Method for preserving litchi and maintaining Vc of litchi by using LED light and modified atmosphere packaging

Abstract

The present application relates to the field of illumination and modified atmosphere combined preservation technology, and discloses a method for preserving litchi and maintaining Vc of litchi by using LED illumination combined with modified atmosphere packaging. The method comprises the following steps: picking fresh litchi, immediately screening out litchi without disease and insect pests and mechanical damage, retaining complete fresh branches and leaves, and precooling the screened litchi; after the precooling of the litchi, the dry end of the litchi is immersed in a nutrient supplement hydrogel, the litchi is placed flat, is packaged by using a fruit and vegetable film, and a slow-release antibacterial sheet is arranged inside; the packaged litchi is placed in a thermostat with an ambient temperature of 4-10 DEG C and a humidity of 85-95% for preservation, and the illumination intensity of white light or red and blue light is 70-90 μmol·m ‑2 ·s ‑1 The present application uses red and blue light combination, white light illumination to promote photosynthesis to form an internal microcirculation system for low-temperature storage for the first time to preserve litchi, effectively prevents loss of nutritional ingredients, and can also increase the vitamin C content of litchi to a certain extent.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of light and modified atmosphere combined preservation technology, and particularly relates to a method for preserving litchi and maintaining Vc by using LED light combined with modified atmosphere packaging. BACKGROUND

[0002] Litchi is a tropical fruit produced in southern China, such as Guangdong and Fujian, and is usually supplied in summer. It is favored for its unique taste and rich nutritional and medicinal value. The thin and juicy peel of litchi still maintains a high physiological metabolism at room temperature after picking, which leads to the accelerated loss of fruit flesh moisture and nutrients, especially vitamin C (Vc), resulting in widespread browning and even rotting of the fruit, which seriously affects the nutritional value, eating quality and economic benefits of litchi.

[0003] At present, the main postharvest preservation method for litchi is cold storage. Chinese patent CN202310960518.9 discloses a litchi preservation powder and its preparation method and application. The litchi preservation powder is prepared by mixing the glycopeptide complex obtained by the reaction of corn alcohol-soluble protein peptide and carboxymethyl chitosan with a food additive solution and then freeze-drying. The litchi preservation powder can effectively delay the browning and deterioration of litchi, and has a small volume, which is convenient for transportation. However, it has the disadvantages of high raw material cost, complex preparation process and non-recyclable use. Chinese patent CN202310214798.9 discloses a litchi preservation and storage method based on static electric field combined with low temperature treatment. The screened litchi is subjected to browning prevention, disinfection and sterilization, and pre-cooling treatment, and then placed in a static electric field and a low-temperature cold storage for preservation. The method has the advantages of long-term use after one-time investment and environmental protection, but the cost of the equipment is high, which is not suitable for large-scale market production.

[0004] At present, the practicality research of LED light source in the field of low-temperature storage is mostly focused on delaying the loss of nutrients and the decline in quality, and there is no research on the use of LED light source in litchi preservation and improvement of litchi storage quality. SUMMARY

[0005] In view of the shortcomings and deficiencies of the above litchi preservation methods, the present application provides a method for preserving litchi by using light combined with modified atmosphere packaging.

[0006] The present application utilizes the light-promoted photosynthesis microcirculation system to effectively prevent the loss of nutrients and is also beneficial to the accumulation of litchi nutrient Vc during storage. The present application combines LED red and blue light, white light and low temperature to treat litchi as test material, and compares and analyzes the influence of different light treatments on the storage quality of litchi, in order to provide a theoretical basis for the research and development and popularization and application of postharvest light preservation technology of litchi.

[0007] The application achieves the objective by the following technical solutions.

[0008] A method for preserving litchi and maintaining Vc of litchi by combining LED light with modified atmosphere packaging, comprising the following steps:

[0009] (1) Immediately after picking fresh litchi, screen out litchi without disease and insect pests, mechanical damage, and retain complete fresh branches and leaves;

[0010] (2) Precool the screened litchi;

[0011] (3) After the precooling treatment, immerse the end of the litchi branch in a nutrient supplement gel, then place it flat, pack it with fruit and vegetable film, and place a slow-release antibacterial tablet inside;

[0012] (4) Place the packed litchi in an incubator with white light or red and blue light, an environmental temperature of 4-10 DEG C, and a humidity of 85-95%; and

[0013] The light intensity of the white light or red and blue light is 70-90 mu mol m -2 ·s -1 .

