Detection method for deteriorated milk, detection test paper and preparation method of detection test paper

Abstract

The invention provides a deteriorated milk detection method, detection test paper and a preparation method thereof, and the deteriorated milk detection method comprises the following steps: mixing a nano-silver particle solution and a cysteine aqueous solution, and uniformly stirring to obtain a functionalized nano-silver particle solution; the functionalized nano-silver particle solution and an isometric milk metamorphic sample are mixed and oscillated, after full reaction, the metamorphic degree of milk in the milk metamorphic sample is judged according to color change, the functionalized nano-silver particles are gathered in a lactic acid environment to develop color, and then the metamorphic degree of the milk is rapidly judged.

Description

Technical Field

[0001] The present invention relates to the technical field of food safety detection, and particularly to a milk spoilage indicator, a preparation method thereof, and a milk spoilage detection test strip. Background Art

[0002] As an important daily nutritional source, milk is extremely susceptible to environmental factors and spoils easily. Its spoilage process is mainly due to lactic acid bacteria metabolizing lactose to produce lactic acid, resulting in an increase in acidity and protein denaturation to form flocculent sediment. In the prior art, the quality of milk packaging usually depends on the marked shelf life, but the actual storage conditions are complex (such as temperature fluctuations, oxygen contact, etc.), and the shelf life is difficult to accurately reflect the true spoilage degree.

[0003] Regarding the problem of the true spoilage degree of milk, the prior art has provided solutions. For example, "a milk carton" disclosed in the Chinese patent literature, with the publication number CN110127203A, uses an irreversible thermochromic ink and a color comparison card to indicate the spoilage of milk. However, it relies on temperature-sensitive materials, has insufficient sensitivity to changes in lactic acid content, and has a high cost, making it difficult to cover the entire process from production to consumption. In addition, most of the existing discoloring materials are based on a single physical parameter (such as temperature) and cannot reflect the chemical process of lactic acid accumulation in real time, resulting in delayed or inaccurate indication.

[0004] Therefore, there is an urgent need for a technology that is inexpensive, highly sensitive, and can visually indicate the spoilage of milk in real time. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for detecting spoiled milk, a detection test strip, and a preparation method thereof, so as to solve the technical problem of difficult to accurately detect the spoilage degree of milk.

[0006] To solve the above problems, the first aspect of the present invention provides a method for detecting spoiled milk, including the following steps:

[0007] Mix the silver nanoparticle solution and the cysteine aqueous solution and stir evenly to obtain a functionalized silver nanoparticle solution;

[0008] Mix the functionalized silver nanoparticle solution with an equal volume of a milk spoilage sample and shake, and after sufficient reaction, judge the spoilage degree of the milk in the milk spoilage sample according to the color change.

[0009] Further, in the above method for detecting spoiled milk, the silver nanoparticle solution is prepared from a sodium borohydride solution and a silver nitrate solution under light-shielded conditions, and no stirring is required during the preparation process.

[0010] Further, in the above-mentioned method for detecting spoiled milk, the concentration of the sodium borohydride solution is 0.002 mol / L, the concentration of the silver nitrate solution is 0.001 mol / L, and the volume ratio of the sodium borohydride solution to the silver nitrate solution is 3:1.

[0011] Further, a trisodium citrate solution is added to the silver nanoparticle solution in the above-mentioned method for detecting spoiled milk.

[0012] Further, the concentration of the cysteine aqueous solution in the above-mentioned method for detecting spoiled milk is: 10 -5 mol / L.

[0013] According to another aspect of the present invention, there is also provided a method for preparing a test strip for detecting spoiled milk, which comprises soaking a nitrocellulose membrane in the functionalized silver nanoparticle solution and taking it out to dry.

[0014] Further, in the above-mentioned method for preparing a test strip for detecting spoiled milk, the soaking time of the nitrocellulose membrane in the functionalized silver nanoparticle solution is not less than 24 hours.

[0015] Further, a trisodium citrate solution is added to the functionalized silver nanoparticle solution in the above-mentioned method for preparing a test strip for detecting spoiled milk.

[0016] According to still another aspect of the present invention, there is also provided a test strip for detecting spoiled milk, which is prepared by the method for preparing a test strip for detecting spoiled milk according to any one of the above.

[0017] The above technical solution of the present invention has the following beneficial technical effects: By mixing the silver nanoparticle solution with cysteine, a functionalized silver nanoparticle solution will be formed, which will aggregate and show color under acidic conditions. Through the correlation between the chromaticity value and the degree of milk spoilage, the degree of milk spoilage can be quickly judged. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a flowchart of an embodiment shown in the present invention;

[0019] Figure 2 is a function relationship diagram between the lactic acid content and the chromaticity in milk. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention.

[0021] Embodiments of the present invention are shown below. In the first aspect, the present invention provides a method for detecting spoiled milk, which specifically includes the following steps:

[0022] Step 100: Under light-shielded conditions, 10 mL of 0.001 mol / L silver nitrate is dropped into 30 mL of freshly prepared sodium borohydride solution with a concentration of 0.002 mol / L without stirring. When the solution changes from transparent and clear to light yellow, it indicates that the reaction is completed, and a silver nanoparticle solution is obtained.

