Methyl salicylate nanoemulsion as well as preparation method and application thereof

Abstract

The invention relates to a nano-emulsion, in particular to a methyl salicylate nano-emulsion as well as a preparation method and application thereof. The methyl salicylate nanoemulsion is prepared from methyl salicylate, a composite surfactant and water, wherein the composite surface active agent is prepared from Tween 80 and Span 80; the HLB (hydrophile-lipophile balance) value of the composite surfactant is 9-10; the mass fraction of methyl salicylate is 8%-12%. The methyl salicylate nano-emulsion not only can prolong the release time of methyl salicylate and effectively inhibit and delay germination of the potatoes in the storage and logistics processes, but also can reduce the nutrient loss of the potatoes and achieve a better fresh-keeping effect; furthermore, methyl salicylate is prepared into the form of methyl salicylate nanoemulsion, so that the use amount of essential oil is greatly reduced, the cost is reduced, and industrial popularization is facilitated.

Description

Technical Field

[0001] The invention relates to a nanoemulsion, in particular to a methyl salicylate nanoemulsion and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Potato (Solanum tuberosum L.), as one of the most important food and vegetable crops in the world, plays an important role in food supply around the world. Due to its rich nutritional value and high yield, potato plays a vital role in ensuring food security. However, the sprouting of potato tubers during storage can lead to quality degradation, affect nutritional value, and even cause storage losses. Therefore, controlling potato sprouting has become a key issue in storage technology.

[0004] At present, the widely used sprout inhibition methods in the potato storage process at home and abroad include the application of chemical sprout inhibitors and physical methods such as irradiation. Although physical methods such as irradiation are relatively environmentally friendly, their high equipment investment and operating costs, as well as limitations in technical operation and safety, have prevented this technology from being widely used. In terms of chemical sprout inhibitors, chlorpropamine (CIPC), as a commonly used plant growth regulator, is widely used due to its low cost and significant sprout inhibition effect. Chlorpropamine can play a good sprout inhibition effect when used during the dormant period, but the sprout inhibition effect of chlorpropamine on potatoes that have passed the dormant period is very poor. Moreover, chlorpropamine belongs to the herbicide class of pesticides, which has mutagenic and carcinogenic effects on humans and other animals, and its use will be gradually cancelled. The development of safe and efficient sprout inhibitor products for potatoes after dormancy release and storage is imminent.

[0005] Essential oils are volatile aromatic substances extracted from plants and have been found to have the potential to inhibit potato germination in recent years. Methyl salicylate (MeSA), the main component of wintergreen essential oil, has been reported to effectively inhibit potato germination. However, methyl salicylate is easily volatilized and lost during use, thereby affecting the durability of its germination inhibition effect. Moreover, due to its strong volatility, special conditions are also required to maintain its active ingredients during storage and transportation, which undoubtedly increases the cost and complexity of operation. In addition, the solubility of methyl salicylate is poor, which may limit its diffusion and range of action in potato tubers, resulting in uneven germination inhibition effect. Summary of the invention

[0006] In order to overcome the above problems, the present invention provides a methyl salicylate nanoemulsion and a preparation method and application thereof.

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

[0008] The first aspect of the present invention provides a methyl salicylate nanoemulsion, comprising methyl salicylate, a composite surfactant and water;

[0009] The composite surfactant includes Tween 80 and Span 80; the HLB value of the composite surfactant is 9 to 10;

[0010] The mass fraction of methyl salicylate is 8% to 12%.

[0011] In one or more embodiments, the particle size of the methyl salicylate nanoemulsion is 100-120 nm.

[0012] In one or more embodiments, the HLB value of the complex surfactant is 10, the mass fraction of the complex surfactant is 5%, and the mass fraction of methyl salicylate is 9.8%.

[0013] The second aspect of the present invention provides a method for preparing the methyl salicylate nanoemulsion according to the first aspect, comprising the following steps:

[0014] (1) mixing methyl salicylate, a composite surfactant and water and subjecting the mixture to shearing treatment to obtain a crude emulsion;

[0015] (2) The crude emulsion is subjected to ultrasonic treatment to obtain the methyl salicylate nanoemulsion.

[0016] In one or more embodiments, in step (1), during the shearing treatment, the shearing rate is 11000-13000 rpm, preferably 12000 rpm; the shearing time is 2.5-3.5 min, preferably 3 min.

[0017] In one or more embodiments, in step (2), during ultrasonic treatment, the ultrasonic rate is 300-500w, preferably 430w; the ultrasonic time is 3-5min, preferably 3.8min; and the ultrasonic interval time is 1.5-2.5s, preferably 2s.

[0018] The third aspect of the present invention provides use of the methyl salicylate nanoemulsion described in the first aspect as a potato sprout inhibitor.

[0019] In one or more embodiments, the potatoes are potatoes that have passed their dormancy period.

[0020] The fourth aspect of the present invention provides a potato sprout inhibitor, comprising the methyl salicylate nanoemulsion described in the first aspect.

