A pelargonium essential oil hydrogel as well as a preparation method and application thereof

Abstract

The present application belongs to the technical field of hydrogel, and particularly relates to a pelargonium essential oil hydrogel and a preparation method and application thereof. The pelargonium essential oil hydrogel is composed of the following components in percentage by mass: 10-12% of pelargonium essential oil, 1.5-3% of sodium alginate, 2-propyl hydroxy- β 2-5% of cyclodextrin, 0.1-0.3% of surfactant, 1.0-3.5% of crosslinking agent, and the balance of deionized water. The pelargonium essential oil hydrogel prepared by the present application can not only prolong the release time of the pelargonium essential oil through the slow-release effect, but also effectively inhibit and delay the germination of potatoes and sweet potatoes in the storage and logistics process, reduce the nutrient loss of the potatoes and sweet potatoes, and achieve a better preservation effect.​

Description

Technical Field

[0001] This invention belongs to the field of hydrogel technology, specifically relating to a geranium essential oil hydrogel, its preparation method, and its application. Background Technology

[0002] Potatoes and sweet potatoes are important food and economic crops globally, but they are prone to sprouting during post-harvest storage, leading to quality deterioration, nutrient loss, and the production of toxic substances (solanine, mesona chinensis), causing significant losses. Currently, the main methods for inhibiting potato sprouting include low-temperature storage, irradiation treatment, and chemical sprout inhibitors.

[0003] Low-temperature storage is energy-intensive, and sweet potatoes are sensitive to low temperatures and prone to chilling injury, limiting its applicability. Irradiation treatment equipment is expensive and has high safety control thresholds, thus it has not been widely adopted. Chemical sprout inhibitors (such as chloranilide and maleic hydrazine) are effective for potatoes, but their application to sweet potatoes can easily cause phytotoxicity and poses a risk of chemical residues, and their use is strictly controlled. Therefore, there is an urgent need to develop a safe, efficient, green sprout inhibitor technology that can be adapted to both types of tubers.

[0004] In recent years, plant essential oils have become a research hotspot due to their natural biodegradability. Among them, geranium essential oil and its main active ingredient, citronellol, have been proven to delay sprouting by interfering with the metabolism of endogenous hormones in tubers and inhibiting meristem activity. However, geranium essential oil faces common challenges in practical applications: citronellol is highly volatile, making it difficult to maintain a stable and effective concentration in storage environments; direct or high-concentration contact of the essential oil with the tuber can easily cause potato skin burns and browning and rotting of sweet potato tubers, affecting marketability and increasing the risk of pathogen infection; the essential oil has low water solubility and uneven diffusion, easily leading to large differences in the sprout-inhibiting effect of stacked tubers, reducing the uniformity of preservation. These problems seriously restrict the industrial application of geranium essential oil in tuber sprout inhibition. Summary of the Invention

[0005] This invention aims to provide a geranium essential oil hydrogel prepared by a double cross-linking method and its application, thereby overcoming the deficiencies of existing technologies. The prepared geranium essential oil hydrogel can not only prolong the slow-release time of geranium essential oil and effectively inhibit sprouting of potatoes and sweet potatoes during storage and logistics, but also reduce the loss of nutrients in potatoes during storage, thus achieving a better preservation effect.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a geranium essential oil hydrogel, which, by weight percentage, comprises the following components: 10-12% geranium essential oil, 1.5-3% sodium alginate, and 2-propionic acid- β - Cyclodextrin 2-5%, surfactant 0.1-0.3%, crosslinking agent 1.0-3.5%, deionized water balance.

[0007] Preferably, by weight percentage, it comprises the following components: 10-11.5% geranium essential oil, 1.5-2.5% sodium alginate, and 2-propionic acid- β - Cyclodextrin 2-3%, surfactant 0.15-0.25%, crosslinking agent 1.5-2.5%, deionized water balance.

[0008] Preferably, the surfactant is one or more of Tween 20, Tween 80, Span 20, Span 80, castor oil polyoxyethylene ether (EL-40), polyethylene glycol (PEG 400), and soybean lecithin (SL), with Span 80 being the most preferred. The HLB value of the Span 80 is 4.3; The crosslinking agent is calcium chloride.

[0009] Secondly, the present invention provides a method for preparing geranium essential oil hydrogel according to the first aspect, comprising the following steps: (1) Sodium alginate and 2-propionic acid β - Dissolve the cyclodextrins separately in water, stir and mix well to obtain a mixed solution; (2) After ultrasonic degassing of the mixed solution, a surfactant is added, followed by stirring emulsification and low-temperature standing treatment to obtain an emulsion matrix; (3) Add geranium essential oil to the emulsion matrix, stir and emulsify, and then let it stand at low temperature to obtain a white emulsion; (4) Add the white emulsion to the crosslinking agent aqueous solution to carry out the crosslinking reaction. After washing and drying, geranium essential oil hydrogel is obtained.

[0010] Preferably, in step (1), the mixture is stirred at a speed of 400-500 rpm for 25-35 minutes.

[0011] Preferably, in step (2), the power of the ultrasonic degassing treatment is 400-600W and the time is 10-30min; In step (2), the stirring and emulsification speed is 450-550 rpm and the time is 10-15 min; In step (2), the temperature of the low-temperature standing is 3-5℃ and the time is 20-40min.

[0012] Preferably, in step (3), the emulsification of geranium essential oil after addition is carried out by gradient stirring: first stirring at 100-300 rpm, then gradually increasing to 500-700 rpm, with a total stirring time of 5-15 min; then ultrasonic mixing is performed, with an ultrasonic power of 400-600 W and a time of 3-10 min; after ultrasonic mixing, stirring is carried out at a speed of 800-1200 rpm for 10-20 min. In step (3), the temperature of the low-temperature standing is 3-5℃ and the time is 20-40min.

[0013] Preferably, in step (4), the mass concentration of the crosslinking agent aqueous solution is 1-3%, the crosslinking reaction time is 40-90 min, and the washing is performed by rinsing with deionized water 2-4 times.

[0014] Thirdly, the present invention provides the application of geranium essential oil hydrogel in the sprout suppression of potatoes and sweet potatoes.

[0015] Preferably, geranium essential oil hydrogel is applied inside the packaging of potatoes and sweet potatoes; the mass ratio of potato to geranium essential oil hydrogel is 1:(0.0075-0.0085), and the mass ratio of sweet potato to geranium essential oil hydrogel is 1:(0.0035-0.0055); the potatoes are potatoes that have passed their dormancy period.

