Sweet potato special fresh-keeping microemulsion as well as preparation method and application thereof

Abstract

The present application belongs to the field of plant preservation technology, in order to solve the problem of large particle size, poor extensibility, poor preservation effect and chemical drug residue of sweet potato preservative effective component in the prior art field, a microemulsion for sweet potato preservation, its preparation method and application are proposed, the microemulsion includes surfactant, co-surfactant, solvent, oil phase, chitosan and water. The microemulsion prepared by the present application contains edible chitosan and natural biological essential oil, by spraying or dipping the sweet potato, a preservation and sterilization film is formed, which has good bacteriostatic function and water loss reduction function, reduces the rot rate of sweet potato during storage, and reduces the product quality decline caused by excessive weight loss. The preparation method of the present application is simple, the preservation and bacteriostasis effect is remarkable, the prepared components are non-toxic and harmless, environment-friendly, non-polluting and easy to degrade, which is used for preservation and storage, and improves the economic benefit.

Description

Technical Field

[0001] This invention relates to the field of plant preservation technology, specifically to a sweet potato-specific preservation microemulsion, its preparation method, and its application. Background Technology

[0002] Currently, sweet potato preservatives are mainly divided into three categories: physical coating types (chitosan, sodium alginate, paraffin emulsion, etc.), chemical antibacterial types (carbendazim, chlorine dioxide, sec-butylamine, isothiazolinone, etc.), and biological preservative types (beneficial microorganisms or plant essential oils). These three types of preservatives mainly achieve the effect of preserving sweet potatoes by reducing water evaporation, chemical antibacterial agents, and biological antibacterial agents. However, these preservatives have limited functions, their bactericidal effect is generally weak, chemical antibacterial preservatives pose food safety issues, and biological antibacterial agents have weak water retention effects. With the extraction and application of various bio-essential oil products, the combination of physical coating and biological antibacterial agents can not only effectively reduce the disease rate of sweet potato tubers during storage, but also effectively slow down the rate of water evaporation from the tubers. Microemulsion technology has gradually moved from the laboratory to industrial applications. Traditional microemulsion preservatives mostly use natural plant extracts such as tea polyphenols and chitosan as active ingredients, combined with nonionic surfactants to construct oil-in-water or water-in-oil systems. By forming a dense protective film on the surface of sweet potatoes, they isolate oxygen and microbial infection, while inhibiting respiration to delay aging. However, these microemulsion systems generally suffer from insufficient stability, and are prone to stratification and demulsification during storage, leading to a rapid decline in preservation effect over time. Furthermore, the release rate of active ingredients is difficult to control precisely, making it unsuitable for the preservation needs of sweet potatoes at different storage stages.

[0003] The nano-microemulsion sweet potato preservative achieves three technological breakthroughs: First, a difference in system structure. Traditional preservatives typically have particle sizes larger than 1000nm, while the nano-microemulsion, through precise control of the surfactant and co-surfactant ratio, compresses droplet sizes to below 500nm, significantly improving the thermodynamic stability of the system. It maintains uniform dispersion at both room temperature and low storage conditions, preventing demulsification and failure. Second, a difference in the loading and release of active ingredients. This technology uses nano-sized droplets as carriers, achieving an encapsulation rate of over 30% for preservative active ingredients. Simultaneously, the use of high-boiling-point bio-essential oils enables slow release of plant essential oils, extending the duration of the preservative microemulsion's effect. Third, through microemulsion treatment, the chitosan particles carried by the bio-essential oils are even smaller. Whether soaked or sprayed, the preservative adheres evenly to the sweet potato skin, even penetrating into the tiny pores of the skin to form a three-dimensional protective layer. This reduces moisture evaporation while significantly extending the shelf life compared to traditional methods. Summary of the Invention

[0004] To address the aforementioned problems, the purpose of this application is to provide a microemulsion formulation with chitosan and plant essential oils as active ingredients. This formulation has the effect of reducing water evaporation and soft rot infection when soaking potato tubers. Furthermore, the microemulsion has good stability, small and uniform particle size, high efficacy, and can be diluted with pure water, groundwater, or tap water. It also has high spreadability and high bactericidal efficiency.

[0005] To achieve the above objectives, the first aspect of the present invention provides a sweet potato-specific preservative microemulsion, which is composed of the following components by mass percentage: Surfactant: 9%–39%; Co-surfactant: 9%–14%; Solvent: 7%–12%; Oil phase: 10%–13%; Chitosan: 2%–7%; Water: Balance.

