Preparation method of hydroxypropyl starch auricularia auricula polysaccharide composite film

Abstract

The present invention relates to the technical field of composite film preparation, specifically a preparation method of a hydroxypropyl starch auricularia auricula polysaccharide composite film, which comprises the following steps: Step 1, mix hydroxypropyl starch and auricularia auricula polysaccharide according to a mass ratio of 3:7 to form a compound system of HPS and AAP; Step 2, add 2.0% glycerol as a plasticizer to the compound system and stir evenly; Step 3, cast the compound system solution of HPS and AAP into a film, and obtain the hydroxypropyl starch auricularia auricula polysaccharide composite film after drying. In the preparation method of the hydroxypropyl starch auricularia auricula polysaccharide composite film of the present invention, in the compound system of HPS and AAP, there is an interaction between HPS and AAP molecules, and a good network structure can be formed.

Description

Technical Field

[0001] The present invention relates to the technical field of composite film preparation, and specifically to a method for preparing a hydroxypropyl starch auricularia auricula polysaccharide composite film. Background Art

[0002] With the continuous enhancement of people's environmental protection awareness, the research, development, utilization, and promotion of renewable natural functional polymer materials have received extensive attention and emphasis worldwide. Generally, biopolymers refer to biological macromolecules in natural resources of plants, animals, and microorganisms in nature. Studying how to more reasonably and effectively utilize biopolymer materials is of extremely important significance for scientific and technological progress, ecological environmental protection, and human development.

[0003] Currently, the natural polymers used for processing bio-functional materials mainly fall into two categories: polysaccharides and proteins. Among them, polysaccharides are the most widely used. They are natural high-molecular compounds composed of monosaccharides and are widely present in animals, plants, and microorganisms. They have good biocompatibility, biodegradability, and low toxicity, and have broad application prospects in the fields of biology, medicine, and pharmacy.

[0004] Starch is one of the most abundant polysaccharide natural polymer materials on earth. It is colorless and odorless, a carbohydrate formed by plants through photosynthesis, a high polymer of glucose, and becomes a transparent liquid when heated with water. Due to its wide source, rich reserves, low price, and the fact that it returns to nature in the form of CO2 and H2O after degradation, it is considered a completely pollution-free natural renewable material. Starch is an important industrial product. Especially in the face of the huge pressure brought by the oil crisis and environmental pollution, as a renewable resource, starch is widely used in fields such as textile and paper industries. Among them, modified starch has a wider application range. In addition to traditional fields such as papermaking, food, textiles, adhesives, foaming materials, and water treatment flocculants, it can also be used to prepare biodegradable plastics, drug release carriers, and tissue engineering scaffolds. With the expansion of the use range of starch, people are eager to understand more properties of starch. Therefore, studying the structure, properties, and uses of starch has very broad prospects.

[0005] HPS is a new modified starch prepared by etherification of natural starch and propylene oxide. It is insoluble in cold water and can be gelatinized into a viscous and somewhat transparent colloid under heating conditions. It has good stability and is a generally recognized safe and edible modified starch. Compared with natural starch, it has better rheological properties, requires milder temperature conditions for gelatinization and dissolution, has higher transparency, and the hydroxyl and ether groups on its groups make it more hydrophilic, with good freeze-thaw stability and being relatively stable to acids, alkalis, and electrolytes, etc. It can be widely used as a thickening agent and stabilizer in the food industry such as beverages, jams, meat products, and ice cream. HPS prepared from cassava, which is inexpensive and resource-rich, has a relatively high cost performance. It is resource-rich, inexpensive, degradable, and has no harmful substance residues, and has good emulsifying, thickening, gelling, and water-retaining properties, and is often used as an additive in food to improve the texture of food. However, HPS has poor stability at high temperatures, weak shear resistance, poor acid tolerance, and poor film-forming properties.

[0006] In order to improve the disadvantages of HPS, physical, chemical, and biological methods are used to modify the structure and physicochemical properties of HPS. However, chemical modification will cause a large amount of pollution to the environment and has poor safety, and the cost of biological modification is too high. Physical modification methods are currently the most environmentally friendly, simple, and fast methods. In recent years, adding non-starch polysaccharides to starch to improve the deficiencies of starch has attracted much attention. In the food industry, the utility of starch-gum blends has been widely studied and applied in various fields, especially to improve the viscosity and gel strength of gums through starch supplementation. For example, the incorporation of agar has been shown to improve the properties of various starch-based films. However, the reaction between starch and edible mushroom polysaccharides is less understood, and its research has important application value.

[0007] Auricularia auricula is an important member of Basidiomycetes, one of the world's leading cultivated edible mushrooms, and also a traditional large edible and medicinal fungus widely cultivated in China. Due to its external characteristics such as gel-like, wrinkled surface, and ear-shaped, A. auricula is also known as jelly ear, tree ear, or wood ear. It is worth noting that A. auricula has a long history of being used as a dietary supplement or herbal medicine in Eastern countries. The medicinal value of A. auricula was first recorded in the famous Chinese medical book "Shennong Ben Cao Jing", which records that eating wood ear can relieve symptoms such as high blood pressure, vascular sclerosis, malignant dysentery, menorrhagia, stomach problems, and hemorrhoids. Due to the rapid development of modern analytical techniques, polysaccharides have been identified as one of the key bioactive components of A. auricula. AAP is a high-molecular-weight viscous polysaccharide with functions such as thickening, gelling, emulsifying, and stabilizing, and is a promising thickening agent and gelling agent, etc. The addition of edible mushroom polysaccharides has an important impact on the gelation and digestibility of starch molecules and the physical quality of products. Adding mushroom powder or edible mushroom polysaccharides to starch-containing foods will affect the decomposition, gelation, and re-aggregation of starch granules, and then affect the rheological and physical properties of the food matrix.

