Extraction and accurate quantitative analysis method for real aroma profile of tea

Abstract

The invention belongs to the field of tea component analysis and detection, and particularly relates to a tea real aroma profile extraction and accurate quantitative analysis method which comprises the following steps: preparing tea soup of tea to be detected by adopting a tea sensory evaluation method; the method comprises the following steps: directly placing a twister stirring rod containing a PDMS (Polydimethylsiloxane) coating into tea soup which is being brewed, and extracting aroma components; after brewing is finished, TD-GC-MS is adopted to desorb and analyze the tea aroma extract, and the molecular structure and abundance composition of the aroma profile of the tea to be detected are identified; carrying out quantitative analysis on target aroma substances of the tea leaves by adopting an improved standard addition method; and adding the concentration obtained by simulation calculation into a tea blank matrix, comparing with the total ion chromatogram of the aroma components of the original tea sample, and finely adjusting, so as to obtain the accurate concentration of each target aroma substance. The method is convenient to operate and short in extraction time, the real aroma profile of the tea can be restored, and the accurate concentration of each aroma component can be obtained.

Description

Technical Field

[0001] The invention belongs to the field of tea component analysis and detection, and specifically relates to a method for extracting and accurately quantitatively analyzing the true aroma profile of tea. Background Art

[0002] Aroma is an important factor in measuring the quality and economic value of tea. High-grade tea often has pleasant aroma characteristics, such as the "light fragrance" and "chestnut fragrance" of green tea, and the "sweet fragrance" and "floral and fruity fragrance" of black tea, which are widely loved by consumers. Finding out the aroma profile composition of tea and the precise content of core aroma components can provide theoretical support for the selection and breeding of high-aroma tea varieties, the improvement of tea aroma quality and targeted regulation. However, tea contains hundreds of aroma components, and the content is generally low, even at trace levels. Therefore, the extraction and quantitative analysis of tea aroma components has always been the focus and difficulty in the field of food analysis and testing.

[0003] With the rapid development of analytical detection technologies, the extraction methods of tea aroma components are changing rapidly. Currently, the mainstream methods include headspace solid phase microextraction (HS-SPME), solvent-assisted flavor evaporation (SAFE), simultaneous distillation and extraction (SDE), stir-bar sorptive extraction (SBSE), etc. Due to many advantages such as large extraction capacity, simple operation, batch offline operation, no need for organic solvents, and direct adsorption extraction in water matrix, the SBSE method has gradually attracted the attention of researchers and has been widely recognized. The SBSE method is affected by many factors such as extraction temperature, extraction time, and material-liquid ratio. In order to extract as many tea aroma substances as possible, the previous research work optimized the above parameters, thus greatly improving the types and contents of analyzable tea aroma substances. However, the above parameters are completely different from the actual brewing methods of tea aroma. The current extraction methods generally use a 20 mL sealed headspace bottle, a tea-water ratio of about 1:1 - 1:10 (such as 1 g of tea powder and 10 mL of boiling water), constant temperature and long-time extraction (such as extraction at 70 ºC for 30 minutes), etc. The types, concentrations, aroma intensities, etc. of the aroma substances obtained under these conditions are all higher than those under the actual tea brewing conditions. Although it has great significance in theoretical research, it has a certain misleading effect on the evaluation of the contribution of tea aroma substances and the practical applications such as tea flavor recombination. GB / T 23776-2018 Tea Sensory Evaluation Method is currently the most widely used and authoritative standard for judging the overall sensory quality of tea in the field of tea science. However, in the current tea aroma research work, it is often only used as an important means to evaluate the overall sensory results of tea, or the tea soup after brewing by this method is extracted. There has been no relevant research report on directly and real-time enriching tea aroma components using SBSE technology when brewing tea.

