A chitosan blended film loaded with natural small molecular phenolic compounds, and a preparation method and application thereof

Abstract

The application belongs to the technical field of materials, and discloses a chitosan blended film loaded with natural small-molecule phenolic compounds, which comprises the following components: a natural eutectic mixture, 1.0wt% of the natural small-molecule phenolic compounds relative to the mass of the natural eutectic mixture, a 3% acetic acid aqueous solution, and chitosan; wherein the mass ratio of chitosan to the natural eutectic mixture is 9:1-1:5, and the mass ratio of the 3% acetic acid aqueous solution to chitosan is 25:75. The chitosan blended film of the application is obtained by physically blending the natural eutectic mixture, the natural small-molecule phenolic compounds, and chitosan, and then performing flat heat pressing, and the blended chitosan film has the advantages of excellent mechanical properties, good ultraviolet blocking performance, good antibacterial properties, and good antioxidant activity.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, and in particular to a chitosan blend film plasticized from a natural eutectic mixture and loaded with a natural small molecule phenolic compound, its preparation method and application. Background Technology

[0002] Food packaging, as a crucial technological means to slow down the decline in food quality, is trending towards the use of biopolymer materials to reduce the environmental damage caused by synthetic polymer waste. Chitosan, a natural, non-toxic, widely available, biodegradable, and biocompatible polysaccharide, is widely used in biology, pharmaceuticals, medicine, food, and other fields. Utilizing chitosan as a base material to prepare food packaging preservation films shows great promise.

[0003] However, the thin films in the current technology have the following problems:

[0004] First, due to the high rigidity of chitosan molecular chains and the presence of numerous hydrogen bonds formed by hydroxyl and amino groups, the strong intermolecular forces result in single chitosan films exhibiting drawbacks such as high brittleness, poor mechanical properties, and weak ultraviolet blocking performance.

[0005] Secondly, most current research uses solution casting to prepare chitosan films, which is time-consuming and inefficient, hindering the industrialization of chitosan in the food packaging field.

[0006] Third, chitosan, with its excellent film-forming properties and antibacterial properties, is a good active packaging substrate for food packaging materials. However, its low antioxidant properties and narrow antibacterial spectrum limit the application of chitosan alone in food packaging materials.

[0007] Therefore, there is an urgent need to develop a new type of thin film. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a chitosan blend film plasticized from a natural eutectic mixture and loaded with a natural small molecule phenolic compound, as well as its preparation method and application.

[0009] The technical solution adopted by this invention to solve its technical problem is:

[0010] A chitosan blend film loaded with natural small molecule phenolic compounds, comprising the following components:

[0011] A natural eutectic mixture, comprising 1.0 wt% of a natural small molecule phenolic compound, a 3% aqueous solution of acetic acid, and chitosan;

[0012] The mass ratio of chitosan to natural eutectic mixture is 9:1-1:5, and the mass ratio of 3% acetic acid aqueous solution to chitosan is 25:75.

[0013] Further, the natural eutectic mixture is composed of citric acid and betaine in a molar ratio of 1:1; or, the natural eutectic mixture is composed of citric acid and fructose in a molar ratio of 1:1; or, the natural eutectic mixture is composed of citric acid and glycine in a molar ratio of 1:1; or, the natural eutectic mixture is composed of citric acid and xylitol in a molar ratio of 1:1.

[0014] Furthermore, the mass ratio of chitosan to natural eutectic mixture is 9:1, 8:2, 7:3, 6:4 or 5:5.

[0015] Furthermore, the natural small molecule phenolic compounds include ferulic acid, caffeic acid, coumaric acid, kaempferol, catechin, and quercetin; the mass fractions of the natural small molecule phenolic compounds include: 0%, 0.5%, 1.0%, 1.5%, and 2.0%.

[0016] The method for preparing the chitosan blend film as described above includes the following steps:

[0017] A preliminary mixture is prepared by mixing and grinding a natural eutectic mixture and chitosan, followed by heating. A natural small molecule phenolic compound is added to the preliminary mixture, and an acetic acid solution is added and mixed and ground to obtain a final film-forming mixture. The film-forming mixture is shaped using a mold, and the mold is removed before compression molding. A chitosan blend film is prepared by hot pressing.

[0018] Furthermore, the mixing and grinding time is 15 minutes.

[0019] Furthermore, the natural eutectic mixture and chitosan are heated at a temperature of 70°C for 30 minutes.

