A clean label high protein milk concentrate and method of making the same

Abstract

This disclosure relates to the field of dairy processing technology, specifically a clean-label high-protein milk concentrate and its preparation method, comprising: S1, centrifuging raw milk to obtain skim milk; S2, ultrafiltration concentration of the skim milk at 10-15°C to obtain an ultrafiltration concentrate; S3, detecting the pH value of the ultrafiltration concentrate and adjusting it to 6.7-7.0 to obtain a pH-adjusted concentrate; S4, maintaining the concentrate at 10-15°C for 1-4 hours, then cooling it to 4-10°C and allowing it to stand for 4-12 hours to stabilize the concentrate system, followed by low-heat sterilization to obtain a high-protein milk concentrate. Combined with micellar reconstruction treatment, the resulting product can achieve long-term storage stability without the addition of phosphates, citrates, and colloidal stabilizers, and the entire process of low-temperature operation preserves the natural flavor, making it suitable for the clean-label high-protein dairy product field.

Description

Technical Field

[0001] This disclosure relates to the field of dairy processing technology, and more specifically, to a clean-label high-protein milk concentrate and its preparation method. Background Technology

[0002] High-protein milk concentrate is widely used in the processing of high-protein beverages, sports nutrition foods, special medical purpose formula foods, and dairy products such as coffee and ice cream. Currently, the industrial process mainly uses ultrafiltration membrane separation technology to concentrate raw milk to increase protein content and reduce lactose content.

[0003] As protein concentration increases, mineral salts such as calcium, magnesium, and phosphates in milk also accumulate, leading to changes in the ionic balance between casein micelles. This results in decreased thermal and storage stability, making the product prone to protein aggregation, precipitation, and even gelation during sterilization and storage. To address these issues, current technologies typically improve system stability by adding stabilizers such as phosphates, citrates, and gellan gum. However, these additives need to be listed in the ingredient list, which is insufficient to meet the needs of clean label products.

[0004] Furthermore, while existing technologies employ ultrafiltration membrane separation to regulate proteins, lactose, and other components in milk systems, they focus more on component separation efficiency and less on changes in the stability of the colloidal structure within the milk system after membrane separation. Particularly during high protein concentration, as protein concentration increases, the interactions between casein micelles strengthen, making the system prone to instability. Simultaneously, changes in the ratio of lactose and soluble components during membrane separation alter the environment of the casein micelles, leading to stability issues such as gelation and precipitation during subsequent sterilization and storage.

[0005] Meanwhile, existing high-protein milk concentrate production processes typically employ high-temperature membrane concentration and sterilization techniques, which can easily lead to the loss of natural flavor compounds and thermal denaturation of whey proteins, resulting in a cooked or oxidized taste in the product. Therefore, there is an urgent need to develop a method for preparing high-protein milk concentrate that achieves good storage stability without the addition of exogenous stabilizers and can better preserve the natural flavor of the milk source. Summary of the Invention

[0006] The purpose of this disclosure is to provide a clean label high-protein milk concentrate and its preparation method, which solves the technical problems of existing high-protein milk concentrates requiring the addition of exogenous stabilizers, insufficient storage stability, and flavor deterioration.

[0007] Other features and advantages of this disclosure will become apparent from the following detailed description, or may be learned in part from practice of this disclosure.

[0008] According to one aspect of this disclosure, a method for preparing a clean-label high-protein emulsion concentrate is provided, comprising: S1, the raw milk is centrifuged to remove fat, resulting in skimmed milk; S2, the skim milk is concentrated by ultrafiltration at 10-15°C to obtain ultrafiltration concentrate; S3, detect the pH value of the ultrafiltration concentrate, adjust it to 6.7-7.0, and obtain a concentrate with pH adjustment; S4. The concentrate is kept at 10-15℃ for 1-4 hours, then cooled to 4-10℃ and allowed to stand for 4-12 hours to allow the concentrate system to reach a stable state. Then, it is sterilized under low heat load to obtain high protein milk concentrate.

[0009] On the other hand, a clean-label high-protein milk concentrate is provided, prepared by the method described in any one of the aspects, wherein the high-protein milk concentrate satisfies: Protein content: 15%–18% (w / w); Fat content: ≤0.6% (w / w); Lactose content: ≤0.5% (w / w); Ash content: ≤0.8% (w / w); The casein micelles in the high-protein emulsion concentrate have an average particle size of 120–180 nm.

[0010] As can be seen from the above technical solutions, the exemplary embodiments disclosed herein possess at least the following advantages and positive effects: On the one hand, by employing a combination of centrifugal defatting to remove fat, low-temperature ultrafiltration to concentrate and enrich protein, and pH adjustment after ultrafiltration concentration, the problem of decreased system stability caused by the simultaneous enrichment of fat, lactose and mineral salts during high-protein milk concentration in existing technologies has been solved. This achieves the goal of increasing protein content while reducing fat and lactose content, and by adjusting pH to restore the concentrate to a suitable ionic environment and pH conditions, providing a favorable premise for the reconstruction of casein micelles.

[0011] On the other hand, by incorporating a micelle reconstruction treatment step after pH adjustment, the existing technology overcomes the problems of imbalanced casein micelle structure after membrane separation and protein aggregation and precipitation during sterilization and storage. This micelle reconstruction treatment, through a combination of staged cooling and long-term low-temperature static incubation, redistributes κ-casein on the surface of casein micelles, reforms the hydration layer, and achieves a new equilibrium of colloidal calcium phosphate, thereby restoring the casein micelle structure and improving the thermal and storage stability of the product.

[0012] On the other hand, by adopting a combination of low-temperature ultrafiltration and low-heat-load sterilization, the problem of loss of natural flavor substances caused by high-temperature concentration and high-temperature sterilization in existing technologies has been solved, thereby reducing the generation of cooking and oxidized flavors and improving the flavor quality of the product.

