Tea polyphenol nano-zinc material and application of tea polyphenol nano-zinc material as fruit preservative

Abstract

The invention discloses a tea polyphenol nano-zinc material which is prepared by the following steps: adding an alkaline aqueous solution into an aqueous solution of a tea polyphenol compound to adjust the pH value to 8-9, and then adding a zinc salt aqueous solution to prepare a solution of the tea polyphenol nano-zinc material. The solution of the tea polyphenol nano-zinc material can be used as a fruit preservative. The raw materials are safe, the synthesis condition of the tea polyphenol-zinc nano material is mild, the reaction time is short, the synthesis can be completed within several seconds, the operation is simple and convenient, the cost is low, and the tea polyphenol-zinc nano material has a very strong antioxidant effect and relatively strong antibacterial and bacteriostatic properties, so that the fresh-keeping effect is good. After the fruit soaking treatment, the shelf life of the strawberries at room temperature can be prolonged to 6-7 days, and the edible and commodity values of the fruits are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit preservation, and particularly relates to a tea polyphenol nano zinc material and an application thereof as a fruit preservative. Background Art

[0002] Fresh fruit is an important part of a healthy diet and one of the most popular foods. Unfortunately, one-third of fruits rot and deteriorate before they are eaten every year, causing serious food waste and economic losses. In particular, fruits containing a lot of water and sugar are prone to rot and deterioration due to oxidation and microbial infection after picking. Affecting the edible and commodity value of fruits. Therefore, it is very important to prolong the freshness of fruits. Nowadays, many technologies have been used to preserve fruits, such as coating, plastic packaging film, low-temperature refrigeration, gas preservation technology, etc. At present, these preservation technologies lack safety and are prone to cause harm to consumer health. For example, wax coating is relatively difficult to clean and remove, which not only affects the taste of fruits, but also causes some potential harm to human health. And most plastic packaging films are petroleum-based, non-degradable, and easily produce microplastic waste, posing long-term health risks to the entire ecosystem. Therefore, the development of an environmentally friendly, simple, efficient, and multi-protective preservation material is of great significance to the field of food preservation. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a fruit preservative, which can form a coating on the surface of the fruit to prevent the fruit from being infected by microorganisms and oxidized by air, so as to increase the shelf life of the fruit. The preservative is safe and does not contain harmful substances such as petroleum-based plastics.

[0004] The technical solution adopted by the present invention is:

[0005] A tea polyphenol nano zinc material is prepared by the following method:

[0006] An alkaline aqueous solution is added to the aqueous solution of tea polyphenol compounds to adjust the pH value to 8-9, and then a zinc salt aqueous solution is added to prepare a solution of tea polyphenol nano-zinc material.

[0007] The tea polyphenols are a complex of polyhydroxyphenol compounds in tea leaves, including more than 30 phenolic substances, among which catechins are the main components of tea polyphenols.

[0008] The raw material of the tea polyphenol compound of the present invention can be tea polyphenol extract (TP for short, tea polyphenol content>96%) which can be purchased commercially, or catechin compounds can be directly used.

[0009] The catechin compound is one or more of epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin (EC), epicatechin gallate (ECG), preferably EGCG.

[0010] Preferably, the mass ratio of tea polyphenols to zinc salt is 2 to 3:1, more preferably 3:1.

[0011] In the prepared tea polyphenol nano-zinc material solution, the zinc ion concentration is preferably 0.1-1 mg / mL.

[0012] The alkaline aqueous solution is an aqueous solution of sodium hydroxide, sodium carbonate or sodium bicarbonate; preferably, the concentration of the alkaline aqueous solution is 0.1-2 mol / L.

[0013] The mass concentration of the tea polyphenol extract or catechin compounds is preferably 1 to 5 mg / mL; more preferably 2 to 3 mg / mL.

[0014] Furthermore, the zinc salt is a water-soluble zinc salt, such as zinc sulfate, zinc chloride, zinc gluconate, zinc nitrate, zinc acetate, etc., preferably zinc sulfate.

