Preparation process of jujube leaf green tea

Abstract

This invention relates to a preparation process for jujube leaf green tea, comprising the following steps: Step 1, material selection and cleaning; Step 2, spreading and fixing: after spreading the leaves to dry at room temperature, stir-frying at 110-130℃ for 1-2 minutes, then removing from the pan and setting aside; Step 3, plasma treatment: spraying deionized water onto the leaves to adjust the moisture content, then performing cold plasma treatment, followed by drying at below 60℃; Step 4, rolling: rolling the leaves for 5-30 minutes until they curl into strips; Step 5, drying, shaping, and aroma enhancement: stir-frying at 60-100℃ for 18-22 minutes, continuing to roll and shape during the stir-frying process, then cooling to 40℃ and stir-frying for 13-17 minutes for aroma enhancement treatment, thus obtaining the final product. The jujube leaf green tea prepared by this invention has a clear and mellow aroma, a sweet aftertaste, and a clear and bright tea soup. It also exhibits high content and high dissolution rate of nutrients and active substances in the green tea.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of jujube leaf processing, and particularly relates to a preparation process of jujube leaf green tea. BACKGROUND

[0002] Jujube leaf, also known as "thorn leaf", is the leaf of Ziziphus jujuba Mill. in the family Rhamnaceae. The jujube leaf contains total flavonoids, total phenols, triterpenes, polysaccharides, vitamins and other nutrients, and has biological activities such as antioxidant, anti-aging, lipid-lowering and sedative and hypnotic. However, there is almost no development and utilization of jujube leaf resources at present, and the treatment of jujube leaf still stays in the traditional livestock feeding and natural degradation stage. Therefore, the development of jujube leaf into jujube leaf green tea has important significance for the utilization of jujube leaf resources.

[0003] At present, although there are some public reports on the preparation technology of jujube leaf green tea, the optimization of the green tea process is usually evaluated by the color, aroma and taste and the content of nutrients and active ingredients in the green tea, which ignores the influence of the brewing method of the green tea on the dissolution of the nutrients and active ingredients. The green tea processing technology optimized by the above index, even if the content of nutrients and active ingredients in the green tea is greatly improved, if these nutrients and active ingredients cannot be dissolved into the tea water during the brewing process of the green tea, they cannot act on the drinker to exert their due effect. For example, during the processing of the green tea, when the rolling time is 25 min, the content of total flavonoids in the green tea is the highest, but the dissolution rate of the total flavonoids is less than 60% under the rolling time, resulting in a low content of total flavonoids in the brewed green tea, and the nutrients and active ingredients in the green tea cannot be fully utilized. When the rolling time is more than 1 h, although a greater total flavonoid dissolution rate is obtained during the brewing of the green tea, the long rolling time leads to the degradation of the total flavonoids, reduces the content of total flavonoids in the prepared green tea, and leads to the breakage of the leaf and the reduction of the integrity rate. Therefore, how to improve the green tea process to obtain a green tea with full color, aroma and taste, high content of nutrients and active ingredients and high dissolution rate is very important. SUMMARY

[0004] The present application aims to overcome the defects in the prior art, and provides a preparation process of jujube leaf green tea, which has a clear and mellow fragrance, a sweet aftertaste, a clear and bright tea soup, a high content of nutrients and active ingredients in the green tea and a high dissolution rate, and greatly improves the utilization rate of the nutrients and active ingredients in the green tea.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present application is as follows:

[0006] A preparation process of jujube leaf green tea, comprising the following steps:

[0007] Step 1, material selection, cleaning: select the jujube tree leaves without disease and insect pests, and with complete shape, wash with clean water, remove the dust on the surface of the leaves, and then drain the water for standby;

[0008] Step 2, spreading, fixation: spread the washed leaves at room temperature for 10-12 hours until the leaves lose luster and the water content is reduced to 68-73%, then stir-fry at 110-130℃ for 1-2min to make the leaf quality soft and the grassy smell disappear, and then take out for standby;

[0009] Step 3, plasma treatment: spray deionized water on the fixed leaves, adjust the water content of the leaves to 68-73%, and then perform cold plasma treatment. After the treatment, dry at 60℃ or below until the water content is 48-53% for standby;

[0010] Step 4, rolling: roll the jujube leaves after plasma treatment for 5-30min until the leaves are curled into strips;

[0011] Step 5, drying, shaping and flavoring: stir-fry at 60-100℃ for 18-22min, and continue to roll and shape during the stir-frying process. Then, reduce the temperature to 40℃ and stir-fry for 13-17min for flavoring treatment, and then obtain the long strip-shaped jujube leaf green tea.

[0012] As a further technical solution, when the cold plasma treatment is performed, the leaves are laid flat, the front surface is treated with a power of 200W for 10-20s, then the leaves are turned over, and then treated again with a power of 200W for 10-20s.

[0013] As a further technical solution, the plasma treatment uses a low-temperature plasma treatment instrument, model SY-DT02S, manufacturer: Suzhou Plasma Technology Co., Ltd.

[0014] As a further technical solution, the jujube tree uses winter jujube tree or sour jujube tree.

[0015] As a further technical solution, the leaves use tender leaves (before flowering), mature leaves (fruiting period), and old leaves (before leaf fall).

[0016] As a further technical solution, when the leaves are tender leaves, the fixation time is 1.3-1.7min, the rolling time is 18-22min, and the drying temperature is 70-76℃.

[0017] As a further technical solution, when the leaves are mature leaves, the fixation time is 1.8-2.2min, the rolling time is 6-9min, and the drying temperature is 81-85℃.

