CN113197242B

CN113197242B - Continuous water bath fixing treatment process for preparing collagen casing by wet method

Info

Publication number: CN113197242B
Application number: CN202110644344.6A
Authority: CN
Inventors: 李国英; 张晓霞
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2020-09-23
Filing date: 2020-09-23
Publication date: 2022-01-18
Anticipated expiration: 2040-09-23
Also published as: CN112042716B; CN113197242A; CN112042716A

Abstract

The invention provides a continuous water bath fixing treatment process for preparing a collagen casing by a wet method. The preparation process comprises the steps of carrying out secondary pretreatment on a leather block subjected to enzyme A pretreatment by utilizing an ionic liquid/acid double-solvent solution system, homogenizing the leather block by a high-shear homogenizer, carrying out treatment by a polyhydroxy alcohol food plasticizer, carrying out extrusion forming, immersing the leather block in a water bath for shaping, carrying out cross-linking and fixing treatment by a continuous water bath, and finally drying to obtain a collagen casing product with the thickness of 0.02-0.04 mm. The collagen casing prepared by the method is light and thin, has uniform thickness, good flexibility, edible mouthfeel similar to that of a natural casing and good mechanical property, and can be widely applied to various packages of food as an edible film.

Description

Continuous water bath fixing treatment process for preparing collagen casing by wet method

The application is a divisional application, and the original application number is as follows: 202011007546.1, filing date: the invention name is as follows on 23 days 9 and 23 in 2020: a collagen casing and its preparation method are provided.

Technical Field

The invention belongs to the technical field of food synthesis bioengineering, relates to a collagen casing and a preparation method thereof, and particularly relates to a method for preparing the collagen casing by a wet method by taking animal two-layer and/or three-layer skins as raw materials.

Background

The two edible casings most commonly used today include natural casings and collagen casings. The natural casing is a transparent tough film from animal body, and has good taste and mechanical strength. But the source is limited, the thickness and the strength are different, the operation is complicated when the sausage is used for food processing, large-scale and continuous production cannot be realized, and the size and the specification of the processed sausages are different. The collagen casing is an edible tubular food packaging film which is prepared by taking collagen fibers in animal skins as raw materials, performing physical and chemical treatment, and drying and shaping. The collagen casing has the characteristics of rich resources, adjustable caliber length and the like, is beneficial to mechanized filling production, and can obtain processed products with consistent specifications.

The existing preparation process of the collagen casing is mainly divided into a dry method and a wet method. In general, both methods employ acid or alkali pretreatment of the skin material to expand the collagen fibers for further mechanical defibration and extrusion. Wherein, the dry method is to extrude and form the grinded and smashed collagen fiber and then directly dry the collagen fiber by hot air to obtain the finished product of the collagen casing; or further fixing and modifying by soaking, spraying and other modes after drying, and finally drying again to obtain the finished product of the collagen casing. The dry method adopts a direct drying and forming method to ensure that collagen fibers are excessively shrunk and bonded, even if the subsequent spraying or dipping modification is adopted, the inner part and the outer part of the casing membrane are difficult to be uniformly treated, and the improvement effect on the membrane performance is very limited. Therefore, the collagen sausage casing prepared by the dry method is hard in taste and poor in flexibility and permeability. The wet method comprises the steps of extruding and forming the smashed collagen fibers, immersing the extruded collagen fibers in water bath for shaping, crosslinking and fixing, and finally drying to obtain the collagen casing product. Because the wet method does not adopt drying and shaping, but directly immerses the tubular film in a water bath for shaping and fixing treatment, the inside and the outside of the formed tubular film can be uniformly treated, and the performance of the collagen casing can be more effectively improved. Thus, conventional wet-laid preparations are softer and have good mechanical strength compared to dry-laid collagen casings.

However, from the perspective of consumers, the products prepared by the wet method on the market still have a distinct difference in taste from the natural casing, because the thickness of the collagen casing prepared by the wet method on the market is significantly higher than that of the natural casing. The inventor of the invention summarizes and finds out in the actual production process, because the conventional acid or alkali pretreatment leather is generally adopted in the current preparation method, the effect on collagen fibers is limited, and the collagen fiber bundles are scattered mainly by mechanical action, so that the prepared collagen fibers are thick and long, the fiber walls are thick, the number of fibers in unit mass of the collagen fiber bundles is small, the specific surface area is small, the formed film is rough and thick, and the mouth feel is hard; and because the homogenization degree is lower, when the thin sausage casing is produced, the gap interval of the extrusion spray heads is small, the movement of thick and long collagen fibers and thin and short collagen fibers in the extrusion forming process is slow, and collagen fiber clusters can not move in an integral form, so that the thickness of the collagen sausage casing film is uneven and even leaks are easily caused. Therefore, for the above reasons, when a casing with a relatively thin thickness is actually produced, the problem of low flexibility and yield of the casing still exists, and the actual production and sale benefits are not obtained. However, according to the current domestic market performance, due to the difference in taste, the collagen casing can not replace the natural casing for a while.

At present, domestic patent technologies related to collagen casings include: a preparation method of a collagen casing with a medium and small caliber (patent number 200810116408.X), "an edible collagen casing and a production method thereof" (patent number 201210206119.5), "an edible collagen casing and a preparation method thereof" (patent number 201210346511.4), "an antibacterial collagen casing and a production method thereof" (patent number 201210376511.4), "a production method of a collagen casing" (patent number 201310321716.7), "an edible halal collagen casing and a preparation method thereof" (patent number 201310373518.5), "an edible casing prepared from collagen and other edible proteins" (patent number 201610505523.0), "a preparation method of a sheepskin collagen casing" (patent number 201710724152.X), "a preparation method of an edible animal collagen casing" (patent number 201910914758.9) are established on the improvement of the traditional or wet process. Generally, the above patent technologies adopt a method of swelling with acid or alkali and then mechanically defibering to prepare collagen fiber clusters; and extruding and molding the collagen fiber clusters, directly drying to obtain the collagen casing, or drying and shaping, and further crosslinking and fixing to obtain the finished collagen casing. The relevant literature is mainly concerned with the use of different kinds of additives, such as plant fibers, other edible proteins, chitosan, alcohols, etc.; and fixing with different cross-linking agents or cross-linking methods, such as aldehydes, cinnamamide cross-linking and UV cross-linking. However, the collagen casings prepared by the above patent technologies and literature technologies have a difference from natural casings in thickness and taste.

The difference is mainly shown in that the thickness of the natural dried sheep sausage casing is only 0.02-0.03 mm, the thickness of the dried pig sausage casing is only 0.03-0.04 mm, and the dried pig sausage casing is light, flexible, soft and palatable and is well pursued by wide consumers. The thickness of the collagen casing product can only be 0.04-0.06 mm, and if the thickness is obviously lower than the thickness, the collagen casing product is easy to damage in the process of filling contents and in the process of storage and transportation, so that the yield and the quality guarantee period of food are greatly influenced. And because the prepared collagen fiber is thicker and longer, the sausage film is harder in taste than the natural sausage casing and is not easy to be bitten, the pleasant experience of the natural sausage casing for consumers cannot be achieved. If the thin collagen casing with uniform thickness and enough toughness can be prepared, the taste and the mechanical property of the natural casing can be expected to be achieved, and the thin collagen casing is greatly beneficial to the promotion of new consumer food and the expansion of market share.

