Method for preparing milk product containing galactooligosaccharide and free of lactose and milk product thereof

Abstract

The invention discloses a method for preparing a milk product containing galactooligosaccharide and free of lactose, which comprises the steps of using common lactase and beta-galactosidase with transgalactosylation activity, and the common lactase decomposes lactose in milk product raw materials into galactose and glucose; wherein the beta-galactosidase with transgalactosylation activity decomposes lactose in a dairy product raw material into galactose and glucose, and transfers the galactose obtained by decomposition to a hydroxyl group of the lactose in the dairy product raw material to be converted into galactooligosaccharide, and optionally, the galactooligosaccharide is converted into higher-order galactooligosaccharide; the galactose obtained by decomposition comprises: 1) galactose obtained by decomposing lactose with common lactase; and / or (2) galactose obtained by decomposing lactose by beta-galactosidase having transgalactosylation activity. According to the method, galactooligosaccharide can be produced in situ to reach a high level, the lactose-free standard is achieved with a simple process and lower cost, and the sugar reducing effect is provided.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese patent application 202111453072.8 filed with the State Intellectual Property Office of China on December 1, 2021, and the entire contents of such priority are incorporated herein by reference. Technical Field

[0003] The present invention relates to a method for preparing a dairy product and a dairy product obtained by the method. Specifically, the present invention relates to a method for preparing a dairy product containing oligogalactose and free of lactose and a dairy product obtained by the method. Background Art

[0004] Galactose oligosaccharide (GOS) is a functional oligosaccharide. It is an excellent nutrient source and effective growth factor for beneficial bacteria in the human intestine, such as Bifidobacterium and Lactobacillus acidophilus, and can improve the digestive and absorptive functions of the human intestine. Furthermore, the lactose contained in dairy products such as milk can cause abdominal pain, flatulence, and diarrhea in people with lactose intolerance. Therefore, the development of lactose-free dairy products containing galactose oligosaccharides is crucial.

[0005] Existing technologies generally achieve the effect of increasing the content of galacto-oligosaccharides and reducing lactose in dairy products through the following two methods:

[0006] 1) Use β-galactosidase with high transgalactosylation activity to convert lactose in dairy raw materials into galacto-oligosaccharides, for example:

[0007] CN101396048A discloses a method for producing galacto-oligosaccharide-rich milk, which includes heating cow's milk, separating the fat to obtain skim milk, pasteurizing it, cooling it, and then hydrolyzing it with immobilized β-galactosidase. UHT sterilization is then followed by cooling and packaging. Specifically, the method hydrolyzes cow's milk with β-galactosidase to produce galacto-oligosaccharide-rich milk. However, the lactose in the dairy product raw material produced by this method is not completely decomposed (see the lactose content described in Examples 1-5).

[0008] CN106455600A discloses a method for producing a galacto-oligosaccharide-containing dairy product at low temperature using β-galactosidase with high transgalactosylation activity, wherein heat treatment is used to inactivate the enzyme. Similarly, however, the lactose in the dairy product raw material produced by this method is not completely decomposed (see the lactose content described in Example 3).

[0009] 2) Use lactase to completely decompose the lactose in dairy raw materials and add galacto-oligosaccharides, for example:

[0010] CN104286174A discloses a method for preparing lactose-free fermented milk, wherein lactose in raw milk is decomposed into glucose and galactose in two steps using lactase produced by yeast and then mold, and oligosaccharides are added to the raw materials as a sweetener (see paragraph

[0014] of the specification and Examples 2 and 4). However, this method requires the additional addition of oligosaccharides, which increases production costs and the risk of introducing external contamination during the production process.

[0011] CN100473283C also discloses a method for producing a dairy composition, which describes the use of multiple separation steps combining ultrafiltration, nanofiltration, and reverse osmosis to obtain a lactose-free dairy raw material. While this combination of ultrafiltration, nanofiltration, and reverse osmosis can remove most lactose, it is complex, energy-intensive, and costly, and results in significant nutrient loss in the fresh milk during operation.

