A method of extending the shelf life of fresh milk

Abstract

The application relates to a method for prolonging the shelf life of fresh milk and belongs to the technical field of food processing. The raw milk is subjected to sterilization centrifugal treatment, and then dynamic ultrahigh pressure jet collision is adopted to convert the mechanical energy of the raw milk into kinetic energy, form a high-speed jet, and simultaneously heat the raw milk, so that the heated raw milk is subjected to heat treatment for sterilization. The sterilization effect of the raw milk reaches 99.99% by adopting the combined sterilization mode of multiple steps. The method is simple in operation, can be industrialized, has low required pressure, can completely kill microorganisms, retains the nutritional components of the raw milk, has good taste, and significantly prolongs the shelf life of the fresh milk.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of food processing, and particularly relates to a method for prolonging the shelf life of fresh milk. BACKGROUND

[0002] The standard process flow of pasteurized milk is as follows: after raw milk is cooled, low-temperature long-time holding sterilization (63 DEG C, holding for 30 min) or high-temperature short-time holding sterilization (72-85 DEG C, holding for at least 15 s) is adopted, and then the milk is cooled to 2-6 DEG C. The sterilization process of the pasteurized milk on the market at present is as follows: ① 72 DEG C holding for 15 s, shelf life of 3-7 days; ② centrifugal sterilization, microfiltration membrane filtration combined with 72 DEG C holding for 15 s, shelf life of 7-10 days; ③ steam instantaneous direct heating sterilization, shelf life of 15-20 days. The milk products treated by the above processes all need to be stored at low temperature. The first two can guarantee the content of active ingredients in the product, but the shelf life is short, and the third can effectively guarantee the shelf life of the product, but the loss is high.

[0003] The ultra-high pressure sterilization technology refers to the use of pressure (usually 100-1000 MPa) to destroy the cell membrane of microorganisms, inhibit biochemical reactions, promote the denaturation of intracellular DNA and the like to achieve the requirement of sterilization. Ultra-high pressure can cause changes in the morphological structure, genetic mechanism, biochemical reaction and cell membrane of microorganisms, thereby further affecting the physiological function of microorganisms, and even destroying or causing irreversible changes to the original function.

[0004] The ultra-high pressure sterilization technology can be divided into static ultra-high pressure and dynamic ultra-high pressure. The static ultra-high pressure refers to placing the sterilization object in a high-pressure container, using water or other fluid as the pressurizing medium, and maintaining pressure at a certain pressure for a certain time, so that the protein maintaining the life activities of microorganisms is denatured and inactivated, thereby achieving the purpose of sterilization. The pressure holding time has a significant effect on the static ultra-high pressure sterilization. Within a certain range, the higher the pressure, the better the sterilization effect. Generally, a pressure of 300 MPa or above can kill bacteria, molds, yeasts and other common microorganism groups in food. The static ultra-high pressure sterilization is a very complex process. For example, some spore-bearing bacteria require a very high pressure to achieve the sterilization effect, the investment in high-pressure equipment is relatively large, the pressure is very high and difficult to control and master, and it is difficult to realize industrialization.

[0005] Dynamic ultra-high pressure refers to pressurizing the object to be sterilized to a specified pressure point, and then releasing the pressure instantaneously or reducing the pressure by gradient, so that the water or other medium permeated into the microbial cells is vaporized and explodes, and the spatial structure of the protein is destroyed under the huge swelling pressure, so as to achieve the purpose of sterilization. Ultra-high pressure jet is a dynamic ultra-high pressure technology in a completely continuous state. The basic working principle is to filter ordinary water or other liquid to be treated, and then convert the mechanical energy of the power source (motor) into pressure energy of the liquid through a specific energy conversion device (high-pressure pump or booster), and the liquid with huge pressure energy is sprayed out through a small nozzle, so that the pressure energy is converted into kinetic energy, thereby forming a high-speed jet. From ordinary liquid to high-speed jet is mainly the conversion process of jet energy, and the booster is the key to the formation of liquid energy accumulation, and the nozzle is the key to the formation of jet.

