Planting method for selenium-enriched hydroponic lettuce in plant factory

Abstract

The invention relates to the technical field of plant planting, in particular to a planting method for selenium-enriched hydroponic lettuce in a plant factory. The preparation method comprises the following steps: preparing the composite glycoside; preparing a chelated selenium solution; and culturing the lettuce and spraying the chelated selenium solution. Chitosan oligosaccharide and L-ascorbic acid are combined through cyclodextrin glycosyl transferase, formation of new glucosidic bonds is specifically catalyzed, the combination degree of ascorbic acid and chitosan oligosaccharide is improved, composite glycoside with the high combination degree can enrich a compound on leaves and roots of lettuce, invalid diffusion is reduced, ascorbic acid has a reduction effect, and the compound can be used for preparing the lettuce. The selenium in the sodium selenite can be reduced, and then the chitosan oligosaccharide is chelated with the selenium, so that the content of free selenium in a system is reduced, the selenium element enters plants in a chelated state, and the selenium element enters plant leaves more quickly to be absorbed by the plants by utilizing the water solubility and biocompatibility of the chitosan oligosaccharide, and thus the selenium absorption amount of the lettuce is increased.

Description

Technical Field

[0001] The invention relates to the technical field of plant planting, and in particular to a method for planting selenium-enriched hydroponic lettuce in a plant factory. Background Art

[0002] Selenium is an important antioxidant with multiple physiological functions such as cancer prevention, anti-oxidation, and immunity enhancement. By increasing the selenium content in agricultural products such as lettuce, the intake of selenium can be increased from the food channel, thereby improving human immunity. Therefore, selenium-rich agricultural products are gradually appearing 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. Studies have shown that adding sodium selenite to the hydroponic nutrient solution can significantly increase the yield of lettuce and has a positive effect on the growth and quality of lettuce. In addition, spraying nano-selenium solution on the leaves has also been shown 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 the lettuce and used for growth and development, which does not reach the level of selenium enrichment, nor can it increase the body's selenium intake. In order to cultivate selenium-rich lettuce, it is necessary to increase the selenium concentration in the hydroponic nutrient solution. When the concentration of the conventional selenium supplement sodium selenite in the water is too high, it not only cannot be absorbed by the plants, but will cause destructive damage to the plants. Therefore, in addition to adding sodium selenite to the hydroponic nutrient solution, foliar spraying is also used to supplement the plant with selenium.

[0004] The concentration requirement of sodium selenite when spraying plants is more stringent. Not only is the concentration of sodium selenite in the spray lower, but there are also requirements for growth light and environment. This is because selenium generally exists in a free state in the spray, so the plant has a poor ability to absorb selenium in the spray, and excessively high free selenium concentration will also have an impact on the plant. Therefore, the present invention provides a method for planting selenium-enriched hydroponic lettuce in a plant factory, which solves the shortcomings of the above-mentioned prior art by reducing free selenium and increasing the content of chelated selenium. Summary of the invention

[0005] In view of the shortcomings of the prior art, the object of the present invention is to provide a method for planting selenium-enriched hydroponic lettuce in a plant factory.

[0006] A method for growing selenium-enriched hydroponic lettuce in a plant factory comprises the following steps: S1: Preparation of complex glycosides The chitosan oligosaccharide is mixed with deionized water and stirred until dissolved, then L-ascorbic acid is added and stirred to dissolve, and then cyclodextrin glycosyltransferase is added, and the reaction product is filtered through an ultrafiltration membrane to remove the cyclodextrin glycosyltransferase to obtain a complex glycoside; S2: Preparation of chelated selenium solution Mix corn meal polypeptide, sodium dodecylbenzene sulfonate and deionized water, heat and stir to obtain a corn meal polypeptide solution, add gallic acid to the corn meal polypeptide solution, add sodium selenite solution after magnetic stirring to obtain a mixed solution, mix complex glycoside with deionized water to obtain a complex glycoside solution, and then drop the complex glycoside solution into the mixed solution to obtain a chelated selenium solution; S3: Growing lettuce and spraying with chelated selenium solution Lettuce seeds are sown on a fully soaked sponge. When the lettuce seeds grow into seedlings, the seedlings are moved into a seedling planting plate. When two leaves of the seedlings are in contact with each other, the seedlings are moved into a seedling raising plate in the middle growth stage. When two leaves of the mid-stage seedlings are in contact with each other, the mid-stage seedlings are moved into a seedling raising plate in the seedling stage. A chelated selenium solution is made into a selenium spray, and the selenium spray is sprayed on the leaves from the second day until they mature, thereby obtaining selenium-enriched hydroponic lettuce.

[0007] Furthermore, step S1 of preparing the complex glycoside comprises the following steps: S1.1: Mix 2.5-3 parts by volume of chitosan oligosaccharide 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 at 50-60°C until completely dissolved; S1.2: Then, the temperature is maintained at 50-60°C, and 5-8% of the system mass of cyclodextrin glycosyltransferase is added, and the reaction is carried out for 12-13 hours. After the reaction is completed, the reaction product is filtered through an ultrafiltration membrane to remove the cyclodextrin glycosyltransferase, and spray-dried to obtain a complex glycoside.

