CN117814299A - A method for freezing fresh milk, a method for reconstitution and thawing of frozen fresh milk and applications thereof - Google Patents
A method for freezing fresh milk, a method for reconstitution and thawing of frozen fresh milk and applications thereof Download PDFInfo
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- CN117814299A CN117814299A CN202311840584.9A CN202311840584A CN117814299A CN 117814299 A CN117814299 A CN 117814299A CN 202311840584 A CN202311840584 A CN 202311840584A CN 117814299 A CN117814299 A CN 117814299A
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- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23B—PRESERVATION OF FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES; CHEMICAL RIPENING OF FRUIT OR VEGETABLES
- A23B11/00—Preservation of milk or dairy products
- A23B11/10—Preservation of milk or milk preparations
- A23B11/14—Preservation of milk or milk preparations by freezing or cooling
- A23B11/145—Preservation of milk or milk preparations by freezing or cooling in packages
- A23B11/1455—Freezing in packages
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- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23B—PRESERVATION OF FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES; CHEMICAL RIPENING OF FRUIT OR VEGETABLES
- A23B11/00—Preservation of milk or dairy products
- A23B11/10—Preservation of milk or milk preparations
- A23B11/14—Preservation of milk or milk preparations by freezing or cooling
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Abstract
本发明属于生鲜乳冻存及乳制品制备技术领域，具体涉及一种生鲜乳的冷冻方法、冷冻生鲜乳的复原解冻方法及其应用。本发明将生鲜乳进行浓缩，在冷冻室转筒壁中形成液体层并迅速冻结，随后被搅拌刮刀铲除，减少大冰晶和不同组分冻结程度不一的问题，以此种快速薄冰冷冻方法减少大冰晶的产生，使冰晶颗粒粒径基本维持一致，减少冷冻对牛奶中蛋白质和脂肪的破坏，解决传统冷冻方式形成的大冰晶会导致蛋白不稳定以及破坏乳脂结构，从而解冻后以及后续加工过程中容易出现分层和沉淀的问题；同时也能解决传统冷冻方式所导致的解冻时间久，牛奶中各组分浓度不一的问题。
The present invention belongs to the technical field of fresh milk freezing and dairy product preparation, and specifically relates to a fresh milk freezing method, a frozen fresh milk recovery and thawing method and its application. The present invention concentrates the fresh milk, forms a liquid layer in the wall of the freezing chamber drum and freezes it quickly, which is then scraped off by a stirring scraper to reduce the problem of large ice crystals and different freezing degrees of different components. This rapid thin ice freezing method reduces the generation of large ice crystals, keeps the particle size of ice crystal particles basically consistent, reduces the damage of freezing to protein and fat in milk, and solves the problem that large ice crystals formed by traditional freezing methods will cause protein instability and destroy the milk fat structure, thus easily causing stratification and precipitation after thawing and in subsequent processing; at the same time, it can also solve the problem of long thawing time and different concentrations of various components in milk caused by traditional freezing methods.
Description
Technical Field
The invention belongs to the technical field of frozen storage of fresh milk and preparation of dairy products, and particularly relates to a freezing method of fresh milk, a restoration and thawing method of frozen fresh milk and application of the restoration and thawing method.
Background
Raw milk is the most important raw material source for dairy processing, but the raw milk has a longer transportation distance from pasture to factory, so that the quality change of the raw milk in the transportation process and the risk of psychrophilic bacteria proliferation are increased. Meanwhile, the production of raw and fresh cow milk is obviously affected by seasons, and the following conditions are often shown: under-feeding of raw milk occurs in summer due to reduced dairy cow production, but is a peak of dairy consumption in summer. However, as the air temperature decreases, milk consumption is at a peak of milk production in the off-season, so that the situation of rich milk production occurs. In order to cope with the contradiction of unbalance of milk quantity, raw milk is usually spray-dried to prepare milk powder, and then reconstituted for use. However, the raw milk is denatured in the spray drying process, and the fat is oxidized to some extent, so that the taste and flavor of the milk powder are defective when the milk powder is reconstituted again for use. Meanwhile, the price of the milk powder prepared by spray drying in China is far higher than that of imported milk powder, and the cost of a dairy enterprise is pressure-bearing under the trend of price hanging.
Freezing is an effective preservation mode and is widely applied to the field of food processing. Cryopreservation achieves the goal of extending the shelf life of food by reducing the temperature of the object to be preserved, thereby slowing or reducing biological, physical, and chemical changes that occur during storage. However, the milk is affected by the freezing speed and the freezing temperature during the freezing process, and the phenomena of dehydration, solid-liquid separation and the like are caused during thawing after freezing, so that the food quality is reduced. In particular, in the freezing process of raw milk, due to different freezing speeds of different components and the generation of crystals such as ice crystals and lactose, proteins in the milk can be denatured to a certain extent during freezing, so that the phenomenon of precipitation and layering can occur due to different concentrations of proteins, fats, carbohydrates and other components at different positions during thawing in a traditional mode. Although deep freezing (-80 ℃ and below) of foods in a short time combined with low-temperature thawing can solve the problem to a certain extent, the economic cost is high, and the method is not suitable for the food processing field with high yield and low added value.