[0013] In summary, this disclosure constructs a stable casein micelle system through the synergistic effect of low-temperature ultrafiltration, pH adjustment, and micelle reconstruction. It achieves stable preparation of high-protein emulsion concentrate without relying on exogenous stabilizers such as phosphate, citrate, gellan gum, and xanthan gum, while taking into account the product's storage stability, thermal stability, and flavor quality.

[0014] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0015] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. In the drawings: Figure 1 This is a schematic diagram of the preparation method of a clean label high-protein emulsion concentrate according to the present invention. Detailed Implementation

[0016] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art.

[0017] Furthermore, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a thorough understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of the specific details, or other methods, components, steps, etc., can be employed. In other instances, well-known methods, implementations, or operations are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0018] The flowcharts shown in the accompanying drawings are merely illustrative and do not necessarily include all content and operations / steps, nor do they necessarily have to be performed in the described order. For example, some operations / steps can be broken down, while others can be combined or partially combined; therefore, the actual execution order may change depending on the specific circumstances.

[0019] Existing technologies typically use ultrafiltration for protein concentration and lactose removal, focusing primarily on increasing protein content, reducing lactose content, and improving concentration efficiency. However, the inventors discovered that when the protein concentration exceeds 15%, the key factor affecting system stability is not the protein content itself, but rather the change in casein micelle stability caused by alterations in mineral salt composition during ultrafiltration concentration. During ultrafiltration, protein and mineral salts are simultaneously enriched, significantly altering the ionic environment of the concentrate. This disrupts the charge distribution on the casein micelle surface and the colloidal calcium phosphate balance, leading to a metastable micelle structure. Existing technologies often proceed directly to sterilization after ultrafiltration concentration, neglecting the resulting non-equilibrium state in the micelle system. This makes the product prone to structural evolution during subsequent storage, leading to problems such as gelation, precipitation, and flavor deterioration. Therefore, additional phosphates, citrates, or colloidal stabilizers are often required to maintain product stability. Furthermore, the high temperatures of ultrafiltration and sterilization processes result in significant loss of natural flavor compounds in milk, resulting in a product with significantly lower flavor quality than fresh milk.

[0020] To address this issue, this invention provides a method for preparing a clean-label high-protein milk concentrate. Unlike existing technologies that simply use membrane separation for component concentration, this invention utilizes centrifugation to remove the impact of fat on membrane flux, effectively increasing the ultrafiltration concentration factor. Low-temperature ultrafiltration is employed to enrich protein while minimizing flavor loss. After ultrafiltration concentration, pH adjustment restores the concentrate to a suitable ionic environment and pH conditions, providing favorable conditions for the stabilization of casein micelles. Following pH adjustment, a micelle reconstruction treatment is implemented, combining staged cooling with prolonged low-temperature settling to allow the casein micelles to transition from a metastable state to a thermodynamically stable state. Finally, low-heat sterilization is performed. The resulting high-protein milk concentrate has a protein content of 15%–18%, exhibits no precipitation or gelation after 6 months of storage at 4°C, and requires no added stabilizers, thus achieving the preparation of a clean-label high-protein milk concentrate.

[0021] In one embodiment, such as Figure 1 As shown, a method for preparing a clean-label high-protein emulsion concentrate is provided, comprising the following steps: S1, the raw milk is centrifuged to remove fat, resulting in skimmed milk.

[0022] S2, the skim milk is concentrated by ultrafiltration at 10-15°C to obtain ultrafiltration concentrate.

[0023] S3, detect the pH value of the ultrafiltration concentrate, adjust it to 6.7-7.0, and obtain the pH-corrected concentrate.

[0024] S4. The concentrate is kept at 10-15℃ for 1-4 hours, then cooled to 4-10℃ and allowed to stand for 4-12 hours to allow the concentrate system to reach a stable state. Then, it is sterilized under low heat load to obtain high protein milk concentrate.

[0025] In one embodiment, step S1 includes: S1.1, After cooling the raw milk to 2-6°C, preheat it to 45-55°C; S1.2, the preheated raw milk is centrifuged at 6500-7500 rpm, and the heavy phase outlet flow rate is controlled at 950-1000 L / h to obtain skim milk with a fat content ≤0.6% (w / w). The skim milk is then cooled to 4-10℃ for later use.

[0026] Raw milk is cooled to 2–6°C and then preheated to 45–55°C. Too low a preheating temperature will result in insufficient fat separation efficiency, while too high a temperature will easily lead to protein denaturation. Centrifugation is performed at 6500–7500 rpm, controlling the heavy phase outlet flow rate at 950–1000 L / h. Too low a speed or too high a flow rate will not effectively remove fat, while too high a speed may generate excessive foam or affect the separation effect. After centrifugation, skim milk with a fat content ≤0.6% (w / w) is obtained. The skim milk is then cooled to 4–10°C for later use.

[0027] In this step, centrifugation removes most of the fat, preventing it from contaminating the membrane surface and causing a decrease in membrane flux during subsequent ultrafiltration. This allows the ultrafiltration concentration factor to be increased to 2.5–5 times, and the protein content to reach 15%–18%. In some preferred embodiments, the fat content of the skim milk after centrifugation is further reduced to ≤0.1% (w / w) to minimize the impact of fat on membrane flux.