[0008] Therefore, in view of the above situation, it is necessary to develop a preparation method of hydroxypropyl starch Auricularia auricula polysaccharide composite film to provide a certain scientific basis for the application of starch and edible mushroom polysaccharide as capsule shell materials. Summary of the Invention

[0009] The purpose of the present invention is to provide a preparation method of hydroxypropyl starch Auricularia auricula polysaccharide composite film to solve the problems raised in the above-mentioned background technology.

[0010] To achieve the above purpose, the present invention provides the following technical solutions:

[0011] A preparation method of hydroxypropyl starch Auricularia auricula polysaccharide composite film includes the following steps:

[0012] Step 1: Mix hydroxypropyl starch and Auricularia auricula polysaccharide according to a mass ratio of (3-4):(6-7) to form a compound system of HPS and AAP;

[0013] Step 2: Add 2.0%-2.5% of glycerol as a plasticizer to the compound system and stir evenly;

[0014] Step 3: Cast the solution of the compound system of HPS and AAP into a film, and obtain the hydroxypropyl starch Auricularia auricula polysaccharide composite film after drying.

[0015] As a further scheme of the present invention: In step 1, the extraction method of the Auricularia auricula polysaccharide includes the following steps:

[0016] S1: Add 120-mesh Auricularia auricula powder to distilled water according to a material-liquid ratio of 1:(50-70), extract in a high-pressure reactor, with a pressure of 0.95-1.05 MPa, a temperature of 108-112 °C, and a time of 55-65 minutes;

[0017] S2: Centrifuge at a speed of 4000 r / min for 20 minutes, and then use the Sevag method to remove proteins from the supernatant;

[0018] S3: After concentration, at 4 °C, precipitate with an ethanol solution four times the volume of the supernatant in step S2 for 12 hours, and then centrifuge at a speed of 4000 r / min for 20 minutes. The precipitate is freeze-dried to obtain Auricularia auricula polysaccharide.

[0019] As a further scheme of the present invention: In step S2, add Sevag reagent to the supernatant and shake for 30 minutes, where the Sevag reagent is a mixed solution of chloroform and n-butanol with a volume ratio of 4:1;

[0020] In step S3, the ethanol solution is a 95% ethanol solution.

[0021] As a further solution of the present invention: in step 1, the preparation method of the compound system of HPS and AAP includes the following steps:

[0022] A1. Weigh 1 g of AAP, dissolve it in distilled water to 100 g, and stir evenly to obtain an AAP solution;

[0023] A2. Weigh 6 g of HPS, dissolve it in distilled water to 100 g, and stir evenly to obtain an HPS solution;

[0024] A3. Weigh the HPS solution and the AAP solution respectively according to the mass ratio of (3-4):(6-7), slowly pour the AAP solution into the HPS solution, and stir while pouring to form a stable gel system.

[0025] As a further solution of the present invention: in steps A1 and A2, the mass concentration of the AAP solution is 1%, and the mass concentration of the HPS solution is 6%.

[0026] As a further solution of the present invention: in step A3, after mixing the HPS solution and the AAP solution, heat it in a water bath at 85 °C for 10 minutes to form a stable gel system.

[0027] As a further solution of the present invention: in step 3, the drying temperature of the composite film is 50 °C - 70 °C, the drying time is 22 - 24 hours, and the drying environment is 20 °C - 30 °C and a humidity of 50% - 75%.

[0028] As a further solution of the present invention: in step 3, the composite film forms a continuous sheet-like combined polymer structure, and the bubble void size decreases; the addition of auricularia auricula polysaccharide in the composite film does not change the crystal form structure of hydroxypropyl starch;

[0029] And the relative crystallinity of the composite film is calculated by the following formula:

[0030] Crystallinity (%) = m1 / (m1 + m2);

[0031] In the formula: m1 is the area of the crystalline region, and m2 is the area of the non-crystalline region.

[0032] As a further solution of the present invention: in step 3, a certain strength of hydrogen bond interaction is formed between the auricularia auricula polysaccharide and the hydroxypropyl starch in the composite film, promoting a more compact and orderly network structure;

[0033] The moisture absorption weight gain rate of the composite film is 8% - 9%, and it is calculated by the following formula:

[0034] Moisture absorption weight gain W (%) = (m1 - m0) / m0 × 100;

[0035] Where: m1 is the weight of the film after moisture absorption (g), and m0 is the initial weight of the film (g);

[0036] And the water vapor permeability WVP of the composite film is calculated by the following formula:

[0037] WVP = Flux / AP0(RH1 - RH2)X;

[0038] Where: Flux is the average mass gain per unit time of the Erlenmeyer flask (g / s), A is the surface area of the film (m 2 ), P0 is the saturated vapor pressure on both sides of the film 3168.74 Pa, (RH1 - RH2) is the humidity difference 0.75, and X is the average thickness of the film (mm).