[0021] A fifth aspect of the present invention provides a method for storing or transporting potatoes, comprising: applying the methyl salicylate nanoemulsion described in the first aspect to the surface of potatoes.

[0022] In one or more embodiments, the mass ratio of the potato weight to the methyl salicylate nanoparticles is 1:0.003-0.006, preferably 1:0.005.

[0023] The beneficial effects of the present invention are:

[0024] In order to solve the problem that methyl salicylate is easy to volatilize, has poor stability and poor solubility during use, the present invention provides a methyl salicylate nanoemulsion, which includes methyl salicylate, a composite surfactant and water; wherein the composite surfactant includes Tween 80 and Span 80; the HLB value of the composite surfactant is 9-10; and the mass fraction of methyl salicylate is 8%-12%. The methyl salicylate nanoemulsion can not only prolong the release time of methyl salicylate, effectively inhibit the germination of potatoes during storage and logistics, but also reduce the nutritional loss of potatoes and better achieve the preservation effect; furthermore, the preparation of methyl salicylate in the form of methyl salicylate nanoemulsion greatly reduces the amount of essential oil used, reduces the cost, and is easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0026] Figure 1 For the screening of surfactants, A is the appearance of the emulsions prepared by different surfactants; B is the particle size and PDI of the emulsions prepared by different surface activities; C is the Zeta potential of the emulsions prepared by different surface activities; D is the embedding rate of the emulsions prepared by different surface activities;

[0027] Figure 2 The influence of surfactants with different HLB values ​​on the emulsion; wherein A is the appearance of the emulsion prepared by the mixed surfactants with different HLB values, B is the particle size and Zeta potential of the emulsion prepared by the mixed surfactants with different HLB values; C is the embedding rate of the emulsion prepared by the mixed surfactants with different HLB values;

[0028] Figure 3 The effect of different surfactant concentrations on the emulsion; A is the appearance of the emulsion prepared with different surfactant concentrations; B is the particle size and Zeta potential of the emulsion prepared with different surfactant concentrations; C is the embedding rate of the emulsion prepared with different surfactant concentrations;

[0029] Figure 4 The effect of different MeSA concentrations on the emulsion; A is the appearance of the emulsion prepared with different MeSA concentrations; B is the particle size and Zeta potential of the emulsion prepared with different MeSA concentrations; C is the embedding rate of the emulsion prepared with different surfactant concentrations;

[0030] Figure 5 The effect of different ultrasonic powers on the emulsion; A is the appearance of the emulsion prepared with different ultrasonic powers; B is the particle size and Zeta potential of the emulsion prepared with different ultrasonic powers; C is the embedding rate of the emulsion prepared with different ultrasonic powers;

[0031] Figure 6 The effect of different ultrasonic time on the emulsion; A is the appearance of the emulsion prepared with different ultrasonic time; B is the particle size and Zeta potential of the emulsion prepared with different ultrasonic time; C is the embedding rate of the emulsion prepared with different ultrasonic time;

[0032] Figure 7 The three-dimensional response surface diagrams and two-dimensional isoline diagrams are the surfactant concentration and MeSA concentration (A, G), surfactant concentration and ultrasonic power (B, H), surfactant concentration and ultrasonic time (C, I), MeSA concentration and ultrasonic power (D, J), MeSA concentration and ultrasonic time (E, K), and ultrasonic power and ultrasonic time (F, L);

[0033] Figure 8 Fourier transform infrared spectrum (A) and rheological properties (B, C) of MeSA nanoemulsion;

[0034] Fig. 9 is the storage stability of MeSA nanoemulsion at different temperatures; A is the appearance of the emulsion after storage at different temperatures for 30 days; B is the particle size of the emulsion after storage at different temperatures; C is the Zeta potential of the emulsion after storage at different temperatures; D is the embedding rate of the emulsion after storage at different temperatures;

[0035] Fig.10 is the centrifugal stability of MeSA nanoemulsion; wherein A is the appearance of the emulsion at different centrifugal speeds; B is the particle size and Zeta potential of the emulsion at different centrifugal speeds; C is the embedding rate of the emulsion at different centrifugal speeds;

[0036] Fig.11 is the pH stability of MeSA nanoemulsion; wherein, A is the appearance of the emulsion at different pH; B is the particle size and Zeta potential of the emulsion at different pH; C is the embedding rate of the emulsion at different pH;

[0037] Fig.12is the sodium ion stability of MeSA nanoemulsion; wherein, A is the appearance of the emulsion at different sodium ion concentrations; B is the particle size and Zeta potential of the emulsion at different sodium ion concentrations; C is the embedding rate of the emulsion at different sodium ion concentrations;

[0038] Fig.13 Effects of different treatments (control, blank emulsion, MeSA fumigation and MeSA nanoemulsion) on potato tuber germination (A), germination rate (B) and germination index (C);

[0039] Fig.14 Effects of different treatments (control, blank emulsion, MeSA fumigation and MeSA nanoemulsion) on potato browning degree (A), total phenols (B), starch (C), reducing sugar (D), PPO activity (E) and POD activity (F). DETAILED DESCRIPTION

[0040] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0041] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0042] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0043] The concentrations in the following examples are by mass unless otherwise specified.

