A method for determining the ester content of baijiu (Chinese liquor) based on Fourier transform infrared transmission spectroscopy

Abstract

A method for determining the ester content of baijiu (Chinese liquor) based on Fourier transform infrared (FTIR) transmission spectroscopy involves collecting the infrared transmission spectra of volatile gases from ethanol-water solutions and ethyl acetate solutions, and then determining the true infrared spectrum of the calibrated sample within the range of 1735-1795 cm⁻¹. ‑1 The integral is applied, and the relationship between the integral area and the concentration change is fitted with a direct proportional function. Then, the infrared transmission spectrum of the volatile gas of the liquor sample to be tested is collected. The ester content in the liquor sample to be tested is calculated based on the integral area of ​​the infrared transmission spectrum. The ester content of the liquor sample to be tested is compared with the calculated national standard reference ester content to obtain the result. This invention has the advantages of good safety, high detection accuracy, simple calculation method, fast testing speed, low sample loss and low testing cost.

Description

Technical Field

[0001] This invention relates to the field of liquor testing technology, specifically to a method for testing the ester content of liquor based on Fourier transform infrared transmission spectroscopy. Background Technology

[0002] The ester content in baijiu (Chinese liquor) is a crucial quality standard. Currently, various methods have been proposed for testing ester content, such as gas chromatography, ultraviolet (UV) absorption spectroscopy, sensory tasting, and atomic force microscopy. Gas chromatography offers high separation efficiency and can simultaneously measure mixtures of multiple substances, but requires complex sample pretreatment and can take up to 40 minutes to test a single sample, resulting in relatively low efficiency. UV absorption spectroscopy involves collecting the UV absorption spectrum of the sample and utilizing the absorption peaks of total acids and esters at 210 nm and furfural at 277 nm for baijiu identification. Using only two points of spectral intensity for identification omits a large amount of spectral information, resulting in low detection accuracy and failing to achieve the goal of determining whether the total ester content in baijiu meets national standards. Sensory tasting involves professional tasters judging the quality of baijiu, but this method not only cannot quantify the results but also relies heavily on the taster's subjective judgment, making it highly susceptible to personal biases and resulting in poor repeatability. Atomic force microscopy can measure the microscopic particle morphology of baijiu, allowing for the differentiation of different aroma types by comparing microscopic particles. However, atomic force microscopy equipment is expensive, requires professional operation, and cannot detect the total ester content in baijiu.

[0003] Patent application number 201310034485.1 provides a method for infrared spectral correction and identification of baijiu (Chinese liquor) quality. The method involves testing the infrared spectra of both samples and baijiu samples. After each sample test, the data is saved, and the average of the sample spectra is used to obtain a standard spectrum. A nonlinear mapping is applied to the standard spectrum, and an optimization algorithm is used to obtain the weighting coefficients of the linear combination. The spectrum is then re-represented using the weighting coefficients and the nonlinear mapping to obtain the corrected spectrum. A baijiu quality identification model is established using partial least squares discriminant analysis and applied to identify unknown samples, outputting the identification results. However, this method requires a large number of baijiu samples, involves cumbersome sample pretreatment, and directly tests liquid baijiu samples, leading to sample deterioration and unusability, resulting in high testing costs. Furthermore, data processing relies on human judgment to compare characteristic peaks, leading to significant errors, and the method is time-consuming, failing to achieve rapid testing. Currently, there is no method for detecting ester content using volatile gases from baijiu. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention aims to provide a method for testing the ester content of baijiu (Chinese liquor) based on Fourier transform infrared transmission spectroscopy. This method involves collecting the infrared transmission spectra of volatile gases from ethanol-water solutions and ethyl acetate solutions, and then determining the true infrared spectrum of the calibrated sample within the range of 1735-1795 cm⁻¹. -1 The integral is applied, and the relationship between the integral area and the concentration change is fitted with a direct proportional function. Then, the infrared transmission spectrum of the volatile gas of the liquor sample to be tested is collected. The ester content in the liquor sample to be tested is calculated based on the integral area of ​​the infrared transmission spectrum. The ester content is compared with the calculated national standard reference ester content to obtain the result. This invention has the advantages of good safety, high detection accuracy, simple calculation method, fast testing speed, low sample loss and low testing cost.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for testing the ester content of baijiu (Chinese liquor) based on Fourier transform infrared transmission spectroscopy includes the following steps:

