Liquid dairy product and preparation method thereof

Abstract

The invention provides a liquid dairy product and a preparation method thereof. The first aspect of the invention provides a liquid dairy product which is prepared by sequentially carrying out nitrogen treatment, homogenization and sterilization on high-protein raw milk, and the protein content in the high-protein raw milk is 3.8-4.2%; the acidity of the high-protein raw milk before nitrogen treatment is X1 degree T, the acidity of the high-protein raw milk after nitrogen treatment is X2 degree T, and (X1-X2) is greater than or equal to 0.5. The nitrogen is introduced into the high-protein raw milk with the protein content of 3.8-4.2%, so that the acidity of the liquid dairy product is reduced, the liquid dairy product with the acidity of 12-18 DEG T is obtained, and the high-protein final product is ensured to meet the industrial requirements.

Description

Technical Field

[0001] The invention relates to a liquid dairy product and a preparation method thereof, and relates to the technical field of food. Background Art

[0002] Protein is the material basis of all life, an important component of body cells, and the main raw material for the renewal and repair of human tissues. The development of the human body and the repair and renewal of damaged cells are inseparable from protein. Liquid dairy products, as one of the important sources of protein in the diet, are widely used.

[0003] At present, the protein content can be increased by adding protein from outside, and the raw milk can also be processed by membrane concentration technology. At present, the products on the market are mainly based on RO membrane concentration technology, but RO membrane concentration of protein will also increase the acidity of dairy products, so that the final product cannot meet the acidity of 12-18°T specified in the "Food Safety Standard for Raw Milk" (GB 19301-2010). The acidity of high-protein dairy products can be improved by adding acidity regulators, but due to the addition of acidity regulators, the finished product cannot be called pasteurized milk or ultra-high temperature sterilized milk, but can only be called modulated milk. Therefore, how to reduce the acidity of high-protein dairy products without adding acidity regulators and make them meet industry requirements during the shelf life of the product has become one of the problems that technicians in this field need to solve. Summary of the invention

[0004] The invention provides a liquid dairy product and a preparation method thereof, which are used to reduce the acidity of a high-protein dairy product to obtain a liquid dairy product with an acidity of 12 to 18°T.

[0005] The first aspect of the present invention provides a liquid dairy product, which is prepared by nitrogen treatment, homogenization and sterilization of high-protein raw milk, wherein the protein content of the high-protein raw milk is 3.8% to 4.2%;

[0006] The acidity of the high-protein raw milk before the nitrogen treatment is X1°T, and the acidity of the high-protein raw milk after the nitrogen treatment is X2°T, (X1-X2)≥0.5.

[0007] In a specific embodiment, the liquid dairy product is pasteurized milk or ultra-high temperature sterilized milk.

[0008] In a specific embodiment, the high-protein raw milk is obtained by filtering raw milk through an RO membrane.

[0009] In a specific embodiment, the nitrogen treatment comprises: inputting nitrogen into the high-protein raw milk after passing through a filter, and after the acidity of the high-protein raw milk is reduced by at least 0.5°T, stopping the introduction of nitrogen to complete the nitrogen treatment.

[0010] In a specific embodiment, the purity of the nitrogen gas is not less than 99.999%.

[0011] In a specific embodiment, the mesh number of the filter screen is 1000 - 2000 meshes.

[0012] In a specific embodiment, the feeding rate of the nitrogen gas is 0.001 - 0.003 L / s.

[0013] In a specific embodiment, the feeding time of the nitrogen gas is 10 - 40 min.

[0014] The second aspect of the present invention provides a method for preparing a liquid dairy product, comprising the following steps:

[0015] The raw milk is sequentially subjected to impurity removal and RO membrane filtration, and the retentate is collected to obtain high-protein raw milk with a protein content of 3.8% - 4.2%; the acidity of the high-protein raw milk is measured and recorded as X1;

[0016] Nitrogen gas is introduced into the high-protein raw milk, and when the acidity of the high-protein raw milk reaches X2, (X1 - X2) ≥ 0.5, the introduction of nitrogen gas is stopped to complete the nitrogen treatment;

[0017] The liquid material after the nitrogen treatment is sequentially subjected to homogenization treatment and sterilization treatment, and the liquid dairy product is obtained after the treatment.