[0044] Example 1

[0045] Determination of the optimal preparation process conditions:

[0046] 1.1 Screening of surfactants: Six nonionic surfactants, including Tween 20, Tween 80, Span 20, Span 80, castor oil polyoxyethylene ether (CEL) and PEG 400, were selected to prepare methyl salicylate (MeSA) nanoemulsion, where the concentration of surfactant was 5%, the concentration of MeSA was 10%, and the rest was distilled water.

[0047] 1.2 Single factor experiment: The HLB values ​​of surfactants (8, 9, 10, 11, 12, 13, 14), the concentrations of surfactants (1%, 3%, 5%, 7% and 9%), the concentrations of methyl salicylate (4%, 6%, 8%, 10% and 12%), the ultrasonic powers (100W, 200W, 300W, 400W and 500W) and the ultrasonic times (1min, 2min, 3min, 4min and 5min) were selected for single factor experiments to determine the particle size, potential and embedding efficiency of the prepared emulsions. When the influence of one factor was investigated, the other conditions were as follows: the HLB value was 10, the concentration of surfactant was 5%, the concentration of methyl salicylate was 10%, the ultrasonic power was 400W, the ultrasonic time was 3min, and the ultrasonic interval time was 2s.

[0048] 1.3 Response surface experiment: Combined with the results of single factor experiment, the response surface methodology was used to optimize the particle size of MeSA nanoemulsion. The response surface Box-Behnken design was used. With the concentration of surfactant (A), essential oil concentration (B), ultrasonic power (C) and ultrasonic time (D) as factors and the particle size of nanoemulsion as the response value, a four-factor three-level response surface experiment was carried out. The coding of the influencing factors is shown in Table 1.

[0049] Table 1 Coding and levels of influencing factors

[0050]

[0051] 1.4 Determination of particle size, PDI and potential: The particle size, PDI and Zeta potential of the nanoemulsion were determined using a laser particle size analyzer. The sample was diluted 50 times before testing to avoid multiple scattering effects.

[0052] 1.5 Determination of embedding efficiency: Take 0.1 mL of emulsion, add 10 mL of 95% anhydrous ethanol, ultrasonicate for 5 min, take the supernatant to a 50 mL volumetric flask, dilute to an appropriate multiple, measure the absorbance at 309 nm, and calculate the MeSA content in the emulsion.

[0053] 1.6 Experimental results:

[0054] (1) Screening of surfactants:

[0055] from Figure 1 As can be seen from Figure A, using PEG 400 as a surfactant does not result in a stable MeSA emulsion. The emulsion aggregates, resulting in droplet breakage and obvious stratification. The emulsions prepared with Span 20 and Span 80 have the smallest particle size ( Figure 1 B), the emulsion has the best stability, followed by Tween 80; except for Tween 20, the particle sizes of other emulsions are all <200nm. Figure 1C shows that the potential values ​​of all emulsions are negative, which is due to the negative charge generated by the free anionic groups on the MeSA molecules and the nonionic surfactant at the oil-water interface. The absolute value of Zeta potential of the emulsion prepared by Span 20 is the highest, followed by Span 80, and the absolute value of potential is >30mV, indicating that the emulsion system is the most stable. The nanoemulsion prepared with Tween 80 and Span 80 has a smaller PDI value, indicating that the emulsion particle size distribution is concentrated and the uniformity is good. The prepared emulsion has the highest embedding rate ( Figure 1 D). After comprehensive consideration, Tween 80 and Span 80 were selected to prepare a mixed surfactant.

[0056] (2) Single factor experimental results:

[0057] HLB value of surfactant:

[0058] The emulsions made from mixed surfactants with different HLB values ​​did not experience demulsification ( Figure 2 A) By Figure 2 B shows that with the increase of HLB value, the particle size of the prepared emulsion shows a trend of decreasing first and then increasing. With the increase of Span 80 addition, the Zeta potential decreases significantly, and the effect of emulsifying MeSA is better. When the HLB value is 10, the particle size of the emulsion is the smallest and the absolute value of the potential is the largest, and the obtained emulsion is the most stable. Figure 2 As shown in Figure C, the embedding rate of MeSA nanoemulsion shows a significant upward trend with the increase of HLB value, and then slightly decreases and tends to be stable. When the HLB value is 10, the embedding rate of the emulsion is the largest, which is 89.38%. Therefore, the emulsion prepared by the mixed surfactant with an HLB value of 10 is better.

[0059] Surfactant concentration:

[0060] like Figure 3 As shown in A, the emulsions prepared by adding mixed surfactants of different concentrations are relatively stable and do not stratify. Figure 3 B It can be seen that the particle size of the MeSA nanoemulsion decreases significantly with the increase of the mixed surfactant concentration. When the surfactant concentration reaches 5%, the particle size is 112.28nm, the potential is -32.53mV, the interfacial tension drops to the minimum, and then increases. Too much surfactant will cause the particles to be too small and aggregate, and the particle size becomes larger. The embedding rate of the emulsion increases first and then stabilizes. Therefore, the MeSA nanoemulsion prepared with a surfactant concentration of 5% is better.

