A composite biological fresh-keeping film for prefabricated dishes and its preparation method

Abstract

The present invention provides a composite biological fresh-keeping film for prefabricated dishes and a preparation method thereof, which comprises the following steps: taking silk fibroin, adding a calcium chloride-ethanol solution, heating and dissolving, and performing ultrafiltration for desalination; spray drying to obtain water-soluble silk fibroin; taking water-soluble silk fibroin, gelatin and water, stirring and dissolving; adding transglutaminase and glutamine to obtain a mixed glue solution; adding porous konjac glucomannan microcapsules, and stirring evenly; casting into a film and reacting at 40°C; drying to obtain the product. The present invention adopts a silk fibroin-gelatin hybrid film doped with porous konjac glucomannan microcapsules, uniformly incorporates the porous konjac glucomannan microcapsules into the silk fibroin-gelatin mixed matrix, obtains a hybrid film with controllable gas permeability, greatly improves the selectivity of CO2 / O2, thereby maintaining an atmosphere with an ideal low O2 concentration and high CO2 concentration, inhibiting the physiological metabolism of prefabricated dishes and inhibiting the reproduction of bacteria, so that the prefabricated dishes can be preserved at room temperature.

Description

Technical Field

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

[0002] Prefabricated dishes are finished or semi-finished products obtained through pre-processing, with diverse varieties and have gradually become the mainstream of consumption. Generally speaking, prefabricated dishes can be roughly classified into cereal-based, meat-based, and fruit and vegetable-based according to the types of raw materials. Among them, fruit and vegetable-based prefabricated dishes refer to fruit and vegetable products that have been preliminarily processed, such as washing, cutting, cooking, etc., for the convenience of consumers to eat quickly and conveniently. With the improvement of the concept of healthy diet and the acceleration of the pace of life, fruit and vegetable-based prefabricated dishes are welcomed by more and more consumers due to their convenience and nutrition. The preservation of fruit and vegetable-based prefabricated dishes is an important research topic, and there are mainly the following preservation technologies and methods: 1. Modified atmosphere packaging (MAP) technology: This is a technology that prolongs the shelf life of food by changing the gas composition inside the package. It can be active, such as gas-flushed packaging, or passive, using the respiration of food and the metabolism of microorganisms to change the gas composition. 2. Vacuum precooling technology: This is a method of quickly reducing the temperature of food. By evacuating air and water vapor in a closed container, the food is rapidly cooled to maintain freshness. 3. Modified atmosphere packaging technology: Develop new modified atmosphere packaging bags, and adjust the concentrations of oxygen and carbon dioxide according to the characteristics of different types of vegetables, forcing the vegetables to "go dormant" and extending the shelf life. 4. New sterilization technologies, etc.: For example, using non-oxidizing bactericides such as dimethyl dicarbonate. These bactericides can quickly sterilize, cause little loss of nutrients, and are safe and harmless to the human body. However, excessive use of bactericides may lead to the bioaccumulation of toxic substances. Heat treatment and irradiation mainly reduce the proliferation of microorganisms, but the ripening of food is inevitable.

[0003] Research has found that most of the decay mechanisms of prefabricated fruit and vegetable dishes are related to the presence of several gas molecules O2 and CO2 that can regulate plant physiological metabolism. A gas-permeable membrane with high CO2 / O2 selectivity can inhibit plant physiological metabolism and the proliferation of bacteria. Therefore, the present invention aims to develop a gas-regulatable biological fresh-keeping film for prefabricated dishes. Summary of the Invention

[0004] Technical problem to be solved: Aiming at the above technical problems, the purpose of the present invention is to provide a composite biological fresh-keeping film for prefabricated dishes and its preparation method. A silk fibroin-gelatin hybrid film doped with porous konjac glucomannan microcapsules is used. The porous konjac glucomannan microcapsules are uniformly incorporated into the silk fibroin-gelatin mixed matrix to obtain a hybrid film with controllable gas permeability. The porous konjac glucomannan microcapsules form "air holes" to regulate the permeability of gases O2 and CO2, greatly improving the selectivity of CO2 / O2, so as to maintain an ideal atmosphere of low O2 concentration and high CO2 concentration, inhibit the physiological metabolism of prefabricated dishes and the reproduction of bacteria, so that the prefabricated dishes can be preserved at room temperature.

