Jujube leaf epidermis wax-protein composite membrane as well as preparation method and application thereof

Abstract

The invention provides a jujube leaf epidermis wax-protein composite membrane as well as a preparation method and application thereof. The composite film is prepared from raw materials including vegetable protein and jujube leaf epidermis wax. Wherein the mass percentage content of the jujube leaf epidermis wax can be 0-2.5%. According to the prepared jujube leaf epidermis wax-protein composite film, one of the raw materials, namely wax, comes from jujube leaves, the materials are safe and non-toxic, and the resource utilization rate of the jujube leaves can be increased; the obtained jujube leaf epidermis wax-protein composite film has excellent waterproofness, antibacterial activity and oxidation resistance, is used for coating preservation of picked blueberries, has slight influence on sensory quality of the blueberries, and meanwhile, obviously reduces weight loss rate and rotting rate of blueberry fruits during storage, effectively delays softening of the fruits and improves preservation quality of the blueberries. The loss of nutrient substances such as soluble solids, anthocyanin, vitamin C and titratable acid is reduced, and the overall quality of the blueberries in the storage period can be effectively maintained. The invention has the advantages of low production cost and no burden on the environment after use.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit and vegetable preservation, and particularly relates to a jujube leaf epidermal wax-protein composite film and a preparation method and application thereof. Background Art

[0002] Common fruit and vegetable preservation technologies include physical preservation, chemical preservation and biological preservation, such as low-temperature storage, modified atmosphere packaging, irradiation preservation, coating preservation, etc. Various preservation technologies have more or less disadvantages. Improper temperature control during low-temperature storage can easily cause low-temperature damage and chilling injury, resulting in softening of the texture and color change of fruits and vegetables, and low-temperature storage consumes a lot of energy, which is costly in large-scale storage and transportation. Modified atmosphere packaging requires special packaging materials and equipment, which is expensive, and there is a risk of packaging damage, which affects the preservation effect. The investment and operating costs of irradiation preservation equipment are high, and some consumers may have reservations about irradiated food. Existing coating preservation materials include natural polymer materials, synthetic polymer materials and composite materials. At present, coating preservation still has some disadvantages. For example, some coating materials may change the original taste, smell or appearance of fruits and vegetables, affecting consumer acceptance, and many coatings still use synthetic polymer materials, which degrade slowly and may bring potential environmental burdens. In addition, high-quality natural coating materials may increase production costs when used on a large scale. Summary of the invention

[0003] The invention aims to provide a jujube leaf epidermal wax-protein composite film.

[0004] The jujube leaf epidermal wax-protein composite film provided by the present invention is made of raw materials including plant protein and jujube leaf epidermal wax;

[0005] Wherein, in the composite film, the mass percentage of the jujube leaf epidermal wax can be 0-2.5%, the endpoint 0 is not desirable, specifically 0.5-2.5%, more specifically 1.0-1.5%;

[0006] The plant protein is at least one of soy protein isolate, wheat gluten, wheat alcohol-soluble protein, glutenin and gluten powder;

[0007] Specifically, the plant protein is a mixture of soy protein isolate and wheat gluten protein;

[0008] More specifically, the plant protein is a mixture of soy protein isolate and wheat gluten protein in a mass ratio of 1:4.

[0009] The jujube leaf epidermal wax is prepared by a method comprising the following steps:

[0010] Weigh dry jujube leaves, add anhydrous ethanol, extract, remove the jujube leaves, collect the extract, extract the jujube leaves again, repeat three times, combine the extracts, concentrate, remove the solvent to obtain a white powder, i.e., jujube leaf epidermal wax.

[0011] The ratio of jujube leaves to anhydrous ethanol can be: 2.8-3.2 g: 50 mL;

[0012] The extraction temperature can be 35°C and the extraction time can be 20 seconds.

[0013] The extraction amount of the obtained jujube leaf epidermal wax reaches 15.03 mg / g (meaning 15.03 mg of wax is extracted from 1 g of dry jujube leaves).