Disclosure of Invention
The invention aims to provide a freezing method of fresh milk, a restoration and thawing method of frozen fresh milk and application thereof, wherein the freezing method can reduce damage of freezing to protein and fat in milk; the quality of the frozen fresh milk after being restored can be effectively ensured by matching with the restoration thawing method, the quality guarantee period of the fresh milk is prolonged, the problem of poor state of milk after being frozen is solved, the influence on the use and the taste of the subsequently processed product is reduced, and the method has the convenience and the economical efficiency of operation.
The invention provides a freezing method of fresh milk, which comprises the following steps:
concentrating the raw milk to obtain concentrated raw milk;
injecting the concentrated fresh milk into a freezing chamber with a rotary drum for freezing, and scraping a formed liquid frozen layer by a stirring scraper connected to the inner wall of the rotary drum in the freezing process to obtain frozen milk;
and filling the frozen milk slurry into a preservation container for quick freezing to obtain frozen raw fresh milk.
Preferably, the freezing and scraping are performed under vacuum conditions, and the vacuum degree of the vacuum conditions is 0.01-0.08 MPa.
Preferably, the concentration mode comprises vacuum falling film concentration, reverse osmosis concentration or ultrafiltration concentration; the protein content in the concentrated fresh milk is 3.5% -10%, the fat content is 3.8% -13.5%, and the lactose content is 4.6% -5.5%.
Preferably, the rotating speed of the rotating drum is 40-100 rpm; the temperature in the freezing chamber with the rotary drum is-25 to-10 ℃, and the freezing chamber with the rotary drum is discharged Mouth(s) At a temperature of -2～-8 ℃ ； The thickness of the liquid frozen layer is 0.1-3 mm.
Preferably, the distance between the edge of the stirring scraper and the inner wall of the rotary drum is 0.1-5 mm, and the angle is 10-30 degrees; the rotating speed of the stirring scraper is 30-150 rpm; the temperature of the stirring scraper and the temperature of the rotary drum are kept consistent.
Preferably, the quick-freezing mode comprises air-cooling quick-freezing, and the temperature of the quick-freezing is not lower than-18 ℃.
The invention also provides frozen raw fresh milk obtained by the freezing method.
The invention also provides a restoration and thawing method for the frozen raw fresh milk, which comprises the following steps:
demolding the frozen raw milk, and performing ice pulping treatment on the obtained demolded frozen raw milk to obtain raw milk ice slurry;
and heating the fresh milk ice slurry to 4-6 ℃ to obtain the thawed reconstituted milk.
Preferably, the demolding mode comprises low-temperature demolding, normal-temperature demolding or thermal demolding; the temperature of the low-temperature demoulding is not higher than 10 ℃; the temperature of the hot demolding is 60-80 ℃.
The invention also provides an application of the freezing method or the restoration thawing method in dairy products.
The beneficial effects are that:
the invention provides a freezing method of fresh milk, which comprises the following steps: concentrating the raw milk to obtain concentrated raw milk; injecting the concentrated fresh milk into a freezing chamber with a rotary drum for freezing, and scraping a formed liquid frozen layer by a stirring scraper connected to the inner wall of the rotary drum to obtain frozen milk; and filling the frozen milk slurry into a preservation container for quick freezing to obtain frozen raw fresh milk. The method has the advantages that fresh milk is concentrated, a liquid layer is formed in the wall of the freezing chamber rotating cylinder and is quickly frozen, then the liquid layer is shoveled by the stirring scraper, the problem that the freezing degree of big ice crystals and different components is different is solved, the generation of big ice crystals is reduced by the quick thin ice freezing method, the particle size of ice crystal particles is basically kept consistent, the damage of freezing to protein and fat in milk is reduced, and the problems that the protein is unstable and the milk fat structure is damaged due to the big ice crystals formed in the traditional freezing mode are solved, so that layering and precipitation are easy to occur after thawing; meanwhile, the problem of different concentrations of each component in milk due to long thawing time caused by the traditional freezing mode can be solved.
On the basis, the invention also provides a method for recovering and thawing the frozen raw fresh milk, which comprises the following steps: demolding the frozen raw milk, and performing ice pulping treatment on the obtained demolded frozen raw milk to obtain raw milk ice slurry; and heating the fresh milk ice slurry to 4-6 ℃ to obtain the thawed reconstituted milk. The restoration and thawing method can realize rapid thawing of the frozen raw milk, effectively ensure the quality of the frozen raw milk after restoration, prolong the shelf life of the frozen raw milk, and has the advantages of convenient operation and economy.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments will be briefly described below.
