A mathematical model for identifying the age of dried orange peel and a method for establishing and applying the same

Abstract

The application discloses a mathematical model for identifying the age of dried orange peel, and a regression equation is obtained by taking X as the horizontal coordinate, Y as the vertical coordinate and fitting a polynomial regression curve, so that the mathematical model is constructed, wherein X is the mass fraction of esterified phenolic acid in total phenolic acid in dried orange peel of each year, and Y is the age of dried orange peel. The application further discloses a method for establishing the mathematical model for identifying the age of dried orange peel. The application further discloses a method for identifying the age of dried orange peel. The mass fraction of esterified phenolic acid in total phenolic acid is used as the independent variable, which conforms to the change rule of the existing form of phenolic acid in the aging process of dried orange peel, and can reduce the deviation caused by individual differences of samples and improve the accuracy of the identification of the age of dried orange peel.

Description

Technical Field

[0001] This invention relates to the field of identification technology of Chinese medicinal materials, and in particular to a mathematical model for identifying the age of dried tangerine peel, its establishment method, and its application. Background Technology

[0002] Dried tangerine peel, also known as tangerine peel or venereum peel, is a nourishing beverage and traditional Chinese medicine made from the mature peel of the tangerine (Citrus reticulata) plant, which has been repeatedly sun-dried and stored for a long time under specific conditions. It is believed to have the effects of regulating qi and strengthening the spleen, as well as drying dampness and resolving phlegm, making it a functional substance that is both food and medicine. Traditionally, it is believed that the longer dried tangerine peel is stored, the higher its medicinal value. Currently, the price of dried tangerine peel sold on the market varies greatly depending on its storage year; dried tangerine peel aged over twenty years can cost tens of thousands of yuan per kilogram. However, it is difficult to distinguish between dried tangerine peel of different years, leading to the phenomenon of inferior products being sold as superior ones. Therefore, establishing an accurate method for identifying the age of dried tangerine peel has become an urgent problem to be solved.

[0003] Currently, the main methods for identifying the age of dried tangerine peel include external characteristic observation, active ingredient determination, and spectral fingerprinting technology. Visual observation primarily utilizes human vision and smell to determine the age of the peel by observing its color, aroma, and texture. This method is highly subjective and requires extensive practical experience from the assessor. Wang Guangning et al. used a colorimeter to quantify the appearance color of Guangchen peel and established a mathematical model based on brightness, red-green component, and yellow-blue component values ​​to reduce the bias caused by human identification to some extent. Determining the content of active ingredients in dried tangerine peel is another commonly used method for age identification. The 2020 Chinese Pharmacopoeia stipulates that the content of hesperidin in Guangchen peel should not be less than 2.0%, and the total amount of norihesperidin and citrusperidin should not be less than 0.42%. Liang Tianyi et al. used gas phase-ion mobility spectrometry (GC-IMS) to analyze the volatile composition of dried tangerine peel from different years, finding significant differences in the volatile oil components, which can be used as a method for age identification. In addition, various spectral fingerprinting techniques have been gradually applied to the identification of the age of dried tangerine peel. Yu Mei et al. used near-infrared spectroscopy to identify dried tangerine peel from different years. Zhou Jie et al. constructed a fingerprint spectrum of dried tangerine peel using high-performance liquid chromatography, providing a reference for the quality control of dried tangerine peel from different years.

[0004] Currently, the age of dried tangerine peel is often determined by detecting the content of hesperidin (a flavonoid). However, the trend of hesperidin content changes with the age of the peel; it sometimes increases and sometimes decreases, making this method inaccurate. Furthermore, the active substances in dried tangerine peel often exist in a dynamic form. For example, flavonoids can exist in free, esterified, and bound-insoluble forms. During active ingredient extraction, usually only free and esterified active ingredients can be extracted, while bound-insoluble active ingredients are difficult to extract. Moreover, when using ultraviolet spectrophotometry and high-performance liquid chromatography (external standard method) for detection, esterified active ingredients often lack ultraviolet absorption or their maximum absorption wavelength is easily shifted, leading to undetectable esterified active ingredients or detection errors. This further reduces the accuracy of determining the age of dried tangerine peel and easily introduces errors.

