Lemon preservation method based on calcium-salicylic acid and tea polyphenol-chitosan

Abstract

The invention discloses a lemon fresh-keeping method based on calcium-salicylic acid and tea polyphenol-chitosan. The lemon fresh-keeping method comprises the steps of pretreatment before picking, soaking treatment after picking and storage management. 14 days before picking, a compound solution of 0.23 g / L chelated calcium and 2.0 mmol / L salicylic acid is sprayed to lemon fruits; after harvesting, the fruits are soaked in a 2% tea polyphenol and 1% chitosan composite fresh-keeping solution for 3 min, and the fruits are stored at the normal temperature of 25 DEG C after being dried in the shade; through the synergistic treatment, the hardness increase, weight loss rate increase and color deterioration of the lemon fruits can be obviously delayed, relatively high contents of total acids, total phenols, ascorbic acid and flavonoids are maintained, the accumulation of malonaldehyde is inhibited, and the activity of superoxide dismutase, peroxidase and catalase is improved; after the fruits are stored for 40 days, the weight loss rate of the fruits is only 30.37%, the total phenol content is 0.486 mg / mL, the SOD activity is 46.63 U / mL, and the fresh-keeping effect is obviously superior to that of a single treatment group and a control group; the method is simple in process, controllable in cost and high in safety.

Description

Technical Field

[0001] This invention relates to the field of fruit storage and preservation technology, specifically a method for preserving lemons based on calcium-salicylic acid and tea polyphenols-chitosan. Background Technology

[0002] Lemons, an important economic fruit of the Rutaceae family and Citrus genus, are widely cultivated in tropical and subtropical regions and are the world's third largest citrus crop. Their fruit is rich in vitamin C, organic acids, flavonoids, phenolic substances, and other bioactive components, possessing edible, medicinal, and health-promoting value. They are widely used in food, beverages, and cosmetics, and market demand continues to grow. However, lemons undergo active post-harvest physiological metabolism, making them susceptible to microbial infection, oxidation, and environmental factors. This leads to fruit rot, stem detachment, water loss, color deterioration, and nutrient degradation, severely impacting their storage quality and commercial value.

[0003] Currently, post-harvest preservation technologies for lemons mainly include physical preservation, chemical preservation, and biological preservation. Although low-temperature storage can delay fruit senescence, it is prone to chilling injury and has high equipment investment and operating costs, making it unsuitable for small and medium-sized growers. Controlled atmosphere storage technology is complex and expensive, making it difficult to popularize and promote. Although chemical preservatives are effective, they pose a risk of residue and do not meet food safety requirements and consumer health needs. Natural preservatives, due to their high safety and environmental friendliness, have become a research hotspot in recent years.

[0004] In existing technologies, pre-harvest calcium supplementation can enhance the stability of fruit cell walls and delay senescence; salicylic acid, as an endogenous active substance in plants, can regulate the physiological metabolism of fruits and improve their storage resistance; tea polyphenols have strong antioxidant properties and can inhibit oxidation reactions and microbial growth; chitosan can form a protective film, blocking oxygen and water exchange and inhibiting pathogen infection; existing studies have reported the application of single or two preservatives, such as pre-harvest spraying of calcium chloride and salicylic acid to improve the storage quality of jujubes, and tea polyphenol-chitosan composite films to extend the shelf life of passion fruit, but these studies mostly focus on single-stage treatment and do not fully utilize the synergistic effect of pre-harvest pretreatment and post-harvest preservation; in addition, the parameters such as preservative concentration and treatment time in existing technologies lack precise optimization, resulting in limited preservation effects, and there are no systematic reports on pre-harvest and post-harvest synergistic preservation technologies for lemons.

