High-protein lactose-free milk rich in native dietary fibers and preparation method of high-protein lactose-free milk

Abstract

The invention relates to the technical field of dairy product processing, in particular to high-protein native-dietary-fiber-rich zero-lactose milk and a preparation method thereof.The method comprises the following steps that 1, raw milk is treated through a reverse osmosis membrane, and RO penetrating fluid and RO retention fluid are obtained; 2) adding a proper amount of No.1 lactase into the RO retention solution, and hydrolyzing until the lactose concentration is less than or equal to 2g / 100mL and the galactooligosaccharide concentration is more than or equal to 3g / 100mL; 3) pasteurizing the hydrolyzed product, and inactivating the No.1 lactase to obtain a semi-finished product milk liquid containing the native dietary fibers; and 4) adding a proper amount of No.2 lactase into the semi-finished product milk liquid, and hydrolyzing until the lactose concentration is less than 0.5 g / 100mL to obtain the high-protein raw milk rich in native dietary fiber and zero in lactose. According to the method, lactase is subjected to enzymolysis on the premise that the sweetness of milk is not improved, galactooligosaccharide (dietary fiber) is generated in a natural enzymolysis mode, and the natural nutritional value of the product is improved.

Description

Technical Field

[0001] This invention relates to the field of dairy processing technology, specifically to a high-protein, lactose-free milk rich in native dietary fiber and its preparation method. Background Technology

[0002] Lactose intolerance, a widespread digestive disorder, is pathologically based on a deficiency or low activity of endogenous lactase in the small intestine, resulting in the incomplete hydrolysis of ingested lactose. Undigested lactose enters the colon and undergoes microbial fermentation, producing metabolites such as hydrogen and short-chain fatty acids, which in turn trigger a series of gastrointestinal symptoms including bloating, abdominal pain, and diarrhea. With the continued growth in global dairy consumption and the increasing genetic diversity of the population, the epidemiological incidence of this condition is showing a significant upward trend, posing new technological challenges to the dairy industry.

[0003] Currently, commercially available low-lactose / lactose-free dairy products mainly rely on two technological approaches: membrane separation technology and enzymatic hydrolysis technology. Membrane separation technology selectively removes lactose through ultrafiltration or nanofiltration, but inevitably results in the loss of inorganic salts (especially calcium and magnesium ions), leading to a disruption of the product's mineral balance and a weakening of its flavor characteristics, resulting in a thin texture and insufficient taste. Enzymatic hydrolysis technology uses β-galactosidase to catalyze the breakdown of lactose into glucose and galactose. While this addresses tolerance issues, it presents taste defects: the enzymatic hydrolysis process significantly increases the reducing sugar content (sweetness increases by 30-40%), altering the flavor profile and causing the final product to deviate from consumers' expectations of traditional milk flavor.

[0004] CN105010539A discloses a method for producing lactose-free milk, including ultrafiltration, nanofiltration, and hydrolysis of raw milk. This method results in the loss of a large amount of lactose and some milk mineral salts, disrupting the natural nutritional balance. CN1287673C discloses a method for preparing lactose-free dairy products, which involves concentrating the dairy product through ultrafiltration, nanofiltration, and reverse osmosis, and adding whey salt to the UF retentate. This method compensates for the loss of milk mineral salts during the production process by adding these salts. However, the ingredient list must include the whey salt in addition to raw milk and lactase. Furthermore, this process leads to lactose loss during production, reducing the product's solids content.

[0005] CN117256674A discloses a method for preparing lactose-free modified milk obtained through reverse osmosis concentration, sterilization, ingredient mixing, enzymatic hydrolysis, and high-temperature sterilization. CN113632836A discloses a method for preparing lactose-free pasteurized milk obtained through low-temperature / high-temperature enzymatic hydrolysis followed by pasteurization. Products prepared using these two methods show a significant increase in sweetness, which does not meet consumers' expectations for the flavor of traditional cow's milk. CN116158463A discloses a method for preparing lactose-free milk containing galactooligosaccharides. However, the product prepared by this method contains only 1.5% galactooligosaccharides, making it impossible to claim high dietary fiber content. Furthermore, this method requires a high initial lactose content in the milk; when the initial lactose content is ≥5.3%, this method cannot produce lactose-free milk. Summary of the Invention

[0006] To address the tolerance issues caused by lactose enrichment in high-protein milk, and in order to increase the content of natural dietary fiber (calculated as galactooligosaccharides) in the product, this invention provides a high-protein, lactose-free milk rich in native dietary fiber and its preparation method.

