Sprayable hydrogel fruit preservative capable of being produced in large scale as well as preparation method and application thereof

Abstract

The invention provides a hydrogel fruit preservative capable of being sprayed and produced on a large scale as well as a preparation method and application of the hydrogel fruit preservative. The hydrogel fruit preservative comprises the following raw materials: a mixed solvent of polyvinyl alcohol, tannic acid, ethanol and deionized water. The hydrogel fruit preservative disclosed by the invention is simple in preparation method and raw material composition, low in cost, capable of being produced on a large scale, environment-friendly, easy to clean, recoverable, recyclable, capable of quickly forming a film (within 50s), uniform and smooth after film forming, high in mechanical strength, and has the characteristics of being antibacterial, antioxidant, uvioresistant, low in water oxygen transmission efficiency and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit preservation and the field of hydrogel, and particularly relates to a sprayable, large-scale produced hydrogel fruit preservative and a preparation method and application thereof. Background Art

[0002] Fruits have become an important part of the human diet due to their high water content and rich nutrients. It is estimated that billions of tons of fruits rot and spoil every year, causing huge economic and food losses. Fruit rot and spoilage are mainly caused by microbial contamination, physical damage and rapid ripening due to respiration. Water evaporation and oxidation reactions during transportation and storage will further reduce the quality of fruits. Traditional fruit preservation methods can extend the storage period of fruits, such as plastic film packaging, low-temperature storage, waxing, etc., but these methods have problems such as high cost, environmental pollution and food safety. In order to achieve better preservation effects and higher economic benefits, people have developed a variety of new fruit preservation methods, such as fresh-keeping boxes, fresh-keeping mats, fresh-keeping paper, fresh-keeping film, preservatives and the comprehensive use of multiple preservation methods.

[0003] Hydrogels are three-dimensional polymer networks with extremely high water content, usually with good biocompatibility and adjustable physicochemical properties, and can be applied in a variety of fields. In the field of fruit preservation, hydrogels have attracted widespread attention due to their biocompatibility, biodegradability and environmental friendliness. Recently, a new type of Janus structured hydrogel membrane (HMs) has been developed. This HMs has excellent water / oxygen barrier capacity and antibacterial properties, which can extend the shelf life of fruits to 5 days (Yuan, L., Liu, R., Zhou, Y., Zhang, R., Chen, S., Yang, Q., Gu, Y., Han, L., & Yan, B. (2024). Janus biopolymer nanocomposite coating with excellent antibacterialandwater / oxygen barrier performance for fruit preservation. Food Hydrocolloids, 149, 109528.). In addition, nano-encapsulated trans-resveratrol / chitosan HM was prepared on the surface of strawberries by impregnation. The HM enhanced the antioxidant activity, antibacterial properties and nutrient retention capacity of strawberry (Hu, Q., Zhou, F., Ly, NK, Ordyna, J., Peterson, T., Fan, Z., & Wang, S. (2023). Development of multifunctional nanoencapsulated trans-resveratrol / chitosannutraceuticaledible coating for strawberry preservation. ACS Nano, 17(9), 8586-8597.). However, most HMs are cost-ineffective and complex in the preparation process and are generally not suitable for large-scale production. The development of HMs with shorter gel time, lower cost and easier large-scale production has become a key technical issue in the field of fruit preservation.

[0004] For the preparation of HMs on fruit surfaces, it is crucial to achieve a rapid transition from sol-gel to ensure the uniformity and timeliness of HMs. Polyvinyl alcohol (PVA) is a popular material for HMs for fruit preservation due to its low price, good biocompatibility, and ability to easily form thin films. However, pure PVA HMs lack antimicrobial ability and mechanical strength, which are insufficient to meet the requirements of fruit preservation. In previous studies, antimicrobial agents have been combined with PVA to enhance the antimicrobial properties of HMs, but it is difficult to completely eliminate the residues of these antimicrobial materials. If these residues are ingested, they may cause health problems. In addition, pure PVA is usually cross-linked by physical methods (such as freeze-thaw cycles) or chemical methods (such as glutaraldehyde), which makes it unsuitable for use on fruit surfaces.

