Kenaf pectin-quinoa protein edible coating film as well as preparation method and application thereof

Abstract

The invention provides a hibiscus cannabinus pectin-quinoa protein edible coating film as well as a preparation method and application thereof, and belongs to the technical field of preservative films. The preparation method comprises the following steps: S1, preparing kenaf pectin; s2, preparing quinoa protein; s3, preparation of a curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion: taking quinoa protein and kenaf pectin, respectively preparing and uniformly stirring to obtain a pectin-protein mixed solution as a water phase; taking curcumin, adding vegetable oil, uniformly stirring in a dark place, ultrasonically dissolving, centrifuging, and taking supernate as an oil phase; and mixing the water phase and the oil phase, and homogenizing to obtain the product. And S4, preparation of the hibiscus cannabinus pectin-quinoa protein edible coating film: mixing the edible plasticizer with the Pickering emulsion, uniformly stirring, and removing bubbles to obtain the hibiscus cannabinus pectin-quinoa protein edible coating film. The Pickering emulsion with better emulsification and embedding performance and antibacterial effect is prepared from the hibiscus cannabinus pectin and the quinoa protein, an edible coating film loaded with curcumin is safe, non-toxic and edible, the shelf life of fruits such as strawberries can be prolonged, and the application prospect is wide.

Description

Technical Field

[0001] This invention relates to the field of food preservation film technology, and more specifically, to an edible coating of kenaf pectin-quinoa protein, its preparation method, and its application. Background Technology

[0002] Edible coatings are made from natural edible substances (such as proteins and pectin), with added edible plasticizers and antibacterial agents. These coatings form through intermolecular interactions, possessing both barrier and antibacterial properties while remaining safe for consumption, representing an important development direction in the food preservation film industry. Utilizing natural proteins and pectin to form Pickering emulsions and encapsulating natural antibacterial agents to create edible coatings is a key research area in edible food preservation coatings.

[0003] Pickering emulsions are emulsions formed by replacing surfactant molecules with colloidal particles such as polysaccharides and proteins. Pickering emulsions are widely used in the food and cosmetic industries due to their anti-agglomeration properties, environmental friendliness, and high stability. They are also extensively used for encapsulating bioactive ingredients and improving their bioavailability. Curcumin is a natural lipophilic polyphenol extracted and isolated from the rhizomes of ginger plants. It has significant antibacterial effects, but its low water solubility and instability under light, high temperature, and alkaline conditions, making it prone to oxidation and degradation, limit its applications.

[0004] Regarding quinoa protein Pickering emulsions, Zhou Wenbo et al. prepared a quinoa protein-citrus pectin Pickering emulsion, but it did not involve the loading of curcumin or its application for antibacterial preservation. Whether the constructed emulsion is suitable for curcumin encapsulation remains unknown. Li Jianan reported the preparation and characteristics of a quinoa protein / sodium alginate composite particle Pickering emulsion. Although it involved loading curcumin into the emulsion, its main purpose was to improve the antioxidant capacity of curcumin and achieve sustained release of curcumin in the gastrointestinal tract.

[0005] Regarding the use of pectin-protein Pickering emulsion systems for encapsulating curcumin, CN120514665A discloses a method for preparing a zein-oxidized starch-Pickering emulsion loaded with curcumin. This method improves the encapsulation rate of curcumin by optimizing concentration and oil phase volume fraction, but does not address its antibacterial and preservative applications. Pectins from different plant sources and extracted with different solvents possess different physicochemical properties. Currently, there are no reports on the preparation of edible coatings using kenaf pectin and quinoa protein. Summary of the Invention

[0006] Based on the problems existing in the prior art, this invention proposes an edible coating film of kenaf pectin and quinoa protein, its preparation method and application. Pickering emulsion with better emulsification and encapsulation properties and antibacterial effect is prepared by kenaf pectin and quinoa protein. The edible coating film loaded with curcumin is safe, non-toxic and edible.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A method for preparing an edible coating of kenaf pectin-quinoa protein includes the following steps:

[0009] S1. Preparation of kenaf pectin;

[0010] S2, Preparation of quinoa protein;

[0011] S3. Preparation of Curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion

[0012] Quinoa protein and kenaf pectin were prepared into protein aqueous solution and pectin aqueous solution, respectively. The mixture was stirred evenly to obtain a pectin-protein mixed solution, which was used as the aqueous phase.

