Preservation method of picked litchis through electromagnetic field treatment

Abstract

The invention discloses a postharvest litchi preservation method treated by an electromagnetic field. The postharvest litchi preservation method comprises the following steps: step 1, screening and pre-treating litchi fruits; step 2, grouping processing and electromagnetic field action; and step 3, packaging and storing. 4, evaluating the fresh-keeping effect; electromagnetic field non-thermal physical treatment is adopted, a large number of chemical agents are not needed, the residual risk caused by chemical preservation is avoided, the food safety requirement is met, and the method is suitable for green fruit production; the lychee fresh-keeping agent can be independently matched with clear water for use, and can also be compounded with conventional bactericides (Sportak and carbendazim) for use, so that different fresh-keeping requirements can be flexibly met, and diversified solutions are provided for storage and transportation of picked lychees.

Description

TECHNICAL FIELD

[0001] The present application relates to the postharvest preservation technology field of litchi, in particular to a litchi postharvest preservation method treated by an electromagnetic field. BACKGROUND

[0002] Litchi (Litchi chinensis Sonn.) belongs to the Sapindaceae family and is a unique and high-quality fruit in southern China, and is also one of the most competitive fruits on the international market. However, litchi is prone to browning and rotting after being harvested in the hot summer season due to its unique fruit structure. At room temperature, it loses its commercial value in 2-3 days, and is said to have "one-day color change, two-day fragrance change, three-day taste change, and four-five-day loss of color, fragrance, and taste". Fruit browning and rotting seriously restrict the long-term storage and transportation of litchi and are the key factors leading to its short shelf life and decreased commercial value.

[0003] The current mainstream postharvest preservation technology for litchi has obvious limitations:

[0004] Chemical preservation method: As a widely used method, it is divided into acid treatment (soaking in edible hydrochloric acid and oxalic acid solution) and sulfur treatment (sulfur fumigation, sulfur immersion, and sulfur dioxide slow release). Although sulfur treatment has a significant effect, it needs to be strictly controlled in terms of concentration, temperature, and time. Excessive treatment can lead to fruit skin softening, loss of fruit flesh elasticity, and the risk of sulfur dioxide residue exceeding the standard;

[0005] Modified atmosphere preservation technology: By controlling the CO2 concentration in the storage environment to inhibit respiration, the preservation period can be moderately extended, but the technical operation control is complex and the application has not been popularized;

[0006] Coating preservation technology: A natural polymer emulsion / solution with antibacterial properties is coated on the surface of the fruit. After film formation, it blocks the invasion of microorganisms and reduces water loss, but the coating concentration needs to be precisely controlled. Too low is ineffective, and too high accelerates rotting and quality decline.

[0007] In recent years, electromagnetic field preservation as a new non-thermal physical preservation technology has attracted attention due to its green and environmentally friendly nature and lack of chemical residues. This technology has been widely used in the preservation of poultry and livestock meat, but research in the fruit and vegetable field is relatively limited. Studies have shown that electromagnetic fields can inhibit cell activity and microbial proliferation by affecting the movement of charged ions within cells, affect cell membrane fluidity to interfere with cell physiological functions, and change enzyme conformation to affect enzyme activity. These characteristics make it have important application potential in the postharvest preservation of litchi and other fruits and vegetables. SUMMARY

[0008] The purpose of the present application is to provide a litchi postharvest preservation method treated by an electromagnetic field to solve the problems raised in the background art.

