Milk and preparation method therefor

Abstract

The present disclosure relates to the technical field of dairy products, and in particular to milk and a preparation method therefor. The preparation method for the milk provided by the present disclosure comprises: performing fat separation on raw milk to obtain light cream and skim milk, and performing separation or filtration on the skim milk for sterilization to obtain a first permeate and a first concentrate; performing cation exchange membrane treatment on the first permeate to obtain an eluent and a permeate, then performing microfiltration on the permeate to obtain a second permeate and a second concentrate, and performing ultrafiltration on the second permeate to obtain a third permeate and a third concentrate. The method can significantly increase the content of active substances in milk, such as lactoferrin, α-lactalbumin, β-Lactoglobulin and immunoglobulin, reduce the attenuation rate of active substances under normal-temperature storage conditions, prolong the shelf life of milk under normal-temperature conditions, and achieve the maximum retention of active substances in raw milk in normal-temperature milk.

Description

Milk and preparation method thereof Technical Field

[0001] The present disclosure relates to the technical field of dairy products, and in particular to milk and a preparation method thereof. Background Art

[0002] In recent years, with the advancement of science and technology and the improvement of living standards, the development of functional foods based on natural bioactive substances has garnered increasing attention. Bioactive substances refer to substances naturally present in food or formed and added during food processing that can induce changes in human physiological and biochemical functions. They are a key manifestation of the physiological activity of functional foods. In addition to providing daily nutrients, cow's milk also contains a wide variety of bioactive components, such as immunoglobulins, lactoferrin, growth factors, and bioactive peptides with various physiological functions. These bioactive substances are the essence of cow's milk and have a significant impact on human metabolism and health.

[0003] The protein content of dairy products is gradually increasing, with products boasting protein levels of 3.6g / 100g, 3.8g / 100g, 4.0g / 100g, 6.0g / 100g, and even higher. In addition to protein and calcium levels, consumers are beginning to pay attention to the content of bioactive substances in products, such as immunoglobulins, lactoferrin, lactoperoxidase, α-lactalbumin, and β-lactoglobulin. However, these substances are heat-sensitive and easily denatured by heat, requiring stringent processing techniques.

[0004] To ensure product safety, raw milk must undergo varying degrees of heat sterilization, such as low-temperature long-time pasteurization, high-temperature short-time pasteurization, ultra-pasteurization, and ultra-high temperature sterilization. Different sterilization intensities result in varying losses of milk's active substances, and storage conditions and shelf life also vary. Currently, low-temperature pasteurized milk is the primary milk product on the market that claims a high content of active substances, but this type of milk requires refrigeration and has a shelf life of only 7-15 days. Existing ambient temperature milk, while long-lasting and refrigerated, has a low content of active substances. Therefore, there is an urgent need to develop ambient temperature milk with a high content of active substances and a long shelf life.

[0005] Summary of the Invention

[0006] Based on the problems described above, the purpose of the present invention is to provide milk and a preparation method thereof, which can significantly increase the content of active substances such as lactoferrin, α-lactalbumin, β-lactoglobulin and immunoglobulin in milk, reduce the decay rate of active substances under room temperature storage conditions, extend the shelf life of milk under room temperature conditions, and achieve maximum retention of active substances in raw milk in room temperature milk.

[0007] According to a first aspect of the present disclosure, there is provided a method for preparing milk, the method comprising:

[0008] The raw milk is subjected to fat separation to obtain cream and skim milk, and the skim milk is subjected to separation or filtration sterilization to obtain a first permeate and a first concentrate;

[0009] The first permeate is treated with a cation exchange membrane to obtain an eluate and a permeate, the permeate is then filtered through microfiltration to obtain a second permeate and a second concentrated solution, and the second permeate is filtered through ultrafiltration to obtain a third permeate and a third concentrated solution.

[0010] According to certain preferred embodiments, the method further comprises: subjecting the third permeate to nanofiltration to obtain a fourth permeate and a fourth concentrated solution, and subjecting the fourth permeate to reverse osmosis to obtain a fifth permeate and a fifth concentrated solution.

[0011] According to certain preferred embodiments, wherein:

[0012] During the microfiltration diafiltration process, the third permeate and the fifth concentrate are eluted in a volume ratio of (7-11):1; and / or

[0013] During the ultrafiltration and diafiltration process, the fourth permeate and the fifth permeate with a volume ratio of (5-9):3 are used for elution.

[0014] According to certain preferred embodiments, wherein:

[0015] The pore size of the cation exchange membrane is 0.8-1.0 μm; and / or

[0016] In the cation exchange membrane treatment, after the first permeate is applied to the membrane, it is first eluted with a 0.4-0.6 mol / L sodium chloride solution, and then eluted with a 0.8-1.2 mol / L sodium chloride solution, and the eluates obtained from the two elutions are ultrafiltered and concentrated; and / or

[0017] In cation exchange membrane treatment, the membrane temperature is 45-55°C or 4-20°C.

[0018] According to certain preferred embodiments, wherein:

[0019] Microfiltration is performed using 0.1-0.2 μm microfiltration ceramic membranes, spiral membranes or hollow fiber membranes; and / or

[0020] Ultrafiltration diafiltration is performed using an ultrafiltration spiral membrane, hollow fiber membrane or ceramic membrane with a molecular weight cut-off of 1000-500000Da; and / or

[0021] Nanofiltration is performed using a nanofiltration spiral membrane with a molecular weight cut-off of 200-1000 Da; and / or

[0022] Reverse osmosis is performed using a reverse osmosis spiral membrane with a feed channel thickness of 0.7-0.9 mm; and / or

[0023] The temperatures for microfiltration, ultrafiltration, nanofiltration, and reverse osmosis treatments are all less than 10°C.

[0024] According to certain preferred embodiments, the method further comprises: mixing the light cream with the first concentrated liquid and then sterilizing the mixture to obtain a milk fat mixture; mixing the milk fat mixture with the second concentrated liquid, the fourth concentrated liquid, the fifth concentrated liquid and the fifth permeate and then heat sterilizing the mixture to obtain the first material.

[0025] According to certain preferred embodiments, the method further comprises: treating the cation exchange membrane to obtain an eluate, concentrating the eluate by ultrafiltration, mixing the eluate with the third concentrated liquid, sterilizing the eluate by microfiltration and / or absolute sterilization to obtain a second material, and mixing the second material with the first material.

[0026] According to certain preferred embodiments, wherein:

[0027] The microfiltration sterilization is performed using a filter membrane with a pore size of 0.25-0.68 μm and a photolithographic silicon material; and / or

[0028] The absolute sterilization efficiency is ≥ log7.

[0029] According to certain preferred embodiments, the first material and the second material are mixed and maintained at 50-70° C. for 180-420 seconds.

[0030] According to a second aspect of the present disclosure, there is provided milk, which is prepared using the method described above.

