Strawberry and grape fresh-keeping composite coating film as well as preparation method and application thereof

Abstract

The invention discloses a strawberry and grape fresh-keeping composite coating film, a preparation method and application, the fresh-keeping composite coating film mainly comprises chitosan, oxidized starch, phytic acid and carvacrol, the rotting rate of strawberries and grapes is reduced, the chromaticity and hardness of the strawberries and the grapes are maintained, the aging of the strawberries and the grapes is delayed, and the fresh-keeping effect of the strawberries and the grapes is improved. The growth of rot-causing fungi alternaria alternata and Penicillium Orsenii in strawberries and grapes is inhibited, the quality of strawberry and grape fruits can be maintained, and the storage period of the strawberries and the grapes can be prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of preservation, and relates to a composite coating film for preserving strawberries and grapes, a preparation method and an application thereof. Background Art

[0002] Strawberries and grapes are favored by consumers due to their unique qualities. However, strawberries and grapes are extremely vulnerable to mechanical damage and microbial infection after harvesting, which leads to decay and deterioration. Microbial infection is one of the main reasons for post-harvest losses of strawberries and grapes, because the physiological characteristics of strawberries and grapes provide favorable conditions for the infection and growth of microorganisms. Strawberries and grapes are often infected by Alternaria alternata and Penicillium olsonii, which cause black spot disease and blue mold disease.

[0003] Phytic acid, also known as inositol hexaphosphate, is widely present in foods such as grains, legumes and nuts. It has the characteristics of wide source, low cost, high safety and convenient use, and is a food additive. Carvacrol is a monoterpenoid phenol compound and the main volatile component in oregano essential oil. It can be extracted from aromatic plants. After strict quality control and safety assessment, it has been proven to have high safety for humans and the environment. Therefore, it has the characteristics of wide material source and high safety.

[0004] Edible coating films are generally divided into lipid-based edible films, protein-based edible films and polysaccharide-based edible films. Chitosan coating film belongs to polysaccharide-based edible film. When using chitosan coating film for preservation, the formed film has relatively poor mechanical strength and limited antibacterial performance, thus restricting the preservation effect. Therefore, it needs to be used in combination with antibacterial active materials such as natural extracts. When chitosan of the present invention is used in combination with phytic acid and carvacrol, phytic acid and carvacrol are embedded in the composite coating film to control their slow release.

[0005] Starch-based coating films have the advantages of wide source, environmental friendliness, biodegradability and safe components, and have broad application prospects in the preservation of fruits and vegetables. However, starch-based coating films have disadvantages such as poor mechanical properties and strong water absorption, so they are often used in combination with other materials. In the present invention, phytic acid and carvacrol are compounded with chitosan and oxidized starch with good film-forming properties. The barrier properties of the composite coating film delay the volatilization and decomposition of phytic acid and carvacrol, and the addition of phytic acid and carvacrol enhances the antibacterial activity of the composite coating film. Summary of the Invention

[0006] The present invention aims at the problems of the above-mentioned existing technologies, and provides a phytic acid / carvacrol-chitosan / oxidized starch preservation composite coating film, a preparation method and an application thereof in the preservation of strawberries and grapes.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention first provides a phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film, which is characterized by comprising components in the following weight ratios: chitosan:oxidized starch = 1-5:1, and the concentration of the oxidized starch is 2.0-4.0%; the addition amount of the phytic acid / carvacrol composite bacteriostatic agent is 0.234-1.170%.

[0009] The preparation method of the above chitosan / oxidized starch fresh-keeping composite coating film solution is as follows: Weigh chitosan and dissolve it in 1.0% acetic acid to prepare a film solution. Add deionized water to the oxidized starch to make its concentration 2.0-4.0%, and gelatinize it at 90°C for 20 min. Mix the chitosan film solution and the oxidized starch film solution, where chitosan:oxidized starch = 2:1, and the concentration of the oxidized starch is 2.89%. Add glycerol as a film-forming agent (0.5%, w:v), and stir magnetically for 1 h.

[0010] The above phytic acid / carvacrol composite bacteriostatic agent is characterized in that the preparation method of the phytic acid / carvacrol composite bacteriostatic agent is as follows: Dissolve phytic acid and carvacrol in deionized water and Tween-80 (0.6%, w:v) respectively, so that their final concentrations are 1.56 g / L and 0.78 g / L respectively, and the addition amount of the phytic acid / carvacrol composite bacteriostatic agent is 0.72%.

