Full-bio-based antibacterial composite film for fruit and vegetable fresh-keeping and preparation method and application of full-bio-based antibacterial composite film

Abstract

The invention discloses a full-bio-based antibacterial composite film for fresh keeping of fruits and vegetables as well as a preparation method and application of the full-bio-based antibacterial composite film, and belongs to the technical field of bio-based food packaging materials. The problems that a pure chitosan film is poor in mechanical property, insufficient in barrier property and single in function are solved. The composite membrane is prepared by taking chitosan as a matrix, introducing a natural cross-linking agent genipin, a reinforcing phase sulfonated nano cellulose whisker and a functional component lemon grass essential oil, and carrying out the steps of curtain coating, drying and the like. Through the synergistic effect of genipin crosslinking and nanocellulose enhancement, the mechanical strength and barrier property of the composite film are remarkably improved, and the composite film is endowed with broad-spectrum antibacterial, antioxidant and excellent anti-ultraviolet functions. All components of the membrane are derived from natural renewable resources, and the membrane is safe and biodegradable. Application experiments show that when the preservative is applied to preservation of perishable fruits and vegetables of cherries and tomatoes, the growth of microorganisms can be effectively inhibited, the quality deterioration is delayed, the weight loss rate is reduced, the hardness is maintained, the shelf life is remarkably prolonged, and the preservative has important application prospects.

Description

Technical Field

[0001] This invention belongs to the field of bio-based food packaging materials technology, specifically relating to a fully bio-based biodegradable composite film with both antibacterial and preservation functions, its preparation method, and its application as a packaging material in extending the shelf life of fruits and vegetables. Background Technology

[0002] Freshly harvested fruits and vegetables are highly susceptible to spoilage and deterioration during storage and distribution due to their own respiration and microbial contamination, leading to quality deterioration and shortened shelf life, resulting in significant economic losses. Currently, widely used petroleum-based plastic packaging materials are non-biodegradable, causing serious "white pollution" problems. Therefore, developing environmentally friendly, biodegradable natural polymer packaging materials has become an important research direction in the food packaging field.

[0003] Chitosan is a natural cationic polysaccharide that is considered a highly promising alternative to petroleum-based packaging materials due to its excellent film-forming properties, biocompatibility, biodegradability, and broad-spectrum antibacterial activity. However, pure chitosan films have significant limitations: firstly, their mechanical strength is poor and their flexibility is insufficient, making it difficult to meet the basic mechanical requirements of packaging materials; secondly, their strong hydrophilicity results in poor water-blocking properties and inadequate barrier performance against water vapor and oxygen, limiting their application in the preservation of perishable foods.

[0004] To improve the performance of chitosan membranes, researchers often employ methods such as blending, crosslinking, or adding nano-reinforcing phases. Crosslinking is an effective means of enhancing the membrane network structure. However, traditional chemical crosslinking agents (such as glutaraldehyde) may pose cytotoxicity and biosafety issues, making them unsuitable for food packaging. Genipin, a natural crosslinking agent extracted from gardenia fruit, boasts high safety and good biocompatibility. It can undergo crosslinking reactions with the amino groups in chitosan molecules, effectively improving the mechanical properties and stability of the membrane. Furthermore, adding nanomaterials such as cellulose whiskers can serve as reinforcing phases, enhancing the mechanical strength and barrier properties of the matrix through interactions such as hydrogen bonding. Introducing plant essential oils (such as lemongrass oil) can endow the membrane with antibacterial, antioxidant, and other bioactive functions.

[0005] However, existing technologies mostly focus on improving a single property, making it difficult to achieve a synergistic balance of multiple excellent properties. For example, simple blending may lead to poor compatibility of the components and uneven dispersion of the functional phase; the addition of essential oils may weaken the mechanical strength of the membrane; and how to use sophisticated component design and preparation processes to enable composite membranes to simultaneously possess high mechanical strength, excellent barrier properties, sustained antibacterial activity, and UV protection, and successfully apply them to the room temperature preservation of perishable fruits and vegetables, remains a technical challenge that urgently needs to be solved. Summary of the Invention

[0006] The primary objective of this invention is to overcome the shortcomings of existing chitosan-based packaging materials in terms of mechanical strength, barrier properties, and functional integration, and to provide a fully bio-based, biodegradable, multifunctional composite film, its preparation method, and its applications. This composite film aims to simultaneously possess excellent mechanical properties, high barrier properties (against oxygen), significant antibacterial activity, and effective UV protection, while effectively extending the shelf life of fruits and vegetables. The preparation method is simple, operates under mild conditions, is easily scalable, and the entire system is safe and non-toxic.

