1. Use of a luminescent film made mainly of a cellulose derivative which is hydroxypropyl methylcellulose modified with methacrylic acid groups as a food packaging film.

2. Use according to claim 1, wherein the luminescent film has a thickness of 1nm to 5 cm.

3. Use according to claim 1, wherein the cellulose derivative has an average molecular weight of 1000-.

4. Use according to claim 1, characterized in that the method for producing luminescent films from cellulose derivatives comprises the steps of:

dissolving the cellulose derivative in a solvent to obtain a cellulose derivative solution;

transferring the cellulose derivative solution to a substrate surface;

and annealing the substrate with the cellulose derivative solution on the surface under vacuum until the solvent is completely evaporated to obtain the luminescent film.

5. Use according to claim 4, characterized in that the concentration of the cellulose derivative solution is between 0.01% and 20%.

6. Use according to claim 4, characterized in that the annealing conditions are: and keeping the temperature for 10 hours in an environment of 40 ℃.

Background

Food packaging is used to protect food from environmental contamination while preventing the effects of other factors, such as microorganisms, humidity, light, and odor, on the food. The package can prolong the shelf life of the food, ensure the safety and the quality of the food, and further reduce the waste of the food. Until now, many different types of films have been developed for food packaging. In recent years, in order to enhance the functionality of food packaging, some studies have started to use different types of luminescent films as food packaging. In the preparation of such films, it is generally necessary to add luminescent agents (such as metal oxide nanoparticles and fullerene C70), so when they are used as packaging, the luminescent agents may penetrate into the protected food, thereby affecting the taste of the food and even causing food safety problems.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, the present invention aims to provide a luminescent film made of cellulose derivatives as a food packaging film, which aims to solve the problem that luminescent substances in the existing luminescent food packaging film may permeate into the protected food, thereby affecting the taste of the food and even bringing about food safety.

The technical scheme of the invention is as follows:

the application of the luminescent film mainly made of cellulose derivative as food packaging film, the cellulose derivative is hydroxypropyl methyl cellulose modified by methacrylic acid group.

Optionally, the thickness of the luminescent thin film is 1 nm-5 cm.

Alternatively, the cellulose derivative has an average molecular weight of 1000-.

Alternatively, a method of making a luminescent film from a cellulose derivative, comprising the steps of:

dissolving the cellulose derivative in a solvent to obtain a cellulose derivative solution;

transferring the cellulose derivative solution to a substrate surface;

and annealing the substrate with the cellulose derivative solution on the surface under vacuum until the solvent is completely evaporated to obtain the luminescent film.

Optionally, the concentration of the cellulose derivative solution is 0.01% to 20%.

Optionally, the annealing conditions are: and keeping the temperature for 10 hours in an environment of 40 ℃.

Has the advantages that: the invention provides an application of a luminescent film made of a cellulose derivative as a food packaging film. The transparent and flexible film not only has higher mechanical strength, biocompatibility and thermal stability, but also has adjustable permeability and good ultraviolet resistance. More importantly, even if the film is exposed to intense uv radiation, the change in properties is negligible, demonstrating the high durability of CT films. In addition, the film possesses self-indicating capability and is capable of exhibiting a change in luminescence intensity during thawing of the frozen meat product. The characteristics show that the film has the potential of serving as a dual self-indicating food packaging material, the material can not only protect food from being influenced by light, but also maintain the environment in a package through adjustable permeability and wettability, and the purpose of prolonging the shelf life of the packaged food is achieved.

Drawings

In fig. 1, (a) is a picture of (a) F0601, (b) F0605, (c) F0610, (d) F1505, and (e) F5005, with a scale bar of 1 cm; (B) average molecular weights of CT06, CT15, and CT 50; (C) FT-IR spectra of (a) CT06, (b) CT15, (c) CT50, (d) F0605, (e) F1505, and (F) F5005; (D) is a thickness of (a) F0606, (b) F0605, (c) F0610, (d) F1505, and (e) F5005; (E) TG curves for different membranes.

In fig. 2, (a) is a photograph in which different films [ (a) F0601, (b) F0605, (c) F0610, (d) F1505 and (e) F5005] are placed on a printed text, for showing high transparency of the films; (B) UV-Vis transmission spectra for different films; (C) ultraviolet blocking factors of different films; (D) the survival rates of the HepG2 cells after 5 hours of different membrane treatment (a) before treatment and (b) after 24 hours of incubation after treatment. (E) For the change of the relative body weight of mice intraperitoneally injected with dimethyl sulfoxide CT solution, the injection of dimethyl sulfoxide solvent was used as a control group.

