Method for rapidly evaluating thermal stability of high-protein beverage

Abstract

The invention discloses a method for rapidly evaluating the thermal stability of a high-protein beverage, and belongs to the technical field of dairy products. The invention finds that the activity of calcium ions in a protein solution system can be used as the effective concentration of calcium ions for flocculation caused by a calcium bridge between casein micelles under a high-temperature condition, so that the activity of calcium ions is selected as an index for evaluating the thermal stability. The prediction equation is obtained by fitting the calcium ion activity and the thermal flocculation time, and the thermal stability of the concentrated milk protein raw material in a high-protein system can be accurately judged, so that whether the concentrated milk protein raw material is suitable for thermal processing production or not is determined.

Description

Technical Field

[0001] The present invention relates to a method for rapidly evaluating the thermal stability of high-protein beverages, and belongs to the technical field of dairy products. Background Art

[0002] Protein is a macronutrient essential for the human body. Dietary high-quality protein can promote the synthesis rate of body muscle protein, improve the adaptability of skeletal muscle to exercise, optimize the body's motor function, enhance immunity, and maintain the health of the body. Milk protein concentrate (MPC) is a high-quality protein source, mainly composed of casein, with the characteristics of high protein, low fat, and low lactose content, and has a wide range of applications in food processing.

[0003] Although both milk protein concentrate (MPC) and whey protein concentrate (WPC) are common protein supplements in dairy products, there are obvious differences in their raw material sources and physical properties. MPC is usually made from skim milk through ultrafiltration and other processing steps, and its protein content can vary between 42% and 92%, including casein and a small amount of whey protein. While WPC is mainly obtained by processing whey after removing casein, and there are significant differences in their protein compositions and applications.

[0004] At the same time, the stabilities of milk protein concentrate (MPC) and whey protein concentrate (WPC) at high protein concentrations vary greatly. WPC is prone to forming protein aggregates and gel-like structures when heated in a high-protein beverage system (protein concentration higher than >6% (g / 100 mL)), which will cause precipitation and a decrease in product stability, restricting its application in high-protein beverages. On the contrary, MPC can maintain good stability even at a protein concentration of 8% (g / 100 mL), is not easy to gel or precipitate, which gives MPC unique advantages in high-protein beverages. However, affected by sources, production areas, and different processing technologies, the thermal stability of MPC also varies greatly, specifically manifested as problems of gelling and flocculation during storage after heating, which has a very adverse impact on product quality. How to accurately predict the thermal stability of MPC raw materials is of great significance for the industry and can effectively avoid product quality problems.

[0005] From an industrial production perspective, predicting the thermal flocculation time of MPC is a complex process that involves multiple physical and chemical properties of proteins. Different from simple parameter prediction, predicting the thermal flocculation time requires considering factors such as the thermal stability of proteins, the influence of shear force, and the enhancement of protein interactions. In the actual production process, the interaction of these factors makes prediction extremely difficult and requires in-depth process understanding and precise control technology. Therefore, the selection of MPC and WPC should be determined according to the application requirements and desired characteristics of the final product. The high stability of MPC makes it more advantageous in liquid high-performance food and nutritional products.

[0006] The thermal stability of the milk protein solution refers to the property that the milk protein solution can withstand high temperatures during heating without flocculation or precipitation, which is an important issue faced during the high-temperature sterilization process of high-protein sports drinks. Li Yan et al. studied the effect of calcium ions on the thermal stability of 3.5% (mass fraction) whey protein concentrate (WPC), but there are significant differences in the protein composition between WPC and MPC; WPC cannot be applied in high-protein beverages either, so the thermal stability of MPC cannot be evaluated based on that of WPC. Currently, scientific research mainly focuses on the thermal stability of cow's milk, but the thermal stability of cow's milk is not completely consistent with that of high-protein beverages, and there are significant differences between them. On the one hand, the protein content differences are large. The protein content (concentration) in cow's milk is about 3%, while the protein content in high-protein beverages is generally higher than 6% (g / 100mL); in addition, their protein compositions are not completely the same; finally, the pH values and mineral ion compositions of the two systems are different, so the thermal stability of high-protein beverages cannot be accurately evaluated based on that of cow's milk.

