High-solubility casein powder and preparation method therefor

Abstract

High-solubility casein powder and a preparation method therefor. The preparation method comprises sequentially performing a microfiltration step, an ultrafiltration step and a drying step on skim milk, wherein in the microfiltration step, the concentration ratio is 1-5; and in the ultrafiltration step, an ultrafiltration membrane having a molecular weight of 30-100 kDa is used, the concentration temperature is 10-20°C, the concentration pressure is 0.1-1 mPa, and upon concentration, the total solid content is 10-25%.

Description

A highly soluble casein powder and its preparation method

[0001] Priority requirements

[0002] This application claims priority to Chinese patent application filed on April 22, 2024, application number 2024104807808, entitled "A Highly Soluble Casein Powder and Its Preparation Method". Technical Field

[0003] This invention relates to the field of dairy processing technology, and in particular to a highly soluble casein powder and its preparation method. Background Technology

[0004] Casein is the most abundant protein in cow's milk, accounting for approximately 80% of the total protein content. It is composed of four proteins: αs1-casein, αs2-casein, β-casein, and κ-casein. The most significant characteristic of casein is the strong interactions between these four casein proteins within the milk system, forming stable micelle structures with Ca and P nanoclusters. Currently, there is no universally accepted model for casein micelles; the subunit model, Holt model, and Horne model are the most frequently studied. Regardless of the model used, micelle integrity has a significant impact on overall micelle properties, milk system stability, product application characteristics, and nutritional properties.

[0005] The solubility of casein or casein powder is particularly affected by the integrity of casein micelles. The four casein subtypes differ significantly in their hydrophilic / hydrophobic structures. αs1-casein, αs2-casein, and β-casein, lacking hydrophilic structures, form nanoclusters with Ca and P ions at the center of the micelles through ionic interactions. κ-casein, on the other hand, is mainly concentrated on the micelle surface and exhibits a distinct amphiphilic structure. The hydrophobic portion maintains the overall micelle structure by binding to the nanoclusters through intermolecular forces, while the hydrophilic portion is located on the outer side of the micelle, maintaining its solubility. In certain special cases, due to the disruption of the micelle structure, the hydrophobic portion is exposed, leading to a decrease in casein solubility or complete precipitation (e.g., in cheese making by lowering the pH or using rennet to precipitate casein). Therefore, improving the integrity of casein micelles is crucial for increasing their solubility. The stability of casein micelle structure can be affected by various factors, such as temperature, heat treatment intensity, pH, pressure, ion concentration, chelating agents, and enzymes.

[0006] There are currently three main methods for preparing casein powder: (1) Acid-based casein: Casein is precipitated by adding a fermenting agent or acid to lower the pH of the solution below the isoelectric point of casein, and then prepared by heating, washing, separation and drying; (2) Enzymatic casein: Casein is coagulated by adding rennet, and then prepared by heating, washing, separation and drying; (3) Membrane separation: Skim milk is used as raw material and separated by microfiltration / ultrafiltration membrane, and then prepared by separation, washing, concentration and drying. Since the acid method and the enzymatic method completely destroy the micelle structure of casein during the preparation process and are irreversible, resulting in extremely poor solubility of casein after reconstitution, they will not be discussed further. Microfiltration membrane separation technology is a highly efficient, energy-saving and environmentally friendly non-thermal physical separation technology, which is suitable for separating heat-sensitive high-value nutrients that are sensitive to temperature and can maintain the integrity of casein micelles to a certain extent during the separation process. However, the solubility of casein powder obtained by existing membrane separation methods is generally poor, such as CN103315128A, and further improvement is needed. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a highly soluble casein powder and its preparation method.

[0008] Specifically, on the one hand, the present invention provides a method for preparing casein powder, comprising the steps of microfiltration, ultrafiltration and drying of skim milk in sequence.

[0009] In the microfiltration step, the concentration ratio is 1-5;

[0010] In the ultrafiltration step, an ultrafiltration membrane with a molecular weight of 30kDa-100kDa is used, the concentration temperature is 10-20℃, the concentration pressure is 0.1-1mPa, and the total solids content after concentration is 10-25%.

[0011] The concentration ratio (VCF) refers to the ratio of the total feed volume to the concentrate volume.

