Method for regulating and controlling postharvest quality of honey pomelo fruits

Abstract

The invention discloses a method for regulating and controlling the quality of picked honey pomelo fruits. The meizhou honey pomelo fruits are soaked by using 1.0 g / L MT and 0.5 g / L NAA exogenous hormone solution and then are preserved after being picked, so that the meizhou honey pomelo treated by the exogenous hormone keeps relatively high quality in the aspects of freshness, smell, moisture content, flavor and mouth feel; the preservative has good effects in the aspects of weight loss, juice sac granulation, respiration, degradation of vitamin C, acid return and the like of meizhou honey pomelo fruits, and has important significance in providing a new thought for post-harvest preservation of the meizhou honey pomelo.

Description

Technical Field

[0001] This invention belongs to the field of postharvest preservation technology, specifically relating to a method for regulating the postharvest quality of pomelo fruits. Background Technology

[0002] Meizhou pomelos often suffer from physiological disorders, primarily juice vesicle granulation, during the late ripening and post-harvest storage stages. This is particularly pronounced in older, late-ripening fruits or those left on the tree for extended periods, posing a significant threat to fruit quality. Juice vesicle granulation is characterized by significant swelling of the juice vesicles, hardening of the texture, reduced juice content, and a bland taste, thus significantly lowering the fruit's edible quality and commercial value, resulting in severe economic losses for fruit growers and distributors. Therefore, researching techniques to control juice vesicle granulation in Meizhou pomelos is crucial for increasing farmers' income and developing the pomelo industry. Furthermore, after harvesting, pomelos gradually lose moisture over time, their flavor weakens, and they may accumulate off-flavor substances. Ethanol is a common off-flavor substance in citrus fruits during storage. Physiological disorders such as brown spots, peel dehydration, and edema that occur during storage are closely related to ethanol accumulation. In-depth research has confirmed that ethanol accumulation is a significant factor affecting the flavor and overall quality of pomelos. These studies also revealed that the accumulation of ethanol in grapefruit fruit is influenced by a variety of factors, including peel thickness, storage temperature, and coating treatment. These factors may also significantly affect other flavor compounds and basic qualities of the fruit.

[0003] Melatonin (MT), a naturally occurring indoleamine compound, is widely found in plants and animals and possesses various physiological effects. It is present in multiple parts of plants, including roots, stems, leaves, flowers, fruits, and seeds. In plants, melatonin exhibits auxin-like properties, promoting adventitious root formation, increasing seed germination rates, and regulating flowering. Therefore, it is considered a novel plant growth regulator and biostimulant. Furthermore, melatonin also possesses significant antioxidant functions in plants, effectively scavenging free radicals and becoming a major antioxidant in plants.

[0004] 1-Naphthaleneacetic acid (NAA) is an organic compound with wide applications, playing an important role in plant growth regulation and medicine. NAA exists in α- and β-forms, with the α-form exhibiting higher activity and being the most commonly used in agriculture and plant growth regulation. Therefore, α-naphthaleneacetic acid is frequently chosen as the target. α-Naphthaleneacetic acid is a broad-spectrum plant growth regulator with auxin-like activity, capable of being absorbed by the roots, stems, and leaves of plants. This substance has wide applications in agriculture, forestry, vegetable cultivation, and fruit tree cultivation, exerting various effects such as inducing adventitious root formation, promoting cell division and expansion, increasing the survival rate of tree cuttings, promoting fruit enlargement, improving fruit set rate, and preventing flower and fruit drop.

[0005] If pomelos are not preserved, they are prone to rotting and spoilage due to physiological aging, bacterial invasion, and mechanical damage. Pomelos undergo continuous metabolic activities during storage and transportation; therefore, it is crucial to explore suitable storage conditions to minimize these metabolic activities and extend the shelf life of pomelos. Summary of the Invention

[0006] Based on the shortcomings and deficiencies of existing technologies, this invention uses Meizhou's specialty fruit, pomelo, as material. It treats Meizhou pomelos with different concentrations of exogenous hormones melatonin and naphthaleneacetic acid to explore the physiological mechanisms of melatonin and naphthaleneacetic acid in their preservation and their effects on the fruit quality and post-harvest lignification of juice sacs. This provides a theoretical basis and technical support for the storage quality and flavor regulation of pomelo fruit, while also meeting the requirements of modern green and organic agricultural development.