[0006] Preferably, the surfactant is Tween 80 and / or Span 80.

[0007] Preferably, the co-surfactant is any one of propylene glycol, ethanol, n-octanol, and polyethylene glycol.

[0008] Preferably, the solvent is one or a combination of several esters or polar solvents.

[0009] Preferably, the oil phase is one or more of cinnamyl alcohol essential oil, calendula essential oil, and citral essential oil.

[0010] Preferably, the water is one of deionized water, standard hard water, or tap water.

[0011] The second aspect of this invention provides a method for preparing a special preservative microemulsion for sweet potatoes. The method involves mixing a surfactant, a co-surfactant, a solvent, and an oil phase in a certain proportion, slowly adding an aqueous solution containing chitosan while stirring, stirring at room temperature (25°C) for 10 minutes to convert the W / O type to the O / W type, and then cooling to room temperature to obtain the final product.

[0012] The third aspect of this invention provides the use of the sweet potato-specific preservative microemulsion described above for the preparation of sweet potato preservation products.

[0013] Compared with the prior art, the beneficial effects of the present invention are: 1. The preservative microemulsion provided by this invention is nanoscale, and its main components are surfactants, plant essential oils, chitosan, and bio-carriers. The advantages of this formulation are its small and uniform particle size, which significantly improves the dispersibility and stability of the active ingredients, thereby enhancing its covering ability and penetration effect on the sweet potato surface. The nanoscale particle size allows the microemulsion to better fill the tiny pores on the surface of the sweet potato tuber, forming a dense and continuous preservative and bactericidal film, effectively blocking the invasion of external pathogens and excessive oxygen contact, thus delaying the physiological aging and spoilage process of the sweet potato.

[0014] 2. The edible chitosan used in this invention has good biocompatibility and film-forming properties. Its molecular structure contains a large number of active groups such as amino and hydroxyl groups, which can interact with polysaccharides, proteins, and other components on the surface of sweet potatoes, enhancing the adhesion and durability of the film. Simultaneously, chitosan itself has certain antibacterial activity, inhibiting the growth and reproduction of various pathogenic microorganisms that cause storage diseases such as soft rot and black spot in sweet potatoes. Synergistically working with natural bio-essential oils, it significantly improves the preservation effect.

[0015] 3. The natural plant essential oils selected in this invention, such as cinnamon oil, tea tree oil, and citral oil, are rich in active ingredients such as terpenes, phenols, and aldehydes, possessing multiple effects including broad-spectrum antibacterial, antioxidant, and insect-repellent properties. Through microemulsion encapsulation and sustained-release, these essential oil components achieve continuous and stable release, avoiding the problems of easy volatility and short duration of action associated with direct application of essential oils. This extends the shelf life, reduces the amount of essential oil used, and lowers costs.

[0016] 4. The microemulsion preparation process of this invention is simple, requiring no special equipment conditions such as high temperature and high pressure. Phase inversion from W / O to O / W can be achieved at room temperature. The operation is safe, energy consumption is low, and it is easy to scale up production. All raw materials used are food-grade or pharmaceutical-grade, non-toxic and harmless. The preservative film formed on the surface of sweet potatoes is edible and easily degradable, and will not have a negative impact on the environment or human health, meeting the development requirements of green agriculture and food safety.

