Antibacterial and antioxidant intelligent indication double-layer preservative film as well as preparation method and application thereof

Abstract

The invention discloses an antibacterial and antioxidant intelligent indication double-layer preservative film and a preparation method and application thereof.The preparation method includes the steps that beet red is modified to generate a beet red-acylation product, so that the beet red-acylation product has better heat stability and higher DPPH free radical scavenging rate, and the beet red-acylation product and a film forming material are prepared into a first-layer preservative film; the plant essential oil is prepared into the Pickering emulsion, and then the Pickering emulsion and the film forming material are prepared into the second-layer preservative film, so that the double-layer preservative film with antibacterial, antioxidant and intelligent indication functions is prepared.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical structure modification and food packaging, and in particular to an antibacterial and antioxidant intelligent indicating double-layer fresh-keeping film, a preparation method thereof, and applications thereof. Background Art

[0002] As consumers' demands for food safety and quality increase, food is becoming more susceptible to microbial contamination, oxidation, and spoilage during storage and transportation, leading to shortened shelf life and economic losses. Traditional food packaging, primarily based on physical barriers, lacks active antibacterial and antioxidant properties, making it impossible to monitor food freshness and safety in real time, making it difficult to meet the modern food industry's demand for active packaging. Furthermore, microbial metabolites (such as volatile basic nitrogen) produced during food spoilage can pose a food safety risk, necessitating the development of intelligent packaging materials with both antibacterial and antioxidant properties and real-time monitoring capabilities.

[0003] Beetroot is a water-soluble nitrogenous pigment primarily extracted and purified from plants such as beetroot and pitaya. Its powder color is purple-red and has excellent coloring power, making it widely used in foods, cosmetics, and pharmaceuticals. Studies have shown that betroot maintains good stability between pH 3 and 7, with peak stability between pH 4 and 6. When exposed to a pH < 3, betroot readily undergoes isomerization or dehydrogenation to form isobetalain or neobetalain, shifting its color from red to purple-red. Due to its high pH sensitivity, betroot is often used as an effective indicator for food freshness testing in active or smart packaging films. Under alkaline conditions, the color change of betroot is useful for detecting the freshness of various protein-rich foods, including shrimp, fish, pork, chicken, and milk. The Chinese patent application number CN202410720840.9 discloses a fungus polysaccharide-curcumin-betalain indicator film and its preparation method and application. Curcumin and betalain are used as indicators, chitosan and fungus polysaccharide are used as film-forming matrices, and the fungus polysaccharide-curcumin-betalain indicator film is prepared by cast drying. The freshness of the salmon is reflected by the color change of the indicator film. The change in the volatile basic nitrogen (TVB-N) content of the salmon during storage is linearly fitted with the change in the color difference of the indicator film, which can be used to monitor the freshness of the salmon. The Chinese patent application number CN202111182867.X discloses a method for preparing anthocyanin-betalain-k-carrageenan freshness indicator film. By mixing anthocyanin, betalain and k-carrageenan, pouring and forming a film. This invention uses anthocyanins to monitor pH changes due to the presence of phenols or conjugated substances, and uses betaine to detect changes in alkaline environments. The two are combined with k-carrageenan polymers to enhance the pH-responsive color change sensitivity of natural pigments and improve their chemical stability to monitor the freshness and spoilage of packaged products.

[0004] The aforementioned patent creates a freshness-indicating film by combining an indicator material with a polymer film-forming material. However, beetroot red's sensitivity to heat, light, and pH limits its practical application. Furthermore, the prepared indicator film only provides an indicator function and lacks effective antibacterial properties. Therefore, developing a cling film with antibacterial, antioxidant, and intelligent indicator properties is of great significance to the field of food packaging technology. Summary of the Invention

[0005] In response to the deficiencies in the prior art, the present invention provides an antibacterial and antioxidant intelligent indicator double-layer cling film, its preparation method, and application. By acylation modification of beetroot red, phenolic acid compounds are associated with betaine glycoside molecules to form acyl glycosides, reducing the breakage of the imine bond, thereby improving the stability of beetroot red. At the same time, antibacterial plant essential oils are loaded into polysaccharide colloidal particles to prepare Pickering emulsions. This system not only improves the compatibility of essential oils with film-forming materials, but also protects essential oils from the influence of the external environment and slows the release rate of essential oils to prolong the duration of antibacterial effects. In addition, a smart indicator double-layer cling film based on natural ingredients is designed to achieve the functions of freshness indication, antibacterial, and preservation of protein foods.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] One of the purposes of the present invention is to disclose a method for preparing a beet red-phenolic acid acylated derivative, comprising the following steps:

[0008] (1) Dissolve betaine in a solvent to form a solution with a solubility of 2.0 to 5.0 mg / mL;

[0009] (2) dissolving the activator, phenolic acid, and condensing agent in a solvent, activating for 0.5 to 3 hours, and then adding dropwise to the beetroot red solution, stirring at 300 to 800 r / min at 25°C to 30°C for 12 to 36 hours;

[0010] (3) After the reaction is complete, remove water and / or organic solvent by rotary evaporation, then add solvent and ultrasonically vibrate to precipitate solid;

[0011] (4) The supernatant was removed by centrifugation, and the bottom precipitate was freeze-dried to obtain the beet red-phenolic acid acylation product.

