Finished tea processing technology for improving flavor of crude and old leaves by using steam explosion technology

Abstract

The invention relates to a finished tea processing technology for improving the flavor of crude and old leaves by using a steam explosion technology. The finished tea processing technology comprises the following steps: picking green tea leaves: picking crude and old leaves and tea stems on tea trees for later use; steam explosion: placing the picked thick and old leaves and tea stems in a steam explosion device for steam explosion; the steam explosion conditions are as follows: the pressure is 0.4-1.0 MPa, the temperature is 140-180 DEG C, and the pressure stabilizing time is 1-5 minutes; and drying: drying the thick old leaves and the tea stems subjected to steam explosion. A traditional tea leaf processing technology is adjusted, the tea leaves are directly subjected to steam explosion after being picked, the coarse and old tea leaves are processed, and the flavor attribute of the coarse and old tea leaves is improved while the original leaf form is reserved. According to the method, the processing steps of the tea leaves are simplified, and the flavor attribute of the crude and old tea leaves which are only used for composting originally can be greatly improved, so that the crude and old tea leaves can be directly drunk, and high-value utilization of the crude and old tea leaves is realized.

Description

Technical Field

[0001] The invention belongs to the technical field of tea processing technology, and in particular relates to a finished tea processing technology for improving the flavor of coarse old leaves by using steam explosion technology. Background Art

[0002] The world's tea plantation area is 5.32 million hectares, of which China's tea plantation area is 3.33 million hectares, ranking first in the world, an increase of 2.0% year-on-year, accounting for 62.6% of the world's total tea plantation area. In 2022, the total global tea production was 6.477 million tons, a year-on-year increase of 0.4%. China continued to rank first in the world with an annual output of 3.181 million tons, accounting for 49.1% of the total output. The full-open fresh leaves, coarse old green leaves, and pruned branches and leaves produced during tea processing and tea garden maintenance cannot be effectively utilized because they do not meet the requirements of graded tea or are not picked in time due to weather reasons. They are almost useless except for being directly discarded, and the amount is astonishing.

[0003] For these rough and old leaves, current research focuses on extracting effective ingredients from them for the production of food additives, health products and daily necessities. In addition, although the fresh tea leaves from most tea gardens in summer, autumn and winter are not suitable for making graded tea, their tea polyphenols and tea polysaccharides content is higher than that of spring tea, and they are an important source of natural bioactive substances. If the flavor of rough and old leaves can be improved so that they can be drunk directly, it will have important industrial significance for the tea industry.

[0004] Steam explosion is a technology that uses pressure to inject water vapor into plant cells and thermally treats the cells through the instantaneous balance of pressure inside and outside the cells. The cell walls of the tea samples that have been steam-exploded are destroyed, the tissue structure is broken, and the dissolution rate of the contents is increased. In addition, the process only uses water vapor to do work, which is low-cost and environmentally friendly.

[0005] Traditional methods mostly use chemical extraction or biological enzymatic hydrolysis to process coarse old leaves, extract biologically active ingredients therein or prepare them into feed or fuel, which is easy to cause environmental pollution and has low utilization rate. It is rarely mentioned to process coarse old leaves into finished tea that can be directly consumed. In addition, the existing processed coarse old leaves are mostly used to prepare instant tea powder, and the tea leaves lose their original shape. The present invention uses steam explosion technology to process coarse old leaves, while retaining their original leaf shape and improving their flavor, and directly prepares them into finished tea that can be directly drunk. Summary of the invention

[0006] The purpose of the present invention is to provide a finished tea processing technology for improving the flavor of coarse and old leaves by using steam explosion technology. The technology can improve the flavor of coarse and old leaves while retaining their original leaf shape, and directly prepare them into finished tea that can be directly drunk.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A finished tea processing technology for improving the flavor of coarse old leaves by using steam explosion technology, comprising the following steps:

[0009] (1) Picking green tea leaves: picking the coarse old leaves and tea stems from the tea tree for later use;

[0010] (2) Steam explosion: The picked coarse old leaves and tea stems are placed in a steam explosion device for steam explosion; wherein the conditions for steam explosion are as follows: pressure of 0.4-1.0 MPa, temperature of 140-180° C., and pressure stabilization time of 1-5 min;

[0011] (3) Drying: Drying the coarse old leaves and tea stems after steam explosion, wherein the drying temperature is 60-100° C. and the drying time is 10 hours.

[0012] Preferably, in step (2), the conditions for steam explosion are as follows: pressure of 0.6 MPa, temperature of 158.86° C., and pressure stabilization time of 3 min.