[0005] Fresh-keeping effect and economic benefit are issues that must be considered in the production and application of fruit preservatives. In the current patented technology, fruit preservatives containing multiple components will face the problem of high production costs, and the interaction between multiple components may also lead to the complication of the production process; for fruit preservatives that achieve fresh-keeping effects by forming a protective layer, the coating method and film-forming time determine whether they can be widely and efficiently used; the random discarding of fruit preservatives may cause environmental pollution, and whether they can be recycled or reused determines the extent of their impact on the environment; appropriate ultraviolet treatment can inhibit the growth of microorganisms and improve the appearance and taste, but excessive treatment may cause oxidation of fruits and loss of nutrients, so fruit preservatives with anti-ultraviolet function are more helpful in maintaining the nutrients of fruits. Therefore, it is of great significance to develop a fruit preservative with simple preparation method and raw material composition, low cost, large-scale production, environmental friendliness, recyclable and recyclable, and excellent antibacterial, antioxidant, anti-ultraviolet functions, low water-oxygen transmission efficiency, fast film-forming speed, and high mechanical strength after film formation. Summary of the invention

[0006] In view of the deficiencies of the prior art, the present invention provides a sprayable, large-scale production hydrogel fruit preservative and its preparation method and application. The preparation method and raw material composition of the hydrogel fruit preservative of the present invention are simple, low in cost, can be produced on a large scale, are environmentally friendly, easy to clean, recyclable, and can be recycled. It can form a film quickly, and the film is uniform and smooth after forming, has high mechanical strength, and has the characteristics of antibacterial, anti-oxidation, anti-ultraviolet, low water-oxygen transmission efficiency, etc.

[0007] The technical solution of the present invention is as follows.

[0008] A sprayable and mass-producible hydrogel fruit preservative comprises the following raw materials: a mixed solvent of polyvinyl alcohol, tannic acid, ethanol and deionized water.

[0009] According to the preferred embodiment of the present invention, the polyvinyl alcohol is polyvinyl alcohol 1799 type.

[0010] Preferably according to the present invention, the mass ratio of polyvinyl alcohol to tannic acid is 1:0.25-1:1, preferably 1:1.

[0011] Preferably according to the present invention, the mass ratio of ethanol to deionized water is 3:6-5:4, preferably 5:4.

[0012] Preferably according to the present invention, the volume ratio of the total mass of polyvinyl alcohol and tannic acid to the mixed solvent is 0.05-1 g / mL.

[0013] The method for preparing the above-mentioned sprayable, large-scale produced hydrogel fruit preservative comprises the following steps:

[0014] Polyvinyl alcohol and tannic acid are added into a mixed solvent of ethanol and deionized water, and the mixture is stirred and mixed, and then ultrasonically treated to obtain a hydrogel fruit preservative.

[0015] Preferably, according to the present invention, the stirring and mixing temperature is 80-100° C., and the stirring and mixing time is 1-3 h; preferably, the stirring and mixing time is 2 h.

[0016] According to the preferred embodiment of the present invention, the ultrasonic treatment time is 5-20 minutes, preferably 10 minutes, and the ultrasonic treatment temperature is room temperature. The ultrasonic treatment is performed to remove bubbles.

[0017] The above-mentioned sprayable and mass-producible hydrogel fruit preservative is used as a preservative for preserving fruits.

[0018] According to the preferred embodiment of the present invention, the application method comprises the steps of: applying the hydrogel fruit preservative to the surface of the fruit by spraying, brushing or dipping, and then drying at room temperature to form a hydrogel film on the surface of the fruit.

[0019] Preferably, the hydrogel fruit preservative is applied to the surface of the fruit by spraying.

[0020] More preferably, spraying is performed using a spray gun with a spraying pressure of 0.25-0.6 MPa and a spraying distance of 15-30 cm, preferably 20 cm.

[0021] According to the present invention, the fruit is a banana, apple, grape, nectarine, cherry, mango, avocado or pear.

[0022] The technical features and beneficial effects of the present invention are as follows:

[0023] (1) The hydrogel fruit preservative provided by the present invention innovatively adopts a preservation method of a polyvinyl alcohol composite hydrogel film. In the hydrogel fruit preservative, the addition of tannic acid enables the polyvinyl alcohol hydrogel to have antibacterial, antioxidant and anti-ultraviolet functions; the hydrogen bonds between polyvinyl alcohol and tannic acid are dynamically regulated by the ethanol content. When the added ethanol evaporates, hydrogen bonds are formed between polyvinyl alcohol and tannic acid to form a stable and uniform hydrogel network structure, that is, a uniform and smooth hydrogel film is quickly formed on the surface of the fruit. At the same time, the hydrogen bonds between polyvinyl alcohol and tannic acid enhance the structural stability and mechanical properties of the hydrogel film, improve the interaction force between the hydrogel film and the fruit surface, significantly reduce the water-oxygen transmission efficiency of the hydrogel film, and further extend the shelf life of the fruit. The hydrogel fruit preservative also has the characteristics of simple preparation, easy cleaning, recyclability and reusability.

