Coffee residue extract composite fresh-keeping coating liquid containing chitosan and hydroxypropyl starch, preparation method of coffee residue extract composite fresh-keeping coating liquid and application of coffee residue extract composite fresh-keeping coating liquid in storage and transportation fresh keeping of thin-skin fruits

Abstract

The invention belongs to the technical field of fruit and vegetable fresh-keeping, and discloses a chitosan and hydroxypropyl starch containing coffee residue extract composite fresh-keeping coating liquid, a preparation method and application in storage and transportation fresh keeping of thin-skin fruits, and every 1000 mL of the fresh-keeping liquid comprises 20 g of chitosan, 20 g of waste coffee residue extract, 7.5 g of hydroxypropyl starch, 2 mL of glycerin and the balance of distilled water. According to the green composite fresh-keeping coating liquid containing the chitosan-hydroxypropyl starch-coffee residue extract, the storage and transportation fresh-keeping quality of thin-leather small-sized vulnerable fruits is improved, and the green composite fresh-keeping coating liquid is completely natural in source, free of peculiar smell, stable, durable and easy to clean, meets the higher requirements of the market for cleaning labels and healthy products, and has a good market prospect. And meanwhile, the problems of insufficient high-value utilization of agricultural by-product coffee grounds and environmental pollution are effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of fruit and vegetable preservation technology, and in particular to a composite preservation coating liquid containing chitosan and hydroxypropyl starch from coffee grounds extract, its preparation method, and its application in the storage and preservation of thin-skinned fruits. Background Technology

[0003] Waste coffee grounds are rich in active ingredients such as chlorogenic acid, caffeine, protocatechuic acid, and flavonoids. Their extract (SCGE) has shown potential in food preservation: SCGE treatment of chicken breast significantly inhibits microbial growth, maintains antioxidant capacity, and extends shelf life; SCGE edible films prepared by combining SCGE with carboxymethyl cellulose, when applied to physalis, reduce weight loss and respiration rate, inhibit microbial growth, and improve storage quality; active packaging using SCGE as an antioxidant also shows good preservation effects in refrigerated foods. Natural extract preservatives, with their advantages of high safety, environmental friendliness, and low cost, are gradually gaining widespread attention in the preservation field. However, existing natural extract preservative coatings reported in the above studies still suffer from low mechanical properties, uneven coating, rapid loss of active ingredients, and residues after pre-consumption washing when storing thin-skinned fruits in high humidity and easily mechanically damaged conditions.

[0004] Specifically, the existing technology has the following problems: (1) The uneven spread and insufficient mechanical properties of the preservative coating make it difficult to meet the requirements of thin-skinned small berries, which are susceptible to mechanical damage and microbial infection; (2) Natural active ingredients are prone to migration and precipitation during coating storage and their efficacy is unstable; (3) It is difficult to clean completely before consumption, resulting in surface residue and other problems.

[0005] The search revealed the following patent publications related to this invention's patent application: 1. Patent document CN 202510457411.1 (publication date: May 27, 2025) discloses a chitosan composite preservation film, which is prepared by combining oxidized starch, phytic acid, carvacrol and chitosan to prepare a preservation film, which reduces the decay rate of strawberries and grapes, delays the senescence of strawberry and grape fruits, and inhibits the growth of putrefactive fungi Alternaria and Penicillium olsenii in strawberries and grapes.

[0006] The problems are: (1) The mechanical properties of the composite coating are not clearly mentioned. Oxidized starch itself has poor mechanical properties and strong water absorption. Even if it is combined with chitosan, it may still have certain limitations in improving the mechanical strength of the coating and is difficult to effectively resist mechanical damage to strawberries and grapes during storage and transportation; (2) Carvacrol depends on plant extraction, which has limited production capacity and high cost; (3) Carvacrol has a volatile odor. When used for the preservation of strawberries and grapes, it may remain on the surface of the fruit, affecting the original flavor of the fruit and the sensory experience of consumers.

[0007] 2. Patent document CN 201610684462.9 (publication date: January 7, 2017) discloses a chitosan composite preservation film. A grape preservative is obtained by dissolving clove extract, calcium chloride, vitamin C, and potassium sorbate in water, followed by adding a chitosan-citric acid solution. The preservative has a simple process, leaves minimal surface chemical residue, and can significantly reduce or delay quality decline and spoilage during grape storage.

[0008] The problems are: (1) Potassium sorbate, as a common chemical preservative, is safe within the prescribed scope of use, but long-term and excessive intake may have a certain impact on human health and cannot meet consumers' higher demand for green and natural preservation; (2) When multiple components are mixed to prepare a preservative, uneven distribution of components may occur during actual production and use, resulting in unstable preservation effect; (3) Vitamin C has poor stability and is easily affected by temperature, light, etc., which may lead to multiphase separation problems and make it impossible to preserve for a long time.

[0009] By comparison, the present invention patent application is fundamentally different from the aforementioned patent publications. Summary of the Invention

[0010] The purpose of this invention is to overcome the shortcomings of the prior art and provide a composite preservative coating liquid containing chitosan and hydroxypropyl starch coffee grounds extract, its preparation method, and its application in the storage and preservation of thin-skinned fruits.

[0011] The technical solution adopted by this invention to solve its technical problem is: A composite preservative coating liquid containing chitosan and hydroxypropyl starch, derived from coffee grounds extract, comprising the following components per 1000 mL of preservative liquid: Chitosan (CS) 20 g, Spent Coffee Grounds Extract (SCGE) 20 g, Hydroxypropyl Starch (HPS) 7.5 g, Glycerin 2 mL, Distilled Water to 1000 mL.

[0012] Furthermore, the 20 g chitosan is food grade with a degree of deacetylation ≥ 85%, conforming to GB 29941-2013.

[0013] Furthermore, the preparation method of the waste coffee grounds extract is as follows: (a) Spread the waste coffee grounds (SCG) evenly on a tray, place it in an oven at 45°C and dry it to constant weight. After drying, vacuum seal it and store it at room temperature away from light. (b) Weigh the waste coffee grounds dried in (a) and mix them thoroughly with an ethanol solution containing 0.1% glacial acetic acid at a volume concentration of 70% (g:mL) at a material-to-liquid ratio of 1:5. Sonicate for 30 min at 240 W and extract by shaking in the dark at room temperature for 2 h. After extraction, place the mixture in a centrifuge at 4℃ and centrifuge at 6000 × g for 20 min. Collect the supernatant and perform a second extraction on the residue to obtain crude SCG extract. (c) Transfer the crude SCG extract to a clean petri dish and dry it in an oven at 50°C for 12 hours. Once drying is complete, the waste coffee grounds extract is obtained.

[0014] Furthermore, the main components of the waste coffee grounds extract are: total phenol content of 12.92 mg / g and total flavonoid content of 85.41 mg / g.

[0015] The method for preparing the composite preservative coating liquid as described above involves using a secondary alcohol extraction process to efficiently extract polyphenolic substances from waste coffee grounds, and then combining chitosan and hydroxypropyl starch to prepare the composite preservative coating liquid.