[0013] In step (3), when the coarse old leaves and tea stems are dried, the coarse old leaves and tea stems are spread flat in an oven, and the drying temperature is 80° C. and the drying time is 10 hours.

[0014] The present invention also provides a finished tea obtained by the finished tea processing technology. The finished tea can generate aroma substances, and the aroma substances are a mixture of 2-formylpyrrole, 2-vinyl-6-methylpyrazine and α-furanmethanol.

[0015] The steam explosion device is a Qingzheng Ecological QBS-200 ICSE steam explosion test unit.

[0016] The tea tree is one of the varieties of green tea, black tea, oolong tea and white tea.

[0017] Compared with the prior art, the advantages of the present invention are: the present invention improves the traditional tea processing technology, adds a steam explosion process, retains the shape of the green tea leaves, and improves the flavor of the coarse old leaves, achieving multiple goals at one stroke. Based on the processing technology of the present invention, the coarse old leaves with thick cell walls can be processed into finished tea that can be directly consumed, thereby improving the utilization rate of the coarse old leaves and reducing damage to the environment. In addition, the green leaves do not require other processing steps except drying before and after steam explosion, which saves energy, and only produces water vapor during the steam explosion process, which is environmentally friendly.

[0018] The present invention adjusts the processing technology of traditional tea leaves, and processes the coarse and old tea leaves by directly steam-exploding the tea leaves after picking, thereby improving the flavor attributes of the coarse and old leaves while retaining the original leaf morphology. Sensory experiments have found that the flavor of the tea leaves after steam explosion is greatly improved compared with the coarse and old tea leaves. Except for the herbal aroma, the other aroma attributes are significantly enhanced; in terms of taste, the bitterness, astringency and green taste attributes are weakened, while the pleasant sweetness, freshness and aftertaste attributes are significantly enhanced, and the tea leaves produced under 0.6MPa have the best quality. Through GC×MS-TOF-MS experiments, it is found that as the steam explosion pressure increases, the number of volatile substances increases, the content of heterocyclic compounds increases significantly, and aroma compounds such as 2-formylpyrrole, 2-vinyl-6-methylpyrazine and α-furan methanol appear, which cannot be produced by traditional processes. Compared with traditional processes, the present invention simplifies the processing steps of tea leaves, can greatly improve the flavor attributes of coarse and old tea leaves that were originally only used for composting, and can be directly drunk, thereby realizing the high-value utilization of coarse and old tea leaves. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the standard curve between polyphenol content and absorbance value;

[0020] Figure 2 It is the standard curve between soluble sugar content and absorbance value;

[0021] Figure 3 Comparison of polyphenols and soluble sugar contents in tea soups prepared from tea leaves of different pressures

[0022] Figure 4 Comparison of polyphenols and soluble sugar contents in tea soups prepared from tea leaves with different stabilization times

[0023] Figure 5 Comparison of polyphenols and soluble sugar contents in tea soup prepared from tea leaves dried at different temperatures

[0024] Figure 6 Comparison of tea morphology of green tea leaves (A), Example 2 before drying (B), Comparative Example 1 (C) and Example 2 after drying (D)

[0025] Figure 7 Comparison of sensory properties of tea leaves in Example 2 and Comparative Examples 1-4;

[0026] Figure 8 Comparison of the distribution of volatile compounds of tea leaves in Example 2 and Comparative Examples 1-4;

[0027] Fig. 9 The heat map of volatile compounds of tea leaves of Example 2 and Comparative Examples 1-4;

[0028] Fig.10The contents of 2-formylpyrrole, 2-vinyl-6-methylpyrazine and α-furanmethanol in the tea leaves of Example 2 and Comparative Examples 1-4 are shown in FIG. DETAILED DESCRIPTION

[0029] The present invention is described in detail below with reference to the accompanying drawings and embodiments:

[0030] Example 1: Determination of pressure and stabilization time during steam explosion and determination of drying temperature during drying

[0031] 1.1 Experiment to determine the steam explosion pressure: 300 g of picked green tea leaves (including coarse old leaves and tea stems) were placed in a steam explosion device and steam exploded at different pressures (0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0 MPa) for 180 seconds. After explosion, the tea leaves were dried at 80°C for 10 hours.

[0032] 1.2 Experiment to determine the stabilization time of steam explosion: 300g of picked green tea leaves (including coarse old leaves and tea stems) were placed in a steam explosion device and stabilized at 0.6MPa for different times (60, 120, 180, 240, 300s). After explosion, the tea leaves were dried at 80℃ for 10h.