[0014] Preferably, the precooling treatment condition in step (1) is precooling treatment for 0.5-1 h at 10-15 DEG C.

[0015] Preferably, the litchi variety is Baotangpiao.

[0016] Preferably, the preparation method of the nutrient supplement hydrogel in step (3) is as follows:

[0017] Slowly add the carboxymethyl chitosan solution to the oxidized sodium alginate solution to obtain a mixed solution, adjust the pH value of the mixed solution to 6.7-6.9, add the nutrient solution to the mixed solution and stir, then add water, and the nutrient supplement hydrogel can be prepared after stirring at room temperature;

[0018] The volume ratio of the carboxymethyl chitosan solution to the oxidized sodium alginate solution is 1:3-5, the concentration of the carboxymethyl chitosan solution is 80-100 mg / mL, and the concentration of the oxidized sodium alginate solution is 30-50 mg / mL;

[0019] The volume ratio of the nutrient solution to the mixed solution is 1:1.5-2.5, and the volume ratio of the total volume of the nutrient solution and the mixed solution to water is 1:(1-1.5);

[0020] The nutrient solution is prepared by dissolving the following components in water according to the mass ratio of 4-6:3-4:0.2-0.3:0.005-0.3 to obtain a 5-15 wt.% nutrient solution: glucose, vitamin C, humic acid, and inorganic salt;

[0021] Preferably, the oxidized sodium alginate is prepared by adding sodium iodate to a sodium alginate solution, stirring at room temperature and in the dark for 5-7 hours, then adding ethylene glycol to terminate the reaction, dialyzing for 72±12 hours, and freeze-drying to obtain;

[0022] The mass ratio of sodium alginate to sodium iodate is 1:1-1.5.

[0023] The molar ratio of ethylene glycol to sodium iodate is 1:1.

[0024] Preferably, the slow-release antibacterial tablet of step (3) is a ClO2-cinnamaldehyde antibacterial tablet.

[0025] Preferably, the preparation method of the slow-release antibacterial tablet of step (3) is as follows:

[0026] (i) Disperse cinnamaldehyde essential oil into whey protein solution, high-speed shear emulsification to form microemulsion, ultrasonic homogenization under ice bath conditions to obtain nanoemulsion;

[0027] (ii) Mix sodium chlorite, tartaric acid, and nanoemulsion in a mass ratio of 1-3:1-3:5-8, uniformly mix with low-density polyethylene masterbatch in a granulator to obtain a composite masterbatch with a mass fraction of 1.2%, then pour the composite masterbatch into an injection molding machine to obtain a slow-release antibacterial tablet.

[0028] Preferably, the mass fraction is the total mass of sodium chlorite, tartaric acid, and nanoemulsion after vortex mixing, accounting for the mass ratio of the masterbatch.

[0029] Preferably, the slow-release antibacterial tablet has a thickness of 1-3 mm and a length and width of 30-40 mm.

[0030] Preferably, the mass-volume ratio g / mL of cinnamaldehyde essential oil to whey protein isolate solution is 1:8-12.

[0031] Preferably, the high-speed shear emulsification of step (i) has a rotation speed of 15000-20000 rpm and an emulsification time of 2-10 min, and the ultrasonic power is 200-450 W and the ultrasonic time is 10-25 min.

[0032] The granulation temperature of step (ii) is 150-170°C, the screw speed is 320 r / min, and the feeding current is 35 mA.

[0033] Preferably, the fruit and vegetable film of step (3) is disclosed in CN2023108943173.

[0034] Preferably, the red and blue light ratio of step (4) is 3:1, the red light wavelength is 650±5 nm, and the blue light wavelength is 450±5 nm.

[0035] Preferably, in step (4), the height of the litchi surface from the white light or red-blue light source is 5-10 cm.

[0036] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0037] (1) The present application first uses LED red-blue light combination and white light illumination to promote photosynthesis to form a low-temperature storage method of internal microcirculation system to preserve litchi. The illumination can promote the photosynthesis, the litchi keeps the complete branches and leaves during the storage process, the litchi leaves absorb light energy after the illumination, synthesize rich-energy organic matter from the exhaled carbon dioxide and water, release oxygen, realize the internal microcirculation system, and still induce the accumulation of nutrients during the storage process. Therefore, the present application can effectively prevent the loss of nutrients, and can improve the nutritional value of litchi to a certain extent, such as the increase of vitamin C content.

