Fruit and vegetable fresh-keeping label for degrading ethylene at room temperature based on MnO2-based catalyst and preparation method thereof

Abstract

The invention belongs to the technical field of fruit and vegetable fresh-keeping, and discloses a fruit and vegetable fresh-keeping label for degrading ethylene at room temperature based on a MnO2-based catalyst and a preparation method of the fruit and vegetable fresh-keeping label. The fruit and vegetable fresh-keeping label comprises a carrier and a MnO2-based catalyst loaded on the carrier, the loading amount of the MnO2-based catalyst on the fruit and vegetable fresh-keeping label is 0.7-4000 mg / cm < 2 >, and the MnO2-based catalyst comprises one or more of MnO2-NH4Cl, MnO2-iso and W / MnO2. The invention solves the problem that the existing powder catalyst is easy to disperse and pollute the environment in practical application, and compared with the existing ethylene scavenger, the invention has the advantages of reusability, lower synthesis cost and easier realization of ethylene degradation conditions, can efficiently degrade ethylene at room temperature, and has wide application prospects. And a novel fresh-keeping technology which is green, energy-saving and low in cost can be provided for picked fruits and vegetables.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of fruit and vegetable preservation, and particularly relates to a fruit and vegetable preservation label based on an MnO2-based catalyst for room-temperature degradation of ethylene and a preparation method thereof. BACKGROUND

[0002] Currently, the common preservation methods for postharvest fruits and vegetables include low-temperature preservation and controlled atmosphere preservation. These two preservation methods can prolong the shelf life of postharvest fruits and vegetables by providing low-temperature conditions and controlling the proportion of gases in the environment, respectively. However, they have the disadvantages of high cost and high energy consumption due to the high requirements for equipment.

[0003] Ethylene is a plant hormone that can widely participate in the growth, maturation and aging of fruits and vegetables. Even a small amount of ethylene can accelerate the maturation and aging of fruits and vegetables, leading to deterioration in color, texture and nutritional quality. According to investigations, the harmful effects of ethylene cause product loss of fruits and vegetables of up to 10-80%. Therefore, how to control the ethylene concentration in the storage environment of fruits and vegetables is of great significance for postharvest storage of fruits and vegetables. The research of Xie et al. shows that the reduction of ethylene in the environment has an excellent effect on delaying the deterioration of postharvest fruit quality.

[0004] The common ethylene removal methods include porous material adsorption, photocatalytic oxidation, KMnO4 and O3, etc. However, these methods have their own shortcomings. Porous materials have no selectivity, are easy to cause adsorption saturation, need to be replaced frequently and are easy to desorb to cause secondary pollution; chemical oxidation has high efficiency, but is easily affected by environmental conditions and may pollute the fruits themselves.

[0005] Compared with the above methods, normal-temperature catalytic oxidation degradation can oxidize and degrade ethylene at normal temperature and pressure, has low energy consumption and is stable. Currently, the main noble metal catalysts used for degradation of ethylene at normal temperature include platinum (Pt) and silver (Ag), which have excellent catalytic performance but also have the shortcomings of resource scarcity and high cost.

[0006] Manganese dioxide (MnO2) is a transition metal oxide, which is often used as a substitute for noble metals due to its high catalytic activity, abundant content, low toxicity, and low cost. There are six crystal forms of MnO2 in nature, namely α, β, γ, ε, δ, and λ. Zhang et al. found that δ-MnO2 has a unique two-dimensional layered structure and a large number of oxygen vacancies and active oxygen on the surface, which makes it have better catalytic activity than other crystal forms. Therefore, δ-MnO2 is often used for the oxidative degradation of gases such as formaldehyde and propane. Based on the high degradation ability of δ-MnO2 to small molecule gases such as formaldehyde and propane, it can be speculated that δ-MnO2 may also have excellent degradation effect on ethylene. In the patent (Patent No. CN106268799B) of Wang Min and Kan Xiaotian, 1% to 5% of platinum is loaded on the crystallized manganese oxide nanosheet to prepare a Pt / δ-MnO2 catalyst, which can effectively degrade ethylene. However, the catalyst is obtained by compounding δ-MnO2 with noble metal Pt, and there is still room for further reduction in the cost of catalyst preparation. Moreover, the MnO2-based catalyst in the existing invention has a low degradation efficiency of ethylene at room temperature, and the powder catalyst has the problems of easy dispersion and difficult recovery in actual use, which may affect the environment and fruits. SUMMARY

[0007] Therefore, the purpose of the present application is to provide a fruit and vegetable preservation label based on a MnO2-based catalyst for degrading ethylene at room temperature and a preparation method thereof. The present application can efficiently degrade ethylene at room temperature, and aims to provide a more green, energy-saving, and low-cost new preservation technology for postharvest fruits and vegetables.