More importantly, unlike natural casings, the preparation of collagen casings belongs to the food synthesis bioengineering technology, and the progress can be realized by innovative improvements on the production technology.

Disclosure of Invention

The invention provides a collagen casing prepared by a wet method of a food synthesis bioengineering technology and a preparation method thereof, aiming at the technical prospect provided by the background technology. The preparation method comprises the steps of carrying out secondary pretreatment on the leather blocks pretreated by the enzyme A by utilizing an ionic liquid/acid double-solvent solution system, homogenizing by a high-shear homogenizer, carrying out treatment by a polyhydroxy alcohol food plasticizer, carrying out extrusion forming, immersing in a water bath for shaping, carrying out cross-linking fixation, and finally drying to obtain the collagen casing product with the thickness of 0.02-0.04 mm. The collagen casing prepared by the method is light and thin, has uniform thickness, good flexibility, edible mouthfeel similar to that of a natural casing and good mechanical property, and can be widely applied to various packages of food as an edible film.

In order to achieve the purpose, the invention adopts the technical scheme formed by the following technical measures.

A method for preparing collagen casing by a wet method of a food synthesis bioengineering technology comprises the following steps:

(1) pretreatment of raw material dermatome: screening two-layer and/or three-layer skins of an untanned animal, cleaning, pretreating by using enzyme A to remove residual hair root hair follicles and non-fibrous proteins, cleaning and cutting into block-shaped skins suitable for preparing a collagen casing by a wet method;

(2) pretreatment of the leather blocks by a double-solvent system: putting the leather blocks obtained in the step (1) into ionic liquid/acid double-solvent solution with the weight of 3-15 times of the leather weight, stirring for 8-16 h at the temperature of 4-10 ℃, filtering to obtain leather blocks, and washing for later use; in the ionic liquid/acid double-solvent solution, the ionic liquid solvent is at least one of a 20-60% volume concentration 1-butyl-3-methylimidazole nitrate solution, a 1-ethyl-3-methylimidazole acetate solution, a 1-butyl-3-methylimidazole methane sulfonate solution, a 1-butyl-3-methylimidazole chloride solution and a 1-ethyl-3-methylimidazole bromine salt solution; the acid solution is 0.1-1 mol/L food grade weak acid; the volume ratio of the ionic liquid to the acid solution is 5: 5-8: 2;

(3) preparing collagen slurry: putting the leather blocks obtained in the step (2) into a high-shear homogenizer for homogenization treatment, adding a polyhydroxy alcohol food plasticizer which is 10-20% of the mass of the homogenized collagen slurry, uniformly stirring, and then adjusting the mixture into short fiber collagen slurry with solid content of 4-7% for later use;

wherein the polyhydric alcohol food plasticizer is any one of glycerol, propylene glycol, polyvinyl alcohol and polyethylene glycol;

wherein the technological parameters of the homogenization treatment are as follows: the rotating speed is 2000-3200 rpm, and the temperature is not higher than 20 ℃ in the homogenizing process;

(4) shaping and fixing: extruding and spraying the short fiber collagen slurry obtained in the step (3) to form a tubular membrane, carrying out setting treatment through saturated NaCl, and then directly immersing in a fixing solution water bath containing a cross-linking agent for fixing treatment;

wherein the gap distance between the nozzle gaps in the extrusion spraying process is 0.02-0.04 mm;

(5) drying to obtain a finished product: and (4) cleaning and hot air drying the tubular membrane subjected to the fixing treatment in the step (4) to obtain a finished product of the collagen casing.

According to the invention, the leather blocks pretreated by the enzyme A are subjected to secondary pretreatment by using an ionic liquid/acid double-solvent solution system, so that the treated animal skin collagen fibers are shorter and have higher homogenization degree. The degradation degree of the collagen fiber bundle prepared by the secondary pretreatment is slightly high, the prepared collagen fiber bundle is thin and short, the fiber wall is thin, the number of fibers in unit mass of the collagen fiber slurry is large, the specific surface area is large, the dispersion uniformity is good, and even if the collagen fiber bundle is extruded and formed by a nozzle with small gap spacing, the collagen fiber slurry can move in an integral form, so that a uniform film with high transparency can be easily obtained.

However, based on the common knowledge in the art, it is known that, since the thickness and length of the collagen fibers obtained by the above treatment are much lower than those of the collagen fiber bundles, although the shorter collagen fibers are beneficial to uniformly weaving the collagen film, the smaller the fibers, the more seriously the hydrogen bonds and ionic bonds that maintain the collagen fiber configuration are damaged, the strength of the prepared film material is adversely affected, so that the mechanical properties of the formed collagen casing are lower than those of the existing products, and the technical effect of combining lightness and flexibility cannot be realized.

However, the inventor of the present invention has found that, by selecting the skin mass after the secondary pretreatment and performing the homogenization treatment by using a homogenizer, and then adding a polyhydric alcohol plasticizer, the plasticizer fills the gaps between the fiber macromolecular polymer chains, and because the plasticizer contains a plurality of hydroxyl groups, hydrogen bonds can be formed between the plasticizer and the collagen macromolecules, so that the slippage between molecules is increased, and the flexibility of the formed film is improved. The collagen membrane is immersed in the fixing solution containing the cross-linking agent for treatment after being formed, a specific covalent cross-linking bond is formed between the fixing solution containing the cross-linking agent and the collagen fiber, the uniform internal and external cross-linking of the collagen casing membrane is ensured, a wider and compact space network structure is formed, and the aim of improving the mechanical performance of the membrane is fulfilled. Therefore, the preparation method provided by the invention not only can enable the prepared collagen casing film to be light, thin, flexible and uniform in thickness, but also can ensure the excellent mechanical property of the collagen casing film.

Wherein the untanned animal second and/or third skins in step (1) are animal skin stock materials selected in the preparation of conventional collagen casings, and preferably any one of pigskin, cow skin and sheep skin for better illustration of the present invention.

Generally, the pretreatment with the enzyme A in the step (1) is a conventional technical method for removing residual hair root hair follicles and non-fibrin in the technical field, and a person skilled in the art can self-establish a proper enzyme A pretreatment process mode according to the prior art and the selection of animal skin material raw materials, to better illustrate the present invention, and to provide a preferred solution selected based on the implementation controls, when the untanned animal second-layer and/or third-layer skin is pigskin, the pretreatment is carried out by adopting the enzyme A, namely, the untanned pigskin is cut into 4-6 cubic centimeters of skin blocks, then the skin blocks are put into a buffer solution with the weight of 1-3 times of the skin weight and the pH value of 6-8, adding 0.05-2% of enzyme A, stirring at 20-25 ℃ for 30-60 min, standing for 2-3 h, repeating for 4-5 times, stirring for 30-60 min, and filtering to remove waste liquid.

Wherein the A enzyme is selected from conventional species in food industry, preferably comprises one or more of 1398 neutral protease, 2709 alkaline protease, pancreatin, bromelain and papain; the buffer solution includes one of disodium hydrogen phosphate-citric acid buffer solution, citric acid-sodium citrate buffer solution, and disodium hydrogen phosphate-sodium dihydrogen phosphate buffer solution.

