A method for processing concentrated milk

Abstract

This invention relates to the field of dairy product technology, and more particularly to a method for processing concentrated milk. The processing method includes: subjecting raw milk to a fat separation process to obtain skim milk and light cream; permeating the skim milk through an MF membrane to obtain MF permeate and MF concentrate; permeating the MF permeate through an NF membrane to obtain NF concentrate and NF permeate; permeating the NF permeate through an RO membrane to obtain RO concentrate and RO water; and recombining multiple components of light cream, MF concentrate, NF concentrate, RO concentrate, and RO water to obtain a semi-finished concentrated milk product, such that the mass ratio of protein, fat, lactose, and ash in the semi-finished concentrated milk product is 1:(0.02-2):(0.32-1.3):(0.08-0.25). This invention, by combining multiple membrane concentration technologies and controlling the proportions of protein, fat, lactose, and ash, effectively improves the shelf-life stability of concentrated milk.

Description

Technical Field

[0001] This invention relates to the field of dairy product technology, and more particularly to a method for processing concentrated milk. Background Technology

[0002] Concentrating milk using membrane technology is one of the commonly used techniques for preparing concentrated dairy products. While it can increase the nutrient content of milk, it also increases the content of fibrinolytic enzymes (sources) and the thermal instability of milk proteins. During storage, fibrinolytic enzymes hydrolyze casein, causing protein aggregation and gel formation, while releasing bitter hydrolysates that severely affect the product's taste. Furthermore, concentrated milk (high-protein milk) generally has a higher protein concentration, leading to increased thermal instability. Casein is more prone to cross-linking with lactose and other casein micelles when heated, forming large particles. According to Stokes' law, these large particles cause precipitation during storage. Simultaneously, mineral salt ions also increase the thermal instability of casein micelles. These problems have hindered the development of membrane-concentrated milk.

[0003] Existing technologies include using low-temperature inactivation of protease activity. For example, heat-treating raw milk or UHT milk at 55°C for 60 minutes can significantly reduce protease activity in the product. However, low-temperature inactivation is impractical for large quantities of raw milk and already packaged products, failing to meet actual production needs. Other existing technologies use sodium hexametaphosphate (HMP). Adding HMP to UHT milk can prevent the aggregation of degraded casein, thus controlling gel formation. Alternatively, lysine and ion chelating agents can be used to improve stability. However, adding salt or amino acids increases production costs, and additional additives contradict current additive-free concepts. Existing technologies also reduce the degree of heat treatment in high-protein milk to decrease heat denaturation. However, reduced heat treatment leads to lower enzyme inactivation levels, resulting in a bitter product. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a method for processing concentrated milk. By combining multiple membrane concentration technologies, the proportions of protein, fat, lactose, and ash in dairy products are controlled, effectively improving the shelf-life stability of concentrated milk.

[0005] In a first aspect, the present invention provides a method for processing concentrated milk, comprising:

[0006] The raw milk undergoes a fat separation process to obtain skim milk and light cream;

[0007] The skim milk is permeated through an MF membrane to obtain MF permeate and MF concentrate. The MF permeate is permeated through an NF membrane to obtain NF concentrate and NF permeate. The NF permeate is permeated through an RO membrane to obtain RO concentrate and RO water. Multiple of the light cream, MF concentrate, NF concentrate, RO concentrate and RO water are recombined to obtain a concentrated milk semi-finished product, such that the mass ratio of protein, fat, lactose and ash in the concentrated milk semi-finished product is 1:(0.02-2):(0.32-1.3):(0.08-0.25).

[0008] This invention separates raw milk into skim milk and light cream through fat separation. The light cream is then used to fill the semi-finished product, so that the protein and fat concentrations reach a certain ratio. This method can accurately control the fat content of the product and meet the requirements of the final product. At the same time, separating the fat before membrane processing can speed up the concentration process, reduce the difficulty of cleaning the MF membrane, and reduce the risk of membrane pore blockage.

