A planting method for selenium-rich hydroponic lettuce in a plant factory

Abstract

The present invention relates to the technical field of plant cultivation, and particularly relates to a method for cultivating selenium-rich hydroponic lettuce in a plant factory. The preparation method comprises the following steps: preparing a composite glycoside; preparing a chelated selenium solution; cultivating lettuce and spraying the chelated selenium solution. In the present invention, chitosan oligosaccharide glycoside and L-ascorbic acid are combined through cyclodextrin glycosyltransferase to specifically catalyze the formation of new glycosidic bonds, improving the binding degree between ascorbic acid and chitosan oligosaccharide glycoside. The composite glycoside with a high binding degree can enrich the complex in the leaves and roots of lettuce, reducing ineffective diffusion. Moreover, ascorbic acid has a reducing effect and can reduce the selenium in sodium selenite. Subsequently, chitosan oligosaccharide glycoside chelates with selenium, thereby reducing the content of free selenium in the system, enabling selenium to enter the plant in a chelated state, and entering the plant leaves faster and being absorbed by the plant by virtue of the water solubility and biocompatibility of chitosan oligosaccharide glycoside, thus increasing the selenium absorption amount of lettuce.

Description

Technical Field

[0001] The present invention relates to the technical field of plant cultivation, and particularly relates to a method for cultivating selenium-rich hydroponic lettuce in a plant factory. Background Art

[0002] Selenium is an important antioxidant with various physiological functions such as cancer prevention, antioxidant activity, and immune enhancement. By increasing the selenium content in agricultural products such as lettuce, the intake of selenium can be increased through food channels, thereby enhancing human immunity. Therefore, selenium-rich agricultural products have gradually emerged on the market. The cultivation of selenium-rich hydroponic lettuce is mainly achieved by adding selenium sources such as sodium selenite to the hydroponic nutrient solution or by spraying selenium solution on the leaves. Some studies have shown that adding sodium selenite to the hydroponic nutrient solution can significantly increase the yield of lettuce and have a positive impact on the growth and quality of lettuce. In addition, spraying nano-selenium solution on the leaves has also been proven to increase the selenium content and quality of lettuce.

[0003] However, although adding sodium selenite to the hydroponic nutrient solution can increase the yield of lettuce, the inorganic selenium in sodium selenite is absorbed by lettuce for growth and development and does not reach the level of selenium enrichment, nor can it increase the human intake of selenium. To cultivate selenium-rich lettuce, it is necessary to increase the selenium concentration in the hydroponic nutrient solution. However, when the concentration of the conventional selenium supplement sodium selenite in water is too high, it cannot be absorbed by plants and will instead cause destructive damage to plants. Therefore, in addition to adding sodium selenite to the hydroponic nutrient solution, the method of spraying on the leaves is also used to supplement selenium for plants.

[0004] When spraying plants, the concentration requirements for sodium selenite are even more stringent. Not only is the concentration of sodium selenite in the spraying agent lower, but there are also requirements for growth light and environment. This is because selenium generally exists in a free state in the spraying agent, so plants have poor absorption ability for selenium in the spraying agent, and too high a concentration of free selenium will also affect plants. Therefore, the present invention provides a method for cultivating selenium-rich hydroponic lettuce in a plant factory to solve the deficiencies of the above-mentioned existing technologies by reducing free selenium and increasing the content of chelated selenium. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method for cultivating selenium-rich hydroponic lettuce in a plant factory.

[0006] A method for cultivating selenium-rich hydroponic lettuce in a plant factory includes the following steps:

[0007] S1: Prepare compound glycoside

[0008] Mix chitosan oligosaccharide glycoside with deionized water and stir until dissolved. Then add L-ascorbic acid and stir to dissolve. Next, add cyclodextrin glycosyltransferase. Filter the reaction product through an ultrafiltration membrane to remove cyclodextrin glycosyltransferase and obtain compound glycoside;

[0009] S2: Prepare the chelated selenium solution

[0010] Mix corn gluten meal polypeptide, sodium dodecylbenzenesulfonate and deionized water, heat and stir to obtain a corn gluten meal polypeptide solution. Add gallic acid to the corn gluten meal polypeptide solution, and then add sodium selenite solution after magnetic stirring to obtain a mixture. Mix compound glycoside and deionized water to obtain a compound glycoside solution, and then dropwise add the compound glycoside solution to the mixture to obtain the chelated selenium solution;

[0011] S3: Cultivate lettuce and spray the chelated selenium solution

[0012] Sow lettuce seeds on a fully wetted sponge. When the lettuce seeds grow into seedlings, transfer the seedlings into a seedling fixing plate. When the two leaves of the seedlings touch each other, transfer the seedlings into a seedling raising plate in the middle growth stage. When the two leaves of the middle-stage seedlings touch each other, transfer the middle-stage seedlings into a seedling raising plate in the adult stage. Prepare the chelated selenium solution into a selenium spraying agent, and start spraying the selenium spraying agent onto the leaves from the second day until maturity to obtain selenium-enriched hydroponic lettuce.

[0013] Further, the preparation of compound glycoside in step S1 includes the following steps:

[0014] S1.1: Mix 2.5 - 3 parts by volume of chitosan oligosaccharide glycoside with 10 - 12 parts by volume of deionized water, and stir until dissolved. Then add 0.1 - 0.3 parts by volume of L-ascorbic acid, and stir at 300 - 350 r / min under heating conditions at 50 - 60 °C until completely dissolved;

[0015] S1.2: Then keep the temperature at 50 - 60 °C, and add 5 - 8% of cyclodextrin glycosyltransferase based on the mass of the system. React for 12 - 13 h. After the reaction, filter the reaction product through an ultrafiltration membrane to remove cyclodextrin glycosyltransferase, and spray dry to obtain the compound glycoside.

