Processing method for directionally regulating and controlling flower and fruit aroma quality of black tea based on static magnetic field assisted drying

Abstract

The invention discloses a processing method for directionally regulating and controlling flower and fruit aroma quality of black tea based on static magnetic field assisted drying. The processing method comprises the following steps: naturally withering fresh tea leaves until the water content is 60-62%; performing gradient rolling on the withered tea leaves; fermenting under the conditions that the temperature is 28-30 DEG C and the RH is 95% + / -0.1%; the moisture content is reduced to 15% + / -1% by adopting hot air gross fire drying at 110 + / -0.2 DEG C; spreading and cooling at room temperature for 30-32 minutes; the full-fire drying temperature is set to be 70 + / -0.1 DEG C, the drying time is 15-16 min, and in the process, a static magnetic field of 3-9 mT is applied for auxiliary treatment till the water content is smaller than or equal to 6%; the static magnetic field assisted drying method can effectively promote the release of linalool, geraniol and cis-jasmonone, so that the odor activity value is obviously improved. The magnetic field drying technology is applied to directional regulation and control of the flower and fruit aroma quality of the black tea for the first time, the aroma metabolism pathway is precisely regulated and controlled through the non-thermal action, and the method has important application prospects.

Description

Technical Field

[0001] This invention relates to the field of tea processing technology, specifically to a processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying. Background Technology

[0002] Black tea, as one of the world's three major beverages, occupies an important position in global tea consumption. China is the birthplace of black tea, which is beloved by consumers for its unique aroma, flavor, and health benefits. Among the six major tea categories (green tea, black tea, oolong tea, white tea, yellow tea, and dark tea), black tea, due to its full fermentation process, possesses the unique characteristics of "red leaves and red liquor," with a rich aroma and mellow taste, especially floral and fruity black teas. Black tea is not only popular in the domestic market but also holds a significant share in the international market, being one of China's main tea export categories. The quality characteristics of black tea are mainly determined by its aroma, flavor, and color, with aroma being one of the core indicators for evaluating black tea quality. Floral and fruity black teas, with their fresh and elegant aroma, represent high-end black teas and have high market value. Therefore, how to enhance the floral and fruity aroma of black tea through processing technology has become an important research direction in the field of black tea processing.

[0003] The processing of black tea mainly includes four key steps: withering, rolling, fermentation, and drying. Drying is the final step in black tea processing, determining not only the moisture content and storage stability of the tea leaves but also significantly influencing aroma formation. Traditional black tea drying processes often employ hot air drying, using high temperatures to remove moisture from the tea leaves while simultaneously promoting aroma formation. However, traditional drying processes have the following problems: First, high-temperature drying easily leads to the thermal degradation of aroma substances, especially key aroma components in floral and fruity teas (such as linalool and cis-jasmone), which are prone to volatilization or decomposition at high temperatures, reducing the aroma quality of the black tea. Second, traditional drying processes provide relatively crude regulation of aroma metabolic pathways, making it difficult to achieve targeted control of aroma components, resulting in less prominent aroma characteristics in the black tea. Finally, traditional drying processes are energy-intensive, which is inconsistent with the development trend of green processing.

[0004] In recent years, with the advancement of food processing technology, some novel drying technologies (such as vacuum drying, microwave drying, and freeze drying) have been introduced into the tea industry, aiming to improve the aroma quality and processing efficiency of tea. However, these technologies still have limitations in practical applications. For example, while vacuum drying and freeze drying can better preserve the aroma components of tea, they are costly to operate and have long processing cycles, making large-scale production difficult. Microwave drying, although highly efficient, can easily lead to uneven heating of the tea leaves, affecting their aroma quality. Therefore, developing a processing technology that can both efficiently dry tea leaves and precisely control their aroma quality has become an urgent problem to be solved in the black tea processing industry.

