Dairy products and methods of preparing the same

Abstract

The present application relates to the field of food, and proposes a dairy product and a preparation method thereof, the method comprising: subjecting raw milk to fat separation and membrane separation treatment to obtain cream, membrane concentrate and permeate; subjecting the permeate to freeze concentration and decanter separation treatment to obtain water, concentrated lactose solution and concentrated skim milk; subjecting the water, concentrated lactose solution and lactase to enzymolysis treatment to obtain lactose-free solution; subjecting the cream, membrane concentrate and concentrated skim milk to ultra-high temperature sterilization treatment to obtain a first sterilization product; subjecting the first sterilization product to a first mixing treatment with the lactose-free solution to obtain the dairy product. The method for preparing dairy products in the present application can effectively reduce the Maillard reaction, retain the natural color and nutrients in the milk source to the greatest extent, improve the nutritional value, flavor, taste, color and stability of the product, have high production efficiency and low cost, and are suitable for industrial production and application.

Description

Technical Field

[0001] The present application relates to the field of food, and in particular, to dairy products and preparation methods thereof. Background Art

[0002] Lactose in milk is a naturally occurring sugar that needs to be broken down into glucose and galactose by lactase in the human body before it can be absorbed by the small intestine. For those who do not secrete enough lactase, the unbroken lactose will be fermented by bacteria in the intestines, causing a series of symptoms, including bloating, diarrhea, abdominal pain, bowel sounds, increased flatulence, nausea, and developmental delay (in children). For those who are lactose intolerant, avoiding or reducing lactose intake can alleviate the above symptoms.

[0003] In order to meet the milk drinking needs of lactose-intolerant consumers, dairy companies have developed a variety of "zero lactose" white milk products, but because these products are often accompanied by certain sensory defects, the repurchase rate of consumers for "zero lactose" products is relatively low. The main reason is that during the processing of "zero lactose" milk, lactose is broken down into glucose and galactose by lactase, which not only makes the milk sweeter, but may also affect the color of the milk. This color change is mainly caused by the Maillard reaction, which is a non-enzymatic browning process that occurs between reducing sugars (such as glucose) and amino acids. When milk is heated or stored at a higher temperature, this reaction will gradually occur, causing the food color to darken. In addition, the glucose content in "zero lactose" milk is higher, and this reaction may be more significant than that of ordinary milk, so that the color of the milk may appear slightly pink or yellow.

[0004] However, the problems faced by the above-mentioned "zero lactose" milk are still industry challenges. Existing studies have shown that it is impossible to effectively inhibit the occurrence of the Maillard reaction by controlling the sterilization temperature and time or using antioxidants. Therefore, the color change of "zero lactose" milk is difficult to solve. Summary of the invention

[0005] The present application aims to solve the technical problems existing in the prior art at least to a certain extent. To this end, the present application proposes a dairy product and a method for preparing the dairy product. The method for preparing the dairy product in the present application can effectively reduce the Maillard reaction, retain the natural color and nutrients in the milk source to the greatest extent, improve the nutritional value, flavor, taste, color and stability of the product, have high production efficiency, low cost, and are suitable for industrial production applications.

[0006] It should be noted that this application is completed based on the following findings of the inventor:

[0007] At present, in the process of producing zero-lactose dairy products using ultra-high temperature sterilization technology (UHT), the addition of lactase is divided into two methods: adding before UHT sterilization and adding after UHT sterilization, but both methods have disadvantages. Specifically:

[0008] (1) Lactase is added before UHT sterilization. Lactase breaks down lactose into glucose and galactose, which increases the sugar content in the system and exacerbates the Maillard reaction during heat treatment and shelf life, resulting in significant differences in the sensory and color properties of the product. In addition, since the optimal enzymatic hydrolysis temperature of lactase is usually room temperature or slightly higher, if raw milk is treated at the optimal enzymatic hydrolysis temperature of lactase, microorganisms are likely to grow, and it is easy to fail to effectively kill microorganisms after UHT sterilization, shortening the shelf life. For this reason, low-temperature and long-term enzymatic hydrolysis is usually required, which reduces production efficiency and increases energy consumption.

[0009] (2) When lactase is added after UHT sterilization, the Maillard reaction will still occur because lactose is always present in the sterilization system. Moreover, after the lactase is added, it will always be present in the product, which may cause other adverse reactions during the shelf life and reduce the stability of the product.

[0010] In view of this, the inventor of the present application tried to separate the lactose in the raw milk, enzymolyze it separately, and then mix the other materials with the enzymolyzed zero lactose liquid after a series of treatments and UHT sterilization to obtain zero lactose dairy products. The inventor tried a variety of separation methods, such as a combined separation method of ultrafiltration and nanofiltration. In this process, in order to achieve zero sugar, ultrafiltration requires multiple diafiltrations, and the system configuration is super large, the investment is high, and the energy consumption is high. In addition, the loss of trace elements such as flavors and minerals during the diafiltration process increases with the increase in the number of diafiltrations.

[0011] After in-depth research, the inventors took advantage of the different freezing points of water, lactose and protein in the milk system (water is about -0.5°C, lactose is about -2°C, and protein is about -2.6°C). Through freeze concentration technology, the permeate is first cooled to the freezing point of water to form ice crystals and separate, and then further cooled to the freezing point of lactose to promote lactose crystallization. Due to the high viscosity of lactose crystals, the horizontal screw separation technology can effectively separate it from the solution to obtain lactose liquid. Therefore, the ingenious combination of freeze concentration and horizontal screw separation technology can achieve efficient separation of protein, lactose and water in milk. In this process, natural ingredients such as protein, enzymes, vitamins, volatile compounds and edible pigments in the milk source can be effectively retained, successfully avoiding the risk of loss of these natural ingredients during separation and concentration processing. In addition, the separated lactose is treated with lactase enzymolysis alone, which significantly improves the process flexibility and enzymolysis efficiency, shortens the waiting time required for early enzymolysis, avoids the adverse effects of late enzymolysis side reactions, and reduces the amount of lactase used. At the same time, it can effectively reduce the Maillard reaction caused by heat treatment, retain the natural color and nutrients in the milk source to the greatest extent, improve the nutritional value, flavor, taste, color and stability of the product, have high production efficiency and low cost, and is suitable for industrial production applications.

[0012] To this end, in a first aspect of the present application, the present application proposes a method for preparing a dairy product. According to an embodiment of the present application, the method comprises:

[0013] The raw milk is subjected to fat separation and membrane separation treatment to obtain cream, membrane concentrate and permeate;

[0014] The permeate is freeze-concentrated and decanter-separated to obtain water, concentrated lactose solution and concentrated skimmed milk;

[0015] The water, the concentrated lactose solution and the lactase are subjected to enzymatic hydrolysis to obtain a lactose-free solution;

[0016] The cream, the membrane concentrate and the concentrated skim milk are subjected to ultra-high temperature sterilization to obtain a first sterilized product;

[0017] The first sterilized product and the lactose-free liquid are subjected to a first mixing treatment to obtain the dairy product.