[0061] MeSA concentration:

[0062] As the concentration of MeSA increases, the appearance of the prepared emulsions has no significant difference and is stable and uniform. Figure 4As shown in B, when the MeSA concentration is 10%, the smallest particle size is 104.41nm, the largest potential absolute value is 33.77mV, and the embedding rate is the highest, indicating that under this condition, the mutual repulsion between particles is high and the stability is high. When the essential oil concentration increases further, the surfactant is difficult to embed the oil due to insufficient content, resulting in an increase in particle size and a larger potential. The embedding rate of the emulsion shows a trend of first increasing and then decreasing ( Figure 4 C), at a concentration of 10% MeSA, the emulsion had the highest encapsulation efficiency.

[0063] Ultrasonic power:

[0064] The particle size of the emulsion decreased significantly with the increase of ultrasonic power, and the smallest particle size and the largest absolute value of potential were obtained at 400 W ( Figure 5 B), then too high ultrasonic power will increase the number of collisions between the emulsion liquids, resulting in droplet breakage, reduced stability, and a decrease in the embedding rate ( Figure 5 C), therefore the emulsion prepared at an ultrasonic power of 400 W is optimal.

[0065] Ultrasound time:

[0066] There is no obvious difference in the appearance of the prepared emulsions with different ultrasonic times. Figure 6 B It can be seen that with the increase of ultrasonic time, the particle size and potential both show a trend of decreasing first and then increasing. When the ultrasonic time is 4 minutes, the particle size and potential are the smallest, and the encapsulation rate is the highest. If the ultrasonic time is too long, the mechanical energy is converted into thermal energy, resulting in an increase in the emulsion temperature, which destroys the interface film of the emulsion and reduces the stability, thus affecting the encapsulation effect of the emulsion on MeSA. Figure 6 As shown in C, the embedding rate was the highest when ultrasound was applied for 4 minutes.

[0067] (3) Response surface experiment results and analysis:

[0068] Combined with the results of the single factor test, a 4-factor 3-level response surface experimental design was adopted, with surfactant concentration (A), MeSA concentration (B), ultrasonic power (C), and ultrasonic time (D) as independent variables and the particle size of the emulsion (Y) as the response value, to optimize the experiment. The experimental design results are shown in Table 2. The obtained data were subjected to regression analysis using Design Expert 12 software, and the results are shown in Table 3.

[0069] Table 2 Experimental design results

[0070]

[0071] Table 3 Regression analysis

[0072]

[0073] As shown in Table 3, the model P < 0.0001, reaching an extremely significant level, and the difference in the lack of fit item was not significant P = 0.6439, indicating that the obtained model has a good fit. 2 =0.9947, R 2 Adj =0.9895, indicating that the model can represent 98.95% of the response value changes. The quadratic polynomial regression equation of Y and A, B, C, D: Y = 112.26-3.08A+0.7B-10.99C+10.1D+8.55AB+3.59AC-10.25AD+5.91BC-10.49BD-2.69CD+41.65A 2 +21.96B 2 +19.64C 2 +25.21D 2 . Linear terms C, D and quadratic term A 2 , B 2 , C 2 , D 2 It reached a very significant level (P<0.01). The influence of the four factors on the emulsion particle size was ranked as follows: C>D>A>B. The P values ​​of the interaction terms AB, AD, and BD were <0.01.

[0074] The interaction of each factor is analyzed according to the regression equation, and the response surface diagram and contour diagram of the interaction relationship of each factor are obtained, such as Figure 7 As shown. The steepness of the response surface is related to the degree of influence of each factor on the response value. The higher the slope of the curve in the 3D graph, the more significant the influence of the corresponding factor on the response value. The tendency of the contour map to an ellipse indicates that the interaction between the two factors is significant, and the tendency to a circle indicates that the interaction between the two factors is not significant. With the increase of surfactant concentration, MeSA concentration, ultrasonic power and ultrasonic time, the particle size of the emulsion first decreases and then gradually increases. The slope of the three-dimensional response surface diagram of BD is large, and the two-dimensional contour map is the most dense and tends to an ellipse, indicating that the interaction between MeSA concentration (B) and ultrasonic time (D) is the most significant. Similarly, the interaction of the above four factors has a significant effect on the particle size of the emulsion. The order of the interaction effect of each factor is: BD>AD>AB>BC>AC>CD. The interaction effect of ultrasonic power and ultrasonic time is the smallest.