[0007] To achieve the above objectives, this invention provides a fully bio-based antibacterial composite film for fruit and vegetable preservation, which is prepared from a raw material system comprising chitosan, genipin, sulfonated nanocellulose whiskers, and lemongrass essential oil. Simultaneously, this invention provides a method for preparing the composite film, comprising the following steps: (1) Preparation of chitosan solution: Chitosan powder with a specific degree of deacetylation is dissolved in dilute acetic acid solution and stirred continuously at a certain temperature until completely dissolved to obtain a homogeneous chitosan solution.

[0008] (2) Genipin crosslinking reaction: Genipin is added to the chitosan solution obtained in step (1), and the crosslinking reaction is carried out by continuous stirring to obtain chitosan-genipin crosslinking solution.

[0009] (3) Introduction of nanocellulose reinforcing phase: Sulfonated nanocellulose whiskers are added to the chitosan-genipin crosslinking solution obtained in step (2), and stirred thoroughly to disperse them evenly, forming a three-dimensional network reinforcing structure, and a chitosan-genipin-nanocellulose composite solution is obtained.

[0010] (4) Preparation of lemongrass essential oil emulsion: The emulsifier Tween 80 is mixed with lemongrass essential oil in deionized water and emulsified by high-speed shearing or stirring to form a stable essential oil emulsion.

[0011] (5) Composite and degassing of film-forming solution: The essential oil emulsion obtained in step (4) is slowly added to the composite solution obtained in step (3), and the mixture is stirred and mixed evenly. Then, ultrasonic treatment is performed to remove bubbles, so as to obtain a final uniform and stable film-forming solution.

[0012] (6) Film formation and drying: The degassed film-forming liquid is cast onto a flat substrate and dried at a specific temperature to constant weight. After peeling off the film, the fully bio-based antibacterial composite film is obtained.

[0013] Preferably, in step (1), the degree of deacetylation of the chitosan is not less than 95%, and the mass fraction in the solution is 1% to 3%; the volume concentration of the acetic acid solution is 0.5% to 2%; and the stirring and dissolving time is 20 to 40 minutes.

[0014] Preferably, in step (2), the amount of genipin added is 0.5% to 2% of the mass of chitosan; the cross-linking reaction time is 20 to 40 minutes.

[0015] Preferably, in step (3), the amount of sulfonated nanocellulose whiskers added is 5% to 20% of the mass of chitosan; the dispersion and stirring time is 2 to 4 hours.

[0016] Preferably, in step (4), the amount of Tween 80 emulsifier added is 5% to 15% of the mass of chitosan; the amount of lemongrass essential oil added is 1% to 10% of the mass of chitosan; and the emulsification time is 1 to 2 hours.

[0017] Preferably, in step (5), the mixing time is 0.5 to 1.5 hours and the ultrasonic degassing time is 15 to 35 minutes.

[0018] Preferably, in step (6), the drying temperature is 40°C to 50°C and the drying time is 36 to 48 hours.

[0019] This invention also claims protection for the application of the all-bio-based antibacterial composite film in fruit and vegetable preservation, particularly suitable for the room temperature or low temperature storage and preservation of perishable fruits and vegetables such as cherry tomatoes, strawberries, and blueberries, which can significantly delay spoilage, maintain quality, and extend shelf life. The film can be used directly as an independent packaging material or applied as an edible coating to the surface of fruits and vegetables.

[0020] Compared with the prior art, the present invention has the following significant advantages: 1. Innovative Components and Green Safety: All components (chitosan, genipin, nanocellulose, lemongrass essential oil) are derived from natural renewable resources, and the entire system is non-toxic and biodegradable. Genipin is specifically used as a natural cross-linking agent, completely avoiding the potential toxicity risks of traditional cross-linking agents such as glutaraldehyde, ensuring food contact safety and meeting the requirements of green and sustainable development.

[0021] 2. Performance Coordination and Functional Integration: Significantly improved mechanical properties: Through the synergistic effect of genipin crosslinking and nano-reinforcing effect of nanocellulose, a dense network structure is constructed, which significantly improves the tensile strength and toughness of the composite film.

[0022] Excellent barrier properties: The dense cross-linked network and the filling effect of nanocellulose effectively reduce oxygen permeability and delay the oxidation of fruits and vegetables.

[0023] Long-lasting antibacterial and antioxidant activity: The introduction of lemongrass essential oil endows the film with broad-spectrum antibacterial and antioxidant capabilities, which can effectively inhibit the growth of microorganisms on the surface of fruits and vegetables and delay spoilage.