[0009] Furthermore, the process of passing through the MF membrane concentrates the skim milk to a protein content of 5.6% to 9.8% by mass. The MF concentration can be carried out in various ways, such as single-pass membrane concentration, multiple-cycle concentration, or repeated addition of RO water for multiple concentrations. The concentration method depends on the equipment capacity and the final product index requirements.

[0010] Furthermore, the permeation through the NF membrane increases the mass percentage of lactose in the MF permeate to 10%–16%.

[0011] Furthermore, the RO membrane is used to increase the mass percentage of ash in the NF permeate to 1% to 2%.

[0012] This invention concentrates protein in skim milk through a microfiltration membrane (MF) to obtain different protein concentrations according to product requirements. Then, the MF permeate is permeated through an NF membrane to remove lactose, resulting in an NF concentrate with a high lactose concentration. While an appropriate amount of lactose in the product helps maintain a good taste, excessively high lactose concentrations can lead to cross-linking of casein micelles with lactose and browning. This invention concentrates lactose to facilitate adjustment of the lactose concentration in the final product based on the protein concentration. Correspondingly, the NF permeate contains mineral salts, which are recovered through an RO membrane concentration. The purpose of this is to control monovalent ions such as Na+, Cl-, and K+ in the product. Soluble salt ions are crucial for the stability of the milk system; for high-protein products, appropriately adjusting the salt ion concentration can improve the stability of casein micelles.

[0013] Furthermore, the fat separation process is as follows: fat separation is carried out at 55-63℃ and 6300-6700r / min until the mass percentage of fat in the skim milk is 0.06-1%.

[0014] Furthermore, the fat content in the cream is 30% to 40% by mass.

[0015] Furthermore, a sterilization process is included before the fat separation process; the sterilization process includes: double-effect centrifugation sterilization at 55-63℃ and 4800-5300r / min, with a processing efficiency of 20-25T / h.

[0016] Furthermore, after obtaining the concentrated milk semi-finished product, a sterilization process is also included; the sterilization process includes: direct steam sterilization at -135-154℃ for 0.2-8 seconds.

[0017] Furthermore, the sterilization process also includes a sterilization process in a holding tube. When the protein concentration is 5-6.5 g / 100 g, the holding tube parameters are set to 75-95 °C for 30-300 s, more preferably 75-85 °C for 180-300 s or 85-95 °C for 30-180 s; when the protein concentration is 6.5-8 g / 100 g, the protein holding tube is set to 72-75 °C for 180-300 s.

[0018] This invention further employs a protein retention tube and a sterilizer for sterilization. The parameters of the sterilizer should be set to meet the conditions required for enzyme inactivation while ensuring that the high-protein product is not overheated. Therefore, the parameters should be set based on the protein concentration to achieve a synergistic effect of enzyme inactivation and maintaining product stability. The final product can be stored at room temperature for more than 3 months.

[0019] The present invention further provides concentrated milk prepared by the aforementioned processing method.

[0020] The present invention has the following beneficial effects:

[0021] This technology provides a membrane concentration technology that combines microfiltration, reverse osmosis, and nanofiltration. By controlling the total protein content and the ratio of total protein to fat, lactose, and ash, the stability of dairy products can be effectively improved. By further synergistically employing direct steam sterilization technology and setting different sterilization and retention parameters according to the protein concentration, the shelf-life stability of the product can be better guaranteed. This is of great significance in the field of preparing concentrated dairy products. Detailed Implementation

[0022] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0023] Example 1

[0024] This embodiment provides a method for preparing high-protein milk, specifically including the following steps.

[0025] (1) After raw milk passes the inspection according to GB19302, it is stored in the milk warehouse at a temperature of 3℃ for 6 hours.

[0026] (2) The selected raw milk was sterilized by double-effect centrifugation technology. The sterilization temperature was 60℃, the rotation speed was 5000r / min, and the processing efficiency was 20-25T / h.

[0027] (3) The sterilized raw milk was centrifuged at a temperature of 60°C and a speed of 6500 r / min. The separated skim milk had a fat content of 0.06% (by mass) and the cream had a fat content of 37% (by mass).