[0008] Furthermore, step S2 prepares the chelated selenium solution, comprising the following steps: S2.1: corn meal polypeptide, sodium dodecylbenzene sulfonate and deionized water are mixed in a volume ratio of 10:(1-3):(14-18), heated to 30-40°C and stirred for 10-15 minutes, then allowed to stand for 3-5 minutes, and deionized water is added to adjust the content of corn meal polypeptide in the system to 5 mg / mL, thereby obtaining a corn meal polypeptide solution; S2.2: Add 0.1-0.5 wt% gallic acid to the corn meal polypeptide solution, stir magnetically for 30-35 min, then add 10 mM sodium selenite solution, stir magnetically at 50-60°C for 3-5 min, then cool to room temperature to obtain a mixed solution; S2.3: Mix the complex glycoside and deionized water at a solid-liquid ratio of 1 g: (10-15) mL and stir evenly to obtain a complex glycoside solution; S2.4: Then add the complex glycoside solution to the mixed solution at a rate of 1-3 mL / s to make the volume ratio of the added complex glycoside solution to the mixed solution be 1:(1-1.2), and finally stir magnetically at 300-350 r / min for 30-40 min to obtain a chelated selenium solution.

[0009] Furthermore, step S3 of culturing lettuce and spraying the chelated selenium solution comprises the following steps: S3.1: Sow lettuce seeds on a fully soaked sponge and start supplementing light on the second day after germination. The light intensity is 120-150 μmol / m 2 / s, 10h of light per day, water once a day within 1-2 days after the seeds germinate to keep the seedling sponge moist, 3-5 days after the seeds germinate, the light intensity is changed to 180-220μmol / m2 / s, the light time is 12h, 1-2 times of nutrient solution per day to keep the sponge moist; S3.2: When the lettuce seeds grow into seedlings and the seedlings grow to four true leaves, move the seedlings into seedling planting plates, light intensity 180-220μmol / m2 / s, light duration 12h per day, nutrient solution circulation 2-3 times a day, each time 1-1.5h; S3.3: When the leaves of two seedlings touch each other, move the seedlings into the seedling plate in the middle growth period, with a light intensity of 180-220 μmol / m2 / s, a light duration of 12 hours per day, and nutrient solution circulated 2-3 times a day, each time for 1-1.5 hours; S3.4: Mix the chelated selenium solution and pure water in a volume ratio of 1:500-550 to obtain a selenium spray agent. When the leaves of two mid-stage seedlings are in contact with each other, move the mid-stage seedlings into the seedling raising plate of the seedling stage. The light intensity is 180-220μmol / m2 / s. After moving into the seedling raising plate of the seedling stage, spray the selenium spray agent onto the leaves at 10-11 am starting from the second day until the lettuce enters the maturity stage. Stop spraying to obtain selenium-enriched hydroponic lettuce.

[0010] Furthermore, the method for preparing corn meal polypeptide comprises the following steps: The corn meal is placed in a high-speed grinder for grinding, then passed through an 80-mesh sieve, 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 hours 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, 1-1.5% of the system mass of alkaline protease, papain and neutral protease are added to the system respectively, and constant temperature enzymolysis is performed for 6-7 hours. During the reaction, the pH value of the enzymolysis solution is maintained constant between 7 and 8 by adding NaOH solution. After the enzymolysis is completed, the obtained enzymolysis mixture is heated at 100-120° C. for 10-15 minutes to inactivate the enzyme, cooled to room temperature, centrifuged at a speed of 4000-4200 r / min for 30-35 minutes to obtain the supernatant, and the obtained supernatant is freeze-dried to obtain the corn meal polypeptide, which is refrigerated and stored for later use.

[0011] Furthermore, 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.

[0012] Furthermore, the alkaline protease is specifically Novo protease.

[0013] Furthermore, the neutral protease is specifically 1398 neutral protease.

[0014] Compared with the prior art, the present invention has at least the following beneficial effects: 1. The present invention combines chitosan oligosaccharide with L-ascorbic acid through cyclodextrin glycosyltransferase, specifically catalyzes the formation of new glycosidic bonds, and improves the binding degree of ascorbic acid and chitosan oligosaccharide. The composite glycoside with high binding degree can enrich the composite in the leaves and root system of lettuce, reduce ineffective diffusion, and enhance the antioxidant property of the composite glycoside after binding, and reduce the degradation rate. In addition, ascorbic acid has a reducing effect and can reduce the selenium in sodium selenite. Subsequently, chitosan oligosaccharide and selenium are chelated, thereby reducing the content of free selenium in the system, allowing the selenium element to enter the plant in a chelated state, and utilizing the water solubility and biocompatibility of chitosan oligosaccharide to enter the plant leaves faster and be absorbed by the plant, thereby increasing the absorption of selenium by lettuce.

