A curcuma, lemon and green tea extract / chitosan composite preservative film and a preparation method and application thereof

Abstract

The application discloses a curcuma, lemon and green tea extract / chitosan composite preservative film and a preparation method and application thereof. The composite preservative film comprises a chitosan matrix and a composite extract composed of curcuma extract, lemon extract and green tea extract at a weight ratio of 1:1:1. The three kinds of natural plant extracts are prepared by ultrasonic-assisted extraction or reflux extraction respectively, and the composite preservative film is prepared by mixing the chitosan solution, centrifugation, pouring and drying. The composite preservative film is used for the preservation packaging of grouper fillets, can significantly inhibit the growth of microorganisms, delay fat oxidation and protein corruption under 4 DEG C cold storage conditions, and prolongs the shelf life of the grouper fillets to more than 12 days. The synergistic effect of the three kinds of plant polyphenol components is utilized, the preservation effect is improved, safety, non-toxicity, green environmental protection are ensured, the preparation process is simple, the cost is low, and the application is suitable for the field of aquatic product preservation.

Description

Technical Field

[0001] This invention relates to the field of food preservation technology, specifically to a composite preservation film of turmeric, lemon and green tea extracts / chitosan, its preparation method and application. Background Technology

[0002] Grouper has white, tender flesh, rich in high-quality protein, unsaturated fatty acids, and various minerals. It is known for its immune-boosting properties, brain-developing benefits, and cardiovascular protection, earning it the nicknames "sea chicken" or "the aristocrat of fish." However, due to its rich nutritional content, grouper is highly susceptible to oxidation and rancidity, as well as bacterial contamination, resulting in a short shelf life. This makes it unsuitable for long-term storage and long-distance transportation. Therefore, inhibiting microbial growth and fat oxidation to preserve the freshness of grouper flesh has been a key research focus for this type of marine fish.

[0003] Currently, the main methods for preserving grouper include low-temperature refrigeration, cold seawater preservation, micro-freezing, modified atmosphere or vacuum preservation, and compound preservatives, with low-temperature preservation being the primary method. However, during low-temperature storage, some degree of spoilage still occurs due to protein denaturation, dehydration, and oxidation of lipids and pigments. Furthermore, under conventional refrigeration conditions, the shelf life can only be maintained for 3-5 days, which cannot meet market demand. Vacuum preservation, on the other hand, has limited inhibitory effect on certain facultative anaerobic spoilage bacteria.

[0004] In recent years, natural plant-derived preservatives have received widespread attention due to their safety, non-toxicity, and environmental friendliness. Extracts from plants such as turmeric, lemon, and green tea have been proven to possess excellent antibacterial and antioxidant activities. For example, curcumin in turmeric exhibits strong free radical scavenging capabilities and broad-spectrum antibacterial effects; flavonoids in lemon can lower environmental pH, chelate metal ions, and inhibit enzymatic browning; and tea polyphenols in green tea are commonly used natural antioxidants and antibacterial components. However, current technologies mostly utilize single plant extracts for preservation, with limited research on the synergistic effects of combining multiple plant extracts, especially in the field of aquatic product preservation, where systematic research on the optimal concentration and synergistic ratio of turmeric, lemon, and green tea extracts is lacking.

[0005] Furthermore, applying single natural extracts directly to the surface of aquatic products suffers from problems such as easy loss and short duration of action. Chitosan, as a natural and biodegradable polysaccharide material, possesses good film-forming properties and biocompatibility, but the mechanical properties and antioxidant activity of pure chitosan films are limited. How to organically combine various natural plant extracts with chitosan to prepare a high-performance, easy-to-use composite preservation film, and determine its optimal working concentration for preserving grouper fillets, is a pressing technical problem to be solved in this field. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a composite preservation film composed of a compound extract of turmeric, lemon, and green tea, along with its preparation method and application, to overcome the shortcomings of the prior art, such as limited preservation effect of single plant extracts, lack of synergistic ratio optimization, and inconvenient application methods.

[0007] The first aspect of the present invention provides a composite food preservation film, the composite food preservation film comprising a chitosan matrix and a composite extract dispersed in the chitosan matrix, the composite extract comprising turmeric extract, lemon extract and green tea extract.