[0014] The jujube leaf epidermal wax-protein composite film is prepared by a method comprising the following steps:

[0015] Weigh soy protein isolate and wheat gluten protein, mix them in a mass ratio of 1:4, take glycerol, dissolve the above materials in ethanol solution (referring to the mixture of soy protein isolate and wheat gluten protein dissolved in ethanol solution, and glycerol dissolved in ethanol solution), heat and stir the two solutions to melt into a mixture, then mix and cool the solutions; adjust the pH value of the solution to 9.8-10.2, continue stirring, add jujube leaf epidermis wax, continue stirring, emulsify and homogenize the obtained film solution, and finally let the film-forming solution stand at 75-85°C (specifically 80°C), take it out after cooling, cast it into a film, and dry it.

[0016] In the above method, the ratio of the mixture of soy protein isolate and wheat gluten protein to glycerol can be: 30g: 8-10mL, specifically 30g: 9mL;

[0017] The ethanol solution may specifically be an ethanol solution with a volume concentration of 50%;

[0018] In the obtained jujube leaf epidermal wax-protein composite film, the mass percentage of the jujube leaf epidermal wax can be 0-2.5%, the endpoint 0 is not desirable, specifically 0.5-2.5%, more specifically 1.0-1.5%;

[0019] The standing time may be 25-35 minutes, specifically 30 minutes;

[0020] The drying is carried out in a drying oven at a temperature of 60° C. and a humidity of about 40% for 10-13 hours.

[0021] The application of the above-mentioned jujube leaf epidermal wax-protein composite film as a packaging film also falls within the protection scope of the present invention.

[0022] The jujube leaf epidermal wax-protein composite film is used as a packaging film, has excellent water resistance, antibacterial and antioxidant properties, and can be used in food and medicine packaging.

[0023] The application of the above-mentioned jujube leaf epidermal wax-protein composite film in the storage and preservation of fruits and vegetables also falls within the protection scope of the present invention.

[0024] In the application, the fruit and vegetable may specifically be blueberry.

[0025] In the application, the jujube leaf epidermal wax-protein composite film has antibacterial and antioxidant properties. The jujube leaf epidermal wax-protein composite film coating treatment can reduce the weight loss rate and decay rate of fruits and vegetables during storage, effectively delay the softening of fruits and vegetables, reduce the loss of nutrients such as soluble solids, anthocyanins, vitamin C and titratable acid, and effectively maintain the overall quality of fruits and vegetables during storage.

[0026] The invention also provides a method for storing and preserving fruits and vegetables.

[0027] The fruit and vegetable storage and preservation method provided by the present invention comprises the following steps: mixing soy protein isolate and wheat gluten protein in a mass ratio of 1:4, taking glycerol, dissolving the above materials in an ethanol solution respectively, heating and stirring the two solutions to melt into a mixture, and then mixing and cooling the solutions; adjusting the pH value of the solution to 9.8-10.2, continuing to stir, adding jujube leaf epidermis wax, continuing to stir, emulsifying and homogenizing the obtained film solution, leaving the film-forming solution at 75-85°C (specifically 80°C), taking it out after cooling, and spraying it on the surface of fruits and vegetables.

[0028] The ratio of the mixture of soy protein isolate and wheat gluten protein to glycerol can be: 30g: 8-10mL, specifically 30g: 9mL;

[0029] The ethanol solution may specifically be an ethanol solution with a volume concentration of 50%;

[0030] The standing time may be 25-35 minutes, specifically 30 minutes;

[0031] In the obtained jujube leaf epidermal wax-protein composite film, the mass percentage content of the jujube leaf epidermal wax can be 0-2.5%, the endpoint 0 is not desirable, and can be specifically 0.5-2.5%, more specifically 1.0-1.5%.