[0011] The above phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film is characterized in that fresh strawberries and grapes are soaked in the prepared phytic acid / carvacrol-chitosan / oxidized starch coating film solution for 2-5 min, and then taken out and dried in a ventilated environment at room temperature (20±2°C) to ensure the formation of a uniform coating film on the surfaces of the strawberries and grapes.

[0012] The present invention also provides a preparation method of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film, which comprises the following steps:

[0013] S1. Prepare the chitosan / oxidized starch fresh-keeping composite coating film solution: Weigh chitosan and dissolve it in 1.0% acetic acid to prepare a film solution. Add deionized water to the oxidized starch to make its concentration 2.89%, and gelatinize it at 90°C for 20 min. Mix the chitosan bacteriostatic agent and the oxidized starch bacteriostatic agent, where chitosan:oxidized starch = 2:1, add glycerol as a film-forming agent (0.5%, w:v), and stir magnetically for 1 h.

[0014] S2. Prepare the phytic acid / carvacrol composite bacteriostatic agent: Dissolve phytic acid and carvacrol in deionized water and Tween-80 (0.6%, w:v) respectively, so that their final concentrations are 1.56 g / L and 0.78 g / L respectively, and the addition amount is 0.72%.

[0015] S3. Preparation of phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film: It is obtained by mixing the above-mentioned chitosan / oxidized starch fresh-keeping composite coating solution with a chitosan:oxidized starch ratio of 2:1 and the phytic acid / carvacrol composite bacteriostatic agent. Among them, the concentration of oxidized starch is 2.89%, the concentration of phytic acid is 1.56 g / L, the concentration of carvacrol is 0.78 g / L, and the addition amount of the phytic acid / carvacrol composite bacteriostatic agent is 0.72%. Preparation of phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film: Soak fresh strawberries and grapes with the prepared phytic acid / carvacrol-chitosan / oxidized starch coating solution for 2 - 5 min, then take them out and dry them in a ventilated environment at room temperature (20 ± 2°C) to ensure the formation of a uniform coating film on the surfaces of strawberries and grapes.

[0016] The present invention also provides the application of the above-mentioned phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film in the fresh-keeping of strawberries and grapes.

[0017] Specifically, the application method is as follows: Soak fresh strawberries and grapes with the above-mentioned phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating solution for 2 - 5 min, then take them out and dry them in a ventilated environment at room temperature (20 ± 2°C) to ensure the formation of a uniform coating film on the surfaces of strawberries and grapes, and finally store them at room temperature (20 ± 2°C).

[0018] The beneficial effects of the present invention are as follows:

[0019] (1) The phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film provided by the present invention has good bacteriostatic activity against the postharvest dominant spoilage fungi Penicillium olsonii and Alternaria alternata of strawberries and grapes, and has an inhibitory effect on the biofilms of the dominant spoilage fungi Penicillium olsonii and Alternaria alternata.

[0020] (2) The phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film provided by the present invention improves problems such as postharvest rot and softening of strawberries and grapes. It delays the deterioration of the quality of strawberries and grapes after harvest, inhibits the invasion of fruits by fungi, delays fruit senescence, improves the antioxidant and anti-softening abilities of strawberries and grapes during storage at room temperature (20 ± 2°C), and extends the storage period of strawberries and grapes at room temperature (20 ± 2°C). Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0022] Figure 1Results graph of the effects of phytic acid / carvacrol composite bacteriostatic agents with different concentrations provided in Experimental Example 3 of the present invention on the biofilm formation ability of Penicillium olsonii (A) and Alternaria alternata (B)

[0023] Figure 2 Results graph of the changes in the hardness of strawberries (A) and grapes (B) during storage at room temperature (20±2°C) provided in Experimental Example 3 of the present invention;

[0024] Figure 3 Results graph of the changes in the appearance quality and morphology of strawberries (A) and grapes (B) during storage at room temperature (20±2°C) provided in Experimental Example 3 of the present invention;