Wherein, the cutting treatment in the step (1) is a block-shaped leather block suitable for preparing the collagen casing by a wet method, and in order to better perform secondary pretreatment on the leather block by an ionic liquid/acid double-solvent system, the cutting treatment is preferably carried out to obtain the block-shaped leather block with the drift diameter of 5-10 mm.

In the ionic liquid/acid double solvent system in the step (2), the ionic liquid solvent is at least one of a 20-60 vol% 1-butyl-3-methylimidazole nitrate solution, a 1-ethyl-3-methylimidazole acetate solution, a 1-butyl-3-methylimidazole methane sulfonate solution, a 1-butyl-3-methylimidazole chloride solution and a 1-ethyl-3-methylimidazole bromide solution. The selection of the ionic liquid solvent is obtained by the inventor of the present invention through practical production verification, and as can be known by the common general knowledge in the art, the ionic liquid has different polarity, for example, but based on the theory in the art, the ionic liquid having a structure greatly different from the chemical formula of the ionic liquid solvent defined above can be also applied to the present invention. And the inventors of the present invention have also found that when an ionic liquid solvent having a concentration lower than the above volume concentration is selected, on the one hand, the treatment time is prolonged to increase the production cost, and on the other hand, the low concentration ionic liquid does not sufficiently act on the collagen fibers, the collagen fibers are insufficiently dispersed, and the uniformity of film formation is somewhat affected; when the ionic liquid solvent with the volume concentration higher than the above is selected, on one hand, the material cost is increased, on the other hand, the production process is difficult to control because the action of the ionic liquid and the collagen fiber is enhanced, and if the ionic liquid solvent is subjected to high concentration treatment for a long time, the mechanical performance of the formed film is influenced to a certain extent.

It is worth to be noted that, in order to further improve the technical effect of the two-solvent system pretreatment (secondary pretreatment), so that the thickness and length of the collagen fibers are appropriate and have higher homogenization degree, and the weaving uniformity and relative thin permeability of the finally prepared collagen casing are ensured, as verified by a large number of control experiments by the inventor of the present invention, in the ionic liquid/acid two-solvent solution in step (2), the ionic liquid is preferably 1-ethyl-3-methylimidazolium acetate solution with a volume concentration of 25-30%, the acid solution is 0.5-0.6 mol/L of glacial acetic acid, and the volume ratio of the two is 7: 3; or the ionic liquid is preferably a 1-butyl-3-methylimidazolium chloride solution with the volume concentration of 45-50%, the acid solution is a lactic acid solution with the volume ratio of 0.8-1.0 mol/L, and the volume ratio of the two is 5: 5. It is verified that if a composite ionic liquid is selected, the difference between the effect of the composite ionic liquid and that of a single ionic liquid is small, and the single ionic liquid is preferred for the reason of production cost. Generally, when preparing the ionic liquid/acid two-solvent solution, it can be mixed uniformly by mechanical stirring for a short time in the volume concentration range defined in step (2).

In addition, the implementation process of the inventor of the invention finds that the thickness of the collagen fiber pulp processed by the ionic liquid/acid double-solvent system in the technical scheme of the invention is obviously lower than that of the collagen fiber pulp processed by acid or alkali which is conventionally used, and the thickness uniformity of each position of the film is better. This is because conventional acid or base solutions, mainly COO, by ionization with collagen side chains^-And NH₃ ⁺Bonding and reinforcing collagen peptide chainNH₃ ⁺Or COO^-The repulsive force between the fibers and the leather achieves the purposes of loosening the fibers and expanding the leather. In the ionic liquid/acid double-solvent solution, cations of the ionic liquid can be combined with C ═ O on collagen peptide bonds to form strong hydrogen bonds, and anions in the solution are combined with-NH-on the collagen peptide bonds, so that the original hydrogen bonds and ionic bonds among collagen molecules are broken. Therefore, the ionic liquid/acid double-solvent system has stronger effect on collagen fibers than the traditional acid or alkali solution, and uniform and short collagen fibers are easier to obtain. Meanwhile, as the fiber wall of the short thin fibers is thinner than that of the long thick fibers, the number of fibers of the collagen pulp in unit mass is more, the specific surface area is larger, the uniform dispersion is easier, and even if the collagen pulp is extruded and formed by the spray heads with small gap spacing, the collagen fibers can move integrally, so that the collagen casing film with better uniformity and thinner thickness is obtained.

It is worth to be noted that the ionic liquid used in the invention is a non-toxic or low-toxic substance, and meets the relevant standards of national food safety standard GB 14967/2015.

Further, the ionic liquid/acid double-solvent solution in the step (2) can be collected after the processed leather block is filtered, and can be recycled after being recycled, so that the production cost is reduced.

In order to further improve the flexibility of the finally prepared collagen casing film, the collagen slurry prepared in the step (3) is preferably added with glycerol which is 15-18% of the mass of the homogenized collagen slurry and uniformly stirred. The glycerol is a common cheap food plasticizer, has small molecular weight and 3 hydroxyl groups, is easy to permeate into gaps of macromolecules of the collagen fibers, forms hydrogen bonds with the collagen molecules, increases the slippage of the collagen fibers and improves the flexibility of a formed film.

In order to prepare a lighter and thinner collagen casing, the invention defines a process mode of forming a tubular film by extrusion spraying, and the thickness of the tubular film is controlled by setting the gap distance of a nozzle in the process, wherein the gap distance of the nozzle is 0.02-0.04 mm, and in a preferred technical scheme, the gap distance of the nozzle can be 0.025 mm. The selection and arrangement of the relevant equipment in the process mode of forming the tubular film by the spray head, the relevant limitations on the relevant parameters such as the thickness, the caliber and the like of the tubular film, and the conventional selection of the extrusion spraying process and the equipment in the technical field.

Generally, the step (4) is performed by setting with saturated NaCl, which is a conventional setting treatment manner in the prior art for preparing collagen casings by a wet method, and the time of the setting treatment is generally 5-10 min.

Wherein, after the setting treatment in the step (4), the collagen casing is directly immersed in a fixing solution water bath containing a cross-linking agent for fixing treatment, and a person skilled in the art can directly refer to the prior art of preparing the collagen casing by a wet method and select a proper fixing solution water bath containing the cross-linking agent for fixing treatment.

It is worth to be noted that, because the secondary pretreatment is performed by using an ionic liquid/acid double-solvent system innovatively, the method is different from the prior art, in order to further improve the mechanical properties of the finally prepared collagen casing and ensure the safety and good biocompatibility of the prepared collagen casing, a set of adaptive wet-process fixing treatment modes is provided:

the shaping and fixing in the step (4) are that the short fiber collagen pulp obtained in the step (3) is extruded and sprayed to form a tubular membrane, and is shaped through saturated NaCl and then is fixed;

the fixing treatment comprises the following steps:

respectively preparing a B enzyme bath solution with the volume concentration of 0.1-1.5% and a genipin bath solution with the volume concentration of 0.1-1%, immersing the tubular membrane subjected to shaping treatment in the B enzyme bath solution, fixing for 10-30 min under the water bath condition at the temperature of 20-30 ℃, then immersing in the genipin bath solution, and fixing for 10-30 min under the water bath condition at the temperature of 20-30 ℃; wherein, the B enzyme is any one of glutaminase, horseradish peroxidase and tyrosinase.