[0018] In a specific embodiment, the acidity of the liquid dairy product is 12 - 18 °T.

[0019] By introducing nitrogen gas into high-protein raw milk with a protein content of 3.8% - 4.2%, the present invention helps to reduce the acidity of the liquid dairy product and maintain stability during the product shelf life, obtaining a liquid dairy product with an acidity of 12 - 18 °T, ensuring that the high-protein final product meets the industry requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0021] Figure 1 It is a flowchart of the method for preparing a dairy product provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will, in conjunction with the embodiments of the present invention, clearly and completely describe the technical solutions in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0023] In the first aspect of the present invention, a liquid dairy product is provided. The liquid dairy product is prepared by successively subjecting high-protein raw milk to nitrogen treatment, homogenization, and sterilization. The protein content in the high-protein raw milk is 3.8% to 4.2%.

[0024] The acidity of the high-protein raw milk before nitrogen treatment is X1°T, and the acidity of the high-protein raw milk after nitrogen treatment is X2°T, where (X1 - X2) ≥ 0.5.

[0025] The liquid dairy product provided by the present invention is a high-protein product, which is obtained by subjecting high-protein raw milk to nitrogen treatment. It helps to reduce the acidity of the liquid dairy product and remains stable during the product shelf life, resulting in a liquid dairy product with an acidity of 12 to 18°T.

[0026] In a specific embodiment, the high-protein raw milk refers to raw milk with a protein content between 3.8% and 4.2%. The protein content can be measured using a protein detector.

[0027] Further, the high-protein raw milk refers to that obtained by filtering raw milk through an RO membrane; the raw milk can be raw cow milk. Further, the temperature of RO membrane filtration is 2 to 15°C, the membrane pressure is 2 to 5 bar, and the membrane pore size is 1.0 to 1.4 μm.

[0028] In addition, before subjecting the raw milk to RO membrane filtration, the raw milk can also be subjected to impurity removal treatment to remove large particle impurities and non-milk cell impurities in the raw milk; specifically, the raw milk can be filtered through a 80 - 600 mesh sieve to remove large particle impurities in the raw milk, and after collecting the filtrate, centrifugation is carried out at a rotational speed of 4000 - 6000 rpm to remove non-milk cell impurities in the raw milk, and after collecting the supernatant, RO membrane filtration is carried out.

[0029] Collect the retentate after RO membrane filtration to obtain high-protein raw milk, and introduce nitrogen into the high-protein raw milk. Stop introducing nitrogen after the acidity of the high-protein raw milk has decreased by at least 0.5°T to complete the nitrogen treatment.

[0030] Further, the purity of the nitrogen used is not less than 99.999%.

[0031] Further, before introducing nitrogen into the high-protein raw milk, it needs to be filtered through a filter screen to avoid the influence of impurities in the nitrogen on the high-protein raw milk; specifically, the mesh number of the filter screen is 1000-2000 meshes.

[0032] Further, the introduction rate of the nitrogen is 0.001-0.003 L / s, the introduction time is 10-40 min, and the acidity of the high-protein raw milk is monitored in real time. When the acidity of the high-protein raw milk is reduced by at least 0.5 °T, the introduction of nitrogen is stopped.

[0033] As the protein content in the high-protein raw milk increases, the difference between (X1-X2) should be appropriately increased. For example, when the protein content in the high-protein raw milk is 4.0-4.2%, (X1-X2) should be not less than 1.5.

[0034] The liquid material after nitrogen treatment is subjected to homogenization treatment to improve the uniformity of the liquid material, avoid the situation of fat floating during the product shelf life, and reduce the oxidation of fat to ensure that the liquid dairy product emits an aromatic smell. Specifically, the temperature of the homogenization treatment is 50-60 °C, and the pressure is 170-230 bar to further improve the stability and flavor of the liquid dairy product.

[0035] Finally, the homogenized liquid material is subjected to sterilization treatment to kill the microorganisms in the material, extend the shelf life of the liquid dairy product, and ensure the stability of the product during the shelf life. Specifically, the sterilization treatment can be pasteurization treatment or high-temperature short-time sterilization. Specifically, the temperature of pasteurization is 75-90 °C, and the time is 15-20 s. The temperature of high-temperature short-time sterilization is 120-140 °C, and the time is 1-4 s.

