Method for improving pepper quality

Abstract

The invention provides a method for improving the quality of peppers. The method comprises the following steps: sowing the peppers according to the line spacing of 50 cm and the plant spacing of 30 cm; the method comprises the following steps: spraying a methyl jasmonate solution with the concentration of 2.5 mmol. L <-1 > on stems and leaves of a whole plant in the initial flowering period of the pepper; thoroughly decomposed sheep manure is applied 7-10 days before field planting; dressing a water-soluble fertilizer along with water after fruit setting of the first pepper; a yellow plate, an insect-proof net and a sex attractant are adopted for integrated insect prevention, and the peppers are harvested in the mature period. The MeJA regulation and control scheme which is accurate in concentration, clear in period, systematic in evaluation and suitable for the continuous cropping obstacle environment is provided for improving the quality of the chilies, and the purposes of synchronously improving the flavor and nutrition of the chilies and cooperatively enhancing stress resistance and commodity are achieved.

Description

Technical Field

[0001] This invention belongs to the field of chili cultivation technology, specifically relating to a method for improving the quality of chili peppers. Background Technology

[0002] Chili pepper (Capsicum annuum L.) is my country's largest vegetable crop, with a cultivation area exceeding 2.26 million hectares in 2020. 2 Chili peppers are rich in capsaicinoids, vitamin C, and soluble sugars, which are core indicators determining their spiciness, nutritional value, and economic grade. However, the quality of chili peppers is regulated by three factors: genetics, environment, and cultivation practices. Especially under continuous cropping in plastic greenhouses, soil nutrient imbalances and frequent abiotic stresses can easily lead to problems such as low capsaicin content, decreased vitamin C, and imbalanced sugar-acid ratios. This results in diluted flavor in commercial fruits and lower grades of processed raw materials, becoming a bottleneck restricting the high-quality development of the industry.

[0003] Plant endogenous hormones play a crucial role in secondary metabolism and quality development. Methyljasmonate (MeJA), a lipid signaling molecule widely found in higher plants, can upregulate phenylalanine ammonia-lyase (PAL) activity through the phenylpropane metabolic pathway, promoting capsaicin synthesis. Simultaneously, it induces antioxidant enzyme systems such as peroxidase (POD) and polyphenol oxidase (PPO), enhancing fruit stress resistance and postharvest tolerance. Existing research largely focuses on single indicators and single harvests, lacking dynamic window studies on the simultaneous improvement of the three-dimensional quality profile of capsaicin, vitamin C, and soluble sugars. Furthermore, its stability and reproducibility have not been verified under multi-year continuous cropping greenhouse conditions, leading to frequent failures when translating laboratory results into field applications. Therefore, there is an urgent need in production for a precise concentration, clearly defined timing, systematic evaluation, and applicable MeJA regulation scheme suitable for continuous cropping obstacles, to achieve the goal of simultaneously improving pepper flavor and nutrition, and synergistically enhancing stress resistance and marketability. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for improving the quality of chili peppers, which addresses the shortcomings of the prior art. This method provides a MeJA regulation scheme with precise concentration, clear timing, systematic evaluation, and applicable to continuous cropping obstacle environments to improve the quality of chili peppers, so as to achieve the goal of simultaneously improving the flavor and nutrition of chili peppers and synergistically enhancing their stress resistance and marketability.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for improving the quality of chili peppers, the method being as follows: S1. Sow peppers with a row spacing of 50 cm and a plant spacing of 30 cm; S2. During the initial flowering stage of chili peppers, spray the entire plant with a concentration of 2.5 mmol·L⁻¹. -1 Methyl jasmonate solution; S3. Apply well-rotted sheep manure 7-10 days before transplanting; S4. Apply water-soluble fertilizer with irrigation water after the first pepper fruit sets. S5. Insect control is achieved by using yellow sticky traps, insect nets, and sex pheromones. Peppers are harvested at maturity.

