Lemon ripening process

Abstract

The invention relates to the technical field of fruit ripening acceleration, in particular to a lemon ripening acceleration process, which comprises the following steps: placing lemons with the ripening grade of grade 1 in an environment with the temperature of 8-12 DEG C and the relative humidity of 85-95% for refrigeration; heating and fermenting: taking out the refrigerated lemons in the step S1, heating the lemon pulp to 23-25 DEG C at a heating speed of 1-2 DEG C / h, and keeping the temperature for 6-12 hours; the lemons are subjected to graded ripening acceleration, the treated lemons are placed in a relatively closed environment, and environmental parameters are regulated and controlled according to the target ripening grade: the lemons subjected to ripening acceleration are placed in an environment with the temperature being 10-12 DEG C, the carbon dioxide concentration being 3000 ppm and the relative humidity being 85%-95%, and the environment is kept for 6-8 hours; and cold storage and preservation: placing the treated lemons in an environment of 10 DEG C for cold storage. Through multi-parameter quantitative control, staged ripening acceleration, a pressure difference circulation system and low-temperature gas cooperative regulation and control, multi-factor precise ripening acceleration, controllable maturity, large-scale efficient production and quality preservation of lemons are achieved, and various requirements are met.

Description

Technical Field

[0001] The invention relates to the technical field of fruit ripening, in particular to a lemon ripening process. Background Art

[0002] Lemons, the iconic "King of Vitamin C" among subtropical fruits, are rich in nutrients, including vitamin C, citric acid, dietary fiber, and various trace elements. They offer antioxidant, digestion-boosting, and immune-boosting benefits, making them a favorite among consumers. In recent years, with the growing popularity of healthy eating concepts, lemons have seen continued growth in market demand due to their refreshing and sour flavor and diverse ways to enjoy them, including as fresh food, seasoning, and beverages. Lemons are primarily produced in subtropical regions around the world, with the highest concentrations in Anyue, Sichuan, and Zhaoqing, Guangdong, in China, and in Brazil and California, USA, abroad. Because lemons require long-distance transportation to reach markets across China and even the world, farmers typically harvest them when they are 50% to 60% ripe. At this point, the lemons appear bluish-green, with a firm skin and a sour, hard flesh, making them inedible. They must undergo a ripening process until they are fully mature before being released to the market.

[0003] As a fruit that ripens after respiratory bursts, traditional ripening methods for lemons have obvious limitations. Natural ripening involves placing lemons in a sealed paper bag at room temperature for ripening, which usually takes 1 to 7 days. However, the degree of maturity is difficult to control, and fruits in the same batch are prone to uneven color change, being undercooked or rotten. The flesh also has a hard texture and a noticeable sour and astringent taste, affecting quality. Chemical ripening often involves applying or soaking the fruit in a diluted ethephon solution. Although this can accelerate ripening, the operation is cumbersome and requires each fruit to be processed individually, which has high labor costs. In addition, the ethephon dosage is difficult to accurately control, which can easily lead to over-ripening of some fruits, cracking, or uneven saccharification. The ripening cycle is as long as 7 to 10 days, which cannot meet the market supply turnover needs.

[0004] With the large-scale development of the lemon industry, traditional ripening processes are no longer able to meet the needs of standardized, mass-produced production. Currently, lemons are mostly transported to distribution centers for centralized ripening and distribution. Different distributors have varying maturity requirements, such as grades 3-4 for fresh consumption and grade 5 for juice processing. Existing processes lack controllable, scalable methods for regulating these different maturity levels, necessitating the development of a precise ripening technology system. Summary of the Invention

[0005] The present invention aims to provide a lemon ripening process, which standardizes the maturity level of lemons by quantitatively controlling factors such as pulp temperature, ethylene gas concentration, and carbon dioxide concentration during the ripening process, and performs large-scale ripening of lemons, thereby achieving the effects of uniform maturity level, high ripening quality, and low waste for lemons in the same batch.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0007] A lemon ripening process specifically comprises the following steps:

[0008] Step S1: refrigeration pretreatment, placing lemons with maturity level 1 in an environment with a temperature of 8°C to 12°C and a relative humidity of 85% to 95%;