[0016] The beneficial effects of this invention are: This invention relies on the synergistic effect between its components, with the surfactant synergistically targeting 2-propionic acid- βA three-dimensional hydrogel network crosslinked with sodium alginate and calcium chloride was constructed using cyclodextrin, successfully encapsulating 10%-12% (w / w) of geranium essential oil, overcoming the inherent defects of existing essential oil sprout-inhibiting products. Firstly, this invention uses 2-propoxy-β-cyclodextrin as a molecular inclusion carrier, utilizing its cavity structure to pre-encapsulate geranium essential oil, thus constraining the escape rate of volatile active ingredients such as citronellol at the molecular level. This overcomes the shortcomings of pure essential oil, such as high volatility and short sprout-inhibiting effect, meeting the long-term storage needs of potatoes without frequent oil replenishment. Secondly, the addition of an appropriate amount of surfactant effectively improves the interfacial compatibility between the hydrophobic essential oil and the aqueous gel system, solving the problems of essential oil aggregation and uneven distribution in the aqueous phase, ensuring uniform essential oil release concentration within the storage space, and preventing localized sprout-inhibiting failure in potato tubers. Furthermore, the combination of sodium alginate and a cross-linking agent constructs a stable three-dimensional gel network structure, which completely encapsulates and isolates the essential oil complex, completely preventing high-concentration free essential oils from directly contacting the potato tuber skin and avoiding problems such as potato skin burn and sweet potato tuber browning and rotting. Finally, all raw materials of this invention have excellent biocompatibility and are biodegradable, with no chemical sprout inhibitor residue pollution or crop phytotoxicity risk. At the same time, one formula can be adapted to both potatoes and sweet potatoes, two types of tubers with different physiological characteristics, breaking the limitation of traditional preservatives that are only applicable to one crop, and taking into account both preservation safety and broad-spectrum applicability. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0018] Figure 1 The apparent and embedding rates of hydrogels prepared with different surfactants in Example 1 of this invention are shown. Figure 2 The effects of different core-to-wall ratios, different CaCl2 concentrations, different Span 80 concentrations, and different crosslinking times on the appearance of the hydrogel in Example 1 of this invention; Figure 3 This illustrates the effect of different core-to-wall ratios on the hydrogel embedding efficiency in Example 1 of the present invention. Figure 4 This illustrates the effect of different CaCl2 concentrations on the hydrogel embedding efficiency in Example 1 of the present invention. Figure 5 This illustrates the effect of different Span 80 concentrations on the hydrogel embedding efficiency in Example 1 of the present invention. Figure 6 This illustrates the effect of different crosslinking times on the hydrogel embedding efficiency in Example 1 of the present invention. Figure 7This is a three-dimensional response surface plot of the core-to-wall ratio and CaCl2 concentration, core-to-wall ratio and Span 80 concentration, core-to-wall ratio and crosslinking time, CaCl2 concentration and Span 80 concentration, CaCl2 concentration and crosslinking time, and Span 80 concentration and crosslinking time in Example 1 of the present invention, where a represents the core-to-wall ratio and CaCl2 concentration, b represents the core-to-wall ratio and Span 80 concentration, c represents the core-to-wall ratio and crosslinking time, d represents the CaCl2 concentration and Span 80 concentration, e represents the CaCl2 concentration and crosslinking time, and f represents the Span 80 concentration and crosslinking time. Figure 8 This is a two-dimensional isoline graph showing the relationship between core-wall ratio and CaCl2 concentration, core-wall ratio and Span 80 concentration, core-wall ratio and crosslinking time, CaCl2 concentration and Span 80 concentration, CaCl2 concentration and crosslinking time, and Span 80 concentration and crosslinking time in Example 1 of the present invention; wherein, a represents core-wall ratio and CaCl2 concentration, b represents core-wall ratio and Span 80 concentration, c represents core-wall ratio and crosslinking time, d represents CaCl2 concentration and Span 80 concentration, e represents CaCl2 concentration and crosslinking time, and f represents Span 80 concentration and crosslinking time; Figure 9 The surface morphology and scanning electron microscope image of the GEO hydrogel in Example 2 of this invention; Figure 10 The images show the Fourier transform infrared spectrum and X-ray diffraction spectrum of the GEO hydrogel in Example 2 of this invention; where A is the Fourier transform infrared spectrum and B is the X-ray diffraction spectrum. Figure 11 This is a thermal stability diagram of the GEO hydrogel in Example 2 of the present invention; where A is TGA and B is DSC. Figure 12 The swelling ratio of the GEO hydrogel in Example 2 of this invention; Figure 13 The release characteristics of the GEO hydrogel in Example 2 of this invention; Figure 14 This invention illustrates the effects of different treatment groups (control, GEO fumigation, and GEO hydrogel) on potato tuber sprouting, sprouting rate, and sprouting index in Example 3 of this invention; where A represents the apparent morphology of potato tuber sprouting, B represents the sprouting rate, and C represents the sprouting index. Figure 15 The morphology of sweet potato tuber sprouting in different treatment groups (control and GEO hydrogel) in Example 3 of the present invention; Figure 16This invention illustrates the effects of different treatment groups (control, GEO fumigation, and GEO hydrogel) on potato browning degree, total phenols, total flavonoids, starch, reducing sugar, ascorbic acid, PPO activity, and POD activity in Example 3 of this invention; wherein, A represents potato browning degree, B represents total phenols, C represents total flavonoids, D represents starch, E represents reducing sugar, F represents ascorbic acid, G represents PPO activity, and H represents POD activity. Detailed Implementation

[0019] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0020] To address the problems of geranium essential oil's volatility, poor stability, poor solubility, and the potential for direct contact or excessive concentration to cause pesticide damage and compromise tuber quality in potatoes, this invention provides a geranium essential oil hydrogel, composed of the following components by weight percentage: 10-12% geranium essential oil, 1.5-3% sodium alginate, and 2-propionic acid- β - Cyclodextrin 2-5%, surfactant 0.1-0.3%, crosslinking agent 1.0-3.5%, deionized water balance.

[0021] 2-Propylhydroxy- β Cyclodextrin molecules possess a hollow truncated pyramidal ring structure, and their hydrophobic inner cavity can encapsulate geranium essential oil, forming a stable inclusion system. This inclusion effect enhances the stability and water solubility of the essential oil at the molecular level, while also contributing to the controlled-release effect. The surfactant further emulsifies with the inclusion complex, forming a uniformly dispersed and stable emulsion. Sodium alginate and a cross-linking agent construct a macroscopic three-dimensional gel network through ionic cross-linking, firmly fixing and encapsulating the emulsion droplets within the gel system. Through the synergistic effect of the components, the core challenges of geranium essential oil—its volatility, poor stability, and strong irritant properties—are successfully addressed.

[0022] This invention utilizes surfactants in synergistic effects with 2-propionic acid- βCyclodextrin was used to construct a three-dimensional hydrogel network crosslinked with sodium alginate and calcium chloride, successfully encapsulating 10%-12% (w / w) of geranium essential oil within it. This system significantly inhibited the volatilization and burst release of the essential oil, endowing it with sustained-release properties to prolong the sprout-inhibiting effect, while avoiding chemical burns caused by direct or high-concentration contact of the essential oil with the potato skin, effectively maintaining the marketability of the tubers. Addressing the problem of sprouting during sweet potato storage, the hydrogel proposed in this invention also exhibits excellent sprout-inhibiting effects. By continuously releasing the active ingredients of geranium essential oil, this hydrogel can effectively inhibit the sprouting of potato tubers, avoiding the potential risks of excessive residues and phytotoxicity associated with traditional chemical sprout inhibitors (such as chloranilide), providing a new technical approach for the green preservation of potatoes.

[0023] In some other embodiments, the product comprises, by weight percentage: 10-11.5% geranium essential oil, 1.5-2.5% sodium alginate, and 2-propionic acid- β - Cyclodextrin 2-3%, surfactant 0.15-0.25%, crosslinking agent 1.5-2.5%, deionized water balance. The effects of crosslinking agent concentration and surfactant concentration on the encapsulation efficiency of geranium essential oil hydrogels were investigated.

[0024] In some other embodiments, the surfactant is one or more of Tween 20, Tween 80, Span 20, Span 80, castor oil polyoxyethylene ether (EL-40), polyethylene glycol (PEG 400), and soybean lecithin (SL), preferably Span 80; The HLB value of the Span 80 is 4.3; The crosslinking agent is calcium chloride.

[0025] Span 80, with an HLB value of 4.3, is a lipophilic emulsifier that effectively disperses geranium essential oil in water to form stable W / O / W or O / W emulsions. Its lipophilic segments have good compatibility with the essential oil, while its hydrophilic heads interact with cyclodextrin and the aqueous phase, promoting the uniform distribution of inclusion complexes. Calcium chloride is the most commonly used ionic crosslinking agent for sodium alginate. + It forms an "egg-box" structure with alginate G units, exhibiting rapid cross-linking and adjustable gel strength. Furthermore, calcium chloride is a food additive, making it safe and non-toxic. Other surfactants listed can be used as alternatives, but Span 80 demonstrates the highest encapsulation rate due to its optimal HLB value matching the essential oil's polarity.

[0026] This invention provides a method for preparing the above-mentioned geranium essential oil hydrogel, comprising the following steps: (1) Sodium alginate and 2-propionic acid β - Dissolve the cyclodextrins separately in water, stir and mix well to obtain a mixed solution; (2) After ultrasonic degassing of the mixed solution, a surfactant is added, followed by stirring emulsification and low-temperature standing treatment to obtain an emulsion matrix; (3) Add geranium essential oil to the emulsion matrix, stir and emulsify, and then let it stand at low temperature to obtain a white emulsion; (4) Add the white emulsion to the crosslinking agent aqueous solution to carry out the crosslinking reaction. After washing and drying, geranium essential oil hydrogel is obtained.

[0027] The two-step emulsification method of this invention pre-disperses cyclodextrin in the aqueous phase. The surfactant first forms a complex interface with the cyclodextrin, and then, when essential oils are added, the essential oils are simultaneously encapsulated by the cyclodextrin and emulsified by the surfactant, achieving a synergistic effect. Ultrasonic degassing and low-temperature settling help eliminate bubbles and stabilize the emulsion. This method is simple to operate, requires no complex equipment such as microfluidics, and is easy to scale up for production.

[0028] In some other embodiments, in step (1), the mixture is stirred at a speed of 400-500 rpm for 25-35 minutes.

[0029] In some other embodiments, in step (2), the power of the ultrasonic degassing treatment is 400-600W and the time is 10-30min; In step (2), the stirring and emulsification speed is 450-550 rpm and the time is 10-15 min; In step (2), the temperature of the low-temperature standing is 3-5℃ and the time is 20-40min.

