A method for improving tea flavor based on supercritical CO2

Abstract

This invention discloses a method for improving tea flavor based on supercritical CO2, belonging to the field of tea processing technology. The method includes: softening raw tea leaves, followed by extraction using supercritical carbon dioxide fluid; wherein the entrainer used in the extraction process is a polar alcohol solution. This invention innovatively utilizes SFE-CO2 as a flavor reshaping tool, significantly reducing bitterness and astringency while enhancing sweetness perception, effectively suppressing grassy / herbal aromas, preserving and highlighting floral characteristics, and without compromising the integrity of the tea leaves. This invention provides a scalable, mild, and precise flavor control strategy, offering technical support for improving the quality and diversifying tea products, combining practicality and innovation.

Description

Technical Field

[0001] This invention belongs to the field of tea processing technology, specifically relating to a method for improving tea flavor based on supercritical CO2. Background Technology

[0002] Tea is one of the world's most popular beverages, and the quality of tea fundamentally depends on the harmony of its aroma and flavor. Subtle variations in volatile aroma components and non-volatile matrices can translate into significant sensory differences. Different processing methods result in a rich variety of tea products.

[0003] Flavor modulation techniques have always been a hot topic because flavor during tea processing is matrix-driven and sensitive, easily tilting the balance towards undesirable sensory outcomes (such as astringency, grassy / off-flavors, or excessive bitterness / astringency). Current research focuses on two main areas: firstly, refining traditional processes by utilizing biochemical transformations and thermal reactions during withering, turning, roasting, and fermentation to generate or transform aromatic compounds and reshape the flavor balance. Recent studies have further demonstrated that incorporating shake-stacking techniques can enhance floral / fruity / sweet aroma components in green tea, highlighting the effectiveness of process-driven aroma formation. Secondly, emerging mild or non-thermal techniques (such as ultrasound, pulsed electric fields, high-voltage treatment, and cold plasma) are being investigated to reduce heat damage to tea and modulate its quality. While these techniques often have limited selectivity for specific subsets of aroma components compared to solvent-phase separation techniques, these advances collectively drive efforts to find a scalable technique that can enhance the sensory prominence of pleasant aroma components in tea while selectively suppressing undesirable aromas.

[0004] At the same time, consumers are increasingly demanding diversified tea products, including options with reduced irritation and improved drinking comfort. Traditional ingredient modification strategies, such as caffeine-based modifications, often lead to sensory loss or damage to the tea's form (tea powder), such as a flattened aroma or loss of distinctive flavor. Balancing "functional" modifications with sensory quality also presents a challenge.

[0005] Supercritical carbon dioxide extraction (SFE-CO2) is a scalable and relatively mild processing technique that has been widely used to selectively remove substances from certain target samples. In early research, SFE-CO2 was most widely used in the tea industry for decaffeination. In this process, process variables (pressure / temperature / time) and polar modifiers (such as ethanol) were used to adjust caffeine solubility and removal efficiency. Existing supercritical carbon dioxide extraction processes require grinding the tea leaves into powder to achieve sufficient contact between the supercritical fluid and the target substance. This grinding process disrupts the cellular structure and physical morphology of the tea leaves, resulting in a large amount of suspended matter in the tea infusion. More seriously, grinding causes uncontrollable escape or oxidation of volatile aroma compounds within the tea leaves during processing and storage, leading to sensory defects such as a "bland aroma" and "weak flavor" in the final product. Therefore, it is highly significant to provide a method for improving tea flavor that significantly reduces bitterness and astringency, enhances sweetness perception, effectively suppresses grassy / herbal aromas, and preserves and highlights floral characteristics without damaging the integrity of the tea leaves. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a method for improving tea flavor based on supercritical CO2, which effectively solves the problems of flavor imbalance and insufficient selective control of flavor components in existing tea processing methods.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for improving tea flavor based on supercritical CO2 is provided, comprising the following steps: The raw tea leaves are softened and then extracted using supercritical carbon dioxide fluid; the entrainer used in the extraction process is a polar alcohol solution.

