Low-fat condensed milk process adopting micronization and low-temperature concentration

Abstract

The invention relates to a low-fat condensed milk process adopting micronization and low-temperature concentration, and belongs to the technical field of dairy product processing. The invention discloses a low-fat condensed milk process adopting micronization and low-temperature concentration. The low-fat condensed milk process comprises the following specific steps: (1) mixing and stirring skimmed milk powder, purified water and a stabilizer to obtain feed liquid; (2) sterilizing the feed liquid, and homogenizing the sterilized feed liquid in a homogenizer to obtain micronized feed liquid; (3) mixing cane sugar with purified water to form a cane sugar solution for later use; (4) adding a sucrose solution into the micronized feed liquid, mixing, and carrying out multi-effect low-temperature vacuum concentration; and (5) adding lactose, cooling and stirring step by step until crystallization, and finally cooling and canning in vacuum. The stability of the condensed milk is further improved by utilizing high-speed shearing and pasting of homogenized feed liquid and combining step-by-step cooling crystallization, in addition, the efficiency is improved by adopting multi-stage low-temperature vacuum concentration, and the loss and deterioration of components in the condensed milk are reduced, so that the low-fat condensed milk which is smooth and soft in mouth feel and sufficient in flavor can be prepared.

Description

Technical Field

[0001] The present invention belongs to the technical field of dairy product processing and relates to a process for low-fat condensed milk with atomization and low-temperature concentration. Background Art

[0002] Condensed milk is a concentrated dairy product, which is made by disinfecting fresh milk and evaporating to remove most of the water. It has the unique flavor of condensed milk and is one of the dairy products generally loved by people.

[0003] Condensed milk is further divided into sweetened condensed milk and unsweetened condensed milk. The production process of sweetened condensed milk includes raw material preheating and sterilization, sugar addition and concentration, and cooling and crystallization. The traditional processing process of concentrated dairy products usually uses heat treatment to remove water, which will cause a series of physical or chemical changes in some components in milk, including whey protein denaturation, casein dissociation, micelle aggregation, Maillard reaction, and dephosphorylation of casein, etc., resulting in a certain degree of damage to its nutritional components. Therefore, more and more research focuses on optimizing the concentration of condensed milk to meet the production of high-quality products under high-yield process conditions.

[0004] The definition of atomization is to reduce the particle size to below 10 µm through different mechanisms. Atomization technology uses hydrodynamic and mechanical methods to break the internal connections of materials and cause their structures to break. Atomization technology has a significant impact on food matrices. Reducing the size of food raw materials to the micron level can improve the functionality and physicochemical properties of foods, such as improving the water retention, swelling, solubility, antioxidant properties, and thermal stability of foods. However, there is less research on the performance of condensed milk by atomization in the current existing technologies. Summary of the Invention

[0005] The present invention relates to a process for low-fat condensed milk with atomization and low-temperature concentration, belonging to the technical field of dairy product processing. The present invention discloses a process for low-fat condensed milk with atomization and low-temperature concentration, and the specific steps are as follows: (1) Mix skim milk powder, purified water, and a stabilizer and stir to obtain a liquid mixture; (2) Sterilize the liquid mixture, and then put it into a homogenizer for homogenization to obtain an atomized liquid mixture; (3) Mix sucrose and purified water to form a sucrose solution for standby; (4) Add the sucrose solution to the atomized liquid mixture and mix, and perform multi-effect low-temperature vacuum concentration; (5) Then add lactose, gradually cool and stir until crystallization, and finally cool and vacuum can. Using high-speed shear homogenization of the liquid mixture and combining with gradual cooling crystallization to further improve the stability of condensed milk. In addition, multi-stage low-temperature vacuum concentration is adopted to improve efficiency and reduce the loss and deterioration of components in condensed milk. Therefore, the present invention can prepare low-fat condensed milk with a smooth and mellow taste and full flavor.

[0006] The object of the present invention can be achieved by the following technical solutions: A process for producing low-fat condensed milk by micronization and low-temperature concentration. The specific steps of the low-fat condensed milk process are as follows: (1) Mix skim milk powder, purified water and stabilizer at room temperature and stir to obtain a liquid mixture; (2) Preheat the liquid mixture, then heat and sterilize it, and then put it into a homogenizer for homogenization to obtain a micronized liquid mixture; (3) Mix sucrose and purified water to form a sucrose solution for standby; (4) Add the sucrose solution to the micronized liquid mixture and mix at room temperature, then put it into a three-stage concentration tower. Each layer of the concentration tower is connected to a vacuum pump through a pipeline, and low-temperature vacuum concentration is carried out step by step from top to bottom by controlling the pipeline valves. The bottom liquid collected is the concentrated liquid mixture; (5) Add lactose to the concentrated liquid mixture to form a pre-crystallized material, cool it step by step with stirring until crystallization occurs, and finally cool and fill it into cans under vacuum.