[0030] In some other embodiments, in step (3), the stirring and emulsification after adding geranium essential oil adopts a gradient stirring method: first stirring at 100-300 rpm, then gradually increasing to 500-700 rpm, with a total stirring time of 5-15 min; then ultrasonic mixing is performed, with an ultrasonic power of 400-600 W and a time of 3-10 min; after ultrasonic mixing, stirring is performed at a speed of 800-1200 rpm for 10-20 min; In step (3), the temperature of the low-temperature standing is 3-5℃ and the time is 20-40min.

[0031] In some other embodiments, in step (4), the mass concentration of the crosslinking agent aqueous solution is 1-3%, the crosslinking reaction time is 40-90 min, and the washing is performed by rinsing with deionized water 2-4 times. The effects of CaCl2 concentration and crosslinking time on the embedding efficiency of geranium essential oil hydrogel.

[0032] In some other embodiments, the volume ratio of the geranium essential oil to the total mass of sodium alginate and 2-propionic-β-cyclodextrin is (1-5):1, where volume is in mL and mass is in g. It should be noted that the volume ratio of the geranium essential oil to the total mass of sodium alginate and 2-propionic-β-cyclodextrin, and the ratio of the oil phase core material to the shell matrix material, is the core-wall ratio. Different core-wall ratios have a significant regulatory effect on the embedding efficiency of the geranium essential oil hydrogel.

[0033] This invention provides the application of the above-mentioned geranium essential oil hydrogel in inhibiting sprouting in potatoes and sweet potatoes.

[0034] In some other embodiments, geranium essential oil hydrogel is applied inside potato and sweet potato packages; the mass ratio of potato to geranium essential oil hydrogel is 1:(0.0075-0.0085), and the mass ratio of sweet potato to geranium essential oil hydrogel is 1:(0.0035-0.0055); the potatoes are potatoes that have passed their dormancy period.

[0035] The geranium essential oil hydrogel of this invention can be applied simultaneously to two tuber crops with different physiological characteristics: potato tubers and sweet potato roots. Experiments have shown that, under room temperature storage conditions, this hydrogel can delay potato sprouting by more than 30 days, and has a similarly significant sprout-inhibiting effect on sweet potatoes, without causing browning or rotting of sweet potato roots. This overcomes the limitation of existing chemical sprout inhibitors being unsuitable for sweet potatoes, achieving cross-crop versatility. Furthermore, different tuber crops have different sensitivities to essential oils, requiring different dosages. Potatoes have thicker skins and are slightly more tolerant, thus requiring a higher proportion of hydrogel to achieve an effective sprout-inhibiting concentration; sweet potatoes have thinner skins and are more sensitive to chemical irritants, so a lower proportion is sufficient to exert a sprout-inhibiting effect while avoiding phytotoxicity.

[0036] The geranium essential oil hydrogel of this invention, when used to treat potatoes, can significantly delay or even inhibit sprouting during storage and transportation. The slow-released essential oil active ingredients in the hydrogel can continuously interfere with the metabolism of endogenous hormones and the activity of meristematic tissues in the tuber, effectively inhibiting the sprouting process from a physiological perspective. While exerting its sprout-inhibiting effect, this method also significantly reduces nutrient loss caused by starch conversion and vitamin loss during storage, achieving a comprehensive preservation effect on the potato tubers.

[0037] Compared to the residual risks associated with chemical sprout inhibitors or the high costs of physical treatment methods, this invention uses natural plant essential oils as the key active ingredient, employing a hydrogel carrier to achieve safe release and precise control, effectively avoiding the irritation and uneven distribution issues caused by direct use of essential oils. This technology provides a green, convenient, stable, and efficient new path for sprout inhibition and preservation in post-harvest storage of potatoes, combining environmental friendliness and ease of operation, demonstrating excellent potential for industrialization.

[0038] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Specific conditions not specified in the embodiments were performed under conventional conditions or conditions recommended by the manufacturer. Components whose manufacturers are not specified are all commercially available conventional products. Unless otherwise specified, all concentrations in the following embodiments are mass fractions.

[0039] Example 1 This embodiment studies the optimal preparation process conditions for geranium essential oil hydrogels, specifically including the following steps: (1) Preparation of mixed solution Dissolve 0.4 g of sodium alginate and 0.6 g of 2-propoxy-β-cyclodextrin separately in 20 mL of deionized water, and mix thoroughly using a magnetic stirrer. Specifically, the sodium alginate was stirred at 400 rpm for 30 min; the 2-propoxy-β-cyclodextrin was stirred at 500 rpm for 5 min; and the mixture was then stirred at 500 rpm for 10 min. In this step, the concentrations of sodium alginate and 2-propoxy-β-cyclodextrin were 2% and 3%, respectively, and the total mass of the wall material was 1.0 g.

[0040] (2) Preparation of emulsion matrix The well-mixed solution was subjected to ultrasonic degassing (500 W, 20 min) to remove air bubbles. Span 80 (0.2% by mass, i.e. 0.04 g) was added for emulsification. The mixture was magnetically stirred at 500 rpm for 10 min. After ultrasonication for 5 min, the mixture was placed in a 4℃ refrigerator and allowed to stand for 30 min to obtain the emulsified matrix.

[0041] (3) Preparation of white emulsion Geranium essential oil was added to the emulsion matrix. Based on the optimal core-to-wall ratio of 3.08:1 (geranium essential oil volume: total wall material mass, unit mL / g), and a total wall material mass of 1.0 g, the volume of geranium essential oil was 3.08 mL (2.74 g, calculated based on a density of 0.89 g / mL). When adding the essential oil, the magnetic stirring speed was gradually increased from 200 rpm to 600 rpm for 10 min, forming a white emulsion. Then, ultrasonic mixing was performed (500 W power, 5 min). Stirring was repeated at 1100 rpm for 15 min to fully encapsulate the essential oil. The mixture was then placed in a 4℃ refrigerator and allowed to stand for 30 min to eliminate air bubbles.

[0042] (4) Crosslinking reaction and post-treatment Using a 1 mL syringe, draw up the white emulsion and slowly drop it dropwise into a 2.0% calcium chloride aqueous solution (20 mL volume) from a height of 12 cm above the surface of the calcium chloride aqueous solution. Wrap the conical flask with plastic wrap and allow it to stand at room temperature for 59 min for crosslinking. After crosslinking is complete, rinse three times quickly with deionized water and blot dry with filter paper to obtain geranium essential oil hydrogel.

[0043] Note: In this method, the core-to-wall ratio of geranium essential oil to wall material (sodium alginate + 2-propionic-β-cyclodextrin) is 3.08:1 (volume:mass, unit mL / g), the total mass of the wall material is 1.0g (sodium alginate 0.4g + 2-propionic-β-cyclodextrin 0.6g), and the amount of geranium essential oil added is approximately 3.08mL (2.74g). In subsequent surfactant screening, single-factor experiments, and response surface methodology experiments, unless otherwise specified, this method will be used as a basis, with variations in the investigated variable parameters (e.g., adjusting the amount of geranium essential oil added when the core-to-wall ratio changes).

[0044] Encapsulation efficiency determination: Weigh 0.2 g of geranium essential oil hydrogel, add 10 mL of 95% ethanol, grind in a mortar until completely broken, and sonicate for 20 min to completely break down and dissolve the hydrogel. Then centrifuge at 10000 r / min for 15 min, take the supernatant and dilute to an appropriate factor, and measure its absorbance at 238 nm using a spectrophotometer. The absorbance is then calculated according to the standard curve (Y=11.73X+0.37217, R...). 2 =0.9995) Calculate the geranium essential oil content in the hydrogel. The encapsulation efficiency is calculated using the following formula:

[0045] 1. Screening of surfactants: Seven nonionic surfactants, namely Tween 20, Tween 80, Span 20, Span 80, castor oil polyoxyethylene ether (EL-40), polyethylene glycol (PEG 400), and soybean lecithin (SL), were selected for the preparation of geranium essential oil (GEO) hydrogels. The surfactant concentration was 0.2%, the CaCl2 concentration was 2%, the core-to-wall ratio was 3:1, and the crosslinking time was 60 min.

[0046] from Figure 1 As can be seen, there are significant differences in the encapsulation effect of hydrogels prepared with different emulsifiers. Among them, the Span80 group has the highest encapsulation rate, followed by Tween 80, and EL... 40, PEG, and Tween 20 showed moderate encapsulation effects, while Span 20 and SL had the lowest encapsulation rates. This is mainly because different emulsifiers have different interaction strengths with oil phase molecules, which can change the interfacial tension of the system and thus affect the dispersion effect of the oil phase in the aqueous phase. Span 80 can effectively reduce interfacial tension, promote the uniform dispersion of the oil phase into the aqueous phase, and form a dense network structure under ionic crosslinking, achieving efficient encapsulation of active substances in the oil phase. Therefore, Span 80 was selected as the surfactant to prepare GEO hydrogels.