[0031] The beneficial effects of the present disclosure are as follows: the milk preparation method provided by the present disclosure can significantly increase the content of active substances such as lactoferrin, α-lactalbumin, β-lactoglobulin, and immunoglobulins in milk, while simultaneously reducing the decay rate of the active substances under room temperature storage conditions, extending the shelf life of milk at room temperature, and maximizing the retention of active substances in raw milk in room temperature milk. This method can be used to produce milk with high protein and high active substance content, enhancing the nutritional value and functionality of milk products. Furthermore, the preparation method of the present disclosure has high processing efficiency, can extend the service life of equipment, and is conducive to improving production efficiency and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the contents of the present disclosure or the technical solutions in the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are some embodiments of the contents of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0033] FIG1 is a schematic diagram of the process path of the milk preparation method in the invention content section of the present disclosure. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of this disclosure more clear, the technical solutions of this disclosure are described clearly and completely below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of this disclosure, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0035] Specifically, the present disclosure provides a method for preparing room-temperature milk with high protein and high active substance content, and the milk prepared by the method.

[0036] Specifically, the present disclosure provides the following technical solutions:

[0037] The present disclosure provides a method for preparing milk, the method comprising: using raw milk as a raw material, separating the raw milk by fat to obtain cream and skim milk, and separating or filtering and sterilizing the skim milk to obtain a first permeate and a first concentrate;

[0038] The first permeate is treated with a cation exchange membrane to obtain an eluate and a permeate, the permeate is then filtered through microfiltration to obtain a second permeate and a second concentrated solution, and the second permeate is filtered through ultrafiltration to obtain a third permeate and a third concentrated solution.

[0039] The present disclosure aims to develop room temperature milk with high lactoferrin, α-lactalbumin, β-lactoglobulin and immunoglobulin content and long shelf life, and improves the method for preparing milk. In order to avoid the destruction of active substances by high temperature treatment, the preparation method of the present disclosure first separates and extracts the active substances in the milk (while concentrating the milk), and then sterilizes the active substances and backfills them into the milk raw material that has been sterilized at high temperature. During the research and development process, the inventors of the present invention found that compared with the separation and extraction technology of other milk-derived active substances, the separation and extraction of active substances by using a combination of a cation exchange membrane (charged membrane) and a diafiltration process can not only ensure a higher separation efficiency of active substances, thereby significantly increasing the content of active substances in milk products, but also significantly reduce the decay rate of active substances during room temperature storage, thereby extending the room temperature shelf life of milk products.

[0040] The milk preparation method further comprises: subjecting the third permeate to nanofiltration to obtain a fourth permeate and a fourth concentrated liquid, and subjecting the fourth permeate to reverse osmosis to obtain a fifth permeate and a fifth concentrated liquid.

[0041] Furthermore, the inventors of the present invention have also found that in different diafiltration processes, different elution solutions used also have a significant impact on the separation efficiency of the active substance and its stability during storage at room temperature, which has rarely been paid attention to in the prior art.

[0042] Preferably, in the microfiltration diafiltration process, the third permeate and the fifth concentrated solution are used in a volume ratio of (7-11):1 for elution.

[0043] Preferably, in the ultrafiltration and diafiltration process, the fourth permeate and the fifth permeate are used for elution in a volume ratio of (5-9):3.

[0044] The inventors of the present invention have discovered that using the above-mentioned mixed solution for elution during the microfiltration and ultrafiltration processes, respectively, can not only significantly improve the separation efficiency of components such as α-lactalbumin, β-lactoglobulin, immunoglobulins, and lactose, but also help reduce the attenuation rate of these active proteins when stored at room temperature.

[0045] In the milk preparation method described above, the cation exchange membrane used preferably has a pore size of 0.8-1.0 μm. Using a cation exchange membrane with these parameters not only improves the separation efficiency of active substances such as lactoferrin, but also better cooperates with microfiltration and diafiltration to achieve the separation and extraction of multiple active substances.

[0046] Preferably, in the cation exchange membrane treatment, after the first permeate is applied to the membrane, it is first eluted with a 0.4-0.6 mol / L sodium chloride solution and then eluted with a 0.8-1.2 mol / L sodium chloride solution, and the eluates obtained from the two elutions are ultrafiltered and concentrated.

[0047] The above-mentioned elution method is more conducive to ensuring that a high content of lactoferrin is obtained by separation using a cation exchange membrane.

[0048] Preferably, during the cation exchange membrane treatment, the membrane temperature is 45-55°C or 4-20°C.

[0049] Preferably, the eluate obtained by the cation exchange membrane treatment is ultrafiltered and concentrated using an ultrafiltration spiral membrane, a hollow fiber membrane or a ceramic membrane with a molecular weight cutoff of 1000-500000 Da.

[0050] In the above-mentioned milk preparation method, the microfiltration diafiltration is performed using a 0.1-0.2 μm microfiltration ceramic membrane, a spiral membrane or a hollow fiber membrane, preferably a spiral membrane.

[0051] The ultrafiltration diafiltration is carried out using an ultrafiltration spiral membrane, hollow fiber membrane or ceramic membrane with a molecular weight cut-off of 1000-500000 Da (preferably 8000-12000 Da), preferably a spiral membrane.

[0052] Preferably, the nanofiltration is performed using a nanofiltration membrane with a molecular weight cut-off of 200-1000 Da. The main purpose of nanofiltration is to separate lactose, which can be backfilled into the high-temperature sterilized milk raw material according to the lactose content requirements of the milk product.

[0053] Preferably, the reverse osmosis process is performed using a spiral wound reverse osmosis membrane with a feed channel thickness of 0.7-0.9 mm. The primary purpose of reverse osmosis is to separate milk mineral salts. The separated milk mineral salts can be backfilled into the high-temperature sterilized milk raw material based on the milk mineral salt content requirements of the milk product. Preferably, the reverse osmosis has a NaCl rejection rate greater than 98%.

[0054] The temperatures of the above-mentioned microfiltration, ultrafiltration, nanofiltration and reverse osmosis treatments are all less than 10°C.

[0055] The above-mentioned method for preparing milk further includes: mixing the light cream with the first concentrated liquid and then sterilizing it to obtain a cream mixture, mixing the cream mixture with the second concentrated liquid, the fourth concentrated liquid, the fifth concentrated liquid and the fifth permeate and then heat sterilizing it to obtain the first material.

[0056] The nutrients in the milk fat mixture, the second concentrate, the fourth concentrate, the fifth concentrate and the fifth permeate are all high-temperature resistant substances. Therefore, according to the demand and design of different nutrients in the milk product, they can be mixed in the required amount and then heat-sterilized.

[0057] Preferably, the heat sterilization is ultra-high temperature sterilization. Preferred ultra-high temperature sterilization conditions are: 145-162°C for no more than 0.9 seconds, or 135-143°C for no more than 3 seconds.

[0058] Preferably, the ultra-high temperature sterilization is high-temperature, short-time direct infusion / injection sterilization.

[0059] Before ultra-high temperature sterilization, the process also includes preheating the material to be sterilized (preferably at a temperature of 68-90° C.).

