Preparation method and application of EGCG nano selenium for improving tea quality

Abstract

The application constructs EGCG nano selenium (ESe) through a one-step green synthesis method in an aqueous phase at normal temperature and pressure, and finds that ESe can effectively promote the increase of free amino acid and theanine content, reduce the content of tea polyphenols, reduce the content of phenolic amine ratio, increase the fresh taste of tea, reduce the bitter taste of tea, and further improve the quality characteristics of tea, especially for summer and autumn tea with high polyphenol content; meanwhile, the material also improves the soil quality; not only provides rich raw materials for the development of high-quality green tea, but also shows excellent performance in soil quality regulation, which is beneficial to the green and sustainable development of tea.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tea planting, and relates to a preparation method of EGCG nano selenium for improving tea quality. BACKGROUND

[0002] China has nearly 47 million mu of tea gardens, and the output of raw tea reaches 298.60 million tons. Both the tea garden area and the tea output rank first in the world. However, the unit area yield is far lower than that of other major tea-producing countries. The main reason is the large amount of abandoned picking of summer and autumn tea. This is because the quality of summer and autumn tea decreases and the labor cost increases, resulting in more and more abandoned picking of summer and autumn tea, which causes serious waste of tea resources. In order to increase the picking of summer and autumn tea and realize the high-value utilization of summer and autumn tea, in recent years, researchers have tried to regulate and improve the quality characteristics of summer and autumn tea through various technical means. Fertilization is an important way to regulate the quality of tea, such as the application of foliar fertilizer and organic fertilizer. According to the research results of predecessors, the above methods still have many problems, such as the uncertainty of foliar fertilizer safety and foliar absorption efficiency, and the low nutrient content of organic fertilizer, which limits the precise regulation of tea quality. In recent years, with the rapid development of materials science, nano materials have been widely used in the precise regulation and efficient absorption and utilization of plants / soil due to their strong surface effect and excellent characteristics.

[0003] Selenium is an essential trace element for living organisms and an important component of various enzymes in living organisms. It plays a role in resisting diseases, delaying aging, and enhancing immune function in life activities. In many regions of China, selenium is abundant and selenium-rich tea has been developed according to local conditions, such as Enshi selenium-rich tea, Ziyang selenium-rich tea, and Fuzhou selenium-rich tea. The development of selenium-rich tea not only improves the income of local tea farmers but also plays an important role in promoting the brand of local tea industry. Due to the health benefits of selenium, selenium-rich tea is in short supply in many regions of China, especially in low-selenium and selenium-deficient areas. Therefore, how to increase the selenium content in tea in low-selenium and selenium-deficient areas is a difficult problem that needs to be solved for the development of selenium-rich products. Previous studies have tried to add inorganic selenium to increase the selenium content in soil and plants, but inorganic selenium is highly toxic. Japan has explicitly prohibited the addition of inorganic selenium in food and feed since 1993. In addition, inorganic selenium has poor stability, especially when combined with various vitamins, it is easy to react with vitamins, has low bioavailability, and reduces the biological efficacy of vitamins. Although organic selenium has strong stability and absorption efficiency, its safety is still uncertain, and the production process of organic selenium is complex and the production cost is high. Compared with inorganic selenium and organic selenium, nano selenium has many advantages: (1) the bioactivity of nano selenium is higher than that of organic selenium and inorganic selenium; (2) nano selenium is the safest selenium product known.

[0004] Studies have shown that bovine serum albumin (BSA) nano selenium can activate the antioxidant system of crops by spraying the leaves, significantly improve the quality of tea, and nano selenium can improve the production of theanine, glutamic acid and arginine and other amino acids. However, BSA is an animal product with a molecular weight of 66.4KD and cannot be directly used by plants. It can only be degraded into polypeptides and amino acids before being absorbed by plants. Therefore, it is not clear whether BSA-coated nano selenium can be directly absorbed by tea tree leaves. If nano selenium can be constructed using tea tree materials, it can be "taken from tea and used for tea", and it is convenient for tea trees to absorb and utilize. Unlike other crops, tea trees need to be pruned 1-2 times a year, and all pruning materials are returned to the field. According to the survey, the pruning material reaches 8000kg per hectare per year. If the polyphenols (EGCG) in the pruning material can be effectively utilized, the raw materials for constructing nano selenium will be obtained at a low cost, saving costs.

