A method, apparatus and package for blow moulding in situ fruit and vegetable spun packs

Abstract

This invention relates to a method, apparatus, and packaging structure for in-situ packaging of fruits and vegetables using blown fiber spinning, addressing the current issues of efficiency and effectiveness in the use of nanofibers in fruit and vegetable packaging. This method selects carboxymethyl chitosan (CMCH) and polycaprolactone (PCL) as base materials, and uses SBS technology to directly deposit CMCH / PCL nanofibers layer by layer onto the surface of fruits and vegetables, forming a tightly adhered and stable fiber coating. The apparatus in this invention uses spiral-patterned conveyor rollers to simultaneously transport fruits and vegetables while performing blown spinning, achieving rapid and continuous in-situ packaging of fruits and vegetables. The in-situ packaging of this invention can be easily peeled off by hand, and it also serves as an excellent carrier for active substances, effectively inhibiting gray mold in fruits and vegetables. The in-situ packaging film forms a barrier on the surface of fruits and vegetables, reducing weight and hardness loss and delaying the ripening period after harvest.

Description

Technical Field

[0001] This invention belongs to the field of fruit and vegetable packaging, and relates to a method, apparatus and packaging structure for in-situ packaging of fruits and vegetables by blow molding and spinning. Background Technology

[0002] Fresh agricultural products such as fruits and vegetables face the challenge of quality degradation after harvest, resulting in a 20-30% loss in the post-harvest stage. Oxidation, metabolism, and microbial contamination are the causes of this post-harvest quality decline. Among these, microbial contamination, especially fruit diseases caused by fungal contamination, is the most significant cause of post-harvest fruit loss. Although synthetic fungicides have been used to control fungal growth during the storage and logistics of harvested fruits and vegetables, overuse not only leads to fungal pathogens developing resistance to synthetic fungicides but also poses threats to the environment and human health. As an alternative to reducing fungal contamination of fruits and vegetables, active food packaging films have received widespread attention in recent years.

[0003] Nanofibers, with their high porosity and specific surface area, are playing an increasingly important role in active packaging. This means that nanofiber materials can more effectively load and release active substances, potentially reducing the amount of active substances needed to maintain the quality of fruits and vegetables while minimizing their impact on sensory properties. On the other hand, the overuse of non-biodegradable petroleum-based plastic packaging materials has caused serious global ecological problems. In contrast, nanofiber matrix materials can be selected from a variety of biodegradable materials, including natural and synthetic polymers. For example, carboxymethyl chitosan (CMCH) is a biodegradable polymer obtained by introducing carboxymethyl groups into chitosan. CMCH exhibits good antibacterial, antioxidant, and biocompatibility, but its spinnability is poor due to chain rigidity and the repulsive forces between ionic groups. A common approach to address this issue is to add synthetic polymers as spinning aids, such as biodegradable and biocompatible polycaprolactone (PCL), which is often used to improve the spinnability of chitosan.

[0004] To date, nanofibers have not been practically applied in food packaging due to several challenges. The biggest challenge is that current nanofiber production primarily relies on electrospinning, which has low efficiency and limits large-scale application. Secondly, the storage conditions for fruits and vegetables are typically high-humidity environments, causing the structure of hydrophilic nanofiber membranes to be damaged during storage; while hydrophobic nanofiber membranes may not adhere tightly to fruits and vegetables, leading to detachment and poor preservation. Furthermore, nanofiber membranes used for fruit and vegetable preservation are usually placed under or under the fruits and vegetables, leaving gaps between them, making it difficult for nanofibers to function effectively in these areas, especially when the loaded active substances are non-volatile. This reduces the utilization efficiency of nanofiber films, increases manufacturing costs, and hinders the practical application of nanofibers in food packaging. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of efficiency and effectiveness of current nanofibers in fruit and vegetable preservation packaging, which hinder the practical application of nanofibers in food packaging. This invention provides a method, device, and packaging structure for in-situ blown spinning packaging of fruits and vegetables. It utilizes blown spinning to perform all-round closed in-situ blown spinning packaging around fruits and vegetables, solving the problem of easy detachment of nanofiber films. At the same time, by using a continuous rolling conveyor combined with blown spinning nozzles, fruits and vegetables can be continuously and rapidly blown spun packaging.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for in-situ packaging of fruits and vegetables by blow molding and spinning, comprising the following steps:

[0007] S1: Preparation of basic spinning solution: Dissolve 0.8 g of PCL and 0.2 g of CMCH in 10 mL of TFEA to prepare a basic spinning solution containing PCL and CMCH;

[0008] S2: Preparation of preservative spinning solution: Add preservative to the basic spinning solution and stir continuously for 6-8 hours to obtain the preservative spinning solution;

[0009] S3: Blow spinning packaging: The preservative spinning solution is fed into the blow spinning equipment, and the spinning nozzle of the equipment is used to directly spin the fruit and vegetable surface. The blowing rate of the preservative spinning solution is 4 mL / h, the blowing pressure is 0.12 MPa, the fruit and vegetables are placed 20-30 cm away from the spinning nozzle, and the fruit and vegetables are kept in a rotating or rolling state. The spinning packaging time for a single fruit and vegetable is 0.5-8 min.

[0010] PCL stands for polycaprolactone, a biodegradable synthetic polymer; CMCH stands for carboxymethyl chitosan, a natural polymer; and TFEA stands for 2,2,2-trifluoroethanol.

[0011] Preferably, the preservative mentioned in S2 is one or more of CUR, NAT, NIS, and THY. CUR is curcumin, NAT is natamycin, NIS is nisin, and THY is thymol. The preservative can also be replaced by an indicator to indicate whether the fruits and vegetables have spoiled.