[0007] Step 1: Prepare an ethanol aqueous solution with a concentration of 30%-60%. Under room temperature conditions, drop the ethanol aqueous solution into the gas cell of the transmission Fourier transform infrared spectroscopy. Measure the Fourier transform infrared transmission spectrum of the volatile gas of the ethanol aqueous solution using a Fourier transform infrared spectrometer. Record the measured Fourier transform infrared transmission spectrum as the background spectrum.

[0008] Step 2: Prepare multiple portions of ethanol aqueous solution with the same concentration. Add ethyl acetate with a concentration range of 1-10 g / L to each of the multiple portions of ethanol aqueous solution with the same concentration to prepare multiple mixed solutions with different ethyl acetate concentrations. Using the same method as in Step 1, collect the Fourier transform infrared transmission spectra of the volatile gases from the mixed solutions of ethyl acetate with different concentrations.

[0009] Step 3: Subtract the background spectrum obtained in Step 1 from the Fourier transform infrared transmission spectra of the volatile gases from the mixed ethyl acetate solution of different concentrations collected in Step 2, and subtract the background spectrum obtained in Step 1 from the overall spectrum. -1 The intensity at that point is reduced to zero, thus obtaining the true infrared spectrum of the calibrated sample;

[0010] Step 4: Set the true infrared spectral intensity of the sample calibrated in Step 3 to 1735-1795 cm⁻¹. -1 Integrate within the range, and denote the integrated area as S. i ;

[0011] Step 5: Using the integral area S from Step 4... i The vertical axis represents the concentration of the different ethyl acetate mixtures in step 1, denoted as C. iUsing the x-axis as the abscissa, a direct proportional function is fitted according to the formula shown in equation (1) to obtain the constant a:

[0012] S i =a*C i (1)

[0013] Step 6: Using the same method as in Step 1, collect the Fourier transform infrared transmission spectrum of the volatile gases from the liquor sample to be tested. Subtract the background spectrum from the collected spectrum, and then subtract the value at 1795 cm⁻¹ from the obtained spectrum. -1 The intensity at that point is reduced to zero, thus obtaining the true infrared spectrum of the liquor sample to be tested;

[0014] Step 7: The true infrared spectral intensity of the liquor sample obtained in Step 6 is integrated within the range of 1735-1795 cm⁻¹ using the same integration method as in Step 4. -1 Integrate within the range, and denote the area of ​​integration as S. t ;

[0015] Step 8: Based on the constant 'a' obtained in Step 5 and S obtained in Step 7... t The ester content E1 in the liquor sample to be tested was calculated using equation (2):

[0016]

[0017] Wherein, the value 88.105 is the relative molecular mass of ethyl acetate, and the unit of E1 is mmol / L;

[0018] Step 9: Consult and obtain the required ester content (E) for a certain type of liquor according to national standards. s The ester content E2, which is the reference standard, is calculated using equation (3):

[0019]

[0020] Where E2 is in mmol / L, E s This refers to the ester content that a certain type of liquor should meet according to national standards, expressed in g / L.

[0021] Step 10: Compare the ester content E1 in the liquor sample to be tested with the calculated national standard reference ester content E2. If E1 ≥ E2, the ester content of the liquor sample to be tested meets the national standard. If E1 < E2, the ester content of the liquor sample to be tested does not meet the national standard.

[0022] The integral calculation method in step 4 is shown in equation (4):

[0023]

[0024] Among them, I i(v) represents the intensity of the spectrum at v.

[0025] In step 7, the true infrared spectrum of the liquor sample to be tested is between 1735-1795 cm⁻¹. -1 The integral calculation method within the range is the same as in step 4.

[0026] The gas cell used to measure transmission Fourier transform infrared spectra uses a window material made of calcium fluoride or potassium bromide.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. By collecting the Fourier transform infrared transmission spectrum of the volatile gases from the liquor sample to be tested, the damage to the total reflection crystal in the Fourier transform instrument caused by directly using liquid samples for detection can be effectively avoided. Therefore, this invention has the advantage of good safety.

