Phytosterol film forming liquid for fresh keeping of fruits and vegetables as well as preparation method and application method of phytosterol film forming liquid

Abstract

The invention relates to the technical field of fruit and vegetable preservation, in particular to phytosterol film forming liquid for fruit and vegetable preservation and a preparation method and application method. The film forming liquid is prepared from the following components in percentage by weight: 0.5 to 2.0 percent of chitosan, 0.1 to 0.5 percent of phytosterol, 0.05 to 0.3 percent of a one-dimensional nano material, 0.1 to 0.5 percent of an emulsifier, 0.5 to 1.5 percent of a plasticizer and the balance of an acid solvent; the preparation method comprises the following steps: S1, pretreatment; S2, preparation of the phytosterol film-forming liquid. According to the application method, the phytosterol film-forming liquid is applied to fruit and vegetable preservation. According to the invention, the ternary structure design of matrix-hydrophobic filler-reinforced skeleton is utilized, so that the film-forming liquid can form a compact nano composite network during film formation, the nanofiber yarns are used as a skeleton to improve the mechanical and barrier properties, and the phytosterol is used as a strong hydrophobic agent and an antioxidant to fill or cover gaps and surfaces of the network, so that the film-forming effect is improved. And the water resistance of the film is greatly improved.

Description

Technical Field

[0001] This invention relates to the field of fruit and vegetable preservation technology, specifically to phytosterol film-forming solutions for fruit and vegetable preservation, their preparation methods, and their application methods. Background Technology

[0002] Fresh fruits and vegetables remain living organisms after harvest, and continuous respiration and transpiration lead to nutrient loss, weight reduction, and quality decline. Simultaneously, due to their high water and nutrient content, they are highly susceptible to microbial infection, resulting in spoilage. Globally, post-harvest spoilage causes 20-30% of fruit and vegetable losses annually. Traditional preservation methods mainly include low-temperature refrigeration and controlled atmosphere storage, but these methods are costly, energy-intensive, and unsuitable for all stages of the distribution chain. While chemical disinfectant soaking is effective, it easily leads to pesticide residues, causing food safety and environmental pollution problems.

[0003] Edible coating technology is considered a green and safe alternative. Among them, chitosan-based coating is one of the most widely studied technologies. Chitosan, derived from shrimp and crab shells, is a natural polysaccharide with good film-forming properties, biocompatibility, and broad-spectrum antibacterial properties. However, pure chitosan films, due to the large number of hydrophilic groups (hydroxyl and amino groups) in their molecules, have limited ability to block water vapor and cannot effectively inhibit the transpiration and water loss of fruits and vegetables. Furthermore, pure chitosan films are brittle and lack flexibility, easily forming microcracks during drying or storage and transportation, leading to the failure of their protective function. At the same time, its main preservation mechanism relies on the antibacterial properties of chitosan, and its functions in inhibiting respiration (oxygen barrier) and antioxidation are weak, resulting in insufficient preservation dimensions. In addition, single chitosan solutions sometimes have high viscosity or are prone to stickiness after film formation, which is not conducive to uniform spraying and the formation of an ideal film.

[0004] To address the aforementioned problems, this invention provides a film-forming liquid that exhibits good water resistance, high mechanical strength, multiple functions (antibacterial, antioxidant, and respiration-inhibiting) and is suitable for spray application. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a phytosterol film-forming liquid for fruit and vegetable preservation, along with its preparation and application methods.

[0006] The technical solution of the present invention is as follows: a phytosterol film-forming liquid for preserving fruits and vegetables, comprising, by weight percentage, 0.5-2.0% chitosan, 0.1-0.5% phytosterol, 0.05-0.3% one-dimensional nanomaterials, 0.1-0.5% emulsifier, 0.5-1.5% plasticizer, and the balance being an acid solvent; The phytosterol is any one or a mixture of two or more of stigmasterol, β-sitosterol, and campesterol; the emulsifier is any one of Tween-80 and Span 80; the plasticizer is any one of glycerol, sorbitol, and polyethylene glycol; the one-dimensional nanomaterial is one of cellulose nanofibers, chitin nanofibers, and starch nanocrystals; the acid solvent is any one of a 1% (v / v) acetic acid solution, a 5% (v / v) lactic acid solution, and a 5-10% (v / v) citric acid solution, or a mixture of one of these solutions and ethanol at a volume ratio of 1:1. Explanation: Chitosan serves as the film-forming matrix and antibacterial agent, phytosterols act as hydrophobic reinforcing and antioxidant components, and one-dimensional nanomaterials play a role in mechanical reinforcement and barrier framework. Through the synergistic combination of phytosterols, nanofibers, and chitosan, a stable, sprayable "oil-in-water" emulsion system is constructed.

