A rapid detection method for the content of polar components in frying vegetable oil based on dielectric loss factor

Abstract

The present application relates to a kind of fast detection methods of frying plant oil polar component content based on dielectric loss factor, comprising the following steps: 1) take multiple frying oils, and the frying oil is pretreated to obtain clear oil product;2) obtain the dielectric loss factor and polar component content of each oil product in step 1);3) with the dielectric loss factor of oil product as independent variable, with the polar component content of oil product as variable fitting, obtain linear equation PC (%) =A×tan delta-B;Wherein, PC (%) is the polar component content in oil product, tan delta is dielectric loss factor, A, B is constant;4) the dielectric loss factor of the frying oil sample to be measured is measured, and the polar component content of frying oil sample is obtained by calculation.The present application solves the problem that the measurement result is not accurate due to the large difference of dielectric constant of different kinds of plant oil, realizes the non-difference measurement of all plant oil varieties, and at the same time, different types of base oil are not needed to be used for calibration.

Description

Technical Field

[0001] The invention relates to the field of food detection, and in particular to a method for quickly detecting the content of polar components in frying vegetable oil based on dielectric loss factor. Background Art

[0002] When edible vegetable oils come into contact with water and air during frying, they undergo a series of complex reactions, producing acrylamide, polycyclic aromatic hydrocarbons, and other harmful substances. Therefore, the quality of frying vegetable oils is directly related to public health. Polar components (PC) are currently one of the most important indicators for evaluating frying oil quality. GB 2716-2018, "National Food Safety Standard for Vegetable Oils," stipulates that the polar component content of frying vegetable oils must be ≤27%.

[0003] The current GB5009.202-2016 "Determination of Polar Components (PC) in Edible Oils" uses column chromatography to determine polar components. This method has disadvantages such as long time consumption, large amount of organic solvents, and complex operation. In order to strengthen the quality and safety control of frying oil, it is necessary to develop a rapid detection method for polar components.

[0004] CN112098571A invented a device that connects a gel chromatography column, a silica gel chromatography column and a differential refractive index detector in series, which realizes the separation and online monitoring of six components in the polar components of frying oil: TGO, TGD, ox-TG and TG mixture, DG, FFA, and degradation products, reducing the measurement time of polar components to 0.5h.

[0005] CN111103259A provides a frying oil quality detection method based on spectral technology. By collecting near-infrared, far-infrared, and Raman spectral data as well as quality data such as acid value and polar components of a large number of samples, chemometrics is used to establish and correct the model through data training to achieve the purpose of non-destructive testing of frying oil quality.

[0006] CN104634823A discloses a method for determining the polar components of frying oil using a frequency domain dielectric spectrum tester. This method obtains the dielectric spectrum of the sample using linear measurement points (N≥1600), extracts the relaxation time τ by spectrum decomposition, and determines the polar component content of the frying oil using a linear model of the polar component content and τ.

[0007] The methods disclosed in the above patents have simplified the detection process to a certain extent and shortened the detection time compared to the national standard, but they either require complex chromatography equipment or require a large amount of data collection and complex data processing.

[0008] Currently, small portable frying oil quality testers from foreign brands such as FOS, FOM, and TESTO are also available on the market. These devices use probe-type sensors to quickly read the content of polar components in frying oil based on the positive correlation between polar components and dielectric constant. However, these devices require calibration with reference oil before use and can only accurately measure a certain type of relatively clean frying oil. Significant deviations will occur in frying oil with a lot of suspended matter or other types of frying oil, resulting in relatively limited application scenarios. Summary of the Invention

[0009] In response to the above problems, a rapid detection method for the polar component content of frying vegetable oil based on dielectric loss factor is provided to achieve rapid, accurate and non-destructive measurement of the polar component content in frying vegetable oil.

[0010] The specific technical solutions are as follows:

[0011] The first aspect of the present invention is to protect the application of dielectric loss factor in determining the content of polar components in frying vegetable oil.

[0012] The second aspect of the present invention is to claim a method for rapidly detecting the polar component content of frying vegetable oil based on dielectric loss factor, which has the following characteristics and comprises the following steps:

[0013] 1) taking a variety of frying vegetable oils and pre-treating the frying vegetable oils to obtain clarified oil products;

[0014] 2) obtaining the dielectric loss factor and polar component content of each oil product in step 1);

[0015] 3) Using the oil's dielectric loss factor as the independent variable and the oil's polar component content as the variable for fitting, the linear equation PC(%) = A × tanδ - B is obtained; where PC(%) is the polar component content in the oil, tanδ is the dielectric loss factor, and A and B are constants;

[0016] 4) Determine the dielectric loss factor of the frying oil sample to be tested, and calculate the polar component content of the frying oil sample using the above linear equation.