[0015] The mass concentration of the zinc salt aqueous solution is preferably 0.5 to 2 mg / mL, more preferably 1 to 2 mg / mL.

[0016] In the present invention, an alkaline aqueous solution is added to the aqueous solution of tea polyphenol compounds to adjust the pH value to 8-9, at which time the solution color changes from light yellow to dark yellow, and then a zinc salt aqueous solution is added, the color changes to reddish brown, thereby preparing a solution of tea polyphenol nano-zinc material.

[0017] The solution of the tea polyphenol nano zinc material can be used as a bactericide for Staphylococcus aureus and Pseudomonas aeruginosa.

[0018] The solution of the tea polyphenol nano-zinc material can be used as a fruit preservative.

[0019] The solution of the tea polyphenol nano-zinc material has a zinc ion concentration of 0.1 to 1 mg / mL, more preferably 0.4 to 0.6 mg / mL.

[0020] Specifically, the application method is:

[0021] The fruit is soaked in a solution of tea polyphenol nano-zinc material, then taken out and dried, to form a tea polyphenol nano-zinc material coating on the surface of the fruit, which is used as a preservative.

[0022] The present invention also provides a method for preserving fruits, which comprises the following steps:

[0023] (1) adding an alkaline aqueous solution to an aqueous solution of tea polyphenol compounds to adjust the pH value to 8-9, and then adding a zinc salt aqueous solution to prepare a solution of tea polyphenol nano-zinc material;

[0024] (2) The fruit is soaked in a solution of tea polyphenol nano-zinc material, and then taken out and dried to form a tea polyphenol nano-zinc material coating on the surface of the fruit.

[0025] The soaking time is preferably 1 to 3 minutes.

[0026] In the step (1), the mass ratio of the tea polyphenols compound to the zinc salt is 2 to 3:1, more preferably 3:1.

[0027] The prepared tea polyphenol nano-zinc material solution contains zinc ion concentration of 0.1-1 mg / mL, more preferably 0.4-0.6 mg / mL.

[0028] The technical effects of the present invention are:

[0029] Natural green raw materials are selected as the ingredients of the preservative, which are safe and non-toxic, and the usage is within the control range of safety standards to ensure the safety of food. The synthesis conditions of tea polyphenol-zinc nanomaterials are mild, the reaction time is fast, and it can be completed within a few seconds. It is easy to operate and has low cost, which is conducive to industrial production. Tea polyphenol-zinc nanomaterials have strong antioxidant effects, strong antibacterial and antibacterial properties, and have good antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa, the main bacteria that cause fruit corruption, so they have good preservation effects. After strawberries are soaked in tea polyphenol-zinc nanomaterials, the shelf life of strawberries at room temperature can be extended to 6-7 days, which improves the edible and commercial value of the fruit. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The photos of the tea polyphenol-zinc nanomaterials and reaction raw materials prepared in Example 1, from left to right are tea polyphenol solution TP, ZnSO4 solution and product tea polyphenol-zinc nanomaterial TPZn solution.

[0031] Figure 2 Transmission electron micrograph of the tea polyphenol-zinc nanomaterial prepared in Example 1.

[0032] Figure 3 Bar graph of the survival rates of Staphylococcus aureus and Pseudomonas aeruginosa after treatment with different concentrations of tea polyphenol-zinc nanomaterials.

[0033] Figure 4 Histogram of the survival rates of Staphylococcus aureus and Pseudomonas aeruginosa after treatment with different concentrations of zinc ion solutions.

[0034] Figure 5Histogram of the survival rates of Staphylococcus aureus and Pseudomonas aeruginosa after treatment with different concentrations of polyphenol alkali solutions.

[0035] Figure 6 Photos of coated plates of Staphylococcus aureus and Pseudomonas aeruginosa treated with different concentrations of tea polyphenol-zinc nanomaterials.