[0016] Furthermore, it includes the following steps: (1) Prepare a 1% (mass concentration) glacial acetic acid aqueous solution: Pipette 5 mL of glacial acetic acid into a volumetric flask, add distilled water to make up to 500 mL, take 400 mL of the solution and preheat it to 55℃ for later use; (2) Accurately weigh 20 g of CS (food grade, degree of deacetylation ≥ 85%, conforming to GB 29941-2013), slowly sprinkle it into the preheated glacial acetic acid aqueous solution, and magnetically stir at 300 rpm for 2 h at 55℃ until the chitosan is completely dissolved to obtain CS base solution; (3) Accurately weigh 20g of SCGE powder, mix it with 400 mL of distilled water, and sonicate it at 40 kHz and 240 W for 10 min to form a uniform dispersion. The SCGE dispersion is then magnetically stirred at 300 rpm at 25℃ for later use. (4) Weigh 7.5 g HPS, mix with 100 mL distilled water, heat in a water bath to 75°C and maintain for 30 min (magnetic stirring at 200 rpm) to form a transparent gelatinized liquid, cool to 55°C and set aside. (5) Under continuous magnetic stirring at 300 rpm, the above HPS gelatinized liquid was slowly added to the CS base liquid. After mixing evenly, the SCGE dispersion was added, followed by 2 mL of glycerol. The mixture was then stirred magnetically at 300 rpm for 30 min until the system was homogeneous. (6) Add distilled water to the above mixture to bring the volume to 900 mL, sonicate at 40 kHz and 200 W for 30 min, and finally bring the volume to 1000 mL with distilled water to obtain a brownish-brown viscous and uniformly dispersed liquid, which is the CS+SCGE+HPS composite preservation coating solution. This coating solution should be prepared and used immediately, and stored at 4℃ in the dark for no more than 12 h.

[0017] The method of using the composite preservative coating liquid as described above includes the following steps: (a) Immersion: Immerse intact, undamaged, thin-skinned, small, and fragile fruits in a composite preservative coating solution at a ratio of 1:3 (kg:L) to ensure that the fruits are completely submerged in the coating solution; after immersion, remove the fruits with a slotted spoon and drain them for 10 min at 25°C and RH ≤ 60%. Alternatively, (b) spraying method: use a small handheld sprayer with a pressure of 0.2 MPa and a nozzle diameter of 0.5 mm, spray evenly twice at a distance of 20 cm from the fruit surface, once on the front and once on the back, with a single spray volume of 1.5 mL / 100 g of fruit. After spraying, let the fruit air dry naturally in a ventilated place. Washing before consumption: Before eating fruits treated with the compound preservative coating liquid, a simple washing process can remove the compound preservative coating liquid.

[0018] Furthermore, after treating the fruit with the composite preservative coating liquid, gently rinse it under clean running water for 10-15 seconds at a water temperature of 15-20℃ to completely remove the surface composite film. After draining for 30 seconds, the fruit can be eaten directly.

[0019] The above-mentioned composite preservative coating liquid is used in the preservation of small, fragile fruits with thin skin (such as grapes, jujubes, and cherry tomatoes).

[0020] The advantages and positive effects of this invention are as follows: 1. This invention provides a green composite preservative coating liquid containing chitosan-hydroxypropyl starch-coffee grounds extract, which improves the storage and preservation quality of thin-skinned, small, and fragile fruits. It is also all-natural, odorless, stable, and long-lasting, meeting the market's higher demand for clean labels and healthy products. At the same time, it effectively solves the problems of insufficient high-value utilization of agricultural by-product coffee grounds and environmental pollution.

[0021] 2. The film-forming base solution of this invention adopts a ternary network of "chitosan-hydroxypropyl starch-coffee ground polyphenols". After gelatinization, hydroxypropyl starch provides flexible linear chains. The amino groups of chitosan and starch hydroxyl groups form hydrogen bonds / electrostatic crosslinks. The coffee ground polyphenols fill the micropores through hydrogen bonds. When the thickness of the resulting CS+SCGE+HPS membrane is 53 μm, the tensile strength is ≥ 24 MPa and the elongation at break is ≥ 31%, which are 57.0% and 76.7% higher than those of the CS+HPS membrane, respectively, significantly reducing the mechanical damage rate of thin-skinned berries caused by bumps.

[0022] 3. The polyphenols in the coffee grounds extract of this invention have strong antioxidant capabilities, which can scavenge free radicals generated in grapes during storage and reduce oxidative damage. Chitosan also has certain antioxidant properties; it can slow down the oxidation process of grapes by chelating with metal ions and inhibiting the activity of oxidases. The combination of the two further enhances the antioxidant properties.

[0023] 4. This invention achieves high-value utilization of waste coffee grounds, reducing environmental pollution. Coffee grounds are usually treated as waste, easily leading to resource waste and environmental pollution. This invention extracts and utilizes them to obtain bioactive components for preservation. This not only reduces the potential environmental harm of coffee grounds but also turns waste into treasure, improving resource utilization and reducing the dependence of preservative production on other resources, resulting in excellent environmental and economic benefits.

[0024] 5. This invention is the first to propose a novel ternary synergistic system constructed from chitosan (CS), hydroxypropyl starch (HPS), and coffee grounds extract (SCGE) through intermolecular interactions, achieving synergistic enhancement in the molecular structure, function, and practicality of the coating film. Chitosan, as a cationic natural polysaccharide, forms a continuous rigid framework, providing basic film-forming properties and structural strength. The linear long chains of hydroxypropyl starch act as flexible fillers, interspersed within the chitosan framework. The introduced hydroxypropyl groups effectively disrupt the rigid, ordered arrangement of the chitosan molecular chains, significantly enhancing the film's flexibility, extensibility, and impact resistance. The two components are bonded together through strong hydrogen bonds, forming a dense and uniform "reinforced concrete" composite network. This structure ensures that the coating liquid can form a continuous, defect-free, and highly adhesive film on the surface of thin-skinned, small, and fragile fruits. Its tensile strength and elongation at break are significantly improved, effectively resisting mechanical damage such as collisions and friction during harvesting, storage, and transportation.

[0025] 6. This invention employs a secondary alcohol extraction method to extract polyphenolic substances from waste coffee grounds. The negatively charged phenolic hydroxyl groups and positively charged chitosan molecular chains are electrostatically complexed and firmly anchored within the composite membrane network. This fundamentally solves the problem of easy migration and precipitation of active ingredients in traditional natural extract preservatives, ensuring that antibacterial and antioxidant components remain stably and persistently on the fruit surface, preventing rapid deterioration and achieving long-lasting preservation. This patented composite preservative coating effectively blocks the permeation of oxygen and moisture, significantly reducing the respiration rate and weight loss of fruit, and delaying aging. Simultaneously, due to the uniform film formation, it avoids localized clumping or spotting, maintaining the appearance and color quality of the fruit.

[0026] 7. For small, fragile fruits with thin skin that can be eaten directly without peeling, the coating agent should be easy to wash off and leave low residue. The hydrophilicity and cold water dispersibility of hydroxypropyl starch effectively enable the coating to form a stable and robust film layer together with chitosan and coffee grounds extract during preservation and storage. When consumers rinse with water, water molecules quickly penetrate and disrupt the hydrogen bond network of hydroxypropyl starch, causing it to swell rapidly. This leads to the complete disintegration and peeling of the ternary composite film from the fruit surface, greatly improving the product's practical safety and consumer experience, and solving the problem of traditional coating agents being difficult to wash off.