[0036] The sterilized liquid material is cooled and filled to obtain the liquid dairy product. According to the different sterilization processes, the liquid dairy product provided by the present invention can be pasteurized milk or ultra-high temperature sterilized milk. The acidity of the obtained liquid dairy product is 12 °T-18 °T and remains stable during the product shelf life.

[0037] The second aspect of the present invention provides a method for preparing a liquid dairy product, comprising the following steps:

[0038] The raw milk is sequentially subjected to impurity removal and RO membrane filtration, and the retentate is collected to obtain high-protein raw milk with a protein content of 3.8%-4.2%; the acidity of the high-protein raw milk is measured and recorded as X1;

[0039] Nitrogen is introduced into the high-protein raw milk. When the acidity of the high-protein raw milk reaches X2 and (X1-X2)≥0.5, the introduction of nitrogen is stopped to complete the nitrogen treatment;

[0040] The liquid material after nitrogen treatment is subjected to homogenization treatment and sterilization treatment in sequence, and the liquid dairy product is obtained after the treatment is completed.

[0041] In a specific embodiment, Figure 1 is a flowchart of a method for preparing a dairy product provided by an embodiment of the present invention. As Figure 1 shown, it specifically includes the following steps:

[0042] Step 1: The raw milk is subjected to impurity removal and RO membrane filtration in sequence, and the retentate is collected to obtain high-protein raw milk with a protein content of 3.8% - 4.2%.

[0043] Specifically, the raw milk used in the present invention can be raw cow milk.

[0044] First, the raw milk is subjected to impurity removal treatment to remove large particle impurities and non-milk cell impurities in the raw milk; specifically, the impurity removal treatment includes filtration and centrifugation. Filtration can be carried out using a sieve mesh of 80 - 600 meshes. After collecting the filtrate, centrifugation is carried out at a rotation speed of 4000 - 6000 rpm, and the supernatant is collected.

[0045] Secondly, the supernatant collected after centrifugation is subjected to RO membrane filtration, and the retentate is collected to obtain high-protein raw milk. Specifically, the temperature of RO membrane filtration is 2 - 15°C, the membrane pressure is 2 - 5 bar, and the membrane pore size is 1.0 - 1.4 μm.

[0046] Step 2: Nitrogen is introduced into the high-protein raw milk. When the acidity of the high-protein raw milk reaches X2, (X1 - X2) ≥ 0.5, the introduction of nitrogen is stopped, and the nitrogen treatment is completed.

[0047] Nitrogen is introduced into the high-protein raw milk to improve the acidity of the finished liquid dairy product. Specifically, the high-protein raw milk storage tank is connected to a nitrogen cylinder through a pipeline. The nitrogen cylinder stores high-purity nitrogen with a purity of more than 99.999%. A filter mesh of 1000 - 2000 meshes is set at the pipe orifice. Nitrogen is continuously introduced into the high-protein raw milk at an introduction rate of 0.001 - 0.003 L / s for 10 - 40 min. During the nitrogen introduction period, the acidity of the high-protein raw milk is continuously monitored. When the acidity is reduced by at least 0.5°T, the introduction of nitrogen is stopped, and the nitrogen treatment is completed. Thereafter, ensure that the high-protein raw milk is in an isolated state from oxygen.

[0048] Step 3: The liquid material after nitrogen treatment is subjected to homogenization treatment and sterilization treatment in sequence, and the liquid dairy product is obtained after the treatment is completed.

[0049] The liquid material after nitrogen treatment is subjected to homogenization treatment. Specifically, the temperature of the homogenization treatment is 50 - 60°C, and the pressure is 170 - 230 bar.

[0050] The homogenized liquid material is subjected to sterilization treatment. Specifically, the sterilization treatment can be pasteurization treatment or ultra-high temperature instantaneous sterilization. Specifically, the temperature of pasteurization is 75-90°C and the time is 15-20 s. The temperature of ultra-high temperature instantaneous sterilization is 120-140°C and the time is 1-4 s.

