Metal-loaded starch aerogel, its preparation method and application

Abstract

The application discloses a kind of metal-loaded starch aerogel and its preparation method and application, comprising the following steps: (1) starch and water are prepared into starch milk, starch milk is heated, and gelatinized starch solution is obtained;(2) sodium laurate is added to the gelatinized starch solution and heated to react, and after the reaction is completed, starch-sodium laurate complex solution is obtained;(3) metal nitrate solution is added to the above-mentioned complex solution, and after stirring uniformly, a reducing agent is added to reduce metal ions, and metal-loaded starch hydrogel is obtained;(4) the above-mentioned hydrogel is pre-frozen and freeze-dried to obtain metal-loaded starch aerogel.The metal-loaded starch aerogel of the application has excellent ethylene adsorption capacity, with an adsorption capacity of about 32 mL / g, good adsorption stability, and the adsorption process can be carried out at normal temperature and pressure, which can be used for fruit preservation.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of food, material and chemical industry, and relates to a metal-loaded starch aerogel, in particular to a starch aerogel loaded with metal nanoparticles and having high ethylene adsorption capacity and a preparation method thereof. BACKGROUND

[0002] Ethylene is a plant hormone that promotes fruit ripening. It accumulates slowly during fruit development and increases to a certain concentration, which can accelerate fruit ripening and decay. Controlling ethylene concentration is an effective means to improve fruit storage time and quality.

[0003] Current ethylene removal agents and adsorption carriers include potassium permanganate, ozone, activated carbon, zeolite, and cyclodextrin. Potassium permanganate oxidizes ethylene into water and carbon dioxide to remove ethylene. Potassium permanganate is loaded on a fiber membrane to adsorb the ethylene produced by oxidized avocado, extending the shelf life by 4 days (Journal of Agricultural and Food Chemistry, 2018, 66, 5635-5643). However, such oxidizing agents have defects such as oxidation corrosion, food contamination, incomplete ethylene removal, and poor fruit preservation effect. Cyclodextrin and V-type crystalline starch materials rely on van der Waals forces and hydrophobic interactions to achieve ethylene adsorption. High-pressure conditions are required for ethylene adsorption, and there are still great challenges in capturing the extremely low concentration of ethylene produced by fruits (Aggregate, 2024, e565). Activated carbon and zeolite have been used for ethylene adsorption due to their large specific surface area, but the adsorption capacity is low, at 3.5-4.1 mL / g and 29.1-439 μL / g, respectively, and the ethylene adsorption is not stable and can be easily released (Environmental Research, 2024, 248, 118247; Comprehensive Reviews in Food Science and Food Safety, 2020, 19, 3980-4007). In summary, existing cyclodextrin and V-type crystalline starch materials require high pressure to promote ethylene contact with the binding sites on the surface or pores of the solid substrate. The binding energy between activated carbon, zeolite and ethylene is not strong, and in the actual low-temperature and high-humidity storage and transportation environment, the ethylene partial pressure produced by fruits is low. The adsorption capacity achieved by physical force is low and can be easily desorbed, which is not suitable for the capture and removal of endogenous ethylene and fruit preservation. Therefore, for the low-temperature, normal-pressure, and high-humidity fruit storage and transportation environment, a stronger binding mode is needed to achieve the adsorption of trace amounts of ethylene to slow down the ripening and decay of fruits.

[0004] Starch-based aerogels, as novel sustainable aerogels, not only possess characteristics such as low density and high specific surface area, but also exhibit novel properties when combined with other materials to form composite materials, leading to their widespread application in food packaging and wastewater treatment. However, there are currently no studies in China on the use of metal-loaded starch aerogels for ethylene removal during fruit preservation. Summary of the Invention

[0005] The purpose of this invention is to provide a convenient, low-cost, and environmentally friendly method for preparing metal-loaded starch aerogels to achieve efficient ethylene adsorption and fruit preservation functions.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for preparing metal-loaded starch aerogel includes the following steps:

[0008] (1) Prepare starch milk by mixing starch and water, and heat the starch milk to obtain gelatinized starch solution;

[0009] (2) Sodium lauryl precipitate was added to the above gelatinized starch solution and heated to react. After the reaction was completed, a starch-sodium lauryl precipitate complex solution was obtained.