[0007] With the wave of the national fitness campaign and the improvement of residents' health awareness in social development, the market for high-protein liquid beverages is increasing day by day. Before producing high-protein beverages, it is first necessary to evaluate the thermal stability of the concentrated milk protein solution system, otherwise scaling or even blocking the pipeline will occur during the high-temperature sterilization process, resulting in economic losses. Under laboratory conditions, the thermal stability is mainly evaluated by visually observing the time (HCT) when flocculation starts to occur during the heating of the concentrated milk protein solution at 140°C. This method has certain subjectivity and is destructive to the sample, and the high temperature also cannot guarantee the safety of the experimenters.

[0008] In the above technical solutions, whether predicting thermal stability through calcium ion concentration or detecting the thermal stability of the protein solution by visual observation is inaccurate. Therefore, there is an urgent need to develop a method for accurately predicting the thermal stability of high-protein solution systems, which has extremely high practical and economic value. Summary of the Invention

[0009] To solve the above problems, the present invention discovers that the calcium ion activity in a high-protein solution system can serve as the effective concentration of calcium ions that act as calcium bridges between casein micelles and cause flocculation under high-temperature conditions. Therefore, the calcium ion activity is selected as an index for evaluating thermal stability. By fitting the calcium ion activity and the thermal flocculation time, the present invention obtains a prediction equation, which can accurately determine the thermal stability of the milk protein concentrate raw material in a high-protein system, thereby determining whether it is suitable for hot processing production, and can serve the purpose of guiding material selection in actual production.

[0010] The first object of the present invention is to provide a method for rapidly predicting the thermal flocculation time of milk protein concentrate based on calcium ion activity, including the steps of:

[0011] (1) By detecting the calcium ion activity and the thermal flocculation time of milk protein concentrate solutions with different calcium ion concentrations, fitting the calcium ion activity and the thermal flocculation time to obtain a prediction equation; the prediction equation is:

[0012] When x is less than or equal to 1.86, y = -18.51x + 36.51;

[0013] When x is greater than 1.86, y = 14.86e -x / 0.83 + 0.18;

[0014] Wherein, x is the calcium ion activity, mM; y is the thermal flocculation time, min;

[0015] (2) Take the milk protein concentrate to be tested, prepare a milk protein concentrate solution to be tested, detect the calcium ion activity of the milk protein concentrate solution to be tested, and substitute the calcium ion activity into the prediction equation to obtain the thermal flocculation time.

[0016] In one embodiment, the calcium ion activity can be calculated by the formula a Ca =γ Ca ×c Ca ; wherein, a Ca (mM) is the calcium ion activity; c Ca (mM) is the free calcium ion concentration; γ Ca is the calcium ion activity coefficient.

[0017] In one embodiment, the free calcium ion concentration can be calculated by the formula Ec Ca =a×ln(c Ca ) + b; wherein, E Ca (mV) is the potential value; a, b are constants related to the ionic strength and can be calculated according to the ionic strength.

[0018] In one embodiment, the preparation method of the milk protein concentrate solutions with different calcium ion concentrations in step (1) is:

[0019] Mix the concentrated milk protein and water, homogenize, and refrigerate to obtain a concentrated milk protein solution; add calcium ions at different concentrations to obtain concentrated milk protein solutions with different calcium ion concentrations.

[0020] In one embodiment, the concentrated milk protein and water are mixed at a dosage ratio of 6 - 8 g:100 mL.

[0021] In one embodiment, the mixing is carried out by stirring at 30 - 50 °C and 300 - 300 rpm for 0.5 - 2 h.

[0022] In one embodiment, the homogenization is carried out at 20 - 30 °C and 25 - 35 MPa for 3 - 5 times.

[0023] In one embodiment, the refrigeration is carried out by placing at 2 - 8 °C for more than 12 h.

