High-protein low-lactose product and preparation method thereof

Abstract

The invention belongs to the field of food, and particularly relates to a high-protein low-lactose product and a preparation method thereof.According to the invention, raw milk is used as a raw material, ultrafiltration and nanofiltration technologies are combined, and nanofiltration conditions capable of removing lactose in the raw milk to the maximum extent are screened out through a large number of experiments; and edible saccharides are added in the ultrafiltration process, so that the protein loss rate during ultrafiltration and nanofiltration is further reduced. By using the method provided by the invention, the lactose content in the raw milk can be reduced to 0.01% or below, and at the same time, the protein content of 95% or above is retained.

Description

Technical Field

[0001] This invention belongs to the food field, specifically, it relates to a high-protein, low-lactose product based on dual-membrane separation technology and its preparation method. Background Technology

[0002] High-protein dairy beverages, as fortified dairy products, have become important products in the fields of sports nutrition and healthy diets due to their high biological value protein content and convenient absorption. In existing technologies, whey protein and casein concentrates are often used as core raw materials in the development of such products because of their complete amino acid profile and excellent digestibility. Traditional industrial production mainly uses a protein powder reconstitution process, which involves reconstituted pre-processed milk protein powder (made through ultrafiltration concentration and spray drying) provided by upstream suppliers with water, followed by blending, sterilization, and other processes to produce the final product. While this process can increase the basic protein content, its core raw material is highly dependent on imported milk protein powder.

[0003] In existing technologies, the protein powder reconstitution process involves high-temperature drying and secondary reconstitution, which intensifies the Maillard reaction and leads to the loss of heat-sensitive flavor compounds, resulting in a noticeable powdery texture and a bitter aftertaste. While ultrafiltration technology directly concentrates raw milk protein, the final product still contains more than 0.5g / 100mL of lactose, failing to meet the needs of lactose-intolerant individuals. Further nanofiltration, although capable of removing a small amount of sugar, increases protein loss, and current nanofiltration technology for sugar removal remains inadequate. These technological shortcomings collectively result in commercially available high-protein dairy beverages generally suffering from low raw material autonomy, poor sensory quality, and limited functional adaptability, hindering industrial technology upgrades and the development of high-end products. Summary of the Invention

[0004] To address at least one of the technical shortcomings of existing high-protein dairy beverage production, such as strong dependence on raw materials, severe flavor loss, incomplete lactose removal, and high protein loss rate after lactose removal, this invention proposes a high-protein, low-lactose product based on dual-membrane separation technology and its preparation method. Using the method of this application, the lactose content in raw milk can be reduced to below 0.01%, while retaining more than 95% of the protein content.

[0005] In a first aspect, the present invention provides a method for preparing a high-protein, low-lactose product. According to an embodiment of the present invention, the method includes the following steps: A. The pretreated raw milk is concentrated by ultrafiltration to obtain ultrafiltration retentate; B. Perform nanofiltration desaccharification treatment on the ultrafiltration retentate to obtain nanofiltration permeate and nanofiltration retentate. C. Mix the nanofiltration retentate with the nanofiltration permeate to obtain the high-protein, low-lactose product. The pressure during the nanofiltration desaccharification process is 1.8-2.2 MPa, and the permeate flow rate is 1-1.5 m³ / h.

[0006] According to the method of the above embodiments of the present invention, the synergistic effect of ultrafiltration and nanofiltration achieves the dual effects of efficient lactose removal and high protein retention. Specifically, in the ultrafiltration stage, proteins are selectively retained by the membrane pore size to form a concentrate, while edible sugars are added to reduce protein permeation loss through osmotic pressure balance. In the nanofiltration stage, under an optimized pressure of 1.8-2.2 MPa, the selective permeation characteristics of the nanofiltration membrane for small-molecule lactose are utilized, causing lactose to be discharged with the permeate while the protein is completely retained. The specific permeate flow rate (1-1.5 m³ / h) ensures sufficient lactose migration while avoiding protein adsorption loss due to membrane fouling. Finally, through the remixing of the nanofiltration retentate and the permeate, a protein recovery rate of over 95% is achieved while reducing the lactose content to below 0.01%.

