Preparation and application of pH-responsive pine needle essential oil microcapsule composite antibacterial and fresh-keeping film

Abstract

The application discloses a preparation process of a pH-responsive slow-release pine needle essential oil food preservative film composed of microcapsules. Pine needle essential oil / gelatin / arabic gum microcapsules are prepared by adopting a complex coagulation method with gelatin and arabic gum as a double-network wall material and the pine needle essential oil as core material; polyvinyl alcohol is used as a film-forming base material, the microcapsules are mixed with the base material, and a film is dried by a flow casting method. The obtained microcapsules are uniformly distributed in a spherical shape, have excellent embedding effect, can effectively protect active ingredients of the pine needle essential oil and delay volatilization. The prepared food preservative film is safe, non-toxic and edible, has good antibacterial performance, can perceive changes in a packaging microenvironment through a pH response mechanism, realizes targeted slow release of antibacterial ingredients, inhibits growth of microorganisms, and significantly prolongs the shelf life of fruits, vegetables and other foods. The process is simple, has good stability, and has important research and application value in the field of intelligent antibacterial food packaging.

Description

Technical Field

[0001] This invention belongs to the field of food packaging materials technology, specifically relating to the preparation and application of a pH-responsive pine needle essential oil microcapsule composite antibacterial preservation film. Background Technology

[0002] Food preservation is a core aspect of the food industry, impacting food quality and safety, extending shelf life, and enhancing the value of the supply chain. It is also a crucial measure for implementing the national food quality and safety strategy, promoting the green and low-carbon development of the food industry, and reducing food waste. In recent years, my country has introduced numerous policies to drive the upgrading of food preservation technologies towards natural, safe, efficient, and environmentally friendly approaches, encouraging the research and development of natural preservation materials to replace chemical preservatives, thus clarifying the development direction for technological innovation in the industry. Traditional preservation methods such as low-temperature refrigeration, vacuum packaging, and the addition of chemical preservatives suffer from high energy consumption, high costs, limited antibacterial effects, and potential health risks, making them difficult to meet the needs of industry development and consumers. Natural antibacterial preservation films, due to their ability to slowly release antibacterial substances and effectively inhibit microbial growth, align with the requirements of green development and have become a research hotspot in the field of food preservation.

[0003] Plant essential oils are ideal natural antibacterial agents, possessing natural safety, broad-spectrum antibacterial properties, and antioxidant effects, aligning with national research and development guidelines for natural preservation materials. Pine needle essential oil, rich in terpenes, alcohols, and other active ingredients, exhibits excellent antibacterial and antioxidant properties, making it a promising candidate for food preservation. However, pine needle essential oil suffers from inherent drawbacks such as high volatility and poor stability. Direct addition to cling film leads to rapid evaporation and loss, significantly shortening the duration of its antibacterial effect and hindering long-term preservation, thus severely limiting its large-scale application. Microencapsulation technology is a core solution to this problem. Physical barrier properties through the wall material reduce essential oil evaporation and improve stability, while the slow-release structure enables the slow and continuous release of antibacterial components, extending the antibacterial time. Furthermore, integrating pH-responsive functionality with the microcapsule's slow-release structure allows for intelligent release of antibacterial components via functional groups such as carboxyl and amino groups. This accelerates drug release when food spoilage causes pH anomalies, precisely enhancing the antibacterial effect and significantly improving preservation efficiency.

[0004] Gelatin and gum arabic, as natural polymer wall materials, possess excellent biocompatibility, film-forming properties, safety, and biodegradability, aligning with the requirements of green and environmentally friendly industries. They are ideal composite wall materials for preparing pine needle oil microcapsules. Using these two materials as wall materials, pine needle oil microcapsules can be prepared via a complex coagulation method. Adjusting the wall material ratio and process parameters can improve the microcapsule encapsulation rate and stability, enabling controlled release of antibacterial components and laying the foundation for the application of pine needle oil in food preservation. However, research on the preparation of pine needle oil microcapsules and their application in food preservation films is still in its early stages. Existing technologies generally suffer from low microcapsule encapsulation rates, poor sustained-release performance, limited antibacterial effects in preservation films, and a lack of intelligent responsiveness, making it difficult to meet the actual preservation needs of the food industry. Developing a natural composite preservation film that combines pH responsiveness, long-lasting sustained release, and highly effective antibacterial properties has become an urgent technical challenge.