Fig. 3 (a) is SEM images of (a) F0601, (b) F0605, (c) F0610, (d) F1505, and (e) F5005; (B) is the contact angle of (a) F0601, (b) F0605, (c) F0610, (d) F1505 and (e) F5005 with water; (C) an average water content of (a) F0601, (b) F0605, (c) F0610, (d) F1505, and (e) F5005; (D) is the weight change of the apple pieces stored in the test tube at 4 ℃; (E) pictures of apple pieces stored in test tubes ((a, g) F0601, (b, h) F0605, (c, i) F0610, (d, j) F1505, (e, k) F5005) and control apple pieces (F, l).

In fig. 4, (a) shows photographs of (a, F) F0601, (b, g) F0605, (c, h) F0610, (d, i) F1505 and (e, j) F5005 under irradiation of (a-e) white light and (F-j) ultraviolet light, wherein the scale bar is 1 cm; (B) PL and PLE spectra for F0605; (C) PL spectra for different films.

FIG. 5 shows (A) photographs (a, d, g) F0601, (b, e, h) F0605 and (c, F, i) F0610 in a dried (a-F) and swollen (g-i) state, and photographs (a-c) under white light and (d-i) ultraviolet light irradiation; (B) PL spectra of the membrane in dry and wet states; (C) a photograph of (a-d) white light and (e-h) uv light exposure of (a-d) fresh chicken breast, (c, g) frozen chicken breast, and (d, h) thawed chicken breast, in a scale of 1cm, made from F0605; (D) is photo of (a-D) chicken breast without package (e-h) with F0605 package, after standing for (a, e)0hr, (b, F) 1hr, (c, g)2hr and (D, h)3hr, the scale bar is 1 cm; (E) the moisture content of the meat changes over time for use and not for use with the F0605 package.

Detailed Description

The present invention provides an application of a luminescent film made of a cellulose derivative as a food packaging film, and the present invention is further described in detail below in order to make the objects, technical solutions and effects of the present invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The existing luminescent film is used as a food packaging film, and a luminescent agent is generally required to be added in the preparation process of the film, so that luminescent substances can permeate into protected food, the taste of the food is further influenced, and even the problem of food safety is brought.

Based on the above, the embodiment of the present invention provides an application of a luminescent film mainly made of a cellulose derivative as a food packaging film, wherein the cellulose derivative is hydroxypropyl methylcellulose modified by methacrylic acid groups. Hereinafter, the methacrylic group-modified hydroxypropylmethylcellulose may be abbreviated as CT.

In the embodiment of the invention, the cellulose derivative is hydroxypropyl methyl cellulose modified by methacrylic acid groups, and the structure of the methacrylic acid groups isModifying modified hydroxypropyl methylcellulose to obtain hydroxypropyl methylcellulose modified by methacrylic acid group.

Hydroxypropyl methyl cellulose (HMPC) is a high molecular compound prepared by cellulose etherification, wherein partial hydroxyl groups are substituted by methoxy groups and/or hydroxypropyl groups, and the hydroxypropyl methyl cellulose modified by methacrylic acid groups is prepared by modifying and modifying the methyl acrylic acid groups, and can drive physical entanglement to form a three-dimensional network structure in a water environment.

It should be noted that the hydroxypropyl methylcellulose modified by methacrylic acid group is the prior art, and other related details and preparation method thereof are disclosed in the patent application publication No. CN 112175204A.

The inventors have surprisingly found that the hydroxypropyl methylcellulose (CT) modified with methacrylic acid groups is capable of emitting light. Although CT has no conjugated structure, the energy gap between polyenic heteroatoms (especially among functional groups such as C ═ O, N ═ O, and C ═ N) narrows down the energy gap between the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO) through steric nonbond interactions, enabling CT to emit light. Because CT self luminous characteristic, and CT is cluster induced emission (CTE), adopt by the film that CT made, the film can give out light, when luminescent film is used for food package, effectively avoided having the problem that the luminous agent of potential toxicity gets into food in the current luminescent film.

