Method for extracting keratin, method for manufacturing keratin molded products, keratin molded products, and biological models.

Abstract

This invention provides a method for extracting keratin and a method for producing keratin molded products suitable for use as biological models, as well as keratin molded products suitable for use as biological models. [Solution] A method for extracting keratin, comprising the step of extracting keratin from a raw material containing keratin in an aqueous solution containing a reducing agent, wherein the temperature of the aqueous solution is 20°C to 35°C.

Description

Technical Field

[0001] The present disclosure relates to a method for extracting keratin, a method for producing a keratin molded article, a keratin molded article, and a biological model.

Background Art

[0002] Keratin extracted from raw materials derived from living organisms is used in various fields such as agriculture, pharmaceutical production, and cosmetic production (Non-Patent Document 1). Since keratin has extremely high chemical stability due to hydrophobic interactions, ionic bonds, hydrogen bonds, disulfide bonds, etc. formed between or within molecular chains, its extraction requires complicated chemical treatments. Therefore, most of the keratin sources are treated as waste. Thus, methods for extracting keratin from these unused keratin sources have been actively studied (Non-Patent Document 2).

[0003] As methods for extracting keratin from keratin sources, there are various methods such as an alkali method, a sulfite decomposition method, a reduction method, an ionic liquid extraction method, an oxidation method, a Steam explosion method, an ultrasonic treatment method, an enzymatic decomposition method by microorganisms, etc. For example, a method for extracting keratin from a keratin source by an alkali method (Patent Document 1), a method for extracting keratin from a keratin source by an oxidative sulfite decomposition method (Patent Document 2), a method for extracting keratin from a keratin source using thioglycolic acid as a reducing agent (Patent Document 3), a method for extracting keratin from a keratin source by using a protein denaturant and a reducing agent in combination, etc. have been proposed (Patent Document 4, Patent Document 5, Non-Patent Document 3, Non-Patent Document 4).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

[0005] [Non-Patent Document 1] Chilakamarry CR et al., 3 Bioteh., Extraction and application of keratin from natural resources: a review, 11:220 (2021) [Non-Patent Document 2] Shavandi A., et al., Keratin: dissolution, extraction and biomedical application, Biomater. Sci., 5,1699-1735 (2017) [Non-Patent Document 3] Nakamura A., et al., A Rapid Extraction Procedure of Human Hair Proteins and Identification of Phosphorylated Species, Biol. Pharm. Bull., 25(5) 569-572 (2002) [Non-Patent Document 4] Fujii T., Ide Y., Preparation of Translucent and Flexible Human Hair Protein Films and Their Properties, Biol. Pharm. Bull., 27(9) 1433-1436 (2004) [Overview of the project] [Problems that the invention aims to solve]

[0006] One application of keratin is the use of keratin molded into desired shapes as bio-models to reproduce the condition of human hair, nails, and skin. For keratin molded products to be used as bio-models, (1) they must have sufficient mechanical strength from the standpoint of handling, and (2) their physical and chemical behavior must approximate that of the object being reproduced from the standpoint of reproducibility. Keratin molded products obtained using keratin extracted by the methods described in Patent Documents 1, 2, and 3 have problems from the perspective of use as a biological model, such as producing keratin with a chemical bonding state different from native keratin, and using biotoxic metal ions in the extraction process. Keratin molded products obtained using keratin extracted by the method described in Patent Document 4 have room for improvement in mechanical strength. One method for improving the mechanical strength of keratin molded products is to add additives such as plasticizers and crosslinking agents to the extracted keratin. However, when additives are added to the extracted keratin, the physical and chemical behavior of the keratin molded product changes due to the influence of the additives, which may impair the reproducibility of the physical and chemical behavior required for biological models. Therefore, there is a need for the development of a technology that can obtain keratin molded products suitable for use in biological models without using additives. In view of the above circumstances, this disclosure aims to provide a method for extracting keratin and a method for producing a keratin molded product suitable for use as a biological model, as well as a keratin molded product suitable for use as a biological model. [Means for solving the problem]

