A preservative film liquid, a preservative film and a preparation method and application thereof in berry preservation

Abstract

The application discloses a preservative film liquid, a preservative film and a preparation method and application thereof in berry preservation, and relates to the technical field of food preservation. The preservative film liquid comprises a self-assembled nanoparticle with a melatonin core and a PEG-40 hydrogenated castor oil shell and a chitosan dispersion liquid, wherein the mass ratio of the PEG-40 hydrogenated castor oil to the melatonin is 0.25:1.2-1.6. The application also provides a preparation method of the preservative film liquid, a preservative film prepared by the preservative film liquid and application thereof in berry preservation. The application loads the melatonin in the chitosan film and overcomes the negative influence of the melatonin on the performance of the chitosan film material, so that the preservative film has good mechanical performance, barrier performance and continuous preservation function, and has important significance for the preservation of perishable foods such as berries.

Description

Technical Field

[0001] This invention relates to a preservation technology, specifically to a preservation film liquid, a preservation film, a method for preparing the same, and its application in berry preservation. Background Technology

[0002] Berries such as blueberries, strawberries, raspberries, and blackberries are rich in anthocyanins, vitamins, and polyphenols, making them highly nutritious. However, their high post-harvest respiration and metabolism, coupled with their fragile protective skin, make them extremely susceptible to dehydration, shrinkage, softening, microbial contamination, and deterioration in nutritional quality. This results in short shelf life and significant post-harvest losses. While traditional methods such as low-temperature storage and modified atmosphere packaging offer some benefits, they suffer from high energy consumption, high costs, and complex operations.

[0003] Nanofilm technology has attracted widespread attention due to its high efficiency, stability, ease of operation, safety, and environmental friendliness. Chitosan (CH) is a natural cationic polysaccharide with good film-forming properties, biocompatibility, and broad-spectrum antibacterial activity, making it a commonly used coating matrix material. However, single-component chitosan films suffer from drawbacks such as insufficient mechanical strength, limited barrier properties, and limited functionality. Melatonin (MT) is an indoleamine widely found in organisms and has been shown to possess excellent antioxidant activity in plants, capable of scavenging reactive oxygen species (ROS), delaying fruit senescence, and inducing systemic resistance. However, melatonin has poor water solubility, is unstable under light and high temperatures, has low bioavailability when applied directly, and high-concentration additions may damage the structure of the film-forming matrix (such as hydrogen bond networks), leading to a decline in the performance of the preservative film.

[0004] CN120381052A discloses a method for extending the shelf life of garlic, using melatonin and glycine betaine as the inner film liquid and chitosan and sodium alginate as the outer film liquid. Currently, there are no reports of using the same preservative film liquid prepared from melatonin and chitosan for berry preservation.

[0005] Therefore, how to stably and efficiently load melatonin, a highly effective bioactive substance, into chitosan membranes, and overcome its negative impact on membrane performance, and develop a novel composite membrane with good mechanical properties, barrier properties, and continuous preservation function, is of great significance for the preservation of perishable foods such as berries. Summary of the Invention

[0006] The first technical problem to be solved by the present invention is to provide a plastic wrap liquid.

[0007] The second technical problem to be solved by the present invention is to provide a method for preparing the aforementioned plastic wrap liquid.

[0008] The third technical problem to be solved by the present invention is to provide a cling film prepared from the aforementioned cling film liquid.

[0009] The fourth technical problem to be solved by the present invention is to provide an application of the aforementioned preservative film liquid in berry preservation.

[0010] The fifth technical problem to be solved by the present invention is to provide a method for preserving berries.

[0011] The technical solution adopted by the present invention to solve its first technical problem is a plastic wrap liquid, which includes: self-assembled nanoparticles having a melatonin core and a PEG-40 hydrogenated castor oil (PHCO) shell, and a chitosan dispersion, wherein the mass ratio of the PEG-40 hydrogenated castor oil to the melatonin is 0.25:1.2-1.6.

[0012] Furthermore, the final concentration of melatonin in the dispersion is 25-100 μg / mL, and the final concentration of chitosan is 2.0wt%-2.5wt%.

