A method for detecting total polar substances in edible oil

Abstract

The present invention discloses a method for rapidly determining total polar substances in edible oil, using wax spray filter paper with perovskite quantum dot solution on the surface as a paper-based sensor, adding the edible oil sample to be tested to the quantum dot solution area; different polar substances in the edible oil sample to be tested will affect the fluorescence in the area to present different intensities, extract the G value of the fluorescent area in the photo by a photographing device, and compare it with a colorimetric card to obtain the content of polar substances; the perovskite quantum dots are organic-inorganic hybrid perovskite quantum dots CH3NH3PbX3, CH(NH2)2PbX3, all-inorganic perovskite quantum dots CsPbX3, (X=Cl, Br, I) One or more. The present invention provides a novel, simple, efficient, and low-cost rapid detection method for total polar substances in edible oil, which plays a role in early warning of edible oil safety, and expands the application range of perovskite quantum dots, providing a basis for the application of perovskite quantum dots in the field of food safety.

Description

Technical Field

[0001] The invention belongs to the field of food safety, and in particular relates to a method for detecting total polar substances in edible oil. Background Art

[0002] When edible oil is used repeatedly at high temperature, a series of reactions such as oxidation, polymerization, cracking, and hydrolysis will occur. In these processes, various compounds containing carbonyl, carboxyl, ketone, and aldehyde groups will be generated. Since the polarity of these compounds is greater than that of triglycerides, they are collectively referred to as polar compounds. In particular, polar compounds will continue to be produced during the frying process of edible oil. These compounds will not only have an adverse effect on the quality of the oil itself, but some substances will directly harm human health, such as causing growth stagnation, liver enlargement, reproductive function and liver dysfunction, lymphocyte aberration, etc. Therefore, it is particularly important to effectively evaluate the quality of edible oil. The main indicators for evaluating the quality of edible oil are sensory, transmittance, acid value, peroxide value, carbonyl value, iodine value, free fatty acids, polymers, and total polar compound content. Among them, the determination of polar compound content has the characteristics of high accuracy and high reliability, and is the most stable indicator. Therefore, it has also become an evaluation indicator recommended by countries around the world. my country's national standard stipulates that the content of polar compounds in frying oil must not be higher than 27% (by mass).

[0003] Column chromatography and preparative rapid column chromatography are methods for determining polar components in edible oils in my country's national food safety standards. However, the above methods are time-consuming and labor-intensive, require the consumption of large amounts of organic solvents, and cannot achieve rapid and real-time monitoring of total polar substances.

[0004] In recent years, there are many methods for detecting total polar substances in edible oil in my country, including infrared spectroscopy, nuclear magnetic resonance, dielectric constant method, etc. However, these methods are cumbersome, highly professional, and the instruments are very expensive. Portable edible oil quality testers based on the dielectric constant method have been commercialized, but the price of such portable instruments is not affordable, and they need to be calibrated regularly, and they are easily affected by electromagnetic fields, temperature, etc., which may affect the accuracy of the measurement results.

[0005] In recent years, perovskite quantum dots have attracted people's attention and research due to their excellent optoelectronic properties. Compared with traditional inorganic semiconductor quantum dots, perovskite quantum dots have higher fluorescence quantum efficiency (PLQY), wider adjustable emission wavelength range, excellent optoelectronic transmission performance, simple synthesis, low cost and other advantages, and have good application prospects in optoelectronic devices. However, perovskite quantum dots are greatly affected by the environment and have poor stability. Factors such as air, humidity, temperature, and polar solvents can cause the luminescence efficiency of perovskite quantum dots to decrease or even completely quench. Among them, polar solvents are one of the most important factors affecting the stability of perovskite quantum dots. Since perovskite quantum dots belong to ionic crystals, their structure will be destroyed in polar solvents and cannot exist stably. By utilizing the unique property of being sensitive to polar substances, perovskite quantum dots can be used for qualitative and quantitative analysis of polar substances. Fluorescence detection methods can overcome the above defects and have the advantages of high sensitivity and high stability. However, the fluorescence detection instruments used in traditional fluorescence detection methods are expensive and inconvenient to carry, showing obvious disadvantages in rapid detection. Compared with fluorescence instrument detection, fluorescence test strips have the advantages of easy portability, obvious phenomena, fast detection speed and low cost. Only a portable ultraviolet lamp is needed for on-site real-time naked eye rapid detection, and therefore it is increasingly valued by researchers. Summary of the invention

