Method for measuring peroxide value of food grease based on differential scanning calorimetry

Abstract

The invention discloses a method for measuring the peroxide value of food grease based on differential scanning calorimetry, and belongs to the technical field of food grease detection. The method comprises the following steps: (1) measuring oxidation induction peak temperature T of a grease sample at different heating rates by using a differential scanning calorimeter, and calculating oxidation reaction activation energy E of the grease sample; (2) substituting the E value into a fitting function, and calculating to obtain the peroxidation value POV of the sample to be detected; the fitting function is constructed through curve fitting on the basis of oxidation reaction activation energy E of a known sample and a peroxide value POV measured by a national standard method. According to the invention, the differential scanning calorimetry is utilized to measure the heat released by the grease oxidation reaction, and the number function relationship between the oxidation reaction activation energy and the peroxide value is established. Compared with a traditional national standard peroxide value measuring method, the method has the advantages that the sample amount is small, no organic reagent is used, and the precision is high.

Description

Technical Field

[0001] The invention relates to the technical field of food oil detection, and in particular to a method for measuring the peroxide value of food oil based on differential scanning calorimetry. Background Art

[0002] As a raw material widely used in the food industry, the quality of oils and fats affects the quality of food. Oil oxidation, commonly known as rancidity, is mainly due to the oxidation of unsaturated fatty acids in oils and fats to produce peroxides, which are degraded into volatile aldehydes, ketones, and acid mixtures, which make the oils and fats produce unpleasant odors and reduce the nutritional quality of food. Therefore, it is of great significance to quickly detect the oxidation of edible oils and fats to ensure the safety of edible oils and fats.

[0003] At present, the detection of the degree of oxidation of food fats and oils is mainly based on the indicator titration method and potentiometric titration method in "GB 5009.227-2023 National Food Safety Standard Determination of Peroxide Value in Food", but this method has a large sample volume, cumbersome steps, and requires the use of a large amount of organic reagents, such as glacial acetic acid, chloroform, petroleum ether, etc., which is not suitable for rapid and intelligent detection.

[0004] Patent document CN 106226286 A discloses a method for rapid detection of edible oil oxidation process based on Raman spectroscopy, which uses a 785nm wavelength incident laser light source to scan the oil sample to be tested, and selects 974cm in the obtained Raman spectrum. -1 and 1265cm -1 The characteristic peaks of the two bands specifically characterize the degree of oil oxidation. This method does not use any chemical reagents during the testing process and has the advantages of being safe and pollution-free. However, there is a problem of fluorescence background interference in Raman spectroscopy detection of edible oil.

[0005] Differential scanning calorimetry (DSC) is used to measure the physical transformation and chemical reaction of samples. Under program-controlled temperature, it can measure the relationship between the power difference input to the sample and the reference and the temperature. DSC can measure the heat absorbed or released during the sample transformation process, the starting temperature of the transformation, the temperature at the maximum reaction, and the temperature at the end of the reaction. DSC has the characteristics of a wide operating temperature range, high resolution, small sample dosage, and no use of organic reagents.

[0006] Oil oxidation is a chemical reaction (exothermic reaction). DSC can measure the heat change during the chemical reaction. Related studies have found that the peak temperature (Tp) and activation energy (E) of oil oxidation reaction decrease with the extension of oil storage time, indicating that there is a qualitative and quantitative relationship between the DSC value of oil and its oxidation stability. At present, there are no related research reports on the characterization of oil peroxide value by differential scanning calorimetry. Therefore, it is an urgent problem to develop a method for determining oil peroxide value using DSC thermal analysis technology with a small sample size, no organic reagents, and a short detection time. Summary of the invention

[0007] The invention aims to develop a method for rapidly and accurately detecting the peroxide value of food fats and oils with a small sample amount (milligram level) and without using organic reagents.