[0007] The first objective of this invention is to provide a postharvest preservative for pomelo fruit, which consists of 1.0 g / L melatonin and 0.5 g / L naphthaleneacetic acid, with the remainder being water.

[0008] A second objective of this invention is to provide the application of the aforementioned preservative in regulating the postharvest quality of pomelo fruit.

[0009] Preferably, the application is the use of the preservative in inhibiting postharvest weight loss, juice granulation, respiration, vitamin C degradation, and / or acidification of pomelo fruit.

[0010] The third objective of this invention is to provide a method for maintaining the post-harvest quality of pomelo fruit, comprising the following steps: soaking pomelo fruit in a preservative and then drying it, and storing it in bags; The preservative consists of 1.0 g / L melatonin and 0.5 g / L naphthaleneacetic acid, with the remainder being water.

[0011] Preferably, the process of soaking the pomelo fruit in the preservative involves soaking the pomelo fruit in the preservative for 20 minutes.

[0012] Preferably, the storage is carried out in a dark environment at 18°C ​​to 22°C.

[0013] Beneficial effects of this invention: This invention utilizes a 1.0 g / L MT + 0.5 g / L NAA exogenous hormone solution to soak Meizhou pomelo fruits for postharvest preservation. The results show that Meizhou pomelos treated with this exogenous hormone maintain high quality in terms of freshness, aroma, moisture content, flavor, and taste. It also effectively inhibits weight loss, juice granulation, respiration, vitamin C degradation, and acid reversion in Meizhou pomelos. This invention provides a new approach to postharvest preservation of Meizhou pomelos, offering theoretical basis and technical support for controlling the storage quality and flavor of pomelos, while also meeting the requirements of modern green and organic agricultural development. Attached Figure Description

[0014] Figure 1 This is the standard curve for pyruvate content.

[0015] Figure 2 The values ​​represent the changes in weight loss rate of pomelo fruits at different times in the same treatment group after different hormone treatments; different lowercase letters a, b, and c indicate significance (P < 0.05).

[0016] Figure 3 The values ​​represent the changes in weight loss rate of pomelo fruits under different hormone treatments at the same time point; different lowercase letters a, b, and c indicate significance (P < 0.05).

[0017] Figure 4 The changes in the granulation index of juice cells in pomelo fruits under different hormone treatments at different time points in the same treatment group; different lowercase letters a, b, and c indicate significance (P < 0.05).

[0018] Figure 5 The changes in the granulation index of juice vesicles in pomelo fruits at the same time point after different hormone treatments; different lowercase letters a, b, and c indicate significance (P < 0.05).

[0019] Figure 6 The values ​​represent the changes in respiration intensity of pomelo fruits at different times within the same treatment group after different hormone treatments; different lowercase letters a, b, and c indicate significance (P < 0.05).

[0020] Figure 7 The values ​​represent the changes in respiration intensity of pomelo fruits under different hormone treatments at the same time point; different lowercase letters a, b, and c indicate significance (P < 0.05).

[0021] Figure 8The values ​​represent the changes in ascorbic acid content in pomelo fruits at different time points after different hormone treatments; different lowercase letters a, b, and c indicate significance (P < 0.05).

[0022] Figure 9 The values ​​represent the changes in ascorbic acid content in pomelo fruits at the same time point after different hormone treatments; different lowercase letters a, b, and c indicate significance (P < 0.05).

[0023] Figure 10 The values ​​represent the changes in pyruvate content in pomelo fruits at different times within the same treatment group after different hormone treatments; different lowercase letters a, b, and c indicate significance (P < 0.05).

[0024] Figure 11 The values ​​represent the changes in pyruvate content in pomelo fruits at the same time point after different hormone treatments; different lowercase letters a, b, and c indicate significance (P < 0.05). Detailed Implementation

[0025] The following embodiments are further illustrations of the present invention, but not limitations thereof.