[0051] After cooling and filling the sterilized liquid material, liquid dairy products can be obtained. According to different sterilization processes, the liquid dairy products provided by the present invention can be pasteurized milk or ultra-high temperature sterilized milk. The acidity of the obtained liquid dairy products is 12°T-18°T and remains stable during the product shelf life.

[0052] The present invention will be elaborated in detail below in conjunction with specific embodiments.

[0053] Example 1

[0054] The preparation method of the liquid dairy product provided in this example includes the following steps:

[0055] (1) Impurity removal and milk clarification:

[0056] The qualified raw milk is subjected to cooling and milk clarification treatment. The cooling temperature is 2-10°C to keep the milk fresh. The raw milk is passed through a 600-mesh sieve, and the filtrate is centrifuged at a speed of 6000 rpm to collect the supernatant.

[0057] (2) RO membrane filtration

[0058] The supernatant is subjected to RO membrane filtration at 2-15°C. The membrane pressure is 2-5 bar and the membrane pore size is 1.0-1.4 microns. The retentate is collected to obtain high-protein raw milk with protein contents of 3.8, 3.9, 4.0, 4.1, and 4.2 g / 100 g respectively.

[0059] (3) Nitrogen treatment:

[0060] Connect the nitrogen cylinder nozzle to the pipeline and connect a 1500-mesh filter screen at the pipe orifice. High-purity nitrogen with a purity of 99.999% is used and filled into 1 L of high-protein raw milk at a volume of 0.002 L / s. The nitrogen filling time is 10, 20, 30, 40 min.

[0061] (4) Homogenization:

[0062] In this step, the sample in (3) is passed through the homogenization treatment process, and the homogenization treatment is carried out at 65°C and a pressure of 30 / 180 bar.

[0063] (5) Sterilization:

[0064] The milk obtained in step (4) is heated to 133±1°C and kept warm for 2 s for sterilization. After sterilization, it is cooled to 20±2°C and filled.

[0065] Example 2

[0066] The preparation method of the liquid dairy product provided in this example can refer to Example 1, except that in Step 3:

[0067] Connect the nozzle of the nitrogen cylinder to the pipeline, and connect a 1000-mesh filter at the pipe orifice. Use high-purity nitrogen with a nitrogen purity of 99.999% and fill 1 L of high-protein raw milk at a volume of 0.001 L / s. The nitrogen filling time is 10, 20, 30, 40 min.

[0068] Example 3

[0069] The preparation method of the liquid dairy product provided in this example can refer to Example 1, except that in Step 3:

[0070] Connect the nozzle of the nitrogen cylinder to the pipeline, and connect a 2000-mesh filter at the pipe orifice. Use high-purity nitrogen with a nitrogen purity of 99.999% and fill 1 L of RO membrane concentrated raw milk at a volume of 0.001 L / s. The nitrogen filling time is 10, 20, 30, 40 min.

[0071] Example 4

[0072] The preparation method of the liquid dairy product provided in this example can refer to Example 1, except that in Step 3:

[0073] Connect the nozzle of the nitrogen cylinder to the pipeline, and connect a 1000-mesh filter at the pipe orifice. Use high-purity nitrogen with a nitrogen purity of 99.999% and fill 1 L of high-protein raw milk at a volume of 0.003 L / s. The nitrogen filling time is 10, 20, 30, 40 min.

[0074] Example 5

[0075] The preparation method of the liquid dairy product provided in this example can refer to Example 1, except that in Step 3:

[0076] Connect the nozzle of the nitrogen cylinder to the pipeline, and connect a 2000-mesh filter at the pipe orifice. Use high-purity nitrogen with a nitrogen purity of 99.999% and fill 1 L of RO membrane concentrated raw milk at a volume of 0.003 L / s. The nitrogen filling time is 10, 20, 30, 40 min.

[0077] Comparative Example 1

[0078] The preparation method of the liquid dairy product provided in this comparative example can refer to Example 1, except that in Step 3:

[0079] Connect the nozzle of the argon gas cylinder to the pipeline, and connect a 1500-mesh filter screen to the pipe orifice. Use high-purity argon gas with an argon purity of 99.999% and fill 1 L of high-protein raw milk at a volume of 0.002 L / s. The argon gas filling time is 10, 20, 30, 40 min.

