A caffeic acid-amino acid complex grafted starch, and a preparation method and application thereof

Abstract

The application discloses a caffeic acid-amino acid composite grafted starch and a preparation method and application thereof. The preparation method comprises the following steps: using a catalytic system comprising 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine to catalyze caffeic acid to be selectively grafted to primary hydroxyl groups at C6 of high amylose starch, so as to prepare caffeic acid selectively grafted starch; then, amino acid is added to continue the reaction, so as to prepare caffeic acid-amino acid composite grafted starch; and the amino acid mainly reacts with secondary hydroxyl groups at C2 and C3 of the high amylose starch. The composite grafted starch in the application has excellent emulsification stability, gelation characteristics and biological activity by using the synergistic effect between functional groups, the prepared emulsion gel has an encapsulation rate of active substances of more than 93%, a storage stability of more than 90 days, and a significant enhancement of antioxidant capacity, and the inhibition rate of pathogenic bacteria is greater than or equal to 99.9%, so that the composite grafted starch can be widely applied to high-end skin care cosmetics such as face cream and sunscreen cream.

Description

Technical Field

[0001] This invention belongs to the field of daily chemical technology, specifically relating to a caffeic acid-amino acid composite grafted starch, its preparation method, and its application. Background Technology

[0002] High-amylose corn starch is a type of natural polysaccharide widely used in the food, pharmaceutical, and cosmetic industries, exhibiting good biocompatibility, biodegradability, and a certain gel-forming ability. However, natural high-amylose corn starch is significantly hydrophilic, and its gelatinized dispersion has limited adsorption capacity at the oil-water interface, making it difficult to form a stable interfacial layer on the surface of oil droplets. Consequently, its direct use in oil-water emulsions often results in insufficient stability. Furthermore, natural starch itself lacks antioxidant and antibacterial activities, failing to meet the current comprehensive requirements for bioactivity and stability in functional emulsions or emulsion gels.

[0003] To improve the interfacial properties and functional attributes of starch, current research generally involves chemically modifying starch to alter its amphiphilicity or introduce active groups. Among these, esterification modification of polysaccharides using polyphenolic compounds such as gallic acid, ferulic acid, and caffeic acid is a common strategy in recent years. The introduction of polyphenolic groups can improve the hydrophobicity and antioxidant capacity of starch to some extent. However, existing single-phenolic acid modified starch still faces significant technical bottlenecks: First, interfacial adsorption and film-forming capabilities remain limited. While introducing single phenolic acid groups improves amphiphilicity, in constructing high internal phase emulsions (HIPE, oil phase volume fraction >74%), insufficient interfacial film mechanical strength or steric hindrance often makes it difficult to resist the compression and aggregation of high-concentration oil droplets, resulting in the inability to form a stable gel-like paste, thus limiting its application in high-oil-phase formulations such as high-end face creams; Second, functional activity has shortcomings. While phenolic acids possess antioxidant properties, their antibacterial mechanism is limited, exhibiting weak cell membrane penetration against some pathogenic bacteria (especially Gram-negative bacteria), making it difficult to achieve highly effective broad-spectrum antibacterial activity. Therefore, developing a novel composite modified starch material that synergistically enhances interfacial adsorption performance, high internal phase emulsion stability, and broad-spectrum bioactivity is of great significance for the construction of functional emulsions and cosmetic matrices. Summary of the Invention

[0004] The main objective of this invention is to provide a caffeic acid-amino acid composite grafted starch, its preparation method, and its application, to solve the technical problems of natural starch, such as weak interfacial adsorption, insufficient stability, lack of functional activity, unstable emulsification, low encapsulation rate of active substances, lack of antioxidant and antibacterial properties, and limited interfacial regulation capabilities due to single modification methods. To achieve the aforementioned objective, the technical solution adopted by this invention includes:

[0005] This invention provides a method for preparing caffeic acid-amino acid composite grafted starch, comprising: using a catalytic system containing 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine to catalyze the selective grafting of caffeic acid onto the C6 primary hydroxyl group of high amylose starch to obtain caffeic acid selectively grafted starch; then adding amino acids to continue the reaction to obtain caffeic acid-amino acid composite grafted starch; wherein the amino acids mainly react with the C2 and C3 secondary hydroxyl groups of high amylose starch.

[0006] The present invention also provides a caffeic acid-amino acid composite grafted starch prepared by the aforementioned preparation method, characterized in that: the caffeic acid grafting degree in the caffeic acid-amino acid composite grafted starch is 2~14%, and the amino acid grafting degree is 1~5%.

[0007] This invention also provides the application of the aforementioned caffeic acid-amino acid composite grafted starch in the preparation of emulsion gels.

[0008] This invention also provides a method for preparing a functional emulsion gel carrying active ingredients, comprising:

[0009] Provide the aforementioned caffeic acid-amino acid composite grafted starch;

[0010] The caffeic acid-amino acid composite grafted starch was mixed with water and gelatinized to obtain a stabilizer solution; the active substance was mixed with vegetable oil to form an oil phase;

[0011] Furthermore, the oil phase is mixed with a stabilizer solution, homogenized, and allowed to stand at low temperature to obtain a functional emulsion gel carrying active ingredients.

[0012] The present invention also provides a functional emulsion gel loaded with active ingredients prepared by the aforementioned preparation method. The functional emulsion gel loaded with active ingredients has a three-dimensional cross-linked network structure and does not flow when the container is inverted. The encapsulation rate of active substances in the functional emulsion gel loaded with active ingredients is above 93%.

[0013] The present invention also provides the application of the aforementioned functional emulsion gel carrying active ingredients in the preparation of skin care cosmetics with antibacterial, antioxidant and anti-aging effects, wherein the skin care cosmetics include face cream, sunscreen and / or face mask.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] (1) A synergistic interface layer with a specific spatial conformation was constructed: This invention utilizes a sequential selective grafting strategy to achieve orthogonal functionalization of caffeic acid (C6 position) and amino acids (C2 / C3 position). In particular, when an amino acid containing an aromatic side chain (such as tryptophan) is introduced, its indole ring can generate a strong π-π stacking effect with the benzene ring of caffeic acid. Combined with hydrophobic interaction, a rigid, dense and highly viscoelastic "armor-like" protective film is constructed at the oil-water interface, which significantly solves the problem of insufficient strength of the interface film of single modified starch.

[0016] (2) The present invention has excellent high internal phase emulsion (HIPE) construction ability: thanks to the excellent amphiphilic balance and interfacial strength brought about by composite grafting, the modified starch can not only stabilize ordinary emulsions, but also stabilize high internal phase emulsions with an oil phase volume fraction of up to 75%~85%; under extremely high oil phase conditions, the modified starch particles can effectively isolate the tightly packed oil droplets (exhibiting a polyhedral structure), prevent them from agglomerating, and induce the continuous phase to form a strong gel network, thereby obtaining a solid emulsion system with a fine texture, high yield stress and self-support, breaking through the bottleneck of traditional starch-based emulsifiers being difficult to prepare high oil phase creams;

[0017] (3) The present invention achieves "dual locking" and efficient protection of fat-soluble active ingredients: the encapsulation rate of active ingredients such as pterostilbene in the emulsion gel is over 93%; this is mainly due to: on the one hand, the aromatic groups (caffeic acid / tryptophan) at the interface strongly adsorb active molecules through the π-π conjugation effect; on the other hand, the dense interface film and the continuous phase gel network form a physical barrier, effectively blocking the leakage of active ingredients; in addition, the system has a significant shielding effect against ultraviolet light, which greatly improves the storage stability of photosensitive ingredients;

[0018] (4) This invention endows the material with broad-spectrum and highly efficient bioactivity: the composite grafted starch combines the electron donor properties of caffeic acid with the special functions of amino acid side chains: for thiol-containing amino acids (such as cysteine), it significantly enhances antioxidant capacity through strong reducing properties; for hydrophobic amino acids (such as tryptophan), it effectively inserts into and disrupts the cell membrane of bacteria (especially Gram-negative bacteria) using its strong hydrophobic side chains. This synergistic mechanism enables the material to enhance antioxidant (DPPH / ABTS) activity. + • It shows significant advantages in terms of high clearance rate and broad-spectrum antibacterial activity (inhibition rate of over 95% against Escherichia coli and Staphylococcus aureus), realizing the integration of efficacy of "carrier as active ingredient";

[0019] (5) The preparation process of the present invention is mild, the reaction raw materials are derived from natural small molecules, the system does not rely on toxic organic solvents and traditional synthetic surfactants, and the resulting emulsion gel has good biocompatibility, thixotropy and spreadability. By adjusting the types of amino acids and the grafting ratio, the rheological properties of the product (from emulsion to cream) can be precisely controlled, providing a new technical path for developing a high-end functional skin care system that combines "natural, safe and highly effective". Attached Figure Description

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

[0021] Figure 1 This is a comparative morphological diagram of natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) in a typical embodiment of the present invention.

[0022] Figure 2 This is a Fourier transform infrared spectrum of natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) in a typical embodiment of the present invention.