More preferably, in order to obtain the collagen casing with oxidation resistance, the tubular membrane is subjected to the fixing treatment by the two-step water bath fixing solution, then is immersed in tannin and/or tannin extract bath liquid containing the enzyme C catalyst, and is subjected to the fixing treatment for 10-30 min at the temperature of 20-30 ℃; wherein, in tannin and/or tannin extract bath liquid containing C enzyme catalyst, tannin is preferably any one of tannic acid, catechin, gallic acid and procyanidine, tannin extract is preferably any one of myrica tannin extract, wattle tannin extract, castanopsis tannin extract and tara tannin extract; the enzyme C catalyst is any one of laccase and tyrosinase, the volume concentration of tannin and/or tannin extract in bath liquid is 0.1-2%, and the dosage of the enzyme C catalyst is 0.1-2% of the total weight of tannin and/or tannin extract.

In order to better illustrate the present invention and provide a most preferred technical solution, a thin collagen casing with uniform thickness, better mechanical properties and oxidation resistance is further obtained, and the fixing treatment in the step (4) comprises the following steps:

preparing a glutaminase bath solution with the volume concentration of 0.2-0.3%, a genipin bath solution with the volume concentration of 0.4-0.5%, a tannic acid bath solution with the volume concentration of 0.5-0.6% and containing a laccase catalyst with the weight of 0.3-0.4 per mill of tannic acid respectively, immersing a tubular membrane subjected to shaping treatment in the glutaminase bath solution, carrying out fixation treatment for 30min under the water bath condition of the temperature of 25 ℃, then immersing the tubular membrane in the genipin bath solution, carrying out fixation treatment for 20min under the water bath condition of the temperature of 28 ℃, finally immersing the tubular membrane in the tannic acid bath solution, and carrying out fixation treatment for 15min under the water bath condition of the temperature of 30 ℃.

It is worth to say that the collagen short fibers are respectively immersed in the water bath stationary liquid for fixation, so that the structural strength of the film formed by the collagen short fibers is further improved, and the collagen casing film is endowed with certain oxidation resistance. Because the collagen casing film is directly immersed in a water bath for crosslinking and fixing, on one hand, the collagen casing film can be uniformly and uniformly crosslinked and fixed inside and outside; on the other hand, the crosslinking sites of the collagen are increased, for example, an enzyme crosslinking agent can catalyze specific amino acid residues on collagen fibers to react, so that two different collagen molecules are crosslinked with each other without generating byproducts; genipin is an excellent natural biological macromolecular cross-linking agent, can react with free residues such as free arginine, lysine and hydroxylysine on collagen polypeptide chains, has basically no difference between the cross-linking degree and glutaraldehyde cross-linking, but has far lower toxicity than glutaraldehyde; tannin and tannin extract are common natural extracts which can be used for food, tannin and/or tannin extract after enzyme catalyst is added, phenolic hydroxyl groups on benzene rings of the tannin and/or tannin extract are oxidized into quinoid structures through enzyme catalysis, and can generate Schiff base reaction or Michael addition reaction with amino groups of collagen to form covalent bonds, and simultaneously can endow a collagen casing with certain antioxidation performance, in addition, the technical scheme of the invention also limits that tannin and/or tannin extract bath solution containing the enzyme catalyst C is carried out after the two-step water bath stationary liquid fixing treatment, which is verified by the actual production of the inventor of the invention, when the three-step sequence of the continuous bath solution fixing treatment is limited, the improvement of mechanical performance is greatly higher than that of the fixing treatment of the tannin and/or tannin extract bath solution containing the enzyme catalyst C which is singly used, and is also obviously higher than other sequences, and further endows the antioxidation performance of the collagen casing, thereby having practical production benefits. In conclusion, the continuous bath solution fixation treatment improves the crosslinking degree of collagen, so that the structure of the casing film is more compact, the stability of the casing film is enhanced, the mechanical performance of the collagen casing is effectively improved, and meanwhile, the yield in the production process is obviously improved.

Through the research of the inventor, the tannin and/or tannin extract adopted in the water bath stationary liquid treatment defined by the invention has good oxidation resistance, and the increase rate of the oxidation resistance of the collagen casing film is not less than 35 percent after the collagen casing film is fixed by the tannin and/or tannin extract through crosslinking. The collagen casing packaging film with oxidation resistance can block the permeation of oxygen to a certain extent and reduce the oxygen content in food, thereby improving the stability of the food and prolonging the storage period.

It should be noted that the bath liquid used in the fixing treatment is selected to be food grade or to comply with the relevant regulations of food additives.

According to the collagen casing prepared by the preparation method, under the condition that the thickness is 0.02-0.04 mm, the moisture content is 15-25%, the wet longitudinal breaking resistance is more than 2.5N, compared with the existing collagen casing product, the thickness is reduced by 20-60%, and meanwhile, excellent mechanical strength is guaranteed.

It should be noted that, because the collagen casing prepared by the invention belongs to an intermediate product in the actual food production process, the specific performance and the taste of the collagen casing are simultaneously influenced by the subsequent production processes such as filling, and from the actual production test, on the premise that the subsequent production processes do not greatly influence the casing, the sausage product finally produced is evaluated from the aspects of appearance and taste and is similar to the natural casing.

The invention has the following beneficial effects:

(1) according to the invention, the leather blocks pretreated by the enzyme A are subjected to secondary pretreatment by using an ionic liquid/acid double-solvent solution system, and the obtained animal skin collagen fibers are shorter and have higher homogenization degree, so that the formed film is thinner and more uniform; after being blended with an alcohol food plasticizer, the mixture is extruded and molded and then is immersed in a water bath fixing solution for treatment, so that the mechanical property of the collagen casing can be effectively improved; finally, the thin collagen casing product with the thickness of 0.02-0.04 mm is prepared, and the wet longitudinal breaking resistance is greater than 2.5N through determination, so that the requirements of the SB/T10373-2012 detection standard are met. The collagen casing prepared by the invention can be widely applied to various packages of food as an edible film and has edible mouthfeel highly similar to that of natural casing.

(2) The preparation method provided by the invention is to adopt an ionic liquid/acid double-solvent system to pretreat the leather blocks so as to prepare the fine and short collagen fibers with higher homogenization degree. Conventional acid or base solutions, COO, mainly by ionization with collagen side chains^-And NH₃ ⁺Bonding and enhancing NH on collagen peptide chain₃ ⁺Or COO^-The repulsive force between the fibers and the leather achieves the purposes of loosening the fibers and expanding the leather. In the ionic liquid/acid double-solvent solution, cations of the ionic liquid can be combined with C ═ O on collagen peptide bonds to form strong hydrogen bonds, and anions in the solution are combined with-NH-on the collagen peptide bonds, so that the original hydrogen bonds and ionic bonds among collagen molecules are broken. Thus, the ionic liquid/acid two-solvent system is more traditionalThe acid or alkali solution has stronger action on the collagen fibers, and the obtained collagen fibers are thinner, shorter and more uniform, thereby being beneficial to obtaining the thin tubular membrane with uniform thickness.