[0010] (3) Add the metal nitrate solution to the above complex solution, stir evenly, and then add a reducing agent to reduce the metal ions to obtain metal-loaded starch hydrogel.

[0011] (4) The above hydrogel was pre-frozen and then freeze-dried to obtain metal-loaded starch aerogel.

[0012] Preferably, in step (3), the reducing agent is sodium borohydride and / or glucose, and the molar ratio of the reducing agent to the metal nitrate is 1:2 to 2:1.

[0013] Preferably, in step (3), the metal nitrate is copper nitrate and / or silver nitrate, and the amount used is 1 to 5% of the dry weight of starch.

[0014] Preferably, in step (2), the mass of sodium lauryl ester is 8-20% of the dry starch.

[0015] Preferably, the sodium laurylate is added in solution, and the sodium laurylate solution needs to be preheated at 80-90°C for 5-10 minutes.

[0016] Preferably, the heating reaction is carried out at a heating temperature of 80–120°C with continuous stirring for 0.5–2 hours.

[0017] Preferably, the molar ratio of the reducing agent to the metal nitrate is 1:1; the mass of the sodium laurylate is 10-15% of the dry starch; and the heating reaction conditions are a heating temperature of 95±5℃ and continuous stirring for 1.2±0.2h.

[0018] Preferably, in step (1), the starch is one of potato starch, corn starch, cassava starch and wheat starch; the starch milk prepared from the starch has a concentration of 5-10% w / w.

[0019] Preferably, in step (1), the starch milk is heated at 100-120°C for 1-2 hours while being stirred; in step (3), the stirring conditions are a speed of 500-2000 rpm for 5-20 minutes; after reduction, it is further subjected to high-speed shearing at a speed of 8000-10000 rpm for 2-5 minutes.

[0020] Preferably, in step 3), the reducing agent is added dropwise while maintaining stirring, at a rate of 20–40 mL / h; in step 4), the pre-freezing conditions are: immersion in liquid nitrogen for 10–20 min; the freeze-drying conditions are: temperature of -60–-30 °C; vacuum degree of 30–10 Pa; and drying time of 24–72 h.

[0021] The metal-loaded starch aerogels prepared by the above method are used in fruit preservation (such as packaging materials) and in the adsorption of ethylene, oxygen and carbon dioxide gases.

[0022] The metal-loaded starch aerogel provided by this invention is prepared by in-situ synthesis of metal nanoparticles on a starch gel matrix. The metal-loaded starch aerogel is prepared by depositing and in-situ reducing metal ions on the starch matrix and then freeze-drying. The aerogel utilizes the special π-complexation between metal and ethylene to achieve stable capture of ethylene, and the capillary adsorption effect of starch aerogel endows it with ethylene adsorption properties and fruit preservation ability.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The metal-loaded starch aerogel prepared in this invention has good ethylene adsorption capacity and adsorption stability. For example, the ethylene adsorption capacity of silver-loaded starch aerogel and copper-loaded starch aerogel under normal temperature and pressure conditions is 25.31-30.49 mL / g and 26.93-32.51 mL / g, respectively; after 80 h, their release rates are only 14-16% and 15-21%, respectively. This metal-loaded starch aerogel exhibits excellent fruit preservation effect and can extend the shelf life of bananas by more than 7 days.

[0025] (2) This invention prepares metal-loaded starch aerogel by in-situ reduction, and obtains an aerogel with high specific area, low density and strong ethylene adsorption capacity. It can be applied to the control of ethylene in the process of fruit preservation. Compared with adsorption matrices such as zeolite and activated carbon, the ethylene adsorption capacity is more prominent. At the same time, the ethylene half-release time is greatly improved, reaching more than 500 hours, and the highest can reach 1580.86 hours. Moreover, the adsorption process can be carried out under normal temperature and pressure conditions. In addition, the bulk material has more advantages than the powder product in the application process.

