Method for identifying oil-tea camellia seed oil based on dynamic ultraviolet absorption characteristics

Abstract

A method for identifying oil-tea camellia seed oil based on dynamic ultraviolet absorption characteristics, comprising: placing the oil sample to be tested after being adsorbed by silica gel in a closed oxygen-free environment and heating from room temperature, collecting absorbance values at 315 nm and 322 nm multiple times during the heating; subtracting the initial absorbance value at room temperature from the absorbance value at each collection time to obtain the absorbance increment ΔA 315 and ΔA 322 at each collection time, subtracting ΔA 322 from ΔA 315 to obtain the double-wavelength difference ΔA 315‑322 at each time; using ΔA 315 as the dependent variable and the collection time t as the independent variable, and using a kinetic equation to perform numerical fitting to obtain the kinetic constant K 315 ; using ΔA 315‑322 as the dependent variable and the collection time t as the independent variable, and using a kinetic equation to perform numerical fitting to obtain the kinetic constant K D315‑322 ; if the value of K D315‑322 is not greater than 0.0005 and the value of K 315 is less than 0, it is determined that the oil sample to be tested is oil-tea camellia seed oil. This method can conveniently and rapidly identify oil-tea camellia seed oil on the spot in production, circulation and consumption scenarios with reliable criteria and simple instruments, and can be used for technical authentication of pure oil-tea camellia seed oil.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of grain and oil processing and food safety, and specifically relates to a method for identifying counterfeit or adulterated oil-tea camellia seed oil, a high-value edible oil. TECHNICAL BACKGROUND

[0002] Oil-tea camellia seed oil is a woody plant oil produced in Jiangxi, Hunan, Hubei, Anhui and other provinces in China. It not only has excellent fatty acid composition and rich oil accompanying nutrients, but also has high thermal stability, making it suitable for Chinese cooking and earning the reputation of "Oriental olive oil". It is a high-end health-care edible oil. Due to the factors of oil-tea camellia mountain planting, difficulty in oil-tea camellia fruit harvesting, and high labor requirement, the production cost and market price of pure oil-tea camellia seed oil are much higher than those of most plant oils in the market. Some unscrupulous processors dump counterfeit or adulterated oil-tea camellia seed oil into the market for profit, which suppresses or even destroys the inherent processing characteristics and nutritional value of oil-tea camellia seed oil, seriously undermines consumer confidence, and has a sustained negative impact on the healthy development of related industries. Therefore, the development of oil-tea camellia seed oil counterfeit or adulteration identification technology is of great significance for the development of rural mountain economy, the upgrading of oil processing industry, and the realization of high-end edible oil import substitution.

[0003] Adulteration of low-value oil in high-value edible oil is a long-standing problem in the relevant industry and consumer field. The identification techniques developed so far can be broadly divided into two categories: one is based on the identification method of target chemical components, which usually uses chemical analysis methods to determine the presence or content of specific chemical components in the oil sample to be tested, and judges the attribution of the oil sample. Because the chemical components of various edible oils are very similar, this method usually needs to select a complex separation method to cooperate with a high-sensitivity analytical instrument to determine the content of trace chemical components. The second is the identification method based on characteristic spectroscopic signals, which usually uses spectroscopy, mass spectrometry or nuclear magnetic resonance technology to collect spectroscopic information of the oil sample to be tested, and then extracts the characteristic signals based on chemometrics methods, which are used as the basis for oil sample attribution discrimination.

[0004] The main chemical characteristic that distinguishes camellia seed oil from other bulk or inexpensive edible oils is its unique fatty acid composition and the content of trace lipid-associated nutrients. One of its core characteristics is its high oleic acid content (over 70%) and almost complete absence of linolenic acid. Gas chromatography analysis can provide information on its fatty acid composition, effectively differentiating it from other bulk and inexpensive edible oils. However, this method involves complex and time-consuming chemical operations and expensive gas chromatography equipment, making it unsuitable for on-site application in production, distribution, and consumption, and it also typically involves the consumption of organic solvents. Alternatively, the content of trace lipid-associated natural products such as tocopherols, squalene, and phytosterols in camellia seed oil can be used as a basis for identification, but these indicators are highly susceptible to changes in raw material origin, harvesting time, and processing methods, resulting in significant fluctuations and making it difficult to provide reliable criteria.