[0038] (2) The present application is energy-saving, environment-friendly and non-polluting. The modified atmosphere preservation film has excellent mechanical properties, gas selectivity and anti-fog performance, and high visibility, and is particularly suitable for the packaging of fruit and vegetable products. Under the condition of low-temperature cold storage, the LED illumination combined with the modified atmosphere packaging can regulate the physiological metabolism of litchi, effectively inhibit the deterioration of the preservation quality of litchi, obtain greater benefits at a lower cost, and maximize the quality and nutrition of litchi.

[0039] (3) In the litchi storage process of the present application, the slow-release antibacterial sheet and the nutrient supplement gel are added. The slow-release antibacterial sheet can slowly release the antibacterial substances ClO2 and cinnamyl aldehyde, and can have broad-spectrum and long-acting antibacterial effect. The slow-release antibacterial sheet can inhibit the influence of various bacteria and molds for a long time. The nutrient supplement hydrogel has a cross-linked network structure, and is rich in multiple nutrients. The nutrient supplement hydrogel can provide nutrients for the photosynthesis and growth of litchi, and greatly prolongs the storage time of litchi.

[0040] (4) The present application has the advantages of simple operation, low cost, obvious preservation effect, large-scale production application, low LED power voltage, energy saving, environmental protection, small size, strong stability, long service life, and great practical application value. The combination of LED red-blue light, white light and low temperature has great practical application value. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 The browning index change of litchi preserved by different illumination in Comparative Example 1 and Examples 1-4 is shown in Table 1.

[0042] Figure 2 The water content change of litchi preserved by different illumination in Comparative Example 1 and Examples 1-4 is shown in Table 2.

[0043] Figure 3 The hardness change of litchi preserved by different illumination in Comparative Example 1 and Examples 1-4 is shown in Table 3.

[0044] Figure 4 Vitamin C content changes of litchi preserved under different light for Comparative Example 1 and Examples 1-4;

[0045] Figure 5 Soluble solids content changes of litchi preserved under different light for Comparative Example 1 and Examples 1-4;

[0046] Figure 6 Total phenol content changes of litchi preserved under different light for Comparative Example 1 and Examples 1-4;

[0047] Figure 7 Antibacterial performance test results of the prepared sustained-release antibacterial tablets.

[0048] Specific experimental methods

[0049] The application will be described in further detail below in conjunction with the examples and drawings, but the embodiments of the application are not limited thereto, and for the process parameters not specifically mentioned, conventional techniques can be referred to.

[0050] Fruit and vegetable film: disclosed in patent CN202310894317.3;

[0051] The preparation method of the nutritional supplement hydrogel is as follows:

[0052] (1) Dissolve sodium alginate (SA) in ultrapure water, fully stir in a 40°C constant temperature water bath until completely dissolved, and prepare a sodium alginate aqueous solution with a mass concentration of 30 mg / mL. Add a certain amount of sodium iodate to the sodium alginate solution, so that m SA :m NaIO3 = 1: (1-1.5), and after stirring for 6 h under room temperature and light shielding conditions, add ethylene glycol with the same mass as sodium iodate to terminate the reaction. After dialysis for 72 h, freeze-drying for 48 h to obtain oxidized sodium alginate (OSA). Dissolve the oxidized sodium alginate in ultrapure water, and prepare an oxidized sodium alginate solution with a concentration of 30 mg / mL.

[0053] (2) Dissolve carboxymethyl chitosan (CMCS) in ultrapure water to prepare a carboxymethyl chitosan solution with a concentration of 100 mg / mL. Slowly add the above carboxymethyl chitosan solution to the oxidized sodium alginate solution (30 mg / mL) (V CMCS :V OSA = 1: (3-5)) and stir at room temperature for 5-10 min, and then adjust the pH value of the mixed solution to 6.7-6.9.

