Vanillin deep eutectic reagent / chitosan coating preservative as well as preparation method and application thereof

Abstract

The invention discloses a vanillin deep eutectic reagent / chitosan coating preservative as well as a preparation method and application thereof, and belongs to the technical field of food preservatives. The vanillin deep eutectic reagent / chitosan composite coating preservative is prepared from the following raw materials in parts by mass: 1 to 9 parts of vanillin deep eutectic reagent and 10 parts of chitosan. Or 2-6 parts by mass of a film-forming agent. The vanillin deep eutectic reagent / chitosan membrane liquid or the vanillin deep eutectic reagent / chitosan membrane prepared by the invention has the technical effects of resisting microorganisms and oxidation. The liquid film can play a fresh-keeping effect on the fresh fruits through an anti-oxidation and anti-microbial mechanism so as to prolong the shelf life. And the shelf life of the food is prolonged in a film-covering and vacuumizing mode on the fresh fruits. The raw materials are natural, safe, environment-friendly, low in price and easy to obtain, the preparation process is simple and convenient, and the potential value of large-scale production and market application is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of food preservatives, and specifically relates to a chitosan coating preservative using a vanillin deep eutectic reagent as a natural plasticizer, and a preparation method and application thereof. Background Art

[0002] Chitosan, as a degradable biopolymer, is safe and edible, has good film-forming and antibacterial properties, and can selectively permeate oxygen, carbon dioxide, and ethylene gases by forming a semipermeable membrane on the surface of fruits and vegetables, inhibit the respiration intensity of fruits and vegetables, regulate the physiological metabolism of fruits and vegetables after harvest, and inhibit many microorganisms to prevent fruits and vegetables from rotting and deteriorating, thereby achieving the effect of preserving fruits and vegetables. It is often prepared with antioxidant functional molecules such as tea polyphenols and citric acid as a composite coating preservative for use in agricultural product preservation. However, the mechanical properties and moisture resistance of pure chitosan film are relatively poor, and the film is hard and brittle, which affects the preservation effect. The common method is to add plasticizers such as glycerol, sorbitol, and even polyvinyl alcohol and polyethylene glycol to optimize its film-forming properties, but these plasticizers have hidden dangers such as safety, pollution, and reduced antibacterial effect. Therefore, it is of great significance to develop a green, safe, natural source plasticizer that can be designed to solve the problem of food preservation and optimize chitosan coating preparations.

[0003] Deep Eutectic Mixture (DEM) is formed by hydrogen bond acceptor (HBA) compounds and hydrogen bond donor (HBD) compounds according to the molar ratio through hydrogen bonding. By screening HBD, functional deep eutectic agents (DEA) with choline chloride (ChCl) as HBA are obtained. This type of DEA has function-oriented design and can specifically solve the preservation problems of different types of food.

[0004] The present invention provides a type of chitosan composite coating preservative prepared by using ChCl as HBA and deep eutectic agents (Deep Eutectic Agents DEA) as plasticizer, namely DEA-chitosan composite coating preservative. The prepared natural DEA with antioxidant and antimicrobial activity from animal and plant sources is used as a plasticizer and functional molecule to prepare a DEA-chitosan composite film with chitosan, which is applied to the preservation of foods such as lychees and tomatoes, thereby enhancing the film-forming mechanical properties, further improving the preservation effect of chitosan through antioxidant and antimicrobial mechanisms, extending the shelf life of food, and reducing safety and pollution hazards. Summary of the invention

[0005] Compared with the prior art, the purpose of the present invention is to provide a chitosan coating preservative with vanillin deep eutectic reagent as a natural plasticizer, and a preparation method and application thereof.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] On the one hand, the present invention provides a vanillin deep eutectic reagent / chitosan coating preservative, comprising the following raw materials in parts by weight: 1 to 9 parts of vanillin deep eutectic reagent and 10 parts of chitosan.

[0008] The vanillin deep eutectic reagent / chitosan coating preservative further comprises 2 to 6 parts by weight of a film-forming agent.

