High-efficiency low-loss extraction method of inorganic salt in milk powder

Abstract

The invention relates to the technical field of inorganic salt extraction, and particularly discloses a high-efficiency low-loss extraction method of inorganic salt in milk powder, which comprises the following steps: S1, competitive coordination pretreatment, S2, slow-speed acid precipitation of protein, S3, organic solvent-assisted precipitation, S4, adsorption purification, S5, color development determination and S6, recovery rate calculation. According to the method, on the premise that the original addition form of calcium is not damaged, calcium loss or interference of other metal ions possibly caused by strong acid digestion is avoided, and the recovery rate and the determination accuracy of target components are improved. Compared with traditional digestion or dry ashing and other methods, the method has the advantages that experimental error sources and uncontrollable variables are reduced through mild operation conditions, and the method is particularly suitable for distinguishing the two forms of'free calcium 'and'protein binding calcium' in milk powder, so that the actual feeding effect of the additional nutrition enhancer is evaluated more accurately.

Description

Technical Field

[0001] This invention belongs to the field of inorganic salt extraction technology, specifically relating to a highly efficient and low-loss extraction method for inorganic salts from milk powder. Background Technology

[0002] In the field of food nutrition and safety, accurately analyzing the inorganic salt composition of milk powder, especially the content and forms of important nutrients such as calcium and zinc, is crucial for assessing milk powder quality and ensuring the accuracy of nutrient intake for infants and consumers. Calcium, as an important nutrient fortifier in milk powder, often exists in two forms: free calcium and protein-bound calcium. Accurately distinguishing and measuring the content of these two forms of calcium can directly reflect the actual effect of added nutrient fortifiers, providing strong evidence for milk powder manufacturers' quality control and product development.

[0003] Accurately determining the content of free calcium (artificially added calcium, an important source of calcium for infants and young children, and one of the important forms of calcium absorbed and utilized by the human body) and total calcium (including inorganic and organic calcium) in infant formula allows for the assessment of the nutritional value of the formula, providing a basis for the scientific formulation of formulas to meet the calcium needs of infants at different ages. Establishing reliable testing methods is of great significance for standardizing the infant formula production process, ensuring the quality of infant formula products on the market, strengthening market supervision, and effectively protecting consumers' legitimate rights and interests.

[0004] However, existing technologies for extracting inorganic salts from milk powder have many shortcomings and cannot meet practical needs. Traditional methods often employ strong acid digestion or drying and ashing to process milk powder samples. Strong acid digestion requires large amounts of strong acid and prolonged reactions at high temperatures, which not only destroys the original form of calcium, leading to calcium loss, but may also introduce interference from other metal ions, severely affecting the accuracy of target component determination. Drying and ashing involves burning the sample to ash at high temperatures. This process also causes some calcium to volatilize and be lost; moreover, it is complex, time-consuming, and has many sources of experimental error and uncontrollable variables, making it difficult to guarantee the stability and reliability of analytical results.

[0005] Furthermore, existing technologies have limited ability to effectively release and selectively enrich free calcium components when processing the complex matrix of milk powder. Milk powder contains abundant organic components such as proteins and fats, which can form complexes or encapsulation structures with inorganic salts such as calcium and zinc, increasing the difficulty of inorganic salt extraction. Traditional methods often lack targeted pretreatment and separation enrichment strategies, failing to effectively disrupt protein network structures, break down fat globules, or efficiently dissociate complexed metal ions, resulting in low extraction efficiency and unsatisfactory recovery rates for the target inorganic salts.

[0006] Regarding detection methods, while existing technologies often combine conventional instrumental analysis methods such as ultraviolet colorimetry or atomic absorption spectrometry, these methods require sophisticated sample pretreatment and involve expensive and complex equipment, limiting their application in resource-constrained or unequipped scenarios. Therefore, developing an extraction method that can efficiently and minimally extract inorganic salts from milk powder under mild operating conditions, accurately distinguish between free calcium and protein-bound calcium, and possess good scalability and applicability, has become a critical issue urgently needing to be addressed in the field of food analysis.

