrane material is ceramic, both of which were purchased from Tetra Pak.

[0094] Example 1

[0095] In this embodiment 1, a method for preparing low-sodium and high-calcium high-protein milk is provided, comprising the following steps:

[0096] 1) Raw milk separation: The raw milk is heated to about 52° C. and separated into skim milk and cream using a centrifuge, wherein the fat content of the skim milk is 0.05%;

[0097] 2) Centrifugal sterilization: the skim milk obtained in step 1) is put into a centrifugal sterilizer at a temperature of about 52° C. After sterilization, the pre-sterilized skim milk is cooled to 6° C. for later use;

[0098] 3) Nanofiltration concentration: adjusting the nanofiltration concentration ratio to a target protein of 4.7 g / 100 g, and performing nanofiltration concentration on the pre-sterilized skim milk obtained in step 2), maintaining the temperature at 4-10° C. during nanofiltration, the nanofiltration feed pressure at 15 bar, and the feed flow rate at 300-400 kg / h;

[0099] 4) Microfiltration sterilization: the concentrated skim milk obtained in step 3) is heated to about 55° C. and sterilized through a ceramic microfiltration membrane;

[0100] 5) Cream sterilization: the cream obtained in step 1) is subjected to high temperature sterilization at a temperature of 120° C. for 15 seconds, and the cream is cooled to 55° C. after sterilization;

[0101] 6) Pasteurization: The sterilized concentrated skim milk obtained in step 4) and the sterilized cream obtained in step 5) are mixed online in a pipeline, and the fat content after mixing is 4.0g / 100g. After heating, they are homogenized and pasteurized. The homogenization temperature is 65°C, the homogenization pressure is 250bar, the pasteurization temperature is 75°C, and the sterilization time is 15s. After sterilization, high-protein milk with low sodium and high calcium is obtained.

[0102] Example 2

[0103] In this embodiment 2, the protein content in milk is further increased by further adjusting the nanofiltration concentration ratio. The specific steps are as follows:

[0104] 1) Raw milk separation: The raw milk is heated to about 52° C. and separated into skim milk and cream using a centrifuge, wherein the fat content of the skim milk is 0.05%;

[0105] 2) Centrifugal sterilization: the skim milk obtained in step 1) is put into a centrifugal sterilizer at a temperature of about 52° C. After sterilization, the pre-sterilized skim milk is cooled to 6° C. for later use;

[0106] 3) Nanofiltration concentration: adjusting the nanofiltration concentration ratio to a target protein of 5.2 g / 100 g, and performing nanofiltration concentration on the pre-sterilized skim milk obtained in step 2), maintaining the temperature at 4-10° C. during nanofiltration, the nanofiltration feed pressure at 15 bar, and the feed flow rate at 300-400 kg / h;

[0107] 4) Microfiltration sterilization: the concentrated skim milk obtained in step 3) is heated to about 55° C. and sterilized through a ceramic microfiltration membrane;

[0108] 5) Cream sterilization: the cream obtained in step 1) is subjected to high temperature sterilization at a temperature of 120° C. for 15 seconds, and the cream is cooled to 55° C. after sterilization;

[0109] 6) Pasteurization: The sterilized concentrated skim milk obtained in step 4) and the sterilized cream obtained in step 5) are mixed online in a pipeline, and the fat content after mixing is 1.5g / 100g. After heating, they are homogenized and pasteurized. The homogenization temperature is 65°C, the homogenization pressure is 250bar, the pasteurization temperature is 75°C, and the sterilization time is 15s. After sterilization, high-protein milk with low sodium and high calcium is obtained.

[0110] Example 3

[0111] The difference between this embodiment 3 and embodiment 1 is that the nanofiltration concentration parameters in step 3) are different, and the pasteurization parameters in step 6) are different. The specific differences are: the nanofiltration feed pressure in step 3) is 17 bar, and the pasteurization temperature in step 6) is 72° C. The rest is the same as embodiment 1.

[0112] Example 4

[0113] The difference between this embodiment 4 and embodiment 2 is that the nanofiltration concentration parameters in step 3) are different, and the homogenization and pasteurization parameters in step 6) are different. The specific differences are: the nanofiltration feed pressure in step 3) is 20 bar, the homogenization pressure in step 6) is 150 bar, and the pasteurization temperature is 72° C. The rest is the same as embodiment 2.