[0006] The invention patent with publication number CN101690515 "Low-temperature ultra-high pressure sterilization method for liquid milk" increases the pressure of cold-chain liquid milk raw milk from normal pressure to 400 MPa through a booster, and then the liquid milk enters an energy accumulator to eliminate high-pressure pulsation, and then the liquid milk is sprayed out through a nozzle, and the supersonic jet collides intensively to sterilize and homogenize, and the temperature of the liquid milk can reach 70℃; finally, the temperature of the sterilized liquid milk is reduced for aseptic packaging. The product obtained by the invention can meet the national standard of pasteurized milk, can help to preserve the nutritional components of cow milk, and can be produced continuously. However, the defect is that the temperature of the sample after ultra-high pressure jet is relatively low, and there are many microbial colonies, which cannot guarantee the inactivation of alkaline phosphatase and lactoperoxidase.

[0007] The thermal stability of alkaline phosphatase is slightly higher than that of most pathogenic microorganisms in milk, such as Mycobacterium tuberculosis and Listeria. When the heat treatment intensity of cow milk is sufficient to make the alkaline phosphatase activity test result negative, it means that other pathogenic microorganisms are also completely inactivated, so the activity index of alkaline phosphatase is a very important index in the dairy processing industry, which indicates whether the pasteurization of dairy products is successful or not.

[0008] Lactoperoxidase is also a representative heat-sensitive enzyme in cow milk, and its thermal stability is higher than that of other endogenous enzymes in milk. Studies have shown that under the heat processing conditions of 68℃ / 15s, lactoperoxidase begins to denature in the dairy processing process. If the heat processing conditions are 74℃ / 15s, lactoperoxidase will lose 60-70% of its activity. The complete denaturation conditions are 78℃ / 15s or 74℃ / 60s. The activity of lactoperoxidase can indicate whether there is excessive heat processing, heat treatment, etc. in the pasteurization process to cause more loss of nutrients in cow milk, and it is also a very important index in the dairy processing industry.

[0009] The conventional raw cow milk sterilization method can only sterilize, and after sterilization, the alkaline phosphatase in the bacteria still has part of the activity and has not been completely inactivated. The inventor found in long-term production practice that the high temperature and high pressure process can activate the activity of the enzyme in the bacteria, so that the raw cow milk sterilization method in the prior art cannot realize the simultaneous and high-efficiency inactivation of the bacteria and the enzyme (such as alkaline phosphatase) in the bacteria. The existence of the alkaline phosphatase in the bacteria can react with the protein, fat and other nutrients in the raw milk, causing the raw milk to spoil and the taste to decrease. To solve this problem, the general technical means is sterilization + enzyme inactivation. The operation of sterilization + the operation of enzyme inactivation can theoretically solve the above-mentioned problems, but in actual operation, it is found that since enzyme inactivation requires higher temperature or pressure, if higher temperature or pressure is selected, the enzyme can indeed be inactivated, but a new problem arises: other milk enzymes such as milk peroxidase in the raw milk are also inactivated, since high temperature and high pressure can damage the protein and fat structure of raw milk, causing protein denaturation and fat denaturation, thereby making the taste of raw milk worse, and high temperature and high pressure are necessarily accompanied by high energy consumption, which is not conducive to the development requirements of enterprise energy saving and environmental protection. Therefore, it is necessary to change the conventional idea and seek a new sterilization and enzyme inactivation method which can solve the above-mentioned main contradictions.

[0010] The invention patent with the publication number 111528279 discloses a sterilization method for liquid milk, which adds bacteriostatic agent nisin to perform bacteriostatic treatment and homogenization on the liquid milk, and then performs ultrahigh pressure water jet sterilization treatment. The product obtained by the invention patent has a longer shelf life, and the flavor, color and taste of the milk are better. However, the technical defects of this technology are that the operation steps are complex, the addition amount of the bacteriostatic agent nisin needs to be controlled, the collection container after high-pressure sterilization treatment has high technical requirements and high cost.

[0011] The sterilization methods for raw milk in the prior art have advantages and disadvantages in production process, nutritional value and shelf life, and how to obtain fresh milk with high nutritional ingredients and long shelf life is a problem to be solved in the field. SUMMARY

[0012] The purpose of the present application is to overcome the various disadvantages of the existing heat sterilization technology, to solve the problems of the short shelf life of the pasteurized milk with low-temperature sterilization, the high requirement for the storage conditions during the storage period, the easy spoilage of the product during the shelf life, the great loss of nutritional ingredients during high-temperature long-time sterilization, the high pressure and high energy consumption of thermal sterilization and static ultrahigh pressure sterilization, and the high cost of the machine, and to provide a sterilization method for low-temperature fresh milk which is suitable for industrial production, has less loss of nutritional ingredients and has a significantly prolonged shelf life, i.e. a method for prolonging the shelf life of fresh milk.