[0005] The present application provides a preparation method of EGCG nano selenium for improving the quality of tea, which is constructed by a one-step green synthesis method in aqueous solution at room temperature and normal pressure. The EGCG nano selenium (ESe) is sprayed into the soil, and it is found that ESe can effectively promote the increase of free amino acid and theanine content, reduce the content of tea polyphenols, reduce the content of phenolic amino acids, increase the fresh taste of tea, reduce the bitter taste of tea, and thus improve the quality characteristics of tea, especially for summer and autumn tea with high polyphenol content. The material also improves the soil quality; not only provides rich raw materials for the development of high-quality green tea, but also shows excellent performance in soil quality regulation, which is conducive to the green and sustainable development of tea. SUMMARY

[0006] The present application provides a preparation method of EGCG nano selenium for improving the quality of tea, which is constructed by a one-step green synthesis method in aqueous solution at room temperature and normal pressure. The EGCG nano selenium (ESe) is sprayed into the soil, and it is found that ESe can effectively promote the increase of free amino acid and theanine content, reduce the content of tea polyphenols, reduce the content of phenolic amino acids, increase the fresh taste of tea, reduce the bitter taste of tea, and thus improve the quality characteristics of tea, especially for summer and autumn tea with high polyphenol content. The material also improves the soil quality; not only provides rich raw materials for the development of high-quality green tea, but also shows excellent performance in soil quality regulation, which is conducive to the green and sustainable development of tea.

[0007] Step one, first configure 1L 2mMol EGCG aqueous solution, add magnetic sonication at room temperature, and the stirring rate is 1000-1500rpm / min;

[0008] Step two, add 10mL alkaline aqueous solution A, so that the pH is 9-10;

[0009] Step three, add 10mL sodium selenite, and the amount-of-substance ratio of EGCG to Se salt is 3:1-3;

[0010] Step four, add 300mg ascorbic acid to the above solution;

[0011] Step five, using a molecular weight cut-off of 3KD ultrafiltration tube to remove unreacted EGCG solution and selenium ions, centrifugal speed is 8500 rpm / min, add deionized water repeatedly centrifugal purification in the ultrafiltration tube, and use UV absorption to detect the liquid in the outer tube, until there is no absorption peak, collect the red liquid in the inner tube, which is the purified ESe.

[0012] Step two includes:

[0013] Add 10 mL of 1Mol / L NaOH aqueous solution, the solution will immediately become light yellow, that is, EGCG molecules are self-assembled polymerization.

[0014] Step three includes

[0015] Add 10 mL of 0.2Mol / L Na2SeSO3 aqueous solution.

[0016] Step four includes:

[0017] Add 300 mg of ascorbic acid, after stirring for a few minutes, EGCG nanoselenium is formed.

[0018] Step five includes

[0019] The reaction of EGCG nanoselenium is purified, the synthesized liquid is placed in a ultrafiltration tube with a molecular weight cut-off of 3KD for centrifugal purification, 8000 rpm centrifugal for 10 min, repeated several times, remove unreacted EGCG and ions, finally collect the liquid in the inner tube, get the purified EGCG nanoselenium ESe, long-term stable storage at 4℃.

[0020] A kind of application for improving tea quality of the preparation method of EGCG nanoselenium for improving tea new shoot selenium content, EGCG nanoselenium ESe is applied to the soil, promotes tea tree root system to absorb Ese.

[0021] A kind of application for improving tea quality of the preparation method of EGCG nanoselenium for improving tea quality, after the application of EGCG nanoselenium ESe, the content of polyphenol TP in tea is significantly reduced, the content of free amino acid AA is significantly increased, and the phenolic amino acid ratio is also significantly reduced with the increase of EGCG nanoselenium concentration.

[0022] A kind of application for improving tea quality of the preparation method of EGCG nanoselenium for improving green tea quality, EGCG is significantly reduced after the application of ESe, and the content of tea amino acid Thea is significantly increased, and the ratio of EGCG / Thea is significantly reduced under the application of ESe.

[0023] A preparation method of the EGCG nano selenium for improving tea quality is used to improve the soil, and the EGCG nano selenium ESe is applied to the soil to improve the soil. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A schematic diagram of the formation of the EGCG nano selenium (ESe) of the present application is shown;

[0025] Figure 2 The ultraviolet absorption spectrum of the EGCG and the EGCG nano selenium (ESe) of the present application is shown;

[0026] Figure 3 The transmission electron microscope image of the EGCG nano selenium (ESe) of the present application is shown;

[0027] Figure 4 The XPS full spectrum spectrum of the EGCG nano selenium (ESe) of the present application is shown;

[0028] Figure 5 The high-resolution XPS spectrum of Se in the EGCG nano selenium (ESe) of the present application is shown;

[0029] Figure 6 The effect of the EGCG nano selenium (ESe) of the present application on the selenium content in the new shoots is shown;

[0030] Figure 7 The effect of the EGCG nano selenium (ESe) of the present application on the tea polyphenols (TP), free amino acids (AA) and the phenol-ammonia ratio (TP / AA) is shown;

[0031] Figure 8 The effect of the EGCG nano selenium (ESe) of the present application on the EGCG, theanine (AA) and the ratio (EGCG / Thea) is shown;

[0032] Figure 9 The effect of the EGCG nano selenium (ESe) of the present application on the soil fertility index is shown. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a 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] Please refer to Figures 1-9 The present application provides a preparation method of EGCG nano selenium for improving tea quality, comprising the following steps:

