Composite biological fresh-keeping film for prefabricated vegetables and preparation method of composite biological fresh-keeping film

Abstract

The invention provides a prefabricated vegetable composite biological fresh-keeping film and a preparation method thereof, and the preparation method comprises the following steps: taking silk fibroin, adding a calcium chloride-ethanol solution, heating for dissolving, and carrying out ultrafiltration desalination; performing spray drying to obtain water-soluble silk fibroin; stirring and dissolving water-soluble silk fibroin, gelatin and water; transglutaminase and glutamine are added, and a mixed glue solution is obtained; adding the porous konjac glucomannan microcapsules, and uniformly stirring; casting to form a film, and reacting at 40 DEG C; and drying. The silk fibroin-gelatin hybrid membrane doped with the porous konjac glucomannan microcapsules is adopted, the porous konjac glucomannan microcapsules are evenly doped into a silk fibroin-gelatin mixed matrix, the hybrid membrane with controllable gas permeation is obtained, the CO2 / O2 selectivity of the hybrid membrane is greatly improved, and therefore the ideal atmosphere with the low O2 concentration and the high CO2 concentration is maintained; the physiological metabolism of the premade vegetables is inhibited, and the reproduction of bacteria is inhibited, so that the premade vegetables can be preserved at room temperature.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and in particular relates to a composite biological fresh-keeping film for pre-prepared dishes and a preparation method thereof. Background Art

[0002] Pre-prepared food is a finished or semi-finished product that has been pre-processed. It has a variety of types and has gradually become the mainstream of consumption. Generally speaking, pre-prepared food can be roughly divided into grains, meat, and fruits and vegetables according to the types of raw materials. Among them, fruit and vegetable pre-prepared food refers to fruit and vegetable products that have undergone preliminary processing, such as washing, cutting, cooking, etc., so that consumers can eat them quickly and conveniently. With the improvement of healthy eating concepts and the acceleration of the pace of life, fruit and vegetable pre-prepared food has been welcomed by more and more consumers due to its convenience and nutrition. The preservation of vegetable pre-prepared food is an important research topic, and the main preservation technologies and methods are as follows: 1. Controlled atmosphere preservation technology: This is a technology that extends the shelf life of food by changing the gas composition in the package. It can be active, such as inflatable packaging, or passive, using food respiration and microbial metabolism to change the gas composition. 2. Vacuum precooling technology: This is a method of quickly reducing the temperature of food. By extracting air and water vapor in a closed container, the food is quickly cooled to maintain freshness. 3. Modified atmosphere packaging technology: Develop new modified atmosphere packaging bags, adjust the concentration of oxygen and carbon dioxide according to the characteristics of different types of vegetables, force vegetables to "dormant", and extend the shelf life. 4. New sterilization technology, etc.: For example, use non-oxidizing fungicides such as dimethyl dicarbonate, which can quickly sterilize, have little loss of nutrients, and are safe and harmless to the human body. However, excessive use of fungicides may lead to bioaccumulation of toxic substances. Heat treatment and irradiation mainly reduce the proliferation of microorganisms, but food maturation is inevitable. Research has found that most of the decay mechanisms of pre-prepared fruits and vegetables are related to the presence of several gas molecules, O2 and CO2, which can regulate plant physiological metabolism. Gas permeable membranes with high CO2 / O2 selectivity can inhibit plant physiological metabolism and inhibit bacterial proliferation. Therefore, the present invention aims to develop a gas-regulatable biological preservative film for pre-prepared dishes. Summary of the invention

[0003] Technical problem to be solved: In view of the above technical problems, the purpose of the present invention is to provide a composite biological preservative film for pre-prepared dishes and a preparation method thereof, using a silk fibroin-gelatin hybrid membrane doped with porous konjac glucomannan microcapsules, and uniformly incorporating the porous konjac glucomannan microcapsules into the silk fibroin-gelatin mixed matrix to obtain a hybrid membrane with controllable gas permeability, wherein the porous konjac glucomannan microcapsules form "pores" to adjust the permeability of gases O2 and CO2, thereby greatly improving the CO2 / O2 selectivity, thereby maintaining an ideal atmosphere of low O2 concentration and high CO2 concentration, inhibiting the physiological metabolism of pre-prepared dishes and inhibiting the reproduction of bacteria, so that pre-prepared dishes can be preserved at room temperature.