[0012] Preferably, the amount of preservative added per 10 ml of TFEA is 0.01-0.04 g.

[0013] This method selects the natural polymer CMCH and the biodegradable synthetic polymer PCL as the matrix materials for blown spinning. TFEA is selected as the solvent for the above matrix materials, which completely evaporates during the blown spinning fiber formation process. In-situ packaging refers to directly blow-spinning the packaging film on the surface of fruits and vegetables, forming a hydrophobic packaging film on the outside of the fruits and vegetables that continuously releases preservative components. This in-situ packaging film does not adhere to the fruits and vegetables and can be easily peeled off when consuming. In-situ packaging is an excellent carrier of active substances and can effectively inhibit gray mold in fruits and vegetables. The in-situ packaging film forms a barrier on the surface of fruits and vegetables, restricting the penetration of water and gas, thereby reducing fruit respiration and reducing weight and firmness loss. In addition, metabolomics and color analysis show that in-situ packaging can delay the post-harvest ripening period of fruits and vegetables. The in-situ packaging method provides a new solution for post-harvest preservation of fruits and vegetables.

[0014] A fruit and vegetable blow molding and spinning in-situ packaging device can realize the above-mentioned packaging method. It includes several conveying rollers arranged in parallel, with the axis of the conveying rollers arranged in the front-to-back direction. The conveying rollers convey fruits and vegetables from front to back. Each conveying roller has a spiral pattern with the same direction and structure on its surface. The conveying rollers rotate synchronously, and there is a gap between adjacent conveying rollers. The gap between adjacent conveying rollers carries and conveys fruits and vegetables along the axis of the conveying rollers. Several spinning nozzles are arranged at equal intervals above the gap between adjacent conveying rollers. A cleaning nozzle is arranged directly above each conveying roller, and a drying nozzle is also arranged in the gap between the cleaning nozzle and the spinning nozzle.

[0015] The laboratory-scale in-situ packaging method involves clamping fruits and vegetables from both top and bottom, rotating them, and then spinning at the side of the fruit and vegetables using a spinning nozzle. The clamps and spinning nozzle move relative to each other to achieve blow molding and film formation. This method is inefficient and costly, and cannot achieve continuous packaging, making it unsuitable for industrial application. This device can implement the aforementioned in-situ blow molding and spinning method for fruits and vegetables, enabling continuous conveying and packaging. In this device, fruits and vegetables are fed in from the front end of the conveyor rollers and positioned in the gap between adjacent rollers. As the conveyor rollers rotate, the spiral pattern on their surface propels the fruits and vegetables forward along the roller's axial direction. During this process, the fruits and vegetables are rolled forward by the spiral pattern. The spinning nozzle detects the presence of fruits and vegetables below and initiates blow molding. As the fruits and vegetables rotate, the spinning nozzle gradually forms a film on their surface. Multiple spinning nozzles can be installed along the conveying direction of fruits and vegetables. When fruits and vegetables leave the front spinning nozzle and enter the range of the rear spinning nozzle, the rear spinning nozzle can take over the spinning and film formation. By adjusting the rotation speed of the conveyor roller, the conveying time of a single fruit or vegetable on the conveyor roller is controlled to be 0.5-8 minutes to complete the packaging. After a batch of fruits and vegetables is continuously packaged, all fruits and vegetables on the conveyor roller are packaged and emptied. Then, the cleaning nozzle sprays the solvent corresponding to the packaging matrix onto the roller surface. At this time, the conveyor roller continues to rotate, and the spinning residue adhering to the conveyor roller is dissolved and cleaned by the solvent. Then, the air-drying nozzle dries the conveyor roller, preparing it for the packaging of the next batch of fruits and vegetables. This device realizes continuous conveying and continuous in-situ packaging of fruits and vegetables, enabling the industrial application of in-situ packaging of fruits and vegetables.

[0016] Preferably, a feeding conveyor belt is provided above the front end of the conveying roller, and a discharging conveyor belt is provided below the rear end of the conveying roller. The conveying speed of the conveyor belt is greater than that of the conveying roller. After the fruits and vegetables on the conveyor belt fall into the conveying roller, they can automatically and tightly arrange themselves in the gap between the conveying roller, keeping the fruits and vegetables tightly arranged, reducing the dwell time of the spinning nozzle, and improving packaging efficiency.

[0017] Preferably, a waste recycling trough is provided below the conveyor roller. Spinning residue adhering to the conveyor roller can fall into the waste recycling trough through the gaps in the conveyor roller during the packaging and cleaning processes.

[0018] Preferably, each spinning nozzle is equipped with a fruit sensor on its front or circumferential side. The fruit sensor can be a visual sensor or an infrared sensor. The fruit sensor can detect whether the fruit or vegetable has reached the corresponding spinning nozzle position, thus avoiding waste.

[0019] Preferably, the cleaning solvent sprayed by the cleaning nozzle is TFEA.

[0020] A fruit and vegetable blow-spun in-situ packaging structure is disclosed. Using the aforementioned packaging method and device, fruits and vegetables are arranged in bunches of 2-10, with adjacent fruits and vegetables within the same bunch abutting against each other. The outer layer of each bunch is a continuous blow-spun packaging film. Because the conveyor rollers transport the fruits and vegetables at a relatively low speed, the fed fruits and vegetables can naturally align themselves tightly on the rollers. During the packaging process, the spinning nozzles continuously blow-spun, packaging adjacent fruits and vegetables together. This packaging structure forms fruit bunches, facilitating the transfer and handling of fruits and vegetables. The length of the fruit bunch is related to the fruit shape but should not be too large, otherwise the packaging film may break. Even if it breaks, it can be considered as splitting into two or more fruit bunches, without affecting the packaging's preservation effect.

