A postharvest citrus biological preservative, preservation method and application

Abstract

The application discloses a postharvest citrus biological preservative and a preservation method and application thereof. The preservative comprises, in terms of volume percentage, 40-100% of lysobacter enzymogenes LE16 autolysis fermentation liquor, 0-60% of propanil and 0.1-0.2% of Tween 80. The application further provides application and a method of the preservative in citrus biological preservation. The biological preservative is mainly the metabolic product of lysobacter enzymogenes LE16, has obvious biocontrol effect on green mold and green rot, reduces the rot rate of citrus fruits in the preservation process, and does not affect the fruit quality. The autolysis fermentation liquor is safe, non-toxic, environment-friendly, convenient to produce and can be applied on a large scale. In cooperation with chemical pesticides, the application can greatly reduce the pesticide application amount and pesticide residues under the condition of obtaining the same control effect, and has potential application value in postharvest citrus preservation.

Description

Technical Field

[0001] The present invention belongs to the technical field of food preservation, and in particular relates to a post-harvest citrus biological preservative, a preservation method and an application thereof. Background Art

[0002] Citrus, a plant of the Rutaceae family and genus Citrus, is widely cultivated in 125 countries and regions worldwide and is a beloved fruit. However, citrus fruits are notoriously difficult to preserve. During post-harvest transportation and storage, rot rates can sometimes reach as high as 50%, resulting in significant economic losses. Penicillium and green mold are the primary pathogens responsible for rot in citrus fruit, accounting for 90% of post-harvest rot in citrus, necessitating effective control measures.

[0003] Chemical control is currently an important and effective method for controlling postharvest diseases in citrus. For example, prochloraz, imazolide, and thiabendazole are effective against penicillium and green mold in postharvest citrus fruit. However, long-term, large-scale, and frequent use of chemical pesticides can pollute the environment, kill non-target organisms, and induce pathogenic resistance, reducing or even rendering control effective. Furthermore, chemical pesticides such as imidacloprid, acetamiprid, carbendazim, prochloraz, dimethoate, and avermectin have been repeatedly detected in citrus fruit preserved with chemical pesticides, posing potential health risks. With the increasing national emphasis on food safety, chemical fungicides are increasingly being strictly restricted in citrus preservation due to their high residual content, the development of pathogenic resistance, and environmental pollution. Biological preservatives offer significant advantages, such as safety, cost-effectiveness, and environmental friendliness, and hold great promise for their application in citrus preservation. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention aims to provide a biological preservative to solve the problem in the prior art, especially in the preservation of citrus fruits, that long-term, large-scale and frequent use of chemical pesticides pollutes the environment and causes potential harm to human health.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The invention provides a post-harvest citrus biological preservative, which comprises, by volume percentage, 40-100% of Lysobacter enzymogenes LE16 autolysis fermentation liquid and 0-60% of prochloraz solution.

[0007] The enzyme-producing Bacillus lysozyme LE16 was deposited in the General Microbiology Center of the China Culture Collection Administration on June 2, 2017, with the deposit number CGMCC No. 14215, and the deposit address is No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing.

[0008] Furthermore, in the biological preservative, the autolytic fermentation broth of Bacillus enzymogenes LE16 is 49-100%, and the prochloraz solution is 0%-51%, calculated by volume percentage.

[0009] Furthermore, Tween 80 is included, and the added amount is 0.1% to 0.2% of the total amount of the preservative.

[0010] The present invention also provides a method for preserving post-harvest citrus using a biological preservative, comprising the following steps:

[0011] (1) Pretreatment: Soak fresh citrus in 2% sodium hypochlorite for 1–2 min, then rinse with tap water and air-dry for later use.

[0012] (2) Fresh-keeping treatment: soak the citrus fruits treated in step (1) in the above-mentioned biological preservative for 2 to 5 minutes; after air-drying, pack the citrus fruits individually in fresh-keeping bags, place them in commercial packaging boxes, and store them at 4 to 6°C.

[0013] The present invention also provides an application of the post-harvest citrus biological preservative, which is not limited to the preservation of citrus, but can also be used for the preservation of apples, grapes, cherries and the like.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] 1. The biological preservative of the present invention utilizes the autolytic fermentation broth of Bacillus enzymolyticus LE16 to demonstrate significant biocontrol effects without affecting fruit quality. When combined with chemical pesticides, the amount of pesticide applied can be significantly reduced while achieving the same control effect. This biological preservative has potential application value in preserving citrus fruits after harvest.