[0026] (3) The present invention achieves reversible adsorption of ethylene gas through metal-gas interaction. Compared with potassium permanganate-based ethylene oxidizing and removing agents, it does not produce byproducts such as water and carbon dioxide during the adsorption process, does not affect the fruit's breathing environment, and can achieve ethylene desorption and reuse through simple heating.

[0027] (4) The present invention achieves fruit preservation by gas adsorption. Compared with the use of 1-methylcyclopropene ethylene inhibitors, the metal-loaded aerogel of the present invention does not have problems such as uneven fruit ripening and irreversibility, which greatly reduces the cost of fruit preservation.

[0028] (5) This invention utilizes inexpensive starch materials to reduce economic costs and achieve environmentally friendly, green, and sustainable ethylene adsorption functions. The preparation process is simple and the conditions are mild, making it suitable for both laboratory operations and industrial production, which greatly expands the application range of starch-based adsorbent materials. The promotion and use of this metal-supported starch aerogel has good socio-economic value. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image of the silver-loaded starch aerogel prepared in Example 1 of the present invention.

[0030] Figure 2 The curve showing the change in banana firmness when the silver-loaded starch aerogel prepared in Example 1 of this invention is used in a banana preservation test.

[0031] Figure 3 The curve showing the change in soluble solids content of bananas when the silver-loaded starch aerogel prepared in Example 1 of this invention was used in a banana preservation test. Detailed Implementation

[0032] The present invention will be described below through specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0033] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the raw materials and reagents used in the following examples are commercially available. Ordinary corn starch was purchased from Changchun Dacheng Industrial Group Co., Ltd., and wheat starch was purchased from Henan Feitian Biotechnology Co., Ltd.

[0034] Determination of ethylene adsorption capacity of metal-loaded starch aerogel

[0035] In this embodiment, the ethylene adsorption capacity of the metal starch aerogel was determined by headspace gas chromatography. Specifically, the sample was degassed at 85°C for 10 h and then placed in a 20 mL gas chromatograph. 2 mL of high-purity ethylene was injected into the bottle. After adsorption under normal pressure for 24 h, 1 mL of headspace gas was extracted using a syringe and analyzed using a gas chromatograph (GC) (Agilent 7890A, Agilent Technologies, Palo Alto, CA, USA) equipped with a DANI HS 86.50 automated headspace sampler (DANI Instruments SpA, Cologno Monzese, Italy). The ethylene concentration was determined with reference to the calibration curve and recorded as V0. Under the same conditions, the ethylene concentration was measured using a control group without the sample and recorded as V1. The ethylene adsorption capacity (C) of the sample was calculated using formula (1):

[0036]

[0037] Where m is the sample mass.

[0038] Determination of ethylene half-release time of metal-loaded starch aerogel

[0039] In this embodiment, the ethylene half-release time of the metal starch aerogel was obtained by calculating the release kinetics. Specifically, the sample after ethylene adsorption was transferred to a 50 mL test tube, and 1 mL of gas was periodically extracted at 25 °C to determine the ethylene concentration. The release kinetics were modeled using the Avrami equation (2):

[0040]

[0041] Where X represents the amount of ethylene released at time t (h), k is the release rate constant, and n is the Avrami parameter. The formula (3) for calculating the half-release time of ethylene (X = 0.5) is as follows:

[0042]

[0043] Determination of fruit ripening indicators in preservation experiments

[0044] In this embodiment, the material's ability to preserve fruit was determined by characterizing the soluble solids content and firmness of the fruit, with bananas being the selected fruit. Specifically, fresh bananas were used in a 2.5L sealed container at a relative humidity of 75.5% and an ambient temperature of 75.5% for the preservation experiment, with 0.2g of material used. A small amount of juice was extracted from each banana and analyzed at 25°C using a portable refractometer (RHB32) to determine the soluble solids content. The firmness of the bananas was evaluated using a handheld durometer (GY-5A).