[0021] Preferably, the fruit or vegetable is cherry tomato, cherry, or date. This packaging structure is suitable for fruits and vegetables with smaller fruit sizes, and can also be applied to fruits and vegetables with larger fruit sizes but higher economic value.

[0022] The packaging method of this invention utilizes blown spinning to directly form a packaging film on the surface of fruits and vegetables. The packaging film can carry preservatives, providing barrier-like preservation of fruits and vegetables, restricting the penetration of moisture and gas, thereby reducing fruit respiration and minimizing weight and firmness loss. It provides in-situ packaging and can be easily peeled off. In addition, the packaging device of this invention uses spiral conveyor rollers to transport fruits and vegetables, realizing the industrial application of continuous in-situ packaging and forming a fruit bunch packaging structure for multiple fruits and vegetables, facilitating handling and placement. Attached Figure Description

[0023] The invention will now be further described with reference to the accompanying drawings.

[0024] Figure 1 These are before-and-after comparison images of the packaging of cherry tomatoes, based on this invention.

[0025] Figure 2 This is the infrared spectrum of the nanofiber thin film of the present invention.

[0026] Figure 3 This is the XRD analysis diagram of the present invention.

[0027] Figure 4 This is the cytotoxicity result of the nanofiber film of the present invention.

[0028] Figure 5 This is a comparison diagram of the preservation effect of the in-situ packaging of the present invention on cherry tomatoes.

[0029] Figure 6 This is a comparison chart showing the changes in cherry tomatoes during 24 days of storage according to the present invention.

[0030] Figure 7 This is a metabolomics analysis diagram of the in-situ packaged cherry tomatoes of the present invention.

[0031] Figure 8 This is a chromatogram of metabolites from the in-situ packaged cherry tomatoes of the present invention.

[0032] Figure 9 This is a schematic diagram of a packaging device according to the present invention.

[0033] Figure 10 This is a schematic diagram of the conveyor roller arrangement of a packaging device according to the present invention.

[0034] Figure 11 This is a schematic diagram of a fruit and vegetable packaging structure according to the present invention.

[0035] In the picture: 1. Conveyor roller, 2. Spiral pattern, 3. Feed conveyor belt, 4. Fruits and vegetables, 5. Spinning nozzle, 6. Cleaning nozzle, 7. Air drying nozzle, 8. Waste recycling tank, 9. Discharge conveyor belt, 10. Guide plate, 11. Packaging film, 41. Fruit bunch. Detailed Implementation

[0036] The present invention will be further described below with reference to specific embodiments and accompanying drawings.

[0037] Example 1: A method for in-situ packaging of fruits and vegetables using blow molding and spinning, comprising the following steps:

[0038] S1: Preparation of basic spinning solution: Dissolve 0.8 g of PCL and 0.2 g of CMCH in 10 mL of TFEA to prepare a basic spinning solution containing PCL and CMCH;

[0039] S2: Preparation of preservative spinning solution: Add preservative to the basic spinning solution and stir continuously for 6-8 hours to obtain the preservative spinning solution; add 0.04 g of CUR as preservative to every 10 ml of TFEA;

[0040] S3: Blow spinning packaging: The preservative spinning solution is fed into the blow spinning equipment, and the spinning nozzle of the equipment is used to directly spin the fruit and vegetable surface. The blowing rate of the preservative spinning solution is 4 mL / h, the blowing pressure is 0.12 MPa, the fruit and vegetables are placed 20-30 cm away from the spinning nozzle, and the fruit and vegetables are kept rotating or rolling. The spinning packaging time for a single fruit and vegetable is 8 minutes.

[0041] Example 2: A method for in-situ packaging of fruits and vegetables using blow molding and spinning, comprising the following steps:

[0042] S1: Preparation of basic spinning solution: Dissolve 0.8 g of PCL and 0.2 g of CMCH in 10 mL of TFEA to prepare a basic spinning solution containing PCL and CMCH;

[0043] S2: Preparation of preservative spinning solution: Add preservative to the basic spinning solution and stir continuously for 6-8 hours to obtain the preservative spinning solution; add 0.04 g of NAT as preservative to every 10 ml of TFEA;

[0044] S3: Blow spinning packaging: The preservative spinning solution is fed into the blow spinning equipment, and the spinning nozzle of the equipment is used to directly spin the fruit and vegetable surface. The blowing rate of the preservative spinning solution is 4 mL / h, the blowing pressure is 0.12 MPa, the fruit and vegetables are placed 20-30 cm away from the spinning nozzle, and the fruit and vegetables are kept rotating or rolling. The spinning packaging time for a single fruit and vegetable is 8 minutes.

[0045] Example 3: A method for in-situ packaging of fruits and vegetables using blow molding and spinning, comprising the following steps:

[0046] S1: Preparation of basic spinning solution: Dissolve 0.8 g of PCL and 0.2 g of CMCH in 10 mL of TFEA to prepare a basic spinning solution containing PCL and CMCH;

[0047] S2: Preparation of preservative spinning solution: Add preservative to the basic spinning solution and stir continuously for 6-8 hours to obtain the preservative spinning solution; add 0.01 g NIS preservative to every 10 ml TFEA;

[0048] S3: Blow spinning packaging: The preservative spinning solution is fed into the blow spinning equipment, and the spinning nozzle of the equipment is used to directly spin the fruit and vegetable surface. The blowing rate of the preservative spinning solution is 4 mL / h, the blowing pressure is 0.12 MPa, the fruit and vegetables are placed 20-30 cm away from the spinning nozzle, and the fruit and vegetables are kept rotating or rolling. The spinning packaging time for a single fruit and vegetable is 8 minutes.