[0008] Furthermore, chitosan, as a film-forming matrix material, serves as the framework and carrier of the composite preservation film. Chitosan is a natural polysaccharide polymer with excellent film-forming properties. After being dissolved in an aqueous acetic acid solution and dried, it self-assembles to form a continuous, uniform, and transparent solid film, providing a stable physical carrier for the turmeric, lemon, and green tea composite extracts. In addition, it can also serve as a slow-release matrix for active ingredients: the hydroxyl and amino groups on the chitosan molecular chain can form hydrogen bonds or electrostatic interactions with polyphenolic compounds (such as curcumin and catechins), effectively immobilizing the three natural extracts within the film and slowly releasing them upon contact with the grouper fillet surface, thereby extending the duration of the preservation effect. Furthermore, the chitosan film has excellent gas barrier properties, reducing oxygen contact with the fish fillet surface, thus synergistically delaying lipid oxidation in conjunction with the three extracts. Chitosan itself possesses certain antibacterial activity (mainly derived from the interaction of its positively charged amino groups with bacterial cell membranes), forming a "dual preservation" effect with the composite extracts of this invention, further enhancing the inhibitory effect on microbial growth in the grouper fillets.

[0009] Furthermore, the mass ratio of turmeric extract, lemon extract, and green tea extract is 1-5:1-5:1-5. Turmeric extract is rich in curcumin-like polyphenolic compounds, possessing strong antioxidant and broad-spectrum antibacterial activity, effectively scavenging free radicals and inhibiting fat oxidation and spoilage growth in grouper fillets. Lemon extract contains citric acid, vitamin C, and flavonoids, providing an acidic environment to inhibit microorganisms while synergistically enhancing antioxidant capacity, delaying color deterioration and rancidity of the fish. Green tea extract is rich in catechins and other polyphenolic components, exhibiting strong antioxidant and antibacterial effects, particularly inhibiting both Gram-positive and Gram-negative bacteria, and helping to stabilize active ingredients in membrane structures.

[0010] Furthermore, the composite preservation film also contains glycerol. Glycerol molecules are small and can insert between chitosan molecular chains, weakening hydrogen bonding and increasing chain fluidity. This significantly improves the tensile strength and elongation at break of the film, allowing the composite preservation film to adhere tightly to the surface of the grouper fillets without breaking, thus improving processing performance. In addition, the hydrophilic hydroxyl groups of glycerol can moderately regulate the moisture permeability and air permeability of the film, preventing moisture condensation or anaerobic spoilage on the surface of the fish fillets due to excessive barrier, while maintaining the activity of the composite extract.

[0011] Furthermore, the mass ratio of the chitosan to the composite extract is 2:3-15.

[0012] A second aspect of the present invention provides a method for preparing a composite food preservation film, comprising the following steps: (a) Prepare turmeric extract, lemon extract and green tea extract separately; (b) Chitosan was dissolved in an aqueous acetic acid solution, and glycerol was added as a plasticizer to obtain a chitosan solution; (c) Add the turmeric extract, lemon extract and green tea extract obtained in step (a) to the chitosan solution obtained in step (b), mix them in a weight ratio of 1-5:1-5:1-5, stir, and obtain a film-forming solution. (d) Centrifuge, pour into a dish, and dry the film-forming solution obtained in step (c) to obtain the composite preservation film.

[0013] Further, the preparation method of the turmeric extract in step (a) is as follows: turmeric is dried, pulverized, and sieved, 70% ethanol is added at a material-to-liquid ratio of 1:10, ultrasonic extraction is performed at 55°C, the extract is collected, centrifuged, and the supernatant is filtered through a micromembrane and then freeze-dried. The method for preparing the lemon extract is as follows: slice lemons, dry them, crush them, sieve them, add 60% ethanol at a material-to-liquid ratio of 1:30, reflux extract at 80°C, collect the extract, centrifuge, filter the supernatant through a micromembrane, and freeze-dry it. The preparation method of the green tea extract is as follows: green tea is dried, pulverized, and sieved. 80% ethanol is added at a material-to-liquid ratio of 1:25. The extract is extracted by ultrasonication at 50°C. The extract is collected, centrifuged, and the supernatant is filtered through a micromembrane and then freeze-dried.

