A fresh-cut chili film and a preparation method and application thereof

Abstract

The present application relates to the technical field of pepper preservation, and relates to a fresh-cut pepper preservative film, a preparation method and application thereof.The preparation method of the fresh-cut pepper preservative film comprises the following steps: S1, preparation of lignin nanoparticles LNP: lignin is dissolved in a solution; then water is added dropwise at a speed of 0.3-1.0 mL / min; after stirring and reaction at room temperature for 1-3 h, standing, dialysis, the lignin nanoparticles LNP are obtained; S2, preparation of a film-forming solution: sodium alginate is dissolved in water to obtain a sodium alginate solution; tea polyphenol and glycerol are added in sequence and uniformly mixed to obtain a film-forming solution; S3, preparation of a composite film: lignin nanoparticles LNP are added to the film-forming solution, and after uniform mixing, casting and drying, the fresh-cut pepper preservative film is obtained.The fresh-cut pepper preservative film has good antibacterial performance, a low water vapor transmission rate, excellent ultraviolet shielding performance and anti-fog performance.

Description

Technical Field

[0001] This invention relates to the field of chili preservation technology, and more specifically, to a fresh-cut chili preservation film, its preparation method, and its application. Background Technology

[0002] Chili peppers are popular due to their rich content of vitamins and minerals. Fresh-cut products have become an indispensable part of people's lives, offering freshness, nutrition, and convenience. They are widely used in the catering industry, and market demand for these products is steadily increasing. However, fresh-cut fruits and vegetables are prone to spoilage due to mechanical processes, as the cut surfaces are susceptible to bacterial growth, leading to short shelf life, moisture loss, enzymatic browning, and nutrient loss. Maintaining the color, firmness, and freshness of fresh-cut fruits and vegetables is crucial for quality control. The cutting and peeling processes of fresh-cut chili peppers damage the plant's tissue structure, causing injury, sap leakage, accelerated respiration, enzymatic and non-enzymatic browning, and increased physiological metabolism. Furthermore, the large exposed surface area and abundant nutrients create a suitable environment for microbial growth, becoming a breeding ground for putrefactive bacteria, making fresh-cut chili peppers more susceptible to spoilage. Therefore, preserving fresh-cut chili peppers is more challenging. Currently, there are no reports on bio-based, green, and low-energy preservation methods for fresh-cut chili peppers, nor are they being used in the market.

[0003] Among current popular chili preservation technologies, food packaging technology is widely used due to its versatility and ease of handling. Its barrier and antibacterial properties determine the rate of food quality deterioration and shelf life. However, most current food packaging films are made from petroleum-based products, which, due to their poor biodegradability, cause serious environmental pollution with their widespread use. Biomass polymers, due to their biocompatibility, biodegradability, low cost, and environmental friendliness, have broad application prospects in the food packaging industry. Lignin is a natural high-molecular polymer with advantages such as abundance, environmental friendliness, biocompatibility, and biodegradability. Using it to prepare composite film materials can improve the strength and functionality of the materials. However, lignin's poor dispersibility limits its application in composite functional materials. Currently, the application of lignin in food packaging is mostly in combination with metal nanoparticles; however, insufficient research on the safety performance of metal nanoparticles hinders their further application in food packaging.

[0004] Existing technology discloses a slow-release antibacterial chitosan-based composite film. However, this chitosan-based composite film has poor UV resistance and cannot meet the requirements for preserving fresh-cut foods.

[0005] Existing technology discloses a ternary composite material of lignin nanoparticles / polyvinyl alcohol / chitosan (LNP / PVA / CH). However, this ternary composite material has poor antibacterial properties and cannot meet the requirements for preserving fresh-cut foods. Summary of the Invention

[0006] The purpose of this invention is to provide a preservation film with antibacterial properties that meets the requirements for preserving fresh-cut chili peppers, as well as its preparation method and application.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a preservation film for fresh-cut chili peppers includes the following steps:

[0009] S1. Preparation of lignin nanoparticles (LNP): Lignin was dissolved in the solution; then water was added dropwise at a rate of 0.3-1.0 mL / min; the mixture was stirred and reacted at room temperature for 1-3 h, then allowed to stand and dialyzed to obtain the lignin nanoparticles (LNP).

[0010] S2. Preparation of film-forming solution: Sodium alginate is dissolved in water to obtain sodium alginate solution; tea polyphenols and glycerin are added sequentially and mixed evenly to obtain film-forming solution;

[0011] S3. Preparation of composite film: Add lignin nanoparticles (LNP) to the film-forming solution, mix evenly, pour and dry to obtain fresh-cut chili preservation film.

[0012] In one preferred embodiment, the stirring speed in S1 is 800-1200 r / min.

[0013] In one preferred embodiment, the lignin nanoparticles (LNPs) are granular with a particle size of 90-160 nm.

[0014] Smaller particle size allows for more uniform dispersion, which helps improve the mechanical properties of composite materials. However, if the particle size is too small or the distribution is uneven, it may lead to stress concentration, thereby reducing the strength of the material. Simultaneously, smaller particle size and more uniform distribution result in higher transparency. Smaller and more uniformly distributed lignin nanoparticles can enhance the barrier properties of composite films, preventing the passage of small molecules.

[0015] If the particle size is too large, it is difficult to distribute evenly during the film formation process, which may lead to a rough and uneven film surface, affecting its appearance. Although lignin itself has a certain degree of thermal and chemical stability, if the prepared LNPs have an excessively large particle size, it may alter its surface properties by exposing more of the internal structure, thereby affecting the performance of the composite film in these two aspects.

[0016] In one preferred embodiment, in S2, the mass ratio of sodium alginate, tea polyphenols, and glycerol is (1-3):(1-3):(0.5-1.5).