[0009] Lemons are a climacteric fruit. Low temperatures can slow their metabolic process but cannot completely inhibit ethylene release. If the temperature is above 12°C, the ethylene-induced ripening reaction will continue slowly, potentially causing premature softening of the flesh or loss of sourness. If the temperature is below 8°C, chilling damage can easily occur, leading to browning of the peel and fibrosis of the flesh. Keeping the temperature between 8°C and 12°C can inhibit enzyme activity and ethylene synthesis while reducing water loss. Maintaining a relative humidity of 85% to 95% effectively maintains the peel's sheen and the flesh's plumpness, thus avoiding overripening or fermentation caused by trace ethylene accumulation.

[0010] Step S2: Heating the lemons to wake them up: take out the lemons refrigerated in step S1, raise the temperature of the lemon pulp to 23°C to 25°C at a heating rate of 1°C to 2°C per hour, and maintain this temperature for 6 to 12 hours;

[0011] When the temperature of lemon pulp is lower than 23℃, the activity of ethylene synthase is insufficient and the rate of starch conversion into sugar is reduced; if it exceeds 25℃, anaerobic respiration will be accelerated, causing the pulp to produce ethanol odor and the risk of mold proliferation to increase; the constant temperature stage can promote the release of endogenous ethylene in lemons, laying the foundation for subsequent ripening.

[0012] Step S3: Ripening by grade: Place the lemons processed in step S2 in a relatively closed environment and adjust the environmental parameters according to the target maturity grade:

[0013] In the lemon ripening process, key parameter control is crucial to the ripening effect and fruit quality: in terms of temperature, 23℃-25℃ is the optimal range for lemon ethylene receptor activity, which can accelerate the saccharification of the pulp; when the temperature drops to 15℃, the metabolic rate of lemon cells decreases by more than 50%, which can effectively delay the over-ripening of the fruit. In terms of gas concentration control, a high ethylene concentration of 500-800ppm can promote the decomposition of chlorophyll in the peel, while a low ethylene concentration of 300-500ppm focuses on promoting the accumulation of sugar in the pulp; and when the carbon dioxide concentration is ≥4000ppm, it can delay the ripening of the fruit by competitively inhibiting the binding of ethylene to the receptor. Humidity control is also critical. Maintaining the humidity at above 90%-95% can prevent the lemon peel from losing water and shrinking, maintain the plumpness of the pulp, and avoid the problem of dry and hard taste caused by water loss during the ripening process.

[0014] Step S4: To stabilize the maturity, place the lemons ripened in step S3 in an environment with a temperature of 10° C. to 12° C., a carbon dioxide concentration of 3000 ppm, and a relative humidity of 85% to 95% for 6 to 8 hours;

[0015] During this stage, low temperature and high carbon dioxide concentration inhibit the respiration of the fruit, thereby delaying the ripening process, stabilizing the maturity, and preventing the fruit from excessive softening.

[0016] Step S5: refrigerate and preserve the lemons after the treatment in step S4. Place the lemons in a refrigerated environment at 10°C.

[0017] The refrigerated environment can continuously inhibit enzyme activity and ethylene release, reduce water loss, and keep the lemons at their best quality after ripening within 15 to 20 days.

[0018] Furthermore, in step S3,

[0019] Step S31: ripening the lemons after the heating and constant temperature treatment in step S2 to level 2-3, controlling the environmental parameters as follows: pulp temperature 23°C-25°C, carbon dioxide concentration 2000-3000 ppm, ethylene concentration 500-800 ppm, relative humidity 85%-95%, for 24-28 hours;

[0020] Step S32: ripening the lemons ripened to level 2-3 in step S31 to level 3-4, controlling the environmental parameters as follows: pulp temperature 23°C-25°C, carbon dioxide concentration 4000-6000 ppm, ethylene concentration 300-500 ppm, relative humidity 85%-95%, for 24-28 hours;

[0021] Step S33: ripening the lemons ripened to level 3-4 in step S32 to level 5, controlling the environmental parameters as follows: pulp temperature 15°C-18°C, carbon dioxide concentration 4500-5000 ppm, ethylene concentration ≤1 ppm, relative humidity 85%-95%, for 24-28 hours.