[0016] 2. The biological preservative and preservation method of the present invention can be used to preserve citrus and other fresh fruits susceptible to penicillium and green mold infection, such as apples, grapes, and cherries, with a wide range of applications. The longest preservation time of citrus fruits after harvest at 4-6°C can reach 120 days, with a strong preservation effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The disease prevention effect diagram of the embodiment and the comparative example on citrus fruits inoculated with Penicillium spores;

[0018] Figure 2 Graph showing the effects of the examples and comparative examples on the rotten fruit rate of citrus fruits;

[0019] Figure 3 The diagram shows the control effect of the biological preservatives of the embodiment and the comparative example;

[0020] Figure 4 The inhibition of the culture medium containing different concentrations of LE16 autolysis fermentation broth on the hyphae of Penicillium and Chlorella;

[0021] Figure 5 The morphology of green mold and penicillium hyphae after solid treatment of the fermentation broth of Lysobacterium enzymogenes LE16 of the present invention is shown in the scanning electron microscope image;

[0022] Figure 6 This is a graph showing the inhibitory effect of volatile substances (VOCs) produced by LE16 of the present invention on the growth of green mold and penicillium hyphae. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described below in conjunction with specific examples, but the embodiments of the present invention are not limited thereto.

[0024] 1. The present invention has found that the application of the autolytic fermentation broth of Bacillus enzymolyticus LE16 in biological preservatives has a significant effect on reducing the pollution of chemical pesticides.

[0025] 2. Preparation of post-harvest citrus biological preservatives

[0026] 1. Culture medium

[0027] Beef extract peptone solid medium (NA): 3.0 g beef extract, 10.0 g peptone, 5.0 g sodium chloride, 15.0 g agar, 1000 mL distilled water, pH 7.4-7.6; its liquid medium does not contain agar and is abbreviated as NB.

[0028] Potato solid medium (PDA): 200.0g potatoes, 20.0g glucose, 15.0g agar, natural pH, 1000mL distilled water; its liquid medium does not contain agar and is abbreviated as PDB.

[0029] 2. Source of Lysozyme-producing Bacillus LE16

[0030] The Lysobacter enzymogenes LE16 (GenBank Number MK044898) strain (hereinafter referred to as LE16) was independently screened and isolated by the applicant's research group in 2016 and has been made public.

[0031] 3. LE16 autolysis fermentation broth and solid preparation method thereof

[0032] Prepare NB culture medium, sterilize (121℃, 103kPa, 30min), cool, and inoculate LE16 bacterial suspension (LE16 bacterial suspension (cell number about 10 7 ~10 9 After 1:100 (V / V), the mixture was incubated at 28°C and 150 r / min. -1The flask was shaken in a constant temperature shaking box until the solution became clear and transparent, thereby obtaining the autolytic fermentation broth of Bacillus enzymolyticus LE16 (hereinafter referred to as the original fermentation broth).

[0033] The LE16 autolyzed fermentation broth was vacuum dried at 28° C. to obtain the LE16 autolyzed fermentation broth solid.

[0034] 4. A biopreservative for post-harvest citrus fruits

[0035] Calculated by volume percentage, the invention comprises 40-100% of the autolytic fermentation liquid of Bacillus enzymogenes LE16, 0-60% of the prochloraz solution, and 0.1-0.2% of Tween 80.

[0036] The autolytic fermentation broth of Bacillus enzymogenes LE16 is directly obtained by dissolving and diluting the original fermentation broth or the fermentation broth solids prepared in step 3; the mass fraction of prochloraz in the prochloraz solution is 25% (the effective concentration of the prochloraz product). Tween 80 is an adhesive used to increase the adhesion of the preservative.

[0037] Table 1 Chemical composition and content of biological preservatives (calculated by volume percentage)

[0038]

[0039] Example 1 was prepared using the original fermentation broth and Tween 80, and Example 2 was prepared using the original fermentation broth, prochloraz solution and Tween 80.