[0012] This invention first uses microfiltration to remove most of the whey protein, followed by ultrafiltration to remove the remaining whey protein and other impurities such as other proteins and minerals. The concentration process of this invention is a non-thermal concentration process, avoiding damage to the micelle structure of casein powder (MCC). This invention does not require the addition of additional processing aids; by controlling the process parameters during separation, the separation of casein micelles from other impurities can be achieved under mild conditions.

[0013] The temperature selection during ultrafiltration concentration is crucial. Too low a temperature may cause β-casein to dissociate from the MCC micelles, leading to micelle structure damage, increased feed viscosity, and reduced production efficiency. Too high a temperature may cause uncontrolled microbial growth in the feed, increasing the microbial risk during production. However, higher temperatures can reduce feed viscosity and improve concentration efficiency. Considering all factors, this invention selects a concentration temperature of 10-20℃, which controls microbial growth while ensuring the integrity of the proportion of casein subtypes within the casein micelles. In a preferred embodiment, the concentration temperature is 15℃. Ultrafiltration membranes have a wide molecular weight range, from 3000 Da to 500 kDa. When the temperature drops to around 10℃, β-CN will dissociate from the casein micelles, resulting in incomplete casein micelles and poor solubility of the final MCC powder. Since the molecular weights of β-casein and whey protein are both around 20 kDa-30 kDa, an ultrafiltration membrane of 30 kDa-100 kDa is selected to filter out impurities and retain casein micelles. Meanwhile, the concentration of the final concentrated solution is also crucial. Too low a concentration results in low preparation efficiency, while too high a concentration may lead to excessive viscosity, poor flowability, and increased gelation, causing atomizer blockage during subsequent drying. Therefore, to ensure product quality and production continuity, the total solids content after concentration needs to be controlled within the range of 10-25%. Furthermore, regarding the concentration temperature and the solids content after concentration, a suitable concentration pressure is required to ensure concentration efficiency and production continuity. In other words, the parameters in this invention are closely interconnected, working together to achieve production continuity and obtain casein powder with high solubility.

[0014] In a preferred embodiment of the present invention, in the ultrafiltration step, an ultrafiltration membrane with a molecular weight of 50 kDa is used, the concentration temperature is 15°C, the concentration pressure is 0.6 MPa, and the total solids content after concentration is 20%.

[0015] In some embodiments of the present invention, in the microfiltration step, the ratio of washing water volume to retentate flow rate is 2:1-6:1; in the ultrafiltration step, the ratio of washing water volume to total feed volume is 0.5:1-3:1.

[0016] More preferably, in both the microfiltration and ultrafiltration steps, the filtration process involves adding filtration water online. This online filtration method is superior to the traditional batch-based filtration method and enables continuous production.

[0017] More preferably, in the microfiltration step, the ratio of washing water volume to retentate flow rate is 4.5:1;

[0018] In the ultrafiltration step, the ratio of washing water to total feed is 1:1.

[0019] In the microfiltration and ultrafiltration steps of this invention, an online washing process is adopted, and an appropriate flow ratio is adjusted to achieve continuous production. This helps to improve the casein separation rate, casein purity, and production efficiency, thereby achieving economic benefits.

[0020] In some embodiments of the present invention, the microfiltration step uses a microfiltration membrane with a pore size of 0.1-0.2 micrometers, a separation temperature of 40-60°C, and a transmembrane pressure of 0.1-0.2 mPa. Preferably, in some embodiments of the present invention, the microfiltration step uses a microfiltration membrane with a pore size of 0.14 micrometers.

[0021] More preferably, in the microfiltration step, a microfiltration membrane with a pore size of 0.14 micrometers is used, the separation temperature is 50°C, the transmembrane pressure is 0.1-0.2 mPa, and the concentration ratio is 3.

[0022] In some embodiments of the present invention, the drying is performed using electrostatic spray drying.

[0023] This invention employs electrostatic spray drying technology. Compared with traditional spray drying processes, electrostatic spray drying can significantly reduce the degree of heating of the liquid during the drying process while maintaining a low moisture content, thereby protecting the structural integrity of casein micelles and improving the solubility of MCC powder after reconstitution.

[0024] In some embodiments of the present invention, in the electrostatic spray drying step, the atomizing nozzle uses a pressure atomizer with an atomization pressure of 0.1-2 mPa, an atomization temperature of 20-60°C, a protective gas of nitrogen, an inlet air temperature of 60-90°C, an outlet air temperature of 30-50°C, an electrostatic field voltage of 1-20 kV, and a material preheating temperature of 30-60°C.

