Yak skin collagen polymer network construction method and preparation method of casing film of yak skin collagen polymer network

Abstract

The invention discloses a preparation method for constructing a yak skin collagen polymer network and a casing film of the yak skin collagen polymer network. The preparation method comprises the following steps: step 1, pretreating yak skin; step 2, preparing a collagen group; step 3, preparing a collagenous fiber membrane; and 4, determining the thickness of the collagenous fiber membrane, the dry and wet tensile strength TS and elongation at break EAB of the collagenous fiber membrane, the light transmittance of the collagenous fiber membrane, the moisture content WC and the swelling ratio SR of the collagenous fiber membrane, and the thermal shrinkage rate HSR and the thermal swelling ratio TSR of the collagenous fiber membrane. The yak skin is prepared into collagen slurry, an edible forming agent, a cross-linking agent or a plasticizer is added, a porous network structure is formed through interaction among molecules, the porous network structure can form a film, and the edible protein film or collagen casing has the advantages of being high in mechanical performance, free of pollution during degradation, good in permeability, resistant to microorganisms and oxidation and the like. And not only can the product packaging problem be solved, but also the key effects of protecting the environment and promoting the food industry progress can be achieved. The method has a wide application prospect in the food field for the nutritional ingredients and characteristics of the yak skin, and provides reference and basis for the application and research of the yak skin in the food field.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of yak leather collagen polymer network construction and its sausage casing film forming preparation, and particularly relates to a method for yak leather collagen polymer network construction and its sausage casing film forming preparation. BACKGROUND

[0002] Yak has been living in the Qinghai-Tibet Plateau for a long time, which is a high-cold, hypoxic and strong ultraviolet region. Yak leather is rich in nutritional value, and the collagen content in yak leather is higher than that in yellow cattle leather, which is more suitable for food raw materials. Yak leather resources are relatively scarce, and in the plateau region, yak leather is often regarded as one of the main wastes of yak industry, so it is a big substitute for yellow cattle leather. At present, the research on yak leather is mainly on the extraction process and performance of collagen, and it has not been deeply researched and developed in the food industry, which has caused a lot of resource waste. Therefore, it is of great significance to utilize yak leather in the food industry.

[0003] Yak leather collagen sausage casing is made of yak leather as raw material, and edible sausage casing is processed by extracting collagen. The existing production technology mainly includes dry method and wet method: the dry method is to extrude the ground collagen fibers into a shape and then dry them directly by hot air, or to modify them by immersion and spraying and then dry them again, which has simple equipment and direct process; the wet method is to immerse the extruded collagen fibers in water bath for shaping and cross-linking, and then dry them to make the tubular film, which can make the inside and outside of the tubular film uniform, and the sausage casing is relatively soft and has good mechanical strength.

[0004] However, the existing technology has some problems:

[0005] The adhesion between the collagen and the meat filling is small during the cooking process, and it is easy to separate; the diameter is difficult to control during the blowing process, and the mechanical strength is insufficient, which affects the production efficiency and the consistency of the specifications; the root cause of these problems is that: in the raw material processing, the conventional acid or alkali pretreatment has limited effect on the collagen fibers, and mainly relies on mechanical dispersion, so that the collagen fibers are long and thick, and the film is rough and thick, and the thickness of yak leather itself is large and uneven, which further increases the processing difficulty; in the process control, the sausage casing is thin and small during drying, and it is difficult to accurately control, and the cross-linking degree and other key links are not properly controlled, which affects the adhesion and mechanical strength.

[0006] Therefore, it is an urgent problem for those skilled in the art to provide a method which can form a porous network structure, so that the edible protein film or collagen sausage casing can be formed, and the method has the advantages of strong mechanical performance, no pollution in degradation, good permeability, and anti-microbial and anti-oxidation. SUMMARY

[0007] Therefore, the present application provides a method for yak leather collagen polymer network construction and sausage casing film forming preparation.