[0009] In order to achieve the above object, the present application provides the following technical scheme: a postharvest preservation method of litchi by electromagnetic field treatment, comprising the following steps:

[0010] Step one, litchi fruit selection and pretreatment: select eight to nine mature litchi, remove diseased and insect fruits, and select healthy fruits without mechanical damage and disease and insect pests;

[0011] Step two, grouping treatment and electromagnetic field action: set up a control group and a treatment group, the control group is soaked in water or 0.05% bactericide (Shibaoke or Multicin) for 3 minutes, and the treatment group is treated by electromagnetic field treatment while being soaked in water or 0.05% bactericide, the electromagnetic field intensity is 2-6 mT, the treatment time is 3 minutes, and all groups are dried at 25±5℃ and relative humidity of 85±10% after treatment;

[0012] Step three, packaging and storage: use 0.03mm thick polyethylene film bag packaging, 20 fruits per bag, every 4 bags are treated, and stored at 25℃ and relative humidity of 85±10% for 8 days;

[0013] Step four, preservation effect evaluation: evaluate the preservation effect by browning degree, specifically grade I-IV, calculate the browning index and the rate of marketable fruits.

[0014] Preferably, in step one, the litchi harvesting time is a sunny day, and the fruit maturity is eight to nine mature.

[0015] Preferably, in step two, the electromagnetic field treatment group includes T1 (2mT), T2 (4mT), and T3 (6mT) three intensity gradients, and the composite treatment group includes FT1 (2mT), FT2 (4mT), and FT3 (6mT) three intensity gradients.

[0016] Preferably, in step two, the bactericide is 0.05% Shibaoke or 0.05% Multicin, and the soaking time and the electromagnetic field treatment time are both 3 minutes.

[0017] Preferably, in step three, the packaging material is a 0.03mm thick polyethylene film bag, 20 fruits per bag, 4 repeated bags are set for each group, the storage temperature is fixed at 25℃, the relative humidity is 85±10%, and the storage period is 8 days.

[0018] Preferably, in step four, the browning degree grading standard is: grade I browning area ≤25%, grade II 25%<browning area ≤50%, grade III 50%<browning area ≤75%, and grade IV browning area >75%; browning index = Σ(browning degree × corresponding grade number) / (highest grade × total fruit number), and marketable fruit rate = (grade I browning fruit number / total fruit number) × 100.

[0019] Preferably, in the step two, the air-drying environment parameters are temperature 25±5℃ and air relative humidity 85±10%, and the air-dried product is packaged again.

[0020] Compared with the prior art, the application has the advantages that:

[0021] The application adopts electromagnetic field non-thermal physical treatment, does not need to rely on a large number of chemical agents, avoids the residual risk brought by chemical preservation, meets the food safety requirements, and is suitable for green fruit production; compared with the water control group, the electromagnetic field treatment can reduce the browning index of litchi by 22.82%-27.2% during 8 days of normal temperature storage, and increase the commodity fruit rate from 2.5% to 17.5%-23.75%; compared with the fungicide control group, the composite treatment can reduce the browning index by 31.25%-38.13%, and increase the commodity fruit rate from 11.25% to 76.25%-87.5%, significantly delaying browning and improving commodity value; the electromagnetic field treatment can be used alone or in combination with conventional fungicides (prochloraz and carbendazim), and is flexible in adapting to different preservation requirements, thereby providing diversified solutions for litchi postharvest storage and transportation. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is the browning of litchi fruits in the control group (water) and the electromagnetic field treatment group during 8 days of normal temperature storage;

[0023] Figure 2 is the browning index of litchi fruits in the control group (water) and the electromagnetic field treatment group during 8 days of normal temperature storage;

[0024] Figure 3 is the commodity fruit rate of litchi fruits in the control group (water) and the electromagnetic field treatment group during 8 days of normal temperature storage;

[0025] Figure 4 is the browning of litchi fruits in the control group (fungicide) and the fungicide / electromagnetic field composite treatment group during 8 days of normal temperature storage;

[0026] Figure 5 is the browning index of litchi fruits in the control group (fungicide) and the fungicide / electromagnetic field composite treatment group during 8 days of normal temperature storage;

[0027] Figure 6 is the browning index of litchi fruits in the control group (fungicide) and the fungicide / electromagnetic field composite treatment group during 8 days of normal temperature storage. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application.

