Pulullan fruit preservative with mildew-proof and fresh-keeping functions as well as preparation method and application of pulullan fruit preservative

Abstract

The invention discloses a pullulan fruit fresh-keeping agent with mildew-proof and fresh-keeping functions as well as a preparation method and application of the pullulan fruit fresh-keeping agent. The preservative is prepared by taking defective apples as a fermentation substrate, synchronously generating pullulan and natural polyphenol through aureobasidium pullulans fermentation, and performing synergistic extraction and compounding of a coalescing agent and calcium salt, and the preparation method comprises the steps of defective fruit pretreatment, fermentation, extraction separation, purification and compounding dissolution. During application, the preservative film is coated on the surfaces of cleaned and aired fruits by adopting a dipping or spraying method to form the composite preservative film. The cost is reduced by 30-50% by utilizing agricultural product wastes, the pullulan provides a physical barrier, the polyphenol endows the broad-spectrum antibacterial activity, the mildew-proof period is prolonged by 2-3 times through the synergism of the pullulan and the polyphenol, the weight loss rate is reduced to 2% or below, and the preservative is suitable for the postharvest preservation of apples, grapes, oranges, berries and other fruits and is safe, non-toxic, simple in process and easy to industrialize.

Description

Technical Field

[0001] This invention belongs to the field of food preservation technology, specifically relating to pullulan polysaccharide fruit preservative with anti-mold and preservation functions, its preparation method, and its application. Background Technology

[0002] Even after harvesting, fruit continues its life processes, making it highly susceptible to problems such as dehydration and wilting, decreased nutritional quality, browning of the peel, and infection by pathogenic microorganisms. In particular, the rate of decay and loss is high during storage and transportation.

[0003] Existing fruit preservation technologies mainly include refrigeration, modified atmosphere packaging (MAP), and chemical preservation. Refrigeration / MAP offers good results, but requires high equipment investment and operating costs, and demands strict control over temperature and gas composition, making it unsuitable for all fruit varieties or large-scale, decentralized applications. Chemical preservation, using preservatives such as sec-butylamine and terbufos, while exhibiting significant antibacterial effects, poses potential food safety and environmental risks. The growing consumer demand for "green" products necessitates the urgent development of safe, non-toxic, and natural biological preservatives.

[0004] Pullulan is a natural, edible extracellular polysaccharide secreted by *Brachystomata*. Pullulan forms a colorless, transparent, and flexible protective film on the surface of fruits. This film effectively blocks oxygen, reducing fruit respiration, inhibiting oxidation and enzymatic browning, while also reducing ethylene release and delaying fruit senescence. Furthermore, the film effectively reduces fruit moisture evaporation, lowers weight loss, and maintains fruit firmness and freshness. Pullulan has been approved as a safe food additive in several countries and is non-toxic and harmless.

[0005] However, using pullulan alone as a preservative coating also has limitations. Pullulan films primarily provide physical protection, with relatively weak inhibitory effects against molds and yeasts. Furthermore, the main raw materials for pullulan production are corn starch or glucose, resulting in high production costs and limiting its widespread application in the low-value-added field of agricultural product preservation.

[0006] Agricultural product processing and cultivation generate a large amount of substandard, inferior, and fallen fruit. Taking Yantai, a major apple-producing area in China, as an example, the yield of substandard apples is enormous, containing abundant nutrients such as sugars, organic acids, vitamins, and polyphenols. Therefore, how to efficiently transform waste resources such as substandard apples into high-value biological products is an urgent technical challenge. Against this backdrop, this invention addresses the two core issues of high raw material costs and insufficient anti-mold effects by proposing a composite fruit preservative that utilizes pullulan from substandard apples and combines it with natural antioxidant polyphenols. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a pullulan polysaccharide fruit preservative with anti-mold and preservation functions. This invention not only makes full use of substandard apple fruit, but also ferments it using *Bacillus buddingus*, simultaneously obtaining pullulan polysaccharide and natural antioxidant polyphenols from the fermentation products, and then combining the two to obtain a compound fruit preservative. This simultaneously solves the two core problems of high raw material costs and insufficient anti-mold effect. To achieve the above objectives, the present invention adopts the following technical solution: a pullulan polysaccharide fruit preservative with anti-mold and preservation functions, characterized in that: the preservative is composed of the following components by weight percentage: Pullulan polysaccharide 0.5%–5.0%; Polyphenol extract 0.5%–5.0%; Film-forming aids: 0.5%–5.0%; Calcium salts 0.5%–5.0%; The remainder is water; The pullulan polysaccharide and polyphenol extracts were obtained by synergistic extraction of apple broth fermented with *Synthia spp.* using apple bleach as a fermentation substrate.

