Membrane concentrated dairy product and preparation method thereof

Abstract

The invention provides a membrane concentrated dairy product and a preparation method thereof. Compared with the prior art, effective separation and concentration of milk active protein, lactose, sodium and other components in the raw and fresh milk are realized through microfiltration, washing filtration, ultrafiltration and optional nanofiltration processes under the condition of lower temperature, and damage of high-temperature concentration to protein, vitamins and other thermosensitive components is avoided; the natural flavor and the nutritional value of dairy products are fully reserved, flexibility is achieved in the aspect of meeting different products and production requirements, micromolecular lactose or salt and the like in permeate liquid can be recycled, the resource utilization rate is increased, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of dairy product processing, in particular to a membrane concentrated dairy product and a preparation method thereof. Background Art

[0002] Dairy products are not only an important source of high-quality protein, fat, and a variety of vitamins and minerals, but the active proteins they contain are also functional ingredients that have received widespread attention in recent years. Generally speaking, cow's milk is rich in a variety of physiologically active proteins, including immunoglobulins, lactoferrin, lactoperoxidase, etc. These active proteins have potential benefits for improving human immunity, iron ion balance, and intestinal health, and therefore have important value in the fields of clinical nutrition, special medical formula foods, and high-end health foods. However, traditional dairy processing often requires high-temperature evaporation or long-term heat treatment to achieve concentration or sterilization, which causes partial or major denaturation and loss of active proteins, reducing the functionality and nutritional value of the end product.

[0003] With the increasing demand for active proteins and the continuous maturity of membrane separation technology, multi-stage membrane separation and enrichment of milk at room temperature or low temperature conditions has become a more ideal technical route.

[0004] However, in the existing technology, if only a single or simple combination of membrane processes are relied upon, it is often difficult to balance the efficient retention and separation purity of active proteins. Some membrane separation processes fail to fully optimize the sensitivity of active proteins to factors such as heat and mechanical shear, resulting in aggregation or denaturation of proteins during the separation process. Moreover, in order to obtain low-lactose or low-sodium product effects, some processes will perform multiple filtrations or repeated heating and sterilization, which will further damage the functionality of active proteins. For the flavor and texture of the end product, unreasonable degreasing, desalting or protein reconstitution processes may also have a negative impact, resulting in a thin taste and insufficient flavor, which is difficult to meet the consumer market's expectations for high-end dairy products. Summary of the invention

[0005] In view of the shortcomings of the prior art mentioned above, the object of the present invention is to provide a membrane concentrated dairy product and a preparation method thereof, which utilizes multi-stage membrane separation technology (including defatting, microfiltration, diafiltration, ultrafiltration and nanofiltration, etc.) to grade and regulate the components such as protein, lactose and sodium in dairy products at a relatively low temperature, thereby obtaining a dairy product with high protein, low lactose and low sodium.

[0006] This method retains active proteins, vitamins and other heat-sensitive nutrients to the greatest extent, while effectively overcoming the problems of nutritional loss, taste deterioration and high energy consumption caused by high temperature. In the specific process, after physical sterilization is achieved through microfiltration, low-temperature pasteurization can be combined to completely remove residual microorganisms; microfiltration first removes most of the bacteria under low pressure and low temperature conditions, and the subsequent short-term low-temperature pasteurization further inactivates the remaining bacteria and avoids the destruction of active substances by repeated high-temperature sterilization. This combination of "physics + low-temperature heat" not only greatly reduces membrane pollution and energy consumption of multiple heating operations, but also enables the product to achieve a balance between safety, nutrition and flavor retention.

[0007] To achieve the above objectives and other related objectives, the present invention is achieved through the following technical solutions.

[0008] In one aspect, the present invention provides a method for preparing a membrane concentrated dairy product, the method comprising the following steps:

[0009] 1) skimming and separating the raw milk to obtain skimmed milk and cream;

[0010] 2) microfiltration of the skim milk to obtain a microfiltration retentate and a microfiltration permeate;

[0011] 3) performing diafiltration on the microfiltration retentate obtained in step 2) to obtain a diafiltration retentate and a diafiltration permeate; performing ultrafiltration on the microfiltration permeate obtained in step 2) to obtain a final retentate and a final permeate;

[0012] 4) The diafiltration retentate is homogenized and sterilized, and then mixed with the final retentate to obtain the membrane concentrated dairy product.

[0013] In some embodiments of the present invention, the fat content of the skim milk in step 1) is 0.01-0.5 g / 100 ml.

[0014] In some embodiments of the present invention, the defatting method is separation.

[0015] In some embodiments of the present invention, the separation method is centrifugal separation.

[0016] In some embodiments of the present invention, the temperature of the centrifugal separation is 40-70°C.

[0017] In some embodiments of the present invention, the centrifugal rotation speed is 3000-8000 rpm.

[0018] In some embodiments of the present invention, the source of the fresh milk can be selected from cows, sheep and / or camels.

[0019] In some embodiments of the present invention, the pore size of the membrane used for microfiltration in step 2) is 0.1-0.8 μm.

[0020] In some embodiments of the present invention, the material of the membrane used for microfiltration in step 2) can be selected from polypropylene, ceramic, polyvinylidene fluoride (PVDF), polyvinylidene fluoride (PVDF), polyether sulfone (PES) or other materials with microfiltration performance.

[0021] In some embodiments of the present invention, the operating pressure of the microfiltration in step 2) is 1 to 5 bar.

[0022] In some embodiments of the present invention, the operating temperature of the microfiltration in step 2) is 30-55°C.

[0023] In some embodiments of the present invention, the microfiltration flux in step 2) can be between 50 and 400 L / m 2 ·h.

[0024] In some embodiments of the present invention, the concentration multiple of the microfiltration in step 2) is 1.2 to 5.0.

[0025] In some embodiments of the present invention, the diafiltration operation is performed according to the following steps: after the microfiltration concentration, water is added to the microfiltration retentate to perform diafiltration until the lactose content in the diafiltration retentate is less than or equal to 2 mg / 100 ml.

[0026] In some embodiments of the present invention, the molecular weight cutoff of the membrane used for ultrafiltration in step 3) is 10,000 to 100,000 Daltons.