[0024] The second object of the present invention is to provide a method for rapidly predicting the thermal flocculation time of high-concentration milk protein beverages based on calcium ion activity:

[0025] (1) By detecting the calcium ion activity and thermal flocculation time of concentrated milk protein solutions with different calcium ion concentrations, fitting the calcium ion activity and thermal flocculation time to obtain a prediction equation; the prediction equation is:

[0026] When x is less than or equal to 1.86, y = -18.51x + 36.51;

[0027] When x is greater than 1.86, y = 14.86e -x / 0.83 + 0.18;

[0028] Wherein, x is the calcium ion activity (mM), and y is the thermal flocculation time (min);

[0029] (2) Take the high-concentration milk protein beverage to be measured, detect the calcium ion activity in the high-concentration milk protein beverage, and substitute the calcium ion activity into the prediction equation to obtain the thermal flocculation time.

[0030] In one embodiment, the protein concentration of the high-concentration milk protein beverage is 6 - 8% (g / 100 mL).

[0031] In one embodiment, the above method can be used to predict the duration of heat sterilization of high-concentration milk protein beverages to ensure that the protein does not denature and precipitate during the heat sterilization process of high-concentration milk protein beverages.

[0032] In one embodiment, the preparation method of the concentrated milk protein solutions with different calcium ion concentrations in step (1) is:

[0033] Mix the concentrated milk protein and water, homogenize, and refrigerate to obtain a concentrated milk protein solution; add calcium ions at different concentrations to obtain concentrated milk protein solutions with different calcium ion concentrations.

[0034] In one embodiment, the concentrated milk protein and water are mixed at a dosage ratio of 6 - 8 g:100 mL.

[0035] In one embodiment, the mixing is carried out with stirring at 30 - 50 °C and 300 - 500 rpm for 0.5 - 2 h.

[0036] In one embodiment, the homogenization is carried out at 20 - 30 °C and 25 - 35 MPa for 3 - 5 times.

[0037] In one embodiment, the refrigeration is carried out at 2 - 8 °C for more than 12 h.

[0038] The third object of the present invention is to provide a method for evaluating the thermal stability of a high-protein beverage based on calcium ion activity, comprising the steps of:

[0039] (1) Detect the calcium ion activity of the high-protein beverage, substitute the calcium ion activity into the prediction equation to obtain the thermal flocculation time; the prediction equation is:

[0040] When x is less than or equal to 1.86, y = -18.51x + 36.51;

[0041] When x is greater than 1.86, y = 14.86e -x / 0.83 + 0.18;

[0042] wherein, x is the calcium ion activity (mM), and y is the thermal flocculation time (min);

[0043] (2) If the thermal flocculation time is greater than 2 min, it is considered that the high-protein beverage has good thermal stability; if the thermal flocculation time is greater than or equal to 1 min and less than or equal to 2 min, it is considered that the high-protein beverage has general thermal stability; if the thermal flocculation time is less than 1 min, it is considered that the high-protein beverage has poor thermal stability;

[0044] The protein concentration of the high-concentration milk protein beverage is 6 - 8% (g / 100 mL).

[0045] The beneficial effects of the present invention:

[0046] The present invention can be a standard method for preparing a concentrated milk protein solution under laboratory conditions, which can minimize the thermal stability difference caused by the difference in the solution preparation method in evaluating thermal stability; the present invention provides a method for evaluating the concentrated milk protein solution based on calcium ion activity, and the prediction model established by this prediction method has good accuracy. By measuring the calcium ion activity, the thermal flocculation time can be simply and quickly calculated without damaging the sample, which can quickly and accurately screen the concentrated milk protein raw materials suitable for processing, help improve the quality and stability of products, meet the market demand for high-protein sports supplements, and provide practical guiding significance for the processing of milk protein beverages under a high-protein system. Description of the Drawings

[0047] Figure 1 It is the fitting curve of the prediction equation for Example 1;

[0048] Figure 2 It is the fitting curve of the prediction equation for Comparative Example 1;

[0049] Figure 3 It is the fitting curve of the prediction equation for Comparative Example 2;

[0050] Figure 4 It is the fitting curve of the prediction equation for Comparative Example 3;

[0051] Figure 5 It is the fitting curve of the prediction equation for Comparative Example 4. Detailed Description of the Invention

[0052] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explaining the present invention and are not used to limit the present invention.