[0075] Determination of the optimal preparation process conditions

[0076] The optimal preparation process conditions of the obtained response surface are: surfactant concentration 5.020%, MeSA concentration 9.792%, ultrasonic power 428.03W, ultrasonic time 3.795min, under which the theoretical prediction value of the emulsion particle size is 109.63nm. According to the actual situation, the conditions are adjusted to surfactant concentration of 5%, MeSA concentration of 9.8%, ultrasonic power 430W, and ultrasonic time 3.8min. Under this condition, the experiment was repeated three times for verification, and the particle size of the prepared emulsion was measured to be 110.12nm, which is close to the predicted value and within the confidence interval. Therefore, the particle size regression model of the obtained MeSA nanoemulsion is reliable.

[0077] Example 2

[0078] The MeSA nanoemulsion prepared under the optimal preparation process conditions in Example 1 was characterized:

[0079] 2.1 Fourier transform infrared spectroscopy (FTIR) of emulsions: The molecular structures of MeSA, blank emulsions and MeSA nanoemulsions were characterized by FTIR spectroscopy in the spectral range of 4000–400 cm -1 , resolution 4cm -1 .

[0080] 2.2 Rheological properties of the emulsion: The PP50 parallel plate geometry measurement system was used, with the gap size set to 1 mm, the frequency set to 1 Hz, and the measurement temperature set to 25 °C. The strain range of 0.01% to 100% was scanned to determine the linear viscoelastic range of the emulsion. Within the measured linear viscoelastic range, dynamic frequency sweep measurements were performed at an angular frequency of 1-10 rad / s and at a frequency of 0.1 to 100 s. -1 The shear rate is used to measure the viscosity of the emulsion.

[0081] 2.3 Determination of storage stability of emulsion: The emulsion was stored at 0°C, 4°C, 15°C, 25°C and 37°C, and the particle size, potential and embedding efficiency of the emulsion were measured every 5 days for 30 consecutive days.

[0082] 2.4 Determination of centrifugal stability of emulsion: The emulsion was centrifuged at 3000 rpm, 6000 rpm, 9000 rpm and 12000 rpm for 20 min respectively, and its particle size, potential and embedding rate were measured, and the flocculation and sedimentation were observed.

[0083] 2.5 Determination of pH stability of emulsion: After adjusting the pH of the emulsion to 3, 5, 7, 9 and 11 with 1 mol / L citric acid and 1 mol / L sodium hydroxide, store it at room temperature for 24 h, record the appearance changes, and determine the particle size, potential and embedding efficiency of the emulsion.

[0084] 2.6 Determination of sodium ion stability of emulsion: NaCl solution of different concentrations was added to the same volume of nanoemulsion, and NaCl was adjusted to 50, 100, 200, 300, 400 and 500 mmol / L, and the particle size, potential and embedding rate were determined.

[0085] Experimental results:

[0086] (1) Fourier transform infrared spectroscopy:

[0087] The FTIR results of MeSA, blank emulsion and MeSA nanoemulsion are shown in Figure 2. Figure 8 As shown in A. 3100~3400cm -1 The peaks in the range represent the stretching vibration of -OH. MeSA at 2950cm -1 The characteristic peaks that appear are related to the stretching vibration of the CH bond of the methyl group, which is at 1672 cm -1 The peak at represents the stretching vibration of C=O. The peak of C=O in MeSA nanoemulsion moves to 1676 cm -1 , and the peak value is reduced. In MeSA and MeSA nanoemulsion, 1088cm -1 and 1090cm -1 The peak at 1584 cm represents the symmetric stretching vibration of COC; -1 and 1585cm -1 The peak at represents the vibration of the carbon-carbon double bond on the benzene ring, indicating that the MeSA nanoemulsion successfully emulsified and encapsulated MeSA.

[0088] (2) Rheological properties of emulsion:

[0089] The processing and application of emulsions are inseparable from their rheological properties. Rheological properties are one of the main indicators to characterize the flow behavior of emulsions. Figure 8 B shows that as the shear rate increases, the viscosity of all emulsions gradually decreases, showing similar shear-thinning rheological behavior, and can be used for spraying. When the shear rate continues to increase, the viscosity approaches 0, which indicates that a higher shear rate will destroy the internal structure of the emulsion, and the droplets need to rearrange to reach a new stable state. Figure 8 C shows that the storage modulus G' and loss modulus G" of all emulsions increase with the increase of frequency. The larger the oscillation frequency, the larger G', and the emulsion is a pure fluid. G'>G" This indicates that the interaction between the emulsion droplets is enhanced, forming a stable network structure.

[0090] Storage stability of emulsion:

[0091] Good storage stability of emulsion is the basic premise for its application. Fig. 9As shown in Figure A, at different temperatures, the appearance of the emulsion did not change significantly after storage for 30 days. The emulsion still showed good stability and no stratification occurred. The particle size of the emulsion at different temperatures increased slightly with the extension of storage time. The higher the temperature, the more significant the change. The increase in temperature increases the kinetic energy of the droplets, promotes the movement, collision and coalescence of the droplets, and thus increases the droplet size. The absolute value of the potential of the emulsion is greater than 25mV ( Fig. 9 C), in a stable state. As the temperature rises, the longer the storage time, the more significantly the embedding rate of MeSA in the emulsion decreases. Therefore, low temperature can effectively maintain the embedding rate of MeSA in the emulsion and maintain good stability.

