Preparation method of difunctional intelligent preservative film based on citric acid modified sweet potato starch

Abstract

The invention belongs to the technical field of deep processing of agricultural and sideline products, and particularly relates to a preparation method of a difunctional intelligent preservative film based on citric acid modified sweet potato starch. According to the invention, sweet potato starch esterified by citric acid in a deep eutectic solvent is used as a matrix, and phenolic acid auxiliary color anthocyanin and beta-cyclodextrin are integrated to encapsulate cinnamon essential oil microcapsules. The film modified by the citric acid with the concentration of 70% is optimal in comprehensive performance and has a remarkable bacteriostasis effect on escherichia coli and staphylococcus aureus; the anthocyanin enables the film to present significant chromatic aberration (delta Egt; 3.5), the pH change of chicken putrefaction can be reflected. When the fresh-keeping film is used for keeping chicken fresh, TBARS and TVB-N indexes are delayed by 35%-40% compared with those of a control group and reach corruption threshold values, and the film color indicates freshness. The method provides a basis for developing starch-based materials for active packaging and intelligent monitoring, and has an application value for reducing food waste and improving cold chain visual supervision.

Description

Technical Field

[0001] This invention belongs to the field of deep processing technology of agricultural and sideline products, and specifically relates to a method for preparing a dual-function intelligent preservation film based on citric acid modified sweet potato starch. Background Technology

[0002] The growing global demand for sustainable food preservation technologies has made smart packaging materials, which combine activity protection and real-time quality monitoring, a hot research topic. While traditional petroleum-based plastics offer advantages in mechanical strength, they are controversial due to their environmental durability and inability to inhibit microbial contamination or indicate food freshness. Against this backdrop, starch-based films based on renewable resources are considered an ideal alternative due to their biodegradability. Sweet potato ( Ipomoea batatas As one of the largest annual grain crops, sweet potato starch holds enormous potential for high-value utilization through sustainable technologies. Developing smart packaging materials based on sweet potato starch can not only increase the added value of agricultural products but also provide new avenues for the efficient utilization of biomass resources.

[0003] In recent years, combining pH-responsive anthocyanins with volatile antimicrobial agents to construct bifunctional active smart packaging has become a cutting-edge research direction in the field of food preservation. These systems achieve real-time, visual monitoring of food freshness through the pH-dependent colorimetric properties of anthocyanins, while actively delaying microbial spoilage through the slow-release effect of antimicrobial agents, thus driving a revolutionary transformation in food packaging from traditional passive isolation to a combination of dynamic sensing and active protection. However, the high sensitivity of anthocyanins to light, heat, and oxygen leads to insufficient color stability and easy degradation and fading, severely limiting their practical application. To address this problem, researchers have attempted to use phenolic acid co-coloring technology, utilizing intermolecular π-π stacking interactions to stabilize the yellow-yellow cation structure of anthocyanins, extending its half-life by 1.8 times and significantly improving the color difference ΔE*ab.

[0004] On the other hand, while volatile antimicrobial agents (such as cinnamaldehyde) exhibit significant antimicrobial activity, their high volatility, poor water solubility, and easy diffusion not only lead to activity loss during processing but also make it difficult to maintain an effective inhibitory concentration on food surfaces. Furthermore, high concentrations may affect food flavor. Currently, microencapsulation strategies are commonly used to achieve controlled release. Previous studies have shown that cinnamon oil microcapsules constructed based on a cellulose / hydroxypropyl-β-cyclodextrin complex system can achieve an encapsulation efficiency as high as 96.26%, successfully extending shelf life to 12 days in grape preservation applications, demonstrating excellent controlled release and preservation potential. In addition, the nanoscale β-cyclodextrin-cinnamaldehyde inclusion complex system exhibits broad-spectrum antimicrobial activity against a variety of common spoilage microorganisms, with minimum inhibitory concentrations (MICs) ranging from 62.5 to 125 mg·L⁻¹ against *Escherichia coli*, *Aspergillus niger*, *Transvaporium niger*, and *Penicillium digitatum*. -1 The results further confirm its significant effect in inhibiting microbial proliferation.

[0005] Although phenolic acid co-coloring strategies and microencapsulation technology have made positive progress in stabilizing anthocyanins and antibacterial agents, respectively, most current research is still limited to simply blending them as independent functional units in the membrane matrix. This physical blending method cannot solve problems such as poor interfacial compatibility between active ingredients and the matrix, potential migration or phase separation during long-term storage, and damage to active ingredients caused by processing conditions. More importantly, traditional film-forming matrices (such as gelatin, carrageenan, and pure starch membranes) have limited mechanical properties, water resistance, and the ability to load and protect active substances. They often struggle to balance high mechanical strength, excellent barrier properties, high active substance loading, and good bioactivity, resulting in limitations in the overall performance and practicality of the membrane. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch, so as to solve the problems of limited mechanical properties, water resistance, and loading and protection capacity of starch films for active substances.

[0007] The technical solution adopted in this invention is:

[0008] The preparation process of a dual-functional smart food preservation film based on citric acid-modified sweet potato starch is as follows:

[0009]

[0010] A method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch, the specific steps of which are as follows:

[0011] 1) Preparation of eutectic solvent DES: Choline chloride and ethylene glycol were mixed in a sealed beaker at a molar ratio of 1:2, heated to 95 °C and stirred continuously for 6 hours until a homogeneous transparent liquid was formed; the resulting homogeneous transparent liquid was filtered and dried in an oven at 50 °C for 12 hours.

[0012] 2) Dissolving sweet potato starch: Weigh 2.0 g of dry sweet potato starch and add it to 100 mL of the eutectic solvent DES obtained in step 1). Stir continuously for 4 h in an oil bath at 100°C until the sweet potato starch is completely dissolved.

[0013] 3) Citric acid modification: Citric acid was added to the sweet potato starch dissolution system obtained in step 2), and sodium hypophosphite was used as a catalyst. The reaction was carried out at 100 °C for 2 h, and then the reaction mixture was cooled to room temperature.