[0014] Furthermore, in step (c), the weight ratio of turmeric extract, lemon extract, and green tea extract is 1:1:1.

[0015] Furthermore, the drying temperature in step (d) is 45°C and the drying time is 12 hours.

[0016] More specifically, the preparation method of turmeric extract is as follows: Turmeric was dried and pulverized at 60 ℃, then passed through a 60-mesh sieve. 50 g of turmeric powder was weighed and added to 70% ethanol at a 1:10 material-to-liquid ratio. The mixture was then ultrasonically extracted at 55 ℃ and 150 W for 30 min. The extract was collected, centrifuged at 9000 rpm for 20 min, and the supernatant was filtered through a micromembrane and then freeze-dried.

[0017] The specific preparation method of lemon extract is as follows: Slice the lemons, dry them at 60 ℃, pulverize them, and pass them through a 60-mesh sieve. Weigh 10 g of the sample, add 60% ethanol at a material-to-liquid ratio of 1:30, and reflux extract at 80 ℃ for 60 min. Collect the extract, centrifuge at 9000 rpm for 20 min, filter the supernatant through a micromembrane filter, and freeze-dry.

[0018] The specific preparation method of lemon extract is as follows: Green tea was dried and pulverized at 60 ℃, then passed through a 60-mesh sieve. 20 g of green tea powder was weighed and added to 80% ethanol at a material-to-liquid ratio of 1:25. The mixture was then ultrasonically extracted at 50 ℃ and 150 W for 20 min. The extract was collected, centrifuged at 9000 rpm for 20 min, and the supernatant was filtered through a micromembrane and then freeze-dried.

[0019] Specifically, 2 wt% chitosan was dissolved in a 1 wt% acetic acid aqueous solution and stirred for 2 h. 30 wt% glycerol was added as a plasticizer. A complex extract of turmeric, lemon, and green tea was added to the solution at a concentration of [mass concentration not specified] and stirred for 30 min. After centrifugation for 3 min, 20 mL was transferred to a 90 mm × 15 mm petri dish and dried at 45 ℃ for 12 h. The composite film was then removed for use.

[0020] A third aspect of this invention provides the application of the aforementioned composite preservation film in the preparation of food packaging materials for preserving grouper fillets. The application includes wrapping the grouper fillets in the composite preservation film and storing them at 4°C.

[0021] This invention combines a mixed extract of turmeric, lemon, and green tea with chitosan for the preservation of grouper fillets, significantly improving the preservation effect and offering a series of advantages over existing processes: Product Formula Advantages: Turmeric, lemon, and green tea are all natural edible plants, rich in polyphenols, flavonoids, and other natural antibacterial and antioxidant active ingredients. The combination of these three extracts produces a significant synergistic effect, greatly enhancing the preservation effect on grouper fillets. Experimental data shows that after treatment with the composite preservation film of this invention, the shelf life of grouper fillets under 4°C refrigeration conditions can be extended to 12 days. Compared to chemically synthesized preservatives, the preservative components of this invention are all derived from natural plants, are safe and non-toxic, meet the modern consumer demand for green and healthy food, and the raw materials are readily available and inexpensive, making them suitable for large-scale application.

[0022] Advantages of the preparation process: This invention uses ultrasound-assisted extraction and reflux extraction processes to prepare active extracts from three plants. The processes are mature, and ultrasound extraction can reduce energy consumption and time costs. The subsequent preparation process of the plastic wrap is simple and controllable, requiring only the mixing of the extract with a chitosan solution to form a film. No complex reaction equipment or harsh process conditions are needed, making it easy to achieve industrial-scale production. Moreover, the preparation process leaves no harmful solvent residues, making it green and environmentally friendly.

[0023] Product Application Advantages: The composite preservation film of this invention is easy to use; it only needs to be wrapped around the treated grouper fillets, requiring no complicated procedures. Experiments have verified its excellent preservation performance: 1. Excellent physical properties: Compared with pure chitosan film, the composite preservation film prepared by this invention has significantly enhanced mechanical properties and active functions.

