CN116035157B

CN116035157B - A kind of Zanthoxylum bungeanum leaf polyphenol-chitosan composite film and preparation method thereof

Info

Publication number: CN116035157B
Application number: CN202211248577.5A
Authority: CN
Inventors: 罗爱国; 胡变芳; 史胜利; 赵佳; 郝建伟; 陈静
Original assignee: Jinzhong University
Current assignee: Jinzhong University
Priority date: 2022-10-12
Filing date: 2022-10-12
Publication date: 2025-02-14
Anticipated expiration: 2042-10-12
Also published as: CN116035157A

Abstract

The invention discloses a method for preparing a Zanthoxylum polyphenol-chitosan composite film. It belongs to the technical field of biofilm preparation. It comprises the following steps: dissolving chitosan in an acidic aqueous solution, heating and stirring evenly, adding a Zanthoxylum polyphenol extract, homogenizing, filtering, and vacuum degassing to obtain a membrane solution, pouring the membrane solution into a mold by a casting film-forming method, and obtaining a Zanthoxylum polyphenol-chitosan composite film by drying. The invention also discloses a Zanthoxylum polyphenol-chitosan composite film prepared by the above method. By combining Zanthoxylum polyphenol and chitosan to form a composite biofilm, the antibacterial and antibacterial and antioxidant functions of the biofilm are improved; at the same time, the cross-linking effect between Zanthoxylum polyphenol and chitosan improves the opacity and flexibility of the biofilm; the casting film-forming method is adopted to ensure the thickness and uniformity of the film; and technical support is provided for the further development of bio-based packaging materials.

Description

Composite film of polyphenol and chitosan from pricklyash leaves and preparation method thereof

Technical Field

The invention relates to the technical field of biological film preparation, in particular to a pepper leaf polyphenol-chitosan composite film and a preparation method thereof.

Background

Today, where environmental and sustainable development issues are of great concern, bio-based packaging materials are of interest to the market and consumers because they are renewable, non-toxic and biodegradable, and can reduce white pollution, prevent oxidative spoilage and microbial spoilage of foods.

Chitosan is a macromolecular compound obtained by deacetylation of chitin widely existing in nature, has good film forming property, biocompatibility and biodegradability, can inhibit the growth and reproduction of microorganisms, prevent water loss and effectively prolong the shelf life, but has certain defects in the aspects of thickness, opacity, solubility, flexibility, antibacterial and antioxidative activity and the like, so that the application of chitosan on biological films is limited. Plant polyphenols are the general names of polyhydroxy compounds in plants, and mainly include flavonoids, tannins, anthocyanins, phenolic acids and the like. The world health organization specialist considers that plant polyphenol is the 7 th nutrient of the sham human beings, a large amount of active phenolic hydroxyl groups lead the plant polyphenol to have unique chemical and physiological activities, mainly shown by oxidation resistance, antibiosis and bacteriostasis and scavenging action on various active oxygen free radicals, and technologies for embedding the plant polyphenol in chitosan to prepare biological films, such as tannins, brown algae polyphenol and tea polyphenol, exist at present, but reports of applying the pepper leaf polyphenol to biological packaging films are not seen in the prior art, and further, the biological films prepared by adding the plant polyphenol such as tannins are low in opacity and barrier property to visible light, so that the release of the plant polyphenol is uneven, long-acting slow release cannot be ensured, and the effect on flexibility is poor.

Therefore, how to provide a pepper leaf polyphenol-chitosan composite film with good improvement effect on film thickness, opacity, flexibility and the like of a bio-based composite film and a preparation method thereof are problems to be solved by the technicians in the field.

Disclosure of Invention

In view of the above, the invention provides a preparation method of a pepper leaf polyphenol-chitosan composite film, which improves the antibacterial and antioxygenic properties of the biological film by combining the pepper leaf polyphenol and the chitosan, has good improvement effects on the physical properties of the biological film, such as flexibility and opacity, and provides a new idea for the utilization of the pepper leaf.