[0027] In some embodiments of the present invention, the material of the membrane used for ultrafiltration in step 3) can be selected from cellulose acetate, polyvinylidene fluoride (PVDF), polyether sulfone (PES), polyamide, polyacrylonitrile (PAN), polyvinyl chloride (PVC), polypropylene (PP) or ceramic membrane or other materials with ultrafiltration performance.

[0028] In some embodiments of the present invention, the operating pressure of the ultrafiltration in step 3) is 1 to 10 bar.

[0029] In some embodiments of the present invention, the operating temperature of the ultrafiltration in step 3) is 5-25°C.

[0030] In some embodiments of the present invention, the ultrafiltration flux in step 3) is 20 to 100 L / m 2 ·h.

[0031] In some embodiments of the present invention, the concentration factor of the ultrafiltration in step 3) is 1 to 3.0.

[0032] In some embodiments of the present invention, step 3) further comprises the step of nanofiltration of the ultrafiltration retentate after ultrafiltration.

[0033] In some embodiments of the present invention, the molecular weight cutoff of the membrane used for nanofiltration is 200 to 1000 Daltons.

[0034] In some embodiments of the present invention, the material of the nanofiltration membrane can be selected from cellulose acetate, polyethersulfone (PES), polytetrafluoroethylene, polyethersulfone resin, polyethersulfone or polyamide composite membrane (TFC membrane) or other materials with nanofiltration performance.

[0035] In some embodiments of the present invention, the operating pressure of the nanofiltration is 10 to 30 bar.

[0036] In some embodiments of the present invention, the operating temperature of the nanofiltration is 5 to 25°C.

[0037] In some embodiments of the present invention, the nanofiltration flux is 10 to 40 L / m 2 ·h.

[0038] In some embodiments of the present invention, the concentration factor of the nanofiltration is 1 to 3.3.

[0039] In some embodiments of the present invention, the final retentate is an ultrafiltration retentate or a nanofiltration retentate; if a high-protein, low-lactose membrane concentrated dairy product is to be prepared, the final retentate is an ultrafiltration retentate; if the sodium content of the membrane concentrated dairy product is to be further reduced, the ultrafiltration retentate after ultrafiltration is further subjected to nanofiltration concentration after ultrafiltration, and the final retentate is the nanofiltration retentate at this time. The nanofiltration retentate after nanofiltration is used as the final retentate, and then mixed with the sterilized wash retentate in step 4) to prepare a high-protein, low-lactose, low-sodium membrane concentrated dairy product.

[0040] In some embodiments of the present invention, step 4) can also be to mix the diafiltration retentate and cream, homogenize and sterilize, and then mix with the final retentate to obtain a membrane concentrated dairy product; by adding cream, it can be used to prepare full-fat dairy products.

[0041] In some embodiments of the present invention, the homogenization temperature in step 4) is 55-65°C.

[0042] In some embodiments of the present invention, the homogenization pressure in step 4) is 150-400 bar.

[0043] In some embodiments of the present invention, the sterilization in step 4) is pasteurization.

[0044] In some embodiments of the present invention, the sterilization temperature in step 4) is 70-80°C.

[0045] In some embodiments of the present invention, the sterilization time in step 4) is 10 to 30 seconds.

[0046] The present invention also provides a membrane concentrated dairy product, which is prepared by the aforementioned preparation method of the present invention.

[0047] Compared with the prior art, the present invention realizes effective separation and concentration of components such as milk-active proteins (such as immunoglobulins, lactoferrin, lactoperoxidase), lactose and sodium in raw milk through microfiltration, diafiltration, ultrafiltration and optional nanofiltration processes under relatively low temperature conditions. The temperature is set to 30-55°C in the microfiltration stage, which can achieve the effects of concentration and sterilization at the same time, avoiding the destruction of heat-sensitive components such as proteins and vitamins by multiple high-temperature sterilizations, and fully retaining the natural flavor and nutritional value of dairy products.

[0048] At the same time, the present invention improves the milk active protein in fresh milk by microfiltration and ultrafiltration, reduces the lactose content by diafiltration, and designs the nanofiltration for reducing the sodium content as an optional step, which is more flexible in meeting different products and production requirements, and the small molecule lactose or sodium in the permeate can be recycled and reused, improving resource utilization and reducing production costs, and by mixing various diafiltration retentates and / or cream in the post-processing stage and homogenizing, high-temperature instant sterilization, and then mixing with ultrafiltration retentates or nanofiltration retentates, avoiding the influence of high temperature on active proteins or heat-sensitive nutrients in ultrafiltration retentates and nanofiltration retentates, and can be used to prepare high-active protein, low-lactose, low-sodium full-fat or skim dairy products. This method not only guarantees product quality, but also significantly outperforms the prior art in terms of heat-sensitive nutrient retention, comprehensive resource utilization, product stability and flavor. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 The present invention is a process flow chart of the method for preparing the membrane concentrated milk beverage. DETAILED DESCRIPTION

[0050] The following is a description of the implementation of the present invention by means of specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0051] Before further describing the specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the examples of the present invention are intended to describe specific embodiments, rather than to limit the scope of protection of the present invention. The test methods in the following examples without specifying specific conditions are generally carried out under conventional conditions or under conditions recommended by the manufacturers.

[0052] When the embodiments give numerical ranges, it should be understood that, unless otherwise specified in the present invention, both endpoints of each numerical range and any numerical value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those generally understood by those skilled in the art. In addition to the specific methods, equipment, and materials used in the embodiments, according to the grasp of the prior art by those skilled in the art and the record of the present invention, any methods, equipment, and materials of the prior art similar or equivalent to the methods, equipment, and materials described in the embodiments of the present invention can also be used to realize the present invention.