[0020] Furthermore, the hot pressing is performed using a flatbed hot press at a temperature of 120°C, a pressure of 3 MPa, and a total time of 5 minutes.

[0021] Furthermore, the mold is a circular mold with a diameter of 5cm and a thickness of 2mm.

[0022] The chitosan blend film described above is used in the field of food packaging for its antioxidant and / or antibacterial properties.

[0023] The advantages and positive effects of this invention are as follows:

[0024] 1. The chitosan blend film of the present invention is a chitosan film obtained by physical blending of natural eutectic mixtures, natural small molecule phenols, and chitosan through flat plate hot pressing. This chitosan blend film has advantages such as excellent mechanical properties, good UV blocking performance, and good antibacterial and antioxidant activity. In terms of mechanical properties, the tensile strength of the chitosan film plasticized by the natural eutectic mixture is much higher than that of the single chitosan film, with the highest tensile strength being about 6 times that of the single chitosan film (the highest tensile strength of the single chitosan film in this experiment is 5.5 MPa, which is only compared with the single chitosan film in this experiment); in terms of UV blocking ability, the chitosan blend film plasticized by the natural eutectic mixture (10mm) has a higher tensile strength than the single chitosan film. -1 The opacity of both (left and right) was significantly higher than that of a single chitosan film (6mm). -1 (Approximately 1000-2000 ppm), with good ultraviolet blocking performance.

[0025] 2. The preparation method of chitosan blend film of the present invention solves the problems of long preparation time and low production efficiency of chitosan film preparation by solution casting method, and greatly improves the production efficiency. The hot pressing technology for film preparation adopted in the present invention greatly shortens the preparation time of chitosan film, and also optimizes the film preparation process, reducing the time of solution casting method from several hours or even days to about 1 hour of flat plate hot pressing method, which greatly improves the film preparation efficiency and is conducive to industrialization.

[0026] 3. The potential applications of the chitosan blend film of the present invention in the field of food packaging in terms of anti-oxidation and antibacterial properties: the blending of different types and mass fractions of natural small molecule phenols with chitosan and natural eutectic mixtures improves the antioxidant and antibacterial activities of the chitosan film, solving the problems of low antioxidant properties and narrow antibacterial spectrum when chitosan is used alone in food packaging materials.

[0027] 4. The chitosan blend film of the present invention uses natural small molecule phenolic substances as a mixing component, which are added to the natural eutectic / chitosan blend in a certain proportion to prepare a chitosan blend film loaded with natural small molecule phenolic compounds plasticized by a natural eutectic mixture that has good antibacterial properties and antioxidant activity. This not only solves the problem of narrow antibacterial spectrum of single chitosan, but also improves the antioxidant properties of chitosan film. Attached Figure Description

[0028] Figure 1 The figure shows the effect of different types of natural eutectic mixtures on the mechanical properties and opacity of the chitosan blend film in Example 1.

[0029] Figure 2 The graph shows the effect of different contents of natural eutectic mixtures on the mechanical properties and opacity of the chitosan blend film in Example 2.

[0030] Figure 3 The graph shows the effect of different types of natural small molecule phenols on the antioxidant properties of the chitosan blend film in Example 3.

[0031] Figure 4 The graph shows the effect of different contents of kaempferol on the antioxidant properties of the chitosan blend film in Example 4 in this invention.

[0032] Figure 5 The graph shows the effect of different quercetin contents on the antioxidant properties of the chitosan blend film in Example 4 in this invention.

[0033] Figure 6 This is a growth curve diagram of Escherichia coli and Staphylococcus aureus under the action of different types of natural small molecule phenols and the control group in this invention;

[0034] Figure 7 This is a growth curve of Escherichia coli and Staphylococcus aureus under different contents of kaempferol and the control group in this invention;

[0035] Figure 8 This is a growth curve diagram of Escherichia coli and Staphylococcus aureus under different contents of quercetin and the control group in this invention. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0037] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0038] A chitosan blend film loaded with natural small molecule phenolic compounds, comprising the following components:

[0039] A natural eutectic mixture, comprising 1.0 wt% of a natural small molecule phenolic compound, a 3% aqueous solution of acetic acid, and chitosan;

[0040] The mass ratio of chitosan to natural eutectic mixture is 9:1-1:5, and the mass ratio of 3% acetic acid aqueous solution to chitosan is 25:75.

