Method for preparing dietary fiber-rich milk and milk prepared using same

Abstract

A method for preparing dietary fiber-rich milk and milk prepared using same. In the method, an ultrafiltration technology and a β-galactosidase enzymolysis process are combined, so as to increase the content of dietary fiber GOS, protein and calcium in the milk, and reduce the content of lactose.

Description

Preparation method of milk rich in dietary fiber and milk prepared thereby

[0001] Priority

[0002] The present application claims the priority of the Chinese invention patent application with the application date of 2024-07-04, the application number of 202410888577.4, and the invention name of "Preparation method of milk rich in dietary fiber and milk prepared thereby". TECHNICAL FIELD

[0003] The present application relates to the technical field of dairy products, and particularly relates to a preparation method of milk rich in dietary fiber and milk prepared thereby. BACKGROUND

[0004] In recent years, with the increasing attention of consumers to health, high-quality high-protein, high-calcium and high-dietary fiber milk is favored by more athletes, social elites, the elderly and children, and becomes a trend of healthy consumption. Therefore, it is urgent to develop raw high-protein, high-calcium and high-dietary fiber pasteurized milk.

[0005] Most of the existing high-nutrition milk realizes the purposes of high protein and high calcium through a membrane combination process, but the dietary fiber content thereof is low. If high dietary fiber content is desired, it needs to rely on exogenous addition of dietary fiber. Dietary fiber generally refers to non-digestible carbohydrate polymers with three or more monomers. Galactooligosaccharides (GOS) is a natural functional oligosaccharide. Intake of GOS as a dietary supplement can increase mineral absorption, stimulate immune regulation, prevent allergy and intestinal inflammation. GOS is composed of a variable number of 2-8 galactose units, which are connected together by β-(1-6) and β-(1-4) glycosidic bonds, and connected to the terminal glucose unit by α-(1-4) glycosidic bond, and the stoichiometric formula is (Gal) i Glc or (Gal) j wherein i=1-8 and j=2-9, wherein lactose and Gal2 do not belong to dietary fiber in strict sense, and GOS of trisaccharide and above belong to dietary fiber.

[0006] Some lactases can convert part of the lactose in milk into GOS, but the concentration of GOS obtained is extremely low. The degree of galactose polymerization (2-8 units) is affected by various factors, including: enzyme properties, enzyme activity, lactose concentration as a substrate, enzyme reaction time, optimal enzyme conditions (pH, temperature, etc.) and enzyme hydrolysis process method (free enzyme or immobilized enzyme). The end point of the enzyme reaction catalyzed by lactase is to produce 3 monosaccharides and above polymerized GOS and Gal2, in addition to low concentrations of lactose, free galactose and free glucose. Currently, there are two main problems in the process of producing GOS by hydrolyzing milk with β-galactosidase with transgalactosylation activity: (1) lactose cannot be completely hydrolyzed, because in the process of hydrolyzing lactose and synthesizing GOS, β-galactosidase will continue to hydrolyze GOS containing α-(1-4) glycosidic bonds in the later stage. Generally speaking, when the lactose system in milk is reduced to 0.5-1 g / 100 mL, the degradation rate of GOS is greater than the synthesis rate, which leads to the fact that in order to retain more GOS content, lactose cannot be excessively hydrolyzed, so it is impossible to achieve 0 lactose (not higher than 0.5 g / 100 mL); (2) the synthesis yield of GOS by lactase hydrolysis of lactose is between 18% and 52.5%, and the synthesis yield of dietary fiber will be lower due to the presence of glucose, lactose and Gal2. Therefore, the problems of incomplete hydrolysis of lactose in milk and low yield of GOS as dietary fiber need to be solved. SUMMARY

[0007] The present application provides a preparation method of milk rich in dietary fiber and milk prepared thereby.

[0008] To solve the problem of the content of dietary fiber in the current high-nutrition milk and the problem of GOS generated by lactase hydrolysis of lactose in milk, the present application develops a method for preparing milk with 0 lactose (not higher than 0.5 g / 100 mL) by significantly improving the yield of GOS generated by lactase hydrolysis of lactose in milk and improving the hydrolysis rate of lactose based on membrane filtration technology and lactase hydrolysis technology.

[0009] Specifically, the present application provides the technical solutions described below.

[0010] The present application provides a preparation method of milk, which comprises the following steps (1)-(4).

[0011] (1) The lactose raw material is subjected to enzyme hydrolysis treatment with β-galactosidase, and the enzyme hydrolysis is stopped when the lactose content is 2-3 g / 100 mL. The enzyme hydrolysis liquid is subjected to ultrafiltration, and the retentate and the permeate are collected as the first retentate and the first permeate, respectively.

[0012] (2) the first permeate is subjected to enzymatic treatment with β-galactosidase until the lactose content is 0.8-1.2 g / 100 mL, and the enzymatic solution is subjected to ultrafiltration to collect the retentate and the permeate as the second retentate and the second permeate, respectively.

[0013] (3) the second permeate is subjected to enzymatic treatment with β-galactosidase until the lactose content is 0.1-0.5 g / 100 mL, and the enzymatic solution is subjected to ultrafiltration to collect the retentate and the permeate as the third retentate and the third permeate, respectively.