[0045] Comparative Example 1

[0046] (1) Preparation of starch-sodium lauryl acid complex solution

[0047] 5g of ordinary corn starch was dispersed in 95g of deionized water to prepare a 5% (w / w) starch suspension. The starch suspension was stirred and heated at 100°C for 1 hour. Then, 0.5g of sodium lauryl precipitate (10% of the dry weight of starch) was added. The mixture was stirred and heated at 90°C for 1 hour to obtain a starch-sodium lauryl precipitate complex solution.

[0048] (2) Preparation of starch hydrogel

[0049] After cooling the obtained starch-sodium lauryl complex solution to room temperature, 0.5 g of gluconolactone (10% of the dry weight of starch) was added, and the solution was allowed to stand overnight to obtain starch hydrogel.

[0050] (3) Preparation of starch aerogel

[0051] The obtained starch hydrogel was immersed in liquid nitrogen for 5 minutes and then freeze-dried to obtain an aerogel. The freeze-drying conditions were: temperature -40℃, vacuum degree 20 Pa, and time 48 h.

[0052] The ethylene adsorption capacity of the obtained starch aerogel was determined to be 15.0 mL / g, and the ethylene half-release time of the obtained starch aerogel was 36.27 h.

[0053] Example 1

[0054] (1) Preparation of starch-sodium lauryl acid complex solution

[0055] 5g of ordinary corn starch was dispersed in 95g of deionized water to prepare a 5% (w / w) starch suspension. The starch suspension was stirred and heated at 100°C for 1 hour. Then, 0.5g of sodium lauryl precipitate (10% of the dry weight of starch) was added. The mixture was stirred and heated at 90°C for 1 hour to obtain a starch-sodium lauryl precipitate complex solution.

[0056] (2) Silver ion loading and reduction

[0057] 2 mL of silver nitrate solution (0.4 mol / L) was added to the starch-sodium lauryl compound solution at 50 °C, while stirring at 1000 rpm. After 10 min, 8 mL of sodium borohydride solution (0.1 mol / L) was added to reduce silver ions in situ to silver nanoparticles.

[0058] (3) Preparation of silver-loaded starch hydrogel

[0059] The above solution was placed under a high-speed shearing machine at a shearing speed of 10,000 rpm for 5 minutes. After standing, silver-loaded starch hydrogel was obtained.

[0060] (4) Preparation of silver-loaded starch aerogel

[0061] The obtained hydrogel was immersed in liquid nitrogen for 10 min and then freeze-dried to obtain an aerogel. The freeze-drying conditions were: temperature -40℃, vacuum degree 20 Pa, and time 48 h.

[0062] The ethylene adsorption capacity of the silver-loaded starch aerogel was determined to be 30.5 mL / g, and the ethylene half-release time of the silver-loaded starch aerogel was 1580.86 h.

[0063] Example 2

[0064] (1) Preparation of starch-sodium lauryl acid complex solution

[0065] 5g of ordinary corn starch was dispersed in 95g of deionized water to prepare a 5% (w / w) starch suspension. The starch suspension was stirred and heated at 100°C for 1 hour. Then, 0.5g of sodium lauryl precipitate (10% of the dry weight of starch) was added. The mixture was stirred and heated at 90°C for 1 hour to obtain a starch-sodium lauryl precipitate complex solution.

[0066] (2) Silver ion loading and reduction

[0067] 2 mL of silver nitrate solution (0.4 mol / L) was added to the above starch-sodium lauryl complex solution at 50 °C, while stirring at 1000 rpm. After 10 min, 8 mL of glucose solution (0.1 mol / L) was added to reduce silver ions in situ to silver cluster particles.