[0016] Further, the preparation of the chelated selenium solution in step S2 includes the following steps:

[0017] S2.1: Mix corn gluten meal polypeptide, sodium dodecylbenzenesulfonate and deionized water at a volume ratio of 10:(1 - 3):(14 - 18), heat to 30 - 40 °C and stir for 10 - 15 min, then let it stand for 3 - 5 min, and then add deionized water to adjust the content of corn gluten meal polypeptide in the system to 5 mg / mL to obtain a corn gluten meal polypeptide solution;

[0018] S2.2: Add 0.1 - 0.5 wt% of gallic acid to the corn gluten meal polypeptide solution, stir magnetically for 30 - 35 min, then add 10 mM sodium selenite solution, and then stir magnetically at 50 - 60 °C for 3 - 5 min, and then let it stand and cool to room temperature to obtain a mixture;

[0019] S2.3: Mix the complex glycoside and deionized water at a material-liquid ratio of 1 g:(10 - 15) mL and stir evenly to obtain a complex glycoside solution;

[0020] S2.4: Then, add the complex glycoside solution to the mixture at a rate of 1 - 3 mL / s, such that the volume ratio of the added complex glycoside solution to the mixture is 1:(1 - 1.2). Finally, stir magnetically at 300 - 350 r / min for 30 - 40 min to obtain a chelated selenium solution.

[0021] Furthermore, step S3 of cultivating lettuce and spraying the chelated selenium solution includes the following steps:

[0022] S3.1: Sow the lettuce seeds on a fully moistened sponge. Start supplementary lighting on the second day after germination, with a light intensity of 120 - 150 μmol / m 2 / s, a daily lighting time of 10 h. Water with clear water once a day within 1 - 2 days after the seeds germinate to keep the seedling-raising sponge moist. From 3 - 5 days after the seeds germinate, change the light intensity to 180 - 220 μmol / m2 / s, with a lighting time of 12 h, and water with the nutrient solution 1 - 2 times a day to keep the sponge moist;

[0023] S3.2: When the lettuce seeds grow into seedlings and the seedlings have four true leaves, transfer the seedlings into a seedling planting board, with a light intensity of 180 - 220 μmol / m2 / s, a daily lighting time of 12 h, and the nutrient solution circulating 2 - 3 times a day, each time for 1 - 1.5 h;

[0024] S3.3: When the leaves of the two seedlings come into contact with each other, transfer the seedlings into a seedling-raising board in the mid-growth stage, with a light intensity of 180 - 220 μmol / m2 / s, a daily lighting time of 12 h, and the nutrient solution circulating 2 - 3 times a day, each time for 1 - 1.5 h;

[0025] S3.4: Mix the chelated selenium solution and pure water at a volume ratio of 1:500 - 550 to obtain a selenium spraying agent. When the leaves of the two mid-stage seedlings come into contact with each other, transfer the mid-stage seedlings into a seedling-raising board in the adult stage, with a light intensity of 180 - 220 μmol / m2 / s. After transferring into the seedling-raising board in the adult stage, starting from the second day, spray the selenium spraying agent onto the leaves at 10 - 11 am until the lettuce enters the mature stage and stop spraying to obtain selenium-enriched hydroponic lettuce.

[0026] Furthermore, the preparation method of corn gluten meal polypeptide includes the following steps:

[0027] Place the corn gluten meal in a high-speed pulverizer for pulverization, then pass through an 80-mesh sieve, and perform decolorization by washing with an acid solution. Adjust the pH value of the system to 3 - 3.5 and wash and decolorize at 50 °C for 2 - 2.5 h to obtain decolorized corn gluten meal;

[0028] Mix the decolorized corn meal with deionized water at a solid-liquid ratio of 1 g : (10 - 12) mL, and adjust the pH value to 7 - 8. Subsequently, add alkaline protease, papain, and neutral protease, each accounting for 1 - 1.5% of the system mass, to the system and carry out enzymatic hydrolysis at a constant temperature for 6 - 7 h. During the reaction process, add NaOH solution to maintain the pH value of the enzymatic hydrolysate constant between 7 and 8. After the enzymatic hydrolysis is completed, heat the obtained enzymatic hydrolysis mixture at 100 - 120 °C for 10 - 15 min to inactivate the enzymes. After cooling to room temperature, centrifuge at a speed of 4000 - 4200 r / min for 30 - 35 min and take the supernatant. Freeze-dry the obtained supernatant to obtain corn meal polypeptide, which is stored refrigerated for later use.

[0029] Furthermore, the nutrient solution is prepared by mixing calcium nitrate tetrahydrate at 236 - 240 mg / L, potassium nitrate at 400 - 404 mg / L, ammonium dihydrogen phosphate at 57 - 60 mg / L, and magnesium sulfate heptahydrate at 123 - 125 mg / L.

[0030] Furthermore, the alkaline protease is specifically Novo protease.

[0031] Furthermore, the neutral protease is specifically 1398 neutral protease.

[0032] Compared with the prior art, the present invention has at least the following beneficial effects:

[0033] 1. In the present invention, chitosan oligosaccharide glycoside and L-ascorbic acid are combined through cyclodextrin glycosyltransferase to specifically catalyze the formation of new glycosidic bonds, improving the binding degree of ascorbic acid and chitosan oligosaccharide glycoside. The composite glycoside with a high binding degree can enrich the complex in the leaves and roots of lettuce, reduce ineffective diffusion, and enhance the antioxidant property and reduce the degradation rate of the combined composite glycoside. Moreover, ascorbic acid has a reducing effect, which can reduce selenium in sodium selenite. Subsequently, chitosan oligosaccharide glycoside chelates with selenium, thereby reducing the content of free selenium in the system, enabling selenium to enter the plant in a chelated state, and using the water solubility and biocompatibility of chitosan oligosaccharide glycoside to enter the plant leaves more quickly and be absorbed by the plant, thus increasing the selenium uptake of lettuce.