[0015] 2. The present invention uses the composite glycoside and the corn meal polypeptide to load the selenium element in sodium selenite. Various groups in the corn meal polypeptide can directly chelate free selenium, and the composite glycoside composed of ascorbic acid and chitosan oligosaccharide can reduce the selenium in sodium selenite to free selenium that is more easily chelated, and further stabilize the selenium through chitosan oligosaccharide to form a corn meal polypeptide-selenium-glycoside ternary complex with a multi-folding structure, thereby increasing the content of chelated selenium in the spray and making selenium more stable in the environment. At the same time, the corn meal polypeptide also contains polypeptide components that regulate plant growth and development. Such polypeptides that promote plant root growth can be transported to plant leaves and roots faster. Therefore, the selenium element loaded by the corn meal polypeptide can also be transported to the lettuce root system faster and fixed along with the physiological effects of the lettuce, thereby increasing the selenium content in the mature lettuce.

[0016] 3. The present invention combines corn meal polypeptide with sodium dodecylbenzene sulfonate. The charged groups of sodium dodecylbenzene sulfonate can combine with the hydrophobic amino acids contained in the corn meal polypeptide through electrostatic repulsion and micelle encapsulation, thereby changing the defect that the hydrophobic amino acids are easily aggregated and precipitated in an aqueous solution alone, so that the corn meal polypeptide can be evenly dispersed in the aqueous solution and the water solubility of the corn meal polypeptide is improved, so that the chelated selenium added with the corn meal polypeptide can better enter the lettuce leaves and fix the selenium element, thereby increasing the selenium content in the lettuce. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate embodiments of the present disclosure and, together with the description, further serve to explain the principles of the present disclosure and to enable those skilled in the relevant art to make and use the present disclosure.

[0018] Figure 1 This is a flow chart of a method for growing selenium-enriched hydroponic lettuce in a plant factory adopted in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The following is a detailed description of a method for growing selenium-enriched hydroponic lettuce in a plant factory provided by the present invention in combination with the accompanying drawings and specific embodiments. At the same time, it is explained here that in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments, and those skilled in the art may also adopt other alternative methods for some known technologies; and the accompanying drawings are only for a more specific description of the embodiments, and are not intended to specifically limit the present invention.

[0020] Embodiment 1: A method for growing selenium-enriched hydroponic lettuce in a plant factory, such as Figure 1 As shown, the following steps are included: S1: Preparation of complex glycosides S1.1: 2.5 parts by volume of chitosan oligosaccharide was mixed with 10 parts by volume of deionized water, and stirred until dissolved, followed by adding 0.1 parts by volume of L-ascorbic acid, and stirring at 300 r / min at 50°C until completely dissolved; S1.2: Then, the temperature is maintained at 50°C, and 5% of the system mass of cyclodextrin glycosyltransferase is added, and the reaction is carried out for 12 hours. After the reaction is completed, the reaction product is filtered through an ultrafiltration membrane to remove the cyclodextrin glycosyltransferase, and spray-dried to obtain a complex glycoside.

[0021] S2: Preparation of chelated selenium solution S2.1: The corn meal is crushed in a high-speed crusher, and 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, and the corn meal is washed and decolorized at 50°C for 2 hours to obtain decolorized corn meal; The decolorized corn meal was mixed with deionized water at a solid-liquid ratio of 1 g: 10 mL, and the pH value was adjusted to 7. Subsequently, 1% of the system mass of Novo protease, papain and 1398 neutral protease were added to the system, and constant temperature enzymolysis was performed for 6 hours. During the reaction, the pH value of the enzymolysis solution was maintained constant between 7 and 8 by adding NaOH solution. After the enzymolysis was completed, the obtained enzymolysis mixture was heated at 100° C. for 10 minutes to inactivate the enzyme, cooled to room temperature, centrifuged at a speed of 4000 r / min for 30 minutes, and the supernatant was obtained. The obtained supernatant was freeze-dried to obtain corn meal polypeptides, which were refrigerated and stored for later use; Corn meal polypeptide, sodium dodecylbenzene sulfonate and deionized water were mixed in a volume ratio of 10:1:14, heated to 30°C and stirred for 10 minutes, then allowed to stand for 3 minutes, and deionized water was added to adjust the content of corn meal polypeptide in the system to 5 mg / mL, to obtain a corn meal polypeptide solution; S2.2: Add 0.1 wt% gallic acid to the corn meal polypeptide solution, stir magnetically for 30 min, then add 10 mM sodium selenite solution, stir magnetically at 50°C for 3 min, and then cool to room temperature to obtain a mixed solution; S2.3: Mix the complex glycoside and deionized water at a solid-liquid ratio of 1 g:10 mL and stir evenly to obtain a complex glycoside solution; S2.4: Then, the complex glycoside solution is added dropwise to the mixed solution at a rate of 1 mL / s to make the volume ratio of the added complex glycoside solution to the mixed solution be 1:1. Finally, magnetic stirring is performed at 300 r / min for 30 min to obtain a chelated selenium solution.

