Casein adhesive and method for its preparation

Abstract

The application provides a casein adhesive and a preparation method thereof. The method comprises the following steps: subjecting skimmed milk to ultrafiltration and nanofiltration in sequence to obtain a micellar casein concentrate; subjecting the micellar casein concentrate and a first additive to first mixing to obtain a first mixed solution, and subjecting the first mixed solution to ultra-high temperature treatment to obtain an ultra-high temperature treatment product; subjecting the ultra-high temperature treatment product and a second additive to second mixing to obtain a second mixed solution, and subjecting the second mixed solution to aging treatment to obtain the casein adhesive. Based on a physical modification method, the casein adhesive is prepared without using any toxic and harmful chemical reagent, the adhesive property of the casein is significantly improved, the casein adhesive is transparent, and the casein adhesive has good adhesion to various materials. Therefore, the casein adhesive has the advantages of high adhesion, high nutritional value, edibility, universality and safety, and can be used for bonding materials made of various materials. Moreover, the method is simple in operation, low in cost and suitable for large-scale production and application.

Description

Technical Field

[0001] This application relates to the food industry, and more specifically, to casein binders and methods for their preparation. Background Technology

[0002] With the development of the food industry, the demand for edible adhesives in food processing is increasing, such as in food shaping, edible packaging, and functional ingredient encapsulation. Casein, as a milk protein, has excellent film-forming properties and adhesive potential, making it an ideal base material for edible adhesives.

[0003] Currently, existing technologies include research on preparing adhesives using casein as a raw material, but most methods employ chemical modification, such as using toxic and harmful cross-linking agents like formaldehyde and glutaraldehyde, or compounding with inedible synthetic polymers. While these methods can improve adhesive performance to some extent, they inevitably introduce chemical residues, leading to biosafety risks and failing to meet the application requirements in the food industry. Furthermore, casein systems based on purely physical treatments or edible gum compounding often suffer from insufficient adhesive strength and poor stability, limiting their practical application.

[0004] Therefore, the preparation methods of casein adhesives still need further research. Summary of the Invention

[0005] This application aims to at least partially address the technical problems existing in the prior art. To this end, this application proposes a casein adhesive and its preparation method. This method, based on physical modification, significantly improves the adhesive properties of casein without the use of any toxic or harmful chemical reagents, resulting in a transparent adhesive with excellent adhesion to a variety of materials. The resulting casein adhesive possesses advantages such as high viscosity, high nutritional value, edibility, versatility, and safety, and can be used to bond various materials. Furthermore, this method is simple to operate, low in cost, and suitable for large-scale production applications.

[0006] In one aspect of this application, a method for preparing casein adhesive is provided. According to an embodiment of this application, the method includes the following steps:

[0007] The raw milk is centrifuged to obtain skim milk;

[0008] The skim milk was subjected to ultrafiltration treatment in sequence, and the ultrafiltration retentate was collected.

[0009] The ultrafiltration retentate is subjected to nanofiltration treatment, and the nanofiltration retentate is collected to obtain micellar casein concentrate;

[0010] The micelle casein concentrate is mixed with a first additive to obtain a first mixture, wherein the first additive includes an acidic substance.

[0011] The first mixture can be subjected to ultra-high temperature treatment to obtain an ultra-high temperature treated product.

[0012] The ultra-high temperature treatment product is mixed with the second additive to obtain a second mixture, wherein the second additive and the first additive form a buffer system.

[0013] The second mixture is subjected to aging treatment to obtain casein binder.

[0014] The inventors of this application discovered that by subjecting skim milk to ultra-high temperature (UHT) treatment, the casein micelle structure is disrupted through purely physical means, exposing active groups. The UHT-treated product is then aged to further enhance casein viscosity. Since casein is difficult to withstand ultra-high temperature conditions, an acidic first additive is added beforehand to adjust its pH value to withstand these conditions. Simultaneously, before aging, a second additive is added to provide an acidic buffer, creating a suitable acidic environment for the subsequent aging process and further enhancing the viscosity-enhancing effect. Furthermore, the inventors found that the concentration of metal ions in the system, especially calcium ions, affects the degree of casein micelle denaturation, thus affecting viscosity. Removing an appropriate amount of these ions is beneficial for increasing casein viscosity. Nanofiltration can remove some metal salts, and the addition of the second additive not only provides an acidic environment but also acts as a chelating agent to remove metal ions such as calcium and magnesium ions, thereby facilitating both the UHT treatment and aging modification, ultimately improving the overall viscosity of casein.

[0015] According to embodiments of this application, the first additive is selected from citric acid, and the second additive is selected from citrate.

[0016] According to embodiments of this application, the micelle casein concentrate satisfies at least one of the following conditions: electrical conductivity of 1700 μs / cm to 1900 μs / cm; calcium ion concentration of 3000 mg / kg to 3400 mg / kg; sodium ion concentration of 80 mg / kg to 90 mg / kg; and potassium ion concentration of 90 mg / kg to 110 mg / kg.

