A method and system for improving pre-harvest and post-harvest storage quality of hydroponically grown leafy greens

Abstract

The present application relates to the technical field of vegetable cultivation, and discloses a method and system for improving the pre-harvest and post-harvest storage quality of water-cultivated lettuce. In view of the fact that the pre-harvest cultivation and post-harvest storage links are disconnected in the prior art, the light environment regulation consumes high energy, the nutrient solution management is prone to cause nitrate accumulation, chemical preservation exists food safety residue risk, and the existing preservation mode is difficult to adapt to the core problem of large-scale standardized production of a plant factory, the present application realizes integrated improvement of pre-harvest quality optimization and post-harvest preservation gain of lettuce by short-term synergistic regulation of the temperature difference between the aboveground part and the underground part and the concentration of the nutrient solution betaine before harvesting. The present technology does not use chemical preservatives throughout the whole process, has no residue risk, is low in energy consumption, simple in operation, can be directly integrated into the existing plant factory production system, is suitable for large-scale and standardized production of lettuce, and has safety and economy.

Description

Technical Field

[0001] This invention belongs to the field of vegetable cultivation technology, specifically relating to a method and system for improving the pre-harvest and post-harvest storage quality of hydroponic lettuce. Background Technology

[0002] Lettuce, a widely cultivated leafy vegetable for fresh consumption worldwide, enjoys a continuously growing market demand due to its crisp texture, rich nutrients, and versatility for both raw and cooked consumption. Plant factories, with their closed and controlled environments, can overcome seasonal, geographical, and climatic limitations, enabling year-round, continuous, standardized, and clean production of lettuce. This effectively avoids quality risks associated with open-field cultivation, such as pests, diseases, and environmental pollution, and has become one of the core models for large-scale, high-quality lettuce cultivation. The lettuce produced through these factories is also a mainstream supply category in the fresh food market due to its high cleanliness and uniform commercial characteristics.

[0003] Lettuce leaves have a high water content and active metabolism, making them highly susceptible to wilting, yellowing, nutrient loss, and microbial invasion after harvest, leading to a rapid decline in commercial value. Pre-harvest treatment is a key strategy for proactively controlling post-harvest quality. Its core lies in using specific agronomic measures or exogenous interventions to induce beneficial changes in the physiological and biochemical characteristics of the crop during its pre-harvest growth and development stage, thereby increasing its post-harvest storability, nutritional quality, and commercial value.

[0004] Currently, research on the formation of pre- and post-harvest quality in lettuce mainly focuses on light environment control, nutrient solution management, and the addition of bioactive substances. While these three technologies are effective in increasing yield, improving nutritional quality (such as vitamin and antioxidant content), and extending shelf life, they each face their own bottlenecks: light environment control, although precise, suffers from high energy costs, complex light quality ratios, and is prone to causing physiological disorders in plants; nutrient solution management, while efficient, is prone to nitrate accumulation due to nutrient imbalances, lacks real-time and accurate monitoring methods, and waste liquid treatment also faces environmental pressures; and while the addition of bioactive substances can effectively induce stress resistance, there are risks of food safety residues, difficulty in controlling dosage effects, and unstable effects.

[0005] In the post-harvest storage of lettuce, existing technologies mostly rely on low-temperature refrigeration as the core method, supplemented by modified atmosphere packaging, chemical preservative treatment, and physical sterilization to extend shelf life. However, auxiliary methods such as modified atmosphere packaging and chemical preservation have problems such as high packaging costs, complex operation procedures, chemical residue risks, and poor adaptability to large-scale applications, making it difficult to form an efficient connection with the standardized and large-scale production and distribution system of lettuce in plant factories.

[0006] Existing technologies generally suffer from a disconnect between pre-harvest planting and post-harvest storage, failing to establish a synergistic system for targeted pre-harvest nutrient regulation and precise post-harvest temperature management. This prevents the simultaneous improvement of pre-harvest commercial quality and post-harvest storage performance of lettuce. Furthermore, existing technologies either struggle to overcome the technical bottleneck of rapid post-harvest deterioration in lettuce or suffer from drawbacks such as food safety risks, high application costs, and difficulties in large-scale implementation. These limitations fail to meet the demands of the plant factory lettuce industry for high-quality, long-shelf-life, high-safety, and fully controllable production and distribution. Therefore, there is an urgent need to develop technical solutions that can synergistically optimize pre-harvest nutrient management and post-harvest temperature control for lettuce, addressing the numerous shortcomings of existing technologies.

[0007] Furthermore, on the one hand, there are differences in understanding among those skilled in the art; on the other hand, the inventors studied a large number of documents and patents when making this invention, but due to space limitations, not all details and contents were listed in detail. However, this does not mean that the present invention does not possess the features of these prior art. On the contrary, the present invention already possesses all the features of the prior art, and the applicant reserves the right to add relevant prior art to the background art. Summary of the Invention

[0008] This invention belongs to the field of vegetable cultivation technology, specifically relating to a method and system for improving the pre-harvest and post-harvest storage quality of hydroponic lettuce.

[0009] To address the aforementioned technical problems, one objective of this invention is to provide a method for improving the pre-harvest and post-harvest storage quality of hydroponic lettuce, comprising the following steps: Light intensity 150~200 μmol m -2 s -1 Under conditions of full-spectrum white light, a photoperiod of 16 / 8 h, and a relative humidity of 60%–70%, lettuce is hydroponically cultivated by adding 2–8 mM betaine to the nutrient solution at least 7 days before harvest. Preferably, a light intensity of 200 μmol / L is used. m -2 s -1 Full-spectrum white light. Preferably, the amount of betaine added is 2 mM. The amount of betaine added is 4 mM. The amount of betaine added is 6 mM. The amount of betaine added is 8 mM.

