Method for improving stability of ultrahigh-temperature sterilized goat milk

Abstract

The invention relates to the technical field of dairy product processing, and discloses a method for improving the stability of ultrahigh-temperature sterilized goat milk. Gradient decalcification regulation and control are performed on a sheep milk casein system by adopting an ultra-high-speed centrifugal dilution method, and a sheep milk casein calcium stabilizing environment adaptive to ultra-high-temperature sterilization is constructed in combination with calcium ion back-adding verification. Experiments show that the particle size of the decalcified sheep milk casein micelle is reduced, the absolute value of Zeta potential is remarkably increased, and the thermal coagulation time is greatly prolonged. When the decalcification rate of the goat milk casein reaches 76%, the thermal coagulation time of the goat milk casein is prolonged to 180 minutes or more when the goat milk casein is heated at 95 DEG C, no precipitate is generated, and the thermal stability of the goat milk casein is superior to that of untreated goat milk and bovine milk casein. The technical problems that the goat milk is easy to aggregate and precipitate and poor in thermal stability under the ultrahigh-temperature sterilization condition are solved, the process is simple and convenient, no exogenous additive exists, the stability of the product can be remarkably improved, the shelf life of the product can be remarkably prolonged, and reliable theoretical basis and technical support are provided for development of high-quality normal-temperature liquid goat milk products.

Description

Technical Field

[0001] This invention relates to the field of dairy processing technology, specifically to a method for improving the stability of ultra-high temperature sterilized goat milk by regulating the calcium ion environment. Background Technology

[0002] Goat milk is highly favored by consumers due to its high nutritional value, easy digestibility and absorption, and low allergenicity. Ultra-high temperature (UHT) sterilization is the core process for producing room-temperature liquid dairy products, effectively killing microorganisms and extending shelf life. However, compared to cow milk, goat milk exhibits extremely poor thermal stability during UHT sterilization, readily experiencing protein aggregation and precipitation. This severely impacts product quality and consumer acceptance, limiting the research and development and promotion of room-temperature liquid goat milk products. Existing technologies primarily improve stability by adding stabilizers and optimizing homogenization processes, but they fail to fundamentally solve the thermal stability problem caused by the inherent composition of goat milk. Summary of the Invention

[0003] The purpose of this invention is to overcome the defect of easy thermal coagulation of casein in goat milk during ultra-high temperature sterilization in existing technologies, and to provide a method for improving the thermal stability of ultra-high temperature sterilized goat milk. This invention, by comparing the physicochemical properties of casein in cow milk and goat milk, reveals the key role of calcium ions in the thermal instability of goat milk casein. Based on this, it proposes a method to partially remove calcium ions from the casein micelle system through physical methods and construct a thermally stable calcium environment for goat milk casein, thereby significantly improving the thermal stability of goat milk casein.

[0004] To achieve the above objectives, the present invention provides a method for improving the stability of ultra-high temperature sterilized goat milk, the method comprising:

[0005] (1) Pretreatment of sheep milk: Take fresh sheep milk and centrifuge it at 4 ℃ and 10000 r / min for 15 min to remove the upper layer of fat and obtain skimmed sheep milk;

[0006] (2) Casein extraction: The skimmed sheep milk was centrifuged at 4 ℃ and 10000 r / min for 1 h, the upper whey was discarded, and the bottom casein precipitate was collected;

[0007] (3) Gradient decalcification: Add an equal volume of ultrapure water to the casein precipitate and resuspend it. Vortex for 3 min to mix well, then centrifuge again and discard the supernatant. Repeat the dilution and centrifugation to obtain sheep milk casein samples with different decalcification rates.

[0008] (4) Sterilization treatment: The sample was subjected to ultra-high temperature sterilization at 140 ℃ for 5 s.

[0009] A second aspect of the present invention provides a highly thermally stable sheep milk casein prepared by the method described above.

[0010] The third aspect of the present invention provides the application of the method described above in the production of room temperature liquid goat milk, goat milk-based beverages, and fermented goat milk.

[0011] The fourth aspect of this invention provides a method for regulating the calcium environment of sheep milk casein, wherein 0.2-0.6 g / L calcium chloride solution is added back after defatting and separating whey to verify the effect of calcium content on thermal stability.

[0012] The fifth aspect of this invention provides control samples of sheep milk casein with different calcium contents prepared by the calcium environment regulation method described above. Attached Figure Description

[0013] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0014] Figure 1 Showing the micelle size distribution of bovine and ovine casein

[0015] Figure 2 Comparison of bovine and ovine casein micelles (Zeta)

[0016] Figure 3 Changes in micelle size of decalcified sheep milk casein

[0017] Figure 4 Changes in micelle potential of decalcified sheep casein Detailed Implementation

[0018] The endpoints and any values ​​of the ranges 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 endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] The present invention will be described in detail below through embodiments.

[0020] Example 1: Undecalcified sheep milk casein

[0021] This is used to illustrate the decalcification method provided by the present invention.