In order to achieve the above purpose, the present invention adopts the following technical scheme:

A process for preparing the composite film of polyphenol-chitosan from Chinese prickly ash leaf includes such steps as dissolving chitosan in acidic aqueous solution, heating while stirring, adding polyphenol extract, homogenizing, filtering, vacuum degassing to obtain film solution, pouring the film solution in mould, and drying.

The technical scheme has the beneficial effects that the pepper leaf polyphenol has the capabilities of resisting oxidation, resisting bacteria and scavenging free radicals, the release process of the polyphenol can be effectively controlled by embedding the pepper leaf polyphenol extract in chitosan, so that the utilization rate of the active ingredients is effectively improved by keeping certain concentration of the functional active ingredients during the storage period of food, the shelf life of the food is prolonged, the antibacterial and bacteriostatic capabilities of the biological film are improved, meanwhile, the crosslinking effect between the pepper leaf polyphenol and the chitosan is improved, the opacity and the flexibility of the biological film are improved, and the thickness and the uniformity of the film are ensured by adopting a casting film forming mode.

Preferably, the ratio relationship of chitosan to xanthoxylum leaf polyphenol to acidic aqueous solution is 2 g:0.5-1.0 g:100mL by weight.

The technical scheme has the beneficial effects that the proper addition amount of the pepper leaf polyphenol and the chitosan ensures that the active film has good light resistance and flexibility.

Preferably, the acidic aqueous solution is a 1% acetic acid solution.

Preferably, a casting film forming technology is adopted, 20ml of film solution is cast on a film making device with the diameter of 9cm, and the prepared film thickness is 39.07-41.19 mu m.

The technical scheme has the beneficial effects that the quantitative film making mode is adopted, so that the thickness and uniformity of the film are ensured.

Preferably, the heating temperature of chitosan dissolved in acidic aqueous solution is 60 ℃, stirring time is 30min, homogenizing time is 10min at the rotating speed of 8000r/min, filtering by a filter membrane with the aperture of 0.45 μm, degassing under the vacuum degree of-0.08 MPa, and pouring the membrane solution into a membrane making device, wherein the drying temperature is 25 ℃, and the drying time is 24h.

The technical scheme has the beneficial effects that the structure uniformity of the active film and the polyphenol release property of the pepper leaves are ensured by proper film preparation process parameters.

Preferably, the polyphenol extract of Zanthoxylum bungeanum leaf contains epicatechin, chlorogenic acid, p-coumaric acid, ferulic acid, quercetin and kaempferol.

The technical scheme has the beneficial effect that the abundance of the polyphenol of the pepper leaves ensures the good antioxidant activity of the active film.

Preferably, the pepper leaf polyphenol extract is prepared by dissolving pepper leaf powder in ethanol solution according to a feed liquid ratio of 1:20, heating in water bath, centrifuging to obtain supernatant, concentrating, and purifying to obtain the pepper leaf polyphenol extract.

Preferably, the water bath heating temperature is 40 ℃, the heating time is 60min, the centrifugation is carried out at 6000r/min for 10min, and the concentration volume is 25%.

Preferably, the pepper leaves are dried for 6 hours at 40 ℃, crushed and sieved by a 60-mesh sieve, and the pepper leaf powder is prepared.

Preferably, the zanthoxylum bungeanum leaf polyphenol is purified by taking polyamide as a stationary phase, loading concentrated zanthoxylum She Duofen crude extract (1.5 BV) for 30min, eluting with ddH2O and 75% ethanol respectively, collecting 2,3BV eluent, and concentrating and purifying to obtain the zanthoxylum bungeanum leaf polyphenol extract.

The invention also relates to the pepper leaf polyphenol-chitosan composite membrane prepared by the method.

