Preparation method of layer-by-layer self-assembled fruit and vegetable fresh-keeping composite coating

Abstract

The invention discloses a method for preparing a fruit and vegetable fresh-keeping composite coating through a layer-by-layer self-assembly technology and application. The coating comprises nanocellulose, chitosan, a natural antibacterial agent, other auxiliaries and deionized water. The prepared composite coating can protect fruits and vegetables from being damaged by microorganisms, use of chemical preservatives is avoided, and harm to the human body is reduced. According to the structural characteristics of different fruits and vegetables, a multi-layer composite micro-nano thin film is formed on the surfaces of the fruits and vegetables in a manner of coating different types of coatings one by one. The composite coating has barrier property and antibacterial property, can delay the rotting process of fruits and vegetables, effectively prolongs the shelf life of the fruits and vegetables, and reduces waste and economic loss; meanwhile, the composite coating is edible and easy to wash, no risk is brought to the edible safety of the fruits and vegetables, and the taste of the fruits and vegetables can be improved to a certain extent. The method can be widely applied to the field of fruit and vegetable preservation and the field of packaging materials, and has high commercial application value.

Description

Technical Field

[0001] The invention belongs to the field of fruit and vegetable fresh-keeping materials and technologies, and relates to a preparation method and application of a layer-by-layer self-assembled fruit and vegetable fresh-keeping composite coating. Background Art

[0002] The quality and storage period of fruits and vegetables will be affected by factors such as the environment, physiological effects and microorganisms, which will lead to significant losses and waste of fruits and vegetables in the entire supply chain after picking. According to statistics, the annual loss rate of fruits and vegetables in circulation in my country is higher than 25%, and the amount of loss is as high as 55 billion yuan, which has caused serious economic losses to the society. Therefore, excellent fruit and vegetable preservation technology is urgently needed, and the commonly used preservatives are mostly chemical preservatives. With the development of social economy, people pay more and more attention to food safety issues. Edible coatings are a very effective method to improve food quality and shelf life, and are currently receiving widespread attention. Edible coatings can protect food from mechanical and microbial damage, prevent the escape of beneficial volatiles, inhibit the aging process of food, and maintain a good appearance. The film-forming matrix of edible coatings mainly includes lipids, proteins and polysaccharides. The fresh-keeping coating used in the present invention belongs to polysaccharides. Since these coatings are based on biodegradable and biocompatible materials, they can meet consumers' needs for safe and healthy food, and in many cases can also replace synthetic packaging.

[0003] Layer-by-layer self-assembly technology is one of the methods that can be actively regulated to prepare composite coatings. Through the method of alternating layer-by-layer deposition, the layers are spontaneously associated with each other to produce molecular aggregates or supramolecular structures with complete structures, stable chemical properties, and certain special functions. Compared with traditional film-forming technology, this technology can assemble a wide variety of materials, and has the properties of controlling edible coatings at the molecular level, and can use templates to accurately adjust the surface structure and thickness of the film. Layer-by-layer self-assembly technology can flexibly control the type of deposited materials, the order of deposition, and the number of deposition layers, so as to prepare edible coatings with diverse functions. It is safe, green and environmentally friendly, and has broad application prospects in the field of fruit and vegetable preservation.

[0004] Based on the above, constructing self-assembled edible composite coatings of different compositions according to the characteristics of different fruits and vegetables can protect food from mechanical and microbial damage, while ensuring food safety, reducing environmental pollution, avoiding the use of chemical preservatives and reducing harm to the human body, thereby improving the quality of life of residents. It is also a much-needed way to preserve fruits and vegetables in the industry. Summary of the invention