[0005] In the chemical analysis of oils and fats, ultraviolet spectroscopy is a simple and commonly used technique. However, conventional ultraviolet absorption spectroscopy analysis of oils and fats can only provide information about the existing binary or ternary conjugated structures in the oils and fats. This information mainly depends on the degree of heat treatment and oxidation that the oils and fats have undergone, and does not directly indicate the variety or origin of the oils and fats, so it cannot be used as a basis for oil identification. Summary of the Invention

[0006] The purpose of this invention is to provide a method for rapidly and sensitively identifying camellia seed oil based on dynamic ultraviolet absorption characteristics.

[0007] The method for identifying camellia seed oil of the present invention includes the following steps: treating the oil sample to be tested with silica gel to remove any possible moisture and / or other impurities; placing the oil sample to be tested under a sealed, oxygen-free condition, heating it from room temperature, and repeatedly collecting its absorbance values ​​at 315 nm and 322 nm during the heating period; subtracting the initial absorbance value collected at room temperature from the absorbance value collected at each collection time during the heating period to obtain the absorbance increment ΔA at each collection time. 315 and ΔA 322 And the ΔA at each acquisition time 315 Subtract ΔA 322 Obtain the dual-wavelength difference ΔA at each acquisition time. 315-322 ; Take ΔA 315 With t as the dependent variable and the acquisition time as the independent variable, the first kinetic equation is used for numerical fitting within the acquisition time range to obtain the kinetic constant K. 315 ; Take ΔA 315-322 With t as the dependent variable and the acquisition time as the independent variable, the second kinetic equation is used for numerical fitting within the acquisition time range to obtain the kinetic constant K. D315-322 ; and if the K of the oil to be tested D315-322 The value is not greater than 0.0005 and K 315 If the value is less than 0, the oil to be tested is determined to be camellia seed oil.

[0008] The silica gel adsorption in the embodiments of the present application is silica gel column adsorption.

[0009] In the preferred embodiments of the present application, the heating is constant-rate heating, and the heating rate is between 8°C / min and 10°C / min.

[0010] In the preferred embodiments of the present application, the absorbance value is collected at an optical path of 0.1-0.5 mm.

[0011] In the preferred embodiments of the present application, the first kinetic equation is y=K 315 ln(1+at), y is the dependent variable ΔA 315 , a is a fitting coefficient; and the second kinetic equation is y'=K D315-322 ln(1+a't), y' is the dependent variable ΔA 315－322 , a' is a fitting coefficient.

[0012] In the preferred embodiments of the present application, if the K D315－322 of the oil product to be tested is greater than 0.0005, it is determined that the oil tea seed oil is adulterated or counterfeited with linolenic acid; if the K D315-322 of the oil product to be tested is less than 0.0005 and the K 315 is greater than 0, it is determined that the oil tea seed oil is counterfeited or adulterated without linolenic acid.

[0013] In the preferred embodiments of the present application, the silica gel adsorption treatment comprises: providing a silica gel column with silica gel particles between 100-200 mesh and a column length of 10-20 mm; and driving the oil product to be tested to flow through the silica gel column based on gravity or centrifugal force.

[0014] By using the method of the present application, the oil tea seed oil can be quickly identified on the spot in the production, circulation and consumption scenarios with convenient operation, simple instrument and reliable criterion. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figures la-lc The dynamic ultraviolet absorption signals and kinetic fitting curves of pure oil tea seed oil produced by different processing technologies are shown.

[0016] Figure 2 The characteristic indexes K 315 and K 315-322 of pure oil tea seed oil and various bulk edible oils are shown.

[0017] Figure 3 The characteristic indexes K 315 and K 315-322 of self-made adulterated oil by primary pressing process are shown.