[0024] 2. Significant antibacterial effect: During refrigeration, the composite preservation film of this invention can effectively inhibit the growth of microorganisms. After 12 days, the total number of colonies in the treatment group was only 5.63 lg (cfu / g), which still meets the national standard requirements of GB 18406.4—2001 for pollution-free aquatic products.

[0025] 3. Effectively delays oxidation and spoilage: This invention can significantly inhibit the oxidation of fat in fish fillets. After 12 days, the peroxide value is only 3.2 Meq O2 / 100g, far lower than the 12.3 Meq O2 / 100g of the control group; the TBA value is only 0.64 mg / kg, only 23% of the control group; at the same time, it effectively delays protein spoilage. The volatile nitrogen content is only 28.9% after 12 days, only 33.8% of the control group, thus preserving the nutrition and fresh taste of the grouper fillets to the greatest extent.

[0026] In summary, this invention combines a complex extract of turmeric, lemon, and green tea with chitosan for the preservation of grouper fillets, providing an efficient, green, and economical technical solution for the natural preservation of grouper, with broad application prospects and market competitiveness. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and experimental data tables. Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. It should be understood that the following description is merely illustrative and not intended to limit the invention.

[0028] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0029] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0030] In some instances, approximate terms may correspond to the precision of the instrument used to measure the value. In this specification and claims, scope definitions may be combined and / or interchanged. Unless otherwise stated, these scopes include all subscopes contained therein.

[0031] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0032] The terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., used in this invention refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms are not necessarily directed at the same embodiment or example. Furthermore, the technical features involved in the various embodiments of the invention can be combined with each other as long as they do not conflict with each other.

[0033] Unless otherwise specified, the raw materials and equipment used in this invention can be purchased from the market or are commonly used in the field. The methods in the embodiments, unless otherwise specified, are conventional methods in the field. The above are all preferred embodiments of this invention and are not intended to limit the scope of protection of this invention. Therefore, all equivalent changes made to the structure, shape, and principle of this invention should be covered within the scope of protection of this invention.

[0034] In some embodiments, the present invention provides a composite food preservation film comprising a chitosan matrix and a composite extract dispersed in the chitosan matrix, wherein the composite extract comprises turmeric extract, lemon extract and green tea extract.

[0035] Furthermore, the mass ratio of the turmeric extract, lemon extract, and green tea extract is 1-5:1-5:1-5. More specifically, it can be 1:1:1.

[0036] Furthermore, the composite preservation film also contains glycerin.

[0037] Furthermore, the mass ratio of chitosan to the composite extract is 2:3-15. Specifically, it can be 2:3, 2:9, or 2:15.

[0038] In some embodiments, the present invention provides a method for preparing a composite food preservation film, comprising the following steps: (a) Prepare turmeric extract, lemon extract and green tea extract separately; (b) Chitosan was dissolved in an aqueous acetic acid solution, and glycerol was added as a plasticizer to obtain a chitosan solution; (c) Add the turmeric extract, lemon extract and green tea extract obtained in step (a) to the chitosan solution obtained in step (b), mix them in a weight ratio of 1-5:1-5:1-5, stir, and obtain a film-forming solution. (d) Centrifuge, pour into a dish, and dry the film-forming solution obtained in step (c) to obtain the composite preservation film.

[0039] Further, the preparation method of the turmeric extract in step (a) is as follows: turmeric is dried, pulverized, and sieved, 70% ethanol is added at a material-to-liquid ratio of 1:10, ultrasonic extraction is performed at 55°C, the extract is collected, centrifuged, and the supernatant is filtered through a micromembrane and then freeze-dried. The method for preparing the lemon extract is as follows: slice lemons, dry them, crush them, sieve them, add 60% ethanol at a material-to-liquid ratio of 1:30, reflux extract at 80°C, collect the extract, centrifuge, filter the supernatant through a micromembrane, and freeze-dry it. The preparation method of the green tea extract is as follows: green tea is dried, pulverized, and sieved. 80% ethanol is added at a material-to-liquid ratio of 1:25. The extract is extracted by ultrasonication at 50°C. The extract is collected, centrifuged, and the supernatant is filtered through a micromembrane and then freeze-dried.