[0028] (4) The skim milk is transported to the MF (microfiltration membrane equipment), the concentration ratio is adjusted according to the index, the concentration temperature is 6.5℃, so that the final protein content reaches 5.6-5.8% (mass percentage content), and the MF concentrate is stored at 6℃.

[0029] (5) Pass the 50% MF permeate through NF, adjust the concentration ratio, and concentrate until the lactose reaches 10-11% (mass percentage content). Store the NF concentrate at 6°C.

[0030] (6) Pass the NF permeate through the RO membrane, adjust the concentration ratio, and stop when the outflow reaches 42-44% of the total NF permeate. Store the RO concentrate at 6°C. At this time, the mineral content in the RO concentrate reaches about 1% (mass percentage).

[0031] (7) Fill the MF concentrate with light cream, NF concentrate and RO concentrate in sequence, so that the semi-finished product has a protein content of 5-5.2g / 100g, a protein:fat ratio of 3:1, a protein:lactose ratio of 1:1 and a protein to ash ratio of 3:0.5.

[0032] (8) The semi-finished product is fed into a steam immersion sterilizer at a sterilization temperature of 139℃ / 4-6s, and the holding tube parameters are 95℃ / 30s. Finally, it is aseptically filled.

[0033] (9) The finished product was stored at room temperature for 3 months. The following indicators were monitored during the 3 months: (The frequency was once a month, with three samples taken, and the results were presented in the form of average and variance). The indicator characterization and detection methods are as follows:

[0034] Table 1. Indicator Characterization and Detection Methods

[0035]

[0036] The results are as follows:

[0037] Table 2 shows the test results and sensory evaluation results for each indicator.

[0038]

[0039]

[0040] The above results indicate that a combination of appropriate protein concentration, sterilization parameters, and storage tube parameters can effectively control the content and activity of fibrinolytic enzymes and the degree of protein hydrolysis during the shelf life, thus maintaining the normal system and taste of the product.

[0041] Example 2

[0042] This embodiment provides a method for preparing high-protein milk, specifically including the following steps.

[0043] (1) After raw milk passes the inspection according to GB19302, it is stored in the milk warehouse at a temperature of 3℃ for 6 hours.

[0044] (2) The selected raw milk was sterilized by double-effect centrifugation technology. The sterilization temperature was 55℃, the rotation speed was 5300r / min, and the processing efficiency was 20-25T / h.

[0045] (3) The sterilized raw milk was centrifuged at 55℃ and 6700 r / min. The separated skim milk had a fat content of 0.09%, and the cream had a fat content of 34%.

[0046] (4) The skim milk is transported to the MF (microfiltration membrane equipment), the concentration ratio is adjusted according to the index, the concentration temperature is 6.5℃, so that the final protein concentration reaches 6.5-6.7% (mass percentage content), and the MF concentrate is stored at 6℃.

[0047] (5) Pass the 60% MF permeate through NF, adjust the concentration ratio, and concentrate until the lactose content reaches 10-12% (mass percentage). Store the NF concentrate at 6°C.

[0048] (6) Pass the NF permeate through the RO membrane, adjust the concentration ratio, and stop when the outflow reaches 50-52% of the total NF permeate. Store the RO concentrate at 6°C, at which point the mineral content of the RO concentrate reaches 1.5-1.6% (mass percentage).

[0049] (7) Fill the MF concentrate with light cream, NF concentrate and RO concentrate in sequence to make the semi-finished product protein 6.1-6.3g / 100g, protein:fat 3:0.6, protein:lactose 1:0.85 and protein to ash 3:0.6.

[0050] (8) The semi-finished product is fed into a steam immersion sterilizer at a sterilization temperature of 139℃ / 4s and a holding tube parameter of 90℃ / 60s. Finally, it is aseptically filled.

[0051] (9) The finished product is stored at room temperature for 3 months. The following indicators of the finished product are monitored during the 3 months: (tested once a month)

[0052] Table 3 shows the test results and sensory evaluation results for each indicator.

