Method for delaying postharvest physiological deterioration of cassava and reducing superoxide anion levels in cassava by nickel sulfate treatment

Abstract

The present invention provides a method for delaying post-harvest physiological deterioration of cassava and reducing the level of superoxide anion in cassava by nickel sulfate treatment, belonging to the technical field of post-harvest preservation of cassava. The method is to treat cassava by contact with nickel sulfate to reduce the level of superoxide anion in cassava, so as to delay post-harvest physiological deterioration of cassava, thereby effectively preventing post-harvest physiological browning and deterioration of cassava, and thus facilitating the maintenance of good storage quality of cassava. The present invention is highly practical, easy to operate, and can effectively extend the storage time of cassava, and has good development and application value in the storage, transportation and industrial production of cassava as an industrial raw material.

Description

Technical Field

[0001] The invention belongs to the technical field of post-harvest cassava preservation, and in particular relates to a method for delaying post-harvest physiological deterioration of cassava and reducing the level of superoxide anions in cassava by treating with nickel sulfate. Background Art

[0002] Cassava (Cassava) belongs to the Euphorbiaceae family, Manihot esculenta, is one of the world's three major tubers (cassava, potato, sweet potato), and is also a specialty crop in tropical regions. As a common industrial raw material, cassava tubers can be used to prepare industrial products such as alcohol, adhesives, and biofuels. Cassava has the characteristics of drought resistance, barrenness tolerance, wide adaptability, and does not compete with grain for land. Therefore, cassava is a high-yield and high-quality industrial raw material. Unlike other tuber crops, cassava tubers have a very short shelf life and usually begin to deteriorate 1 to 3 days after harvesting. This unique phenomenon is called "postharvest physiological deterioration (PPD)". During storage and processing, fresh cassava tissues quickly develop PPD (1 to 3 days), causing the tubers to brown and rot and deteriorate, thereby restricting the comprehensive industrial utilization of cassava after harvest, causing direct economic losses of more than US$200 million each year, and greatly restricting the development of the cassava industry. Effectively curbing the occurrence of PPD has become a major production problem that needs to be urgently solved in the development of the cassava industry.

[0003] The occurrence of cassava PPD is strongly associated with the level of reactive oxygen species. Studies have shown that the occurrence of cassava PPD is accompanied by the outbreak of various types of reactive oxygen species (ROS), including hydrogen peroxide (H2O2), superoxide anion (O2 -), etc. These reactive oxygen levels are important markers for the physiological deterioration of cassava after harvest. In most cases, researchers curb postharvest physiological decay by inhibiting the outbreak of reactive oxygen, such as calcium signals and plant hormones (such as jasmonate, abscisic acid, ethylene, gibberellins), reduced substances (such as melatonin, cyanogenic glycosides, phenylpropanoids, flavonoids, coumarins, carotenoids and other molecules) and proteases (such as polyphenol oxidase, phenylalanine ammonia lyase, peroxidase, etc.). There are other methods for storing postharvest cassava tubers in the field, such as sand burial and trench storage. These burial methods can extend the storage period of fresh cassava. Although this technology can extend the shelf life of cassava to 2 months, cassava tubers will deteriorate after storage by this method and are no longer suitable as raw materials for industrial production. Because traditional methods are difficult to manage and the control effect is unstable, the cost of organic chemical molecules such as hormones is too high, and the inhibition efficiency of inorganic molecules such as calcium chloride is low. Recently, Hu Shuai et al. inhibited the production of superoxide anions in cassava by soaking in cobalt chloride solution, ascorbic acid and potassium iodide, which delayed the occurrence of PPD, providing new ideas and new technologies for post-harvest storage of cassava. However, such methods are still relatively rare and need further development. Therefore, it is of great significance to develop more similar low-cost and efficient molecules that inhibit the physiological deterioration of cassava after harvest. Summary of the invention

[0004] In view of the above problems, the present invention provides a method for delaying the post-harvest physiological deterioration of cassava by treating with nickel sulfate and a method for reducing the level of superoxide anions in cassava. Through a chemical substance screening method, it is found that nickel sulfate has good effect in preventing and controlling the post-harvest physiological deterioration of cassava, has the characteristics of strong practicability and simple operation for cassava storage, can effectively prevent the browning and deterioration of cassava after harvest, thereby extending the storage period of cassava, improving the value and economic benefits of cassava as an industrial raw material, and has good development and application prospects.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A method for reducing the level of superoxide anions in cassava comprises contacting cassava with a nickel sulfate aqueous solution having a concentration of 0.1 to 100 mmol / L to reduce the level of superoxide anions in cassava.