[0005] This invention aligns with the national green development policy for the food preservation industry. Addressing the application deficiencies and shortcomings of existing technologies for pine needle oil, it utilizes gelatin and gum arabic as composite wall materials. By studying the effects of single factors such as core-to-wall ratio and pH value on the performance of pine needle oil microcapsules, the preparation process is optimized to produce pH-responsive pine needle oil microcapsules with high encapsulation efficiency and excellent sustained-release properties. Furthermore, these microcapsules are composited with a polyvinyl alcohol film-forming substrate to prepare a composite antibacterial food preservation film with excellent pH-responsive sustained-release properties and high antibacterial effects. The aim is to provide novel, natural, and efficient preservation materials and preparation technologies for the food preservation field, promoting the large-scale and industrialized application of natural plant essential oils in the food preservation industry. Summary of the Invention

[0006] The purpose of this invention is to provide a pH-responsive pine needle essential oil microcapsule composite preservation film material, its preparation method, and its application. The prepared composite preservation film material has good film-forming properties, pH responsiveness, and antibacterial preservation properties. It can effectively protect the bioactive components of pine needle essential oil, delay the volatilization of essential oil, achieve targeted and sustained release of antibacterial components, and significantly extend the shelf life of food.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a pH-responsive pine needle oil microcapsule composite preservation film material. The composite preservation film material is composed of a polyvinyl alcohol film-forming substrate and pine needle oil / gelatin / gum arabic microcapsules loaded therein. The pine needle oil / gelatin / gum arabic microcapsules are prepared by complex coagulation method with gelatin and gum arabic as wall materials and pine needle oil as core material. The core-to-wall ratio is 3:1, 2:1, 1:1, 1:2, and 1:3. The film material has the function of pH-responsive slow-release pine needle oil and exhibits antibacterial preservation activity.

[0009] Preferably, the raw materials for preparing the pine needle oil / gelatin / gum arabic microcapsules include gelatin, gum arabic, pine needle oil, acetic acid solution, sodium hydroxide solution, and glutaraldehyde. The gelatin is prepared as an aqueous solution with a mass fraction of 4-6%, and the gum arabic is prepared as an aqueous solution with a mass fraction of 4-6%.

[0010] Preferably, in the preparation process of the pine needle oil / gelatin / gum arabic microcapsules, the pH of the system is adjusted to 5.2~6.8 by sodium hydroxide solution, the amount of glutaraldehyde added for cross-linking and curing is 0.1~0.3 mL, and the performance of the microcapsules is optimized by controlling the core-to-wall ratio and the pH of the system adjusted by sodium hydroxide solution.

[0011] Preferably, in step (1), after cross-linking and curing, the mixture is centrifuged at a speed of 2500~3500 r / min for 8~12 min, the centrifuged precipitate is collected and placed in a freeze dryer, and freeze-dried at -55~-45 ℃ and 5~15 Pa for 20~28 h.

[0012] Preferably, in the preparation of the polyvinyl alcohol film-forming solution in step (2), the heating and stirring temperature is 90~100 ℃ and the time is 5~7 h.

[0013] Preferably, in step (2), after the pine needle oil / gelatin / gum arabic microcapsule suspension is mixed with the polyvinyl alcohol film-forming solution, it is continuously stirred for 0.5~1.5 h.

[0014] Preferably, in step (2), the drying temperature is 45~55 ℃ and the time is 4~6 h.

[0015] The present invention also provides an application of the above-mentioned pH-responsive pine needle essential oil microcapsule composite preservation film material in the preparation of preservation and / or antibacterial food packaging products.

[0016] The beneficial effects of this invention compared to the prior art are as follows:

[0017] (1) This invention uses gelatin and gum arabic as double-wall materials and pine needle oil as core material to prepare microcapsules, and loads them on polyvinyl alcohol film-forming substrate to obtain a composite preservation film. Pine needle oil is used as a natural antibacterial and preservation ingredient, which realizes the efficient utilization of plant-derived bioactive ingredients. There are no potential safety hazards of artificially synthesized antibacterial agents. It has important practical significance for inhibiting the growth of microorganisms on the surface of food and extending the shelf life of fruits, vegetables, and meat.

[0018] (2) The pine needle oil / gelatin / gum arabic microcapsules prepared by the present invention can effectively encapsulate pine needle oil, protect its bioactive components from being destroyed, and delay the volatilization and loss of essential oil. Combined with the pH response release mechanism, it can achieve targeted sustained release of antibacterial components, which solves the problem of excessively fast release of essential oil and short preservation time in traditional essential oil films. Moreover, the composite film has excellent film-forming properties, stable mechanical properties, and high safety in use.