[0025] Furthermore, in a preferred embodiment of the present invention, the atomization pressure is 0.3 mPa, the atomization temperature is 40°C, the protective gas is nitrogen, the inlet air temperature is 70°C, the outlet air temperature is 40°C, the electrostatic field voltage is 12 kV, and the material preheating temperature is 50°C.

[0026] The skim milk described in this invention is obtained by standardizing raw milk, followed by skimming and pasteurization. The skimming temperature is 45-55℃, preferably 50℃. The pasteurization temperature is 60-90℃, and the pasteurization time is 10-60 seconds.

[0027] Furthermore, the fat content in the skim milk is 0.01-0.1%. This invention has found that the fat content in skim milk has little impact on product solubility, but it does affect the sustainability of membrane processing. For continuous production, this invention preferably controls the fat content in the skim milk to 0.01-0.1%.

[0028] In some embodiments of the present invention, the method for preparing the casein powder includes the following steps:

[0029] (1) Fresh raw milk is standardized after being processed to obtain standardized raw milk. The raw milk is defatting at a temperature of 45-55℃, and the fat content in the defatting milk is 0.01-0.1%. The defatting milk is pasteurized at a temperature of 60-90℃ for 10-60 seconds. (2) Microfiltration membrane separation process: The pasteurized defatting milk enters the microfiltration membrane separation equipment, where the separation temperature is 40-60℃, the transmembrane pressure is 0.1-0.2mPa, the concentration ratio is 1-5, the ratio of washing water flow rate to retentate flow rate is 2:1-6:1, and the washing method is online addition washing. (3) Ultrafiltration membrane concentration process: The casein raw material liquid separated by microfiltration membrane enters the ultrafiltration membrane equipment for further processing. Ultrafiltration concentration is carried out, with a concentration temperature of 10-20℃, a concentration pressure of 0.1-1mPa, and an online addition of washing filter. The ratio of washing filter water to total feed is 0.5:1-3:1. After concentration, the total solid content is 10-25%, the protein content is 17-19%, and the casein content accounts for 85-97% of the total protein content. (4) Drying process: The atomizing nozzle uses a pressure atomizer with an atomization pressure of 0.1-2mPa, an atomization temperature of 20-60℃, a protective gas of nitrogen, an inlet air temperature of 60-90℃, an outlet air temperature of 30-50℃, an electrostatic field voltage of 1-20kV, and a material preheating temperature of 30-60℃.

[0030] This invention controls process conditions to maximize the preservation of casein's relatively complete micellar structure throughout the entire process from pretreatment to concentration and drying, ensuring that MCC powder retains excellent solubility after reconstitution, thus solving the core problem of poor solubility of MCC powder that hinders its application.

[0031] On the other hand, the present invention provides a casein powder prepared by the above preparation method.

[0032] The casein powder obtained by this invention has a relatively complete micelle structure and exhibits good solubility after reconstitution, which is superior to mainstream casein powders currently on the market. The casein powder, tested according to GB5413.29-2010, has a centrifugal sedimentation rate of less than 28%; the casein powder, tested according to IDF 87:1979, has a dispersibility greater than 46%.

[0033] This invention provides a highly soluble casein powder and its preparation method. By controlling the key process parameters in each production step, the resulting casein powder can be guaranteed to have a relatively complete micelle structure, so that the casein powder still has excellent solubility after reconstitution, thus expanding its application prospects. Moreover, the preparation method of this invention has high production efficiency, strong continuous production capability, and is economical. Attached Figure Description

[0034] Figure 1 is a process flow diagram for preparing casein powder according to an embodiment of the present invention;

[0035] Figure 2 is a SEM image of the casein powder obtained in Example 1 of the present invention;

[0036] Figure 3 is a SEM image of the MCC powder obtained by conventional spray drying in Comparative Example 3;

[0037] Figure 4 is a SEM image of the MCC powder obtained by freeze-drying in Comparative Example 4;

[0038] Figure 5 shows the static solubility test results of the casein powder obtained in Examples 1-7 (from left to right, Examples 1-7 are respectively);

[0039] Figure 6 shows the static solubility test results of the casein powders obtained from Comparative Examples 1-6 (from left to right, they are Comparative Examples 1-6 respectively);

[0040] Figure 7 shows the stability test results of the casein powder obtained in Examples 1-3 (from left to right, Examples 1-3 are respectively);

[0041] Figure 8 shows the stability test results of the casein powder obtained in Examples 4-7 (from left to right, Examples 4-7 are respectively);

[0042] Figure 9 shows the stability test results of the casein powder obtained from Comparative Examples 1-3 (from left to right, they are Comparative Examples 1-3 respectively);

[0043] Figure 10 shows the stability test results of the casein powder obtained from Comparative Examples 4-6 (from left to right, Comparative Examples 4-6 are respectively). Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0045] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased through legitimate channels.