[0007] In response, the inventors proposed a highly efficient and low-loss extraction method for inorganic salts from milk powder to solve the above problems. Summary of the Invention

[0008] The purpose of this invention is to provide a highly efficient and low-loss extraction method for inorganic salts from milk powder, so as to solve the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A highly efficient and low-loss extraction method for inorganic salts from milk powder includes the following steps:

[0011] S1, competitive coordination pretreatment, used to release free Ca2+ encapsulated by proteins or lipids. 2+ Mix milk powder and water at a mass ratio of 1:4, add a competitive ligand and mix well to obtain a pretreated mixture;

[0012] S2, slow-speed acid precipitation protein, is used for selective precipitation of proteins without encapsulating free calcium. 2+ Add acid precipitant to the pretreatment mixture stepwise, adjust the pH to the isoelectric point of the protein, and let it stand to obtain protein precipitate and supernatant A;

[0013] S3. Organic solvent-assisted precipitation: After adding organic solvent to supernatant A, mix, sonicate or vortex, and then centrifuge to further remove residual protein and fat, to obtain supernatant B.

[0014] S4. Adsorption purification: Add adsorbent material to supernatant B and mix, then filter to remove pigments and particulate impurities from supernatant B to obtain purified liquid.

[0015] S5. Colorimetric determination, used to determine the free Ca in the purified solution. 2+ The solution is converted into a colorimetric complex and its absorbance is measured to obtain the measurement results.

[0016] S6. Recovery rate calculation, used to calculate the recovery rate based on the test results and the theoretical added Ca in the sample. 2+ Calculate the recovery rate.

[0017] Preferably, in step S1, the competing ligand is disodium ethylenediaminetetraacetate or sodium citrate, with a concentration range of 0.2 mM to 2 mM; the mixing volume is 0.5% to 2.0% of the sample suspension volume.

[0018] Preferably, in step S2, the acid precipitant is trichloroacetic acid with a concentration of 3% to 6% (w / v), added in three portions with a 1-minute interval, and the pH is adjusted to 4.4 to 4.7 before standing for 5 to 15 minutes.

[0019] Preferably, in step S3, the organic solvent is acetonitrile, the pre-cooling temperature is 0℃~4℃, the amount added is 30%~50% of the volume of the sample suspension, and the supernatant is collected after sonication for 5 min or vortexing for 1 min and centrifugation at 4000 rpm for 5 min.

[0020] Preferably, in step S4, the adsorbent material is food-grade activated carbon or diatomaceous earth, and the amount added is 0.5% to 2% (w / v) of the supernatant volume. After stirring for 3 to 5 minutes, the material is filtered using a 0.22 μm to 0.45 μm filter membrane.

[0021] Preferably, in step S5, the colorimetric agent is o-cresolphthalein complex ketone with a concentration of 0.2 mM to 1.0 mM, and after reacting in a pH 5.0 to 6.0 buffer for 5 min to 10 min, the absorbance is measured at 550 nm to 580 nm.

[0022] Preferably, the formula for calculating the recovery rate in step S6 is:

[0023] Recovery rate (%) = (Ctest × V ...fixed / Vsample) ÷ (msample × Cstandard) × 100%

[0024] Among them, C measure: the calcium concentration corresponding to the absorbance, μg / mL;

[0025] Vmeasurement: The volume of the solution used for the measurement, in mL;

[0026] Vfixed: The total volume of the sample after treatment and final volume adjustment, in mL;

[0027] Vtake: The volume (mL) of the final volume solution used for the measurement;

[0028] m sample: Mass of milk powder used for extraction, in grams;

[0029] C-standard: The theoretical concentration of free calcium added to the sample, in μg / g.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] (1) This invention achieves effective release and selective enrichment of free calcium components in the complex matrix of milk powder by using mild acid precipitation, acetonitrile-assisted removal of organic matter, trichloroacetic acid to regulate protein precipitation behavior, and a combined strategy of adsorption purification and multi-stage filtration.

[0032] (2) This invention avoids calcium loss or interference from other metal ions that may be caused by strong acid digestion without destroying the original form of added calcium, thus improving the recovery rate and accuracy of the target component. Compared with traditional digestion or drying and ashing methods, this invention reduces experimental error sources and uncontrollable variables through mild operating conditions, and is particularly suitable for distinguishing between the two forms of "free calcium" and "protein-bound calcium" in milk powder, thereby more accurately evaluating the actual effect of added nutritional fortifiers;

[0033] (3) This invention combines conventional instrumental analysis methods such as ultraviolet colorimetry or atomic absorption spectroscopy, and can also be adapted to digital image colorimetry systems for detection in instrument-free scenarios, with good scalability and universality. Attached Figure Description

[0034] Figure 1 This is a flowchart of a method for efficient and low-loss extraction of inorganic salts from milk powder according to the present invention.

