Prepared vegetable fragrance and freshness retaining film and preparation method thereof

Abstract

The invention provides a fragrance-keeping and fresh-keeping film for prefabricated vegetables and a preparation method thereof, the fragrance-keeping and fresh-keeping film is a double-layer film, the lower layer is a fragrance-keeping layer, the upper layer is a fresh-keeping layer, and the film is laid in a casting manner. Wherein the main components of the fragrance keeping layer are amidated algin and cellulose, and can be combined with flavor substances to achieve the purposes of controlled release and fragrance keeping; the main components of the fresh-keeping layer are grape seed enzymolysis polypeptide liquid, starch and cinnamon essential oil, the three components have a synergistic effect to achieve the effects of inhibiting bacteria and keeping fresh, and a new thought is provided for fragrance keeping and fresh keeping of the prefabricated vegetables.

Description

Technical Field

[0001] The invention belongs to the technical field of food processing, and in particular relates to a film for pre-prepared food aroma preservation and freshness preservation and a preparation method thereof. Background Art

[0002] Pre-prepared food is a kind of finished or semi-finished product that has been processed and treated in advance. 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, meat pre-prepared food is mainly divided into fermented meat products and pre-prepared conditioned meat products. The former is a product made of fresh or frozen livestock meat as the main raw material, and is made through pretreatment and fermentation processes; the latter is a non-ready-to-eat product made of fresh or frozen livestock meat or other edible by-products as the main raw materials, and is conditioned and refrigerated, and stored at a temperature of 0 to 4°C. At present, pre-prepared conditioned meat products are processed with auxiliary materials, condiments, etc. to improve their flavor. However, since meat is rich in nutrients, it is easily contaminated by microorganisms during storage and transportation, which leads to the deterioration of product quality during the maturation process, and the decline of taste and flavor, which has become a common problem restricting the development of pre-prepared food. Most of the current cling films are petroleum-based plastics, which are difficult to degrade and non-renewable materials. Therefore, the development of biodegradable and renewable natural fragrance cling films has very important research significance. Flavor is one of the important indicators of food sensory quality. There are many kinds of flavor substances, most of which are volatile small molecules. However, their stability is relatively poor and they are easily affected by external environments such as light, heat, and oxygen, causing them to evaporate or deteriorate. Cellulose is the most widely distributed and abundant natural renewable polymer in nature. It mainly comes from plants, including natural vegetation and crops, and can also be synthesized by fermentation of certain microorganisms. Cellulose has excellent stability, good biocompatibility and degradability, and can be combined with flavor molecules in a variety of ways. It has a wide range of applications in the field of flavor substance adsorption and embedding. Carbohydrates are widely present in various foods and are an extremely important nutrient. Their impact on food flavor quality is complex and difficult to predict. Carbohydrates can serve as food flavor precursors and become the main source of food characteristic flavor compounds under the action of enzymatic hydrolysis. They can also play an important role in the formation of food derived flavors (such as the Maillard reaction causing the formation of heterocyclic compounds in food). On the other hand, after the formation of flavor compounds, carbohydrates can inhibit the release of volatile flavor compounds by direct encapsulation or entrapment, or indirectly affect the retention of flavor compounds in food by affecting food quality (such as texture) and food physicochemical properties (such as pH, ionic strength, water activity). With the deepening of research, carbohydrates are often added to food to improve the sensory quality of food or hide odors. For example, starch, cyclodextrin, alginate, pectin, etc. have been used as flavor encapsulation carriers to protect volatile compounds or achieve the purpose of controlled release. Amidated alginate can also combine with flavor substances to achieve the purpose of controlled release. At present, the preservation technologies for meat products at home and abroad mainly include coating preservation, high pressure preservation, irradiation preservation, and modified atmosphere preservation. Natural antioxidant coating preservation is more environmentally friendly, safe, and reliable than other preservation technologies, and has low equipment requirements and is easy to operate. However, there are few natural antioxidant products that can be truly applied to meat product preservation. On the one hand, the cost of developing and producing natural antioxidants is high, and on the other hand, some natural antioxidants have limited antibacterial effects and cannot achieve a good preservation effect. Grape seed peptides are a class of biologically active peptides extracted from grape seeds. They have significant antioxidant activity and also show multiple biological activities such as antibacterial activity, emulsification stability, immunomodulation, and anti-tumor. Cinnamon essential oil has significant antibacterial and antioxidant activities due to its unique chemical composition, such as cinnamaldehyde, which makes it have a wide range of application potential in the field of food preservation. Studies have shown that cinnamon essential oil can effectively inhibit the growth of microorganisms, slow down the oxidation process of food, and thus extend the shelf life of food. In terms of meat preservation, cinnamon essential oil can be used as a natural preservative. It can effectively extend the shelf life of fresh meat through coating treatment or in combination with other preservation technologies such as modified atmosphere packaging. Summary of the invention