[0023] Figure 3 The fluorescence spectra of natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) are shown in a typical embodiment of the present invention.

[0024] Figure 4 These are scanning electron microscope (SEM) images of natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) in a typical embodiment of the present invention, wherein the top row is an image at ×500 magnification and the bottom row is an image at ×2.0k magnification.

[0025] Figure 5This is a comparison chart of the DPPH free radical scavenging rates of natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) in a typical embodiment of the present invention.

[0026] Figure 6 This is an ABTS of natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) in a typical embodiment of the present invention. +• Free radical scavenging rate comparison chart;

[0027] Figure 7 This is a comparison chart of the iron ion reduction antioxidant capacity (FRAP value) of natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) in a typical embodiment of the present invention.

[0028] Figure 8 This is a typical embodiment of the present invention showing the antibacterial effects of natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​complex grafted starch (8%Cf-3%Cys-HAMS) on Escherichia coli and Staphylococcus aureus, including photos of inhibition zones and statistical charts of inhibition zone diameters;

[0029] Figure 9 These are plate coating count photos and antibacterial rate statistics of natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) against Escherichia coli and Staphylococcus aureus in the embodiments of the present invention.

[0030] Figure 10 This is a fluorescence staining image of live / dead bacteria after treating Escherichia coli and Staphylococcus aureus with natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) in a typical embodiment of the present invention. SYTO 9 shows live bacteria (green), PI shows dead bacteria (red), and MERGE is a merged image.

[0031] Figure 11These are comparative images showing the appearance stability and texture of active ingredient-loaded emulsion gels prepared from natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) in the embodiments of the present invention.

[0032] Figure 12 This is a comparison chart of the emulsifying activity index (EAI) of natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) in a typical embodiment of the present invention.

[0033] Figure 13 This is an optical microscope image (scale bar is 200 μm) of an active ingredient-loaded emulsion gel prepared from natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) in the embodiments of the present invention.

[0034] Figure 14 This is a comparison chart of the encapsulation rates of the active ingredient pterostilbene in emulsion gels prepared from natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS) in embodiments of the present invention.

[0035] Figure 15 The Fourier transform infrared spectra of natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-tryptophan composite grafted starch (8%Cf-3%Trp-HAMS) in a typical embodiment of the present invention are shown below.

[0036] Figure 16 This is a visual appearance diagram of a high internal phase emulsion gel prepared from natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS), and caffeic acid-tryptophan composite grafted starch (8%Cf-3%Trp-HAMS) in a typical embodiment of the present invention.

[0037] Figure 17 This is an optical microscope image (scale bar is 200 μm) of the high internal phase emulsion gel loaded with active ingredients prepared by natural high amylose corn starch (HAMS), caffeic acid grafted starch (8%Cf-HAMS) and caffeic acid-tryptophan composite grafted starch (8%Cf-3%Trp-HAMS) in Example 2 of the present invention. Detailed Implementation

[0038] In view of the deficiencies of the prior art, the applicant of this case has proposed the technical solution of the present invention through long-term research and extensive practice. The present invention constructs a dual grafting structure of "aromatic ester structure + amino acid ester structure", so that high amylose starch has aromatic ester bonds, amino or thiol side chains at the same time, thereby improving the amphiphilicity and interfacial behavior of starch and enhancing its ability to form emulsion gel during gelatinization-cooling process, thereby achieving effective encapsulation and protection of fat-soluble active ingredients.

[0039] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Specifically, as one aspect of the technical solution of this invention, a method for preparing a caffeic acid-amino acid composite grafted starch includes:

[0041] A catalytic system comprising 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC·HCl) and 4-dimethylaminopyridine (DMAP) was used to selectively graft caffeic acid onto the C6 primary hydroxyl group of high amylose starch to prepare caffeic acid selectively grafted starch. Then, amino acids were added to continue the reaction to prepare caffeic acid-amino acid composite grafted starch. The amino acids mainly react with the C2 and C3 secondary hydroxyl groups of high amylose starch.

[0042] In some preferred embodiments, the preparation method specifically includes:

[0043] (1) Disperse high amylose in a solvent and stir at 70~90℃, then cool to 30~50℃ and add caffeic acid, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine and react for 8~16h, so that caffeic acid forms an ester bond with the C6 primary hydroxyl group in high amylose.

[0044] (2) Add amino acids to step (1) and supplement with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC·HCl), and then continue the reaction at 20~40℃ for 6~12h, so that the amino acids and the secondary hydroxyl groups at C2 and C3 in starch undergo esterification reaction. Then, after ethanol precipitation, dialysis and freeze drying, caffeic acid-amino acid composite grafted starch is obtained.

[0045] Furthermore, the high amylose includes any one or more combinations of high amylose corn starch, high amylose pea starch, high amylose potato starch, and high amylose rice starch, and is not limited thereto.

[0046] Furthermore, the amylose content in the high amylose content is ≥50%.

[0047] Furthermore, the solvent includes one or a combination of two of N,N-dimethylformamide and dimethyl sulfoxide (DMSO), and is not limited thereto.

[0048] Further, the mass ratio of high amylose to caffeic acid in step (1) is 10: (0.5~4.0).

[0049] Further, in step (1), the molar ratio of the carboxyl group of caffeic acid, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine is 1 : (1.0~2.0) : (0.05~0.5).

[0050] Furthermore, the amino acid includes any one or more combinations of lysine, cysteine, serine, and glycine, but is not limited thereto.

[0051] Furthermore, the mass ratio of the amino acid to the high amylose is (0.02~0.3):1.

[0052] This invention uses high-amylose corn starch as a matrix and grafts it with caffeic acid through a carbodiimide-catalyzed esterification reaction, introducing aromatic structures and phenolic hydroxyl groups into the starch molecules. Subsequently, amino acids are added, and polar side chains are further introduced through an esterification reaction. After washing and drying, a composite grafted starch containing aromatic ester bonds and amino / thiol side chains is obtained, wherein the grafting degree of caffeic acid is 2-14% and the grafting degree of amino acids is 1-8%. After the caffeic acid esterification is completed, amino acids are added. The carboxyl groups in the amino acid molecules are activated under the action of EDC and continue to undergo esterification reaction with the remaining hydroxyl groups of starch. The amino or other groups of the amino acid molecules do not participate in esterification and are thus completely preserved, becoming active sites for adsorption, hydrogen bonding, or polar interactions at the emulsion interface.

[0053] Another aspect of the present invention provides a caffeic acid-amino acid composite grafted starch prepared by the aforementioned preparation method, wherein the caffeic acid grafting degree in the caffeic acid-amino acid composite grafted starch is 2-14%, and the amino acid grafting degree is 1-8%.

[0054] Furthermore, the caffeic acid grafting degree in the caffeic acid-amino acid composite grafted starch is 4-12%, and the amino acid grafting degree is 1-5%.

[0055] Another aspect of the present invention provides the application of the aforementioned caffeic acid-amino acid composite grafted starch in the preparation of emulsion gels.

[0056] Another aspect of this invention provides a method for preparing a functional emulsion gel carrying active ingredients, comprising:

[0057] Provide the aforementioned caffeic acid-amino acid composite grafted starch;

[0058] The caffeic acid-amino acid composite grafted starch was mixed with water and gelatinized to obtain a stabilizer solution; the active substance was mixed with vegetable oil to form an oil phase;

[0059] Furthermore, the oil phase is mixed with a stabilizer solution and homogenized, and then allowed to stand at 0~10°C to obtain a functional emulsion gel carrying active ingredients.

[0060] In some preferred embodiments, the active substance includes any one or more combinations of polyphenols, flavonoids, carotenoids, and fat-soluble vitamins, but is not limited thereto.

[0061] Furthermore, the active substances include, but are not limited to, pterostilbene and / or resveratrol.

[0062] In some preferred embodiments, the content of caffeic acid-amino acid composite grafted starch in the functional emulsion gel carrying the active ingredient is 1-10 wt%, and the oil phase content is 30-85 wt%.

[0063] In some preferred embodiments, the gelatinization treatment is carried out at a temperature of 120~130℃ for a time of 0.5~2h.

[0064] In some preferred embodiments, the volume ratio of the oil phase to the stabilizer solution is 2:8 to 8.5:1.5.

[0065] In some preferred embodiments, the concentration of caffeic acid-amino acid composite grafted starch in the stabilizer solution is 3-8 wt%.

[0066] In some preferred embodiments, the mass fraction of the active substance in the oil phase is 0.1~1.0%.

[0067] In some preferred embodiments, the settling time is 4 to 24 hours.

[0068] This invention disperses composite grafted starch in an aqueous phase and heats it to gelatinize, forming a homogeneous starch system. An oil phase containing active ingredients is added to the thermally gelatinized system and homogenized and emulsified to obtain an emulsion. The emulsion, upon cooling, forms an emulsion gel with a three-dimensional network structure. The composite grafted starch simultaneously participates in oil droplet interface adsorption, continuous phase network construction, and gel structure reinforcement, thereby improving the stability of the emulsion gel and the encapsulation ability of active ingredients.