[0029] Please refer to Figures 1-6 The present application provides a postharvest preservation method of litchi by electromagnetic field treatment, comprising the following steps:

[0030] Step one, litchi fruit selection and pretreatment: select litchi fruits with 80-90% maturity, remove diseased, insect-damaged and substandard fruits, and select healthy fruits without mechanical damage and disease and insect pests;

[0031] Step two, grouping treatment and electromagnetic field action: set a control group and a treatment group, the control group is soaked in water or 0.05% fungicide (chlorothalonil or carbendazim) for 3 min, and the treatment group is subjected to electromagnetic field treatment while being soaked in water or 0.05% fungicide, the electromagnetic field intensity is 2-6 mT, the treatment time is 3 min, and all groups are dried at 25±5℃ and 85±10% relative humidity after treatment;

[0032] Step three, packaging and storage: use 0.03 mm thick polyethylene film bags for packaging, 20 fruits per bag, 4 bags per treatment, and store at 25℃ and 85±10% relative humidity for 8 days;

[0033] Step four, preservation effect evaluation: evaluate the preservation effect by calculating the browning index and the rate of marketable fruits according to the browning grades, specifically grades I-IV.

[0034] In step one, the litchi harvesting time is a sunny day, and the fruit maturity is 80-90% maturity.

[0035] In step two, the electromagnetic field treatment group includes T1 (2 mT), T2 (4 mT), and T3 (6 mT) three intensity gradients, and the composite treatment group includes FT1 (2 mT), FT2 (4 mT), and FT3 (6 mT) three intensity gradients.

[0036] In step two, the fungicide is 0.05% chlorothalonil or 0.05% carbendazim, and the soaking time and the electromagnetic field treatment time are both 3 min.

[0037] In step three, the packaging material is a 0.03 mm thick polyethylene film bag, 20 fruits per bag, 4 repeated bags per group, the storage temperature is fixed at 25℃, the relative humidity is 85±10%, and the storage period is 8 days.

[0038] In step four, the browning level classification criteria are: grade I browning area ≤ 25%, grade II 25% < browning area ≤ 50%, grade III 50% < browning area ≤ 75%, and grade IV browning area > 75%; browning index = Σ(browning level × corresponding level fruit number) / (highest level × total fruit number); and commodity fruit rate = (grade I browning fruit number / total fruit number) × 100.

[0039] In step two, the drying environment parameters are temperature 25 ± 5°C and air relative humidity 85 ± 10%.

[0040] Example 1: Fresh water-electromagnetic field treatment of litchi postharvest preservation

[0041] Material: Litchi (Litchi chinensis Sonn.) is collected from Zengcheng District, Guangzhou City, Guangdong Province, and the variety is "Feixiaoshuo".

[0042] Treatment method: Freshly harvested litchi fruits at 80-90% maturity are selected, and diseased, insect-damaged and substandard fruits are removed. The control group (CK1) is soaked in fresh water for 3 min, and then dried in an environment with temperature 25 ± 5°C and air relative humidity 85 ± 10%. The treatment group 1 (T1) is soaked in fresh water, and then treated with an electromagnetic field intensity of 2 mT for 3 min, and then dried in an environment with temperature 25 ± 5°C and air relative humidity 85 ± 10%. The treatment group 2 (T2) is soaked in fresh water, and then treated with an electromagnetic field intensity of 4 mT for 3 min, and then dried in an environment with temperature 25 ± 5°C and air relative humidity 85 ± 10%. The treatment group 3 (T3) is soaked in fresh water, and then treated with an electromagnetic field intensity of 6 mT for 3 min, and then dried in an environment with temperature 25 ± 5°C and air relative humidity 85 ± 10%. The control group and the treatment groups are packaged with 0.03 mm thick polyethylene film bags, 20 fruits per bag, and 4 bags of fruits per treatment are stored in an environment with temperature 25°C and air relative humidity 85 ± 10% for 8 days.