[0060] Preferably, the ash content in the first material is 0.65-1.1 g / 100 g, preferably 0.7-1.0 g / 100 g.

[0061] The milk preparation method further comprises: treating the cation exchange membrane to obtain an eluate, concentrating the eluate by ultrafiltration, mixing the eluate with the third concentrate, sterilizing the eluate by microfiltration and / or absolute sterilization to obtain a second material, and mixing the second material with the first material.

[0062] The eluate (containing active substances such as lactoferrin) and the third concentrated liquid (containing active substances such as whey protein) obtained by cation exchange membrane treatment mainly contain heat-sensitive active substances that are easily denatured by heat. Therefore, they are sterilized by microfiltration sterilization and absolute sterilization (biological grade) to avoid high-temperature treatment to destroy the active substances.

[0063] Preferably, the microfiltration sterilization is performed using a filter membrane with a pore size of 0.25-0.68 μm and a photolithographic silicon material.

[0064] The temperature for microfiltration sterilization is preferably 45-65°C or 4-20°C.

[0065] Preferably, the absolute sterilization has a sterilization efficiency of ≥ log 7, and the sterilization temperature is 4-20°C.

[0066] Currently, biological-grade absolute sterilization is primarily used in the biopharmaceutical field, with limited application in food products such as dairy products. The inventors of the present invention have discovered that combining microfiltration sterilization with absolute sterilization, performing microfiltration sterilization before absolute sterilization, can significantly extend the operating time of sterilization equipment and reduce production costs.

[0067] Preferably, the eluate obtained by treating the cation exchange membrane is concentrated by ultrafiltration, mixed with the third concentrated liquid, sterilized by microfiltration, and then absolutely sterilized to obtain the second material, which is then mixed with the first material.

[0068] In the above method, the first material and the second material are mixed and maintained at 50-70° C. (preferably 55-65° C.) for 180-420 seconds (preferably 300-360 seconds).

[0069] The inventors of the present invention have found that mixing the first material and the second material and maintaining them at a relatively low temperature (50-70°C) for a certain period of time can significantly reduce the decay rate of the active substance under room temperature storage, which is beneficial to further extend the shelf life of the product.

[0070] After the first material and the second material are mixed, the temperature is maintained at 50-70° C. for 180-420 seconds, and then the mixture of the first material and the second material is cooled to below 25° C. and temporarily stored in a sterile tank.

[0071] Optionally, after cooling, lactase is added using an aseptic online lactase addition process and then aseptic filling is performed.

[0072] Preferably, the second material is mixed with the first material by aseptic online addition, that is, the second material is added to the first material by aseptic online addition.

[0073] Preferably, the first material is flash evaporated and homogenised before being mixed with the second material.

[0074] In some embodiments of the present disclosure, the method for preparing milk comprises the following steps (a schematic diagram of the process is shown in FIG1 ):

[0075] (1) Clean milk

[0076] The raw milk is purified by a centrifugal purifier at a temperature of 1-10°C, preferably 4-7°C;

[0077] (2) Fat separation

[0078] The raw milk after milk purification is subjected to fat separation in a centrifugal separator at a temperature of 45-70°C, preferably 55°C, or a temperature of 4-20°C, preferably 4-7°C; a rotation speed of 3500-5500 rpm, preferably 4000-5000 rpm;

[0079] (3) Sterilization separation / microfiltration sterilization (ceramic membrane or hollow fiber membrane)

[0080] sterilizing the skimmed milk produced in (2) by using a sterilizing separator, a microfiltration ceramic membrane, or a microfiltration hollow fiber membrane, or a combination of these processes;

[0081] Among them, the separation process of the sterilization separator is as follows: centrifugal sterilization is performed using a self-cleaning airtight centrifugal sterilizer, the conditions are temperature 40-65°C, preferably 55°C; rotation speed 6000-7000 rpm, preferably 6800 rpm; time 30-40s, preferably 35s.

[0082] The microfiltration ceramic membrane sterilization process is as follows: the conditions are: pore size 0.45-1.4 μm, preferably 0.8 μm; sterilization temperature 45-65°C, preferably 55°C, or temperature 4-20°C, preferably 4-7°C; the microfiltration concentrate is mixed with the cream and then sterilized, and the permeate is treated with an ion exchange membrane and then concentrated by diafiltration (MF);

[0083] The sterilization process of the microfiltration hollow fiber membrane is as follows: the conditions are: pore size 0.45-1.4 μm, preferably 0.8 μm; sterilization temperature 4-45°C, preferably 40-45°C or preferably 4-7°C; the microfiltration concentrate is mixed with the cream and then sterilized, and the permeate is concentrated by diafiltration (MF) after passing through a charged membrane;

[0084] (4) Cream sterilization

[0085] The mixture of the cream and the microfiltration concentrate is treated by an indirect or direct sterilization method. For an indirect tubular sterilizer, the temperature is 120-140°C, preferably 130°C, and the time is 5-20 seconds, preferably 10 seconds. For a direct infusion sterilizer, the temperature is 120-140°C, preferably 135°C, and the time is 5-20 seconds, preferably 7 seconds.

[0086] (5) Cation exchange membrane treatment

[0087] The sterilized skim milk (3) is passed through a cation exchange membrane at a temperature of 45-55°C, or 4-20°C, preferably 7-13°C; the flow-through liquid (permeate) is further subjected to a diafiltration (MF) process;

[0088] When the ratio of sterilized skim milk to filler reaches 250:1, the cation exchange membrane becomes saturated and automatically switches to another set of cation exchange membranes, thus achieving continuous operation. Gradient elution of the saturated charged membrane is performed using 0.4-0.6 mol / L and 0.8-1.2 mol / L sodium chloride solutions, respectively, to obtain two eluates. These can be mixed and purified and concentrated according to the target product index requirements, or purified and concentrated separately.

[0089] (6) Filtration (MF)

[0090] The permeate obtained in (5) is subjected to diafiltration (MF) concentration using a microfiltration ceramic membrane, a spiral membrane or a hollow fiber membrane with a pore size of 0.1-0.2 μm, preferably a 0.14 μm membrane assembly, and the diafiltration temperature is less than 10°C; during the diafiltration process, a third permeate and a fifth concentrated solution are used for elution in a volume ratio of (8-10):1, and the third permeate and the fifth concentrated solution are prepared by the method of the present disclosure; the diafiltration (MF) concentrated solution is temporarily stored in a tank, and the permeate is subjected to the next diafiltration (UF) concentration;

[0091] (7) UF

[0092] The permeate obtained in (6) is subjected to diafiltration (UF) concentration using an ultrafiltration roll membrane, a hollow fiber membrane or a ceramic membrane with a molecular weight cutoff of 1000-500000Da, preferably an 8000-12000Da membrane assembly, and the ultrafiltration temperature is less than 10°C; the fourth permeate and the fifth permeate are eluted with a volume ratio of (6-8):3, and the fourth permeate and the fifth permeate are prepared by the method of the present disclosure; the ultrafiltration concentrate is temporarily stored in a tank, and the permeate is concentrated by a nanofiltration membrane;