[0017] 5. The preservative microemulsion of this invention offers flexible application methods. It can be used for rapid treatment of large quantities of sweet potatoes through soaking or spraying, or for precise treatment of individual sweet potatoes through wetting, adapting to different storage needs. The treated sweet potatoes exhibit excellent preservation effects under both ambient and low-temperature storage conditions, with significantly reduced weight loss and rot rates, effectively improving product quality and shelf life. This provides reliable technical support for reducing post-harvest losses and increasing added value in sweet potatoes. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0019] In the attached diagram: Figure 1 Example 1: Soft rot infection status after 48 hours of culture under different treatments; Figure 2 Example 2: Soft rot infection status after 48 hours of culture under different treatments; Figure 3 Example 3: Soft rot infection status after 48 hours of culture under different treatments; Figure 4Example 1 Chitosan particle size distribution curve (original solution diluted 100 times, average particle size 195.8 nm). Figure 5 Example 2 Chitosan particle size distribution curve (original solution diluted 100 times, average particle size 364.2 nm). Figure 6 Example 3 Chitosan particle size distribution curve (original solution diluted 100 times, average particle size 24.32 nm). Figure 7 Example 1: Difference in tuber infection diameter (mg / L) 48 hours after inoculation with soft rot tissue; Note: based on effective cinnamon oil concentration; Figure 8 Example 2: Difference in tuber infection diameter (mg / L) 48 hours after inoculation with soft rot tissue; Note: based on effective concentration of Melaleuca lyrata. Figure 9 Example 3: Antibacterial effect of different treatments on sweet potato soft rot; Note: based on effective concentration of citral; Figure 10 Antimicrobial effects of different treatments of citral microemulsion on sweet potato soft rot; Note: This microemulsion does not contain chitosan, based on the effective concentration of citral. Figure 11 Antimicrobial effects of different treatments of cinnamon oil microemulsion on sweet potato soft rot (mg / L); Note: This microemulsion does not contain chitosan, based on the effective concentration of cinnamon oil. Figure 12 Antibacterial effects of different treatments of Melaleuca lyrata microemulsion on sweet potato soft rot (mg / L); Note: This microemulsion does not contain chitosan, based on the effective concentration of Melaleuca lyrata. Figure 13 Antimicrobial effect of chitosan microemulsion on sweet potato soft rot (mg / L); Note: based on effective chitosan concentration; Figure 14 The effect of different types and contents of microemulsions on the weight loss rate of sweet potatoes; Figure 15 Effects of different microemulsion treatments on the weight loss rate of sweet potatoes. Detailed Implementation

[0020] The following combination Figure 1 - Figure 15 The preferred embodiments of the present invention will be described herein. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0021] Raw materials and reagents: Tween 80 (Tianjin Dengfeng Chemical Reagent), Span 80 (Guangdong Runhua Chemical Co., Ltd.), 1,2-propanediol (Tianjin Beichen Fangzheng Reagent Factory), ε-caprolactone (Shanghai Dibai Biotechnology Co., Ltd.), cinnamon oil (Guangxi), chitosan (Jinan Sanhe Biotechnology), n-octanol (Tianjin Bailunsi Biotechnology Co., Ltd.), ethyl acetate (Tianjin Fuchen Chemical Reagent Factory), melaleuca essential oil (Guangdong), citral (Guangdong Fangxin Biotechnology Co., Ltd.).

[0022] Example 1, a preservative microemulsion, composed of the following components by weight percentage: Surfactants: Tween 80, 28%; Span 80, 10%; Co-surfactant: Propylene glycol, 13%; Solvent: ξ-caprolactone, 10%; Oil phase: cinnamon oil, 13%; Chitosan, 3%; Deionized water, balance.

[0023] Mix the above components thoroughly in proportion, slowly add an aqueous solution containing 13% chitosan while stirring, stir at 25°C for 10 minutes, the system changes from W / O type to O / W type, and is then cooled to room temperature to obtain the final product.

[0024] Example 2, a preservative microemulsion, composed of the following components by weight percentage: Surfactants: Tween 80, 29%; Span 80, 10%; Co-surfactant: n-Octanol, 14%; Solvent: Ethyl acetate, 12%; Oil phase: Melaleuca alba oil, 12%; Chitosan, 2%; Deionized water, balance.

[0025] Mix the above components thoroughly in proportion, slowly add an aqueous solution containing 13% chitosan while stirring, stir at 25°C for 10 minutes, and the system will change from W / O type to O / W type. Cool to room temperature to obtain the final product.

[0026] Example 3, a preservative microemulsion, composed of the following components by weight percentage: Surfactants: Tween 80, 23%; Span 80, 8%; Co-surfactant: n-Octanol, 10%; Solvent: ξ-caprolactone, 8%; Oil phase: citral, 10%; Chitosan, 7%; Deionized water, balance.

[0027] Mix the above components thoroughly in proportion. First, add an aqueous solution containing 20% ​​chitosan while stirring. Stir slowly at 25°C for 5 minutes. Then, add an aqueous solution containing 13% chitosan and stir for 5 minutes. The system will change from W / O type to O / W type. Cool to room temperature to obtain the final product.

[0028] Experimental procedure: 1. Chitosan particle size distribution curves after 100-fold dilution of formulations in Examples 1-3 After sample preparation, the samples were packaged and sent to the Zhengzhou Testing Center of eTest Company for analysis using liquid Zeta particle size / potential analysis (DLS). The samples were diluted 100 times, and each sample was repeated 3 times to determine the particle size distribution curve.

