Fresh-keeping method for reducing high-temperature damage of litchi pericarp

Abstract

The invention discloses a fresh-keeping method for reducing high-temperature damage of litchi peels. The method comprises the following steps: soaking litchis in a propylene glycol solution, taking out the litchis, airing, soaking the litchis in a glutathione solution, and carrying out quarantine high-temperature treatment. The moisturizing and antioxidant treatment method can effectively prolong the shelf life of the litchis and reduce the problem of quality degradation after high-temperature treatment, so that the litchis keep good commodity value in the export process.

Description

Technical Field

[0001] The invention relates to a fruit preservation technology, in particular to a preservation technology for reducing the damage to the peel of litchi during high-temperature treatment, in particular to improving the quality and safety of litchi after high-temperature treatment by using propylene glycol and glutathione. Background Art

[0002] Litchi is a specialty fruit in my country, with a cultivated area of ​​about 8 million mu, an output of about 2.3 million tons, accounting for about 77% of the world's output, and an output value of about 30 billion yuan. my country has a long history of lychee cultivation and rich cultural heritage. In recent years, as a business card product of agricultural products, it has been loved by the public and the lychee industry has been rapidly improved. Because lychees mature in high temperature and high humidity seasons, and the lychee fruit itself has a fast metabolism, the quality deteriorates very quickly after harvesting, and it is extremely difficult to store and transport to keep fresh, and the harvest period of lychees is very short. Therefore, it brings great pressure to the sales of lychees, and also seriously restricts the circulation and trade of fresh lychees, affecting the overall benefits of the industry. According to incomplete statistics, the loss of lychees in the circulation process after harvesting exceeds 30%, and the annual loss is about 5 billion yuan.

[0003] As a high-value fruit, the export of litchi can bring significant economic benefits to producing countries, help increase farmers' income and promote local economic development. Due to the special storage conditions of litchi and the strict customs clearance requirements of various countries, the export volume of fresh litchi in my country is very small, with an annual export volume of less than 10,000 tons, accounting for about 0.3% of the total litchi production. Different countries have different requirements for litchi quarantine. For example, in order to eliminate quarantine pests, the temperature of the litchi core needs to be evenly increased from 30℃ to 41℃ within 50min, and then increased to ≥46.5℃ for 10min, and then cooled by cold water spray, and then soaked in ice water. The core temperature drops to ≤2℃ within 6h and is maintained for more than 40h. If the litchi treated in this way is not preserved, the peel will turn brown or black, bacteria and mold will multiply, the fruit will shrivel, the taste will decrease, and the commodity value will deteriorate. Summary of the invention

[0004] The present invention provides a preservation technology for reducing the damage of the peel of litchi during high-temperature treatment, utilizing the synergistic effect of propylene glycol and glutathione to protect the litchi from oxidative damage during high-temperature treatment, reduce water loss, maintain the peel color and pulp flavor, thereby improving the commercial value and export volume of litchi.

[0005] High temperature treatment will trigger oxidation reactions inside litchi, resulting in loss of nutrients and color. Glutathione, as an important antioxidant, can neutralize free radicals and slow down the oxidation process, thereby protecting the color and taste of litchi. Glutathione helps maintain the sensory quality of litchi, including aroma, sweetness and crispness, helps reduce the damage to cells caused by heat stress, improves cell survival rate, and ensures the stability of litchi during processing; it can help delay the ripening and corruption of litchi and extend its shelf life; in summary, the role of glutathione in high temperature treatment of litchi is multifaceted, including antioxidant protection, maintaining quality, enhancing resistance to adversity, promoting freshness, detoxification and improving the stability of nutrients. By using glutathione rationally, the quality and safety of litchi after high temperature treatment can be effectively improved.

[0006] Propylene glycol protects the water loss of litchi peel during high temperature treatment: Propylene glycol is an effective moisturizer that can reduce the water loss of litchi during high temperature treatment, maintain the moisture and elasticity of the peel, and prevent the peel from drying and turning brown due to dehydration. Propylene glycol also has a certain antioxidant effect, which can slow down the oxidation reaction of litchi during high temperature treatment and protect the color and flavor of the peel and flesh.