[0028] In one embodiment, step S2 includes: S2.1, Adjust the temperature of the skim milk to 12-14℃, pump in a ceramic ultrafiltration membrane module with a molecular weight cutoff of 10-20 kDa, control the transmembrane pressure to 0.2-0.4 MPa, the circulation flow rate to 3-5 m / s, and the concentration factor to 2.5-5 times; A molecular weight cutoff below 10 kDa results in the retention of some proteins, while simultaneously increasing the retention rates of lactose and minerals, hindering the removal of lactose and mineral salts with the permeate. A molecular weight cutoff above 20 kDa may cause some low-molecular-weight whey proteins (approximately 14-18 kDa) to permeate through the membrane, affecting protein recovery. The transmembrane pressure should be controlled at 0.2–0.4 MPa, the circulation flow rate at 3–5 m / s, and the concentration factor at 2.5–5 times. A transmembrane pressure below 0.2 MPa results in insufficient membrane flux, while a pressure above 0.4 MPa can exacerbate membrane fouling or protein deposition. A circulation flow rate below 3 m / s results in insufficient membrane shear force, allowing contaminants to accumulate on the membrane surface, while a flow rate above 5 m / s leads to excessive energy consumption and potential mechanical damage to the membrane module.

[0029] S2.2 During ultrafiltration, the membrane surface is cleaned by backwashing every 20–30 minutes to maintain a membrane flux ≥20 L / (m²). 2 When the protein content in the concentrate reaches 15%–18% (w / w), stop ultrafiltration and collect the ultrafiltration concentrate.

[0030] In this step, the low-temperature ultrafiltration conditions of 10–15°C effectively inhibit microbial proliferation while avoiding the thermal destruction of natural flavor substances in milk (such as lactones, methyl ketones, sulfides, etc.) by high temperatures, making the finished product flavor close to that of fresh milk. In some preferred embodiments, the ratio of transmembrane pressure to circulation flow rate is controlled at 0.05–0.1 MPa·s / m, and the temperature fluctuation throughout the ultrafiltration process is ≤±1°C to ensure stable membrane flux and process reproducibility.

[0031] In one embodiment, step S3 includes: S3.1, Adjust the temperature of the ultrafiltration concentrate to 10-15℃, stir slowly at 40-60 rpm, and add food-grade sodium hydroxide dropwise as a processing aid to the concentrate, controlling the addition rate to ensure that the pH change rate of the concentrate does not exceed 0.05 / min. The sodium hydroxide, used as a processing aid in the food industry, plays a regulatory role during the pH readjustment process. During this process, sodium hydroxide reacts with acidic substances in the concentrate to neutralize them, producing sodium salt and water. After the readjustment is complete, the pH of the concentrate returns to a neutral range of 6.7-7.0, consistent with the natural pH of raw milk. The system does not contain any residual free sodium hydroxide used as an ingredient, complying with the requirements of GB 2760 for the use of processing aids.

[0032] Adding the casein micelles too quickly can cause the local pH to deviate excessively from the target value, resulting in drastic fluctuations in the surface charge of the casein micelles and inducing hydrophobic aggregation between micelles. Adding the casein micelles too slowly prolongs the conditioning time, increasing energy consumption and microbial risk. Adjusting the pH to 6.7–7.0, which is consistent with the natural pH range of raw milk, allows the negative charge carried by κ-casein on the surface of the casein micelles to maintain a suitable electrostatic repulsion, preventing micelle aggregation or structural loosening due to pH deviation, while providing a stable initial state for subsequent micelle reconstruction.

[0033] S3.2, monitor the pH of the concentrate in real time. When the pH reaches 6.7–7.0, stop adding the regulator and continue stirring for 5–10 minutes to homogenize the system, obtaining the concentrated solution after pH adjustment. Throughout this step, the temperature is controlled at 10–15℃ to avoid thermal disturbance to the casein micelle structure caused by temperature fluctuations. Low temperature also reduces the frequency of micelle collisions, minimizing the risk of micelle aggregation caused by local environmental changes during adjustment. Because lactose and mineral salts are enriched simultaneously with proteins during ultrafiltration concentration, the pH of the concentrate usually shifts. Adjusting it to the neutral range restores the ionic environment and pH conditions of the concentrate to a suitable state, providing a stable system basis for subsequent adjustment of the casein micelle structure under low-temperature static conditions.

[0034] In some preferred embodiments, the concentrate after pH adjustment meets the following condition: the average particle size change rate of casein micelles is ≤10%. This indicator is used to characterize that no significant aggregation or dissociation of micelles occurs during the pH adjustment process, ensuring that the disturbance to the micelle structure caused by the adjustment operation is controlled within an acceptable range, thereby providing an initial micelle system with good structural integrity for subsequent micelle reconstruction.

[0035] In one embodiment, step S4 includes: S4.1, transfer the concentrate to a sealed equilibrium tank, maintain it at 10-15°C for 1-4 hours, cool it down to 4-10°C at a rate of 0.5-1°C / min, and let it stand at this temperature for 4-12 hours. During the standing period, keep the system in a state of no stirring and no shearing. Although the pH adjustment operation restores the pH of the concentrate to the neutral range, local pH fluctuations and changes in the ionic environment during the addition of the regulator can still disturb the structure of casein micelles to some extent, causing the micelles to deviate from their original thermodynamic equilibrium. If heat sterilization is performed directly after pH adjustment, the micelles are prone to aggregation and precipitation when heated while the pH disturbance is not fully restored. Therefore, after pH adjustment, the micelles are first kept at 10–15°C for 1–4 hours to allow them to initially adapt to the adjusted ionic environment and pH conditions, avoiding structural disorder caused by sudden environmental changes. Then, the temperature is lowered to 4–10°C at a rate of 0.5–1°C / min and allowed to stand at this temperature for 4–12 hours. A cooling rate lower than 0.5°C / min results in an excessively long production cycle and a significant increase in energy consumption; a rate higher than 1°C / min causes the micelles to shrink or become structurally disordered due to thermal shock, which is not conducive to uniform reconstruction. During the settling period, the system is kept in a state of no stirring and no shearing, allowing the κ-casein on the surface of the casein micelles to redistribute under the drive of hydrophobic interactions and hydrogen bonds. The hydration layer on the surface of the micelles reforms, and colloidal calcium phosphate (CCP) reaches a new dissolution equilibrium. Ultimately, the micelles transition from a metastable state to a thermodynamically stable state, forming a casein micelle system with uniform particle size distribution and stable structure.