[0025] Figure 4 Results graph of the changes in the decay rate of strawberries (A) and grapes (B) during storage at room temperature (20±2°C) provided in Experimental Example 3 of the present invention;

[0026] Figure 5 Results graph of the changes in the peroxidase (POD) activity of strawberries (A) and grapes (B) during storage at room temperature (20±2°C) provided in Experimental Example 3 of the present invention;

[0027] Figure 6 Results graph of the changes in the catalase (CAT) activity of strawberries (A) and grapes (B) during storage at room temperature (20±2°C) provided in Experimental Example 3 of the present invention;

[0028] Figure 7 Results graph of the changes in the malondialdehyde (MDA) content of strawberries (A) and grapes (B) during storage at room temperature (20±2°C) provided in Experimental Example 3 of the present invention. Specific implementation method

[0030] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below in conjunction with embodiments. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art, and the raw materials used are all commercially available products. Among them, phytic acid and carvacrol are purchased from Macklin Biochemical Technology Co., Ltd., chitosan is purchased from Sinopharm Chemical Reagent Co., Ltd., and oxidized starch is purchased from Dongguan Dongmei Food Co., Ltd.

[0031] Example 1 Preparation of phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating

[0032] The preparation method of the chitosan / oxidized starch fresh-keeping composite coating film is as follows: Weigh chitosan and dissolve it in 1.0% acetic acid to make a film solution. Add deionized water to oxidized starch to make its concentration 2.0 - 4.0%, and gelatinize it at 90°C for 20 min. Mix the chitosan film solution and the oxidized starch film solution, where chitosan:oxidized starch = 2:1, and the concentration of oxidized starch is 2.89%. Add glycerol as a film-forming agent (0.5%, w:v), and stir magnetically for 1 h.

[0033] The preparation method of the phytic acid / carvacrol composite bacteriostatic agent is as follows: Dissolve phytic acid and carvacrol in deionized water and Tween-80 (0.6%, w:v) respectively, so that their final concentrations are 1.56 g / L and 0.78 g / L respectively, and the addition amount of the phytic acid / carvacrol composite bacteriostatic agent is 0.72%.

[0034] Preparation of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film: Soak fresh strawberries and grapes in the prepared phytic acid / carvacrol-chitosan / oxidized starch coating solution for 2 - 5 min, then take them out and dry them in a ventilated environment at room temperature (20 ± 2°C) to ensure the formation of a uniform coating film on the surfaces of strawberries and grapes.

[0035] Application method of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film in Example 2

[0036] Soak fresh strawberries and grapes separately in the prepared phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating solution for 2 - 5 min, take them out and let them dry, then dry them in a ventilated environment at room temperature (20 ± 2°C) to ensure the formation of a uniform coating film on the surfaces of strawberries and grapes, and finally store them at room temperature (20 ± 2°C).

[0037] Application of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film in the fresh-keeping of strawberries and grapes in Example 3

[0038] 1. Determination of the bacteriostatic activity of the phytic acid / carvacrol composite bacteriostatic agent

[0039] (1) Determination of the minimum inhibitory concentration (MIC): The minimum inhibitory concentrations of phytic acid and carvacrol are determined by the doubling dilution method. Take sterilized test tubes, add 5 mL of potato dextrose broth, and then add phytic acid and carvacrol respectively to make the final concentrations in the tubes: 50 mg / mL, 25 mg / mL, 12.5 mg / mL, 6.25 mg / mL, 3.125 mg / mL, 1.56 mg / mL, 0.78 mg / mL, 0.39 mg / mL, and use sterile water as a blank control. Add 100 μL of the spore suspensions of Penicillium olsonii and Alternaria alternata (1×10 6(CFU / mL), incubated at 28 °C for 48 h. After the incubation, observe whether the liquid in the test tube becomes turbid or mycelial growth occurs. If the liquid becomes turbid or mycelial growth appears, it indicates that colonies have formed. If the liquid in the test tube remains clear and no mycelial growth is observed, the final concentration of this test tube is taken as the minimum inhibitory concentration of the test bacteria.

[0040] (2) Determination of the minimum fungicidal concentration (MFC): Prepare sterilized potato dextrose agar medium. Take 100 μL of the liquid from the above-mentioned minimum inhibitory concentration tube and add it to the potato dextrose agar medium. After spreading evenly, incubate at 28 °C for 48 h. Set three parallel groups for each experiment. If no colony growth occurs, it is the minimum fungicidal concentration.