[0005] Magnetic field drying technology, as an emerging non-thermal processing technology, has shown broad application prospects in the food processing field in recent years. This technology achieves a highly efficient and energy-saving drying process by applying a static or alternating magnetic field of specific intensity, utilizing the magnetic field's ability to regulate the molecular structure and water migration of substances. Studies have shown that magnetic fields can induce the directional migration of water molecules in food, improving drying efficiency. Simultaneously, through non-thermal effects, it alters the conformation of macromolecules such as proteins and polysaccharides, promoting Maillard reactions and the formation of aroma compounds. Compared with traditional thermal drying, magnetic field drying has advantages such as low energy consumption, high efficiency, and minimal damage to heat-sensitive substances, providing a new technical pathway for the targeted enhancement of aroma quality in black tea processing. This invention is the first to introduce magnetic field drying technology into black tea processing, providing an innovative solution for the targeted enhancement of floral and fruity aromas in black tea by optimizing magnetic field parameters and precisely regulating aroma metabolic pathways. Summary of the Invention

[0006] This invention provides a processing method for directionally regulating the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying. This invention is the first to apply magnetic field drying technology to the directional regulation of floral and fruity aroma quality in black tea, precisely controlling aroma metabolism pathways through non-thermal effects, providing an innovative solution for green food processing.

[0007] The specific technical solution is as follows: A processing method for directionally regulating the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying includes the following steps: (1) Withering of fresh leaves: Fresh tea leaves are naturally withered until the moisture content of the tea leaves drops to 60%~62%; (2) Gradient rolling: Roll the withered tea leaves according to the following procedure: empty rolling → light rolling → heavy rolling → light rolling → empty rolling to break up clumps; (3) Temperature and humidity controlled fermentation: The tea leaves after breaking up the clumps are fermented at 28~30℃ and 95%±0.1% relative humidity (RH); (4) After fermentation, the tea leaves are dried in sections by initial drying, cooling, and final drying: Drying process: 110±0.2℃ hot air drying until moisture content is 15%±1%; Cool: Let it cool at room temperature for 30-32 minutes; Sufficient drying: Set the drying temperature to 70±0.1°C and the drying time to 15~16 min. During the sufficient drying process, apply a static magnetic field of 3~9 mT, preferably 5~7 mT, and even more preferably 6 mT, until the moisture content is ≤6%. The processing method promotes the release of linalool, geraniol and cis-jasmone, thereby increasing the odor activity value (OAV) of linalool, geraniol and cis-jasmone.

[0008] This invention introduces magnetic field-assisted drying, which can enhance the aroma quality of black tea, especially floral and fruity aromas. Magnetic field drying induces a shift in the secondary structure of proteins from disorder to order (β-sheet / β-turn dominant), thereby regulating enzyme activity and protein hydrolysis, and promoting the release of floral and fruity aroma components such as linalool, geraniol, and cis-jasmine. At the same time, magnetic field drying alters the physical distribution of water molecules in tea leaves (bound water rises, free water sinks) and their mobility. More water molecules in the tea leaves are converted into bound water, while free water, which easily leads to flavor loss, is significantly reduced, thus most effectively preserving and stabilizing the volatile flavors of the tea.

[0009] Step (4) preferably involves applying a 6 mT static magnetic field during the foot drying process. The magnetic field strength is as follows: 1) Quantitative descriptive analysis (QDA) showed that the floral aroma (4.8) and fruity aroma (4.5) intensities reached their peak values; 2) Significantly improved the odor activity values ​​of key odor active substances in floral and fruity aromas, with linalool increasing by 80.5%, geraniol by 77.5%, and cis-jasmone by 165.31%; 3) Fourier transform infrared spectroscopy (FT-IR) results showed that the magnetic field induced protein secondary structure reorganization, with β-sheets decreasing to 32.1% and α-helices increasing to a peak of 25.0% at 6 mT, thereby regulating enzyme activity and promoting protein hydrolysis, thus promoting the formation of floral and fruity aromas; 4) The magnetic field affected the physical distribution and mobility of water molecules in the tea sample, significantly reducing the proportion of free water (T23), reaching its lowest value (0.22%) at 6 mT. Lower free water content can slow down the loss of flavor components and is beneficial for the retention and stability of volatile flavors in tea.

[0010] In the processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying, in step (1), the fresh tea leaves are preferably Fuding Da Bai tea leaves with one bud and two leaves.

[0011] Preferably, in the processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying, in step (1), the fresh tea leaves are naturally withered in a well-ventilated indoor area.

[0012] Preferably, in the processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying, in step (1), the leaf thickness is 2 cm during natural withering, and the leaves are turned over once every 120 minutes.

[0013] Preferably, in the processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying, in step (2), the kneading is carried out in a kneading machine.

[0014] Preferably, in the processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying, the kneading temperature in step (2) is 25±0.5℃.

