Controlled release type chitosan-based coating liquid as well as preparation method and application thereof

Abstract

The invention discloses a controlled release type chitosan-based coating liquid as well as a preparation method and application thereof. According to the preparation method, trans-2-hexenal and a chitosan-stearic acid nano-cluster embedded with trans-2-hexenal are adopted as core materials, dimyristoyl phosphatidylcholine and cholesterol are adopted as wall materials, and the temperature-sensitive liposome is prepared; then taking chitosan as a matrix, and mixing the chitosan with the temperature-sensitive lipidosome to prepare a temperature-sensitive lipidosome / chitosan composite coating liquid; finally, the composite coating liquid is combined with cold shock treatment, and the novel normal-temperature preservation method for the postharvest vegetable soybeans is obtained. When the temperature-sensitive liposome / chitosan composite coating liquid is applied to normal-temperature storage and fresh-keeping of harvested vegetable soybeans, the antibacterial and antioxidant effects are achieved, and trans-2-hexenal has the characteristics of temperature response and on-demand regulation and release.

Description

Technical Field

[0001] The invention relates to the field of fruit and vegetable preservation, and in particular to a thermosensitive liposome / chitosan composite coating liquid and a preparation method thereof, and an application of the composite coating liquid combined with cold shock treatment in postharvest storage and preservation of vegetable soybeans at room temperature. Background Art

[0002] Trans-2-hexenal is a naturally derived plant essential oil with strong antibacterial effects. It can be used to prepare edible flavors such as strawberry and apple. However, it has a strong odor, is sensitive to heat, and is volatile. Direct use will affect the sensory quality of fruits and vegetables, limiting the widespread application of trans-2-hexenal in the storage and preservation of agricultural products.

[0003] With the continuous improvement of people's living standards, the field of fruit and vegetable preservation has developed rapidly. Traditional physical and chemical preservation methods cannot meet the needs of modern food storage and preservation. Therefore, it is imperative to develop a new type of temperature-responsive antibacterial preservation material for fruits and vegetables.

[0004] Polysaccharides are macromolecular polymers whose functional groups give them diverse biological activities. Chitosan is a natural polysaccharide with good film-forming properties, non-toxicity, and biodegradability. It can be widely used in the field of food storage and preservation through coating, soaking, etc. However, chitosan itself has low antibacterial activity, single function, and poor mechanical properties. It cannot meet the needs of modern food active packaging materials, and its application is limited. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies in the prior art and provide a thermosensitive liposome / chitosan composite coating liquid for storage and preservation of post-harvest edible soybeans, specifically a method for preserving edible soybeans at room temperature by regulating release on demand within a temperature response range, reducing browning of edible soybeans and delaying aging.

[0006] The present invention also aims to provide a method for preparing the thermosensitive liposome / chitosan composite coating liquid that can regulate release on demand within the temperature response range. The preparation method uses chitosan-stearic acid nanoclusters embedded with trans-2-hexenal and trans-2-hexenal as core materials, dimyristoylphosphatidylcholine and cholesterol as wall materials to prepare a thermosensitive liposome composite material; then chitosan is used as a matrix and mixed with the thermosensitive liposome composite material to prepare a thermosensitive liposome / chitosan composite coating liquid.

[0007] The purpose of the present invention is achieved through the following technical solutions.

[0008] A method for preparing a controlled-release chitosan-based coating liquid, the steps of the method are as follows:

[0009] (1) chitosan and stearic acid are used as raw materials, carbodiimide is used as a cross-linking coupling agent, and a reaction is carried out under stirring conditions to obtain a chitosan-stearic acid nanocluster emulsion;

[0010] (2) adding trans-2-hexenal and chitosan-stearic acid nanocluster emulsion into an organic solvent under stirring conditions to obtain a chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal;

[0011] adding trans-2-hexenal into an organic solvent to obtain a trans-2-hexenal solution;

[0012] (3) under stirring conditions, the chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal, the trans-2-hexenal solution, the synthetic phospholipid and cholesterol are fully mixed, and the solvent is removed to form a composite film, namely, the thermosensitive liposome;

[0013] (4) placing the obtained thermosensitive liposome in the chitosan-stearic acid nanocluster solution containing trans-2-hexenal as described in step (2) for shaking and hydration, then hydrating, and then sonicating with an ultrasonic cell disruptor to obtain a composite thermosensitive liposome;

[0014] (5) adding chitosan to the acetic acid solution and fully dissolving it to obtain a chitosan acetic acid solution, which is then mixed with the composite thermosensitive liposome to obtain the composite thermosensitive liposome / chitosan coating solution encapsulating the trans-2-hexenal essential oil.