[0017] In one preferred embodiment, in step S2, the mass ratio of sodium alginate to tea polyphenols is 1-2:1-2.

[0018] In one preferred embodiment, in step S2, the mass ratio of sodium alginate to tea polyphenols is 1:1.

[0019] Too little sodium alginate will result in poor water vapor permeability of the composite membrane and poor film-forming properties; while too much sodium alginate will cause changes in the mechanical properties of the composite membrane, making the membrane too stiff or brittle and prone to breakage.

[0020] Excessive tea polyphenols increase the cost of the composite film too much; insufficient content results in weak antibacterial properties.

[0021] In one preferred embodiment, in S2, the mass ratio of sodium alginate to water is 1-3:90-110.

[0022] In one preferred embodiment, in S3, the casting is performed on an acrylic board.

[0023] In one preferred embodiment, in step S3, the drying temperature is 50-70°C and the drying time is 24-72 hours.

[0024] In one preferred embodiment, in step S3, the amount of lignin nanoparticles (LNP) added is 1%-5% of the total mass of sodium alginate and tea polyphenols.

[0025] If the LNP content is too low, the mechanical properties and UV shielding performance of the composite film will be weak. However, if the LNP content is too high, it will interfere with the hydrogen bonds between sodium alginate molecules, weaken the bonds between sodium alginate molecules, and reduce the mechanical properties, as well as the dispersibility and stability.

[0026] In one preferred embodiment, in step S3, the amount of lignin nanoparticles (LNP) added is 3%-5% of the total mass of sodium alginate and tea polyphenols.

[0027] In one preferred embodiment, in S3, the amount of lignin nanoparticles (LNP) added is 5% of the total mass of sodium alginate and tea polyphenols.

[0028] Based on the same inventive concept, the present invention also claims protection for the fresh-cut chili preservation film prepared by the preparation method.

[0029] In one preferred embodiment, the thickness of the fresh-cut chili preservation film is 0.090-0.095 mm.

[0030] In one preferred embodiment, the maximum thermal decomposition temperature of the fresh-cut chili preservation film is 183-194°C.

[0031] In one preferred embodiment, the moisture content of the fresh-cut chili preservation film is 31%-37%.

[0032] In one preferred embodiment, the water vapor permeability of the fresh-cut chili pepper preservation film is 0.02-0.05%.

[0033] Based on the same inventive concept, this invention also claims protection for the application of the fresh-cut chili preservation film in the preservation of fresh-cut vegetables.

[0034] In one preferred embodiment, the fresh-cut vegetable is fresh-cut chili pepper.

[0035] Based on the same inventive concept, this invention also claims protection for the application of fresh-cut chili pepper preservation film in terms of antibacterial, antioxidant and UV protection properties.

[0036] Compared with the prior art, the fresh-cut chili pepper preservation film prepared by the present invention has the following advantages and significant progress: (1) The combination of LNPs and TP produces a synergistic antibacterial effect, which disrupts the cell membrane structure of bacteria, interferes with the normal function of bacterial DNA, hinders the synthesis and expression of bacterial proteins, accelerates the exudation of contents and leads to cell death. (2) LNPs and TP can be evenly distributed in SA, resulting in better integrity of the composite film. The addition of LNPs and TP not only improves the mechanical properties of the composite film, but also improves the structural properties of SA. The prepared composite film has a low water vapor permeability, and due to the coloring of lignin and TP itself, the prepared composite film is brown, giving it excellent ultraviolet shielding performance in both UVA and UVB bands. (3) The composite film can significantly improve the freshness of fresh-cut chili peppers and extend their shelf life. (4) The composite film has good thermal anti-fogging performance and cold anti-fogging performance. Attached Figure Description

[0037] Figure 1 The results show the morphology and size of LNPs; where a represents the microstructure of 1-LNPs lignin nanoparticles; b represents the microstructure of 3-LNPs lignin nanoparticles; c represents the microstructure of 5-LNPs lignin nanoparticles; A represents the particle size distribution of 1-LNPs; B represents the particle size distribution of 3-LNPs; and C represents the particle size distribution of 5-LNPs.

[0038] Figure 2 Photographs of the SA / TP / LNPs composite membrane; (a) is the control group membrane; (b)-(d) show the addition amounts of lignin nanoparticles of 1%, 3%, and 5%, respectively.

[0039] Figure 3SEM images of SA / TP / LNPs composite membranes; (a) control group membrane; (b) lignin nanoparticles with an addition of 5%;

[0040] Figure 4 The blocking properties of SA / TP / LNPs composite film for visible and ultraviolet light;

[0041] Figure 5 Here are the TG-DTG curves of the thin film, where A is the TG curve and B is the DTG curve.

[0042] Figure 6 The anti-fogging performance of the SA / TP / LNPs composite membrane;

[0043] Figure 7 The antibacterial properties of SA / TP / LNPs composite membrane against Escherichia coli and Staphylococcus aureus;

[0044] Figure 8 The SA / TP / LNPs composite membrane exhibits high free radical scavenging capacity and total antioxidant capacity.

[0045] Figure 9 The effects of different treatment groups on the appearance of fresh-cut chili peppers;

[0046] Figure 10 This represents the change in weight loss rate of fresh-cut chili peppers during storage.