[0069] In some preferred embodiments, the method for preparing the functional emulsion gel carrying the active ingredient includes the following steps:

[0070] (1) First step of selective esterification: High straight-chain corn starch is added to N,N-dimethylformamide, stirred at 80°C for 1 h, and then cooled to 30°C. Caffeic acid, EDC·HCl and DMAP are added and reacted for 8~16 h, so that caffeic acid preferentially forms ester bonds with the C6 primary hydroxyl group with less steric hindrance on starch.

[0071] (2) Second step of orthogonal functionalization: Small molecule amino acids are directly added to the above reaction system, EDC·HCl is added, and the reaction is continued at 25℃ for 6-8h, so that the amino acids mainly undergo esterification with the remaining secondary hydroxyl groups;

[0072] (3) By ethanol precipitation, dialysis and freeze drying, composite grafted starch with caffeic acid and amino acids grafted at different hydroxyl sites was obtained, wherein the grafting degree of caffeic acid was 4~12% and the grafting degree of amino acids was 1~5%, and the two types of functional groups were spatially complementary.

[0073] (4) Gelatinization of high amylose corn starch grafted with caffeic acid-amino acid composite: caffeic acid modified high amylose corn starch was dispersed in deionized water and gelatinized at 120°C for 1 hour. After cooling to 50°C, gelatinized modified starch slurry was obtained.

[0074] (5) Evaluation of the functional activity of modified high amylose corn starch: The DPPH free radical scavenging method and ABTS were used. +• The antioxidant activity of gelatinized modified starch was evaluated using the free radical scavenging method; the antibacterial activity against Escherichia coli and Staphylococcus aureus was evaluated using the inhibition zone method and the plate coating method, with natural high amylose corn starch gelatinized liquid as the control group.

[0075] (6) Preparation of functional emulsion gels carrying active ingredients: ① Preparation of stabilizer solution: Caffeic acid modified high amylose corn starch was gelatinized to obtain a gelatinized liquid; ② Preparation of oil phase containing active ingredients: Pterostilbene was dissolved in a suitable carrier oil and stirred evenly in the dark to obtain an oil phase containing Pterostilbene; ③ Preparation of emulsion gel: Under the condition of avoiding light, the oil phase containing Pterostilbene was slowly added to the stabilizer solution, emulsified using a high shear homogenizer, and refrigerated at 4°C to obtain a stable functional emulsion gel carrying active ingredients.

[0076] In some more specific embodiments, the method for preparing the functional emulsion gel carrying the active ingredient includes the following steps:

[0077] 1. Preparation of high amylose corn starch selectively grafted with caffeic acid

[0078] This invention preferably uses high-amylose corn starch as the natural polysaccharide base material, and employs an esterification reaction to covalently graft the carboxyl groups of caffeic acid molecules onto the hydroxyl groups of starch molecules. The modification reaction is preferably carried out in N,N-dimethylformamide (DMF) as a solvent. First, the starch is thoroughly stirred and dissolved at 80°C, then cooled to 30°C, and caffeic acid, EDC·HCl (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride), and DMAP (4-dimethylaminopyridine) are added sequentially to catalyze the reaction. The molar ratio is usually carboxyl:EDC:DMAP ≈ 1:1.2:0.1, and the reaction time is controlled at 8~16 hours.

[0079] 2. Preparation of caffeic acid-amino acid composite grafted high amylose corn starch

[0080] After the esterification of coffee, without changing the reaction system, small molecule amino acids, such as cysteine ​​or tryptophan, can be directly added, along with an appropriate amount of EDC·HCl. This activates the carboxyl groups of the amino acids under the action of the carbodiimide condensing agent in the system, allowing them to further undergo esterification with other hydroxyl groups in the starch molecule. This process covalently introduces amino acid groups with amino or thiol side chains onto the starch molecule, forming a second type of ester bond, starch-O-CO-amino acid. The amino group (lysine) or thiol group (cysteine) in the amino acid molecule is retained during the reaction and can serve as active groups for subsequent interfacial adsorption, hydrogen bonding, or polar interactions. After filtration, washing, and drying, a composite grafted high amylose starch containing both aromatic ester and amino acid ester structures can be obtained.

[0081] 3. Gelatinization treatment of high amylose corn starch grafted with caffeic acid-amino acid complex.

[0082] The obtained caffeic acid-amino acid composite grafted high amylose corn starch was dispersed in deionized water and gelatinized under high temperature conditions, preferably at 120°C for 1 hour to achieve full gelatinization. The reaction system required certain stirring conditions to prevent agglomeration. Subsequently, the system was cooled to 50°C to obtain a gelatinized starch slurry, which was used for subsequent functional evaluation and emulsion construction.

[0083] 4. Construction and Functional Evaluation of Functional Emulsion Gels

[0084] This invention uses gelatinized caffeic acid-amino acid composite grafted high amylose corn starch as a stabilizer for the emulsion (as the aqueous phase of the stabilizer). Specifically, the gelatinized caffeic acid-amino acid composite grafted high amylose corn starch slurry is cooled to approximately 50°C. Pterostilbene, as a fat-soluble active ingredient, is first dissolved in an appropriate amount of carrier oil at a specific ratio, and stirred in the dark at 40-50°C until fully dissolved, forming a clear oil phase. During emulsion construction, the oil phase is slowly added dropwise to the aqueous stabilizer phase, and homogenized using a high-shear homogenizer at 12000 rpm for approximately 10 minutes to obtain a dense, milky-white emulsion dispersion system. Subsequently, the emulsion is allowed to stand at 4°C for 6 hours to induce gelation, promoting stable adsorption of modified starch particles at the oil-water interface, rearrangement and improvement of the interfacial membrane structure, and formation of a gel network structure, thereby obtaining a functional emulsion gel with excellent stability and carrying the active ingredient.

[0085] The functional emulsion gel constructed in this invention can load natural active ingredients such as pterostilbene, with an encapsulation efficiency of up to 95%. This functional emulsion gel exhibits excellent long-term storage stability, showing no significant stratification or oil separation within 3 months at room temperature. Based on the synergistic effect of caffeic acid and amino acids with pterostilbene, this functional emulsion gel also demonstrates enhanced free radical scavenging ability and antibacterial effects, making it suitable for the development of natural skincare cosmetics such as lotions, serums, creams, and masks.

[0086] Another aspect of the present invention provides a functional emulsion gel loaded with active ingredients prepared by the aforementioned preparation method. The functional emulsion gel loaded with active ingredients has a three-dimensional cross-linked network structure and does not flow when the container is inverted. The encapsulation rate of active substances in the functional emulsion gel loaded with active ingredients is above 93%.

[0087] Furthermore, the functional emulsion gel carrying the active ingredient has good mechanical strength and self-support.

[0088] Furthermore, the functional emulsion gel carrying the active ingredient showed no obvious stratification, water separation, or oil droplet aggregation after storage for more than 90 days, demonstrating good structural stability and bioactivity retention.

[0089] Another aspect of the present invention provides the application of the aforementioned functional emulsion gel carrying active ingredients in the preparation of skin care cosmetics with antibacterial, antioxidant and anti-aging effects, the skin care cosmetics including face cream, sunscreen or face mask.

[0090] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0091] Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0092] The testing and characterization methods used in this invention are as follows:

[0093] (1) Grafting Degree Determination: The UV-Vis absorption characteristics and caffeic acid grafting rate of the modified starch samples were determined using a UV-Vis spectrophotometer. Specifically, 0.1% (mass-volume ratio) of the sample was heated to complete dissolution using distilled water. The absorbance of each sample was recorded at 311 nm. The caffeic acid content was calculated by substituting the absorbance value into a calibration curve prepared using a caffeic acid standard solution under the same conditions. The grafting rate was expressed as the mass percentage of caffeic acid covalently bonded to the starch sample. The amino acid grafting rate was indirectly determined by elemental analysis. The composite modified starch sample was vacuum dried to constant weight at 105℃, then pulverized and sieved. An appropriate amount of sample was placed in an elemental analyzer to determine the mass fraction of nitrogen (N) (%). Since neither starch nor caffeic acid contains nitrogen, it can be assumed that all nitrogen in the sample comes from the grafted amino acid groups. Based on this, the amino acid grafting rate (expressed as the mass percentage of amino acids covalently bonded in the sample) was calculated using the following formula:

[0094] Amino acid grafting rate (%) = N (%) ×

[0095] Among them, M AA m represents the relative molecular mass of the grafted amino acid. N 14 represents the number of nitrogen atoms in the amino acid molecule, and 14 is the relative atomic mass of nitrogen. For different amino acids such as cysteine, lysine, histidine, tryptophan, and tyrosine, their respective M values ​​can be substituted. AA and m N Calculate the corresponding grafting rate. Since caffeic acid does not contain nitrogen, the above-mentioned amino acid grafting rate determination process will not be interfered with by the caffeic acid grafted portion, and will not affect the UV determination of the caffeic acid grafting rate.