[0043] Preservation effect: The browning index and the commodity fruit rate are often used to evaluate the occurrence of litchi fruit browning. The browning level is divided into four levels from low to high: grade I, browning area ≤ 25% (slight browning); grade II, 25% < browning area ≤ 50%; grade III, 50% < browning area ≤ 75%; and grade IV, browning area > 75% or more. The browning index = Σ(browning level × fruit number) / total fruit number. According to the browning classification results, the commodity fruit rate is calculated, grade I fruit is considered to have commercial value, and grades II-IV fruit is considered to be inferior fruit without commercial value. The commodity fruit rate calculation formula is: commodity fruit rate = grade I browning fruit number × 100 / total fruit number.

[0044] The browning of litchi fruits in the control group (water) and the electromagnetic field treatment group after 8 days of storage at room temperature is shown in Table 1. Figure 1 As can be observed from the physical pictures, compared with the control, the electromagnetic field treatment significantly delayed the occurrence of browning of litchi fruits.

[0045] After 8 days of storage, the browning index of the control group CK1 was 93.13%, and the browning indexes of the electromagnetic field treatment groups T1, T2 and T3 were 68.44%, 70.31% and 65.93%, respectively, which were reduced by about 24.69%, 22.82% and 27.2%, respectively. Figure 2 Meanwhile, the rate of marketable fruits of the control group CK1 was 2.5%, and the rates of marketable fruits of the electromagnetic field treatment groups T1, T2 and T3 were 17.5%, 21.25% and 23.75%, respectively, which were increased by about 7.27 times. Figure 3

[0046] Example 2: 0.05% Prochloraz-electromagnetic field composite treatment for postharvest preservation of litchi

[0047] Materials: Litchi (Litchi chinenis Sonn.) was collected from Zengcheng District, Guangzhou City, Guangdong Province, and the variety was "Feixiaoshuo".

[0048] Treatment method: Freshly harvested litchi fruits at 80-90% maturity on sunny days were selected after sorting out diseased, insect-damaged and substandard fruits, and selecting litchi fruits without mechanical damage and disease and insect pests. The control group (CK2) of litchi fruits was soaked in 0.05% fungicide Prochloraz for 3 minutes, and then taken out and dried in an environment with a temperature of 25±5°C and an air relative humidity of 85±10%. The composite treatment group 1 (FT1) of litchi fruits was soaked in 0.05% Prochloraz, and an electromagnetic field intensity of 2mT was set for 3 minutes of treatment, and then taken out and dried in an environment with a temperature of 25±5°C and an air relative humidity of 85±10%. The composite treatment group 2 (FT2) of litchi fruits was soaked in 0.05% Prochloraz, and an electromagnetic field intensity of 4mT was set for 3 minutes of treatment, and then taken out and dried in an environment with a temperature of 25±5°C and an air relative humidity of 85±10%. The composite treatment group 3 (FT3) of litchi fruits was soaked in 0.05% Prochloraz, and an electromagnetic field intensity of 6mT was set for 3 minutes of treatment, and then taken out and dried in an environment with a temperature of 25±5°C and an air relative humidity of 85±10%. The control group and the composite treatment groups were packaged with 0.03mm thick polyethylene film bags, 20 fruits per bag, and 4 bags of fruits per treatment, and stored in an environment with a temperature of 25°C and an air relative humidity of 85±10% for 8 days.

[0049] Preservation effect:

[0050] The browning of litchi fruits in the control group (fungicide) and the fungicide / electromagnetic field composite treatment group after 8 days of storage at room temperature is shown in Table 1. Figure 4 ​As can be observed from the actual images, compared with the control, electromagnetic field treatment significantly delayed the occurrence of browning in litchi fruit, and the treatment groups FT2 and FT3 were more effective than FT1.

[0051] After 8 days of storage, the browning index of the control group CK2 was 68.44%, while the browning indices of the electromagnetic field treatment groups FT1, FT2, and FT3 were 37.19%, 30.31%, and 30.63%, respectively, representing reductions of approximately 31.25%, 38.13%, and 37.81%. Figure 5 Meanwhile, the marketable fruit rate of the control group CK2 was 11.25%, while the marketable fruit rates of the electromagnetic field treated groups FT1, FT2, and FT3 were 76.25%, 82.5%, and 87.5%, respectively, representing increases of 65%, 71.25%, and 76.25%. Figure 6 ).

