Milk protein base material rich in beta-casein

Abstract

The invention discloses a milk protein base material rich in beta-casein and a preparation method of the milk protein base material. The method comprises the following steps: firstly, obtaining a casein micelle trapped fluid through a membrane separation technology, and secondly, promoting casein micelles to be partially dissociated and partially precipitated by adopting a pH conversion combined ultrasonic technology, so that the interaction between a casein monomer and whey protein is destroyed; adjusting the pH value of the solution to be neutral, and dissolving the casein; the preparation method comprises the following steps: adding calcium chloride to promote the aggregation of the alpha-casein by utilizing the sensitivity of the alpha-casein to calcium ions, and intercepting the alpha-casein by utilizing a membrane separation technology to realize the enrichment of the beta-casein so as to prepare the milk protein base material rich in the beta-casein. Compared with the traditional column chromatography technology, the technology has the advantages that the efficient enrichment of beta-casein and the efficient separation of alpha-casein can be realized through the membrane separation and pH conversion combined ultrasonic technology; in the separation process, only pH needs to be adjusted, other auxiliaries are not needed, and the process is environmentally friendly, simple, easy to implement and suitable for large-scale processing; the prepared milk protein base material rich in beta-casein can be used as a main material and a base material of infant food, and is high in nutritional value and wide in application prospect.

Description

Technical Field

[0001] The invention belongs to the field of food processing, and in particular relates to a milk protein base material rich in beta-casein and a preparation method thereof. Technical Background

[0002] Breast milk is the most ideal food for infants. The protein content is about 9~11g / L, mainly whey protein and casein, with a ratio of about 6:4; among them, casein is mainly β-casein. β-casein is rich in essential amino acids and is one of the important sources of amino acids in infant food. The main function of breast milk protein is to provide a source of essential amino acids for breastfed infants. It also participates in physiological activities and promotes infant health in many ways, including assisting in the digestion of lipids and carbohydrates, promoting the absorption of nutrients, antibacterial, prebiotic effects, participating in the improvement of immunity and promoting gastrointestinal development. After gastrointestinal digestion in the body, β-casein will produce casein phosphopeptide, which has been shown to form chelates with metal ions and promote the body's absorption of mineral nutrients.

[0003] When breast milk is insufficient or breastfeeding is impossible, infant formula should be chosen to ensure the normal growth and development of infants and young children, and the composition of breast milk is the gold standard for infant formula. The demand for infant formula in my country has increased year by year. According to statistics, the demand for infant milk powder in my country increased to 1.4583 million tons in 2020 and exceeded 1.7968 million tons in 2022. From January to February 2022, the import value of infant formula industry in my country was nearly US$600 million. It can be seen that the market demand for infant formula is huge, and the related base materials, auxiliary materials and nutritional enhancers industries have considerable prospects and huge development potential.

[0004] Existing formula milk powders are all made from cow's milk, simulating the composition of breast milk, and processed by nutrient compounding and protein ratio adjustment. However, the ratio of whey protein and casein in cow's milk protein is about 20:80, and casein is mainly αs-casein and β-casein. If there is a certain difference between the protein composition of formula milk powder and breast milk, it will seriously affect the subsequent digestion characteristics of milk protein and the functional activity after digestion of infants and young children. This requires that the protein ratio in cow's milk must be adjusted, the αs-casein content must be reduced, and β-casein must be enriched, so that it can be used as a raw material to develop infant formula milk powder to meet the needs of infant growth and development.