[0006] Preferably, the concentration in S2 is 2.5 mmol·L⁻¹. -1 The method for preparing the methyl jasmonate solution is as follows: dissolve 56 mg of methyl jasmonate in 1 mL of anhydrous ethanol to obtain a concentration of 250 mmol·L⁻¹. -1 The mother liquor, 1 mL of which yielded a concentration of 250 mmol·L⁻¹ -1 Add 99 mL of water to the mother liquor and mix well to obtain a concentration of 2.5 mmol·L⁻¹. -1 Methyl jasmonate solution.

[0007] Preferably, the application rate of the decomposed sheep manure in S3 is 45 t·hm. -2 .

[0008] Preferably, the application rate of the water-soluble fertilizer in S4 is 150 kg·hm. -2 The water-soluble fertilizer has a total nitrogen content of 15%, a phosphorus pentoxide content of 5%, a potassium oxide content of 35%, an iron content of 0.15%, and a manganese content of 0.08%.

[0009] Preferably, in S5, the stem diameter and plant height of the chili pepper are increased; the content of soluble sugar, vitamin C, capsaicin, dihydrocapsaicin, and total capsaicin in the chili pepper fruit is increased; and the activities of phenylalanine ammonia-lyase, peroxidase, and polyphenol oxidase in the chili pepper fruit are increased.

[0010] Compared with the prior art, the present invention has the following advantages: 1. This invention addresses the technical challenge of unstable content, weakened flavor, and reduced marketability of key quality indicators such as capsaicin, vitamin C, and soluble sugars in chili peppers during fruit quality formation due to environmental fluctuations and imbalances in endogenous hormone regulation. It proposes a comprehensive regulation scheme based on exogenous methyl jasmonate (MeJA), a two-year continuous cropping experiment in plastic greenhouses, and dynamic measurement at multiple time points and multivariate statistical verification to achieve synergistic improvement in high yield, high quality, and stress resistance of chili peppers.

[0011] 2. This invention provides a precise concentration, clear timing, systematic evaluation, and applicable MeJA regulation scheme for improving the quality of chili peppers, so as to achieve the goal of simultaneously improving the flavor and nutrition of chili peppers and synergistically enhancing their stress resistance and marketability.

[0012] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0013] Figure 1 This is a graph showing the soluble sugar content of pepper fruits treated with different concentrations of MeJA for 20-60 days in 2024 and 2025, according to Example 1 of the present invention.

[0014] Figure 2 This is a graph showing the vitamin C content of pepper fruits treated with different concentrations of MeJA for 20-60 days in 2024 and 2025, according to Example 1 of the present invention.

[0015] Figure 3 This is a graph showing the phenylalanine ammonia-lyase (PAL) activity of pepper fruits treated with different concentrations of MeJA in 2024 and 2025 for 20-60 days according to Example 1 of the present invention.

[0016] Figure 4 This is a graph showing the peroxidase (POD) activity of pepper fruits treated with different concentrations of MeJA in 2024 and 2025 for 20-60 days, according to Example 1 of the present invention.

[0017] Figure 5 This is a graph showing the polyphenol oxidase (PPO) activity of pepper fruits treated with different concentrations of MeJA in 2024 and 2025 for 20-60 days, according to Example 1 of the present invention.

[0018] Figure 6 This is a bipolar diagram of the principal components of Example 1 of the present invention. In the diagram, TS: stem diameter; PH: plant height; VC: vitamin C; SS: soluble sugar; C: capsaicin; D: dihydrocapsaicin; TC: total capsaicin; PAL: phenylalanine ammonia-lyase activity; POD: peroxidase activity; PPO: polyphenol oxidase activity.

[0019] Different lowercase letters in the above figures represent significant differences between treatments (p<0.05). Detailed Implementation

[0020] Example 1 The experiment was conducted in 2024-2025 at the Chili Science and Technology Courtyard in Ligao Township, Tunliu District, Changzhi City, Shanxi Province (113°E, 36.27°N). The area has an altitude of 946 m, an average temperature of 10.3℃, an average sunshine duration of 2548.5 h, and a soil pH of 7.2.