[0027] 8. The green composite preservative coating liquid of this invention is a green, efficient, and user-friendly natural preservative coating agent. When this patented CS+SCGE+HPS composite preservative coating liquid is applied to the preservation of grapes, winter jujubes, and cherry tomatoes, it exhibits outstanding advantages such as good mechanical strength, uniform extensibility, long-lasting functional activity, and easy cleaning. Its preservation effect is significantly better than CS+HPS, SCGE+HPS coating liquid and the control group.

[0028] 9. Innovative combination of raw materials in this invention: For the first time, an edible ternary network is constructed by combining "chitosan-hydroxypropyl starch-coffee grounds extract" in a fixed weight ratio (20:7.5:20). The gelatinized linear chain of hydroxypropyl starch provides a flexible framework, the amino groups of chitosan and the hydroxyl groups of starch form hydrogen bonds / electrostatic crosslinks, and the polyphenols of coffee grounds fill the micropores through hydrogen bonds and endow them with antioxidant-antibacterial dual functions. This makes the 53 μm composite membrane have a tensile strength ≥ 24 MPa and an elongation at break ≥ 31%, which is significantly better than the CS+HPS membrane.

[0029] 10. High-value utilization of waste in this invention: Using waste coffee grounds as raw material, SCGE is obtained through "drying at 55℃ → secondary ultrasonic extraction with 70% ethanol → concentration and drying at 50℃" to replace synthetic antioxidants, thereby increasing the resource utilization rate of coffee grounds to ≥ 12% and reducing the cost of preservative raw materials. Attached Figure Description

[0030] Figure 1 This is a diagram illustrating the SCG raw materials, extracts, and solutions used in this invention. Figure 2 This is a diagram illustrating the preservation effect of Kyoho grapes in this invention. Figure 3 The weight loss (A), respiration rate (B), soluble solids (TSS) (C), and volume (V) of Kyoho grapes under different treatments in this invention are shown in Figure 1. C Content (D) plot; where, for the same storage time, different lowercase letters indicate significant differences between groups ( P <0.05), the same applies to the following figures; Figure 4 The graph shows the total phenols (A), flavonoids (B), anthocyanins (C), malondialdehyde (MDA) (D), polyphenol oxidase (PPO) activity (E), and hydrogen peroxide (H2O2) content (F) of Kyoho grapes under different treatments in this invention. Figure 5 The graph shows the total number of colonies (A), mold (B), and yeast (C) of Kyoho grapes under different treatments in this invention. Figure 6 This is a diagram illustrating the preservation effect of winter jujubes in this invention. Figure 7 The graph shows the weight loss rate (A), decay rate (B), and respiration rate (C) of jujube under different treatments in this invention. Figure 8 The TSS(A) and V of jujube under different treatments in this invention C Content (B) chart; Figure 9 This is a diagram illustrating the preservation effect of cherry tomatoes in this invention. Figure 10 The graph shows the weight loss rate (A), decay rate (B), and respiration rate (C) of cherry tomatoes under different treatments in this invention. Figure 11 The TSS(A) and V of cherry tomatoes under different treatments in this invention C Content (B) chart; Figure 12 This is a schematic diagram illustrating an extraction process for waste coffee grounds and the preparation of a composite coating liquid in this invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0032] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0033] Applications in the storage, transportation, and preservation of fruits with thin skin.

[0034] A composite preservative coating liquid containing chitosan and hydroxypropyl starch, derived from coffee grounds extract, comprising the following components per 1000 mL of preservative liquid: Chitosan (CS) 20 g, coffee grounds extract (SCGE) 20 g, hydroxypropyl starch (HPS) 7.5 g, glycerin 2 mL, distilled water to 1000 mL.

[0035] Furthermore, the 20 g chitosan is food grade with a degree of deacetylation ≥ 85%, conforming to GB 29941-2013.

[0036] Furthermore, the preparation method of the waste coffee grounds extract is as follows: (a) Spread the waste coffee grounds evenly on a tray, place them in a 45°C oven to dry to constant weight, vacuum seal after drying and store at room temperature away from light; (b) Weigh the waste coffee grounds dried in (a) and mix them thoroughly with an ethanol solution containing 0.1% glacial acetic acid at a volume concentration of 70% (g:mL) at a material-to-liquid ratio of 1:5. Sonicate for 30 min at 240 W and extract by shaking in the dark at room temperature for 2 h. After extraction, place the mixture in a centrifuge at 4℃ and centrifuge at 6000 × g for 20 min. Collect the supernatant and perform a second extraction on the residue to obtain crude SCG extract. (c) Transfer the crude SCG extract to a clean petri dish and dry it in an oven at 50°C for 12 h. Once drying is complete, SCGE is obtained.

[0037] Furthermore, the main components of the SCGE are: total phenol content of 12.92 mg / g and total flavonoid content of 85.41 mg / g.

[0038] The method for preparing the composite preservative coating liquid as described above involves using a secondary alcohol extraction process to efficiently extract polyphenolic substances from waste coffee grounds, and then combining CS and HPS to prepare the composite preservative coating liquid.

[0039] Furthermore, it includes the following steps: (1) Prepare a 1% (mass concentration) glacial acetic acid aqueous solution: Pipette 5 mL of glacial acetic acid into a volumetric flask, add distilled water to make up to 500 mL, take 400 mL of the solution and preheat it to 55℃ for later use; (2) Accurately weigh 20 g of CS (food grade, degree of deacetylation ≥ 85%, conforming to GB 29941-2013), slowly sprinkle it into the preheated glacial acetic acid aqueous solution, and magnetically stir at 300 rpm for 2 h at 55℃ until the chitosan is completely dissolved to obtain CS base solution; (3) Accurately weigh 20g of SCGE powder, mix it with 400 mL of distilled water, and sonicate it at 40 kHz and 240 W for 10 min to form a uniform dispersion. The SCGE dispersion is then magnetically stirred at 300 rpm at 25℃ for later use. (4) Weigh 7.5 g HPS, mix with 100 mL distilled water, heat in a water bath to 75°C and maintain for 30 min (magnetic stirring at 200 rpm) to form a transparent gelatinized liquid, cool to 55°C and set aside. (5) Under continuous magnetic stirring at 300 rpm, the above HPS gelatinized liquid was slowly added to the CS base liquid. After mixing evenly, the SCGE dispersion was added, followed by 2 mL of glycerol. The mixture was then stirred magnetically at 300 rpm for 30 min until the system was homogeneous. (6) Add distilled water to the above mixture to bring the volume to 900 mL, sonicate at 40 kHz and 200 W for 30 min, and finally bring the volume to 1000 mL with distilled water to obtain a brownish-brown viscous and uniformly dispersed liquid, which is the CS+SCGE+HPS composite preservation coating solution. This coating solution should be prepared and used immediately, and stored at 4℃ in the dark for no more than 12 h.