[0054] (3) Nutrients were dissolved in ultrapure water in a mass ratio of glucose: vitamin C: humic acid: inorganic salt (containing nitrogen, phosphorus, potassium) = (4-6): (3-4): (0.2-0.3): (0.005-0.3) to prepare a 10 wt.% nutrient solution. The nutrient solution was added to the mixed solution described above (V 营 : V 混 = 1: (1.5-2.5)) and stirred at room temperature for 10-20 min, then ultrapure water (V 营+混 : V 超纯水 = 1: (1-1.5)) was added, and the nutrient supplement hydrogel was prepared after sufficient stirring at room temperature.

[0055] Sustained-release antibacterial tablets: specifically ClO2-cinnamaldehyde antibacterial tablets, prepared as follows:

[0056] (1) Cinnamaldehyde essential oil was dispersed into a whey protein isolate solution (w / v = 1:10), and emulsified with a high-shear emulsifier at a speed of 18000 rpm for 5 min to form a microemulsion. The microemulsion was then converted into a nanoemulsion in an ice bath by an ultrasonic homogenizer, with an ultrasonic time of 10-25 min and an ultrasonic power of 200-450 W.

[0057] (2) Sodium chlorite, tartaric acid, and the above nanoemulsion were vortex mixed in a mass ratio of (2-4): 1: (4-6), and then uniformly mixed with a low-density polyethylene (LDPE) masterbatch in a granulator to prepare a composite masterbatch with a mass fraction of 1.2%. The temperature of the granulator was 150-170°C, the screw speed was 320 r / min, and the feeding current was 35 mA. Then the composite masterbatch was poured into an injection molding machine (set at 260°C) to be injection molded into a plastic sheet with a thickness of 2 mm and a length and width of 35 mm, which was the sustained-release antibacterial tablet.

[0058] Example 1

[0059] (1) Fresh litchi was picked immediately after picking and screened for no pests and mechanical damage, and fresh branches and leaves were retained, with a variety of Baizhao; (2) The screened litchi was pre-cooled at 15°C for about 1 h; (3) The pre-cooled litchi was then packaged in batches using fruit and vegetable film, with each layer being laid flat and each package containing about 400 g of litchi; (4) The packaged litchi was placed in a low-temperature humidification box with white light (light intensity of 80 μmol·m -2 ·s -1 ) at an ambient temperature of 8°C and a humidity of 90% for preservation for 15 d. The LED light source was placed directly above the incubator, and the litchi surface was 6 cm away from the LED light source. The browning index, water content, hardness, vitamin C content, soluble solids, and total phenol content of each batch of litchi were measured every 5 d.

[0060] Example 2

[0061] (1) Immediately after picking fresh lychee, screen out and select lychee without disease and insect pests and mechanical damage, keep the complete fresh branches and leaves, and the variety is Baizhao Pang; (2) Put the screened lychee in a 15℃ environment for precooling for about 1h; (3) Then batch-pack the precooling-treated lychee with fruit and vegetable film, place them flat, about 450g lychee per pack, and put 3 slow-release antibacterial tablets inside; (4) Put the packed lychee in a low-temperature and humidity box with white light (light intensity is 80μmol·m -2 ·s -1 ) and an environmental temperature of 8℃ and a humidity of 90% for preservation for 15d, the LED light source is placed above the preservation box, and the height of the lychee surface from the LED light source is 8cm, and the browning index, water content, hardness, vitamin C content, soluble solids, and total phenol content of each batch of lychee are measured every 5d.

[0062] Example 3

[0063] (1) Immediately after picking fresh lychee, screen out and select lychee without disease and insect pests and mechanical damage, keep the complete fresh branches and leaves, and the variety is Baizhao Pang; (2) Put the screened lychee in a 10℃ environment for precooling for about 0.5h; (3) Then immerse the ends of the branches and trunks of the precooling-treated lychee in 10g nutrient supplement gel, place them flat, batch-pack them with fruit and vegetable film, about 350g lychee per pack, and put 3 slow-release antibacterial tablets inside; (4) Put the packed lychee in a low-temperature and humidity box with white light (light intensity is 80μmol·m -2 ·s -1 ) and an environmental temperature of 4℃ and a humidity of 95% for preservation for 15d, the LED light source is placed above the preservation box, and the height of the lychee surface from the LED light source is 5cm, and the browning index, water content, hardness, vitamin C content, soluble solids, and total phenol content of each batch of lychee are measured every 5d.