Compared with the prior art, the invention has the following beneficial effects:

(1) According to the invention, the chitosan is used for embedding the polyphenol extract of the pepper leaves, so that the oxidation resistance of the biological film is improved, the blocking effect of the biological film on visible light is improved, the polyphenol release is effectively controlled, the shelf life of food is further prolonged, and a new idea is provided for the utilization of the pepper leaves through the proportion of the chitosan and the polyphenol of the pepper leaves and the arrangement of the technological parameters of the preparation of the film.

(2) The casting film forming mode realizes quantitative film making and ensures the thickness and uniformity of the film.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.

FIG. 1 is a graph of gallic acid standard curve;

the regression equation is that y=0.1463x+0.0082, R2=0.9995 and has good linear relation in the range of 1.463-5.850 mg/L;

FIG. 2 is a graph showing the analytical chromatogram of the polyphenol extract of Zanthoxylum bungeanum leaf;

Wherein 1 represents epicatechin, 2, chlorogenic acid, 3, catechin, 4, vanillin, 5, p-coumaric acid, 6, ferulic acid, 7, m-coumaric acid, 8, rutin, 9, o-coumaric acid, 10, quercitrin, 11, quercetin, 12, naringenin, 13, kaempferol;

FIG. 3a-h are the scanning electron microscope images of C-film, TA/C-film and ZMP/C-film;

FIG. 4 is a chart showing FTIR spectra of C-film, TA/C-film and ZMP/C-film;

FIG. 5 is a XRD spectrum showing the patterns C-film, TA/C-film and ZMP/C-film;

FIG. 6 is a graph showing ZMP release profiles in three different food simulants;

FIG. 7 is a graph showing the release profile of antioxidant activity of ZMP/C-film in various food simulants;

FIG. 8 is a graph showing the effect of ZMP/C-film on appearance, moisture and Vc of strawberries during storage.

Detailed Description

The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

Example 1

Taking pepper leaves, drying for 6 hours at the temperature of 40 ℃, crushing and sieving with a 60-mesh sieve to obtain pepper leaf powder, dissolving the pepper leaf powder in a 60% ethanol solution according to a feed liquid ratio of 1:20 to obtain a mixed solution, centrifuging the mixed solution at the temperature of 40 ℃ for 60 minutes in a water bath for 10 minutes at the temperature of 6000r/min, concentrating the supernatant to 25% to obtain pepper She Duofen crude extract, purifying the pepper leaf polyphenol crude extract by taking polyamide as a stationary phase and respectively taking ddH ₂ O and 75% ethanol as eluent to obtain the pepper leaf polyphenol extract (ZMP).

2G of chitosan is weighed and dissolved in 100ml of 1% acetic acid solution, heating and stirring are carried out for 30min at 60 ℃, then 0.5g of pepper leaf polyphenol extract is added into the obtained chitosan film solution, the pepper leaf polyphenol-chitosan film solution is obtained after homogenization, filtration and vacuum degassing, a casting film forming technology is adopted, 20ml of film solution is cast into a film making device with the diameter of 9cm, and drying is carried out for 24h at 25 ℃, thus obtaining the 0.5% pepper leaf polyphenol-chitosan composite film (0.5% ZMP/C-film).

Example 2:

Taking the chitosan film solution prepared in the example 1, adding 1.0g of the pepper leaf polyphenol extract, homogenizing, filtering, and vacuum degassing to obtain the pepper leaf polyphenol-chitosan film solution, pouring 20ml of the film solution into a film making device with the diameter of 9cm by adopting a pouring film forming technology, and drying at 25 ℃ for 24 hours to obtain the 1.0% pepper leaf polyphenol-chitosan composite film (1.0% ZMP/C-film).

Control group 1

Taking the chitosan film solution prepared in the example 1, adding 1g of glycerol, homogenizing, filtering, vacuum degassing to obtain a control chitosan film solution, pouring 20ml of the film solution into a film making device with the diameter of 9cm by adopting a pouring film forming technology, and drying at 25 ℃ for 24 hours to obtain a control chitosan film (C-film).