[0013] In the long-term research on the raw milk sterilization process, it is found that the static ultra-high pressure treatment of liquid milk has the following disadvantages: the microorganism killing effect is limited, although the low and high pressure alternation and the cyclic pressurization can achieve partial killing of spores, but cannot achieve the total number of colonies <1 CFU / ml; the enzyme cannot be completely inactivated, when the pressure is higher than 400 MPa, the protein starts to denature, and the taste of milk is poor; and the investment of the ultra-high pressure equipment is relatively large, the sterilization requires high pressure, the high pressure resistance of the equipment is required, the purchase and maintenance cost of the equipment is high, and the static ultra-high pressure technology requires a certain pressure bearing time in the fixed container during the sterilization of the milk, and the industrialization is difficult.

[0014] The application considers adopting the dynamic ultra-high pressure technology combined with other sterilization technologies, and provides a method for prolonging the shelf life of fresh milk, which comprises four steps,

[0015] The first step is to perform sterilization centrifugal treatment on the raw milk to remove part of the spores and bacteria;

[0016] The second step is to perform high-pressure pump energy storage on the raw milk to remove high-pressure pulses;

[0017] The third step is to use dynamic ultra-high pressure jet collision on the raw milk to convert the mechanical energy of the raw milk into kinetic energy to form a high-speed jet, and the collision releases energy while heating;

[0018] The fourth step is to perform low-temperature heat treatment on the heated raw milk to complete sterilization and enzyme inactivation.

[0019] In the first step of the above method, the water pressure of the sterilization centrifugal is 2-5 bar, the inlet pressure is 2-6 bar, the outlet pressure is 2-6 bar, the compressed air pressure is 6-8 bar, the separation temperature is 50-55 DEG C, the water pressure is ≤2.5 bar when the residue is discharged, and the separation speed is 4000-7000 rpm.

[0020] In the second step of the above method, before the dynamic ultra-high pressure jet collision method is used, the raw milk cooled to 2-6 DEG C is subjected to high-pressure pump energy storage to remove high-pressure pulses, the high-pressure energy storage pump uses 38.5 kW / 380V alternating current, and the pressurization time is ≤30 s. It is found that when the pressurization time is not greater than 30 s, the pressure can be stabilized, thereby effectively ensuring the improvement of the sterilization efficiency.

[0021] In the second step of the above method, the total pressure of the dynamic ultra-high pressure jet is 50-350 MPa, preferably 150-250 MPa, and more preferably 200 MPa; the secondary pressure of the dynamic ultra-high pressure jet is 5-10 MPa, preferably 7.5-10 MPa, and more preferably 10 MPa; and the secondary pressure / total pressure of the dynamic ultra-high pressure jet is 10-20%.

[0022] The third step of the above method provided by the application is that the collision nozzle of the dynamic ultra-high pressure jet collision method is a coaxial equal (0°) collision nozzle, the nozzle aperture is the same, the aperture range is 0.1-0.4 mm, the jet hole distance is 2-10 mm, and the pressure fluctuation during the collision process is kept ± 5 MPa. In the third step, the temperature of the raw milk after energy release by collision is increased to 28-80℃.

[0023] The fourth step of the above method provided by the application is that the temperature of the raw milk is increased by 10-30℃ before heat treatment and sterilization.

[0024] The low-temperature heat treatment refers to a sterilization temperature of 72-85℃, a sterilization time of 12-15 s, and a cooling temperature of 2-6℃.

[0025] The increase of the sample temperature by 10-30℃ in the fourth step of the application is a necessary process, and the sample temperature is optimized according to the total pressure range of the ultra-high pressure jet.

[0026] The environmental conditions of the above method provided by the application are that the environmental temperature of the dynamic ultra-high pressure jet collision is 20-26℃, the environmental humidity is 30-70%, and the total number of colonies of air settling microorganisms is ≤ 50 CFU / dish.

[0027] The equipment conditions of the above method provided by the application are that the dynamic ultra-high pressure equipment is resistant to a high temperature of ≤ 150℃ and a pressure of ≤ 400 MPa.

[0028] Other conditions of the above method provided by the application are that the total hardness (in terms of CaCO3) of the ice water for cyclic cooling is ≤ 450 mg / L.

[0029] The milk product prepared by the above method belongs to the protection scope of the application.