[0005] The casein structure in cow's milk is highly similar, the specific groups are not prominent, and it does not exist in the state of free monomers in milk protein, but forms supramolecular aggregates with a certain structure, which makes it extremely difficult to enrich and separate milk protein components. There are four monomers of casein in milk, including αs1-casein, αs2-casein, β-casein, and κ-casein. The four monomers are combined by calcium bridges and hydrophobic interactions to form nearly spherical particles with an average diameter of about 100nm, called casein micelles; among them, κ-casein is located on the surface of the micelles, while β-casein is wrapped inside the micelles. Therefore, it is very difficult to enrich β-casein, the existing separation process is complicated, the separation efficiency is not high, and the component extraction rate is low. In addition, cow's milk is easy to spoil, has high requirements for the storage environment, and the processing cycle is not too long, which makes it difficult to enrich β-casein and process the base materials of infant formula milk powder. There is still a lack of efficient and convenient β-casein enrichment technology.

[0006] In the early stage, the team conducted research on the structure and formation mechanism of casein micelles, analyzed the dissociation and aggregation rules of casein micelles in different pH systems, mastered the technology of regulating the structure of casein micelles, and on this basis, formed the independent intellectual property technology "Method for simultaneous separation of three main components of bovine casein", with the authorization number: ZL201711286755.2. In addition, based on the structure and properties of casein micelles, the team formed the independent intellectual property technology "Functional and easily digestible micellar casein powder and its preparation method", with the authorization number: ZL202110386435.4. The study found that due to high temperature sterilization, casein micelles bind to whey protein, and the casein micelles prepared by membrane separation contain some whey protein. In the subsequent separation process, the binding effect between whey protein and casein micelles must be destroyed first to increase the casein content. In addition, pH has a great influence on the structure of casein micelles, and the rate of pH change significantly affects the type and degree of dissociation of casein monomers in micelles.

[0007] Low-frequency ultrasound technology is a non-thermal processing technology that has emerged in recent years. Ultrasound can produce cavitation, thermal and microjet effects in liquid matrices, causing strong turbulence, generating high shear forces, and increasing the frequency of collisions between particles, thereby weakening particle agglomeration and changing their physical properties. The team's previous research found that ultrasound-assisted technology can promote changes in the structure of casein micelles and promote the dissociation of casein monomers.

[0008] Based on the above research conclusions, the present invention uses pH conversion technology combined with ultrasonic technology to promote partial dissociation of casein micelles, and then the undissociated micelles are aggregated by acidification, so that β-casein is enriched in the clear liquid; then by adjusting the pH to neutral, using the sensitivity of αs-casein to calcium ions, adding an appropriate amount of calcium chloride to promote αs-casein to form aggregates of a certain size, and finally intercepting them through ultrafiltration technology, thereby achieving the enrichment of β-casein. It has been determined that the β-casein content of the filtrate after drying is more than 40%, and the αs-casein content is less than 10%.

[0009] It can be seen that the milk protein base prepared by the technology of the present invention is rich in β-casein and whey protein, and can be used as infant formula milk powder and infant food base and main ingredients. The milk protein base does not require any heat treatment, enzyme treatment or other processes during preparation, and does not add other chemical reagents. It has the advantages of simple process, low processing cost, and natural green, and retains the nutritional value of milk protein to the greatest extent. The milk protein base can also be used as a functional food base to strengthen protein and improve the nutritional properties of the product. Summary of the invention

[0010] The technical problem to be solved by the present invention is, on the one hand, to achieve the enrichment of β-casein and reduce the content of αs-casein; on the other hand, to simplify the milk protein separation process, provide a simple and easy β-casein enrichment technology for industrial production, and achieve green and efficient preparation of base materials rich in different monomers of milk protein. In addition, the technology of the present invention not only enriches β-casein to form a milk protein base rich in β-casein, but also obtains a milk protein base rich in αs-casein, providing a variety of protein raw materials for the functional food industry.

