Oxidation-assisted sheepskin enzyme depilation method

Abstract

The invention belongs to the technical field of animal skin processing, and discloses an oxidation-assisted sheepskin enzyme unhairing method, which comprises the following steps: in a sheepskin unhairing process, firstly adding protease to carry out enzyme unhairing, after the protease fully permeates into the skin, adding a protease inhibitor to inhibit the protease activity on the surface of the skin, and when the unhairing area reaches 80-90%, stopping unhairing; and carrying out oxidation depilation under an alkaline condition by using a strong oxidant until the depilation is completed. According to the method, the acting time and acting strength of protease on sheepskin surface collagenous fibers are reduced, meanwhile, wool at the positions such as the back and the side belly of the sheepskin is completely removed, the problems that when an existing enzyme unhairing technology is used for the sheepskin, unhairing is incomplete, and the sheepskin collagenous fibers are seriously damaged are solved, and high-quality unhaired bare skin can be obtained. The sheepskin unhairing method is convenient to operate, mild in condition and environmentally friendly, and the prepared unhaired bare skin can be used for industries such as leather making and food.

Description

Technical Field

[0001] The present invention belongs to the technical field of animal skin processing, and particularly relates to an oxidative-assisted enzymatic hair removal method for sheepskin and the dehaired naked skin obtained by using this method. Background Art

[0002] Sheepskin has extensive application values in the fields of textile, leather manufacturing, food processing, etc. In the process of sheepskin processing, hair removal, as a key process, aims to efficiently separate wool from sheepskin to obtain high-quality wool and naked skin raw materials. In recent years, due to advantages such as environmental protection and high efficiency, the enzymatic hair removal technology based on protease has become an important research direction in this field and has received extensive attention from the industrial community. However, there are still certain limitations in simply using protease for enzymatic hair removal of sheepskin. On the one hand, the wool on the back, side abdomen and other parts of sheepskin has characteristics such as large diameter, deep hair follicles and high strength, making it difficult to be completely removed in a short time. On the other hand, since the epidermis and subcutaneous tissue layer of sheepskin are relatively thin, with a high fat content and low structural strength, if the action time of protease is too long, the collagen fibers on the surface layer of sheepskin are likely to be excessively degraded, resulting in a significant decrease in the strength of the leather board. This technical bottleneck needs to be solved urgently through process optimization and other means.

[0003] In view of this, the present invention is specifically proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide an oxidative-assisted enzymatic hair removal method for sheepskin, which can improve the hair removal efficiency and reduce the damage of collagen fibers in sheepskin during hair removal to obtain high-quality dehaired naked skin.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: An oxidative-assisted enzymatic hair removal method for sheepskin. During the hair removal process of sheepskin, protease is first added for enzymatic hair removal. After the protease fully penetrates the skin, a protease inhibitor is added to inhibit the protease activity on the surface of the skin. When the hair removal area reaches 85%-95%, an oxidizing agent is then used for oxidative hair removal under alkaline conditions until the hair removal is complete.

[0006] Preferably, the protease is selected from any one or more of microbial protease, animal protease and plant protease.

[0007] Preferably, the oxidizing agent is hydrogen peroxide solution.

[0008] Preferably, a protease inhibitor is added to inhibit the protease activity on the surface layer of the skin at 1 / 2 - 7 / 8 of the total protease hair removal time.

[0009] Preferably, the protease inhibitor is selected from any one or more of protein, polypeptide, short peptide and amino acid.

[0010] Preferably, the sheepskin is pretreated by washing, soaking, fleshing, degreasing, etc.

[0011] Preferably, based on the mass percentage of the pretreated sheepskin, the dosage of the protease is 0.05%-1.0%, the dosage of the protease inhibitor is 0.05%-2.0%, and the dosage of the strong oxidant is 0.5%-5.0%.

[0012] The present invention also discloses a dehaired bare skin obtained by using the oxidative-assisted enzymatic dehairing method for sheepskin described in any one of the above.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The oxidative-assisted enzymatic dehairing method for sheepskin proposed by the present invention, with the assistance of a strong oxidant, reduces the action time and intensity of the protease on the collagen fibers of the sheepskin during the dehairing process, and at the same time effectively removes the wool on the back, side abdomen and other parts of the sheepskin, solving the problems that the existing enzymatic dehairing technology may not be completely dehaired or easily damage the collagen fibers of the sheepskin when used on sheepskin, and can obtain high-quality dehaired bare skin.