[0017] Furthermore, the pre-treatment method in step 1) includes but is not limited to filtration and centrifugation.

[0018] Furthermore, in step 2), the oil temperature is maintained at 90° C. using a temperature control device, and then the dielectric loss factor of the frying oil sample to be tested is obtained using an insulating oil dielectric loss resistance tester at 50 Hz and 2 kV AC, and the polar component content of the frying oil sample is calculated by substituting the dielectric loss factor into the calculated value.

[0019] Furthermore, it is characterized in that the polar component content of the frying oil sample in step 4) is tested in the range of 3%-40%.

[0020] The beneficial effects of the above scheme are:

[0021] 1) The present invention realizes the rapid, convenient and non-destructive determination of polar components in frying oil;

[0022] 2) Compared with existing frying oil quality testers based on dielectric constant, this invention solves the problem of inaccurate measurement results caused by the large differences in dielectric constants of different types of vegetable oils. It achieves the same measurement of all vegetable oil varieties and does not require calibration with different types of base oils (standard oils). BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the effect of moisture content on the dielectric loss factor of vegetable oil;

[0024] Figure 2 The changes in acid value and polar component content of palm oil during frying at 180℃. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0026] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0027] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to limit the present invention.

[0028] A rapid detection method for the polar component content of frying vegetable oil based on dielectric loss factor has the following characteristics and comprises the following steps:

[0029] 1) Taking various frying oils, pre-treating the frying oils to obtain clarified oil products;

[0030] 2) obtaining the dielectric loss factor and polar component content of each oil product in step 1);

[0031] 3) Fitting the dielectric loss factor and polar component content of the oil yields PC(%) = A × tanδ - B; where PC(%) is the polar component content in the oil, tanδ is the measured dielectric loss factor, and A and B are constants;

[0032] 4) Determine the dielectric loss factor of the frying oil sample and use it to calculate the polar component content of the frying oil sample.

[0033] The dielectric constant is an inherent property that characterizes the polarity of a substance. The dielectric constant of vegetable oils ranges from 2.5 to 3.0, with significant variations in dielectric constants depending on the fatty acid composition of different vegetable oils. Frying oil quality testers available on the market, such as FOS, FOM, and TESTO, utilize the principle that the dielectric constant of an oil is positively correlated with its polar component content during frying. If the linear equation y = A × x + B is used to determine the polar component content of a vegetable oil, B represents the dielectric constant of the base oil (the oil with zero polar component content). This value varies significantly relative to the slope A of the equation. Therefore, frying oil quality testers must be calibrated with base oil (standard oil) to determine the B value for high accuracy. However, due to the wide variety of vegetable oils, and the lack of a base oil for many blended oils, frying oil quality testers based on dielectric constant measurement can experience significant measurement errors in many applications. However, this application study found that the dielectric loss factor is an indicator that is only sensitive to polar components. The dielectric loss factor of refined vegetable oil is close to 0, and the dielectric loss factor of frying oil is entirely contributed by the polar components it contains. Therefore, for the linear equation of dielectric loss factor-polar component content y=A×x+B, the dielectric loss factor B of blank oil is close to 0. The type of oil has basically no effect on this technical route, and no base oil is needed to correct B.

[0034] Based on the above principle, the present invention takes a variety of commercially available frying oils and processes them according to the above steps 1) and 2) to obtain the linear equation PC(%)=94.462tanδ-0.4132.

[0035] This test method requires that the oil be clarified when determining the polar component content of frying oil (clarification methods include but are not limited to filtration, centrifugation, etc.). This is mainly because the presence of suspended solids or salt in the frying oil will significantly affect the determination of the dielectric loss factor, thereby greatly affecting the determination of the polar component content.

[0036] Table 1 Effect of solids and salt on dielectric loss factor test

[0037]

[0038] This test method does not need to consider the water content in frying oil when determining the polar component content of frying oil. Figure 1 As shown in the figure, the moisture content in oil and the dielectric loss factor are linearly correlated in deeply refined vegetable oils, but the effect is small and can be ignored in the determination of polar components in frying oils.