[0008] To achieve the above purpose, the present application discloses a fruit and vegetable preservation label based on a MnO2-based catalyst for degrading ethylene at room temperature, which comprises a carrier and a MnO2-based catalyst loaded on the carrier. The loading amount of the MnO2-based catalyst on the fruit and vegetable preservation label is 0.7 to 4000 mg / cm2. 2 The size of each fruit and vegetable label can be prepared according to needs.

[0009] Among them, the MnO2-based catalyst comprises one or more of MnO2-NH4Cl, MnO2-iso, and W / MnO2.

[0010] Further, the carrier uses a cellulose paper with a high specific surface area.

[0011] The present application also discloses a preparation method of a fruit and vegetable preservation label based on a MnO2-based catalyst for degrading ethylene at room temperature, which comprises the following steps:

[0012] S1. Preparation of a MnO2-based catalyst;

[0013] S2. Preparation of a MnO2-based catalyst suspension;

[0014] The MnO2-based catalyst prepared in the S1 step is dissolved in deionized water and stirred, and the catalyst particles are uniformly distributed in the deionized water by ultrasonic treatment, to obtain a MnO2-based catalyst suspension;

[0015] S3. Preparation of the MnO2-based fruit and vegetable preservation label;

[0016] The high specific surface area cellulose paper is directly immersed in the MnO2-based catalyst suspension prepared in the step S2, and after soaking for a certain time, it is taken out and dried in an oven. After drying, the MnO2-based fruit and vegetable preservation label is obtained.

[0017] Further, the MnO2-based catalyst in the step S1 includes one or more of MnO2-NH4Cl, MnO2-iso, and W / MnO2;

[0018] The preparation steps of the three MnO2-based catalysts are as follows:

[0019] The preparation steps of MnO2-NH4Cl are as follows: KMnO4 is dissolved in deionized water to obtain a KMnO4 solution, NH4Cl is added to the KMnO4 solution, and after stirring until the NH4Cl is completely dissolved, a hydrothermal reaction is carried out in a high-pressure reaction kettle, the reaction temperature is 100-160°C, and the reaction time is 10-36 h. After the hydrothermal reaction, a brown slurry is obtained, which is centrifuged, washed, purified, and dried to obtain the MnO2-NH4Cl catalyst;

[0020] The preparation steps of MnO2-iso are as follows: KMnO4 is dissolved in deionized water to obtain a KMnO4 solution, and under stirring conditions, isopropyl alcohol solution is slowly added dropwise to the KMnO4 solution. After the isopropyl alcohol solution is added dropwise, a heating reaction is carried out, the reaction temperature is 10-50°C, and the reaction time is 0.1-10 h. After the heating reaction, a brown slurry is obtained, which is centrifuged, washed, purified, and dried to obtain the MnO2-iso catalyst;

[0021] The preparation steps of W / MnO2 are as follows: KMnO4 is dissolved in deionized water to obtain a KMnO4 solution, WCl6 is added to the KMnO4 solution, and after the WCl6 in the KMnO4 solution is completely dissolved, a heating reaction is carried out by mixing with a manganese chloride solution, the reaction temperature is 10-50°C, and the reaction time is 1-72 h. After the heating reaction, a brown slurry is obtained, which is centrifuged, washed, purified, and dried to obtain the W / MnO2 catalyst.

[0022] Further, in the step S1, the washing, centrifugation, and drying processes are as follows:

[0023] Washing: The product is washed with deionized water until the supernatant is clear;

[0024] Centrifugation: centrifugal speed is 8000-10000 rpm, centrifugation time is 8-15 min;

[0025] Drying: drying temperature is 70-110℃, drying time is 12-24h.

[0026] Further, in the step S2, the stirring and ultrasonic treatment time is 5-10 min.

[0027] Further, in the step S3, the carrier is high specific surface area cellulose paper, and the loading amount is 0.7-4000 mg / cm 2 The size of each fruit and vegetable label can be prepared according to the need, the soaking time is 5-20 min, the drying temperature is 30-100℃, and the drying time is 0.1-24h.

