Hydrogel coating based on corn protein-based turmeric carbon nanodots, preparation method of hydrogel coating and application of hydrogel coating in fresh keeping of fruits and vegetables

Abstract

The invention discloses a hydrogel coating based on corn protein-based turmeric carbon nanodots, a preparation method of the hydrogel coating and application of the hydrogel coating in fruit and vegetable fresh-keeping, and belongs to the technical field of fruit and vegetable fresh-keeping materials. The preparation method of the hydrogel coating comprises the following steps: mixing a turmeric carbon nanodot solution and a solution phase, adding a citric acid solution, fully stirring, pouring into a mold, and standing to obtain the hydrogel coating. The corn protein-based turmeric carbon nanodot hydrogel coating has the beneficial effects that the corn protein-based turmeric carbon nanodot hydrogel coating has good broad-spectrum antibacterial property, oxidation resistance, biological solubility and stability, the storage requirement of low pollution in the transportation process after fruits and vegetables are harvested can be met, and meanwhile, the corn protein-based turmeric carbon nanodot hydrogel coating can be completely washed away through simple water washing before being eaten; the method meets the safe and non-toxic use requirements in the field of fruit and vegetable preservation, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of fruit and vegetable preservation materials, specifically to a hydrogel coating based on corn protein-based turmeric carbon nanodots, its preparation method, and its application in fruit and vegetable preservation. Background Technology

[0002] Turmeric has wide applications in medicine, food, cosmetics, and agriculture. The growing global demand for natural and health products, coupled with technological advancements, has brought new development opportunities to the turmeric industry. While curcumin possesses potential health benefits such as antioxidant, anticancer, anti-inflammatory, and antibacterial properties, its low bioavailability and water solubility limit its use. In recent years, nanomaterials, with their superior performance and delivery efficiency compared to traditional bulk materials, and the unique physicochemical properties resulting from their size effect, have brought revolutionary changes to multiple fields such as materials science, biomedicine, electronic information, and modern agriculture and food. The preparation of turmeric carbon nanodots has attracted widespread attention due to its significantly increased bioavailability, solubility, cycle life, targeting specificity, stability, cell delivery efficiency, and lower biodegradability. Zein, a byproduct of renewable resources in the corn processing chain, with its unique hydrophobic / hydrophilic properties, excellent coating, film-forming and fiber-forming capabilities, and powerful antioxidant functions, has opened up limitless possibilities in the food and nutrition field, becoming one of the most highly regarded biopolymers.

[0003] The adsorption of turmeric carbon nanodots onto corn gluten may enhance the antioxidant properties, solubility, and stability of lipids and bioactive compounds. However, there are no reports on how to cleverly combine these two methods for fruit and vegetable preservation.

[0004] Chinese patent application CN117158440A discloses the application of turmeric carbon nanodots in the control of wheat scab. The turmeric carbon nanodots are prepared by a method including the following steps: 1) taking turmeric powder and drying it for later use; 2) subjecting the system of the turmeric powder and solvent to a hydrothermal reaction, centrifuging after the reaction, and collecting the supernatant; 3) purifying and drying the supernatant to obtain the turmeric carbon nanodots. This patent uses the naturally occurring herbaceous plant turmeric as a precursor and combines it with carbon nanodot technology to prepare turmeric CDs. Turmeric is widely available and easy to obtain. The prepared turmeric CDs have excellent antibacterial ability against Fusarium graminearum spores and a good control effect on wheat scab, without adversely affecting wheat seedling growth, and are expected to serve as an ideal green agricultural fungicide. However, this patent does not disclose its application in the field of fruit and vegetable preservation, therefore further improvement is needed. Summary of the Invention

[0005] The technical problem to be solved by this invention is how to solve the problems of poor preservation effect, poor antibacterial properties and poor degradation performance of existing fruit and vegetable preservation materials.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] The first aspect of this invention provides a method for preparing a corn protein-based turmeric carbon nanoparticle hydrogel coating with both preservation and antibacterial functions, comprising the following steps:

[0008] (1) Dissolve the dried turmeric carbon nanodots in anhydrous ethanol aqueous solution to obtain a turmeric carbon nanodot solution; the final concentration of the turmeric carbon nanodot solution is 0.05-5 mg / mL;

[0009] (2) Dissolve zein in anhydrous ethanol aqueous solution to obtain zein solution, add glycerol and mix thoroughly to obtain zein-glycerol mixed solution; the final concentration of zein solution is 4-8 mg / mL; the amount of glycerol added is 10-30% of the zein mass;

[0010] (3) Mix the turmeric carbon nanodot solution obtained in step (1) and the zein-glycerol mixed solution obtained in step (2), add citric acid solution, stir thoroughly, pour into a mold, and let stand to obtain the product;

[0011] The mass ratio of turmeric carbon nanodot solution to zein-glycerol mixed solution is (0.8-1.5):(20-25); the amount of citric acid solution added is 5-15% of the mass of zein.

[0012] Preferably, in (1), the final concentration of the turmeric carbon nanodot solution is 0.2 mg / mL.

[0013] Preferably, in (2), the final concentration of the zein solution is 6 mg / mL.

[0014] Preferably, in (2), a magnetic stirrer is used to stir until the zein is completely dissolved. The stirring speed is 300-500 rpm and the stirring time is about 1-2 hours to ensure that the solution is uniform and transparent and free of particles.

[0015] Preferably, in (2), the amount of glycerol added is 20% of the amount of corn alcohol-soluble protein.

[0016] The amount of glycerin added can be adjusted according to the required stretchability and flexibility of the hydrogel.

[0017] Preferably, in (3), the mass ratio of turmeric carbon nanodot solution and zein-glycerol mixed solution is 1:20 and 1.4:22.

[0018] Preferably, in (3), the phase is mixed evenly by stirring for 15 to 30 minutes to ensure that the carbon dots are evenly distributed in the solution.

[0019] Preferably, in (3), the amount of citric acid solution added is 10% of the amount of corn alcohol-soluble protein.

[0020] Preferably, in (3), during the addition of citric acid solution, the mixture is continuously stirred at a speed of 200-300 rpm. After the addition is completed, the mixture is stirred for 1-2 hours to promote the cross-linking reaction.

[0021] Preferably, in step (3), the solution is poured into the mold to ensure that the solution is evenly distributed and to avoid air bubbles.

[0022] Preferably, in (3), the mold is placed in a constant temperature environment of 30-50°C and left to stand for 12-24 hours to allow the hydrogel to fully cross-link and form.

[0023] A second aspect of the present invention provides a hydrogel coating prepared by the above-described preparation method.

[0024] A third aspect of the present invention proposes the application of the above-mentioned hydrogel coating in the field of fruit and vegetable preservation.

[0025] The beneficial effects of this invention are as follows:

[0026] (1) This invention uses the plant tuber of turmeric, a traditional Chinese herbal medicine, as raw material and ethanol as solvent to prepare natural, low-toxicity, and biocompatible turmeric carbon nanodot materials (TCDs) with a particle size of less than 10 nm by hydrothermal method. Under natural light, TCDs generate abundant active oxygen (ROS) components, which can play an efficient cleaning and sterilization role on the surface of fruits and vegetables and the storage environment (aerosol).

[0027] (2) Compared with other ROS sterilization technologies, the corn protein-based turmeric carbon nanoparticle hydrogel coating method of the present invention uses the slow-release function of corn protein to retain TCDs on the surface of fruits and vegetables for a longer period of time. Under external light, it continuously generates ROS and exerts a sterilization effect continuously. This will provide a continuously clean storage environment for fruits and vegetables after harvest, greatly reduce the risk of contamination of fruits and vegetables, and reduce waste after harvest.