[0092] Centrifugal stability of emulsions:

[0093] After the MeSA nanoemulsion was centrifuged at different speeds for 20 minutes, the effect of the centrifugal treatment on the emulsion was equivalent to the effect of the MeSA nanoemulsion droplets being naturally left to stand and settle for a certain period of time under the action of gravity. Fig.10 As shown in A, with the increase of centrifugal speed, the emulsion did not stratify. By measuring the particle size of the emulsion before and after centrifugation, it can be seen that the potential of the emulsion increases slightly just after centrifugation. It may be that the centrifugal force causes the emulsion to slightly aggregate. The particle size of the emulsion does not change much compared with that before centrifugation, indicating that the emulsion has good anti-centrifugal stability. Fig.10 C shows that the centrifugal rate has no significant effect on the final MeSA encapsulation rate of the emulsion.

[0094] pH stability of emulsion:

[0095] The emulsion will be affected by the environment during preparation and use. External factors will lead to different pH environments. Therefore, it is necessary to study the effects of different pH values ​​on MeSA nanoemulsion. The original pH value of MeSA nanoemulsion is 5.9. Fig.11 As shown in B, when the pH value is in the range of 3 to 11, the hydrogen ion content in the emulsion decreases, the absolute value of the Zeta potential decreases significantly, and the particle size increases. In the lower pH range, due to the large amount of charge between the droplets, the strong electrostatic repulsion makes the droplets have a strong repulsiveness. The embedding rate of the emulsion does not change significantly with the increase of pH value in the early stage, but decreases significantly in a weak alkaline environment. This shows that the MeSA nanoemulsion is more stable in a slightly acidic environment and unstable in a weak alkaline environment.

[0096] Sodium ion stability of emulsion:

[0097] The NaCl content in different food systems is different. Fig.12It can be seen that after adding NaCl, the apparent state of the nanoemulsion did not change. The particle size of the nanoemulsion tended to increase, and the absolute value of the nanoemulsion potential decreased with the increase of the NaCl content in the nanoemulsion. This may be because the electrostatic repulsion between droplets was strong, and NaCl could destroy the stability of the emulsion by weakening the electrostatic repulsion, but did not cause the emulsion to delaminate. The encapsulation rate of the emulsion decreased with the increase of the NaCl concentration, which may be due to the fact that after the stability of the emulsion decreased, the encapsulated MeSA was easily released from it, resulting in the decrease of the encapsulation rate.

[0098] Example 3

[0099] 3.1 Application of the emulsion in potato bud inhibition: Select potatoes that have passed the dormancy period, are free of mechanical damage, pests, diseases and rot, wash them with clean water and dry them for later use. Divide them into four treatment groups: control group, blank emulsion, MeSA fumigation, and MeSA nanoemulsion. The MeSA fumigation concentration was 50 μL / L. Drop MeSA on filter paper and stick it on a plastic basket for airtight fumigation. The treatment concentration was calculated according to the volume of the basket. For the blank emulsion and MeSA nanoemulsion treatment groups, 5 mL of the emulsion was sprayed per 1 kg of potatoes, and after drying, they were put into plastic baskets. Store them at room temperature (25 °C) for 16 d, observe the bud inhibition effect every 4 d, and take samples to measure the quality indexes.

[0100] 3.2 Germination rate and germination index: Randomly select 5 potatoes for each treatment, record the number of buds on each tuber and measure the length of the longest bud with a vernier caliper, and take the average value. The bud length was divided into 8 levels. When the bud length was less than 2 mm, it was regarded as not germinated or in the germinating state and was determined as not germinated. When the potato germinated to a length of ≥2 mm, it was regarded as germinated. The grading standard for potato tuber germination was: level 0 (0 < L ≤ 2); level 1 (2 < L ≤ 5); level 2 (5 < L ≤ 10); level 3 (10 < L ≤ 15); level 4 (15 < L ≤ 20); level 5 (20 < L ≤ 25); level 6 (25 < L ≤ 30); level 7 (L ≥ 30) (L: bud length / mm). Calculate the germination rate and germination index according to the following formulas:

[0101]

[0102] 3.3 Determination of browning degree content: Randomly weigh 2.0 g of potato samples into a mortar, add 20 mL of distilled water, grind them into a homogenate in an ice bath, transfer them to a centrifuge tube and centrifuge at 10000 r / min for 5 min. Take the supernatant and keep it warm in a water bath at 25 °C for 5 min. Measure the absorbance at 410 nm using a spectrophotometer. The browning degree is expressed as A 410 ×10.

[0103] 3.4 Determination of total phenol content: Take 2g of ground sample, extract with 5mL cold ethanol, place in a refrigerator at 4℃ overnight, centrifuge at 12000rpm, take 0.5mL supernatant and mix with 1.5mL distilled water, 1mL Folin phenol reagent and 1mL 7.5% anhydrous sodium carbonate solution, incubate at 25℃ for 2h. Determine the absorbance value of the reaction solution at a wavelength of 765nm, and the result is calculated as gallic acid.