[0030] Specifically, the application provides a preparation method for prolonging the shelf life of fresh milk, comprising the following steps:

[0031] (1) Net milk: centrifugal net milk of raw milk; the net milk temperature is 2-6℃;

[0032] (2) Sterilization centrifugation: preheat the raw milk after net milk and perform sterilization centrifugation, and cool after separation; the water pressure of the sterilization centrifugation is 2-5 bar, the inlet pressure is 2-6 bar, the outlet pressure is 2-6 bar, the compressed air pressure is 6-8 bar, the separation temperature is 50-55℃, the water pressure during slag discharge is ≤ 2.5 bar, the separation speed is 4000-7000 rpm, and the cooling temperature is reduced to 2-6℃.

[0033] (3) high-pressure pump energy storage: the cooled raw milk is subjected to high-pressure pump energy storage, and high-pressure pulses are removed; the high-pressure pump energy storage pressure is 50-350, and the secondary pressure is 5-10 MPa; the high-pressure pump energy storage uses 38.5 kW / 380V alternating current, and the pressurization time is ≤30 s.

[0034] (4) collision heating: the raw milk subjected to high-pressure pump energy storage is subjected to collision energy release while being heated; the collision energy release nozzle uses coaxial equal (0°) collision nozzles, and the symmetrical nozzles use the same aperture, the aperture range is 0.1-0.4 mm, and the jet hole distance is 2-10 mm; the pressure fluctuation during the collision process is kept ±5 MPa. The heating temperature after the collision is 28-80℃.

[0035] (5) sterilization: before heat treatment for sterilization, the raw milk sample temperature is increased by 10-30℃. The raw milk subjected to heating is subjected to low-temperature heat treatment; the low-temperature heat treatment temperature is 72-85℃, and the sterilization time is 12-15 s.

[0036] (6) cooling: the raw milk subjected to sterilization is cooled and cooled;

[0037] (7) filling: the raw milk subjected to cooling is filled.

[0038] In step (3), preferably, the high-pressure pump energy storage pressure is 150-250, and the secondary pressure is 7.5-10 MPa.

[0039] In step (3), more preferably, the high-pressure pump energy storage pressure is 200 / 10 MPa (referring to the primary pressure 200 MPa and the secondary pressure 10 MPa)

[0040] In step (6), the cooling temperature is 2-6℃.

[0041] In step (7), the filling uses super-clean filling or sterile filling.

[0042] The raw milk is raw cow milk, skimmed milk or formula milk.

[0043] When the single super-high-pressure jet method is used for sterilization, the alkaline phosphatase detection is positive, which indicates that the process alone cannot completely kill the pathogenic bacteria in the milk; after the combined process of the application is used, the alkaline phosphatase detection is negative, and the milk peroxidase detection is positive, which indicates that the combined process can completely kill the pathogenic bacteria in the milk while effectively retaining the nutritional ingredients of the raw milk, and can significantly prolong the shelf life of the raw milk.

[0044] The excellent effect of the application is that:

[0045] 1. This invention differs from traditional heat treatment sterilization processes. It employs a process combining ultra-high pressure jet collision with low-temperature heat treatment, which ensures sterilization and the elimination of alkaline phosphatase within the bacteria while also ensuring a low inactivation rate of the inherent enzymes in the dairy product.

[0046] In preliminary research, the applicant discovered that the taste of raw milk deteriorates when the ultra-high pressure jet pressure reaches above 250 MPa. Therefore, this invention strictly controls the pressure below 250 MPa. This ensures both sufficient sterilization rate and product taste, while also preserving over 80% of the lactoperoxidase activity. This pressure is relatively low compared to static ultra-high pressure (>400 MPa), and the pressure increase and decrease are instantaneous, without a pressure holding process. This results in lower denaturation rates of proteins and fats, and higher retention rates of active proteins.

[0047] In the fourth step of this invention, the raw milk after heating is subjected to low-temperature heat treatment, i.e., the operation of the aforementioned step (5), in order not to damage the taste of the milk and to better inactivate the enzyme, this invention does not use high temperature, but uses a relatively mild enzyme inactivation temperature, which not only achieves excellent sterilization and enzyme inactivation effect, but also ensures that the unique flavor of the dairy product is not lost.

[0048] 2. Under the condition that the terminal cold chain conditions are met, the shelf life of fresh milk produced by the method of the present invention can be extended to more than 20 days compared to the 3-7 days of high temperature short-time pasteurization.