[0032] The jujube leaf epidermal wax-protein composite film prepared by the present invention has one of the raw materials, wax, which comes from jujube leaves, and the material is safe and non-toxic, and can improve the resource utilization rate of jujube leaves; the obtained jujube leaf epidermal wax-protein composite film has excellent water resistance, antibacterial property and antioxidant property, and is used for the coating preservation of blueberries after harvesting. The composite coating has a slight effect on the sensory quality of blueberries. At the same time, the composite coating significantly reduces the weight loss rate and decay rate of blueberry fruits during storage, effectively delays fruit softening, reduces the loss of nutrients such as soluble solids, anthocyanins, vitamin C and titratable acid, and can effectively maintain the overall quality of blueberries during storage. The production cost of the present invention is low, and there is no burden on the environment after use. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the effect of extraction time, extraction temperature and ethanol concentration on the extraction amount of jujube leaf epidermal wax in Example 1 of the present invention.

[0034] Figure 2 It is the percentage of epidermal wax content at different storage times in Example 1 of the present invention.

[0035] Figure 3 The figure shows the effect of the epidermal wax content on the light transmittance and DPPH·free radical scavenging rate of the composite film in Example 2 of the present invention.

[0036] Figure 4 The following are Fourier infrared spectra and X-ray diffraction patterns of epidermal wax composite coatings with different addition amounts in Example 2 of the present invention.

[0037] Figure 5 These are scanning electron microscope images of the cross-section (CK1-A5) and surface (CK2-B5) of the epidermal wax composite coating films with different added amounts in Example 2 of the present invention, wherein A1, A2, A3, A4 and A5 are scanning electron microscope images of the cross-section of the epidermal wax composite coating films prepared with epidermal wax added amounts of 0.5%, 1.0%, 1.5%, 2.0% and 2.5%, respectively; B1, B2, B3, B4 and B5 are scanning electron microscope images of the surface of the epidermal wax composite coating films prepared with epidermal wax added amounts of 0.5%, 1.0%, 1.5%, 2.0% and 2.5%, respectively.

[0038] Figure 6 The sensory evaluation, decay rate, weight loss rate and hardness of blueberries under different coating treatments in Example 3 of the present invention are shown.

[0039] Figure 7 The titratable acid and soluble solid contents of blueberries under different coating treatments in Example 3 of the present invention.

[0040] Figure 8 The total phenols, anthocyanins and Vc contents of blueberries under different coating treatments in Example 3 of the present invention. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below in conjunction with specific embodiments, and the examples provided are only for illustrating the present invention, rather than for limiting the scope of the present invention. The examples provided below can be used as a guide for further improvements by those of ordinary skill in the art, and do not constitute a limitation of the present invention in any way.

[0042] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels.

[0043] The jujube leaves in the following embodiments were from the National Jujube Seed Base in Cang County, Hebei Province. Fresh jujube leaves were picked from winter jujube trees and immediately sent to the laboratory after being dried in the sun.

[0044] Example 1: Determining the Optimal Extraction Process for Jujube Leaf Epidermal Wax

[0045] Weigh 3 g of dried jujube leaves, add 50 ml of ethanol of different concentrations (volume concentration 60%, 70%, 80%, 90%, 100%) respectively, extract for different times (5s, 10s, 15s, 20s, 25s) at different temperatures (25, 30, 35, 40, 45°C), collect the extracts, concentrate them, determine the amount of jujube leaf cuticle wax extraction, and investigate the effect of different conditions on the amount of jujube leaf cuticle wax extraction. Figure 1 To investigate the effects of extraction time, extraction temperature and ethanol concentration on the extraction amount of jujube leaf epidermal wax.

[0046] After orthogonal experimental verification (Table 1, Table 2, Table 3), it was determined that the optimal extraction process for jujube leaf epidermal wax was to use anhydrous ethanol for extraction at 35°C for 20s.