[0047] Figure 11 The effect of different treatments on the decay index of fresh-cut peppers after 10 days of storage;

[0048] Figure 12 This refers to the change in soluble solids content during the storage of fresh-cut chili peppers;

[0049] Figure 13 The change in vitamin C content during the storage of fresh-cut chili peppers;

[0050] Figure 14 Changes in respiration rate during the storage of fresh-cut chili peppers;

[0051] Figure 15 Changes in chlorophyll content during the storage of fresh-cut chili peppers;

[0052] Figure 16 The changes in malondialdehyde during the storage of fresh-cut chili peppers. Detailed Implementation

[0053] This invention is not limited to the specific embodiments listed below. Those skilled in the art can implement this invention using various other specific embodiments based on the content disclosed herein. Any modifications or alterations made to the design structure and concept of this invention fall within the protection scope of this invention. It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0054] Data statistics and analysis of this invention: All experiments were repeated three times, and the results are expressed as mean ± standard deviation. One-way ANOVA was performed using SPSS 20.0 software, and graphs were plotted using Origin 8.5.

[0055] The strains, materials, and reagents used in this invention are as follows:

[0056] Staphylococcus aureus and Escherichia coli were both laboratory-preserved strains; alkaline lignin; tetrahydrofuran (AR), sodium alginate (chemically pure), glycerol (AR), methanol (AR), and other analytical grade reagents were purchased from Sinopharm Chemical Reagent Co., Ltd.; tea polyphenols (99%) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; chromatographically pure 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) was purchased from Hangzhou Huipu Chemical Co., Ltd.; 2,2'-azido-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), anhydrous calcium chloride, and deionized water were used in the laboratory; Zhangshugang chili peppers were also used. Other reagents not explicitly mentioned were all commercially available products.

[0057] The instruments and equipment used in this invention are as follows:

[0058] Nano ZS90 Malvern laser particle size analyzer, Malvern Instruments, UK; Evolution201 UV-Vis spectrophotometer, Thermo Fisher Scientific; Discovery TGA550 thermogravimetric analyzer, Thermal Analysis Instruments, USA; Nicolet iS50 Fourier transform infrared spectrometer, Nicolet Instruments, USA; ZEISS Sigma300 scanning electron microscope, Carl Zeiss AG, Germany; MTS CMT6103 electronic universal testing machine, Shenzhen Century Tianyuan Instrument Co., Ltd.; forced-air drying oven, Suzhou Ruizhifeng Oven Manufacturing Co., Ltd.; magnetic heating stirrer, Guohua Electric Co., Ltd.; JA2003 electronic balance, Shanghai Hengping Scientific Instruments Co., Ltd.; GZ-280-S biochemical incubator, Shaoguan Guangzhi Technology Equipment Co., Ltd.; BBS-SDC clean bench, Jinan Xinbeixi Biotechnology Co., Ltd.; digital micrometer, Dongguan Sanliang Hardware Instrument Co., Ltd.; PAL-BX / ACID1 saccharimeter, ATAGO Ltd., Japan.

[0059] Example 1

[0060] 1. Preparation method of lignin nanoparticles

[0061] Weigh an appropriate amount of lignin and prepare LNPs using water as the antisolvent. Add an appropriate amount of lignin dissolved in a H2O-tetrahydrofuran cosolvent (H2O-tetrahydrofuran v / v, 3 / 7) to a round-bottom flask and stir magnetically to fully dissolve the lignin, obtaining LNPs solutions with mass concentrations of 1%, 3%, and 5%. Then, use a dropping funnel to add 40 mL of deionized water dropwise to the lignin solution at a rate of approximately 0.5 mL / min, and stir continuously at a stirring rate of 1000 r / min at room temperature for 2 h. The resulting LNPs are designated as 1-LNPs, 3-LNPs, and 5-LNPs, respectively. Place the suspension in a dialysis bag, and then immerse the dialysis bag in excess deionized water to remove tetrahydrofuran (the deionized water needs to be replaced periodically).

[0062] The morphology and particle size of 1-LNPs, 3-LNPs, and 5-LNPs were characterized using SEM and a nanoparticle size analyzer, respectively. The results are as follows: Figure 1 As shown in the SEM images, the prepared lignin products are nanoscale particles, exhibiting spherical and granular structural characteristics. The average particle size of 1-LNPs is the smallest (98.33±4.58 nm), while that of 5-LNPs is the largest (150±2.31 nm), showing good dispersibility. However, when the LNPs solution concentration is too high, such as when preparing 10-LNPs at a mass concentration of 10%, the particle size is too large (573±6.98 nm), and the dispersibility (dispersion index PDI of 2.231) and stability are poor.

[0063] 2. Preparation of film-forming solutions and composite films

[0064] Preparation of SA / TP film-forming solution: First, weigh 2g of sodium alginate (SA) and dissolve it in 100mL of deionized water. Stir at 60℃ for 2 hours until the solution is clear and free of bubbles, preparing a 2wt% SA solution. Then, weigh 2g of tea polyphenols (TP) and dissolve it in the SA solution. Stir well, then add 1% glycerol and mix well to obtain the SA / TP mixed film solution for later use.

[0065] Preparation of SA / TP / LNPs film-forming solution: The SA / TP mixed film-forming solution was mixed with a certain amount of LNPs with a mass concentration of 1% and mixed evenly. Finally, the film-forming solution was poured onto an acrylic plate, leveled, and dried at 60℃ for 48 hours to form a film. According to the amount of LNPs added (relative to the mass fraction of SA / TP), which were 1%, 3%, and 5% by mass, the composite membranes were named: SA / TP / LNPs-1, SA / TP / LNPs-3, and SA / TP / LNPs-5.

[0066] Composite membrane testing and characterization

[0067] 1. SEM characterization of the composite membrane

[0068] The composite film was cut into strips of appropriate size, sputtered with gold, and then the surface morphology of the film was examined using a scanning electron microscope (ZEISS Sigma300).