[0007] Further, in step (1), the mass ratio of skim milk powder, purified water and stabilizer is 30 - 40:50 - 60:0.002 - 0.003, and the stabilizer is guar gum or carrageenan.

[0008] Further, in step (2), the preheating temperature is 60 - 70°C, the heating means heating the temperature to 90 - 120°C, the heating time is 5 - 8 s, and the rotation speed, temperature and time of homogenization are 10000 - 12000 r / min, 40 - 50°C, and 10 - 12 min respectively.

[0009] Further, in step (3), the mass ratio of sucrose to purified water is 50 - 60:100.

[0010] Further, in step (4), the mass ratio of the sucrose solution to the micronized liquid mixture is 52 - 55:100. The temperatures of the three-stage concentration tower from top to bottom are 40 - 45°C, 48 - 55°C, and 63 - 65°C respectively. The times for low-temperature vacuum concentration step by step from top to bottom are 5 - 8 min, 10 - 12 min, and 8 - 10 min respectively. The pressure for low-temperature vacuum concentration step by step from top to bottom is 0.025 - 0.045 MPa.

[0011] Further, in step (5), the mass ratio of the concentrated liquid mixture to lactose is 100:0.03 - 0.05, and the fineness of lactose is 400 - 500 mesh.

[0012] Further, in step (5), the specific steps of cooling step by step are as follows: the pre-crystallized material is cooled at a rate of 8 - 10°C / min to 35 - 36°C, then cooled to 25 - 26°C and continuously stirred for 25 - 30 min, and finally cooled to 18 - 20°C and stirred until crystallization occurs.

[0013] Further, the cooling temperature in step (5) is 15-18°C.

[0014] Advantages of the present invention: 1. The present invention atomizes the liquid material by high-speed shearing homogenization, and its micron-sized particles improve the stability of condensed milk. At the same time, the method of step-by-step cooling crystallization is adopted to refine the crystals, further enhancing the stability of condensed milk, achieving the purpose of extending the shelf life, and also enhancing the delicate, smooth and mellow taste. In addition, the temperature of the concentration tower gradually increases from top to bottom to avoid bubbles in the liquid material, and when the temperature rises to 63-65°C, it has a sterilizing effect on the liquid material, eliminating the need for re-sterilization steps and improving production efficiency. Low-temperature vacuum concentration reduces the loss and deterioration of nutrients in condensed milk, and both the natural flavor and high protein are retained, improving the quality of the product. Specific embodiments

[0015] To further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following combines examples to detail the specific embodiments, structures, features and their effects according to the present invention as follows.

[0016] The skim milk powder involved in the present invention is purchased from Guangzhou Qiongqi Biotechnology Co., Ltd. Example

[0017] A low-fat condensed milk process with atomization and low-temperature concentration. The low-fat condensed milk process specifically comprises the following steps: (1) Mix skim milk powder, purified water and stabilizer at room temperature and stir to obtain a liquid material; (2) Preheat the liquid material, then heat and sterilize it, and then put it into a homogenizer for homogenization to obtain atomized liquid material; (3) Mix sucrose with purified water to form a sucrose solution for standby; (4) Add the sucrose solution to the atomized liquid material and mix at room temperature, and then put it into a three-stage concentration tower. Each layer of the concentration tower is connected to a vacuum pump through a pipeline, and low-temperature vacuum concentration is carried out step by step from top to bottom by controlling the pipeline valves. The liquid collected at the bottom layer is the concentrated liquid material; (5) Add lactose to the concentrated liquid material to form a pre-crystallized material, cool step by step and stir until crystallization, and finally cool and vacuum pack into cans.

[0018] In step (1), the mass ratio of skim milk powder, purified water and stabilizer is 30:50:0.002, and the stabilizer is guar gum.

[0019] In step (2), the preheating temperature is 60°C, the heating means heating to 90°C, the heating time is 5 s, and the rotation speed, temperature and time of the homogenization are 10000 r / min, 40°C and 10 min respectively.