[0039] Example 1

[0040] Soybean oil was purchased from a supermarket and maintained at 90°C using a temperature control device. The dielectric loss factor was measured using an AI-6000 insulating oil dielectric loss resistance tester at 50 Hz and 2 kV AC voltage. Six parallel tests were performed and the average value was taken.

[0041] Example 2

[0042] Rapeseed oil was purchased from a supermarket and the oil temperature was maintained at 90°C using a temperature control device. The dielectric loss factor was measured using an AI-6000 insulating oil dielectric loss resistance tester at 50 Hz and 2 kV AC voltage. Six parallel tests were performed and the average value was taken.

[0043] Example 3

[0044] Palm oil was purchased from a supermarket and the oil temperature was maintained at 90°C using a temperature control device. The dielectric loss factor was measured using an AI-6000 insulating oil dissipation factor resistance tester at 50 Hz and 2 kV AC voltage. Six parallel tests were performed and the average value was taken.

[0045] Example 4

[0046] Purchase soybean oil from a supermarket, add 3% activated clay by weight, distill under reduced pressure at 90°C for 30 minutes, filter, add 2% basic alumina by weight, stir at 60°C for 120 minutes, and filter to obtain deeply refined soybean oil after dehydration, decolorization, and acid reduction. Measure the dielectric loss factor using an AI-6000 insulating oil dissipation factor tester at 50 Hz and 2 kV AC. Repeat six tests in parallel and take the average value.

[0047] Example 5

[0048] Purchase rapeseed oil from a supermarket, add 3% activated clay by weight of the oil, distill under reduced pressure at 90°C for 30 min, filter, add 2% alkaline alumina by weight of the oil, stir at 60°C for 120 min, filter, and obtain deeply refined rapeseed oil after dehydration, decolorization, and acid reduction; use an AI-6000 insulating oil dielectric loss factor resistance tester to measure the dielectric loss factor at 50 Hz and 2 kV AC voltage. Repeat 6 parallel tests and take the average value.

[0049] Example 6

[0050] Peanut oil was purchased from a supermarket, activated clay (3% by weight of the oil) was added, and the oil was distilled under reduced pressure at 90°C for 30 min, filtered, and basic alumina (2% by weight of the oil) was added at 60°C, stirred for 120 min, and filtered to obtain deeply refined peanut oil after dehydration, decolorization, and acid reduction. The dielectric loss factor was measured using an AI-6000 insulating oil dielectric loss resistance tester at 50 Hz and 2 kV AC voltage. Six parallel tests were conducted and the average value was taken.

[0051] Example 7

[0052] Commercially available palm oil was purchased and added to a frying pan set at 140°C. The batter was placed in the pan and fried until crispy and golden brown. The batter was removed and frying was continued for 36 h without adding oil. The frying oil was collected. The oil temperature was maintained at 90°C using a temperature control device. The dielectric loss factor was measured using a ULYDC-3 fully automatic insulating oil tester at 50 Hz and 2 kV AC voltage, and the average value was taken. Six parallel tests were performed, and the average value was taken.

[0053] Example 8

[0054] Commercially available palm oil was purchased and added to a frying pan set at 150°C. The batter was placed in the pan and fried until crispy and golden brown. The batter was removed and frying was continued for 28 h without adding oil. The frying oil was collected. The oil temperature was maintained at 90°C using a temperature control device. The dielectric loss factor was measured using a ULYDC-3 fully automatic insulating oil tester at 50 Hz and 2 kV AC voltage, and the average value was taken. Six parallel tests were performed, and the average value was taken.

[0055] Example 9

[0056] Purchase commercially available palm oil, add it to a frying pan, set the heating temperature to 170℃, put the batter into the pan and fry until it is crispy and golden, then remove it and fry it for 24 hours without adding oil, and collect the frying oil; use a temperature control device to maintain the oil temperature at 90℃, use a ULYDC-3 fully automatic insulating oil tester to measure the dielectric loss factor at 50Hz and 2kV AC voltage, and take the average value. Repeat the test 6 times in parallel and take the average value.