[0041] The final measurement results are shown in Table 1-1.

[0042] Table 1-1 Minimum inhibitory concentration and minimum fungicidal concentration of phytic acid and carvacrol against Penicillium olsonii and Alternaria alternata

[0043]

[0044] (3) Evaluation of combined antibacterial effect: First, set the maximum concentration of the antibacterial agent to 8 times the minimum inhibitory concentration of a single antibacterial agent, and then sequentially dilute it to 4, 2, 1, 1 / 2, 1 / 4, 1 / 8, and 1 / 16 of the minimum inhibitory concentration using the two-fold dilution method. Conduct a 7×7 combined test on a 96-well plate and incubate at 28 °C for 48 h. When no fungal colonies grow, determine the fractional inhibitory concentration (FIC) and calculate the fractional inhibitory concentration index (FICI) to confirm and verify the existence of combined antifungal activity. The specific method is as follows: Take 7 rows and 7 columns on the 96-well plate. Add phytic acid in a horizontal row (concentration decreasing), and add carvacrol in a vertical column (concentration decreasing). Take 100 μL of each antibacterial agent, and then add 100 μL of Penicillium olsonii and Alternaria alternata spore suspensions (concentration about 1×10 6 CFU / mL) respectively. Use the group without adding antibacterial agent as the control group. The final measurement results are shown in Table 1-2.

[0045] Table 1-2 Combined antibacterial effect of phytic acid and carvacrol against Penicillium olsonii and Alternaria alternata

[0046]

[0047] In summary, the combined use of phytic acid and carvacrol can better inhibit the spore germination and mycelial growth of Penicillium olsonii and Alternaria alternata. To expand the inhibitory effect on spoilage fungi, select concentrations of phytic acid and carvacrol as 1.56 mg / mL and 0.78 mg / mL respectively for subsequent experiments.

[0048] 2. Effect of phytic acid / carvacrol composite bacteriostatic agent on the biofilm formation ability of spoilage fungi in strawberries and grapes

[0049] Take 20 μL of Penicillium olsonii and Alternaria alternata spore suspensions (1×10 8 CFU / mL) and inoculate them into 96-well plates. Then add 180 μL of phytic acid and carvacrol respectively to make their final concentrations 4MIC 联合 , 2MIC 联合 , MIC 联合 and 1 / 2MIC 联合 . Set three parallel wells for each strain, and the negative control group is replaced with the addition of the same volume of PDB medium. Incubate statically at 28 °C for 12 h, 24 h, and 48 h. After the incubation, measure the biofilm amount by the crystal violet staining method to preliminarily determine the effect of the composite bacteriostatic agent at different concentrations on the biofilm formation ability of spoilage fungi.

[0050] The spore suspensions of Penicillium olsonii and Alternaria alternata (1×10 8 CFU / mL) added with different concentrations of phytic acid / carvacrol composite bacteriostatic agent, compared with the control group added with PDB medium, the effects of the phytic acid / carvacrol composite bacteriostatic agent at different concentrations on the biofilm formation ability at different times (0 h, 4 h, 8 h, 12 h, 24 h, and 48 h) are shown in Figure 1 . There are significant differences in the biofilm amounts of Penicillium olsonii and Alternaria alternata with different concentrations of phytic acid / carvacrol composite bacteriostatic agent. As shown in Figure 1 -A, at 48 h, the inhibitory effect of 1 / 2MIC 联合 on Penicillium olsonii is less than that of 4MIC 联合 and 2MIC 联合 , but it is significantly better than the control group added with PDB medium. Figure 1 As shown in

[0051] -B. Compared with the control group added with PDB medium, at 48 h, the high MIC concentration of phytic acid / carvacrol composite bacteriostatic agent can significantly reduce the biofilm amount, and the higher the concentration, the lower the biofilm amount. This may be due to the good permeability and bacteriostatic effect of phytic acid and carvacrol, which play a role in dispersing fungal colonies and inhibiting their film formation. In summary, the phytic acid / carvacrol composite bacteriostatic agent has a good inhibitory effect on the biofilm formation of Penicillium olsonii and Alternaria alternata.