[0012] Further, the solvent includes one or more of water, methanol, ethanol, acetone, isopropanol, chloroform, ethyl acetate, tetrahydrofuran and N,N-dimethylformamide;

[0013] At least one of the activators 1-hydroxy-benzotriazole, benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-benzotriazole-N,N,N',N'-tetramethyluronium tetrafluoroboric acid, and N-hydroxysuccinimide;

[0014] The condensing agent is at least one of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, dicyclohexylcarbodiimide, and diisopropylcarbodiimide (DIC);

[0015] The phenolic acid is at least one of chlorogenic acid, ferulic acid, gentisic acid, vanillic acid, cinnamic acid, syringic acid, sinapic acid, p-coumaric acid, caffeic acid, protocatechuic acid, and gallic acid.

[0016] Furthermore, the molar ratio of the activator to the phenolic acid is 1:1 to 5:1, the molar ratio of the condensing agent to the phenolic acid is 1:1 to 5:1, and the molar ratio of the phenolic acid to beetroot red is 0.1:1 to 3:1.

[0017] The second object of the present invention is to provide a beet red-phenolic acid acylated derivative prepared by any of the above preparation methods.

[0018] A third object of the present invention is to provide a method for preparing an antibacterial and antioxidant intelligent indicating double-layer cling film, comprising the following steps:

[0019] S1. Dispersing polysaccharide in deionized water to obtain a polysaccharide dispersion, and then dripping plant essential oil into the aqueous phase while performing shear emulsification to obtain a plant essential oil Pickering emulsion;

[0020] S2. dissolving the film-forming material in deionized water, stirring the solution under magnetic stirring, adding a plasticizer to obtain a film-forming solution A, adding the beet red-phenolic acid acylated derivative according to claim 4, pouring the solution into a mold, and drying at room temperature to obtain an indicator layer;

[0021] S2. Dissolve the film-forming material in deionized water, stir magnetically to dissolve, add a plasticizer to obtain a film-forming liquid B; then mix the emulsion prepared in step S1 with the film-forming liquid in a volume ratio of 1:9 to 9:1, pour into a mold, and dry at room temperature to obtain a double-layer plastic wrap.

[0022] Furthermore, in step S1,

[0023] The polysaccharide is one or more of carrageenan, gellan gum, konjac gum, gum arabic, pectin, xanthan gum, agar, guar gum, karaya gum, tamarind gum, and locust bean gum;

[0024] The shear emulsification speed is 10000-12000 r / min, and the shear emulsification time is 3-8 min;

[0025] The plant essential oil comprises at least one of thyme essential oil, galangal essential oil, tea tree essential oil, lemon essential oil, citronella essential oil, oil peel essential oil, mustard essential oil, peppermint essential oil, cinnamon essential oil, clove essential oil, garlic essential oil, almond essential oil, eucalyptus essential oil, ylang-ylang essential oil and lavender essential oil;

[0026] The concentration of the polysaccharide is 0.1-3.0%, and the concentration of the plant essential oil is 1.0-50%.

[0027] Furthermore, the film-forming material is at least one of chitosan, carboxymethyl chitosan, quaternary ammonium chitosan, quaternary phosphonium chitosan, soluble starch, cellulose, polyvinyl alcohol, zein, cyclodextrin, gelatin, sodium alginate, carboxymethyl fiber bundle, konjac glucomannan, and pullulan;

[0028] The plasticizer is at least one of ethylene glycol, glycerol, sorbitol, polyethylene glycol with a molecular weight lower than 4000, ethylenediamine, and triethanolamine.

[0029] Furthermore, in step S2, the amount of the plasticizer added is 20 to 30 wt% of the mass of the film-forming material; the amount of the beet red-phenolic acid acylated derivative added is 5 to 40 wt% of the mass of the film-forming material;

[0030] In step S3, the amount of plasticizer added is 20-30 wt% of the mass of the film-forming material;

[0031] The mass concentration of the film-forming material in the film-forming solution A and the film-forming solution B is 0.5%-10%.

[0032] The fourth object of the present invention is to provide an antibacterial, antioxidant, intelligent indicating double-layer cling film prepared by any of the above-mentioned preparation methods.

[0033] The present invention also aims to provide an application of the antibacterial and antioxidant intelligent indicating double-layer cling film in food packaging or food freshness detection.

[0034] The beneficial effects of the present invention include at least:

[0035] (1) The present invention provides a method for reducing the beetroot red chromophore (breakage of the aldehyde imine bond) by structurally modifying the unstable group of the beetroot red molecule, and grafting biologically active phenolic acids onto the beetroot red molecule, which not only improves the stability of beetroot red but also increases its antioxidant activity.

[0036] (2) The acylation reaction conditions involved in the present invention are mild, simple to handle, and do not require harsh conditions such as high temperature and high pressure, thereby avoiding degradation of betaine during the structural modification process due to external environments such as high temperature, strong acid or strong base, thereby reducing its stability.

[0037] (3) The present invention utilizes polysaccharide colloids to construct a Pickering emulsion of plant essential oils. The polysaccharide used is a high-viscosity colloid containing multiple carboxyl groups. The spatial network structure enhances the strength of the interfacial film, prevents droplet aggregation, and maintains the stability of the emulsion. The preparation method is simple and suitable for large-scale synthesis.