FIG. 1 is a diagram of a frozen milk slurry prepared by the freezing method of the invention;
FIG. 2 is a diagram of a frozen raw fresh milk prepared by the freezing method of the invention;
FIG. 3 is a reconstituted milk after thawing prepared by the reconstituted thawing method of the invention;
FIG. 4 is a graph showing the relationship between the stirring scraper and the inner wall of the rotary drum.
Detailed Description
The invention provides a freezing method of fresh milk, which comprises the following steps:
concentrating the raw milk to obtain concentrated raw milk;
injecting the concentrated fresh milk into a freezing chamber with a rotary drum for freezing, and scraping a formed liquid frozen layer by using a stirring scraper connected to the inner wall of the rotary drum in the freezing process to obtain frozen milk;
and filling the frozen milk slurry into a preservation container for quick freezing to obtain frozen raw fresh milk.
The invention concentrates the fresh milk to obtain the concentrated fresh milk. The invention relates to fresh milkPreferably including but not limited to raw milk, pasteurized milk or whole or skim milk prepared by other sterilization means. The fresh milk is preferably raw milk meeting the national standard, and the total bacterial count of the raw milk is preferably less than 1 multiplied by 10 4 cfu/mL, the number of somatic cells is preferably less than 2X 10 5 individual/mL; the protein content is preferably not less than 3.1%, and the fat content is preferably not less than 3.4%. The concentration according to the invention preferably comprises vacuum falling film concentration, reverse osmosis concentration or ultrafiltration concentration, more preferably reverse osmosis concentration or ultrafiltration concentration; the temperature of the concentration is preferably 4-6 ℃; the protein content in the concentrated fresh milk obtained by concentration is preferably 3.5-10%, the fat content is preferably 3.8-13.5%, and the lactose content is preferably 4.6-5.5%. Through the concentration, a part of water in the milk can be removed, and the cost of subsequent transportation and storage is reduced.
After the concentrated fresh milk is obtained, the concentrated fresh milk is injected into a freezing chamber with a rotary drum for freezing, and a stirring scraper connected to the inner wall of the rotary drum is used for scraping the formed liquid frozen layer, so that frozen milk slurry is obtained. The invention preferably injects the concentrated raw milk into a freezing chamber with a rotating drum through a centrifugal pump under stirring. The raw milk of the present invention is preferably stirred after concentration, that is, stirred after concentration and injected into a freezing chamber with a drum under stirring conditions, and the rotation speed of the stirring conditions is preferably 40 to 100rpm, more preferably 60 to 80rpm.
The concentrated raw milk of the present invention is preferably injected tangentially into the freezer compartment with the drum. The temperature in the freezing chamber with the rotary drum is preferably-25 to-10 ℃, more preferably-20 to-18 ℃; the freezer compartment with the drum is set at its temperature by a freezing medium which is located in a jacket outside the drum and flows in the jacket. The thickness of the liquid freezing layer is preferably 0.1 to 3mm. The rotation speed of the drum according to the invention is preferably 60 to 120rpm, more preferably 100rpm.
After the liquid freezing layer is formed on the inner wall of the rotary drum, the liquid freezing layer is scraped by the stirring scraper connected to the inner wall of the rotary drum, so that frozen milk slurry is obtained. The scraping according to the invention is preferably performed simultaneously with the freezing. The distance between the edge of the stirring scraper and the inner wall of the rotary drum is preferably 0.1-5 mm, more preferably 0.2-3 mm, and even more preferably 0.3-2.5 mm; the distance between the edge of the stirring scraper and the inner wall of the rotary drum can be preferably changed manually before the scraping operation is carried out, so that the distance between the stirring scraper and the inner wall of the rotary drum can be adjusted, or the distance between the stirring scraper and the inner wall of the rotary drum can be adjusted in a hydraulic mode; the angle between the stirring scraper and the inner wall of the rotary drum is preferably 10-30 degrees, and the relative relation between the stirring scraper and the inner wall of the rotary drum is shown in figure 4; the specific process of hydraulically adjusting the distance between the stirring scraper and the inner wall of the rotary drum is preferably as follows: the opening angle of the stirring scraper is controlled by adjusting the pressure of compressed air in the hydraulic connecting rod cavity, so that the distance between the edge of the stirring scraper and the cylinder wall is adjusted; the rotation speed of the stirring blade is preferably 30 to 150rpm, and more preferably 60 to 80rpm. The stirring scraper can control the temperature preferably, maintain the temperature of the stirring scraper to be consistent with the temperature of the freezing chamber during operation, and reduce the temperature difference generated between the stirring scraper and the frozen milk thin layer during stirring, thereby influencing the scraping effect. In order to reduce the mixing of air, the freezing chamber of the present invention preferably maintains a vacuum, and the vacuum degree is preferably 0.01 to 0.08MPa, more preferably 0.04 to 0.06MPa, which is preferably achieved by a conventional vacuuming device. The outlet temperature of the freezing chamber with the rotary drum is preferably-8 to-2 ℃, more preferably-5 to-2 ℃; the outlet temperature can ensure that the frozen milk slurry has certain fluidity, so that the frozen milk slurry is conveniently input into a storage container, and the figure 1 is a physical diagram of the obtained frozen milk slurry.