[0008] The beneficial effects of this invention are as follows: First, this invention abandons the traditional method of pulverizing and damaging the cell walls of tea leaves. Without damaging the integrity of the tea leaves, it re-softens raw tea leaves and utilizes the swelling effect of water molecules to reshape the microenvironment of the tea matrix, opening up mass transfer and diffusion pathways such as intercellular spaces and micropores, effectively reducing the mass transfer resistance of supercritical fluids penetrating into the leaf interior. Second, based on opening the mass transfer channels, a polar entrainer (polar alcohol solution) is introduced to adjust the effective polarity and solubility parameters of the supercritical carbon dioxide phase. The mixed solvent system formed by this polar entrainer and the supercritical fluid can specifically target, dissolve, and extract polar and moderately polar undesirable flavor precursors (such as bitter-tasting monomeric polyphenols and volatile alcohols and aldehydes exhibiting grassy / woody off-flavors) from the tea matrix, while preferentially stripping away the hydrophobic wax and lipid barriers on the leaf surface. Finally, due to the targeted removal of undesirable flavor substances (such as astringency and oxidative off-flavors) and the stripping of hydrophobic barriers, not only is the bitterness of the tea soup reduced, but also, due to the reduction of total matrix solids and the improvement of pore structure, pleasant volatile components (such as phenylacetaldehyde) and specific polyphenols (such as epigallocatechin gallate) that contribute positively to floral, fruity, and sweet aromas are significantly enriched in the tea matrix. Furthermore, non-volatile matrix components (total polyphenols and total free amino acids) are steadily retained. In summary, this method significantly reduces the bitterness of tea, enhances the perception of sweetness, effectively suppresses grassy / herbal aromas, preserves and highlights floral characteristics, and does not damage the integrity of the tea leaves. This invention provides a scalable, mild, and precise flavor control strategy, offering technical support for the quality improvement and diversification of tea products, combining practicality and innovation.

[0009] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, the raw tea refers to Pu'er raw tea.

[0010] Furthermore, the specific process for softening raw tea is as follows: spray water on the surface of the raw tea and then let it stand for 20-40 minutes; the water should be 20-40% of the weight of the raw tea.

[0011] The softening process for raw Pu-erh tea is a process that allows the tea leaves to fully absorb moisture. This involves spraying an appropriate amount of water onto the surface of the raw Pu-erh tea leaves, and then subjecting the tea leaves to supercritical carbon dioxide extraction after they have fully absorbed the moisture.

[0012] Further, spray water onto the surface of the raw tea leaves and let it stand for 30 minutes; the water should be 30% of the weight of the raw tea leaves.

[0013] Furthermore, the polar alcohol solution is a C1-C4 fatty alcohol or an aqueous solution thereof.

[0014] Furthermore, the polar alcohol solution is edible alcohol; the volume fraction of edible alcohol is 95%.

[0015] Furthermore, the amount of polar alcohol solution added is 20-40% of the weight of raw tea; preferably, the amount of polar alcohol solution added is 30% of the weight of raw tea.

[0016] Furthermore, the extraction pressure during the extraction process is 25-35 MPa, the extraction temperature is 55-65℃, and the extraction time is 2-4 h.

[0017] Furthermore, the extraction pressure during the extraction process was 30 MPa, the extraction temperature was 60℃, and the extraction time was 3 hours.

[0018] Furthermore, the flow rate of the supercritical carbon dioxide fluid is 60-70 L / h, the temperature of the separation vessel is 35-45℃, and the pressure of the separation vessel adopts a two-stage separation of 8-12 MPa and 3-5 MPa.

[0019] Furthermore, the flow rate of the supercritical carbon dioxide fluid is 65 L / h, the temperature of the separation vessel is 40 °C, and the pressure of the separation vessel is 10 MPa and 4 MPa for two-stage separation.

[0020] The tea produced using the above-mentioned improved method can be used to prepare tea beverages that have reduced bitterness, enhanced sweetness, and reduced grassy aroma.