[0046] In the following embodiments, the pore size of the microfiltration membrane in the microfiltration step is 0.14 micrometers;

[0047] The ultrafiltration process uses an ultrafiltration membrane with a molecular weight of 50 kDa.

[0048] Example 1

[0049] This embodiment provides a highly soluble casein powder, the preparation process of which is shown in Figure 1. The specific preparation method is as follows:

[0050] (1) Fresh raw milk is standardized after being processed to obtain standardized raw milk. The raw milk is processed by defatting, with a defatting temperature of 50℃ and a fat content of 0.06% in the defatted milk; the defatted milk is pasteurized, with a pasteurization temperature of 75℃ and a pasteurization time of 30s; (2) Microfiltration membrane separation process: The pasteurized defatted milk enters the microfiltration membrane separation equipment, with a separation temperature of 50℃, a transmembrane pressure of 0.15mPa, a concentration ratio of 3, a washing water flow rate: retentate flow rate ratio of 4.5:1, and the washing method is online addition washing; (3) Ultrafiltration membrane concentration process: The casein raw material liquid separated by microfiltration membrane enters the ultrafiltration membrane. The membrane equipment is used for ultrafiltration concentration, with a concentration temperature of 15℃, a concentration pressure of 0.6mPa, and an online addition of washing filter. The ratio of washing filter water to total feed is 1:1. After concentration, the total solid content is 20%, the protein content is 18%, and the casein content accounts for 94% of the total protein content. (4) Electrostatic spray drying process: The atomizing nozzle uses a pressure atomizer with an atomization pressure of 0.3mPa, an atomization temperature of 40℃, a protective gas of nitrogen, an inlet air temperature of 70℃, an outlet air temperature of 40℃, an electrostatic field voltage of 12kV, and a material preheating temperature of 50℃.

[0051] The casein powder obtained in this embodiment was examined by scanning electron microscopy. The resulting SEM image is shown in Figure 2. It can be seen that the particle size distribution of the powder is uniform, with the overall particle size between 80 and 100 micrometers, and there is obvious collapse on the particle surface.

[0052] Example 2

[0053] This embodiment provides a highly soluble casein powder, the preparation method of which is as follows:

[0054] (1) Fresh raw milk is standardized after being processed to obtain standardized raw milk. The raw milk is processed by defatting, with a defatting temperature of 45℃ and a fat content of 0.05% in the defatted milk; the defatted milk is pasteurized, with a pasteurization temperature of 70℃ and a pasteurization time of 40s; (2) Microfiltration membrane separation process: The pasteurized defatted milk enters the microfiltration membrane separation equipment, with a separation temperature of 50℃, a transmembrane pressure of 0.15mPa, a concentration ratio of 4, a washing water flow rate: retentate flow rate ratio of 4:1, and the washing method is online addition washing; (3) Ultrafiltration membrane concentration process: The casein raw material liquid separated by microfiltration membrane enters the ultrafiltration membrane concentration process. The filter membrane equipment performs ultrafiltration concentration, with a concentration temperature of 10℃, a concentration pressure of 0.5mPa, and an online addition of washing filter. The ratio of washing water to total feed is 2:1. After concentration, the total solid content is 20%, the protein content is 18%, and the casein content accounts for 96% of the total protein content. (4) Drying process: The atomizing nozzle uses a pressure atomizer with an atomization pressure of 0.5mPa, an atomization temperature of 40℃, a protective gas of nitrogen, an inlet air temperature of 75℃, an outlet air temperature of 40℃, an electrostatic field voltage of 10kV, and a material preheating temperature of 45℃.