[0011] The technical solution adopted by the present invention is: A milk protein base rich in beta-casein, comprising the following specific steps: (1) Preparation of casein micelle solution: sterilized milk was centrifuged and skimmed at 4000-6000g for 20-30min, the upper fat layer was discarded, the lower skim milk was collected, and the skim milk was concentrated using an ultrafiltration membrane with a molecular weight cutoff of 100kDa. The membrane inlet pressure was 0.5-1.0MPa, and the concentration factor was 3-5. Deionized water 3-6 times the volume of the skim milk raw material was added to dilute the retentate. After low-speed circulation balance for 20-60min, ultrafiltration was continued to concentrate 3-5 times to obtain the casein micelle retentate. (2) Ultrasonic-assisted alkalization treatment: Take 1000-2000 mL of casein micelle retentate, add 0.5-1.0 mol / L sodium hydroxide at a rate of 2-4 mL / min under magnetic stirring at 500-1000 r / min, adjust the pH to 10.0-11.0 and stabilize it, monitor the pH in real time during the addition process, and perform ultrasonic treatment on the solution every time the pH increases by 0.8-1.2; the diameter of the ultrasonic probe is 12.7 mm, the depth of immersion in the center of the sample is 2-4 cm, the ultrasonic frequency is 20 kHz, the amplitude is 20-40%, the ultrasonic time is 6-10 min, and the pulse mode is on for 3-5 s and off for 2-4 s; (3) Acidification treatment: hydrochloric acid with a concentration of 0.8-1.2 mol / L was added dropwise to the solution of step (2) at a rate of 2-4 mL / min, and the pH was adjusted to 5.0-5.5 and stabilized under magnetic stirring at 500-1000 r / min, and ultrasonic treatment was performed; the diameter of the ultrasonic probe was 12.7 mm, the depth of immersion in the center of the sample was 2-4 cm, the ultrasonic frequency was 20 kHz, the amplitude was 20-40%, the ultrasonic time was 6-10 min, and the pulse mode was on for 3-5 s and off for 2-4 s; (4) аs-casein aggregation: 0.5-1.0 mol / L sodium hydroxide was added to the solution of step (3) at a rate of 2-4 mL / min, and the pH was adjusted to be stable at 6.8-7.2 under magnetic stirring at 500-1000 r / min. 50-100 mL of 0.06-0.08 mol / L calcium chloride solution was added dropwise at a rate of 2-4 mL / min under magnetic stirring. After the addition, the solution was subjected to ultrasonic treatment; the diameter of the ultrasonic probe was 12.7 mm, the depth of immersion in the center of the sample was 2-4 cm, the ultrasonic frequency was 20 kHz, the amplitude was 20-40%, the ultrasonic time was 6-10 min, and the pulse mode was on for 3-5 s and off for 2-4 s; (5) Membrane separation: using the solution of step (4) as raw material, using an ultrafiltration membrane with a molecular weight cutoff of 50 kDa for concentration, the membrane inlet pressure is 0.5-1.0 MPa, the concentration multiple is 3-5, and the filtrate is a solution rich in β-casein and whey protein; (6) Spray drying: The retentate and filtrate solutions are spray dried respectively, with an inlet temperature of 130-150°C, an atomization pressure of 0.05-0.1 MPa, an impactor interval of 1 second, an impactor execution time of 1 second, and a material flow rate of 200-300 mL / h. After the filtrate is dried, a milk protein base rich in β-casein is obtained, and after the retentate is dried, a milk protein base rich in аs-casein is obtained.

[0012] Beneficial effects or advantages of the present invention: (1) The present invention utilizes pH conversion technology, takes casein micelles as raw materials, first partially dissociates them by slowly alkalizing them, promotes the dissolution of β-casein, and then further promotes the dissociation and dissolution of β-casein by slowly acidifying; finally, adjusts the pH of the solution to neutral, and achieves the aggregation of аs-casein by slowly adding calcium ions. The technology utilizes the distribution law of casein monomers in casein micelles and their precipitation characteristics, and cleverly promotes the separation of β-casein and аs-casein by pH conversion; the separation process only requires pH fine-tuning, and no other chemical reagents are added. The process is green and pollution-free, simple and feasible, and low in cost.