[0018] According to the method for preparing dairy products in the embodiment of the present application, the use of freeze concentration and horizontal snail separation can effectively separate lactose, reduce the occurrence of Maillard reaction caused by subsequent ultra-high pressure sterilization due to the presence of lactose, retain the natural color and nutrients of the milk source to the greatest extent, and perform lactase enzymolysis on the separated lactose separately, which can improve the enzymolysis efficiency and process flexibility. Therefore, the method of the present application can effectively improve the nutritional value, flavor, taste, color and stability of dairy products, with high production efficiency and low cost, and is suitable for industrial production applications.

[0019] According to the embodiments of the present application, the above method for preparing dairy products may also have the following additional technical features:

[0020] According to an embodiment of the present application, the freeze concentration process includes an ice crystal stage and a lactose crystallization stage;

[0021] The ice crystal stage comprises: placing the permeate in an ice crystal crystallizer, controlling the temperature of the permeate to a first temperature so that ice crystals are generated in the permeate, and collecting concentrated material and the ice crystals;

[0022] The lactose crystallization stage comprises: placing the concentrated material in a lactose crystallizer, controlling the temperature of the concentrated material to a second temperature so as to generate lactose crystals in the concentrated material;

[0023] The concentrated material producing lactose crystals is subjected to horizontal screw separation to separate the concentrated lactose liquid;

[0024] Among them, the first temperature is -0.6℃~-1.3℃, and the second temperature is -1.5℃~-2.2℃.

[0025] According to the embodiments of the present application, the average particle size of the ice crystals is 500 μm~900 μm; the average particle size of the lactose crystals is 200 μm~600 μm; the growth rate of the ice crystals is 2 μm / min~6 μm / min; the growth rate of the lactose crystals is 0.3 μm / min~2.7 μm / min.

[0026] According to an embodiment of the present application, the refrigerant temperature of the ice crystal stage is -1°C~-18°C and lower than the first temperature; the refrigerant temperature of the lactose crystallization stage is -5°C~-23°C and lower than the second temperature; the stirring speed of the ice crystal crystallizer is 300 rpm~1000 rpm; the stirring speed of the lactose crystallizer is 30 rpm~150 rpm; the centrifugal speed of the horizontal screw separation process is 2300 rpm~4700 rpm.

[0027] According to the embodiment of the present application, 40% to 60% by volume of the concentrated lactose solution obtained by the decanter separation process is used for the enzymatic hydrolysis process; the lactase is selected from Nurica TM Lactase.

[0028] According to an embodiment of the present application, the temperature of the enzymatic hydrolysis treatment is 2°C~60°C, and the time is 1 h~2 h; before the enzymatic hydrolysis treatment, the water, concentrated lactose solution and lactase are subjected to a second mixing and sterilization treatment; after the enzymatic hydrolysis treatment, the obtained enzymatic hydrolysis product is subjected to an enzyme inactivation treatment to obtain the lactose-free solution, and the temperature of the enzyme inactivation treatment is 80°C~100°C, and the time is 90 s~180 s.

[0029] According to an embodiment of the present application, the temperature of the enzymatic hydrolysis treatment is 45°C~50°C.

[0030] According to an embodiment of the present application, the membrane separation treatment includes microfiltration membrane treatment; the temperature of the ultra-high temperature sterilization treatment is 140°C~162°C, and the time is 0.09 s~3.5 s; before the ultra-high temperature sterilization treatment, the method further includes at least one of the following steps: subjecting the mixture of the light cream and the membrane concentrate to a second sterilization treatment to obtain a second sterilized product; subjecting the second sterilized product and the concentrated skim milk to fat standardization treatment to obtain a standardized material; subjecting the standardized material to a first homogenization treatment; after the ultra-high temperature sterilization treatment, subjecting the obtained ultra-high temperature sterilization product to a flash evaporation treatment; after the first mixing treatment, subjecting the obtained mixed liquid to a second homogenization, cooling and filling treatment.

[0031] According to an embodiment of the present application, the temperature of the second sterilization treatment is 120°C~140°C, and the time is 5 s~20 s; the temperature of the first homogenization treatment is 68°C~90°C, the total pressure is 160 bar~200 bar, and the secondary pressure is 20 bar~35 bar; the outlet temperature after the flash evaporation treatment is 68°C~90°C; the temperature of the second homogenization treatment is 55°C~90°C, the total pressure is 160 bar~400 bar, and the secondary pressure is 20 bar~35 bar.

[0032] In the second aspect of the present application, the present application proposes a dairy product. According to an embodiment of the present application, the dairy product is obtained by the method for preparing a dairy product according to the first aspect. Thus, the dairy product according to the embodiment of the present application has excellent nutritional value, flavor, taste, color and stability.

[0033] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0035] Figure 1 and Figure 2 The flowcharts of the method for preparing dairy products according to one embodiment of the present application are respectively shown. DETAILED DESCRIPTION

[0036] The following is a detailed description of the embodiments of the technical solution of the present application. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0037] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0038] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 listed, and if the maximum range values ​​3,4 and 5 are listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers, and the scope limited in this way can be including end values ​​a and b. 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.

[0039] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0040] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0041] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0042] The present application proposes a method for preparing a dairy product and a dairy product, which will be described in detail below.

[0043] Method for preparing dairy products

[0044] In the first aspect of the present application, the present application proposes a method for preparing a dairy product. According to the embodiments of the present application, see Figure 1 The method includes: S100 fat separation treatment, S200 membrane separation treatment, S300 freeze concentration treatment, S400 horizontal snail separation treatment, S500 enzymatic hydrolysis treatment, S600 ultra-high temperature sterilization treatment, S700 first mixing treatment, and each step will be described in detail below.

[0045] S100 Fat Separation Process

[0046] In this step, the raw milk is subjected to a fat separation process, and the fat globules in the raw milk are separated and aggregated to form cream.

[0047] According to the embodiment of the present application, the fat separation process can be carried out by centrifugation, under the conditions of temperature 45-70°C or temperature 4-20°C, preferably 4-7°C; rotation speed 3500-5500 rpm, preferably 4500 rpm. In this way, the milk fat can be separated quickly and fully, and the heat denaturation of the milk fat or protein can be reduced.

[0048] It should be noted that before the fat separation process, the collected raw milk can be purified to remove impurities and foreign matter in the raw milk, such as dust, impurities, and some bacteria, so as to improve the purity of the milk, and also help improve the flavor and taste of the milk and enhance the product quality. In some embodiments, a milk purifier can be used for milk purification at a temperature of 1-10°C.

[0049] S200 membrane separation treatment

[0050] In this step, the liquid obtained by the S100 fat separation treatment to obtain the cream is subjected to a membrane separation treatment to achieve the purpose of preliminary sterilization.

[0051] According to an embodiment of the present application, the membrane separation process includes microfiltration membrane processing, thereby achieving the purpose of sterilization.

[0052] In some embodiments, one or more combinations of microfiltration ceramic membranes or microfiltration hollow fiber membranes are used for sterilization, and the pore size of the filter membrane is 0.45-1.4 μm, for example, 0.45 μm, 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, preferably 0.8 μm; the temperature of the membrane separation treatment is 45-65°C or 4-20°C, preferably 4-7°C. Thus, effective sterilization is achieved and the loss of nutrients is reduced. After the membrane separation treatment, the permeate passing through the membrane is used for subsequent freeze concentration and horizontal snail separation treatment.