[0008] To achieve the above object, the present invention adopts the following technical solution:

[0009] The present invention provides a method for measuring the peroxide value of food fats and oils based on differential scanning calorimetry, comprising the following steps:

[0010] (1) Using a differential scanning calorimeter, the food fat sample to be tested was heated from 100°C to 390°C at several heating rate gradients for oxidation induction, the oxidation induction peak temperature T of the fat sample at different heating rates was measured, and the activation energy E of the oxidation reaction was calculated;

[0011] (2) Substituting the calculated activation energy E of the oxidation reaction into the fitting function, the peroxide value POV of the sample to be tested is calculated;

[0012] The method for constructing the fitting function comprises: 1) taking a number of food oil samples with different oxidation degrees, determining the oxidation induction peak temperature T of each sample at different heating rates according to the method in step (1), and calculating the activation energy E of the oxidation reaction; and at the same time determining the peroxide value POV of each sample by indicator titration or potentiometric titration; and 2) performing function fitting with the peroxide value POV as the dependent variable and the activation energy E as the independent variable to obtain the fitting function.

[0013] The present invention has found that there is a correlation between the activation energy E of the oxidation reaction of oil samples and the peroxide value POV, and a quantitative function relationship is established between the activation energy E and the peroxide value POV of known samples. Based on the obtained fitting function, the differential scanning calorimetric oxidation activation energy E of any oil with an unknown oxidation degree is measured and calculated, and the peroxide value POV of the sample can be calculated by substituting it into the fitting function.

[0014] The food fat may be, but is not limited to, edible vegetable oil or animal oil.

[0015] In step (1), the oxidation induction test based on differential scanning calorimetry is specifically performed by heating the sample from 100°C to 390°C at a constant heating rate, introducing oxygen into the oil during the heating process to induce oxidation of the sample, and measuring the oxidation induction peak temperature T of the oil sample. The oxidation induction peak temperature T at different heating rates is measured, and the activation energy E of the oxidation reaction is calculated.

[0016] Specifically, the amount of the fat sample weighed is 3 to 10 mg. Preferably, the amount of the fat sample weighed is 3 to 5 mg.

[0017] Preferably, during oxidation induction, oxygen is introduced into the sample at a carrier gas flow rate of 50 mL / min.

[0018] Preferably, the heating rate ranges from 5 to 15 K / min. More preferably, four heating rate gradients are set, namely 5 K / min, 7.5 K / min, 10 K / min, and 15 K / min.

[0019] Preferably, the activation energy E of the oxidation reaction of oil is calculated using the Ozawa equation lgβ=-0.4567E / (RT)+C, where β is the heating rate in K / min; E is the activation energy in kJ / mol; R is the gas constant, 8.314J / (K·mol); T is the peak absolute temperature of oxidation measured by a differential scanning calorimeter in K; C is a constant;

[0020] A straight line was fitted to 1 / T using lgβ to obtain the slope of the straight line, which was then substituted into the Ozawa equation to calculate the activation energy E.

[0021] In the present invention, a corresponding fitting function is constructed according to the specific type of the food oil sample to be tested. Specifically, a number of food oil samples with different oxidation degrees are taken, and the oxidation induction peak temperature T of each sample at different heating rates is determined by differential scanning calorimetry, and the activation energy E of the oxidation reaction is calculated; at the same time, the peroxide value POV of each sample is determined by referring to the method in "GB 5009.227-2023 National Food Safety Standard Determination of Peroxide Value in Food", and then the peroxide value POV is taken as y and the activation energy E is taken as x, and the function fitting is performed.

[0022] Preferably, in step 1), the food fat samples with different oxidation degrees are prepared by evenly dividing the same food fat into 5 to 8 portions and heating them at 80 to 120° C. for different time periods. The fat samples are in contact with air during the heating process.

[0023] More preferably, the food fat is heated at 90°C, with the heating time being stepped every 12 hours.

[0024] As a preference, in step 2), the R of the fitting function2 ≥0.99.

[0025] The food oil in the present invention may be but is not limited to camellia oil.

[0026] In a specific embodiment of the present invention, the fitting function constructed for camellia oil is: POV = 0.0004308335E 4 -0.1190936436E 3 +12.2904736266E 2 -561.4458320339E+9590, the unit of POV is mmol / kg. There is no significant difference between the POV value calculated based on the function and the POV value measured by the national standard method, indicating that the method provided by the present invention is scientific and reliable.