[0093] (8) Nanofiltration

[0094] The permeate after ultrafiltration (7) is concentrated by nanofiltration using a nanofiltration membrane with a molecular weight cutoff of 200-1000Da, preferably a 250-350Da membrane assembly, and the nanofiltration temperature is less than 10°C; the nanofiltration concentrate is temporarily stored in a tank, and the permeate is concentrated by reverse osmosis membrane;

[0095] (9) Reverse Osmosis

[0096] The permeate after nanofiltration concentration (8) is subjected to reverse osmosis concentration using a reverse osmosis wound membrane with a feed flow channel thickness of 0.7-0.9 mm, preferably a membrane assembly with a flow channel thickness of 0.8 mm, a reverse osmosis temperature of <10°C, and a NaCl retention rate of >98%; the reverse osmosis concentrate and the permeate are temporarily stored in tanks respectively;

[0097] (10) Component Recombination

[0098] According to the product index requirements, the mixture of the sterilized cream and the microfiltration concentrate in step (4), the diafiltration (MF) concentrate (concentrated casein), the nanofiltration concentrate (lactose solution), the reverse osmosis concentrate (milk mineral salt solution) and the reverse osmosis permeate (RO water) are mixed in proportion and recombined to form a semi-finished product, wherein the ash content is 0.65-1.1g / 100g, preferably 0.7-1.0g / 100g; during the component recombining process, an online near-infrared detection device is used to achieve precise control of physical and chemical indicators such as protein, fat, lactose and ash, and stirring is started in the mixing tank for 15-25 minutes before transferring to the ultra-high temperature sterilization system;

[0099] (11) Purification and concentration

[0100] The eluate obtained in (5) is purified and concentrated using an ultrafiltration roll membrane, hollow fiber membrane or ceramic membrane with a molecular weight cutoff of 1000-500000Da, preferably a 30000Da membrane assembly, at a temperature of <10°C; RO water is added for purification during the process, and the RO water is mainly prepared in the process;

[0101] (12) Mixing

[0102] The concentrated solution obtained in (11) and the ultrafiltration concentrated solution (whey protein concentrate) obtained in (7) are subjected to microfiltration sterilization and / or biological grade absolute sterilization, or mixed and then subjected to microfiltration sterilization and / or biological grade absolute sterilization to achieve the purpose of commercial sterility, and after sterilization, they are aseptically added online to the semi-finished product after heat treatment in step (10) to achieve maximum retention of milk-derived active substances;

[0103] (13) Microfiltration sterilization, biological grade absolute sterilization

[0104] The microfiltration sterilization process is as follows: using a filter membrane made of photolithographic silicon with a pore size of 0.25-0.68 μm, preferably 0.3 μm; the sterilization temperature is 45-65°C, preferably 55°C, or the temperature is 4-20°C, preferably 4-7°C;

[0105] The biological grade absolute sterilization process is as follows: select a suitable sterilization filter element according to the sterilization efficiency, which is required to be ≥ log7, and the sterilization temperature is 4-20℃, preferably <10℃;

[0106] (14) Preheating

[0107] Preheating the semi-finished product after heat treatment in step (10) to 68-90° C., preferably 70° C.;

[0108] (15)Ultra-high temperature sterilization (direct)

[0109] After preheating in (14), the semi-finished product is directly sterilized by injection or infusion, and the sterilization temperature and time parameters are 145-162℃ for no more than 0.9s, or 135-143℃ for no more than 3s;

[0110] (16) Flash evaporation

[0111] The semi-finished product after sterilization in (15) is flash-evaporated, and the outlet temperature after flash evaporation is 68-90°C, preferably 68°C;

[0112] (17) Homogenization

[0113] The sterilized product is homogenized using a two-stage homogenization process of a sterile homogenizer. The homogenization temperature is 55-90°C, preferably 65-75°C, the total homogenization pressure is 160-400 bar, and the secondary homogenization pressure is 20-50 bar. The secondary pressure is preferably 20-25 bar or 0.2 times the total pressure. The lower the homogenization pressure, the better, provided that the homogenization efficiency is met.

[0114] (18) Sterile online addition

[0115] The semi-finished product after homogenization is cooled to 45-75°C, and then (13) the sterilized heat-sensitive substance is aseptically added online to the semi-finished product in a quantitative manner;

[0116] (19) Long-term maintenance of low temperature

[0117] The semi-finished product with added heat-sensitive substances is kept at low temperature for a long time to achieve the purpose of low-temperature enzyme inactivation and extend the shelf life while ensuring the activity of the heat-sensitive substances; the conditions are to maintain the temperature at 50-70°C, preferably 55°C, and the holding time is 180-420s, preferably 360s;

[0118] (20) Cooling and temporary storage in sterile tanks

[0119] After being kept at low temperature for a long time (19), the product is cooled to below 25°C and temporarily stored in a sterile tank;

[0120] (21) Lactase addition

[0121] Adopt aseptic online lactase addition process, the lactase addition amount is 0.3 per thousand;

[0122] (22) Aseptic filling

[0123] The sterilized product is filled using aseptic cold filling technology, that is, aseptic filling is performed below 25°C.

[0124] The present disclosure provides milk, which is prepared by the method described above.

[0125] Preferably, the milk is room temperature milk.

[0126] Preferably, the milk has a protein content of 3.6-11.17 g / 100 g, a fat content of 0.1-6.0 g / 100 g, a lactose content of 0.5-6.5 g / 100 g, a lactoferrin content of >60 mg / L, an α-lactalbumin content of >500 mg / L, a β-lactoglobulin content of >800 mg / L, and an immunoglobulin content of >100 mg / L.

[0127] Preferably, the milk has a protein content of 3.6-11.17 g / 100 g, a fat content of 0.1-6.0 g / 100 g, a lactose content of 0.5-6.5 g / 100 g, a lactoferrin content of >100 mg / L, an α-lactalbumin content of >900 mg / L, a β-lactoglobulin content of >4000 mg / L, and an immunoglobulin content of >200 mg / L.

[0128] The present invention will be described in more detail below with reference to the examples. It should be noted that these descriptions and examples are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The scope of protection of the present invention shall be subject to the appended claims.

[0129] Example 1

[0130] This embodiment provides a method for preparing milk, the steps of which are as follows:

[0131] (1) Clean milk

[0132] The raw milk is purified by a centrifugal purifier at a temperature of 4-7°C.

[0133] (2) Fat separation

[0134] The raw milk after milk purification is centrifuged to separate fat at a temperature of 4-7°C and a speed of 4500 rpm. After the whole milk is skimmed, the skim milk is sterilized. The cream is mixed with the concentrated solution obtained by microfiltration and sterilization of the skim milk and then recombined with other components online.

