Konjac glucomannan emulsion film and preparation method thereof

Abstract

The present invention provides a konjac glucomannan emulsion film and a preparation method thereof. The konjac glucomannan emulsion film comprises the following components: a konjac glucomannan solution, a Pickering emulsion, glycerin, and water. The konjac glucomannan emulsion film prepared by the preparation method can slowly release essential oils while improving the thermal stability and mechanical properties of the film. The composite film not only improves the ability of the konjac glucomannan film to load active substances, but also improves its antioxidant and antibacterial properties. In addition, a raspberry preservation experiment shows that the film prolongs the shelf life of the raspberries by about 6 days, thereby providing a new optional material for the field of food packaging.

Description

Technical Field

[0001] The invention belongs to the technical field of new materials and relates to a konjac glucomannan emulsion film and a preparation method thereof. Background Art

[0002] Konjac glucomannan (KGM) is a high-molecular-weight natural polymer extracted from the tubers of the konjac plant. It is considered a safe and sustainable edible polysaccharide film-forming material. The KGM backbone consists of D-mannose and D-glucose units linked by β-1,4-linked units in a molar ratio of 1.6:1, with side chains linked by β-1,6-glycosyl units. KGM is widely used in food packaging due to its excellent film-forming and biodegradable properties.

[0003] However, conventional food packaging materials in the existing art have poor activity or limited functionality, failing to meet current requirements for active packaging materials. KGM's low mechanical strength and poor bioactivity also limit its further application in areas such as edible or biodegradable packaging and food preservation. On the other hand, existing KGM technology improves the physical, chemical, mechanical, and antimicrobial properties of KGM films by adding natural plant extracts. However, this technology suffers from drawbacks such as uneven essential oil dispersion, rapid release, and high cost. Summary of the Invention

[0004] The purpose of the present invention is to provide a new material and method that can improve the material properties of traditional konjac glucomannan and stably protect the loaded active substance.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] The first aspect of the present invention provides a konjac glucomannan emulsion film, comprising the following components: konjac glucomannan solution, Pickering emulsion, glycerol, and water.

[0007] Preferably, the Pickering emulsion comprises β-cyclodextrin, sodium caseinate, Tween-20, eugenol and water.

[0008] Preferably, in the Pickering emulsion, the eugenol content accounts for 1-10% of the total mass; further preferably, in the Pickering emulsion, the eugenol content accounts for 3-5% of the total mass.

[0009] Preferably, in the Pickering emulsion, the β-cyclodextrin accounts for 0.5%-1%, the sodium caseinate accounts for 0.5-3% of the total mass, and the Tween-20 accounts for 0.5-2% of the total mass; further preferably, the β-cyclodextrin accounts for 0.725%, the sodium caseinate accounts for 2.895% of the total mass, and the Tween-20 accounts for 1.38% of the total mass.

[0010] Preferably, the konjac glucomannan solution accounts for 0.8-2% of the total mass, the glycerol accounts for 0.1-1% of the total mass, and the Pickering emulsion accounts for 0.5-2% of the total mass; further preferably, the konjac glucomannan solution accounts for 1% of the total mass, the glycerol accounts for 0.3% of the total mass, and the Pickering emulsion accounts for 2% of the total mass.

[0011] A second aspect of the present invention provides a method for preparing a konjac glucomannan emulsion film, comprising the following steps:

[0012] S1, stirring konjac glucomannan and water to obtain a mixture A;

[0013] S2, adding the Pickering emulsion to mixture A;

[0014] S3, adding glycerol, and then stirring to obtain a mixture B;

[0015] S4, treating the mixture B at 10000-15000 rpm and room temperature for 8-10 min, and then ultrasonically treating it at 50-60° C. for 2 h to remove bubbles, thereby obtaining a film-forming liquid;

[0016] S5. Pour the membrane-forming liquid completely onto a polytetrafluoroethylene plate and dry it at 50-60°C.

[0017] Preferably, the Pickering emulsion in step S2 is prepared by the following method:

[0018] R1. Add β-cyclodextrin to heated deionized water at 60°C-70°C, stir until β-cyclodextrin is completely dissolved at a stirring speed of 600-800 rpm, and then cool down.