[0013] (2) The present invention uses casein micelles as raw material instead of skim milk, which greatly reduces the difficulty of enriching β-casein and simplifies the difficulty of enriching milk protein monomers. While achieving the enrichment of β-casein, the enrichment of аs-casein is also completed, and two milk protein bases rich in β-casein and аs-casein can be obtained at the same time, providing the food industry and the health care product industry with an optional milk protein monomer base. The separation process is gentle, and the nutritional value of the milk protein is retained to the maximum extent.

[0014] (3) The present invention uses ultrasound-assisted technology to promote the dissociation of casein micelles, weaken the non-covalent interaction between milk proteins, and promote the separation of casein monomers, so as to better enrich β-casein monomers. In addition, ultrasound treatment can effectively prevent the aggregation of acidified casein and prevent a large amount of β-casein from aggregating and precipitating with other milk proteins during the acidification process. In addition, under the action of cavitation and microfluidization generated by ultrasound, аs-casein fully interacts with calcium ions to form supramolecular aggregates, which are easier to separate by ultrafiltration technology.

[0015] In summary, the present invention utilizes pH conversion combined with ultrasonic technology to achieve the enrichment of β-casein, and develops two milk protein bases rich in β-casein and аs-casein, which provides high-quality raw materials for infant formula milk powder and also provides milk protein bases for the food and health care products industry; the processing process is simple, the product has a wide range of applications, and the market prospects are broad. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Attached Figure 1 These are the electrophoresis bands of the milk protein standard and the milk protein product in the examples of the present invention. DETAILED DESCRIPTION

[0017] In order to better understand the present invention, the present invention is further described below in conjunction with the accompanying drawings and examples, but the scope of protection claimed by the present invention is not limited to the scope described in the examples. The gel electrophoresis method in the examples is as follows.

[0018] The milk protein product was dissolved in deionized water to prepare an aqueous solution with a concentration of 2 mg / mL, and then mixed with the electrophoresis buffer at a volume ratio of 2:1. After boiling in a water bath for 4 minutes, the solution was centrifuged at 4000 r / min for 4 minutes. Then 10 μL of the supernatant was injected into the gel track and electrophoresed at a constant voltage of 130 V. The gel slices were stained in Coomassie Brilliant Blue R-250 staining solution and photographed after decolorization.

[0019] Example 1, a milk protein base rich in β-casein, the specific steps are as follows: (1) Preparation of casein micelle solution: sterilized milk was centrifuged and skimmed at 4000g for 30 min, the upper fat layer was discarded, the lower skim milk was collected, and the skim milk was concentrated using an ultrafiltration membrane with a molecular weight cutoff of 100 kDa. The membrane inlet pressure was 0.5 MPa, the concentration factor was 3, and 3 times the volume of deionized water as the skim milk raw material was added to dilute the retentate. After low-speed circulation balance for 20 min, ultrafiltration was continued to concentrate 3 times to obtain the casein micelle retentate. (2) Ultrasonic-assisted alkalization treatment: Take 1000 mL of casein micelle retentate, add 0.5 mol / L sodium hydroxide at a rate of 4 mL / min under magnetic stirring at 500 r / min, adjust the pH to 8.0, and then perform ultrasonic treatment on the solution. The diameter of the ultrasonic probe is 12.7 mm, the depth of immersion in the center of the sample is 2 cm, the ultrasonic frequency is 20 kHz, the amplitude is 20%, the ultrasonic time is 6 min, and the pulse mode is on for 3 s and off for 2 s. After the ultrasonic treatment, continue to add 0.5 mol / L sodium hydroxide at a rate of 4 mL / min under magnetic stirring at 500 r / min to adjust the pH to 9.0. Afterwards, the solution was treated with ultrasound, with the diameter of the ultrasound probe being 12.7 mm, the depth of immersion in the center of the sample being 2 cm, the ultrasonic frequency being 20 kHz, the amplitude being 20%, the ultrasonic time being 6 min, and the pulse mode being on for 3 s and off for 2 s; after the ultrasound was completed, 0.5 mol / L sodium hydroxide was added dropwise at a rate of 4 mL / min under 500 r / min magnetic stirring, and the pH was adjusted to 10.0, and the solution was treated with ultrasound, with the diameter of the ultrasound probe being 12.7 mm, the depth of immersion in the center of the sample being 2 cm, the ultrasonic frequency being 20 kHz, the amplitude being 20%, the ultrasonic time being 6 min, and the pulse mode being on for 3 s and off for 2 s.