[0028] (3) Compared with other sterilization methods, the raw materials used in this invention—turmeric tubers and corn protein—are derived from pure natural plants, are widely available and inexpensive, and have simple and easy synthesis conditions, making them easy to promote and apply on a large scale. They have a good application prospect in the modern agriculture and food fields.

[0029] (4) The corn protein-based turmeric carbon nanoparticle hydrogel coating of the present invention has good broad-spectrum antibacterial, antioxidant, biocompatibility and stability, which can meet the low pollution storage requirements during the post-harvest transportation of fruits and vegetables. At the same time, it can be completely washed off with water before consumption, which meets the requirements for safe and non-toxic use in the field of fruit and vegetable preservation.

[0030] (5) Zealysin is a plant protein extracted from corn, and turmeric carbon nanodots are derived from natural turmeric. The entire system is non-toxic and conforms to the concept of sustainable development. Moreover, the coating is biodegradable, reducing environmental pollution, and is suitable for fields with high environmental protection requirements such as food packaging and medical dressings.

[0031] (6) Curcumin possesses broad-spectrum antibacterial and strong antioxidant activity. Combined with the photocatalytic or photothermal properties of carbon nanodots, it can enhance the inhibitory effect on bacteria and fungi, and extend the shelf life of food. Furthermore, the introduction of carbon nanodots can improve the mechanical strength of the coating (such as toughness and wear resistance), compensating for the brittleness of zein film formation. In addition, the hydrophobicity of zein and the surface modification of carbon nanodots work synergistically to improve the light and heat stability of curcumin and extend the functional life of the coating.

[0032] (7) Turmeric carbon nanodots are environmentally responsive materials (photo-triggered), enabling the intelligent release of antibacterial agents and antioxidants, thus improving the coating's adaptability in complex environments. In addition, the film-forming properties of zein combined with the high loading capacity of carbon nanodots allow for precise control of the release rate of active ingredients.

[0033] (8) The solution blending process can be carried out at room temperature or low temperature, avoiding the damage of active ingredients (such as curcumin) to high temperatures. This colloidal coating can be uniformly coated on the surface of various materials (such as metals, plastics, and textiles), and is suitable for diverse applications such as food packaging films, medical devices, and agricultural preservation films. Moreover, the raw materials are widely available, the colloidal synthesis process is simple, and it is suitable for large-scale production.

[0034] (9) A hydrogel coating with excellent preservation properties was prepared by organically combining turmeric carbon nanodots and zein. This combination can leverage the synergistic effect of both to further enhance the preservation of fruits and vegetables. This hydrogel coating can not only effectively extend the shelf life of fruits and vegetables, but also maintain their freshness and taste. In addition, since both turmeric carbon nanodots and zein are natural materials, this hydrogel coating has the advantages of being environmentally friendly, non-toxic, and biodegradable, which is in line with the current trend of green and environmentally friendly development. Attached Figure Description

[0035] Figure 1This invention demonstrates the antibacterial effect of different concentrations of turmeric carbon dots-corn protein-based hydrogel coatings on *Colletotrichum gloeosporioides* spores in Example 1. A: Comparison of spore survival counts on plate coatings; B: Comparison of spore germination rates 4 hours after treatment; C: Comparison of spore germ tube elongation.

[0036] Figure 2 This invention demonstrates the antibacterial effect of different concentrations of turmeric carbon dots-corn protein-based hydrogel coatings on *Colletotrichum gloeosporioides* spores in Example 1. A: Comparison of mycelial growth photographs; B: Comparison of mycelial inhibition rates;

[0037] Figure 3 This study investigates the effects of different concentrations of turmeric carbon dots-corn protein-based hydrogel coatings on the preservation effects of various fruits and vegetables during storage, as described in Example 1 of this invention.