[0010] According to a preferred embodiment, the method further includes: subjecting the aboveground and underground parts of the lettuce to a temperature difference treatment at least 7 days before harvesting, with the temperature difference ranging from 13 to 21°C. Preferably, the temperature difference range is 13°C. Preferably, the temperature difference range is 17°C. Preferably, the temperature difference range is 21°C.

[0011] According to a preferred embodiment, the temperature of the above-ground part of the lettuce is 37°C. The temperature range of the underground part of the lettuce is 16~24°C. Preferably, the temperature of the underground part of the lettuce is 16°C. Preferably, the temperature of the underground part of the lettuce is 20°C. Preferably, the temperature of the underground part of the lettuce is 24°C.

[0012] According to a preferred embodiment, the pH of the nutrient solution is maintained at 5.7 ± 0.1, and the EC value is maintained at 1.8 ± 0.1 mS. cm -1 .

[0013] According to a preferred embodiment, the nutrient solution contains nutrients at concentrations of: N ≥ 7 mM L -1 P2O5 ≥ 0.1 mM L -1 K2O≥2 mM L -1 Mg≥0.4 mM L -1 S≥0.6 mM L -1 Fe≥0.07 mM L -1 Mn≥0.09 mM L -1 B≥0.05 mM L -1 Zn≥0.01 mM L -1 Mo≥6×10 -4 mM L -1 Ca≥2.5 mM L -1 .

[0014] According to a preferred embodiment, in order to improve the quality of lettuce before and after harvest and for post-harvest storage, lettuce is treated with 2-8 mM betaine and temperature difference 7 days before harvest.

[0015] According to a preferred embodiment, the lettuce is 'Zhong Sheng No. 1' hydroponic lettuce.

[0016] According to a preferred embodiment, lettuce that has undergone pre-harvest co-regulation treatment is individually packaged in vegetable preservation bags and stored at 4°C in the dark.

[0017] like Figure 7 As shown, one of the objectives of this invention is to provide a system for achieving the above-mentioned method of improving the pre-harvest and post-harvest storage quality of hydroponic lettuce, comprising: Temperature control units, installed above and below ground, are used to treat the temperature difference between the above-ground and underground parts of the lettuce at least 7 days before harvesting, with a temperature difference range of 13~21℃. The nutrient solution circulation unit is used to circulate nutrient solution to lettuce and add 2-8 mM betaine to the nutrient solution at least 7 days before the lettuce is harvested. The illumination control unit is used to provide an illumination intensity of 150~200 μmol. m -2 s -1 Full-spectrum white light; The environmental monitoring unit is used to monitor environmental temperature, rhizosphere temperature, light intensity, relative humidity, and nutrient solution pH and EC values ​​in real time. The central control unit communicates with the environmental monitoring unit, connects to the light control unit, the nutrient solution circulation unit, and the temperature control unit, and is configured to: when receiving the detection signal from the environmental monitoring unit, adjust the operating parameters of each unit based on the set parameters so that the light control unit, the nutrient solution circulation unit, and the temperature control unit can maintain the growth conditions required for the lettuce growth stage.

[0018] According to a preferred embodiment, the illumination control unit is a full-band white spectrum LED tube whose light intensity and spectrum can be controlled by a central control unit.

[0019] According to a preferred embodiment, the light, humidity, and nutrient solution formula of the preset cultivation conditions is provided starting 14 days after transplanting the lettuce. Preferably, the preset cultivation conditions of light, humidity, and nutrient solution formula are provided starting after the lettuce enters the rosette stage. More preferably, transplanting is carried out 15 days after the lettuce germinates and grows, and treatment begins 14 days after transplanting.

[0020] According to a preferred embodiment, the nutrient solution circulation unit includes a water storage tank, a chiller, a water pump, a filter, a cultivation trough, an inlet pipe, a drain pipe, and a temperature recorder; the water storage tank is connected to the inlet pipe of the cultivation trough through the water pump and the filter, and the drain pipe of the cultivation trough is connected to the water storage tank to form a closed circulation loop.

[0021] According to a preferred embodiment, the temperature control unit is equipped with a chiller connected to a water storage tank for regulating the temperature of the nutrient solution in the tank. A temperature recorder is installed in the rhizosphere region of the cultivation trough to collect rhizosphere temperature data in real time and transmit it to the central control unit.

[0022] According to a preferred embodiment, the environmental monitoring unit includes an air temperature and humidity sensor, a rhizosphere temperature sensor, a light intensity sensor, a nutrient solution pH sensor, and a nutrient solution EC sensor, all of which are communicatively connected to the central control unit.

[0023] One of the objectives of this invention is to provide the above-mentioned method for improving the pre-harvest and post-harvest storage quality of hydroponic lettuce for use in slowing down the rate of nutrient degradation of lettuce during storage and increasing its shelf life.

[0024] According to a preferred embodiment, the lettuce contains soluble sugars, soluble proteins, and total flavonoids. The improved shelf life is specifically achieved through a reduction in nitrate content.