[0014] (4) the third permeate is mixed with the first retentate, the second retentate and the third retentate to obtain a mixed solution.

[0015] Preferably, the β-galactosidase is a β-galactosidase having transgalactosyl activity.

[0016] The present application discloses a method for preparing milk containing dietary fiber GOS by using β-galactosidase to enzymatically hydrolyze milk. i Glc or (Gal) j (wherein i≥2, j≥3) oligosaccharides, which can greatly reduce the possibility of further enzymatic hydrolysis of the dietary fiber GOS produced above by β-galactosidase, and further improve the yield of GOS; the lactose, Gal2, glucose and galactose remaining in the permeate obtained by ultrafiltration re-form a new sugar system, and through the above-mentioned control of the end point of enzymatic hydrolysis and the ultrafiltration technology, the new sugar system in the permeate can still ensure a high lactose hydrolysis efficiency and a high GOS synthesis efficiency after being treated by β-galactosidase, further improving the yield of GOS.

[0017] Preferably, the synthesis rate of the trisaccharide and above oligogalactose in the preparation method is 60% or more.

[0018] The synthesis rate of the trisaccharide and above oligogalactose is the ratio of the content of the trisaccharide and above oligogalactose in the milk prepared by the preparation method to the content of lactose in the milk raw material.

[0019] Preferably, the membrane core used for ultrafiltration has a pore size of 1-20 Dal. The ultrafiltration membrane with the above-mentioned pore size can retain the (Gal) i Glc or (Gal) j (wherein i≥2, j≥3) oligosaccharides produced by enzymatic hydrolysis, and also can retain the protein, fat and calcium and other components in the milk. The present application finds that the ultrafiltration membrane with the above-mentioned pore size can not only ensure the (Gal) i Glc or (Gal) jThe ultrafiltration has a cut-off effect on oligosaccharides with i≥2 and j≥3, and can permeate lactose, Gal2, glucose and galactose. The concentration ratio of the ultrafiltration is preferably 1.1-1.5. The pressure of the ultrafiltration is preferably 1-4 bar.

[0020] The ultrafiltration is performed until the permeate is completely filtered out.

[0021] The above-mentioned ultrafiltration technology can be well combined with the end-point control of lactase hydrolysis, and can make glucose more involved in the synthesis of dietary fiber, thereby ensuring a higher oligosaccharide content in the cut-off liquid, and ensuring a higher lactose hydrolysis efficiency and dietary fiber GOS synthesis efficiency after the new sugar system in the permeate is treated by β-galactosidase, thereby improving the yield of GOS and reducing the amount of residual lactose.

[0022] Preferably, the temperature of the enzymatic hydrolysis is 40-60℃.

[0023] In the present application, the temperature of the enzymatic hydrolysis can be adjusted according to the optimum reaction temperature of the β-galactosidase with transgalactosyl activity used.

[0024] In some embodiments of the present application, the β-galactosidase is Nurica lactase. The temperature of the enzymatic hydrolysis is 48-52℃.

[0025] For the amount of β-galactosidase, in step (1), the amount of the β-galactosidase added is 1-3 g / L. In steps (2) and (3), the amount of the β-galactosidase added is 0.5-2 g / L.

[0026] According to the control range of the lactose content at the end of the enzymatic hydrolysis, the temperature of the enzymatic hydrolysis and the amount of the enzyme added, the person skilled in the art can determine the time of the enzymatic hydrolysis.

[0027] In the above-mentioned method, the end of the enzymatic hydrolysis is achieved by passivation treatment of the β-galactosidase.

[0028] The passivation treatment of the β-galactosidase can use common enzyme passivation treatment methods, such as high-temperature passivation, etc.

[0029] Preferably, the passivation treatment is at 90-95℃ for 280-320 s.

[0030] In the above-mentioned method, the lactose content of the lactose raw material is 4-5 g / 100 mL, and / or the protein content is 2.9-4 g / 100 mL, and / or the fat content is 2.7-4 g / 100 mL, and / or the calcium content is 100-120 mg / 100 mL.

[0031] In some embodiments of the present application, the milk raw material is obtained by subjecting raw cow milk to fat standardization and filter sterilization. The fat content after standardization is in the range of 3.0±0.3 g / 100 mL, and the filter sterilization is performed using a filter with a pore size of 0.50 mm.

[0032] The method for preparing milk described above further comprises the steps of subjecting the mixed liquid to homogenization and sterilization.

[0033] Preferably, the temperature for homogenization is 65-70℃, and the pressure for homogenization is 220-240 bar.

[0034] The sterilization is performed at 126±6℃ for 0.5-2 s.

[0035] The present application further provides a milk prepared by the method for preparing milk described above.

[0036] Preferably, the content of tri-galactose and above oligosaccharides in the milk is not less than 5.5 g / 100 mL; and / or, the content of protein is not less than 5.0 g / 100 mL, and / or, the content of calcium is not less than 170 mg / 100 mL.

[0037] Preferably, the content of oligosaccharides in the milk is 5.5-6.5 g / 100 mL. More preferably, the content of protein in the milk is 5.0-6.0 g / 100 mL, and the content of calcium is 170-200 mg / 100 mL.