[0013] Take curcumin, add vegetable oil, stir evenly in the dark, sonicate to dissolve, centrifuge to remove insoluble matter, and take the supernatant as the oil phase;

[0014] The aqueous and oil phases were mixed and homogenized to obtain a curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion.

[0015] S4. Preparation of edible coating of kenaf pectin-quinoa protein

[0016] The edible plasticizer is mixed with the curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion, stirred evenly, and the air bubbles are removed to obtain the edible kenaf pectin-quinoa protein coating.

[0017] Preferably, in step S3, the mass ratio of quinoa protein to kenaf pectin is 1-5:1.

[0018] In this invention, the concentrations of the protein aqueous solution and the pectin aqueous solution are not limited, as long as the protein and pectin can be completely dissolved.

[0019] Preferably, the mass-to-volume ratio of curcumin to corn oil is 0.4-4g:100-800mL.

[0020] Preferably, in step S3, the volume ratio of the aqueous phase to the oil phase is 5-7:5-3.

[0021] Preferably, in step S3, the vegetable oil is any one or more of corn oil, soybean oil, and peanut oil.

[0022] Preferably, in step S4, the volume ratio of the edible plasticizer to the curcumin-loaded sesame pectin-quinoa protein Pickering emulsion is 1:3-5.

[0023] Preferably, in step S1, the preparation specifically includes the following steps:

[0024] The bast bark of kenaf is crushed, soaked in alcohol, and filtered to obtain defatted kenaf powder. Citric acid solution is added to the defatted kenaf powder, and the mixture is extracted by shaking in a water bath. After cooling to room temperature, it is filtered, the filtrate is collected, and concentrated by rotary evaporation. After alcohol precipitation, washing, and drying, kenaf pectin is obtained.

[0025] Preferably, the concentration of the citric acid solution is 0.05-0.2 mol / L.

[0026] Preferably, the volume ratio of defatted sesame powder to citric acid solution is 1:6-20.

[0027] Preferably, the water bath temperature is 80-90℃ and the extraction time is 4-6 h.

[0028] Preferably, the temperature for rotary evaporation concentration is 50-60℃.

[0029] In step S2, the preparation specifically includes the following steps:

[0030] Quinoa rice flour was crushed and soaked in alcohol to obtain defatted quinoa rice flour. NaCl solution and α-amylase were added to the defatted quinoa rice flour, and the mixture was extracted by shaking in a water bath under neutral conditions. After centrifugation, the supernatant was collected. The supernatant was dialyzed and then freeze-dried to obtain quinoa protein.

[0031] Preferably, the concentration of the NaCl solution is 0.2-0.5 mol / L, and the volume ratio of defatted quinoa rice flour to NaCl solution is 1:10-20.

[0032] Preferably, the water bath temperature is 55-65℃ and the extraction time is 3-6 h.

[0033] Preferably, the dialysis bag has a molecular weight cutoff of 1000-3000 Da and the dialysis time is 48-62 h.

[0034] Preferably, in step S4, the edible plasticizer is any one or more of glycerin, propylene glycol, and polyethylene glycol. The plasticizer is used to improve the film-forming properties of the coating. Glycerin is a food additive and is edible. In addition, propylene glycol, polyethylene glycol, etc., are also food additives and have plasticizing functions.

[0035] The edible coating film made from kenaf pectin and quinoa protein prepared by the method described above.

[0036] The application of the aforementioned edible sesame pectin-quinoa protein coating in fruit preservation.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] The preparation method of this invention uses kenaf pectin and quinoa protein as raw materials to prepare a Pickering emulsion. This emulsion can load more curcumin, and the resulting edible coating has good preservation and antibacterial effects. The raw materials are widely available and inexpensive, which helps to achieve high-value conversion of kenaf and quinoa.

[0039] In the preparation method of the present invention, kenaf pectin is extracted with citric acid. Compared with kenaf pectin extracted with ammonium oxalate (CN202211192326.X), kenaf pectin has a higher content of galacturonic acid, and the Pickering emulsion prepared with it exhibits better emulsification and encapsulation properties and antibacterial effect.