[0017] According to an embodiment of this application, the mass ratio of the first additive to the micelle casein in the micelle casein concentrate is (0.005~0.015):1.

[0018] According to an embodiment of this application, the mass ratio of the amount of the second additive to the micelle casein in the micelle casein concentrate is (0.005~0.05):1.

[0019] According to an embodiment of this application, the pH value of the first mixture is 5.0 to 6.0, and the pH value of the second mixture is 4.7 to 4.9.

[0020] According to an embodiment of this application, the ultrafiltration process satisfies at least one of the following conditions: the molecular weight cutoff of the ultrafiltration membrane is 50~300 kDa; the temperature of the ultrafiltration process is 40~60°C; and the pressure of the ultrafiltration process is 0.1~1.5 MPa.

[0021] According to an embodiment of this application, the nanofiltration process satisfies at least one of the following conditions: the molecular weight cutoff of the nanofiltration membrane is 200-500 Da; the temperature of the nanofiltration process is 40-60°C; the pressure of the nanofiltration process is 1-3 MPa; and the solid content of the micelle casein concentrate is 25-35% by mass.

[0022] According to an embodiment of this application, the ultra-high temperature treatment is performed at a temperature of 137~145℃ for a duration of 0.09~30 seconds.

[0023] According to an embodiment of this application, the aging treatment is performed at a temperature of 10~20°C for 4~24 hours.

[0024] According to an embodiment of this application, the preparation method further includes: spray drying the aged material; the inlet air temperature of the spray drying process is 160~200℃, and the outlet air temperature is 60~100℃.

[0025] According to an embodiment of this application, the preparation method further includes: reconstitute the powder obtained by spray drying to obtain a liquid; the reconstituted treatment includes: hydrating the powder with water at a mass ratio of (0.2~0.4):1, the hydration temperature being 50~70℃ and the time being 0.5~1.5 hours.

[0026] In another aspect of this application, a casein adhesive is proposed. According to an embodiment of this application, the casein adhesive is prepared using the aforementioned method for preparing casein adhesive. Therefore, the casein adhesive of this application possesses high viscosity, edibility, and safety.

[0027] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] Figure 1 A flowchart of a method for preparing casein adhesive according to an embodiment of this application is shown;

[0030] Figure 2 The image shows a physical photograph illustrating the bonding effect between wood materials according to an embodiment of this application;

[0031] Figure 3 The image shows a physical photograph illustrating the adhesive effect between paper materials according to an embodiment of this application;

[0032] Figure 4 This image shows a physical photograph illustrating the bonding effect between paper and glass materials according to an embodiment of this application.

[0033] Figure 5 The image shows a physical photograph of the adhesive effect of a food product according to an embodiment of this application;

[0034] Figure 6 The image shows a physical diagram of the clarity of food when an adhesive according to an embodiment of this application is used to bond food. Detailed Implementation

[0035] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0036] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0037] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0038] In this document, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this application but do not exclude other contents.

[0039] This application discloses a casein adhesive and its preparation method, which will be described in detail below.

[0040] Preparation method of casein binder

[0041] In one aspect of this application, a method for preparing a casein adhesive is provided. According to embodiments of this application, see [link to embodiment]. Figure 1 The method includes: S100 centrifugal separation treatment, S200 ultrafiltration treatment, S300 nanofiltration treatment; S400 first mixing treatment, S500 ultra-high temperature treatment, S600 second mixing treatment, and S700 aging treatment. Each step will be described in detail below.

[0042] S100 centrifugal separation process

[0043] In this step, the raw milk is centrifuged to obtain skim milk. Thus, centrifugation removes fat from the milk, resulting in skim milk.

[0044] S200 ultrafiltration treatment

[0045] In this step, the skim milk is subjected to ultrafiltration sequentially, and the ultrafiltration retentate is collected. This facilitates the concentration and removal of whey protein, lactose, and water.

[0046] According to embodiments of this application, the ultrafiltration process satisfies at least one of the following conditions:

[0047] Ultrafiltration membranes have a molecular weight cutoff of 50~300 kDa, for example 50 kDa, 100 kDa, 150 kDa, 200 kDa, 250 kDa, and 300 kDa;

[0048] The ultrafiltration treatment temperature is 40~60℃, for example 40℃, 45℃, 50℃, 55℃, 60℃;

[0049] The pressure of the ultrafiltration process is 0.1~1.5 MPa, for example 0.1 MPa, 0.2 MPa, 0.5 MPa, 0.8 MPa, 1.0 MPa, 1.2 MPa, 1.5 MPa.

[0050] Meeting the above ultrafiltration conditions can effectively remove whey protein, lactose, and water while retaining casein, thus achieving the purpose of concentration and impurity removal.

[0051] S300 nanofiltration treatment

[0052] In this step, the ultrafiltration retentate is subjected to nanofiltration, and the nanofiltration retentate is collected to obtain a concentrated micelle casein solution. The concentration of metal ions in the system, especially calcium ions, affects the degree of micelle casein denaturation, and thus the viscosity. Therefore, by using nanofiltration, some metal ions can be removed to improve the modification effect of micelle casein and increase its viscosity.