[0038] The present application has at least the following beneficial effects: the method for preparing milk of the present application combines ultrafiltration technology with β-galactosidase enzymolysis process, which not only increases the content of protein and calcium in milk, but also increases the yield of GOS (tri-galactose and above GOS) generated from lactose in milk to 70%, significantly increases the content of dietary fiber in milk, and realizes 0 lactose, thereby preparing high-nutrition milk with high protein, high calcium and high dietary fiber, which can better meet the needs of consumers for nutrition and health, and has good taste and flavor. BRIEF DESCRIPTION OF DRAWINGS

[0039] In order to more clearly illustrate the technical solutions of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0040] Figure 1 is a graph showing the content change of lactose and GOS with the enzymolysis time in the enzymolysis process of the milk preparation method of Comparative Example 1.

[0041] Figure 2 is a graph showing the change in the content of lactose and GOS with the enzyme hydrolysis time during the first enzyme hydrolysis process of the milk preparation method of Example 1.

[0042] Figure 3 is a graph showing the change in the content of lactose and GOS with the enzyme hydrolysis time during the second enzyme hydrolysis process of the milk preparation method of Example 1.

[0043] Figure 4 is a graph showing the change in the content of lactose and GOS with the enzyme hydrolysis time during the third enzyme hydrolysis process of the milk preparation method of Example 1. DETAILED DESCRIPTION

[0044] The present application provides a milk preparation method, which comprises the following steps:

[0045] (1) filtering the chilled raw milk after standardization to obtain partially defatted milk, the standardization fat being in the range of 3.0±0.3 g / 100 mL, and the filter mesh size being 0.50 mm; the protein content of the partially defatted milk being 2.9-4 g / 100 mL, the calcium content being 100-120 mg / 100 mL, and the lactose content being 4-5 g / 100 mL;

[0046] (2) adding β-galactosidase with transgalactosyl activity to the partially defatted milk obtained in step (1) for enzyme hydrolysis treatment, the addition amount of the β-galactosidase being 1-3 g / L, the enzyme hydrolysis temperature being 40-60°C, and the enzyme hydrolysis being stopped when the lactose content is 2-3 g / 100 mL;

[0047] (3) performing β-galactosidase inactivation on the enzyme-hydrolyzed raw milk obtained in step (2), the inactivation conditions being 90-95°C and 300 s;

[0048] (4) performing UF filtration on the enzyme-hydrolyzed raw milk after inactivation in step (3), the membrane core filtration pore size of the UF membrane being 1-20 Dal, the concentration ratio being 1.1-1.5, and the pressure being 1-4 bar, until the permeate is completely filtered out, and the retentate and the permeate are collected;

[0049] (5) adding β-galactosidase with transgalactosyl activity to the permeate obtained in step (4) for enzyme hydrolysis treatment, the addition amount of the β-galactosidase being 0.5-2 g / L, the enzyme hydrolysis temperature being 40-60°C, and the enzyme hydrolysis being stopped when the lactose content is 0.8-1.2 g / 100 mL;

[0050] (6) performing β-galactosidase inactivation on the enzyme-hydrolyzed permeate obtained in step (5), the inactivation conditions being 90-95°C and 300 s;

[0051] (7) the permeate obtained in step (6) is subjected to UF filtration, the membrane core filtration pore size of the UF membrane is 1-20 Dal, the concentration ratio is 1.1-1.5, the pressure is 1-4 bar, until the permeate is completely filtered out, the retentate and the permeate are collected;

[0052] (8) β-galactosidase with transgalactosyl activity is added to the permeate obtained in step (7) for enzymatic treatment, the addition amount of the β-galactosidase is 0.5-2 g / L, the enzymatic temperature is 40-60 ℃, and the enzymolysis is stopped when the lactose content is 0.1-0.5 g / 100 mL;

[0053] (9) the enzymatic permeate obtained in step (8) is subjected to β-galactosidase passivation, the passivation condition is 90-95 ℃, 300 s;

[0054] (10) the passivated enzymatic permeate obtained in step (9) is subjected to UF filtration, the membrane core filtration pore size of the UF membrane is 1-20 Dal, the concentration ratio is 1.1-1.5, the pressure is 1-4 bar, until the permeate is completely filtered out, the retentate and the permeate are collected;

[0055] (11) the permeate obtained in step (10) is backfilled into the retentate obtained in steps (4), (7) and (10) to prepare a standard protein content of 5.0-6.0 g / 100 mL, a calcium content of 170-200 mg / 100 mL, and a dietary fiber content of 5.5-6.5 g / 100 mL, at this time, the cow milk has better taste and flavor; then homogenization and sterilization treatment are performed, the homogenization process is as follows: the preheating temperature is 65-70 ℃, and the homogenization pressure is 220-240 bar; the sterilization is sterilized at 126±6 ℃ for 0.5-2 s, and a high-nutrient milk is obtained.

[0056] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be described clearly and completely below in combination with the drawings in the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0057] The materials, reagents, methods and instruments used in the following embodiments are not specially described, and are conventional materials, reagents, methods and instruments in the art, which can be obtained by market purchase or the like.