[0040] Furthermore, the drying temperature in step (d) is 45°C and the drying time is 12 hours.

[0041] In some embodiments, the composite preservation film provided by the present invention is used for preserving grouper fillets. Further, this includes wrapping the grouper fillets in the composite preservation film and storing them at 4°C.

[0042] The present invention will be further described below with reference to specific embodiments.

[0043] Example 1 Step 1: Preparation of Turmeric Extract Turmeric was dried and pulverized at 60 ℃, then passed through a 60-mesh sieve. 50 g of turmeric powder was weighed and added to 70% ethanol at a 1:10 material-to-liquid ratio. The mixture was then ultrasonically extracted at 55 ℃ and 150 W for 30 min. The extract was collected, centrifuged at 9000 rpm for 20 min, and the supernatant was filtered through a micromembrane and then freeze-dried.

[0044] Step 2: Preparation of lemon extract Slice the lemons, dry them at 60 ℃, pulverize them, and pass them through a 60-mesh sieve. Weigh 10 g of the sample, add 60% ethanol at a material-to-liquid ratio of 1:30, and reflux extract at 80 ℃ for 60 min. Collect the extract, centrifuge at 9000 rpm for 20 min, filter the supernatant through a micromembrane filter, and freeze-dry.

[0045] Step 3: Preparation of Green Tea Extract Green tea was dried and pulverized at 60 ℃, then passed through a 60-mesh sieve. 20 g of green tea powder was weighed and added to 80% ethanol at a material-to-liquid ratio of 1:25. The mixture was then ultrasonically extracted at 50 ℃ and 150 W for 20 min. The extract was collected, centrifuged at 9000 rpm for 20 min, and the supernatant was filtered through a micromembrane and then freeze-dried.

[0046] Step 4: Preparation of Turmeric Composite Preservative Film Dissolve 2% chitosan in a 1% acetic acid aqueous solution and stir for 2 h. Add 30% glycerol as a plasticizer. Add 1% turmeric, 1% lemon and 1% green tea compound extract to the solution and stir for 30 min. After centrifugation for 3 min, take 20 mL and pour it into a 90 mm × 15 mm petri dish. Dry at 45 ℃ for 12 h and remove the composite film for later use.

[0047] Step 5: Physical property testing of turmeric composite plastic wrap The tensile strength and elongation at break of the composite food preservation film were measured using a tensile testing machine. The prepared film samples were cut into 5×2 cm pieces, placed in the fixture of the tensile testing machine, and stretched with a force of 10 N. The thickness of the film was calculated using a micrometer.

[0048] Step Six: Preservation of Grouper Fillets After slaughtering and scaling the live grouper, wash it thoroughly, take the back meat and slice it into pieces, each about 20 g. Rinse the slices with sterile water and drain them on a sterile wire mesh. Wrap the fish slices in turmeric composite plastic wrap.

[0049] Step 7: Evaluation of the preservation effect of grouper fillets The grouper fillets from the three treatment groups were stored in a refrigerator at 4 ℃, and the total bacterial count, pH value, peroxide content, thiobarbituric acid (TBA) content, and volatile nitrogen content were measured every 3 days.

[0050] Example 2 Step 1: Preparation of Turmeric Extract Turmeric was dried and pulverized at 60 ℃, then passed through a 60-mesh sieve. 50 g of turmeric powder was weighed and added to 70% ethanol at a 1:10 material-to-liquid ratio. The mixture was then ultrasonically extracted at 55 ℃ and 150 W for 30 min. The extract was collected, centrifuged at 9000 rpm for 20 min, and the supernatant was filtered through a micromembrane and then freeze-dried.

[0051] Step 2: Preparation of lemon extract Slice the lemons, dry them at 60 ℃, pulverize them, and pass them through a 60-mesh sieve. Weigh 10 g of the sample, add 60% ethanol at a material-to-liquid ratio of 1:30, and reflux extract at 80 ℃ for 60 min. Collect the extract, centrifuge at 9000 rpm for 20 min, filter the supernatant through a micromembrane filter, and freeze-dry.