[0055] Example 3

[0056] This embodiment provides a highly soluble casein powder, the preparation method of which is as follows:

[0057] (1) Fresh raw milk is standardized after being processed to obtain standardized raw milk. The raw milk is processed by defatting, with a defatting temperature of 50℃ and a fat content of 0.06% in the defatted milk; the defatted milk is pasteurized, with a pasteurization temperature of 75℃ and a pasteurization time of 30s; (2) Microfiltration membrane separation process: The pasteurized defatted milk enters the microfiltration membrane separation equipment, with a separation temperature of 50℃, a transmembrane pressure of 0.2mPa, a concentration ratio of 3, a washing water flow rate: retentate flow rate ratio of 5:1, and the washing method is online addition washing; (3) Ultrafiltration membrane concentration process: The casein raw material liquid separated by microfiltration membrane enters the ultrafiltration membrane. The membrane equipment is used for ultrafiltration concentration, with a concentration temperature of 20°C, a concentration pressure of 0.4 MPa, and an online addition of washing filter. The ratio of washing filter water to total feed is 0.8:1. After concentration, the total solid content is 20%, the protein content is 19%, and the casein content accounts for 94% of the total protein content. (4) Drying process: The atomizing nozzle uses a pressure atomizer with an atomization pressure of 0.8 MPa, an atomization temperature of 40°C, a protective gas of nitrogen, an inlet air temperature of 70°C, an outlet air temperature of 40°C, an electrostatic field voltage of 14 kV, and a material preheating temperature of 50°C.

[0058] Example 4

[0059] This embodiment provides a highly soluble casein powder, the preparation method of which is as follows:

[0060] (1) Fresh raw milk is standardized after being processed to obtain standardized raw milk. The raw milk is processed by defatting, with a defatting temperature of 50℃ and a fat content of 0.06% in the defatted milk; the defatted milk is pasteurized, with a pasteurization temperature of 75℃ and a pasteurization time of 30s; (2) Microfiltration membrane separation process: the pasteurized defatted milk enters the microfiltration membrane separation equipment, with a separation temperature of 40℃, a transmembrane pressure of 0.13mPa, a concentration ratio of 5, a washing water flow rate: retentate flow rate ratio of 4:1, and the washing method is online addition washing; (3) Ultrafiltration membrane concentration process: the casein raw material liquid separated by microfiltration membrane enters The ultrafiltration membrane equipment is used for ultrafiltration concentration, with a concentration temperature of 10℃, a concentration pressure of 0.3mPa, and an online addition of washing filter. The ratio of washing water to total feed is 3:1. After concentration, the total solid content is 20%, the protein content is 17%, and the casein content accounts for 88% of the total protein content. (4) Drying process: The atomizing nozzle uses a pressure atomizer with an atomization pressure of 2mPa, an atomization temperature of 30℃, a protective gas of nitrogen, an inlet air temperature of 60℃, an outlet air temperature of 40℃, an electrostatic field voltage of 20kV, and a material preheating temperature of 50℃.

[0061] Example 5

[0062] This embodiment provides a highly soluble casein powder, the preparation method of which is as follows:

[0063] (1) Fresh raw milk is standardized after being processed to obtain standardized raw milk. The raw milk is processed by defatting, with a defatting temperature of 50℃ and a fat content of 0.06% in the defatted milk; the defatted milk is pasteurized, with a pasteurization temperature of 75℃ and a pasteurization time of 30s; (2) Microfiltration membrane separation process: the pasteurized defatted milk enters the microfiltration membrane separation equipment, with a separation temperature of 50℃, a transmembrane pressure of 0.1mPa, a concentration ratio of 3, a washing water flow rate: retentate flow rate ratio of 6:1, and the washing method is online addition washing; (3) Ultrafiltration membrane concentration process: the casein raw material liquid separated by microfiltration membrane enters The ultrafiltration membrane equipment is used for ultrafiltration concentration, with a concentration temperature of 14℃, a concentration pressure of 0.1mPa, and an online addition of washing filter. The ratio of washing water to total feed is 2:1. After concentration, the total solid content is 25%, the protein content is 19%, and the casein content accounts for 85% of the total protein content. (4) Drying process: The atomizing nozzle uses a pressure atomizer with an atomization pressure of 1mPa, an atomization temperature of 60℃, a protective gas of nitrogen, an inlet air temperature of 70℃, an outlet air temperature of 30℃, an electrostatic field voltage of 10kV, and a material preheating temperature of 60℃.