[0058] Embodiment 1

[0059] The present embodiment provides a preparation method of cow milk, which comprises the following steps:

[0060] (1) The 2℃ refrigerated raw milk was filtered after standardization to obtain partially defatted milk, the standardization of fat was 3.0g / 100mL, the filter aperture was 0.50mm, the protein content of the partially defatted milk was 3.2g / 100mL, the calcium content was 108mg / 100mL, and the lactose content was 5g / 100mL;

[0061] (2) The nurica enzyme was added to the partially defatted milk obtained in step (1) for enzymatic treatment, the addition amount of the nurica enzyme was 2g / L, the enzymatic temperature was 50℃, and the enzymatic treatment was stopped when the lactose content was 2.5g / 100mL;

[0062] (3) The β-galactosidase of the enzymatic milk obtained in step (2) was inactivated, the inactivation condition was 95℃, 300s;

[0063] (4) The inactivated enzymatic milk obtained in step (3) was subjected to UF filtration, the membrane core filtration aperture of the UF membrane was 1Dal, the concentration ratio was 1.5, the pressure was 4bar, until the permeate was completely filtered out, the retentate and the permeate were collected;

[0064] (5) The nurica enzyme was added to the permeate obtained in step (4) for enzymatic treatment, the addition amount of the nurica enzyme was 1g / L, the enzymatic temperature was 50℃, and the enzymatic treatment was stopped when the lactose content was 1g / 100mL;

[0065] (6) The β-galactosidase of the enzymatic permeate obtained in step (5) was inactivated, the inactivation condition was 95℃, 300s;

[0066] (7) The inactivated enzymatic permeate obtained in step (6) was subjected to UF filtration, the membrane core filtration aperture of the UF membrane was 1Dal, the concentration ratio was 1.5, the pressure was 4bar, until the permeate was completely filtered out, the retentate and the permeate were collected;

[0067] (8) The nurica enzyme was added to the permeate obtained in step (7) for enzymatic treatment, the addition amount of the nurica enzyme was 1g / L, the enzymatic temperature was 50℃, and the enzymatic treatment was stopped when the lactose content was 0.5g / 100mL;

[0068] (9) The β-galactosidase of the enzymatic permeate obtained in step (8) was inactivated, the inactivation condition was 95℃, 300s;

[0069] (10) The inactivated enzymatic permeate obtained in step (9) was subjected to UF filtration, the membrane core filtration aperture of the UF membrane was 1Dal, the concentration ratio was 1.5, the pressure was 4bar, until the permeate was completely filtered out, the retentate and the permeate were collected;

[0070] (11) the permeate obtained in step (10) is backfilled into the retentate obtained in steps (4), (7) and (10); and then homogenization and sterilization are performed, the homogenization process is: preheating temperature is 70℃, homogenization pressure is 230bar; sterilization is at 126℃ for 2s, thereby high-fold nutritional milk is prepared. The protein content of the high-fold nutritional milk is 5.5g / 100mL, and the calcium content is 185mg / 100mL.

[0071] Example 2

[0072] The present embodiment provides a preparation method of milk, which comprises the following steps:

[0073] (1) the milk chilled at 2℃ is filtered after standardization to obtain partially defatted milk, the standardization fat is 3.0g / 100mL, the filter screen with a pore size of 0.50mm is selected for filtering, the protein content of the partially defatted milk is 3.2g / 100mL, the calcium content is 108mg / 100mL, and the lactose content is 5g / 100mL;

[0074] (2) nurica enzyme is added to the partially defatted milk obtained in step (1) for enzymatic hydrolysis, the addition amount of the nurica enzyme is 2g / L, the enzymatic hydrolysis temperature is 50℃, and the enzymatic hydrolysis is stopped when the lactose content is 3g / 100mL;

[0075] (3) the enzymatic hydrolysis milk obtained in step (2) is subjected to β-galactosidase passivation, the passivation condition is 95℃ for 300s;

[0076] (4) the passivated enzymatic hydrolysis milk obtained in step (3) is subjected to UF filtration, the membrane core filtration pore size of the UF membrane is 1Dal, the concentration ratio is 1.5, and the pressure is 4bar, until the permeate is completely filtered out, the retentate and the permeate are collected;

[0077] (5) nurica enzyme is added to the permeate obtained in step (4) for enzymatic hydrolysis, the addition amount of the nurica enzyme is 1g / L, the enzymatic hydrolysis temperature is 50℃, and the enzymatic hydrolysis is stopped when the lactose content is 1.2g / 100mL;

[0078] (6) the enzymatically hydrolyzed permeate obtained in step (5) is subjected to β-galactosidase passivation, the passivation condition is 95℃ for 300s;

[0079] (7) the passivated enzymatic hydrolysis permeate obtained in step (6) is subjected to UF filtration, the membrane core filtration pore size of the UF membrane is 1Dal, the concentration ratio is 1.5, and the pressure is 4bar, until the permeate is completely filtered out, the retentate and the permeate are collected;

[0080] (8) adding nurica enzyme to the permeate obtained in step (7) for enzymatic treatment, the addition amount of nurica enzyme is 1 g / L, the enzymatic temperature is 50°C, and the enzymatic treatment is stopped when the lactose content is 0.1 g / 100 mL;

[0081] (9) performing β-galactosidase passivation on the enzymatic permeate obtained in step (8), the passivation condition is 95°C, 300s;

[0082] (10) performing UF filtration on the passivated enzymatic permeate obtained in step (9), the membrane core filtration pore size of the UF membrane is 1 Dal, the concentration ratio is 1.5, the pressure is 4 bar, until the permeate is completely filtered out, and the retentate and the permeate are collected;

[0083] (11) back-filling the permeate obtained in step (10) into the retentate obtained in steps (4), (7) and (10); then performing homogenization and sterilization treatment, the homogenization process is: the preheating temperature is 70°C, the homogenization pressure is 230 bar, and the sterilization is at 126°C for 2s; thus high-nutrition milk is prepared. The protein content of the high-nutrition milk is 5.5 g / 100 mL, and the calcium content is 185 mg / 100 mL.