[0029] 2. Because this invention converts the liquor to be tested from a liquid state to a gaseous state for measurement, it eliminates the complex matrix interference of liquid liquor, reduces intermolecular forces, improves spectral resolution, and thus improves the accuracy of testing.

[0030] 3. Because the calculation methods used in steps 8 and 9 of this invention are simple, the verification is faster.

[0031] 4. The method of the present invention does not require sample pretreatment and measures are performed by dripping a solution into it to allow it to evaporate, which reduces the loss of the sample to be tested and thus reduces the testing cost.

[0032] In summary, this invention, by measuring the volatile gases of the liquor sample to be tested, avoids damage to the Fourier transform analyzer, ensuring good safety. Furthermore, directly measuring the volatile gases eliminates interference from the complex matrix of liquid liquor and reduces intermolecular forces, resulting in high testing accuracy. The invention's calculation method is simple, thus accelerating the testing process. Moreover, this invention requires no sample pretreatment; by measuring the volatile gases through the addition of a solution, sample loss is reduced, thereby lowering testing costs. Attached Figure Description

[0033] Figure 1 This is a flowchart of the method of the present invention.

[0034] Figure 2 The six calibration samples in this embodiment of the invention are located at 1735-1795 cm⁻¹. -1 The true infrared spectrum within the range.

[0035] Figure 3 The graph shows the relationship between the ethyl acetate concentration and the integral area fitting function for the six calibrated samples in the embodiments of the present invention.

[0036] Figure 4 These are the true infrared spectra of 17 different brands and aroma types of baijiu samples tested in this embodiment of the invention.

[0037] Figure 5 This is a graph showing the test results of 17 different brands and aroma types of baijiu samples in this embodiment of the invention. Detailed Implementation

[0038] This invention provides an embodiment, such as Figure 1 As shown, a method for testing the ester content of baijiu (Chinese liquor) based on Fourier transform infrared transmission spectroscopy includes the following steps:

[0039] Step 1: Prepare 100 mL of 50% ethanol aqueous solution. At room temperature, drop the ethanol aqueous solution into the gas cell of the transmission Fourier transform infrared spectroscopy. Measure the Fourier transform infrared transmission spectrum of the volatile gas of the ethanol aqueous solution using a Fourier transform infrared spectrometer. Record the measured Fourier transform infrared transmission spectrum as the background spectrum.

[0040] Step 2: Prepare 6 100 mL 50% ethanol aqueous solutions, and add 6 different concentrations of ethyl acetate to them respectively: C1, 1 g / L, C2, 2 g / L, C3, 3 g / L, C4, 4 g / L, C5, 6 g / L and C6, 8 g / L, to prepare 6 mixed solutions of ethyl acetate with different concentrations. Then, using the same method as in Step 1, collect the Fourier transform infrared transmission spectra of the volatile gases from the mixed solutions of the above 6 ethyl acetates.

[0041] Step 3: Subtract the background spectrum obtained in Step 1 from the Fourier transform infrared transmission spectra of the volatile gases from the mixed ethyl acetate solution of different concentrations collected in Step 2, and subtract the background spectrum obtained in Step 1 from the overall spectrum. -1 The intensity at that point is reduced to zero, thus obtaining the true infrared spectrum of the calibrated sample;

[0042] Step 4: Set the true infrared spectral intensity of the calibration sample from Step 3 to 1735-1795 cm⁻¹. -1 Integrate within the range, and denote the integrated area as S. i ;

[0043] Step 5: Using the integral area S from Step 4... i The vertical axis represents the concentration of the different ethyl acetate mixtures in step 1, denoted as C. i Using the x-axis as the abscissa, a direct proportional function is fitted according to the formula shown in equation (1) to obtain the constant a:

[0044] S i =a*C i (1)