[0019] (3) This invention optimizes the performance of microcapsules by adjusting key parameters such as core-to-wall ratio and system pH. The overall preparation process is simple to operate and the parameters are easy to control. The raw materials used, such as gelatin and gum arabic, are common biomass materials, which are in line with the development trend of green and environmentally friendly food packaging. It can meet the needs of industrial mass production and has extremely high practical application value and broad industrialization prospects in the field of antibacterial and fresh food packaging. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 Images showing the encapsulation efficiency of pine needle essential oil microcapsules with different core-to-wall ratios in Experimental Example 1 of this invention;

[0022] Figure 2 Images showing the microcapsule encapsulation efficiency of pine needle essential oil at different pH values ​​in Experiment Example 1 of this invention;

[0023] Figure 3 The image shown is a scanning electron microscope image of pine needle essential oil microcapsules from Experimental Example 1 of this invention.

[0024] Figure 4 Images showing the surface morphology of the composite film and blank film of pine needle essential oil microcapsules at different concentrations in Experiment Example 1 of this invention;

[0025] Figure 5 These are scanning electron microscope (SEM) images of the surface morphology of composite films and blank films containing microcapsules of pine needle essential oil at different concentrations in Experimental Example 1 of this invention; where a is the blank film; b is PNEO@GA-PVA-1; c is PNEO@GA-PVA-2; and d is PNEO@GA-PVA-3.

[0026] Figure 6 This is a schematic diagram showing the light transmittance of the composite film of pine needle essential oil microcapsules at different concentrations in Experiment Example 1 of the present invention;

[0027] Figure 7This is a schematic diagram showing the surface contact angles of the composite film and blank film of pine needle essential oil microcapsules with different concentrations in Experiment 1 of the present invention with water; where a is the blank film; b is PNEO@GA-PVA-1; c is PNEO@GA-PVA-2; and d is PNEO@GA-PVA-3.

[0028] Figure 8 This is a schematic diagram illustrating the antibacterial effects of microcapsule composite films and blank films of pine needle essential oil at different concentrations in Experiment Example 1 of the present invention.

[0029] Figure 9 This is a schematic diagram illustrating the sustained-release effect of microcapsule composite films containing different concentrations of pine needle essential oil in Experiment Example 1 of this invention;

[0030] Figure 10 This is a schematic diagram of strawberry preservation using microcapsule composite films of pine needle oil at different concentrations in Experiment Example 1 of this invention;

[0031] Figure 11 This is a schematic diagram of pork preserved using microcapsule composite films of pine needle oil at different concentrations in Experiment 1 of this invention. Detailed Implementation

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0033] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0035] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0036] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0037] The pine needle essential oil used in this invention is derived from pine needle essential oil extracted using a microwave-assisted method with a low eutectic solvent.

[0038] Example 1

[0039] Example 1 of this invention provides a method for preparing a pH-responsive pine needle essential oil microcapsule composite film material, the specific steps of which are as follows:

[0040] (1) Preparation of pine needle essential oil microcapsules

[0041] Pine needle essential oil was added to a 5% (w / w) gelatin aqueous solution at core-to-wall ratios of 3:1, 2:1, 1:1, 1:2, and 1:3. The mixture was homogenized at 12000 r / min for 2 min using a high-speed homogenizer to obtain a homogenized essential oil solution. A 5% (w / w) gum arabic aqueous solution was added to the homogenized essential oil solution, and the mixture was stirred at 50 °C for 30 min. The pH of the system was adjusted to 4.0 by slowly adding 1 mol / L acetic acid solution until the solution became turbid, indicating preliminary microcapsule formation. The preliminarily formed microcapsule system was cooled in an ice-water bath and stirred continuously for 1 h until the system temperature dropped to 10 °C. The pH of the system was adjusted to 5.2, 5.6, 6.0, 6.4, and 6.8 using sodium hydroxide solution. 0.2 mL of glutaraldehyde was added for cross-linking and curing. After the reaction was complete, a pine needle essential oil-gelatin-gum arabic microcapsule suspension was obtained. The mixture was centrifuged at 3000 r / min for 10 min. The precipitate obtained by centrifugation was collected and placed in a freeze dryer, where it was freeze-dried at -50 °C and 10 Pa for 24 h. During the preparation process, the microcapsule performance was optimized using the core-to-wall ratio and the pH of the system adjusted with sodium hydroxide solution as single factors.

