Preparation method of composite film for blueberry preservation

Abstract

The invention discloses a preparation method of a composite film for blueberry preservation. Natural chitosan is adopted as a base material, active ingredients of phellinus igniarius hypha acid polysaccharide (APFP) and a glycerin plasticizer are matched, no chemical preservative is added, the residual risk caused by traditional chemical preservation is avoided from the source, and the requirements for green consumption and food safety are met; the antibacterial and antioxidant characteristics of APFP and the barrier property of chitosan form a synergistic effect, putrefying bacteria reproduction after blueberry picking can be effectively inhibited, water loss and pulp softening can be slowed down, the method is simple in step and clear in parameter, complex and precise equipment is not needed, the technologies such as magnetic stirring dissolution, standing defoaming and constant-temperature drying are easy to regulate and control in a standardized mode, and the production difficulty and cost can be reduced; the viscosity, the pH value and other indexes of the composite film forming solution are stable, the mechanical strength and the barrier property of the prepared composite film reach the standard, the batch consistency is good, the bottlenecks that an existing bio-based composite film is insufficient in mechanical strength and the technology is difficult to scale are overcome, and both the creativity and the industrialization price are considered.

Description

Technical Field

[0001] This invention relates to the field of food preservation packaging materials technology, specifically a method for preparing a composite film for blueberry preservation. Background Technology

[0002] Blueberries are rich in nutrients, but they are prone to softening, dehydration, and microbial contamination after harvest, leading to rapid quality deterioration and severely restricting market circulation. Efficient preservation technology is crucial for the development of the blueberry industry. Traditional blueberry preservation relies mainly on low-temperature storage and chemical preservatives, which suffers from high energy consumption and preservative residues, failing to meet the demands of green consumption. In recent years, research on blueberry preservation films has focused on natural polysaccharide-based composite films. Introducing active ingredients such as polysaccharides to construct antibacterial and antioxidant multifunctional composite films to improve preservation effects has become the mainstream approach. Currently, bio-based composite films face bottlenecks such as insufficient mechanical strength, easy volatilization of active ingredients, and difficulties in scaling up the preparation process. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a composite film for preserving blueberries, so as to solve the problems in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a composite film for blueberry preservation, comprising the following steps:

[0005] (1) Preparation of chitosan solution: Accurately weigh 3g of chitosan and dissolve it in 200mL of 2% citric acid solution. Use a magnetic stirrer of model 81-2 to stir at 60℃ and 3000 rpm until the chitosan is completely dissolved to obtain a chitosan solution with a mass fraction of 1.5%. At the same time, add 30% glycerol by mass of chitosan to the solution.

[0006] (2) Preparation of composite film-forming solution: The aqueous solution of acidic polysaccharide (APFP) of Phellinus linteus mycelium with mass fractions of 0.25%, 0.5%, 0.75% and 1% respectively is mixed with the chitosan solution obtained in step (1) in equal volume ratio and stirred evenly to obtain APFP-CS composite film-forming solution;

[0007] (3) Degassing treatment: Take 25 ml of the above composite film-forming solution and pour it into a plastic petri dish with a diameter of 90 mm. Let it stand for 1 hour to remove the air bubbles in the solution.

[0008] (4) Film drying: The culture dish after degassing was placed in a constant temperature drying oven of model GF-9030A and dried at 50°C for 8 hours to form a composite film.

[0009] As a preferred embodiment of the present invention, the acidic polysaccharide (APFP) of the Phellinus linteus mycelium in step (2) is prepared by the following method:

[0010] (1) Extraction of crude polysaccharides: Weigh the mycelial powder of Phellinus linteus and mix it with distilled water at a solid-liquid ratio of 1:90 (w / v, g / mL). Extract it in hot water at 90℃ for 3 hours. After extraction, centrifuge the extract at 3500 rpm for 15 minutes and collect the supernatant.