[0034] 2. The present invention combines compound glycosides with corn gluten meal polypeptides for loading selenium in sodium selenite. Multiple groups in corn gluten meal polypeptides can directly chelate free selenium, while the compound glycosides composed of ascorbic acid and chitosan oligosaccharide glycosides can reduce the selenium in sodium selenite into free selenium that is more easily chelated, and further stabilize selenium through chitosan oligosaccharide glycosides, forming a ternary complex of corn gluten meal polypeptide - selenium - glycoside with a multiple folded structure, increasing the content of chelated selenium in the spraying agent and making selenium more stable in the environment. At the same time, corn gluten meal polypeptides also contain polypeptide components that regulate plant growth and development. These polypeptides that promote plant root growth can be transported to plant leaves and roots more quickly. Therefore, the selenium element loaded by corn gluten meal polypeptides can also be transported to lettuce roots more quickly and fixed with the physiological action of lettuce, thereby increasing the selenium content in mature lettuce.

[0035] 3. The present invention combines corn gluten meal polypeptides with sodium dodecylbenzenesulfonate. The charged groups of sodium dodecylbenzenesulfonate can bind to the hydrophobic amino acids contained in corn gluten meal polypeptides through electrostatic repulsion and micelle encapsulation, thereby changing the defect that hydrophobic amino acids are prone to aggregation and precipitation when alone in an aqueous solution, enabling corn gluten meal polypeptides to be evenly dispersed in the aqueous solution and increasing the water solubility of corn gluten meal polypeptides. As a result, the chelated selenium added with corn gluten meal polypeptides can better enter lettuce leaves and fix selenium elements, thereby increasing the selenium element content in lettuce. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings incorporated herein and constituting a part of the specification illustrate embodiments of the present disclosure and, together with the specification, are further used to explain the principles of the present disclosure and enable those skilled in the relevant art to implement and use the present disclosure.

[0037] Figure 1 It is a flowchart of a method for planting selenium - enriched hydroponic lettuce in a plant factory according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The following describes in detail a method for planting selenium - enriched hydroponic lettuce in a plant factory provided by the present invention with reference to the accompanying drawings and specific embodiments. At the same time, it should be noted here that in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments. For some well - known technologies, those skilled in the art can also adopt other alternative methods for implementation; moreover, the drawing part is only for more specifically describing the embodiments and is not intended to specifically limit the present invention.

[0039] Example 1:

[0040] A method for planting selenium - enriched hydroponic lettuce in a plant factory, as Figure 1 shown, includes the following steps:

[0041] S1: Prepare compound glycosides

[0042] S1.1: Mix 2.5 parts by volume of chitosan oligosaccharide glycoside with 10 parts by volume of deionized water, and stir until dissolved. Then add 0.1 part by volume of L-ascorbic acid, and stir at 300 r / min until completely dissolved under the heating condition of 50°C.

[0043] S1.2: Then keep the temperature at 50°C, add cyclodextrin glycosyltransferase accounting for 5% of the system mass, react for 12 h. After the reaction, filter the reaction product through an ultrafiltration membrane to remove cyclodextrin glycosyltransferase, and spray dry to obtain the composite glycoside.

[0044] S2: Prepare the chelated selenium solution

[0045] S2.1: Place corn gluten meal in a high-speed grinder for grinding, then pass through an 80-mesh sieve, and perform decolorization by washing with an acid solution. Adjust the pH value of the system to 3, and wash and decolorize at 50°C for 2 h to obtain decolorized corn gluten meal.

[0046] Mix the decolorized corn gluten meal with deionized water at a solid-liquid ratio of 1 g:10 mL, and adjust the pH value to 7. Then add Novo protease, papain, and 1398 neutral protease accounting for 1% of the system mass to the system respectively, and perform constant-temperature enzymatic hydrolysis for 6 h. During the reaction, add NaOH solution to maintain the pH value of the enzymatic hydrolysis solution constantly between 7 and 8. After the enzymatic hydrolysis, heat the obtained enzymatic hydrolysis mixture at 100°C for 10 min to inactivate the enzyme. After cooling to room temperature, centrifuge at 4000 r / min for 30 min to take the supernatant, and freeze-dry the obtained supernatant to obtain corn gluten meal polypeptide, which is stored refrigerated for later use.

[0047] Mix corn gluten meal polypeptide, sodium dodecylbenzenesulfonate, and deionized water at a volume ratio of 10:1:14, heat to 30°C and stir for 10 min, then let it stand for 3 min, and then add deionized water to adjust the content of corn gluten meal polypeptide in the system to 5 mg / mL to obtain the corn gluten meal polypeptide solution.

[0048] S2.2: Add 0.1 wt% of gallic acid to the corn gluten meal polypeptide solution, stir magnetically for 30 min, then add 10 mM sodium selenite solution, and then stir magnetically at 50°C for 3 min, and then let it stand and cool to room temperature to obtain a mixed solution.

[0049] S2.3: Mix the composite glycoside with deionized water at a solid-liquid ratio of 1 g:10 mL and stir evenly to obtain the composite glycoside solution.

[0050] S2.4: Then add the composite glycoside solution to the mixed solution at a rate of 1 mL / s, so that the volume ratio of the added composite glycoside solution to the mixed solution is 1:1. Finally, stir magnetically at 300 r / min for 30 min to obtain the chelated selenium solution.

