Preparation method of hydroxypropyl starch and auricularia auricula polysaccharide composite membrane

Abstract

The invention relates to the technical field of preparation of composite membranes, in particular to a preparation method of a hydroxypropyl starch and auricularia auricula polysaccharide composite membrane, which comprises the following steps: step 1, mixing 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, adding 2.0% of glycerol into the compounded system as a plasticizer, and uniformly stirring; 3, the compound system solution of the HPS and the AAP is subjected to film casting and drying, and then the hydroxypropyl starch and auricularia auricula-judae polysaccharide composite film is obtained.According to the preparation method of the hydroxypropyl starch and auricularia auricula-judae polysaccharide composite film, in the compound system of the HPS and the AAP, interaction exists between HPS molecules and AAP molecules, and a good network structure can be formed.

Description

Technical Field

[0001] The invention relates to the technical field of composite film preparation, in particular to a method for preparing a hydroxypropyl starch and black fungus polysaccharide composite film. Background Art

[0002] As people's environmental awareness continues to increase, the research, development, utilization and promotion of renewable natural functional polymer materials have received widespread attention and attention worldwide. Generally, biopolymers refer to biological macromolecules in plants, animals and microbial resources in nature. Research on how to use biopolymer materials more reasonably and effectively is of great significance to scientific and technological progress, ecological environmental protection and human development.

[0003] At present, there are two main categories of natural polymers used to process biofunctional materials: polysaccharides and proteins. Among them, polysaccharides are the most widely used. They are natural polymer compounds composed of monosaccharides, widely present in animals, plants and microorganisms, with good biocompatibility, degradability and low toxicity, and have broad application prospects in the fields of biology, medicine and pharmacy.

[0004] Starch is one of the most abundant natural polymer materials of polysaccharides on the earth. It is colorless and tasteless. It is a carbohydrate formed by photosynthesis of plants, a polymer of glucose, and becomes a transparent liquid when it comes into contact with water and is heated. Due to its wide source, abundant reserves, low price, and return to nature in the form of CO2 and H20 after degradation, it is considered to be 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 materials, textiles and papermaking industries. Among them, the application range of modified starch is more extensive. In addition to being used in 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 scope of starch use, people are eager to understand more properties of starch. Therefore, studying the structure, properties and uses of starch has a very broad prospect.

[0005] HPS is a new modified starch made by etherification of natural starch and propylene oxide. It is insoluble in cold water and can be gelatinized into a viscous colloid with a certain degree of transparency under heating conditions. It has good stability and is a universally recognized safe and edible modified starch. Compared with natural starch, it has good rheological properties, milder temperature conditions required for gelatinization and dissolution, higher transparency, and hydroxyl and ether groups on the groups make it more hydrophilic, with good freeze-thaw stability. It is relatively stable to acids, alkalis and electrolytes, and can be widely used as a thickener and stability in food industries such as beverages, jams, meat products and ice cream. HPS prepared from cassava, which is cheap and abundant in resources, has a high cost-effectiveness. It is abundant in resources, cheap and easy to obtain, degradable, and has no harmful substance residues. It has good emulsification, thickening, gelling and water retention 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 shortcomings of HPS, physical, chemical and biological methods are used to modify the structure and physicochemical properties of HPS. However, chemical modification will cause a lot of pollution to the environment and has poor safety. The cost of biological modification is too high. Physical modification is currently the most economical, environmentally friendly, simple and fast method. In recent years, adding non-starch polysaccharides to starch to improve the shortcomings of starch has attracted much attention. In the food industry, the effectiveness of starch-gum blends has been widely studied and applied in various fields, especially by starch supplementation to increase the viscosity and gel strength of gum. For example, the incorporation of agar has been shown to improve the performance of various starch-based films. However, the reaction between starch and edible fungus polysaccharides is less understood, and its research has important application value.

