阅读说明：本技术 一种鱼皮胶原蛋白的提取方法及应用 (Extraction method and application of fish skin collagen ) 是由 刘茹 吴丹 胡杨 熊善柏 于 2021-03-17 设计创作，主要内容包括：本发明属于胶原蛋白提取技术领域,尤其涉及一种鱼皮胶原蛋白的提取方法及应用。本发明提供了一种快速提取非变性鱼皮胶原的方法,解决淡水鱼加工副产物浪费的问题,克服了传统胶原蛋白提取方法提取率低,提取时间长的缺点；本发明技术方法简单可行,提取时间短,提取效率高,最重要的是保证了胶原大分子结构的完整性,相比于其他方法大大缩短了提取时间。本发明在传统“酸-酶”结合法提取胶原蛋白之前对其进行超声处理,保证所提鱼皮胶原分子的天然活性,通过测定得到的鱼皮胶原保持Ⅰ型胶原蛋白的天然结构,为非变性的Ⅰ型胶原蛋白。该方法操作简单,耗能较低,提取效率高,易于放大应用于生产。(The invention belongs to the technical field of collagen extraction, and particularly relates to a method for extracting fish skin collagen and application thereof. The invention provides a method for rapidly extracting non-denatured fish skin collagen, which solves the problem of waste of freshwater fish processing by-products and overcomes the defects of low extraction rate and long extraction time of the traditional collagen extraction method; the method is simple and feasible, short in extraction time and high in extraction efficiency, and most importantly, the integrity of the collagen macromolecular structure is ensured, and the extraction time is greatly shortened compared with other methods. The invention carries out ultrasonic treatment before extracting the collagen by the traditional acid-enzyme combination method, ensures the natural activity of the extracted fish skin collagen molecules, and the fish skin collagen obtained by determination keeps the natural structure of the I type collagen and is the non-denatured I type collagen. The method has the advantages of simple operation, low energy consumption, high extraction efficiency, and easy application in production.)

1. The method for extracting the fish skin collagen is characterized by comprising the following steps:

s1 fish skin pretreatment: removing fish meat and pigment;

s2 degreasing and removing foreign proteins: according to the material-liquid ratio of 1:20, stirring by using a NaOH solution, and periodically replacing the NaOH solution; then washing the mixture with distilled water to be neutral, and mixing the raw materials according to a feed-liquid ratio of 1:20, stirring and treating by using isopropanol, washing to be neutral by using distilled water, and draining;

s3 ultrasonic treatment: placing the fish skin after degreasing and protein removal into feed liquid according to the proportion of 1: carrying out ultrasonic crushing treatment in 20 acetic acid solution, wherein the ultrasonic condition is 150-550W, and the time is 10-30 min;

s4 enzymatic extraction: drying pretreated fish skin, weighing pepsin according to 2% of the dry weight of the fish skin, dissolving the pepsin in an acetic acid solution with the pH of 2 and the volume of the acetic acid being calculated according to the ratio of material to liquid of 1: 20;

s5 centrifuging and taking the supernatant;

s6 salting out: adjusting the pH of the supernatant to be neutral, adding ammonium sulfate, and standing;

s7 centrifuging to obtain precipitate;

s8 precipitation dissolution: dissolving the precipitate in acetic acid solution; repeating the operations of S6-S8;

dialysis with S9 saline solution: dialyzing with dialysis bag with cut-off molecular weight of 10000D, dialyzing with 0.04M disodium hydrogen phosphate for 2 days, dialyzing with 0.02M disodium hydrogen phosphate for 1 day, and dialyzing with distilled water for 2 days;

s10 freeze-drying: and subpackaging the dialyzed solution into drying containers, and freeze-drying for 36-50 hours to prepare a finished product which is a white spongy solid.

2. The method for extracting collagen from fish skin according to claim 1, wherein the method comprises the following steps: in the step S2, the concentration of the NaOH solution is 0.01M, the treatment temperature of the NaOH solution is 4 ℃, the treatment time is 24 hours, and the NaOH is replaced every 8 hours; the concentration of the isopropanol solution is 10 percent, and the treatment condition is that the isopropanol solution is stirred for 8 hours at 4 ℃.