[0004] On the other hand, in previous studies, the internal standard method or the external standard method was usually used for quantitative analysis of tea aroma substances. The internal standard substance of the former has a significant difference in abundance on the GC-MS chromatogram from many aroma substances to be measured, and the representativeness of the substance is relatively lacking; although the latter uses the standard substance of the corresponding substance, it is generally prepared with organic reagents, which is completely different from the nature of the aqueous solution medium of tea, and the matrix effect is not considered, and the obtained data is not very reliable; although the stable isotope labeling quantitative method (belonging to the internal standard method) that is more recognized internationally can avoid the matrix effect, it has a high cost. The price of the labeled standard substance is more than 10 times that of the unlabeled one, and the types of commercial standard substances are also less, which limits the wide application of this method; although the standard addition method (belonging to the external standard method) can also avoid the matrix effect, it is necessary to establish a standard curve for each sample, and the workload is huge, making it difficult to achieve quantitative analysis of batch tea samples. Combining the standard addition method with the traditional external standard method to prepare a blank matrix can largely avoid the above defects. However, due to the large number of trace substances in tea, there is a certain degree of competitive adsorption, and there are human errors in the operation of preparing the standard substance. Therefore, the obtained quantitative analysis results may not completely match the actual situation.

[0005] For the first time, the present invention can visually adjust the addition amount of a single target compound by comparing and adjusting with the GC-MS chromatographic peaks in the original tea sample, so as to obtain accurate quantitative analysis results, which have not been reported yet.

[0006] It can be seen that in view of the technical bottlenecks such as distorted aroma profiles, inaccurate quantitative analysis of tea aroma substances, or high costs in tea aroma analysis, there is an urgent need for an extraction method that can directly enrich the aroma substances generated during the brewing process of tea and an accurate, convenient, and economical quantitative analysis technology to achieve the extraction of the true aroma profile of tea and the precise quantitative analysis of target aroma substances. Summary of the Invention

[0007] Aiming at the problems existing in the prior art, the purpose of the present invention is to design and provide a technical solution for an extraction and precise quantitative analysis method of the true aroma profile of tea. The present invention uses the tea sensory evaluation method adopted by the national standard to brew the tea to be measured, and adopts the SBSE method for real-time adsorption extraction during the brewing stage. After the brewing is completed, the extract is analyzed and detected by TD-GC-MS to obtain the true aroma profile information of the tea; then, the standard addition method is combined with the external standard curve method to quantitatively analyze the target aroma substances, and the precise concentration of each target aroma substance is obtained by comparing and adjusting with the corresponding substance peaks of the original tea sample.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention provides an extraction and precise quantitative analysis method for the true aroma profile of tea, which includes the following steps: 1) Brewing of the tea leaves to be tested Prepare the tea soup of the tea leaves to be tested by using the method of tea sensory evaluation; 2) Real-time adsorption extraction of the aroma profile of the tea leaves to be tested Enrich the aroma components released during the brewing process of the tea leaves by using the stir bar sorptive extraction (SBSE) method, and stop the extraction immediately after the brewing is completed; 3) Detection and qualitative analysis of the aroma profile of the tea leaves to be tested After the brewing is completed, use the thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) technology to desorb and analyze the tea aroma extract, and identify the molecular structure and abundance composition of the aroma profile of the tea leaves to be tested; 4) Quantitative analysis of the target aroma substances of the tea leaves to be tested Use the improved standard addition method to quantitatively analyze the target aroma substances of the tea leaves; 5) Precise adjustment of the concentration of the target aroma substances of the tea leaves to be tested Add the concentration obtained by simulation calculation to the tea blank matrix, compare and fine-tune it with the total ion current chromatogram of the aroma components of the original tea sample, so as to obtain the accurate concentration of each target aroma substance.