[0038] Figure 4 This invention illustrates the effect of different concentrations of turmeric carbon dots-corn protein-based hydrogel coatings on the sensory quality changes of peaches during storage, as described in Example 1. A: Hardness; B: Weight loss; C: Decay rate;

[0039] Figure 5 The images show a comparison between the hydrogel coatings prepared in Example 1 and Comparative Example 1 of the present invention, where A is a physical image and B is a result image of CFU coating.

[0040] Figure 6 The images show a comparison between the hydrogel coatings prepared in Example 1 and Comparative Example 8 of this invention, where A is a physical image and B is a result image of CFU coating. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0043] Unless otherwise specified, all techniques or conditions described in the embodiments can be performed in accordance with the techniques or conditions described in the literature in this field or in the product manual. Unless otherwise specified, the quantitative experiments in the following embodiments are all repeated three times or more, and the results are averaged.

[0044] The turmeric carbon nanodots were prepared using the method described in Example 1 of the patent document with publication number CN117158440A.

[0045] Example 1:

[0046] A method for preparing a corn protein-based turmeric carbon nanoparticle hydrogel coating with both preservation and antibacterial functions includes the following steps:

[0047] (1) Dissolve the dried turmeric carbon nanodots in a 75% (v / v) anhydrous ethanol aqueous solution to obtain a turmeric carbon nanodot solution (final concentration of 0.2 mg / mL);

[0048] (2) Add zein to an 80% (v / v) anhydrous ethanol aqueous solution and stir with a magnetic stirrer until the zein is completely dissolved. The stirring speed is 400 rpm and the stirring time is about 1.5 h to obtain a zein solution (final concentration is 6 mg / mL); add glycerol (the amount added is 20% of the zein mass) and stir for 30 min to mix thoroughly to obtain a zein-glycerol mixed solution;

[0049] (3) Mix the turmeric carbon nanodot solution from step (1) and the zein-glycerol mixed solution obtained in step (2) at a mass ratio of 1:20, and stir for 20 minutes to ensure uniform mixing and that the carbon dots are evenly distributed in the solution; add citric acid solution (10% of the mass of zein) dropwise while stirring at a speed of 250 rpm. After the addition is complete, continue stirring for 1.5 hours; then pour it into a mold, ensuring that the solution is evenly distributed and avoiding air bubbles. Place the mold in a constant temperature environment of 35°C and let it stand for 22 hours to allow the hydrogel to fully cross-link and form.

[0050] Further sterilization verification will be conducted.

[0051] Example 2:

[0052] The difference between this embodiment and embodiment 1 is that the final concentration of the turmeric carbon nanodot solution in step (1) is 0.05 mg / mL, and the rest is the same as in embodiment 1.

[0053] Example 3:

[0054] The difference between this embodiment and Embodiment 1 is that the final concentration of the turmeric carbon nanodot solution in step (1) is 0.1 mg / mL, and the rest is the same as in Embodiment 1.

[0055] Example 4:

[0056] A method for preparing a corn protein-based turmeric carbon nanoparticle hydrogel coating with both preservation and antibacterial functions includes the following steps:

[0057] (1) Dissolve the dried turmeric carbon nanodots in 75% (v / v) anhydrous ethanol aqueous solution to obtain a turmeric carbon nanodot solution (final concentration of 5 mg / mL);

[0058] (2) Add zein to an 80% (v / v) anhydrous ethanol aqueous solution and stir with a magnetic stirrer until the zein is completely dissolved. The stirring speed is 300 rpm and the stirring time is about 2 hours to obtain a zein solution (final concentration is 8 mg / mL). Add glycerol (the amount added is 10% of the zein mass) and stir for 30 minutes to mix thoroughly to obtain a zein-glycerol mixed solution.

[0059] (3) Mix the turmeric carbon nanodot solution from step (1) and the zein-glycerol mixed solution obtained in step (2) at a mass ratio of 1.4:22, and stir for 15 min to ensure uniform mixing and that the carbon dots are evenly distributed in the solution; add citric acid solution (15% of the mass of zein) dropwise while stirring at a speed of 200 rpm. After the addition is complete, continue stirring for 2 h; then pour into a mold, ensuring that the solution is evenly distributed and avoiding air bubbles. Place the mold in a constant temperature environment of 50°C and let it stand for 12 h to allow the hydrogel to fully cross-link and form, thus obtaining the final product.