3. The method for extracting collagen from fish skin according to claim 1, wherein the method comprises the following steps: the concentration of the acetic acid solution in step S3 was 0.5M.

4. The method for extracting collagen from fish skin according to claim 1, wherein the method comprises the following steps: in step S3, the ultrasonic condition is 350W, and the time is 30 min.

5. The method for extracting collagen from fish skin according to claim 1, wherein the method comprises the following steps: stirring at 4 deg.C for 4 hr in step S5, and freeze-centrifuging at 10000rpm for 10 min.

6. The method for extracting collagen from fish skin according to claim 1, wherein the method comprises the following steps: in step S7, freezing and centrifuging at 10000r/min and 4 ℃ for 15min, and taking the precipitate.

7. The method for extracting collagen from fish skin according to claim 1, wherein the method comprises the following steps: freeze-drying for 36-50 hours in step S10.

8. Use of a method for the extraction of fish skin collagen according to any one of claims 1 to 7 for the extraction of fish skin collagen.

Technical Field

The invention belongs to the technical field of collagen extraction, and particularly relates to a method for extracting fish skin collagen and application thereof.

Background

The aquatic product resources in China are rich, and a large amount of processing byproducts such as fish skin and fish scales are generated in the processing process of freshwater fish and account for about 40-60% of the total amount of the aquatic products. Collagen is mainly distributed in the byproducts of fish skin and fish scales, wherein the content of the collagen in the fish skin is up to 25 percent, and the collagen is mainly high-value type I collagen. Because the source is sufficient, the fish skin is taken as the main raw material for extracting the type I collagen, so that the waste of a large amount of precious resources can be avoided, the additional value of fish processing is improved, and the environmental pollution is reduced; meanwhile, good economic benefit and social benefit can be obtained; in addition, the antigenicity of aquatic organisms is weaker than that of collagen of terrestrial mammal origin, and the aquatic organisms are easier to extract; and has higher water solubility; most importantly, collagen of aquatic animal origin avoids the risk of terrestrial mammalian-derived diseases and pathogen transmission. Therefore, the utilization of the processing byproducts such as fish skin and fish scale as raw materials for extracting type I collagen has a broad research prospect, and how to avoid the damage to the molecular structure of collagen while quickly and efficiently extracting the collagen gradually becomes a hot spot and a key point of the current research.

Type i collagen has been recognized as one of the most useful biomaterials, and has excellent biocompatibility and is capable of promoting cell adhesion, growth, proliferation, and differentiation, compared to other biomaterials. Widely applied to bone tissue repair materials, artificial skin materials, artificial blood vessels, heart valves, cell transplantation devices and the like. Common methods for extracting collagen from aquatic products at home and abroad include an acid method, an alkaline method, a salt method and an enzyme extraction method. The acid extraction method has short extraction time, can keep the integrity of the collagen molecular structure to the maximum extent and keep the natural activity, and is particularly suitable for preparing biomedical materials. But the tail end of the collagen has aldehyde group interaction and molecule covalent crosslinking, so that the amount of collagen dissolved out by acid is less; in addition, the acid extraction method also has the problems of solvent residue, equipment corrosion, environmental pollution and the like. The alkaline method is simple to operate and high in extraction speed, but the alkaline method can cause peptide bond hydrolysis, and all amino acids containing hydroxyl and sulfhydryl in collagen molecules are damaged to generate racemization. Therefore, practical applications are relatively few. The salt method refers to a method in which a certain concentration of neutral salt solution such as NaCl, Tris-HCl, citrate, etc. can dissolve collagen. NaCl is used in the extraction process to increase the surface charge of the collagen, so that the acting force between the NaCl and water molecules is enhanced, and the dissolution of the collagen is accelerated. However, when the salt concentration is too high, the salting-out reaction lowers the yield. The enzymatic extraction is the most common method at present, and the enzymatic extraction of collagen has the characteristics of short extraction time, high yield, less environmental pollution and the like; meanwhile, the enzyme method has mild extraction conditions, so that the collagen with good biological activity can be obtained. However, the biggest problem of enzymatic extraction is that hydrolysis is not thorough enough, and it is very important to explore a novel extraction method in order to improve the yield of collagen and ensure that the collagen has good biological activity.