[0040] In the preparation method of the present invention, quinoa protein is extracted using a low-concentration food-grade NaCl solution as a solvent, which does not pose a food safety risk. Moreover, compared with quinoa protein extracted with NaOH, it has a higher total protein content. The Pickering emulsion prepared with this quinoa protein exhibits better emulsification and encapsulation properties as well as antibacterial effects.

[0041] The edible coating prepared by this invention is based on kenaf pectin extracted with citric acid and quinoa protein extracted with NaCl solution. It has better antibacterial and preservation effects, is safe and non-toxic and edible, and can improve the quality of fruits such as strawberries during storage and extend the shelf life of fruits. Attached Figure Description

[0042] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided and described:

[0043] Figure 1 The infrared spectra of kenaf pectin prepared in Examples 1-3 and Control Group 1 of this invention are shown.

[0044] Figure 2 The monosaccharide composition of the kenaf pectin prepared in Examples 1-3 and Control Group 1 of this invention. Detailed Implementation

[0045] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways than those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0047] It should be noted that the raw materials, instruments, etc. involved in this invention are all commercially available products.

[0048] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0049] Example 1

[0050] This embodiment provides a method for preparing an edible coating of kenaf pectin-quinoa protein, comprising the following steps:

[0051] (1) Preparation of kenaf pectin

[0052] The harvested fresh kenaf bast was cut into small sections using a guillotine cutter and transferred to a homogenizer. Twice the volume (w / v) of deionized water was added, and the mixture was homogenized and broken down. The homogenate was then filtered. The residue was soaked in eight times the volume (w / v) of 95% ethanol for 24 hours to remove impurities such as lipids and fat-soluble pigments. The residue was then filtered again and air-dried in a fume hood to obtain defatted kenaf powder.

[0053] Place defatted sesame powder in a flask, add 10 times the amount of 0.1 mol / L citric acid solution, and extract by shaking in a water bath at 85°C for 4 hours. After cooling to room temperature, filter, collect the filtrate, and concentrate it to a smaller volume by rotary evaporation at 55°C.

[0054] Add twice the volume (v / v) of anhydrous ethanol to the concentrate for alcohol precipitation, let stand at 4°C for 12 hours, filter, and obtain the precipitate. Wash the precipitate twice with anhydrous ethanol, dry at 50°C, grind, and obtain kenaf pectin.

[0055] (2) Preparation of quinoa protein

[0056] Quinoa rice was ground through a 60-mesh sieve, and 5 times (w / v) of 95% ethanol was added. The mixture was soaked for 12 hours, filtered, and the residue was soaked twice more with 5 times (w / v) of 95% ethanol added. The residue was then air-dried in a fume hood to obtain defatted quinoa flour.

[0057] Defatted quinoa powder was placed in a flask, and 15 times (w / v) of 0.5 mol / L NaCl solution and 40 U / g of α-amylase were added. The mixture was extracted by shaking in a water bath at 60°C for 4 h at pH=7. After cooling to room temperature, the mixture was centrifuged at 4000 rpm for 15 min and the supernatant was collected.

[0058] Adjust the pH of the solution to 4.5, let it stand for 1 hour, and centrifuge at 8000 rpm and 4℃ for 20 minutes. Transfer the precipitate to a dialysis bag with a molecular weight cutoff of 3000 Da, dialyze it in deionized water for 48 hours, freeze-dry the dialysate, and grind it to obtain quinoa protein.

[0059] (3) Preparation of curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion

[0060] Take 0.5g of quinoa protein and 0.1g of kenaf pectin, add deionized water, and prepare protein solutions of 5g / L and pectin solutions of 1g / L, respectively. Take 100mL of protein solution and 100mL of pectin solution, and mix them evenly on a magnetic stirrer at 400rpm to obtain a pectin-protein mixed solution, which will be used as the aqueous phase.

[0061] Take 0.2g of curcumin, add 50mL of corn oil, stir in the dark for 12h, then sonicate for 30min to fully dissolve, centrifuge at 4000rpm for 20min, and take the supernatant as the oil phase.

[0062] Take 50 mL of the aqueous phase and 50 mL of the oil phase, and homogenize them in a high-speed homogenizer at 14,000 rpm for 3 min to obtain the curcumin-loaded sesame pectin-quinoa protein Pickering emulsion.