[0022] S3: Growing lettuce and spraying with chelated selenium solution S3.1: Sow lettuce seeds on a fully soaked sponge and start supplementing light on the second day after germination. The light intensity is 120 μmol / m 2 / s, with a light intensity of 10 h per day, water the seeds once a day within 1 day after germination to keep the seedling sponge moist. 3 days after germination, the light intensity was changed to 180 μmol / m 2 / s, light duration 12h, water once a day with nutrient solution, the nutrient solution is prepared by mixing 236mg / L calcium nitrate tetrahydrate, 400mg / L potassium nitrate, 57mg / L ammonium dihydrogen phosphate, and 123mg / L magnesium sulfate heptahydrate, and keep the sponge moist; S3.2: When the lettuce seeds grow into seedlings and the seedlings have four true leaves, they are moved into seedling planting plates with a light intensity of 180 μmol / m 2 / s, daily light duration 12h, nutrient solution circulated twice a day, each time 1h; S3.3: When the leaves of two seedlings touch each other, move the seedlings into the seedling plate in the middle growth period, and light intensity is 180 μmol / m 2 / s, daily light duration 12h, nutrient solution circulated twice a day, each time 1h; S3.4: Mix the chelated selenium solution with purified water at a volume ratio of 1:500 to obtain a selenium spray. When the leaves of two mid-stage seedlings are in contact with each other, move the mid-stage seedlings into the seedling raising plate at the seedling stage. The light intensity is 180 μmol / m 2 / s, after being moved into the seedling raising plate in the seedling stage, starting from the second day, at 10 am, the selenium spray agent was sprayed on the leaves until the lettuce entered the maturity stage, and the spraying was stopped to obtain selenium-enriched hydroponic lettuce.

[0023] Embodiment 2: A method for growing selenium-enriched hydroponic lettuce in a plant factory, such as Figure 1 As shown, the following steps are included: S1: Preparation of complex glycosides S1.1: 3 parts by volume of chitosan oligosaccharide was mixed with 12 parts by volume of deionized water, and stirred until dissolved, then 0.3 parts by volume of L-ascorbic acid was added, and stirred at 300 r / min at 50°C until completely dissolved; S1.2: Then, the temperature is maintained at 50°C, and 8% of the system mass of cyclodextrin glycosyltransferase is added, and the reaction is carried out for 12 hours. After the reaction is completed, the reaction product is filtered through an ultrafiltration membrane to remove the cyclodextrin glycosyltransferase, and spray-dried to obtain a complex glycoside.

[0024] S2: Preparation of chelated selenium solution S2.1: The corn meal is crushed in a high-speed crusher, and 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, and the corn meal is washed and decolorized at 50°C for 2 hours to obtain decolorized corn meal; The decolorized corn meal was mixed with deionized water at a solid-liquid ratio of 1 g: 12 mL, and the pH value was adjusted to 7. Subsequently, 1.5% of the system mass of Novo protease, papain and 1398 neutral protease were added to the system respectively, and constant temperature enzymolysis was performed for 6 hours. During the reaction, the pH value of the enzymolysis solution was maintained constant between 7 and 8 by adding NaOH solution. After the enzymolysis was completed, the obtained enzymolysis mixture was heated at 100°C for 10 minutes to inactivate the enzyme, cooled to room temperature, centrifuged at a speed of 4000 r / min for 30 minutes, and the supernatant was obtained. The obtained supernatant was freeze-dried to obtain corn meal polypeptides, which were refrigerated and stored for later use; Corn meal polypeptide, sodium dodecylbenzene sulfonate and deionized water were mixed in a volume ratio of 10:3:18, heated to 30°C and stirred for 10 minutes, then allowed to stand for 3 minutes, and deionized water was added to adjust the content of corn meal polypeptide in the system to 5 mg / mL, to obtain a corn meal polypeptide solution; S2.2: Add 0.5 wt% gallic acid to the corn meal polypeptide solution, stir magnetically for 30 min, then add 10 mM sodium selenite solution, stir magnetically at 50°C for 3 min, and then cool to room temperature to obtain a mixed solution; S2.3: Mix the complex glycoside and deionized water at a solid-liquid ratio of 1 g:15 mL and stir evenly to obtain a complex glycoside solution; S2.4: The complex glycoside solution is then added dropwise to the mixed solution at a rate of 1 mL / s to make the volume ratio of the added complex glycoside solution to the mixed solution be 1:1.2. Finally, magnetic stirring is performed at 300 r / min for 30 min to obtain a chelated selenium solution.