[0052] Step 3: Preparation of Green Tea Extract Green tea was dried and pulverized at 60 ℃, then passed through a 60-mesh sieve. 20 g of green tea powder was weighed and added to 80% ethanol at a material-to-liquid ratio of 1:25. The mixture was then ultrasonically extracted at 50 ℃ and 150 W for 20 min. The extract was collected, centrifuged at 9000 rpm for 20 min, and the supernatant was filtered through a micromembrane and then freeze-dried.

[0053] Step 4: Preparation of Turmeric Composite Preservative Film Dissolve 2% chitosan in a 1% acetic acid aqueous solution to a concentration of 2%, and stir for 2 h. Add 30% glycerol as a plasticizer. Add a complex extract of 3% turmeric, 3% lemon, and 3% green tea to the solution and stir for 30 min. After centrifugation for 3 min, take 20 mL and pour it into a 90 mm × 15 mm petri dish. Dry at 45 ℃ for 12 h, and then remove the composite film for later use.

[0054] Step 5: Physical property testing of turmeric composite plastic wrap The tensile strength and elongation at break of the composite food preservation film were measured using a tensile testing machine. The prepared film samples were cut into 5×2 cm pieces, placed in the fixture of the tensile testing machine, and stretched with a force of 10 N. The thickness of the film was calculated using a micrometer.

[0055] Step Six: Preservation of Grouper Fillets After slaughtering and scaling the live grouper, wash it thoroughly, take the back meat and slice it into pieces, each about 20 g. Rinse the slices with sterile water and drain them on a sterile wire mesh. Wrap the fish slices in turmeric composite plastic wrap.

[0056] Step 7: Evaluation of the preservation effect of grouper fillets The grouper fillets from the three treatment groups were stored in a refrigerator at 4 ℃, and the total bacterial count, pH value, peroxide content, thiobarbituric acid (TBA) content, and volatile nitrogen content were measured every 3 days. Example 3 Step 1: Preparation of Turmeric Extract Turmeric was dried and pulverized at 60 ℃, then passed through a 60-mesh sieve. 50 g of turmeric powder was weighed and added to 70% ethanol at a 1:10 material-to-liquid ratio. The mixture was then ultrasonically extracted at 55 ℃ and 150 W for 30 min. The extract was collected, centrifuged at 9000 rpm for 20 min, and the supernatant was filtered through a micromembrane and then freeze-dried.

[0057] Step 2: Preparation of lemon extract Slice the lemons, dry them at 60 ℃, pulverize them, and pass them through a 60-mesh sieve. Weigh 10 g of the sample, add 60% ethanol at a material-to-liquid ratio of 1:30, and reflux extract at 80 ℃ for 60 min. Collect the extract, centrifuge at 9000 rpm for 20 min, filter the supernatant through a micromembrane filter, and freeze-dry.

[0058] Step 3: Preparation of Green Tea Extract Green tea was dried and pulverized at 60 ℃, then passed through a 60-mesh sieve. 20 g of green tea powder was weighed and added to 80% ethanol at a material-to-liquid ratio of 1:25. The mixture was then ultrasonically extracted at 50 ℃ and 150 W for 20 min. The extract was collected, centrifuged at 9000 rpm for 20 min, and the supernatant was filtered through a micromembrane and then freeze-dried.

[0059] Step 4: Preparation of Turmeric Composite Preservative Film Dissolve 2% chitosan in a 1% acetic acid aqueous solution to a concentration of 2%, and stir for 2 h. Add 30% glycerol as a plasticizer. Add 5% turmeric, 5% lemon, and 5% green tea compound extract to the solution, and stir for 30 min. After centrifugation for 3 min, take 20 mL and pour it into a 90 mm × 15 mm petri dish. Dry at 45 ℃ for 12 h, and then remove the composite film for later use.

[0060] Step 5: Physical property testing of turmeric composite plastic wrap The tensile strength and elongation at break of the composite food preservation film were measured using a tensile testing machine. The prepared film samples were cut into 5×2 cm pieces, placed in the fixture of the tensile testing machine, and stretched with a force of 10 N. The thickness of the film was calculated using a micrometer.

