Method for preparing lactose-free dairy products containing galactooligosaccharides and dairy products obtained by said method

Abstract

Disclosed is a method for preparing a lactose-free dairy product containing galactooligosaccharides, comprising the steps of using normal lactase and β-galactosidase having transgalactosylation activity, where normal lactase degrades lactose in the dairy starting material into galactose and glucose; where β-galactosidase having transgalactosylation activity degrades lactose in the dairy starting material into galactose and glucose and transfers the galactose obtained through degradation to hydroxyl groups of lactose in the dairy starting material to achieve conversion to galactooligosaccharides, and optionally to galactooligosaccharides with higher linkages; where the galactose obtained through degradation comprises: 1) galactose obtained by degradation of lactose with normal lactase; and / or 2) galactose obtained by degradation of lactose with β-galactosidase having transgalactosylation activity. The disclosed method is capable of producing high levels of galactooligosaccharides in situ, achieving lactose-free standards through a low-cost, simple process, and providing sugar-reducing benefits.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to China Patent Application No. 202111453072.8, filed with the State Intellectual Property Office on December 1, 2021, the entire contents of which are incorporated by reference.

[0002] The present invention relates to a method for preparing a dairy product and to the dairy product obtained by this method. In particular, the present invention relates to a method for preparing a lactose-free dairy product containing galactooligosaccharides and to the dairy product obtained by this method. [Background technology]

[0003] Galactooligosaccharides (galactose oligosaccharides, GOS) are a type of functional oligosaccharide. Galactooligosaccharides are effective growth factors and good nutritional sources for beneficial bacteria such as Bifidobacterium and Lactobacillus acidophilus in the human intestine, and therefore can improve digestion and absorption in the human intestine. In addition, lactose contained in, for example, milk and dairy products will cause adverse reactions such as stomach pain, flatulence, and diarrhea in people with lactose intolerance. Therefore, it is absolutely necessary to develop dairy products that contain galactooligosaccharides but are lactose-free.

[0004] In the prior art, the effect of increasing the content of galactooligosaccharides in dairy products while lowering lactose is generally achieved in two ways:

[0005] 1) Using β-galactosidase with high levels of transgalactosylation activity to convert lactose in dairy starting materials to galactooligosaccharides, for example: China Patent Publication No. 101396048 (Patent Document 1) discloses a method for producing milk rich in galactooligosaccharides, including heating milk, isolating fat to obtain skim milk, pasteurizing, then cooling, followed by hydrolysis with immobilized β-galactosidase, UHT sterilization, and then cooling and packaging. Thus, the method hydrolyzes milk with β-galactosidase to prepare milk rich in galactooligosaccharides. However, the lactose in the starting material of the dairy product prepared by such a method is not completely decomposed (see the lactose content recorded in Examples 1-5 of the patent).

[0006] China Patent Publication No. 106455600 (Patent Document 2) discloses a method for using β-galactosidase with high levels of transgalactosylation activity at low temperature to produce dairy products containing galactooligosaccharides, in which heat treatment is used to inactivate the enzyme. Similarly, lactose in the starting material of the dairy product prepared by such a method is also not completely decomposed (see the lactose content recorded in Example 3 of the patent).

[0007] 2) Using lactase to completely break down lactose in dairy starting materials and add galactooligosaccharides, for example: CN104286174 discloses a method for preparing lactose-free fermented milk, in which yeast lactase and fungal lactase are successively used in two steps to decompose lactose in the starting milk material into glucose and galactose to obtain lactose-free fermented milk, and galactooligosaccharides are added to the starting material as sweeteners (see paragraph

[0014] and Examples 2 and 4 of this specification). However, such a method requires the addition of galactooligosaccharides, which increases the production cost and creates the risk of external contamination during production.

[0008] In addition, Chinese Patent No. 100473283 (Patent Document 4) further discloses a method for producing a dairy composition, in which the use of multiple separation steps combining ultrafiltration, nanofiltration and reverse osmosis to obtain lactose-free dairy starting material is recorded. Although the combination of ultrafiltration, nanofiltration and reverse osmosis can achieve the effect of removing most of the lactose, this process is compounded with high energy consumption and high cost, and the loss of nutrients from raw milk during the operation is significant.