[0029] Depend on Figure 4 , Figure 5 , Figure 6 It can be seen that the average particle size of chitosan in Example 1 is 195.8 nm, the average particle size of chitosan in Example 2 is 264.2 nm, and the average particle size of chitosan in Example 3 is 24.32 nm. After preparation, stable oil-in-water nanoemulsions were formed.

[0030] The above analysis shows that the average particle size of chitosan in Example 2 is the largest, followed by Example 1 and Example 3.

[0031] In Example 1, the particle size of chitosan was mainly distributed between 106-342 nm. The volume content of 190 nm particles was the highest at 23.96%, followed by 164 nm particles at 22.13%, 220 nm particles at 19.56%, 142 nm particles at 13.12%, and 255 nm particles at 12.03%. The volume content of other particle sizes was less than 10%.

[0032] In Example 2, the particle size of chitosan was mainly distributed between 142-459 nm. The volume content of 255 nm particles was the highest at 24.05%, followed by 295 nm particles at 21.19%, 220 nm particles at 20.06%, 342 nm particles at 12.94%, and 190 nm particles at 11.75%. The volume content of other particle sizes was less than 10%.

[0033] In Example 3, the particle size of chitosan was mainly distributed between 13-58 nm, with the highest volume content of 21 nm particles at 20.75%, followed by 24 nm particles at 18.57%, 18 nm particles at 17.54%, and 28 nm particles at 12.94%. The volume content of other particle sizes was less than 10%.

[0034] In summary, the chitosan microemulsions prepared using different surfactants, solvents, and bio-extracted essential oils all achieved nanoscale particle sizes, and the dispersion effects on chitosan varied: Example 3 showed the best dispersion effect on chitosan molecules, followed by Examples 1 and 2.

[0035] The smaller the particle size of chitosan, the better its dispersibility and extensibility during use, and the better its penetration into the surface of potato skin. Its bactericidal and preservative effects still need further verification.

[0036] 2. Antibacterial effects of different treatments on sweet potato soft rot To further verify the inhibitory effect of the combination of bio-extracted essential oil and chitosan on sweet potato soft rot pathogen, the following experiment was conducted.

[0037] Potato variety: Leshu 01. After cleaning the long strip-shaped potato tubers with a diameter of 5-8 cm with tap water, spray them with alcohol for disinfection and place them in a clean bench for later use.

[0038] Reagent preparation: Example 1 Microemulsion concentration gradient (mg / L): 0, 50, 100, 200, 400.

[0039] Example 2 Microemulsion concentration gradient (mg / L): 0, 50, 100, 200, 400.

[0040] Example 3 Microemulsion concentration gradient (mg / L): 0, 50, 100, 200, 400.

[0041] Melaleuca lycopersicum microemulsion concentration gradient (mg / L): 0, 50, 100, 200, 400.

[0042] Cinnamon oil microemulsion concentration gradient (mg / L): 0, 50, 100, 200, 400.

[0043] Citral microemulsion concentration gradient (mg / L): 0, 50, 100, 200, 400.

[0044] Chitosan microemulsion concentration gradient (mg / L): 0, 50, 100, 200, 400.

[0045] Inoculation treatment: The strain was obtained from rotten potato tubers infected with soft rot and stored in a constant temperature warehouse. A certain amount of rotten tissue was taken from the rotten potato tubers, placed in a sterile petri dish, and then placed in an ultra-clean workbench.

[0046] On a clean bench, cut the sweet potato chunks into 3-4mm thick slices from the middle. Dip the slices in microemulsion solutions of different concentrations and place them in sterile petri dishes. Then, use tweezers to take a soybean-sized piece of rotten sweet potato tissue infected with soft rot fungus and place it in the middle of the slice. Seal the slice and incubate it in a 25℃ incubator. Take pictures after a certain period of time and observe the diameter of the infection zone.