[0025] S3: Growing lettuce and spraying with chelated selenium solution S3.1: Sow lettuce seeds on a fully soaked sponge and start supplementing light on the second day after germination. The light intensity is 120 μmol / m 2 / s, with a light intensity of 10 h per day, water the seeds once a day within 1 day after germination to keep the seedling sponge moist. 3 days after germination, the light intensity was changed to 180 μmol / m 2 / s, light duration 12h, water once a day with nutrient solution, the nutrient solution is prepared by mixing 240mg / L calcium nitrate tetrahydrate, 404mg / L potassium nitrate, 60mg / L ammonium dihydrogen phosphate, and 125mg / L magnesium sulfate heptahydrate, and keep the sponge moist; S3.2: When the lettuce seeds grow into seedlings and the seedlings have four true leaves, they are moved into seedling planting plates with a light intensity of 180 μmol / m 2 / s, daily light duration 12h, nutrient solution circulated twice a day, each time 1h; S3.3: When the leaves of two seedlings touch each other, move the seedlings into the seedling plate in the middle growth period, and light intensity is 180 μmol / m 2 / s, daily light duration 12h, nutrient solution circulated twice a day, each time 1h; S3.4: Mix the chelated selenium solution with purified water at a volume ratio of 1:500 to obtain a selenium spray. When the leaves of two mid-stage seedlings are in contact with each other, move the mid-stage seedlings into the seedling raising plate at the seedling stage. The light intensity is 180 μmol / m 2 / s, after being moved into the seedling raising plate in the seedling stage, starting from the second day, at 10 am, the selenium spray agent was sprayed on the leaves until the lettuce entered the maturity stage, and the spraying was stopped to obtain selenium-enriched hydroponic lettuce.

[0026] Embodiment 3: A method for growing selenium-enriched hydroponic lettuce in a plant factory, such as Figure 1 As shown, the following steps are included: S1: Preparation of complex glycosides S1.1: 2.5 parts by volume of chitosan oligosaccharide was mixed with 10 parts by volume of deionized water, and stirred until dissolved, followed by adding 0.1 parts by volume of L-ascorbic acid, and stirring at 350 r / min at 60°C until completely dissolved; S1.2: Then, the temperature is maintained at 60°C, and 5% of the system mass of cyclodextrin glycosyltransferase is added, and the reaction is carried out for 13 hours. After the reaction is completed, the reaction product is filtered through an ultrafiltration membrane to remove the cyclodextrin glycosyltransferase, and spray-dried to obtain a complex glycoside.

[0027] S2: Preparation of chelated selenium solution S2.1: The corn meal is crushed in a high-speed crusher, then passed through an 80-mesh sieve, and decolorized by washing with an acid solution. The pH value of the system is adjusted to 3.5, and the corn meal is washed and decolorized at 50°C for 2.5 hours to obtain decolorized corn meal; The decolorized corn meal was mixed with deionized water at a solid-liquid ratio of 1 g: 10 mL, and the pH value was adjusted to 8. Subsequently, 1% of the system mass of Novo protease, papain and 1398 neutral protease were added to the system, and constant temperature enzymolysis was performed for 6 hours. During the reaction, the pH value of the enzymolysis solution was maintained constant between 7 and 8 by adding NaOH solution. After the enzymolysis was completed, the obtained enzymolysis mixture was heated at 120°C for 15 minutes to inactivate the enzyme, cooled to room temperature, centrifuged at a speed of 4200 r / min for 35 minutes, and the supernatant was obtained. The obtained supernatant was freeze-dried to obtain corn meal polypeptides, which were refrigerated and stored for later use. Corn meal polypeptide, sodium dodecylbenzene sulfonate and deionized water were mixed in a volume ratio of 10:1:14, heated to 30°C and stirred for 10 minutes, then allowed to stand for 3 minutes, and deionized water was added to adjust the content of corn meal polypeptide in the system to 5 mg / mL, to obtain a corn meal polypeptide solution; S2.2: Add 0.1 wt% gallic acid to the corn meal polypeptide solution, add 10 mM sodium selenite solution after magnetic stirring for 35 min, and then magnetically stir at 60°C for 5 min, then cool to room temperature to obtain a mixed solution; S2.3: Mix the complex glycoside and deionized water at a solid-liquid ratio of 1 g:10 mL and stir evenly to obtain a complex glycoside solution; S2.4: Add the complex glycoside solution to the mixed solution at a rate of 3 mL / s to make the volume ratio of the added complex glycoside solution to the mixed solution be 1:1. Finally, stir magnetically at 350 r / min for 40 min to obtain a chelated selenium solution.

[0028] S3: Growing lettuce and spraying with chelated selenium solution S3.1: Sow lettuce seeds on a fully soaked sponge and start supplementing light on the second day after germination. The light intensity is 150 μmol / m 2 / s, 10h of light per day, water once a day within 2 days after seeds germinate, keep the seedling sponge moist, 5 days after seeds germinate, light intensity changed to 220μmol / m 2 / s, light duration 12h, water once a day with nutrient solution, the nutrient solution is prepared by mixing 236mg / L calcium nitrate tetrahydrate, 400mg / L potassium nitrate, 57mg / L ammonium dihydrogen phosphate, and 123mg / L magnesium sulfate heptahydrate, and keep the sponge moist; S3.2: When the lettuce seeds grow into seedlings and the seedlings have four true leaves, they are moved into seedling planting plates with a light intensity of 180 μmol / m 2 / s, daily light duration 12h, nutrient solution circulated 3 times a day, each time 1.5h; S3.3: When the leaves of two seedlings touch each other, move the seedlings into the seedling plate in the middle growth period, and place the light intensity at 180 μmol / m 2 / s, daily light duration 12h, nutrient solution circulated 3 times a day, each time 1.5h; S3.4: Mix the chelated selenium solution and purified water at a volume ratio of 1:550 to obtain a selenium spray. When the leaves of two mid-stage seedlings are in contact with each other, move the mid-stage seedlings into the seedling raising plate at the seedling stage. The light intensity is 220 μmol / m 2 / s, after being moved into the seedling raising plate in the seedling stage, starting from the second day, at 14:00 in the morning, the selenium spray agent was sprayed on the leaves until the lettuce entered the maturity stage, and the spraying was stopped to obtain selenium-enriched hydroponic lettuce.