[0012] In summary, there is an urgent need for a method for preparing a lactose-free dairy product containing galacto-oligosaccharides that can overcome the above defects, especially a method for preparing a lactose-free dairy product containing galacto-oligosaccharides, which can produce galacto-oligosaccharides in situ without adding additional galacto-oligosaccharides and achieve a high level of galacto-oligosaccharides, and can also achieve the lactose-free standard in the final dairy product with a simple process and low cost. Summary of the Invention

[0013] The technical problem to be solved by the present invention is to overcome the following disadvantages of the current method for preparing a galacto-oligosaccharide-containing and lactose-free dairy product:

[0014] 1) The method of converting lactose in dairy raw materials into galacto-oligosaccharides by simply using β-galactosidase with high transgalactosylation activity has the problem that the lactose in the prepared dairy raw materials is not completely decomposed.

[0015] 2) The method of simply using lactase to completely decompose lactose in dairy raw materials and adding galacto-oligosaccharides cannot produce enough galacto-oligosaccharides in situ, so additional galacto-oligosaccharides need to be added, which increases production costs and the risk of introducing external contamination during the production process.

[0016] The present invention provides a method for preparing a lactose-free dairy product containing galacto-oligosaccharides, wherein:

[0017] The method comprises the steps of using common lactase and β-galactosidase having transgalactosylation activity,

[0018] The common lactase decomposes lactose in dairy raw materials into galactose and glucose;

[0019] wherein the β-galactosidase having transgalactosylation activity decomposes lactose in the dairy raw material into galactose and glucose, and transfers the decomposed galactose to the hydroxyl group of the lactose in the dairy raw material to convert it into galacto-oligosaccharides; optionally, the β-galactosidase having transgalactosylation activity transfers the decomposed galactose to the hydroxyl group of the galacto-oligosaccharides to convert them into higher-order galacto-oligosaccharides; and

[0020] The galactose obtained by the decomposition includes galactose selected from the group consisting of:

[0021] 1) galactose obtained by decomposing lactose by the common lactase; and

[0022] 2) Galactose obtained by decomposing lactose with the β-galactosidase having transgalactosylation activity.

[0023] The present invention also provides a lactose-free dairy product containing galacto-oligosaccharide prepared by the method of the present invention.

[0024] Compared with the existing technology, the present invention has the following advantages: the method can produce a high level of galacto-oligosaccharide content in dairy products without adding additional galacto-oligosaccharides to the dairy raw materials. Moreover, due to the combined use of β-galactosidase with transgalactosylation activity and ordinary lactase, the method can also achieve lactose-free standards for dairy products with a simple process and low cost. Moreover, because galacto-oligosaccharides are produced using lactose and monosaccharides originally contained in the dairy raw materials, galacto-oligosaccharides cannot be absorbed by the human body, thus achieving the effect of reducing sugar.

[0025] From the following detailed description, other objects, features and advantages of the present invention will become apparent. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of example only, as various changes and modifications within the spirit and scope of the present invention will become apparent to those skilled in the art from this detailed description. DETAILED DESCRIPTION

[0026] The present invention provides a method for preparing a lactose-free dairy product containing galacto-oligosaccharides, wherein:

[0027] The method comprises the steps of using common lactase and β-galactosidase having transgalactosylation activity,

[0028] The common lactase decomposes lactose in dairy raw materials into galactose and glucose;

[0029] wherein the β-galactosidase having transgalactosylation activity decomposes lactose in the dairy raw material into galactose and glucose, and transfers the decomposed galactose to the hydroxyl group of the lactose in the dairy raw material to convert it into galacto-oligosaccharides; optionally, the β-galactosidase having transgalactosylation activity transfers the decomposed galactose to the hydroxyl group of the galacto-oligosaccharides to convert them into higher-order galacto-oligosaccharides; and

[0030] The galactose obtained by the decomposition includes galactose selected from the group consisting of:

[0031] 1) galactose obtained by decomposing lactose by the common lactase; and

[0032] 2) Galactose obtained by decomposing lactose with the β-galactosidase having transgalactosylation activity.

[0033] The method of the present invention can produce a high level of galacto-oligosaccharide content in dairy products without adding additional galacto-oligosaccharide to the dairy raw materials. Moreover, due to the combined use of β-galactosidase with transgalactosylation activity and ordinary lactase, the method can also enable dairy products to meet lactose-free standards with a simple process, low cost and high production efficiency. In addition, since galacto-oligosaccharide is produced using lactose and monosaccharides originally contained in the dairy raw materials, galacto-oligosaccharide cannot be absorbed by the human body, thus achieving the effect of reducing sugar (i.e., reducing the sum of monosaccharides and disaccharides).