[0096] (2) Infrared spectroscopy analysis: 10-20 mg of sample was mixed with KBr powder and pressed into tablets. Fourier transform infrared spectroscopy (FTIR) was used to analyze the sample at 4000-500 cm⁻¹. -1 Scan within the range, with a resolution of 4 cm. -1 The chemical structure changes of the modified starch were analyzed by scanning 32 times.

[0097] (3) Fluorescence spectroscopy analysis: Prepare a 1% starch sample solution and measure it using a fluorescence spectrophotometer. Set the excitation wavelength (Ex) to 350 nm, the scanning emission spectrum (Em) range to 360-650 nm, and the slit width to 5 nm. Record the fluorescence emission intensity to characterize the introduction of aromatic groups and amino acid side chains and their interactions.

[0098] (4) Scanning electron microscopy (SEM): The surface microstructure of natural and modified starch granules was observed using a field emission scanning electron microscope. After gold sputtering, the morphology of the granules was observed and photographed at magnifications of 500× and 2000×.

[0099] (5) Contact angle test: The powder sample was pressed into a uniform thin sheet using a tablet press, and the contact angle of water on the sample surface was determined by the static drop method. Using a JY-PHA contact angle meter, a drop of distilled water was carefully placed on the surface of the thin sheet, and the contact angles on both sides of the drop were recorded and the average value was calculated. All measurements were performed under room temperature and ambient humidity conditions.

[0100] (6) Evaluation of antioxidant performance:

[0101] DPPH method: Mix the sample solution with DPPH ethanol solution, react in the dark for 30 min, and measure the absorbance at 517 nm.

[0102] ABTS method: Mix the sample solution with ABTS +• The working solutions were mixed and reacted for 6 min. The absorbance was then measured at 734 nm.

[0103] FRAP method: Mix the sample solution with TPTZ working solution, react at 37℃ for 10 min, and measure the absorbance at 593 nm. The results are expressed as millimoles of ferrous sulfate equivalent (mmol Fe). 2+ / g) indicates.

[0104] (7) Evaluation of antibacterial properties:

[0105] Escherichia coli (ATCC 25922) and Staphylococcus aureus (ATCC 6538) were selected as target strains, and the antibacterial effects were evaluated using the inhibition zone method and the plate coating method, respectively.

[0106] In the inhibition zone method, after activating and culturing Escherichia coli and Staphylococcus aureus, the bacterial concentration is adjusted to 1×10⁻⁶. 8 CFU / mL was evenly spread onto the surface of nutrient broth agar plates. Using a sterile punch, holes (approximately 6 mm in diameter) were made in the surface of the medium, and 100 μL of gelatinized modified starch solution was added to each hole. The plates were incubated at 37°C for 18–24 hours, and the diameter of the inhibition zone was observed and measured for qualitative evaluation of the antibacterial effect.

[0107] In the plate spread method, the gelatinized modified starch solution and the test bacterial solution were mixed at a 1:1 volume ratio and incubated at 37°C for 8-10 hours. After incubation, the bacterial solution was serially diluted 10-fold, and an appropriate amount of the diluted solution (e.g., 100 μL) was evenly spread onto nutrient agar plates and incubated at 37°C for 18-24 hours. After incubation, the number of colonies was counted, and the inhibition rate relative to the control group was calculated to quantitatively evaluate the inhibitory effect of modified starch on bacterial growth. Natural high-amylose corn starch gelatinized solution served as a negative control group.

[0108] In live / dead bacteria staining (CLSM), the bacterial suspension is treated with sample solution and then stained with SYTO 9 and PI dyes. The survival status of the bacteria is observed through a laser confocal microscope (live bacteria appear green, and dead bacteria appear red).

[0109] (8) Determination of Emulsifying Activity Index (EAI) and Emulsifying Index (CI): Take 50 μL of freshly prepared emulsion and add it to 10 mL of 0.1% (w / v) SDS solution. Vortex for 10 seconds to ensure uniform dispersion. Measure the absorbance of the diluted emulsion at 510 nm at 0 minutes using a UV-Vis spectrophotometer. EAI is calculated using the following formula: EAI (m 2 / g) = 2×2.303×A0×N / (L×φ×C×10000), where A0 is the absorbance at 0 minutes, N is the dilution factor, C is the initial starch concentration, φ is the oil phase volume fraction, and L is the optical path length. After storage for a certain period of time, the emulsion layer height (H1) and the total emulsion height (H0) are measured. The emulsification index is calculated using the following formula: CI = H1 / H0×100%.

[0110] (9) Observation of the microstructure of emulsion gel: Take a small amount of emulsion and place it on a glass slide. Use an optical microscope under a 10× or 20× objective lens to observe the size and distribution of oil droplets and take a photomicrograph.

[0111] (10) Determination of emulsion gel strength: The emulsion sample was dispensed into containers of fixed size and cooled into a gel. A texture analyzer was used to perform puncture or compression tests. The probe was inserted into the gel at a fixed speed to a certain depth, and the maximum peak force (g) was recorded as an indicator of the emulsion gel strength.

[0112] (11) Encapsulation efficiency and UV stability determination:

[0113] Encapsulation efficiency: Solvent extraction method was used. The emulsion was separated by centrifugation, and the lower supernatant was collected or the content of free active ingredients (such as pterostilbene) was determined by demulsification extraction. The proportion of active ingredients encapsulated inside the oil droplets was calculated.

[0114] UV stability: The emulsion gel loaded with active ingredients was irradiated under a UV lamp for 10 h, the residual active ingredients were extracted and their content was determined, and the retention rate after UV irradiation was calculated.

[0115] Example 1

[0116] 1. Preparation of caffeic acid-grafted high amylose corn starch

[0117] 10.0 g of high-amylose corn starch was weighed and added to 250 mL of N,N-dimethylformamide (DMF). The mixture was stirred at 80 °C for 1 h to loosen the starch granules and expose more reactive hydroxyl groups. After cooling to 30 °C, 1.0 g, 2.0 g, and 3.2 g of caffeic acid were added, respectively. 5.0 g of EDC·HCl and 1.0 g of DMAP were added to each group, and the reaction was carried out for 12 h under dark conditions. After the reaction, an equal volume of anhydrous ethanol was added to precipitate the product. The precipitate was centrifuged and washed four times with ethanol. The precipitate was then transferred to a dialysis bag and dialyzed against deionized water for 72 hours, with the water changed every 12 hours. After dialysis, the precipitate was freeze-dried to obtain caffeic acid-grafted high-amylose corn starch with different grafting rates. These samples were named 4%Cf-HAMS, 8%Cf-HAMS, and 12%Cf-HAMS based on the grafting rate of caffeic acid in the samples.

[0118] 2. Preparation of caffeic acid-amino acid composite grafted high amylose corn starch

[0119] After the caffeic acid reaction was completed, 0.2-2.5 g of cysteine ​​was added under the same reaction conditions, along with 2.5 g of EDC·HCl. The reaction was continued for 8 h, allowing the carboxyl groups in the amino acid molecules to be reactivated by the carbodiimide condensing agent, resulting in esterification with the remaining hydroxyl groups in the starch molecules. This yielded a composite grafted starch containing amino acid side chains. The resulting composite grafted starch molecule possessed both aromatic ester and amino acid ester structures on its molecular backbone. After the reaction, an equal volume of anhydrous ethanol was added to precipitate the product. The precipitate was then centrifuged and washed four times with ethanol. Subsequently, the precipitate was transferred to a dialysis bag and dialyzed against deionized water for 72 hours, with the water changed every 12 hours. After dialysis, the precipitate was freeze-dried to obtain caffeic acid-amino acid composite grafted high amylose corn starch samples with different caffeic acid and amino acid grafting rates. Based on the grafting rates of caffeic acid and amino acids in the obtained samples, they were named 4%Cf-1%Cys-HAMS, 4%Cf-3%Cys-HAMS, 4%Cf-5%Cys-HAMS, 8%Cf-1%Cys-HAMS, 8%Cf-3%Cys-HAMS, 8%Cf-5%Cys-HAMS, 12%Cf-3%Cys-HAMS, 12%Cf-5%Cys-HAMS, and 12%Cf-1%Cys-HAMS.

[0120] As a comparison with the 8%Cf-3%Cys-HAMS (8% caffeic acid-3% cysteine ​​composite grafted high amylose corn starch) sample, this application also prepared comparative samples of 8%Cf–HAMS (caffeic acid grafted only, 8% caffeic acid grafted high amylose corn starch), 3%Cys-HAMS (amino acid grafted only), 1%Cf-3%Cys-HAMS (caffeic acid grafting too low), 15%Cf-3%Cys-HAMS (caffeic acid grafting too high), 8%Cf-0.5%Cys-HAMS (amino acid grafting too low), and 8%Cf-10%Cys-HAMS (amino acid grafting too high). (Note: The amount of feed for the comparative samples can be adjusted accordingly based on the target grafting degree.)

[0121] 3. Gelatinization treatment

[0122] The modified starch sample and the unmodified high amylose corn starch were added to 100 mL of deionized water at a ratio of 3.0 g, heated to 120°C, and stirred continuously for 1 h until completely gelatinized. The mixture was then cooled to 50°C to obtain starch paste, which was used for subsequent antioxidant and antibacterial tests.