[0024] (2) The raw material composition and preparation method of the present invention are simple and convenient for large-scale production. Compared with the existing hydrogel fruit preservative technology, the components involved in the present invention are polyvinyl alcohol, tannic acid, ethanol and deionized water, which are low in cost and can be purchased from the market or prepared by simple methods; and the ingredients will not have an adverse effect on human health, and the fruit can be eaten normally after washing, which is environmentally friendly. The production process only involves conventional operations such as weighing, heating, stirring, etc., which is convenient for transformation to industrial production.

[0025] (3) The hydrogel fruit preservative of the present invention is easy to use and can be directly sprayed on the surface of the fruit to form a film quickly. The obtained gel film is uniform and smooth. The present invention preferably adopts the spraying method, which has a simple preparation process and can be mass-produced. After the hydrogel fruit preservative is sprayed on the cleaned fruit surface, the ethanol therein can evaporate within 50 seconds, and a dense cross-linked network is formed between polyvinyl alcohol and tannic acid through hydrogen bonds, thereby enhancing the mechanical strength of the hydrogel film, improving the interaction force between the hydrogel film and the fruit surface, and reducing the water-oxygen transmission efficiency of the hydrogel film. In addition, the existing preservative film needs to be formed into a film first, and then the preservative film is transferred to the food. During the transfer process, the film is prone to adhesion, contamination, and damage. In addition, since the fruit is irregular in shape, it is very easy to have incomplete coverage when wrapped with this type of film, and the fruit rots due to contact with air, water vapor, etc. The present invention uses a spraying method to directly form a hydrogel film on the surface of the fruit, without the need for secondary transfer, and can achieve 100% coverage, eliminating the contamination and damage caused by transfer, and is particularly suitable for irregularly shaped foods such as fruits.

[0026] (4) The hydrogel film obtained after the hydrogel fruit preservative of the present invention is formed has the characteristics of being recyclable and reusable. The hydrogel film obtained by the present invention can be peeled off from the surface of the fruit by washing or soaking, and can be redissolved by placing it in a mixed solution of ethanol and deionized water at 80-100°C; when the ethanol evaporates again, the solution can form a hydrogel film again, and still maintain a certain mechanical strength, visible light transmittance, UV resistance, antibacterial, antioxidant and ability to reduce water-oxygen transmission efficiency.

[0027] (5) The hydrogel fruit preservative of the present invention has good antibacterial, antioxidant and anti-ultraviolet effects. The natural antibacterial properties of tannic acid can make the hydrogel film have good antibacterial activity against Staphylococcus aureus and Escherichia coli; the DPPH method to evaluate the antioxidant capacity of the hydrogel film shows that the addition of tannic acid makes the hydrogel film have antioxidant capacity, which can be used to delay the browning and wrinkling of fruits; the hydrogel film has a transmittance of more than 80% for visible light and has a significant absorption capacity for ultraviolet light. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 :(a) Light transmittance of hydrogel films formed by the preservatives of Comparative Example 1, Example 1, Example 2 and Example 3 in the wavelength range of 200-700nm; (b) Changes of G' and G" of the preservatives of Comparative Example 1, Example 1, Example 2 and Example 3 over time; (c) Film formation time of the preservatives of Comparative Example 1, Example 1, Example 2 and Example 3; (d) Surface wettability of mango, grape, banana and cherry before and after treatment with the preservative of Example 3; (e) and (f) Fourier infrared spectra of hydrogel films formed by the preservatives of Comparative Example 1 and Example 3 and tannic acid; (g) Surface morphology and thickness of the hydrogel film formed by the preservative of Example 3; (h) Optical photograph of the flexibility and foldability of the hydrogel film formed by the preservative of Example 3.

[0029] Figure 2 :(a) strain amplitude sweep test of hydrogel film formed by preservatives in comparative example 1 and example 3; (b) and (c) frequency sweep test of hydrogel film formed by preservatives in comparative example 1, example 1, example 2 and example 3; (d) strain amplitude sweep test of hydrogel film formed by preservatives in example 3 at 0.1-1000s -1 Viscosity change test within shear rate range.

