CN114015094B

CN114015094B - High-strength hordein chitosan composite membrane and preparation method thereof

Info

Publication number: CN114015094B
Application number: CN202210014398.9A
Authority: CN
Inventors: 梅晓宏; 程思琪; 李非凡; 张晓云; 赵天瑜
Original assignee: China Agricultural University
Current assignee: China Agricultural University
Priority date: 2022-01-07
Filing date: 2022-01-07
Publication date: 2022-03-11
Anticipated expiration: 2042-01-07
Also published as: CN114015094A

Abstract

The invention discloses a high-strength hordein chitosan composite membrane and a preparation method thereof. The composite membrane is prepared by dissolving and uniformly mixing hordein and chitosan serving as base materials and finally adopting a drop casting technology. The method has simple process, and the prepared composite membrane has uniform texture, has the highest mechanical strength compared with similar composite membranes, and can meet the requirements of food and medicine packaging.

Description

High-strength hordein chitosan composite membrane and preparation method thereof

Technical Field

The invention belongs to the technical field of food preservation, and particularly relates to a high-strength hordein chitosan composite film and a preparation method thereof.

Background

Food packaging plays an important role in the food industry, primarily to prevent biological, chemical and physical hazards in food circulation and transportation. However, with the development of scientific technology, the environmental hazard of non-degradable packaging materials is receiving more and more attention from countries around the world. Therefore, the development of renewable and environmentally friendly biopolymer materials is imminent. Natural polysaccharides, proteins, lipids, etc. are biopolymers with the advantages of being renewable, degradable, edible, and biocompatible, etc., and are promising alternatives because they can be used as replicators for synthetic organic polymers (e.g., plastics).

In recent years, edible films have attracted considerable attention from researchers due to their biodegradable, renewable, non-toxic properties. Currently, edible films are mainly classified into four types: 1) proteins (whey protein, soy protein); 2) polysaccharides (starch, chitosan, cellulose and derivatives thereof); 3) lipids (waxes, acylglycerols and fatty acids); 4) composite materials (containing a mixture of two or more components that produce films with improved physicochemical properties). In recent years, consumer awareness of edible, biodegradable and environmentally friendly packaging materials is continuously improved, and edible films and coatings are one of the emerging strategies for optimizing food quality.

Chitosan (CH) is a renewable natural resource obtained from alkaline deacetylation of chitin at high temperatures. It has been studied as early as the middle of the 20 th century and has been widely reported as a natural food preservative. In addition, chitosan is an excellent film forming material, and in recent years, studies on chitosan-based composite films such as chitosan/pectin composite films, chitosan/gelatin blended films, chitosan/soy protein, chitosan/zein blended films and the like have been carried out, and the results show that the chitosan-based thin films have good mechanical properties and gas (CO) resistance₂And O₂) Selective permeability of. However, the use of chitosan alone as a film forming agent has certain drawbacks, not to be neglected, that is, its high hydrophilicity, which limits its application in food packaging. Therefore, the hydrophobic property of the hydrophobic fiber is improved. Previous studies have indicated that the addition of lipids and clay can increase the hydrophobicity of chitosan membranes in cases where the composite membranes are mechanically weak.

CHENGUIYUN (antibacterial zein/chitosan composite film preparation and properties, CHENGUIYUN, food science, volume 38, stage 15) chitosan with different concentrations is added into zein, the chitosan mass fraction is controlled within the range of 2% -8%, the properties of the composite film are remarkably changed, the tensile strength is 28MPa, and the water vapor transmission rate reaches 9.16 g.m/(m.m/(m.m.M.M.²h.Pa), large intestineThe bacillus bacteriostasis experiment shows that the composite membrane has stronger antibacterial property by adding the chitosan. The composite membrane is prepared from the composite membrane by the ultrasonic microblog synergy method, such as liuting and the like (the process for preparing the composite membrane is optimized by the ultrasonic microwave synergy method, and liuting and the like are prepared from the composite membrane by the ultrasonic microwave synergy method in the 37 th volume and the 20 th volume of food science), the tensile strength can reach (19.98 +/-0.34) MPa, the microstructure of the composite membrane is improved, the surface is smooth, and the granular sensation is less. Wangcao et al (preparation and performance of crosslinking agent modified wheat alcohol soluble protein/chitosan composite membrane, Wangcao et al, material science and engineering journal, volume 31, stage 1) adopt solution casting method to prepare crosslinked wheat alcohol soluble protein/chitosan composite membrane, use glutaraldehyde and L-cysteine as crosslinking agent, can improve the tensile strength of the composite membrane to 20MPa, swelling degree, solubility increase obviously with the increase of L-cysteine content.