[0041] Preferably, the natural eutectic mixture is composed of citric acid and betaine in a molar ratio of 1:1; or, the natural eutectic mixture is composed of citric acid and fructose in a molar ratio of 1:1; or, the natural eutectic mixture is composed of citric acid and glycine in a molar ratio of 1:1; or, the natural eutectic mixture is composed of citric acid and xylitol in a molar ratio of 1:1.

[0042] Preferably, the mass ratio of chitosan to natural eutectic mixture is 9:1, 8:2, 7:3, 6:4 or 5:5.

[0043] Preferably, the natural small molecule phenolic compounds include ferulic acid, caffeic acid, coumaric acid, kaempferol, catechin, and quercetin; the mass fractions of the natural small molecule phenolic compounds include: 0%, 0.5%, 1.0%, 1.5%, and 2.0%.

[0044] The method for preparing the chitosan blend film as described above includes the following steps:

[0045] A preliminary mixture is prepared by mixing and grinding a natural eutectic mixture and chitosan, followed by heating. A natural small molecule phenolic compound is added to the preliminary mixture, and an acetic acid solution is added and mixed and ground to obtain a final film-forming mixture. The film-forming mixture is shaped using a mold, and the mold is removed before compression molding. A chitosan blend film is prepared by hot pressing.

[0046] Preferably, the mixing and grinding time is 15 minutes.

[0047] Preferably, the natural eutectic mixture and chitosan are heated at a temperature of 70°C for a time of 30 minutes.

[0048] Preferably, the hot pressing is performed using a flatbed hot press at a temperature of 120°C, a pressure of 3 MPa, and a total time of 5 minutes.

[0049] Preferably, the mold is a circular mold with a diameter of 5cm and a thickness of 2mm.

[0050] The chitosan blend film described above is used in the field of food packaging for its antioxidant and / or antibacterial properties.

[0051] Specifically, the relevant preparation and testing methods are as follows:

[0052] Example 1: Effect of different types of natural eutectic mixtures on the properties of chitosan blend films

[0053] A method for preparing a chitosan blend film loaded with natural small molecule phenolic compounds, the specific steps of which are as follows:

[0054] First, the chitosan was dried in an oven for at least 24 hours before use. The following blend was weighed: 4g chitosan and 1.72g natural eutectic mixture. The mixture was ground for 15 minutes using a pestle and mortar. Then, the ground mixture was placed in a 70°C oven for 30 minutes. Next, the hot powdery paste was removed from the oven, and 12mL of acetic acid aqueous solution (3% w / w) was slowly added, along with 0.06g ferulic acid (1.0wt%). The mixture was then ground for another 15 minutes. Approximately 3g of the above mixture was shaped using a circular mold (5cm diameter, 2mm thickness). Before compression molding, the circular mold was removed, and the chitosan blend film was prepared by hot pressing at 120°C, 3MPa, and 5min using a flatbed hot press. All prepared films were stored in an incubator at 25°C and 50% humidity for at least 48 hours.

[0055] The natural eutectic mixture is composed of: citric acid and betaine in a molar ratio of 1:1; or citric acid and fructose in a molar ratio of 1:1; or citric acid and glycine in a molar ratio of 1:1; or citric acid and xylitol in a molar ratio of 1:1.

[0056] Opacity Measurement: The opacity of the film was measured using a UV-Vis spectrophotometer. The prepared chitosan blend film was cut into rectangles approximately 10×30 mm and placed on one side of the inner wall of a 1 cm cuvette, with a blank cuvette as a control. The absorbance of the film sample was measured at 600 nm using a UV-Vis spectrophotometer. Each experiment was repeated at least three times. The calculation formula is as follows:

[0057]

[0058] In the formula: opacity, mm -1 A represents the absorbance of the chitosan blend film at 600 nm; d represents the thickness of the chitosan blend film, in mm.

[0059] Mechanical strength determination: The mechanical strength determination in this invention includes tensile strength, elongation at break, and Young's modulus. The chitosan blend film is cut into dumbbell-shaped films with a width of 2 mm using a mold. The mechanical properties are determined using a universal testing machine. The film is clamped between clamps with an initial distance of 10 mm, and the tensile speed is 5 mm / min. Each test is repeated at least 5 times. The elastic modulus can be read directly. The formulas for calculating tensile strength and elongation at break are as follows:

[0060]

[0061] In the formula: TS is the tensile strength, MPa; F is the maximum tension when the membrane breaks, N; d is the membrane thickness, mm; W is the membrane width, mm.