[0040] The method of using the CS+SCGE+HPS composite preservative coating liquid as described above includes the following steps: (a) Immersion: Immerse intact, undamaged, thin-skinned, small, and fragile fruits in a composite preservative coating solution at a ratio of 1:3 (kg:L) to ensure that the fruits are completely submerged in the coating solution; after immersion, remove the fruits with a slotted spoon and drain them for 10 min at 25°C and RH ≤ 60%. Alternatively, (b) spraying method: use a small handheld sprayer with a pressure of 0.2 MPa and a nozzle diameter of 0.5 mm, spray evenly twice at a distance of 20 cm from the fruit surface, once on the front and once on the back, with a single spray volume of 1.5 mL / 100 g of fruit. After spraying, let the fruit air dry naturally in a ventilated place. Washing before consumption: Before eating fruits treated with the compound preservative coating liquid, a simple washing process can remove the compound preservative coating liquid.

[0041] Furthermore, after treating the fruit with the composite preservative coating liquid, gently rinse it under clean running water for 10-15 seconds at a water temperature of 15-20℃ to completely remove the surface composite film. After draining for 30 seconds, the fruit can be eaten directly.

[0042] The above-mentioned composite preservative coating liquid is used in the preservation of small, fragile fruits with thin skin (such as grapes, jujubes, and cherry tomatoes).

[0043] Specifically, the relevant preparation and testing methods are as follows: Example 1 This invention provides a method for preparing a green composite preservative coating liquid containing chitosan, hydroxypropyl starch, and coffee grounds extract, and its application. The method utilizes a secondary alcohol extraction process to efficiently extract polyphenols from waste coffee grounds. Chitosan and hydroxypropyl starch are then combined to prepare the preservative coating liquid. This liquid is applied by soaking or spraying thin-skinned, small, and fragile fruits. After film formation, the fruits are packaged and rinsed with water before consumption, thereby improving their preservation quality. Figure 12 As shown, the specific steps are as follows: (1) Extraction of active ingredients from waste coffee grounds (SCG): (a) SCG was evenly spread on a tray and dried in a 45℃ oven (DHG-9140A, Anhui Ninghuai Instrument Co., Ltd.) until constant weight. After drying, it was vacuum sealed and stored at room temperature away from light. (b) 200 g of SCG dried in (a) was weighed and mixed thoroughly with 1000 mL of 70% ethanol solution (containing 0.1% glacial acetic acid) at a material-to-liquid ratio of 1:5 (g:mL). The mixture was ultrasonically extracted at 240 W (SB-6000DT, Ningbo Xinzhi Biotechnology Co., Ltd.) for 30 min and then shaken in the dark at room temperature (SHA-B, Changzhou Tianjing Experimental Instrument Factory) for 2 h. After extraction, the mixture was centrifuged at 4℃, 6000 × g for 20 min in a centrifuge (TGL-16, Sichuan Shuke Instrument Co., Ltd.). The supernatant was collected and the residue was extracted a second time to obtain crude SCG extract. (c) Transfer the crude SCG extract to a clean petri dish and dry it in an oven at 50°C for 12 hours. After drying, the waste coffee grounds extract (SCGE) is obtained, as follows: Figure 1 As shown. The main components of SCGE were determined to be: total phenol content 12.92 mg / g, total flavonoid content 85.41 mg / g, and the extract was stored at -20℃ after sealing.

[0044] (2) Preparation of CS+HPS coating solution (2% SCGE-0.75% HPS-0.2% glycerol): Based on a 1000 mL system, the coating solution contains 2% (w / v, mass concentration) CS, 0.75% (w / v, mass concentration) HPS, and 0.2% (v / v, volume concentration) glycerol, as detailed below: (a) Prepare a 1% (mass concentration) aqueous solution of glacial acetic acid: Pipette 5 mL of glacial acetic acid into a volumetric flask, add distilled water to make up to 500 mL, take 400 mL of this solution and preheat it to 55°C for later use; (b) Accurately weigh 20 g of CS (food grade, degree of deacetylation ≥ 85%, conforming to GB 29941-2013), slowly sprinkle it into the preheated glacial acetic acid aqueous solution, and magnetically stir at 300 rpm for 2 h at 55°C until the chitosan is completely dissolved to obtain CS base solution; (c) Weigh 7.5 g HPS, mix with 100 mL distilled water, heat in a water bath to 75°C and maintain for 30 min (magnetic stirring at 200 rpm) to form a transparent gelatinized liquid. After cooling to 55°C, slowly add the above CS base liquid while stirring continuously at 300 rpm and mix evenly. (d) Add 2 mL of glycerol to the mixture and continue to stir magnetically at 300 rpm for 30 min until the system is homogeneous. Then add distilled water to make up to 900 mL. Sonicate at 40 kHz and 200 W for 30 min. Finally, make up to 1000 mL with distilled water to obtain a colorless, transparent, viscous liquid with a pH of 4.2 ± 0.2, which is the CS+HPS coating solution. Prepare and use immediately.

[0045] (3) Preparation of SCGE+HPS coating solution (2%SCGE-0.75%HPS-0.2%glycerin): Based on a 1000 mL system, the coating solution contains 2% (w / v, mass concentration) SCGE, 0.75% (w / v, mass concentration) HPS, and 0.2% (v / v, volume concentration) glycerol, as detailed below: (a) Accurately weigh 20g of SCGE powder, mix it with 400 mL of distilled water, and sonicate it at 40 kHz and 240 W for 10 min to form a uniform dispersion. The SCGE dispersion is then magnetically stirred at 300 rpm at 25°C for later use. (b) Weigh 7.5 g HPS, mix with 100 mL distilled water, heat in a water bath to 75°C and maintain for 30 min (magnetic stirring at 200 rpm) to form a transparent gelatinized liquid. After cooling to 25°C, slowly add the above SCGE dispersion while stirring continuously at 300 rpm and mix evenly. (c) Add 2 mL of glycerol to the mixture and continue to stir magnetically at 300 rpm for 30 min until the system is homogeneous. Then add distilled water to make up to 900 mL. Sonicate at 40 kHz and 200 W for 20 min. Finally, make up to 1000 mL with distilled water to obtain a brownish-brown uniform dispersion, which is the SCGE+HPS coating solution. The coating solution should be prepared and used immediately and stored at 4℃ in the dark for no more than 12 h.

[0046] (4) Preparation of CS+SCGE+HPS composite preservative coating solution (2%CS-2%SCGE-0.75%HPS-0.2%glycerin): A preservative coating liquid containing chitosan-hydroxypropyl starch-waste coffee grounds extract, wherein each 1000 mL of preservative liquid contains: Chitosan (CS) 20 g (food grade, degree of deacetylation ≥ 85%, conforming to GB 29941-2013), waste coffee grounds extract (SCGE) 20 g, hydroxypropyl starch (HPS) 7.5 g, glycerin 2 mL, distilled water to 1000 mL, details as follows: (a) Preparation of CS base liquid: Same as steps (a) and (b) in Example 1 (2), CS base liquid was prepared and magnetically stirred at 300 rpm at 55°C for later use; (b) Preparation of HPS gelatinized liquid and SCGE dispersion: The preparation of HPS gelatinized liquid is the same as the first half of step (c) in Example 1 (2). After obtaining transparent gelatinized liquid, it is cooled to 55°C for later use; The preparation of SCGE dispersion is the same as step (a) in Example 1 (3). SCGE dispersion is obtained for later use. (c) Base material mixing and plasticizer addition: Under continuous magnetic stirring at 300 rpm, the above HPS gelatinized liquid was slowly added to the CS base liquid. After mixing evenly, SCGE dispersion was added, followed by 2 mL of glycerol. The mixture was then stirred magnetically at 300 rpm for 30 min until the system was homogeneous. (d) Volume adjustment and ultrasonic treatment: Add distilled water to the above mixture to a final volume of 900 mL, sonicate at 40 kHz and 200 W for 30 min, and finally adjust the volume to 1000 mL with distilled water to obtain a brownish-red, viscous, uniformly dispersed solution, which is the CS+SCGE+HPS composite preservative coating solution. This coating solution should be prepared and used immediately, and stored at 4℃ in the dark for no more than 12 h.