[0007] In addition, the preparation method according to the above embodiments of the present invention may also have the following additional technical features: In some embodiments of the present invention, the pressure during the ultrafiltration concentration process is 0.5-1.5 MPa, the temperature is 10-20°C, and the cross-flow velocity is 2-3 m³ / h. Limiting the ultrafiltration pressure to 0.5-1.5 MPa, the temperature to 10-20°C, and the cross-flow velocity to 2-3 m³ / h optimizes membrane flux and reduces protein denaturation, ensuring a high protein rejection rate (>95%) while maintaining stable ultrafiltration efficiency.

[0008] In some embodiments of the present invention, the ultrafiltration membrane used in the ultrafiltration concentration process is a ceramic membrane, specifically a zirconia ceramic membrane. This reduces membrane flux decline while efficiently concentrating proteins, ensuring the stability of the subsequent nanofiltration desaccharification process.

[0009] In some embodiments of the present invention, the zirconia ceramic membrane has a molecular weight cutoff of 50-100 kDa. This effectively reduces the sugar removal load of subsequent nanofiltration while initially concentrating proteins, thereby improving overall process efficiency.

[0010] In some embodiments of the present invention, the nanofiltration membrane used for desaccharification is a polyamide composite nanofiltration membrane, and the temperature for desaccharification is 23-27°C. Therefore, using a polyamide composite nanofiltration membrane and performing desaccharification at 23-27°C fully utilizes the high selective separation performance of this membrane material.

[0011] In some embodiments of the present invention, the polyamide composite nanofiltration membrane has a molecular weight cutoff of 200-300 Da. This allows for highly efficient sugar removal while achieving near-zero protein loss.

[0012] In some embodiments of the present invention, the mass ratio of the nanofiltration retentate to the nanofiltration permeate is (3-4):1. This ensures that while removing lactose to the maximum extent, the stable conformation of the protein and the colloidal stability of the product system are maintained, avoiding nutrient loss or decline in sensory quality due to excessive dilution or concentration.

[0013] In some embodiments of the present invention, step A is further included by adding a protein protectant to the raw milk. This reduces protein denaturation loss during ultrafiltration due to shear forces or membrane surface adsorption, maintaining the native structure and recovery rate of the proteins.

[0014] In some embodiments of the present invention, the protein protectant is a glycoprotein protectant, which includes at least one of sucrose and trehalose. This improves the protein recovery rate.

[0015] In some embodiments of the present invention, the protein protectant is trehalose, and the concentration of trehalose in the raw milk is 0.002 g / ml. This improves the protein recovery rate.

[0016] In some embodiments of the present invention, step A is further followed by adding a protein protectant to the ultrafiltration retentate. This suppresses conformational changes and membrane surface adsorption of proteins under subsequent nanofiltration high-pressure conditions, effectively reducing protein denaturation or loss caused by mechanical shear forces and interfacial effects.

[0017] In some embodiments of the present invention, the protein protectant is a glycoprotein protectant, which includes at least one of sucrose and trehalose. This achieves highly efficient protein protection under dynamic filtration conditions.

[0018] In some embodiments of the present invention, the protein protectant is trehalose, and the concentration of trehalose in the ultrafiltration retentate is 0.002 g / ml. This improves the protein recovery rate.

[0019] In a second aspect of the invention, this application provides a high-protein, low-lactose product, which, according to an embodiment of this application, is prepared using the method described above.

[0020] Additional aspects and advantages of the invention 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 the invention. Detailed Implementation

[0021] The embodiments of the present invention are described in detail below. 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 indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of the present invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0022] In this document, the terms "about," "substantially," or "essentially" can mean that a value includes the standard deviation of the error of the apparatus or method used to determine that value. The numerical ranges and parameters used to define the present invention are approximate values, and the relevant values ​​in the specific embodiments have been presented as precisely as possible. However, any value inevitably contains a standard deviation due to the aforementioned testing apparatus or method. Therefore, unless explicitly stated otherwise, it should be understood that all ranges, quantities, values, and percentages used in the present invention are modified with "about." Here, "about" generally means that the standard deviation of the actual value from the theoretical model or theoretical data is within the range of 3%, preferably 2%, more preferably 1%.