After the frozen milk slurry is obtained, the frozen milk slurry is filled into a preservation container for quick freezing, so that the frozen raw fresh milk is obtained. A physical diagram of the frozen raw fresh milk is shown in figure 2. The preservation container of the present invention preferably comprises a plastic bag or a cask; the quick-freezing mode preferably comprises air-cooling quick-freezing, and the temperature of the quick-freezing is preferably not lower than-18 ℃.
Compared with the traditional freezing mode, the freezing mode can reduce the generation of large ice crystals, the sizes of the ice crystal particles are more uniform, the influence of freezing on the physicochemical properties of raw and fresh milk is reduced, layering and precipitation of finished products are not easy to occur, and the shelf life of the product is longer. Based on the advantages, the frozen raw milk obtained by the freezing method provided by the invention also belongs to the protection scope of the invention.
The invention also provides a restoration and thawing method for the frozen raw fresh milk, which comprises the following steps:
demolding the frozen raw milk, and performing ice pulping treatment on the obtained demolded frozen raw milk to obtain raw milk ice slurry;
and heating the fresh milk ice slurry to 4-6 ℃ to obtain the thawed reconstituted milk.
The invention carries out demoulding on the frozen raw milk to obtain the demoulded frozen raw milk. The demolding mode of the invention preferably comprises low-temperature demolding, normal-temperature demolding or thermal demolding, more preferably low-temperature demolding or thermal demolding; the temperature of the low temperature demolding is preferably not higher than 10 ℃; the temperature of the hot demolding is preferably 60-80 ℃; the present invention preferably performs the thermal stripping in a hot air tunnel. The time for demolding according to the present invention is preferably not more than 5 hours, more preferably 0.1 to 0.5 hours.
After the demolded frozen raw milk is obtained, the invention carries out ice pulping treatment on the demolded frozen raw milk to obtain raw milk ice slurry. In the invention, the frozen fresh milk after demoulding is poured into a refiner for carrying out the ice pulping treatment, and the ice pulp is in a flowable mud shape, and the temperature is preferably between-4 ℃ and-2 ℃.
Before the ice pulping treatment, the invention preferably further comprises the step of placing the demolded frozen raw milk into an ice crusher with ice claws for crushing, and carrying out subsequent ice pulping treatment on the obtained crushed milk blocks. The volume of the crushed milk pieces according to the invention is preferably 10cm by 5cm.
After the fresh milk ice slurry is obtained, the temperature of the fresh milk ice slurry is raised to 4-6 ℃ to obtain the thawed reconstituted milk. The thawed cow milk can be directly processed or processed by adding other raw materials such as water and the like. The physical diagram of the thawed reconstituted milk prepared by the invention is shown in fig. 3. The invention preferably adopts a heat exchanger to heat, and the source of the temperature is preferably waste heat generated by dairy product processing, so as to achieve the effects of fully utilizing the redundant heat source and reducing the energy cost. In the heating process of the invention, stirring is preferably carried out, and the rotating speed of stirring is preferably 40-80 rpm, more preferably 60-70 rpm; the stirring speed is relatively suitable, not fast and slow, and the effect of avoiding generating excessive foam while increasing the heat exchange efficiency is achieved.
In order to adjust seasonal differences in milk source yield and contradiction of unbalance of production places and consumption areas of the raw milk, compared with the traditional mode that the redundant raw fresh milk is prepared into milk powder after spray drying, the frozen raw fresh milk prepared by the freezing method has small influence on the flavor and quality of the milk, and does not generate bad flavor and texture. Compared with the traditional freezing mode, the invention can reduce the generation of large ice crystals during freezing, the sizes of the ice crystal particles are more uniform, the influence of freezing on the physicochemical properties of milk is reduced, layering and precipitation of finished products are not easy to occur, and the shelf life of the products is longer. Meanwhile, the pulping mode adopted by the invention reduces the occurrence of uneven concentration caused by different speeds of different components in milk in the freezing and thawing processes. The freezing method can achieve the effect of deep freezing (-80 ℃), but has lower cost, and avoids the problems of high construction cost and high operation and maintenance cost of deep freezing (-80 ℃).
Based on the advantages, the invention also provides an application of the freezing method or the restoration thawing method in dairy products. Specifically, in the present invention, when preparing a dairy product from the thawed reconstituted milk obtained by the reconstituted thawing method, it is preferable to prepare the dairy product after heating, stirring and homogenizing the thawed reconstituted milk. In the invention, the thawed reconstituted milk is preferably heated to 45-60 ℃, more preferably 50-55 ℃; the stirring time is preferably 10 to 20 minutes, more preferably 15 minutes. The temperature of the homogenization is preferably 50-60 ℃, and the pressure is preferably 15-18 Mpa. The heating, stirring and homogenizing operations of the present invention can produce a uniform reconstituted milk.