[0019] R2, then add Tween-20 and sodium caseinate pre-mixed in deionized water to the solution in step R1, the deionized water temperature is 45°C-60°C;

[0020] R3. Cool the suspension obtained in step R2 to room temperature, reduce the stirring speed to 200 rpm-400 rpm, and stir for 1 h-3 h.

[0021] R4, reheating the suspension in step R3;

[0022] R5. Add eugenol dropwise to the suspension described in step R4 at a rate of 0.4 μL / min-1 μL / min using a fully automatic syringe pump and continue stirring;

[0023] R6, stirring the solution obtained in step R5 at a speed of 400-800 rpm / min;

[0024] R7, shearing the emulsion obtained in step R6 at a speed of 10000 rpm-20000 rpm by a high-speed shearing device to finally obtain the Pickering emulsion loaded with eugenol;

[0025] Preferably, the eugenol content accounts for 1-10% of the total mass of the Pickering emulsion.

[0026] Preferably, the stirring time in step S1 is no more than 1 hour. If the stirring time is too long, lumps will form.

[0027] Preferably, the preparation method of konjac glucomannan emulsion film comprises the following steps:

[0028] Step 1: Add β-cyclodextrin to heated deionized water at 60°C-70°C, stir until the β-cyclodextrin is completely dissolved at a stirring speed of 600-800 rpm, and then cool to 45°C.

[0029] Step 2: Then, Tween-20 and sodium caseinate pre-mixed in deionized water are added to the solution of step 1, and the deionized water temperature is 45°C-60°C;

[0030] Step 3: Cool the suspension obtained in step 2 to room temperature, reduce the stirring speed to 200 rpm-400 rpm, and stir for 1 h-3 h.

[0031] Step 4: reheat the suspension in step 3 to 45°C.

[0032] Step 5: Add eugenol dropwise into the suspension described in step 4 at a rate of 0.4 μL / min-1 μL / min using a fully automatic syringe pump, and continue stirring for 10 minutes.

[0033] Step 6: Stir the solution obtained in step 5 at a speed of 400-800 rpm / min for 30 min.

[0034] Step 7: The emulsion obtained in step 6 is sheared by a high-speed shearing device at a speed of 10,000 rpm to 20,000 rpm for 8 minutes to finally obtain the Pickering nanoemulsion loaded with eugenol.

[0035] Step 8: Konjac glucomannan and water were stirred at 95°C for 1 hour to obtain a mixture A. The Pickering emulsion obtained in step 7 was added to mixture A in varying proportions, followed by the addition of glycerol, and then stirred for 30-50 minutes to obtain a mixture B. Mixture B was treated with the aforementioned high-speed shear at 10,000-15,000 rpm and room temperature for 8-10 minutes, followed by ultrasonic treatment at 50-60°C for 2 hours to remove bubbles, thereby obtaining a membrane-forming liquid. Finally, the membrane-forming liquid was completely poured onto a polytetrafluoroethylene plate and dried at 50-60°C for 8 hours.

[0036] Compared with the prior art, the present invention has the following advantages:

[0037] 1. The present invention provides a simple, efficient and rapid method for improving the physical and mechanical properties of the Magic Domain Glucomannan film. The required raw materials are common, easily available and low in cost.

[0038] 2. The present invention imparts stronger antibacterial and antioxidant properties to the Magic Domain Glucomannan film by adding eugenol active substances. Compared with adding essential oils, it has fewer impurities, a clearer mechanism, and can achieve a more direct and effective effect.

[0039] 3. In the present invention, eugenol is loaded in Pickering emulsion, which makes the active substance more stable and the loading rate on the film higher, while its biological activity can be better slowly released;

[0040] 4. The film prepared by the present invention can be used to keep fruits fresh and extend the shelf life of fruits. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The initial appearance of the Pickering emulsion after implementation of 1 (A: 1% eugenol-Pickering; B: 3% eugenol-Pickering; C: 5% eugenol-Pickering; D: 10% eugenol-Pickering);

[0042] Figure 2 The Pickering emulsion centrifugal stability test diagram of 1 was implemented;

[0043] Figure 3 The graph of emulsification index change during storage stability of 1 is implemented;

[0044] Figure 4 Schematic diagram of the process for preparing konjac glucomannan emulsion film according to step 2;

[0045] Figure 5 Surface morphology and cross-sectional images (SEM images) of the composite film obtained by implementing 2;

[0046] Figure 6 The mechanical performance diagram of 2 was implemented;

[0047] Figure 7 Thermogravimetric analysis diagram of 2 was implemented;

[0048] Figure 8 Inhibition zones of KGM and Pickering-KGM films implemented for 2 (test bacteria: Staphylococcus aureus);

[0049] Figure 9 The graph shows the weight loss rate and visual appearance changes of raspberries after the implementation of 2 film packaging. DETAILED DESCRIPTION

[0050] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0051] In the following examples, unless otherwise specified, raw materials or processing techniques are conventional commercially available raw materials or conventional processing techniques in the art.