[0052] Soak fresh strawberries and grapes separately in the prepared phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating solution for 2 - 5 min, take them out and dry them, then dry them in a ventilated environment at room temperature (20 ± 2 °C) to ensure the formation of a uniform coating on the surfaces of strawberries and grapes, and finally store them at room temperature (20 ± 2 °C).

[0053] Fresh strawberries and grapes of the same variety with uniform quality were evenly divided into a control group and an experimental group. The control group consisted of strawberries and grapes soaked in sterile water. The strawberries and grapes in the experimental group were respectively soaked in phytic acid / carvacrol-chitosan / oxidized starch, chitosan / oxidized starch, phytic acid-chitosan / oxidized starch, carvacrol-chitosan / oxidized starch fresh-keeping composite coating solutions and phytic acid, carvacrol, and phytic acid / carvacrol bacteriostatic agents. After being fished out and air-dried, they were stored at room temperature (20 ± 2°C).

[0054] (1) Determination of hardness

[0055] The fruit hardness was measured using a food texture analyzer with a P75 disc extrusion probe; the force sensor had a range of 1000 N; the deformation was 20%; the downward pressing speed was 2 mm / s; and the height of the probe rising back to the sample surface was 20 mm.

[0056] As can be seen from Figure 2 -A, the hardness of strawberries in each treatment group showed a trend of first increasing and then decreasing during storage. The phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating had a significant effect on inhibiting the decrease in hardness (p < 0.05). At 10 days of storage, the hardness of strawberry fruits in the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group was also higher than that of other treatment groups. This indicates that the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment can better slow down the decrease in strawberry fruit hardness in the early stage of storage and maintain the fruit hardness in the later stage of storage. As Figure 2 shown in -B, the hardness of grapes in each treatment group showed a downward trend during storage. At the 10th day of storage, the hardness of grapes in the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group was still the highest, indicating that this treatment method can better maintain the hardness of grape fruits.

[0057] (2) Chromaticity detection

[0058] The change in fruit color can reflect its freshness. Therefore, a color difference meter was used to measure the chromaticity of strawberries and grapes, and the color changes of strawberries and grapes during storage were represented by L*, a*, b*, and ΔE values. Among them, the L* value represents brightness, the a* value reflects the change from green to red, the b* value represents the change from blue to yellow, and ΔE represents the color difference value. Two points on the epidermis of the equatorial region of strawberry and grape fruits were measured, and six strawberries and grapes were taken for each group. The ΔE was calculated according to formula (1.1).

[0059]

[0060] The results of the change in chromaticity during the storage of strawberries at room temperature (20±2°C) are shown in Table 2-1. During the entire storage period, the ΔE values of the chromaticity of strawberry fruits in each group showed an upward trend. Among them, at the 10th day of storage, the change in the ΔE value of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group was the smallest. This indicates that the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment effectively inhibits the color transformation rate of strawberry fruits during storage at room temperature.

[0061] Table 2-1 Changes in chromaticity during the storage of strawberries at room temperature (20±2°C)

[0062]

[0063] Continued Table 2-1

[0064]

[0065] Note: Different letters indicate significant differences between groups (p<0.05).

[0066] The changes in chromaticity during the storage of grapes at room temperature (20±2°C) are shown in Table 2-2. During the entire storage period, the color difference of grape fruits did not change much. However, at the 10th day of storage, the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group still had the smallest color difference change among the 8 groups. Therefore, it can be shown that the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating can effectively slow down the color change of grape fruits during storage at room temperature.

[0067] Table 2-2 Changes in chromaticity during the storage of grapes at room temperature (20±2°C)

[0068]

[0069] Continued Table 2-2

[0070]

[0071] Note: Different letters indicate significant differences between groups (p<0.05).

[0072] (3) Evaluation of appearance quality and morphology

[0073] The appearance and overall acceptability of strawberries and grapes were used as indicators to evaluate the appearance quality and morphology of strawberries and grapes. The results are as Figure 3 shown.