[0007] Black fungus (A. auricula) is an important member of the basidiomycetes and one of the world's leading cultivated edible fungi. It is also a traditional edible and medicinal macrofungus widely cultivated in my country. Due to its external characteristics, such as gelatinous, wrinkled and ear-like, black fungus is also called jelly ear, tree ear or wood ear. It is worth noting that black fungus has a long history of being used as a dietary supplement or herbal medicine in Eastern countries. The medicinal value of black fungus was first recorded in the Chinese famous doctor Shennong's Herbal Classic, which records that eating black fungus can relieve symptoms such as hypertension, vascular sclerosis, malignant dysentery, menorrhagia, gastric disease and hemorrhoids. Due to the rapid development of modern analytical techniques, polysaccharides have been identified as one of the key bioactive components of black fungus. AAP is a high-molecular-weight viscous polysaccharide with thickening, gelling, emulsification and stabilization functions. It is a promising thickener and gelling agent. The addition of edible fungus polysaccharides has an important influence on the gelation and digestibility of starch molecules and the physical quality of the product. Adding mushroom powder or edible fungus polysaccharides to starch-containing foods can affect the decomposition, gelation, and reaggregation 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 method for preparing a hydroxypropyl starch and black fungus polysaccharide composite film to provide a certain scientific basis for the application of starch and edible fungus polysaccharide capsule shell materials. Summary of the invention

[0009] The object of the present invention is to provide a method for preparing a hydroxypropyl starch-black fungus polysaccharide composite film to solve the problems raised in the above background technology.

[0010] To achieve the above object, the present invention provides the following technical solutions: A method for preparing a hydroxypropyl starch black fungus polysaccharide composite film comprises the following steps: Step 1, mixing hydroxypropyl starch and black fungus polysaccharide in a mass ratio of (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.

[0011] As a further solution of the present invention: 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, the supernatant in step S2 is precipitated with an ethanol solution having a volume four times that of the supernatant at 4°C for 12 hours, and centrifuged at 4000 r / min for 20 minutes. The precipitate is freeze-dried to obtain black fungus polysaccharide.

[0012] As a further solution of the present invention: 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.

[0013] As a further solution of the present invention: 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 to 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) respectively, and slowly pour the AAP solution into the HPS solution while stirring to form a stable gel system.

[0014] As a further solution of the present invention: 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%.

[0015] As a further solution of the present invention: in step A3, the HPS solution and the AAP solution are mixed and then heated in a water bath at 85° C. for 10 minutes to form a stable gel system.

[0016] 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, the drying environment is 20°C-30°C and the humidity is 50%-75%.

[0017] As a further solution of the present invention: in step 3, the composite film will form a polymer structure with continuous sheets and the size of the pores 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 ​​the crystalline region, and m2 is the area of ​​the non-crystalline region.

[0018] As a further solution of the present invention: in step 3, a certain strength of hydrogen bonding is formed between the black fungus polysaccharide and the 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; Where: m1 is the weight of the membrane after moisture absorption (g), m0 is the initial weight of the membrane (g); 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 bottle per unit time (g / s), A is the surface area of ​​the membrane (m 2 ), P0 is the saturated vapor pressure on both sides of the membrane 3168.74Pa, (RH1-RH2) is the humidity difference 0.75, and X is the average thickness of the membrane (mm).

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. In the HPS and AAP compound system, there is interaction between HPS and AAP molecules, and a good network structure can be formed; 2. As the AAP concentration increases, the AAP molecules wrap around the HPS particles, which leads to the formation of an interface layer with opposite charges, increasing the electrostatic repulsion and steric hindrance between the droplets, preventing further droplet-droplet aggregation, so that the mixed system can remain stable for a certain period of time; 3. The peak value was reached at HA-7. The addition of AAP solution led to an increase in hydrogen bonds and covalent bonds between the composite system, which made the network structure of the polysaccharide more compact and dense, thus having stronger tensile strength and greater elasticity. The increase in EAB value may be due to a plasticizing effect, that is, AAP increased the spacing and fluidity between HPS by relieving the interaction. HA-7 membrane has the lowest hygroscopicity, which may be due to good compatibility and dense structure; HA-7 film has the lowest water vapor permeability, can play a good barrier role, and can maintain the quality of the sealed substance. From the perspective of food coating and packaging, consumer acceptability is greatly affected by the transparency of the film. The higher the transparency, the lower the opacity. HA-7 film has good light transmittance; 4. The addition of AAP disturbs the starch in the crystallization zone, inhibiting the rearrangement of amylose. The AAP concentration of HA-7 accelerates the rearrangement of amylose in the composite film and increases the crystallinity; 5. The AAP concentration of HA-7 makes the structure of the composite membrane regular, forming a network structure with strong order and crystallinity; 6. The surface of HA-7 is the smoothest. This observation indicates that there is good interaction between HPS and AAP, and the molecular distance between molecules is reduced, making the structure more compact. This produces a more uniform and stable rigid biopolymer structure, provides the best compatibility, and effectively improves the barrier properties of the film. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of cryo-electron microscopy in an embodiment of the present invention.