[0053] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0054] The multi-stage membrane concentration method of the present invention first performs centrifugal defatting on the raw milk, then sequentially uses a microfiltration membrane to separate and sterilize and intercept large molecular active proteins, reduces the lactose content by diafiltration, then uses an ultrafiltration membrane to enrich whey protein and partially remove small molecular components such as lactose and sodium, and finally uses a nanofiltration membrane to further accurately control the lactose and sodium content. Under this multi-stage membrane coupling process, dairy products can be enriched and separated under low or normal temperature conditions, avoiding the destruction of product nutrition by multiple high-temperature sterilizations. By mixing the diafiltration retentate and the retentate after microfiltration or nanofiltration treatment according to the required formula, and performing mild sterilization or drying, functional dairy products in liquid or powder form can be prepared to meet different consumer needs.

[0055] In addition, the present invention also proposes a scheme of using the cream obtained after centrifugation as a raw material for processing other dairy products, and can also be mixed with the retentate after ultrafiltration or nanofiltration to further balance the protein content, taste and functionality of the terminal product, and can be used to prepare full-fat dairy products. This flexible hierarchical regulation method enables the product to not only perform outstandingly in terms of low lactose, low sodium or high protein, but also take into account diversified market application needs, and is suitable for wide application in the industrial production of high-protein (such as immunoglobulin, lactoferrin, lactoperoxidase), low lactose and other functional dairy products, and has significant economic benefits and application value.

[0056] The present invention achieves precise separation and enrichment of fat, protein, lactose and sodium components by regulating membrane separation processes such as microfiltration, ultrafiltration and optional nanofiltration, and mixes the obtained different concentrated liquids in the required ratio, and then backfills the necessary fat and functional nutrients (active proteins (such as immunoglobulins, lactoferrin, lactoperoxidase), calcium, sodium), etc.) according to the requirements of the target product. After homogenization, sterilization and aseptic filling, it can not only effectively retain heat-sensitive active proteins, but also accurately control the content of milk fat, flavor and nutrients.

[0057] The present invention is suitable for the industrial production of high-protein, low-lactose, low-sodium and other functional dairy products. It is particularly suitable for the efficient separation and enrichment of active proteins that are easily destroyed by heat, and for achieving precise control of milk fat, flavor (low sodium, low lactose) and nutrients in subsequent formulation steps. It has significant economic benefits and application potential.

[0058] The present invention provides a method for preparing a membrane concentrated dairy product, the preparation method comprising the following steps:

[0059] 1) skimming and separating the raw milk to obtain skimmed milk and cream;

[0060] 2) microfiltration of the skim milk to obtain a microfiltration retentate and a microfiltration permeate;

[0061] 3) performing diafiltration on the microfiltration retentate obtained in step 2) to obtain a diafiltration retentate and a diafiltration permeate; performing ultrafiltration on the microfiltration permeate obtained in step 2) to obtain a final retentate and a final permeate;

[0062] 4) The diafiltration retentate is homogenized and sterilized, and then mixed with the final retentate to obtain the membrane concentrated dairy product.

[0063] In a further embodiment, in step 1) of the present invention, the fat content in the skim milk is 0.01-0.5 g / 100 ml; it may also be 0.01-0.05 g / 100 ml, 0.05 g / 100 ml-0.1 g / 100 ml, 0.1 g / 100 ml-0.2 g / 100 ml, 0.2 g / 100 ml-0.3 g / 100 ml, 0.3 g / 100 ml-0.4 g / 100 ml or 0.4 g / 100 ml-0.5 g / 100 ml.

[0064] In a further embodiment, the degreasing method is separation.

[0065] In a further embodiment, the separation method is centrifugal separation.

[0066] In a further embodiment, the centrifugal separation temperature is 40-70°C, and can also be 40-55°C, 55-60°C, 55-65°C or 65-70°C, preferably 55-65°C, such as 50°C, 55°C or 60°C.

[0067] In a further embodiment, the rotation speed of the centrifugal separation is 3000-8000rpm; it can also be 3000-4000rpm, 4000-5000rpm, 5000-6000rpm, 6000-7000rpm, 7000-8000rpm or 5000-7000rpm; it can also be 4000rpm, 5000rpm, 6000rpm or 7000rpm.

[0068] In a further embodiment, the source of the raw milk can be selected from cows, sheep and / or camels, etc.; for example, raw cow milk, raw sheep milk and / or camel milk.

[0069] In a further embodiment, when the fat content of the raw milk is high, the fat content in the skim milk can be reduced to 0.01g / 100ml~0.5g / 100ml through multiple centrifugation operations. In order to reduce damage to protein and other nutritional components, the centrifugation time is generally controlled at 1 to 5 minutes; it can be appropriately adjusted according to the specifications and rotation speed (such as 3000~8000rpm) of the centrifugal equipment.

[0070] In step 2) of the present invention, skim milk is passed into a microfiltration device for membrane separation, wherein the microfiltration interception liquid is sterilized concentrated milk, and its components include minerals such as calcium and phosphorus bound to casein micelles; and the microfiltration permeate contains whey protein, small molecular weight mineral ions, part of lactose, vitamins, etc.

[0071] In step 2) of the present invention, the pore size of the membrane used for microfiltration is 0.1-0.8 μm; it can also be 0.1-0.3 μm, 0.3-0.5 μm, 0.5-0.6 μm or 0.6-0.8 μm; it can also be 0.2 μm, 0.3 μm or 0.5 μm.

[0072] In step 2) of the present invention, the material of the membrane used for microfiltration can be selected from polypropylene, ceramics, polyvinylidene fluoride (PVDF), polyvinylidene fluoride (PVDF), polyether sulfone (PES) or other materials with microfiltration performance.

[0073] In step 2) of the present invention, the operating pressure of the microfiltration is 1 to 5 bar, and can also be 1 to 3 bar or 3 to 5 bar.

[0074] In step 2) of the present invention, the operating temperature of the microfiltration is 30-55°C; it can also be 30-40°C, 40-50°C or 50-55°C, and can also be 40°C, 45°C, 50°C or 55°C.

[0075] In a further embodiment, the microfiltration flux can be between 50 and 400 L / m 2 ·h; can also be 50~100L / m 2 h, 100~200L / m 2 ·h, 200~300L / m 2 h or 300~400L / m 2 h, can also be 100L / m 2 h, 150L / m 2 h, 180L / m 2 h, 200L / m 2 h or 300L / m 2 h; By adjusting the feed flow rate and reflux ratio, a stable transmembrane pressure difference is maintained to delay membrane fouling.