[0123] 4. Emulsion-Gel Construction

[0124] High-amylose corn starch gelatinized liquid and composite grafted starch were prepared at a mass concentration of 5%, respectively. Gelatinization was carried out at 120℃ for 1 hour, followed by cooling to 50℃ for later use. Pterostilbene, as a fat-soluble active ingredient, was dissolved in soybean oil at a mass concentration of 0.3%, and stirred thoroughly at a constant temperature of 45℃ to ensure complete dissolution and the formation of a clear oil phase. During emulsion preparation, the oil phase containing pterostilbene was slowly added dropwise to the stabilizer aqueous phase under light-protected conditions, with an oil-to-water volume ratio controlled at 4:6. The mixture was homogenized and emulsified using a high-shear emulsifier (12000 rpm) for 10 minutes. After emulsification, the resulting emulsion was refrigerated at 4℃ for 6 hours to promote the formation of a dense interfacial film at the oil-water interface of the composite grafted starch and to induce the formation of a stable gel network structure in the continuous phase. The final emulsion gel was uniformly milky white in appearance, with a fine texture, and no stratification or oil separation, exhibiting good storage stability and physical stability. This emulsion gel can be used for subsequent testing of pterostilbene encapsulation efficiency, stability analysis, and functional evaluation, and has good application prospects.

[0125] Figure 1The image shows a comparison of the morphology of natural high amylose corn starch (HAMS), caffeic acid-grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite-grafted starch (8%Cf-3%Cys-HAMS). As can be seen from the image, natural HAMS is a white powder; 8%Cf-HAMS turns light yellow and is more porous, indicating successful caffeic acid grafting; 8%Cf-3%Cys-HAMS further deepens in color to a bright yellow, and the powder becomes even more fluffy. This significant gradient in appearance directly confirms that the dual functional groups of caffeic acid and cysteine ​​have been successfully modified into the starch system.

[0126] Figure 2 The image shows the FTIR spectral characteristics of natural HAMS, caffeic acid-grafted starch (8%Cf-HAMS), and caffeic acid-cysteine ​​composite grafted starch (8%Cf-3%Cys-HAMS). Natural HAMS exhibits FTIR spectra at approximately 3400 cm⁻¹. -1 It exhibits a broad and strong O–H stretching vibration peak at 1647 cm⁻¹, and at 1647 cm⁻¹... -1 A bending vibration peak of adsorbed water appears nearby. After caffeic acid grafting, the peak shape of 8% Cf-HAMS in this region changes and slightly redshifts, indicating that the intermolecular hydrogen bond network of starch molecules is reconstructed; simultaneously, at 1714 cm⁻¹... -1 A distinct C=O absorption peak appears at 1606 cm⁻¹. -1 The enhanced aromatic ring skeletal vibration observed indicates that the caffeic acid carboxyl group underwent esterification with the starch hydroxyl group, and the aromatic structure was successfully introduced. Further introduction of cysteine ​​resulted in the formation of an 8% Cf-3% Cys-HAMS mixture at 3400 cm⁻¹. -1 The peak shape in the region continued to broaden, accompanied by a slight red shift, indicating that the N–H / O–H groups participated in the new hydrogen bond rearrangement; at 2552 cm⁻¹ -1 A weak S–H stretching vibration peak was observed, indicating that the thiol moiety of the cysteine ​​side chain was retained; the characteristic absorption of its ester group C=O was located at approximately 1712 cm⁻¹. -1 The aromatic ring vibration is still at 1606 cm. -1 The surrounding area maintained a relatively strong intensity. Comprehensive characterization results verified that both caffeic acid and cysteine ​​underwent esterification with starch hydroxyl groups, successfully constructing a thiol-containing composite grafted starch structure.

[0127] Figure 3The fluorescence emission spectra of natural HAMS, 8%Cf-HAMS, and 8%Cf-3%Cys-HAMS are shown. Natural HAMS exhibits almost no significant fluorescence signal, showing only a near-baseline background level. After caffeic acid grafting, 8%Cf-HAMS shows a broad and distinct emission peak at approximately 451 nm, indicating that the introduction of the aromatic structure endows starch with a certain fluorescence response. Further introduction of cysteine ​​significantly enhances the fluorescence intensity of 8%Cf-3%Cys-HAMS at both 367 nm and 451 nm. The characteristic peak near 367 nm is related to the energy level changes caused by the thiol group and its adjacent environment, while the 451 nm peak corresponds to the characteristic emission of the caffeic acid aromatic structure. Overall, the fluorescence emission intensity of the composite grafted sample is significantly higher than that of the single caffeic acid grafted system, indicating that the introduction of cysteine ​​alters the microenvironment and energy transition behavior of starch molecules, enhancing the intermolecular electronic coupling effect and thus improving the fluorescence response characteristics of the system.

[0128] Figure 4 The images shown are scanning electron microscope (SEM) images of HAMS, 8%Cf-HAMS, and 8%Cf-3%Cys-HAMS at different magnifications. Natural HAMS has a smooth and flat surface; the surface roughness of 8%Cf-HAMS increases and flaky adhesions appear, indicating that caffeic acid alters the chemical environment of the particle surface; the surface of 8%Cf-3%Cys-HAMS further exhibits pits, cracks, and irregular contours. This gradual roughening and loosening of the microstructure directly confirms the introduction of more substituents and the occurrence of complex grafting reactions.

[0129] Static water contact angle testing: Natural HAMS had a contact angle of only 26.8°, exhibiting strong hydrophilicity; 8%Cf-HAMS increased to 51.1°, indicating the introduction of a hydrophobic aromatic structure; 8%Cf-3%Cys-HAMS further increased to 87.3°, approaching the hydrophobic critical value. The significant stepwise increase in contact angle validates the synergistic hydrophobic regulatory effect of the dual components, which is beneficial for enhancing the directional adsorption and emulsification stability of starch at the oil-water interface.

[0130] Figure 5 The figures show the DPPH radical scavenging capabilities of HAMS, 8%Cf-HAMS, and 8%Cf-3%Cys-HAMS. Natural HAMS showed almost no scavenging activity; the significantly improved scavenging rate of 8%Cf-HAMS was attributed to the introduction of the caffeic acid phenolic hydroxyl group. 8%Cf-3%Cys-HAMS achieved the highest value, indicating a significant synergistic effect between the electron-donating properties of caffeic acid and the hydrogen-donating ability of cysteine ​​sulfhydryl groups, effectively enhancing the radical capture efficiency.

[0131] Figure 6The figures show the effects of HAMS, 8%Cf-HAMS, and 8%Cf-3%Cys-HAMS on ABTS. +• Free radical scavenging ability. Natural HAMS showed extremely weak activity; 8% Cf-HAMS showed a significantly improved scavenging rate; and 8% Cf-3% Cys-HAMS exhibited the highest activity. The results further confirmed that the dual mechanism of electron and hydrogen donors in the composite grafting structure significantly enhanced the total antioxidant capacity of starch in the water-soluble system.

[0132] Figure 7 The results of FRAP reducing power determination for HAMS, 8%Cf-HAMS, and 8%Cf-3%Cys-HAMS are shown. Natural HAMS contains almost no Fe. 3+ →Fe 2+ The reducing power of 8%Cf-HAMS was close to zero; after grafting with caffeic acid, the reducing power of 8%Cf-HAMS was significantly enhanced, indicating that the ortho-diphenol structure in caffeic acid can efficiently participate in electron transfer reactions. Further grafting with cysteine ​​further increased the FRAP value of 8%Cf-3%Cys-HAMS, reaching the highest level among the three, demonstrating the synergistic electron transfer ability of phenolic hydroxyl and thiol groups. The results show that this invention, through the composite grafting of caffeic acid and cysteine, can effectively enhance the electron donor capacity of starch, giving it stronger reducing antioxidant activity.

[0133] Figure 8 This image shows the antibacterial effects of natural high-amylose corn starch (HAMS), caffeic acid-grafted starch (8%Cf-HAMS), and caffeic acid-cysteine-grafted starch (8%Cf-3%Cys-HAMS) against *Escherichia coli* and *Staphylococcus aureus*, including photographs of inhibition zones and statistical graphs of inhibition zone diameters. Natural HAMS produced almost no obvious inhibition zones, exhibiting only very weak or near-background antibacterial activity. After caffeic acid grafting, 8%Cf-HAMS formed observable inhibition zones against both indicator bacteria, indicating that the phenolic hydroxyl groups in the caffeic acid structure endow starch with certain antibacterial activity. Further grafting with cysteine ​​resulted in the strongest inhibitory effect in both strains, with a statistically significant difference (p<0.05). Of particular note is that the diameter of the inhibition zones against *Escherichia coli* and *Staphylococcus aureus* in the composite-grafted samples was significantly increased compared to the single-grafted samples (from approximately 14.7 mm and 25.3 mm to approximately 26.0 mm and 30 mm, respectively). This enhancement effect stems from the synergistic contribution of the oxidative stress effect of caffeic acid and the membrane disruption mechanism of cysteine ​​sulfhydryl groups, resulting in a significant advantage for the composite-grafted starch in microbial inhibition. These results demonstrate that the composite modification strategy of this invention can effectively improve the basic antibacterial properties of starch materials.