[0009] In summary, there is an urgent need for a method for preparing a lactose-free dairy product containing galactooligosaccharides that is able to overcome the above mentioned drawbacks, in particular a method for preparing a lactose-free dairy product containing galactooligosaccharides that does not require the addition of additional galactooligosaccharides and is even able to generate galactooligosaccharides in situ, and that achieves high levels of galactooligosaccharides and can achieve lactose-free standards in the final dairy product through a low-cost and simple process. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] China Patent Application Publication No. 101396048 [Patent Document 2] China Patent Application Publication No. 106455600 [Patent Document 3] China Patent Publication No. 104286174 [Patent Document 4] Chinese Patent No. 100473283 Summary of the Invention [Problem to be solved by the invention]

[0011] The technical problem addressed by the present invention is to overcome the following drawbacks of existing methods for preparing lactose-free dairy products containing galactooligosaccharides: 1) The method of simply using β-galactosidase with high levels of transgalactosylation activity to convert lactose in the dairy starting material to galactooligosaccharides has the problem that the lactose in the starting material of the dairy product being prepared is not completely degraded. 2) The method of simply using lactase to completely degrade lactose in dairy starting materials and adding galactooligosaccharides has the problem that the addition of galactooligosaccharides is required due to the inability to generate galactooligosaccharides in situ, which increases production costs and creates a risk of external contamination during production. [Means for solving the problem]

[0012] The present invention relates to a method for preparing a lactose-free dairy product containing galactooligosaccharides, comprising the steps of: using normal lactase and a β-galactosidase having transgalactosylation activity, Normal lactase breaks down lactose in dairy starting materials into galactose and glucose; a β-galactosidase having transgalactosylation activity degrades lactose in the dairy starting material into galactose and glucose, and transfers the galactose obtained through the degradation to a hydroxyl group of lactose in the dairy starting material to achieve conversion to galactooligosaccharides, and optionally a β-galactosidase having transgalactosylation activity transfers the galactose obtained through the degradation to a hydroxyl group of galactooligosaccharides to achieve conversion to galactooligosaccharides with higher linkages; The galactose obtained through degradation is as follows: 1) galactose, obtained by the degradation of lactose by normal lactase; and 2) Galactose obtained by hydrolysis of lactose with β-galactosidase having transgalactosylation activity containing galactose obtained through degradation, selected from the group consisting of A method is provided.

[0013] The present invention further provides lactose-free dairy products containing galactooligosaccharides prepared by the methods of the present invention.

[0014] Compared with the conventional technology, the present invention has the following beneficial effects: the method can produce a high level of galactooligosaccharides in dairy products without the need to add galactooligosaccharides to the dairy starting material, and the method also enables dairy products to achieve lactose-free standard through a simple process at low cost thanks to the combined use of β-galactosidase with transgalactosylation activity and normal lactase. In addition, the galactooligosaccharides are produced using lactose and monosaccharides originally contained in the dairy starting material, and the effect of sugar reduction is also achieved because galactooligosaccharides cannot be absorbed by the human body.

[0015] Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that this detailed description and the specific examples, while specifying preferred embodiments of the present invention, are given by way of example only, since various changes and improvements within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present invention relates to a method for preparing a lactose-free dairy product containing galactooligosaccharides, comprising the steps of: using normal lactase and a β-galactosidase having transgalactosylation activity, Normal lactase breaks down lactose in dairy starting materials into galactose and glucose; a β-galactosidase having transgalactosylation activity degrades lactose in the dairy starting material into galactose and glucose, and transfers the galactose obtained through the degradation to a hydroxyl group of lactose in the dairy starting material to achieve conversion to galactooligosaccharides, and optionally a β-galactosidase having transgalactosylation activity transfers the galactose obtained through the degradation to a hydroxyl group of galactooligosaccharides to achieve conversion to galactooligosaccharides with higher linkages; The galactose obtained through degradation is as follows: 1) galactose, obtained by the degradation of lactose by normal lactase; and 2) Galactose obtained by hydrolysis of lactose with β-galactosidase having transgalactosylation activity containing galactose obtained through degradation, selected from the group consisting of A method is provided.