[0036] S4.2, the micelle size change is monitored by an online particle size analyzer. When the deviation between two consecutive particle size detection results does not exceed 5%, the micelle reconstruction is determined to be complete. The reconstructed concentrate is degassed under -0.064 to -0.08 MPa to remove dissolved oxygen and bubbles. Microfiltration sterilization is performed by passing the concentrate through a ceramic membrane with a pore size of 0.1 to 0.5 μm for cold sterilization. Then, pasteurization is carried out at 72 to 75 °C for 15 s to obtain a high-protein emulsion concentrate.

[0037] Micellar particle size changes are monitored using an online particle size analyzer. When the deviation between two consecutive particle size measurements does not exceed 5%, micelle reconstruction is considered complete. In this step, low-temperature static equilibration treatment gradually stabilizes the casein micelle structure, manifested as a decrease in particle size distribution width and improved micelle dispersion stability. The reduction in particle size and narrowing of the distribution width indicate that the micelle structure is becoming more homogeneous and stable. The larger particle size before reconstruction is usually caused by reversible micelle aggregation due to changes in the ionic environment during ultrafiltration concentration. With the redistribution of the κ-casein surface layer and the reconstruction of colloidal calcium phosphate equilibrium during reconstruction, these aggregated structures gradually dissociate and form more homogeneous and stable micelles, thus providing a structural basis for subsequent heat sterilization. After reconstruction, the concentrate is degassed at -0.064 to -0.08 MPa to remove dissolved oxygen and bubbles, preventing bubble expansion during subsequent sterilization that could lead to boiling over or product oxidation. Microfiltration sterilization is employed, using a ceramic membrane with a pore size of 0.1–0.5 μm for cold sterilization, followed by pasteurization at 72–75 °C for 15 seconds to obtain a high-protein milk concentrate. In this step, the low-heat sterilization method of microfiltration combined with pasteurization avoids the thermal denaturation of whey proteins and further damage to flavor compounds caused by UHT sterilization at 137–142 °C. Simultaneously, microfiltration effectively removes microorganisms from the system, reducing the microbial load in the product and improving its storage safety. In some preferred embodiments, low-temperature UHT sterilization at 125–130 °C for 2–4 seconds can also be used to adapt to different production line configurations.

[0038] The aforementioned micelle reconstruction treatment refers to the process in which, during the membrane separation and concentration process, the relative proportions of protein, lactose, and mineral salt components change, leading to alterations in the ionic environment, hydration state, and colloidal stability of casein micelles. Under low-temperature static conditions, the casein micelles are restored to a stable dispersion state through molecular diffusion, ion balance adjustment, and recovery of the hydration layer on the micelle surface.

[0039] After ultrafiltration, the proteins in the milk system are in a highly concentrated state, the distance between casein micelles is shortened, and the charge environment and hydration state of the micelle surface change. If heat treatment is performed directly, it can easily induce micelle aggregation, particle size increase, and continuous structural changes during storage. This application reduces the tendency of micelle aggregation and improves the stability of the concentrated milk system by setting a static equilibrium stage under low temperature conditions, allowing the milk system to complete structural adjustment before heat treatment.

[0040] The high-protein milk concentrate prepared by the above method has a protein content of 15%–18% (w / w), a fat content of ≤0.6% (w / w), a lactose content of ≤0.5% (w / w), and an ash content of ≤0.8% (w / w). The average particle size of the casein micelles is 120–180 nm. This concentrate does not contain any phosphates, citrates, gellan gum, or xanthan gum. The ingredient list contains only raw milk. Sodium hydroxide is used only as a processing aid for pH adjustment and is neutralized and consumed during subsequent processing; it is not used as a product ingredient and meets clean labeling requirements. Example 1:

[0041] 1000 kg of raw milk was cooled to 4°C and then preheated to 50°C. It was then centrifuged at 7500 rpm, and the flow rate of the heavy phase outlet was controlled at 950 L / h to obtain skim milk with a fat content of 0.08% (w / w). The skim milk was then cooled to 4°C for later use.

[0042] The skim milk temperature was adjusted to 13℃, and a ceramic ultrafiltration membrane module with a molecular weight cutoff of 10 kDa was pumped in. The transmembrane pressure was controlled at 0.3 MPa, the circulation flow rate at 4 m / s, and the concentration factor at 4.0 times. During ultrafiltration, the membrane surface was cleaned by backwashing every 25 minutes to maintain a membrane flux ≥22 L / (m²). 2 (h) When the protein content in the concentrate reaches 16-18% (w / w), ultrafiltration is stopped, and approximately 200 kg of ultrafiltration concentrate is collected. Testing revealed that the pH of the ultrafiltration concentrate was 6.3, the lactose content was 0.4% (w / w), and the ash content was 0.6% (w / w).

[0043] The temperature of the ultrafiltration concentrate was adjusted to 12℃, and the solution was slowly stirred at 50 rpm. A 5% (w / w) food-grade sodium hydroxide solution was added dropwise to the concentrate, controlling the addition rate to ensure that the pH change rate did not exceed 0.05 / min. The pH value of the concentrate was monitored in real time. When the pH reached 6.8, the addition of alkali solution was stopped, and stirring was continued for 8 minutes to homogenize the system, resulting in a concentrate with pH adjustment. The temperature was controlled at 12℃ ± 0.5℃ throughout the process. The average particle size change rate of casein micelles in the concentrate after pH adjustment was measured to be 3.2%.