[0074] As Figure 3 shown in -A, the control group of strawberries soaked in sterile water had lesions spreading to the entire strawberry at the 10th day, and the fruits were severely shriveled and wrinkled. The phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group had better quality than other treatment groups during the entire storage period and maintained a better appearance quality and morphology. As Figure 3As can be seen from -B, for the control group of grapes soaked in sterile water, the fruits lost a significant amount of water after 10 days of storage, the pulp texture was relatively loose, and they were inedible. Water loss occurred in all other treatment groups, and depressions appeared on the surfaces of some fruits. However, the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group could still better maintain the quality of the grapes.

[0075] (4) Determination of decay rate

[0076] The decay degree of strawberries was classified and calculated according to the fruit decay area. The decay degree was divided into 5 levels according to the size of the fruit decay area: level 0: no decay; level 1: the decay area was less than 1 / 4 of the fruit area; level 2: the decay area was in the range of 1 / 4 - 1 / 2 of the fruit area; level 3: the decay area was in the range of 1 / 2 - 3 / 4 of the fruit area; level 4: the decay area was greater than 3 / 4 of the fruit area. The decay rate was calculated according to formula (1.2).

[0077]

[0078] The decay rate of grapes was calculated according to formula (1.3).

[0079]

[0080] From Figure 4 -A, it can be seen that the decay rate of strawberries in all treatment groups showed an upward trend during storage. The decay rate of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group was still lower than that of the control group soaked in sterile water after 10 days of storage. This was because after the coating treatment of strawberries, the external environment was isolated outside the coating, thus avoiding the contamination of strawberries by harmful microorganisms such as bacteria or fungi. Moreover, phytic acid and carvacrol had good antibacterial and antioxidant properties, effectively inhibiting the growth and reproduction of microorganisms. From Figure 4 -B, it can be seen that during storage, the decay rate of grapes with different treatments showed an upward trend. The decay rate of grapes treated with phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating was significantly lower than that of the control group soaked in sterile water (p < 0.05), which had an inhibitory effect on the increase in the decay rate of postharvest grapes. In summary, phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating could effectively inhibit the decay of grapes caused by fungal infection during storage.

[0081] (5) Determination of senescence-related indicators

[0082] S1. The peroxidase (POD) activity was determined by the guaiacol colorimetric method, and the results were as Figure 5As shown in Figure -A, during the entire storage period, the activity of peroxidase (POD) in strawberries showed a trend of first increasing and then decreasing. The activity of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group was significantly (p<0.05) higher than that of the control group soaked in sterile water. As Figure 5 As shown in Figure -B, during the storage of grapes, the POD enzyme activity of the control group soaked in sterile water, the carvacrol solution treatment group, and the phytic acid solution treatment group showed a trend of first increasing and then slightly decreasing, while the other treatment groups all showed an increasing trend. There was a significant difference (p<0.05) between the control group soaked in sterile water and the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group. The enzyme activity of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group was significantly higher than that of other groups, indicating that it could effectively delay the senescence process of grapes.

[0083] S2. The activity of catalase (CAT) was determined by ultraviolet spectrophotometry. The results are as Figure 6 As shown in Figure -A, during the storage of strawberries, the decline rate of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group was slower than that of other treatment groups, and the inhibitory effect of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating was the most significant. As Figure 6 As shown in Figure -B, during the storage period, the CAT activity of grapes in the control group soaked in sterile water showed a downward trend, while the other treatment groups showed a trend of first increasing and then decreasing. At the end of storage, the CAT activity of grapes in the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group was higher than that of the control group soaked in sterile water. By comparing the above results, the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment could better protect the activity of CAT in grapes.

[0084] S3. The content of malondialdehyde (MDA) was determined by the thiobarbituric acid colorimetric method. The results are as Figure 7 As shown in Figure -A, during the storage process, the content of malondialdehyde (MDA) in strawberries in each treatment group showed an increasing trend. At the 10th day of storage, the MDA content of strawberries in the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group was lower than that of other treatment groups. This indicates that the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating can effectively delay the accumulation of MDA in fruits, inhibit lipid peroxidation reactions, and delay cell oxidation. As Figure 7 As shown in Figure -B, the overall content of MDA in grapes showed an upward trend. At the 10th day of storage, the MDA content of other treatment groups was higher than that of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment group. It can be seen that the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating treatment can effectively reduce the increase in MDA content.