[0018] As a further technical scheme, when the leaf is a mature leaf, the fixation time is 1.3-1.7 min, the rolling time is 18-22 min, and the drying temperature is 70-76 DEG C.

[0019] As a further technical scheme, the light pressure rolling-twist-middle pressure rolling-light pressure rolling mode is adopted.

[0020] Compared with the prior art, the beneficial effects of the present application are that:

[0021] 1. The present application applies the plasma treatment technology to the preparation process of jujube leaf green tea, which not only improves the dissolution of the nutritional components and active components in the tea-making process, but also improves the conversion of the nutritional components and active components, and improves the content of the nutritional components and active components in the jujube leaf green tea.

[0022] 2. By optimizing the timing of the plasma treatment, it is found that after the jujube leaf cell is fixed and softened, the plasma treatment can improve the soup color, leaf shape and leaf bottom quality of the jujube leaf green tea, and improve the strip rate of the jujube leaf green tea. Compared with the low moisture content, increasing the moisture content of the jujube leaf to about 70% before the plasma treatment can further improve the dissolution of the nutritional components and active components in the tea-making process, and further improve the conversion of the nutritional components and active components, and further improve the content of the nutritional components and active components in the jujube leaf green tea.

[0023] 3. By screening the jujube leaf variety and picking period for preparing jujube leaf green tea, optimizing the fixation time, rolling time and drying temperature in the preparation process, and combining with the plasma treatment after fixation, while controlling the moisture content of the leaf during the plasma treatment, the prepared jujube leaf green tea not only has a clear and sweet aroma, a sweet aftertaste, a clear and bright tea soup, and an excellent sensory quality, but also has a high content of nutritional substances and active substances, a high dissolution rate, and a greatly improved utilization rate of the nutritional substances and active substances in the green tea. In addition, the jujube leaf green tea prepared by the process of the present application has a significantly improved antioxidant effect. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The response surface graph of each factor for preparing jujube leaf green tea from tender jujube leaves;

[0025] Figure 2 The response surface graph of each factor for preparing jujube leaf green tea from mature leaves;

[0026] Figure 3 The response surface graph of each factor for preparing jujube leaf green tea from old leaves;

[0027] In Figures 1-3 , a: rolling time and fixation time interaction response surface graph;

[0028] b: Response surface plot of the interaction of drying temperature and fixation time;

[0029] c: Response surface plot of the interaction of drying temperature and twisting time;

[0030] Figure 4 Comparison chart of the scavenging ability of DPPH free radicals by fresh jujube leaves, jujube leaf green tea and commercially available green tea;

[0031] Figure 5 Comparison chart of the scavenging ability of hydroxyl free radicals by fresh jujube leaves, jujube leaf green tea and commercially available green tea;

[0032] Figure 6 Comparison chart of the scavenging ability of superoxide anion free radicals by fresh jujube leaves, jujube leaf green tea and commercially available green tea. DETAILED DESCRIPTION

[0033] The technical solutions of the present application will be described below in conjunction with specific embodiments, obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0034] In the present application,

[0035] 1) The plasma treatment adopts a low-temperature plasma treatment instrument (SY-DT02S) purchased from Suzhou Plasma Technology Co., Ltd.;

[0036] 2) Commercially available green tea: Xinyang Maojian green tea is adopted;

[0037] 3) The determination method of total flavonoids content:

[0038] Accurately take rutin standard product to prepare rutin standard working solution with 70% ethanol solution. Accurately take 0, 1, 2, 3, 4, 5, 6 mL of rutin standard solution into a 10 mL centrifuge tube with a stopper, add 0.6 mL of 5% sodium nitrite solution, shake well and stand for 6 min, then add 0.4 mL of 10% aluminum nitrate solution, shake well and stand for 6 min, add 2 mL of 4% sodium hydroxide solution, and dilute to 10 mL with 70% anhydrous ethanol, and stand for 30 min. With 70% anhydrous ethanol solution as blank control, the absorbance of the reaction solution at 511 nm is determined, and the rutin standard curve is drawn. Take 1 mL of the sample to be tested to determine the absorbance of the sample solution by the above method, and calculate the total flavonoid content in the sample to be tested according to the rutin standard curve.

[0039] 4) The determination method of soluble sugar content:

[0040] The soluble sugar content in the sample solution to be measured is determined by anthrone colorimetry. The glucose standard is accurately weighed to prepare a glucose working solution with deionized water. 0, 0.2, 0.4, 0.8, 1.2, and 1.6 mL of the standard working solution are accurately removed and added to 2 mL of distilled water. Then, 0.5 mL of anthrone reagent and 5 mL of concentrated sulfuric acid are added, and the mixture is shaken well and placed in a boiling water bath for 10 min. After the reaction solution is cooled to room temperature, deionized water is used as a blank control. The absorbance of the reaction solution at 630 nm is measured, and a glucose standard curve is drawn. 0.5 mL of the sample solution to be measured is taken and the absorbance of the sample solution is determined by the above method. The soluble sugar content of the sample solution to be measured is calculated according to the glucose standard curve.

[0041] 5) Determination method of polyphenol content:

[0042] A gallic acid working solution is prepared with deionized water. 0, 0.1, 0.2, 0.3, 0.4, and 0.5 mL of the standard working solution are accurately removed and added to 3 mL of distilled water. Then, 0.5 mL of Folin-phenol reagent and 1.5 mL of 7.5% sodium carbonate solution are added. After being kept in the dark for 2 h, deionized water is used as a blank control. The absorbance of the reaction solution at 765 nm is measured, and a gallic acid standard curve is drawn. 0.1 mL of the sample solution to be measured is taken and the absorbance of the sample solution is determined by the above method. The polyphenol content of the sample solution to be measured is calculated according to the gallic acid standard curve.