The present invention preferably includes, but is not limited to, liquid milk, yogurt or milk drinks for the dairy products; the production mode of the dairy product is not particularly limited, and the dairy product can be prepared according to the type of the product. The freezing method and the restoration and thawing method of the invention are used for improving the processing stability in the process of producing dairy products.
The technical solutions provided by the present invention are described in detail below with reference to the drawings and examples for further illustrating the present invention, but they should not be construed as limiting the scope of the present invention.
Example 1
1. A freezing method of fresh milk comprises the following steps:
(1) Selecting raw milk meeting national standard, wherein the total bacterial count is less than 1×10 4 cfu/mL, somatic cell count less than 2X 10 5 The raw milk protein content is not less than 3.1 percent per mL, and the fat content is not less than 3.4 percent.
(2) Removing partial water from raw milk by reverse osmosis at 4-6deg.C to make protein content reach 4.0%, fat content reach 4.5%, and lactose content reach 5.3%; stirring at 60rpm/min in a milk tank for later use.
(3) Pumping the raw milk obtained in the step (2) to a freezing chamber through a centrifugal pump for freezing. The temperature of the freezing medium in the jacket of the freezing chamber was set at-20 ℃. The distance between the stirring knife and the surface of the rotary drum is set to be 0.2mm, the rotating speed is 80rpm/min, and the temperature is controlled to be-18 to-20 ℃; the temperature of the resulting frozen milk slurry was set at-3 ℃. In order to reduce the air mixing, the vacuum in the freezer compartment was set at 60kPa.
(4) Filling the frozen fresh whey obtained in the step (3) into a packaging bag or an iron drum for sealing, and performing air cooling quick freezing in time; setting the quick-freezing temperature at-18 ℃ and preserving for standby.
2. A method for thawing frozen raw milk by restoration comprises the following steps:
(1) Demoulding the frozen raw milk prepared in the step 1 in a refrigerator at 4 ℃ for 6 hours, and delivering the demoulded product into a refiner to prepare ice slurry.
(2) And (3) heating the fresh milk ice slurry prepared in the step (1) to 4-6 ℃ through a pipeline by a heat exchanger, and stirring at 60rpm/min to obtain the reconstituted frozen fresh milk.
(3) Heating the recovered frozen raw milk obtained in the step (2) to 50 ℃ and homogenizing under 18MPa.
Pasteurizing and filling the homogenized reconstituted raw milk to obtain a final product (dairy product); pasteurization conditions were 75 ℃,15s.
Example 2
1. A freezing method of fresh milk comprises the following steps:
(1) Selecting raw milk meeting national standard, wherein the total bacterial count is less than 1×10 4 cfu/mL, somatic cell count less than 2X 10 5 The raw milk protein content is not less than 3.1 percent per mL, and the fat content is not less than 3.4 percent.
(2) Removing partial water from raw milk by reverse osmosis at 4-6deg.C to make protein content reach 4.0%, fat content reach 4.5%, and lactose content reach 5.3%; stirring at 60rpm/min in a milk tank for later use.
(3) Pumping the raw milk obtained in the step (2) to a freezing chamber through a centrifugal pump for freezing. The temperature of the freezing medium in the jacket of the freezing chamber was set at-20 ℃. The distance between the stirring knife and the surface of the rotary drum is set to be 0.2mm, the rotating speed is 80rpm/min, and the temperature is controlled to be-18 to-20 ℃. The temperature of the resulting frozen milk slurry was set at-3 ℃. In order to reduce the air mixing, the vacuum in the freezer compartment was set at 60kPa.
(4) And (3) filling the frozen fresh whey obtained in the step (3) into a packaging bag or an iron drum for sealing, and performing air cooling quick freezing in time. Setting the quick-freezing temperature at-18 ℃ and preserving for standby.
2. A method for restoring frozen fresh milk comprises the following steps:
(1) Demolding the frozen fresh milk prepared in the step 1 in a hot air tunnel at 80 ℃ for 0.1h, crushing the demolded product, and preparing ice slurry by a homogenizer.
(2) And (3) heating the fresh milk ice slurry prepared in the step (1) to 4-6 ℃ through a pipeline by a heat exchanger, and stirring at 60rpm/min to obtain the reconstituted frozen fresh milk.
(3) Heating the reconstituted frozen raw milk obtained in the step (2) to 50 ℃, stirring for 15min, homogenizing and pre-pasteurizing at 55 ℃ and 18MPa, and cooling for later use.
Homogenizing and ultra-high temperature sterilizing the pre-pasteurized product in the step (3) and filling to obtain a final product. The ultra-high temperature sterilization condition is 137 ℃ for 6s.
Example 3
1. A freezing method of fresh milk comprises the following steps:
(1) Selecting raw milk meeting national standard, wherein the total bacterial count is less than 1×10 4 cfu/mL, somatic cell count less than 2X 10 5 The raw milk protein content is not less than 3.1 percent per mL, and the fat content is not less than 3.4 percent.