[0003] Technical problems to be solved: In view of the above technical problems, the purpose of the present invention is to provide a pre-prepared food aroma preservation and fresh-keeping film and a preparation method thereof, wherein the aroma preservation and fresh-keeping film is a double-layer film, wherein the lower layer is an aroma preservation layer and the upper layer is a fresh-keeping layer, and is laid by casting. Among them, the main components of the aroma preservation layer are amidated alginate and cellulose, which can be combined with flavor substances to achieve the purpose of controlled release and aroma preservation; the main components of the fresh-keeping layer are grape seed enzymatic polypeptide liquid, starch, and cinnamon essential oil, and the three synergistically enhance the effect of antibacterial preservation.

[0004] Technical solution: A fragrance-preserving and fresh-keeping film for pre-prepared dishes, wherein the fragrance-preserving and fresh-keeping film is a double-layer film, wherein the lower layer is a fragrance-preserving layer, and the upper layer is a fresh-keeping layer, and is laid in a casting manner. Furthermore, the main components of the aroma-preserving layer are amidated alginate and cellulose; the main components of the fresh-keeping layer are grape seed enzymatic polypeptide liquid, starch, and cinnamon essential oil. Furthermore, the preparation steps of the grape seed enzymatic polypeptide solution are as follows: S1. Grind the de-oiled grape seeds and pass them through a 20-50 mesh sieve to obtain grape seed powder; S2. dissolving grape seed powder in water and subjecting it to heat denaturation treatment at 100°C for 10-15 minutes; S3. Add pectinase to the solution obtained in S2, stir evenly, heat in a water bath at 80°C for 5 min, and then quickly adjust the pH to 8-9 with NaHCO3 solution to obtain a preliminary enzymatic solution; S4. Add alkaline protease to the preliminary enzymatic hydrolysis solution, stir and mix, and then perform enzymatic hydrolysis at 50°C for 3-4 hours to inactivate the enzyme to obtain the grape seed enzymatic hydrolyzed polypeptide solution. Furthermore, in step S2, the mass volume ratio of grape seed powder to water is 1 g: (15-35) mL. Furthermore, the mass ratio of the grape seed powder to pectinase and alkaline protease is 1:(0.03-0.06):(0.02-0.04). Furthermore, the preparation steps of the fresh-keeping layer are: Step 1: Weigh starch, add 10-15 times the volume of water, and stir evenly at 50-60°C to obtain a starch solution; Step 2: Add grape seed enzymatic polypeptide solution and cinnamon essential oil to the starch solution and stir evenly to obtain a plastic wrap solution; Step 3: Spread the plastic wrap liquid evenly on the polytetrafluoroethylene plate and dry it to obtain the fresh-keeping layer. Furthermore, in step 2, the volume ratio of the starch solution, the grape seed enzymatic polypeptide solution and the cinnamon essential oil is 5:(1-2):(2-3). Furthermore, the pre-prepared food fragrance and fresh-keeping film comprises the following steps: (1) dissolving 1-4 parts of chitosan in an acetic acid solution having a concentration of 1-2%, stirring at 800-1000 rpm for 30-40 minutes, ultrasonically treating for 5-10 minutes, and then stirring at room temperature for 5-8 minutes to obtain a chitosan solution; (2) dissolving 1-2 parts of glycerol and 2-5 parts of alginate in deionized water, stirring at 1000-1200 rpm for 40-60 min to obtain an alginate solution; (3) mixing the chitosan solution and the alginate solution, and stirring at 600-800 rpm for 60 min to obtain an amidated alginate solution; (4) Weigh a certain amount of cellulose, dissolve it in deionized water, heat it at 85-90°C to dissolve it, and prepare it into a mass fraction It is a 1-2% cellulose solution; (5) mixing the amidated alginate solution with the cellulose solution and stirring them evenly to prepare a fragrance-retaining layer mixed membrane solution; (6) Casting the aroma-preserving layer mixed film solution on the fresh-keeping layer and drying it to obtain an aroma-preserving fresh-keeping film. Furthermore, in step S13, the volume ratio of the chitosan solution to the alginate solution is 2:(3-4). Furthermore, in step S15, the volume ratio of the amidated alginate solution to the cellulose solution is (2-3):1. Beneficial effects: 1. The main components of the aroma-preserving layer prepared by the present invention are amidated alginate and cellulose. The -COOH in alginate reacts with the -NH2 of chitosan to generate amidated alginate, which can combine with flavor substances through hydrophobic interaction and hydrogen bonding to control the release of flavor substances. The various fine channels and pores of alginate will have a certain adsorption capacity for flavor compounds, and can also form a macromolecular network to produce a physical retention effect on flavor components. In addition, the hydroxyl groups in cellulose are easy to form hydrogen bonds with the polar functional groups of flavor substances, thereby playing a role in adsorbing flavor substances. The amidated alginate is combined with the cellulose microfibers, and the prepared aroma-preserving layer can better adsorb and control the release of flavor components of pre-prepared dishes. At the same time, the mechanical properties of the aroma-preserving and fresh-keeping film after the two are combined are also enhanced. 