[0009] In a second aspect, the present invention provides a method for preparing the vanillin deep eutectic reagent / chitosan coating preservative, comprising the following steps:

[0010] (1) Weighing vanillin and choline chloride, mixing, and stirring while heating until clear and homogeneous to obtain a vanillin deep eutectic reagent;

[0011] (2) weighing chitosan, dissolving it in an acetic acid aqueous solution, heating and stirring until completely dissolved, adding a vanillin deep eutectic reagent, and continuing to stir after heating to obtain a vanillin deep eutectic reagent / chitosan film solution;

[0012] Optionally, (3) is evenly spread on a glass plate and dried to obtain a vanillin deep eutectic reagent / chitosan film preservative.

[0013] In a third aspect, the present invention provides a method for preparing the vanillin deep eutectic reagent / chitosan coating preservative, characterized in that it comprises the following steps:

[0014] (1) Weighing vanillin and choline chloride, mixing, and stirring while heating until clear and homogeneous to obtain a vanillin deep eutectic reagent;

[0015] (2) weighing chitosan, dissolving it in an acetic acid aqueous solution, heating and stirring until completely dissolved, adding a vanillin deep eutectic reagent, and continuing to stir after heating to obtain a vanillin deep eutectic reagent / chitosan film solution;

[0016] (3) adding a film-forming agent, stirring and dissolving after continuous heating, stopping stirring after the reaction is completed, cooling to room temperature, and obtaining a vanillin deep eutectic reagent / chitosan composite film solution;

[0017] Optionally, (4) is evenly spread on a glass plate and dried to obtain a vanillin deep eutectic reagent / chitosan film composite preservative.

[0018] The method for preparing a vanillin deep eutectic reagent / chitosan coating preservative, wherein the molar ratio of vanillin to choline chloride in step (1) is (1-5):(1-3);

[0019] The heating is to a temperature of 60-100°C.

[0020] The preparation method of the vanillin deep eutectic reagent / chitosan coating preservative, the conditions for continuing stirring after heating in step (2) are: temperature 50-100° C., time 0.5-5 hours;

[0021] The mass ratio of V-DEA to chitosan is (1-9):10;

[0022] The concentration of the acetic acid aqueous solution is 1-3%.

[0023] In the method for preparing the vanillin deep eutectic reagent / chitosan coating preservative, the film-forming agent in step (3) is polyvinyl alcohol, cyclodextrin, hydrolyzed starch, citrate or glycerol.

[0024] The choice of film-forming agent is changed according to the preservation needs of various foods; the addition of polyvinyl alcohol film-forming agent can further enhance the mechanical strength of the film while also improving its wettability; glycerol as a plasticizer greatly improves the flexibility of the cling film; cyclodextrin and citrate esters greatly improve the mechanical properties of the cling film and exhibit certain moisture resistance.

[0025] The method for preparing a vanillin deep eutectic reagent / chitosan coating preservative, wherein the step (3) is to continuously heat to 80-100° C.;

[0026] The stirring and dissolving reaction time is 2 to 5 hours;

[0027] The mass ratio of the film-forming agent to chitosan is (2-6):10.

[0028] In a fourth aspect, the present invention provides a use of the vanillin deep eutectic reagent / chitosan coating preservative in preserving fresh fruits or vegetables.

[0029] In the application, the fresh fruit is lychee, longan, tomato, cherry tomato, strawberry, cherry, citrus, pomelo or grape.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The vanillin deep eutectic reagent / chitosan film liquid (two types, the raw materials contain or do not contain a film-forming agent) and the vanillin deep eutectic reagent / chitosan film (two types, the raw materials contain or do not contain a film-forming agent) prepared by the present invention have antimicrobial and antioxidant technical effects. Among them, the vanillin deep eutectic reagent / chitosan film liquid can have a preservation effect on lychee, longan, tomato, grape and other fruits through antioxidant and antimicrobial mechanisms at a relatively low concentration to extend the shelf life. The vanillin deep eutectic reagent / chitosan film extends the shelf life of lychee, longan, tomato, grape and the like by coating and vacuuming. The raw materials of the present invention are natural, safe and environmentally friendly, low-priced and easily available, and the preparation process is simple and convenient. It has the potential value of large-scale production and market application. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The preparation diagram of V-DEA / chitosan membrane and membrane solution;

[0033] Figure 2 It is a comparison chart of H NMR spectra of 0%-80% vanillin DEA / chitosan film and vanillin DEA;