[0084] Example 3

[0085] The present embodiment provides a preparation method of milk, which comprises the following steps:

[0086] (1) filtering the standardized milk obtained by filtering raw milk stored at 2°C to obtain partially defatted milk, the standardized fat is 3.0 g / 100 mL, the filter screen with a pore size of 0.50 mm is selected for filtering, the protein content of the partially defatted milk is 3.2 g / 100 mL, the calcium content is 108 mg / 100 mL, and the lactose content is 5 g / 100 mL;

[0087] (2) adding nurica enzyme to the partially defatted milk obtained in step (1) for enzymatic treatment, the addition amount of nurica enzyme is 2 g / L, the enzymatic temperature is 50°C, and the enzymatic treatment is stopped when the lactose content is 2 g / 100 mL;

[0088] (3) performing β-galactosidase passivation on the enzymatic milk obtained in step (2), the passivation condition is 95°C, 300s;

[0089] (4) performing UF filtration on the passivated enzymatic milk obtained in step (3), the membrane core filtration pore size of the UF membrane is 1 Dal, the concentration ratio is 1.5, the pressure is 4 bar, until the permeate is completely filtered out, and the retentate and the permeate are collected;

[0090] (5) adding nurica enzyme to the permeate obtained in step (4) for enzymatic treatment, the addition amount of nurica enzyme is 1 g / L, the enzymatic temperature is 50℃, and the enzymatic treatment is stopped when the lactose content is 0.8 g / 100 mL;

[0091] (6) performing β-galactosidase passivation on the enzymatic permeate obtained in step (5), the passivation condition is 95℃, 300s;

[0092] (7) performing UF filtration on the passivated enzymatic permeate obtained in step (6), the membrane core filtration pore size of the UF membrane is 1 Dal, the concentration ratio is 1.5, the pressure is 4 bar, until the permeate is completely filtered out, and the retentate and the permeate are collected;

[0093] (8) adding nurica enzyme to the permeate obtained in step (7) for enzymatic treatment, the addition amount of nurica enzyme is 1 g / L, the enzymatic temperature is 50℃, and the enzymatic treatment is stopped when the lactose content is 0.5 g / 100 mL;

[0094] (9) performing β-galactosidase passivation on the enzymatic permeate obtained in step (8), the passivation condition is 95℃, 300s;

[0095] (10) performing UF filtration on the passivated enzymatic permeate obtained in step (9), the membrane core filtration pore size of the UF membrane is 1 Dal, the concentration ratio is 1.5, the pressure is 4 bar, until the permeate is completely filtered out, and the retentate and the permeate are collected;

[0096] (11) backfilling the permeate obtained in step (10) into the retentate obtained in steps (4), (7) and (10), and then performing homogenization and sterilization treatment, the homogenization process is: the preheating temperature is 70℃, and the homogenization pressure is 230 bar; the sterilization is at 126℃ for 2s; thus, the high-nutrition milk is prepared. The protein content of the high-nutrition milk is 5.5 g / 100 mL, and the calcium content is 185 mg / 100 mL.

[0097] Example 4

[0098] The present embodiment provides a preparation method of milk, which comprises the following steps:

[0099] (1) filtering the standardized milk obtained by filtering and standardizing the milk stored at 2℃ to obtain partial skim milk, the standardized fat is 3.0 g / 100 mL, the filter screen with a pore size of 0.50 mm is selected for filtering, the protein content of the partial skim milk is 4 g / 100 mL, the calcium content is 120 mg / 100 mL, and the lactose content is 5 g / 100 mL;

[0100] (2) adding nurica enzyme to the partial skim milk obtained in step (1) for enzymatic treatment, the addition amount of nurica enzyme is 3 g / L, the enzymatic temperature is 60℃, and the enzymatic treatment is stopped when the lactose content is 3 g / 100 mL;

[0101] (3) β-galactosidase inactivation of the enzymatic milk obtained in step (2) is carried out under the conditions of 95℃ and 320s;

[0102] (4) UF filtration is carried out on the inactivated enzymatic milk obtained in step (3), the membrane core filtration pore size of the UF membrane is 20 Dal, the concentration ratio is 1.5, the pressure is 4 bar, until the permeate is completely filtered out, the retentate and the permeate are collected;

[0103] (5) adding nurica enzyme to the permeate obtained in step (4) for enzymatic treatment, the addition amount of nurica enzyme is 2 g / L, the enzymatic temperature is 60℃, and the enzymatic treatment is stopped when the lactose content is 1.2 g / 100 mL;

[0104] (6) β-galactosidase inactivation of the enzymatic permeate obtained in step (5) is carried out under the conditions of 95℃ and 320s;