[0005] Therefore, developing a simple, low-cost, safe, and efficient method for the synergistic preservation of lemons, which combines pre-harvest treatment with post-harvest preservative coating, to achieve multi-dimensional regulation of lemon storage quality, delay fruit aging, and extend storage period, is of great practical significance and application value for enhancing the added value of the lemon industry and ensuring market supply stability. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a lemon preservation method based on calcium-salicylic acid and tea polyphenols-chitosan, which solves the problems mentioned in the background section.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preserving lemons based on calcium-salicylic acid and tea polyphenols-chitosan, comprising the following steps:

[0008] S1. Select lemon trees with consistent growth and vigorous growth, aged 5-8 years, planted in a planting area at 24.97°±0.5°N, 106.14°±0.5°E. One month before harvest, check the fruit trees for diseases and pests to ensure that the fruit is free from mechanical damage and disease and pest infection, and that the fruit maturity reaches 70-80% (soluble solids content 8.0%-8.8%). Harvest in mid-to-late August by hand to avoid damage to the fruit stem. Within 2 hours after harvest, transport the fruit to the processing site, remove deformed, diseased, and damaged fruit, and select fruits of uniform size (single fruit weight 120-150g) and consistent color for later use.

[0009] S2. Using chelated calcium (Ca content ≥150g / L) and salicylic acid (purity ≥99%) as raw materials and distilled water as solvent, a pre-harvest composite treatment solution was prepared. First, salicylic acid was dissolved in a small amount of ethanol (95% by volume), stirred until completely dissolved, then diluted with distilled water. Next, chelated calcium was added, stirred evenly, and the pH was adjusted to 5.5-6.5, ultimately yielding a composite solution of 0.23g / L calcium ions and 2.0mmol / L salicylic acid. After preparation, the concentration was calibrated using an FA-004 electronic analytical balance to ensure the error did not exceed ±5%.

[0010] S3. Spray treatment 14 days before lemon harvest, choosing a cloudy day or sunny evening (avoiding periods of high temperature and strong sunlight); use a backpack electric sprayer (working pressure 0.3-0.5MPa) to evenly spray the compound solution onto the surface of the fruit and the back of the leaves, with a spray volume of 1.5-2.0L per tree, ensuring that a uniform water film forms on the fruit surface without dripping; if it rains within 4 hours after spraying, re-spray within 24 hours after the rain; set up a control group (CK), spraying an equal amount of distilled water, with 3 replicates per group, and 5 trees per replicate;

[0011] S4. Select tea polyphenols (purity ≥98%) and chitosan (food grade, degree of deacetylation >90%) as raw materials, and distilled water as solvent. First, add chitosan to 60℃ distilled water and stir until completely dissolved. After cooling to room temperature, add tea polyphenols and stir continuously for 30 minutes. Adjust the pH value to 5.0-6.0 to finally obtain a composite preservation solution with a mass fraction of 2% tea polyphenols and 1% chitosan. During the preparation process, a KQ-500DE type CNC ultrasonic cleaner is used to assist in dissolution. The ultrasonic power is 500W and the ultrasonic time is 15 minutes to ensure that the preservation solution is uniform and stable.

[0012] S5. Divide the harvested and screened lemon fruits into two groups: one group is directly soaked (post-harvest treatment group), and the other group is fruits treated with pre-harvest spraying (pre-harvest and post-harvest combined treatment group); completely immerse the fruits in the compound preservative solution at a temperature of 20-25℃ for 3 minutes, using a multi-layer mesh basket to ensure that each fruit is fully in contact with the preservative solution; after soaking, remove the fruits and place them in a ventilated and cool place to air dry naturally for 4-6 hours at a relative humidity of 60%-70%, avoiding direct sunlight and high-temperature baking.

[0013] S6. After air-drying, the naked lemon fruits are placed on storage racks. The storage environment temperature is controlled at 25℃±1℃, the relative humidity is 65%-75%, and the ventilation rate is 0.5-1.0m / s. During the storage period, sampling tests are conducted every 10 days, with a sampling ratio of 5% of the total number of fruits in each group. Before the test, the fruits are placed at room temperature for 2 hours to equilibrate. The storage racks are made of stainless steel, with a spacing of 15cm between each layer and a spacing of 2-3cm between fruits to avoid squeezing and stacking.