[0020] (3) Acidification treatment: hydrochloric acid with a concentration of 0.8 mol / L was added dropwise to the solution of step (2) at a rate of 4 mL / min, and the pH was adjusted to 5.0 under magnetic stirring at 500 r / min. After stabilization, ultrasonic treatment was performed; the diameter of the ultrasonic probe was 12.7 mm, the immersion depth in the center of the sample was 2 cm, the ultrasonic frequency was 20 kHz, the amplitude was 20%, the ultrasonic time was 6 min, and the pulse mode was on for 3 s and off for 2 s.

[0021] (4) аs-casein aggregation: 0.5 mol / L sodium hydroxide was added to the solution of step (3) at a rate of 4 mL / min, and the pH was adjusted to be stable at 6.8 under magnetic stirring at 500 r / min. 50 mL of 0.06 mol / L calcium chloride solution was added dropwise at a rate of 4 mL / min under magnetic stirring. After the addition, the solution was subjected to ultrasonic treatment; the diameter of the ultrasonic probe was 12.7 mm, the depth of immersion in the center of the sample was 2 cm, the ultrasonic frequency was 20 kHz, the amplitude was 20%, the ultrasonic time was 6 min, and the pulse mode was on for 3 s and off for 2 s.

[0022] (5) Membrane separation: The solution of step (4) is used as raw material and concentrated using an ultrafiltration membrane with a molecular weight cutoff of 50 kDa. The membrane inlet pressure is 0.5 MPa, the concentration factor is 3, and the filtrate is a solution rich in β-casein and whey protein.

[0023] (6) Spray drying: The retentate and the filtrate were spray dried respectively, with an inlet temperature of 130°C, an atomization pressure of 0.05 MPa, an impactor interval of 1 s, an impactor execution time of 1 s, and a material flow rate of 200 mL / h. After the filtrate was dried, a milk protein base rich in β-casein was obtained, and after the retentate was dried, a milk protein base rich in аs-casein was obtained.

[0024] The gel electrophoresis results of the two base materials are shown in the attached figure. It was determined that the content of β-casein in the milk protein powder after the filtrate was dried was 43.75±2.13%; the content of аs-casein in the milk protein powder after the retentate was dried was 52.17±2.78%.