[0062]

[0063] Where: EAB is the elongation at break, %; L is the distance between the markings when the membrane breaks, mm; L0 is the original distance between the markings on the membrane, mm.

[0064] Figure 1 This paper presents the effects of different types of natural eutectic mixtures on the mechanical properties and opacity of the chitosan film in Example 1 of this invention. After obtaining the chitosan film, its mechanical properties were characterized using a universal testing machine, and its opacity was characterized using a UV spectrophotometer. Compared to single-component chitosan films, chitosan films plasticized with natural eutectic mixtures exhibited superior mechanical properties. Specifically, the Xyl-plasticized chitosan film demonstrated excellent mechanical properties, with a tensile strength of 33 MPa, an elongation at break of 43%, and an elastic modulus of 780 MPa, exhibiting high tensile strength, elongation at break, and elastic modulus. This may be because, under hot pressing, the natural eutectic mixture enters the chitosan molecular chain, disrupting its crystal structure. The numerous polar groups it contains interact with the hydroxyl and amino groups on the chitosan molecular chain to form hydrogen bonds, increasing intermolecular forces and improving the tensile strength of the film. Furthermore, the electrostatic interactions between molecules and the covalent cross-linking effect imparted by the natural eutectic mixture contribute to the film's toughness and increase its elongation at break. Compared to other plasticizing systems, the Fru-plasticized chitosan film has the lowest tensile strength (18 MPa) and the highest elongation at break (49%), indicating that it exhibits typical elastomer behavior under tension. However, its elastic modulus is the lowest (124 MPa), indicating that the film is easily deformed and does not meet the characteristics of excellent material performance. In addition, higher opacity indicates better light-blocking function. Compared to the opacity of a single chitosan film (6 mm...),... -1 The opacity of chitosan films plasticized from four natural eutectic blends was significantly increased (10 mm). -1 It has good light-blocking properties.

[0065] Wherein: CS: single chitosan film; Beta: chitosan film plasticized with betaine / citric acid; Fru: chitosan film plasticized with fructose / citric acid; Gly: chitosan film plasticized with glycine / citric acid; Xyl: chitosan film plasticized with xylitol / citric acid.

[0066] Example 2: Effect of different contents of natural eutectic mixtures on the properties of chitosan blend films

[0067] A method for preparing a chitosan blend film loaded with natural small molecule phenolic compounds, the specific steps of which are as follows:

[0068] First, the chitosan was dried in an oven for at least 24 hours before use. Weigh out the following blend: 4g chitosan and a natural eutectic mixture (composed of citric acid and xylitol in a 1:1 molar ratio). Grind the natural eutectic / chitosan mixture for 15 minutes using a pestle and mortar. Then, place the ground mixture in a 70°C oven for 30 minutes. Next, remove the hot powdery paste from the oven and slowly add 12mL of an aqueous acetic acid solution (3% w / w), along with 0.06g of ferulic acid (1.0wt%), and mix and grind for 15 minutes. Shape approximately 3g of the above mixture into a circular mold (5cm diameter, 2mm thickness). Before compression molding, remove the circular mold and hot-press the mixture using a flatbed hot press at 120°C, 3MPa, for 5 minutes to prepare the chitosan blend film. All prepared films were stored in an incubator at 25°C and 50% humidity for at least 48 hours.

[0069] The natural eutectic / chitosan mixture comprises chitosan and a natural eutectic mixture in a mass ratio of 9:1, 8:2, 7:3, 6:4, or 5:5.

[0070] The relevant detection methods are the same as in Example 1. Other examples are the same.

[0071] Figure 2 The results show the effect of different contents of natural eutectic mixtures on the mechanical properties and opacity of the chitosan film in Example 2 of this invention. The chitosan film plasticized with 30Xyl exhibits superior mechanical properties, with a measured tensile strength of 31 MPa and an elastic modulus of 780 MPa, demonstrating high tensile strength and elastic modulus. The elongation at break experiment results show that the elongation at break increases with increasing plasticizer content, with the 50Xyl plasticized chitosan film reaching approximately 100%. This indicates that a higher plasticizer content results in more typical elastomer behavior during stretching. However, its low elastic modulus (56 MPa) suggests that the film is easily deformed and does not meet the characteristics of excellent material properties. Therefore, it is considered that 30Xyl has the most significant effect on plasticizing the chitosan film.