[0029] Comparative Example 1: Compared with Example 1, the difference of Comparative Example 1 is that step S1 is not performed, and the complex glycoside in step S2.3 is replaced by chitosan oligosaccharide, specifically “S2.3: mixing chitosan oligosaccharide with deionized water at a solid-liquid ratio of 1 g: 10 mL and stirring uniformly to obtain a chitosan oligosaccharide solution; S2.4: Add the chitosan oligosaccharide solution to the mixed solution at a rate of 1 mL / s to make the volume ratio of the chitosan oligosaccharide solution to the mixed solution 1:1, and finally stir magnetically at 300 r / min for 30 min to obtain a chelated selenium solution. The remaining steps remain unchanged.

[0030] Comparative Example 2: Compared with Example 1, the difference of Comparative Example 2 is that step S1 is not performed, and the complex glycoside in step S2.3 is replaced by L-ascorbic acid, specifically, “S2.3: L-ascorbic acid and deionized water are mixed at a solid-liquid ratio of 1 g: 10 mL and stirred to obtain an L-ascorbic acid solution; S2.4: then add L-ascorbic acid solution to the mixed solution at a rate of 1 mL / s to make the volume ratio of the added L-ascorbic acid solution to the mixed solution be 1:1, and finally stir magnetically at 300 r / min for 30 min to obtain a chelated selenium solution. The remaining steps remain unchanged.

[0031] Comparative Example 3: Compared with Example 1, the difference of Comparative Example 3 is that step S2.3 and step S2.4 are not performed, and the mixed solution is directly added as a chelated selenium solution in step S3.4, specifically "S3.4: the mixed solution is mixed with purified water at a volume ratio of 1:500 to obtain a selenium spray agent, and when the leaves of two mid-stage seedlings are in contact with each other, the mid-stage seedlings are moved into the seedling raising plate at the seedling stage, and the light intensity is 180 μmol / m 2 / s, after being moved into the seedling raising plate in the seedling stage, starting from the second day, at 10 a.m., the selenium spray agent is sprayed on the leaves until the lettuce enters the maturity stage, and the spraying is stopped to obtain selenium-enriched hydroponic lettuce. The other steps remain unchanged.

[0032] Comparative Example 4: Compared with Example 1, the difference of Comparative Example 4 is that step S2.1 is not performed, and in step S2.2, the corn meal polypeptide solution is not added, but the complex glycoside solution is added, specifically, "S2: preparing the chelated selenium solution S2.1: Mix the complex glycoside and deionized water at a solid-liquid ratio of 1 g:10 mL and stir evenly to obtain a complex glycoside solution; S2.2: add 0.1wt% gallic acid to the complex glycoside solution, stir magnetically for 30 min, then add 10mM sodium selenite solution, stir magnetically at 50°C for 3 min, then cool to room temperature to obtain a chelated selenium solution. The remaining steps remain unchanged.

[0033] Comparative Example 5: Compared with Example 1, the difference of Comparative Example 5 is that sodium dodecylbenzene sulfonate is not added in step S2.1, specifically, "S2.1: placing corn meal in a high-speed grinder for grinding, then passing through an 80-mesh sieve, decolorizing by washing with an acid solution, adjusting the pH value of the system to 3, washing and decolorizing at 50° C. for 2 hours, to obtain decolorized corn meal; The decolorized corn meal was mixed with deionized water at a solid-liquid ratio of 1 g: 10 mL, and the pH value was adjusted to 7. Subsequently, 1% of the system mass of Novo protease, papain and 1398 neutral protease were added to the system, and constant temperature enzymolysis was performed for 6 hours. During the reaction, the pH value of the enzymolysis solution was maintained constant between 7 and 8 by adding NaOH solution. After the enzymolysis was completed, the obtained enzymolysis mixture was heated at 100° C. for 10 minutes to inactivate the enzyme, cooled to room temperature, centrifuged at a speed of 4000 r / min for 30 minutes, and the supernatant was obtained. The obtained supernatant was freeze-dried to obtain corn meal polypeptides, which were refrigerated and stored for later use; The corn meal polypeptide was mixed with deionized water, heated to 30°C and stirred for 10 minutes, then allowed to stand for 3 minutes, and deionized water was added to adjust the content of the corn meal polypeptide in the system to 5 mg / mL to obtain a corn meal polypeptide solution. The other steps remained unchanged.

