Preservation solution containing walnut green seedcase polyphenol and application of preservation solution in grape preservation

Abstract

The invention belongs to the technical field of preservatives, and particularly relates to a fresh-keeping solution containing walnut green seedcase polyphenol and application thereof in grape preservation, and the fresh-keeping solution is prepared by the following steps: S1, taking dry walnut green seedcases, crushing the walnut green seedcases into powder, putting the powder into a conical flask with a plug, mixing the powder with ethanol, extracting, filtering, collecting filtrate, and concentrating; s2, taking a nano-silver particle solution, adding the nano-silver particle solution into the walnut green seedcase polyphenol extract, and stirring in a stirrer; and S3, adding the modified cyclodextrin into the polyphenol-nano-silver complex solution, stirring, putting into an ultrasonic generator for ultrasonic treatment, centrifuging by using a centrifugal machine, and taking supernate. The polyphenol molecules and the nano-silver particles are included in the cavities of the modified cyclodextrin to form a stable ternary complex, so that the stability of the polyphenol and the nano-silver is improved, and the preservation effect is further enhanced through the antibacterial and antioxidant properties of the chitosan.

Description

Technical Field

[0001] The invention belongs to the technical field of preservatives, and in particular relates to a preservative liquid containing walnut green peel polyphenols and application thereof in grape preservation. Background Art

[0002] Grapes are one of the fruits with the largest cultivation area and the highest yield in the world. They are deeply loved by people for their rich nutritional value and sweet taste. However, the preservation of grapes has always been a problem that has troubled fruit farmers and merchants. The high sugar content, thin skin and juicy characteristics of grapes make them extremely vulnerable to mechanical damage and microbial invasion, leading to rot and deterioration. In order to extend the shelf life and shelf life of grapes, preservatives play a vital role in grape preservation. Although traditional chemical preservatives such as sulfur dioxide preservatives can effectively inhibit pathogens and delay the aging of grapes, their impact on the human body and the environment cannot be ignored. In addition, natural plant-based preservatives are usually made from natural plant extracts or microbial fermentation products, which are not only harmless to the human body, but also environmentally friendly. The shelf life of grapes can be extended by inhibiting the growth of microorganisms, reducing the respiration intensity of grapes, and reducing the consumption of nutrients. In addition to preservatives, other preservation technologies are also developing. For example, by adjusting the temperature and humidity of the storage environment, the metabolism of grapes and the reproduction rate of pathogens can be slowed down. Controlled atmosphere storage technology inhibits the respiration of grapes and the growth of microorganisms by changing the gas composition in the storage environment. In addition, there are advanced technologies such as radiation preservation and ozone treatment, which extend the shelf life of grapes in different ways.

[0003] In the prior art, the use effect of traditional chemical preservatives such as plant-based preservatives may not be as stable as that of chemical-based preservatives. The effect of preservatives is easily affected by environmental factors such as temperature and humidity. Too high or too low temperature will cause the plant-based preservatives to fail. At the same time, the preservation effect may be relatively poor, and the speed of natural failure is also relatively fast. Although some traditional preservatives are widely used in countries around the world, such as benzoic acid, long-term consumption of foods containing these preservatives may have a certain impact on human health. For example, the main components of preservatives such as nitrites and benzoic acid may bind to hemoglobin in the body after being absorbed by the human body, affecting the oxygen carrying capacity of hemoglobin, and then affecting the human body's breathing and acid-base balance. Long-term and large-scale intake may affect the digestion and absorption function of the human body, leading to symptoms such as nausea, vomiting, and abdominal pain. In addition, some traditional preservatives may pollute the environment after use, which is not conducive to environmental protection and sustainable development. Summary of the invention

[0004] The purpose of the present invention is to provide a fresh-keeping liquid containing walnut green peel polyphenols and the application of the fresh-keeping liquid in grape preservation in view of the deficiencies of the prior art.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A fresh-keeping liquid containing walnut green peel polyphenols is prepared by the following steps:

[0007] S1. Take dried walnut green peel, crush it into powder, put it into a conical flask with a stopper, mix it with 70% ethanol, and extract it in a constant temperature water bath at 60°C for 2-4 hours, shake it every 30 minutes, filter it, collect the filtrate, and concentrate it to 1 / 4 of the original volume by a rotary evaporator to obtain a walnut green peel extract;