[0043] 6) Determination method of soluble protein content:

[0044] Bovine serum albumin is accurately weighed to prepare a bovine serum albumin working solution with deionized water. 0, 1, 2, 3, 4, and 5 mL of the standard working solution are taken and added to 5 mL of Coomassie brilliant blue staining agent. After reacting for 2-3 min, deionized water is used as a sample blank to immediately measure the absorbance of the reaction solution at 595 nm. A standard curve is drawn. 1 mL of the jujube leaf green tea water extract is accurately removed and the absorbance of the sample solution is determined by the above method. The soluble protein content in the sample to be measured is calculated according to the bovine serum albumin standard curve.

[0045] 7) Determination method of total free amino acid content:

[0046] Glutamic acid standard is accurately weighed to prepare a glutamic acid standard working solution with deionized water. 1 mL of the glutamic acid working solution, 0.5 mL of pH 8.0 phosphate buffer, and 0.5 mL of indantrione solution are placed in a 25 mL test tube with a stopper, shaken well, and heated in a boiling water bath for 15 min. After cooling to room temperature, the volume is adjusted to 25 mL. After reacting for 10 min, the absorbance of the reaction solution at 570 nm is measured, and a glutamic acid standard curve is drawn. 1 mL of the sample solution to be measured is accurately removed and the absorbance of the sample solution is determined by the above method. The total free amino acid content of the sample solution to be measured is calculated according to the glutamic acid standard curve.

[0047] 8) Amino acid composition and content determination: LC-MS / MS method:

[0048] Liquid chromatography conditions: Exion LC AD system, Waters BEH Amide (100 x 2.1 mm, 1.7 μm) liquid chromatography column, column temperature 35℃, sample size 2 μL. Mobile phase A (0.4% formic acid 20 mM ammonium formate-95% acetonitrile solution), mobile phase B (0.4% formic acid 20 mM ammonium formate-5% acetonitrile aqueous solution).

[0049] The mobile phase elution gradient is shown in Table 1;

[0050] Table 1

[0051] Time (min) Flow rate (mL / min) Phase A (%) Phase B (%) 0 1 100 0 1 1 90 10 2.6 1 85 15 3.5 1 70 30 4 1 70 30 4.1 1 100 0 6 1 100 0

[0052] Mass spectrometry conditions: AB SCIEX QTRAP 6500+, positive mode detection, Curtain Gas (CUR) 35, Collision Gas (CAD) Medium, IonSpray Voltage (IS) 5500, Temperature (TEM) 350, Ion Source Gas1 (GS1) 70, Ion Source Gas2 (GS2) 70.

[0053] 9) The raw materials used in the present application are commercially available unless otherwise specified.

[0054] Example 1: Effects of fixation time, rolling time and drying temperature on total flavonoids in jujube leaf green tea

[0055] I. Test method:

[0056] Step 1, material selection and cleaning: select jujube tree leaves without disease and insect damage, complete in shape, wash with clean water, remove dust on the surface of the leaves, drain the water, and prepare for use;

[0057] Step 2, spreading and fixation: spread and dry the washed leaves at room temperature for 10-12 hours until the leaves lose luster and the water content is reduced to 70%, then perform stir-frying fixation at 120℃ for 1-2 min, so that the leaf quality becomes soft and the grassy smell disappears, and the pan is taken out at this time. The water content of the leaves is 50%, and they are ready for use;

[0058] Step 3, rolling: roll the jujube leaves after ionization by light pressure rolling, medium pressure rolling and light pressure rolling for 5-20 min, until the leaves are rolled into strips;

[0059] Step 4, drying, shaping, and flavoring: frying at 70-90℃ for 15min, and continuously kneading and shaping during frying, then reducing temperature to 40℃, frying for 20min for flavoring treatment, to obtain long strip-shaped jujube leaf green tea.

[0060] The killing time, kneading time, and drying temperature in the preparation process of the jujube leaf green tea were optimized by response surface method, and the parameter combinations were obtained, as shown in Tables 2-3.

[0061] II. Index detection

[0062] The content of total flavonoids in the jujube leaf green tea prepared under each parameter combination was detected, and the results are shown in Tables 2-3; the results in Tables 2-3 were analyzed and 3D response surface graphs were drawn, and the results are shown in Tables 4-6 and Figures 1-3 ;

[0063] III. Results and analysis

[0064] Table 2: Response surface results of total flavonoid content in jujube leaf green tea

[0065]

[0066] Table 3: Response surface results of total flavonoid content in jujube leaf green tea

[0067]

[0068]

[0069] Table 4: Quadratic regression model and variance analysis of jujube leaf green tea

[0070] Source Sum of squares Degrees of freedom Mean square F value p value Significance Model 1.74 9 0.1935 6.64 0.0103 * A - Fixation time 0.0036 1 0.0036 0.124 0.7351 B - Twisting time 0.0312 1 0.0312 1.07 0.3348 C - Drying temperature 0.1035 1 0.1035 3.55 0.1014 AB 0.497 1 0.497 17.06 0.0044 ** AC 0.0004 1 0.0004 0.0137 0.91 BC 0.0506 1 0.0506 1.74 0.2289 A 2 ]]> 0.1727 1 0.1727 5.93 0.0451 * B 2 ]]> 0.2132 1 0.2132 7.32 0.0304 * [C 2 ]]> 0.5687 1 0.5687 19.52 0.0031 ** Residual 0.2039 7 0.0291 Residual error 0.1673 3 0.0558 6.1 0.0567 Not significant Pure error 0.0366 4 0.0092 Adjusted total 1.95 16

[0071] Note: * indicates significant difference, P<0.05; ** indicates extremely significant difference, P<0.01, and the same below.