[0104] 3.5 Determination of starch content: The starch content was determined by iodine-starch colorimetry. Weigh 1.0 g of frozen potato sample, add 20 mL of petroleum ether and ethanol, grind thoroughly and filter. Then place the filter residue in a boiling water bath and heat and stir until all the starch is gelatinized into a transparent solution. Prepare the starch extract and then perform colorimetric analysis.

[0105] 3.6 Determination of reducing sugar content: Weigh 1.0 g of sample and fix it to 25 mL with distilled water. After mixing, extract the sample in a water bath at 80°C for 30 min, then take it out and cool it to room temperature. Centrifuge the filtrate at 12000 rpm for 10 min and transfer it to a 100 mL container to a constant volume. Measure the absorbance of the solution at 540 nm.

[0106] 3.7 Determination of polyphenol oxidase (PPO) content: Add 5.0 mL of extraction buffer (containing 1 mmol polyethylene glycol, 4% polyvinyl polypyrrolidone and 1% Triton X-100) to 2 g of ground sample, mix well, and centrifuge at 12000 rpm for 20 min at 4 ° C. Collect the supernatant as the enzyme extract and store it at low temperature. Mix 100 μL of enzyme extract with 4 mL of 50 mmol / L acetic acid and sodium acetate buffer and 1 mL of 50 mmol / L catechol solution. Use a spectrophotometer to immediately measure the absorbance value at a wavelength of 398 nm and record the reading for 2 minutes. The absorbance change of 0.01 per gram of sample per minute is taken as an enzyme activity unit.

[0107] 3.8 Determination of peroxidase (POD) content: The enzyme extract was the same as that for PPO. 1 mL of the enzyme extract was mixed with 0.1 mL of 25 mmol / L guaiacol solution and 2.0 mL of 50 mmol / L acetic acid-sodium acetate buffer, and then 0.1 mL of 0.5 mol / L H 2 O 2 The solution was added to start the reaction. The absorbance was measured at 460 nm and the reading was recorded for 2 min. The change of 0.01 absorbance per gram of sample per minute was regarded as one unit of enzyme activity.

[0108] Experimental results:

[0109] Effect of MeSA nanoemulsion on potato germination stored at room temperature:

[0110] like Fig.13 As shown in A, the potato tubers in the control group began to germinate at 4 days of storage. In the later stage, the buds gradually became longer, the terminal buds were severely divided and clustered. The blank emulsion treatment group also began to germinate on the 4th day, and its germination rate and germination index were not significantly different from those of the control group. The MeSA fumigation concentration was 50μL / L, which was the same as the effective concentration of MeSA applied to potatoes in the MeSA nanoemulsion, and was only half of the previous effective dose of MeSA direct fumigation (100μL / L). Under the same storage conditions, the inhibitory effect of the MeSA nanoemulsion treatment group on potato germination was significantly better than that of MeSA direct fumigation. The bud tips of the potato tubers in the MeSA nanoemulsion treatment group turned black and showed bud necrosis. After 16 days of storage, the germination rate was only 20.95%, while the other treatment groups reached 100%. After 16 days of storage at room temperature, the germination index of the MeSA nanoemulsion treatment group was only 10.48%, while that of the CK group was 44.76% ( Fig.13 C). The results showed that the emulsion prepared under the optimal response surface conditions could effectively delay the germination of potato tubers by 9 days (Table 4), maintaining the germination rate and germination index at a low level; secondly, after the preparation of MeSA nanoemulsion, the amount of MeSA used to treat each kilogram of potato tubers could be reduced by 50%, achieving the purpose of reducing the amount and increasing the efficiency.

[0111] Table 4 Germination rate and germination index

[0112]

[0113] Effect of MeSA nanoemulsion on browning degree of potatoes stored at room temperature:

[0114] Effects of different treatments on the browning degree of potatoes Fig.14 As shown in A. Under different treatments, the browning degree of all potato tubers showed an increasing trend with time. The CK group increased significantly in the first 4 days, and then the blank emulsion increased significantly. At the end of storage (16 days), the browning degrees of the CK group, blank emulsion group, MeSA fumigation group and MeSA nanoemulsion treatment group were 2.91, 2.90, 2.63 and 2.39, respectively. Compared with the CK group, the MeSA nanoemulsion treatment group can significantly reduce the browning of potatoes.

[0115] Effect of MeSA nanoemulsion on total phenolic content of potatoes stored at room temperature:

[0116] A large number of phenolic substances exist in fruit and vegetable tissues. They are closely related to the appearance, flavor formation, maturation and aging process, health status and tissue browning of fruits and vegetables. They are an important substance in fruit and vegetable tissues. Fig.14B shows that during the storage process, the total phenol content of potato tubers in the CK group showed a trend of first decreasing and then increasing, reaching the highest value of 1.44 mg GAE g at the end of storage. -1 The total phenol content in the MeSA nanoemulsion treatment group was 1.18 mg GAE g -1 , indicating that potato germination is accompanied by an increase in total phenolic content, and MeSA emulsion treatment can inhibit the increase of total phenolic content in tubers.