[0021] Figure 2 Schematic diagram of a confocal laser scanning microscope in an embodiment of the present invention.

[0022] Figure 3 Schematic diagram of the water contact angle of HA-7 membrane in an embodiment of the present invention.

[0023] Figure 4 This is the diffraction pattern of the HPS and AAP complex system in the embodiment of the present invention.

[0024] Figure 5 This is a differential scanning calorimeter analysis diagram in an embodiment of the present invention.

[0025] Figure 6 This is a scanning electron microscope analysis diagram in an embodiment of the present invention.

[0026] Figure 7 It is a Fourier infrared spectrum analysis diagram in the embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0029] See also Figure 1-Figure 7 The present invention provides a method for preparing a hydroxypropyl starch black fungus polysaccharide composite film, comprising the following steps: Step 1, mixing hydroxypropyl starch and black fungus polysaccharide in a mass ratio of (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.

[0030] In one embodiment of the present invention, see Figure 1-Figure 7 In step 1, the method for extracting black fungus polysaccharide (AAP) 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, the supernatant in step S2 was precipitated with an ethanol solution having a volume four times that of the supernatant at 4°C for 12 hours, and centrifuged at 4000 r / min for 20 minutes. The precipitate was freeze-dried to obtain Auricularia auricula polysaccharide (AAP).

[0031] 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.

[0032] 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) respectively, and slowly pour the AAP solution into the HPS solution while stirring to form a stable gel system.

[0033] 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%.

[0034] In step A3, the HPS solution and the AAP solution are mixed and then heated in a water bath at 85° C. for 10 minutes to form a stable gel system.

[0035] In one embodiment of the present invention, see Figure 1-Figure 7 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%.

[0036] 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, but will disrupt the crystallization area and change the rearrangement rate of amylose; And the relative crystallinity of the composite film was calculated by the following formula: Crystallinity (%) = m1 / m1+m2; Where: m1 is the area of ​​the crystalline region, and m2 is the area of ​​the non-crystalline region.

[0037] In step 3, a strong hydrogen bond 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; Where: m1 is the weight of the membrane after moisture absorption (g), m0 is the initial weight of the membrane (g); And 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 bottle per unit time (g / s), A is the surface area of ​​the membrane (m 2 ), P0 is the saturated vapor pressure on both sides of the membrane 3168.74Pa, (RH1-RH2) is the humidity difference 0.75, and X is the average thickness of the membrane (mm).

[0038] Example 1: A method for preparing a hydroxypropyl starch black fungus polysaccharide composite film, as follows: Extraction of black fungus polysaccharide (AAP): Accurately weigh 5 g of 120 mesh black fungus powder, add distilled water at a 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), deproteinize the supernatant by Sevag method (Sevag reagent, V (chloroform): V (n-butanol) = 4:1, oscillate for 30 min), concentrate, and precipitate with 4 times the volume of alcohol at 4 °C for 12 h (95% ethanol solution), centrifuge (4000 r / min, 20 min), and freeze-dry the precipitate to obtain AAP.

[0039] Preparation of HPS and AAP compound system: Prepare mixed systems of different concentrations. First, weigh 1g of AAP, dissolve it in distilled water to 100g, and stir evenly to obtain a black, viscous, transparent AAP liquid with a mass concentration of 1%; weigh 6g of HPS, dissolve it in distilled water to 100g, and stir evenly to obtain a white HPS liquid with a mass concentration of 6%. According to Table 1, take out different masses of HPS liquid and AAP liquid, slowly pour the AAP liquid into the HPS liquid, stir while pouring, and place it in a water bath at 85℃ for 10 minutes. This is a fresh HPS and AAP mixed system, which will produce gel after a few hours. The ingredient list of the HPS and AAP compound system is as follows: Table 1 HPS and AAP compound system

[0040] Texture determination: Texture determination was performed at room temperature using a texture analyzer. The parameters were as follows: P / 36R stainless steel cylindrical probe, pre-test and test speed 1.0 mm / s, post-test speed 10.0 mm / s, compression 30%, trigger force 5.0 g, and 5 s interval between two repetitions. Each set of tests was performed three times in parallel and the average value was taken.