[0030] Figure 3: (a) tensile stress-strain diagram of the hydrogel films formed by the preservatives of Comparative Example 1, Example 1, Example 2, and Example 3; (b) tensile strength of the hydrogel films formed by the preservatives of Comparative Example 1, Example 1, Example 2, and Example 3; (c) adhesion of the hydrogel films formed by the preservatives of Comparative Example 1 and Example 3 on the surfaces of mango, banana, and apple; (d) adhesion of the hydrogel films formed by Comparative Example 1 and Example 3 on the surface of banana.

[0031] Figure 4 : (a) Tensile stress-strain curves of the hydrogel film formed by the preservative in Example 3 before and after recycling; (b) Optical transmittance of the hydrogel film formed by the preservative in Example 3 before and after recycling; (c) Washability of the hydrogel film formed by the preservative in Example 3 on the surface of the fruit.

[0032] Figure 5 : (a) Water vapor permeability of hydrogel films formed with preservatives in Comparative Example 1, Example 1, Example 2, and Example 3 over time; (b) Apparent oxygen permeability of hydrogel films formed with preservatives in Comparative Example 1, Example 1, Example 2, and Example 3 over time; (c) Scanning electron microscope images of the surface morphology of hydrogel films formed with preservatives in Comparative Example 1, Example 1, Example 2, and Example 3, with a scale size of 500 μm.

[0033] Figure 6 : (a) Photographs of the antibacterial zones of the hydrogel films formed by the preservatives in Comparative Example 1, Example 1, Example 2, and Example 3 after being co-cultured with Escherichia coli and Staphylococcus aureus for 1 day; (b) Measurement of the diameters of the antibacterial zones of the hydrogel films formed by the preservatives in Comparative Example 1, Example 1, Example 2, and Example 3 after being co-cultured with Escherichia coli and Staphylococcus aureus for 1 day; (c) Measurement of the diameters of the antibacterial zones of the hydrogel films formed by the preservative in Example 3 after being co-cultured with Staphylococcus aureus and Escherichia coli for 7 days.

[0034] Figure 7 :(a) Photographs of the appearance changes of bananas sprayed with the preservative of Example 3 and without the preservative during storage; (b) Weight changes of bananas sprayed with the preservative of Example 3 and without the preservative during storage; (c) Photographs of the appearance changes of grapes sprayed with the preservative of Example 3 and without the preservative during storage; (d) Weight changes of grapes sprayed with the preservative of Example 3 and without the preservative during storage; (e) Photographs of the appearance changes of cherries sprayed with the preservative of Example 3 and without the preservative during storage; (f) Weight changes of cherries sprayed with the preservative of Example 3 and without the preservative during storage; (g), (h) and (i) Hardness tests of bananas, grapes and cherries sprayed with the preservative of Example 3 and without the preservative after storage for 0 day and 7 days, respectively.

[0035] Figure 8 : (a) The ability of the hydrogel films formed by the preservatives of Comparative Example 1, Example 1, Example 2, and Example 3 to remove DPPH; (b) Photos of fresh-cut apples of the control group, Comparative Example 1 group, and Example 3 group (PVA-TA-3) during 24h storage; (c) Biocompatibility of the hydrogel films formed by the preservatives of the control group, Comparative Example 1, and Example 3. DETAILED DESCRIPTION

[0036] The present invention is described in detail below through specific examples and comparative examples, but the use and purpose of these exemplary implementation modes are only used to illustrate the present invention, and do not constitute any form of limitation on the actual protection scope of the present invention, nor limit the protection scope of the present invention to these.

[0037] Example 1

[0038] Preparation of a sprayable, mass-producible hydrogel fruit preservative:

[0039] (1) Weigh 1.25 g of polyvinyl alcohol (polyvinyl alcohol 1799 type, alcoholysis degree 98-99% (mol / mol)) and tannic acid in a mass ratio of 1:0.25, and dissolve them in 12 mL of a mixed solvent of ethanol and deionized water in a mass ratio of 5:4;

[0040] (2) stirring the mixed solution at 90° C. for 2 h;

[0041] (3) The mixed solution was ultrasonically treated at room temperature for 10 min to remove bubbles and obtain a hydrogel fruit preservative (PVA@TA 0.25 ).