[0105] (7) UF filtration is carried out on the inactivated enzymatic permeate obtained in step (6), the membrane core filtration pore size of the UF membrane is 20 Dal, the concentration ratio is 1.5, the pressure is 4 bar, until the permeate is completely filtered out, the retentate and the permeate are collected;

[0106] (8) adding nurica enzyme to the permeate obtained in step (7) for enzymatic treatment, the addition amount of nurica enzyme is 2 g / L, the enzymatic temperature is 60℃, and the enzymatic treatment is stopped when the lactose content is 0.1 g / 100 mL;

[0107] (9) β-galactosidase inactivation of the enzymatic permeate obtained in step (8) is carried out under the conditions of 95℃ and 320s;

[0108] (10) UF filtration is carried out on the inactivated enzymatic permeate obtained in step (9), the membrane core filtration pore size of the UF membrane is 20 Dal, the concentration ratio is 1.5, the pressure is 4 bar, until the permeate is completely filtered out, the retentate and the permeate are collected;

[0109] (11) the permeate obtained in step (10) is backfilled into the retentate obtained in steps (4), (7) and (10); then homogenization and sterilization treatment are carried out, the homogenization process is: preheating temperature is 70℃, homogenization pressure is 230 bar, sterilization is at 126℃ for 2s; high-nutrition milk is prepared. The protein content of the high-nutrition milk is 6.5 g / 100 mL, and the calcium content is 200 mg / 100 mL.

[0110] Example 5

[0111] The present embodiment provides a method for preparing milk, comprising the following steps:

[0112] (1) filtering the milk standardized at 2℃ to obtain partially defatted milk, the standardized fat being 3.0 g / 100 mL, the filter aperture being 0.50 mm, the protein content of the partially defatted milk being 2.9 g / 100 mL, the calcium content being 100 mg / 100 mL, and the lactose content being 4 g / 100 mL;

[0113] (2) adding nurica enzyme to the partially defatted milk obtained in step (1) for enzymatic treatment, the addition amount of the nurica enzyme being 1 g / L, the enzymatic temperature being 40℃, and the enzymatic treatment being stopped when the lactose content is 2 g / 100 mL;

[0114] (3) β-galactosidase inactivation of the enzymatic milk obtained in step (2), the inactivation condition being 90℃, 280 s;

[0115] (4) UF filtration of the inactivated enzymatic milk obtained in step (3), the membrane core filtration aperture of the UF membrane being 1 Dal, the concentration ratio being 1.1, the pressure being 1 bar, until the permeate is completely filtered out, and the retentate and the permeate being collected;

[0116] (5) adding nurica enzyme to the permeate obtained in step (4) for enzymatic treatment, the addition amount of the nurica enzyme being 0.5 g / L, the enzymatic temperature being 40℃, and the enzymatic treatment being stopped when the lactose content is 0.8 g / 100 mL;

[0117] (6) β-galactosidase inactivation of the enzymatic permeate obtained in step (5), the inactivation condition being 95℃, 300 s;

[0118] (7) UF filtration of the inactivated enzymatic permeate obtained in step (6), the membrane core filtration aperture of the UF membrane being 20 Dal, the concentration ratio being 1.1, the pressure being 1 bar, until the permeate is completely filtered out, and the retentate and the permeate being collected;

[0119] (8) adding nurica enzyme to the permeate obtained in step (7) for enzymatic treatment, the addition amount of the nurica enzyme being 0.5 g / L, the enzymatic temperature being 50℃, and the enzymatic treatment being stopped when the lactose content is 0.1 g / 100 mL;

[0120] (9) β-galactosidase inactivation of the enzymatic permeate obtained in step (8), the inactivation condition being 90℃, 280 s;

[0121] (10) The permeate obtained in step (9) is subjected to UF filtration, the membrane core filtration pore size of the UF membrane is 20 Dal, the concentration ratio is 1.1, the pressure is 1 bar, until the permeate is completely filtered out, the retentate and the permeate are collected;

[0122] (11) The permeate obtained in step (10) is backfilled into the retentate obtained in steps (4), (7) and (10), and then subjected to homogenization and sterilization treatment, the homogenization process is: the preheating temperature is 70℃, the homogenization pressure is 220 bar; the sterilization is sterilized at 126℃ for 2s; thus high-nutrition milk is prepared. The protein content of the high-nutrition milk is 5g / 100mL, and the calcium content is 170mg / 100mL.

[0123] Comparative Example 1

[0124] The present comparative example provides a preparation method of milk, which comprises the following steps:

[0125] (1) The raw milk stored at 2℃ is filtered after standardization to obtain partially defatted milk, the standardization fat is 3.0g / 100mL, the filter screen with a pore size of 0.50mm is selected for filtration, the protein content of the partially defatted milk is 3.2g / 100mL, the calcium content is 108mg / 100mL, and the lactose content is 5g / 100mL;

[0126] (2) The nurica enzyme is added to the partially defatted milk obtained in step (1) for enzymatic treatment, the addition amount of the nurica enzyme is 2g / L, the enzymatic treatment is stopped when the lactose content is 0.5g / 100mL at an enzymatic temperature of 50℃;

[0127] (3) The enzymatic milk obtained in step (2) is subjected to β-galactosidase passivation, the passivation condition is 95℃ for 300s;

[0128] (4) The passivated enzymatic milk obtained in step (3) is subjected to UF filtration, the membrane core filtration pore size of the UF membrane is 1 Dal, the concentration ratio is 1.5, the pressure is 4 bar, until the protein concentration in the retentate reaches 5.5g / 100mL, the concentration is stopped; then subjected to homogenization and sterilization treatment, the homogenization process is: the preheating temperature is 70℃, the homogenization pressure is 230 bar, the sterilization is sterilized at 126℃ for 2s, thus high-nutrition milk is prepared.