[0025] In recent years, the role of pre-harvest cultivation environment in improving the post-harvest performance of agricultural products has received increasing attention from both academia and industry. Among numerous environmental factors, temperature plays a central role. The rise of controlled-environment agriculture, such as plant factories, has provided unprecedented possibilities for precise temperature control. Beyond conventional appropriate temperature management, pre-harvest low temperatures, as an abiotic stress factor, have a dual effect: on the one hand, they may inhibit growth and induce chilling injury symptoms; on the other hand, increasing evidence suggests that moderate, controlled low-temperature exposure can serve as an effective ecological stimulus or pre-adaptive signal, initiating and optimizing stress resistance and quality-forming metabolic pathways within the plant before harvest. Based on this, this invention achieves stable storage and quality control of lettuce after harvest by adjusting the temperature supply above and below ground and coupling nutrient solutions, through transient growth regulation before harvest.

[0026] Twenty-eight days after transplanting, when the lettuce was growing normally, a 7-day pre-harvest intensive treatment was initiated: a constant aboveground temperature of 37°C and a precise rhizosphere temperature of 20°C were set to create an optimal temperature difference of 17°C; 6 mM betaine was added to the modified hydroponic nutrient solution, along with 200 μmol of full-spectrum white light. m - ² s - ¹ Environmental conditions: photoperiod 16 / 8 h, relative humidity 60%~70%. This invention can significantly improve the dry matter accumulation efficiency of lettuce, greatly increase the content of soluble sugar, soluble protein and total flavonoids, while reducing the nitrate content to a level far below the national standard. After 6 days of storage at 4℃ in the dark, lettuce treated with the synergistic method showed a weight loss rate of only 4.99% and a decrease in soluble sugar of only 2.82%, effectively delaying post-harvest senescence and nutrient degradation.

[0027] Based on relevant experimental results regarding lettuce growth traits, core nutritional quality indicators, and post-harvest storage characteristics, it can be seen that in the pre-harvest treatment stage of hydroponic lettuce, precise regulation of rhizosphere temperature using temperature control equipment induces physiological stress responses in the plants by utilizing changes in underground temperature, significantly improving the nutritional quality of lettuce and delaying post-harvest senescence. This approach achieves quality improvement using a single variable.

[0028] In existing technologies, hydroponic cultivation of lettuce and other crops typically involves continuously adding glycine betaine to the nutrient solution throughout the entire crop growth cycle. This relies on betaine to replace some of the inorganic nitrogen source, reducing leaf necrosis and improving post-harvest storage quality. However, this method requires maintaining an effective concentration of betaine in the nutrient solution for an extended period, resulting in high consumption of the agent, cumbersome daily water and fertilizer management, and reliance solely on betaine as a single osmotic regulator for preservation without supporting environmental control measures to enhance its effectiveness, thus limiting its potential for improved preservation. Furthermore, there is a lack of observation and research on post-harvest storage. This invention breaks away from the conventional approach of continuously applying betaine throughout the entire growth cycle. It applies glycine betaine in a short period, equivalent to the amount used in conventional techniques, only a few days before lettuce harvest. This significantly shortens the application cycle and reduces the input of betaine raw materials and the workload of water and fertilizer maintenance. Simultaneously, it incorporates limited pre-harvest light intensity supplementation and synergistic regulation of root and aboveground temperature differences, constructing a composite preservation system with short-term exogenous betaine, light-enriched endogenous stress-resistance substances, and root-stem temperature difference-regulated plant metabolism. Appropriate light intensity before harvest promotes the accumulation of antioxidants such as soluble sugars and ascorbic acid in lettuce leaves, strengthening the plant's pre-harvest resilience. Significant temperature differences in the roots and stems stabilize root absorption activity, inhibit senescence-related ethylene production, and reduce membrane lipid peroxidation damage during storage. Exogenous betaine plays a role in osmotic protection, stabilizing chloroplast structure, and scavenging light-induced reactive oxygen species. Light, temperature differences, and betaine regulatory pathways are complementary, without any physiological antagonistic conflict. Observations show that this technical solution can effectively inhibit leaf margin necrosis, leaf yellowing, browning, and senescence during post-harvest storage. Water loss and wilting are minimal throughout the storage process, effectively extending the shelf life of lettuce. The effect on maintaining the commercial appearance, crispness, and nutritional components of lettuce during storage is comparable to or even superior to existing long-term betaine-addition treatments.

[0029] Specifically, such as Figure 1 As shown, after lettuce has grown normally to the 28-day mark, the cultivation method involved in this invention is provided to lettuce. It has good compatibility and can be used in conjunction with technologies such as light environment optimization, precise management of nutrient solution and application of exogenous bioactive substances. It can effectively improve the quality of lettuce and slow down the rate of quality degradation after harvesting and storage. It can also create a suitable rhizosphere microenvironment for lettuce in extreme high temperature environments, effectively alleviating the quality deterioration caused by adverse stress. Attached Figure Description

