Application of nicotinic acid in preservation of apple fruit

Abstract

The application discloses application of nicotinic acid in apple fruit preservation and relates to the technical field of fruit preservation. The apple fruit is soaked or sprayed with a nicotinic acid aqueous solution, so that the appearance of the fruit is kept, the fruit hardness, the original pectin content and the soluble pectin content of the fruit during storage are maintained, the superoxide dismutase and catalase activities of the fruit are improved, and the antioxidant capacity of the fruit is enhanced. The application uses nicotinic acid for fruit preservation, and the preservation effect is good and safe and reliable.

Description

Technical Field

[0001] This invention relates to the field of fruit preservation technology, and in particular to the application of niacin in apple fruit preservation. Background Technology

[0002] Apples (Malus domestica), a plant of the Rosaceae family, are rich in various nutrients beneficial to the human body, such as polyphenols, flavonoids, and vitamins. my country's annual apple production reaches 45 million tons, accounting for approximately 55% of global production. However, with prolonged post-harvest storage, fruit quality declines and antioxidant capacity decreases. Fruit quality mainly refers to the fruit's appearance, flavor, and nutritional value. During storage, changes in respiration and metabolism alter the pectin content, leading to decreased fruit firmness and softening, thus affecting edibility, limiting shelf life, and reducing transportation efficiency. Simultaneously, the reduced antioxidant capacity accelerates fruit aging, softening, and nutrient loss, decreasing the apple's resilience and shelf life. Therefore, researching apple storage techniques is crucial for extending shelf life and preserving nutritional value.

[0003] Currently, apple preservation strategies include chemical preservation, low-temperature storage, coating preservation technology, and microbial antagonistic preservation. Chemical preservation uses chemical agents to inhibit or kill microorganisms, thereby extending the apple's shelf life. While effective in inhibiting microbial growth and reproduction and reducing the probability of spoilage due to microbial attack during storage, chemical residues can remain on the apple's surface or inside, posing potential health risks. Low-temperature storage uses low temperatures to reduce respiration, metabolism, and ethylene production in apples, thus extending their shelf life. However, this method relies on refrigeration equipment, consumes a lot of energy, and requires precise humidity control. Microbial antagonistic preservation utilizes the antagonistic effects between microorganisms. This method offers good preservation results, and some beneficial microorganisms may produce substances that improve apple quality. However, the apple variety and storage environment affect the preservation effect, and microbial activity is influenced by temperature, humidity, and pH. Furthermore, this method requires advanced technology and is not suitable for large-scale application. Coating preservation technology involves applying a coating to the surface of apples to reduce respiration and moisture loss. Therefore, finding natural, safe, efficient, and even beneficial methods for preserving fruits and vegetables is particularly important.

[0004] Niacin, also known as vitamin B3, is an important bioactive molecule with various physiological functions in organisms, such as antioxidation, regulation of fat and protein metabolism, promotion of cell growth and repair, and construction of coenzymes. Niacin synthesizes NAD (nicotinamide adenine dinucleotide) through the Preiss-Handler pathway, a conserved metabolic pathway in terrestrial plants. However, there are no reports on the application of niacin in fruit preservation. Summary of the Invention

[0005] The purpose of this invention is to provide the application of niacin in apple fruit preservation, addressing the aforementioned limitations of existing technologies. This invention employs an aqueous solution of niacin to soak or spray apple fruits, which can maintain the fruit's appearance and shape, preserve fruit firmness, protopectin content, and soluble pectin content during storage; simultaneously, it increases the activity of superoxide dismutase and catalase in the fruit, enhancing its antioxidant capacity. This invention utilizes niacin for fruit preservation with good preservation effects and is safe and reliable.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides the application of nicotinic acid in fruit preservation.

[0008] Preferably, the fruit is an apple.

[0009] More preferably, the apple fruit includes Fuji apple fruit and Fanta apple fruit.

[0010] Preferably, the nicotinic acid achieves fruit preservation through at least one of the following methods (1)-(4):

[0011] (1) Maintain the appearance of the fruit during storage;

[0012] (2) Maintain fruit firmness during storage;

[0013] (3) Maintain the content of protopectin and soluble pectin during fruit storage;

[0014] (4) Increase the activity of superoxide dismutase and catalase during fruit storage.