[0068] (3) Preparation of silver-loaded starch hydrogel

[0069] The above solution was placed under a high-speed shearing machine at a shearing speed of 10,000 rpm for 5 minutes. After standing, silver-loaded starch hydrogel was obtained.

[0070] (4) Preparation of silver-loaded starch aerogel

[0071] The obtained hydrogel was immersed in liquid nitrogen for 10 min and then freeze-dried to obtain an aerogel. The freeze-drying conditions were: temperature -40℃, vacuum degree 20 Pa, and time 48 h.

[0072] The ethylene adsorption capacity of the silver-loaded starch aerogel was determined to be 25.3 mL / g, and the ethylene half-release time of the silver-loaded starch aerogel was 974.87 h.

[0073] Example 3

[0074] (1) Preparation of starch-sodium lauryl acid complex solution

[0075] 5g of ordinary corn starch was dispersed in 95g of deionized water to prepare a 5% (w / w) starch suspension. The starch suspension was stirred and heated at 100°C for 1 hour. Then, 0.5g of sodium lauryl precipitate (10% of the dry weight of starch) was added. The mixture was stirred and heated at 90°C for 1 hour to obtain a starch-sodium lauryl precipitate complex solution.

[0076] (2) Copper ion loading and reduction

[0077] 2 mL of copper nitrate solution (0.4 mol / L) was added to the above starch-sodium lauryl compound solution at 50 °C, while stirring at 1000 rpm. After 10 min, 8 mL of sodium borohydride solution (0.1 mol / L) was added to reduce copper ions in situ to copper nanoparticles.

[0078] (3) Preparation of copper-loaded starch hydrogel

[0079] The above solution was placed under a high-speed shearing machine at a shearing speed of 10,000 rpm for 5 minutes. After standing, copper-loaded starch hydrogel was obtained.

[0080] (4) Preparation of copper-loaded starch aerogel

[0081] The obtained hydrogel was immersed in liquid nitrogen for 10 min and then freeze-dried to obtain an aerogel. The freeze-drying conditions were: temperature -40℃, vacuum degree 20 Pa, and time 48 h.

[0082] The ethylene adsorption capacity of the copper-loaded starch aerogel was determined to be 32.5 mL / g, and the ethylene half-release time of the copper-loaded starch aerogel was 574.96 h.

[0083] Example 4

[0084] (1) Preparation of starch-sodium lauryl acid complex solution

[0085] 5g of ordinary corn starch was dispersed in 95g of deionized water to prepare a 5% (w / w) starch suspension. The starch suspension was stirred and heated at 100°C for 1 hour. Then, 0.5g of sodium lauryl precipitate (10% of the dry weight of starch) was added. The mixture was stirred and heated at 90°C for 1 hour to obtain a starch-sodium lauryl precipitate complex solution.

[0086] (2) Copper ion loading and reduction

[0087] 2 mL of copper nitrate solution (0.4 mol / L) was added to the above starch-sodium lauryl compound solution at 50 °C, while stirring at 1000 rpm. After 10 min, 8 mL of glucose solution (0.1 mol / L) was added to reduce copper ions in situ to copper cluster particles.

[0088] (3) Preparation of copper-loaded starch hydrogel

[0089] The above solution was placed under a high-speed shearing machine at a shearing speed of 10,000 rpm for 5 minutes. After standing, copper-loaded starch hydrogel was obtained.

[0090] (4) Preparation of copper-loaded starch aerogel

[0091] The obtained hydrogel was immersed in liquid nitrogen for 10 min and then freeze-dried to obtain an aerogel. The freeze-drying conditions were: temperature -40℃, vacuum degree 20 Pa, and time 48 h.

[0092] The ethylene adsorption capacity of the copper-loaded starch aerogel was determined to be 26.9 mL / g, and the ethylene half-release time of the copper-loaded starch aerogel was 1157.38 h.