[0069] Since LNPs and TP are brown, the composite membrane made from LNPs and TP materials is also brown. A photograph of the composite membrane is shown below. Figure 2 As shown, the SEM characterization results are as follows: Figure 3 As shown. By Figure 2 It can be seen that as the LNP content increases, the appearance of the composite film changes from light brown to dark brown, and its transparency decreases accordingly. Figure 3 It can be seen that the SA / TP / LNPs composite membrane exhibits a relatively uniform and continuous surface without large-scale aggregation, indicating that LNPs and TP have good dispersion in SA and no phase separation occurs. No pores or cracks appear between LNPs and SA, suggesting that the good interfacial bonding can act as a bridge for load transfer, reducing stress concentration under strain, thereby improving the toughness and ductility of the antibacterial composite membrane.

[0070] 2. Transmittance test of composite film

[0071] The composite film was cut into a rectangle of 10mm × 40mm, and its transmission spectrum was measured in the wavelength range of 200–800nm ​​using a UV-Vis spectrophotometer, with a blank cuvette as a control.

[0072] The results are as follows Figure 4 As shown, SA films, SA / TP films, and PE films all exhibit poor blocking performance for visible and ultraviolet light, with visible light transmittance exceeding 70%. Compared to SA films and SA / TP films, the SA / TP / LNPs composite film almost completely blocks UVB (320–275 nm), UVC (275–200 nm), and most of the UVA (400–320 nm) spectrum. Even with a small amount of LNPs added, the ultraviolet shielding performance of the composite film can be significantly enhanced.

[0073] 3. Thermogravimetric analysis

[0074] Weigh an appropriate amount of composite membrane sample and, under a nitrogen atmosphere, raise the temperature from room temperature to 600℃ at a rate of 10℃ / min to determine the thermal stability of the composite membrane.

[0075] The thermal stability of several thin films was investigated. The TG-DTG curves of the thin films are shown below. Figure 5As shown, A represents the TG curve, and B represents the DTG curve. The maximum thermal decomposition temperature of the SA film is 179.5℃. With the addition of LNPs and TP, the maximum thermal decomposition temperature of the composite film is increased. The maximum thermal decomposition temperatures of SA / TP / LNPs-1, SA / TP / LNPs-3, and SA / TP / LNPs-5 are 183.2℃, 190.3℃, and 193.4℃, respectively. The results indicate that the composite film has good thermal stability.

[0076] 4. Antibacterial effect of composite membrane solution

[0077] Pour nutrient agar medium into a sterile petri dish. After it solidifies, add 0.1 mL of 10% nutrient agar medium. 6 CFU / mL bacterial suspension was evenly spread onto the surface of the culture medium using a spreader. Four wells were punched in the agar using a sterile puncher. Three wells were filled with composite membrane solution, and one well was filled with LNPs solution as a blank. The mixture was incubated at 37°C for 12–24 h. The size of the inhibition zone was observed, and the colony diameter was determined using the cross-hatching method.

[0078] The results showed that the composite membrane solution had a good inhibitory effect on both Staphylococcus aureus and Escherichia coli, as shown in Table 1. The inhibitory effect on Staphylococcus aureus was the most significant, while the inhibitory activity against Escherichia coli was relatively weak. Furthermore, the inhibitory effect was positively correlated with the mass concentration of tea polyphenols.

[0079] Table 1. Results of the determination of inhibition zones of the composite film solution against two foodborne pathogens.

[0080]

[0081]

[0082] Note: Different lowercase letters after the values ​​in the same column indicate significant differences (P < 0.05).

[0083] When the mass ratio of SA to TP is 3:1, the antibacterial performance of the prepared composite membrane decreases, and the increased amount of sodium alginate makes the composite membrane prone to breakage. When the mass ratio of SA to TP is 4:1, the composite membrane solution has poor fluidity and high viscosity, making it difficult to stir and resulting in uneven mixing, thus hindering the formation of a uniform thin film during casting.

[0084] Determination of Physicochemical Indicators of Composite Membranes

[0085] 1 thickness

[0086] The thickness of the film was measured at 10 random locations on the thin film sample using a digital micrometer.

[0087] 2. Determination of moisture content and water solubility

[0088] The film was divided into 20mm × 20mm squares, and the initial mass was measured. The film was dried at 105℃ until a constant mass was obtained. The water content was calculated using formula (1). The film was completely dried and then soaked in 50mL of distilled water at room temperature for 24h. The swollen film was then removed from the solution and dried at 105℃ until a constant mass was obtained. The water solubility (%) was calculated using formula (2).

[0089]

[0090] In the formula: m0 is the initial mass of the film / g; m1 is the dry mass of the film after drying / g; m2 is the dry mass of the film after swelling / g.

[0091] 3 Mechanical properties

[0092] The film was cut into 100mm × 10mm rectangles, and its tensile strength (TS, MPa) and elongation at break (EAB, %) were determined using an automatic tensile testing machine. The initial clamping distance was 50mm, and the clamping speed was 1mm / s.

[0093] 4 Water vapor transmission rate

[0094] A 60mm × 60mm membrane containing anhydrous calcium chloride (particle size less than 2mm) was fixed at the mouth of a test cup, with the distance between the calcium chloride and the cup mouth less than 6mm. The test cup was placed in a desiccator containing saturated sodium chloride solution (25℃, 75% relative humidity), maintaining a certain vapor pressure difference across the membrane. The test cup was removed, and the membrane was weighed periodically until the mass change was less than 0.001g. Each experiment was repeated three times. The WVP calculation formula is as follows:

[0095]

[0096] In the formula: m is the mass change of water during the test, in g; L is the thickness of the thin film sample, in mm; A is the area of ​​the weighing bottle opening, in m². 2 ; t is the test time, s; p2 is the partial pressure of water vapor at 20℃, 2.337 kPa; p1 is the partial pressure of water vapor in the silica gel dryer, 0.0280 kPa.

