Method for measuring peroxide value in oil-containing food

Abstract

The application belongs to the technical field of detecting substances by optical means, and relates to a method for measuring the peroxide value of oil-containing food. In view of the technical problems of low detection efficiency, low accuracy, and unfriendliness to the detector and environment of the existing method for measuring the peroxide value of oil-containing food, the application provides a method for measuring the peroxide value of oil-containing food, which comprises the following steps: dissolving iodine into a fatty amine and mixing to prepare iodine-doped carbon dots, establishing a standard curve by using the carbon dots and fresh oil-containing food as a standard oil sample, and finally adding the iodine-doped carbon dots into a sample to be measured to react, and calculating the peroxide value by means of fluorescence intensity, so that the peroxide value can be quickly and accurately measured. The preparation method is simple, has good oil solubility, does not use heavy metals, has high fluorescence quantum yield, stable performance, good reproducibility, and good consistency with the national standard result, and expands the application scope of the carbon dots, a fluorescent nanomaterial, in the field of food safety detection.

Description

Technical Field

[0001] This invention belongs to the field of optical detection technology, specifically relating to a method for determining the peroxide value in oily foods. Background Technology

[0002] Foods rich in oils, such as oily nuts, vegetable oils, and fried foods, are susceptible to oxidative rancidity during storage and processing due to factors such as temperature, light, and air. During rancidity, triglycerides and fatty acids break down to produce peroxides, which further oxidize and decompose to produce small-molecule compounds such as aldehydes, ketones, and acids, severely affecting food quality and safety. Peroxides can damage cell membrane structures, and long-term consumption of foods with excessive peroxide values ​​poses significant health risks. Therefore, peroxide value is an important indicator reflecting the degree of oxidation in oil-rich foods and can be used to monitor food safety. Current national standards use iodometric titration and potentiometric titration to detect peroxide value in food, as specified in GB5009.227-2016, "National Food Safety Standard: Determination of Peroxide Value in Food." The reaction mechanism involves peroxides and hydroperoxides formed during the oxidative rancidity of oils in an acidic medium, oxidizing iodide ions to elemental iodine. The titration endpoint is then determined using a starch standard solution as an indicator or a potentiometric titrator, and titrated with a sodium thiosulfate standard solution. The peroxide value is calculated based on the amount of iodine precipitated. Conventional iodometric and potentiometric methods are complex and cumbersome, have low sensitivity, cannot provide real-time monitoring, and are inefficient. Therefore, there is an urgent need for a more accurate and rapid detection method to monitor the peroxide value of oil-rich foods.

[0003] Fluorescence visualization analysis boasts high sensitivity and rapid detection speed, making it a promising application in numerous fields such as food safety monitoring, environmental monitoring, and clinical diagnosis. Compared to methods like iodometric titration, which rely on color changes for qualitative and quantitative analysis, fluorescence signal-based visualization detection offers significant advantages, including high sensitivity, clear signal gradient changes, and less susceptibility to external interference. This enables rapid and highly sensitive detection of peroxide values ​​in food. For example, Zhu et al. synthesized all-inorganic perovskite quantum dots CsPbX3 (X being Cl, Br, or I), and utilized the redox reaction between iodide ions and peroxides in food, combined with the halogen exchange reaction of the perovskite quantum dots, to achieve rapid and visual detection of peroxide value in oils (Anal. Chem. 2019, 91, 14183-14187); Wu et al. synthesized fluorescent metal-organic framework materials (Pb-MOF), and utilized the property that iodide ions can efficiently quench Pb-MOF, combined with the redox reaction between iodide ions and peroxides in food, to achieve rapid and visual detection of peroxide value in oils (Food Chem. 2022, 385, 132710). For example, Chinese patent application publication number CN110146496A, filed on May 28, 2019, entitled "A Method for Rapidly Determining the Peroxide Value of Edible Oils," discloses a method that uses oleamine iodine as a reducing agent for the target peroxide, uses the fluorescence color of CsPbBr3 perovskite nanocrystals after halogen exchange as a visual indicator of the degree of peroxide oxidation in edible oils, and uses molecular fluorescence detection as the detection method. While the above scheme can achieve rapid detection of peroxide value, the synthesis of the fluorescent signal probe materials used, such as perovskite quantum dots and metal-organic frameworks, requires complex and demanding reaction conditions, and involves the use of raw materials containing heavy metals like lead and the consumption of large amounts of organic reagents. Therefore, exploring a new method for peroxide value detection, achieving sensitive and rapid determination of peroxide value in oily foods, is of great significance for ensuring food safety. Summary of the Invention