[0021] The present invention has the following beneficial effects: This invention innovatively utilizes SFE-CO2 as a flavor reshaping tool. By optimizing process conditions (pressure, temperature, time) and co-solvent polarity (e.g., 95 vol% edible alcohol) and matrix moisture adjustment (softening treatment), it achieves precise removal of unpleasant odor components (such as astringency and oxidative off-odors) and enhancement of pleasant aromas (floral, fruity, and sweet aromas). A combination of multi-platform chemical characterization (LC-UV, LC-QQQ-MS / MS, HS-SPME-GC-MS) and sensory evaluation reveals the steady-state retention of non-volatile matrices (total polyphenols, total free amino acids) and the reorganization effect of monomeric polyphenols and volatile components by SFE-CO2 treatment, clarifying the changes in marker compounds (e.g., significantly increased ECG content and significantly decreased off-odor compound 3-octanol). This method significantly reduces bitterness and astringency in tea, enhances sweetness perception, effectively suppresses grassy / herbal aromas, retains and highlights floral characteristics, and does not damage the integrity of the tea leaves. This invention provides a scalable, mild, and precise flavor control strategy, offering technical support for improving the quality and diversifying the development of tea products, and combining practicality and innovation. Attached Figure Description

[0022] Figure 1 Cluster heatmap of monomeric polyphenol content in different treatment groups.

[0023] Figure 2This is a comparison of the differences in polyphenol monomer content between different treatment groups using logFC values. Detailed Implementation

[0024] The tea samples selected for this invention are raw Pu'er tea from Yunnan Province, which come from the same manufacturer and the same production batch.

[0025] The examples given below are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, conditions in the examples are performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products. Example 1:

[0026] A method for improving tea flavor based on supercritical CO2 (the treatment group is denoted as RH-E-SFE) includes the following steps: Raw Pu-erh tea was used as raw material. Water, at 30% of the tea's weight, was sprayed onto the surface of the tea leaves to soften them for 30 minutes (this process allows the tea leaves to fully absorb moisture). The softened tea leaves were then placed in a 10L supercritical carbon dioxide fluid extraction apparatus. 95% vol% edible alcohol, at 30% of the tea's weight, was added as an entrainer. Extraction was carried out for 3 hours at an extraction pressure of 30 MPa and an extraction temperature of 60°C. During extraction, the carbon dioxide fluid flow rate was kept constant at 65 L / h, the separation vessel temperature was 40°C, and the separation vessel pressures were 10 MPa and 4 MPa, respectively. The extract was collected every 30 minutes. After extraction, the extracted tea leaves were collected as flavor-improved tea and stored in a light-proof, sealed container. Example 2:

[0027] A method for improving tea flavor based on supercritical CO2 includes the following steps: Raw Pu-erh tea was used as raw material. Water, at 30% of the tea's weight, was sprayed onto the surface of the tea leaves to soften them for 40 minutes (this process allows the tea leaves to fully absorb moisture). The softened tea leaves were then placed in a 10L supercritical carbon dioxide fluid extraction apparatus. 20% of the tea's weight in 95% vol edible alcohol was added as an entrainer. Extraction was carried out for 2 hours at an extraction pressure of 35 MPa and an extraction temperature of 65°C. During extraction, the carbon dioxide fluid flow rate was kept constant at 60 L / h, the separation vessel temperature was 45°C, and the separation vessel pressures were 10 MPa and 4 MPa, respectively. The extract was collected every 30 minutes. After extraction, the extracted tea leaves were collected as flavor-improved tea and stored in a light-proof, sealed container. Example 3:

[0028] A method for improving tea flavor based on supercritical CO2 includes the following steps: Raw Pu-erh tea was used as raw material. Water, at 30% of the tea's weight, was sprayed onto the surface of the tea leaves to soften them for 20 minutes (this process allows the tea leaves to fully absorb moisture). The softened tea leaves were then placed in a 10L supercritical carbon dioxide fluid extraction apparatus. 95% vol% edible alcohol, at 40% of the tea's weight, was added as an entrainer. Extraction was carried out for 4 hours at an extraction pressure of 25 MPa and an extraction temperature of 55°C. During extraction, the carbon dioxide fluid flow rate was kept constant at 70 L / h, the separation vessel temperature was 35°C, and the separation vessel pressures were 10 MPa and 4 MPa, respectively. The extract was collected every 30 minutes. After extraction, the extracted tea leaves were collected as flavor-improved tea and stored in a light-proof, sealed container.