[0022] Furthermore, in step S3, the closed environment is a ripening warehouse with a pressure difference control circulation system.

[0023] Furthermore, in step S3, the maturity level is divided based on the peel, pulp and smell, and the specific standards are:

[0024] Grade 1: The fruit is in the raw stage and has not yet matured. The skin is green and firm. It does not deform when pressed by a thumb. The surface is smooth and has no yellowing areas. The flesh is white. The pectin between cells is tightly connected. The texture is firm and does not sink when pressed. The flesh and skin are tightly attached. It has a distinct green and astringent taste and no lemon aroma.

[0025] Grade 2: Early maturity, at the beginning of color change, 70% to 80% of the peel is turquoise, and 15% to 30% turns yellow-green. The color transition is uneven and the texture is slightly hard. The flesh is white and slightly rebounds when pressed. The astringent taste in the smell is weakened, and a light lemon aroma appears.

[0026] Grade 3: Half-ripe, mid-color change stage, with the rind 40% to 60% each of bluish-green and yellowish-green, showing a mottled pattern. The texture is soft, and a thumb press yields 30% to 50%. The flesh is golden yellow, with a slightly milky white core, a soft texture, and noticeable deformation upon pressing. The fruit is less juicy, exudes a fresh lemon aroma, and has a significantly reduced sour taste.

[0027] Grade 4: Fully ripe, suitable for fresh consumption. 70% to 95% of the peel is light yellow, with the remaining green area concentrated in the fruit stem. The texture is soft and easily dents when pressed. The flesh is light yellow, with a moderate texture, soft and juicy, with loose connections between cells and juice oozing out. The aroma exudes a strong lemon aroma, with a balanced sweet and sour taste and no astringency.

[0028] Level 5: Overripe, suitable for deep processing. The peel is completely yellow with a glossy luster, and some areas are dark yellow. The texture is extremely soft, and it is difficult to rebound after being pressed. The flesh is golden yellow, extremely soft and juicy, and there is obvious juice oozing out when pressed. The flesh fibers are softened; the aroma is strong, slightly sweet, and the sugar content reaches its peak.

[0029] The advantages of the present invention compared with the prior art are:

[0030] 1. The present invention incorporates a temperature of 8°C to 28°C, a humidity of 85% to 90%, an ethylene concentration of ≤100ppm to 800ppm, and a carbon dioxide concentration of 2000 to 6000ppm into a quantitative control system during each step of lemon ripening: cold pretreatment, temperature awakening, graded ripening, maturity stabilization, and cold storage preservation. For example, cold pretreatment controls the temperature at 8°C to 12°C and the humidity at 85% to 95%, while graded ripening regulates the concentrations and temperatures of different gases according to the target grade. This overcomes the limitations of traditional natural ripening, which relies on room temperature and chemical ripening, which uses only ethephon, and achieves precise ripening through the coordinated use of multiple factors.

[0031] 2. The present invention uses staged parameter control to set the corresponding pulp temperature, carbon dioxide concentration, ethylene concentration and duration for target maturity levels 2-3, 3-4 and 5 in the graded ripening steps. Combined with the maturity level standards based on the smell of the peel and pulp, lemons can be ripened to different levels as needed to meet diverse needs such as fresh consumption and processing, achieving standardized and controllable maturity and solving the problem of uncontrollable maturity in traditional processes.

[0032] 3. The present invention places the lemons in the graded ripening step in a ripening warehouse equipped with a pressure differential control circulation system, and coordinates precise parameter control of each step. For example, the temperature is raised at 1°C-2°C / hour for waking up the fruit and kept at a constant temperature for 6-12 hours, and the graded ripening lasts for 24-28 hours. This achieves a ripening uniformity of ≥95% for the same batch of lemons, shortens the ripening cycle to 3-5 days, and reduces the cargo damage rate to ≤0.8%, significantly improving industrial production efficiency and overcoming the shortcomings of traditional processes such as long cycles and high cargo damage.