[0007] Further, the method for reducing the level of superoxide anion in cassava comprises the following specific steps:

[0008] 1) Harvesting: dig out the cassava, keep the cassava stem intact and the outer skin undamaged, and get the dug cassava;

[0009] 2) Cleaning: Clean and drain the cassava;

[0010] 3) Soaking: Cassava was treated by soaking with nickel sulfate to reduce the level of superoxide anions in cassava.

[0011] Furthermore, in step 3), the soaking time is 1 to 30 minutes.

[0012] Furthermore, the method for reducing the level of superoxide anions in cassava also includes taking out the cassava and directly storing it after the nickel sulfate soaking treatment is completed.

[0013] Furthermore, the storage temperature is 25±2°C and the relative humidity is 65~85%.

[0014] A method for delaying postharvest physiological deterioration of cassava by nickel sulfate treatment, comprising contacting cassava with a nickel sulfate aqueous solution with a concentration of 0.1-100 mmol / L to reduce the level of superoxide anions in cassava, thereby delaying postharvest physiological deterioration of cassava.

[0015] Furthermore, the method for delaying the physiological deterioration of cassava after harvest by nickel sulfate treatment comprises the following specific steps:

[0016] S1. Harvesting: dig out the cassava, keep the cassava stem intact and the outer skin undamaged, and get the dug cassava;

[0017] S2. Cleaning: Clean the dug cassava and drain it for later use;

[0018] S3. Soaking: Soak cassava in a nickel sulfate aqueous solution to reduce the level of superoxide anions in cassava, thereby delaying the physiological deterioration of cassava after harvest.

[0019] Furthermore, in step S3, the soaking time is 1 to 30 minutes.

[0020] Furthermore, the method for delaying post-harvest physiological deterioration of cassava by nickel sulfate treatment also includes taking out the cassava and directly storing it after the nickel sulfate soaking treatment is completed.

[0021] Furthermore, the storage temperature is 25±2°C and the relative humidity is 65~85%.

[0022] The beneficial effects of the method of delaying postharvest physiological deterioration of cassava and reducing the level of superoxide anion in cassava by nickel sulfate treatment of the present invention are:

[0023] Based on superoxide anion (O2 - ) is an important reason for the physiological deterioration of cassava after harvest. The method for reducing the level of superoxide anion in cassava of the present invention can effectively and quickly reduce the level of superoxide anion, which is the main active oxygen component, and can significantly inhibit the occurrence of physiological deterioration of cassava after harvest at a certain concentration;

[0024] The method for reducing the superoxide anion level of cassava of the present invention is a method for rapidly reducing the superoxide anion level of cassava by using nickel sulfate, thereby effectively preventing the occurrence of post-harvest physiological deterioration of cassava. The collected fresh cassava can be soaked in a nickel sulfate aqueous solution to effectively avoid the occurrence of post-harvest physiological deterioration of cassava.

[0025] The method of delaying the physiological deterioration of cassava after harvest by nickel sulfate treatment of the present invention can prevent the cassava from browning and rotting after harvest, significantly delay the occurrence of physiological deterioration of cassava after harvest, effectively prolong the storage period of cassava, and improve the value and economic benefits of cassava industrial raw materials;

[0026] The method of delaying post-harvest physiological deterioration of cassava by nickel sulfate treatment of the present invention can effectively inhibit post-harvest physiological decay, has low reagent cost, is easy to operate, and has strong practicality;

[0027] The invention has strong practicability, is easy to operate, and can effectively prolong the storage time of cassava, and has good development and application value in the storage, transportation and industrial production of cassava as an industrial raw material.

