A method for extracting and accurately quantifying the true aroma profile of tea

Abstract

The present invention belongs to the field of tea component analysis and detection, and specifically relates to a method for extracting and accurately quantifying the true aroma profile of tea leaves, comprising: preparing a tea soup of tea to be tested using a tea sensory evaluation method; placing a twister stirring rod containing a PDMS coating directly in the brewing tea soup to extract the aroma components; after brewing, desorbing and analyzing the tea aroma extract using TD-GC-MS to identify the molecular structure and abundance composition of the aroma profile of the tea to be tested; quantitatively analyzing the target aroma substances in the tea leaves using an improved standard addition method; and adding the concentrations calculated by simulation to a blank tea matrix, comparing and fine-tuning the total ion current diagram of the aroma components of the original tea sample, thereby obtaining the precise concentrations of each target aroma substance. This method is easy to operate, has a short extraction time, can restore the true aroma profile of tea leaves, and obtain the precise concentrations of each aroma component.

Description

Technical Field

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

[0002] Aroma is a crucial factor in measuring tea quality and its economic value. High-grade teas often possess pleasing aroma characteristics, such as the "light fragrance" and "chestnut aroma" of green tea and the "sweet fragrance" and "floral and fruity aroma" of black tea, making them widely popular among consumers. Identifying the aroma profile of tea and the precise content of core aroma components provides theoretical support for the selection and breeding of high-fragrant tea varieties, as well as for improving and regulating tea aroma quality. However, tea contains hundreds of aroma components, and their contents are generally low, even at trace levels. Therefore, the extraction and quantitative analysis of tea aroma components has always been a key and challenging issue in food analysis and testing.

[0003] With the rapid advancement of analytical and detection technologies, methods for extracting tea aroma components are evolving rapidly. Currently, mainstream methods include headspace solid phase microextraction (HS-SPME), solvent-assisted flavor evaporation (SAFE), simultaneous distillation and extraction (SDE), and stir-bar sorptive extraction (SBSE). SBSE has gradually attracted the attention of researchers and gained widespread recognition due to its advantages, including large extraction capacity, ease of operation, batch offline operation, the absence of organic solvents, and direct sorptive extraction in an aqueous matrix. SBSE is influenced by numerous factors, including extraction temperature, extraction time, and material-to-liquid ratio. To maximize the extraction of tea aroma compounds, previous research has optimized these parameters, significantly increasing the variety and content of tea aroma compounds that can be analyzed. However, these parameters are completely different from the actual tea aroma brewing method. Current extraction methods generally use 20 mL sealed headspace vials, a tea-to-water ratio of approximately 1:1-1:10 (e.g., 1 g tea powder to 10 mL boiling water), and a constant temperature and prolonged extraction time (e.g., 70°C for 30 minutes). The variety, concentration, and aroma intensity of aroma compounds obtained under these conditions are higher than those obtained under actual tea brewing conditions. While of great theoretical significance, these methods are somewhat misleading in practical applications such as evaluating the contribution of tea aroma compounds and reconstructing tea flavors. The GB / T 23776-2018 tea sensory evaluation method is currently the most widely used and authoritative standard for determining the overall sensory quality of tea in the field of tea science. However, in current tea aroma research, it is often used only as a key tool for evaluating the overall sensory results of tea, or for extracting the tea infusion after brewing using this method. No studies have yet reported on the direct, real-time enrichment of tea aroma components using SBSE technology during tea brewing.