[0038] (4) The present invention uses an acylated beetroot red derivative indicator material and a polysaccharide-stabilized essential oil Pickering emulsion antibacterial material to prepare an antibacterial indicator fresh-keeping film. The antioxidant activity of beetroot red is enhanced by aromatic acid modification; the essential oil is stabilized by polysaccharide, achieving solubilization, synergistic effects, and efficient transport of the essential oil. This also improves the antibacterial properties of the packaging material, and the packaging film is applied to food freshness testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The infrared spectra of the prepared beetroot red-caffeic acid acylated derivatives are beetroot red (BT), caffeic acid (CA), and beetroot red-caffeic acid acylated derivatives (BT-g-CA).

[0040] Figure 2 The UV-visible spectra of the prepared beetroot red-caffeic acid acylated derivatives are beetroot red (BT), caffeic acid (CA), and beetroot red-caffeic acid acylated derivatives (BT-g-CA).

[0041] Figure 3 The retention curves of beetroot red (BT) and beetroot red-caffeic acid acylated derivative (BT-g-CA) at different temperatures.

[0042] Figure 4 This is the retention curve of beetroot red (BT) and beetroot red-caffeic acid acylated derivative (BT-g-CA) under ultraviolet light (500W).

[0043] Figure 5 The DPPH free radical scavenging ability of vitamin C (VC), beetroot red (BT), and beetroot red-caffeic acid acylated derivative (BT-g-CA) is

[0044] Figure 6 This is an optical microscope image of the prepared cinnamon essential oil (CEO) Pickerin emulsion.

[0045] Figure 7 This is the particle size distribution diagram of the prepared cinnamon essential oil (CEO) Pickerin emulsion.

[0046] Figure 8 The antibacterial properties of the prepared cinnamon essential oil (CEO) Pickerin emulsion.

[0047] Figure 9The light blocking performance of the prepared intelligent indicator double-layer cling film.

[0048] Figure 10 The application of the prepared intelligent indicating double-layer cling film in the freshness detection of fresh shrimp.

[0049] Figure 11 The growth trend diagram of volatile basic nitrogen (TVB-N) in the prepared intelligent indicating double-layer cling film during the storage of fresh shrimp. DETAILED DESCRIPTION

[0050] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0051] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0052] One of the purposes of the present invention is to disclose a method for preparing a beet red-phenolic acid acylated derivative, comprising the following steps:

[0053] Betaine is dissolved in a solvent to a concentration of 2.0 to 5.0 mg / mL. An activator, phenolic acid, and condensing agent are dissolved in the solvent and activated for 0.5 to 3 hours. The solution is then added dropwise to the betaine solution and stirred at 300 to 800 rpm for 12 to 36 hours at room temperature (25 to 30°C). After the reaction is complete, water and organic solvent are removed by rotary evaporation. An appropriate amount of solvent is then added to remove unreacted phenolic acid, and the solid is precipitated by ultrasonication. The supernatant is then removed by centrifugation, and the above process is repeated three times. Finally, the precipitate is freeze-dried to obtain the betaine-phenolic acid acylation product.

[0054] In some embodiments, the activator is preferably at least one of 1-hydroxybenzotriazole (HOBT), benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate (HBTU), O-benzotriazole-N,N,N',N'-tetramethyluronium tetrafluoroborate (TBTU), and N-hydroxysuccinimide (NHS). Thus, the activator is used to activate the carboxylic acid, which can increase the reaction rate and inhibit the occurrence of side reactions, thereby increasing the yield of the target product. Among them, HBTU, TBTU, HOBt, and NHS are urea ion-type polypeptide condensing agents and are multifunctional reagents for activating carboxylic acids. They can react and combine betaine with phenolic acids in one step, without the need for pre-activation of acids. Their advantages include rapid in situ activation, minimal side reactions, good stability, and good solubility.

[0055] In some embodiments, the condensing agent is preferably at least one of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC), dicyclohexylcarbodiimide (DCC), and diisopropylcarbodiimide (DIC). A condensing agent refers to a reaction aid added during a condensation reaction, generally serving as a catalyst. EDC, DCC, and DIC are inexpensive, solid, convenient, and practical, and their byproducts are easily removed. Furthermore, EDC, DCC, and DIC are suitable for the amide condensation reaction of carboxylic acids and amines.

[0056] In some embodiments, the molar ratio of the activator to the phenolic acid is 1:1 to 5:1, the molar ratio of the condensing agent to the phenolic acid is 1:1 to 5:1, and the molar ratio of the phenolic acid to betaine is 0.1:1 to 3:1.

[0057] In some embodiments, the polyphenol is at least one of chlorogenic acid, ferulic acid, gentisic acid, vanillic acid, cinnamic acid, syringic acid, sinapic acid, p-coumaric acid, caffeic acid, protocatechuic acid, and gallic acid.

[0058] In some embodiments, the solvent includes one or more of water, methanol, ethanol, acetone, isopropanol, chloroform, ethyl acetate, tetrahydrofuran, and N,N-dimethylformamide.

[0059] A second object of the present invention is to disclose a method for preparing a plant essential oil Pickering emulsion, comprising the following steps:

[0060] The polysaccharide is dispersed in deionized water to obtain a polysaccharide dispersion, and then the plant essence is dropped into the aqueous phase while being shear-emulsified to obtain a plant essential oil Pickering emulsion.