[0028] The application also discloses a fruit and vegetable preservation label based on the MnO2-based catalyst for degrading ethylene at room temperature, and the fruit and vegetable preservation label is applied to preservation of different postharvest fruits during storage.

[0029] Advantages:

[0030] (1) The MnO2-based fruit and vegetable preservation label provided by the application solves the problem of easy dispersion and environmental pollution of the existing powder catalyst in practical application by using a simple preparation process and low cost.

[0031] (2) The MnO2-based catalyst prepared by potassium permanganate reduction has high specific surface area, high Mn 3+ / Mn 4+ and other properties conducive to ethylene degradation;

[0032] (3) The MnO2-based catalyst and the preservation label provided by the application have excellent ethylene oxidation and degradation performance under normal temperature and pressure conditions, and the ethylene (100mL, 100ppm) degradation rates of the three preservation label examples MnO2-NH4Cl, MnO2-iso and W / MnO2 reach 48.69%, 68.48% and 45.60% within 8h. By degrading ethylene at room temperature, the problem of secondary pollution caused by easy desorption of the existing adsorbent (such as activated carbon) is solved. Compared with the existing ethylene scavenger, the application has the advantages of lower synthesis cost and easier degradation conditions.

[0033] (4) MnO2-NH4Cl, MnO2-iso and W / MnO2 three kinds of label examples are applied to postharvest storage of Wushan crisp plum fruits, so that the ethylene production rate of the postharvest crisp plum in the storage process is reduced by 20.3%, 28.5% and 12.1% respectively compared with the comparative example; the respiration peak is delayed by 2d; in addition, the color transition speed of bananas in the storage experiment is also slowed down.

[0034] (5) The final product of the MnO2-based fresh-keeping label prepared in the application is carbon dioxide, no chemical additive residues, and has the advantages of green environmental protection, convenient use, reusability and the like.

[0035] Other advantages, objects and features of the present application will be in part apparent and in part pointed out hereinafter in the specification, and will be learned from a reading of the following specification and by practicing the application according to the claims hereinafter set forth. The objects and other advantages of the present application will be realized and attained by the structure particularly pointed out in the written description and claims hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 Flow chart of the fruit and vegetable fresh-keeping label preparation method of the present application;

[0037] Figure 2 XRD images of the three manganese-based catalysts A1, A2 and A3 obtained in Example 1;

[0038] Figure 3a N2 adsorption isotherm curves of the three manganese-based catalysts A1, A2 and A3 obtained in Example 1;

[0039] Figure 3b Pore size distribution images of the three manganese-based catalysts A1, A2 and A3 obtained in Example 1;

[0040] Figure 4a XPS images of the Mn 2p orbit of the three manganese-based catalysts A1, A2 and A3 obtained in Example 1;

[0041] Figure 4b XPS images of the O1s orbit of the three manganese-based catalysts A1, A2 and A3 obtained in Example 1;

[0042] Figure 5a Ethylene degradation rates of the three manganese-based catalysts A1, A2 and A3 obtained in Example 1 at room temperature;

[0043] Figure 5b Ethylene degradation rates of the three manganese-based catalysts A1, A2 and A3 obtained in Example 1 after three cycles at room temperature;

[0044] Figure 6XRD images of three manganese-based catalysts A1, A2 and A3 obtained in Example 1;

[0045] Figure 7 XRD images of three manganese-based fruit and vegetable fresh-keeping labels B1, B2 and B3 obtained in Example 2;

[0046] Figure 8 Comparison of XRD images of three manganese-based fruit and vegetable fresh-keeping labels B1, B2 and B3 obtained in Example 2 before and after labeling treatment;

[0047] Figure 9a Ethylene degradation rates of three manganese-based fruit and vegetable fresh-keeping labels B1, B2 and B3 obtained in Example 2 at room temperature;

[0048] Figure 9b Ethylene degradation rates of three manganese-based fruit and vegetable fresh-keeping labels B1, B2 and B3 obtained in Example 2 at room temperature after three cycles;

[0049] Figure 10 Changes in ethylene production rates of fruits in each group during storage for comparative analysis;

[0050] Figure 11 Changes in respiration intensity of fruits in each group during storage for comparative analysis;

[0051] Figure 12 Changes in hardness of fruits in each group during storage for comparative analysis;