[0014] 2. The oxidative-assisted enzymatic dehairing method for sheepskin provided by the present invention is convenient to operate, has mild conditions, is environmentally friendly, and the obtained dehaired bare skin can be used in various industries such as leather making and food. Specific Embodiments

[0015] To make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that these descriptions are exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present invention. Those not specified in the examples are carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0016] The first embodiment provided by the present invention is: In the oxidative-assisted enzymatic dehairing method for sheepskin, during the sheepskin dehairing process, protease is first added for enzymatic dehairing. After the protease fully penetrates the hide, a protease inhibitor is added to inhibit the protease activity on the surface of the hide. When the dehaired area reaches 80%-90%, a strong oxidant is then used for oxidative dehairing under alkaline conditions until the dehairing is complete.

[0017] The key to the embodiment of the present invention lies in the control of the degree of enzymatic hair removal and oxidative hair removal. When the hair removal area of the sheepskin reaches 80%-90% under the action of protease, that is, when most of the wool has been removed and only a small amount of wool remains on the back and the side abdomen, a strong oxidant is used for oxidative hair removal. This can not only shorten the action time of protease on the sheepskin, but also reduce the dosage and action time of the strong oxidant at the same time, thereby achieving the effects of reducing the damage degree of the collagen fibers of the sheepskin and improving the hair removal efficiency. In addition, after the protease fully penetrates the hide, a protease inhibitor needs to be used to inhibit the protease activity on the surface of the hide, further reducing the action time and intensity of the protease on the collagen fibers on the surface of the sheepskin, so as to achieve the beneficial effects of the present invention.

[0018] It should be noted that the process parameters and hair removal degree of enzymatic hair removal of sheepskin are determined by targeted optimization according to the differences in skin sources (such as different storage methods such as fresh skin, frozen skin, salted skin, etc., different ages, areas, thicknesses of lambskin, old sheepskin, etc., as well as different varieties and origins). A large number of our studies have shown that for salted skin or lambskin with relatively low hair removal difficulty, when the enzymatic hair removal area reaches about 90%, transferring to the oxidative hair removal stage can obtain ideal results; while for fresh skin, frozen skin or old sheepskin with relatively high hair removal difficulty, the degree of enzymatic hair removal needs to be reduced, and when the enzymatic hair removal area reaches about 80%, it is transferred to the oxidative hair removal stage to achieve the best hair removal effect. Experimental data shows that when the hair removal area of the sheepskin reaches 80%-90%, the damage rate of the collagen fibers of the sheepskin can be as low as about 2%; if the enzymatic hair removal time is continued until the hair removal rate is greater than 98%, the damage rate of the collagen fibers will rise sharply to more than 20%. This embodiment adopts an "enzymatic-oxidative" synergistic hair removal process. After most of the hair is removed enzymatically, mild oxidative treatment is supplemented to remove the remaining 20%-10% of the wool. Compared with simple enzymatic hair removal treatment, it can significantly reduce the damage of the collagen fibers of the sheepskin. In this embodiment, the protease is selected from any one or more of microbial protease, animal protease and plant protease. The key process control point is that when the protease fully penetrates the hide, a protease inhibitor needs to be added within the time period of 1 / 2-7 / 8 of the total protease hair removal time to inhibit the protease activity on the surface of the hide, so as to reduce the damage of the collagen fibers of the hide while not affecting the hair removal effect of the protease preparation. The total protease hair removal time described here is the duration from the addition of protease to the hair removal area reaching 80%-90%. The protease inhibitor can be selected from any one or more of protein, polypeptide, short peptide and amino acid.

[0019] In this embodiment, the purpose of performing oxidative depilation under alkaline conditions is to enhance the oxidation efficiency of strong oxidants by increasing the environmental pH, thereby obtaining a more efficient depilation effect. Specifically, during the oxidative depilation stage, an appropriate amount of alkali agent can be added while adding a strong oxidant to adjust the pH of the depilation system to not less than 12.5. The alkali agent can be selected from commonly used, colorless and transparent strong alkalis, such as sodium hydroxide. The strong oxidant can be selected from common strong oxidants used for oxidative depilation of animal skins, such as hydrogen peroxide solution with a mass concentration of 45%-55%.

[0020] In this embodiment, based on the mass percentage of the pretreated sheepskin, the dosage of protease is 0.05%-1.0%, the dosage of protease inhibitor is 0.05%-2.0%, and the dosage of strong oxidant is 0.5%-5.0%.

[0021] The second embodiment provided by the present invention is as follows: The depilated naked skin obtained according to the above oxidative-assisted enzymatic depilation method for sheepskin.

[0022] To further elaborate on the technical solution of the present invention, multiple examples will be used below to illustrate the oxidative-assisted enzymatic depilation method for sheepskin and its effects in detail.