[0076] In a further embodiment, the concentration factor of the microfiltration is 1.2 to 5; it can also be 1.2 to 1.5, 1.5 to 2, 2 to 3, 3 to 4 or 4 to 5, or it can be 1.3, 1.5, 1.8, 2.5, 3 or 3.3 (wherein the concentration factor of the microfiltration is defined as the ratio of the protein concentration in the microfiltration retentate to the protein concentration in the microfiltration feed liquid).

[0077] In a further embodiment, the diafiltration operation is performed according to the following steps: after the microfiltration concentration, water is added to the microfiltration retentate to perform diafiltration until the lactose content in the diafiltration retentate is less than or equal to 2 mg / 100 ml, and can also be less than or equal to 1.5 mg / 100 ml, 1.3 mg / 100 ml, 1 mg / 100 ml, 0.8 mg / 100 ml, 0.7 mg / 100 ml or 0.5 mg / 100 ml; the purpose of the diafiltration is to reduce the lactose content; specifically, the microfiltration retentate and water are circulated into the microfiltration membrane to achieve the effect of reducing lactose; the ratio of the amount of diafiltration water to the volume of the microfiltration retentate (diafiltration ratio) can be adjusted according to the lactose removal target. For example, the diafiltration ratio is 1:1 to 5:1 (i.e., 1 to 5 volumes of water are added for every 1 volume of microfiltration retentate). The higher the diafiltration ratio, the better the lactose removal effect. Constant volume diafiltration (keeping the volume of the retentate unchanged, continuously adding water and discharging the permeate) is used. Through the diafiltration step, the lactose in the microfiltration retentate can be effectively removed, so that the lactose content in the obtained diafiltration retentate is less than or equal to 2 mg / 100 ml, and the final product is more in line with the standard of low-lactose dairy products.

[0078] In step 3) of the present invention, the molecular weight cutoff of the membrane used for ultrafiltration is 10,000 to 100,000 Daltons; it can also be 10,000 to 50,000 Daltons, 50,000 to 80,000 Daltons, or 80,000 to 100,000 Daltons.

[0079] In step 3) of the present invention, the material of the membrane used for ultrafiltration can be selected from cellulose acetate, polyvinylidene fluoride (PVDF), polyether sulfone (PES), polyamide, polyacrylonitrile (PAN), polyvinyl chloride (PVC), polypropylene (PP), ceramic membrane or other materials with ultrafiltration performance.

[0080] In step 3) of the present invention, the operating pressure of the ultrafiltration is 1-10 bar; it can also be 1-3 bar, 3-6 bar or 6-10 bar, and can also be 3 bar, 4 bar, 5 bar, 6 bar or 7 bar.

[0081] In step 3) of the present invention, the operating temperature of the ultrafiltration is 5-25°C; it can also be 5-10°C, 10-15°C, 15-20°C or 20-25°C.

[0082] In step 3) of the present invention, the ultrafiltration can achieve the enrichment of milk protein under mild conditions, and allow lactose, sodium, etc. to enter the permeate for subsequent recovery and utilization.

[0083] In a further embodiment, the ultrafiltration flux can generally be maintained at 20 to 100 L / m 2 h; can also be 20 to 40 L / m 2 ·h, 40~60L / m 2 ·h, 60~80L / m2 h or 80~100L / m 2 h, can also be 45L / m 2 h, 50L / m 2 h, 55L / m 2 h, 60L / m 2 h, 70L / m 2 h or 80L / m 2 h; Achieve higher protein concentration multiples through continuous or segmented operations.

[0084] In a further embodiment, the ultrafiltration concentration factor is 1 to 3 (wherein the ultrafiltration concentration factor is defined as: the ratio of the protein concentration in the ultrafiltration retentate to the protein concentration in the ultrafiltration feed liquid); it can also be 1 to 1.5, 1.5 to 2 or 2 to 3, and can also be 1.3, 1.5, 2, 2.5 or 3.

[0085] In a further embodiment, for products that wish to significantly reduce specific sodium, nanofiltration technology can be used to treat the ultrafiltration retentate so that the sodium content in the final retentate is reduced. According to the actual situation of existing dairy membrane filtration processes, the removal rate of sodium by nanofiltration operation under appropriate conditions can generally reach about 10% to 40%. The permeate produced by the nanofiltration process is rich in the removed sodium and other minerals, which can be recycled later to achieve the goal of low-sodium dairy products and further increase the concentration of protein and solids in the concentrate. Therefore, after ultrafiltration, the process also includes the step of nanofiltration of the ultrafiltration concentrate to obtain a final retentate and a final permeate.

[0086] In some embodiments, the molecular weight cutoff of the membrane used for nanofiltration is 200-1000 Daltons; it can also be 200-300 Daltons, 300-500 Daltons, 500-700 or 700-1000 Daltons, and can also be 300, 400, 500, 600 or 800 Daltons.

[0087] In some embodiments, the material of the nanofiltration membrane can be selected from polyethersulfone (PES), cellulose acetate, polytetrafluoroethylene, polyethersulfone resin, polyethersulfone, polyamide composite membrane (TFC membrane) or other materials with nanofiltration performance.

[0088] In some embodiments, the operating pressure of the nanofiltration is 10 to 30 bar; it can also be 10 to 15 bar or 15 to 30 bar, or it can also be 15 bar, 18 bar, 20 bar or 25 bar.

[0089] In some embodiments, the operating temperature of the nanofiltration is 5-25°C; it can also be 5-10°C, 10-15°C, 15-20°C or 20-25°C.

[0090] In some embodiments, the flux of the nanofiltration is 10 to 40 L / m 2 h, and can also be 10 to 20 L / m 2 ·h, 20~30L / m 2 ·h or 30~40L / m 2 h, can also be 20L / m 2 h, 25L / m 2 h, 30L / m 2 h or 35L / m 2 ·h.