[0023] 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.

[0024] A first aspect of the present invention provides a method for preparing a high-protein, low-lactose product. According to an embodiment of the present invention, the method includes the following steps: A. The pretreated raw milk is concentrated by ultrafiltration to obtain ultrafiltration retentate; B. Perform nanofiltration desaccharification treatment on the ultrafiltration retentate to obtain nanofiltration permeate and nanofiltration retentate. C. Mix the nanofiltration retentate with the nanofiltration permeate to obtain the high-protein, low-lactose product. The pressure during the nanofiltration desaccharification process is 1.8-2.2 MPa, and the permeate flow rate is 1-1.5 m³ / h.

[0025] According to the method of the above embodiments of the present invention, the synergistic effect of ultrafiltration and nanofiltration achieves the dual effects of efficient lactose removal and high protein retention. Specifically, in the ultrafiltration stage, proteins are selectively retained by the membrane pore size to form a concentrate, while edible sugars are added to reduce protein permeation loss through osmotic pressure balance. In the nanofiltration stage, under an optimized pressure of 1.8-2.2 MPa, the selective permeation characteristics of the nanofiltration membrane for small-molecule lactose are utilized, causing lactose to be discharged with the permeate while the protein is completely retained. The specific permeate flow rate (1-1.5 m³ / h) ensures sufficient lactose migration while avoiding protein adsorption loss due to membrane fouling. Finally, through the remixing of the nanofiltration retentate and the permeate, a protein recovery rate of over 95% is achieved while reducing the lactose content to below 0.01%.

[0026] As an example, the pressure during the nanofiltration desaccharification process can be 1.8 MPa, 2.0 MPa, 2.2 MPa, etc.; the permeate flow rate can be 1 m³ / h, 1.2 m³ / h, 1.4 m³ / h, 1.5 m³ / h, etc.

[0027] In some embodiments of this application, the pressure during the ultrafiltration concentration process is 0.5-1.5 MPa, the temperature is 10-20°C, and the cross-flow velocity is 2-3 m³ / h. By controlling the low pressure (0.5-1.5 MPa) and low temperature (10-20°C), the risks of membrane compression and protein thermal denaturation are reduced. At the same time, optimizing the cross-flow velocity (2-3 m³ / h) maintains turbulence on the membrane surface, effectively mitigating concentration polarization, thereby improving protein retention and reducing membrane fouling, ensuring high protein recovery and stable ultrafiltration efficiency.

[0028] As an example, the pressure during the ultrafiltration concentration process can be 0.5 MPa, 1.0 MPa, 1.5 MPa, etc.; the temperature can be 10℃, 15℃, 20℃, etc.; and the crossflow velocity can be 2 m³ / h, 2.5 m³ / h, 3 m³ / h, etc.

[0029] In some embodiments of this application, the ultrafiltration membrane used in the ultrafiltration concentration process is a ceramic membrane, specifically a zirconia ceramic membrane. Zirconia ceramic membranes possess high mechanical strength, high temperature resistance, acid and alkali resistance, and antifouling properties. They can maintain a stable pore structure under high pressure, preventing protein leakage caused by membrane deformation. Furthermore, their smooth, hydrophilic surface reduces protein adsorption loss, thereby minimizing membrane flux decline while efficiently concentrating protein and ensuring the stability of the subsequent nanofiltration desaccharification process.

[0030] In some embodiments of this application, the molecular weight cutoff of the zirconia ceramic membrane is 50-100 kDa. Limiting the molecular weight cutoff of the zirconia ceramic membrane to the above range ensures efficient retention of milk proteins in the ultrafiltration stage, while allowing lactose and small molecule salts to permeate freely. This effectively reduces the sugar removal load of subsequent nanofiltration while initially concentrating the protein, thereby improving the overall process efficiency.