[0135] (3) Microfiltration sterilization

[0136] The skim milk produced in step (2) is sterilized using a microfiltration hollow fiber membrane to obtain a permeate and a concentrate, under the following conditions: a membrane pore size of 0.8 μm and a sterilization temperature of 4-7° C.; the microfiltration concentrate is mixed with cream and then sterilized, and the permeate is concentrated by diafiltration (MF) after passing through an ion exchange membrane (charged membrane);

[0137] (4) Cream sterilization

[0138] The mixture of the cream of step (2) and the microfiltration concentrate of step (3) was treated by direct infusion at a temperature of 135° C. and a time of 7 seconds;

[0139] (5) Cation exchange membrane treatment

[0140] The skim milk (permeate) sterilized in step (3) is passed through a cation exchange membrane at a temperature of 13° C.; the flow-through (permeate) is further subjected to a diafiltration (MF) process;

[0141] When the ratio of sterilized skim milk to filler reaches 250:1, the cation exchange membrane becomes saturated and automatically switches to another set of cation exchange membranes, thus achieving continuous operation. Gradient elution of the saturated cation exchange membrane is performed using 0.4 mol / L and 0.8 mol / L sodium chloride solutions, respectively, to obtain two eluates, which are then purified and concentrated according to the target product indicators.

[0142] (6) Microfiltration (MF)

[0143] The cation exchange membrane permeate obtained in step (5) is subjected to microfiltration diafiltration (MF) concentration using a wound membrane with a pore size of 0.14 μm, and the diafiltration temperature is less than 10° C. During the diafiltration process, a mixed solution consisting of an ultrafiltration permeate and a reverse osmosis concentrate with a volume ratio of 9:1 is used for elution; the obtained microfiltration diafiltration (MF) concentrate is temporarily stored in a tank for component recombining in step (10), and the permeate is subjected to the next ultrafiltration diafiltration (UF) concentration;

[0144] (7) Ultrafiltration (UF)

[0145] The microfiltration (MF) permeate obtained in step (6) is subjected to ultrafiltration (UF) concentration using an ultrafiltration wound membrane with a molecular weight cutoff of 10,000 Da, and the ultrafiltration temperature is less than 10° C. During the diafiltration process, a mixture of nanofiltration permeate and reverse osmosis permeate in a volume ratio of 7:3 is used for elution; the obtained ultrafiltration concentrate is temporarily stored in a tank, and the ultrafiltration permeate is concentrated using a nanofiltration membrane;

[0146] (8) Nanofiltration

[0147] The permeate after ultrafiltration concentration in step (7) is subjected to nanofiltration concentration using a nanofiltration membrane with a molecular weight cutoff of 300 Da, and the nanofiltration temperature is less than 10° C. The nanofiltration concentrate is temporarily stored in a tank, and the permeate is subjected to reverse osmosis membrane concentration;

[0148] (9) Reverse Osmosis

[0149] The permeate after nanofiltration concentration in step (7) is subjected to reverse osmosis concentration using a reverse osmosis wound membrane having a feed flow channel thickness of 0.8 mm, the reverse osmosis temperature being less than 10° C., and the NaCl retention rate being greater than 98%; the obtained reverse osmosis concentrate and permeate are temporarily stored in tanks respectively;

[0150] (10) Component Recombination

[0151] According to the product index requirements, the mixture of the sterilized cream and the microfiltration concentrate in step (4), the microfiltration diafiltration (MF) concentrate (concentrated casein) in step (6), the nanofiltration concentrate (lactose solution) in step (8), the reverse osmosis concentrate (milk mineral salt solution) in step (9) and the reverse osmosis permeate (RO water) are mixed in proportion and recombined to form a semi-finished product, wherein the ash content is 0.7-1.0g / 100g; during the component recombining process, an online near-infrared detection device is required to achieve precise control of physical and chemical indicators such as protein, fat, lactose and ash, and stirring is started in the mixing tank for 20 minutes before entering the ultra-high temperature sterilization system;

[0152] (11) Purification and concentration

[0153] The eluate obtained in step (5) is purified and concentrated using an ultrafiltration hollow fiber membrane with a molecular weight cutoff of 30,000 Da at a temperature of <10° C. RO water is added for purification during the process, and the RO water is mainly prepared in the process;

[0154] (12) Mixing

[0155] Mixing the concentrated solution obtained in step (11) with the ultrafiltration concentrated solution (whey protein concentrate) obtained in step (7);

[0156] (13) Sterilization of heat-sensitive substances

[0157] The mixture of step (12) is physically sterilized by microfiltration and biological grade absolute sterilization in series to achieve the purpose of commercial sterility, and after sterilization, it is aseptically added online to the semi-finished product after heat treatment;

[0158] The microfiltration sterilization process is as follows: the membrane core is made of silicon and processed by photolithography technology. The membrane pore size is 0.3μm and the pore size distribution is uniform and stable. The sterilization efficiency of active substances can reach log6 or above. The microfiltration sterilization temperature is 4-7℃.

[0159] The biological grade absolute sterilization process is as follows: select the appropriate sterilization filter according to the sterilization efficiency, the sterilization efficiency is ≥ log7, and the sterilization temperature is <10°C;

[0160] (14) Preheating

[0161] Preheating the semi-finished product after the components are reassembled in step (10) to 70° C.

[0162] (15)Ultra-high temperature sterilization (direct)

[0163] The semi-finished product preheated in step (14) is directly sterilized by infusion at ultra-high temperature, and the sterilization temperature and time parameters are 157°C and 0.1s;

[0164] (16) Flash evaporation

[0165] The semi-finished product sterilized in step (15) is flash-evaporated, and the outlet temperature after flash evaporation is 68° C.

[0166] (17) Homogenization

[0167] The semi-finished product after flash evaporation in step (16) is homogenized by a two-stage homogenization process using a sterile homogenizer, with a homogenization temperature of 65-75° C., a total homogenization pressure of 160-400 bar, and a secondary homogenization pressure of 25 bar;

[0168] (18) Sterile online addition

[0169] After homogenization, the semi-finished product is cooled to 55° C. according to the low temperature and long-term temperature maintenance design, and then the sterilized heat-sensitive substance in step (13) is aseptically added to the semi-finished product online in a quantitative manner;

[0170] (19) Long-term maintenance of low temperature

[0171] The semi-finished product with heat-sensitive substances added is kept at low temperature for a long time, maintaining the temperature at 55°C for 360 seconds;

[0172] (20) Cooling and temporary storage in sterile tanks

[0173] The product after long-term low temperature maintenance in step (19) is cooled to below 25° C. and temporarily stored in a sterile tank;

[0174] (21) Lactase addition

[0175] Lactase was added using a sterile online lactase addition process, with the added amount of lactase being 0.3 per thousand;

[0176] (22) Aseptic filling

[0177] The product obtained in step (21) is aseptically cold-filled, i.e., aseptically filled at a temperature below 25°C.

[0178] This embodiment also provides milk, which is prepared by the above method, and the product target indicators are designed to be: protein: 4.0g / 100g, fat: 4.5g / 100g, lactose (before adding lactase): 3.2g / 100g.