[0091] In some embodiments, the concentration factor of the nanofiltration is 1 to 3.3 (wherein the nanofiltration concentration factor is defined as: the ratio of the protein concentration in the nanofiltration retentate to the protein concentration in the nanofiltration feed liquid); it can also be 1 to 1.5, 1.5 to 2 or 2 to 3.3, or 1.2, 1.5 or 1.8; the small molecule lactose or sodium contained in the nanofiltration permeate can also be recovered and reused.

[0092] In some embodiments of the invention, step 4) can also be to mix the diafiltration retentate and cream, homogenize and sterilize, and then mix with the final retentate to obtain a membrane concentrated dairy product; by adding cream, it can be used to prepare full-fat dairy products.

[0093] In step 4) of the present invention, the homogenization temperature is 55-65°C, and can be 55-60°C or 60-65°C, and can also be 58°C, 60°C or 63°C.

[0094] In step 4) of the present invention, the homogenization pressure is 150-400 bar, and can be 150-180 bar, 180-250 bar or 250-400 bar, and can also be 200 bar, 250 bar or 300 bar.

[0095] In step 4) of the present invention, the sterilization is preferably pasteurization, specifically high temperature short time sterilization.

[0096] In step 4) of the present invention, the sterilization temperature is 70-80°C, and can also be 70-75°C or 75-80°C, and can also be 72°C, 73°C, 74°C or 76°C.

[0097] In step 4) of the present invention, the sterilization time is 10 to 30 seconds; it can also be 10 to 15 seconds, 15 to 20 seconds, 20 to 25 seconds or 25 to 30 seconds; it can also be 10 seconds, 15 seconds or 20 seconds.

[0098] In step 4) of the present invention, aseptic filling is performed after mixing.

[0099] The present invention also provides a membrane concentrated dairy product, which is prepared by the aforementioned preparation method of the present invention.

[0100] In some embodiments, based on the total volume of the membrane concentrated dairy product, the protein content in the membrane concentrated dairy product is ≥ 6.0 g / L; it can also be 6-20 g / L, 6-10 g / L, 10-15 g / L or 15-20 g / L.

[0101] In some embodiments, based on the total volume of the membrane concentrated dairy product, the content of immunoglobulin in the membrane concentrated dairy product is ≥250 mg / L; it can also be 250-600 mg / L, 250-300 mg / L, 300-400 mg / L, 400-500 mg / L or 500-600 mg / L.

[0102] In some embodiments, based on the total volume of the membrane concentrated dairy product, the lactoferrin content in the membrane concentrated dairy product is ≥80 mg / L; it can also be 80-200 mg / L, 80-120 mg / L, 120-170 mg / L or 170-200 mg / L.

[0103] In some embodiments, based on the total volume of the membrane concentrated dairy product, the activity of lactoperoxidase in the membrane concentrated dairy product is ≥1600 U / L; it may also be 1600-8000 U / L, 1600-3500 U / L, 3500-6000 U / L or 6000-8000 U / L.

[0104] In some embodiments, based on the total volume of the membrane concentrated dairy product, the sodium content in the membrane concentrated dairy product is ≤120 mg / L, and can also be 1-120 mg / L, 1-30 mg / L, 30-60 mg / L, 60-90 mg / L or 90-120 mg / L.

[0105] In some embodiments, based on the total volume of the membrane concentrated dairy product, the lactose content in the membrane concentrated dairy product is ≤1 mg / L, and can also be 0.01-1 mg / L, 0.01-0.1 mg / L, 0.1-0.3 mg / L, 0.3-0.6 mg / L or 0.6-1 mg / L.

[0106] By adopting the above technical scheme, the present invention realizes effective separation and concentration of components such as milk active protein, lactose and sodium in raw milk by microfiltration, diafiltration, ultrafiltration and optional nanofiltration process under relatively low temperature conditions, avoids the destruction of heat-sensitive components such as protein and vitamins by multiple high-temperature sterilization, and fully retains the nutritional value of dairy products. At the same time, the present invention designs nanofiltration as an optional step, which is more flexible in meeting different products and production requirements, and the small molecule lactose or sodium in the permeate can be recycled and reused, improving resource utilization and reducing production costs. By mixing the relevant ingredients (such as diafiltration retentate, ultrafiltration retentate, nanofiltration retentate, cream) in sections and partially sterilizing them in the post-processing stage, not only the product quality and safety are guaranteed, but also the shelf life is extended, so that the heat-sensitive nutrients are retained, the comprehensive utilization of resources, and the product stability and flavor (low sodium, low lactose) are significantly superior to the prior art.

[0107] The present invention is committed to retaining and enriching the active protein in fresh milk to the greatest extent, while effectively reducing the content of small molecules such as lactose and salt. By optimizing the connection and conditions of the multi-stage membrane process of centrifugal degreasing, microfiltration, diafiltration, ultrafiltration, and nanofiltration, and combining the reasonable combination of microfiltration physical sterilization and low-temperature pasteurization, a membrane concentrated dairy product with high protein activity, low lactose, and low sodium is finally prepared; the process flow chart of the preparation method of the membrane concentrated dairy product of the present invention can be referred to ( Figure 1 ); preparing full-fat or skim dairy products with or without the addition of cream.

[0108] In the prior art, fresh milk is generally sterilized at high temperature to obtain sterilized milk, which is then skimmed and concentrated. However, the present invention obtains sterilized milk by removing most of the bacteria and impurities through low-temperature physical separation during microfiltration, thus avoiding the early destruction of protein by multiple high-temperature sterilization treatments; then low-temperature pasteurization is performed under mild conditions of 70 to 75°C to further inactivate residual microorganisms, thereby minimizing the impact of heat treatment on active proteins on the basis of a double sterilization effect. Compared with traditional high-temperature sterilization, this "physical + low-temperature thermal" sterilization scheme can significantly reduce nutritional losses and flavor deterioration, while avoiding protein denaturation and aggregation problems caused by multiple high-temperature treatments.

[0109] By rationally utilizing the synergistic advantages of microfiltration sterilization and low-temperature pasteurization, the present invention effectively overcomes the problem of active protein loss caused by traditional high-temperature concentration or single membrane operation, and at the same time has more advantages in energy consumption, production capacity and economic feasibility. The optimized process flow achieves seamless connection of the conditions of each membrane separation stage, and combined with the final low-temperature sterilization treatment, it produces skimmed or full-fat membrane concentrated dairy products with high active protein and high-quality flavor (low sodium, low lactose), providing reliable technical support for the development and large-scale production of high-active protein dairy products.