[0014] S7. During storage, fruit quality indicators should be tested regularly, including: measuring fruit firmness using a GY-4 hardness tester (probe diameter 0.35cm, indentation depth 1cm), measuring two points on the equatorial region of each fruit, and taking the average value; and determining the weight loss rate using a weighing method, calculated using the following formula.

[0015]

[0016] The L*, a*, and b* values ​​of the fruit peel were determined using a CR-400 colorimeter, with four points near the equator measured for each fruit, and the average value was taken. The soluble solids content was determined using a PAL-1 handheld saccharimeter. Ascorbic acid content was determined according to GB5009.86—2016, and total acid content was determined according to GB12456—2021. Total phenols (absorbance at 760 nm) and flavonoids (absorbance at 510 nm) content were determined using ultrasonic extraction combined with a SynergyLX multifunctional microplate reader. Malondialdehyde (MDA) content and the activities of superoxide dismutase (SOD, absorbance at 450 nm), peroxidase (POD, absorbance at 470 nm), and catalase (CAT, absorbance at 240 nm) were determined using a kit method. The test kits were purchased from Beijing Box Biotechnology Co., Ltd., and the operation procedures were strictly followed according to the instructions.

[0017] S8. The core evaluation index is the quality of the fruit after 40 days of storage. When the fruit weight loss rate is ≤31%, the firmness is ≤16.5kg / cm², the L* value is ≤50, the a* value is ≥-12.5, the b* value is ≤42, and the total phenol content is ≥0.48mg / mL, the SOD activity is ≥46U / mL, and the MDA content is ≤3.6nmol / mL, the preservation effect is considered qualified. The combined treatment group must meet the above indicators and be significantly better than the single treatment group and the control group (P<0.05).

[0018] Optionally, the chelated calcium in step S2 is EDTA chelated calcium, and the ethanol dissolution ratio of salicylic acid is 1g of salicylic acid added to 5mL of ethanol, ensuring complete dissolution before dilution.

[0019] Optionally, the tea polyphenols mentioned in step S4 are green tea extracts, and the molecular weight of chitosan is 50,000-100,000 Da. The composite preservative solution should be used within 24 hours after preparation to avoid deterioration.

[0020] Optionally, during the soaking treatment described in step S5, the mass-to-volume ratio of the preservative solution to the fruit is 3:1 (L / kg), and the mixture is stirred every 30 seconds during the soaking process to ensure uniform treatment.

[0021] Optionally, the storage environment described in step S6 uses a JW-1042 high-speed refrigerated centrifuge to assist in humidity control and a DW-86L490J ultra-low temperature freezer as a backup for emergency cooling to ensure temperature stability.

[0022] Optionally, in step S7, the sample extraction conditions for determining the total phenol content are as follows: weigh 0.1g of lemon pulp sample, add 2.5mL of 60% ethanol extraction solution, ultrasonically extract at 25℃ for 20min, centrifuge at 12000r / min for 10min, and take the supernatant to make up to 2.5mL. Use gallic acid as the standard curve ( , ) Calculate the content.

[0023] Optionally, the sample extraction conditions for the flavonoid content determination in step S7 are as follows:

[0024] Weigh 0.1g of lemon pulp sample, add 1mL of 60% ethanol extraction solution, sonicate at 25℃ for 20min, centrifuge at 12000r / min for 10min, take the supernatant and dilute to 1mL, using rutin as the standard curve ( , ) Calculate the content.

[0025] Optionally, the harvesting criteria for lemons in step S1 are: fruit diameter 6-7cm, peel thickness 2.5-3.0mm, and titratable acid content 5.0-5.5g / 100mL.