[0004] Technical solution: A composite biological cling film for pre-prepared dishes, wherein the biological cling film is a silk fibroin-gelatin hybrid film doped with porous konjac glucomannan microcapsules. The preparation method of the composite biological preservative film for pre-prepared dishes comprises the following steps, measured in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, heat to dissolve at 95°C, and perform ultrafiltration desalination using a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin, gelatin and water, and stir to dissolve; S4: add transglutaminase and glutamine, stir for 5-10 minutes, and obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done. Furthermore, the calcium chloride concentration in the calcium chloride-ethanol solution in S1 is 4 mol / L, and the volume fraction of ethanol is 30%. Furthermore, the mass ratio of water-soluble silk fibroin, gelatin and water in S3 is 2:(1-2):40. Furthermore, the amount of transglutaminase added in the S4 is 15-20 U / g water-soluble silk fibroin; and the amount of glutamine added is 2-3 g / g water-soluble silk fibroin. Furthermore, the volume ratio of the porous konjac glucomannan microcapsules to the mixed colloid in S5 is (0.5-0.8):10. Furthermore, the preparation method of the porous konjac glucomannan microcapsules in S5 is as follows: S51: dissolving konjac glucomannan, xanthan gum, tannic acid and citric acid in distilled water to obtain an aqueous phase; S52: mixing corn oil and Tween in a mass ratio of 20:1 to obtain an oil phase; S53: pour the oil phase into the water phase, the volume ratio of the oil phase to the water phase is (5-10):1, and react for 2-5 hours at a speed of 100-150 rpm, a temperature of 50-95° C., and a pH value of 4.5; S54: filtering the product and washing it with deionized water to obtain porous konjac glucomannan microcapsules. Furthermore, the mass ratio of the konjac glucomannan, xanthan gum, tannic acid, citric acid and distilled water is (7-10):3:3:0.1:50. Furthermore, the particle size of the porous konjac glucomannan microcapsules is 20-50 μm. Beneficial effects: 1. The present invention adopts a silk fibroin-gelatin hybrid membrane doped with porous konjac glucomannan microcapsules, and the porous konjac glucomannan microcapsules are uniformly incorporated into the silk fibroin-gelatin mixed matrix to obtain a hybrid membrane with controllable gas permeability. The porous konjac glucomannan microcapsules form "pores" to adjust the permeability of gases O2 and CO2, thereby greatly improving the CO2 / O2 selectivity, thereby maintaining an ideal atmosphere of low O2 concentration and high CO2 concentration, inhibiting the physiological metabolism of pre-prepared dishes and inhibiting the reproduction of bacteria, so that the pre-prepared dishes can be kept fresh at room temperature. 2. The present invention uses xanthan gum to increase the cross-linking of konjac glucomannan, and uses citric acid to further cross-link and form a porous structure. 3. The present invention uses tannic acid to change the microstructure of konjac glucomannan microcapsules, greatly affecting the gas permeability and having a certain antibacterial effect. 4. The present invention introduces glutamine into the silk fibroin-gelatin hybrid membrane to improve the cross-linking reaction between silk fibroin proteins, because under the action of transglutaminase, glutamine participates in the cross-linking reaction as an acyl receptor, thereby increasing the action sites of silk fibroin proteins, improving its cross-linking degree, and improving the mechanical properties of the hybrid membrane. 5. The present invention also uses gelatin and silk fibroin to perform non-covalent and covalent cross-linking to form two independent but mutually penetrating network structures, thereby improving the toughness and mechanical strength of the hybrid membrane. DETAILED DESCRIPTION The present invention will be further described below in conjunction with embodiments, which are explanations of the present invention and are not limited to the following embodiments: Example 1 The preparation method of porous konjac glucomannan microcapsules is as follows: S1: dissolving konjac glucomannan, xanthan gum, tannic acid and citric acid in distilled water to obtain an aqueous phase; the mass ratio of konjac glucomannan, xanthan gum, tannic acid, citric acid and distilled water is 7:3:3:0.1:50; S2: mixing corn oil and Tween in a mass ratio of 20:1 to obtain an oil phase; S3: Pour the oil phase into the water phase, the volume ratio of the oil phase to the water phase is 8:1, and react for 4 hours at a speed of 130 rpm, a temperature of 80°C, and a pH value of 4.5; S4: filtering the product and washing it with deionized water to obtain porous konjac glucomannan microcapsules. Example 2 The preparation method of porous konjac glucomannan microcapsules is as follows: S1: dissolving konjac glucomannan, xanthan gum, tannic acid and citric acid in distilled water to obtain an aqueous phase; the mass ratio of konjac glucomannan, xanthan gum, tannic acid, citric acid and distilled water is 9:3:3:0.1:50; S2: mixing corn oil and Tween in a mass ratio of 20:1 to obtain an oil phase; S3: Pour the oil phase into the water phase, the volume ratio of the oil phase to the water phase is 8:1, and react for 4 hours at a speed of 130 rpm, a temperature of 80°C, and a pH value of 4.5; S4: filtering the product and washing it with deionized water to obtain porous konjac glucomannan microcapsules. Example 3 The preparation method of porous konjac glucomannan microcapsules is as follows: S1: dissolving konjac glucomannan, xanthan gum, tannic acid and citric acid in distilled water to obtain an aqueous phase; the mass ratio of konjac glucomannan, xanthan gum, tannic acid, citric acid and distilled water is 10:3:3:0.1:50; S2: mixing corn oil and Tween in a mass ratio of 20:1 to obtain an oil phase; S3: Pour the oil phase into the water phase, the volume ratio of the oil phase to the water phase is 8:1, and react for 4 hours at a speed of 130 rpm, a temperature of 80°C, and a pH value of 4.5; S4: filtering the product and washing it with deionized water to obtain porous konjac glucomannan microcapsules. Example 4 The preparation method of porous konjac glucomannan microcapsules is as follows: S1: dissolving konjac glucomannan, xanthan gum, tannic acid and citric acid in distilled water to obtain an aqueous phase; the mass ratio of konjac glucomannan, xanthan gum, tannic acid, citric acid and distilled water is 9:3:3:0.1:50; S2: mixing corn oil and Tween in a mass ratio of 20:1 to obtain an oil phase; S3: Pour the oil phase into the water phase, the volume ratio of the oil phase to the water phase is 5:1, and react for 4 hours at a speed of 130 rpm, a temperature of 80°C, and a pH value of 4.5; S4: filtering the product and washing it with deionized water to obtain porous konjac glucomannan microcapsules. The particle size of the porous konjac glucomannan microcapsules is 20-50 μm. Example 5 The preparation method of porous konjac glucomannan microcapsules is as follows: S1: dissolving konjac glucomannan, xanthan gum, tannic acid and citric acid in distilled water to obtain an aqueous phase; the mass ratio of konjac glucomannan, xanthan gum, tannic acid, citric acid and distilled water is 9:3:3:0.1:50; S2: mixing corn oil and Tween in a mass ratio of 20:1 to obtain an oil phase; S3: Pour the oil phase into the water phase, the volume ratio of the oil phase to the water phase is 10:1, and react for 4 hours at a speed of 130 rpm, a temperature of 80°C, and a pH value of 4.5; S4: filtering the product and washing it with deionized water to obtain porous konjac glucomannan microcapsules. Example 6 The preparation method of porous konjac glucomannan microcapsules is as follows: S1: dissolving konjac glucomannan, xanthan gum, tannic acid and citric acid in distilled water to obtain an aqueous phase; the mass ratio of konjac glucomannan, xanthan gum, tannic acid, citric acid and distilled water is 9:3:3:0.1:50; S2: mixing corn oil and Tween in a mass ratio of 20:1 to obtain an oil phase; S3: Pour the oil phase into the water phase, the volume ratio of the oil phase to the water phase is 8:1, and react for 4 hours at a speed of 100 rpm, a temperature of 80°C, and a pH value of 4.5; S4: filtering the product and washing it with deionized water to obtain porous konjac glucomannan microcapsules. Example 7 The preparation method of porous konjac glucomannan microcapsules is as follows: S1: dissolving konjac glucomannan, xanthan gum, tannic acid and citric acid in distilled water to obtain an aqueous phase; the mass ratio of konjac glucomannan, xanthan gum, tannic acid, citric acid and distilled water is 9:3:3:0.1:50; S2: mixing corn oil and Tween in a mass ratio of 20:1 to obtain an oil phase; S3: Pour the oil phase into the water phase, the volume ratio of the oil phase to the water phase is 8:1, and react for 4 hours at a speed of 150 rpm, a temperature of 80°C, and a pH value of 4.5; S4: filtering the product and washing it with deionized water to obtain porous konjac glucomannan microcapsules. The properties of porous konjac glucomannan microcapsules were measured, and the results are shown in Table 1 below: Table 1 Average particle size (μm) <![CDATA[Specific surface area is (m 2 / g)]]> Average pore size (nm) Example 1 35.2 62.4 6.4 Example 2 35.1 62.8 6.0 Example 3 35.2 62.7 5.9 Example 4 35.0 62.8 5.6 Example 5 35.5 62.5 6.3 Example 6 36.0 61.4 6.1 Example 7 34.3 62.9 6.0 The porous konjac glucomannan microcapsules prepared in Example 2 were selected for the next experiment. Example 8 A method for preparing a composite biological preservative film for pre-prepared dishes comprises the following steps, measured in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, the calcium chloride concentration in the calcium chloride-ethanol solution is 4 mol / L, the volume fraction of ethanol is 30%, heat to dissolve at 95°C, and perform ultrafiltration desalination with a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:1:40 and stir to dissolve; S4: adding transglutaminase and glutamine, wherein the amount of transglutaminase added is 18 U / g water-soluble silk protein; the amount of glutamine added is 2.5 g / g water-soluble silk protein, stirring for 10 min to obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules, wherein the volume ratio of porous konjac glucomannan microcapsules to the mixed glue is 0.7:10, and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done. Example 9 A method for preparing a composite biological preservative film for pre-prepared dishes comprises the following steps, measured in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, the calcium chloride concentration in the calcium chloride-ethanol solution is 4 