[0053] Raw Materials

[0054] The milk protein concentrate is purchased from Fonterra, standard milk protein concentrate (hereinafter referred to as milk protein concentrate in the following examples).

[0055] Calculation method of calcium ion activity:

[0056] Referring to the method of Crowley et al. (Heat stability of reconstituted milk protein concentrate powders; doi.org / 10.1016 / j.idairyj.2014.03.005), a series of standard solutions are prepared using potassium chloride and calcium chloride, with total ionic strengths of 5, 10, 20, 40, 60 or 80 mM, and at each ionic strength, c Ca = 0, 0.25, 0.50, 1, 2, 3 mM. The potential value E Ca (mV) and the conductivity value κ (ms·cm -1 ) of the standard solutions are measured using a calcium ion selective electrode and a conductivity meter respectively.

[0057] (1) Establish a standard curve of ionic strength I (mM) and conductivity value κ (ms·cm -1 ) as follows:

[0058] κ = 0.1339I + 0.3385 Equation (1)

[0059] The ionic strength can be calculated by measuring the conductivity of the sample using Equation (1).

[0060] (2) Potential value E Ca (mV) and free calcium ion concentration c Ca (mM)

[0061] Using a calcium ion selective electrode to establish the relationship between the potential value E Ca (mV) of a standard solution (i.e., a series of standard solutions prepared from the above potassium chloride and calcium chloride) and the free calcium ion concentration c Ca (mM), the formula is:

[0062] Ec Ca = a × ln(c Ca ) + b Formula (2)

[0063] Wherein, a and b are constants related to the ionic strength, and their relationship is as follows,

[0064] a = -0.73 × ln(I) + 16.30 Formula (3)

[0065] b = -3.72 × ln(I) - 16.61 Formula (4)

[0066] According to the above formulas (1) to (4), the free calcium ion concentration c Ca (mM) in the sample can be calculated.

[0067] (3) Calcium ion activity a Ca (mM) and free calcium ion concentration c Ca (mM)

[0068] Calcium ion activity coefficient γ Ca Then it is calculated from the Debye-Hückel limiting formula, and the formula is as follows:

[0069]

[0070] In Formula (5), Z is the charge number of Ca 2+ , that is, Z = 2; I is the ionic strength (mM);

[0071] Calcium ion activity a Ca (mM) can be obtained by the formula a Ca = γ Ca × c Ca Formula calculation.

[0072] Thermal flocculation time detection method

[0073] Take 2 mL of the sample and put it into an ampoule bottle. After heat sealing, place it in an oil bath at a temperature of 140 °C, and shake the ampoule bottle at a constant speed of 8 times per minute. Record the time when flocculation first appears by visual observation, which is the thermal flocculation time;

[0074] Taking the centrifugal precipitation rate as another index to measure the concentrated milk protein solution, 2 mL of the samples with different calcium addition amounts were filled into ampoules. The re-dissolved solution after heat treatment at 140 °C was immediately cooled to room temperature under flowing cold water, centrifuged at 3000 g for 30 min, and then the precipitate was dried at 105 °C for 7 h until the weight was constant. The percentage of the weight of the dried precipitate to the weight of the corresponding non-centrifuged re-dissolved solution after drying was taken as the centrifugal precipitation rate.

[0075] Unless otherwise specified, the meaning of the concentration % in the text is g / 100 mL.

[0076] Example 1: Piecewise fitting of the calcium ion activity and heat flocculation time curves

[0077] 1. Prepare the concentrated milk protein solution according to the following steps:

[0078] (1) Mix the concentrated milk protein and water according to the dosage ratio of 8:100 (8 g / 100 mL), and stir at 50 °C and 300 rpm for 1 h;

[0079] (2) After stirring, homogenize 3 times at 25 °C and 30 MPa, and refrigerate at 4 °C to obtain a concentrated milk protein solution with good homogeneity, and the solubility is 97.8%.

[0080] 2. Detect the influence of different calcium activities on the heat flocculation time of the concentrated milk protein solution

[0081] Take the concentrated milk protein solution prepared in 1, add different amounts of CaCl 2 , and adjust the pH to 6.8 to obtain samples with different calcium addition amounts, and detect and calculate the calcium ion activity (a Ca , mM), heat flocculation time (t, min), free calcium content (c Ca , mM), particle size (D, nm) and Zeta potential (ζ, mV).