[0117] Effect of MeSA nanoemulsion on starch content of potatoes stored at room temperature:

[0118] Starch is the main storage carbohydrate in potato tubers and is also the component of most of the dry matter in potato tubers. Starch content is usually used as an important indicator to evaluate the storage quality of potatoes. Fig.14 As shown in Figure C, the starch content of all treatment groups showed a downward trend during storage. The starch content of the CK group was the lowest, reaching 11.76% at the end of storage. The CK group decreased rapidly in the first 8 days of storage, from 24.54% to 12.57%, when the potato tubers were in the budding stage. The starch content of the MeSA nanoemulsion treatment group was 17.04% at the end of storage, which effectively delayed the decline of starch content and maintained the good quality and commercial value of potatoes.

[0119] Effect of MeSA nanoemulsion on reducing sugar content of potatoes stored at room temperature:

[0120] Reducing sugar content is an important indicator for measuring the storage quality of potato tubers. Changes in the balance between starch and sugar metabolism cause abnormal accumulation of reducing sugars, leading to the Maillard reaction and the production of bitter brown substances, which will affect the color and quality of potatoes after frying. Fig.14 D shows that the reducing sugar content of all treatment groups decreased rapidly with the extension of storage time. The reducing sugar content of the MeSA nanoemulsion treatment group was 0.56% in the late storage period. During the entire storage period, the reducing sugar content of the MeSA nanoemulsion treatment group was always higher than that of the control group. On the 16th day, it was 0.19% higher than that of the control group. This shows that the MeSA nanoemulsion treatment group inhibited the decline of reducing sugar content.

[0121] Effect of MeSA nanoemulsion on PPO activity of potatoes stored at room temperature:

[0122] PPO catalyzes phenolic substances to form quinones in the presence of oxygen, and quinones further react to form melanoidins, the final product of browning, leading to browning of potatoes. Fig.14As shown in Figure E, with the extension of storage time, the PPO activity of potatoes in each treatment group showed an upward trend. The MeSA nanoemulsion treatment group could significantly inhibit the enhancement of potato PPO activity. On the 16th day of storage, it was 31.43% lower than that of the control group, which significantly inhibited enzymatic browning and reduced the nutritional loss of potatoes caused by browning.

[0123] Effect of MeSA nanoemulsion on POD activity of potatoes stored at room temperature:

[0124] POD is closely related to plant metabolism. POD has dual characteristics. It can participate in the production of reactive oxygen species and can also act as a protective enzyme in plants, promoting the decomposition of highly oxidizing substances accumulated in tissues, thereby reducing oxidative damage. Fig.14 As shown in Figure F, with the extension of storage time, the POD activity of each treatment group showed a trend of first decreasing and then increasing. The MeSA nanoemulsion treatment group could effectively inhibit the increase of potato POD activity, thereby delaying potato senescence and achieving a better preservation effect.

[0125] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A methyl salicylate nanoemulsion, characterized in that: Includes methyl salicylate, complex surfactants and water; The composite surfactant includes Tween 80 and Span 80; the HLB value of the composite surfactant is 9 to 10; The mass fraction of methyl salicylate is 8% to 12%.

2. The methyl salicylate nanoemulsion according to claim 1, characterized in that The particle size of the methyl salicylate nanoemulsion is 100-120 nm.

3. The methyl salicylate nanoemulsion according to claim 1, characterized in that The HLB value of the composite surfactant is 10, the mass fraction of the composite surfactant is 5%, and the mass fraction of methyl salicylate is 9.8%.

4. The method for preparing the methyl salicylate nanoemulsion according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) mixing methyl salicylate, a composite surfactant and water and subjecting the mixture to shearing treatment to obtain a crude emulsion; (2) The crude emulsion is subjected to ultrasonic treatment to obtain the methyl salicylate nanoemulsion.

5. The preparation method according to claim 4, characterized in that: In step (1), during the shearing treatment, the shearing rate is 11000-13000 rpm, preferably 12000 rpm; the shearing time is 2.5-3.5 min, preferably 3 min.

6. The preparation method according to claim 4, characterized in that: In step (2), during ultrasonic treatment, the ultrasonic rate is 300-500w, preferably 430w; the ultrasonic time is 3-5min, preferably 3.8min; and the ultrasonic interval time is 1.5-2.5s, preferably 2s.

7. Use of the methyl salicylate nanoemulsion according to any one of claims 1 to 3 as a potato sprout inhibitor.

8. The use according to claim 7, characterized in that The potatoes are potatoes that have passed their dormancy period.

9. A potato sprout inhibitor, characterized in that: The invention comprises the methyl salicylate nanoemulsion according to any one of claims 1 to 3.

10. A method for storing or transporting potatoes, characterized in that include: The methyl salicylate nanoemulsion according to any one of claims 1 to 3 is applied to the surface of potatoes.

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