[0040] In fact, the dosage ratio of the autolytic fermentation broth of Bacillus enzymolyticus LE16 and the prochloraz solution can be any ratio between (40% and 100%) and (0% and 60%), including 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, 70:30, 80:20, 85:15, 90:10, etc.; or adding a small amount of adhesion agent (such as Tween 80) will have a better effect.

[0041] 3. Application of a biological preservative. An example of the biological preservative is shown in Table 1.

[0042] Application Example 1

[0043] Take citrus fruits (variety: Ponkan) and dip a 2mm diameter sterile iron nail into a suspension of Penicillium spores (3×10 6 / mL), pierce the peel of the citrus fruit at 5 points evenly along the equator (depth of about 2mm), and dry it; then soak the fruit for 2 minutes with the preservatives described in Example 1-2 and Comparative Example 1-2 respectively. After drying, pack the fruits individually in citrus fresh-keeping bags, place them in a room at 22-25°C and a relative humidity of about 80%. Treat 20 fruits with each preservative in Example 1-2 and Comparative Example 1-2, and repeat 4 times. The test was carried out 3 times, with a total of 960 citrus fruits, and the average value was taken. 5 days after the treatment, the disease index, rotten fruit rate and prevention and control effect of the fruits were calculated.

[0044] Among them, the grading standard of citrus diseased fruit refers to the method disclosed by Yu Linhua et al. "The antibacterial effect of Ginkgo biloba extract on citrus Penicillium spp. Food and Machinery, 2010, 11(6)".

[0045] Fruit rot rate (%) = number of rotten holes / total number of holes × 100;

[0046] Disease index = [∑(number of diseased fruits surveyed × the level of the diseased fruit)] / (total number of fruits × the highest level) × 100;

[0047] Control effect (%) = (control rotten fruit rate - treatment rotten fruit rate) / control rotten fruit rate × 100.

[0048] The processing results are shown in Table 2

[0049] Table 2 Statistics of rotten fruit rate, disease index and control effect

[0050]

[0051] As shown in Table 2, the rotten fruit rate of citrus fruits was as follows: treatment with sterile water only (62.67%) > treatment with LE16 autolysis fermentation broth and prochloraz only (28% to 29.33%) > treatment with LE16 autolysis fermentation broth + 50% prochloraz (16%);

[0052] Disease index: The change of disease index is similar to the rotten fruit rate;

[0053] Control effect: LE16 autolysis fermentation liquid + 50% prochloraz (75.84%) > LE16 autolysis fermentation liquid alone (53.72%) > prochloraz alone (50.81%). However, there were no significant differences in fruit rot rate, disease index and control effect between the two groups (e.g. Figure 1 shown).

[0054] This shows that:

[0055] (1) The citrus fruit treated with LE16 autolytic fermentation liquid had a significantly lower rate of penicillium rot than that treated with sterile water. LE16 autolytic fermentation liquid has a good inhibitory ability against citrus penicillium rot.

[0056] (2) Citrus fruits treated with LE16 autolytic fermentation broth alone and those treated with prochloraz alone showed comparable efficacy in preventing and controlling penicillium, indicating that LE16 autolytic fermentation broth can replace prochloraz as a citrus penicillium control agent. This can reduce the use of pesticides, environmental pollution, and threats to human health.

[0057] The activities of peroxidase, catalase, and superoxide dismutase, as well as the malondialdehyde content and cell membrane permeability of non-diseased citrus peels treated with preservatives were determined by guaiacol method, potassium permanganate titration method, nitroblue tetrazolium method, thiobarbituric acid method, and conductivity method, respectively. The results are shown in Table 3.

[0058] Table 3 Antioxidant content of healthy citrus peels after treatment with preservatives

[0059]

[0060] Note: The data in the table are mean ± standard deviation. The significance of differences among different treatments were compared by univariate statistical analysis and the least significant difference (LSD) method. Different lowercase letters represent the same storage time, and the differences among treatments were significant at the 0.05 level.

[0061] As shown in Table 3, compared with Comparative Example 2, the malondialdehyde content and cell membrane permeability in citrus peels were reduced after treatment with Examples 1-2 and Comparative Example 1, and the activities of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase) were increased. Specifically, the activities of superoxide dismutase and peroxidase after treatment with LE16 autolyzed fermentation broth + 50% prochloraz were greater than those after treatment with LE16 autolyzed fermentation broth, but there was no significant difference between the treatment with prochloraz alone and the treatment with LE16 autolyzed fermentation broth.