[0018] Figure 4 The characteristic indexes K 315 and K D315-322 . DETAILED DESCRIPTION

[0019] Among the commonly used edible oils, only camellia seed oil and olive oil have much higher oleic acid content (up to 70-80%) than other oils, and the contents of linoleic acid and linolenic acid are relatively low. Both of them are high-value oils, and there is no benefit in counterfeiting or adulterating each other. Other low-value edible oils with low linolenic acid and linoleic acid content mainly include palm oil, coconut oil and hydrogenated vegetable oil, etc., which have high solid ester content. For example, if camellia seed oil is counterfeited or adulterated, it can be directly identified by transparency detection, viscosity detection, and even naked eye observation. The market for such counterfeiting or adulteration may be small. Even if a large proportion of liquid oils such as soybean oil, rapeseed oil and sunflower seed oil is adulterated in camellia seed oil, it is difficult to identify by the above simple methods, which is a problem that needs to be solved urgently in the market.

[0020] Therefore, the main purpose and effect of the method of the present application is to identify camellia seed oil counterfeited or adulterated with bulk oils such as soybean oil and rapeseed oil with high linolenic acid content, and to identify camellia seed oil counterfeited or adulterated with high linoleic acid content oils such as peanut oil, sunflower seed oil and cottonseed oil, so as to realize the technical certification of pure camellia seed oil and the rapid and effective identification of most of the adulterated and counterfeited camellia seed oil in the market.

[0021] Unlike conventional static ultraviolet absorption analysis, the principle of the oil dynamic ultraviolet spectrum analysis used in the present application is that the oil to be tested is placed in a closed oxygen-sealed heating environment to cause thermal rearrangement of the olefinic bond to produce new olefinic bond conjugated structure products and their ultraviolet absorption characteristics. The generation rate and type of the olefinic bond conjugated structure products are related to the content and type of the polyunsaturated fatty acids in the oil, so the dynamic change characteristics of the ultraviolet absorption signal can be used to identify the type of the oil. The use of closed oxygen-sealed heating can avoid the oxidation of the oil by air, thereby reducing the complex interference of various oil oxidation products on the dynamic ultraviolet absorption signal.

[0022] The saturated fatty acids (no olefinic bond) and monounsaturated fatty acids (one olefinic bond) contained in edible oils will not produce conjugated olefinic bond structures due to thermal rearrangement; while polyunsaturated fatty acids, such as commonly seen linoleic acid (two olefinic bonds) and linolenic acid (three olefinic bonds), can undergo thermal rearrangement to produce di-, tri-, and further tetra-conjugated products. The generation rate and type of the above conjugated products have a high correlation with the content and type of the polyunsaturated fatty acids.

[0023] Camellia seed oil contains more than 70% oleic acid and trace amounts of saturated fatty acids, as well as 7-14% linoleic acid and 0-1.4% linolenic acid. In the thermal rearrangement reaction, di- and tri-conjugated structure products can be slowly generated, and trace amounts of tetra-conjugated structure products can be further generated.

[0024] Correspondingly, when camellia seed oil is heated and thermal rearrangement is initiated, its dynamic ultraviolet absorption shows the following: the absorbance in the 225nm-240nm band (reflecting the binary conjugated structure) and the 260nm-280nm band (reflecting the ternary conjugated structure) shows a significant and continuous increase; while the absorbance in the 310nm-325nm band (reflecting the quaternary conjugated structure) shows an overall decreasing trend. This is because during the heating process, the absorbance of the oil shows a slight decreasing trend in the entire ultraviolet band, and the formation of the quaternary conjugated structure product of camellia seed oil is extremely slow, and its ultraviolet absorption is extremely weak, resulting in a decrease in absorbance in this band instead of an increase.

[0025] Extensive experimental observations revealed that during the process of heating camellia seed oil in a sealed, oxygen-free environment, the absorbance at 315nm and 322nm continuously decreased over time. Stable kinetic constants with values ​​less than 0 were obtained through data fitting.