Control group 2

Taking the chitosan film solution prepared in the example 1, adding 1.0g of tannic acid, homogenizing, filtering, and vacuum degassing to obtain tannic acid-chitosan film solution, pouring 20ml of film solution into a film-making device with the diameter of 9cm by adopting a pouring film-forming technology, and drying at 25 ℃ for 24 hours to obtain the tannic acid-chitosan composite film (TA/C-film).

Determination of total phenol content in pepper She Duofen crude extract

Taking the crude extract of pepper She Duofen prepared in example 1, measuring the total phenol content, and calculating according to a gallic acid standard curve, wherein the total phenol content in the extracted pepper leaf polyphenol is 41.85mg/g as shown in the figure of figure 1.

Component analysis of polyphenol extract of Zanthoxylum bungeanum leaf

The components of the polyphenol extract of Zanthoxylum bungeanum leaf prepared in example 1 were analyzed by HPLC, chromatographic conditions are that a chromatographic column SYMMETRY C-18 column (3.9 mm. Times.150 mm,5 μm), mobile phase 0.1% formic acid (A) and methanol (B) are subjected to gradient elution (0min,90％A,10％B;5min,80％A,20％B;10min,60％A,40％B;20min,50％A,50％B;30min,20％A,80％B;40min,70％A,30％B;50min,90％A,10％B),ZMP, the sample injection amount is 1 μl, the flow rate is 1.0mL/min, the column temperature is 30 ℃, and the detection wavelength is 280nm.

13 Polyphenol compound standard substances such as catechin and the like are precisely weighed, 20.00mg of each standard substance is dissolved by methanol to prepare stock solution with the concentration of 2mg/mL, a series of 1,5,10,20,40,60 mu g/mL mixed standard solutions are prepared, the mixed standard solutions are filtered by a microporous filter membrane with the concentration of 0.22 mu m, and sample injection analysis is carried out according to the chromatographic conditions, and the detection result is shown in the figure of figure 2.

The polyphenol extract of the pepper leaves can be detected to contain 7 components of epicatechin, chlorogenic acid, p-coumaric acid, ferulic acid, quercetin, kaempferol, and the contents of the components are 3.24mg/g, 3.59mg/g, 1.40mg/g, 4.36mg/g, 7.61mg/g, 4.52mg/g and 2.51mg/g in sequence.

Determination of physical Properties of biological films

Control experiments were performed in examples 1 and 2 and control groups 1 and 2, and film thickness, opacity, solubility, tensile strength, and elongation at break were measured, respectively, and the experimental results are shown in table 1.

Film thickness was measured by randomly selecting 10 locations on the surface of the sample and measuring with a micrometer (0.01 mm) of 0-25 mm.

Opacity measurement by cutting the film into 30mm×10mm strips by UV method, fixing the strips on the inner wall of cuvette, measuring absorbance A at 600nm, repeating the measurement 3 times with an empty cuvette as a control, and calculating the opacity as A divided by film thickness d.

Solubility measurement, namely immersing a certain amount of film into distilled water at 25 ℃ for 24 hours, taking out, removing surface moisture, placing the film in an oven for drying at 105 ℃ for 24 hours, placing the film in a dryer for balancing for 12 hours, weighing the mass of the film before and after drying, and calculating the solubility according to a formula (1).

Solubility (%) = [ (m 1-m 2)/m 1] ×100 (1)

Wherein m1 is the initial mass (g) of the sample, and m2 is the final mass (g) of the sample.

The Tensile Strength (TS) and elongation at break (E%) of the film were measured according to the method of GB/T1040.3-2006, the original gauge length was set to 100mm, the stretching speed was 50mm/min, the maximum length and the maximum tensile force at break of the film were measured by an electronic universal tensile machine, each treatment was repeated 5 times, and TS and E% were expressed by the formula (2) and the formula (3), respectively:

TS(MPa)=F/(b×d) (2)

where F is the maximum tensile force (N), b is the sample width (mm), and d is the sample thickness (mm).

E(%)=[(L-L0)/L0]×100 (3)

Where L is the distance (mm) at which the film sample breaks and L0 is the original gauge length (mm) of the film sample.