[0047] Table 1. Levels of factors in orthogonal experiment

[0048]

[0049] Table 2L9(3 4 )Orthogonal Experiment Results and Analysis

[0050]

[0051]

[0052] Table 3 Analysis of variance of orthogonal experiment results

[0053] factor Sum of Squared Deviations Degrees of Freedom Mean Square F-number P-value Significance A 24.700 2 12.350 288.250 0.003 * B 6.545 2 3.273 76.385 0.013 * C 10.967 2 5.484 127.987 0.008 * error 0.086 2 0.043 1.000 0.500

[0054] Note: * indicates significant difference (P<0.05).

[0055] The qualitative and quantitative analysis of jujube leaf epidermal wax by gas chromatography-mass spectrometry showed that the wax components mainly included alkanes, alcohols, esters and fatty acids. The results are shown in Table 4.

[0056] Table 4 Analysis results of wax components in jujube leaf epidermis

[0057]

[0058]

[0059] During the storage process, it was observed that the alcohol substances gradually decreased and then disappeared, the proportion of esters and fatty acids first increased and then decreased, while the proportion of alkanes continued to increase.

[0060] Figure 2 It is the percentage of epidermal wax content under different storage time.

[0061] Example 2: Investigating the effect of the amount of jujube leaf epidermal wax added on the performance of the composite coating

[0062] Weigh 3 g of dried jujube leaves, add them to 50 ml of anhydrous ethanol, and extract at 35°C for 20 seconds. Then remove the jujube leaves, collect the extract, and extract the jujube leaves again. Repeat this process three times, combine the extracts, concentrate them, and remove the solvent to obtain a white powder, i.e., jujube leaf epidermal wax (extraction amount 15.03 mg / g).

[0063] Weigh 30g of soy protein isolate and wheat gluten protein, mix them in a ratio of 1:4, take 9mL of glycerol, dissolve the above materials in 50% volume fraction of ethanol solution respectively, place both solutions in an 80℃ water bath and stir to melt into a mixture, then mix and cool the solutions; use sodium hydroxide and hydrochloric acid solution to adjust the pH value of the membrane solution to about 10.0, continue to stir the membrane solution at 80℃ on a magnetic stirrer, then add an appropriate amount of jujube leaf epidermal wax (added amount 0, 0.5%, 1.0%, 1.5%, 2.0% and 2.5%), and continue stirring for 10 minutes. The film solution was emulsified and homogenized using a shearing instrument, and the film-forming solution was placed in a constant temperature water bath at 80°C for 30 minutes. After cooling, it was taken out and the film-forming solution was drawn with a pipette and cast into a square acrylic culture dish to ensure that the amount of film-forming solution used in the film making was consistent. A certain volume of film-forming solution was poured into a glass box covered with projection film and spread out. The bubbles in the solution were eliminated by shaking and other means to ensure that the film surface was smooth and flat. After that, it was dried in a drying oven at a temperature of 60°C and a humidity of about 40% for 12 hours. After the film was dried, the film was peeled off with pointed tweezers, and the prepared film was placed in a dryer (room temperature, relative humidity of about 50%) and stored for 3 days before the film properties were measured. Table 5 shows the color difference of the composite coating film with different addition amounts of epidermal wax; Table 6 shows the effect of the amount of epidermal wax added on the moisture content, water solubility and water vapor permeability (WVP) of the composite coating; Table 7 shows the effect of the amount of epidermal wax added on the total number of molds, yeasts and colonies of the composite coating.

[0064] Table 5 Color difference of epidermal wax composite coatings with different addition amounts

[0065]

[0066] Note: All data are derived from at least 5 parallel experiments. The results are presented as mean ± standard deviation. Different letters in the same column indicate significant differences (p<0.05).

[0067] Table 6 Effect of epidermal wax addition on moisture content, water solubility and water vapor permeability of composite coatings

[0068]

[0069]

[0070] Note: The unit of WVP is g·m / (h·Pa·m 2 ).