mol / L, the volume fraction of ethanol is 30%, heat to dissolve at 95°C, and perform ultrafiltration desalination with a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:2:40 and stir to dissolve; S4: adding transglutaminase and glutamine, wherein the amount of transglutaminase added is 18 U / g water-soluble silk protein; the amount of glutamine added is 2.5 g / g water-soluble silk protein, stirring for 10 min to obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules, wherein the volume ratio of porous konjac glucomannan microcapsules to the mixed glue is 0.7:10, and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done. Example 10 A method for preparing a composite biological preservative film for pre-prepared dishes comprises the following steps, measured in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, the calcium chloride concentration in the calcium chloride-ethanol solution is 4 mol / L, the volume fraction of ethanol is 30%, heat to dissolve at 95°C, and perform ultrafiltration desalination with a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:1:40 and stir to dissolve; S4: adding transglutaminase and glutamine, wherein the amount of transglutaminase added is 15 U / g water-soluble silk protein; the amount of glutamine added is 2.5 g / g water-soluble silk protein, stirring for 10 min to obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules, wherein the volume ratio of porous konjac glucomannan microcapsules to the mixed glue is 0.7:10, and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done. Embodiment 11 A method for preparing a composite biological preservative film for pre-prepared dishes comprises the following steps, measured in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, the calcium chloride concentration in the calcium chloride-ethanol solution is 4 mol / L, the volume fraction of ethanol is 30%, heat to dissolve at 95°C, and perform ultrafiltration desalination with a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:1:40 and stir to dissolve; S4: adding transglutaminase and glutamine, wherein the amount of transglutaminase added is 20 U / g water-soluble silk protein; the amount of glutamine added is 2.5 g / g water-soluble silk protein, stirring for 10 min to obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules, wherein the volume ratio of porous konjac glucomannan microcapsules to the mixed glue is 0.7:10, and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done. Example 12 A method for preparing a composite biological preservative film for pre-prepared dishes comprises the following steps, measured in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, the calcium chloride concentration in the calcium chloride-ethanol solution is 4 mol / L, the volume fraction of ethanol is 30%, heat to dissolve at 95°C, and perform ultrafiltration desalination with a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:1:40 and stir to dissolve; S4: adding transglutaminase and glutamine, wherein the amount of transglutaminase added is 18 U / g water-soluble silk protein; the amount of glutamine added is 2 g / g water-soluble silk protein, stirring for 10 min to obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules, wherein the volume ratio of porous konjac glucomannan microcapsules to the mixed glue is 0.7:10, and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done. Embodiment 13 A method for preparing a composite biological preservative film for pre-prepared dishes comprises the following steps, measured in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, the calcium chloride concentration in the calcium chloride-ethanol solution is 4 mol / L, the volume fraction of ethanol is 30%, heat to dissolve at 95°C, and perform ultrafiltration desalination with a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:1:40 and stir to dissolve; S4: adding transglutaminase and glutamine, wherein the amount of transglutaminase added is 18 U / g water-soluble silk protein; the amount of glutamine added is 3 g / g water-soluble silk protein, stirring for 10 min to obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules, wherein the volume ratio of porous konjac glucomannan microcapsules to the mixed glue is 0.7:10, and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done. Embodiment 14 A method for preparing a composite biological preservative film for pre-prepared dishes comprises the following steps, measured in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, the calcium chloride concentration in the calcium chloride-ethanol solution is 4 mol / L, the volume fraction of ethanol is 30%, heat to dissolve at 95°C, and perform ultrafiltration desalination with a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:1:40 and stir to dissolve; S4: adding transglutaminase and glutamine, wherein the amount of transglutaminase added is 18 U / g water-soluble silk protein; the amount of glutamine added is 2.5 g / g water-soluble silk protein, stirring for 10 min to obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules, wherein the volume ratio of porous konjac glucomannan microcapsules to the mixed glue is 0.5:10, and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done. Embodiment 15 A method for preparing a composite biological preservative film for pre-prepared dishes comprises the following steps, measured in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, the