2. The main components of the fresh-keeping layer prepared by the present invention are grape seed enzymatic polypeptide liquid, starch, and cinnamon essential oil, wherein the grape seed enzymatic polypeptide liquid has significant antioxidant activity and antibacterial properties; the starch-based fresh-keeping film can form a protective film on the surface of the pre-prepared dish, inhibit respiration, reduce water volatilization, and delay quality deterioration, thereby achieving a long-term fresh-keeping effect and effectively extending the shelf life of the food; the cinnamon essential oil can inhibit the growth of spoilage bacteria, delay the decline in meat quality, and extend its shelf life. The three synergistically enhance the effect of antibacterial preservation. 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 steps of grape seed enzymatic polypeptide solution are as follows: S1. Grind the de-oiled grape seeds and pass them through a 20-mesh sieve to obtain grape seed powder; S2. dissolve grape seed powder in water at a mass volume ratio of 1 g:15 mL, and heat denature at 100°C for 10 min; S3. Add pectinase to the solution obtained in S2, stir evenly, heat in a water bath at 80°C for 5 min, and then quickly adjust the pH to 8 with NaHCO3 solution to obtain a preliminary enzymatic solution; S4. Add alkaline protease to the preliminary enzymatic hydrolysis solution. The mass ratio of grape seed powder to pectinase and alkaline protease is 1:0.03:0.02. After stirring and mixing, perform enzymatic hydrolysis at 50°C for 3 hours, inactivate the enzyme, and obtain grape seed enzymatic polypeptide solution. Example 2 The preparation steps of grape seed enzymatic polypeptide solution are as follows: S1. Grind the de-oiled grape seeds and pass them through a 30-mesh sieve to obtain grape seed powder; S2. dissolve grape seed powder in water at a mass volume ratio of 1 g:25 mL, and heat denature at 100°C for 12 min; S3. Add pectinase to the solution obtained in S2, stir evenly, heat in a water bath at 80°C for 5 min, and then quickly adjust the pH to 8.5 with NaHCO3 solution to obtain a preliminary enzymatic solution; S4. Add alkaline protease to the preliminary enzymatic hydrolysis solution. The mass ratio of grape seed powder to pectinase and alkaline protease is 1:0.04:0.03. After stirring and mixing, perform enzymatic hydrolysis at 50°C for 3.5 hours and inactivate the enzyme to obtain grape seed enzymatic polypeptide solution. Example 3 The preparation steps of grape seed enzymatic polypeptide solution are as follows: S1. Grind the de-oiled grape seeds and pass them through a 50-mesh sieve to obtain grape seed powder; S2. dissolving grape seed powder in water at a mass volume ratio of 1 g:35 mL, and heat denaturing at 100°C for 15 min; S3. Add pectinase to the solution obtained in S2, stir evenly, heat in a water bath at 80°C for 5 min, and then quickly adjust the pH to 9 with NaHCO3 solution to obtain a preliminary enzymatic solution; S4. Add alkaline protease to the preliminary enzymatic hydrolysis solution. The mass ratio of grape seed powder to pectinase and alkaline protease is 1:0.06:0.04. After stirring and mixing, perform enzymatic hydrolysis at 50°C for 4 hours, inactivate the enzyme, and obtain grape seed enzymatic polypeptide solution. Performance Test: (1) Antioxidant Determination of DPPH free radical scavenging ability: 1 mL of the grape seed enzymatic polypeptide solution prepared in Example 1-3 was reacted with 3 mL of DPPH, and the absorbance was measured at 517 nm when the reaction was in equilibrium to study its scavenging rate for DPPH free radicals. Where: A0 is the blank absorbance value; A is the absorbance value of DPPH added to the sample at 517nm; Ab It is the absorbance value of DPPH without adding sample at 517nm. Table 1 DPPH removal rate of grape seed enzymatic polypeptide solution Example 1 Example 2 Example 3 Clearance rate (%) 43.03 43.26 43.15 As shown in Table 1, the DPPH scavenging rates of the grape seed enzymatic polypeptide solutions prepared in Examples 1-3 were 43.03-43.26%. The higher the DPPH scavenging rate, the stronger the antioxidant activity. It can be seen that Example 2 has the best antioxidant activity. (2) Antibacterial properties The antibacterial diameter is used as the standard for evaluating the antibacterial performance of the grape seed enzymatic polypeptide liquid. The experimental strains used meat spoilage bacteria Escherichia coli and Pseudomonas fluorescens. The two strains were added to LB broth respectively and cultured at 35°C for 24 hours. Sterile water was added to dilute the bacterial liquid 10 times as the initial bacterial liquid. 