[0026] Example 1 1. Material handling Meizhou pomelos were selected from Meixian County, Meizhou City. Fruits of uniform maturity, size, and without mechanical damage were chosen at harvest and transported to the laboratory immediately after harvest. The fruits were randomly divided into 7 groups and treated with the following solutions: water (CK, control group); 1.0 g / L melatonin aqueous solution (1.0 g / L MT, 1.0M); 2.0 g / L melatonin aqueous solution (2.0 g / L MT, 2.0M); 0.5 g / L naphthaleneacetic acid (NAA, 0.5N); 1.0 g / L NAA aqueous solution (1.0 g / L NAA, 1.0N); 1.0 g / L MT + 0.5 g / L NAA aqueous solution (1.0M + 0.5N); or 1.0 g / L MT + 1.0 g / L NAA aqueous solution (1.0M + 1.0N). Each pomelo was soaked for 20 minutes. After drying, the fruits are packaged in special bags and then stored in a dark environment at 18℃~22℃. Relevant indicators are measured and analyzed at 0, 20, 40, 60, and 80 days after storage.

[0027] 2. Detection Indicators and Methods 2.1 Sensory evaluation Table 1 Sensory evaluation items and scoring criteria Sensory evaluation adopted the descriptive test method, referring to the method of OBENLAND (OBENLAND D, COLLIN S, MACKEY B, et al. Storage temperature and time influences sensory quality of mandarins by altering soluble solids, acidity and aroma volatile composition[J]. Postharvest Biology and Technology, 2011, 59(2):187-193.), with slight modifications, to form the evaluation items and scoring criteria shown in Table 1, and sensory evaluation of Meizhou pomelo under different exogenous hormone treatments was carried out according to Table 1.

[0028] 2.2 Weightlessness rate The weight loss rate was determined according to the method of Wu Binbin et al. (Wu Binbin, Rao Jingping, Li Baiyun, et al. Effects of harvest time on the quality and storage resistance of kiwifruit[J]. Northwest Botanical Journal, 2008, (04): 4788-4792.). Two pomelo fruit samples were randomly selected, the fruits were photographed and weighed, and the weight loss rate was calculated by formula (1).

[0029] Formula (1): Weight loss rate % = (Original single fruit weight - Single fruit weight after storage) / Original single fruit weight × 100%.

[0030] 2.3 Determination of granulation index of juice cells The granulation index was based on the method of Pan Tengfei et al. (Pan Tengfei, Zhu Xueliang, Pan Dongming et al. Effects of low temperature storage on granulation of juice vesicles and lignin metabolism in Guanxi pomelo [J]. Journal of Tropical Crops, 2013, 34(4):710-714.), with slight modifications. After removing the outer pericarp, the fruit was divided into several segments, and after removing the inner pericarp, it was divided into 4 grades according to the granulation range of the juice vesicles in the pulp.

[0031] Table 2 classifies cellular granulation into four levels based on granulation area. The granulation index of juice cells is calculated according to formula (2).

[0032] Formula (2): Juice cell granulation index = ∑ (juice cell granulation level × number of fruit segments at that level) / total number of fruit segments.

[0033] 2.4 Respiratory intensity measurement The static alkaline absorption method was adopted (refer to: Zhang Gui. Determination of postharvest respiration intensity of fruits and vegetables [J]. Physical and Chemical Testing (Chemical Section), 2005(8):596-597.). The glass desiccator was cleaned and dried. A petri dish was placed underneath. 10 mL of 0.4 mol / L NaOH standard solution was pipetted into the petri dish. A partition was placed, and one pomelo fruit was placed inside. The desiccator was covered and the dish was left to stand at 6℃~8℃ for 2 h. Then, the NaOH standard solution was transferred to an Erlenmeyer flask (rinsed 3 times). 5 mL of saturated BaCl2 solution and 2 drops of phenolphthalein indicator were added. The solution was titrated with 0.2 mol / L oxalic acid standard solution. The titration endpoint was reached when the pink precipitate turned white. The amount of oxalic acid used was recorded. The determination was repeated 3 times. The respiration intensity was calculated according to formula (3).