[0060] Example 5:

[0061] A method for preparing a corn protein-based turmeric carbon nanoparticle hydrogel coating with both preservation and antibacterial functions includes the following steps:

[0062] (4) Dissolve the dried turmeric carbon nanodots in a 75% (v / v) anhydrous ethanol aqueous solution to obtain a turmeric carbon nanodot solution (final concentration of 0.2 mg / mL);

[0063] (5) Add zein to an 80% (v / v) anhydrous ethanol aqueous solution and stir with a magnetic stirrer until the zein is completely dissolved. The stirring speed is 500 rpm and the stirring time is about 1 hour to obtain a zein solution (final concentration is 4 mg / mL). Add glycerol (the amount added is 30% of the zein mass) and stir for 30 minutes to mix thoroughly to obtain a zein-glycerol mixed solution.

[0064] (6) Mix the turmeric carbon nanodot solution from step (1) and the zein-glycerol mixed solution obtained from step (2) at a mass ratio of 1.5:25, and stir for 30 minutes to ensure uniform mixing and that the carbon dots are evenly distributed in the solution; add citric acid solution (5% of the zein mass) dropwise while stirring at a speed of 300 rpm. After the addition is complete, continue stirring for 1 hour; then pour into a mold, ensuring that the solution is evenly distributed and avoiding air bubbles. Place the mold in a constant temperature environment of 30°C and let it stand for 24 hours to allow the hydrogel to fully cross-link and form.

[0065] The hydrogel coatings prepared in Examples 4 and 5 have similar properties to those in Example 1.

[0066] Comparative Example 1:

[0067] The difference between this comparative example and Example 1 is that the final concentration of the turmeric carbon nanodot solution in step (1) is 20 mg / mL, and the rest is the same as in Example 1.

[0068] The product obtained in this comparative example has the following solubility characteristics: Figure 5 As shown in Figure A, the results of CFU coating are as follows: Figure 5 As shown in B. Turmeric carbon dots are a type of photo-driven bactericidal material. In the early experiments, it was indeed found that the bactericidal efficiency was not good when the concentration exceeded a certain range. This is mainly because the higher the concentration, the less light transmittance the solution has, and incomplete light exposure will affect the bactericidal efficiency.

[0069] Comparative Example 2:

[0070] The difference between this comparative example and Example 1 is that the final concentration of the turmeric carbon nanodot solution in step (1) is 0.01 mg / mL, and the rest is the same as in Example 1.

[0071] The comparative study showed that the antibacterial rate of *Colletotrichum gloeosporioides* spores was only 9.8%, which is poor and not conducive to the antibacterial preservation of fruits and vegetables.

[0072] Comparative Example 3:

[0073] The difference between this comparative example and Example 1 is that glycerol is not added in step (2), while the rest is the same as in Example 1.

[0074] Results: During low-temperature freezing storage, the coating lost its room-temperature ductility because there was no glycerin as an antifreeze to absorb and retain moisture from the environment. The low-temperature environment made the coating brittle and hard, and the water retention of the coating was greatly reduced, making it unusable.

[0075] Comparative Example 4:

[0076] The difference between this comparative example and Example 1 is that the amount of glycerol added in step (2) is 2% of the amount of corn alcohol-soluble protein, and the rest is the same as in Example 1.

[0077] Results: Adding 2% glycerol to the entire coating system made the originally hard and brittle coating significantly softer, more flexible and impact-resistant, but the coating had insufficient extensibility, the gel could not be fully formed, the stability was poor, and the coating properties could not be maintained for a long time.

[0078] Comparative Example 5:

[0079] The difference between this comparative example and Example 1 is that the final concentration of the zein solution in step (2) is 0.5 mg / mL, while the rest is the same as in Example 1.