[0052] Figure 13 Changes in total color difference values (ΔE) of fruits in each group during storage for comparative analysis;

[0053] Figure 14 Changes in weight loss rates of fruits in each group during storage for comparative analysis;

[0054] Figure 15 Changes in rot rates of fruits in each group during storage for comparative analysis;

[0055] Figure 16 Changes in appearance of fruits in each group during storage for comparative analysis;

[0056] Figure 17 Changes in cross-sectional views of fruits in each group during storage for comparative analysis. DETAILED DESCRIPTION

[0057] In order to make the technical solutions, advantages and objectives of the present application clearer, the technical solutions of the embodiments of the present application will be described clearly and completely below in conjunction with the drawings of the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the described embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without any inventive effort fall within the protection scope of the present application.

[0058] The application discloses a fruit and vegetable preservation label based on an MnO2-based catalyst for degrading ethylene at room temperature, which comprises a carrier and an MnO2-based catalyst loaded on the carrier, and the loading amount of the MnO2-based catalyst on the fruit and vegetable preservation label is 0.7-4000 mg / cm 2 The size of each fruit and vegetable label can be prepared according to requirements.

[0059] The MnO2-based catalyst comprises one or more of MnO2-NH4Cl, MnO2-iso and W / MnO2.

[0060] The carrier is high-specific-surface-area cellulose paper.

[0061] As shown in Figure 1 The application further discloses a preparation method of the fruit and vegetable preservation label based on the MnO2-based catalyst for degrading ethylene at room temperature, which comprises the following steps:

[0062] S1. Preparation of the MnO2-based catalyst;

[0063] The MnO2-based catalyst in step S1 comprises one or more of MnO2-NH4Cl, MnO2-iso and W / MnO2.

[0064] The preparation steps of the three MnO2-based catalysts are as follows:

[0065] The preparation steps of the MnO2-NH4Cl are as follows: KMnO4 is dissolved in deionized water to obtain a KMnO4 solution, NH4Cl is added to the KMnO4 solution, and after stirring until the NH4Cl is completely dissolved, a hydrothermal reaction is performed in a high-pressure reaction kettle, the reaction temperature is 100-160 DEG C, the reaction time is 10-36 h, and after the hydrothermal reaction, a brown slurry is obtained, and the brown slurry is centrifuged, washed, purified, and dried to obtain the MnO2-NH4Cl catalyst.

[0066] Preparation steps of MnO2-iso: KMnO4 was dissolved in deionized water to obtain a KMnO4 solution, and isopropyl alcohol solution was slowly added dropwise to the KMnO4 solution under stirring, and then a heating reaction was performed after the isopropyl alcohol solution was completely added, the reaction temperature was 10-50°C, and the reaction time was 0.1-10 h, and then a brown slurry was obtained after the heating reaction, and the brown slurry was centrifuged, washed, purified, and dried to obtain the MnO2-iso catalyst;

[0067] Preparation steps of W / MnO2: KMnO4 was dissolved in deionized water to obtain a KMnO4 solution, WCl6 was added to the KMnO4 solution, and then a heating reaction was performed after the WCl6 in the KMnO4 solution was completely dissolved and mixed with a manganese chloride solution, the reaction temperature was 10-50°C, and the reaction time was 1-72 h, and then a brown slurry was obtained after the heating reaction, and the brown slurry was centrifuged, washed, purified, and dried to obtain the W / MnO2 catalyst;

[0068] In the preparation processes of the above three kinds of MnO2-based catalysts, the steps of centrifugation, washing, purification, and drying are the same;

[0069] Washing: The product was washed with deionized water until the supernatant was clear;

[0070] Centrifugation: The centrifugal speed was 8000-10000 rpm, and the centrifugation time was 8-15 min;

[0071] Drying: The drying temperature was 70-110°C, and the drying time was 12-24 h.

[0072] S2. Preparation of a MnO2-based catalyst suspension;

[0073] The MnO2-based catalyst prepared in step S1 was dissolved in deionized water and stirred, and the catalyst particles were uniformly distributed in the deionized water by ultrasonic treatment, thereby obtaining a MnO2-based catalyst suspension;

[0074] In step S2, the stirring and ultrasonic treatment time was 5-10 min;

[0075] S3. Preparation of a MnO2-based fruit and vegetable preservation label;

[0076] The high specific surface area cellulose paper was directly soaked in the MnO2-based catalyst suspension prepared in step S2, and then taken out and dried in an oven after soaking for a certain time, thereby obtaining a MnO2-based fruit and vegetable preservation label.