[0007] Furthermore, the chitosan is blue light-resistant modified chitosan; The preparation method of the blue light-resistant modified chitosan is as follows: Step (1): Chitosan pretreatment Add 1% acetic acid solution at a ratio of 1g:80-100mL, and stir for 4-6 hours at 23-27℃ and 450-550rpm with magnetic stirring to obtain a 0.8-1wt% chitosan solution. Dilute acetic acid is used to dissolve the chitosan by protonating the amino groups, making it soluble in water, and providing reaction sites for subsequent reactions. Step (2): Preparation of carboxylated picrate blue light protectant The leaves of *Ilex chinensis* were ground and passed through an 80-100 mesh sieve, and then subjected to supercritical extraction to obtain *Ilex chinensis* extract rich in photoprotective active ingredients. The extract was dissolved in anhydrous pyridine at a ratio of 1 g: 10-15 mL, and succinic anhydride was added at a molar ratio of 1:3-5. The mixture was stirred at 60-70°C under nitrogen protection for 4-6 hours to obtain a reaction solution. This solution was then filtered, washed, and vacuum dried in a drying oven at 35-40°C for 12-24 hours to obtain the activated carboxylated *Ilex chinensis* photoprotectant. Step (3): Preparation of blue light-resistant modified chitosan Adjust the pH of the chitosan solution to 4.5-5.5; then weigh the activated carboxylated picolinate blue photoprotectant according to a weight ratio of chitosan to activated carboxylated picolinate blue photoprotectant of 1:0.3-0.5; then dissolve the activated carboxylated picolinate blue photoprotectant in dimethyl sulfoxide according to a ratio of 1g:20-30mL to obtain a mixed solution. Finally, the mixture was added dropwise to the chitosan solution at a rate of 1-2 drops / s, and carbodiimide hydrochloride was added according to a molar ratio of carboxylated picrine blue light protectant to carbodiimide hydrochloride of 1:1.3-1.7. The mixture was then reacted with shaking in the dark at 23-27°C for 18-24 hours to obtain modified chitosan with anti-blue light function; the carbodiimide hydrochloride was 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride. Note: Chitosan possesses strong film-forming properties, biocompatibility, degradability, antibacterial properties, and non-toxicity. However, while chitosan membranes exhibit some selective permeability to oxygen and carbon dioxide, their extremely high hydrophilicity results in very poor water vapor barrier properties. Furthermore, due to their hydrophilicity, they have poor water barrier properties, and because their primary function is antibacterial, they cannot effectively meet complex preservation requirements. The main harms of blue light to fruits and vegetables include: accelerated chlorophyll degradation: Many green vegetables exposed to blue light lose their vibrant green color more quickly because chlorophyll decomposes more rapidly, leading to yellowing. Induction of oxidative stress: Blue light has high energy, which promotes the production of more reactive oxygen species within fruit and vegetable cells, thereby accelerating oxidative damage to cell membranes and organelles, leading to aging and spoilage. Bitter lettuce is rich in various furan diterpenoids (such as bitter lettuce ketone), which have a good inhibitory effect on fungi such as Penicillium and Botrytis cinerea that cause fruit and vegetable rot, making up for the lack of antibacterial function of chitosan itself. The flavonoids and phenolic acids it contains can effectively remove reactive oxygen species generated by physiological metabolism and stress after fruit and vegetable harvesting, delay aging, and form a synergistic effect with the antioxidant effect of phytosterols, inhibiting the spoilage of fruits and vegetables from multiple aspects. The conjugated structure of flavonoids can also effectively absorb blue light in the 400-500nm wavelength band, converting it into harmless heat energy, reducing the transmission of blue light to fruit and vegetable tissues, thereby improving the anti-blue light effect of the film-forming liquid. In addition, the terpenoid components contained in bitter lettuce have a certain degree of hydrophobicity. By utilizing the hydrophobic terpenoids and long-chain fatty acids in bitter lettuce extract, they can be chemically bonded to the chitosan molecular chain, transforming the hydrophilic chitosan into an amphiphilic or even hydrophobic polymer. This can significantly reduce the water vapor permeability of the membrane material after film formation, effectively preventing moisture loss from fruits and vegetables and the intrusion of environmental moisture.

[0008] Furthermore, in step (2), the conditions for supercritical extraction are as follows: the mobile phase is carbon dioxide and a polar entrainer accounting for 5-10% of the volume of the carbon dioxide; the extraction pressure is 15-20 MPa; the extraction temperature is 30-35℃; and the extraction time is 30-60 min. Note: The above extraction parameters effectively prevent the dissolution of a large number of highly polar impurities (such as chlorophyll, proteins, polysaccharides, and tannins). This simplifies subsequent purification steps, resulting in a lighter-colored extract with fewer impurities and a higher concentration of active ingredients. Furthermore, it effectively optimizes the extraction of blue light-sensitive active ingredients (flavonoids and phenylethyl glycosides).

[0009] Furthermore, the polar entrainer is composed of ethanol and water in a volume ratio of 90-95:5-10; Note: Pure ethanol has good solubility for some phenylethanol glycosides with slightly higher polarity, but may also carry out a small amount of impurities; adding a small amount of water can more selectively dissolve the target phenylethanol glycosides and flavonoid glycosides in gentian, while continuing to effectively remove highly polar impurities such as chlorophyll, polysaccharides, and proteins.

[0010] Furthermore, in step (3), the volume ratio of chitosan solution to mixture is controlled to be 5-10:1; Note: Controlling the volume ratio of chitosan solution to mixture within the above range avoids local overdose of gentian. If the mixture is added too quickly or in too much, the local concentration of gentian will be too high, leading to side reactions between gentian molecules, wasting raw materials and generating impurities, which will affect the performance of modified chitosan.

[0011] Further, in step (2), the filtration and washing method is as follows: first, add the reaction solution to ice-cold ether and let it stand for 30-60 minutes, filter to obtain the solid product, and wash with cold ether 2-3 times; Explanation: Ice-cold ether causes the product to precipitate from the solution by changing the solvent environment. Then, cold ether further dissolves the precipitate and washes away impurities adsorbed on the surface of the precipitate, resulting in a purer solid product.