[0005] Technical solution: A composite biological fresh-keeping film for prefabricated dishes, wherein the biological fresh-keeping film is a silk fibroin-gelatin hybrid film doped with porous konjac glucomannan microcapsules.

[0006] The preparation method of the above-mentioned composite biological fresh-keeping film for prefabricated dishes includes the following steps, in parts by weight:

[0007] S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution, heat and dissolve at 95 °C, and perform ultrafiltration and desalination with a 5000 Da ultrafiltration membrane;

[0008] S2: Perform spray drying, with an inlet air temperature of 170 °C and an outlet air temperature of 80 °C, to obtain water-soluble silk fibroin;

[0009] S3: Take water-soluble silk fibroin, gelatin and water, and stir to dissolve;

[0010] S4: Add transglutaminase and glutamine, stir for 5 - 10 min to obtain a mixed glue solution;

[0011] S5: Add porous konjac glucomannan microcapsules and stir evenly;

[0012] S6: Cast into a film and react at 40 °C for 3 h;

[0013] S7: Dry to obtain.

[0014] Further, in the calcium chloride-ethanol solution in S1, the concentration of calcium chloride is 4 mol / L, and the volume fraction of ethanol is 30%.

[0015] Further, in S3, the mass ratio of water-soluble silk fibroin, gelatin and water is 2:(1 - 2):40.

[0016] Further, in S4, the addition amount of transglutaminase is 15 - 20 U / g of water-soluble silk fibroin; the addition amount of glutamine is 2 - 3 g / g of water-soluble silk fibroin.

[0017] Further, the volume ratio of the porous konjac glucomannan microcapsules to the mixed glue solution in S5 is (0.5 - 0.8):10.

[0018] Further, the preparation method of the porous konjac glucomannan microcapsules in S5 is as follows:

[0019] S51: Dissolve konjac glucomannan, xanthan gum, tannic acid, and citric acid in distilled water to obtain an aqueous phase;

[0020] S52: Mix corn oil and Tween with a mass ratio of 20:1 to obtain an oil phase;

[0021] S53: Pour the oil phase into the aqueous phase, with the volume ratio of the oil phase to the aqueous phase being (5 - 10):1, and react at a rotation speed of 100 - 150 rpm, a temperature of 50 - 95 °C, and a pH value of 4.5 for 2 - 5 h;

[0022] S54: Filter the product and wash it with distilled water to obtain the porous konjac glucomannan microcapsules.

[0023] Further, the mass ratio of the konjac glucomannan, xanthan gum, tannic acid, citric acid, and distilled water is (7 - 10):3:3:0.1:50.

[0024] Further, the particle size of the porous konjac glucomannan microcapsules is 20 - 50 μm. Beneficial effects

[0025] The present invention uses a silk fibroin - gelatin hybrid membrane doped with porous konjac glucomannan microcapsules. 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 "air holes" to regulate the permeability of gases O2 and CO2, greatly improving the selectivity of CO2 / O2, thereby maintaining an ideal atmosphere with a low O2 concentration and a high CO2 concentration, inhibiting the physiological metabolism of pre - prepared dishes and the reproduction of bacteria, so that the pre - prepared dishes can be preserved at room temperature.

[0026] The present invention uses xanthan gum to increase the cross - linking of konjac glucomannan, and at the same time uses citric acid for further cross - linking and forms a porous structure.

[0027] The present invention uses tannic acid to change the microstructure of the konjac glucomannan microcapsules, which greatly affects the gas permeability and also has a certain antibacterial effect.

[0028] The present invention introduces glutamine into the silk fibroin-gelatin hybrid membrane to enhance the cross-linking reaction between silk fibroins. Because under the action of transglutaminase, glutamine participates in the cross-linking reaction as an acyl acceptor, thereby increasing the action sites of silk fibroins, improving their cross-linking degree, and enhancing the mechanical properties of the hybrid membrane.

