Preparation method of standard sample for detecting peroxide value of edible oil

Abstract

The application belongs to the technical field of edible oil detection, and particularly relates to a preparation method of a standard sample for detecting the peroxide value of edible oil. The method uses edible oil to prepare peroxide by first heating under low oxygen and then heating under oxygen at a rising temperature, and the prepared peroxide is dispersed in a plant oil in a reverse micelle system, and dimethyl phthalate and diglyceride are added. The obtained standard sample has high stability, and the effective period is significantly prolonged, and is suitable for being applied to laboratory capability verification, internal quality control, method verification and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of edible oil detection, and particularly relates to a preparation method of a standard sample for detecting the peroxide value of edible oil. BACKGROUND

[0002] Edible oil is animal or vegetable fat used in the process of making food. Common edible oils are mostly vegetable fats, including rapeseed oil, peanut oil, corn oil, olive oil, camellia oil, palm oil, sunflower oil, soybean oil, sesame oil, etc. As a necessity for daily life, the choice and use of edible oil directly affect health. However, during storage and processing, oil is prone to a chemical reaction called "oil oxidation". This process not only significantly affects the quality of food, but also can potentially harm our health.

[0003] Peroxide value (PV) is an important indicator of the degree of oil oxidation in food and a key indicator of the degree of oil oxidation and spoilage. As oil oxidation progresses, the accumulation of oxidation products not only affects the flavor of food, but also can significantly change its color. Especially in high-temperature or long-term exposure to air, the color of oil can become turbid, even discolored or precipitated, further reducing the sensory quality of food. Oil oxidation not only affects the sensory quality of food, but also destroys its nutritional ingredients, greatly reducing its nutritional value. In addition, oxidation consumes oxidation substances such as tocopherols and polyphenols, and produces free radicals and peroxidized lipids, destroying its nutritional ingredients and even harming human health.

[0004] The detection of the peroxide value of edible oil presents a pattern of "standard method as the basis, rapid technology as the supplement, and intelligent equipment to promote popularization". Iodometric titration is still the national standard method and official method. The end point of iodometric titration needs to be judged by color change, but in actual operation, it is easily affected by subjective factors. For example, near the end point, the sample may show color for a short time and then fade, making it difficult for beginners to identify the discoloration point. Dark-colored oil (such as sesame oil and rapeseed oil) also interferes with the observation of the end point.

[0005] Peroxide value standard sample refers to a standard substance used for calibration and quality control, which is usually used in laboratory analysis to ensure the accuracy and reliability of measurement results. The detection unit can use samples with known values (peroxide value standard samples) as reference standards to evaluate the accuracy of laboratory analysis methods by comparing the measured peroxide value with the standard value of the known standard sample. It can directly assess the accuracy of the laboratory analysis method and determine whether there are systematic errors or accidental errors. However, since the peroxide value itself is a dynamic oxidation indicator, it is easily affected by environmental factors, which may cause the standard value of the standard sample to gradually increase due to continuous oxidation during storage or use, losing its initial reference value. Therefore, it is necessary to develop stable and reliable peroxide value analysis standard samples for edible oil. SUMMARY

[0006] In view of this, the purpose of the present application is to provide a preparation method of standard sample for detecting peroxide value of edible oil.

[0007] In order to achieve the above-mentioned target, the technical scheme adopted by the present application is as follows:

[0008] A preparation method of standard sample for detecting peroxide value of edible oil, the preparation method comprises the following steps:

[0009] S1 Preparation of peroxide concentrate: using the method of low oxygen heating first and then heating with oxygen, peroxide is prepared from raw material edible oil (which can be soybean oil, including its peroxide value quality control sample), the heating product is cooled, pre-cooled ethanol-water mixed solvent is added after cooling, polar peroxide is extracted, and peroxide concentrate is obtained by dehydration with molecular sieve;

[0010] S2 Preparation of reverse micelle system of peroxide concentrate: using soybean lecithin and phytosterol complex as surfactant, the surfactant is dissolved in cyclohexane to obtain a cyclohexane solution; the peroxide concentrate is injected into the cyclohexane solution and ultrasonically treated to obtain a reverse micelle system;

[0011] S3 Preparation of standard sample: adding dimethyl phthalate to the reverse micelle system and stirring to obtain pretreated reverse micelle; mixing the pretreated reverse micelle with the dispersion medium soybean oil, and obtaining a reverse micelle mixture liquid by gradient decompression of supercritical CO2, adding diglyceride as stabilizer, mixing uniformly, vacuumizing, filling nitrogen, and then packaging with brown glass bottle.