[0007] The following embodiments are included as specific means for solving the above problems. <1> The process includes a step of extracting keratin from a keratin-containing raw material in an aqueous solution containing a reducing agent, A method for extracting keratin, wherein the temperature of the aqueous solution is 20°C to 35°C. <2> The reducing agent includes an organophosphorus compound. <1> The method for extracting keratin described in [the document]. <3> <1> or <2> A method for producing a molded keratin product, comprising the steps of: extracting keratin by the keratin extraction method described herein; and molding the keratin. <4> The aforementioned keratin molded product consists of keratin and water, and the keratin content is 85% by mass or more of the total keratin molded product. <3> A method for producing keratin molded products as described above. <5> A keratin molded product containing keratin, wherein a yield point is observed in the stress-strain curve obtained by performing a tensile test as specified in JIS K7127:1999 under conditions of 25°C and 60% relative humidity. <6> The yield point is observed in the region where the strain in the stress-strain curve is 4% or more. <5> Keratin molded product as described. <7> The elongation at break measured by a tensile test conducted according to JIS K7127:1999 under conditions of 25°C and 60% relative humidity is 5% or more. <5> or <6> Keratin molded product as described. <8> The breaking strength measured by a tensile test conducted according to JIS K7127:1999 under conditions of 25°C and 60% relative humidity is 10 MPa or higher. <5> ~ <7> A keratin molded product as described in any one of the following. <9> The aforementioned keratin molded product consists of keratin and water, and the keratin content is 85% by mass or more of the total keratin molded product. <5> ~ <8> A keratin molded product as described in any one of the following. <10> It is in the form of a film. <5> ~ <9> A keratin molded product as described in any one of the following. <11> <5> ~ <10> A biological model comprising a keratin molded product as described in any one of the following. <12> Hair model, <11> The biological model described. [Effects of the Invention]

[0008] This disclosure provides a method for extracting keratin and a method for producing a keratin molded product suitable for use as a biological model, as well as a keratin molded product suitable for use as a biological model. [Brief explanation of the drawing]

[0009] [Figure 1] This is an example of a stress-strain curve obtained from a tensile test of a keratin molded product conducted under Condition 1 (25°C, relative humidity 60%). [Figure 2] This is a graph showing the elongation at break in the tensile test of a keratin molded product conducted under Condition 1 (25°C, relative humidity 60%). [Figure 3] This is a graph showing the breaking strength in the tensile test of a keratin molded product conducted under Condition 1 (25°C, relative humidity 60%). [Figure 4] This is an example of a stress-strain curve obtained from a tensile test of a keratin molded product conducted under Condition 2 (25°C, relative humidity 40%). [Figure 5] This is a graph showing the elongation at break in the tensile test of a keratin molded product conducted under Condition 2 (25°C, relative humidity 40%). [Figure 6] This is a graph showing the breaking strength in the tensile test of a keratin molded product conducted under Condition 2 (25°C, relative humidity 40%).

Mode for Carrying Out the Invention

[0010] Hereinafter, the content according to the present disclosure will be described in detail. The description of the constituent elements described below may be made based on typical embodiments according to the present disclosure, but the present disclosure is not limited to such embodiments. In the present disclosure, a numerical range indicated by using "~" means a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerically described stepwise range. Also, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment.

[0011] <Method for extracting keratin> One embodiment of this disclosure is, The process includes a step of extracting keratin from a keratin-containing raw material in an aqueous solution containing a reducing agent, This is a method for extracting keratin, wherein the temperature of the aqueous solution is 20°C to 35°C.

[0012] As shown in the examples described later, keratin molded products produced using keratin extracted by the method of this disclosure possess properties suitable for use as a biological model. The reason for this is presumed to be, for example, as follows. The method of extracting keratin using an aqueous solution containing a reducing agent (hereinafter also referred to as the reduction method) has advantages such as being able to be carried out under mild conditions, but the molecular chains of keratin are easily broken down during the extraction process. For this reason, keratin molded products containing keratin extracted by the conventional reduction method tend to have lower mechanical strength compared to keratin molded products containing keratin extracted by other methods. According to the method disclosed herein, even when keratin is extracted by a reduction method, a keratin molded product with excellent mechanical strength can be obtained. In particular, keratin molded products produced using keratin extracted by the method disclosed herein show a remarkable improvement in elongation properties. This property is suitable when the keratin molded product is used as a biological model, especially a hair model.

