5-oxo-l-proline in the preservation of fruits and vegetables

Abstract

The application discloses application of 5-oxo-L-proline in fruit and vegetable preservation, and further discloses a fruit and vegetable preservation method, which is characterized in that: picked fruits and vegetables are soaked in a 5-oxo-L-proline solution with a mass concentration of 0.5% to 0.8% for 2 to 5 minutes, taken out, dried, packed, and preserved under the conditions of 20 to 25 DEG C and 80% to 95% relative humidity, or under the conditions of 3 to 5 DEG C and 80% to 90% relative humidity. The fruits and vegetables can be preserved for 10 to 30 days under the conditions of 20 to 25 DEG C, and the citrus fruits can be preserved for 3 months under the conditions of 3 to 5 DEG C, and the rotten fruit rate is less than 5%. The inventor of the application finds that the 5-oxo-L-proline can inhibit the main pathogenic bacteria causing citrus fruit rot in different degrees, including green mold, penicillium, acid rot fungus, anthracnose fungus and alternaria alternata; meanwhile, the pathogenic bacteria are also the main pathogenic bacteria causing the rot of other fruits and vegetables (such as apples, strawberries, cherries, solanaceous vegetables and the like). The 5-oxo-L-proline has the characteristics of "one dose for multiple prevention" and "one dose for multiple use" when used for fruit and vegetable preservation. When used for fruit and vegetable preservation, the 5-oxo-L-proline has long preservation time and good preservation effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of biological preservation technology, and particularly relates to application of 5-oxo-L-proline in fruit and vegetable preservation. BACKGROUND

[0002] In developed countries such as Europe and North America, the use of antibiotics and chemical pesticides is decreasing year by year, and instead, natural substances (such as plant extracts and microbial metabolites) and physical methods are used for the preservation of postharvest fruits and vegetables. In China, there are few natural substances that can replace antibiotics and chemical pesticides for the preservation of fruits and vegetables, and large-scale application is rare. At present, in addition to antibiotics and chemical pesticides, methods for preserving fruits and vegetables can be summarized as follows: ① biological control: using biocontrol bacteria (such as yeast, lactic acid bacteria, Trichoderma, Bacillus subtilis, Bacillus licheniformis, and photosynthetic bacteria) to prevent postharvest fruits and vegetables from rotting, the main mechanism of which is to use the hydrolytic enzymes (such as chitinase and β-1,3 glucosidase) and antibacterial substances secreted by biocontrol bacteria to antagonize pathogenic microorganisms and induce disease resistance in fruits; ② inorganic salts and disinfectants: mainly including sodium chloride, calcium chloride, sodium bicarbonate, ethanol, and organic acids, which can clean the surface of fruits, change the pH value of the fruit surface, or increase the osmotic pressure to inhibit the growth and reproduction of pathogenic microorganisms; ③ natural extract substances: such as chitosan, vitamins, and polysaccharides, which can mainly nourish the peel and maintain the health of fruits, thereby enhancing disease resistance. ④ physical methods: including low temperature, filling N2, CO2, etc., which can reduce the respiration intensity of fruits and the growth and reproduction rate of pathogens. Although the above methods are environmentally friendly, safe for humans and animals, and can inhibit pathogenic microorganisms and reduce fruit rot to varying degrees. However, these methods have some obvious defects: first, the number of biocontrol bacteria that can be actually applied is limited, and the growth and reproduction of microorganisms are closely related to environmental conditions, so the biocontrol effect of microbial inoculants is easily affected by environmental conditions and has poor stability; second, high concentrations of inorganic salts and ethanol can damage fruits and shorten the preservation time; if the concentration is reduced, the effect is poor; third, the concentration of natural extract substances in the original plant is low, which is difficult to extract and expensive, limiting its application; fourth, physical methods are suitable for large-scale centralized preservation, but small-scale production of fruits and vegetables by farmers accounts for a high proportion in China, and the cost of physical preservation is increased. In summary, the current methods for preserving fruits and vegetables are few, the preservation effect is poor, and the number of methods needs to be increased and the preservation effect needs to be improved.