[0015] In the above preparation method, in step (1), the molecular weight of the chitosan is 20-40 kDa; the mass ratio of the chitosan, stearic acid and carbodiimide is 1-3:1-3:3-8; the reaction temperature is 70°C-90°C, and the reaction is carried out for 12-24 hours.

[0016] In the above preparation method, in step (2), the volume ratio of the solvent, trans-2-hexenal and chitosan-stearic acid nanocluster emulsion in the chitosan-stearic acid nanocluster solution of trans-2-hexenal is 5-15:0.1-1:1-5; the volume ratio of trans-2-hexenal and solvent in the trans-2-hexenal solution is 1:250-750.

[0017] In the above preparation method, in step (3), the synthetic phospholipid is dimyristoylphosphatidylcholine (DMPC);

[0018] In step (3), the volume ratio of the chitosan-stearic acid nanocluster solution of trans-2-hexenal to trans-2-hexenal is 1:0.5-1.5; the mass ratio of the synthetic phospholipid to cholesterol is 1-3:1-3, wherein the volume ratio of the cholesterol content to trans-2-hexenal is 0.1-1%.

[0019] In the above preparation method, in step (4), the hydration temperature is 30°C to 50°C, the hydration time is 5 to 15 minutes, the ultrasonic power of the ultrasonic cell disruptor is 200W-300W, and the ultrasonic time is 5 minutes to 15 minutes;

[0020] In step (5), the concentration of chitosan in the chitosan acetate solution is 0.05 g / L-0.15 g / L; the composite thermosensitive liposome accounts for 1%-10% of the chitosan solid.

[0021] A controlled-release chitosan-based coating liquid is characterized in that it is prepared by the above method.

[0022] In the technical solution of the present invention, the controlled-release chitosan-based coating liquid prepared by the method is used in the preservation of vegetables.

[0023] Further, the vegetables are subjected to a cold shock treatment of -5 to 0°C ice-water mixture for 5 to 15 minutes, and then air-dried; after drying, the vegetables are immersed in a controlled-release chitosan-based coating solution for 5 to 15 minutes, and then air-dried again. Preferably, the vegetables are edible soybeans.

[0024] The present invention is conceived as follows:

[0025] The method for preparing the thermosensitive liposome / chitosan composite coating liquid provided by the present invention regulates the release rate of the thermosensitive liposome by designed different temperatures, and has the characteristics of temperature response and on-demand regulation of release.

[0026] The invention utilizes the property of liposomes that can simultaneously embed hydrophobic and hydrophilic substances, and the dynamic effect of the phospholipid bilayer of dimyristoylphosphatidylcholine regulated by temperature, embeds trans-2-hexenal and chitosan-stearic acid nanoclusters compounded with trans-2-hexenal in thermosensitive liposomes, and solves the problems of instability of chitosan-stearic acid nanoclusters and limited embedding space; utilizes the embedding properties of chitosan-stearic acid nanoclusters and thermosensitive liposomes to encapsulate trans-2-hexenal, slow down its release rate, and release trans-2-hexenal while ensuring its long-term antibacterial effect. The problem of rapid release of trans-2-hexenal leading to decreased freshness-keeping effect is solved; the surface and interface effects of thermosensitive liposomes and chitosan are utilized to improve the disadvantage of weak mechanical strength of chitosan; trans-2-hexenal is utilized as a long-acting antibacterial preservative to solve the problem of weak antibacterial activity and unstable effect of chitosan packaging; trans-2-hexenal is utilized as the encapsulation core material to solve the disadvantages of strong odor, strong volatility and heat sensitivity of trans-2-hexenal; the composite chitosan coating has excellent antibacterial properties, expanding the application of chitosan in the field of degradable antibacterial packaging.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] (1) The preparation method provided by the present invention adopts dimyristoylphosphatidylcholine as the synthetic phospholipid, which is temperature-sensitive and safe; the core material trans-2-hexenal is a natural essential oil derived from plants, which is low in price, widely available, safe and non-toxic, and has antioxidant and antibacterial activities;

[0029] (2) The preparation method provided by the present invention utilizes thin film hydration and ultrasound to composite trans-2-hexenal and chitosan-stearic acid nanoclusters encapsulating trans-2-hexenal into the hydrophobic layer and the hydrophilic layer of the thermosensitive liposome, thereby ingeniously slowing down the volatilization of trans-2-hexenal without introducing other substances. The method is green and safe, and expands its application in the field of fruit and vegetable storage and preservation.