[0110] In the following examples, unless otherwise specified, various raw materials of the present invention can be purchased from the market or prepared according to conventional methods in the art.

[0111] Embodiment 1:

[0112] 1) Degreasing and separation

[0113] 1000L of raw milk with a fat content of about 3.0g / 100mL was selected and centrifuged for degreasing at 60°C and 6000rpm / min to obtain cream and skim milk (with a fat content of about 0.5g / 100mL).

[0114] 2) Microfiltration

[0115] Microfiltration of skim milk was performed using a ceramic membrane with a pore size of 0.2 μm, an operating pressure of 2 bar, a temperature of 50 °C, and a microfiltration flux of 100 L / m 2 h, the concentration multiple is 1.5, and the microfiltration interception liquid (also known as sterilized milk, main components: lactose 6.5g / 100mL, protein 3.8g / 100mL) and microfiltration permeate are obtained. RO water is added to the obtained microfiltration interception liquid for diafiltration, and the microfiltration membrane is continued to be used for diafiltration. The operating conditions remain unchanged, and low lactose diafiltration retentate (lactose content is 0.8mg / 100ml, protein 6.5g / 100mL) and diafiltration permeate are obtained after diafiltration.

[0116] 3) Ultrafiltration

[0117] The microfiltration permeate was subjected to ultrafiltration, and the concentration factor was set to 1.5. The ultrafiltration membrane material was PES, the molecular weight cutoff was 50,000 Daltons, and the ultrafiltration flux was maintained at 50 L / m 2 h, the operating pressure was 3 bar, the temperature was 10°C, and the ultrafiltration retentate (active protein concentrate) and ultrafiltration permeate were obtained.

[0118] 4) Post-processing

[0119] The diafiltration retentate is mixed with the cream, homogenized (60°C, 200 bar), and pasteurized (72°C, 15 seconds) to obtain mixed sterilized whole milk, and then the ultrafiltration retentate (active protein concentrate) and the mixed sterilized whole milk are aseptically backfilled to obtain a low-lactose, high-concentration active protein, full-fat dairy product.

[0120] Embodiment 2:

[0121] 1) Degreasing and separation

[0122] 1000L of raw milk (fat content 4.5g / 100mL) was selected and centrifuged at 55°C and 6000rpm / min for degreasing to obtain cream and skim milk (fat content 0.05g / 100mL).

[0123] 2) Microfiltration

[0124] Microfiltration of skim milk using a ceramic membrane with a pore size of 0.3 μm, an operating pressure of 3 bar, a temperature of 50 °C, and a flux of 300 L / m 2 / h, the concentration multiple is 3.3, and the microfiltration retentate and microfiltration permeate are obtained. RO water is added to the obtained microfiltration intercepted liquid for diafiltration, and the microfiltration membrane is continued to be used for diafiltration. The operating conditions remain unchanged, and low lactose diafiltration retentate (lactose content is 1.0 mg / 100 ml, protein is 12.8 g / 100 ml) and diafiltration permeate are obtained after diafiltration.

[0125] 3) Ultrafiltration

[0126] The microfiltration liquid is ultrafiltered, the material is polyethersulfone, the flux is 50L / m 2 / h, the cut-off molecular weight is 80,000 Daltons, the operating pressure is 4 bar, the concentration factor is 3, the temperature is 15°C, and the ultrafiltration retentate and ultrafiltration permeate are obtained.

[0127] 4) Nanofiltration

[0128] The ultrafiltration retentate was nanofiltered using cellulose acetate at a flux of 30 L / m 2 / h, concentration multiple of 1.5, membrane cut-off molecular weight of 300 Daltons, operating pressure of 15 bar, temperature of 10°C, and nanofiltration retentate and nanofiltration permeate were obtained.

[0129] 5) Post-processing

[0130] The diafiltration retentate is homogenized (60°C, 180 bar), pasteurized (72°C, 20 seconds), and then mixed with the nanofiltration retentate. After cooling, it is aseptically backfilled to obtain a high-activity protein, low-lactose, low-sodium, skimmed dairy product.

[0131] Embodiment 3:

[0132] 1) Degreasing and separation

[0133] 1000L of raw milk (fat content 3.5g / 100mL) was selected and centrifuged at 55°C and 6500rpm / min for degreasing to obtain cream and skim milk (fat content 0.1g / 100mL).

[0134] 2) Microfiltration

[0135] Microfiltration of skim milk, the pore size of the microfiltration membrane is 0.5μm, the material is ceramic membrane, the operating pressure is 1.8bar, the temperature is 40℃, and the flux is 250L / m 2 / h, the concentration multiple is 2.0, and the microfiltration retentate and microfiltration permeate are obtained. RO water is added to the obtained microfiltration intercepted liquid for diafiltration, and the microfiltration membrane is continued to be used for diafiltration. The operating conditions remain unchanged, and low lactose diafiltration retentate (lactose content is 1.5mg / 100ml, protein 5.2g / 100mL) and diafiltration permeate are obtained after diafiltration.

[0136] 3) Ultrafiltration

[0137] The microfiltration permeate was subjected to ultrafiltration, the material was cellulose acetate, the molecular weight cut-off was 50,000 Daltons, the operating pressure was 5 bar, the temperature was 10°C, and the flux was 60 L / m 2 / h, the concentration factor is 1.5, and ultrafiltration retentate and ultrafiltration permeate are obtained.

[0138] 4) Post-processing

[0139] The diafiltration retentate is homogenized (60°C, 200 bar), pasteurized (72°C, 15 seconds), and then mixed with the ultrafiltration retentate and aseptically backfilled to obtain a high-activity protein, low-lactose, skim dairy product.