[0008] To solve the above technical problems, the present application adopts the following technical solutions:

[0009] The yak leather collagen polymer network construction and its casing film forming preparation method comprises the following steps:

[0010] Step 1: yak leather pretreatment

[0011] Take the cowhide, soak it in NaOH, remove the surface skin, wash it to neutral, add sodium carbonate solution, soak it, rinse it, cut it into small pieces, soak it in HCl+NaCl demineralization solution, rinse it to neutral, and store it in the refrigerator;

[0012] Step 2: preparation of collagen group

[0013] Break the yak leather and crushed ice, swell, break into collagen groups, add sodium carboxymethyl cellulose, mix and knead evenly, and put it in a vacuum drying box for degassing treatment, ready for use;

[0014] Step 3: preparation of collagen fiber film

[0015] Take the collagen group, roll it, soak the film in ammonia solution for solidification, wash it until the pH is neutral, soak it in glycerol solution, dry it, put it in a desiccator for balance, and measure the related indexes of the film;

[0016] Step 4: measurement of collagen fiber film thickness, collagen fiber film dry and wet tensile strength TS and elongation at break EAB, collagen fiber film light transmittance, collagen fiber film moisture content WC and swelling rate SR, collagen fiber film heat shrinkage rate HSR and thermal expansion rate TSR.

[0017] Preferably, in step 1, the cowhide is soaked in 0.1M NaOH at a sample:solution ratio of 1:6 for 24h, and washed with distilled water to remove NaOH;

[0018] Add 5% sodium carbonate solution at a sample:solution ratio of 1:6 to remove fat, soak for 24h, rinse with distilled water to achieve neutral pH, soak in 0.1M HCl+0.1M NaCl demineralization solution at 4℃, the sample to solution ratio is 1:6(w / v), soak for 2h; store in a-80℃ refrigerator.

[0019] Preferably, in step 2, the yak leather and crushed ice are added to a high-speed shearing machine at a ratio of 1:2, the sample is respectively swelled in 0.96WT% hydrochloric acid and 0.7M acetic acid at 4℃ for 24h, and the sample to solution ratio is 1:2(w / v);

[0020] Take the collagen group and add 1% carboxymethyl cellulose sodium by mass fraction, and the mass of carboxymethyl cellulose sodium is 1 / 4 based on the mass of the collagen group;

[0021] Drying temperature 20℃, drying time 60min.

[0022] Preferably, in step 3, 5g collagen group is taken, and is rolled by a stainless steel roller with a 0.5mm groove, and is immersed in 5% ammonia water solution for 10min for solidification, and is washed in deionized water;

[0023] Is immersed in glycerol solution for 30min, and is air-dried at room temperature for 24h, and then is placed in a dryer with a temperature of 25℃ and a relative humidity of 58±3 for 48h.

[0024] Preferably, in step 4, the wet tensile strength TS and the breaking elongation EAB are calculated according to the following formula:

[0025]

[0026] In the formula, F is the maximum force, N; S is the cross-sectional area of the film, mm 2 ; d is the maximum deformation, mm; d0 is the original length of the film, mm.

[0027] Preferably, in step 4, the light transmittance of the collagen fiber film is calculated according to the following formula:

[0028]

[0029] In the formula, T is the transparency value, A 600 is the absorbance value of the thin film at a wavelength of 600nm, and X is the thickness of the thin film.

[0030] Preferably, in step 4, the moisture content WC and the swelling rate SR of the collagen fiber film are calculated according to the following formula:

[0031]

[0032] Each film sample is W0, and the weight is W d ;

[0033]

[0034] The constant weight is Ws.

[0035] Preferably, in step 1, the thermal shrinkage rate HSR and the thermal swelling rate TSR of the collagen fiber film are calculated according to the following formula:

[0036]

[0037] The present application has the following technical effects relative to the prior art:

[0038] The application studies the application potential of yak leather collagen fiber membrane in the field of food casing, and reveals the directional reconstruction mechanism of strong acid controllable hydrolysis on the microstructure of collagen by comparing the influence of hydrochloric acid and acetic acid as swelling acid on the preparation of collagen fiber casing.

[0039] The research finds that, compared with the acetic acid group, the collagen fiber membrane prepared by hydrochloric acid swelling shows comprehensive physical and mechanical properties, and through SEM, FTIR, XRD and TGA research, it is found that the hydrochloric acid treatment group presents a highly ordered parallel arrangement, and the chemical bonds between and within the molecules after treatment increase, and the interaction force increases, indicating that hydrochloric acid can promote its crosslinking, form a more dense network structure, and increase the mechanical properties, thereby providing a theoretical basis for the high-value utilization of yak leather collagen fiber casing. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 For the application Figure 1 SEM images of two kinds of collagen fiber membranes;

[0041] Figure 2 FTIR images of two kinds of collagen fiber membranes in the application;