Hordeins are one of the major endosperm storage proteins of barley grain. Hordeins contain about 40% hydrophobic amino acids and are highly hydrophobic. Guan et al (2020) report a well performing edible hordein/TiO protein₂Composite membranes, indicating that hordein is a promising edible membrane matrix. However, the use of hordein alone as a film forming agent has certain disadvantages, such as low mechanical strength, poor flexibility, poor stability, and brittleness and fragility of the film formed by hordein, which limits the practical application thereof. Recent studies have demonstrated that chitosan can interact with hydrophobins such as hordein by non-covalent interactions. However, the study of the formation of composite membranes by chitosan and hordein complexes has not been reported. The hordein and the chitosan are combined to play a role in complementing advantages, so that the edible composite film with good physical and mechanical properties and barrier property is prepared.

Chinese invention patent application CN110628064A discloses a high-ductility rice protein edible composite membrane prepared by an ultrasonic-enzyme method. The rice protein hydrolysate is prepared by an enzyme method, is prepared into a film forming solution with chitosan according to a certain proportion, and is subjected to ultrasonic treatment and then is subjected to casting film forming under constant temperature and humidity. The rice protein edible composite film has the advantages of smooth surface, compact microstructure, high ductility, and poor oxidation resistance and bacterial inhibition.

The Chinese invention patent application CN102964847A discloses a protein/chitosan composite edible film raw material which comprises the following components: 50 parts of zein, 50 parts of wheat gliadin, 20-50 parts of chitosan and 20-30 parts of glycerol. The edible composite film has good mechanical property, oxidation resistance, water resistance and oil resistance. But no specific cross-linking strength was measured.

Based on the prior art, the invention provides the harmless edible composite film which is simple in ingredients, low in cost, high in crosslinking degree, good in mechanical strength and harmless.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides the high-strength hordein chitosan composite membrane and the preparation method thereof.

Specifically, the invention provides the following technical scheme:

a preparation method of a high-strength hordein chitosan composite membrane comprises the following steps:

(1) preparation of hordeins: grinding barley seeds into powder, mixing the powder with n-hexane, stirring to obtain homogenate, centrifuging to obtain precipitate, and sequentially washing with ultrapure water and sodium chloride solution; mixing the precipitate and barley flour in ethanol solution, stirring and mixing; centrifuging to collect supernatant, and removing ethanol by rotary evaporation; freeze drying to obtain freeze dried powder;

(2) preparing a hordein stock solution: dissolving the hordein obtained in the step (1) in an ethanol solution, and heating and stirring to obtain a hordein stock solution;

(3) preparing a chitosan stock solution: dissolving Chitosan (CH) in an acetic acid solution, heating and stirring to obtain a chitosan stock solution;

(4) preparing a film forming solution: mixing the hordein stock solution and the chitosan stock solution obtained in the steps (2) and (3) according to a certain proportion, stirring at room temperature to obtain a hordein/chitosan (HCH) solution, and carrying out ultrasonic treatment to obtain a film-forming solution;

(5) preparing a hordein chitosan composite membrane: and (4) dripping the film-forming liquid obtained in the step (4) into a mould, drying in an oven, peeling the film, and balancing in the oven to obtain the hordein chitosan composite film.

To further achieve the object of the present invention, preferably, in step (1), hordeins are prepared by the following method:

barley seeds were ground to powder and then stirred continuously with n-hexane at a ratio of 5:1 (v/w) for 2h at 25 ℃. The homogenate was centrifuged at 2000 Xg for 5min at 25 ℃ in a high-speed refrigerated centrifuge. The resulting precipitate was washed once by centrifugation with ultrapure water and 0.1M sodium chloride solution, respectively. The precipitate was dispersed in 75% (v/v) ethanol aqueous solution at a ratio of solvent to barley flour of 10:1 (v/w), and stirred at 500rpm for 2h at 55 ℃. The supernatant was collected by centrifugation, centrifuged at 4000 Xg for 5min, and residual ethanol was removed using a rotary evaporator at 45 ℃. The samples were freeze dried in a freeze dryer for 48 h and the dry powder was stored at 4 ℃ for further use.