[0029] The present invention also cross-links gelatin and silk fibroin through non-covalent and covalent bonds to form two independent but interpenetrating network structures, thereby improving the toughness and mechanical strength of the hybrid membrane. Detailed implementation mode

[0030] The present invention will be further described below in conjunction with embodiments. The following embodiments are explanations of the present invention and the present invention is not limited to the following embodiments: Embodiment 1

[0031] The preparation method of porous konjac glucomannan microcapsules is as follows:

[0032] S1: Dissolve 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;

[0033] S2: Mix corn oil and Tween with a mass ratio of 20:1 to obtain an oil phase;

[0034] S3: Pour the oil phase into the aqueous phase, with the volume ratio of the oil phase to the aqueous phase being 8:1, and react at a rotation speed of 130 rpm, a temperature of 80 °C, and a pH value of 4.5 for 4 h;

[0035] S4: Filter the product and wash it with distilled water to obtain porous konjac glucomannan microcapsules. Embodiment 2

[0036] The preparation method of porous konjac glucomannan microcapsules is as follows:

[0037] S1: Dissolve 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;

[0038] S2: Mix corn oil and Tween with a mass ratio of 20:1 to obtain an oil phase;

[0039] S3: Pour the oil phase into the aqueous phase, with the volume ratio of the oil phase to the aqueous phase being 8:1, and react at a rotation speed of 130 rpm, a temperature of 80 °C, and a pH value of 4.5 for 4 h;

[0040] S4: Filter the product and wash it with distilled water to obtain porous konjac glucomannan microcapsules. Example 3

[0041] The preparation method of the porous konjac glucomannan microcapsules is as follows:

[0042] S1: Dissolve 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;

[0043] S2: Mix corn oil and Tween with a mass ratio of 20:1 to obtain an oil phase;

[0044] S3: Pour the oil phase into the aqueous phase, with the volume ratio of the oil phase to the aqueous phase being 8:1, and react at a rotation speed of 130 rpm, a temperature of 80 °C and a pH value of 4.5 for 4 h;

[0045] S4: Filter the product and wash it with distilled water to obtain the porous konjac glucomannan microcapsules. Example 4

[0046] The preparation method of the porous konjac glucomannan microcapsules is as follows:

[0047] S1: Dissolve 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;

[0048] S2: Mix corn oil and Tween with a mass ratio of 20:1 to obtain an oil phase;

[0049] S3: Pour the oil phase into the aqueous phase, with the volume ratio of the oil phase to the aqueous phase being 5:1, and react at a rotation speed of 130 rpm, a temperature of 80 °C and a pH value of 4.5 for 4 h;

[0050] S4: Filter the product and wash it with distilled water to obtain the porous konjac glucomannan microcapsules.

[0051] The particle size of the porous konjac glucomannan microcapsules is 20 - 50 μm. Example 5

[0052] The preparation method of the porous konjac glucomannan microcapsules is as follows:

[0053] S1: Dissolve 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;

[0054] S2: Mix corn oil and Tween with a mass ratio of 20:1 to obtain an oil phase;

[0055] S3: Pour the oil phase into the water phase with a volume ratio of the oil phase to the water phase of 10:1, and react for 4 h at a rotation speed of 130 rpm, a temperature of 80 °C, and a pH value of 4.5;

[0056] S4: Filter the product and wash it with distilled water to obtain the porous konjac glucomannan microcapsules. Example 6

[0057] The preparation method of the porous konjac glucomannan microcapsules is as follows:

[0058] S1: Dissolve konjac glucomannan, xanthan gum, tannic acid, and citric acid in distilled water to obtain the water phase; the mass ratio of konjac glucomannan, xanthan gum, tannic acid, citric acid, and distilled water is 9:3:3:0.1:50;

[0059] S2: Mix corn oil and Tween with a mass ratio of 20:1 to obtain the oil phase;

[0060] S3: Pour the oil phase into the water phase with a volume ratio of the oil phase to the water phase of 8:1, and react for 4 h at a rotation speed of 100 rpm, a temperature of 80 °C, and a pH value of 4.5;

[0061] S4: Filter the product and wash it with distilled water to obtain the porous konjac glucomannan microcapsules. Example 7

[0062] The preparation method of the porous konjac glucomannan microcapsules is as follows:

[0063] S1: Dissolve konjac glucomannan, xanthan gum, tannic acid, and citric acid in distilled water to obtain the water phase; the mass ratio of konjac glucomannan, xanthan gum, tannic acid, citric acid, and distilled water is 9:3:3:0.1:50;

[0064] S2: Mix corn oil and Tween with a mass ratio of 20:1 to obtain the oil phase;

[0065] S3: Pour the oil phase into the water phase with a volume ratio of the oil phase to the water phase of 8:1, and react for 4 h at a rotation speed of 150 rpm, a temperature of 80 °C, and a pH value of 4.5;

[0066] S4: Filter the product and wash it with distilled water to obtain the porous konjac glucomannan microcapsules.