[0064] Example 4

[0065] (1) Immediately after picking fresh lychee, screen out and select lychee without disease and insect pests and mechanical damage, keep the complete fresh branches and leaves, and the variety is Baizhao Pang; (2) Put the screened lychee in a 10℃ environment for precooling for about 0.5h; (3) Then immerse the ends of the branches and trunks of the precooling-treated lychee in 10g nutrient supplement gel, place them flat, batch-pack them with fruit and vegetable film, about 350g lychee per pack, and put 3 slow-release antibacterial tablets inside; (4) Put the packed lychee in a low-temperature and humidity box with red and blue light (red light wavelength 650±5nm, blue light wavelength 450±5nm, red and blue combined light light ratio 3:1, light intensity 80μmol·m -2 ·s -1(1) The fresh litchi was picked and screened immediately, and the litchi without pests and mechanical damage was selected, and the fresh branches and leaves were reserved. The variety was Baotangpang. (2) The screened litchi was pre-cooled at 10°C for about 0.5 h. (3) The pre-cooled litchi was packaged in batches with fruit and vegetable film, about 500 g of litchi per package, and placed in a single layer. (4) The packaged litchi was placed in a low-temperature humidifying box with an environmental temperature of 8°C and a humidity of 90% for 15 days of light-proof preservation. The browning index, water content, hardness, vitamin C content, soluble solids, and total phenol content of each batch of litchi were measured every 5 days.

[0066] Comparative Example 1

[0067] (1) The fresh litchi was picked and screened immediately, and the litchi without pests and mechanical damage was selected, and the fresh branches and leaves were reserved. The variety was Baotangpang. (2) The screened litchi was pre-cooled at 10°C for about 0.5 h. (3) The pre-cooled litchi was packaged in batches with fruit and vegetable film, about 500 g of litchi per package, and placed in a single layer. (4) The packaged litchi was placed in a low-temperature humidifying box with an environmental temperature of 8°C and a humidity of 90% for 15 days of light-proof preservation. The browning index, water content, hardness, vitamin C content, soluble solids, and total phenol content of each batch of litchi were measured every 5 days.

[0068] Comparative Example 2

[0069] (1) Different from Example 3, after the pre-cooled litchi was immersed in 10 g of nutrient supplement gel, it was placed flat, packaged in batches with fruit and vegetable film, about 350 g of litchi per package, and 3 pieces of fruit and vegetable preservation cards were placed inside and cut into the size of 35*35 mm (purchased from the store: Fruit and Vegetable Preservation Application Technology Center); (4) The packaged litchi was placed in a low-temperature humidifying box with an environmental temperature of 8°C and a humidity of 90% for 15 days of light-proof preservation. The browning index, water content, hardness, vitamin C content, soluble solids, and total phenol content of each batch of litchi were measured every 5 days. -2 ·s -1 (1) The fresh litchi was picked and screened immediately, and the litchi without pests and mechanical damage was selected, and the fresh branches and leaves were reserved. The variety was Baotangpang. (2) The screened litchi was pre-cooled at 10°C for about 0.5 h. (3) The pre-cooled litchi was packaged in batches with fruit and vegetable film, about 500 g of litchi per package, and placed in a single layer. (4) The packaged litchi was placed in a low-temperature humidifying box with an environmental temperature of 8°C and a humidity of 90% for 15 days of light-proof preservation. The browning index, water content, hardness, vitamin C content, soluble solids, and total phenol content of each batch of litchi were measured every 5 days.

[0070] Comparative Example 3

[0071] (2) Different from Example 3, after the pre-cooled litchi was immersed in 10 g of vegetable and fruit nutrient diluent (diluted at a ratio of 1:400, purchased from the store: DeWuDo Fertilizer Flagship Store), it was placed flat, packaged in batches with fruit and vegetable film, about 350 g of litchi per package, and 3 pieces of slow-release antibacterial tablets were placed inside. (4) The packaged litchi was placed in a low-temperature humidifying box with an environmental temperature of 8°C and a humidity of 90% for 15 days of light-proof preservation. The browning index, water content, hardness, vitamin C content, soluble solids, and total phenol content of each batch of litchi were measured every 5 days. -2 ·s -1The environmental temperature of the low-temperature moisture box was 4°C, and the humidity was 95%, and the preservation time was 15 days. The height of the litchi surface from the LED light source was 5 cm. The browning index, water content, hardness, vitamin C content, soluble solids, and total phenol content of each batch of litchi were measured every 5 days.