[0053]

[0054] Example 3

[0055] This embodiment provides a method for preparing high-protein milk, specifically including the following steps.

[0056] (1) After raw milk passes the inspection according to GB19302, it is stored in the milk warehouse at a temperature of 3℃ for 6 hours.

[0057] (2) The selected raw milk was sterilized by double-effect centrifugation technology. The sterilization temperature was 63℃, the rotation speed was 4800r / min, and the processing efficiency was 20-25T / h.

[0058] (3) The sterilized raw milk was centrifuged at 63℃ and 6300 r / min. The separated skim milk had a fat content of 0.08%, and the cream had a fat content of 34%.

[0059] (4) The skim milk is transported to the MF (microfiltration membrane equipment), the concentration ratio is adjusted according to the index, the concentration temperature is 6.5℃, so that the final protein concentration reaches 7.8-8% (mass percentage content), and the MF concentrate is stored at 6℃.

[0060] (5) Pass 70% MF permeate through NF, adjust the concentration ratio, and concentrate to 13-14% lactose (mass percentage content). Store the NF concentrate at 6°C.

[0061] (6) Pass the NF permeate through the RO membrane, adjust the concentration ratio, and stop when the outflow reaches 48-50% of the total NF permeate. Store the RO concentrate at 6°C, at which point the mineral content of the RO concentrate reaches 1.3-1.4% (mass percentage).

[0062] (7) Fill the MF concentrate with light cream, NF concentrate and RO concentrate in sequence, so that the protein content of the semi-finished product is 7.1-7.3g / 100g, the protein:fat ratio is 3:0.8, the protein:lactose ratio is 1:0.9 and the protein to ash ratio is 3:0.45.

[0063] (8) The semi-finished product is fed into a steam immersion sterilizer at a sterilization temperature of 154℃ / 0.25s and the tube parameters are maintained at 75℃ / 180. Finally, it is aseptically filled.

[0064] (9) The finished product is stored at room temperature for 3 months. The following indicators of the finished product are monitored during the 3 months (tested once a month):

[0065] Table 4 shows the test results and sensory evaluation results for each indicator.

[0066]

[0067] Example 4

[0068] This embodiment provides a method for preparing high-protein milk, specifically including the following steps.

[0069] (1) After raw milk passes the inspection according to GB19302, it is stored in the milk warehouse at a temperature of 3℃ for 6 hours.

[0070] (2) The selected raw milk was sterilized by double-effect centrifugation technology. The sterilization temperature was 63℃, the rotation speed was 4800r / min, and the processing efficiency was 20-25T / h.

[0071] (3) The sterilized raw milk was centrifuged at 63℃ and 6300 r / min. The separated skim milk had a fat content of 0.08%, and the cream had a fat content of 34%.

[0072] (4) The skim milk is transported to the MF (microfiltration membrane equipment), the concentration ratio is adjusted according to the index, the concentration temperature is 6.5℃, so that the final protein concentration reaches 9.5-9.8% (mass percentage content), and the MF concentrate is stored at 6℃.

[0073] (5) Pass 80% MF permeate through NF, adjust the concentration ratio, and concentrate to 14-16% lactose (mass percentage). Store the NF concentrate at 6°C.

[0074] (6) Pass the NF permeate through the RO membrane, adjust the concentration ratio, and stop when the outflow reaches 55-60% of the total NF permeate. Store the RO concentrate at 6°C, at which point the mineral content of the RO concentrate reaches 1.6-1.8% (mass percentage).

[0075] (7) Fill the MF concentrate with light cream, NF concentrate and RO concentrate in sequence, so that the protein content of the semi-finished product is 8.1-8.3g / 100g, the protein:fat ratio is 3:1.5, the protein:lactose ratio is 1:1.2 and the protein to ash ratio is 3:0.6.

[0076] (8) The semi-finished product is fed into a steam immersion sterilizer at a sterilization temperature of 154℃ / 0.25s and a holding tube parameter of 72℃ / 300s. Finally, it is aseptically filled.