[0013] The technical solution adopted by this invention to solve its second technical problem is a method for preparing a plastic wrap liquid, characterized by comprising the following steps: Melatonin was dissolved in ethyl acetate and then mixed with PEG-40 hydrogenated castor oil. The mixture was heated and stirred to form an oil phase. Chitosan was dissolved in an aqueous acetic acid solution to form an aqueous phase. The oil phase was rapidly added to the aqueous phase under continuous stirring. After cooling, the mixture self-assembled to form a dispersion of nanoparticles with a melatonin core and a PEG-40 hydrogenated castor oil shell.

[0014] Furthermore, the mass fraction of acetic acid in the aqueous acetic acid solution is 0.5-2%.

[0015] Furthermore, the heating temperature is 60-80℃.

[0016] The technical solution adopted by the present invention to solve its third technical problem is a plastic wrap, which is obtained by drying the plastic wrap liquid.

[0017] The technical solution adopted by the present invention to solve its fourth technical problem is the application of the aforementioned preservation film liquid in berry preservation.

[0018] Furthermore, the berries are blueberries, strawberries, raspberries, or blackberries.

[0019] The technical solution adopted by the present invention to solve its fifth technical problem is a method for preserving berries, which includes the following steps: soaking the berries in the preservative film liquid, taking them out and drying them, and then refrigerating them.

[0020] Furthermore, the soaking time is 20-60 seconds.

[0021] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention utilizes PHCO to efficiently encapsulate hydrophobic melatonin, forming stable nanoparticles (PHCO-MTNPs), which solves the problems of poor water dispersibility and instability when melatonin is applied directly, and improves its bioavailability in composite systems.

[0022] 2. This invention introduces PHCO-MT NPs into a chitosan matrix to prepare PMC nanofilms. PHCO-MT NPs play a dual role in the film as both a "plasticizer-like agent" and a "nanofiller." On the one hand, it moderately reduces the tensile strength of the film but significantly increases the elongation at break, enhancing the flexibility of the food preservation film. On the other hand, the nanoparticles fill the gaps between the chitosan molecular chains and interact with chitosan through hydrogen bonds and other mechanisms to form a denser structure, significantly reducing the water vapor permeability of the food preservation film and improving its moisture-blocking performance.

[0023] 3. The preservative film liquid prepared in this invention, when applied to blueberry preservation, forms a protective film with a microporous structure on the fruit surface. This film effectively reduces water evaporation, inhibits respiration, and hinders pathogen infection. Simultaneously, the melatonin loaded in the film is slowly released, continuously scavenging reactive oxygen species within the fruit and inhibiting membrane lipid peroxidation and cell wall degrading enzyme activity. Thus, it delays fruit senescence and quality deterioration through both physical barriers and physiological regulation.

[0024] 4. Blueberries treated with the preservation film liquid prepared in this invention, after being stored at 4°C for 14 days, showed a weight loss rate of about 26% and a rot rate of about 58% compared with the control group. The retention rates of nutrients and functional components such as firmness, vitamin C, total phenols, and anthocyanins were significantly higher, and the preservation effect was better than that of single chitosan film or single melatonin treatment.

[0025] 5. All raw materials used in this invention (chitosan, melatonin, and PEG-40 hydrogenated castor oil) are safe, biodegradable, or derived from nature. The preparation process is simple and suitable for industrial production, and it has broad application prospects in the field of green preservation of berries and other high-value fruits and vegetables. Attached Figure Description

[0026] Figure 1 Photographs of the various groups of nano-dispersions prepared in Example 1.

[0027] Figure 2 The particle size and PDI index of each group of nano-dispersions prepared in Example 1 are shown.

[0028] Figure 3 The zeta potential of nano-dispersions with different PHCO addition amounts prepared in Example 1.

[0029] Figure 4 The image shows the FIIR spectrum of the nanofilm prepared in Example 2.

[0030] Figure 5 The images show the SEM spectra of the CH (A), MC-50 (B), PMC-0 (C), and PMC-50 (D) nanofilms prepared in Example 2. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to the embodiments.

[0032] Example 1: Preparation and characterization of PHCO-MT NPs 250 mg of melatonin (MT) was dissolved in 3 mL of ethyl acetate. This solution was then added to Erlenmeyer flasks containing 0 g (CK), 1.0 g, 1.1 g, 1.2 g, 1.3 g, 1.4 g, 1.5 g, 1.6 g, 1.7 g, and 1.8 g of PEG-40 hydrogenated castor oil (PHCO), respectively. The mixture was placed on a magnetic stirrer at 70 °C and stirred at 600 rpm / min for 2 minutes until homogeneous. Subsequently, while continuing high-speed stirring, 20 mL of ultrapure water was rapidly injected into the oil phase mixture, and stirring was continued for 1 minute. The Erlenmeyer flasks were then quickly transferred to an ice-water bath to cool to room temperature, yielding a PEG-40 hydrogenated castor oil-melatonin nanoparticle (PHCO-MT NPs) dispersion.