[0072] Table 5: Quadratic regression model and variance analysis of jujube leaf green tea

[0073] Source Sum of squares Degrees of freedom Mean square F value p value Significance Model 2.52 9 0.2795 8.38 0.0052 ** A - Fixation time 0.099 1 0.099 2.97 0.1285 B - Twisting time 0.1081 1 0.1081 3.24 0.1148 C - Drying temperature 0.0421 1 0.0421 1.26 0.2985 AB 0.1296 1 0.1296 3.89 0.0493 * AC 0.0306 1 0.0306 0.9184 0.3698 BC 0.4032 1 0.4032 12.09 0.0103 * A2 0.5084 1 0.5084 15.25 0.0059 ** B2 0.0095 1 0.0095 0.2849 0.61 C2 1.07 1 1.07 32.2 0.0008 ** Residual 0.2334 7 0.0333 Residual error 0.1836 3 0.0612 4.92 0.079 Not significant Pure error 0.0498 4 0.0124 Adjusted total 2.75 16

[0074] Note: * indicates significant difference, P<0.05; ** indicates extremely significant difference, P<0.01, and the same below.

[0075] Table 6: Quadratic regression model and variance analysis of jujube leaf green tea

[0076]

[0077]

[0078] Note: * indicates significant difference, P < 0.05; ** indicates extremely significant difference, P < 0.01, the same below.

[0079] The response surface analysis chart reveals the mutual influence relationship between the factors. The steepness of the response surface reflects the strength of the interaction, and the shape of the contour line can also reflect the strength of the interaction. When the contour chart presents an elliptical shape, it indicates that the interaction is more obvious; and when the contour line presents a circular shape, it indicates that the interaction is weaker.

[0080] 1、From Figure 1 and Table 2, Table 4 can be seen:

[0081] 1) When preparing jujube leaf green tea with tender leaves, the interaction of the fixation time and the rolling time is significant;

[0082] 2) When preparing jujube leaf green tea with tender leaves, the regression equation is calculated by Design-Expert.11.0 software, and the process is verified, and the optimal process parameters are determined as follows: the fixation time is 1.3-1.7 min, the rolling time is 18-22 min, the drying temperature is 70-76℃, and the total flavonoid content is 3.48-4.07 mg / g;

[0083] 2、From Figure 2 , Table 2 and Table 5 can be seen:

[0084] 1) When the leaves are mature leaves, the interaction of the rolling time with the fixation time and the drying temperature is significant;

[0085] 2) When the leaves are mature leaves, the regression equation is calculated by Design-Expert.11.0 software, and the process is verified, and the optimal process parameters are determined as follows: the fixation time is 1.8-2.2 min, the rolling time is 6-9 min, the drying temperature is 81-85℃, and the total flavonoid content is 3.54-4.17 mg / g;

[0086] 3、From Figure 3 , Table 3 and Table 6 can be seen:

[0087] 1) When the leaves are old leaves, the interaction of the rolling time with the fixation time and the drying temperature is significant;

[0088] 2) When the leaves are old leaves, the regression equation is calculated by Design-Expert.11.0 software, and the process is verified, and the optimal process parameters are determined as follows: the fixation time is 1.3-1.7 min, the rolling time is 18-22 min, the drying temperature is 70-76℃, and the total flavonoid content is 2.67-3.28 mg / g.

[0089] Example 2-6: Influence of the timing of plasma treatment and the moisture content of the leaves on the content of the nutritional active ingredients in jujube leaf tea and their dissolution and on the sensory quality of green tea

[0090] I. Test method:

[0091] Flavonoids are the main bioactive components in jujube leaves, so the content and dissolution of total flavonoids in jujube leaf green tea were used as indicators to select and optimize the green tea preparation process:

[0092] Example 2:

[0093] A jujube leaf green tea preparation method comprises the following steps:

[0094] Step 1, material selection and cleaning: select healthy and intact winter jujube leaf blades, wash them with clean water to remove dust on the surface, and then drain the water for standby;

[0095] Step 2, spreading and fixation: spread and dry the washed leaves at room temperature for 10-12 hours until the leaves lose luster and the moisture content decreases to 70%, then perform stir-frying fixation at 120℃ for 1.5min to make the leaf quality soft and the grassy smell disappear, and the leaves are taken out at this time, with a moisture content of 50%, for standby;

[0096] Step 3, plasma treatment: spray deionized water on the fixed leaves, adjust the moisture content of the leaves to 70%, and then perform cold plasma treatment, and after the treatment, dry at 55℃ until the moisture content is 50% for standby;

[0097] During cold plasma treatment, the leaves are spread flat, the front side is treated with a power of 200W for 13s, then the leaves are turned over, and then treated again with a power of 200W for 13s.

[0098] Step 4, rolling: roll the jujube leaves after plasma treatment in the way of light pressure rolling, medium pressure rolling, and light pressure rolling for 20min until the leaves are curled into strips;

[0099] Step 5, drying, shaping, and flavoring: fry the rolled leaves at 73℃ for 15min, and continue to roll and shape during frying, then reduce the temperature to 40℃, and fry for 20min for flavoring treatment, and the long strip-shaped jujube leaf green tea is obtained.