[0011] (2) Ethanol precipitation: Add 95% ethanol to the supernatant at a volume ratio of 4:1 and precipitate at 4°C for 12 hours. Then centrifuge again under the same centrifugation conditions and collect the precipitate as crude polysaccharide (PFP).

[0012] (3) Purification treatment: Weigh 2g of crude polysaccharide (PFP) and dissolve it in 100mL of distilled water. Centrifuge at 4000rpm for 15 minutes. Take the supernatant and add it to a DEAE-52 cellulose column (35mm×40cm). After the sample has completely penetrated the cellulose matrix, elute the acidic polysaccharide component with 0.2mol / L sodium chloride solution at a flow rate of 1.5mL / min.

[0013] (4) Dialysis and drying: The collected eluent was transferred to a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed with distilled water for 48 hours. The dialysate was concentrated by rotary evaporation and then freeze-dried to obtain Sanghuang mycelium acid polysaccharide (APFP).

[0014] As a preferred embodiment of the present invention, the composite membrane uses chitosan as the base material, acidic polysaccharide (APFP) of Phellinus linteus as the active ingredient, and glycerol as the plasticizer. The mass fraction of acidic polysaccharide (APFP) of Phellinus linteus in the composite film-forming solution is 0.25%-1%, and the amount of glycerol added is 30% of the mass of chitosan.

[0015] As a preferred embodiment of the present invention, the composite membrane has a mechanical strength of 20-35 MPa, an elongation at break of 35%-55%, an oxygen permeability of ≤5.0 cm³ / (m²・d・atm), and a moisture permeability of ≤8.0 g / (m²・d).

[0016] As a preferred application method of the present invention, the composite film is used to make packaging material to wrap blueberries, or a film liquid is prepared to coat blueberries and then dried.

[0017] As a preferred embodiment of the present invention, when a coating treatment method is used, the coating thickness is 0.05-0.15 mm, the drying temperature is 55°C, and the drying time is 8 hours.

[0018] As a preferred embodiment of the present invention, a method for preserving blueberries involves using a composite film to preserve the blueberries, specifically including the following steps:

[0019] (1) Blueberry pretreatment: Select fresh blueberries that are uniformly ripe, undamaged, and free from pests and diseases. Rinse them with clean water and then air dry the surface moisture at 25-30℃.

[0020] (2) Preservation treatment: The pretreated blueberries are wrapped in the composite film of claim 3, or immersed in the composite film-forming solution of claim 1 for 10-20 seconds and then dried at 25-30°C for 1-2 hours.

[0021] (3) Storage: Store the blueberries that have undergone preservation treatment in an environment with a temperature of 0-4℃ and a relative humidity of 85%-90%.

[0022] As a preferred embodiment of the present invention, blueberries preserved by this method exhibit a weight loss rate of ≤18%, a rot rate of ≤16%, and a flesh firmness of ≥20kg / cm² after 15 days of storage.

[0023] As a preferred embodiment of the present invention, the mixture comprises a chitosan solution, an aqueous solution of acidic polysaccharide (APFP) from Phellinus linteus mycelium, and glycerol. The chitosan solution is a 1.5% (w / w) citric acid-chitosan solution, the aqueous solution of acidic polysaccharide (APFP) from Phellinus linteus mycelium has a (w / w) fraction of 0.25%-1%, the volume ratio of the chitosan solution to the aqueous solution of acidic polysaccharide (APFP) from Phellinus linteus mycelium is 1:1, and the amount of glycerol added is 30% of the mass of chitosan.

[0024] As a preferred embodiment of the present invention, the viscosity of the composite film-forming solution is 50-150 mPa·s (25℃), the pH value is 4.0-5.5, the inhibition rate of common postharvest spoilage bacteria of blueberries is ≥80%, and the DPPH free radical scavenging rate is ≥65%.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. This invention uses natural chitosan as the base material, combined with active ingredients such as acidic polysaccharide (APFP) from Phellinus linteus mycelium and glycerol plasticizer. No chemical preservatives are added, thus avoiding the residual risks brought by traditional chemical preservation from the source, which meets the demands of green consumption and food safety. The antibacterial and antioxidant properties of APFP and the barrier properties of chitosan form a synergistic effect, which can effectively inhibit the reproduction of spoilage bacteria in blueberries after harvest, slow down moisture loss and softening of fruit pulp, significantly extend the shelf life of blueberries, and solve the industry pain point of easy deterioration of blueberries after harvest.