TABLE 1 thickness, opacity, solubility, tensile Strength and elongation at break of Zanthoxylum leaf polyphenol/chitosan composite film

Note that the different lowercase letters (a-c) of the superscript in the table indicate that the difference in the same column of data is significant (p < 0.05).

Film thickness measurement the thicknesses of the four films C-film, TA/C-film and ZMP/C-film were measured by micrometer, the average film thickness was 41.42 μm, and ZMP/C-film showed a smaller thickness than TA/C-film.

And the opacity measurement is that the opacity of the four films at 600nm is measured respectively, and the TA/C-film and the ZMP/C-film have significant differences, so that the transmittance of the ZMP/C-film is lower, and the film has a certain barrier property to visible light.

And (3) measuring the solubility, namely soaking the film in distilled water for 24 hours, wherein the shape of the C-film basically keeps integrity, the shape of the chitosan film added with TA and ZMP is changed to a certain extent, and the solubility is improved, but the difference is not obvious.

The Tensile Strength (TS) and the elongation at break (E%) of the film are important parameters affecting the film as a packaging material, and the table shows that the tensile strength of TA/C-film and ZMP/C-film is reduced compared with that of C-film, the elongation at break of ZMP/C-film is obviously increased compared with that of TA/C-film, and the film has extremely obvious difference, so that the flexibility of the film can be greatly improved by adding the xanthoxylum leaf polyphenol compared with that of tannic acid plant polyphenol.

Scanning Electron Microscope (SEM) of biomembrane

A Zeiss MERLIN Compact scanning electron microscope is adopted for observation, a film sample with the thickness of 5mm multiplied by 5mm is taken and fixed on a copper table after vacuum metal spraying, and the surface and the cross section of the sample are scanned by an electron beam with the accelerating voltage of 5kV for electron microscope observation, and the result is shown in the figures of figures 3 a-h.

From the results, a significant difference in the microstructure of the composite film was observed. From the surface scan, the C-film surface microstructure is continuous, uniform, without any voids, cracks, or irregularities (FIG. 3-a). Different morphologies were observed for the composite films with either TA or ZMP added. The addition of TA alters the apparent structure of the biofilm, the surface appears non-uniform, and the surface has some uniformly dispersed white spots and raised small pieces (FIG. 3-c), indicating some heterogeneity in the membrane matrix. After ZMP is added, the surface of 0.5% or 1.0% of ZMP/C-film can be observed to be uneven or uneven, some white spots are dispersed, and some small pits appear (figures 3-e and 3-g), which shows that the addition of ZMP damages the network structure of CS matrix to a certain extent, and causes discontinuity of CS matrix, which has a certain influence on the mechanical strength of the composite film.

From a cross-sectional scan of the film (FIGS. 3-b, d, f, h), the cross-section of C-film shows a loose network structure, compared to the cross-sections of TA/C-film and ZMP/C-film which are more dense, the phenols and chitosan polymer may have a denser, compact cross-section due to interaction forces.

Fourier transform infrared spectroscopy (FTIR)

The method adopts Nicolet 670 Fourier infrared spectrum, the resolution is 4cm < -1 >, the scanning range is 4000-650 cm < -1 >, the scanning is 64 times, the internal structure change condition of a sample is observed, the FTIR can reveal the information about the molecular interaction of chemical components of a composite film, the FTIR is an important means for representing chemical bonds in film polymers, the result is shown in the figure of figure 4, the FTIR of C-film presents typical aminopolysaccharide characteristic bands, the broadband of 3262-3383cm ^-1 is the characteristic bands due to-OH stretching vibration and-NH symmetrical stretching vibration, the peak near 2926-2878cm ^-1 is the vibration absorption of CH, and the amide I band (1636-1771 cm ^-1), the amide II band (1548-1600 cm ^-1) and the amide III band (1366-1404 cm ^-1) correspond to C=O stretching, N-H bending and C-N bending respectively. Peaks at 1249cm ^-1 and 1152cm ^-1 are associated with symmetrical and asymmetrical stretching of C-O-C in the fingerprint region, and bands at 1024-1074cm ^-1 are caused by C-O backbone stretching. When polyphenols (ZMP, TA) were added, the spectrum of the composite film was similar to that of chitosan, and no new characteristic absorption band was found. These results indicate that insufficient amounts of TA or ZMP added cause significant changes in the chitosan structural matrix, but the change in the intensity of the FTIR absorption peak and the mechanical property data of the composite membrane reveal the crosslinking effect between chitosan and TA or ZMP molecules.