[0026] Furthermore, the quaternary conjugated structure of the oil exhibits characteristic absorption at 315 nm, which can partially offset the decreasing trend of absorbance with increasing temperature. Therefore, the dual-wavelength difference ΔA can be utilized. 315-322 The changes in absorbance at 315 nm and 322 nm over time, ΔA 315 With ΔA 322 The difference (ΔA) represents the accumulation of quaternary conjugated structure products. The unique fatty acid composition of camellia seed oil determines that the formation of quaternary conjugated structure products is very slow; therefore, ΔA... 315-322 The value increases extremely slowly over time, and a stable kinetic constant can be obtained by data fitting, with a value no greater than 0.0005.

[0027] Before acquiring dynamic ultraviolet spectra, the method of this invention allows for the dehydration and drying of the test oil, which may contain water. This eliminates the interference of water vaporization during heating, especially in the later stages when the temperature exceeds 100 degrees Celsius, on the detection. For example, sodium sulfate can be used to absorb water to obtain a dry test oil. Alternatively, silica gel adsorption can be used to treat the test oil, removing not only any water but also other impurities, thus eliminating their interference with the spectral signal.

[0028] The process of collecting signals includes placing the oil sample to be tested in a closed oxygen-isolated condition, starting from room temperature and gradually heating to start the thermal rearrangement reaction, and collecting the absorbance values at 315 nm and 322 nm during the process. In order to improve the stability of the kinetic parameters, it is best to use a constant heating rate. For example, the oil sample to be tested is heated from room temperature to not more than 120℃, for example, not more than 100℃, at a heating rate of 5-12℃, preferably 8-10℃ / min. There is enough time to collect the absorbance data at the above wavelengths multiple times to obtain reliable kinetic constants, and the time consumed is controllable, which is beneficial to quickly obtain the identification conclusion. The heating rate and the maximum temperature used in the embodiments of the present application are widely applicable to various types of ultraviolet spectrophotometers. Limiting the maximum heating temperature can protect the spectral equipment and prolong its service life.

[0029] In a preferred embodiment of the method of the present application, the absorbance values at 315 nm and 322 nm of the oil sample to be tested are collected under a small optical path (for example, 0.1 mm optical path), and the collection times are not less than 4 times, preferably not less than 5 times.

[0030] Traditional oil ultraviolet spectrum analysis usually involves dilution of the oil sample, and the solvents used are mainly alkanes, which are flammable, explosive and volatile, and cannot be used for dynamic ultraviolet spectrum analysis described in the present method. However, the use of a small optical path such as 0.1 mm can directly collect the ultraviolet signal of the oil, which is simple, safe and environmentally friendly. Other small optical paths such as 0.05-0.5 mm, preferably 0.1-0.2 mm, can also be used. In order to obtain reliable kinetic constants, sufficient absorbance and collection time data need to be collected, so it is required to maintain sufficient collection frequency under the total collection time. According to the analysis of test data, the total collection time is 450-750 s, and the collection frequency is not less than 1 time / 120 s, which can meet the stable fitting requirement of kinetic constants. The use of high-frequency collection method can further shorten the analysis time and improve the detection efficiency.

[0031] After collecting the absorbance values at 315 nm and 322 nm multiple times, the collected absorbance values are processed. The absorbance values collected at each collection time are subtracted from the absorbance value collected at room temperature for the first time, to obtain the absorbance increment ΔA 315 and ΔA 322 at each collection time; and the difference between ΔA 315 and ΔA 322 is used to calculate the dual-wavelength difference ΔA 315-322 at each collection time.

[0032] Then feature extraction is performed: taking ΔA 315 as the dependent variable and the collection time t as the independent variable, the kinetic equation is used for numerical fitting in the range of continuous collection time to obtain the kinetic constant K 315 ; and ΔA 315-322For dependent variable, collection time t is independent variable, in collection time range, dynamic equation is used for numerical fitting, and dynamic constant K is obtained D315-322 .

[0033] In the embodiment of the present application, ΔA 315 -t is fitted to obtain the dynamic equation in the form of y=K 315 ln(1+at), wherein y is dependent variable ΔA 315 , t is independent variable, K 315 is the dynamic constant to be solved, and a is fitting coefficient.