[0097] Table 2 shows that the thickness of the SA / TP / LNPs composite films with different ratios did not differ significantly (P>0.05), ranging from 0.090 to 0.093 mm. Compared with the SA film, the thickness of the composite film increased with the addition of TP and LNPs. The thickness of the PE film was 0.089 mm, and the thickness of the SA / TP / LNPs composite films with different ratios did not differ significantly from that of the PE film (P>0.05).

[0098] Table 2 Physical properties of 7 membrane materials

[0099]

[0100] Note: Data in the same column with completely different lowercase letters indicates a significant difference between groups (P<0.05), while data with any identical lowercase letters indicates no significant difference (P>0.05).

[0101] The moisture content of SA films is significantly higher than that of other composite films. With the addition of TP, the moisture content of SA / TP composite films decreases to 47.20%. When LNPs are introduced, the moisture content of SA / TP / LNPs composite films decreases significantly, with SA / TP / LNPs-5 having the lowest moisture content at 31.06%, followed by SA / TP / LNPs-3 (34.72%) and SA / TP / LNPs-1 (36.81%). Overall, the moisture content of composite films gradually decreases with increasing LNP content.

[0102] Of all the prepared membranes, the SA membrane exhibited the highest water solubility at room temperature (79.62%), which is attributed to the hydrophilicity of both SA and glycerol. The water solubility of the composite membranes significantly decreased upon the addition of LNPs and TP (P<0.05). SA / TP / LNPs-5 had the lowest solubility at 44.54%, followed by SA / TP / LNPs-3 (54.29%) and SA / TP / LNPs-1 (62.42%). The high water resistance of the composite membranes indicates the crosslinking and miscibility of the phenolic compounds in lignin with the hydrophilic sodium alginate portion.

[0103] Water vapor transmission rate (WVP) is a crucial indicator of atmospheric water vapor transfer to the other side of a film, affecting the shelf life of packaged products. Table 2 shows the WVP data for the composite films. The SA film has the highest WVP at 0.101%. The hydrophilicity of SA reduces the barrier properties of the composite film. The WVP of the SA / TP / LNPs composite film is significantly lower than that of the SA film and PE film (P<0.05), with the SA / TP / LNPs-5 having the lowest WVP at 0.028%. Under the same conditions, the WVP of the composite film prepared according to prior art CN 113292753 B with a w(LNP):w(ASPNG) ratio of 3:5 was 2.608. A composite film prepared using the lignin nanoparticle / polyvinyl alcohol / chitosan (3LNP / PVA / CH) ternary composite material prepared in Example 10 of prior art CN 113652047B had a WVP of 3.154. Both of these WVP values ​​are significantly higher than those of the SA / TP / LNPs composite film prepared in this invention.

[0104] Food packaging materials should possess good mechanical properties to meet the requirements of food packaging. Mechanical properties are an indispensable parameter for determining the structural integrity of active packaging films. As shown in Table 2, SA films have high elongation at break (EB) and low tensile strength (TS). Compared to SA films alone, the composite film SA / TP has improved tensile strength and reduced elongation at break. The TS of the composite films SA / TP / LNPs-3 and SA / TP / LNPs-5 are significantly higher than those of sodium alginate and other composite films, at 5.33 MPa and 6.44 MPa, respectively.

[0105] 5. Determination of the anti-fogging performance of composite film

[0106] Thermal anti-fogging test: Cover a beaker containing 50℃ water (about 60mL) with a composite membrane and place it in a 50℃ water bath. Observe the fogging on the membrane surface at 0min, 60min and 120min respectively to evaluate its thermal anti-fogging performance.

[0107] Cold anti-fogging test: Cover the beaker with the composite film and place it at -20℃ for 2 hours, then place it at room temperature (25℃) for 30 seconds. Observe the fogging on the film surface and evaluate its cold anti-fogging performance.

[0108] Due to changes in ambient temperature, packaging materials can fog up, causing water molecules to condense and form droplets. This droplet formation can promote microbial growth, thus requiring packaging materials to have excellent anti-fogging properties. Figure 6 As shown, after 60 and 120 minutes of water bath, droplets accumulated on the surface of the PE film, blurring the background text. However, no water droplets formed on the surface of the SA / TP / LNPs composite film, indicating its good hydrophobicity, water absorption, and anti-fogging properties. At the same water bath time, the transparency of the SA / TP / LNPs composite film was higher than that of the SA film. For low-temperature anti-fogging, the PE film surface rapidly fogged upon transfer from -20°C to room temperature. No fog droplets formed on the surface of the composite film, demonstrating better cold fog resistance than the SA film alone.

[0109] Under the same conditions, the antifogging performance of the composite film prepared by the prior art CN 113292753 B with a w(LNP):w(ASPNG) ratio of 3:5 and the composite film prepared by the prior art CN 113652047 B Example 10 with a lignin nanoparticle / polyvinyl alcohol / chitosan (3LNP / PVA / CH) ternary composite material was worse than that of the SA / TP film.

[0110] 6. Determination of the antibacterial properties of the composite membrane

[0111] Immerse an appropriate amount of the composite membrane in liquid culture medium (20 mL), and inoculate with 500 μL of E. coli or S. aureus suspension (10 mL). 8The sample (CFU / mL) was cultured in a constant temperature shaker (150 r / min, 37℃) for 12 h. After diluting to an appropriate concentration, the sample was evenly spread on the culture medium and counted. The inhibition rate was calculated according to formula (4).