[0093] Example 5

[0094] (1) Preparation of starch-sodium lauryl acid complex solution

[0095] 5g of ordinary corn starch was dispersed in 95g of deionized water to prepare a 5% (w / w) starch suspension. The starch suspension was stirred and heated at 100°C for 1 hour. Then, 0.5g of sodium lauryl precipitate (10% of the dry weight of starch) was added. The mixture was stirred and heated at 90°C for 1 hour to obtain a starch-sodium lauryl precipitate complex solution.

[0096] (2) Silver ion loading and reduction

[0097] 2 mL of silver nitrate solution (0.4 mol / L) was added to the above starch-sodium lauryl compound solution at 50 °C, while stirring at 1000 rpm. After 10 min, 4 mL of sodium borohydride solution (0.1 mol / L) was added to reduce silver ions in situ into silver nanoparticles.

[0098] (3) Preparation of silver-loaded starch hydrogel

[0099] The above solution was placed under a high-speed shearing machine at a shearing speed of 10,000 rpm for 5 minutes. After standing, silver-loaded starch hydrogel was obtained.

[0100] (4) Preparation of silver-loaded starch aerogel

[0101] The obtained hydrogel was immersed in liquid nitrogen for 10 min and then freeze-dried to obtain an aerogel. The freeze-drying conditions were: temperature -40℃, vacuum degree 20 Pa, and time 48 h.

[0102] The ethylene adsorption capacity of the silver-loaded starch aerogel was determined to be 28.2 mL / g, and the ethylene half-release time of the silver-loaded starch aerogel was 1273.47 h.

[0103] Example 6

[0104] (1) Preparation of starch-sodium lauryl acid complex solution

[0105] 5g of ordinary corn starch was dispersed in 95g of deionized water to prepare a 5% (w / w) starch suspension. The starch suspension was stirred and heated at 100°C for 1 hour. Then, 0.5g of sodium lauryl precipitate (10% of the dry weight of starch) was added. The mixture was stirred and heated at 90°C for 1 hour to obtain a starch-sodium lauryl precipitate complex solution.

[0106] (2) Silver ion loading and reduction

[0107] 2 mL of silver nitrate solution (0.4 mol / L) was added to the above starch-sodium lauryl compound solution at 50 °C, while stirring at 1000 rpm. After 10 min, 4 mL of glucose solution (0.1 mol / L) was added to reduce silver ions in situ to silver cluster particles.

[0108] (3) Preparation of silver-loaded starch hydrogel

[0109] The above solution was placed under a high-speed shearing machine at a shearing speed of 10,000 rpm for 5 minutes. After standing, silver-loaded starch hydrogel was obtained.

[0110] (4) Preparation of silver-loaded starch aerogel

[0111] The obtained hydrogel was immersed in liquid nitrogen for 10 min and then freeze-dried to obtain an aerogel. The freeze-drying conditions were: temperature -40℃, vacuum degree 20 Pa, and time 48 h.

[0112] The ethylene adsorption capacity of the silver-loaded starch aerogel was determined to be 21.8 mL / g, and the ethylene half-release time of the silver-loaded starch aerogel was 692.13 h.

[0113] Example 7

[0114] (1) Preparation of starch-sodium lauryl acid complex solution

[0115] 5g of ordinary corn starch was dispersed in 95g of deionized water to prepare a 5% (w / w) starch suspension. The starch suspension was stirred and heated at 100°C for 1 hour. Then, 0.5g of sodium lauryl precipitate (10% of the dry weight of starch) was added. The mixture was stirred and heated at 90°C for 1 hour to obtain a starch-sodium lauryl precipitate complex solution.

[0116] (2) Copper ion loading and reduction

[0117] 2 mL of copper nitrate solution (0.4 mol / L) was added to the above starch-sodium lauryl compound solution at 50 °C, while stirring at 1000 rpm. After 10 min, 4 mL of sodium borohydride solution (0.1 mol / L) was added to reduce copper ions in situ to copper nanoparticles.

[0118] (3) Preparation of copper-loaded starch hydrogel

[0119] The above solution was placed under a high-speed shearing machine at a shearing speed of 10,000 rpm for 5 minutes. After standing, copper-loaded starch hydrogel was obtained.