[0028] The cassava treated by the method of the present invention can be used as an industrial raw material for the production of subsequent industrial products (such as alcohol, adhesives, biofuels, etc.). BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The diagram of physiological deterioration effect of postharvest cassava and the quantitative statistical diagram of physiological browning of postharvest cassava in Example 1 of the present invention; wherein, Figure A on the left is the diagram of physiological deterioration effect of postharvest cassava after treatment with nickel sulfate aqueous solution for 24 hours and 48 hours, and Figure B on the right is the quantitative statistical diagram of physiological browning of postharvest cassava after treatment with nickel sulfate aqueous solution in Example 1 of the present invention for 24 hours and 48 hours; in the concentration of nickel sulfate aqueous solution (mM) in Figures A and B, 0 represents the control group (i.e., the concentration of nickel sulfate in the distilled water used for treatment is 0 mmol / L), 0.1 represents treatment group 1 (i.e., the concentration of nickel sulfate in the nickel sulfate aqueous solution used for treatment is 0.1mmol / L), 1 represents treatment group 2 (i.e., the concentration of nickel sulfate in the nickel sulfate aqueous solution used for treatment is 1mmol / L), 10 represents treatment group 3 (i.e., the concentration of nickel sulfate in the nickel sulfate aqueous solution used for treatment is 10mmol / L), 50 represents treatment group 4 (i.e., the concentration of nickel sulfate in the nickel sulfate aqueous solution used for treatment is 50mmol / L), and 100 represents treatment group 5 (i.e., the concentration of nickel sulfate in the nickel sulfate aqueous solution used for treatment is 100mmol / L);

[0030] Figure 2 The superoxide anion (O2) of cassava after being treated with 50 mol / L nickel sulfate aqueous solution and distilled water for 2 min in Example 2 of the present invention -) of NBT staining and NBT staining grayscale statistics; the left picture is the NBT staining picture, and the right picture is the NBT staining grayscale statistics picture; distilled water represents the control group, and nickel sulfate represents the experimental group;

[0031] Figure 3 In Example 3 of the present invention, the cassava superoxide anion (O2 - ) relative content detection diagram and relative content grayscale statistical diagram; the left figure is superoxide anion (O2 - ) is the relative content detection diagram, and the right figure is the relative content grayscale statistical diagram; distilled water represents the control group, and nickel sulfate represents the experimental group. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention are described clearly and completely below. In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0033] Nickel sulfate and nitrotetrazolyl blue chloride (NBT) were both domestic analytical grade. Nickel sulfate was provided by Sinopharm Chemical Reagent Co., Ltd. All distilled water used was deionized distilled water.

[0034] During the harvesting process, cassava is very prone to physical (mechanical) damage, and slicing is also a kind of mechanical (physical) damage to cassava, which can accelerate the deterioration of cassava after harvest. Therefore, in order to facilitate the observation of the whole process of cassava physiological deterioration and quickly obtain the test results, cassava slices are used as experimental materials in the embodiments of the present invention.

[0035] Example 1 A method for delaying postharvest physiological deterioration of cassava by nickel sulfate treatment

[0036] This embodiment is a method for controlling postharvest physiological deterioration of cassava by nickel sulfate treatment, comprising the following specific steps:

[0037] S1. Harvesting: Carefully dig out the cassava, keeping the cassava stem intact and the outer skin undamaged, and get the dug cassava;

[0038] S2, cleaning: clean the dug cassava with clean water and drain it for later use, and prevent the outer skin of the cassava from being damaged during cleaning to obtain the cleaned cassava;

[0039] Slicing: Slice the cleaned cassava into slices to obtain cassava slices with a thickness of 5-10 mm;

[0040] S3. Soaking: The cassava slices were divided into six groups, namely control group and treatment group one to five, with about 20 cassava slices in each group (biological replicates);

[0041] Among them, the control group was immersed in distilled water;

[0042] Treatment groups one to five were immersed in nickel sulfate aqueous solutions with different concentration gradients; the concentration gradients of nickel sulfate in the nickel sulfate aqueous solution were 0.1mmol / L, 1mmol / L, 10mmol / L, 50mmol / L, and 100mmol / L, respectively.

[0043] During immersion, the volume of distilled water or nickel sulfate aqueous solution with different concentration gradients was 20 mL, and the immersion time was 2 min.

[0044] S4. Storage: After soaking, the treated cassava slices were placed in a culture room at 25±2°C and a relative humidity of 65-85%. The color changes of the cassava slices were observed and recorded at 0h, 24h and 48h. The results were as follows: Figure 1 shown.