[0072] Wherein: 10Xyl: chitosan film plasticized with 10% xylitol / citric acid by mass; 20Xyl: chitosan film plasticized with 20% xylitol / citric acid by mass; 30Xyl: chitosan film plasticized with 30% xylitol / citric acid by mass; 40Xyl: chitosan film plasticized with 40% xylitol / citric acid by mass; 50Xyl: chitosan film plasticized with 50% xylitol / citric acid by mass.

[0073] Example 3: Effects of different types of natural small molecule phenolic compounds on the antioxidant capacity and antibacterial activity of chitosan blend films plasticized from natural eutectic mixtures

[0074] A method for preparing a chitosan blend film loaded with natural small molecule phenolic compounds, the specific steps of which are as follows:

[0075] First, the chitosan was dried in an oven for at least 24 hours before use. Weigh out the following blend: 4g chitosan and 1.72g of a natural eutectic mixture (composed of citric acid and xylitol in a 1:1 molar ratio). Grind the natural eutectic / chitosan mixture for 15 minutes using a pestle and mortar. Then, place the ground mixture in a 70°C oven for 30 minutes. Next, remove the hot powdery paste from the oven and slowly add 12mL of an aqueous acetic acid solution (3% w / w). Simultaneously, add 0.06g of different types of natural small molecule phenols and mix and grind for 15 minutes. Shape approximately 3g of the above mixture into a circular mold (5cm in diameter, 2mm thick). Before compression molding, remove the circular mold and hot-press the mixture using a flatbed hot press at 120°C, 3MPa, and 5min to prepare the chitosan blend film. All prepared films were stored in an incubator at 25°C and 50% humidity for at least 48 hours.

[0076] The natural small molecule phenols include: ferulic acid, caffeic acid, coumaric acid, kaempferol, catechin, and quercetin.

[0077] Antioxidant activity assay:

[0078] 1. DPPH Determination. A 0.1 mM DPPH solution was prepared using 95% ethanol and stored in the dark. Approximately 25 mg of the film sample was placed in 5 mL of 0.1 mM DPPH solution in the dark for 30 min. After 30 min, the film sample was removed, and the absorbance of the DPPH solution at 517 nm was recorded using a UV-Vis spectrophotometer. The DPPH ethanol solution served as a control group. Each experiment was repeated at least three times. The antioxidant activity of the film was calculated as follows:

[0079]

[0080] In the formula: A1 is the absorbance of the sample at 517 nm; A0 is the absorbance of the control at 517 nm.

[0081] 2. ABTS Determination. First, prepare the required ABTS solution. Mix ABTS (7 mM) and potassium persulfate (2.4 mM) solution at a ratio of 1:0.5 (volume ratio, v / v) to prepare the ABTS solution and store it in the dark for 12-16 hours. Then, dilute the ABTS solution with distilled water to achieve an absorbance of 0.70 (±0.10) at 734 nm. Next, place approximately 25 mg of the film sample in 5 mL of the ABTS solution in the dark for 30 min. After 30 min, remove the film sample and record the absorbance of the ABTS solution at 734 nm using a UV-Vis spectrophotometer. Pure ABTS solution serves as the control group. Each experiment is repeated at least three times. The antioxidant activity of the film is calculated as follows:

[0082]

[0083] In the formula: A1 is the absorbance of the sample at 734 nm; A0 is the absorbance of the control at 734 nm.

[0084] 3. Determination of Ferric Ion Reducing Power. Take approximately 100 mg of the film, cut it into small pieces, and soak it in 5 mL of 95% ethanol solution for 12 h. Take 1 mL of the soaking solution and mix it thoroughly with 2.5 mL of phosphate buffer (0.2 M, pH 7.2-7.4) and 2.5 mL of 1% (w / v) potassium ferricyanide. Heat the mixture in a 50℃ water bath for 20 min, then quickly cool it in a cold water bath. Add 2.5 mL of trichloroacetic acid (10%, w / v) and mix thoroughly. Centrifuge for 10 min (10000 x g) to obtain the supernatant. Mix 2.5 mL of the supernatant, 2.5 mL of ultrapure water, and 0.5 mL of 0.1% (w / v) ferric chloride thoroughly. After standing for 10 min, measure the absorbance of the mixed solution at 700 nm using a UV-Vis spectrophotometer. Higher absorbance indicates stronger reducing power.