[0005] The present invention provides a preparation method and application of a layer-by-layer self-assembled composite coating for preserving fruits and vegetables. The invention studies the properties of materials such as nanocellulose, chitosan and plant essential oils, and in particular, conducts antibacterial experiments on peppermint essential oil, ginger essential oil and lemon essential oil, which have antibacterial effects; according to the characteristics of different fruits and vegetables, the layer-by-layer self-assembly technology is used to construct edible coatings with different concentrations of nanocellulose, different concentrations of chitosan, different concentrations of natural plant essential oils, and different numbers of preservation layers, and a nanocellulose / plant essential oil / chitosan composite coating is prepared. The coating forms a micro-nano film with barrier and antibacterial properties on the surface of fruits and vegetables by dipping or spraying, which can effectively delay the decay process of fruits and vegetables after picking, extend the shelf life of fruits and vegetables, and reduce waste. At the same time, the preservative coating is edible and easy to wash, which will not only not affect the flavor of fruits and vegetables, but also improve the taste of fruits and vegetables to a certain extent. The present invention can be widely used in the field of fruit and vegetable preservation and the field of packaging materials, and has high commercial application value.

[0006] The technical solution of the present invention:

[0007] A layer-by-layer self-assembled composite coating for preserving fruits and vegetables is characterized in that, according to the characteristics of the fruits and vegetables, one or more of a nanocellulose coating, a chitosan coating and a natural antibacterial agent coating are selected and combined to be coated on the surface of the fruits and vegetables.

[0008] The present invention provides a nanocellulose coating, characterized in that the nanocellulose is selected from one or more of carboxylated cellulose (CNF-C), sulfonated cellulose (CNC-C), and carboxylated cellulose (C-CNC), and is food grade.

[0009] In one embodiment of the present invention, it is characterized in that the solubility of carboxylated cellulose (CNF-C) is 0.2wt% to 1.0wt%, the concentration of sulfonated cellulose (CNC-C) is 2wt% to 8wt%, and the solubility of carboxylated cellulose (C-CNC) is 1wt% to 4wt%.

[0010] The invention provides a chitosan coating, characterized in that the chitosan coating is selected from one or more chitosans with a deacetylation degree of 85%, 90% and 95%, and is food grade.

[0011] In one embodiment of the present invention, the chitosan concentration is 0.5 wt% to 2.5 wt%.

[0012] The present invention provides a natural antibacterial coating, characterized in that the natural antibacterial is selected from one or more of clove essential oil, lemon essential oil, peppermint essential oil, and ginger essential oil, and is food grade.

[0013] In one embodiment of the present invention, the solubility of the natural antibacterial agent is 0.1wt% to 0.5wt%.

[0014] The present invention provides a coating composite method, which is characterized by a layer-by-layer self-assembly technology, that is, according to the structural characteristics of different fruits and vegetables, a single coating is attached to the surface of fruits and vegetables by a layer-by-layer alternating deposition method, so that the layers spontaneously associate with each other to produce a composite coating of molecular aggregates or supramolecular structures with complete structure, stable chemical properties and certain special functions.

[0015] The present invention provides a method for preparing a composite coating for preserving fruits and vegetables, which is characterized by comprising the following steps:

[0016] (1) Nanocellulose coating: Nanocellulose and deionized water (w / w) are mixed in a certain proportion and stirred at room temperature for 15 to 20 minutes to obtain a nanocellulose solution, thereby obtaining product 1;

[0017] (2) Chitosan coating: glacial acetic acid and deionized water (w / w) were mixed at a ratio of 1:99 to obtain a 1 wt% glacial acetic acid solution, chitosan was added, and the mixture was stirred at room temperature for 15 to 20 minutes to obtain chitosan solutions of different mass concentrations to obtain product 2;

[0018] (3) Natural antibacterial agent coating: natural plant oil and deionized water (w / w) were mixed in proportion, ultrasonically dispersed at room temperature and frequency of 25 kHz for 5 min, Tween-80 was added, and ultrasonic dispersion was continued for 20 min to prepare natural antibacterial agent solutions of different mass concentrations to obtain product three;

[0019] (4) Coating composite: According to the structural characteristics of each fruit and vegetable, one or more of the three products are coated on the surface of the fruit and vegetable to obtain a layer-by-layer self-assembled fruit and vegetable fresh-keeping composite coating.