[0003] During postharvest storage and marketing of citrus, the pathogenic fungi such as Penicillium digitatum, Penicillium italicum, Geotrichum citri-aurantii, Colletotrichum gloeosporioides and Alternaria alternata infect the fruit and cause decay, and the total incidence rate of decayed fruit can reach more than 20%. At present, chemical pesticides (such as prochloraz and thiophanate-methyl) are the main means to inhibit the growth and reproduction of pathogenic microorganisms and prevent the decay of citrus fruit. However, the chemical pesticides remaining on the surface of the fruit or soaked into the fruit can cause acute and chronic poisoning and harm health when ingested by human body. In addition, antibiotics (such as clotrimazole and natamycin) can also inhibit the growth and reproduction of pathogenic microorganisms and prevent the decay of citrus, but long-term, large-scale and frequent use of antibiotics can lead to drug resistance of pathogenic bacteria, and there are also risks to human and animal health and the environment.

[0004] In the prior art, 5-oxo-L-proline is an organic synthesis precursor or intermediate. It is an enantiomeric body with biological activity in the human body, an intermediate in glutathione metabolism, and is commonly added to cosmetics for moisturizing and whitening. It is non-toxic, safe and non-irritating to humans, and can be synthesized by dehydration of two molecules of glutamic acid at 140-150 DEG C, which is easy to be industrially synthesized and has low cost.

[0005] The inventors of the present application independently isolated Lysobacter enzymogenes LE16 and Bacillus velezensis HY19, which can also secrete 5-oxo-L-proline. So far, no one has found that 5-oxo-L-proline has the phenomenon of antagonizing Penicillium, Penicillium, Geotrichum, Colletotrichum and Alternaria alternaria, and no report has been made on the use of 5-oxo-L-proline for fruit and vegetable preservation. SUMMARY

[0006] In view of the above-mentioned deficiencies in the prior art, the purpose of the present application is to provide the application of 5-oxo-L-proline in fruit and vegetable preservation, to solve the problems of poor preservation effect, short preservation time, easy to be affected by the environment, poor stability and high cost in the existing fruit and vegetable preservation methods.

[0007] In order to solve the above technical problems, the technical scheme adopted by the present application is as follows:

[0008] The present application discloses the application of 5-oxo-L-proline in fruit and vegetable preservation.

[0009] Further, 5-oxo-L-proline is used for fruit preservation.

[0010] Further, 5-oxo-L-proline is used for citrus preservation.

[0011] Further, the method for fruit and vegetable preservation is as follows: picking fruits and vegetables are soaked in 5-oxo-L-proline solution with mass concentration of 0.5%-0.8% for 2-5 minutes, taken out, dried, packed, and preserved under the condition of 20-25℃ and relative humidity of 80-95%.

[0012] Further, the method for fruit and vegetable preservation is as follows: picking fruits and vegetables are soaked in 5-oxo-L-proline solution with mass concentration of 0.5%-0.8% for 2-5 minutes, taken out, dried, packed, and preserved under the condition of 20-25℃ and relative humidity of 80-95%.

[0013] Compared with the prior art, the present application has the following beneficial effects:

[0014] 1. The inventor of the present application accidentally finds that 5-oxo-L-proline can inhibit the main pathogenic bacteria of citrus fruit rot, including green mold, penicillium, sour rot bacteria, anthracnose and alternaria, which are also the main pathogenic bacteria causing the rot of other fruits and vegetables (such as apples, strawberries, cherries, solanaceous vegetables, etc.). Therefore, 5-oxo-L-proline can be used not only for postharvest citrus preservation, but also for the preservation of other fruits and solanaceous vegetables, having the characteristics of "one dose for multiple prevention" and "one dose for multiple use". When used for fruit and vegetable preservation, the preservation time is long, and the preservation effect is good. At room temperature (20-25℃), fruits and vegetables can be preserved for 10-30 days, and at low temperature (3-5℃), citrus fruits can be preserved for 3 months, and the rot rate is less than 5%.

[0015] 2. When the fruit and vegetable preservation is performed, 5-oxo-L-proline is prepared into a solution with a specified concentration, and then the fruits are soaked and dried, so that the operation is completed, which is simple and convenient for popularization and application. As the types of pathogenic bacteria causing fruit rot are different in different regions and different fruits and vegetables, and the half-inhibitory concentration (IC 50 ) of 5-oxo-L-proline to different pathogenic bacteria is different, the concentration of 5-oxo-L-proline can be increased or decreased to obtain an ideal prevention and treatment effect, and the application range is wide.