[0047] (5) Preservation treatment with coating solution: (a) Immersion: Immerse intact, undamaged, thin-skinned, small, and fragile fruits in the above coating solution at a ratio of 1:3 (kg:L), ensuring that the fruits are completely submerged. After immersion, remove the fruits with a slotted spoon and drain them for 10 min in an environment of 25℃ and RH ≤ 60%. (b) Spraying method: Use a small handheld sprayer (0.2 MPa, nozzle diameter 0.5 mm) to spray evenly twice (once on each side) from a distance of 20 cm from the fruit surface. The amount of liquid sprayed at one time is 1.5 mL / 100 g of fruit. After spraying, allow the fruit to air dry naturally in a ventilated place.

[0048] (6) Packaging: (a) Bag type: Choose plastic food storage bags with good air permeability and preservation performance, such as polyethylene (PE) food storage bags or polypropylene (PP) food storage bags. (b) Box type: Choose food-grade plastic food storage boxes or foam food storage boxes.

[0049] Washing before consumption: The green composite preservative coating liquid containing chitosan-hydroxypropyl starch-coffee grounds extract prepared in this invention can be removed from fruits by a simple washing step before consumption. Gently rinse the fruit under clean running water for 10-15 seconds at a water temperature of 15-20℃ to completely remove the surface composite film. After draining for 30 seconds, the fruit can be eaten directly.

[0050] Example 2 Preservation experiment of Kyoho grapes: 1. Raw material pretreatment Kyoho grapes with similar appearance, uniform ripeness, and no diseases, pests, or mechanical damage were selected as experimental materials. The grapes were randomly divided into four groups (A, B, C, and D), with each group weighing approximately 10.0 ± 0.5 kg. The grapes were placed in a PE microporous membrane (O2 permeability: 6000-8000 cm / (m²)). 2 ·d), CO2 transmission rate: 12000-16000 cm⁻¹ 2 / (m 2 ·d), Water vapor transmission rate: 20-30 g / (m 2 Place the grapes in plastic turnover baskets (with simple sealing to prevent water loss). Pre-cool each group of grapes in a cold storage at 0 ± 1℃ (relative humidity RH 90%-95%) for 12 h.

[0051] 2. Coating treatment The pre-cooled grapes were immersed in the CS+HPS coating solution, SCGE+HPS coating solution, and CS+SCGE+HPS composite preservative coating solution prepared in Example 1, respectively. 1000 mL of each coating solution was prepared, ensuring that the liquid level was more than 2 cm above the fruit. After immersion for 3 min, the grapes were removed and ventilated to dry for 25 min. The fourth group of grapes served as a control group (immersed in distilled water under the same conditions).

[0052] 3. Storage conditions The four groups of grapes were placed into food-grade PP preservation boxes (5 L capacity, with ventilation holes) and stored in a cold storage for 35 days, with the temperature controlled at 0 ± 1℃ and the relative humidity at 90%-95%.

[0053] 4. Physiological and quality indicator testing Samples were taken on days 0, 5, 10, 15, 20, 25, 30, and 35 of storage to determine weight loss, respiratory rate, TSS, and vitamin C (V). C The total phenols, flavonoids, anthocyanins, malondialdehyde (MDA), polyphenol oxidase (PPO), hydrogen peroxide (H2O2), and microbial indicators were measured.

[0054] Respiration intensity: The respiration intensity of grapes was measured using a fruit and vegetable respiration meter (FS-GH100, Shandong Lainede Intelligent Technology Co., Ltd.). Grapes were placed in a 2 L respiration chamber and left to stand for 15 min. The data from the fruit and vegetable respiration meter after standing were recorded. The test was repeated 3 times, and the average value was taken (unit: mg / kg·h).

[0055] TSS: Place 2 drops of grape juice on a handheld digital saccharimeter (AK002B, Shenzhen Ceyou Technology Co., Ltd.) to measure TSS. The result is expressed as a percentage.

[0056] V C Total phenols, flavonoids, anthocyanins, PPO activity, and MDA: According to "Guide to Postharvest Physiological and Biochemical Experiments in Fruits and Vegetables" (edited by Cao Jiankang, Jiang Weibo, and Zhao Yumei, 1st edition), the results were expressed as mg / 100 g, OD... 280 / g、OD 325 / g、(OD 530 -OD 600 / g) / g, U / g, μmol / g are used to express this.

[0057] H2O2: The H2O2 content was detected using a hydrogen peroxide detection kit (Shanghai Ruifan Biotechnology Co., Ltd.), and the results are expressed in µmol / mL.

[0058] Microbiological indicators: The total number of grape colonies was determined according to GB 4789.2-2022, and the number of grape molds and yeasts was determined according to GB 4789.15-2016.

[0059] Experimental data were analyzed using SPSS 22.0 and Origin 2021 software. Significant differences were analyzed using one-way ANOVA. Data are expressed as mean ± standard deviation, and the LSD test was used to determine the statistical significance level. P A difference of <0.05 is statistically significant.

[0060] Depend on Figure 2 It can be seen that the preservation effect (loose fruit bunches, berry drop, and water loss of fruit and stems) of grapes in the three coating treatment groups after 35 days of storage was better than that of the untreated control group. However, the CS+SCGE+HPS composite preservation coating treatment group of this invention still had relatively firm fruit bunches and good stem condition after 35 days, which was significantly better than the CS+HPS and SCGE+HPS treatment groups.

[0061] Depend on Figure 3 As shown in Figure A, the weight loss rate of Kyoho grapes increased over time during storage, while the weight loss rate of the CS+SCGE+HPS composite preservative coating solution treatment group was significantly lower than that of the CS+HPS, SCGE+HPS treatment groups, and the control group. P<0.05). After 35 days of storage, the weight loss rate of the CS+SCGE+HPS composite preservative coating liquid treatment group was only 3.22%, while the CS+HPS and SCGE+HPS single treatment groups were 3.97% and 4.62%, respectively, and the weight loss rate of the control group was as high as 4.88%.

[0062] Depend on Figure 3 As shown in B, the peak respiratory rate of grape bunches treated with the CS+SCGE+HPS composite preservative coating solution of the present invention (5.92 mg / kg·h) occurred on the 10th day of storage, while the peak respiratory rates of the CS+HPS and SCGE+HPS treatment groups and the control (6.11 mg / kg·h, 6.40 mg / kg·h, and 6.71 mg / kg·h, respectively) all occurred on the 5th day. This indicates that the application of the CS+SCGE+HPS coating solution of the present invention significantly reduced the postharvest respiratory intensity of grape bunches and delayed their peak respiratory rate.