[0044] The concentrated solution after pH adjustment was transferred to a sealed equilibrium tank and maintained at 12°C for 2 hours. Then, it was cooled to 6°C at a rate of 0.8°C / min and allowed to stand at this temperature for 8 hours, during which time the system was kept in a state of no stirring and no shearing. The micelle size change was monitored using an online particle size analyzer. When the deviation between two consecutive particle size measurements was 2.5%, micelle reconstruction was considered complete.

[0045] The reconstituted concentrate was degassed at -0.07 MPa for 15 minutes to remove dissolved oxygen and air bubbles. It was then cold sterilized by passing it through a ceramic membrane with a pore size of 0.2 μm, followed by pasteurization at 73℃ for 15 seconds, and then refrigerated and filled to obtain a high-protein milk concentrate. Example 2:

[0046] 1000 kg of raw milk was cooled to 2°C and then preheated to 45°C. It was then centrifuged at 6500 rpm, and the flow rate of the heavy phase outlet was controlled at 1000 L / h to obtain skim milk with a fat content of 0.15% (w / w). The skim milk was then cooled to 4°C for later use.

[0047] The skim milk temperature was adjusted to 12℃, and a ceramic ultrafiltration membrane module with a molecular weight cutoff of 15 kDa was pumped in. The transmembrane pressure was controlled at 0.25 MPa, the circulation flow rate at 3.5 m / s, and the concentration factor at 3.5 times. During ultrafiltration, the membrane surface was cleaned by backwashing every 20 minutes to maintain a membrane flux ≥ 21 L / (m²). 2 (h) When the protein content in the concentrate reaches 16-18% (w / w), ultrafiltration is stopped, and approximately 230 kg of ultrafiltration concentrate is collected. Testing revealed that the pH of the ultrafiltration concentrate is 6.4, the lactose content is 0.5% (w / w), and the ash content is 0.7% (w / w).

[0048] The temperature of the ultrafiltration concentrate was adjusted to 10℃, and the solution was slowly stirred at 40 rpm. A 5% (w / w) food-grade sodium hydroxide solution was added dropwise to the concentrate, controlling the addition rate to ensure that the pH change rate did not exceed 0.05 / min. The pH value of the concentrate was monitored in real time. When the pH reached 6.7, the addition of alkali solution was stopped, and stirring was continued for 10 minutes to homogenize the system, resulting in a concentrate with pH adjustment. The temperature was controlled at 10℃ ± 0.5℃ throughout the process. Testing showed that the average particle size change rate of casein micelles in the concentrate after pH adjustment was 4.1%.

[0049] The concentrated solution after pH adjustment was transferred to a sealed equilibrium tank and kept at 10°C for 3 hours. Then, it was cooled to 4°C at a rate of 0.6°C / min and allowed to stand at this temperature for 10 hours, during which time the system was kept in a state of no stirring and no shearing. The micelle size change was monitored using an online particle size analyzer. When the deviation between two consecutive particle size measurements was 3.0%, micelle reconstruction was considered complete.

[0050] The reconstituted concentrate was degassed at -0.064 MPa for 20 minutes to remove dissolved oxygen and air bubbles. It was then cold sterilized by passing it through a ceramic membrane with a pore size of 0.3 μm, followed by pasteurization at 72℃ for 15 seconds, and then refrigerated and filled to obtain a high-protein milk concentrate. Example 3:

[0051] 1000 kg of raw milk was cooled to 6°C and then preheated to 55°C. It was then centrifuged at 7000 rpm, and the flow rate of the heavy phase outlet was controlled at 980 L / h to obtain skim milk with a fat content of 0.05% (w / w). The skim milk was then cooled to 10°C for later use.

[0052] The skim milk temperature was adjusted to 14℃, and a ceramic ultrafiltration membrane module with a molecular weight cutoff of 20 kDa was pumped in. The transmembrane pressure was controlled at 0.35 MPa, the circulation flow rate at 4.5 m / s, and the concentration factor at 4.8 times. During ultrafiltration, the membrane surface was cleaned by backwashing every 30 minutes to maintain a membrane flux ≥23 L / (m²). 2 (h) When the protein content in the concentrate reaches 16-18% (w / w), ultrafiltration is stopped, and approximately 170 kg of ultrafiltration concentrate is collected. Testing revealed that the pH of the ultrafiltration concentrate is 6.2, the lactose content is 0.3% (w / w), and the ash content is 0.5% (w / w).

[0053] The temperature of the ultrafiltration concentrate was adjusted to 15℃, and the solution was slowly stirred at 60 rpm. A 5% (w / w) food-grade sodium hydroxide solution was added dropwise to the concentrate, controlling the addition rate to ensure that the pH change rate did not exceed 0.05 / min. The pH value of the concentrate was monitored in real time. When the pH reached 7.0, the addition of alkali solution was stopped, and the system was stirred for another 5 minutes to homogenize, resulting in a concentrate with pH adjustment. The temperature was controlled at 15℃ ± 0.5℃ throughout the process. Testing showed that the average particle size change rate of casein micelles in the concentrate after pH adjustment was 2.8%.

[0054] The concentrated solution after pH adjustment was transferred to a sealed equilibrium vessel and kept at 15°C for 1 hour. Then, it was cooled to 8°C at a rate of 0.9°C / min and allowed to stand at this temperature for 6 hours, during which time the system was kept in a state of no stirring and no shearing. The micelle size change was monitored using an online particle size analyzer. When the deviation between two consecutive particle size measurements was 2.0%, micelle reconstruction was considered complete.

[0055] The reconstituted concentrate was degassed at -0.08 MPa for 12 minutes to remove dissolved oxygen and air bubbles. It was then cold sterilized by passing it through a ceramic membrane with a pore size of 0.15 μm, followed by pasteurization at 75℃ for 15 seconds, and then refrigerated and filled to obtain a high-protein milk concentrate.