[0008] Furthermore, the fermentation broth from the substandard apples is obtained through the following steps: (1) Pretreatment of substandard apples: wash and drain the substandard apples, cut off the rotten and spoiled parts, and pulp them in a pulper for 10 minutes to obtain jam. Then, place the jam in a homogenizer for 15 minutes and concentrate it in a jam concentrator for 30 minutes to make concentrated jam for later use. (2) Prepare fermentation medium with apple defective fruit mass concentration of 100-200 g / L and nitrogen source mass concentration of 2-16 g / L respectively; (3) Fermentation: The budding short-stem mold AS3.3984 was fermented in a fermentation medium at 26-32℃ for 24-120h. After centrifugation, the bacterial cells and residues were removed to obtain a fermentation broth of apple substandard fruit rich in pullulan polysaccharide and polyphenols.

[0009] Furthermore, the polyphenol extract is obtained through the following steps: (a) Add 50%–70% of a hydrophilic organic solvent (such as ethanol) to the fermentation broth of the apple substandard fruit and perform shake extraction; (b) After centrifugation, collect the supernatant rich in polyphenols and concentrate it to 10% of the original supernatant volume to obtain the polyphenol extract. The pullulan polysaccharide was obtained through the following steps: (c) Precipitate the lower layer residue separated in step (b) with ethanol, and collect the crude polysaccharide by centrifugation. (d) Polysaccharide purification: The crude polysaccharide obtained in step (c) is dissolved and subjected to decolorization and protein removal purification operations to obtain pullulan polysaccharide.

[0010] Furthermore, the nitrogen source is selected from at least one of yeast extract, peptone, corn steep liquor, beef powder, ammonium nitrate, ammonium chloride, sodium nitrate, and ammonium sulfate.

[0011] Furthermore, the film-forming aid is glycerol.

[0012] Furthermore, the calcium salt is calcium chloride.

[0013] This invention also discloses a method for preparing pullulan polysaccharide fruit preservative with anti-mold and preservation functions. The raw materials are weighed according to weight percentages, and pullulan polysaccharide, polyphenol extract, film-forming aid, and calcium salt are added sequentially to water under stirring. After stirring evenly, the pullulan polysaccharide fruit preservative with anti-mold and preservation functions is obtained. In addition, the application of pullulan polysaccharide fruit preservative with anti-mold and preservation functions in the preparation of fruit preservation films, fruit coating agents, or in the post-harvest anti-mold and preservation of fruits is also disclosed.

[0014] Furthermore, the fruits include, but are not limited to, apples, papayas, citrus fruits, berries, grapes, etc. The application method is as follows: after washing and drying the fruit, the preservative is applied to the fruit surface using an immersion or spraying method, followed by drying at room temperature or under ventilated conditions, allowing pullulan polysaccharides to form a continuous composite preservative film.

[0015] The beneficial effects of this invention are: This invention creatively uses discarded and substandard apples instead of traditional corn starch or glucose as the carbon source for pullulan fermentation, which greatly reduces the production cost of pullulan, improves the utilization rate of substandard fruit, and realizes the high-value transformation of agricultural waste, with significant economic benefits and environmental significance.

[0016] Pullulan and polyphenol extracts work synergistically to enhance preservation: Pullulan forms a continuous, transparent film on the fruit surface, effectively blocking oxygen, inhibiting respiration, and reducing moisture evaporation, thus achieving basic preservation. It also incorporates natural polyphenols extracted from fermentation broth. As powerful antioxidants, polyphenols significantly inhibit post-harvest enzymatic browning and oxidation reactions in fruits, maintaining peel color and delaying fruit senescence.