[0007] Glutathione Antioxidant Protection: Glutathione is a natural strong antioxidant that can neutralize free radicals, slow down the oxidation process, and prevent the browning of the peel and the loss of nutrients during high-temperature processing of litchi. Glutathione can enhance the resistance of litchi to adversity, protect cells from high temperature damage, and extend the shelf life of litchi while maintaining its sweetness, crispness and aroma.

[0008] The preservation method for reducing high temperature damage of litchi peel of the present invention comprises the following specific steps: soaking litchi in propylene glycol solution for 3-5 minutes, taking out and drying, soaking in glutathione solution for 3-5 minutes, and then performing quarantine high temperature treatment.

[0009] Preferably, the quarantine high-temperature treatment is: placing the litchi in a heating device, the core temperature is uniformly increased from 30°C to 41°C within 50 minutes, and then increased to ≥46.5°C and maintained for 10 minutes; then spraying cold water to cool down, and then soaking in ice water, the core temperature is reduced to ≤2°C within 6 hours, maintained for more than 40 hours, and after refrigeration for 40 hours, it is packaged in a moisture-permeable and breathable functional fresh-keeping bag for storage.

[0010] Preferably, the storage is at 4°C.

[0011] Preferably, the refrigerated storage for 40 hours is performed by covering the fruit with textiles to prevent the fruit peel from losing water.

[0012] Preferably, the concentration of the propylene glycol solution is 0.1-1.5% by mass, and the soaking time is 3-5 minutes.

[0013] Preferably, the concentration of the glutathione solution is 0.1-1% by mass, and the soaking time is 3-5 minutes.

[0014] The processing method of the present invention can effectively reduce the browning of the peel and the shriveling of the fruit after high-temperature treatment of litchi, and improve its stability during low-temperature storage.

[0015] Effects and advantages:

[0016] 1. Technological advancement: We have overcome the technical barriers of heat treatment quarantine requirements and for the first time successfully maintained the fruit quality of litchi that was immediately refrigerated (2°C, 40h) after heat treatment (fumigation in a high temperature environment for 1.5 hours), thus safeguarding my country's litchi exports to Japan and other countries with heat treatment quarantine requirements.

[0017] 2. Efficiently maintain the water activity of the peel: Propylene glycol can maintain the effective water activity of the lychee peel during high temperature treatment, preventing browning caused by dehydration, while glutathione can neutralize free radicals and delay the oxidation process, thereby maintaining the color and nutritional value of the peel.

[0018] 3. Improving the storage stability of litchi: The moisturizing and antioxidant treatment method of the present invention can effectively prolong the quality of litchi stored in a high temperature and low temperature dual stress environment, while reducing the quality change problem after high temperature treatment, so that litchi maintains a good commodity value during the export process.

[0019] 4. Replace sulfur treatment: In order to maintain the color of the peel, lychees currently exported internationally are mainly treated with sulfur fumigation, which has been banned in many countries. This innovative technology uses propylene glycol to maintain the water activity of the lychee peel and uses glutathione to effectively reduce the damage caused by high temperature to the lychee peel. Both substances are harmless to the human body, will not produce harmful chemical residues or pollute the environment, and meet modern food safety standards.

[0020] 5. Improve the competitiveness of Chinese litchi in the international market: The preservation technology of the present invention can improve the competitiveness of litchi in the international market, increase the export volume of litchi, and create greater economic benefits for producing countries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the preservation effect of the control example 1 stored at 4°C for 15 days;

[0022] Figure 2 This is the preservation effect of control example 2 stored at 4°C for 15 days;

[0023] Figure 3 This is the preservation effect of the control example 3 stored at 4°C for 15 days;

[0024] Figure 4This is the preservation effect of the control example 4 stored at 4°C for 15 days;

[0025] Figure 5 This is the preservation effect of Example 1 stored at 4°C for 15 days;

[0026] Figure 6 This is the preservation effect of Example 2 stored at 4°C for 15 days;

[0027] Figure 7 This is the preservation effect of Example 3 after storage at 4°C for 15 days. DETAILED DESCRIPTION

[0028] The following examples are provided to further illustrate the present invention, rather than to limit the present invention.