[0021] This embodiment describes a method for improving the quality of chili peppers. The method is as follows: S1. Cultivation Technical Conditions: A north-south oriented steel-framed plastic greenhouse was used, with a top height of 3.2 m and a shoulder height of 1.8 m, covered with 0.12 mm PO film. A 50 cm top ventilation opening and a 60 cm skirt ventilation opening were provided. For two consecutive years (2024-2025), six treatments were set up in a randomized block design with three replicates, for a total of 18 plots. Each plot contained 30 plants, with a row spacing of 50 cm and a plant spacing of 30 cm. Peppers were sown, and protective rows were set up around the perimeter. The pepper variety was "Jin Jiao 301". S2. At the initial flowering stage of chili peppers (when the first flower of 10% of the plants has opened), spray the entire plant with a concentration of 2.5 mmol·L⁻¹. -1 The application of methyl jasmonate (MeJA) solution should be done at a rate that ensures the entire plant is evenly moistened and the leaves begin to drip. This should be completed between 9:00 and 10:00 AM to avoid decomposition caused by strong sunlight and high temperatures. The concentration is 2.5 mmol·L. -1 The method for preparing the methyl jasmonate solution is as follows: dissolve 56 mg of methyl jasmonate in 1 mL of anhydrous ethanol to obtain a concentration of 250 mmol·L⁻¹. -1 The mother liquor, 1 mL of which yielded a concentration of 250 mmol·L⁻¹ -1 Add 99 mL of water to the mother liquor and mix well to obtain a concentration of 2.5 mmol·L⁻¹. -1 Methyl jasmonate solution; This embodiment tested both water spray (CK) and five concentrations of MeJA: 1 mmol·L⁻¹. -1 (M1), 1.5 mmol·L -1 (M2), 2.5 mmol·L -1 (M3), 3.5 mmol·L -1 (M4), 5 mmol·L -1 (M5) processing; S3. Apply 45 t·hm² 7-10 days before transplanting (7 days before transplanting in this example). -2 Well-rotted sheep manure; S4. After the first fruit set of peppers, the application rate with irrigation water is 150 kg·hm. -2 The water-soluble fertilizer contains 15% total nitrogen, 5% phosphorus pentoxide, 35% potassium oxide, 0.15% iron, and 0.08% manganese. S5. Use yellow sticky traps, insect nets, and sex pheromones to control aphids, whiteflies, and tobacco budworms. Do not use any plant growth regulators or foliar fertilizers containing jasmonic acid throughout the process to eliminate background interference. Harvest the peppers at maturity.

[0022] Measurement contents: (1) Morphological indicators: 20, 30, 40, 50 and 60 days after flowering, 10 representative plants were selected in each plot. The stem diameter was measured 1 cm below the first true leaf node using a digital vernier caliper (accuracy 0.01 mm); the plant height from the base of the rhizome to the growing point was measured using a steel tape measure (accuracy 0.1 cm).

[0023] (2) Fruit quality: Five fruits with the same flowering node, free from pests and diseases, and weighing 5 ± 0.5 g each were collected at the same time, flash-frozen in liquid nitrogen, and stored at −80 ℃. ① Soluble sugars: Boxbio kit (colorimetric method, λ=620 nm); ② Vitamin C: Boxbio kit (molybdenum blue colorimetric method, λ=760 nm); ③ Capsaicin and dihydrocapsaicin: According to the modified method of GB / T 21266-2007, the samples were dried at 80 ℃ for 48 h, ground through a 40-mesh sieve, and extracted by ultrasonication. HPLC conditions: C18 column, mobile phase methanol-water (80:20), flow rate 1.0 mL·min -1 The column temperature was 30 ℃, and the detection wavelength was 280 nm. The formula for calculating total capsaicin is: (capsaicin content + dihydrocapsaicin content) / 0.9.

[0024] (3) Key enzyme activities: The following were measured in the same batch of samples: ① Phenylalanine ammonia-lyase (PAL): Boxbio kit (colorimetric method, λ=290 nm); ② Peroxidase (POD): Boxbio kit (colorimetric method, λ=470 nm); ③ Polyphenol oxidase (PPO): Boxbio kit (colorimetric method, λ=420 nm); all were measured on a fresh weight basis and were repeated 3 times.