[0034] The term "galacto-oligosaccharide" or "GOS" refers to a stoichiometric formula (Gal) i Glc or (Gal) j Oligosaccharides wherein i = 1-8 and j = 2-9. GOS typically exist as a mixture of various GOS molecules with different degrees of polymerization and different linkage structures. The mixture may include both linear GOS molecules and branched GOS molecules. Lactose is not considered a GOS molecule.

[0035] The method of the present invention can use various "β-galactosidases with transgalactosylation activity" available in the art, as long as the β-galactosidase with transgalactosylation activity decomposes lactose in the dairy raw material into galactose and glucose, and transfers the decomposed galactose to the hydroxyl group of the lactose in the dairy raw material to convert it into oligomeric galactose. Most preferably, the β-galactosidase with transgalactosylation activity is the trade name Nurica® produced by International Flavors & Fragrances (IFF). TM Enzyme preparations, Nurica TM It can utilize lactose in dairy products to naturally produce dietary fiber in the form of galacto-oligosaccharides. TMThe enzyme activity of the enzyme preparation ranges from 500-800 BLU / g, preferably 540-760 BLU / g, and the Nurica TM The content of β-galactosidase in the enzyme preparation is 5-8% (w / w).

[0036] The method of the present invention can utilize any conventional lactase available in the art, as long as the conventional lactase breaks down lactose in the dairy raw material into galactose and glucose. Examples include DuPont's GODO-YNL2 lactase and Maxilact LGI 5000. Most preferably, the conventional lactase is DSM's Maxilact LGI 5000, which has an enzyme activity of 5000 NLU / g or greater.

[0037] Preferably, the amount of the β-galactosidase with transgalactosylation activity ranges from 0.5 to 12 g / L of dairy raw material, further preferably 2.0 to 11.0 g / L of dairy raw material, preferably 0.5 to 6.0 g / L of dairy raw material, further preferably 3.0 to 4.0 g / L of dairy raw material; and the weight ratio of the common lactase to the β-galactosidase with transgalactosylation activity ranges from 1:1 to 1:25, preferably the weight ratio of the common lactase to the β-galactosidase with transgalactosylation activity ranges from 1:1 to 1:10, further preferably the weight ratio of the common lactase to the β-galactosidase with transgalactosylation activity ranges from 1:6 to 1:7, more preferably the weight ratio of the common lactase to the β-galactosidase with transgalactosylation activity ranges from 1:4 to 1:22.

[0038] The present invention has no particular requirements for the order of adding the β-galactosidase with transgalactosylation activity and the ordinary lactase. Preferably, the method first adds the β-galactosidase with transgalactosylation activity and then adds the ordinary lactase. More preferably, the method adds the ordinary lactase after inactivating or partially inactivating the β-galactosidase with transgalactosylation activity. More preferably, the method adds the β-galactosidase with transgalactosylation activity and the ordinary lactase at the same time. Adding the two enzymes at the same time can further shorten the total time used for enzymolysis in the entire production process. In addition, the step of separate enzyme inactivation can also be omitted, and other step conditions after enzymolysis (such as sterilization) can achieve the effect of enzyme inactivation.

[0039] The method of the present invention has no particular limitations on the dairy raw materials that can be used, and the raw materials can be selected from the group consisting of fresh milk, reconstituted milk, formula milk, and concentrated milk. The animal sources of the dairy raw materials include, but are not limited to, humans, cows, sheep, goats, buffaloes, camels, llamas, mares, and deer, preferably from cows and sheep. Specifically, the dairy raw materials that can be used in the method of the present invention can preferably be selected from one or more of the following:

[0040] 1. Fresh whole milk or skim milk;

[0041] 2. Reconstituted milk with whole milk powder, skim milk powder or concentrated milk protein;

[0042] 3. After skimming and any membrane filtration technology to concentrate and backfill the cream to form fresh milk with the required fat, protein and lactose content;

[0043] 4. Fresh milk concentrated by freeze concentration technology; and

[0044] 5. Fresh milk concentrated by membrane evaporation technology.