[0114] Comparative Example 1

[0115] The only difference between this comparative example 1 and example 2 is that the nanofiltration feed pressure in step 3) is increased to 25 bar to investigate the effect of the increased nanofiltration feed pressure on the sodium content in milk. The rest is the same as example 2 to prepare comparative high-protein milk.

[0116] Comparative Example 2

[0117] The difference between this comparative example 2 and example 2 is that the pasteurization temperature in step 6) is increased to 80°C to investigate the effect of the increase in pasteurization temperature on the active protein content and shelf life in milk. The rest is the same as example 2 to prepare comparative high-protein milk.

[0118] Comparative Example 3

[0119] The difference between this comparative example 3 and example 2 is that the nanofiltration concentration in step 3) is changed to reverse osmosis concentration (RO), and the specific steps are as follows:

[0120] 1) Raw milk separation: The raw milk is heated to about 52° C. and separated into skim milk and cream using a centrifuge, wherein the fat content of the skim milk is 0.05%;

[0121] 2) Centrifugal sterilization: the skim milk obtained in step 1) is put into a centrifugal sterilizer at a temperature of about 52° C. After sterilization, the pre-sterilized skim milk is cooled to 6° C. for later use;

[0122] 3) Reverse osmosis concentration (RO): the reverse osmosis concentration ratio is adjusted to a target protein content of 5.2 g / 100 g, and the pre-sterilized skim milk obtained in step 2) is subjected to RO concentration. During the RO concentration, the temperature is maintained at 4-10° C., the RO concentration feed pressure is 15 bar, and the feed flow rate is 300-400 kg / h;

[0123] 4) Microfiltration sterilization: the concentrated skim milk obtained in step 3) is heated to about 55° C. and sterilized through a ceramic microfiltration membrane;

[0124] 5) Cream sterilization: the cream obtained in step 1) is subjected to high temperature sterilization at a temperature of 120° C. for 15 seconds, and the cream is cooled to 55° C. after sterilization;

[0125] 6) Pasteurization: The sterilized concentrated skim milk obtained in step 4) and the sterilized cream obtained in step 5) are mixed online in a pipeline, and the fat content after mixing is 1.5g / 100g. After heating, they are homogenized and pasteurized. The homogenization temperature is 65°C, the homogenization pressure is 250bar, the pasteurization temperature is 75°C, and the sterilization time is 15s. After sterilization, a comparative high-protein milk is obtained.

[0126] Comparative Example 4

[0127] The difference between this comparative example 4 and example 2 is that the raw milk which has been centrifugally sterilized and not skimmed is first concentrated by nanofiltration and then skimmed and separated. The specific steps are as follows:

[0128] 1) Centrifugal sterilization: The raw milk is heated to about 52°C and enters the centrifugal sterilizer at a temperature of about 52°C. After sterilization, the pre-sterilized raw milk is cooled to 6°C for later use;

[0129] 2) Nanofiltration concentration: adjusting the nanofiltration concentration ratio to a target protein content of 5.2 g / 100 g, and performing nanofiltration concentration on the pre-sterilized raw milk obtained in step 1), wherein the temperature during nanofiltration is maintained at 4-10° C. and the nanofiltration feed pressure is 15 bar;

[0130] 3) skimming and separation: heating the concentrated milk obtained in step 2) to about 52° C., and using a centrifugal separator to separate the raw milk into skimmed milk and cream, wherein the fat content of the skimmed milk is 0.05%;

[0131] 4) Microfiltration sterilization: the concentrated skim milk obtained in step 3) is heated to about 55° C. and sterilized through a ceramic microfiltration membrane;

[0132] 5) Cream sterilization: The cream obtained in step 3) is subjected to high temperature sterilization at a temperature of 120° C. for 15 seconds, and the cream is cooled to 55° C. after sterilization;

[0133] 6) Pasteurization: The concentrated skim milk obtained in step 4) and the sterilized cream obtained in step 5) are mixed online in a pipeline, and the fat content after mixing is 1.5 g / 100 g. After heating, they are homogenized and pasteurized. The homogenization temperature is 65° C., the homogenization pressure is 250 bar, the pasteurization temperature is 75° C., and the sterilization time is 15 s. After sterilization, a comparative high-protein milk is obtained.