[0134] Figure 9 The bactericidal efficacy of different modified starches was quantitatively demonstrated using the plate coating method. Results showed that the natural HAMS group exhibited dense colony growth on the plates, confirming its lack of bactericidal activity. The 8%Cf-HAMS group showed a significant reduction in colony count, with an inhibition rate of nearly 100% against Staphylococcus aureus, but an inhibition rate of approximately 89% against Escherichia coli, with a small number of colonies still surviving. In contrast, the composite-grafted 8%Cf-3%Cys-HAMS group showed no colony growth on either indicator bacteria plate, exhibiting a "sterile plate" state. Statistical results indicate that the composite-grafted starch achieved a 100% inhibition rate against both bacteria. Overall, the antibacterial rate of the composite-grafted sample was higher than that of the single-caffeic acid-grafted sample, indicating a synergistic effect between the oxidative stress effect of caffeic acid and the membrane disruption mechanism of cysteine ​​sulfhydryl groups, thereby significantly enhancing the broad-spectrum antibacterial performance of the composite modified starch of this invention.

[0135] Figure 10 The results show the fluorescence staining of live / dead E. coli and S. aureus by HAMS, 8%Cf-HAMS, and 8%Cf-3%Cys-HAMS. In the natural HAMS treatment group, cells mainly showed green fluorescence (SYTO 9), with almost no red fluorescence signal, indicating that it did not cause significant damage to the bacterial cell membrane. After caffeic acid grafting, the red fluorescence (PI) in the bacterial samples treated with 8%Cf-HAMS increased significantly, indicating partial cell membrane damage and reduced cell viability. Further grafting with cysteine ​​resulted in a significant increase in red fluorescence and a significant decrease in green fluorescence in the 8%Cf-3%Cys-HAMS group, with a higher proportion of yellow-red mixed color in the composite image, indicating that this composite grafted starch had the most significant destructive effect on the bacterial cell membrane. These results indicate a synergistic effect between caffeic acid and cysteine ​​in the antibacterial mechanism; caffeic acid can induce oxidative stress, while the sulfhydryl structure of cysteine ​​can further disrupt cell membrane integrity, resulting in a stronger bactericidal ability of the composite grafted starch.

[0136] Figure 11 This study visually demonstrates the differences in the macroscopic state of emulsions and gels prepared from different starch matrices. The natural HAMS emulsion exhibited severe oil-water separation and a thin texture, indicating insufficient interfacial adsorption. 8% Cf-HAMS formed a homogeneous and stable emulsion. 8% Cf-3% Cys-HAMS further exhibited a fine and dense "creamy" gel appearance, demonstrating the strongest structure retention. This confirms that composite grafting significantly enhances interfacial adsorption capacity and constructs a robust three-dimensional gel network, giving it excellent properties as a high-end cosmetic matrix.

[0137] Figure 12The emulsifying activity index (EAI) of HAMS, 8%Cf-HAMS, and 8%Cf-3%Cys-HAMS is shown. Natural HAMS has the lowest EAI due to limited interfacial adsorption; 8%Cf-HAMS shows a significant increase, attributed to the introduction of hydrophobic aromatic groups which improves amphiphilicity; 8%Cf-3%Cys-HAMS reaches the highest value, confirming that cysteine ​​and caffeic acid synergistically optimize interfacial behavior and significantly improve emulsification efficiency.

[0138] Long-term stability tests of the emulsions after 90 days of storage at room temperature: the natural HAMS emulsion exhibited severe stratification, with only about 23% of the emulsion layer remaining; the 8%Cf-HAMS emulsion retained over 97%; and the 8%Cf-3%Cys-HAMS emulsion maintained 100% retention, remaining homogeneous throughout. This superior stability is attributed to the enhanced interfacial adsorption through modification to inhibit oil droplet aggregation, while the antioxidant and antibacterial properties imparted by the composite grafting reduced oxidation and microbial damage during storage, further maintaining the integrity of the emulsion structure.

[0139] Figure 13 Natural HAMS emulsions exhibit large and unevenly distributed oil droplets, resulting in insufficient interfacial film strength; 8% Cf-HAMS oil droplets show a significant reduction in size. 8% Cf-3% Cys-HAMS exhibits the best morphology, with small, uniform, and densely packed oil droplets, confirming that composite grafting effectively enhances interfacial film strength to prevent oil droplet aggregation.

[0140] Gel strength tests of emulsion gels prepared from three starch systems: The gel strength test results showed that the natural HAMS had extremely low strength because the oil droplets acted as "inert fillers" and blocked the gel network; the strength of 8%Cf-HAMS increased to about 14 g, which was attributed to the modified starch transforming the oil droplets into "active fillers" that reinforced the structure; the strength of 8%Cf-3%Cys-HAMS further jumped to about 23 g, confirming that the cysteine ​​side chain introduced additional cross-linking effects, which significantly improved the mechanical strength of the system.

[0141] Figure 14The loading capacity of different emulsion-gel systems for the fat-soluble active ingredient pterostilbene was quantitatively evaluated. As shown in the figure, the encapsulation efficiency of natural HAMS was extremely low, only about 25%, indicating that natural starch particles could not form a dense barrier layer on the surface of oil droplets, resulting in the loss or exudation of a large amount of active ingredient during processing. After grafting with caffeic acid, the encapsulation efficiency of 8%Cf-HAMS was significantly improved, which may be related to the fact that the aromatic structure introduced by caffeic acid enhanced the hydrophobic interaction between starch and pterostilbene. Furthermore, the 8%Cf-3%Cys-HAMS composite grafted starch achieved the highest encapsulation efficiency, reaching over 93% (p<0.05). This is because the synergistically introduced cysteine ​​side chain provides additional active sites such as amino and thiol groups, which can form multiple hydrogen bonds and polar interactions with active molecules; at the same time, the interfacial film formed by the composite grafted particles is denser and tougher, and together with the enhanced gel network structure in the continuous phase, a dual physical barrier of "interfacial adsorption-network capture" is constructed, thereby achieving the encapsulation and locking of active ingredients.

[0142] The UV protection capabilities of different emulsion-gel systems for the photosensitive active ingredient pterostilbene were evaluated: In the natural HAMS emulsion, due to interfacial barrier failure, the pterostilbene retention rate was only about 38%; the retention rate of 8%Cf-HAMS significantly increased to about 74%, attributed to the UV absorption effect of the conjugated benzene ring of caffeic acid, which exerted an effect similar to a "chemical sunscreen". 8%Cf-3%Cys-HAMS performed best (retention rate ~83%), thanks to the denser physical interfacial barrier and the antioxidant system synergistically constructed by cysteine ​​and caffeic acid, which effectively scavenged UV-induced free radicals and significantly improved the stability of the photosensitive active ingredient.

[0143] Example 2

[0144] Construction and performance evaluation of high internal phase emulsion gel based on tryptophan-grafted starch.

[0145] This embodiment aims to construct a high internal phase emulsion gel system using high amylose corn starch (HAMS), 8% caffeic acid-grafted high amylose corn starch (8%Cf-HAMS), and 8% caffeic acid-3% tryptophan-grafted high amylose corn starch (8%Cf-3%Trp-HAMS) as stabilizers, and to evaluate its molding characteristics, microstructure, and physical stability.

[0146] 1. Preparation of experimental materials (1) Preparation of 8%Cf-3%Trp-HAMS. The preparation method described in Example 1 is the same as described in Example 1, except that after the first step of the reaction of caffeic acid (the amount of feed corresponds to 8% grafting rate), L-tryptophan (Trp) is added to the same reaction system to replace cysteine, and the feed ratio is controlled to achieve an amino acid grafting rate of about 3%. The reaction conditions (EDC / DMAP catalytic system, room temperature reaction for 8 h) and the post-treatment steps (alcohol precipitation, dialysis, freeze drying) are consistent with those in Example 1. (2) Control samples Natural high amylose corn starch (HAMS) and 8% caffeic acid grafted starch (8%Cf-HAMS) prepared in Example 1 are selected as control samples.

[0147] 2. Construction of high internal phase emulsion gel. The preparation process of the high internal phase emulsion gel is the same as that described in Example 1, except that the oil-water volume ratio is adjusted to 7.5:2.5 (i.e., oil phase volume fraction 75%), the active substance concentration is 0.5%, and the mixture is homogenized at 12,000 rpm for 10 min using a high shear homogenizer to construct the high internal phase system.