[0004] On the other hand, previous studies usually use internal standard method or external standard method to quantitatively analyze tea aroma substances. The abundance of internal standard substances in the former on the GC-MS chromatogram is significantly different from that of the many aroma substances to be tested, and the substances are relatively lacking in representativeness; although the latter uses standard substances of the corresponding substances, they are generally prepared with organic reagents, which are completely different from the aqueous medium properties of tea. The matrix effect is not taken into account, and the data obtained are not very reliable; the currently internationally recognized stable isotope labeling quantification method (internal standard method) can avoid matrix effects, but the cost is high. The price of labeled standards is more than 10 times that of unlabeled standards, and there are fewer types of commercial standards, which limits the widespread application of this method; although the standard addition method (external standard method) can also avoid matrix effects, it requires the establishment of a standard curve for each sample, which is a huge workload and makes 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 avoid the above-mentioned defects to a large extent. However, due to the large number of trace substances contained in tea, there is a certain degree of competitive adsorption, and there are human errors in the preparation of standard samples. Therefore, the quantitative analysis results obtained may not be completely consistent with the actual situation.

[0005] The present invention is the first to intuitively adjust the addition amount of a single target compound by adjusting and comparing with the GC-MS chromatographic peaks in the original tea sample, thereby obtaining accurate quantitative analysis results, which has not been reported yet.

[0006] It can be seen that, given the technical bottlenecks in tea aroma analysis such as aroma profile distortion, inaccurate quantitative analysis of tea aroma substances or high cost, there is an urgent need for an extraction method that can directly enrich the aroma substances produced during the tea brewing process 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] In response to the problems existing in the prior art, the present invention aims to provide a technical solution for extracting and accurately quantifying the true aroma profile of tea. This method uses the tea sensory evaluation method adopted by the national standard to brew the tea to be tested. During the brewing process, the SBSE method is used for real-time adsorption extraction. After brewing, the extract is analyzed by TD-GC-MS to obtain the true aroma profile of the tea. The target aroma compounds are then quantitatively analyzed using the standard addition method combined with the external standard curve method. The precise concentration of each target aroma compound is then determined by comparing and adjusting the corresponding compound peaks with those of the original tea sample.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for extracting and accurately quantitatively analyzing the true aroma profile of tea leaves, which comprises the following steps:

[0010] 1) Brewing of the tea to be tested

[0011] Prepare tea soup of the tea to be tested using the tea sensory evaluation method;

[0012] 2) Real-time adsorption extraction of the aroma profile of the tea leaves to be tested

[0013] Stir bar sorptive extraction (SBSE) was used to enrich the aroma components released during the tea brewing process, and the extraction was stopped immediately after the brewing process was completed.

[0014] 3) Detection and qualitative analysis of the aroma profile of the tea to be tested

[0015] After brewing, the tea aroma extract is desorbed and analyzed using thermal desorption-gaschromatography-mass spectrometry (TD-GC-MS) to identify the molecular structure and abundance composition of the aroma profile of the tea.

[0016] 4) Quantitative analysis of target aroma substances in tea leaves

[0017] The improved standard addition method was used to quantitatively analyze the target aroma compounds in tea.

[0018] 5) Accurate adjustment of the concentration of target aroma substances in the tea to be tested

[0019] The concentration obtained by simulation calculation is added to the blank tea matrix, compared with the total ion current diagram of the aroma components of the original tea sample, and fine-tuned to obtain the precise concentration of each target aroma substance.

[0020] Furthermore, the step 1) is specifically as follows: 3 g of uniformly mixed whole tea leaves and 150 mL of boiling water are used, and the brewing utensil is a 150 mL cylindrical evaluation cup. Depending on the type of tea, the brewing time is 4 minutes for green tea; 5 minutes for black tea, white tea, yellow tea, strip-shaped or curled oolong tea; and 6 minutes for round-shaped, fist-shaped or granular oolong tea. Except for black tea, the brewing time is once; black tea adopts a two-time brewing method, with the first brewing time being 2 minutes and the second brewing time being 5 minutes.