[0008] S2, taking a 1-2 mg / mL nanosilver particle solution, adding it to the walnut peel polyphenol extract, stirring it in a stirrer at a speed of 500-600 rpm for 30 min to obtain a polyphenol-nanosilver complex solution;

[0009] S3. Add modified cyclodextrin to the polyphenol-nanosilver complex solution, stir at a speed of 300-400rpm for 30-60min, put it into an ultrasonic generator for ultrasonic treatment, and then centrifuge it at a speed of 3000-4000rpm for 10-20min, take the supernatant, and obtain a fresh-keeping solution containing walnut green peel polyphenols.

[0010] Furthermore, in step S1, the ratio of walnut green peel to ethanol is (12-14) g: (50-55) mL.

[0011] In step S2, the volume ratio of the nanosilver particle solution to the walnut peel polyphenol extract is (1.2-1.8): (5-7).

[0012] In the step S3, the dosage ratio of the modified cyclodextrin to the polyphenol-nanosilver composite solution is (2-3) g: (11-17) mL.

[0013] The modified cyclodextrin in step S3 comprises the following steps:

[0014] Take 2g of chitosan and add it to 100mL of 1% acetic acid solution, heat it to 60-70℃ and stir until the chitosan is completely dissolved, add β-cyclodextrin, stir it at 300-400rpm for 2-4min, filter it, and dry it in an oven at 60℃ for 12-24h to obtain modified cyclodextrin.

[0015] The frequency of the ultrasonic treatment in step S3 is 40-50 kHz, and the time of the ultrasonic treatment is 10-20 min.

[0016] The usage ratio of the chitosan, the acetic acid solution and the beta-cyclodextrin is (2-5) g: (100-150) mL: (10-18) g.

[0017] According to another aspect of the present invention, there is provided an application of the above-mentioned preservative solution containing walnut green peel polyphenols in grape preservation. After the grapes are washed, they are soaked in the preservative solution for 5-15 minutes, then taken out and naturally dried, and stored in an environment with a relative humidity of 85-95% and a temperature of 0-4°C.

[0018] The fresh-keeping liquid can also be used in combination with other food-grade preservatives or antioxidants to improve the fresh-keeping effect of grapes.

[0019] Beneficial effects of the present invention:

[0020] 1. In the technical solution of the present invention, the nano silver particles can more easily penetrate the cell wall of bacteria due to their extremely small size, combine with atoms such as sulfur and phosphorus in the cells, destroy the DNA structure of bacteria, and thus achieve a bactericidal effect. The phenolic hydroxyl group in the polyphenol molecule can form a weak coordination bond with the nano silver surface, thereby enhancing the dispersibility and stability of the nano silver. At the same time, the antibacterial property of the polyphenol itself is combined with the antibacterial property of the nano silver, resulting in a synergistic effect.

[0021] 2. In the technical solution of the present invention, the cyclodextrin molecule has a hydrophobic internal cavity and a hydrophilic external surface, so that the cyclodextrin can include a variety of organic molecules to form a stable inclusion complex. The polyphenol molecules and nanosilver particles are included in the cavity of the modified cyclodextrin to form a stable ternary complex, which not only improves the stability of polyphenols and nanosilver, but also further enhances the preservation effect through the antibacterial and antioxidant properties of chitosan. DETAILED DESCRIPTION

[0022] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] Example 1

[0024] The modified cyclodextrin is prepared by the following steps:

[0025] Take 20g of chitosan and add it to 1000mL of 1% acetic acid solution, heat it to 60°C and stir it until the chitosan is completely dissolved, add 100g of β-cyclodextrin, stir it at 300rpm for 2min, filter it, and dry it in an oven at 60°C for 12h to obtain modified cyclodextrin.

[0026] Example 2

[0027] The modified cyclodextrin is prepared by the following steps:

[0028] Take 35g of chitosan and add it to 1250mL of 1% acetic acid solution, heat it to 65°C and stir until the chitosan is completely dissolved, add 140g of β-cyclodextrin, stir it at 350rpm for 3min, filter it, and dry it in an oven at 60°C for 18h to obtain modified cyclodextrin.