[0030] Figure 1 This is a diagram of the growth process of lettuce after pre-harvest synergistic regulation treatment in Example 1 of the present invention. From left to right, the diagram shows lettuce transplanting, before treatment, temperature difference between aboveground and underground parts and betaine treatment. Figure 2This is a diagram of the plant growth status of lettuce after pre-harvest synergistic regulation treatment in Embodiment 1 of the present invention. It is used to show the overall growth morphology and growth performance of lettuce after 7 days of treatment with aboveground-rhizosphere temperature difference. Among them, (a) is the phenotype of lettuce at harvest after no pre-harvest treatment, (b) is the phenotype of lettuce after storage for 6 days after no pre-harvest treatment, (c) is the phenotype of lettuce at harvest after pre-harvest synergistic treatment, and (d) is the phenotype of lettuce after storage for 6 days after pre-harvest synergistic treatment. Figure 3 This is a bar chart illustrating the effects of different aboveground-underground temperature differences on the pre-harvest growth and quality indicators of lettuce in Example 1 of the present invention. (a) is a comparison chart of the fresh weight of a single lettuce plant under different temperature difference treatments; (b) is a comparison chart of the dry weight of a single lettuce plant under different temperature difference treatments; (c) is a comparison chart of the soluble sugar content of lettuce under different temperature difference treatments; (d) is a comparison chart of the soluble protein content of lettuce under different temperature difference treatments; (e) is a comparison chart of the total flavonoid content of lettuce under different temperature difference treatments; and (f) is a comparison chart of the nitrate content of lettuce under different temperature difference treatments. Figure 4 This is a comparison chart of the quality indicators of lettuce after different aboveground-rhizosphere temperature differences in Example 1 of the present invention, stored at 4℃ in the dark for 6 days. It is used to show the effects of three temperature difference treatments of 13℃, 17℃, and 21℃ on the changes in postharvest weight loss, soluble sugar, soluble protein, total flavonoids, and nitrate content of lettuce. Among them, (a) is a comparison chart of the weight loss rate of lettuce after storage under different temperature difference treatments; (b) is a comparison chart of the nitrate content of lettuce after storage under different temperature difference treatments; (c) is a comparison chart of the soluble sugar content of lettuce after storage under different temperature difference treatments; (d) is a comparison chart of the soluble protein content of lettuce after storage under different temperature difference treatments; and (e) is a comparison chart of the total flavonoid content of lettuce after storage under different temperature difference treatments. Figure 5 This is a bar chart showing the effects of different betaine concentrations on the pre-harvest growth and quality indicators of lettuce in Example 2 of the present invention. (a) is a comparison of the fresh weight of a single lettuce plant under different betaine concentrations; (b) is a comparison of the dry weight of a single lettuce plant under different betaine concentrations; (c) is a comparison of the soluble sugar content of lettuce under different betaine concentrations; (d) is a comparison of the soluble protein content of lettuce under different betaine concentrations; (e) is a comparison of the total flavonoid content of lettuce under different betaine concentrations; and (f) is a comparison of the nitrate content of lettuce under different betaine concentrations. Figure 6This study presents a comparison of quality indicators of lettuce treated with different betaine concentrations and stored at 4℃ in the dark for 6 days. The effects of five betaine concentrations (0 mM, 2 mM, 4 mM, 6 mM, and 8 mM) on postharvest weight loss, soluble sugar, soluble protein, total flavonoids, and nitrate content are shown in the graphs. (a) shows the effect of different betaine concentrations on weight loss after storage; (b) shows the effect of different betaine concentrations on nitrate content; (c) shows the effect of different betaine concentrations on soluble sugar content; (d) shows the effect of different betaine concentrations on soluble protein content; and (e) shows the effect of different betaine concentrations on total flavonoid content. Figure 7 This refers to a cultivation system that can be used with the cultivation method involved in this invention. Detailed Implementation

[0031] In the description of this invention, terminology is used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly defined.

[0032] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials, reagents or instruments used, unless otherwise specified by the manufacturer, are all commercially available reagents and materials; the conditions not specified in the examples are all carried out according to conventional conditions or conditions recommended by the manufacturer. At the same time, the present invention does not limit the source of the raw materials used. Unless otherwise specified, the raw materials used in the present invention are all commercially available products in this technical field.

[0033] The following examples use 8 mM of N, 1 mM of P, 5 mM of K, 2 mM of Ca, 1 mM of Mg, 1 mM of S, 80 μM of Fe, 14 μM of B, 5 μM of Mn, 0.7 μM of Cu, 4.9 μM of Mo, and 3 μM of Zn [the concentrations of each component are consistent with those described in "Pre-harvest nitrogen limitation and continuous lighting improve the quality and flavor of lettuce (Lactuca sativa L.) under hydroponic conditions in greenhouse."].

[0034] Example 1: Effects of different aboveground-underground temperature differences on lettuce growth and quality This embodiment provides a method for cultivating lettuce after the normal 28-day cultivation period.

[0035] 1. Test Methods (1) Seedling raising Place filter paper in the germination box, moisten the filter paper with pure water, and then remove the air between the filter paper and the germination box. Arrange the 'Zhong Sheng No. 1' seeds evenly on the moistened filter paper and germinate them in a dark environment at 20℃ until the seeds show white sprouts (time is 30~38 hours).

[0036] Select uniformly growing, sprouting seeds and sow them into the small hole in the center of a 2×2×2 cm black sponge block that has been pre-soaked in water. Incubate the seeds at an ambient temperature of 24℃ and a light intensity of 150 μmol·m⁻². -2 ·s -1 Under an environment with a photoperiod of 16 / 8 h and a relative humidity of 60-70%, the culture was carried out for 14 days, during which the nutrient solution was added every 2 days and replaced every 7 days. The nutrient solution, modified from a classic hydroponics formula, contained N ≥ 7 mM·L. -1 P2O5 ≥ 0.1 mM·L -1 K2O≥2 mM·L -1 Mg≥0.4mM·L -1 S≥0.6 mM·L -1 Fe≥0.07 mM·L -1 Mn≥0.09 mM·L -1 B≥0.05 mM·L -1 Zn≥0.01 mM·L -1 Mo≥6×10 -4 mM·L -1 Ca ≥ 2.5 mM·L -1 The nutrient solution was set to pH 5.7 and EC 1.8 mS·cm. -1 .