Further, in the step (2), the final volume concentration of the ethanol solution is 70-80%, the stirring temperature is 45 ℃, and the mass percentage concentration of the obtained hordein stock solution is 1.0%.

Further, in the step (3), the mass percentage concentration of the acetic acid solution is 2.0%, the stirring temperature is 100 ℃, and the mass percentage concentration of the obtained chitosan stock solution is 3.0%.

Further, in the step (4), the ratio of the hordein stock solution to the chitosan stock solution is 1:3, 1:5, 1:7 and 1:9 (v/v);

preferably, the stirring and mixing conditions are magnetic stirring at the speed of 500 rpm;

preferably, the stirring and mixing time is 15 min.

Further, step (4), the ultrasonic power is 200W;

preferably, the sonication time is 12 min.

Further, step (5), the film pouring method is a drop casting method; the mould is a polytetrafluoroethylene mould;

preferably, the diameter of the die is 10 cm-20 cm, and preferably, the diameter is 15 cm;

preferably, the oven temperature is 37 ± 1 ℃;

preferably, the drying time is 24 h;

preferably, the equilibrium temperature is 37 ± 1 ℃;

preferably, the equilibrium humidity is 54 ± 2%;

preferably, the equilibration time is 72 h.

The invention provides a high-strength hordein chitosan composite film which is characterized in that the raw materials are all edible.

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

(1) the hordein chitosan composite membrane prepared by the invention has excellent mechanical strength, thermal stability, transparency and hydrophobicity, so that the hordein chitosan composite membrane has higher operability in the field of food packaging.

(2) The preparation method disclosed by the invention is low in production cost, simple in preparation process, green and environment-friendly, high in production efficiency and convenient to popularize and use.

Drawings

Fig. 1 scanning electron micrographs of the surface (a 1-E1) and cross section (a 2-E2) of cast films from chitosan film (a 1, a 2), hordein/chitosan =1:9 composite film (B1, B2), hordein/chitosan =1:7 composite film (C1, C2), hordein/chitosan =1:5 composite film (D1, D2), hordein/chitosan =1:3 composite film (E1, E2).

FIG. 2 is a Fourier transform infrared spectrum of chitosan film and hordein chitosan composite film.

FIG. 3 is a differential scanning calorimetry trace of chitosan films and hordein chitosan composite films.

FIG. 4 is a schematic thickness diagram of a chitosan film and a hordein chitosan composite film.

FIG. 5 is a schematic drawing showing the tensile strength of chitosan films and hordein chitosan composite films.

FIG. 6 is a schematic diagram of the elongation at break of chitosan films and hordein chitosan composite films.

FIG. 7 is a comparison of the mechanical strength of the composite films obtained in example 6 by the same film-forming process.

In the figure, different capital letters indicate that the difference among groups is significant (P is less than 0.05) (namely the difference among a gliadin/chitosan composite membrane, a zein/chitosan composite membrane and a hordein/chitosan composite membrane is significant), and different lower letters indicate that the difference among groups is significant (P is less than 0.05) (the difference among different ratios of the gliadin/chitosan is significant).

Detailed Description

The conception and the resulting technical effects of the present invention will be further described with reference to specific embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention. The method is a conventional method unless otherwise specified. The materials are commercially available from the open literature unless otherwise specified.

Example 1 preparation method of high-strength hordein chitosan composite membrane

The preparation method comprises the following steps:

s1 extraction of hordeins: barley seeds were ground into powder using a grinder and then continuously stirred with n-hexane at a ratio of 5:1 (v/w) at 25 ℃ for 2 hours. The homogenate was centrifuged at 2000 Xg for 5min at 25 ℃ in a high-speed refrigerated centrifuge. The resulting precipitate was washed once by centrifugation with ultrapure water and 0.1M sodium chloride solution, respectively. The precipitate was dispersed in 75% (v/v) ethanol aqueous solution at a ratio of solvent to barley flour of 10:1 (v/w), and stirred at 500rpm for 2h at 55 ℃. The supernatant was collected by centrifugation, centrifuged at 4000 Xg for 5min, and residual ethanol was removed using a rotary evaporator at 45 ℃. The samples were freeze dried in a freeze dryer for 48 h and the dry powder was stored in plastic tubes at 4 ℃ for further use.