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. In the HPS and AAP compounding system, there is an interaction between HPS and AAP molecules, and a good network structure can be formed;

[0041] 2. As the concentration of AAP increases, AAP molecules wrap around HPS particles, which leads to the formation of an interfacial layer with opposite charges, increasing the electrostatic repulsion and steric hindrance between droplets and preventing further droplet-droplet aggregation. Therefore, the mixed system can remain stable for a certain period of time;

[0042] 3. When HA - 7 reaches the peak, the addition of AAP solution causes an increase in hydrogen bonds and covalent bonds between the composite systems, promoting the network structure of the polysaccharide to be more compact and dense, thus having stronger tensile strength and greater elasticity. The increase in the EAB value may be due to a plasticizing effect, that is, AAP increases the spacing and fluidity between HPS by alleviating the interaction. The HA - 7 film has the lowest hygroscopicity, probably because of good compatibility and a dense structure;

[0043] The HA - 7 film has the lowest water vapor permeability, can play a good barrier role, and can maintain the quality of the enclosed substance. From the perspective of food coatings and packaging, the acceptability of consumers is greatly affected by the transparency of the film. The higher the transparency, the lower the opacity. The HA - 7 film has good light transmittance;

[0044] 4. The addition of AAP disrupts the crystalline region of starch, inhibiting the rearrangement of amylose. The AAP concentration of HA - 7 accelerates the rearrangement rate of amylose in the composite film and increases the crystallinity;

[0045] 5. The AAP concentration of HA - 7 makes the structure of the composite film regular, forming a network structure with strong order and strong crystallinity;

[0046] 6. The surface of HA-7 is the smoothest. This observation indicates good interaction between HPS and AAP, with a reduced intermolecular distance between molecules, making the structure more compact. This results in a more uniform and stable rigid biopolymer structure, providing optimal compatibility and effectively improving the barrier properties of the film. Description of the Drawings

[0047] Figure 1 Schematic diagram of cryo-electron microscopy in the embodiment of the present invention.

[0048] Figure 2 Schematic diagram of confocal laser scanning microscopy in the embodiment of the present invention.

[0049] Figure 3 Schematic diagram of the water contact angle of the HA-7 film in the embodiment of the present invention.

[0050] Figure 4 Diffraction pattern of the HPS and AAP compound system in the embodiment of the present invention.

[0051] Figure 5 Analysis diagram of differential scanning calorimetry in the embodiment of the present invention.

[0052] Figure 6 Analysis diagram of scanning electron microscopy in the embodiment of the present invention.

[0053] Figure 7 Analysis diagram of Fourier transform infrared spectroscopy in the embodiment of the present invention. Detailed Embodiments

[0054] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0055] The following describes in detail the specific implementation of the present invention with specific embodiments.

[0056] Please refer to Figures 1-7 , a preparation method of a hydroxypropyl starch auricularia auricula polysaccharide composite film provided by an embodiment of the present invention, includes the following steps:

[0057] Step 1: Mix hydroxypropyl starch and auricularia auricula polysaccharide in a mass ratio of (3 - 4):(6 - 7) to form a compound system of HPS and AAP;

[0058] Step 2: Add 2.0% - 2.5% of glycerol as a plasticizer to the compound system and stir evenly;

[0059] Step 3: Cast the composite solution of HPS and AAP into a film, and dry it to obtain the hydroxypropyl starch - auricularia auricula polysaccharide composite film.

[0060] In one embodiment of the present invention, refer to Figures 1-7 , in Step 1, the extraction method of the auricularia auricula polysaccharide (AAP) includes the following steps:

[0061] S1: Add 120 - mesh auricularia auricula powder to distilled water according to a solid - liquid ratio of 1:(50 - 70), extract in a high - pressure reactor, with a pressure of 0.95 - 1.05 MPa, a temperature of 108 - 112 °C, and a time of 55 - 65 minutes;

[0062] S2: Centrifuge at a speed of 4000 r / min for 20 minutes, and then use the Sevag method to remove proteins from the supernatant;

[0063] S3: After concentration, at 4 °C, precipitate with an ethanol solution four times the volume of the supernatant in Step S2 for 12 hours, and then centrifuge at a speed of 4000 r / min for 20 minutes. The precipitate is freeze - dried to obtain the auricularia auricula polysaccharide (AAP).

[0064] In Step S2, add Sevag reagent to the supernatant and shake for 30 minutes. Among them, the Sevag reagent is a mixed solution of chloroform and n - butanol with a volume ratio of 4:1;

[0065] In Step S3, the ethanol solution is a 95% ethanol solution.

[0066] In Step 1, the preparation method of the composite system of HPS and AAP includes the following steps:

[0067] A1: Weigh 1 g of AAP, dissolve it in distilled water to 100 g, and stir evenly to obtain the AAP solution;

[0068] A2: Weigh 6 g of HPS, dissolve it in distilled water to 100 g, and stir evenly to obtain the HPS solution;

[0069] A3: Weigh the HPS solution and the AAP solution according to a mass ratio of (3 - 4):(6 - 7) respectively, slowly pour the AAP solution into the HPS solution, and stir while pouring to form a stable gel system.

[0070] In Step A1 and Step A2, the mass concentration of the AAP solution is 1%, and the mass concentration of the HPS solution is 6%.

[0071] In Step A3, after mixing the HPS solution and the AAP solution, heat it in a water bath at 85 °C for 10 minutes to form a stable gel system.

[0072] In one embodiment of the present invention, refer toFigures 1-7 In step 3, the drying temperature of the composite film is 50°C - 70°C, the drying time is 22 - 24 hours, and the drying environment is 20°C - 30°C and a humidity of 50% - 75%.

[0073] In step 3, the composite film forms a polymer structure with continuous sheet-like binding, and the bubble void size decreases; the addition of Auricularia auricula polysaccharide in the composite film does not change the crystal form structure of hydroxypropyl starch, but disrupts the crystalline region and changes the rearrangement rate of amylose;

[0074] And the relative crystallinity of the composite film is calculated by the following formula:

[0075] Crystallinity (%) = m1 / (m1 + m2);

[0076] In the formula: m1 is the area of the crystalline region, and m2 is the area of the non-crystalline region.