[0033] 4. The present invention combines low-temperature refrigeration with gas regulation. The cold storage pretreatment and cold preservation steps adopt a low-temperature environment, the maturity stabilization step controls the temperature and carbon dioxide concentration, and the graded ripening step controls the gas concentration. This achieves uniform saccharification of lemon pulp, rich aroma, and a soluble solids content of ≥12%. At the same time, it extends the shelf life to more than 20 days, meeting the requirements of cross-regional distribution for fruit quality and storage time, and ensuring terminal quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings constituting a part of this application are used to provide a further understanding of this application and make other features, purposes and advantages of this application more apparent. The drawings and descriptions of the exemplary embodiments of this application are used to explain this application and do not constitute an improper limitation on this application.

[0035] In the attached figure:

[0036] Figure 1 The present invention is a flow chart of a lemon ripening process in Example 1.

[0037] Figure 2 This is a diagram showing the appearance of a lemon with a maturity level of 1 in the embodiment.

[0038] Figure 3 This is a diagram showing the appearance of a lemon with a maturity level of 2 in the embodiment.

[0039] Figure 4 This is a diagram showing the appearance of a lemon with a maturity level of 3 in the embodiment.

[0040] Figure 5 This is a diagram showing the appearance of a lemon with a maturity level of 4 in the embodiment.

[0041] Figure 6 This is a diagram showing the appearance of a lemon with a maturity level of 5 in the embodiment. DETAILED DESCRIPTION

[0042] The detailed descriptions of the following embodiments are used to exemplify the principles of the present application, but are not intended to limit the scope of the present application. That is, the lemon ripening process of the present application is not limited to the described embodiments.

[0043] Example 1

[0044] like Figure 1-4 As shown, step S1: refrigerate lemons with maturity level 1 in an environment of 8° C. to 12° C. and relative humidity of 85% to 95% for 3-7 days.

[0045] Step S2: After taking the lemon out of the refrigerated environment, heating it, raising the temperature of the lemon pulp from 8°C to 12°C at a heating rate of 1°C to 2°C per hour to 20°C, and maintaining the constant temperature for 6 hours;

[0046] In this step, if the temperature is higher than 25°C, the respiration intensity of the pulp will increase sharply, accelerating the production of ethanol odor from anaerobic respiration and increasing the risk of mold proliferation; when it is lower than 20°C, the activity of ethylene synthase in the pulp is insufficient, and the rate of starch conversion to sugar is reduced.

[0047] Step S3: ripening the lemons to a maturity level of 2-3, placing the lemons after the heating and constant temperature treatment in step S2 in a relatively closed environment, heating the lemon pulp to a temperature of 23° C., and controlling the carbon dioxide concentration in the environment to 2500 ppm, the ethylene gas concentration to 700 ppm, and the humidity to 90%-95% for 30 hours;

[0048] In a relatively closed environment, the air inside the storage chamber and outside the storage chamber do not exchange naturally, requiring controlled exchange through the coordination of relevant equipment. Step S4: Control the temperature of the ripened lemon pulp at 10°C to 12°C, and control the carbon dioxide concentration in the environment to 3000ppm and the humidity to 90% to 95% for 8 hours.

[0049] Step S5: refrigerate the lemons processed in step S4 at 10°C.

[0050] Example 2

[0051] like Figure 1-4 As shown, step S1: refrigerate lemons with maturity level 1 in an environment of 8° C. to 12° C. and relative humidity of 85% to 90% for 3-7 days.

[0052] Step S2: After taking the lemon out of the refrigerated environment, heating it, raising the temperature of the lemon pulp from 8°C to 12°C at a heating rate of 1°C to 2°C / hour to 24°C, and maintaining the constant temperature for 6 hours;

[0053] Step S3: ripen the lemons to maturity level 3-4.