[0022] (1) Take fresh goat milk, divide it into centrifuge tubes, and balance them symmetrically;

[0023] (2) Centrifuge at 4 ℃ and 10000 r / min for 15 min, remove the upper layer of fat, and obtain skimmed sheep milk;

[0024] (3) Centrifuge at 4 ℃ and 10000 r / min for 1 h, collect whey, and collect casein precipitate;

[0025] (4) Add an equal volume of ultrapure water to each centrifuge tube to the original milk and vortex for 3 min to resuspend the casein.

[0026] Examples 2-4: Decalcified sheep milk casein

[0027] This is used to illustrate the decalcification method provided by the present invention.

[0028] (1) Take fresh goat milk, divide it into centrifuge tubes, and balance them symmetrically;

[0029] (2) Centrifuge at 4 ℃ and 10000 r / min for 15 min, remove the upper layer of fat, and obtain skimmed sheep milk;

[0030] (3) Centrifuge at 4 ℃ and 10000 r / min for 1 h, discard the whey, and collect the casein precipitate;

[0031] (4) Add an equal volume of ultrapure water to each centrifuge tube to the original milk and vortex for 3 min to resuspend the casein.

[0032] (5) Centrifuge at 4 ℃ and 10000 r / min for 15 min, discard the supernatant, and complete 1-3 dilutions for decalcification;

[0033] (5) Add an equal volume of ultrapure water to the original milk and sterilize at 140 °C for 5 s. After cooling, store at 4 °C.

[0034] Comparative Example 1: Undecalcified bovine casein

[0035] This comparative example is used to illustrate the casein sample as a reference.

[0036] Undecalcified bovine casein was prepared using the same method as in Example 1, using undecalcified goat milk.

[0037] Comparative Example 2: Re-addition of 0.2 g / L calcium chloride sheep milk casein

[0038] This comparative example is used to illustrate the casein sample as a reference.

[0039] Take the undecalcified sample from Example 1, add 0.2 g / L calcium chloride, and vortex for 3 min to mix.

[0040] Comparative Example 3: Re-addition of 0.4 g / L calcium chloride sheep milk casein

[0041] This comparative example is used to illustrate the casein sample as a reference.

[0042] Take the undecalcified sample from Example 1, add 0.4 g / L calcium chloride, and vortex for 3 min to mix.

[0043] Comparative Example 4: Re-addition of 0.6 g / L calcium chloride sheep milk casein

[0044] This comparative example is used to illustrate the casein sample as a reference.

[0045] Take the undecalcified sample from Example 1, add 0.6 g / L calcium chloride, and vortex for 3 min to mix.

[0046] Test Example 1

[0047] SDS-PAGE electrophoresis was used to analyze the casein components of the sheep milk casein solution from Example 1 and the bovine milk casein solution from Comparative Example 1. The casein micelles and whey calcium content, micelle size, zeta potential, and 95°C coagulation time were determined.

[0048] The casein composition results are shown in Table 1. In sheep milk casein, α... s The proportion of casein (38.68%) in goat milk was significantly lower than that in cow milk (56.98%), while the proportion of β-casein (51.62%) was significantly higher than that in cow milk (34.81%). The content of κ-casein was similar, with goat milk slightly higher than cow milk.

[0049] Table 1. Proportion of Casein Components in Bovine and Sheep Milk

[0050] Casein components Milk casein percentage (%) Casein content of sheep milk (%) <![CDATA[α s -Casein]]> 56.98 38.68 β-casein 34.81 51.62 κ-casein 8.21 9.7 Total casein 100 100

[0051] Distribution of calcium content in cow and sheep milk: The results of calcium content determination are shown in Table 2. The total calcium content of sheep milk (1.36 mg / mL) is higher than that of cow milk (1.11 mg / mL), and the proportion of whey phase calcium in sheep milk (39.71%) is higher than that in cow milk (36.94%). Sheep milk has more free calcium and is more sensitive to calcium ions. This part of free calcium is more likely to induce casein aggregation when heated.

[0052] Table 2 Distribution of calcium content in bovine and mutton milk

[0053] Comparison of mouse size of bovine and mutton casein micelles: particle size distribution diagram, see Figure 1 The average particle size of casein micelles from sheep milk (276.2 nm) was significantly smaller than that from cow milk (323.5 nm).

[0054] Comparison of bovine and ovine casein micelles with zeta potentials: See [link to zeta potential diagram]. Figure 2 The results showed that the absolute value of the Zeta potential of sheep milk casein was 18.5 mV, which was lower than that of cow milk (26.4 mV), indicating that the micelle system of sheep milk casein was less stable.

[0055] Coagulation time of bovine and ovine casein: See Table 3. Under conditions of 95℃ and pH 6.8, the coagulation time of bovine casein was 60.22 minutes, while that of ovine casein was 45.20 minutes. Both showed loose flocculent precipitates. This result directly confirms that the thermal stability of ovine casein is significantly inferior to that of bovine casein.