[0077] The loading amount of MnO2 on the cellulose paper was 0.7-4000 mg / cm 2 , the soaking time was 5-20 min, the drying temperature was 30-100°C, and the drying time was 0.1-24 h.

[0078] The application further discloses a preservation application of the fruit and vegetable preservation label based on the MnO2-based catalyst for degrading ethylene at room temperature during different postharvest fruit storage periods, wherein the application object, i.e., the fruit type, is a climacteric fruit, and the storage application condition is a temperature of 0-40 ℃ and a humidity of 40-95% RH.

[0079] Example 1

[0080] Preparation of three MnO2-based catalysts

[0081] A1: 0.922 g of KMnO4 and 0.313 g of NH4Cl are dissolved in 210 ml of deionized water, and after being stirred to be uniformly dissolved, the solution is transferred into a reaction kettle to be hydrothermally reacted at 140 ℃ for 24 h; after the product is cooled to room temperature, centrifugal washing is performed, and the product is dried at 70 ℃ for 12 h to obtain a granular final product, i.e., MnO2-NH4Cl;

[0082] A2: 5.0 g of KMnO4 is dissolved in 150 ml of deionized water, and then 25 ml of isopropyl alcohol is added under stirring, and the obtained brown slurry is aged at 25 ℃ for 1 h; after centrifugal washing, the product is placed into an oven to be dried at 110 ℃ for 12 h to obtain granular manganese dioxide, i.e., MnO2-iso;

[0083] A3: 1.264 g of KMnO4 is added into 200 ml of deionized water, 0.635 g of WCl6 is added into the KMnO4 solution, and additionally, 1.728 g of MnCl2 is added into 200 ml of deionized water; the obtained MnCl2 solution which is stirred to be uniformly dissolved is slowly added dropwise into the KMnO4 solution, the obtained brown slurry is aged at 30 ℃ for 12 h, centrifugal washing is performed, and the product is dried at 105 ℃ for 12 h to obtain a product W / MnO2.

[0084] Figure 2 It can be seen that the three manganese-based catalysts A1, A2 and A3 obtained in Example 1 all have diffraction peaks at θ=12.4°, 37.2° and 66.2°. The several diffraction peaks correspond to the (001), (-111) and (005) crystal faces of manganese dioxide (JCPDS No. 80-1098) respectively, which proves that the three manganese-based catalysts are all δ-crystal manganese dioxide. Figure 3a It can be seen that the three catalysts all belong to type IV isotherm, which indicates that the materials all contain mesopores, and A3 has the largest specific surface area, which is 204.5309 m 2 / g. The Mn 3+ has an inducing effect on the Jahn-Teller distortion phenomenon, thereby promoting the formation of oxygen vacancies, so that the catalyst is more likely to produce reactive oxygen for reaction; in addition, the O AMost of the low coordination number of unsaturated oxygen, also easy to produce active oxygen species, so the content can reflect the side of the catalyst oxygen vacancy and active oxygen. Figure 4a , b and Table 1 can be seen, A2 and A3 have the highest Mn 3+ and surface adsorbed oxygen (O A ) ratio, more conducive to the progress of catalytic reaction.

[0085] Table 1

[0086]

[0087] Experimental analysis of three MnO2-based catalysts for degrading ethylene

[0088] The manganese-based catalysts A1, A2 and A3 prepared in Example 1 were applied to the catalytic degradation of ethylene at room temperature. The manganese-based catalyst (0.1 g) was placed in a sealed container containing ethylene with a concentration of about 100 ppm, and the ethylene concentration in the container was measured every 2 h. The degradation efficiency of ethylene was (C0-C t ) / C0, wherein C t was the ethylene concentration in the container at time t, and C0 was the initial ethylene concentration. The ethylene degradation experiment was repeated three times in succession according to the above method.

[0089] Figure 5a It can be seen that after 8 h, the ethylene degradation rates of A1, A2 and A3 were 46.12%, 66.92% and 54.97%, respectively, and the three MnO2-based catalysts all had good ethylene degradation performance. In addition, Figure 5b It can be seen that after three cycles, the ethylene degradation rates of A1, A2 and A3 were 44.06%, 62.34% and 52.47%, respectively. The above results prove that the MnO2-based catalysts obtained by the present application have high and stable ethylene degradation performance under normal temperature and pressure conditions, and have good potential for reuse.