[0035] Configuration 1L 2mMol of EGCG aqueous solution, then the reaction system is added to the stirring son constant temperature stirring (speed: 1300rpm). Then add 10mL concentration of 1M NaOH aqueous solution, the solution will immediately become light yellow, that is, EGCG molecules are self-assembled polymerization, followed by the addition of 10mL concentration of 0.2M Na2SeSO3 aqueous solution, and add 300mg ascorbic acid, stirring, a few minutes can form EGCG nano selenium (ESe). Figure 1 For EGCG nano selenium synthesis schematic. Then the reaction of EGCG nano selenium purification, the synthesis of liquid into the molecular weight of 3KD ultrafiltration tube (Millipore) centrifugal purification, 8000rpm centrifugation 10min, repeatedly several times, remove unreacted EGCG and ions, finally collected the inner tube liquid, get purified ESe, at 4 degrees can be long-term stable storage. EGCG and EGCG nano selenium absorption spectrum as shown in Figure 2 Compared with the absorption peak of EGCG (275nm), EGCG nano selenium has obvious absorption peak at 253nm. From high resolution transmission electron microscopy, ESe particle size is 4nm, and gathered on the surface of EGCG self-assembly nanosphere. From X-ray photoelectron spectroscopy (XPS), the corresponding elements in ESe were also detected. Figure 4 High resolution XPS also observed Se element fine spectrum, proved the phenolic hydroxyl on EGCG and Se interaction to form nanoparticles. Figure 5

[0036] In June 2021, EGCG nano selenium (ESe) was applied to the soil, and in April 2022, the new shoots of tea tree were sampled and the selenium content in the new shoots was determined. It was found that with the increase of Ese concentration applied to the soil, the Se content in the new shoots of tea tree increased significantly, when the Ese concentration applied was 10mg / kg, the Se content in the new shoots reached 2.41mg / kg Figure 6 ), which is within the standard range of selenium content of selenium-rich tea (0.25~4.00mg / kg, GB / T 12399), indicating that the root system of tea tree has good absorption effect on Ese.

[0037] After the application of ESe, the content of polyphenols (TP) in tea leaves decreased significantly, the content of free amino acids (AA) increased significantly, and the phenolic amino acid ratio also decreased significantly with the increase of ESe concentration Figure 5 ​). The application of Ese significantly increased the fresh taste in tea and reduced the bitterness in tea, which was beneficial to the formation of green tea quality. In addition, further analysis of the catechin and amino acid components was carried out, and the changes in the contents of epigallocatechin gallate (EGCG) and thea (Thea) in the catechin and amino acid components were mainly concerned. It was found that EGCG was significantly reduced after the application of ESe, while the content of Thea was significantly increased. We also calculated the ratio of EGCG / Thea, and found that EGCG / Thea was significantly reduced after the application of ESe Figure 8 ). In summary, the application of ESe is very beneficial to the formation of tea quality, especially the formation of green tea quality.

[0038] By constructing a comprehensive index of soil quality, it was further found that the application of Ese at an appropriate concentration significantly increased the comprehensive index of soil fertility Figure 9 In recent years, with the use of chemical fertilizers and pesticides, many problems such as acidification of red soil in the south and degradation of black soil in the northeast have occurred, and soil health problems have attracted more and more attention. Therefore, how to cultivate healthy soil is also a scientific research problem that the state has paid special attention to in recent years. Our results show that the soil quality index is improved to a certain extent after the application of Ese, and this material has an important role in soil improvement, and plays an important role in realizing the green and sustainable development of tea industry.

[0039] Although embodiments of the present application have been shown and described, it will be understood by those having ordinary skill in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. Use of EGCG nano-selenium in improving soil, characterized by, The EGCG nano selenium is prepared by the following method: Step one, first configure 1L 2 mM EGCG aqueous solution, add magnetic sonication at room temperature, and the stirring rate is 1000-1500 rpm / min; Step two, add 10 mL of 1 mol / L NaOH aqueous solution, the solution will immediately become light yellow, that is, the EGCG molecules are self-assembled and polymerized, and the pH is 9-10; Step three, add 10 mL of 0.2 mol / L Na2SeSO3 aqueous solution; Step four, add 300 mg of ascorbic acid to the solution, stir, and form EGCG nano selenium; Step five, use a molecular cut-off of 3KD ultrafiltration tube to remove unreacted EGCG solution and selenium ions, the centrifugal rate is 8500 rpm / min, add deionized water to the ultrafiltration tube repeatedly, centrifuge and purify, and detect the supernatant of the outer tube by ultraviolet absorption until there is no absorption peak, collect the red liquid in the inner tube, and obtain purified EGCG nano selenium ESe, which is stored at 4℃ for long-term stable preservation.

2. Use according to claim 1, wherein The application method is: The EGCG nano selenium is applied to the soil.

3. The use according to claim 1, wherein Application of EGCG nano selenium in improving soil quality index.

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