[0027] 2. The method and steps in this invention are simple and the parameters are clear. There is no need for complex and precision equipment. Processes such as magnetic stirring and dissolution, static degassing, and constant temperature drying are easy to standardize and control, which can reduce production difficulty and cost. The viscosity, pH value and other indicators of the composite film-forming solution are stable. The mechanical strength and barrier performance of the obtained composite film meet the standards and the batch consistency is good. It overcomes the bottleneck of insufficient mechanical strength and difficulty in scaling up the process of existing bio-based composite films, and takes into account both inventiveness and industrialization value. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the overall process flow of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] In the description of this invention, it should be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, in the description of this invention, "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or a connection through an intermediate medium; and they can refer to the internal communication between two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances. "Multiple" means two or more, and unless otherwise explicitly limited, all such meanings fall within the scope of protection of this invention.

[0032] Example 1

[0033] A method for preparing a composite film for preserving blueberries, comprising the following steps:

[0034] 1. Preparation of chitosan solution: Accurately weigh 3g of chitosan and dissolve it in 200mL of 2% citric acid solution. Use an 81-2 type magnetic stirrer to stir at 60℃ and 3000r / min until completely dissolved to obtain a 1.5% chitosan solution. Add 0.9g of glycerol (30% of the chitosan mass) to the solution and stir until homogeneous.

[0035] 2. Preparation of composite film-forming solution: Take 0.5% by mass of the aqueous solution of acidic polysaccharide (APFP) of Phellinus linteus mycelium and mix it with the chitosan solution obtained in step 1 at a volume ratio of 1:1. Stir for 20 minutes until the mixture is uniform to obtain the APFP-CS composite film-forming solution.

[0036] 3. Degassing treatment: Pour 25 mL of the above composite film-forming solution into a 90 mm diameter plastic petri dish and let it stand at room temperature for 1 hour to completely remove air bubbles from the solution.

[0037] 4. Film drying: Place the degassed petri dishes in a GF-9030A constant temperature drying oven and dry at 50℃ for 8 hours. After removing the petri dishes, peel them off to obtain a composite film for blueberry preservation.

[0038] Beneficial effects: The composite film prepared in this embodiment has a mechanical strength of 28 MPa, an elongation at break of 45%, an oxygen permeability of 3.2 cm³ / (m²·d·atm), and a water permeability of 6.5 g / (m²·d), exhibiting balanced overall performance. When used to wrap and package blueberries, after 15 days of storage at 0-4℃ and 85%-90% relative humidity, the blueberries experienced a weight loss of 12%, a rot rate of 10%, and a pulp firmness of 25 kg / cm², demonstrating a significant preservation effect. Furthermore, the film material has excellent flexibility, easily adheres to blueberry fruits, and is convenient to operate.

[0039] Example 2

[0040] A method for preparing a composite film for preserving blueberries and its application, the specific steps of which are as follows:

[0041] 1. Preparation of acidic polysaccharide (APFP) from Phellinus linteus mycelium:

[0042] Crude polysaccharide extraction: Weigh 10g of Phellinus linteus mycelium powder, mix it with distilled water at a solid-liquid ratio of 1:90 (w / v, g / mL), extract with hot water at 90℃ for 3 hours, centrifuge the extract at 3500rpm for 15 minutes, and collect the supernatant.

[0043] Ethanol precipitation: Add 95% ethanol (volume ratio of ethanol to supernatant 4:1) to the supernatant, let it stand at 4℃ for 12 hours to precipitate, centrifuge at 3500 rpm for 15 minutes, and collect the precipitate as crude polysaccharide (PFP).