[0025] Example 2, a milk protein base rich in β-casein, the specific steps are as follows: (1) Preparation of casein micelle solution: sterilized milk was centrifuged and skimmed at 6000g for 20 min, the upper fat layer was discarded, the lower skim milk was collected, and the skim milk was concentrated using an ultrafiltration membrane with a molecular weight cutoff of 100 kDa. The membrane inlet pressure was 1.0 MPa, the concentration factor was 5, and 6 times the volume of deionized water as the skim milk raw material was added to dilute the retentate. After low-speed circulation balance for 60 min, ultrafiltration was continued to concentrate 5 times to obtain the casein micelle retentate. (2) Ultrasonic-assisted alkalization treatment: Take 2000 mL of casein micelle retentate, add 1.0 mol / L sodium hydroxide at a rate of 2 mL / min under magnetic stirring at 1000 r / min, adjust the pH to 8.2, and then treat the solution with ultrasound. The diameter of the ultrasound probe is 12.7 mm, the depth of immersion into the center of the sample is 4 cm, the ultrasonic frequency is 20 kHz, the amplitude is 40%, the ultrasonic time is 10 min, and the pulse mode is on for 5 s and off for 4 s; after the ultrasound is completed, continue to add 1.0 mol / L sodium hydroxide at a rate of 2 mL / min under magnetic stirring at 1000 r / min. After adjusting the pH to 9.4, treat the solution with ultrasound. The diameter of the ultrasound probe is 12.7 mm, the depth of immersion into the center of the sample is 4 cm, the ultrasonic frequency is 20 kHz, the amplitude is 40%, the ultrasonic time is 10 min, and the pulse mode is on for 5 s and off for 4 s. The ultrasonic mode was turned on for 5s and stopped for 4s. After the ultrasonic treatment, 1.0 mol / L sodium hydroxide was added dropwise at a rate of 2 mL / min under 1000 r / min magnetic stirring. After the pH was adjusted to 10.2, the solution was treated with ultrasound. The diameter of the ultrasonic probe was 12.7 mm, the depth of immersion in the center of the sample was 4 cm, the ultrasonic frequency was 20 kHz, the amplitude was 40%, the ultrasonic time was 10 min, and the pulse mode was turned on for 5s and stopped for 4s. After the ultrasonic treatment, 1.0 mol / L sodium hydroxide was added dropwise at a rate of 2 mL / min under 1000 r / min magnetic stirring. After the pH was adjusted to 11.0, the solution was treated with ultrasound. The diameter of the ultrasonic probe was 12.7 mm, the depth of immersion in the center of the sample was 4 cm, the ultrasonic frequency was 20 kHz, the amplitude was 40%, the ultrasonic time was 10 min, and the pulse mode was turned on for 5s and stopped for 4s.

[0026] (3) Acidification treatment: hydrochloric acid with a concentration of 1.2 mol / L was added dropwise to the solution of step (2) at a rate of 2 mL / min, and the pH was adjusted to 5.5 under magnetic stirring at 1000 r / min. After stabilization, ultrasonic treatment was performed; the diameter of the ultrasonic probe was 12.7 mm, the immersion depth in the center of the sample was 4 cm, the ultrasonic frequency was 20 kHz, the amplitude was 40%, the ultrasonic time was 10 min, and the pulse mode was on for 5 s and off for 4 s.

[0027] (4) аs-casein aggregation: 1.0 mol / L sodium hydroxide was added to the solution of step (3) at a rate of 2 mL / min, and the pH was adjusted to be stable at 7.2 under magnetic stirring at 1000 r / min. 100 mL of 0.08 mol / L calcium chloride solution was added dropwise at a rate of 2 mL / min under magnetic stirring. After the addition, the solution was subjected to ultrasonic treatment; the diameter of the ultrasonic probe was 12.7 mm, the depth of immersion in the center of the sample was 4 cm, the ultrasonic frequency was 20 kHz, the amplitude was 40%, the ultrasonic time was 10 min, and the pulse mode was on for 5 s and off for 4 s.

[0028] (5) Membrane separation: The solution of step (4) is used as raw material and concentrated using an ultrafiltration membrane with a molecular weight cutoff of 50 kDa. The membrane inlet pressure is 1.0 MPa, the concentration factor is 5, and the filtrate is a solution rich in β-casein and whey protein.

[0029] (6) Spray drying: The retentate and the filtrate were spray dried respectively, with an inlet temperature of 150°C, an atomization pressure of 0.1 MPa, an impactor interval of 1 s, an impactor execution time of 1 s, and a material flow rate of 300 mL / h. After the filtrate was dried, a milk protein base rich in β-casein was obtained, and after the retentate was dried, a milk protein base rich in аs-casein was obtained.

[0030] The gel electrophoresis results of the two base materials are shown in the attached figure. It was determined that the content of β-casein in the milk protein powder after the filtrate was dried was 48.67±1.86%; the content of аs-casein in the milk protein powder after the retentate was dried was 49.57±1.22%.