[0057] Example 10

[0058] Commercially available soybean oil was frying at a temperature of approximately 160-200°C. French fries and chicken nuggets were fried for approximately 6 hours daily for 3 days without adding oil. The oil was collected from a fried chicken shop. The oil temperature was maintained at 90°C using a temperature control device. The dielectric loss factor was measured using a ULYDC-3 fully automatic insulating oil tester at 50 Hz and 2 kV AC voltage, and the average value was taken. Six parallel tests were conducted, and the average value was taken.

[0059] Example 11

[0060] Commercially available soybean oil was frying at a temperature of about 150-180°C. The oil was frying for about 1.5 hours daily for one week without adding oil during the frying period and the oil was collected in the cafeteria. The oil temperature was maintained at 90°C using a temperature control device. The dielectric loss factor was measured using a ULYDC-3 fully automatic insulating oil tester at 50Hz and 2kV AC voltage, and the average value was taken. Six parallel tests were conducted, and the average value was taken.

[0061] Example 12

[0062] Commercially available soybean oil was frying at a temperature of approximately 160-200°C. The fried foods were meat and pasta. The frying time was unknown and no oil was added during the frying period. The oil was collected from a restaurant. The oil temperature was maintained at 90°C using a temperature control device. The dielectric loss factor was measured using a ULYDC-3 fully automatic insulating oil tester at 50 Hz and 2 kV AC voltage, and the average value was taken. Six parallel tests were conducted, and the average value was taken.

[0063] The measurement results of Examples 1-12 of the present invention are shown in the following table:

[0064]

[0065] The values ​​measured using the Chinese standard method in the above table are the polar component contents of the corresponding oils measured in accordance with GB5009.202-2016 “Determination of Polar Components (PC) in Edible Oils”.

[0066] It can be seen from Examples 1-3 in the above table that for unfried edible vegetable oils, when the polar component content is ≤3%, the dielectric loss factor will be significantly affected by the acid value, and the measurement error is large, about ±40%, indicating that the rapid detection method of the present invention has low accuracy when the polar component content is measured to be ≤3%, and is unreliable; it can be seen from Examples 4-6 that different types of vegetable oils are deeply refined to remove moisture, free fatty acids and polar components. The dielectric loss factor is less than or equal to 0.005, which shows that the difference in the category of vegetable oils will not affect the method of determining the polar component content by the dielectric loss factor; the polar component content measured in Examples 7-12 is basically similar to the value measured by the national standard method, which shows that the detection method provided in this application has good accuracy.

[0067] It should be noted that when the polar component content is greater than 40%, the rapid detection method provided in this application cannot be accurately determined. Here, the frying process of palm oil at 180°C is taken as an example. The polar component content in the frying oil increases linearly with the frying time, while the acid value increases linearly with the frying time in the initial stage, and stabilizes at a fixed level after reaching a certain level. When the polar component content is ≤40%, the acid value and polar component content of the frying oil increase in the same proportion. A large amount of measured data in the early stage shows that the dielectric loss factor and polar component content of the frying oil at this stage are positively correlated. The present method can obtain a more accurate polar component content by measuring the dielectric loss factor, with a measurement error of ±10%; when the polar component content is greater than 40%, the acid value and polar component of the frying oil no longer maintain the same change pattern, and the polar component content cannot be determined by the dielectric loss factor at this time.

[0068] The above description is only a preferred embodiment of the present invention and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the description and illustrations of the present invention should be included in the protection scope of the present invention.

Claims

1. A rapid detection method for the polar component content of frying vegetable oil based on dielectric loss factor, characterized in that: The steps include: 1) Taking various frying oils, pre-treating the frying oils to obtain clarified oil products; 2) obtaining the dielectric loss factor and polar component content of each oil product in step 1); 3) Using the oil's dielectric loss factor as the independent variable and the oil's polar component content as the variable for fitting, the linear equation PC=94.462tanδ-0.4132 is obtained, where PC is the polar component content in the oil and tanδ is the dielectric loss factor; 4) Determine the dielectric loss factor of the frying oil sample to be tested, and calculate the polar component content of the frying oil sample using the above linear equation; The polar component content of the frying oil sample in step 4) is tested in the range of 3%-40%.

2. The rapid detection method according to claim 1, characterized in that The pre-treatment method in step 1) includes filtration and centrifugation.

3. The rapid detection method according to claim 1, characterized in that In step 2), the oil temperature is maintained at 90° C. using a temperature control device, and the dielectric loss factor of the frying oil sample to be tested is obtained using an insulating oil dielectric loss resistance tester at 50 Hz and 2 kV AC.

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