[0042] Figure 3 XRD images of two kinds of collagen fiber membranes in the application;

[0043] Figure 4 TG and DTG curves of two kinds of collagen fiber membranes in the application. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0045] Pretreatment of yak leather

[0046] Most of the hair on the yak leather hair layer is removed by acid enzyme method, the cowhide is taken, the cowhide is soaked in 0.1M NaOH for 24h with a sample:solution ratio of 1:6, the surface layer of the skin is removed with a scalpel, and then the NaOH is washed away with distilled water until the pH reaches neutral;

[0047] First, 5% sodium carbonate solution is added at a sample:solution ratio of 1:6 to remove fat, and soaked for 24h, and then washed with distilled water to reach neutral pH, cut into small pieces, and soaked in 0.1M HCl+0.1M NaCl demineralization solution at 4℃, with a sample:solution ratio of 1:6(w / v), and soaked for 2h;

[0048] Rinse with distilled water until the pH of the rinse water reaches neutral pH, and store in a -80°C refrigerator.

[0049] Preparation of collagen mass

[0050] Take the cowhide, and add yak hide and crushed ice at a ratio of 1:2 to a high-speed shearing machine to break up, and swell the sample in 0.96 WT% hydrochloric acid and 0.7 M acetic acid at 4°C for 24 h, with the sample to solution ratio being 1:2 (w / v);

[0051] Put the swollen sample into a meat grinder to break it into collagen mass, and add collagen mass to 1% carboxymethyl cellulose sodium CMC, with the mass of CMC being 1 / 4 based on the mass of the collagen mass, and mix and knead uniformly;

[0052] And put it into a vacuum drying oven for degassing treatment, with the drying temperature being 20°C and the drying time being 60 min, take it out, and reserve it for use.

[0053] Preparation of collagen fiber membrane

[0054] Take 5 g of collagen mass, and use a 0.5 mm recessed stainless steel roller to roll it, and immerse the membrane in a 5% ammonia water solution for 10 min for solidification, and wash it in deionized water until the pH is neutral, and immerse it in a glycerol solution of a certain concentration for 30 min;

[0055] Air dry at room temperature for 24 h, and then put it into a desiccator at 25°C and a relative humidity of 58±3 for 48 h, and measure the relevant indices of the membrane.

[0056] Measurement of thickness of collagen fiber membrane

[0057] Use a thickness gauge to measure, measure each membrane 5 times, and take the average value as the membrane thickness.

[0058] Measurement of dry and wet tensile strength (TS) and elongation at break (EAB) of collagen fiber membrane

[0059] Cut the collagen protein casing membrane into a rectangle of 10 mm x 50 mm, and use a tensile testing machine to measure the tensile strength and elongation at break of the sample in dry and wet states, repeat 3-5 times, and take the average value.

[0060] Test parameters: automatic breakage judgment (reach force) 30%, automatic breakage judgment (sensitivity) 30%, running speed 100 mm / min.

[0061] The calculation formula is as follows:

[0062]

[0063] In the formula: F is the maximum force, N; S is the cross-sectional area of the membrane, mm2 d is the maximum deformation, mm; d0 is the original length of the film, mm;

[0064] Measurement of light transmittance of collagen fiber film

[0065] The light transmittance of the film was evaluated using the absorbance value of the film at a wavelength of 600 nm measured using a UV spectrophotometer. The film was cut into a 10*50 mm long strip, placed in a cuvette, and the cuvette was placed in a test cell to test the absorbance of the sample, with the empty cuvette as the reference value. Three samples were taken for each treatment, and the average value was calculated.

[0066] The formula for calculating the transparency value is as follows:

[0067]

[0068] In the formula: T is the transparency value, A 600 is the absorbance value of the film at a wavelength of 600 nm, and X is the thickness of the film.

[0069] Measurement of water content (WC) and swelling rate (SR) of collagen fiber film

[0070] Each film sample (W0) was accurately weighed, then dried at 105°C for 5h until the weight (W d ) was constant, and the WC value of each film sample was calculated:

[0071]

[0072] Each film sample (W0) was accurately weighed, then completely immersed in a PBS solution (pH 7.4).

