Preparation method of gallic acid coating based on radiation modification

Abstract

The invention provides a preparation method of a gallic acid coating based on radiation modification, and belongs to the technical field of preservation, and the preparation method comprises the following steps: cleaning walnut green seedcases with distilled water, airing, drying, and crushing to obtain walnut green seedcase powder; weighing walnut green seedcase powder, putting the walnut green seedcase powder into a dry centrifugal tube, adding an ethanol water solution, soaking, and carrying out ultrasonic extraction; cooling and centrifuging the crude gallic acid extracting solution, and collecting the crude gallic acid extracting solution; pouring the crude gallic acid extracting solution into activated macroporous resin, adsorbing and purifying, and concentrating under reduced pressure to obtain a gallic acid product; the method comprises the following steps: diluting gallic acid, irradiating and filtering to obtain an irradiated gallic acid solution; and adding the irradiated gallic acid solution into the beta-cyclodextrin solution, carrying out alcohol washing and vacuum filtration after the reaction is finished to obtain a filter cake, and re-dissolving the filter cake in water to obtain the irradiated gallic acid microcapsule suspension. The radiation modified gallic acid coating can isolate food from the external environment, and the purpose of food preservation is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of aquatic product processing, and in particular to a preparation method of a radiation-modified gallic acid coating. Background Art

[0002] Bioactive substances (such as organic acids, phenolic compounds, essential oils, etc.) are added to edible coatings to prevent oxidation, degradation and enzymatic browning of coated foods and improve food quality and safety. Gallic acid is one of the main active ingredients in walnut green peel. It has multiple phenolic hydroxyl structures and belongs to polyphenol compounds. Its chemical name is 3,4,5-trihydroxybenzoic acid. Gallic acid has multiple biological activities such as antioxidant, anti-tumor, antibacterial and antiviral, and is a low-molecular-weight natural antioxidant. It is considered to be an ideal bioactive ingredient with antibacterial and antioxidant activities, which can extend the shelf life of the product; in addition, it can also improve the antioxidant properties of the coating. The use of active packaging containing GA during food storage has a better preservation effect in delaying lipid oxidation or microbial growth.

[0003] Refrigeration can effectively inhibit the activity of endogenous enzymes in the muscle tissue of aquatic products and the growth and reproduction of surface microorganisms. It is widely used in the preservation of aquatic products, but it cannot completely inhibit microorganisms and is difficult to meet the needs of long-distance transportation and large-scale production. Spoilage caused by microbial contamination is an important problem that the food industry needs to solve. Food packaging is not only used to store food, but also to extend the shelf life of food, thereby ensuring food safety and improving food quality. Therefore, the use of appropriate preservation methods, such as active packaging and natural phenolic compounds, can protect the quality of seafood products and prevent the generation of odors.

[0004] Therefore, a method for preparing a radiation-modified gallic acid coating is needed to extend the shelf life of seafood. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a radiation-modified gallic acid coating. The present invention uses walnut green peel as a raw material to extract gallic acid, uses the gallic acid as a coating after ultraviolet irradiation, and uses the gallic acid as a coating for aquatic products to extend the shelf life of aquatic products.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a radiation-modified gallic acid coating comprises the following steps:

[0008] (1) washing walnut green peel with distilled water and drying it, and then crushing the dried walnut green peel with a grinder and passing it through an 80-mesh sieve to obtain walnut green peel powder;

[0009] (2) Weigh 1.0-1.3 g of walnut green peel powder into a 50 mL dry centrifuge tube, add 30-40 mL of 70-80% ethanol aqueous solution, soak and then place in an ultrasonic cleaner for extraction;

[0010] Since gallic acid has a large polarity, according to the principle of similar polarity dissolving each other, too high or too low ethanol concentration is not conducive to extraction; when the solid-liquid ratio is 1.0-1.3:30-40, it can promote the contact between the solid and liquid phases, thereby reducing the dissolution resistance of gallic acid. Too low solid-liquid ratio is not conducive to the extraction of gallic acid;