[0034] Formula (3): Respiratory intensity (mg / g·h) = (C 标 ×V1×44) / (V2×t; Among them, C 标 V1 is the molar concentration of oxalic acid standard solution (mol / L), V2 is the amount of oxalic acid used in the sample titration (mL), V3 is the molar mass of carbon dioxide (CO2) (g / mol), V4 is the volume of the sample (mL), and t is the determination time (h).

[0035] 2.5 Determination of ascorbic acid content The ascorbic acid content in food was determined using the national food safety standard method. Approximately 50 g of minced fruit pulp was placed in a 100 mL dry beaker, and the contents were then transferred to a 250 mL Erlenmeyer flask. The beaker was rinsed once or twice with a small amount of water, and the rinse water was also poured into the Erlenmeyer flask. Next, 10 mL of 2 mol / L acetic acid solution (HAc), 20 mL of 25% potassium iodide (KI) solution, and 5 mL of 1% starch solution were added sequentially to the Erlenmeyer flask. Titration was then performed using potassium iodate (KIO3) standard solution. The titration endpoint was reached when the solution color changed from red to blue-purple, and the vitamin C (VitC) content (unit: mg / 100 g) was calculated. The ascorbic acid content was calculated using formula (4).

[0036] Formula (4): Ascorbic acid content (mg / 100 g) = (V×C×176.12×100) / W; where V is the volume of iodine solution consumed during titration (mL), C is the concentration of iodine solution (mol / L), W is the weight of the sample (g), and 176.12 is the molar mass of ascorbic acid (g / mol).

[0037] 2.6 Determination of Pyruvic Acid Content The pyruvate content was determined using the 2,4-dinitrophenylhydrazine method (ANDREIA P, OLIVERIRA, LUIS R, et al. Determination of low molecular weight volatiles in Ficus carica using HS-SPME and GC / FID [J]. Food Chemistry, 2010, 121(4): 1289-1295.), with a slight modification: the frozen fruit pulp sample was ground into powder using liquid nitrogen, 8.00 g of fruit pulp was weighed and 18 mL of 5% trichloroacetic acid (TCA) was added, and the mixture was incubated on ice for 20 min. Then, it was centrifuged at 4℃ and 10000 r / min for 15 min. After centrifugation, the precipitate was removed, and only the supernatant was retained as the extraction solution. The extraction solution (400 μL) was placed in a test tube and 2 mL of DNPH (prepared by dissolving 0.25 g of 2,4-dinitrophenylhydrazine in 500 mL of 1 mol / L HCl) was added. Place the test tube in a water bath at 37°C for 10 min. Then add 2 mL of 1.5 mol / L NaOH, mix by vortexing, and immediately measure the absorbance of the mixture at 515 nm after 1 min. The pyruvate content is calculated according to formula (5).

[0038] Formula (5): Pyruvic acid content (mg / g) = (C×V) / W; where C is the value according to the standard curve ( Figure 1 The pyruvate concentration (mg / mL) is calculated, V is the total volume of the fruit extract (mL), and W is the weight of the fruit sample (g).

[0039] 3. Results 3.1 Sensory evaluation of Meizhou pomelo fruit after exogenous hormone treatment Meizhou pomelos are typically smooth and plump after harvesting, with a fragrant aroma, full juice sacs, and a sweet and sour taste. After 80 days of storage, the fruit surface shows some wrinkling, the aroma fades, the flesh texture deteriorates, acidity and bitterness increase, and significant dehydration and granulation occur. Table 3 shows that after 80 days of storage, among the exogenous hormone treatment groups, the 1.0 g / L MT + 0.5 g / L NAA group had the highest evaluation in terms of aroma, moisture content, flavor, and taste; its freshness evaluation was second only to the 1.0 g / L NAA treatment group, but the difference was not statistically significant. When the NAA concentration increased to 1.0 g / L (i.e., the 1.0 g / L MT + 1.0 g / L NAA group), the sensory evaluation of the Meizhou pomelos deteriorated in all aspects. In addition, Meizhou pomelos were rated poorly in terms of aroma, flavor and taste under the 1.0 g / LMT treatment, poorly in all aspects under the 2.0 g / LMT treatment, poorly in terms of freshness, aroma and taste under the 0.5 g / LNAA treatment, and poorly in terms of aroma and moisture content under the 0.1 g / LNAA treatment.