[0020] In one embodiment of the present invention, step (4) is a layer-by-layer self-assembly technology. According to the characteristics of different types of fruits and vegetables, one or more of nanocellulose, chitosan, and natural plant essential oils are sequentially coated on the surface of fruit and vegetable products at room temperature using the layer-by-layer self-assembly technology. By controlling the coating sequence and the number of coating layers, an edible micro-nano composite fresh-keeping coating is formed on the surface of the fruits and vegetables. The fresh-keeping effect is continuously monitored by observing the appearance of the fruits and vegetables and measuring the weight loss rate, and the evaluation is performed by extending the shelf life of the fruits and vegetables.

[0021] The beneficial effects of the present invention are:

[0022] 1. The fresh-keeping coating of the present invention includes nanocellulose, chitosan, and natural plant essential oil, all of which are food grade, and the raw materials are green and environmentally friendly. The coating is edible and easy to wash, and will not cause harm to the health of consumers. It will not only not affect the flavor of fruits and vegetables, but also improve the taste of fruits and vegetables to a certain extent.

[0023] 2. In the present invention, nanocellulose, chitosan and natural plant essential oil are coated on the surface of fruits and vegetables to form a micro-nano film with barrier and antibacterial properties. The coating can effectively delay the decay process of fruits and vegetables after picking, extend the shelf life of fruits and vegetables, reduce waste and economic losses, and has high commercial application value.

[0024] 3. The layer-by-layer self-assembly technology in the present invention is a generally applicable method for preserving fruits and vegetables. According to the structural characteristics of different fruits and vegetables, the layer-by-layer self-assembly method can be used to control the coating sequence and number of coating layers of the preservative coating to form a personalized preservative coating. Its application methods are flexible and diverse, suitable for the post-harvest preservation of most fruits and vegetables, and can be widely used in the field of fruit and vegetable preservation and packaging materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a comparison chart of the preservation effect of the layer-by-layer self-assembled fruit and vegetable preservation composite coating on bananas;

[0026] Figure 2 This is a comparison chart of the preservation effect of layer-by-layer self-assembled fruit and vegetable preservation composite coating on mango;

[0027] Figure 3 This is a comparison chart of the preservation effect of the layer-by-layer self-assembled fruit and vegetable preservation composite coating on oranges;

[0028] Figure 4 This is a comparison chart of the antibacterial effects of different types of natural plant essential oils on Penicillium. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0030] Example 1

[0031] Provided is a method for preparing a layer-by-layer self-assembled "nanocellulose / chitosan / nanocellulose / chitosan" fruit and vegetable fresh-keeping composite coating, comprising the following steps:

[0032] (1) Carboxylated cellulose (CNF-C) and deionized water were mixed at a ratio of 1:500 and stirred at room temperature to prepare a CNF-C solution;

[0033] (2) glacial acetic acid: deionized water = 1:99, to prepare a 1 wt% glacial acetic acid solution;

[0034] (3) chitosan (CS): 1 w't% glacial acetic acid solution = 1:50, stirring at room temperature for 15-20 minutes to prepare a CS solution;

[0035] (4) Under room temperature conditions, CNF-C solution, CS solution, CNF-C solution, and CS solution were sequentially coated on the surface of bananas. After drying, a four-layer composite edible micro-nanoscale fresh-keeping coating of CNF-C / CS / CNF-C / CS was formed on the surface of the fruit. The fresh-keeping effect was continuously monitored by observing the appearance and measuring the weight loss rate, and the evaluation was performed by extending the shelf life of fruits and vegetables.

[0036] See attached Figure 1 , Figure 1 This is a diagram of the banana preservation effect under 20℃ and 40%RH conditions. In the figure, bananas No. 1 and No. 2 are blank controls without any coating, and bananas No. 3 and No. 4 are bananas coated with four layers of CNF-C / CS / CNF-C / CS composite fresh-keeping coating. It can be clearly observed that the composite coating on the surface of bananas No. 3 and No. 4 can reduce the respiration intensity of fruits and vegetables, delay the appearance of banana spots, make them less likely to rot and deteriorate, and effectively extend the shelf life of bananas to 8 days.