[0021] Furthermore, the tool used in the step 2) stirring rod adsorption extraction method is a twister stirring rod, and the extraction coating is polydimethylsiloxane (PDMS), with specifications of 10 mm length × 1.0 mm film thickness × 24 μL capacity; the stirring rod adsorption extraction method specifically includes placing a twister stirring rod during the tea brewing process, brewing for 4-6 minutes under natural conditions at room temperature, draining the tea, taking out the stirring rod, and rinsing its surface with deionized water. After wiping it with non-woven fabric until the surface is dry, it is placed in a special glass liner tube for thermal desorption for standby use, and each sample is repeated in parallel 3 times.

[0022] Furthermore, the specific parameter conditions of the thermal desorption-gas chromatography-mass spectrometry technology in step 3) are:

[0023] Thermal desorption conditions: solvent evacuation mode, initial temperature 40 °C, hold for 2 min, heat to 240 °C at a rate of 100 °C / min, hold for 4 min; large volume inlet cooled to -100 °C with liquid nitrogen, equilibrated for 1.0 min, then heated to 280 °C at a rate of 12 °C / s, hold for 3.0 min;

[0024] Gas chromatography conditions: Tea aroma extracts were analyzed using an HP-5MS or DB-5MS column (30 m × 0.25 mm × 0.25 μm). The carrier gas was high-purity He (99.999%) at a flow rate of 1.6 mL / min. The column oven heating program was as follows: initial temperature at 50°C for 2.0 min, then increased to 265°C at a rate of 4.0°C / min and held for 5 min.

[0025] 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.

[0026] Furthermore, the improved standard addition method in step 4) is an external standard curve quantification method, with pre-deodorized tea leaves as a blank matrix.

[0027] Furthermore, the preparation steps of the tea blank matrix are as follows: weigh 500 g of original tea sample, repeatedly brew it with 2500 mL of boiling water for 3-5 times until the tea soup has no obvious aroma; fully soak the tea residue in 1000 mL of anhydrous ethanol overnight, and after removing the ethanol, remove the residual ethanol and aroma substances in the tea leaves in batches using a rotary evaporator (60 ºC, 10 minutes each time, repeated 2-3 times); the initially dried residue is fully dried using a vacuum pump (2 hours) and an oven (60 ºC, 3 days), and its aroma components are detected by GC-MS. The overall chromatographic peak S / N is <3, excluding column bleed products, and is considered to be a qualified blank matrix.

[0028] Furthermore, the improved standard addition method in step 4) specifically adds target aroma substances with different gradient concentrations to a pre-prepared blank tea matrix, establishes a standard working curve for each target substance, and then substitutes the quantitative ion peak area data of each target substance detected in step 3) into the working curve to preliminarily calculate the concentration of the target substance in the tea soup.

[0029] Furthermore, the calculated concentration of the target substance is backfilled into the blank tea matrix, and adjusted proportionally after comparison with the corresponding peak area in the original tea sample. The adjustment is considered complete when the peak area data of the target substance in the simulated sample and the original tea sample reach no statistical difference P>0.05, and the precise concentration of the target aroma substance in the tea soup is obtained.

[0030] Furthermore, the linear correlation coefficient of the standard working curve must be above 0.99.

[0031] The present invention has the following beneficial effects:

[0032] 1) For the first time, direct extraction is achieved under real tea brewing conditions. The specially designed 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 odor distortion, compound conversion and deterioration caused by conditional control.

[0033] 2) The operation is simple and the extraction time is short. The extraction time is only 4-7 minutes, which is shorter than the 30-60 minutes required by the conventional method, significantly improving work efficiency.

[0034] 3) SBSE can be used for batch extraction without immediate injection. Samples can be stored in the stir bar for up to 7 days. The intra-day and inter-day repeatability of aroma compounds in the samples are good, with relative standard deviations generally below 10%.

[0035] 3) The quantitative analysis method for target aroma compounds combines the technical advantages of the standard addition method and the external standard curve method, avoiding matrix effects and improving quantitative analysis efficiency. The tea blank matrix can be recycled repeatedly, avoiding significant waste of tea samples.