[0041] As shown in Table 2, the entanglement between HPS and AAP molecules makes their compound system form an elastic system with better texture, providing a reference for product development.

[0042] Table 2 Texture characteristics of HPS / AAP compound system

[0043] Example 2: Preparation of composite film with a mass ratio of hydroxypropyl starch to black fungus polysaccharide of 3:6; Step 1: Mix hydroxypropyl starch (HPS) and black fungus polysaccharide (AAP) in a mass ratio of 3:6 to form a composite system of HPS and AAP.

[0044] Step 2: Add 2.0% glycerin as a plasticizer to the compound system and stir evenly.

[0045] Step 3: Cast the composite system solution of HPS and AAP into a film, the drying temperature is 50°C, the drying time is 22 hours, the drying environment is 20°C and the humidity is 50%. After drying, a hydroxypropyl starch black fungus polysaccharide composite film is obtained.

[0046] The composite film prepared in this example has good mechanical properties, but compared with the composite film with a mass ratio of 3:7, its tensile strength and elastic modulus are slightly lower, and its water vapor permeability is slightly higher, indicating that the mass ratio of 3:7 has more advantages in mechanical properties and barrier properties.

[0047] Example 3: Preparation of composite film with a mass ratio of hydroxypropyl starch to black fungus polysaccharide of 4:7; Step 1: Mix hydroxypropyl starch (HPS) and black fungus polysaccharide (AAP) in a mass ratio of 4:7 to form a composite system of HPS and AAP.

[0048] Step 2: Add 2.5% glycerin as a plasticizer to the compound system and stir evenly.

[0049] Step 3: Cast the composite system solution of HPS and AAP into a film, the drying temperature is 70°C, the drying time is 24 hours, the drying environment is 30°C and the humidity is 75%. After drying, a hydroxypropyl starch black fungus polysaccharide composite film is obtained.

[0050] The composite film prepared in this example performs well in mechanical properties and barrier properties, but compared with the composite film with a mass ratio of 3:7, its moisture absorption weight gain rate is slightly higher and its water vapor permeability is slightly larger, indicating that the mass ratio of 3:7 is more superior in hygroscopicity and barrier properties.

[0051] Example 4: Different conditions for extracting black fungus polysaccharides; Step 1: Add 120-mesh black fungus powder to distilled water at a solid-liquid ratio of 1:50, and extract in a high-pressure reactor at a pressure of 0.95 MPa, a temperature of 108° C., and a time of 55 minutes.

[0052] Step 2: After centrifugation at 4000 r / min for 20 min, the supernatant was deproteinized using the Sevag method.

[0053] Step 3: After concentration, the supernatant in step S2 is precipitated with 95% ethanol solution in a volume four times that of the supernatant at 4°C for 12 hours, and centrifuged at 4000 r / min for 20 minutes. The precipitate is freeze-dried to obtain black fungus polysaccharide.

[0054] The yield of black fungus polysaccharide extracted in this embodiment is high, but compared with the extraction conditions of solid-liquid ratio 1:70, pressure 1.0 MPa, temperature 110°C, and time 60 minutes, the polysaccharide purity and molecular weight are slightly lower, indicating that the optimal extraction conditions have more advantages in polysaccharide quality and yield.

[0055] Example 5: Different conditions for extracting black fungus polysaccharides; Step 1: Add 120-mesh black fungus powder to distilled water at a solid-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.

[0056] Step 2: After centrifugation at 4000 r / min for 20 min, the supernatant was deproteinized using the Sevag method.

[0057] Step 3: After concentration, the supernatant in step S2 is precipitated with 95% ethanol solution in a volume four times that of the supernatant at 4°C for 12 hours, and centrifuged at 4000 r / min for 20 minutes. The precipitate is freeze-dried to obtain black fungus polysaccharide.