[0031] As an example, the molecular weight cutoff of zirconia ceramic membranes can be 50 kDa, 70 kDa, 90 kDa, 100 kDa, etc.

[0032] In some embodiments of this application, the nanofiltration membrane used for desaccharification is a polyamide composite nanofiltration membrane, and the temperature during desaccharification is 23-27°C. Using a polyamide composite nanofiltration membrane and performing desaccharification at 23-27°C fully utilizes the high selective separation performance of this membrane material. The dense charged layer on the surface of the polyamide composite membrane can precisely retain proteins while allowing lactose to permeate. The temperature control range of 23-27°C maintains membrane pore size stability and ensures lactose diffusion efficiency, thereby achieving efficient lactose removal and minimal protein loss through a dual mechanism of molecular size exclusion and charge repulsion.

[0033] As an example, the temperature during nanofiltration desugaring can be 23°C, 25°C, 27°C, etc.

[0034] In some embodiments of this application, the polyamide composite nanofiltration membrane has a molecular weight cutoff of 200-300 Da.

[0035] As an example, the molecular weight cutoff of the polyamide composite nanofiltration membrane can be 200 Da, 240 Da, 280 Da, 300 Da, etc. Limiting the molecular weight cutoff of the polyamide composite nanofiltration membrane to the above range allows for precise matching of the molecular weight difference between lactose and milk protein, ensuring both sufficient lactose removal and complete protein retention, thus achieving near-zero protein loss while efficiently removing lactose.

[0036] In some embodiments of this application, the mass ratio of the nanofiltration retentate to the nanofiltration permeate is (3-4):1. The retentate is rich in protein but contains trace amounts of lactose, while the permeate contains removed lactose but with very low protein loss. By adjusting the mixing ratio of the nanofiltration retentate to the nanofiltration permeate, the stable conformation of the protein and the colloidal stability of the product system are maintained while removing lactose to the maximum extent, avoiding nutritional loss or decline in sensory quality due to excessive dilution or concentration.

[0037] As an example, the mass ratio of the nanofiltration retentate to the nanofiltration permeate when mixed can be 3:1, 3.5:1, 4:1, etc.

[0038] In some embodiments of this application, step A is further included by adding a protein protectant to the raw milk. Adding a protein protectant (such as a sugar or polyhydroxy compound) to the raw milk can stabilize the protein conformation through steric hindrance and hydrogen bonding, reducing protein denaturation loss during ultrafiltration caused by shear forces or membrane surface adsorption. Simultaneously, it reduces passive protein migration with the filtrate by adjusting osmotic pressure, thereby maintaining the native structure and recovery rate of proteins more efficiently in subsequent membrane separation processes.

[0039] In some embodiments of this application, the protein protectant is a glycoprotein protectant, including at least one of sucrose and trehalose. Adding sucrose or trehalose as a protein protectant allows these sugar molecules to bind to the protein surface through hydrogen bonding, forming a hydration layer protective film. This reduces protein denaturation or loss during ultrafiltration and nanofiltration caused by mechanical shearing, concentration polarization, or membrane surface adsorption. Simultaneously, it inhibits protein migration with the filtrate by regulating osmotic pressure balance, thereby significantly improving protein recovery.

[0040] In some embodiments of this application, the protein protectant is trehalose, and the concentration of trehalose in the raw milk is 0.002 g / ml. Adding a specific concentration of trehalose as a protein protectant allows it to interact with milk proteins through hydrogen bonding and steric hindrance, forming a dynamic protective layer during ultrafiltration and nanofiltration. This reduces non-specific adsorption loss of proteins on the membrane surface and maintains the native conformational stability of the proteins, thereby significantly improving protein recovery.

[0041] In some embodiments of this application, step A is further followed by adding a protein protectant to the ultrafiltration retentate. The purpose of adding the protein protectant is to bind to the polar regions of the protein surface through its active groups (such as hydroxyl and carboxyl groups) to form a stable hydration layer, thereby inhibiting conformational changes and membrane surface adsorption of proteins under subsequent nanofiltration high-pressure conditions, effectively reducing protein denaturation or loss caused by mechanical shear forces and interfacial effects.