[0082] The correlation coefficients (r) of the above indexes are shown in Table 1. When |r| ≥ 0.8, it can be considered that these two factors are significantly correlated. The results show that there is a significant correlation among pH, free calcium content, calcium ion activity and heat flocculation time.

[0083] Table 1 Results of correlation coefficients

[0084] r in the table pH Free calcium content Zeta potential Average particle size Calcium ion activity Thermal flocculation time Total calcium content pH 1.00 -0.94 -0.47 0.34 -0.90 0.95 0.00 Free calcium content -0.94 1.00 0.65 -0.16 0.91 -0.95 0.29 Zeta potential -0.47 0.65 1.00 0.07 0.56 -0.54 0.70 Average particle size 0.34 -0.16 0.07 1.00 0.05 0.15 0.50 Calcium ion activity -0.90 0.91 0.56 0.05 1.00 -0.95 0.27 Thermal flocculation time 0.95 -0.95 -0.54 0.15 -0.95 1.00 -0.18 Total calcium content 0.00 0.29 0.70 0.50 0.27 -0.18 1.00

[0085] By linear fitting and non-linear fitting of the calcium ion activity and heat flocculation time in the samples with different calcium addition amounts, it is found that:

[0086] When the calcium ion activity is less than or equal to 1.86 and greater than 0.82, it shows a linear decreasing relationship with the heat flocculation time (R 2= 0.99); when the calcium ion activity is greater than 1.86 and less than 5.22, it shows an exponential decreasing relationship with the thermal flocculation time (R 2 = 0.97). Finally, a piecewise function of calcium ion activity (mM) with respect to thermal flocculation time (min) is obtained, and the results are as Figure 1 shown.

[0087] That is, y = -18.51x + 36.51 (0.82 < x ≤ 1.86); y = 14.86e -x / -0.83x + 0.18 (5.22 > x > 1.86).

[0088] 3. Protein thermal flocculation time and thermal stability

[0089] Table 2 shows the thermal flocculation time and corresponding centrifugal precipitation rate of samples with different calcium addition amounts. The results show that with the increase of calcium addition amount, the thermal flocculation time decreases while the centrifugal precipitation rate increases, and the increase of calcium makes the sample more easily thermally induced to be unstable, manifested as flocculation occurring in a shorter time and more protein sedimentation after heat treatment.

[0090] That is, when the thermal flocculation time (y) is greater than 2 minutes, the thermal stability of the concentrated milk protein solution is relatively good; when the thermal flocculation time is greater than 1 minute and less than or equal to 2 minutes, the thermal stability of the concentrated milk protein solution is average; when the thermal flocculation time is less than or equal to 1 minute, the thermal stability of the concentrated milk protein solution is poor.

[0091] Table 2 Thermal flocculation time and centrifugal precipitation rate under different calcium addition amounts

[0092] Calcium addition amount Thermal flocculation time Centrifugal precipitation rate 0 19.08 3.48％ 0.1 11.31 9.56％ 0.2 1.86 14.08％ 0.3 1.08 20.75％ 0.4 0.84 35.34％ 0.5 0.46 58.16％ 0.6 0.34 73.41％ 0.7 0.20 80.16％ 0.8 0.13 82.15％

[0093] Comparative Example 1: Directly fitting the calcium ion activity and thermal flocculation time curves

[0094] On the basis of Example 1, the fitting method is changed to non-linear fitting, and the remaining steps are the same as those in Example 1.

[0095] The fitting curve is as Figure 2 shown. The results show that non-linear fitting reveals that the calcium ion activity and the thermal flocculation time show an exponential decreasing relationship (R 2 = 0.96), and the function of calcium ion activity and thermal flocculation time is obtained as y = 98.50e -x / -0.57x - 0.09;

[0096] When y > 2, the thermal stability of the concentrated milk protein solution is relatively good; when 1 < y ≤ 2, the thermal stability of the concentrated milk protein solution is average; when y ≤ 1, the thermal stability of the concentrated milk protein solution is poor.