[0017] A synergistic extraction process for pullulan and polyphenols was employed. Before alcohol precipitation of the polyphenols, a mild organic solvent extraction was performed on the polyphenols. This process maximized the preservation of the polyphenols' bioactivity while avoiding the damage to polyphenols caused by high-temperature and strong acid / alkali treatments during pullulan extraction and purification. This simplified the subsequent separation process and improved the overall yield and purity of both high-value products. Detailed Implementation

[0018] To better understand the present invention, specific embodiments are described in further detail below. These embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0019] Example 1: Preparation of fermentation broth from substandard apple fruit (1) Raw material pretreatment 500 kg of freshly harvested, substandard Fuji apples from Qixia production area, Yantai City, Shandong Province were selected. This batch of substandard fruit mainly included mechanically damaged, insect-bitten, deformed, and small fruits, with rotten or spoiled portions accounting for less than 5%. First, the apples were rinsed with running water to remove mud and pesticide residues for at least 5 minutes until the water became clear. Then, they were placed on a stainless steel drain rack to air dry naturally for 30 minutes until no obvious water droplets remained on the surface. Severely rotten, blackened, or moldy areas were manually removed using a stainless steel fruit and vegetable knife, with a total removed weight of approximately 22 kg. The remaining apples were then pulped in an industrial-grade pulper for 10 minutes to obtain a smooth and uniform jam with fruit pulp particles ≤2 mm in diameter. The jam was transferred to a high-pressure homogenizer and homogenized for 15 minutes to further refine the jam and ensure even dispersion of solids. The homogenized jam was then pumped into a vacuum rotary evaporator for 30 minutes to concentrate and remove some of the water, ultimately yielding 425 kg of concentrated jam with a solids content of 45%, pH 4.2, and soluble solids of 42%.

[0020] (2) Preparation of fermentation culture medium Add the above concentrated fruit jam to a 1000 L stainless steel fermentation tank. Based on a mass concentration of 150 g / L, the actual input is 120 kg (equivalent to the original fruit jam mass concentration of 150 g / L). Then add 8 g / L yeast extract and 2 g / L potassium dihydrogen phosphate (i.e., a total mass of 2 kg), and replenish with deionized water to a total mass of 1000 L. After mixing thoroughly with the agitator, heat to 121°C using a steam jacket and maintain for 20 minutes for moist heat sterilization. After sterilization, circulate sterile cooling water to lower the tank temperature to 30°C, maintaining the tank pressure at 0.05 MPa.

[0021] (3) Inoculation and fermentation Seed culture preparation: *Berberidosis brevis* AS3.3984, preserved on a slant culture medium, was inoculated into a 250 mL shake flask containing 100 mL of YPD liquid medium and cultured at 28°C and 180 rpm for 24 h with shaking to obtain primary seed culture. This was then transferred to a 5 L seed tank at a 5% inoculum level and cultured at 28°C and 200 rpm for 24 h with aeration to obtain secondary seed culture, with a viable count of approximately 2.5 × 10⁻⁶ cells / mL. 8 CFU / mL. 50 L of secondary seed culture (5% inoculum) was added to the fermenter. The temperature was controlled at 28℃, the stirring speed at 200 rpm, the aeration rate at 1:0.8 vvm (volume air / volume culture medium / min), and the fermentation pressure at 0.05 MPa for 72 h. Samples were taken every 12 h for microscopic examination to confirm the absence of contamination. The fermentation endpoint was defined as the pullulan content no longer showing a significant increase. After fermentation, the material in the fermenter was centrifuged at 4000 rpm for 20 min to separate and remove bacterial cells and pomace, yielding 920 L of clear fermentation supernatant. Sampling and analysis revealed: pullulan content 18.5 g / L (enzymatic hydrolysis-anthrone colorimetric method), polyphenol content 3.2 g / L (Folin-Ciocalteu method), pH 4.8.

[0022] Example 2: Synergistic extraction of pullulan polysaccharide and polyphenol extracts Step 1: Polyphenol Extraction 920 L of fermentation supernatant obtained in Example 1 was slowly added to a final ethanol concentration of 65% (v / v). Extraction was performed at a constant temperature of 25°C using an in-tank stirrer for 2 h to promote the transfer of polyphenols from the aqueous phase to the alcohol phase. After extraction, the material was pumped into a high-speed tubular centrifuge (8000 rpm, throughput 500 L / h) and centrifuged continuously for 15 min. 850 L of the polyphenol-rich supernatant was collected, and the lower layer was temporarily stored.