[0034] Comparative Example 6: The selenium spraying agent in step S3 is replaced with a sodium selenite solution, and the concentration of the sodium selenite solution is controlled to be 10 mg / L, specifically: Lettuce seeds were sown on a fully soaked sponge and supplemented with light on the second day after germination, with a light intensity of 120 μmol / m 2 / s, 10h of light per day, water once a day within 1 day after the seeds germinate, keep the seedling sponge moist, and 3 days after the seeds germinate, the light intensity is changed to 180μmol / m 2 / s, light duration 12h, water once a day with nutrient solution, the nutrient solution is prepared by mixing 236mg / L calcium nitrate tetrahydrate, 400mg / L potassium nitrate, 57mg / L ammonium dihydrogen phosphate, and 123mg / L magnesium sulfate heptahydrate, and keep the sponge moist; When the lettuce seeds grew into seedlings and the seedlings had four true leaves, they were moved into seedling planting plates with a light intensity of 180 μmol / m 2 / s, daily light duration 12h, nutrient solution circulated twice a day, each time 1h; When the leaves of two seedlings touch each other, the seedlings are moved into the seedling plate in the middle growth period, and the light intensity is 180 μmol / m 2 / s, daily light duration 12h, nutrient solution circulated twice a day, each time 1h; When the leaves of two mid-stage seedlings touch each other, move the mid-stage seedlings into the seedling raising plate at the seedling stage, and light intensity is 180 μmol / m 2 / s, after being moved into the seedling plate in the seedling stage, starting from the second day, at 10 am, 10 mg / L sodium selenite solution was sprayed on the leaves until the lettuce entered the maturity stage, and then spraying was stopped to obtain selenium-enriched hydroponic lettuce.

[0035] After sowing lettuce seeds on a fully soaked sponge, 10 sponges sown with lettuce seeds were grouped together, and a total of 9 groups of sponges were cultivated according to the lettuce planting methods of Examples 1-3 and Comparative Examples 1-6. After the lettuces were 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 HPLC-ICP-MS, as shown in Table 1.

[0036] 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

[0037] Table 1

[0038] The average selenium content of the mature lettuces of Examples 1-3 and Comparative Examples 1-6 is shown in Table 2.

[0039] Table 2

[0040] The proportion of free selenium in the chelated selenium solutions of Examples 1-3 and Comparative Examples 1-4 was detected, and the free selenium and total selenium contents were detected by high performance liquid chromatography-inductively coupled plasma mass spectrometry, respectively. , the results are shown in Table 3.

[0041] Table 3

[0042] It can be seen that the selenium conversion rate of Examples 1-3 is 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%. The selenium conversion rate and the average selenium content are all higher than those of the comparative example, while the proportion of free selenium is all lower than that of the comparative example. It can be seen that the hydroponic lettuce planting method of the present invention has a higher selenium conversion rate, and the obtained agricultural product lettuce has a higher selenium content. Moreover, the chelated selenium solution prepared by the method recorded in the present invention has a lower proportion of free selenium and more chelated selenium components, so it is easier to be absorbed by lettuce. It can be seen that the proportion of chelated selenium components is higher, which also increases the selenium content in mature lettuce to a certain extent, and can also prove from the side that chelated selenium is easier to absorb by lettuce.

[0043] In Comparative Examples 1-4 of the present invention, L-ascorbic acid, chitosan oligosaccharide, complex glycoside and corn meal polypeptide were respectively removed from the preparation of the chelated selenium solution, indicating that the above ingredients are effective in 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 effect that can be achieved by a single ingredient is not as good as that achieved by the synergistic ingredients.

[0044] The selenium conversion rate and selenium content of Comparative Example 5 of the present invention are lower than those of the embodiment, indicating that after sodium dodecylbenzene sulfonate is combined with corn meal polypeptide, the water solubility of corn meal polypeptide can be improved, thereby improving the selenium conversion rate.

[0045] Comparative Example 6 of the present invention is lettuce obtained by directly using sodium selenite as a leaf spray agent. The average selenium content in the lettuce is only 0.13 mg / kg, and the selenium conversion rate is 31.8%. It can be seen that when sodium selenite is directly used for spraying the leaves, the absorption rate and conversion ability of the lettuce for selenium are not as good as the effects achieved by the present invention.

[0046] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for growing selenium-enriched hydroponic lettuce in a plant factory, characterized in that: The steps include: S1: Preparation of complex glycosides The chitosan oligosaccharide is mixed with deionized water and stirred until dissolved, then L-ascorbic acid is added and stirred to dissolve, and then cyclodextrin glycosyltransferase is added, and the reaction product is filtered through an ultrafiltration membrane to remove the cyclodextrin glycosyltransferase to obtain a complex glycoside; S2: Preparation of chelated selenium solution Mix corn meal polypeptide, sodium dodecylbenzene sulfonate and deionized water, heat and stir to obtain a corn meal polypeptide solution, add gallic acid to the corn meal polypeptide solution, add sodium selenite solution after magnetic stirring to obtain a mixed solution, mix complex glycoside with deionized water to obtain a complex glycoside solution, and then drop the complex glycoside solution into the mixed solution to obtain a chelated selenium solution; S3: Growing lettuce and spraying with chelated selenium solution Lettuce seeds are sown on a fully soaked sponge. When the lettuce seeds grow into seedlings, the seedlings are moved into a seedling planting plate. When two leaves of the seedlings are in contact with each other, the seedlings are moved into a seedling raising plate in the middle growth stage. When two leaves of the mid-stage seedlings are in contact with each other, the mid-stage seedlings are moved into a seedling raising plate in the seedling stage. A chelated selenium solution is made into a selenium spray, and the selenium spray is sprayed on the leaves from the second day until they mature, thereby obtaining selenium-enriched hydroponic lettuce.