The principle of ultrasonic-assisted extraction of fish skin collagen mainly comprises two principles: firstly, the solvent can effectively and rapidly enter the tissue due to the cavitation effect and the mechanical effect generated by the ultrasonic wave, so that the tissue structure becomes loose, the collagen fiber expands, and the speed of the acetic acid solution entering the fiber gaps in the subsequent extraction is increased, thereby increasing the extraction efficiency; secondly, the loose tissue structure is more easily combined with the enzyme cutting site of pepsin in the subsequent enzymolysis process, and the enzymolysis efficiency is improved (Defu Li, 2009). Research shows that ultrasonic treatment only slightly destroys part of hydrogen bonds of collagen under proper power, does not affect the integrity of a triple helix structure, improves the extraction rate of active collagen, and has obvious effect on the separation and extraction of biomacromolecules (Liangjianhua 2016). The research of Liangjianhua et al on the method for extracting the non-denatured collagen from fish skin by ultrasonic wave assisted extraction can remarkably improve the yield of the collagen, the yield of the collagen extracted by ultrasonic wave assisted extraction for 30min is 28.32% (higher than that extracted by traditional stirring for 12h by 8.0%), the yield of the collagen is also increased along with the increase of the ultrasonic pulse time, and SDS electrophoresis shows that the ultrasonic wave assisted extraction can promote the dissolution of collagen polymer chains (Liangjianhua, 2015). The process for extracting the bighead carp scale collagen by ultrasonic-assisted pepsinase is researched, and the ultrasonic power of 420W, the ultrasonic time of 30min and the solid-liquid ratio of 1: 15(g/mL), 6 percent of pepsin dosage, 1 percent of enzymolysis liquid pH and 3 hours of enzyme extraction time. Under these conditions, the collagen extraction rate was 56.01%. The characterization of the uv-vis spectrophotometer, the fourier transform infrared spectrometer and the X-ray diffraction analyzer and the analysis of the amino acid analyzer indicate that the product is type i collagen, and the amino acid composition and content of the collagen are substantially the same as those of typical mammalian and fish collagen (marijuan, pandai, 2017).

The invention belongs to the technical field of natural protein extraction, and particularly relates to a method for extracting collagen by taking tuna skin as a raw material and adopting pulsed ultrasound-assisted enzymolysis, wherein the granted publication number is CN 190336966A. Comprises the steps of raw material degreasing, impurity protein removing treatment, extraction, salting out, purification, dialysis and drying. Wherein, the raw material treatment adopts ether and NaOH to carry out degreasing and impurity protein removal. The ultrasonic auxiliary extraction step comprises: soaking the raw materials in 0.5M acetic acid solution in a material-to-liquid ratio of 1:200(mg/mL), and homogenizing in an ice bath for 5min at a frequency of 28kHz and a power of 100-400W for 10-50 min; and (3) after the ultrasonic treatment is finished, adding 0.06% (W/V)1800U/g pepsin (pH is 2) enzyme for 48 hours, centrifuging at 4 ℃ to obtain a supernatant, dialyzing, and freeze-drying to obtain a freeze-dried collagen sample. The ultrasonic-assisted enzyme extraction accelerates the extraction process of collagen, and finally, the I-type tuna skin collagen with a complete structure is prepared, so that the energy consumption is low. Although the extraction rate of the method is improved, the enzyme extraction time is still longer after the ultrasonic-assisted treatment, and the extraction efficiency is not high. And long-time high-power ultrasonic treatment can not only cause collagen macromolecules to form heat aggregation, but also can damage the integrity of collagen molecular structures by the shearing force generated by high-intensity ultrasound, so that the extracted collagen loses bioactivity. Therefore, in order to maintain the helical structure and bioactivity of collagen, the sonication conditions must be strictly controlled.

Disclosure of Invention

The invention provides a method for extracting fish skin collagen, aiming at solving part of problems in the prior art or at least relieving part of problems in the prior art.