[0053] S300 freeze concentration and S400 decanter separation

[0054] In this step, the permeate is subjected to freeze concentration and decanter separation to separate water and lactose solution in turn.

[0055] In view of the technical drawbacks of adding lactase to hydrolyze lactose before and after UHT sterilization, the inventors of the present application tried to separate the lactose in raw milk and hydrolyze it separately, and then mix the other materials with the zero-lactose liquid after hydrolysis after a series of treatments and UHT sterilization to obtain zero-lactose dairy products.

[0056] The inventors tried a variety of separation methods, such as the combined separation method of ultrafiltration and nanofiltration. In this process, in order to achieve zero sugar, ultrafiltration requires multiple diafiltrations, and the system configuration is super large, the investment is high, and the energy consumption is high. In addition, the loss of trace elements such as flavors and minerals during the diafiltration process increases with the increase in the number of diafiltrations. Finally, the inventors took advantage of the characteristics of water, lactose and protein in the milk system, each with different freezing points (water is about -0.5°C, lactose is about -2°C, and protein is about -2.6°C). Through freeze concentration technology, the permeate is first cooled to the freezing point of water to form ice crystals and separate (i.e., ice crystal stage), and then further cooled to the freezing point of lactose to promote lactose crystallization (i.e., lactose crystallization stage). Due to the high viscosity of lactose crystals, the horizontal screw separation technology can effectively separate it from the solution to obtain lactose solution. Therefore, the ingenious combination of freeze concentration and horizontal screw separation technology can achieve efficient separation of protein, lactose and water in milk. In this process, the natural ingredients in the milk source, such as proteins, enzymes, vitamins, volatile compounds, and food coloring, can be effectively retained, successfully avoiding the risk of loss of these natural ingredients during the separation and concentration process. In addition, the process flexibility and enzymatic efficiency of the separated lactose are significantly improved by enzymatic hydrolysis with lactase alone, shortening the waiting time required for the early enzymatic hydrolysis, avoiding the adverse effects of the side reactions of the later enzymatic hydrolysis, and reducing the amount of lactase used. At the same time, it can effectively reduce the Maillard reaction caused by heat treatment, and retain the natural color and nutrients in the milk source to the greatest extent.

[0057] It should be noted that the freeze concentration process of the present application adopts a conventional freeze concentration system, which usually includes a crystallizer and a washing column. The feed liquid is first freeze concentrated in the ice crystal crystallizer. When the ice crystal growth reaches a suitable size range, the feed liquid enters the washing column equipment, and the concentrated liquid flows out from the screen. Since the ice crystal viscosity is small, it can be separated and taken away by flushing the screen with water, thereby effectively separating the ice crystals. The concentrated liquid enters the lactose crystallizer and is freeze concentrated. When the lactose crystals grow to a suitable size range, due to the high viscosity of lactose, it cannot be separated by the washing column, and can be separated by centrifugation. Compared with the traditional vertical centrifuge, the horizontal screw centrifuge can handle the feed liquid with high solid content and viscosity. Therefore, the concentrated material that produces lactose crystals is subjected to horizontal screw separation treatment to achieve the purpose of separating lactose. Exemplarily, the freeze concentration system can use the GEAIceCon equipment, and the horizontal screw centrifuge can use the Flottweg horizontal screw centrifuge.

[0058] According to an embodiment of the present application, the ice crystal stage includes: placing the permeate in an ice crystal crystallizer, controlling the temperature of the permeate to a first temperature so that ice crystals are generated in the permeate, collecting concentrated materials and ice crystals, the first temperature is -0.6°C to -1.3°C, for example, it can be -0.6°C, -0.8°C, -0.9°C, -1.0°C, -1.2°C, -1.3°C, preferably -0.9°C to -1.3°C. In the ice crystal stage, the permeate is frozen to the freezing point (first temperature), ice crystals are generated, and the ice crystals on the washing column are collected to achieve a separation effect.

[0059] According to the embodiments of the present application, the average particle size of the ice crystals is 500 μm to 900 μm, for example, 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm, 800 μm, 850 μm, 900 μm. Thus, while ensuring that the ice crystals can be separated smoothly, it also avoids the long growth time and high energy consumption of the ice crystals caused by the ice crystals being too large. The ice crystals being too large are also prone to causing other components to be mixed, resulting in the loss of nutrients in the milk.

[0060] According to an embodiment of the present application, the refrigerant temperature in the ice crystal stage is -1°C to -18°C and is lower than the first temperature, for example, it can be -1°C, -3°C, -5°C, -8°C, -10°C, -13°C, -15°C, -18°C. Thus, the ambient temperature is lowered, water crystallization is promoted, and the growth rate of ice crystals is appropriate, so that the ice crystals can maintain a uniform spherical shape and a smooth surface. If the surface shape of the ice crystal is irregular, the risk of carrying nutrients such as minerals is increased, resulting in the loss of nutrients, and the viscosity of the material is increased, the fluidity of the material is reduced, and more materials are hung on the surface of the ice crystals, increasing the difficulty of separation.

[0061] According to an embodiment of the present application, the stirring speed of the ice crystal crystallizer is 300 rpm to 1000 rpm, for example, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, preferably 400 rpm to 600 rpm. Thus, it is conducive to the uniform growth of ice crystals, so that the ice crystals can maintain a uniform spherical shape and a smooth surface, avoid local oversaturation and crystal aggregation, thereby improving the efficiency of ice crystal crystallization and product quality, while reducing energy consumption and avoiding equipment wear, ensuring the stability and controllability of the entire crystallization process.

[0062] According to the embodiments of the present application, the growth rate of ice crystals is 2 to 6 μm / min, for example, 2 μm / min, 3 μm / min, 4 μm / min, 5 μm / min, and 6 μm / min. Thus, the ice crystals can maintain a uniform spherical shape and a smooth surface. If the surface shape of the ice crystals is irregular, the risk of carrying nutrients such as minerals increases, resulting in loss of nutrients, and also increases the viscosity of the material, reduces the fluidity of the material, causes more material to hang on the surface of the ice crystals, and increases the difficulty of separation.

[0063] The temperature of the ice crystals coming out of the washing column is about 1-4°C and is temporarily stored in a pure water tank until it is mixed with concentrated lactose in the next step. The excess water can be used for other purposes.

[0064] According to an embodiment of the present application, the lactose crystallization stage includes: placing the concentrated material in a lactose crystallizer, controlling the temperature of the concentrated material to a second temperature so that lactose crystals are generated in the concentrated material; subjecting the concentrated material that produces lactose crystals to a horizontal screw separation process to separate a concentrated lactose liquid, and the second temperature is -1.5°C to -2.2°C, for example, it can be -1.5°C, -1.6°C, -1.8°C, -2.0°C, -2.2°C, preferably -1.8°C to -2.2°C.