[0015] A second aspect of the present invention provides a method for preserving apples, comprising the following steps:

[0016] Apple fruits can be preserved by spraying or soaking them with a nicotinic acid aqueous solution and then drying them after treatment.

[0017] Preferably, the concentration of the nicotinic acid aqueous solution is 1-100 mmol / L.

[0018] More preferably, the concentration of the nicotinic acid aqueous solution is 10 mmol / L.

[0019] Preferably, the specific operation of the spraying treatment is as follows: spray the nicotinic acid aqueous solution evenly on the surface of the apple fruit, and repeat the spraying 2-4 times.

[0020] Further preferred, the total spraying amount per apple is 1.5-2.5 mL.

[0021] Preferably, the soaking treatment is performed by immersing the apple fruit in a nicotinic acid aqueous solution for 60-120 minutes.

[0022] Preferably, the dried fruit is stored at 20-25℃.

[0023] The beneficial effects of this invention are:

[0024] This invention utilizes an aqueous solution of nicotinic acid to soak or spray apple fruits for preservation. Treating apples with this solution maintains their appearance, preserves firmness, protopectin content, and soluble pectin content during storage, and simultaneously increases the activity of superoxide dismutase and catalase, enhancing the fruit's antioxidant capacity. This invention employs nicotinic acid for fruit preservation, ensuring both effective preservation and the safety and reliability of the preservation method. Attached Figure Description

[0025] Figure 1 Effects of different concentrations of nicotinic acid aqueous solution on Fuji apples;

[0026] Figure 2 Changes in the appearance and morphology of Fuji and Huaniu apples after treatment with 10 mmol / L nicotinic acid aqueous solution and distilled water;

[0027] Figure 3 Changes in firmness of Fuji and Huaniu apples after treatment with 10 mmol / L nicotinic acid aqueous solution and distilled water;

[0028] Figure 4 Changes in protopectin in Fuji and Huaniu apples treated with 10 mmol / L nicotinic acid aqueous solution and distilled water;

[0029] Figure 5 Changes in soluble pectin in Fuji and Huaniu apples under treatment with 10 mmol / L nicotinic acid aqueous solution and distilled water;

[0030] Figure 6 Changes in superoxide dismutase activity in Fuji and Vanilla apples treated with 10 mmol / L nicotinic acid aqueous solution and distilled water;

[0031] Figure 7Changes in catalase activity in Fuji and Huaniu apples treated with 10 mmol / L nicotinic acid aqueous solution and distilled water. Detailed Implementation

[0032] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0033] In existing technologies, fruit quality and antioxidant capacity decline with prolonged post-harvest storage. Therefore, apples require preservation treatment to extend their shelf life and maintain their nutritional value. Currently, while chemical preservation can inhibit microbial growth, its safety is not high. Low-temperature storage relies on equipment, and microbial antagonism requires advanced technology and is not suitable for large-scale application. Niacin, as a water-soluble vitamin, is an essential nutrient for organisms, playing a crucial role in energy metabolism and oxidative phosphorylation, and is vital for the metabolism of proteins, fats, and carbohydrates. However, there are currently no studies applying niacin to fruit preservation.

[0034] Previous studies have shown that apples experience a decrease in niacin and NAD content during storage. Therefore, the inventors hypothesized that niacin might possess excellent properties for delaying fruit quality decline, and that exogenous application of niacin could potentially play a preservative role in apples. Based on this, a systematic study was conducted on the effects of niacin on fruit preservation. Specifically, this invention selected Fuji apples (which are resistant to storage) and Huaniu apples (which are not) as test subjects. Niacin aqueous solution was sprayed onto these apples, and the effects of niacin on physiological indicators such as fruit firmness, protopectin, soluble pectin, superoxide dismutase (SOD), and catalase were investigated. The results showed that niacin significantly maintained the appearance of the fruit; effectively maintained the stability of fruit firmness, protopectin, and soluble pectin during storage; and significantly increased the activity of SOD and catalase, enhancing the fruit's antioxidant capacity. In conclusion, niacin demonstrates broad application potential in delaying apple senescence and extending storage and shelf life.