[0029] Example 3

[0030] The modified cyclodextrin is prepared by the following steps:

[0031] Take 50g of chitosan and add it to 1500mL of 1% acetic acid solution, heat it to 70℃ and stir it until the chitosan is completely dissolved, add 180g of β-cyclodextrin, stir it at 400rpm for 4min, filter it, and dry it in an oven at 60℃ for 24h to obtain modified cyclodextrin.

[0032] Example 4

[0033] A fresh-keeping liquid containing walnut green peel polyphenols, characterized in that it comprises the following steps:

[0034] S1. Take 120g of dried walnut green peel, crush it into powder, put it into a conical flask with a stopper, mix it with 500mL of 70% ethanol, and extract it in a constant temperature water bath at 60°C for 2h, shake it every 30min, filter it, collect the filtrate, and concentrate it to 1 / 4 of the original volume by a rotary evaporator to obtain a walnut green peel extract;

[0035] S2, taking 12 mL of a 1 mg / mL nanosilver particle solution, adding it to 50 mL of walnut peel polyphenol extract, stirring at 500 rpm for 30 min in a stirrer to obtain a polyphenol-nanosilver complex solution;

[0036] S3. Add 20 g of the modified cyclodextrin prepared in Example 1 to 110 mL of the polyphenol-nanosilver complex solution, stir at 300 rpm for 30 min, put into an ultrasonic generator, and ultrasonically treat at a frequency of 40 kHz for 10 min. Centrifuge at 3000 rpm for 10 min, take the supernatant, and obtain a fresh-keeping solution containing walnut peel polyphenols.

[0037] Example 5

[0038] A fresh-keeping liquid containing walnut green peel polyphenols, characterized in that it comprises the following steps:

[0039] S1. Take 130g of dried walnut green peel, crush it into powder, put it into a conical flask with a stopper, mix it with 525mL of 70% ethanol, and extract it in a constant temperature water bath at 60°C for 3h, shake it every 30min, filter it, collect the filtrate, and concentrate it to 1 / 4 of the original volume by rotary evaporator to obtain walnut green peel extract;

[0040] S2, taking 15 mL of a 1.5 mg / mL nanosilver particle solution, adding it to 60 mL of walnut peel polyphenol extract, stirring at 550 rpm for 30 min in a stirrer to obtain a polyphenol-nanosilver complex solution;

[0041] S3. Add 25 g of the modified cyclodextrin prepared in Example 2 to 140 mL of the polyphenol-nanosilver complex solution, stir at 350 rpm for 45 min, put into an ultrasonic generator, and ultrasonically treat at a frequency of 45 kHz for 15 min. Centrifuge at 3500 rpm for 15 min, take the supernatant, and obtain a fresh-keeping solution containing walnut peel polyphenols.

[0042] Example 6

[0043] A fresh-keeping liquid containing walnut green peel polyphenols, characterized in that it comprises the following steps:

[0044] S1. Take 140g of dried walnut green peel, crush it into powder, put it into a conical flask with a stopper, mix it with 550mL of 70% ethanol, and extract it in a constant temperature water bath at 60°C for 4h, shake it every 30min, filter it, collect the filtrate, and concentrate it to 1 / 4 of the original volume by rotary evaporator to obtain walnut green peel extract;

[0045] S2, taking 18 mL of 2 mg / mL nanosilver particle solution, adding it to 70 mL of walnut peel polyphenol extract, stirring at 600 rpm for 30 min in a stirrer to obtain a polyphenol-nanosilver complex solution;

[0046] S3. Add 30 g of the modified cyclodextrin prepared in Example 3 to 170 mL of the polyphenol-nanosilver complex solution, stir at 400 rpm for 60 min, put into an ultrasonic generator, and ultrasonically treat at a frequency of 50 kHz for 20 min. Centrifuge at 4000 rpm for 20 min, take the supernatant, and obtain a fresh-keeping solution containing walnut peel polyphenols.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 4 is that chitosan is used instead of modified cyclodextrin, and the remaining steps are the same as those of Example 4, namely:

[0049] S1. Take 120g of dried walnut green peel, crush it into powder, put it into a conical flask with a stopper, mix it with 500mL of 70% ethanol, and extract it in a constant temperature water bath at 60°C for 2h, shake it every 30min, filter it, collect the filtrate, and concentrate it to 1 / 4 of the original volume by a rotary evaporator to obtain a walnut green peel extract;

[0050] S2, taking 12 mL of a 1 mg / mL nanosilver particle solution, adding it to 50 mL of walnut peel polyphenol extract, stirring at 500 rpm for 30 min in a stirrer to obtain a polyphenol-nanosilver complex solution;

[0051] S3. Add 20 g of chitosan to 110 mL of polyphenol-nanosilver complex solution, stir at 300 rpm for 30 min, put into an ultrasonic generator, ultrasonicate at 40 kHz for 10 min, centrifuge at 3000 rpm for 10 min, and take the supernatant.