[0058] The yield and purity of the black fungus polysaccharide extracted in this embodiment are high, but compared with the extraction conditions of a solid-liquid ratio of 1:70, a pressure of 1.0 MPa, a temperature of 110° C., and a time of 60 minutes, the polysaccharide molecular weight distribution is slightly wider, indicating that the optimal extraction conditions have more advantages in controlling the polysaccharide molecular weight.

[0059] Example 6: Different conditions of composite film drying temperature; Step 1: Mix hydroxypropyl starch (HPS) and black fungus polysaccharide (AAP) in a mass ratio of 3:7 to form a composite system of HPS and AAP.

[0060] Step 2: Add 2.0% glycerin as a plasticizer to the compound system and stir evenly.

[0061] Step 3: Cast the composite system solution of HPS and AAP into a film, the drying temperature is 60°C, the drying time is 24 hours, the drying environment is 25°C and the humidity is 60%. After drying, a hydroxypropyl starch black fungus polysaccharide composite film is obtained.

[0062] Under suitable drying conditions, the composite film can form a good network structure with advantages such as low water vapor permeability and high tensile strength.

[0063] Example 7: Different conditions of composite film drying temperature; Step 1: Mix hydroxypropyl starch (HPS) and black fungus polysaccharide (AAP) in a mass ratio of 3:7 to form a composite system of HPS and AAP.

[0064] Step 2: Add 2.0% glycerin as a plasticizer to the compound system and stir evenly.

[0065] Step 3: Cast the composite system solution of HPS and AAP into a film, the drying temperature is 60°C, the drying time is 23 hours, the drying environment is 25°C and the humidity is 60%. After drying, a hydroxypropyl starch black fungus polysaccharide composite film is obtained.

[0066] The composite film prepared in this example has excellent mechanical properties and barrier properties, but 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 have more advantages in the structure and performance of the film.

[0067] Example 8: Different conditions of composite film drying temperature Step 1: Mix hydroxypropyl starch (HPS) and black fungus polysaccharide (AAP) in a mass ratio of 3:7 to form a composite system of HPS and AAP.

[0068] Step 2: Add 2.5% glycerin as a plasticizer to the compound system and stir evenly.

[0069] Step 3: Cast the composite system solution of HPS and AAP into a film, the drying temperature is 55°C, the drying time is 22.5 hours, the drying environment is 22°C and the humidity is 65%. After drying, a hydroxypropyl starch black fungus polysaccharide composite film is obtained.

[0070] The composite film prepared in this embodiment performs well in mechanical properties and barrier properties, but compared with the conditions of drying temperature 60°C and drying time 24 hours, the moisture absorption weight gain rate of the film is slightly higher and the water vapor permeability is slightly larger, indicating that the optimal drying conditions are more superior in the hygroscopicity and barrier properties of the film.

[0071] Example 9: Microstructure; Cryo-SEM observation: The experiment was conducted in a scanning electron microscope equipped with a cryo-transfer device. The HPS and AAP compound samples were fixed on the sample cup, pre-cooled at -25℃, and placed in the sample tank after being frozen through. After vacuuming, the samples were observed and photographed under an electron cryo-microscope. Experimental conditions: voltage value: 5kV; magnification: 1000 times. Figure 1 As shown, in the HPS and AAP complex system, there is interaction between HPS and AAP molecules, and a good network structure can be formed.

[0072] Confocal laser scanning microscopy (CLMS): Confocal laser scanning microscopy analysis was observed within 30 minutes after the preparation of the HPS / AAP mixed system. Take 1 ml of the freshly prepared sample and carefully transfer it to a 1.5 ml centrifuge tube. Mix it thoroughly with 30 μl FITC (fluorescein isothiocyanate) (2 mg / ml, dissolved in DMSO) of starch stain and 30 μl fluorescent brightener 28 (10 mg / ml, dissolved in DMSO) of polysaccharide stain, and stain it in the dark for 5 minutes. Place 2 μl of the stained sample on a glass slide, cover it with a coverslip, and seal it with silicone oil on all sides. Place the glass slide on the stage and use a 0x objective to observe the sample. 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 with a scanning density of 10 24 ×10 24 .like Figure 2 As shown in the figure, with the increase of AAP concentration, AAP molecules are wrapped around the HPS particles, which leads to the formation of an interface layer with opposite charge, increases the electrostatic repulsion and steric hindrance between the droplets, and prevents further aggregation of droplets. Therefore, the mixed system can remain stable for a certain period of time.