[0035] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0036] The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0037] The nicotinic acid used in this invention was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with product number N814565.

[0038] Example 1: Apple Fruit Preservation Method

[0039] Prepare a 10 mmol / L nicotinic acid aqueous solution and spray it evenly onto the surface of the apple fruit using a top-to-bottom spraying method. Repeat the spraying 3 times to ensure that the total spraying volume for each apple is 2 mL. After treatment, air dry the fruit and store it at 20℃.

[0040] Example 2:

[0041] Prepare a nicotinic acid aqueous solution with a concentration of 1 mmol / L. Apply the nicotinic acid aqueous solution evenly to the surface of the apple fruit using a top-to-bottom spraying method. Repeat the spraying 3 times to ensure that the total spraying amount for each apple is 1.5 mL. After treatment, air dry the fruit and store it at 20℃.

[0042] Example 3:

[0043] Prepare a 100 mmol / L nicotinic acid aqueous solution and spray it evenly onto the surface of the apple fruit using a top-to-bottom spraying method. Repeat the spraying 3 times to ensure that the total spraying amount for each apple is 2.5 mL. After treatment, air dry the fruit and store it at 20℃.

[0044] Example 4: Apple Fruit Preservation Method

[0045] Prepare a 10 mmol / L nicotinic acid aqueous solution, immerse apple fruits in the solution for 100 min, remove them, air dry them, and store them at 20°C.

[0046] Experimental Example 1:

[0047] 1. Test method:

[0048] 1.1 Experimental grouping and treatment:

[0049] Two hundred Fuji apples (each weighing 206.4g ± 41.2g) from the same batch, of the same variety and specifications, and with no difference in freshness or other indicators were selected and randomly divided into four groups of 50 apples each.

[0050] Experimental group: Apple fruits were preserved using aqueous solutions of nicotinic acid at different concentrations;

[0051] Blank control group: Apple fruits were preserved using distilled water.

[0052] Samples were taken at 0, 15, 30, and 60 days after treatment to observe apple fruit phenotype and measure fruit firmness, protopectin and soluble pectin content, superoxide dismutase activity, and catalase activity. The results are as follows: Figures 1-7 As shown.

[0053] Meanwhile, 100 Huaniu apples (each weighing 225.6g±36.6g) from the same batch, of the same variety and specifications, and with no difference in freshness and other indicators were selected and randomly divided into 2 groups of 50 apples each.

[0054] Experimental group: Apple fruits were preserved using an aqueous solution of nicotinic acid at the optimal concentration.

[0055] Blank control group: Apple fruits were preserved using distilled water.

[0056] Apple phenotypes were observed and samples were taken at 0, 15, 30, and 45 days after treatment. Changes in fruit firmness, protopectin content, soluble pectin content, superoxide dismutase activity, and catalase activity were measured. The results are as follows: Figures 2-7 As shown.

[0057] The specific operation for preservation treatment is as follows: spray different concentrations of nicotinic acid aqueous solution or distilled water evenly on the surface of apple fruit using the top-to-bottom spraying method, repeat the spraying 3 times, and ensure that the total spraying amount for each apple is 2mL. After the treatment is completed, dry the apple and store it at 20℃.

[0058] 1.2 Test Method:

[0059] 1.2.1 Hardness testing method:

[0060] Apple firmness was measured using a Stable Micro Systems TA.XT plus texture analyzer.

[0061] Measurements were performed using a P / 2 cylindrical probe (2 mm in diameter). The initial speed was 2 mm / s, the measurement speed was 1 mm / s, and the subsequent speed was 5 mm / s. The penetration depth was 10 mm, and the minimum sensing force was 10 grams. For each sampling day, 10 apples of each concentration were randomly selected. Four evenly spaced points were randomly chosen around the central equator of each apple for puncture testing perpendicular to the fruit surface. The measured fruit firmness values ​​were analyzed using TextureExponent 32 software. The firmness result for each apple was the average of the four test points.