[0025] Analytical methods: Data quality control: All indicators were measured independently for two years, and outliers were removed using the Grubbs method; the instrument was calibrated daily with national standard reference material (capsaicin purity ≥98%), and the relative error was <3%.

[0026] Significance test: Two-way (concentration × time) ANOVA was performed using IBM SPSS Statistics 27, with Duncan multiple comparisons (α=0.05).

[0027] Principal component analysis (PCA): After KMO and Bartlett's test of sphericity (P<0.01), PCA dimensionality reduction was performed using Origin 2021 to extract principal components with eigenvalues ​​>1, calculate loadings and scores, clarify the influence weights of different concentrations of MeJA on the overall quality of chili peppers, and determine the optimal harvest window.

[0028] Existing reports mostly focus on potted plants or one-year field trials, which are insufficient to withstand real-world production variables such as continuous cropping obstacles and soil background fluctuations. Using the method of this invention, the stem diameter and plant height of chili peppers treated with different concentrations of MeJA for 20–60 days in 2024 and 2025 are shown in Tables 1-2.

[0029] Table 1. Stem diameter of chili peppers treated with different concentrations of MeJA for 20–60 days in 2024 and 2025. Note: Lowercase letters in the table indicate significant differences between different treatments (p<0.05).

[0030] Table 1 shows that, in a typical greenhouse in Shanxi Province with five consecutive years of cropping, the soil pH and pathogen population were both at the critical values ​​for continuous cropping obstacles in peppers. The stem diameter of peppers treated with different concentrations of MeJA generally showed an increasing trend over both years. At all time points over the two years, 2.5 mmol·L⁻¹ was the most effective concentration. -1 MeJA performed best and was significantly higher than CK. The results showed that the stem diameter of the treatment group was 12%~14.29% and 8.89%~14.1% higher than the control in 2024 and 2025, respectively, proving that the scheme remained stable and effective under continuous cropping adversity and significantly improved the credibility of the technology implementation.

[0031] Table 2. Plant height of chili peppers treated with different concentrations of MeJA for 20–60 days in 2024 and 2025. Note: Lowercase letters in the table indicate significant differences between different treatments (p<0.05).

[0032] Table 2 shows that the levels of all treatments in 2024 and 2025 showed a continuous upward trend with the passage of sampling time. The overall level, from highest to lowest, was M3 > M5 ≈ M4 > M2 > M1 > CK, indicating that an appropriate exogenous MeJA concentration can significantly increase the plant height of peppers, with M3 showing the most significant effect. The optimal concentration for both 2024 and 2025 was 2.5 mmol·L⁻¹. -1 The plant height in the treatment groups increased by 4.77%–10.27% and 4.44%–9.75% compared to the control group, respectively. Data from both years together indicate that M3 not only rapidly improves early indicators but also maintains rapid accumulation in the middle and late stages, demonstrating stable and highly reproducible effects, making it an optimal treatment condition.

[0033] Traditional cultivation often uses the ripening of fruit or the maximum weight of a single fruit as the basis for harvesting, resulting in the loss of key indicators such as soluble sugar and vitamin C during the decline phase.

[0034] Depend on Figure 1As can be seen, this invention, through five consecutive samplings at 20-60 days post-flowering, showed an overall upward trend in the soluble sugar content of pepper fruits treated with different concentrations of MeJA over two years, reaching its highest level at 60 days post-flowering. (Left figure, 2024, 60 days post-flowering, 2.5 mmol·L⁻¹) -1 The soluble sugar content of M3 was still higher than other treatments and reached its maximum value, increasing by 148.52% compared to the control (CK). The soluble sugar content of other MeJA treatments also increased, by 75.3%, 86.67%, 81.09%, and 8.91% respectively compared to the CK. In 2025 (right figure), 60 days after flowering, M3 was still higher than other treatments and reached its maximum value, significantly increasing by 123.95% compared to the CK. The soluble sugar content of other MeJA treatments increased by 68.62%, 81.09%, 105.54%, and 28.78% respectively compared to the CK.