[0049] Example 4: A method for in-situ packaging of fruits and vegetables using blow molding and spinning, comprising the following steps:

[0050] S1: Preparation of basic spinning solution: Dissolve 0.8 g of PCL and 0.2 g of CMCH in 10 mL of TFEA to prepare a basic spinning solution containing PCL and CMCH;

[0051] S2: Preparation of preservative spinning solution: Add preservative to the basic spinning solution and stir continuously for 6-8 hours to obtain the preservative spinning solution; add 0.04 g THY preservative to every 10 ml TFEA;

[0052] S3: Blow spinning packaging: The preservative spinning solution is fed into the blow spinning equipment, and the spinning nozzle of the equipment is used to directly spin the fruit and vegetable surface. The blowing rate of the preservative spinning solution is 4 mL / h, the blowing pressure is 0.12 MPa, the fruit and vegetables are placed 20-30 cm away from the spinning nozzle, and the fruit and vegetables are kept rotating or rolling. The spinning packaging time for a single fruit and vegetable is 8 minutes.

[0053] Examples 1-4 above all use cherry tomatoes as raw materials. The specific materials and methods are as follows:

[0054] Chemicals: Nisin (NIS, high purity) was purchased from Hefei Bomei Biotechnology Co., Ltd. (Hefei, China). Curcumin (CUR, analytical grade, Mw = 368.38 Da), thymol (THY, biotechnology grade), CMCH (90% deacetylation, Mn = 240 kDa, DS = 90%, approximately 80% O-carboxymethyl chitosan, approximately 20% N-carboxymethyl chitosan as impurities), and 2,2,2-trifluoroethanol (TFEA, analytical grade) were purchased from Maclean's Ltd. (Shanghai, China). PCL (Mn = 80 kDa) and natamycin (NAT, 95% purity) were purchased from Aladdin Ltd. (Shanghai, China). The gray mold strain was obtained from the Institute of Fruit Science, Zhejiang University.

[0055] Spinning solution and in-situ packaging process: SBS was used to achieve rapid in-situ packaging of fruits and vegetables. Natural polymer CMCH and biodegradable synthetic polymer PCL were selected as matrix materials. TFEA was chosen as the solvent, as it completely evaporates during fiber formation. Cherry tomatoes were selected as the demonstration subject in this study. Cherry tomatoes are susceptible to fungal infection after harvest, leading to rot and severe economic losses, making them a suitable subject for testing the effectiveness of this in-situ packaging method.

[0056] Dissolve 0.8 g PCL and 0.2 g CMCH in 10 mL TFEA to prepare basic spinning solutions of PCL (8% w / v) and CMCH (2% w / v). Then, add 0.04 g CUR, 0.04 g NAT, 0.01 g NIS and 0.04 g THY to four of the basic spinning solutions to prepare four different preservative spinning solutions.

[0057] The blow spinning process for in-situ packaging of cherry tomatoes was completed using an SBS device (JNS-SBS-01, Nanjing Zhangzidao New Material Co., Ltd., China). Specifically, during the in-situ packaging process, a mixed solution was pumped into 20 ml syringes at a feed rate of 4 mL / h, with a pressure of 0.12 MPa. The cherry tomatoes were placed 20 cm away from the spinning nozzle to form in-situ packaging. The spinning process for each cherry tomato lasted 8 minutes. After the in-situ packaging process, nanofiber packaging films formed on the surface of the fruits and vegetables. Based on the different active substances they contained, these films were named CUR / PCL / CMCH (curcumin / chitosan / polycaprolactone) film, NAT / PCL / CMCH (natamycin / chitosan / polycaprolactone) film, NIS / PCL / CMCH (nisin / chitosan / polycaprolactone) film, and THY / PCL / CMCH (thymol / chitosan / polycaprolactone) film. The nanofiber films used for characterization were peeled from the cherry tomato surface, placed in sealed bags, and stored in the dark until the characterization time.

[0058] Characterization of in-situ encapsulation: The morphology of the gold sputtered samples was studied using field emission scanning electron microscopy (FE-SEM) images with a GeminiSEM 300 (ZEISS, Germany). Using Nano Measurer software (V1.2), 100 nanofibers were randomly selected from each SEM image to determine the distribution and average diameter of the nanofibers.

[0059] ATR-FTIR spectra in the wavelength range of 4000–400 cm⁻¹ were obtained using a Thermo Scientific Nicolet iS20 instrument (Thermo Nicolet Ltd., USA). The wavelength range of the ATR-FTIR spectral signal of the sample was 4000–400 cm⁻¹, the scanning resolution was 4 cm⁻¹, and a total of 32 scans were performed.

[0060] The XRD patterns of the nanofiber films were recorded using an X'Pert Pro diffractometer (PAAnalytical BV, Netherlands) equipped with a Cu Kα radiation source. The parameters were set as follows: diffraction range 5–90° (2θ), scan rate 2° min⁻¹, voltage 40 kV, and tube current 35 mA.

[0061] Thermal stability was measured using a TG 209 F3 analyzer (Netzsch, Germany) under nitrogen atmosphere, in a temperature range of 50–600 °C. The heating rate was 10 °C / min.

[0062] The mechanical properties of the nanofiber films were tested using a mechanical analyzer (INSTRON 3343, Instron, USA), equipped with a 10 N load cell, a crosshead speed of 10 mm / min, and at room temperature.