[0053] According to embodiments of this application, the nanofiltration process satisfies at least one of the following conditions:

[0054] Nanofiltration membranes have a molecular weight cutoff of 200~500 Da, for example 200 Da, 250 Da, 300 Da, 350 Da, 400 Da, 450 Da, and 500 Da;

[0055] The nanofiltration process is performed at a temperature of 40~60℃, for example, 40℃, 45℃, 50℃, 55℃, or 60℃.

[0056] The pressure of the nanofiltration process is 1~3 MPa, for example 1.5 MPa, 2 MPa, 2.5 MPa, 3 MPa;

[0057] The solids content of the micelle casein concentrate is 25-35% by mass, for example, 25% by mass, 26% by mass, 28% by mass, 30% by mass, 32% by mass, and 35% by mass.

[0058] Meeting the above nanofiltration conditions can effectively remove some metal ions, such as sodium and potassium ions, which not only effectively concentrates casein but also facilitates subsequent ultra-high temperature and aging treatments, further increasing the viscosity of casein. Furthermore, the resulting casein is clear and transparent, exhibiting excellent adhesion to various materials.

[0059] According to embodiments of this application, the micelle casein concentrate satisfies at least one of the following conditions:

[0060] The electrical conductivity is 1700 μs / cm to 1900 μs / cm, for example, 1700 μs / cm, 1750 μs / cm, 1800 μs / cm, 1850 μs / cm, and 1900 μs / cm.

[0061] The calcium ion concentration is 3000 mg / kg to 3400 mg / kg, for example, 3000 mg / kg, 3050 mg / kg, 3100 mg / kg, 3150 mg / kg, 3200 mg / kg, 3250 mg / kg, 3300 mg / kg, 3350 mg / kg, and 3400 mg / kg;

[0062] Sodium ion concentration is 80 mg / kg to 90 mg / kg, for example 80 mg / kg, 82 mg / kg, 85 mg / kg, 88 mg / kg, 90 mg / kg;

[0063] The potassium ion concentration is 90 mg / kg to 110 mg / kg, for example, 90 mg / kg, 95 mg / kg, 100 mg / kg, 105 mg / kg, and 110 mg / kg.

[0064] Therefore, this micellar casein concentrate has a suitable concentration of metal ions, which enables subsequent ultra-high temperature and aging treatments to achieve better denaturation conditions, thereby obtaining casein with high adhesion and clear transparency.

[0065] S400 First Mixing Process

[0066] In this step, the micelle casein concentrate is mixed with a first additive to obtain a first mixture, wherein the first additive includes an acidic substance. Adding the first additive to provide an acidic environment helps improve the heat resistance of the micelle casein and avoids precipitation or coagulation caused by localized short-term temperature changes.

[0067] According to embodiments of this application, the mass ratio of the first additive to the micelle casein in the micelle casein concentrate is (0.005~0.015):1, for example, 0.005:1, 0.006:1, 0.008:1, 0.010:1, 0.012:1, or 0.015:1. This provides a suitable acidic environment, improving the heat resistance of the micelle casein, thereby effectively denaturing it to increase its viscosity, while avoiding excessive acidity that could damage the micelle structure and cause casein precipitation, thus preventing pipe blockage.

[0068] According to an embodiment of this application, the pH value of the first mixture is 5.0 to 6.0. This provides a suitable acidic environment, enhancing the heat resistance of micelle casein, thereby effectively denaturing it to increase its viscosity, while preventing excessive acidity that could damage the micelle structure and cause casein precipitation, thus reducing the likelihood of clogging the pipeline.

[0069] S500 Ultra-High Temperature Processing

[0070] In this step, the first mixture is subjected to ultra-high temperature treatment to obtain an ultra-high temperature treated product. The casein micelle structure is disrupted by purely physical means to expose active groups, and then the ultra-high temperature treated product is aged to further enhance the viscosity of casein.

[0071] According to embodiments of this application, the ultra-high temperature treatment is performed at a temperature of 137~145℃ for a time of 0.09~30 seconds. In some embodiments, the ultra-high temperature treatment is performed at temperatures of 137℃, 139℃, 140℃, 142℃, and 145℃ for times of 0.09 seconds, 1 second, 5 seconds, 10 seconds, 15 seconds, 20 seconds, 25 seconds, and 30 seconds, respectively. This allows for a better degree of denaturation of the micelle casein, resulting in better adhesive properties and preventing excessive denaturation that could damage the micelle structure.

[0072] S600 Second Mixing Process

[0073] In this step, the ultra-high temperature treated product is mixed with a second additive to obtain a second mixture, whereby the second additive and the first additive form a buffer system. This provides a buffer environment for the aging process, which is beneficial for further improving casein viscosity. Simultaneously, some buffer salts can chelate metal salts in the system, separating them from the casein, which also helps to further improve casein viscosity.