[0052] Example 1 Preparation and Testing of Pickering Emulsion

[0053] Experimental methods

[0054] 1.1. Pickering emulsions of groups 1-4 were prepared. The components and contents of the Pickering emulsions are shown in Table 1 below.

[0055] Table 1 Pickering emulsion components and contents

[0056]

[0057] First, β-CD (0.725%, w / v) was added to deionized water at 70°C and stirred at 800 rpm until completely dissolved, then cooled to 45°C. Subsequently, an aqueous solution of Tween-20 (1.38%, w / v) and SC (2.895%, w / v) pre-mixed at 45°C was added to the β-CD solution. After thorough mixing, the suspension was cooled to room temperature (25°C), the stirring speed was reduced to 200 rpm, and the mixture was stirred for 3 hours. The suspension was then reheated to 45°C. Eugenol (3% / 5% / 10%, w / v) was added dropwise to the suspension at a rate of 0.4 mL / min using an automatic syringe pump, and stirring was continued for 10 minutes. Finally, the mixture was stirred at 800 rpm / min for 30 min, and the emulsion sample was sheared by a high-speed shear for 8 min (the effects of three shear speeds of 3000 rpm, 10000 rpm, and 20000 rpm on the emulsion were investigated). Finally, Pickering nanoemulsions with 1%, 3%, 5%, and 10% eugenol loading were obtained, respectively.

[0058] 1.2. The Pickering emulsions of groups 1-4 were subjected to the following centrifugal stability and storage stability tests:

[0059] Centrifugal stability

[0060] The centrifugal stability of the Pickering emulsions of Groups 1 to 4 was investigated using a centrifuge. The sample (3 mL) in the centrifuge tube was centrifuged at 10,000 rpm for 8 minutes, and the presence or absence of phase separation was recorded.

[0061] Storage stability

[0062] The Pickering emulsions from Groups 1-4 were placed in sealed glass bottles and observed for three months in a controlled environment chamber (-18°C, 5°C, 25°C, 40°C, 50°C, under UV). The stability of the eugenol-loaded Pickering emulsions was first monitored and recorded over time for changes in appearance (e.g., color change, phase separation, etc.). Furthermore, the storage stability of the emulsions can be characterized by the emulsification index (CI, %), which is calculated as follows:

[0063] CI = (v2 / v1) × 100%

[0064] In the formula, v1 and v2 represent the total height of the sample and the height of the emulsion phase (25°C), respectively.

[0065] The mean particle size and distribution of the nanoemulsions (Pickering emulsions loaded with 3%, 5%, and 10% eugenol) were measured using a Zetasizer Nano ZS (Malvern Instruments Ltd., Worcestershire, UK). Samples were diluted to 0.5% aqueous solution to avoid multiple scattering effects during the measurement. The refractive index of water and temperature were set to 1.59 and 25°C, respectively. The average and standard deviation of three measurements were taken. The breadth of the droplet size distribution is represented by the polydispersity index (PDI), which ranges from 0 (monodisperse) to 1 (polydisperse).

[0066] After measuring the average particle size and distribution, the zeta potential value was directly measured using the same capillary cuvette DTS 1070 (Brookhaven Instruments, USA). To avoid the influence of multiple scattering effects, the Pickering emulsion (loaded with 3%, 5%, and 10% eugenol) was diluted to a 0.5% aqueous solution before measurement. The zeta potential was determined by measuring the direction and speed of particle movement in an applied electric field, and the zeta potential value was calculated using the Smoluchowski equation. The average and standard deviation of three measurements are given.