[0051] S3: Cultivate lettuce and spray chelated selenium solution

[0052] S3.1: Sow lettuce seeds on a fully moistened sponge. Start supplementary lighting on the 2nd day after germination. The light intensity is 120 μmol / m 2 / s, with a daily lighting time of 10 h. Water with clear water once a day within 1 day after the seeds germinate to keep the seedling-raising sponge moist. On the 3rd day after the seeds germinate, change the light intensity to 180 μmol / m 2 / s, with a lighting time of 12 h. Water with the nutrient solution once a day. The nutrient solution is prepared by mixing 236 mg / L of calcium nitrate tetrahydrate, 400 mg / L of potassium nitrate, 57 mg / L of ammonium dihydrogen phosphate, and 123 mg / L of magnesium sulfate heptahydrate to keep the sponge moist;

[0053] S3.2: When the lettuce seeds grow into seedlings and the seedlings have four true leaves, transfer the seedlings into the seedling planting board. The light intensity is 180 μmol / m 2 / s, with a daily lighting time of 12 h. The nutrient solution circulates 2 times a day, each time for 1 h;

[0054] S3.3: When the leaves of the two seedlings come into contact with each other, transfer the seedlings into the seedling-raising board in the mid-growth stage. The light intensity is 180 μmol / m 2 / s, with a daily lighting time of 12 h. The nutrient solution circulates 2 times a day, each time for 1 h;

[0055] S3.4: Mix the chelated selenium solution and pure water in a volume ratio of 1:500 to obtain a selenium spraying agent. When the leaves of the two mid-stage seedlings come into contact with each other, transfer the mid-stage seedlings into the seedling-raising board in the adult stage. The light intensity is 180 μmol / m 2 / s. After transferring into the seedling-raising board in the adult stage, starting from the 2nd day, spray the selenium spraying agent onto the leaves at 10 am until the lettuce enters the mature stage and stop spraying to obtain selenium-enriched hydroponic lettuce.

[0056] Example 2:

[0057] A method for planting selenium-enriched hydroponic lettuce in a plant factory, as Figure 1 shown, includes the following steps:

[0058] S1: Prepare composite glycoside

[0059] S1.1: Mix 3 parts by volume of chitosan oligosaccharide glycoside with 12 parts by volume of deionized water and stir until dissolved. Then add 0.3 parts by volume of L-ascorbic acid and stir at 300 r / min until completely dissolved under the heating condition of 50 °C;

[0060] S1.2: Then maintain the temperature at 50 °C, and then add cyclodextrin glycosyltransferase accounting for 8% of the system mass. React for 12 h. After the reaction, filter the reaction product through an ultrafiltration membrane to remove cyclodextrin glycosyltransferase, and then perform spray drying to obtain the composite glycoside.

[0061] S2: Prepare the chelated selenium solution

[0062] S2.1: Place the corn gluten meal in a high-speed crusher for crushing, then pass through an 80-mesh sieve, and perform decolorization by washing with an acid solution. Adjust the pH value of the system to 3, and wash and decolorize at 50 °C for 2 h to obtain the decolorized corn gluten meal;

[0063] Mix the decolorized corn gluten meal with deionized water at a material-liquid ratio of 1 g: 12 mL, and adjust the pH value to 7. Subsequently, add Novo protease, papain, and 1398 neutral protease accounting for 1.5% of the system mass to the system, and perform constant-temperature enzymatic hydrolysis for 6 h. During the reaction, add NaOH solution to maintain the pH value of the enzymatic hydrolysate between 7 and 8. After the enzymatic hydrolysis, heat the obtained enzymatic hydrolysis mixture at 100 °C for 10 min to inactivate the enzyme. After cooling to room temperature, centrifuge at a rotation speed of 4000 r / min for 30 min and take the supernatant. Freeze-dry the obtained supernatant to obtain corn gluten meal polypeptide, and store it refrigerated for later use;

[0064] Mix the corn gluten meal polypeptide, sodium dodecylbenzenesulfonate, and deionized water at a volume ratio of 10: 3: 18, heat up to 30 °C and stir for 10 min, then let it stand for 3 min, and then add deionized water to adjust the content of corn gluten meal polypeptide in the system to 5 mg / mL to obtain the corn gluten meal polypeptide solution;

[0065] S2.2: Add 0.5 wt% gallic acid to the corn gluten meal polypeptide solution, stir magnetically for 30 min, then add 10 mM sodium selenite solution, and then stir magnetically at 50 °C for 3 min, and then let it stand and cool to room temperature to obtain the mixed solution;

[0066] S2.3: Mix the composite glycoside with deionized water at a material-liquid ratio of 1 g: 15 mL and stir evenly to obtain the composite glycoside solution;

[0067] S2.4: Then dropwise add the composite glycoside solution to the mixed solution at a speed of 1 mL / s, so that the volume ratio of the dropped composite glycoside solution to the mixed solution is 1: 1.2. Finally, stir magnetically at 300 r / min for 30 min to obtain the chelated selenium solution.

[0068] S3: Cultivate lettuce and spray the chelated selenium solution

[0069] S3.1: Sow lettuce seeds on the fully moistened sponge, and start supplementary lighting on the 2nd day after germination. The light intensity is 120 μmol / m 2 / s, with a daily light exposure time of 10 h. After the seeds germinate, water them with clear water once a day within 1 day to keep the seedling sponge moist. Three days after the seeds germinate, change the light intensity to 180 μmol / m 2 / s, with a light exposure time of 12 h. Water with nutrient solution once a day. The nutrient solution is prepared by mixing 240 mg / L of calcium nitrate tetrahydrate, 404 mg / L of potassium nitrate, 60 mg / L of ammonium dihydrogen phosphate, and 125 mg / L of magnesium sulfate heptahydrate, and keep the sponge moist;

[0070] S3.2: When the lettuce seeds grow into seedlings and the seedlings have four true leaves, transfer the seedlings into the seedling planting board. The light intensity is 180 μmol / m 2 / s, with a daily light exposure time of 12 h. The nutrient solution circulates 2 times a day, each time for 1 h;

[0071] S3.3: When the leaves of the two seedlings come into contact with each other, transfer the seedlings into the seedling board in the mid - growth stage. The light intensity is 180 μmol / m 2 / s, with a daily light exposure time of 12 h. The nutrient solution circulates 2 times a day, each time for 1 h;

[0072] S3.4: Mix the chelated selenium solution and pure water in a volume ratio of 1:500 to obtain the selenium spraying agent. When the leaves of the two mid - stage seedlings come into contact with each other, transfer the mid - stage seedlings into the seedling board in the adult - growth stage. The light intensity is 180 μmol / m 2 / s. After transferring them into the seedling board in the adult - growth stage, starting from the second day, spray the selenium spraying agent onto the leaves at 10:00 in the morning until the lettuce enters the mature stage and stop spraying to obtain selenium - enriched hydroponic lettuce.