[0006] The purpose of the present invention is to make up for the shortcomings of the existing edible oil polar substance detection method, and proposes a method for detecting total polar substances in edible oil. Wax spray filter paper is used as a paper-based sensor, and the surface of the wax spray filter paper contains a perovskite quantum dot solution. The method is to add the edible oil sample to be tested to the area containing the quantum dot solution on the surface of the wax spray filter paper; different polar substances in the edible oil sample to be tested will affect the fluorescence in the area to present different intensities, and the G value of the fluorescent area in the photo is extracted by a photographing device, and compared with a colorimetric card to obtain the content of the polar substance; the perovskite quantum dots are one or more of organic-inorganic hybrid perovskite quantum dots CH3NH3PbX3, CH(NH2)2PbX3, and all-inorganic perovskite quantum dots CsPbX3 (X=Cl, Br, I).

[0007] Preferably, the edible oil is at least one of soybean oil, corn oil, sunflower oil, olive oil, peanut oil, rice bran oil and palm oil.

[0008] Preferably, the solvent for dissolving the quantum dots in the method is one of n-hexane, cyclohexane and toluene.

[0009] Preferably, the polar substance content of the edible oil sample to be tested is between 17% and 33%.

[0010] Preferably, the edible oil drop volume is 5-50 μL, the quantum dot concentration is 10-30 mg / mL, the quantum dot solution volume is 0.1-3 mL, and the reaction time is 1 minute to 10 minutes.

[0011] The present invention has the following advantages and beneficial effects:

[0012] (1) Compared with the traditional column chromatography method, the method of the present invention is simple to operate, greatly shortens the detection time, reduces the amount of organic reagents used, and is based on the fluorescence quenching principle of quantum dots, has high reaction sensitivity, higher precision, and good reproducibility;

[0013] (2) Compared with the previously reported detection methods and traditional fluorescence analysis methods, the method of the present invention is simple to operate, the detection results are clear and intuitive, and it is more operator-friendly;

[0014] (3) Compared with commercial edible oil quality detectors, the method of the present invention can detect the total polar substances in edible oil at room temperature without heating, thereby avoiding the influence of temperature on the test results;

[0015] (4) The present invention provides a novel, simple, rapid, efficient and low-cost fluorescent test paper for total polar substances in edible oil, and expands the application scope of perovskite quantum dots, providing a basis for the application of perovskite quantum dots in the field of food safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of a square test paper;

[0017] Figure 2 Example 1 of the present invention, a colorimetric chart of polar substance content and fluorescence intensity of olive oil;

[0018] Figure 3 Example 2 of the present invention, colorimetric chart of polar substance content and fluorescence intensity of soybean oil;

[0019] Figure 4 Example 3 of the present invention is a colorimetric chart of polar substance content and fluorescence intensity of sunflower seed oil. DETAILED DESCRIPTION

[0020] In order to make the above-mentioned objects, features and advantages of the present invention more clearly understood, the specific embodiments of the present invention are described in detail below.

[0021] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described again, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0022] (1) Preparation of a test paper for total polar substances in edible oil. The test paper is a square wax-sprayed filter paper with a circular blank sample area in the middle. The filter paper is printed by a wax printer and placed in an oven for drying. The polymer solution is fully mixed with a certain amount of quantum dot solution, and the solution is dripped into the circular sample area of ​​the paper-based sensor, dried naturally at room temperature, and placed in a nitrogen sealed bag for storage.

[0023] (2) The polar substance content in all oil samples was determined by using the national standard column chromatography method to obtain a series of oil samples with different polar substance contents;

[0024] (3) Pipette the oil sample and add it to the central sample adding area of ​​the prepared test paper. Fully react at room temperature and place it under an ultraviolet lamp with an excitation wavelength of 365nm. Due to the different contents of polar substances, different oil samples have different degrees of quenching of quantum dot fluorescence, and the fluorescence intensity presented by the test paper is also different. Use a digital camera to take pictures of all the fluorescence photos after the reaction of oil samples and quantum dot solutions to make a standard colorimetric card;

[0025] (4) According to the operation method of step (3) and the obtained colorimetric card, the fluorescence intensity photograph of the oil sample with unknown polar substance content after the reaction on the test paper is compared with the standard colorimetric card, so as to realize the semi-quantitative detection of the content of polar substance in the oil sample, and then the content of polar substance in the oil sample is verified by column chromatography.