[0037] Example 2

[0038] Provided is a method for preparing a layer-by-layer self-assembled "chitosan / nanocellulose / chitosan" fruit and vegetable fresh-keeping composite coating, comprising the following steps:

[0039] (1) Carboxylated cellulose (C-CNC) and deionized water in a ratio of 1:25 were stirred at room temperature to prepare a C-CNC solution;

[0040] (2) glacial acetic acid: deionized water = 1:100 to prepare a 1 wt% glacial acetic acid solution;

[0041] (3) chitosan (CS): 1 wt% glacial acetic acid solution = 1:40, stirring at room temperature for 15-20 minutes to prepare a CS solution;

[0042] (4) Under room temperature conditions, CS solution, C-CNC solution, and CS solution were sequentially coated on the surface of mangoes. After drying, a three-layer composite edible micro-nanoscale fresh-keeping coating of CS / C-CNC / CS was formed on the surface of the fruit. The fresh-keeping effect was continuously observed by observing the appearance and measuring the weight loss rate, and the evaluation was carried out by extending the shelf life of fruits and vegetables.

[0043] See attached Figure 2 , Figure 2 This is a diagram of the preservation effect of mangoes at 20℃ and 40%RH. In the figure, mangoes No. 1 and No. 2 are blank controls without any coating, and mangoes No. 3, No. 4 and No. 5 are mangoes coated with CS / C-CNC / CS three-layer composite fresh-keeping coating. It can be clearly observed that the composite coating on the surface of mangoes No. 3, No. 4 and No. 5 can reduce the respiration intensity of fruits and vegetables, delay the appearance of mango wrinkles and spots, make it less likely to rot and deteriorate, and effectively extend the shelf life of mangoes to 9 days.

[0044] Example 3

[0045] Provided is a method for preparing a layer-by-layer self-assembled "chitosan / nanocellulose / plant essential oil / chitosan" fruit and vegetable fresh-keeping composite coating, comprising the following steps:

[0046] (1) sulfonated cellulose (CNC-C) and deionized water in a ratio of 1:40, stirred at room temperature to prepare a CNC-C solution;

[0047] (2) glacial acetic acid: deionized water = 1:100 to prepare a 1 wt% glacial acetic acid solution;

[0048] (3) chitosan (CS): 1 wt% glacial acetic acid solution = 1:25, stirring at room temperature for 15 to 20 minutes to prepare a CS solution;

[0049] (4) lemon essential oil: deionized water = 1:200 ratio, ultrasonic dispersion at room temperature and frequency of 25 kHz for 5 min, Tween-80 was added, ultrasonic dispersion was continued for 20 min, and stirring was continued for 15-20 min to prepare a lemon essential oil solution;

[0050] (5) Under room temperature conditions, CS solution, CNC-C solution, lemon essential oil solution, and CS solution were sequentially coated on the surface of oranges. After drying, a four-layer composite edible nanoscale preservative coating of CS / CNC-C / lemon essential oil / CS was formed on the surface of the fruit. The freshness-keeping effect was continuously observed by observing the appearance and measuring the weight loss rate, and was evaluated by extending the shelf life of fruits and vegetables.

[0051] See attached Figure 3 , Figure 3 This is a picture of the preservation effect of oranges under 20℃ and 40%RH. In the picture, orange No. 2 is a blank control group without any coating, orange No. 1 is an orange coated with a three-layer composite fresh-keeping coating of CS / CNC-C / CS, and orange No. 3 is an orange coated with a four-layer composite fresh-keeping coating of CS / CNC-C / lemon essential oil / CS. It can be clearly observed that the coating on the surface of oranges No. 1 and No. 3 can reduce the respiration intensity of fruits and vegetables, delay the appearance of orange wrinkles and spots, and make them less likely to rot and deteriorate. In particular, the preservation effect of orange No. 3, which is added with natural antibacterial agent lemon essential oil, is better. Among them, the shelf life of orange No. 1 can be effectively extended to 11 days, and the shelf life of orange No. 3 can be effectively extended to 16 days.

