Method for improving texture of camel fermented milk and application thereof

Abstract

The invention provides a method for improving texture of camel fermented milk and application thereof, and the method comprises the following steps: (1) degreasing: centrifuging and filtering fresh camel milk to obtain degreased camel milk; (2) dissociation: adding sodium citrate into the degreased camel milk to dissociate calcium ions in camel milk casein micelles, and then adjusting the pH value to 6.6 to obtain dissociated camel milk; (3) heat treatment: heating the dissociated camel milk at 70-90 DEG C for 5-20 minutes; and (4) TG enzyme treatment: after the temperature of the camel milk is reduced to 40-45 DEG C, adding glutamine transaminase into the camel milk, incubating for a certain time, adding an acidifying agent, and acidifying for 3-5 hours to finally obtain the camel fermented milk. Wherein sodium citrate treatment is adopted, TG enzyme crosslinking and heat treatment are combined, formation of camel lactic acid gel is promoted from multiple aspects, and the industrial problem that camel milk cannot be acidified and curded is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of fermented milk product processing, and in particular relates to a method for improving the texture of camel fermented milk and an application thereof. Background Art

[0002] After acidification and fermentation, camel milk maintains a largely unchanged viscosity, resulting in camel yogurt that is fragile, uneven, and lacks texture. Yogurt's texture significantly impacts its quality, including appearance and taste, and thus influences consumer acceptance. Therefore, improving camel yogurt's texture and resolving the problem of camel milk's inability to curdle are crucial to its development and industrialization.

[0003] Camel milk differs from cow's milk in many ways, both in composition and properties. This makes it difficult to simply compare the texture of camel-milk fermented milk to that of cow's milk. Camel milk has a low kappa-casein content, lacks beta-lactoglobulin, and has large casein micelles. These factors contribute to its loose, liquid texture after fermentation, making it difficult to form curds. In contrast, cow's milk fermentation readily forms a dense, uniform curd structure.

[0004] Among the many technologies used to enhance the texture of dairy yogurt, heat treatment is the most widely used. Heat-denatured whey protein reacts with casein micelles, significantly optimizing yogurt texture and improving its textural properties, rheological properties, and water-holding capacity. However, camel milk casein micelles are relatively large, approximately 260 to 300 nm in size, and lack β-lactoglobulin. Heat treatment under these conditions causes casein particles to fuse together, forming large aggregates, which degrades the thermal stability of camel milk and causes precipitation. Given the inherent differences in composition and structure between camel milk and cow milk, heat treatment alone not only fails to promote camel milk gel formation, but can actually cause it to become unstable.

[0005] Therefore, how to solve the problem that fermented camel milk cannot be acidified and curdled is a problem that needs to be solved urgently. Summary of the Invention

[0006] In response to the problems existing in the prior art, the present invention aims to provide a method for improving the texture of camel fermented milk and its application. The method uses sodium citrate treatment, combined with TG enzyme cross-linking and heat treatment, to promote the formation of camel lactic acid gel from multiple aspects, thereby solving the industry problem that camel milk cannot be acidified and coagulated.

[0007] Through research on the camel milk acidification gelation process, it was found that simple heat treatment has a negative effect on camel milk acidification gelation, causing the storage modulus of skim milk during the acidification process to be lower than that of untreated camel milk. Therefore, the inventors conducted research on this and found that sodium citrate treatment, TG enzyme treatment, and the combined treatment of the two can all improve the gelation properties of camel milk to a certain extent, but the gel structure of camel fermented lactic acid still has room for improvement. Based on this, when further studying how to increase the gel strength of camel fermented milk, the inventors found that adding a heat treatment step between sodium citrate treatment and TG enzyme treatment can significantly improve the gelation properties of camel milk, increasing the storage modulus of camel fermented milk by 126 times. In view of this, the inventors provide the following solution of the present invention.

[0008] In order to achieve the above object, the first aspect of the present invention provides a method for improving the texture of camel fermented milk, comprising the following steps:

[0009] (1) Degreasing: fresh camel milk is centrifuged and filtered to obtain degreased camel milk;

[0010] (2) Dissociation: Sodium citrate is added to skimmed camel milk to dissociate calcium ions in camel milk casein micelles, and then the pH is adjusted to 6.6 to obtain dissociated camel milk;

[0011] (3) Heat treatment: heat the dissociated camel milk at 70-90°C for 5-20 min;

[0012] (4) TG enzyme treatment: After the temperature of camel milk drops to 40-45°C, add glutamine transaminase to it and incubate at 40-45°C for a certain period of time;

[0013] (5) Acidification treatment: Add an acidifier to the incubated camel milk and perform acidification treatment for 3 to 5 hours to finally obtain camel fermented milk.