[0148] Figure 15 The Fourier transform infrared (FTIR) spectra of different starch samples are shown. Natural HAMS spectra are observed at approximately 3400 cm⁻¹. -1 A broad and strong O–H stretching vibration band was observed at 1712 cm⁻¹; after modification with caffeic acid and tryptophan, this absorption band broadened further, indicating that the introduction of these two groups led to a redistribution of hydrogen bond structures in the starch system, possibly accompanied by the participation of tryptophan N–H. Compared to HAMS, 8% Cf-HAMS showed a stronger O–H stretching vibration band at 1712 cm⁻¹. -1 A distinct C=O stretching vibration peak of the ester group appears at 1603 cm⁻¹. -1 The vibrations of the nearby aromatic ring skeleton were also significantly enhanced; both of the above characteristic peaks persisted in the 8%Cf-3%Trp-HAMS composite grafted sample, and were at 1603 cm⁻¹. -1 The absorption was further enhanced, reflecting the contribution of aromatic vibrations resulting from the superposition of the aromatic ring of caffeic acid and the indole ring of tryptophan. Overall, the spectral results indicate that both caffeic acid and tryptophan have been successfully grafted onto starch molecules via esterification, simultaneously causing significant changes in the absorption characteristics of the starch hydrogen bond network and aromatic region.

[0149] Fluorescence emission characteristics of different starch samples were tested: Natural HAMS exhibited almost no intrinsic fluorescence, showing only a low and flat baseline signal; after grafting with caffeic acid (8%Cf-HAMS), a significant broad peak appeared around 450 nm, originating from the characteristic emission of the aromatic structure of caffeic acid. The fluorescence intensity of the composite grafted sample 8%Cf-3%Trp-HAMS was further significantly enhanced, with two more prominent emission peaks at approximately 368 nm and 458 nm. The 368 nm peak is attributed to the characteristic fluorescence of the tryptophan indole ring, while the 458 nm peak reflects the superimposed emission effect of caffeic acid and tryptophan. Overall, the results indicate that grafting caffeic acid and tryptophan significantly alters the optical emission behavior of the starch system. The composite grafted sample exhibits a stronger fluorescence response from the aromatic group, which can serve as an important spectral basis for judging the success of the modification.

[0150] Contact angle tests on solid surfaces of different starch samples: The contact angle of natural HAMS was approximately 26.8°, exhibiting typical strong hydrophilicity; after grafting with caffeic acid (8%Cf-HAMS), the contact angle increased to approximately 51.1°, indicating that the introduction of the aromatic structure enhanced the hydrophobicity of the particle surface. Further grafting with tryptophan (8%Cf-3%Trp-HAMS) significantly increased the contact angle to approximately 98.3°, exhibiting obvious hydrophobic surface characteristics. Tryptophan itself is a hydrophobic amino acid, and its indole aromatic ring can further reduce the polarity exposure of the particle surface, thereby further enhancing hydrophobicity on the basis of caffeic acid. Overall results show that the synergistic grafting of caffeic acid and hydrophobic tryptophan can significantly regulate the interfacial wettability of starch particles, giving them stronger hydrophobicity and interfacial adsorption capacity, providing a structural basis for the subsequent formation of stable high internal phase emulsion gels.

[0151] The antioxidant and antibacterial properties of HAMS, 8%Cf-HAMS, and 8%Cf-3%Trp-HAMS are shown in Table 1.

[0152] Table 1. Antioxidant and antibacterial properties of HAMS, 8%Cf-HAMS, and 8%Cf-3%Trp-HAMS

[0153]

[0154] As shown in Table 1, natural HAMS exhibits extremely low antioxidant activity, with low DPPH and ABTS levels. +• The clearance rates were only 2.1% and 6.3%, respectively, and the FRAP value was also 0 mmol Fe. 2+ / g, it has almost no free radical scavenging and reducing ability. After grafting with caffeic acid (8% Cf-HAMS), the antioxidant indicators are significantly improved: DPPH and ABTS. +• The clearance rates increased by 56.4% and 62.2%, respectively, and the FRAP value reached 50.5 mmol Fe.2+ / g indicates that the introduction of aromatic phenolic hydroxyl groups in caffeic acid significantly enhanced free radical scavenging ability. Further introduction of hydrophobic tryptophan (8%Cf-3%Trp-HAMS) further improved the three antioxidant indicators, particularly DPPH and ABTS. +• The clearance rates reached 68.5% and 80.2%, respectively, and the FRAP value increased to 62.1 mmol Fe. 2+ / g. This trend indicates that the tryptophan indole ring structure has a synergistic enhancing effect on aromatic domain interactions and hydrogen donor capacity, resulting in dual-modified starch exhibiting stronger overall antioxidant properties.

[0155] The antibacterial results showed that natural HAMS had virtually no antibacterial ability, with inhibition zone diameters of 8.0 mm (equal to the size of the blank well) against both *Escherichia coli* and *Staphylococcus aureus*, and a plate-coating inhibition rate of 0%. After grafting with caffeic acid (8%Cf-HAMS), the antibacterial performance of both model bacteria was significantly improved: the inhibition zone diameters for *E. coli* and *Staphylococcus aureus* increased to 16.1 mm and 25.3 mm, respectively, corresponding to inhibition rates of 88.8% and 100%, indicating that the phenolic hydroxyl groups of caffeic acid provide significant antibacterial effects in cell membrane disruption and free radical interference. Further grafting with tryptophan (8%Cf-3%Trp-HAMS) further enhanced the antibacterial effect: the inhibition zone diameters for *E. coli* and *Staphylococcus aureus* increased to 19.8 mm and 28.5 mm, respectively, with inhibition rates reaching 100% for both bacteria. This result indicates that the hydrophobic side chain of tryptophan and the aromatic structure of caffeic acid work synergistically to enhance the efficacy of the grafted starch in interacting with bacterial cell membranes, disrupting interfaces, and providing antioxidant and bactericidal effects.

[0156] Figure 16 The image shows the differences in appearance of high internal phase emulsion gels prepared from natural HAMS, 8%Cf-HAMS, and 8%Cf-3%Trp-HAMS samples. The natural HAMS system exhibits significant stratification, forming only a thin, highly fluid emulsion. The caffeic acid-grafted 8%Cf-HAMS forms a relatively uniform gel appearance, but its gel strength and morphology remain weak. In contrast, the 8%Cf-3%Trp-HAMS sample displays a nearly "creamy" yet flexible and thick texture, maintaining its upright peak structure after standing, demonstrating excellent self-support and plasticity. This significantly enhanced macroscopic morphological stability is attributed to the synergistic grafting of caffeic acid and the hydrophobic amino acid tryptophan, which significantly improves the interfacial adsorption capacity and hydrophobic interaction of the particles, thereby constructing a denser and stronger three-dimensional particle network under high internal phase conditions. Overall, the results indicate that composite-grafted starch is an excellent structural unit for preparing high-stability, high-texture high internal phase emulsion gels.

[0157] like Figure 17 The images show the microstructures of high internal phase emulsion gels prepared from natural HAMS, 8%Cf-HAMS, and 8%Cf-3%Trp-HAMS samples. Due to insufficient interfacial activity, the oil droplets in natural HAMS are severely aggregated and unevenly distributed, making it difficult to form a stable network. The oil droplets in 8%Cf-HAMS are significantly refined, indicating that the introduction of caffeic acid enhances interfacial adsorption. 8%Cf-3%Trp-HAMS exhibits the densest and most uniform microstructure, with oil droplets tightly packed to form a continuous network. This is attributed to the strong hydrophobic tryptophan significantly enhancing the interfacial anchoring ability, constructing a stable colloidal framework under high internal phase conditions.

[0158] Table 2. Emulsifying and activity-protecting properties of HAMS, 8%Cf-HAMS, and 8%Cf-3%Trp-HAMS high internal phase emulsion gels.

[0159]

[0160] As shown in Table 2, the original HAMS, lacking hydrophobic groups, exhibits weak emulsifying properties and active substance protection capabilities, as evidenced by an emulsifying activity index (EAI) of only 4.2 m. 2 The emulsion gel strength was insufficient (2.8 g), with a 90-day emulsion separation index (EI) of only 2.5%, and UV irradiation retention and pterostilbene encapsulation rates of only 12.5% ​​and 15.6%, respectively. After modification with caffeic acid (8% Cf-HAMS), the amphiphilicity and interfacial adsorption capacity of starch were significantly enhanced, and the EAI increased to 21.5 m. 2 The EI (Encapsulation Intensity) increased to 82.3%, and the emulsion gel strength increased to 24.5 g. Simultaneously, due to the aromatic structure and antioxidant properties of caffeic acid, the UV irradiation retention and encapsulation efficiency of the sample significantly improved to 75.2% and 78.4%, respectively. Further introduction of tryptophan (8%Cf-3%Trp-HAMS), which has stronger hydrophobicity and contains an indole aromatic ring, further enhanced the interfacial construction ability and hydrophobic interactions of the modified starch, increasing the EAI to 38.5 m² / g, achieving an EI of 95.4%, and further improving the emulsion gel strength to 42.6 g. Simultaneously, the stronger hydrophobic encapsulation and aromatic stacking effects significantly improved the protection ability of active substances, resulting in a UV irradiation retention rate and a pterostilbene encapsulation efficiency of 86.2% and 95.6%, respectively. In summary, the composite grafting of caffeic acid and tryptophan significantly enhanced the interfacial activity and protective efficacy of starch, making it the most outstanding performer in constructing highly stable, high-internal-phase emulsion gels.