0.1 mL of the initial bacterial liquid was dropped on the PCA agar solid culture medium and spread on the plate. The grape seed enzymatic polypeptide liquid prepared by the present invention was dropped into the center of the culture medium, cultured at 37°C for 24 hours, and the diameter of the antibacterial zone was observed and measured. Table 2 Diameter of inhibition zone of grape seed enzymatic polypeptide solution (mm) Example 1 Example 2 Example 3 Escherichia coli 13.9±0.3 13.4±0.4 13.6±0.3 Pseudomonas fluorescens 15.3±0.5 15.1±0.3 15.7±0.6 As shown in Table 2, the grape seed enzymatic polypeptide liquid prepared in Examples 1-3 has a better antibacterial effect on Escherichia coli than on Pseudomonas fluorescens, and the grape seed enzymatic polypeptide liquid prepared in Example 2 has the smallest antibacterial zone diameter and the best antibacterial property. Therefore, the grape seed enzymatic polypeptide liquid prepared in Example 2 was selected for the subsequent preparation of the fresh-keeping layer. Example 4 A film for pre-prepared food aroma preservation and freshness preservation, the preparation steps are as follows: Step 1: Weigh starch, add 10 times the volume of water, and stir evenly at 50°C to obtain a starch solution; Step 2: Add the grape seed enzymatic polypeptide solution prepared in Example 2 and cinnamon essential oil to the starch solution in a volume ratio of 5:1:2, and stir evenly to obtain a preservative film solution; Step 3: Spread the cling film liquid evenly on the polytetrafluoroethylene plate and dry it to obtain a cling film layer; Step 4: dissolving 1 part of chitosan in 1% acetic acid solution, stirring at 800 rpm for 40 min, ultrasonically treating for 5 min, and stirring at room temperature for 5 min to obtain a chitosan solution; Step 5: Dissolve 1 part of glycerol and 2 parts of alginate in deionized water, and stir at 1000 rpm for 60 min to obtain an alginate solution; Step 6: Mix the chitosan solution and the alginate solution in a volume ratio of 2:3, and stir at 600 rpm for 60 min to obtain an amidated alginate solution; Step 7: Weigh a certain amount of cellulose, dissolve it in deionized water, heat it at 85°C to dissolve it, and prepare a cellulose solution with a mass fraction of 1%; Step 8: Mix the amidated alginate solution and the cellulose solution in a volume ratio of 2:1, stir evenly, and prepare a fragrance-retaining layer mixed membrane solution; Step 9: Cast the aroma-preserving layer mixed film solution on the fresh-keeping layer and dry it to obtain the aroma-preserving fresh-keeping film. Example 5 A film for pre-prepared food aroma preservation and freshness preservation, the preparation steps are as follows: Step 1: Weigh starch, add 12 times the volume of water, and stir evenly at 54°C to obtain a starch solution; Step 2: Add the grape seed enzymatic polypeptide solution prepared in Example 2 and cinnamon essential oil to the starch solution in a volume ratio of 5:1:2, and stir evenly to obtain a preservative film solution; Step 3: Spread the cling film liquid evenly on the polytetrafluoroethylene plate and dry it to obtain a cling film layer; Step 4: dissolving 2 parts of chitosan in a 1% acetic acid solution, stirring at 900 rpm for 35 minutes, ultrasonically treating for 8 minutes, and then stirring at room temperature for 7 minutes to obtain a chitosan solution; Step 5: Dissolve 1.5 parts of glycerol and 4 parts of alginate in deionized water, and stir at 1100 rpm for 50 min to obtain an alginate solution; Step 6: Mix the chitosan solution and the alginate solution in a volume ratio of 2:3.5, and stir at 700 rpm for 60 min to obtain an amidated alginate solution; Step 7: Weigh a certain amount of cellulose, dissolve it in deionized water, heat it at 88°C to dissolve it, and prepare a cellulose solution with a mass fraction of 1.5%; Step 8: Mix the amidated alginate solution and the cellulose solution at a volume ratio of 2.5:1, stir evenly, and prepare a fragrance-retaining layer mixed membrane solution; Step 9: Cast the aroma-preserving layer mixed film solution on the fresh-keeping layer and dry it to obtain the aroma-preserving fresh-keeping film. Example 6 A film for pre-prepared food aroma preservation and freshness preservation, the preparation steps are as follows: Step 1: Weigh starch, add 14 times the volume of water, and stir evenly at 56°C to obtain a starch solution; Step 2: Add the grape seed enzymatic polypeptide solution prepared in Example 2 and cinnamon essential oil to the starch solution in a volume ratio of 5:2:2.5, and stir evenly to obtain a plastic wrap solution; Step 3: Spread the cling film liquid evenly on the polytetrafluoroethylene plate and dry it to obtain a cling film layer; Step 4: dissolving 4 parts of chitosan in a 2% acetic acid solution, stirring at 1000 rpm for 30 minutes, ultrasonically treating for 10 minutes, and then stirring at room temperature for 8 minutes to obtain a chitosan solution; Step 5: Dissolve 2 parts of glycerol and 5 parts of alginate in deionized water, and stir at 1200 rpm for 40 minutes to obtain an alginate solution; Step 6: Mix the chitosan solution and the alginate solution in a volume ratio of 2:4, and stir at 800 rpm for 60 minutes to obtain an amidated alginate solution; Step 7: Weigh a certain amount of cellulose, dissolve it in deionized water, heat it at 89°C to dissolve it, and prepare a cellulose solution with a mass fraction of 2%; Step 8: Mix the amidated alginate solution and the cellulose solution in a volume ratio of 3:1, stir evenly, and prepare a fragrance-retaining layer mixed membrane solution; Step 9: Cast the aroma-preserving layer mixed film solution on the fresh-keeping layer and dry it to obtain the aroma-preserving fresh-keeping film. Example 7 A film for pre-prepared food fragrance preservation and freshness preservation, the preparation steps are as follows: Step 1: Weigh starch, add 15 times the volume of water, and stir evenly at 60°C to obtain a starch solution; Step 2: Add the grape seed enzymatic polypeptide solution prepared in Example 2 and cinnamon essential oil to the starch solution in a volume ratio of 5:2:3, and stir evenly to obtain a plastic wrap solution; Step 3: Spread the cling film liquid