[0014] Furthermore, in step (2), sodium citrate is added to the skimmed camel milk so that the final concentration of the sodium citrate solution reaches 10 to 50 mmol / L.

[0015] Furthermore, in step (3), the heat treatment condition is heating at 80° C. for 15 minutes.

[0016] Furthermore, in steps (4) and (5), based on 1 L of the skimmed camel milk, the amount of the acidifier is 10 to 20 g; the amount of the transglutaminase is 5 to 20 U / g protein.

[0017] Furthermore, in step (5), the acidulant is glucono-δ-lactone.

[0018] Furthermore, in steps (4) and (5), transglutaminase is added to the camel milk, and after incubation at 42° C. for 1 hour, an acidifier is added, and the acidification treatment is continued at 42° C. for 4 hours.

[0019] The second aspect of the present invention provides camel fermented milk prepared by the method described in the first aspect.

[0020] Furthermore, the camel fermented milk has a gel strength of at least 1.615N and a water holding capacity of at least 96.79%.

[0021] The third aspect of the present invention provides use of the method of the first aspect in improving the texture of camel fermented milk.

[0022] Furthermore, the method can improve the gel strength and water holding capacity of camel fermented milk.

[0023] The beneficial effects of the present invention compared to the prior art are:

[0024] The existing method uses sodium citrate and TG enzyme combined treatment with significant results, which can increase the storage modulus of camel milk by 44 times compared with untreated state. The reason is that sodium citrate treatment increases the cross-linking sites of TG enzyme, improves the degree of covalent cross-linking, and thus enhances the gel strength. In the method of the present invention, the use of sodium citrate and heat synergistic TG enzyme treatment can further optimize the gel performance of camel lactic acid, and its storage modulus can be significantly increased by 126 times, successfully overcoming the industry problem of camel milk not coagulating after acidification, and greatly improving the acidification gel effect of camel milk. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0026] Figure 1 The rheological properties of camel lactation during acidification after different treatments in various embodiments and comparative examples are shown;

[0027] Figure 2 This is an enlarged view of some groups in Example 1;

[0028] Figure 3 The texture of camel lactic acid gel after different treatments in various examples and comparative examples is shown;

[0029] Figure 4 The water holding capacity of camel lactic acid gels treated differently in various embodiments and comparative examples is shown. DETAILED DESCRIPTION

[0030] The examples are provided to better illustrate the present invention, but are not intended to limit the present invention to the examples. Therefore, non-essential improvements and adjustments to the embodiments made by those skilled in the art based on the above-mentioned invention still fall within the scope of protection of the present invention.

[0031] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0032] The present invention will be described in detail below through examples. It should be understood that the following examples are only used to further explain and illustrate the content of the present invention in detail, and are not intended to limit the present invention.

[0033] In the following examples, some of the raw materials involved are:

[0034] Camel milk was obtained from Inner Mongolia Yinggesu Biotechnology Co., Ltd., sodium citrate was purchased from Sinopharm Group, transglutaminase (TGase) was purchased from C&P Group Co., Ltd., and glucono-δ-lactone (GDL) was purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd.

[0035] The detection methods involved in the following embodiments include:

[0036] 1. Rheological properties determination: Camel milk samples with different treatments were immediately placed in a rheological test barrel after adding GDL. A time sweep program was performed with a scanning temperature of 42°C, a frequency of 1 Hz, a strain of 0.1%, and a scanning time of 4 hours.

[0037] 2. Texture determination: Place the sample to be tested on the texture analyzer platform and use the puncture procedure. The specific method is to use an aluminum cylindrical probe with a diameter of 25 mm and insert the probe into the gel at a constant speed of 30 mm / min to a distance of 10 mm. The trigger force is 0.05N.

[0038] 3. Water holding capacity determination: After the acidified camel fermented milk sample is returned to room temperature, it is centrifuged at 3000 rpm / min for 10 minutes. After the supernatant is separated, the water holding capacity is calculated. The water holding capacity calculation formula is:

[0039] Water holding capacity = (total mass of acid gel - mass of whey) / total mass of acid gel × 100%.

[0040] Example 1

[0041] This embodiment provides a method for improving the texture of camel fermented milk, and the specific processing method is as follows:

[0042] (1) Degreasing: Fresh camel milk was centrifuged (1589 g, 15 min) and filtered through gauze to obtain defatted camel milk.