[0012] Preferably, in step S1, the low oxygen heating condition is O2<5%, 65~75℃ for 16~20h.

[0013] Preferably, in step S1, the heating with oxygen is heated to 110~130℃, and oxygen is introduced at a flow rate of 0.2~0.4L / min, and the heating continues for 18~22h.

[0014] Preferably, in step S1, the volume ratio of ethanol to water in the pre-cooled ethanol-water mixed solvent is (7~9):2.

[0015] Preferably, in step S1, the amount of pre-cooled ethanol-water mixed solvent is 150~250ml / kg of edible oil.

[0016] Preferably, in step S2, the molar ratio of soybean lecithin to phytosterol in the soybean lecithin and phytosterol complex is (2~4):1.

[0017] Preferably, in step S2, the concentration of soy lecithin in the cyclohexane solution is 2g / 100mL~5g / 100mL.

[0018] Preferably, in step S2, the volume of the cyclohexane solution is 5~10 times the volume of the peroxide concentrate.

[0019] Preferably, in step S2, the phytosterol is beta-sitosterol.

[0020] Preferably, in step S2, the ultrasonic treatment condition is 100W~200W ultrasonic power for 5min~15min.

[0021] Preferably, in step S3, the concentration of dimethyl phthalate in the pre-treatment reverse micelle system is 0.3mg / kg~0.7mg / kg.

[0022] Preferably, in step S3, the stirring condition of the pre-treatment reverse micelle is 200rpm~400rpm stirring for 0.5h~2h.

[0023] Preferably, in step S3, the amount of the dispersion medium soybean oil is 0.5~1.5 times the mass of the raw edible oil in step S1.

[0024] Preferably, in step S3, the gradient pressure condition of the supercritical CO2 gradient decompression is gradient pressure: 25MPa→15MPa→8MPa; temperature 30℃~50℃, time 80min~120min, CO2 flow rate 40L / h~60L / h.

[0025] Preferably, in step S3, the concentration of diglyceride in the reverse micelle mixture is 1g / 100g~3g / 100g.

[0026] Compared with the prior art, the beneficial effects of the present application include:

[0027] The present application provides a preparation method of a standard sample for detecting the peroxide value of edible oil, which breaks through the technical bottleneck of stable storage of high-activity peroxide in oil and fat by steps of directional oxidation extraction, reverse micelle wrapping to reduce free radical contact, supercritical dispersion, and a large number of auxiliary agent screening, including surfactant and stabilizer screening, and provides a new path for the preparation of a standard sample for detecting the peroxide value of edible oil.

[0028] The standard sample prepared by the present application has good uniformity and high stability, and can significantly prolong the shelf life of the standard sample, thereby improving the utilization rate of the standard sample. The standard sample of the present application will be mainly applied to laboratory capability verification, internal quality control, method verification and other activities; it is helpful for laboratory quality control and ensures the accuracy of quantitative detection results; it is helpful for strengthening the quality and safety control of edible oil production and improving the detection level of inspection and testing institutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the validity period prediction chart for the experimental group samples;

[0030] Figure 2 This is a graph predicting the shelf life of 5 groups of samples in the comparative example. DETAILED DESCRIPTION

[0031] The technical solutions and effects of the present invention are described clearly and completely below in conjunction with the accompanying drawings and specific examples. The examples are only used to illustrate the technical solutions of the present invention and should not be regarded as limiting the scope of protection of the present invention. Unless otherwise specified, the test methods used in the following examples are all conventional methods; the raw materials used, unless otherwise specified, are all materials commonly used in the art, available to the public or available through commercial channels. Due to the lack of nationally recognized standard samples for the detection of edible oil peroxide values, the edible oil peroxide value quality control samples used as comparisons in the examples use commercially available soybean oil in accordance with industry practice. The soybean oil used as the raw material for preparing peroxide in step S1 of Example 1, the soybean oil used as the dispersion medium in step S3, and the commercially available edible oil peroxide value quality control sample of Comparative Example 5 are all commercially available soybean oil.