[0004] 1. The problem to be solved

[0005] To address the technical problems of existing methods for determining peroxide value in oily foods, which require complex and demanding reaction conditions for the synthesis of fluorescent signal probe materials, involve cumbersome detection steps, and consume large amounts of organic reagents due to the presence of heavy metals in the raw materials, resulting in low detection efficiency, low accuracy, and unfriendly technology to testing personnel and the environment, this application provides a method for determining peroxide value in oily foods. This method enables rapid and accurate detection of peroxide value. The proposed method is simple to prepare, has good oil solubility, does not use heavy metals, has high fluorescence quantum yield, stable performance, good reproducibility, and the detection results are in good agreement with national standards. This expands the application scope of carbon dots, a fluorescent nanomaterial, in the field of food safety testing.

[0006] 2. Technical Solution

[0007] To achieve the above objectives, the provided technical solution is as follows:

[0008] The method for determining the peroxide value in oil-containing foods according to this application includes the following steps:

[0009] The steps include preparing iodine-doped carbon dots: dissolving elemental iodine in a fatty amine and mixing to obtain a precursor solution, and heating the precursor solution to obtain iodine-doped carbon dots;

[0010] The process includes the following steps for preparing a standard curve: using fresh oily food as a standard oil sample, mixing the standard oil sample with an organic solvent to prepare standard oil sample solutions with different peroxide value gradients; adding the iodine-doped carbon dots to the standard oil sample solutions and reacting them, then detecting the fluorescence signal intensity to obtain fluorescence signal data; and establishing a standard curve with the peroxide value of the standard oil sample solutions on the x-axis and the fluorescence signal data on the y-axis.

[0011] This includes the steps of pre-treating the oily food to be tested to obtain the sample to be tested;

[0012] The process includes the steps of adding the iodine-doped carbon dots to the sample to be tested and reacting them, and then calculating the peroxide value in the oil-containing food using the standard curve.

[0013] Preferably, the peroxide value of the standard oil sample is determined according to the method recommended in the national standard GB 5009.227-2016 "Determination of Peroxide Value in Food". The synthesized oily solid I-CDs are diluted 200 times with n-butanol; the I-CDs solution and the standard oil sample solution are mixed at a ratio of 9:1.

[0014] Furthermore, the fluorescence signal intensity was measured using 365 nm as the excitation wavelength and 440 nm as the emission wavelength, and the standard curve was plotted.

[0015] Furthermore, the fatty amine is one or more of octadecylamine, hexadecylamine, tetradecylamine, and dodecylamine.

[0016] Furthermore, the mass ratio of elemental iodine to fatty amine in the precursor solution is 1:3 to 1:5.

[0017] Furthermore, the temperature range for heating the precursor solution is 180–210°C, and the heating time is 6–12 hours.

[0018] Preferably, the precursor solution is uniformly mixed under heating and stirring at 80°C, and 10 mL of the precursor solution is transferred to a 25 mL reactor; after heating at 200°C for 8 h, it is naturally cooled to room temperature. The heating temperature range of the reactor is 180–210°C, and the heating time is 6–12 h; finally, an oily I-CDs solid is obtained.

[0019] Furthermore, the organic solvent is one or more of n-butanol, isopropanol, toluene, and n-hexane.

[0020] Furthermore, the fresh oily food is subjected to constant temperature treatment at a temperature of 60°C.

[0021] Furthermore, the parameters for the reaction of adding the iodine-doped carbon dots to the standard oil sample solution are: temperature from room temperature to 100°C, and reaction time from 10 to 60 minutes.

[0022] Furthermore, the oil-containing food is a liquid; it is diluted with an organic solvent, which is one or more of n-butanol, isopropanol, toluene, and n-hexane.

[0023] Preferably, the oil-containing food is one or more of peanut oil, rapeseed oil, soybean oil, corn oil, and palm oil.

[0024] Furthermore, the oil-containing food is a solid; it is extracted using a non-polar organic solvent by leaching, wherein the non-polar organic solvent is one or more of petroleum ether, hexane, and toluene; the mass ratio of the oil-containing food to the non-polar organic solvent is 1:5 to 1:10.