[0017] The method of the present invention can produce high levels of galactooligosaccharides in dairy products without the need to add galactooligosaccharides to the dairy starting material, and the method also allows dairy products to achieve lactose-free standards through a simple process with low cost and higher productivity thanks to the combined use of β-galactosidase with transgalactosylation activity and normal lactase. Furthermore, since galactooligosaccharides are produced using lactose and monosaccharides originally contained in the dairy starting material, and galactooligosaccharides cannot be absorbed by the human body, the effect of sugar reduction (i.e., reduction in the total amount of monosaccharides and disaccharides) is also achieved.

[0018] The term "galactooligosaccharide" or "GOS" refers to a galactosidase having the stoichiometric formula (Gal). i Glc or (Gal) jwhere i=1-8 and j=2-9. GOS generally exists as a mixture of various GOS molecules with different degrees of polymerization and different linkage structures. The mixture can contain linear and branched GOS molecules. Lactose is not considered a GOS molecule.

[0019] The method of the present invention can use various kinds of "β-galactosidases with transgalactosylation activity" available in the art, as long as the β-galactosidases with transgalactosylation activity can degrade lactose in dairy starting materials into galactose and glucose, and transfer the galactose obtained through the decomposition to the hydroxyl group of lactose in dairy starting materials to achieve conversion to galactooligosaccharides. Most preferably, the β-galactosidase with transgalactosylation activity is an enzyme preparation with the trade name Nurica™ by the US company International Flavors & Fragrances; Nurica™ can utilize lactose in dairy products to naturally produce dietary fiber in the form of galactooligosaccharides. The enzymatic activity range of the Nurica™ enzyme preparation is 500-800 BLU / g, preferably 540-760 BLU / g, and the content of β-galactosidase (beta-galactosidase) in the Nurica™ enzyme preparation is 5-8% (w / w).

[0020] The method of the present invention can use various types of "conventional lactases" available in the art, provided that the conventional lactase breaks down lactose in the dairy starting material into galactose and glucose. Examples are Maxilact LGI 5000 and GODO-YNL2 lactase by Dupont. Most preferably, the conventional lactase is Maxilact LGI 5000 by DSM; the enzyme activity range of the Maxilact LGI 5000 enzyme preparation is 5000 NLU / g or higher.

[0021] Preferably, the β-galactosidase with transgalactosylation activity is used in an amount of 0.5-12 g per liter of dairy starting material, more preferably 2.0-11.0 g / L (dairy raw material), preferably 0.5-6.0 g / L (dairy raw material), even more preferably 3.0-4.0 g per liter of dairy starting material; the weight ratio of normal lactase to the β-galactosidase with transgalactosylation activity is 1:1-1:25, preferably the weight ratio of normal lactase to the β-galactosidase with transgalactosylation activity is in the range of 1:1-1:10, even more preferably 1:6-1:7, and the weight ratio of normal lactase to the β-galactosidase with transgalactosylation activity is in the range of 1:4-1:22.

[0022] The present invention has no specific requirement regarding the order in which the β-galactosidase with transgalactosylation activity and the normal lactase are added. Preferably, the method adds the β-galactosidase with transgalactosylation activity first, and then adds the normal lactase. More preferably, the method adds the normal lactase after inactivating or partially inactivating the β-galactosidase with transgalactosylation activity. More preferably, the method can add the β-galactosidase with transgalactosylation activity and the normal lactase simultaneously. Adding the two enzymes simultaneously can further shorten the total time of enzymatic hydrolysis in the whole production process. In addition, a separate step of enzyme inactivation can be omitted. Other conditions after enzymatic hydrolysis (such as pasteurization) can play a role in enzyme inactivation.