[0012] This application also provides a method for preparing a phytosterol film-forming solution for preserving fruits and vegetables, comprising the following steps: S1, Preprocessing S1-1, Chitosan pretreatment: First, dissolve chitosan in an acid solvent that accounts for 2 / 4 to 3 / 4 of the total acid solvent volume, and then magnetically stir at 25℃ and 400-600 rpm until clear to obtain a chitosan solution; S1-2, Pretreatment of one-dimensional nanomaterials: The one-dimensional nanomaterials are sheared at 8000-12000 rpm in an ice-water bath for 10-20 min to form a 0.5-1.5 wt% dispersion of one-dimensional nanomaterials; S2. Preparation of phytosterol film-forming solution Phytosterols are mixed with emulsifiers and the remaining acid solvent, and heated at 70-80℃ for 30-45 min to dissolve, obtaining an oil phase. Then, the oil phase is sheared at 8000-10000 rpm for 10-15 min, and the one-dimensional nanomaterial dispersion is added to the chitosan solution to obtain the first composite solution. Next, the oil phase is added dropwise to the first composite solution at a dropping rate of 1-2 mL / min. After the addition is complete, shearing is continued for 5-10 min to obtain a uniform O / W type emulsion, which is the second composite solution. Finally, a plasticizer is added to the second composite solution, and the mixture is stirred at 300-500 rpm for 15-20 min to mix. The mixture is then ultrasonically treated at an ultrasonic power of 300-400 W for 10-15 min, and filtered to obtain the phytosterol film-forming solution. Explanation: By combining high-speed shear emulsification with ultrasonic treatment, hydrophobic phytosterols are stably dispersed as micro- and nano-sized droplets in the aqueous phase of hydrophilic chitosan / nanofiber filaments, forming an O / W type emulsion with good stability and that is not prone to clogging the nozzle.

[0013] Based on the above-mentioned application method of phytosterol film-forming liquid for fruit and vegetable preservation, the phytosterol film-forming liquid is loaded into a spraying device and sprayed at a spraying pressure of 0.1-0.3MPa at a distance of 15-25cm from the surface of the fruit and vegetables. The spraying volume is 50-150mL of phytosterol film-forming liquid per square meter of fruit and vegetable surface area. The product is then naturally air-dried or dried with the help of airflow with a wind speed of <1 m / s at 20-25°C and relative humidity <65% to form a film. Note: Under the above parameters, a uniform, ultra-thin liquid film covering layer can be formed, which can reduce water evaporation, regulate respiration, and block germs. Furthermore, slow and uniform drying can form a dense film, ensuring that the antibacterial and antioxidant components are evenly distributed and have a long-lasting effect.

[0014] Furthermore, the fruit or vegetable in question is either bayberry or leafy greens; Fruits and vegetables such as bayberries and leafy greens, which are difficult to treat with traditional soaking methods or single coatings, require a spray-type preservation film liquid that can evenly cover, is easy to operate, and has extremely low loss. Blue light has high energy and directly catalyzes the photo-oxidation reaction of the abundant anthocyanins and vitamin C in bayberries, causing their characteristic purplish-red color to fade rapidly, turning brown, accompanied by nutrient loss. Common pathogens of bayberries (such as Botrytis cinerea) multiply rapidly under suitable conditions, and light is one of their growth environmental factors. For bayberries, the film of this application can directly block the contact between blue light photons and the surface of the bayberry pulp, thereby physically cutting off the photo-oxidation reaction pathway, delaying fading and nutrient loss, and providing the most basic and direct protection for bayberries. For post-harvest leafy vegetables, blue light stimulates the opening of stomata, leading to a rapid loss of water through transpiration, which is the main cause of wilting and yellowing. Under post-harvest conditions, photosynthesis is hindered, and the absorbed light energy (especially blue light) cannot be effectively utilized. The resulting large amount of reactive oxygen species causes leaves to yellow, age, and rot. For leafy vegetables, "anti-blue light" films filter / reflect some blue light, inhibiting stomatal opening, reducing water transpiration, keeping leaves firm, reducing photo-oxidative stress, protecting chlorophyll, delaying yellowing, and extending shelf life.

[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) This application utilizes a ternary structure design of “matrix-hydrophobic filler-reinforcing skeleton” to enable the film-forming liquid to form a dense nanocomposite network during film formation. The nanofibers serve as the skeleton to enhance mechanical and barrier properties, while phytosterols, as strong hydrophobic agents and antioxidants, fill or cover the gaps and surface of the network, greatly improving the water resistance of the film. Through the combination of high-speed shear emulsification and ultrasonic treatment, it is ensured that the hydrophobic phytosterols can be stably dispersed in the hydrophilic chitosan / nanofiber aqueous phase as micro-nano scale droplets, forming an O / W type emulsion with good stability and not easy to clog the nozzle.