[0073] Example 3:

[0074] A planting method for selenium - enriched hydroponic lettuce in a plant factory, as Figure 1 shown, including the following steps:

[0075] S1: Prepare compound glycoside

[0076] S1.1: Mix 2.5 parts by volume of chitosan oligosaccharide glycoside with 10 parts by volume of deionized water and stir until dissolved. Then add 0.1 part by volume of L - ascorbic acid and stir at 350 r / min until completely dissolved under the heating condition of 60 °C;

[0077] S1.2: Then keep the temperature at 60 °C, add cyclodextrin glycosyltransferase accounting for 5% of the system mass, react for 13 h. After the reaction ends, filter the reaction product through an ultrafiltration membrane to remove cyclodextrin glycosyltransferase, and spray - dry to obtain compound glycoside.

[0078] S2: Prepare chelated selenium solution

[0079] S2.1: Place the corn meal in a high-speed grinder for grinding, then pass it through an 80-mesh sieve, and perform decolorization by washing with an acid solution. Adjust the pH value of the system to 3.5, and wash and decolorize at 50 °C for 2.5 h to obtain decolorized corn meal;

[0080] Mix the decolorized corn meal with deionized water at a solid-liquid ratio of 1 g: 10 mL, and adjust the pH value to 8. Subsequently, add 1% Novo protease, papain, and 1398 neutral protease based on the mass of the system to the system, and carry out constant-temperature enzymatic hydrolysis for 6 h. During the reaction, add NaOH solution to maintain the pH value of the enzymatic hydrolysate between 7 and 8. After the enzymatic hydrolysis is completed, heat the obtained enzymatic hydrolysis mixture at 120 °C for 15 min to inactivate the enzyme. After cooling to room temperature, centrifuge at a speed of 4200 r / min for 35 min to obtain the supernatant. Freeze-dry the obtained supernatant to obtain corn meal polypeptide, and store it refrigerated for later use;

[0081] Mix the corn meal polypeptide, sodium dodecyl benzene sulfonate, and deionized water at a volume ratio of 10: 1: 14, heat to 30 °C and stir for 10 min, then let it stand for 3 min, and then add deionized water to adjust the content of corn meal polypeptide in the system to 5 mg / mL to obtain a corn meal polypeptide solution;

[0082] S2.2: Add 0.1 wt% gallic acid to the corn meal polypeptide solution, magnetically stir for 35 min, then add 10 mM sodium selenite solution, and then magnetically stir at 60 °C for 5 min, and then let it stand and cool to room temperature to obtain a mixed solution;

[0083] S2.3: Mix the complex glycoside with deionized water at a solid-liquid ratio of 1 g: 10 mL and stir evenly to obtain a complex glycoside solution;

[0084] S2.4: Then, add the complex glycoside solution to the mixed solution at a rate of 3 mL / s, so that the volume ratio of the added complex glycoside solution to the mixed solution is 1: 1. Finally, magnetically stir at 350 r / min for 40 min to obtain a chelated selenium solution.

[0085] S3: Cultivate lettuce and spray the chelated selenium solution

[0086] S3.1: Sow lettuce seeds on a fully moistened sponge, start supplementary lighting on the 2nd day after germination, with a light intensity of 150 μmol / m 2 / s, with a daily lighting time of 10 h. Water with clear water once a day within 2 days after the seeds germinate to keep the seedling-raising sponge moist. On the 5th day after the seeds germinate, change the light intensity to 220 μmol / m 2 / s, with a light exposure time of 12 h, watering once a day with a nutrient solution prepared by mixing 236 mg / L of calcium nitrate tetrahydrate, 400 mg / L of potassium nitrate, 57 mg / L of ammonium dihydrogen phosphate, and 123 mg / L of magnesium sulfate heptahydrate, and keeping the sponge moist;

[0087] S3.2: When the lettuce seeds grow into seedlings and the seedlings have four true leaves, transplant the seedlings into the seedling fixing board, with a light intensity of 180 μmol / m 2 / s, with a daily light exposure time of 12 h, and the nutrient solution is circulated 3 times a day, each time for 1.5 h;

[0088] S3.3: When the leaves of the two seedlings come into contact with each other, transplant the seedlings into the seedling raising board in the middle growth stage, with a light intensity of 180 μmol / m 2 / s, with a daily light exposure time of 12 h, and the nutrient solution is circulated 3 times a day, each time for 1.5 h;

[0089] S3.4: Mix the chelated selenium solution and pure water in a volume ratio of 1:550 to obtain a selenium spraying agent. When the leaves of the two middle-stage seedlings come into contact with each other, transplant the middle-stage seedlings into the seedling raising board in the adult stage, with a light intensity of 220 μmol / m 2 / s. After transplanting into the seedling raising board in the adult stage, starting from the second day, at 14:00 in the morning, spray the selenium spraying agent onto the leaves until the lettuce enters the mature stage and stop spraying to obtain selenium-enriched hydroponic lettuce.