[0023] The method of the present invention does not impose any particular restriction on the dairy starting material that can be used, and the dairy starting material that can be used may be selected from the group consisting of: raw milk, reconstituted milk, formula milk, and concentrated milk. Animal sources of dairy starting materials include, but are not limited to, humans, dairy cows, sheep, goats, buffaloes, camels, llamas, mares, and deer. Among these, cows and sheep are preferred. Specifically, the dairy starting material that can be used in the method of the present invention may preferably be one or more of the following: 1. Raw whole or skim milk; 2. Reconstituted milk from whole milk powder, skim milk powder, or concentrated milk proteins; 3. Raw milk that has been skimmed and concentrated by any membrane filtration technique and backfilled with thin cream to produce the required fat, protein, and lactose content; 4. Raw milk concentrated by freeze-concentration technology; and 5.Raw milk concentrated by membrane evaporation technology.

[0024] Preferably, the dairy starting material that can be used is the dairy starting material of items 3 to 5 above, and the content of components such as fat, protein, and lactose in the dairy starting material may vary according to the needs of different population groups. For example, enrichment can significantly increase the protein content and improve intake efficiency.

[0025] Generally, raw whole milk or skim milk has a lactose content of 4.0-5.4%, preferably 4.5-5.4%. Preferably, the dairy starting material can have a lactose content of 5.0% or more. The dairy starting material can also have a lactose content as high as 15.0%. Preferably, the dairy starting material has a lactose content of 6.0%-10.0%; preferably, the dairy starting material has a lactose content of 7.0%-8.0%; further, the dairy starting material has a lactose content of 8.0%-9.0%; further, the dairy starting material has a lactose content of 9.0%-10.0%. This preferred range of lactose can serve as starting material for the in situ production of GOS in sufficient quantities as required.

[0026] Generally, raw whole milk or skim milk has a total protein content of 3.2-3.8%. Preferably, concentrated milk has a total protein content of 4.0% or more. Preferably, concentrated milk has a protein content of 4.0%-10.0%. Preferably, concentrated milk has a protein content of 5.0%-9.0%. More preferably, concentrated milk has a protein content of 5.0%-6.0%; concentrated milk in this protein content range easily meets the body's demand for protein, is easily absorbed in the intestine, and does not require the intake of excessive amounts of liquid, thus avoiding increased intestinal load.

[0027] The concentrated milk can be obtained by various concentration methods commonly used in the art, for example, prepared by one or a combination of two or more of reverse osmosis concentration, ultrafiltration, nanofiltration, and membrane filtration. The reverse osmosis concentration is preferably carried out at 25°C, more preferably at 2-10°C. The membrane filtration can be ultrafiltration, nanofiltration, or reverse osmosis. The concentrated raw milk preferably has a total protein content of 4.0% or more; and optionally has a protein content of 4.0%-10.0%; more preferably has a protein content of 5.0%-9.0%, and even more preferably has a protein content of 5.0%-6.0%.

[0028] Furthermore, the applicant of the present application has found that when using a concentrated high-protein dairy starting material with a total protein content of 4.0% or more, the lactose in the high-protein dairy starting material cannot be completely hydrolyzed by using a β-galactosidase with transgalactosylation activity by itself. Furthermore, if the β-galactosidase with transgalactosylation activity is not inactivated after the enzymatic degradation step, during storage, the presence of this enzyme will instead degrade the already formed GOS, for example, causing a reduction in GOS in the final product. In particular, when a fermentation step is further performed after the enzymatic degradation step to prepare a dairy product such as yogurt, if both lactic acid bacteria and an uninactivated β-galactosidase with transgalactosylation activity are present in the fermentation step, more GOS produced in the enzymatic degradation step will be consumed, resulting in a significant reduction in GOS in the final product.