[0054] Step S31: placing the lemons after the heating and constant temperature treatment in step S2 in a relatively closed environment, heating the lemon pulp to a temperature of 23° C., and controlling the carbon dioxide concentration in the environment to 2500 ppm, the ethylene gas concentration to 700 ppm, and the humidity to 90% to 95% for 30 hours;

[0055] Step S32: heating the lemons ripened to maturity level 2-3 in step S31 to a pulp temperature of 25° C., and controlling the carbon dioxide concentration in the environment to 5000 ppm, the ethylene gas concentration to 400 ppm, and the humidity to 90%-95% for 24 hours;

[0056] Step S4: controlling the temperature of the ripened lemon pulp to 10° C. to 12° C., and controlling the carbon dioxide concentration in the environment to 3000 ppm and the humidity to 85% to 95% for 8 hours;

[0057] Step S5: refrigerate the lemons processed in step S4 at 10°C.

[0058] Example 3

[0059] like Figure 1-4 As shown, step S1: refrigerate lemons with maturity level 1 at 8°C to 12°C and relative humidity of 85% to 95% for 3-7 days;

[0060] Step S2: After taking the lemon out of the refrigerated environment, heating it, raising the temperature of the lemon pulp from 8°C to 12°C at a heating rate of 1°C to 2°C / hour to 24°C, and maintaining the constant temperature for 6 hours;

[0061] Step S3: ripening the lemon to level 5;

[0062] Step S31: placing the lemons after the heating and constant temperature treatment in step S2 in a relatively closed environment, heating the lemon pulp to a temperature of 24° C., and controlling the carbon dioxide concentration in the environment to 2500 ppm, the ethylene gas concentration to 700 ppm, and the humidity to 85% to 90% for 30 hours;

[0063] Step S32: heating the lemons ripened to maturity level 2-3 in step S31 to a pulp temperature of 25° C., and controlling the carbon dioxide concentration in the environment to 5000 ppm, the ethylene gas concentration to 400 ppm, and the humidity to 90%-95% for 24 hours;

[0064] Step S33: Cooling the lemons ripened to maturity level 3-4 in step S32 to a pulp temperature of 16° C., and controlling the carbon dioxide concentration in the environment to 4800 ppm and the humidity to 85%-90% for 24 hours.

[0065] Step S4: controlling the temperature of the ripened lemon pulp to 10° C. to 12° C., and controlling the carbon dioxide concentration in the environment to 3000 ppm and the humidity to 85% to 90% for 8 hours;

[0066] Step S5: refrigerate the lemons processed in step S4 at 10°C.

[0067] Example 4

[0068] like Figure 1-4 As shown, 2 tons of lemons were ripened from Anyue, Sichuan to the ripening base in Hunan.

[0069] Lemons shipped from Anyue, Sichuan, to our Hunan base arrive at grade 1 ripeness upon arrival. They are then stored in cold storage or freezers, where the ambient temperature is maintained at 8°C to 12°C and the relative humidity is 85% to 90%. Based on customer needs, we plan to ripen 300kg of lemons to grades 2-3, 700kg to grades 3-4, and the remainder to grade 5.

[0070] Step S1: First, 2 tons of lemons are transferred to the first ripening warehouse and stacked in sections according to the planned ripening maturity level, namely 300 kg, 700 kg, and 1 ton. The ripening warehouse is heated in the chamber under the condition of natural air circulation. After the temperature of the lemon pulp is raised from 8°C to 12°C to 20.5°C, the constant temperature is maintained for 6 hours to 12 hours.

[0071] Lemon is a late-ripening fruit with respiratory climacteric. When stored in a cold environment of 8℃ to 12℃, its respiration is inhibited. When the temperature is raised and maintained at a constant temperature, the respiration intensity of the lemon gradually increases during the heating process and the process of maintaining the temperature. The carbon dioxide in the storage gradually increases. This stage is the fruit awakening process.

[0072] Step S2: The ripening warehouse is sealed, and the lemons that have been heated and kept at a constant temperature are placed in a relatively closed environment. The temperature is raised to 23° C., and the carbon dioxide concentration, ethylene gas concentration, and humidity in the environment are controlled to be 2500 ppm, 700 ppm, and 85% to 90%. After maintaining these conditions for 30 hours, the lemons are ripe at level 2 to 3.