[0179] Example 2

[0180] This embodiment provides a method for preparing milk, which differs from the method in Example 1 only in that: Step (13) sterilization of heat-sensitive substances: biological-grade absolute sterilization is removed, and only physical sterilization is performed by microfiltration sterilization.

[0181] This embodiment also provides milk, which is prepared by the above method, and the product target indicators are designed to be: protein: 4.0g / 100g, fat: 4.5g / 100g, lactose (before adding lactase): 3.2g / 100g.

[0182] Example 3

[0183] This embodiment provides a method for preparing milk, which differs from the method in Example 1 only in that: Step (13) sterilization of heat-sensitive substances: microfiltration sterilization is eliminated, and only biological-grade absolute sterilization is used for physical sterilization.

[0184] This embodiment also provides milk, which is prepared by the above method, and the product target indicators are designed to be: protein: 4.0g / 100g, fat: 4.5g / 100g, lactose (before adding lactase): 3.2g / 100g.

[0185] Example 4

[0186] This embodiment provides a method for preparing milk, which differs from the method of embodiment 1 only in that: in step (6), a mixture of ultrafiltration permeate and reverse osmosis concentrate in a volume ratio of 7:1 is used for elution during the diafiltration process;

[0187] In step (7), a mixture of nanofiltration permeate and reverse osmosis permeate in a volume ratio of 9:3 is used for elution during the diafiltration process.

[0188] This embodiment also provides milk, which is prepared by the above method, and the product target indicators are designed to be: protein: 4.0g / 100g, fat: 4.5g / 100g, lactose (before adding lactase): 3.2g / 100g.

[0189] Example 5

[0190] This embodiment provides a method for preparing milk, which differs from the method in Example 1 only in that: Step (19) low temperature long-term maintenance: the semi-finished product with the heat-sensitive substance added is maintained at a low temperature for a long time, maintaining the temperature at 65°C for 300 seconds.

[0191] This embodiment also provides milk, which is prepared by the above method, and the product target indicators are designed to be: protein: 10.0g / 100g, fat: 0.2g / 100g, lactose (before adding lactase): 1.0g / 100g.

[0192] Example 6

[0193] This embodiment provides a method for preparing milk, which differs from the method in Example 1 only in that: in step (5), the cation exchange membrane treatment temperature is 50°C, the saturated cation exchange membrane is gradient eluted using 0.6 mol / L and 1.2 mol / L sodium chloride solutions, and the membrane flow temperature of the cation exchange membrane in step (5) is 50°C.

[0194] This embodiment also provides milk, which is prepared by the above method, and the product target indicators are designed to be: protein: 10.0g / 100g, fat: 0.2g / 100g, lactose (before adding lactase): 1.0g / 100g.

[0195] Comparative Example 1

[0196] This comparative example provides a method for preparing milk, which differs from the method of Example 1 only in that: steps (5), (6), (11), (12), (13), and (18) are omitted, and step (7) diafiltration (UF) is as follows: ultrafiltration (UF) is performed on the skimmed milk sterilized in step (3) using an ultrafiltration roll membrane with a molecular weight cutoff of 10,000 Da, and the ultrafiltration temperature is less than 10°C; during the diafiltration process, a mixture of nanofiltration permeate and reverse osmosis permeate in a volume ratio of 7:3 is used for elution; the obtained ultrafiltration concentrate is temporarily stored in a tank for component recombining in step (10) and the ultrafiltration permeate is concentrated by nanofiltration membrane.

[0197] This comparative example also provides a milk prepared by the above method, and the target product indicators are designed as follows: protein: 4.0g / 100g, fat: 4.5g / 100g, lactose (before adding lactase): 3.2g / 100g.

[0198] Comparative Example 2

[0199] This comparative example provides a method for preparing milk, which differs from the method of Example 1 only in that: steps (5), (11) and (12) are omitted, and step (6) microfiltration (MF) is as follows: the skimmed milk sterilized in step (3) is subjected to microfiltration (MF) concentration using a roll membrane with a pore size of 0.14 μm, and the filtration temperature is less than 10°C; during the filtration process, a mixed solution consisting of ultrafiltration permeate and reverse osmosis concentrate in a volume ratio of 9:1 is used for elution; the obtained microfiltration (MF) concentrate is temporarily stored in a tank for component recombining in step (10), and the filtrate is subjected to the next step of ultrafiltration (UF) concentration.

[0200] This comparative example also provides a milk prepared by the above method, and the target product indicators are designed as follows: protein: 4.0g / 100g, fat: 4.5g / 100g, lactose (before adding lactase): 3.9g / 100g.

[0201] Comparative Example 3

[0202] This comparative example provides a method for preparing milk, which differs from the method of Example 1 only in that: steps (6) and (12) are omitted, and step (7) diafiltration (UF) is as follows: the permeate of step (5) is subjected to ultrafiltration diafiltration (UF) concentration using an ultrafiltration roll membrane with a molecular weight cutoff of 10,000 Da, and the ultrafiltration temperature is less than 10°C; during the diafiltration process, a mixture of nanofiltration permeate and reverse osmosis permeate in a volume ratio of 7:3 is used for elution; the obtained ultrafiltration concentrate is temporarily stored in a tank for step (10) component recombining and ultrafiltration permeate concentration using a nanofiltration membrane.

[0203] This comparative example also provides a milk prepared by the above method, and the target product indicators are designed as follows: protein: 4.0g / 100g, fat: 4.5g / 100g, lactose (before adding lactase): 3.2g / 100g.

[0204] Comparative Example 4

[0205] This comparative example provides a method for preparing milk, which differs from the method in Example 1 only in that an ion exchange chromatography column is used in step (5) 20 instead of a cation exchange membrane, as follows:

[0206] Pass the sterilized skim milk (permeate) from step (3) through a cation chromatography column at a temperature of 4-7°C;

[0207] The flow-through liquid (permeate) continues to undergo the diafiltration (MF) process;

[0208] When the ratio of the amount of sterilized skimmed milk to the amount of filler in the chromatographic column reaches 250:1, the chromatographic column is saturated. Gradient elution is performed on the saturated chromatographic column using 0.4 mol / L and 0.8 mol / L sodium chloride solutions, respectively, to obtain two eluates, which are purified and concentrated according to the target product index requirements.

[0209] This comparative example also provides a milk prepared by the above method, and the target product indicators are designed as follows: protein: 4.0g / 100g, fat: 4.5g / 100g, lactose (before adding lactase): 3.2g / 100g.

[0210] Comparative Example 5

[0211] This comparative example provides a method for preparing milk, which differs from the method in Example 1 only in that the skimmed milk sterilized in step (3) is divided into two equal parts, one of which is used to prepare the active substance using the rennet method, and the processing method of the other part differs from the method in Example 1 in that steps (5), (6) and (12) are omitted.