[0062] The malondialdehyde (cell membrane oxidation product) content and cell membrane permeability in citrus peels decreased, indicating that after the application of the fermentation liquid, the pathogenic bacteria reduced the damage to citrus peel cells. The antioxidant enzyme activity increased, indicating that the fermentation liquid reduced the damage caused by pathogens to citrus fruit. This is because when plants are infected with pathogens, they stimulate the production of reactive oxygen species that damage cells and tissues. Increasing the activity of antioxidant enzymes is beneficial for eliminating reactive oxygen species, thereby reducing the damage caused by pathogens to the fruit. The combination of LE16 autolytic fermentation liquid and myclobutanil increased antioxidant enzyme activity by a similar amount as the application of myclobutanil alone, indicating that the combination of LE16 autolytic fermentation liquid and myclobutanil can replace the application of myclobutanil alone as a preservative, thereby reducing the use of pesticides, environmental pollution, and potential threats to the human body.

[0063] Application Example 2

[0064] Citrus fruits (cultivar: Ponkan) were soaked in 2% sodium hypochlorite by mass for 2 minutes, rinsed with tap water, and air-dried. The fruits were then soaked in the preservatives of Examples 1-2 and Comparative Examples 1-2 for 2 minutes, respectively. After air-drying, the fruits were individually packaged in fresh-keeping bags and placed in commercial packaging boxes. The fruit was stored at 4-6°C and a relative humidity of 90%-95%. 440 citrus fruits were treated with each preservative four times, for a total of 7,040 citrus fruits. The fruit rot rate, control efficacy, and fruit weight loss were measured at 0, 15, and 30 days of storage.

[0065] Weight loss rate (%) = (mass before storage - mass after storage) / (mass before storage) × 100.

[0066] The fruit rot rate and control effect are shown in Table 4.

[0067] Table 4 Fruit rot rate and control effect

[0068]

[0069] As shown in Table 4, the rotten fruit rate of citrus fruits increased with the extension of storage time. There was no significant difference between the LE16 autolysis fermentation liquid treatment and the sterile water treatment alone. The prochloraz and LE16 autolysis fermentation liquid + 50% prochloraz treatments were significantly lower than the sterile water treatment alone (e.g. Figure 2 ). It can be seen that prochloraz and LE16 autolysis fermentation liquid + 50% prochloraz can significantly reduce the rot rate of citrus fruits. Control effect: After 15 days of storage, the control effects of LE16 autolysis fermentation liquid, prochloraz and LE16 autolysis fermentation liquid + 50% prochloraz were 50.00%, 83.33% and 75.93%, respectively, and after 30 days of storage, they were 26.90%, 73.68% and 72.51%, respectively (such as Figure 3 Thus, there was no significant difference between the treatment with LE16 autolytic fermentation broth and 50% prochloraz and the treatment with prochloraz. This means that the combination of fermentation broth and chemical pesticides can significantly reduce the amount of pesticide applied while achieving the same control effect, ensuring food safety and having potential application value in the post-harvest preservation of citrus.

[0070] The nutritional content of citrus fruits after preservation treatment is shown in Table 5:

[0071] Table 5 Nutrient content of citrus fruits after preservation treatment

[0072]

[0073] Note: The data in the table are mean ± standard deviation. The significance of differences among different treatments were compared by univariate statistical analysis and the least significant difference (LSD) method. Different lowercase letters represent the same storage time, and the differences among treatments were significant at the 0.05 level.

[0074] As shown in Table 5, reducing sugars, soluble solids, and weight loss in citrus fruits increased to varying degrees with extended storage, while fruit firmness showed the opposite effect. During storage, vitamin C content initially decreased and then increased. Overall, there were no significant differences in citrus quality between the various treatments for the same storage time. This indicates that preserving citrus fruits with the biological preservative of the present invention does not affect their quality.