[0029] Therefore, in order to reduce or avoid significant loss of GOS during subsequent storage or further processing (e.g., fermentation or another step), the β-galactosidase with transgalactosylation activity is preferably inactivated immediately after the β-galactosidase with transgalactosylation activity completes the production of GOS. The inactivation of the β-galactosidase with transgalactosylation activity can be carried out using inactivation methods commonly used in the art, such as heat inactivation (e.g., maintaining at 90-95°C for 5-10 minutes) or acid inactivation (e.g., lowering the pH value of the system to less than 4.5 by fermentation). The method of the present invention can not only produce a high level of GOS in situ and ensure the stability of GOS, but also achieve the lactose-free standard through a simple process with low cost and high production efficiency, and also achieve the effect of sugar reduction.

[0030] The present invention also provides a lactose-free dairy product containing galactooligosaccharides prepared by the method of the present invention, wherein the galactooligosaccharide content is preferably 0.5-3.8g per 100ml dairy product, preferably 0.5-2.3g / 100ml, preferably 1.0g / 100ml, and the lactose content is less than 0.2g per 100ml dairy product, more preferably less than 0.1g per 100ml dairy product, and most preferably the lactose content is 0%. The dairy product may be unflavored milk, flavored milk, ice cream, yogurt, and any liquid nutritional product that can be prepared from milk or dairy ingredients.

[0031] The objectives, structural features and advantages of the present invention will be described in more detail below by enumerating specific examples. These examples are only enumerated below for the purpose of more fully illustrating the present invention, and do not limit the scope of protection. EXAMPLES

[0032] Example 1 This example is used to demonstrate a method for preparing a lactose-free dairy product containing galactooligosaccharides, and the dairy product obtained from that method.

[0033] (1) Preparation of high-protein, high-lactose milk base 188 kg of raw skimmed milk (total protein 3.5%, lactose content 4.5%) is subjected to reverse osmosis concentration at 4±2°C and cream with a fat content of 45.0% is added to adjust the fat in the reconstituted raw milk, finally obtaining a high-protein, high-lactose milk base with a total protein content amounting to 5.3%, a fat content amounting to 4.0% and a lactose content amounting to 7.5%.

[0034] (2) Enzymatic hydrolysis of high-protein, high-lactose milk-based To the high protein milk base obtained in step (1) (5.3% protein + 4.0% fat + 7.5% lactose) Nurica™ enzyme preparation (enzyme activity 650 ± 150 BLU / g) is added at a concentration of 3.2 g per kg of high protein milk base; after 15 hours of enzymatic degradation at 10°C, Maxilact LGI 5000 (enzyme activity of more than 5000 NLU / g) is added at a concentration of 0.5 g per kg of high protein milk base and the enzymatic degradation is continued for 15 hours at a temperature of 10°C.

[0035] (3) Fermentation after enzymatic decomposition The high protein, high lactose milk base after enzymatic degradation obtained in step (2) is heated to 30° C., kefir fermentation preparation (Choozit Kefir Mild 01 purchased from Dupont) is added at a concentration of 0.0050 g / L, and then maintained at 30° C. for 20 hours. Finally, yogurt with a pH of 4.45 is obtained.

[0036] Example 2 This example is used to demonstrate a method for preparing a lactose-free dairy product containing galactooligosaccharides, and the dairy product obtained from that method.

[0037] (1) Preparation of high-protein, high-lactose milk base 188 kg of raw skimmed milk (total protein 3.5%, lactose content 4.5%) is subjected to reverse osmosis concentration at 4±2°C and cream with a fat content of 45.0% is added to adjust the fat in the reconstituted raw milk, finally obtaining a high-protein, high-lactose milk base with a total protein content amounting to 5.3%, a fat content amounting to 4.0% and a lactose content amounting to 7.5%.

[0038] (2) Enzymatic hydrolysis of high-protein, high-lactose milk-based To the high protein milk base obtained in step (1) (5.3% protein + 4.0% fat + 7.5% lactose) Nurica™ enzyme preparation (enzyme activity 650 ± 150 BLU / g) is added at a concentration of 3.2 g per kg of high protein milk base; after 15 hours of enzymatic degradation at 10°C, Maxilact LGI 5000 (enzyme activity of more than 5000 NLU / g) is added at a concentration of 0.5 g per kg of high protein milk base and the enzymatic degradation is continued for 15 hours at a temperature of 10°C.