[0007] In existing technologies, milk containing galactooligosaccharides (GOS) is mostly prepared by directly adding GOS. This invention, however, uses a specific lactase to catalyze the hydrolysis of lactose in milk under mild conditions (producing galactose and glucose), and utilizes its transgalactosidase activity to transfer galactose groups to other lactose molecules, thereby synthesizing GOS in situ within the system. This enzyme is highly specific, acting only on lactose, and has no effect on the core nutrients in milk, such as fat, protein, vitamins, and minerals.

[0008] Specifically, the present invention provides the following technical solution: A method for preparing high-protein, lactose-free milk rich in native dietary fiber includes the following steps: 1) Raw milk, whether or not it has undergone defatting and standardization treatment, is pasteurized and then processed through a reverse osmosis membrane system to obtain RO permeate and RO retention solution; the RO retention solution is high-protein raw milk. 2) Add an appropriate amount of lactase No. 1 to the high-protein raw milk to hydrolyze until the lactose concentration is ≤2g / 100mL and the galactooligosaccharide concentration is ≥3g / 100mL; the lactase No. 1 is NOLA from Kerry Company. ® GOS lactase; 3) Pasteurize the hydrolyzed product to inactivate lactase No. 1, and obtain a semi-finished milk containing native dietary fiber. 4) Add an appropriate amount of lactase No. 2 to the semi-finished milk liquid to hydrolyze until the lactose concentration is <0.5g / 100mL to obtain high-protein, high-fiber, lactose-free raw milk; the lactase No. 2 is KERRY's Ha-Lactase™ 5200 lactase.

[0009] In step 1), the raw milk is either skimmed or not, and pasteurized or not; the protein content of the raw milk is 3.0-3.5%, and the lactose content is 4.2-5.2%. The pore size of the reverse osmosis membrane is 0.1-0.2 nm, and the concentration ratio is 1.5-3.

[0010] In step 2), the amount of lactase No. 1 added is 0.1-0.6% of the weight of the high-protein raw milk, and the enzyme activity of lactase No. 1 is ≥5500 NLU / g.

[0011] In step 3), the pasteurization temperature range is 72-85℃, and the pasteurization time is 12-18s.

[0012] In step 4), the amount of lactase No. 2 added is 0.02-0.06% of the weight of the semi-finished milk containing native dietary fiber, and the enzyme activity of lactase No. 2 is ≥4800 NLU / g.

[0013] Furthermore, it also includes an INF sterilization step on the obtained high-protein, native dietary fiber, lactose-free raw milk.

[0014] The INF sterilization process includes the following steps: ① Preheating: The high-protein, fiber-rich, lactose-free raw milk is heated to 65-75℃ via plate heat exchanger; ② Steam immersion sterilization and degassing and cooling: After preheating, the raw milk is sterilized by steam immersion and then enters the degassing system by centrifugal pump for degassing and cooling; the steam immersion sterilization is 140~155℃ for 2-5 seconds. ③ Homogenization: After degassing and cooling, the product enters a sterile homogenizer. The homogenization temperature is 60-75℃ and the total homogenization pressure is 200-250 bar. ④ Filling: Cool the homogenized product to below 20℃ and fill it to obtain a high-protein, dietary fiber-rich, lactose-free milk product.

[0015] The high-protein, lactose-rich, lactose-free milk prepared by the above-described preparation method of the present invention has a lactose content of more than 3.0% based on the content of galactooligosaccharides and less than 0.5%.

[0016] This invention utilizes a specific lactase combined with dual-temperature gradient enzymatic hydrolysis to precisely control the hydrolysis time and temperature. This process hydrolyzes lactose into glucose and galactooligosaccharides in the final product without enhancing its sensory sweetness. This innovative process not only hydrolyzes lactose without increasing the milk's sweetness but also generates galactooligosaccharides (dietary fiber) through natural enzymatic hydrolysis, thus improving the product's natural nutritional value. Furthermore, the steam immersion sterilization process, through direct contact heat transfer that breaks through the conductive boundary layer, improves heat conduction efficiency and minimizes the impact of heat damage on the milk's flavor. Therefore, the high-protein, naturally occurring dietary fiber-rich, lactose-free milk prepared using this method is particularly suitable for individuals with lactose intolerance who have an extreme need for the taste and nutritional content of dairy products.

[0017] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention improves the native protein in milk by reverse osmosis, and then uses a specific novel lactase to hydrolyze lactose into glucose and galactooligosaccharides. With only the addition of lactase, the final product can contain 6.0g / 100mL of protein, ≥3g / 100mL of dietary fiber (calculated as galactooligosaccharides), and less than 0.5g / 100mL of lactose, thus obtaining a lactose-free milk that can be claimed to be high in protein and rich in native dietary fiber.