[0100] Example 3:

[0101] A jujube leaf green tea preparation method comprises the following steps:

[0102] Step 1, material selection and cleaning: same as example 2;

[0103] Step 2, spreading: spread the cleaned leaves at room temperature for 10-12 hours until the leaves lose luster and the water content is reduced to 70%;

[0104] Step 3, plasma treatment: cold plasma treatment is performed on the spreaded leaves,

[0105] During the cold plasma treatment, the leaves are laid flat, the front side is treated with a power of 200W for 13s, then the leaves are turned over and treated again with a power of 200W for 13s;

[0106] Step 4, fixation: the cold plasma treated leaves are fried at 120°C for 1.5min to make the leaves soft and the grassy smell disappear, and the leaves are taken out when the water content is 50%, ready for use;

[0107] Step 5, rolling: the fixed jujube leaves are rolled in the way of light pressure rolling-middle pressure rolling-light pressure rolling for 20min until the leaves are rolled into strips;

[0108] Step 5, drying, shaping and flavoring: the rolled leaves are fried at 73°C for 15min, and continue to roll and shape during the frying process, then the temperature is reduced to 40°C, fried for 20min for flavoring treatment, and the long strip-shaped jujube leaf green tea is obtained.

[0109] Example 4:

[0110] A preparation method of jujube leaf green tea, comprising the following steps:

[0111] Step 1, material selection and cleaning: same as example 2

[0112] Step 2, spreading and fixation: same as example 2

[0113] Step 3, rolling: the fixed jujube leaves are rolled in the way of light pressure rolling-middle pressure rolling-light pressure rolling for 20min until the leaves are rolled into strips;

[0114] Step 4, plasma treatment: the rolled leaves are spreaded and treated with cold plasma, and after the treatment, the leaves are rolled into strips (rolled into strips once, without long time rolling), ready for use;

[0115] During the cold plasma treatment, the leaves are laid flat, the front side is treated with a power of 200W for 13s, then the leaves are turned over and treated again with a power of 200W for 13s.

[0116] Step 5, drying, shaping and flavoring: the plasma treated leaves are fried at 73°C for 15min, and continue to roll and shape during the frying process, then the temperature is reduced to 40°C, fried for 20min for flavoring treatment, and the long strip-shaped jujube leaf green tea is obtained.

[0117] Example 5

[0118] A preparation method of jujube leaf green tea, comprising the following steps:

[0119] Step 1, material selection and cleaning: same as example 2

[0120] Step 2, spreading and fixation: same as example 2

[0121] Step 3, plasma treatment: after fixation, the leaves are treated by cold plasma, and then standby;

[0122] During cold plasma treatment, the leaves are laid flat, and the front side is treated with a power of 200W for 13s, then the leaves are turned over, and then treated again with a power of 200W for 13s;

[0123] Step 4, rolling: same as example 2;

[0124] Step 5, drying, shaping and flavoring: same as example 2;

[0125] Example 6

[0126] A preparation method of jujube leaf green tea, comprising the following steps:

[0127] Step 1, material selection and cleaning: same as example 2;

[0128] Step 2, spreading and fixation: same as example 2;

[0129] Step 3, rolling: after fixation, the jujube leaves are rolled in the mode of light pressure rolling-middle pressure rolling-light pressure rolling for 20min, until the leaves are curled into strips;

[0130] Step 4, drying, shaping and flavoring: same as example 2.

[0131] II. Index detection

[0132] 1. In the form of scoring, 25 professionals evaluate the jujube leaf green tea of examples 2-6 according to the evaluation standard in table 7, and the results are shown in table 8;

[0133] Table 7 Sensory evaluation table

[0134]

[0135] 2. In the preparation process of jujube leaf green tea of examples 2-6, the leaf residues in the rolling step and the drying, shaping and flavoring step, and the jujube leaf green tea strips are collected respectively, and weighed (in dry product), and the strip rate is calculated, and the results are shown in table 8;

[0136] Strip rate % = weight of jujube leaf green tea strips / (weight of jujube leaf green tea strips + weight of residues) * 100%;

[0137] 3. The contents of total flavonoids, soluble sugar, polyphenol, soluble protein and free amino acid in fresh jujube leaf, jujube leaf green tea prepared in Example 2-6 and commercially available green tea (Maojian) were determined respectively. Then, jujube leaf green tea prepared in Example 2-6 and commercially available green tea were respectively brewed into tea water by using tea brewing process, and the contents of total flavonoids, soluble sugar, polyphenol, soluble protein and free amino acid in tea water were determined, the dissolution of each component was calculated, 3 parallel tests were carried out for each test, the results were represented by the average value of parallel tests, and the contents of each component in tea water were calculated by converting into the contents in tea leaves, and the results are shown in Table 9;

[0138] The tea brewing process was as follows: according to the material to liquid weight ratio of 1:20, 80℃ hot water was added to fresh jujube leaf or green tea, and the tea water was prepared by keeping warm for 30 min.

[0139] 1) The sample treatment method for determination of the content of total flavonoids:

[0140] Sample treatment of fresh jujube leaf, jujube leaf green tea and commercially available green tea: after the fresh jujube leaf, jujube leaf green tea or commercially available green tea was broken, 70% ethanol was used for extraction according to the material to liquid mass ratio of 1:30, and the sample solution for determination was obtained.

[0141] Sample treatment method of tea water: the tea water was directly used as the sample solution for determination.

[0142] 2) The sample treatment method for determination of the content of soluble sugar:

[0143] Sample treatment of fresh jujube leaf, jujube leaf green tea and commercially available green tea: after the fresh jujube leaf, jujube leaf green tea or commercially available green tea was broken, hot water with a temperature of 80-90℃ was used for extraction according to the material to liquid mass ratio of 1:20, and the sample solution for determination was obtained.

[0144] Sample treatment method of tea water: the tea water was directly used as the sample solution for determination.