[0064] Example 6

[0065] This embodiment provides a highly soluble casein powder, the preparation method of which is as follows:

[0066] (1) Fresh raw milk is standardized after being processed to obtain standardized raw milk. The raw milk is defatting at 50°C and the fat content in the defatting milk is 0.06%. The defatting milk is pasteurized at 75°C for 30 seconds. (2) Microfiltration membrane separation process: The pasteurized defatting milk enters the microfiltration membrane separation equipment, where the separation temperature is 60°C, the transmembrane pressure is 0.18 mPa, the concentration ratio is 1, the ratio of washing water flow rate to retentate flow rate is 5:1, and the washing method is online addition washing. (3) Ultrafiltration membrane concentration process: The casein raw material liquid separated by microfiltration membrane enters the ultrafiltration membrane concentration process. The filter membrane equipment performs ultrafiltration concentration, with a concentration temperature of 20℃, a concentration pressure of 0.9mPa, and an online addition of washing filter. The ratio of washing filter water to total feed is 0.5:1. After concentration, the total solid content is 14%, the protein content is 19%, and the casein content accounts for 95% of the total protein content. (4) Drying process: The atomizing nozzle uses a pressure atomizer with an atomization pressure of 0.1mPa, an atomization temperature of 40℃, a protective gas of nitrogen, an inlet air temperature of 90℃, an outlet air temperature of 50℃, an electrostatic field voltage of 1kV, and a material preheating temperature of 40℃.

[0067] Example 7

[0068] This embodiment provides a highly soluble casein powder, the preparation method of which is as follows:

[0069] (1) Fresh raw milk is standardized after being processed to obtain standardized raw milk. The raw milk is processed by defatting, with a defatting temperature of 50℃ and a fat content of 0.06% in the defatted milk; the defatted milk is pasteurized, with a pasteurization temperature of 75℃ and a pasteurization time of 30s; (2) Microfiltration membrane separation process: The pasteurized defatted milk enters the microfiltration membrane separation equipment, with a separation temperature of 55℃, a transmembrane pressure of 0.2mPa, a concentration ratio of 4, a washing water flow rate: retentate flow rate ratio of 2:1, and the washing method is online addition washing; (3) Ultrafiltration membrane concentration process: The casein raw material liquid separated by microfiltration membrane enters the ultrafiltration membrane concentration process. The filter membrane equipment performs ultrafiltration concentration, with a concentration temperature of 18℃, a concentration pressure of 1mPa, and an online addition of washing filter. The ratio of washing filter water to total feed is 2.5:1. After concentration, the total solid content is 10%, the protein content is 17%, and the casein content accounts for 97% of the total protein content. (4) Drying process: The atomizing nozzle uses a pressure atomizer with an atomization pressure of 0.8mPa, an atomization temperature of 20℃, a protective gas of nitrogen, an inlet air temperature of 80℃, an outlet air temperature of 50℃, an electrostatic field voltage of 15kV, and a material preheating temperature of 30℃.

[0070] Comparative Example 1

[0071] This comparative example provides a conventional acid-processed casein powder.

[0072] Comparative Example 2

[0073] This comparative example provides a conventional enzymatic casein powder.

[0074] Comparative Example 3

[0075] This comparative example provides a casein powder, which differs from Example 1 in that step (4) uses a conventional spray drying process: inlet air temperature 150°C and outlet air temperature 80°C.

[0076] Figure 3 shows the SEM image of the MCC powder obtained by conventional spray drying in this comparative example. The particle size distribution is uneven, ranging from 60 to 200 micrometers. The morphology of the powder particles is different, with some particles having a collapsed surface and others having a smooth surface.

[0077] Comparative Example 4

[0078] This comparative example provides a casein powder, which differs from Example 1 in that step (4) is freeze-dried at a freezing temperature of -89°C.

[0079] Figure 4 is a SEM image of the MCC powder obtained by freeze-drying in this comparative example. It can be seen that the appearance of the freeze-dried MCC powder is different from that of the MCC powder obtained by spray drying in the embodiment of the present invention, and it is in the form of flake crystals.

[0080] Comparative Example 5

[0081] This comparative example provides a casein powder, which differs from Example 1 in that the concentration temperature in step (3) is 30°C.

[0082] Comparative Example 6

[0083] This comparative example provides a casein powder, which differs from Example 1 in that, in step (3), the total solids content after concentration is 40%.

[0084] Performance testing

[0085] The casein powders obtained in each embodiment and comparative example were subjected to performance tests, including:

[0086] 1. Static solubility test

[0087] Take the same mass of purified water and place it in a test tube. Pour the same mass of MCC powder into the test tube at the same time and observe the dissolution of the MCC powder under no external force conditions.