[0056] Comparative Example 1: The difference from Example 1 is that no pH adjustment process is performed during ultrafiltration.

[0057] Specifically, the ultrafiltration steps of Example 1 were followed, but without pH adjustment after ultrafiltration. Instead, the micelle reconstruction and sterilization steps of Example 1 were followed directly to obtain a high-protein emulsion concentrate.

[0058] Comparative Example 2: The difference from Example 1 is that: no low-temperature static stabilization treatment is performed, and degassing and sterilization are performed directly.

[0059] Specifically, after obtaining the pH-adjusted concentrate according to the ultrafiltration and pH adjustment steps of Example 1, without performing the 10-15°C incubation stage and the 4-10°C low-temperature standing treatment, the concentrate is directly subjected to degassing and sterilization to obtain a high-protein milk concentrate.

[0060] Comparative Example 3: The difference from Example 1 is that the ultrafiltration temperature is 50°C, and high-temperature ultrafiltration is used.

[0061] Specifically, the temperature of the skim milk was adjusted to 50°C, and ultrafiltration concentration was performed according to the ultrafiltration parameters of Example 1. The subsequent micelle reconstruction and sterilization steps were the same as in Example 1 to obtain a high-protein milk concentrate.

[0062] Comparative Example 4: The difference from Example 1 is that the sterilization method is traditional UHT sterilization at 137℃ for 4 seconds.

[0063] Specifically, after obtaining the reconstituted concentrate according to the ultrafiltration and micelle reconstruction steps of Example 1, the concentrate was degassed and then sterilized at 137°C / 4s using UHT instead of microfiltration sterilization and pasteurization to obtain a high-protein emulsion concentrate.

[0064] Performance testing: Performance tests were conducted on the above embodiments and comparative examples. The test items and methods are as follows.

[0065] The method for determining protein content is as follows: the total nitrogen content is determined by the Kjeldahl method according to GB 5009.5-2016 standard, and the protein content is obtained by multiplying by the conversion factor. Each sample is tested 3 times and the average value is taken.

[0066] The method for determining fat content is as follows: according to GB 5009.6-2016 standard, the Soxhlet extraction method or acid hydrolysis method is used for determination, and each sample is tested 3 times and the average value is taken.

[0067] The method for determining lactose content is as follows: according to GB 5413.5-2010 standard, the lactose content is determined by high performance liquid chromatography, and each sample is tested 3 times and the average value is taken.

[0068] The method for determining ash content is as follows: according to GB 5009.4-2016 standard, the sample is ignited in a muffle furnace at 550℃ to constant weight, the mass of the residue is weighed, and each sample is tested 3 times and the average value is taken.

[0069] The method for determining the micelle size is as follows: using a dynamic light scattering particle size analyzer, the sample is diluted to a suitable concentration and the average particle size and particle size distribution width (Span) of casein micelles are measured at 25℃. Each sample is tested 3 times and the average value is taken.

[0070] The method for determining zeta potential is as follows: using a zeta potential analyzer, the sample is diluted to a suitable concentration and the zeta potential of the micelles is measured at 25℃. Each sample is tested 3 times and the average value is taken.

[0071] The method for determining the centrifugal sedimentation rate is as follows: take 10 mL of sample into a centrifuge tube, centrifuge at 4000 rpm for 10 minutes, discard the supernatant, weigh the mass of the precipitate, and the sedimentation rate = mass of precipitate / total mass of sample × 100%. Each sample is tested 3 times and the average value is taken.

[0072] The method for observing storage stability is as follows: the sample is stored at 4℃ for 6 months, and the appearance of the sample is observed regularly to record whether there are any phenomena such as precipitation, gelation, or layering.

[0073] The method for determining the thermal solidification time is as follows: take 10 mL of sample in a glass tube, place it in an oil bath at 130℃ and heat it. Record the time when visible aggregates or precipitates begin to appear on the sample. Test each sample 3 times and take the average value.

[0074] The method for determining apparent viscosity is as follows: according to GB / T 10247-2008 standard, the apparent viscosity of the sample is measured using a rotational viscometer at 10℃, the shear rate is set to 100s⁻¹, and each sample is tested 3 times and the average value is taken.

[0075] The flavor evaluation method is as follows: a quantitative descriptive analysis method is adopted, and a trained sensory evaluation team (at least 10 people) scores the flavor of the samples. The scoring dimensions include milky aroma, steamed taste, sweetness, off-flavor, etc. A 10-point scale is used (1-3 points is poor, 4-6 points is fair, 7-8 points is good, and 9-10 points is excellent). Blind sample evaluation is carried out on the sample of the example and the comparative sample, and the average value is taken.

[0076] Table 1: Basic physicochemical properties and micelle structure parameters of the products in the examples and comparative examples.

[0077]

[0078] As shown in Table 1, the lactose content of the high-protein milk concentrates obtained in Examples 1-3 was ≤0.5% (w / w), the ash content was ≤0.8% (w / w), the average particle size of casein micelles was controlled within the range of 120-180 nm, and the Span value was ≤0.88. This indicates that after low-temperature ultrafiltration concentration, pH adjustment, and subsequent stabilization treatment, the casein micelles in the concentrated milk system can maintain a good dispersion state. Comparative Example 1, without pH adjustment treatment, had lactose and ash contents similar to the examples. However, because the pH of the system did not return to the stable range of casein micelles after ultrafiltration concentration, the average micelle size increased to 210 nm, the Span reached 1.35, and the absolute value of the Zeta potential decreased to 18.5 mV. This indicates that the acid-base environment change during ultrafiltration concentration weakens the surface charge stability of micelles, reduces inter-micelle repulsion, and promotes micelle aggregation.