X-ray diffraction spectrum

And (3) observing a sample diffraction diagram by using a D/max 2550X-ray powder diffractometer at a voltage of 40kV, a current of 100mA, a scanning range of 10-80 degrees and a scanning speed of 5 DEG/min, and observing the influence of ZMP on the crystal characteristics of the chitosan composite film, wherein the result is shown in a figure of fig. 5. The C-film based composite film has two diffraction peaks at the Bragg angle (2 theta) of 11.6 DEG and around 22.1 DEG, according to previous literature reports, the diffraction peak around 11.6 DEG reflects the hydrated crystal structure of the chitosan film, and the diffraction peak around 22.1 DEG reflects the amorphous structure of the chitosan film, which is the characteristic fingerprint of chitosan. After ZMP is added into chitosan, two diffraction peaks become flat gradually, the diffraction intensity becomes smaller, and especially the characteristic peak at 22.1 degrees is reduced, and the addition of TA has the same effect, so that ZMP or TA induces the chitosan film to be converted into an amorphous structure from a result structure, and the crystallinity of the composite film is reduced. In TA/C-film and ZMP/C-film, interaction between the polyphenol and the chitosan may obstruct formation of intramolecular or intermolecular hydrogen bonds of the chitosan itself due to competition effect of hydrogen bonds between the chitosan and the polyphenol, resulting in further formation of amorphous complex in the structure, reduced crystallinity, increased solubility, and increased film forming property of the chitosan.

Kinetics of polyphenol release

The water, 3% (v/v) acetic acid and 10% (v/v) ethanol are adopted to simulate water-based, acid and alcohol foods, and the release process of the ZMP/C-film composite film polyphenol of 1.0% (m/v) in the food simulation liquid is examined. Cutting film sample into 1cm×1cm pieces, weighing, placing into volumetric flasks containing 20mL of simulation solution, releasing from light at 25deg.C for 48 hr, taking 0.3mL of the above release solution at different time points (timely supplementing the same amount of simulation solution into volumetric flasks), mixing with 0.3mL of Fulin reagent, standing for 5min, transferring into 0.6mL of Na2CO3 (10%, v/v), fixing volume to 3mL, developing for 2 hr at 25deg.C, measuring absorbance (A760 nm), calculating total polyphenol content from 1.3.1 gallic acid standard curve, and expressing (mg GAE/g film) in milliequivalents of gallic acid per gram of sample. The experiment was repeated 3 times and the cumulative release rate of polyphenols was calculated according to formula (4):

cumulative release rate (%) = (m _t/m₀) ×100 (4)