[0025] Preferably, solid oil-containing food samples, such as oily nuts and fried foods, are pulverized and the oil is extracted according to the method recommended in the national standard GB5009.227-2016 "Determination of Peroxide Value in Food". The sample is allowed to stand for at least 12 hours for extraction. The crude oil extract is filtered through an anhydrous sodium sulfate funnel, and the filtrate is rotary evaporated, then subjected to nitrogen blowing and centrifugation to further remove residual solvent impurities. The collected oil sample is stored in a refrigerator at 4°C in the dark for later use. The organic solvent used to dilute the liquid vegetable oil can be n-butanol, isopropanol, toluene, n-hexane, etc., with n-butanol being preferred.

[0026] 3. Beneficial effects

[0027] Compared with existing known technologies, the technical solution provided by this invention has the following beneficial effects:

[0028] This invention discloses a method for determining the peroxide value in oily foods. Iodine is dissolved in a fatty amine and mixed thoroughly to prepare I-CDs. A standard curve is established using the I-CDs and fresh oily foods as standard oil samples, with the peroxide value of the standard oil sample solution on the x-axis and the fluorescence signal data on the y-axis. Finally, the I-CDs are added to the test sample to react, and the peroxide value in the oily food is calculated. The prepared fluorescent probe I-CDs material is not only low-cost, but its synthesis and use are also environmentally friendly and easy for operators to operate. The fluorescence of the prepared I-CDs can be efficiently quenched by peroxides in the oil, thus achieving rapid and accurate detection of peroxide value. For rapid peroxide value detection, the preparation method is simple, has good oil solubility, does not use heavy metals, has high fluorescence quantum yield, and is stable. This method has good reproducibility; the results of actual oily food sample testing are in good agreement with national standard results, indicating that this method has great potential in food safety testing and expands the application scope of carbon dots, a "green" fluorescent nanomaterial, in the field of food safety testing, providing a new approach for food peroxide value detection. Attached Figure Description

[0029] Figure 1 The image shows the transmission electron microscopy (TEM) characterization results of the I-CDs prepared in Example 1.

[0030] Figure 2 The image shows the XPS characterization results of the I-CDs prepared in Example 1.

[0031] Figure 3 Photographs of the iodine I-CDs solution prepared in Example 1 under sunlight (left) and 365nm excitation (right).

[0032] Figure 4 The excitation-emission fluorescence spectrum of the I-CDs solution prepared in Example 1 is shown.

[0033] Figure 5 The fluorescence response of the I-CDs prepared in Example 1 to different peroxide values ​​is shown in the diagram.

[0034] Figure 6 The working curve of the I-CDs prepared in Example 1 for detecting the peroxide value of edible oil based on fluorescence quenching is shown. Detailed Implementation

[0035] To further understand the content of this invention, the invention will be described in detail with reference to the embodiments.

[0036] Example 1

[0037] This embodiment describes a method for determining the peroxide value in oil-containing foods. The oil-containing food being tested is soybean oil. In some embodiments, the oil-containing food may also be one or more of peanut oil, rapeseed oil, soybean oil, corn oil, and palm oil. The specific determination steps are as follows:

[0038] (1) Accurately weigh 2.0 g of elemental iodine and mix with 10.0 g of octadecylamine. Octadecylamine is used in this embodiment; in some embodiments, one or more of hexadecylamine, tetradecylamine, and dodecylamine may also be selected; in some embodiments, 2.0 g of elemental iodine and 6.0 g of octadecylamine may also be weighed and mixed. Good results are obtained when the mass ratio of elemental iodine to aliphatic amine in the precursor solution is 1:3 to 1:5.

[0039] The two components were stirred and mixed at 80°C to dissolve them and form a homogeneous precursor solution. 10 mL of the above precursor solution was transferred to a 25 mL hydrothermal reactor and heated at 200°C for 8 hours, followed by natural cooling to room temperature. In some embodiments, the heating temperature range of the precursor solution was 180–210°C, and the heating time was 6–12 hours, all of which yielded ideal oily I-CDs solids.

[0040] After obtaining the oily solid I-CDs, they are dispersed in n-butanol for use.