[0016] (2) This application modifies chitosan by extracting crape myrtle. The modified chitosan film-forming solution prepared has anti-blue light function. It is beneficial to the conjugated structure of flavonoids rich in crape myrtle, which can effectively absorb blue light in the 400-500nm wavelength band and convert it into harmless heat energy, reducing the transmission of blue light to fruit and vegetable tissues. In addition, the above-mentioned active ingredients are highly efficient natural antioxidants, which can quickly remove superoxide anions, hydrogen peroxide and other reactive oxygen species generated in fruit and vegetable cells under blue light irradiation, thereby alleviating oxidative damage to fruits and vegetables and delaying aging. At the same time, the chitosan matrix provides excellent barrier properties (waterproofing and regulating respiration), which works synergistically with the photoprotective and antioxidant functions of crape myrtle extract to jointly improve the preservation effect of fruits and vegetables under light. Attached Figure Description

[0017] Figure 1 This is a graph showing the effect of phytosterol film-forming solution treatment on the total sugar content of bayberries during storage; Figure 2 This is a graph showing the effect of phytosterol film-forming solution treatment on the resistance of bayberry to light radiation. Detailed Implementation

[0018] To further illustrate the methods and effects of this invention, the technical solution of this invention will be clearly and completely described below in conjunction with experiments.

[0019] Example 1: A phytosterol film-forming solution for preserving fruits and vegetables, comprising, by weight percentage, 1.2% chitosan, 0.3% phytosterol, 0.15% one-dimensional nanomaterials, 0.3% emulsifier, 1.0% plasticizer, and the balance being an acid solvent. The phytosterol is stigmasterol; the emulsifier is Tween-80; the plasticizer is glycerol; the one-dimensional nanomaterial is cellulose nanofibers; and the acid solvent is a 1% (v / v) acetic acid solution. Chitosan is blue light resistant modified chitosan; The preparation method of blue light resistant modified chitosan is as follows: Step (1): Chitosan pretreatment Add 1% acetic acid solution at a ratio of 1g:90mL, and stir for 5h at 25℃ and 500rpm with magnetic stirring to obtain a 0.9wt% chitosan solution. Step (2): Preparation of carboxylated picrate blue light protectant The leaves of *Ilex chinensis* were ground and passed through an 80-100 mesh sieve, followed by supercritical extraction to obtain a *Ilex chinensis* extract rich in photoprotective active ingredients. The extract was dissolved in anhydrous pyridine at a ratio of 1 g: 13 mL, and succinic anhydride was added at a molar ratio of 1:4. The mixture was stirred at 65°C for 5 hours under nitrogen protection to obtain a reaction solution. After filtration and washing, the solution was vacuum dried in a drying oven at 38°C for 18 hours to obtain the activated carboxylated *Ilex chinensis* photoprotectant. The filtration and washing method was as follows: the reaction solution was first added to icy ether and allowed to stand for 45 minutes, then filtered to obtain a solid product, which was washed three times with cold ether. In step (2), the conditions for supercritical extraction are as follows: the mobile phase is carbon dioxide and a polar entrainer accounting for 8% of the volume of carbon dioxide, the extraction pressure is 18 MPa, the extraction temperature is 33 °C, and the extraction time is 45 min; the polar entrainer is composed of ethanol and water in a volume ratio of 93:7. Step (3): Preparation of blue light-resistant modified chitosan Adjust the pH of the chitosan solution to 5.0; then weigh the activated carboxylated picolinate blue photoprotectant according to a weight ratio of chitosan to activated carboxylated picolinate blue photoprotectant of 1:0.4; then dissolve the activated carboxylated picolinate blue photoprotectant in dimethyl sulfoxide according to a ratio of 1g:25mL to obtain a mixed solution. Finally, the mixture was added dropwise to the chitosan solution at a rate of 1 drop / s, and carbodiimide hydrochloride was added according to a molar ratio of carboxylated picrate blue light protectant to carbodiimide hydrochloride of 2:3. The mixture was reacted with shaking in the dark at 25°C for 21 hours to obtain modified chitosan with anti-blue light function. The volume ratio of chitosan solution to mixture was controlled at 8:1. The application method of phytosterol film-forming liquid for fruit and vegetable preservation is as follows: The phytosterol film-forming liquid is loaded into a spraying device and sprayed at a spray pressure of 0.2 MPa at a distance of 20 cm from the surface of the fruit and vegetables. The spray volume is 100 mL of phytosterol film-forming liquid per square meter of fruit and vegetable surface area. The film is formed by blowing it dry under the conditions of 23°C and 63% relative humidity with an airflow of 0.9 m / s. The fruit and vegetables are leafy vegetables.

[0020] Example 2: This example is based on the preparation method of the phytosterol film-forming solution for fruit and vegetable preservation in Example 1, including the following steps: S1, Preprocessing S1-1, Chitosan pretreatment: First, dissolve chitosan in an acid solvent that accounts for 5 / 8 of the total amount of acid solvent, and then magnetically stir at 25℃ and 500 rpm until clear to obtain a chitosan solution; S1-2, Pretreatment of one-dimensional nanomaterials: The one-dimensional nanomaterials were sheared at 10,000 rpm in an ice-water bath for 15 min to form a 1.0 wt% dispersion of one-dimensional nanomaterials; S2. Preparation of phytosterol film-forming solution Phytosterols were mixed with emulsifiers and the remaining acid solvent and heated at 75°C for 38 min to dissolve, yielding an oil phase. Then, the oil phase was sheared at 9000 rpm for 13 min, and the one-dimensional nanomaterial dispersion was added to the chitosan solution to obtain the first composite solution. Next, the oil phase was added dropwise to the first composite solution at a dropping rate of 1 mL / min. After the addition was complete, shearing continued for 8 min to obtain a uniform O / W emulsion, which is the second composite solution. Finally, a plasticizer was added to the second composite solution, and the mixture was stirred at 400 rpm for 18 min to homogenize. The mixture was then sonicated at 350 W for 13 min, and filtered to obtain the phytosterol film-forming solution.