[0011] (3) After the ultrasonic treatment, the crude gallic acid extract was cooled to room temperature, centrifuged at 5000 r / min for 10 min in a high-speed centrifuge, and the supernatant was collected to obtain the crude gallic acid extract;

[0012] (4) Pour the crude gallic acid extract into the activated macroporous resin, place it in a constant temperature shaker at a temperature of 25° C. and an oscillation frequency of 110 r / min for static adsorption purification for 24 hours, and then use a rotary evaporator to reduce the pressure and concentrate it to obtain a gallic acid product;

[0013] (5) Dilute gallic acid with deionized water to a volume fraction of 0.25%, transfer to a sterilized crystal culture dish, and heat at 4.5 J / cm 2 The irradiation was continued at high intensity for 10 hours; the irradiated gallic acid was filtered through a sterile filter with a pore size of 0.2 μm to obtain an irradiated gallic acid solution;

[0014] (6) adding the irradiated gallic acid solution to the β-cyclodextrin solution, washing with alcohol after the reaction is completed, vacuum filtering to obtain a filter cake, and redissolving the filter cake in water to obtain an irradiated gallic acid coating solution.

[0015] Furthermore, in step (1), the specific operation of drying is: putting the dried walnut green peel into an oven, adjusting the temperature to 60° C. for drying until the mass is constant.

[0016] Furthermore, in step (2), the specific operation of extraction is: extraction is performed under the conditions of ultrasonic power of 600 W, ultrasonic temperature of 40-50° C. and ultrasonic time of 50 min. Gallic acid oxidation at too high a temperature or too high an ultrasonic time will cause structural changes, and at the same time will lead to an increase in the dissolution amount of some impurities and degradation of unstable components, which is not conducive to the extraction of gallic acid.

[0017] Furthermore, in step (4), the specific operation of adsorption purification is: adsorption purification is performed at an adsorption rate of 1-2BV / h, a desorption rate of 1-2BV / h and a desorption volume of 1-2BV.

[0018] Furthermore, in step (5), the irradiation is performed using a desktop UV-C intermittent light source with a wavelength of 254 nm and an average intensity of 4540 μW / cm 2 , the maximum liquid penetration is 17cm.

[0019] Furthermore, in step (6), the irradiated gallic acid solution and the β-cyclodextrin solution are reacted for 80 minutes.

[0020] Based on the application of radiation-modified gallic acid coating in aquatic products, the aquatic products are shelled and the meat is immersed in the irradiated gallic acid coating solution for 60-65s. After being taken out, it is air-dried at 25℃ for 10min, then placed in a food-grade PP plastic packaging box, sealed and marked, and stored in a 0℃ refrigerator.

[0021] Furthermore, the aquatic product is oysters.

[0022] The present invention has the following beneficial effects due to the adoption of the above technical solution:

[0023] In the present invention, gallic acid is an organic phenolic acid existing in plants, which has antioxidant and antibacterial effects and can inhibit the deterioration of aquatic products; radiation-modified gallic acid has antioxidant activity for scavenging free radicals, can delay lipid oxidation and reduce the oxygen permeability of the coating, and the radiation-modified gallic acid coating can isolate food from the external environment, achieve the purpose of food preservation, and thus extend the shelf life of aquatic products. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, preferred embodiments are given below to further describe the present invention in detail. However, it should be noted that many details listed in the specification are only for the purpose of enabling the reader to have a thorough understanding of one or more aspects of the present invention, and these aspects of the present invention can be implemented even without these specific details.

[0025] A method for preparing a radiation-modified gallic acid coating comprises the following steps:

[0026] (1) washing walnut green peel with distilled water and drying it, and then crushing the dried walnut green peel with a grinder and passing it through an 80-mesh sieve to obtain walnut green peel powder;

[0027] (2) Weigh 1.0-1.3 g of walnut green peel powder into a 50 mL dry centrifuge tube, add 30-40 mL of 70-80% ethanol aqueous solution, soak and then place in an ultrasonic cleaner for extraction;

[0028] (3) After the ultrasonic treatment, the crude gallic acid extract was cooled to room temperature, centrifuged at 5000 r / min for 10 min in a high-speed centrifuge, and the supernatant was collected to obtain the crude gallic acid extract;