S2 preparation of hordein stock solution: dissolving hordein in 75% ethanol solution at 45 deg.C to obtain 1.0% hordein stock solution, and cooling the stock solution to room temperature before use.

S3, preparing a chitosan stock solution: chitosan (CH) was dissolved in 2.0% acetic acid solution to give a 3.0% chitosan stock solution at 100 ℃.

S4, preparing a film forming solution: mixing the hordein stock solution obtained in the step S2 and the chitosan stock solution obtained in the step S3 in a ratio of 1:3, 1:5, 1:7 and 1:9 (v/v), and stirring the HCH solution for 15min at a speed of 500rpm by using a magnetic stirrer to prepare a hordein/chitosan (HCH) solution. Then, the HCH solution was treated with a sonicator at 200W for 12 min to obtain a deposition solution.

S5 preparation of the hordein chitosan composite membrane: and (3) preparing the hordein chitosan composite membrane by adopting a drop casting method, and dropping 15 mL of the membrane-forming liquid obtained in the step S4 into a polytetrafluoroethylene mould with the diameter of 15 cm. Then, the mold was placed in an oven at 37. + -. 1 ℃ for 24 hours, dried and stripped, and then incubated in a desiccator at 37. + -. 1 ℃ with a relative humidity of 54. + -. 2% for at least 72 hours to reach equilibrium.

Example 2 characterization of hordein Chitosan composite membranes

Further analyzing the obtained composite membrane, namely fixing the hordein chitosan composite membrane on an aluminum support by using a double-sided carbon belt, coating a fine gold-palladium layer, observing the surface appearance of the membrane by adopting a scanning electron microscope under the acceleration voltage of 3Kv, the working distance of 10.9-11.7 mm and the magnification of 10000 times, and finding that the surface crack of the chitosan membrane (A in the figure 1) is small and the rice grains protrude more; the surface of the composite membrane (B in figure 1) obtained by mixing hordein and chitosan according to the proportion of 1:3 has large protrusions and small holes; the surface of the composite membrane (C in figure 1) obtained by mixing hordein and chitosan according to the proportion of 1:5 has slight stripes, and the whole composite membrane is smooth; the surface of the composite membrane (D in figure 1) obtained by mixing hordein and chitosan according to the proportion of 1:7 has smaller cracks and bulges; the surface of the composite membrane (E in figure 1) obtained by mixing hordein and chitosan according to the ratio of 1:9 is similar to that of the control group, and the bulges are relatively less. By observing the cross section of the membrane, the pores in the composite membrane are more regular than those in the chitosan membrane. Furthermore, the greater the protein fraction, the more dense the composite membrane. The intermolecular interaction exists between the chitosan and the hordein, so that the chitosan can be crosslinked or adsorbed on the surface of the hordein, and the membrane density is increased.

The sample was subjected to fourier transform spectroscopy using a fourier transform spectrophotometer. The spectrum is 4000-400 cm^-1The resolution is 4cm by 32 times of scanning^-1. Analysis of the ir spectra of hordein, hordein/chitosan =1:3, hordein/chitosan =1:5, hordein/chitosan =1:7, hordein/chitosan =1:9 and chitosan film (fig. 2) revealed that the ir spectrum of the chitosan film was 3191cm^-1There is a broad peak nearby, which may be due to stretching vibrations of O-H and N-H groups. At 1656cm^-1，1598cm^-1，1380cm^-1The peaks at (A) are amide I band (C = O), amide II band (N-H) and amide III band (C-N), respectively. Meanwhile, the chitosan is 1080.4 cm^-1The obvious peak appeared in the (C-O) peak is probably caused by the stretching vibration of the C-O in the CH-OH group of the chitosan. The hordein is 3310cm^-1The wide characteristic peak represents O-H stretching vibration, 1661cm^-1And 1534cm^-1The other two characteristic peaks in (b) belong to the amide i band (C = O) and the amide ii band (N-H), respectively. Compared with chitosan, with the increase of chitosan content, the O-H stretching vibration of the hordein chitosan composite membrane is respectively 3191, 3271, 3278 and 3278cm^-1The change of the peak position of the absorption peak shows that hydrogen bonds are formed between the chitosan and the hordein. The peak position of the amide II band shifts significantly as the hordein content increases.