[0075] Application Example 3

[0076] Citrus fruits (variety: sweet orange) were collected and soaked in 2% sodium hypochlorite by mass for 2 minutes. After being rinsed with tap water and air-dried, the fruits were then soaked for 2 minutes in each of the preservatives described in Examples 1-2, Comparative Examples 1-2, and a 50% prochloraz solution (with a prochloraz active content of 50%). After air-drying, the fruits were individually packaged in fresh-keeping bags and placed in commercial packaging boxes. Thirty-two citrus fruits were treated with each of Examples 1-2, Comparative Examples 1-2, and the 50% prochloraz solution, and the preservatives were repeated four times. Four trials were conducted, totaling 2,560 citrus fruits. The rotten fruit rate and control efficacy are shown in Table 6.

[0077] Table 6 Citrus fruit rot rate and control effect

[0078]

[0079] As shown in Table 6, the rot rate of citrus fruits treated with the fermentation broth was significantly lower than that of citrus fruits treated with sterile water alone, indicating that the fermentation broth has a positive control effect on preventing citrus fruit rot. Furthermore, the pathogen control efficacy of citrus fruits treated with the LE16 autolysis fermentation broth plus 50% prochloraz was comparable to that of citrus fruits treated with prochloraz. This indicates that, given comparable pathogen control efficacy, the use of the LE16 autolysis fermentation broth plus 50% prochloraz solution of the present invention can effectively reduce pesticide usage, thereby reducing environmental pollution and threats to human health.

[0080] The nutritional content of citrus fruits after preservation treatment is shown in Table 7:

[0081] Table 7 Nutrient content of citrus fruits after fresh-keeping treatment

[0082]

[0083]

[0084]

[0085] Note: The data in the table are mean ± standard deviation. The significance of differences among different treatments were compared by univariate statistical analysis and the least significant difference (LSD) method. Different lowercase letters represent the same storage time, and the differences among treatments were significant at the 0.05 level.

[0086] As shown in Table 7, the contents of vitamin C, soluble sugars, firmness, and titratable acid in citrus fruit decreased with prolonged storage. After 30 days of storage, the soluble solids content of the fruit increased slightly. However, there were no significant differences in fruit quality between the different treatments. This indicates that the use of the biological preservative of the present invention for preserving citrus fruit does not affect its quality.

[0087] In summary, the present invention utilizes the autolytic fermentation broth of strain LE16. In wound inoculation and preservation tests, the broth demonstrated significant biocontrol efficacy without compromising fruit quality. When combined with chemical pesticides, the broth can significantly reduce pesticide application while achieving the same control efficacy, demonstrating potential application value in postharvest citrus preservation. Furthermore, the broth exhibits thermal stability (maintaining antimicrobial activity at 100°C), resulting in a longer shelf life and greater suitability for practical applications.

[0088] 4. Determination of the inhibitory ability of LE16 against Penicillium and Green mold

[0089] 1. LE16 solids inhibition of mycelial growth test

[0090] (1) Measurement method

[0091] Different weights of LE16 autolyzed fermentation broth solids were weighed and added to sterilized PDA cooled to approximately 55°C at concentrations of 0 (control), 0.05%, 0.10%, 0.20%, and 0.40%. 5-mm-diameter cakes of Penicillium and Chlorella were inoculated in the center of each PDA plate and incubated in the dark at (28±1)°C for 8 days. Colony area was measured using a scanner. Five replicates were performed for each concentration, and the inhibition rate was calculated.

[0092] Inhibition rate / %=[(control colony area-treated colony area) / control colony area]×100.

[0093] A 2cm x 2cm piece of tinfoil was placed on the surface of a control plate and a plate containing LE16 autolyzed fermentation broth. The pathogen was inoculated onto the PDA and allowed to grow onto the foil. The foil was removed and fixed with 2.5% glutaraldehyde. After drying, the hyphae were observed using a scanning electron microscope.

[0094] (2) Result analysis

[0095] like Figure 4As shown, compared with the control, the culture medium supplemented with LE16 autolyzed fermentation broth solids had an inhibition rate of 56.54% to 100% on the mycelia of green mold and 55.66% to 100% on the mycelia of penicillium.

[0096] like Figure 5 As shown, scanning electron microscopy observation revealed that the hyphae of Penicillium and Green mold on the PDA culture medium of the control group had clear edges, obvious transverse septa, uniform thickness, and smooth outer walls; on the PDA containing the solids of the autolytic fermentation broth of Bacillus enzymolyticus LE16, the hyphae of Penicillium and Green mold were shriveled, twisted and deformed.