[0033] 1.3 Drying temperature determination experiment: The tea leaves after steam explosion (0.6 MPa, 180 s) were spread in an electric blast drying oven (DHG-9240A, Shanghai Yiheng Scientific Instrument Co., Ltd.) with a thickness of about 1 cm and dried at different temperatures (60, 70, 80, 90, 100 °C) for 10 h.

[0034] 1.4 Determination of the content of polyphenols (taking gallic acid as an example) and soluble sugar (taking glucose as an example) in the tea leaves obtained in steps 1.1, 1.2 and 1.3

[0035] 1.4.1 Experiment on polyphenols and soluble sugar content in tea soup

[0036] 1.4.1.1 Reagent preparation

[0037] Preparation of tea soup: Take 4.00 g of the dry tea leaves described in steps 1.1, 1.2, and 1.3 respectively, and brew them with 200 mL of boiling deionized water for 5 minutes.

[0038] Dilute the tea soup 100 times: measure 1mL of tea soup and dilute to 100mL with deionized water.

[0039] 7.5% sodium carbonate solution: Weigh 7.50 g of sodium carbonate and dilute to 100 mL with deionized water.

[0040] 10% Folin phenol solution: Take 10 mL of Folin phenol and dilute to 90 mL with deionized water.

[0041] 100 μg / mL gallic acid standard solution: Weigh 0.011 g of gallic acid and dilute to 100 mL with deionized water.

[0042] Drawing of the gallic acid standard curve: Take 200, 400, 800, 1200, 1600, and 2000 μL of gallic acid standard solution, respectively, add 1800, 1600, 1200, 800, 400, and 0 μL of deionized water, respectively, to prepare 6 gradients (10 μg / L, 20 μg / L, 40 μg / L, 60 μg / L, 80 μg / L, and 100 μg / L) of gallic acid solutions and determine the standard curve.

[0043] Anthrone ethyl acetate: Take 1 g of analytically pure anthrone, dissolve it in 50 mL of ethyl acetate, and store it in a brown bottle.

[0044] Concentrated sulfuric acid (specific gravity 1.84)

[0045] 1% glucose standard solution: Dry analytical grade glucose at 80°C to constant weight, accurately weigh 1.000g, add a small amount of water to dissolve, transfer to a 100mL volumetric flask, and dilute to the mark with distilled water.

[0046] 100ug / mL glucose standard solution: Accurately absorb 1mL of 1% glucose standard solution into a 100mL volumetric flask and add water to the scale.

[0047] 1.4.1.2 Testing Process

[0048] Experimental group: Take 200 μL of diluted tea soup and add 1 mL of Folin phenol reagent. After reacting for 5 minutes, add 800 μL of 7.5% sodium carbonate solution, shake evenly, and place at room temperature for 60 minutes. Then, measure the absorbance at a wavelength of 765 nm with a spectrophotometer and use the standard curve to calculate the polyphenol content.

[0049] Control group: Take 200 μL of deionized water into 1 mL of Folin phenol reagent, react for 5 minutes, then add 800 μL of 7.5% sodium carbonate solution, shake evenly, place at room temperature for 60 minutes, measure the absorbance at 765 nm with a spectrophotometer, and use the standard curve to calculate the polyphenol content.

[0050] The method for drawing the standard curve between gallic acid content (μg) and absorbance value is shown in Table 1. The obtained standard curve is shown in Figure 1 .

[0051] Table 1 Gallic acid standard curve detection steps

[0052]

[0053] Experimental group: Take 0.4 mL of diluted tea soup, add 0.1 mL of anthrone ethyl acetate reagent and 1 mL of concentrated sulfuric acid, keep the temperature in a boiling water bath for 10 min, and detect the absorbance at a wavelength of 620 nm after cooling.

[0054] Control group: Take 0.4 mL of distilled water, add 0.1 mL of anthrone ethyl acetate reagent and 1 mL of concentrated sulfuric acid, keep the temperature in a boiling water bath for 10 min, and detect the absorbance at a wavelength of 620 nm after cooling.

[0055] The method for drawing the standard curve between glucose content (μg) and absorbance value is shown in Table 2. The obtained standard curve is shown in Figure 2 .

[0056] Table 2 Standard curve detection steps for glucose

[0057]

[0058] 1.4.1.3 Calculation method of polyphenol and soluble sugar content

[0059] The data of the experimental group and the control group were inserted into the standard curve and multiplied by the dilution factor to calculate the content of polyphenols and soluble sugars. The experimental results are as follows: Figure 3-5 shown.