[0212] Preparation of active substance by rennet method: After sterilization in step (3), the skim milk is kept at 42℃ for 30min, citric acid is added to adjust the pH value to 6.2, 0.006% calf rennet is added, the enzyme reaction temperature is 42℃, and the clotting time is 40min. When the clotting time is reached, cut the milk into 1cm pieces with a cheese knife. 3 The mixed active substance is prepared by slowly stirring for 2 minutes and then centrifuging to remove casein, which is purified and concentrated by step (11), and then the heat-sensitive substance is sterilized by step (13). The sterilized heat-sensitive substance is aseptically added online to the other processed skim milk in step (18).

[0213] This comparative example also provides a milk prepared by the above method, and the target product indicators are designed as follows: protein: 4.0g / 100g, fat: 4.5g / 100g, lactose (before adding lactase): 3.2g / 100g.

[0214] Comparative Example 6

[0215] This comparative example provides a method for preparing milk, which differs from the method in Example 1 only in that, in step (6), microfiltration (MF) is performed on the cation exchange membrane permeate obtained in step (5) using a spiral membrane with a pore size of 0.14 μm, and the filtration temperature is less than 10° C.; ultrafiltration permeate is used for elution during the diafiltration process; the obtained microfiltration (MF) concentrate is temporarily stored in a tank, and the permeate is subjected to the next step of ultrafiltration (UF) concentration.

[0216] This comparative example also provides a milk prepared by the above method, and the target product indicators are designed as follows: protein: 4.0g / 100g, fat: 4.5g / 100g, lactose (before adding lactase): 3.2g / 100g.

[0217] Comparative Example 7

[0218] This comparative example provides a method for preparing milk, which differs from the method in Example 1 only in that, in step (6), microfiltration (MF) is performed on the cation exchange membrane permeate obtained in step (5) using a spiral membrane with a pore size of 0.14 μm, and the filtration temperature is less than 10° C.; during the diafiltration process, a mixed solution consisting of an ultrafiltration permeate and a reverse osmosis concentrate in a volume ratio of 8:2 is used for elution; the obtained microfiltration (MF) concentrate is temporarily stored in a tank for component recombining in step (10), and the permeate is subjected to the next step of ultrafiltration (UF) concentration.

[0219] This comparative example also provides a milk prepared by the above method, and the target product indicators are designed as follows: protein: 4.0g / 100g, fat: 4.5g / 100g, lactose (before adding lactase): 3.2g / 100g.

[0220] Comparative Example 8

[0221] This comparative example provides a method for preparing milk, which differs from the method in Example 1 only in that: Step (19) low temperature long-term maintenance: the semi-finished product with the heat-sensitive substance added is maintained at a low temperature for a long time, maintaining the temperature at 45°C for 420 seconds.

[0222] This comparative example also provides a milk prepared by the above method, and the target product indicators are designed as follows: protein: 10.0g / 100g, fat: 0.2g / 100g, lactose (before adding lactase): 1.0g / 100g.

[0223] Comparative Example 9

[0224] This comparative example provides a method for preparing milk, which differs from the method in Example 1 only in that: Step (19) low temperature long-term maintenance: the semi-finished product with the heat-sensitive substance added is maintained at a low temperature for a long time, maintaining the temperature at 75°C for 240s.

[0225] This comparative example also provides a milk prepared by the above method, and the target product indicators are designed as follows: protein: 10.0g / 100g, fat: 0.2g / 100g, lactose (before adding lactase): 1.0g / 100g.

[0226] Comparative Example 10

[0227] This comparative example provides a method for preparing milk, which differs from the method in Example 1 only in that: Step (19) low temperature long-term maintenance: the semi-finished product with the heat-sensitive substance added is maintained at a low temperature for a long time, maintaining the temperature at 80°C for 180 seconds.

[0228] This comparative example also provides a milk, which is prepared by the above method, and the product target indicators are designed to be: protein: 10.0g / 100g, fat: 0.2g / 100g, lactose (before adding lactase): 1.0g / 100g.

[0229] Comparative Example 11

[0230] This comparative example provides a method for preparing milk, which differs from the method in Example 1 only in that step (19) is omitted.

[0231] This comparative example also provides a milk prepared by the above method, and the target product indicators are designed as follows: protein: 10.0g / 100g, fat: 0.2g / 100g, lactose (before adding lactase): 1.0g / 100g.

[0232] Experimental example

[0233] The milk prepared by the methods of the above embodiments and comparative examples was subjected to product index testing, and the results are shown in Table 1.

[0234] Table 1 Results of milk product index determination

[0235] The milk prepared by the methods of the above examples and comparative examples was subjected to determination of active substance content, shelf life, active substance decay rate, and sensory evaluation, and production performance was also evaluated, as follows:

[0236] 1. Method for determining the content of active substances in the product before it comes off the production line: The content of active substances in the product shall be tested within 7 days after the product comes off the production line.

[0237] 2. Separation time determination method: Calculate the time required for an ion exchange membrane (charged membrane) and an ion exchange chromatography column loaded with 600 L of filler to process 100 T of skim milk respectively.

[0238] 3. Continuous operation time determination method: The longest continuous operation time of the prepared active substance microfiltration / biological grade absolute sterilization equipment is the time from the start of the sterilization equipment to the serious decrease in the membrane flux of the equipment, resulting in the inability to feed normally.

[0239] 4. Shelf life determination method: The time it takes to ensure product safety and achieve the required flavor, chemical, physical and microbiological properties under storage conditions at room temperature of 25°C.

[0240] 5. Sensory preference test method: After 10 days, 50 professional tasters were invited to rate the product's preference for the prepared milk. The score range was 1 to 10, with higher scores indicating higher preference. The obtained scores were averaged to obtain the sensory preference test results.

[0241] 6. Active substance decay rate determination method: Under normal temperature and storage conditions of 25°C, the active substance content in the sample is tested after 30, 60, 90, 120, 150, and 180 days (storage time is determined according to the shelf life). The decay rate is calculated as follows:

[0242] Decay rate = ((active substance content immediately after production - active substance content at 30 / 60 / 90 / 120 / 150 / 180 days) / active substance content immediately after production) × 100%.

[0243] The results are shown in Tables 2, 3 and 4.

[0244] Table 2 Test results of performance indicators such as the content of active substances in milk products

[0245] Table 3 Results of active substance decay rate determination (1)

[0246] Table 4 Active substance decay rate measurement results (2)

[0247] As shown in Tables 2, 3, and 4, considering the contents of lactoferrin, α-lactalbumin, β-lactoglobulin, and immunoglobulin, the active substance separation time, the continuous operation time of the active substance sterilization equipment, the shelf life, the active substance decay rate, and other test results, the comprehensive performance indicators of the milk prepared by the preparation methods of the embodiments are significantly better than those of the comparative examples.