[0026] In the step (1), the side length of the square test paper is 1 to 5 cm, and the diameter of the dot in the sample addition area is 0.1 to 2 cm. The filter paper is placed in an oven for drying, the oven temperature is 30-130°C, and the drying time is 5-30 minutes. The polymer solution is one or more of polyvinyl acetate, polyvinyl alcohol, polydimethylsilane (PDMS), polyvinyl butyral, and polyvinyl chloride. The perovskite quantum dots are one or more of organic-inorganic hybrid perovskite quantum dots CH3NH3PbX3, CH(NH2)2PbX3, and all-inorganic perovskite quantum dots CsPbX3, X=Cl, Br, I, and the concentration of quantum dots is 10-30 mg / mL. The solvent for dissolving quantum dots is one of n-hexane, cyclohexane, and toluene. The mixing ratio of the polymer solution quantum dot solution is 0.1-0.9, and the volume of the mixed solution added dropwise is 1-10 μL.

[0027] Example 1

[0028] The side length of the square test paper is 1 cm, and the diameter of the dot in the sample area is 0.2 cm. After the filter paper is printed by a wax printer, it is placed in a 120°C oven for 5 minutes and taken out. 1 mL of PDMS and 500 μL of CsPbBr3 quantum dot toluene solution are fully mixed, and 1 μL of the above solution is dripped into the circular sample area of ​​the paper-based sensor, dried naturally at room temperature, and placed in a nitrogen sealed bag and sealed for storage.

[0029] Different olive oil samples came from several restaurant kitchens. The polar substance content of the above oil samples was measured by column chromatography, and the results were 25%, 26%, 27%, 28%, and 29%, respectively. So far, 5 groups of olive oil samples with polar substance contents ranging from 25% to 29% were obtained.

[0030] Pipette 10 μL of oil sample and add it to the central sample adding area of ​​the prepared test paper. React at room temperature for 3 minutes. Place it under an ultraviolet lamp with an excitation wavelength of 365 nm. Use a digital camera to record the fluorescence photos of all oil samples and quantum dot solutions after the reaction. Arrange them from strong to weak in terms of fluorescence intensity to make a standard colorimetric card.

[0031] 50 μL of oil sample with unknown polar substance content was added dropwise to the central sample adding area of ​​the prepared test paper, fully reacted at room temperature, placed under an ultraviolet lamp with an excitation wavelength of 365 nm, and recorded with a digital camera the fluorescence photos of all oil samples and quantum dot solutions after the reaction. The test paper photos taken after the reaction were compared with the standard colorimetric card. The fluorescence intensity was close to the fluorescence intensity of the total polar substance content of 28% on the colorimetric card. The oil sample was then verified by column chromatography, and the result was 28.5%. Thus, the semi-quantitative determination of polar components of olive oil using a rapid test paper based on perovskite quantum dot fluorescence quenching was achieved.

[0032] Example 2

[0033] The side length of the square test paper is 5 cm, and the diameter of the dot in the sample area is 1 cm. After the filter paper is printed by a wax printer, it is placed in a 100°C oven for 20 minutes and taken out. 0.5 mL of PDMS and 1 mL of CsPbBr3 quantum dot toluene solution are fully mixed, and 1 μL of the above solution is dripped into the circular sample area of ​​the paper-based sensor, dried naturally at room temperature, and placed in a nitrogen sealed bag and sealed for storage.

[0034] Different sunflower seed oils were collected from different household kitchens, and the polar substance content of each oil sample was measured by column chromatography. The polar substance content of the above mixed oil samples was measured by column chromatography, and the results were 25%, 26%, 27%, 28%, and 29%, respectively. So far, 5 groups of sunflower seed oil samples with polar substance contents ranging from 25% to 29% were obtained.

[0035] Pipette 50 μL of oil sample and add it to the central sample adding area of ​​the prepared test paper. React at room temperature for 8 minutes. Place it under an ultraviolet lamp with an excitation wavelength of 365 nm. Use a digital camera to record the fluorescence photos of all oil samples and quantum dot solutions after the reaction. Arrange them from strong to weak in terms of fluorescence intensity to make a standard colorimetric card.