[0067] Measure the performance of the porous konjac glucomannan microcapsules, and the results are shown in Table 1 below:

[0068] Table 1

[0069] Average particle size (μm) <![CDATA[Specific surface area is (m 2 / g)]]> Porous 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

[0070] Select the porous konjac glucomannan microcapsules prepared in Example 2 for the next experiment. Example 8

[0071] A preparation method of a composite biological fresh-keeping film for prefabricated dishes, comprising the following steps, by weight:

[0072] 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 ethanol volume fraction is 30%, heat and dissolve at 95°C, and perform ultrafiltration desalination with a 5000 Da ultrafiltration membrane;

[0073] S2: Perform spray drying, with an inlet air temperature of 170°C and an outlet air temperature of 80°C, to obtain water-soluble silk fibroin;

[0074] S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:1:40, and stir to dissolve;

[0075] S4: Add transglutaminase and glutamine, the addition amount of transglutaminase is 18 U / g of water-soluble silk fibroin; the addition amount of glutamine is 2.5 g / g of water-soluble silk fibroin, stir for 10 min to obtain a mixed glue solution;

[0076] S5: Add porous konjac glucomannan microcapsules, and the volume ratio of the porous konjac glucomannan microcapsules to the mixed glue solution is 0.7:10, and stir evenly;

[0077] S6: Cast into a film and react at 40°C for 3 h;

[0078] S7: Dry to obtain. Example 9

[0079] A preparation method of a composite biological fresh-keeping film for prefabricated dishes, comprising the following steps, by weight:

[0080] 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 ethanol volume fraction is 30%, heat and dissolve at 95°C, and perform ultrafiltration desalination with a 5000 Da ultrafiltration membrane;

[0081] S2: Perform spray drying, with an inlet air temperature of 170°C and an outlet air temperature of 80°C, to obtain water-soluble silk fibroin;

[0082] S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:2:40, and stir to dissolve;

[0083] S4: Add transglutaminase and glutamine. The addition amount of transglutaminase is 18 U / g of water-soluble silk fibroin; the addition amount of glutamine is 2.5 g / g of water-soluble silk fibroin. Stir for 10 min to obtain a mixed glue solution;

[0084] S5: Add porous konjac glucomannan microcapsules. The volume ratio of porous konjac glucomannan microcapsules to the mixed glue solution is 0.7:10. Stir evenly;

[0085] S6: Cast into a film and react at 40 °C for 3 h;

[0086] S7: Dry to obtain. Example 10

[0087] A preparation method of a composite biological fresh-keeping film for prefabricated dishes, comprising the following steps, in parts by weight:

[0088] 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 ethanol volume fraction is 30%, heat and dissolve at 95 °C, and perform ultrafiltration and desalination with a 5000 Da ultrafiltration membrane;

[0089] S2: Perform spray drying. The inlet air temperature is 170 °C and the outlet air temperature is 80 °C to obtain water-soluble silk fibroin;

[0090] S3: Take water-soluble silk fibroin, gelatin and water with a mass ratio of 2:1:40, and stir to dissolve;

[0091] S4: Add transglutaminase and glutamine. The addition amount of transglutaminase is 15 U / g of water-soluble silk fibroin; the addition amount of glutamine is 2.5 g / g of water-soluble silk fibroin. Stir for 10 min to obtain a mixed glue solution;

[0092] S5: Add porous konjac glucomannan microcapsules. The volume ratio of porous konjac glucomannan microcapsules to the mixed glue solution is 0.7:10. Stir evenly;

[0093] S6: Cast into a film and react at 40 °C for 3 h;

[0094] S7: Dry to obtain. Example 11

[0095] A preparation method of a composite biological fresh-keeping film for prefabricated dishes, comprising the following steps, in parts by weight:

[0096] S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution with a calcium chloride concentration of 4 mol / L and an ethanol volume fraction of 30% in the calcium chloride-ethanol solution, heat and dissolve at 95°C, and perform ultrafiltration desalination with a 5000 Da ultrafiltration membrane;

[0097] S2: Perform spray drying at an inlet air temperature of 170°C and an outlet air temperature of 80°C to obtain water-soluble silk fibroin;

[0098] S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:1:40, and stir to dissolve;

[0099] S4: Add transglutaminase and glutamine. The addition amount of transglutaminase is 20 U / g of water-soluble silk fibroin; the addition amount of glutamine is 2.5 g / g of water-soluble silk fibroin, and stir for 10 min to obtain a mixed glue solution;