[0026] This invention provides a method for preserving lemons based on calcium-salicylic acid and tea polyphenols-chitosan, which has the following beneficial effects:

[0027] This lemon preservation method based on calcium-salicylic acid and tea polyphenols-chitosan constructs a multi-dimensional, full-chain lemon preservation technology system through synergistic treatment of pre-harvest calcium-salicylic acid compound spraying and post-harvest tea polyphenols-chitosan compound soaking. Compared with existing single preservation methods, it has significant technical advantages and practical value, with the following specific beneficial effects:

[0028] First, the preservation effect is significantly improved, and the storage period is greatly extended. This invention achieves precise control over the aging process of lemon fruit through the synergistic effect of pre-harvest treatment and post-harvest preservation. Pre-harvest spraying of calcium and salicylic acid can enhance the stability of the fruit's cell wall structure and improve the fruit's own resistance to adverse conditions. Post-harvest tea polyphenol-chitosan composite membrane can effectively block oxygen and water exchange, inhibiting microbial infection and oxidation reactions. Experimental results show that after treatment with the method of this invention, the storage period of lemons at room temperature (25℃) can be extended to 40 days, which is twice that of the control group (CK) of 20 days. After 40 days of storage, the fruit... The weight loss rate was only 30.37%, a decrease of 14.2% compared to the control group's 35.28%. The firmness was 16.34 kg / cm², significantly lower than the control group's 18.42 kg / cm², effectively preventing the fruit from hardening and spoiling due to moisture loss. At the same time, this method can significantly delay the deterioration of the fruit peel color. After 40 days of storage, the combined treatment group had L* values ​​of 49.27, a* values ​​of -12.13, and b* values ​​of 41.55, which were 12.35%, 28.36%, and 16.75% lower than the control group, respectively. The fruit still maintained a good green appearance, without obvious browning or spots.

[0029] Secondly, the nutritional components are fully preserved, and the fruit quality remains stable. The core value of lemons lies in their rich content of vitamin C, total phenols, flavonoids, and other nutrients. This invention effectively inhibits the degradation of these components through synergistic treatment. After 40 days of storage, the ascorbic acid content in the combined treatment group was 106.18 mg / mL, an increase of 25.7% compared to the control group's 84.45 mg / mL; the total phenol content was 0.486 mg / mL, an increase of 21.5% compared to the control group's 0.400 mg / mL; the flavonoid content was 0.036 mg / mL, an increase of 33.3% compared to the control group's 0.027 mg / mL; and the total acid content was 49.17 g / 100 mL, an increase of 7.5% compared to the control group's 45.72 g / 100 mL, effectively maintaining the lemon's flavor and nutritional value. Furthermore, the treatment groups had minimal impact on the soluble solids content, which remained between 8.42% and 10.33% during storage, showing no significant difference from the control group, thus avoiding the problem of the fruit becoming overly sweet or losing its flavor.

[0030] Furthermore, the antioxidant metabolic balance was well maintained, delaying fruit senescence. Fruit senescence is closely related to the accumulation of reactive oxygen species. This invention significantly improved the antioxidant capacity of fruits through synergistic treatment. After 40 days of storage, the MDA content in the combined treatment group was 3.58 nmol / mL, which was 29.1% lower than the 5.05 nmol / mL in the control group, effectively reducing cell membrane lipid peroxidation damage. The SOD activity was 46.63 U / mL, the POD activity was 12.63 U / mL, which were 66.4% and 57.6% higher than the control group, respectively, and the CAT activity was 5.63 U / mL, which was 27.7% higher than the control group. The three antioxidant enzymes worked synergistically to effectively scavenge reactive oxygen free radicals in the fruit, maintain the oxidative metabolic balance, delay the fruit senescence process from a physiological mechanism, and reduce the occurrence of decay and spoilage.

[0031] Finally, the process of this invention is simple and feasible, cost-controllable, safe, and easy to scale up; pre-harvest spraying and post-harvest soaking are simple to operate, and the required equipment (sprayers, soaking baskets, storage racks, etc.) are all commonly used agricultural production equipment, without the need for additional expensive facilities; the preservatives used (calcium, salicylic acid, tea polyphenols, chitosan) are all natural substances or food-grade raw materials, with no residue risk and meeting food safety requirements; the concentration of preservatives has been precisely optimized, the dosage is small, and the cost is low, with a processing cost of only 0.1-0.2 yuan per kilogram of lemons, making it suitable for small and medium-sized growers and large storage enterprises; at the same time, this invention provides detailed operating parameters and detection methods, with good repeatability and high stability, providing technical support for the standardized storage and preservation of lemons, helping to enhance the market competitiveness of lemon products and promote the sustainable development of the industry. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the invention process;

[0033] Figure 2 This invention provides a schematic diagram illustrating the effect of different treatments on the firmness of lemon fruits.