[0033] Measured by a Malvern laser particle size analyzer, such as Figure 1 As shown, the average particle size of the nanoparticles is 20.63 nm, and the polydispersity index (PDI) is 0.23; Figure 2 As shown, when the amount of PHCO is 1.4 g, the Zeta potential is -18.29 ± 0.42 mV, indicating that the system is stable and the particle size distribution is uniform. Figure 3 As shown, when the amount of PHCO added is less than 1.2 g, the prepared nanoemulsion is milky white, with large and unevenly distributed particles (PDI>0.3), poor stability, and prone to precipitation or stratification after standing. When the amount of PHCO added exceeds 1.6 g, the initial emulsion is clear, but the absolute value of the Zeta potential decreases, and the long-term stability of the system deteriorates, possibly due to flocculation caused by excessive surfactant. Therefore, subsequent examples use a PHCO-MT NPs dispersion prepared with 1.4 g of PHCO for further analysis.

[0034] Example 2: Preparation of PMC nanofilms (1) Prepare a 2.5% (w / v) chitosan solution: Weigh 2.5 g of chitosan (degree of deacetylation ≥ 95%) and slowly add it to 97.5 mL of 1% (v / v) acetic acid aqueous solution. Stir magnetically at room temperature for 3 hours until completely dissolved to obtain a uniform and transparent chitosan solution.

[0035] (2) Preparation of composite membrane solution: Take a certain volume of the PHCO-MT NPs dispersion prepared in Example 1 (where the MT concentration is 0.5 mg / mL), add it to the above chitosan solution, and stir magnetically for 20 minutes to mix it evenly. By adjusting the amount of PHCO-MT NPs dispersion added, composite membrane solutions with final melatonin concentrations of 25, 50, 75, and 100 μg / mL were prepared, and the corresponding groups were named PMC-25, PMC-50, PMC-75, and PMC-100. A pure chitosan membrane without any added active ingredients (CH group) and a chitosan membrane with melatonin directly added to 50 μg / mL (MC-50 group) were set as controls.

[0036] (3) Film formation: Each composite membrane solution was ultrasonically degassed for 30 minutes to remove air bubbles. 10 mL of membrane solution was measured and poured into a 90 mm × 90 mm disposable plastic petri dish, and gently shaken to level it. After initial solidification at room temperature for 15 minutes, it was transferred to a 50°C oven to dry for 12 hours. After removal, it was equilibrated at 25°C and 50% relative humidity for 24 hours, and then carefully peeled off from the petri dish to obtain a transparent PMC nano-preservative film, which was then sealed for later use.

[0037] The performance of each group of plastic wraps prepared in Example 2 was tested: (1) Mechanical properties: Tensile strength (TS, unit MPa) and elongation at break (EAB, %) were determined using an XLW (M) automatic tensile testing machine (PARAM, China). The assembled samples were cut into rectangular blocks (1 cm × 5 cm), mounted on the extension fixture of the testing machine, and tested at 50 mm / min. -1 The rate of axial stretching was measured. The tensile strength of the PMC-50 group decreased by about 26% compared with the pure chitosan film (CH group), but the elongation at break increased by about 38%, indicating that the flexibility of the plastic wrap was significantly enhanced.

[0038] (2) Barrier performance: Weigh 3 g ± 0.1 g CaCl2 and place it in a weighing bottle. Cover the weighing bottle with the film sample and secure it with an elastic band. Place the bottle in a desiccator at 25℃ and 50% relative humidity, and measure the mass of the bottle at 24-hour intervals. The water vapor transmission rate of the PMC-50 group was significantly lower than that of the MC-50 group with directly added melatonin, proving that the PHCO-coated nanoparticles effectively improved the moisture barrier properties of the plastic wrap.

[0039] The mechanical and barrier properties of the films in different groups are shown in Table 1.