[0043] (2) Dissociation: Sodium citrate was added to skimmed camel milk to a final concentration of 30 mmol / L to dissociate the calcium ions in the camel milk casein micelles, and then the pH was adjusted to 6.6 to obtain dissociated camel milk.

[0044] (3) Heat treatment: Heat the dissociated camel milk at 80°C for 15 min.

[0045] (4) TG enzyme treatment: After the temperature of camel milk drops to 42°C, add glutamine transaminase to make the final enzyme activity 10U / g protein, and incubate at 42°C for 1h.

[0046] (5) Acidification treatment: 1.5 wt% of glucono-δ-lactone was added to the incubated camel milk and acidified at 42°C for 4 h to obtain camel fermented milk (sodium citrate and heat-synergistic TG enzyme treatment group: TC-H-TG).

[0047] Comparative Example

[0048] In this comparative example, the effects of different treatment methods on the texture of camel fermented milk were studied. The specific methods are as follows:

[0049] Blank group (K): Camel fermented milk was prepared according to the method of step (1) in Example 1, except that the skimmed camel milk obtained in step (1) was directly subjected to the acidification treatment in step (5).

[0050] Sodium citrate treatment group (TC): Camel fermented milk was prepared according to the method of Example 1, except that steps (3) and (4) were omitted. Sodium citrate was added to skimmed camel milk to a final concentration of 30 mmol / L to dissociate calcium ions in the camel milk casein micelles, and then the pH was adjusted to 6.6 to obtain dissociated camel milk. 1.5 wt% glucono-δ-lactone was added to the dissociated camel milk, and the milk was acidified at 42°C for 4 h to obtain camel fermented milk (TC).

[0051] Heat Treatment Group (H): Camel fermented milk was prepared according to the method of Example 1, except that steps (2) and (4) were omitted. Skimmed camel milk was heated at 80°C for 15 min, 1.5 wt% glucono-δ-lactone was added to the camel milk, and the milk was acidified at 42°C for 4 h to obtain camel fermented milk (H).

[0052] TG enzyme treatment group (TG): Camel fermented milk was prepared according to the method of Example 1, except that steps (2) and (3) were omitted. Transglutaminase was added to skimmed camel milk to a final enzyme activity of 10 U / g protein, and the milk was incubated at 42°C for 1 h. 1.5 wt% glucono-δ-lactone was added to the incubated camel milk, and the milk was acidified at 42°C for 4 h to obtain camel fermented milk (TG).

[0053] Heat treatment combined with TG enzyme treatment (H-TG): Camel fermented milk was prepared according to the method of Example 1, except that step (2) was not included. Skimmed camel milk was heated at 80°C for 15 min. After the temperature of the camel milk dropped to 42°C, transglutaminase was added to the milk to a final enzyme activity of 10 U / g protein, and the milk was incubated at 42°C for 1 h. 1.5 wt% of glucono-δ-lactone was added to the incubated camel milk, and the milk was acidified at 42°C for 4 h to obtain camel fermented milk (H-TG).

[0054] Sodium citrate synergistic TG enzyme treatment group (TC-TG): Camel fermented milk was prepared according to the method of Example 1, except that step (3) was not included. Sodium citrate was added to skimmed camel milk to a final concentration of 30 mmol / L to dissociate calcium ions in camel milk casein micelles, and then the pH was adjusted to 6.6 to obtain dissociated camel milk; transglutaminase was added to the dissociated camel milk to a final enzyme activity of 10 U / g protein, and the milk was incubated at 42°C for 1 hour; 1.5 wt% of glucono-δ-lactone was added to the incubated camel milk, and the milk was acidified at 42°C for 4 hours to obtain camel fermented milk.

[0055] Test example:

[0056] The rheological properties, texture properties and water holding capacity of the camel fermented lactic acid gels prepared in the above examples and comparative examples were measured respectively.

[0057] The gelling process of camel fermented lactic acid in 7 treatment groups in Example 1 and the comparative example is as follows: Figure 1 and Figure 2 As shown. It can be found that the storage modulus of the skimmed camel milk of the simple heat treatment group (H) during the acidification process is lower than that of the camel fermented milk without any treatment, indicating that simple heat treatment is unfavorable for the camel fermented milk acidification gel. The sodium citrate treatment group (TC), the TG enzyme treatment group (TG) and the heat treatment synergistic TG enzyme treatment group (H-TG) all increased the gel properties of the camel fermented milk, but the camel fermented lactic acid gel structure is still very weak. The sodium citrate synergistic TG enzyme treatment group (TC-TG) can significantly improve the camel fermented lactic acid gel performance. Compared with the untreated camel fermented milk, the storage modulus increased by 44 times. This is because the sodium citrate treatment increases the cross-linking sites of the TG enzyme, increases the degree of covalent cross-linking and thus increases the gel strength. The sodium citrate and heat synergistic TG enzyme treatment groups (TC-H-TG) described in Example 1 can further improve the camel fermented lactic acid gel performance, increase the storage modulus of the camel fermented lactic acid gel by 126 times, and completely solve the industry problem of camel fermented lactic acid acidification not curdling.