[0062] 1.2.2 Protopectin Determination Method:

[0063] The protopectin content was determined using a kit (YGJ-2-G, Keming, Suzhou, China). The specific detection method is as follows:

[0064] (1) Weigh 0.05g of apple sample, put it into a mortar, add 1mL of extraction solution one, wherein the extraction solution one is 80% ethanol by mass, grind quickly, transfer the whole homogenate into a 2mL centrifuge tube, tighten the centrifuge tube, bathe in a 90℃ water bath for 30min, cool, centrifuge at 5000×g and 25℃ for 10min, remove the supernatant and keep the precipitate.

[0065] (2) Take 1 mL of the extract and add it to the precipitate in step (1). Secure the centrifuge tube, heat it in a 90°C water bath for 30 min, cool it, centrifuge it at 5000×g and 25°C for 10 min, remove the supernatant and keep the precipitate.

[0066] (3) Take 1 mL of extract solution II, which is 0.5 mol / L sulfuric acid, add it to the precipitate in step (2), bathe in a 90℃ water bath for 1 h, cool, centrifuge at 8000×g and 25℃ for 15 min, and keep the supernatant for testing.

[0067] (4) The supernatant obtained in step (3) is tested on the instrument. The absorbance is detected by a UV spectrophotometer. The UV spectrophotometer is preheated for 30 minutes, the wavelength is set to 530 nm, and ddH2O is used to zero it.

[0068] The order and amount of samples added to each EP tube before testing are shown in Table 1.

[0069] Table 1 Sample Addition Table

[0070]

[0071]

[0072] Thoroughly mix the liquids in the blank tube, standard tube, control tube, and test tube, and transfer them separately into 1 mL glass cuvettes. Use a UV spectrophotometer to read the absorbance values ​​of the blank tube, standard tube, control tube, and test tube at 530 nm, and record them as A1, A2, A3, and A4, respectively. Calculate the protopectin content using the above absorbance values. The formula for calculating the protopectin content is as follows:

[0073] Protopectin content (mg g) -1 )=0.25×(A4-A3)÷(A2-A1)÷W;

[0074] In the formula, W: fresh weight of sample (g); A1 is the absorbance of blank tube, A2 is the absorbance of standard tube, A3 is the absorbance of control tube, and A41 is the absorbance of test tube.

[0075] 1.2.3 Method for determining soluble pectin:

[0076] The pectin content was determined using a water-soluble pectin assay kit (WSP-2-Y, Keming, Suzhou, China). The specific detection method is as follows:

[0077] (1) Weigh 0.3g of apple sample, place it in a mortar, add 1mL of 80% ethanol, and grind rapidly. Transfer the homogenate to a 2mL centrifuge tube, seal the tube tightly, and incubate in a 95℃ water bath for 20min. After cooling, centrifuge at 4000×g and 25℃ for 10min. Discard the supernatant and retain the precipitate. Wash the precipitate once with 1.5mL of 80% ethanol and once with acetone (vortex for 2min, centrifuge at 4000×g and 25℃ for 10min, and retain the precipitate).

[0078] (2) Add 1 mL of reagent to the washed precipitate obtained in step (1), let it soak for 15 hours, centrifuge at 4000×g and 25℃ for 10 min, discard the supernatant and keep the precipitate. Place the precipitate in a 65℃ oven to dry and weigh it.

[0079] (3) Weigh 3mg of the dried precipitate obtained in step (2), put it into a mortar, add 1mL of reagent II, grind quickly, transfer the homogenate into a 1.5mL centrifuge tube, centrifuge at 8000×g, 4℃ for 10min, and take the supernatant for testing.

[0080] (4) The supernatant obtained in step (3) is tested on the instrument. The absorbance is measured by a UV spectrophotometer. The UV spectrophotometer is preheated for 30 minutes, the wavelength is set to 530 nm, and zeroed with ddH2O. Reagents 3 and 4 are placed in a water bath at 37°C for more than 10 minutes before use.

[0081] The order and amount of samples added to each EP tube before testing are shown in Table 2.