[0040] The above results indicate that the combined treatment of Meizhou pomelo with 1.0 g / L MT and 0.5 g / L NAA can comprehensively delay the changes in the quality of Meizhou pomelo and effectively preserve the freshness of Meizhou pomelo.

[0041] Table 3 Sensory evaluation results after 80 days of storage Note: Different lowercase letters a, b, and c indicate the significance of different treatment groups at the same time for the same indicator (P < 0.05). The order of the letters is as follows.

[0042] 3.2 Effects of exogenous hormones on the basic quality of pomelos 3.2.1 Determination of weight loss rate and juice cell granulation index Depend on Figures 2 to 5 It can be seen that during the storage of pomelos, the weight loss rate and juice cell granulation index of the water group and each treatment group all showed an increasing trend with the increase of storage time.

[0043] from Figure 2 , Figure 3The results showed that the weight loss rate and juice granulation index of the fruits in each hormone treatment group were lower than those in the water group (P<0.05). After 40 days of storage, the Meizhou pomelo fruits treated with 1.0 g / L NAA and 1.0 g / L MT + 0.5 g / L NAA had the lowest weight loss rate. After 60 days of storage, the Meizhou pomelo fruits treated with 2.0 g / L MT and 1.0 g / L MT + 0.5 g / L NAA had the lowest weight loss rate. After 80 days of storage, the Meizhou pomelo fruits treated with 1.0 g / L MT had a significantly higher weight loss rate than the other hormone treatment groups. The Meizhou pomelo fruits treated with 2.0 g / L MT had the lowest weight loss rate. The Meizhou pomelo fruits treated with 1.0 g / L MT + 0.5 g / L NAA had a weight loss rate that was only slightly higher than that of the 2.0 g / L MT treatment group, but there was no significant difference between the two.

[0044] Depend on Figure 4 , Figure 5 It can be seen that the granulation index of Meizhou pomelo fruits treated with exogenous hormones was significantly lower than that of the water group at all storage times. Among them, the granulation index of Meizhou pomelo fruits treated with 0.5 g / L NAA was the lowest at 80 days, at 1.42, which was significantly lower than that of the water group (3.30). The second lowest was the granulation index of the 1.0 g / L MT + 0.5 g / L NAA treatment group.

[0045] The above results indicate that the 1.0 g / L MT + 0.5 g / L NAA treatment group has a good effect on inhibiting weight loss and juice cell granulation in Meizhou pomelo.

[0046] 3.2.2 Measurement of respiratory intensity Respiration intensity reflects the consumption of nutrients within the fruit and the overall aging of the fruit. The respiration intensity of fruit gradually decreases over time during storage, and fruit respiration is one of the reasons for the deterioration of citrus flavor. Figure 6 , Figure 7 It was found that the respiration rate of Meizhou pomelo fruit decreased over time in both the water treatment group and the hormone treatment group; the most significant decrease was observed between 20 and 40 days, followed by a gradual decline. At 20 and 40 days of storage, the respiration rate of Meizhou pomelo fruit treated with 1.0 g / L MT + 0.5 g / L NAA was 0.0004951 × 10⁻⁶. 3 (mg / g·h) and 0.0002602×10 3 The respiration rate (mg / g·h) was significantly lower than that of Meizhou pomelos stored for the same period of time in other hormone treatment groups (P<0.05). These results indicate that exogenous 1.0 g / L MT + 0.5 g / L NAA treatment can better inhibit the respiration rate of Meizhou pomelos in the early stages of storage, thus delaying fruit senescence and maintaining better freshness.