[0005] Furthermore, while volatile oils are an important active ingredient in aged tangerine peel, their high volatility means their concentration often decreases with aging, making it difficult to establish a reliable determination model. Although fingerprint and other spectroscopic techniques can determine the age of aged tangerine peel, they require expensive equipment and specialized expertise, which is not conducive to actual production by enterprises. Summary of the Invention

[0006] Based on the technical problems existing in the background technology, this invention proposes a mathematical model for identifying the age of dried tangerine peel, its establishment method, and its application. This invention uses the mass fraction of esterified phenolic acid in total phenolic acid as the independent variable. On the one hand, it conforms to the changing law of the existence form of phenolic acid in the aging process of dried tangerine peel. On the other hand, it can reduce the deviation caused by individual differences in samples and improve the accuracy of identifying the age of dried tangerine peel.

[0007] This invention proposes a mathematical model for identifying the age of dried tangerine peel. Using X as the abscissa and Y as the ordinate, a polynomial regression curve is fitted to obtain the regression equation, thereby constructing a mathematical model. Here, X is the mass fraction of esterified phenolic acid in the total phenolic acid of dried tangerine peel from each year, and Y is the year of dried tangerine peel.

[0008] Preferably, the total phenolic acids are the sum of free phenolic acids, esterified phenolic acids, and bound phenolic acids.

[0009] Besides flavonoids and volatile oils, dried tangerine peel also contains a large amount of phenolic acids, exceeding 2.0%. Phenolic acids structurally contain phenolic hydroxyl groups, which can form ester bonds with carboxyl groups. The most abundant carbohydrate in dried tangerine peel is a type of pectin, which contains a large amount of galacturonic acid, capable of undergoing esterification reactions with phenolic acids. Therefore, phenolic acids in dried tangerine peel exist in free, esterified, and bound (i.e., insoluble) forms.

[0010] The inventors discovered through research that the content of esterified phenolic acids in dried tangerine peel increases with age. Therefore, the inventors proposed using the mass fraction of esterified phenolic acids in total phenolic acids as the independent variable and the age of dried tangerine peel as the dependent variable to establish a mathematical model for the identification of the age of dried tangerine peel.

[0011] Using the mass fraction of esterified phenolic acids in total phenolic acids as the independent variable not only conforms to the changing patterns of phenolic acids during the aging process of dried tangerine peel, but also reduces deviations caused by individual sample differences, thus improving the accuracy of tangerine peel age identification. Furthermore, the mathematical model described in this invention is unprecedented. In addition, the method for establishing the mathematical model described in this invention is simple, and the method for identifying the age of dried tangerine peel is also convenient and easy to operate.

[0012] This invention also proposes a method for establishing the mathematical model for identifying the age of tangerine peel, comprising the following steps: extracting free phenolic acids, esterified phenolic acids, and bound phenolic acids from tangerine peel of each year; then detecting the content of free phenolic acids, esterified phenolic acids, and bound phenolic acids in tangerine peel of each year; calculating the mass fraction of esterified phenolic acids in total phenolic acids in tangerine peel of each year; then fitting a polynomial regression curve with X as the abscissa and Y as the ordinate to obtain a regression equation and thus constructing a mathematical model, wherein X is the mass fraction of esterified phenolic acids in total phenolic acids in tangerine peel of each year, and Y is the year of tangerine peel.

[0013] The extraction methods for free phenolic acids, esterified phenolic acids, and bound phenolic acids from dried tangerine peel can employ conventional methods in the field, or the following methods can be used.

[0014] Preferably, the extraction steps for free phenolic acids from dried tangerine peel include: ultrasonically extracting dried tangerine peel with an ethanol-water solution to obtain a precipitate and a supernatant; removing the ethanol from the supernatant; adjusting the pH to 1.8-2.2 to obtain solution A; adding ethyl acetate to solution A for extraction; concentrating the ethyl acetate phase to dryness to obtain substance B; and dissolving substance B with a methanol-water solution to obtain the free phenolic acid test solution.

[0015] Preferably, the volume fraction of ethanol in the aqueous ethanol solution is 45-55%.

[0016] Preferably, the pH is adjusted using an inorganic acid; more preferably, hydrochloric acid is used to adjust the pH.