[0047] 2. Single-factor experiments: Single-factor experiments were conducted using the following parameters: Span 80 concentration (0.1%, 0.15%, 0.2%, 0.25%, and 0.3%), CaCl2 concentration (1.0%, 1.5%, 2.0%, 2.5%, and 3.0%), core-to-wall ratio (1:1, 2:1, 3:1, 4:1, and 5:1), and cross-linking time (20 min, 40 min, 60 min, 90 min, and 120 min). The embedding efficiency of the prepared hydrogel was determined. When investigating the effect of one factor, the other conditions were: Span 80 concentration 0.2%, CaCl2 concentration 2.0%, cross-linking time 60 min, and core-to-wall ratio 2:1.

[0048] Results of the single-factor experiment: Core-to-wall ratio: Figure 3 It can be seen that different core-to-wall ratios have a significant regulatory effect on the encapsulation efficiency of geranium essential oil hydrogels, showing an overall trend of first increasing and then decreasing. As the core-to-wall ratio gradually increases from 1:1 to 3:1, the encapsulation efficiency of the hydrogel continues to rise and reaches its maximum value. Among them, the encapsulation efficiency of the 3:1 core-to-wall ratio group is the highest, significantly higher than that of the 1:1, 4:1 and 5:1 groups. P <0.05). When the core-to-wall ratio continued to increase to 4:1 and 5:1, the encapsulation efficiency showed a continuous downward trend, and the encapsulation efficiency of the 5:1 group was significantly lower than that of all other experimental groups. When the core-to-wall ratio was too low, the shell matrix material was relatively excessive, and the resulting hydrogel network was too dense, hindering the uniform dispersion and penetration of the oil phase core material, resulting in a low encapsulation efficiency. As the core-to-wall ratio increased to 3:1, the ratio of shell material to oil phase core material reached the optimal match, and the surfactant could fully exert its interfacial regulation effect, promoting the uniform dispersion of the oil phase in the form of micro-droplets and complete encapsulation by the three-dimensional hydrogel network, thus achieving the highest encapsulation efficiency. However, when the core-to-wall ratio exceeded 3:1, the oil phase core material was excessive, and the limited shell material could not form a continuous and dense encapsulation structure. The hydrogel network exhibited a large number of structural defects, and the oil phase that was not effectively encapsulated was prone to aggregation and leakage, ultimately leading to a significant decrease in the encapsulation efficiency. Considering both the encapsulation effect and material utilization rate, 3:1 was the optimal core-to-wall ratio for preparing geranium essential oil hydrogels with high encapsulation efficiency.

[0049] CaCl2 concentration: Figure 4 The study showed the regulatory effect of CaCl2 crosslinking agent concentration on the encapsulation efficiency of geranium essential oil hydrogels, exhibiting an overall trend of increasing concentration followed by decreasing concentration. When the CaCl2 concentration increased from 1% to 2%, the encapsulation efficiency continuously increased and reached a peak. There was no significant difference in encapsulation efficiency between the 2% and 2.5% groups, and the 2% group was significantly higher than the other groups. P When the concentration was less than 0.05%, the encapsulation efficiency decreased significantly when the concentration was further increased to 3%. This is because at low concentrations, Ca²⁺... + Insufficient supply prevents the construction of a complete and continuous three-dimensional cross-linked network, making essential oils prone to leakage; at a concentration of 2%, the cross-linking reaction is sufficient and moderate, resulting in a dense and uniform hydrogel network that can stably encapsulate the essential oil core material; however, at excessively high concentrations, excess Ca²⁺… + It can cause rapid and excessive cross-linking on the surface, forming a dense hard shell that hinders the internal cross-linking process. At the same time, it can easily cause the microsphere structure to crack, which reduces the embedding effect. Therefore, 2% is the optimal CaCl2 cross-linking concentration for this system.

[0050] Span 80 concentration: Figure 5 The effect of Span 80 concentration on the encapsulation efficiency of geranium essential oil hydrogels was demonstrated, showing an overall unimodal pattern of first increasing and then decreasing. As the Span 80 concentration increased from 0.1% to 0.2%, the encapsulation efficiency continuously rose and reached its maximum value, with the 0.2% group showing a significantly higher encapsulation efficiency than all other groups. P <0.05). When the concentration exceeds 0.2%, the encapsulation efficiency shows a continuous downward trend, with the encapsulation efficiency of the 0.3% group significantly decreasing to the lowest level. This is because at low concentrations, Span 80 cannot adequately cover the oil-water interface, and the oil phase is prone to aggregation, leading to incomplete encapsulation. At a concentration of 0.2%, the emulsifier effectively reduces interfacial tension, promoting the uniform dispersion of essential oils as fine droplets in the aqueous phase, providing a good foundation for the encapsulation of the hydrogel network. Excessive Span 80, however, interferes with the reaction between sodium alginate and Ca²⁺. + The cross-linking reaction disrupts the compactness of the three-dimensional hydrogel network, leading to essential oil leakage and a decrease in encapsulation rate. Therefore, 0.2% is the optimal concentration of Span 80 for this system.

[0051] Crosslinking time: Figure 6 This reflects the effect of cross-linking time on the encapsulation efficiency of geranium essential oil hydrogels, showing an overall trend of first increasing and then decreasing: as the cross-linking time increased from 20 min to 60 min, the encapsulation efficiency continued to rise and reached its maximum value, with the 60 min group showing a significantly higher encapsulation efficiency than all other groups. P <0.05), when the cross-linking time exceeded 60 min, the encapsulation efficiency significantly decreased, and there was no statistically significant difference between the 90 min and 120 min groups. This is because when the cross-linking time is too short, Ca²⁺… +Insufficient ionic crosslinking with the hydrogel matrix results in a loose network structure, making essential oils prone to leakage. A crosslinking reaction at 60 min is sufficient and moderate, constructing a dense and uniform three-dimensional network for stable encapsulation of essential oils. Excessive crosslinking time leads to over-crosslinking on the surface, forming a dense, hard shell, while excessive network shrinkage causes the encapsulated essential oils to precipitate, ultimately reducing the encapsulation rate. Therefore, 60 min is the optimal crosslinking time for this system.

[0052] 3. Response Surface Methodology: Based on the results of the single-factor experiments, the embedding efficiency of the GEO hydrogel was optimized using the response surface methodology. The Box-Behnken response surface design was used, with the core-to-wall ratio (A), CaCl2 concentration (B), Span 80 concentration (C), and crosslinking time (D) as factors, and the embedding efficiency of the hydrogel as the response value. A four-factor, three-level response surface experiment was conducted, and the coding of the influencing factors is shown in Table 1.

[0053] Table 1. Coding and Levels of Influencing Factors

[0054] Response surface methodology experimental results and analysis: Based on the parameter range determined in the previous single-factor experiments, four key influencing factors were selected: core-to-wall ratio (A), CaCl2 concentration (B), Span 80 concentration (C), and crosslinking time (D). A four-factor, three-level response surface methodology was employed, with the encapsulation rate of geranium essential oil (GEO) hydrogel as the response value, to conduct process optimization experiments. Specific experimental schemes and results are shown in Table 2. Design Expert 12 software was used to perform multiple regression fitting and analysis of variance on the experimental data. The obtained regression model and significance test results are shown in Table 3.

[0055] Table 2 Experimental Design Results

[0056] Table 3 Regression Analysis

[0057] As shown in Table 3, the quadratic regression model is highly significant (F=113.15). P <0.0001, the lack-of-fit term is not significant ( P =0.5089), indicating good fit. The model's coefficient of determination R² = 0.9912, and the adjusted coefficient of determination R²Adj = 0.9825, indicating that the model can represent 98.25% of the response value changes. The regression equation is Y = 82.07 + 0.5775A + 0.0241B + 0.2186C 0.3795D 0.9110AB 0.9110AC 0.4555AD 0.3475BC 0.4097BD 1.14CD 3.78A² 4.02B² 3.88C² 4.15D². The first-order terms A and D are highly significant, the interaction terms AB, AC, and CD are highly significant, AD is significant, and all quadratic terms are highly significant; the influence of each factor is as follows: core-to-wall ratio > crosslinking time > Span 80 concentration > CaCl2 concentration.