[0077] In step 3, a strong hydrogen bond is formed between Auricularia auricula polysaccharide and hydroxypropyl starch in the composite film, promoting a more compact and ordered network structure;

[0078] The moisture absorption weight gain rate of the composite film is 8% - 9%, and it is calculated by the following formula:

[0079] Moisture absorption weight gain W (%) = (m1 - m0) / m0 × 100;

[0080] In the formula: m1 is the weight of the film after moisture absorption (g), and m0 is the initial weight of the film (g);

[0081] And the water vapor permeability (WVP) of the composite film is calculated by the following formula:

[0082] WVP = Flux / AP0(RH1 - RH2)X;

[0083] In the formula: Flux is the average weight gain mass per unit time of the Erlenmeyer flask (g / s), A is the surface area of the film (m 2 )), P0 is the saturated vapor pressure on both sides of the film 3168.74 Pa, (RH1 - RH2) is the humidity difference 0.75, and X is the average thickness of the film (mm).

[0084] Example 1: A preparation method of hydroxypropyl starch Auricularia auricula polysaccharide composite film is as follows:

[0085] Extraction of Auricularia auricula polysaccharide (AAP): Accurately weigh 5 g of Auricularia auricula powder with 120 mesh, add distilled water according to the solid-liquid ratio of 1:70, extract in a high-pressure reactor at a pressure of 1.0 MPa, a temperature of 110 °C, and a time of 60 min. Centrifuge (4000 r / min, 20 min), and deproteinize the supernatant by the Sevag method (Sevag reagent, V(chloroform):V(n-butyl alcohol)=4:1, shake for 30 min). After concentration, precipitate with 4 times the volume of ethanol at 4 °C for 12 h (95% ethanol solution), centrifuge (4000 r / min, 20 min), and freeze-dry the precipitate to obtain AAP.

[0086] Preparation of the HPS and AAP compound system: Prepare mixed systems with different concentrations. First, weigh 1 g of AAP, dissolve it in distilled water to 100 g, and stir evenly to obtain a black, viscous, and transparent AAP solution with a mass concentration of 1%. Weigh 6 g of HPS, dissolve it in distilled water to 100 g, and stir evenly to obtain a white HPS solution with a mass concentration of 6%. According to Table 1, take different masses of the HPS solution and AAP solution, slowly pour the AAP solution into the HPS solution while stirring, and place it in a water bath at 85 °C for 10 min to obtain a fresh HPS and AAP mixed system. Gelation will occur after a few hours. The ingredient list of the HPS and AAP compound system is as follows:

[0087] Table 1 HPS and AAP compound system table

[0088]

[0089] Texture measurement: Texture measurement was carried out at room temperature using a texture analyzer. The parameters are as follows: P / 36R stainless steel cylindrical probe, pre-test speed and in-test speed of 1.0 mm / s, post-test speed of 10.0 mm / s, compression degree of 30%, trigger force of 5.0 g, and interval of 5 s between two repeated reciprocating motions. Each group of experiments was carried out in parallel three times, and the average value was taken.

[0090] As shown in Table 2, the entanglement between HPS and AAP molecules makes the compound system form an elastic system with better texture, providing a reference basis for product development.

[0091] Table 2 Texture properties of the HPS / AAP compound system

[0092]

[0093] Example 2: Preparation of a composite film with a mass ratio of hydroxypropyl starch to Auricularia auricula polysaccharide of 3:6;

[0094] Step 1: Mix hydroxypropyl starch (HPS) and Auricularia auricula polysaccharide (AAP) according to a mass ratio of 3:6 to form a compound system of HPS and AAP.

[0095] Step 2: Add 2.0% glycerol as a plasticizer to the compounding system and stir evenly.

[0096] Step 3: Cast the compounding system solution of HPS and AAP into a film. The drying temperature is 50 °C, the drying time is 22 hours, and the drying environment is 20 °C and 50% humidity. After drying, a hydroxypropyl starch - auricularia auricula polysaccharide composite film is obtained.

[0097] The composite film prepared in this example has good mechanical properties. However, compared with the composite film with a mass ratio of 3:7, its tensile strength and elastic modulus are slightly lower, and the water vapor transmission rate is slightly higher, indicating that the mass ratio of 3:7 has more advantages in mechanical properties and barrier properties.

[0098] Example 3: Preparation of a composite film with a mass ratio of hydroxypropyl starch to auricularia auricula polysaccharide of 4:7;

[0099] Step 1: Mix hydroxypropyl starch (HPS) and auricularia auricula polysaccharide (AAP) according to a mass ratio of 4:7 to form a compounding system of HPS and AAP.

[0100] Step 2: Add 2.5% glycerol as a plasticizer to the compounding system and stir evenly.

[0101] Step 3: Cast the compounding system solution of HPS and AAP into a film. The drying temperature is 70 °C, the drying time is 24 hours, and the drying environment is 30 °C and 75% humidity. After drying, a hydroxypropyl starch - auricularia auricula polysaccharide composite film is obtained.

[0102] The composite film prepared in this example shows good performance in mechanical properties and barrier properties. However, compared with the composite film with a mass ratio of 3:7, its moisture absorption weight gain rate is slightly higher, and the water vapor transmission rate is slightly larger, indicating that the mass ratio of 3:7 has more superiority in moisture absorption and barrier properties.

[0103] Example 4: Different conditions for the extraction of auricularia auricula polysaccharide;

[0104] Step 1: Add 120 - mesh auricularia auricula powder to distilled water according to a solid - liquid ratio of 1:50, and extract it in a high - pressure reactor. The pressure is 0.95 MPa, the temperature is 108 °C, and the time is 55 minutes.