[0061] Step Six: Preservation of Grouper Fillets After slaughtering and scaling the live grouper, wash it thoroughly, take the back meat and slice it into pieces, each about 20 g. Rinse the slices with sterile water and drain them on a sterile wire mesh. Wrap the fish slices in turmeric composite plastic wrap.

[0062] Step 7: Evaluation of the preservation effect of grouper fillets The grouper fillets from the three treatment groups were stored in a refrigerator at 4 ℃, and the total bacterial count, pH value, peroxide content, thiobarbituric acid (TBA) content, and volatile nitrogen content were measured every 3 days.

[0063] Comparative Example 1 The difference between this comparative example and Example 1 is that the grouper fillets were not treated with any plastic wrap.

[0064] Comparative Example 2 The difference between this comparative example and Example 1 is that the plastic wrap in step four contains only 2% chitosan.

[0065] Comparative Example 3 The difference between this comparative example and Example 1 is that the plastic wrap in step four contains 2% chitosan and 5% turmeric extract.

[0066] Comparative Example 4 The difference between this comparative example and Example 1 is that the plastic wrap in step four contains 2% chitosan and 5% lemon extract.

[0067] Comparative Example 5 The difference between this comparative example and Example 1 is that the plastic wrap in step four contains 2% chitosan and 5% green tea extract.

[0068] Comparative Example 6 The difference between this comparative example and Example 1 is that the plastic wrap in step four contains 2% chitosan, 5% turmeric extract, and 5% lemon extract.

[0069] Comparative Example 7 The difference between this comparative example and Example 1 is that the plastic wrap in step four contains 2% chitosan, 5% turmeric extract, and 5% green tea extract.

[0070] Comparative Example 8 The difference between this comparative example and Example 1 is that the plastic wrap in step four contains 2% chitosan, 5% lemon extract, and 5% green tea extract.

[0071] The above are the test data for the examples and comparative examples, as shown in Tables 1-6.

[0072] Table 1 Physical properties of turmeric composite food preservation film Table 2. Effects of turmeric composite preservation film treatment on the total bacterial count of grouper fillets. Note: According to GB 18406.4—2001 "Safety Requirements for Pollution-Free Aquatic Products", the total bacterial count should not exceed 5.90 lg (cfu / g). Table 3. Effects of turmeric-composite preservation film treatment on pH changes in grouper fillets. Table 4. Effect of turmeric composite preservation film treatment on the peroxide content of grouper fillets (Meq O2 / 100 g) Table 5. Effect of turmeric composite plastic wrap treatment on the TBA content of grouper fillets (mg / kg) Table 6. Effect of turmeric composite preservation film treatment on the change of volatile nitrogen content in grouper fillets (%) The data above shows that the composite preservation film prepared by the ratio of 5% turmeric extract, 5% lemon extract, 5% green leaf extract and 2% chitosan used in Example 3 has the best physical properties, the strongest antioxidant capacity, and the best preservation effect on grouper fillets, which can extend the shelf life of the fillets to 12 days.

[0073] Comparing the data from each group, it is evident that Comparative Example 2, which contains only chitosan, had the worst performance in all indicators. While Comparative Examples 3-5, which added a single plant extract, showed improved preservation effects, they were still inferior to Comparative Examples 6-8, which added two plant extracts. Even among the comparative examples that added two extracts, the lowest total bacterial count at 12 days was 6.54 lg (cfu / g), and the lowest volatile nitrogen was 33.8%, still lower than Example 1, which only added 1% of the three extracts. This fully demonstrates that the combination of turmeric, lemon, and green tea extracts produced a significant synergistic effect, far superior to the combination of single or two extracts.

[0074] Regarding preservation effects, after 12 days of refrigeration at 4℃, the total bacterial count of the grouper fillets treated in Example 3 was only 5.63 lg (cfu / g), fully meeting the requirements of GB 18406.4—2001 for pollution-free aquatic products. In contrast, the total bacterial count of the blank control group (Comparative Example 1) had risen to 10.97 lg (cfu / g), and the pure chitosan membrane group (Comparative Example 2) had reached 7.45 lg (cfu / g), both far exceeding the limits. Meanwhile, the peroxide value of Example 3 was only 3.2 Meq O2 / 100g, only 26.0% of the blank group; the TBA value was 0.64 mg / kg, only 23.3% of the blank group; and the volatile basic nitrogen content was 28.9%, only 33.8% of the blank group. All indicators were far superior to other groups, fully demonstrating its effective inhibition of lipid oxidation and protein spoilage.