[0024] Outstanding UV protection: The chromophores generated after genipin crosslinking work together with nanocellulose to give the film excellent UV shielding effect, protecting fruits and vegetables from photo-oxidative damage.

[0025] 3. Excellent preservation effect: Application experiments show that this composite film can effectively reduce the weight loss rate of fruits and vegetables during storage, delay the decrease in firmness, and significantly extend the shelf life.

[0026] 4. Simple and efficient preparation process: The preparation process does not require complex equipment, the conditions are mild, the parameters are highly controllable, it is easy to achieve large-scale production, and the cost is low. Attached Figure Description

[0027] Figure 1 This is a schematic diagram showing the UV resistance test results of different films.

[0028] Figure 2 This is a schematic diagram showing the test results of the antibacterial properties of different films.

[0029] Figure 3 This is a graph showing the weight loss rate of cherry tomatoes during storage.

[0030] Figure 4 This is a graph showing the change in firmness of cherry tomatoes during storage.

[0031] Figure 5 A comparison chart showing the changes in the appearance of cherry tomatoes during storage. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0033] Comparative Example 1: (1) Add 2g of chitosan powder to 100mL of 1% (v / v) acetic acid solution, stir magnetically for 30min, and then degas by ultrasonication for 30min to obtain chitosan film solution; (2) Pour the chitosan film liquid onto a polytetrafluoroethylene plate, and then dry it in an oven at 40°C for 48 hours. Peel off the chitosan film (referred to as CS film).

[0034] Comparative Example 2: (1) Add 2g of chitosan powder to 100mL of 1% (v / v) acetic acid solution and stir magnetically for 30min to obtain chitosan solution; (2) Add 1% (by weight of chitosan) of genipin (G) to the chitosan solution, stir for 30 min, and then sonicate for 30 min to obtain chitosan / genipin composite membrane solution; (3) The chitosan / genipin film liquid was cast onto a polytetrafluoroethylene plate and then dried in an oven at 40°C for 48 hours. The chitosan / genipin film composite film (referred to as CS / G film) was then peeled off.

[0035] Example 1: (1) Add 2g of chitosan powder to 100mL of 1% (v / v) acetic acid solution and stir magnetically for 30min to obtain chitosan solution; (2) Add 1% (by weight of chitosan) of genipin (G) to the chitosan solution, stir for 30 min, and then sonicate for 30 min to obtain chitosan / genipin composite membrane solution; (3) Add 15% of the chitosan mass of sulfonated cellulose nanofibers (CNC) to the CS / G solution obtained in step (2), and disperse by magnetic stirring for 3 hours to obtain a chitosan / genipin / sulfonated cellulose nanofiber composite solution (referred to as CS / G / CNC solution). (4) Add 10% of the chitosan mass of Tween 80 to 10 mL of water and stir at 40°C for 1 h. Then add 5% of the chitosan mass of lemongrass essential oil (LEO) and stir for 30 min to obtain a stable lemongrass essential oil emulsion.

[0036] (5) Slowly add the essential oil emulsion obtained in step (4) to the CS / G / CNC solution obtained in step (3), stir for 1 hour to mix evenly, and then degas by ultrasonication for 30 minutes to obtain the final film-forming solution.

[0037] (6) The film-forming liquid in step (5) is cast onto a polytetrafluoroethylene plate and then dried in an oven at 40°C for 48 hours to obtain a chitosan / genipin / sulfonated cellulose nanofibers / lemongrass essential oil composite film (denoted as CS / G / CNC / LEO film).

[0038] Example 2: The only difference between this embodiment and embodiment 1 is the amount of lemongrass essential oil added in step (4): 10% of the chitosan mass of lemongrass essential oil (LEO) is added. The other raw material ratios and preparation steps are exactly the same as in embodiment 1. The resulting composite membrane is also referred to as CS / G / CNC / LEO membrane.

[0039] Performance testing methods: Mechanical performance testing The tensile strength and elongation at break of the film were determined according to GB / T 1040.3-2006.

[0040] UV resistance test The film was cut into rectangles of 2cm × 2cm and scanned using a UV-Vis spectrophotometer (UV-2700i) with a wavelength range of 200-800nm.

[0041] Oxygen barrier test The oxygen permeability coefficient of the composite membrane was determined according to GB / T 1038.1-2022.

[0042] Fruit and vegetable preservation application test: Using cherry tomatoes as the subject, we recorded changes in indicators such as weight loss rate and firmness of the fruit during storage, and observed their appearance quality.