The freshwater biogenic collagen is a biological material which has more superiority than the mammalian collagen, has weaker antigenicity and is easy to extract; has better biological safety, can not cause mammal-derived diseases and pathogen transmission, and has sufficient sources. However, the traditional extraction method has the problems of long extraction period, low extraction rate, incapability of ensuring the integrity of the collagen structure and the like, and how to ensure the integrity of the collagen structure while improving the extraction rate and shortening the extraction time needs to explore a novel extraction method. The extraction method of the fish skin collagen mainly comprises the steps of degreasing, impurity protein removal, ultrasonic treatment, enzyme extraction, centrifugation, salting out, centrifugation, precipitation dissolution, salt solution dialysis, pure water dialysis, freeze drying and the like. The extracted collagen is in the form of white filamentous powder, and aggregated into white sponge solid with good solubility. The fish skin collagen prepared by the invention can be applied to the product fields of wound repair materials, artificial skin, implantable medical materials and the like.

The invention is realized in such a way that the method for extracting the fish skin collagen comprises the following steps:

s1 fish skin pretreatment: removing fish meat and pigment;

s2 degreasing and removing foreign proteins: according to the material-liquid ratio of 1:20, stirring by using a NaOH solution, and periodically replacing the NaOH solution; then washing the mixture with distilled water to be neutral, and mixing the raw materials according to a feed-liquid ratio of 1:20, stirring and treating by using isopropanol, washing to be neutral by using distilled water, and draining;

s3 ultrasonic treatment: placing the fish skin after degreasing and protein removal into feed liquid according to the proportion of 1: carrying out ultrasonic crushing treatment in 20 acetic acid solution, wherein the ultrasonic condition is 150-550W, and the time is 10-30 min;

s4 enzymatic extraction: drying pretreated fish skin, weighing pepsin according to 2% of the dry weight of the fish skin, dissolving the pepsin in an acetic acid solution with the pH of 2 and the volume of the acetic acid being calculated according to the ratio of material to liquid of 1: 20;

s5 centrifuging and taking the supernatant;

s6 salting out: adjusting the pH of the supernatant to be neutral, adding ammonium sulfate, and standing;

s7 centrifuging to obtain precipitate;

s8 precipitation dissolution: dissolving the precipitate in acetic acid solution; repeating the operations of S6-S8;

dialysis with S9 saline solution: dialyzing with dialysis bag with cut-off molecular weight of 10000D, dialyzing with 0.04M disodium hydrogen phosphate for 2 days, dialyzing with 0.02M disodium hydrogen phosphate for 1 day, and dialyzing with distilled water for 2 days;

s10 freeze-drying: and subpackaging the dialyzed solution into drying containers, and freeze-drying for 36-50 hours to prepare a finished product which is a white spongy solid.

Further, in the step S2, the concentration of the NaOH solution is 0.01M, the treatment temperature of the NaOH solution is 4 ℃, the treatment time is 24 hours, and the NaOH is replaced every 8 hours; the concentration of the isopropanol solution is 10 percent, and the treatment condition is that the isopropanol solution is stirred for 8 hours at 4 ℃.

Further, the concentration of the acetic acid solution in step S3 was 0.5M.

Further, the ultrasonic condition in step S3 was 350W for 30 min.

Further, in step S5, after stirring at 4 ℃ for 4 hours, it was subjected to refrigerated centrifugation at 10000rpm for 10 min.

Further, in step S7, the precipitate is collected by freezing and centrifuging at 10000r/min and 4 ℃ for 15 min.

Further, freeze-drying is performed in step S10 for 36-50 hours.

The invention also discloses application of the fish skin collagen extraction method in fish skin collagen extraction.

The invention provides a method for rapidly extracting non-denatured fish skin collagen, which solves the problem of waste of freshwater fish processing by-products and overcomes the defects of low extraction rate and long extraction time of the traditional collagen extraction method; the method is simple and feasible, short in extraction time and high in extraction efficiency, and most importantly, the integrity of the collagen macromolecular structure is ensured, and the extraction time is greatly shortened compared with other methods.

In summary, the advantages and positive effects of the invention are:

(1) the invention carries out ultrasonic treatment before extracting the collagen by the traditional acid-enzyme combination method, greatly shortens the extraction time, improves the extraction rate and simultaneously ensures the natural activity of the extracted fish skin collagen molecules, and the fish skin collagen obtained by determination keeps the natural structure of the type I collagen and is the non-denatured type I collagen. The method has the advantages of simple operation, low energy consumption, high extraction efficiency, and easy application in production.

(2) The processing byproducts of aquatic products such as fish skin and the like not only avoid wasting a large amount of precious resources, but also improve the added value of fish processing and reduce environmental pollution.