[0014] 4) Filtration: Wash the reaction mixture obtained in step 3) with anhydrous ethanol and filter it three times to remove residual reagents;

[0015] 5) Drying: Place the product obtained in step 4) in a vacuum drying oven and dry at 50 °C for 48 h to obtain the modified sweet potato starch sample;

[0016] 6) Dissolving ferulic acid: Dissolve ferulic acid in anhydrous ethanol to form a ferulic acid stock solution;

[0017] 7) Dissolving anthocyanins: Dissolve anthocyanins in acidified ethanol at pH 3.0 to form an anthocyanin solution;

[0018] 8) Mixing: The ferulic acid stock solution obtained in step 6) and the anthocyanin solution obtained in step 7) are mixed and magnetically stirred at 1000 rpm for 20 min at 25 °C to obtain a ferulic acid co-pigment anthocyanin mixed solution.

[0019] 9) Mixing β-cyclodextrin and cinnamon essential oil: Dissolve β-CD as a wall material in distilled water and stir at 800 rpm for 30 minutes at 55 °C to obtain a clear β-CD solution; dissolve CIN as a core material in anhydrous ethanol and add it dropwise to the β-CD solution under controlled pressure using a peristaltic pump;

[0020] 10) Heating: After stirring the mixture obtained in step 19) at 45 °C for 2 h, let it cool naturally to 25 °C and maintain for 2 h, then heat it to 45 °C and react for 2 h.

[0021] 11) Refrigeration: Refrigerate the mixture obtained in step 10) at 4 °C overnight;

[0022] 12) Vacuum filtration: The mixture obtained in step 11) is vacuum filtered to collect the precipitate, which is then washed three times with anhydrous ethanol;

[0023] 13) Drying: The product obtained in step 12) was dried in a convection oven at 50 °C. The resulting powder was equilibrated in air at 25 °C for 24 h to allow the moisture content to reach equilibrium, thus obtaining cinnamon essential oil microcapsules CIN@β-CD. The microcapsules CIN@β-CD were dispersed in distilled water to prepare a 20 mg / mL CIN@β-CD suspension.

[0024] 14) Mixing: Dissolve the modified sweet potato starch obtained in step 5) in distilled water, and gradually heat it to 65°C under magnetic stirring until it is completely gelatinized. After cooling to 45°C, add the CIN@β-CD suspension prepared in step 13) and stir for 1 h. Then add the ferulic acid co-pigment anthocyanin mixture obtained in step 8) and stir for 30 min. Add the composite plasticizer, stir vigorously, and then sonicate for 20 min to remove bubbles. Adjust the pH to 3.5 with 1 mol / L HCl to obtain the film-forming solution.

[0025] 15) Film formation: Pour 20 mL of film-forming solution into a sterile petri dish with a diameter of 9 cm, dry at 45 ℃ for 48 h, and equilibrate the dried film at 25 ℃ and 85% relative humidity for more than 48 h until the quality of the film is constant, thus obtaining a dual-function intelligent preservation film based on citric acid modified sweet potato starch.

[0026] Furthermore, in the above-mentioned method for preparing a dual-function smart food preservation film based on citric acid-modified sweet potato starch, in step 3), the amount of citric acid added is 55% or 70% based on the dry basis mass fraction of sweet potato starch.

[0027] Preferably, in step 3), the amount of citric acid added is 70% based on the dry weight fraction of sweet potato starch.

[0028] Furthermore, in the above-mentioned method for preparing a dual-function smart food preservation film based on citric acid modified sweet potato starch, in step 3), the amount of sodium hypophosphite added is 50% of the mass of citric acid.

[0029] Furthermore, in the above-mentioned method for preparing a dual-function smart food preservation film based on citric acid-modified sweet potato starch, in step 6), the concentration of ferulic acid stock solution is 1 mg / mL.

[0030] Furthermore, in the above-mentioned method for preparing a dual-function smart food preservation film based on citric acid-modified sweet potato starch, in step 7), the concentration of the anthocyanin solution is 0.2 mg / mL.

[0031] Furthermore, in the above-mentioned method for preparing a dual-functional smart food preservation film based on citric acid modified sweet potato starch, in step 8), the mass ratio of ferulic acid to anthocyanin in the ferulic acid co-pigment anthocyanin mixture is 5:1.

[0032] Furthermore, in the above-mentioned method for preparing a dual-function smart food preservation film based on citric acid modified sweet potato starch, in step 9), the mass ratio of the core material CIN to the wall material β-CD is 1:1, 1:2, 1:4 or 1:8, and the ratio of the total mass of the core material CIN and the wall material β-CD to the volume of distilled water is 10%, 15%, 20% or 25%.

[0033] Preferably, in step 9), the mass ratio of the core material CIN to the wall material β-CD is 1:2, and the ratio of the total mass of the core material CIN and the wall material β-CD to the volume of distilled water is 20%.

[0034] Furthermore, in the above-mentioned method for preparing a dual-function smart food preservation film based on citric acid modified sweet potato starch, in step 14), the modified sweet potato starch is dissolved in distilled water at a concentration of 25 mg / mL.

[0035] Furthermore, in the above-mentioned method for preparing a dual-functional smart food preservation film based on citric acid modified sweet potato starch, in step 14), the film-forming solution contains CIN@β-CD at a concentration of 2 mg / mL, anthocyanins at a concentration of 0.2 mg / mL, and ferulic acid at a concentration of 1 mg / mL.

[0036] Furthermore, in the above-mentioned method for preparing a dual-function smart food preservation film based on citric acid modified sweet potato starch, in step 14), the composite plasticizer is composed of glycerol and D-sorbitol in a mass ratio of 1:1, and the added mass of the composite plasticizer is 35% of the total mass of the dry polymer in the film-forming solution.

[0037] The beneficial effects of this invention are as follows: This invention, through a method for preparing a dual-functional intelligent food preservation film based on citric acid-modified sweet potato starch, not only achieves integrated "structure-function" design but also establishes a controllable construction method from molecular modification to macroscopic properties, providing a new approach for the green preparation of multifunctional bio-based membrane materials. Testing showed that in a DES medium with 70% citric acid mass fraction, the esterification substitution degree of starch reached 62%, significantly higher than the highest value of 45.3% for aqueous phase modification. After modification, the average particle size of starch decreased from 14.376 μm to 7.206 μm, solubility increased to 68%, gelatinization enthalpy decreased, and thermal stability enhanced, indicating that DES modification effectively disrupted the crystalline region of starch, forming a continuous phase dominated by an amorphous structure. The prepared film has a water contact angle of approximately 118.9° and an oxygen barrier performance of approximately 6.53 cm⁻¹. 3 ·m -2 ·day -1 This film possesses excellent hydrophobicity and barrier properties; simultaneously, it exhibits real-time pH-responsive color-changing functionality, showing a correlation of over 0.8 with the chicken spoilage index—TVB-N / TBARS—and can extend shelf life by approximately 35-40% at room temperature. By integrating dynamic antibacterial properties with real-time visual monitoring, this invention provides a practical solution for reducing food spoilage in cold chain logistics, while also opening up new avenues for the high-value utilization of sweet potato starch. Attached Figure Description

[0038] Figure 1 This is the FT-IR spectrum of a starch sample.