[0032] Example 1 Preparation of Standard Samples for Detection of Edible Oil Peroxide Value

[0033] Standard samples of the experimental group:

[0034] Preparation of S1 peroxide concentrate: 5 kg of a commercially available edible oil peroxide value quality control sample (soybean oil) was taken and heated continuously for 18 hours at 70°C using a heater in a low-oxygen environment (O2 <5%. As a specific example, the O2 concentration in this study was controlled at 4.9%); then the temperature was rapidly raised to 120°C, oxygen was introduced at an oxygen flow rate of 0.3 L / min, and heating was continued for 20 hours. After the heating was completed, the sample was first cooled to room temperature, and then the oil sample was cooled to -20°C. 1000 mL of a pre-cooled ethanol-water mixed solvent (v:v = 8:2) was added to extract the polar peroxides (the extraction layer was divided into two layers, and the extract was in the non-oil polar phase), and the sample was dehydrated through a 3A molecular sieve to obtain a peroxide concentrate.

[0035] Preparation of S2 peroxide concentrate reverse micelle system: A mixture of soybean lecithin and β-sitosterol was used as a surfactant (the molar ratio of soybean lecithin to β-sitosterol was 3:1) and dissolved in cyclohexane to obtain a cyclohexane solution (the concentration of soybean lecithin in the cyclohexane solution was 3 g / 100 mL).

[0036] The peroxide concentrate was injected into a cyclohexane solution (the volume of the cyclohexane solution was 6 times the volume of the peroxide concentrate), and treated at an ultrasonic power of 150 W for 10 minutes to obtain a reverse micelle system.

[0037] S3 standard sample preparation: add dimethyl phthalate with a mass concentration of 0.5 mg / kg to the reverse micelle system, mix the pretreated reverse micelle by stirring at 300 rpm for 1 h using an overhead stirrer, mix the pretreated reverse micelle with 5 kg of soybean oil, and after supercritical CO2 gradient pressure reduction under the conditions of gradient pressure (25 MPa→15 MPa→8 MPa), temperature 40℃, time 100 min, CO2 flow rate 50 L / h, add 1.5% (i.e. 1.5 g / 100 g) diglyceride as a colloidal stabilizer, mix well, and then vacuumize and fill with nitrogen before packaging in a brown glass bottle.

[0038] Comparative Example 1 group standard sample: different from the experimental example group, the peroxide concentrate is injected into the cyclohexane solution step (step S2), and no ultrasonic treatment is performed.

[0039] Comparative Example 2 group standard sample: different from the experimental example group, in step S2, the surfactant is only soy lecithin (β-sitosterol is also replaced with an equal molar amount of soy lecithin).

[0040] Comparative Example 3 group standard sample: different from the experimental example group, in step S3, no dimethyl phthalate is added.

[0041] Comparative Example 4 group standard sample: different from the experimental example group, in step S3, no diglyceride is added.

[0042] Comparative Example 5 group standard sample: commercially available edible oil peroxide value quality control sample.

[0043] Example 2 Analysis and testing of standard sample for edible oil peroxide value detection

[0044] The standard sample of the present application can be stored for a long time under refrigeration at 2℃-8℃ in the dark and sealed (the storage temperature selected for the following experiments is 4℃).

[0045] 1. Homogeneity test

[0046] The standard samples of the experimental examples and comparative examples were subjected to homogeneity testing. The detection method used the method specified in GB 5009.227-2023 "National Food Safety Standard Determination of Peroxide Value in Food". The statistical method used single factor variance statistical analysis method, and F test was used to test the homogeneity of the three level samples. The specific method was to randomly select 15 bottles from the samples prepared in each group above, each sample was tested as an independent sub-sample, and each sub-sample was also tested in triplicate. The experimental results were the average of the parallel measurements. All samples were tested under repeatability conditions in random order. The test results are shown in Tables 1-6.