[0045] Preferably, the dairy raw materials are those described in items 3-5 above. The content of fat, protein, lactose and other ingredients in the dairy raw materials can be varied according to the needs of different groups of people. For example, concentration can significantly increase the protein content and improve intake efficiency.

[0046] Generally, the lactose content of fresh whole milk or skim milk is 4.0-5.4%, preferably 4.5-5.4%. Preferably, the dairy raw material may have a lactose content of not less than 5.0%. The dairy raw material may also have a lactose content of up to 15.0%. Preferably, the dairy raw material has a lactose content of 6.0%-10.0%, preferably the dairy raw material has a lactose content of 7.0%-8.0%; more preferably the dairy raw material has a lactose content of 8.0%-9.0%; more preferably the dairy raw material has a lactose content of 9.0%-10.0%. The lactose in the preferred range can serve as a raw material for in situ production of a sufficient amount of galacto-oligosaccharides.

[0047] Generally, the total protein content of fresh whole or skim milk is 3.2-3.8%. Preferably, the condensed milk has a total protein content of no less than 4.0%. Preferably, the condensed milk has a protein content of 4.0%-10.0%. More preferably, the condensed milk has a protein content of 5.0%-9.0%, and preferably, the condensed milk has a protein content of 5.0%-6.0%. Concentrated milk within this protein content range easily meets the body's protein needs, is easily absorbed by the gastrointestinal tract, and does not require excessive fluid intake, thereby avoiding increasing gastrointestinal burden.

[0048] The concentrated milk can be obtained by various concentration methods commonly used in the art, for example, by one or a combination of reverse osmosis concentration, ultrafiltration, nanofiltration, and membrane filtration. Preferably, the reverse osmosis concentration is performed below 25°C, more preferably at 2-10°C. The membrane filtration can be ultrafiltration, nanofiltration, or reverse osmosis. Preferably, the concentrated fresh milk has a total protein content of not less than 4.0%; more preferably, a protein content of 4.0%-10.0%; more preferably, a protein content of 5.0%-9.0%, and even more preferably, a protein content of 5.0%-6.0%.

[0049] In addition, the applicants of the present application have discovered that, when using a concentrated high-protein dairy raw material with a total protein content of not less than 4.0%, the use of β-galactosidase with transgalactosylation activity alone is unable to completely hydrolyze the lactose in the high-protein dairy raw material. Furthermore, if the β-galactosidase with transgalactosylation activity is not inactivated after the enzymatic hydrolysis step, the presence of the enzyme during storage may actually decompose the already formed galacto-oligosaccharides, for example, reducing the GOS in the final product. In particular, when a fermentation step is performed after the enzymatic hydrolysis step to prepare dairy products such as yogurt, the coexistence of lactic acid bacteria and the uninactivated β-galactosidase with transgalactosylation activity in the fermentation step will further consume the GOS produced in the enzymatic hydrolysis step, significantly reducing the GOS in the final product.

[0050] Therefore, it is preferred that after the β-galactosidase with transgalactosylation activity completes the generation of galacto-oligosaccharides, the β-galactosidase with transgalactosylation activity is promptly inactivated, thereby reducing or avoiding a significant reduction in galacto-oligosaccharides during subsequent storage or further processing (such as fermentation). The inactivation of the β-galactosidase with transgalactosylation activity can be carried out by inactivation methods such as heating inactivation (such as keeping at 90-95° C. for 5-10 minutes) and acid inactivation (such as reducing the pH value of the system to below 4.5 by fermentation) commonly used in the art. The method of the present invention can not only produce galacto-oligosaccharides in situ at a high level and ensure the stability of galacto-oligosaccharides, but also achieve the lactose-free standard with a simple process, lower cost and higher production efficiency, and achieve a sugar reduction effect.

[0051] The present invention also provides a lactose-free dairy product containing galacto-oligosaccharides prepared by the method of the present invention, wherein, preferably, based on the dairy product, the galacto-oligosaccharide content is 0.5-3.8 g / 100 ml, 0.5-2.3 g / 100 ml, preferably >1.0 g / 100 ml, and the lactose content is less than 0.2 g / 100 ml of the dairy product, more preferably less than 0.1 g / 100 ml of the dairy product, and most preferably the lactose content is 0%. The dairy product can be plain milk, flavored milk, ice cream, yogurt, or any liquid nutritional product that can be prepared from milk or milk components.