[0063] Depend on Figure 3 As shown in C, the TSS content of Kyoho grapes generally showed a trend of first increasing and then decreasing during storage. After 20 days of storage, the TSS content of grapes treated with the CS+SCGE+HPS composite preservative coating solution of this invention was 15.6%, which was significantly higher than that of the control group (14.9%) by 4.7%.

[0064] Depend on Figure 3 D indicates that V was present during the storage of the four groups of grapes. C The content of all components decreased significantly. After 35 days, the content of the CS+SCGE+HPS composite preservative coating treatment group V was significantly lower. C The content retention rate was 53.7%, with 49.9% and 38.7% in the CS+HPS and SCGE+HPS treatment groups, respectively, while the control group had only 34.6%.

[0065] Depend on Figure 4 As shown in A and 4B, the total phenol and flavonoid contents of the four groups of grapes all showed a trend of first increasing and then decreasing, and reached their peak values ​​in each group after 20 days of storage. The total phenol content of the CS+SCGE+HPS composite preservative coating liquid of this invention was 6.1% and 16.7% higher than that of the CS+HPS and SCGE+HPS treatment groups, and 34.6% higher than that of the control group; the flavonoid content was 8.8% and 32.1% higher than that of the CS+HPS and SCGE+HPS treatment groups, and 48.0% higher than that of the control group.

[0066] Depend on Figure 4 As shown in C, the anthocyanin content of all four groups of grapes increased significantly during storage. At 35 days, the anthocyanin content of the group treated with the CS+SCGE+HPS composite preservative coating of this invention was significantly higher than that of the control group by 37.5%. Figure 4As shown in D, the MDA content of all four groups of grapes increased significantly during storage. Throughout the entire storage period, the cumulative MDA content in the CS+SCGE+HPS composite preservative coating group was only 15.49 nmol / g, which was 18.3% and 28.3% lower than the CS+HPS and SCGE+HPS treatment groups, respectively, and significantly lower than the control group by 39.1%.

[0067] Depend on Figure 4 E shows that after 35 days of storage, the PPO activity of the CS+SCGE+HPS composite preservative coating liquid group of the present invention was 1.58 U / g, which was 25.5% and 30.7% lower than that of the CS+HPS and SCGE+HPS treatment groups, respectively, and 38.3% lower than that of the control group.

[0068] Depend on Figure 4 As can be seen from F, after 35 days of storage, the H2O2 content of the CS+SCGE+HPS composite preservative coating liquid of this invention was only 0.11 μmol / mL, which was significantly reduced by 35.3% compared with the control group.

[0069] According to the Chinese national standard (GB 2763-2021) and the guidelines of the International Committee for Microbiological Standards in Food (ICMSF), a TVC < ​​4.0 lg CFU / g is considered a safe threshold, while a TVC > 5.0 lg CFU / g indicates a significantly increased risk of spoilage. Figure 5 As shown in Figure A, the TVC values ​​of the CS+SCGE+HPS composite coating treatment group of this invention were all below 3 lg CFU / g during the 35-day storage period, while the control group reached 4.16 lg CFU / g after 25 days of storage. Referring to GB 2763-2021, when the total number of molds and yeasts > 3.0 lg CFU / g, Kyoho grapes enter the spoilage stage. Figure 5 As shown in B and 5C, after 35 days of storage, the number of molds and yeasts in the composite coating treatment group of the present invention was significantly reduced by 37.5% compared with the control group.

[0070] Meanwhile, it can also be seen that the composite preservative coating liquid (CS+SCGE+HPS) of the present invention has significantly better comprehensive preservation effects than single chitosan-based coating liquid (CS+HPS) and single coffee grounds extract-based coating liquid (SCGE+HPS) in terms of delaying postharvest weight loss of grapes, retaining nutrients, enhancing the antioxidant capacity of fruits, and inhibiting microbial proliferation. This indicates that chitosan (CS) and waste coffee grounds extract (SCGE) exhibit a significant complementary and synergistic effect in the composite coating system. The combination of the two can optimize the physical barrier and biological activity functions of the coating, thereby significantly improving the comprehensive preservation effect on grapes.

[0071] Example 3 Winter jujube preservation experiment: 1. Raw material pretreatment Jujubes with similar appearance, uniform maturity, and freedom from pests, diseases, and mechanical damage were selected as experimental materials. The jujubes were randomly divided into four groups (A, B, C, and D), with each group weighing approximately 4.0 ± 0.1 kg. They were placed in a PE microporous membrane (O2 permeability: 6000-8000 cm⁻¹) lining. 3 / (m 2 •d), CO2 transmission rate: 12000-16000 cm⁻¹ 3 / (m 2 •d), Water vapor transmission rate: 20-30 g / (m 2 Place the jujubes in plastic turnover baskets (simply seal to prevent water loss). Pre-cool each group of jujubes in a cold storage at 0 ± 1℃ (relative humidity RH 90%-95%) for 12 h.

[0072] 2. Coating treatment Same as Example 2.

[0073] 3. Storage conditions Four groups of jujubes were placed in food-grade PP preservation boxes (5 L capacity, with ventilation holes) and stored in a cold storage for 30 days, with the temperature controlled at 4 ± 1℃ and the relative humidity at 90 ± 5%.

[0074] 4. Indicator Testing Samples were taken on days 0, 5, 10, 15, 20, 25, and 30 of storage to determine weight loss, decay rate, respiration rate, TSS, and V. C (The above indicators were measured in the same way as in Example 2).

[0075] Depend on Figure 6 It can be seen that the preservation effect (color deterioration and degree of rot) of the three coating treatment groups of winter jujubes after 30 days of storage was better than that of the untreated control group (CK). However, the winter jujubes treated with the CS+SCGE+HPS composite preservation coating liquid of this invention still had relatively bright color and less water loss from fruit wrinkles after 30 days, which was significantly better than the CS+HPS and SCGE+HPS treatment groups.

[0076] Depend on Figure 7 As can be seen from A, the weight loss rate of winter jujubes showed a significant upward trend during storage. P <0.05). After 30 days of storage, the weight loss rate of the CS+SCGE+HPS composite preservative coating liquid treatment group was only 2.12%, while the CS+HPS and SCGE+HPS treatment groups were 2.55% and 2.81%, respectively, and the weight loss rate of the control group was as high as 3.79%.

[0077] Depend on Figure 7As shown in B, after 30 days of storage, the rot rate of the CS+SCGE+HPS composite preservative coating liquid group of the present invention was only 6.67%, while the rot rate of the control group was as high as 20%.

[0078] Depend on Figure 7 As can be seen from C, after 30 days of storage, the respiration intensity of the CS+SCGE+HPS composite preservative coating liquid group of the present invention decreased to 27.4 mg / kg·h, which was 2.14% and 4.7% lower than the CS+HPS and SCGE+HPS treatment groups, respectively, and 8.3% lower than the control group.