[0047] Table 1 Record of measurement results of sample uniformity evaluation of experimental example group (g / 100g)

[0048]

[0049] Table 2 Record of measurement results of sample uniformity evaluation of comparative example 1 group (g / 100g)

[0050]

[0051] Table 3 Record of measurement results of sample uniformity evaluation of comparative example 2 group (g / 100g)

[0052]

[0053] Table 4 Record of measurement results of sample uniformity evaluation of comparative example 3 group (g / 100g)

[0054]

[0055] Table 5 Record of measurement results of sample uniformity evaluation of comparative example 4 group (g / 100g)

[0056]

[0057] Table 6 Record of measurement results of sample uniformity evaluation of comparative example 5 group (g / 100g)

[0058]

[0059] The above data is subjected to one-way analysis of variance, and the following analysis of variance results are obtained: at a confidence probability of 0.95, degrees of freedom f1=14, f2=30, by F test table, F 0.05（14，30） =2.04, the F values of the standard samples of comparative example 1 group, comparative example 2 group, and comparative example 3 group are 2.37, 2.07, and 2.52 respectively, all of which are greater than the critical value F 0.05（14，30） , indicating that these standard samples are not uniform. The F values of the standard samples of experimental example group, comparative example 4 group, and comparative example 5 group are 0.98, 1.26, and 1.69 respectively, all of which are less than the critical value F 0.05（14，30） , indicating that there is no significant difference within and between groups of the standard samples of experimental example group, comparative example 4 group, and comparative example 5 group, and the samples are uniform. The above results show that the physical isolation of oxygen free radicals by reverse micelles is very critical for improving the uniformity of the standard samples. The uniformity of the standard sample lacking dimethyl phthalate still does not meet the requirements, which may be related to the polar structure of the double ester group of dimethyl phthalate.

[0060] 2. Stability test

[0061] The results of the above target substance content (i.e. peroxide value) are shown in Tables 7-9.

[0062] Table 7 Long-term stability results of samples stored at 4°C (g / 100g)

[0063]

[0064] Table 8 Long-term stability results of 4 groups of samples in the comparative example stored at 4°C (g / 100g)

[0065]

[0066] Table 9 Long-term stability results of 5 groups of samples in the comparative example stored at 4°C (g / 100g)

[0067]

[0068] As can be seen from Table 7, the standard samples prepared by the method of the present invention in the experimental group and the comparative example 5 samples were all less than t in the 12-month long-term stability study. 0.95，n-2 ×s(b1), the peroxide content in the matrix standard sample tends to be stable, and the storage environment of 2-8°C can be determined as the storage environment of the matrix standard sample.

[0069] It can be seen from Tables 8 and 9 that the samples in Group 4 of the comparative example showed good stability in the 12-month long-term stability study. β 1|(0.011308564)is greater than t 0.95，n-2 ×s(β1) (0.004551065), indicating that the peroxide content in this matrix standard sample varied significantly, and the long-term stability of the sample did not meet the expected requirements. In addition, the peroxide values ​​of the four groups of samples in the comparative example showed an overall upward trend, indicating that the lack of diglyceride-stabilized peroxide reverse micelle system accelerated sample degradation, leading to an increase in peroxide levels.

[0070] 3. Prediction and measurement of validity period

[0071] According to GB / T 15000.3-2023, "Guidelines for Reference Standards Part 3: Determination of Values ​​and Evaluation of Homogeneity and Stability of Reference Standards," the initial monitoring point is predicted based on the results of the stability study. This principle takes into account the estimated degradation rate, estimates a 95% confidence interval for future values, and selects the shortest time at which one of the confidence limits (upper or lower) intersects the specified limit as the shelf life of the reference standard.

[0072] Using the long-term stability data of the experimental and comparative examples, the confidence interval of the fitted line can be obtained, that is, the long-term trend of the standard value. Usually, the 95% confidence interval of the regression line is represented by two curves around the regression line. The equations of these two curves are as follows:

[0073]

[0074] wherein,

[0075] is the standard value at time x;

[0076] is the designed measurement time;

[0077] t0.95,n-2is the t-test two-sided critical value at a confidence level of 95% with a degree of freedom of n-2;

[0078] xiis the time of the long-term stability study;

[0079] is the arithmetic mean of all xiinvolved in fitting the regression line.

[0080] Let the upper limit and the lower limit of the acceptable range of the standard value of the standard sample be Luprand Llwr, respectively, and the calculation method of the limit value is as follows:

[0081]

[0082]

[0083] wherein,

[0084] Xis the average value of the homogeneity test;

[0085] Uis the expanded uncertainty introduced by the long-term stability.