[0067] The stability of Pickering emulsions loaded with varying eugenol contents (1%, 3%, 5%, and 10%) during storage was evaluated by recording changes in appearance. The stability of each Pickering emulsion was recorded and photographed at -18°C, 5°C, 25°C, 40°C, and 50°C under UV light after 0 days and 90 days of storage.

[0068] Experimental results

[0069] like Figure 1 The following are the Pickering emulsions of groups 1-4 prepared in step 1.1. Among them, A: 1% eugenol-Pickering; B: 3% eugenol-Pickering; C: 5% eugenol-Pickering; D: 10% eugenol-Pickering. Figure 1 From the initial appearance of the emulsion, it can be seen that the Pickering emulsion loaded with 1% eugenol is translucent, and the Pickering emulsions loaded with 3%, 5%, and 10% eugenol are milky white.

[0070] Centrifugal stability can reflect the water and oil retention capacity of the Pickering emulsion. Emulsification of the emulsion can be accelerated by centrifugation at 10,000 rpm for 8 minutes. The phase separation of the Pickering emulsions with different eugenol contents (1%, 3%, 5%, 10%) is shown in Figure 2. Figure 2As shown in the figure, A: Initial fresh Pickering emulsion; B: After centrifugation at 10,000 rpm for 8 minutes, from left to right: 1% eugenol-Pickering; 3% eugenol-Pickering; 5% eugenol-Pickering; 10% eugenol-Pickering. It can be seen that the Pickering emulsion loaded with 1% eugenol has the most obvious phase separation, while the Pickering emulsions loaded with 3% and 5% eugenol show almost no phase separation, and the Pickering emulsion loaded with 10% eugenol shows less phase separation.

[0071] like Figure 3-4 As shown, after 90 days under various storage conditions, the Pickering emulsions of groups 1-4 also showed good stability. Specifically, the Pickering emulsion loaded with 1% eugenol showed varying degrees of stratification and severe discoloration under all storage conditions except -18°C, and the oil phase and solid particles leaked out from the interface layer structure. The Pickering emulsions loaded with 3%, 5%, and 10% eugenol had better stability, maintaining a uniform liquid state under various storage conditions and maintaining good stability under UV. However, the color deepened at 40°C and 50°C, which may be related to the sodium caseinate SC in the emulsion. The storage stability of the emulsion can be characterized by the emulsification index (CI, %). Figure 4 It can be clearly seen that after 90 days, the Pickering emulsion index CI of 3%, 5% and 10% eugenol loadings were all 100%, and the Pickering emulsion index CI of 1% eugenol loading was 70.39%. There was no demulsification in the prepared Pickering emulsions, which indicates that the Pickering emulsion stabilized by β-CD has excellent stability.

[0072] In summary, Pickering emulsions loaded with 3%, 5%, and 10% eugenol exhibited stronger centrifugal and storage stability than those loaded with 1%. Therefore, subsequent experiments focused on characterizing the Pickering emulsions loaded with 3%, 5%, and 10% eugenol. The characterization results are shown in Table 2 below.

[0073] Table 2 Particle size, PDI and zeta potential of Pickering emulsions loaded with 3%, 5% and 10% eugenol

[0074]

[0075]

[0076] As can be seen from Table 2, the initial average particle size of the Pickering emulsion with 3% eugenol is 87.94 ± 0.64 nm. As the amount of eugenol increases, the particle size of the Pickering emulsion increases to 101.98 ± 3.92 nm (5% eugenol) and 145.79 ± 1.25 nm (10% eugenol). That is, at the same particle concentration, the particle size of the Pickering emulsion increases with increasing oil content. The corresponding polydispersity index (PDI) is 0.21 ± 0.012, 0.299 ± 0.022, and 0.194 ± 0.03, respectively. The polydispersities of the three are all low, indicating that the prepared nanoemulsions have long-term stability.

[0077] Generally speaking, the greater the absolute value of the emulsion potential, the stronger the electrostatic interaction between particles and the better the emulsion stability. An absolute value of 30 mV is sufficient to maintain droplet stability. The zeta potential of a 3% eugenol Pickering emulsion is -38.61 ± 0.14 mV, that of a 5% eugenol Pickering emulsion is -11.98 ± 6.78 mV, and that of a 10% eugenol Pickering emulsion is -41.68 ± 1.15 mV. In summary, the 3%, 5%, and 10% eugenol Pickering emulsions stabilized by β-CD / SC / T-20 demonstrate stable structures and properties.