calcium chloride concentration in the calcium chloride-ethanol solution is 4 mol / L, the volume fraction of ethanol is 30%, heat to dissolve at 95°C, and perform ultrafiltration desalination with a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:1:40 and stir to dissolve; S4: adding transglutaminase and glutamine, wherein the amount of transglutaminase added is 18 U / g water-soluble silk protein; the amount of glutamine added is 2.5 g / g water-soluble silk protein, stirring for 10 min to obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules, wherein the volume ratio of porous konjac glucomannan microcapsules to the mixed glue is 0.8:10, and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done. Comparative Example 1 The difference between this comparative example and Example 8 is that no porous konjac glucomannan microcapsules are added, specifically as follows: A method for preparing a composite biological preservative film for pre-prepared dishes comprises the following steps, measured in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, the calcium chloride concentration in the calcium chloride-ethanol solution is 4 mol / L, the volume fraction of ethanol is 30%, heat to dissolve at 95°C, and perform ultrafiltration desalination with a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:1:40 and stir to dissolve; S4: adding transglutaminase and glutamine, wherein the amount of transglutaminase added is 18 U / g water-soluble silk protein; the amount of glutamine added is 2.5 g / g water-soluble silk protein, stirring for 10 min to obtain a mixed glue solution; S5: film casting, placed at 40 ° C for 3 hours; S6: Dry and you are done. Comparative Example 2 The difference between this comparative example and Example 8 is that no tannic acid is added to the porous konjac glucomannan microcapsules. Specifically, a method for preparing a composite biological preservative film for pre-prepared dishes comprises the following steps, calculated by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, the calcium chloride concentration in the calcium chloride-ethanol solution is 4 mol / L, the volume fraction of ethanol is 30%, heat to dissolve at 95°C, and perform ultrafiltration desalination with a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin and water in a mass ratio of 3:40 and stir to dissolve; S4: adding transglutaminase and glutamine, wherein the amount of transglutaminase added is 18 U / g water-soluble silk protein; the amount of glutamine added is 2.5 g / g water-soluble silk protein, stirring for 10 min to obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules, wherein the volume ratio of porous konjac glucomannan microcapsules to the mixed glue is 0.7:10, and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done. The preparation method of porous konjac glucomannan microcapsules is as follows: S1: dissolving konjac glucomannan, xanthan gum and citric acid in distilled water to obtain an aqueous phase; the mass ratio of konjac glucomannan, xanthan gum, citric acid and distilled water is 9:3:0.1:50; S2: mixing corn oil and Tween in a mass ratio of 20:1 to obtain an oil phase; S3: Pour the oil phase into the water phase, the volume ratio of the oil phase to the water phase is 8:1, and react for 4 hours at a speed of 130 rpm, a temperature of 80°C, and a pH value of 4.5; S4: filtering the product and washing it with deionized water to obtain porous konjac glucomannan microcapsules. Comparative Example 3 The difference between this comparative example and Example 8 is that no gelatin is added, specifically as follows: A method for preparing a composite biological preservative film for pre-prepared dishes comprises the following steps, measured in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, the calcium chloride concentration in the calcium chloride-ethanol solution is 4 mol / L, the volume fraction of ethanol is 30%, heat to dissolve at 95°C, and perform ultrafiltration desalination with a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin and water in a mass ratio of 3:40 and stir to dissolve; S4: adding transglutaminase and glutamine, wherein the amount of transglutaminase added is 18 U / g water-soluble silk protein; the amount of glutamine added is 2.5 g / g water-soluble silk protein, stirring for 10 min to obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules, wherein the volume ratio of porous konjac glucomannan microcapsules to the mixed glue is 0.7:10, and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done. Table 2 The composite biological preservative films for pre-prepared dishes prepared in Example 8, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were used to preserve the pre-prepared dishes. The pre-prepared dishes were covered and sealed with the preservative films of the above embodiments, and the weight loss rate (%) after storage at refrigeration (4° C.) and room temperature (25° C.) for 10 days was measured. The results are shown in Table 3: Table 3 Refrigeration weight loss rate (%) Weight loss rate at room temperature (%) Example 8 3.1 7.8 Comparative Example 1 10.2 14.3 Comparative Example 2 6.0 10.5 Comparative Example 3 4.5 8.7 The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the above disclosed methods and technical contents without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of protection of the technical solution of the present invention.