evenly on the polytetrafluoroethylene plate and dry it to obtain a cling film layer; Step 4: dissolving 2 parts of chitosan in a 2% acetic acid solution, stirring at 900 rpm for 35 minutes, ultrasonically treating for 8 minutes, and then stirring at room temperature for 7 minutes to obtain a chitosan solution; Step 5: Dissolve 1.5 parts of glycerol and 4 parts of alginate in deionized water, and stir at 1100 rpm for 50 min to obtain an alginate solution; Step 6: Mix the chitosan solution and the alginate solution in a volume ratio of 2:4, and stir at 700 rpm for 60 min to obtain an amidated alginate solution; Step 7: Weigh a certain mass of cellulose, dissolve it in deionized water, heat it at 90° C. to dissolve it, and prepare a cellulose solution with a mass fraction of 1.5%; Step 8: Mix the amidated alginate solution and the cellulose solution in a volume ratio of 2.5:1, stir evenly, and prepare a fragrance-retaining layer mixed membrane solution; Step 9: Cast the aroma-preserving layer mixed film solution on the fresh-keeping layer and dry it to obtain the aroma-preserving fresh-keeping film. Comparative Example 1 The difference between this comparative example and Example 5 is that unmodified alginate is used to prepare the fragrance-preserving layer, specifically as follows: A film for pre-prepared food aroma preservation and freshness preservation, the preparation steps are as follows: Step 1: Weigh starch, add 12 times the volume of water, and stir evenly at 54°C to obtain a starch solution; Step 2: Add the grape seed enzymatic polypeptide solution prepared in Example 2 and cinnamon essential oil to the starch solution in a volume ratio of 5:1:2, and stir evenly to obtain a preservative film solution; Step 3: Spread the cling film liquid evenly on the polytetrafluoroethylene plate and dry it to obtain a cling film layer; Step 4: Dissolve 1.5 parts of glycerol and 4 parts of alginate in deionized water, and stir at 1100 rpm for 50 min to obtain an alginate solution; Step 5: Weigh a certain mass of cellulose, dissolve it in deionized water, heat it at 88°C to dissolve it, and prepare a cellulose solution with a mass fraction of 1.5%; Step 6: Mix the alginate solution and the cellulose solution in a volume ratio of 2.5:1, stir evenly, and prepare a fragrance-retaining layer mixed membrane solution; Step 7: Cast the aroma-preserving layer mixed film solution on the fresh-keeping layer and dry it to obtain the aroma-preserving fresh-keeping film. Comparative Example 2 The difference between this comparative example and Example 5 is that no cellulose is added to prepare the aroma-retaining layer, which is as follows: A film for pre-prepared food aroma preservation and freshness preservation, the preparation steps are as follows: Step 1: Weigh starch, add 12 times the volume of water, and stir evenly at 54°C to obtain a starch solution; Step 2: Add the grape seed enzymatic polypeptide solution prepared in Example 2 and cinnamon essential oil to the starch solution in a volume ratio of 5:1:2, and stir evenly to obtain a preservative film solution; Step 3: Spread the cling film liquid evenly on the polytetrafluoroethylene plate and dry it to obtain a cling film layer; Step 4: dissolving 2 parts of chitosan in a 1% acetic acid solution, stirring at 900 rpm for 35 minutes, ultrasonically treating for 8 minutes, and then stirring at room temperature for 7 minutes to obtain a chitosan solution; Step 5: Dissolve 1.5 parts of glycerol and 4 parts of alginate in deionized water, and stir at 1100 rpm for 50 min to obtain an alginate solution; Step 6: Mix the chitosan solution and the alginate solution in a volume ratio of 2:3.5, and stir at 700 rpm for 60 min to obtain an amidated alginate solution; Step 7: Cast the amidated alginate solution on the fresh-keeping layer and dry it to obtain a fragrance-preserving fresh-keeping film. Comparative Example 3 The difference between this comparative example and Example 5 is that cinnamon essential oil is not added to prepare the fresh-keeping layer, which is as follows: A film for pre-prepared food fragrance preservation and freshness preservation, the preparation steps are as follows: Step 1: Weigh starch, add 12 times the volume of water, and stir evenly at 54°C to obtain a starch solution; Step 2: Add the grape seed enzymatic polypeptide solution prepared in Example 2 to the starch solution at a volume ratio of 5:1, and stir evenly to obtain a plastic wrap solution; Step 3: Spread the cling film liquid evenly on the polytetrafluoroethylene plate and dry it to obtain a cling film layer; Step 4: dissolving 2 parts of chitosan in a 1% acetic acid solution, stirring at 900 rpm for 35 minutes, ultrasonically treating for 8 minutes, and then stirring at room temperature for 7 minutes to obtain a chitosan solution; Step 5: Dissolve 1.5 parts of glycerol and 4 parts of alginate in deionized water, and stir at 1100 rpm for 50 min to obtain an alginate solution; Step 6: Mix the chitosan solution and the alginate solution in a volume ratio of 2:3.5, and stir at 700 rpm for 60 min to obtain an amidated alginate solution; Step 7: Weigh a certain amount of cellulose, dissolve it in deionized water, heat it at 88°C to dissolve it, and prepare a cellulose solution with a mass fraction of 1.5%; Step 8: Mix the amidated alginate solution and the cellulose solution in a volume ratio of 2.5:1, stir evenly, and prepare a fragrance-retaining layer mixed membrane