[0077] (9) The finished product is stored at room temperature for 3 months. The following indicators of the finished product are monitored during the 3 months (tested once a month):

[0078] Table 5 shows the test results and sensory evaluation results for each indicator.

[0079]

[0080] Experimental Example 1

[0081] This experimental example provides other concentration methods used in the study for comparison, as follows:

[0082] Control group 1: The procedure is as follows (same as in Example 1, but with a different protein to lactose ratio).

[0083] (1) After raw milk passes the inspection according to GB19302, it is stored in the milk warehouse at a temperature of 3℃ for 6 hours.

[0084] (2) The selected raw milk was sterilized by double-effect centrifugation technology. The sterilization temperature was 60℃, the rotation speed was 5000r / min, and the processing efficiency was 20-25T / h.

[0085] (3) The sterilized raw milk was centrifuged at a temperature of 60°C and a speed of 6500 r / min. The fat content of the separated skim milk was 0.07% (mass percentage) and the fat content of the light cream was 35% (mass percentage).

[0086] (4) The skim milk is transported to the MF (microfiltration membrane equipment), the concentration ratio is adjusted according to the index, the concentration temperature is 6.5℃, so that the final protein concentration reaches 5.6-5.8%, and the MF concentrate is stored at 6℃.

[0087] (5) Pass the 50% MF permeate through NF, adjust the concentration ratio, and concentrate to 15% lactose (mass percentage content). Store the NF concentrate at 6°C.

[0088] (6) Pass the NF permeate through the RO membrane, adjust the concentration ratio, and stop when the outflow reaches 42-44% of the total NF permeate. Store the RO concentrate at 6°C, at which point the mineral content of the RO concentrate reaches 1% (mass percentage).

[0089] (7) Fill the MF concentrate with light cream, NF concentrate and RO concentrate in sequence, so that the semi-finished product has a protein content of 5-5.2g / 100g, a protein:fat ratio of 3:1, a protein:lactose ratio of 1:1.4 and a protein to ash ratio of 3:0.5.

[0090] (8) The semi-finished product is fed into a steam immersion sterilizer at a sterilization temperature of 139℃ / 4-6s, and the holding tube parameters are 95℃ / 30s. Finally, it is aseptically filled.

[0091] (9) The finished product is stored at room temperature for 3 months. The following indicators of the finished product are monitored during the 3 months (tested once a month):

[0092] Table 6 shows the test results and sensory evaluation results for each indicator.

[0093]

[0094] The results showed that when the lactose and protein content were outside the range defined in this invention, the casein micelle size of the product increased and the zeta potential increased, indicating that the micelles were unstable. Slight browning occurred after 2 months of storage and a small amount of precipitation occurred after 3 months, indicating that the product stability was affected when the ratio of protein to lactose was unreasonable.

[0095] Control group 2: The steps are as follows (same as in Example 2, only the holding tube parameters are changed):

[0096] (1) After raw milk passes the inspection according to GB19302, it is stored in the milk warehouse at a temperature of 3℃ for 6 hours.

[0097] (2) The selected raw milk was sterilized by double-effect centrifugation technology. The sterilization temperature was 55℃, the rotation speed was 5300r / min, and the processing efficiency was 20-25T / h.

[0098] (3) The sterilized raw milk was centrifuged at a temperature of 55°C and a speed of 6700 r / min. The separated skim milk had a fat content of 0.08% (by weight) and the cream had a fat content of 35% (by weight).

[0099] (4) The skim milk is transported to the MF (microfiltration membrane equipment), the concentration ratio is adjusted according to the index, the concentration temperature is 6.5℃, so that the final protein concentration reaches 6.5-6.7% (mass percentage content), and the MF concentrate is stored at 6℃.

[0100] (5) Pass the 60% MF permeate through NF, adjust the concentration ratio, and concentrate to 10-12% lactose (mass percentage content). Store the NF concentrate at 6°C.