[0145] 3) The sample treatment method for determination of the content of polyphenol:

[0146] Sample treatment method of fresh jujube leaf, jujube leaf green tea, commercially available green tea and tea water: the same as the sample treatment method described in total flavonoids.

[0147] 4) The sample treatment method for determination of the content of soluble protein:

[0148] Sample treatment method of fresh jujube leaf, jujube leaf green tea, commercially available green tea and tea water: the same as the sample treatment method described in soluble sugar.

[0149] 5) The determination method of the content of free amino acid:

[0150] Sample treatment method of fresh jujube leaf, jujube leaf green tea, commercially available green tea and tea water: the same as the sample treatment method described in soluble sugar.

[0151] 4. The amino acids in fresh jujube leaves, jujube leaf green tea prepared in Example 1 and 5, and tea water thereof were analyzed, respectively; each test was in triplicate, the results were expressed by the average of parallel tests, the content of each component in tea water was calculated by converting into the content of tea leaves, and the results were shown in Table 10;

[0152] The process of brewing tea water was the same as above;

[0153] The content of amino acids was detected by LC-MS / MS;

[0154] The sample treatment method of fresh jujube leaves and jujube leaf green tea was as follows: 50 mg of fresh jujube leaves and jujube leaf green tea samples (calculated by dry weight) were mixed with 750 μL of acetonitrile, ultrasonicated for 30 minutes, centrifuged at 13000 rpm for 5 minutes, repeated once, and the supernatant was subjected to LC-MS / MS detection;

[0155] The sample treatment method of tea water was as follows: the tea water was concentrated under vacuum at 60°C, and then subjected to sample determination.

[0156] III. Results and analysis:

[0157] 1. Evaluation of sensory quality and rate of tea leaf into strips

[0158] Table 8

[0159]

[0160]

[0161] Table 9

[0162]

[0163] Table 10

[0164]

[0165]

[0166] From Tables 8-10, it can be seen that:

[0167] 1) From the comparison of Example 2-5 with Example 6 and fresh jujube leaves and commercially available green tea, it can be seen that after the leaf blades are treated by plasma, on the one hand, the transformation of the nutritional active ingredients is promoted, and the contents of total flavonoids, polyphenols, soluble sugar, soluble protein and free amino acids in the jujube leaf green tea are increased, among which, the increase in the contents of soluble sugar, soluble protein and free amino acids is relatively large; compared with Example 6 which is not treated by plasma, the contents of soluble protein and free amino acids in Example 2 are simultaneously increased, which may be due to the transformation of non-soluble protein into soluble protein under the action of plasma. On the other hand, after the leaf blades are treated by plasma, the dissolution of total flavonoids, polyphenols, soluble sugar, soluble protein and free amino acids in tea water is greatly promoted, especially for soluble sugar and soluble protein, the increase is relatively large, which may be due to the fact that after the plasma treatment, the permeability of the cytoplasmic membrane is improved, so that the substances with large molecules are easily dissolved from the cells.

[0168] 2) From the comparison of Example 2 and Example 3, it can be seen that the plasma treatment is moved forward from after fixation in Example 2 to before fixation in Example 3. Since the cells that have not been fixed have a high water content and have not been softened by dehydration, the cell wall is brittle. At this time, the plasma treatment is more likely to damage the cell wall under the action of plasma than after fixation, thereby affecting the sensory quality of the soup color, leaf bottom and leaf shape of the jujube leaf green tea, and also leading to the fact that the leaf blades are easily broken and the leaf strip rate is reduced in the subsequent rolling, drying and shaping. In Example 2, the plasma treatment is before fixation, and the dehydration occurs during the fixation process, so that the cell wall is elastic. Even if the cells are sprayed with water, the cell wall is still tough, and the damage degree is relatively low compared with the brittle cell wall.

[0169] From the comparison of Example 2 and Example 4-5, it can be seen that when the water content of the leaf blades is reduced to about 50% (the water content of the leaf blades after rolling in Example 4 is about 50%, and the water content is also about 50% when the leaf blades are not sprayed with water during the plasma treatment in Example 5), the cells are in a semi-dehydrated state, and the cytoplasmic membrane is wrinkled and stored in the cell wall. Under this condition, compared with Example 2 in which the cytoplasmic membrane is full, the plasma will mainly act on the cell wall, thereby causing the damage degree of the cytoplasmic membrane to be relatively small and the damage degree of the cell wall to be relatively large. Therefore, the dissolution, aroma, taste, sensory quality of the soup color, leaf bottom and leaf shape, and the strip rate are all inferior to those of Example 2. In addition, when the plasma treatment is performed on cells with a high water content, it is more conducive to the transformation of active ingredients than when the plasma treatment is performed on cells with a low water content, so that the content of nutritional active ingredients in the prepared jujube leaf green tea is increased.

[0170] Examples 7-14: Effect of plasma treatment power and time on the content and dissolution of total flavonoids in jujube leaf green tea and the strip rate of green tea

[0171] I. Test method:

[0172] A preparation method of jujube leaf green tea, comprising the following steps:

[0173] Step 1, material selection and cleaning: selecting healthy and intact winter jujube leaf blades without diseases and insect pests, washing with clean water to remove dust on the surface of the leaf blades, and draining water for standby;

[0174] Step 2, spreading and fixation: spreading and airing the washed leaf blades at room temperature for 10-12 hours until the leaf loses luster and the water content is reduced to 70%, and then performing stir-frying fixation at 120℃ for 1.5 min to make the leaf soft and the grassy smell disappear, and the leaf blades are taken out when the water content is 50%, and standby;

[0175] Step 3, plasma treatment: spraying deionized water on the fixed leaf blades, adjusting the water content of the leaf blades to 70%, and then performing cold plasma treatment, and after the treatment, drying at 55℃ until the water content is 50%, and standby;

[0176] During the cold plasma treatment, the leaf blades are placed flat with the front face upward for plasma treatment, and then the leaf blades are turned over and the back face is upward for plasma treatment again with the same power and treatment time.