[0042] (2) Preparation of pH-responsive sustained-release thin film material containing pine needle essential oil

[0043] Preparation of pH-responsive pine needle oil microcapsule composite preservation film: Polyvinyl alcohol was dissolved in water and stirred in a 95 ℃ water bath for 6 h to obtain a 4% (w / v) PVA film-forming solution; 2.5 g, 10 g, and 40 g of pine needle oil / gelatin / gum arabic microcapsule suspensions were added to 10 g of PVA and stirred continuously for 1 h to obtain a composite film-forming solution; the composite film-forming solution was cast onto a petri dish plate and dried in a 50 ℃ oven for 5 h to obtain the pH-responsive pine needle oil microcapsule composite preservation film.

[0044] Example 2

[0045] Example 2 of this invention provides a method for preparing a pH-responsive pine needle oil microcapsule composite film material based on the pine needle oil / gelatin / gum arabic microcapsule described in Example 1. The specific steps are as follows:

[0046] Preparation of pH-responsive pine needle oil microcapsule composite preservation film: Polyvinyl alcohol was dissolved in water and stirred in a 95 ℃ water bath for 6 h to obtain a 4% (w / v) PVA film-forming solution; the prepared pine needle oil / gelatin / gum arabic microcapsule suspension was added to the PVA film-forming solution at a mass ratio of 2.5:10 g, and stirred continuously for 1 h to obtain a composite film-forming solution; the composite film-forming solution was cast onto a petri dish plate and dried in a 50 ℃ oven for 5 h to obtain the pH-responsive pine needle oil microcapsule composite preservation film.

[0047] Example 3

[0048] Example 3 of this invention provides a method for preparing a pH-responsive pine needle oil microcapsule composite film material based on the pine needle oil / gelatin / gum arabic microcapsule described in Example 1. The specific steps are as follows:

[0049] Preparation of pH-responsive pine needle oil microcapsule composite preservation film: Polyvinyl alcohol was dissolved in water and stirred in a 95 ℃ water bath for 6 h to obtain a 4% (w / v) PVA film-forming solution; the prepared pine needle oil / gelatin / gum arabic microcapsule suspension was added to the PVA film-forming solution at a mass ratio of 10:10 g, and stirred continuously for 1 h to obtain a composite film-forming solution; the composite film-forming solution was cast onto a petri dish plate and dried in a 50 ℃ oven for 5 h to obtain the pH-responsive pine needle oil microcapsule composite preservation film.

[0050] Example 4

[0051] Example 4 of this invention provides a method for preparing a pH-responsive pine needle oil microcapsule composite film material based on the pine needle oil / gelatin / gum arabic microcapsule described in Example 1. The specific steps are as follows:

[0052] Preparation of pH-responsive pine needle oil microcapsule composite preservation film: Polyvinyl alcohol was dissolved in water and stirred in a 95 ℃ water bath for 6 h to obtain a 4% (w / v) PVA film-forming solution; the prepared pine needle oil / gelatin / gum arabic microcapsule suspension was added to the PVA film-forming solution at a mass ratio of 40:10 g, and stirred continuously for 1 h to obtain a composite film-forming solution; the composite film-forming solution was cast onto a petri dish plate and dried in a 50 ℃ oven for 5 h to obtain the pH-responsive pine needle oil microcapsule composite preservation film.

[0053] Experimental Example 1

[0054] Experimental Example 1 of this invention tested the effect of a pH-responsive pine needle essential oil microcapsule composite film material prepared in Example 1. The specific steps are as follows:

[0055] (1) Preparation of pine needle essential oil microcapsules with different core-wall ratios

[0056] Take 0.5 g of each of the five microcapsules with different core-to-wall ratios from Example 1, dissolve them in 10 mL of anhydrous ethanol and soak for 1 h. Filter the above solution through a membrane, and use a UV-Vis-NIR spectrophotometer to measure the absorbance of the solution at 215 nm. The results are as follows: Figure 1 As shown, when the core-to-wall ratio is between 3:1 and 1:1, the encapsulation efficiency continuously increases, reaching a peak of approximately 90% at a core-to-wall ratio of 1:1. Further reducing the core-to-wall ratio to 1:2 and 1:3 leads to a gradual decrease in encapsulation efficiency, dropping to approximately 73% at 1:3. This indicates that at a core-to-wall ratio of 1:1, the wall material composed of gelatin and gum arabic can fully combine with pine needle essential oil to form structurally stable microcapsules with excellent encapsulation effects, representing the optimal core-to-wall ratio for this preparation process.