In addition, since the intensity of cluster-induced luminescence is affected by molecular entanglement of cellulose derivative molecules, the change in luminescence intensity of the luminescent thin film can be used to indicate the properties of the film itself and the degree of wetting. The embodiment of the invention takes the frozen chicken breast as a food model, and verifies the protection effect and double indication capability of the film on food when the film is used for food packaging.

Furthermore, the luminescent film has a great potential in food packaging, allowing for a high degree of adjustability, negligible toxicity and a certain uv screening effect, allowing for a double indication while effectively achieving versatile protection.

In one embodiment, the thickness of the luminescent film is 1nm to 5 cm.

In one embodiment, the cellulose derivative has an average molecular weight of 1000-.

In one embodiment, a method of making a light emitting film from a cellulose derivative comprises the steps of:

(1) dissolving the cellulose derivative in a solvent (such as ethanol, etc.) to obtain a cellulose derivative solution;

(2) transferring the cellulose derivative solution to a substrate (e.g., glass) surface;

(3) and annealing the substrate with the cellulose derivative solution on the surface under vacuum until the solvent is completely evaporated to obtain the luminescent film.

In the embodiment of the invention, the luminescent film is successfully prepared by adopting a solution film-making method.

In one embodiment, the concentration of the cellulose derivative solution is between 0.01% and 20%.

In one embodiment, the annealing conditions are: and keeping the temperature for 10 hours in an environment of 40 ℃.

The invention is further illustrated by the following specific examples.

The preparation steps of the film of this example are as follows: dissolving a proper amount of CT in ethanol to reach the required concentration to obtain a CT solution; pouring the CT solution into the clean glass surface; the glass sheet was placed in an environment of 40 ℃ and kept under vacuum for 10 hours until the solvent was completely evaporated to obtain a thin film.

The characterization test performed in this example is as follows:

structural characterization: CT and its film structures were characterized using FT-IR spectroscopy, and the reported spectra were the average of 16 scans.

Contact angle measurement: the contact angle of the film was analyzed using a contact angle measuring system, and the measurement was performed using water.

PL characteristics: PL characterisation was performed using FLS920P fluorescence spectrometer, fluorescence spectroscopy was performed at an excitation wavelength of 370nm and PLE spectra were obtained at a fixed emission wavelength of 450 nm.

Ultraviolet-visible spectroscopy: the transmission spectra of the film samples were recorded using a UV-visible spectrophotometer in the 200-700 nm range, and the UV blocking factor was calculated by dividing the average transmission at 400-700 nm by the transmission at 350 nm.

GPC: 100mg of CT06, CT15, or CT50 was dissolved in 10mL of Tetrahydrofuran (THF) which was used as the mobile phase in subsequent GPC analysis and sonicated for 10min to enhance the solubility of CT. During the analysis, the flow rate of the mobile phase was set to 1.0 mL-min^-1. Dissolution detection was performed by a refractive index detector.

And (3) measuring the film thickness: the thickness of the film was measured with a digital micrometer to a precision of 0.001 mm.

Thermogravimetric analysis (TGA): thermogravimetric analysis was performed on different membrane samples using a thermogravimetric analyzer in a nitrogen inert atmosphere at 40 ℃ to 600 ℃. The heating rate was set to 10 ℃ min in all cases^-1。

Scanning Electron Microscopy (SEM) analysis: the samples were first sputter plated with gold and then the microstructure of the film sample cross section was observed with SEM.

Equilibrium Water Content (EWC) evaluation: 0.05g of the film was immersed in 100mL of distilled water. At various time intervals, excess surface moisture was removed from the film by filter paper and the weight of the film sample was measured. This procedure was repeated until no further increase in weight of the sample was observed. The EWC of the sample was calculated using the following equation:

wherein m is_sAnd m_dRespectively representing the mass of the film after water absorption and the mass of the film before water absorption.

Moisture retention evaluation: each ripe Garland apple was cut into 12 pieces of similar weight (8.5. + -. 0.5 g), each piece was placed in a 50 ml centrifuge tube, and a 1.5 cm diameter hole was drilled in the lid. The hole is covered with a film. One of the lid wells was not covered to serve as a control. All tubes were kept at 4. + -.1C. The test tube weight was measured periodically. Three measurements were made each time.