[0039] Figure 2 This is the XRD pattern of a starch sample.

[0040] Figure 3 This refers to the color changes of anthocyanins in the presence of different phenolic acids.

[0041] Figure 4 These are the UV-Vis spectra of CK, AA-BA, and FA-BA under different pH conditions.

[0042] Figure 5It is the encapsulation efficiency (EE) of CIN@β-CD.

[0043] Figure 6 It refers to the color and appearance of the smart food preservation film at different pH values.

[0044] Figure 7 It refers to the mechanical and textural properties of smart food preservation film.

[0045] Figure 8 These are SEM images of the surface (top) and fracture surface (bottom) of the smart food preservation film, where (a) to (e) correspond to NS, 55% CA-DES, 70% CA-DES, 55% CA-AQ and 70% CA-AQ, respectively.

[0046] Figure 9 The images show the AFM height diagram (top) and three-dimensional morphology diagram (bottom) of the smart food preservation film, where (a) to (e) correspond to NS, 55% CA-DES, 70% CA-DES, 55% CA-AQ and 70% CA-AQ, respectively.

[0047] Figure 10 It is the water contact angle of the smart food preservation film.

[0048] Figure 11 The antibacterial activity of the smart food preservation film was determined, where (a) and (b) correspond to Staphylococcus aureus, and (c) and (d) correspond to Escherichia coli; numbers (1) to (6) represent control film (without microcapsules) and film containing microcapsules (NS, 55% CA-DES, 70% CA-DES, 55% CA-AQ and 70% CA-AQ).

[0049] Figure 12 The visual appearance of chicken breast in different packages, where (a) to (e) correspond to NS, 55% CA-DES, 70% CA-DES, 55% CA-AQ and 70% CA-AQ, respectively.

[0050] Figure 13 These are the TBARS values ​​of chicken breast packaged in different films.

[0051] Figure 14 The TVB-N value is the value of chicken breast packaged in different films.

[0052] Figure 15 The time evolution of the correlation between the color of the smart plastic wrap and the freshness of chicken, day 4 (A), day 8 (B), and day 12 (C).

[0053] Figure 16 These are representative images of soil degradation using different films. Detailed Implementation

[0054] Example 1: Preparation of citric acid modified starch in water and DES respectively

[0055] (a) Preparation of eutectic solvent (DES)

[0056] 1.1) Mix choline chloride and ethylene glycol in a 1:2 molar ratio in a sealed beaker, heat to 95 °C and stir continuously for 6 hours until a homogeneous and transparent liquid is formed;

[0057] 1.2) After filtering the homogeneous and transparent liquid obtained in step 1.1), place it in a 50 ℃ oven to dry for 12 hours for later use.

[0058] (II) Preparation of citric acid modified sweet potato starch

[0059] 2.1) Weigh two portions of 2.0 g sweet potato starch and add them to 100 mL DES and 100 mL deionized water respectively. Stir continuously for 4 h in an oil bath at 100℃ until the sweet potato starch is completely dissolved.

[0060] 2.2) Citric acid (based on the dry weight of sweet potato starch) of 55% and 70% (corresponding to the experimental variables of each group) was added to the obtained sweet potato starch dissolution system, and sodium hypophosphite of 50% of the citric acid mass was used as a catalyst. After reacting at 100 °C for 2 h, the reaction mixture was cooled to room temperature.

[0061] 2.3) The resulting reaction mixture was washed with anhydrous ethanol and filtered three times to remove residual reagents;

[0062] 2.4) The product obtained in step 2.3) was placed in a vacuum drying oven and dried at 50 °C for 48 h to obtain modified sweet potato starch samples. Based on the different starch matrix modification conditions, the starch samples were named NS-S (natural starch, control), 55%CA-DES-S (based on starch esterified with 55% citric acid in DES), 70% CA-DES-S (based on starch esterified with 70% citric acid in DES), 55% CA-AQ-S (based on starch esterified with 55% citric acid in an aqueous medium), and 70% CA-AQ-S (based on starch esterified with 70% citric acid in an aqueous medium).

[0063] (III) Preparation of ferulic acid co-pigment anthocyanins

[0064] 3.1) Dissolve ferulic acid (FA) in anhydrous ethanol to prepare a ferulic acid stock solution with a concentration of 1 mg / mL;

[0065] 3.2) Dissolve anthocyanins (BA) in acidified ethanol (pH 3.0) to form an anthocyanin solution of 0.2 mg / mL;

[0066] 3.3) Mix the ferulic acid stock solution obtained in step 3.1) and the anthocyanin solution obtained in step 3.2) (ferulic acid and anthocyanin in a mass ratio of 5:1) and stir magnetically at 1000 rpm for 20 min at 25 °C to obtain a ferulic acid co-pigment anthocyanin (FA-BA) mixture.

[0067] (iv) Preparation of β-cyclodextrin (β-CD) encapsulated cinnamon oil (CIN)

[0068] 4.1) Dissolve 5 g of wall material β-CD in 37.5 mL of distilled water and stir at 800 rpm for 30 minutes at 55 °C to obtain a clear β-CD solution; dissolve 2.5 g of core material CIN in anhydrous ethanol and add it dropwise to the β-CD solution under controlled pressure using a peristaltic pump to make the total solids content (the ratio of the total mass of core material CIN and wall material β-CD to the volume of distilled water) 20%, w / v;

[0069] 4.2) After stirring the mixture obtained in step 4.1) at 45 °C for 2 h, let it cool naturally to 25 °C and maintain for 2 h, then heat it to 45 °C and react for 2 h, and then refrigerate it at 4 °C overnight.

[0070] 4.3) The mixture obtained in step 4.2) was vacuum filtered to collect the precipitate, washed three times with anhydrous ethanol, and dried at 50 °C in a convection oven (DHG-9247A, Shanghai Jinghong). The resulting powder was equilibrated in air at 25 °C for 24 h to allow the moisture content to reach equilibrium, thus obtaining cinnamon essential oil microcapsules (CIN@β-CD). The microcapsules (CIN@β-CD) were dispersed in distilled water to prepare a 20 mg / mL CIN@β-CD suspension.