[0042] In some embodiments of this application, the protein protectant is a glycoprotein protectant, which includes at least one of sucrose and trehalose. The glycoprotein protectant is specifically defined as sucrose and / or trehalose, which binds to polar groups on the protein surface via hydrogen bonds to form a hydration protective layer. This stabilizes the protein conformation during ultrafiltration and nanofiltration, reduces denaturation losses caused by membrane surface adsorption and shear forces, and simultaneously inhibits protein migration with the filtrate by regulating osmotic pressure, thereby achieving highly efficient protein protection under dynamic filtration conditions.

[0043] In some embodiments of this application, the protein protectant is trehalose, and the concentration of trehalose in the ultrafiltration retentate is 0.002 g / ml. As a protein protectant, trehalose molecules bind to the protein surface through hydrogen bonds to form a hydration layer, effectively stabilizing the protein conformation during ultrafiltration and preventing protein denaturation or adsorption loss caused by membrane surface shear forces and concentration polarization. Furthermore, by limiting the concentration of trehalose, its molecular osmotic pressure effect balances the transmembrane pressure during ultrafiltration, reducing protein deposition loss on the membrane surface due to concentration polarization, while avoiding excessively high concentrations that could affect the lactose removal efficiency of subsequent nanofiltration.

[0044] In this application, ultrafiltration concentration uses a ceramic ultrafiltration membrane with a molecular weight cutoff of 50-100 kDa, and nanofiltration desaccharification uses a polyamide composite nanofiltration membrane with a molecular weight cutoff of 200-300 Da.

[0045] According to the specific implementation scheme of this application, the high-protein, low-lactose product is subjected to two-stage pasteurization using a step-by-step sterilization method. The parameters for the two-stage pasteurization are 75℃ / 20s→85℃ / 10s.

[0046] According to embodiments of this application, the inventors used raw milk as raw material and combined ultrafiltration and nanofiltration technologies. Through extensive experimentation, they selected nanofiltration conditions that could maximally remove lactose from raw milk. Edible sugars were added during the ultrafiltration process to further reduce protein loss during both ultrafiltration and nanofiltration. Using the method of this application, the lactose content in raw milk can be reduced to below 0.01%, while retaining more than 95% of the protein content.

[0047] A second aspect of the present invention provides a high-protein, low-lactose product, which, according to embodiments of this application, is prepared using the method of the first aspect. The high-protein, low-lactose product contains less than 0.01% lactose and more than 95% protein.

[0048] The present invention will be explained below 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 the invention. 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 field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially. Example 1

[0049] 1. Raw milk pretreatment: Turn on the centrifuge (Westfalia Separator SA1) to pre-cool to 4°C, set the speed to 6500 rpm, pump 5L of raw milk (from local farms, protein ≥3.2%, fat ≤3.8%) into the feed tank, control the flow rate to 200 L / h, centrifuge for 15 min for 4 cycles to remove fat, collect the skimmed milk (fat content ≤0.1%), and pasteurize at 72°C / 15 s (using APVHTST plate heat exchanger). The pasteurized skimmed milk is then pre-filtered (Pall Supor® PES 1.5μm filter cartridge) to remove particulate impurities. 2. Ultrafiltration Concentration: The pretreated emulsion was concentrated by ultrafiltration (TAMI Industries INSIDE CeRAM® 6-channel ceramic membrane, ZrO2 material, molecular weight cutoff 50 kDa, membrane area 0.8 m²). The feed temperature was maintained at 12±1℃ (controlled by a plate heat exchanger), the transmembrane pressure at 0.55 MPa (adjusted by a variable frequency pump), and the crossflow velocity at 2.5 m³ / h. The protein content ratio of feed to permeate was recorded every 15 min (Kjeldahl method, GB 5009.5) and the membrane flux decrease rate (≤3% / h allowed). When the volume concentration factor (VCF) = 5 (feed liquid reduced to 20% of its original volume), concentration was stopped, and the retentate was obtained. 3. Nanofiltration desugaring: The retentate was subjected to nanofiltration desugaring (Dow FilmTec™ NF270-400 / 34i spiral wound membrane), and the feed temperature during nanofiltration was 25±2℃. The experimental groups were set up according to the operating pressure and permeate flow rate shown in the table below. The nanofiltration permeate and nanofiltration retentate were mixed at a mass ratio of 1:3. The protein loss rate and lactose residue rate of the experimental groups were measured. The protein loss rate was compared with the difference between nanofiltration and ultrafiltration by the Kjeldahl method. The lactose content was tested by HPLC (GB5413.5-2010). The test results are shown in Table 1.