[0049] 3. In this invention, the raw milk is heated at 50°C for less than 15 seconds throughout the entire production cycle (all steps), which can minimize the heat load, ensure that the produced fresh milk has the flavor and nutrition of pasteurized milk, and at the same time eliminate the unpleasant flavors of pasteurized milk itself, such as fishy smell and silage smell, while maintaining a high content of nutrients.

[0050] 4. In the method of the present invention, the ultra-high pressure jet sterilization requires a low pressure, is easy to operate, can be continuously produced, and is easy to connect with the existing pretreatment system, sterilization system, filling system and packaging system in the factory, so as to realize industrial production quickly and efficiently. Detailed Implementation

[0051] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0052] The alkaline phosphatase detection method adopts NY / T 3799 method, and the lactoperoxidase detection method refers to the industry standard T / TDSTIA 001-2021 “Determination of Lactoperoxidase in Milk and Milk Products”. In this embodiment, the standards for evaluating the freshness of milk and the total number of colonies are based on GB 19645-2010 Food Safety National Standard Pasteurized Milk Requirements. The fat detection method refers to the “GB 5009.6 Third French Standard Detailed Fat Detection Operation Instruction”, the protein detection method refers to the “Kjeldahl Nitrogen Detection Protein Operation Instruction”, the non-fat milk solid detection method refers to the “GB 5413.39-2010 National Standard Detailed Dry Matter (Total Solid), Non-fat Milk Solid Operation Instruction”, and the acidity detection method refers to the “GB 5009.239 First French Standard Detailed Acidity Detection Operation Instruction” and “GB 5009.239 Third French Standard Detailed Acidity Detection Operation Instruction”.

[0053] If the specific technology or condition is not specified in the examples, it is performed according to the technology or condition described in the literature in the field, or according to the product manual. If the reagent or instrument used is not specified by the manufacturer, it is a conventional product that can be purchased through a regular channel.

[0054] Example 1

[0055] The present embodiment provides a method for prolonging the shelf life of fresh milk, which also maintains the effective nutritional ingredients and flavor of raw milk in fresh milk.

[0056] (1) Net milk: centrifugal net milk is performed on raw cow milk, and the cooling temperature is 6℃;

[0057] (2) Sterilization centrifugation: the raw milk after net milk is preheated and subjected to sterilization centrifugation, the water pressure of the sterilization centrifugation is 5 bar, the inlet pressure is 6 bar, the outlet pressure is 6 bar, the compressed air pressure is 8 bar, the separation temperature is 50℃, the water pressure during slagging is 2.5 bar, and the separation speed is 4200 rpm, and the cooling temperature is reduced to 6℃;

[0058] (3) High-pressure pump energy storage: high-pressure pump energy storage is performed on the cooled raw milk, the pressure parameters are first-stage pressure 150 MPa and second-stage pressure 10 MPa, and high-pressure pulse is removed; the high-pressure energy storage pump uses 38.5kW / 380V alternating current, and the pressurization time is ≤30s;

[0059] (4) Opposite collision heating: opposite collision energy release is performed on the raw milk after high-pressure pump energy storage, the pore size range is 0.3mm, the jet hole distance is 3mm, and the pressure fluctuation during the opposite collision process is kept ±5MPa;

[0060] (5) Sterilization: low-temperature heat treatment is performed on the raw milk after heating, the sterilization temperature is 75℃, and the sterilization time is 12s;

[0061] (6) Cooling: The cooling conditions are conventional in the art, and the homogenized raw milk is cooled to 6°C;

[0062] (7) Filling: The cooled raw milk is filled, and the filling is performed by super-clean filling or sterile filling, and the final product temperature is reduced to 6°C.

[0063] Example 2

[0064] The present embodiment provides a method for prolonging the shelf life of fresh milk, which also maintains the effective nutritional ingredients and flavor of raw milk in fresh milk.