[0023] Step 200: Add 2 mL of 1 g / mL trisodium citrate solution and mix, and continuously stir for 5 minutes. The trisodium citrate will coat the surface of the silver nanoparticles to ensure that the silver nanoparticles are not oxidized and inactivated, and their chemical properties are stable.

[0024] Step 300: Add and mix evenly with 10 -5 mol / L cysteine aqueous solution prepared on-site to obtain a functionalized silver nanoparticle solution.

[0025] Step 400: Mix the functionalized silver nanoparticle solution with an equal volume of spoiled milk sample and shake. React for 15 minutes, and judge the spoilage of the spoiled milk sample according to the chromaticity measured by a colorimeter.

[0026] The silver nanoparticle solution is a bright yellow, transparent and clear liquid. It does not show color under acidic conditions. However, when the silver nanoparticles are mixed with cysteine, a stable complex will be formed. Therefore, the silver nanoparticles in the functionalized silver nanoparticle solution will aggregate and show color due to the change of the pH value of the current solution. During the spoilage process of milk, lactic acid will be continuously produced and the pH value will gradually decrease. That is, the spoilage degree of milk is correlated with the pH value. The silver nanoparticles will gradually aggregate and change color, changing from pink to purple and then gradually to gray. Therefore, the spoilage degree of milk can be quickly and accurately judged according to the chromaticity value. The relationship between the chromaticity value and the lactic acid concentration is as Figure 1 shown.

[0027] In the second aspect, the present invention also provides a method for preparing a spoiled milk detection test strip. The specific operation is to immerse a nitrocellulose membrane in the functionalized silver nanoparticle solution for no less than 24 hours and then take it out to dry. The functionalized silver nanoparticles will adsorb on the surface of the nitrocellulose membrane to form a uniform light yellow coating with stable chemical properties and no volatile gas released. At the same time, trisodium citrate solution can also be added to the functionalized silver nanoparticle solution as a protective agent. The trisodium citrate can only coat the surface of the silver nanoparticles to protect them from being oxidized and inactivated.

[0028] In the third aspect, the present invention also provides a spoiled milk detection test strip prepared by the above method.

[0029] When using test paper to detect the degree of milk spoilage, when the chromaticity value of the test paper reaches 180 or above, it means that the milk is seriously spoiled, and the rancid odor of the milk can also be smelled at this time; when the chromaticity value is below 150, the milk has no special odor, and the test paper can be used to accurately measure the degree of milk spoilage. Compared with pH test paper, this test paper has higher sensitivity and accuracy, and can monitor smaller pH changes. pH test paper detects pH value through acid-base balance chemical reaction, while this method is based on the change of optical properties caused by the aggregation of nanosilver particles at the physical level, which can be used for dynamic monitoring, and pH test paper is disposable, while this test paper can be reused. Secondly, the silver nano solution has strong anti-interference ability in detecting acidity and is not easily affected by other heavy gold ions or oxidant components in the solution.

[0030] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. A method for detecting spoiled milk, characterized in that: The steps include: The silver nanoparticle solution and the cysteine ​​aqueous solution are mixed and stirred evenly to obtain a functionalized silver nanoparticle solution; The functionalized nanosilver particle solution is mixed and shaken with an equal volume of a spoiled milk sample, and after sufficient reaction, the degree of deterioration of the milk in the spoiled milk sample is determined based on the color change.

2. The method for detecting spoiled milk according to claim 1, characterized in that: The nano silver particle solution is prepared from a sodium borohydride solution and a silver nitrate solution under light-proof conditions, and stirring is not required during the preparation process.

3. The method for detecting spoiled milk according to claim 2, characterized in that: The concentration of the sodium borohydride solution is 0.002 mol / L, the concentration of the silver nitrate solution is 0.001 mol / L, and the volume ratio of the sodium borohydride solution to the silver nitrate solution is 3:

1.

4. The method for detecting spoiled milk according to claim 3, characterized in that: A trisodium citrate solution is added into the nano silver particle solution.

5. The method for detecting spoiled milk according to claim 3, characterized in that: The concentration of the cysteine ​​aqueous solution is: 10 -5 mol / L.

6. A method for preparing a test paper for detecting spoiled milk, characterized in that: The nitrocellulose membrane is immersed in the functionalized nanosilver particle solution, and then taken out and air-dried.

7. The method for preparing a test strip for detecting spoiled milk according to claim 6, characterized in that: The nitrocellulose membrane is immersed in the functionalized nanosilver particle solution for no less than 24 hours.

8. The method for preparing a test strip for detecting spoiled milk according to claim 6, characterized in that: The trisodium citrate solution is added into the functionalized nanosilver particle solution.

9. A test strip for detecting spoiled milk, characterized in that The method for preparing the spoiled milk detection test paper is described in any one of claims 6 to 7.

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