[0248] The current dairy liquid milk market is dominated by low-temperature pasteurized milk and ambient temperature (UHT) milk. Low-temperature pasteurized milk primarily uses pasteurization at temperatures of 72-90°C for 5-20 seconds. This method offers low sterilization intensity but relatively good activity retention. Lactoferrin content is approximately 20-60 mg / L, α-lactalbumin is approximately 800-1200 mg / L, and β-lactoglobulin is approximately 1800-3000 mg / L. The currently claimed maximum immunoglobulin content is 230 mg / L. Compared to ambient temperature (UHT) milk, low-temperature pasteurized milk exhibits better activity retention. However, its shelf life is shorter, approximately 7-15 days, and it requires refrigeration at temperatures of 2-6°C. Therefore, low-temperature pasteurized milk has limited reach and cannot reach areas with underdeveloped cold chains. UHT milk, on the other hand, uses ultra-high temperature (UHT) sterilization at temperatures of 135-150°C for 4-15 seconds. This method offers high sterilization intensity but low activity retention. β-lactoglobulin content is approximately 300 mg / L, and other active substances are almost undetectable. The present disclosure utilizes a cation exchange membrane combined diafiltration process to first separate and sterilize active substances such as lactoferrin, α-lactalbumin, β-lactoglobulin, and immunoglobulins in raw cow milk, and then backfill them into the sterilized semi-finished product. Combined with technologies such as low temperature and long-term preservation, a method for preparing room-temperature milk with high protein, high active substance content, and a long shelf life has been developed, which provides the possibility for the incubation of high-end, high-nutrition, and multifunctional products. The combination of a cation exchange membrane and a diafiltration process enables efficient and non-destructive separation and extraction of active substances from skim milk, preventing them from being damaged by heat treatment. This significantly increases the content of active substances in milk products without affecting other components of the milk. This method is more efficient than traditional acid precipitation and enzymatic coagulation methods and is more suitable for dairy processing primarily based on liquid milk. Furthermore, the cation exchange membrane has a large pore size and low resistance, with a pressure of less than 1 bar for skim milk to pass through the membrane and a residence time of approximately 0.2 minutes. Traditional chromatographic column packing particles are compact and have high resistance, with a pressure of approximately 3 bar for skim milk to pass through the column and a residence time of approximately 2-3 minutes, or even longer. Therefore, when loaded with the same packing amount, the cation exchange membrane is significantly more efficient at processing skim milk than a chromatographic column and can be operated continuously in series with the diafiltration (MF) process, saving milk transfer and storage time, improving process efficiency, and further facilitating product quality assurance.

[0249] At present, centrifuges or microfiltration are often used for sterilization in dairy products, and the sterilization efficiency is about log2-4, which can only be used as a pretreatment to achieve the purpose of locking the freshness of the product and extending the shelf life. The microfiltration sterilization technology used in the present disclosure uses silicon as the material for the membrane core, which is processed by photolithography technology. The sterilization efficiency of active substances can reach log6 and above, achieving the purpose of commercial sterility. At the same time, drawing on the absolute sterilization technology of biology and pharmaceuticals, the absolute sterilization filter element adopts the "vertical filtration" form, which has a higher sterilization efficiency and can reach log7 and above for active substances. The present disclosure connects microfiltration sterilization with a biological-grade absolute sterilization membrane in series, which has a higher sterilization efficiency and a longer continuous sterilization time, and can achieve the effect of commercial sterility. After sterilization by the combination of microfiltration and biological-grade absolute sterilization, the active substance is aseptically added online to the semi-finished product after heat treatment to achieve maximum retention of milk-derived active substances.

[0250] The inventors of the present invention have discovered that while direct infusion / injection sterilization, performed at high temperatures and for a short time, effectively preserves the product's original flavor, it also results in higher enzyme content after sterilization compared to indirect sterilization. While active substances are highly effective in removing bacteria independently, enzymes are difficult to effectively remove due to their molecular weight and particle size being similar to proteins, resulting in a shorter shelf life. To address this issue, the inventors of the present invention, through continuous experimentation, discovered that maintaining the product at low temperatures for a long period of time after sterilization can help inactivate enzymes, extending shelf life without significantly impacting active substances.

[0251] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A method for preparing milk, the method comprising: include: The raw milk is subjected to fat separation to obtain cream and skim milk, and the skim milk is subjected to separation or filtration sterilization to obtain a first permeate and a first concentrate; The first permeate is treated with a cation exchange membrane to obtain an eluate and a permeate, the permeate is then filtered through microfiltration to obtain a second permeate and a second concentrated solution, and the second permeate is filtered through ultrafiltration to obtain a third permeate and a third concentrated solution.

2. The method according to claim 1, further comprising: include: The third permeate is subjected to nanofiltration to obtain a fourth permeate and a fourth concentrated solution, and the fourth permeate is subjected to reverse osmosis to obtain a fifth permeate and a fifth concentrated solution.

3. The method according to claim 2, in: In the microfiltration diafiltration process, the third permeate and the fifth concentrated solution are eluted in a volume ratio of (7-11):1; and / or In the ultrafiltration and diafiltration process, the fourth permeate and the fifth permeate with a volume ratio of (5-9):3 are used for elution.

4. The method according to any one of claims 1 to 3, in: The pore size of the cation exchange membrane is 0.8-1.0 μm; and / or In the cation exchange membrane treatment, after the first permeate is applied to the membrane, it is first eluted with a 0.4-0.6 mol / L sodium chloride solution, and then eluted with a 0.8-1.2 mol / L sodium chloride solution, and the eluate obtained by the two elutions is ultrafiltered and concentrated; and / or In the cation exchange membrane treatment, the membrane temperature is 45-55°C or 4-20°C.

5. The method according to any one of claims 1 to 3, in: Microfiltration is performed using 0.1-0.2 μm microfiltration ceramic membranes, spiral membranes or hollow fiber membranes; and / or The ultrafiltration is carried out using an ultrafiltration membrane, a hollow fiber membrane or a ceramic membrane with a molecular weight cutoff of 1000-500000Da; and / or Nanofiltration is performed using a nanofiltration membrane with a molecular weight cut-off of 200-1000Da; and / or The reverse osmosis is carried out using a reverse osmosis spiral membrane with a feed channel thickness of 0.7-0.9 mm; and / or The temperatures for microfiltration, ultrafiltration, nanofiltration, and reverse osmosis treatments are all less than 10°C.

6. The method according to any one of claims 1 to 3, further comprising: include: The cream is mixed with the first concentrated liquid and then sterilized to obtain a cream mixture, and the cream mixture is mixed with the second concentrated liquid, the fourth concentrated liquid, the fifth concentrated liquid and the fifth permeate and then heat-sterilized to obtain the first material.

7. The method according to claim 6, further comprising: include: The eluted liquid obtained by treating the cation exchange membrane is concentrated by ultrafiltration and then mixed with the third concentrated liquid, sterilized by microfiltration and / or absolute sterilization to obtain the second material, and the second material is mixed with the first material.

8. The method according to claim 7, in: The microfiltration sterilization is performed using a filter membrane with a pore size of 0.25-0.68 μm and a photolithographic silicon material; and / or The absolute sterilization efficiency is ≥ log 7.

9. The method according to claim 7 or 8, wherein the first material and the second material are mixed and maintained at 50-70°C for 180-420s.

10. Milk, prepared by the method according to any one of claims 1 to 9.

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