[0061] In some embodiments, the polysaccharide is preferably carrageenan, gellan gum, konjac gum, gum arabic, pectin, xanthan gum, agar, guar gum, karaya gum, tamarind gum, locust bean gum, or the like.

[0062] In some embodiments, the shear emulsification speed is 10,000 to 12,000 r / min, and the shear emulsification time is 3 to 8 minutes.

[0063] In some embodiments, the plant essential oil includes at least one of thyme essential oil, galangal essential oil, tea tree essential oil, lemon essential oil, citronella essential oil, oil peel essential oil, mustard essential oil, peppermint essential oil, cinnamon essential oil, clove essential oil, garlic essential oil, almond essential oil, eucalyptus essential oil, ylang-ylang essential oil, and lavender essential oil.

[0064] In some embodiments, the concentration of the polysaccharide is 0.1 to 3.0% (w / v), wherein w / v refers to the "mass / volume" percentage concentration of the polysaccharide in the polysaccharide aqueous solution, and the unit is g / mL; the volume concentration of the plant essential oil (unit is mL / mL) is 1.0 to 50% (v / v).

[0065] The present invention also aims to disclose a method for preparing a double-layered cling film with an intelligent indicator based on the above-mentioned natural ingredients, which can realize the functions of indicating the freshness of protein foods, antibacterial, and preserving freshness. The method comprises the following steps:

[0066] A two-step casting method is used to prepare an intelligent indicating double-layer cling film. First, the film-forming material is dissolved in deionized water, magnetically stirred to dissolve, a plasticizer (20-30wt%, based on the mass of the film-forming matrix) is added, and then the indicator material beet red-phenolic acid acylation product (5-40wt%, based on the mass of the film-forming matrix) is added, poured into a mold, and dried at room temperature to obtain an indicating layer. Then, the film-forming material is dissolved in deionized water, magnetically stirred to dissolve, a plasticizer (20-30wt%, based on the mass of the film-forming matrix) is added, the emulsion prepared above is mixed with the film-forming liquid in a volume ratio of (1:9-9:1), poured into a mold, and dried at room temperature to obtain a double-layer cling film.

[0067] In some embodiments, the film-forming material is at least one of chitosan, carboxymethyl chitosan, quaternary ammonium chitosan, quaternary phosphonium chitosan, soluble starch, cellulose, polyvinyl alcohol, zein, cyclodextrin, gelatin, sodium alginate, carboxymethyl fiber bundle, konjac glucomannan, and pullulan; the plasticizer is at least one of ethylene glycol, glycerol, sorbitol, polyethylene glycol with a molecular weight of less than 4000, ethylenediamine, and triethanolamine; and the mass concentration of the film-forming material in the film-forming base liquid is 0.5%-10%.

[0068] The present invention also provides a method for applying the intelligent indicating double-layer fresh-keeping film to the detection of the freshness of protein foods; the method comprises the following steps:

[0069] Fresh shrimp, beef, pork, fish, and other protein foods are placed in a mold (9 cm diameter) and sealed with a double-layer film (with the indicator layer facing outward). The shrimp is then stored at either 25°C or 4°C. The volatile basic nitrogen (TVB-N) and pH values of the food are measured, and the color change of the film is recorded. The freshness of the food is determined by colorimetry.

[0070] The solution proposed by the present invention is described in detail below through specific embodiments:

[0071] Example 1 Beetroot-caffeic acid acylated derivatives

[0072] At 25°C, beetroot red (0.275 g, 0.5 mmol) was weighed and dissolved in 5 mL of water and 2.5 mL of tetrahydrofuran (THF) until fully dissolved. Next, 0.5 mmol of caffeic acid (0.09 g) was weighed and added to 7.5 mL of THF. 0.5 mmol (0.09585 g) of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and 0.5 mmol (0.0575 g) of N-hydroxysuccinimide (NHS) were dissolved in 7.5 mL of water and mixed thoroughly with the caffeic acid solution. The mixture was stirred at room temperature in the dark for 2 h to fully activate the mixture. Subsequently, the activation solution was slowly added dropwise to the beetroot red solution with stirring. The mixture was stirred at room temperature in the dark for 24 h. After the reaction was complete, the water and THF were removed by rotary evaporation at 55°C. 25 mL of anhydrous ethanol was added to remove unreacted caffeic acid, and the solid was precipitated by ultrasonication. Subsequently, the mixture was transferred to a 50 mL centrifuge tube and centrifuged at 10,000 rpm for 10 min. The supernatant was removed and the above operation (adding 25 mL of anhydrous ethanol, precipitating the solid, and centrifuging for 10 min) was repeated three times. Finally, the bottom precipitate was freeze-dried to obtain the beet red-caffeic acid acylation product (BT-g-CA).