[0112]

[0113] Where: N 对照 The number of colonies on the control group plate (in units); N 样品 The number of colonies per plate on which the composite membrane sample group was added.

[0114] The results are as follows Figure 7 As shown, compared with SA film and PE film, SA / TP / LNPs composite film has better antibacterial effect. Among them, composite film SA / TP / LNPs-5 has the best antibacterial efficiency, with an antibacterial rate of 91.28% against S. aureus and 89.20% against E. coli, which is better than composite films SA / TP / LNPs-1 and SA / TP / LNPs-3. Composite film SA / TP / LNPs-5 also has better antibacterial efficiency than SA / TP film.

[0115] 7. Determination of the antioxidant properties of composite films

[0116] To improve the reliability of the experiment, the ABTS and DPPH free radical scavenging rates of the composite membrane were simultaneously determined. 0.1 g of the composite membrane sample was weighed and added to an Erlenmeyer flask containing distilled water. The mixture was magnetically stirred at 25°C (150 r / min) for 24 h until completely dissolved. 1 mL of 1 mmol / L DPPH methanol solution was thoroughly mixed with 3 mL of the composite membrane solution and stored at room temperature in the dark for 30 min for antioxidant activity testing. The absorbance of the mixture was then measured at 517 nm using a UV spectrophotometer. Methanol was used as a blank control for absorbance measurement. The DPPH free radical scavenging rate was calculated according to formula (5).

[0117]

[0118] In the formula: A sample A represents the absorbance of the sample. control The absorbance is for the control group.

[0119] The ABTS cation radical scavenging rate was determined according to the method of Yuan et al. with slight modifications. 1.0 mL of eluent and 2.0 mL of ABTS reaction solution were mixed, with 50% ethanol as a blank control, and reacted at room temperature in the dark for 1 h. The absorbance of the mixed solution at 734 nm was measured using a UV-Vis spectrophotometer. The ABTS cation radical scavenging rate was calculated according to formula (6).

[0120]

[0121] In the formula: A sample A represents the absorbance of the sample. control The absorbance is for the control group.

[0122] The results are as follows Figure 8 As shown in the figure, the SA / TP / LNPs composite membrane has better free radical scavenging ability and total antioxidant capacity than the SA film, SA / TP film and PE film. With the increase of LNPs content in the composite membrane, the free radical scavenging ability and total antioxidant capacity of the composite membrane gradually increase, with the SA / TP / LNPs-5 composite membrane showing the best effect.

[0123] Under the same conditions, the composite membrane prepared by the prior art CN 113292753 B with a w(LNP):w(ASPNG) ratio of 3:5 and the composite membrane prepared by the prior art CN 113652047 B Example 10 with a lignin nanoparticle / polyvinyl alcohol / chitosan (3LNP / PVA / CH) ternary composite material were compared to the composite membrane prepared by the prior art CN 113652047 B. The scavenging rate of the composite membrane was only half that of the SA / TP membrane.

[0124] Example 2

[0125] SA / TP / LNPs composite film application for fresh-cut chili pepper preservation

[0126] 1. Chili pepper sample processing

[0127] Processing of fresh-cut chili peppers: Rinse and dry the chili peppers, then cut them into uniform small pieces and place them in food-grade polypropylene preservation containers. All chili peppers were randomly divided into 5 groups: blank control (CK), PE film, SA film, SA / TP composite film, and SA / TP / LNPs-5 composite film. All chili peppers were stored at room temperature (25±2℃) and humidity (85%-90%) for 10 days. Every 2 days, samples were randomly selected from each group for various index measurements.

[0128] The appearance of freshly cut chili peppers can be observed with the naked eye, and the results are as follows: Figure 9As shown in the figure. During the initial storage period, there was no significant difference in appearance among the samples. From day 8, both the CK and PE groups showed obvious color changes, with the CK group exhibiting partial tissue decay. Without any treatment, the fragile cellular structure of the fresh-cut bell pepper cross-section led to nutrient loss. Simultaneously, the attachment and proliferation of microorganisms further damaged the pepper's internal defense mechanisms, causing a rapid decline in quality during the later stages of storage. By day 10, the quality of the CK and SA groups had further deteriorated, showing more severe decay, while the color change of the fresh-cut peppers in the PE group was more pronounced than in the early stages of storage. Conversely, the SA / TP / LNPs-5 composite film group and the SA / TP group did not show obvious color changes or signs of decay. In conclusion, the SA / TP / LNPs-5 composite film effectively delayed the deterioration of the quality of fresh-cut bell peppers.

[0129] Under the same conditions, the composite film prepared by the prior art CN 113292753 B with a w(LNP):w(ASPNG) ratio of 3:5 and the composite film prepared by the prior art CN 113652047 B Example 10 with a lignin nanoparticle / polyvinyl alcohol / chitosan (3LNP / PVA / CH) ternary composite material showed obvious color changes and signs of decay when tested on fresh-cut chili peppers.

[0130] 2. Determination of weight loss rate

[0131] The weight loss rate is calculated using the following formula.

[0132]

[0133] In the formula: m0 is the initial mass of the chili pepper before treatment, in g; m1 is the mass of the chili pepper after soaking and leaving it for several days, in g.

[0134] During storage, moisture loss due to cutting is considered the main cause of weight loss in fresh-cut chili peppers. For example... Figure 10 As shown, the weight loss rate of all peppers increased with the extension of storage time. On the 6th day of storage, the weight loss rate of peppers in the CK group increased sharply to 33.83%, while the weight loss rate of the PE group was 22.62%. This was significantly different from the weight loss rate of peppers in the SA / TP / LNPs-5 composite film group (13.28%) (P<0.05). On the 10th day of storage, the weight loss rate of the SA / TP / LNPs-5 composite film group was only 16.62%, much lower than that of the CK group, SA / TP group, and PE group. This may be because the film on the surface of the green peppers formed an effective barrier, reducing water loss and respiration, thus maintaining the quality of fresh-cut peppers. At the same time, TP effectively inhibited the adhesion and growth of microorganisms, thereby slowing down the consumption of nutrients.