[0042] Example 2

[0043] Preparation of a sprayable, mass-producible hydrogel fruit preservative:

[0044] (1) Weigh 1.5 g of polyvinyl alcohol (polyvinyl alcohol 1799 type, alcoholysis degree 98-99% (mol / mol)) and tannic acid in a mass ratio of 1:0.5, and dissolve them in 12 mL of a mixed solvent of ethanol and deionized water in a mass ratio of 5:4;

[0045] (2) stirring the mixed solution at 90° C. for 2 h;

[0046] (3) The mixed solution was ultrasonically treated at room temperature for 10 min to remove bubbles and obtain a hydrogel fruit preservative (PVA@TA 0.5 ).

[0047] Example 3

[0048] Preparation of a sprayable, mass-producible hydrogel fruit preservative:

[0049] (1) Weigh 2 g of polyvinyl alcohol (polyvinyl alcohol 1799 type, alcoholysis degree 98-99% (mol / mol)) and tannic acid in a mass ratio of 1:1, and dissolve them in 12 mL of a mixed solvent of ethanol and deionized water in a mass ratio of 5:4;

[0050] (2) stirring the mixed solution at 90° C. for 2 h;

[0051] (3) The mixed solution was ultrasonically treated at room temperature for 10 min to remove bubbles and obtain a hydrogel fruit preservative (PVA@TA1).

[0052] Comparative Example 1

[0053] Preparation of a polyvinyl alcohol hydrogel:

[0054] (1) Weigh 1 g of polyvinyl alcohol (polyvinyl alcohol 1799 type, alcoholysis degree 98-99% (mol / mol)) and dissolve it in 12 mL of a mixed solvent of ethanol and deionized water in a mass ratio of 5:4;

[0055] (2) stirring the mixed solution at 90° C. for 2 h;

[0056] (3) The mixed solution was ultrasonically treated at room temperature for 10 min to remove bubbles, and then dried at room temperature for 10 min to obtain polyvinyl alcohol hydrogel (PVA).

[0057] Test Example 1

[0058] Effect of the mass ratio of ethanol to deionized water on hydrogel fruit preservatives

[0059] The mass ratio of ethanol to deionized water in Example 3 was changed (0:9, 1:8, 3:6, 1:1, 4:5, 5:4, 6:3, 8:1) to observe the state of the hydrogel fruit preservative.

[0060] The preservatives with a mass ratio of ethanol to deionized water of 0:9, 1:8, 6:3, and 8:1 contained gelatinous precipitates formed by hydrogen bonding interactions between polyvinyl alcohol and tannic acid, and could not form a uniform and stable hydrogel fruit preservative. The preservatives with a mass ratio of ethanol to deionized water of 3:6, 1:1, 4:5, and 5:4 contained no gelatinous precipitates and could be used as hydrogel fruit preservatives.

[0061] Test Example 2

[0062] Structural characterization of hydrogel films and film formation of hydrogel fruit preservatives

[0063] The transmittance of the hydrogel film formed by the fruit preservatives of Comparative Example 1, Example 1, Example 2, and Example 3 at room temperature was measured by an ultraviolet-visible spectrophotometer in the wavelength range of 200-700 nm. The thickness of the film was 50±5 μm. Figure 1 As shown in (a), the hydrogel film obtained by the present invention has excellent transparency in the visible light range. The transmittance of the hydrogel films formed in Example 1, Example 2, and Example 3 is maintained above 80%, and exhibits significant ultraviolet absorption ability in the ultraviolet range.

[0064] Under the conditions of constant strain and frequency, the film-forming time of the fruit preservatives of Comparative Example 1, Example 1, Example 2, and Example 3 at room temperature was measured using a rheometer. Figure 1 As shown in (b) and (c), the film-forming time of Example 1, Example 2 and Example 3 is significantly lower than that of Comparative Example 1, indicating that the present invention can form a film quickly. The film-forming time of Comparative Example 1, Example 1, Example 2 and Example 3 are 500, 50, 45 and 42 s, respectively.

[0065] The surface wettability of mango, grape, banana and cherry before and after treatment with the preservative in Example 3 was measured using a contact angle meter. Figure 1 As shown in (d), the present invention can form a hydrogel film on the surface of fruits such as bananas, grapes, cherries, and mangoes with a low contact angle, indicating that the hydrogel film has good hydrophilicity, can reduce water loss in fruits, and prolong the storage period.