[0039] (3) Preparation of yogurt by fermentation after enzymatic hydrolysis The high protein, high lactose milk base after enzymatic degradation obtained in step (2) is heated to 42°C, and YO-MIX 558 fermentation preparation (a complex lactic acid bacteria preparation containing Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus purchased from Dupont) is added at a concentration of 0.0274g / L, and then maintained at 42°C for 20 hours. Finally, yogurt with a pH of 3.95 is obtained.

[0040] Example 3 This example is used to demonstrate a method for preparing a lactose-free dairy product containing galactooligosaccharides, and the dairy product obtained from that method.

[0041] (1) Preparation of high-protein, high-lactose milk base 188 kg of raw skimmed milk (total protein 3.5%, lactose content 4.5%) is subjected to reverse osmosis concentration at 5°C and cream with a fat content of 45.0% is added to adjust the fat in the reconstituted raw milk, finally obtaining a high-protein, high-lactose milk base with a total protein content amounting to 5.3%, a fat content amounting to 4.0% and a lactose content amounting to 7.5%.

[0042] (2) Enzymatic hydrolysis of high-protein, high-lactose milk-based To the high protein milk base (5.3% protein + 4.0% fat + 7.5% lactose) obtained in step (1), Nurica™ enzyme preparation (enzyme activity 650 ± 150 BLU / g) is added at a concentration of 3.2 g per kg of high protein milk base; after 15 hours of enzymatic degradation at 10°C, a heat treatment is carried out at 95°C for 7 minutes. After the end of the heat treatment, the temperature is reduced to 42°C and Maxilact LGI 5000 (enzyme activity above 5000 NLU / g) is added at a concentration of 0.5 g per kg of high protein milk base and the enzymatic degradation is continued at a temperature of 10°C for 15 hours to obtain the final dairy product.

[0043] Examples 4 to 9 These examples are used to demonstrate methods for preparing lactose-free dairy products containing galactooligosaccharides, and the dairy products produced thereby.

[0044] (1) Preparation of high-protein, high-lactose milk base 188 kg of raw milk (total protein 3.3%, lactose content 4.3%) was subjected to reverse osmosis concentration at 5°C and cream with a fat content of 30-45.0% was added to adjust the fat in the reconstituted raw milk, finally obtaining 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).

[0045] (2) Enzymatic hydrolysis of high-protein, high-lactose milk-based Nurica™ enzyme preparation (enzyme activity 650±150 BLU / g) and Maxilact LGI 5000 (enzyme activity above 5000 NLU / g) are added simultaneously 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); after 18-20 hours of enzymatic degradation at 10°C, heat treatment is carried out at 90°C for 10 minutes to obtain the final dairy product. The concentrations of Nurica™ enzyme preparation and Maxilact LGI 5000 are as shown in Table 1 below.

[0046] [Table 1]

[0047] Comparative Example 1 This comparative example is used to illustrate a prior art method for preparing a lactose-free dairy product containing galactooligosaccharides, and the resulting dairy product.

[0048] (1) Preparation of high-protein, high-lactose milk base 188 kg of raw skimmed milk (total protein 3.5%, lactose content 4.5%) is subjected to reverse osmosis concentration at 5°C and cream with a fat content of 45.0% is added to adjust the fat in the reconstituted raw milk, finally obtaining a high-protein, high-lactose milk base with a total protein content amounting to 5.3%, a fat content amounting to 4.0% and a lactose content amounting to 7.5%.

[0049] (2) Enzymatic digestion of high protein, high lactose milk-based products using only Maxilact LGI 5000 To the high protein milk base (5.3% protein + 4.0% fat + 7.5% lactose) obtained in step (1), Maxilact LGI 5000 (enzyme activity of more than 5000 NLU / g) is added at a concentration of 0.5 g per kg of high protein milk base and after 15 hours of enzymatic degradation at a temperature of 10°C, the final dairy product is obtained.

[0050] Comparative Example 2 This comparative example is used to illustrate a prior art method for preparing a lactose-free dairy product containing galactooligosaccharides, and the resulting dairy product.