[0140] Embodiment 4:

[0141] 1) Degreasing and separation

[0142] 300L of raw cow's milk (fat content: 3.7g / 100mL) and 200L of raw goat's milk (fat content: 4.5g / 100mL) were mixed and centrifuged at 60°C with a speed of 6000rpm / min for degreasing to obtain light cream and skimmed milk (fat content: 0.08g / 100mL).

[0143] 2) Microfiltration

[0144] Microfiltration of skim milk, the pore size of the microfiltration membrane is 0.2μm, the material is ceramic membrane, the operating pressure is 2bar, the temperature is 45℃, and the flux is 180L / m 2 / h, the concentration multiple is 3.0, and the microfiltration retentate and microfiltration permeate are obtained. RO water is added to the obtained microfiltration intercepted liquid for diafiltration, and the microfiltration membrane is continued to be used for diafiltration. The operating conditions remain unchanged, and low lactose diafiltration retentate (lactose content is 1.3mg / 100ml, protein 10.2g / 100mL) and diafiltration permeate are obtained after diafiltration.

[0145] 3) Ultrafiltration

[0146] The microfiltration permeate was subjected to ultrafiltration. The ultrafiltration membrane had a molecular weight cutoff of 50,000 Daltons, was made of PES, had an operating pressure of 3 bar, a temperature of 10°C, and a flux of 80 L / m 2 / h, the concentration factor is 2.0, and ultrafiltration retentate and ultrafiltration permeate are obtained.

[0147] 4) Post-processing

[0148] The diafiltration retentate is homogenized (60°C, 200 bar), pasteurized (72°C, 20 seconds), and then mixed with the ultrafiltration retentate and aseptically backfilled to obtain a high-activity protein, low-lactose, skim dairy product.

[0149] Embodiment 5:

[0150] 1) Degreasing and separation

[0151] 800L of raw milk (fat content 3.5g / 100mL) was selected and centrifuged for degreasing at a speed of 6500rmp / min and a temperature of 60°C until the fat content reached 0.2g / 100mL, thereby obtaining cream and skimmed milk.

[0152] 2) Microfiltration

[0153] Microfiltration of skim milk, the pore size of the microfiltration membrane is 0.3μm ceramic membrane, the operating pressure is 2.5bar, the temperature is 45℃, and the flux is 100L / m 2 / h, the concentration multiple is 3.5, and the microfiltration retentate and microfiltration permeate are obtained. RO water is added to the obtained microfiltration intercepted liquid for diafiltration, and the microfiltration membrane is continued to be used for diafiltration. The operating conditions remain unchanged, and low lactose diafiltration retentate (lactose content is 0.7mg / 100ml, protein is 14.2g / 100mL) and diafiltration permeate are obtained after diafiltration.

[0154] 3) Ultrafiltration

[0155] The microfiltration permeate was subjected to ultrafiltration. The ultrafiltration membrane had a molecular weight cutoff of 80,000 Daltons, was made of PVDF, had an operating pressure of 4 bar, a temperature of 15°C, and a flux of 60 L / m 2 / h, the concentration factor is 1.3, and ultrafiltration retentate and permeate are obtained.

[0156] 4) Nanofiltration

[0157] The ultrafiltration retentate was subjected to nanofiltration, the membrane material was polyethersulfone, the molecular weight cutoff was 300 Daltons, and the flux was 20 L / m 2 / h, the concentration multiple is 1.2, the operating pressure is 18 bar, the temperature is 10°C, and the nanofiltration retentate and nanofiltration permeate are obtained.

[0158] 5) Post-processing

[0159] The microfiltration retentate is homogenized (60°C, 200 bar), pasteurized (72°C, 20 seconds), mixed with the nanofiltration retentate, and aseptically backfilled to obtain a high-protein, low-lactose, low-sodium skimmed dairy product.

[0160] Comparative Example 1:

[0161] The difference between this comparative example 1 and example 1 is that in step 1), a first pasteurization (75°C, 15s) is added before centrifugation, and the skim milk microfiltration temperature in step 2) is set to 10°C, and the diafiltration step is not performed. The other steps are the same as example 1.

[0162] Comparative Example 2:

[0163] The difference between Comparative Example 1 and Example 1 is that in step 4), the mixed sterilized whole milk and the ultrafiltration intercepted liquid are first mixed and then pasteurized (72° C., 15 seconds). The other steps are the same as Example 1.

[0164] Effect Example 1

[0165] The dairy products obtained in Examples 1 to 5 and Comparative Examples 1 to 2 were tested, and the test indicators included lactoferrin, lactoperoxidase, immunoglobulin, protein, sodium, lactose content, and shelf life at 2 to 6°C;

[0166] The detection methods are as follows:

[0167] Shelf life test method: After aseptic filling, the liquid dairy product is placed in a 2-6℃ environment to determine the shelf life. When fat in the sample obviously floats or microorganisms are detected exceeding the limit specified in Table 3 of 4.6 of GB 19645-2010 Pasteurized Milk, it is considered to have reached the end of the shelf life.

[0168] Immunoglobulin content inspection: Determined according to the standard "NY / T 2070-2011 Determination of immunoglobulin IgG in bovine colostrum and its products by spectrophotometry";

[0169] Lactoperoxidase activity test: Determined according to the standard "T / CIFST008-2022 Colorimetric method for determination of lactoperoxidase activity in milk";

[0170] Lactoferrin content investigation: Determined according to the standard "T / CIFST 006-2021 Enzyme-linked immunosorbent assay for the determination of lactoferrin in food";

[0171] Protein content inspection: Determined according to the standard "GB / T 14771-1993 Method for determination of protein in food";

[0172] Lactose content inspection: Determined according to the standard "CNS 3445-2007 Dairy Inspection Method - Determination of Lactose";

[0173] Sodium content investigation: Determined according to the standard "IS12760-2012 Determination of calcium, sodium, potassium and magnesium content in milk and dairy products - Atomic absorption spectrometry".

[0174] Among them, immunoglobulin, lactoferrin and lactoperoxidase are used to characterize the content or activity of active proteins in liquid dairy products.

[0175] The results are shown in Table 1.