[0045] Step 6: Using the same method as in Step 1, collect the Fourier transform infrared transmission spectrum of the volatile gases from the liquor sample to be tested. Subtract the background spectrum from the collected spectrum, and then subtract the value at 1795 cm⁻¹ from the obtained spectrum. -1 The intensity at that point is reduced to zero, thus obtaining the true infrared spectrum of the liquor sample to be tested;

[0046] Step 7: The true infrared spectral intensity of the liquor sample obtained in Step 6 is integrated within the range of 1735-1795 cm⁻¹ using the same integration method as in Step 4. -1 Integrate within the range, and denote the area of ​​integration as S. t ;

[0047] Step 8: Based on the constant 'a' obtained in Step 5 and S obtained in Step 7... t The ester content E1 in the liquor sample to be tested was calculated using equation (2):

[0048]

[0049] Wherein, the value 88.105 is the relative molecular mass of ethyl acetate, and the unit of E1 is mmol / L;

[0050] Step 9: Consult and obtain the required ester content (E) for a certain type of liquor according to national standards. s The ester content E2, which is the reference standard, is calculated using equation (3):

[0051]

[0052] Where E2 is in mmol / L, E s This refers to the ester content that a certain type of liquor should meet according to national standards, expressed in g / L.

[0053] Step 10: Compare the ester content E1 in the liquor sample to be tested with the calculated national standard reference ester content E2. If E1 ≥ E2, the ester content of the liquor sample to be tested meets the national standard. If E1 < E2, the ester content of the liquor sample to be tested does not meet the national standard.

[0054] Furthermore, the gas cell window used for measuring transmission Fourier transform infrared spectroscopy is made of calcium fluoride or potassium bromide. In this embodiment, calcium fluoride is preferred as the gas cell window because this material is not easily deliquescent and has a transmission wavelength range of 1100-1800 cm⁻¹. -1 The transmittance is greater than 90% in the 1-9µm range.

[0055] Figure 2 The image shows ethanol-water solutions of ethyl acetate at six different concentrations at 1735-1795 cm⁻¹. -1The true infrared spectrum of the range shows that the spectral shapes of ethyl acetate-ethanol aqueous solutions of different concentrations are regular and uniform, basically only around 1758 cm⁻¹. -1 and 1770cm -1 Two absorption peaks are observed, corresponding to the absorption peaks of ester substances. The area of ​​the spectral peaks increases with the increase of ethyl acetate concentration. Therefore, it can be seen that this method can accurately measure the true infrared spectrum of ethyl acetate in ethanol aqueous solution. Compared with existing ester content detection technologies, this embodiment shows that by using the present invention to detect the ester content in ethanol aqueous solution, the detection accuracy can be guaranteed while reducing the loss of the test sample, thereby reducing the testing cost.

[0056] like Figure 3 As shown, the spectral density of the calibration sample is 1735-1795 cm⁻¹. -1 Using the integral area within the range as the ordinate and the ethyl acetate concentration as the abscissa, a fitting function was obtained for these six sets of data to derive the relationship between ethyl acetate concentration and integral area. The fitting function obtained after six sets of data is S. i =0.82*C i That is, the value of the constant a is 0.82.

[0057] like Figure 4 The figure shows the true infrared spectra of 17 different brands and aroma types of baijiu samples obtained according to the testing method described in this invention. As can be seen from the figure, the spectra of various brands and aroma types of baijiu are similar in shape to the spectra of ethyl acetate-ethanol aqueous solutions of different concentrations, and are basically only around 1758 cm⁻¹. -1 and 1770cm -1 Two absorption peaks, which correspond to the absorption peaks of esters in baijiu.

[0058] like Figure 5 The figure shows the results obtained by testing 17 different brands and aroma types of baijiu samples according to the testing method described in this invention. The results show that the method of this invention can accurately identify whether the ester content of the baijiu samples meets the national standards they are labeled with. The experimental results show that among the 17 baijiu samples tested, 12 have national standards labeled with their respective ester contents; 5 baijiu do not have national standards, of which 3 have low ester contents and are of poor quality. Therefore, the national standards for ester content labeled on the bottles of the 17 baijiu samples tested are consistent with the results obtained by the method provided in this invention. Compared with existing technologies, this embodiment demonstrates that the ester content detection of baijiu using this invention does not require pretreatment of the baijiu samples, can obtain test results more quickly, and the tested baijiu samples do not deteriorate and can be reused.