[0027] The present invention has the following beneficial effects:

[0028] The present invention uses differential scanning calorimetry to measure the heat released by the oxidation reaction of oils and fats, and establishes a quantitative function relationship between the activation energy of the oxidation reaction and the peroxide value. Compared with the traditional national standard method for measuring peroxide value, the method of the present invention has a small sample size, does not use organic reagents, and has high precision, which solves the current practical problems of large sample size, cumbersome steps, and large consumption of organic reagents in the detection of oil oxidation stability. The detection method of the present invention is simple and easy, the test time is short, the reagent sample consumption is small, and it is easy to actually detect and operate, which meets the market's needs for the detection of oil oxidation stability and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the method for determining the peroxide value of food fats and oils using differential scanning calorimetry. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with specific embodiments. The following embodiments are only used to illustrate the present invention and are not intended to limit the scope of application of the present invention. Without departing from the spirit and essence of the present invention, modifications or replacements made to the inventive method, steps or conditions all belong to the scope of the present invention.

[0031] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0032] The camellia oils C and S used in the following examples were purchased from supermarkets and are commercially available materials.

[0033] Example 1

[0034] 1. Preparation of oil samples with different oxidation degrees: Weigh camellia oil C sample and divide it into 7 portions (100 g each), place them in 125 mL wide-mouth brown reagent bottles, and place them in a constant temperature oven at 90 ° C. The 7 samples are heated open for 0 h, 12 h, 24 h, 36 h, 48 h, 60 h, and 72 h to obtain camellia oil with different oxidation degrees, which are numbered as C0, C12, C24, C36, C48, C60, and C72 respectively. After heating, seal the bottles away from light and store them in a 4 ° C refrigerator for testing.

[0035] 2. Differential scanning calorimetry: 5 mg of the camellia oil with different oxidation degrees were accurately weighed into a 40 μL aluminum crucible with a lid, and 4 holes were pierced on the lid. The carrier gas was O2, and the carrier gas flow rate was 50 mL / min. Each sample was heated from 100°C to 390°C at four gradient heating rates (5K / min, 7.5K / min, 10K / min, 15K / min), and the oxidation induced peak temperature T of the oil sample at different heating rates was measured.

[0036] 3. Calculation of activation energy of oxidation reaction: Use Ozawa equation lgβ=-0.4567E / (RT)+C, where β is the heating rate (K / min), E is the activation energy (kJ / mol), R is the gas constant (8.314J / (K·mol)), T is the peak absolute temperature of differential scanning calorimetry oxidation of oil (K), and C is a constant; a straight line is obtained by plotting lgβ against 1 / T, and the activation energy E is calculated by substituting the slope of the straight line into the formula "lgβ=-0.4567E / (RT)+C". The results are shown in Table 1.

[0037] Table 1

[0038]

[0039] 4. The peroxide value POV of the oil samples was measured using "GB 5009.227-2023 National Food Safety Standard Determination of Peroxide Value in Food". The results are shown in Table 2.

[0040] Table 2

[0041] C0 C12 C24 C36 C48 C60 C72 POV(mmol / kg) 3.78 5.91 7.88 10.24 12.21 14.58 18.91

[0042] 5. Perform function fitting on the peroxide value POV of oil and fat and its differential scanning calorimetry oxidation activation energy E, with the peroxide value POV as the dependent variable and the activation energy E as the independent variable, and obtain the optimal fitting function: POV = 0.0004308335E 4 -0.1190936436E 3 +12.2904736266E 2 -561.4458320339E+9590, R 2=0.996.

[0043] Application Example 1

[0044] 1. Referring to the method of steps 2 and 3 of Example 1, the differential scanning calorimetry oxidation activation energy E of three camellia oils with unknown oxidation degrees (S1, S2, S3, randomly stored for different lengths of time) was determined, which were 70.43 kJ / mol, 57.67 kJ / mol, and 55.62 kJ / mol, respectively. Substituting into the fitting function of step 5 of Example 1, the peroxide values ​​POV were calculated to be 7.14 mmol / kg, 10.71 mmol / kg, and 15.32 mmol / kg, respectively.