[0044] Purification: Weigh 2g of crude polysaccharide (PFP) and dissolve it in 100mL of distilled water. Centrifuge at 4000rpm for 15 minutes. Pass the supernatant through a DEAE-52 cellulose column (35mm×40cm). After the sample has completely penetrated, elute the acidic polysaccharide component with 0.2mol / L sodium chloride solution at a flow rate of 1.5mL / min and collect the eluent.

[0045] Dialysis drying: The eluent was transferred into a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed with distilled water for 48 hours (the distilled water was changed every 12 hours). The dialysate was concentrated by rotary evaporation and then freeze-dried to obtain acidic polysaccharide (APFP) from Phellinus linteus mycelium.

[0046] 2. Composite membrane preparation:

[0047] Preparation of chitosan solution: Same as step 1 in Example 1.

[0048] Preparation of composite film-forming solution: Take 0.75% APFP aqueous solution by mass and mix it with chitosan solution at a volume ratio of 1:1 to obtain composite film-forming solution (viscosity 100 mPa·s, 25℃; pH value 4.8).

[0049] Defoaming, film formation and drying: Same as steps 3 and 4 in Example 1.

[0050] 3. Blueberry preservation treatment:

[0051] Pretreatment: Select fresh blueberries that are uniformly ripe, undamaged, and free from pests and diseases. Rinse them thoroughly with clean water and air dry them at 28°C to remove surface moisture.

[0052] Preservation treatment: Immerse the pretreated blueberries in the above composite film-forming solution for 15 seconds, then remove them and air dry at 28°C for 1.5 hours, controlling the coating thickness to be 0.1 mm.

[0053] Storage: Store the coated blueberries in an environment of 2°C and 88% relative humidity.

[0054] Beneficial effects: The APFP prepared in this embodiment has high purity. The composite film-forming solution has an 88% inhibition rate against common post-harvest spoilage bacteria of blueberries (such as Penicillium and Botrytis), a 72% DPPH free radical scavenging rate, and outstanding antibacterial and antioxidant capabilities. Blueberries preserved by this method have a weight loss rate of only 10% and a rot rate of 8% after 15 days of storage, with a pulp firmness of 28 kg / cm². The quality preservation effect is significantly improved compared with traditional low-temperature storage of blueberries. Moreover, the coating method is easy to operate in batches and is suitable for the industrial preservation needs of blueberries.

[0055] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a composite film for preserving blueberries, characterized in that, Includes the following steps: (1) Preparation of chitosan solution: Accurately weigh 3g of chitosan and dissolve it in 200mL of 2% citric acid solution. Use a magnetic stirrer of model 81-2 to stir at 60℃ and 3000 rpm until the chitosan is completely dissolved to obtain a chitosan solution with a mass fraction of 1.5%. At the same time, add 30% glycerol by mass of chitosan to the solution. (2) Preparation of composite film-forming solution: The aqueous solution of acidic polysaccharide (APFP) of Phellinus linteus mycelium with mass fractions of 0.25%, 0.5%, 0.75% and 1% respectively is mixed with the chitosan solution obtained in step (1) in equal volume ratio and stirred evenly to obtain APFP-CS composite film-forming solution; (3) Degassing treatment: Take 25 ml of the above composite film-forming solution and pour it into a plastic petri dish with a diameter of 90 mm. Let it stand for 1 hour to remove the air bubbles in the solution. (4) Film drying: The culture dish after degassing was placed in a constant temperature drying oven of model GF-9030A and dried at 50°C for 8 hours to form a composite film.