[0073] When the soaked film reached its constant weight (Ws), the swelling rate (SR) was obtained:

[0074]

[0075] Measurement of heat shrinkage rate (HSR) and heat swelling rate (TSR) of collagen fiber film

[0076] The collagen protein casing sample was cut into a 30*10 mm strip, and after cooking in boiling water for 1 min, the length and width of the casing sample were measured respectively;

[0077] Then according to the change of length (MD, longitudinal direction) and width (TD, transverse direction) before and after cooking, the HSR was calculated using the following formula:

[0078]

[0079] Fourier transform infrared (FTIR) spectroscopy analysis

[0080] Collagen fiber membranes were cut into powder, and then pressed into tablets with a sample:KBr ratio of 1:100. Fourier transform infrared spectroscopy was used in the range of 400 to 4000 cm -1 , with 32 scans and a resolution of 1 cm -1 .

[0081] X-ray diffraction (XRD) analysis

[0082] The crystallinity of the samples was determined using an X-ray diffractometer. Each sample was scanned in the range of 5-50° with a step width of 0.02° and a scan rate of 0.02° / 0.1 s.

[0083] Scanning electron microscope (SEM) analysis

[0084] The samples were quenched in liquid nitrogen, and the cross-sectional features of the collagen fiber membranes were observed at magnifications of x3000 and x5000, respectively, at a voltage of 10 kV.

[0085] Thermogravimetric (TG) analysis

[0086] The thermal degradation behavior of the collagen fiber membranes was explored using TGA. A 5-microgram film sample was weighed and heated from 25 to 600°C at a heating rate of 10°C / min under N2 atmosphere

[0087] Data processing

[0088] Statistical analysis was performed on the experimental data, and all data were repeated three times. The experimental results were expressed as the mean ± standard deviation. IBM SPSS Statistics 26 software was used for analysis, t-test was used for two-sample comparison, ANOVA was used for single-factor variance analysis, and Duncan's multiple comparison method (p<0.05) was used for significant difference analysis.

[0089] Example 1: Analysis of collagen fiber membrane thickness and mechanical properties

[0090] The thickness and mechanical properties of the two collagen fiber membranes are shown in Table 1. The thickness of the collagen fiber membranes in the hydrochloric acid group and the acetic acid group was 0.059 mm and 0.072 mm, respectively. The thickness of the collagen fiber membrane prepared in the hydrochloric acid group was smaller than that in the acetic acid group. The thickness of the commercial collagen casing was about 0.050 mm, and the thickness of the collagen fiber membrane in the hydrochloric acid group was closer.

[0091] The tensile strength and elongation at break of the collagen fiber membranes in dry and wet states were measured, respectively, and the results are shown in Table 1. The tensile strength and elongation at break of the collagen fiber membranes in the hydrochloric acid group were significantly higher than those in the acetic acid group (p<0.05). In general, the mechanical properties of the collagen fiber membranes in the hydrochloric acid group were better than those in the acetic acid group.

[0092] As shown in the table, the tensile strength of the hydrochloric acid treated yak skin collagen fiber membrane in dry and wet state reached 69.70 MPa and 10.73 MPa, respectively. The collagen fiber membrane was prepared from cow skin, and mineralized carboxymethyl cellulose sodium was added to enhance the wet tensile properties, and the wet tensile strength after treatment reached 2.5 MPa; the edible film was prepared by using transglutaminase cross-linked loach collagen protein, and the tensile strength after cross-linking reached 3.07 MPa; glycerol was used as a plasticizer to prepare a gelatin-based edible film, and the tensile strength of the prepared edible film was 17.3 MPa; the edible film was prepared by using TG enzyme cross-linked citrus pectin and mung bean protein, and the tensile strength was 36.71 MPa, and the elongation at break was 2.4%. Compared with other animal collagen sausage casings, the film showed more excellent mechanical properties in dry and wet states.

[0093] Table 1 Physicochemical indexes of collagen fiber membrane

[0094]

[0095] Example 2: Moisture content and light transmission analysis of collagen fiber membrane

[0096] The water content of the film is related to its waterproof ability, and plays a key role in the storage stability of sausage casings and sausage industry. As shown in Table 1, the moisture content of the hydrochloric acid group was significantly less than that of the acetic acid group, which may be because the "densification hydrophobic reconstruction" induced by hydrochloric acid significantly reduced the hydrophilicity of the collagen fiber surface, while acetic acid as a weak acid only swelled the surface, so the hydrophilic groups (-OH, -COOH) still dominated.