(2) Removing part of water from raw milk by reverse osmosis at 4-6deg.C to make protein content reach 6.0%, fat content reach 8.0%, and lactose content reach 8.8%. Stirring at 60rpm/min in a milk tank for later use.
(3) Pumping the raw milk obtained in the step (2) to a freezing chamber through a centrifugal pump for freezing. The temperature of the freezing medium in the jacket of the freezing chamber was set at-20 ℃. The distance between the stirring knife and the surface of the rotary drum is set to be 3mm, the rotating speed is 80rpm/min, and the temperature is controlled to be-18 to-20 ℃. The temperature of the resulting frozen milk slurry was set at-4 ℃. In order to reduce the air mixing, the vacuum in the freezer compartment was set at 80kPa.
(4) And (3) filling the frozen fresh whey obtained in the step (3) into a packaging bag or an iron drum for sealing, and performing air cooling quick freezing in time. Setting the quick-freezing temperature at-18 ℃ and preserving for standby.
2. A method for restoring frozen fresh milk comprises the following steps:
(1) Demolding the frozen fresh milk prepared in the step 1 in a hot air tunnel at 80 ℃ for 0.2h, crushing the demolded product, and preparing ice slurry by a refiner.
(2) And (3) heating the fresh milk ice slurry prepared in the step (1) to 4-6 ℃ through a pipeline by a heat exchanger, and stirring at 60rpm/min to obtain the reconstituted frozen fresh milk.
(3) Heating the reconstituted frozen raw milk obtained in the step (2) to 50 ℃, stirring for 15min, homogenizing and pre-pasteurizing at 60 ℃ and 15MPa, and cooling for later use.
(4) Homogenizing and ultra-high temperature sterilizing the pre-pasteurized product in the step (3) and filling to obtain a final product. The ultra-high temperature sterilization condition is 137 ℃ for 6s.
Example 4
1. A freezing method of fresh milk comprises the following steps:
(1) Selecting raw milk meeting national standard, wherein the total bacterial count is less than 1×10 4 cfu/mL, somatic cell count less than 2X 10 5 The raw milk protein content is not less than 3.1 percent per mL, and the fat content is not less than 3.4 percent.
(2) Removing partial water from raw milk by reverse osmosis at 4-6deg.C to make protein content reach 8.0%, fat content reach 9.2%, and lactose content reach 12%. Stirring at 80rpm/min in a milk jar for use.
(3) Pumping the raw milk obtained in the step (2) to a freezing chamber through a centrifugal pump for freezing. The temperature of the freezing medium in the jacket of the freezing chamber was set at-20 ℃. The distance between the stirring knife and the surface of the rotary drum is set to be 0.3mm, the rotating speed is 80rpm/min, and the temperature is controlled to be-18 to-20 ℃. The temperature of the resulting frozen milk slurry was set at-2.5 ℃. In order to reduce the air mixing, the vacuum in the freezer compartment was set at 80kPa.
(4) And (3) filling the frozen fresh whey obtained in the step (3) into a packaging bag or an iron drum for sealing, and performing air cooling quick freezing in time. Setting the quick-freezing temperature at-18 ℃ and preserving for standby.
2. A method for restoring frozen fresh milk comprises the following steps:
(1) Demolding the frozen fresh milk prepared in the step 1 in a hot air tunnel at 60 ℃ for 0.2h, crushing the demolded product, and preparing ice slurry by a refiner.
(2) And (3) heating the fresh milk ice slurry prepared in the step (1) to 4-6 ℃ through a pipeline by a heat exchanger, and stirring at 60rpm/min to obtain the reconstituted frozen fresh milk.
(3) Heating the recovered frozen fresh milk prepared in the step (2) to 50 ℃, stirring for 15min, homogenizing and pre-pasteurizing at 50-60 ℃ and 15-18MPa, and cooling for later use.
(4) Homogenizing and sterilizing the pre-pasteurized product in the step (3) and filling to obtain a final product. The sterilization adopts steam immersion sterilization, and the conditions are 147 ℃ and 4s. And (3) sterilizing, and preferably carrying out sterile homogenization again before filling, wherein the homogenization condition is 60 ℃ and 23MPa.
Example 5
1. A freezing method of fresh milk comprises the following steps:
(1) Selecting raw milk meeting national standard, wherein the total bacterial count is less than 1×10 4 cfu/mL, somatic cell count less than 2X 10 5 The raw milk protein content is not less than 3.1 percent per mL, and the fat content is not less than 3.4 percent.
(2) Under the condition of 4-6 ℃, the raw milk is ultrafiltered to remove partial water, so that the protein content reaches 10.0%, the fat content reaches 13.2%, and the lactose content is 6.0%. Stirring at 60rpm/min in a milk tank for later use.
(3) Pumping the raw milk obtained in the step (2) to a freezing chamber through a centrifugal pump for freezing. The temperature of the freezing medium in the jacket of the freezing chamber was set at-20 ℃. The distance between the stirring knife and the surface of the rotary drum is set to be 0.1mm, the rotating speed is 80rpm/min, and the temperature is controlled to be-18 to-20 ℃. The temperature of the resulting frozen milk slurry was set at-2.5 ℃. In order to reduce the air mixing, the vacuum in the freezer compartment was set at 80kPa.