(3) The extracted collagen molecule has complete spiral structure and bioactivity, has very stable collagen molecule structure, and has wide application prospect in the fields of biological medicine, tissue engineering, biological materials and the like.

Drawings

FIG. 1 is a raw material diagram of silver carp skin;

FIG. 2 is a point diagram of the collagen yield of silver carp skin obtained by performing ultrasonic treatment on the silver carp skin at the same frequency for different times and different powers;

FIGS. 3 and 4 are SDS-PAGE electrophoretograms of the collagen extracted from silver carp skin by ultrasonic treatment at 20Hkz and different times and powers;

FIG. 5 is a CD map of collagen extracted from silver carp skin by different power ultrasonic treatment at 20Hkz for 30 min;

FIG. 6 is FT-IR spectrum of collagen extracted from silver carp skin by sonication at 20Hkz for 30min at different power;

fig. 7 and 8 are scanning electron micrographs of silver carp skin extracted by different power ultrasonic treatment for 30min at the frequency of 20 Hkz.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples, and the equipment and reagents used in the examples and test examples are commercially available without specific reference. The specific embodiments described herein are merely illustrative of the invention and are not intended to be limiting.

Various modifications to the precise description of the invention will be readily apparent to those skilled in the art from the information contained herein without departing from the spirit and scope of the appended claims. It is to be understood that the scope of the invention is not limited to the procedures, properties, or components defined, as these embodiments, as well as others described, are intended to be merely illustrative of particular aspects of the invention. Indeed, various modifications of the embodiments of the invention which are obvious to those skilled in the art or related fields are intended to be covered by the scope of the appended claims.

For a better understanding of the invention, and not as a limitation on the scope thereof, all numbers expressing quantities, percentages, and other numerical values used in this application are to be understood as being modified in all instances by the term "about". Accordingly, unless expressly indicated otherwise, the numerical parameters set forth in the specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. In the present invention, "about" means within 10%, preferably within 5% of a given value or range.

The normal temperature in the following embodiments of the present invention refers to a natural room temperature condition in four seasons, and is not subjected to additional cooling or heating treatment, and is generally controlled at 10 to 30 ℃, preferably 15 to 25 ℃.

The invention discloses an extraction method and application of fish skin collagen, the obtained fish skin collagen has extremely high similarity with human collagen in components, the extraction time is greatly shortened, the extraction rate is improved, and simultaneously the integrity of a collagen molecule triple helix structure is ensured, the prepared collagen has the advantages of no toxicity, low antigenicity, good biocompatibility, easy biodegradation, easy processing and the like, and has great application potential in the fields of medical treatment, beauty treatment, health care and the like. The details are shown in the following examples.

Example 1 preparation of Fish skin collagen with sonication power of 150W, 250W, 350W, 450W, 550W for 20min

The raw material of the silver carp skin is shown in figure 1, the silver carp skin is obtained by an automatic skinning machine, and the residual fish and black impurities in the silver carp skin are manually removed. The fish skin was cut into 5mm by 5mm, washed, drained with a coarse gauze and weighed 163.93 g.

Degreasing and removing foreign protein:

(1) stirring 0.01M NaOH with volume of 3L at 4 deg.C for 24 hr, changing NaOH every 8 hr, repeatedly washing with distilled water to neutral, and draining

(2) The volume of 10% isopropyl alcohol was 3L, and the mixture was stirred at 4 ℃ for 8 hours, repeatedly washed with distilled water to neutrality, thoroughly drained, and weighed 365.69 g.

Ultrasonic treatment:

60.16g, 60.13g, 60.28 g, 60.35g and 60.80g of fish skin after degreasing and protein removal are respectively weighed and placed in 1L of 0.5M acetic acid solution for ultrasonic treatment; ultrasonic cell disruptor with frequency of 20KHz is used, and the probe is placed at 1-2cm of liquid level for ultrasonic treatment. The ultrasonic power gradient was set at 150W, 250W, 350W, 450W, 550W; the ultrasound time was set to 20 min.