[0060] 1.4.1.4 According to this testing process, the content of polyphenols and soluble sugars in the tea brewed from steam-exploded tea leaves is higher than that in the control group. Moreover, under the conditions of 0.4-1.0MPa, constant pressure for 180s, and drying at 80℃ for 10h, the content of polyphenols and soluble sugars in the tea soup is relatively high, which will be used for the subsequent analysis of flavor attributes.

[0061] Example 2 A finished tea processing technology using steam explosion technology to improve the flavor of coarse old leaves

[0062] In this embodiment, finished tea is processed under the optimum pressure, pressure stabilization time and drying temperature, specifically:

[0063] (1) Preparation of tea leaves

[0064] Choose Wuyi Narcissus tea, and collect fresh coarse old leaves and tea stems in mid-July for later use.

[0065] (2) Steam explosion

[0066] Steam explosion was carried out in the test unit using the Qingzheng Ecological QBS-200 ICSE steam explosion test unit. 300g of green tea leaves were added to the test unit. Under a pressure of 0.6MPa, the temperature was 158.86℃, and the pressure was maintained for 3 minutes before being released instantly.

[0067] (3) Drying: Spread the steam-exploded tea leaves in an oven to a thickness of 1-2 cm and dry them at 80°C for 10 h to obtain steam-exploded white tea. The resulting tea leaves are complete in shape, such as Figure 6 shown.

[0068] In order to explore the effect of steam explosion on the sensory properties of tea, the present invention also conducted the following comparative experiments, as follows:

[0069] Comparative Example 1

[0070] The green tea leaves prepared in Example 2 (1) were directly dried at 80° C. for 10 h without steam explosion.

[0071] Comparative Example 2

[0072] It is basically the same as Example 2, except that the steam explosion pressure is 0.4 MPa and the temperature is 143.64°C.

[0073] Comparative Example 3

[0074] It is basically the same as Example 2, except that the steam explosion pressure is 0.8 MPa and the temperature is 170.44°C.

[0075] Comparative Example 4

[0076] It is basically the same as Example 2, except that the steam explosion pressure is 1.0 MPa and the temperature is 179.92°C.

[0077] Effects of steam explosion on sensory attributes of tea

[0078] The sensory attributes of the tea leaves prepared in Example 2 and Comparative Examples 1-4 were evaluated using the following evaluation method: refer to GB / T 23776-2018 "Tea Sensory Evaluation Method", tea-to-water ratio of 1:50, water temperature of 100°C, brewing for 5 minutes. A sensory panel of 22 trained volunteers reached consensus on the definitions of aroma and taste descriptors, scoring the aroma in six aspects: floral, fruity, grassy, ​​nutty, fatty, and woody; the taste was scored in six aspects: sweetness, bitterness, astringency, green, aftertaste, and freshness, with a full score of 8 points, 0 for no perception, and 8 for the strongest perception. The definitions of the descriptors are shown in Table 3, and the sensory results are shown in Table 3. Figure 7 shown.

[0079] Table 3

[0080]

[0081] Steam explosion improves the sensory attributes of tea. The sensory attributes of comparative example 1 and the other samples are quite different. After steam explosion, except for the herbal aroma of tea, the other aroma attributes are significantly increased. In terms of taste, the unpleasant bitterness, astringency and green taste scores are significantly reduced, and correspondingly, the pleasant sweetness, freshness and aftertaste are significantly enhanced. Interestingly, after steam explosion, the bitterness and astringency of Example 2 and comparative examples 2-4 are reduced to different degrees, indicating that steam explosion can reduce the bitterness of tea.

[0082] Steam explosion improves the sensory attributes of tea. The green and bitter tastes of comparative example 1 are stronger, while the intensity of each aroma attribute of tea after steam explosion increases, the bitter and green tastes decrease, and the fresh and sweet aftertaste are enhanced. Example 2 obtains the highest scores for floral aroma, fruity aroma, sweetness, freshness and sweet aftertaste.

[0083] Effect of steam explosion on volatile compounds of tea leaves

[0084] The volatile components of the tea leaves prepared in Example 2 and Comparative Examples 1-4 were detected by the following method:

[0085] The aroma of tea leaves was extracted using headspace solid phase microextraction technology, and the aroma was analyzed using a 7890B comprehensive two-dimensional gas chromatograph combined with an EI-TOF MS 0620 time-of-flight mass spectrometer as follows:

[0086] (1) Aroma extraction method:

[0087] Extraction fiber model: 50 / 30μm CAR / DVB / PDMS 57348-U.