solution; Step 9: Cast the aroma-preserving layer mixed film solution on the fresh-keeping layer and dry it to obtain the aroma-preserving fresh-keeping film. Performance Testing: (3) Determination of volatile flavor components The aroma-preserving layer films prepared in Examples 4-7 and Comparative Examples 1-3 were applied to pre-prepared meat dishes, and the volatile flavor components were measured after being left for one month. Table 3 Relative content of volatile flavor substances in pre-prepared dishes As shown in Table 3, the aroma-preserving and fresh-keeping films prepared in Examples 4-7 make the total content of volatile flavor substances in the prepared dishes 48.34-49.12 μg / kg, while the total content of volatile flavor substances in the aroma-preserving and fresh-keeping films prepared by unmodified alginate in Comparative Example 1 is slightly reduced to 45.72 μg / kg; the total content of volatile flavor substances in the aroma-preserving and fresh-keeping films prepared by Comparative Example 2 without adding cellulose is 42.68 μg / kg, which is significantly reduced; the aroma-preserving and fresh-keeping films prepared by Comparative Example 3 without adding cinnamon essential oil have little effect on volatile flavor substances. It can be seen that both amidated alginate and cellulose can combine with flavor substances to achieve the purpose of aroma preservation. (4) Mechanical properties The fragrance-preserving and fresh-keeping film prepared by the present invention is cut into 4 cm×1.5 cm samples, and the tensile strength (TS) and elongation at break (EAB) are measured by a texture analyzer, the probe is AT / G, the test component spacing is 3 cm, and the stretching speed is 0.5 mm / s. The tensile strength and elongation at break are calculated as follows: TS=F / S Where: TS is the tensile strength (MPa); F is the maximum tensile force received when the membrane breaks (N); S is the cross-sectional area of ​​the membrane (m 2 ). EAB=(L0-L) / L*100% Where: EAB is the elongation at break (%); L0 is the length of the film when it breaks (cm); L is the initial spacing of the test parts of the film (cm), which is 3 cm. Table 4 Mechanical properties of aroma and freshness-preserving films Tensile strength(MPa) Elongation at break (%) Example 4 58.46 83.45 Example 5 59.22 84.36 Example 6 58.57 83.29 Example 7 58.68 83.74 Comparative Example 1 56.24 81.74 Comparative Example 2 52.13 78.28 Comparative Example 3 57.84 82.47 It can be seen from Table 4 that the fragrance-preserving layer prepared by combining amidated alginate with cellulose microfibers improves the mechanical properties of the fragrance-preserving and fresh-keeping film. The mechanical properties of the fragrance-preserving and fresh-keeping film prepared by using unmodified alginate in Comparative Example 1 have no significant difference; while the tensile strength and elongation at break of the fragrance-preserving and fresh-keeping film prepared by using no cellulose in Comparative Example 2 are both reduced; the mechanical properties of the fragrance-preserving and fresh-keeping film prepared by using no cinnamon essential oil in Comparative Example 3 are not greatly affected. (5) Air and water permeability The moisture permeability and air permeability are measured using the national standard method. Table 5 Air and water permeability of aroma and freshness-preserving films As can be seen from Table 5, the fragrance-preserving and fresh-keeping film prepared by the present invention has a low water vapor permeability coefficient, which can increase the water resistance of the film, and can inhibit the permeation of oxygen, increase the permeation of carbon dioxide, and create a low-oxygen and high-carbon dioxide environment, thereby achieving a fresh-keeping effect. The moisture permeability and air permeability of the fragrance-preserving and fresh-keeping film prepared in Comparative Example 3 without adding cinnamon essential oil is slightly reduced. (6) Antibacterial properties The operation steps are the same as the above performance test step (2). Table 6 Diameter of the antibacterial zone of the fragrance and freshness-preserving film (mm) Example 4 Example 5 Example 6 Example 7 Comparative Example 1 Comparative Example 2 Comparative Example 3 Escherichia coli 12.3±0.3 12.1±0.4 12.5±0.3 12.4±0.5 12.4±0.3 12.7±0.4 13.9±0.6 Pseudomonas fluorescens 13.6±0.5 13.1±0.3 14.1±0.6 13.8±0.4 13.9±0.3 13.8±0.3 15.4±0.3 As shown in Table 6, the diameter of the antibacterial zone of the fresh-keeping layer prepared in Examples 4-7 for Escherichia coli is 12.1-12.5 mm, and the diameter of the antibacterial zone for Pseudomonas fluorescens is 13.1-14.1 mm, while the diameter of the antibacterial zone of the fragrance-preserving and fresh-keeping film prepared in Comparative Example 3 without adding cinnamon essential oil is relatively large, and the antibacterial performance is slightly reduced. It can be seen that the grape seed enzymatic polypeptide liquid, cinnamon essential oil and starch synergize to better inhibit the growth of spoilage bacteria and exert the effect of antibacterial preservation. 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 film for pre-prepared food, characterized in that: The aroma-preserving and fresh-keeping film is a double-layer film, wherein the lower layer is the aroma-preserving layer and the upper layer is the fresh-keeping layer, and is laid in a casting manner.