[0036] 50 μL of oil sample with unknown polar substance content was added dropwise to the central sample adding area of ​​the prepared test paper, fully reacted at room temperature, placed under an ultraviolet lamp with an excitation wavelength of 365 nm, and recorded with a digital camera the fluorescence photos of all oil samples and quantum dot solutions after the reaction, and the test paper photos taken after the reaction were compared with the standard colorimetric card. The fluorescence intensity was close to the fluorescence intensity of the total polar substance content of 27% on the colorimetric card, and then the oil sample was verified by column chromatography, and the result was 27%. Thus, the semi-quantitative determination of polar components of sunflower oil using a rapid test paper based on perovskite quantum dot fluorescence quenching was achieved.

[0037] Example 3

[0038] The side length of the square test paper is 1.6 cm, and the diameter of the dot in the sample area is 0.6 cm. After the filter paper is printed by a wax printer, it is placed in a 130°C oven for 8 minutes and then taken out. 0.1 mL of PDMS and 0.1 mL of CsPbBr3 quantum dot n-hexane solution are fully mixed, and 5 μL of the above solution is dripped into the circular sample area of ​​the paper-based sensor, dried naturally at room temperature, and placed in a nitrogen sealed bag and sealed for storage.

[0039] Different soybean oils were collected from various stalls in the cafeteria, and the polar substance content of each oil sample was measured by column chromatography. The results were 25%, 26%, 27%, 28%, and 29%, respectively. So far, 5 groups of soybean oil samples with polar substance content ranging from 25% to 29% were obtained.

[0040] Pipette 20 μL of oil sample and add it to the central sample adding area of ​​the prepared test paper. React at room temperature for 5 minutes. Place it under an ultraviolet lamp with an excitation wavelength of 365 nm. Use a digital camera to record the fluorescence photos of all oil samples and quantum dot solutions after the reaction. Arrange them from strong to weak in fluorescence intensity to make a standard colorimetric card.

[0041] 50 μL of oil sample with unknown polar substance content was added dropwise to the central sample adding area of ​​the prepared test paper, fully reacted at room temperature, placed under an ultraviolet lamp with an excitation wavelength of 365 nm, and recorded with a digital camera the fluorescence photos of all oil samples and quantum dot solutions after the reaction, and compared the test paper photos taken after the reaction with the standard colorimetric card. The fluorescence intensity was close to the fluorescence intensity of the total polar substance content of 25% on the colorimetric card, and then the oil sample was verified by column chromatography, and the result was 25%. Thus, the semi-quantitative determination of polar components of soybean oil using a rapid test paper based on perovskite quantum dot fluorescence quenching was achieved.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for detecting total polar substances in edible oil, characterized in that: A wax-sprayed filter paper is used as a paper-based sensor, a polymer solution and a quantum dot solution are mixed and dripped onto a specific area of ​​the paper-based sensor and dried, so that the specific area on the surface of the wax-sprayed filter paper contains perovskite quantum dots. The method is to add a sample of edible oil to be tested to the area on the surface of the wax-sprayed filter paper containing the quantum dot solution; different polar substances in the sample of edible oil to be tested will affect the fluorescence in the area to present different intensities, and the G value of the fluorescent area in the photo is extracted by a camera, and compared with a colorimetric card to obtain the content of the polar substance; The perovskite quantum dots are organic-inorganic hybrid perovskite quantum dots CH3NH3PbX3, CH(NH2)2PbX3, all-inorganic perovskite quantum dots CsPbX3, and X=Cl, Br, I, or one or more thereof.

2. The method for determining total polar substances in edible oil according to claim 1, characterized in that: The edible oil is at least one of soybean oil, corn oil, sunflower oil, olive oil, peanut oil, rice bran oil and palm oil.

3. The method for determining total polar substances in edible oil according to claim 2, characterized in that: The solvent in the quantum dot solution in the method is one of n-hexane, cyclohexane and toluene; The polymer is selected from at least one of polyvinyl acetate, polyvinyl alcohol, polydimethylsilane, polyvinyl butyral and polyvinyl chloride.

4. The method for determining total polar substances in edible oil according to claim 2, characterized in that: The polar matter content of the edible oil sample to be tested is between 17% and 33%.

5. The method for determining total polar substances in edible oil according to claim 1, characterized in that: The edible oil drop volume is 5-50 μL, the quantum dot concentration is 10-30 mg / mL, the quantum dot solution volume is 0.1-3 mL, and the reaction time is 1 minute to 10 minutes.

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