[0129] Comparative Example 2

[0130] The present comparative example provides a preparation method of milk, which comprises the following steps:

[0131] (1) The 2℃ refrigerated cow milk was filtered after standardization to obtain partially defatted milk, the standardization fat was 3.0 g / 100 mL, the filter aperture was 0.50 mm, the protein content of the partially defatted milk was 3.2 g / 100 mL, the calcium content was 108 mg / 100 mL, and the lactose content was 5 g / 100 mL;

[0132] (2) The nurica enzyme was added to the partially defatted milk obtained in step (1) for enzymatic treatment, the addition amount of the nurica enzyme was 2 g / L, the enzymatic temperature was 50℃, and the enzymatic treatment was stopped when the lactose content was 1 g / 100 mL;

[0133] (3) The β-galactosidase of the enzymatic milk obtained in step (2) was inactivated, the inactivation condition was 95℃, 300 s;

[0134] (4) The inactivated enzymatic milk obtained in step (3) was subjected to UF filtration, the membrane core filtration aperture of the UF membrane was 1 Dal, the concentration ratio was 1.5, the pressure was 4 bar, until the permeate was completely filtered out, the retentate and the permeate were collected;

[0135] (5) The nurica enzyme was added to the permeate obtained in step (4) for enzymatic treatment, the addition amount of the nurica enzyme was 1 g / L, the enzymatic temperature was 50℃, and the enzymatic treatment was stopped when the lactose content was 0.6 g / 100 mL;

[0136] (6) The β-galactosidase of the enzymatic permeate obtained in step (5) was inactivated, the inactivation condition was 95℃, 300 s;

[0137] (7) The inactivated enzymatic permeate obtained in step (6) was subjected to UF filtration, the membrane core filtration aperture of the UF membrane was 1 Dal, the concentration ratio was 1.5, the pressure was 4 bar, until the permeate was completely filtered out, the retentate and the permeate were collected;

[0138] (8) The nurica enzyme was added to the permeate obtained in step (7) for enzymatic treatment, the addition amount of the nurica enzyme was 1 g / L, the enzymatic temperature was 50℃, and the enzymatic treatment was stopped when the lactose content was 0.3 g / 100 mL;

[0139] (9) The β-galactosidase of the enzymatic permeate obtained in step (8) was inactivated, the inactivation condition was 95℃, 300 s;

[0140] (10) The inactivated enzymatic permeate obtained in step (9) was subjected to UF filtration, the membrane core filtration aperture of the UF membrane was 1 Dal, the concentration ratio was 1.5, the pressure was 4 bar, until the permeate was completely filtered out, the retentate and the permeate were collected;

[0141] (11) The permeate obtained in step (10) is backfilled into the retentate obtained in steps (4), (7) and (10); and then homogenized and sterilized, the homogenization process being: preheating temperature 70℃, homogenization pressure 230bar; sterilization being at 126℃ for 2s, to obtain the high-nutrition milk. The protein content of the high-nutrition milk is 5.5g / 100mL, and the calcium content is 185mg / 100mL.

[0142] Experimental Example 1: Detection of dietary fiber content of high-nutrition milk

[0143] The milk of each of the above examples and comparative examples was detected for the content of trisaccharide group and above oligogalactose (GOS), and the detection method referred to GB 5009.289-2023 "Determination of oligogalactose in food". The detection results are shown in Table 1. The calculation formula of GOS synthesis rate is: GOS (trisaccharide and above) synthesis rate = GOS (trisaccharide and above) content / original milk lactose content.

[0144] Table 1

[0145] The changes in the contents of lactose and GOS during the enzymatic hydrolysis of Comparative Example 1 are shown in Figure 1. At 0-4min, one molecule of lactose is rapidly hydrolyzed to produce one molecule of galactose and one molecule of glucose, one molecule of galactose is combined with one molecule of lactose under the action of transgalactosylase to produce (Gal)2Glc, and one molecule of galactose is combined with one molecule of (Gal)2Glc under the action of transgalactosylase to produce (Gal)3Glc, and so on. Therefore, at 0-4min, the content of oligogalactose also rapidly increases. When the content of lactose continuously decreases and the content of GOS continuously increases, the β-galactosidase not only hydrolyzes lactose, but also gradually hydrolyzes the α-(1-4) glycosidic bond in GOS, and the (Gal)2Glc molecule is hydrolyzed into one molecule of Gal2 and one molecule of glucose. Gal2 does not belong to dietary fiber, which leads to a decrease in the rate of β-galactosidase hydrolysis of lactose, a decrease in the rate of galactose production, and a decrease in the rate of GOS synthesis. After 20min, the rate of hydrolysis of GOS is greater than the rate of synthesis of GOS, thereby showing a downward trend of GOS. The final sugar system product of Comparative Example 1 is oligosaccharide of (Gal) i Glc or (Gal) j , wherein i = 2-8 and j = 2-8, in addition to GOS, there is also part of lactose, glucose and galactose.