[0034] Figure 3 A schematic diagram illustrating the effect of different treatments on the weight loss rate of lemon fruits according to this invention;

[0035] Figure 4 Schematic diagram of the appearance phenotypes of lemon fruits treated with different methods according to the invention;

[0036] Figure 5 This is a schematic diagram illustrating the effect of the soluble solids content of this invention on the nutritional components of lemon fruit.

[0037] Figure 6 A schematic diagram illustrating the effect of total acid content on the nutritional components of lemon fruit according to this invention;

[0038] Figure 7 A schematic diagram illustrating the effect of ascorbic acid content on the nutritional components of lemon fruit according to this invention;

[0039] Figure 8 This is a schematic diagram illustrating the effect of the total phenol content of this invention on the nutritional components of lemon fruit;

[0040] Figure 9 A schematic diagram illustrating the effect of flavonoid content on the nutritional components of lemon fruit according to this invention;

[0041] Figure 10 This is a schematic diagram illustrating the effect of MDA content on the antioxidant enzyme activity of lemon fruit.

[0042] Figure 11 This is a schematic diagram illustrating the effect of SOD activity on the antioxidant enzyme activity of lemon fruit.

[0043] Figure 12 This is a schematic diagram illustrating the effect of POD activity on the antioxidant enzyme activity of lemon fruit.

[0044] Figure 13 This is a schematic diagram illustrating the effect of CAT activity on the antioxidant enzyme activity of lemon fruit. Detailed Implementation

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0046] In the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0047] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0048] Example 1: A method for preserving lemons based on calcium-salicylic acid and tea polyphenols-chitosan, with a pre-harvest and post-harvest combined treatment group, as detailed below:

[0049] (1) Sixty lemon trees with a height of 6 years and uniform vigor were selected from 24.97°N and 106.14°E. They were harvested on August 20, 2024. Eighty hundred fruits with a single fruit weight of 120-150g, a transverse diameter of 6-7cm, no diseases or pests, and no mechanical damage were selected and randomly divided into 4 groups of 200 fruits each, with 3 replicates.

[0050] (2) Weigh 0.23 g / L chelated calcium (Ca content 150 g / L) and 2.0 mmol / L salicylic acid. Dissolve 1 g of salicylic acid in 5 mL of 95% ethanol, dilute with distilled water, add chelated calcium, stir evenly, adjust pH to 6.0, and calibrate the concentration using FA-004 electronic analytical balance.

[0051] (3) On August 6, 2024 (14 days before harvest), the experimental group fruit trees were sprayed with a compound solution using a backpack electric sprayer (pressure 0.4MPa), 2.0L per tree, while the control group was sprayed with an equal amount of distilled water;

[0052] (4) Weigh 2% tea polyphenols and 1% chitosan, dissolve the chitosan in 60℃ distilled water, cool and add tea polyphenols, sonicate at 500W for 15min, stir for 30min, adjust pH to 5.5, and use within 24h after preparation.

[0053] (5) After harvesting, wash and drain the fruits. Immerse the fruits of the pre-harvest treatment group in the compound preservation solution at 25°C for 3 minutes. The volume ratio of the preservation solution to the fruit is 3:1. Stir once every 30 seconds. After taking them out, place them in a ventilated and cool place (humidity 65%) to air dry for 5 hours.

[0054] (6) After air drying, the naked fruit is placed on a stainless steel storage rack and stored at 25℃±1℃, humidity 70%, and ventilation rate 0.8m / s. The spacing between each layer is 15cm and the spacing between fruits is 2cm.

[0055] (7) Sampling and testing shall be conducted every 10 days. The test indicators include hardness, weight loss rate, color (L, a, b values), soluble solids, total acid, ascorbic acid, total phenols, flavonoid content, MDA content, SOD, POD, CAT activity, and the test methods are the same as those described in claim 1.