[0036] 4) By comparing with the original tea sample, the added dosage of the target substance can be precisely adjusted, which largely avoids quantitative errors caused by multi-component competitive adsorption and human operation errors. Accurate quantitative analysis of trace and micro-amounts of aroma substances can be achieved without the use of expensive stable isotope standards, significantly reducing technical costs.

[0037] 5) The SBSE method of the present invention can be directly extracted in water, without the need for additional organic reagents during the extraction stage, thus avoiding environmental pollution and a large amount of waste of tea samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Comparison of total ion chromatograms of the brewing SBSE method and the conventional SBSE method for tea sensory evaluation;

[0039] Figure 2 Comparison of the inter-day repeatability of total ion current patterns of the SBSE method for tea sensory evaluation;

[0040] Figure 3 Comparison of total ion currents between simulated tea sample and original tea sample;

[0041] Figure 4 This is the quantitative ion peak overlay diagram of geraniol in the simulated tea sample and the original tea sample;

[0042] Figure 5 This is the overlay diagram of the quantitative ion peaks of the target aroma substances in the simulated tea sample and the original tea sample. DETAILED DESCRIPTION

[0043] The present invention will be further explained below with reference to 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 scope of protection of the present invention.

[0044] In this application, the tea to be tested was brewed using the national standard GB / T 23776-2018 tea sensory evaluation method. Specifically, the method involves: 3 g of uniformly mixed whole tea leaves, 150 mL of boiling water, and 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, and strip or curled oolong tea), and 6 minutes (knot, fist, or granular oolong tea). Except for dark tea, the brewing frequency is one. For dark tea, a two-step brewing method is used: the first step is 2 minutes, and the second step is 5 minutes.

[0045] In this study, stir bars sorptive extraction (SBSE) was used to extract the aroma profile of the tea leaves in real time. The extraction tool used was a twister bar coated with PDMS (10 mm (length) × 1.0 mm (thickness) × 24 μL (volume)). The SBSE procedure involved weighing 3 g of uniformly mixed tea leaves into a specially designed 150 mL cylindrical evaluation cup. 150 mL of boiling water was then poured into the cup, followed by the rapid introduction of a PDMS-coated twister bar (10 mm × 1.0 mm × 24 μL). The cup was then covered and allowed to infuse at room temperature for 4-6 minutes. The tea was then drained, the bar removed, and its surface rinsed with deionized water. After wiping dry with a non-woven fabric, the bar was placed in a glass liner designed for thermal desorption. This procedure was repeated three times for each sample.

[0046] 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% with 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 chemical structure of the remaining compounds is accurately verified using a self-built tea aroma substance library; and the composition and abundance distribution of the tea aroma profile are obtained.

[0047] The improved standard addition method employed in this invention utilizes an external standard curve for quantification, using pre-deodorized tea leaves as a blank matrix. The tea blank matrix preparation steps are as follows: 500 g of raw tea sample is weighed and repeatedly brewed with 2500 mL of boiling water 3-5 times until the tea soup loses its noticeable aroma. The tea residue is then thoroughly soaked in 1000 mL of anhydrous ethanol overnight. After removing the ethanol, the residual ethanol and aroma compounds in the tea leaves are removed in batches using a rotary evaporator (60°C, 10 minutes each, repeated 2-3 times). The pre-dried residue is then thoroughly dried using a vacuum pump (2 hours) and an oven (60°C, 3 days). The aroma components are then analyzed using GC-MS. A S / N ratio of the overall chromatographic peak is less than 3, excluding column bleed products, and the blank matrix is ​​considered acceptable.

[0048] The improved standard addition method specifically adds target aroma substances of different gradient concentrations into a pre-prepared tea blank matrix, establishes a standard working curve for each target substance, and then substitutes the detected quantitative ion peak area data of each target substance into the working curve to preliminarily calculate the concentration of the target substance in the tea soup; the calculated target substance concentration is backfilled into the tea blank matrix, and adjusted proportionally after comparison with the corresponding peak area in the original tea sample. The adjustment is considered complete when the peak area data of the target substance in the simulated sample and the original tea sample reach no statistical difference P>0.05, and the precise 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.