[0034] Through analysis of a large number of observation data of various oil products, it is found that the dynamic equation is used to fit the series ΔA 315 -t observation values of the oil products, and the stability and correlation are good, and thus the reliable characteristic value K 315 of the oil product to be measured can be extracted, which is beneficial to improve the identification resolution and reliability, and the fitting effect is better than that of linear equation, exponential equation or other model equation. The dynamic constant is a parameter that does not change with observation time, and the numerical fitting of multiple observations can significantly eliminate accidental errors and careless errors in single observation, and is a reliable parameter reflecting the dynamic change of oil absorption signal, and is more beneficial to reflect the essential characteristics of the oil product to be measured.

[0035] Similarly, the dynamic equation in the form of y=K 315-322 ln(1+at) is used to fit ΔA D315-322 -t, wherein y is dependent variable ΔA 315－322 , t is independent variable, K D315-322 is the dynamic constant to be solved, and a is fitting coefficient.

[0036] Through analysis of a large number of observation data of various oil products, it is found that the dynamic equation is used to fit the series ΔA 315-322 -t observation values of the oil products, and the stability and correlation are good, and thus the reliable characteristic value K D315-322 of the oil product to be measured can be extracted, which is beneficial to improve the identification resolution and reliability, and the fitting stability is better than that of linear equation, exponential equation or other model equation. The dynamic constant is a parameter that does not change with observation time, and the numerical fitting of multiple observations can significantly eliminate accidental errors and careless errors in single observation, and is a reliable parameter reflecting the dynamic change of oil absorption signal, and is more beneficial to reflect the essential characteristics of the oil product to be measured.

[0037] The dynamic constants K 315 and K D315-322 obtained based on the fitted dynamic equation are used to determine whether the oil product to be measured is adulterated oil or counterfeit oil.

[0038] If the K D315-322 value of the measured oil product is not greater than 0.0005 and K315 If the value is less than 0, it is determined to be, or essentially determined to be, pure camellia seed oil.

[0039] If the K of the oil to be tested D315-322 A value greater than 0.0005 indicates that the tested oil is an adulterated or counterfeit oil containing linolenic acid. Analysis of extensive observational data from various oil products revealed that bulk oils with high linolenic acid content, such as soybean oil and rapeseed oil, have a K... D315-322 The eigenvalue is typically an order of magnitude higher than that of camellia seed oil, making it highly likely to detect counterfeit or adulterated camellia seed oil. This is because linoleic acid contains three unsaturated double bonds, which readily form quaternary conjugated structures under thermal rearrangement and polymerization reactions, leading to the higher eigenvalue K. D315-322 It is far higher than that of camellia seed oil, which contains virtually no or only trace amounts of linolenic acid.

[0040] If the K of the oil to be tested D315-322 Less than 0.0005 and K 315 A value greater than 0 indicates that the tested oil is an adulterated or counterfeit oil that does not contain linolenic acid. Analysis of extensive observational data from various oil products revealed that bulk oils with low or no linolenic acid content, such as certain varieties of peanut oil, sunflower oil, and cottonseed oil, have a lower K content. D315-322 The value can be less than 0.0005. However, its linoleic acid content is much higher than that of camellia seed oil, which allows it to form binary conjugated products more quickly. Therefore, the rate of further polymerization to form quaternary conjugated products remains high, resulting in its K... 315 It is greater than 0, which also distinguishes it from camellia seed oil.

[0041] The method for identifying counterfeit or adulterated camellia seed oil described in this invention is not only fast and reliable, easy to operate, and uses universal instruments, but it can also effectively identify most possible counterfeit or adulterated camellia seed oil phenomena.

[0042] As mentioned above, this invention can pretreat the oil sample to be tested using silica gel adsorption. Specifically, the silica gel column used for adsorbing the oil sample is filled with dried silica gel particles. The particle size is between 100-200 mesh, and the column length is between 10-20 mm. Column adsorption treatment of the oil sample is simple and rapid, effectively removing any moisture and other impurities that may be present by utilizing the drying properties, polar component adsorption properties, and filtration function of the silica gel column.