[0052] The following examples are provided to further illustrate the purpose, structural features and advantages of the present invention. The following examples are provided only for the purpose of better illustrating the present invention and do not limit the scope of protection.

[0053] Example 1

[0054] This example is used to illustrate the method for preparing a galacto-oligosaccharide-containing and lactose-free dairy product and the dairy product.

[0055] (1) Preparation of high-protein and high-lactose milk base

[0056] 188 kg of fresh skim milk (total protein content of 3.5% and lactose content of 4.5%) was concentrated by reverse osmosis at 4±2°C, and cream with a fat content of 45.0% was added to adjust the fat content in the reconstituted fresh milk, ultimately obtaining a high-protein and high-lactose milk base with a total protein content of 5.3%, a fat content of 4.0%, and a lactose content of 7.5%.

[0057] (2) Enzymatic hydrolysis of high-protein and high-lactose milk base

[0058] Nurica was added to the high protein milk base (5.3% protein + 4.0% fat + 7.5% lactose) obtained in step (1) at a concentration of 3.2 g / kg high protein milk base. TM After enzymatic hydrolysis of the enzyme preparation (enzyme activity 650±150 BLU / g) at 10°C for 15 hours, Maxilact LGI 5000 (enzyme activity greater than 5000 NLU / g) was added at a concentration of 0.5 g / kg high-protein milk base and enzymatic hydrolysis was continued at 10°C for 15 hours.

[0059] (3) Fermentation after enzymatic hydrolysis

[0060] The high-protein, high-lactose milk base obtained after enzymatic hydrolysis in step (2) was heated to 30°C, and a kefir fermentation preparation (Choozit Kefir Mild 01 commercially available from DuPont) was added at a concentration of 0.0050 g / L, and the mixture was maintained at 30°C for 20 hours. Finally, yogurt with a pH of 4.45 was obtained.

[0061] Example 2

[0062] This example is used to illustrate the method for preparing a galacto-oligosaccharide-containing and lactose-free dairy product and the dairy product.

[0063] (1) Preparation of high-protein and high-lactose milk base

[0064] 188 kg of fresh skim milk (total protein content of 3.5% and lactose content of 4.5%) was concentrated by reverse osmosis at 4±2°C, and cream with a fat content of 45.0% was added to adjust the fat content in the reconstituted fresh milk, ultimately obtaining a high-protein and high-lactose milk base with a total protein content of 5.3%, a fat content of 4.0%, and a lactose content of 7.5%.

[0065] (2) Enzymatic hydrolysis of high-protein and high-lactose milk base

[0066] Nurica was added to the high protein milk base (5.3% protein + 4.0% fat + 7.5% lactose) obtained in step (1) at a concentration of 3.2 g / kg high protein milk base. TM After enzymatic hydrolysis of the enzyme preparation (enzyme activity 650±150 BLU / g) at 10°C for 15 hours, Maxilact LGI 5000 (enzyme activity greater than 5000 NLU / g) was added at a concentration of 0.5 g / kg high-protein milk base and enzymatic hydrolysis was continued at 10°C for 15 hours.

[0067] (3) Enzymatic hydrolysis followed by fermentation to prepare yogurt

[0068] The enzymatically hydrolyzed high-protein, high-lactose milk base obtained in step (2) was heated to 42°C, and a YO-MIX 558 fermentation preparation (a commercially available lactic acid bacteria preparation containing Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus) was added at a concentration of 0.0274 g / L. The mixture was then maintained at 42°C for 20 hours. Finally, a yogurt with a pH of 3.95 was obtained.

[0069] Example 3

[0070] This example is used to illustrate the method for preparing a galacto-oligosaccharide-containing and lactose-free dairy product and the dairy product.

[0071] (1) Preparation of high-protein and high-lactose milk base

[0072] 188 kg of fresh skim milk (total protein content of 3.5% and lactose content of 4.5%) was concentrated by reverse osmosis at 5°C, and cream with a fat content of 45.0% was added to adjust the fat content in the reconstituted fresh milk, ultimately obtaining a high-protein and high-lactose milk base with a total protein content of 5.3%, a fat content of 4.0%, and a lactose content of 7.5%.