[0090] Analysis of the practical application of the three MnO2-based catalysts

[0091] Green banana fruits with mature fruits, uniform size, no mechanical damage, and no disease and insect pests were selected. The obtained fruits were randomly divided into four groups, with 9 banana fruits in each group. The fruits were placed in PET transparent preservation boxes with holes, and 3 banana fruits were placed in each box, of which the blank group was added without any catalyst; the remaining three groups were placed in the three manganese-based catalysts A1, A2 and A3 obtained in Example 1; the use amount was 0.2 g / 500 g of fruits, and the treated banana fruits were stored in an environment with a temperature of 27±3℃ (room temperature) and a humidity of 55±5% RH. The banana fruits were photographed and recorded at regular intervals during storage.

[0092] Figure 6 It is evident that black spots began to appear on the banana peel in the control group from day 4, and the area covered by these black spots increased with prolonged storage, indicating fruit deterioration. In contrast, groups A1, A2, and A3 delayed the appearance of black spots on the banana peel, thus extending the shelf life of the bananas to some extent.

[0093] Example 2

[0094] Preparation of Fruit and Vegetable Preservation Labels Corresponding to Three MnO2-based Catalysts

[0095] B1: Add 0.2g of MnO2-NH4Cl particles (obtained in Example 1) to 20mL of deionized water and stir for 5min. Then, ultrasonically disperse for 10min to obtain a MnO2-NH4Cl suspension. Cut cellulose paper into squares with a side length of 10cm and add them to the suspension. Soak for 10min and dry at 80℃ for 3h to obtain a MnO2-NH4Cl catalytic tag.

[0096] B2: Add 0.2g of MnO2-iso particles (obtained in Example 1) to 20ml of deionized water and stir for 5min. Then, ultrasonically disperse for 10min to obtain MnO2-iso suspension. Cut cellulose paper into squares with a side length of 10cm and add them to the suspension. Soak for 10min and dry at 80℃ for 3h to obtain MnO2-iso catalytic tags.

[0097] B3: Add 0.2g of W / MnO2 particles (obtained in Example 1) to 20ml of deionized water and stir for 5min. Then, ultrasonically disperse for 10min to obtain a W / MnO2 suspension. Cut cellulose paper into squares with a side length of 10cm and add them to the suspension. Soak for 10min and dry at 80℃ for 3h to obtain a W / MnO2 catalytic tag.

[0098] Figure 7 As can be seen, the uncatalyst-supported substrate exhibited three diffraction peaks at θ = 15.4°, 16.8°, and 22.9°, corresponding to (110), (22.9°), and (32.9°) of cellulose (JCPDS No. 50-2241), respectively. (200) Crystal plane. After loading the material, the characteristic peak of δ-MnO2 appeared in both labels B1 and B3. Figure 8 As can be seen, the XRD diffraction peak positions of the catalyst did not change significantly before and after the labeling treatment. These results demonstrate that the MnO2-based fruit and vegetable preservation label preparation method provided by this invention does not significantly affect the morphology and structure of the catalyst.

[0099] Experimental Analysis of Ethylene Degradation in Three Types of Fruit and Vegetable Preservation Labels

[0100] The manganese-based catalytic labels B1, B2 and B3 prepared in Example 2 were applied to the catalytic degradation of ethylene at room temperature. The labels loaded with 0.1 g of manganese-based catalyst were placed in a closed container containing ethylene at a concentration of about 100 ppm, and the ethylene concentration in the container was measured every 2 h. The ethylene degradation efficiency was C t / C0, where C t is the ethylene concentration in the container at time t, and C0is the initial ethylene concentration. The ethylene degradation experiment was repeated three times in succession for the samples in the container according to the above method.

[0101] Figure 9a It can be seen that the ethylene degradation rates of B1, B2 and B3 at room temperature for 8 h were 48.69%, 68.48% and 45.60%, respectively, which were similar to the results of the powder catalyst. In addition, the stability and reusability of the three types of fresh-keeping labels were also investigated, and the results of the three repeated experiments are shown in Table 2. Figure 9b The ethylene degradation rates of B1, B2 and B3 after three cycles were 42.29%, 62.34% and 46.52%, respectively, and no significant decrease occurred. The above results show that the MnO2-based fruit and vegetable fresh-keeping labels have high and stable ethylene degradation capacity at room temperature.

