Preparation method of low-GI lactose-free milk

Abstract

The invention provides a preparation method of low-GI lactose-free milk. The RO penetrating fluid obtained by the reverse osmosis technology is backfilled into the UF penetrating fluid, so that more salt ions in the UF penetrating fluid are eluted into a final product. The innovative process not only improves the natural nutritional value of the product, but also restores the original taste of the milk as much as possible. In addition, an INF (steam immersion sterilization) process is adopted, so that the taste of the cow milk is reserved to the maximum extent. Therefore, the milk powder is particularly suitable for patients with lactose intolerance, so that the patients can obtain richer nutrition and better taste experience while enjoying the delicious milk. In addition, the product is detected to belong to low-GI food, and people do not need to worry about increase of blood sugar when eating the product.

Description

Technical Field

[0001] The product belongs to the technical field of dairy processing, and specifically relates to a method for preparing low-GI lactose-free milk. Background Art

[0002] Lactose intolerance is a common digestive disease characterized by insufficient lactase activity, which results in insufficient breakdown of lactose in the small intestine. Lactose is then fermented by microorganisms in the large intestine, producing gas and other metabolites, triggering a series of digestive symptoms. As the global population grows, the prevalence of lactose intolerance is also rising, posing new challenges to the dairy industry. Although there are some low-lactose or lactose-free dairy products on the market, they often cannot compare with traditional milk in terms of taste and nutritional value.

[0003] Currently, lactose-free milk on the market is mainly prepared by two methods: membrane filtration technology and lactase hydrolysis technology. Membrane filtration technology removes lactose from milk by physical means, but this process is often accompanied by the loss of salt ions in the milk, resulting in a bland taste for the final product. On the other hand, lactase hydrolysis technology converts lactose into glucose and galactose by biocatalysis, but this method increases production costs, and because the hydrolysis of lactose increases the sweetness of milk, it may not meet the taste preferences of some consumers.

[0004] In the field of dairy processing, membrane technology plays a key role in the ultrafiltration process, which can remove lactose from milk, but it is also accompanied by a partial loss of salt ions. According to the description in WO Gazette 2010 / 023362, controlling the loss of salt ions is a key technical challenge to maintain the taste of lactose-free milk. One solution mentioned in WO Gazette 2003 / 094623 is to add milk mineral salts to lactose-free milk after membrane filtration to improve the taste of the product. These technical documents show that in current membrane technology applications, in order to compensate for the loss of taste caused by the loss of salt ions, it is usually necessary to add additional milk mineral salts.

[0005] In the domestic market, lactose-free milk is mainly produced by adding lactase, a process that breaks down lactose into glucose, thereby increasing the sweetness of milk. Although some lactases may produce oligosaccharides that do not increase sweetness during the hydrolysis process, this addition does not reduce the carbohydrate content in milk. Therefore, for consumers who prefer a low-carb diet, this lactose-free milk may not meet their needs. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing low GI lactose-free milk. The present invention efficiently recovers part of the salt ions lost in the ultrafiltration process of membrane technology, and backfills the RO permeate obtained by reverse osmosis (RO) technology into UF permeate, raw milk or NF retention liquid, thereby eluting more salt ions in the UF permeate into the final product, so as to retain the taste of lactose-free milk to the greatest extent.

[0007] The method for preparing low GI lactose-free milk provided by the present invention comprises the following steps:

[0008] 1) treating raw milk through an ultrafiltration (UF) membrane to obtain a UF permeate and a UF retentate; storing the UF retentate for later use;

[0009] 2) treating the UF permeate through a nanofiltration (NF) membrane to obtain a NF permeate and a NF retained solution; the NF retained solution is retained for later use;

[0010] 3) The NF permeate is concentrated by a reverse osmosis (RO) membrane according to a certain ratio to obtain RO concentrate and RO permeate;

[0011] 4) Mix the RO concentrate with the UF retained solution to obtain a standard solution;