[0120] (4) Preparation of copper-loaded starch aerogel

[0121] The obtained hydrogel was immersed in liquid nitrogen for 10 min and then freeze-dried to obtain an aerogel. The freeze-drying conditions were: temperature -40℃, vacuum degree 20 Pa, and time 48 h.

[0122] The ethylene adsorption capacity of the copper-loaded starch aerogel was determined to be 29.7 mL / g, and the ethylene half-release time of the copper-loaded starch aerogel was 864.58 h.

[0123] Example 8

[0124] (1) Preparation of starch-sodium lauryl acid complex solution

[0125] 5g of wheat starch was dispersed in 95g of deionized water to prepare a 5% (w / w) starch suspension. The starch suspension was stirred and heated at 100°C for 1 hour. Then, 0.5g of sodium lauryl precipitate (10% of the dry weight of starch) was added. The mixture was stirred and heated at 90°C for 1 hour to obtain a starch-sodium lauryl precipitate complex solution.

[0126] (2) Silver ion loading and reduction

[0127] 2 mL of silver nitrate solution (0.4 mol / L) was added to the starch-sodium lauryl compound solution at 50 °C, while stirring at 1000 rpm. After 10 min, 8 mL of sodium borohydride solution (0.1 mol / L) was added to reduce silver ions in situ to silver nanoparticles.

[0128] (3) Preparation of silver-loaded starch hydrogel

[0129] The above solution was placed under a high-speed shearing machine at a shearing speed of 10,000 rpm for 5 minutes. After standing, silver-loaded starch hydrogel was obtained.

[0130] (4) Preparation of silver-loaded starch aerogel

[0131] The obtained hydrogel was immersed in liquid nitrogen for 10 min and then freeze-dried to obtain an aerogel. The freeze-drying conditions were: temperature -40℃, vacuum degree 20 Pa, and time 48 h.

[0132] The ethylene adsorption capacity of the silver-loaded starch aerogel was determined to be 28.3 mL / g, and the ethylene half-release time of the silver-loaded starch aerogel was 1357.3 h.

[0133] Analysis of the ethylene adsorption capacity of metal-loaded starch aerogels prepared in Comparative Example 1 and Examples 1-8:

[0134] Table 1. Ethylene adsorption capacity of metal starch-loaded aerogels

[0135]

[0136]

[0137] Table 1 shows that the ethylene adsorption capacity of metal-loaded starch aerogels is related to the type of metal, the type of reducing agent, and their ratio. The ethylene adsorption capacity of the obtained metal-loaded starch aerogels is much higher than that of starch aerogels, and the ethylene adsorption capacity of metal-loaded starch aerogels using sodium borohydride as a reducing agent is even higher. This is because, in addition to the capillary effect provided by the porous structure, the metal in the metal-loaded starch aerogels acts as an active site for ethylene adsorption, binding ethylene through π-complexation, thereby increasing the ethylene adsorption capacity. Furthermore, sodium borohydride, as a strong reducing agent, has a faster reduction rate than glucose, resulting in smaller metal particle sizes, reducing the metal aggregation effect, and improving the utilization rate of metal sites, thus exhibiting a higher ethylene adsorption capacity.

[0138] Depend on Figure 1It is evident that the starch aerogel loaded with silver nanoparticles exhibits a three-dimensional network-like open-pore structure. This open-pore structure endows the metal-loaded starch aerogel with a high specific surface area and uniform dispersion of metal particles. The adsorption capacity of the obtained metal-loaded starch aerogel for ethylene at ambient pressure is 21.8–32.5 mL / g, and the ethylene half-release time is 574.96–1580.86 h, far exceeding the ethylene adsorption capacity of starch aerogel.