[0074] According to embodiments of this application, the first additive is selected from citric acid, and the second additive is selected from citrate. Citric acid-citrate not only provides a suitable acidic buffering environment, which is beneficial for further improving casein viscosity during aging treatment, but also citrate can chelate metal salts in the system, such as calcium and magnesium ions, which also helps to improve casein viscosity. However, the overall effect of other buffer combinations is relatively low. For example, the pH range of lactic acid / lactate and malic acid / maltate buffers is too low, making it difficult to provide a suitable acidic buffering environment; the phosphate system has a weak chelating ability for calcium and magnesium ions (mainly chelating calcium ions, with a low magnesium ion content), and the acetic acid / acetate system has a weak calcium ion chelating ability.

[0075] According to embodiments of this application, the pH value of the second mixture is 4.7 to 4.9, for example, 4.7, 4.72, 4.75, 4.78, 4.8, 4.82, 4.85, 4.88, or 4.9. This provides an acidic environment, offering a continuous and stable environment for micellar casein denaturation, thereby further enhancing casein viscosity.

[0076] S700 Aging Treatment

[0077] In this step, the second mixture is aged to obtain a casein binder. This provides a continuous and stable environment for micellar casein denaturation, thereby further enhancing the casein's viscosity.

[0078] According to embodiments of this application, the aging treatment temperature is 10~20°C, and the time is 4~24 hours. In some embodiments, the aging treatment temperature is 10°C, 12°C, 15°C, 16°C, 18°C, or 20°C, and the time is 4 hours, 8 hours, 12 hours, 15 hours, 18 hours, 20 hours, or 24 hours, respectively. This results in a better degree of denaturation of the micelle casein, leading to better adhesive properties, avoiding excessive denaturation that could damage the micelle structure, reducing microbial residue and spoilage, and producing a clear and transparent casein with excellent adhesion to various materials.

[0079] According to an embodiment of this application, the preparation method further includes: spray drying the aged material; the inlet air temperature of the spray drying process is 160~200℃, and the outlet air temperature is 60~100℃. This allows the liquid material to be dried into powder, reducing the loss of active ingredients. Further, the spray-dried powder can be reconstituted with the supporting casein binder liquid under the following reconstitution conditions: the powder is reconstituted at a mass ratio of micelle casein powder:water = (0.2~0.4):1. The reconstitution water temperature is 50~70℃, and the hydration time is 0.5~1.5 hours.

[0080] According to an embodiment of this application, the preparation method includes:

[0081] 1. Raw milk standardization: Raw milk is standardized by adjusting its fat-to-protein ratio, controlling the protein content at 3.20-3.25% (w / w) and the total solids content at 13.00-13.10% (w / w) to ensure the stability of raw material composition and the consistency of the final product.

[0082] 2. Centrifugation: Standardized milk is centrifuged at 50~65℃ and 5000~8000 r / min to remove milk fat and obtain skim milk.

[0083] 3. Membrane separation and concentration:

[0084] Ultrafiltration (UF): Skim milk is initially concentrated using an ultrafiltration membrane with a molecular weight cutoff of 50~300 kDa under operating conditions of 40~60℃ and 0.1~1.5 MPa.

[0085] Nanofiltration (NF): Using a nanofiltration membrane with a molecular weight cutoff of 200–500 Da, the concentration is further achieved under operating conditions of 40–60 °C and 1–3 MPa. The final product is a micellar casein concentrate with a solids content of 25–35% (w / w).

[0086] 4. Food additive compound 1: Add citric acid to the nanofiltration concentrated micelle casein, with a mass ratio of citric acid to micelle casein of (0.005~0.015):1, stir for 2~4 hours to mix thoroughly.

[0087] 5. Ultra-high temperature physical modification: The above-mentioned micellar casein concentrate was subjected to ultra-high temperature transient (UHT) treatment at a temperature of 137~145℃ for 0.09~30 seconds. This step aims to disrupt the casein micelle structure through purely physical means, exposing active groups and laying the foundation for subsequent enhanced viscosity.

[0088] 6. Food Additive Compound 2: Add food-grade sodium citrate to the modified micellar casein system. The mass ratio of sodium citrate to micellar casein (on a dry basis) is (0.005~0.05):1. Mix thoroughly under stirring conditions.

[0089] 7. Aging: The compounded mixture is left to stand at a low temperature of 10~20℃ for 4~24 hours to allow the modification reaction and synergistic effect to proceed fully and thoroughly.

[0090] 8. Spray drying (if preparing powder): The aged material is spray dried, with the inlet air temperature controlled at 160~200℃ and the outlet air temperature controlled at 60~100℃, to obtain dried micelle casein binder powder.

[0091] 9. Reconstitution (if preparing a liquid): Reconstitute the spray-dried powder at a mass ratio of micelle casein powder to water of (0.2~0.4):1. The reconstitution temperature is 50~70℃, and the hydration time is 0.5~1.5 hours. After filling, a ready-to-use edible adhesive liquid is obtained.