(3) In the preferred technical scheme provided by the invention, three-step continuous bath fixing treatment is adopted, wherein the tannin and/or tannin extract bath containing enzyme catalyst is innovatively adopted to fix the collagen casing through crosslinking. The tannin and/or tannin extract of traditional enzyme catalyst is mainly combined with collagen by multipoint hydrogen bonds, and tannin and/or tannin extract of enzyme catalyst is added, phenolic hydroxyl on benzene ring is oxidized into quinoid structure by enzyme catalysis, and then generates Schiff base reaction or Michael addition reaction with amino of collagen to form covalent bond, so the tannin and/or tannin extract containing enzyme catalyst provided by the invention can improve the crosslinking degree with collagen, and shorten the reaction time. And the tannin and/or tannin extract have good oxidation resistance, and the increase rate of the oxidation resistance of the collagen casing film is not less than 35 percent after the collagen casing film is subjected to three-step continuous bath fixing treatment. By the preferable technical scheme, the prepared collagen casing with oxidation resistance can obstruct the permeation of oxygen to a certain extent when being used as a food packaging film, and reduce the oxygen content in food, thereby improving the stability of the food and prolonging the storage period.

(4) In the preferred technical scheme provided by the invention, at least two steps of continuous bath liquid fixing treatment are adopted, so that the inside and the outside of the collagen casing film are uniformly treated, the crosslinking sites of the casing film are increased, the collagen casing film forms a more compact net structure, and the problem of lower mechanical property of the casing film woven by thin and short collagen fibers is solved. The collagen casing with relatively thinner thickness is obtained, the excellent mechanical property is ensured, and meanwhile, the selected fixative is food-grade, has no or very low biological toxicity, ensures the safety and biocompatibility of the prepared collagen casing, and provides a new way for diversification of the collagen casing.

Drawings

FIG. 1 is a photograph of a collagen casing finished product prepared in example 1 of the present invention.

FIG. 2 is a photograph of a tubular film obtained after the fixing treatment in step (4) in example 1 of the present invention.

Fig. 3 is a photograph of a tensile test experiment of a collagen casing finished product prepared in example 1 of the present invention.

FIG. 4 is a graph showing a comparison of the ABTS radical scavenging ability of tubular collagen membranes before and after the fixation treatment in example 8 of the present invention.

Detailed Description

The invention is further illustrated by the following examples in conjunction with the accompanying drawings. It should be noted that the examples given are not to be construed as limiting the scope of the invention, and that those skilled in the art, on the basis of the teachings of the present invention, will be able to make numerous insubstantial modifications and adaptations of the invention without departing from its scope.

Note that: the antioxidant properties, thickness and wet longitudinal breaking resistance of the collagen casings in the following examples were determined by the following methods and using the prior art.

(1) Thickness of collagen casing: randomly extracting a section of collagen casing finished product, measuring the thickness of different parts of the collagen casing finished product by using an electronic digital display micrometer, wherein the number of measuring parts is not less than 10, and the thickness reading is accurate to 0.001 mm.

(2) Wet longitudinal breaking resistance: refer to SB/T10373-. A strip sample of 120X 15mm (length X width) is cut along the longitudinal direction of the collagen casing and soaked in normal temperature water for 5 min. And (3) testing the tensile property of the collagen casing by using a tensile machine, wherein the force borne by the sample when the sample is broken is the breaking resistance (N). Adjusting the distance between the clamps of the tensile machine to be 100mm, taking out the sample, absorbing surface moisture by using filter paper, clamping the sample in a chuck, and carrying out tensile test by using the chuck at the speed of 100 mm/min.

(3) The increase rate of the antioxidant capacity: the ABTS method is used for measuring the free radical scavenging capacity of the collagen enteric-coated membrane after tannin and/or tannin extract crosslinking and fixing. ABTS can be K₂S₂O₈Oxidizing to generate blue-green free radical cation ABTS +, which is stable and has maximum absorption peak at 734 nm. ABTS + reacts with the antioxidant in the presence of the antioxidant, becoming colorless ABTS. ABTS stock solution and K are firstly mixed₂S₂O₈And uniformly mixing the stock solution to prepare the ABTS working solution. Get 5The collagen casing membranes before and after the cross-linking and fixing of the tannin and/or tannin extract with the length of cm are respectively immersed in 100ml of ABTS working solution, after a period of reaction, the absorbance of each solution at 734nm is measured by a spectrophotometer, and the free radical clearance rate of the casing membranes is calculated (formula 1). The difference of the clearance rate of free radicals of the collagen casing membrane before and after tannin and/or tannin extract crosslinking fixation is the increase rate of the antioxidant capacity of the collagen casing (formula 2).

ABTS free radical clearance (%) - (absorbance of ABTS working solution-absorbance of ABTS working solution added to the sample)/absorbance of ABTS working solution × 100% (formula 1);

the collagen casing oxidation resistance increase rate (%) -tannin and/or collagen casing free radical clearance rate (%) after tannin extract crosslinking and fixing, tannin and/or collagen casing free radical clearance rate (%) before tannin extract crosslinking and fixing (formula 2).

In order to further illustrate the beneficial effects obtained by the invention and embody the accuracy of the test results, the dried collagen casings of each batch are set to be a packaging unit according to 14m, and no broken hole exists continuously. And cutting the collagen casing finished product according to each packaging unit to carry out a wet fracture resistance test, wherein the good grade is that the wet fracture resistance of the sample is more than or equal to 2.5N, otherwise, the product of the packaging unit is considered to be unqualified. If the sausage casing product has a hole, the front and rear 2cm sections of the hole are considered as unqualified sections. And (4) not less than 10 test samples per packaging unit, and taking the average value as a test result.

And (3) the yield (%) of each batch of the sausage casing is equal to the length of the sausage casing of a good grade/the total length of the sausage casing product of the batch.

Further, for the collagen casing treated by the three-step stationary liquid defined by the invention, the batch of casing products are sampled to measure the antioxidant capacity thereof according to the sampling mode, and the average value is taken as the test result.

Example 1

The method for preparing the collagen casing by the wet method comprises the following steps:

(1) pretreatment of raw material dermatome: screening 100kg of untanned second layer cowhide, cleaning, cutting into 4-6 cubic centimeters of leather blocks, putting the leather blocks into a disodium hydrogen phosphate-sodium dihydrogen phosphate solution with the weight 2 times of the leather weight and the pH value of 7.0, adding neutral protease with the weight 0.5 percent of the leather weight while stirring, standing for 3 hours at the temperature of 20 ℃ every 40min of stirring, repeating for 4 times, stirring for 30min, filtering to remove waste liquid to remove residual hair root hair follicles and non-fibrin, cleaning and chopping into block leather blocks with the diameter of 5-6 mm;

(2) pretreatment of the leather blocks by a double-solvent system: putting the leather blocks obtained in the step (1) into ionic liquid/acid double-solvent solution with the weight 8 times of the leather weight, stirring for 10 hours at the temperature of 5 ℃, filtering to obtain leather blocks, and washing for later use; wherein the ionic liquid solvent is 560kg of 1-ethyl-3-methylimidazole acetate solution with the volume concentration of 30%; the acid solution is 240kg of glacial acetic acid solution of 0.5 mol/L; uniformly mixing an ionic liquid solvent and an acid solution through mechanical stirring to prepare an ionic liquid/acid double-solvent solution;

(3) preparing collagen slurry: putting the leather blocks obtained in the step (2) into a high-shear homogenizer for homogenization treatment, adding glycerol with the mass of 16% of that of the homogenized collagen slurry, uniformly stirring, and then adjusting to short fiber collagen slurry with the solid content of 5.5% for later use;

wherein the technological parameters of the homogenization treatment are as follows: the rotating speed is 2400rpm, and the temperature is 6 ℃ in the homogenizing process;

(4) shaping and fixing: extruding and spraying the short fiber collagen slurry obtained in the step (3) to form a tubular membrane, carrying out setting treatment for 8min through saturated NaCl, and then directly immersing in a fixing solution water bath containing a cross-linking agent for fixing treatment;

wherein the fixing treatment is specifically that 0.2 percent glutaraldehyde bath solution is soaked for 2min at the temperature of 30 ℃;

wherein, the gap distance of the nozzle in the extrusion spraying process is 0.025 mm.