2. The film for preserving aroma and freshness of pre-prepared food according to claim 1, characterized in that: The main components of the aroma-preserving layer are amidated alginate and cellulose; the main components of the fresh-keeping layer are grape seed enzymatic polypeptide liquid, starch and cinnamon essential oil.

3. The film for pre-prepared food aroma preservation and freshness preservation according to claim 2, characterized in that: The preparation steps of the grape seed enzymatic polypeptide solution are as follows: S1. Grind the de-oiled grape seeds and pass them through a 20-50 mesh sieve to obtain grape seed powder; S2. dissolving grape seed powder in water and subjecting it to thermal denaturation treatment at 100°C for 10-15 minutes; S3. Add pectinase to the solution obtained in S2, stir evenly, heat in a water bath at 80°C for 5 min, and then quickly adjust the pH to 8-9 with NaHCO3 solution to obtain a preliminary enzymatic solution; S4. Add alkaline protease to the preliminary enzymatic hydrolysis solution, stir and mix, and then perform enzymatic hydrolysis at 50°C for 3-4 hours to inactivate the enzyme to obtain the grape seed enzymatic hydrolyzed polypeptide solution.

4. The film for preserving aroma and freshness of pre-prepared food according to claim 3, characterized in that: The mass volume ratio of grape seed powder to water in step S2 is 1 g: (15-35) mL.