[0071] (v) Preparation of dual-function intelligent food preservation film

[0072] 5.1) Dissolve the modified sweet potato starch (25 mg / mL) obtained in step 2.4) in distilled water, and gradually heat it to 65 °C until it is completely gelatinized under magnetic stirring. After cooling to 45 °C, first add the CIN@β-CD suspension prepared in step 4.3) and stir for 1 h, then add the FA-BA mixture prepared in step 3.3) and stir for 30 min to make the final film-forming solution have a BA concentration of 0.2 mg / mL, a FA concentration of 1 mg / mL, and a CIN@β-CD concentration of 2 mg / mL. Add a composite plasticizer to the film-forming solution: composed of glycerol and D-sorbitol in a mass ratio of 1:1. The mass of the composite plasticizer added is 35% (w / w) of the total mass of the dry polymer in the film-forming solution. After vigorous stirring, sonicate for 20 min to remove bubbles, and adjust the pH to 3.5 with 1 mol / L HCl to obtain the final film-forming solution.

[0073] 5.2) Pour 20 mL of the film-forming solution into a sterile petri dish with a diameter of 9 cm and dry at 45 ℃ for 48 h. Equilibrate the dried film at 25 ℃ and 85% relative humidity for more than 48 h until the film mass is constant. According to different starch matrix modification conditions, the films were named NS (natural starch film, control), 55% CA-DES (film based on starch esterified with 55% citric acid in DES), 70% CA-DES (film based on starch esterified with 70% citric acid in DES), 55% CA-AQ (film based on starch esterified with 55% citric acid in aqueous medium), and 70% CA-AQ (film based on starch esterified with 70% citric acid in aqueous medium).

[0074] Example 2: Performance Testing of Modified Sweet Potato Starch and Dual-Functional Smart Food Preservation Film

[0075] 1) Fourier transform infrared spectroscopy analysis

[0076] The ordered structure of starch samples was analyzed using a Fourier transform infrared spectroscopy (IRTracer-100, Shimadzu Corporation Co., Ltd., Japan), with a scanning range of 400-4000 cm⁻¹. -1 The resolution is 4 cm. -1 . Figure 1 The results show that the FT-IR spectra of all starch samples exhibit the characteristic absorption bands of natural starch, mainly including the band at approximately 3414 cm⁻¹. -1 The wide OH stretching vibration at approximately 2931 cm -1 The CH stretching vibration at [location missing]. Key evidence for successful citric acid grafting is the presence of [spectral density missing] at ~1730 cm⁻¹ in all modified starch samples. -1A new, distinct absorption peak appeared, attributed to the C=O stretching vibration of the ester carbonyl group formed between citric acid and starch hydroxyl groups, indicating that the esterification reaction occurred in both aqueous and DES media. However, compared to the aqueous system, the OH region (3300-3500 cm⁻¹) of the citric acid-modified sample in DES was significantly larger. -1 The reaction exhibited more pronounced broadening and intensity changes. This can be attributed to the unique role of DES as a solvent. FT-IR results indicate that DES, as a reaction medium, more effectively promoted the esterification reaction.

[0077] 2) X-ray diffraction analysis

[0078] The crystal structure of starch was characterized using an X-ray diffractometer (S2 PUMA, Bruker AXS GmbH Co., Ltd., Germany). The test conditions were as follows: Cu Kα radiation (λ=0.154 nm), scan range 5°–35° (2θ), step size 0.01°, scan speed 5° / min, operating voltage 40 kV, and operating current 40 mA. Figure 2 X-ray diffraction patterns of sweet potato starch modified in DES and aqueous solution are shown. NS-S exhibits characteristic diffraction peaks at 15°, 17°, 18°, and 23° (2θ), indicating a typical A-type crystal structure. CA-AQ-S retains distinct diffraction peaks with additional sharp peaks at 7°, 13°, and 20° (2θ), showing a typical Vh-type crystal pattern. This structure typically originates from the rapid rearrangement and recrystallization of amylose into single helices during processing. In contrast, the sharp diffraction peaks in the corresponding angular range in the CA-DES-S sample are significantly weakened and transformed into broad, diffuse peaks, indicating that the crystal structure is disrupted and transitions to an amorphous state, a trend that becomes more pronounced with increasing citric acid content.

[0079] 3) Co-pigmentation of anthocyanins by phenolic acids

[0080] Stock solutions of caffeic acid (AA) and ferulic acid (FA) were prepared in anhydrous ethanol (1 mg / mL), and anthocyanins (BA) were dissolved in acidified ethanol (pH 3.0) at 0.2 mg / mL. Each phenolic acid solution was mixed with the BA solution at a mass ratio of 5:1. The mixtures were homogenized at 25 °C and 1000 rpm for 20 min using a magnetic stirrer. A control containing only BA solution was prepared under the same conditions. Color changes of BA (control group, CK), ferulic acid-anthocyanin (FA-BA), and caffeic acid-anthocyanin (AA-BA) in buffer solutions (pH 3.0–11.0) were recorded using a camera (EOS 90D, Canon China). All samples were stored in clear glass vials at 25 °C for 8 days to assess color stability.

[0081] like Figure 3 As shown, CK, FA-BA, and AA-BA exhibit significant color changes in different pH buffer solutions. In acidic to neutral environments (pH 3-5), the anthocyanin solution gradually changes from red to pink, which is mainly attributed to the red 2-phenylbenzoylbenzodiazepine cation (…). flavylium cation The dominant form of flavonoids is flavonoid cations. As the pH increases, flavonoid cations react with hydroxide ions to form colorless methanolic pseudobases and chalcone structures, causing the solution to gradually fade to a light purple color. Under alkaline conditions (pH 8-9), the flavonoid cation structure is extremely unstable and undergoes deprotonation to form quinone bases, making the solution appear blue-green. When the pH is further increased to above 11, the solution turns yellow due to the increased proportion of chalcone forms.