[0100] S5: Add porous konjac glucomannan microcapsules. The volume ratio of the porous konjac glucomannan microcapsules to the mixed glue solution is 0.7:10, and stir evenly;

[0101] S6: Cast into a film and react at 40°C for 3 h;

[0102] S7: Dry to obtain. Example 12

[0103] A preparation method of a composite biological fresh-keeping film for prefabricated dishes, comprising the following steps, in parts by weight:

[0104] S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride-ethanol solution with a calcium chloride concentration of 4 mol / L and an ethanol volume fraction of 30% in the calcium chloride-ethanol solution, heat and dissolve at 95°C, and perform ultrafiltration desalination with a 5000 Da ultrafiltration membrane;

[0105] S2: Perform spray drying at an inlet air temperature of 170°C and an outlet air temperature of 80°C to obtain water-soluble silk fibroin;

[0106] S3: Take water-soluble silk fibroin, gelatin and water in a mass ratio of 2:1:40, and stir to dissolve;

[0107] S4: Add transglutaminase and glutamine. The addition amount of transglutaminase is 18 U / g of water-soluble silk fibroin; the addition amount of glutamine is 2 g / g of water-soluble silk fibroin, and stir for 10 min to obtain a mixed glue solution;

[0108] S5: Add porous konjac glucomannan microcapsules. The volume ratio of the porous konjac glucomannan microcapsules to the mixed glue solution is 0.7:10, and stir evenly;

[0109] S6: Cast the film by casting method and place it at 40 °C for reaction for 3 h;

[0110] S7: Obtain the product by drying. Example 13

[0111] A preparation method of a composite biological fresh-keeping film for prefabricated dishes, comprising the following steps, by weight:

[0112] 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 ethanol volume fraction is 30%, heat and dissolve at 95 °C, and perform ultrafiltration desalination with a 5000 Da ultrafiltration membrane;

[0113] S2: Perform spray drying, with an inlet air temperature of 170 °C and an outlet air temperature of 80 °C to obtain water-soluble silk fibroin;

[0114] S3: Take water-soluble silk fibroin, gelatin and water with a mass ratio of 2:1:40, and stir to dissolve;

[0115] S4: Add transglutaminase and glutamine, the addition amount of transglutaminase is 18 U / g of water-soluble silk fibroin; the addition amount of glutamine is 3 g / g of water-soluble silk fibroin, stir for 10 min to obtain a mixed glue solution;

[0116] S5: Add porous konjac glucomannan microcapsules, and the volume ratio of the porous konjac glucomannan microcapsules to the mixed glue solution is 0.7:10, and stir evenly;

[0117] S6: Cast the film by casting method and place it at 40 °C for reaction for 3 h;

[0118] S7: Obtain the product by drying. Example 14

[0119] A preparation method of a composite biological fresh-keeping film for prefabricated dishes, comprising the following steps, by weight:

[0120] 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 ethanol volume fraction is 30%, heat and dissolve at 95 °C, and perform ultrafiltration desalination with a 5000 Da ultrafiltration membrane;

[0121] S2: Perform spray drying, with an inlet air temperature of 170 °C and an outlet air temperature of 80 °C to obtain water-soluble silk fibroin;

[0122] S3: Take water-soluble silk fibroin, gelatin and water with a mass ratio of 2:1:40, and stir to dissolve;

[0123] S4: Add transglutaminase and glutamine. The addition amount of transglutaminase is 18 U / g of water-soluble silk fibroin; the addition amount of glutamine is 2.5 g / g of water-soluble silk fibroin. Stir for 10 min to obtain a mixed glue solution;

[0124] S5: Add porous konjac glucomannan microcapsules. The volume ratio of porous konjac glucomannan microcapsules to the mixed glue solution is 0.5:10. Stir evenly;

[0125] S6: Cast into a film and react at 40 °C for 3 h;

[0126] S7: Dry to obtain. Example 15

[0127] A preparation method of a composite biological fresh-keeping film for prefabricated dishes, comprising the following steps, in parts by weight:

[0128] 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, and the ethanol volume fraction is 30%. Heat and dissolve at 95 °C, and perform ultrafiltration desalination with a 5000 Da ultrafiltration membrane;

[0129] S2: Perform spray drying. The inlet air temperature is 170 °C and the outlet air temperature is 80 °C to obtain water-soluble silk fibroin;