[0086] The stability trend of the standard value is analyzed, and the standard value limit and the standard value confidence interval curve obtained from the long-term stability study are plotted on a graph. The shortest time of intersection is the initial monitoring point for post-issuance stability monitoring.

[0087] The results are shown in Tables 1 and 2, respectively. Figure 1 and Figure 2 The long-term stability of the standard samples in the experimental example group and the comparative example 5 group was studied for 12 months. The experimental example group sample may have a lack of standard sample stability at the predicted stability of 21 months, and the comparative example 5 group sample may have a lack of standard sample stability at the predicted stability of 17 months. The standard samples in the experimental example group and the comparative example 5 group were stored at 4°C for a long time, and were regularly tested. The test results were consistent with the predicted results.

[0088] Therefore, by using a scientific evaluation method, it is concluded that the standard sample prepared by the method of the experimental example group has a longer shelf life than the commercially available sample group of comparative example 5, and the stability is significantly improved.

Claims

1. A method for preparing a standard sample for detecting the peroxide value of edible oil, characterized in that: The preparation method comprises the following steps: S1 Preparation of peroxide concentrate: using a method of first heating under low oxygen conditions and then heating with oxygen, the raw material edible oil is used to prepare peroxide, the heated product is cooled, and after cooling, a pre-cooled ethanol-water mixed solvent is added to extract polar peroxides, and dehydrated through molecular sieves to obtain a peroxide concentrate; Preparation of reverse micelle system of S2 peroxide concentrate: using soybean lecithin and phytosterol compound as surfactant, dissolving the surfactant in cyclohexane to obtain cyclohexane solution; The concentrated peroxide solution was injected into the cyclohexane solution and ultrasonically treated to obtain a reverse micelle system; S3 standard sample preparation: add dimethyl phthalate to the reverse micelle system and stir to obtain pretreated reverse micelles; The pretreated reverse micelles were mixed with soybean oil as a dispersion medium, and the reverse micelle mixture was obtained by gradient decompression with supercritical CO2. Diglyceride was added as a stabilizer, and the mixture was mixed evenly. The mixture was vacuumed, filled with nitrogen, and then packaged in brown glass bottles. In step S1, the hypoxic heating conditions are: O2 <5%, 65°C to 75°C, and continuous heating for 16 hours to 20 hours; the heating method is: heating to 110°C to 130°C, introducing oxygen at an oxygen flow rate of 0.2L / min to 0.4L / min, and continuing heating for 18 hours to 22 hours; In the step S1, the volume ratio of ethanol to water in the pre-cooled ethanol-water mixed solvent is (7-9):2; in the step S1, the amount of the pre-cooled ethanol-water mixed solvent is 150ml / kg edible oil to 250ml / kg edible oil; In step S2, the molar ratio of soybean lecithin to phytosterol in the soybean lecithin and phytosterol compound is (2-4):1; the concentration of soybean lecithin in the cyclohexane solution is 2 g / 100 mL-5 g / 100 mL; In the step S2, the volume of the cyclohexane solution is 5 to 10 times the volume of the peroxide concentrate; and in the step S2, the phytosterol is β-sitosterol.

2. The method for preparing a standard sample for detecting the peroxide value of edible oil according to claim 1, wherein: In step S2, the ultrasonic treatment condition is 100W-200W ultrasonic power for 5min-15min.

3. The method for preparing a standard sample for detecting the peroxide value of edible oil according to claim 1, wherein: In step S3, the concentration of dimethyl phthalate in the pretreated reverse micelle system is 0.3 mg / kg to 0.7 mg / kg.

4. The method for preparing a standard sample for detecting the peroxide value of edible oil according to claim 1, wherein: In step S3, the amount of soybean oil used as the dispersion medium is 0.5 to 1.5 times the mass of the raw edible oil in step S1.

5. The method for preparing a standard sample for detecting the peroxide value of edible oil according to claim 1, wherein: In step S3, the conditions for the supercritical CO2 gradient pressure reduction are: gradient pressure: 25 MPa→15 MPa→8 MPa; temperature 30°C~50°C, time 80min~120min, CO2 flow rate 40L / h~60L / h; and the concentration of diglyceride in the reverse micelle mixture is 1g / 100g~3g / 100g.

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