[0034] Figure 3 Thermogravimetric analysis of vanillin DEA / chitosan films with different percentages;

[0035] Figure 4 The cross-sectional SEM images of vanillin DEA / chitosan films with different percentages are shown;

[0036] Figure 5 is the transmittance of V-DEA / chitosan films with different ratios at 600nm wavelength;

[0037] Figure 6 is the water vapor transmission rate of V-DEA / chitosan membranes with different ratios;

[0038] Figure 7 The tensile strength and elongation at break results of V-DEA / chitosan films with different ratios;

[0039] Figure 8 The half-inhibition activity of V-DEA / chitosan films with different ratios on DPPH and ABTs free radicals;

[0040] Fig. 9 The inhibitory activity of V-DEA / chitosan films with different ratios against Staphylococcus aureus and Escherichia coli;

[0041] Fig.10The figure is a graph showing the preservation effect of 80% V-DEA / chitosan membrane solution on the lychee of Guiwei variety, wherein T1 is a deionized water immersion treatment group; T2 is a 1mL / L 80% V-DEA / chitosan membrane solution aqueous solution immersion treatment group; T3 is a 2mL / L 80% V-DEA / chitosan membrane solution aqueous solution immersion treatment group; T4 is a 4mL / L 80% V-DEA / chitosan membrane solution aqueous solution immersion treatment group; T5 is a 6mL / L 80% V-DEA / chitosan membrane solution aqueous solution immersion treatment group; T6 is a 4mL / L 0% V-DEA / chitosan membrane solution aqueous solution immersion treatment group;

[0042] Fig.11 This is a graph showing the daily weight loss changes of fresh litchi fruit;

[0043] Fig.12 This is a diagram showing the browning changes in the skin of fresh lychee fruit;

[0044] Fig.13 The soluble solid content TSS of fresh litchi fruit pulp after 6 days of preservation treatment;

[0045] Fig.14 To measure the vitamin C content in fresh litchi pulp after 6 days of preservation treatment;

[0046] Fig.15 For preservation purposes, the acidity of fresh lychee fruit pulp can be titrated after 6 days of treatment;

[0047] Fig.16 The relative permeability of electrolytes in the peel of fresh litchi fruit after 6 days of preservation treatment;

[0048] Fig.17 The content of malondialdehyde in the peel of fresh litchi fruit after 6 days of preservation treatment;

[0049] Fig.18 Total quinone content in the peel of fresh litchi fruit after 6 days of preservation treatment. DETAILED DESCRIPTION

[0050] The present invention will be further described below by means of drawings and embodiments.

[0051] Embodiment 1:

[0052] 1. Preparation of V-DEA:

[0053] Weigh 4.56 g of vanillin and 1.40 g of choline chloride (vanillin to choline chloride in a molar ratio of 3:1), mix and add into a round-bottom flask with a mechanical stirrer, heat to 70°C while stirring, continue stirring for 30 minutes, the solid gradually turns into a clear homogeneous liquid, stop stirring, transfer while hot, cool to room temperature, and obtain 5.96 g of white solid, i.e., vanillin deep eutectic reagent (abbreviated as V-DEA).

[0054] 2. Preparation of V-DEA / chitosan coating preservative

[0055] 5 g of chitosan was dissolved in 1.5% acetic acid aqueous solution, heated to 60°C and stirred for 2 hours until completely dissolved, 0 g of the above-prepared V-DEA was added, heated to 70°C and stirred for 2 hours to obtain a yellow liquid, that is, a V-DEA / chitosan film liquid preservative with a mass ratio of V-DEA to chitosan of 0% was obtained, as shown in the physical picture. Figure 1 . Evenly spread on a glass plate, and bake at 30-60°C for 6-12 hours to obtain a yellow chitosan film with a vanilla aroma and a mass ratio of V-DEA to chitosan of 0%, such as Figure 1 shown.

[0056] Embodiment 2:

[0057] The steps for preparing the V-DEA / chitosan composite coating preservative were the same as those in Example 1, except that 0 g of the V-DEA prepared above was added instead of 1 g of V-DEA. Finally, a 20% V-DEA / chitosan coating preservative was prepared.