[0101] (6) Pass the NF permeate through the RO membrane, adjust the concentration ratio, and stop when the outflow reaches 50-52% of the total NF permeate. Store the RO concentrate at 6°C, at which point the mineral content of the RO concentrate reaches 1.5-1.6% (mass percentage).

[0102] (7) Fill the MF concentrate with light cream, NF concentrate and RO concentrate in sequence to make the semi-finished product protein 6.1-6.3g / 100g, protein:fat 3:0.6, protein:lactose 1:0.85 and protein to ash 3:0.6.

[0103] (8) The semi-finished product is fed into a steam immersion sterilizer at a sterilization temperature of 139℃ / 4s and a holding tube parameter of 90℃ / 300s. Finally, it is aseptically filled.

[0104] (9) The finished product is stored at room temperature for 3 months. The following indicators of the finished product are monitored during the 3 months (tested once a month):

[0105] Table 7 shows the test results and sensory evaluation results for each indicator.

[0106]

[0107] The results showed that when the protein ratio and sterilization parameters did not match, the system could not work together to maintain stability, resulting in protein aggregation and precipitation in the product.

[0108] Control group 3: The steps are as follows (except for the sterilization parameters, they are exactly the same as in Example 3):

[0109] (1) After raw milk passes the inspection according to GB19302, it is stored in the milk warehouse at a temperature of 3℃ for 6 hours.

[0110] (2) The selected raw milk was sterilized by double-effect centrifugation technology. The sterilization temperature was 63℃, the rotation speed was 4800r / min, and the processing efficiency was 20-25T / h.

[0111] (3) The sterilized raw milk was centrifuged at a temperature of 63°C and a speed of 6300 r / min. The separated skim milk had a fat content of 0.08% (by mass) and the cream had a fat content of 34% (by mass).

[0112] (4) The skim milk is transported to the MF (microfiltration membrane equipment), the concentration ratio is adjusted according to the index, the concentration temperature is 6.5℃, so that the final protein concentration reaches 8.5-8.7% (mass percentage content), and the MF concentrate is stored at 6℃.

[0113] (5) Pass 70% MF permeate through NF, adjust the concentration ratio, and concentrate to 13-14% lactose (mass percentage content). Store the NF concentrate at 6°C.

[0114] (6) Pass the NF permeate through the RO membrane, adjust the concentration ratio, and stop when the outflow reaches 48-50% of the total NF permeate. Store the RO concentrate at 6°C, at which point the mineral content of the RO concentrate reaches 1.3-1.4% (mass percentage).

[0115] (7) Fill the MF concentrate with light cream, NF concentrate and RO concentrate in sequence, so that the protein content of the semi-finished product is 8.1-8.2g / 100g, the protein:fat ratio is 3:0.8, the protein:lactose ratio is 1:0.9 and the protein to ash ratio is 3:0.45.

[0116] (8) The semi-finished product is fed into a steam immersion sterilizer at a sterilization temperature of 154℃ / 0.125s and a holding tube parameter of 75℃ / 180s. Finally, it is aseptically filled.

[0117] (9) The finished product is stored at room temperature for 3 months. The following indicators of the finished product are monitored during the 3 months (tested once a month):

[0118] Table 8 shows the test results and sensory evaluation results for each indicator.

[0119]

[0120] The results showed that when the protein concentration and sterilization parameters were mismatched, the system tended to be unstable and a large amount of gel appeared after prolonged standing.

[0121] Control group 4: The steps are as follows (except for the ratio of protein to small molecules, everything else is the same as in Example 4):

[0122] (1) After raw milk passes the inspection according to GB19302, it is stored in the milk warehouse at a temperature of 3℃ for 6 hours.

[0123] (2) The selected raw milk was sterilized by double-effect centrifugation technology. The sterilization temperature was 63℃, the rotation speed was 4800r / min, and the processing efficiency was 20-25T / h.

[0124] (3) The sterilized raw milk was centrifuged at a temperature of 63℃ and a speed of 6300 r / min. The fat content of the skim milk was 0.08% (by weight), and the fat content of the cream was 34% (by weight).