[0073] Example 10: Preparation of hybrid system membrane; Take 5g of mixed solution with different proportions, add 2.0% glycerol, keep warm in a water bath at 40℃ for half an hour, then pour into a polyethylene plate and cast into a film. The drying temperature is 60℃. After drying is complete, place it in a constant temperature dryer at 25℃ and humidity (RH) 65% for 24 hours to balance, and then the performance of the film can be measured.

[0074] Hybrid system membrane characterization: (1) Mechanical properties - tensile strength measurement: The mechanical properties of the membrane were measured using an American TA.DHR-1 rheometer, in MPa. The membrane was cut into strips of 1.0 × 7 cm, a tensile fixture was selected, the probe movement speed was set to 100 μm / s, and the mechanical properties were measured at 25°C. Five points were randomly selected, the thickness and width of the membrane were measured with a micrometer and the average was taken. The length was automatically read, and the tensile strength result was directly read.

[0075] (2) Transmittance: The prepared HPS / AAP mixed system membrane was cut into strips of 1 cm × 4 cm and then fixed inside a cuvette. The transmittance of the HPS / AAP mixed system membrane was measured at visible light λ = 500 nm, with an empty cuvette as a reference.

[0076] (3) Water vapor permeability: The water vapor permeability of the film was measured by gravimetric analysis. The prepared film was cut into a circular shape and fixed with wax on the mouth of a conical bottle containing 2g of CaCl2. The internal humidity was 0. The weighed sample bottle was sealed and stored in a humidity environment of 75% (saturated salt water) at a temperature of 25°C. The sample was taken out and weighed every 24 hours until the value changed less than 0.001g. Three parallel experiments were performed for each group of samples to calculate the water vapor permeability WVP of the film.

[0077] Water vapor transmission rate (WVP) = Flux / AP0(RH1-RH2)X (4); Where: Flux is the average weight gain of the triangular bottle per unit time (g / s), A is the surface area of ​​the membrane (m 2 ), P0 is the saturated vapor pressure on both sides of the membrane 3168.74Pa, (RH1-RH2) is the humidity difference 0.75, and X is the average thickness of the membrane (mm).

[0078] (4) Moisture absorption and weight gain: The prepared membrane was cut into 1 × 1 cm squares and placed in a forced air drying oven at 40 °C for 6 h. The initial mass of the membrane was weighed, m0. The membrane was then sealed and stored in a humidity environment of 75% (saturated salt water). After 12 h, the mass of the membrane was taken out and weighed, m1. The moisture absorption and weight gain of the membrane was calculated according to the following equation.

[0079] Moisture absorption weight gain W (%) = (m1-m0) / m0×100 (5); Where: m1 is the weight of the membrane after moisture absorption (g), m0 is the initial weight of the membrane (g).

[0080] Table 3 Membrane Characterization

[0081] The peak value was reached at HA-7 (hydroxypropyl starch and black fungus polysaccharide in a mass ratio of 3:7, referred to as HA-7). The addition of AAP solution led to an increase in hydrogen bonds and covalent bonds between the composite system, making the network structure of the polysaccharide more compact and dense, thus having stronger tensile strength and greater elasticity. The increase in EAB value may be due to a plasticizing effect, that is, AAP increases the spacing and fluidity between HPS by relieving interactions. HA-7 film has the lowest hygroscopicity, which may be due to good compatibility and a dense structure.

[0082] HA-7 film has the lowest water vapor transmission rate, can play a good barrier role, and can maintain the quality of the sealed material. From the perspective of food coating and packaging, consumer acceptability is greatly affected by the transparency of the film. The higher the transparency, the lower the opacity, because they are negatively correlated. HA-7 film has good light transmittance.