[0058] Embodiment 3:

[0059] The steps for preparing the V-DEA / chitosan composite coating preservative were the same as those in Example 1, except that 2 g of V-DEA was added instead of 0 g of the V-DEA prepared above, and finally a 40% V-DEA / chitosan coating preservative was prepared.

[0060] Embodiment 4:

[0061] The steps for preparing the V-DEA / chitosan composite coating preservative were the same as those in Example 1, except that 3 g of V-DEA was added instead of 0 g of the V-DEA prepared above, and finally a 60% V-DEA / chitosan coating preservative was prepared.

[0062] Embodiment 5:

[0063] The steps for preparing the V-DEA / chitosan composite coating preservative were the same as those in Example 1, except that 4 g of V-DEA was added instead of 0 g of the V-DEA prepared above, and finally an 80% V-DEA / chitosan coating preservative was prepared.

[0064] The comparison of H NMR spectra of 0%, 20%, 40%, 60%, 80% vanillin DEA / chitosan films and pure vanillin DEA prepared in Examples 1-5 is shown in the figure below: Figure 2As shown. Among them, V-DEA is vanillin DEA, and 80%-0% is 80%-0% vanillin DEA / chitosan film. It can be seen that, relative to vanillin DEA, all vanillin DEA / chitosan films have both chitosan peaks and vanillin and choline peaks in the H-NMR spectra. It is worth noting that, relative to the H-NMR spectrum of vanillin DEA, the peaks of vanillin and choline have undergone chemical shift changes in the membrane solution, all moving to the high field, indicating that chitosan and vanillin DEA reagents have been successfully grafted, most likely in the form of Schiff bases formed between vanillin and the amino groups of chitosan.

[0065] Thermo Gravimetric Analysis (TGA) was used to characterize the chitosan films with five concentrations of 0%, 20%, 40%, 60% and 80% vanillin DEA prepared in Examples 1-5, and the thermodynamic stability of the chitosan films with five different concentrations of vanillin DEA was analyzed. Figure 3 As shown in the figure, there are two weight loss stages at 0% mass concentration. The first stage of weight loss is caused by the release of water from chitosan itself and the crystal water in chitosan. The second stage of weight loss is caused by the main chain of chitosan starting to decompose under heat and oxidation. From the TGA curves of each concentration, it can be seen that the thermal decomposition temperature (Td, equivalent to the temperature at which the thermal weight loss is 5%) of the five concentrations of vanillin DEA chitosan film of 0%, 20%, 40%, 60% and 80% is all around 55°C. The water content of the 20% vanillin DEA / chitosan film is relatively high, and the decomposition of DEA makes the weight loss most obvious at 55°C; the weight loss of chitosan at 250°C is also more obvious than that of 0%, indicating that its stability is also the worst. The weight loss at 40%, 60% and 80% mass concentrations was greatly alleviated compared with 20%. Due to the presence of vanillin DEA, the weight loss at 55°C was aggravated compared with 0%, which is normal; but the weight loss at 250°C was greatly alleviated compared with 0%, indicating that the addition of DEA is beneficial to the enhancement of the stability of the chitosan structure, and that with the increase in concentration, the weight loss at 40%, 60% and 80% concentrations at 55°C gradually increased, while the stability of chitosan at 250°C increased.

[0066] like Figure 4 As shown in the figure, under the scanning electron microscope, there is no obvious difference on the front of the membrane, but under the scanning electron microscope 3700 times magnification, it can be clearly seen that the smoothness and roughness of the cross section of the membrane are different at different DEA concentrations. It can be seen that the addition of V-DEA makes the cross section of the chitosan membrane denser and smoother. With the increase of concentration, the smoothness increases, but the smoothness of the cross section of the 80% membrane decreases, which is slightly rougher than 60%.

[0067] Embodiment 6:

[0068] Weigh 1 g of film-forming agent (polyvinyl alcohol, cyclodextrin, hydrolyzed starch, citrate, and glycerol, a total of 1 g), add it to the 60% V-DEA / chitosan film liquid preservative prepared in Example 4, continue heating to 80°C and stirring to dissolve for 2 hours, then stop stirring, cool to room temperature, spread the film liquid onto a glass plate, and dry it at room temperature for 5-10 hours until it is dry to obtain a V-DEA / chitosan composite preservative film.