[0066] The functional group composition and interaction of the hydrogel film formed by the fruit preservatives of Comparative Example 1 and Example 3 and tannic acid were analyzed by infrared spectrometer. Figure 1 As shown in (e) and (f), PVA at 2940 cm -1 The characteristic absorption peak at 1714 cm -1 and 1612cm -1 The absorption peaks at 1087 cm-1 correspond to the stretching vibrations of C=O and C=C bonds. -1 Transferred to 1032cm -1 This shift to a lower value may be related to the formation of intramolecular or intermolecular hydrogen bonds, resulting in a red shift in the vibration frequency. The presence of characteristic groups such as CH, C=O, and C=C in PVA@TA1 indicates that PVA@TA1 achieves an effective combination of PVA and tannic acid.

[0067] The surface morphology and thickness of the hydrogel film formed by room temperature film formation in Example 3 were analyzed using a 3D laser scanning microscope. Figure 1As shown in (g), the thickness of PVA@TA1 is 50±5μm and the surface is relatively uniform and smooth.

[0068] The optical photographs of the flexibility and foldability of the hydrogel film formed in Example 3 are as follows: Figure 1 As shown in (h), it shows that the hydrogel film formed in Example 3 is flexible and foldable.

[0069] Test Example 3

[0070] Rheology of hydrogel films and preservatives

[0071] The G' and G" of the hydrogel films formed by room temperature film formation in Comparative Example 1 and Example 3 were measured in the strain amplitude range of 1-1000%. The G' and G" of the hydrogel films formed by room temperature film formation in Comparative Example 1 and Examples 1-3 were measured in the frequency range of 0.1-100 Hz. Figure 2 (a)-(c), indicating that the hydrogen bonding interaction between polyvinyl alcohol and tannic acid molecules enhances the mechanical properties of the hydrogel. The addition of tannic acid improves the structural stability and mechanical properties of the hydrogel.

[0072] In 0.1-1000s -1 The viscosity of the preservative obtained in Example 3 was measured within the shear rate range. Figure 2 (d) Example 3 exhibits shear thinning behavior, which can effectively improve the spraying efficiency of the fruit preservative.

[0073] Test Example 4

[0074] Adhesion properties of hydrogel films

[0075] The tensile strength of the hydrogel films formed by room temperature film formation in Example 1, Example 2, Example 3 and Comparative Example 1 was tested using a testing machine. Figure 3 As shown in (a) and (b), compared with the hydrogel film formed in Comparative Example 1, the addition of tannic acid reduces the tensile strength of the hydrogel film, but increases the elongation at break, indicating that the hydrogel film has strong toughness.

[0076] The adhesion performance of the hydrogel films formed by room temperature film formation in Comparative Example 1 and Example 3 on the surfaces of different fruits was tested by overlapping shear adhesion test. The microscopic adhesion between the hydrogel films formed by room temperature film formation in Comparative Example 1 and Example 3 and the fruit surfaces was measured by atomic force microscopy. Figure 3 As shown in (c) and (d), tannic acid improves the adhesion of the hydrogel film by tightly hydrogen bonding with polyvinyl alcohol. At the same time, tannic acid improves the interaction between the hydrogel film and the fruit surface through non-covalent interactions such as hydrogen bonding and van der Waals forces.

[0077] Test Example 5

[0078] Recyclability of hydrogel films

[0079] Use a spray gun to spray the hydrogel fruit preservative prepared by the method of Example 3 on the surface of nectarines. The spraying method is as follows: Use a spray gun to spray the surface of the fruit under the conditions of a spraying pressure of 0.25-0.6MPa and a spraying distance of 20cm. After spraying, dry at room temperature for 1 minute to form a hydrogel film. Peel off the hydrogel film on the surface of the fruit, add it to a mixed solution of ethanol and deionized water (the mass ratio of ethanol and deionized water is 5:4), heat it at 80°C until the hydrogel film is completely dissolved, spray it again on the surface of nectarines and dry it at room temperature to form a hydrogel film again. Repeat the cycle and use it repeatedly. The tensile stress-strain curves of the hydrogel film before and after recycling and reuse are shown in Figure 4 As shown in (a), the optical transmittance of the hydrogel film before and after recycling is Figure 4 (b) shows, where Recycled 2th Recycled once, used twice in total; 4th The hydrogel fruit preservative of the present invention can be recycled and reused three times, and used four times in total.