[0047] 3.2.3 Determination of ascorbic acid content Citrus fruits are an important source of vitamin C (ascorbic acid), which helps protect cells from free radical damage, boosts immunity, prevents cancer, and improves the body's stress response. Therefore, the vitamin C content of fruits is one of the important indicators for assessing their quality. Figure 8 , Figure 9 It was found that the ascorbic acid content in Meizhou pomelo fruits decreases over time. Specifically, the water group showed a rapid decrease after 20 days of storage, while the hormone-treated group showed a relatively slower decline in ascorbic acid content. Figure 8 , Figure 9 As shown, after 80 days of storage, the ascorbic acid content of Meizhou pomelo fruit treated with 1.0 g / L MT + 0.5 g / L NAA was 0.6173 × 10⁻⁶. 3 The ascorbic acid content in the treated groups was significantly higher than that in other treatment groups (P<0.05). This indicates that treatment with 1.0 g / L MT + 0.5 g / L NAA can, to some extent, slow down the decline in ascorbic acid content in Meizhou pomelo fruits, and is superior to the effect of MT or NAA treatment alone, allowing the fruits to maintain good quality after storage.

[0048] 3.2.4 Effects of exogenous hormones on the metabolic quality of pyruvate content in pomelo Organic acids are a key factor influencing fruit flavor, and their composition and content vary among different fruits. Typically, fruits contain one or two main organic acids, while other organic acids are present in lower amounts and have a smaller impact on fruit acidity. The acidity reversion phenomenon in pomelos is mainly caused by the abnormal accumulation of citric acid. During citric acid synthesis, the concentration of pyruvate increases with storage time, showing a positive correlation with changes in citric acid concentration. Therefore, detecting pyruvate content can indirectly indicate the corresponding citric acid concentration. Figure 10 , Figure 11It was found that during the storage of Meizhou pomelos, the pyruvate content in the fruit generally showed an increasing trend with the increase of storage time. A significant increase was observed after 20-40 days, followed by a slowdown in the increase. Significant differences were found between the hormone treatment groups and the water group (P<0.05), with the water group showing significantly higher pyruvate content than the hormone treatment groups. Among the hormone treatment groups, the pyruvate content of fruits treated with 1.0 g / L MT + 0.5 g / L NAA and 1.0 g / L MT + 1.0 g / L NAA was generally lower than that of other groups. Specifically, at 80 days, the pyruvate content of Meizhou pomelos treated with 1.0 g / L MT + 0.5 g / L NAA and 1.0 g / L MT + 1.0 g / L NAA was 1.5054 × 10⁻⁶. 3 mg / 100 g and 1.5311×10 3 The pyruvate concentration (mg / 100 g) was significantly lower than that in other groups. These results indicate that the fruits treated with all exogenous hormones showed a slower rate of acid reversion, with the combined treatment of exogenous MT and NAA showing a better effect in delaying acid reversion.

[0049] In summary, the 1.0 g / L MT + 0.5 g / L NAA treatment group can better regulate the quality of Meizhou pomelo in multiple aspects during post-harvest storage, which is better than the effect of using MT or NAA treatment alone, especially in delaying acidification.

Claims

1. A postharvest preservative for grapefruits, characterized by comprising, It is composed of 1.0 g / L melatonin and 0.5 g / L naphthalene acetic acid, and the rest is water.

2. The application of the preservative in claim 1 in regulating the postharvest quality of honey pomelo fruits.

3. Use according to claim 2, characterized in that, The application of the preservative in inhibiting the postharvest weight loss, juice cell granulation, respiration, vitamin C degradation and / or acid return of honey pomelo fruits.

4. A method of maintaining postharvest quality of grapefruit fruit, characterized by, It comprises the following steps: After the honey pomelo fruits are soaked with the preservative, they are dried, bagged and stored; the preservative is composed of 1.0 g / L melatonin and 0.5 g / L naphthalene acetic acid, and the rest is water.

5. The method of claim 4, wherein, The soaking of the honey pomelo fruits with the preservative is for 20 min.

6. The method of claim 4, wherein, The storage is in a dark environment at 18-22℃.

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