[0069] Embodiment 7:

[0070] Weigh 2 g of film-forming agent (1 g in total of polyvinyl alcohol, cyclodextrin, hydrolyzed starch, citrate, and glycerol) and add it to the 60% V-DEA / chitosan film liquid prepared in Example 4. After continuously heating to 90°C and stirring to dissolve for 3 hours, stop stirring, cool to room temperature, spread the film liquid onto a glass plate, and dry it at room temperature for 5-10 hours to obtain a V-DEA / chitosan composite preservative film.

[0071] Embodiment 8:

[0072] Weigh 3 g of film-forming agent (polyvinyl alcohol, cyclodextrin, hydrolyzed starch, citrate, glycerol, a total of 1 g), add it to the 60% V-DEA / chitosan film liquid prepared in Example 4, continue heating to 100°C and stirring to dissolve for 5 hours, then stop stirring, cool to room temperature, spread the film liquid onto a glass plate, and dry it at room temperature for 5-10 hours until it is dry to obtain a V-DEA / chitosan composite preservative film.

[0073] Example 9: Performance analysis of V-DEA / chitosan coating preservative

[0074] 1. Light transmittance

[0075] The 0%, 20%, 40%, 60%, and 80% vanillin DEA / chitosan films prepared in Examples 1-5 were cut into the same size as the side of the cuvette and attached to the side of the cuvette. The wavelength was set to 600nm in a UV-visible spectrophotometer to measure their transmittance. The blank cuvette was used as a blank, and the measurements were repeated three times in parallel to obtain the average value. The results are shown in Table 1. Figure 5 As shown in the figure, with the increase of DEA content, the transmittance decreased.

[0076] 2. Water vapor transmission rate

[0077] The 0%, 20%, 40%, 60%, and 80% vanillin DEA / chitosan films prepared in Examples 1-5 were cut into circular shapes with a diameter of 3 cm, and the water vapor transmission rate tester was set at 37.5°C and 89.6% humidity to measure the water vapor transmission rate of each group of sample films. The results are shown in FIG. Figure 6As shown in the figure, with the addition of DEA, the water vapor permeability of the chitosan film containing 20% ​​vanillin DEA only slightly increased compared with the pure chitosan film (0%), but the water vapor permeability of the chitosan film containing 40%-80% vanillin DEA increased significantly, and 80% increased to 2 times, which shows that vanillin DEA has a significant effect on improving water vapor permeability. The increase of vanillin DEA increases the water vapor permeability, because DEA is essentially an ionic liquid with water solubility. The increase in water vapor permeability is a foreseeable result as its content increases. It is also noted that the water vapor permeability of the 60% vanillin DEA / chitosan film is lower than 40% and 80%, reaching a moderate level. Combining other test results, it can be concluded that the water vapor permeability of the 60% vanillin DEA / chitosan film is moderate.

[0078] 3. Mechanical strength

[0079] According to the national standard "Test Method for Tensile Properties of Plastic Films" (GB13022-91), the 0%, 20%, 40%, 60%, and 80% vanillin DEA / chitosan films prepared in Examples 1-5 were cut into 10 mm x 80 mm strips, and the tensile strength and elongation at break of the cling film were measured using a universal tensile machine. The test results of tensile strength and elongation at break are shown in Figure 1. Figure 7 As shown, with the increase of DEA addition, there is a trend of increasing tensile strength and elongation at break, but the tensile strength and elongation at break of 60% are the best, indicating that 60% V-DEA / chitosan film has the best mechanical strength.

[0080] 4. Antioxidant

[0081] The DPPH and ABTs free radical scavenging rate method is a common method for in vitro antioxidant activity testing. The 0%, 20%, 40%, 60%, and 80% vanillin DEA / chitosan films prepared in Examples 1-5 were cut into pieces and soaked in methanol solutions. A series of methanol solutions with different concentration gradients were prepared as samples, and their DPPH and ABTs free radical scavenging rates were tested, and the half-inhibitory concentrations of the films with different ratios were calculated. The results are shown in Figure 2. Figure 8 As shown in the figure, as the proportion of DEA increases, its half-inhibitory concentration decreases significantly, and the lower the IC50, the better the antioxidant effect. Figure 8 It can be seen that the 60% V-DEA / chitosan film has the best scavenging effect on DPPH free radicals, and the scavenging of ABTs free radicals is concentration-dependent. It can be seen that with the addition of vanillin DEA, the antioxidant effect of chitosan film is significantly enhanced, and the higher the content, the better the effect. The comprehensive results show that 60% has the best antioxidant effect.