[0065] According to the embodiments of the present application, the average particle size of lactose crystals is 200 μm to 600 μm, for example, 200 μm, 250 μm, 300 μm, 350 μm, 400 μm, 450 μm, 500 μm, 550 μm, 600 μm. As the total solid content of the material increases, the heat transfer efficiency decreases, and the crystal growth rate decreases, the lactose crystals are controlled to the above size, which can ensure that the lactose crystals can be separated smoothly while avoiding the long crystal growth time and high energy consumption caused by excessive crystals. Excessive crystals are also prone to cause other components to be mixed, resulting in the loss of nutrients in milk.

[0066] According to the embodiments of the present application, the growth rate of lactose crystals is 0.3 μm / min~2.7 μm / min, for example, it can be 0.3 μm / min, 0.5 μm / min, 0.8 μm / min, 1 μm / min, 1.2 μm / min, 1.5 μm / min, 1.8 μm / min, 2 μm / min, 2.2 μm / min, 2.5 μm / min, 2.7 μm / min. Thus, the lactose crystals can maintain a uniform spherical shape and a smooth surface. If the surface shape of the lactose crystals is irregular, the risk of carrying nutrients such as minerals is increased, resulting in loss of nutrients, and the viscosity of the material is increased, the fluidity of the material is reduced, and more materials are hung on the surface of the lactose crystals, increasing the difficulty of separation.

[0067] According to an embodiment of the present application, the refrigerant temperature during the lactose crystallization stage is -5°C to -23°C and is lower than the second temperature, for example, it can be -5°C, -8°C, -10°C, -12°C, -15°C, -18°C, -20°C, -23°C. Thus, the ambient temperature is lowered to promote lactose crystallization, and the growth rate of lactose crystals is appropriate, maintaining a uniform spherical shape and a smooth surface. If the surface shape of the lactose crystals is irregular, the risk of carrying nutrients such as minerals is increased, resulting in loss of nutrients, and the viscosity of the material is increased, the fluidity of the material is reduced, and more materials are hung on the surface of the lactose crystals, increasing the difficulty of separation.

[0068] According to an embodiment of the present application, the stirring speed of the lactose crystallizer is 30 rpm to 150 rpm, for example, 30 rpm, 50 rpm, 60 rpm, 80 rpm, 100 rpm, 120 rpm, 140 rpm, 150 rpm, preferably 80 rpm to 100 rpm. Thus, it is conducive to the uniform growth of lactose crystals, making the lactose crystal growth rate suitable, maintaining a uniform spherical shape and a smooth surface, avoiding local supersaturation and crystal aggregation, thereby improving lactose crystallization efficiency and product quality, while reducing energy consumption and avoiding equipment wear, ensuring the stability and controllability of the entire crystallization process.

[0069] According to an embodiment of the present application, the centrifugal speed of the horizontal screw separation process is 2300 rpm to 4700 rpm, for example, 2300 rpm, 2500 rpm, 3000 rpm, 3500 rpm, 4000 rpm, 4500 rpm, 4700 rpm. Thus, lactose crystals can be separated from the material.

[0070] S500 enzymatic treatment

[0071] In this step, water, concentrated lactose solution and lactase are enzymatically treated to obtain lactose-free solution.

[0072] According to an embodiment of the present application, 40% to 60% by volume of the concentrated lactose solution obtained by the horizontal snail separation process is used for the enzymatic hydrolysis process, for example, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, and 60% by volume. The above-mentioned partial concentrated lactose solution is subjected to enzymatic hydrolysis, so that the sweetness of the resulting product is suitable and closer to the taste of milk. If the entire concentrated lactose solution is subjected to enzymatic hydrolysis, the sweetness of the product will be higher. The unused concentrated lactose solution can be used elsewhere.

[0073] According to an embodiment of the present application, the lactase is selected from Nurica TM Lactase. NuricaTM Lactase can further convert the enzymatically hydrolyzed galactose into galacto-oligosaccharides (GOS), reducing the sweetness of the product and making it closer to the original sweetness of milk.

[0074] According to an embodiment of the present application, the temperature of the enzymatic hydrolysis treatment is 2°C~60°C, for example, it can be 2°C, 10°C, 20°C, 30°C, 40°C, 45°C, 50°C, 55°C, 60°C, preferably 45°C~50°C; the time is 1 h~2 h, for example, it can be 1 h, 2 h. As a result, the lactase activity is relatively high, and lactose can be efficiently and quickly enzymolyzed with high enzymolysis efficiency. In addition, by separating lactose separately for enzymolysis, the optimal enzymolysis conditions of lactase can be selected, thereby reducing the amount of lactase used. After enzymolysis, the lactose content is ≤0.2%, and the product has an appropriate sweetness, close to the original sweetness of milk.

[0075] According to an embodiment of the present application, before enzymolysis treatment, water, concentrated lactose solution and lactase are subjected to a second mixing and sterilization treatment. Exemplarily, the concentrated lactose solution is mixed with water and then heated to 25-30°C, and lactase is added to the mixed solution, and sterilization treatment is performed after mixing to avoid the presence of a small amount of miscellaneous bacteria in the subsequent enzymolysis process. The bacteria content in the product is too high, affecting the shelf life stability. The enzymolysis temperature can be appropriately increased in a sterile environment to reach the optimal enzymolysis temperature of lactase, and the enzymolysis effect is high. Due to the physical sterilization method after sterilization in some embodiments, specifically filtration sterilization, the pore size of the sterilization filter element is 0.22-0.45 μm, preferably 0.22 μm, and the sterilization efficiency is ≥ log 7.

[0076] According to the embodiments of the present application, after enzymolysis treatment, enzyme inactivation treatment is performed. In order to prevent lactase and other enzymes from reacting continuously during the shelf life of the product, enzyme inactivation is performed in advance, thereby ensuring the shelf life stability of the product and avoiding color change. In some embodiments, the temperature of enzyme inactivation treatment is 80°C to 100°C, for example, 80°C, 85°C, 90°C, 95°C, 100°C, and the time is 90 s to 180 s, for example, 90 s, 100 s, 120 s, 140 s, 150 s, 160 s, 180 s. Thus, in order to fully inactivate lactase and reduce the loss of other components.

[0077] S600 ultra-high temperature sterilization

[0078] In this step, the cream, the membrane concentrate and the concentrated skim milk are subjected to ultra-high temperature sterilization to obtain a first sterilized product. Thus, the ultra-high temperature sterilization can effectively kill microorganisms and reduce the loss of nutrients.

[0079] According to the embodiments of the present application, the temperature of the ultra-high temperature sterilization treatment is 140°C to 162°C, for example, it can be 140°C, 142°C, 144°C, 145°C, 146°C, 148°C, 150°C, 152°C, 154°C, 155°C, 156°C, 158°C, 160°C, 162°C, and the time is 0.09 s to 3.5 s, for example, it can be 0.09 s, 0.1 s, 0.5 s, 1 s, 1.5 s, 2 s, 2.5 s, 3 s, 3.5 s. Thus, microorganisms can be effectively killed and the loss of nutrients can be reduced.