And evaluating the thermal performance of the composite membrane by using a DSC-60 differential scanning calorimeter, wherein the analysis temperature is 30-250 ℃, and the heating rate is 20 ℃/min. The nitrogen flow was set at 25mL/min, and an empty crucible was used as a control. After cooling the film sample, about 5mg, to room temperature, it was analyzed for thermal stability, and individual chitosan and hordein showed endothermic peaks at 136.5 ℃ and 163.5 ℃ (fig. 3). The endothermic peak of the composite membrane increased from 136.5 ℃ to 167.1 ℃ with increasing hordein content. The hordein is connected with the chitosan, and the structure of the composite membrane is more compact through hydrogen bond and hydrophobic interaction, so that the composite membrane has better thermal stability.

Example 3 measurement of thickness and mechanical Properties of hordein Chitosan composite membranes

The thickness of the sample is measured by a digital micrometer, and 6 points are randomly selected around the composite membrane to calculate the average thickness. The Tensile Strength (TS) and Elongation At Break (EAB) of the composite film were measured using a physical property analyzer, the initial distance was 60mm, and the probe speed was 0.5 mm/s. The composite film was cut into strips of 20X 80 mm, each set being repeated at least 3 times. The calculation formula for TS and EAB is as follows:

TS(MPa)=P/(b×d)

EAB(%)=(L-L₀)/L₀ ×100%

wherein P is the maximum force (N), b is the thickness (mm), and d is the film width (mm);

l is the length (mm) of the film at the time of rupture, L₀Is the initial length (mm) of the film.

The thickness of the hordein/chitosan-based composite membrane is reduced compared to the chitosan film alone. The lowest thickness of the composite membrane of hordein and chitosan mixed in a ratio of 1:5 was 26 ± 5 μm, which is significantly lower than that of the composite membrane of hordein and chitosan mixed in a ratio of 1:3 (p < 0.05) (fig. 4). As the hordein content decreased, the thickness of the hordein/chitosan =1:7, hordein/chitosan =1:9 composite membrane gradually increased. This result indicates that the hordein content is an important factor in determining the physicochemical properties of the film.

Mechanical properties are critical to the adequate design of biopolymer packaging films and must be somewhat resistant. The addition of hordeins significantly improved the tensile strength of the film. With the decrease of the content of the hordein, the tensile strength of the composite membrane gradually increases, and when the ratio of the hordein to the chitosan reaches 1:7, the tensile strength of the composite membrane is the highest and is about 36 +/-5 MPa (figure 5). However, as the prolamin content is further reduced, the tensile strength of the composite film begins to decrease. The tensile strength of whey protein isolate/chitosan composite membrane is reported to be about 3MPa, the tensile strength of polysaccharide/soy protein/lauric acid composite membrane is reported to be about 4MPa, and the hordein chitosan composite membrane disclosed by the patent has good tensile strength and is obviously superior to other similar composite membranes (Table 1).

TABLE 1 comparison of tensile Strength of similar composite films

The elongation at break reflects the elongation ability of the film before breaking, and the elongation at break of the composite film is slightly increased due to the addition of hordein, i.e., the ductility and flexibility of the film are improved (fig. 6). Intermolecular hydrogen bonds play a role therein.

Example 4 measurement of physical Properties of hordein-chitosan composite Membrane

(1) Water Vapor Permeability (WVP): adopting Poplar and Jersen method, improving, collecting dried filter paper with diameter of 7cm, and accurately weighing to 0.1mg (m)₁) Wrapping with composite membrane, sealing with the stock solution of membrane-forming solution, placing in a dryer containing saturated potassium bromide, placing in an oven at 60 deg.C with relative humidity of 79 + -2%, incubating for 72 hr, collecting filter paper, and weighing (m₂) All tests were performed in 5 replicates. The calculation formula of WVP is as follows:

WVP(%)=(m₂-m₁)/m₁ ×100%

in the formula m₁Is the initial weight of the filter paper, m₂The weight of the filter paper after the culture.

When hordein is added, the moisture permeability of the composite membrane is remarkably reduced (p is less than 0.05), and the water-blocking performance of the composite membrane is enhanced (table 2). The hydrophobic property of the chitosan can be improved by adding the prolamin, so that the composite membrane has better waterproof property compared with a single chitosan membrane. When the mass ratio of the chitosan to the hordein is 5:1, the water vapor transmission rate is the lowest and is 2.86% +/-0.03%.