[0023] Step 2: Polyphenol Concentration The supernatant was pumped into a thin-film evaporator at a pressure of 850 L and concentrated under reduced pressure to 10% of its original volume (i.e., 85 L), yielding a dark brown concentrated polyphenol solution. Sampling and analysis revealed a polyphenol content of 32.6 g / L and a yield of 92.1% (based on total polyphenols in the fermentation broth). This concentrate is the polyphenol extract and should be stored at 4°C in a sealed container, protected from light.

[0024] Step 3: Precipitation and Crude Product Preparation of Pullulan Add 3 times the volume of 95% ethanol (approximately 2400 L) to the lower layer residue (approximately 800 L) after centrifugation, stir thoroughly, and then place in a 4°C cold storage to allow precipitation overnight (12 h). Pullulan polysaccharide precipitates as a white flocculent precipitate. Collect the crude polysaccharide precipitate by centrifugation using a basket centrifuge; the precipitate mass is approximately 85 kg (wet weight).

[0025] Step 4: Purification of pullulan The crude polysaccharide precipitate was reconstituted with deionized water to a concentration of 5% (w / v), and 0.5% (w / w) pharmaceutical-grade activated carbon was added. The mixture was stirred at 50°C for 30 min to decolorize. The activated carbon was removed by diatomaceous earth plate and frame filtration, yielding a light yellow polysaccharide solution. Protein removal was performed using the Sevag method: 1 / 4 volume of Sevag reagent (chloroform:n-butanol volume ratio 4:1) was added to the polysaccharide solution, and the mixture was vigorously shaken for 15 min. After standing and separating the layers, the solution was centrifuged (5000 rpm, 10 min) to remove the intermediate denatured protein layer. This process was repeated three times until no obvious protein layer was observed. The purified polysaccharide solution was placed in a dialysis bag (molecular weight cutoff 8000-14000 Da), dialyzed against running tap water for 24 h, and then against deionized water for 12 h to remove salts and small molecules. The dialysate was freeze-dried at -50°C for 48 h to obtain 15.8 kg of white powdered pullulan polysaccharide. Sampling and testing: purity 96.5% (HPLC area normalization method), yield 92.7% (based on pullulan polysaccharide in fermentation broth), moisture <5%, ash <0.5%.

[0026] Example 3: Preparation of Preservative Step 1: Weighing the raw materials In the cleanroom, accurately weigh the following by weight percentage: pullulan (purified product of Example 2), 2.0 kg, polyphenol extract (dry weight of concentrated solution of Example 2), 1.5 kg, food-grade glycerol, 1.0 kg, food-grade calcium chloride, and 94.5 kg of deionized water.

[0027] Step 2: Dissolving and compounding Add 94.5 kg of 40°C deionized water to a stainless steel mixing tank and start stirring. Slowly add pullulan powder sequentially, stirring for 15 min until completely dissolved and the solution is clear and viscous. Add polyphenol concentrate and stir for 10 min until the solution turns light brown. Add glycerol and stir for 5 min. Finally, add calcium chloride and stir for 10 min until the system is homogeneous. The total stirring time is 30 min. After stirring, allow to stand for 30 min to remove bubbles, obtaining a clear, homogeneous, slightly viscous composite preservative solution with pH 5.5 and a viscosity of approximately 250 mPa·s. Aseptically fill into 5 L food-grade plastic drums and seal with labels.

[0028] Example 4: Evaluation of the effect of preservatives on Fuji apples Step 1: Apple Preprocessing Freshly harvested Fuji apples from the Yantai production area (single fruit weight 180-220 g, diameter 75-80 mm, 80% ripeness) were selected, free from pests, diseases, and mechanical damage. They were washed with running water for 3 minutes, soaked in 1% sodium bicarbonate solution for 2 minutes for sterilization, rinsed twice with pure water, and air-dried naturally on a drain rack for 30 minutes until there were no water droplets on the surface.

[0029] Step 2: Coating Treatment Treatment group: Apples were immersed in the preservative of Example 3 for 10 seconds, then removed and dried in a fume hood (wind speed 0.5 m / s) for 30 minutes to form a uniform transparent film with a thickness of about 100 μm. Control group: Soaked and dried in deionized water using the same method. Each group contains 300 apples, randomly divided into 3 duplicates of 100 apples each.