[0049] Example: Extraction of the true aroma profile of white tea and quantitative analysis of important aroma compounds

[0050] (1) Weigh 3 g of the uniformly mixed 2017 Shoumei tea sample into a 150 mL cylindrical evaluation cup. Pour 150 mL of boiling water into the cup, then quickly place a PDMS-coated twister rod. Cover the cup and extract at room temperature for 5 minutes. Drain the tea and remove the twister rod. Rinse its surface with deionized water, wipe it with a non-woven fabric until it is dry, and place it in a glass liner tube for thermal desorption. Repeat three times for each sample.

[0051] (2) The aroma extracts were analyzed by TD-GC-MS. TD conditions were as follows: solvent evacuation mode, initial temperature 40 °C, hold for 2 minutes, then heat to 240 °C at a rate of 100 °C / min and hold for 4 minutes. The large volume inlet was cooled to -100 °C with liquid nitrogen, equilibrated for 1.0 min, then heated to 280 °C at a rate of 12 °C / s and held for 3.0 min. GC conditions: HP-5MS column (30 m × 0.25 mm × 0.25 μm), carrier gas was high-purity He (purity 99.999%), flow rate 1.6 mL / min, column oven heating program: initial temperature 50 °C, hold for 2.0 minutes, then heat to 265 °C at a rate of 4.0 °C / min and hold for 5 minutes. MS conditions: electron ionization: 70 eV; line temperature: 250 °C; ion source temperature: 220 °C; quadrupole temperature: 150 °C; mass range: m / z 50–450 u; no solvent delay.

[0052] About 500 chromatographic peaks were initially identified using this method, and the peak response was significantly lower than that of aroma substances extracted using 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 2After similarity sorting using the NIST 2020 library, removal of exogenous volatile substances such as column bleed and plasticizers, retention index verification, and standard sample validation, a total of 108 volatile components were identified. Based on their chemical structure, they can be divided into 10 categories: esters, alcohols, alkenes, ketones, aldehydes, acids, oxygen heterocycles, nitrogen-containing compounds, aromatic compounds, and lactones. In terms of quantitative distribution, alcohols are the most abundant, followed by ketones and aldehydes, and nitrogen-containing compounds are the least abundant. The specific aroma compound composition and quantitative ion peak areas are shown in Tables 1(a)-1(d).

[0053] Table 1 (a) Shoumei aroma components identified by sensory evaluation, extraction, and brewing SBSE method

[0054]

[0055] [1] Retention index calculation value; [2] Retention index reported by NIST2020 library.

[0056] Table 1 (b) Aroma components of Shoumei identified by sensory evaluation, extraction and brewing SBSE method

[0057]

[0058] [1] Retention index calculation value; [2] Retention index reported by NIST2020 library.

[0059] Table 1 (c) Aroma components of Shoumei identified by sensory evaluation, extraction and brewing SBSE method

[0060]

[0061] [1] Retention index calculation value; [2] Retention index reported by NIST2020 library.

[0062] Table 1 (d) Shoumei aroma components identified by sensory evaluation extraction and brewing SBSE method

[0063]

[0064] [1] Retention index calculation value; [2] Retention index reported by NIST2020 library.

[0065] (3) Ten common aroma compounds with high content in Shoumei tea were accurately quantitatively analyzed, including geraniol, linalool, phenylethyl alcohol, benzaldehyde, dihydroactinol, limonene, nonanoic acid, 2-methylbutanal, 3-methylbutanal, and γ-nonalactone. The target aroma compounds were quantitatively analyzed using the improved standard addition method. Fifteen target aroma compounds with different gradient concentrations were added to the pre-prepared tea blank matrix, and standard working curves for each target compound were established. The qualitative parameters, quantitative ions, linear equations, linear correlation coefficients, and the calculated concentrations of each target compound in Shoumei tea are shown in Table 2.