[0080] According to an embodiment of the present application, before the ultra-high temperature sterilization treatment is performed, the method further comprises at least one of the following steps:

[0081] The mixture of the cream and the membrane concentrate is subjected to a second sterilization treatment to obtain a second sterilized product;

[0082] The second sterilized product and the concentrated skim milk are subjected to fat standardization treatment to obtain a standardized material;

[0083] The standardized material is subjected to a first homogenization process.

[0084] By sterilizing the mixture of the cream and the membrane concentrate, the bacteria can be effectively killed and the stability during the shelf life can be ensured. In some embodiments, the temperature of the sterilization treatment is 120°C to 140°C, for example, 120°C, 122°C, 124°C, 125°C, 126°C, 128°C, 130°C, 132°C, 134°C, 135°C, 136°C, 138°C, 140°C; the time is 5 s to 20 s, for example, 5 s, 8 s, 10 s, 12 s, 15 s, 18 s, 20 s. Thus, the bacteria can be effectively killed and the loss of nutrients can be reduced. Exemplarily, indirect and / or direct sterilization methods can be used.

[0085] The fat content of the product is adjusted to meet industry requirements and ensure batch consistency by subjecting the liquid (i.e., concentrated skim milk) from which lactose is separated by decanter separation and the above-mentioned sterilization product to fat standardization.

[0086] Through the first homogenization treatment, the material is refined to reduce the occurrence of floating or precipitation. In some embodiments, the temperature of the first homogenization treatment is 68°C~90°C, for example, it can be 68°C, 70°C, 75°C, 80°C, 85°C, 90°C, the total pressure is 160 bar~200 bar, for example, it can be 160 bar, 170 bar, 180 bar, 190 bar, 200 bar, and the secondary pressure is 20 bar~35 bar, for example, it can be 20 bar, 25 bar, 30 bar, 35 bar. Therefore, the above homogenization effect is better. Before the first homogenization treatment, the standardized material is heated to the homogenization temperature in advance.

[0087] According to the embodiments of the present application, after the ultra-high temperature sterilization treatment, the obtained ultra-high temperature sterilization product is flash-treated. Thus, part of the water in the feed liquid is removed, the water activity of the product is reduced, and the shelf life of the product is extended. At the same time, flash evaporation can also help concentrate the flavor and nutrients in the product and improve the taste and texture of the product. In some embodiments, the outlet temperature after flash evaporation is 68°C to 90°C, for example, it can be 68°C, 70°C, 75°C, 80°C, 85°C, 90°C, which is more effective.

[0088] S700 First Mixing Process

[0089] In this step, the first sterilized product and the lactose-free liquid are subjected to a first mixing treatment to obtain a dairy product. Specifically, the lactose-free liquid is added to the sterilized product in an aseptic addition manner.

[0090] According to an embodiment of the present application, after the first mixing process, the obtained mixed liquid is subjected to a second homogenization, cooling and filling process.

[0091] In some embodiments, the temperature of the second homogenization treatment is 55°C to 90°C, for example, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C; the total pressure is 160 bar to 400 bar, for example, 160 bar, 200 bar, 250 bar, 300 bar, 350 bar, 400 bar; the secondary pressure is 20 bar to 35 bar, for example, 20 bar, 25 bar, 30 bar, 35 bar. In order to refine the material and reduce the occurrence of floating or precipitation. Before the second homogenization treatment, the mixed liquid is heated to the homogenization temperature in advance.

[0092] In some embodiments, the feed liquid after the second homogenization treatment is cooled to below 25°C and temporarily stored in a sterile tank, and the aseptic cold filling technology is adopted, that is, aseptic filling is performed below 25°C.

[0093] Dairy

[0094] In the second aspect of the present application, the present application proposes a dairy product. According to an embodiment of the present application, the dairy product is obtained by the aforementioned method for preparing a dairy product. Therefore, the dairy product according to the embodiment of the present application retains the natural color and nutrients in the milk source to the greatest extent, is not prone to Maillard reaction during the shelf life, and has excellent nutritional value, flavor, taste, color and stability.

[0095] According to the embodiments of the present application, the protein content of the dairy product is 3.8-15.0 g / 100 g, the fat content is 0.1-20.0 g / 100 g, and the nutritional value is high. The content of carbohydrates and oligosaccharides can be adjusted according to different product requirements or consumer preferences.

[0096] It should be noted that the features and advantages described above for the method for preparing dairy products are also applicable to the dairy products and will not be repeated here.

[0097] The scheme of the present application will be explained below in conjunction with the embodiments. It will be appreciated by those skilled in the art that the following embodiments are only used to illustrate the present application and should not be considered as limiting the scope of the present application. If no specific technology or conditions are indicated in the embodiments, the technology or conditions described in the literature in this area or the product specification are carried out. The reagents used or the instruments that do not indicate the manufacturer are all conventional products that can be obtained commercially.

[0098] Example 1

[0099] In this embodiment, see Figure 2 , prepare zero lactose dairy products according to the following method, product target indicators: protein: 4.5g / 100g, fat: 1.2g / 100g, Nurica lactase addition: 4g / kg.

[0100] (1) Clean milk

[0101] A centrifugal milk purifier is used at a temperature of 4-7°C.

[0102] (2) Fat separation

[0103] The fat is separated by a centrifuge at a temperature of 4-7°C and a rotation speed of 4500 rpm to obtain cream and skim milk.

[0104] (3) MF membrane sterilization

[0105] The skim milk produced in (2) is sterilized by a microfiltration ceramic membrane with a pore size of 0.8 μm; the sterilization temperature is 4-7°C.

[0106] (4) Cream sterilization

[0107] The mixture of light cream and microfiltration concentrate was treated by direct sterilization, using a direct infusion sterilizer at a temperature of 135°C and a time of 7 seconds.

[0108] (5) Freezing point concentration

[0109] (3) The sterilized skim milk is concentrated through the freezing point. The system uses GEA IceCon equipment, which is mainly composed of a crystallizer and a washing column. The temperature is controlled in steps to achieve ice crystal (water) separation and lactose crystallization.

[0110] ① Ice crystal separation: material temperature is -1.0℃; stirring speed in the crystallizer is 550 rpm; refrigerant temperature is -10℃; ice crystal growth rate is 4.5 μm / min. When the average particle size of ice crystals reaches about 700μm, the material enters the washing column equipment, large ice crystals are separated from the washing column, and the concentrated material enters the next lactose crystallizer. After the ice crystals come out of the washing column, the temperature is about 1-4℃, and they are temporarily stored in a pure water tank until they are mixed with concentrated lactose in the next step. The excess water can be used for other purposes.

[0111] ② Lactose crystallization: After the concentrated material enters the lactose crystallizer, the refrigerant temperature, material temperature and stirring speed are further adjusted to achieve the purpose of lactose crystallization. Among them, the material temperature is -2.0℃; the stirring speed in the crystallizer is 90 rpm; the refrigerant temperature is -18℃, and the lactose crystallization speed is 1.8μm / min. When the average particle size of the lactose crystals reaches about 400μm, the material is put into the horizontal screw separator, and the lactose crystals are separated from the horizontal screw separator, and the remaining is concentrated skim milk.