[0105] Step 2: Centrifuge at a speed of 4000 r / min for 20 minutes, and then use the Sevag method to remove proteins from the supernatant.

[0106] Step 3: After concentration, at 4 °C, precipitate with 95% ethanol solution at four times the volume of the supernatant in step S2 for 12 hours, and then centrifuge at a speed of 4000 r / min for 20 minutes. The precipitate is freeze - dried to obtain auricularia auricula polysaccharide.

[0107] The yield of Auricularia auricula polysaccharide extracted in this example is relatively high. However, compared with the extraction conditions of a material-liquid ratio of 1:70, a pressure of 1.0 MPa, a temperature of 110 °C, and a time of 60 minutes, its polysaccharide purity and molecular weight are slightly lower, indicating that the optimal extraction conditions are more advantageous in terms of polysaccharide quality and yield.

[0108] Example 5: Different conditions for the extraction of Auricularia auricula polysaccharide;

[0109] Step 1: Add Auricularia auricula powder with 120 meshes to distilled water according to a material-liquid ratio of 1:70, and extract in a high-pressure reactor at a pressure of 1.05 MPa, a temperature of 112 °C, and a time of 65 minutes.

[0110] Step 2: After centrifuging at a speed of 4000 r / min for 20 minutes, the supernatant is deproteinized by the Sevag method.

[0111] Step 3: After concentration, at 4 °C, precipitate with 95% ethanol solution at four times the volume of the supernatant in Step S2 for 12 hours, and after centrifuging at a speed of 4000 r / min for 20 minutes, the precipitate is freeze-dried to obtain Auricularia auricula polysaccharide.

[0112] The yield and purity of Auricularia auricula polysaccharide extracted in this example are relatively high. However, compared with the extraction conditions of a material-liquid ratio of 1:70, a pressure of 1.0 MPa, a temperature of 110 °C, and a time of 60 minutes, the molecular weight distribution of its polysaccharide is slightly wider, indicating that the optimal extraction conditions are more advantageous in terms of polysaccharide molecular weight control.

[0113] Example 6: Different conditions for the drying temperature of the composite film;

[0114] Step 1: Mix hydroxypropyl starch (HPS) and Auricularia auricula polysaccharide (AAP) in a mass ratio of 3:7 to form a compound system of HPS and AAP.

[0115] Step 2: Add 2.0% glycerol as a plasticizer to the compound system and stir evenly.

[0116] Step 3: Cast the solution of the compound system of HPS and AAP into a film, with a drying temperature of 60 °C, a drying time of 24 hours, and a drying environment of 25 °C and a humidity of 60%. After drying, a hydroxypropyl starch Auricularia auricula polysaccharide composite film is obtained.

[0117] Under suitable drying conditions, the composite film can form a good network structure and has advantages such as a low water vapor transmission rate and a high tensile strength.

[0118] Example 7: Different conditions for the drying temperature of the composite film;

[0119] Step 1: Mix hydroxypropyl starch (HPS) and Auricularia auricula polysaccharide (AAP) in a mass ratio of 3:7 to form a compound system of HPS and AAP.

[0120] Step 2: Add 2.0% glycerol as a plasticizer to the compounding system and stir evenly.

[0121] Step 3: Cast the compounding system solution of HPS and AAP into a film. The drying temperature is 60 °C, the drying time is 23 hours, and the drying environment is 25 °C and 60% humidity. After drying, a hydroxypropyl starch - auricularia auricula polysaccharide composite film is obtained.

[0122] The composite film prepared in this example shows excellent mechanical properties and barrier properties. However, compared with the conditions of a drying temperature of 60 °C and a drying time of 24 hours, the surface smoothness and crystallinity of the film are slightly lower, indicating that the optimal drying conditions are more advantageous in terms of the structure and properties of the film.

[0123] Example 8: Different conditions of the drying temperature of the composite film

[0124] Step 1: Mix hydroxypropyl starch (HPS) and auricularia auricula polysaccharide (AAP) in a mass ratio of 3:7 to form a compounding system of HPS and AAP.

[0125] Step 2: Add 2.5% glycerol as a plasticizer to the compounding system and stir evenly.

[0126] Step 3: Cast the compounding system solution of HPS and AAP into a film. The drying temperature is 55 °C, the drying time is 22.5 hours, and the drying environment is 22 °C and 65% humidity. After drying, a hydroxypropyl starch - auricularia auricula polysaccharide composite film is obtained.

[0127] The composite film prepared in this example shows good mechanical properties and barrier properties. However, compared with the conditions of a drying temperature of 60 °C and a drying time of 24 hours, its moisture absorption weight gain rate is slightly higher and the water vapor transmission rate is slightly larger, indicating that the optimal drying conditions are more superior in terms of the moisture absorption and barrier properties of the film.

[0128] Example 9: Microstructure;

[0129] Observation by cryo - scanning electron microscope (cryo SEM): The experiment was carried out in a scanning electron microscope equipped with a cryo - transfer device. The compound sample of HPS and AAP was fixed on the sample cup, pre - cooled at - 25 °C, and after the sample was frozen through, it was placed in the sample slot. After vacuum pumping, it was observed and photographed under the electron cryo - microscope. Experimental conditions: voltage value: 5 kV; magnification: 1000 times. As Figure 1 shown, in the compounding system of HPS and AAP, there are interactions between HPS and AAP molecules, and a good network structure can be formed.