[0177] Step 4, rolling: rolling the jujube leaf after plasma treatment by light pressure rolling, medium pressure rolling and light pressure rolling for 20 min until the leaf blades are curled into strips;

[0178] Step 5, drying, shaping and flavoring: frying the rolled leaf blades at 73℃ for 15 min, and continuing to roll and shape during the frying process, and then reducing the temperature to 40℃ and frying for 20 min for flavoring treatment, and obtaining the long strip-shaped jujube leaf green tea.

[0179] In Examples 7-14, the power and time of plasma treatment are shown in Table 5;

[0180] II. Index detection:

[0181] 1. According to the method described in Examples 2-6, the jujube leaf green tea of Examples 7-14 was subjected to tea leaf sensory evaluation in the form of scoring, and the results are shown in Table 11;

[0182] 2. The strip forming rate of Examples 7-14 was detected respectively, and the detection method is shown in Examples 2-6, and the results are shown in Table 11;

[0183] 3. The content of total flavonoids in the jujube leaf green tea prepared in Examples 7-14 and the content of total flavonoids in the tea water thereof were detected respectively, the dissolution rate of total flavonoids was calculated, 3 parallel tests were carried out, the results were represented by the average value of parallel tests, the content of each component in the tea water was calculated by converting into the content of tea leaves, and the results were shown in Table 11.

[0184] The method for preparing the jujube leaf green tea, the method for preparing the tea water of the green tea, and the sample processing method and detection method for determining the content of total flavonoids were the same as those in Examples 2-6.

[0185] III. Results and analysis:

[0186] Table 11

[0187]

[0188]

[0189] From the data in Table 10, it can be seen that when the plasma treatment power is 200 W and the treatment time is 10-20 s, the sensory score of the prepared jujube leaf green tea, the content of total flavonoids and the dissolution of total flavonoids in the tea water thereof are all better.

[0190] Example 15: Effect of jujube varieties on the sensory quality of jujube leaf green tea

[0191] I. Test method:

[0192] A preparation method of jujube leaf green tea, comprising the following steps:

[0193] Step 1, material selection and cleaning: select the tender leaf blades of jujube trees without diseases and insect pests and with complete morphology, wash them with clean water to remove the dust on the surface of the leaf blades, drain the water, and then prepare for use;

[0194] Step 2, spreading and fixation: spread and dry the washed leaf blades at room temperature for 10-12 hours until the leaf loses luster and the water content decreases to 70%, then perform stir-frying fixation at 120℃ for 1.5 min to make the leaf quality soft and the grassy smell disappear, and take out the pot at this time, at which time the water content of the leaf blades is 50%, and then prepare for use;

[0195] Step 3, plasma treatment: spray deionized water on the fixed leaf blades, adjust the water content of the leaf blades to 70%, and then perform cold plasma treatment, after the treatment, dry at 55℃ until the water content is 50%, and then prepare for use;

[0196] During the cold plasma treatment, the leaf blades are spread flat with the front face upward, and then plasma treatment is performed at a power of 200 W for 13 s, the leaf blades are turned over, and then plasma treatment is performed at a power of 200 W for 13 s with the back face upward.

[0197] Step 4, kneading: after the jujube leaves are treated by plasma, the leaves are subjected to light pressure kneading, medium pressure kneading and light pressure kneading for 20 min, until the leaves are curled into strips;

[0198] Step 5, drying, shaping and flavoring: the kneaded leaves are fried at 73℃ for 15 min, and continue to be kneaded and shaped during the frying process, then the temperature is lowered to 40℃, and the leaves are fried for 20 min for flavoring treatment, to obtain the jujube leaf green tea in the form of long strip rolls.

[0199] II. Index detection

[0200] According to the method described in Examples 2-6, the jujube leaf green tea prepared from each variety of jujube leaves is scored, and the results are shown in Table 12.

[0201] III. Results and analysis

[0202] Table 12

[0203] Variety Soup color Aroma Taste Leaf bottom Leaf shape Total score Rain Shuai 13.2 11.9 9.1 11 10.6 55.8 Winter jujube 16.1 14.4 14.3 16 14.7 77.5 Gold silk small jujube 14.6 11.2 15.4 14.1 11.9 67.2 Fuxiang 13.2 11.5 10.6 11.9 10.2 57.4 Zanshu 9.8 11.3 11.6 11 7.9 51.6 Moonlight 12.2 15.7 11.5 12.2 6.9 58.5 Mao Boyan Zhongjue 13.1 14 13.9 12.2 11.2 64.4 Starlight 13 11.6 11.2 11.9 12.8 60.5 Gray jujube 13.9 15 12.4 12.2 12.3 65.8 Round bell 11.5 11.7 11 11.1 7.5 52.8 Acid jujube 16.8 12.9 12.5 15.3 15.7 73.2

[0204] As can be seen from the data in Table 12, the jujube leaf green tea prepared from the leaves of winter jujube and sour jujube has the best sensory quality.