Wherein Mt is the cumulative amount of polyphenol released (μg) at time t, and M0 is the total polyphenol loading (μg), and the results are shown in the graph of FIG. 6. In each simulated food system, all films had similar release profiles, starting at a faster release rate and then slowing down. The time for the ZMP to reach equilibrium in three systems of water, 3.0% acetic acid and 10% ethanol is 720min, 540min and 1440min respectively, and the ZMP release in the acid food simulation system is sequentially higher than that in the water-based and alcoholic food simulation system (p < 0.05). This suggests that ZMP/C-film has the highest solubility in acidic media and that the release of polyphenols from the polymer matrix is related to many factors such as the nature of the polymer itself (swelling, molecular weight distribution, density, size, etc.), the nature of the polyphenols themselves (molecular size, shape, density, polarity, solubility, etc.), and the factors related to the interaction of the polymer matrix with polyphenols (plasticization, plasticization resistance, etc.). In this study, the high solubility of chitosan in acidic media resulted in dissociation of hydrogen bonds between amino groups and phenolic groups, thereby facilitating the entrance of acetic acid solvent into the membrane matrix and increasing the release rate of ZMP, and in addition, the release rate of polyphenols depends on the ZMP partition coefficient between the organic phase and the aqueous phase, which is slightly soluble in water, and the ZMP partition coefficient in 10% acetic acid volume is greater relative to the aqueous simulated liquid. From the above analysis it can be deduced that the release process of ZMP may be a system solution penetration into the matrix, resulting in swelling of the polymer backbone, an increase of free volume, widening of the polymer cross-linked network, after which the amorphous polyphenols dissolved in the chitosan polymer matrix diffuse throughout the polymer network space, migrating to the external solution system. It can be seen that the release of the polyphenols from ZMP/C-film is affected by the polarity and pH of the environmental system, with the maximum release in acetic acid solution.

Antioxidant capacity

The antioxidant capacity of the 1.0% ZMP/C-film releasing liquid is determined by measuring DPPH and ABTS+ free radical clearance, the result is shown in figure 7, the antioxidant activity of the composite film is positively correlated with the releasing time, the scavenging effect of the ZMP/C-film under different food simulation systems is obviously different (p < 0.05), the antioxidant capacity of the film under 3% acetic acid system is strongest, the scavenging rate of the DPPH and the ABTS+ free radical is 73.25% and 81.06% respectively, the scavenging rate of the DPPH and the ABTS+ free radical is 0.83 times and 0.82 times of Vc under the same condition, and the lowest free radical scavenging rate is shown in 10% ethanol solution, which is basically consistent with the research result of the ZMP releasing rate.

ZMP/C-film fresh-keeping strawberry research

Fresh strawberries were collected from the Shanxi Yuci farm, samples of consistent color, size, weight and maturity were selected and split equally into three groups (n=15) of untreated control, C-film, ZMP/C-film. Strawberry was placed in a 4L polystyrene container, the mouth of the container was covered with ZMP/C-film, the samples were kept at room temperature at 25℃and 50% relative humidity for 7 days, and the weight loss rate and Vitamin C (Vitamin C, vc) were measured at 0,1,2,3,4,5,6,7 days, respectively, and each set of fresh-keeping tests was repeated three times.

The weight loss rate is calculated according to the formula (11)

Wherein m0 is the weight of the strawberries stored for 0 day, and mt is the weight of the strawberries stored for different time periods.

Measuring Vc content, namely diluting 10g of ground strawberry pulp to 20mL by using 1.0mol/L HCl solution, carrying out vortex oscillation for 5min, centrifuging for 5min at 4 ℃ 7500r/min, filtering by using a 0.45 mu m filter membrane, taking supernatant, carrying out absorbance measurement, and calculating according to a standard Vc standard curve equation.

Results and analysis:

As shown in fig. 8-a, control (CK) strawberries began to lose gloss and moisture on day 2, withered and blackened markedly on day 4, rotted on day 5, no significant change in appearance was observed with the film-covered fresh-keeping treatment, and the weight and Vc changes of the three strawberries at different storage times were significantly different (p < 0.05). With the increase of the storage time, the weight loss of the strawberries in the three groups gradually increases (figure 8-B), the weight loss rate of the strawberries in the control group which is not covered by the film is obviously higher than that of the samples in the treatment group, and the film can effectively prevent the water of the strawberries samples in the container from diffusing to the external environment. After 7d storage, the weight loss rate of the ZMP/C-film treated strawberries (4.85%) was significantly lower than the weight loss of the uncovered fresh-kept strawberries (15.47%) and the weight loss rate of the C-film treated group (6.33%). The addition of ZMP to C-film significantly reduced strawberry weight loss, possibly associated with ZMP/C-film having denser structural properties (see SEM results), inhibiting the diffusion of strawberry moisture into the external environment.