[0130] S3: Take water-soluble silk fibroin, gelatin and water with a mass ratio of 2:1:40, and stir to dissolve;

[0131] S4: Add transglutaminase and glutamine. The addition amount of transglutaminase is 18 U / g of water-soluble silk fibroin; the addition amount of glutamine is 2.5 g / g of water-soluble silk fibroin. Stir for 10 min to obtain a mixed glue solution;

[0132] S5: Add porous konjac glucomannan microcapsules. The volume ratio of porous konjac glucomannan microcapsules to the mixed glue solution is 0.8:10. Stir evenly;

[0133] S6: Cast into a film and react at 40 °C for 3 h;

[0134] S7: Dry to obtain. Comparative Example 1

[0135] The difference between this comparative example and Example 8 is: Do not add porous konjac glucomannan microcapsules, specifically as follows:

[0136] A preparation method of a composite biological fresh-keeping film for prefabricated dishes, comprising the following steps, in parts by weight:

[0137] S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride - ethanol solution, where the calcium chloride concentration in the calcium chloride - ethanol solution is 4 mol / L and the ethanol volume fraction is 30%. Heat and dissolve at 95°C, and perform ultrafiltration desalination with a 5000 Da ultrafiltration membrane;

[0138] S2: Perform spray drying, with an inlet air temperature of 170°C and an outlet air temperature of 80°C, to obtain water - soluble silk fibroin;

[0139] S3: Take water - soluble silk fibroin, gelatin, and water in a mass ratio of 2:1:40, and stir to dissolve;

[0140] S4: Add transglutaminase and glutamine. The addition amount of transglutaminase is 18 U / g of water - soluble silk fibroin; the addition amount of glutamine is 2.5 g / g of water - soluble silk fibroin, and stir for 10 min to obtain a mixed glue solution;

[0141] S5: Cast into a film and place it at 40°C for reaction for 3 h;

[0142] S6: Dry to obtain. Comparative Example 2

[0143] The difference between this comparative example and Example 8 is that: tannic acid is not added to the porous konjac glucomannan microcapsule, specifically as follows:

[0144] A preparation method of a composite biological fresh - keeping film for pre - prepared dishes, comprising the following steps, in parts by weight:

[0145] S1: Take 8 parts of silk fibroin, add 140 parts of calcium chloride - ethanol solution, where the calcium chloride concentration in the calcium chloride - ethanol solution is 4 mol / L and the ethanol volume fraction is 30%. Heat and dissolve at 95°C, and perform ultrafiltration desalination with a 5000 Da ultrafiltration membrane;

[0146] S2: Perform spray drying, with an inlet air temperature of 170°C and an outlet air temperature of 80°C, to obtain water - soluble silk fibroin;

[0147] S3: Take water - soluble silk fibroin and water in a mass ratio of 3:40, and stir to dissolve;

[0148] S4: Add transglutaminase and glutamine. The addition amount of transglutaminase is 18 U / g of water - soluble silk fibroin; the addition amount of glutamine is 2.5 g / g of water - soluble silk fibroin, and stir for 10 min to obtain a mixed glue solution;

[0149] S5: Add porous konjac glucomannan microcapsules, and the volume ratio of the porous konjac glucomannan microcapsules to the mixed glue solution is 0.7:10, and stir evenly;

[0150] S6: Cast the film and react at 40 °C for 3 h;

[0151] S7: Dry to obtain the product.

[0152] The preparation method of the porous konjac glucomannan microcapsule is as follows:

[0153] S1: Dissolve 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;

[0154] S2: Mix corn oil and Tween with a mass ratio of 20:1 to obtain an oil phase;

[0155] S3: Pour the oil phase into the aqueous phase, with the volume ratio of the oil phase to the aqueous phase being 8:1, and react at a rotation speed of 130 rpm, a temperature of 80 °C, and a pH value of 4.5 for 4 h;

[0156] S4: Filter the product and wash it with distilled water to obtain the porous konjac glucomannan microcapsule. Comparative Example 3

[0157] The difference between this comparative example and Example 8 is that gelatin is not added, specifically as follows:

[0158] A preparation method of a composite biological fresh-keeping film for prefabricated dishes, comprising the following steps, in parts by weight:

[0159] 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 ethanol volume fraction is 30%, heat and dissolve at 95 °C, and perform ultrafiltration desalination with a 5000 Da ultrafiltration membrane;