[0041] The properties of the I-CDs fluorescent materials prepared by the above steps were characterized. Figure 1 The image shows the transmission electron microscopy (TEM) characterization results of I-CDs. The TEM results show that the nanoparticles have a relatively uniform particle size, mostly concentrated in the range of 3–5 nm, which is consistent with the characteristics of carbon dot nanoparticles.

[0042] The X-ray photoelectron spectrum of the prepared I-CDs is as follows: Figure 2 As shown, the results indicate that I-CDs have typical characteristic peak information of iodine, indicating that iodine has been successfully doped into I-CDs.

[0043] Fluorescence image of I-CDs solution at 365nm as shown in the image. Figure 3 As shown, the I-CDs solution exhibits bright blue fluorescence.

[0044] The excitation and emission spectra of I-CDs are as follows: Figure 4 As shown, the results indicate that I-CDs exhibit the strongest fluorescence emission at 440 nm at the optimal excitation wavelength of 365 nm.

[0045] (2) Peroxide value standard curve

[0046] Take 100 mL of fresh soybean oil sample and place it in a constant temperature incubator. Store it at 60℃ for 7 days, then remove it as a standard oil sample. Determine the peroxide value of the standard oil sample according to the method recommended in the national standard GB5009.227-2016 "Determination of Peroxide Value in Food".

[0047] The standard oil sample is uniformly mixed with an appropriate proportion of the organic solvent n-butanol to form a series of standard oil samples with different peroxide values. In some embodiments, the organic solvent may also be one or more of isopropanol, toluene, and n-hexane.

[0048] The prepared solid I-CDs were diluted 200-fold with n-butanol. The I-CDs solution and standard oil samples with different peroxide values ​​were mixed at a ratio of 9:1. The mixture was allowed to react for 30 minutes. In some embodiments, the reaction temperature was from room temperature to 100°C, and the reaction time was from 10 to 60 minutes, all of which yielded ideal results. 200 μL of the above-prepared mixture was transferred to an ELISA plate, and the fluorescence intensity was measured using an ELISA reader at an excitation wavelength of 365 nm and an emission wavelength of 440 nm. Figure 5 The results showed that the fluorescence signal of I-CDs exhibited good responsiveness to peroxides in food, and the fluorescence intensity of I-CDs in the detection system decreased significantly with increasing peroxide value. This fluorescence method demonstrated good linearity within the peroxide value range of 0–0.1 g / 100 g. A standard curve R was established using peroxide value concentration and fluorescence intensity. 2 The result was 0.99, indicating that this method can be applied to the determination of peroxide value in actual edible oils.

[0049] (3) Soybean oil (liquid vegetable oil) is mixed evenly with an appropriate proportion of organic solvent and then used for the next step of testing. The organic solvent used to dilute the liquid vegetable oil can be n-butanol, isopropanol, toluene, n-hexane, etc., with n-butanol being preferred.

[0050] (4) I-CDs were added to the soybean oil sample to react, and the peroxide value of the oil-containing food was calculated by using the standard curve.

[0051] In this embodiment, the peroxide value of soybean oil was measured to be 0.129 g / kg.

[0052] Example 2

[0053] The method for determining the peroxide value in oily foods in this embodiment uses almonds as the oily food sample. The method is basically the same as in Example 1, and the specific determination steps are as follows:

[0054] (1) Step (1) is the same as in Example 1.

[0055] (2) Step (2) is the same as in Example 1.

[0056] (3) Different almond samples were pulverized, and the oil was extracted using petroleum ether, a non-polar organic solvent, according to the method recommended in the national standard GB5009.227-2016 "Determination of Peroxide Value in Food". In some embodiments, the non-polar organic solvent may also be one or more of hexane or toluene. Good results can be obtained when the mass ratio of almonds to petroleum ether in oily foods is 1:5 to 1:10. The mass ratio used in this embodiment is 1:5.

[0057] The crushed almond sample and solvent were placed in a conical flask at a mass ratio of 1:5 and thoroughly mixed. The mixture was allowed to stand for extraction for more than 12 hours. The mixture was then filtered through a funnel containing anhydrous sodium sulfate. The filtrate was evaporated at 50°C to remove the solvent. Nitrogen blowing and centrifugation were performed at 10,000 r / min for 10 min to further remove residual solvent and impurities. The collected almond oil samples were stored in a refrigerator below 4°C in the dark for later use. In this example, the samples were stored in a refrigerator at -20°C in the dark for later use.