(2) Water solubility: according to the Gennadios method, a 2.0X 2.0cm film was dried in an oven at 80. + -. 2 ℃ for 24 hours and then weighed (m)₁) Put into a beaker filled with 50mL of distilled water to incubate for 24h at room temperature. Then the wet film is put into an oven, dried for 24 hours at 80 +/-2 ℃, and then weighed to obtain the final weight (m)₂). All experiments were repeated three times. The water solubility calculation is as follows:

Water solubility(%)=(m₁-m₂)/m₁ ×100%

in the formula m₁Is the initial weight of the film, m₂Is the weight of the wet film after drying.

The water solubility of the chitosan film (13.1%) was significantly higher than the composite film (p < 0.05) (table 2). On the one hand, factors such as molecular weight, degree of deacetylation, plasticizer concentration and content affect the water solubility of the chitosan film. On the other hand, the addition of the hydrophobic alcohol soluble protein inhibits the permeation of water molecules and reduces the water solubility of the composite membrane. It should be noted that such low solubility is advantageous, since high solubility is a significant disadvantage in the industrial application of hydrocolloid based films.

(3) Water content: the moisture content was determined by measuring the weight loss of the film after drying at 80. + -. 2 ℃ for 24 h. All measurements were performed in 3 replicates. Film samples (2.0X 2.0 cm) were weighed (w)₁) Drying in an oven at 80 +/-2 ℃ for 24h and then weighing (w)₂). The water content calculation formula is as follows:

Moisture content(%)=(W₀-W₁)/W₀ ×100%

wherein W₀Is the initial weight of the film, W₁Is the dry weight of the film.

The water content of the chitosan film was 15.03%, and the water content of the composite film was significantly reduced from 13.73% to 7.44% (p < 0.05) with increasing prolamin content (table 2). Prolamines can bind to chitosan molecules through hydrogen bonding and hydrophobic interactions, which limit the interaction between the hydrophilic groups of chitosan and water molecules. Thus, less water is bound to the chitosan, resulting in a reduced water content.

TABLE 2 physical properties of chitosan and hordein chitosan composite membranes

Wherein H stands for hordein abbreviation, CH is chitosan abbreviation, HCH refers to composite membrane HCH mixed with the two; HCH3 represents a protein: the ratio of sugar is 1: 3; HCH5 is a protein: the sugar ratio is 1: 5; HCH7 is a protein: the sugar ratio is 1: 7; HCH9 is a protein: the sugar ratio is 1: 9.

a. the same letter of b, c and d represents no significant difference, the different letter represents significant difference, and the standard deviation is calculated as: each group is at least 3 groups of parallels, after the standard deviation is calculated by using the sps, the result data has overlapping condition, namely the two data have no obvious difference directly, otherwise, the difference is obvious.

Example 5 comparison of mechanical Strength of composite films for optimal film formation Process

In order to detect the mechanical strength characteristic of the hordein-chitosan composite membrane, the currently known optimal processes of a zein/chitosan composite membrane, a wheat prolamin/chitosan composite membrane and a hordein/chitosan composite membrane are used for membrane preparation, and comparison is further carried out.

1. Zein/chitosan composite film (27 MPa)

The optimal film preparation process comprises the following steps: dissolving a certain amount of chitosan in 2% acetic acid solution, standing for 24h to fully hydrate the chitosan, and obtaining 2% chitosan acetic acid solution. Dissolving zein in 80% ethanol solution, wherein the mass concentration of zein is 100 mg/mL, the mass fraction of chitosan is 8% of that of zein, heating in water bath at 65 ℃ for 10 min, standing for defoaming, measuring the solution property, casting into zein/chitosan composite film by using a tape casting method, and drying at room temperature for 24 h. The film is placed in a dryer with relative humidity (50 +/-4)%, temperature (23 +/-2) ° C for storage for 48 h, and the film property is measured.