(5) Drying to obtain a finished product: and (4) repeatedly washing the tubular membrane subjected to the fixing treatment in the step (4), drying the tubular membrane in a drying line at 50 ℃ by hot air, and taking the tubular membrane out of the drying line to obtain the collagen casing. The collagen casing is inspected, folded and packaged to obtain a finished product.

The thickness of the finished collagen casing is 0.025 plus or minus 0.01mm, and the wet longitudinal breaking resistance is 5.325N. The yield of the product produced by the embodiment is 90.2%.

Example 2

(1) pretreatment of raw material dermatome: screening 100kg of untanned second-layer pigskin, cleaning and cutting into 4-6 cubic centimeters of skin blocks. The pieces were put into a disodium hydrogenphosphate-sodium dihydrogenphosphate buffer solution having a pH of 7.8, which was 1.5 times the tare weight. Adding 0.3% trypsin while stirring, standing for 2h at 22 ℃ for 60min every time after stirring, repeating for 4 times, stirring for 60min, filtering to remove waste liquid to remove residual hair root hair follicles and non-fibrous proteins, cleaning and chopping into block-shaped skin blocks with the diameter of 5-6 mm;

(2) pretreatment of the leather blocks by a double-solvent system: putting the leather blocks obtained in the step (1) into ionic liquid/acid double-solvent solution with the weight 10 times of the leather weight, stirring for 12 hours at the temperature of 5 ℃, filtering to obtain leather blocks, and washing for later use; wherein the ionic liquid solvent is 500kg of 1-butyl-3-methylimidazole chlorine salt solution with the volume concentration of 50%; the acid solution is 500kg of lactic acid solution with 0.8 mol/L; uniformly mixing an ionic liquid solvent and an acid solution through mechanical stirring to prepare an ionic liquid/acid double-solvent solution;

(3) preparing collagen slurry: putting the leather blocks obtained in the step (2) into a high-shear homogenizer for homogenization treatment, adding glycerol with the mass of 17% of that of the homogenized collagen slurry, uniformly stirring, and then adjusting to short fiber collagen slurry with the solid content of 5% for later use;

wherein the technological parameters of the homogenization treatment are as follows: the rotating speed is 2800rpm, and the temperature is 6 ℃ in the homogenizing process;

The thickness of the finished collagen casing is measured to be 0.027 +/-0.01 mm, and the wet longitudinal breaking resistance is 5.472N. The yield of the product produced by the embodiment is 90.5%.

Example 3

(1) pretreatment of raw material dermatome: and screening 100kg of untanned second-layer sheepskin, cleaning and cutting into 4-6 cubic centimeters of skin blocks. The pieces were added to a disodium hydrogen phosphate-citric acid buffer solution having a pH of 6.8, which was 2 times the tare weight. Adding 0.2% of papain and 0.05% of neutral protease 1398 while stirring, standing for 2h at 20 ℃ every 45min of stirring, repeating for 4 times, stirring for 60min, filtering to remove waste liquid to remove residual hair root hair follicles and non-fibrous proteins, cleaning and chopping into block-shaped skin blocks with the diameter of 5-6 mm;

(2) pretreatment of the leather blocks by a double-solvent system: putting the leather blocks obtained in the step (1) into ionic liquid/acid double-solvent solution with the weight 6 times of the leather weight, stirring for 8 hours at the temperature of 5 ℃, filtering to obtain leather blocks, and washing for later use; wherein the ionic liquid solvent is 450kg of 1-butyl-3-methylimidazole nitrate solution with the volume concentration of 25%; 150kg of citric acid solution with the acid solution of 0.6 mol/L; uniformly mixing an ionic liquid solvent and an acid solution through mechanical stirring to prepare an ionic liquid/acid double-solvent solution;

(3) preparing collagen slurry: putting the leather blocks obtained in the step (2) into a high-shear homogenizer for homogenization treatment, adding propylene glycol with the mass of 15% of that of the homogenized collagen slurry, uniformly stirring, and then adjusting to short-fiber collagen slurry with the solid content of 7% for later use;

wherein the technological parameters of the homogenization treatment are as follows: the rotating speed is 2000rpm, and the temperature is 6 ℃ in the homogenizing process;

The thickness of the finished collagen casing is 0.024 +/-0.01 mm, and the wet longitudinal breaking resistance is 4.983N. The yield of the product in this embodiment is 83.2%.

Example 4

(1) pretreatment of raw material dermatome: screening 100kg of untanned second layer cowhide, cleaning and cutting into 4-6 cubic centimeters of leather blocks. The pieces were put into a disodium hydrogenphosphate-sodium dihydrogenphosphate buffer solution having a pH of 8 and a tare weight of 1.5 times. Adding 0.35% of alkaline protease while stirring, standing for 2h at the temperature of 20 ℃ for 30min every time after stirring, repeating for 5 times, stirring for 45min, filtering to remove waste liquid to remove residual hair root hair follicles and non-fibrous proteins, cleaning and chopping into block-shaped skin blocks with the diameter of 5-6 mm;

(2) pretreatment of the leather blocks by a double-solvent system: putting the leather blocks obtained in the step (1) into ionic liquid/acid double-solvent solution with the weight 9 times of the leather weight, stirring for 14 hours at the temperature of 5 ℃, filtering to obtain leather blocks, and washing for later use; wherein the ionic liquid solvent is 540kg of 1-butyl-3-methylimidazole mesylate with the volume concentration of 40%; the acid solution is 360kg of malic acid solution with the concentration of 0.8 mol/L; uniformly mixing an ionic liquid solvent and an acid solution through mechanical stirring to prepare an ionic liquid/acid double-solvent solution;

(3) preparing collagen slurry: putting the leather blocks obtained in the step (2) into a high-shear homogenizer for homogenization treatment, adding glycerol with the mass of 16.5% of that of the homogenized collagen slurry, uniformly stirring, and then adjusting to short fiber collagen slurry with the solid content of 6% for later use;

wherein the technological parameters of the homogenization treatment are as follows: the rotating speed is 2200rpm, and the temperature is 6 ℃ in the homogenizing process;

The thickness of the finished collagen casing is 0.025 plus or minus 0.01mm and the wet longitudinal breaking resistance is 5.112N. The yield of the product in this embodiment is 85.6%.