[0097] It can be seen that the LE16 autolysis fermentation broth has a significant inhibitory effect on both Penicillium and Chlorella mycelium, and the higher the concentration of LE16 autolysis fermentation broth, the stronger the inhibitory effect.

[0098] 2. LE16 solids inhibition spore germination test

[0099] (1) Measurement method

[0100] LE16 autolyzed fermentation broth solids were added to PDB medium to make the concentrations 0 (control) and 0.4%, respectively. Then, pathogenic bacteria (Penicillium or Chlorella) spore suspension (3×10 6 Spores were cultured in the dark at 28°C for 12 and 24 h. Spore germination was observed under a microscope. Spores were considered germinated if the length of the germ tube exceeded the diameter of the swollen spore. Each concentration was repeated five times.

[0101] Spore germination rate / % = number of spores germinated in the field of view / total number of spores in the field of view × 100;

[0102] Germination inhibition rate / % = (control germination rate - treatment germination rate) / control germination rate × 100.

[0103] (2) Result analysis

[0104] Calculations showed that the culture medium supplemented with LE16 autolysis fermentation broth solids had a maximum inhibition rate of 96.03% to 99.16% on the spore germination of Penicillium and Chlorella compared to the control group. This indicates that LE16 autolysis fermentation broth also has a significant inhibitory effect on the spore germination of Penicillium and Chlorella.

[0105] 3. Test on the inhibition of mycelial growth by volatile substances

[0106] (1) Measurement method

[0107] Pour PDA and NA culture media into separate Petri dishes. Inoculate 5 mm diameter cakes of Penicillium and Chlorella in the center of the PDA, respectively, and LE16 in the center of the NA. Then, place the two plates face-to-face and seal with Parafilm. A plate inoculated with the pathogen alone serves as a control. Incubate at 28°C in the dark for 8 days. Repeat five times, and calculate the inhibition rate.

[0108] (2) Result analysis

[0109] like Figure 6 As shown in the figure, after 8 days of culture, the colony diameters of Penicillium and Chloride mold were 7.42 mm and 10.41 mm, respectively, and the inhibition rates reached 91.11% and 77.52%, respectively. This shows that the volatile substances produced by LE16 can also significantly inhibit the growth of Penicillium and Chloride mold.

[0110] In summary, the LE16 autolytic fermentation broth has an inhibitory effect on the growth of both Penicillium and Green mold. Combined with the fact that the LE16 autolytic fermentation broth has a good inhibitory ability against citrus Penicillium disease, the inventors analyzed and believed that the LE16 autolytic fermentation broth also has a good inhibitory ability against citrus Green mold disease.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the technical solutions. Those skilled in the art should understand that modifications or equivalent replacements of the technical solutions of the present invention that do not depart from the purpose and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A post-harvest citrus biological preservative, characterized in that: By volume percentage, it includes 40%-55% of Bacillus lysozyme-producing bacteria ( Lysobacter enzymogenes ) LE16 autolytic fermentation broth, 45%-60% prochloraz solution, the mass fraction of prochloraz in the prochloraz solution is 25%; wherein, the enzyme-producing Bacillus lysozyme LE16 was deposited in the General Microbiology Center of China Microorganism Culture Collection on June 2, 2017, with the deposit number CGMCC No. 14215, and the deposit address is No. 3, Yard 1, Beichen West Road, Chaoyang District, Beijing.

2. The post-harvest citrus biological preservative according to claim 1, characterized in that: It includes 49.9% autolytic fermentation broth of Bacillus enzymogenes LE16, 50% prochloraz solution, and 0.1% Tween 80.

3. A method for preserving post-harvest citrus using a biological preservative, characterized in that: The steps include: (1) Pretreatment: Soak fresh citrus in 2% sodium hypochlorite for 1-2 min, then rinse with tap water and air-dry for later use; (2) Fresh-keeping treatment: soak the citrus fruits treated in step (1) in the biological preservative according to any one of claims 1 to 2 for 2 to 5 minutes; after air-drying, pack the citrus fruits individually in fresh-keeping bags, place them in commercial packaging boxes, and store them at 4 to 6°C.

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