[0029] Comparative Example 1: Comparative Example 1 was direct supercritical carbon dioxide extraction (this treatment group is denoted as D-SFE), and the specific process was as follows: Raw Pu-erh tea leaves were directly placed into a 10L supercritical carbon dioxide fluid extraction apparatus and extracted for 3 hours at an extraction pressure of 30 MPa and an extraction temperature of 60℃. During the extraction process, the flow rate of the carbon dioxide fluid was kept constant at 65 L / h, the temperature of the separation vessel was 40℃, and the pressures of the separation vessel were 10 MPa and 4 MPa, respectively. The extract was collected every 30 minutes. After extraction, the extracted tea leaves were collected and stored in a sealed container away from light.

[0030] Comparative Example 2: Comparative Example 2 was based on direct supercritical carbon dioxide extraction, with water used as an entrainer (this treatment group is denoted as W-SFE). The specific process was as follows: Raw Pu-erh tea was directly placed into a 10L supercritical carbon dioxide fluid extraction apparatus, and then water (30% of the tea's mass by weight) was added as an entrainer. Extraction was carried out for 3 hours at an extraction pressure of 30 MPa and an extraction temperature of 60℃. During the extraction process, the flow rate of carbon dioxide fluid was kept constant at 65 L / h, the temperature of the separation vessel was 40℃, and the pressures of the separation vessel were 10 MPa and 4 MPa, respectively. The extract was collected every 30 minutes. After extraction, the extracted tea leaves were collected and stored in a sealed container away from light.

[0031] Comparative Example 3: Comparative Example 3 was based on direct supercritical carbon dioxide extraction, with ethanol used as an entrainer (this treatment group is denoted as E-SFE). The specific process was as follows: Raw Pu-erh tea was directly placed into a 10L supercritical carbon dioxide fluid extraction apparatus, and then 30% (by weight of the raw tea) of 95 vol% edible alcohol was added as an entrainer. Extraction was carried out for 3 hours at an extraction pressure of 30 MPa and an extraction temperature of 60℃. During the extraction process, the flow rate of carbon dioxide fluid was kept constant at 65 L / h, the temperature of the separation vessel was 40℃, and the pressures of the separation vessel were 10 MPa and 4 MPa, respectively. The extract was collected every 30 minutes. After extraction, the extracted tea leaves were collected and stored in a sealed container away from light.

[0032] Comparative Example 4: Comparative Example 4 involved softening the tea leaves, but without adding any entrainer during the supercritical carbon dioxide extraction process (this treatment group is designated RH-SFE). The specific process was as follows: Raw Pu-erh tea was used as raw material. Water, equal to 30% of the tea's weight, was sprayed onto the surface of the tea leaves to soften them for 30 minutes (this process allows the tea leaves to fully absorb moisture). The softened tea leaves were then placed in a 10L supercritical carbon dioxide fluid extraction apparatus and extracted for 3 hours at an extraction pressure of 30 MPa and an extraction temperature of 60℃. During extraction, the carbon dioxide fluid flow rate was kept constant at 65 L / h, the separation vessel temperature was 40℃, and the separation vessel pressures were 10 MPa and 4 MPa, respectively. The extract was collected every 30 minutes. After extraction, the extracted tea leaves were collected and stored in a light-proof, sealed container.

[0033] The tea leaves prepared in Example 1 and Comparative Examples 1-4 were first tested as follows: I. Experimental Methods 1. Analysis of total polyphenols and total free amino acids in tea (1) The analysis of total polyphenols was based on the national standard GB / T8313-2018 "Determination of the content of tea polyphenols and catechins in tea", with slight modifications, as follows: Sample preparation: The tea leaves obtained in Example 1 and Comparative Examples 1-4 were ground into tea powder. 0.2000 g of tea powder was accurately weighed into a 10 mL centrifuge tube, and 5 mL of 70% (v / v) methanol-water solution was added. The mixture was incubated in a water bath at 70°C for 10 min, followed by centrifugation at 3500 rpm for 10 min. The supernatant was collected. The tea powder precipitate was repeated once, and the supernatants were combined. The extract was brought to a final volume of 10 mL and then diluted 100 times for later use.