[0130] Confocal Laser Scanning Microscope (CLMS): Confocal laser scanning microscope analysis was carried out within 30 min after the preparation of the HPS / AAP hybrid system. Take 1 ml of freshly prepared sample, carefully transfer it to a 1.5 ml centrifuge tube, and mix it well with 30 μl of FITC (fluorescein isothiocyanate) (2 mg / ml, dissolved in DMSO) of starch staining solution and 30 μl of fluorescent brightener 28 (10 mg / ml, dissolved in DMSO) of polysaccharide staining solution. Stain in the dark for 5 min. Place 2 μl of the stained sample on a glass slide, cover it with a coverslip, and seal it with silicone oil around. Place the glass slide on the stage, and observe the sample with a 0-fold objective lens. Select the dual-laser mode to scan the sample (495 nm He / Ne laser and 488 nm Ar laser), and use LAS AF Lite software to collect fluorescence images, and the scanning density is 10 24 ×10 24 . As Figure 2 shown, with the increase in the concentration of AAP, AAP molecules wrap around HPS particles, which will lead to the formation of an interfacial layer with opposite charges, increasing the electrostatic repulsion and steric hindrance between droplets, preventing further droplet-droplet aggregation, so the hybrid system can remain stable within a certain period of time.

[0131] Example 10: Preparation of the hybrid system membrane;

[0132] Take 5 g of mixed solution with different ratios, add 2.0% glycerol, keep it warm at 40 °C in a water bath for half an hour, then pour it into a polyethylene dish to cast a film, the drying temperature is 60 °C, and place it in a constant temperature dryer at 25 °C and humidity (RH) 65% to balance for 24 h after complete drying, and then the performance of the film can be measured.

[0133] Characterization of the hybrid system membrane:

[0134] (1) Mechanical properties - Tensile strength measurement: The mechanical properties of the film were measured using a TA.DHR-1 rheometer from the United States, with the unit of MPa. Cut the film into strips of 1.0 × 7 cm, select the tensile fixture, set the moving speed of the probe to 100 μm / s, and measure the mechanical properties at 25 °C. Randomly select five points, measure the thickness and width of the film with a micrometer and take the average value, the length is automatically read, and the tensile strength result is directly read.

[0135] (2) Transmittance: Cut the prepared HPS / AAP hybrid system membrane into strips of 1 cm × 4 cm in size, then fix it inside the cuvette, and measure it at the visible light λ = 500 nm, using an empty cuvette as a reference to measure the transmittance of the HPS / AAP hybrid system membrane.

[0136] (3)Water vapor permeability: The water vapor permeability of the film was measured by gravimetric analysis. The prepared film was cut into a circle and sealed with wax on the mouth of a conical flask containing 2 g of CaCl2. The internal humidity was 0. The weighed sample bottle was placed in a sealed environment with a humidity of 75% (saturated brine) and stored at a temperature of 25 °C. It was taken out and weighed every 24 h until the numerical change was less than 0.001 g. Three parallel experiments were conducted for each group of samples, and the water vapor permeability WVP of the film was calculated.

[0137] Water vapor permeability (WVP) = Flux / AP0(RH1 - RH2)X (4);

[0138] Where: Flux is the average mass gain per unit time of the Erlenmeyer flask (g / s), A is the surface area of the film (m 2 ), P0 is the saturated vapor pressure on both sides of the film 3168.74 Pa, (RH1 - RH2) is the humidity difference 0.75, and X is the average thickness of the film (mm).

[0139] (4)Moisture absorption weight gain: The prepared film was cut into a 1×1 cm square and placed in a forced-air drying oven. It was dried at 40 °C for 6 h, and the initial mass m0 of the film was weighed. Then it was placed in a sealed environment with a humidity of 75% (saturated brine) and stored. After 12 h, it was taken out and the mass m1 of the film was weighed. The moisture absorption weight gain of the film was calculated according to the following equation.

[0140] Moisture absorption weight gain W (%) = (m1 - m0) / m0×100 (5);

[0141] Where: m1 is the weight of the film after moisture absorption (g), and m0 is the initial weight of the film (g).

[0142] Table III Film Characterization

[0143]

[0144] The peak was reached at HA-7 (hydroxypropyl starch and auricularia auricula polysaccharide in a mass ratio of 3:7, abbreviated as HA-7). The addition of the AAP solution led to an increase in hydrogen bonds and covalent bonds between the composite systems, promoting the network structure of the polysaccharide to be more compact and dense, thus having stronger tensile strength and greater elasticity. The increase in the EAB value may be due to a plasticizing effect, that is, AAP increased the spacing and fluidity between HPS by alleviating the interaction. The HA-7 film had the lowest hygroscopicity, probably because of good compatibility and a dense structure.

[0145] The HA-7 film has the lowest water vapor transmission rate, which can play a good barrier role and maintain the quality of the enclosed substances. From the perspective of food coatings and packaging, the acceptability of consumers is greatly affected by the transparency of the film. The higher the transparency, the lower the opacity, because they are negatively correlated. The HA-7 film has good light transmittance.

[0146] (5) Contact angle analysis: The water contact angle (WCA) of the film is measured using a standard contact angle measuring instrument (OCA50, database). Small droplets are added to a 2 cm x 2 cm thin film. The contact interface is captured at regular intervals. The water contact angle (WCA) of the starch thin film is measured using a contact angle meter (OCA50, Data Physics). Small droplets are added to a 2 cm x 2 cm thin film. The contact interface is captured at regular intervals. As Figure 3 shown, the water contact angle value of the HA-7 film is small, possibly due to the interaction between HPS and AAP, which increases the number of hydroxyl groups on the surface. Smooth surfaces also lead to a reduction in WCA.