[0092] Casein binder

[0093] In another aspect of this application, a casein adhesive is proposed. According to an embodiment of this application, the casein adhesive is prepared using the aforementioned method for preparing casein adhesive. Therefore, the casein adhesive of this application possesses high viscosity, edibility, and safety. It should be noted that the features and advantages described above regarding the preparation method of casein adhesive also apply to this casein adhesive, and will not be repeated here.

[0094] The casein binder and its preparation method of this application also have the following advantages:

[0095] (1) Excellent adhesive properties:

[0096] By modifying and activating casein at ultra-high temperatures, and through its synergistic effect with citrate, the adhesive strength of the final product is significantly improved. Testing shows that its 90° peel strength reaches 180 g / cm², a performance far exceeding that of traditional edible adhesives such as gelatin and starch, meeting the strength requirements for strong material bonding in food processing.

[0097] (2) Outstanding nutritional fortification function:

[0098] The base material used in this application—micelle casein (MCC)—is itself a high-quality milk protein with a complete structure and extremely high bioavailability. Its amino acid composition is balanced, making it a recognized source of high-quality protein. Furthermore, micellar casein naturally contains abundant calcium, which exists in the form of casein phosphopeptide-calcium complexes, making it easily absorbed by the human body.

[0099] As a protein supplement: the final product (whether in powder or liquid form) is itself a high-protein base. For example, the solid content of a reconstituted liquid can reach 30%, and the dry protein content can exceed 85%, making it a highly effective protein fortifier.

[0100] As a calcium supplement: The binder in this application is naturally rich in calcium, avoiding the problems of bitter taste or low absorption rate that may result from adding inorganic calcium. It is a natural, efficient and easily absorbed calcium fortification carrier.

[0101] This means that using the adhesive of this application for food processing (such as cereal bars, nutritional meal replacements, and healthy snacks) not only achieves the adhesive function, but also naturally achieves dual nutritional fortification of protein and calcium, thus achieving a perfect unity of "function and nutrition".

[0102] (3) Absolute safety and edibility:

[0103] This application fundamentally eliminates the use of toxic and harmful chemical reagents. All raw materials are food-grade, and the final product is safe and non-toxic. Third-party testing results show that the product's safety indicators are far superior to national standard limits.

[0104] (4) Extremely long shelf life and application flexibility:

[0105] Powder products have a shelf life of up to 24 months under normal temperature and dry conditions, while liquid products have a shelf life of up to 6 months under refrigeration. Users can choose flexibly according to their needs, greatly improving the commercial circulation and ease of use of the products.

[0106] The following will explain the solution of this application with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0107] Example 1

[0108] Prepare an edible casein adhesive powder with high bonding strength and high protein content using the following method:

[0109] 1. Raw material pretreatment: Raw milk is standardized (protein content 3.20%, total solids content 13w / w%) and centrifuged (55℃, 6500 r / min) to obtain skim milk.

[0110] 2. Membrane separation and concentration: Skim milk was subjected to ultrafiltration (100 kDa, 1.0 MPa, 50℃) and nanofiltration (300 Da, 2.0 MPa, 50℃) to obtain a micellar casein concentrate with a solids content of 30%, a conductivity of 1800 μs / cm, a calcium ion concentration of 3200 mg / kg, a sodium ion concentration of 85 mg / kg, and a potassium ion concentration of 100 mg / kg.

[0111] 3. Add citric acid, with a dry weight ratio of citric acid to micelle casein of 0.01:1, and stir to mix thoroughly. The pH of the mixture should be 5.5.

[0112] 4. Ultra-high temperature modification: treated at 142℃ for 4 seconds.

[0113] 5. Additive formulation: Add sodium citrate, with a dry basis mass ratio of sodium citrate to micelle casein of 0.015:1, stir and mix evenly, and the pH value of the mixture is 4.8.

[0114] 6. Aging: Let it stand at 15℃ for 8 hours to age.

[0115] 7. Spray drying: Inlet air temperature 190℃, outlet air temperature 100℃, to obtain adhesive powder.

[0116] Example 2

[0117] Prepare an edible casein adhesive powder with high bonding strength and high protein content using the following method:

[0118] 1. Raw material pretreatment: Raw milk is standardized (protein content 3.20%, total solids content 13.10 w / w%) and centrifuged (65℃, 5000 r / min) to obtain skim milk.

[0119] 2. Membrane separation and concentration: Skim milk was subjected to ultrafiltration (300 kDa, 0.1 MPa, 60℃) and nanofiltration (500 Da, 3.0 MPa, 40℃) to obtain a micellar casein concentrate with a solids content of 30%, a conductivity of 1700 μs / cm, a calcium ion concentration of 3000 mg / kg, a sodium ion concentration of 90 mg / kg, and a potassium ion concentration of 90 mg / kg.

[0120] 3. Add citric acid, with a dry weight ratio of citric acid to micelle casein of 0.005:1. Stir and mix thoroughly. The pH of the mixture should be 5.8.