[0073] The changes in the molecular structure of the prepared beet red-caffeic acid acylated derivatives were analyzed using German Tensor27 infrared spectroscopy (FT-IR). Figure 1 In the infrared spectrum of beetroot red (BT), the wavelengths of 3500-3000 cm -1 The broad absorption band is the superposition vibration absorption peak of -COOH, -OH, =CH, -NH- and pyridine heteroaromatic ring in beet red, at 2933 cm -1 、2886cm -1 It is the asymmetric stretching vibration and symmetric stretching vibration of -CH2 of beet red glucosyl group, at 1640cm -1 It is the characteristic absorption peak of the benzene ring skeleton structure of beetroot red, at 1016cm -1 It is the vibration absorption peak of -CH2-OH of beet red glucosyl. In the infrared spectrum of caffeic acid (CA), 3398cm-1 It is the vibration absorption peak of the phenolic hydroxyl group -OH of the benzene ring of caffeic acid, 3219cm -1 It is the stretching vibration absorption peak of the free -OH in the carboxyl group of caffeic acid, 1632 and 1450 cm -1 The characteristic absorption peak of the benzene ring skeleton structure of caffeic acid. Compared with the infrared spectrum of beet red (BT), in the infrared spectrum of beet red-caffeic acid acylated derivative (BT-g-CA), 3292 cm -1 The stretching vibration absorption peak of -OH at 2933 cm -1 The CH vibration absorption peak at 1707 cm-1 becomes stronger, indicating that a methyl or methylene group is introduced into the beet red structure. The C=O characteristic absorption peak of the ester group (COO) appears at 1640 and 1562 cm-1. -1 The characteristic absorption peak of the benzene ring skeleton structure appeared at , indicating that a benzene ring was introduced into the glucoside bond structure of betalain. These results show that caffeic acid was grafted onto the structure of betalain, and the betalain-caffeic acid acylated derivative was successfully prepared.

[0074] The functional group structure changes of the prepared beet red-caffeic acid acylated derivatives were analyzed using a UV spectrophotometer (U765S) from Shimadzu, Japan. The results are as follows: Figure 2 As shown. In the UV-visible spectrum of beetroot red (BT), a maximum absorption wavelength appeared in the visible light region at 523nm, and a lower absorption peak appeared in the UV region at 265nm. In the UV-visible spectrum of caffeic acid (CA), a maximum absorption wavelength appeared at 328nm, which is the characteristic peak of the benzene ring. In the UV-visible spectrum of the beetroot red-caffeic acid acylated derivative (BT-g-CA), a lower absorption peak appeared at 523nm, which is the characteristic peak of betaine aldehyde, and a strong absorption peak appeared at 281nm, which is mainly due to the grafting of caffeic acid into the molecular structure of beetroot red. The above results also prove that caffeic acid has been successfully grafted onto the structure of beetroot red.

[0075] Time and temperature stability test: 10 mg / mL beet red solution before and after modification was heated in a constant temperature water bath at 60℃ and 80℃ for different time periods in the dark. The absorbance was measured, the retention rate was calculated, and the curve was drawn. The results are shown in the figure. Figure 3As shown in the figure, under high temperature conditions (60°C and 80°C), the retention rate of acylated beetroot red (BT-g-CA) was significantly higher than that of beetroot red at the same concentration. When heated at 60°C for 4 hours, the retention rate of beetroot red BT was 32.78%, while the retention rate of beetroot red-caffeic acid acylated derivative (BT-g-CA) was 44.64%. When heated at 80°C for 2 hours, the retention rate of beetroot red BT was 8.87%, while the retention rate of beetroot red-caffeic acid acylated derivative (BT-g-CA) was 19.79%. This indicates that caffeic acid acylation of beetroot red improves its thermal stability.

[0076] UV stability test: 10 mg / mL beetroot red solution before and after modification was irradiated with UV light (500W) for different time periods, the absorbance was measured, the retention rate was calculated, and the curve was drawn. The results are shown in the figure. Figure 4 As shown in the figure, the retention rate of beetroot red-caffeic acid acylated derivative (BT-g-CA) under UV irradiation conditions is significantly higher than that of beetroot red at the same concentration. After 2 hours (120 minutes) of illumination, the retention rate of beetroot red is only 2.27%, while the retention rate of beetroot red-caffeic acid acylated derivative (BT-g-CA) is as high as 38.69%. This is mainly because the molecular structure of beetroot red-caffeic acid acylated derivative (BT-g-CA) introduces phenolic hydroxyl groups with UV resistance. During UV irradiation, the phenolic hydroxyl groups help protect the chromophore of beetroot red (betainalanine) from degradation.

[0077] The in vitro antioxidant activity of betaine-caffeic acid acylated derivatives was determined by scavenging DPPH free radicals.

[0078] Determination of DPPH free radical scavenging ability: dilute with anhydrous ethanol to obtain Vc solutions of different concentrations, and dilute with ultrapure water to obtain sample solutions of different concentrations. Weigh a certain amount of DPPH powder and dissolve it in anhydrous ethanol to obtain a 0.2mM DPPH working solution. Take 1mL of sample or Vc solution of different concentrations, mix it evenly with an equal volume of DPPH working solution, react at 25℃ in the dark for 30min, and measure the absorbance of the mixed solution at 517nm. Take Vc as the positive control, and adjust the solution to zero with an equal volume of anhydrous ethanol and ultrapure water. The absorbance of the mixed solution of sample and DPPH is As, and the absorbance of the mixed solution of equal volume of anhydrous ethanol and DPPH is the blank control Ac. The DPPH free radical scavenging rate is calculated using the following formula:

[0079]

[0080] The DPPH free radical scavenging rate of Vc was compared and calculated, and the DPPH value of the sample was expressed as μmol Vcequiv. / g.