[0016] 3. 5-oxo-L-proline is easy to be synthesized industrially, and has low cost; and has stable chemical properties (heat-resistant, acid-resistant, and alkali-resistant), is not easily affected by the environment during the preservation process, and has high stability; is non-toxic, safe and non-irritating to the human body, and is suitable for fruit and vegetable preservation. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1Figure of the antagonistic effect of different concentrations of 5-oxo-L-proline on Penicillium digitatum, Penicillium italicum, Guignardia citric-aurantii, Colletotrichum gloeosporioides and Alternaria alternata; P. digitatum, green mold; P. italicum, Penicillium; G. citri-aurantii, sour rot; C. gloeosporioides, anthracnose; A. alternata, Alternaria alternate. DETAILED DESCRIPTION

[0018] The specific embodiments of the present application will be further described in conjunction with the specific examples below.

[0019] The numerical ranges recited herein are inclusive of the recited endpoints and of every integer and fraction within the range. All intermediate ranges and subranges are also included herein. The endpoints of the ranges and subranges are independently combinable with each other.

[0020] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, preferred methods and materials are described. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and / or materials in connection with which the publications are cited. In case of conflict, the content of the present specification will control. As used herein, the terms "comprises", "comprising", "includes", "including", "has", "having", and the like are open-ended terms that are intended to permit but not limit the inclusion of elements or the number of elements, and that do not exclude additional elements or the number of elements.

[0021] The experimental methods used in the present application are conventional methods unless otherwise specified.

[0022] The materials, reagents and the like used in the present application can be purchased or synthesized by known methods unless otherwise specified.

[0023] The quantitative test in the present application is set up with three repeated experiments, and the average value is taken.

[0024] Note: The concentrations involved in the present application are mass concentrations.

[0025] The present application verifies that 5-oxo-L-proline has a significant inhibitory effect on the main rotten fruit pathogens of postharvest citrus, such as green mold, penicillium, sour rot, anthracnose and alternaria, and can reduce the rotten fruit rate of postharvest citrus. Moreover, the virulence equation of 5-oxo-L-proline is established, and the half inhibitory concentration is determined; the application method and effect of 5-oxo-L-proline as a new type of preservative for citrus are determined, and can be extended to the preservation of other fruits and solanaceous vegetables (because green mold, penicillium, sour rot, anthracnose and alternaria are also the main pathogens causing the rot of other fruits such as apples, strawberries and cherries, and solanaceous vegetables). The following steps are realized in turn:

[0026] I. Inhibition of 5-oxo-L-proline on the main rotten fruit pathogens of postharvest citrus

[0027] ① Preparation of PDA medium containing 5-oxo-L-proline: different amounts of 5-oxo-L-proline are added to PDA medium (potato 200 g, glucose 20 g, agar 20 g, deionized water 1000 mL, pH 5.60) to make the mass concentration (%) of 5-oxo-L-proline in PDA medium reach 0 (CK), 0.05, 0.10, 0.20, 0.40 and 0.80 respectively, and then sterilized at 121℃ for 20 minutes to obtain PDA medium containing different concentrations of 5-oxo-L-proline.

[0028] ② Preparation of toxin-containing plates: when the PDA medium containing 5-oxo-L-proline is cooled to 50-60℃, 15 mL of the obtained medium is added to different culture dishes (φ≈10 cm) respectively, and then cooled to obtain toxin-containing plates.

[0029] ③ Inoculation and culture of pathogens: one piece of activated green mold, penicillium, sour rot, anthracnose and alternaria cake (φ≈3 mm) is inoculated in the center of the PDA toxin-containing plate respectively, and then cultured in the dark at 25℃ for 5-7 days, the colony area is measured, and the inhibition rate of different concentrations of 5-oxo-L-proline on the pathogens is calculated.

[0030] Inhibition rate (%)=(colony area of CK-colony area of Ct) / colony area of CK×100; wherein, CK is the colony area without 5-oxo-L-proline; Ct is the colony area with different concentrations of 5-oxo-L-proline.