[0121] 4. Ultra-high temperature modification: treated at 145℃ for 0.09 seconds.

[0122] 5. Additive formulation: Add sodium citrate, with a dry basis mass ratio of sodium citrate to micelle casein of 0.005:1, stir and mix evenly, and the pH value of the mixture is 4.72.

[0123] 6. Aging: Let it stand at 20℃ for 4 hours to age.

[0124] 7. Spray drying: Inlet air temperature 200℃, outlet air temperature 60℃, to obtain adhesive powder.

[0125] Example 3

[0126] Prepare an edible casein adhesive powder with high bonding strength and high protein content using the following method:

[0127] 1. Raw material pretreatment: Raw milk is standardized (protein content 3.25%, total solids content 13.00w / w%) and centrifuged (50℃, 8000 r / min) to obtain skim milk.

[0128] 2. Membrane separation and concentration: Skim milk was subjected to ultrafiltration (50 kDa, 1.5 MPa, 40℃) and nanofiltration (200 Da, 1.0 MPa, 60℃) to obtain a micellar casein concentrate with a solids content of 35%, a conductivity of 1900 μs / cm, a calcium ion concentration of 3400 mg / kg, a sodium ion concentration of 80 mg / kg, and a potassium ion concentration of 110 mg / kg.

[0129] 3. Add citric acid, with a dry weight ratio of citric acid to micelle casein of 0.015:1. Stir and mix thoroughly. The pH of the mixture should be 5.3.

[0130] 4. Ultra-high temperature modification: treated at 137℃ for 30 seconds.

[0131] 5. Additive formulation: Add sodium citrate, with a dry basis mass ratio of sodium citrate to micelle casein of 0.05:1, stir and mix evenly, and the pH value of the mixture is 4.75.

[0132] 6. Aging: Let it stand at 10℃ for 24 hours to age.

[0133] 7. Spray drying: Inlet air temperature 160℃, outlet air temperature 100℃, to obtain adhesive powder.

[0134] Example 4

[0135] The casein adhesive was prepared according to the method of Example 1, except that in step 3, the mass ratio of citric acid to micelle casein dry basis was 0.02:1, and the pH of the resulting mixture was 4.9.

[0136] Example 5

[0137] The casein adhesive was prepared according to the method of Example 1, except that in step 5, the mass ratio of sodium citrate to micelle casein dry basis was 0.08:1, and the pH of the resulting mixture was 5.13.

[0138] Example 6

[0139] The casein adhesive was prepared according to the method in Example 1, except that step 2 is as follows:

[0140] Membrane separation concentration: Skim milk was subjected to ultrafiltration (100 kDa, 1.0 MPa, 50℃) and nanofiltration (300 Da, 3.0 MPa, 55℃) to obtain a micellar casein concentrate with a solids content of 30%, a conductivity of 1963 μs / cm, a calcium ion concentration of 3570 mg / kg, a sodium ion concentration of 125 mg / kg, and a potassium ion concentration of 131 mg / kg.

[0141] Example 7

[0142] The casein adhesive was prepared according to the method in Example 1, except that step 2 is as follows:

[0143] Membrane separation concentration: Skim milk was subjected to ultrafiltration (100 kDa, 1.0 MPa, 50℃) and nanofiltration (500 Da, 1.0 MPa, 40℃) to obtain a micellar casein concentrate with a solid content of 30%, a conductivity of 1630 μs / cm, a calcium ion concentration of 2890 mg / kg, a sodium ion concentration of 77 mg / kg, and a potassium ion concentration of 81 mg / kg.

[0144] Example 8

[0145] Casein adhesive was prepared according to the method of Example 1, except that the aging temperature was 25°C.

[0146] Example 9

[0147] Casein adhesive was prepared according to the method of Example 1, except that the aging treatment time was 28 hours.

[0148] Example 10

[0149] Casein adhesive was prepared according to the method in Example 1, except that the ultra-high temperature modification temperature was 150°C and the time was 10 seconds.

[0150] Example 11

[0151] Casein adhesive was prepared according to the method in Example 1, except that the ultra-high temperature modification temperature was 130°C and the time was 2 seconds.

[0152] Example 12

[0153] The casein adhesive was prepared according to the method of Example 1, except that step 7 was omitted and the solution obtained from aging was used directly as the liquid.

[0154] Comparative Example 1

[0155] The casein adhesive was prepared according to the method in Example 1, except that...

[0156] Step 4 is as follows: Add 0.5% (w / w) of glutaraldehyde and react at 50°C for 2 hours.

[0157] Step 5 is excluded.

[0158] Comparative Example 2

[0159] The casein adhesive was prepared according to the method of Example 1, except that step 5 was omitted.

[0160] Comparative Example 3

[0161] The casein adhesive was prepared according to the method of Example 1, except that step 4 was omitted.

[0162] Comparative Example 4

[0163] Casein binder was prepared according to the method of Example 1, except that the nanofiltration step was omitted.