Enzyme extraction:

(1) the water content of the fish skin after degreasing and protein removal is 87.69%, and 0.156g of pepsin (1:3000) is weighed according to 2% of the dry weight of the fish skin

(2) The mixture was stirred at 4 ℃ for 4h with an electric stirrer. And (3) carrying out refrigerated centrifugation on the enzymolysis liquid for 10min at the rotation speed of 10000rpm by using a refrigerated centrifuge at 4 ℃, and taking the volume of the supernatant as 720 ml.

(3) Adjusting pH of the enzymolysis supernatant to 7.0 with 10mol/L NaOH solution to adjust the volume of the enzymolysis solution to be neutral to 780ml, weighing 154.60g of ammonium sulfate according to the final concentration of the ammonium sulfate to be 1.5mol/L, immediately adding the ammonium sulfate into the enzymolysis solution, and stirring to dissolve the ammonium sulfate. Standing overnight in a refrigerator at 4 deg.C, and the volume of salting-out solution is 850 ml.

(4) Freezing and centrifuging the salting-out solution at 10000r/min and 4 ℃ for 15min, taking out the precipitate, and dissolving with 800ml of 0.5mol/L acetic acid. Adjusting pH to about 7 according to the operation of first salting out, weighing 105.71g ammonium sulfate according to the final concentration of ammonium sulfate of 1mol/L, immediately adding ammonium sulfate into the enzymolysis solution, and stirring to dissolve. The mixture was left to stand overnight in a refrigerator at 4 ℃. Freezing and centrifuging the salting-out solution at 10000r/min and 4 ℃ for 15min, taking the precipitate, and dissolving the precipitate with 600ml of 0.5mol/L acetic acid.

(5) Dialyzing with pretreated dialysis bag with molecular weight cutoff of 10000D. The dialysate was 10L, dialyzed against 0.04M disodium hydrogen phosphate for 2 days, dissolved 143.256g disodium hydrogen phosphate in 6L distilled water, mixed with 4kg crushed ice to make an ice-water mixture, and the filled dialysis bag was put therein. The dialyzate was replaced every 8 hours and the incubator was used for storage. Dialysis was further performed with 0.042M disodium hydrogenphosphate for 1 day, 71.56g disodium hydrogenphosphate was sufficiently dissolved in 6L distilled water and mixed with 4kg crushed ice to prepare an ice-water mixture, and finally, dialysis was performed with distilled water for 2 days.

(6) And (4) subpackaging the dialyzed solution into five dishes, and freeze-drying for 48 hours to prepare a finished product which is a white spongy solid.

Example 2 preparation of Fish skin collagen with sonication power of 150W, 250W, 350W, 450W, 550W for 30min

And (3) obtaining fish skin by adopting an automatic skinning machine, and manually removing residual fish and black impurities from the fish skin. The skin of the fish was cut into 5mm by 5mm, washed, drained with a coarse gauze and weighed 121.68 g.

Degreasing and removing foreign protein:

(1) the volume of 0.01M NaOH is 3L, the NaOH is stirred for 24h at 4 ℃, the NaOH is changed every 8h, the solution is repeatedly washed by distilled water until the solution is neutral, and the solution is fully drained.

(2) The volume of 10% isopropyl alcohol was 3L, and the mixture was stirred at 4 ℃ for 8 hours, repeatedly washed with distilled water to neutrality, thoroughly drained, and weighed 271.44 g.

Ultrasonic treatment:

60.04g, 60.35g, 60.07 g, 60.15 g and 60.89g of fish skin after degreasing and protein removal are respectively weighed and placed in 1L of 0.5M acetic acid solution for ultrasonic treatment; ultrasonic cell disruptor with frequency of 20KHz is used, and the probe is placed at 1-2cm of liquid level for ultrasonic treatment. The ultrasonic power gradient was set at 150W, 250W, 350W, 450W, 550W; the ultrasound time was set to 30 min.

Enzyme extraction:

(1) 3.04g of pretreated fish skin is dried at 105 ℃ to constant weight, the water content is measured to be 87.69%, and 0.156g of pepsin (1:3000) is weighed according to 2% of the dry weight of the fish skin.

(2) The mixture was stirred at 4 ℃ for 4h with an electric stirrer. And (3) carrying out refrigerated centrifugation on the enzymolysis liquid for 10min at the rotation speed of 10000rpm by using a refrigerated centrifuge at 4 ℃, and taking the volume of the supernatant to be about 700 ml.