[0063] Surface wettability was measured using a contact angle meter (OCA20, Data Physics Instruments GmbH, Germany) via water contact angle analysis. The sample was adhered to a glass slide, and 3.0 μL of deionized water was dropped onto the sample surface using deionized water as the probe solvent. After equilibration for 60 s, the water contact angle (WCA) was measured on both the left and right sides. Each sample was tested three times.

[0064] Cytotoxicity was assessed using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT). Specifically, 10 g of nanofiber membranes were autoclaved under UV irradiation for 2 hours (inverted after one hour) on a sterile bench, then added to 10 mL of minimum essential culture medium and incubated at 37°C for 24 hours. The supernatant was filtered through a 0.22 μm filter to obtain the extract. Human foreskin fibroblasts (L929) in logarithmic growth phase were numbered and cultured in 96-well plates at approximately 6 × 10³ cells per well, and cultured at 37°C with 5% CO₂ until cell adhesion occurred. Then, 100 μL of sample extracts at different concentrations (25, 50, 100, 200, and 400 μg / mL) were added to each well and incubated for 24 hours. Next, 100 μL of minimum essential medium containing 0.5 mg / mL MTT solution was added to each well and incubated for another 4 hours. Then, 100 μL of dimethyl sulfoxide was added to each well, and the mixture was gently shaken for 10 minutes before the absorbance was recorded at 570 nm.

[0065] To further investigate the biocompatibility of the samples, a live / dead assay was also performed. Specifically, the cell suspension co-cultured with the sample extract was mixed with a dye solution, incubated at 37°C for 15 minutes, and then observed using a laser scanning confocal microscope (FV1200, OLYMPUS, Japan).

[0066] Preservation Analysis of Cherry Tomatoes Infected with Gray Mold: Before in-situ packaging, cherry tomatoes were inoculated with gray mold. Specifically, cherry tomatoes were immersed in a 300 ppm sodium hypochlorite solution for 3 minutes, rinsed three times with deionized water, and finally air-dried on a sterile surface. Subsequently, the cherry tomatoes were inoculated with gray mold. A 0.1 mm deep wound was punctured on the surface of each cherry tomato using a sterile stainless steel needle, and 10 μL of a 10⁵ log mL⁻¹ suspension of Aspergillus fumigatus spores was injected into each wound using a pipette. The inoculated cherry tomatoes were air-dried on a sterile surface and then packaged in situ. The cherry tomatoes covered with a nanofiber film were then placed in a 25 °C incubator, and the infection status was observed after 14 days.

[0067] Physicochemical properties and metabolomics analysis: Washed cherry tomatoes were packaged in situ and then stored at ambient temperature. Cherry tomatoes were randomly selected every four days, and their hardness was measured using a TA-XT2i texture analyzer (Stable MicroSystems, UK), their color was measured using a MiniScan XE Plus colorimeter (HunterLab, Reston, Virginia, USA), and their weight loss was also measured.

[0068] To further investigate the effects of the in-situ packaging system on cherry tomato fruit, metabolomics analysis was performed to identify different metabolites and analyze their pathways. Specifically, at the end of storage, cherry tomatoes from both the control and in-situ packaged groups were frozen, ground, and weighed in 100 mg increments. Before ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS / MS) analysis, each sample was extracted overnight at 4 °C with 0.6 mL of 70% methanol solution, followed by high-speed centrifugation for 10 min and filtration through a 0.22 μm microporous membrane. Equal volumes of cherry tomato powder from the control and in-situ packaged groups were mixed to prepare quality control (QC) samples to evaluate the mass spectrometry results. Data acquisition was performed using UPLC and tandem mass spectrometry.

[0069] Statistical analysis: The experiment was conducted in triplicate, and the results are expressed as mean ± standard deviation (SD). SPSS (V 19.0, IBM, USA) was used for statistical analysis. Paired-samples t-test and Tukey's multiple test were employed. P < 0.05 was considered statistically significant.

[0070] Metabolite labeling was performed using the internal MS2 spectral tag (MS2T) library (MetWave Biotechnology Co., Ltd., China). Principal component analysis (PCA) was performed using the built-in prcomp function in the R project. Metabolite maps from the Kyoto Genome Encyclopedia (KEGG) database were used to identify associated pathways. Metabolic pathway enrichment analysis was performed using a web server; pathways with P < 0.05 were considered significantly enriched after Bonferroni correction. Upregulated metabolites with a refractory period ≥ 2.0, downregulated metabolites with a refractory period ≤ 0.5, and metabolites with a VIP score ≥ 1 were identified.

[0071] Conclusion: Rapid in-situ packaging of fruits and vegetables was achieved using SBS. The substrate materials were the natural polymer CMCH and the biodegradable synthetic polymer PCL. TFEA was used as the solvent, as it can completely evaporate during fiber formation. Cherry tomatoes were chosen as the demonstration subject in this study because they are susceptible to fungal infection after harvest, leading to rot and significant economic losses, making them suitable for testing the effectiveness of this in-situ packaging method. Here, we prepared CMCH / PCL nanofibers using the SBS method and directly deposited these nanofibers layer by layer onto the surface of cherry tomatoes. A tightly adhered and stable CMCH / PCL (chitosan / polycaprolactone) fiber coating was formed in less than ten minutes. Figure 1 The images show comparisons of cherry tomatoes before, after, and after the packaging has been removed. The horizontal line in the lower right corner serves as a reference scale, with the line length representing 2cm. It's worth noting that although this nanofiber coating adheres tightly to the fruits and vegetables, it is easily peeled off by hand. Therefore, the in-situ packaging does not affect the consumer's ability to eat the fruits and vegetables.