[0097] The higher the light transmission value, the lower the transparency of the film; and the transparency of the sausage casing product is an important factor affecting the willingness of consumers to purchase. As shown in Table 2, compared with the acetic acid group, the hydrochloric acid treatment significantly reduced the light transmission value of the collagen fiber membrane, and improved its transparency and apparent quality.

[0098] Table 2 SR, HSR and TSR values of two collagen fiber membranes

[0099]

[0100]

[0101] Example 3: Swelling properties analysis of collagen fiber membrane

[0102] The heat shrinkage rate reflects the degree of shrinkage of the fiber film along the fiber orientation due to thermal denaturation in hot water, which is closely related to the application of collagen sausage casing. The HSR values of the two collagen fiber films are shown in Table 2. The MD of the hydrochloric acid group is significantly lower than that of the acetic acid group, and the TD has no significant change (p < 0.05). The overall performance of the hydrochloric acid group is lower heat shrinkage rate, which may be due to the fact that the cross-linking and entanglement between the molecules of the collagen fiber film of the hydrochloric acid group are more compact and orderly, forming a dense structure, and thus forming a dense film. It was found that the addition of glutaraldehyde to the collagen fiber film could enhance the cross-linking degree, reduce the heat shrinkage rate of the collagen fiber film, and improve its thermal stability. This is consistent with the results of the SEM images described above.

[0103] SR and TSR are the water absorption and swelling of collagen fiber film at room temperature and boiling water, which is related to the water resistance of collagen fiber film. As shown in Table 2, the SR and TSR values of the collagen fiber film of the hydrochloric acid group are less than those of the acetic acid group, indicating that the water resistance of the fiber film of the hydrochloric acid group is enhanced. This may be due to the fact that the fiber bundle formed after the yak skin is swelled by hydrochloric acid is small, which promotes the intermolecular and intramolecular cross-linking, forms covalent bonds, and makes the fiber structure compact, so that the water resistance is enhanced, which is consistent with the results of the moisture content described above.

[0104] Example 4: SEM analysis

[0105] In order to understand the effect of different swelling acids on the structure of collagen fiber film, the microstructure of collagen fiber film and yak skin pulp after acid swelling was evaluated, as shown in Figure 1

[0106] The results of the scanning electron microscope show that the cross section of the collagen fiber film of the hydrochloric acid group is uniform and dense, which may be because the collagen fiber of the yak skin swelled by hydrochloric acid is more loose, while the collagen fiber swelled by acetic acid presents a sheet shape. Hydrochloric acid can fully swell, while acetic acid only swells the surface. The carboxyl groups in CMC can fully enter between the collagen fiber bundles, and the intermolecular entanglement between the carboxyl groups and the amino groups at the end of the collagen fiber peptide chain forms a more compact cross-linked structure, making the structure more compact. The uneven, broken and hole appearance of the collagen fiber film of the acetic acid group was observed. In general, the mechanical properties of the film depend on the distribution and density of intermolecular and intramolecular interactions in the polymer matrix. The compact and dense structure of the edible film may be the reason for its high tensile strength, which is also consistent with the fact that the mechanical strength of the fiber film swelled by hydrochloric acid is greater.

[0107] Example 5: FTIR analysis

[0108] In order to evaluate the interaction between the components in the film, the Fourier transform infrared (FTIR) spectra of the collagen fiber films swelled by different acids are shown in Figure 2

[0109] ​​Both of the two different acid-swelled fiber membranes showed characteristic peaks of collagen fibers; corresponding to O-H stretching vibration and intermolecular and intramolecular hydrogen bond amide A band, the greater the degree of cross-linking, the more obvious the stretching vibration of the hydroxyl group will occur, moving to a higher wavelength. The peak positions of the hydrochloric acid group and the acetic acid group were 3431.1 cm -1 and 3434.7 cm -1 , respectively. The absorption peak moved to a lower wave number, indicating that the N-H group participated in the formation of stronger or more hydrogen bonds; the amide B band corresponding to the N-H stretching vibration appeared at -2923 cm -1 ; the amide I band (1600-1700 -1 ) region can be more sensitive to the secondary structure of the protein, and belongs to the stretching vibration of the C=O group in the amide or polypeptide. Compared with the acetic acid group, the collagen fiber membrane of the hydrochloric acid group showed a red shift, and the peak width increased, which may be due to the formation of more hydrogen bonds in the hydrochloric acid group, resulting in a decrease in the stretching vibration frequency; amide II is related to N-H plane bending and C-N stretching vibration, and the position is at 1540 cm -1 ; amide III appears at about 1240 cm -1 , caused by the C-N stretching vibration and N-H bending vibration of the amide bond and the CH2 vibration from the glycine backbone and Pro side chain group. There were no significant changes in the functional groups of the collagen group after different acid treatment, but it can be seen that the intensity of these characteristic absorption peaks of the hydrochloric acid group increased, which may be related to the strong force of the hydrochloric acid group.