[0029] (4) Pour the crude gallic acid extract into the activated macroporous resin, place it in a constant temperature shaker at a temperature of 25° C. and an oscillation frequency of 110 r / min for static adsorption purification for 24 hours, and then use a rotary evaporator to reduce the pressure and concentrate it to obtain a gallic acid product;

[0030] (5) Dilute gallic acid with deionized water to a volume fraction of 0.25%, transfer to a sterilized crystal culture dish, and heat at 4.5 J / cm 2 The irradiation was continued at high intensity for 10 hours; the irradiated gallic acid was filtered through a sterile filter with a pore size of 0.2 μm to obtain an irradiated gallic acid solution;

[0031] (6) adding the irradiated gallic acid solution to the β-cyclodextrin solution, washing with alcohol after the reaction is completed, vacuum filtering to obtain a filter cake, and redissolving the filter cake in water to obtain an irradiated gallic acid coating solution.

[0032] In step (1), the specific operation of drying is: putting the dried walnut green peel into an oven, adjusting the temperature to 60° C. for drying until the mass is constant.

[0033] In step (2), the specific operation of extraction is: extraction is carried out under the conditions of ultrasonic power of 600W, ultrasonic temperature of 40-50°C and ultrasonic time of 50min.

[0034] In step (4), the specific operation of adsorption purification is: adsorption purification is carried out at an adsorption rate of 1-2 BV / h, a desorption rate of 1-2 BV / h and a desorption volume of 1-2 BV.

[0035] In step (5), the irradiation is carried out using a desktop UV-C intermittent light source with a wavelength of 254 nm and an average intensity of 4540 μW / cm 2 , the maximum liquid penetration is 17cm.

[0036] In step (6), the irradiated gallic acid solution and the β-cyclodextrin solution are reacted for 80 minutes.

[0037] Based on the application of radiation-modified gallic acid coating in aquatic products, the aquatic products are shelled and the meat is immersed in the irradiated gallic acid coating solution for 60-65s. After being taken out, it is air-dried at 25℃ for 10min, then placed in a food-grade PP plastic packaging box, sealed and marked, and stored in a 0℃ refrigerator.

[0038] The aquatic product is oysters.

[0039] Example 1

[0040] A method for preparing a radiation-modified gallic acid coating comprises the following steps:

[0041] (1) washing walnut green peel with distilled water and drying it, placing it in an oven, adjusting the temperature to 60° C. for drying until the mass is constant, and then crushing the dried walnut green peel with a grinder and passing it through an 80-mesh sieve to obtain walnut green peel powder;

[0042] (2) Weigh 1.0 g of walnut green peel powder into a 50 mL dry centrifuge tube, add 30 mL of 70% ethanol aqueous solution, soak and place in an ultrasonic cleaning machine, and extract under the conditions of ultrasonic power of 600 W, ultrasonic temperature of 40° C. and ultrasonic time of 50 min;

[0043] (3) After the ultrasonic treatment, the crude gallic acid extract was cooled to room temperature, centrifuged at 5000 r / min for 10 min in a high-speed centrifuge, and the supernatant was collected to obtain the crude gallic acid extract;

[0044] (4) Pour the crude gallic acid extract into the activated macroporous resin, place it in a constant temperature shaker at a temperature of 25° C. and an oscillation frequency of 110 r / min for static adsorption purification for 24 hours, and then use a rotary evaporator to reduce pressure and concentrate it to obtain a gallic acid product; adsorption purification is performed at an adsorption rate of 1 BV / h, a desorption rate of 1 BV / h, and a desorption volume of 1 BV;

[0045] (5) Dilute gallic acid with deionized water to a volume fraction of 0.25%, transfer to a sterilized crystal culture dish, and heat at 4.5 J / cm 2 The irradiation was continued for 10 hours; the irradiated gallic acid was filtered through a sterile filter with a pore size of 0.2 μm to obtain an irradiated gallic acid solution; the irradiation was carried out using a desktop UV-C intermittent light source with a wavelength of 254 nm and an average intensity of 4540 μW / cm 2 , the maximum liquid penetration is 17cm;

[0046] (6) The irradiated gallic acid solution was added to the β-cyclodextrin solution and reacted for 80 minutes. After the reaction, the solution was washed with alcohol and vacuum filtered to obtain a filter cake. The filter cake was redissolved in water to obtain an irradiated gallic acid coating solution, which was labeled as UVC-GA1.