[0052] Comparative Example 2

[0053] The difference between this comparative example and Example 5 is that β-cyclodextrin is used instead of modified cyclodextrin, and the remaining steps are the same as those in Example 5, namely:

[0054] S1. Take 130g of dried walnut green peel, crush it into powder, put it into a conical flask with a stopper, mix it with 525mL of 70% ethanol, and extract it in a constant temperature water bath at 60°C for 3h, shake it every 30min, filter it, collect the filtrate, and concentrate it to 1 / 4 of the original volume by rotary evaporator to obtain walnut green peel extract;

[0055] S2, taking 15 mL of a 1.5 mg / mL nanosilver particle solution, adding it to 60 mL of walnut peel polyphenol extract, stirring at 550 rpm for 30 min in a stirrer to obtain a polyphenol-nanosilver complex solution;

[0056] S3. Add 25 g of β-cyclodextrin to 140 mL of polyphenol-nanosilver complex solution, stir at 350 rpm for 45 min, put into an ultrasonic generator, ultrasonically treat at a frequency of 45 kHz for 15 min, and then centrifuge at 3500 rpm for 15 min. Take the supernatant to obtain a fresh-keeping solution containing walnut peel polyphenols.

[0057] E. coli was inoculated on the culture medium and cultured at 37°C for 24 hours. The bacteria were then washed with sterile saline and the bacterial concentration was adjusted to about 10^6 CFU / mL. A certain amount of bacterial suspension was taken and the same amount of the preservative solution prepared in Examples 4-6 and Comparative Examples 1-2 was added. The mixture was incubated at 37°C for 1 hour. The results are shown in Table 1:

[0058] Table 1. Antibacterial effect results of Examples 4-6 and Comparative Examples 1-2

[0059]

[0060] Select several bunches of healthy grapes of similar maturity, cut off the grape stems, rinse with running water, and dry them. Randomly divide the grapes into several groups, each group containing the same number of grapes. Ensure that the initial quality, color and hardness of each group of grapes are similar. Each group of grapes is soaked in the fresh-keeping solution prepared in Examples 4-6 and Comparative Examples 1-2, respectively, to ensure that the grapes are completely covered by the fresh-keeping solution, and soak for 5 minutes. Set up another control group and soak them in clean water for the same time. Store the treated grapes in an environment with a relative humidity of 85% and a temperature of 0°C. After 14 days of storage, analyze the effect of the fresh-keeping solution on the preservation effect of grapes, including color retention rate, hardness retention rate and rot rate. Among them, color retention rate = [1-(color change value / initial color value)] × 100%, hardness retention rate = (hardness measurement value after storage / initial hardness measurement value) × 100%, rot rate = (number of rotten grapes / total number of grapes) × 100%. The results are shown in Table 2:

[0061] Table 2. Grape preservation effects of Examples 4-6, Comparative Examples 1-2 and the control group

[0062]

[0063] As shown in Table 1, the fresh-keeping solutions of Examples 4-6 have significant antibacterial effects on Escherichia coli, and the bacterial reduction rates are all above 93%, which is significantly higher than that of Comparative Examples 1-2. This may be because the addition of modified cyclodextrin enhances the antibacterial properties of the fresh-keeping solution. Modified cyclodextrin is prepared by compounding chitosan and β-cyclodextrin. Chitosan itself has certain antibacterial activity, while β-cyclodextrin can enhance the antibacterial effect of chitosan. The modified cyclodextrin formed by the combination of the two may play a synergistic antibacterial role in the fresh-keeping solution.