[0072] Test Example

[0073] (1) Browning index determination

[0074] Determination method: observe the browning of litchi in each treatment group and grade:

[0075] Grade 1 fruit has no browning or browning area less than 1 / 4 of the fruit skin area; Grade 2 fruit has browning area accounting for 1 / 4-1 / 2 of the fruit skin area; Grade 3 fruit has browning area accounting for 1 / 2-3 / 4 of the fruit skin area; Grade 4 fruit has browning area greater than 3 / 4 of the fruit skin area; and Grade 5 fruit is completely browned.

[0076] Browning index = ∑(browning grade * number of each browning fruit) / total number of fruit in the treatment group

[0077] (2) Water content determination

[0078] The determination method refers to the direct drying method of GB5009.3-2016 to determine the water content of litchi in each treatment group on the 0th day and during the preservation process.

[0079] (3) Hardness determination

[0080] Determination method: use a hardness tester with model GY-4 to measure the hardness, measure each litchi 3 times, and take the average value.

[0081] (4) Vitamin C content determination

[0082] Determination method: use spectrophotometry to determine the Vc content in litchi juice.

[0083] Establishment of standard curve: prepare a Vc standard solution with a concentration of 2.5 μg / mL, take 0, 1.0, 2.0, 3.0, 4.0, and 5.0 mL of the standard solution into 10 mL test tubes, dilute to the mark with deionized water, use deionized water as a blank reference solution, measure the absorbance at 267 nm, and draw a standard curve.

[0084] Determination of sample Vc content: grind the litchi and load it into a centrifuge tube, take 1.0 mL of supernatant and dilute it 100 times, use deionized water as a blank reference, measure the absorbance of the sample solution at 267 nm, and calculate the Vc content in litchi juice according to the formula.

[0085] W = 100 × C

[0086] W—Vc content in litchi juice, μg / mL;

[0087] 100—dilution multiple of litchi peach juice;

[0088] C—Vc content in sample solution after dilution, μg / mL.

[0089] (5) Determination of soluble solids

[0090] Determination method: 3-4 litchi fruits were randomly selected from each treatment group, the peel was removed, the core was removed, the pulp was squeezed to obtain juice, and the juice was centrifuged at 8000 r / min for 10 min, and the supernatant was taken for standby. The sugar content was determined by sugar meter PAL-108.

[0091] (6) Determination of total phenol

[0092] Determination method: 2.5 mg of gallic acid standard was accurately weighed into a volumetric flask, and the volume was made to 25 mL. 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 mL were respectively taken into test tubes, 1 mL of Folin phenol reagent was added, shaken, 10 mL of 7% sodium carbonate was added, and the volume was made to 25 mL with distilled water, mixed, and placed in the dark for 1 h. The absorbance value was determined at 750 nm by multifunctional enzyme label instrument, repeated for 3 times, and the standard curve was drawn.

[0093] 5.0 g of chopped litchi was weighed, 20 mL of 80% ethanol was added, and homogenized in ice bath for 2 times, 6 s each time, ice was added, and ultrasonic was performed for 1 h. The precipitate was discarded after centrifugation at 4 ℃ and 10000 g for 15 min. 1 mL of supernatant was taken, 1 mL of Folin phenol reagent and 10 mL of 7% sodium carbonate were added, and the volume was made to 25 mL with distilled water, mixed, and placed in the dark for 1 h. The absorbance value was determined at 750 nm by multifunctional enzyme label instrument, and the absorbance value was brought into the standard curve to obtain C value, and the total phenol content was calculated.

[0094]

[0095] The unit of total phenol content in the formula is mg·g -1 ; C is the mass concentration of total phenol in the measurement liquid, the unit is mg·mL -1 ; V is the volume of the crude extract, the unit is mL; W is the sample mass, the unit is g.

[0096] (7) Test of antibacterial performance

[0097] Test method: according to national standard GB / T 31402-2015, taking blank aluminum foil as blank control group. The calculation formula of antibacterial rate R is:

[0098]

[0099] In the formula: R is the antibacterial rate; A is the number of viable bacteria obtained after inoculation of blank aluminum foil; B is the number of viable bacteria obtained after inoculation of sustained-release antibacterial tablets.