[0020] In step (3), the mass ratio of sucrose to pure water is 50:100.

[0021] In step (4), the mass ratio of the sucrose solution to the atomized feed liquid is 52:100. The temperatures of the three-stage concentration tower from top to bottom are 40°C, 48°C, and 63°C respectively. The times for low-temperature vacuum concentration step by step from top to bottom are 5 min, 10 min, and 8 min respectively. The pressure for low-temperature vacuum concentration step by step from top to bottom is 0.025 MPa.

[0022] In step (5), the mass ratio of the concentrated feed liquid to lactose is 100:0.03, and the fineness of the lactose is 400 mesh.

[0023] In step (5), the step of gradually decreasing the temperature is specifically as follows: The pre-crystallization material is cooled at a rate of 8°C / min to 35°C, then cooled to 25°C and continuously stirred for 25 min, and finally cooled to 18°C and stirred until crystallization.

[0024] In step (5), the cooling temperature is 15°C. Example

[0025] A low-fat condensed milk process with atomization and low-temperature concentration. The low-fat condensed milk process specifically comprises the following steps: (1) Mix skim milk powder, pure water, and a stabilizer at room temperature and stir to obtain a feed liquid; (2) Preheat the feed liquid, then heat and sterilize it, and then put it into a homogenizer for homogenization to obtain an atomized feed liquid; (3) Mix sucrose and pure water to form a sucrose solution for standby; (4) Add the sucrose solution to the atomized feed liquid and mix at room temperature, then put it into a three-stage concentration tower. Each layer of the concentration tower is connected to a vacuum pump through a pipeline, and low-temperature vacuum concentration is carried out step by step from top to bottom by controlling the pipeline valves. The bottom-layer liquid collected is the concentrated feed liquid; (5) Add lactose to the concentrated feed liquid to form a pre-crystallization material, gradually decrease the temperature and stir until crystallization, and finally cool and vacuum-fill into cans.

[0026] In step (1), the mass ratio among skim milk powder, pure water, and the stabilizer is 35:55:0.0025, and the stabilizer is carrageenan.

[0027] In step (2), the preheating temperature is 65°C. The heating means heating to a temperature of 105°C, and the heating time is 6 s. The rotation speed, temperature, and time of the homogenization are 11000 r / min, 45°C, and 11 min respectively.

[0028] In step (3), the mass ratio of sucrose to pure water is 55:100.

[0029] In step (4), the mass ratio of the sucrose solution to the atomized feed liquid is 54:100. The temperatures of the three-stage concentration tower from top to bottom are 42 °C, 52 °C, and 64 °C respectively. The times for low-temperature vacuum concentration step by step from top to bottom are 6 min, 11 min, and 9 min respectively. The pressure for low-temperature vacuum concentration step by step from top to bottom is 0.035 MPa.

[0030] In step (5), the mass ratio of the concentrated feed liquid to lactose is 100:0.04, and the fineness of the lactose is 450 mesh.

[0031] In step (5), the step of gradually decreasing the temperature is specifically as follows: the precrystallized material is cooled at a rate of 9 °C / min to 35 °C, then cooled to 25 °C and continuously stirred for 27 min, and finally cooled to 19 °C and stirred until crystallization.

[0032] In step (5), the cooling temperature is 17 °C. Example

[0033] A low-fat condensed milk process with atomization and low-temperature concentration. The low-fat condensed milk process specifically comprises the following steps: (1) Mix skim milk powder, pure water, and a stabilizer at room temperature and stir to obtain a feed liquid; (2) Preheat the feed liquid, then heat and sterilize it, and then put it into a homogenizer for homogenization to obtain an atomized feed liquid; (3) Mix sucrose and pure water to form a sucrose solution for standby; (4) Add the sucrose solution to the atomized feed liquid and mix at room temperature, then put it into a three-stage concentration tower. Each layer of the concentration tower is connected to a vacuum pump through a pipeline, and low-temperature vacuum concentration is carried out step by step from top to bottom by controlling the pipeline valves. The bottom-layer liquid collected is the concentrated feed liquid; (5) Add lactose to the concentrated feed liquid to form a precrystallized material, gradually cool and stir until crystallization, and finally cool and vacuum pack into cans.

[0034] In step (1), the mass ratio among the skim milk powder, pure water, and the stabilizer is 40:60:0.003, and the stabilizer is guar gum.