2. Wheat alcohol soluble protein/chitosan composite film (18 MPa)

The optimal film preparation process comprises the following steps: mixing 10% wheat gliadin solution and 2% chitosan acetic acid solution at a mass ratio of 3:10 to make the mass ratio of prolamin/chitosan dry matter be 6:4, adding metered glycerol as plasticizer (glycerol/dry matter is 20g/100 g), and magnetically stirring the mixed solution at room temperature for 30 min. Pouring onto plastic culture dish, heating in 50 deg.C oven for 30min, vacuumizing at 25 deg.C until most of solvent volatilizes, and naturally drying to constant weight. After the sample had completely dried to a film, the sample was removed and placed at 25 ℃ and 57.5% relative humidity for 3 days.

3. Hordein/chitosan composite membrane (35 MPa)

The optimal film preparation process comprises the following steps: an appropriate amount of CH3COOH was dissolved in water to prepare an acetic acid buffer solution (2%). Dispersing proper amount of low viscosity chitosan (CH, deacetylation degree is more than or equal to 95%) in acetic acid buffer solution, heating at 100 + -2 deg.C, stirring at 500rpm/min for 2h until chitosan is fully dissolved, and cooling to room temperature to obtain chitosan solution (3%, w/v). Dissolving appropriate amount of hordein (H) lyophilized powder in 75% ethanol solution, stirring and heating at 55 deg.C for 2 hr to dissolve sufficiently to obtain hordein solution (1%). Hordein and chitosan solution were mixed at H: CH =1:7, a film forming solution was prepared using a magnetic stirrer at a speed of 500rpm/min for 15min, and then the resulting film forming solution was sonicated at a power of 200W for 12 min, with the chitosan solution as a control. The film is then prepared by drop casting techniques, the solution containing the polymeric material is placed on a suitable substrate and the solvent is controlled to evaporate. Using a disposable plastic sterile petri dish as a mold, 10ml of the solution was added to a petri dish with a diameter of 15 cm and left to dry at 37 ℃ for 24 hours. After separation from the petri dish, the membrane was equilibrated with saturated sodium bromide solution in a desiccator at 35 ℃ and 54% relative humidity for at least 72h, ready for use.

All three composite films described above were measured by the Tensile Strength (TS) increase method in example 3. Results the results of mechanical strength measurements were as follows: the mechanical strength of the zein/chitosan composite film is 27MPa, the mechanical strength of the wheat zein/chitosan composite film is 18MPa, and the mechanical strength of the barley zein/chitosan composite film is 35 MPa.

Analysis conjectures that in the zein/chitosan composite film, the chain segment of chitosan is fully entangled with zein molecular chains, the interaction between protein and polysaccharide groups is mainly used, the network structure formed by crosslinking is uniformly distributed, the hydrogel property of chitosan enables the formed film network structure to keep more water, and the water in the composite film plays a certain plasticizing role; in the wheat alcohol soluble protein/chitosan composite membrane, interaction exists between chitosan and wheat alcohol soluble protein molecules, and the interaction may be hydrogen bond interaction and hydrophobic interaction; in the hordein/chitosan composite membrane, the chain segment of chitosan is fully entangled with a hordein molecular chain, and at the moment, hydrogen bond action and hydrophobic action exist between protein and polysaccharide groups, so that a network-shaped structure is formed and is uniformly and compactly distributed.

The principle of the composite membrane formed by the three components is similar, and the composite membrane contains similar groups, but the amino acid type, the number and the structure are greatly different, and finally the mechanical strength results are different.

Example 6 comparison of mechanical Strength of composite Membrane for optimal Process of hordein Chitosan

A film making process:

an appropriate amount of CH3COOH was dissolved in water to prepare an acetic acid buffer solution (2%). Dispersing proper amount of low viscosity chitosan (CH, deacetylation degree is more than or equal to 95%) in acetic acid buffer solution, heating at 100 + -2 deg.C, stirring at 500rpm/min for 2h until chitosan is fully dissolved, and cooling to room temperature to obtain chitosan solution (3%, w/v). Dissolving appropriate amount of hordein (H) (or zein/wheat gliadin) lyophilized powder in 75% ethanol solution, stirring and heating at 55 deg.C for 2 hr to dissolve sufficiently to obtain hordein solution (1%). Hordein and chitosan solution were mixed at H: CH =1:7, a film forming solution was prepared using a magnetic stirrer at a speed of 500rpm/min for 15min, and then the resulting film forming solution was sonicated at a power of 200W for 12 min, with the chitosan solution as a control. The film is then prepared by drop casting techniques, the solution containing the polymeric material is placed on a suitable substrate and the solvent is controlled to evaporate. Using a disposable plastic sterile petri dish as a mold, 10ml of the solution was added to a petri dish with a diameter of 15 cm and left to dry at 37 ℃ for 24 hours. After separation from the petri dish, the membrane was equilibrated with saturated sodium bromide solution in a desiccator at 35 ℃ and 54% relative humidity for at least 72h, ready for use.