[0082] Table 2 Sample Addition Table

[0083]

[0084]

[0085] After thoroughly mixing the solutions in the blank tube, standard tube, control tube, and test tube, incubate them in a 95℃ water bath for 5 minutes. Measure the absorbance at 530 nm using a UV spectrophotometer. Record the absorbance values ​​of each tube as A1, A2, A3, and A4. If A is greater than 2, the sample needs to be diluted with ddH2O (10-fold or 20-fold). Prepare one blank tube and one standard tube, and one control tube for each test tube.

[0086] The soluble pectin content was then calculated using the absorbance values ​​of the blank tube, standard tube, control tube, and test tube. The calculation formula is shown below:

[0087] Soluble pectin content (mg g) -1 ) = 0.05 × (A4 - A3) ÷ (A2 - A1) ÷ W × dilution factor;

[0088] In the formula, A1 is the absorbance value of the blank tube; A2 is the absorbance value of the standard tube; A3 is the absorbance value of the control tube; A4 is the absorbance value of the test tube; and W is the dry weight of the sample, in g.

[0089] 1.2.4 Superoxide dismutase assay method:

[0090] (1) Weigh 0.5g of the well-mixed apple sample, add 1mL of phosphate buffer (0.05mol / L, pH=7.8), grind in an ice bath, add another 1mL of phosphate buffer, pour into a centrifuge tube, wash the mortar with 2mL of phosphate buffer, pour into a centrifuge tube, equilibrate, centrifuge at low temperature for 20min, and then take the supernatant and store it in the refrigerator.

[0091] (2) Take test tubes of the same type and add 50 μL of supernatant to each of the four control test tubes (add 50 μL of phosphate buffer to each of the four control test tubes). Add 3 mL of reaction solution to each tube. Place two control test tubes in the dark, and react the remaining tubes under 4000 lx sunlight for 20-30 min (the light exposure of each tube should be consistent; higher temperature requires a shorter time, and lower temperature requires a longer time). After the reaction is complete, use the unlit control test tubes as blanks and measure the absorbance at 560 nm.

[0092] (3) 150mL reaction solution composition: water 12.7mL, phosphate buffer 76.5mL, Met 15.25mL, NBT 15.25mL, EDTA-Na 2 15.25mL, riboflavin 15.25mL.

[0093] (4) Calculation formula: The amount required to inhibit 50% photochemical reduction of NBT is the enzyme activity unit (U);

[0094] SOD activity (U g) -1 FW)=(A ck -A s )×V / (A ck ×0.5×FW×V1).

[0095] In the formula, A ck A represents the absorbance of the control tube. s V represents the absorbance of the sample tube; V represents the total sample volume (mL); V1 represents the amount of sample used during the determination (mL); FW represents the apple mass (g).

[0096] Superoxide dismutase activity was calculated at each sampling time, and the results for each experimental group were the average of 6 apples.

[0097] 1.2.5 Hydrogen peroxide determination method:

[0098] The peroxidase (POD) assay was performed using a peroxidase (POD-2-Y) kit (Keming, Suzhou, China). The specific detection procedure is as follows:

[0099] (1) Weigh 0.1g of apple sample, put it into a mortar, add 1mL of acetone as the extraction solution, place it on ice, and homogenize it in an ice bath. Transfer the homogenate to a 1.5mL centrifuge tube, centrifuge at 8000×g, 4℃ for 10min, take the supernatant, store it at 4℃, and wait for analysis.

[0100] (2) Detection of absorbance:

[0101] Preheat the UV spectrophotometer for 30 minutes, set the wavelength to 470 nm, and zero it using ddH2O. Mix reagents 1, 2, and 3 in a ratio of 2.6 (mL): 1.5 (μL): 1 (μL) to prepare the working solution. Before use, incubate in a 25°C water bath for 10 minutes and prepare immediately.

[0102] Mix 0.05 mL of supernatant and 0.95 mL of working solution, transfer to a 1 mL glass cuvette, and use a UV spectrophotometer to measure the absorbance value A1 at 470 nm for 1 min and the absorbance value A2 after 2 min.