[0035] Figure 2 This is an absorption wavelength diagram of the ultraviolet-visible spectrophotometer of the present invention;

[0036] Figure 3 A standard curve was obtained by measuring absorbance in the ultraviolet spectrophotometer of the present invention.

[0037] Figure 4 For the determination of Fe in o-phenanthroline of the present invention 2+ The experimental diagram. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1:

[0040] Please see Figures 1-2 As shown, a highly efficient and low-loss extraction method for inorganic salts from milk powder includes:

[0041] Sample: Infant formula milk powder A, labeled as containing 500mg of calcium carbonate per 100g of milk powder (approximately 200mg of Ca). 2+ )

[0042] Sample size: 3.00 g, corresponding to theoretical free Ca 2+ The dosage is 6.00 mg (6000 μg).

[0043] Method and steps:

[0044] 1. Competitive coordination pretreatment: Add 3.00g of milk powder to 12mL of deionized water and vortex for 30s; add 0.5mM (0.1mL) of disodium ethylenediaminetetraacetate (EDTA) as a coordination agent and stir gently for 1min; add 0.01% (v / v) of Tween-20.

[0045] 2. Slow-release TCA acid-precipitated proteins: such as Figure 2 As shown, the absorbance is highest when the trichloroacetic acid solution concentration is around 4%. Therefore, in this invention, 15 mL of 4% trichloroacetic acid solution is added, and the pH is adjusted to 4.5. That is, 5 mL of 4% trichloroacetic acid solution is slowly added in 3 portions, with an interval of 1 min, and the pH is adjusted to 4.5. The mixture is then allowed to stand at room temperature for 10 min until the protein coagulates.

[0046] 3. Acetonitrile-assisted precipitation: Add 5 mL of pre-cooled (0℃) acetonitrile at once, vortex for 30 s; ultrasonic bath (25℃) for 5 min; centrifuge at 4000 rpm for 5 min, and collect 10 mL of clear supernatant;

[0047] 4. Activated carbon adsorption: Add 0.1 g of activated carbon to the supernatant and stir at room temperature for 5 min; filter through a 0.45 μm filter membrane to obtain the purified solution;

[0048] 5. Colorimetric determination: The purified solution was brought to a final volume of 10 mL; 0.5 mM (2 mL) o-cresolphthalein complex ketone and 1 mL of 1 M sodium acetate buffer (pH 5.5) were added; the reaction was carried out at room temperature for 10 min; the absorbance was measured at 565 nm.

[0049] 6. Recovery rate calculation: such as Figure 3 As shown, the maximum absorption wavelength was scanned in the range of 400 to 600 nm. The maximum absorption wavelength was determined by peak and valley detection. The wavelength of 580 nm was selected for colorimetric determination using a UV-Vis spectrophotometer (UV-1801).

[0050] Using Ca 2+ Standard solutions were used to construct a standard curve (linear range 0–10 μg / mL, R²>0.9995).

[0051] Calculate the recovery rate:

[0052] Assume the measured absorbance corresponds to a Ca concentration of 1.60 μg / mL; the total amount in 10 mL of treatment solution is 16.0 μg.

[0053] Magnification: Final liquid to original sample ratio = 10mL / (3g) × 100g = 333.3;

[0054] The estimated content is 5.33 mg / 100g;

[0055] Recovery rate = 5.33 / 6.00 × 100% = 88.83;

[0056] Example 2:

[0057] Extraction and determination of free calcium in milk powder based on the combined use of food-grade citric acid and acetonitrile:

[0058] Sample: Student Nutritional Milk Powder B, labeled as containing an additional 400mg of calcium carbonate (approximately 160mg Ca) per 100g of milk powder. 2+ )

[0059] Sample size: 3.00 g, corresponding to theoretical free Ca 2+ The dosage was 4.80 mg (4800 μg).