[0066] Table 2 Qualitative and quantitative parameters and concentration distribution of common aroma substances in Shoumei

[0067]

[0068] [1] The numbers marked in black are the quantitative ions of the target aroma substances; [2] This concentration is the concentration of each substance in 3g of Shoumei and 150mL of water.

[0069] (4) Next, the above compounds were simulated and added to 3 g of Shoumei blank matrix according to the calculated concentrations, and the corresponding substances were extracted according to the sensory evaluation SBSE method, and analyzed using 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, with each sample repeated 3 times in parallel. Process the GC-MS data, extract the quantitative ions of each target compound, and compare the multiple difference 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, the multiple average value in the original tea sample is adjusted accordingly, and the above experiment is repeated until there is no significant difference ( Figure 3 Finally, the precise concentrations of the above 10 aroma compounds in Shoumei tea were obtained, and the adjustments of each compound 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 adjustments were made ( Figure 4 ); Although there are certain differences among other compounds, the overall reproducibility is good, with adjustment factors ranging from 0.88 to 2.46 ( Figure 5 After adding these adjusted compounds back to the blank matrix, no significant difference in peak area was observed between the simulated and original tea samples, indicating that the adjustment was complete. Through these steps, the authentic aroma profile of Shoumei 2017 was extracted, and accurate quantification of 10 key aroma compounds was achieved. (Due to space limitations, these 10 compounds are only used as examples; accurate quantification of all aroma compounds is achievable.)

[0070] Table 3 Concentration adjustment of 10 target aroma substances in Shoumei

[0071]

[0072] [1] Difference factor: quantitative ion peak of target substance in original tea sample / quantitative ion peak of target substance in simulated sample.

[0073] In summary, the present invention uses SBSE combined with TD-GC-MS technology to achieve for the first time the efficient enrichment of aroma components in the tea evaluation and brewing stage, extracting the true aroma profile of the tea. The extraction process only takes 4-7 minutes to complete, and is simple to operate, does not require organic solvents, and is environmentally friendly. Subsequently, the quantitative analysis of the target aroma substances in tea was achieved by combining the external standard method with the standard addition method, and for the first time, the precise concentration of the target aroma substances in tea was calculated by intuitively comparing with the original tea samples. 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 selection and breeding of high-fragrant tea 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 a quantitative analysis of aroma substances in similar fields such as other teas, plants and foods, the ideas are basically consistent with the present invention. The extraction method and quantitative ideas in the present invention can be referred to for detection and analysis. When the resulting functions 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 accurately analyzing the true aroma profile of tea, characterized in that: The following steps are involved: 1) Brewing of the tea to be tested Prepare tea soup of the tea to be tested using the tea sensory evaluation method; 2) Real-time adsorption extraction of the aroma profile of the tea leaves to be tested A stir bar adsorption extraction method is used to enrich the aroma components released during the tea brewing process, and the extraction is stopped immediately after the brewing is completed; 3) Detection and qualitative analysis of the aroma profile of the tea to be tested After brewing, the tea aroma extract is desorbed and analyzed using thermal desorption-gas chromatography-mass spectrometry to identify the molecular structure and abundance composition of the aroma profile of the tea to be tested; 4) Quantitative analysis of target aroma substances in tea leaves The target aroma compounds in tea were quantitatively analyzed using the improved standard addition method, which used external standard curve quantification and pre-deodorized tea as blank matrix. 5) Accurate adjustment of the concentration of target aroma substances in the tea to be tested The target aroma substance concentrations of tea obtained by simulation calculation are added to the blank tea matrix, and compared and fine-tuned with the total ion current diagram of the aroma components of the original tea sample to obtain the precise concentration of each target aroma substance.