[0082] 4) Ultraviolet-Visible Absorption Spectrum

[0083] The UV-Vis absorption spectra of CK, AA-BA, and FA-BA were determined using a UV spectrophotometer in the wavelength range of 350–800 nm. McIlvaine buffer solutions with pH values ​​of 2–8 were prepared using a citrate-disodium hydrogen phosphate system. Samples were diluted with the appropriate pH buffer to the linear absorbance range (0.2–1.0 AU), and measurements were performed using 1 cm quartz cuvettes at 25 °C. Figure 4 In the BA solution, the maximum UV-Vis absorption peak red-shifted with increasing pH, from 500 nm to 550 nm. Notably, the addition of phenolic acids (especially FA) significantly increased both the maximum absorption wavelength and absorbance of the composite solution, indicating intermolecular cochromaticization and a strong red-shift and color-enhancing effect. pH 8-9 is a critical range in the spoilage process of high-protein foods; the FA-BA system still exhibited significant color responsiveness and optical enhancement within this range, demonstrating its promising application potential in real-time monitoring of intelligent packaging. (Solution color change trend) Figure 3 ) and ultraviolet-visible spectroscopy ( Figure 4 The data were highly consistent, further verifying the enhancing effect of ferulic acid on the stability and color development of anthocyanins.

[0084] 5) Preparation optimization and characterization of cinnamon essential oil microcapsules

[0085] β-CD was dissolved in distilled water as the wall material and stirred at 800 rpm for 30 minutes at 55 °C to obtain a clear β-CD solution. Cinnamon oil (CIN) was dissolved in anhydrous ethanol as the core material. Different preparation conditions were set by adjusting the mass ratio of core material to wall material (CIN:β-CD, w / w) and the total solids content (the ratio of the total mass of core material and wall material to the volume of distilled water, w / v). The mass ratio of core material to wall material (core-to-wall ratio) was set to 1:1, 1:2, 1:4, and 1:8, and the total solids content was set to 10%, 15%, 20%, and 25%, respectively. Experiments determined that the optimal conditions for microcapsule preparation were a core-to-wall ratio of 1:2 and a total solids content of 20%. β-CD (5 g) was dissolved in 37.5 mL of distilled water (to achieve a total solids content of 20%, w / v) and stirred at 800 rpm for 30 minutes at 55 °C. CIN (2.5 g) was dissolved in anhydrous ethanol and added dropwise to the β-CD solution under controlled pressure using a peristaltic pump. The mixture was stirred at 45 °C for 2 hours, gradually cooled to 25 °C and held for 2 hours, then reheated to 45 °C and held for another 2 hours. It was then refrigerated overnight at 4 °C to complete precipitation. The precipitate was collected by vacuum filtration, washed three times with anhydrous ethanol, and dried at 50 °C. Finally, the powder was equilibrated at 25 °C for 24 hours.

[0086] Accurately weigh 0.15 g of microcapsule powder into a centrifuge tube, add 30 mL of anhydrous ethanol solution, and soak for 12 h to ensure complete extraction. Centrifuge at 4500 rpm for 10 min, take the supernatant, dilute appropriately, and measure the absorbance at the maximum absorption wavelength of 289 nm. Calculate the essential oil content (V1) in the microcapsules according to the standard curve. The encapsulation efficiency is calculated using the following formula:

[0087]

[0088] In the formula: V1 is the amount of essential oil in the microcapsule (mL), and V2 is the amount of essential oil added during preparation (mL).

[0089] like Figure 5As shown, the core-to-wall ratio and total solids content significantly affect the encapsulation efficiency of cinnamon essential oil microcapsules. Within a certain range, the encapsulation rate first increases and then decreases with the increase of the core-to-wall ratio, reaching its maximum at a core-to-wall ratio of 1:2. This phenomenon can be attributed to the saturation effect of the wall material's encapsulation capacity: when the core material ratio is too low, the wall material is not fully utilized, resulting in a low encapsulation rate; while when the core material ratio is too high, it exceeds the effective encapsulation capacity of the wall material, causing some essential oil to be lost during preparation and drying. On the other hand, the total solids content also significantly affects the encapsulation efficiency. The encapsulation effect is optimal when the total solids content is 20%. Both excessively high and excessively low total solids contents are detrimental to the formation of a stable encapsulation structure: when the total solids content is low, the wall material concentration is insufficient, and the encapsulation interface is incomplete; when the content is too high, it may lead to increased system viscosity, restricted molecular motion, and affect the self-assembly efficiency during the encapsulation process.

[0090] In summary, this invention determines that a core-to-wall ratio of 1:2 (CIN:β-CD, w / w) and a total solids content of 20% (the ratio of the total mass of the core material and wall material to the volume of distilled water, w / v) are the optimal conditions for microcapsule preparation. This combination not only exhibits the best encapsulation efficiency but also balances the stability of the microcapsules with the feasibility of practical production, laying the foundation for their subsequent application in active packaging systems.

[0091] 6) Preparation of bifunctional composite membranes

[0092] FA was dissolved in anhydrous ethanol, and BA was dissolved in citrate-phosphate buffer (pH 3.0) to prepare stock solutions, which were then mixed to obtain a mixed FA-BA solution. Simultaneously, the CIN@β-CD microcapsules with the highest encapsulation efficiency were dispersed in distilled water to obtain a 20 mg / mL suspension. Modified sweet potato starch (25 mg / mL, in distilled water) was gelatinized by stirring and heating to 65 °C, then cooled to 45 °C. 80 mL of this gelatinized starch solution was used as the matrix. 10 mL of the CIN@β-CD suspension (20 mg / mL) was added and stirred for 1 hour, followed by the addition of the FA-BA stock solution (10 mL, containing 2 mg / mL BA and 10 mg / mL FA), and stirring for 30 minutes. The final volume of the film-forming solution was 100 mL, with target concentrations of 2 mg / mL CIN@β-CD, 0.2 mg / mL BA, and 1 mg / mL FA. A glycerol-D-sorbitol mixture (1:1, 35% w / w based on dry polymer) was incorporated as a plasticizer under vigorous stirring. The mixture was sonicated (F-040FR80, Shenzhen Fuyang Technology Group Co., Ltd., China) for 20 minutes to remove air bubbles, and the pH was adjusted to 3.5 with 1 mol / L HCl to obtain the film-forming solution.

[0093] 20 mL of the film-forming solution was poured onto 9 cm culture dishes and dried at 45 °C for 48 hours. Prior to characterization, the dried films were conditioned at 25 °C and 85% RH for ≥48 hours. Films were designated according to the starch matrix modification conditions as follows: NS (natural starch film, control), 55% CA-DES (film based on starch esterified with 55% citrate in DES), 70% CA-DES (film based on starch esterified with 70% citrate in DES), 55% CA-AQ (film based on starch esterified with 55% citrate in aqueous medium), and 70% CA-AQ (film based on starch esterified with 70% citrate in aqueous medium).