[0047] Depend on Figure 1 , Figure 2 , Figure 3 , Figure 7 , Figure 8 , Figure 9 , Figure 10 , Figure 11 , Figure 12 , Figure 13 It can be seen that Examples 1-3 demonstrate the infection effects of three plant essential oil-chitosan-based microemulsions on sweet potato soft rot pathogens, as well as the effects of using plant essential oils or chitosan microemulsions alone on sweet potato soft rot pathogen infection. The combination of plant essential oils and chitosan significantly inhibits the infection of sweet potato soft rot pathogens, and the antibacterial effect gradually increases with the increase of plant essential oil concentration in the microemulsion. Under the same concentration conditions, the antibacterial effect of the microemulsion treatment group containing chitosan is significantly better than that of the single essential oil microemulsion treatment group, indicating a synergistic effect between chitosan and plant essential oils.

[0048] from Figure 7 As can be seen, in Example 1, at a concentration of 50 mg / L, the diameter of the infected tuber was 4.75 cm 48 hours after inoculation with soft rot tissue, while the diameter of the infected tuber in the blank control group reached 6.45 cm, with an inhibition rate of 26.35%. As the concentration of Example 1 increased, the diameter of the infected tuber did not decrease significantly, indicating that Example 1 achieved the highest inhibition effect on soft rot at a concentration of 50 mg / L.

[0049] Figure 8 The results show that the antibacterial effect of Example 2 differs from that of cinnamon oil microemulsion. Example 2 exhibits the best antibacterial effect against soft rot at a concentration of 200 mg / L, with an inhibition rate of 66.7%, followed by treatments at 400 mg / L and 100 mg / L. The antibacterial effect of the 50 mg / L treatment is moderate.

[0050] Figure 9 The results showed that Example 3 had the most significant antibacterial effect. The antibacterial effect was significant from 50 mg / L to 400 mg / L, with antibacterial rates of 74.41%, 75.19%, 75.96%, and 79.84%, respectively.

[0051] Figure 7 , Figure 8 , Figure 9It can be seen that, based on comprehensive analysis, Example 3 showed the best antibacterial effect, followed by Example 2, and lastly Example 1. (Combined with...) Figure 4 , Figure 5 , Figure 6 Example 3 showed the best dispersion effect on chitosan, the smallest average particle size of chitosan, and the best antibacterial effect. The two had a significant effect on synergistic antibacterial activity.

[0052] Figure 10 It was found that the antibacterial effect of citral microemulsion (without chitosan) on sweet potato soft rot increased with increasing citral content, reaching the highest efficiency at 200 mg / L. The antibacterial efficiencies at 50, 100, 200, and 400 mg / L were 2.35%, 40.00%, 52.94%, and 51.76%, respectively.

[0053] Figure 11 It can be seen that the antibacterial effect of Melaleuca lycopersicum microemulsion (without chitosan) on sweet potato soft rot increases with the increase of Melaleuca lycopersicum content, and the antibacterial efficiency is the highest at 100 mg / L. The antibacterial efficiencies of 50, 100, 200, and 400 mg / L are 37.65%, 51.76%, 51.76%, and 45.88%, respectively.

[0054] Figure 12 It was found that the antibacterial effect of cinnamon oil microemulsion (without chitosan) against sweet potato soft rot increased with increasing cinnamon oil content, reaching its highest efficiency at 400 mg / L. The antibacterial efficiencies at 50, 100, 200, and 400 mg / L were 37.64%, 45.88%, 52.94%, and 56.47%, respectively.

[0055] Figure 13 It can be seen that the antibacterial effect of chitosan solution on sweet potato soft rot increases with the increase of chitosan content, and the antibacterial efficiency is the highest when it reaches 200 mg / L. The antibacterial efficiencies of 50, 100, 200, and 400 mg / L are 40.00%, 54.11%, 58.82%, and 54.17%, respectively.

[0056] have Figure 7 , Figure 8 , Figure 9 , Figure 10 , Figure 11 , Figure 12 , Figure 13 The above data, from the same batch of tests, indicate that citral, melaleuca lanceolata, cinnamon oil, and chitosan all have inhibitory effects on soft rot pathogens. The combination of citral and chitosan significantly enhanced their inhibitory effects on soft rot, as did the combination of melaleuca lanceolata and chitosan. The antibacterial effect of the combination of cinnamon oil and chitosan was slightly lower than that of either ingredient alone.

[0057] This antibacterial test was conducted under the condition that the sweet potatoes were cut open. In actual production, the sweet potatoes are not cut open during storage and are protected by the skin. Therefore, the antibacterial effect of these preparations can significantly reduce the rot rate and infection speed of sweet potatoes during storage, thereby achieving the effect of reducing the rot rate of sweet potatoes.