[0043] Example

[0044] The following examples further illustrate the implementation and technical effects of the method described in this invention. All the oil samples used in the following examples were treated with silica gel column adsorption: 0.25g of each oil sample was dropped onto a silica gel adsorption column (6mm in diameter, 16mm in length, filled with 120-mesh silica gel) at room temperature (around 24°C), and centrifuged at 1000×g to obtain the adsorbed oil.

[0045] Comparison of dynamic ultraviolet absorption characteristics of pure camellia seed oil processed by different methods

[0046] The oils tested were first-grade pressed camellia seed oil, cold-pressed refined camellia seed oil, and freshly pressed camellia seed oil. A 0.1 mm path length UV absorption sample cell was injected at room temperature (approximately 24°C), filled, and sealed in an oxygen-free environment within the sample chamber of a UV spectrophotometer. The sample was heated at a constant rate of 8°C / min, and absorbance values ​​at 315 nm and 322 nm were continuously collected five times every 120 seconds. The absorbance increment ΔA at each collection time was obtained by subtracting the absorbance value collected at room temperature from each collected absorbance value. 315 Value and ΔA 322 Value; then based on ΔA 315 and ΔA 322 Calculate the difference between the two wavelengths ΔA at each acquisition time. 315-322 Value. ΔA 315 ΔA 322 and ΔA 315-322 The relationship with the acquisition time t is as follows: Figures la-lc As shown in the figures, these figures illustrate the dynamic ultraviolet absorption signals and kinetic fitting curves of pure camellia seed oil processed using different techniques.

[0047] Take ΔA 315 and ΔA 315-322 With t as the dependent variable and the acquisition time as the independent variable, a first-order kinetic equation is used for numerical fitting within the continuous acquisition time range to obtain the kinetic constant K. 315 and K D315-322 Shown Figures la-lc In each figure, the values ​​for first-grade pressed camellia seed oil, cold-pressed refined camellia seed oil, and freshly pressed camellia seed oil are represented by ΔA. 315 The kinetic constant K of -t 315 They are -2.7x10 -3 -1.3x10 -2 and -1.3x10 -3 ΔA 315-322 The kinetic constant K of -t D315-322 They are 9.6x10 -6 5x10 -4 and 5x10 -4 Regardless of the processing method used, the K content of pure camellia seed oil is... D315-322 Not greater than 0.0005 and K 315 Less than 0.

[0048] Example 1: Comparison of dynamic ultraviolet absorption characteristics of pure camellia seed oil and various bulk edible oils

[0049] The tested oil products are first grade pressed tea seed oil, edible palm oil, first grade pressed peanut oil, first grade leached soybean oil and first grade pressed rapeseed oil. The adsorbed oil is injected into a UV absorption sample cell with an optical path of 0.1 mm at room temperature, and is placed in the sample chamber of a UV spectrophotometer under the condition of being filled and sealed to prevent oxygen. The absorbance values at 315 nm and 322 nm are continuously collected at a constant heating rate of 10°C / min and a frequency of 100 seconds per time. The absorbance values collected at each time are subtracted from the absorbance value collected at room temperature for the first time to obtain the absorbance increment ΔA 315 at each collection time 322 ; and the two-wavelength difference ΔA 315 at each collection time is calculated according to the difference between ΔA 322 and ΔA 315-322 ; and the absorbance increment ΔA 315 and ΔA 315-322 are taken as dependent variables, and the collection time t is taken as an independent variable, and the first order kinetic equation is used for numerical fitting in the range of continuous collection time. The dynamic UV absorbance kinetic constants K 315 and K D315-322 of pure tea seed oil and various edible oils are shown in Figure 2 .