[0031] Example 3, a milk protein base rich in β-casein, the specific steps are as follows: (1) Preparation of casein micelle solution: sterilized milk was centrifuged and defatted at 5000 g for 25 min, the upper fat layer was discarded, and the lower layer of skim milk was collected. The skim milk was concentrated using an ultrafiltration membrane with a molecular weight cutoff of 100 kDa. The membrane inlet pressure was 0.75 MPa, the concentration factor was 4, and 4.5 times the volume of deionized water as the skim milk raw material was added to dilute the retentate. After low-speed circulation balance for 40 min, ultrafiltration was continued and concentrated by 4 times to obtain the casein micelle retentate.

[0032] (2) Ultrasonic-assisted alkalization treatment: 1500 mL of casein micelle retentate was added dropwise with 0.75 mol / L sodium hydroxide at a rate of 3 mL / min under magnetic stirring at 750 r / min. After adjusting the pH to 8.2, the solution was subjected to ultrasonic treatment. The diameter of the ultrasonic probe was 12.7 mm, the depth of immersion in the center of the sample was 3 cm, the ultrasonic frequency was 20 kHz, the amplitude was 30%, the ultrasonic time was 8 min, and the pulse mode was on for 4 s and off for 3 s. After the ultrasonic treatment, 0.75 mol / L sodium hydroxide was added dropwise at a rate of 3 mL / min under magnetic stirring at 750 r / min. The pH was adjusted to 8.2. After adjusting the pH to 9.4, the solution was treated with ultrasound, with the diameter of the ultrasound probe being 12.7 mm, the depth of immersion in the center of the sample being 3 cm, the ultrasonic frequency being 20 kHz, the amplitude being 30%, the ultrasonic time being 8 min, and the pulse mode being on for 4 s and off for 3 s; after the ultrasound was completed, sodium hydroxide with a concentration of 0.75 mol / L was continued to be added at a rate of 3 mL / min. After adjusting the pH to 10.5, the solution was treated with ultrasound, with the diameter of the ultrasound probe being 12.7 mm, the depth of immersion in the center of the sample being 3 cm, the ultrasonic frequency being 20 kHz, the amplitude being 30%, the ultrasonic time being 8 min, and the pulse mode being on for 4 s and off for 3 s.

[0033] (3) Acidification treatment: hydrochloric acid with a concentration of 1.0 mol / L was added dropwise to the solution of step (2) at a rate of 3 mL / min, and the pH was adjusted to 5.3 under magnetic stirring at 750 r / min. After stabilization, ultrasonic treatment was performed; the diameter of the ultrasonic probe was 12.7 mm, the depth of immersion in the center of the sample was 3 cm, the ultrasonic frequency was 20 kHz, the amplitude was 30%, the ultrasonic time was 8 min, and the pulse mode was on for 4 s and off for 3 s.

[0034] (4) аs-casein aggregation: 0.75 mol / L sodium hydroxide was added to the solution of step (3) at a rate of 3 mL / min, and the pH was adjusted to be stable at 7.0 under magnetic stirring at 750 r / min. 75 mL of 0.07 mol / L calcium chloride solution was added dropwise at a rate of 3 mL / min under magnetic stirring. After the addition, the solution was subjected to ultrasonic treatment; the diameter of the ultrasonic probe was 12.7 mm, the depth of immersion in the center of the sample was 3 cm, the ultrasonic frequency was 20 kHz, the amplitude was 30%, the ultrasonic time was 8 min, and the pulse mode was on for 4 s and off for 3 s.

[0035] (5) Membrane separation: The solution of step (4) is used as raw material and concentrated using an ultrafiltration membrane with a molecular weight cutoff of 50 kDa. The membrane inlet pressure is 0.75 MPa, the concentration factor is 4, and the filtrate is a solution rich in β-casein and whey protein.