[0047] 150 fresh oysters were purchased from the Tancun Seafood Wholesale Market in Nanning City, from the Beibu Gulf. The oysters were shelled and the meat was immersed in the irradiated gallic acid coating solution for 60-65s. After being taken out, the oyster meat was air-dried at room temperature (25℃) for 10min, and then placed in a food-grade PP plastic packaging box, sealed and marked, and stored in a refrigerator at 0℃; 30 oysters were placed in each plastic box, and a total of 10 plastic boxes were placed for 8 days. After the start of the experiment, oysters were taken on the 0th, 2nd, 4th, 6th, and 8th days, and their surface color and sensory properties were comprehensively evaluated, pH was tested, muscle tissue structure was observed by sectioning, total colony counts, and total volatile basic nitrogen (TVB-N) and biogenic amines were determined to comprehensively evaluate the preservation effect of the coating on oysters. All measurements were performed on three independent samples.

[0048] Example 2

[0049] A method for preparing a radiation-modified gallic acid coating comprises the following steps:

[0050] (1) washing walnut green peel with distilled water and drying it, placing it in an oven, adjusting the temperature to 60° C. for drying until the mass is constant, and then crushing the dried walnut green peel with a grinder and passing it through an 80-mesh sieve to obtain walnut green peel powder;

[0051] (2) Weigh 1.3 g of walnut green peel powder into a 50 mL dry centrifuge tube, add 40 mL of 80% ethanol aqueous solution, soak and place in an ultrasonic cleaning machine, and extract under the conditions of ultrasonic power of 600 W, ultrasonic temperature of 50° C. and ultrasonic time of 50 min;

[0052] (3) After the ultrasonic treatment, the crude gallic acid extract was cooled to room temperature, centrifuged at 5000 r / min for 10 min in a high-speed centrifuge, and the supernatant was collected to obtain the crude gallic acid extract;

[0053] (4) Pour the crude gallic acid extract into the activated macroporous resin, place it in a constant temperature shaker at a temperature of 25° C. and an oscillation frequency of 110 r / min for static adsorption purification for 24 hours, and then use a rotary evaporator to reduce the pressure and concentrate it to obtain a gallic acid product; adsorption purification is carried out at an adsorption rate of 2 BV / h, a desorption rate of 2 BV / h, and a desorption volume of 2 BV;

[0054] (5) Dilute gallic acid with deionized water to a volume fraction of 0.25%, transfer to a sterilized crystal culture dish, and heat at 4.5 J / cm 2 The irradiation was continued for 10 hours; the irradiated gallic acid was filtered through a sterile filter with a pore size of 0.2 μm to obtain an irradiated gallic acid solution; the irradiation was carried out using a desktop UV-C intermittent light source with a wavelength of 254 nm and an average intensity of 4540 μW / cm2 , the maximum liquid penetration is 17cm;

[0055] (6) The irradiated gallic acid solution was added to the β-cyclodextrin solution and reacted for 80 minutes. After the reaction, the solution was washed with alcohol and vacuum filtered to obtain a filter cake. The filter cake was redissolved in water to obtain an irradiated gallic acid coating solution, which was labeled as UVC-GA2.

[0056] (7) 150 fresh oysters were purchased from the Beibu Gulf Seafood Wholesale Market in Nanning. The oysters were shelled and the meat was immersed in the irradiated gallic acid coating solution for 60-65 seconds. After being taken out, the oyster meat was air-dried at room temperature (25°C) for 10 minutes, and then placed in a food-grade PP plastic packaging box, sealed and marked, and stored in a refrigerator at 0°C; 30 oysters were placed in each plastic box, and a total of 10 plastic boxes were placed for 8 days. After the start of the experiment, oysters were taken on the 0th, 2nd, 4th, 6th, and 8th days, and their surface color and sensory properties were comprehensively evaluated, pH was tested, muscle tissue structure was observed by sectioning, total colony counts were counted, and total volatile basic nitrogen (TVB-N) and biogenic amines were determined to comprehensively evaluate the preservation effect of the coating on oysters. All measurements were performed on three independent samples.