[0072] Active substances, including curcumin (CUR), natamycin (NAT), nisin (NIS), and thymol (THY), were added to the spinning solution to impart antibacterial activity to the in-situ packaging. To verify that the SBS-prepared nanofibers could serve as carriers for antibacterial agents, the functionalized in-situ packaging material was comprehensively characterized. The microstructure of the in-situ packaging material was observed using scanning electron microscopy (SEM). All SEM images showed a similar morphology: a continuous and uniform nanofiber structure, indicating that the addition of the antibacterial agent did not disrupt nanofiber formation. The average diameter of the nanofibers increased after the addition of the antibacterial agent, which may be due to the antibacterial agent increasing the viscosity of the spinning solution, thus hindering the stretching during nanofiber formation.

[0073] Fourier transform infrared spectroscopy was used to analyze the encapsulation of antibacterial agents in nanofiber films, such as... Figure 2 As shown. In CMCH / PCL nanofiber films, [the following conditions were observed] at 2945 and 2867 cm⁻¹. -1CH extension vibration, 1723 cm -1 The C=O stretch is 1292 cm. -1 CO and CC stretch, 1238 cm -1 The asymmetric COC stretch and 1164 cm -1 The characteristic peaks of symmetrical COC extension were observed. These characteristic peaks remained unchanged after the addition of the antibacterial agent, indicating that the structure of the composite nanofibers was not destroyed. On the other hand, after the addition of the antibacterial agent, CUR (1627 cm⁻¹) was observed. -1 C=O stretching vibration at 1604 cm -1 The stretching vibration of the benzene ring at 1509 cm -1 C=C stretching vibration on the benzene ring at the location), NAT (1005 cm -1 (cyclic ether) and THY (1090 cm) -1 The presence of characteristic peaks (in-plane CH bending at the location) indicates successful loading. However, no characteristic peaks of NIS were recorded in the Fourier transform infrared spectrum of the nanofibers, which may be related to the relatively small amount of NIS added.

[0074] To further determine the distribution of the added antibacterial agent within the nanofibers, XRD analysis was performed to investigate the presence of crystalline domains, which could represent aggregation or incomplete dissolution. Figure 3 As shown in the AD diagram, two sharp peaks were observed in the XRD pattern of the CMCH / PCL film, located at 2θ = 21.3° and 23.6°, representing a semi-crystalline structure. Only after the addition of CUR did the characteristic peaks at 2θ = 8.8° and 17.2° appear in the XRD pattern, indicating the presence of non-uniform distribution. In contrast, no crystalline domains were observed in the XRD pattern of the nanofibers after the addition of other antibacterial agents, indicating that the antibacterial agents can be uniformly distributed within the nanofibers.

[0075] The thermal stability of nanofiber films is as follows Figure 3 As shown in E, the high volatility and thermal instability of THY accelerate the thermal degradation of the nanofiber membrane. The residual weight of the CMCH / PCL nanofiber membrane was 1.43%, which increased to 4.49%, 3.73%, and 2.51% after the addition of CUR, NAT, and NIS, respectively, indicating that the thermal stability was improved.

[0076] Mechanical properties are important indicators for packaging material applications. As shown in Figures 3G and H, the elastic modulus and tensile strength of CMCH / PCL nanofiber films are 1.43 and 1.21 MPa, respectively, while those of CUR / CMCH / PCL nanofiber films are 2.62 and 2.28 MPa, and those of NAT / CMCH / PCL nanofiber films are 3.87 and 2.61 MPa, respectively. This indicates that CUR and NAT improve the mechanical properties of the nanofiber films. The addition of NIS and THY does not affect the elastic modulus and tensile strength of CMCH / PCL nanofiber films, indicating that they have little impact on the mechanical properties of the films. After adding antibacterial agents, there is no significant difference in the elongation at break of the nanofibers, indicating that the addition of antibacterial agents does not affect the ductility of the nanofibers.

[0077] Hydrophobicity is a fundamental property of packaging materials, enabling them to be used in high-humidity environments without structural damage from moisture and preventing microbial adhesion. Due to the presence of hydrophilic CMCH, the water contact angle of the CMCH / PCL film was 132.7° at 0 seconds, decreasing to 49.9° after stabilization (60 seconds). The addition of CUR, NAT, NIS, and THY resulted in stable water contact angles of 89.3°, 127.3°, 70.4°, and 135.4° for the nanofiber films, respectively, indicating increased hydrophobicity.

[0078] The safety of nanofiber food packaging materials is related to human health and should be given high priority. Figure 4 The images show the cytotoxicity results of CMCH / PCL (methylchitosan / polycaprolactone), CUR / CMCH / PCL (curcumin / methylchitosan / polycaprolactone), NAT / CMCH / PCL (natamycin / methylchitosan / polycaprolactone), NIS / CMCH / PCL (nisin / methylchitosan / polycaprolactone), and THY / CMCH / PCL (thymol / methylchitosan / polycaprolactone) nanofiber films, respectively. After co-culturing with different concentrations of nanofiber samples for 24 hours, the relative survival rate of L292 cells exceeded 86%, indicating that the CMCH / PCL nanofiber membranes loaded with antibacterial agents have good biocompatibility and low toxicity. This study demonstrates the feasibility of using CMCH / PCL nanofibers as an in-situ packaging carrier for antibacterial agents due to their good biocompatibility.