[0037] (2) Transplanting To minimize root damage to lettuce and avoid errors caused by growth, lettuce seedlings with uniform growth, no yellowing leaves, and no pests or diseases were selected and transplanted into 6-cell planting trays. The ambient temperature was set at 24℃ and the light intensity at 200 μmol·m². -2 ·s -1 Under an environment with a photoperiod of 16 / 8 h and a relative humidity of 60-70%, the nutrient solution was replenished every 2 days for 14 days, during which the nutrient solution was replaced once. Then, the temperature difference treatment experiment of the aboveground and underground parts was carried out. The specific temperature settings are shown in Table 1, and other culture conditions were not changed.

[0038] After treatment, the fresh weight and dry weight of plants in each treatment group were measured, and relevant physiological indicators were analyzed. Lettuce samples used for storage experiments were individually packaged in vegetable preservation bags and stored at 4℃ in the dark for 6 days, after which their weight loss rate and physiological indicators were measured.

[0039] Table 1 Temperature difference between above-ground and underground parts

[0040] 2. Test Results This invention systematically studies the effects of rhizosphere temperature regulation on the growth, nutritional quality, and safety of lettuce by setting three temperature gradients of 13℃, 17℃, and 21℃ for the aboveground and underground parts.

[0041] Figure 2 It is evident from the data that there are significant differences in phenotypic changes between untreated and treated lettuce at the time of harvest and after 6 days of storage.

[0042] Figure 3 a and 3b indicate that, in terms of growth and yield, lettuce growth was significantly inhibited at a temperature difference of 13℃, with the lowest values ​​for both fresh and dry weight per plant among the three treatments, at 90.92 g and 5.11 g, respectively, and a dry matter content of only 5.62%. At a temperature difference of 17℃, lettuce dry matter accumulation efficiency reached its peak, with a dry weight per plant of 7.72 g, significantly higher than 13℃ by 51.08% and higher than 21℃ by 22.35%, and a dry matter content as high as 7.06%, which are 1.26 times and 1.40 times higher than at temperature differences of 13℃ and 21℃, respectively. Under the 21℃ treatment, lettuce had the highest fresh weight per plant, reaching 125.41 g, but the dry weight decreased by 18.26% compared to 17℃, and the dry matter content dropped to the lowest of 5.03%, showing obvious signs of bloating, indicating that photosynthetic products were used more for maintaining respiration than for dry matter accumulation.

[0043] Figure 3c~f indicates that, in terms of nutritional quality, the effect of rhizosphere temperature on the main nutrients in lettuce shows a trend of first increasing and then decreasing. Under the 17℃ temperature difference treatment, the soluble sugar content reached 1184.42 mg / 100 g, an increase of 24.00% compared to 13℃ and 7.12% compared to 21℃; the soluble protein content reached 153.89 mg / 100 g, an increase of 20.44% compared to 13℃ and 16.33% compared to 21℃; the total flavonoid content showed very little difference among the three temperature difference treatments, with a change of only 0.75%. The nitrate content in all three treatments was far below the nitrate limit for leafy vegetables (3000 mg / kg) stipulated in the National Food Safety Standard for Limits of Contaminants in Food (GB2762-2022), and all met food safety requirements. Among them, the nitrate content was lowest at a temperature difference of 21℃, at 232.06 mg / 100 g, and highest at a temperature difference of 17℃, at 268.51 mg / 100 g, but both were still within the safe range.

[0044] This experiment analyzed the physiological indicators of lettuce stored for 6 days after treatment with three temperature differences: 13℃, 17℃, and 21℃. The results are as follows: Figure 4 As shown, a temperature difference of 17℃ is the optimal treatment temperature for overall effect. The soluble sugar content reaches 782.83 mg / g, which is significantly higher than the 13℃ group by 24.9% and higher than the 21℃ group. At the same time, the weight loss rate is only 6.00%, only 0.4% higher than the 13℃ group with the best preservation effect. The nitrate content is 4.5% lower than the 13℃ group, and there is no significant effect on the soluble protein content. Only the total flavonoid content is slightly lower than the 13℃ group by 7.9%, but still remains above 55 mg / 100 g. Although the 13℃ group has the highest total flavonoid content and the lowest weight loss rate, it has the lowest soluble sugar content and the highest nitrate content. Although the 21℃ group has the lowest nitrate content, the weight loss rate is significantly higher than the 13℃ group by 27.3%, and the soluble sugar content is somewhat lower. Therefore, the 17℃ treatment achieves the best balance between lettuce flavor quality, storage stability, and food safety.

[0045] To scientifically and objectively evaluate the comprehensive effects of different rhizosphere temperature treatments, this invention employs a linear weighted comprehensive evaluation method for multi-index comprehensive analysis. Post-harvest indicators have a weight of 55% (fresh weight 16.50%, dry weight 5.50%, soluble sugar 11.00%, soluble protein 11.00%, total flavonoids 5.50%, nitrate 5.50%), while post-storage indicators have a weight of 45% (soluble sugar 10.80%, soluble protein 9.45%, total flavonoids 6.75%, nitrate 4.50%).