[0057] (2) Preparation of pine needle essential oil microcapsules with different pH responses

[0058] Take 0.5 g of each of the five microcapsules at different pH values ​​from Example 1, dissolve them in 10 mL of anhydrous ethanol and soak for 1 h. Filter the solution through a membrane, and use a UV-Vis-NIR spectrophotometer to measure the absorbance of the solution at 215 nm. The results are as follows: Figure 2 As shown, when the pH is between 5.4 and 6.0, the encapsulation efficiency continuously increases, reaching a peak of approximately 89.13% at pH 6.0. With further increases in pH, the encapsulation efficiency gradually decreases, dropping to approximately 49.89% at pH 6.4. At pH 6.0, which is close to the isoelectric point of gelatin, the electrostatic attraction between the positive charge of gelatin molecules and the negative charge of gum arabic reaches its optimal balance, resulting in the most complete coagulation reaction. The resulting wall material structure is dense and stable, exhibiting the strongest encapsulation and retention capacity for pine needle essential oil, thus achieving the maximum encapsulation efficiency.

[0059] (3) Surface morphology characterization of pine needle essential oil microcapsules

[0060] The surface structural features of pine needle essential oil microcapsules were examined using field emission scanning electron microscopy. The results are as follows: Figure 3 As shown, the surface of the microcapsule is convex and spherical. The core material essential oil is encapsulated by the wall material formed by the coagulation of gelatin and gum arabic. During the freeze-drying process, the internal water sublimates and generates supporting force, causing the wall material to bulge outward and solidify into a spherical convex structure.

[0061] (4) Surface morphology of microcapsule composite film and blank film of pine needle essential oil at different concentrations

[0062] The prepared pine needle essential oil, gelatin, and gum arabic microcapsule suspensions were added to PVA film-forming solution at mass ratios of 2.5:10 g, 10:10 g, and 40:10 g, and stirred continuously for 1 h to obtain a composite film-forming solution. The composite film-forming solution was cast onto a petri dish and dried in a 50 ℃ oven for 5 h. The resulting film was the pH-responsive pine needle essential oil microcapsule composite preservation film. Films were cut to 1×1 cm size, and the results are shown below. Figure 4 As shown, the slow-release film has a certain degree of transparency, which decreases with increasing essential oil concentration. These films can block ultraviolet light, protecting food from oxidation and are beneficial for the packaging of photosensitive foods.

[0063] (5) Surface morphology characterization of microcapsule composite films and blank films of pine needle essential oil at different concentrations

[0064] A 0.5 × 0.5 cm film was cut, sputter-coated with gold, and then the surface morphology of the microcapsule films of different concentrations of essential oil and the blank film were analyzed by scanning electron microscopy. The results are as follows. Figure 5 As shown, compared to the blank membrane, the composite membrane has a rougher and more uneven surface, and the number of microspheres in the microstructure increases with increasing essential oil concentration. This is because the essential oil is encapsulated within microcapsules. During drying, the microcapsules, as intact particles, tend to accumulate on the surface. Obvious microcapsule protrusions or aggregates can be observed on the surface. With increasing microcapsule concentration, the particle packing density on the surface increases, and the roughness increases accordingly.

[0065] (6) Transmittance of microcapsule composite films and blank films of pine needle essential oil at different concentrations

[0066] Films measuring 2 × 2 cm were cut, and their UV-Vis light blocking properties were evaluated using a UV-Vis spectrometer, measuring from 200 to 800 nm. Three replicate tests were performed for each type of film. Results are shown below. Figure 6 As shown, the transmittance decreased slightly with increasing pine needle microcapsule essential oil content. These results indicate that pine needle essential oil can effectively block the transmission of ultraviolet light through the film.

[0067] (7) Hydrophobicity of microcapsule composite films and blank films of pine needle essential oil at different concentrations

[0068] Cut a 1.0 × 1.0 cm film and test its hydrophilicity using a contact angle meter. The results are as follows. Figure 7 As shown, the surface contact angle between the slow-release membrane and water increases with the increase of essential oil content. Compared with the blank membrane, the hydrophobicity of the slow-release membrane is slightly increased, with a maximum contact angle of 119.9°. It effectively blocks the penetration of water vapor, water droplets, and external moisture.