[0034] Construction of standard curve: Accurately weigh 0.0010 g of gallic acid and dissolve it in 10 mL of 70% (v / v) methanol-water as a stock solution, and then dilute it to 10, 20, 30, 40 and 50 μg / mL gallic acid working solutions respectively.

[0035] Sample Analysis: Pipette 1.0 mL of sample, water, and gallic acid working solutions of different concentrations into separate glass test tubes. Add 5 mL of 10% Folin-Ciocalteu reagent to each tube, shake well, and react for 5 min. Then add 4 mL of 7.5% sodium carbonate solution and react at room temperature for 60 min. Measure the absorbance at 765 nm and calculate the total polyphenol content in the sample using a standard curve. Three copies are required.

[0036] (2) The total free amino acid content was determined by referring to the national standard GB / T8314-2013 "Determination of Total Free Amino Acid Content in Tea" and making slight modifications, as follows: Accurately weigh 0.0010 g of theanine and dissolve it in 10 mL of 70% (v / v) methanol-water as a stock solution. Then dilute this stock solution to prepare theanine standard solutions of 0.2, 0.3, 0.4, 0.5, and 0.6 mg / mL. Accurately pipette 1.0 mL of the sample, water, and the theanine standard solutions of different concentrations into glass test tubes. Add 0.5 mL of phosphate buffer (pH 8.0) and 0.5 mL of 2% (v / v) ninhydrin solution to each tube, and incubate in a boiling water bath for 15 min. After cooling, bring the volume to 25 mL, let stand for 10 min, and then measure the absorbance at 570 nm. Calculate the total free amino acid content based on the standard curve. Prepare three copies.

[0037] 2. Analysis of monomeric polyphenols The sample pretreatment method was the same as that for total polyphenols, and the extract was filtered through a 0.22 μm filter membrane before determination.

[0038] The determination of monomeric polyphenols was performed using high-performance liquid chromatography-tandem mass spectrometry combined with multiple reaction monitoring mode in negative ion mode. The specific procedure is as follows: Mobile phase A was 0.1% (v / v) formic acid aqueous solution, and mobile phase B was acetonitrile. The column oven temperature was 35℃. The injection volume was 1 μL. The flow rate was 0.3 mL / min, and the elution program was as follows: 0–8 min, 2–10% B; 8–15 min, 10–20% B; 15–20 min, 20–28% B; 20–25 min, 28–37% B; 25–30 min, 37–47% B; 30–35 min, 47–50% B; 35–36 min, 50–2% B. Mass spectrometry analysis was performed using multiple reaction monitoring (MRM) mode. Data acquisition was performed in negative ion mode using an electrospray ionization (ESI) source. The ESI parameters were set as follows: nebulizer gas 55 psi; curtain gas 30 psi; auxiliary heating gas 60 psi; ion source temperature 500℃; capillary voltage -4.5 kV.

[0039] 3. GC-MS analysis of aroma The parameters for HS-SPME (headspace-solid phase microextraction) were set as follows: incubation temperature was set to 80℃, and shaking rate was 500 rpm. Before sample injection, the fiber extraction head was conditioned for 15 min, and then immediately inserted into the sample, adsorbing at the same temperature for 50 min to reach equilibrium. After adsorption, the fiber extraction head was desorbed at 250℃ for 5 min. Gas chromatography-mass spectrometry (GC-MS, Agilent 5977B GC / MSD, Agilent Technologies, USA) was used, with an HP-5 capillary column (30 m × 0.25 mm × 0.25 μm, Agilent Technologies). Helium was used as the carrier gas, flowing continuously at a rate of 1 mL / min in a splitless manner. The interface temperature was maintained stably at 250℃. The temperature program was as follows: initial temperature set at 40℃ and held for 5 min, then increased to 100℃ at a rate of 5℃ / min, then increased to 220℃ at a rate of 6℃ / min, and then increased to 250℃ at a rate of 15℃ / min, held for 5 min. Mass spectrometry was performed using an electron impact ionization (EI) source with an ionization energy of 70 eV. The ion source temperature was 230 °C, and the transfer line temperature was 250 °C. Data acquisition was performed in full scan mode, with a scan range of 30–350 m / s. Qualitative analysis was conducted using standards. Quantitative analysis was performed using standard curves and internal standards.