[0031] Figure 1 The pathogen inhibition effect of different concentrations of 5-oxo-L-proline. Figure 1 It can be seen that different concentrations of 5-oxo-L-proline solution have a significant inhibitory effect on green mold, penicillium, sour rot, anthracnose and alternaria, and the higher the concentration of 5-oxo-L-proline, the better the antibacterial effect.

[0032] II. Establishing the toxicity equation of 5-oxo-L-proline to determine the half-inhibitory concentration

[0033] According to the concentration of 5-oxo-L-proline (x) and the corresponding inhibitory rate (y) in PDA, the toxicity equation (y = alog 10 x + b, a and b are coefficients) was established, and the half-inhibitory concentration IC 50 of 5-oxo-L-proline to green mold, penicillium, sour rot, anthracnose and alternaria was calculated according to the toxicity equation, as shown in Table 1.

[0034] Table 1 Inhibitory effect of 5-oxo-L-proline on citrus fruit rot pathogens

[0035]

[0036] In Table 1, P. digitatum, green mold; P. italicum, penicillium; G. citri-aurantii, sour rot; C. gloeosporioides, anthracnose; A. alternata, alternaria; y is the inhibitory rate; x is the concentration of 5-oxo-L-proline; n is the sample size; r 2 and p are statistical concepts, r 2 is the absolute coefficient, and p is the probability; IC 50 is the half-inhibitory concentration, indicating the inhibitory ability of 5-oxo-L-proline on different pathogens, and the lower the value, the stronger the inhibitory effect.

[0037] As shown in Table 1, the inhibitory effect of 5-oxo-L-proline on pathogens is highly related to the concentration of 5-oxo-L-proline, and the inhibitory effect of 5-oxo-L-proline on different pathogens is also different, so increasing or decreasing the concentration of 5-oxo-L-proline can achieve ideal antibacterial effect.

[0038] III. Preservation method and effect of 5-oxo-L-proline (food grade) on postharvest fruits and vegetables

[0039] Due to the non-toxicity and easy synthesis of 5-oxo-L-proline, using 5-oxo-L-proline for the preservation of fruits and vegetables has the characteristics of economy, convenience, high efficiency, non-toxicity, safety, etc., and can overcome the defects of the current common preservation technology of fruits and vegetables.

[0040] (1) Citrus preservation: pick up the picked citrus and soak it in 0.8% mass concentration of 5-oxo-L-proline solution for 2 minutes, take it out and dry, pack; store at room temperature (20-25°C, relative humidity 80-95%) for 30 days or store at low temperature (3-5°C, relative humidity 80-90%) for 90 days, and the fruit rot rate is less than 5%.

[0041] Example 1

[0042] The present example provides a method for preserving citrus fruits using 5-oxo-L-proline, comprising the following steps:

[0043] Dissolve 400 g of 5-oxo-L-proline in 50 kg of tap water to prepare a 5-oxo-L-proline solution with a mass fraction of 0.8%. Collect 500 kg of citrus fruits (variety: Ponkan; fruit without damage, no pests and diseases), and immerse them in the 5-oxo-L-proline solution for 2 minutes in 5 batches (100 kg per batch), dry, and pack into fruit boxes (10 kg per box). Take 500 kg of citrus fruits as a control group without soaking in the 5-oxo-L-proline solution, and treat the rest of the citrus fruits in the same way as the 5-oxo-L-proline solution. Store them in a cold storage room at 3-5°C and a relative humidity of 80-90% for 3 months. The rotten fruit rate of the control group is 24.25%, and the rotten fruit rate of the 5-oxo-L-proline solution treated group is 3.25%.

[0044] Example 2

[0045] The present example provides a method for preserving citrus fruits using 5-oxo-L-proline, comprising the following steps:

[0046] Dissolve 400 g of 5-oxo-L-proline in 50 kg of tap water to prepare a 5-oxo-L-proline solution with a mass fraction of 0.8%. Collect 500 kg of citrus fruits (variety: Ponkan; fruit without damage, no pests and diseases), and immerse them in the 5-oxo-L-proline solution for 2 minutes in 5 batches (100 kg per batch), dry, and pack into fruit boxes (10 kg per box). Take 500 kg of citrus fruits as a control group without soaking in the 5-oxo-L-proline solution, and treat the rest of the citrus fruits in the same way as the 5-oxo-L-proline solution. Store them in a cold storage room at 3-5°C and a relative humidity of 80-90% for 3 months. The rotten fruit rate of the control group is 24.25%, and the rotten fruit rate of the 5-oxo-L-proline solution treated group is 3.25%.