[0090] Comparative Example 1:

[0091] Compared with Example 1, the difference in Comparative Example 1 is that step S1 is not carried out, and the composite glycoside in step S2.3 is replaced with chitosan oligosaccharide, specifically as follows: "S2.3: Mix chitosan oligosaccharide and deionized water at a material-liquid ratio of 1 g:10 mL and stir evenly to obtain a chitosan oligosaccharide solution;

[0092] S2.4: Then, drop the chitosan oligosaccharide solution into the mixture at a speed of 1 mL / s, so that the volume ratio of the dropped chitosan oligosaccharide solution to the mixture is 1:1, and finally stir magnetically at 300 r / min for 30 min to obtain a chelated selenium solution", and the other steps remain unchanged.

[0093] Comparative Example 2:

[0094] Compared with Example 1, the difference in Comparative Example 2 is that step S1 is not carried out, and the composite glycoside in step S2.3 is replaced with L-ascorbic acid, specifically as follows: "S2.3: Mix L-ascorbic acid and deionized water at a material-liquid ratio of 1 g:10 mL and stir evenly to obtain an L-ascorbic acid solution;

[0095] S2.4: Then, dropwise add the L-ascorbic acid solution to the mixed solution at a speed of 1 mL / s, so that the volume ratio of the added L-ascorbic acid solution to the mixed solution is 1:1. Finally, stir magnetically at 300 r / min for 30 min to obtain the chelated selenium solution, and the rest of the steps remain unchanged.

[0096] Comparative Example 3:

[0097] Compared with Example 1, the difference in Comparative Example 3 is that steps S2.3 and S2.4 are not carried out, and the mixed solution is directly added as the chelated selenium solution in step S3.4. Specifically, it is "S3.4: Mix the mixed solution and pure water at a volume ratio of 1:500 to obtain the selenium spraying agent. When the leaves of two middle-stage seedlings come into contact with each other, transfer the middle-stage seedlings to the seedling-raising plate in the adult seedling stage. The light intensity is 180 μmol / m 2 / s. After transferring to the seedling-raising plate in the adult seedling stage, starting from the second day, at 10:00 am, spray the selenium spraying agent onto the leaves until the lettuce enters the mature stage and stop spraying to obtain selenium-enriched hydroponic lettuce", and the rest of the steps remain unchanged.

[0098] Comparative Example 4:

[0099] Compared with Example 1, the difference in Comparative Example 4 is that step S2.1 is not carried out, and in step S2.2, instead of adding the corn gluten meal polypeptide solution, a composite glycoside solution is added. Specifically, it is "S2: Prepare the chelated selenium solution

[0100] S2.1: Mix the composite glycoside and deionized water at a material-liquid ratio of 1 g:10 mL and stir evenly to obtain the composite glycoside solution;

[0101] S2.2: Add 0.1 wt% of gallic acid to the composite glycoside solution, stir magnetically for 30 min, then add a 10 mM sodium selenite solution, and then stir magnetically at 50 °C for 3 min, and then let it stand and cool to room temperature to obtain the chelated selenium solution", and the rest of the steps remain unchanged.

[0102] Comparative Example 5:

[0103] Compared with Example 1, the difference in Comparative Example 5 is that sodium dodecylbenzenesulfonate is not added in step S2.1. Specifically, it is "S2.1: Place the corn gluten meal in a high-speed crusher for crushing, then pass through an 80-mesh sieve, and perform decolorization by washing with an acid solution. Adjust the pH value of the system to 3 and wash and decolorize at 50 °C for 2 h to obtain the decolorized corn gluten meal;

[0104] Mix the decolorized corn gluten meal with deionized water at a solid-liquid ratio of 1 g:10 mL, and adjust the pH value to 7. Subsequently, add Novo protease, papain, and 1398 neutral protease, each accounting for 1% of the system mass, to the system, and perform constant-temperature enzymatic hydrolysis for 6 h. During the reaction, add NaOH solution to maintain the pH value of the enzymatic hydrolysate between 7 and 8. After the enzymatic hydrolysis is completed, heat the obtained enzymatic hydrolysis mixture at 100 °C for 10 min to inactivate the enzyme. After cooling to room temperature, centrifuge at 4000 r / min for 30 min and take the supernatant. Freeze-dry the obtained supernatant to obtain corn gluten meal polypeptide, and store it refrigerated for later use;

[0105] Mix the corn gluten meal polypeptide with deionized water, heat it to 30 °C and stir for 10 min, then let it stand for 3 min, and add deionized water to adjust the content of corn gluten meal polypeptide in the system to 5 mg / mL to obtain the corn gluten meal polypeptide solution, and the remaining steps remain unchanged.

[0106] Control Example 6:

[0107] Replace the selenium spraying agent in step S3 with sodium selenite solution, and control the concentration of the sodium selenite solution to be 10 mg / L. Specifically:

[0108] Sow the lettuce seeds on the fully moistened sponge. Start supplementary lighting on the 2nd day after germination, with a light intensity of 120 μmol / m 2 / s, and the daily lighting time is 10 h. Pour clear water once a day within 1 day after the seeds germinate to keep the seedling-raising sponge moist. On the 3rd day after the seeds germinate, change the light intensity to 180 μmol / m 2 / s, the lighting time is 12 h, and pour 1 time of nutrient solution every day. The nutrient solution is prepared by mixing 236 mg / L of calcium nitrate tetrahydrate, 400 mg / L of potassium nitrate, 57 mg / L of ammonium dihydrogen phosphate, and 123 mg / L of magnesium sulfate heptahydrate, and keep the sponge moist;

[0109] When the lettuce seeds grow into seedlings and the seedlings have four true leaves, transfer the seedlings into the seedling fixing plate, with a light intensity of 180 μmol / m 2 / s, the daily lighting time is 12 h, and the nutrient solution circulates 2 times a day, each time for 1 h;

[0110] When the two leaves of the seedlings touch each other, transfer the seedlings into the seedling-raising plate in the mid-growth stage, with a light intensity of 180 μmol / m 2 / s, the daily lighting time is 12 h, and the nutrient solution circulates 2 times a day, each time for 1 h;

[0111] When the two leaves of the mid-stage seedlings touch each other, transfer the mid-stage seedlings into the seedling-raising plate in the adult stage, with a light intensity of 180 μmol / m 2 / s, after transplanting the seedling trays into the seedling stage, starting from the second day, at 10:00 in the morning, spray the sodium selenite solution at a concentration of 10 mg / L onto the leaves until the lettuce enters the mature stage, then stop spraying to obtain selenium-enriched hydroponic lettuce.