[0112] (6) Horizontal screw separation

[0113] The horizontal screw separator uses Flottweg horizontal screw centrifuge, which can separate lactose crystals from the material through centrifugal force at a rotation speed of 3500 rpm to obtain concentrated lactose liquid.

[0114] (7) Mixing

[0115] Take 60% concentrated lactose solution and mix it with water in a volume ratio of 1:4.5, then heat it to 25±1°C, and add lactase (4g / kg) into the solution for mixing. The lactase used is Nurica lactase.

[0116] (8) Sterilization

[0117] The mixed solution after (7) is physically sterilized, the pore size of the sterilization filter is 0.22 μm, and the sterilization efficiency is ≥ log 7.

[0118] (9) Enzymatic hydrolysis

[0119] The lactose solution after the sterilization in the previous step was enzymatically hydrolyzed with Nurica lactase at a temperature of 48±1°C for 1.5 hours. After enzymatic hydrolysis, the lactose content was ≤0.2%, and a certain concentration of galacto-oligosaccharides GOS was produced.

[0120] (10) Enzyme inactivation

[0121] The material obtained by enzymatic hydrolysis in the previous step was subjected to enzyme inactivation treatment at 85°C for 90s.

[0122] (11) Fat standardization

[0123] The sterilized cream from step (4) and the concentrated skim milk from step (5) were subjected to fat standardization at a fat to protein ratio of 1:3.68.

[0124] (12) Preheating

[0125] Preheat the standardized semi-finished product to 70°C.

[0126] (13) Homogenization

[0127] Homogenizing temperature is 70℃, total homogenizing pressure is 160bar, and secondary pressure is 30bar.

[0128] (14) Ultra-high temperature sterilization (direct type)

[0129] The semi-finished product homogenized by (13) is sterilized by direct infusion ultra-high temperature sterilization, and the sterilization temperature and time parameters are 153°C and 0.15s.

[0130] (15) Flash evaporation

[0131] The semi-finished product sterilized by (14) is flash-steamed, and the outlet temperature after flash-steaming is 68°C.

[0132] (16) Aseptic online addition

[0133] The mixed solution after enzyme inactivation in step (10) is added aseptically online to the semi-finished product in step (15).

[0134] (17) Homogenization

[0135] The sterilized product is homogenized using a two-stage homogenization process of a sterile homogenizer, with a homogenization temperature of 70°C, a total homogenization pressure of 200 bar, and a secondary homogenization pressure of 30 bar.

[0136] (18) Cooling and temporary storage in sterile tanks

[0137] The product homogenized in (17) is cooled to below 25°C and temporarily stored in a sterile tank.

[0138] (19) Aseptic filling

[0139] The sterilized product is filled using aseptic cold filling technology, that is, aseptic filling is carried out below 25°C.

[0140] Example 2

[0141] The difference from Example 1 is that step (5) is as follows:

[0142] ① Ice crystal separation: material temperature is -0.7℃; stirring speed in the crystallizer is 350 rpm; refrigerant temperature is -8℃; ice crystal growth rate is 2.6μm / min. When the average particle size of ice crystals is about 700μm, the material enters the washing column equipment, large ice crystals are separated from the washing column, and the concentrated material enters the next lactose crystallizer. After the ice crystals come out of the washing column, the temperature is about 1-4℃, and they are temporarily stored in a pure water tank to be mixed with concentrated lactose in the next step. The excess water can be used for other purposes.

[0143] ② Lactose crystallization: After the concentrated material enters the lactose crystallizer, the refrigerant temperature, material temperature and stirring speed are further adjusted to achieve the purpose of lactose crystallization. Among them, the material temperature is -1.6℃; the stirring speed in the crystallizer is 50 rpm; the refrigerant temperature is -13℃, and the lactose crystal growth rate is 0.5 μm / min. When the average particle size of the lactose crystal is about 400μm, the material is put into the horizontal screw separator, and the lactose crystals are separated from the horizontal screw separator, and the remaining is concentrated skim milk.

[0144] Example 3

[0145] The difference from Example 1 is that step (5) is as follows:

[0146] ① Ice crystal separation: material temperature is -1.3℃; stirring speed in the crystallizer is 900 rpm; refrigerant temperature is -16.5℃; ice crystal growth rate is 6μm / min. When the average particle size of ice crystals is about 700μm, the material enters the washing column equipment, large ice crystals are separated from the washing column, and the concentrated material enters the next lactose crystallizer. After the ice crystals come out of the washing column, the temperature is about 1-4℃, and they are temporarily stored in a pure water tank to be mixed with concentrated lactose in the next step. The excess water can be used for other purposes.

[0147] ② Lactose crystallization: After the concentrated material enters the lactose crystallizer, the refrigerant temperature, material temperature and stirring speed are further adjusted to achieve the purpose of lactose crystallization. Among them, the material temperature is -2.2℃; the stirring speed in the crystallizer is 120 rpm; the refrigerant temperature is -22℃, and the lactose crystal growth rate is 2.7 μm / min. When the average particle size of the lactose crystal is about 400μm, the material is put into the horizontal screw separator, and the lactose crystals are separated from the horizontal screw separator, and the remaining is concentrated skim milk.

[0148] Example 4

[0149] The difference from Example 1 is that in step (5), the ice crystal separation step, when the average particle size of the ice crystals is about 550 μm, the material enters the washing column equipment.

[0150] Example 5

[0151] The difference from Example 1 is that in step (5), the ice crystal separation step, when the average particle size of the ice crystals is about 850 μm, the material enters the washing column equipment.

[0152] Example 6

[0153] The difference from Example 1 is that in step (5), the lactose crystallization step, when the average particle size of the lactose crystals is about 250 μm, the material enters the horizontal screw centrifuge.

[0154] Example 7

[0155] The difference from Example 1 is that in step (5), the lactose crystallization step, when the average particle size of the lactose crystals is about 600 μm, the material is fed into a horizontal screw separator.

[0156] Example 8

[0157] The difference from Example 1 is that in step (5), the ice crystal separation step, when the average particle size of the ice crystals is about 300 μm, the material enters the washing column equipment.

[0158] Example 9

[0159] The difference from Example 1 is that in step (5) the ice crystal separation step, when the average particle size of the ice crystals is about 1000 μm, the material enters the washing column equipment.

[0160] Example 10

[0161] The difference from Example 1 is that in step (5), the lactose crystallization step, when the average particle size of the lactose crystals is about 100 μm, the material is fed into a horizontal screw separator.

[0162] Embodiment 11

[0163] The difference from Example 1 is that in step (5), the lactose crystallization step, when the average particle size of the lactose crystals is about 700 μm, the material is fed into a horizontal screw separator.

[0164] Example 12

[0165] The difference from Example 1 is that in step (5) the ice crystal separation step, the material temperature range is -0.4°C; the stirring speed in the crystallizer is 550 rpm; the refrigerant temperature is -5°C, and the ice crystal growth rate is 1 μm / min.

[0166] Embodiment 13

[0167] The difference from Example 1 is that in step (5) the ice crystal separation step, the material temperature range is -1.5°C; the stirring speed in the crystallizer is 550 rpm; the refrigerant temperature is -18°C, and the ice crystal growth rate is 8 μm / min.