[0085] Antibacterial Activity Assay: This invention conducted antibacterial experiments on *Escherichia coli* (Gram-negative bacteria) and *Staphylococcus aureus* (Gram-positive bacteria), using a growth curve method to determine the antibacterial properties of different chitosan blend films. A certain amount of the test bacteria (*Escherichia coli* and *Staphylococcus aureus*) was inoculated into sterile liquid culture medium and activated for 24 hours in a shaker at 37°C and 120 rpm. 50 mg of the film sample was weighed and added to 10 ml of sterile liquid culture medium, while 100 μL of the bacterial stock solution was added to the sterile liquid culture medium. The mixture was then incubated in a shaker at 37°C and 200 rpm. After 12 hours of incubation, 200 μL of liquid culture medium was collected every 2 hours, and the absorbance at 600 nm was measured using a UV-Vis spectrophotometer. The average value of the three groups was calculated each time to prepare a growth curve.

[0086] Figure 3 The effects of different types of natural small molecule phenols on the antioxidant properties of the chitosan film in Example 3 of this invention are presented. After the chitosan film was prepared, its antioxidant properties were characterized using DPPH, ABTS, and ferric ion reducing power methods. The results showed that the chitosan film with added KA and QUE exhibited high DPPH scavenging abilities, at 55% and 21%, respectively; the chitosan film with added CAT exhibited high ABTS free radical scavenging ability, reaching 90%; and the chitosan film with added KA and QUE exhibited high ferric ion reducing power, with absorbance values ​​reaching 0.35 and 0.46, respectively. Therefore, the chitosan film with added KA and QUE exhibits relatively comprehensive and excellent antioxidant properties.

[0087] Among them: CT: chitosan film without added natural small molecule phenolic compounds; FA: chitosan film with added 1% (wt) ferulic acid; CA1: chitosan film with added 1% (wt) caffeic acid; CA2: chitosan film with added 1% (wt) coumaric acid; KA: chitosan film with added 1% (wt) kaempferol; CAT: chitosan film with added 1% (wt) catechin; QUE: chitosan film with added 1% (wt) quercetin.

[0088] Example 4: Effects of different contents of natural small molecule phenols on the antioxidant capacity and antibacterial activity of chitosan blend films plasticized from natural eutectic mixtures

[0089] A method for preparing a chitosan blend film loaded with natural small molecule phenolic compounds, the specific steps of which are as follows:

[0090] First, the chitosan was dried in an oven for at least 24 hours before use. Weigh out the following blend: 4g chitosan and 1.72g of a natural eutectic mixture (composed of citric acid and xylitol in a 1:1 molar ratio). Grind the natural eutectic / chitosan mixture for 15 minutes using a pestle and mortar. Then, place the ground mixture in a 70°C oven for 30 minutes. Next, remove the hot powdery paste from the oven and slowly add 12mL of an aqueous acetic acid solution (3% w / w). Simultaneously, add different amounts of natural small molecule phenols and mix and grind for 15 minutes. Shape approximately 3g of the above mixture into a circular mold (5cm in diameter, 2mm thick). Before compression molding, remove the circular mold and hot-press the mixture using a flatbed hot press at 120°C, 3MPa, and 5min to prepare the chitosan blend film. All prepared films were stored in an incubator at 25°C and 50% humidity for at least 48 hours.

[0091] The natural small molecule phenol is either kaempferol or quercetin. The mass fraction of the added natural small molecule phenol is 0%, 0.5%, 1.0%, 1.5%, or 2.0%.

[0092] The relevant detection methods are the same as in Example 3. Other examples are the same.

[0093] Figure 4 The results show the effect of different contents of kaempferol on the antioxidant properties of the chitosan film in Example 4 of this invention. The results indicate that the chitosan film with 2.0% (wt) kaempferol exhibits the best antioxidant performance, with DPPH scavenging capacity reaching 58%, ABTS free radical scavenging capacity reaching 17%, and iron ion reducing capacity reaching 0.35 (absorbance value). All antioxidant performance indicators are the highest values ​​among different contents of kaempferol.

[0094] Figure 5 The results show the effect of different quercetin contents on the antioxidant properties of the chitosan film in Example 4 of this invention. The results indicate that the chitosan film with 2.0% (wt) quercetin content exhibited the best ABTS free radical scavenging ability, reaching 40%, followed by the chitosan film with 1.0% (wt) quercetin content. Chitosan films with 0.5%, 1.0%, and 1.5% (wt) quercetin content showed similar DPPH scavenging abilities, all above 10%. Chitosan films with different quercetin contents showed similar iron ion reducing abilities, with the chitosan film with 2.0% (wt) quercetin content exhibiting a higher iron ion reducing ability, reaching an absorbance of 0.30.