[0147] (6) X-ray diffractometer (X-RD): The film is freeze-dried in a vacuum freeze dryer (0.05 MPa, -55 °C), the freeze-dried film is crushed, passed through a 200-mesh sieve, and dried in an oven at 80 °C to constant weight. Take 0.5 g of the film and place it in the groove of a glass slide. Press the sample with a cover glass, pull it forcefully to the side to make the sample form a flat surface without cracks, and wipe off the excess sample. The diffractometer operates at 40 mA and 40 kV, uses Cu-Kα radiation with a wavelength of 0.1542 nm as the X-ray source, sets the parameter scanning range from 2 to 60°, the scanning speed is 4° / min, and the data is analyzed and processed by the supporting software. The relative crystallinity is calculated from the ratio of the peak area of the crystalline region to the total diffraction area.

[0148] Crystallinity (%) = m1 / (m1 + m2) (6);

[0149] Where: m1 is the area of the crystalline region, and m2 is the area of the non-crystalline region.

[0150] As Figure 4 shown, the addition of AAP disrupts the crystalline region of starch and inhibits the rearrangement of amylose. The AAP concentration in HA-7 accelerates the rearrangement rate of amylose in the composite film and increases the crystallinity.

[0151] (7) Differential scanning calorimeter (DSC): The DSC25 differential scanning calorimeter is used to study the thermal properties of the samples. Weigh 5.0 ± 0.2 mg of the film and place it in an alloy dish, cover and seal it. Use an empty alloy dish as a comparison. The heating rate is 10 °C / min, the test range is 20 - 120 °C, N2 gas is used as the protective gas, and the protective gas flow rate is 20 ml / min. Record the thermal difference curve.

[0152] AsFigure 5 As shown, the AAP concentration of HA-7 makes the structure of the composite film regular, forming a network structure with strong order and crystallinity.

[0153] (8) Scanning electron microscopy (SEM) analysis: After sputtering different mixed films with gold, they were scanned using an SSE-550 scanning electron microscope from Shimadzu Corporation of Japan under a vacuum of 0.1 t, and the microscopic morphology of the film surface and cross-section was observed at magnifications of 500 and 6000 times respectively. SEM operating conditions: high voltage 25 kV, beam current 5×10 -9 mA, working distance 15 mm. As Figure 6 shown, the surface of HA-7 is the smoothest. This observation indicates good interaction between HPS and AAP, with the intermolecular distance between molecules decreasing, making the structure more compact. This produces a more uniform and stable rigid biopolymer structure, providing optimal compatibility and effectively improving the barrier properties of the thin film.

[0154] (9) Fourier transform infrared spectroscopy (FT-IR) analysis: An IR RESTIGE-21 Fourier transform infrared spectrometer from Shimadzu Corporation of Japan was used to measure the infrared spectrum of the samples by the potassium bromide tablet method. The frozen film samples were freeze-dried and made into powders, which were then mixed with potassium bromide in a ratio of 1:100, and then ground into a uniform powder in a mortar and pressed into tablets under 9 MPa. The scanning conditions were set as follows: spectral range 400 - 4000 cm -1 scanning times 32 times, resolution 4 cm -1 . Potassium bromide was used as a blank control. The spectral acquisition of each sample was repeated three times under the same conditions.

[0155] As Figure 7 shown, no new peaks were detected in the spectrum, indicating that there is no new covalent interaction between the polysaccharide and starch, mainly hydrogen bond interaction. The peak at 3200 - 3500 cm-1 of HA-7 gradually broadens, and the hydrogen bond interaction gradually strengthens.

[0156] Therefore, based on the actual processing and application requirements of preparing starch films, a comprehensive characterization was carried out on the composite solution and composite film of hydroxypropyl starch and Auricularia auricular polysaccharide. The compound solution is a typical non-Newtonian fluid. As the proportion of AAP increases, the fluidity decreases, the pseudoplasticity weakens, the consistency coefficient decreases, and the apparent viscosity decreases. As the proportion of AAP increases, the hardness and viscosity of its compound system decrease significantly, while the elasticity and cohesiveness increase, indicating that AAP can improve the properties of the HPS solution. When the mixing ratio of hydroxypropyl starch and Auricularia auricular polysaccharide is 3:7, the composite solution presents a polymer combined in a continuous sheet-like form, and the mixed system can remain stable within a certain period of time. An appropriate proportion of AAP can improve the microstructure. When prepared into a composite film, the polysaccharide can form a strong hydrogen bond with the starch, thereby promoting the formation of a more compact and ordered network structure, making it have a lower water vapor transmission rate and a higher tensile strength. The diffraction pattern obtained by XRD analysis shows that the addition of Auricularia auricular polysaccharide does not change its crystal form structure, but disrupts the crystalline region and changes the rearrangement rate of amylose, thus changing its properties. The thermal properties of the composite film show that the addition of an appropriate amount of Auricularia auricular polysaccharide can improve the thermal stability of the composite film. The figure obtained by SEN shows that the addition of Auricularia auricular polysaccharide increases the intermolecular interaction of the film, making the matrix of the film more dense and the surface smooth without cracks. The addition of polysaccharide not only improves the physical and chemical properties of the starch film, but also, as two natural, renewable and biodegradable polymers, the prepared composite film can significantly improve its biodegradability, meet the requirements of green labels, and has the potential significance to replace food and drug packaging materials.