[0017] Preferably, the extraction steps for esterified phenolic acids from dried tangerine peel include: taking the aqueous phase remaining after ethyl acetate extraction in the free phenolic acid extraction step, removing the residual ethyl acetate in the aqueous phase, adding an alkaline substance and mixing to obtain solution C; carrying out an alkaline hydrolysis reaction in an inert gas atmosphere, then adjusting the pH to 1.8-2.2, adding ethyl acetate for extraction, taking the ethyl acetate phase and concentrating it to dryness to obtain substance D, and dissolving substance D in a methanol aqueous solution to obtain the esterified phenolic acid test solution.

[0018] Preferably, the concentration of the alkaline substance in solution C is 3.8-4.2 mol / L; preferably, the alkaline substance is an inorganic base, more preferably sodium hydroxide.

[0019] Preferably, the alkaline hydrolysis reaction is carried out at room temperature for 3.5-4.5 hours.

[0020] Preferably, the pH is adjusted using an inorganic acid; more preferably, hydrochloric acid is used to adjust the pH.

[0021] Preferably, the extraction step of bound phenolic acids in dried tangerine peel includes: taking the precipitate from the free phenolic acid extraction step, mixing it with an alkaline aqueous solution, carrying out an alkaline hydrolysis reaction in an inert gas atmosphere, then adjusting the pH to 1.8-2.2, and separating the solid and liquid to obtain solution E; adding ethyl acetate to solution E for extraction, concentrating the ethyl acetate phase to dryness to obtain substance F, and dissolving substance F with an aqueous methanol solution to obtain the bound phenolic acid test solution.

[0022] Preferably, the concentration of the alkaline aqueous solution is 3.8-4.2 mol / L; preferably, the alkaline substance is an inorganic base, and more preferably, sodium hydroxide.

[0023] Preferably, the alkaline hydrolysis reaction is carried out at room temperature for 3.5-4.5 hours.

[0024] Preferably, the pH is adjusted using an inorganic acid; more preferably, hydrochloric acid is used to adjust the pH.

[0025] When extracting free phenolic acids, esterified phenolic acids, and bound phenolic acids, the preferred weight-to-volume ratio of dried tangerine peel to methanol aqueous solution is 1 g: 20 mL; the preferred volume fraction of methanol in the methanol aqueous solution is 45-55%.

[0026] When extracting free phenolic acids, esterified phenolic acids, and bound phenolic acids, ultrasonic extraction and extraction should be performed at least once.

[0027] The inventors used the above extraction steps to extract free phenolic acids, esterified phenolic acids, and bound phenolic acids from the same dried tangerine peel, ensuring that the phenolic acids in each test solution are ultimately in a free state. This allows the phenolic acids to be accurately detected by ultraviolet or high-performance liquid chromatography, thereby improving the accuracy of the model.

[0028] Preferably, the contents of free phenolic acids, esterified phenolic acids, and bound phenolic acids in tangerine peel are detected by ultraviolet spectroscopy, high-performance liquid chromatography, or gas chromatography, and calculated by external standard method.

[0029] Preferably, gallic acid is used as the reference standard in the external standard method.

[0030] The specific steps of the preferred external standard method include: preparing reference solutions of different concentrations, detecting the absorbance of each reference solution using an ultraviolet spectrometer, plotting a standard curve, and obtaining a linear regression equation; then detecting the absorbance of the free phenolic acid test solution, the esterified phenolic acid test solution, and the bound phenolic acid test solution respectively, calculating the content of free phenolic acid, esterified phenolic acid, and bound phenolic acid in tangerine peel according to the linear regression equation, and then calculating the mass fraction of esterified phenolic acid in total phenolic acid in tangerine peel.

[0031] The formula for calculating the mass fraction of esterified phenolic acid in total phenolic acid is: Esterified phenolic acid content / (Free phenolic acid content + Esterified phenolic acid content + Bound phenolic acid content) × 100%.

[0032] This invention also proposes a method for identifying the age of dried tangerine peel, comprising the following steps: detecting the mass fraction of esterified phenolic acid in the total phenolic acid of the tangerine peel to be tested; and, based on the mathematical model for identifying the age of tangerine peel described above, substituting the detection result of the mass fraction of esterified phenolic acid in the total phenolic acid into the regression curve and regression equation to calculate the age of the tangerine peel to be tested.

[0033] Beneficial effects:

[0034] The inventors discovered through research that the content of esterified phenolic acids in dried tangerine peel increases with age. Therefore, the inventors proposed to establish a mathematical model using the mass fraction of esterified phenolic acids in total phenolic acids as the independent variable and the age of dried tangerine peel as the dependent variable, for the identification of the age of dried tangerine peel.