[0168] Embodiment 14

[0169] The difference from Example 1 is that in step (5) the lactose crystallization step, the material temperature range is -1.25°C; the stirring speed in the crystallizer is 90 rpm; the refrigerant temperature is -7°C, and the lactose crystal growth rate is 0.1 μm / min.

[0170] Embodiment 15

[0171] The difference from Example 1 is that in step (5) the lactose crystallization step, the material temperature range is -2.6°C; the stirring speed in the crystallizer is 90 rpm; the refrigerant temperature is -25°C, and the lactose crystal growth rate is 3.0 μm / min.

[0172] Comparative Example 1

[0173] The difference from Example 1 is that steps (5) ② lactose crystallization, (6), (7), (8), and (16) are omitted, and the steps after step (5) ① and before step (14) are as follows:

[0174] (a) Fat standardization: The sterilized cream from step (4) and the concentrated skim milk from step (5) (i.e., the concentrated material obtained by ice crystal separation in step ①) are subjected to fat standardization at a fat to protein ratio of 1:3.68.

[0175] (b) Preheating: Same as step (12) of Example 1.

[0176] (c) Homogenization: Same as step (13) of Example 1.

[0177] (d) Enzymatic hydrolysis: the same as step (9) of Example 1, except that the enzymatic hydrolysis time was 24 h.

[0178] (e) Enzyme inactivation: same as step (10) of Example 1.

[0179] Comparative Example 2

[0180] The difference from Comparative Example 1 is that step (5) ① is as follows: the skimmed milk sterilized in (4) is concentrated by RO membrane (NaCl retention rate > 97%) at a temperature < 10°C.

[0181] Comparative Example 3

[0182] The difference from Comparative Example 1 is that step (5) ① is as follows: the sterilized skim milk is concentrated by falling film evaporation (double-effect evaporation system), with the first-effect evaporation temperature being 70°C and the second-effect evaporation temperature being 52°C.

[0183] Comparative Example 4

[0184] The difference from Example 1 is that steps (5) and (6) have the following differences:

[0185] Step (5) Freezing point concentration: Replace with UF membrane concentration (molecular weight cutoff 10 kDa), temperature <10°C, concentrate skim milk (retentate) for fat standardization, and the effluent contains lactose.

[0186] Step (6) Horizontal screw separation: The effluent obtained in the previous step is concentrated by NF membrane (molecular weight cutoff is 300Da) to obtain concentrated lactose solution and NF permeate water, respectively. The NF permeate water is used as the permeate added during the UF membrane diafiltration process in step (5). The concentrated lactose solution is subjected to the operation of step (7).

[0187] Test Case

[0188] The lactose-free dairy products prepared in Examples 1-15 and Comparative Examples 1-4 were tested respectively, and the specific steps were as follows:

[0189] 1. Concentration capacity: the total solid (TS) content of the concentrated material obtained in step (5) and step (6).

[0190] 2. Lactose removal rate:

[0191] Removal rate = (1 - lactose content after concentration / initial lactose content of skimmed milk) * 100%, wherein the lactose content after concentration refers to the lactose content in the concentrated skimmed milk in step (6), and the initial lactose content of skimmed milk refers to the lactose content in the skimmed milk in step (2).

[0192] 3. COD (chemical oxygen demand) of removed water: COD test is performed on the water removed during freezing point concentration, RO membrane concentration, falling film concentration and UF+NF concentration in step (5).

[0193] 4. Concentration cost determination method: Comprehensively compare the energy consumption (water, electricity, steam, etc.), cleaning, operation and maintenance, and consumables costs in the processes of freezing point concentration, combination of freezing point concentration and horizontal screw separation, RO membrane concentration, falling film concentration, and combined membrane (UF+RO), and convert them into the cost per ton of finished product.

[0194] 5. Enzymatic hydrolysis time: The time taken for the lactose content of the milk product to be ≤0.2% after enzymatic hydrolysis with Nurica lactase.

[0195] 6. Crystal size: Observe the shape and size of ice crystals and lactose crystals through an optical microscope. The crystals can be clearly imaged under the microscope. Use the ruler in the eyepiece and image analysis software to measure their size and calculate the average particle size.

[0196] 7. Method for determining the content of heat-sensitive substances before the product comes off the production line: Detect the content of heat-sensitive substances (α-lactalbumin, β-lactoglobulin, furosine) in the product on the 7th day after the product comes off the production line.

[0197] 8. Sensory test method: The prepared milk was stored at room temperature of 37°C. After 7 days, 30 days, 60 days and 90 days, 50 professional tasters were invited to rate the degree of preference for the product. The preference score ranged from 1 to 10 points. The higher the score, the higher the preference. The obtained scores were averaged to obtain the result of the sensory preference test.

[0198] The results are shown in Table 1, Table 2 and Table 3.

[0199] Table 1 Comparison of milk product processing efficiency

[0200]

[0201] Table 2 Comparison of milk product quality

[0202]

[0203] Table 3 Details of sensory scores of milk products during shelf life

[0204]

[0205] It can be seen from Tables 1-3 that the product quality of the zero lactose dairy products of Examples 1-15 is better than that of Comparative Examples 1-4 as a whole.

[0206] Compared with Comparative Examples 1-3, Examples 1-15 show that the combination of freezing point concentration and horizontal snail separation can efficiently separate the water and lactose components in skimmed milk and improve product quality. ① By comparing the concentration capacity, it can be found that the concentration capacity of the combination of freezing point concentration and horizontal snail separation is higher than that of single freezing point concentration, RO membrane, and falling film, and the treatment effect and component range are wider, and more product categories are suitable for development. ② By comparing the lactose removal rate, it can be found that single freezing point concentration, RO membrane, and falling film only have the characteristics of full component concentration, and lactose cannot be regulated. ③ By comparing the active protein and furosine content, it can be found that before enzyme inactivation and heat sterilization, lactose is separated and processed separately, which can effectively retain the natural ingredients such as protein, enzyme, vitamin, volatile compound and edible pigment in the milk source, and avoid the Maillard reaction between protein and reducing sugar (such as lactose, glucose, etc.) during the thermal processing, so as not to affect the product quality. In addition, the separated lactose is sterilized, enzymolyzed and enzyme inactivated separately, which has higher efficiency and minimal impact on product quality. Mixing lactose and lactase and sterilizing them can make both the lactose solution and lactase achieve commercial sterility, and at the same time, the selectivity of lactase increases, for example, non-sterile enzymes with high enzyme activity can be selected, which are cheaper. ④ By comparing the enzymatic hydrolysis time, it can be found that when lactose is hydrolyzed alone, the optimal temperature range can be selected according to the characteristics of lactase, thereby improving the enzymatic hydrolysis efficiency and the conversion efficiency of galacto-oligosaccharides (GOS), greatly shortening the processing time (the enzymatic hydrolysis time of lactose alone is about 1 to 2 hours, while the traditional lactase pre-addition time is about 20 to 28 hours), and reducing the total amount of lactase added. ⑤ By comparing the results of the shelf life sensory evaluation, it can be found that due to the long enzyme inactivation and heat sterilization time and high temperature, the enzyme inactivation operation is performed separately after the lactose enzymatic hydrolysis, which can not only ensure the safety of the product, but also avoid the loss of nutrients in the milk due to excessive heating. At the same time, the color and sensory performance of the product are more stable during the shelf life. Compared with the traditional method of adding lactase before and after aseptic addition, the products using this method perform better in terms of shelf life consistency.