All three composite films described above were measured by the Tensile Strength (TS) increase method in example 3. Results the results of mechanical strength measurements were as follows:

the membrane preparation treatment is carried out by using the same process, and the hordein/chitosan composite membrane can still keep higher mechanical strength; wheat and zein, however, may be mainly deficient in substances such as glycerin as a plasticizer due to non-optimal processes, resulting in a decrease in mechanical strength on the contrary (as shown in fig. 7).

Although the present invention has been described in detail hereinabove by way of general description, specific embodiments and experiments, it is not limited to the above-described embodiments, but may be modified or improved on the basis of the present invention, as will be apparent to those skilled in the art. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims

1. A preparation method of a high-strength hordein chitosan composite membrane is characterized by comprising the following steps:

(3) preparing a chitosan stock solution: dissolving chitosan in acetic acid solution, heating and stirring to obtain chitosan stock solution;

(4) preparing a film forming solution: mixing the hordein stock solution and the chitosan stock solution obtained in the steps (2) and (3) according to a certain proportion, stirring at room temperature to obtain a hordein/chitosan solution, and carrying out ultrasonic treatment to obtain a film-forming solution;

2. The preparation method according to claim 1, wherein the thickness of the hordein chitosan composite membrane is 0.02-0.03 mm.

3. The preparation method according to claim 1, wherein the tensile strength of the hordein chitosan composite membrane is 20-40 MPa.

4. The method according to claim 1, wherein for step (1), the preparation of hordeins comprises in particular:

grinding barley seeds into powder, and continuously stirring the powder and n-hexane at 25 ℃ for 2 hours according to the ratio of the mass of the barley powder to the volume of the n-hexane being 5: 1; centrifuging homogenate at 25 deg.C for 5min at 2000 × g with a high-speed refrigerated centrifuge; centrifuging and washing the obtained precipitate once by using ultrapure water and 0.1M sodium chloride solution respectively; dispersing the precipitate in 75% ethanol water solution at a ratio of 10:1 of solvent volume to barley flour mass, stirring at 55 deg.C and 500rpm for 2 h; centrifuging to collect supernatant, centrifuging at 4000 Xg for 5min, and removing residual ethanol at 45 deg.C with rotary evaporator; the samples were freeze dried in a freeze dryer for 48 h and the dry powder was stored at 4 ℃ for further use.

5. The method according to claim 1, wherein for step (2), the final volume concentration of the ethanol solution is 70% to 80%, the stirring temperature is 45 ℃, and the mass percentage concentration of the obtained hordein stock solution is 1.0%.

6. The method according to claim 1, wherein in the step (3), the acetic acid solution has a concentration of 2.0% by mass, the stirring temperature is 100 ℃, and the chitosan stock solution has a concentration of 3.0% by mass.

7. The method of claim 1, wherein for step (4), the ratio of the volume of the hordein stock solution to the volume of the chitosan stock solution is 1:3, 1:5, 1:7, 1: 9;

and/or the stirring and mixing conditions are magnetic stirring, and the speed is 500 rpm;

and/or, the stirring and mixing time is 15 min.

8. The production method according to claim 1, wherein, for step (4), the ultrasonic power is 200W;

and/or the ultrasonic treatment time is 12 min.

9. The method for preparing a high-strength hordein chitosan composite membrane according to claim 1, wherein for step (5), the membrane inversion method is a drop casting method;

the mould is a polytetrafluoroethylene mould;

and/or the diameter of the die is 10 cm-20 cm;

and/or the temperature of the oven is 37 +/-1 ℃;

and/or the drying time is 24 h;

and/or, the equilibrium temperature is 37 ± 1 ℃;

and/or, equilibrium humidity is 54 ± 2%;

and/or the equilibrium time is 72 h.

10. The hordein chitosan composite membrane prepared by the preparation method according to any one of claims 1 to 9, wherein the raw materials for the membrane are all food grade.