[0139] Analysis of the banana preservation ability of the metal-loaded starch aerogel prepared in Example 1:

[0140] Starch aerogel loaded with metallic silver exhibits excellent ethylene adsorption capacity, effectively adsorbing trace amounts of endogenous ethylene released during banana ripening, thus preserving the bananas. This is because ethylene, as a plant hormone, initiates the ripening process of fruit. When the endogenous ethylene released by the banana into the storage environment is adsorbed by the metal-loaded starch aerogel, the ethylene receptors on the banana cannot be stimulated, and starch, pectin, and cellulose cannot be degraded by enzymes, thereby maintaining the freshness of the banana. By placing an appropriate amount of metal-loaded starch aerogel into the banana storage environment, the degree of ripeness is characterized by measuring the firmness and soluble solids content of the bananas during the preservation process. Figure 2 It can be seen that after 16 days of storage, bananas without any treatment and without starch aerogel began to ripen from the 7th day, while bananas with silver-loaded starch aerogel showed only slight changes in hardness and soluble solids content within 16 days. This indicates that starch aerogel loaded with metallic silver has a good effect on fruit preservation.

[0141] This invention proposes a method for preparing metal-loaded starch aerogel for ethylene adsorption and its application, which can achieve efficient adsorption of endogenous ethylene in fruits and has good adsorption stability; it is low in cost and simple in preparation process, suitable for both laboratory operation and easy industrial production.

[0142] It should be noted that, for those skilled in the art, the implementation of this invention is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this invention should be considered equivalent substitutions and are included within the protection scope of this invention.

Claims

1. A method of preparing a metal-loaded starch aerogel, characterized by, It comprises the following steps: (1) starch and water are prepared into starch milk, and the starch milk is heated to obtain a gelatinized starch solution; (2) sodium laurate is added to the gelatinized starch solution for heating reaction, and a starch-sodium laurate complex solution is obtained after the reaction is completed; (3) a metal nitrate solution is added to the complex solution, and after uniform stirring, a reducing agent is added to reduce the metal ions, and a metal-loaded starch hydrogel is obtained; (4) the hydrogel is pre-frozen and freeze-dried to obtain a metal-loaded starch aerogel; In step (3), the reducing agent is sodium borohydride and / or glucose, and the molar ratio of the reducing agent to the metal nitrate is 1:2-2:1; the metal nitrate is copper nitrate and / or silver nitrate, and the amount used is 1-5% of the dry mass of the starch; In step (2), the mass of sodium laurate is 8-20% of the dry mass of the starch; and the heating reaction conditions are a heating temperature of 80-120℃ and continuous stirring for 0.5-2 h.

2. The production method according to claim 1, characterized by, The molar ratio of the reducing agent to the metal nitrate is 1:1; the mass of sodium laurate is 10-15% of the dry mass of the starch; and the heating reaction conditions are a heating temperature of 95±5℃ and continuous stirring for 1.2±0.2 h.

3. The method according to claim 1 or 2, characterized in that, In step (1), the starch is one of potato starch, corn starch, cassava starch and wheat starch; and the starch milk prepared from the starch has a concentration of 5-10% w / w.

4. The method of claim 1 or 2, wherein: In step (1), the starch milk is heated at 100-120℃ for 1-2 h while stirring; in step (3), the stirring conditions are a speed of 500-2000 rpm and a time of 5-20 min; and after reduction, high-speed shearing is performed at a shearing speed of 8000-10000 rpm for 2-5 min.

5. The method according to claim 1 or 2, characterized in that, In step 3), the reducing agent is added dropwise while stirring, and the dropwise addition speed is 20-40 mL / h; in step 4), the pre-freezing conditions are soaking in liquid nitrogen for 10-20 min; and the freeze-drying conditions are a temperature of -60 to -30℃, a vacuum degree of 30-10 Pa, and a drying time of 24-72 h.

6. The metal-loaded starch aerogel prepared by the preparation method of the metal-loaded starch aerogel according to any one of claims 1-5.

7. The metal-loaded starch aerogel according to claim 6 for use in fruit preservation and ethylene adsorption.

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