[0015] Preferably, in the processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying, in step (2), the following kneading procedure is followed: kneading without air for 25~26 min → kneading lightly for 20~21 min → kneading heavily for 10~11 min → kneading lightly for 15~16 min → kneading without air for 5~6 min.

[0016] Preferably, in the processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying, the kneading frequency in step (2) is 45~50 r / min.

[0017] Preferably, in the processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying, fermentation is carried out in a fermenter in step (3).

[0018] Preferably, in the processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying, the fermentation time in step (3) is 3.5 ± 0.5 h.

[0019] Preferably, in the processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying, in step (4) the initial drying is carried out by box-type hot air drying for 20-21 minutes.

[0020] Compared with the prior art, the beneficial effects of this invention are as follows: 1. Precisely regulate aroma components to significantly improve the quality of floral and fruity aromas.

[0021] This invention introduces magnetic field-assisted drying technology to regulate the aroma metabolism pathway of black tea, significantly increasing the OAV value of key aroma active substances in floral and fruity aromas. Among them, linalool increased by 80.5%, geraniol by 77.5%, and cis-jasmone by 165.31%, thus optimizing the aroma characteristics of black tea and making it more floral and fruity.

[0022] 2. Optimized protein secondary structure, promoting the synthesis of floral and fruity volatile compounds.

[0023] Magnetic field-assisted drying induces a shift in the secondary structure of proteins in tea leaves from disorder to order (reduction of β-sheets and increase of α-helices), thereby regulating enzyme activity and promoting the synthesis of floral and fruity volatile compounds, providing molecular-level theoretical support for improving aroma quality.

[0024] 3. Improves moisture distribution and stabilizes volatile substances.

[0025] Magnetic field drying alters the physical distribution of water molecules in tea leaves, converting more water molecules into bound water while significantly reducing free water that easily leads to flavor loss. This effectively stabilizes volatile flavor components, making the aroma of tea more lasting.

[0026] 4. Improves drying efficiency, saves energy and is environmentally friendly.

[0027] Magnetic field-assisted drying technology improves moisture migration efficiency through non-thermal action, simplifies the complex process of traditional black tea processing, lowers drying temperature, shortens drying time, and reduces energy consumption, providing a green and energy-saving innovative solution for tea processing.

[0028] In summary, this invention is the first to apply magnetic field drying technology to the targeted regulation of floral and fruity aromas in black tea. By precisely regulating aroma metabolism pathways through non-thermal processes, it avoids aroma loss or quality degradation that may occur with traditional thermal processing. This provides a green and efficient innovative method for black tea processing and has significant application prospects. Attached Figure Description

[0029] Figure 1 The figure shows the ODA analysis results of tea samples under different magnetic field intensities in a specific implementation method.

[0030] Figure 2 The images show the LF-NMR spectra of tea samples treated with different magnetic field intensities in a specific implementation method.

[0031] Figure 3 The image shows the FT-IR characterization results of tea samples treated with different magnetic field intensities in a specific implementation method.

[0032] Figure 4 The figure shows the analysis results of aroma components of tea samples under different magnetic field intensities in a specific implementation method.

[0033] Figure 5 The figure shows the OAV analysis results of the aroma components of tea samples under different magnetic field intensities in a specific implementation method. The data in the figure have been Z-score normalized. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Operating methods not specifically specified in the following embodiments are generally performed under conventional conditions or as recommended by the manufacturer.

[0035] Experimental section: Instruments and apparatus: Gas chromatography-triple quadrupole mass spectrometry (GC-MS), Agilent 7890B-7000C (USA); constant temperature mixer, Hangzhou Mio Instrument Co., Ltd.; electronic balance, Beijing Sartorius Scientific Instruments Co., Ltd.; 6CR-25 tea rolling machine, Zhejiang Chunjiang Tea Machinery Co., Ltd.; 6CJK-20 de-clumping machine, Zhejiang Lvfeng Machinery Co., Ltd.; JY-6CFJ-0.7 black tea fermentation machine, Fujian Jiayou Tea Machinery Intelligent Technology Co., Ltd.; 6CHT-16 box-type aroma enhancer, Zhejiang Zhufeng Machinery Co., Ltd.; MFT10 magnetic field drying oven, Induster (Wuxi) Induction Technology Co., Ltd.