[0058] The texture of camel fermented lactic acid gel in 7 treatment groups Figure 3The results showed that only the sodium citrate treatment group (TC), the sodium citrate combined with TG enzyme treatment group (TC-TG), and the sodium citrate and heat-assisted TG enzyme treatment group (TC-H-TG) showed a significant improvement in texture compared to the blank group. Among them, the sodium citrate treatment group (TC) showed severe whey precipitation (gel shrinkage). The results show that the sodium citrate and heat-assisted TG enzyme treatment group (TC-H-TG) described in Example 1 can maximize the improvement of the gel properties of camel fermented milk, forming a firm yogurt gel.

[0059] The water holding capacity of camel fermented milk gel in 7 treatment groups Figure 4 The results showed that the sodium citrate and heat-synergistic TG enzyme treatment group (TC-H-TG) described in Example 1 could significantly increase the water holding capacity of camel fermented milk, and almost no whey was precipitated after centrifugation, forming a yogurt gel with good water holding performance.

[0060] In summary, the present invention first uses sodium citrate to process skimmed camel milk, so that the calcium ions in its casein micelles are dissociated so that the casein micelle particle size is reduced. On the one hand, the micelle particle size is reduced to increase the reaction site of transglutaminase (TG enzyme); on the other hand, the micelles with small particle size may not cause thermal aggregation precipitation after heat treatment with whey protein, and the denatured whey protein is attached to the surface of the casein micelles and may play a similar "nodule" effect as in cow's milk during gel formation, thereby enhancing gel properties. Therefore, sodium citrate is used to treat the formation of camel fermented lactic acid gel in combination with TG enzyme cross-linking and heat treatment, and the industry problem that camel milk cannot be acidified and coagulated is solved.

[0061] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and is not limiting. Although the present invention is described in detail with reference to the preferred arrangement scheme, ordinary technicians in this field should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for improving the texture of camel fermented milk, characterized in that: The method comprises the following steps: (1) Degreasing: fresh camel milk is centrifuged and filtered to obtain degreased camel milk; (2) Dissociation: Sodium citrate is added to skimmed camel milk to dissociate calcium ions in camel milk casein micelles, and then the pH is adjusted to 6.6 to obtain dissociated camel milk; (3) Heat treatment: heat the dissociated camel milk at 70-90°C for 5-20 min; (4) TG enzyme treatment: After the temperature of camel milk drops to 40-45°C, add glutamine transaminase to it and incubate at 40-45°C for a certain period of time; (5) Acidification treatment: Add an acidifier to the incubated camel milk and perform acidification treatment for 3 to 5 hours to finally obtain camel fermented milk.

2. The method according to claim 1, characterized in that In step (2), sodium citrate is added to the skimmed camel milk to make the final concentration of the sodium citrate solution reach 10 to 50 mmol / L.

3. The method according to claim 1, characterized in that In step (3), the heat treatment condition is heating at 80° C. for 15 minutes.

4. The method according to claim 1, wherein In steps (4) and (5), based on 1 L of the skimmed camel milk, the amount of the acidifier is 10 to 20 g; the amount of the transglutaminase is 5 to 20 U / g protein.

5. The method according to claim 4, characterized in that In step (5), the acidulant is glucono-δ-lactone.

6. The method according to any one of claims 1, 4 or 5, characterized in that In steps (4) and (5), transglutaminase is added to camel milk, and after incubation at 42° C. for 1 hour, an acidifier is added, and the acidification treatment is continued at 42° C. for 4 hours.

7. Camel fermented milk prepared by the method according to any one of claims 1 to 6.

8. Camel fermented milk according to claim 7, characterized in that The camel fermented milk has a gel strength of at least 1.615N and a water holding capacity of at least 96.79%.

9. Use of the method according to any one of claims 1 to 6 in improving the texture of camel fermented milk.

10. The use according to claim 9, characterized in that The method can improve the gel strength and water holding capacity of camel fermented milk.

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