[0060] Method and steps:

[0061] 1. Competitive coordination of sodium citrate: 3.00g milk powder + 12mL deionized water; vortex for 30s; add 1mM sodium citrate (0.2mL), and gently mix for 1min;

[0062] 2. Slow-release TCA precipitation: Add 5 mL of 4% trichloroacetic acid solution in three portions, ensuring pH≈4.4; allow protein to coagulate for 5 min; centrifuge at 4000 rpm for 5 min.

[0063] 3. Acetonitrile-assisted precipitation: Add 5 mL of room temperature acetonitrile, vortex for 30 s; sonicate for 5 min; centrifuge for 5 min; collect 10 mL of supernatant;

[0064] 4. Diatomaceous earth filtration: Add 0.2g of diatomaceous earth to the supernatant and stir for 3min; then filter through a 0.22μm filter membrane to obtain the treated solution;

[0065] 5. Colorimetric analysis: Adjust the volume of treatment solution B to 10 mL; add 0.5 mM (2 mL) o-cresolphthalein complex ketone + 1 mL 1 M sodium acetate buffer (pH 5.5); measure the absorbance at 565 nm;

[0066] The absorbance was measured at a wavelength of 580 nm, and Ca was calculated. 2+ Concentration conversion standard curve.

[0067] Calculation results:

[0068] Absorbance corresponding to Ca 2+ Concentration = 1.25 μg / mL, total Ca = 12.5 μg;

[0069] Content = 12.5 × (100g / 3g) = 4.17mg / 100g;

[0070] Recovery rate = 4.17 / 4.80 × 100% = 86.88%;

[0071] Table 1

[0072] project Example 1 Example 2 Types of milk powder Infant formula milk powder A Student Nutritional Milk Powder B Theoretical Ca addition amount 6.00mg / 100g 4.80mg / 100g Measured content 5.33mg / 100g 4.17mg / 100g Recovery rate 88.83% 86.88% Separation method Trichloroacetic acid + acetonitrile Food-grade citric acid + acetonitrile Measurement method Ultraviolet-Vis Spectrophotometry Ultraviolet-Vis Spectrophotometry Does it meet the target accuracy? yes yes

[0073] As can be seen from the above, both embodiments employ a triple separation strategy of isoelectric point precipitation + organic solvent assistance + adsorption filtration, which is suitable for different milk powder matrices.

[0074] With a recovery rate controlled at 80%–90%, the free calcium added to milk powder can be accurately measured, avoiding interference from naturally bound calcium.

[0075] By optimizing the acid type, dosage, pH control, and adsorbent selection, the applicability and potential for promotion of this method in actual food testing were further verified.

[0076] Example 3:

[0077] Obtain the supernatant:

[0078] Add 5 mL of a 10% milk powder solution to a centrifuge tube (50 mL).

[0079] Add 5 mL of 0.6 mL disodium ethylenediaminetetraacetate (EDTA) as a complexing agent; this is to prevent metal ions from being adsorbed or encapsulated by proteins, which could lead to their loss.

[0080] Vortex mix for 5-10 minutes

[0081] Add 20 mL of 2.5% trichloroacetic acid and vortex to mix (for protein precipitation).

[0082] Add 5 mL of acetonitrile and mix again (to promote the precipitation of proteins by trichloroacetic acid and reduce the encapsulation of metal ions by fat).

[0083] After sonication for 5 minutes, centrifugation is performed for 5-10 minutes, and the supernatant is collected.

[0084] The supernatant was filtered through a 0.45 μm filter membrane to obtain a more transparent supernatant for analysis;

[0085] Determination of calcium by o-cresolphthalein complex ketone:

[0086] Solution preparation:

[0087] 1.0.4% o-cresolphthalein complex ketone solution: Weigh 0.4 g of o-cresolphthalein complex ketone, add 0.1 mol of sodium hydroxide solution until completely dissolved, and then dilute to 100 mL.

[0088] 2. Ammonium chloride-ammonium hydroxide buffer solution: Weigh 13.5 g of ammonium chloride, measure 87.5 mL of ammonium hydroxide, mix and dilute to 250 mL.

[0089] 3. Calcium Standard Stock Solution (100 mg / L): Accurately weigh 0.1249 g of dried and cooled calcium carbonate solid, moisten with pure water, and add 20% hydrochloric acid dropwise until the solid is completely dissolved. Transfer to a 500 mL volumetric flask and dilute to volume. This yields a calcium standard stock solution of 100 mg / L.