[0012] 5) adding an appropriate amount of lactase to the standard solution to hydrolyze it to a lactose concentration of ≤0.5 g / 100 g to obtain lactose-free raw milk;

[0013] or 4') adding an appropriate amount of lactase to the UF retentate to hydrolyze the solution to a lactose concentration of ≤0.5 g / 100 g;

[0014] 5') mixing the hydrolyzed product with RO concentrate to obtain lactose-free raw milk;

[0015] wherein the RO permeate obtained in step 3) is recycled to the UF permeate obtained in step 1) to dilute the UF permeate; the diluted UF permeate is sequentially subjected to the processes of steps 2)-5) or steps 2)-5') to obtain lactose-free raw milk;

[0016] Or, the RO permeate obtained in step 3) is recycled into raw milk, and then the processes of steps 1) to 5) or steps 1) to 5') are sequentially performed to obtain lactose-free raw milk;

[0017] Alternatively, the RO permeate obtained in step 3) is recycled into the NF retained solution obtained in step 2), and together with the UF permeate obtained in step 1), the processes of steps 2)-5) or steps 2)-5') are sequentially performed to obtain lactose-free raw milk.

[0018] In step 1) of the above method, the raw milk may or may not be defatted, and may or may not be pasteurized; the protein content of the raw milk is 3.0-3.5%, and the ash content is 0.5-0.8%;

[0019] In step 1), the molecular weight cut-off range of the ultrafiltration (UF) membrane is 10,000 to 20,000 Daltons;

[0020] In step 2), the pore size of the nanofiltration (NF) membrane is 1 to 2 nm;

[0021] In step 3), the pore size of the reverse osmosis (RO) membrane is 0.1-0.2 nm; the concentration ratio is 1-3;

[0022] In step 4), the volume ratio of RO concentrate to UF retained solution is 0.25 to 1:1;

[0023] In step 5), based on the weight of the standard solution, the amount of lactase added is 0.02% to 0.06% of the weight of the standard solution (RO concentrate and UF retained solution), and the enzyme activity of lactase is 4000 to 5000 NLU;

[0024] In step 4'), based on the weight of the UF retentate, the amount of lactase added is 0.02-0.06%, and the enzyme activity of the lactase is 4000-5000 NLU;

[0025] In step 5'), the volume ratio of the hydrolysis product to the RO concentrate is 1:0.25-1;

[0026] In steps 5) and 5'), the hydrolysis temperature may be 40±5°C and the time may be 1 to 2 hours.

[0027] During reuse, the volume ratio of RO permeate to UF permeate is 0.25 to 2:1; specifically, it can be 0.25:1;

[0028] The volume ratio of RO permeate to raw milk during reuse is 0.25 to 2:1;

[0029] During reuse, the volume ratio of RO permeate to NF retained liquid is 0.25 to 2:1.

[0030] The above method further comprises, after step 5) or 5'), performing INF sterilization on the obtained lactose-free raw milk.

[0031] The INF sterilization comprises the following steps:

[0032] Preheating: The lactose-free raw milk obtained in step 5) or 5') is rapidly preheated by plate heating, the preheating temperature is 50-65° C., and the time (referring to the time kept at this preheating temperature) is 5-8 seconds;

[0033] Steam immersion sterilization and instant degassing cooling: the preheated raw milk is subjected to steam immersion sterilization at 135℃~155℃ for 0.09~0.2s (specifically, it can be regarded as 0.09s), and then pumped into the degassing system for degassing using a centrifugal pump. It is instantaneously degassed to 55~60℃ within 0.1s~0.2s and cooled for standby use;

[0034] Homogenization: The degassed sample is homogenized under sterile conditions at a temperature of 55-60°C;

[0035] The homogenized sample is aseptically filled at 4-10°C to obtain the finished lactose-free milk.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] The present invention adopts a unique process step, that is, the RO permeate obtained by reverse osmosis (RO) technology is backfilled into the UF permeate, so that more salt ions in the UF permeate are eluted into the final product. This innovative process not only improves the natural nutritional value of the product, but also restores the original taste of milk as much as possible. In addition, the INF (steam immersion sterilization) process is adopted to retain the taste of cow's milk to the maximum extent. Therefore, the present invention is particularly suitable for patients with lactose intolerance, so that they can enjoy the delicious milk while obtaining richer nutrition and better taste experience. In addition, the product of the present invention has been tested and is a low GI food, and there is no need to worry about blood sugar increasing when eating this product.