[0080] Result: Low concentration of zein prevented the gel from forming properly, failed to evenly coat the fruits and vegetables, was easy to peel off, and was unusable.

[0081] Comparative Example 6:

[0082] The difference between this comparative example and Example 1 is that the final concentration of the zein solution in step (2) is 20 mg / mL, and the rest is the same as in Example 1.

[0083] Results: The addition of excessive zein will damage the mechanical properties of the entire coating system, leading to increased coating brittleness, decreased flexibility, intensified water vapor and oil penetration, reduced barrier function, insufficient coating stability, functional coating failure, and limited application performance.

[0084] Comparative Example 7: The difference between this comparative example and Example 1 is that the amount of glycerol added in step (2) is 50% of the amount of corn alcohol-soluble protein, and the rest is the same as in Example 1.

[0085] Results: The addition of a high proportion of glycerol greatly increased the viscosity of the coating system, affecting the coating's application performance and flowability. In practical applications, the coating is difficult to wash off the surface of fruits and vegetables, seriously affecting the consumer's user experience.

[0086] Comparative Example 8:

[0087] The difference between this comparative example and Example 1 is that in step (3), the turmeric carbon nanodot solution and the zein-glycerol mixed solution are mixed at a mass ratio of 1:10, and the rest is the same as in Example 1.

[0088] Results: The hydrogel coating prepared in this comparative example is as follows. Figure 6 As shown in Figure A, the results of CFU coating are as follows: Figure 6 As shown in B.

[0089] Comparative Example 9:

[0090] The difference between this comparative example and Example 1 is that in step (3), the turmeric carbon nanodot solution and the zein-glycerol mixed solution are mixed at a mass ratio of 1:50, and the rest is the same as in Example 1.

[0091] Results: The product obtained at this ratio had excellent bactericidal effect, but its flexibility and moisture retention were insufficient in the storage experiment. In practical applications, it did not perform well in terms of barrier function, which affected the final use effect.

[0092] Comparative Example 10:

[0093] The difference between this comparative example and Example 1 is that the amount of citric acid solution added in step (3) is 1% of the amount of corn alcohol-soluble protein, and the rest is the same as in Example 1.

[0094] Results: The product obtained at this ratio has large particles, increased porosity, and a loose "cauliflower"-like structure on the surface. It has poor corrosion resistance and insufficient adhesion to fruits and vegetables in practical applications, making it easy to fall off.

[0095] Comparative Example 11:

[0096] The difference between this comparative example and Example 1 is that the amount of citric acid solution added in step (3) is 30% of the amount of corn alcohol-soluble protein, and the rest is the same as in Example 1.

[0097] Results: At this ratio, the product has a slow deposition rate, cannot form a gel for a long time, prolongs the production cycle, increases the brittleness of the coating, and is prone to citric acid residue during subsequent water washing, increasing the difficulty of post-processing and wastewater treatment costs.

[0098] Research Results

[0099] This study selected *C. gloeosporioides*, the pathogen most susceptible to anthracnose after fruit and vegetable harvesting, as the treatment target and evaluated the antibacterial efficiency of different concentrations of turmeric carbon dots-corn protein-based hydrogel coatings against *C. gloeosporioides*.

[0100] First, an antibacterial rate experiment was conducted by culturing C. gloeosporioides on PDA plates and applying different concentrations of turmeric carbon dots-corn protein-based hydrogel coatings. The antibacterial efficiency of the turmeric carbon dots-corn protein-based hydrogel coatings against C. gloeosporioides was evaluated by CFU coating, spore germination number, germ tube elongation, and colony diameter.

[0101] Secondly, by inoculating fruits and vegetables, samples were taken every 5 days during the 30-day storage period to test the disease incidence and sensory quality (firmness, weight loss, and decay rate).