[0125] (4) The skim milk is transported to the MF (microfiltration membrane equipment), the concentration ratio is adjusted according to the index, the concentration temperature is 6.5℃, so that the final protein concentration reaches 9.5-9.8% (mass percentage content), and the MF concentrate is stored at 6℃.

[0126] (5) Pass 80% MF permeate through NF, adjust the concentration ratio, and concentrate to 14-16% lactose (mass percentage). Store the NF concentrate at 6°C.

[0127] (6) Pass the NF permeate through the RO membrane, adjust the concentration ratio, and stop when the outflow reaches 70-75% of the total NF permeate. Store the RO concentrate at 6°C, at which point the mineral content of the RO concentrate reaches 1.9-2.1% (mass percentage).

[0128] (7) Fill the MF concentrate with light cream, NF concentrate and RO concentrate in sequence, so that the protein content of the semi-finished product is 8.1-8.3g / 100g, the protein:fat ratio is 3:1.5, the protein:lactose ratio is 1:1.2 and the protein to ash ratio is 3:0.8.

[0129] (8) The semi-finished product is fed into a steam immersion sterilizer at a sterilization temperature of 154℃ / 0.25s and a holding tube parameter of 72℃ / 300s. Finally, it is aseptically filled.

[0130] (9) The finished product is stored at room temperature for 3 months. The following indicators of the finished product are monitored during the 3 months (tested once a month):

[0131] Table 9 shows the test results and sensory evaluation results for each indicator.

[0132]

[0133]

[0134] The results showed that when the protein to ash ratio was outside the range defined in this invention, casein micelles aggregated, the particle size increased, and significant precipitation occurred.

[0135] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for processing concentrated milk, characterized in that, include: The raw milk undergoes a fat separation process to obtain skim milk and light cream; The skim milk is permeated through an MF membrane to obtain MF permeate and MF concentrate. The MF permeate is permeated through an NF membrane to obtain NF concentrate and NF permeate. The NF permeate is permeated through an RO membrane to obtain RO concentrate and RO water. Multiple components of the light cream, MF concentrate, NF concentrate, RO concentrate, and RO water are recombined to obtain a concentrated milk semi-finished product, such that the mass ratio of protein, fat, lactose, and ash in the concentrated milk semi-finished product is 1:(0.02-2):(0.32-1.3):(0.08-0.25). The MF membrane is used to concentrate the skim milk until the protein content in the MF concentrate is 5.6% to 9.8% by mass. After obtaining the concentrated milk semi-finished product, a sterilization process is also included; The sterilization process includes: direct steam sterilization at 139~154℃ for 0.2-8 seconds; When the protein concentration is 5-6.5 g / 100g, the holding tube parameters are set to 75-95℃ for 30-300s. When the protein concentration is 6.5-8 g / 100g, excluding a protein concentration of 6.5 g / 100g, the protein holding tube should be set to 72-75℃ for 180-300s.

2. The processing method according to claim 1, characterized in that, The permeable NF membrane is used to increase the mass percentage of lactose in the MF permeate to 10%~16%.

3. The processing method according to claim 1, characterized in that, The RO membrane is used to increase the mass percentage of ash in the NF permeate to 1%~2%.

4. The processing method according to claim 1, characterized in that, The fat separation process is as follows: fat separation is carried out at 55-63℃ and 6300-6700r / min until the mass percentage of fat in the skim milk is 0.06~1%.

5. The processing method according to claim 4, characterized in that, The fat content of the light cream is 30% to 40% by mass.

6. The processing method according to claim 1, characterized in that, The process includes a sterilization process before the fat separation process; the sterilization process includes: double-effect centrifugation sterilization at 55-63℃ and 4800-5300r / min, with a processing efficiency of 20-25T / h.

7. The processing method according to claim 1, characterized in that, When the protein concentration is 5-6.5 g / 100g, the holding tube parameters are set to 75-85℃ for 180-300s or 85-95℃ for 30-180s.

8. Concentrated milk prepared by the processing method according to any one of claims 1-7.

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