[0047] (2) Strawberry preservation: immerse the picked strawberries in a 5-oxo-L-proline solution with a mass concentration of 0.6% for 2 minutes, dry, and pack; store at room temperature (20-25°C, relative humidity 80-95%) for 10 days, and the rotten fruit rate is less than 5%.

[0048] Example 3

[0049] The present example provides a method for preserving strawberries using 5-oxo-L-proline, comprising the following steps:

[0050] Take 5-oxo-L-proline 150 grams dissolved in 25 kg tap water, prepared 0.6% by mass fraction of 5-oxo-L-proline solution. Collection of strawberries 100 kg (fruit no injury, no disease and pests), 10 batches (10 kg each batch) soaked in 5-oxo-L-proline solution for 2 minutes, dry, packed into fruit box (2 kg per box); with 100 kg not soaked 5-oxo-L-proline solution for control, the rest of the 5-oxo-L-proline solution treatment. Normal temperature storage (20-25 °C, relative humidity 85-95%) for 10 days. The control group rotten fruit rate 61.50%, 5-oxo-L-proline solution treatment of rotten fruit rate 4.85%.

[0051] (3) Tomato preservation: the picked tomatoes are soaked in 0.6% by mass concentration of 5-oxo-L-proline solution for 5 minutes, taken out and dried, and packed; normal temperature storage (20-25 °C, relative humidity 80-95%) for 28 days, and the rotten fruit rate is less than 5%.

[0052] Example 4

[0053] The embodiment provides a method for preserving tomatoes by using 5-oxo-L-proline, which comprises the following steps:

[0054] Take 5-oxo-L-proline 300 grams dissolved in 50 kg tap water, prepared 0.6% by mass fraction of 5-oxo-L-proline solution. Collection of tomatoes 200 kg (fruit no injury, no disease and pests), 10 batches (20 kg each batch) soaked in 5-oxo-L-proline solution for 5 minutes, dry, packed into fruit box (10 kg per box); with 200 kg not soaked 5-oxo-L-proline solution for control, the rest of the 5-oxo-L-proline solution treatment. Normal temperature storage (20-25 °C, relative humidity 85-95%) for 28 days. The control group rotten fruit rate 26.01%, 5-oxo-L-proline solution treatment of rotten fruit rate 3.57%.

[0055] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application, but not to limit the technical solutions, and those of ordinary skill in the art should understand that those who modify or equivalently replace the technical solutions of the present application without departing from the purpose and scope of the technical solutions should be covered in the scope of claims of the present application.

Claims

1. Use of 5-oxo-L-proline for the preservation of postharvest fruits and vegetables, characterized in that, 5-oxo-L-proline has inhibitory effect on green mold, penicillium, aspergillus, anthracnose and alternaria which cause postharvest fruit and vegetable to rot, and 5-oxo-L-proline is prepared into a solution with mass concentration of 0.5%-0.8% when postharvest fruit and vegetable preservation is carried out.

2. The use of 5-oxo-L-proline according to claim 1 for the preservation of postharvest fruits and vegetables, characterized in that, 5-oxo-L-proline is used for postharvest fruit preservation.

3. The use of 5-oxo-L-proline according to claim 1 for the preservation of postharvest fruits and vegetables, characterized in that, 5-oxo-L-proline is used for postharvest citrus preservation.

4. The use of 5-oxo-L-proline according to claim 1 for the preservation of fruits and vegetables, characterized in that, The method for fruit and vegetable preservation is that the picked fruit and vegetable is soaked in 5-oxo-L-proline solution with mass concentration of 0.5%-0.8% for 2-5 minutes, taken out, dried, packed and preserved under the condition of 20-25°C and relative humidity of 80-95%.

5. The use of 5-oxo-L-proline according to claim 1 for the preservation of fruits and vegetables, characterized in that, The method for fruit and vegetable preservation is that the picked fruit and vegetable is soaked in 5-oxo-L-proline solution with mass concentration of 0.5%-0.8% for 2-5 minutes, taken out, dried, packed and preserved under the condition of 3-5°C and relative humidity of 80-90%.

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