[0018] (2) This invention overcomes the reversible reaction of novel lactases through a specific dual-temperature zone enzymatic hydrolysis technology, while ensuring that the lactose content in the final product is below 0.5%. Simultaneously, this invention uses a specific lactase to break down lactose in milk into galactose and glucose. While hydrolyzing lactose molecules, the lactase provided by this invention transfers galactose molecules to another lactose molecule, extending the molecular length to form galactooligosaccharides (GOS). The formed galactooligosaccharides are a type of dietary fiber, enhancing the nutritional value of milk without the need for additional dietary fiber.

[0019] (3) This invention utilizes the properties of a novel lactase to promote the recombination of lactose and galactose to form galactooligosaccharides, rather than completely hydrolyzing them into glucose and galactose. Because the content of glucose and galactose in the final product is significantly reduced, the lactose-free product made by this invention has a lower sweetness compared to traditional lactose-free products made using ordinary lactase. Simultaneously, the low glucose content effectively inhibits browning, significantly improving the shelf-life stability of lactose-free milk containing galactooligosaccharides, without affecting other nutritional components. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation process of the high-protein, fiber-rich, lactose-free milk of this invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The lactase No. 1 used in this invention is NOLA from Kerry Corporation. ® GOS lactase; lactase No. 2 is Kerry's Ha-Lactase™ 5200 lactase, both of which are commercially available.

[0023] A method for preparing high-protein, lactose-free milk rich in native dietary fiber, specifically as follows: Includes the following steps: 1) Raw milk, whether or not it has undergone defatting and standardization treatment, is pasteurized and then processed through a reverse osmosis membrane system to obtain RO permeate and RO retentate; the RO retentate is high-protein raw milk; wherein the raw milk is defatted or not, and pasteurized or not; the protein content of the raw milk is 3.0-3.5%, and the lactose content is 4.2-5.2%. The pore size of the reverse osmosis membrane is 0.1~0.2nm, and the concentration ratio is 1.5~3.

[0024] 2) Add an appropriate amount of lactase No. 1 to the high-protein raw milk to hydrolyze until the lactose concentration is ≤2g / 100mL and the galactooligosaccharide concentration is ≥3g / 100mL; the lactase No. 1 is NOLA from Kerry Company. ® GOS lactase; the addition amount of lactase No. 1 is 0.1-0.6% of the weight of high-protein raw milk, and the enzyme activity of lactase No. 1 is ≥5500 NLU / g.

[0025] 3) The hydrolyzed product is pasteurized to inactivate lactase No. 1, resulting in a semi-finished milk containing native dietary fiber; the pasteurization temperature range is 72-85℃, and the pasteurization time is 12-18s.

[0026] 4) Add an appropriate amount of lactase No. 2 to the semi-finished milk liquid to hydrolyze until the lactose concentration is <0.5g / 100mL, to obtain high-protein, lactose-free raw milk rich in native dietary fiber; the lactase No. 2 is Ha-Lactase™ 5200 lactase from Kerry Corporation. The amount of lactase No. 2 added is 0.02-0.06% of the weight of the semi-finished milk liquid containing native dietary fiber, and the enzyme activity of lactase No. 2 is ≥4800 NLU / g.

[0027] 5) INF sterilization ① Preheating: The high-protein, fiber-rich, lactose-free raw milk is heated to 65-75℃ via plate heat exchanger; ② Steam immersion sterilization and degassing and cooling: After preheating, the raw milk is sterilized by steam immersion and then enters the degassing system by centrifugal pump for degassing and cooling; the steam immersion sterilization is 140~155℃ for 2-5 seconds. ③ Homogenization: After degassing and cooling, the product enters a sterile homogenizer. The homogenization temperature is 60-75℃ and the total homogenization pressure is 200-250 bar. ④ Filling: Cool the homogenized product to below 20℃ and fill it to obtain a high-protein, dietary fiber-rich, lactose-free milk product.

[0028] Example 1 A method for preparing high-protein, lactose-free milk rich in native dietary fiber, specifically as follows: In this embodiment, the protein content of the raw milk is 3.32% and the lactose content is 4.82%. During the milk production process, the amount of lactase No. 1 added is 0.2% of the weight of the high-protein raw milk, with an enzyme activity ≥5500 NLU / g and an enzymatic hydrolysis temperature of 50±5℃. The amount of lactase No. 2 added is 0.03% of the weight of the semi-finished milk containing native dietary fiber, with an enzyme activity ≥4800 NLU / g and an enzymatic hydrolysis temperature of 45±5℃.