Vc is an important indicator of fresh fruit. As shown in FIG. 8-C, the Vc content of the three strawberries in the storage period tended to decrease, and the Vc content of the strawberries in the ZMP/C-film treatment was slowly decreased from 712.77mg/kg to 546.84mg/kg on day 7, but higher than 513.16mg/kg of the strawberries in the C-film treatment group and 314.62g/kg of the strawberries in the uncovered treatment group. In contrast, the CK group decreased significantly, while the ZMP/C-film and C-film treated groups decreased slowly, especially ZMP/C-film. The loss of Vc of the strawberries is related to self respiration, external oxidation and microbial spoilage in the storage process, most probably oxygen exists, the oxidation loss of vitamin of the strawberries is promoted, the chitosan film prevents the strawberries from being contacted with the oxygen, the oxidation loss of Vc is inhibited, and the release of polyphenol in ZMP/C-film can prevent Vc from being oxidized, so that the quality of the strawberries is more effectively protected.

In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Dissolving chitosan in an acidic aqueous solution, heating and stirring uniformly, adding a pepper leaf polyphenol extract, homogenizing, filtering, vacuum degassing to prepare a film solution, pouring the film solution into a mould in a pouring film forming mode, and drying to prepare the pepper leaf polyphenol-chitosan composite film;

The ratio relationship between the chitosan and the polyphenol extract of the pepper leaves and the acidic aqueous solution is 2g, 0.5-1.0 g and 100mL;

The polyphenol extract of the pepper leaves comprises epicatechin, chlorogenic acid, p-coumaric acid, ferulic acid, quercitrin, quercetin and kaempferol.

2. The method for preparing the pepper leaf polyphenol-chitosan composite membrane according to claim 1, wherein the acidic aqueous solution is 1% acetic acid solution.

3. The preparation method of the pepper leaf polyphenol-chitosan composite film according to claim 1, characterized in that a casting film forming technology is adopted, 20ml of film solution is cast in a mold with the diameter of 9cm, the mold is a film making device, and the prepared film thickness is 39.07-41.19 μm.

4. The preparation method of the pepper leaf polyphenol-chitosan composite membrane according to claim 1 is characterized in that the heating temperature of chitosan dissolved in an acidic aqueous solution is 60 ℃, the stirring time is 30min, the homogenizing time is 10min at the rotating speed of 8000 r/min after the pepper leaf polyphenol extract is added, the pore diameter of a filtering membrane is 0.45 μm, the degassing vacuum degree is-0.08 MPa, the drying temperature is 25 ℃ after the membrane solution is poured into a mould, and the drying time is 24h, wherein the mould is a membrane making device.

5. The preparation method of the pepper leaf polyphenol-chitosan composite membrane according to claim 1, wherein the pepper leaf polyphenol extract is prepared by dissolving pepper leaf powder in ethanol solution according to a feed liquid ratio of 1:20, heating in a water bath, centrifuging to obtain supernatant, concentrating, and purifying to obtain the pepper leaf polyphenol extract.

6. The preparation method of the pepper leaf polyphenol-chitosan composite film according to claim 5, wherein the heating temperature in a water bath is 40 ℃, the heating time is 60min, the centrifugation is carried out at 6000r/min for 10min, and the concentration volume is 25%.

7. The method for preparing the pepper leaf polyphenol-chitosan composite membrane according to claim 5 is characterized in that the pepper leaf polyphenol extract is purified by taking polyamide as a stationary phase, loading concentrated pepper She Duofen crude extract 1.5 BV to be 30 min, eluting with ddH ₂ O and 75% ethanol respectively, collecting 2 BV eluent and 3 BV eluent respectively, and concentrating and purifying to obtain the pepper leaf polyphenol extract.

8. The pepper leaf polyphenol-chitosan composite membrane prepared by the method according to any one of claims 1-7.