(3) The enzymolysis solution volume of which the pH value of the enzymolysis supernatant is adjusted to 7.0 and adjusted to be neutral is about 750ml by 10mol/L NaOH solution, 148.65g of ammonium sulfate is weighed according to the final concentration of the ammonium sulfate of 1.5mol/L and is immediately added into the enzymolysis solution, and the solution is stirred to be dissolved. Standing overnight in a refrigerator at 4 deg.C, and the volume of salting-out solution is 850 ml.

(4) Freezing and centrifuging the salting-out solution at 10000r/min and 4 ℃ for 15min, taking out the precipitate, and dissolving with 800ml of 0.5mol/L acetic acid. Adjusting pH to about 7 according to the operation of first salting out, weighing 105.71g ammonium sulfate according to the final concentration of ammonium sulfate of 1mol/L, immediately adding ammonium sulfate into the enzymolysis solution, and stirring to dissolve. The mixture was left to stand overnight in a refrigerator at 4 ℃. Freezing and centrifuging the salting-out solution at 10000r/min and 4 ℃ for 15min, taking the precipitate, and dissolving the precipitate with 500ml of 0.5mol/L acetic acid.

(5) Dialyzing with pretreated dialysis bag with cut-off molecular weight of 10000D. The dialysate was 10L, dialyzed against 0.04M disodium hydrogen phosphate for 2 days, dissolved 143.256g disodium hydrogen phosphate in 6L distilled water, mixed with 4kg crushed ice to make an ice-water mixture, and the filled dialysis bag was put therein. The dialyzate was replaced every 8 hours and the incubator was used for storage. Dialysis was further performed with 0.042M disodium hydrogenphosphate for 1 day, 71.56g disodium hydrogenphosphate was sufficiently dissolved in 6L distilled water and mixed with 4kg crushed ice to prepare an ice-water mixture, and finally, dialysis was performed with distilled water for 2 days.

(6) And (4) subpackaging the dialyzed solution into five dishes, and freeze-drying for 48 hours to prepare a finished product which is a white spongy solid.

Calculation of collagen yield: weighing the dried silver carp skin and the collagen after freeze drying respectively, and calculating the collagen yield according to the following formula:

collagen yield (%) — extract dry weight (g) ÷ fish skin dry weight (g) × 100%

As can be seen from FIG. 2, the ultrasonic treatment can significantly improve the collagen yield, the collagen yield increases and then decreases with the increase of the ultrasonic power, and when the ultrasonic power is 350W30min, the collagen yield reaches the maximum value of 46%, and then starts to decrease. When the ultrasonic power is less than 250W, the influence of the ultrasonic time on the collagen yield is small, and when the ultrasonic power is more than 350W, the collagen yield is rapidly reduced along with the extension of the ultrasonic time. This is probably due to the interference with bubble dynamics with increasing ultrasound power and with increasing ultrasound time, leading to a worsening of cavitation effects and consequently to an impact on yield. The low-power ultrasonic treatment can obviously improve the collagen yield, but the ultrasonic power is not beneficial to extraction when continuously increasing. Therefore, ultrasonic treatment for 350W30min is determined as the optimal condition for extracting the fish skin collagen.

Analysis of collagen by Polyacrylamide gel electrophoresis (SDS-PAGE) in examples 1 and 2

7% separation gel and 4% concentrated gel are selected, and the sample loading amount is 20 mu L. And (3) processing of a sample: the sample is a collagen solution of 5mg/ml, the insoluble substances are removed by centrifugation for 10min at 10000r/min, and the supernatant and a Sodium Dodecyl Sulfate (SDS) loading buffer solution are mixed according to the volume ratio of 2: 3 mixing to make collagen concentration be 2 mg/ml. Electrophoresis conditions: the initial voltage is 80V, the electrophoresis time is 40min, then the voltage is adjusted to 110V, the electrophoresis time is about 90min, and the electrophoresis is stopped until the dye in the sample migrates to 2cm from the lower end. After electrophoresis, the gel was stained with Coomassie Brilliant blue R-250 for 30min, followed by ethanol: acetic acid: distilled water 5: 1: 4 for 1h, and finally soaking in distilled water overnight.