[0097] Comparative Example 2: Fitting the calcium content and thermal flocculation time curves

[0098] Fit the curve of calcium ion concentration and thermal flocculation time as follows:

[0099] On the basis of Example 1, fit the curve of calcium content and thermal flocculation time. The fitting result is as Figure 3 shown. The result shows that there is a decreasing relationship between calcium content and thermal flocculation time (R 2 = 0.99);

[0100] The function obtained by fitting is Comparative Example 3: Fit the curve of free calcium ion concentration and thermal flocculation time

[0101] Fit the curve of free calcium ion concentration and thermal flocculation time as follows:

[0102] On the basis of Example 1, fit the curve of free calcium ion concentration and thermal flocculation time. The fitting result is as Figure 4 shown. The result shows that there is a decreasing relationship between free calcium ion concentration and thermal flocculation time (R 2 = 0.97);

[0103] The function obtained by fitting is y = 61.58e -x / 0.15 -0.46.

[0104] Comparative Example 4: Fit the curve of pH value and thermal flocculation time

[0105] Fit the curve of pH and thermal flocculation time as follows:

[0106] Prepare the concentrated milk protein solution according to the method in Example 1, and adjust the pH to 6.3 - 7.1 with 1 mol / L hydrochloric acid and sodium hydroxide solution, and measure the thermal flocculation time respectively.

[0107] Obtain the curve of pH and thermal flocculation time through non - linear fitting. The fitting result is as Figure 5 shown. The result shows that there is an increasing relationship between pH and thermal flocculation time (R 2 = 0.99)

[0108] The function obtained by fitting is Example 2: A method for rapidly evaluating the thermal stability of high - protein beverages containing concentrated milk protein

[0109] In the industrial production process of high - protein beverages, due to the different calcium contents of concentrated milk proteins from different sources and the different pH values under different ingredient systems, it is difficult to predict the inconsistent thermal stability during actual production. Therefore, adjust the pH and calcium content of the high - protein beverage to verify the accuracy of the prediction model.

[0110] Prepare a high-protein sports drink by referring to the ingredient list of commercially available high-protein sports drinks. Using water, concentrated milk protein, fructooligosaccharide, whey protein powder, collagen peptide, and coconut oil as the main raw materials, by weight, its components include: 100 parts of water, 7.5 parts of concentrated milk protein, 0.5 part of fructooligosaccharide, 0.5 part of whey protein, 0.5 part of collagen peptide, and 0.3 part of coconut oil. Prepare it into a uniform and stable solution according to the method in Example 1 and divide it into 6 equal parts.

[0111] Adjust the pH of three of them to 6.5, 6.8, and 7.1 respectively with 1 mol / L hydrochloric acid and sodium hydroxide solution, and add calcium chloride to the other three parts so that their calcium content (mg / mL) is 1.95, 2.05, and 2.15 respectively. Adjust the pH to 6.8 with 1 mol / L hydrochloric acid and sodium hydroxide solution, and detect the calcium ion activity of the 6 samples. Calculate the predicted values of the thermal flocculation time with different functions and judge the stability according to them.

[0112] The results are shown in Table 3. The results show that only the predicted thermal stability of Example 1 is completely consistent with the actual thermal stability. Compared with Comparative Example 1 with direct fitting, the predicted value of Example 1 with piecewise fitting has a smaller error value and higher accuracy; Comparative Example 2 fitted according to the calcium content has a higher accuracy when the pH remains unchanged, but when the system pH changes, Comparative Example 2 cannot be used for prediction; Comparative Example 3 fitted according to the pH has a higher accuracy when the calcium content remains unchanged, but when the system calcium content changes, Comparative Example 3 cannot be used for prediction.

[0113] In summary, only Example 1 fitted based on the calcium ion activity can ignore the influence of the system pH and calcium content and accurately predict the thermal stability of the concentrated milk protein solution.

[0114] Table 3 Detection of prediction effect

[0115]

[0116]

[0117] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this technology can make various modifications and decorations without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be defined by the claims.