[0050] Table 1 As shown in Table 1, when the nanofiltration pressure is 2 MPa, lactose can be removed with maximum efficiency. However, if the nanofiltration pressure is further increased, the efficiency of lactose removal will not increase, but the protein loss rate will increase. Therefore, in order to remove lactose with maximum efficiency and relatively small protein loss, the pressure of nanofiltration should be around 2 MPa and the permeate flow rate should be between 1 and 1.5 m³ / h. Example 2

[0051] 1. Raw milk pretreatment: Turn on the centrifuge (Westfalia Separator SA1) to pre-cool to 4°C, set the speed to 6500 rpm, pump 5L raw milk into the feed tank, control the flow rate to 200 L / h, centrifuge for 4 times and skim for 15 min, collect the skim milk (fat content ≤0.1%), and pasteurize at 72°C / 15 s (using APV HTST plate heat exchanger). The pasteurized skim milk is then pre-filtered (Pall Supor® PES 1.5μm filter cartridge) to remove particulate impurities. 2. Ultrafiltration Concentration: The pretreated emulsion was concentrated by ultrafiltration (TAMI Industries INSIDE CeRAM® 6-channel ceramic membrane, ZrO2 material, molecular weight cutoff 50 kDa, membrane area 0.8 m²). The feed temperature was maintained at 12±1℃ (controlled by plate heat exchanger), the transmembrane pressure at 0.55 MPa (adjusted by variable frequency pump), and the crossflow velocity at 2.5 m³ / h. The protein content ratio of feed to permeate was recorded every 15 min (Kjeldahl method, GB 5009.5) and the membrane flux decrease rate (≤3% / h allowed). Concentration was stopped when the volume concentration factor (VCF) = 5 (feed liquid reduced to 20% of its original volume). 3. Nanofiltration desugaring: Trehalose (0.002 g / ml) was added to the retentate after ultrafiltration concentration, and nanofiltration desugaring was performed on the retentate after adding trehalose (Dow FilmTec™ NF270-400 / 34i spiral wound membrane). The parameters for nanofiltration desugaring were: temperature 25±2℃, nanofiltration pressure 2MPa, and permeate flow rate 1.5 m³ / h. Example 3

[0052] 1. Raw milk pretreatment: Turn on the centrifuge (Westfalia Separator SA1) to pre-cool to 4°C, set the speed to 6500 rpm, pump 5L raw milk into the feed tank, control the flow rate to 200 L / h, centrifuge for 4 times and skim for 15 min, collect the skim milk (fat content ≤0.1%), and pasteurize at 72°C / 15 s (using APV HTST plate heat exchanger). The pasteurized skim milk is then pre-filtered (Pall Supor® PES 1.5μm filter cartridge) to remove particulate impurities. 2. Ultrafiltration Concentration: Trehalose (0.002 g / ml) was added to the pretreated emulsion, and the emulsion with added trehalose was subjected to ultrafiltration concentration (TAMI Industries INSIDE CeRAM® 6-channel ceramic membrane, ZrO2 material, molecular weight cutoff 50 kDa, membrane area 0.8 m²). The feed temperature was maintained at 12±1℃ (controlled by plate heat exchanger), the transmembrane pressure at 0.55 MPa (adjusted by variable frequency pump), and the cross-flow velocity at 2.5 m³ / h. The protein content ratio of feed to permeate was recorded every 15 min (Kjeldahl method, GB 5009.5) and the membrane flux decrease rate (≤3% / h allowed). When the volume concentration factor VCF=5 (feed liquid reduced to 20% of the original volume), the concentration was stopped. 3. Nanofiltration desugaring: The retentate after ultrafiltration is desugared by nanofiltration (Dow FilmTec™ NF270-400 / 34i spiral wound membrane). The parameters for nanofiltration desugaring are: temperature 25±2℃, nanofiltration pressure 2MPa, and permeate flow rate 1.5m³ / h. Example 4