[0063] (4) Preparation of edible coating of kenaf pectin-quinoa protein

[0064] Glycerin and kenaf pectin-quinoa protein Pickering emulsion were mixed at a volume ratio of 1:3 and stirred at 400 rpm for 1 hour on a magnetic stirrer. After standing to remove air bubbles, an edible kenaf pectin-quinoa protein coating was obtained.

[0065] Example 2

[0066] This embodiment provides another method for preparing an edible coating of kenaf pectin-quinoa protein, comprising the following steps:

[0067] (1) Preparation of kenaf pectin

[0068] Freshly harvested kenaf bast was cut into small sections using a guillotine cutter and transferred to a homogenizer. Twice the volume (w / v) of deionized water was added, and the mixture was homogenized and broken down. The homogenate was then filtered. The residue was soaked in nine times the volume (w / v) of 90% ethanol for 20 hours to remove impurities such as lipids and fat-soluble pigments. The residue was then filtered again and air-dried in a fume hood to obtain defatted kenaf powder.

[0069] Place defatted sesame powder in a flask, add 8 times the volume of 0.2 mol / L citric acid solution, and extract by shaking in a water bath at 80°C for 5 hours. After cooling to room temperature, filter, collect the filtrate, and concentrate it to a smaller volume by rotary evaporation at 55°C.

[0070] Add 3 times (v / v) anhydrous ethanol to the concentrate for alcohol precipitation, let stand at 4°C for 12 hours, filter, and obtain the precipitate. Wash the precipitate twice with anhydrous ethanol, dry at 50°C, grind, and obtain kenaf pectin.

[0071] (2) Preparation of quinoa protein

[0072] Quinoa rice was ground through a 60-mesh sieve, and then soaked for 16 hours with 4 times the amount (w / v) of 95% ethanol. After filtration, the residue was soaked twice with 4 times the amount (w / v) of 95% ethanol. The residue was then dried in a fume hood to obtain defatted quinoa flour.

[0073] Defatted quinoa powder was placed in a flask, and 18 times (w / v) of 0.4 mol / L NaCl solution and 50 U / g of α-amylase were added. The mixture was extracted by shaking in a water bath at 55°C for 6 hours under pH=7 conditions. After cooling to room temperature, the mixture was centrifuged at 4000 rpm for 15 minutes, and the supernatant was collected.

[0074] Adjust the pH of the solution to 4.2, let it stand for 2 hours, and centrifuge at 8000 rpm and 4℃ for 20 minutes. Transfer the precipitate to a dialysis bag with a molecular weight cutoff of 3000 Da, dialyze it in deionized water for 52 hours, freeze-dry the dialysate, and grind it to obtain quinoa protein.

[0075] (3) Preparation of curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion

[0076] Take 0.4g of quinoa protein and 0.2g of kenaf pectin, add deionized water, and prepare protein solutions of 4g / L and pectin solutions of 2g / L, respectively. Take 100mL of protein solution and 100mL of pectin solution, and mix them evenly on a magnetic stirrer at 400rpm to obtain a pectin-protein mixed solution, which will be used as the aqueous phase.

[0077] Take 0.2g of curcumin, add 50mL of corn oil, stir in the dark for 12h, then sonicate for 30min to fully dissolve, centrifuge at 4000rpm for 20min, and take the supernatant as the oil phase.

[0078] Take 60 mL of the aqueous phase and 40 mL of the oil phase, and homogenize them in a high-speed homogenizer at 13,000 rpm for 3 min to obtain the curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion.

[0079] (4) Preparation of edible coating of kenaf pectin-quinoa protein

[0080] Glycerin and kenaf pectin-quinoa protein Pickering emulsion were mixed at a volume ratio of 1:4 and stirred at 400 rpm for 1 hour on a magnetic stirrer. After standing to remove air bubbles, an edible kenaf pectin-quinoa protein coating was obtained.