[0073] During this process, the lemon's respiration rate increases, allowing the fruit to better absorb ethylene. Ethylene in the air triggers the synthesis and activity of cell wall hydrolases in the lemon pulp, such as cellulase and pectinase. These enzymes break down the cellulose and pectin components of the cell walls. Ethylene accelerates the breakdown of polysaccharides such as starch in the lemon pulp into monosaccharides like glucose and fructose. The soluble sugar content in the lemon fruit increases, and the lemon reaches its peak respiration rate at this time.

[0074] In this embodiment, the ripening warehouse utilizes the Chinese patent application number CN222465911U, "An Energy-Saving Fruit Pressure-Differential Ripening Warehouse," which discloses a ripening warehouse with a pressure-differential control circulation system. This pressure-differential circulation system ensures uniform exposure to ethylene for a more even temperature distribution, allowing the fruit to ripen uniformly from the inside out. In practice, lemons are randomly and evenly sampled, and after a hole is made, a temperature sensor probe is inserted into the fruit to monitor its temperature.

[0075] Step S3: After transferring 300 kg of lemons ripened to maturity level 2-3 to a second ripening warehouse, the lemon pulp temperature is controlled at 10° C. to 12° C., and the carbon dioxide concentration and humidity in the environment are controlled at 3000 ppm and 90% to 95% for 8 hours; and then refrigerated at 10° C.

[0076] The temperature of the remaining lemons in the first ripening warehouse is raised to 24°C, and the carbon dioxide concentration in the environment is controlled at 5000ppm and the humidity is 85% to 90% for 24 hours. At this time, the maturity level of the lemons in the first ripening warehouse is 3 to 4. In the process of ripening lemons with maturity levels of 2-3 to 3 to 4, the color of the lemon shell will gradually change, the chlorophyll in the lemon shell will gradually decompose, and the physiological metabolic activity of its pulp will continue to increase. At the cellular level, mitochondrial respiration will further accelerate, and at the same time, the synthesis of some pigments such as carotenoids will increase, continuously consuming oxygen and producing carbon dioxide.

[0077] In this embodiment, during the process of transferring 300 kg of lemons to the second ripening warehouse, random samples were taken to confirm the maturity and yield of the lemons. The number of samples randomly sampled was 15, of which 14 samples had a maturity level of 2 to 3. The remaining sample had a damaged peel when it was put into storage and was not counted in the maturity statistics.

[0078] Step S4: After transferring the 700 kg of lemons from the first ripening warehouse to the third ripening warehouse, the lemon pulp temperature is controlled at 10°C to 12°C, and the ambient carbon dioxide concentration is controlled at 3000 ppm and the humidity at 90% to 95% for 8 hours; the lemons are then refrigerated at 10°C. The remaining lemons in the first ripening warehouse are cooled to a pulp temperature of 16°C, and the ambient carbon dioxide concentration is controlled at 4800 ppm and the humidity at 85% to 90% for 24 hours. At this point, the lemons in the first ripening warehouse are at maturity level 5. The lemon pulp temperature is controlled at 10°C to 12°C, and the ambient carbon dioxide concentration is controlled at 3000 ppm and the humidity at 90% to 95% for 8 hours; the lemons are then refrigerated at 10°C.

[0079] During the ripening process of lemons from maturity levels 3-4 to 5, all ethylene is expelled, reaching a concentration of zero. The fruit temperature is then lowered, allowing the air inside the storage chamber to exchange with the air outside, reducing the carbon dioxide concentration inside. At this point, the lemon shell loses its chlorophyll color, becoming golden yellow. The flesh firmness and starch content decrease, and the fruit gradually turns yellow, with some areas still showing signs of being undercooked. Correspondingly, the soluble solids and total sugar content increase.

[0080] In this embodiment, during the process of transferring 700 kg of lemons to the third ripening warehouse, random samples were taken to confirm the maturity and yield of the lemons. The number of samples randomly sampled was 25, of which 23 samples had a maturity level of 3 to 4, and the remaining 2 samples still had a maturity level of 2 to 3.

[0081] Furthermore, a random sampling inspection was conducted on 35 lemons that were expected to be ripened to maturity level 5. Of these, 29 samples reached maturity level 5, 2 were overripe, 3 were at maturity levels 3-4, and 1 was at maturity level 2-3. Statistics on the damage rate of this example showed a low damage rate of only 0.8%.