[0029] according to Figure 1 The process flow diagram shown is as follows: Raw milk is pasteurized (75℃, 15s) and then passed through an RO membrane (pore size 0.2nm, concentration ratio 1.87) to obtain RO concentrate. The protein content of the RO concentrate is 6.10%, and the lactose content is 8.56%. The RO concentrate is heated to 50±5℃, and lactase No. 1 is added. After enzymatic hydrolysis for 90 minutes, it is pasteurized (75℃, 15s) to obtain high-protein, low-lactose milk. Lactase No. 2 is added to the high-protein, low-lactose milk and enzymatically hydrolyzed for 90 minutes. After INF sterilization (145±4℃, 2-5s), high-protein, fiber-rich, lactose-free milk is obtained.

[0030] To highlight the beneficial effects of the present invention, the following comparative experiments are provided.

[0031] Comparative Example 1 This comparative example provides a method for preparing lactose-free milk containing galactooligosaccharides (CN116158463A).

[0032] The protein content of the raw milk in this comparative example is 3.29g / 100mL, and the lactose content is 4.95g / 100mL. The raw materials for producing the finished milk product contain the following components by weight: 996.0 parts by weight of raw milk, 4.0 parts by weight of lactase, and the lactase donor is Bifidobacterium bifidum.

[0033] Production process: Raw milk is filtered using a milk purifier and pasteurized at 75℃ for 15 seconds. It is then cooled to 5℃, and lactase is added for enzymatic hydrolysis. The hydrolysis temperature is 5℃, and the hydrolysis time is 24 hours. UHT sterilization is performed at 137±2℃ for 4-6 seconds.

[0034] Comparative Example 2 Based on Comparative Example 1, this comparative example first concentrates raw milk through an RO membrane to obtain high-protein milk, and then follows the steps in Comparative Example 1 to provide a method for preparing high-protein lactose-free milk containing galactooligosaccharides.

[0035] The protein content of the raw milk in this comparative example is 3.31g / 100mL, and the lactose content is 4.95g / 100mL. The raw materials for producing the finished milk product contain the following components by weight: 996.0 parts by weight of raw milk, 4.0 parts by weight of lactase, and the lactase donor is Bifidobacterium bifidum.

[0036] Production process: Raw milk is filtered through a milk purifier, then concentrated using a 1.85x RO membrane (0.2nm pore size, concentration ratio 1.87), and pasteurized at 75℃ for 15 seconds. It is then cooled to 5℃, and lactase is added for enzymatic hydrolysis. The hydrolysis temperature is 5℃, and the hydrolysis time is 24 hours. UHT sterilization is performed at 137±2℃ for 4-6 seconds.

[0037] Comparative Example 3 This comparative example provides a method for preparing lactose-free pasteurized milk (CN 113632836 A).

[0038] In this comparative example, the raw milk protein content was 3.29 g / 100 mL, and the lactose content was 4.93 g / 100 mL. The specific steps are as follows: 1) Place the qualified raw milk or skim milk with an initial temperature of 6±1℃ into a milk storage tank for later use; 2) Raw milk or skim milk is pasteurized at 85℃ for 15 seconds, and then cooled to 40±1℃ to obtain pasteurized milk; 3) Add β-galactosidase to the milk obtained in step 2, at a rate of 0.05%-0.1%, and stir well; 4) Store at 40±1℃ for 1.5-3 hours; 5) Sampling, testing, filling, and you will get the lactose-free pasteurized milk product.

[0039] Comparative Example 4 This comparative example, based on Comparative Example 3, first concentrates raw milk through RO membrane filtration to obtain high-protein milk, and then, following the steps in Comparative Example 3, provides a method for preparing high-protein lactose-free milk. The specific steps are as follows: 1) Place the qualified raw milk or skim milk with an initial temperature of 6±1℃ into a milk storage tank for later use; 2) The raw milk is concentrated by passing it through a 1.85x RO membrane (pore size 0.2nm, concentration ratio 1.88), and the concentrated milk is placed in a milk storage tank for later use; 2) Raw milk or skim milk is pasteurized at 85℃ for 15 seconds, and then cooled to 40±1℃ to obtain pasteurized milk; 3) Add β-galactosidase to the milk obtained in step 2, at a rate of 0.05%-0.1%, and stir well; 4) Store at 40±1℃ for 1.5-3 hours; 5) Sampling, testing, filling, and you will get high-protein, lactose-free pasteurized milk.

[0040] Table 1 shows the content of protein, lactose, and dietary fiber (calculated as galactooligosaccharides) in Comparative Examples 1-4 and Example 1. The results show that the finished product of the present invention has the highest dietary fiber (calculated as galactooligosaccharides) content, at 3.95%, and also meets the zero lactose claim (lactose < 0.5%), indicating that the preparation method of the present invention has achieved a significant breakthrough in this field.

[0041] Table 1. Content of various physicochemical indicators in lactose-free milk The results in Table 2 show that the present invention scored the highest in terms of overall likability, milky aroma and thickness, and the milky sweetness score was closest to 5 (the most suitable). The product taste was also improved after the present invention increased the original dietary fiber (calculated as galactooligosaccharides).