[0040] Table 1 Mechanical and barrier properties of films in different groups

[0041] (3) Structural characterization: such as Figure 4 As shown, Fourier transform infrared spectroscopy (FTIR) revealed new characteristic absorption peaks in the PMC film, indicating that PHCO-MT NPs were successfully introduced and interacted with chitosan. Figure 5 As shown, scanning electron microscopy (SEM) reveals that the PMC-50 membrane has the smoothest and flattest cross-section, indicating good compatibility.

[0042] Example 3: Application of plastic wrap in preserving blueberries Material preparation: Select uniformly sized "Brilliant" rabbiteye blueberries free from pests, diseases, and mechanical damage. The blueberries were randomly divided into 7 groups: blank control group (CK, soaked in deionized water), MT-25 group (soaked in 25 μg / mL melatonin aqueous solution), CH group (soaked in 2.5% chitosan solution), and PMC-25, PMC-50, PMC-75, and PMC-100 groups (soaked in the corresponding concentration of composite membrane solution, i.e., the membrane solution from Example 2 used directly as the coating agent). Each group had 3 replicates, with approximately 1 kg per replicate. The soaking time was 30 seconds for all groups, and the blueberries were then air-dried in a clean, well-ventilated area.

[0043] Storage and testing: The treated blueberries were packaged into perforated plastic bags and stored in a cold storage at (4±0.5)℃. Samples were taken every 2 days to measure relevant indicators.

[0044] The results are shown in Table 2. After 14 days of storage, the blueberries in the CK group showed a weight loss rate of 18.9%, a rot rate of 52.8%, a significant decrease in firmness, and a substantial reduction in the content of vitamin C and total phenols. The PMC treatment group showed significantly better results than the CK group in all indicators. Among them, the PMC-50 group showed the most balanced and outstanding results: a weight loss rate of only 14.0%, a rot rate of 22.3%, and the best firmness retention; the vitamin C content was 21.3 mg / 100g, far higher than the CK group's 1.58 mg / 100g; and the retention rates of total phenols and anthocyanins were also the highest. The preservation effect of the PMC-50 group was also better than that of the single chitosan membrane treatment (CH group) and the single low-concentration melatonin treatment group (MT-25 group).

[0045] Table 2. Effects of different treatments on the nutritional composition and quality of blueberries

[0046] The above results demonstrate that this invention successfully developed a high-performance active preservation nanofilm through a specific PHCO-MT NPs preparation process and a composite technology with chitosan. This film effectively solves the application challenges of melatonin and, through the nanocomposite effect, synergistically enhances the mechanical, barrier, and preservation functions of the preservation film, exhibiting excellent preservation effects on berries such as blueberries.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A plastic wrap liquid, characterized in that, It includes: The nanoparticles formed by self-assembly have a melatonin core and a PEG-40 hydrogenated castor oil shell, and a dispersion of chitosan, wherein the mass ratio of the PEG-40 hydrogenated castor oil to the melatonin is 0.25:1.2-1.

6.

2. The preservative film liquid according to claim 1, characterized in that, The final concentration of melatonin in the dispersion is 25-100 μg / mL, and the final concentration of chitosan is 2.0wt%-2.5wt%.

3. A method for preparing a plastic wrap liquid according to claim 1 or 2, characterized in that, Includes the following steps: Melatonin was dissolved in ethyl acetate and then mixed with PEG-40 hydrogenated castor oil. The mixture was heated and stirred to form an oil phase. Chitosan was dissolved in an aqueous acetic acid solution to form an aqueous phase. The oil phase was rapidly added to the aqueous phase under continuous stirring. After cooling, the mixture self-assembled to form a dispersion of nanoparticles with a melatonin core and a PEG-40 hydrogenated castor oil shell.

4. The preparation method according to claim 3, characterized in that, The mass fraction of acetic acid in the acetic acid aqueous solution is 0.5-2%.

5. The preparation method according to claim 3, characterized in that, The heating temperature is 60-80℃.

6. A plastic wrap, which is obtained by drying the plastic wrap liquid according to claim 1 or 2.

7. The application of the preservative film liquid according to claim 1 or 2 in berry preservation.

8. The application according to claim 7, characterized in that, The berries are blueberries, strawberries, raspberries, or blackberries.

9. A method for preserving berries, characterized in that, Includes the following steps: Soak the berries in the plastic wrap solution as described in claim 1 or 2, remove them, air dry, and refrigerate.

10. The method for preserving berries according to claim 9, characterized in that, The soaking time is 20-60 seconds.

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