[0071] Table 7. Total number of molds, yeasts and colonies in composite coatings

[0072]

[0073] It can be seen from Tables 5 to 7 that during the preparation of epidermal wax-protein composite coatings, as the amount of epidermal wax added increased, the brightness of the composite coating decreased, the color gradually turned yellow, and the transmittance ( Figure 3 ), moisture content and water solubility all showed a downward trend, and the water vapor permeability showed a characteristic of first decreasing and then increasing. In addition, the addition of epidermal wax significantly improved the antibacterial and antioxidant properties of the composite coating. Comprehensive analysis by Fourier infrared spectroscopy, X-ray diffraction and scanning electron microscopy found that a stable network structure was formed between the epidermal wax and the protein coating, and showed a high degree of compatibility.

[0074] Figure 3 Effect of epidermal wax content on the light transmittance and DPPH· free radical scavenging rate of the composite film.

[0075] Figure 4 Fourier infrared spectra and X-ray diffraction patterns of epidermal wax composite coatings with different addition amounts.

[0076] Figure 5 The figures are scanning electron micrographs of the cross-section (CK1-A5) and surface (CK2-B5) of epidermal wax composite coatings with different addition amounts, wherein A1, A2, A3, A4 and A5 are scanning electron micrographs of the cross-section of epidermal wax composite coatings prepared with epidermal wax addition amounts of 0.5%, 1.0%, 1.5%, 2.0% and 2.5%, respectively; B1, B2, B3, B4 and B5 are scanning electron micrographs of the surface of epidermal wax composite coatings prepared with epidermal wax addition amounts of 0.5%, 1.0%, 1.5%, 2.0% and 2.5%, respectively.

[0077] From the above experimental results, it can be seen that the lower the WVP, the less likely the contents of the film packaging are to be affected by moisture and deteriorate. The optimal amount of epidermal wax added is determined to be 1.0%-1.5%.

[0078] Example 3: Effect of composite film on blueberry quality

[0079] Weigh 30g of soy protein isolate and wheat gluten protein, mix them in a ratio of 1:4, take 9mL of glycerol, dissolve the above materials in 50% volume ethanol solution respectively, place both solutions in an 80°C water bath and stir to melt into a mixture, then mix and cool the solutions; use sodium hydroxide and hydrochloric acid solution to adjust the pH value of the membrane solution to about 10.0, continue to stir the membrane solution at 80°C on a magnetic stirrer, then add jujube leaf epidermal wax (the addition amount is 1.5%, determined on the basis of WVP according to moisture content, water solubility, mold, yeast and total colony count), continue stirring for 10 minutes, emulsify and homogenize the obtained membrane solution, let the film-forming solution stand at 80°C for 30 minutes, take it out after cooling, and spray it on the surface of blueberries.

[0080] Figure 6 Sensory evaluation, decay rate, weight loss rate and hardness of blueberries under different coating treatments.

[0081] Figure 7 Titratable acid and soluble solids content of blueberries under different coating treatments.

[0082] Figure 8 Total phenols, anthocyanins and Vc contents of blueberries under different coating treatments.

[0083] Among them, CK is a blank control group, NC is a negative control group treated with ethanol solution (volume fraction 50%), SG is a protein coating (the step of adding jujube leaf epidermal wax is removed in the above process) treatment group, and SG-CW is an epidermal wax-protein composite coating (1.5% epidermal wax content) treatment group

[0084] The experimental results show that in the blueberry storage and preservation experiment, the composite coating has a slight effect on the sensory quality of blueberries. At the same time, the composite coating significantly reduces the weight loss rate and decay rate of blueberry fruits during storage, effectively delays fruit softening, and reduces the loss of nutrients such as soluble solids, anthocyanins, vitamin C and titratable acid, which can effectively maintain the overall quality of blueberries during storage.

[0085] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, and without the need to carry out unnecessary experimental conditions, the present invention can be implemented in a wide range under equivalent parameters, concentrations and conditions. Although the present invention provides specific embodiments, it should be understood that the present invention can be further improved. In a word, according to the principles of the present invention, the application is intended to include any changes, uses or improvements to the present invention, including departure from the disclosed scope in the application, and changes made with conventional techniques known in the art.