[0135] 3. Determination of the decay index

[0136]

[0137] Decomposition level assessment:

[0138] Grade 0: No signs of decay;

[0139] Grade 1: Rotten area accounts for 0% to 10% of the total fruit area;

[0140] Grade 2: Rotten area accounts for 10% to 30% of the total fruit area;

[0141] Grade 3: Rotten area accounts for 30% to 50% of the total fruit area;

[0142] Level 4: Rotten area accounts for 50%-100% of the total fruit area.

[0143] Figure 11 The effects of each treatment on the decay index of chili peppers were investigated on the 10th day of storage. The decay index of the control group reached 67.67%, the lowest was 20.67% in the SA / TP / LNPs-5 composite film group, followed by the SA / TP composite film group at 26.33%, and the PE group at 36.32%. The SA / TP / LNPs-5 composite film group showed a decrease of 69.45% and 43.09% compared to the control and PE groups, respectively. This indicates that the SA / TP / LNPs-5 composite film can inhibit the rate of decay and spoilage of chili peppers.

[0144] 4. Determination of soluble solids

[0145] The soluble solids content of the fruit was determined using a PAL-BX / ACID1 saccharimeter. Soluble solids content is expressed as a percentage (%).

[0146] Juice was extracted from chili peppers from different treatment groups and then transferred to 10 mL centrifuge tubes. The tubes were centrifuged at 4 °C and 7000 × g for 5 min. 20 μL of the supernatant was accurately aspirated for analysis.

[0147] like Figure 12As shown, the soluble solids content of fresh-cut peppers in all groups continuously decreased during storage. The cutting process causes mechanical damage to the peppers, increasing their respiration and consuming soluble solids, thus reducing their content. The PE group showed the fastest decline in soluble solids content, decreasing from 6.02% at the beginning of storage to 4.46%, and remained significantly lower than the composite membrane treatment group throughout the storage process. In contrast, the SA / TP / LNPs-5 composite membrane treatment maintained a higher soluble solids content, reaching 4.88% on day 10 of storage, only 18.94% lower than before storage, significantly lower than the CK group's 36.88% and the PE group's 25.91%. The SA / TP composite membrane group also showed a lower soluble solids content compared to the SA / TP / LNPs-5 composite membrane treatment group.

[0148] 5. Determination of Vitamin C Content

[0149] The vitamin C content was determined by titration with 2,6-dichloroindophenol.

[0150] The effects of different packaging methods on the vitamin C content of fresh-cut chili peppers during storage, such as Figure 13 As shown, during storage, the vitamin C content of peppers in the control group (CK) decreased from 63 mg / 100g at the beginning of storage to 30 mg / 100g. PE, SA / TP / LNPs-5, and SA / TP composite films all delayed the decrease in vitamin C in fresh-cut peppers, but their effect was less than that of SA / TP / LNPs-5. On day 10 of storage, the vitamin C content of fresh-cut peppers in the PE group was 41.33 mg / 100g, while the vitamin C content of fresh-cut peppers in the SA / TP / LNPs-5 composite film group was 49.33 mg / 100g. Compared with the CK and PE groups, the vitamin C content increased by 39.19% and 16.22% respectively, showing a significant difference (p < 0.05). This indicates that the self-made composite film containing TP and LNPs can prevent vitamin C oxidation and has good antioxidant capacity.

[0151] 6. Measurement of respiratory intensity

[0152] The respiration intensity of chili peppers was determined using the static method. During the test, the sample was placed in a desiccator with a measured amount of alkaline solution at the bottom. The CO2 released by the respiration of the fruit and vegetables naturally settled and was absorbed by the alkaline solution. After standing for 30 minutes, the alkaline solution was removed, titrated with oxalic acid, and the amount of CO2 released by the sample during respiration was calculated.

[0153]

[0154] Where: molar concentration of C—H2C2O4 solution, mol / L;

[0155] V1—Volume of H2C2O4 used in blank titration, mL;

[0156] V2—Determines the amount of H2C2O4 used in the titration, in mL;

[0157] m—Weight of fruits and vegetables, kg;

[0158] T—Measurement time, h;

[0159] 22—Mass conversion number between NaOH and CO2 during determination.

[0160] like Figure 14 As shown, the respiration rate of the five groups of samples gradually increased throughout the storage period. On day 0 of storage, the respiration rates of the CK group and the treatment group were basically the same. However, on day 4 of storage, the respiration rate of the CK group increased sharply to 23 mg / (kg·h), while the respiration rate of the SA / TP / LNPs-5 group increased slightly to 17.16 mg / (kg·h). On day 10 of storage, compared with the initial storage period, the respiration rate of the CK group increased significantly by 102.44%, and the respiration rate of the SA / TP / LNPs-5 group increased by 52.66%. The results indicate that the SA / TP / LNPs-5 composite membrane has a significant effect on regulating the respiration rate of fresh-cut peppers, leading to a decrease in oxidative metabolism.

[0161] 7. Determination of chlorophyll content

[0162] Take 0.2g of fresh sample in a mortar, add a small amount of quartz sand, 0.2g of calcium carbonate, and 5mL of 95% ethanol, grind into a homogenate, add 95% ethanol and continue grinding until the tissue turns white, let stand for 5 minutes. Pour the extract into a funnel, filter with 95% ethanol into a brown volumetric flask, rinse repeatedly until no green residue remains, and finally make up to 25mL. Using 95% ethanol as a blank, measure the absorbance at wavelengths of 665nm and 649nm.