[0056] Table 3. Thermal coagulation time of bovine and mutton casein

[0057] name pH value Temperature (°C) Thermal solidification time (min) state Bovine casein 6.8 95 60.22 Loose flocculent precipitate appeared sheep casein 6.8 95 45.20 Loose flocculent precipitate appeared

[0058] Test Example 2

[0059] The calcium content, average particle size, zeta potential, and 95°C thermal solidification time were determined in Examples 1-4.

[0060] Calcium content and degree of decalcification in the decalcified group: see Table 4, with decalcification rates of 0%, 48%, 62%, and 76%, respectively.

[0061] Table 4. Calcium content and decalcification rate of decalcified casein

[0062] name Calcium content (mg / mL) Decalcification rate (%) Dilution 0 times 0.82 0 control Dilute once 0.43 48 Dilute twice 0.31 62 Dilute 3 times 0.20 76

[0063] Changes in the size of decalcified sheep milk casein micelles: See particle size distribution diagram. Figure 3 This indicates that as the decalcification rate increases, casein micelles dissociate and the particle size decreases significantly, with the smallest particle size observed at 48% decalcification.

[0064] Changes in micelle potential of decalcified sheep milk casein: See Zeta potential diagram. Figure 4 As the decalcification rate increased, the absolute value of the Zeta potential increased significantly from 18.5 mV in the control group to -21.3 mV in the 76% decalcification group, indicating that the electrostatic repulsion of the system was enhanced and the stability was improved.

[0065] Improved thermal stability: Table 5 shows the results of the thermal solidification time measurement. The thermal solidification time increased significantly with the increase of decalcification rate. Precipitation appeared in the control group at 45.20 minutes; in the 48% decalcification group, it increased to 98.53 minutes; in the 62% decalcification group, it increased to 143.20 minutes; while in the 76% decalcification group, no precipitation appeared within 180 minutes.

[0066] Table 5. Thermal coagulation time of casein in the decalcified group.

[0067] name pH value Temperature (°C) Thermal solidification time (min) state control group 6.8 95 45.20 Loose flocculent precipitate appeared 48% decalcification 6.8 95 98.53 Loose flocculent precipitate appeared 62% decalcification 6.8 95 143.20 Loose flocculent precipitate appeared 76% decalcification 6.8 95 >180.00 No sedimentation was observed.

[0068] Test Example 3

[0069] To verify the crucial role of calcium ions, different amounts (0, 0.2, 0.4, and 0.6 g / L) of calcium chloride solution were added back to decalcified sheep casein. Table 6 shows that with increasing calcium ion addition, the coagulation time decreased sharply, from 45.20 minutes in the control group to 11.65 minutes in the 0.6 g / L addition group, indicating a significant deterioration in thermal stability. This result conversely confirms that calcium ions are the core factor regulating the thermal stability of sheep casein.

[0070] Table 6. Casein coagulation time in the calcium-added group

[0071] name pH value Temperature (°C) Thermal solidification time (min) state Comparison 6.8 95 45.20 Loose flocculent precipitate appeared Add 0.2 g / L calcium chloride 6.8 95 23.42 Loose flocculent precipitate appeared Add 0.4 g / L calcium chloride 6.8 95 17.25 Loose flocculent precipitate appeared Add 0.6 g / L calcium chloride 6.8 95 11.65 Loose flocculent precipitate appeared

[0072] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for improving the stability of ultra-high temperature sterilized goat milk, characterized in that, The method includes: defatting sheep milk raw material, separating whey to obtain casein; partially removing calcium ions from the casein micelle system by ultra-high speed centrifugation dilution method, constructing a thermally stable calcium ion microenvironment, and significantly improving the anti-thermal coagulation ability of sheep milk casein during heating.

2. The method according to claim 1, characterized in that, The ultra-high speed centrifugation dilution method includes: resuspending the defatted casein precipitate in ultrapure water of the same volume as the original milk, centrifuging at 4 ℃ and 10000 r / min, discarding the supernatant and retaining the casein precipitate; repeating the above resuspension and centrifugation steps 1-3 times.

3. The method according to claim 2, characterized in that, By controlling the number of repeated centrifugations, the calcium removal rate in the casein micelle system was adjusted to 48% to 76%.

4. The method according to claim 1, characterized in that, The defatting process includes: centrifuging fresh sheep milk at 4 ℃ and 10000 r / min for 15 minutes to remove the upper layer of fat and obtain defatted milk.

5. The method according to claim 1, characterized in that, The method also includes ultra-high temperature sterilization of the treated sheep milk casein at 140 °C for 5 seconds.

6. Highly thermally stable sheep milk casein prepared by the method according to any one of claims 1-5.

7. The application of the method according to any one of claims 1-5 in the production of room temperature liquid goat milk, goat milk-based beverages, and fermented goat milk.

8. The application according to claim 7, characterized in that, It is used to inhibit protein precipitation, stratification, and flocculation in sheep milk-based products during ultra-high temperature sterilization.

9. A method for regulating the calcium environment of sheep milk casein, characterized in that, After the defatting and whey separation process described in claim 1, 0.2-0.6 g / L calcium chloride solution is added back to verify the effect of calcium content on thermal stability.

10. Control samples of sheep milk casein with different calcium contents prepared by the method of claim 10.

Images