[0051] (1) Preparation of high-protein, high-lactose milk base 188 kg of raw skimmed milk (total protein 3.5%, lactose content 4.5%) is subjected to reverse osmosis concentration at 5°C and cream with a fat content of 45.0% is added to adjust the fat in the reconstituted raw milk, finally obtaining a high-protein, high-lactose milk base with a total protein content amounting to 5.3%, a fat content amounting to 4.0% and a lactose content amounting to 7.5%.

[0052] (2) Enzymatic hydrolysis of high protein, high lactose milk-based products using only Nurica™ enzyme preparations To the high protein milk base obtained in step (1) (5.3% protein + 4.0% fat + 7.5% lactose) Nurica™ enzyme preparation (enzyme activity 650±150 BLU / g) is added at a concentration of 3.2 g per kg of high protein milk base and after 15 hours of enzymatic degradation at 10° C. the final dairy product is obtained.

[0053] Comparative Example 3 This comparative example is used to illustrate a prior art method for preparing a lactose-free dairy product containing galactooligosaccharides, and the resulting dairy product.

[0054] (1) Preparation of high-protein, high-lactose milk base 188 kg of raw milk (total protein 3.3%, lactose content 4.3%) is subjected to reverse osmosis concentration at 5°C, and cream with a fat content of 30-45.0% is added to adjust the fat in the reconstituted raw milk, finally obtaining 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 9.8%.

[0055] (2) Enzymatic hydrolysis of high protein, high lactose milk-based products using only Nurica™ enzyme preparations To the high protein milk base (6.5% protein + 3.8% fat + 9.8% lactose) obtained in step (1), Nurica™ enzyme preparation (enzyme activity 650±150 BLU / g) is added at a concentration of 2.0 g per kg of high protein milk base, and enzymatic degradation at 10° C. for 20 hours followed by heat treatment at 90° C. for 10 minutes is carried out to obtain the final dairy product.

[0056] The dairy products obtained in the above-mentioned Examples 1 to 9 and Comparative Examples 1 to 3 are all sterilized by ultra-high temperature (UHT) flash sterilization, the sterilization temperature is 137° C., and the sterilization time is 4 seconds.

[0057] Example of effectiveness verification The dairy products obtained in Examples 1 to 3 and Comparative Examples 1 and 2 were tested for sugar composition under the same conditions.

[0058] The method for testing the sugar composition was as follows:

[0059] Carrez reagents 1 and 2 were added to 1 ml of the sample to be tested in sufficient amounts to coagulate all solids. The two-phase mixture was centrifuged (6000 rpm) for 15 minutes and a disposable PTFE microfilter (0.22 micron) was used for further filtration. The final clear solution of sugars was then placed in an HPLC vial and analyzed.

[0060] The HPLC method used was as follows: System: Waters Column: Agilent HiPlex Ca polymeric ion exchange column Eluent: MilliQ water Column temperature: 60℃ Flow rate: 0.6mL / min Pressure: 600 psi (for such columns, the maximum is 1000 psi) Detector: RID, 35℃

[0061] Quantification was based on peak area and known lactose concentration. Response coefficients for all sugars were also calculated. Oligosaccharide retention times were previously determined using Sigma DP2, DP3, and DP4 oligosaccharide and monosaccharide analytical standards.

[0062] The sugar composition was tested when the dairy products were freshly prepared, after 3 days of storage at 10° C., and after 17 days of storage at 10° C. The test results are shown in Table 2 below:

[0063] [Table 2]

[0064] From Table 2, it can be seen that after the concentration of the dairy starting material used in Examples 1-3, the protein and lactose concentrations are both increased, and since β-galactosidase with a high level of transgalactosylation activity and normal lactase are used in combination, the high content of lactose in the concentrated milk is completely decomposed and converted into GOS, thereby obtaining a dairy product with high protein, high GOS, and low monosaccharides. In Comparative Examples 1-2, β-galactosidase with a high level of transgalactosylation activity is used independently, or normal lactase is used independently; lactose cannot be completely decomposed, or GOS is not produced, so the excellent properties of the dairy product prepared by the method of the present invention cannot be achieved in either case.