[0030] (3) The preparation method provided by the present invention mixes the thermosensitive liposome with the chitosan matrix, thereby improving the mechanical properties of the chitosan;

[0031] (4) The preparation method of the present invention has simple process, is easy to operate, has a wide source of raw materials, and is conducive to large-scale industrial production;

[0032] (5) The preservation method provided by the present invention combines the thermosensitive liposome / chitosan composite coating with the cold shock treatment, which is simple to operate and solves the problem of easy residue and unsafety of chemical preservation methods;

[0033] (5) The preservation method provided by the present invention combines the thermosensitive liposome / chitosan composite coating with cold shock treatment, which effectively delays the aging of post-harvest vegetable soybeans and prolongs the storage period. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a data graph of the cumulative release rate of trans-2-hexenal in the thermosensitive liposomes obtained in Example 2 under different temperature conditions; DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and drawings, but the embodiments and protection scope of the present invention are not limited thereto.

[0036] Example 1

[0037] The method for preserving soybeans for vegetable use at room temperature after harvesting, the specific steps are as follows:

[0038] (1) Chitosan (molecular weight 30 kDa), stearic acid and carbodiimide were reacted at a mass ratio of 1:1:5 at 70°C for 20 h with stirring to obtain a chitosan-stearic acid nanocluster emulsion;

[0039] (2) under stirring conditions, anhydrous ethanol, trans-2-hexenal and chitosan-stearic acid nanocluster emulsion in a volume ratio of 10:0.2:2 were mixed to obtain a chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal;

[0040] The anhydrous ethanol and trans-2-hexenal are mixed uniformly in a volume ratio of 250:1 to obtain a trans-2-hexenal solution;

[0041] (3) under stirring conditions, the chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal, the trans-2-hexenal solution, the synthetic phospholipid (dimyristoylphosphatidylcholine), and the cholesterol are fully mixed, and the solvent is removed to form a composite film, and the obtained film is the thermosensitive liposome;

[0042] Wherein: the chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal and the trans-2-hexenal solution are mixed in a volume ratio of 1:0.5; the mass ratio of synthetic phospholipid and cholesterol is 1:1 and the volume ratio of cholesterol content to trans-2-hexenal is 0.4%.

[0043] (4) placing the obtained thermosensitive liposome in the chitosan-stearic acid nanocluster emulsion containing trans-2-hexenal as described in step (2) for shaking and hydration, then hydrating at 30° C. for 10 min, and then ultrasonicating with an ultrasonic cell disruptor at 200 W for 5 min to obtain a composite thermosensitive liposome;

[0044] (5) A chitosan acetic acid solution with a chitosan concentration of 0.05 g / L is taken and then mixed with the composite thermosensitive liposome to obtain a controlled release chitosan-based coating solution, wherein the composite thermosensitive liposome accounts for 1% of the solid content of the chitosan.

[0045] (6) Preparation of edible soybean raw materials: Select edible soybeans of uniform size and color, without obvious mechanical damage and pests, and of the same weight;

[0046] (7) Cold shock treatment of vegetable soybeans: The selected vegetable soybeans were subjected to cold shock treatment with a mixture of ice and water at 0°C for 5 min;

[0047] (8) Coating treatment of vegetable soybeans: After cold shock treatment, the vegetable soybeans were fully dried, immersed in 5 L of the prepared composite coating solution for coating treatment for 5 min, and fully dried;

[0048] (9) Storage of edible soybeans: The dried edible soybeans were placed in a constant temperature box at 20°C ± 1°C and stored for 10 days (the experimental time was set to 10 days).

[0049] Example 2

[0050] The method for preserving soybeans for vegetable use at room temperature after harvesting, the specific steps are as follows:

[0051] (1) Chitosan (30 kDa), stearic acid and carbodiimide were stirred at a mass ratio of 2:1:5 at 80 °C for 18 h to obtain a chitosan-stearic acid nanocluster emulsion;

[0052] (2) under stirring conditions, anhydrous ethanol, trans-2-hexenal and chitosan-stearic acid nanocluster emulsion in a volume ratio of 10:0.2:2 were mixed to obtain a chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal;

[0053] The anhydrous ethanol and trans-2-hexenal are mixed uniformly in a volume ratio of 250:1 to obtain a trans-2-hexenal solution;

[0054] (3) under stirring conditions, the chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal, the trans-2-hexenal solution, the synthetic phospholipid (dimyristoylphosphatidylcholine), and the cholesterol are fully mixed, and the solvent is removed to form a composite film, and the obtained film is the thermosensitive liposome;

[0055] Wherein: the chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal and the trans-2-hexenal solution are mixed in a volume ratio of 1:1; the mass ratio of synthetic phospholipids and cholesterol is 1:2, and the volume ratio of cholesterol content to trans-2-hexenal is 0.4%.