2. The method for planting selenium-enriched hydroponic lettuce in a plant factory according to claim 1, characterized in that: Step S1: preparing a complex glycoside, comprising the following steps: S1.1: Mix 2.5-3 parts by volume of chitosan oligosaccharide 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 at 50-60°C until completely dissolved; S1.2: Then, the temperature is maintained at 50-60°C, and 5-8% of the system mass of cyclodextrin glycosyltransferase is added, and the reaction is carried out for 12-13 hours. After the reaction is completed, the reaction product is filtered through an ultrafiltration membrane to remove the cyclodextrin glycosyltransferase, and spray-dried to obtain a complex glycoside.

3. The method for planting selenium-enriched hydroponic lettuce in a plant factory according to claim 2, characterized in that: Step S2 prepares a chelated selenium solution, comprising the following steps: S2.1: corn meal polypeptide, sodium dodecylbenzene sulfonate and deionized water are mixed in a volume ratio of 10:(1-3):(14-18), heated to 30-40°C and stirred for 10-15 minutes, then allowed to stand for 3-5 minutes, and deionized water is added to adjust the content of corn meal polypeptide in the system to 5 mg / mL, thereby obtaining a corn meal polypeptide solution; S2.2: Add 0.1-0.5 wt% gallic acid to the corn meal polypeptide solution, stir magnetically for 30-35 min, then add 10 mM sodium selenite solution, stir magnetically at 50-60°C for 3-5 min, then cool to room temperature to obtain a mixed solution; S2.3: Mix the complex glycoside and deionized water at a solid-liquid ratio of 1 g: (10-15) mL and stir evenly to obtain a complex glycoside solution; S2.4: Then add the complex glycoside solution to the mixed solution at a rate of 1-3 mL / s to make the volume ratio of the added complex glycoside solution to the mixed solution be 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 method for planting selenium-enriched hydroponic lettuce in a plant factory according to claim 3, characterized in that: Step S3, culturing lettuce and spraying the chelated selenium solution, comprises the following steps: S3.1: Sow lettuce seeds on a fully soaked sponge and start supplementing light on the second day after germination. The light intensity is 120-150 μmol / m 2 / s, 10h of light per day, water once a day within 1-2 days after the seeds germinate, keep the seedling sponge moist, 3-5 days after the seeds germinate, change the light intensity to 180-220μmol / m 2 / s, photoperiod 12h, 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, move the seedlings into seedling planting plates and place them under a light intensity of 180-220 μmol / m 2 / s, daily light duration 12h, nutrient solution circulated 2-3 times a day, each time 1-1.5h; S3.3: When the leaves of two seedlings touch each other, move the seedlings into the seedling plate in the middle growth period, and light intensity is 180-220 μmol / m 2 / s, daily light duration 12h, nutrient solution circulated 2-3 times a day, each time 1-1.5h; S3.4: Mix the chelated selenium solution with purified water at a volume ratio of 1:500-550 to obtain a selenium spray. When the leaves of two mid-stage seedlings are in contact with each other, move the mid-stage seedlings into the seedling raising plate at the seedling stage. The light intensity is 180-220 μmol / m 2 / s, after being moved into the seedling raising plate in the seedling stage, starting from the second day, at 10-11 am, the selenium spray agent is sprayed on the leaves until the lettuce enters the maturity stage, and the spraying is stopped to obtain selenium-enriched hydroponic lettuce.

5. The method for planting selenium-enriched hydroponic lettuce in a plant factory according to claim 3, characterized in that: The preparation method of corn meal polypeptide comprises the following steps: The corn meal is placed in a high-speed grinder for grinding, then passed through an 80-mesh sieve, 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 hours 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, 1-1.5% of the system mass of alkaline protease, papain and neutral protease are added to the system respectively, and constant temperature enzymolysis is performed for 6-7 hours. During the reaction, the pH value of the enzymolysis solution is maintained constant between 7 and 8 by adding NaOH solution. After the enzymolysis is completed, the obtained enzymolysis mixture is heated at 100-120° C. for 10-15 minutes to inactivate the enzyme, cooled to room temperature, centrifuged at a speed of 4000-4200 r / min for 30-35 minutes to obtain the supernatant, and the obtained supernatant is freeze-dried to obtain the corn meal polypeptide, which is refrigerated and stored for later use.

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

8. The method for planting 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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