[0043] Measurement results Mechanical properties The mechanical strengths of various films are shown in Table 1. Compared with CS film and CS / G film, the tensile strength and elongation at break of CS / G / CNC / LEO composite film are significantly improved. Specifically, the tensile strength is more than doubled, and the elongation at break is nearly 10 times higher. This is mainly attributed to the chemical cross-linking reaction between genipin and chitosan, as well as the nano-reinforcing effect of nanocellulose, making the composite film more suitable for the preservation and packaging of fruits and vegetables.

[0044] Table 1 Mechanical strength of different films

[0045] UV protection For the UV resistance properties of various films, see Figure 1 In the ultraviolet light range of 200-400 nm, the composite films of Examples 1 and 2 exhibit extremely low ultraviolet light transmittance, indicating that the composite films have excellent anti-ultraviolet properties.

[0046] oxygen barrier properties of membranes The oxygen permeability coefficients of various films are shown in Table 2. The oxygen barrier properties of CS / G / CNC / LEO films are significantly improved compared to CS films.

[0047] Table 2 Oxygen barrier properties of different films

[0048] Antibacterial properties For the antibacterial properties of various films, see [link to relevant documentation]. Figure 2 The composite membranes prepared in Examples 1 and 2 both exhibited obvious antibacterial zones against Staphylococcus aureus and Escherichia coli, indicating that they have good antibacterial effects.

[0049] Preservation effect like Figure 3 , Figure 4 and Figure 5 As shown, cherry tomatoes packaged with the composite film of this invention exhibited a significantly lower weight loss rate during storage compared to the comparative example, maintained better firmness, and showed slower deterioration in appearance quality. Experimental results indicate that the composite film of this invention can extend the shelf life of cherry tomatoes from approximately 5 days to at least 11 days, demonstrating a significant preservation effect.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A fully bio-based antibacterial composite film for preserving fruits and vegetables, characterized in that, It is prepared from a raw material system containing chitosan, genipin, sulfonated nanocellulose whiskers and lemongrass essential oil.

2. A method for preparing a fully bio-based antibacterial composite membrane as described in claim 1, characterized in that, Includes the following steps: (1) Dissolve chitosan in acetic acid solution and stir until completely dissolved to obtain a homogeneous chitosan solution; (2) Add genipin to the chitosan solution obtained in step (1) and stir continuously to carry out the cross-linking reaction to obtain a chitosan-genipin cross-linking solution; (3) Add sulfonated nanocellulose whiskers to the chitosan-genipin crosslinking solution obtained in step (2), stir thoroughly to disperse them evenly, and obtain a chitosan-genipin-nanocellulose composite solution. (4) Mix the emulsifier Tween 80 with lemongrass essential oil in deionized water and emulsify to form a stable lemongrass essential oil emulsion. (5) Add the lemongrass essential oil emulsion obtained in step (4) to the composite solution obtained in step (3), stir and mix evenly, and then perform ultrasonic degassing to obtain a uniform film-forming solution. (6) Cast the film-forming liquid obtained in step (5) onto a flat substrate, dry it, and then peel off the film to obtain the all-bio-based antibacterial composite film.

3. The preparation method according to claim 2, characterized in that: In step (1), the degree of deacetylation of the chitosan is not less than 95%; the mass fraction of the chitosan in the solution is 1% to 3%; and the volume concentration of the acetic acid solution is 0.5% to 2%.

4. The preparation method according to claim 2, characterized in that: In step (2), the amount of genipin added is 0.5% to 2% of the mass of chitosan.

5. The preparation method according to claim 2, characterized in that: In step (3), the amount of sulfonated nanocellulose whiskers added is 5% to 20% of the mass of chitosan.

6. The preparation method according to claim 2, characterized in that: In step (4), the amount of the emulsifier Tween 80 added is 5% to 15% of the mass of chitosan; the amount of lemongrass essential oil added is 1% to 10% of the mass of chitosan.

7. The preparation method according to claim 2, characterized in that: In step (1), the stirring and dissolving time is 20 to 40 minutes; In step (2), the crosslinking reaction time is 20 to 40 minutes; In step (3), the dispersion and stirring time is 2 to 4 hours; In step (4), the emulsification time is 1 to 2 hours; In step (5), the mixing time is 0.5 to 1.5 hours, and the ultrasonic degassing time is 15 to 35 minutes; In step (6), the drying temperature is 40°C to 50°C and the drying time is 36 to 48 hours.

8. The application of the all-bio-based antibacterial composite film as described in claim 1 in the preservation of fruits and vegetables.

9. The application according to claim 8, characterized in that, The fruits and vegetables mentioned are perishable, including cherry tomatoes, strawberries, or blueberries.

10. The application according to claim 8 or 9, characterized in that, The composite film is used as a stand-alone packaging material or an edible coating.

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