[0040] 4. Sensory evaluation The sensory evaluation process for flavor includes screening, training, and analysis. Volunteers who pass the initial screening receive training, with each training session lasting at least one hour, conducted twice a week for a total training period of two months. Training content includes an introduction to basic knowledge of raw Pu'er tea, flavor identification training, aroma identification training, and scale usage training. Trained sensory evaluators are then assessed according to GB / T10220-2012 "Sensory Analysis - Methodology - General Introduction". Ultimately, a sensory evaluation team of 18 people was established, aged 21-32, including 10 male and 8 female evaluators.

[0041] II. Experimental Results 1. Characteristics of matrix content composed of total polyphenols and total free amino acids The matrix component contents of the four comparative examples are shown in Table 1. The total polyphenol content ranged from 19.75% to 20.28%, which is basically consistent with RAPT (raw Pu-erh tea raw material, 20.14%). The total free amino acid content ranged from 3.37% to 3.89%, with no significant difference from RAPT (3.63%). This indicates that the total polyphenols and amino acids, these core flavor and nutritional components in tea, remain stable in total quantity.

[0042] In general, Example 1 and Comparative Examples 1-4 showed good overall retention of non-volatile key substrates (total polyphenols, total free amino acids).

[0043] Table 1. Content of non-volatile matrix components in different groups of tea 2. Results of monomeric polyphenol determination The polyphenol monomer contents in different treatment groups are shown in Table 2-3. A total of 28 polyphenolic substances were analyzed and classified into 5 categories according to their material structure: 7 flavanols, 7 flavonols, 8 phenolic acids, 2 flavonol glycosides and 4 anthocyanins.

[0044] Table 2. Polyphenol monomer content in tea leaves of different treatment groups Table 3. Polyphenol monomer content in tea leaves of different treatment groups From Table 2-3 and Figure 1 It was found that the total content of targeted polyphenols in the raw Pu-erh tea was 160,984.40 mg / kg, which decreased to 156,438.65 mg / kg in the treatment group, but there was no significant difference between them. Among them, the content of flavanol polyphenols was the highest (>125,875.13 mg / kg). Among all monomeric compounds, epicatechin gallate had the highest content (>72,453.87 mg / kg).

[0045] Meanwhile, cluster analysis was performed on the composition of monomeric polyphenols in different tea samples, and the results are as follows: Figure 1 As shown. By Figure 1 It was found that the W-SFE group was most similar to the RAPT group in terms of polyphenol composition. The polyphenol compositions of the RH-SFE and RH-E-SFE groups, which underwent softening pretreatment, were even closer. The D-SFE and E-SFE groups were grouped together. This result indicates that the influence of SFE on the non-volatile profile of tea is significantly regulated by two types of factors: firstly, the type of entrainer, which determines the effective polarity and selectivity of the supercritical phase; and secondly, the moisture content of the matrix (softening pretreatment) potentially alters the leaf microenvironment, diffusion pathway, and extraction efficiency.

[0046] Furthermore, this invention further analyzed the differences in polyphenol compounds between the five treatment groups and the RAPT raw material using logFC values, and the results are as follows: Figure 2 As shown. By Figure 2It was found that most polyphenol compounds showed varying degrees of downregulation, especially quercetin, dihydromyricetin, and luteolin. Quercetin decreased from 7.0 mg / kg to 4.3 mg / kg, a decrease of 37.7%. Dihydromyricetin decreased from 19.2 mg / kg to 11.1 mg / kg, a decrease of 41.2%. Luteolin decreased from 0.9 mg / kg to 0.4 mg / kg, a decrease of 53.3%. Some compounds, such as epigallocatechin gallate, gallic acid, and proanthocyanidins A1, showed a significant upward trend in content after supercritical extraction. For example, epigallocatechin gallate increased from 216.5 mg / kg in tea raw materials to 390.7 mg / kg, an increase of 80.5%; gallic acid increased from 541.8 mg / kg to 829.0 mg / kg, an increase of 53%; and proanthocyanidin A1 increased from 2.5 mg / kg to 6.2 mg / kg, an increase of 148.8%. These substances are also typical components of tea. Due to the preferential removal of other extractables during SFE, especially waxes, lipids, and other low-molecular-weight solids, the quality of the tea itself is reduced. Furthermore, the removal of these hydrophobic barriers (waxes and lipids) further alters the solid surface and pore structure, leading to significant enrichment and improved sample efficiency in solvent extraction. This rebalancing and enrichment pattern indicates that the core role of SFE in the composition of non-volatile substances is not a simple loss, but rather a combined effect through the partial selective removal and alteration of monomer contributions.