[0078] Taking into account the stability of the emulsion and the actual cost, 3% eugenol can be preferably used as the oil phase to prepare the Pickeringr emulsion.

[0079] Example 2 Preparation and Testing of Konjac Glucomannan Emulsion Film

[0080] Experimental methods

[0081] 1.1. Reference Figure 5 The konjac glucomannan emulsion film was prepared according to the process shown in the figure. However, the konjac glucomannan emulsion film prepared in the comparative example did not contain Pickering emulsion.

[0082] A konjac glucomannan solution (1%, w / v) was stirred at 75°C for 1 hour. The 3% eugenol-loaded Pickering emulsion (prepared in step 1) was then added to the konjac glucomannan solution at a 2% concentration to prepare a konjac glucomannan film. 0.3% glycerol (w / w, based on the weight of the konjac glucomannan) was then added and stirred for 30 minutes. The resulting mixture was treated with a high-speed shear at 10,000 rpm and room temperature for 8 minutes, followed by ultrasonic treatment at 60°C for 2 hours to remove bubbles, thereby obtaining a film-forming liquid. Finally, the film-forming liquid was completely cast onto a polytetrafluoroethylene plate and dried at 60°C for 8 hours to obtain a finished film.

[0083] 1.2. Electron microscopy scanning: The experimental group and the control group konjac glucomannan emulsion films prepared in step 1.1 were subjected to electron microscopy scanning.

[0084] 1.3 Thermal Stability Test: The experimental and control konjac glucomannan emulsion films prepared in step 1.1 were tested using a thermogravimetric analyzer (TGA-Q5000, America). The film samples were placed in a sample tray and heated from 30°C to 600°C in a nitrogen atmosphere at a heating rate of 10°C / min and a flow rate of 20 mL / min. A curve showing the change in sample mass with increasing temperature was obtained.

[0085] 1.4 Mechanical properties test: The thickness of the experimental and control konjac glucomannan emulsion films prepared in step 1.1 was measured: a digital micrometer (Mitu toyo Absolute Tester, Japan) was used to measure the average thickness of the film. Five points were randomly selected for testing with a resolution of 0.001 mm. A texture analyzer (TA-XT plus, England) was used to measure the tensile strength (TS, MPa) and elongation at break (EAB, %) of the film. The film was cut into 4*4 cm pieces. The initial clamping distance and speed were 60 mm and 50 mm / s, respectively.

[0086] 1.5. Antioxidant test, (i) The antioxidant capacity of the film samples was measured using the DPPH free radical scavenging assay. 20 mg of the film sample was immersed in 4 mL of DPPH ethanol solution (100 μM), shaken well, and placed in the dark for 1 hour. The absorbance of the film was recorded at 517 nm using a UV-visible spectrophotometer. Finally, the DPPH free radical scavenging activity of the film sample was calculated using the formula. (ii) The PTIO free radical scavenging ability assay was performed according to (Li et al., 2023). 0.5 mL of the sample solution was mixed with 3.5 mL of PTIO solution (0.1 mg / mL) and placed at 37°C for 2 hours. The absorbance at 557 nm was then measured using a UV-visible spectrophotometer.

[0087] 1.6 Antibacterial Activity Test: The antibacterial activity of the films was analyzed using the agar diffusion method. Specifically, after the culture medium solidified, a certain amount of bacterial culture (Staphylococcus aureus and Escherichia coli) was evenly spread on an agar plate. Before biofilm formation, a 6mm diameter film sample was placed in the agar medium and incubated in a biochemical incubator at 37°C for 24 hours.

[0088] 1.7. Raspberry Preservation Test: Six raspberries were placed in a 30 mL airline cup and sealed with pure konjac glucomannan film (Pure-KGM), konjac glucomannan film supplemented with 2% Pickering emulsion (2%-Pickering-KGM), and konjac glucomannan film supplemented with 2% Pickering emulsion and containing an equivalent amount of eugenol (Eugeno-KGM). A blank control group (Blank) and a control group (sealed with plastic wrap) served as comparison. All samples were stored at room temperature (24±1°C) and relative humidity (65±5%). The strawberries' weight loss rate and visual appearance changes were measured every two days for a total of eight measurements.