[0112] After sowing the lettuce seeds on the fully moistened sponge, taking 10 sponges sown with lettuce seeds as a group, a total of 9 groups of sponges were cultivated using the lettuce cultivation methods in Examples 1-3 and Comparative Examples 1-6 respectively. After the lettuce was mature and harvested, the selenium conversion rates of Examples 1-3 and Comparative Examples 1-6 were calculated, and the selenium content was detected by high performance liquid chromatography - inductively coupled plasma mass spectrometry (HPLC-ICP-MS), as shown in Table 1.

[0113] Where LAI = leaf area index, W = unit target yield (kg / m 2 ), T0 = background value of selenium content in lettuce (mg / kg), Tx = selenium content in lettuce after spraying, C = concentration of chelated selenium solution, Vx = volume of chelated selenium solution, X = selenium conversion rate

[0114]

[0115] Table 1

[0116]

[0117] The average selenium content of the mature lettuce in Examples 1-3 and Comparative Examples 1-6 is shown in Table 2.

[0118] Table 2

[0119]

[0120] Detect the proportion of free selenium in the chelated selenium solutions of Examples 1-3 and Comparative Examples 1-4. The free selenium and the total selenium content were detected by high performance liquid chromatography - inductively coupled plasma mass spectrometry (HPLC-ICP-MS) respectively. , and the results are shown in Table 3.

[0121] Table 3

[0122]

[0123] It can be seen that the selenium conversion rates of Examples 1-3 are above 64.6%, the average selenium content is above 0.24 mg / kg, and the proportion of free selenium in the solution is below 23.4%. Their selenium conversion rates and average selenium contents are all higher than those of the comparative examples, while the proportion of free selenium is all lower than that of the comparative examples. It can be seen that the planting method of hydroponic lettuce in the present invention has a higher selenium conversion rate, the selenium content in the obtained agricultural product lettuce is higher, and moreover, for the chelated selenium solution prepared by the recording method in the present invention, the proportion of free selenium is lower and the content of chelated selenium is higher, so it is easier to be absorbed by lettuce. It can be seen that the higher proportion of chelated selenium also increases the selenium content in mature lettuce to a certain extent, which also proves from the side that chelated selenium is more easily absorbed by lettuce.

[0124] In Comparative Examples 1-4 of the present invention, L-ascorbic acid, chitosan oligosaccharide glycoside, compound glycoside and corn germ meal polypeptide in the preparation of the chelated selenium solution were removed respectively, indicating that the above components have an effect on increasing the proportion of chelated selenium in the chelated selenium solution, and at the same time the selenium conversion rate is also improved. It can be seen that the effects that can be achieved by single components are not as good as those achieved by synergistic components.

[0125] In Comparative Example 5 of the present invention, both the selenium conversion rate and the selenium content are lower than those of the examples, indicating that after sodium dodecylbenzenesulfonate is combined with corn germ meal polypeptide, the water solubility of corn germ meal polypeptide can be improved, thereby improving the selenium conversion rate.

[0126] In Comparative Example 6 of the present invention, the lettuce obtained by directly using sodium selenite as a leaf spraying agent was used. The average selenium content in the lettuce was only 0.13 mg / kg, and the selenium conversion rate was 31.8%. It can be seen that when directly spraying sodium selenite on the leaves, the absorption rate and conversion ability of lettuce to selenium elements are not as good as the effects that can be achieved by the present invention.

[0127] The above examples only illustrate the principles and effects of the present invention by way of example, and are not used to limit the present invention. Any person familiar with this technology can modify or change the above examples without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A method for cultivating selenium-enriched hydroponic lettuce in a plant factory, characterized in that, It includes the following steps: S1: Prepare compound glycoside Mix chitosan oligosaccharide glycoside with deionized water and stir until dissolved. Then add L-ascorbic acid and stir until dissolved. Next, add cyclodextrin glycosyltransferase. Filter the reaction product through an ultrafiltration membrane to remove cyclodextrin glycosyltransferase, and obtain compound glycoside; S2: Prepare chelated selenium solution Mix corn gluten meal polypeptide, sodium dodecylbenzenesulfonate with deionized water, heat up and stir to obtain a corn gluten meal polypeptide solution. Add gallic acid to the corn gluten meal polypeptide solution, stir magnetically and then add sodium selenite solution to obtain a mixture. Mix compound glycoside with deionized water to obtain a compound glycoside solution, and then dropwise add the compound glycoside solution to the mixture to obtain a chelated selenium solution; S3: Cultivate lettuce and spray chelated selenium solution Sow lettuce seeds on a fully moistened sponge. When the lettuce seeds grow into seedlings, transfer the seedlings into a seedling planting board. When the two leaves of the seedlings touch each other, transfer the seedlings into a seedling raising board in the middle growth stage. When the two leaves of the middle-stage seedlings touch each other, transfer the middle-stage seedlings into a seedling raising board in the adult growth stage. Prepare the chelated selenium solution into a selenium spraying agent, and start spraying the selenium spraying agent onto the leaves from the second day until maturity to obtain selenium-enriched hydroponic lettuce.