[0038] The present invention combines membrane filtration technology and lactase technology to produce lactose-free milk. This invention not only combines the advantages of the two technologies, but also effectively recovers the salt ions lost in the membrane filtration process through a unique process method, and reduces the sweetness increased by lactose hydrolysis while reducing carbon water. These innovations make the taste of lactose-free milk closer to pure milk, providing a healthy and delicious alternative for patients with lactose intolerance. In addition, this product has also been certified as a low-GI food. While using lactase to hydrolyze lactose, the glycemic index does not increase, and it is also suitable for people with high blood sugar. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The process flow chart of the present invention is shown in Figure 1. A is a process flow chart for preparing zero-lactose milk by adding lactase to UF retained solution for hydrolysis, and B is a process flow chart for preparing zero-lactose milk by adding lactase to RO concentrated solution and UF retained solution for hydrolysis.

[0040] Figure 2 This is the process flow chart of Comparative Example 1.

[0041] Figure 3This is the process flow chart of Comparative Example 2.

[0042] Figure 4 This is the process flow chart of Comparative Example 3. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below in conjunction with specific embodiments, and the examples provided are only for illustrating the present invention, rather than for limiting the scope of the present invention. The examples provided below can be used as a guide for further improvements by those of ordinary skill in the art, and do not constitute a limitation of the present invention in any way.

[0044] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels.

[0045] Example 1

[0046] The protein content of the raw milk in this example is 3.22%, and the ash content is 0.67%. In the process of producing the finished milk product, the amount of lactase added is 0.03% of the weight of the standard solution, the enzyme activity is ≥4000 NLU, the hydrolysis time is 90 min, and the hydrolysis temperature is 40±5°C.

[0047] according to Figure 1 The process flow chart shown in B is operated as follows: the raw milk is pasteurized and passed through a UF membrane (molecular weight cutoff 20,000 Daltons), the RO permeate is mixed and diluted with the UF permeate, the dilution ratio is 1:1, the dilution passes through a NF membrane (pore size 2nm), and the NF permeate passes through a RO membrane (pore size 0.2nm) to obtain a RO concentrate. The RO concentrate, UF retained liquid and lactase are mixed and hydrolyzed to obtain raw milk with a protein content of 3.4% and a lactose content of less than 0.5g / 100g. The raw milk is sterilized by INF to obtain lactose-free milk.

[0048] Comparative Example 1

[0049] This comparative example provides a lactose-free process (Method for producing lactose-free milk, H.H. Horst, K. Lauridsen, WO2009 / 043356).

[0050] Step 1, whole fat raw milk (protein content of 3.31%, ash content of 0.66%) passes through an ultrafiltration (UF) membrane (molecular weight cutoff of 20,000 Daltons) to obtain UF permeate and UF retentate; the UF retentate is stored for later use.

[0051] Step 2, passing the UF permeate in step 1 through a nanofiltration (NF) membrane (pore size of 2 nm) to obtain NF permeate and NF retained liquid; the NF permeate is retained for later use.

[0052] Step 3, mixing the UF retentate in step 1 and the NF permeate in step 2 to obtain a standard solution from which part of the lactose has been removed. At this time, the lactose content of the standard solution is 3.00 g / 100 g.

[0053] Step 4, adding 0.03% by weight of the standard solution and lactase with an enzyme activity of ≥4000 NLU to hydrolyze the residual lactose to a lactose concentration of ≤0.5 g / 100 g, thereby obtaining lactose-free raw milk.

[0054] Step 5: The lactose-free raw milk is standardized to a protein content of 3.40%.