[0035] In step (2), the preheating temperature is 70 °C. The heating means heating to 120 °C, and the heating time is 8 s. The rotation speed, temperature, and time of the homogenization are 12000 r / min, 50 °C, and 12 min respectively.

[0036] In step (3), the mass ratio of sucrose to pure water is 60:100.

[0037] In step (4), the mass ratio of the sucrose solution to the atomized feed liquid is 55:100. The temperatures of the three-stage concentration tower from top to bottom are 45°C, 55°C, and 65°C respectively. The times for low-temperature vacuum concentration step by step from top to bottom are 8 min, 12 min, and 10 min respectively. The pressure for low-temperature vacuum concentration step by step from top to bottom is 0.045 MPa.

[0038] In step (5), the mass ratio of the concentrated feed liquid to lactose is 100:0.05, and the fineness of the lactose is 500 mesh.

[0039] In step (5), the step of gradually decreasing the temperature is specifically as follows: the pre-crystallized material is cooled at a rate of 10°C / min to 36°C, then cooled to 26°C and continuously stirred for 30 min, and finally cooled to 20°C and stirred until crystallization.

[0040] In step (5), the cooling temperature is 18°C.

[0041] Comparative Example 1 Based on Example 2, a low-fat condensed milk process with atomization and low-temperature concentration, the specific steps of the low-fat condensed milk process are as follows: (1) Mix skim milk powder, pure water, and a stabilizer at room temperature and stir to obtain a feed liquid; (2) Preheat the feed liquid, then heat and sterilize it, and then put it into a homogenizer for homogenization to obtain an atomized feed liquid; (3) Mix sucrose and pure water to form a sucrose solution for standby; (4) Add the sucrose solution to the atomized feed liquid and mix at room temperature, and heat and sterilize it after vacuum concentration to obtain a concentrated feed liquid; (5) Add lactose to the concentrated feed liquid to form a pre-crystallized material, gradually cool and stir until crystallization, and finally cool and vacuum pack into cans.

[0042] In step (1), the mass ratio among the skim milk powder, pure water, and the stabilizer is 35:55:0.0025, and the stabilizer is carrageenan.

[0043] In step (2), the preheating temperature is 65°C. The heating means heating to 105°C, and the heating time is 6 s. The rotation speed, temperature, and time of the homogenization are 11000 r / min, 45°C, and 11 min respectively.

[0044] In step (3), the mass ratio of sucrose to pure water is 55:100.

[0045] In step (4), the mass ratio of the sucrose solution to the atomized feed liquid is 54:100. The temperature, time, and pressure of the vacuum concentration are 52°C, 26 min, and 0.035 MPa respectively. The temperature and time of the heat sterilization are 64°C and 9 min respectively.

[0046] In step (5), the mass ratio of the concentrated feed liquid to lactose is 100:0.04, and the fineness of the lactose is 450 mesh.

[0047] The specific steps of the step-by-step cooling in step (5) are as follows: the precrystallized material is cooled at a rate of 9°C / min to 35°C, then cooled to 25°C and continuously stirred for 27 min, and finally cooled to 19°C and stirred until crystallization.

[0048] The temperature of the cooling in step (5) is 17°C.

[0049] Comparative Example 2 Based on Example 2, a low-fat condensed milk process with atomization and low-temperature concentration, the specific steps of the low-fat condensed milk process are as follows: (1) Mix skim milk powder, purified water, and stabilizer at room temperature and stir to obtain a feed liquid; (2) Preheat the feed liquid, then heat and sterilize it, and then put it into a homogenizer for homogenization to obtain an atomized feed liquid; (3) Mix sucrose and purified water to form a sucrose solution for standby; (4) Add the sucrose solution to the atomized feed liquid and mix at room temperature, then put it into a secondary concentration tower. Each layer of the concentration tower is connected to a vacuum pump through a pipeline, and low-temperature vacuum concentration is carried out step by step from top to bottom by controlling the pipeline valves. The liquid collected at the bottom layer is the concentrated feed liquid; (5) Add lactose to the concentrated feed liquid to form a precrystallized material, cool step by step and stir until crystallization, and finally cool and vacuum can.

[0050] In step (1), the mass ratio among the skim milk powder, purified water, and stabilizer is 35:55:0.0025, and the stabilizer is carrageenan.