2. The cultivation method of selenium-rich hydroponic lettuce in a plant factory according to claim 1, characterized in that, Step S1 for preparing compound glycoside includes the following steps: S1.1: Mix 2.5 - 3 parts by volume of chitosan oligosaccharide glycoside with 10 - 12 parts by volume of deionized water and stir until dissolved. Then add 0.1 - 0.3 parts by volume of L-ascorbic acid, and stir at 300 - 350 r / min until completely dissolved under the heating condition of 50 - 60 °C; S1.2: Then keep the temperature at 50 - 60 °C, add 5 - 8% by mass of cyclodextrin glycosyltransferase in the system, react for 12 - 13 h. After the reaction ends, filter the reaction product through an ultrafiltration membrane to remove cyclodextrin glycosyltransferase, and perform spray drying to obtain compound glycoside.

3. The planting method of selenium-rich hydroponic lettuce in a plant factory according to claim 2, characterized in that, Step S2 for preparing chelated selenium solution includes the following steps: S2.1: Mix corn gluten meal polypeptide, sodium dodecylbenzenesulfonate with deionized water at a volume ratio of 10:(1 - 3):(14 - 18), heat up to 30 - 40 °C and stir for 10 - 15 min, then let it stand for 3 - 5 min, and then add deionized water to adjust the content of corn gluten meal polypeptide in the system to 5 mg / mL to obtain a corn gluten meal polypeptide solution; S2.2: Add 0.1 - 0.5 wt% of gallic acid to the corn gluten meal polypeptide solution, stir magnetically for 30 - 35 min and then add 10 mM sodium selenite solution, and then stir magnetically at 50 - 60 °C for 3 - 5 min, then let it stand and cool to room temperature to obtain a mixture; S2.3: Mix compound glycoside with deionized water at a material-liquid ratio of 1 g:(10 - 15) mL and stir evenly to obtain a compound glycoside solution; S2.4: Then dropwise add the compound glycoside solution to the mixture at a speed of 1 - 3 mL / s, so that the volume ratio of the added compound glycoside solution to the mixture is 1:(1 - 1.2), and finally stir magnetically at 300 - 350 r / min for 30 - 40 min to obtain a chelated selenium solution.

4. The planting method of selenium-enriched hydroponic lettuce in a plant factory according to claim 3, characterized in that, Step S3 for cultivating lettuce and spraying chelated selenium solution includes the following steps: S3.1: Sow lettuce seeds on a fully soaked sponge. Start supplementary lighting on the 2nd day after germination. The light intensity is 120 - 150 μmol / m 2 / s, with a daily lighting time of 10 h. Water with clean water once a day within 1 - 2 days after the seeds germinate to keep the seedling-raising sponge moist. From 3 - 5 days after the seeds germinate, change the light intensity to 180 - 220 μmol / m 2 / s, with a lighting time of 12 h, and water with nutrient solution 1 - 2 times a day to keep the sponge moist; S3.2: When the lettuce seeds grow into seedlings and the seedlings have four true leaves, transplant the seedlings into the seedling planting board, with a light intensity of 180 - 220 μmol / m 2 / s, a daily light duration of 12 h, and the nutrient solution circulates 2 - 3 times a day, each time for 1 - 1.5 h; S3.3: When the leaves of two seedlings come into contact with each other, transfer the seedlings into the seedling plate in the mid-growth stage, with a light intensity of 180 - 220 μmol / m 2 / s, a daily light duration of 12 h, and the nutrient solution is circulated 2 - 3 times a day, each time for 1 - 1.5 h; S3.4: Mix the chelated selenium solution and pure water at a volume ratio of 1:500 - 550 to obtain a selenium spraying agent. When the leaves of two mid-stage seedlings come into contact with each other, transfer the mid-stage seedlings into the seedling-raising plate at the adult seedling stage. The light intensity is 180 - 220 μmol / m 2 / s. After transferring into the seedling-raising plate at the adult seedling stage, starting from the second day, at 10 - 11 am, spray the selenium spraying agent onto the leaves until the lettuce enters the mature stage and stop spraying to obtain selenium-enriched hydroponic lettuce.

5. The planting method of selenium-rich hydroponic lettuce in a plant factory according to claim 3, characterized in that, The preparation method of corn gluten meal polypeptide includes the following steps: The corn meal is placed in a high-speed grinder for grinding, then passed through an 80-mesh sieve, and decolorized by washing with an acid solution. The pH value of the system is adjusted to 3 - 3.5, and washed and decolorized at 50 °C for 2 - 2.5 h to obtain decolorized corn meal; The decolorized corn meal is mixed with deionized water at a solid-liquid ratio of 1 g:(10 - 12) mL, and the pH value is adjusted to 7 - 8. Subsequently, alkaline protease, papain and neutral protease accounting for 1 - 1.5% of the mass of the system are added to the system respectively, and subjected to constant-temperature enzymatic hydrolysis for 6 - 7 h. During the reaction process, the pH value of the enzymatic hydrolysate is maintained between 7 - 8 by adding NaOH solution. After the enzymatic hydrolysis is completed, the obtained enzymatic hydrolysis mixture is heated at 100 - 120 °C for 10 - 15 min to inactivate the enzyme. After cooling to room temperature, it is centrifuged at a speed of 4000 - 4200 r / min for 30 - 35 min to take the supernatant. The obtained supernatant is freeze-dried to obtain corn meal polypeptide, which is stored refrigerated for standby.

6. The planting method of selenium-rich hydroponic lettuce in a plant factory according to claim 4, characterized in that, The nutrient solution is prepared by mixing 236 - 240 mg / L of calcium nitrate tetrahydrate, 400 - 404 mg / L of potassium nitrate, 57 - 60 mg / L of ammonium dihydrogen phosphate, and 123 - 125 mg / L of magnesium sulfate heptahydrate.

7. A method for cultivating selenium-enriched hydroponic lettuce in a plant factory according to claim 5, characterized in that The alkaline protease is specifically Novo protease.

8. The planting method of selenium-enriched hydroponic lettuce in a plant factory according to claim 5, characterized in that, The neutral protease is specifically 1398 neutral protease.

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