[0030] Step 3: Storage and Index Testing Store in a constant temperature and humidity chamber (20±2℃, relative humidity 65%) for 30 days. Take samples for testing every 5 days. Weight loss rate: by weighing method, 8.7% in the control group and 2.1% in the treatment group; Hardness: GY-4 fruit hardness tester (Φ8 mm probe), the retention rate of the control group was 68%, and that of the treatment group was 89%; Vitamin C: 2,6-dichlorophenolindophenol titration method, retention rate of the control group was 52%, and that of the treatment group was 78%; Mold rate: The number of fruits with mold spots >5 mm² was visually counted, with 28% in the control group and 3% in the treatment group; Sensory evaluation: A professional panel of 9 people (out of 9) evaluated the color, flavor and texture. The control group scored 4.2 and the treatment group scored 7.8.

[0031] Example 5: Evaluation of the effect of preservatives on Shine Muscat grapes Step 1: Grape Pretreatment Select freshly harvested Shine Muscat grapes (500-600 g per bunch, 18-20°Brix sugar content) from the Penglai production area of ​​Yantai. Remove diseased and damaged berries, but retain the fruit brush. Soak in a 1% potassium permanganate solution for 1 minute, rinse three times with pure water, and drain.

[0032] Step 2: Spray coating treatment The preservative from Example 3 was evenly sprayed using a pneumatic sprayer (pressure 0.3 MPa, droplet diameter 100-150 μm) at a dosage of 1.5 L / t of grapes. After spraying, the grapes were placed in a cool, ventilated place to air dry naturally for 1 hour, resulting in the formation of an extremely thin, transparent film on the fruit surface.

[0033] Step 3: Refrigeration and Indicator Testing Store in a cold storage (0±0.5℃, relative humidity 90%) for 45 days. Take samples every 7 days. Threshing rate: The number of threshed berries was counted after gently shaking the rachis. The control group had a threshing rate of 12.3%, while the treatment group had a threshing rate of 1.8%. Gray mold incidence: Visually observed grayish-white mold layer, 35% in control group, 6% in treatment group; Total sugars: Anthrone colorimetric method, the retention rate of the treated group increased by 18%; Fruit stalk freshness: 92% of the fruit stalks in the treatment group remained green, compared to 45% in the control group.

[0034] Example 6: Preservative Formulation Optimization and Performance Verification Experimental Design Using L9(3) 4 The formulation was optimized using an orthogonal experiment. The factor levels were: pullulan 1.0%, 2.5%, 4.0%; polyphenol extract 0.8%, 1.8%, 3.0%; glycerol 0.5%, 1.5%, 2.5%; and calcium chloride 0.5%, 1.0%, 1.5%. The diameter of the inhibition zone (Penicillium), water vapor transmission rate, and membrane tensile strength were used as evaluation indicators.

[0035] Key conclusions The diameter of the inhibition zone showed a linear positive correlation with the increase of polyphenol concentration, with a regression equation of y=5.2x+8.1 and a correlation coefficient R²=0.97. When the glycerol concentration is >2.0%, the membrane elongation at break is >60%, exhibiting optimal flexibility; The water vapor permeability was lowest at a calcium chloride concentration of 1.5%, at 1.2 × 10⁻¹. 0 g·m⁻¹·s⁻¹·Pa⁻¹; The optimal formula is: pullulan 2.5%, polyphenols 1.8%, glycerol 2.0%, and calcium chloride 1.5%, which has the best overall performance.

[0036] Comparative Example 1: Commercially available pullulan polysaccharide coating agent A commercially available 1% pullulan polysaccharide solution (without polyphenols or calcium salts) was used to treat Fuji apples using the same method as in Example 4. After 30 days of storage at room temperature, the mold rate was 18%, the weight loss rate was 4.5%, and the firmness retention rate was 75%, which was significantly inferior to that of the present invention.

[0037] Comparative Example 2: Chemical antibacterial agents Although the mold rate of a 0.05% tebuconazole aqueous solution treated in the same way was <5%, liquid chromatography detected a drug residue of 0.8 mg / kg, the sensory score dropped to 5.5, and there were concerns about consumer safety.