[0079] Although Comparative Example 2 underwent pH adjustment, it did not undergo low-temperature static stabilization. Its average micelle size still reached 180 nm, Span was 1.12, and Zeta potential was 23.0 mV, all lower than the levels in the examples. This indicates that pH adjustment can improve the acid-base environment of the system, but it cannot completely restore the micelle structure disturbed during concentration. Further static stabilization is still needed to promote further adjustment of the micelle structure.

[0080] Comparative Example 3 underwent ultrafiltration at 50℃, resulting in an average micelle size of 185 nm and a span of 1.18. This indicates that higher ultrafiltration temperatures increase the risk of changes in milk protein structure and are detrimental to maintaining stable dispersion of casein micelles.

[0081] Comparative Example 4 was treated with traditional high-temperature sterilization, which increased the average micelle size to 170 nm, raised the Span to 1.05, and reduced the absolute value of the Zeta potential to 24.0 mV. This indicates that high heat load treatment enhances the interaction between proteins, causing some micelles to aggregate and reducing the stability of the system.

[0082] Table 2: Thermal stability and storage stability test results of the examples and comparative examples.

[0083]

[0084] As shown in Table 2, the high-protein milk concentrates obtained in Examples 1-3 all had a thermal coagulation time of ≥25 min and a centrifugal sedimentation rate of ≤0.20%. Furthermore, no precipitation, gelation, or stratification occurred after storage at 4°C for 6 months. This indicates that by controlling the pH environment of the concentrated milk system and combining it with low-temperature static stabilization treatment, this application has improved the structural stability of the product during heat treatment and long-term storage.

[0085] In Comparative Example 1, since no pH adjustment treatment was performed, the pH of the system deviated from the stable range of casein micelles, resulting in a decrease in electrostatic repulsion between micelles and easier aggregation during heat treatment. Therefore, the heat coagulation time was reduced to 12 min and the centrifugal sedimentation rate increased to 1.50%.

[0086] Although Comparative Example 2 underwent pH adjustment, it did not receive subsequent low-temperature stabilization. Its thermal coagulation time was only 18 minutes, and gelation occurred after one month of storage. This indicates that pH adjustment primarily improved the acid-base environment of the system but could not completely eliminate the disturbances to the micelle structure during concentration. Further stabilization through a settling process is needed to promote the recovery of the micelle structure.

[0087] Comparative Example 3 underwent ultrafiltration at 50℃, resulting in a reduced coagulation time of 21 min and an increased centrifugal sedimentation rate of 0.40%. Slight precipitation was observed after 3 months of storage. This indicates that higher temperature membrane treatment can easily cause changes in protein structure, potentially altering the structure of some proteins and affecting subsequent micellar stabilization processes.

[0088] Comparative Example 4 used the traditional UHT sterilization method at 137℃ / 4s, which reduced the heat coagulation time to 17min. After 3 months of storage, slight precipitation occurred, indicating that the heat-induced protein aggregation generated during the high-temperature sterilization process weakens the stable micelle structure formed in the early stage.

[0089] Table 3: Flavor evaluation and viscosity test results of the examples and comparative examples.

[0090] Example 1 8.5 150 Example 2 8.2 140 Example 3 8.8 160 Comparative Example 1 7.8 380 Comparative Example 2 8.3 175 Comparative Example 3 6.5 220 Comparative Example 4 6.0 280

[0091] As shown in Table 3, the flavor scores of Examples 1-3 all reached above 8.2 points, and the apparent viscosity was ≤160 mPa·s, demonstrating good flavor retention and flow properties. Among them, Example 3, due to the use of superior concentration and stabilization conditions, had a higher flavor score and lower viscosity change.

[0092] In Comparative Example 1, the protein micelles were in an unstable state due to the lack of pH adjustment treatment, resulting in an apparent viscosity of 380 mPa·s, significantly higher than that of the Example. The pH shift led to a decrease in the surface charge of the casein micelles, enhanced the interaction between micelles, and formed a higher viscosity system.

[0093] Although Comparative Example 2 underwent pH adjustment, it was not subjected to low-temperature static stabilization treatment. Its apparent viscosity was 175 mPa·s, which was slightly higher than that of the Example, indicating that when the micelle structure was not fully adjusted, the system still had a certain degree of aggregation tendency.

[0094] Comparative Example 3, which used 50℃ high-temperature ultrafiltration, had a flavor score that decreased to 6.5 points, while its viscosity increased to 220 mPa·s. This indicates that higher temperature membrane treatment increases the loss of heat-sensitive flavor substances and promotes changes in protein structure.

[0095] Comparative Example 4, which was sterilized using traditional UHT, had a flavor score of 6.0 and an apparent viscosity of 280 mPa·s. This indicates that high-temperature sterilization can easily lead to heat-induced aggregation of milk proteins, resulting in a decrease in product flavor and rheological properties.

[0096] As can be seen from the comparative examples of the above implementation methods: First, in Comparative Example 1, no pH adjustment was performed. Although the protein concentration process was completed normally, the pH of the concentrated system deviated from the stable range of casein micelles, leading to a decrease in micelle surface charge, an increase in particle size, and further a decline in thermal and storage stability. Therefore, simply increasing the protein concentration cannot obtain a stable high-protein milk concentration system; it is necessary to restore a suitable micelle environment through pH adjustment.

[0097] Second, pH was adjusted in Comparative Example 2, but no low-temperature static stabilization treatment was performed. Its micelle size, span, and storage stability were still lower than those of the Example. This indicates that pH adjustment can only solve the acid-base environment problem of the system, but cannot completely eliminate the disturbance to the micelle structure during the concentration process. Stabilization can further improve the micelle dispersion state and improve product stability.