[0058] Figure 7 This is a 3D response surface plot showing the effect of the interaction of various factors on the embedding rate of geranium essential oil hydrogel. Figure 8 The corresponding contour plot visually reflects the strength of the interaction between the two factors and the trend of response value changes. The steepness of the response surface directly reflects the degree of influence of the factors on the embedding rate; the greater the slope of the surface, the more significant the regulatory effect of the combination of factors on the embedding rate, and vice versa. The density and shape of the contour lines can also indicate the strength of the interaction; the denser the contour lines, the faster the response value changes; an elliptical shape indicates a significant interaction between the two factors, while a tendency towards a circle indicates an insignificant interaction. As shown in the figure, the highly significant interaction terms AB (core-to-wall ratio - CaCl2 concentration), AC (core-to-wall ratio - Span 80 concentration), and CD (Span 80 concentration - crosslinking time) correspond to response surfaces with steep slopes and significant undulations, and the contour lines are densely packed ellipses, indicating that the interaction of these three factors has a very strong impact on the encapsulation efficiency. The significant interaction term AD (core-to-wall ratio - crosslinking time) corresponds to a response surface with a moderate slope and relatively obvious elliptical contour lines, indicating a significant interaction. The insignificant interaction term BC (CaCl2 concentration - Span 80 concentration) corresponds to a response surface with gentle slopes and minimal undulations, and the contour lines are sparse and nearly circular, indicating that its interaction has a negligible impact on the encapsulation efficiency. These results are completely consistent with the analysis of variance conclusions, further verifying the accuracy and reliability of the established regression model.

[0059] Based on the established quadratic regression model, the optimal preparation conditions for geranium essential oil hydrogel were determined using Design Expert 12 software: core-to-wall ratio 3.077:1, CaCl2 concentration 1.9971%, Span 80 concentration 0.2013%, and crosslinking time 58.935 min. Under these conditions, the theoretical predicted embedding efficiency of the hydrogel was 82.82%. Considering the practical feasibility of the experimental operation, the process parameters were adjusted to: core-to-wall ratio 3.08:1, CaCl2 concentration 2.00%, Span 80 concentration 0.20%, and crosslinking time 59 min. Three parallel verification experiments were conducted under these adjusted conditions, and the average embedding efficiency of the prepared hydrogel was measured to be 82.08%. The actual measured value was very close to the theoretical predicted value of the model and was within the 95% confidence interval, indicating that the regression model for the embedding efficiency of the geranium essential oil hydrogel has good predictive accuracy and high reliability and practical application value.

[0060] Example 2 This embodiment characterizes the GEO hydrogel prepared under the optimal preparation conditions in Example 1: 1. Surface morphology and scanning electron microscopy (SEM) of the hydrogel: After preparation, the surface moisture of the hydrogel was blotted dry with filter paper, and the macroscopic morphology of the hydrogel surface was observed and photographed using a camera. A layer of conductive adhesive was attached to the SEM stage, and the sample powder was gently adhered to it. Excess powder was removed, and then gold was sputtered for 40 seconds. The sample was then placed in the SEM for observation. The distribution of inclusion particles was observed and photographed in different fields of view.

[0061] Figure 9 The macroscopic morphology and surface scanning electron microscopy (SEM) characterization results of the hollow hydrogel and GEO hydrogel are presented. Macroscopically, the hollow hydrogel is translucent, with plump and relatively large particles; the GEO hydrogel is uniformly milky white and opaque, with smaller and more evenly distributed particles. 25x surface SEM images show numerous wrinkles and sheet-like protrusions on the surface of the hollow hydrogel, indicating a loose structure and irregular edges; the GEO hydrogel is a complete sphere with a rough surface and fine texture. 50x high-magnification surface images further reveal that the hollow hydrogel surface has a continuous, large-sized sheet-like cross-linked structure with very few pores; while the GEO hydrogel surface is covered with dense micropores and uneven structures. This rough, porous structure not only provides more sites for the adsorption and encapsulation of essential oils but also facilitates the slow release of essential oils during storage, indicating that the introduction of geranium essential oil significantly alters the surface microstructure and cross-linking mode of the hydrogel.

[0062] 2. Fourier Transform Infrared (FTIR) and X-ray Diffraction (XRD) Spectra of Hydrogels: The molecular structures of SA, HP-β-CD, GEO, empty hydrogels, and GEO hydrogels were characterized using Fourier Transform Infrared (FTIR) spectroscopy, with a spectral range of 400–4000 cm⁻¹ and a resolution of 4 cm⁻¹. -1 The sample was scanned 32 / 64 times. The prepared hydrogel was pre-frozen at -80 °C for 12 h, then freeze-dried for 24 h. After freeze-drying, 5 mg of the sample was mixed with 100 mg of potassium bromide and ground into powder. The powder was then placed on a diamond crystal plate for scanning. The crystallinity of the sample was determined by Cu-Kα radiation using an X-ray diffractometer. The test voltage was 30 kV, the current was 20 mA, the diffraction angle range was 5°–50°, and the scanning speed was 8° / min.

[0063] SA, HP- β -FTIR results for CD, GEO, empty hydrogel, and GEO hydrogel are as follows: Figure 10 As shown in A in the diagram. 3000~3600cm -1 The region is the stretching vibration region of the hydroxyl group (-OH), SA (3368 cm). -1 HP- β -CD (3406 cm) -1 This region exhibits the typical broad and strong absorption peak of polysaccharides, corresponding to the presence of numerous hydroxyl groups in the molecule. The peak in this region of the GEO hydrogel shifts to 3336 cm⁻¹. -1 Furthermore, the wider peak shape indicates that hydrogen bonding interactions have formed between the hydroxyl groups of the hydrogel matrix and the polar groups of the GEO essential oil; 2800~3000 cm⁻¹ -1 The interval is the stretching vibration region of saturated CH bonds, HP- β -CD (2944 cm) -1 SA (2938 cm) -1 ), GEO (2964, 2919 cm) -1 The characteristic peaks of ) are retained at 2964 and 2912 cm⁻¹ in GEO hydrogel. -1 This indicates that the hydrogel completely preserves the hydrocarbon framework structure of each component; 1600~1700 cm -1 The region represents the stretching vibration region of the carbonyl group (C=O) and double bond; GEO is located at 1674 cm⁻¹. -1 The characteristic carbonyl peak at 1616 cm⁻¹ is clearly preserved in the GEO hydrogel, and SA is at 1616 cm⁻¹. -1 The characteristic peak of carboxylate at this location shifted to 1629 cm⁻¹ in both the empty hydrogel and the GEO hydrogel. -1 Near the vicinity, the weak interactions between components were further verified; 1000~1500 cm -1 Within the specified range, the peak shapes of the GEO hydrogel were SA and HP-.β The superposition and fusion of the characteristic peaks of CD and GEO did not produce any new characteristic absorption peaks, indicating that the components are only bound by physical interactions such as hydrogen bonds and van der Waals forces, without any chemical reaction. In conclusion, the GEO hydrogel successfully encapsulated geranium essential oil.

[0064] SA, HP- β XRD results for -CD, empty hydrogel, and GEO hydrogel are as follows: Figure 10 As shown in B in the diagram. Pure HP- β -CD exhibits sharp characteristic crystallization peaks at 11.1° and 18.9°, while pure SA shows peaks at 13.1°, 21.7°, 29.9°, and 39.5°, indicating high crystallinity of both raw materials. After the two materials are ionically crosslinked to form a blank hydrogel, the original sharp peaks are significantly broadened and their intensity decreases, leaving only weak broad diffraction bulges at 13.3°, 30.7°, and 41.4°. This demonstrates that the crosslinking network disrupts the orderly molecular stacking of the raw materials, increasing the system's disorder and significantly decreasing its crystallinity. The diffraction peak positions and shapes of the GEO composite hydrogel are highly consistent with those of the blank hydrogel, with only broadened diffraction signals at 13.1°, 18.6°, 29.6°, and 42.2°, and no essential oil-specific crystallization peaks appear. The results indicate that geranium essential oil is uniformly dispersed in the gel network in an amorphous form, suggesting that GEO was successfully embedded in the hydrogel matrix through physical interactions such as hydrogen bonding. The embedding process did not trigger a chemical reaction; it only altered the microstructure of the material through physical interactions, providing a structural basis for the stable loading of the essential oil.

[0065] 3. Thermal stability of the hydrogel: The thermal stability of the hydrogel was determined using differential scanning calorimetry. 5 mg of sample was accurately weighed into a sealed aluminum crucible and placed in the sample chamber for testing. Nitrogen purging (flow rate 30 mL / min) and a protective gas-air mixture (flow rate 50 mL / min) were used. The temperature range was 20 ℃ to 600 ℃, and the heating rate was 10 ℃ / min.