[0035] Using the mass fraction of esterified phenolic acids in total phenolic acids as the independent variable not only conforms to the changing patterns of phenolic acids during the aging process of dried tangerine peel, but also reduces deviations caused by individual sample differences, thus improving the accuracy of tangerine peel age identification. Furthermore, the mathematical model described in this invention is unprecedented. In addition, the method for establishing the mathematical model described in this invention is simple, and the method for identifying the age of dried tangerine peel is also convenient and easy to operate. Attached Figure Description

[0036] Figure 1 This is the linear standard curve of gallic acid in Example 4.

[0037] Figure 2 This is the fitted polynomial regression curve in Example 6. Detailed Implementation

[0038] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0039] The sample and reagent information used in the following examples is as follows:

[0040] The aged tangerine peels (1, 3, 5, 7, 10, 15, and 20 years) were purchased from Xinbaotang Tea Co., Ltd., Xinhui District, Jiangmen City, Guangdong Province. They are dried peels of Dahonggan (a type of tangerine). The tangerine peel samples were dried to constant weight in an oven at 40℃, pulverized using a tissue pulverizer, and passed through an 18-mesh sieve. The sieved particles were collected and set aside for later use.

[0041] Gallic acid (analytical grade) was purchased from Sinopharm Group; anhydrous ethanol, ethyl acetate, methanol, hydrochloric acid, sodium carbonate, etc. were all analytical grade.

[0042] The water used in the following examples is distilled water.

[0043] Example 1

[0044] Free phenolic acids were extracted from dried tangerine peel from different years. The extraction steps were as follows:

[0045] Accurately weigh 1.0g of dried tangerine peel granules and extract them three times with a 50% ethanol aqueous solution at 30℃ and 40KHz (each extraction using 20mL of ethanol aqueous solution, each extraction time being 1.0h, and each extraction centrifuged at 8000rpm for 10min). Combine the supernatants from the three extractions (dry the precipitate in a 50℃ oven for later use). Concentrate the supernatant at 50℃ using a vacuum rotary evaporator (RE-2000B, Gongyi Yuhua Instrument Co., Ltd.) to remove the ethanol. The volume of the concentrated supernatant should be approximately 30-40mL. Adjust the pH to 2.0 with a 6.0mol / L HCl aqueous solution to obtain solution A. Add ethyl acetate to solution A and extract three times (each extraction using the same volume of ethyl acetate as solution A). Combine the ethyl acetate phases from the three extractions and concentrate them to dryness using a vacuum rotary evaporator to obtain substance B. Dissolve substance B in 20mL of a 50% methanol aqueous solution to obtain the free phenolic acid test solution.

[0046] Example 2

[0047] Esterified phenolic acids were extracted from dried tangerine peel from different years. The extraction steps were as follows:

[0048] The aqueous phase remaining after ethyl acetate extraction in Example 1 was concentrated using a vacuum rotary evaporator to remove residual ethyl acetate. The volume was adjusted to 30-40 mL with water, and sodium hydroxide was added and mixed to obtain a solution C with a sodium hydroxide concentration of 4 mol / L. Nitrogen gas was then introduced to purge oxygen, and the reaction was carried out at room temperature for 4.0 h. The pH was then adjusted to 2.0 with a 6.0 mol / L HCl aqueous solution, and an equal volume of ethyl acetate was added for extraction three times. The ethyl acetate phases from the three extractions were combined and then concentrated under vacuum to dryness to obtain substance D. Substance D was dissolved in 20 mL of a 50% methanol aqueous solution to obtain the esterified phenolic acid test solution.

[0049] Example 3

[0050] Phenolic acids were extracted from dried tangerine peel from different years. The extraction steps were as follows:

[0051] Take the precipitate from the extraction step of Example 1, add a 4.0 mol / L sodium hydroxide aqueous solution and mix well (the ratio of precipitate to sodium hydroxide aqueous solution is 1 g: 10 mL), then purge with nitrogen to remove oxygen, react at room temperature for 4.0 h, adjust the pH to 2.0 with a 6.0 mol / L HCl aqueous solution, then centrifuge at 8000 rpm for 10 min and take the supernatant to obtain solution E; add an equal volume of ethyl acetate to solution E for extraction 3 times, combine the ethyl acetate phases from the 3 extractions, concentrate under vacuum to dryness to obtain substance F, dissolve substance F in 20 mL of 50% methanol aqueous solution to obtain the bound phenolic acid test solution.