[0069] (8) Antibacterial effect of pH-responsive pine needle essential oil microcapsule composite film

[0070] Prepare buffer solutions with pH=6 and pH=9 respectively, and cut films and blank films of different concentrations with a diameter of 1 cm. Immerse the films in buffer solutions of different pH values ​​to achieve different acidity and alkalinity. Prepare solid culture medium, and add 200 μL of diluted bacterial suspension to the surface of the solid culture medium, then spread the bacterial suspension evenly using a spreader. Place the films of different pH values ​​in the culture medium and incubate at 37 ℃ for 24 h. Figure 7 As shown, compared to the blank membrane, the diameter of the inhibition zone of the sustained-release membrane is larger, and the concentration of the inhibition zone also increases slightly with increasing concentration. Furthermore, the diameter of the inhibition zone increases with increasing inhibition time, exhibiting a sustained-release antibacterial effect. Simultaneously, with changes in the membrane's pH, the diameter of the inhibition zone significantly increases. This is because pine needle essential oil has stronger antibacterial activity under alkaline conditions, and the gelatin / gum arabic / PVA membrane structure is more stable, resulting in more uniform essential oil release; therefore, the antibacterial effect is superior to that under acidic conditions.

[0071] (9) Sustained-release effect of pH-responsive pine needle essential oil microcapsule composite film

[0072] Buffer solutions with pH values ​​of 4, 6, and 9 were prepared, and films and blank films of different concentrations with a diameter of 1 cm were cut. The films were immersed in buffer solutions at different pH values, and appropriate amounts of solution were collected at 1, 2, 3, 4, 5, and 6 days for UV absorbance testing. Figure 7 As shown, the film exhibits a certain pH responsiveness, and the release amount increases with increasing pH. Simultaneously, the film's essential oil release demonstrates a slow-release characteristic, with the cumulative release amount increasing over time.

[0073] (10) The effect of different packaging films on preserving strawberries

[0074] Take strawberries of equal weight and place them separately under commercial plastic wrap, blank film, and slow-release film of different concentrations of essential oil. Store them at room temperature. Observe the surface of the strawberries daily for bacterial growth and freshness. If the strawberries show signs of spoilage, record the time and a picture of the spoiled strawberries. Figure 10 As shown, after 7 days of storage, strawberries wrapped in blank film and commercial plastic wrap showed obvious oxidative deterioration, while strawberries wrapped in slow-release films of different concentrations of essential oils did not show obvious oxidation even after 7 days.

[0075] (11) The effect of different packaging films on preserving pork

[0076] Take equal weights of pork and place them separately under commercial plastic wrap, blank film, and slow-release film of different concentrations of essential oil, then store at room temperature. Observe the surface of the pork daily for bacterial growth and freshness. If the pork shows signs of spoilage, record the time and a photo of the product. Figure 11 As shown, after 11 days of storage, pork wrapped in blank film and commercial plastic wrap showed obvious spoilage, while pork wrapped in slow-release films of different concentrations of essential oils did not show obvious spoilage even after 11 days.

[0077] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A pH-responsive pine needle essential oil microcapsule composite preservation film material, characterized in that, The composite preservation film material is composed of a polyvinyl alcohol film-forming substrate and pine needle oil / gelatin / gum arabic microcapsules loaded therein. The pine needle oil / gelatin / gum arabic microcapsules are prepared by complex coagulation method with gelatin and gum arabic as wall materials and pine needle oil as core material. The core-to-wall ratio is 3:1, 2:1, 1:1, 1:2, and 1:

3. The film material has the function of pH-responsive slow-release pine needle oil and exhibits antibacterial preservation activity.

2. The pH-responsive pine needle essential oil microcapsule composite preservation film material according to claim 1, characterized in that, The raw materials for preparing the pine needle oil / gelatin / gum arabic microcapsules include gelatin, gum arabic, pine needle oil, acetic acid solution, sodium hydroxide solution, and glutaraldehyde. The gelatin is prepared as an aqueous solution with a mass fraction of 4-6%, and the gum arabic is prepared as an aqueous solution with a mass fraction of 4-6%.