[0021] Example 3: Unlike Example 1, the phytosterol film-forming solution for preserving fruits and vegetables includes, by weight percentage, 0.5% chitosan, 0.1% phytosterol, 0.05% one-dimensional nanomaterials, 0.1% emulsifier, 0.5% plasticizer, and the balance being an acid solvent.

[0022] Example 4: Unlike Example 1, the phytosterol film-forming solution for preserving fruits and vegetables includes, by weight percentage, 2.0% chitosan, 0.5% phytosterol, 0.3% one-dimensional nanomaterials, 0.5% emulsifier, 1.5% plasticizer, and the balance being an acid solvent.

[0023] Example 5: Unlike Example 1, the phytosterol is campesterol.

[0024] Example 6: Unlike Example 1, the phytosterol is β-sitosterol.

[0025] Example 7: Unlike Example 1, the emulsifier is any of Span 80.

[0026] Example 8: Unlike Example 1, the plasticizer is sorbitol.

[0027] Example 9: Unlike Example 1, the plasticizer is polyethylene glycol.

[0028] Example 10: Unlike Example 1, the one-dimensional nanomaterial is chitin nanofiber.

[0029] Example 11: Unlike Example 1, the one-dimensional nanomaterial is starch nanocrystals.

[0030] Example 12: Unlike Example 1, the acid solvent is lactic acid with a volume concentration of 5%.

[0031] Example 13: Unlike Example 1, the acid solvent is a citric acid solution with a volume concentration of 10%.

[0032] Example 14: Unlike Example 1, the acid solvent is a mixture of acetic acid solution with a volume concentration of 1% and ethanol at a volume ratio of 1:1.

[0033] Example 15: Unlike Example 1, step (1): chitosan pretreatment Add 1% acetic acid solution at a ratio of 1g:80mL, and stir for 4 hours at 23℃ and 450rpm with magnetic stirring to obtain a 0.8wt% chitosan solution.

[0034] Example 16: Unlike Example 1, step (1): chitosan pretreatment Add 1% acetic acid solution at a ratio of 1g:100mL, and stir for 6 hours at 27℃ and 550rpm with magnetic stirring to obtain a 1wt% chitosan solution.

[0035] Example 17: Unlike Example 1, the leaves of *Ilex chinensis* were ground through an 80-100 mesh sieve and then subjected to supercritical extraction to obtain *Ilex chinensis* extract rich in photoprotective active ingredients. The *Ilex chinensis* extract was dissolved in anhydrous pyridine at a ratio of 1 g: 10 mL, and succinic anhydride was added at a molar ratio of 1:3. The reaction was carried out under nitrogen protection and stirred at 60°C for 4 hours to obtain the reaction solution.

[0036] Example 18: Unlike Example 1, the leaves of *Ilex chinensis* were ground through an 80-100 mesh sieve and then subjected to supercritical extraction to obtain *Ilex chinensis* extract rich in photoprotective active ingredients. The *Ilex chinensis* extract was dissolved in anhydrous pyridine at a ratio of 1 g: 15 mL, and succinic anhydride was added at a molar ratio of 1:5. The reaction was carried out under nitrogen protection and stirred at 70°C for 6 hours to obtain the reaction solution.

[0037] Example 19: Unlike Example 1, the reaction solution was first added to ice-cold ether and allowed to stand for 30 minutes. The solid product was then filtered and washed twice with cold ether. The product was then vacuum dried in a drying oven at 35°C for 12 hours to obtain the activated carboxylated picrate blue light protectant.

[0038] Example 20: Unlike Example 1, the reaction solution was first added to ice-cold ether and allowed to stand for 60 minutes. The solid product was then filtered and washed three times with cold ether. The product was then vacuum dried in a drying oven at 40°C for 24 hours to obtain the activated carboxylated picrate blue light protectant.

[0039] Example 21: Unlike Example 1, the supercritical extraction conditions are as follows: the mobile phase is carbon dioxide and a polar entrainer accounting for 5% of the volume of carbon dioxide, the extraction pressure is 15 MPa, the extraction temperature is 30°C, and the extraction time is 30 min; the polar entrainer is composed of ethanol and water in a volume ratio of 19:1.

[0040] Example 22: Unlike Example 1, the supercritical extraction conditions are as follows: the mobile phase is carbon dioxide and a polar entrainer accounting for 10% of the volume of carbon dioxide, the extraction pressure is 20 MPa, the extraction temperature is 35 °C, and the extraction time is 60 min; the polar entrainer is composed of ethanol and water in a volume ratio of 9:1.

[0041] Example 23: Unlike Example 1, the pH of the chitosan solution was adjusted to 4.5; then, the activated carboxylated picolinate blue photoprotectant was weighed according to a weight ratio of chitosan to activated carboxylated picolinate blue photoprotectant of 1:0.3; then, the activated carboxylated picolinate blue photoprotectant was dissolved in dimethyl sulfoxide at a ratio of 1g:20mL to obtain a mixed solution.