[0052] Example 4

[0053] Plot the standard curve:

[0054] Gallic acid standard solutions with concentrations of 0.004, 0.008, 0.02, 0.032, 0.04, 0.048, and 0.06 mg / mL were prepared using a 50% methanol aqueous solution. Then, 0.5 mL of each gallic acid standard solution was mixed with 0.5 mL of 0.25 mol / L Folin-ciocalteu reagent, and the mixture was stirred using a turbine for 3 min. Next, 1.0 mL of a 10% sodium carbonate aqueous solution was added, and the mixture was allowed to stand at 25°C for 30 min. After centrifugation at 3500 rpm for 3 min, the supernatant was collected. Using a 15% sodium carbonate aqueous solution as a blank solution, the absorbance of each supernatant was measured at 760 nm using a UV-Vis spectrophotometer (L4, Shanghai Youke Instrument Co., Ltd.). A standard curve was plotted between absorbance and gallic acid concentration, yielding the linear regression equation: y = 26.942x + 0.0484 (R²). 2 =0.9961), where x is the gallic acid concentration and y is the absorbance; the standard curve is as follows: Figure 1 As shown.

[0055] Example 5

[0056] The mass fraction of esterified phenolic acids in total phenolic acids in dried tangerine peel from different years was determined:

[0057] The free phenolic acid test solutions, esterified phenolic acid test solutions, and bound phenolic acid test solutions of dried tangerine peel from various years obtained in Examples 1-3 were tested according to the following steps: 0.5 mL of the test solution was mixed with 0.5 mL of 0.25 mol / L Folin-ciocalteu reagent, and the mixture was stirred with a turbine for 3 min. Then, 1.0 mL of 10% sodium carbonate aqueous solution was added to each solution, and the mixture was allowed to stand at 25°C for 30 min. After centrifugation at 3500 rpm for 3 min, the supernatant was collected. Using 15% sodium carbonate aqueous solution as a blank solution, the absorbance of the supernatant was measured at 760 nm using a UV-Vis spectrophotometer (L4, Shanghai Youke Instrument Co., Ltd.). The absorbance was then used in a linear regression equation to calculate the phenolic acid concentration in each test solution (each sample was tested three times, and the average value was taken).

[0058] Then, the contents of free phenolic acid, esterified phenolic acid, and bound phenolic acid in tangerine peel from different years are calculated according to the formula (phenolic acid content = phenolic acid concentration in the test solution × volume of methanol aqueous solution / weight of tangerine peel = phenolic acid concentration in the test solution × 20 mL / 1 g, where the unit of phenolic acid concentration in the test solution is mg / mL).

[0059] The mass fraction of esterified phenolic acid in total phenolic acid was calculated according to the formula (esterified phenolic acid content / (free phenolic acid content + esterified phenolic acid content + bound phenolic acid content) × 100%).

[0060] Example 6

[0061] Establishing a mathematical model for identifying the age of dried tangerine peel includes the following steps:

[0062] Using the mass fraction of esterified phenolic acids in total phenolic acids in dried tangerine peel from each year, as measured in Example 5, as the independent variable X, and the corresponding year of dried tangerine peel as the dependent variable Y, a curve was plotted and a polynomial regression curve was fitted, yielding the regression equation: Y = 0.0488X. 2 -1.8964X+19.297(R 2 =0.999), thus constructing a mathematical model for identifying the age of dried tangerine peel, and fitting a polynomial regression curve as shown. Figure 2 As shown.

[0063] Example 7

[0064] Verify the accuracy of the mathematical model in Example 6.

[0065] Three-year-old and seven-year-old tangerine peels were taken, and free phenolic acid test solutions, esterified phenolic acid test solutions, and bound phenolic acid test solutions were extracted according to Examples 1-3, respectively. Then, according to Examples 4-5, the mass fraction of esterified phenolic acid in the total phenolic acid of tangerine peels of each year was detected. The mass fraction results were then substituted into the regression equation described in Example 6 to calculate the year of the tangerine peel. The results are shown in Table 1.