[0081] Figure 5Figure 1 shows the DPPH radical scavenging ability of vitamin C (VC), betalain (BT), and betalain-caffeic acid acylated derivative (BT-g-CA). The figure shows that BT-g-CA exhibits far greater radical scavenging ability than betalain (BT). At a concentration of 125 μg / mL, BT-g-CA achieved a DPPH radical scavenging rate of 94.98%, while BT achieved a rate of only 3.34%. This indicates that modification significantly enhanced the antioxidant capacity of betalain. This is because BT-g-CA introduces the catechol hydroxyl group on caffeic acid into BT through an esterification reaction, conferring antioxidant activity on betalain phenolics. BT's inherent antioxidant capacity primarily relies on the isolated hydroxyl groups and sugar groups in betanin, which have weak hydrogen-donating capacity and a low reaction rate, resulting in an overall low scavenging rate.

[0082] Example 2 Carrageenan stabilized cinnamon essential oil Pickering emulsion

[0083] 1g of carrageenan was dissolved in 100mL of deionized water at 80°C to prepare a 1% (w / v, g / mL) carrageenan aqueous solution. Cinnamon essential oil was then added to the carrageenan aqueous solution at varying volume fractions of 1%, 3%, 5%, and 7%. Emulsification was performed using a high-speed disperser at 10,000 rpm for 3 minutes to obtain a carrageenan-stabilized cinnamon essential oil Pickering emulsion.

[0084] The microstructure of the prepared carrageenan-stabilized cinnamon essential oil Pickering emulsion was observed using an EVOS XL Core inverted optical microscope from Thermo Fisher Scientific, USA. Figure 6 As shown in the figure, the emulsion droplets are all regular circles with clear boundaries between the droplets. As can be seen from the figure, as the proportion of cinnamon essential oil (CEO) increases, the particle size of the emulsion gradually increases.

[0085] The particle size of the emulsion was measured using a Mastersizer 3000 laser scattering particle size analyzer. The pump stirring speed of the dispersion device was 1800 rpm. The refractive indices of the dispersant and cinnamon essential oil were 1.333 and 1.592, respectively. The emulsion particle size was expressed as the volume-weighted mean diameter (D4,3). The results are shown in Figure 2. Figure 7As shown, the particle size of the cinnamon essential oil Pickering emulsion exhibits a normal distribution and gradually increases with increasing essential oil addition. When the essential oil addition is 3%, the emulsion has a relatively concentrated distribution, with an average particle size of 6.019±0.816μm. The rheological properties curve shows that the apparent viscosity of the carrageenan-stabilized cinnamon essential oil Pickering emulsion decreases with increasing shear rate, exhibiting a shear-thinning phenomenon. This indicates that the carrageenan-stabilized cinnamon essential oil Pickering emulsion is a pseudoplastic fluid. This is because carrageenan, as a polysaccharide solid particle, can form a three-dimensional network structure or particle aggregates through hydrogen bonding or van der Waals forces under static or low shear conditions, increasing flow resistance. As the shear rate increases, the shear force disrupts this temporary three-dimensional network structure or particle aggregates, causing the particles or droplets to rearrange, thereby reducing the apparent viscosity. Furthermore, the figure shows that the viscosity of the emulsion decreases with increasing essential oil concentration. This is because the low viscosity of cinnamon essential oil dilutes the carrageenan network structure of the continuous phase (aqueous phase), weakening its thickening ability.

[0086] The rheological properties of the carrageenan-stabilized cinnamon oil Pickering emulsion in this example were investigated at 25°C using a Thermofisher / MARS Hake rheometer. Parallel steel plates (60 mm diameter, 0.5 mm gap) were used in a dynamic oscillation experiment to measure the apparent viscosity of the sample at shear rates ranging from 0.1 to 300 s⁻¹. Figure 8 As shown. The figure shows the antibacterial effect and size of the emulsion prepared with 1.0% carrageenan and different volume fractions of cinnamon essential oil (0%, 1%, 3%, 5%, 7%) on Escherichia coli (E.coli) and Staphylococcus aureus (S.aureus). As can be seen from the figure, the antibacterial ability of the emulsion is positively correlated with the essential oil content in the emulsion. When the essential oil addition amount is 1%, the inhibition zone can be clearly seen, which significantly inhibits the growth of Escherichia coli and Staphylococcus aureus. The diameter of the inhibition zone of the emulsion against these two bacteria was measured, and the results are shown in Table 1. The larger the diameter of the inhibition zone, the better the effect of the substance in inhibiting microbial growth. The diameter of the inhibition zone is less than 7mm, which means the antibacterial ability is weak; the diameter of the inhibition zone is greater than 20mm, which means the antibacterial ability is extremely strong. When the essential oil addition amount in the emulsion is 3%, the diameters of the inhibition zones against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) are 35.2±0.22mm and 30.6±0.13mm, respectively, showing extremely strong antibacterial activity.