[0157] In summary, the interaction mechanism of the compound system of Auricularia auricular polysaccharide (AAP) and hydroxypropyl starch (HPS) in this invention at different ratios was studied, and the casting method was used to prepare a composite film to prove the influence of this interaction on the macroscopic properties and microstructure of the composite material. As the proportion of Auricularia auricular polysaccharide increases, the texture property results show that its hardness decreases, while the elasticity and cohesiveness increase; the rheological property results show that the fluidity, apparent viscosity and pseudoplasticity weaken. The results of cryo-electron microscopy and confocal microscopy show that an appropriate polysaccharide addition ratio can improve the porous structure of the compound system, and the bubble void size decreases to form a good network structure. The composite film prepared by mixing hydroxypropyl starch and Auricularia auricular polysaccharide at a ratio of 3:7 has a lower water vapor transmission rate and a higher tensile strength. The diffraction pattern obtained by XRD analysis shows that the addition of Auricularia auricular polysaccharide does not change its crystal form structure, but disrupts the crystalline region and changes the rearrangement rate of amylose. The thermal properties of the composite film show that the addition of an appropriate amount of Auricularia auricular polysaccharide can improve the thermal stability of the composite film. The figure obtained by SEN shows that the addition of Auricularia auricular polysaccharide increases the intermolecular interaction of the film, making the matrix of the film more dense and the surface smooth without cracks.

[0158] Taking auricularia auricula polysaccharide and hydroxypropyl starch as the research objects, the interaction mechanism was studied by means of a texture analyzer, a rheometer and an electron scanning microscope, etc. The HPS / AAP composite film was prepared by the casting method, and the effects of different ratios on the physical properties, mechanical properties and microstructure of the composite film were studied. It provides a certain scientific basis for the application of starch and edible mushroom polysaccharide as capsule shell materials.

[0159] It should be noted that in the present invention, it should be understood that although this specification is described according to the embodiments, not each embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a hydroxypropyl starch black fungus polysaccharide composite film, characterized in that: The following steps are involved: Step 1, mixing hydroxypropyl starch (HPS) and black fungus polysaccharide (AAP) according to the solution mass ratio (3-4): (6-7) to form a composite system of HPS and AAP; Step 2: Add 2.0%-2.5% glycerin as a plasticizer to the compound system and stir evenly; Step 3, casting the composite system solution of HPS and AAP into a film, and drying to obtain a hydroxypropyl starch black fungus polysaccharide composite film; In step 1, the method for extracting black fungus polysaccharide comprises the following steps: S1. Add 120 mesh black fungus powder to distilled water at a material-liquid ratio of 1: (50-70), and extract in a high-pressure reactor at a pressure of 0.95-1.05 MPa, a temperature of 108-112°C, and a time of 55-65 minutes; S2, after centrifugation at 4000 r / min for 20 min, the supernatant was deproteinized using the Sevag method; S3, after concentration, at 4°C, using an ethanol solution with a volume four times that of the supernatant in step S2 for alcohol precipitation for 12 hours, and centrifuging at a speed of 4000 r / min for 20 minutes, and then freeze-drying the precipitate to obtain black fungus polysaccharide; In step 1, the preparation method of the composite system of HPS and AAP comprises the following steps: A1. Weigh 1g of AAP, dissolve it into 100g with distilled water, and stir evenly to obtain AAP solution; A2. Weigh 6 g of HPS, dissolve it into 100 g with distilled water, and stir evenly to obtain an HPS solution; A3. Weigh the HPS solution and AAP solution in the mass ratio of (3-4):(6-7), and slowly pour the AAP solution into the HPS solution while stirring to form a stable gel system; In step 3, the composite film is dried at a temperature of 50°C-70°C, for a drying time of 22-24 hours, in a drying environment of 20°C-30°C and a humidity of 50%-75%.

2. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 1, characterized in that: In step S2, Sevag reagent is added to the supernatant and shaken for 30 minutes, wherein the Sevag reagent is a mixed solution of chloroform and n-butanol in a volume ratio of 4:1; In step S3, the ethanol solution is a 95% ethanol solution.

3. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 1, characterized in that: In step A1 and step A2, the mass concentration of the AAP solution is 1%, and the mass concentration of the HPS solution is 6%.

4. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 1, characterized in that: In step A3, after the HPS solution and the AAP solution are mixed, they are heated in a water bath at 85° C. for 10 minutes to form a stable gel system.

5. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 1, characterized in that: In step 3, the composite film will form a polymer structure with continuous sheets and the bubble size will be reduced; the addition of black fungus polysaccharide in the composite film will not change the crystal structure of hydroxypropyl starch; And the relative crystallinity of the composite film was calculated by the following formula: Crystallinity = m1 / m1+m2; Where: m1 is the area of ​​crystalline region, m2 is the area of ​​non-crystalline region, and the unit of crystallinity is %.

6. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 1, characterized in that: In step 3, a certain strength of hydrogen bonding is formed between black fungus polysaccharide and hydroxypropyl starch in the composite film, promoting a more compact and ordered network structure; The moisture absorption weight gain rate of the composite film is 8%-9%, which is calculated by the following formula: Moisture absorption weight gain W = (m1-m0) / m0×100; In the formula: m1 is the weight of the membrane after moisture absorption, the unit of m1 is g, m0 is the initial weight of the membrane, the unit of m0 is g, and the unit of moisture absorption weight gain W is %; The water vapor transmission rate WVP of the composite film is calculated by the following formula: WVP=Flux / AP0(RH1-RH2)X; Where: Flux is the average weight gain of the triangular flask per unit time, the unit of Flux is g / s, A is the surface area of ​​the membrane, the unit of A is m 2 , P0 is the saturated vapor pressure on both sides of the membrane 3168.74Pa, (RH1-RH2) is the humidity difference 0.75, X is the average thickness of the membrane, and the unit of X is mm.

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