[0052] Comparative Example 1

[0053] Clove essential oil, lemon essential oil, peppermint essential oil and ginger essential oil were used in the Penicillium inhibition experiment; at the same time, a blank control group (no essential oil was added to the Penicillium culture medium) was carried out to observe its changes under the same culture conditions.

[0054] See attached Figure 4 , the antibacterial effects of various essential oils were evaluated and compared. The diameters of the antibacterial circles of ginger essential oil were 8.19mm, 7.55mm, and 7.24mm from large to small, respectively, which indicates that these two essential oils have a certain inhibitory effect on Penicillium; the diameters of the antibacterial circles of peppermint essential oil were 16.49mm, 16.29mm, and 12.44mm from large to small, respectively, indicating that peppermint essential oil has a good inhibitory effect on Penicillium; and the inhibitory effect of lemon essential oil on Penicillium is the most obvious, and Penicillium cannot grow. The lemon essential oil selected in the example of the present invention has a strong inhibitory effect on mold growth.

[0055] The above description is a detailed description of the preferred feasible embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modified changes completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A layer-by-layer self-assembled fresh-keeping composite coating, characterized in that: According to the characteristics of fruits and vegetables, one or more of nanocellulose coating, chitosan coating and natural antibacterial agent coating are selected and combined for coating on the surface of fruits and vegetables. The specific preparation steps are as follows: (1) Nanocellulose coating: Nanocellulose and deionized water (w / w) were mixed in a certain proportion and stirred at room temperature for 15 to 20 minutes to prepare nanocellulose solutions with different mass concentrations to obtain product 1; (2) Chitosan coating: glacial acetic acid and deionized water (w / w) were mixed at a ratio of 1:99 to obtain a 1 wt% glacial acetic acid solution, chitosan was added, and the mixture was stirred at room temperature for 15 to 20 minutes to obtain chitosan solutions of different mass concentrations to obtain product 2; (3) Natural antibacterial agent coating: natural plant oil and deionized water (w / w) were mixed in proportion, ultrasonically dispersed at room temperature and frequency of 25 kHz for 5 min, Tween-80 was added, and ultrasonic dispersion was continued for 20 min to prepare natural antibacterial agent solutions of different mass concentrations to obtain product three; (4) Composite coating: According to the structural characteristics of different fruits and vegetables, one or more of the three products are applied to the surface of fruits and vegetables to obtain a layer-by-layer self-assembled fruit and vegetable fresh-keeping composite coating.

2. According to claim 1, the nano-cellulose, chitosan and natural plant essential oil are food grade.

3. The nanocellulose coating according to claim 1, characterized in that The nanocellulose in step (1) is selected from one or more of carboxylated cellulose (CNF-C), sulfonated cellulose (CNC-C), and carboxylated cellulose (C-CNC), wherein the solubility of the carboxylated cellulose (CNF-C) is 0.2wt% to 1.0wt%, the concentration of the sulfonated cellulose (CNC-C) is 2wt% to 8wt%, and the solubility of the carboxylated cellulose (C-CNC) is 1wt% to 4wt%.

4. The chitosan coating according to claim 1, characterized in that: The chitosan coating in step (2) is selected from one or more chitosans with a deacetylation degree of 85%, 90%, and 95%, and the chitosan concentration is 0.5wt% to 2.5wt%.

5. The natural antimicrobial coating according to claim 1, characterized in that: The natural antibacterial agent in step (3) is selected from one or more of clove essential oil, lemon essential oil, peppermint essential oil, and ginger essential oil, and the solubility of the natural antibacterial agent is 0.1wt% to 0.5wt%.

6. The coating composite method according to claim 1, characterized in that: The layer-by-layer self-assembly technology is to attach a single coating to the surface of fruits and vegetables by alternating layer-by-layer deposition according to the structural characteristics of different fruits and vegetables, so that the layers spontaneously associate with each other to produce a composite coating of molecular aggregates or supramolecular structures with complete structure, stable chemical properties and certain special functions.

7. A layer-by-layer self-assembled fruit and vegetable fresh-keeping composite coating obtained according to the preparation method of claims 1-6 and its application.

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