[0102] Comparative Example 1

[0103] The filter paper substrate was cut into a square size with a side length of 10 cm, completely immersed in deionized water, taken out after 10 min and placed in an oven, and dried at 60°C for 30 min to obtain Comparative Example 1.

[0104] Comparative Example 2

[0105] 1 g of commercially available KMnO4 balls (carrier: Al2O3, KMnO4 content: 10 wt%) was weighed and placed in a breathable non-woven bag and sealed to obtain Comparative Example 2.

[0106] Comparative Analysis

[0107] The experimental crisp plum fruits were harvested from a fruit garden in Wushan, Chongqing. The selected Wushan crisp plum fruits were blown with cold air to remove surface dust and then randomly divided into 5 groups, each containing about 200 fruits. 30 fruits were used for the determination of weight loss rate, respiration intensity and ethylene production rate, and the appearance of the fruits was recorded by taking photos. The remaining fruits were used for the determination of other quality indicators. The 5 groups of fruits were placed in PET transparent fresh-keeping boxes with holes, and 6 fruits were placed in each box. The 5 groups of fruits were placed in fruit and vegetable fresh-keeping labels B1, B2, B3, Comparative Example 1 and Comparative Example 2 (catalyst dosage: 0.2 g / 500 g of fruits). The treated crisp plum fruits were stored in an environment with a temperature of 25±2°C (room temperature) and a humidity of 52±2% RH. During the storage process, a portion of the fruits were randomly selected at regular intervals for the determination of indicators.

[0108] Figure 10 It can be seen that the ethylene production rate of the fruit of the Wushan crisp plum on the 12th day of storage is significantly reduced under the action of the three manganese-based fresh-keeping labels. Compared with Comparative Example 1, the ethylene production rate of the fruit of the fresh-keeping label groups B1, B2 and B3 is reduced by 20.3%, 28.5% and 12.1%, respectively. Figure 11 It can be seen that, compared with Comparative Example 1, the respiration intensity of the fruit in the fresh-keeping label group is lower, and the fresh-keeping label successfully delays the respiration peak of the crisp plum fruit from the fifth day to the seventh day. The crisp and tender taste and the fresh green peel color are the signature characteristics of the Wushan crisp plum, so the hardness and color are important indicators for evaluating the quality thereof. Figure 12 The change in the hardness of the fruit in the fresh-keeping label groups B1, B2 and B3 is significantly higher than that in Comparative Examples 1 and 2 on the 12th day of storage, proving that the fresh-keeping label delays the softening of the fruit. In addition, Figure 13 It can be seen that the total color difference value of the fruit in the fresh-keeping label group is significantly lower than that in Comparative Example 1 during the storage period, and is also reduced to a certain extent compared with Comparative Example 2. Figure 14 And 15 It can be seen that the fresh-keeping label also delays the weight loss and rotting of the crisp plum fruit to a certain extent. Figure 16 And 17 The appearance changes of the peel and the cross section of the green crisp plum fruit during the storage period are recorded, respectively, and it can be seen that the fruit in Comparative Examples 1 and 2 appears black and is infected by microorganisms in the late storage period, while the fruit treated by the label, especially the fruit in groups B1 and B2, still maintains a fresh green appearance; the cross section of the fruit in groups B1, B2 and B3 is also fresher than that in the two comparative examples.

[0109] The above results prove that the fruit and vegetable fresh-keeping label prepared in the present application can degrade ethylene in the storage environment at room temperature through the MnO2-based catalyst loaded on the label, thereby inhibiting the respiration and metabolism of the fruit and delaying the weight loss and rotting of the fruit. In addition, the degradation of ethylene can also reduce the degradation of pectin and chlorophyll caused by ethylene, so that the softening and color change of the fruit are inhibited, thereby achieving the purpose of prolonging the shelf life of the fruit.

[0110] Finally, it should be explained that the above examples are only used to illustrate the technical solutions of the present application and not to limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the present technical solutions, and all of them should be covered in the protection scope of the present application.

Claims

1. A fruit and vegetable fresh-keeping label based on MnO2-based catalyst for room temperature degradation of ethylene, characterized in that: The fruit and vegetable fresh-keeping label comprises a carrier and a MnO2-based catalyst loaded on the carrier, and the loading amount of the MnO2-based catalyst on the fruit and vegetable fresh-keeping label is 0.7-4000 mg / cm 2 The size of each fruit and vegetable label can be prepared according to requirements. The MnO2-based catalyst comprises one or more of MnO2-NH4Cl, MnO2-iso, and W / MnO2.