[0079] To evaluate the preservation effect of in-situ packaging containing antimicrobial agents on cherry tomatoes, the diameter of lesions in cherry tomatoes inoculated with gray mold was tested after 14 days of storage at room temperature. Figure 5 As shown, Figure 5 Image A shows the condition of cherry tomatoes inoculated with gray mold and treated with different in-situ packaging coatings, as well as the control group. Figure 5 Part B represents the condition after 14 days of storage and removal of packaging, compared to the control group. Figure 5 In the diagram, C represents the diameter of the lesion, and the horizontal line in the lower right corner of area B is a reference scale, with a line length representing 3 cm. Cherry tomatoes without in-situ packaging were severely infected with *Botrytis cinerea*, exhibiting severe gray mold, with an average lesion diameter of 14.7 mm. In contrast, cherry tomatoes with in-situ packaging showed significantly less gray mold. In particular, cherry tomatoes wrapped with a NAT / CMCH / PCL nanofiber film had an average lesion diameter of only 3.7 mm, showing almost no effect from gray mold. These results indicate that in-situ packaging containing antimicrobial agents effectively protects cherry tomatoes from postharvest fungal infection.

[0080] The NAT / CMCH / PCL nanofiber film with the strongest antifungal activity was selected to determine the effect of in-situ packaging on the physicochemical properties of cherry tomatoes. Figure 6 Figure A shows the weight loss of cherry tomatoes during 24 days of storage. Compared to cherry tomatoes without in-situ wrapping, those coated with in-situ wrapping showed significantly less weight loss throughout storage. This is likely because the in-situ wrapping forms a barrier on the surface of the cherry tomatoes, restricting the penetration of moisture and gases, thereby reducing fruit respiration and resulting in less weight loss.

[0081] Figure 6B shows the firmness of cherry tomatoes during 24 days of storage. Throughout the storage period, the cherry tomatoes coated with in-situ filler were firmer than the control group (the differences were statistically significant at days 4, 8, and 12). Firmness is related to fruit maturity. During ripening, cell wall components such as pectin and cellulose are degraded by related enzymes, causing the fruit to soften. This indicates that in-situ packaging can effectively delay the ripening of cherry tomatoes and extend their shelf life.

[0082] To assess the color changes of cherry tomatoes during storage, a* values ​​were recorded and hue angles were calculated, as shown in Figures C and D of Figure 6. From day 8 onwards, the a* values ​​of the control group cherry tomatoes were higher than those of the in-situ packaged cherry tomatoes. This result indicates that in-situ packaging delays the color deepening of cherry tomatoes, suggesting that it can effectively delay post-harvest ripening. Furthermore, throughout the storage period, the hue angles of the control group cherry tomatoes were significantly lower than those of the in-situ packaged cherry tomatoes.

[0083] To determine the impact of in-situ packaging on the metabolites and metabolic pathways of cherry tomatoes, further metabolomics analysis was performed. A total of 1870 metabolites were measured, mainly including flavonoids, phenolic acids, alkaloids, lipids, amino acids and their derivatives, lignans, and coumarins, such as... Figure 7 As shown in Figure A, the principal components of in-situ packaged cherry tomatoes and control group cherry tomatoes are clearly separated, indicating differences in metabolites between the two groups. Hierarchical cluster analysis based on the log10 transformation of metabolite peak areas showed that the two groups of metabolites were divided into two distinct components, such as... Figure 7 As shown in B.

[0084] A total of 230 metabolites with significant changes were identified, of which 88 were upregulated and 142 were downregulated, such as... Figure 8 As shown in A, the 88 upregulated differential metabolites mainly include organic acids (such as shikimic acid, homocitric acid, and sebacic acid), phenolic acids (such as vanillic acid, cyanidin, and veratrine), tannic acids (such as tannic acid), flavonoids (such as gallic acid, 3,7-di-O-methylquercetin, and 3',4',5,6,7-pentamethoxyflavanone), alkaloids (such as dihydroshikimic acid), nucleotides and derivatives (such as β-nicotinamide mononucleotide), and lipids (such as buperidin and methyl linolenic acid). The 142 downregulated differentially expressed metabolites mainly included flavonoids (such as hesperidin, hesperidin, and quercetin-7-O-glucoside), phenolic acids (such as punicin, 3-OO-punicin, and quercetin-7-O-glucoside), lipids (such as juglone, methyl linolenic acid, and DL-2-hydroxystearic acid), amino acids and their derivatives (such as N-acetyl-L-glutamic acid, γ-glutamyltyrosine, and glycyl-L-leucine), and alkaloids (such as cannabinoid D and lycopene).

[0085] The 230 identified differentially metabolites were compared with KEGG data to retrieve pathway profiles. Figure 8 As shown in B, the differentially metabolites were categorized into 25 metabolic pathways, of which 54.84% were classified as "Biosynthesis of Secondary Metabolites," 51.61% as "Metabolic Pathways," 22.58% as "Biosynthesis of Flavonoids," 19.35% as "Biosynthesis of Flavonoids and Flavonols," and 12.9% as "Biosynthesis of Cofactors." KEGG enrichment analysis showed that the differentially metabolites enriched in "Biosynthesis of Flavonoids and Flavonols" and "Biosynthesis of Flavonoids" differed significantly between the in-situ packaged cherry tomato group and the control group, such as... Figure 8 As shown in C.

[0086] Numerous studies have shown that many fruits and vegetables accumulate flavonoids during ripening. In this study, at the end of storage, the flavonoid content of in-situ packaged cherry tomatoes was significantly lower than that of the control group. Furthermore, fruits and vegetables consume organic acids during ripening, and the organic acid content of the control group cherry tomatoes was significantly lower than that of the in-situ packaged cherry tomatoes. These results indicate that in-situ packaging delays the ripening process of cherry tomatoes.