[0038] In summary, this invention achieves the preparation of a low-cost, highly antibacterial, and uniformly film-forming green preservative through key technologies such as simultaneous fermentation of substandard apples to produce pullulan and polyphenols, synergistic extraction, and ionic cross-linking compounding. The process is stable and controllable, suitable for post-harvest treatment of various fruits including apples, grapes, citrus, and berries, demonstrating significant technological advancement and broad industrialization prospects. The above embodiments are merely illustrative of the technical concept of this invention and do not constitute a limitation on the scope of protection. All equivalent substitutions or modifications made based on the substantive content of this invention should fall within the scope of protection of the claims of this invention.

[0039] The above embodiments are merely illustrative of the technical concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A pullulan polysaccharide fruit preservative with anti-mold and preservation functions, characterized in that: The preservative is composed of the following components by weight percentage: Pullulan polysaccharide 0.5%–5.0%; Polyphenol extract 0.5%–5.0%; Film-forming aids: 0.5%–5.0%; Calcium salts 0.5%–5.0%; The remainder is water; The pullulan polysaccharide and polyphenol extracts were obtained by synergistic extraction of apple broth fermented with *Synthia spp.* using apple bleach as a fermentation substrate.

2. The pullulan polysaccharide fruit preservative with anti-mold and preservation functions according to claim 1, characterized in that, The fermentation broth from the substandard apples was obtained through the following steps: (1) Pretreatment of substandard apples: wash and drain the substandard apples, cut off the rotten and spoiled parts, and pulp them in a pulper for 10 minutes to obtain jam. Then, place the jam in a homogenizer for 15 minutes and concentrate it in a jam concentrator for 30 minutes to make concentrated jam for later use. (2) Prepare fermentation medium with apple defective fruit mass concentration of 100-200 g / L and nitrogen source mass concentration of 2-16 g / L respectively; (3) Fermentation: The budding short-stem mold AS3.3984 was fermented in a fermentation medium at 26-32℃ for 24-120h. After centrifugation, the bacterial cells and residues were removed to obtain a fermentation broth of apple substandard fruit rich in pullulan polysaccharide and polyphenols.

3. The pullulan polysaccharide fruit preservative with anti-mold and preservation functions according to claim 2, characterized in that, The polyphenol extract was obtained through the following steps: (a) Add 50%–70% of a hydrophilic organic solvent (such as ethanol) to the fermentation broth of the apple substandard fruit and perform shake extraction; (b) After centrifugation, collect the supernatant rich in polyphenols and concentrate it to 10% of the original supernatant volume to obtain the polyphenol extract. The pullulan polysaccharide was obtained through the following steps: (c) Precipitate the lower layer residue separated in step (b) with ethanol, and collect the crude polysaccharide by centrifugation. (d) Polysaccharide purification: The crude polysaccharide obtained in step (c) is dissolved and subjected to decolorization and protein removal purification operations to obtain pullulan polysaccharide.

4. The pullulan polysaccharide fruit preservative with anti-mold and preservation functions according to claim 2, characterized in that: The nitrogen source is selected from at least one of yeast extract, peptone, corn steep liquor, beef powder, ammonium nitrate, ammonium chloride, sodium nitrate, and ammonium sulfate.

5. The pullulan polysaccharide fruit preservative with anti-mold and preservation functions according to claim 1, characterized in that: The film-forming aid is glycerin.

6. The pullulan polysaccharide fruit preservative with anti-mold and preservation functions according to claim 1, characterized in that: The calcium salt is calcium chloride.

7. A method for preparing a pullulan polysaccharide fruit preservative with anti-mold and preservation functions according to any one of claims 1-6, characterized in that: Weigh the raw materials according to the weight percentage, add pullulan polysaccharide, polyphenol extract, film-forming aid, and calcium salt to the water in sequence, and stir evenly to obtain pullulan polysaccharide fruit preservative with anti-mold and preservation functions.

8. The application of pullulan polysaccharide fruit preservative with anti-mold and preservation function according to any one of claims 1-6 in the preparation of fruit preservation film, fruit coating agent or for post-harvest anti-mold and preservation of fruit.

9. The application according to claim 8, characterized in that: The fruits mentioned include, but are not limited to, apples, papayas, citrus fruits, berries, grapes, etc.

10. The application according to claim 8, characterized in that: The application method is as follows: after washing and drying the fruit, the preservative is applied to the surface of the fruit by immersion or spraying, and then dried at room temperature or under ventilated conditions, so that pullulan polysaccharide forms a continuous composite preservative film.