[0090] 4. Calcium standard working solution (10 mg / L): Accurately transfer 10.00 mL of calcium standard stock solution to a 100 mL volumetric flask, and dilute to volume to obtain a 10 mg / L calcium standard working solution.

[0091] II. Establishment of Standard System

[0092] Prepare six 25 mL volumetric flasks, numbered 0, 1-5. Accurately transfer 1.00, 2.00, 3.00, 4.00, and 5.00 mL of calcium standard working solution to flasks 1-5, respectively. Then, transfer 1 mL of 0.4% o-cresolphthalein complex ketone solution and 3 mL of ammonium chloride-ammonium hydroxide buffer solution to each flask. Dilute to the mark in each flask to obtain a series of calcium standard solutions with concentrations of 0, 0.4, 0.8, 1.2, 1.6, and 1.8 mg / L (µg / mL).

[0093] The absorbance was measured in a UV spectrophotometer with a wavelength set to 570-580 nm to obtain a standard curve, as shown in Table 2. Figure 3 As shown;

[0094] Table 2

[0095] c(mg / L) A 0.4 0.192 0.8 0.323 1.2 0.436 1.6 0.567 2 0.678

[0096] This invention proposes a highly efficient and low-loss extraction method for the external addition of inorganic calcium to milk powder. By employing a combined strategy of mild acid precipitation, acetonitrile-assisted removal of organic matter, trichloroacetic acid regulation of protein precipitation behavior, and adsorption purification and multi-stage filtration, the method achieves effective release and selective enrichment of free calcium components in the complex matrix of milk powder.

[0097] Example 4:

[0098] Determination of Fe by o-phenanthroline 2+

[0099] Obtain the supernatant:

[0100] The experiment was divided into 5 groups, including:

[0101] 1. Take 5 mL of 10% milk powder solution and 200 μg / mL Fe 2+Add the sample to a centrifuge tube, add 20 mL of 3.5% trichloroacetic acid, and vortex to mix; then add 5 mL of acetonitrile and mix again; then sonicate for 5 min, centrifuge for 5-10 min, and take the supernatant to obtain sample 1;

[0102] 2. Take 5 mL of 10% milk powder solution and 200 μg / mL Fe 2+ Add the sample to a centrifuge tube, add 3.5% trichloroacetic acid (spiked), and vortex to mix; then add 5 mL of acetonitrile and mix again; then sonicate for 5 min, centrifuge for 5-10 min, and take the supernatant to obtain sample 2;

[0103] 3. Take 5 mL of 10% milk powder solution and 200 μg / mL Fe 2+ Add the sample to a centrifuge tube, add 4% trichloroacetic acid (spiked), and vortex to mix; then add 5 mL of acetonitrile and mix again; then sonicate for 5 min, centrifuge for 5-10 min, and take the supernatant to obtain sample 3;

[0104] 4. Take 5 mL of 10% milk powder solution and 200 μg / mL Fe 2+ Add the sample to a centrifuge tube, add 4.5% trichloroacetic acid (spiked), and vortex to mix; then add 5 mL of acetonitrile and mix again; then sonicate for 5 min, centrifuge for 5-10 min, and take the supernatant to obtain sample 4;

[0105] 5. Take 5 mL of 10% milk powder solution and 200 μg / mL Fe 2+ Add the sample to a centrifuge tube, add 5% trichloroacetic acid (spiked), and vortex to mix; then add 5 mL of acetonitrile and mix again; then sonicate for 5 min, centrifuge for 5-10 min, and take the supernatant to obtain sample 5;

[0106] like Figure 4 As shown, the Fe content of samples 1 to 5 was determined using the o-phenanthroline method. 2+ ;

[0107] The obtained data is shown in Table 3 below:

[0108] Table 3

[0109] Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 A 0.116 0.554 0.551 0.552 0.530 C 0.5969 2.8546 2.8392 2.8443 2.7309 Content (mg / 100g) 8.9535 45.74 45.44 45.54 43.28

[0110] As shown above, this method, without destroying the original form of added calcium, avoids calcium loss or interference from other metal ions that may occur during strong acid digestion, thus improving the recovery rate and accuracy of the target component. Compared with traditional digestion or drying and ashing methods, this invention reduces experimental error sources and uncontrollable variables through mild operating conditions. It is particularly suitable for distinguishing between "free calcium" and "protein-bound calcium," and "free iron" and "protein-bound iron" in milk powder, thereby more accurately evaluating the actual effect of added nutritional fortifiers.