In vitro toxicity evaluation: HepG2 cells were cultured in DMEM supplemented with 10% FBS, 100UI/mL penicillin, 100. mu.g/mL streptomycin and 2mM L-glutamine. 24 hours before assay, cells were seeded separately in 96-well plates at an initial density of 5,000 cells per well at 5% CO₂Incubated at 37 ℃ in a humid atmosphere. At the same time, an appropriate amount of the membrane is ground and resuspended in fresh cell culture medium to obtain a suspension with the desired concentration. The suspension was filtered using a 0.45 μm Polytetrafluoroethylene (PTFE) filter. During the experiment, the culture fluid in each well was replaced with 100 μ L of filtrate and cell viability was determined in each well using the CellTiter 96AQueous nonradioactive cell proliferation assay after 5 hours of incubation at 37 ℃.

In vivo toxicity assessment: in vivo toxicity of CT was evaluated using BALB/c nude mice as a model. F1505 was dissolved in dimethyl sulfoxide to give a 5% (w/v) CT solution. The solution was injected into nude mice in the form of intraperitoneal injection at a dose of 20mg kg-1. Mice were weighed daily.

Evaluation of food packaging performance: the boneless peeled chicken breast was cut uniformly to obtain a similar thickness and a surface area of about 3.5cm²The meat chunk of (1). The meat pieces were placed in bags made from F0601 (dimensions 5cm x 5cm) and stored under ambient conditions. The other meat piece is straightThe samples were then stored under ambient conditions for comparison and weighed periodically.

The characterization test results and analysis of this example are as follows:

1. film formation and structural analysis

CT is a cellulose-based derivative, and the synthetic CT starts from hydroxypropylation and methylation of cellulose, followed by promotion of transesterification by using a polar aprotic solvent as a reaction medium. CT showed its ability to form macroscopically uniform films without creating brittle regions (see a in fig. 1). The average molecular weights of the CT produced by CT06, CT15 and CT50 were estimated to be about 33.9kDa, 45.1kDa and 55.9kDa, respectively, by GPC (see B in FIG. 1). When the CT concentration was increased from 1% (w/v) to 10% (w/v), the thickness of the film was increased from 22.2. + -. 4.5. mu.m to 85.3. + -. 11.4. mu.m, while when the average molecular weight of CT was increased from 33.9kDa to 55.9kDa, the thickness of the film was increased from 71.1. + -. 8.1. mu.m to 117.4. + -. 10.0. mu.m (see D in FIG. 1). The film thickness changes with the CT concentration or average molecular weight, due to the differences in film-forming solution viscosity, which in turn leads to differences in solution spreadability. The higher the concentration or molecular weight of CT, the greater the viscosity of the solution used for film formation, which may result in a decrease in dispersibility of the solution during film formation, resulting in an increase in film thickness.

The CT structure was obtained by FT-IR spectroscopy (see C in FIG. 1). FT-IR spectrum of CT at 1720 cm^-1The peak at (a) is derived from the C ═ O stretching vibration of the methacrylate group. At the same time, at 2800 and 3000cm^-1The detected signal in the wavenumber range in between comes from the C-H stretching vibration. The spectra before and after film formation by CT are not obviously different, which shows that the film formation process has no obvious influence on the structure of CT. Meanwhile, the thermal stability of different film samples was derived by TGA. The TG curves of all samples show that, regardless of the concentration of CT or average molecular weight employed, the film is thermally stable at temperatures around 300 ℃ and thermal decomposition occurs between 300 and 400 ℃, with a significant reduction in weight percent (Δ m — 80.98%) (see E in fig. 1) in this section.

2. Transparency and UV resistance of the film

The opacity of the film is an important factor that affects consumer choice. The UV-vis spectra show that all film samples are optically transparent with a transmission in the visible range (400-700 nm) of about 60-85% (see A-B in FIG. 2). An increase in the CT concentration or molecular weight can result in a decrease in the transmission value in the visible range. It is noted that all film samples showed the ability to absorb UV in both the UVA (320-400 nm, long wavelength radiation) and UVB (280-320 nm, short wavelength radiation) regions with UV blocking factors between 1.05-1.24 (see C in FIG. 2)). Thus, the films of the present embodiments can avoid ultraviolet degradation of food products by significantly reducing or eliminating ultraviolet transmission.