[0036] (6) Spray drying: The retentate and the filtrate were spray dried respectively, with an inlet temperature of 140°C, an atomization pressure of 0.08 MPa, an impactor interval of 1 s, an impactor execution time of 1 s, and a material flow rate of 250 mL / h. After the filtrate was dried, a milk protein base rich in β-casein was obtained, and after the retentate was dried, a milk protein base rich in аs-casein was obtained.

[0037] The gel electrophoresis results of the two base materials are shown in the attached figure. According to the determination, the content of β-casein in the milk protein powder after the filtrate is dried is 52.33±2.12%; the content of аs-casein in the milk protein powder after the retentate is dried is 42.77±2.08%.

Claims

1. A milk protein base rich in β-casein, characterized in that The process includes the following steps and process conditions: (1) Preparation of casein micelle solution: sterilized milk was centrifuged and skimmed at 4000-6000g for 20-30min, the upper fat layer was discarded, the lower skim milk was collected, and the skim milk was concentrated using an ultrafiltration membrane with a molecular weight cutoff of 100kDa. The membrane inlet pressure was 0.5-1.0MPa, and the concentration factor was 3-5. Deionized water 3-6 times the volume of the skim milk raw material was added to dilute the retentate. After low-speed circulation balance for 20-60min, ultrafiltration was continued to concentrate 3-5 times to obtain the casein micelle retentate. (2) Ultrasonic-assisted alkalization treatment: Take 1000-2000 mL of casein micelle retentate and slowly add 0.5-1.0 mol / L sodium hydroxide under magnetic stirring to adjust the pH to 10.0-11.0 and stabilize it. Monitor the pH in real time during the addition process. Ultrasonic treatment is performed on the solution every time the pH increases by 0.8-1.

2. (3) Acidification treatment: slowly add hydrochloric acid with a concentration of 0.8-1.2 mol / L to the solution of step (2), adjust the pH of the solution to 5.0-5.5 and stabilize it under magnetic stirring, and then perform ultrasonic treatment; (4) аs-casein aggregation: slowly drop 0.5-1.0 mol / L sodium hydroxide into the solution of step (3), adjust the pH to 6.8-7.2 under magnetic stirring, then slowly drop 50-100 mL of 0.06-0.08 mol / L calcium chloride solution, and ultrasonically treat the solution; (5) Membrane separation: using the solution of step (4) as raw material, using an ultrafiltration membrane with a molecular weight cutoff of 50 kDa for concentration, the membrane inlet pressure is 0.5-1.0 MPa, the concentration multiple is 3-5, and the filtrate is a solution rich in β-casein and whey protein; (6) Spray drying: The retentate and the filtrate are spray dried respectively, with an inlet temperature of 130-150°C, an atomization pressure of 0.05-0.1 MPa, an impactor interval of 1 second, an impactor execution time of 1 second, and a material flow rate of 200-300 mL / h. After the filtrate is dried, a milk protein base rich in β-casein is obtained, and after the retentate is dried, a milk protein base rich in аs-casein is obtained.

2. A milk protein base rich in β-casein and a preparation method thereof according to claim 1, characterized in that: The casein micelle solution described in step (1) can also be a solution prepared by dissolving casein micelle powder in deionized water with a pH of 6.5 to 7.5, wherein the mass concentration of casein micelles is 6 to 10%.

3. A milk protein base rich in β-casein and a preparation method thereof according to claim 1, characterized in that: The ultrasonic treatment conditions described in steps (2), (3) and (4) are as follows: the diameter of the ultrasonic probe is 12.7 mm, the depth of immersion in the center of the sample is 2 to 4 cm, the ultrasonic frequency is 20 kHz, the amplitude is 20 to 40%, the ultrasonic time is 6 to 10 min, and the pulse mode is on for 3 to 5 s and off for 2 to 4 s; the dropping speed of the sodium hydroxide, hydrochloric acid and calcium chloride described in steps (2), (3) and (4) is 2 to 4 mL / min, and the magnetic stirring speed is 500 to 1000 r / min.

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