[0059] Furthermore, the same conclusion can be drawn by using 100 mL of ethanol aqueous solutions with concentrations of 30%, 45%, and 60% in steps one and two of the present invention as test examples.

Claims

1. A method for detecting the ester content of Baijiu based on Fourier infrared transmission spectrum, characterized in that, The method comprises the following steps: Step 1, an ethanol aqueous solution with a concentration of 30%-60% is configured, the ethanol aqueous solution is dropped into a transmission Fourier infrared gas cell under room temperature, a Fourier infrared transmission spectrum of the volatile gas of the ethanol aqueous solution is measured by a Fourier infrared spectrometer, and the measured Fourier infrared transmission spectrum is recorded as a background spectrum; Step 2, multiple portions of the same concentration of the ethanol aqueous solution are configured, ethyl acetate with a concentration range of 1-10 g / L is added into the multiple portions of the same concentration of the ethanol aqueous solution respectively, mixed solutions with different concentrations of ethyl acetate are configured, and Fourier infrared transmission spectra of volatile gases of the mixed solutions with different concentrations of ethyl acetate are collected by using the same manner as that in step 1; Step 3, subtract the background spectrum obtained in Step 1 from the Fourier infrared transmission spectrum of the volatile gas of the ethyl acetate mixed solution of different concentrations collected in Step 2, and subtract the intensity at 1795 cm -1 from the obtained spectrum as a whole, so that the relative intensity at this point is zero, to obtain the true infrared spectrum of the calibration sample; Step 4, the true infrared spectrum intensity of the calibration sample in step 3 is integrated in the range of 1735-1795 cm -1 , and the integral area is recorded as S i , respectively. Step 5, integral area S in step 4 i As the ordinate, the concentration of the different ethyl acetate mixed solutions in step 1 is denoted as C i As the abscissa, the constant a is obtained by a proportional function fitting according to the formula (1): S i = a * C i (I) Step 6, collect the Fourier infrared transmission spectrum of the volatile gas of the liquor sample to be tested in the same way as step 1, subtract the background spectrum from the collected spectrum, and subtract the intensity of the obtained spectrum at 1795 cm -1 to make the relative intensity at this point zero, to obtain the true infrared spectrum of the liquor sample to be tested; Step 7, the true infrared spectrum intensity of the liquor sample to be tested obtained in step 6 is integrated in the range of 1735-1795 cm -1 in the same way as in step 4, and the obtained integral area is recorded as S t ; Step 8, according to the constant a obtained in step 5 and S obtained in step 7 t The ester content E1 in the liquor sample to be tested is calculated by formula (2): Wherein, the numerical value 88.105 is the relative molecular mass of ethyl acetate, and the unit of E1 is mmol / L; Step 9, refer to the ester content E that a certain kind of liquor should reach in the national standard s and calculate the national standard control ester content E2 by formula (3): wherein E2 is in mmol / L, E s is the ester content that a certain Baijiu should reach in the national standard, in g / L; Step 10, the ester content E1 of the to-be-tested liquor sample is compared with the calculated national standard control ester content E2, if E1 is greater than or equal to E2, the ester content of the to-be-tested liquor sample meets the national standard, and if E1 is less than E2, the ester content of the to-be-tested liquor sample does not meet the national standard.

2. The method for detecting the ester content of Baijiu based on Fourier infrared transmission spectrum according to claim 1, characterized in that, The integral calculation mode in the step 4 is shown in the formula (4): where I i (v) represents the intensity of the spectrum at v.

3. The method for detecting the ester content of Baijiu based on Fourier infrared transmission spectrum according to claim 1, characterized in that, The integral calculation of the real infrared spectrum of the liquor sample to be tested in step 7 is the same as that in step 4 in the range of 1735-1795 cm -1 .

4. The method for detecting the ester content of Baijiu based on Fourier infrared transmission spectrum according to claim 1, characterized in that, The window sheet material used for the gas cell for measuring the transmission Fourier infrared spectrum is calcium fluoride or potassium bromide.

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