[0036] Materials and reagents: This study used fresh leaves of Fuding Da Bai tea as experimental material, which were collected from the Shengzhou Experimental Base of the Tea Research Institute of the Chinese Academy of Agricultural Sciences. The picking standard was one bud and two leaves, and the moisture content of the fresh leaves was 79.85%. The picking time was early April 2024. The 20mL headspace vials and matching 18 mm magnetic PTFE / silicone caps were purchased from Agilent Technologies, Inc., USA. The purified water was purchased from Hangzhou Wahaha Group Co., Ltd., USA. The SPME handle and DVB / CAR / PDMS extraction head were purchased from Supelco, Inc., USA.

[0037] Tea making process: The harvested one-bud-two-leaf Fuding Da Bai tea leaves are naturally withered indoors in a well-ventilated area. The leaves are spread out to a thickness of 2 cm, and turned every two hours or so. Withering is stopped when the moisture content of the tea leaves drops to 60%~62%. Then, the leaves are rolled in a rolling machine at 25°C. The rolling procedure is: 25 min of empty rolling → 20 min of light rolling → 10 min of heavy rolling → 15 min of light rolling → 5 min of empty rolling, at a rolling frequency of 45 r / min. After rolling, the leaves are broken up using a de-clumping machine. The broken-up tea leaves are then placed in a fermentation machine for temperature and humidity controlled fermentation at 28°C and 95% RH for 3~4 hours. A box-type hot air drying oven is used for initial drying at 110°C for 20 minutes, until the moisture content of the tea leaves drops to about 15%. After cooling to room temperature for half an hour, the leaves are then subjected to final drying at 70°C for 15 minutes. During the drying process, a static magnetic field of specific intensity was applied to assist in the treatment. The intensity of the gradient magnetic field was compared by setting 0 mT, 3 mT, 6 mT and 9 mT respectively until the moisture content was ≤6%.

[0038] Quantitative descriptive analysis (QDA) of aroma characteristics: A panel of six trained expert evaluators conducted quantitative descriptive analysis (QDA) of the aroma characteristics of black tea samples processed under different magnetic field intensities. The specific procedure was as follows: First, 3 grams of tea sample were placed in a tasting cup and steeped with 150 ml of boiling water for 5 minutes. Then, the tea liquor was filtered and poured into tasting bowls. The evaluators assessed multiple aroma dimensions, including oily, malty, floral, fruity, and grassy notes. Each attribute was evaluated using a 5-point intensity scale (0 = none, 5 = very strong), and each sample was evaluated three times.

[0039] Low-field nuclear magnetic resonance analysis: Low-field nuclear magnetic resonance (LF-NMR) analysis was performed using a MesoMR23-060H-I instrument (Suzhou Numai Analytical Instruments Co., Ltd., Suzhou, China). In this study, transverse relaxation (T2) decay profiles were acquired using a CarrPurcell-Meiboom-Gill (CPMG) sequence. Optimized acquisition parameters were as follows: 90° pulse width (P1) = 6.6 μs, 180° pulse width (P2) = 10.64 μs, receiver frequency width = 250 kHz, spectrometer frequency = 12 MHz, RF delay time = 0.02 ms, wait time = 3500 ms, number of scans = 16, number of echoes = 5000, TE = 0.12 ms. The raw T2 decay data were then subjected to inverse Laplace transform using dedicated software to generate the relaxation time distribution spectrum.

[0040] Fourier transform infrared spectroscopy (FT-IR) analysis: Fourier transform infrared (FT-IR) spectroscopy analysis was performed using a Nicolet iS20 spectrometer (Thermo Fisher Scientific, USA). Samples were pre-ground into powder. In a dry environment, a small amount of sample was mixed with dry potassium bromide (KBr) powder in an agate mortar and ground thoroughly. The homogeneous mixture was then pressed into transparent thin films using a hydraulic press. Background spectra were acquired before sample analysis. Sample spectra were collected in the range of 400–4000 cm⁻¹. -1 Recorded within the range, with a resolution of 4 cm. -1 A total of 32 scans were performed.