[0082] 5. Antimicrobial activity

[0083] Chitosan naturally has antibacterial activity, while V-DEA itself has no antibacterial activity. After UV sterilization of the 0%, 20%, 40%, 60%, and 80% vanillin DEA / chitosan films prepared in Examples 1-5, the antibacterial activity of the films of various proportions was studied by coating method. The results are shown as follows: Fig. 9 As shown in the figure, the antibacterial activity of 0%-40% V-DEA / chitosan membrane did not change significantly, while the 60% membrane had a significant antibacterial effect, and there was basically no Escherichia coli and Staphylococcus aureus in the bacterial culture medium after 80% membrane treatment. It can be seen that the addition of V-DEA significantly improved the antibacterial activity of the chitosan membrane itself when the concentration reached 60%.

[0084] Embodiment 10:

[0085] Freshly picked Guiwei lychees from the orchard were selected and divided into 6 groups with basically the same color and size, three replicates in each group, and 9 lychees in each replicate. After preservation, they were placed at a constant temperature of 26℃, weighed daily to observe the browning, and on the 6th day, the lychees were peeled and sampled. Detailed grouping: T1: deionized water immersion treatment; T2: 1mL / L 80% V-DEA / chitosan membrane solution immersion treatment; T3: 2mL / L 80% V-DEA / chitosan membrane solution immersion treatment; T4: 4mL / L 80% V-DEA / chitosan membrane solution immersion treatment; T5: 6mL / L 80% V-DEA / chitosan membrane solution immersion treatment; T6: 4mL / L 0% V-DEA / chitosan membrane solution immersion treatment.

[0086] The results are as follows Fig.10 The following are photos of the appearance of the fruit 4 days after preservation. It can be seen that the control group T1, the high concentration groups T4 and T5, and the chitosan film liquid preservation group T6 without V-DEA all had moldy phenomena, while the three groups T2, T3 and T4 had no bad fruits, especially T2 and T3, which had less browning.

[0087] The results of daily weighing and observation of epidermal browning are shown in Fig.11 and Fig.12 . It can be seen that with the extension of storage time, the weight loss phenomenon of each group is aggravated, but relatively speaking, the weight loss of groups T1, T2, and T3 has been alleviated, but the browning of group T1 is serious. Although the browning of group T3 has increased with the extension of time, it has been alleviated compared with other groups. Therefore, the T3 group has the best effect overall, that is, the fresh-keeping effect of litchi fruit after being treated with 2mL / L 80% V-DEA / chitosan membrane solution is the best.

[0088] On the sixth day after the lychee was preserved, the skin was peeled and the pulp and peel were sampled. In order to evaluate the quality of the fresh fruit, the soluble solid content (TSS) of the pulp, the vitamin C content (Vat.C) of the pulp, and the titratable acidity (TA) were determined. The results are as follows: Fig.13 , 14 As shown in Figures 1 and 15, the soluble solid content of the pulp reflects the sugar content of litchi, that is, the sweetness of the pulp. The test results show that the TSS content of litchi pulp in each group is not much different. However, the Vc content of the T3 group is significantly higher than that of the other treatment groups, and the acidity is also lower than that of the other groups. It can be seen that the quality of fresh litchi fruit after preservation treatment with 2mL / L 80% V-DEA / chitosan membrane solution is the best.

[0089] The electrolyte relative permeability (REL) data of the peel was measured. The electrolyte relative permeability of the fresh fruit peel reflects the integrity of the peel cells. The better the preservation effect, the lower the permeability. Fig.16 As shown in the figure, compared with the control group, the T2 and T3 groups were slightly lower, but the T5 group had the best effect. The oxidation of the peel will accelerate the wilting, aging and corruption of fresh fruits. The degree of peel preservation is often evaluated by testing the content of malondialdehyde and quinone, the oxidation products in the peel. Since the antioxidant test results of the V-DEA / chitosan film preservation reagent show that it has a clear antioxidant effect, it can delay the browning of the skin through the antioxidant mechanism to achieve a preservation effect in the preservation of litchi.