[0134] Comparative Example 5

[0135] The difference between this comparative example 5 and example 2 is that the microfiltration sterilization in step 4) is removed to investigate the effect of microfiltration sterilization on the shelf life of milk. The rest is the same as example 2 to prepare comparative high-protein milk.

[0136] Comparative Example 6

[0137] The difference between this comparative example 6 and example 2 is that when the raw milk is separated in step 1), the fat content in the skimmed milk is appropriately retained, so that the fat content is changed from 0.05% to 0.1%, and the rest is the same as example 2 to prepare comparative high-protein milk.

[0138] The protein, calcium, sodium, α-lactalbumin, β-lactoglobulin, lactoferrin and immunoglobulin contents in the low-sodium and high-calcium high-protein milk obtained in the above Examples 1-4 and Comparative Examples 1-6 and the comparative high-protein milk were tested, and the shelf life under refrigerated conditions was tracked. The results are shown in Table 1.

[0139] Study on the shelf life under refrigerated conditions: After filling, the above high-protein milk samples were placed in a constant temperature box at 10°C to determine the shelf life. The shelf life is considered to end when the total colony count in the sample exceeds 10,000 CFU / mL or the appearance is obviously deteriorated (for example: flocculation, agglomeration, sourness, odor of milk, large amount of fat floating, etc.).

[0140] The total colony count test is carried out in accordance with the standard "GB 4789.2-2022 National Food Safety Standard Food Microbiology Inspection Determination of Total Colony Count".

[0141] Investigation of α-lactalbumin content: Determined according to the standard "T / TDSTIA 002-2021 Determination of α-lactalbumin in milk and dairy products - High Performance Liquid Chromatography".

[0142] Investigation of β-lactoglobulin content: Determined according to the standard "T / TDSTIA 007-2019 Liquid chromatography method for determination of β-lactoglobulin in milk and dairy products".

[0143] Investigation of lactoferrin content: The content of lactoferrin was determined according to the standard "GB 5009.299-2024 National Food Safety Standard Determination of Lactoferrin in Food".

[0144] Investigation of immunoglobulin content: The content of immunoglobulin was determined according to the standard "T / TDSTIA 003-2021 High Performance Liquid Chromatography for the Determination of Immunoglobulin IgG in Milk and Dairy Products".

[0145] The content of α-lactalbumin, β-lactoglobulin, lactoferrin and immunoglobulin was used to characterize the content of active proteins in high-protein milk.

[0146] Table 1

[0147]

[0148]

[0149] Note: The unit of protein and fat is g / 100g, the unit of calcium and sodium is mg / 100g, the unit of α-lactalbumin, β-lactoglobulin, lactoferrin content and immunoglobulin is mg / L, the shelf life test condition is 10℃ constant temperature box, the unit is day. The sodium reduction efficiency (%) is calculated based on the sodium content of Comparative Example 3.

[0150] From the results in Table 1, we can see that:

[0151] 1) In Example 2, Example 3, Example 4 and Comparative Example 1, as the nanofiltration feed pressure continued to increase until 25 bar, the sodium content in the milk also continued to increase until it reached 68 mg / 100 g. Therefore, the increase in the nanofiltration feed pressure will cause the sodium content in the milk to increase at the same time; the feed pressure of Examples 1-4 is in the range of 15-20 bar, and the sodium content is reduced by more than 25% compared with Comparative Example 3.

[0152] 2) In Comparative Example 2, the pasteurization temperature was changed from 75°C to 80°C, resulting in a significant increase in the inactivation ratio of active proteins.

[0153] 3) Comparative Example 3 uses RO concentration, which is a complete concentration of all components in milk. When the protein is concentrated to 5.0g / 100g, the sodium content reaches 75mg / 100g. The increase in sodium content causes the taste to be significantly salty.

[0154] 4) Comparative Example 4 used whole milk for nanofiltration concentration without first skimming, resulting in a lower sodium reduction efficiency of only about 20%.