[0095] Figure 6 The growth curves of *Escherichia coli* and *Staphylococcus aureus* under the influence of different types of natural small molecule phenols and the control group are shown. The results indicate that the absorbance values ​​of the growth curves of *E. coli* and *Staphylococcus aureus* on chitosan films with different types of natural small molecule phenols were lower than those of the control group. Specifically, the absorbance value of the *Staphylococcus aureus* growth curve on chitosan films with added kaempferol (approximately 0.60) was significantly lower than that of the control group (approximately 1.10). This demonstrates that the addition of different types of natural small molecule phenols has a significant antibacterial effect.

[0096] Figure 7 The growth curves of *Escherichia coli* and *Staphylococcus aureus* under different concentrations of kaempferol and the control group are shown. The results indicate that the absorbance values ​​of the chitosan films with different kaempferol concentrations for both *E. coli* and *S. aureus* were lower than those in the control group. Specifically, a significant difference was observed in the growth curves of *E. coli* at 10 h, and in the growth curves of *S. aureus* between 6 h and 8 h.

[0097] Figure 8The growth curves of *Escherichia coli* and *Staphylococcus aureus* under different concentrations of quercetin and the control group are shown. The results indicate that the absorbance values ​​of the chitosan films containing different concentrations of quercetin for both *E. coli* and *Staphylococcus aureus* were lower than those of the control group, with significant differences observed between 6 and 12 hours. Specifically, the absorbance value of the chitosan film containing 2.0% (wt) quercetin for *Staphylococcus aureus* (approximately 0.40) was significantly lower than that of the control group (approximately 0.63). Therefore, the chitosan film containing 2.0% (wt) quercetin exhibits a good antibacterial effect against *Staphylococcus aureus*.

[0098] Comparative Example 1

[0099] The raw materials and preparation method are the same as in Example 1, except that the natural eutectic mixture prepared by mixing citric acid with betaine, fructose, glycine, or xylitol is replaced with citric acid and glycerol. The comparative example involved mixing chitosan powder with 10% and 20% citric acid powder (mass ratio, based on chitosan mass). 3 mL of deionized water and 15% glycerol (mass ratio, based on chitosan mass) were added to the powder mixture, and then chitosan films were prepared by hot pressing. The results showed that the chitosan film with 10% citric acid had a tensile strength, elongation at break, and Young's modulus of 8.0 MPa, 16.6%, and 309 MPa, respectively; while the chitosan film with 20% citric acid had a tensile strength, elongation at break, and Young's modulus of 12.8 MPa, 48.1%, and 487 MPa, respectively. [Reference: Crosslinking of chitosan films processed by compression molding]

[0100] Comparative Example 2

[0101] The raw materials and preparation method are the same as in Example 1, except that the natural eutectic mixture prepared by mixing citric acid with betaine, fructose, glycine, or xylitol is replaced by a natural eutectic system prepared by mixing malic acid and betaine in the comparative example. The specific implementation process of the comparative example is as follows: a certain amount of betaine, malic acid, and water are weighed and mixed and stirred at 130°C for 6 hours to obtain a yellow transparent eutectic solvent. The molar ratio of betaine, malic acid, and water is 1:1:2. The above eutectic solvent is mixed with water at a molar ratio of 1:8 and transferred to a stainless steel reactor. Hydrogen gas at 20 bar is introduced into the reactor, and the mixture is stirred thoroughly for 1 hour to allow the hydrogen gas to fully dissolve in the solution, thus preparing a hydrogen-rich antioxidant. The results show that the DPPH free radical scavenging capacity of this antioxidant is 2.39 × 10⁻⁶. -2 mg / mL. [Reference Patent: A hydrogen-rich antioxidant based on a eutectic solvent, preparation method and application, CN112340696A]

[0102] Comparative Example 3

[0103] The raw materials and preparation method are the same as in Example 2, except that the natural eutectic mixture prepared by mixing citric acid and xylitol is replaced by citric acid and choline chloride. The specific implementation process for the comparative example is as follows: Citric acid and choline chloride are mixed in a molar ratio of 1:1 and ball-milled at 600 rpm for 30 min at 50°C to obtain an organic acid-based eutectic solvent. The results show that the chitosan film with added citric acid / choline chloride exhibits weaker UV blocking ability. [Reference Patent: A method for preparing a green biodegradable antibacterial paper with a bioactive coating for fruit cultivation bags, CN114657815A]