[0056] (4) placing the obtained composite membrane in the chitosan-stearic acid nanocluster emulsion containing trans-2-hexenal as described in step (3) for shaking and hydration, then hydrating at 40° C. for 10 min, and then ultrasonicating with an ultrasonic cell disruptor at 250 W for 10 min to obtain a composite thermosensitive liposome;

[0057] (5) taking a chitosan dilute acetic acid solution with a concentration of 0.1 g / L, and then mixing it with the composite thermosensitive liposome to obtain the composite thermosensitive liposome / chitosan coating solution encapsulating the trans-2-hexenal essential oil; the trans-2-hexenal composite thermosensitive liposome preservative accounts for 5% of the solid content of the chitosan;

[0058] (6) Preparation of edible soybean raw materials: Select edible soybeans of uniform size and color, without obvious mechanical damage and pests, and of the same weight;

[0059] (7) Cold shock treatment of vegetable soybeans: The selected vegetable soybeans were subjected to cold shock treatment with a mixture of ice and water at 0°C for 10 min;

[0060] (8) Coating treatment of vegetable soybeans: After the cold shock treatment, the vegetable soybeans are fully dried, immersed in the prepared composite coating solution for coating treatment for 10 minutes, and fully dried;

[0061] (9) Storage of edible soybeans: Store the dried edible soybeans in a constant temperature box at 20℃±1℃ for 10 days.

[0062] The cumulative release rate of trans-2-hexenal in the prepared composite thermosensitive liposomes is as follows: Figure 1 As shown. Figure 1 It can be seen that the cumulative release rate of E2H in the composite liposomes increases with time in the temperature range of 10℃-35℃. In the first 8h of release, the cumulative release rate of the composite liposomes at 10℃ did not show a significant trend of acceleration; at 25℃ and 35℃, the release rate of the composite liposomes accelerated rapidly, and the release rate of the composite liposomes at 35℃ was higher than that of the composite liposomes at 25℃. In addition, after 8h of release, the cumulative release rate of the composite liposomes at 10℃ changed slowly, while its release rate at 25℃ and 35℃ increased, and the release rate of E2H in the composite liposomes at 35℃ was faster. At 72h of release, the cumulative release rates of the composite liposomes at 25℃ and 35℃ were 21% and 37%, respectively, while the cumulative release rate of E2H at 10℃ was only 4%. This indicates that the composite thermosensitive liposomes have a good encapsulation efficiency for the hydrophobic trans-2-hexenal essential oil, and can release trans-2-hexenal on demand under different temperature conditions, thereby improving the efficiency of the trans-2-hexenal essential oil and prolonging its action time.

[0063] Example 3

[0064] The method for preserving soybeans for vegetable use at room temperature after harvesting, the specific steps are as follows:

[0065] (1) Chitosan (30 kDa), stearic acid and carbodiimide were stirred at a mass ratio of 3:1:5 at 80 °C for 15 h to obtain a chitosan-stearic acid nanocluster emulsion;

[0066] (2) under stirring conditions, anhydrous ethanol, trans-2-hexenal and chitosan-stearic acid nanocluster emulsion were mixed in a volume ratio of 10:0.2:2 to obtain a chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal;

[0067] The anhydrous ethanol and trans-2-hexenal are mixed uniformly in a volume ratio of 250:1 to obtain a trans-2-hexenal solution;

[0068] (3) under stirring conditions, the chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal, the trans-2-hexenal solution, the synthetic phospholipid (dimyristoylphosphatidylcholine), and the cholesterol are fully mixed, and the solvent is removed to form a composite film, and the obtained film is the thermosensitive liposome;

[0069] The chitosan-stearic acid nanocluster emulsion encapsulating trans-2-hexenal and the trans-2-hexenal solution are mixed at a volume ratio of 1:1.5; the mass ratio of synthetic phospholipids to cholesterol is 1:3, and the volume ratio of cholesterol content to trans-2-hexenal is 0.4%.