[0089] Experimental results

[0090] The scanning electron microscopy results are as follows Figure 6 As shown in the figure, the pure konjac glucomannan film in the control group showed a smooth and uniform surface, and its cross-sectional surface was also slightly uniform. However, the addition of Pickering emulsion to the experimental group reduced the smoothness of the film surface, making it rough and uneven, which may be the microscopic reason for enhancing the mechanical strength of the film.

[0091] The thermal properties of the films obtained in the experimental and control groups are shown in Figure 2. Figure 7 As shown in the data, in the range of 150-300 °C, the residual mass of the konjac glucomannan film loaded with eugenol Pickering emulsion was higher than that of the pure konjac glucomannan film, indicating that the addition of the emulsion hindered the thermal degradation and thermal decomposition of the components in the film material, thereby improving the thermal stability of the konjac glucomannan film.

[0092] The mechanical properties of the films prepared in the experimental group and the control group are shown in Table 3. Tensile strength (TS) and elongation at break (EAB) are key parameters for describing the mechanical properties of the films. Adding Pickering emulsion to konjac glucomannan can significantly increase (p < 0.05) the tensile strength (TS) of the film, and the EAB of the film is also significantly increased (p < 0.05). In summary, compared with pure konjac glucomannan, the Pickering-konjac glucomannan film-forming solution has higher mechanical elasticity.

[0093] Table 3 Comparison of mechanical properties

[0094]

[0095] The PTIO and DPPH antioxidant properties of the films are shown in Table 4. The antioxidant activity of the pure KGM film (13.5%) was significantly lower than that of the Pickering-KGM film (p < 0.0001), due to the limited hydrogen supply capacity of the pure KGM film for scavenging free radicals. The pure KGM film also had a weak PTIO radical scavenging ability (only approximately 6.25%). However, with the addition of 2% Pickering to the system, the PTIO radical scavenging ability of the KGM film was significantly enhanced (p < 0.0001), reaching 24%. This indicates that the combination of eugenol-loaded Pickering and KGM can significantly improve the antioxidant capacity of the KGM system.

[0096] Table 4 Comparison of antioxidant properties

[0097]

[0098] The antibacterial results of the films are shown in Table 5 and Figure 8 As shown, the antibacterial activity of Pickering-KGM film against Staphylococcus aureus was evaluated by inhibition zone ( Figure 8 The diameters of the inhibition zones of pure KGM and Pickering-KGM films against Staphylococcus aureus (diluted 104 times) were 8.11 and 15.23 mm, respectively, and there were significant differences in their antibacterial activities (P<0.0001). Pickering-KGM films showed good inhibitory effect against Staphylococcus aureus.

[0099] Table 5 Comparison of antibacterial properties

[0100]

[0101] The weight loss rate and visual appearance changes of raspberries after being packaged with film are as follows: Figure 9 As shown, uncoated raspberries developed noticeable shrinkage and dulling due to water loss on the 7th day. By the 9th day, the rotten fruit rate exceeded 20%, making them inedible. Raspberries covered with plastic wrap began to become severely infested with fungi on the 3rd day. Compared to the konjac glucomannan composite film, plastic wrap has poor water permeability, preventing the release of water produced by respiration. This encloses the raspberries in a high-humidity environment, promoting the growth of fungi and other microorganisms, ultimately leading to the earliest fruit rot. Compared to raspberries covered with 2% Pickering KGM and Eugenol KGM, raspberries covered with Pure KGM showed the earliest signs of spoilage. Raspberries covered with Eugenol KGM developed some fungal infection on the 7th day, while raspberries covered with 2% Pickering KGM showed no fungal infection for the first 13 days.

[0102] All raspberries experienced varying degrees of weight loss after storage began, with the unfilmed raspberries experiencing the highest weight loss (44.32%) and the plastic wrap-covered raspberries experiencing the lowest weight loss (1.68%). This is because raspberries are rich in water, which increases water loss through transpiration and respiration, while plastic wrap provides a strong barrier to evaporative water. The weight loss of raspberries covered with Eugenol-KGM was higher than that of those covered with Pure-KGM and 2%-Pickering-KGM, likely due to the unencapsulated release of eugenol, consistent with the release profile of eugenol from KGM-based films.