Claims

1. A method for rapidly predicting the thermal flocculation time of concentrated milk protein based on calcium ion activity, characterized in that: Includes steps: (1) The calcium ion activity and thermal flocculation time of concentrated milk protein solutions with different calcium ion concentrations were detected, and the calcium ion activity and thermal flocculation time were fitted to obtain a prediction equation; the prediction equation is: When x is less than or equal to 1.86, y = -18.51x + 36.51; When x is greater than 1.86, y = 14.86e -x / 0.83 +0.18; Wherein, x is the calcium ion activity, mM; y is the thermal flocculation time, min; (2) taking the concentrated milk protein to be tested, preparing a concentrated milk protein test solution, detecting the calcium ion activity of the concentrated milk protein test solution, substituting the calcium ion activity into a prediction equation, and obtaining the thermal flocculation time.

2. The method according to claim 1, characterized in that The preparation method of concentrated milk protein solutions with different calcium ion concentrations in step (1) is as follows: The concentrated milk protein and water are mixed in a dosage ratio of 6-8 g:100 mL, homogenized, and refrigerated to obtain a concentrated milk protein solution; different concentrations of calcium ions are added to obtain concentrated milk protein solutions with different calcium ion concentrations.

3. The method according to claim 2, characterized in that The mixing is carried out by stirring at 30-50°C and 300-500 rpm for 0.5h-2h; the homogenization is carried out at 20-30°C and 25-35 MPa for 3-5 times; the refrigeration is carried out by placing at 2-8°C for more than 12h.

4. A method for quickly predicting the thermal flocculation time of a high-concentration milk protein beverage based on calcium ion activity, characterized in that: Includes steps: (1) The calcium ion activity and thermal flocculation time of concentrated milk protein solutions with different calcium ion concentrations were detected, and the calcium ion activity and thermal flocculation time were fitted to obtain a prediction equation; the prediction equation is: When x is less than or equal to 1.86, y = -18.51x + 36.51; When x is greater than 1.86, y = 14.86e -x / 0.83+0.18; Wherein, x is the calcium ion activity, mM; y is the thermal flocculation time, min; (2) Taking a high-concentration milk protein beverage to be tested, detecting the calcium ion activity in the high-concentration milk protein beverage, substituting the calcium ion activity into a prediction equation, and obtaining the thermal flocculation time.

5. The method according to claim 4, characterized in that The protein concentration of high-concentration milk protein beverages is 6 to 8% (g / 100 mL).

6. The method according to claim 4, characterized in that The preparation method of concentrated milk protein solutions with different calcium ion concentrations in step (1) is as follows: The concentrated milk protein and water are mixed in a dosage ratio of 6-8 g:100 mL, homogenized, and refrigerated to obtain a concentrated milk protein solution; different concentrations of calcium ions are added to obtain concentrated milk protein solutions with different calcium ion concentrations.

7. The method according to claim 6, characterized in that The mixing is carried out at 30-50°C and 300-500 rpm for 0.5-2 h.

8. The method according to claim 6, characterized in that The homogenization is carried out at 20-30°C and 25-35 MPa for 3-5 times.

9. The method according to claim 6, characterized in that Refrigeration means keeping it at 2-8℃ for more than 12 hours.

10. A method for evaluating the thermal stability of a high-protein beverage based on calcium ion activity, characterized in that: Includes steps: (1) Detect the calcium ion activity of the high-protein beverage, substitute the calcium ion activity into the prediction equation, and obtain the thermal flocculation time; the prediction equation is: When x is less than or equal to 1.86, y = -18.51x + 36.51; When x is greater than 1.86, y = 14.86e -x / 0.83+0.18; Wherein, x is the calcium ion activity, mM; y is the thermal flocculation time, min; (2) If the thermal flocculation time is greater than 2 min, the high-protein beverage is considered to have good thermal stability; if the thermal flocculation time is greater than or equal to 1 min and less than or equal to 2 min, the high-protein beverage is considered to have average thermal stability; if the thermal flocculation time is less than 1 min, the high-protein beverage is considered to have poor thermal stability; The protein concentration of high-concentration milk protein beverages is 6 to 8% (g / 100 mL).

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