[0042] Table 2 Sensory Comparison of Lactose-Free Milk Example 2 This embodiment changes the enzymatic hydrolysis time of lactase No. 1 in Example 1.

[0043] In this embodiment, the protein content of the raw milk is 3.32% and the lactose content is 4.82%. During the milk production process, the amount of lactase No. 1 added is 0.2% of the weight of the high-protein raw milk, with an enzyme activity ≥5500 NLU / g and an enzymatic hydrolysis temperature of 50±5℃. The amount of lactase No. 2 added is 0.03% of the weight of the semi-finished milk containing native dietary fiber, with an enzyme activity ≥4800 NLU / g and an enzymatic hydrolysis temperature of 45±5℃.

[0044] according to Figure 1The process flow diagram shown is as follows: Raw milk is pasteurized (75℃, 15s) and then passed through an RO membrane (pore size 0.2nm, concentration ratio 1.87) to obtain RO concentrate. The protein content of the RO concentrate is 6.10%, and the lactose content is 8.56%. The RO concentrate is heated to 50±5℃, and lactase No. 1 is added. After enzymatic hydrolysis for 60 minutes, it is pasteurized (75℃, 15s) to obtain high-protein, low-lactose milk. Lactase No. 2 is added to the high-protein, low-lactose milk and enzymatically hydrolyzed for 90 minutes. After INF sterilization (145±4℃, 2-5s), high-protein, fiber-rich, lactose-free milk is obtained.

[0045] Example 3 This embodiment changes the enzymatic hydrolysis time of lactase No. 2 in Example 1.

[0046] In this embodiment, the protein content of the raw milk is 3.32% and the lactose content is 4.82%. During the milk production process, the amount of lactase No. 1 added is 0.2% of the weight of the high-protein raw milk, with an enzyme activity ≥5500 NLU / g and an enzymatic hydrolysis temperature of 50±5℃. The amount of lactase No. 2 added is 0.03% of the weight of the semi-finished milk containing native dietary fiber, with an enzyme activity ≥4800 NLU / g and an enzymatic hydrolysis temperature of 45±5℃.

[0047] according to Figure 1 The process flow diagram shown is as follows: Raw milk is pasteurized (75℃, 15s) and then passed through an RO membrane (pore size 0.2nm, concentration ratio 1.87) to obtain RO concentrate. The protein content of the RO concentrate is 6.10%, and the lactose content is 8.56%. The RO concentrate is heated to 50±5℃, and lactase No. 1 is added. After enzymatic hydrolysis for 90 minutes, it is pasteurized (75℃, 15s) to obtain high-protein, low-lactose milk. Lactase No. 2 is added to the high-protein, low-lactose milk and enzymatically hydrolyzed for 60 minutes. After INF sterilization (145±4℃, 2-5s), high-protein, fiber-rich, lactose-free milk is obtained.

[0048] Example 4 This embodiment changes the amount of lactase No. 1 added in Example 1.

[0049] In this embodiment, the protein content of the raw milk is 3.32% and the lactose content is 4.82%. During the milk production process, the amount of lactase No. 1 added is 0.3% of the weight of the high-protein raw milk, with an enzyme activity ≥5500 NLU / g and an enzymatic hydrolysis temperature of 50±5℃. The amount of lactase No. 2 added is 0.03% of the weight of the semi-finished milk containing native dietary fiber, with an enzyme activity ≥4800 NLU / g and an enzymatic hydrolysis temperature of 45±5℃.

[0050] according to Figure 1The process flow diagram shown is as follows: Raw milk is pasteurized (75℃, 15s) and then passed through an RO membrane (pore size 0.2nm, concentration ratio 1.87) to obtain RO concentrate. The protein content of the RO concentrate is 6.10%, and the lactose content is 8.56%. The RO concentrate is heated to 50±5℃, and lactase No. 1 is added. After enzymatic hydrolysis for 90 minutes, it is pasteurized (75℃, 15s) to obtain high-protein, low-lactose milk. Lactase No. 2 is added to the high-protein, low-lactose milk and enzymatically hydrolyzed for 90 minutes. After INF sterilization (145±4℃, 2-5s), high-protein, fiber-rich, lactose-free milk is obtained.

[0051] Example 5 This embodiment changes the amount of lactase No. 1 added in Example 1.

[0052] In this embodiment, the protein content of the raw milk is 3.32% and the lactose content is 4.82%. During the milk production process, the amount of lactase No. 1 added is 0.1% of the weight of the high-protein raw milk, with an enzyme activity ≥5500 NLU / g and an enzymatic hydrolysis temperature of 50±5℃. The amount of lactase No. 2 added is 0.03% of the weight of the semi-finished milk containing native dietary fiber, with an enzyme activity ≥4800 NLU / g and an enzymatic hydrolysis temperature of 45±5℃.