[0081] Example 3

[0082] This embodiment provides another method for preparing an edible coating of kenaf pectin-quinoa protein, including the following steps:

[0083] (1) Preparation of kenaf pectin

[0084] The harvested fresh kenaf bast was cut into small sections using a guillotine cutter and transferred to a homogenizer. Twice the volume (w / v) of deionized water was added, and the mixture was homogenized and broken down. The homogenate was then filtered. Ten times the volume (w / v) of 95% ethanol was added to the filter residue, and the residue was soaked for 18 hours to remove impurities such as lipids and fat-soluble pigments. The residue was then filtered again and air-dried in a fume hood to obtain defatted kenaf powder.

[0085] Place defatted sesame powder in a flask, add 12 times the amount of 0.05mol / L citric acid solution, and extract by shaking in a water bath at 90℃ for 6 hours. After cooling to room temperature, filter, collect the filtrate, and concentrate it to a smaller volume by rotary evaporation at 55℃.

[0086] Add 4 times (v / v) anhydrous ethanol to the concentrate for alcohol precipitation, let stand at 4°C for 12 hours, filter, and obtain the precipitate. Wash the precipitate twice with anhydrous ethanol, dry at 50°C, grind, and obtain kenaf pectin.

[0087] (2) Preparation of quinoa protein

[0088] Quinoa rice was ground through a 60-mesh sieve, and 6 times (w / v) of 95% ethanol was added. The mixture was soaked for 10 hours, filtered, and the residue was soaked twice more with 6 times (w / v) of 95% ethanol added. The residue was then air-dried in a fume hood to obtain defatted quinoa flour.

[0089] Place defatted quinoa powder in a flask, add 20 times (w / v) of 0.2 mol / L NaCl solution and 60 U / g of α-amylase, and extract by shaking in a water bath at 65°C for 3 h at pH=7. After cooling to room temperature, centrifuge at 4000 rpm for 15 min and collect the supernatant.

[0090] Adjust the pH of the solution to 4.7, let it stand for 3 hours, and centrifuge at 8000 rpm and 4℃ for 20 minutes. Transfer the precipitate to a dialysis bag with a molecular weight cutoff of 3000 Da, dialyze it in deionized water for 60 hours, freeze-dry the dialysate, and grind it to obtain quinoa protein.

[0091] (3) Preparation of curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion

[0092] Take 0.3g of quinoa protein and 0.3g of kenaf pectin, add deionized water, and prepare protein solutions and pectin solutions of 3g / L and 3g / L respectively. Take 100mL of protein solution and 100mL of pectin solution, and mix them evenly on a magnetic stirrer at 400rpm to obtain a pectin-protein mixed solution, which is used as the aqueous phase.

[0093] Take 0.2g of curcumin, add 50mL of corn oil, stir in the dark for 12h, then sonicate for 30min to fully dissolve, centrifuge at 4000rpm for 20min, and take the supernatant as the oil phase.

[0094] Take 70 mL of the aqueous phase and 30 mL of the oil phase, and homogenize them in a high-speed homogenizer at 13000 rpm for 3 min to obtain the curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion.

[0095] (4) Preparation of edible coating of kenaf pectin-quinoa protein

[0096] Glycerin and kenaf pectin-quinoa protein Pickering emulsion were mixed at a volume ratio of 1:5 and stirred at 400 rpm for 1 hour on a magnetic stirrer. After standing to remove air bubbles, an edible kenaf pectin-quinoa protein coating was obtained.

[0097] Control group 1

[0098] Based on Example 1, the citric acid solution for extracting kenaf pectin in step (1) was replaced with a 4% ammonium oxalate solution. The other steps were completely consistent with Example 1. The kenaf pectin, kenaf pectin-quinoa protein Pickering emulsion and edible coating prepared were used as control group 1.

[0099] Control group 2

[0100] Based on Example 1, the NaCl solution used to extract quinoa protein in step (2) was replaced with NaOH solution (pH=8), and the other steps were the same as in Example 1. The quinoa protein, sesame pectin-quinoa protein Pickering emulsion and edible coating prepared were used as control group 2.

[0101] Control group 3

[0102] Based on Example 1, kenaf pectin was replaced with citrus pectin (pectin content >65%, purchased from Shanghai Yuanye Biotechnology Co., Ltd.), and other subsequent steps were completely consistent with Example 1. The citrus pectin-quinoa protein Pickering emulsion and edible coating prepared were used as control group 3.