[0083] (5) Contact angle analysis: The water contact angle (WCA) of the film is measured using a standard contact angle meter (OCA50, Data Physics). Small droplets were added to a 2cmx2cm film. The contact interface was captured at normal intervals. The water contact angle (WCA) of the starch film was measured using a contact angle meter (OCA50, Data Physics). Small droplets were added to a 2cmx2cm film. The contact interface was captured at normal intervals. Figure 3 As shown in Figure 3, the water contact angle of HA-7 film is smaller, which may be due to the interaction between HPS and AAP, which increases the number of hydroxyl groups on the surface. Smooth surface can also lead to a decrease in WCA.

[0084] (6) X-ray diffractometer (X-RD): freeze-dry the membrane in a vacuum freeze dryer (0.05 MPa, -55 °C), crush the freeze-dried membrane, pass through a 200-mesh sieve, and dry in an oven at 80 °C to constant weight. Take 0.5 g of the membrane and place it in the groove of the slide. Compact the sample with a cover glass and pull it sideways with force to make the sample flat and without cracks. Wipe off excess sample. The diffractometer operates at 40 mA and 40 kV, using Cu-Kα radiation with a wavelength of 0.1542 nm as the X-ray source. Set the parameters to scan in the range of 2-60° and at a scanning speed of 4° / min. 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.

[0085] Crystallinity (%) = m1 / m1+m2 (6); Where: m1 is the area of ​​the crystalline region, and m2 is the area of ​​the non-crystalline region.

[0086] like Figure 4 As shown in the figure, the addition of AAP disturbed the starch in the crystalline region and inhibited the rearrangement of amylose. The AAP concentration of HA-7 accelerated the rearrangement of amylose in the composite film and increased the crystallinity.

[0087] (7) Differential Scanning Calorimeter (DSC): A DSC25 differential scanning calorimeter was used to study the thermal properties of the sample. 5.0±0.2 mg of the film was weighed and placed in an alloy dish, which was sealed with a lid. An empty alloy dish was used for comparison. The heating rate was 10°C / min, the test range was 20-120°C, N2 gas was used as the protective gas, and the protective gas flow rate was 20 ml / min. The thermal differential curve was recorded.

[0088] like Figure 5 As shown, the AAP concentration of HA-7 makes the structure of the composite membrane regular, forming a network structure with strong order and crystallinity.

[0089] (8) Scanning electron microscopy (SEM) analysis: After the different mixed films were sprayed with gold, they were scanned using a SSE-550 scanning electron microscope from Shimadzu Corporation of Japan at a vacuum of 0.1t, and the film surface and cross-section micromorphology were observed at magnifications of 500 and 6000 times, respectively. The working conditions of the scanning electron microscope were: high voltage 25 kV, beam current 5×10 -9 mA, working distance 15mm. Figure 6 As shown in the figure, HA-7 has the smoothest surface, an observation that indicates good interaction between HPS and AAP, and a decrease in the molecular distance between molecules, 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 film.

[0090] (9) Fourier transform infrared spectroscopy (FT-IR) analysis: The infrared spectrum of the sample was measured using the IR RESTIGE-21 Fourier transform infrared spectrometer of Shimadzu Corporation of Japan and the potassium bromide tablet method. The frozen membrane sample was freeze-dried and powdered, and mixed with potassium bromide at a ratio of 1:100, then ground into a uniform powder in a mortar and pressed into a tablet at 9 MPa. The scanning conditions were set as follows: spectral range 400-4000cm -1 Scan times: 32 times, resolution: 4cm -1 Potassium bromide was used as a blank control. The spectrum acquisition of each sample was repeated three times under the same conditions.

[0091] like Figure 7 As shown, no new peaks were detected in the spectrum, indicating that there was no new covalent interaction between the polysaccharide and starch, and the main interaction was hydrogen bonding. The peak at 3200-3500 cm-1 of HA-7 gradually broadened, and the hydrogen bonding interaction gradually strengthened.