[0064] As shown in Table 2, the fresh-keeping solutions of Examples 4-6 also showed excellent effects in grape preservation. The color retention rate and hardness retention rate were significantly higher than those of Comparative Examples 1-2 and the control group, while the decay rate was significantly lower than that of the other groups. This may be related to the unique properties of the modified cyclodextrin, which not only has good antibacterial properties, but also forms a more stable composite system through interaction with polyphenols and nano-silver particles, thereby improving the fresh-keeping effect of the fresh-keeping solution.

[0065] Specifically, polyphenols are a class of compounds with antioxidant and antibacterial activity, while nanosilver particles have a broad-spectrum antibacterial effect. Modified cyclodextrins may enhance the stability and dispersibility of polyphenols and nanosilver particles in the preservation solution through interaction with them, allowing these active ingredients to play a better role. In addition, modified cyclodextrins themselves may also protect grapes from external environmental damage by forming inclusion compounds, thereby extending the shelf life of grapes.

[0066] In summary, the fresh-keeping solutions of Examples 4-6 showed significantly better effects in antibacterial and grape fresh-keeping than those of Comparative Examples 1-2 and the control group. The reason why the fresh-keeping solutions of Examples 4-6 showed excellent effects in antibacterial and fresh-keeping may be related to the addition of modified cyclodextrin and its interaction with polyphenols and nano-silver particles.

[0067] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0068] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A fresh-keeping liquid containing walnut green peel polyphenols, characterized in that: The method comprises the following steps: S1. Take dried walnut green peel, crush it into powder, put it into a conical flask with a stopper, mix it with 70% ethanol, and extract it in a constant temperature water bath at 60°C for 2-4 hours, shake it every 30 minutes, filter it, collect the filtrate, and concentrate it to 1 / 4 of the original volume by a rotary evaporator to obtain a walnut green peel extract; S2, taking a 1-2 mg / mL nanosilver particle solution, adding it to the walnut peel polyphenol extract, stirring it in a stirrer at a speed of 500-600 rpm for 30 min to obtain a polyphenol-nanosilver complex solution; S3. Add modified cyclodextrin to the polyphenol-nanosilver complex solution, stir at a speed of 300-400rpm for 30-60min, put it into an ultrasonic generator for ultrasonic treatment, and then centrifuge it at a speed of 3000-4000rpm for 10-20min, take the supernatant, and obtain a fresh-keeping solution containing walnut green peel polyphenols.

2. The fresh-keeping liquid containing walnut peel polyphenols according to claim 1, characterized in that: In step S1, the usage ratio of walnut green peel and ethanol is (12-14) g: (50-55) mL.

3. The fresh-keeping liquid containing walnut green peel polyphenols according to claim 1, characterized in that: In step S2, the volume ratio of the nanosilver particle solution to the walnut peel polyphenol extract is (1.2-1.8):(5-7).

4. The fresh-keeping liquid containing walnut green peel polyphenols according to claim 1, characterized in that: In step S3, the dosage ratio of modified cyclodextrin and polyphenol-nanosilver composite solution is (2-3) g: (11-17) mL.

5. The fresh-keeping liquid containing walnut green peel polyphenols according to claim 1, characterized in that: The modified cyclodextrin in step S3 comprises the following steps: Take 2g of chitosan and add it to 100mL of 1% acetic acid solution, heat it to 60-70℃ and stir until the chitosan is completely dissolved, add β-cyclodextrin, stir it at 300-400rpm for 2-4min, filter it, and dry it in an oven at 60℃ for 12-24h to obtain modified cyclodextrin.

6. The fresh-keeping liquid containing walnut peel polyphenols according to claim 1, characterized in that: The frequency of the ultrasonic treatment in step S3 is 40-50 kHz, and the time of the ultrasonic treatment is 10-20 min.

7. The fresh-keeping liquid containing walnut green peel polyphenols according to claim 5, characterized in that: The dosage ratio of chitosan, acetic acid solution and β-cyclodextrin is (2-5) g: (100-150) mL: (10-18) g.

8. Use of a fresh-keeping liquid containing walnut peel polyphenols according to claim 1 in grape preservation, characterized in that: After the grapes are cleaned, they are soaked in the fresh-keeping liquid for 5-15 minutes, then taken out and naturally dried, and stored in an environment with a relative humidity of 85-95% and a temperature of 0-4°C.

9. The use according to claim 8, characterized in that: The preservative solution can also be used in combination with other food-grade preservatives or antioxidants to improve the preservation effect of grapes.

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