[0087] Table 1 Antibacterial diameters of different essential oil contents

[0088]

[0089] Example 3 Intelligent Indicating Double-Layer Fresh-Preservative Film

[0090] A two-step casting method was used to prepare a smart indicating double-layer cling film. First, carboxymethyl cellulose (CMC) was dissolved in deionized water at 60°C, magnetically stirred to dissolve, cooled to 25°C, and prepared into a 2% (w / v, g / mL) aqueous solution. At the same time, 20wt% (based on the mass of the solute) glycerol was added as a plasticizer. 0.2g of beet red-caffeic acid acylated derivative (MBT, 20wt% of the mass of the CMC matrix) was added to 50mL of 2% CMC solution, poured into a mold, and dried at room temperature to obtain an indicator layer. Then, sodium alginate (SA) was added to deionized water, stirred and dissolved at 60°C, then cooled to 25°C, and 30wt% of glycerol (based on the mass of the solute SA) was added to obtain a 2% (w / v, g / mL) SA solution. 17.5 mL of the SA solution was mixed with 7.5 mL of the carrageenan-stabilized cinnamon essential oil Pickering emulsion (PE) prepared above at a ratio of 7:3 (v / v). 25 mL of the mixture was poured onto the dried indicator layer and dried at 25°C to obtain a double-layer plastic wrap (CMC-SA-MBT-PE). Three control groups (CMC-SA, CMC-SA-MBT, and CMC-SA-PE) were also set up.

[0091] Figure 9 The light-barrier properties of the prepared smart indicator double-layer cling film were investigated. A UV-visible light barrier is crucial for food packaging, as light can cause oxidative deterioration. As shown in the figure, the double-layer cling film CMC-SA-MBT-PE, incorporating both acylated betaine and essential oil emulsion, exhibits significant light-barrier properties from 200 to 800 nm. The optical transmittance of the CMC-SA composite film at 350 nm is 58.73%, while that of the CMC-SA-MBT composite film is only 0.38%, indicating that the addition of acylated betaine enhances the composite film's light-barrier properties. The light transmittance of the CMC-SA-PE and CMC-SA-MBT-PE composite films incorporating essential oil emulsion is significantly lower than that of the CMC-SA and CMC-SA-MBT composite films. At 550nm, the optical transmittance of CMC-SA was 71.05%, that of CMC-SA-MBT was 46.32%, that of CMC-SA-PE was 1.44%, and that of CMC-SA-MBT-PE was 0.83%, indicating that the addition of the emulsion improved the material's light barrier properties. This is primarily because MBT and essential oil emulsions contain unsaturated bonds, such as benzene rings, phenolic hydroxyl groups, and double bonds, that can absorb UV-visible radiation. In summary, the addition of MBT and essential oil Pickering emulsions significantly improves the film's light barrier properties.

[0092] Example 4 Application of intelligent indicating double-layer cling film in shrimp freshness detection

[0093] Fresh shrimp (80 g) were placed in a plastic Petri dish (9 cm diameter) and sealed with a double-layer film (with the indicator layer facing outward). The shrimp were then stored at either 25°C or 4°C for 48 hours. The volatile basic nitrogen (TVB-N) content of the shrimp was measured every 8 hours, and the color change of the film was recorded. Food freshness was determined by colorimetry.

[0094] Figure 10 The application of the prepared intelligent indicator double-layer plastic wrap in shrimp freshness testing. As shown in the figure, over time (2-day intervals), the white shrimp in the KB (blank) and CMCS-SA groups deteriorated by the sixth day. By the eighth day, the shrimp heads had turned a distinct yellow, and the surface white shrimp flesh began to rot. In contrast, the color of the composite film CMC-SA-MBT-PE gradually turned yellow over time, and the white shrimp began to deteriorate by the eighth day.

[0095] Figure 11 The prepared smart indicator double-layer plastic wrap was used to monitor volatile basic nitrogen (TVB-N) during storage of fresh shrimp. Shrimp have a high water activity and their muscle components (protein and amino acids) are rich in nitrogen. Therefore, they are susceptible to rapid spoilage under refrigerated conditions (4°C). Endogenous enzymes and microbial activity produce TVB-N and biogenic amines. The initial TVB-N level (7.23 ± 1.02 mg / 100 g) classified the sample as first-class freshness. On day 4, TVB-N values for the blank, CMCS-SA, and CMC-SA-MBT-PE films were 28.5 ± 1.19, 23.1 ± 1.71, and 17.43 ± 1.75 mg / 100 g, respectively. The blank and CMCS-SA films exceeded the Chinese regulatory limit (GB2707-2016: ≤ 20 mg / 100 g). In contrast, CMC-SA-MBT-PE demonstrated superior performance, maintaining TVB-N at 17.43 ± 1.75 mg / 100g. This was attributed to the synergistic effect of the CMC-SA-MBT-PE bilayer film, along with the antioxidant MBT and antibacterial PE. By day 8, TVB-N accumulation in the KB (blank) (39.82 ± 2.14 mg / 100g) and CMCS-SA groups (30.33 ± 1.87 mg / 100g) exceeded the international threshold (≤30 mg / 100g), while the CMC-SA-MBT-PE bilayer film maintained a level of 21.27 ± 1.19 mg / 100g. These results suggest that bilayer films containing antioxidant and antibacterial materials can extend the shelf life of shrimp by 2-4 days.

[0096] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0097] The serial numbers of the above embodiments of the present invention are for description only and do not represent the advantages or disadvantages of the embodiments.