[0051] In step (2), the preheating temperature is 65°C, the heating means heating to 105°C, the heating time is 6 s, and the rotation speed, temperature, and time of the homogenization are 11000 r / min, 45°C, and 11 min respectively.

[0052] In step (3), the mass ratio of sucrose to purified water is 55:100.

[0053] In step (4), the mass ratio of the sucrose solution to the atomized feed liquid is 54:100. The temperatures of the secondary concentrator tower from top to bottom are 42 °C and 64 °C respectively. The times for low-temperature vacuum concentration step by step from top to bottom are 17 min and 9 min respectively. The pressure for low-temperature vacuum concentration step by step from top to bottom is 0.035 MPa.

[0054] In step (5), the mass ratio of the concentrated feed liquid to lactose is 100:0.04, and the fineness of the lactose is 450 mesh.

[0055] In step (5), the step of gradually decreasing the temperature is specifically as follows: the pre-crystallized material is cooled at a rate of 9 °C / min to 35 °C, then cooled to 25 °C and continuously stirred for 27 min, and finally cooled to 19 °C and stirred until crystallization.

[0056] In step (5), the cooling temperature is 17 °C.

[0057] Comparative Example 3 Based on Example 2, a low-fat condensed milk process with atomization and low-temperature concentration, the specific steps of the low-fat condensed milk process are as follows: (1) Mix skim milk powder, pure water and stabilizer at room temperature and stir to obtain a feed liquid; (2) Preheat the feed liquid, then heat and sterilize it, and then put it into a homogenizer for homogenization to obtain an atomized feed liquid; (3) Mix sucrose and pure water to form a sucrose solution for standby; (4) Add the sucrose solution to the atomized feed liquid and mix at room temperature, then put it into a three-stage concentrator tower. Each layer of the concentrator tower is connected to a vacuum pump through a pipeline, and low-temperature vacuum concentration is carried out step by step from top to bottom by controlling the pipeline valves. The bottom liquid collected is the concentrated feed liquid; (5) Add lactose to the concentrated feed liquid to form a pre-crystallized material, gradually cool and stir until crystallization, and finally cool and vacuum can.

[0058] In step (1), the mass ratio among skim milk powder, pure water and stabilizer is 35:55:0.0025, and the stabilizer is carrageenan.

[0059] In step (2), the preheating temperature is 65 °C, the heating means heating to 105 °C, the heating time is 6 s, and the rotation speed, temperature and time of the homogenization are 11000 r / min, 45 °C and 11 min respectively.

[0060] In step (3), the mass ratio of sucrose to pure water is 55:100.

[0061] In step (4), the mass ratio of the sucrose solution to the atomized feed liquid is 54:100. The temperatures of the three-stage concentration tower from top to bottom are 42 °C, 52 °C, and 60 °C respectively. The times for low-temperature vacuum concentration from top to bottom are 6 min, 11 min, and 9 min respectively. The pressure for low-temperature vacuum concentration from top to bottom is 0.035 MPa.

[0062] In step (5), the mass ratio of the concentrated feed liquid to lactose is 100:0.04, and the fineness of the lactose is 450 mesh.

[0063] In step (5), the step of gradually decreasing the temperature is specifically as follows: The precrystallized material is cooled at a rate of 9 °C / min to 35 °C, then cooled to 25 °C and continuously stirred for 27 min, and finally cooled to 19 °C and stirred until crystallization.

[0064] In step (5), the cooling temperature is 17 °C.

[0065] Comparative Example 4 On the basis of Example 2, the precrystallization cooling rate in step (5) is adjusted to 7 °C / min, and other conditions are the same as those in Example 2.

[0066] Comparative Example 5 On the basis of Example 2, the precrystallization cooling rate in step (5) is adjusted to 11 °C / min, and other conditions are the same as those in Example 2.

[0067] Comparative Example 6 On the basis of Example 2, a low-fat sweetened condensed milk process with atomization and low-temperature concentration is as follows: (1) Mix skim milk powder, purified water, and stabilizer at room temperature and stir to obtain a feed liquid; (2) Preheat the feed liquid, then heat and sterilize it, and then put it into a homogenizer for homogenization to obtain an atomized feed liquid; (3) Mix sucrose and purified water to form a sucrose solution for standby; (4) Add the sucrose solution to the atomized feed liquid and mix at room temperature, then put it into a three-stage concentration tower. Each layer of the concentration tower is connected to a vacuum pump through a pipeline, and low-temperature vacuum concentration is carried out step by step from top to bottom by controlling the pipeline valves. The bottom liquid collected is the concentrated feed liquid; (5) Add lactose to the concentrated feed liquid to form a precrystallized material, cool and stir it in a constant-temperature ice bath until crystallization, and finally cool and vacuum pack it into cans.