Claims

1. A jujube leaf epidermal wax-protein composite film, made from raw materials including plant protein and jujube leaf epidermal wax; wherein: In the composite film, the mass percentage of the jujube leaf epidermal wax is 0-2.5%, and the endpoint 0 is not desirable.

2. The jujube leaf epidermal wax-protein composite film according to claim 1, characterized in that: The plant protein is at least one of soy protein isolate, wheat gluten protein, wheat alcohol-soluble protein, glutenin and gluten powder, and specifically can be a mixture of soy protein isolate and wheat gluten protein.

3. The jujube leaf epidermal wax-protein composite film according to claim 1, characterized in that: The jujube leaf epidermal wax is prepared by a method comprising the following steps: Weigh the dried jujube leaves, add anhydrous ethanol, extract, remove the jujube leaves, collect the extract, extract the jujube leaves again, repeat three times, combine the extracts, concentrate, remove the solvent to obtain a white powder, i.e., jujube leaf epidermal wax; The ratio of jujube leaves to anhydrous ethanol is: 2.8-3.2 g: 50 mL; The extraction temperature is 35°C and the extraction time is 20s. The extraction amount of the obtained jujube leaf epidermal wax reaches 15.03 mg / g.

4. A method for preparing the jujube leaf epidermal wax-protein composite film according to any one of claims 1 to 3, comprising the following steps: Weigh soy protein isolate and wheat gluten protein, mix them in a mass ratio of 1:4, take glycerol, dissolve the above materials in ethanol solution respectively, heat and stir the two solutions to melt into a mixture, then mix and cool the solutions; adjust the pH value of the solution to about 9.8-10.2, continue stirring, add jujube leaf epidermis wax, continue stirring, emulsify and homogenize the obtained film solution, finally let the film-forming solution stand at 75-85°C, take it out after cooling, cast it into a film, and dry it.

5. The method according to claim 4, characterized in that The ratio of the mixture of soy protein isolate and wheat gluten protein to glycerol is: 30g: 8-10mL; The ethanol solution is an ethanol solution with a volume concentration of 50%; In the obtained jujube leaf epidermal wax-protein composite film, the mass percentage of the jujube leaf epidermal wax is 0-2.5%, and the endpoint 0 is not desirable; The standing time is 25-35min; The drying is carried out in a drying oven at a temperature of 60° C. and a humidity of about 40% for 10-13 hours.

6. Use of the jujube leaf epidermal wax-protein composite film according to any one of claims 1 to 3 in the storage and preservation of fruits and vegetables.

7. The use according to claim 6, characterized in that: In the application, the jujube leaf epidermal wax-protein composite film has antibacterial and antioxidant properties. The jujube leaf epidermal wax-protein composite film coating treatment can reduce the weight loss rate and decay rate of fruits and vegetables during storage, effectively delay the softening of fruits and vegetables, reduce the loss of nutrients such as soluble solids, anthocyanins, vitamin C and titratable acid, and effectively maintain the overall quality of fruits and vegetables during storage.

8. A method for storing and preserving fruits and vegetables, comprising: mixing soy protein isolate and wheat gluten protein in a mass ratio of 1:4, taking glycerol, dissolving the above materials in an ethanol solution respectively, heating and stirring the two solutions to melt into a mixture, and then mixing and cooling the solutions; adjusting the pH value of the solution to 9.8-10.2, continuing to stir, adding jujube leaf epidermal wax, continuing to stir, emulsifying and homogenizing the obtained film solution, allowing the film-forming solution to stand at 75-85°C (specifically 80°C), taking it out after cooling, and spraying it on the surface of fruits and vegetables.

9. The jujube leaf epidermal wax-protein composite film according to any one of claims 1 to 3 is used as a packaging film for food and medicine packaging.

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