[0023] In the following examples and comparative examples, the dosages of materials are all based on the mass percentage (wt%) of the pretreated sheepskin.

[0024] Example 1 Load the pretreated sheepskin (frozen lamb skin) into a drum, add 250% water and 0.2% microbial protease, adjust the temperature to 30°C, rotate for 105 min, add 0.05% soybean trypsin inhibitor, and continue to rotate for 15 min. The depilation area reaches about 90%; change the liquid, add 100% water, 0.5% hydrogen peroxide solution (mass concentration 45%) and 1% sodium hydroxide, adjust the temperature to 20°C, and rotate until depilation is completed. The total depilation time is 240 min to obtain the depilated naked skin.

[0025] Comparative Example 1 The traditional enzymatic depilation method is specifically as follows: Load the pretreated sheepskin (frozen lamb skin) into a drum, add 250% water and 0.2% microbial protease, adjust the temperature to 30°C, and rotate until depilation is completed. The total depilation time is 320 min to obtain the depilated naked skin.

[0026] Comparative Example 2 Compared with Example 1, the difference is that the addition of soybean trypsin inhibitor is cancelled, and the enzymatic depilation time is 120 min. That is, the depilation process is as follows: Load the pretreated sheepskin (frozen lamb skin) into a rotating drum, add 250% water and 0.2% microbial protease, adjust the temperature to 30 °C, rotate for 120 min, and the hair removal area reaches about 90%; change the liquid, add 100% water, 0.5% hydrogen peroxide solution (mass concentration 45%) and 1% sodium hydroxide, adjust the temperature to 20 °C, rotate until hair removal is completed, and the total hair removal time is 240 min to obtain the hair-removed bare skin.

[0027] Comparative Example 3 Compared with Example 1, the difference is that enzymatic hair removal is carried out until the hair removal area reaches 75%, that is, the hair removal process is as follows: Load the pretreated sheepskin (frozen lamb skin) into a rotating drum, add 250% water and 0.2% microbial protease, adjust the temperature to 30 °C, rotate for 75 min, add 0.05% soybean trypsin inhibitor, and continue to rotate for 15 min. The hair removal area reaches about 75%; change the liquid, add 100% water, 0.5% hydrogen peroxide solution (mass concentration 45%) and 1% sodium hydroxide, adjust the temperature to 20 °C, rotate until hair removal is completed, and the total hair removal time is 400 min to obtain the hair-removed bare skin.

[0028] Comparative Example 4 Compared with Example 1, the difference is that the addition of soybean trypsin inhibitor is cancelled, and the enzymatic hair removal time is 105 min, that is, the hair removal process is as follows: Load the pretreated sheepskin (frozen lamb skin) into a rotating drum, add 250% water and 0.2% microbial protease, adjust the temperature to 30 °C, rotate for 105 min, and the hair removal area reaches about 83%; change the liquid, add 100% water, 0.5% hydrogen peroxide solution (mass concentration 45%) and 1% sodium hydroxide, adjust the temperature to 20 °C, rotate until hair removal is completed, and the total hair removal time is 320 min to obtain the hair-removed bare skin.

[0029] Comparative Example 5 Compared with Example 1, the difference is that the addition of sodium hydroxide solution is cancelled, that is, the hair removal process is as follows: Load the pretreated sheepskin (frozen lamb skin) into a rotating drum, add 250% water and 0.2% microbial protease, adjust the temperature to 30 °C, rotate for 105 min, add 0.05% soybean trypsin inhibitor, and continue to rotate for 15 min. The hair removal area reaches about 90%; change the liquid, add 100% water and 0.5% hydrogen peroxide solution (mass concentration 45%), adjust the temperature to 20 °C, rotate until hair removal is completed, and the total hair removal time is 540 min to obtain the hair-removed bare skin.

[0030] Comparative Example 6 Compared with Example 1, the difference is that the addition of hydrogen peroxide solution is cancelled, that is, the hair removal process is as follows: Load the pretreated sheepskin (frozen lamb skin) into a rotating drum, add 250% water and 0.2% microbial protease, adjust the temperature to 30 °C, rotate for 105 min, add 0.05% soybean trypsin inhibitor, and continue to rotate for 15 min. The hair removal area reaches about 90%. Change the liquid, add 100% water and 1% sodium hydroxide, adjust the temperature to 20 °C, and rotate until hair removal is completed. The total hair removal time is 640 min to obtain the dehaired naked skin.

[0031] Test the hydroxyproline concentration of the hair removal waste liquid in Example 1 and Comparative Examples 1-6 above. The higher the concentration of hydroxyproline (a characteristic amino acid of collagen) in the hair removal waste liquid, the greater the degree of damage to the skin collagen fibers. In addition, the hair removal effect is characterized by the protease hair removal time, oxidative hair removal time, total hair removal time, and hair removal rate. The results are shown in Table 1.