[0047] 3. Volatile component grouping analysis This invention uses GC-MS to analyze specific aroma components, and a total of 62 aroma compounds were identified (see Tables 4-6 for details), including 16 alcohols, 13 ketones, 7 terpenes, 5 esters, 6 aldehydes, 7 alkanes, and 8 other substances.

[0048] The contents of aldehydes, alkanes, and esters all increased to varying degrees in Example 1 and the five comparative examples 1-4. For example, the content of aldehydes in RATP was 93.39 μg / L, reaching a maximum of 190.50 μg / L in RH-E-SFE, a change of more than two times. These results suggest that the effect of SFE is not only reflected in the total loss, but more likely in the redistribution of volatile components, which is consistent with the aforementioned aroma sensory trajectory of overall aroma sensory intensity decreasing but different aroma dimensions changing at different rates. Benzaldehyde increased from 24.6 μg / L in tea raw materials to 39.6 μg / L, an increase of 60.8%, and phenylacetaldehyde increased from 51.9 μg / L to 133.4 μg / L, an increase of 156.9%.

[0049] Furthermore, some components showed a significant decrease after SFE treatment. For example, 3-octanol, whose OAV value decreased from 1.80 in RAPT to 0.55 in RH-E-SFE (81.2 μg / L to 24.6 μg / L), had a mushroom aroma, but after SFE treatment, it fell below its effective contribution range. Similarly, saffron aldehyde decreased from 2.85 to 0.94 (8.5 μg / L to 2.8 μg / L), which provides herbal and woody aromas. Neraldehyde, with its sweet aroma characteristics, saw its OAV value increase from <1 (imperceptible) in RAPT to a maximum of 7.30 (from <1 μg / L to 11.0 μg / L). These results provide concrete evidence of aroma alterations, demonstrating that changes in SFE only reduce aroma compounds and weaken aroma perception.

[0050] Table 4. Content of volatile components in tea leaves of different control groups Table 5. Content of volatile components in tea leaves of different control groups Table 6. Content of volatile components in tea leaves of different control groups 4. Sensory characteristics of the taste and aroma of tea products Non-volatile components provide the necessary "baseline" support for the flavor and mouthfeel of tea soup. Sensory evaluators, who have undergone screening and systematic training, evaluated the intensity of seven flavors in raw Pu-erh tea soup under different treatments, including sourness, sweetness, bitterness, saltiness, umami, astringency, and aftertaste. The specific results are shown in Table 7.

[0051] Table 7. Flavor scores of tea leaves from different treatment groups As shown in Table 7, compared with RAPT, all treatment groups showed an overall decrease in bitterness and astringency: bitterness decreased from 4.06 to 2.83 (RH-E-SFE); astringency also decreased from 3.06 to 2.11. Corresponding to the simultaneous reduction in bitterness and astringency, sweetness showed an upward trend. The sweetness value of RH-E-SFE was 1.94, significantly higher than that of the control group (1.39), suggesting that the reduction in bitterness and astringency may have enhanced the perceived significance of sweetness. In terms of aftertaste, it decreased from 3.39 to 2.61, consistent with the overall reduction in bitterness and astringency, indicating that SFE not only reduced the instantaneous bitterness and astringency intensity but may also have weakened or shortened the unpleasant aftertaste.

[0052] Conversely, umami remained relatively stable during processing, while sourness and saltiness showed only slight fluctuations without a clear trend. In summary, the sensory differences influenced by SFE were mainly concentrated on the bitterness, astringency, and aftertaste axes. Moisture pretreatment appeared to further enhance the mitigation of bitterness and astringency, while improving sweetness perception and aftertaste cleanliness. Further chemical analysis was conducted to identify non-volatile markers supporting the mitigation of bitterness and astringency and the enhancement of sweetness.