[0161] Comparative Example 1

[0162] The method is the same as in Example 1, except that only caffeic acid is grafted and only amino acid (cysteine) is grafted.

[0163] Comparative Example 1 aims to verify the necessity and irreplaceability of each functional component in the "aromatic acid + amino acid" dual grafting strategy. For the sample grafted with only caffeic acid (8%Cf-HAMS), although the introduction of the benzene ring structure increased its contact angle to 51.1° and endowed it with certain antioxidant properties, its emulsifying activity (19.8 m² / g) and gel strength (14.3 g) were significantly lower than those of the composite grafting group in Example 1. This indicates that the lack of additional hydrogen bond crosslinking sites and auxiliary antioxidant effects provided by the cysteine ​​side chain limited the improvement of the overall performance of the material. Conversely, for the sample grafted with only cysteine ​​(3%Cys-HAMS), due to the lack of hydrophobic anchoring sites provided by caffeic acid, its surface properties still tend to be strongly hydrophilic (contact angle only 30.5°), making it difficult to form effective adsorption at the oil-water interface. This resulted in extremely poor emulsifying ability (EAI only 6.2 m² / g) and almost no carrier function (encapsulation rate only 30.2%). In summary, Comparative Example 1 strongly demonstrates that the caffeic acid hydrophobic framework and the cysteine ​​active side chain described in this invention are both indispensable, and only the synergistic coexistence of the two can achieve the optimal balance between interfacial activity, gel structure and functional activity.

[0164] Comparative Example 2

[0165] The method is the same as in Example 1, except that the caffeic acid grafting rate is too low or too high.

[0166] Comparative Example 2 aims to demonstrate the scientific validity and criticality of the preferred grafting degree range (2~12%) of the present invention by examining extreme cases of excessively low (1%) and excessively high (15%) caffeic acid grafting. For the low grafting degree sample (1%Cf-3%Cys-HAMS), due to insufficient introduction of caffeic acid, the degree of hydrophobic modification of the particle surface is limited (contact angle only 38.2°), which cannot provide sufficient interfacial driving force for effective adsorption of starch particles at the oil-water interface. As a result, its emulsifying activity index (EAI) is only 10.5 m² / g, the emulsification index drops to 62.4%, and the encapsulation efficiency of fat-soluble active ingredients is only 52.6%, which is difficult to meet the requirements for constructing a high-stability carrier. Conversely, for the high grafting degree sample (15%Cf-3%Cys-HAMS), the excessive introduction of hydrophobic benzene rings disrupted the hydrophilic-hydrophobic balance and hydration capacity of starch molecules, resulting in poor dispersion of the material in the aqueous phase and even the formation of insoluble precipitates (marked as "-"), completely losing its processing suitability as an emulsion stabilizer. In summary, Comparative Example 2 strongly demonstrates that there is a specific "optimal window" for the grafting degree of caffeic acid; too low a degree leads to insufficient interfacial activity, while too high a degree leads to loss of solubility and dispersibility. Only by controlling it within a suitable range (such as 8% in this invention) can a balance between emulsifying performance and processing suitability be achieved.

[0167] Comparative Example 3

[0168] The method is the same as in Example 1, except that the grafting rate of amino acids (cysteine) is too low or too high.

[0169] Comparative Example 3 aimed to investigate the effect of the amount of amino acid (cysteine) grafted on the properties of the composite modified starch, in order to demonstrate the rationality of the preferred grafting range of the present invention. For the low grafting degree sample (8%Cf-0.5%Cys-HAMS), although a small amount of amino acid was introduced, its synergistic effect was very limited due to insufficient density of active side chains, and its emulsion gel strength (16.8 g) and emulsifying activity (23.5 m) were significantly lower. 2 While slightly better than the single-graft group, the formulation (23.2 g and 32.4 m g / g) was still significantly lower than the optimal formulation in Example 1 (23.2 g and 32.4 m g / g). 2 The presence of trace amounts of amino acids ( / g) indicates that insufficient modification is necessary to construct a robust three-dimensional network structure. Conversely, for high-grafting-degree samples (8%Cf-10%Cys-HAMS), excessive amino acid introduction leads to over-enhanced intermolecular hydrogen or disulfide crosslinking, severely altering the dissolution behavior and hydrophilic / hydrophobic distribution of starch granules. This results in the material failing to disperse uniformly or exhibiting uncontrolled aggregation during gelatinization (data marked "-"), thus losing its practical application value. In summary, Comparative Example 3 confirms that the amount of amino acid grafting also exhibits a threshold effect; only by controlling it within an appropriate ratio can its synergistic function of assisting emulsification and structural enhancement be maximized.

[0170] Table 3 Comparison of physicochemical properties and functional activities of Example 1 with each comparative example

[0171]

[0172] Note: The data in the table are mean ± standard deviation; "-" indicates that the sample has extremely poor solubility due to excessive grafting and cannot be prepared into a uniform dispersion for testing.

[0173] In addition, the applicant also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0174] It should be understood that the technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made to the technical solutions of the present invention without departing from the spirit and scope of the claims are within the scope of protection of the present invention.

Claims

1. A method for preparing caffeic acid-amino acid composite grafted starch, characterized in that, include: (1) Disperse high amylose in a solvent and stir at 70~90℃, then cool to 30~50℃ and add caffeic acid, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine. React for 8~16h to form an ester bond between caffeic acid and the primary hydroxyl group at C6 in high amylose to obtain caffeic acid selectively grafted starch. (2) Add amino acids to step (1) and supplement with 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and then continue the reaction at 20~40℃ for 6~12h, so that the amino acids react with the secondary hydroxyl groups at C2 and C3 positions of starch to undergo esterification reaction. Then, after ethanol precipitation, dialysis and freeze drying, caffeic acid-amino acid composite grafted starch is obtained; the amino acids include any one of lysine, cysteine, serine and glycine; The caffeic acid-amino acid composite grafted starch has a grafting degree of 2-14% and an amino acid grafting degree of 1-8%.

2. The preparation method according to claim 1, characterized in that: The high amylose includes any one or more combinations of high amylose corn starch, high amylose pea starch, high amylose potato starch, and high amylose rice starch; And / or, the amylose content in the high amylose content is ≥50%; And / or, the solvent includes N,N-dimethylformamide and / or dimethyl sulfoxide.

3. The preparation method according to claim 1, characterized in that: The mass ratio of high amylose to caffeic acid in step (1) is 10: (0.5~4.0); And / or, the molar ratio of the carboxyl group of caffeic acid, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and 4-dimethylaminopyridine in step (1) is 1 : (1.0~2.0) : (0.05~0.5); And / or, the mass ratio of the amino acid to high amylose is (0.02~0.3):

1.

4. Caffeic acid-amino acid composite grafted starch prepared by any one of claims 1-3.

5. The caffeic acid-amino acid composite grafted starch according to claim 4, characterized in that: The caffeic acid-amino acid composite grafted starch has a grafting degree of 4-12% and an amino acid grafting degree of 1-5%.

6. The application of the caffeic acid-amino acid composite grafted starch according to claim 4 or 5 in the preparation of emulsion gels.

7. A method for preparing a functional emulsion gel carrying active ingredients, characterized in that, include: Provide the caffeic acid-amino acid composite grafted starch as described in claim 4 or 5; The caffeic acid-amino acid composite grafted starch was mixed with water and gelatinized to obtain a stabilizer solution; the active substance was mixed with vegetable oil to form an oil phase; Furthermore, the oil phase is mixed with a stabilizer solution and homogenized, and then allowed to stand at 0~10°C to obtain a functional emulsion gel carrying active ingredients.

8. The preparation method according to claim 7, characterized in that: The active substances include any one or more combinations of polyphenols, flavonoids, carotenoids, and fat-soluble vitamins. And / or, the content of caffeic acid-amino acid composite grafted starch in the functional emulsion gel carrying the active ingredient is 1~10 wt%, and the oil phase content is 30~85 wt%; And / or, the gelatinization treatment is performed at a temperature of 120~130℃ for a time of 0.5~2h; And / or, the volume ratio of the oil phase to the stabilizer solution is 2:8~8.5:1.5; And / or, the concentration of the stabilizer solution is 3-8 wt%; And / or, the mass fraction of the active substance in the oil phase is 0.1~1.0%; And / or, the settling time is 4~24h.

9. A functional emulsion gel carrying an active ingredient, prepared by the method according to claim 7 or 8, characterized in that: The functional emulsion gel carrying active ingredients has a three-dimensional cross-linked network structure and does not flow when the container is inverted. The encapsulation rate of active substances in the functional emulsion gel carrying active ingredients is above 93%.

10. The application of the functional emulsion gel carrying active ingredients as described in claim 9 in the preparation of skin care cosmetics with antibacterial, antioxidant and anti-aging effects, wherein the skin care cosmetics include face cream, sunscreen or face mask.

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