[0094] 7) Color stability of bifunctional membranes

[0095] The morphology of NS, 55% CA-DES, 70% CA-DES, 55% CA-AQ, and 70% CA-AQ films was photographed at preparation time (day 0) and after exposure to buffer solutions ranging from pH 2 to 12. As a core functionality, the pH response behavior of the films was demonstrated by significant color changes over a wide pH range (2.0–12.0). Figure 6 As shown, the film exhibits a rapid and visually distinguishable color transition, evolving from red under acidic conditions to pink, then blue-green, and finally turning yellowish-brown under strongly alkaline conditions (pH 12.0). This behavior is closely related to that of free BA, confirming that BA retains its inherent pH-responsive properties within the film matrix. Even under extreme pH conditions, the rapid response indicates excellent ion permeability and molecular mobility, highlighting the effectiveness of the starch matrix in promoting the dispersion and mass transfer of functional components.

[0096] 8) Determination of mechanical properties

[0097] The film sample was placed in an environment of 25 ℃ and 50% relative humidity for 48 h to achieve moisture equilibrium. The equilibrated film was then cut into rectangular strips of 50 mm × 10 mm. The thickness and width of the strips were measured at five random locations using a digital micrometer, and the initial gauge length between the fixtures was recorded. Tensile properties were determined using a texture analyzer, stretching the strips at a beam speed of 50 mm / min until fracture. The tensile strength (MPa) and elongation at break (%) were calculated based on the stress-strain curve. Figure 7As shown, the NS film exhibits poor mechanical properties, with low peak loading and deformation, attributed to weak intermolecular forces and disordered polymer arrangement in natural starch. After citric acid modification, both tensile strength and flexibility are significantly improved. The peak loadings of 55% CA-DES and 70% CA-DES are 9.31 N and 9.59 N, respectively, with deformations of 11.58 mm and 10.82 mm, significantly higher than that of the NS film (6.31 mm). This enhancement can be attributed to the introduction of ester bonds between starch chains through citric acid modification, thereby strengthening the polymer network and improving stress dissipation. The superior performance of the 70% CA-DES film indicates higher esterification efficiency. In contrast, the improvement of CA-AQ is limited, possibly due to insufficient reaction efficiency and poor dispersibility of citric acid in water, leading to heterogeneity.

[0098] 9) Scanning electron microscope (SEM)

[0099] The surface and cross-sectional morphology of the thin film samples were observed using a scanning electron microscope (SEM). Images were captured at an accelerating voltage of 10 kV and a magnification of 700x. The SEM images provide a detailed understanding of the surface and cross-sectional morphology of the thin films. Figure 8 NS films exhibit a relatively loose and heterogeneous structure, indicating limited intermolecular interactions and inherent film-forming discontinuities. In contrast, CA-AQ film media exhibit a rough surface with identifiable granular protrusions and porous, fractured cross-sections. This microstructure not only indicates insufficient cross-linking but also poor compatibility and inhomogeneity within the formed network, potentially leading to phase separation. This directly results in compromised mechanical integrity and barrier properties of the film. Conversely, CA-DES film media exhibit a distinctly different morphology. Their surfaces are quite smooth, and the cross-sections show dense, uniform, and viscous fractured surfaces. This uniform microstructure is characteristic of a well-integrated three-dimensional network, resulting from a more efficient and uniform esterification cross-linking reaction. The unique solvation properties of DES facilitate the penetration and molecular-level dispersion of citric acid in the starch matrix, thereby promoting extensive esterification and forming films with enhanced structural integrity and stability.

[0100] 10) Atomic Force Microscopy (AFM)

[0101] The surface morphology of the thin film samples was studied using atomic force microscopy. Measurements were taken in tapping mode at 5 × 5 μm. 2 The scanning area was scanned at a speed of 0.5 Hz. AFM images ( Figure 9The results show significant morphological variations among starch-based films, directly reflecting differences in their internal structure. NS films exhibit a moderately rough surface, while CA-AQ films show significantly increased roughness and pronounced protrusions. The observed surface morphology suggests the formation of heterogeneous and poorly integrated crosslinked networks during aqueous modification, which may limit the effective stacking and fusion of starch molecular chains. Conversely, CA-DES films exhibit an exceptionally smooth and uniform surface morphology. This surface smoothness indicates that the DES environment promotes a more uniform and thorough crosslinking reaction between citric acid and starch macromolecules, forming a highly continuous and dense network, thereby enhancing starch chain mobility and promoting better film formation.

[0102] 11) Water contact angle test

[0103] The hydrophilicity of cross-linked starch membranes was evaluated using a contact angle meter. The membrane sample was fixed to a glass slide with double-sided tape, and a 5 μL drop of distilled water was dropped onto the membrane surface using a microsyringe via the seat-drop method. Images were acquired and contact angle values ​​were measured within 5 seconds of droplet deposition. Figure 10 As shown, CA-DES significantly enhances the overall performance of starch-based films, promoting a functional transition from hydrophilic to hydrophobic, from limited antioxidant activity to enhanced antioxidant activity, and from low barrier properties to high barrier properties. The hydrophobicity is improved after DES-mediated modification, with the 55% CA-DES group achieving a contact angle of 118.9°. This enhancement is attributed to the slow and controlled esterification reaction in DES, which promotes the uniform formation of hydrophobic ester bonds and effective shielding of hydrophilic hydroxyl groups. In contrast, water modification results in limited hydrophobicity (90.9°) due to low reaction efficiency and significant hydrolysis.