[0164] Comparative Example 5

[0165] The casein adhesive was prepared according to the method of Example 1, except that step 3 was omitted.

[0166] Comparative Example 6

[0167] The casein adhesive was prepared according to the method of Example 1, except that step 6 was omitted.

[0168] Comparative Example 7

[0169] Casein adhesive was prepared according to the method of Example 1, except that sodium citrate was replaced with sodium tripolyphosphate.

[0170] Comparative Example 8

[0171] Konjac gum and xanthan gum are mixed in a 1:1 mass ratio to obtain an adhesive.

[0172] Test case

[0173] The adhesives prepared in each embodiment and comparative example were tested under the following conditions:

[0174] I. Adhesion Strength

[0175] The adhesives prepared in Examples 1-12 and Comparative Examples 1-8 were subjected to a 90° peel strength test according to the following method:

[0176] 1. Test principle:

[0177] An adhesive is applied between two substrates to form an adhesive sample. After curing under specified temperature, humidity and time conditions, the two substrates are peeled off at a constant speed along a 90° direction using a universal testing machine, and the average peel force per unit width is measured.

[0178] 2. Sample preparation

[0179] Take a sample of adhesive powder, hydrate it at 60°C for 1 hour at a mass ratio of adhesive powder to water of 0.3:1, and then cool it to room temperature before use.

[0180] 3. Coating and bonding

[0181] 3.1 Clean the surface of the stainless steel sheet and PET film with anhydrous ethanol and let them air dry.

[0182] 3.2 Thoroughly stir the adhesive liquid until homogeneous, and apply it evenly to one end of the stainless steel plate using a coater. The coating size is 100 mm × 25 mm, and the coating amount is controlled at 15 ± 2 g / m². 2 ;

[0183] 3.3 Immediately align and adhere the PET film to the adhesive area, and roll it three times in one direction with a standard roller at a speed of approximately 10 mm / s to remove air bubbles;

[0184] 3.4 Place the bonded sample in a constant temperature and humidity chamber and cure for 24 hours at 23±2℃ and 50±5% RH.

[0185] 4. Test steps:

[0186] 4.1 Take out the cured sample and place it in the same temperature and humidity environment for 2 hours;

[0187] 4.2 Clamp the unbonded end of the stainless steel plate onto the upper fixture of the testing machine, and clamp the unbonded end of the PET film onto the lower fixture in the opposite direction, so that the peeling angle is 90° and the initial peeling length is about 20 mm.

[0188] 4.3 Set the tensile speed of the testing machine to 100±5 mm / min and start the test;

[0189] 4.4 The continuous peeling length shall not be less than 75 mm, and the force-displacement curve during the peeling process shall be recorded;

[0190] 4.5 Each sample shall be tested with no fewer than 5 valid specimens, and the arithmetic mean shall be taken.

[0191] 5. Result Calculation

[0192] 90° peel strength is calculated using the following formula:

[0193] σ = F / b

[0194] in:

[0195] σ—peel strength, expressed in grams per square centimeter (g / cm²) 2 );

[0196] F—The average force during the peeling process, in grams (g).

[0197] b—Sample width, in centimeters (cm).

[0198] Table 1 Adhesion Strength

[0199]

[0200] As can be seen from Table 1, the adhesive strength of the adhesives prepared in Examples 1-12 is better than that of Comparative Examples 2-8, with the adhesive strength of Examples 1-3 being even better.

[0201] The adhesives prepared in Examples 1-3 all exhibit good adhesive properties to various materials:

[0202] Figure 2 The bonding effect between wood materials. Figure 3 This refers to the adhesion effect between paper materials. Figure 4 This describes the bonding effect between paper and glass materials. Figure 5 For the adhesive effect of food, Figure 6 This refers to the clarity of food when using adhesives to bond it together.

[0203] II. Clarity

[0204] The adhesives prepared in Examples 1-12 and Comparative Examples 1-8 were subjected to clarification tests, and the specific methods are as follows:

[0205] 1. Test principle:

[0206] The transmittance of the adhesive solution at a specific wavelength was determined by spectrophotometry, and the clarity of the sample was quantitatively characterized by the transmittance value (%T). The higher the transmittance, the better the clarity and transparency of the sample.

[0207] 2. Sample preparation: Same as above.

[0208] 3. Preparation of reference solution: Distilled water is used as the reference solution for instrument zeroing.

[0209] 4. Test conditions: Measurement wavelength 600 nm, cuvette optical path: 10 mm, test temperature 25±2℃.

[0210] 5. Test steps:

[0211] 5.1 After the instrument is preheated, use distilled water to adjust the instrument zero point so that the transmittance display is 100.0%T;

[0212] 5.2 Rinse the quartz cuvette three times with the sample solution to be tested;

[0213] 5.3 Add the sample solution to the cuvette, filling it to approximately 3 / 4 of its volume, ensuring that there are no air bubbles in the light path;

[0214] 5.4 Place the cuvette into the sample cell, cover it with the dust cover, and read the transmittance value after stabilizing for 30 seconds;

[0215] 5.5 Each sample was measured in triplicate, and the sample was reloaded after each measurement;

[0216] 5.6 Record the transmittance values ​​T1, T2, and T3 for each measurement;

[0217] 5.7 Simultaneously measure the transmittance of the same batch of distilled water as a blank control T0 (the theoretical value should be 100.0%).