5. The film for preserving aroma and freshness of pre-prepared food according to claim 3, characterized in that: The mass ratio of the grape seed powder to pectinase and alkaline protease is 1:(0.03-0.06):(0.02-0.04).

6. The film for pre-prepared food aroma preservation and freshness preservation according to claim 2, characterized in that: The preparation steps of the fresh-keeping layer are as follows: Step 1: Weigh starch, add 10-15 times the volume of water, and stir evenly at 50-60°C to obtain a starch solution; Step 2: Add grape seed enzymatic polypeptide solution and cinnamon essential oil to the starch solution and stir evenly to obtain a plastic wrap solution; Step 3: Spread the plastic wrap liquid evenly on the polytetrafluoroethylene plate and dry it to obtain the fresh-keeping layer.

7. The film for preserving aroma and freshness of pre-prepared food according to claim 6, characterized in that: In step 2, the volume ratio of the starch solution, the grape seed enzymatic polypeptide solution and the cinnamon essential oil is 5:(1-2):(2-3).

8. The film for preserving aroma and freshness of pre-prepared food according to claim 2, characterized in that: The following steps are involved: (1) dissolving 1-4 parts of chitosan in an acetic acid solution having a concentration of 1-2%, stirring at 800-1000 rpm for 30-40 minutes, ultrasonically treating for 5-10 minutes, and then stirring at room temperature for 5-8 minutes to obtain a chitosan solution; (2) dissolving 1-2 parts of glycerol and 2-5 parts of alginate in deionized water, stirring at 1000-1200 rpm for 40-60 min to obtain an alginate solution; (3) mixing the chitosan solution and the alginate solution, and stirring at 600-800 rpm for 60 min to obtain an amidated alginate solution; (4) Weigh a certain amount of cellulose, dissolve it in deionized water, heat it at 85-90°C to dissolve it, and prepare it into a mass fraction It is a 1-2% cellulose solution; (5) mixing the amidated alginate solution with the cellulose solution and stirring them evenly to obtain a fragrance-retaining layer mixed membrane solution; (6) Casting the aroma-preserving layer mixed film solution on the fresh-keeping layer and drying it to obtain an aroma-preserving fresh-keeping film.

9. The film for preserving aroma and freshness of pre-prepared food according to claim 8, characterized in that: In step S13, the volume ratio of the chitosan solution to the alginate solution is 2:(3-4).

10. The film for preserving aroma and freshness of pre-prepared food according to claim 8, characterized in that: In step S15, the volume ratio of the amidated alginate solution to the cellulose solution is (2-3):1.

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