[0058] (4) The solid I-CDs synthesized in Example 1 were diluted 200 times with n-butanol. The iodine-doped carbon dot I-CDs solution and the extracted almond oil sample were mixed at a ratio of 9:1. The mixture was allowed to react fully for 30 minutes. In some examples, the reaction temperature was between room temperature and 100°C, and the reaction time was between 10 and 60 minutes, all of which yielded ideal results. 200 μL of the above-mentioned mixture was transferred to an ELISA plate, and the fluorescence intensity was measured on an ELISA reader at an excitation wavelength of 365 nm and an emission wavelength of 440 nm. Based on the measured fluorescence signal intensity of different almond oil samples, the peroxide value of different almond samples was calculated using a standard curve.

[0059] In this embodiment, the peroxide value of almonds was measured to be 0.110 g / kg.

[0060] Example 3

[0061] The method for determining the peroxide value in oily foods in this embodiment uses peanut oil as the oily food to be tested, and the steps are basically the same as in Embodiment 1.

[0062] In this embodiment, the peroxide value of peanut oil was measured to be 0.251 g / kg.

[0063] Almond, soybean oil, and peanut oil samples were tested using the titration method recommended by national standards and the fluorescence rapid detection method developed in this invention, respectively. The test results are shown in Table 1, indicating that the fluorescence rapid detection method of this scheme has good accuracy and can be applied to the rapid and accurate detection of peroxide value in oily foods.

[0064] Table 1. Results of peroxide value detection in different foods using the fluorescence method in the examples and national standard methods.

[0065]

[0066] The embodiments described above are merely preferred embodiments of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications, improvements, and substitutions without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for determining the peroxide value in oil-containing foods, characterized in that: Includes the following steps: Preparation of iodine-doped carbon dots: iodine is dissolved in a fatty amine and mixed to obtain a precursor solution. The precursor solution is then heated to obtain iodine-doped carbon dots. The fatty amine is one or more of octadecylamine, hexadecylamine, tetradecylamine, and dodecylamine; the mass ratio of elemental iodine to fatty amine in the precursor solution is 1:3 to 1:5; the heating temperature range of the precursor solution is 180 to 210 °C, and the heating time is 6 to 12 h; Preparation of standard curves: Fresh oily food was used as a standard oil sample. The standard oil sample was mixed with an organic solvent to prepare standard oil sample solutions with different peroxide value gradients. Iodine-doped carbon dots were added to the standard oil sample solutions respectively, and the fluorescence signal intensity was detected to obtain fluorescence signal data. A standard curve was established with the peroxide value of the standard oil sample solution on the x-axis and the fluorescence signal data on the y-axis. The fluorescence signal intensity was measured with an excitation wavelength of 365 nm and an emission wavelength of 440 nm, and the standard curve was plotted. The parameters for the reaction of adding the iodine-doped carbon dots to the standard oil sample solution were: temperature from room temperature to 100 °C, and reaction time of 10 to 60 min. The prepared iodine-doped carbon dots were diluted 200 times with n-butanol, and the iodine-doped carbon dot solution and standard oil samples with different peroxide values ​​were mixed at a ratio of 9:

1. The food containing oil to be tested is pretreated to obtain the sample to be tested; The iodine-doped carbon dots are added to the sample to be tested, and the peroxide value in the oil-containing food is calculated using the standard curve.

2. The method for determining the peroxide value in oil-containing foods according to claim 1, characterized in that: The organic solvent is one or more of n-butanol, isopropanol, toluene, and n-hexane.

3. The method for determining the peroxide value in oil-containing foods according to claim 2, characterized in that: The fresh oily food is subjected to constant temperature treatment at a temperature of 60 ℃.

4. The method for determining the peroxide value in oil-containing foods according to any one of claims 1-3, characterized in that: The oil-containing food is a liquid; it is diluted with an organic solvent, which is one or more of n-butanol, isopropanol, toluene, and n-hexane.

5. The method for determining the peroxide value in oil-containing foods according to any one of claims 1-3, characterized in that: The oil-containing food is a solid; it is extracted using a non-polar organic solvent by leaching, wherein the non-polar organic solvent is one or more of petroleum ether, hexane, and toluene; the mass ratio of the oil-containing food to the non-polar organic solvent is 1:5 to 1:10.

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