[0070] (4) placing the obtained composite membrane in the chitosan-stearic acid nanocluster emulsion containing trans-2-hexenal embedded in step (3) for shaking and hydration, then hydrating at a temperature of 50° C. for 10 min, and then ultrasonicating with an ultrasonic cell disruptor at 300 W for 15 min to obtain a composite thermosensitive liposome;

[0071] (5) taking a chitosan dilute acetic acid solution with a concentration of 0.2 g / L, and then mixing it with the composite thermosensitive liposome to obtain the composite thermosensitive liposome / chitosan coating solution encapsulating the trans-2-hexenal essential oil; the trans-2-hexenal composite thermosensitive liposome preservative accounts for 10% of the solid content of the chitosan;

[0072] (6) Preparation of edible soybean raw materials: Select edible soybeans of uniform size and color, without obvious mechanical damage and pests, and of the same weight;

[0073] (7) Cold shock treatment of vegetable soybeans: The selected vegetable soybeans were subjected to cold shock treatment with a mixture of ice and water at 0°C for 15 min;

[0074] (8) Coating treatment of vegetable soybeans: After the cold shock treatment, the vegetable soybeans were fully dried, immersed in the prepared 7L composite coating solution for coating treatment for 15 minutes, and fully dried;

[0075] (9) Storage of edible soybeans: Store the dried edible soybeans in a constant temperature box at 20℃±1℃ for 10 days.

[0076] The above embodiments are only preferred implementation modes of the present invention and are only used to explain the present invention rather than to limit the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a controlled-release chitosan-based coating solution, characterized in that: The steps of this method are as follows: (1) Chitosan and stearic acid are used as raw materials, carbodiimide is used as a cross-linking coupling agent, and the reaction is carried out under stirring conditions to obtain a chitosan-stearic acid nanocluster emulsion; (2) adding trans-2-hexenal and chitosan-stearic acid nanocluster emulsion into an organic solvent under stirring conditions to obtain a chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal; adding trans-2-hexenal into an organic solvent to obtain a trans-2-hexenal solution; (3) Under stirring conditions, the chitosan-stearic acid nanocluster solution encapsulating trans-2-hexenal, the trans-2-hexenal solution, the synthetic phospholipid and cholesterol are fully mixed, and the solvent is removed to form a composite film, namely, the thermosensitive liposome; (4) placing the obtained thermosensitive liposome in the chitosan-stearic acid nanocluster solution containing trans-2-hexenal as described in step (2) for shaking and hydration, then hydrating, and then sonicating with an ultrasonic cell disruptor to obtain a composite thermosensitive liposome; (5) adding chitosan to the acetic acid solution and fully dissolving it to obtain a chitosan acetic acid solution, which is then mixed with the composite thermosensitive liposome to obtain the composite thermosensitive liposome / chitosan coating solution encapsulating the trans-2-hexenal essential oil.

2. The preparation method according to claim 1, characterized in that: In step (1), the molecular weight of the chitosan is 20-40 kDa; the mass ratio of the chitosan, stearic acid and carbodiimide is 1-3:1-3:3-8; the reaction temperature is 70°C-90°C, and the reaction is carried out for 12-24 hours.

3. The preparation method according to claim 1, characterized in that: In step (2), the volume ratio of the solvent, trans-2-hexenal and chitosan-stearic acid nanocluster emulsion in the chitosan-stearic acid nanocluster solution of trans-2-hexenal is 5-15:0.1-1:1-5; the volume ratio of trans-2-hexenal and the solvent in the trans-2-hexenal solution is 1:250-750.

4. The preparation method according to claim 1, characterized in that: In step (3), the synthetic phospholipid is dimyristoylphosphatidylcholine DMPC; In step (3), the volume ratio of the chitosan-stearic acid nanocluster solution of trans-2-hexenal to trans-2-hexenal is 1:0.5-1.5; the mass ratio of the synthetic phospholipid to cholesterol is 1-3:1-3, wherein the volume ratio of the cholesterol content to trans-2-hexenal is 0.1-1%.

5. The preparation method according to claim 1, characterized in that: In step (4), the hydration temperature is 30°C to 50°C, the hydration time is 5 to 15 minutes, the ultrasonic power of the ultrasonic cell disruptor is 200 W to 300 W, and the ultrasonic time is 5 min to 15 min; In step (5), the concentration of chitosan in the chitosan acetate solution is 0.05 g / L-0.3 g / L; the composite thermosensitive liposome accounts for 1%-10% of the chitosan solid.

6. A controlled release chitosan-based coating solution, characterized in that: The method is prepared by any one of claims 1 to 5.

7. Use of the controlled-release chitosan-based coating liquid prepared by the method of claim 1 in preserving vegetables.

8. The use according to claim 7, characterized in that: The vegetables are subjected to a cold shock treatment with a mixture of ice and water at -5 to 0°C for 5 minutes to 15 minutes, and then air-dried; after drying, they are immersed in a controlled-release chitosan-based coating liquid for coating treatment for 5 minutes to 15 minutes, and then air-dried again; preferably, the vegetables are edible soybeans.

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