[0053] according to Figure 1 The process flow diagram shown is as follows: Raw milk is pasteurized (75℃, 15s) and then passed through an RO membrane (pore size 0.2nm, concentration ratio 1.87) to obtain RO concentrate. The protein content of the RO concentrate is 6.10%, and the lactose content is 8.56%. The RO concentrate is heated to 50±5℃, and lactase No. 1 is added. After enzymatic hydrolysis for 90 minutes, it is pasteurized (75℃, 15s) to obtain high-protein, low-lactose milk. Lactase No. 2 is added to the high-protein, low-lactose milk and enzymatically hydrolyzed for 90 minutes. After INF sterilization (145±4℃, 2-5s), high-protein, fiber-rich, lactose-free milk is obtained.

[0054] Example 6 This embodiment changes the amount of lactase No. 2 added in Example 1.

[0055] In this embodiment, the protein content of the raw milk is 3.32% and the lactose content is 4.82%. During the milk production process, the amount of lactase No. 1 added is 0.2% of the weight of the high-protein raw milk, with an enzyme activity ≥5500 NLU / g and an enzymatic hydrolysis temperature of 50±5℃. The amount of lactase No. 2 added is 0.04% of the weight of the semi-finished milk containing native dietary fiber, with an enzyme activity ≥4800 NLU / g and an enzymatic hydrolysis temperature of 45±5℃.

[0056] according to Figure 1The process flow diagram shown is as follows: Raw milk is pasteurized (75℃, 15s) and then passed through an RO membrane (pore size 0.2nm, concentration ratio 1.87) to obtain RO concentrate. The protein content of the RO concentrate is 6.10%, and the lactose content is 8.56%. The RO concentrate is heated to 50±5℃, and lactase No. 1 is added. After enzymatic hydrolysis for 90 minutes, it is pasteurized (75℃, 15s) to obtain high-protein, low-lactose milk. Lactase No. 2 is added to the high-protein, low-lactose milk and enzymatically hydrolyzed for 90 minutes. After INF sterilization (145±4℃, 2-5s), high-protein, fiber-rich, lactose-free milk is obtained.

[0057] Example 7 This embodiment changes the amount of lactase No. 2 added in Example 1.

[0058] In this embodiment, the protein content of the raw milk is 3.32% and the lactose content is 4.82%. During the milk production process, the amount of lactase No. 1 added is 0.2% of the weight of the high-protein raw milk, with an enzyme activity ≥5500 NLU / g and an enzymatic hydrolysis temperature of 50±5℃. The amount of lactase No. 2 added is 0.02% of the weight of the semi-finished milk containing native dietary fiber, with an enzyme activity ≥4800 NLU / g and an enzymatic hydrolysis temperature of 45±5℃.

[0059] according to Figure 1 The process flow diagram shown is as follows: Raw milk is pasteurized (75℃, 15s) and then passed through an RO membrane (pore size 0.2nm, concentration ratio 1.87) to obtain RO concentrate. The protein content of the RO concentrate is 6.10%, and the lactose content is 8.56%. The RO concentrate is heated to 50±5℃, and lactase No. 1 is added. After enzymatic hydrolysis for 90 minutes, it is pasteurized (75℃, 15s) to obtain high-protein, low-lactose milk. Lactase No. 2 is added to the high-protein, low-lactose milk and enzymatically hydrolyzed for 90 minutes. After INF sterilization (145±4℃, 2-5s), high-protein, fiber-rich, lactose-free milk is obtained.

[0060] Example 8 This embodiment changes the enzymatic hydrolysis temperature of lactase No. 1 in Example 1.

[0061] In this embodiment, the protein content of the raw milk is 3.32% and the lactose content is 4.82%. During the milk production process, the amount of lactase No. 1 added is 0.2% of the weight of the high-protein raw milk, with an enzyme activity ≥5500 NLU / g and an enzymatic hydrolysis temperature of 55±5℃. The amount of lactase No. 2 added is 0.03% of the weight of the semi-finished milk containing native dietary fiber, with an enzyme activity ≥4800 NLU / g and an enzymatic hydrolysis temperature of 45±5℃.