[0055] Step 6, the lactose-free raw milk is sterilized by INF to obtain lactose-free milk.

[0056] Figure 2 It is the process flow chart of comparative example 1.

[0057] Comparative Example 2

[0058] Production and separation of milk fractions using forward osmosis, Shaken O. Ureman, Timothy P. Delman, Michael J. McCloskey, WO2020 / 009804.

[0059] Step 1: skim raw milk (protein content of 3.31%, ash content of 0.67%) to obtain skim milk and cream, and the cream is retained for later use.

[0060] Step 2: The skimmed milk in step 1 is passed through an ultrafiltration (UF) membrane (molecular weight cut-off of 20,000 Daltons) to obtain a UF permeate and a UF retentate; the UF retentate is stored for later use.

[0061] Step 3, the UF permeate in step 2 is treated through a nanofiltration (NF) membrane (pore size of 2 nm) to separate the permeate and the retained liquid; the NF permeate is retained for later use.

[0062] Step 4, mixing the cream in step 1, the NF permeate in step 3 and the UF retentate in step 2 to obtain a standard solution from which part of the lactose has been removed, wherein the lactose content of the standard solution is 3.22 g / 100 g.

[0063] Step 5, adding 0.03% by weight of the standard solution and lactase with an enzyme activity of ≥4000 NLU to hydrolyze the residual lactose.

[0064] Step 6: Standardize the lactose-free raw milk to a protein content of 3.4%.

[0065] Step 7, the lactose-free raw milk is subjected to INF sterilization to obtain lactose-free milk.

[0066] Figure 3 It is the process flow chart of comparative example 2.

[0067] Comparative Example 3

[0068] Method for producing lactose-free dairy products, O. Tossiain, J. Sachstein, WO 2003 / 094623.

[0069] Step 1: Raw milk (with a protein content of 3.28% and an ash content of 0.64%) passes through an ultrafiltration (UF) membrane to obtain a UF permeate and a UF retentate; the UF retentate is stored for later use.

[0070] Step 2: passing the UF permeate in step 1 through a nanofiltration (NF) membrane to obtain a NF permeate and a NF retentate.

[0071] Step 3, passing the NF permeate in step 2 through a reverse osmosis (RO) membrane to obtain RO permeate and RO concentrate.

[0072] Step 4: Mix the RO concentrate with the UF retentate to obtain a standard solution from which part of the lactose has been removed.

[0073] Step 5, adding 0.03% by weight of the standard solution and lactase with an enzyme activity of ≥4000 NLU to hydrolyze the residual lactose.

[0074] Step 6: Add 18% water by weight of the standard solution to the lactose-free raw milk to standardize the protein content to 3.4%.

[0075] Step 7, the lactose-free raw milk is subjected to INF sterilization to obtain lactose-free milk.

[0076] Figure 4 It is the process flow chart of comparative example 3.

[0077] Table 1: Ash recovery of lactose-free milk

[0078]

[0079] Table 1 shows the ash recovery of each comparative example and Example 1. The results show that the ash recovery rate of the present invention is the highest, close to 90%. The present invention has made a significant breakthrough in this field.

[0080] Table 2: Sensory comparison of lactose-free milk in comparative example

[0081]

[0082] The results in Table 2 show that the present invention has the highest score in terms of overall preference, and also has the highest scores in terms of milk aroma, milk sweetness and thickness. After the ash recovery rate is improved, the taste of lactose-free milk is also improved.

[0083] Example 2

[0084] In this embodiment, the protein content of the raw milk is 3.27%, and the ash content is 0.65%. In the process of producing the finished milk product, the amount of lactase added is 0.03% of the weight of the standard solution, the hydrolysis time is 90 minutes, and the hydrolysis temperature is 40±5°C.