2. The method for extracting and accurately analyzing the true aroma profile of tea leaves according to claim 1, wherein: Step 1) Specifically, use 3 g of evenly mixed whole tea leaves, 150 mL of boiling water, and a 150 mL cylindrical evaluation cup. Depending on the type of tea, the brewing time is 4 minutes for green tea; 5 minutes for black tea, white tea, yellow tea, and strip-shaped or curled oolong tea; and 6 minutes for round-shaped, fist-shaped, or granular oolong tea. Except for black tea, the brewing time is once for all other teas; black tea uses a double brewing method, with the first brewing time being 2 minutes and the second brewing time being 5 minutes.

3. The method for extracting and accurately analyzing the true aroma profile of tea according to claim 1, wherein: Step 2) The stir bar adsorption extraction method uses a twister stir bar with a polydimethylsiloxane coating and specifications of 10 mm length × 1.0 mm film thickness × 24 μL capacity. The stir bar adsorption extraction method specifically involves placing a twister stir bar during the tea brewing process. After brewing at room temperature for 4-6 minutes, the tea is drained, the stir bar is removed, and its surface is rinsed with deionized water. After wiping it with non-woven fabric until the surface is dry, it is placed in a special glass liner tube for thermal desorption and set aside. Each sample is repeated in parallel 3 times.

4. The method for extracting and accurately analyzing the true aroma profile of tea according to claim 1, wherein: Step 3) The specific parameters of the thermal desorption-gas chromatography-mass spectrometry technique are as follows: Thermal desorption conditions: solvent evacuation mode, initial temperature 40 °C, hold for 2 min, heat to 240 °C at a rate of 100 °C / min, hold for 4 min; large volume inlet cooled to -100 °C with liquid nitrogen, equilibrated for 1.0 min, then heated to 280 °C at a rate of 12 °C / s, hold for 3.0 min; Gas chromatography conditions: Tea aroma extracts were analyzed using an HP-5MS or DB-5MS column. The carrier gas was high-purity He at a flow rate of 1.6 mL / min. The column oven heating program was as follows: initial temperature at 50°C for 2.0 min, then the temperature was increased to 265°C at a rate of 4.0°C / min and held for 5 min. 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 accurately analyzing the true aroma profile of tea leaves according to claim 1, wherein: The preparation steps of the tea blank matrix are as follows: weigh 500 g of the original tea sample, repeatedly brew it with 2500 mL of boiling water for 3-5 times until the tea soup has no obvious aroma; fully soak the tea residue in 1000 mL of anhydrous ethanol overnight, remove the ethanol, and then remove the residual ethanol and aroma substances in the tea leaves in batches using a rotary evaporator; after the preliminary dried residue is fully dried using a vacuum pump and an oven, its aroma components are detected by GC-MS. The overall chromatographic peak S / N is less than 3, excluding column bleed products, and is considered to be a qualified blank matrix.

6. The method for extracting and accurately analyzing the true aroma profile of tea leaves according to claim 1 or 5, wherein: In step 4), the improved standard addition method specifically adds target aroma substances at different gradient concentrations to a pre-prepared blank tea matrix, establishes a standard working curve for each target substance, and then substitutes the quantitative ion peak area data of each target substance detected in step 3) into the working curve to preliminarily calculate the concentration of the target substance in the tea soup.

7. The method for extracting and accurately analyzing the true aroma profile of tea according to claim 6, characterized in that: The calculated concentration of the target substance is backfilled into the blank tea matrix and adjusted proportionally after comparison with the corresponding peak area in the original tea sample. The adjustment is considered complete when the peak area data of the target substance in the simulated sample and the original tea sample reach no statistical difference P>0.05, and the precise concentration of the target aroma substance in the tea soup is obtained.

8. The method for extracting and accurately analyzing the true aroma profile of tea leaves according to claim 6, wherein: The linear correlation coefficient of the standard working curve must be above 0.99.

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