[0080] Comparative Example 2

[0081] The preparation method of the liquid dairy product provided in this comparative example can refer to Example 2, except that in step 3:

[0082] Connect the nozzle of the argon gas cylinder to the pipeline, and connect a 1000-mesh filter screen to the pipe orifice. Use high-purity argon gas with an argon purity of 99.999% and fill 1 L of high-protein raw milk at a volume of 0.001 L / s. The argon gas filling time is 10, 20, 30, 40 min.

[0083] Comparative Example 3

[0084] The preparation method of the liquid dairy product provided in this comparative example can refer to Example 3, except that in step 3:

[0085] Connect the nozzle of the argon gas cylinder to the pipeline, and connect a 2000-mesh filter screen to the pipe orifice. Use high-purity argon gas with an argon purity of 99.999% and fill 1 L of high-protein raw milk at a volume of 0.001 L / s. The argon gas filling time is 10, 20, 30, 40 min.

[0086] Comparative Example 4

[0087] The preparation method of the liquid dairy product provided in this comparative example can refer to Example 4, except that in step 3:

[0088] Connect the nozzle of the argon gas cylinder to the pipeline, and connect a 1000-mesh filter screen to the pipe orifice. Use high-purity argon gas with an argon purity of 99.999% and fill 1 L of high-protein raw milk at a volume of 0.003 L / s. The argon gas filling time is 10, 20, 30, 40 min.

[0089] Comparative Example 5

[0090] The preparation method of the liquid dairy product provided in this comparative example can refer to Example 5, except that in step 3:

[0091] Connect the nozzle of the argon gas cylinder to the pipeline, and connect a 2000-mesh filter screen to the pipe orifice. Use high-purity argon gas with an argon purity of 99.999% and fill 1 L of high-protein raw milk at a volume of 0.003 L / s. The argon gas filling time is 10, 20, 30, 40 min.

[0092] The ultra-high temperature sterilized milk provided in Examples 1 to 5 and Comparative Examples 1 to 5 was subjected to acidity tests, and the acidity was tested after 60 days of storage. The acidity test method refers to GB-5413.34-2010. Among them, the acidity test results of the ultra-high temperature sterilized milk after preparation are shown in Tables 1-1 to 10-1 respectively, and the acidity test results after 60 days of storage at room temperature are shown in Tables 1-2 to 10-2.

[0093] Table 1-1 Acidity test results of the ultra-high temperature sterilized milk provided in Example 1

[0094]

[0095] Table 1-2 Acidity results of the ultra-high temperature sterilized milk provided in Example 1 after 60 days of storage at room temperature

[0096]

[0097]

[0098] Table 2-1 Acidity test results of the ultra-high temperature sterilized milk provided in Example 2

[0099]

[0100] Table 2-2 Acidity results of the ultra-high temperature sterilized milk provided in Example 2 after 60 days of storage at room temperature

[0101]

[0102] Table 3-1 Acidity test results of the ultra-high temperature sterilized milk provided in Example 3

[0103]

[0104]

[0105] Table 3-2 Acidity results of the ultra-high temperature sterilized milk provided in Example 3 after 60 days of storage at room temperature

[0106]

[0107] Table 4-1 Acidity test results of the ultra-high temperature sterilized milk provided in Example 4

[0108]

[0109] Table 4-2 Acidity results of the ultra-high temperature sterilized milk provided in Example 4 after 60 days of storage at room temperature

[0110]

[0111]

[0112] Table 5-1 Acidity test results of ultra-high temperature sterilized milk provided in Example 5

[0113]

[0114] Table 5-2 Acidity results of ultra-high temperature sterilized milk provided in Example 5 after being placed at room temperature for 60 days

[0115]

[0116] Table 6-1 Acidity test results of ultra-high temperature sterilized milk provided in Comparative Example 1

[0117]

[0118]

[0119] Table 6-2 Acidity results of ultra-high temperature sterilized milk provided in Comparative Example 1 after being placed at room temperature for 60 days

[0120]

[0121] Table 7-1 Acidity test results of ultra-high temperature sterilized milk provided in Comparative Example 2

[0122]