[0090] like Fig.17 , 18 As shown, the content of oxidation products malondialdehyde (MDA) and total quinone (SQ) was measured to evaluate the preservation effect. It can be seen that the content of malondialdehyde and total quinone in T3 group was the lowest. 2mL of V-DEA / chitosan membrane solution had a significant inhibitory effect on the oxidation of litchi epidermis.

[0091] In summary, through the analysis of the test results of the pulp and peel, the low concentration of 80% V-DEA / chitosan membrane solution has the effect of preserving fresh lychee fruit. The same test experiment also proved that 60% and 40% also showed the effect of preserving other lychees.

Claims

1. A vanillin deep eutectic reagent / chitosan coating preservative, characterized in that: The method comprises the following raw materials in parts by weight: 1 to 9 parts of vanillin deep eutectic reagent and 10 parts of chitosan.

2. The vanillin deep eutectic reagent / chitosan coating preservative according to claim 1, characterized in that: It also contains 2 to 6 parts by weight of a film-forming agent.

3. The method for preparing a vanillin deep eutectic reagent / chitosan coating preservative according to claim 1, characterized in that: The following steps are involved: (1) Weighing vanillin and choline chloride, mixing, and stirring while heating until clear and homogeneous to obtain a vanillin deep eutectic reagent; (2) weighing chitosan, dissolving it in an acetic acid aqueous solution, heating and stirring until completely dissolved, adding a vanillin deep eutectic reagent, and continuing to stir after heating to obtain a vanillin deep eutectic reagent / chitosan film solution; Optionally, (3) is evenly spread on a glass plate and dried to obtain a vanillin deep eutectic reagent / chitosan film preservative.

4. The method for preparing a vanillin deep eutectic reagent / chitosan coating preservative according to claim 2, characterized in that: The following steps are involved: (1) Weighing vanillin and choline chloride, mixing, and stirring while heating until clear and homogeneous to obtain a vanillin deep eutectic reagent; (2) weighing chitosan, dissolving it in an acetic acid aqueous solution, heating and stirring until completely dissolved, adding a vanillin deep eutectic reagent, and continuing to stir after heating to obtain a vanillin deep eutectic reagent / chitosan film solution; (3) adding a film-forming agent, stirring and dissolving after continuous heating, stopping stirring after the reaction is completed, cooling to room temperature, and obtaining a vanillin deep eutectic reagent / chitosan composite film solution; Optionally, (4) is evenly spread on a glass plate and dried to obtain a vanillin deep eutectic reagent / chitosan film composite preservative.

5. The method for preparing a vanillin deep eutectic reagent / chitosan coating preservative according to claim 3 or 4, characterized in that: The molar ratio of vanillin to choline chloride in step (1) is (1-5):(1-3); The heating is to a temperature of 60-100°C.

6. The method for preparing a vanillin deep eutectic reagent / chitosan coating preservative according to claim 3 or 4, characterized in that: The conditions for continuing stirring after heating in step (2) are: temperature 50-100° C., time 0.5-5 hours; The mass ratio of V-DEA to chitosan is (1-9):10; The concentration of the acetic acid aqueous solution is 1-3%.

7. The method for preparing a vanillin deep eutectic reagent / chitosan coating preservative according to claim 4, characterized in that: The film-forming agent in step (3) is polyvinyl alcohol, cyclodextrin, hydrolyzed starch, citrate or glycerol.

8. The method for preparing a vanillin deep eutectic reagent / chitosan coating preservative according to claim 4, characterized in that: The step (3) is continued to heat to 80-100° C.; The stirring and dissolving reaction time is 2 to 5 hours; The mass ratio of the film-forming agent to chitosan is (2-6):

10.

9. Use of a vanillin deep eutectic reagent / chitosan coating preservative as claimed in claim 1 or 2 in preserving fresh fruits or vegetables.

10. The use according to claim 9, characterized in that The fresh fruit is lychee, longan, tomato, cherry tomato, strawberry, cherry, citrus, honey pomelo or grape.

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