[0104] Comparative Example 4

[0105] The raw materials and preparation method are the same as in Example 2, except that the chitosan base is replaced with a gelatin-chitosan composite base. The specific implementation process for the comparative example is as follows: Natural carboxylic acids (lactic acid and acetylsalicylic acid) are added to choline chloride, and a natural eutectic solvent is obtained by heating and stirring. The gelatin solution and chitosan solution are mixed in different proportions to obtain a mixed substrate solution. The natural eutectic solvent is added to the mixed substrate solution in different proportions and stirred until homogeneous to obtain an antibacterial gel solution. The antibacterial gel solution is placed in a substrate (such as a circular petri dish) and dried by heating to obtain an antibacterial gel film. The results show that the antibacterial gel film achieves a DPPH free radical scavenging rate of over 58% and an ABTS free radical scavenging rate of over 32%. [Reference: Patent Publication: A Method for Preparing a Biocompatible Antibacterial Gel Film CN 114949324A]

[0106] As can be seen from Comparative Examples 3, 4 and 2, the natural eutectic mixture prepared by mixing citric acid and xylitol in the chitosan blend film of the present invention has a synergistic effect with chitosan, which can synergistically improve the relevant properties of the prepared chitosan blend film.

[0107] Comparative Example 5

[0108] The raw materials and preparation method are the same as in Example 2, except that the chitosan-based film is replaced with a starch-based film. The comparative example was carried out by mixing a natural eutectic system with a starch-based film at concentrations of 20%, 30%, 40%, 50%, and 60% relative to the dry weight of starch. The results showed that the starch film with a 30% concentration of the natural eutectic system exhibited a higher elongation at break, indicating the plasticizing effect of the natural eutectic system on the starch-based film. [Reference: Naturaldeep eutectic solvent of choline chloride with oxalic or ascorbic acids as efficient starch-based film plasticizers]

[0109] Comparative Example 6

[0110] The raw materials and preparation method were the same as in Example 3, except that ferulic acid or caffeic acid, coumaric acid, kaempferol, catechin, and quercetin were replaced with tannic acid and gallic acid. The results showed that the DPPH scavenging abilities of the chitosan films with added tannic acid and gallic acid were 17% and 56%, respectively. [Reference: The Physicochemical, Antioxidant, and Color Properties of Thin Films Based on Chitosan Modified by Different Phenolic Acids]

[0111] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A chitosan blended film loaded with natural small molecule phenolic compounds, characterized in that: The composition comprises: a natural eutectic mixture, a natural small molecule phenolic compound with a mass of 1.0 wt% of the natural eutectic mixture, a 3% acetic acid aqueous solution, and chitosan; wherein the mass ratio of chitosan to the natural eutectic mixture is 9:1-1:5, and the mass ratio of the 3% acetic acid aqueous solution to chitosan is 25:75; the natural eutectic mixture is a mixture of citric acid and xylitol with a molar ratio of 1:1; the natural small molecule phenolic compound is kaempferol, catechol, or quercetin.

2. The blend film according to claim 1, wherein: The mass ratio of chitosan to the natural eutectic mixture is 9:1, 8:2, 7:3, 6:4, or 5:

5.

3. The method for preparing chitosan blend films as described in claim 1 or 2, characterized in that: The method comprises the following steps: The natural eutectic mixture and chitosan are mixed and ground, and heated to obtain a preliminary mixture; the natural small molecule phenolic compound is added to the preliminary mixture, and an acetic acid solution is added and mixed and ground to obtain a final film-forming mixture; the film-forming mixture is shaped with a mold, and the mold is removed before compression molding; and hot-pressing molding is performed to obtain the chitosan blended film.

4. The method of claim 3, wherein: The mixing and grinding time is 15 min.

5. The method of claim 3, wherein: The temperature for mixing and heating the natural eutectic mixture and chitosan is 70℃, and the heating time is 30 min.

6. The method of claim 3, wherein: The hot-pressing is performed using a flat hot press, at a temperature of 120℃, a pressure of 3 MPa, and a total time of 5 min.

7. The method of claim 3, wherein: The mold is a circular mold with a diameter of 5 cm and a thickness of 2 mm.

8. Use of the chitosan blended film according to claim 1 or 2 in the field of food packaging for antioxidant and / or antibacterial purposes.

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