[0056] Comparative Example 1: Control Group (CK)

[0057] (1) The experimental materials used were the same as those used in Example 1;

[0058] (2) Spray an equal amount of distilled water before harvesting, and do not soak after harvesting. After drying directly in the shade, store according to the storage conditions in Example 1.

[0059] (3) The quality testing method is the same as in Example 1;

[0060] Comparative Example 2: Pre-harvest separate treatment group

[0061] (1) The experimental materials used were the same as those used in Example 1;

[0062] (2) The pre-harvest spraying treatment is the same as in Example 1. After harvesting, no soaking treatment is performed. After air drying, the product is stored according to the storage conditions in Example 1.

[0063] (3) Quality inspection: The method is the same as in Example 1;

[0064] Comparative Example 3: Postharvest Separate Treatment Group

[0065] (1) The experimental materials used were the same as those used in Example 1;

[0066] (2) Spray distilled water before harvesting, soak in the same way as in Example 1 after harvesting, and store in the same way as in Example 1 after air drying;

[0067] (3) Quality inspection: The method is the same as in Example 1;

[0068] The specific experimental data is recorded as follows:

[0069] Table 1 shows the effects of different treatments on the L value of lemon fruits.

[0070]

[0071] Note: Different lowercase letters after the data in the same row indicate significant differences between groups (P < 0.05); L value reflects the lightness or darkness of the peel, and the larger the value, the darker the peel color and the more severe the browning; there were no significant differences among the groups in the first 20 days of storage, but the L value of the control group increased rapidly after 30 days, and was 14.1% higher than that of the combined treatment group at 40 days, indicating that the combined treatment can significantly inhibit the abnormal increase in the lightness or darkness of the peel and delay browning;

[0072] Table 2 shows the effects of different treatments on the a value of lemon fruits.

[0073]

[0074] Note: Different lowercase letters after the data in the same row indicate significant differences between groups (P < 0.05); the a value reflects the redness and greenness of the peel, and the larger the value (closer to 0), the redder the peel and the more obvious the color deterioration; at 40 days, the a value of the control group (-9.45) was significantly higher than that of the combined treatment group (-12.13), and the combined treatment group was 28.36% lower than the control group, indicating that it can effectively inhibit the peel from turning red and maintain the green tone;

[0075] Table 3 shows the effects of different treatments on the b-value of lemon fruits.

[0076]

[0077] Note: Different lowercase letters after the data in the same row indicate significant differences between groups (P < 0.05); b value reflects the yellowness of the peel, the larger the value, the more yellow the peel and the lower the freshness; at 40 days, the b value of the control group (49.91) was significantly higher than that of the combined treatment group (41.55), and the combined treatment group was 16.75% lower than that of the control group, indicating that it can delay the excessive yellowing of the peel and maintain good appearance quality.

[0078] The experimental results and analysis are as follows:

[0079] A. Changes in hardness, such as Figure 2 As shown:

[0080] During storage, the firmness of the fruits in all groups showed an increasing trend. The control group showed the fastest increase, reaching 18.42 kg / cm² after 40 days of storage. Example 1 (combined treatment group) had the lowest firmness at 16.34 kg / cm², which was significantly lower than that of Comparative Examples 1-3 (P < 0.05), indicating that the combined treatment can effectively inhibit the abnormal increase in fruit firmness.

[0081] B. Changes in weightlessness rate, such as Figure 3 As shown:

[0082] The weight loss rate in the control group continued to rise, reaching 35.28% after 40 days; the weight loss rate in Example 1 was only 30.37%, which was 14.2% lower than that in the control group and significantly lower than that in Comparative Example 2 (31.74%) and Comparative Example 3 (31.89%), indicating that the combined treatment had a better inhibitory effect on water loss.

[0083] C. Color changes, as shown in Table 1-3:

[0084] After 40 days of storage, the L value (49.27), a value (-12.13), and b value (41.55) of Example 1 were all significantly lower than those of the control group (L=56.22, a=-9.45, b=49.91). Furthermore, the combined treatment group showed the slowest rate of color deterioration and the best fruit greening effect among all treatment groups. Figure 4 The appearance is consistent with the description.