[0066] Figure 11 This study reflects the thermal behavior of SA, HP-β-CD, empty hydrogels, and GEO hydrogels. TGA curves show that all samples exhibit multi-stage weight loss. In the room temperature to 200℃ range, the main process is the evaporation of free and bound water. GEO hydrogel shows a weight loss of 64.83%, significantly higher than the 14.46% of empty hydrogels, corresponding to a broader endothermic peak at 91.2℃ in the DSC curve. This is due to the initial volatilization of light volatile components in the essential oils within this temperature range; therefore, the thermal stability of GEO hydrogels is slightly lower than that of empty hydrogels in this stage. The 200–600℃ range represents the main thermal decomposition stage of the polysaccharide matrix. SA and HP-β-CD... β-CD lost 33.16% and 91.35% of their weight, respectively, while the empty hydrogel and GEO hydrogel lost 45.87% and 14.08%, respectively. The thermal weight loss trends of the two were highly consistent. DSC curves showed that the main decomposition peak of the empty hydrogel was at 293.5℃, while the main decomposition peak of the GEO hydrogel shifted to 338.9℃. Furthermore, both exhibited significantly better thermal stability than pure HP-. β -CD indicates that the encapsulation of essential oils did not weaken the structural stability of the hydrogel matrix. On the contrary, the three-dimensional network of the hydrogel provided excellent thermal protection for the essential oils, effectively inhibiting their rapid decomposition and volatilization under medium and high temperature environments. In summary, the encapsulation of essential oils only slightly affected the low-temperature thermal stability of the hydrogel, while achieving effective thermal protection for the essential oils, meeting the temperature requirements of applications such as food preservation.

[0067] 4. Swelling rate of hydrogels: The swelling rate of dried hydrogels was studied by immersing them in deionized water. The experiment was conducted at 25℃ and 60% humidity. The three treatments were: empty hydrogel, hydrogel treated with Ca... 2+ Cross-linked GEO hydrogels, without Ca 2+ Cross-linked GEO hydrogels. The swelling degree was measured at 10 min, 20 min, 30 min, 40 min, 50 min, 60 min and 90 min, and the changes in the swelling rate of hydrogels in different treatment groups within 90 min were observed.

[0068] Swelling degree (SD) = (m t -m1) / m1×100%; Where m1 is the mass before water absorption, m t This refers to the mass after water absorption.

[0069] Figure 12 The swelling kinetics curves of the empty hydrogel and the GEO hydrogel reflect the differences in their water absorption and swelling behavior. The swelling rate of the empty hydrogel shows a typical trend of rapid increase followed by a plateau over time. The rapid swelling stage occurs from 0 to 20 minutes, with the swelling rate rising rapidly from 3.2% to 3.9%. Subsequently, the swelling rate gradually slows down, reaching 5.4% at 90 minutes, reflecting the water absorption and expansion process of the three-dimensional hydrogel network. In contrast, the swelling rate of the GEO hydrogel remains at an extremely low level, consistently below 1%, with minimal increase over time. This indicates that the introduction of geranium essential oil significantly inhibits the swelling capacity of the hydrogel. This is because the essential oil molecules fill the network pores of the hydrogel and form hydrogen bonds with the hydroxyl groups in the gel matrix, reducing the active sites that can bind to water molecules and hindering water molecule penetration and network expansion. This low swelling characteristic helps maintain the structural stability of the hydrogel microspheres, reduces the burst release of essential oil, and provides a structural basis for achieving long-term sustained release of essential oil.

[0070] 5. Release characteristics of hydrogel: Weigh several 0.2 g samples and place them in centrifuge tubes. Place them in an environment of 25 ℃. Every 12 h, add 10 mL of 95% ethanol and grind and dissolve them thoroughly. After ultrasonic centrifugation, measure the absorbance value and calculate the content of GEO essential oil.

[0071] Figure 13 SA-HP- β The sustained-release performance curves of geranium essential oil in CD-GEO hydrogel and SA-GEO hydrogel showed that the residual GEO content of both hydrogels gradually decreased with prolonged storage time, but SA-HP- β The release rate of -CD-GEO was significantly more gradual, and the residual GEO levels at all time points were significantly higher than those in the SA-GEO group. Initially, SA-HP- β The GEO content of CD-GEO was approximately 159.3 μL / g, slightly higher than that of SA-GEO (156.8 μL / g). At 60 h, SA-HP- β CD-GEO retains 140.1 μL / g of essential oil, while SA-GEO only retains 132.3 μL / g. The reason for this lies in HP- β The hydrophobic cavity of the -CD can form a stable host-guest inclusion complex with GEO molecules, enhancing the binding ability of essential oil molecules. Simultaneously, the three-dimensional cross-linked network of the composite hydrogel further hinders the diffusion and volatilization of essential oils, thus effectively delaying the release process. This indicates that the introduction of HP- β -CD significantly enhances the sustained-release effect of hydrogel on geranium essential oil, maintaining the effective essential oil concentration in the system for a longer period, making it more suitable for applications such as food preservation that require long-lasting antibacterial properties.

[0072] Example 3 1. Application of hydrogel in inhibiting potato sprouting: Select potatoes that have passed dormancy and are free from mechanical damage, pests, diseases, and rot. Wash them with clean water and air dry them for later use. Three treatment groups were established: a control group, GEO fumigation, and GEO hydrogel treatment. The GEO fumigation concentration was 200 µL / L. GEO was dropped onto filter paper, which was then placed on a plastic basket for sealed fumigation. The treatment concentration was calculated based on the basket volume. For GEO hydrogel treatment, 16 g of hydrogel was sprinkled per 2 kg of potatoes for sealed fumigation. Potatoes were stored at room temperature (25 ℃) for 20 days, and the sprouting inhibition effect was observed every 4 days. Samples were taken to determine quality indicators.

[0073] 2. Germination rate and germination index: 5 potatoes or sweet potatoes were randomly selected for each treatment, the number of buds on each tuber was recorded, and the length of the longest bud was measured with a vernier caliper, and the average value was taken. Bud length is divided into 8 grades. A bud with a length less than 2 mm is regarded as not germinated or in a germinating state, and is determined as not germinated; when the germination length is ≥ 2 mm, it is regarded as germinated. The grading standard for tuber germination is: Grade 0 (0 < L ≤ 2); Grade 1 (2 < L ≤ 5); Grade 2 (5 < L ≤ 10); Grade 3 (10 < L ≤ 15); Grade 4 (15 < L ≤ 20); Grade 5 (20 < L ≤ 25); Grade 6 (25 < L ≤ 30); Grade 7 (L ≥ 30) (L: bud length / mm). The germination rate and germination index were calculated according to the following formulas: ; .

[0074] Figure 14 and Table 4 show the effects of CK, direct GEO fumigation and GEO hydrogel treatment on the germination characteristics of potatoes during normal-temperature storage. The results showed that potatoes in the CK group started to germinate on the 3rd day of storage, the germination rate reached 100% at 12 d, and the buds grew vigorously and apical buds branched and clustered at 20 d. Direct GEO fumigation can delay the initial germination time of potatoes to 11 d, the germination rate was 22.22% at 12 d, and rose to 58.33% at 20 d. The GEO hydrogel treatment has a better bud-inhibiting effect, the initial germination time is further extended to 15 d, the germination rate was 0 at 12 d, and the germination rate was only 44.45% at 20 d, which is significantly lower than that of the first two groups. Figure 14 B The change trend of germination rate is consistent with that of 14C germination index. The germination index of the GEO hydrogel group at 20 d is also significantly lower than that of the CK and GEO fumigation groups, and bud tip necrosis occurred in potatoes of the treatment groups. The above results show that the GEO hydrogel prepared by response surface optimization can achieve continuous and stable release of essential oil by virtue of its slow-release property. It can not only effectively delay potato germination for more than 12 d, but also significantly inhibit bud growth, and its bud-inhibiting effect is obviously better than that of direct GEO fumigation.

[0075] Table 4 Initial germination time and germination rate of potatoes

[0076] 3. Application of hydrogel for bud inhibition in sweet potatoes: Select sweet potatoes without mechanical damage, diseases, insect pests and rot, wash them with clean water and dry them for later use. They were divided into a control group and a GEO hydrogel group. For the GEO hydrogel group, 8 potatoes were placed per crate, 16 g of hydrogel was sprinkled in for closed fumigation. The sweet potatoes were stored at room temperature (25 °C) for 20 d, and the bud-inhibiting effect was observed every 10 d.