[0041] GC-MS / MS analysis: Volatile compounds were extracted using headspace solid-phase microextraction (HS-SPME). The specific procedure was as follows: 0.5 g of tea leaves were weighed using an electronic balance and placed in a 20 mL headspace vial. 5 mL of purified water was added, and the vial was tightly sealed. A DVB / CAR / PDMS fiber was inserted into the headspace vial to absorb the volatile components, and the vial was fixed in a constant-temperature mixer for aroma enrichment. Extraction was performed at a constant temperature of 60°C for 60 minutes. After extraction, the fiber tip was inserted into the GC inlet, and desorption was performed at 250°C for 5 minutes. Each sample was tested in triplicate. Volatile compounds were analyzed using an Agilent 7890B-7000C GC-MS / MS. A DB-5MS column (30 m × 0.25 mm × 0.25 μm, Agilent, USA) was used. The initial column temperature was 40 °C for 5 min, followed by a ramp-up to 160 °C at a rate of 4 °C / min (hold for 5 min). Splitless mode was used with helium (purity >99.999%) as the carrier gas at a constant flow rate of 1.0 mL / min. High-purity nitrogen (purity >99.999%) was used as the collision gas at a flow rate of 1.5 mL / min, while helium was used as the quencher at a flow rate of 2.25 mL / min. Mass spectrometry was run in multiple reaction monitoring (MRM) mode with a collision-induced dissociation energy of 20 V. The injector temperature was 230 °C, and the transfer line and ion source temperatures were set to 270 °C and 230 °C, respectively. Set the quality resolution of MS1 to the widest setting, and set the quality resolution of MS2 to units.

[0042] Volatile compounds were accurately quantified using the external standard method. A standard curve was constructed using a series of mixed calibration solutions with different concentration gradients, R0 2 ≥0.99.

[0043] Aroma activity value analysis: Aroma Activity (OAV) is a commonly used method to assess the contribution of volatile compounds to the aroma quality of tea. It is calculated by dividing the concentration (C) of a volatile compound by its perceived threshold (OT) in water, specifically using the formula: OAV = C / OT.

[0044] Data Analysis: All tea samples were tested three times. The concentrations of volatile compounds are expressed as mean ± variance. Pie charts and radar charts were generated using Origin 2021 software; HCl analysis and OAV heatmaps of key odor compounds were performed using TBtools software.

[0045] The effects of different magnetic field strengths on the aroma and quality of black tea: Quantitative descriptive analysis (QDA) results on the evaluation of aroma quality of black tea treated with different magnetic field strengths ( Figure 1The results showed significant differences in aroma properties among the treatment groups. The floral aroma intensity was 6 mT (4.8) > 9 mT (4.2) > 0 mT (3.9) > 3 mT (3.5), while the fruity aroma characteristics followed a pattern of 6 mT (4.5) > 3 mT (4.0) > 9 mT (3.9) > 0 mT (2.9). Furthermore, the 6 mT treatment group exhibited significantly better fatty aromas than other treatment groups and had the lowest grassy aroma content. These data indicate that 6 mT magnetic field treatment can enhance the floral and fruity aromas of black tea while effectively reducing undesirable grassy aromas, thus significantly optimizing the aroma quality of black tea. These findings confirm that magnetic field drying, as a precise means of controlling the aroma chemistry of tea, has a specific impact on the formation and degradation pathways of volatile compounds.

[0046] Low-field nuclear magnetic resonance (LF-NMR) analysis of moisture state changes during magnetic field-assisted drying: Figure 2 LF-NMR spectra of black tea samples treated with different magnetic field intensities are presented. The T2 relaxation time can be used to describe the mobility of three water states (bound water, semi-bound water, and free water). A smaller T2 value indicates lower water mobility and stronger binding to the material; conversely, a larger T2 value indicates higher mobility. Three distinct relaxation peaks were identified in the samples treated with different magnetic fields: T21 (0.01–4 ms) corresponds to bound water, which interacts with intracellular molecules through hydrogen bonds; T23 (38–622 ms) represents free water, located in the extracellular space and exhibiting the highest mobility; and T22 (1.8–33.7 ms) represents semi-bound water, falling between the two. These three water states can be quantified by changes in their respective peak areas (P21, P22, and P23, respectively). The T21 signal peak has the largest proportion, indicating that bound water dominates in all magnetic field treatments. Crucially, the proportion of bound water (T21) generally increased, reaching its peak at 9 mT (92.99%), indicating that magnetic field treatment promoted the conversion of water molecules into bound water. We hypothesize that the magnetic field, by influencing molecular polarity or hydrogen bond networks, promoted hydrogen bonding between water molecules and macromolecules such as tea polyphenols and polysaccharides. The proportion of weakly bound water (T22) first increased and then decreased, peaking at 3 mT (11.11%). After magnetic field drying, the proportion of free water (T23) decreased significantly, reaching its lowest content (0.22%) at 6 mT. Lower free water content can mitigate the loss of flavor components, which is beneficial for the retention and stability of volatile flavors in tea. These results suggest that different magnetic field treatments affect the physical distribution and mobility of water molecules in tea samples, which may contribute to the retention of volatile flavors, with the 6 mT treatment showing the most significant effect.