3. Membrane toxicity detection

Food packaging films need to be in direct contact with food, and therefore must ensure low toxicity of the film. This example examined the toxicity of the films in vitro and in vivo. The former uses HepG2 cell as model to detect the cytotoxicity of the membrane. This cell line was chosen for its availability, phenotypic stability and, more importantly, for its multiple genotypic characteristics typical of normal hepatocytes. Therefore, this cell line has been considered as a human hepatocyte substitute for cytotoxicity studies and has been used to test the toxicity of food packaging films. In this example, at all concentrations, the loss of cell viability 5 hours after CT addition was negligible (see D in fig. 2), and therefore, these membranes had low cytotoxicity. To test for potential chronic cytotoxicity, cell viability was tested 24 hours after treatment and the results demonstrated no loss of cell viability. In an in vivo environment, the CT solution did not result in significant weight loss in mice (see E in fig. 2). The above results demonstrate that the food packaging film of this example brings negligible toxicity.

4. Barrier properties of the film

SEM analysis of the membrane cross-section showed that all membranes showed a highly dense microstructure and low porosity regardless of the CT concentration or average molecular weight used during the production of the thin film (see a in fig. 3). Swelling and wettability are two important factors that affect the water resistance of the film. The wettability of the film can be determined by contact angle measurements, which indicate that as the concentration or average molecular weight of CT increases, the wettability of the film decreases (see B in fig. 3), partly because the hydrophobicity of CT increases with increasing molecular weight of CT. Meanwhile, with the increase of the concentration of the film preparation solution, the entanglement degree among CT molecules in the film is increased, and the interaction among the CT molecules is gradually strengthened. The interaction between CT hydrophilic groups and water molecules may be reduced due to competitive binding effects, and thus the membrane wettability decreases as the membrane-making solution concentration increases. In addition, the decrease in membrane wettability is also the reason why its swelling capacity decreases with the increase in CT concentration or average molecular weight (see C in fig. 3).

5. Dual indicating application of food packaging film

All films in this example exhibited varying degrees of luminescence under uv irradiation (see a in fig. 4). This luminescence is attributed to the CTE of CT. Despite the absence of a conjugated structure, the energy gap between the HOMO and LUMO is reduced by steric nonbond interactions between the multiple electron heteroatoms, enabling CT to emit light. The film exhibited a PL peak at about 450nm and a PL excitation (PLE) peak at about 370nm (see B in FIG. 4). The film emission intensity was directly correlated with the concentration of film-formed CT and the molecular weight (see C in FIG. 4). The concentration and molecular weight of the CT not only determine the barrier property and wettability of the film, but also have a positive correlation with the luminescence intensity, so the CT film can indicate its own barrier property.

In addition, the film's luminous intensity significantly decreased when the film swelled (see A-B in FIG. 5), due to the increased volume of the film, the decreased molecular entanglement, and the resulting decrease in CTE intensity during swelling. The membrane of this example has dual self-indicating capability, since the luminescence intensity of the membrane is positively correlated with the CT concentration and molecular weight. To demonstrate the effectiveness of the dual self-indicating ability of the film in food packaging applications, the present example uses chicken breast as a food model to verify the protection and dual indicating ability of the film on food when used in food packaging (see C-E in fig. 5). An early study showed that repeated freezing and thawing had an effect on the eating quality of food products, particularly meat products, and that repeated freezing and thawing could lead to changes in beef color and a decrease in beef tenderness and juice content. Similar research is carried out in the prior art, which detects the influence of freeze-thaw cycles on the edible quality and biochemical characteristics of the catfish fillets and indicates that repeated freeze-thaw cycles can damage cells and hemoproteins, thereby releasing pro-oxidants.

In conclusion, the invention provides the application of the luminescent film made of the cellulose derivative as the food packaging film. The transparent and flexible film not only has higher mechanical strength, biocompatibility and thermal stability, but also has adjustable permeability and good ultraviolet resistance. More importantly, even if the film is exposed to intense uv radiation, the change in properties is negligible, demonstrating the high durability of CT films. In addition, the film possesses self-indicating capability and is capable of exhibiting a change in luminescence intensity during thawing of the frozen meat product. The characteristics show that the film has the potential of serving as a dual self-indicating food packaging material, the material can not only protect food from being influenced by light, but also maintain the environment in a package through adjustable permeability and wettability, and the purpose of prolonging the shelf life of the packaged food is achieved.

It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.