[0066] Table 1 Verification accuracy results

[0067]

[0068]

[0069] As can be seen from Table 1, the mathematical model for identifying the age of tangerine peel described in this invention can accurately determine the aging age of tangerine peel.

[0070] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for establishing a mathematical model for identifying the age of dried tangerine peel, characterized in that, The process includes the following steps: extracting free phenolic acids, esterified phenolic acids, and bound phenolic acids from tangerine peels of different years; then detecting the content of free phenolic acids, esterified phenolic acids, and bound phenolic acids in tangerine peels of different years; calculating the mass fraction of esterified phenolic acids in total phenolic acids in tangerine peels of different years; and then fitting a polynomial regression curve with X as the abscissa and Y as the ordinate to obtain the regression equation and thus construct a mathematical model, where X is the mass fraction of esterified phenolic acids in total phenolic acids in tangerine peels of different years, and Y is the year of tangerine peel. Total phenolic acids are the sum of free phenolic acids, esterified phenolic acids, and bound phenolic acids; The tangerine peel mentioned is the dried peel of the tangerine.

2. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 1, characterized in that, The extraction steps for free phenolic acids from dried tangerine peel include: ultrasonic extraction of dried tangerine peel with ethanol aqueous solution to obtain precipitate and supernatant; removal of ethanol from supernatant; adjustment of pH to 1.8-2.2 to obtain solution A; extraction with ethyl acetate; concentration of ethyl acetate phase to dryness to obtain substance B; and dissolution of substance B with methanol aqueous solution to obtain the test solution for free phenolic acids.

3. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 2, characterized in that, In an aqueous ethanol solution, the volume fraction of ethanol is 45-55%.

4. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 2, characterized in that, Adjust the pH using inorganic acids.

5. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 1, characterized in that, The extraction steps of esterified phenolic acids from dried tangerine peel include: taking the aqueous phase remaining after ethyl acetate extraction in the free phenolic acid extraction step, removing the residual ethyl acetate in the aqueous phase, adding an alkaline substance and mixing to obtain solution C; carrying out an alkaline hydrolysis reaction in an inert gas atmosphere, then adjusting the pH to 1.8-2.2, adding ethyl acetate for extraction, taking the ethyl acetate phase and concentrating it to dryness to obtain substance D, dissolving substance D in methanol aqueous solution to obtain the esterified phenolic acid test solution.

6. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 5, characterized in that, In solution C, the concentration of alkaline substances is 3.8-4.2 mol / L.

7. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 5, characterized in that, The alkaline hydrolysis reaction was carried out at room temperature for 3.5-4.5 hours.

8. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 5, characterized in that, Adjust the pH using inorganic acids.

9. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 1, characterized in that, The extraction steps for bound phenolic acids in dried tangerine peel include: taking the precipitate from the free phenolic acid extraction step, mixing it with an alkaline aqueous solution, carrying out an alkaline hydrolysis reaction in an inert gas atmosphere, then adjusting the pH to 1.8-2.2, and separating the solid and liquid to obtain solution E; adding ethyl acetate to solution E for extraction, concentrating the ethyl acetate phase to dryness to obtain substance F, and dissolving substance F in an aqueous methanol solution to obtain the bound phenolic acid test solution.

10. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 9, characterized in that, The concentration of the alkaline substance in the aqueous solution is 3.8-4.2 mol / L.

11. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 9, characterized in that, The alkaline hydrolysis reaction was carried out at room temperature for 3.5-4.5 hours.

12. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 9, characterized in that, Adjust the pH using inorganic acids.

13. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 1, characterized in that, The contents of free phenolic acids, esterified phenolic acids, and bound phenolic acids in tangerine peel were detected by ultraviolet spectroscopy, high performance liquid chromatography, or gas chromatography, and calculated by external standard method.

14. The method for establishing a mathematical model for identifying the age of dried tangerine peel according to claim 13, characterized in that, Gallic acid was used as the reference standard in the external standard method.

15. A method for identifying the age of dried tangerine peel, characterized in that, The method includes the following steps: detecting the mass fraction of esterified phenolic acid in total phenolic acid in the tangerine peel to be tested; using the mathematical model for identifying the age of tangerine peel established by the method described in any one of claims 1-14; and substituting the detection result of the mass fraction of esterified phenolic acid in total phenolic acid into the regression curve and regression equation to calculate the age of the tangerine peel to be tested.

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