[0092] Therefore, this application is based on the actual processing and application needs of preparing starch films, and comprehensively characterizes the composite solution and composite film of hydroxypropyl starch and black fungus polysaccharide. The composite 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. With the increase of the proportion of AAP, the hardness and viscosity of the composite system decrease significantly, and the elasticity and cohesion increase, indicating that AAP can improve the properties of the HPS solution. When the mixing ratio of hydroxypropyl starch and black fungus polysaccharide is 3:7, the composite solution presents a continuous sheet-like polymer, and the mixed system can remain stable for a certain period of time. The appropriate AAP ratio can improve the microstructure. Prepared into a composite film, the polysaccharide can form a strong hydrogen bond with starch, thereby promoting the formation of a more compact and ordered network structure, so that it has a lower water vapor permeability and a higher tensile strength. The diffraction pattern obtained by XRD analysis shows that the addition of black fungus polysaccharide does not change its crystal structure, but disrupts the crystallization area, changes the rearrangement rate of amylose, and thus changes its properties. The thermal properties of the composite film show that the appropriate addition of black fungus polysaccharide can improve the thermal stability of the composite film. The image obtained by SEN shows that the addition of black fungus polysaccharide increases the molecular interaction of the film, making the matrix of the film denser and the surface smoother without cracks. The addition of polysaccharide not only improves the physicochemical properties of the starch film, but also the two raw materials are natural, renewable and biodegradable polymers. The composite film prepared can significantly improve its biodegradability, meet the requirements of the green label, and has the potential significance of replacing food and drug packaging materials.

[0093] In summary, the interaction mechanism of the composite system of Auricularia auricular polysaccharide (AAP) and hydroxypropyl starch (HPS) at different ratios of the present invention is studied, and the composite film prepared by the casting method is used to prove the influence of this interaction on the macroscopic properties and microstructure of the composite material. With the increase of the proportion of Auricularia auricular polysaccharide, the texture property results show that its hardness decreases, and its elasticity and cohesion increase; the rheological property results show that its fluidity, apparent viscosity and pseudoplasticity weaken. The results of cryo-electron microscopy and confocal microscopy show that the appropriate addition ratio of polysaccharide can improve the multi-void structure of the composite system, and the size of the pores is reduced to form a good network structure. The composite film prepared by mixing hydroxypropyl starch and Auricularia auricular polysaccharide in a ratio of 3:7 has a lower water vapor permeability 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 structure, but disrupts the crystallization area and changes the rearrangement rate of amylose. The thermal properties of the composite film show that the appropriate addition of Auricularia auricular polysaccharide can improve the thermal stability of the composite film. The images obtained by SEN showed that the addition of black fungus polysaccharide increased the molecular interactions of the membrane, making the matrix of the membrane denser and the surface smoother without cracks.

[0094] The black fungus polysaccharide and hydroxypropyl starch were used as research objects, and their interaction mechanism was studied by means of texture analyzer, rheometer and electron scanning microscope. HPS / AAP composite film was prepared by casting method, and the influence of different proportions on the physical properties, mechanical properties and microstructure of the composite film was studied. This provides a certain scientific basis for the application of starch and edible fungus polysaccharides in capsule shell materials.

[0095] It should be noted that in the present invention, it should be understood that although this specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that those skilled in the art can understand.

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 and black fungus polysaccharide in a mass ratio of (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.

2. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 1, characterized in that: 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, the supernatant in step S2 is precipitated with an ethanol solution having a volume four times that of the supernatant at 4° C. for 12 hours, and centrifuged at 4000 r / min for 20 minutes. The precipitate is freeze-dried to obtain black fungus polysaccharide.

3. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 2, 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.

4. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 1, characterized in that: 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) respectively, and slowly pour the AAP solution into the HPS solution while stirring to form a stable gel system.

5. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 4, 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%.

6. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 5, characterized in that: In step A3, the HPS solution and the AAP solution are mixed and then heated in a water bath at 85° C. for 10 minutes to form a stable gel system.

7. The method for preparing the hydroxypropyl starch and black fungus polysaccharide composite film according to any one of claims 1 to 6, characterized in that: 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%.

8. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 7, 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 ​​the crystalline region, and m2 is the area of ​​the non-crystalline region.

9. The method for preparing the hydroxypropyl starch black fungus polysaccharide composite film according to claim 8, 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; Where: m1 is the weight of the membrane after moisture absorption (g), m0 is the initial weight of the membrane (g); 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 bottle per unit time (g / s), A is the surface area of ​​the membrane (m 2 ), P0 is the saturated vapor pressure on both sides of the membrane 3168.74Pa, (RH1-RH2) is the humidity difference 0.75, and X is the average thickness of the membrane (mm).

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