2. The method for preparing a composite film for blueberry preservation according to claim 1, characterized in that, The acidic polysaccharide (APFP) of Phellinus linteus mycelium mentioned in step (2) was prepared by the following method: (1) Extraction of crude polysaccharides: Weigh the mycelial powder of Phellinus linteus and mix it with distilled water at a solid-liquid ratio of 1:90 (w / v, g / mL). Extract it in hot water at 90℃ for 3 hours. After extraction, centrifuge the extract at 3500 rpm for 15 minutes and collect the supernatant. (2) Ethanol precipitation: Add 95% ethanol to the supernatant at a volume ratio of 4:1 and precipitate at 4°C for 12 hours. Then centrifuge again under the same centrifugation conditions and collect the precipitate as crude polysaccharide (PFP). (3) Purification treatment: Weigh 2g of crude polysaccharide (PFP) and dissolve it in 100mL of distilled water. Centrifuge at 4000rpm for 15 minutes. Take the supernatant and add it to a DEAE-52 cellulose column (35mm×40cm). After the sample has completely penetrated the cellulose matrix, elute the acidic polysaccharide component with 0.2mol / L sodium chloride solution at a flow rate of 1.5mL / min. (4) Dialysis and drying: The collected eluent was transferred to a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed with distilled water for 48 hours. The dialysate was concentrated by rotary evaporation and then freeze-dried to obtain Sanghuang mycelium acid polysaccharide (APFP).

3. A composite film for blueberry preservation obtained by the preparation method according to claim 1 or 2, characterized in that, The composite membrane uses chitosan as the base material, acidic polysaccharide (APFP) of Phellinus linteus as the active ingredient, and glycerol as the plasticizer. The mass fraction of APFP in the composite film-forming solution is 0.25%-1%, and the amount of glycerol added is 30% of the mass of chitosan.

4. The composite film for blueberry preservation according to claim 3, characterized in that, The composite membrane has a mechanical strength of 20-35 MPa, an elongation at break of 35%-55%, an oxygen permeability of ≤5.0 cm³ / (m²・d・atm), and a moisture permeability of ≤8.0 g / (m²・d).

5. The application of the composite film according to claim 3 in postharvest preservation of blueberries, characterized in that, The application method involves making the composite film into packaging material to wrap blueberries, or preparing a film liquid to coat blueberries and then drying them.

6. The application according to claim 5, characterized in that, When using a coating treatment, the coating thickness is 0.05-0.15 mm, the drying temperature is 55℃, and the drying time is 8 hours.

7. A method for preserving blueberries, characterized in that, The preservation treatment of blueberries using the composite film described in claim 3 specifically includes the following steps: (1) Blueberry pretreatment: Select fresh blueberries that are uniformly ripe, undamaged, and free from pests and diseases. Rinse them with clean water and then air dry the surface moisture at 25-30℃. (2) Preservation treatment: The pretreated blueberries are wrapped in the composite film of claim 3, or immersed in the composite film-forming solution of claim 1 for 10-20 seconds and then dried at 25-30°C for 1-2 hours. (3) Storage: Store the blueberries that have undergone preservation treatment in an environment with a temperature of 0-4℃ and a relative humidity of 85%-90%.

8. The blueberry preservation method according to claim 7, characterized in that, Blueberries preserved using this method exhibit a weight loss rate of ≤18%, a rot rate of ≤16%, and a flesh firmness of ≥20 kg / cm² after 15 days of storage.

9. A composite film-forming solution for preparing a blueberry preservation composite film, characterized in that, It is composed of chitosan solution, aqueous solution of acidic polysaccharide (APFP) from Phellinus linteus mycelium and glycerol. The chitosan solution is a 1.5% (w / w) citric acid-chitosan solution, the aqueous solution of acidic polysaccharide (APFP) from Phellinus linteus mycelium has a (w / w) fraction of 0.25%-1%, the volume ratio of chitosan solution to aqueous solution of acidic polysaccharide (APFP) from Phellinus linteus mycelium is 1:1, and the amount of glycerol added is 30% of the mass of chitosan.

10. The composite film-forming solution according to claim 9, characterized in that, The composite film-forming solution has a viscosity of 50-150 mPa·s (25℃), a pH of 4.0-5.5, an inhibition rate of ≥80% against common postharvest spoilage bacteria of blueberries, and a DPPH free radical scavenging rate of ≥65%.

Images