[0088] The results are shown in Figures 5 and 6. The samples with excellent solubility spontaneously and rapidly sank and dissolved during sedimentation, forming a white solution. The casein powder in the samples with poor solubility floated on the surface, with a significantly slower sedimentation rate, and the liquid color showed no obvious change. It can be seen that the static solubility of Examples 1-7 is significantly better than that of Comparative Examples 1-6, especially compared to Comparative Examples 1-4.

[0089] 2. Stability Test

[0090] Dissolve the same mass of MCC powder in pure water at 50℃ to prepare a 3% casein solution. Keep warm and stir to hydrate for 30 minutes. Let stand at room temperature for 8 hours to observe stability.

[0091] The results are shown in Figure 7-10. It can be seen from the figure that the highly soluble MCC solution prepared by the process in the example showed no obvious precipitate at the bottom of the bottle after standing, which proves that the solution is stable and has good solubility. The MCC powder prepared by the process in the comparative example had poor solubility after rehydration, and obvious precipitate could be observed at the bottom of the bottle, with only a small portion being soluble in water.

[0092] 3. Centrifugal sedimentation rate test

[0093] Referring to the national standard test method GB5413.29-2010, a method for quantifying the solubility of MCC powder was used. A lower centrifugal sedimentation rate indicates that more solute dissolves in the solvent, and the better the powder solubility. The results are shown in Table 1.

[0094] Table 1

[0095] 4. Dissolution rate test (dispersion determination)

[0096] Referring to the International Dairy Federation standard testing method IDF 87:1979, a method for quantifying the dissolution rate of MCC powder was used; the greater the dispersion, the faster the dissolution rate. The results are shown in Table 2.

[0097] Table 2

[0098] 5. Economic efficiency

[0099] The continuous production time and continuous powdering time of each embodiment and comparative example were statistically analyzed, and the results are shown in Table 3.

[0100] Table 3

[0101] The results above show that the casein powder obtained by the preparation method of the present invention has excellent solubility after reconstitution, and the preparation method of the present invention has high production efficiency, strong continuous production capability, and is economical.

[0102] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing casein powder, characterized in that, This includes the steps of microfiltration, ultrafiltration, and drying of skim milk. In the microfiltration step, the concentration ratio is 1-5; In the ultrafiltration step, an ultrafiltration membrane with a molecular weight of 30kDa-100kDa is used, the concentration temperature is 10-20℃, the concentration pressure is 0.1-1mPa, and the total solids content after concentration is 10-25%.

2. The method for preparing casein powder according to claim 1, characterized in that, In the microfiltration step, the ratio of washing water volume to retentate flow rate is 2:1-6:1; In the ultrafiltration step, the ratio of washing water to total feed is 0.5:1-3:

1.

3. The method for preparing casein powder according to claim 1 or 2, characterized in that, In the microfiltration step, the ratio of washing water volume to retentate flow rate is 4.5:1; In the ultrafiltration step, the ratio of washing water to total feed is 1:

1.

4. The method for preparing casein powder according to any one of claims 1-3, characterized in that, In the microfiltration step, a microfiltration membrane with a pore size of 0.1-0.2 micrometers is used, the separation temperature is 40-60℃, and the transmembrane pressure is 0.1-0.2mPa.

5. The method for preparing casein powder according to any one of claims 1-4, characterized in that, The drying process employs electrostatic spray drying.

6. The method for preparing casein powder according to any one of claims 1-5, characterized in that, In the electrostatic spray drying step, the atomizing nozzle uses a pressure atomizer with an atomization pressure of 0.1-2 mPa, an atomization temperature of 20-60℃, a protective gas of nitrogen, an inlet air temperature of 60-90℃, an outlet air temperature of 30-50℃, an electrostatic field voltage of 1-20 kV, and a material preheating temperature of 30-60℃.

7. The method for preparing casein powder according to any one of claims 1-6, characterized in that, The skimmed milk is obtained by standardizing raw milk, followed by skimming and pasteurization.

8. The method for preparing casein powder according to any one of claims 1-7, characterized in that, The fat content of the skim milk is 0.01-0.1%.

9. A casein powder, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The casein powder according to claim 9, characterized in that, The casein powder was tested according to GB5413.29-2010, and the centrifugal sedimentation rate was less than 28%. The casein powder was tested according to IDF 87:1979 and the dispersibility was greater than 46%.