[0053] To evaluate the impact of different SFE flavor modification strategies on aroma perception, trained tasters scored the typical aroma attributes of six groups of samples, including green, herbal, floral, woody, and fresh. The specific results are shown in Table 8. The treatment groups showed the most significant reduction in green and herbal aromas. For example, the RH-SFE group saw a 40% decrease in the green aroma sensory score and a 38% decrease in the herbal aroma score, but floral and fresh aromas still accounted for 97% and 77% of the RAPT, respectively. Overall, the softening pretreatment was the most effective in reducing green and herbal aromas, thus demonstrating an advantage in suppressing unpleasant aroma dimensions, while also preserving floral aromas well.

[0054] Table 8 Aroma scores of tea leaves from different treatment groups In summary, this invention provides a method for improving the flavor of raw Pu-erh tea based on supercritical carbon dioxide extraction (SFE-CO2) technology, aiming to selectively regulate the aroma and taste of tea and enhance its sensory quality. Addressing the issues of flavor imbalance in traditional tea processing and the insufficient selective regulation of flavor components by existing technologies, this invention innovatively utilizes SFE-CO2 as a flavor reshaping tool. By optimizing process conditions (pressure, temperature, time) and co-solvent polarity (e.g., 95% vol edible alcohol) and matrix moisture adjustment (softening treatment), it achieves precise removal of unpleasant odor components (such as astringency and oxidative off-odors) and enhancement of pleasant aromas (floral, fruity, and sweet aromas). A combination of multi-platform chemical characterization (LC-UV, LC-QQQ-MS / MS, HS-SPME-GC-MS) and sensory evaluation reveals the steady-state retention of non-volatile matrices (total polyphenols, total free amino acids) and the recombination effect of monomeric polyphenols and volatile components by SFE-CO2 treatment, clarifying the changes in marker compounds (e.g., significantly increased ECG content and significantly decreased off-odor compound 3-octanol). This method significantly reduces the bitterness and astringency of tea while enhancing the perception of sweetness, effectively suppressing grassy / herbal aromas, preserving and highlighting floral characteristics, and without compromising the integrity of the tea leaves. This invention provides a scalable, mild, and precise flavor control strategy, offering technical support for improving the quality and diversifying tea products, combining practicality and innovation.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the flavor of tea leaves based on supercritical CO2, characterized by, Includes the following steps: The raw tea leaves are softened and then extracted using supercritical carbon dioxide fluid; the entrainer used in the extraction process is a polar alcohol solution.

2. The supercritical CO2-based tea flavor modification method according to claim 1, characterized by, The raw tea is Pu-erh raw tea.

3. The supercritical CO2-based tea flavor modification method according to claim 1 or 2, characterized by, The specific process for softening raw tea is as follows: spray water on the surface of the raw tea and then let it stand for 20-40 minutes; the water should be 20-40% of the weight of the raw tea.

4. The supercritical CO2-based tea flavor modification method according to claim 3, characterized by, Spray water onto the surface of the raw tea leaves and let it stand for 30 minutes; the water should be 30% of the weight of the raw tea leaves.

5. The supercritical CO2-based tea flavor modification method according to claim 1 or 2, characterized by, The polar alcohol solution is a C1-C4 fatty alcohol or an aqueous solution thereof.

6. The method for improving tea flavor based on supercritical CO2 according to claim 5, characterized in that, The polar alcohol solution is edible alcohol.

7. The method for improving tea flavor based on supercritical CO2 according to claim 1 or 2, characterized in that, The extraction pressure during the extraction process is 25-35 MPa, the extraction temperature is 55-65℃, and the extraction time is 2-4 h.

8. The method for improving tea flavor based on supercritical CO2 according to claim 7, characterized in that, The extraction pressure during the extraction process was 30 MPa, the extraction temperature was 60℃, and the extraction time was 3 hours.

9. The method for improving tea flavor based on supercritical CO2 according to claim 1 or 2, characterized in that, The flow rate of supercritical carbon dioxide fluid is 60-70 L / h, the temperature of the separation vessel is 35-45℃, and the pressure of the separation vessel adopts a two-stage separation of 8-12 MPa and 3-5 MPa.

10. Tea leaves improved by any one of the improvement methods described in claims 1-9.

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