[0098] Third, although the protein concentration was achieved by ultrafiltration at 50°C in Comparative Example 3, the flavor evaluation and stability were significantly reduced, indicating that the use of low-temperature ultrafiltration at 10-15°C in this application is beneficial to reducing the adverse effects of heat treatment on the structure of the milk system.

[0099] Fourth, Comparative Example 4, which used traditional UHT sterilization, resulted in a decrease in the product's thermal stability, storage stability, and flavor, indicating that low-heat sterilization plays an important role in maintaining the stable micelle structure formed in the early stage.

[0100] In summary, this disclosure achieves protein enrichment while preserving natural flavor compounds through low-temperature ultrafiltration; the pH of the concentrate is restored to the neutral range after ultrafiltration, providing suitable pH conditions and ionic environment for stable initial state for micelle reconstruction; the micelle reconstruction treatment after pH restoration promotes the recovery of casein micelles from a disturbed state to a stable dispersion state, reducing micelle size and fundamentally solving the structural evolution problem during the storage of high-protein concentrates; finally, a low-heat sterilization method combining microfiltration and pasteurization avoids further damage to flavor and thermal shock to the micelle structure caused by high temperatures. This method achieves long-term storage stability of the product without the addition of any exogenous stabilizers, solving the technical problems of high-protein milk concentrates relying on chemical additives, flavor deterioration, and poor storage stability in existing technologies.

[0101] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the following claims.

[0102] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.

Claims

1. A method for preparing a clean label high-protein emulsion concentrate, characterized in that, include: S1, the raw milk is centrifuged to remove fat, resulting in skimmed milk; S2, the skim milk is concentrated by ultrafiltration at 10-15°C to obtain ultrafiltration concentrate; S3, detect the pH value of the ultrafiltration concentrate, adjust it to 6.7-7.0, and obtain a concentrate with pH adjustment; S4. The concentrate is kept at 10-15℃ for 1-4 hours, then cooled to 4-10℃ and allowed to stand for 4-12 hours to allow the concentrate system to reach a stable state. Then, it is sterilized under low heat load to obtain high protein milk concentrate.

2. The method for preparing the clean label high-protein emulsion concentrate according to claim 1, characterized in that, Step S1 includes: S1.1, After cooling the raw milk to 2-6°C, preheat it to 45-55°C; S1.2, centrifuge at 6500-7500 rpm, control the flow rate at 950-1000 L / h, to obtain skim milk with a fat content ≤0.6% (w / w), and cool the skim milk to 4-10℃ for later use.

3. The method for preparing the clean label high-protein emulsion concentrate according to claim 2, characterized in that, The fat content of the skim milk after centrifugation in S1.2 is ≤0.1% (w / w).

4. The method for preparing the clean label high-protein emulsion concentrate according to claim 1, characterized in that, Step S2 includes: S2.1, Adjust the temperature of the skim milk to 12-14℃, pump in a ceramic ultrafiltration membrane module with a molecular weight cutoff of 10-20 kDa, control the transmembrane pressure to 0.2-0.4 MPa, the circulation flow rate to 3-5 m / s, and the concentration factor to 2.5-5 times; S2.2 During ultrafiltration, the membrane surface is cleaned by backwashing every 20–30 minutes to maintain a membrane flux ≥ 20 L / (m²). 2 When the protein content in the concentrate reaches 15%–18% (w / w), stop ultrafiltration and collect the ultrafiltration concentrate.

5. The method for preparing the clean label high-protein emulsion concentrate according to claim 4, characterized in that, In S2.1, the ratio of transmembrane pressure to circulation flow rate is controlled between 0.05 and 0.1 MPa·s / m, and the temperature fluctuation throughout the ultrafiltration process is ≤ ±1℃.

6. The method for preparing the clean label high-protein emulsion concentrate according to claim 1, characterized in that, Step S3 includes: S3.1 Adjust the temperature of the ultrafiltration concentrate to 10-15℃, stir slowly at 40-60 rpm, add food-grade sodium hydroxide dropwise to the concentrate as a processing aid, and control the addition rate so that the pH change rate of the concentrate does not exceed 0.05 / min. S3.2, monitor the pH value of the concentrate. When the pH reaches 6.7-7.0, stop adding the regulator and continue stirring for 5-10 minutes to make the system uniform, thus obtaining the concentrate after pH adjustment.

7. The method for preparing the clean label high-protein emulsion concentrate according to claim 1, characterized in that, Step S4 includes: S4.1, transfer the concentrate to a sealed equilibrium tank, maintain it at 10-15°C for 1-4 hours, cool it down to 4-10°C at a rate of 0.5-1°C / min, and let it stand at this temperature for 4-12 hours. During the standing period, keep the system in a state of no stirring and no shearing. S4.2, the micelle size change is monitored by an online particle size analyzer. The reconstructed concentrate is degassed under -0.064 to -0.08 MPa to remove dissolved oxygen and bubbles. Microfiltration sterilization is performed by passing the concentrate through a ceramic membrane with a pore size of 0.1 to 0.5 μm for cold sterilization. Then, pasteurization is carried out at 72 to 75 °C for 15 seconds to obtain a high-protein emulsion concentrate.

8. The method for preparing the clean label high-protein emulsion concentrate according to claim 7, characterized in that, In step S4.2, when the deviation between two consecutive particle size detection results does not exceed 5%, the micelle reconstruction is determined to be complete.

9. A clean label high-protein emulsion concentrate, characterized in that, The high-protein emulsion concentrate prepared by the method according to any one of claims 1-8 satisfies the following: Protein content: 15%–18% (w / w); Fat content: ≤0.6% (w / w); Lactose content: ≤0.5% (w / w); Ash content: ≤0.8% (w / w); The casein micelles in the high-protein emulsion concentrate have an average particle size of 120–180 nm.

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