[0073] (2) Enzymatic hydrolysis of high-protein and high-lactose milk base

[0074] Nurica was added to the high protein milk base (5.3% protein + 4.0% fat + 7.5% lactose) obtained in step (1) at a concentration of 3.2 g / kg high protein milk base. TM The enzyme preparation (enzyme activity 650±150 BLU / g) was hydrolyzed at 10°C for 15 hours and then heat-treated at 95°C for 7 minutes. After the heat treatment, the temperature was lowered to 42°C, and Maxilact LGI 5000 (enzyme activity greater than 5000 NLU / g) was added at a concentration of 0.5g / kg high-protein milk base. The enzymatic hydrolysis was continued at 10°C for 15 hours to obtain the final dairy product.

[0075] Examples 4-9

[0076] This example is used to illustrate the method for preparing a galacto-oligosaccharide-containing and lactose-free dairy product and the dairy product.

[0077] (1) Preparation of high-protein and high-lactose milk base

[0078] 188 kg of fresh milk (total protein content of 3.3% and lactose content of 4.3%) was concentrated by reverse osmosis at 5°C, and cream with a fat content of 30-45.0% was added to adjust the fat content in the reconstituted fresh milk. The result was a high-protein, high-lactose milk base with a total protein content of 6.5%, a fat content of 3.8%, and a lactose content of 7.5-9.8% (see Table 1 for details).

[0079] (2) Enzymatic hydrolysis of high-protein and high-lactose milk base

[0080] Add Nurica to the high protein milk base (6.5% protein + 3.8% fat + 7.5% lactose or 6.5% protein + 3.8% fat + 9.8% lactose) obtained in step (1) TM The enzyme preparation (enzyme activity 650±150 BLU / g) and MaxilactLGI 5000 (enzyme activity greater than 5000 NLU / g) were enzymatically hydrolyzed at 10°C for 18-20 hours and then heat-treated at 90°C for 10 minutes to obtain the final dairy product. TM The concentrations of enzyme preparations and Maxilact LGI 5000 are shown in Table 1 below.

[0081] Table 1

[0082]

[0083] Comparative Example 1

[0084] This comparative example is used to illustrate the prior art method for preparing a galacto-oligosaccharide-containing and lactose-free dairy product and the dairy product.

[0085] (1) Preparation of high-protein and high-lactose milk base

[0086] 188 kg of fresh skim milk (total protein content of 3.5% and lactose content of 4.5%) was concentrated by reverse osmosis at 5°C, and cream with a fat content of 45.0% was added to adjust the fat content in the reconstituted fresh milk, ultimately obtaining a high-protein and high-lactose milk base with a total protein content of 5.3%, a fat content of 4.0%, and a lactose content of 7.5%.

[0087] (2) Only Maxilact LGI 5000 is used to enzymatically hydrolyze high-protein and high-lactose milk-based

[0088] Maxilact LGI 5000 (enzyme activity greater than 5000 NLU / g) was added to the high-protein milk base (5.3% protein + 4.0% fat + 7.5% lactose) obtained in step (1) at a concentration of 0.5 g / kg high-protein milk base, and the final dairy product was obtained after enzymatic hydrolysis at a temperature of 10°C for 15 hours.

[0089] Comparative Example 2

[0090] This comparative example is used to illustrate the prior art method for preparing a galacto-oligosaccharide-containing and lactose-free dairy product and the dairy product.

[0091] (1) Preparation of high-protein and high-lactose milk base

[0092] 188 kg of fresh skim milk (total protein content of 3.5% and lactose content of 4.5%) was concentrated by reverse osmosis at 5°C, and cream with a fat content of 45.0% was added to adjust the fat content in the reconstituted fresh milk, ultimately obtaining a high-protein and high-lactose milk base with a total protein content of 5.3%, a fat content of 4.0%, and a lactose content of 7.5%.

[0093] (2) Only use Nurica TM Enzyme preparation for enzymatic hydrolysis of high protein and high lactose milk base

[0094] Nurica was added to the high protein milk base (5.3% protein + 4.0% fat + 7.5% lactose) obtained in step (1) at a concentration of 3.2 g / kg high protein milk base. TM The enzyme preparation (enzyme activity 650±150 BLU / g) was enzymatically hydrolyzed at 10°C for 15 hours to obtain the final dairy product.