[0103] Control group 4

[0104] Based on Example 1, kenaf pectin was replaced with apple pectin (pectin content >65%, purchased from Shanghai Yuanye Biotechnology Co., Ltd.), and other subsequent steps were completely consistent with Example 1. The apple pectin-quinoa protein Pickering emulsion and edible coating prepared were used as control group 4.

[0105] Experimental Example 1

[0106] The galacturonic acid content of the kenaf pectin of this invention was determined with reference to the literature "Tullia MCC Filisetti-Cozzi, Nicholas C. Carpita. Measurement of uronic acids without interference from neutral sugars. Analytical Biochemistry, 1991, 197(1): 157-162".

[0107] The results of galacturonic acid content determination in Examples 1 to 3 and Control Group 1 are shown in Table 1.

[0108] Table 1

[0109]

[0110] The experimental results above show that the galacturonic acid content of kenaf pectin prepared in Examples 1 to 3 did not differ significantly. Compared with control group 1, the galacturonic acid content of kenaf pectin extracted with citric acid in Examples 1 to 3 was significantly increased.

[0111] Citric acid and ammonium oxalate are both solvents used for extracting pectin, but their extraction mechanisms and effects differ. Citric acid primarily utilizes the hydrolysis of pectin in acidic solutions to convert insoluble pectin into soluble pectin. This solvent causes less damage to the polymer chains of pectin, preserving their integrity. Furthermore, as a green extraction agent, it offers advantages such as safety, non-toxicity, low cost, and high efficiency, leading to its widespread application in the food industry.

[0112] Ammonium oxalate belongs to the ammonium salt class. Its oxalate ions can complex with metal ions such as calcium and magnesium in plant cell walls, disrupting pectin-metal ion complexes and thus converting water-insoluble calcium pectate into water-soluble ammonium pectate, increasing pectin solubility. However, ammonium oxalate also dissolves impurities such as hemicellulose bound to pectin, leading to a decrease in the purity of the pectin sample. Therefore, the galacturonic acid content of kenaf pectin extracted by this method is lower than that extracted with citric acid. In addition, ammonium oxalate is toxic to organisms; ingestion or inhalation may cause poisoning.

[0113] Experiment Example 2

[0114] The near-infrared characteristics of kenaf pectin were analyzed according to the literature “Tang JL, Qin XL, Repo-Carrasco-Valencia, R., et al. Physicochemical, functional and antioxidant properties of four polysaccharides sequentially extracted from jute (Corchorus olitorius L.) leaves. International Journal of Biological Macromolecules. 2025, 323:147223”. Figure 1 ) and monosaccharide composition were analyzed ( Figure 2 It can be seen that the infrared absorption characteristics of the kenaf pectin prepared in Examples 1 to 3 are not significantly different. The infrared absorption characteristics of the kenaf pectin prepared in Control Group 1 are somewhat different from those in Examples 1 to 3, for example, at 3190 cm⁻¹... -1 1976cm -1 1645cm -1 738cm -1 There are distinct characteristic absorption peaks near the isowavenumber.

[0115] From the perspective of monosaccharide composition, there was no significant difference in the monosaccharide composition of the kenaf pectin prepared in Examples 1 to 3. Compared with the three examples, the kenaf pectin prepared in Control Group 1 had higher contents of xylose, arabinose, and mannose, while having lower contents of rhamnose, galactose, and galacturonic acid.

[0116] The differences in the structural characteristics of kenaf pectin between the examples and the control group are also due to the different extraction solvents. As mentioned earlier, ammonium oxalate can promote the dissolution of hemicellulose, thereby increasing the content of monosaccharides such as xylose and arabinose in kenaf pectin.

[0117] Experimental Example 3

[0118] The total protein content in quinoa protein was determined according to the literature “Bradford, MM A Rapid and Sensitive Method for the Quantitation of Microgram Quantities of Protein Utilizing the Principle of Protein-Dye Binding. Analytical Biochemistry. 1976, 72, 248–254”.

[0119] The protein extraction rate and total protein content of Examples 1 to 3 and Control Group 2 are shown in Table 2.

[0120] Table 2

[0121]

[0122] The experimental results above show that there were no significant differences in the quinoa protein extraction rate and total protein content among Examples 1 to 3. Compared with control group 2, the quinoa protein extraction rate obtained using NaCl solution in Examples 1 to 3 was lower, but the total protein content was significantly increased.