[0077] Figure 15Table 5 shows the effects of CK and GEO hydrogel treatments on the sprouting characteristics of sweet potatoes during room temperature storage. Initially, there was no significant difference in appearance between the two groups of sweet potatoes. At 10 days, the control group showed obvious sprouts, corresponding to a sprouting rate of 58.33% and a sprouting index of 31.94% in Table 5. In contrast, the GEO hydrogel-treated group showed intact appearance with no signs of sprouting, and both the sprouting rate and sprouting index were 0. At 20 days, the control group showed dense and vigorous sprouting, with a sprouting rate of 100%, while the GEO hydrogel-treated group showed only a few small sprouts, with a sprouting rate of only 45.83% and a sprouting index of 36.11%. These results indicate that the prepared GEO hydrogel can significantly delay the initial sprouting time of sweet potatoes by 8 days, not only greatly reducing the sprouting rate and sprouting index during storage but also effectively maintaining the appearance quality of sweet potatoes, verifying its good application potential in the preservation of sweet potatoes and other root vegetables.

[0078] Table 5. Initial sprouting time, sprouting rate, and sprouting index of sweet potatoes

[0079] 4. Determination of browning content: Take 2g of sample, add 20 mL of distilled water, transfer to a 50 mL centrifuge tube, centrifuge at 10000 r / min for 5 min, take the supernatant and incubate at 25 ℃ for 5 min, and measure the absorbance at 410 nm using a spectrophotometer. The browning degree is expressed as A. 410 ×10, measured every 4 days.

[0080] The effects of different treatments on the browning degree of potatoes, such as Figure 16 As shown in A, with prolonged storage time, the browning degree of the CK group increased rapidly and continuously, the rate of increase in the GEO fumigation group slowed down, while the browning degree of the GEO hydrogel group increased the most gradually, and from day 4 onwards, the browning degree at each time point was significantly lower than that of the first two groups. P <0.05). After 20 days of storage, the browning degree of the CK group increased to 2.62, the GEO fumigation group to 2.58, while the GEO hydrogel group remained at a low level of only 2.25. These results indicate that GEO treatment can effectively delay the browning process of potatoes during storage. GEO hydrogel, with its slow-release properties, can continuously and stably release essential oils, thus inhibiting browning-related oxidation reactions more effectively, and its browning inhibition effect is significantly better than that of direct GEO fumigation.

[0081] 5. Determination of total phenol content: Weigh 2.0 g of sample into a 10 mL centrifuge tube, add 5 mL of cold ethanol for extraction, incubate overnight at 4 ℃, centrifuge at 12000 r / min for 20 min at 4 ℃, and collect the supernatant for later use. Take 0.5 mL of the sample extract into a 5 mL test tube, add 1.5 mL of distilled water, 1 mL of Folin-Ciocalteu reagent, and 1 mL of 7.5% anhydrous sodium carbonate solution, mix well, and incubate in a water bath at 25 ℃ for 2 h. Measure the absorbance at 765 nm. The unit is mg GAEg. -1 .

[0082] Phenolic compounds are important substances in fruit and vegetable tissues that are associated with processes such as appearance, flavor, and browning. Figure 16 As shown in Figure B, the total phenol content in the CK group increased rapidly and continuously with prolonged storage time, reaching 1.28 mg GAE g at 20 days. - ¹, the rate of increase in the GEO fumigation group slowed down, reaching 1.20 mg GAE g at 20 days. - ¹, while the total phenol content in the GEO hydrogel group increased the most gradually, and the total phenol content at each time point from day 4 onwards was significantly lower than that in the first two groups ( P <0.05), at 20 days only 1.00 mg GAE g - ¹. Increased total phenol content is closely related to potato sprouting and browning processes. GEO hydrogel inhibits the physiological metabolic activities of tubers by continuously releasing essential oils, effectively delaying the accumulation of total phenolic substances, which also corresponds to its excellent sprout-inhibiting and anti-browning effects.

[0083] 6. Determination of total flavonoid content: Weigh 2.0 g of sample into a 10 mL centrifuge tube, add 5 mL of cold ethanol for extraction, incubate overnight at 4 ℃, centrifuge at 12000 r / min for 20 min at 4 ℃, and collect the supernatant for later use. Take 3 mL of the sample extract, and add 0.3 mL of 5% sodium nitrite solution, 0.3 mL of 10% aluminum nitrate solution, and 2 mL of 4% sodium hydroxide solution sequentially every 6 min. Add 4.4 mL of ethanol to a 10 mL centrifuge tube. After stabilizing for 15 min, measure the absorbance at 510 nm.

[0084] Figure 16 C shows the effects of different treatments on the total flavonoid content of potatoes during room temperature storage. With prolonged storage, the total flavonoid content in the control group (CK) showed a continuous and rapid upward trend, reaching 1.57 mg / g at 20 days. The rate of increase in the GEO fumigation group slowed down, reaching 1.42 mg / g at 20 days. The increase in the GEO hydrogel group was the most gradual, and from day 4 onwards, the total flavonoid content at all time points was significantly lower than that in the CK and GEO fumigation groups. P<0.05), and only 1.01 mg / g at 20 days. Total flavonoids, as secondary metabolites of potatoes in response to stress, are closely related to the sprouting and browning process. GEO hydrogel inhibits the physiological stress response of tubers by continuously releasing essential oils, effectively delaying the excessive accumulation of total flavonoids. Its regulatory effect is significantly better than that of direct GEO fumigation, which is consistent with the previous results on sprout inhibition and anti-browning.

[0085] 7. Determination of starch content: Weigh 0.5 g of sample into a 50 mL centrifuge tube, add 50 mL of diethyl ether, mix, centrifuge at 10000 rpm for 10 min, discard the liquid, and keep the filter residue. Add 20 mL of 80% ethanol, mix, centrifuge for 10 min, discard the liquid, and keep the filter residue. Wash the filter residue with 25 mL of distilled water into a graduated test tube and heat in a boiling water bath until transparent. Pipette 1 mL of starch extract into 6.8 mL of distilled water and 0.2 mL of iodine solution into a 10 mL centrifuge tube, shake well, stabilize for 10 min, and then measure the absorbance at 660 nm.

[0086] Starch is the most abundant storage carbohydrate in potato tubers, and its content changes directly reflect the physiological metabolic activity and storage quality of the tubers. Figure 16 As shown in D, the starch content of all treatment groups decreased with prolonged storage time, with the CK group showing the most significant decrease, dropping from an initial 22.0% to 11.3% at 20 days, and exhibiting the fastest rate of decline in the early stages. The starch consumption rate in the GEO fumigation group slowed down, reaching 13.5% at 20 days; while the starch content in the GEO hydrogel group remained consistently high, retaining 15.4% at 20 days, and from day 4 onwards, the starch content at all time points was significantly higher than that of the CK group and the GEO fumigation group. P <0.05). Starch degradation is closely related to respiration and energy metabolism during germination. GEO hydrogel inhibits the physiological metabolic activities of tubers by continuously releasing essential oils, effectively delaying the hydrolysis and consumption of starch, and better maintaining the storage quality and commercial value of potatoes. Its effect is significantly better than direct GEO fumigation treatment.

[0087] 8. Determination of reducing sugar content: Weigh 1 g of sample and place it in a 25 mL graduated test tube, then dilute to volume. Place in an 80 ℃ water bath for 30 min, remove and cool, centrifuge at 12000 rpm for 10 min, collect the filtrate in a 100 mL volumetric flask, add 20 mL of distilled water and centrifuge again, collecting the filtrates twice into a 100 mL volumetric flask. Add 2 mL of extraction solution and 1.5 mL of DNS to a 25 mL graduated test tube, shake well, and incubate in a boiling water bath for 5 min. Immediately remove and place in a beaker containing cold water to cool to room temperature, dilute to 25 mL, and measure the absorbance at 540 nm.

[0088] Reducing sugars are key metabolic products during potato storage, and changes in their content directly reflect the degree of starch degradation and the physiological activity of tubers, making them an important indicator affecting potato processing quality. Figure 16 As shown in Figure E, the reducing sugar content of all treatment groups decreased with prolonged storage time, with the CK group showing the most significant decrease, from an initial 0.89% to 0.28% at 20 days, and the rate of decrease was the fastest in the early stages. The reducing sugar consumption rate of the GEO fumigation group slowed down, reaching 0.34% at 20 days, while the reducing sugar content of the GEO hydrogel group remained at a high level, still retaining 0.40% at 20 days. Furthermore, from day 8 onwards, the reducing sugar content at each time point was significantly higher than that of the CK group and the GEO fumigation group. P <0.05). The decrease in reducing sugar is closely related to starch hydrolysis and respiratory metabolism during germination. GEO hydrogel inhibits the physiological metabolic activities of tubers by continuously releasing essential oils, effectively delaying the excessive consumption of reducing sugar, maintaining the dynamic balance of starch and sugar metabolism, and helping to maintain the storage and processing quality of potatoes. Its effect is significantly better than direct GEO fumigation treatment.