[0085] D. Changes in nutritional composition, combined with Figures 5 to 9 data:

[0086] After 40 days of storage, the total acid content of Example 1 was 49.17 g / 100 mL, ascorbic acid was 106.18 mg / mL, total phenols were 0.486 mg / mL, and flavonoids were 0.036 mg / mL, all of which were significantly higher than those of Comparative Examples 1-3. The total phenol content was 3.1% higher than that of Comparative Example 2 and 11.7% higher than that of Comparative Example 3, indicating that the combined treatment can better preserve the nutrients.

[0087] E. Changes in antioxidant indicators, such as Figures 10 to 13 As shown:

[0088] In Example 1, after 40 days of storage, the MDA content was 3.58 nmol / mL, which was significantly lower than that of the control group (5.05 nmol / mL), Comparative Example 2 (3.41 nmol / mL), and Comparative Example 3 (4.09 nmol / mL). The SOD activity was 46.63 U / mL and the POD activity was 12.63 U / mL, both of which were significantly higher than those of other groups, indicating that the combined treatment can effectively maintain the activity of antioxidant enzymes and inhibit oxidative damage.

[0089] In summary, the pre-harvest and post-harvest combined treatment method in Example 1 is significantly better than the other comparative methods in terms of lemon preservation effect. It can effectively extend the storage period, maintain fruit quality and nutritional components, and has significant application advantages.

[0090] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preserving lemons based on calcium-salicylic acid and tea polyphenols-chitosan, characterized in that, Includes the following steps: S1. Select lemon trees with consistent growth and vigorous growth. One month before harvest, check the trees for diseases and pests to ensure that the fruit is free from mechanical damage and disease and pest infection, and that the fruit is 70-80% ripe. Harvest in mid-to-late August by hand to avoid damage to the fruit stem. Within 2 hours after harvest, transport the fruit to the processing site, remove deformed, diseased, and damaged fruit, and select fruits that are uniform in size and color for later use. S2. Select chelated calcium and salicylic acid as raw materials and distilled water as solvent to prepare a pre-harvest composite treatment solution. First, dissolve salicylic acid in a small amount of ethanol and stir until completely dissolved. Then add distilled water to dilute it. Next, add chelated calcium, stir evenly, and adjust the pH value to 5.5-6.