[0053] 1. Raw milk pretreatment: Turn on the centrifuge (Westfalia Separator SA1) to pre-cool to 4°C, set the speed to 6500 rpm, pump 5L raw milk into the feed tank, control the flow rate to 200 L / h, centrifuge for 4 times and skim for 15 min, collect the skim milk (fat content ≤0.1%), and pasteurize at 72°C / 15 s (using APV HTST plate heat exchanger). The pasteurized skim milk is then pre-filtered (Pall Supor® PES 1.5μm filter cartridge) to remove particulate impurities. 2. Ultrafiltration Concentration: Trehalose (0.002 g / ml) was added to the pretreated emulsion, and the emulsion with added trehalose was subjected to ultrafiltration concentration (TAMI Industries INSIDE CeRAM® 6-channel ceramic membrane, ZrO2 material, molecular weight cutoff 50 kDa, membrane area 0.8 m²). The feed temperature was maintained at 12±1℃ (controlled by plate heat exchanger), the transmembrane pressure at 0.55 MPa (adjusted by variable frequency pump), and the cross-flow velocity at 2.5 m³ / h. The protein content ratio of feed to permeate was recorded every 15 min (Kjeldahl method, GB 5009.5) and the membrane flux decrease rate (≤3% / h allowed). When the volume concentration factor VCF=5 (feed liquid reduced to 20% of the original volume), the concentration was stopped. 3. Nanofiltration desugaring: Trehalose (0.002 g / ml) was added to the retentate after ultrafiltration concentration, and the emulsion after adding trehalose was subjected to nanofiltration desugaring (Dow FilmTec™ NF270-400 / 34i spiral wound membrane). The parameters for nanofiltration desugaring were: temperature 25±2℃, nanofiltration pressure 2MPa, and permeate flow rate 1.5 m³ / h. Example 5

[0054] 1. Raw milk pretreatment: Turn on the centrifuge (Westfalia Separator SA1) to pre-cool to 4°C, set the speed to 6500 rpm, pump 5L raw milk into the feed tank, control the flow rate to 200 L / h, centrifuge for 4 times and skim for 15 min, collect the skim milk (fat content ≤0.1%), and pasteurize at 72°C / 15 s (using APV HTST plate heat exchanger). The pasteurized skim milk is then pre-filtered (Pall Supor® PES 1.5μm filter cartridge) to remove particulate impurities. 2. Ultrafiltration Concentration: Sucrose (0.002 g / ml) was added to the pretreated emulsion, and the emulsion with added trehalose was subjected to ultrafiltration concentration (TAMI Industries INSIDE CeRAM® 6-channel ceramic membrane, ZrO2 material, molecular weight cutoff 50 kDa, membrane area 0.8 m²). The feed temperature was maintained at 12±1℃ (controlled by plate heat exchanger), the transmembrane pressure at 0.55 MPa (adjusted by variable frequency pump), and the cross-flow velocity at 2.5 m³ / h. The protein content ratio of feed to permeate (Kjeldahl method, GB 5009.5) and the membrane flux decline rate (≤3% / h allowed) were recorded every 15 min. When the volume concentration factor VCF=5 (feed liquid reduced to 20% of the original volume), concentration was stopped. 3. Nanofiltration desugaring: Sucrose (0.002 g / ml) was added to the retentate after ultrafiltration concentration, and nanofiltration desugaring was performed on the emulsion after adding trehalose (Dow FilmTec™ NF270-400 / 34i spiral wound membrane). The parameters for nanofiltration desugaring were: temperature 25±2℃, nanofiltration pressure 2MPa, and permeate flow rate 1.5 m³ / h.