[0080] like Figure 4 As shown in (c), after the fruit preservative was coated on the surface of nectarine according to the above method, a uniform and smooth hydrogel film was formed. After the nectarine was immersed in a mixed solution of ethanol and deionized water at 80°C (the mass ratio of ethanol and deionized water was 5:4) for 60 seconds, the hydrogel film was separated from the nectarine surface. After washing with water, the hydrogel film fell off completely, and the nectarine surface was not damaged.

[0081] Test Example 6

[0082] Determination of water vapor permeability (WVP) and apparent oxygen permeability (OTR) of hydrogel films

[0083] The water vapor permeability of the hydrogel films formed by room temperature film formation in Comparative Example 1, Example 1, Example 2, and Example 3 was measured by differential weight method. The apparent oxygen permeability of the hydrogel films formed by room temperature film formation in Comparative Example 1, Example 1, Example 2, and Example 3 was measured by deoxidizer adsorption method. The test results are shown in Table 1. Figure 5 As shown in Figures 5(a) and 5(b), with the increase of tannic acid content, a high-density network structure is formed inside the hydrogel film, which limits the transmission of water and oxygen. The water vapor permeability of the hydrogel film formed in Example 3 is 2.65×10 -7 g.h -1 ·m -1 ·Pa -1 The apparent oxygen permeability is 1.31×10 -3 g·s-1 ·m -2 During the 7-day observation period, the daily average water vapor permeability and apparent oxygen permeability of the hydrogel films formed in Comparative Example 1, Example 1, Example 2, and Example 3 did not change significantly, and had good stability.

[0084] The surface microstructure of the hydrogel films formed by room temperature film formation in Comparative Example 1, Example 1, Example 2, and Example 3 was characterized by scanning electron microscopy. Figure 5 As shown in (c), the hydrogel films formed in Comparative Example 1, Example 1, and Example 2 have pores or cracks on their surfaces, while the hydrogel film formed in Example 3 has a uniform and smooth surface due to its high crosslinking density, thereby improving its barrier capacity against water and oxygen.

[0085] Test Example 7

[0086] Antibacterial activity of hydrogel films

[0087] The inhibition ring test was used to determine the antibacterial activity of the hydrogel films formed by room temperature film formation in Comparative Example 1, Example 1, Example 2, and Example 3 against Escherichia coli and Staphylococcus aureus, and the plate method was used to calculate the antibacterial rate.

[0088] The photos of the antibacterial bands after the hydrogel films formed in Comparative Example 1, Example 1, Example 2, and Example 3 were co-cultured with Escherichia coli and Staphylococcus aureus for 1 day are shown in the figure. Figure 6 As shown in (a), the diameter of the inhibition zone is measured as Figure 6 (b) As shown; the diameter of the antibacterial zone after the hydrogel film formed in Example 3 was co-cultured with Staphylococcus aureus and Escherichia coli for 7 days was measured as follows Figure 6 The above test results show that compared with comparative example 1, the hydrogel film formed in the embodiment has higher antibacterial activity against Staphylococcus aureus and Escherichia coli, and with the increase of tannic acid, the antibacterial activity of the hydrogel films formed in examples 1, 2 and 3 increases successively, and the antibacterial rates of the hydrogel film formed in example 3 against Staphylococcus aureus and Escherichia coli are 100% and 99.9%, respectively.

[0089] Test Example 8

[0090] Effect of hydrogel fruit preservative on the preservation of bananas, grapes and cherries

[0091] Fresh bananas, grapes and cherries were washed with deionized water and divided into a test group and a control group. The hydrogel fruit preservative prepared in Example 3 was sprayed on the fruit of the test group. The surface of the fruit was sprayed with a spray gun under the conditions of a spraying pressure of 0.25-0.6MPa and a spraying distance of 20cm. After the spraying, the fruit was dried at room temperature for 1min to form a hydrogel film. Both groups of fruits were stored in an environment of 25°C and 40% relative humidity. The fruits were placed on plastic trays with sufficient spacing between each fruit to ensure air circulation and minimize compression damage. The weight of the fruit was also measured to evaluate its weight reduction, and their morphological changes were photographed. The hardness of the pulp was evaluated at the beginning and end of the test.