[0009] Furthermore, the specific steps of step 1) are as follows: Use 3 g of uniformly mixed whole tea leaves, 150 mL of boiling water, and the brewing utensil is a 150-milliliter cylindrical evaluation cup. According to different tea categories, the brewing time is 4 minutes for green tea; 5 minutes for black tea, white tea, yellow tea, strip-shaped or curly oolong tea; 6 minutes for round-knotted, curly or granular oolong tea; except for dark tea, the number of brewing times is 1 time; for dark tea, the two-brewing method is adopted, the first brewing is 2 minutes, and the second brewing is 5 minutes.

[0010] Furthermore, the tool used in the stir bar sorptive extraction method in step 2) is a twister stir bar, the extraction coating is polydimethylsiloxane (PDMS), and the specifications are 10 mm in length × 1.0 mm in film thickness × 24 μL in volume; the specific operation of the stir bar sorptive extraction method is to put the twister stir bar during the brewing process of the tea leaves. After brewing at room temperature under natural conditions for 4-6 minutes, drain the tea water, take out the stir bar, rinse its surface with deionized water, wipe it with non-woven fabric until the surface is dry, and then put it into a special glass liner for thermal desorption for standby. Each sample is repeated in parallel 3 times.

[0011] Furthermore, the specific parameter conditions of the thermal desorption-gas chromatography-mass spectrometry technology in step 3) are as follows: Thermal desorption conditions: Solvent evacuation mode, initial temperature 40 °C, hold for 2 minutes, heat to 240 °C at a rate of 100 °C / min, hold for 4 minutes; The large volume injection port is cooled to -100 °C with liquid nitrogen, after equilibration for 1.0 min, heat to 280 °C at a rate of 12 °C / s, hold for 3.0 min; Gas chromatography conditions: Analyze the tea aroma extract using an HP-5MS or DB-5MS chromatographic column (30 m × 0.25 mm × 0.25 μm), the carrier gas is high-purity He (purity 99.999%), the flow rate is 1.6 mL / min, the column oven heating program: The initial temperature is 50 °C, hold for 2.0 minutes, then increase the temperature to 265 °C at a rate of 4.0 °C / min, hold for 5 minutes; Mass spectrometry conditions: Electron ionization: 70 eV; Transmission line temperature: 250 °C; Ion source temperature: 220 °C; Quadrupole temperature: 150 °C; Mass range: m / z 50 - 450 u; No solvent delay.

[0012] Furthermore, the improved standard addition method in step 4) is external standard curve quantification, using pre-deodorized tea as the blank matrix.

[0013] Furthermore, the preparation steps of the tea blank matrix are as follows: Weigh 500 g of the original tea sample, repeatedly brew it 3 - 5 times with 2500 mL of boiling water until there is no obvious aroma in the tea soup; Fully soak the tea residue with 1000 mL of anhydrous ethanol overnight, after removing the ethanol, use a rotary evaporator to remove the residual ethanol and aroma substances in the tea in batches (60 °C, 10 minutes each time, repeat 2 - 3 times); After the preliminarily dried residue is fully dried with a vacuum pump (2 hours) and an oven (60 °C, 3 days), detect its aroma components by GC-MS, and when the overall chromatographic peak S / N < 3, it is regarded as a qualified blank matrix except for the column bleed products.

[0014] Furthermore, the improved standard addition method in step 4) specifically involves adding target aroma substances with different gradient concentrations to the pre-prepared tea blank matrix, establishing the standard working curves of each target substance respectively, and then substituting the quantitative ion peak area data of each target substance detected in step 3) into the working curves to preliminarily calculate the concentration of the target substance in the tea soup.

[0015] Furthermore, backfill the calculated concentration of the target substance into the tea blank matrix, and after comparing with the corresponding peak area in the original tea sample and adjusting proportionally, when the peak area data of the target substance in the simulated sample and the original tea sample show no statistically significant difference P > 0.05, it is regarded as the adjustment completed, and the accurate concentration of the target aroma substance in the tea soup is obtained.

[0016] Furthermore, the linear correlation coefficient of the standard working curve must reach above 0.99.