[0095] Comparative Example 3

[0096] This comparative example is used to illustrate the prior art method for preparing a galacto-oligosaccharide-containing and lactose-free dairy product and the dairy product.

[0097] (1) Preparation of high-protein and high-lactose milk base

[0098] 188 kg of fresh milk (total protein content of 3.3% and lactose content of 4.3%) was concentrated by reverse osmosis at 5°C, and cream with a fat content of 30-45.0% was added to adjust the fat content in the reconstituted fresh milk, ultimately obtaining a high-protein and high-lactose milk base with a total protein content of 6.5%, a fat content of 3.8% and a lactose content of 9.8%.

[0099] (2) Only use Nurica TM Enzyme preparation for enzymatic hydrolysis of high protein and high lactose milk base

[0100] Nurica was added to the high protein milk base (6.5% protein + 3.8% fat + 9.8% lactose) obtained in step (1) at a concentration of 2.0 g / kg high protein milk base. TM The enzyme preparation (enzyme activity 650±150 BLU / g) was enzymatically hydrolyzed at 10°C for 20 hours and then heat-treated at 90°C for 10 minutes to obtain the final dairy product.

[0101] The dairy products obtained in the above Examples 1-9 and Comparative Examples 1-3 were all sterilized by ultra-high temperature instantaneous sterilization (UHT) at a sterilization temperature of 137 degrees Celsius and a sterilization time of 4 seconds.

[0102] Effect verification example

[0103] The sugar composition of the dairy products obtained in Examples 1-3 and Comparative Examples 1-2 was tested under the same conditions.

[0104] The test method for sugar composition is as follows:

[0105] Carrez reagents 1 & 2 were added to 1 ml of the sample to be tested in an amount sufficient to cause all solids to condense. The biphasic mixture was centrifuged for 15 minutes (6000 rpm) and filtered again using a disposable PTFE microfilter (0.22 micron). The final clear solution of sugars was then placed in an HPLC vial and analyzed.

[0106] The HPLC method used was as follows:

[0107] System: Waters

[0108] Column Agilent HiPlex Ca polymeric ion exchange column

[0109] Eluent: MilliQ water

[0110] Column: Temperature: 60°C

[0111] Flow rate: 0.6 mL / min

[0112] Pressure: 600 psi (1000 psi maximum for this column)

[0113] Detector: RID, at 35°C

[0114] Quantification is based on peak area and known lactose concentration.Also calculated the response coefficient of all sugars.Previously, the retention time of oligosaccharides has been determined using analytical standards of monosaccharides and DP2, DP3 and DP4 oligosaccharides from Sigma.

[0115] The sugar composition test was conducted on the dairy product immediately after preparation, after storage at 10°C for 3 days, and after storage at 10°C for 17 days. The test results are shown in Table 2 below:

[0116] Table 2

[0117]

[0118] The unit of the test results in the above sugar composition test is g / 100g

[0119] ***The storage temperature for this test was 10°C. At this temperature, the shelf life of yogurt products generally does not exceed 7 days. Therefore, the sugar composition of Examples 1-2 after 17 days of storage was not measured.

[0120] As can be seen from Table 2, the protein and lactose concentrations of the dairy raw materials used in Examples 1-3 were increased after concentration. Due to the combined use of β-galactosidase with high transgalactosylation activity and conventional lactase, the high lactose content in the concentrated milk was completely broken down and converted into GOS, resulting in a dairy product high in protein, high in galacto-oligosaccharides, and low in monosaccharides. In Comparative Examples 1-2, where either β-galactosidase with high transgalactosylation activity or conventional lactase was used alone, either the lactose was not completely broken down or no galacto-oligosaccharides were produced, failing to achieve the superior properties of the dairy products prepared by the method of the present invention.

[0121] In addition, since the preparation process of yogurt also includes a fermentation step, those skilled in the art generally believe that fermentation will cause the decomposition of galacto-oligosaccharides. However, the results shown in Table 3 below show that before and after the yogurt fermentation step of different processes in Examples 1-2 of the present invention, the content of naturally produced galacto-oligosaccharides is not significantly reduced due to the fermentation step, and still meets the amount of galacto-oligosaccharides required to produce a prebiotic effect.