[0110] The stability of the fiber membrane is related to the secondary structure of the protein, and the secondary structure of the protein is the intermolecular and intramolecular force, such as disulfide bond, hydrogen bond, etc. The content of the secondary structure calculated by deconvolution using Omnic software is shown in the table above. It can be seen that the a-helix content of the collagen fiber membrane of the hydrochloric acid group is higher than that of the acetic acid group. Related research shows that the higher the content of a-helix in the secondary structure of the protein, the higher the stability of the protein. This may be due to the introduction of disulfide bonds into the double-chain a-helix coil helix to produce a hydrophobic core. Compared with the acetic acid group, the content of random coil in the hydrochloric acid group is greatly reduced. Previous related research reports that the increase in the ordered structure content of collagen protein is the basis of protein stability, and the increase in the content of random coil represents the loss of ordered structure. Therefore, the great reduction in the content of random coil in the hydrochloric acid group indicates that the ordered structure has higher stability.

[0111] Table 3 Secondary structure of the sample obtained by FTIR

[0112]

[0113] Example 6: XRD analysis

[0114] The structure of the collagen fiber membranes, such as the distance between the molecular chains and the content of the triple helix structure of the protein, was analyzed using XRD, as shown in Figure 3 Both collagen fiber membrane patterns showed a sharp peak near 7.62° (2θ) and a broad peak near 22.2° (2θ).

[0115] The first peak is related to the diameter of the triple helix structure, and the intensity is related to the content of the triple helix of the protein. The second broad amorphous peak is related to the distance between the amino acid residues along the triple helix chain of collagen protein. As can be seen from the figure, the hydrochloric acid group has a higher triple helix content than the acetic acid group, which is similar to the result of FTIR.

[0116] Example 7: Thermodynamic analysis

[0117] The thermal stability of the fiber membranes was evaluated by thermogravimetric analysis to determine the thermal degradation rate of the thin film. The TGA and DGA curves of the collagen fiber membranes treated with two different acids are shown in the figure, and there are three main weight loss stages. The degradation temperature (T d ), weight loss (w i ) and residue of the fiber membrane are listed in the table. At a temperature below 150℃, the weight loss of the hydrochloric acid group and the acetic acid group samples was 4.15% and 4.88% respectively. At this temperature, the main loss is the evaporation of free water and other volatile substances in the fiber membrane; in addition, the second stage occurs at 240-250℃, which is attributed to the evaporation of glycerol and the breaking of the glycosidic bond of the sodium carboxymethyl cellulose backbone (reference literature), and the third stage above 300℃ is related to the degradation behavior of low molecular weight proteins and biopolymers, especially the mixture or crosslinking components, which is consistent with the observation of other bovine collagen fiber membranes (reference related literature). As can be seen from the figure, the main DTG peak temperature of the hydrochloric acid group is higher than that of the acetic acid group, indicating that the thermal stability of the hydrochloric acid group is higher than that of the acetic acid group. Compared with the acetic acid group, the collagen fiber membrane of the hydrochloric acid group shows higher degradation temperature and lower weight loss in the two main loss stages, which may be due to the presence of high hydrophobicity and less free and bound water in the hydrochloric acid group, and the residue content of the collagen fiber membrane of the hydrochloric acid group is higher than that of the acetic acid group. The results show that the swelling by hydrochloric acid can improve the thermal stability of the collagen fiber membrane, which may be because the chemical bonds such as hydrogen bonds between and within the molecules increase after hydrochloric acid treatment, and the interaction force is enhanced. It shows that different types of acid have certain influence on the preparation of collagen fiber membrane. This is consistent with the mechanism of hydrochloric acid promoting crosslinking.

[0118] Table 4 Thermal degradation temperature (T d ) and weight loss (W i ) of two collagen fiber membranes

[0119]

[0120] The above merely describes preferred embodiments of the present application, and is not intended to limit the technical scope of the present application in any way. Any minor modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application shall still fall within the technical scope of the present application.