Claims

1. A composite biological fresh-keeping film for pre-prepared dishes, characterized in that: The biological fresh-keeping film is a silk fibroin-gelatin hybrid film doped with porous konjac glucomannan microcapsules.

2. The method for preparing a composite biological fresh-keeping film for pre-prepared dishes according to claim 1, characterized in that: The method comprises the following steps, in parts by weight: S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, heat to dissolve at 95°C, and perform ultrafiltration desalination using a 5000Da ultrafiltration membrane; S2: spray drying with an air inlet temperature of 170°C and an air outlet temperature of 80°C to obtain water-soluble silk fibroin; S3: Take water-soluble silk fibroin, gelatin and water, and stir to dissolve; S4: add transglutaminase and glutamine, stir for 5-10 minutes, and obtain a mixed glue solution; S5: adding porous konjac glucomannan microcapsules and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and you are done.

3. The method for preparing a composite biological preservative film for pre-prepared dishes according to claim 2, characterized in that: The calcium chloride concentration in the calcium chloride-ethanol solution in S1 is 4 mol / L, and the volume fraction of ethanol is 30%.

4. The method for preparing a composite biological preservative film for pre-prepared dishes according to claim 2, characterized in that: The mass ratio of water-soluble silk fibroin, gelatin and water in S3 is 2:(1-2):

40.

5. The method for preparing a composite biological preservative film for pre-prepared dishes according to claim 2, characterized in that: The amount of transglutaminase added in the S4 is 15-20 U / g water-soluble silk fibroin; the amount of glutamine added is 2-3 g / g water-soluble silk fibroin.

6. The method for preparing a composite biological preservative film for pre-prepared dishes according to claim 2, characterized in that: The volume ratio of the porous konjac glucomannan microcapsules to the mixed colloid in S5 is (0.5-0.8):

10.

7. The method for preparing a composite biological preservative film for pre-prepared dishes according to claim 2, characterized in that: The preparation method of the porous konjac glucomannan microcapsules in S5 is as follows: S51: dissolving konjac glucomannan, xanthan gum, tannic acid and citric acid in distilled water to obtain an aqueous phase; S52: mixing corn oil and Tween in a mass ratio of 20:1 to obtain an oil phase; S53: pour the oil phase into the water phase, the volume ratio of the oil phase to the water phase is (5-10):1, and react for 2-5 hours at a speed of 100-150 rpm, a temperature of 50-95° C., and a pH value of 4.5; S54: filtering the product and washing it with deionized water to obtain porous konjac glucomannan microcapsules.

8. The method for preparing a composite biological preservative film for pre-prepared dishes according to claim 7, characterized in that: The mass ratio of the konjac glucomannan, xanthan gum, tannic acid, citric acid and distilled water is (7-10):3:3:0.1:

50.

9. The method for preparing a composite biological fresh-keeping film for pre-prepared dishes according to claim 7, characterized in that: The particle size of the porous konjac glucomannan microcapsule is 20-50 μm.

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