Electrophoresis strips with different ultrasonic powers and ultrasonic times are shown in figures 3 and 4: wherein, the A band is Marker, and proteins with known molecular weights of 250KDa, 150KDa, 100KDa and 75KDa are selected for electrophoretic analysis. M-maker; k-no ultrasound; a-ultrasonic 150W10, 20, 30 min; b-ultrasonic 250W10, 20 and 30 min; c-ultrasonic 350W10, 20 and 30 min; d-ultrasonic 450W10, 20 and 30 min; E-550W10, 20, 30min, 4 clear bands were present for all collagen samples: α 1, α 2, β and γ. The alpha chain consists of alpha 1 and alpha 2, wherein the width of the alpha 1 spectrum is significantly greater than that of alpha 2, indicating that the collagen is a trimer consisting of 2 alpha 1 and 1 alpha 2 peptide chains, and the beta chain content is higher and contains a small amount of gamma chain, which is characteristic of typical type I collagen. Wherein, the gamma strip is a collagen molecule formed by three peptide chains which are twisted together; the beta chain is a polymer of two alpha peptide chains, the molecular weight of the beta chain is twice that of the alpha peptide chain, and the molecular weight is about 260 kDa; the molecular weight of the alpha 1 chain is higher than that of the alpha 2 chain, and the molecular weight is about 130 kDa. The electrophoresis result shows that the collagen molecule prepared by the experiment is complete, the molecular weight is more than 300kDa, and the extracted collagen is type I collagen. The impurity bands in the sample are gradually increased along with the increase of the ultrasonic power, because the collagen molecules are broken due to the long-time high-power ultrasonic treatment, and the collagen molecules are sheared into small molecules by the shearing force during the ultrasonic treatment. The low-power processing of the fish skin collagen electrophoresis pattern is clear, no impurity band appears, the protein purity is good, and the original structure is basically maintained.

The circular dichroism spectrum of collagen treated by different ultrasonic powers is shown in figure 5. By using the product obtained in the above example 2, a collagen solution of 0.1mg/mL is prepared by pretreatment, the thickness of a liquid pool is 1cm, the scanning wavelength range is 190-250 nm, and the scanning speed is 50nm/min for analysis. The positive absorption peak appears at the position of about 220nm of the wavelength of the I type collagen solution, the negative absorption peak appears at the position of about 198nm of the wavelength of the I type collagen solution, the positive absorption peak and the negative absorption peak exist, and the phenomenon that the positive absorption peak disappears or the negative absorption peak is red-shifted does not appear, which indicates that the prepared collagen triple-helix structure is kept complete and the secondary structure is not changed.

FIG. 6 is FT-IR spectrum of collagen extracted from silver carp skin by sonication at 20Hkz for 30min at different power. Wherein A-is not sonicated; B-150W for 30 min; C-250W for 30 min; D-350W for 30 min; E-450W for 30 min; F-550W30 min. Compared with the un-sonicated group, the amide A band showed a tendency to decrease at sonication power of 450W and 550W, indicating that higher power sonication was able to break the N-H groups in collagen and participate in the formation of H bonds. When the H bond is reduced, the position of the group is shifted to a low frequency. The fish skin collagen amide B bands treated by ultrasonic waves with different powers have no difference, and the absorption peaks are 2924cm^-1It is shown that the ultrasonic treatment with different frequencies has no influence on the absorption of the fish skin collagen amide B band. The vibration frequency of the amide I and II peaks is positively correlated with the molecular order of the collagen. With the increase of ultrasonic power, the absorption peak of the amide I band is 1633cm^-1Has not changed, butWhen the ultrasonic power is 550W for 30min, the absorption peak of the amide II band is from 1545cm^-1Down to 1536cm^-1The low-power ultrasonic treatment has little influence on the order degree of collagen molecules, and when the high-power ultrasonic treatment is carried out for a long time, the secondary structure of collagen is changed, so that the order degree of the collagen molecules is reduced. The secondary structure of collagen molecules is not destroyed in 350W30min, and the structure of natural type I collagen is still kept.

FIGS. 7 and 8 are scanning electron micrographs of collagen extracted from silver carp skin by sonication at a frequency of 20 Hkz. At 600 and 1000 times the collagen presents a uniform and dense network structure. The prepared collagen is shown to be loose and porous collagen sponge.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.