5. Finally, a composite solution of calcium ions with a concentration of 0.23 g / L and salicylic acid with a concentration of 2.0 mmol / L is obtained. After preparation, the concentration was calibrated using an electronic analytical balance. S3. Spray the solution 14 days before lemon harvest, choosing a cloudy day or a sunny evening. Use a backpack electric sprayer to evenly spray the compound solution onto the surface of the fruit and the back of the leaves. The spray volume is 1.5-2.0L per tree, ensuring that a uniform water film forms on the fruit surface without dripping. If it rains within 4 hours after spraying, re-spray within 24 hours after the rain. Set up a control group, spraying an equal amount of distilled water. Each treatment has 3 replicates, with 5 trees per replicate. S4. Select tea polyphenols and chitosan as raw materials, and distilled water as solvent; first, add chitosan to 60℃ distilled water, stir until completely dissolved, cool to room temperature, add tea polyphenols, continue stirring for 30 minutes, adjust the pH value to 5.0-6.0, and finally obtain a composite preservation solution with a mass fraction of 2% tea polyphenols and 1% chitosan; during the preparation process, a CNC ultrasonic cleaner is used to assist in dissolution, and the ultrasonic time is 15 minutes to ensure that the preservation solution is uniform and stable; S5. Divide the harvested and screened lemon fruits into two groups. One group will be directly soaked, and the other group will be fruits that have been sprayed before harvest. Immerse the fruits completely in the compound preservative solution at a temperature of 20-25℃ for 3 minutes. Use a multi-layer mesh basket for soaking to ensure that each fruit is fully in contact with the preservative solution. After soaking, remove the fruits and place them in a ventilated and cool place to air dry naturally for 4-6 hours. The relative humidity of the air drying environment should be 60%-70%. Avoid direct sunlight and high-temperature baking. S6. After air-drying, the naked lemon fruits are placed on storage racks. The storage environment temperature is controlled at 25℃±1℃, the relative humidity is 65%-75%, and the ventilation rate is 0.5-1.0m / s. During the storage period, sampling tests are conducted every 10 days, with a sampling ratio of 5% of the total number of fruits in each group. Before the test, the fruits are placed at room temperature for 2 hours to equilibrate. The storage racks are made of stainless steel, with a spacing of 15cm between each layer and a spacing of 2-3cm between fruits to avoid squeezing and stacking. S7. During storage, fruit quality indicators should be tested regularly. Fruit firmness should be measured using a hardness tester with a probe diameter of 0.35 cm and an indentation depth of 1 cm. Two points should be measured at the equator for each fruit, and the average value should be taken. The weight loss rate should be determined by weighing, and the calculation formula is as follows: The L*, a*, and b* values ​​of the fruit peel were determined using a colorimeter, with four points near the equator measured for each fruit, and the average value was taken. The soluble solids content was determined using a handheld saccharimeter. Ascorbic acid content was determined according to GB5009.86—2016, and total acid content was determined according to GB12456—2021. Total phenols and flavonoids content were determined using ultrasonic extraction combined with a Synergy LX multifunctional microplate reader. Malondialdehyde content and the activities of superoxide dismutase, peroxidase, and catalase were determined using a kit method. S8. The core evaluation index is the quality of the fruit after 40 days of storage. When the fruit weight loss rate is ≤31%, the firmness is ≤16.5kg / cm², the L* value is ≤50, the a* value is ≥-12.5, the b* value is ≤42, and the total phenol content is ≥0.48mg / mL, the SOD activity is ≥46U / mL, and the MDA content is ≤3.6nmol / mL, the preservation effect is considered qualified. The combined treatment group must meet the above indicators and be significantly better than the single treatment group and the control group.

2. The lemon preservation method according to claim 1, characterized in that, The chelated calcium mentioned in step S2 is EDTA chelated calcium. The ethanol dissolution ratio of salicylic acid is 1g of salicylic acid to 5mL of ethanol, ensuring complete dissolution before dilution.

3. The lemon preservation method according to claim 1, characterized in that, The tea polyphenols mentioned in step S4 are green tea extracts, and the molecular weight of chitosan is 50,000-100,000 Da. The composite preservation liquid should be used within 24 hours after preparation to avoid failure.

4. The lemon preservation method according to claim 1, characterized in that, In step S5, during the soaking process, the mass-to-volume ratio of the preservative solution to the fruit is 3:1 (L / kg), and the mixture is stirred every 30 seconds to ensure uniform processing.

5. The lemon preservation method according to claim 1, characterized in that, The storage environment described in step S6 uses a high-speed refrigerated centrifuge to assist in humidity control and an ultra-low temperature freezer as a backup for emergency cooling to ensure temperature stability.

6. The lemon preservation method according to claim 1, characterized in that, In step S7, the total phenol content determination was performed under the following sample extraction conditions: 0.1 g of lemon pulp sample was weighed, 2.5 mL of 60% ethanol extract was added, and the sample was ultrasonically extracted at 25°C for 20 min, centrifuged at 12000 r / min for 10 min, and the supernatant was diluted to 2.5 mL. Gallic acid was used as the standard curve. , ) Calculate the content.

7. The lemon preservation method according to claim 1, characterized in that, When determining the flavonoid content in step S7, the sample extraction conditions are as follows: Weigh 0.1g of lemon pulp sample, add 1mL of 60% ethanol extraction solution, sonicate at 25℃ for 20min, centrifuge at 12000r / min for 10min, take the supernatant and dilute to 1mL, using rutin as the standard curve ( , ) Calculate the content.

8. The lemon preservation method according to claim 1, characterized in that, The harvesting standards for lemons mentioned in step S1 are: fruit diameter 6-7cm, peel thickness 2.5-3.0mm, and titratable acid content 5.0-5.5g / 100mL.

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