[0055] The protein loss rate of the emulsions obtained in Examples 2-5 was calculated (by comparing the difference between nanofiltration and ultrafiltration using the Kjeldahl method, protein loss rate = (protein content before ultrafiltration - protein content after nanofiltration) / protein content before ultrafiltration * 100%). The results showed that the protein loss rate obtained in Example 2 was 5.3%, the protein loss rate obtained in Example 3 was 4.2%, the protein loss rate obtained in Example 4 was 4.1%, and the protein loss rate shown in Example 5 was 5.8%. Therefore, adding sugars can reduce the protein loss rate during ultrafiltration and nanofiltration, and the effect of adding sugars during ultrafiltration is greater than that during nanofiltration. In terms of reducing the protein loss rate, trehalose is more effective than sucrose.

[0056] In summary, to remove lactose with maximum efficiency and relatively minimal protein loss, a combination of ultrafiltration and nanofiltration is necessary. Through extensive experimentation, the inventors of this application have determined the optimal reaction conditions for nanofiltration: a nanofiltration pressure of approximately 2 MPa and a permeate flow rate of 1-1.5 m³ / h. Furthermore, the inventors have found that adding a glycoprotein protectant during ultrafiltration can further reduce the protein loss rate during both ultrafiltration and nanofiltration, with trehalose showing a greater effect than sucrose. Through extensive experimentation, the inventors have been able to reduce the lactose content in raw milk to below 0.01% while retaining over 95% of the protein content.

[0057] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0058] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method of making a high protein, low lactose product, characterized in that, The method comprises the following steps: A. performing ultrafiltration concentration treatment on the pretreated raw milk to obtain an ultrafiltration retentate; B. performing nanofiltration desugaring treatment on the ultrafiltration retentate to obtain a nanofiltration permeate and a nanofiltration retentate, C. mixing the nanofiltration retentate and the nanofiltration permeate to obtain the high-protein low-lactose product, wherein the pressure during the nanofiltration desugaring treatment is 1.8-2.2 MPa, and the permeate flow rate is 1-1.5 m³ / h.

2. The method of claim 1, wherein, The pressure during the ultrafiltration concentration treatment is 0.5-1.5 MPa, the temperature is 10-20°C, and the cross-flow speed is 2-3 m³ / h.

3. The method of claim 1, wherein, The ultrafiltration membrane during the ultrafiltration concentration treatment is a ceramic membrane, and the ceramic membrane is a zirconia ceramic membrane.

4. The method of claim 3, wherein, The molecular weight cut-off of the zirconia ceramic membrane is 50-100 kDa.

5. The method of claim 1, wherein, The nanofiltration membrane during the nanofiltration desugaring treatment is a polyamide composite nanofiltration membrane, and the temperature during the nanofiltration desugaring is 23-27°C.

6. The method of claim 5, wherein, The molecular weight cut-off of the polyamide composite nanofiltration membrane is 200-300 Da.

7. The method of claim 1, wherein, The mass ratio of the nanofiltration retentate to the nanofiltration permeate during mixing is (3-4):

1.

8. The method of claim 1, wherein, Step A is further preceded by adding a protein protective agent to the raw milk; Optionally, the protein protective agent is a saccharide protein protective agent, and the saccharide protein protective agent comprises at least one of sucrose and trehalose; Optionally, the protein protective agent is trehalose, and the concentration of the trehalose in the raw milk is 0.002 g / ml.

9. The method of claim 1, wherein, Step A is further followed by adding a protein protective agent to the ultrafiltration retentate; Optionally, the protein protective agent is a saccharide protein protective agent, and the saccharide protein protective agent comprises at least one of sucrose and trehalose; Optionally, the protein protective agent is trehalose, and the concentration of the trehalose in the ultrafiltration retentate is 0.002 g / ml.

10. A high protein, low lactose product, characterized in that, Prepared by the method of any one of claims 1-9.

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