[0047] Fourier transform infrared spectroscopy (FT-IR) analysis: FT-IR characterization was performed on tea samples treated with different magnetic field intensities, and the results are as follows: Figure 3 As shown. The infrared spectrum at 3410 cm⁻¹ -1 A broad peak is observed nearby, attributed to the NH / OH stretching vibrations of proteins and polysaccharides; 2923 cm⁻¹ -1 The nearby peak corresponds to the asymmetric CH stretching vibration of the methyl group; 1648 cm⁻¹ -1 The nearby peaks are mainly attributed to the C=O stretching vibration in the amide I region; 1517 cm⁻¹ -1 The nearby characteristic peaks indicate the presence of aromatic rings, confirming the skeletal characteristics of polyphenols; 1455 cm⁻¹ -1 The nearby peak originates from the asymmetric bending vibration of CH3, 1369 cm⁻¹ -1 The nearby peak is due to the shear vibration of CH3; 1238 cm⁻¹ -1 and 1147 cm -1 The nearby peaks reflect CO stretching vibrations.

[0048] Infrared spectra of the amide I band region (1700-1600 cm⁻¹) of four samples -1 Deconvolution analysis was performed to obtain the values ​​corresponding to β-folds (1610-1640 cm). -1 ), random curls (1640-1650 cm) -1 ), α-helix (1650-1658 cm) -1 ) and β-turn (1660-1695 cm) -1 The relative peak area percentage of the amide I band (1700-1600 cm⁻¹). -1 Analysis revealed that the drying process induced conformational remodeling of the protein. As the magnetic field strength increased from 0 mT to 6 mT, the β-sheet content decreased from 38.1% to 32.1%, then rebounded to 37.9% at 9 mT, indicating unfolding and refolding of the structure. Simultaneously, the β-turn content steadily increased from 6.7% to 19.1%, indicating molecular compression. The increase in β-sheet and β-turn may inhibit enzyme activity (such as oxidases and hydrolases), thereby reducing adverse reactions, such as off-flavors produced by lipid oxidation. At a moderate magnetic field strength (6 mT), the α-helix content peaked (25.0%). The increase in α-helix may expose proteolytic sites, promoting protein hydrolysis to release free amino acids (such as theanine), serving as precursors for Maillard reactions and Streak degradation. The random coil content steadily decreased from 37.5% to 22.1%, reflecting a trend towards molecular ordering. Furthermore, with increasing magnetic field strength, the FT-IR band increased from 1037 cm⁻¹. -1 To 1046 cm -1The movement of these sugars indicates that the carbohydrates have changed. These sugars, as substrates for the Maillard reaction, generate characteristic aroma compounds such as malty notes.

[0049] Analysis of the effects of different magnetic field strengths on the aroma components of black tea: Volatile compounds were analyzed in black tea samples treated with different magnetic field intensities using GC-MS / MS, identifying a total of 56 volatile compounds. These compounds covered eight major classes, including 12 esters, 16 aldehydes, 14 alcohols, 6 ketones, 3 alkenes, 2 aromatic compounds, 2 phenols, and 1 heterocyclic compound. Aldehydes and alcohols accounted for the highest proportions, at 28.6% and 25%, respectively. Figure 4 ).

[0050] Analysis of the effects of different magnetic field strengths on key aroma components of black tea: OAV (Odor Activity Value) analysis results showed that 24 aromatic compounds played important roles in the aroma formation process of black tea under magnetic field treatment. These compounds mainly exhibited characteristic aroma properties such as fatty, floral, and fruity aromas. Figure 5 As shown, magnetic field treatment significantly altered the OAV values ​​of key aromatic active compounds in black tea, with the 6 mT magnetic field treatment exhibiting the most significant enrichment effect on characteristic aromas. Notably, compounds with floral and fruity aroma characteristics all reached peak levels in this treatment group. Specifically, the 6 mT magnetic field treatment increased the OAV value of linalool (floral aroma) by 80.5%, geraniol (floral aroma) by 77.5%, and cis-jasmone (fruity aroma) by a substantial 165.31%, thus significantly improving the overall aroma characteristics of black tea. This result suggests that an appropriate magnetic field strength may optimize the aroma quality of black tea by regulating the accumulation of specific aroma compounds.