[0089] 9. Determination of ascorbic acid content: The 2,6-dichlorophenolindophenol method was used. 10 mL of the supernatant was pipetted into a 100 mL Erlenmeyer flask and titrated with standardized 2,6-dichlorophenolindophenol solution until a faint red color appeared and did not fade within 15 seconds. The amount of dye used was recorded. Simultaneously, 10 mL of 20 g / L oxalic acid solution was used as a blank, and titration was performed using the same method, repeated three times. The results are expressed as mg / 100 g.

[0090] Ascorbic acid (VC) is an important antioxidant and nutrient in potatoes, and changes in its content directly reflect the level of oxidative stress and nutrient retention during storage. Figure 16 As shown in Figure F, the VC content in all treatment groups decreased with prolonged storage time, with the CK group showing the most significant decrease, dropping from an initial 7.02 mg / 100g to 1.50 mg / 100g at 20 days, and exhibiting the fastest rate of decline in the early stages. The VC degradation rate in the GEO fumigation group slowed down, reaching 2.67 mg / 100g at 20 days, while the VC content in the GEO hydrogel group remained consistently high, retaining 3.89 mg / 100g at 20 days. Furthermore, from day 4 onwards, the VC content at all time points was significantly higher than that in the CK and GEO fumigation groups. P <0.05). The degradation of vitamin C is closely related to respiratory metabolism and oxidative stress during the sprouting process. GEO hydrogel exerts an antioxidant effect by continuously releasing essential oils, effectively inhibiting the oxidative decomposition of vitamin C, significantly delaying its content decline, and better preserving the nutritional quality of potatoes. The effect is significantly better than direct GEO fumigation treatment.

[0091] 10. Polyphenol oxidase (PPO) assay: Take a 15 mL centrifuge tube, add 2.5 mL of 0.1 mol / L pH 5.5 acetate-sodium acetate buffer and 1.0 mol / L 50 mol / L catechol solution, and finally add 400 μL of enzyme extraction buffer. Start timing immediately. Pour the reaction mixture into a cuvette and place it in the sample chamber of a spectrophotometer. Using distilled water as a reference, start recording the absorbance of the reaction system at a wavelength of 420 nm after 15 s of reaction as the initial value. Then record every 1 min, continuously measuring at least 6 points. Repeat three times.

[0092] Polyphenol oxidase (PPO) is a key enzyme catalyzing enzymatic browning in fruits and vegetables. With the participation of oxygen, it oxidizes phenolic substances into quinones, which then polymerize to form melanoidins, directly leading to browning and quality deterioration in potatoes. Figure 16 As shown in G, with the extension of storage time, the PPO activity of both the CK group and the GEO fumigation group showed a trend of first increasing and then slowly decreasing, and remained at a high level throughout. The activity of the CK group reached a peak of 1298.75 U / (min) after 8 days of storage. g), and still as high as 1116.24 U / (min) at 20 d. g). Although the PPO activity in the GEO fumigation group was lower than that in the CK group, it was still 1028.72 U / (min) at 20 days. g), while the increase in PPO activity in the GEO hydrogel group was significantly slower, and the PPO activity at each time point from day 4 onwards was significantly lower than that in the CK group and the GEO fumigation group ( P <0.05), and at 20 days it was only 858.14 U / (min g). GEO hydrogel inhibited the physiological stress response of tubers by continuously releasing essential oils, significantly reduced PPO activity, effectively blocked the key steps of enzymatic browning, and reduced the appearance deterioration and nutrient loss of potatoes caused by browning. Its inhibitory effect was significantly better than that of direct GEO fumigation treatment.

[0093] 11. Peroxidase (POD) assay: Take a 15 mL centrifuge tube, add 0.1 mL of 25 mmol guaiacol solution and 1 mL of enzyme extraction solution, then add 0.1 mL of 0.5 mol / L H2O2 and 2 mL of 0.05 mol / L buffer. Quickly mix the solutions to start the reaction and start timing immediately. Pour the reaction mixture into a cuvette and place it in the sample chamber of a spectrophotometer. Using distilled water as a reference, start recording the absorbance of the reaction system at a wavelength of 470 nm after 15 s of reaction as the initial value, and then record every 30 s. Continuously measure at least 6 points and repeat 3 times.

[0094] Peroxidase (POD) is a key enzyme in the potato's antioxidant defense system, and its activity level is closely related to the oxidative stress state of tissues and the process of quality deterioration. Figure 16 H indicates that the POD activity of all treatment groups increased with prolonged storage time. The CK group showed the fastest increase in POD activity at the beginning of storage, significantly higher than the other two groups at 4 days, and then continued to fluctuate upwards, reaching 120.42 U / (min) at 20 days. g). The rate of increase in POD activity in the GEO fumigation group slowed down, reaching 124.86 U / (min) at 20 days. g), while the POD activity of the GEO hydrogel group increased most gradually, reaching 129.38 U / (min) at 20 days. g) Overall, it remained at a low level. The increase in POD activity is a stress response of potatoes to storage stress. GEO hydrogel alleviated the oxidative stress of tubers by continuously releasing essential oils, avoiding excessive upregulation of POD activity, effectively maintaining the oxidative metabolic balance of potatoes during storage, reducing oxidative damage, and thus delaying the process of quality deterioration. Its regulatory effect is better than that of direct GEO fumigation treatment.

[0095] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A geranium essential oil hydrogel, characterized in that, By weight percentage, it consists of the following components: 10-12% geranium essential oil, 1.5-3% sodium alginate, and 2-propionic acid- β - Cyclodextrin 2-5%, surfactant 0.1-0.3%, crosslinking agent 1.0-3.5%, deionized water balance.

2. The geranium essential oil hydrogel according to claim 1, characterized in that, By weight percentage, it consists of the following components: 10-11.5% geranium essential oil, 1.5-2.5% sodium alginate, and 2-propionic acid- β - Cyclodextrin 2-3%, surfactant 0.15-0.25%, crosslinking agent 1.5-2.5%, deionized water balance.

3. The geranium essential oil hydrogel according to claim 1, characterized in that, The surfactant is one or more of Tween20, Tween 80, Span 20, Span 80, castor oil polyoxyethylene ether (EL-40), polyethylene glycol (PEG 400), and soybean lecithin (SL), preferably Span 80; The HLB value of the Span 80 is 4.3; The crosslinking agent is calcium chloride.

4. A method for preparing geranium essential oil hydrogel according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Sodium alginate and 2-propionic acid β - Dissolve the cyclodextrins separately in water, stir and mix well to obtain a mixed solution; (2) After ultrasonic degassing of the mixed solution, a surfactant is added, followed by stirring emulsification and low-temperature standing treatment to obtain an emulsion matrix; (3) Add geranium essential oil to the emulsion matrix, stir and emulsify, and then let it stand at low temperature to obtain a white emulsion; (4) Add the white emulsion to the crosslinking agent aqueous solution to carry out the crosslinking reaction. After washing and drying, geranium essential oil hydrogel is obtained.

5. The preparation method according to claim 4, characterized in that, In step (1), stir and mix at a speed of 400-500 rpm for 25-35 minutes.

6. The preparation method according to claim 4, characterized in that, In step (2), the power of the ultrasonic degassing treatment is 400-600W, and the time is 10-30min; In step (2), the stirring and emulsification speed is 450-550 rpm and the time is 10-15 min; In step (2), the temperature of the low-temperature standing is 3-5℃ and the time is 20-40min.

7. The preparation method according to claim 4, characterized in that, In step (3), the emulsification of geranium essential oil after addition is carried out by gradient stirring: first stirring at 100-300 rpm, then gradually increasing to 500-700 rpm, with a total stirring time of 5-15 min; then ultrasonic mixing is performed, with an ultrasonic power of 400-600 W for 3-10 min; after ultrasonic mixing, stirring is carried out at 800-1200 rpm for 10-20 min. In step (3), the temperature of the low-temperature standing is 3-5℃ and the time is 20-40min.

8. The preparation method according to claim 4, characterized in that, In step (4), the mass concentration of the crosslinking agent aqueous solution is 1-3%, the crosslinking reaction time is 40-90 min, and the washing is performed by rinsing with deionized water 2-4 times.

9. The application of the geranium essential oil hydrogel according to any one of claims 1-3 in inhibiting sprouting in potatoes and sweet potatoes.

10. The application according to claim 9, characterized in that, Geranium essential oil hydrogel was applied to the packaging of potatoes and sweet potatoes; the mass ratio of potato to geranium essential oil hydrogel was 1:(0.0075-0.0085), and the mass ratio of sweet potato to geranium essential oil hydrogel was 1:(0.0035-0.0055); the potatoes were potatoes that had passed their dormancy period.

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