[0082] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0083] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therefrom that can be directly derived from or easily conceived by those skilled in the art based on the disclosure of the present invention are intended to fall within the scope of protection of the present invention.

Claims

1. A lemon ripening process, characterized in that: The specific steps include: Step S1: refrigeration pretreatment, placing lemons with maturity level 1 in an environment with a temperature of 8°C to 12°C and a relative humidity of 85% to 95%; Step S2: Heating the lemons to wake them up: take out the lemons refrigerated in step S1, raise the temperature of the lemon pulp to 23°C to 25°C at a heating rate of 1°C to 2°C per hour, and maintain this temperature for 6 to 12 hours; Step S3: Ripening by grade: Place the lemons processed in step S2 in a relatively closed environment and adjust the environmental parameters according to the target maturity grade: Step S4: To stabilize the maturity, place the lemons ripened in step S3 in an environment with a temperature of 10° C. to 12° C., a carbon dioxide concentration of 3000 ppm, and a relative humidity of 85% to 95% for 6 to 8 hours; Step S5: refrigerate and preserve the lemons after the treatment in step S4. Place the lemons in a refrigerated environment at 10°C.

2. A lemon ripening process according to claim 1, characterized in that: In step S3, Step S31: ripening the lemons after the heating and constant temperature treatment in step S2 to level 2-3, controlling the environmental parameters as follows: pulp temperature 23°C-25°C, carbon dioxide concentration 2000-3000 ppm, ethylene concentration 500-800 ppm, relative humidity 85%-95%, for 24-28 hours; Step S32: ripening the lemons ripened to level 2-3 in step S31 to level 3-4, controlling the environmental parameters as follows: pulp temperature 23°C-25°C, carbon dioxide concentration 4000-6000 ppm, ethylene concentration 300-500 ppm, relative humidity 85%-95%, for 24-28 hours; Step S33: ripening the lemons ripened to level 3-4 in step S32 to level 5, controlling the environmental parameters as follows: pulp temperature 15°C-18°C, carbon dioxide concentration 4500-5000 ppm, ethylene concentration ≤1 ppm, relative humidity 85%-95%, for 24-28 hours.

3. A lemon ripening process according to claim 2, characterized in that: In step S3, the closed environment is a ripening warehouse with a pressure difference control circulation system.

4. A lemon ripening process according to claim 3, characterized in that: In step S3, the maturity level is divided based on the peel, flesh and smell, and the specific standards are: Grade 1: In the early stages of fruit development, the peel is green and firm, with no deformation when pressed by the thumb, a smooth surface with no yellowing areas, white flesh, tightly connected pectin between cells, a firm texture, no sinking when pressed, the flesh and peel adhere tightly, and a distinct green and astringent smell with no lemon aroma. Grade 2: Early maturity: 70% to 80% of the peel is bluish green, with 15% to 30% turning yellowish green. The color transition is uneven and the texture is slightly hard. The flesh is white and slightly springs back when pressed. The astringency in the aroma is reduced, and a light lemon aroma appears. Grade 3: Half-ripe, with the peel 40% to 60% bluish-green and 40% yellowish-green respectively, showing a mottled pattern. The texture is soft and 30% to 50% dents when pressed with a thumb. The flesh is golden yellow with a slightly milky white core, soft in texture, and noticeably deforms when pressed. The fruit has less juice and emits a fresh lemon aroma with significantly less sourness. Grade 4: Fully ripe, with 70% to 95% of the peel light yellow, and the remaining green area concentrated in the fruit stem. The texture is soft and easily dents when pressed. The flesh is light yellow, with a moderate texture, soft and juicy, with loose connections between cells and juice oozing out. The aroma exudes a strong lemon aroma, with a balanced sweet and sour taste and no astringency. Level 5: Overripe, the skin is completely yellow with a glossy luster, and some areas are dark yellow. The texture is extremely soft, and it is difficult to rebound after being pressed. The flesh is golden yellow, extremely soft and juicy, and there is obvious juice oozing out when pressed. The flesh fibers are softened; the aroma is strong, slightly sweet, and the sugar content reaches its peak.

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