Example 5

(1) pretreatment of raw material dermatome: screening 100kg of untanned second-layer pigskin, cleaning and cutting into 4-6 cubic centimeters of skin blocks. The pieces were put into a disodium hydrogenphosphate-citric acid buffer solution having a pH of 6.8 and a tare weight of 1.5 times. Adding 0.1% bromelain while stirring, standing for 2h at 20 ℃ every 45min of stirring, repeating for 5 times, stirring for 45min, filtering to remove waste liquid to remove residual hair root hair follicles and non-fibrous proteins, cleaning and chopping into block-shaped skin blocks with the diameter of 5-6 mm;

(2) pretreatment of the leather blocks by a double-solvent system: putting the leather blocks obtained in the step (1) into ionic liquid/acid double-solvent solution with the weight of 12 times of the leather weight, stirring for 15 hours at the temperature of 5 ℃, filtering to obtain leather blocks, and washing for later use; wherein, the ionic liquid solvent is 960kg of 1-ethyl-3-methylimidazolium bromide with the volume concentration of 60 percent; the acid solution is 240kg of 0.6mol/L acetic acid solution; uniformly mixing an ionic liquid solvent and an acid solution through mechanical stirring to prepare an ionic liquid/acid double-solvent solution;

(3) preparing collagen slurry: putting the leather blocks obtained in the step (2) into a high-shear homogenizer for homogenization treatment, adding glycerol with the mass of 18% of that of the homogenized collagen slurry, uniformly stirring, and then adjusting to short-fiber collagen slurry with the solid content of 4% for later use;

wherein the technological parameters of the homogenization treatment are as follows: the rotating speed is 3200rpm, and the temperature is 6 ℃ in the homogenizing process;

The thickness of the finished collagen casing is measured to be 0.028 +/-0.01 mm, and the wet longitudinal breaking resistance is 5.207N. The yield of the product in this embodiment is 85.8%.

Example 6

(2) pretreatment of the leather blocks by a double-solvent system: putting the leather blocks obtained in the step (1) into ionic liquid/acid double-solvent solution with the weight 10 times of the leather weight, stirring for 9 hours at the temperature of 5 ℃, filtering to obtain leather blocks, and washing for later use; wherein the ionic liquid solvent is 450kg of 1-ethyl-3-methylimidazole acetate solution with the volume concentration of 30% and 250kg of 1-butyl-3-methylimidazole chloride solution with the volume concentration of 50%; the acid solution is 300kg of glacial acetic acid solution with 0.6 mol/L; uniformly mixing an ionic liquid solvent and an acid solution through mechanical stirring to prepare an ionic liquid/acid double-solvent solution;

(3) preparing collagen slurry: putting the leather blocks obtained in the step (2) into a high-shear homogenizer for homogenization treatment, adding glycerol with the mass of 16% of that of the homogenized collagen slurry, uniformly stirring, and then adjusting to short fiber collagen slurry with the solid content of 6% for later use;

wherein the technological parameters of the homogenization treatment are as follows: the rotating speed is 2600rpm, and the temperature is 6 ℃ in the homogenizing process;

The thickness of the finished collagen casing is 0.026 +/-0.01 mm, and the wet longitudinal breaking strength is 5.386N. The yield of the product in this embodiment is 89.5%.

Example 7

wherein the fixing treatment comprises immersing in 0.25% glutaminase bath solution, fixing at 25 deg.C for 30min, immersing in 0.5% genipin bath solution, and fixing at 28 deg.C for 20 min;

The thickness of the finished product of the collagen casing is 0.026 +/-0.01 mm through measurement, and the wet longitudinal breaking resistance is 5.763N. The yield of the product produced by the embodiment is 96.4%.

Example 8

wherein the fixing treatment comprises immersing in 0.25% glutaminase bath solution, fixing at 25 deg.C for 30min, immersing in 0.5% genipin bath solution, fixing at 28 deg.C for 20min, immersing in 0.6% tannic acid bath solution containing 0.3 ‰ of laccase catalyst based on tannic acid weight, and fixing at 30 deg.C for 15 min.

The thickness of the finished collagen casing is measured to be 0.027 +/-0.01 mm, and the wet longitudinal breaking resistance is 6.132N. The yield of the product in this embodiment is 97.5%.

The determination shows that the oxidation resistance of the collagen casing film after the tannin cross-linking and fixing is improved by 45.05 percent. FIG. 4 is a graph comparing the effect of tubular collagen membrane on scavenging ABTS free radicals before and after immobilization treatment according to the present example. As can be seen from the figure, after the ABTS working solution is added into the collagen tubular membrane which is subjected to the fixation treatment in the embodiment, the color is changed from dark blue-green to light blue-green, and the capability of the collagen tubular membrane for removing ABTS free radicals is obviously improved.

Example 9

wherein the fixing treatment comprises immersing in 0.6% tyrosinase bath solution, fixing at 28 deg.C for 25min, immersing in 1.0% genipin bath solution, fixing at 28 deg.C for 30min, immersing in 0.6% catechin bath solution containing 0.4 ‰ of laccase catalyst based on catechin weight, and fixing at 30 deg.C for 20 min.

The thickness of the finished collagen casing is measured to be 0.027 +/-0.01 mm, and the wet longitudinal breaking resistance is 5.964N. The yield of the product produced by the embodiment is 97.2%.

The oxidation resistance of the collagen casing membrane after catechin crosslinking and fixation is improved by 43.48 percent through measurement.

Example 10

wherein the fixing treatment comprises immersing in a bath solution containing 1.2% horseradish peroxidase, fixing at 25 deg.C for 15min, immersing in a genipin bath solution with concentration of 0.2%, fixing at 28 deg.C for 25min, immersing in a bayberry extract bath solution containing laccase catalyst with volume concentration of 1.6% and bayberry extract weight of 0.4 ‰, and fixing at 30 deg.C for 25 min.

The thickness of the finished collagen casing is 0.030 +/-0.01 mm through measurement, and the wet longitudinal breaking resistance is 6.093N. The yield of the product produced by the embodiment is 96.8%.

Through measurement, the oxidation resistance of the collagen casing film after the bayberry tannin extract is fixed by crosslinking is improved by 39.85 percent.

Comparative example 1

The comparative example adopts a single acid solution in the traditional wet preparation process to pretreat the leather blocks, and other process conditions are consistent with those of the example 1, and the method comprises the following steps:

(2) acid solution pretreatment of the leather blocks: putting the leather blocks obtained in the step (1) into an acid solution with the weight 8 times of the leather weight, stirring for 10 hours at the temperature of 5 ℃, filtering to obtain leather blocks, and washing for later use; wherein the acid solution is 0.3mol/L HCl.

The thickness distribution of the finished collagen casing is very uneven and is 0.030-0.048 mm, the average thickness is 0.041, and the wet longitudinal breaking resistance is 3.136N. The yield of the comparative example is 70.2%.

Comparative example 2

The comparative example adopts a single alkali solution to pretreat the leather blocks in the traditional wet preparation process, the other process conditions are consistent with those of the example 1 and the comparative example 1, and the description is not repeated, and the difference steps are as follows:

(2) pretreating the leather blocks with an alkali solution: putting the leather blocks obtained in the step (1) into an alkali solution with the weight 8 times of the leather weight, stirring for 10 hours at the temperature of 5 ℃, filtering to obtain leather blocks, and washing for later use; wherein the alkali solution is 0.3mol/L NaOH solution.