[0123] A certain concentration of NaCl solution can promote protein dissolution by regulating the binding affinity of proteins, thereby increasing protein purity. Therefore, NaCl solution yields quinoa protein with a higher total protein content. Furthermore, dilute salt solutions have the advantage of protecting proteins from denaturation because salt ions partially bind to them.

[0124] Experiment Example 4

[0125] The emulsifying activity index and emulsifying stability index of the kenaf pectin-quinoa protein mixed solution were determined according to the reference "Jia Shuohong, Xu Yujuan, Wu Jijun, et al. Preparation and stability study of cellulose nanofiber synergistic pectin-stabilized Pickering emulsion. Food and Fermentation Industries, 2025, https: / / doi.org / 10.13995 / j.cnki.11-1802 / ts.042501".

[0126] Table 3 shows the results of emulsifying activity index and emulsifying stability index determination for the kenaf pectin-quinoa protein mixed solutions of Examples 1 to 3, Control Groups 1 to 2, Control Group 3 (citrus pectin-quinoa protein mixed solution), and Control Group 4 (apple pectin-quinoa protein).

[0127] Table 3

[0128]

[0129] The experimental results above show that the emulsifying activity index and emulsifying stability index of the kenaf pectin-quinoa protein mixed solutions in Examples 1 to 3 are not significantly different. Compared with the control groups 1 to 4, the emulsifying activity index and emulsifying stability index of the kenaf pectin-quinoa protein mixed solutions in Examples 1 to 3 are significantly improved.

[0130] Experimental Example 5

[0131] The encapsulation rate of curcumin in sesquiterpenoid pectin-quinoa protein Pickering solution was determined according to the reference “Xu Bingxin, Liu Chaoran, Feng Xinyi, et al. Antioxidant properties and environmental stability of zein-tea saponin composite nanoparticles loaded with curcumin. Food Industry Technology, 2025, 46(05): 26-34.”

[0132] The results of curcumin encapsulation rate determination in Examples 1 to 3 and Control Groups 1 to 4 are shown in Table 4.

[0133] Table 4

[0134]

[0135] The experimental results above show that the encapsulation efficiency of curcumin in the kenaf pectin-quinoa protein Pickering solutions prepared in Examples 1 to 3 did not differ significantly. Compared with control groups 1 to 4, the encapsulation efficiency of curcumin in the kenaf pectin-quinoa protein Pickering solutions prepared in Examples 1 to 3 was significantly improved.

[0136] Experimental Example 6

[0137] Referring to the literature "Li Yanpeng, Xia Wei, Chen Ting, et al. Optimization of Compound Shikonin Effervescent Tablets and Study on Antibacterial Activity. Food Industry, 2025, 46(09): 31-36", the antibacterial activity of the curcumin-loaded sesame pectin-quinoa protein Pickering emulsion of the present invention was detected by measuring the diameter of the inhibition zone against Escherichia coli and Staphylococcus aureus. The results of the inhibition zone diameter measurement of Examples 1 to 3 and Control Groups 1 to 4 are shown in Table 5.

[0138] Table 5

[0139]

[0140] The results above show that the diameters of the inhibition zones of the curcumin-loaded kenaf pectin-quinoa protein Pickering emulsions prepared in Examples 1 to 3 against *Escherichia coli* and *Staphylococcus aureus* were not significantly different. Compared with the four control groups, the inhibition zone diameters of Examples 1 to 3 were larger, indicating stronger antibacterial activity.

[0141] Experimental Example 7

[0142] Strawberries were immersed in the pectin-protein edible coating of this invention for 2 minutes, air-dried naturally, and stored at 20°C and 80% relative humidity for 8 days. The preservation effect of the pectin-protein edible coating of this invention was tested by measuring the spoilage rate, weight loss rate, and firmness of the strawberries after 8 days of storage, referring to the literature "Chen Wei, Gong Yanjing, Chen Lu, et al. Application study of chitosan and Lactobacillus plantarum CM-3 composite coating agent in strawberry preservation. China Food Additives, 2024, 35(10):29-35".