[0068] In step (1), the mass ratio among the skim milk powder, purified water, and stabilizer is 35:55:0.0025, and the stabilizer is carrageenan.

[0069] In step (2), the preheating temperature is 65°C. The heating means heating to 105°C, and the heating time is 6 s. The rotation speed, temperature, and time of homogenization are 11000 r / min, 45°C, and 11 min respectively.

[0070] In step (3), the mass ratio of sucrose to pure water is 55:100.

[0071] In step (4), the mass ratio of the sucrose solution to the atomized feed liquid is 54:100. The temperatures of the three-stage concentration tower from top to bottom are 42°C, 52°C, and 64°C respectively. The times for low-temperature vacuum concentration from top to bottom are 6 min, 11 min, and 9 min respectively. The pressure for low-temperature vacuum concentration from top to bottom is 0.035 MPa.

[0072] In step (5), the mass ratio of the concentrated feed liquid to lactose is 100:0.04, and the fineness of lactose is 450 mesh.

[0073] In step (5), the temperature reduction means reducing the temperature to 19°C and stirring until crystallization.

[0074] In step (5), the cooling temperature is 17°C, and other conditions are the same as those in Example 2.

[0075] Performance Test The low-fat condensed milk prepared in Examples 1-3 and Comparative Examples 1-2 was used as a sample. The sample was measured by the national standard test method. For fat ≥ 1.5%: determined by the method specified in GB13102-2010 National Food Safety Standard "Condensed Milk"; for protein ≥ 4.6%: determined by the method specified in GB13102-2010 National Food Safety Standard "Condensed Milk"; for total number of bacteria < 1×10 5 CFU / mL: determined by the total number of colonies in GB4789.2-2010 National Food Safety Standard "Food Microbiology Examination". At the same time, the protein content of the low-fat milk powder was detected, and the protein retention rate of the sample was calculated. The calculation formula is: protein retention rate % = protein content of the sample / protein content of the low-fat milk powder × 100%. In addition, the color change of the sample was observed for browning. The test results are shown in Table 1.

[0076] Table 1 Sample Fat % Protein % Total number of bacteria CFU / mL Retention rate % Whether browning occurs Example 1 1.22 30.59 <![CDATA[2.26×10 3 > 90.23 No Example 2 1.24 30.62 <![CDATA[2.24×10 3 > 90.31 No Example 3 1.22 30.56 <![CDATA[2.28×10 3 > 90.16 No Comparative example 1 1.21 24.48 <![CDATA[2.25×10 3 > 72.23 Yes Comparative example 2 1.24 30.05 <![CDATA[2.26×10 3 > 88.65 Yes Comparative example 3 1.23 30.53 <![CDATA[1.98×10 5 > 90.06 No Low-fat milk powder - 33.9 - - - From the result analysis of Table 1, it can be obtained that the various indicators of Examples 1-3 meet the requirements of national standards, and the retention rate of protein is above 90%. In Comparative Example 1, the vacuum concentration method is used, and heat sterilization needs to be carried out again, which increases the loss of protein and promotes the Maillard reaction to cause color browning; in Comparative Example 2, secondary concentration is used, and the omission of the concentration of the intermediate layer causes a temperature jump, resulting in a large amount of bubbles in the feed liquid. The whey protein is adsorbed at the gas-liquid interface, triggering the Maillard reaction to cause color browning and also consuming protein; in Comparative Example 3, the final concentration temperature of the tertiary concentration is reduced, and the sterilization effect cannot be achieved, resulting in the reproduction of bacteria, and the total number of bacteria exceeds the requirements of national standards.

[0077] Stability test: Take the low-fat condensed milk prepared in Examples 1-3 and Comparative Examples 4-6 in the last month of the shelf life as samples, and use a BT-2600 laser particle size analyzer to measure the particle size of the samples. In addition, observe the stable state of the samples, and the test results are shown in Table 2.