(4) And (3) filling the frozen fresh whey obtained in the step (3) into a packaging bag or an iron drum for sealing, and performing air cooling quick freezing in time. Setting the quick-freezing temperature at-18 ℃ and preserving for standby.
2. A method for restoring frozen fresh milk comprises the following steps:
(1) Demolding the frozen fresh milk prepared in the step 1 in a hot air tunnel at 60 ℃ for 0.1h, crushing the demolded product, and preparing ice slurry by a refiner.
The subsequent procedure is as in example 3.
Comparative example 1
A preparation method of fresh milk comprises the following steps:
(1) Selecting full-fat milk powder meeting national standard, and adding water according to a certain proportion to reduce the full-fat milk powder into reconstituted milk with 3.1% of protein and 3.4% of fat.
(2) Stirring the reconstituted milk obtained in the step (1) at a speed of 50rpm/min, heating to 55 ℃ for homogenization, wherein the homogenization pressure is 18MPa.
(3) Sterilizing the reconstituted fresh milk homogenized in the step (2), wherein the sterilization condition is 137 ℃ for 4s.
(4) And (5) filling and refrigerating the sterilized cow milk at 25 ℃.
Comparative example 2
1. A freezing method of fresh milk comprises the following steps:
(1) Selecting raw milk meeting national standard, wherein the total bacterial count is less than 1×10 4 cfu/mL, somatic cell count less than 2X 10 5 The raw milk protein content is not less than 3.1 percent per mL, and the fat content is not less than 3.4 percent.
(2) The raw milk is subjected to reverse osmosis to remove part of water, the protein content reaches 5.0%, the fat content reaches 7.8%, and the lactose content reaches 7.5%. Stirring at 60rpm/min in a milk tank for later use.
(3) And (3) filling the raw milk obtained in the step (2) into a plastic bag or a barrel at the temperature of 4-6 ℃, sealing, and then transferring the sealed raw milk into a freezer at the temperature of-18 ℃ for freezing for later use.
2. A method for restoring frozen fresh milk comprises the following steps:
(1) Transferring the frozen raw fresh milk prepared in the step 1 into a thawing warehouse for thawing; the thawing warehouse temperature is 10 ℃, and the thawing time is 12 hours.
(2) Heating the thawed raw milk obtained in the step (1) to 55 ℃, stirring for 15min, homogenizing under 18-20MPa, and then carrying out pre-pasteurization. Pasteurization conditions were 85 ℃,15s, and then cooled for use.
(3) And (3) performing ultrahigh temperature sterilization on the pre-pasteurized cow milk obtained in the step (2), wherein the sterilization condition is 137 ℃ for 6s. Homogenizing at 55deg.C and 20MPa before sterilizing. And then cooling to below 20 ℃ and filling.
Comparative example 3
1. A freezing method of fresh milk comprises the following steps:
(1) Selecting raw milk meeting national standard, wherein the total bacterial count is less than 1×10 4 cfu/mL, somatic cell count less than 2X 10 5 The raw milk protein content is not less than 3.1 percent per mL, and the fat content is not less than 3.4 percent.
(2) The raw milk is ultrafiltered to remove partial water, the protein content reaches 6.0%, the fat content reaches 8.0%, and the lactose content reaches 5.0%. Stirring at 60rpm/min in a milk tank for later use.
(3) And (3) filling the raw milk obtained in the step (2) into a plastic bag or a barrel at the temperature of 4-6 ℃, sealing, and then transferring the sealed raw milk into a freezer at the temperature of-18 ℃ for freezing for later use.
2. A method for restoring frozen fresh milk comprises the following steps:
(1) And (3) transferring the frozen raw milk prepared in the step (1) into a thawing warehouse for thawing. The thawing warehouse temperature is 4 ℃ and the thawing time is 20h.
(2) Heating the thawed raw milk obtained in the step (1) to 55 ℃, stirring for 15min, homogenizing under 18-20MPa, and then carrying out pre-pasteurization. Pasteurization conditions were 85 ℃,15s, and then cooled for use.
(3) And (3) performing ultrahigh temperature sterilization on the pre-pasteurized cow milk obtained in the step (2), wherein the sterilization condition is 137 ℃ for 6s. Homogenizing at 50deg.C and 20MPa before sterilizing. And then cooling to below 20 ℃ and filling.
Comparative example 4
1. A freezing method of fresh milk comprises the following steps:
(1) Selecting raw milk meeting national standard, wherein the total bacterial count is less than 1×10 4 cfu/mL, somatic cell count less than 2X 10 5 The raw milk protein content is not less than 3.1 percent per mL, and the fat content is not less than 3.4 percent.
(2) The raw milk is subjected to reverse osmosis to remove part of water, the protein content reaches 6.0%, the fat content reaches 8.0%, and the lactose content is 8.8%. Stirring at 60rpm/min in a milk tank for later use.