[0052] Example 3: Post-harvest preservation of litchi treated with a combination of 0.05% carbendazim and electromagnetic field

[0053] Materials, pretreatment, packaging and storage: Each group was packaged in 0.03mm polyethylene film bags, 20 fruits / bag, 4 bags per treatment, and stored in an environment of 25℃ and 85±10% relative humidity for 8 days;

[0054] Group treatment: The control group (CK2) was soaked in 0.05% carbendazim solution for 3 minutes, and the combined treatment group (FT1-FT3) was soaked in 0.05% carbendazim solution while being treated with an electromagnetic field of 2-6 mT for 3 minutes. After treatment, the fruits were air-dried under the same conditions.

[0055] Preservation effect: It can effectively reduce the occurrence of browning in litchi fruit, with a browning index significantly lower than CK2 and a marketable fruit rate significantly higher than CK2. The effect is similar to that of the Spoker-electromagnetic field composite treatment in Example 2.

[0056] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for post-harvest preservation of litchi treated with electromagnetic fields, characterized in that: Includes the following steps: Step 1: Selection and pretreatment of litchi fruit: Select litchis that are 80-90% ripe, remove diseased, insect-infested, and substandard fruit, and select healthy fruit that is free from mechanical damage and pests. Step 2, Grouping and Electromagnetic Field Treatment: A control group and a treatment group were set up. The control group was soaked in water or 0.05% bactericide for 3 minutes. The treatment group was soaked in water or 0.05% bactericide while being treated with an electromagnetic field with an intensity of 2-6 mT for 3 minutes. All groups were dried at 25±5℃ and 85±10% relative humidity after treatment. Step 3, Packaging and Storage: Pack 20 fruits per bag in 0.03mm thick polyethylene film bags, 4 bags per treatment, and store for 8 days at 25℃ and 85±10% relative humidity. Step 4: Evaluation of preservation effect: The browning index and the percentage of marketable fruit are calculated based on the browning level, specifically levels I-IV, to assess the preservation effect.

2. The method for post-harvest preservation of litchi treated with electromagnetic field according to claim 1, characterized in that: In step one, the lychees are harvested on a sunny day when they are eight to nine tenths ripe.

3. The method for post-harvest preservation of litchi treated with electromagnetic field according to claim 1, characterized in that: In step two, the electromagnetic field processing group includes three intensity gradients: T1, T2, and T3, and the composite processing group includes three intensity gradients: FT1, FT2, and FT3.

4. The method for post-harvest preservation of litchi treated with electromagnetic field according to claim 1, characterized in that: In step two, the bactericide is 0.05% cyproconazole or 0.05% carbendazim, and the soaking time and electromagnetic field treatment time are both 3 minutes.

5. The method for post-harvest preservation of litchi treated with electromagnetic field according to claim 1, characterized in that: In step three, the packaging material is a 0.03mm thick polyethylene film bag, with 20 fruits per bag. Four duplicate bags are set for each group. The storage temperature is fixed at 25℃, the relative humidity is 85±10%, and the storage period is 8 days.

6. The method for post-harvest preservation of litchi treated with electromagnetic field according to claim 1, characterized in that: In step four, the browning grade classification criteria are as follows: Grade I browning area ≤ 25%, Grade II 25% < browning area ≤ 50%, Grade III 50% < browning area ≤ 75%, Grade IV browning area > 75%; Browning index = Σ(browning grade × number of fruits of the corresponding grade) / (highest grade × total number of fruits), and marketable fruit rate % = (number of Grade I browning fruits / total number of fruits) × 100.

7. The method for post-harvest preservation of litchi treated with electromagnetic field according to claim 1, characterized in that: In step two, the drying environment parameters are a temperature of 25±5℃ and a relative humidity of 85±10%. The product is then packaged after drying.

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