[0085] according to Figure 1 The process flow chart shown in B is operated as follows: the raw milk is passed through a UF membrane (molecular weight cutoff of 20,000 Daltons), the RO permeate is mixed and diluted with the UF permeate, the dilution ratio is 0.25:1, the dilution is passed through a NF membrane (pore size of 2nm), and the NF permeate is passed through a RO membrane (pore size of 0.2nm) to obtain a RO concentrate. The RO concentrate, the UF retained liquid and lactase are mixed and hydrolyzed to obtain raw milk with a protein content of 3.4% and a lactose content of less than 0.5g / 100g. The raw milk is sterilized by INF to obtain lactose-free milk.

[0086] This embodiment changes the dilution ratio of the RO permeate to the UF permeate in Embodiment 1.

[0087] Example 3

[0088] In this example, the protein content of the raw milk is 3.21%, and the ash content is 0.63%. In the process of producing the finished milk product, the amount of lactase added is 0.03% of the weight of the standard solution, the hydrolysis time is 90 minutes, and the hydrolysis temperature is 40±5°C.

[0089] according to Figure 1 The process flow chart shown in B is operated as follows: the raw milk is passed through a UF membrane (molecular weight cutoff of 20,000 Daltons), the RO permeate is mixed and diluted with the UF permeate, the dilution ratio is 0.5:1, the dilution is passed through a NF membrane (pore size of 2nm), and the NF permeate is passed through a RO membrane (pore size of 0.2nm) to obtain a RO concentrate. The RO concentrate, UF retentate and lactase are mixed and hydrolyzed to obtain raw milk with a protein content of 3.4% and a lactose content of less than 0.5g / 100g. The raw milk is sterilized by INF to obtain lactose-free milk.

[0090] This embodiment changes the dilution ratio of the RO permeate to the UF permeate in Embodiment 1.

[0091] Example 4

[0092] In this embodiment, the protein content of the raw milk is 3.27%, and the ash content is 0.65%. In the process of producing the finished milk product, the amount of lactase added is 0.03% of the weight of the standard solution, the hydrolysis time is 90 minutes, and the hydrolysis temperature is 40±5°C.

[0093] according to Figure 1 The process flow chart shown in B is operated as follows: the raw milk is passed through a UF membrane (molecular weight cutoff of 20,000 Daltons), the RO permeate is mixed and diluted with the UF permeate, the dilution ratio is 0.75:1, the dilution is passed through a NF membrane (pore size of 2nm), and the NF permeate is passed through a RO membrane (pore size of 0.2nm) to obtain a RO concentrate. The RO concentrate, the UF retentate and lactase are mixed and hydrolyzed to obtain raw milk with a protein content of 3.4% and a lactose content of less than 0.5g / 100g. The raw milk is sterilized by INF to obtain lactose-free milk.

[0094] This embodiment changes the dilution ratio of the RO permeate to the UF permeate in Embodiment 1.

[0095] Example 5

[0096] In this embodiment, the protein content of the raw milk is 3.28%, and the ash content is 0.59%. In the process of producing the finished milk product, the amount of lactase added is 0.03% of the weight of the standard solution, the hydrolysis time is 90 minutes, and the hydrolysis temperature is 40±5°C.

[0097] according to Figure 1 The process flow chart shown in B is operated as follows: the raw milk is passed through a UF membrane (molecular weight cutoff of 20,000 Daltons), the RO permeate is mixed and diluted with the UF permeate, the dilution ratio is 2:1, the dilution is passed through a NF membrane (pore size of 2nm), and the NF permeate is passed through a RO membrane (pore size of 0.2nm) to obtain a RO concentrate. The RO concentrate, the UF retentate and lactase are mixed and hydrolyzed to obtain raw milk with a protein content of 3.4% and a lactose content of less than 0.5g / 100g. The raw milk is sterilized by INF to obtain lactose-free milk.

[0098] This example changes the dilution ratio of the RO permeate to the UF permeate in Example 1.

[0099] Example 6

[0100] In this embodiment, the protein content of the raw milk is 3.25%, and the ash content is 0.60%. In the process of producing the finished milk product, the amount of lactase added is 0.03% of the weight of the standard solution (RO concentrate and UF retained solution), the hydrolysis time is 90 minutes, and the hydrolysis temperature is 40±5°C.