[0102] In addition, hydrogen peroxide (H2O2) was used as a positive sterilization control in the coating preparation process to evaluate the gelation and sterilization of the coating under different coating ratio systems, and the optimal coating system ratio parameters were obtained in this study.

[0103] like Figure 1As shown in Figure A, the CFU coating results indicate that, within a certain concentration range, increasing the concentration of turmeric carbon dots leads to a continuous decrease in the logarithmic value of spore numbers. The 0.2 mg / mL turmeric carbon dot-corn protein-based hydrogel coating reduced spore numbers by 3 log values ​​compared to the control group (0 mg / mL turmeric carbon dot concentration), indicating that the 0.2 mg / mL turmeric carbon dot-corn protein-based hydrogel coating can inhibit the germination of over 99.9% of fungal spores. Similarly, the turmeric carbon dot-corn protein-based hydrogel coating also inhibited spore germination and germ tube elongation of *C. gloeosporioides*.

[0104] like Figure 1 As shown in Figures BC, spore germination and germ tube elongation were monitored 4 hours after treatment. The results indicated that the turmeric carbon dot-corn protein-based hydrogel coating effectively inhibited the development of *C. gloeosporioides* spores, with the inhibitory effect positively correlated with the concentration of turmeric carbon dots. Furthermore, there were significant differences in germination rate and germ tube length between the treated and control groups. These results demonstrate that the turmeric carbon dot-corn protein-based hydrogel coating possesses antifungal properties and can effectively inhibit spore germination and mycelial growth of *C. gloeosporioides*, highlighting its potential as a fruit and vegetable preservation technology.

[0105] To further evaluate the effects of different concentrations of turmeric carbon dots-corn protein-based hydrogel coatings on the spore growth of *C. gloeosporioides*, the CM plate method was used to determine the effects of different concentrations of turmeric carbon dots-corn protein-based hydrogel coatings on the mycelial growth of *C. gloeosporioides*. Figure 2 As shown in Figures A and B, the fungal colonies on the CM plates clearly demonstrate the inhibitory effect of the hydrogel coating on mycelial growth. Mycelial growth was gradually inhibited with increasing turmeric carbon dot concentration, reaching complete inhibition at a maximum concentration of 0.2 mg / mL. The inhibition rates of mycelial growth by different concentrations of the turmeric carbon dot-corn protein-based hydrogel coating were 9.8%, 36.4%, 57.8%, and 94.9%, respectively, with significant differences among the different treatment groups.

[0106] To further scientifically evaluate the efficacy of turmeric carbon dot-corn protein-based hydrogel coating treatment (soaking and then drying or spraying onto the surface of fruits and vegetables) in controlling postharvest anthracnose in fruits and vegetables, such as... Figure 3 As shown, experiments with inoculated fruits and vegetables (peaches, tomatoes, green peppers, and bananas) also confirmed that the turmeric carbon dot-corn protein-based hydrogel coating has a significant preservation effect on fruits and vegetables artificially inoculated with C. gloeosporioides. Figure 3 The study demonstrated the disease incidence and sensory characteristics of peaches stored under low temperature and high humidity conditions for 30 days.

[0107] The results showed that peaches without hydrogel coating were more susceptible to pathogen infection and prone to mold and rot during storage. In contrast, hydrogel coating treatment effectively reduced the incidence of disease and improved the preservation quality of peaches. Figure 4 A. Results on peach firmness changes over storage time showed that firmness gradually decreased during storage. After 10 days, significant differences were observed between treatment groups, with high-concentration turmeric carbon dot-corn protein-based hydrogel coatings improving fruit firmness. By day 30, the firmness of peaches in each treatment group increased by 43%, 61%, 73%, and 82%, respectively. The 0.1 and 0.2 mg / mL hydrogel coating treatments were particularly effective in maintaining firmness, possibly due to reduced microbial contamination.