[0036] Figure 7 This is a graph showing the test results of tea polyphenol-zinc nanomaterials, tea polyphenols and zinc ion free radical scavenging rate.

[0037] Figure 8 This is a graph showing the weight loss rate of strawberries treated with tea polyphenols preservative, tea polyphenols-zinc preservative and control example 1.

[0038] Fig. 9 This is a graph showing the results of determining the vitamin C content of strawberries treated with tea polyphenol preservative, tea polyphenol-zinc preservative and control example 1. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with specific embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0040] Example 1

[0041] Preparation of tea polyphenols-zinc solution

[0042] Weigh 100 mg of tea polyphenol extract (TP) and put it into 50 mL of deionized water to dissolve, and prepare a tea polyphenol (TP) aqueous solution with a mass concentration of 2 mg / mL. Weigh 50 mg of zinc sulfate and put it into 50 mL of deionized water to dissolve, and prepare a zinc sulfate (ZnSO4) aqueous solution with a mass concentration of 1 mg / mL. Then drop 1M NaOH solution into 600 μL of tea polyphenol aqueous solution and mix until the pH value of the tea polyphenol aqueous solution is equal to 9, then add 400 μL of ZnSO4 solution and mix to obtain a tea polyphenol-zinc solution. The photo under visible light irradiation is shown in the figure. Figure 1 As shown, from left to right are tea polyphenol solution TP, ZnSO4 solution, and product tea polyphenol-zinc nanomaterial TPZn solution. Tea polyphenol solution TP is light yellow. After adding alkali to the tea polyphenol solution to adjust the pH to 9, the color will change to dark yellow. After adding zinc sulfate, the obtained tea polyphenol-zinc nanomaterial solution is a reddish brown clear and transparent liquid, which can be stored stably for a long time at 4°C. Take 5μL of the prepared 0.4mg / mL (in terms of zinc ion concentration) tea polyphenol-zinc nanomaterial solution and drop it on the ultra-thin carbon film. The transmission electron microscope image is shown as follows Figure 2 As shown, TPZn is evenly distributed in a spherical shape on the ultrathin carbon film and has good dispersion.

[0043] Example 2

[0044] Antibacterial activity of tea polyphenol-zinc nanomaterials against Staphylococcus aureus and Pseudomonas aeruginosa, the main bacteria causing fruit spoilage

[0045] The tea polyphenol-zinc nanomaterial TPZn prepared in Example 1 was incubated with Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA) in a 96-well plate, respectively, with the final concentrations being (0, 5, 10, 20, 40 μg / mL), 0 representing the blank control group, and incubated for about 8 h until the OD600 of the blank control group reached about 1, then the incubation was stopped, and then the absorbance (OD600) of the suspension at 600 nm was detected by an ELISA instrument, and the antibacterial activity of TPZn on SA and PA was evaluated based on the absorbance. The survival rates of SA and PA after treatment with different concentrations of TPZn are shown in Figure 2. Figure 3 As shown in the figure, tea polyphenol-zinc nanomaterials inhibited the growth of SA and PA, and had a significant concentration dependence. 6 After multiples, the plate was spread onto an agar plate and cultured for 24 hours. Figure 6 It can be seen that the colony forming units of SA and PA were significantly reduced after TPZn treatment, which further proved the antibacterial activity of tea polyphenols-zinc nanomaterials against SA and PA.