[0032] As can be seen from Table 1, compared with Example 1, the hydroxyproline concentration in the hair removal waste liquid of Comparative Examples 1 and 2 increased significantly, indicating an increase in the degree of damage to the sheepskin collagen fibers. Although the treatment time in the enzyme hair removal stage of Comparative Examples 3 and 4 was short, the treatment time in the oxidative hair removal stage was long. Compared with Example 1, the damage to the sheepskin collagen fibers increased, and the total hair removal time was also significantly extended, resulting in low hair removal efficiency. In Comparative Example 5, sodium hydroxide solution was not used, and it was difficult to completely remove the wool even though the total hair removal time was significantly extended. In Comparative Example 6, hydrogen peroxide solution was not used, and the wool could not be completely removed. Although the hair removal time reached 640 min, the hair removal rate was still 90%. Therefore, only the oxidative-assisted enzymatic hair removal method for sheepskin provided by the present invention can balance hair removal efficiency and sheepskin quality, with short hair removal time, complete hair removal, and little damage to the sheepskin collagen fibers, and finally obtain high-quality dehaired naked skin.

[0033] Table 1 Test results of hair removal effect 。

[0034] Example 2 Load the pretreated sheepskin (fresh lamb skin) into a rotating drum, add 250% water and 0.05% protease (including plant protease and animal protease), adjust the temperature to 35 °C, rotate for 90 min, add 0.8% protein hydrolysate, and continue to rotate for 90 min. The hair removal area reaches about 85%. Change the liquid, add 200% water, 2% hydrogen peroxide solution (mass concentration 50%), and 2% sodium hydroxide, adjust the temperature to 20 °C, and rotate until hair removal is completed. The total hair removal time is 360 min to obtain the dehaired naked skin.

[0035] After testing, the hydroxyproline concentration of the hair removal waste liquid in this example is 24.67 mg / L, and the hair removal rate is 100%.

[0036] Example 3 Load the pretreated sheepskin (from 5-year-old sheep, frozen skin) into a rotary drum, add 250% water and 1.0% protease (including microbial protease, plant protease and animal protease), adjust the temperature to 32 °C, rotate for 160 min, add 2.0% protein hydrolyzate, and continue to rotate for 80 min. The hair removal area reaches about 80%. Change the liquid, add 200% water, 5% hydrogen peroxide solution (mass concentration 55%) and 1.5% sodium hydroxide, adjust the temperature to 20 °C, and rotate until hair removal is completed. The total hair removal time is 400 min to obtain the dehaired naked skin.

[0037] After testing, the hydroxyproline concentration of the hair removal waste liquid in this example is 25.39 mg / L, and the hair removal rate is 100%.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. Oxidation-assisted enzymatic hair removal method for sheepskin, characterized in that, During the process of sheepskin hair removal, protease is first added for enzymatic hair removal. After the protease has fully penetrated the skin, a protease inhibitor is added to inhibit the protease activity on the surface of the skin. When the hair removal area reaches 80%-90%, a strong oxidant is then used for oxidative hair removal under alkaline conditions until the hair removal is complete.

2. The oxidative auxiliary enzyme hair removal method according to claim 1, characterized in that, The protease is selected from any one or more of microbial protease, animal protease, and plant protease.

3. The oxidative auxiliary enzyme hair removal method according to claim 1, characterized in that, The strong oxidant is hydrogen peroxide solution.

4. The oxidative auxiliary enzyme hair removal method according to claim 1, characterized in that, A protease inhibitor is added to inhibit the protease activity on the surface of the skin at 1 / 2 - 7 / 8 of the total protease hair removal time.

5. The oxidative auxiliary enzyme hair removal method according to claim 4, wherein The protease inhibitor is selected from any one or more of protein, polypeptide, short peptide, and amino acid.

6. The oxidative auxiliary enzymatic sheepskin dehairing method according to claim 1, wherein, The sheepskin is pretreated by washing, soaking, fleshing, degreasing, etc.

7. The oxidative-assisted enzymatic sheepskin dehairing method according to claim 1, characterized in that, Calculated by the mass percentage of the pretreated sheepskin, the dosage of the protease is 0.05%-1.0%, the dosage of the protease inhibitor is 0.05%-2.0%, and the dosage of the strong oxidant is 0.5%-5.0%.

8. The dehaired bare skin obtained by the oxidative-assisted enzymatic sheepskin hair removal method according to any one of claims 1-7.