2. The fruit and vegetable fresh-keeping label based on MnO2 catalyst for degrading ethylene at room temperature according to claim 1, characterized in that: The carrier is high specific surface area cellulose paper.

3. A method for preparing a fruit and vegetable fresh-keeping label based on MnO2 catalyst for degrading ethylene at room temperature, characterized in that, The method comprises the following steps: S1. Preparation of the MnO2-based catalyst; S2. Preparation of the MnO2-based catalyst suspension; The MnO2-based catalyst prepared in step S1 is dissolved in deionized water and stirred, and the catalyst particles are uniformly distributed in the deionized water by ultrasonic treatment, thereby obtaining the MnO2-based catalyst suspension; S3. Preparation of the MnO2-based fruit and vegetable fresh-keeping label; The high specific surface area cellulose paper is directly soaked in the MnO2-based catalyst suspension prepared in step S2, and then taken out and dried in an oven after soaking for a certain period of time, thereby obtaining the MnO2-based fruit and vegetable fresh-keeping label.

4. The method for preparing the ethylene-degrading fruit and vegetable preservation label based on Mn02 catalysts at room temperature according to claim 3, characterized in that: The MnO2-based catalyst in step S1 comprises one or more of MnO2-NH4Cl, MnO2-iso, and W / MnO2. The preparation steps of the three kinds of MnO2-based catalysts are as follows: The preparation steps of MnO2-NH4Cl are as follows: KMnO4 is dissolved in deionized water to obtain a KMnO4 solution, NH4Cl is added to the KMnO4 solution, and the solution is stirred until the NH4Cl is completely dissolved, and then a hydrothermal reaction is performed in a high-pressure reaction kettle, the reaction temperature is 100-160°C, and the reaction time is 10-36 h; after the hydrothermal reaction, a brown slurry is obtained, and the brown slurry is centrifuged, washed, purified, and dried to obtain the MnO2-NH4Cl catalyst; The preparation steps of MnO2-iso are as follows: KMnO4 is dissolved in deionized water to obtain a KMnO4 solution, and an isopropyl alcohol solution is slowly added to the KMnO4 solution under stirring, and then a heating reaction is performed, the reaction temperature is 10-50°C, and the reaction time is 0.1-10 h; after the heating reaction, a brown slurry is obtained, and the brown slurry is centrifuged, washed, purified, and dried to obtain the MnO2-iso catalyst; The preparation steps of W / MnO2 are as follows: KMnO4 is dissolved in deionized water to obtain a KMnO4 solution, WCl6 is added to the KMnO4 solution, and after the WCl6 in the KMnO4 solution is completely dissolved, a heating reaction is performed by mixing with a manganese chloride solution, the reaction temperature is 10-50°C, and the temperature reaction time is 1-72 h; after the heating reaction, a brown slurry is obtained, and the brown slurry is centrifuged, washed, purified, and dried to obtain the W / MnO2 catalyst.

5. The method for preparing the ethylene-degrading fruit and vegetable preservation label based on Mn02 catalysts at room temperature according to claim 4, characterized in that, In step S1, the washing, centrifugation, and drying processes are as follows: Washing: the product is washed with deionized water until the supernatant is clear; Centrifugation: the centrifugation speed is 8000-10000 rpm, and the centrifugation time is 8-15 min; Drying: the drying temperature is 70-110°C, and the drying time is 12-24 h.

6. The method for preparing the ethylene-degrading fruit and vegetable preservation label based on MnO2 catalysts at room temperature according to claim 4, characterized in that: In step S2, the stirring and ultrasonic treatment times are both 5-10 min.

7. The method for preparing the ethylene-degrading fruit and vegetable preservation label based on MnO2 catalysts at room temperature according to claim 4, characterized in that: The carrier in the step S3 is high specific surface area cellulose paper, and the loading capacity is 0.7-4000 mg / cm 2 The size of each fruit and vegetable label can be prepared according to the needs, the soaking time is 5-20 min, the drying temperature is 30-100℃, and the drying time is 0.1-24 h.

8. The fruit and vegetable fresh-keeping label based on the MnO2-based catalyst for room temperature degradation of ethylene according to any one of claims 1-2 for fresh-keeping application during different postharvest fruit storage periods.

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