[0088] Accurately weigh 0.1g tea powder and 1.5g NaCl in an 18mL headspace vial, then add 20μL 2-octanol (10mg / L, as internal standard). Then, add 5mL boiling water to the headspace vial and brew the tea for 5min. The headspace vial is sealed with a silicone septum. Subsequently, the vial is placed in a 50℃ water bath for 10 minutes. Then, the SPME extraction fiber is inserted into the headspace of the vial, and the volatile compounds are extracted in a 50℃ water bath for 50min. Next, the SPME extraction fiber is inserted into the gas chromatograph inlet and thermally decomposed at 250℃ for 5min.

[0089] (2) Aroma detection method:

[0090] Chromatographic conditions: The first-dimensional GC column was an HP-INNOWAX column (30.0 m × 0.25 mm × 0.25 μm, Agilent Technologies, USA), and the second-dimensional column was an Rxi-17 Sil MS column (2 m × 0.25 mm × 0.25 μm, Restech, USA). The injection port temperature was set at 250 °C, and high-purity He (99.999%) was used as the carrier gas at a flow rate of 1.4 mL / min.

[0091] The temperature program of the first-dimensional column oven was as follows: initial column temperature 40°C, 5 min; temperature increased to 120°C at 3°C / min; temperature further increased to 240°C at 6°C / min and maintained at 240°C for 5 min. The temperature of the second-dimensional column oven was 5°C higher than that of the first-dimensional column oven; the second-dimensional modulation cycle was 6s.

[0092] Mass spectrometry conditions: EI ion source temperature was set to 250 °C, scan rate was 101 spectra / s, solvent delay time was 300 s, EM voltage was 70 eV, and MS scan range was 45 to 550 amu.

[0093] pass Figure 8 By comparing the chromatograms, it can be seen that the profiles of volatile components of tea leaves after traditional process and steam explosion have changed greatly, and the number and content of aroma compounds have increased significantly. Among them, Example 2 produced the most volatile components and had the richest aroma attributes.

[0094] (3) Further analysis of the distribution of aroma compounds in the samples revealed a total of 56 volatile compounds, including 16 alcohol compounds, 7 aldehyde compounds, 5 hydrocarbon compounds, 8 ketone compounds, 14 heterocyclic compounds, 4 ester compounds, and 2 other compounds. Fig. 9 As shown, after steam explosion, 5 ketone compounds, 13 heterocyclic compounds and 2 ester compounds are newly generated, among which Pyrrole-2-carboxaldehyde (2-formylpyrrole), 2-Ethenyl-6-methyl-pyrazine (2-vinyl-6-methylpyrazine), Furfuryl alcohol (α-furan methanol) have never been found in tea, but in this patent, they are not detected in Comparative Example 1, and the content gradually increases in Comparative Example 2, Example 2, Comparative Examples 3-4. They are newly generated compounds in this process, and they show caramel and nut aroma ( Fig.10). Although Pyrrole-2-carboxaldehyde (2-formylpyrrole), 2-Ethenyl-6-methyl-pyrazine (2-vinyl-6-methylpyrazine), and Furfuryl alcohol (α-furan methanol) are not the most in Example 2, from a comprehensive evaluation, Example 2 has the best flavor. That is, when the steam explosion pressure is 0.6MPa, the temperature is 158.86℃, the pressure stabilization time is 3min, the drying temperature is 80℃, and the drying time is 10h. The obtained finished tea has the best flavor.

[0095] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A finished tea processing technology using steam explosion technology to improve the flavor of coarse old leaves, characterized by: It includes the following steps: (1) Picking green tea leaves: picking the coarse old leaves and tea stems from the tea tree for later use; (2) Steam explosion: The picked coarse old leaves and tea stems are placed in a steam explosion device for steam explosion; wherein the conditions for steam explosion are as follows: pressure of 0.4-1.0 MPa, temperature of 140-180° C., and pressure stabilization time of 1-5 min; (3) Drying: Drying the coarse old leaves and tea stems after steam explosion, wherein the drying temperature is 60-100° C. and the drying time is 10 hours.

2. The finished tea processing technology according to claim 1, characterized in that: In step (2), the conditions of steam explosion are as follows: pressure is 0.6 MPa, temperature is 158.86° C., and pressure stabilization time is 3 min.

3. The finished tea processing technology according to claim 2, characterized in that: In step (3), when the coarse old leaves and tea stems are dried, the coarse old leaves and tea stems are spread flat in an oven with a leaf thickness of 1-2 cm and the drying temperature is 80°C.

4. A finished tea obtained by the finished tea processing process according to any one of claims 1 to 3, characterized in that: The finished tea product can generate aroma substances, which are a mixture of 2-formylpyrrole, 2-vinyl-6-methylpyrazine and α-furanmethanol.

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