Claims

1. A method for constructing a collagen polymer network from yak hide and preparing its casing film, characterized in that, Includes the following steps: Step 1: Pre-treatment of yak hide Take cowhide, soak it in NaOH to remove the outer skin, wash it until neutral, add sodium carbonate solution, soak it, rinse it, cut it into small pieces, soak it in HCl + NaCl demineralization solution, rinse it until neutral, and store it in the refrigerator. Step 2: Preparation of collagen clusters Crush the yak hide and crushed ice, let them swell, break them into collagen clumps, add sodium carboxymethyl cellulose, mix well, and place them in a vacuum drying oven for degassing treatment, then set aside. Step 3: Preparation of collagen fiber membrane Take collagen clumps, roll them out, immerse the membrane in an ammonia solution for curing, wash until the pH is neutral, immerse in a glycerol solution, air dry, place in a desiccator for equilibration, and measure the relevant indices of the membrane. Step 4: Determine the thickness of the collagen fiber membrane, the dry and wet tensile strength (TS) and elongation at break (EAB) of the collagen fiber membrane, the light transmittance of the collagen fiber membrane, the moisture content (WC) and swelling ratio (SR) of the collagen fiber membrane, and the thermal shrinkage rate (HSR) and thermal swelling rate (TSR) of the collagen fiber membrane.

2. The method for constructing a yak hide collagen polymer network and preparing its casing film according to claim 1, characterized in that, In step 1, the cowhide is soaked in 0.1M NaOH at a sample:solution ratio of 1:6 for 24 hours, and then washed with distilled water to remove the NaOH. Add 5% sodium carbonate solution at a sample:solution ratio of 1:6 to remove fat, soak for 24 hours, rinse with distilled water to achieve neutral pH, soak in 0.1M HCl + 0.1M NaCl demineralization solution at 4℃ with a sample:solution ratio of 1:6 (w / v) for 2 hours, and store in a -80℃ refrigerator.

3. The method for constructing a yak hide collagen polymer network and preparing its casing film according to claim 1, characterized in that, In step 2, yak hide and crushed ice are added to a high-speed shearing machine at a ratio of 1:2 and crushed. The samples are then placed in 0.96 WT% hydrochloric acid and 0.7 M acetic acid and swelled at 4°C for 24 h. The ratio of sample to solution is 1:2 (w / v). Add 1% sodium carboxymethyl cellulose by mass to the collagen group, where the mass of sodium carboxymethyl cellulose is based on 1 / 4 of the mass of the collagen group; Drying temperature 20℃, drying time 60min.

4. The method for constructing a yak hide collagen polymer network and preparing its casing film according to claim 1, characterized in that, In step 3, take 5g of collagen clumps, roll them out using a stainless steel roller with a 0.5mm groove, immerse the membrane in a 5% ammonia solution for 10 minutes to solidify it, and then wash it in deionized water. Soak in glycerin solution for 30 minutes, air dry at room temperature for 24 hours, and then place in a desiccator at 25°C and a relative humidity of 58±3 for 48 hours to equilibrate.

5. The method for constructing a yak hide collagen polymer network and preparing its casing film according to claim 1, characterized in that, In step 4, the formulas for calculating the wet tensile strength TS and the elongation at break EAB are as follows: In the formula: F is the maximum force, N; S is the cross-sectional area of ​​the membrane, mm. 2 ; d is the maximum deformation, mm; d0 is the original length of the membrane, mm.

6. The method for constructing a yak hide collagen polymer network and preparing its casing film according to claim 1, characterized in that, In step 4, the formula for calculating the transmittance of the collagen fiber membrane is as follows: In the formula: T is the transparency value, A 600 X is the absorbance value of the thin film at a wavelength of 600 nm, and X is the thickness of the thin film.

7. The method for constructing a yak hide collagen polymer network and preparing its casing film according to claim 1, characterized in that, In step 4, the formulas for calculating the moisture content (WC) and swelling ratio (SR) of the collagen fiber membrane are as follows: Each membrane sample is W0, and its weight is W. d ; The constant weight is Ws.

8. The method for constructing a yak hide collagen polymer network and preparing its casing film according to claim 1, characterized in that, In step 1, the calculation formulas for the thermal shrinkage rate (HSR) and thermal swelling rate (TSR) of the collagen fiber membrane are as follows:

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