[0079] Depend on Figure 8 As shown in Figure A, the TSS content of winter jujubes generally showed a trend of first increasing and then decreasing during storage. The TSS retention rate of the CS+SCGE+HPS composite preservative coating solution treatment group reached 91.5%, which was significantly improved by 25.2% compared with the control group.

[0080] Depend on Figure 8 B indicates that V was present during the storage of the four groups of winter jujubes. C The content of all components continued to decrease, and the V-type of the CS+SCGE+HPS composite preservative coating treatment group of this invention... C The content retention rate was 97.66%, while that of the control group was only 81.93%.

[0081] Meanwhile, it can also be seen that the composite preservative coating liquid (CS+SCGE+HPS) of the present invention has a significantly better overall preservation effect than the single chitosan-based coating liquid (CS+HPS) and the single coffee grounds extract-based coating liquid (SCGE+HPS) in delaying postharvest weight loss of winter jujubes, inhibiting decay, maintaining respiratory metabolic homeostasis, and retaining nutrients. This indicates that chitosan (CS) and waste coffee grounds extract (SCGE) exhibit a significant complementary and synergistic effect in the composite coating system. The combination of the two can optimize the physical barrier and biological activity functions of the coating, thereby improving the overall preservation performance of winter jujubes.

[0082] Example 4 Cherry tomato preservation experiment: 1. Raw material pretreatment Cherry tomatoes with similar appearance, uniform maturity, and no pests, diseases, or mechanical damage were selected as experimental materials. The cherry tomatoes were randomly divided into four groups (A, B, C, and D), with each group weighing approximately 2.0 ± 0.1 kg. They were placed in a PE microporous membrane (O2 permeability: 6000-8000 cm⁻¹) lining. 3 / (m 2 •d), CO2 transmission rate: 12000-16000 cm⁻¹ 3 / (m 2 •d), Water vapor transmission rate: 20-30 g / (m 2Place the cherry tomatoes in plastic turnover baskets (simply seal to prevent water loss). Pre-cool each group of cherry tomatoes in a cold storage at 0 ± 1℃ (relative humidity RH 90%-95%) for 12 h.

[0083] 2. Coating treatment Same as Example 2.

[0084] 3. Storage conditions Four groups of cherry tomatoes were placed in food-grade PP storage boxes (5 L capacity, with ventilation holes) and stored in a cold storage for 25 days, with the temperature controlled at 4 ± 1℃ and the relative humidity at 90 ± 5%.

[0085] 4. Indicator Testing Samples were taken on days 0, 5, 10, 15, 20, and 25 of storage to determine weight loss, decay rate, respiration rate, TSS, and V. C (The testing methods for the above indicators are the same as in Example 2).

[0086] like Figure 9 As shown, the preservation effect (fruit shrinkage, rot spots, and color deterioration) of cherry tomatoes in the three coating treatment groups after 25 days of storage was better than that of the untreated control group (CK). Furthermore, the cherry tomatoes treated with the CS+SCGE+HPS composite preservation coating solution of this invention maintained good plumpness, less shrinkage, and relatively brighter color after 25 days, significantly better than the CS+HPS and SCGE+HPS treatment groups.

[0087] Depend on Figure 10 As can be seen from A, the weight loss rate of cherry tomatoes in all treatment groups showed a significant upward trend during storage. P <0.05), the weight loss rate of the CS+SCGE+HPS composite preservative coating liquid treatment group of the present invention was only 4.86%, which was significantly reduced by 37.9% compared with the control group.

[0088] Depend on Figure 10 As shown in B, the decay rate of cherry tomatoes in the four groups increased with the extension of storage time. After 25 days of storage, the decay rate of the group treated with the CS+SCGE+HPS composite preservative coating liquid of this invention was only 20.3%, the decay rates of the CS+HPS and SCGE+HPS treatment groups were 35.0% and 38.6% respectively, while the control group was as high as 50.1%.

[0089] Depend on Figure 10 As can be seen from C, the respiratory peak of cherry tomatoes treated with the CS+SCGE+HPS composite preservative coating solution of the present invention (1.76 mg / kg·h) occurred on the 10th day of storage, while the respiratory peaks of the CS+HPS and SCGE+HPS treatment groups and the control (1.75 mg / kg·h, 1.78 mg / kg·h, and 1.90 mg / kg·h, respectively) all occurred on the 5th day.

[0090] Depend on Figure 11 As shown in A, the TSS content of the four groups of cherry tomatoes gradually decreased with the extension of storage time. After 25 days of storage, the TSS retention rate of the group treated with the CS+SCGE+HPS composite preservative coating liquid of this invention reached 69.1%, which was 3.7% and 4.8% higher than the CS+HPS and SCGE+HPS treatment groups, respectively, and significantly higher than the control group by 19.6%.

[0091] Depend on Figure 11 B indicates that during storage, the levels of cherry tomatoes in each group V... C The content showed a trend of first increasing and then decreasing. The CS+SCGE+HPS composite preservative coating liquid composition of this invention (V) C The content retention rate was 96.41%, with 93.67% and 91.31% in the CS+HPS and SCGE+HPS treatment groups, respectively, while the control group had only 87.08%.

[0092] Meanwhile, it can also be seen that the composite preservative coating liquid (CS+SCGE+HPS) of the present invention has a significantly better overall preservation effect than the single chitosan-based coating liquid (CS+HPS) and the single coffee grounds extract-based coating liquid (SCGE+HPS) in delaying postharvest weight loss of cherry tomatoes, inhibiting decay, maintaining respiratory metabolic homeostasis, and retaining nutrients. This indicates that chitosan (CS) and waste coffee grounds extract (SCGE) exhibit a significant complementary and synergistic effect in the composite coating system. The combination of the two can optimize the physical barrier and biological activity functions of the coating, thereby improving the overall preservation performance of cherry tomatoes.

[0093] Example 5 Performance testing of plastic wrap: 1. Grouping (a) 30 mL of CS+HPS solution. (The 2% CS-0.75% HPS-0.2% glycerol coating solution prepared in step (2) of Example 1.) (b) 30 mL of SCGE+HPS solution. (This SCGE+HPS solution is the 2% SCGE-0.75% HPS-0.2% glycerol coating solution prepared in step (3) of Example 1.) (c) 30 mL of composite preservation solution. (This composite preservation solution is the 2%CS-2%SCGE-0.75%HPS-0.2% glycerol composite preservation coating solution prepared in step (4) of Example 1.) 2. Drying to form a film Pour the three liquids into disposable polystyrene petri dishes, dry them in a 45°C hot air oven for 9 hours, then transfer them to a 23°C, 50% RH constant temperature and humidity chamber for 24 hours to equilibrate. The plastic wrap can then be obtained by peeling off the film.

[0094] 3. Performance Testing (1) Thickness: Five locations were randomly selected on a flat, smooth, non-porous film, and the thickness of the film was measured using a millimeter (CH-1-S, Shanghai Liuling Instrument Factory). The measurement was repeated three times and the average value was taken.

[0095] (2) Mechanical properties: The film samples were cut into rectangular strips of 40 mm × 10 mm. The tensile strength and elongation at break of the film were tested at room temperature using a texture analyzer (TA. TOUCH, Shanghai Baosheng Industrial Development Co., Ltd., China) (TCA probe). The tensile speed force and scale distance were set to 10 mm / min and 50 mm, respectively.