[0017] The present invention has the following beneficial effects: 1) For the first time, direct extraction is realized under the true brewing conditions of tea. The specially designed evaluation cylindrical cup has exhaust holes, and the temperature during brewing is cooled under natural conditions. Therefore, the composition of the aroma substances obtained is close to the comprehensive odor information perceived by the human olfactory system, avoiding phenomena such as odor distortion and compound transformation and deterioration caused by condition control.

[0018] 2) The operation is simple, the extraction time is short, and the extraction time is only 4 - 7 min, which is lower than the 30 - 60 min required by the conventional method, significantly improving the work efficiency.

[0019] 3) SBSE can be batch - extracted without immediate injection. The samples can be stored on the stir bar for up to 7 days, and the intra - day and inter - day repeatabilities of the aroma substances in the samples are good, and the relative standard deviation is generally lower than 10%.

[0020] 3) The quantitative analysis method of the target aroma substances combines the technical advantages of the standard addition method and the external standard curve method, avoiding matrix effects and also improving the work efficiency of quantitative analysis. The tea blank matrix can be recycled repeatedly, avoiding a large amount of waste of tea samples.

[0021] 4) By comparing with the original tea sample, the addition amount of the target substance can be accurately adjusted, largely avoiding quantitative errors caused by multi - component competitive adsorption, human operation errors, etc. Precise quantitative analysis of trace and micro - amount aroma substances can be achieved without using expensive stable isotope standards, significantly reducing the technical cost.

[0022] 5) The SBSE method of the present invention can be directly extracted in water, without the need to use additional organic reagents during the extraction stage, avoiding environmental pollution and a large amount of waste of tea samples. Description of the Drawings

[0023] Figure 1 It is a comparison of the total ion current chromatograms of the SBSE method for tea sensory evaluation brewing and the conventional SBSE method; Figure 2 It is a comparison of the inter - day repeatability of the total ion current chromatograms of the SBSE method for tea sensory evaluation brewing; Figure 3 It is a comparison of the total ion current chromatograms of the simulated tea sample and the original tea sample; Figure 4 It is a superposition diagram of the quantitative ion peaks of geraniol in the simulated tea sample and the original tea sample; Figure 5 It is a superposition diagram of the quantitative ion peaks of the target aroma substances in the simulated tea sample and the original tea sample. Detailed Embodiments

[0024] The present invention will be further explained below in conjunction with the examples and drawings. This example is only used to specifically illustrate the method, and is not intended to limit the scope of the present invention. Any changes or improvements made according to the teachings of the present invention fall within the protection scope of the present invention.

[0025] In this application, the brewing of the tea to be tested adopts the national standard GB / T 23776-2018 tea sensory evaluation method, which is as follows: 3 g of uniformly mixed whole tea leaves, 150 mL of boiling water, and the brewing utensil is a 150 mL cylindrical evaluation cup; depending on the type of tea, the brewing time is 4 minutes (green tea), 5 minutes (black tea, white tea, yellow tea, strip or curled oolong tea), and 6 minutes (round, fist or granular oolong tea); except for black tea, the brewing times are all 1 time. Black tea adopts a two-time brewing method, with the first brewing time of 2 minutes and the second brewing time of 5 minutes.

[0026] In the present invention, the stir bars adsorption extraction (SBSE) method is used for the real-time adsorption extraction of the aroma profile of the tea to be tested. The extraction tool is a twister stirring bar, and the extraction coating is a PDMS material with a specification of 10 mm (length) × 1.0 mm (film thickness) × 24 μL (capacity). The specific operation steps of SBSE are: weigh 3 g of uniformly mixed tea leaves into a special 150 mL cylindrical evaluation cup, pour 150 mL of boiling water into the cup, and quickly put in a twister stirring bar (10 mm × 1.0 mm × 24 μL) with a PDMS coating, cover the cup, and brew at room temperature for 4-6 minutes. After that, drain the tea water, take out the stirring bar, and rinse its surface with deionized water. After wiping the surface with non-woven fabric until it is dry, put it in a special glass liner for thermal desorption for standby use. Each sample is repeated 3 times in parallel.