[0046] The comprehensive scoring results are shown in Table 2. The optimal technical treatment of this invention is a temperature difference of 17℃ between the above-ground and underground parts. This treatment achieves synergistic optimization of yield and quality, reaching maximum values ​​in core indicators such as dry matter accumulation, soluble sugar, and soluble protein content. The higher dry matter content gives lettuce better storage and transportation resistance and a longer shelf life, a richer flavor, and significantly enhanced commercial value.

[0047] Example 2: Effects of different betaine concentrations on lettuce growth and quality This embodiment provides a method for cultivating lettuce by adding betaine to the nutrient solution after 28 days of normal cultivation. The invention systematically studied the effects of betaine concentration (0, 2, 4, 6, and 8 mM) on lettuce growth, nutritional quality, and safety by setting five betaine concentration treatments.

[0048] 1. Test Methods (1) Seedling raising Place filter paper in the germination box, moisten the filter paper with pure water, and then remove the air between the filter paper and the germination box. Arrange the 'Zhong Sheng No. 1' seeds evenly on the moistened filter paper and germinate them in a dark environment at 20℃ until the seeds show white sprouts (30~38 h). Select uniformly growing, white sprouted seeds and sow them into the small hole in the center of a 2×2×2 cm black sponge block that has been moistened with water beforehand. Germinate the seeds at an ambient temperature of 24℃ and a light intensity of 150 μmol·m². -2 ·s -1 Under an environment with a photoperiod of 16 / 8 h and a relative humidity of 60-70%, the culture was carried out for 14 days, during which the nutrient solution was added every 2 days and replaced every 7 days. The nutrient solution, modified from a classic hydroponics formula, contained N ≥ 7 mM·L. -1 P2O5 ≥ 0.1 mM·L -1 K2O≥2 mM·L -1 Mg≥0.4 mM·L -1 S≥0.6 mM·L -1 Fe≥0.07 mM·L -1 Mn≥0.09 mM·L -1 B≥0.05 mM·L -1 Zn≥0.01 mM·L -1 Mo≥6×10 -4 mM·L -1 Ca ≥ 2.5 mM·L -1 The nutrient solution was set to pH 5.7 and EC 1.8 mS·cm. -1 .

[0049] (2) Transplanting To minimize root damage to lettuce and avoid errors caused by growth, lettuce seedlings with uniform growth, no yellowing leaves, and no pests or diseases were selected and transplanted into 6-cell planting trays. The ambient temperature was set at 24℃ and the light intensity at 200 μmol·m². -2 ·s -1 Under an environment with a photoperiod of 16 / 8 h and a relative humidity of 60-70%, the nutrient solution was replenished every 2 days for 14 days, during which the nutrient solution was replaced once. Then, a temperature difference treatment experiment was carried out on the aboveground and underground parts. The temperature was set at 37℃, and the betaine concentration in the nutrient solution was 0, 2, 4, 6, and 8 mM, respectively.

[0050] After treatment, the fresh and dry weights of plants in each treatment group were measured, and the contents of soluble sugars and soluble proteins were analyzed. Lettuce samples used for storage experiments were individually packaged in vegetable preservation bags and stored at 4°C in the dark for 6 days, after which their weight loss rate and physiological index contents were measured.

[0051] 2. Test Results This study set up five gradients of betaine treatment: 0 (CK), 2, 4, 6, and 8 mM. Pre-harvest measurements showed that the fresh weight of the raw plantlets continuously decreased with increasing betaine concentration. Figure 5 a~b show that the 2, 4, 6, and 8 mM treatment groups decreased by 6.29%, 13.08%, 14.12%, and 42.63% respectively compared with the control, while the dry weight of individual plants showed a parabolic trend of first increasing and then decreasing. The 2, 4, 6, and 8 mM treatment groups increased by 20.61%, 14.65%, 100.72%, and 31.46% respectively compared with the control, among which the 6 mM treatment group reached a peak dry weight of 11.10 g, achieving a doubling.

[0052] Figure 5c~f indicates that, in terms of nutritional quality, the soluble sugar content showed a trend of first increasing and then decreasing. The 2, 4, 6, and 8 mM treatment groups increased by 12.98%, 10.90%, 27.82%, and 25.58% compared to the control, respectively, with the 6 mM treatment group reaching the maximum value of 2042.04 mg / 100g. The soluble protein content showed a continuous upward trend, with the 2, 4, 6, and 8 mM treatment groups increasing by 10.71%, 23.37%, 40.25%, and 40.97% compared to the control, respectively. The 6 mM and 8 mM treatment groups showed comparable effects. The nitrate content showed a trend of first decreasing and then increasing. The 2, 4, 6, and 8 mM treatment groups decreased by 7.98%, 33.37%, 40.00%, and 26.40% compared to the control, respectively, with the 6 mM treatment group reaching the lowest value of 144.89 mg / 100g. The total flavonoid content showed a trend of first increasing sharply and then decreasing sharply. Compared with the control, the mM treatment groups increased by 5.46%, 24.21%, 65.71%, and 3.70%, respectively. The 6 mM treatment group reached a peak of 94.44 mg / kg, while the 8 mM treatment group dropped sharply to near the control level.