[0103] (5) Calculation formula: Peroxidase activity (△OD470 min) -1 g -1 FW)=2000×(A2-A1)÷W;

[0104] In the formula, A1 is the absorbance value at 1 minute; A2 is the absorbance value after 2 minutes;

[0105] Definition of activity unit: One enzyme activity unit is defined as a change of 0.01 in A470 per minute per gram of tissue in a reaction system per mL.

[0106] 1.3 Experimental Results:

[0107] Figure 1 The effect of different concentrations of nicotinic acid on Fuji apples after 60 days of storage at room temperature. Figure 1 As can be seen, the control group fruit skin showed obvious wrinkling at 60 days. Treatment with 1 mmol / L nicotinic acid had a slight improvement, while treatments with 10 mmol / L and 100 mmol / L nicotinic acid significantly improved fruit wrinkling and effectively maintained the fruit's appearance. To save costs and achieve the same effect, 10 mmol / L was used as the optimal concentration for subsequent experiments.

[0108] Figure 2The changes in appearance and morphology of Fuji and Huaniu apples after treatment with 10 mmol / L nicotinic acid aqueous solution and distilled water. Figure 2 It can be seen that Fuji apples showed significant phenotypic changes on day 60, with the control group exhibiting more severe skin wrinkling compared to the niacin-treated group. Huaniu apples showed similar changes on day 45 of storage. This indicates that niacin can significantly maintain the appearance of the fruit, and the time it takes for its effect to appear varies depending on the storage tolerance of the apple.

[0109] Figure 3 The change in firmness of Fuji and Huaniu apples after treatment with 10 mmol / L nicotinic acid aqueous solution and distilled water. Figure 3 It can be seen that on day 60 of storage, the firmness of Fuji apples treated with niacin was significantly higher than that of the control group. Similarly, on day 45 of storage, the firmness of Huaniu apples treated with niacin was also significantly higher than that of the control group. This indicates that niacin can effectively maintain fruit firmness during storage.

[0110] Figure 4 and Figure 5 Changes in protopectin and soluble pectin in Fuji and Huaniu apples after treatment with 10 mmol / L nicotinic acid aqueous solution and distilled water. Figure 4 and Figure 5 As can be seen, on days 60 and 45 of storage, the protopectin content of Fuji and Huaniu apples treated with niacin was significantly higher than that of the control group, while the soluble pectin content was significantly lower. This indicates that niacin effectively inhibits the conversion of protopectin to soluble pectin, maintaining the content of both protopectin and soluble pectin during storage.

[0111] Figure 6 and Figure 7 Changes in superoxide dismutase and catalase activities in Fuji and Huaniu apples treated with 10 mmol / L nicotinic acid aqueous solution and distilled water. Figure 6 and Figure 7 As can be seen, niacin treatment increased the activities of superoxide dismutase and catalase in Fuji and Huaniu apples, enhancing the fruit's antioxidant capacity. Based on the above experiments, it is clear that treatment with a 10 mmol / L niacin aqueous solution has a good preservation effect on apples.

[0112] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. The application of niacin in apple fruit preservation, characterized in that, The application method is as follows: spray or soak apple fruits with nicotinic acid aqueous solution, and then dry them after treatment to preserve the freshness of the apple fruits. Niacin preserves apples through either (1) or (2) the following pathways: (1) Maintain the content of protopectin and soluble pectin during fruit storage; (2) Maintain the firmness of the fruit during storage.

2. The application as described in claim 1, characterized in that, The concentration of nicotinic acid aqueous solution is 1-100 mmol / L.

3. The application as described in claim 1, characterized in that, The specific procedure for spraying is as follows: spray the nicotinic acid aqueous solution evenly onto the surface of the apple fruit, and repeat the spraying 2-4 times.

4. The application as described in claim 3, characterized in that, Repeat the spraying 2-4 times, with a total spraying amount of 1.5-2.5 mL per apple fruit.

5. The method for preserving apple fruit as described in claim 1, characterized in that, The specific procedure for soaking is as follows: Immerse the apples in a nicotinic acid aqueous solution for 60-120 minutes.

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