[0065] Furthermore, since the yogurt preparation process also includes a fermentation step, those skilled in the art would generally consider that fermentation would cause the degradation of GOS; however, it can be seen from the results shown in Table 3 below that the content of naturally occurring GOS is not significantly reduced by the yogurt fermentation step of different processes in Examples 1-2 of the present invention, and is still sufficient to produce a prebiotic effect.

[0066] [Table 3]

[0067] That is, in the methods of Examples 1-2 of the present invention, a fermentation step is also carried out after the enzymatic hydrolysis step to prepare yogurt; the fermentation step does not significantly affect the GOS content, and furthermore, compared with the technical solution of Example 3 in which β-galactosidase with a high level of 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 effects of increasing production efficiency and reducing production costs.

[0068] The samples of Examples 4-9 and Comparative Example 3 were subjected to sugar composition testing when the dairy products were freshly prepared.

[0069] [Table 4]

[0070] From Table 4, it can be seen that by adding two kinds of enzymes simultaneously, the time required for enzymatic hydrolysis can be significantly shortened, and the final dairy product can meet the content requirement of the Chinese national standard GB28050-2011 for being lactose-free.

[0071] The invention generally disclosed herein may be suitably practiced in the absence of any element not specifically disclosed herein. However, it will be apparent to those skilled in the art that many variations, modifications, and improvements to the method, and other uses and applications thereof, are possible; variations, modifications, improvements, other uses, and applications that do not depart from the spirit and scope of the invention are deemed to be encompassed by the invention as defined solely by the appended claims.

Claims

1. 1. A method for preparing a lactose-free dairy product containing galactooligosaccharides, comprising: using normal lactase and β-galactosidase with transgalactosylation activity, The normal lactase breaks down lactose in the dairy starting material into galactose and glucose; the β-galactosidase having transgalactosylation activity degrades lactose in the dairy starting material into galactose and glucose, and transfers the galactose obtained through the degradation to a hydroxyl group of lactose in the dairy starting material to achieve conversion to galactooligosaccharides, and optionally the β-galactosidase having transgalactosylation activity transfers the galactose obtained through the degradation to a hydroxyl group of the galactooligosaccharide to achieve conversion to galactooligosaccharides with higher linkages; The galactose obtained through the degradation is: 1) galactose obtained by the degradation of lactose by the normal lactase; and 2) Galactose obtained by decomposing lactose with the β-galactosidase having transgalactosylation activity containing galactose obtained through degradation, selected from the group consisting of A method characterized by:

2. 2. The method of claim 1, wherein the β-galactosidase with transgalactosylation activity is used in an amount of 0.5 to 12.0 g per liter of dairy starting material; and the weight ratio of the normal lactase to the β-galactosidase with transgalactosylation activity is 1:1 to 1:

25.

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

10.

4. 3. The method according to claim 2, wherein the amount of the β-galactosidase with transgalactosylation activity applied is in the range of 2.0 g / L to 11.0 g / L of dairy raw material, and the weight ratio of the normal 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, characterized in that the β-galactosidase with transgalactosylating activity is added first, followed by the normal lactase.

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

7. The method according to any one of claims 1 to 4, characterized in that the β-galactosidase having transgalactosylation activity and the normal lactase are added simultaneously.

8. 2. The method of claim 1, wherein the dairy starting material is selected from the group consisting of raw milk, reconstituted milk, formula milk, and concentrated milk.

9. 9. The method of claim 8, wherein the dairy starting material has a lactose content of 5.0% or greater.

10. 10. The method of claim 8 or 9, wherein the concentrated milk has a total protein content of 4.0% or more.

11. 11. The method of claim 10, wherein the concentrated milk is prepared by one or a combination of two or more of the following: reverse osmosis concentration, ultrafiltration, nanofiltration, and membrane filtration.

12. 10. A lactose-free dairy product containing galactooligosaccharides prepared by the method of claim 1.