[0053] The results of the postharvest storage test further showed that preharvest treatment with betaine could significantly delay the degradation of nutrients in lettuce during storage and improve the preservation effect. All the indicators after storage also showed a trend of first rising and then falling. Figure 6 The results showed that after storage, the soluble sugar content in the 6 mM treatment group reached 1918.48 mg / 100 g, a significant increase of 51.08% compared to the control group; the soluble protein content was 182.74 mg / 100 g, an increase of 24.41% compared to the control group, approaching the peak value; the nitrate content decreased to 162.72 mg / 100 g, a decrease of 36.81% compared to the control group; the total flavonoid content reached 85.56 mg / 100 g, an increase of 109.65% compared to the control group, more than doubling; and the weight loss rate decreased to the lowest value of 5.45%, a decrease of 47.19% compared to the control group, demonstrating the most significant preservation effect. The 4 mM treatment group showed good performance in all indicators and can be used as an alternative, while the 2 mM low-concentration treatment had limited effect, and the 8 mM high-concentration treatment caused a significant decrease in all indicators because it exceeded the suitable tolerance range for lettuce.

[0054] To scientifically and objectively evaluate the comprehensive effects of different rhizosphere temperature treatments, this invention employs a linear weighted comprehensive evaluation method for multi-index comprehensive analysis. Post-harvest indicators have a weight of 55% (fresh weight 16.50%, dry weight 5.50%, soluble sugar 11.00%, soluble protein 11.00%, total flavonoids 5.50%, nitrate 5.50%), while post-storage indicators have a weight of 45% (soluble sugar 10.80%, soluble protein 9.45%, total flavonoids 6.75%, nitrate 4.50%).

[0055] The analysis results of all indicators before and after mining are shown in Table 2. Figure 6 As shown, 6 mM is the optimal concentration of betaine for regulating lettuce quality. Adding 6 mM betaine to the pre-harvest nutrient solution can significantly improve the dry matter accumulation of lettuce, while comprehensively improving its nutritional quality, food safety, and health benefits, and greatly extending its post-harvest shelf life. It is a highly efficient cultivation technique that combines pre-harvest quality improvement and post-harvest preservation. A concentration of 4 mM can be considered as an alternative.

[0056] Example 3: Effects of combined treatment of aboveground and underground temperature difference and betaine on lettuce quality This embodiment provides a method for cultivating lettuce for 7 days after the normal 28-day cultivation period. The specific implementation plan is to screen out a suitable temperature difference (17°C) and betaine concentration (6mM) according to Embodiments 1 and 2.

[0057] 1. Test Methods (1) Seedling raising Place filter paper in the germination box, moisten the filter paper with pure water, and then remove the air between the filter paper and the germination box. Arrange the 'Zhong Sheng No. 1' seeds evenly on the moistened filter paper and germinate them in a dark environment at 20℃ until the seeds show white sprouts (30~38 h). Select uniformly growing, white sprouted seeds and sow them into the small hole in the center of a 2×2×2 cm black sponge block that has been moistened with water beforehand. Germinate the seeds at an ambient temperature of 24℃ and a light intensity of 150 μmol·m². -2 ·s -1 Under an environment with a photoperiod of 16 / 8 h and a relative humidity of 60-70%, the plants were cultivated until they developed three leaves and one bud (14 days), during which time nutrient solution was added once a day. The nutrient solution was a modified version of the classic hydroponics formula containing N ≥ 7 mM·L. -1 P2O5 ≥ 0.1 mM·L -1 K2O≥2 mM·L -1 Mg≥0.4 mM·L -1 S≥0.6 mM·L -1 Fe≥0.07 mM·L -1 Mn≥0.09 mM·L -1 B≥0.05 mM·L -1 Zn≥0.01 mM·L -1 Mo≥6×10 - 4 mM·L -1 Ca ≥ 2.5 mM·L -1 The nutrient solution was set to pH 5.7 and EC 1.8 mS·cm. -1 .

[0058] (2) Transplanting To minimize root damage to lettuce and avoid errors caused by growth, lettuce seedlings with uniform growth, no yellowing leaves, and no pests or diseases were selected and transplanted into 6-cell planting trays. The ambient temperature was set at 24℃ and the light intensity at 200 μmol·m². -2 ·s -1 Under an environment with a photoperiod of 16 / 8 h and a relative humidity of 60-70%, the nutrient solution was replenished every 2 days for 14 days, during which the nutrient solution was replaced once. Then, the temperature difference treatment experiment of the aboveground and underground parts was carried out. The specific temperature settings are shown in Table 1, and other culture conditions were not changed.

[0059] After treatment, the fresh weight and dry weight of plants in each treatment group were measured, and relevant physiological indicators were analyzed. Lettuce samples used for storage experiments were individually packaged in vegetable preservation bags and stored at 4℃ in the dark for 6 days, after which their weight loss rate and physiological indicators were measured.

[0060] 2. Test Results In this experiment, a temperature difference of 17°C was set between the aboveground and underground parts of lettuce after 28 days of cultivation. At the same time, 6 mM betaine was added to the nutrient solution. This experiment explored the synergistic effect of temperature difference and betaine on the postharvest quality of lettuce by setting up an initial group and a 6-day storage group. Each group was biologically replicated 4 times, and the data showed good stability and reliable results.

[0061] The results in Tables 3 and 4 show that the fresh lettuce treated with this compound method exhibited excellent performance in various nutritional, safety, and growth indicators. After 6 days of storage at 4℃, the soluble sugar content reached 2637.81 mg / 100 g, a slight decrease of only 2.82% compared to the pre-harvest level. The soluble protein content increased to 280.27 mg / 100 g due to the water loss concentration effect, a slight increase of 3.23% compared to the pre-harvest level. The degradation rate of total flavonoids was effectively mitigated, with a decrease of 8.80%, while the nitrate content increased by 8.32%. Moreover, the weight loss rate was only 4.99%, far below the critical value for the marketability of leafy vegetables.