[0087] Example 5: A fruit and vegetable blow molding spinning in-situ packaging device, such as... Figure 9 , 10 As shown, the packaging methods in Examples 1-4 can be implemented. This device includes several parallel conveyor rollers 1, with their axes arranged along the front-to-back direction. The conveyor rollers transport fruits and vegetables from front to back. Each conveyor roller surface is provided with spiral patterns 2 of the same direction and structure. The conveyor rollers rotate synchronously, with gaps between adjacent conveyor rollers. These gaps carry and transport fruits and vegetables 4 along the conveyor roller axis. Several spinning nozzles 5 are evenly spaced above the gaps between adjacent conveyor rollers. A fruit sensor is attached to the front side of each spinning nozzle to sense whether the fruits and vegetables have reached below the spinning nozzle; the fruit sensor is an infrared sensor. The spinning nozzles 5 spray the preservation spinning solution described in Example 1. A cleaning nozzle 6 is located directly above each conveyor roller, spraying TFEA as the cleaning solvent. A drying nozzle 7 is also located between the cleaning nozzle and the spinning nozzle. A waste recycling tank is located below the conveyor rollers. A feeding conveyor belt 3 is located above the front end of the conveyor roller 1, and a discharge conveyor belt 9 is located below the rear end of the conveyor roller. The power to the conveyor roller is input from the front end, and an inclined guide plate 10 is provided between the rear end of the conveyor roller and the discharge belt. In this example, cherry tomatoes are used as the fruits and vegetables.

[0088] Example 6: A fruit and vegetable blow molding and spinning in-situ packaging structure, such as... Figure 11 As shown, the methods of Examples 1-4 and the apparatus of Example 5 are used. Fruits and vegetables 4 are arranged in bunches of 2-10, 41, with adjacent fruits and vegetables in the same bunch touching each other. The outside of each bunch is a continuous blow-blown packaging film 11. In this example, cherry tomatoes are used.

Claims

1. A fruit and vegetable blow molding spinning in-situ packaging device, characterized in that: It includes several conveyor rollers arranged in parallel, with the axis of the conveyor rollers arranged in the front-to-back direction. The conveyor rollers convey fruits and vegetables from front to back. Each conveyor roller surface is provided with spiral patterns of the same direction and structure. The conveyor rollers rotate synchronously, and there is a gap between adjacent conveyor rollers. The gap between adjacent conveyor rollers carries and conveys fruits and vegetables along the axis of the conveyor rollers. Several spinning nozzles are arranged at equal intervals above the gap between adjacent conveyor rollers. A cleaning nozzle is arranged directly above each conveyor roller. A drying nozzle is also arranged in the gap between the cleaning nozzle and the spinning nozzle. The in-situ packaging method for fruits and vegetables via blow molding and spinning includes the following steps: S1: Preparation of basic spinning solution: Dissolve 0.6-1.2 g of polycaprolactone and 0.1-0.3 g of carboxymethyl chitosan in 10 mL of 2,2,2-trifluoroethanol to prepare a basic spinning solution containing polycaprolactone and carboxymethyl chitosan; S2: Preparation of preservative spinning solution: Add preservative to the basic spinning solution and stir continuously for 6-8 hours to obtain the preservative spinning solution; S3: Blow spinning packaging: The preservative spinning solution is fed into the blow spinning equipment, and the spinning nozzle of the equipment is used to directly spin the fruit and vegetable surface. The blowing rate of the preservative spinning solution is 3-5 mL / h, the blowing pressure is 0.12-0.15 MPa, the fruit and vegetable are placed 20-30 cm away from the spinning nozzle, and the fruit and vegetable are kept rotating or rolling. The spinning packaging time for a single fruit and vegetable is 0.5-8 min.

2. The fruit and vegetable blow molding spinning in-situ packaging device according to claim 1, characterized in that: A feeding conveyor belt is provided above the front end of the conveying roller, and a discharging conveyor belt is provided below the rear end of the conveying roller.

3. The fruit and vegetable blow molding spinning in-situ packaging device according to claim 1, characterized in that: A waste recycling tank is provided below the conveyor roller.

4. The fruit and vegetable blow molding spinning in-situ packaging device according to claim 1, characterized in that: Each spinning nozzle is equipped with a fruit sensor on its front or circumferential side. The fruit sensor is either a visual sensor or an infrared sensor.

5. The fruit and vegetable blow molding spinning in-situ packaging device according to claim 1, characterized in that: The cleaning solvent sprayed by the cleaning nozzle is 2,2,2-trifluoroethanol.

6. The fruit and vegetable blow molding spinning in-situ packaging device according to claim 1, characterized in that: The preservative mentioned in S2 is one or more of CUR, NAT, NIS and THY.

7. The fruit and vegetable blow molding spinning in-situ packaging device according to claim 6, characterized in that: The amount of preservative added per 10 ml of 2,2,2-trifluoroethanol is 0.01-0.04 g.

8. A fruit and vegetable blow molding and spinning in-situ packaging structure, characterized in that: The fruit and vegetable blown spinning in-situ packaging device as described in claim 1 is used for packaging. The fruit and vegetables are arranged in bunches of 2-10, with adjacent fruits and vegetables in the same bunch abutting each other. The outside of the same bunch is a continuous packaging film formed by blown spinning.

9. The fruit and vegetable blow molding and spinning in-situ packaging structure according to claim 8, characterized in that: The fruits and vegetables mentioned are cherry tomatoes, cherries, or dates.

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