[0160] S2: Perform spray drying, with an inlet air temperature of 170 °C and an outlet air temperature of 80 °C, to obtain water-soluble silk fibroin;

[0161] S3: Take water-soluble silk fibroin and water with a mass ratio of 3:40, and stir to dissolve;

[0162] S4: Add transglutaminase and glutamine, the addition amount of transglutaminase is 18 U / g of water-soluble silk fibroin; the addition amount of glutamine is 2.5 g / g of water-soluble silk fibroin, stir for 10 min to obtain a mixed glue solution;

[0163] S5: Add the porous konjac glucomannan microcapsule, with the volume ratio of the porous konjac glucomannan microcapsule to the mixed glue solution being 0.7:10, and stir evenly;

[0164] S6: Cast the film and react at 40 °C for 3 h;

[0165] S7: Obtain by drying.

[0166] Table 2

[0167] Oxygen permeability (mol / (m·s·Pa)) Carbon dioxide permeability (mol / (m·s·Pa)) <![CDATA[CO2 / O2 selectivity]]> Breaking strength Example 8 <![CDATA[2.63×10 -16 > <![CDATA[2.21×10 -15 > 8.9 4.8 Example 9 <![CDATA[2.49×10 -16 > <![CDATA[2.02×10 -15 > 8.3 5.1 Example 10 <![CDATA[3.12×10 -16 > <![CDATA[2.68×10 -15 > 8.5 4.7 Example 11 <![CDATA[2.45×10 -16 > <![CDATA[2.10×10 -15 > 8.8 4.9 Example 12 <![CDATA[2.77×10 -16 > <![CDATA[2.26×10 -15 > 8.8 4..7 Example 13 <![CDATA[2.60×10 -16 > <![CDATA[2.18×10 -15 > 8.9 4.9 Example 14 <![CDATA[1.02×10 -16 > <![CDATA[1.03×10 -15 > 7.9 4.9 Example 15 <![CDATA[2.81×10 -16 > <![CDATA[2.33×10 -15 > 9.1 4.6 Comparative Example 1 <![CDATA[5.77×10 -17 > <![CDATA[2.76×10 -16 > 4.4 5.1 Comparative Example 2 <![CDATA[9.96×10 -17 > <![CDATA[7.74×10 -16 > 6.0 4.8 Comparative Example 3 <![CDATA[2.69×10 -16 > <![CDATA[2.33×10 -15 > 8.9 4.4

[0168] Use the composite biological fresh-keeping films for prefabricated dishes prepared in Example 8, Comparative Example 1, Comparative Example 2, and Comparative Example 3 to preserve prefabricated dishes. Wrap and seal the prefabricated dishes with the fresh-keeping films of the above examples, and measure the weight loss rate (%) after storage at 4°C (refrigerated) and 25°C (room temperature) for 10 days. The results are shown in Table 3:

[0169] Table 3

[0170] Refrigerated weight loss rate (%) Normal temperature weight loss rate (%) 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

[0171] The above are only the preferred embodiments of the present invention and do not impose any form of limitation on the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes, without departing from the spirit and technical solution of the present invention. Therefore, any simple modification, equivalent replacement, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention still fall 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 preservative film is a silk fibroin-gelatin hybrid film doped with porous konjac glucomannan microcapsules; The preparation method comprises the following steps, measured 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 5000 Da 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: adding transglutaminase and glutamine, stirring for 5-10 minutes, to obtain a mixed glue solution; the amount of transglutaminase added is 15-20 U / g water-soluble silk fibroin; the amount of glutamine added is 2-3 g / g water-soluble silk fibroin; S5: adding porous konjac glucomannan microcapsules and stirring evenly; S6: Casting film, reacting at 40°C for 3h; S7: Dry and ready to use; 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 distilled water to obtain porous konjac glucomannan microcapsules.

2. The composite biological preservative film for pre-prepared dishes according to claim 1, 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%.

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

40.

4. The composite biological preservative film for pre-prepared dishes according to claim 1, characterized in that: The volume ratio of the porous konjac glucomannan microcapsules to the mixed colloid in S5 is (0.5-0.8):

10.

5. The composite biological preservative film for pre-prepared dishes according to claim 1, 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.

6. The composite biological preservative film for pre-prepared dishes according to claim 1, characterized in that: The particle size of the porous konjac glucomannan microcapsule is 20-50 μm.