[0046] Example 3

[0047] Antibacterial activity of zinc ions and tea polyphenols at pH = 9 against Staphylococcus aureus and Pseudomonas aeruginosa

[0048] The prepared zinc ion solution (Zn 2+ ) and tea polyphenol solution (TP) with pH = 9 were incubated with Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA) in 96-well plates, and the final concentrations of TP (0, 15, 30, 60, 120 μg / mL) and Zn were set according to the concentrations of polyphenols and zinc ions in TPZn in Example 2. 2+ (0, 5, 10, 20, 40 μg / mL). 0 represents the blank control group. The incubation was stopped for about 8 h until the OD600 of the blank control group reached 1. The absorbance of the suspension at 600 nm (OD600) was measured with an ELISA reader. The Zn 2+ and TP against SA and PA. 2+ The survival rates of SA and PA after TP treatment were as follows Figure 4 and Figure 5 As shown, compared with TPZn, at the same concentration, Zn 2+It has basically no antibacterial activity against the two bacteria. TP has antibacterial activity against the two bacteria, but compared with TPZn, the antibacterial activity of TP is weaker than that of TPZn nanomaterials at the same concentration. Especially for the antibacterial activity against Pseudomonas aeruginosa, the TPZn nanomaterial obtained after zinc ions and tea polyphenols are assembled significantly improves the antibacterial activity against Pseudomonas aeruginosa.

[0049] Example 4

[0050] Evaluation of the antioxidant properties of tea polyphenols-zinc nanomaterials

[0051] The antioxidant activity of tea polyphenol-zinc nanomaterials was determined by measuring the ABTS radical cation scavenging activity, which was determined according to the instructions of the Biotech Research Institute. The ABTS working stock solution was prepared by mixing 200 μL of ABTS solution and oxidant solution in equal amounts and kept in the dark at room temperature for 16 hours. Before use, the ABTS working stock solution was diluted with PBS to form the ABTS working solution. The absorbance of the ABTS working solution minus the corresponding PBS blank control was required to be 0.7±0.05. Then 10 μL of tea polyphenol-zinc solution, tea polyphenol solution and zinc ion solution were mixed with 200 μL of ABTS working solution respectively. The mixture was placed at room temperature for 6 minutes. The absorbance was then measured at 734 nm. The ABTS radical scavenging activity of the sample was calculated as follows:

[0052] ABTS free radical scavenging rate (%) = (A 空白 -A 测定 )÷A 空白 ×100%

[0053] The results are as follows Figure 7 As shown, the TPZn solution inherits the excellent antioxidant activity of tea polyphenols, so that the tea polyphenols-zinc material can be coated on the surface of fruits to achieve the effect of preserving fruits through antioxidant effect.

[0054] Example 5

[0055] Preparation of tea polyphenol preservative (TP): weigh 0.6 g of tea polyphenol, put it into 500 mL of aqueous solution, stir until completely dissolved, and prepare a tea polyphenol solution with a concentration of 1.2 mg / mL as a tea polyphenol preservative; then soak the strawberries in the tea polyphenol preservative for 1 minute, take them out, and then place them in a cool place to dry.

[0056] Preparation of tea polyphenol-zinc preservative (TPZn): Weigh 0.6g tea polyphenol, put it into 300mL aqueous solution, stir until completely dissolved, prepare a tea polyphenol solution with a concentration of 2mg / mL, weigh 0.2g zinc sulfate, put it into 200mL aqueous solution, stir until completely dissolved, prepare a zinc sulfate solution with a concentration of 1mg / mL, then drop 1M NaOH solution into the tea polyphenol solution until the pH value of the tea polyphenol solution is equal to 9, then add 200mL zinc sulfate solution. Prepare a tea polyphenol-zinc preservative with a concentration of 0.4mg / mL (in terms of zinc ion concentration). Then soak the strawberries in the tea polyphenol-zinc preservative for 1 minute, take them out, and then place them in a cool place to dry.

[0057] Comparative Example 1

[0058] In Control Example 1, no treatment was performed on the strawberries.

[0059] Then, the strawberry samples treated with the tea polyphenol preservative, the tea polyphenol-zinc preservative, and the strawberries of Control Example 1 were respectively measured in the following manners.