[0062] In summary, the synergistic treatment of temperature difference and betaine can effectively delay post-harvest senescence and quality deterioration of lettuce through multiple pathways, such as inhibiting respiratory consumption, stabilizing protein metabolism, slowing down the loss of antioxidants, regulating nitrogen metabolism disorders, and reducing water loss. This significantly extends the shelf life of lettuce and preserves its marketability, demonstrating promising prospects for industrial application.

[0063] Table 2. Overall score of the effects of different treatments on lettuce

[0064] Table 3. Effects of simultaneous temperature difference and betaine on lettuce quality.

[0065] Table 4. Effects of temperature difference and betaine on the quality of lettuce after 6 days of storage.

[0066] It should be noted that the specific embodiments described above are exemplary, and those skilled in the art can devise various solutions inspired by the disclosure of this invention, all of which fall within the scope of this invention and its protection. Those skilled in the art should understand that this specification is illustrative and not intended to limit the scope of the claims. The scope of protection of this invention is defined by the claims and their equivalents.

Claims

1. A method for improving the pre-harvest and post-harvest storage quality of hydroponic lettuce, characterized in that, Includes the following steps: Add 2-8 mM betaine to the nutrient solution at least 7 days before harvesting the lettuce, and perform a temperature difference treatment between the above-ground and underground parts at least 7 days before harvesting the lettuce, with a temperature difference range of 13-21℃, and carry out hydroponic cultivation of the lettuce.

2. The method for improving the pre-harvest and post-harvest storage quality of hydroponically grown lettuce according to claim 1, characterized in that, The environmental conditions are as follows: Light intensity 150~200 μmol m -2 s -1 Full-band white light, photoperiod 16 / 8 h, relative humidity 60%~70%.

3. The method for improving the pre-harvest and post-harvest storage quality of hydroponically grown lettuce according to claim 1, characterized in that, The pH of the nutrient solution was maintained at 5.7 ± 0.1, and the EC value was maintained at 1.8 ± 0.1 mS. cm -1 .

4. The method for improving the pre-harvest and post-harvest storage quality of hydroponically grown lettuce according to claim 1, characterized in that, The nutrient solution contains the following nutrient concentrations: N ≥ 7 mM L -1 P2O5 ≥ 0.1 mM L -1 K2O≥2 mM L -1 Mg≥0.4 mM L -1 S≥0.6 mM L -1 Fe≥0.07 mM L -1 Mn≥0.09 mM L -1 B≥0.05 mM L -1 Zn≥0.01 mM L -1 Mo≥6×10 -4 mM L -1 Ca≥2.5 mM L -1 .

5. The method for improving the pre-harvest and post-harvest storage quality of hydroponic lettuce according to claim 2, characterized in that, To improve the quality of lettuce before and after harvest and during storage, lettuce is treated with 2-8 mM betaine and temperature difference 7 days before harvest.

6. The method for improving the pre-harvest and post-harvest storage quality of hydroponically grown lettuce according to claim 1, characterized in that, The lettuce in question is 'Zhong Sheng No. 1' hydroponic lettuce.

7. The method for improving the pre-harvest and post-harvest storage quality of hydroponically grown lettuce according to claim 1, characterized in that, Lettuce that has undergone pre-harvest co-regulation treatment is individually packaged in vegetable preservation bags and stored at 4℃ in the dark.

8. A system for implementing the method for improving the pre-harvest and post-harvest storage quality of hydroponic lettuce as described in any one of claims 1 to 7, characterized in that, include: Temperature control units, installed above and below ground, are used to treat the temperature difference between the above-ground and underground parts of the lettuce at least 7 days before harvesting, with a temperature difference range of 13~21℃. The nutrient solution circulation unit is used to circulate nutrient solution to lettuce and add 2-8 mM betaine to the nutrient solution at least 7 days before the lettuce is harvested. The illumination control unit is used to provide an illumination intensity of 150~200 μmol. m -2 s -1 Full-spectrum white light; The environmental monitoring unit is used to monitor environmental temperature, rhizosphere temperature, light intensity, relative humidity, and nutrient solution pH and EC values ​​in real time. The central control unit communicates with the environmental monitoring unit, connects to the light control unit, the nutrient solution circulation unit, and the temperature control unit, and is configured to: when receiving the detection signal from the environmental monitoring unit, adjust the operating parameters of each unit based on the set parameters so that the light control unit, the nutrient solution circulation unit, and the temperature control unit can maintain the growth conditions required for the lettuce growth stage.

9. The system for improving the pre-harvest and post-harvest storage quality of hydroponic lettuce according to claim 8, characterized in that, The nutrient solution circulation unit includes a water storage tank, a chiller, a water pump, a filter, a cultivation trough, an inlet pipe, a drain pipe, and a temperature recorder. The water storage tank is connected to the inlet pipe of the cultivation trough through the water pump and the filter, and the drain pipe of the cultivation trough is connected to the water storage tank to form a closed circulation loop.

10. The method for improving the pre-harvest and post-harvest storage quality of hydroponic lettuce according to any one of claims 1 to 7 is used to slow down the rate of nutrient degradation of lettuce during storage and to increase the shelf life.

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