[0108] Weight loss is an important indicator of peach storage quality. After harvesting, peaches continue to metabolize, leading to water evaporation and nutrient consumption, resulting in weight loss. This loss not only affects appearance but also accelerates wilting, spoilage, and rot. Figure 4 As shown in Figure B, under optimal storage conditions, the weight loss of peaches remained below 15%, while the weight loss of peaches treated with hydrogel coating was less than 10%. After 10 days, untreated peaches showed greater weight loss compared to treated peaches. After 30 days of treatment with 0.1 and 0.2 mg / mL hydrogel coatings, the weight loss of peaches was significantly reduced, indicating that hydrogel coating treatment effectively reduced spoilage and maintained the freshness and quality of the fruit.

[0109] During the sensory evaluation, the severity of rot was classified into five levels based on the infected area: Level 0: No rot; Level 1: Rotten area less than 10%; Level 2: Rotten area 10-30%; Level 3: Rotten area 30-50%; Level 4: Rotten area greater than 50%. Weight loss was calculated using the formula: Weight Loss (%) = (M0 - MI) / M0 × 100%. Fruit firmness was measured using a GY-4 fruit firmness tester (manufactured by Zhejiang Aidebao Instrument Co., Ltd.).

[0110] like Figure 4 As shown in Figure C, significant differences existed between the control and treatment groups starting from day 10. On day 30, the decay rate in the control group reached 28.67%, significantly higher than that in all treatment groups. Notably, the 0.2 mg / mL treatment group had the lowest decay rate (4%), with almost no noticeable decay. These results indicate that under specific treatment conditions, turmeric carbon dot-corn protein-based hydrogel coating can significantly reduce decay, improve fruit disease resistance, lower decay rate, maintain fruit quality, and extend shelf life.

[0111] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a corn protein-based turmeric carbon nanoparticle hydrogel coating with both preservation and antibacterial functions, characterized in that, Includes the following steps: (1) Dissolve the dried turmeric carbon nanodots in anhydrous ethanol aqueous solution to obtain a turmeric carbon nanodot solution. The final concentration of the turmeric carbon nanodot solution is 0.05–5 mg / mL; (2) Dissolve zein in anhydrous ethanol aqueous solution to obtain zein solution, add glycerol and mix thoroughly to obtain zein-glycerol mixed solution; the final concentration of zein solution is 4-8 mg / mL; the amount of glycerol added is 10-30% of the zein mass; (3) Mix the turmeric carbon nanodot solution obtained in step (1) and the zein-glycerol mixed solution obtained in step (2), add citric acid solution, stir thoroughly, pour into a mold, and let stand to obtain the product; The mass ratio of turmeric carbon nanodot solution to zein-glycerol mixed solution is (0.8-1.5):(20-25); the amount of citric acid solution added is 5-15% of the mass of zein.

2. The preparation method according to claim 1, characterized in that, In (1), the final concentration of the turmeric carbon nanodot solution is 0.2 mg / mL.

3. The preparation method according to claim 1, characterized in that, (2) The final concentration of the zein solution is 6 mg / mL.

4. The preparation method according to claim 1, characterized in that, In (2), the amount of glycerol added is 20% of the amount of corn alcohol-soluble protein.

5. The preparation method according to claim 1, characterized in that, In (3), the mass ratio of turmeric carbon nanodot solution and zein-glycerol mixed solution is 1:

20.

6. The preparation method according to claim 1, characterized in that, In (3), the amount of citric acid solution added is 10% of the amount of corn alcohol-soluble protein.

7. The preparation method according to claim 1, characterized in that, (3) During the addition of citric acid solution, the mixture is continuously stirred at a speed of 200-300 rpm. After the addition is completed, the mixture is stirred for 1-2 hours.

8. The preparation method according to claim 1, characterized in that, (3) In this process, the mold is placed in a constant temperature environment of 30-50℃ and left to stand for 12-24 hours to allow the hydrogel to fully cross-link and form.

9. The hydrogel coating prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the hydrogel coating according to claim 9 in the field of fruit and vegetable preservation.

Images