[0042] Example 24: Unlike Example 1, the pH of the chitosan solution was adjusted to 5.5; then, the activated carboxylated picolinate blue photoprotectant was weighed according to a weight ratio of chitosan to activated carboxylated picolinate blue photoprotectant of 1:0.5; then, the activated carboxylated picolinate blue photoprotectant was dissolved in dimethyl sulfoxide at a ratio of 1g:30mL to obtain a mixed solution.

[0043] Example 25: Unlike Example 1, the mixture was added to the chitosan solution at a rate of 1 drop / s, and carbodiimide hydrochloride was added at a molar ratio of 1:1.3 for carboxylated picrine blue light protectant and carbodiimide hydrochloride. The mixture was reacted with shaking at 23°C in the dark for 18 hours to obtain modified chitosan with anti-blue light function. The volume ratio of chitosan solution to mixture was controlled at 5:1.

[0044] Example 26: Unlike Example 1, the mixture was added to the chitosan solution at a rate of 2 drops / s, and carbodiimide hydrochloride was added at a molar ratio of 1:1.7 to carbodiimide hydrochloride. The mixture was reacted with shaking at 27°C in the dark for 24 hours to obtain modified chitosan with anti-blue light function. The volume ratio of chitosan solution to mixture was controlled at 10:1.

[0045] Example 27: Unlike Example 1, the phytosterol film-forming liquid was loaded into a spraying device and sprayed at a spray pressure of 0.1 MPa at a distance of 15 cm from the surface of fruits and vegetables. The spray volume was 50 mL of phytosterol film-forming liquid per square meter of fruit and vegetable surface area. The film was dried by airflow with a wind speed of 0.8 m / s under the conditions of 20°C and 60% relative humidity.

[0046] Example 28: Unlike Example 1, the phytosterol film-forming liquid was loaded into a spraying device and sprayed at a spraying pressure of 0.3 MPa at a distance of 25 cm from the surface of fruits and vegetables. The spray volume was 150 mL of phytosterol film-forming liquid per square meter of fruit and vegetable surface area. The film was then naturally air-dried at 25°C and 60% relative humidity to form a film.

[0047] Example 29: Unlike Example 2, S1-1, chitosan pretreatment: chitosan is first dissolved in an acid solvent accounting for 2 / 4 of the total amount of acid solvent, and then magnetically stirred at 25°C and 400 rpm until clear to obtain a chitosan solution.

[0048] Example 30: Unlike Example 2, S1-1, chitosan pretreatment: chitosan is first dissolved in an acid solvent accounting for 3 / 4 of the total acid solvent volume, and then magnetically stirred at 25°C and 600 rpm until clear to obtain a chitosan solution.

[0049] Example 31: Unlike Example 2, S1-2, one-dimensional nanomaterial pretreatment: one-dimensional nanomaterial pretreatment: the one-dimensional nanomaterial was sheared at 8000 rpm in an ice-water bath for 10 min to form a 0.5 wt% one-dimensional nanomaterial dispersion.

[0050] Example 32: Unlike Example 2, S1-2, one-dimensional nanomaterial pretreatment: one-dimensional nanomaterial pretreatment: the one-dimensional nanomaterial was sheared at 12000 rpm in an ice-water bath for 20 min to form a 1.5 wt% one-dimensional nanomaterial dispersion.

[0051] Example 33: Unlike Example 2, in S2, the preparation of the phytosterol film-forming solution involved mixing phytosterol with an emulsifier and the remaining acid solvent, heating at 70°C for 30 min to dissolve it, and obtaining an oil phase. Then, the solution was sheared at 8000 rpm for 10 min, and a one-dimensional nanomaterial dispersion was added to the chitosan solution to obtain the first composite solution. Next, the oil phase was added dropwise to the first composite solution at a dropping rate of 1 mL / min. After the addition was complete, the solution was sheared for another 5 min to obtain a uniform O / W type emulsion, which is the second composite solution. Finally, a plasticizer was added to the second composite solution, and the mixture was stirred at 300 rpm for 15 min to mix. The mixture was then ultrasonically treated at an ultrasonic power of 300 W for 10 min, and filtered to obtain the phytosterol film-forming solution.

[0052] Example 34: Unlike Example 2, in S2, the preparation of the phytosterol film-forming solution involved mixing phytosterol with an emulsifier and the remaining acid solvent, heating at 80°C for 45 min to dissolve it, and obtaining an oil phase. Then, the solution was sheared at 10,000 rpm for 15 min, and the one-dimensional nanomaterial dispersion was added to the chitosan solution to obtain the first composite solution. Next, the oil phase was added dropwise to the first composite solution at a dropping rate of 2 mL / min. After the addition was complete, shearing was continued for 10 min to obtain a uniform O / W type emulsion, which is the second composite solution. Finally, a plasticizer was added to the second composite solution, and the mixture was stirred at 500 rpm for 20 min to mix it. The mixture was then ultrasonically treated at an ultrasonic power of 400 W for 15 min, and filtered to obtain the phytosterol film-forming solution.

[0053] Experimental Example: The description of this experimental example is based on the scheme described in Examples 1 / 2, and aims to illustrate the practical application effect of the present invention.