[0065] (1) Clarification: The raw milk is centrifugally clarified, and the cooling temperature is 6°C;

[0066] (2) Bacterial removal centrifugation: The clarified raw milk is preheated and subjected to bacterial removal centrifugation, the water pressure of which is 5 bar, the inlet pressure is 6 bar, the outlet pressure is 6 bar, the compressed air pressure is 8 bar, the separation temperature is 50°C, the water pressure during slagging is 2.5 bar, the separation speed is 4200 rpm, and the cooling temperature is reduced to 6°C;

[0067] (3) High-pressure pump energy storage: The cooled raw milk is subjected to high-pressure pump energy storage, and the pressure parameters are first-stage pressure 150 MPa and second-stage pressure 10 MPa, and high-pressure pulses are removed; the high-pressure energy storage pump uses 38.5 kW / 380V alternating current, and the pressurization time is ≤30s;

[0068] (4) Opposed jet heating: The raw milk after high-pressure pump energy storage is subjected to opposed jet energy release, the pore size range is 0.3 mm, the jet hole distance is 3 mm, and the pressure fluctuation during the opposed jet process is maintained at ±5 MPa;

[0069] (5) Sterilization: The heated raw milk is subjected to low-temperature heat treatment, and the sterilization temperature is 75°C and the sterilization time is 15s;

[0070] (6) Cooling: The cooling conditions are conventional in the art, and the homogenized raw milk is cooled to 6°C;

[0071] (7) Filling: The cooled raw milk is filled, and the filling is performed by super-clean filling or sterile filling, and the final product temperature is reduced to 6°C.

[0072] Example 3

[0073] The present embodiment provides a method for prolonging the shelf life of fresh milk, which also maintains the effective nutritional ingredients and flavor of raw milk in fresh milk.

[0074] (1) Clarification: The raw milk is centrifugally clarified, and the cooling temperature is 6°C;

[0075] (2) Bacterial removal centrifugation: the raw milk after net milk is preheated and subjected to bacterial removal centrifugation, the water pressure of the bacterial removal centrifugation is 5 bar, the inlet pressure is 6 bar, the outlet pressure is 6 bar, the compressed air pressure is 8 bar, the separation temperature is 50°C, the water pressure when discharging slag is 2.5 bar, the separation speed is 4200 rpm, and the cooling temperature is reduced to 6°C;

[0076] (3) High-pressure pump energy storage: the cooled raw milk is subjected to high-pressure pump energy storage, the pressure parameters are first-stage pressure 200 MPa and second-stage pressure 10 MPa, and high-pressure pulses are removed; the high-pressure energy storage pump uses 38.5 kW / 380V alternating current, and the pressurization time is ≤30 s;

[0077] (4) Opposed jet heating: the raw milk after high-pressure pump energy storage is subjected to opposed jet energy release, the pore size range is 0.3 mm, the jet hole distance is 3 mm, and the pressure fluctuation during the opposed jet process is kept ±5 MPa;

[0078] (5) Sterilization: the raw milk after heating is subjected to low-temperature heat treatment, the sterilization temperature is 75°C, and the sterilization time is 15 s;

[0079] (6) Cooling: the cooling conditions are conventional in the art, and the homogenized raw milk is cooled to 6°C;

[0080] (7) Filling: the cooled raw milk is subjected to filling, the filling adopts super-clean filling or aseptic filling, and the final product temperature is reduced to 6°C.

[0081] Example 4

[0082] The embodiment provides a method for prolonging the shelf life of fresh milk, which also enables the fresh milk to maintain effective nutrient components and flavors of raw milk.

[0083] (1) Net milk: raw cow milk is subjected to centrifugal net milk, and the cooling temperature is 6°C;

[0084] (2) Bacterial removal centrifugation: the raw milk after net milk is preheated and subjected to bacterial removal centrifugation, the water pressure of the bacterial removal centrifugation is 5 bar, the inlet pressure is 6 bar, the outlet pressure is 6 bar, the compressed air pressure is 8 bar, the separation temperature is 50°C, the water pressure when discharging slag is 2.5 bar, the separation speed is 4200 rpm, and the cooling temperature is reduced to 6°C;

[0085] (3) High-pressure pump energy storage: the cooled raw milk is subjected to high-pressure pump energy storage, the pressure parameters are first-stage pressure 200 MPa and second-stage pressure 10 MPa, and high-pressure pulses are removed; the high-pressure energy storage pump uses 38.5 kW / 380V alternating current, and the pressurization time is ≤30 s;

[0086] (4) Collision warming: the raw milk after energy storage of high pressure pump is collided to release energy, the aperture range is 0.3mm, the jet hole distance is 3mm, and the pressure fluctuation during the collision process is kept ±5MPa;

[0087] (5) Sterilization: the raw milk after warming is subjected to low-temperature heat treatment, the sterilization temperature is 85℃, and the sterilization time is 15s;

[0088] (6) Cooling: the cooling condition is conventional in the art, and the raw milk after homogenization is cooled to 6℃;

[0089] (7) Filling: the raw milk after cooling is filled, the filling adopts super-clean filling or aseptic filling, and the final product temperature is reduced to 6℃.