[0029] Comparative Example 1

[0030] Take 8-9 ripe fresh lychees, remove branches and leaves, and keep the bare fruits; pass through the sorting line to pick out the defective fruits; then soak in clean water for 5 minutes, pass through the drain conveyor belt, drain the water, and place the lychees in a heating device. The core temperature needs to be evenly increased from 30℃ to 41℃ within 50min, and then increased to ≥46.5℃ and maintained for 10min; then spray cold water to cool down, transfer to ice water soaking, and the core temperature drops to ≤2℃ within 6h, and maintain for more than 40h. Cover with textiles during refrigeration to prevent moisture loss; after refrigeration for 40 hours, place in an ordinary 3-wire PE bag, and store at 4℃ for 15 days. The lychee peel is 100% browned, the flesh has a fermented taste, loses sugar, and partially autolyzes, such as Figure 1 .

[0031] Comparative Example 2

[0032] Take 8-9 ripe fresh lychees, remove branches and leaves, and keep the light fruits; pass through the sorting line to pick out the defective fruits; then soak in a 0.2% propylene glycol solution for 5 minutes, pass through a drain conveyor belt, drain the water, and place the lychees in a heating device. The core temperature needs to be evenly increased from 30°C to 41°C within 50 minutes, and then increased to ≥46.5°C and maintained for 10 minutes; then spray cold water to cool down, transfer to ice water soaking, and the core temperature drops to ≤2°C within 6 hours, and maintain for more than 40 hours. Cover with textiles during refrigeration to prevent moisture loss; after refrigeration for 40 hours, use ordinary 3-wire PE bags for packaging. After storage at 4°C for 15 days, 42% of the lychee peels turn brown, and some of the pulp loses sugar and has a fermented taste, such as Figure 2 .

[0033] Comparative Example 3

[0034] Take 8-9 ripe fresh lychees, remove branches and leaves, and keep the light fruits; pass through the sorting line to pick out the defective fruits; then soak in a 0.2% glutathione solution for 5 minutes; drain the water through a drain conveyor belt, place the lychees in a heating device, and the fruit core temperature needs to be evenly increased from 30°C to 41°C within 50 minutes, and then increased to ≥46.5°C and maintained for 10 minutes; then spray cold water to cool down, transfer to ice water soaking, and the fruit core temperature drops to ≤2°C within 6 hours, and maintain for more than 40 hours. Cover with textiles during refrigeration to prevent moisture loss; after refrigeration for 40 hours, use ordinary 3-wire PE bags for packaging. After storage at 4°C for 15 days, 44% of the lychee peels turn brown, the flesh has a fermented smell, loses sugar, and is not transparent, such as Figure 3 .

[0035] Comparative Example 4

[0036] Take 8-9 ripe fresh lychees, remove branches and leaves, and keep the bare fruits; pass through the sorting line to pick out the defective fruits; then soak in clean water for 5 minutes, pass through the drain conveyor belt, drain the water, and place the lychees in a heating device. The core temperature needs to be evenly increased from 30°C to 41°C within 50 minutes, and then increased to ≥46.5°C and maintained for 10 minutes; then spray cold water to cool down, transfer to ice water soaking, and the core temperature drops to ≤2°C within 6 hours, and maintain for more than 40 hours. When refrigerating, cover with textile fabric to prevent moisture loss; after refrigerating for 40 hours, place in a moisture-permeable and breathable functional fresh-keeping bag. After 15 days of storage at 4°C, 38% of the lychee peel turns brown, the flesh is not transparent, the sugar is lost, and part of it is autolyzed. Figure 4 .