[0045] Depend on Figure 1 It can be seen that as time goes by, the browning of cassava slices in the control group significantly worsens, while the treatment groups 4 to 5 treated with nickel sulfate aqueous solution of different concentration gradients can inhibit the occurrence of physiological browning deterioration of cassava after harvest (that is, nickel sulfate concentrations of 50mmol / L and 100mmol / L have a certain inhibitory effect at 24h), and the higher the concentration, the more obvious the inhibitory effect. At the 48h stage, nickel sulfate aqueous solution with a nickel sulfate concentration of 10mmol / L and above can also significantly inhibit the browning of cassava slices, especially when the nickel sulfate concentration in the nickel sulfate aqueous solution is 50mmol / L and 100mmol / L.

[0046] The grayscale of cassava slices was analyzed by ImageJ software. Figure 2 As shown, it can be seen that the average gray value of the cassava slices in the control group increased from the initial 39.97 to 81.24 (2.03 times) at 24h and 92.99 (2.33 times) at 48h, while the gray value of the cassava slices was effectively reduced after 24h treatment with nickel sulfate aqueous solution of different concentration gradients, and a complete inhibition effect was achieved when the concentration of nickel sulfate aqueous solution reached 50mmol / L (the gray value was equivalent to the initial stage); similarly, at the 48h stage, the gray value of the cassava slices treated with nickel sulfate aqueous solution of 10mmol / L and above was significantly lower than that of the control group treated with distilled water. These results show that nickel sulfate can effectively inhibit the physiological deterioration of cassava tubers after harvest.

[0047] Example 2 A method of reducing superoxide anion (O2- ) Horizontal method

[0048] Superoxide anion (O2 - ) and other active oxygen bursts are important reasons for the physiological deterioration of cassava after harvest. In the study, nitro tetrazolium blue chloride (NBT) is often used to stain superoxide anions (blue-purple). The higher the level of superoxide anions, the deeper the blue-purple color. In this example, the newly collected cassava root slices in Example 1 were used for the experiment. The control group was treated by soaking in distilled water, and the experimental group was treated by soaking in a nickel sulfate aqueous solution with a nickel sulfate concentration of 50 mmol / L. The cassava slices in the control group and the cassava slices in the experimental group were adjacent slices. During the soaking treatment, the volume of distilled water or nickel sulfate aqueous solution used was 20 mL, and the soaking time was 2 min. After the soaking treatment, the cassava slices were kept away from light for 30 min, and then 1 mg / mL nitro tetrazolium blue chloride (NBT) solution was taken out and dripped. The cassava slices were stained at room temperature away from light for 10 min, and then photographed and the grayscale value of the stained cassava slices was analyzed using Image J software. The results are as follows Figure 2 shown.

[0049] Depend on Figure 2 It can be seen that the outer circle of the cassava slices in the control group treated with distilled water was significantly dyed blue, indicating that the level of superoxide anions in this part was high, while the NBT staining of the cassava slices in the experimental group treated with nickel sulfate aqueous solution was significantly lighter, indicating that the use of nickel sulfate treatment can quickly reduce the level of superoxide anions in cassava tubers. The relative level of superoxide anions displayed by the grayscale analysis of NBT staining also shows that nickel sulfate can significantly reduce the level of superoxide anions.

[0050] Example 3 A method of reducing superoxide anion (O2 - ) Horizontal method

[0051] Superoxide anion (O2 - ) and other active oxygen bursts are important reasons for the physiological deterioration of cassava after harvest. In the study, nitrotetrazolyl blue chloride (NBT) is often used to stain superoxide anions (blue-purple). The higher the level of superoxide anions, the deeper the blue-purple color. In this example, the grinded extract of the newly collected cassava root slices in Example 1 was used for the experiment. The control group was treated with distilled water immersion, and the experimental group was treated with a nickel sulfate aqueous solution with a nickel sulfate concentration of 50 mmol / L. The cassava slices in the control group were adjacent to the cassava slices in the experimental group. During the immersion treatment, the volume of distilled water or nickel sulfate aqueous solution used was 20 mL, and the immersion time was 2 min. After the immersion treatment, the cassava slices were placed away from light for 24 h or 48 h, and then the cassava slices were taken out and ground on ice, and superoxide anions (O2 -) The extract was fully ground and extracted, centrifuged at 14000rpm, 4℃ to obtain the supernatant, 100μL of the supernatant was added with 1mg / mL nitrotetrazolyl blue chloride (NBT) solution, and the reaction was carried out at room temperature in the dark for 10min, and then the gray value of the solution was analyzed using Image J software. The results are as follows Figure 3 shown.