[0078] Table 2 Sample Particle size μm Stable state Example 1 8.01±0.1 Uniform and stable Example 2 7.98±0.1 Uniform and stable Example 3 8.03±0.1 Uniform and stable Comparative example 4 9.23±0.08 Slight delamination Comparative example 5 9.56±1.52 Precipitation and delamination Comparative example 6 10.52±0.63 Precipitation and delamination From the analysis of Table 2, it can be obtained that the particle sizes of Examples 1-3 are smaller than those of Comparative Examples 4-6, and the particle size distribution is uniform, and the sample state is uniform and stable. In Comparative Example 4, the rate of stepwise temperature reduction is reduced, and slow cooling allows the crystals to have a longer growth time, resulting in larger crystal sizes. Its particle size distribution is uniform, and there is slight stratification in the sample; in Comparative Example 5, the crystal particle sizes are different, and the particle size distribution range is large. Due to the too large cooling rate, rapid cooling produces an excessive amount of small crystals that are prone to agglomeration, resulting in obvious stratification; in Comparative Example 6, the feed liquid is directly cooled, and the crystals cannot be refined, resulting in obvious stratification in the sample.

[0079] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content within the scope of the technical solution of the present invention to make equivalent embodiments with equivalent changes. However, as long as it does not depart from the content of the technical solution of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A process for producing low-fat condensed milk by micronization and low-temperature concentration, characterized in that, The low-fat condensed milk process is as follows: (1) Mix skim milk powder, purified water, and stabilizer at room temperature and stir to obtain a liquid mixture; (2) Preheat the liquid mixture, then heat and sterilize it, and then put it into a homogenizer for homogenization to obtain a micronized liquid mixture; (3) Mix sucrose and purified water to form a sucrose solution for later use; (4) Add the sucrose solution to the micronized liquid mixture and mix at room temperature, then put it into a three-stage concentration tower. Each layer of the concentration tower is connected to a vacuum pump through a pipeline. Control the pipeline valves to perform low-temperature vacuum concentration step by step from top to bottom. Collect the bottom liquid as the concentrated liquid mixture; (5) Add lactose to the concentrated liquid mixture to form a pre-crystallized material, cool it step by step with stirring until crystallization, and finally cool and vacuum pack it into cans.

2. A process for producing low-fat condensed milk by micronization and low-temperature concentration according to claim 1, characterized in that, In step (1), the mass ratio of skim milk powder, purified water, and stabilizer is 30 - 40:50 - 60:0.002 - 0.003, and the stabilizer is guar gum or carrageenan.

3. A process for producing low-fat condensed milk by micronization and low-temperature concentration according to claim 1, characterized in that, In step (2), the preheating temperature is 60 - 70°C, the heating means heating to 90 - 120°C, the heating time is 5 - 8 s, and the rotation speed, temperature, and time of homogenization are 10000 - 12000 r / min, 40 - 50°C, and 10 - 12 min respectively.

4. A process for producing low-fat condensed milk by micronization and low-temperature concentration according to claim 1, characterized in that, In step (3), the mass ratio of sucrose to purified water is 50 - 60:

100.

5. A process for producing low-fat condensed milk by micronization and low-temperature concentration according to claim 1, characterized in that, In step (4), the mass ratio of the sucrose solution to the micronized liquid mixture is 52 - 55:

100. The temperatures of the three-stage concentration tower from top to bottom are 40 - 45°C, 48 - 55°C, and 63 - 65°C respectively. The times for low-temperature vacuum concentration step by step from top to bottom are 5 - 8 min, 10 - 12 min, and 8 - 10 min respectively. The pressure for low-temperature vacuum concentration step by step from top to bottom is 0.025 - 0.045 MPa.

6. A process for producing low-fat condensed milk by micronization and low-temperature concentration according to claim 1, characterized in that, In step (5), the mass ratio of the concentrated liquid mixture to lactose is 100:0.03 - 0.05, and the fineness of lactose is 400 - 500 mesh.

7. A process for producing low-fat condensed milk by micronization and low-temperature concentration according to claim 1, characterized in that, In step (5), the step of cooling step by step is specifically as follows: The pre-crystallized material is cooled at a rate of 8 - 10°C / min to 35 - 36°C, then cooled to 25 - 26°C and continuously stirred for 25 - 30 min, and finally cooled to 18 - 20°C and stirred until crystallization.

8. A process for producing low-fat condensed milk by micronization and low-temperature concentration according to claim 1, characterized in that, In step (5), the cooling temperature is 15 - 18°C.