[0111] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0112] The accompanying drawings of the embodiments disclosed in this invention only involve structures relevant to the embodiments disclosed in this invention. Other structures can be referred to with common designs. Unless otherwise specified, the same embodiment and different embodiments of this invention can be combined with each other.

[0113] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for efficient and low-loss extraction of inorganic salts from milk powder, characterized in that, Includes the following steps: S1, competitive coordination pretreatment, used to release free Ca2+ encapsulated by proteins or lipids. 2+ Mix milk powder and water at a mass ratio of 1:4, add a competitive ligand and mix well to obtain a pretreated mixture; S2, slow-speed acid precipitation protein, is used for selective precipitation of proteins without encapsulating free calcium. 2+ Add acid precipitant to the pretreatment mixture stepwise, adjust the pH to the isoelectric point of the protein, and let it stand to obtain protein precipitate and supernatant A; S3. Organic solvent-assisted precipitation: After adding organic solvent to supernatant A, mix, sonicate or vortex, and then centrifuge to further remove residual protein and fat, to obtain supernatant B. S4. Adsorption purification: Add adsorbent material to supernatant B and mix, then filter to remove pigments and particulate impurities from supernatant B to obtain purified liquid. S5. Colorimetric determination, used to determine the free Ca in the purified solution. 2+ The solution is converted into a colorimetric complex and its absorbance is measured to obtain the measurement results. S6. Recovery rate calculation, used to calculate the recovery rate based on the test results and the theoretical added Ca in the sample. 2+ Calculate the recovery rate.

2. The efficient and low-loss extraction method for inorganic salts from milk powder according to claim 1, characterized in that, In step S1, the competing ligand is disodium ethylenediaminetetraacetate or sodium citrate, with a concentration range of 0.2 mM to 2 mM; the mixing volume is 0.5% to 2.0% of the sample suspension volume.

3. The efficient and low-loss extraction method for inorganic salts from milk powder according to claim 1, characterized in that, In step S2, the acid precipitant is trichloroacetic acid with a concentration of 3% to 6% (w / v), added in three portions with a 1-minute interval, and the pH is adjusted to 4.4 to 4.7 before standing for 5 to 15 minutes.

4. The efficient and low-loss extraction method for inorganic salts from milk powder according to claim 1, characterized in that, In step S3, the organic solvent is acetonitrile, the pre-cooling temperature is 0℃~4℃, the amount added is 30%~50% of the sample suspension volume, and the supernatant is collected after sonication for 5 min or vortexing for 1 min and centrifugation at 4000 rpm for 5 min.

5. The efficient and low-loss extraction method for inorganic salts from milk powder according to claim 1, characterized in that, In step S4, the adsorbent material is food-grade activated carbon or diatomaceous earth, and the amount added is 0.5% to 2% (w / v) of the supernatant volume. After stirring for 3 to 5 minutes, the material is filtered using a 0.22 μm to 0.45 μm filter membrane.

6. The efficient and low-loss extraction method for inorganic salts from milk powder according to claim 1, characterized in that, In step S5, the colorimetric reagent is o-cresolphthalein complex ketone with a concentration of 0.2 mM to 1.0 mM. After reacting in a pH 5.0 to 6.0 buffer for 5 min to 10 min, the absorbance is measured at 550 nm to 580 nm.

7. The efficient and low-loss extraction method for inorganic salts from milk powder according to claim 1, characterized in that, The formula for calculating the recovery rate in step S6 is as follows: Recovery rate (%) = (Ctest × V ...fixed / Vsample) ÷ (msample × Cstandard) × 100% Among them, C measure: the calcium concentration corresponding to the absorbance, μg / mL; Vmeasurement: The volume of the solution used for the measurement, in mL; Vfixed: The total volume of the sample after treatment and final volume adjustment, in mL; Vtake: The volume (mL) of the final volume solution used for the measurement; m sample: Mass of milk powder used for extraction, in grams; C-standard: The theoretical concentration of free calcium added to the sample, in μg / g.

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