[0027] In the present invention, for the detection and qualitative analysis of the aroma profile of the tea to be tested, TD-GC-MS technology is used to desorb and detect the composition of the tea aroma extract, and the NIST 2020 spectral library is used to preliminarily match 10 candidate compounds. The compounds with a mass spectral similarity of 75% between the compounds and the library are retained, and exogenous volatile substances such as column bleed and plasticizers are deleted; by comparing with the retention index reported in the NIST spectral library, compounds with a difference of more than ±25 from the reported value are deleted; the self-built tea aroma substance library is used to accurately verify the chemical structure of the remaining compounds; the composition and abundance distribution of the tea aroma profile are obtained.

[0028] In the present invention, the improved standard addition method is external standard curve quantification, with the pre-deodorized tea as the blank matrix. The preparation steps of the tea blank matrix are as follows: Weigh 500 g of the original tea sample, and repeatedly steep it with 2500 mL of boiling water for 3 - 5 times until there is no obvious aroma in the tea soup; soak the tea dregs thoroughly with 1000 mL of absolute ethanol overnight. After removing the ethanol, use a rotary evaporator to remove the residual ethanol and aroma substances in the tea in batches (60 °C, 10 minutes each time, repeat 2 - 3 times); after the preliminarily dried residue is fully dried with a vacuum pump (2 hours) and an oven (60 °C, 3 days), detect its aroma components by GC-MS. When the overall chromatographic peak S / N < 3, it is regarded as a qualified blank matrix except for the column bleed products.

[0029] The improved standard addition method specifically involves adding target aroma substances with different gradient concentrations into the pre-prepared tea blank matrix, respectively establishing standard working curves for each target substance, and then substituting the quantitative ion peak area data of each detected target substance into the working curve to preliminarily calculate the concentration of the target substance in the tea soup; backfill the calculated concentration of the target substance into the tea blank matrix, and adjust it proportionally after comparing with the corresponding peak area in the original tea sample. When the peak area data of the target substance in the simulated sample and the original tea sample have no statistical difference P > 0.05, it is regarded as the adjustment completed, and the accurate concentration of the target aroma substance in the tea soup is obtained; the linear correlation coefficient of the standard working curve must reach above 0.99.

[0030] Example: Extraction of the true aroma profile of white tea and quantitative analysis of important aroma substances (1) Weigh 3 g of the evenly mixed 2017 Shoumei sample into a 150 mL cylindrical evaluation cup. After injecting 150 mL of boiling water into the cup, quickly put in a twister stir bar with a PDMS coating, cover the cup lid, extract at room temperature for 5 minutes, then drain the tea soup, take out the stir bar, rinse its surface with deionized water, wipe it with a non-woven fabric until it is in a dry surface state, and then put it into a special glass liner for thermal desorption for standby. Each sample is repeated in parallel 3 times.

[0031] (2)The obtained aroma extract was detected and analyzed by TD-GC-MS. TD conditions: solvent venting mode, initial temperature 40 °C, held for 2 minutes, heated to 240 °C at a rate of 100 °C / min, and held for 4 minutes. The large-volume injection port was cooled to -100 °C with liquid nitrogen. After equilibration for 1.0 min, it was heated to 280 °C at a rate of 12 °C / s and held for 3.0 min. GC conditions: HP-5MS chromatographic column (30 m × 0.25 mm × 0.25 μm), carrier gas was high-purity He (purity 99.999%), flow rate was 1.6 mL / min, column oven heating program: initial temperature was 50 °C, held for 2.0 minutes, then the temperature was increased to 265 °C at a rate of 4.0 °C / min and held for 5 minutes. MS conditions: electron ionization: 70 eV; transmission line temperature: 250 °C; ion source temperature: 220 °C; quadrupole temperature: 150 °C; mass range: m / z 50 - 450 u; no solvent delay.