[0143] Table 6

[0144]

[0145] The results above show that there were no significant differences in the spoilage rate, weight loss rate, and firmness of strawberries after immersion in the coatings prepared in Examples 1 to 3 for 8 days. Compared with the four control groups, Examples 1 to 3 showed lower spoilage rates and weight losses, and greater firmness, indicating better preservation effects on strawberries. It can be seen from the above that, compared with the control groups, the sesame pectin-quinoa protein edible film prepared in this invention has stronger antibacterial activity and better preservation effects on strawberries.

[0146] The membrane preparation process of this invention is safe and non-toxic, and the resulting membrane is edible.

[0147] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing an edible coating of kenaf pectin-quinoa protein, characterized in that, Includes the following steps: S1. Preparation of kenaf pectin; S2, Preparation of quinoa protein; S3. Preparation of Curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion Quinoa protein and kenaf pectin were prepared into protein aqueous solution and pectin aqueous solution, respectively. The mixture was stirred evenly to obtain a pectin-protein mixed solution, which was used as the aqueous phase. Take curcumin, add vegetable oil, stir evenly in the dark, sonicate to dissolve, centrifuge to remove insoluble matter, and take the supernatant as the oil phase; The aqueous and oil phases were mixed and homogenized to obtain a curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion. S4. Preparation of edible coating of kenaf pectin-quinoa protein The edible plasticizer is mixed with the curcumin-loaded kenaf pectin-quinoa protein Pickering emulsion, stirred evenly, and the air bubbles are removed to obtain the edible kenaf pectin-quinoa protein coating.

2. The preparation method according to claim 1, characterized in that, In step S3, the mass ratio of quinoa protein to kenaf pectin is 1-5:1; preferably, the volume ratio of the aqueous phase to the oil phase is 5-7:5-3; preferably, the mass-volume ratio of curcumin to corn oil is 0.4-4g:100-800mL; preferably, the vegetable oil includes any one or more of corn oil, soybean oil, and peanut oil.

3. The preparation method according to claim 1, characterized in that, In step S4, the volume ratio of glycerol to curcumin-loaded sesame pectin-quinoa protein Pickering emulsion is 1:3-5; the edible plasticizer is any one or more of glycerol, propylene glycol, and polyethylene glycol.

4. The preparation method according to claim 1, characterized in that, In step S1, the preparation specifically includes the following steps: The bast bark of kenaf is crushed, soaked in alcohol, and filtered to obtain defatted kenaf powder. Citric acid solution is added to the defatted kenaf powder, and the mixture is extracted by shaking in a water bath. After cooling to room temperature, it is filtered, the filtrate is collected, and concentrated by rotary evaporation. After alcohol precipitation, washing, and drying, kenaf pectin is obtained.

5. The preparation method according to claim 4, characterized in that, The concentration of the citric acid solution is 0.05-0.2 mol / L; preferably, the volume ratio of defatted sesame powder to citric acid solution is 1:6-20.

6. The preparation method according to claim 4, characterized in that, The water bath temperature is 80-90℃, and the extraction time is 4-6 hours; preferably, the rotary evaporation concentration temperature is 50-60℃.

7. The preparation method according to claim 1, characterized in that, In step S2, the preparation specifically includes the following steps: Quinoa rice flour was crushed and soaked in alcohol to obtain defatted quinoa rice flour. NaCl solution and α-amylase were added to the defatted quinoa rice flour, and the mixture was extracted by shaking in a water bath under neutral conditions. After centrifugation, the supernatant was collected. The supernatant was dialyzed and then freeze-dried to obtain quinoa protein.

8. The preparation method according to claim 7, characterized in that, The concentration of the NaCl solution is 0.2-0.5 mol / L, and the volume ratio of defatted quinoa rice flour to NaCl solution is 1:10-20; preferably, the water bath temperature is 55-65℃, and the extraction time is 3-6 h; preferably, the dialysis bag has a molecular weight cutoff of 3000 Da, and the dialysis time is 48-62 h.

9. An edible coating of kenaf pectin-quinoa protein prepared by the method for preparing an edible coating of kenaf pectin-quinoa protein as described in any one of claims 1-8.

10. The application of the edible coating of kenaf pectin-quinoa protein as described in claim 9 in fruit preservation.

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