[0051] In summary, this invention provides a processing method for directionally enhancing the floral and fruity aroma quality of black tea based on magnetic field-assisted drying. This is the first time magnetic field drying technology has been applied to black tea processing, precisely regulating aroma metabolism pathways through non-thermal effects and significantly improving the aroma quality of black tea. By comparing magnetic field strengths of 0, 3, 6, and 9 mT, 6 mT was determined to be the optimal magnetic field parameter. At this strength, magnetic field-assisted drying can significantly improve the floral and fruity aroma quality of black tea. The 6 mT magnetic field treatment significantly increased the OAV values ​​of key aroma active substances in floral and fruity aromas, with linalool increasing by 80.5%, geraniol by 77.5%, and cis-jasmone by 165.31%, thus optimizing the aroma characteristics of black tea. FT-IR analysis revealed that magnetic field-induced protein secondary structure transition from disorder to order (β-sheet / β-turn dominant), thereby regulating enzyme activity and Maillard reactions. Simultaneously, LF-NMR confirmed that magnetic field drying altered the physical distribution and mobility of water molecules in tea leaves, converting more water molecules into bound water while significantly reducing free water, which easily leads to flavor loss. This effectively preserves and stabilizes the volatile flavors of tea. This invention is the first to apply magnetic field drying technology to the targeted regulation of floral and fruity aromas in black tea. By precisely controlling aroma metabolism pathways through non-thermal effects, it provides a green and efficient processing method for improving the quality of black tea, possessing significant theoretical importance and application prospects.

[0052] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A processing method for directionally regulating the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying, characterized in that, Including the following steps: (1) Withering of fresh leaves: Fresh tea leaves are naturally withered until the moisture content of the tea leaves drops to 60%~62%; (2) Gradient rolling: Roll the withered tea leaves according to the following procedure: empty rolling → light rolling → heavy rolling → light rolling → empty rolling to break up clumps; (3) Temperature and humidity controlled fermentation: The tea leaves after breaking up the clumps are fermented at 28~30℃ and 95%±0.1% RH; (4) After fermentation, the tea leaves are dried in sections by initial drying, cooling, and final drying: Drying process: 110±0.2℃ hot air drying until moisture content is 15%±1%; Cool: Let it cool at room temperature for 30-32 minutes; Sufficient drying: Set the drying temperature to 70±0.1°C and the drying time to 15~16 min. During the sufficient drying process, apply a static magnetic field of 3~9 mT, preferably 5~7 mT, and even more preferably 6 mT, until the moisture content is ≤6%. The processing method promotes the release of linalool, geraniol and cis-jasmone, thereby increasing the odor activity values ​​of linalool, geraniol and cis-jasmone.

2. The processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying according to claim 1, characterized in that, In step (1), the fresh tea leaves are Fuding Da Bai tea leaves with one bud and two leaves.

3. The processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying according to claim 1, characterized in that, In step (1): Fresh tea leaves are naturally withered indoors in a well-ventilated area. During natural withering, the leaves are spread out to a thickness of 2 cm, and turned over every 120 minutes.

4. The processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying according to claim 1, characterized in that, In step (2), the kneading is carried out in a kneading machine.

5. The processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying according to claim 1, characterized in that, In step (2), the kneading temperature is 25±0.5℃.

6. The processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying according to claim 1, characterized in that, In step (2), knead according to the following procedure: knead without kneading for 25~26 min → knead lightly for 20~21 min → knead heavily for 10~11 min → knead lightly for 15~16 min → knead without kneading for 5~6 min.

7. The processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying according to claim 1, characterized in that, In step (2), the kneading frequency is 45~50 r / min.

8. The processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying according to claim 1, characterized in that, In step (3), fermentation is carried out in a fermenter.

9. The processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying according to claim 1, characterized in that, In step (3), the fermentation time is 3.5 ± 0.5 h.

10. The processing method for directional regulation of the floral and fruity aroma quality of black tea based on static magnetic field-assisted drying according to claim 1, characterized in that, In step (4), the raw material is dried using a box-type hot air dryer for 20-21 minutes.

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