[0035] Depend on Figure 2 It can be seen that in 2024 (left figure), the vitamin C content reached its highest level of 2.5 mmol·L⁻¹ 40 days after flowering. -1 The vitamin C content increased significantly by 22.95% compared to the control (CK); it began to decline after 50-60 days. In 2025 (right figure), the vitamin C content reached its peak at 2.5 mmol·L⁻¹ 40 days after flowering. -1 It increased significantly by 38.1% compared to the control group (CK).

[0036] Table 3. Capsaicin content of pepper fruits treated with different MeJA methods 20–60 days in 2024 and 2025. Table 4. Dihydrocapsaicin content in pepper fruits treated with different MeJA methods for 20–60 days in 2024 and 2025. Table 5. Total capsaicin content of pepper fruits under different MeJA treatments from 20 to 60 days in 2024 and 2025. As shown in Tables 3, 4, and 5, the present invention utilizes 1.0, 1.5, 2.5, 3.5, and 5.0 mmol·L⁻¹. -1 Five-level gradient spectroscopy and two-year repeated localization confirmed 2.5 mmol·L⁻¹. -1 This concentration represents the optimal threshold for capsaicin synthesis. In 2024 and 2025, 50 days after flowering, capsaicin, dihydrocapsaicin, and total capsaicin levels significantly increased by 68.13%–71.85%, 64.08%–73.02%, and 182.25%–192.98% respectively compared to the control (CK), and were significantly higher than 1.0 mmol·L⁻¹. -1(Capsaicin increased by 15.19%~30.4% and 20%~29.26% over two years, respectively; dihydrocapsaicin increased by 11.54%~31.75% and 12.16%~38.35%, respectively; and total capsaicin increased by 28.57%~73.68% and 28.57%~74.42%, respectively) and 5.0 mmol·L -1 (Capsaicin decreased by 7.59%~59.34% and 1.18%~8.89% respectively within two years, dihydrocapsaicin decreased by 3.85%~6.34% and -1.35%~5.34% respectively, and total capsaicin decreased by 14.29%~61.4% and 0%~44.64% respectively), thus solving the technical bottleneck of low concentration ineffectiveness and high concentration poisoning, and providing a precise and replicable dosage standard for production.

[0037] Traditional research has focused on capsaicin itself, neglecting the dynamic balance between its synthesis and oxidative consumption.

[0038] Depend on Figure 3 , Figure 4 and Figure 5 It can be seen that this invention simultaneously measured three key enzyme systems: PAL (phenylalanine ammonia-lyase), POD (peroxidase), and PPO (polyphenol oxidase), and found a concentration of 2.5 mmol·L⁻¹. -1 MeJA reduced PAL activity to a lower level than the control (CK), reaching its peak activity 50 days after flowering, increasing it by 30.3%–34.2%, thus providing sufficient precursors for capsaicin synthesis. Figure 3 POD enzyme activity was highest 20 days after flowering, lowest at 50 days, and began to rise again after 60 days, with an activity 2.5 mmol·L higher than at 50 days. -1 MeJA processing improved by 27.91% ( Figure 4 PPO activity was highest at 20 days after flowering and lowest at 50 days, with an activity 2.5 mmol·L⁻¹ lower than that at 50 days. -1 MeJA processing improved by 19.69%~41.08% ( Figure 5 This significantly enhances the fruit's defense against pathogens and oxidative stress, extending its shelf life. This "synthesis-protection" dual-track mechanism has not been systematically reported in existing literature, providing a new perspective for explaining the synergistic effect of MeJA.

[0039] Unlike previous extensive comparisons based on single indicators and single years, this invention introduces a two-way ANOVA + PCA dual model to construct a 10-dimensional quality-enzyme activity-morphology matrix. This can compress the indicators into two principal components, enabling a single measurement and comprehensive scoring, providing farmers or enterprises with a visualized quality index, and solving the practical pain points of numerous, incomprehensible, and difficult-to-determine indicators.