[0062] according to Figure 1The process flow diagram shown is as follows: Raw milk is pasteurized (75℃, 15s) and then passed through an RO membrane (pore size 0.2nm, concentration ratio 1.87) to obtain RO concentrate. The protein content of the RO concentrate is 6.10%, and the lactose content is 8.56%. The RO concentrate is heated to 50±5℃, and lactase No. 1 is added. After enzymatic hydrolysis for 90 minutes, it is pasteurized (75℃, 15s) to obtain high-protein, low-lactose milk. Lactase No. 2 is added to the high-protein, low-lactose milk and enzymatically hydrolyzed for 90 minutes. After INF sterilization (145±4℃, 2-5s), high-protein, fiber-rich, lactose-free milk is obtained.

[0063] Example 9 This embodiment changes the enzymatic hydrolysis temperature of lactase No. 1 in Example 1.

[0064] In this embodiment, the protein content of the raw milk is 3.32% and the lactose content is 4.82%. During the milk production process, the amount of lactase No. 1 added is 0.2% of the weight of the high-protein raw milk, with an enzyme activity ≥5500 NLU / g and an enzymatic hydrolysis temperature of 45±5℃. The amount of lactase No. 2 added is 0.03% of the weight of the semi-finished milk containing native dietary fiber, with an enzyme activity ≥4800 NLU / g and an enzymatic hydrolysis temperature of 45±5℃.

[0065] according to Figure 1 The process flow diagram shown is as follows: Raw milk is pasteurized (75℃, 15s) and then passed through an RO membrane (pore size 0.2nm, concentration ratio 1.87) to obtain RO concentrate. The protein content of the RO concentrate is 6.10%, and the lactose content is 8.56%. The RO concentrate is heated to 50±5℃, and lactase No. 1 is added. After enzymatic hydrolysis for 90 minutes, it is pasteurized (75℃, 15s) to obtain high-protein, low-lactose milk. Lactase No. 2 is added to the high-protein, low-lactose milk and enzymatically hydrolyzed for 90 minutes. After INF sterilization (145±4℃, 2-5s), high-protein, fiber-rich, lactose-free milk is obtained.

[0066] Example 10 This embodiment changes the enzymatic hydrolysis temperature of lactase No. 2 in Example 1.

[0067] In this embodiment, the protein content of the raw milk is 3.32% and the lactose content is 4.82%. During the milk production process, the amount of lactase No. 1 added is 0.2% of the weight of the high-protein raw milk, with an enzyme activity ≥5500 NLU / g and an enzymatic hydrolysis temperature of 50±5℃. The amount of lactase No. 2 added is 0.03% of the weight of the semi-finished milk containing native dietary fiber, with an enzyme activity ≥4800 NLU / g and an enzymatic hydrolysis temperature of 50±5℃.

[0068] according to Figure 1The process flow diagram shown is as follows: Raw milk is pasteurized (75℃, 15s) and then passed through an RO membrane (pore size 0.2nm, concentration ratio 1.87) to obtain RO concentrate. The protein content of the RO concentrate is 6.10%, and the lactose content is 8.56%. The RO concentrate is heated to 50±5℃, and lactase No. 1 is added. After enzymatic hydrolysis for 90 minutes, it is pasteurized (75℃, 15s) to obtain high-protein, low-lactose milk. Lactase No. 2 is added to the high-protein, low-lactose milk and enzymatically hydrolyzed for 90 minutes. After INF sterilization (145±4℃, 2-5s), high-protein, fiber-rich, lactose-free milk is obtained.

[0069] Example 11 This embodiment changes the enzymatic hydrolysis temperature of lactase No. 2 in Example 1.

[0070] In this embodiment, the protein content of the raw milk is 3.32% and the lactose content is 4.82%. During the milk production process, the amount of lactase No. 1 added is 0.2% of the weight of the high-protein raw milk, with an enzyme activity ≥5500 NLU / g and an enzymatic hydrolysis temperature of 50±5℃. The amount of lactase No. 2 added is 0.03% of the weight of the semi-finished milk containing native dietary fiber, with an enzyme activity ≥4800 NLU / g and an enzymatic hydrolysis temperature of 40±5℃.

[0071] according to Figure 1 The process flow diagram shown is as follows: Raw milk is pasteurized (75℃, 15s) and then passed through an RO membrane (pore size 0.2nm, concentration ratio 1.87) to obtain RO concentrate. The protein content of the RO concentrate is 6.10%, and the lactose content is 8.56%. The RO concentrate is heated to 50±5℃, and lactase No. 1 is added. After enzymatic hydrolysis for 90 minutes, it is pasteurized (75℃, 15s) to obtain high-protein, low-lactose milk. Lactase No. 2 is added to the high-protein, low-lactose milk and enzymatically hydrolyzed for 90 minutes. After INF sterilization (145±4℃, 2-5s), high-protein, fiber-rich, lactose-free milk is obtained.