[0122] Table 3

[0123]

[0124] That is, the methods of Examples 1-2 of the present invention further include a fermentation step after the enzymatic hydrolysis step to prepare yogurt. The fermentation step not only does not significantly affect the GOS content, but also, compared with the technical solution of Example 3 in which β-galactosidase with high transgalactosylation activity is inactivated by heating, the technical solution including the fermentation step can also omit the special step of inactivating the enzyme, thereby achieving the technical effect of improving production efficiency and saving production costs.

[0125] For the samples of Examples 4-9 and Comparative Example 3, sugar composition tests were performed immediately after the dairy products were prepared:

[0126] Table 4

[0127]

[0128] As can be seen from Table 4, the simultaneous addition of the two enzymes can significantly reduce the time required for enzymatic hydrolysis, and the final dairy product can meet the lactose-free national standard GB28050-2011 content requirements.

[0129] The invention illustratively disclosed herein suitably can be practiced in the absence of any element not specifically disclosed herein. However, it will be apparent to those skilled in the art that many changes, variations, improvements, other uses and applications of the method are possible, and changes, variations, improvements, other uses and applications that do not depart from the spirit and scope of the invention are also considered to be encompassed by the invention, which is limited only by the appended claims.

Claims

1. A method for preparing a lactose-free dairy product containing galacto-oligosaccharides, characterized in that: The method comprises the steps of using common lactase and β-galactosidase having transgalactosylation activity, The common lactase decomposes lactose in dairy raw materials into galactose and glucose; wherein the β-galactosidase having transgalactosylation activity decomposes lactose in the dairy raw material into galactose and glucose, and transfers the decomposed galactose to the hydroxyl group of the lactose in the dairy raw material to convert it into galacto-oligosaccharides; optionally, the β-galactosidase having transgalactosylation activity transfers the decomposed galactose to the hydroxyl group of the galacto-oligosaccharides to convert them into higher-order galacto-oligosaccharides; and The galactose obtained by the decomposition includes galactose selected from the group consisting of: 1) galactose obtained by decomposing lactose by the common lactase; and 2) Galactose obtained by decomposing lactose with the β-galactosidase having transgalactosylation activity.

2. The method according to claim 1, wherein The dosage of the β-galactosidase with transgalactosylation activity is in the range of 0.5-12.0 g / L of dairy raw material; and the weight ratio of the common lactase to the β-galactosidase with transgalactosylation activity is in the range of 1:1 to 1:

25.

3. The method according to claim 2, wherein The dosage of the β-galactosidase with transgalactosylation activity is in the range of 0.5-6.0 g / L of dairy raw material; and the weight ratio of the common lactase to the β-galactosidase with transgalactosylation activity is in the range of 1:1 to 1:

10.

4. The method according to claim 2, wherein The dosage of the β-galactosidase with transgalactosylation activity is in the range of 2.0-11.0 g / L of dairy raw material; and the weight ratio of the common lactase to the β-galactosidase with transgalactosylation activity is in the range of 1:4 to 1:

22.

5. The method according to any one of claims 1 to 4, wherein: The method comprises first adding the β-galactosidase with transgalactosylation activity and then adding the common lactase.

6. The method according to claim 5, wherein In the method, the conventional lactase is added after the β-galactosidase having transgalactosylation activity is inactivated or partially inactivated.

7. The method according to any one of claims 1 to 4, wherein: The method simultaneously adds the β-galactosidase with transgalactosylation activity and the common lactase.

8. The method according to any one of claims 1 to 7, wherein: The dairy raw material is selected from the group consisting of fresh milk, reconstituted milk, recombined milk and concentrated milk.

9. The method according to claim 8, wherein The dairy raw material has a lactose content of not less than 5.0%.

10. The method according to claim 8 or 9, characterized in that The concentrated milk has a total protein content of not less than 4.0%.

11. The method according to claim 10, wherein The concentrated milk is prepared by one or a combination of several selected from reverse osmosis concentration, ultrafiltration, nanofiltration and membrane filtration.

12. The method according to any one of claims 1 to 11, wherein: The β-galactosidase having transgalactosylation activity is Nurica TM .

13. The method according to any one of claims 1 to 12, wherein: The common lactase is MaxilactLGI 5000.

14. A galacto-oligosaccharide-containing and lactose-free dairy product prepared by the method according to any one of claims 1 to 13.

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