[0032] Using this method, approximately 500 chromatographic peaks were initially identified, and the peak response was significantly lower than that of the aroma substances extracted by the traditional SBSE method ( Figure 1 ), but the day-to-day repeatability of the samples was good, almost completely overlapping, and the relative standard deviation of most chromatographic peaks was less than 10% ( Figure 2 ). After similarity ranking in the NIST2020 spectral library, deletion of exogenous volatile substances such as column bleed and plasticizers, retention index verification, and standard substance verification, a total of 108 volatile components were identified. According to their chemical structures, they could be divided into 10 categories: esters, alcohols, alkenes, ketones, aldehydes, acids, oxacycles, nitrogen-containing compounds, aromatic compounds, lactones, etc.; in terms of quantity distribution, alcohols were the most, followed by ketones and aldehydes, and nitrogen-containing compounds were the least. The specific aroma substance composition and quantitative ion peak areas are shown in Table 1(a) - Table 1(d).

[0033] Table 1(a) Aroma components of Shoumei tea identified by sensory evaluation extraction and infusion SBSE method

[0034] [1] Calculated value of retention index; [2] Reported value of retention index in the NIST2020 spectral library. Table 1(b) Aroma components of Shoumei tea identified by sensory evaluation extraction and infusion SBSE method

[0035] [1] Calculated value of retention index; [2] Reported value of retention index in the NIST2020 spectral library. Table 1 (c) Aroma components of Shoumei tea identified by sensory evaluation extraction and SBSE method

[0036] [1] Calculated retention index value; [2] Reported retention index value in NIST2020 spectral library. Table 1 (d) Aroma components of Shoumei tea identified by sensory evaluation extraction and SBSE method

[0037] [1] Calculated retention index value; [2] Reported retention index value in NIST2020 spectral library. (3) Precise quantitative analysis was carried out on 10 common and high-content aroma compounds in Shoumei tea, including geraniol, linalool, phenethyl alcohol, benzaldehyde, dihydroactinidiolide, limonene, nonanoic acid, 2-methylbutyraldehyde, 3-methylbutyraldehyde, and γ-nonalactone. The improved standard addition method was used to quantitatively analyze the target aroma substances. The target aroma substances with 15 different gradient concentrations were added to the pre-prepared tea blank matrix, and the standard working curves of each target substance were established respectively. The qualitative parameters, quantitative ions, linear equations, linear correlation coefficients of each substance, and the calculated concentrations of each target substance in Shoumei tea are shown in Table 2.

[0038] Table 2 Qualitative and quantitative parameters and concentration distribution of common aroma substances in Shoumei tea

[0039] [1] The bolded numbers are the quantitative ions of the target aroma substances; [2] This concentration is the concentration of each substance in 3 g of Shoumei tea and 150 mL of water. (4) Next, the above compounds were added to 3 g of Shoumei tea blank matrix according to the calculated concentration, and the corresponding substances were extracted by sensory evaluation extraction and SBSE method, and analyzed by the TD-GC-MS method in step 2. At the same time, the original tea sample was used as a control, and the above aroma substances were extracted and analyzed in the same way. Each sample was repeated in parallel 3 times. Process the GC-MS data, extract the quantitative ions of each target compound, and compare the difference multiples of the corresponding peaks in the original tea sample and the simulated tea sample: If there is no significant difference (P>0.05), no adjustment is required; if there is a significant difference, after corresponding adjustment according to the average multiple in the original tea sample, repeat the above experiment until there is no significant difference ( Figure 3); Finally, the exact concentrations of the above 10 aroma substances in the tea soup of Shoumei tea were obtained, and the adjustment situations of each substance are shown in Table 3. There was no significant difference in the peak areas of geraniol and nonanoic acid between the simulated tea sample and the original tea sample, so no adjustment was made ( Figure 4 ); Although there were certain differences in other compounds, the overall reproducibility was good, and the adjustment multiples were between 0.88 and 2.46 ( Figure 5 ). After adding the above-adjusted substances to the blank matrix again, there was no significant difference in their peak areas between the simulated tea sample and the original tea sample, and it was regarded as the adjustment being completed. Through the above steps, the true aroma profile of Shoumei tea in 2017 was extracted, and the precise quantification of 10 important aroma substances was achieved (for the sake of example, only 10 are mentioned due to space limitations, and the precise quantification of all aroma substances can be achieved).