[0163] The calculation formula is as follows:

[0164]

[0165] In the formula:

[0166] C a —Chlorophyll a concentration at a wavelength of 665 nm;

[0167] C b —Chlorophyll b concentration at a wavelength of 649 nm;

[0168] V—Total volume of sample extract, mL;

[0169] W—Sample weight, g.

[0170] Chlorophyll is the main pigment affecting the color of chili peppers, and changes in pigmentation during storage are related to various factors, including the physiological state of the peppers. For example... Figure 15 As shown, on the 10th day of storage, the chlorophyll content in the SA / TP / LNPs-5 composite membrane group decreased from 0.26 mg / g to 0.17 mg / g, while the chlorophyll content in the CK and PE groups decreased from 0.26 mg / g at the beginning of storage to 0.08 mg / g and 0.12 mg / g, respectively. This is consistent with the color changes of fresh-cut peppers observed in the figure. The SA / TP / LNPs-5 treatment group showed the smallest decrease in chlorophyll content, effectively maintaining the appearance and color of the fresh-cut green pepper slices.

[0171] 8. Determination of malondialdehyde content

[0172] Perform the determination according to the malondialdehyde reagent kit procedure.

[0173] The effect of different packaging methods on the MDA content of fresh-cut chili peppers during preservation, such as Figure 16 As shown in the figure. The results showed that the MDA content of all five groups of samples increased during storage. On day 6 of storage, the malondialdehyde content in the CK group increased sharply (1.26 nmol / g), which was significantly different from the MDA content in the PE group (0.816 nmol / g) and the SA / TP / LNPs composite membrane group (0.59 nmol / g) (p < 0.05). This indicates that the accumulation of free radicals and reactive oxygen species on the cross-section of fresh-cut sweet peppers led to a continuous increase in lipid oxidation of cell membranes. On day 10 of storage, the MDA content of the CK group and the PE group was 1.74 nmol / g and 1.43 nmol / g, respectively, while the MDA content of the SA / TP / LNPs-5 composite membrane group was 0.95 nmol / g. The MDA content of the SA / TP / LNPs-5 group was lower than that of the CK group, the PE group, and the SA / TP group. This indicates that composite film packaging containing LNPs and TP can effectively inhibit the accumulation of MDA in bell peppers during storage and reduce membrane peroxidation damage to bell peppers.

[0174] It should be noted that the above embodiments are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of this invention are still within the scope of protection of this invention.

Claims

1. An application of a fresh-cut chili pepper preservation film in the preservation of fresh-cut chili peppers, characterized in that, The method for preparing the fresh-cut chili pepper preservation film includes the following steps: S1. Preparation of lignin nanoparticles (LNPs): Lignin was dissolved in a solution; then water was added dropwise at a rate of 0.3-1.0 mL / min; the mixture was stirred, and after reacting at room temperature for 1-3 hours, it was allowed to stand and dialyzed to obtain the lignin nanoparticles (LNPs); the solution was H2O. Tetrahydrofuran cosolvent; S2. Preparation of film-forming solution: Sodium alginate is dissolved in water to obtain sodium alginate solution; tea polyphenols and glycerin are added sequentially and mixed evenly to obtain film-forming solution; S3. Preparation of composite film: Add lignin nanoparticles (LNP) to the film-forming solution, mix evenly, pour and dry to obtain fresh-cut chili preservation film. The lignin nanoparticles (LNP) are granular with a particle size of 90-160 nm. In S2, the mass ratio of sodium alginate, tea polyphenols, and glycerol is (1-3):(1-3):(0.5-1.5). In S3, the amount of lignin nanoparticles (LNP) added is 1%-5% of the total mass of sodium alginate and tea polyphenols.

2. The application according to claim 1, characterized in that, In S2, the mass ratio of sodium alginate to tea polyphenols is 1-2:1-2.

3. The application according to claim 1, characterized in that, In S2, the mass ratio of sodium alginate to water is 1-3:90-110.

4. The application according to any one of claims 1-3, characterized in that, In S3, the amount of lignin nanoparticles (LNP) added is 3%-5% of the total mass of sodium alginate and tea polyphenols.

5. The application of a fresh-cut chili pepper preservation film in terms of antibacterial, antioxidant, and UV-resistant properties, characterized in that... The method for preparing the fresh-cut chili pepper preservation film includes the following steps: S1. Preparation of lignin nanoparticles (LNPs): Lignin was dissolved in a solution; then water was added dropwise at a rate of 0.3-1.0 mL / min; the mixture was stirred, and after reacting at room temperature for 1-3 hours, it was allowed to stand and dialyzed to obtain the lignin nanoparticles (LNPs); the solution was H2O. Tetrahydrofuran cosolvent; S2. Preparation of film-forming solution: Sodium alginate is dissolved in water to obtain sodium alginate solution; tea polyphenols and glycerin are added sequentially and mixed evenly to obtain film-forming solution; S3. Preparation of composite film: Add lignin nanoparticles (LNP) to the film-forming solution, mix evenly, pour and dry to obtain fresh-cut chili preservation film. The lignin nanoparticles (LNP) are granular with a particle size of 90-160 nm. In S2, the mass ratio of sodium alginate, tea polyphenols, and glycerol is (1-3):(1-3):(0.5-1.5). In S3, the amount of lignin nanoparticles (LNP) added is 1%-5% of the total mass of sodium alginate and tea polyphenols.

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