[0085] Only certain exemplary embodiments of the present invention have been described by way of illustration, and it is understood that, without departing from the spirit and scope of the present invention, various modifications can be made to the described embodiments by those of ordinary skill in the art. Therefore, the above description is illustrative in nature and should not be construed as limiting the scope of the claims of the present invention.

Claims

1. A phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating, characterized in that: The invention comprises the following components in a weight ratio: chitosan: oxidized starch = 1-5:1, the concentration of oxidized starch is 2.0-4.0%; and the addition amount of phytic acid / carvacrol composite antibacterial agent is 0.234-1.170%.

2. The phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating according to claim 1, characterized in that: The preparation method of the chitosan / oxidized starch fresh-keeping composite coating liquid is as follows: weigh chitosan and dissolve it in 1.0% acetic acid to prepare a film liquid, add deionized water to the oxidized starch to make its concentration 2.0-4.0%, gelatinize at 90° C. for 20 minutes, mix the chitosan film liquid and the oxidized starch film liquid, wherein the chitosan:oxidized starch=2:1, the oxidized starch concentration is 2.89%, add glycerol as a film-forming agent (0.5%, w:v), and stir magnetically for 1 hour.

3. The phytic acid / carvacrol composite antibacterial agent according to claim 1, characterized in that The preparation method of the phytic acid / carvacrol composite antibacterial agent is as follows: phytic acid and carvacrol are dissolved in deionized water and Tween-80 (0.6%, w:v) respectively, so that the final concentrations are 1.56 g / L and 0.78 g / L respectively, and the addition amount of the phytic acid / carvacrol composite antibacterial agent is 0.72%.

4. The phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating according to claim 1, characterized in that: Fresh strawberries and grapes were soaked in the prepared phytic acid / carvacrol-chitosan / oxidized starch coating solution for 2 to 5 minutes, and then taken out and dried in a ventilated environment at room temperature (20±2°C) to ensure that a uniform coating was formed on the surface of the strawberries and grapes.

5. The method for preparing the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating liquid according to claim 1, characterized in that: The following steps are involved: S1. Preparation of chitosan / oxidized starch preservative composite coating liquid: weigh chitosan and dissolve it in 1.0% acetic acid to make a film liquid, add deionized water to the oxidized starch to make its concentration 2.89%, gelatinize at 90°C for 20 minutes, mix the chitosan antibacterial agent and the oxidized starch antibacterial agent, wherein the chitosan:oxidized starch = 2:1, add glycerol as a film-forming agent (0.5%, w:v), and stir magnetically for 1 hour. S2. Preparation of phytic acid / carvacrol composite antibacterial agent: phytic acid and carvacrol were dissolved in deionized water and Tween-80 (0.6%, w:v) respectively, so that the final concentrations were 1.56 g / L and 0.78 g / L respectively, and the addition amount was 0.72%. S3. Preparation of phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating: The chitosan / oxidized starch fresh-keeping composite coating liquid with a ratio of chitosan to oxidized starch = 2:1 is mixed with a phytic acid / carvacrol composite antibacterial agent, wherein the concentration of oxidized starch is 2.89%, the concentration of phytic acid is 1.56 g / L, the concentration of carvacrol is 0.78 g / L, and the amount of phytic acid / carvacrol composite antibacterial agent added is 0.72%. Preparation of phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating: Soak fresh strawberries and grapes in the prepared phytic acid / carvacrol-chitosan / oxidized starch coating liquid for 2 to 5 minutes, then remove and dry in a ventilated environment at room temperature (20±2°C) to ensure that a uniform coating is formed on the surface of the strawberries and grapes.

6. Use of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating as claimed in claim 1 in the preservation of strawberries and grapes.

7. The use of the phytic acid / carvacrol-chitosan / oxidized starch fresh-keeping composite coating film as claimed in claim 8 in the preservation of strawberries and grapes, characterized in that: The application method is: soak fresh strawberries and grapes in the above-mentioned phytic acid / carvacrol-chitosan / oxidized starch preservative composite coating liquid for 2 to 5 minutes, then take them out and dry them in a ventilated environment at room temperature (20±2°C) to ensure that a uniform coating is formed on the surface of the strawberries and grapes, and finally store them at room temperature (20±2°C).

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