[0218] 6. Calculation results:

[0219] Clarity is expressed as the average transmittance, and the calculation formula is as follows:

[0220] T = (T1 + T2 + T3) / 3

[0221] in:

[0222] T—Clarity of the sample, %

[0223] T1, T2, T3 — transmittance values ​​from three parallel measurements.

[0224] The results are shown in Table 2. The adhesives prepared in Examples 1-12 have better clarity, with Examples 1-3 being even better.

[0225] Table 2 Clarity

[0226]

[0227] III. Protein and Calcium Content

[0228] The protein content and calcium ion content in the adhesives prepared in Examples 1-12 and Comparative Examples 1-8 were detected, respectively, using the following methods:

[0229] Protein detection reference: GB 5009.5-2016 National Food Safety Standard - Determination of Protein in Food

[0230] Calcium ion content detection reference: GB 5009.92-2016 National Food Safety Standard - Determination of Calcium in Food

[0231] The results are shown in Table 3. The adhesives prepared in Examples 1-12 have higher protein and calcium ion content, which can improve the nutritional value of the product. Among them, the adhesives prepared in Examples 1-3 are better.

[0232] Table 3 Protein and Calcium Content

[0233]

[0234] IV. Shelf life

[0235] The adhesives prepared in Examples 1-12 and Comparative Examples 1-8 were stored at room temperature. When obvious darkening of color, clumping, mold growth, etc. appeared, they were considered to have reached their shelf life.

[0236] The results are shown in Table 4. The adhesives prepared in Examples 1-12 have a longer shelf life, with Examples 1-3 being superior.

[0237] Table 4 Shelf life

[0238]

[0239] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for preparing a casein adhesive, characterized in that, include: The raw milk is centrifuged to obtain skim milk; The skim milk was subjected to ultrafiltration treatment in sequence, and the ultrafiltration retentate was collected. The ultrafiltration retentate is subjected to nanofiltration treatment, and the nanofiltration retentate is collected to obtain micellar casein concentrate; The micelle casein concentrate is mixed with a first additive to obtain a first mixture. The first mixture can be subjected to ultra-high temperature treatment to obtain an ultra-high temperature treated product. The ultra-high temperature treatment product is mixed with the second additive to obtain a second mixture, wherein the second additive and the first additive form a buffer system. The second mixture is subjected to aging treatment to obtain casein binder; The first additive is selected from citric acid, and the second additive is selected from citrate. The ultrafiltration treatment satisfies at least one of the following conditions: Ultrafiltration membranes have a molecular weight cutoff of 50~300 kDa; The temperature for the ultrafiltration process is 40~60℃; The pressure for the ultrafiltration process is 0.1~1.5 MPa; The nanofiltration process satisfies the following conditions: Nanofiltration membranes have a molecular weight cutoff of 200-500 Da; The temperature for nanofiltration is 40~60℃; The pressure for nanofiltration is 1~3 MPa; The solids content of the micelle casein concentrate is 25-35% by mass. The ultra-high temperature treatment is performed at a temperature of 137~145℃ for a time of 0.09~30 seconds. The aging treatment is performed at a temperature of 10~20℃ for 4~24 hours.

2. The preparation method according to claim 1, characterized in that, The micelle casein concentrate meets at least one of the following conditions: Electrical conductivity ranges from 1700 μs / cm to 1900 μs / cm. The calcium ion concentration is 3000 mg / kg to 3400 mg / kg; Sodium ion concentration is 80 mg / kg to 90 mg / kg; The potassium ion concentration is 90 mg / kg to 110 mg / kg.

3. The preparation method according to claim 1, characterized in that, The ratio of the amount of the first additive to the mass of micelle casein in the micelle casein concentrate is (0.005~0.015):1; The ratio of the amount of the second additive to the mass of micelle casein in the micelle casein concentrate is (0.005~0.05):

1.

4. The preparation method according to claim 1, characterized in that, The first mixture has a pH value of 5.0 to 6.0, and the second mixture has a pH value of 4.7 to 4.

9.

5. The preparation method according to claim 1, characterized in that, Further includes: The aged material is then subjected to spray drying. The inlet air temperature of the spray drying process is 160~200℃, and the outlet air temperature is 60~100℃.

6. The preparation method according to claim 5, characterized in that, Further includes: The powder obtained from the spray drying process is reconstituted to obtain a liquid; The reconstitution process includes hydrating the powder with water at a mass ratio of (0.2~0.4):1, wherein the hydration temperature is 50~70℃ and the time is 0.5~1.5 hours.

7. A casein adhesive, characterized in that, The casein adhesive is prepared by the method described in any one of claims 1 to 6.

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