[0037] Embodiment 1:

[0038] Take 8-9 ripe fresh lychees, remove branches and leaves, and keep the light fruits; pass through a sorting line to pick out defective fruits; then soak in a 0.1% propylene glycol solution for 5 minutes, pass through a drain conveyor belt, and then soak in a 0.1% glutathione solution for 5 minutes; after drying the water, place the lychees in a heating device, and the fruit core temperature needs to be evenly increased from 30°C to 41°C within 50 minutes, and then increased to ≥46.5°C and maintained for 10 minutes; then spray cold water to cool down, transfer to ice water soaking, and the fruit core temperature drops to ≤2°C within 6 hours, and is maintained for more than 40 hours. When refrigerated, cover with textiles to prevent moisture loss; after refrigeration for 40 hours, use a moisture-permeable and breathable functional fresh-keeping bag to package, and after storage at 4°C for 15 days, the browning of the lychee peel is less than 8%, the flesh maintains a good taste and flavor, and the circulation loss is reduced. Figure 5 .

[0039] Embodiment 2:

[0040] Take 8-9 ripe fresh lychees, remove branches and leaves, and keep the light fruits; pass through the sorting line to pick out the defective fruits; then soak in a 1.5% propylene glycol solution for 5 minutes, pass through a drain conveyor belt, and then soak in a 0.1% glutathione solution for 5 minutes; after draining the water, place the lychees in a heating device, and the fruit core temperature needs to be evenly increased from 30°C to 41°C within 50 minutes, and then increased to ≥46.5°C and maintained for 10 minutes; then spray cold water to cool down, transfer to ice water soaking, and the fruit core temperature drops to ≤2°C within 6 hours, and is maintained for more than 40 hours. When refrigerated, cover with textiles to prevent moisture loss; after refrigeration for 40 hours, use a moisture-permeable and breathable functional fresh-keeping bag to package, and after storage at 4°C for 15 days, the browning of the lychee peel is less than 5%, the flesh maintains a good taste and flavor, and the circulation loss is reduced. Figure 6 .

[0041] Embodiment 3:

[0042] Take 8-9 ripe fresh lychees, remove branches and leaves, and keep the light fruits; pass through the sorting line to pick out the defective fruits; then soak in a 1.5% propylene glycol solution for 5 minutes, pass through a drain conveyor belt, and then soak in a 1% glutathione solution for 5 minutes; after draining the water, place the lychees in a heating device, and the core temperature needs to be evenly increased from 30°C to 41°C within 50 minutes, and then increased to ≥46.5°C and maintained for 10 minutes; then spray cold water to cool down, transfer to ice water soaking, and the core temperature drops to ≤2°C within 6 hours, and is maintained for more than 40 hours. When refrigerated, cover with textiles to prevent moisture loss; after refrigeration for 40 hours, use a moisture-permeable and breathable functional fresh-keeping bag to package, and after storage at 4°C for 15 days, the browning of the lychee peel is less than 4%, the flesh maintains a good taste and flavor, and the circulation loss is reduced. Figure 7 .

Claims

1. A method for preserving litchi peels to reduce high temperature damage, characterized in that: Soak the litchi in propylene glycol solution, take it out and dry it, then soak it in glutathione solution, and then carry out quarantine high temperature treatment.

2. The preservation method according to claim 1, characterized in that: The quarantine high-temperature treatment is as follows: placing the litchi in a heating device, the temperature of the fruit core is uniformly raised from 30°C to 41°C within 50 minutes, and then raised to ≥46.5°C and maintained for 10 minutes; then spraying cold water to cool down, and then soaking in ice water, the temperature of the fruit core is reduced to ≤2°C within 6 hours, and maintained for more than 40 hours. After refrigeration for 40 hours, it is packaged in a moisture-permeable and breathable functional fresh-keeping bag for storage.

3. The preservation method according to claim 2, characterized in that: The storage is at 4°C.

4. The preservation method according to claim 2, characterized in that: The refrigerated storage for 40 hours is to cover the fruit peel with textiles during refrigeration to prevent water loss from the peel.

5. The preservation method according to claim 1, characterized in that: The concentration of the propylene glycol solution is 0.1-1.5% by mass, and the soaking time is 3-5 minutes.

6. The preservation method according to claim 1, characterized in that: The concentration of the glutathione solution is 0.1-1% by mass, and the soaking time is 3-5 minutes.

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