[0146] The changes in the contents of lactose and GOS during the three-stage enzymatic hydrolysis of Example 1 are shown in Figures 2, 3 and 4. It can be seen that the enzyme is inactivated after the lactose content is controlled to be 2.5g / 100mL, and then the ultrafiltration technology is used to retain (Gal) i Glc or (Gal)j The oligosaccharide of (wherein i≥2, j≥3) avoids the possibility of hydrolysis of dietary fiber by β-galactosidase, and re-forms lactose, Gal2, glucose and galactose into a new sugar system. By controlling the composition of the sugar system, the synthesis of GOS and the hydrolysis of lactose can be kept at the highest rate, and when the lactose is reduced to 1 g / 100 mL, the β-galactosidase is inactivated again and re-ultrafiltration and concentration are performed, the lactose can be fully hydrolyzed to below 0.5 g / 100 mL, and the Gal2, glucose and galactose are converted into GOS to a great extent, thereby significantly increasing the content and yield of GOS.

[0147] Experimental Example 2 Sensory test of high-nutrition milk

[0148] The high-nutrition milk samples of Examples 1-3 and Comparative Examples 1-2 were subjected to a sensory test of 100 consumers, and the sensory test was performed by using a 7-point preference scale method (a conventional method, i.e., a sample was edited with a 3-digit random number, and the preference score of each sample was scored with a full score of 7 points). The results showed that the preference scores of the high-nutrition milk of Examples 1-5 were 5.53, 5.19, 5.33, 5.26 and 5.12, respectively, the preference score of the high-nutrition milk of Comparative Example 1 was 4.22, and the preference score of the high-nutrition milk of Comparative Example 2 was 4.56. Within a 95% confidence interval, the consumers had significant differences in the preference of the high-nutrition milk of Examples 1-5 and Comparative Examples 1-2, which indicated that the overall preference of the high-nutrition milk of Examples 1-5 was more acceptable to consumers, which might be due to the optimization of the sugar system in the enzymatic process in the preparation method of Examples 1-5, resulting in less glucose and more dietary fiber in the prepared high-nutrition milk, and the overall sweetness and milk aroma synergistically made the flavor more suitable.

[0149] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for part of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method of preparing milk, characterized in that, The method comprises: (1) treating the milk raw material with β-galactosidase to end the enzymatic hydrolysis when the lactose content is 2-3 g / 100 mL, and then performing ultrafiltration on the enzymatic hydrolysis solution to collect the retentate and the permeate as the first retentate and the first permeate, respectively; (2) treating the first permeate with β-galactosidase to end the enzymatic hydrolysis when the lactose content is 0.8-1.2 g / 100 mL, and then performing ultrafiltration on the enzymatic hydrolysis solution to collect the retentate and the permeate as the second retentate and the second permeate, respectively; (3) treating the second permeate with β-galactosidase to end the enzymatic hydrolysis when the lactose content is 0.1-0.5 g / 100 mL, and then performing ultrafiltration on the enzymatic hydrolysis solution to collect the retentate and the permeate as the third retentate and the third permeate, respectively; (4) mixing the third permeate with the first retentate, the second retentate and the third retentate to obtain a mixed solution. The β-galactosidase is a β-galactosidase having transgalactosyl activity.

2. The method of claim 1, wherein The synthesis rate of the trisaccharide and higher oligogalactose in the preparation method is 60% or more.

3. The method of preparing milk according to claim 1 or 2, characterized in that, The membrane core used in the ultrafiltration has a pore size of 1-20 Dal; and / or, the concentration ratio is 1.1-1.5, and / or, the pressure is 1-4 bar.

4. The method of preparing milk according to any one of claims 1 to 3, characterized in that, The temperature of the enzymatic hydrolysis is 40-60℃; In step (1), the β-galactosidase is added in an amount of 1-3 g / L; In steps (2) and (3), the β-galactosidase is added in an amount of 0.5-2 g / L.

5. The method of preparing milk according to any one of claims 1 to 3, characterized in that, The end of the enzymatic hydrolysis is achieved by passivation treatment of the β-galactosidase.

6. The method of claim 5, wherein the milk is prepared by, The passivation treatment is performed at 90-95℃ for 280-320 s.

7. The method of preparing milk according to any one of claims 1 to 6, characterized in that, The lactose content of the milk raw material is 4-5 g / 100 mL, and / or, the protein content is 2.9-4 g / 100 mL, and / or, the fat content is 2.7-4 g / 100 mL, and / or, the calcium content is 100-120 mg / 100 mL.

8. The method of preparing milk according to any one of claims 1 to 6, characterized in that, The method further comprises the steps of homogenizing and sterilizing the mixed solution.

9. A milk, characterized in that, The milk is prepared by the method of any one of claims 1-8.

10. The milk according to claim 9, characterized in that, The content of the trisaccharide and higher oligogalactose in the milk is not less than 5.5 g / 100 mL; and / or, the protein content is not less than 5.0 g / 100 mL, and / or, the calcium content is not less than 170 mg / 100 mL.

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