3. The pH-responsive pine needle essential oil microcapsule composite preservation film material according to claim 2, characterized in that, In the preparation process of the pine needle oil / gelatin / gum arabic microcapsules, the pH of the system is adjusted to 5.2~6.8 by sodium hydroxide solution, the amount of glutaraldehyde added for cross-linking and curing is 0.1~0.3 mL, and the performance of the microcapsules is optimized by controlling the core-to-wall ratio and the pH of the system adjusted by sodium hydroxide solution.

4. The pH-responsive pine needle essential oil microcapsule composite preservation film material according to claim 1, characterized in that, The polyvinyl alcohol film-forming substrate is formed by preparing a polyvinyl alcohol solution with a mass-volume fraction of 3-5% (W / V), and the mass ratio of pine needle oil / gelatin / gum arabic microcapsule suspension to polyvinyl alcohol film-forming solution is 2.5-40 g:10 g.

5. A method for preparing a pH-responsive pine needle essential oil microcapsule composite preservative film material as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Preparation of pine needle essential oil / gelatin / gum arabic microcapsules: Pine needle essential oil was added to gelatin aqueous solution according to core-wall ratio of 3:1, 2:1, 1:1, 1:2, 1:3 and homogenized at high speed. Gum arabic aqueous solution was added and stirred to react. Acetic acid solution was added dropwise to adjust the pH of the system until the solution was turbid to achieve the initial formation of microcapsules. The system was cooled in an ice water bath and stirred continuously. The pH of the system was adjusted with sodium hydroxide solution and glutaraldehyde was added for cross-linking and curing. After centrifugation and freeze drying, pine needle essential oil / gelatin / gum arabic microcapsules were obtained. (2) Preparation of composite preservation film: Polyvinyl alcohol is dissolved in water and heated and stirred to obtain polyvinyl alcohol film-forming solution. Pine needle oil / gelatin / gum arabic microcapsule suspension is added to polyvinyl alcohol film-forming solution at a mass ratio of 2.5~40 g:10 g and stirred evenly to obtain composite film-forming solution. The composite film-forming solution is cast into a film and dried to obtain the pH-responsive pine needle oil microcapsule composite preservation film material.

6. The preparation method of the pH-responsive pine needle essential oil microcapsule composite preservation film material according to claim 5, characterized in that, The high-speed homogenization process in step (1) uses a high-speed homogenizer with a homogenization speed of 10,000~14,000 r / min and a homogenization time of 1~3 min.

7. The preparation method of the pH-responsive pine needle essential oil microcapsule composite preservation film material according to claim 5, characterized in that, In step (1), after adding the gum arabic aqueous solution, the mixture is stirred at 45-55 °C for 20-40 min. The concentration of the acetic acid solution added is 0.8-1.2 mol / L, and the pH of the system is adjusted to 3.5-4.

5.

8. The preparation method of the pH-responsive pine needle essential oil microcapsule composite preservation film material according to claim 5, characterized in that, In step (1), the system is cooled to 8-12 °C in an ice-water bath, and stirring is continued for 0.5-1.5 h during cooling. After cooling, the pH of the system is adjusted to 5.2-6.8 with sodium hydroxide solution.

9. The preparation method of the pH-responsive pine needle essential oil microcapsule composite preservation film material according to claim 5, characterized in that, In step (1), after cross-linking and curing, the mixture is centrifuged at 2500~3500 r / min for 8~12 min, the centrifuged precipitate is collected and placed in a freeze dryer, and freeze-dried at -55~-45 ℃ and 5~15 Pa for 20~28 h.

10. The preparation method of the pH-responsive pine needle essential oil microcapsule composite preservation film material according to claim 5, characterized in that, In step (2), the polyvinyl alcohol film-forming solution is prepared by heating and stirring at a temperature of 90-100 °C for 5-7 h.

11. The preparation method of the pH-responsive pine needle essential oil microcapsule composite preservation film material according to claim 5, characterized in that, In step (2), the pine needle oil / gelatin / gum arabic microcapsule suspension is mixed with polyvinyl alcohol film-forming solution and stirred continuously for 0.5~1.5 h.

12. The preparation method of the pH-responsive pine needle essential oil microcapsule composite preservation film material according to claim 5, characterized in that, In step (2), the drying temperature is 45~55 ℃ and the time is 4~6 h.

13. The application of a pH-responsive pine needle oil microcapsule composite preservation film material as described in any one of claims 1 to 4, or a pH-responsive pine needle oil microcapsule composite preservation film material prepared by the preparation method described in any one of claims 5 to 12, in the preparation of food packaging products for preservation and / or antibacterial purposes.

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