[0057] Control group

[0058] Oyster meat not coated with the coating was marked as CON as a control group. Except that the immersion solution was changed to pure water, the other operation steps were the same as those in the embodiment.

[0059] The irradiated gallic acid coating solution (UVC-GA) in Example 1-2 was tested for antioxidant properties. The results of the test solution concentration (ug / mL) and the scavenging rate (%) of DPP free radicals are shown in Table 1:

[0060] Concentration of test solution 1(ug / mL) 2(ug / mL) 3(ug / mL) 4(ug / mL) 5(ug / mL) Example 1 Clearance 26％ 48％ 58％ 67％ 72％ Example 2 Clearance 28％ 50％ 63％ 70％ 75％

[0061] The irradiated gallic acid coating solution has a good scavenging effect on DPPH free radicals. And with the gallic acid mass concentration as an indicator, the scavenging efficiency of DPPH free radicals gradually increases with the increase of sample mass concentration.

[0062] The main reason for the deterioration of aquatic products is protein oxidation. The antioxidant property of the coating determines whether the protein and lipid are oxidized and the degree of oxidation, which in turn determines the shelf life of the aquatic products. The irradiated gallic acid coating can delay lipid oxidation and reduce the oxygen permeability of the coating due to its antioxidant activity of scavenging free radicals. In the present invention, the irradiated GA coating has good antioxidant properties and can improve the preservation effect of aquatic products.

[0063] Testing the indexes of fresh oysters

[0064] On day 0, there was no difference in the L*, a*, and b* values ​​of the oysters in each group (P>0.05). As the storage time increased, the L* and a* values ​​of the oysters in each group decreased (P<0.05), and the degree of decrease was different. The L* and a* values ​​of the oysters in the control group decreased sharply, and the L* and a* values ​​of the oysters in the Example 1-2 (UVC-GA) coating group decreased less. During the entire storage period, the L* and a* values ​​of the oysters in the Example 1-2 (UVC-GA) coating group were significantly higher than those of the control group samples (P<0.05), indicating that the coating effectively prevented the decrease in the brightness of the oyster meat. In addition, the b* values ​​of all samples gradually increased with the extension of storage time. On the 4th day, the coating had a significant effect on the b* value (P<0.05). On the 8th day, the b* values ​​of the oysters in the coating group were much lower than those in the control group (P<0.05), indicating that the coating effectively prevented the increase in the yellowness of the oyster meat. It can be seen that the coating prepared by UVC-GA has a good effect on maintaining the color of oyster meat.

[0065] Fresh oyster meat is milky white, with brown or black mantle, strong sweet flavor, tight and elastic meat, and sensory score close to the full score of 15. During storage, the scores of the coating group were higher than those of the control group. After 4 days of storage, the sensory score of the oysters in the coating group was higher than that of the control group. On the 8th day, the oysters in the control group were inedible, while the oysters in the coating group were still within the acceptable range. This shows that the coating can effectively maintain the sensory properties of oysters during refrigeration.

[0066] The initial pH value of oysters in each group was 6.36. As the storage time increased, the pH value of oysters in each group showed a downward trend. The pH value of oysters in the coating group was higher than that in the control group, indicating that the coating effectively prevented the decrease of pH in oysters. The protective effect of the coating began to appear on the second day of refrigeration. On the sixth day, the pH value of oysters in the coating group was still greater than 6, while that of the control group samples was less than 6. Obviously, the coating has a good effect on preventing the corruption of refrigerated oysters, and the coating prepared by UVC-GA has a better effect.