[0040] Table 6. Two-way ANOVA among various indicators of chili peppers under different MeJA treatments in 2024 and 2025. Table 6 shows that a two-way multivariate ANOVA was performed on the 10 indicators using treatment (T) and year (Y). Table 6 reveals that the year × treatment interaction was not significant (P>0.05), indicating that the MeJA treatments showed consistent performance over the two years, with no year-specificity and stable results. In the ANOVA of the 10 indicators, treatment was the most influential factor. Except for stem diameter, the main effects of different high concentrations of MeJA treatment on the other nine indicators were all significant (P<0.05).

[0041] Table 7. Principal component analysis of the relationship between growth, quality and enzyme activity of peppers treated with MeJA over two consecutive years. Table 7 shows that after merging the data from 2024 and 2025, standardizing them, and performing KMO and Bartlett's test of sphericity, the KMO value was 0.792, greater than 0.7, and the significance of the Bartlett's test of sphericity was less than 0.01, indicating that principal component extraction could be performed. The results are shown in Table 7. Principal component analysis was performed on 10 indicators of chili pepper growth, quality, and related enzyme activities. The analysis results showed that two principal components with eigenvalues ​​greater than 1 were present in both years, with cumulative variance contribution rates of 60.314% and 81.598%, respectively. This indicates that these two principal components can effectively reflect most of the information of the 10 indicators. The eigenvalues ​​of PC1 and PC2 are 6.031 and 2.128, respectively, with variance contribution rates of 60.314% and 21.285%, and a cumulative contribution rate of 81.598%. Among them, the largest contribution of PC1 is total capsaicin, with a loading value of 0.242, followed by dihydrocapsaicin, with a loading value of 0.233. The largest contribution of PC2 is plant height, followed by stem diameter, with loading values ​​of 0.249 and 0.238, respectively.

[0042] Figure 6 It can be seen that the upper right load area concentrates capsaicin-like substances and PAL activity, and has a long vector, which is the core trait of PC1; the load concentration includes POD, PPO, stem diameter and plant height, indicating that the more vigorous the plant growth, the relatively lower the spiciness.

[0043] In summary, the concentration is 2.5 mmol·L⁻¹ -1 MeJA (methyl jasmonate) improves the quality of chili peppers.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method of improving the quality of a pepper, characterized by, The method comprises the following steps: S1, sowing peppers according to a row spacing of 50 cm and a plant spacing of 30 cm; S2, at the initial flowering stage of pepper, the whole plant stem and leaf is sprayed with methyl jasmonate solution with a concentration of 2.5 mmol·L -1 ; S3, applying mature sheep manure 7-10 days before planting; S4, applying water-soluble fertilizer after the setting of the first fruits of the peppers; S5, adopting integrated insect prevention by using yellow plates, insect prevention nets and sex lures, and harvesting the peppers at the mature stage.

2. The method for improving the quality of pepper according to claim 1, characterized in that, The concentration in S2 is 2.5 mmol·L -1 The preparation method of the methyl jasmonate solution with a concentration of 250 mmol·L -1 is to dissolve 56 mg of methyl jasmonate in 1 mL of anhydrous ethanol to obtain a mother liquor with a concentration of 250 mmol·L -1 of methyl jasmonate solution with a concentration of 2.5 mmol·L -1 is to add 99 mL of water to 1 mL of the obtained mother liquor with a concentration of 250 mmol·L -1 .

3. The method of improving quality of pepper according to claim 1, characterized in that, The application amount of the matured sheep manure in S3 is 45 t·hm -2 .

4. The method for improving the quality of pepper according to claim 1, characterized in that, The application amount of the water-soluble fertilizer in S4 is 150 kg·hm -2 ; the water-soluble fertilizer has a mass fraction of 15% of total nitrogen, a mass fraction of 5% of diaphosphine pentoxide, a mass fraction of 35% of potassium oxide, a mass fraction of 0.15% of iron element, and a mass fraction of 0.08% of manganese element.

5. The method for improving the quality of pepper according to claim 1, characterized in that, In S5, the stem diameter and plant height of the peppers are increased; the contents of soluble sugar, vitamin C, capsaicin, dihydrocapsaicin and total capsaicin in the pepper fruits are increased; and the activities of phenylalanine ammonia-lyase, peroxidase and polyphenol oxidase in the pepper fruits are increased.

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