[0101] according to Figure 1The process flow chart shown in B is operated as follows: raw milk is passed through the UF membrane, the UF permeate is passed through the NF membrane (molecular weight cutoff is 20,000 Daltons), the RO permeate is mixed and diluted with the NF retained liquid, the dilution ratio is 1:1, the dilution is passed through the NF membrane (pore size is 2nm) again, and the NF permeate is passed through the RO membrane (pore size is 0.2nm) to obtain RO concentrate. The RO concentrate, UF retained liquid and lactase are mixed and hydrolyzed to obtain raw milk with a protein content of 3.4% and a lactose content of less than 0.5g / 100g. The raw milk is sterilized by INF to obtain lactose-free milk.

[0102] This embodiment changes the dilution process of the RO permeate in Embodiment 1.

[0103] Example 7

[0104] The protein content of the raw milk in this embodiment is 3.28%, and the ash content is 0.65%. In the process of producing the finished milk product, the amount of lactase added is 0.03% of the weight of the standard solution (RO concentrate and UF retained solution), the hydrolysis time is 90 minutes, and the hydrolysis temperature is 40±5°C.

[0105] according to Figure 1 The process flow chart shown in B is operated as follows: before the raw milk passes through the UF membrane (molecular weight cutoff is 20,000 Daltons), it is mixed and diluted with the RO permeate at a dilution ratio of 1:1. The UF permeate passes through the NF membrane (pore size is 2nm), and the NF permeate passes through the RO membrane (pore size is 0.2nm) to obtain the RO concentrate. The RO concentrate, the UF retentate and lactase are mixed and hydrolyzed to obtain raw milk with a protein content of 3.4% and a lactose content of less than 0.5g / 100g. The raw milk is sterilized by INF to obtain lactose-free milk.

[0106] This embodiment changes the dilution process of the RO permeate in Embodiment 1.

[0107] Example 8

[0108] The protein content of the raw milk in this embodiment is 3.22%, and the ash content is 0.67%. In the process of producing the finished milk product, the amount of lactase added is 0.06% of the weight of the UF retained liquid, the enzyme activity is ≥4000 NLU, the hydrolysis time is 90 minutes, and the hydrolysis temperature is 40±5°C.

[0109] according to Figure 1The process flow chart shown in A is operated as follows: the raw milk is pasteurized and passed through a UF membrane (molecular weight cutoff 20,000 Daltons), the UF retained solution is mixed with lactase for hydrolysis to obtain concentrated milk with a lactose content of less than 0.5g / 100g, the RO permeate is mixed and diluted with the UF permeate, the dilution ratio is 1:1, the dilution passes through a NF membrane (pore size 2nm), and the NF permeate passes through a RO membrane (pore size 0.2nm) to obtain a RO concentrate. The RO concentrate is mixed with the concentrated milk to obtain a raw milk with a protein content of 3.4% and a lactose content of less than 0.5g / 100g. The raw milk is sterilized by INF to obtain lactose-free milk.

[0110] This example changes the lactase addition process in Example 1.

[0111] Table 3: Ash recovery and salt ion concentration of lactose-free milk

[0112]

[0113]

[0114] Table 3 shows the ash recovery and salt ion concentration of each embodiment. According to the results, the ash recovery rates of embodiment 1 and embodiment 5 both reached more than 90%, which is higher than the other 5 embodiments. The RO permeate dilution in embodiment 5 is twice that in embodiment 1, but the ash recovery rates of the two are basically the same, which shows that the dilution ratio in embodiment 1 is the optimal dilution ratio.

[0115] Table 4: Sensory comparison of lactose-free milk in various embodiments

[0116]

[0117] Table 4 shows the sensory scores of lactose-free milk in various embodiments. According to the results, when the ash recovery rate of embodiments 1, 5, 6, and 7 reaches 85% or more, the overall preference score is above 7.00. Therefore, in the present invention, when the ash recovery rate reaches 85% or more, the taste of lactose-free milk will be significantly improved.