[0040] Table 3 Concentration adjustment situations of 10 target aroma substances in Shoumei tea

[0041] [1] Difference multiple: Quantitative ion peak of the target substance in the original tea sample / Quantitative ion peak of the target substance in the simulated sample. In summary, the present invention first realized the efficient enrichment of aroma components in the tea evaluation brewing stage by using SBSE combined with TD-GC-MS technology, extracted the true aroma profile of tea, and the extraction process only takes 4 - 7 minutes to complete, and the operation is simple, without the need for organic solvents, and is environmentally friendly. Subsequently, the quantitative analysis of target aroma substances in tea was achieved by combining the external standard method with the standard addition method, and the exact concentrations of target aroma substances in tea were calculated for the first time by directly comparing with the original tea sample. The above method provides a reliable technical guarantee for the scientific evaluation and diversified utilization of tea aroma quality, and lays a theoretical foundation for the breeding of high-aroma tea tree varieties and the improvement and directional regulation of tea aroma quality. The linear equations and concentration adjustment parameters mentioned in this embodiment are only applicable to the samples used in the embodiment. If there is quantitative analysis of aroma substances in other tea categories, plants, foods and other similar fields, the idea is basically the same as that of the present invention, and the detection and analysis can be carried out with reference to the extraction method and quantitative idea in the present invention. When the functions generated do not exceed the scope of the technical solution of the present invention, they all belong to the protection scope of the present invention.

Claims

1. A method for extracting and precisely quantitatively analyzing the true aroma profile of tea leaves, characterized in that, It includes the following steps: 1) Brewing of the tea leaves to be tested Prepare the tea soup of the tea leaves to be tested by using the tea sensory evaluation method; 2) Real-time adsorption extraction of the aroma profile of the tea leaves to be tested Enrich the aroma components released during the brewing process of the tea leaves by using the stir bar sorptive extraction method, and stop the extraction immediately after the brewing ends; 3) Detection and qualitative analysis of the aroma profile of the tea leaves to be tested After the brewing ends, use the thermal desorption-gas chromatography-mass spectrometry coupling technology to desorb and analyze the tea aroma extract, and identify the molecular structure and abundance composition of the aroma profile of the tea leaves to be tested; 4) Quantitative analysis of the target aroma substances of the tea leaves to be tested Use the improved standard addition method to quantitatively analyze the target aroma substances of the tea leaves; 5) Precise adjustment of the concentration of the target aroma substances of the tea leaves to be tested Add the concentration obtained by simulation calculation to the tea blank matrix, compare it with the total ion current chromatogram of the aroma components of the original tea sample, and make fine adjustments to obtain the precise concentration of each target aroma substance.

2. The method for extracting and precisely quantitatively analyzing the true aroma profile of tea according to claim 1, characterized in that, The specific content of step 1) is as follows: Use 3 g of uniformly mixed whole tea leaves, 150 mL of boiling water, and the brewing utensil is a 150-milliliter cylindrical evaluation cup. According to different tea categories, the brewing time is 4 minutes for green tea; 5 minutes for black tea, white tea, yellow tea, strip-shaped or curly oolong tea; 6 minutes for round-knotted, curly or granular oolong tea; except for dark tea, the number of brewing times is 1 time; for dark tea, the two-time brewing method is adopted, the first brewing is 2 minutes, and the second brewing is 5 minutes.