[0052] The dyeing condition after the extract reacts with NBT is as follows Figure 3 As shown in the left figure, the cassava tissue extract treated with distilled water in the control group was significantly stained with NBT at 0h, 24h and 48h, while the NBT staining of the cassava tissue extract treated with nickel sulfate aqueous solution in the experimental group was significantly lighter, which is consistent with the cassava chip staining results in Example 2. Further, the statistical results of A630 per unit weight of tissue show that Figure 3 In the right figure, at 0h, 24h and 48h, the cassava tissues treated with distilled water in the control group had higher absorbance values, while the A630 absorbance values ​​in the cassava tissues treated with nickel sulfate aqueous solution in the experimental group were significantly lower than those treated with distilled water, and there was no significant change in the values ​​in the three time periods, indicating that nickel sulfate can effectively and sustainably curb the production of superoxide anions.

[0053] Based on the fact that the level of active oxygen is an important reason for the physiological deterioration of cassava after harvest, nickel sulfate effectively and quickly reduces the level of superoxide anion, the main active oxygen component, and can significantly inhibit the occurrence of physiological deterioration of cassava after harvest at a certain concentration. Therefore, the present invention provides a method for delaying the physiological deterioration of cassava after harvest by nickel sulfate treatment and a method for reducing the level of superoxide anion in cassava by nickel sulfate, which uses nickel sulfate to quickly reduce superoxide anion, thereby effectively curbing the occurrence of physiological deterioration of cassava after harvest. The collected fresh cassava tubers are soaked in a nickel sulfate aqueous solution to effectively reduce the level of superoxide anion and avoid the occurrence of physiological deterioration of cassava after harvest.

[0054] Examples 4-7 Methods for delaying postharvest physiological deterioration of cassava by nickel sulfate treatment and methods for reducing superoxide anion levels in cassava by nickel sulfate

[0055] Examples 4 to 7 are respectively a method for delaying postharvest physiological deterioration of cassava by nickel sulfate treatment and a method for reducing superoxide anion levels in cassava by nickel sulfate, which are basically the same as Example 1, except that some process parameters are different, as shown in Table 1 for details:

[0056] Table 1 List of process parameters in Examples 4 to 7

[0057]

[0058] The contents and results of other parts of Examples 4 to 7 are the same as those of Example 1 and will not be repeated here.

[0059] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Claims

1. A method for reducing the level of superoxide anion in cassava to delay the physiological deterioration of cassava after harvest, characterized in that: The method for reducing the level of superoxide anion in cassava is to contact cassava with a nickel sulfate aqueous solution with a concentration of 0.1-100 mmol / L to reduce the level of superoxide anion in cassava; The physiological deterioration is physiological browning.

2. The method for reducing superoxide anion levels in cassava to delay postharvest physiological deterioration of cassava according to claim 1, characterized in that: The method for reducing the level of superoxide anions in cassava comprises the following specific steps: 1) Harvesting: dig out the cassava, keep the cassava stem intact and the outer skin undamaged, and get the dug cassava; 2) Cleaning: Clean and drain the cassava; 3) Soaking: Cassava was soaked in nickel sulfate aqueous solution to reduce the level of superoxide anion in cassava.

3. The method for reducing superoxide anion levels in cassava to delay postharvest physiological deterioration of cassava according to claim 2, characterized in that: In step 3), the soaking time is 1 to 30 minutes.

4. The method for reducing the level of superoxide anion in cassava to delay the physiological deterioration of cassava after harvest according to claim 2 or 3, characterized in that: The method for reducing the superoxide anion level of cassava also includes taking out the cassava and directly storing it after the immersion treatment with the nickel sulfate aqueous solution is completed.

5. The method for reducing superoxide anion levels in cassava to delay postharvest physiological deterioration of cassava according to claim 4, characterized in that: The storage temperature is 25±2℃ and the relative humidity is 65~85%.

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