According to the measurement, the thickness distribution of the finished collagen casing is uneven and is 0.022-0.040 mm, the average thickness is 0.032 +/-0.01 mm, and the wet longitudinal breaking resistance is 2.745N. The collagen casing produced by the comparative example has more holes, and the yield is only 52.6%.

Comparative example 3

The comparative example adopts the ionic liquid solvent with the volume concentration lower than that defined by the technical scheme of the invention, the other process conditions are consistent with those of the example 1, the description is not repeated, and the difference steps are as follows:

pretreatment of the leather blocks by a double-solvent system: putting the leather blocks obtained in the step (1) into ionic liquid/acid double-solvent solution with the weight 8 times of the leather weight, stirring for 10 hours at the temperature of 5 ℃, filtering to obtain leather blocks, and washing for later use; wherein the ionic liquid solvent is 560kg of 1-ethyl-3-methylimidazole acetate solution with the volume concentration of 10%; the acid solution is 240kg of glacial acetic acid solution of 0.5 mol/L; uniformly mixing an ionic liquid solvent and an acid solution through mechanical stirring to prepare an ionic liquid/acid double-solvent solution;

according to the determination, the thickness distribution of the finished collagen casing is uneven and is 0.027-0.031 mm, the average thickness distribution is 0.029 +/-0.01 mm, the wet longitudinal breaking resistance is 4.293N, and the production yield of the comparative example is 82.3%.

Comparative example 4

The comparative example adopts the ionic liquid solvent with the volume concentration higher than that defined by the technical scheme of the invention, the other process conditions are consistent with those of the example 1, the description is not repeated, and the difference steps are as follows:

(2) pretreatment of the leather blocks by a double-solvent system: putting the leather blocks obtained in the step (1) into ionic liquid/acid double-solvent solution with the weight 8 times of the leather weight, stirring for 10 hours at the temperature of 5 ℃, filtering to obtain leather blocks, and washing for later use; wherein the ionic liquid solvent is 560kg of 1-ethyl-3-methylimidazole acetate solution with the volume concentration of 70%; the acid solution is 240kg of glacial acetic acid solution of 0.5 mol/L; uniformly mixing an ionic liquid solvent and an acid solution through mechanical stirring to prepare an ionic liquid/acid double-solvent solution;

according to the measurement, the thickness of the finished collagen casing is 0.024 +/-0.01 mm, the wet longitudinal breaking resistance is 4.157N, and the production yield of the comparative example is 81.5%.

Table 1 shows the results of the analysis of each index of collagen casing in each example and comparative example

Claims

1. A continuous water bath fixing treatment process for preparing a collagen casing by a wet method is characterized by comprising the following steps:

(4) shaping and fixing: extruding and spraying the short fiber collagen slurry obtained in the step (3) to form a tubular membrane, carrying out setting treatment through saturated NaCl, and then carrying out fixing treatment;

the fixing treatment comprises the following steps:

b enzyme bath liquid with the volume concentration of 0.1-1.5% and genipin bath liquid with the volume concentration of 0.1-1% are respectively prepared;

immersing the tubular membrane subjected to shaping treatment in B enzyme bath liquid, fixing for 10-30 min under the water bath condition at the temperature of 20-30 ℃, then immersing in genipin bath liquid, and fixing for 10-30 min under the water bath condition at the temperature of 20-30 ℃; wherein, the enzyme B is any one of glutaminase, horseradish peroxidase and tyrosinase;

2. The continuous water bath fixing treatment process as claimed in claim 1, wherein: the pretreatment by using the enzyme A in the step (1) is carried out, namely, firstly, unttanned animal two-layer and/or three-layer skins are cut into 4-6 cubic centimeters of skin blocks, then, the skin blocks are put into a buffer solution which is 1-3 times of the skin weight and has the pH value of 6-8, the enzyme A with the skin weight of 0.05-2% is added, the mixture is stirred for 30-60 min at the temperature of 20-25 ℃ for 2-3 h, the standing is repeated for 4-5 times, and the mixture is stirred for 30-60 min and then filtered to remove waste liquid.

3. The continuous water bath fixing treatment process as claimed in claim 2, which is characterized in that: the A enzyme comprises any one or more of 1398 neutral protease, 2709 alkaline protease, pancreatin, bromelain and papain; the buffer solution comprises any one of disodium hydrogen phosphate-citric acid buffer solution, citric acid-sodium citrate buffer solution and disodium hydrogen phosphate-sodium dihydrogen phosphate buffer solution.

4. The continuous water bath fixing treatment process as claimed in claim 1, wherein: the cutting treatment in the step (1) is to cut the collagen casing into block-shaped leather blocks suitable for preparing the collagen casing by a wet method, and the collagen casing is to cut the collagen casing into block-shaped leather blocks with the drift diameter of 5-10 mm.

5. The continuous water bath fixing treatment process as claimed in claim 1, wherein: in the ionic liquid/acid double-solvent solution in the step (2), the ionic liquid is a 25-30% volume concentration 1-ethyl-3-methylimidazolium acetate solution, the acid solution is 0.5-0.6 mol/L glacial acetic acid, and the volume ratio of the ionic liquid to the acid double-solvent solution is 7: 3; or the ionic liquid is a 1-butyl-3-methylimidazolium chloride solution with the volume concentration of 45-50%, the acid solution is a lactic acid solution with the volume ratio of 0.8-1.0 mol/L, and the volume ratio of the two is 5: 5.

6. The continuous water bath fixing treatment process as claimed in claim 1, wherein: and (3) preparing the collagen slurry in the step (3), namely adding glycerol with the mass of 15-18% of that of the homogenized collagen slurry and uniformly stirring.

7. The continuous water bath fixing treatment process as claimed in claim 1, wherein: the fixing treatment in the step (4) is carried out, after the fixing treatment is carried out through the two-step water bath fixing solution, the fixing treatment is carried out for 10-30 min by immersing the fixing solution into tannin and/or tannin extract bath liquid containing the enzyme C catalyst under the condition of 20-30 ℃; wherein, in tannin and/or tannin extract bath liquid containing enzyme C catalyst, tannin is any one of tannic acid, catechin, gallic acid and procyanidine, and tannin extract is any one of myrica tannin extract, wattle tannin extract, castanopsis mollissima tannin extract and tara tannin extract; the enzyme C catalyst is any one of laccase and tyrosinase, the volume concentration of tannin and/or tannin extract in bath liquid is 0.1-2%, and the dosage of the enzyme C catalyst is 0.1-2% of the total weight of tannin and/or tannin extract.

8. The continuous water bath fixing treatment process as claimed in claim 1, wherein: the fixing treatment in the step (4) comprises the following steps:

preparing glutaminase bath solution with volume concentration of 0.2-0.3%, genipin bath solution with volume concentration of 0.4-0.5% and tannic acid bath solution with volume concentration of 0.5-0.6% and containing laccase catalyst with weight of 0.3-0.4 per mill of tannic acid respectively;

immersing the tubular membrane after shaping treatment in glutaminase bath solution, fixing for 30min under the condition of water bath at the temperature of 25 ℃, then immersing in genipin bath solution, fixing for 20min under the condition of water bath at the temperature of 28 ℃, finally immersing in tannic acid bath solution, and fixing for 15min under the condition of water bath at the temperature of 30 ℃.