[0054] Experimental Design: To elucidate the fruit and vegetable preservation performance of the phytosterol film-forming liquid prepared in this invention, the following experimental groups were designed: 1. The effect of phytosterol film-forming solution on alleviating the degree of rotting in bayberries. Freshly picked bayberries were used as the experimental subjects. The control group (CK) was treated with ultrapure water spray, while the experimental group was treated with the phytosterol film-forming liquid of this invention. After spraying, the bayberries were air-dried and placed in polyethylene preservation boxes, with 20 bayberries per box. The experimental group and the control group were stored in a refrigerator at 4℃ and at room temperature, respectively. During the process, samples were taken and the following indicators were measured: the rot rate of the bayberries. The rot rate of each experimental group was observed and statistically analyzed at fixed times every day. The rot grading and rot rate statistics were carried out according to the following table and formula.

[0055] Table 1. Grading of Waxberry Rot

[0056] The formula for calculating the decay rate is as follows: Experimental results: Table 2. Rot of bayberries treated with the phytosterol film-forming solution in Examples 1 and 2 under different storage conditions.

[0057] The experimental results above show that, compared with the control group, the rotting process of fresh bayberries treated with phytosterol film-forming solution was effectively delayed when stored at 25℃ and 4℃.

[0058] 2. Effects of phytosterol film-forming solution on the total sugar content of bayberries under low-temperature storage Freshly picked bayberries were used as experimental subjects. The control group (CK) was treated with ultrapure water spray, while the experimental group was treated with the phytosterol film-forming solution of this invention. After spraying, the bayberries were air-dried and placed in polyethylene preservation boxes, with 20 bayberries per box. The experimental and control groups were stored in a refrigerator at 4°C.

[0059] Total sugar content was measured every 3 days using the Fehling's reagent method. 5 g of fruit pulp was weighed, chopped, and finely ground. The mixture was transferred to a 250 mL volumetric flask with distilled water and heated in an 80 °C water bath for 20 min. After cooling, 5 mL of 6 mol / L hydrochloric acid was added, and the mixture was heated again in a 70 °C water bath for 15 min. After cooling, 2 drops of methyl red indicator solution were added, and the mixture was neutralized with 20% sodium hydroxide solution. Water was added to bring the volume to a final volume, and the mixture was shaken well. After filtration, the sample solution was injected into a burette and titrated using the standardization method. 5.0 mL of solution A and 5.0 mL of solution B were pipetted into a 150 mL Erlenmeyer flask, 10 mL of water was added, and 2 glass beads were added. The solution was titrated using the sample solution in the burette, heated to boiling within 2 min, and titrated at a rate of one drop every 2 s until the blue color just faded. This process was repeated three times to obtain the average volume consumed.

[0060] In the formula, m1 is the amount of invert sugar equivalent to 10 mL of Fehling's reagent in the direct titration method, in mg; m is the sample mass, in g; V is the total volume of the sample solution consumed on average during calibration, in mL; and V1 is the total volume of the sample processing solution, in mL.

[0061] Experimental results are as follows Figure 1 As shown, by Figure 1 It can be seen that the direct substrate for postharvest respiration in fruits is the sugar content, which is also the energy source for maintaining respiration metabolism. As storage time increases, the sugar content in fruits gradually decreases. Measuring the change in total sugar can, to some extent, reflect the respiration intensity during fruit storage. Figure 1 It can be seen that the rate of decrease in total sugar content in the experimental group treated with phytosterol film-forming liquid was significantly lower than that in the control group, indicating that treatment with the phytosterol film-forming liquid prepared in this application can reduce the respiration of bayberry fruit during storage and help extend the shelf life of bayberry.

[0062] 3. Effects of phytosterol film-forming solution on the resistance of bayberry to photodamage Freshly picked bayberries were used as experimental subjects. The control group (CK) was treated with ultrapure water spray, while the experimental group was treated with the phytosterol film-forming solution of this invention. After spraying, the bayberries were air-dried and placed in polyethylene preservation boxes, with 20 bayberries per box. There were 5 boxes for each of the experimental and control groups. The experimental and control groups were placed in a 4°C cold storage and irradiated with LED fluorescent lamps to control the photosynthetic photon flux density on the surface of the bayberries in each experimental group to be 200 µmol / m². 2 / s. Samples were taken every 6 hours to test the vitamin C content of the bayberry fruit.

[0063] Experimental results are as follows Figure 2 As shown, and by Figure 2 It can be seen that under light radiation, especially blue light in the 400-600nm range, the antioxidant active ingredients in bayberries are rapidly depleted. Therefore, detecting the vitamin C content in blueberries can reflect the effect of phytosterol film-forming fluid on the bayberry's ability to resist light radiation. Figure 2 It was found that within 72 hours, the VC loss rate in the experimental group treated with the phytosterol film-forming solution was reduced by approximately 66% compared to the control group. This indicates that the phytosterol film-forming solution prepared in this application helps to reduce photodamage to bayberries.

Claims

1. A phytosterol film-forming liquid for preserving fruits and vegetables, characterized in that, By weight percentage, it includes 0.5-2.0% chitosan, 0.1-0.5% phytosterols, 0.05-0.3% one-dimensional nanomaterials, 0.1-0.5% emulsifiers, 0.5-1.5% plasticizers, and the balance being acid solvents. The phytosterol is any one or a mixture of two or more of stigmasterol, β-sitosterol, and campesterol; the emulsifier is any one of Tween-80 and Span 80; the plasticizer is any one of glycerol, sorbitol, and polyethylene glycol; the one-dimensional nanomaterial is one of cellulose nanofibers, chitin nanofibers, and starch nanocrystals; the acid solvent is any one of a 1% (v / v) acetic acid solution, a 5% (v / v) lactic acid solution, and a 5-10% (v / v) citric acid solution, or a mixture of one of these solutions and ethanol at a volume ratio of 1:

1.