[0050] The pure tea seed oil (characteristic index K D315-322 is not greater than 0.0005 and K 315 is less than 0) and various edible oils (characteristic index K 315 is greater than 0) have significant differences, so the present application provides K D315-322 not greater than 0.0005 and K 315 less than 0 as the characteristic index for distinguishing pure tea seed oil. Figure 2 The identification characteristic index of various edible oils shown in the table is that the two kinetic constant values are outside the specified index range. Further subdivision, if the K D315－322 of the tested oil product is greater than 0.0005, it can be determined that the tested oil product belongs to high linolenic acid content oil, such as first grade leached soybean oil and first grade pressed rapeseed oil, and the present application method can be used to distinguish the adulteration or counterfeiting of high linolenic acid content oil in practical application; if the K D315-322 of the tested oil product is less than 0.0005 and K 315 is greater than 0, it is determined that the tested oil product is an oil without linolenic acid, such as edible palm oil and first grade pressed peanut oil, and the present application method can be used to distinguish the adulteration or counterfeiting of such oil in practical application. Therefore, the method can effectively identify most of the possible tea seed oil counterfeiting or adulteration problems.

[0051] Example 2

[0052] The to-be-tested oil product is a self-made adulterated oil by main stream processing technology, and the first pressed rapeseed oil is adulterated with the first pressed oil-tea camellia seed oil in proportions of 5%, 10%, 20%, 40% and 80%. After being treated by silica gel column adsorption, the adulterated oil sample is injected into a UV absorption sample cell with an optical path of 0.1 mm at room temperature, and is placed in the sample room of a UV spectrophotometer under the condition of being filled and sealed to prevent oxygen. The sample is heated at a constant heating rate of 8 ℃ / min, and the absorbance values at 315 nm and 322 nm are continuously collected for 5 times every 120 seconds. The absorbance values collected each time are subtracted by the absorbance value collected at room temperature for the first time, to obtain the absorbance increment ΔA 315 at each collection time 322 . The two-wavelength difference ΔA 315 at each collection time is calculated according to the difference between ΔA 322 and ΔA 315-322 . Taking ΔA 315 and ΔA 315-322 as dependent variables and the collection time t as an independent variable, the first-order kinetic equation is used for numerical fitting in the range of continuous collection time, to obtain the kinetic constants K 315 and K D315-322 . As shown in Figure 3 .

[0053] It can be seen that the pure oil-tea camellia seed oil (characteristic index K D315-322 is not greater than 0.0005 and K 315 is less than 0) has a significant difference with the 5%, 10%, 20%, 40% and 80% adulterated oil (characteristic index K D315-322 is greater than 0.0005) in the dynamic UV light absorption characteristic index, the characteristic index of the adulterated oil is outside the range specified above, and it can be judged that the adulterated oil belongs to the adulterated oil containing linolenic acid or the counterfeit oil, which is consistent with the actual adulterated rapeseed oil. Further, the linear equation fitted by taking the characteristic index K D315-322 as a dependent variable and the adulterated concentration (mass percentage) as an independent variable is y=6E-05x+0.0003 (R 2 =0.992), and the detection limit is 5%.

[0054] Therefore, the identification index K D315-322 of the present application can identify the first pressed rapeseed oil adulterated with the first pressed oil-tea camellia seed oil produced by the main stream processing technology, and the adulteration of 5% can be identified, which has high sensitivity.

[0055] Example 3

[0056] The to-be-tested oil product is self-made doped oil by advanced processing technology, cold-pressed refined rapeseed oil doped with cold-pressed refined oil-tea camellia seed oil, and the doped proportion is 5%, 10%, 20%, 40% and 80%. After being treated by passing through a silica gel column, each doped oil sample is injected into a UV absorption sample cell with an optical path of 0.1 mm, and is placed in the sample chamber of a UV spectrophotometer under the condition of being filled and sealed and oxygen isolation. Heating is performed at a constant heating rate of 8 ℃ / min, and the absorbance values at 315 nm and 322 nm are continuously collected for 5 times every 120 seconds. The absorbance values collected each time are subtracted by the absorbance value collected at room temperature for the first time, to obtain the absorbance increment ΔA 315 at each collection time 322 The difference between ΔA 315 and ΔA 322 is used to calculate the dual-wavelength difference ΔA 315-322 at each collection time, and ΔA 315 and ΔA 315-322 are used as dependent variables, and the collection time t is used as an independent variable. In the range of continuous collection time, a first-order kinetic equation is used for numerical fitting to obtain the kinetic constants K 315 and K D315-322 , which are shown in Figure 4 .