[0060] Method 1: Weight loss rate determination

[0061] The weight loss rate is calculated by weighing method. The calculation formula is as follows:

[0062]

[0063] Strawberries contain a lot of water, which is the condition for maintaining their life activities and fresh quality. The loss of water will cause metabolic disorders in strawberries and reduce the nutritional content of the fruit. The weight loss rate of strawberry samples was measured, and the results were as follows: Figure 8 As shown. Figure 8 It can be seen that with the passage of time, the weight loss rate of each sample increased, but after 5 days of storage, the weight loss rate of control example 1 and the tea polyphenols group increased significantly, indicating that the tea polyphenols-zinc solution can significantly improve the water loss of strawberries during storage.

[0064] Method 2: Determination of vitamin C content

[0065] Weigh 10g of the edible part of the strawberry, crush it, add 10g of 20g / L oxalic acid solution, and quickly mash it into a homogenate. Accurately weigh 10.00g of the homogenate sample in a beaker, transfer the sample to a 100mL volumetric flask with 20g / L oxalic acid solution, and dilute to the scale, shake well and filter. Accurately pipette 10mL of the filtrate into a 50mL conical flask, and titrate with a calibrated 2,6-dichloroindophenol solution until the solution turns pink and does not fade for 15s. Perform a blank test at the same time. The vitamin C content in the sample is calculated as follows:

[0066]

[0067] Vitamin C is one of the main nutrients of strawberries. During storage, vitamin C gradually decreases due to oxidation. Fig. 9 It can be seen that after the strawberries were stored for 6 days, the Vc content in the tea polyphenols-zinc group was significantly higher than that in the tea polyphenols group and the control group, indicating that the tea polyphenols-zinc solution can enable the strawberries to maintain higher nutritional content during the storage process.

Claims

1. A tea polyphenol nano zinc material, characterized in that The tea polyphenol nano zinc material is prepared by the following method: An alkaline aqueous solution is added to the aqueous solution of tea polyphenol compounds to adjust the pH value to 8-9, and then a zinc salt aqueous solution is added to prepare a solution of tea polyphenol nano-zinc material.

2. The tea polyphenol nano zinc material according to claim 1, characterized in that The tea polyphenol compounds include tea polyphenol extracts, or are catechin compounds; the catechin compounds are one or more of epigallocatechin gallate, epigallocatechin, epicatechin, and epicatechin gallate.

3. The tea polyphenol nano zinc material according to claim 1, characterized in that The alkaline aqueous solution is an aqueous solution of sodium hydroxide, sodium carbonate or sodium bicarbonate; the concentration of the alkaline aqueous solution is 0.1-2 mol / L.

4. The tea polyphenol nano zinc material according to claim 1, characterized in that The mass ratio of the tea polyphenol extract or catechin compound to the zinc salt is 2-3:

1.

5. The tea polyphenol nano zinc material according to claim 1, characterized in that The solution of the tea polyphenol nano-zinc material contains zinc ions at a concentration of 0.1-1 mg / mL.

6. Use of the solution of tea polyphenol nano-zinc material as claimed in any one of claims 1 to 5 as a fruit preservative.

7. The use according to claim 6, characterized in that The method of application is: The fruit is soaked in a solution of tea polyphenol nano-zinc material, then taken out and dried, to form a tea polyphenol nano-zinc material coating on the surface of the fruit, which is used as a preservative.

8. A method for preserving fruit, characterized in that The method comprises the following steps: (1) Adding an alkaline aqueous solution to an aqueous solution of tea polyphenol extract or catechin compounds to adjust the pH value to 8-9, and then adding a zinc salt aqueous solution to prepare a solution of tea polyphenol nano-zinc material; (2) Soaking the fruit in a solution of tea polyphenol nano-zinc material, then taking it out and drying it, thereby forming a tea polyphenol nano-zinc material coating on the surface of the fruit.

9. The method according to claim 8, characterized in that In the step (1), the mass ratio of the tea polyphenol extract or catechin compound to the zinc salt is 2-3:1, and the obtained tea polyphenol nano-zinc material solution contains a zinc ion concentration of 0.1-1 mg / mL; in the step (2), the soaking time is 1-3 min.

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