[0090] Experimental Example 1

[0091] The shelf life analysis of the products prepared in each example is shown in Table 1.

[0092] Table 1 Shelf life experiment of fresh milk after filling under cold storage condition (6℃)

[0093]

[0094]

[0095] Experimental Example 2

[0096] The microbial detection data of each example is shown in Table 2, and the nutritional ingredient data is shown in Table 3.

[0097] Table 2 Microbial data of ultra-high pressure jet sterilization process

[0098]

[0099] Table 3 Nutritional ingredient data of ultra-high pressure jet sterilization process

[0100]

[0101]

[0102] Comparative Example 1

[0103] On the basis of Example 4, the collision angle of step (4) is adjusted, and gradient tests are carried out at 10° and 20°: the raw milk after warming is subjected to low-temperature heat treatment, the sterilization temperature is 85℃, and the sterilization time is 15s; the raw material and the remaining steps are the same as those of Example 4.

[0104] It is detected that the total number of finished product colonies increases with the increase of the collision angle. The shelf life of the milk sample obtained under the treatment condition of the comparative example 1 is less than 7 days under the condition of low-temperature refrigeration (6℃), the acidity exceeds the national standard requirement (>18°T) during the shelf life, the sensory evaluation of the sample is unqualified (the milk flavor is weak, and there is an acid smell), the color is white, and more coagulation is generated. This shows that the angle of the collision nozzle for releasing energy in the dynamic ultra-high pressure jet collision process of the application is very critical. The sterilization effect of the coaxial equal amount (0°) collision nozzle is better than that of the nozzle angle of 10° and 20°, and the sterilization is more thorough.

[0105] Comparative example 2

[0106] On the basis of example 4, the nozzle aperture is adjusted in step (4), and 0.6 mm and 0.9 mm are selected for gradient test: the raw milk after temperature rise is subjected to low-temperature heat treatment, the sterilization temperature is 85℃, and the sterilization time is 15 s; the raw material and the remaining steps are the same as those in example 4.

[0107] It is detected that the total number of finished product colonies increases with the increase of the nozzle aperture. The shelf life of the milk sample obtained under the treatment condition of the comparative example 2 is less than 7 days under the condition of low-temperature refrigeration (4℃), the acidity exceeds the national standard requirement (>18°T) during the shelf life, the sensory evaluation of the sample is unqualified (the milk flavor is weak, and there is a slight acid smell), the color is white, and slight coagulation is generated. This shows that the size of the nozzle aperture is one of the key factors in the dynamic ultra-high pressure jet collision process of the application. The sterilization effect of the nozzle aperture of 0.3 mm is the best.

[0108] Comparative example 3

[0109] On the basis of example 4, the jet hole distance is adjusted in step (4), and 13 mm and 23 mm are selected for gradient test: the raw milk after temperature rise is subjected to low-temperature heat treatment, the sterilization temperature is 85℃, and the sterilization time is 15 s; the raw material and the remaining steps are the same as those in example 4.

[0110] It is detected that the total number of finished product colonies increases with the increase of the jet hole distance. The shelf life of the milk sample obtained under the treatment condition of the comparative example 3 is less than 7 days under the condition of low-temperature refrigeration (6℃), the acidity exceeds the national standard requirement (>18°T) during the shelf life, the sensory evaluation of the sample is unqualified (the milk flavor is weak, and there is a slight acid smell), the color is white, and slight coagulation is generated. This shows that the jet hole distance is one of the key factors affecting the sterilization effect in the dynamic ultra-high pressure jet collision process of the application. The sterilization effect of the jet hole distance greater than 10 mm is far less than that of the jet hole distance of 2-10 mm.

[0111] Comparative example 4

[0112] On the basis of Example 4, the separation temperature of step (2) is adjusted, and 40℃ and 45℃ are selected for gradient test: the raw milk after warming is subjected to low-temperature heat treatment, the sterilization temperature is 85℃, and the sterilization time is 15s; the raw material and the remaining steps are the same as those in Example 4.

[0113] It is detected that the total number of colonies of the finished product increases with the decrease of the separation temperature. The shelf life of the milk sample obtained under the treatment conditions of Comparative Example 4 under low-temperature refrigeration (6℃) can reach 10 days, the acidity after storage for 10 days has exceeded the national standard requirement (>18°T) for pasteurized milk, the sensory evaluation of the sample is unqualified (the milk aroma is weak, and there is a slight sour smell), the color is slightly white, and slight coagulation is produced.