[0104] 12) Antibacterial properties

[0105] Antibacterial activity against Staphylococcus aureus (ATCC 6538) and Escherichia coli (ATCC 8739) was evaluated using the agar diffusion method. The composite membrane was cut into 7 mm diameter discs and sterilized under UV light for 30 minutes. 100 μL of bacterial suspension (10... 5 The sterile membrane (CFU / mL) was evenly spread onto a nutrient agar plate, and then placed on the agar surface inoculated with the bacterial solution. After incubation at 36±1 ℃ for 24 h, the diameter of the inhibition zone was measured. Antibacterial performance test (… Figure 11Quantitative studies confirmed the practical potential of these bifunctional films. Films doped with CIN@β-CD exhibited significant inhibition zones against Staphylococcus aureus and Escherichia coli, indicating effective antibacterial activity through the release of volatile compounds. Even films modified solely with citric acid and lacking CIN@β-CD showed measurable antibacterial properties; this inherent activity highlights the antibacterial contribution of the citric acid crosslinking network. Notably, the 70% CA-DES film showed the strongest efficacy against Staphylococcus aureus (inhibition zone radius: 8.05 ± 0.05 mm), while the 55% CA-DES film was most effective against Escherichia coli (inhibition zone radius: 11.15 ± 0.10 mm). This differential inhibition is closely related to the film's microstructure, which controls the release of volatiles. The dense and coherent network formed in the CA-DES film (e.g., Figure 8 , Figure 9 The structural features shown in the encapsulated CIN may contribute to more controlled and sustained release of the encapsulated CIN, preventing rapid dissipation and thus improving antimicrobial efficacy.

[0106] 13) Observation of the apparent changes of the film and chicken meat

[0107] The color changes of chicken breast samples (CB), dual-function smart preservation film (BF), and chicken samples wrapped in film (F-WC) were recorded using a digital camera under constant lighting conditions during storage. Photos were taken every 4 days for 12 consecutive days. Figure 12 As shown, significant differences in the visual appearance of chicken samples across treatment groups were observed during storage. By day 12, all samples exhibited varying degrees of spoilage, including mold, blackening, yellowing, and surface slime. This sustained preservation efficacy under non-refrigerated conditions demonstrates the film's ability to maintain a protective microenvironment through synergistic barrier and antimicrobial functions. The film combines effective oxygen / moisture barrier properties with sustained antimicrobial activity by controlling CIN release, properties particularly valuable for practical applications with limited temperature control. Notably, the bifunctional film not only effectively preserves the chicken but also provides real-time visual monitoring of freshness: its color ranges from pink (fresh) to light purple (early spoilage) and finally to dark green (late spoilage), consistent with the gradual decline in packaging quality.

[0108] 14) TBARS value determination

[0109] Weigh 4 g of meat sample and add 10 mL of 20% trichloroacetic acid solution to homogenize for 1.5 minutes. Incubate at 25 °C for 15 minutes, then add 10 mL of deionized water and filter through Whatman 6 filter paper. Mix 5 mL of the filtrate with 5 mL of 0.005 M thiobarbituric acid solution, heat in a water bath at 80±1 °C for 30 minutes, cool to 25 °C, centrifuge, and measure the absorbance of the supernatant at 530 nm. Correct with a blank sample and calculate the TBARS value (mg MDA / kg meat) using a malondialdehyde standard curve. Lipid oxidation (...) is assessed by the TBARS value. Figure 13 The effects of CIN@β-CD were also effectively mitigated. The control sample exceeded the threshold for high-quality meat (0.66 mg / kg) on ​​day 6 (0.68 mg / kg), while the 70% CA-DES group (exhibiting the best preservation performance) remained within acceptable limits (0.59 mg / kg) until day 8. This delay in lipid oxidation can be attributed to the antioxidant activity of released CIN.

[0110] 14) TVB-N value determination

[0111] Take 10 g of meat sample and homogenize it with 60 mL of 5% trichloroacetic acid solution for 5 minutes. After standing for 30 minutes, filter. Take 10 mL of the filtrate and add it to a digestion tube. Add 0.5 g of magnesium oxide and distill using a micro Kjeldahl nitrogen determination apparatus. Collect the distillate with an absorbent containing boric acid and titrate with 0.01 N hydrochloric acid. The result is expressed as milligrams of nitrogen per 100 g of meat (mg N / 100 g). TVB-N value ( Figure 14 TVB-N is a key indicator for assessing meat freshness, and its increase is mainly attributed to microbial degradation of proteins. According to the standard GB2707-2016 for fresh (chilled) livestock and poultry products, the TVB-N content in fresh meat must not exceed 15 mg / 100g. The TVB-N value in the control group reached 15.31 mg / 100g on day 6, making the product commercially unacceptable. In contrast, the CIN@β-CD group did not exceed this threshold until day 8 and maintained a significantly lower TVB-N value than the control group at the end of storage (day 12; P<0.05). This finding indicates that microcapsules effectively inhibit microbial degradation of proteins, thereby preserving meat quality.

[0112] 16) Correlation analysis between chicken quality and color response of bifunctional membrane

[0113] To evaluate the applicability of the bifunctional membrane in monitoring chicken freshness, a time correlation analysis was conducted on key chicken quality indicators and membrane color parameters during storage (days 4, 8, and 12). Figure 15The heatmap illustrates the Pearson correlation coefficient, with red and blue shading representing positive and negative correlations, respectively; color intensity corresponds to the strength of the correlation. Notably, the color depth in the heatmap increases significantly over time, particularly after day 8, indicating the color parameters of the film (…). L*, a*, b* The correlation between the color value and chicken spoilage indicators gradually increased with prolonged storage time. Total volatile base nitrogen (TVB-N) and thiobarbituric acid reactive substances (TBARS) showed a strong negative correlation with color value (|r|>0.8), and these correlations became more pronounced with increasing spoilage, indicating that changes in the film color are increasingly sensitive to meat deterioration. Conversely, firmness consistently showed a weak correlation with color changes.

[0114] 17) Environmental degradation behavior of dual-function smart food preservation film

[0115] To evaluate the biodegradability of five starch-based films, soil degradation tests were conducted, with commercial food wrap (FWP) used as a control. Experiments were performed at 25 ± 2 °C and soil moisture maintained at 60–80%. All film samples were cut into discs with a radius of 2 cm. After measuring the initial dry weight, the samples were buried 3 cm deep in the soil and retrieved after 7, 14, 21, 28, and 35 days. The recovered samples were washed, dried to constant weight, and weighed to determine the percentage of mass loss. Morphological changes were photographed at each interval. Figure 16 Macroscopic changes in the films during soil burial were recorded. The films in the experimental group showed gradual degradation over a 35-day burial period, while the changes in the control group were negligible, confirming their non-biodegradable nature. Notably, compared to citric acid-modified starch films (CA-DES, CA-AQ), the NS films degraded more slowly. Before day 21, the NS films maintained their basic structural integrity but exhibited significant shrinkage and hardening. This delayed degradation pattern of the NS films can be attributed to their more compact molecular structure, which may limit microbial accessibility and enzymatic activity. After 7 days, a significant color change to dark blue was observed in all experimental films, consistent with the measured soil pH range of 7.5.