[0103] The konjac glucomannan composite film prepared in this experiment can not only effectively isolate dust in the air, but also release eugenol while maintaining the moisture of raspberries, which can effectively inhibit the growth of fungi. This shows that adding eugenol-loaded Pickering emulsion to konjac glucomannan film can extend the shelf life of raspberries by about 6 days.

[0104] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A konjac glucomannan emulsion film, characterized in that: The invention comprises the following components: konjac glucomannan solution, Pickering emulsion, glycerin and water; the Pickering emulsion comprises beta-cyclodextrin, sodium caseinate, Tween-20, eugenol and water; Pickering emulsions were prepared using the following method: R1. Add β-cyclodextrin to heated deionized water at 60°C-70°C, stir until β-cyclodextrin is completely dissolved at a stirring speed of 600-800 rpm, and then cool down. R2, then add Tween-20 and sodium caseinate pre-mixed in deionized water to the solution in step R1, the deionized water temperature is 45°C-60°C; R3, cool the suspension obtained in step R2 to room temperature, reduce the stirring speed to 200 rpm-400 rpm, and stir for 1 h-3 h; R4, reheating the suspension in step R3; R5. Add eugenol dropwise to the suspension described in step R4 at a rate of 0.4 μL / min-1 μL / min using a fully automatic syringe pump and continue stirring; R6, stirring the solution obtained in step R5 at a speed of 400-800 rpm / min; R7. The emulsion obtained in step R6 is sheared by a high-speed shearing device at a speed of 10,000 rpm to 20,000 rpm to finally obtain a Pickering emulsion loaded with eugenol.

2. A konjac glucomannan emulsion film according to claim 1, characterized in that, In the Pickering emulsion, the eugenol content accounts for 1-10% of the total mass.

3. A konjac glucomannan emulsion film according to claim 2, characterized in that, In the Pickering emulsion, the eugenol content accounts for 3-5% of the total mass.

4. A konjac glucomannan emulsion film according to claim 1, characterized in that, In the Pickering emulsion, the beta-cyclodextrin accounts for 0.5%-1%, the sodium caseinate accounts for 0.5-3% of the total mass, and the Tween-20 accounts for 0.5-2% of the total mass.

5. A konjac glucomannan emulsion film according to claim 1, characterized in that, The konjac glucomannan solution accounts for 0.8-2% of the total mass, the glycerol accounts for 0.1-1% of the total mass, and the Pickering emulsion accounts for 0.5-2% of the total mass.

6. A method for preparing a konjac glucomannan emulsion film, characterized in that: The following steps are involved: S1, stirring konjac glucomannan and water to obtain a mixture A; S2, adding the Pickering emulsion to mixture A; S3, adding glycerol, and then stirring to obtain a mixture B; S4, treating the mixture B at 10000-15000 rpm and room temperature for 8-10 min, and then ultrasonically treating it at 50-60° C. for 2 h to remove bubbles, thereby obtaining a film-forming liquid; S5, pouring the film-forming liquid and drying it at 50-60° C.; The Pickering emulsion in step S2 is prepared by the following method: R1. Add β-cyclodextrin to heated deionized water at 60°C-70°C, stir until β-cyclodextrin is completely dissolved at a stirring speed of 600-800 rpm, and then cool down. R2, then add Tween-20 and sodium caseinate pre-mixed in deionized water to the solution in step R1, the deionized water temperature is 45°C-60°C; R3, cool the suspension obtained in step R2 to room temperature, reduce the stirring speed to 200 rpm-400 rpm, and stir for 1 h-3 h; R4, reheating the suspension in step R3; R5. Add eugenol dropwise to the suspension described in step R4 at a rate of 0.4 μL / min-1 μL / min using a fully automatic syringe pump and continue stirring; R6, stirring the solution obtained in step R5 at a speed of 400-800 rpm / min; R7. The emulsion obtained in step R6 is sheared by a high-speed shearing device at a speed of 10,000 rpm to 20,000 rpm to finally obtain a Pickering emulsion loaded with eugenol.

7. The method for preparing a konjac glucomannan emulsion film according to claim 6, wherein The eugenol content accounts for 1-10% of the total mass of the Pickering emulsion.

8. The method for preparing a konjac glucomannan emulsion film according to claim 6, wherein The stirring time in step S1 is no more than 1 h.

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