[0155] 5) In Comparative Example 5, after nanofiltration concentration, no microfiltration sterilization treatment was performed, resulting in the presence of spores and some microorganisms that could not be killed by 75°C pasteurization. The shelf life of the milk was significantly shortened and deterioration occurred in only 7 days.

[0156] 6) In Comparative Example 6, in the degreasing stage, the fat content of skimmed milk was 0.1%. Blockage and flow rate reduction were found during microfiltration and sterilization, resulting in a large amount of raw milk waste, and the method was not suitable for industrial production.

[0157] In summary, the method of the present invention not only reduces the sodium content in high-protein milk, but also prolongs the shelf life of fresh milk while retaining active protein by separating the raw milk, first performing nanofiltration concentration, and then performing microfiltration sterilization. Without using any processing aids, high-protein milk with low sodium and high calcium and a long shelf life can be obtained.

[0158] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and evolutions of the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing low-sodium, high-calcium, high-protein milk, characterized in that: The steps include: 1) Separating the raw milk to obtain skimmed milk and cream; 2) Nanofiltration concentration and sterilization of skimmed milk and sterilization of cream; 3) The concentrated and sterilized skimmed milk is mixed with the sterilized cream as required, and then homogenized and pasteurized to obtain a high-protein milk with low sodium and high calcium.

2. The preparation method according to claim 1, characterized in that: The raw milk is raw cow milk, and the raw milk separation is performed by centrifugation at a temperature of 40 to 60° C. and a rotation speed of 4000 to 5000 rpm; And / or, the fat content of the skimmed milk obtained after the centrifugal separation is ≤0.05wt%.

3. The preparation method according to claim 1, characterized in that: The pore size of the nanofiltration membrane used in the nanofiltration concentration is 0.5 to 2 nm; And / or, the temperature of the nanofiltration concentration is 4-10°C.

4. The preparation method according to claim 1, characterized in that: The feed pressure during the nanofiltration concentration is 15 to 20 bar, preferably 15 to 17 bar; And / or, the feed flow rate during the nanofiltration concentration is 300 to 500 kg / h, preferably 300 to 400 kg / h.

5. The preparation method according to claim 1, characterized in that: The sterilization includes one or both of centrifugal sterilization and microfiltration sterilization; the temperature of the centrifugal sterilization is 40-60°C, the rotation speed is 5000-6000rpm, the microfiltration sterilization adopts a microfiltration ceramic membrane, the pore size of the microfiltration ceramic membrane is 1.0-1.5μm, and the temperature of the microfiltration sterilization is 50-60°C.

6. The preparation method according to claim 5, characterized in that: The sterilization includes centrifugal sterilization and microfiltration sterilization. Centrifugal sterilization is performed before nanofiltration concentration, and microfiltration sterilization is performed after nanofiltration concentration.

7. The preparation method according to claim 1, characterized in that: The cream sterilization temperature is 115-125° C., and the sterilization time is 15-25 seconds.

8. The preparation method according to claim 1, characterized in that: The homogenization temperature is 55-65°C, and the homogenization pressure is 150-400 bar; And / or, the pasteurization temperature is 72-75° C., and the pasteurization time is 15-18 s.

9. A low-sodium, high-calcium, high-protein milk obtained by the preparation method according to any one of claims 1 to 8.

10. The low-sodium, high-calcium, high-protein milk according to claim 9, characterized in that: Based on the total mass of milk, the protein content of the high-protein milk is ≥4.5g / 100g. And / or, based on the total mass of milk, the calcium content of the high-protein milk is ≥ 175 mg / 100 g. And / or, based on the total mass of milk, the sodium content of the high-protein milk is ≤50mg / 100g. And / or, based on the total volume of the milk, the α-lactalbumin content in the high-protein milk is ≥1800 mg / L. And / or, based on the total volume of the milk, the β-lactoglobulin content in the high-protein milk is ≥4000 mg / L. And / or, based on the total volume of the milk, the lactoferrin content in the high-protein milk is ≥65 mg / L. And / or, based on the total volume of milk, the immunoglobulin content in the high-protein milk is ≥ 250 mg / L And / or, the milk is fresh milk, and the shelf life of the milk is greater than 20 days.

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