[0098] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, and all of these should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a beet red-phenolic acid acylated derivative, characterized in that: The following steps are involved: (1) Dissolve betaine in a solvent to form a solution with a solubility of 2.0 to 5.0 mg / mL; (2) dissolving the activator, phenolic acid, and condensing agent in a solvent, activating for 0.5 to 3 hours, and then adding dropwise to the beetroot red solution, stirring at 300 to 800 r / min at 25°C to 30°C for 12 to 36 hours; (3) After the reaction is complete, remove water and / or organic solvent by rotary evaporation, then add solvent and ultrasonically vibrate to precipitate solid; (4) The supernatant was removed by centrifugation, and the bottom precipitate was freeze-dried to obtain the beet red-phenolic acid acylation product.

2. The preparation method according to claim 1, characterized in that The solvent includes one or more of water, methanol, ethanol, acetone, isopropanol, chloroform, ethyl acetate, tetrahydrofuran and N,N-dimethylformamide; At least one of the activators 1-hydroxy-benzotriazole, benzotriazole-N,N,N',N'-tetramethyluronium hexafluorophosphate, O-benzotriazole-N,N,N',N'-tetramethyluronium tetrafluoroboric acid, and N-hydroxysuccinimide; The condensing agent is at least one of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, dicyclohexylcarbodiimide, and diisopropylcarbodiimide (DIC); The phenolic acid is at least one of chlorogenic acid, ferulic acid, gentisic acid, vanillic acid, cinnamic acid, syringic acid, sinapic acid, p-coumaric acid, caffeic acid, protocatechuic acid, and gallic acid.

3. The preparation method according to claim 1, characterized in that The molar ratio of the activator to the phenolic acid is 1:1-5:1, the molar ratio of the condensing agent to the phenolic acid is 1:1-5:1, and the molar ratio of the phenolic acid to beetroot red is 0.1:1-3:

1.

4. The beet red-phenolic acid acylated derivative prepared by the preparation method according to any one of claims 1 to 3.

5. A method for preparing an antibacterial and antioxidant intelligent indicator double-layer cling film, characterized in that: The following steps are involved: S1. Dispersing polysaccharide in deionized water to obtain a polysaccharide dispersion, and then dripping plant essential oil into the aqueous phase while performing shear emulsification to obtain a plant essential oil Pickering emulsion; S2. dissolving the film-forming material in deionized water, stirring the solution under magnetic stirring, adding a plasticizer to obtain a film-forming solution A, adding the beet red-phenolic acid acylated derivative according to claim 4, pouring the solution into a mold, and drying at room temperature to obtain an indicator layer; S2. Dissolve the film-forming material in deionized water, stir magnetically to dissolve, add a plasticizer to obtain a film-forming liquid B; then mix the emulsion prepared in step S1 with the film-forming liquid in a volume ratio of 1:9 to 9:1, pour into a mold, and dry at room temperature to obtain a double-layer plastic wrap.

6. The method for preparing the antibacterial and antioxidant intelligent indicating double-layer fresh-keeping film according to claim 5, characterized in that: In step S1, The polysaccharide is one or more of carrageenan, gellan gum, konjac gum, gum arabic, pectin, xanthan gum, agar, guar gum, karaya gum, tamarind gum, and locust bean gum; The shear emulsification speed is 10000-12000 r / min, and the shear emulsification time is 3-8 min; The plant essential oil comprises at least one of thyme essential oil, galangal essential oil, tea tree essential oil, lemon essential oil, citronella essential oil, oil peel essential oil, mustard essential oil, peppermint essential oil, cinnamon essential oil, clove essential oil, garlic essential oil, almond essential oil, eucalyptus essential oil, ylang-ylang essential oil and lavender essential oil; The concentration of the polysaccharide is 0.1-3.0%, and the concentration of the plant essential oil is 1.0-50%.

7. The method for preparing the antibacterial and antioxidant intelligent indicator double-layer fresh-keeping film according to claim 5, characterized in that: The film-forming material is at least one of chitosan, carboxymethyl chitosan, quaternary ammonium salt chitosan, quaternary phosphonium salt chitosan, soluble starch, cellulose, polyvinyl alcohol, zein, cyclodextrin, gelatin, sodium alginate, carboxymethyl fiber bundle, konjac glucomannan, and pullulan; The plasticizer is at least one of ethylene glycol, glycerol, sorbitol, polyethylene glycol with a molecular weight lower than 4000, ethylenediamine, and triethanolamine.

8. The method for preparing the antibacterial and antioxidant intelligent indicating double-layer fresh-keeping film according to claim 5, characterized in that: In step S2, the amount of the plasticizer added is 20-30 wt% of the mass of the film-forming material; the amount of the beet red-phenolic acid acylated derivative added is 5-40 wt% of the mass of the film-forming material; In step S3, the amount of plasticizer added is 20-30 wt% of the mass of the film-forming material; The mass concentration of the film-forming material in the film-forming solution A and the film-forming solution B is 0.5%-10%.

9. The antibacterial and antioxidant intelligent indicator double-layer fresh-keeping film prepared by any one of the preparation methods of claims 5-8.

10. Use of the antibacterial and antioxidant intelligent indicating double-layer cling film according to claim 9 in food packaging or food freshness detection.

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