[0092] The appearance and weight changes of bananas during storage are as follows: Figure 7 As shown in (a) and (b), the changes in appearance and weight of grapes during storage are Figure 7 As shown in (c) and (d), the changes in appearance and weight of cherries during storage are Figure 7 As shown in (e) and (f), the hardness tests of bananas, grapes and cherries after 0 and 7 days of storage are shown in Figure 7 The above test results show that the preservative of the present invention forms a protective layer on the surface of bananas, grapes and cherries, reduces the transmission of water and oxygen, and effectively prolongs the storage period of fruits.

[0093] Test Example 9

[0094] Antioxidant and biocompatibility tests of hydrogel films

[0095] The DPPH method was used to evaluate the antioxidant capacity of the hydrogel films formed by room temperature film formation in Comparative Example 1, Example 1, Example 2, and Example 3. Figure 8 As shown in (a), compared with Comparative Example 1, the present invention has excellent antioxidant capacity.

[0096] Fresh-cut apples were used to evaluate the effects of Comparative Example 1 and Example 3 in delaying browning and wrinkling. The apples in the experimental group were coated with the preservatives of Comparative Example 1 and Example 3, while the apples in the control group were not coated with any preservative. The changes in color and surface wrinkles of the fresh-cut apples were monitored over 24 hours and photographed. Figure 8 As shown in (b), the apples in the control group began to brown after 2 hours, and wrinkles were obvious after 4 hours. The apples in the comparative example 1 group also began to brown after 2 hours, and obvious wrinkles were observed after 6 hours. The apples in the example 3 group did not begin to brown until 8 hours later, and only some wrinkles occurred after 12 hours. This shows that the preservative of the present invention can effectively delay the browning and wrinkling of fresh-cut fruits for at least 12 hours.

[0097] The biocompatibility of the hydrogel film formed by room temperature film formation in Example 3 was tested using a CCK-8 cell counting kit. Figure 8 During the 3-day culture period, the cell survival rates of the control group, the comparative example 1 group and the example 3 group were all maintained above 95%, showing good biocompatibility.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sprayable, mass-producible hydrogel fruit preservative, characterized in that: The invention comprises the following raw materials: a mixed solvent of polyvinyl alcohol, tannic acid, ethanol and deionized water.

2. The sprayable, mass-producible hydrogel fruit preservative according to claim 1, characterized in that: The polyvinyl alcohol used is polyvinyl alcohol 1799 type.

3. The sprayable, mass-producible hydrogel fruit preservative according to claim 1, characterized in that: The mass ratio of polyvinyl alcohol to tannic acid is 1:0.25-1:1, preferably 1:

1.

4. The sprayable, mass-producible hydrogel fruit preservative according to claim 1, characterized in that: The mass ratio of ethanol to deionized water is 3:6-5:4, preferably 5:

4.

5. The sprayable, mass-producible hydrogel fruit preservative according to claim 1, characterized in that: The volume ratio of the total mass of polyvinyl alcohol and tannic acid to the mixed solvent is 0.05-1 g / mL.

6. A method for preparing a sprayable, mass-producible hydrogel fruit preservative according to any one of claims 1 to 5, comprising the steps of: Polyvinyl alcohol and tannic acid are added into a mixed solvent of ethanol and deionized water, and the mixture is stirred and mixed, and then ultrasonically treated to obtain a hydrogel fruit preservative.

7. The method for preparing the sprayable, mass-producible hydrogel fruit preservative according to claim 6, characterized in that: Includes one or more of the following conditions: i. The stirring and mixing temperature is 80-100°C, and the stirring and mixing time is 1-3h; preferably, the stirring and mixing time is 2h; ii. The ultrasonic treatment time is 5-20 min, preferably 10 min; the ultrasonic treatment temperature is room temperature.

8. The use of a sprayable, mass-producible hydrogel fruit preservative according to any one of claims 1 to 5, characterized in that: Used as a preservative to preserve fruits.

9. The use of the sprayable, mass-produced hydrogel fruit preservative according to claim 8, characterized in that: The application method comprises the steps of: applying the hydrogel fruit preservative on the surface of the fruit in the manner of spraying, brushing or dipping, and then drying at room temperature to form a hydrogel film on the surface of the fruit.

10. The use of the sprayable, mass-producible hydrogel fruit preservative according to claim 9, characterized in that: Applying the hydrogel fruit preservative on the surface of the fruit by spraying; Preferably, spraying is performed using a spray gun, the spraying pressure is 0.25-0.6 MPa, and the spraying distance is 15-30 cm, preferably 20 cm.

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