[0114] Comparative Example 5

[0115] On the basis of Example 4, the separation speed of step (2) is adjusted, and 3800rpm and 4000rpm are selected for gradient test: the raw milk after warming is subjected to low-temperature heat treatment, the sterilization temperature is 85℃, and the sterilization time is 15s; the raw material and the remaining steps are the same as those in Example 4.

[0116] It is detected that the total number of colonies of the finished product increases with the decrease of the separation speed. The shelf life of the milk sample obtained under the treatment conditions of Comparative Example 5 under low-temperature refrigeration (6℃) can reach 12 days, the acidity after storage for 12 days has exceeded the national standard requirement (>18°T) for pasteurized milk, the sensory evaluation of the sample is unqualified (the milk aroma is weak, and there is a slight sour smell), the color is slightly white, and slight coagulation is produced.

[0117] Comparative Example 6

[0118] On the basis of Example 1, the step (5) is deleted, and different primary homogenization pressures are selected in step (3) as shown in Table 4, and the other steps are the same as those in Example 1. The nutritional ingredient data of the fresh milk prepared are shown in Table 4.

[0119] Table 4

[0120] Pressure (MPa) Furosine (mg / 100 g protein) Alkaline phosphatase Lactoperoxidase Raw cow milk 5.8 Positive 10236 50 5.5 Positive 7693 100 4.4 Positive 9044 150 4.6 Positive 7220 200 4.4 Positive 8011 250 5.0 Positive 8792 300 6.4 Positive Positive 7926

[0121] Although the present application has been described in detail in the foregoing description with general principles and specific embodiments, modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application, all belong to the scope of the present application claimed.

Claims

1. A method for effectively maintaining nutritional components and dairy flavor, while extending the shelf life of fresh milk, characterized by, It comprises four steps, The first step: the raw milk is subjected to sterilization centrifugal treatment to remove part of the spores and bacteria; the separation temperature of the centrifugal is 50-55℃, and the separation rotation speed is 4000-7000 rpm; The second step: the raw milk is subjected to high-pressure pump energy storage, and high-pressure pulses are removed; the pressurization time of the high-pressure pump energy storage is not more than 30 s; The third step: the raw milk is subjected to dynamic ultra-high pressure jet collision, the mechanical energy of the raw milk is converted into kinetic energy, a high-speed jet is formed, and the collision energy is released while being heated; the total pressure of the dynamic ultra-high pressure jet is 150-250 MPa, the secondary pressure is 7.5-10 MPa, and the secondary pressure / total pressure is 10-20%; The collision nozzle of the dynamic ultra-high pressure jet collision adopts a coaxial equal collision nozzle, the nozzle apertures are the same, and the aperture range is 0.1-0.4 mm; the jet hole distance of the collision nozzle is 2-10 mm, and the pressure fluctuation during the collision process is kept ±5 MPa; The heating is to heat the raw milk after the collision energy release to 28-80℃; The fourth step: the raw milk after heating is subjected to low-temperature heat treatment to realize sterilization and enzyme inactivation; the low-temperature heat treatment refers to a sterilization temperature of 72-85℃, a sterilization time of 12-15 s, and a cooling temperature of 2-6℃; The prolonged shelf life of fresh milk refers to a shelf life of more than 20 days.

2. The method of claim 1, wherein, In the second step, before the dynamic ultra-high pressure jet collision method is used, the raw milk cooled to 2-6℃ is subjected to high-pressure pump energy storage to remove high-pressure pulses; the high-pressure energy storage pump uses 38.5 kW / 380V alternating current.

3. The method of claim 2, wherein, The total pressure of the dynamic ultra-high pressure jet is 200-250 MPa; the secondary pressure of the dynamic ultra-high pressure jet is 10 MPa.

4. The method of claim 3, wherein, The total pressure of the dynamic ultra-high pressure jet is 200 MPa.

5. The milk product obtained by the method of any one of claims 1-4, which retains high nutritional ingredients and milk flavor, and has a prolonged shelf life of fresh milk, and the prolonged shelf life of fresh milk refers to a shelf life of more than 20 days.

6. The method of any one of claims 1-4 for use in retaining the nutritional ingredients of raw milk and / or significantly prolonging the shelf life of low-temperature fresh milk.

Images