[0075] In terms of physical properties, the tensile strength of the film in Example 3 reached 37.43 MPa, which is 62.8% higher than that of the pure chitosan film (Comparative Example 2) at 22.99 MPa. Its antioxidant capacity reached 47.6%, which is 3.28 times that of the pure chitosan film. At the same time, the elongation at break was maintained at 51.05%, which takes into account both excellent mechanical strength and flexibility, and fully meets the requirements for food packaging.

[0076] The effects of Examples 1 and 2 are not as good as those of Example 3. This indicates that increasing the concentration of the plant mixed extract can not only improve the tensile strength of the film, enhance the physical properties of the film, and improve the antioxidant capacity of the film, but also improve its preservation effect.

[0077] By adjusting the composition and concentration of turmeric, lemon, and green tea, this invention optimizes the formula of the composite preservation film, thereby providing a natural and green new preservation method for grouper fillets.

[0078] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A composite food preservation film, characterized in that, The composite preservation film comprises a chitosan matrix and a composite extract dispersed in the chitosan matrix, wherein the composite extract comprises turmeric extract, lemon extract and green tea extract.

2. The composite food preservation film according to claim 1, characterized in that, The mass ratio of the turmeric extract, lemon extract, and green tea extract is 1-5:1-5:1-5.

3. The composite food preservation film according to claim 1 or 2, characterized in that, The composite preservation film also contains glycerin.

4. The composite food preservation film according to claim 1 or 2, characterized in that, The mass ratio of the chitosan to the composite extract is 2:3-15.

5. A method for preparing the composite food preservation film according to any one of claims 1 to 4, characterized in that, Includes the following steps: (a) Prepare turmeric extract, lemon extract and green tea extract separately; (b) Chitosan was dissolved in an aqueous acetic acid solution, and glycerol was added as a plasticizer to obtain a chitosan solution; (c) Add the turmeric extract, lemon extract and green tea extract obtained in step (a) to the chitosan solution obtained in step (b), mix them in a weight ratio of 1-5:1-5:1-5, stir, and obtain a film-forming solution. (d) Centrifuge, pour into a dish, and dry the film-forming solution obtained in step (c) to obtain the composite preservation film.

6. The method according to claim 5, characterized in that, The preparation method of the turmeric extract in step (a) is as follows: turmeric is dried, pulverized, and sieved. 70% ethanol is added at a material-to-liquid ratio of 1:

10. The extract is extracted by ultrasonication at 55°C. The extract is collected, centrifuged, and the supernatant is filtered through a micromembrane and then freeze-dried. The method for preparing the lemon extract is as follows: slice lemons, dry them, crush them, sieve them, add 60% ethanol at a material-to-liquid ratio of 1:30, reflux extract at 80°C, collect the extract, centrifuge, filter the supernatant through a micromembrane, and freeze-dry it. The preparation method of the green tea extract is as follows: green tea is dried, pulverized, and sieved. 80% ethanol is added at a material-to-liquid ratio of 1:

25. The extract is extracted by ultrasonication at 50°C. The extract is collected, centrifuged, and the supernatant is filtered through a micromembrane and then freeze-dried.

7. The method according to claim 5 or 6, characterized in that, In step (c), the weight ratio of turmeric extract, lemon extract and green tea extract is 1:1:

1.

8. The method according to claim 5 or 6, characterized in that, The drying temperature in step (d) is 45°C and the drying time is 12 hours.

9. The use of the composite preservation film according to any one of claims 1 to 4 or the composite preservation film prepared by the method according to any one of claims 5 to 8 in the preparation of food packaging materials for the preservation of grouper fillets.

10. The application according to claim 9, characterized in that, The application includes wrapping grouper fillets in the composite preservation film and storing them at 4°C.

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