[0176] Table 1

[0177]

[0178] It can be seen from Examples 1-5 and Comparative Examples 1 and 2 that, compared with traditional pasteurization or multiple pasteurization, microfiltration membrane sterilization followed by pasteurization can significantly increase the shelf life of liquid dairy products from 7 to 10 days to 21 to 25 days, with good storage stability. Moreover, compared with the comparative examples, the content or activity of milk active proteins (such as milk immunoglobulin, lactoferrin, lactoperoxidase) in the embodiments is significantly higher, for example, the lactoferrin content in Example 1 is 85 mg / L, while that in Comparative Example 1 is only 45 mg / L, and that in Comparative Example 2 is only 50 mg / L, it can be seen that even on the basis of the approximate total protein content, the milk active protein content or activity in the present embodiments (such as Example 1 and Example 3) is also significantly higher than that in the comparative examples, because multiple high temperature sterilizations are performed in Comparative Example 1, and high temperature sterilization is also performed on the ultrafiltration intercepted liquid in Comparative Example 2, which will reduce the content of milk active proteins in the dairy products. Secondly, compared with Example 1 and Example 3, the content or activity of milk active proteins (such as milk immunoglobulin, lactoferrin, and lactoperoxidase) was further increased in Example 2 and Examples 4-5 by increasing the concentration multiple or adding the nanofiltration step.

[0179] In summary, the present invention significantly increases the content of key functional ingredients in dairy products, such as immunoglobulin and lactoferrin, through microfiltration and ultrafiltration processes, while effectively retaining thermosensitive active substances such as lactoperoxidase, and further concentrates functional ingredients through nanofiltration, thereby significantly increasing the content of immunoglobulin and reducing the content of lactose and sodium.

[0180] The coupled membrane separation process of the present invention avoids the destruction of functional ingredients by traditional sterilization methods; the preparation method of the present invention has significant advantages in improving the nutritional value, functionality and protection of heat-sensitive ingredients of dairy products, and is suitable for the development of high-protein, low-lactose and low-sodium dairy products.

[0181] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a membrane concentrated dairy product, the method comprising the following steps: 1) skimming and separating the raw milk to obtain skimmed milk and cream; 2) microfiltration of the skim milk to obtain a microfiltration retentate and a microfiltration permeate; 3) performing diafiltration on the microfiltration retentate obtained in step 2) to obtain a diafiltration retentate and a diafiltration permeate; performing ultrafiltration on the microfiltration permeate obtained in step 2) to obtain a final retentate and a final permeate; 4) The diafiltration retentate is homogenized and sterilized, and then mixed with the final retentate to obtain a membrane concentrated dairy product.

2. The preparation method according to claim 1, characterized in that: The fat content of the skim milk in step 1) is 0.01-0.5 g / 100 ml; Preferably, the source of the fresh milk is selected from cattle, sheep and / or camel.

3. The preparation method according to claim 1, characterized in that: The pore size of the membrane used for microfiltration in step 2) is 0.1 to 0.8 μm; Preferably, the pressure of the microfiltration in step 2) is 1 to 5 bar; Preferably, the temperature of the microfiltration in step 2) is 30-55°C; Preferably, the flux of the microfiltration in step 2) is 50 to 400 L / m 2 ·h; Preferably, the concentration multiple of the microfiltration in step 2) is 1.2 to 5.

0.

4. The preparation method according to claim 1, characterized in that: The diafiltration operation in step 3) is performed according to the following steps: after the microfiltration concentration, water is added to the microfiltration retentate to perform diafiltration; Preferably, the lactose content in the diafiltration retentate is less than or equal to 2 mg / 100 ml.

5. The preparation method according to claim 1, characterized in that: The molecular weight cut-off of the membrane used for ultrafiltration in step 3) is 100,000 to 100,000 Daltons; Preferably, the ultrafiltration pressure in step 3) is 1 to 10 bar; Preferably, the ultrafiltration temperature in step 3) is 5 to 25°C; Preferably, the flux of the ultrafiltration in step 3) is 20 to 100 L / m 2 ·h; Preferably, the concentration multiple of the ultrafiltration in step 3) is 1 to 3.

0.

6. The preparation method according to claim 1, characterized in that: Step 3) also includes the step of nanofiltration of the ultrafiltration retentate after ultrafiltration; Preferably, the molecular weight cut-off of the membrane used for nanofiltration is 200 to 1000 Daltons; Preferably, the nanofiltration pressure is 10 to 30 bar; Preferably, the nanofiltration temperature is 5 to 25°C; Preferably, the flux of the nanofiltration is 10 to 40 L / m 2 ·h; Preferably, the concentration multiple of the nanofiltration is 1 to 3.

3.

7. The preparation method according to claim 1, characterized in that: Step 4) also includes mixing the diafiltration retentate and the cream, homogenizing and sterilizing them, and then mixing them with the final retentate to obtain the membrane concentrated dairy product.

8. The preparation method according to claim 1 or 7, characterized in that: The homogenization temperature in step 4) is 55-65°C; Preferably, the homogenization pressure in step 4) is 150 to 400 bar; Preferably, the sterilization temperature in step 4) is 70-80°C; Preferably, the sterilization time in step 4) is 10 to 30 seconds.

9. A membrane concentrated dairy product, characterized in that: The membrane concentrated dairy product is prepared by the preparation method according to any one of claims 1 to 8.

10. The membrane concentrated dairy product according to claim 9, characterized in that: Based on the total volume of the membrane concentrated dairy product, the protein content in the membrane concentrated dairy product is ≥ 6.0 g / L; and / or, Based on the total volume of the membrane concentrated dairy product, the content of immunoglobulin in the membrane concentrated dairy product is ≥ 250 mg / L; and / or, Based on the total volume of the membrane concentrated dairy product, the content of lactoferrin in the membrane concentrated dairy product is ≥80 mg / L; and / or, Based on the total volume of the membrane concentrated dairy product, the activity of lactoperoxidase in the membrane concentrated dairy product is ≥1600 U / L; and / or, Based on the total volume of the membrane concentrated dairy product, the sodium content in the membrane concentrated dairy product is ≤120 mg / L; and / or, based on the total volume of the membrane concentrated dairy product, the lactose content in the membrane concentrated dairy product is ≤1 mg / L.

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