[0045] 2. The three camellia oil samples (S1, S2, S3) were measured using the method of “GB 5009.227-2023 National Food Safety Standard Determination of Peroxide Value in Food”, and their actual peroxide values ​​(POV) were 7.17 mmol / kg, 10.84 mmol / kg, and 15.14 mmol / kg.

[0046] 3. The POV value calculated by the function established based on the differential scanning calorimetry test in step 1 was compared with the POV value measured based on the national standard in step 2. The results showed that there was no significant difference between the POV value measured by the method of the present invention and the actual POV value (p>0.05), indicating that the method established by the present invention is scientific and reliable.

Claims

1. A method for determining the peroxide value of food fats and oils based on differential scanning calorimetry, characterized in that: The following steps are involved: (1) Using a differential scanning calorimeter, the food fat sample to be tested was heated from 100°C to 390°C at several heating rate gradients for oxidation induction, the oxidation induction peak temperature T of the fat sample at different heating rates was measured, and the activation energy E of the oxidation reaction was calculated; (2) Substituting the calculated activation energy E of the oxidation reaction into the fitting function, the peroxide value POV of the sample to be tested is calculated; The method for constructing the fitting function comprises: 1) taking a number of food oil samples with different oxidation degrees, determining the oxidation induction peak temperature T of each sample at different heating rates according to the method in step (1), and calculating the activation energy E of the oxidation reaction; and at the same time determining the peroxide value POV of each sample by indicator titration or potentiometric titration; and 2) performing function fitting with the peroxide value POV as the dependent variable and the activation energy E as the independent variable to obtain the fitting function.

2. The method for determining the peroxide value of food fats and oils based on differential scanning calorimetry according to claim 1, characterized in that: In step (1), the weighed amount of the oil sample is 3 to 10 mg.

3. The method for measuring the peroxide value of food fats and oils based on differential scanning calorimetry according to claim 1 or 2, characterized in that: In step (1), during oxidation induction, oxygen with a carrier gas flow rate of 50 mL / min was introduced into the sample.

4. The method for measuring the peroxide value of food fats and oils based on differential scanning calorimetry according to claim 1 or 2, characterized in that: In step (1), the heating rate gradients are 5 K / min, 7.5 K / min, 10 K / min, and 15 K / min, respectively.

5. The method for measuring the peroxide value of food fats and oils based on differential scanning calorimetry according to claim 1, characterized in that: In step (1), the activation energy E of the oxidation reaction of the oil is calculated using the Ozawa equation lgβ=-0.4567E / (RT)+C, where β is the heating rate in K / min; E is the activation energy in kJ / mol; R is the gas constant, 8.314 J / (K·mol); T is the absolute temperature of the oxidation peak measured by a differential scanning calorimeter in K; and C is a constant; A straight line was fitted to 1 / T using lgβ to obtain the slope of the straight line, which was then substituted into the Ozawa equation to calculate the activation energy E.

6. The method for measuring the peroxide value of food fats and oils based on differential scanning calorimetry according to claim 1, characterized in that: In step 1), the food fat samples with different oxidation degrees are prepared by evenly dividing the same food fat into 5 to 8 portions and heating them at 80 to 120° C. for different periods of time.

7. The method for measuring the peroxide value of food fats and oils based on differential scanning calorimetry according to claim 6, characterized in that: The food fat is heated at 90°C, and the heating time is stepped every 12 hours.

8. The method for measuring the peroxide value of food fats and oils based on differential scanning calorimetry according to claim 1, characterized in that: In step 2), the R of the fitting function 2 ≥0.

99.

9. The method for measuring the peroxide value of food fats and oils based on differential scanning calorimetry according to claim 1, characterized in that: The food oil is camellia oil.

10. The method for measuring the peroxide value of food fats and oils based on differential scanning calorimetry according to claim 9, characterized in that: The fitting function is: POV = 0.0004308335E 4 -0.1190936436E 3 +12.2904736266E 2 -561.4458320339E+9590.

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