[0067] The muscle fibers of fresh (0d) oyster muscles are long and tightly arranged, and the endomysium tightly wraps the muscle fibers. After the oysters in the control group were refrigerated, the gaps between the muscle fibers gradually increased. Myofibrils broke after 6d of refrigeration. As the refrigeration time increased, the gaps continued to increase, the breaks became more obvious, the endomysium gradually disappeared, and the boundaries between the muscle fibers were unclear, indicating that both myofibrillar proteins and connective tissue proteins had been degraded. The shape of the oyster muscle fibers in the coating group was well maintained, but as the refrigeration time increased, the gaps between the muscle fibers also began to increase. The coating has the best effect on maintaining the muscle fiber structure of oyster muscles. On the 8th day of refrigeration, the boundaries between the oyster muscle fibers in the coating group were still clear.

[0068] The TVC values ​​of oysters in each group increased with the extension of storage time. Compared with the control group, the TVC value of the coating group was lower, indicating that the reproduction of microorganisms in the coating group was inhibited. This showed that UVC-GA could enhance its antibacterial effect. There was no significant difference between the coating groups.

[0069] During the cold storage period, the TVB-N content of oysters in each group showed an upward trend. The TVB-N content of the control group showed a linear upward trend and reached a maximum value of 26.08 mg / 100 g on the 8th day. The TVB-N content of oysters in the coating group rose slowly and also reached a maximum value on the 8th day, with a maximum value of 15.17 mg / 100 g. The TVB-N content of oysters in the coating group was significantly lower than that in the control group, and there was no significant difference between the coating groups. The results show that the coating has excellent barrier properties and can effectively slow down the increase of TVB-N in oysters and the corruption of oysters during cold storage.

[0070] In the present invention, the contents of the four biogenic amines in each group of oysters showed an upward trend during the cold storage period. In the first four days of cold storage, the content of biogenic amines increased slowly, but began to increase rapidly after the fourth day, which was basically consistent with the change trend of TVC. Compared with the experimental groups, the content of biogenic amines in the control group was always higher than that in the coating group, especially after the fourth day of cold storage. On the eighth day of cold storage, the content of cadaverine and putrescine in the oysters of the control group was twice the maximum value of the coating group. The results show that the coating prepared by UVC-GA has the effect of inhibiting the production of biogenic amines in cold-stored oysters.

[0071] In the present invention, the L* value of oysters decreased significantly with the extension of refrigeration time, and the L* value and a* value of oysters in the coating group were significantly higher than those in the control group. The color of refrigerated aquatic products is a comprehensive reflection of the degree of oxidation of proteins and pigments. The antioxidant capacity of irradiated gallic acid can inhibit the oxidation of proteins. The coating in the present invention has good antioxidant properties, effectively alleviates the oxidation of myoglobin, and causes the a* value of oysters to decrease during refrigeration.

[0072] In the present invention, on the 6th day of refrigeration, the control group samples had an obvious spoilage smell and the comprehensive sensory score decreased. Meanwhile, the coating groups all had higher sensory scores, mainly because the coating had good antibacterial and antioxidant properties.

[0073] In the present invention, as the refrigeration time increases, the pH value of the oysters shows a downward trend. After the oysters die, different biochemical reactions occur in the body, and lactic acid and phosphoric acid produced by the decomposition of ATP and glycogen accumulate. The pH values ​​of oysters in all coating groups are higher than those in the control group, indicating that the coating effectively prevents the decrease in the pH of the oysters and the coating has a better preservation effect. During the refrigeration period, the TVB-N content of oysters in each group generally shows an upward trend. This is due to the combined action of endogenous enzymes and microbial enzymes, which generate nitrogen-containing compounds such as ammonia, trimethylamine, and histamine. The TVB-N content in the coating group is significantly lower than that in the control group. This significant difference is related to the antibacterial properties of the coating, indicating that the irradiated gallic acid coating has the effect of inhibiting the growth of microorganisms and delaying the decomposition of proteins caused by microorganisms, effectively reducing the production rate of TVB-N.