3. The method for extracting and precisely quantitatively analyzing the true aroma profile of tea according to claim 1, characterized in that The tool used in the stir bar sorptive extraction method in step 2) is a twister stir bar, the extraction coating is polydimethylsiloxane, and the specifications are 10 mm in length × 1.0 mm in film thickness × 24 μL in volume; the stir bar sorptive extraction method is specifically to put the twister stir bar during the tea brewing process. After brewing at room temperature under natural conditions for 4 - 6 minutes, drain the tea water, take out the stir bar, rinse its surface with deionized water, wipe it with a non-woven fabric until the surface is in a dry state, and then put it into a special glass liner for thermal desorption for standby. Each sample is repeated in parallel 3 times.

4. The method for extracting and precisely quantitatively analyzing the true aroma profile of tea leaves according to claim 1, wherein, The specific parameter conditions of the thermal desorption-gas chromatography-mass spectrometry coupling technology in step 3) are as follows: Thermal desorption conditions: Solvent evacuation mode, initial temperature 40 °C, hold for 2 minutes, heat to 240 °C at a rate of 100 °C / min, and hold for 4 minutes; the large volume injection port is cooled to -100 °C with liquid nitrogen, after equilibration for 1.0 min, heat to 280 °C at a rate of 12 °C / s, and hold for 3.0 min; Gas chromatography conditions: Use an HP-5MS or DB-5MS chromatographic column to analyze the tea aroma extract, the carrier gas is high-purity He, the flow rate is 1.6 mL / min, and the column oven heating program: the initial temperature is 50 °C, hold for 2.0 minutes, then increase the temperature to 265 °C at a rate of 4.0 °C / min, and hold for 5 minutes; Mass spectrometry conditions: Electron ionization: 70 eV; Transmission line temperature: 250 °C; Ion source temperature: 220 °C; Quadrupole temperature: 150 °C; Mass range: m / z 50 - 450 u; No solvent delay.

5. The method for extracting and precisely quantitatively analyzing the true aroma profile of tea according to claim 1, wherein The improved standard addition method in step 4) is quantitative analysis using an external standard curve, with the pre-deodorized tea as the blank matrix.

6. The method for extracting and accurately quantitatively analyzing the true aroma profile of tea according to claim 5, characterized in that, The preparation steps of the tea blank matrix are as follows: Weigh 500 g of the original tea sample and repeatedly steep it 3 - 5 times with 2500 mL of boiling water until the tea soup has no obvious aroma; soak the tea dregs thoroughly with 1000 mL of absolute ethanol overnight. After removing the ethanol, use a rotary evaporator to remove the residual ethanol and aroma substances in the tea in batches; after the preliminarily dried residue is fully dried with a vacuum pump and an oven respectively, use GC-MS to detect its aroma components. When the overall chromatographic peak S / N < 3, it is regarded as a qualified blank matrix except for column bleed products.

7. A method for extracting and precisely quantitatively analyzing the true aroma profile of tea leaves according to claim 5 or 6, characterized in that, Specifically, the improved standard addition method in step 4) is to add target aroma substances with different gradient concentrations to the pre-prepared tea blank matrix, establish the standard working curves of each target substance respectively, and then substitute the quantitative ion peak area data of each target substance detected in step 3) into the working curves to preliminarily calculate the concentration of the target substance in the tea soup.

8. The method for extracting and precisely quantitatively analyzing the true aroma profile of tea according to claim 7, characterized in that, Backfill the calculated concentration of the target substance into the tea blank matrix, and adjust it proportionally by comparing with the corresponding peak area in the original tea sample. When the peak area data of the target substance in the simulated sample and the original tea sample show no statistical difference (P > 0.05), it is regarded as the adjustment completed, and the accurate concentration of the target aroma substance in the tea soup is obtained.

9. The method for extracting and precisely quantitatively analyzing the true aroma profile of tea leaves according to claim 7, characterized in that, The linear correlation coefficient of the standard working curve must reach above 0.99.

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