[0118] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, and without the need to carry out unnecessary experimental conditions, the present invention can be implemented in a wide range under equivalent parameters, concentrations and conditions. Although the present invention provides specific embodiments, it should be understood that the present invention can be further improved. In a word, according to the principles of the present invention, the application is intended to include any changes, uses or improvements to the present invention, including departure from the disclosed scope in the application, and changes made with conventional techniques known in the art.

Claims

1. A method for preparing low GI lactose-free milk, comprising the following steps: 1) treating raw milk through an ultrafiltration (UF) membrane to obtain a UF permeate and a UF retentate; storing the UF retentate for later use; 2) treating the UF permeate through a nanofiltration (NF) membrane to obtain a NF permeate and a NF retentate; The NF retention solution is retained for later use; 3) The NF permeate is concentrated by a reverse osmosis (RO) membrane according to a certain ratio to obtain RO concentrate and RO permeate; 4) Mix the RO concentrate with the UF retained solution to obtain a standard solution; 5) adding an appropriate amount of lactase to the standard solution to hydrolyze it to a lactose concentration of ≤0.5 g / 100 g to obtain lactose-free raw milk; or 4') adding an appropriate amount of lactase to the UF retentate to hydrolyze the solution to a lactose concentration of ≤0.5 g / 100 g; 5') mixing the hydrolyzed product with RO concentrate to obtain lactose-free raw milk; The RO permeate obtained in step 3) is recycled to the UF permeate obtained in step 1) to dilute the UF permeate; the diluted UF permeate is sequentially subjected to the processes of steps 2)-5) or steps 2)-5') to obtain lactose-free raw milk.

2. The method according to claim 1, characterized in that: The RO permeate obtained in step 3) is recycled into raw milk, and then the processes of steps 1) to 5) or steps 1) to 5') are sequentially performed to obtain lactose-free raw milk.

3. The method according to claim 1, characterized in that: The RO permeate obtained in step 3) is recycled into the NF retained solution obtained in step 2), and together with the UF permeate obtained in step 1), the processes of steps 2)-5) or steps 2)-5') are sequentially performed to obtain lactose-free raw milk.

4. The method according to claim 1, characterized in that: In step 1), the raw milk may or may not be defatted, and may or may not be pasteurized; the protein content of the raw milk is 3.0-3.5%, and the ash content is 0.5-0.8%.

5. The method according to claim 1, characterized in that: In step 1), the molecular weight cut-off range of the ultrafiltration (UF) membrane is 10,000 to 20,000 Daltons; In step 2), the pore size of the nanofiltration (NF) membrane is 1 to 2 nm; In step 3), the pore size of the reverse osmosis (RO) membrane is 0.1-0.2 nm; the concentration ratio is 1-3; In step 4), the volume ratio of the RO concentrate to the UF retained solution is 0.25 to 1:

1.

6. The method according to claim 1, characterized in that: In step 5), based on the weight of the standard solution, the amount of lactase added is 0.02% to 0.06% of the weight of the standard solution (RO concentrate and UF retained solution), and the enzyme activity of lactase is 4000 to 5000 NLU.

7. The method according to claim 1, characterized in that: In step 4'), based on the weight of the UF retentate, the amount of lactase added is 0.02-0.06%, and the enzyme activity of the lactase is 4000-5000 NLU.

8. The method according to claim 1, characterized in that: In step 5'), the volume ratio of the hydrolysis product to the RO concentrate is 1:0.25-1; In steps 5) and 5'), the hydrolysis temperature is 40±5°C and the time is 1 to 2 hours.

9. The method according to any one of claims 1 to 3, characterized in that: During reuse, the volume ratio of RO permeate to UF permeate is 0.25 to 2:1; The volume ratio of RO permeate to raw milk during reuse is 0.25 to 2:1; During reuse, the volume ratio of RO permeate to NF retained liquid is 0.25 to 2:

1.

10. Low GI lactose-free milk prepared by the method according to any one of claims 1 to 9.

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