The rest of the procedure is the same as in comparative example 3.
2. A method for restoring frozen fresh milk comprises the following steps:
the procedure is as in comparative example 3.
Comparative example 5
1. A freezing method of fresh milk comprises the following steps:
(1) Selecting raw milk meeting national standard, wherein the total bacterial count is less than 1×10 4 cfu/mL, somatic cell count less than 2X 10 5 The raw milk protein content is not less than 3.1 percent per mL, and the fat content is not less than 3.4 percent.
(2) Removing partial water from raw milk by reverse osmosis at 4-6deg.C to make protein content reach 8.0%, fat content reach 9.2%, and lactose content reach 12%. Stirring at 80rpm/min in a milk jar for use.
(3) And (3) filling the raw milk obtained in the step (2) into a plastic bag or a barrel at the temperature of 4-6 ℃, sealing, and then transferring the sealed raw milk into a freezer at the temperature of-18 ℃ for freezing for later use.
2. A method for restoring frozen fresh milk comprises the following steps:
(1) And (3) transferring the frozen raw milk prepared in the step (1) into a thawing warehouse for thawing. The thawing warehouse temperature is 4 ℃ and the thawing time is 36h.
(2) Heating the reconstituted frozen fresh milk prepared in the step (1) to 50 ℃, stirring for 15min, homogenizing and pre-pasteurizing at 50-60 ℃ and 15-18MPa, and cooling for later use.
(3) Homogenizing and sterilizing the pre-pasteurized product in the step (2) and filling to obtain a final product. The sterilization adopts steam immersion sterilization, and the conditions are 147 ℃ and 4s. And (3) sterilizing, and preferably carrying out sterile homogenization again before filling, wherein the homogenization condition is 60 ℃ and 23MPa.
Test example 1
1) Measurement of thawing state and heat treatment stability of frozen raw milk:
in order to evaluate the condition of the frozen samples after thawing, about 1kg of frozen samples were thawed according to the thawing methods corresponding to examples and comparative examples, and the thawed samples were passed through a 6mm neck funnel, and the thawing rate was evaluated as shown in Table 1, wherein the ratio of the liquid weight to the total mass of the frozen samples was more than 95%.
Table 1 thawing rate evaluation table
| Thawing speed | Quick speed | Faster | In general | Slower | Slow speed |
| Thawing time, T | 0<T≤1h | 1<T≤4h | 4<T≤8h | 8<T≤20h | T>20h |
After about 1kg of frozen sample was stored for 30d, the sample of the example was thawed according to the corresponding thawing method, and then placed in a 1L plastic bottle and allowed to stand for 30min for observation. Comparative samples were directly observed after thawing in 1L plastic bottles according to the corresponding method. After observing the inside of the package, the sample was slowly poured along the glass plate side to observe whether there was particulate matter or coagulum, and the quality and state evaluation criteria of the sample were as shown in Table 2.
Table 2 sample texture and status evaluation table
The thawing state and heat treatment stability of the frozen raw milk in examples 1 to 5 and comparative examples 1 to 5 were evaluated according to the above-described methods, and the results are shown in Table 3.
Table 3 evaluation results of frozen raw fresh milk in examples 1 to 5 and comparative examples 1 to 5 after thawing
2) Evaluation of the shelf-life status and mouthfeel of the finished milk prepared in examples 1 to 5 and comparative examples 1 to 5:
the finished milk samples prepared in examples 1 to 5 and comparative examples 1 to 5 were filled into 100mL plastic bottles, and were evaluated for shelf life status and mouthfeel. In order to reduce the shelf life tracking time, the shelf life tracking adopts a light-shielding acceleration experiment at 37 ℃. For better sensory evaluation of the raw milk samples prepared in examples 1 to 5 and comparative examples 1 to 5, 10 technicians were selected to perform sensory evaluation with reference to the industry specifications of "RHB 101 pasteurized milk sensory quality evaluation rule" and "RHB 102 sterilized milk sensory quality evaluation rule", the evaluation rule is shown in tables 4 to 5, the evaluation results were equally divided by 10 technicians, and the results are shown in Table 6.
Table 4 pasteurized milk sensory evaluation table
TABLE 5 sensory evaluation Table of sterilized milk
TABLE 6 sensory evaluation results of raw milk in examples 1 to 5 and comparative examples 1 to 5
The invention can solve the contradiction between milk source and output mismatch through the examples and the comparative examples, thereby reducing the waste of raw milk and the problems of higher production cost and poor flavor faced by processing into milk powder. Meanwhile, the method solves the problems that the traditional freezing mode has low freezing and thawing speed and particularly has influence on the stability of the subsequent recovery use when ice crystals formed in the freezing process of milk with high dry matter content.
Although the foregoing embodiments have been described in some, but not all, embodiments of the invention, it should be understood that other embodiments may be devised in accordance with the present embodiments without departing from the spirit and scope of the invention.
Claims (10)
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