[0123] Table 7-2 Acidity results of ultra-high temperature sterilized milk provided in Comparative Example 2 after being placed at room temperature for 60 days

[0124]

[0125] Table 8-1 Acidity test results of ultra-high temperature sterilized milk provided in Comparative Example 3

[0126]

[0127] Table 8-2 Acidity results of ultra-high temperature sterilized milk provided in Comparative Example 3 after being placed at room temperature for 60 days

[0128]

[0129]

[0130] Table 9-1 Acidity test results of ultra-high temperature sterilized milk provided in Comparative Example 4

[0131]

[0132] Table 9-2 Acidity results of ultra-high temperature sterilized milk provided in Comparative Example 4 after being placed at room temperature for 60 days

[0133]

[0134] Table 10-1 Acidity test results of ultra-high temperature sterilized milk provided in Comparative Example 5

[0135]

[0136]

[0137] Table 10-2 Acidity results of ultra-high temperature sterilized milk provided in Comparative Example 5 after being placed at room temperature for 60 days

[0138]

[0139] Acidity is not only an important indicator reflecting the freshness of milk but also an indicator reflecting whether there is fraud such as milk protein in products in the industry. However, with the rapid iteration of current technologies, products using membrane concentration technology can concentrate the protein in milk, enabling the products to have better claims and higher added value. However, the acidity problem has always restricted the products from achieving higher protein content. According to the above acidity test data, in the preparation methods provided in Examples 1 to 5, since the homogenization and sterilization treatments do not affect the acidity of the products, therefore, by controlling the acidity of the high-protein raw milk before and after nitrogen treatment, the acidity of the liquid dairy products and the acidity during the product shelf life can both meet the industry requirements. In Comparative Examples 1 to 5, the reduction value of acidity is limited, resulting in the acidity of the finished milk not meeting the industry requirements. Therefore, the present invention provides a new solution to the problem that the acidity of membrane-concentrated high-protein products is too high to meet the industry requirements.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A liquid dairy product, characterized in that, the liquid dairy product is prepared by sequentially subjecting high-protein raw milk to nitrogen treatment, homogenization, and sterilization, and the protein content in the high-protein raw milk is 3.8% to 4.2%; the acidity of the high-protein raw milk before nitrogen treatment is X1 °T, and the acidity of the high-protein raw milk after nitrogen treatment is X2 °T, (X1 - X2) ≥ 0.

5.

2. The liquid dairy product according to claim 1, characterized in that, the liquid dairy product is pasteurized milk or ultra-high temperature sterilized milk.

3. The liquid dairy product according to claim 1, characterized in that, the high-protein raw milk is obtained by filtering raw milk through an RO membrane.

4. The liquid dairy product according to claim 1, characterized in that, the nitrogen treatment includes: inputting nitrogen into the high-protein raw milk after passing through a filter screen, and stopping the nitrogen input after the acidity of the high-protein raw milk is reduced by at least 0.5 °T to complete the nitrogen treatment.

5. The liquid dairy product according to claim 4, characterized in that, the nitrogen purity is not less than 99.999%.

6. The liquid dairy product according to claim 4, characterized in that, the mesh number of the filter screen is 1000 to 2000 meshes.

7. The liquid dairy product according to claim 4, characterized in that, the nitrogen input rate is 0.001 to 0.003 L / s.

8. The liquid dairy product according to claim 4, characterized in that, the nitrogen input time is 10 to 40 min.

9. A preparation method of a liquid dairy product, characterized in that, comprises the following steps: removing impurities and filtering the raw milk through an RO membrane in sequence, collecting the retentate to obtain high-protein raw milk with a protein content of 3.8% to 4.2%; testing the acidity of the high-protein raw milk, denoted as X1; introducing nitrogen into the high-protein raw milk, and stopping the nitrogen input when the acidity of the high-protein raw milk reaches X2, (X1 - X2) ≥ 0.5, to complete the nitrogen treatment; performing homogenization treatment and sterilization treatment on the liquid after nitrogen treatment in sequence, and obtaining the liquid dairy product after the treatment ends.

10. The preparation method according to claim 9, characterized in that, the acidity of the liquid dairy product is 12 to 18 °T.

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