2. The phytosterol film-forming liquid for fruit and vegetable preservation as described in claim 1, characterized in that, The chitosan is blue light resistant modified chitosan; The preparation method of the blue light-resistant modified chitosan is as follows: Step (1): Chitosan pretreatment Add 1% acetic acid solution at a ratio of 1g:80-100mL, and stir for 4-6 hours at 23-27℃ and 450-550rpm with magnetic stirring to obtain a 0.8-1wt% chitosan solution. Step (2): Preparation of carboxylated picrate blue light protectant The leaves of *Ilex chinensis* were ground and passed through an 80-100 mesh sieve, and then subjected to supercritical extraction to obtain *Ilex chinensis* extract rich in photoprotective active ingredients. The extract was dissolved in anhydrous pyridine at a ratio of 1 g: 10-15 mL, and succinic anhydride was added at a molar ratio of 1:3-5. The mixture was stirred at 60-70°C under nitrogen protection for 4-6 hours to obtain a reaction solution. This solution was then filtered, washed, and vacuum dried in a drying oven at 35-40°C for 12-24 hours to obtain the activated carboxylated *Ilex chinensis* photoprotectant. Step (3): Preparation of blue light-resistant modified chitosan Adjust the pH of the chitosan solution to 4.5-5.5; then weigh the activated carboxylated picolinate blue photoprotectant according to a weight ratio of chitosan to activated carboxylated picolinate blue photoprotectant of 1:0.3-0.5; then dissolve the activated carboxylated picolinate blue photoprotectant in dimethyl sulfoxide according to a ratio of 1g:20-30mL to obtain a mixed solution. Finally, the mixture was added to the chitosan solution at a rate of 1-2 drops / s, and carbodiimide hydrochloride was added at a molar ratio of 1:1.3-1.

7. The mixture was then reacted with shaking at 23-27°C in the dark for 18-24 hours to obtain the blue light resistant modified chitosan.

3. The phytosterol film-forming liquid for fruit and vegetable preservation as described in claim 2, characterized in that, In step (2), the conditions for supercritical extraction are as follows: the mobile phase is carbon dioxide and a polar entrainer accounting for 5-10% of the volume of the carbon dioxide; the extraction pressure is 15-20 MPa; the extraction temperature is 30-35℃; and the extraction time is 30-60 min.

4. The phytosterol film-forming liquid for fruit and vegetable preservation as described in claim 3, characterized in that, The polar entrainer is composed of ethanol and water in a volume ratio of 90-95:5-10.

5. A phytosterol film-forming liquid for fruit and vegetable preservation as described in claim 2, characterized in that, In step (3), the volume ratio of chitosan solution to mixture is controlled to be 5-10:

1.

6. A phytosterol film-forming liquid for fruit and vegetable preservation as described in claim 2, characterized in that, In step (2), the filtration and washing method is as follows: first, add the reaction solution to ice-cold ether and let it stand for 30-60 minutes, filter to obtain solid product, and wash with cold ether 2-3 times.

7. The method for preparing the phytosterol film-forming liquid for fruit and vegetable preservation as described in any one of claims 1-6, characterized in that, Includes the following steps: S1, Preprocessing S1-1, Chitosan pretreatment: First, dissolve chitosan in an acid solvent that accounts for 2 / 4 to 3 / 4 of the total acid solvent volume, and then magnetically stir at 25℃ and 400-600 rpm until clear to obtain a chitosan solution; S1-2, Pretreatment of one-dimensional nanomaterials: The one-dimensional nanomaterials are sheared at 8000-12000 rpm in an ice-water bath for 10-20 min to form a 0.5-1.5 wt% dispersion of one-dimensional nanomaterials; S2. Preparation of phytosterol film-forming solution Phytosterols are mixed with emulsifiers and the remaining acid solvent, and heated at 70-80℃ for 30-45 min to dissolve, obtaining an oil phase. Then, the oil phase is sheared at 8000-10000 rpm for 10-15 min, and the one-dimensional nanomaterial dispersion is added to the chitosan solution to obtain the first composite solution. Next, the oil phase is added dropwise to the first composite solution at a dropping rate of 1-2 mL / min. After the addition is complete, shearing is continued for 5-10 min to obtain a uniform O / W type emulsion, which is the second composite solution. Finally, a plasticizer is added to the second composite solution, and the mixture is stirred at 300-500 rpm for 15-20 min to mix. The mixture is then ultrasonically treated at an ultrasonic power of 300-400 W for 10-15 min, and filtered to obtain the phytosterol film-forming solution.

8. The method of applying the phytosterol film-forming liquid for fruit and vegetable preservation as described in any one of claims 1-6, characterized in that, The phytosterol film-forming liquid is loaded into a spraying device and sprayed at a spraying pressure of 0.1-0.3 MPa at a distance of 15-25 cm from the surface of fruits and vegetables. The spray volume is 50-150 mL of phytosterol film-forming liquid per square meter of fruit and vegetable surface area. The mixture is then allowed to air dry naturally at 20-25°C and relative humidity <65% or dried with an airflow of <1 m / s to form a film.

9. The application method as described in claim 8, characterized in that, The fruits and vegetables mentioned are bayberries or leafy greens.

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