[0072] Table 3 shows the lactose and dietary fiber (calculated as galactooligosaccharides) content of the finished products from each example. The results show that the dietary fiber (calculated as galactooligosaccharides) content of the finished products from Examples 1, 3, 7, and 11 reached over 3g / 100mL, meeting the national standard for claiming rich dietary fiber content. However, the lactose content of Examples 3, 7, and 11 was all greater than 0.5g / 100mL, failing to meet the zero-lactose claim. This indicates that the dual-temperature gradient enzymatic hydrolysis process in Example 1 is the optimal process.

[0073] Table 3 Content of various physicochemical indicators in lactose-free milk Table 4 shows the sensory scores of the lactose-free milk from each example. The results show that when the dietary fiber (calculated as galactooligosaccharides) content of the finished products in Examples 1, 3, 7, and 11 reached 3g / 100mL or more, the overall preference score was 7 or higher. Therefore, in this invention, when the dietary fiber (calculated as galactooligosaccharides) content of the finished product reaches 3g / 100mL or more, the lactose-free milk has a better taste.

[0074] Table 4 Sensory Comparison of Lactose-Free Milk from Various Examples Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-protein, lactose-free milk rich in native dietary fiber, characterized in that, Includes the following steps: 1) Raw milk, whether or not it has undergone defatting and standardization treatment, is pasteurized and then fed into a reverse osmosis membrane system for processing to obtain RO permeate and RO retentate; The RO retention solution is high-protein raw milk; 2) Add an appropriate amount of lactase No. 1 to the high-protein raw milk to hydrolyze until the lactose concentration is ≤2g / 100mL and the galactooligosaccharide concentration is ≥3g / 100mL; the lactase No. 1 is NOLA from Kerry Company. ® GOS lactase; 3) Pasteurize the hydrolyzed product to inactivate lactase No. 1, and obtain a semi-finished milk containing native dietary fiber. 4) Add an appropriate amount of lactase No. 2 to the semi-finished milk liquid to hydrolyze until the lactose concentration is <0.5g / 100mL to obtain high-protein, high-fiber, lactose-free raw milk; the lactase No. 2 is KERRY's Ha-Lactase™ 5200 lactase.

2. The method for preparing high-protein, lactose-free milk rich in native dietary fiber according to claim 1, characterized in that: In step 1), the raw milk is either skimmed or not, and is either pasteurized or not; the protein content of the raw milk is 3.0-3.5%, and the lactose content is 4.2-5.2%.

3. The method for preparing high-protein, lactose-free milk rich in native dietary fiber according to claim 1, characterized in that: In step 1), the pore size of the reverse osmosis membrane is 0.1~0.2nm, and the concentration ratio is 1.5~3.

4. The method for preparing high-protein, lactose-free milk rich in native dietary fiber according to claim 1, characterized in that: In step 2), the amount of lactase No. 1 added is 0.1-0.6% of the weight of the high-protein raw milk, and the enzyme activity of lactase No. 1 is ≥5500 NLU / g.

5. The method for preparing high-protein, lactose-free milk rich in native dietary fiber according to claim 1, characterized in that: In step 3), the pasteurization temperature range is 72-85℃, and the pasteurization time is 12-18s.

6. The method for preparing high-protein, lactose-free milk rich in native dietary fiber according to claim 1, characterized in that: In step 4), the amount of lactase No. 2 added is 0.02-0.06% of the weight of the semi-finished milk containing native dietary fiber, and the enzyme activity of lactase No. 2 is ≥4800 NLU / g.

7. The method for preparing high-protein, lactose-free milk rich in native dietary fiber according to claim 1, characterized in that: It also includes an INF sterilization step on the obtained high-protein, native dietary fiber, lactose-free raw milk.

8. The method for preparing high-protein, lactose-free milk rich in native dietary fiber according to claim 7, characterized in that, The INF sterilization process includes the following steps: ① Preheating: The high-protein, fiber-rich, lactose-free raw milk is heated to 65-75℃ via plate heat exchanger; ② Steam immersion sterilization and degassing and cooling: After preheating, the raw milk is sterilized by steam immersion and then enters the degassing system by centrifugal pump for degassing and cooling; the steam immersion sterilization is 140~155℃ for 2-5 seconds. ③ Homogenization: After degassing and cooling, the product enters a sterile homogenizer. The homogenization temperature is 60-75℃ and the total homogenization pressure is 200-250 bar. ④ Filling: Cool the homogenized product to below 20℃ and fill it to obtain a high-protein, dietary fiber-rich, lactose-free milk product.

9. High-protein, lactose-free milk rich in native dietary fiber prepared by the preparation method according to any one of claims 1-8.

10. The high-protein, lactose-rich, lactose-free milk according to claim 9, characterized in that: The milk contains at least 3.0% native dietary fiber, calculated as galactooligosaccharide, and less than 0.5% lactose.

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