[0057] Similar to the embodiment, the pure oil-tea camellia seed oil (characteristic index K D315-322 is not greater than 0.0005 and K 315 is less than 0) has a significant difference with the 5%, 10%, 20%, 40% and 80% doped oil (characteristic index K D315-322 is greater than 0.0005) in the characteristic index, the identification index of the doped oil is outside the specified range, and it can be judged that the doped oil belongs to the doped oil containing linolenic acid or the counterfeit oil, which is consistent with the actual type of the doped oil. Further, the linear equation fitted by taking the characteristic index K D315-322 as the dependent variable and the doped concentration (mass percentage) as the independent variable is y=0.0001x+0.0008 (R 2 =0.999), and the detection limit is 5%.

[0058] Therefore, the identification index K D315-322 of the application can identify the cold-pressed refined rapeseed oil doped with cold-pressed refined oil-tea camellia seed oil produced by advanced processing technology, and the doped oil can be identified even at a doped proportion of 5%.

[0059] The same series of doped oil identification tests are also performed on soybean oil and sunflower seed oil as in Examples 2 and 3, and it is shown that the characteristic indexes K 315 and K D315-322 of the application can be used to sensitively identify the doped oil.

Claims

1. A method for identifying oil-tea camellia seed oil, comprising the steps of: subjecting the oil sample to be tested to silica gel adsorption treatment to remove possible moisture and / or other impurities; placing the oil sample to be tested after adsorption in a closed oxygen-isolated condition, starting heating from room temperature, and collecting the absorbance values of the oil sample to be tested at 315 nm and 322 nm multiple times during the heating process; The absorbance increment ΔA at each sampling time is obtained by subtracting the initial absorbance value collected at room temperature from the absorbance values ​​collected at each sampling time during the heating period. 315 and ΔA 322 And the ΔA at each acquisition time 315 Subtract ΔA 322 Obtain the dual-wavelength difference ΔA at each acquisition time. 315-322 ; Take ΔA 315 With t as the dependent variable and the acquisition time as the independent variable, the first kinetic equation is used for numerical fitting within the acquisition time range to obtain the kinetic constant K. 315 ; Take ΔA 315-322 With t as the dependent variable and the acquisition time as the independent variable, the second kinetic equation is used for numerical fitting within the acquisition time range to obtain the kinetic constant K. D315-322 ;and If the K D315-322 value of the oil to be tested is not greater than 0.0005 and the K 315 value is less than 0, it is determined that the oil to be tested is camellia seed oil.

2. The method of claim 1, wherein the silica gel adsorption is silica gel column adsorption.

3. The method of claim 1, wherein the heating is constant-rate heating, and the heating rate is between 8 ℃ / min and 10 ℃ / min.

4. The method of claim 1, wherein the absorbance values are collected at an optical path of 0.1-0.5 mm.

5. The method of any one of claims 1-3, wherein the first kinetic equation is y = K 315 ln(l + at), y is the dependent variable ΔA 315 , a is a fitting coefficient; and the second kinetic equation is y' = K D315-322 ln(l + a't), y' is the dependent variable ΔA 315－322 , a' is a fitting coefficient.

6. The method according to any one of claims 1-3, if the K D315－322 value of the oil to be tested is greater than 0.0005, it is determined that the oil is adulterated or counterfeit tea seed oil containing linolenic acid; if the K D315-322 value of the oil to be tested is less than 0.0005 and the K 315 value is greater than 0, it is determined that the oil is counterfeit or adulterated tea seed oil not containing linolenic acid.

7. The method of any one of claims 1-3, wherein the silica gel adsorption treatment comprises: providing a silica gel column with silica gel particles between 100-200 mesh and a column length of 10-20 mm; and making the oil sample to be tested flow through the silica gel column based on gravity or centrifugal force.

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