[0116] In summary, this invention creates an ideal starch matrix through DES-mediated citric acid esterification, integrating BA indicators and CIN microcapsules to produce a bifunctional smart preservation film with superior barrier properties, real-time pH-responsive color indication, and sustained antimicrobial activity. The film's color change is closely correlated with chicken spoilage indicators, and due to its effective inhibition of microbial growth and lipid oxidation, it extends shelf life at room temperature by approximately 35%-40%. The successful development of this smart film system not only validates DES-mediated citric acid-modified starch as a promising smart packaging material but also provides technical support for enhancing the properties of sweet potato starch to achieve high-value utilization and promote sustainable agriculture. These findings ensure future scalability and commercial storage evaluation while opening new avenues for development.

Claims

1. A method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch, characterized in that, Includes the following steps: 1) Preparation of eutectic solvent DES: Choline chloride and ethylene glycol were mixed in a sealed beaker at a molar ratio of 1:2, heated to 95 °C and stirred continuously for 6 hours until a homogeneous transparent liquid was formed; the resulting homogeneous transparent liquid was filtered and dried in an oven at 50 °C for 12 hours. 2) Dissolving sweet potato starch: Weigh 2.0 g of dry sweet potato starch and add it to 100 mL of the eutectic solvent DES obtained in step 1). Stir continuously for 4 h in an oil bath at 100°C until the sweet potato starch is completely dissolved. 3) Citric acid modification: Citric acid was added to the sweet potato starch dissolution system obtained in step 2), and sodium hypophosphite was used as a catalyst. The reaction was carried out at 100 °C for 2 h, and then the reaction mixture was cooled to room temperature. 4) Filtration: Wash the reaction mixture obtained in step 3) with anhydrous ethanol and filter it three times to remove residual reagents; 5) Drying: Place the product obtained in step 4) in a vacuum drying oven and dry at 50 °C for 48 h to obtain the modified sweet potato starch sample; 6) Dissolving ferulic acid: Dissolve ferulic acid in anhydrous ethanol to form a ferulic acid stock solution; 7) Dissolving anthocyanins: Dissolve anthocyanins in acidified ethanol at pH 3.0 to form an anthocyanin solution; 8) Mixing: The ferulic acid stock solution obtained in step 6) and the anthocyanin solution obtained in step 7) are mixed and magnetically stirred at 1000 rpm for 20 min at 25 °C to obtain a ferulic acid co-pigment anthocyanin mixed solution. 9) Mixing β-cyclodextrin and cinnamon essential oil: Dissolve β-CD as a wall material in distilled water and stir at 800 rpm for 30 minutes at 55 °C to obtain a clear β-CD solution; dissolve CIN as a core material in anhydrous ethanol and add it dropwise to the β-CD solution under controlled pressure using a peristaltic pump; 10) Heating: After stirring the mixture obtained in step 19) at 45 °C for 2 h, let it cool naturally to 25 °C and maintain for 2 h, then heat it to 45 °C and react for 2 h. 11) Refrigeration: Refrigerate the mixture obtained in step 10) at 4 °C overnight; 12) Vacuum filtration: The mixture obtained in step 11) is vacuum filtered to collect the precipitate, which is then washed three times with anhydrous ethanol; 13) Drying: The product obtained in step 12) was dried in a convection oven at 50 °C. The resulting powder was equilibrated in air at 25 °C for 24 h to allow the moisture content to reach equilibrium, thus obtaining cinnamon essential oil microcapsules CIN@β-CD. The microcapsules CIN@β-CD were dispersed in distilled water to prepare a 20 mg / mL CIN@β-CD suspension. 14) Mixing: Dissolve the modified sweet potato starch obtained in step 5) in distilled water, and gradually heat it to 65 ℃ under magnetic stirring until it is completely gelatinized. After cooling to 45 ℃, add the CIN@β-CD suspension prepared in step 13) and stir for 1 h. Then add the ferulic acid co-pigment anthocyanin mixture obtained in step 8) and stir for 30 min. Add the composite plasticizer, stir vigorously, and then sonicate for 20 min to remove bubbles. Adjust the pH to 3.5 with 1 mol / L HCl to obtain the film-forming solution. 15) Film formation: Pour 20 mL of film-forming solution into a sterile petri dish with a diameter of 9 cm, dry at 45 ℃ for 48 h, and equilibrate the dried film at 25 ℃ and 85% relative humidity for more than 48 h until the quality of the film is constant, thus obtaining a dual-function intelligent preservation film based on citric acid modified sweet potato starch.

2. The method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch according to claim 1, characterized in that, In step 3), the amount of citric acid added is 55% or 70% of the dry weight of sweet potato starch.

3. The method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch according to claim 2, characterized in that, In step 3), the amount of citric acid added is 70% based on the dry weight of sweet potato starch.

4. The method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch according to claim 1, characterized in that, In step 3), the amount of sodium hypophosphite added is 50% of the mass of citric acid.

5. The method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch according to claim 1, characterized in that, In step 6), the concentration of ferulic acid stock solution is 1 mg / mL; in step 7), the concentration of anthocyanin solution is 0.2 mg / mL.

6. The method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch according to claim 1, characterized in that, In step 8), the mass ratio of ferulic acid to anthocyanin in the ferulic acid co-pigment anthocyanin mixture is 5:

1.

7. The method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch according to claim 1, characterized in that, In step 9), the mass ratio of core material CIN to wall material β-CD is 1:2, and the ratio of the total mass of core material CIN and wall material β-CD to the volume of distilled water is 20%.

8. The method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch according to claim 1, characterized in that, In step 14), the modified sweet potato starch is dissolved in distilled water at a concentration of 25 mg / mL.

9. The method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch according to claim 1, characterized in that, In step 14), the film-forming solution contains CIN@β-CD at a concentration of 2 mg / mL, anthocyanins at a concentration of 0.2 mg / mL, and ferulic acid at a concentration of 1 mg / mL.

10. The method for preparing a dual-functional smart food preservation film based on citric acid-modified sweet potato starch according to claim 1, characterized in that, In step 14), the composite plasticizer is composed of glycerol and D-sorbitol in a mass ratio of 1:1, and the added mass of the composite plasticizer is 35% of the total mass of the dry polymer in the film-forming solution.

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