[0100] Browning is a significant factor reflecting the deterioration of lychee quality. Browning of the peel can directly affect consumer demand, leading to a decline in lychee quality and sales. For example... Figure 1 As shown, under refrigeration conditions, the browning index of lychees treated with different methods showed an increasing trend to varying degrees with the increase of storage time. Comparing the browning indices of Examples 1-4 with Comparative Example 1, it can be found that the addition of white light, slow-release antibacterial tablets, and nutritional supplements can effectively reduce the increase of browning index. Comparing Example 3 with Comparative Example 2, it can be found that the self-made slow-release antibacterial tablets have a better preservation effect than the existing preservation cards on the market, and the slow-released antibacterial substances have better bactericidal and long-lasting antibacterial effects. Comparing Example 3 with Comparative Example 3, it can be found that the preservation effect of the nutritional supplement gel is better than that of the existing fruit and vegetable nutrient solutions on the market, and the network structure and fixed morphology inside the gel are more conducive to the preservation treatment of lychees. Compared with Example 4, it can be found that the anti-browning effect of red and blue light is better than that of white light.

[0101] Water content reflects the water content within the lychee. For example... Figure 2 As shown, the water content of Comparative Examples 2-3 and Examples 1-4 is slightly lower than that of Comparative Example 1, and photosynthesis consumes a small amount of its own water.

[0102] Firmness is an important physical indicator of the ripeness and softening degree of fruits and vegetables. During photosynthesis, a small amount of water in lychees is consumed to synthesize soluble solids and other organic matter, increasing firmness. For example... Figure 3 As shown, the hardness of Comparative Examples 2-3 and Examples 1-4 is higher than that of Comparative Example 1. Among them, Examples 1-2 consumed more nutrients in the early stage than Examples 3-4 because no nutrient supplements were added. In the later stage, photosynthesis increased the organic matter in the litchi, and the hardness showed a slight upward trend.

[0103] Vitamin C (V) C Vitamin C is an antioxidant that the human body cannot synthesize. During photosynthesis, enzymes involved in vitamin synthesis are activated, increasing the vitamin C content in lychees. Figure 4 As shown, the Vc content in Comparative Examples 2-3 and Examples 1-4 exhibited a trend of first increasing and then decreasing. In the early stage of storage, the Vc content in Comparative Examples 2-3 and Examples 1-4... C The content is a cumulative state. Compared with Example 4, the effect of synthesizing vitamin C by red and blue light is better than that by white light.

[0104] Soluble solids mainly refer to soluble sugars, acids, and other small molecules in litchi fruit, and their content reflects the ripeness of the fruit. For example... Figure 5As shown, compared with Comparative Example 1, the soluble solids content of Comparative Examples 2-3 and Examples 1-4 all increased to varying degrees after light treatment. Among them, Examples 1-2, due to the lack of nutrient supplements, showed a trend of smaller increase in the early stage and larger increase in the later stage under the combined influence of photosynthesis and respiration. The difference between the two examples was small, indicating that the addition of antibacterial tablets had a weak effect on promoting the increase of soluble solids content. The soluble solids content of Examples 3-4 after the addition of nutrient supplements was higher than that of the unsupplemented examples, and the effect of white light was slightly better than that of red and blue light.

[0105] Total phenols can reflect the antioxidant capacity of litchi. As a substrate for enzymatic browning, they are gradually consumed and converted into dark brown quinones during storage, leading to browning, spoilage, and even rot in the litchi fruit, thus reducing its quality. Figure 6 As shown, the total phenol content of Comparative Examples 2-3 and Examples 1-4 gradually decreased with the extension of storage time. However, the total phenol content of Comparative Examples 2-3 and Examples 1-4 was higher than that of Comparative Example 1, indicating that different treatment methods can effectively delay the consumption of total phenol content.

[0106] The antibacterial rate of sustained-release antibacterial tablets is as follows: Figure 7 As shown, with the increase of contact time, the antibacterial tablets gradually increased their inhibition rate against Escherichia coli and Staphylococcus aureus. At 36 h, the antibacterial tablets achieved an inhibition rate of 99.99% against E. coli and S. aureus, indicating that the sustained-release antibacterial tablets have excellent bactericidal effect.