[0205] In summary of Examples 1-15, it can be determined that the best process for preparing jujube leaf green tea is as follows: the tender leaves or mature leaves of winter jujube and sour jujube are used to prepare jujube leaf green tea according to the steps of selection, spreading, fixation, adjusting the water content to 78-83%, plasma treatment, drying below 60℃ to a water content of 48-52%, kneading, drying, shaping and flavoring, and during the preparation of jujube leaf green tea, when the leaves are tender leaves, the fixation time is controlled to be 1.3-1.7 min, the kneading time is controlled to be 18-22 min, and the drying temperature is controlled to be 70-76℃; when the leaves are mature leaves, the fixation time is controlled to be 1.8-2.2 min, the kneading time is controlled to be 6-9 min, and the drying temperature is controlled to be 81-85℃; in addition, the power for each plasma treatment is controlled to be 200W, and the time is controlled to be 10-20s. Under this process, each parameter interacts and is indispensable, so that jujube leaf green tea with high strip rate, good sensory quality, high content of nutritional active ingredients and easy dissolution can be prepared.

[0206] Example 16: Antioxidant effect of fresh jujube leaves, jujube leaf green tea and commercially available green tea

[0207] The jujube leaf green tea prepared in Example 2, fresh jujube leaves and commercially available green tea were subjected to antioxidant activity determination, and the determination items included DPPH free radical scavenging capacity, hydroxyl free radical scavenging capacity and superoxide anion free radical scavenging capacity; the results are shown in Table 13. Figures 4-6 ;

[0208] 1. From Figure 4It can be seen that the DPPH scavenging ability of fresh jujube leaves, jujube leaf green tea and commercially available green tea increases with the increase of sample concentration, but the change range is not large. The DPPH scavenging ability of tea (commercially available green tea and jujube leaf green tea) is obviously higher than that of fresh jujube leaves. The DPPH scavenging ability of jujube leaf green tea is stronger than that of commercially available green tea, and the clearance rate reaches about 90% in the concentration range of 2-10 mg / ml.

[0209] 2、from Figure 5 It can be seen that the scavenging ability of commercially available green tea on hydroxyl radicals is the strongest, reaching 75.51%, compared with the other two samples. In the concentration range of 2-6 mg / ml, the clearance rate increases significantly, and then changes little. In the concentration range of 2-8 mg / ml, the clearance rates of fresh jujube leaves and jujube leaf green tea are not much different, but in the concentration range of 8-10 mg / ml, the clearance rate of jujube leaf green tea increases greatly, and the clearance rate is 51.58% at 10 mg / ml.

[0210] 3、from Figure 6 It can be seen that the scavenging ability of fresh jujube leaves, jujube leaf green tea and commercially available green tea on superoxide anion radicals is concentration-dependent. In the concentration range of 2-10 mg / ml, the clearance rate of jujube leaf green tea fluctuates the most, and the clearance rate of fresh jujube leaves is always the lowest. In the concentration range of 2-6 mg / ml, the scavenging ability of commercially available green tea on superoxide anion radicals is higher than that of jujube leaf green tea, but after 6 mg / ml, the scavenging ability of jujube leaf green tea exceeds that of commercially available green tea, and the clearance rate can reach 86.86%.

[0211] In summary, jujube leaf green tea has good antioxidant capacity.

[0212] The above-described embodiments are only preferred embodiments of the present application, and are not exhaustive of the feasible implementations of the present application. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present application should be considered to be included in the protection scope of the claims of the present application.

Claims

1. A process for the preparation of jujube leaf green tea, characterized in that, It comprises the following steps: Step 1, material selection and cleaning: select jujube tree leaves without diseases and insect pests, and with complete morphology, wash with clean water, remove dust on the surface of the leaves, and then drain the water for standby; Step 2, spreading and fixation: spread the washed leaves at room temperature for 10-12 hours until the leaves lose luster and the water content is reduced to 68-73%, then stir-fry at 110-130℃ for 1-2min to make the leaf quality soft and the grassy smell disappear, and then take out for standby; Step 3, plasma treatment: spray deionized water on the fixed leaves, adjust the water content of the leaves to 68-73%, and then perform cold plasma treatment, and after the treatment, dry at 60℃ or below until the water content is 48-53% for standby; During cold plasma treatment, the leaves are laid flat, the front surface is treated with a power of 200W for 10-20s, then the leaves are turned over, and then treated again with a power of 200W for 10-20s; Step 4, rolling: roll the jujube leaves after plasma treatment for 5-30min until the leaves are curled into strips; Step 5, drying, shaping and flavoring: stir-fry at 60-100℃ for 18-22min, and continue to roll and shape during the stir-frying process, then reduce the temperature to 40℃, stir-fry for 13-17min for flavoring treatment, and then obtain the long strip-shaped jujube leaf green tea.

2. The preparation process of the jujube leaf green tea according to claim 1, characterized in that the jujube tree is a winter jujube tree or an acid jujube tree.

3. The preparation process of the jujube leaf green tea according to claim 1, characterized in that the leaves are tender leaves, mature leaves or old leaves.

4. The preparation process of the jujube leaf green tea according to claim 3, characterized in that when the leaves are tender leaves, the fixation time is 1.3-1.7min, the rolling time is 18-22min, and the drying temperature is 70-76℃.

5. The preparation process of the jujube leaf green tea according to claim 3, characterized in that when the leaves are mature leaves, the fixation time is 1.8-2.2min, the rolling time is 6-9min, and the drying temperature is 81-85℃.

6. The preparation process of the jujube leaf green tea according to claim 3, characterized in that when the leaves are old leaves, the fixation time is 1.3-1.7min, the rolling time is 18-22min, and the drying temperature is 70-76℃.

7. The preparation process of the jujube leaf green tea according to claim 1, characterized in that the rolling is performed in the mode of light pressure rolling-middle pressure rolling-light pressure rolling. ​ ​ ​ ​ ​ ​

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