[0096] The specific test results are shown in Table 1. Compared with the CS+HPS membrane, the tensile strength and elongation at break of the CS+SCGE+HPS membrane prepared in this invention are increased by 57.0% and 76.7%, respectively. Compared with the SCGE+HPS membrane, the improvement is more significant, with tensile strength and elongation at break increasing by approximately 2.0 times and 1.6 times, respectively.

[0097] Table 1

[0098] Meanwhile, it can also be seen that the CS+SCGE+HPS prepared by this invention exhibits a synergistic effect in terms of tensile strength and elongation at break, which can significantly improve the relevant properties of the prepared coating liquid after film formation.

[0099] Furthermore, Chinese patent publication CN119751938A discloses a "composite antibacterial and food preservation film of iron-cobalt oxide / two-dimensional nitride / chitosan and its preparation method and application," whose optimal composite group (CS / 5%CM) has a film thickness of 72.54 ± 0.07 μm and a tensile strength of 24.06 ± 0.08 MPa. In contrast, the composite food preservation film of this invention has a thickness of only 53 ± 0.03 μm (approximately 27% thinner than the CS / 5%CM film), yet achieves a tensile strength of 24.28 ± 0.21 MPa.

[0100] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A composite preservative coating liquid containing chitosan and hydroxypropyl starch from coffee grounds extract, characterized in that: Each 1000mL of preservative solution includes: 20 g chitosan, 20 g waste coffee grounds extract, 7.5 g hydroxypropyl starch, 2 mL glycerin, and distilled water to bring the total volume to 1000 mL.

2. The composite preservative coating liquid according to claim 1, characterized in that: The chitosan is food grade, with a degree of deacetylation ≥ 85%, conforming to GB 29941-2013.

3. The composite preservative coating liquid according to claim 1 or 2, characterized in that: The preparation method of the waste coffee grounds extract is as follows: (a) Spread the waste coffee grounds evenly on a tray, place them in a 45°C oven to dry to constant weight, vacuum seal after drying and store at room temperature away from light; (b) Weigh the waste coffee grounds dried in (a) and mix them thoroughly with a 70% volume concentration ethanol solution containing 0.1% mass concentration glacial acetic acid at a material-to-liquid ratio of 1:5 (g:mL). Sonicate the mixture for 30 min at 240 W and extract it by shaking in the dark at room temperature for 2 h. After extraction, place the mixture in a centrifuge at 4℃ and centrifuge at 6000 × g for 20 min. Collect the supernatant and perform a second extraction on the residue to obtain the crude extract of SCG. (c) Transfer the crude SCG extract to a clean petri dish and dry it in an oven at 50°C for 12 hours. Once drying is complete, the waste coffee grounds extract is obtained.

4. The composite preservative coating liquid according to claim 1 or 2, characterized in that: The main components of the waste coffee grounds extract are: total phenol content of 12.92 mg / g and total flavonoid content of 85.41 mg / g.

5. The method for preparing the composite preservative coating liquid according to any one of claims 1 to 4, characterized in that: The method employs a secondary alcohol extraction process to efficiently extract polyphenolic substances from waste coffee grounds, and then combines chitosan and hydroxypropyl starch to prepare a composite preservative coating liquid.

6. The preparation method according to claim 5, characterized in that: Includes the following steps: (1) Add chitosan to distilled water containing 1% glacial acetic acid preheated to 55°C. The ratio of chitosan to distilled water (g:mL) is 20:

400. Stir magnetically at 300 rpm for 2 h until completely dissolved to obtain chitosan base solution. (2) Weigh hydroxypropyl starch and mix it with distilled water. The ratio of hydroxypropyl starch to distilled water is 7.5:100 g:mL. Heat the mixture in a water bath to 75°C and stir at 200 rpm for 30 min to form a transparent gelatinized liquid. The hydroxypropyl starch gelatinized liquid is then cooled to room temperature for later use. (3) Mix the waste coffee grounds extract with distilled water. The ratio of waste coffee grounds extract to distilled water is 20:400 g:mL. Sonicate at 40 kHz and 240 W for 10 min to form a uniform dispersion and obtain SCGE dispersion. (4) Under continuous magnetic stirring at 300 rpm, the hydroxypropyl starch gelatinized liquid was slowly added to the chitosan-based liquid. After mixing evenly, the SCGE dispersion was added, followed by glycerol. The mixture was then stirred magnetically at 300 rpm for 30 min until the system was homogeneous. (5) Add some distilled water to the above mixture, sonicate at 40 kHz and 200 W for 30 min, and finally add the remaining distilled water to obtain a brownish-brown viscous and uniformly dispersed liquid, which is the composite preservation coating liquid. The coating liquid should be prepared and used immediately, and stored at 4℃ in the dark for no more than 12 h.

7. The preparation method according to claim 5 or 6, characterized in that: The preparation method of the waste coffee grounds extract is as follows: (a) Spread the waste coffee grounds evenly on a tray, place them in a 45°C oven to dry to constant weight, vacuum seal after drying and store at room temperature away from light; (b) Weigh the waste coffee grounds dried in (a) and mix them thoroughly with a 70% volume concentration ethanol solution containing 0.1% mass concentration glacial acetic acid at a material-to-liquid ratio of 1:5 (g:mL). Sonicate the mixture for 30 min at 240 W and extract it by shaking in the dark at room temperature for 2 h. After extraction, place the mixture in a centrifuge at 4℃ and centrifuge at 6000 × g for 20 min. Collect the supernatant and perform a second extraction on the residue to obtain the crude extract of SCG. (c) Transfer the crude SCG extract to a clean petri dish and dry it in an oven at 50°C for 12 hours. Once drying is complete, the waste coffee grounds extract is obtained.

8. The method of using the composite preservative coating liquid as described in any one of claims 1 to 4, characterized in that: Includes the following steps: (a) Immersion: Immerse intact, undamaged, thin-skinned, small, and fragile fruits in a composite preservative coating solution at a ratio of 1:3 (kg:L) to ensure that the fruits are completely submerged in the coating solution; after immersion, remove the fruits with a slotted spoon and drain them for 10 min at 25°C and RH ≤ 60%. Alternatively, (b) spraying method: use a small handheld sprayer with a pressure of 0.2 MPa and a nozzle diameter of 0.5 mm, spray evenly twice at a distance of 20 cm from the fruit surface, once on the front and once on the back, with a single spray volume of 1.5 mL / 100 g of fruit. After spraying, let the fruit air dry naturally in a ventilated place. Washing before consumption: Before eating fruits treated with the compound preservative coating liquid, a simple washing step can remove the compound preservative coating liquid.

9. The method of use according to claim 8, characterized in that: After treating the fruit with the composite preservative coating liquid, gently rinse it under clean running water for 10-15 seconds at a water temperature of 15-20℃ to completely remove the surface composite film. After draining for 30 seconds, the fruit can be eaten directly.

10. The application of the composite preservative coating liquid as described in any one of claims 1 to 4 in the preservation of thin-skinned, small, and fragile fruits (such as grapes, jujubes, and cherry tomatoes).

Images