[0207] Compared with Example 4, the freezing point concentration and decanter separation combined process is simpler, has lower operating costs, higher separation efficiency, and better sensory stability of products during the shelf life compared with a variety of membrane combinations (UF+NF). ① By comparing the concentration capacity, it can be clearly found that the freezing point concentration and decanter separation combination has a higher concentration capacity than the UF+NF combination membrane, with a wider treatment effect and component range, and more suitable product categories for development; ② By comparing the lactose removal rate and the COD of the removed water quality, it can be found that within the optimal parameter range, the freezing point concentration and decanter separation have a better effect on lactose removal, and the impurities of the removed lactose and water are low, and the material components are pure; within a wider parameter range, a lactose removal rate similar to that of UF+NF can be achieved, and the possibility of minerals and flavor substances being mixed in the components is smaller. Even if the lactose removal rate of UF+NF is improved by multiple diafiltration, its economic efficiency is poor and the loss of trace components is serious. Therefore, the freezing point concentration and decanter separation combined process has great advantages for component concentration and lactose regulation. ③Examples 1-15 and Comparative Example 4 are both lactose separation and lactase hydrolysis processes. By comparing the concentration costs, it can be found that freezing point concentration and decanter separation have obvious operating cost advantages over multiple membrane combinations (UF+NF), and are more energy-saving and low-carbon. ④Comparing the shelf life sensory data, it can be found that the freezing point concentration and decanter separation component processes have better sensory stability and high consistency in consumer preference evaluation.

[0208] Compared with Examples 1-7 and 8-15, the overall effect is better when the ice crystal size is 500-900 μm and the lactose crystal size is 200-600 μm. If the ice crystal size is too small, the small ice crystals will mix with the concentrated material and are not easy to separate, and the ice crystals will even flow out with the material; if the ice crystals are too large, the ice crystal growth time will be long and the energy consumption will be high. If the ice crystals are too large, it will easily cause other components to be mixed, resulting in the loss of nutrients such as milk minerals. If the lactose ice crystals are too small and mixed with the material, it will be necessary to increase the rotation speed and energy consumption costs, and it may even be impossible to separate under higher centrifugal forces; at the same time, if the lactose crystals are too large, the lactose crystallization time will be long and the energy consumption will be high, which may also cause the loss of nutrients such as milk protein.

[0209] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for preparing a dairy product, characterized in that: include: The raw milk is subjected to fat separation and membrane separation treatment to obtain cream, membrane concentrate and permeate; The permeate is subjected to freeze concentration and decanter separation to obtain water, concentrated lactose solution and concentrated skimmed milk; The water, the concentrated lactose solution and the lactase are subjected to enzymatic hydrolysis to obtain a lactose-free solution; The cream, the membrane concentrate and the concentrated skim milk are subjected to ultra-high temperature sterilization to obtain a first sterilized product; The first sterilized product and the lactose-free liquid are subjected to a first mixing treatment to obtain the dairy product.

2. The method according to claim 1, characterized in that The freeze concentration process includes an ice crystal stage and a lactose crystal stage; The ice crystal stage comprises: placing the permeate in an ice crystal crystallizer, controlling the temperature of the permeate to a first temperature so that ice crystals are generated in the permeate, and collecting concentrated material and the ice crystals; The lactose crystallization stage comprises: placing the concentrated material in a lactose crystallizer, controlling the temperature of the concentrated material to a second temperature so as to generate lactose crystals in the concentrated material; The concentrated material producing lactose crystals is subjected to horizontal screw separation to separate the concentrated lactose liquid; Among them, the first temperature is -0.6℃~-1.3℃, and the second temperature is -1.5℃~-2.2℃.

3. The method according to claim 2, characterized in that The average particle size of the ice crystals is 500 μm to 900 μm; The average particle size of the lactose crystals is 200 μm to 600 μm; The growth rate of the ice crystals is 2 μm / min~6 μm / min; The growth rate of the lactose crystals is 0.3 μm / min~2.7 μm / min.

4. The method according to claim 2 or 3, characterized in that The refrigerant temperature in the ice crystal stage is -1°C to -18°C and is lower than the first temperature; The refrigerant temperature during the lactose crystallization stage is -5°C to -23°C and is lower than the second temperature; The stirring speed of the ice crystal crystallizer is 300 rpm to 1000 rpm; The stirring speed of the lactose crystallizer is 30 rpm to 150 rpm; The centrifugal speed of the decanter separation process is 2300 rpm to 4700 rpm.

5. The method according to claim 1, characterized in that 40% to 60% by volume of the concentrated lactose solution obtained by the horizontal snail separation process is used for the enzymatic hydrolysis process; The lactase is selected from Nurica TM Lactase.

6. The method according to claim 1 or 5, characterized in that The temperature of the enzymatic hydrolysis treatment is 2°C to 60°C, and the time is 1 h to 2 h; Before the enzymatic hydrolysis treatment, the water, concentrated lactose solution and lactase are subjected to a second mixing and sterilization treatment; After the enzymatic hydrolysis, the obtained enzymatic hydrolysis product is subjected to an enzyme inactivation treatment to obtain the lactose-free liquid. The temperature of the enzyme inactivation treatment is 80° C. to 100° C., and the time is 90 s to 180 s.

7. The method according to claim 1 or 5, characterized in that: The temperature of the enzymatic hydrolysis treatment is 45°C to 50°C.

8. The method according to claim 1, characterized in that The membrane separation treatment includes microfiltration membrane treatment; The ultra-high temperature sterilization treatment is performed at a temperature of 140°C to 162°C and a time of 0.09 s to 3.5 s; Before the ultra-high temperature sterilization treatment is performed, the method further comprises at least one of the following steps: subjecting the mixture of the cream and the membrane concentrate to a second sterilization treatment to obtain a second sterilized product; The second sterilized product and the concentrated skim milk are subjected to fat standardization treatment to obtain a standardized material; Subjecting the standardized material to a first homogenization process; After the ultra-high temperature sterilization treatment, the obtained ultra-high temperature sterilization product is flash-distilled; After the first mixing process, the obtained mixed liquid is subjected to a second homogenization process, a cooling process and a filling process.

9. The method according to claim 8, characterized in that The temperature of the second sterilization treatment is 120°C to 140°C, and the time is 5 s to 20 s; The temperature of the first homogenization treatment is 68°C to 90°C, the total pressure is 160 bar to 200 bar, and the secondary pressure is 20 bar to 35 bar; The outlet temperature after the flash treatment is 68°C to 90°C; The temperature of the second homogenization treatment is 55°C~90°C, the total pressure is 160 bar~400 bar, and the secondary pressure is 20 bar~35 bar.

10. A dairy product, characterized in that The dairy product is obtained by the method for preparing a dairy product according to any one of claims 1 to 9.

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