[0058] 3. Effect of tuber treatment on sweet potato weight loss rate Potato variety: Baishu 54, each tuber weighs 120-230g, the tubers were harvested in mid-October 2025, and stored in a constant temperature warehouse for nearly 3 months without any treatment.

[0059] Preservative treatment: A preservative microemulsion with cinnamyl alcohol, catechuic acid, and citral as the oil phase was diluted with tap water to prepare emulsions containing 200, 400, and 800 mg / L of cinnamyl alcohol, catechuic acid, and citral, respectively. The potato tubers were washed, dried, and weighed individually. Then, the potato tubers were moistened with the microemulsions at concentrations of 200, 400, and 800 mg / L, respectively. All the potato tubers were placed in order on a tray and incubated in an incubator (temperature set at 25℃). The tubers were weighed every 24 hours for 9 consecutive days. The weight loss rate was calculated using potato tubers moistened with tap water as a control.

[0060] Meanwhile, potato pieces were moistened with emulsions containing chitosan at concentrations of 0, 50, 100, 200, and 400 mg / L, and then cultured as described above. The weight loss rate was then observed.

[0061]

[0062] Depend on Figure 14 The results showed that cinnamon oil, cajeput, citral-chitosan microemulsion, and chitosan microemulsion had preservation effects on sweet potatoes. The 200 mg / L cinnamon oil-chitosan microemulsion treatment reduced water loss by approximately 40.82% compared to the control, while the 800 mg / L treatment reduced water loss by 35.88%. The 200 mg / L and 400 mg / L cajeput chitosan microemulsion treatments reduced the weight loss rate of sweet potatoes, but the differences were not significant. The 200 mg / L treatment reduced water loss by 31.21% compared to the control, while the 800 mg / L treatment had no inhibitory effect on the weight loss rate. The citral-chitosan microemulsion had a relatively small effect on the weight loss rate of sweet potatoes, with no significant difference. The 50 mg / L chitosan microemulsion treatment resulted in the highest weight loss rate, while the 100 mg / L and 400 mg / L treatments had the most significant effects, reducing the weight loss rate by 19.90% and 24.78% respectively compared to the control.

[0063] Depend on Figure 15 It can be seen that the cinnamon oil chitosan microemulsion treatment resulted in the lowest overall weight loss rate for sweet potatoes, followed by citral chitosan microemulsion and melaleuca chitosan microemulsion, while the chitosan microemulsion treatment resulted in the highest weight loss rate for sweet potatoes.

[0064] Among the microemulsions prepared by combining chitosan with cinnamon oil, tea tree oil, and citral, the citral-chitosan microemulsion showed the best antibacterial effect; while the cinnamon oil-chitosan microemulsion exhibited the best weight-loss inhibition effect in terms of preservation. All three microemulsions significantly inhibited the infection of sweet potato soft rot and reduced moisture evaporation, thus playing a preservative role.

[0065] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A preservative microemulsion for sweet potato characterized by comprising, Composed of the following components by mass percentage: Surfactant: 9%–39%; Co-surfactant: 9%–14%; Solvent: 7%–12%; Oil phase: 10%–13%; Chitosan: 2%–7%; Water: Balance.

2. A special preservative microemulsion for sweet potato as claimed in claim 1, characterized in that, The surfactant is Tween 80 and / or Span 80.

3. The special preservative microemulsion for sweet potato according to claim 2, characterized in that, The co-surfactant is any one of propylene glycol, ethanol, n-octanol, and polyethylene glycol.

4. The sweet potato special fresh-keeping microemulsion according to claim 3, characterized in that, The solvent is one or a combination of several esters or polar solvents.

5. The special preservative microemulsion for sweet potato according to claim 4, characterized in that, The oil phase is one or more of cinnamyl alcohol essential oil, tea tree essential oil, and citral essential oil.

6. The method for preparing the special fresh-keeping microemulsion for sweet potato according to any one of claims 1-5, characterized in that, The surfactant, co-surfactant, solvent, and oil phase are mixed in proportion, and an aqueous solution containing chitosan is slowly added while stirring. The mixture is stirred at 25°C for 10 minutes to convert the W / O type to the O / W type. The mixture is then cooled to room temperature to obtain the final product.

7. The use of a sweet potato-specific preservative microemulsion as described in any one of claims 1-5 for the preparation of sweet potato preservation products.

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