[0074] In the present invention, the TVC value of each group of oysters increases with the extension of storage time, and the TVC value of the oysters in the coating group is significantly lower than that in the control group, indicating that the coating has good antibacterial properties and effectively inhibits the reproduction of microorganisms. Microorganisms decompose oyster proteins and amino acids, leading to the formation of biogenic amines. Histamine, tryptamine, putrescine and cadaverine are usually used as indicators for determining the degree of corruption of aquatic products, and are formed by decarboxylation of histidine, tryptophan, ornithine and lysine, respectively. In the present invention, the contents of the four biogenic amines in oysters all showed an upward trend during the cold storage period, which was basically consistent with the changing trend of TVC. The content of biogenic amines in the control group was always higher than that in the coating group, indicating that the coating has good antibacterial properties.

[0075] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a radiation-modified gallic acid coating, characterized in that: The following steps are involved: (1) washing walnut green peel with distilled water and drying it, and then crushing the dried walnut green peel with a grinder and passing it through an 80-mesh sieve to obtain walnut green peel powder; (2) Weigh 1.0-1.3 g of walnut green peel powder into a 50 mL dry centrifuge tube, add 30-40 mL of 70-80% ethanol aqueous solution, soak and then place in an ultrasonic cleaner for extraction; (3) After the ultrasonic treatment, the crude gallic acid extract was cooled to room temperature, centrifuged at 5000 r / min for 10 min in a high-speed centrifuge, and the supernatant was collected to obtain the crude gallic acid extract; (4) Pour the crude gallic acid extract into the activated macroporous resin, place it in a constant temperature shaker at a temperature of 25° C. and an oscillation frequency of 110 r / min for static adsorption purification for 24 hours, and then use a rotary evaporator to reduce the pressure and concentrate it to obtain a gallic acid product; (5) Dilute gallic acid with deionized water to a volume fraction of 0.25%, transfer to a sterilized crystal culture dish, and heat at 4.5 J / cm 2 The irradiation was continued at high intensity for 10 hours; the irradiated gallic acid was filtered through a sterile filter with a pore size of 0.2 μm to obtain an irradiated gallic acid solution; (6) adding the irradiated gallic acid solution to the β-cyclodextrin solution, washing with alcohol after the reaction is completed, vacuum filtering to obtain a filter cake, and redissolving the filter cake in water to obtain an irradiated gallic acid coating solution.

2. The method for preparing a radiation-modified gallic acid coating according to claim 1, characterized in that: In step (1), the specific operation of drying is: putting the dried walnut green peel into an oven, adjusting the temperature to 60° C. for drying until the mass is constant.

3. The method for preparing a radiation-modified gallic acid coating according to claim 1, characterized in that: In step (2), the specific operation of extraction is: extraction is carried out under the conditions of ultrasonic power of 600W, ultrasonic temperature of 40-50°C and ultrasonic time of 50min.

4. The method for preparing a radiation-modified gallic acid coating according to claim 1, characterized in that: In step (4), the specific operation of adsorption purification is: adsorption purification is carried out at an adsorption rate of 1-2 BV / h, a desorption rate of 1-2 BV / h and a desorption volume of 1-2 BV.

5. The method for preparing a radiation-modified gallic acid coating according to claim 1, characterized in that: In step (5), the irradiation is carried out using a desktop UV-C intermittent light source with a wavelength of 254 nm and an average intensity of 4540 μW / cm 2 , the maximum liquid penetration is 17cm.

6. The method for preparing a radiation-modified gallic acid coating according to claim 1, characterized in that: In step (6), the irradiated gallic acid solution and the β-cyclodextrin solution are reacted for 80 minutes.

7. The use of the radiation-modified gallic acid coating in aquatic products according to any one of claims 1 to 6, characterized in that: Remove the shell of the aquatic product and keep the meat, immerse the meat of the aquatic product in the irradiated gallic acid coating solution for 60-65 seconds, take it out and air-dry it at 25°C for 10 minutes, then put it into a food-grade PP plastic packaging box, seal it, mark it, and store it in a 0°C refrigerator.

8. The use of the radiation-modified gallic acid coating in aquatic products according to claim 7, characterized in that: The aquatic product is oysters.