[0107] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preserving lychees and maintaining their vitamin C content using LED lighting combined with modified atmosphere packaging, characterized in that... Includes the following steps: (1) Immediately after picking fresh lychees, sieve out those free from pests, diseases, and mechanical damage, and retain the whole fresh branches and leaves; (2) Pre-cool the selected lychees; (3) After the pre-cooled lychee branches are immersed in the nutrient supplement hydrogel, they are laid flat and packaged with fruit and vegetable film, with slow-release antibacterial tablets inside. (4) Place the packaged lychees in an insulated box with a temperature of 4~10℃ and a humidity of 85~95% under white light or red and blue light for preservation; The intensity of the white light or red-blue light is 70~90 μmol·m⁻². -2 ·s -1 ; The preparation method of the nutritional supplement hydrogel in step (3) is as follows: Carboxymethyl chitosan solution was slowly added to sodium alginate solution to obtain a mixed solution. The pH of the mixed solution was adjusted to 6.7-6.

9. Nutrient solution was added to the mixed solution and stirred. Then water was added and stirred at room temperature to obtain the nutrient supplement hydrogel. The volume ratio of the carboxymethyl chitosan solution to the sodium alginate oxidized solution is 1:3~5, the concentration of the carboxymethyl chitosan solution is 80~100mg / mL, and the concentration of the sodium alginate oxidized solution is 30~50mg / mL. The volume ratio of the nutrient solution to the mixed solution is 1:1.5~2.5, and the volume ratio of the total volume of the nutrient solution and the mixed solution to the volume of water is 1:1~1.

5. The nutrient solution is prepared by dissolving glucose in water at a mass ratio of 4~6:3~4:0.2~0.3:0.005~0.3 to obtain a nutrient solution of 5~15 wt.%. The sustained-release antibacterial tablets mentioned in step (3) are ClO2-cinnamaldehyde antibacterial tablets.

2. The method for preserving lychees and maintaining their vitamin C content using LED lighting combined with modified atmosphere packaging according to claim 1, characterized in that... The pre-cooling conditions in step (1) are 0.5 to 1 h at 10 to 15 °C.

3. The method for preserving lychees and maintaining their vitamin C content using LED lighting combined with modified atmosphere packaging according to claim 1, characterized in that... The oxidized sodium alginate was prepared by the following method: sodium iodate was added to the sodium alginate solution, and the reaction was stirred at room temperature and protected from light for 5-7 hours. Ethylene glycol was added to terminate the reaction, and the solution was dialyzed for 72±12 hours and then freeze-dried. The mass ratio of sodium alginate to sodium iodate is 1:1~1.5; The molar ratio of ethylene glycol to sodium iodate is 1:

1.

4. The method for preserving lychees and maintaining their vitamin C content using LED lighting combined with modified atmosphere packaging according to claim 1, characterized in that... The method for preparing the sustained-release antibacterial tablets in step (3) is as follows: (i) Cinnamaldehyde essential oil was dispersed in whey protein isolate solution, and high-speed shear emulsification was performed to form a microemulsion. After ultrasonic homogenization under ice bath conditions, a nanoemulsion was obtained. (ii) Sodium chlorite, tartaric acid and nanoemulsion are mixed in a mass ratio of 1~3:1~3:5~8 and then mixed evenly with low-density polyethylene masterbatch in a granulator to obtain a composite masterbatch with a mass fraction of 1.2%. The composite masterbatch is then poured into an injection molding machine to obtain a slow-release antibacterial tablet.

5. The method for preserving lychees and maintaining their vitamin C content using LED lighting combined with modified atmosphere packaging according to claim 4, characterized in that... In step (i), the high-speed shear emulsification rotation speed is 15,000~20,000 rpm, the emulsification time is 2~10 min, the ultrasonic power is 200~450 W, and the ultrasonic time is 10~25 min; In step (ii), the granulation temperature is 150~170℃, the screw speed is 320 r / min, and the feed current is 35mA.

6. The method for preserving lychees and maintaining their vitamin C content using LED lighting combined with modified atmosphere packaging according to claim 1, characterized in that, The red-blue light ratio in step (4) is 3:1, the red light wavelength is 650±5nm, and the blue light wavelength is 450±5nm.

7. The method for preserving lychees and maintaining their vitamin C content using LED lighting combined with modified atmosphere packaging according to claim 1, characterized in that... In step (4), the distance between the surface of the lychee and the white light or red and blue light source is 5~10cm.

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