[0013] The types of keratin-containing raw materials used in the method of this disclosure are not particularly limited and include hair, skin, hooves, horns, scales, claws, etc. Among these, hair is preferred as the raw material for keratin. Examples of hair include human hair and animal hair, and examples of animal hair include sheep's wool and feathers. From the standpoint of raw material availability, wool is preferable as the raw material containing keratin.

[0014] The reducing agent used in the method of this disclosure cleaves the intermolecular and intramolecular disulfide bonds (SS bonds) of the keratin contained in the raw material. Keratin from which the disulfide bonds have been cleaved becomes soluble in water and ready for extraction. The type of reducing agent is not particularly limited as long as it can cleave the disulfide bonds (SS bonds) of keratin, and examples include organophosphorus compounds, thioglycolic acid, sodium thioglycolate, and mercaptoethanol. From the viewpoint of extracting keratin that yields keratin molded products with properties suitable for handling and use as a biological model, organophosphorus compounds are preferred as reducing agents, phosphine compounds are more preferred, and trialkylphosphines are even more preferred. In this disclosure, trialkylphosphine means an organophosphorus compound represented by PR3 (where R is an alkyl group which may have substituents). The alkyl group represented by R has 1 to 5 carbon atoms, more preferably 2 or 3, and even more preferably 3 carbon atoms. R is preferably a hydroxyalkyl group, and more preferably a hydroxypropyl group. A specific example of a trialkylphosphine is tris(3-hydroxypropyl)phosphine. The reducing agent used in the method disclosed herein may be a single agent or a combination of two or more agents.

[0015] The concentration of the reducing agent in the aqueous solution is not particularly limited. From the viewpoint of keratin extraction efficiency and economics, the concentration of the reducing agent can be selected from, for example, a range of 40% to 80% by mass.

[0016] From the viewpoint of improving the extraction efficiency of keratin, the aqueous solution containing the reducing agent may further contain a chaotropic agent. Chaotropic compounds are thought to cleave the hydrogen bonds present in between and within the keratin molecule, thereby increasing the solubility of keratin in water. Examples of chaotropic agents include urea compounds, formamides, and guanidine salts. Among these, urea compounds are preferred from the viewpoint of ease of handling. Specific examples of urea compounds include urea, thiourea, and their derivatives. The chaotropic agent used in the method of this disclosure may be a single agent or a combination of two or more agents. For example, the chaotropic agent used in the method of this disclosure may be a combination of urea and thiourea.

[0017] The concentration of the chaotropic agent in the aqueous solution is not particularly limited. From the viewpoint of keratin extraction efficiency and economics, the concentration of the chaotropic agent can be selected from, for example, a range of 30% to 70% by mass.

[0018] From the viewpoint of ensuring stable keratin extraction, the aqueous solution may further contain a buffering agent. As a pH adjuster, known buffering agents such as tris(hydroxymethyl)aminomethane hydrochloride (also called tris hydrochloride) can be used without particular limitation.

[0019] From the viewpoint of extracting keratin suitable for biological models, it is preferable to adjust the pH of the aqueous solution containing the reducing agent to within the range of 8 to 10.

[0020] In the method disclosed herein, the time required for the step of extracting keratin from a keratin-containing raw material in an aqueous solution containing a reducing agent (hereinafter also referred to as the extraction step) is not particularly limited and can be selected according to the type and amount of the keratin-containing raw material. For example, the time required for the extraction step can be selected from a range of 1 hour to 100 hours. As shown in the examples described later, the method of this disclosure can extract keratin of stable quality even when the extraction process time is varied. In the extraction process, the temperature of the aqueous solution may or may not be constant, as long as it is within the range of 20°C to 35°C. In the extraction process, the temperature of the aqueous solution may be 20°C to 30°C or 20°C to 25°C.

[0021] The method disclosed herein may include a step of pre-treating a keratin-containing raw material before the extraction step. Pretreatment of keratin-containing raw materials includes washing the keratin-containing raw materials and cutting or grinding the keratin-containing raw materials. It is preferable to wash the keratin-containing raw materials using a neutral detergent.

[0022] The method disclosed herein may include a step of post-treatment of the extracted keratin after the extraction step. Post-treatment of extracted keratin may include purifying the extracted keratin, drying the extracted keratin, or pulverizing it. The purification method is not particularly limited and can be carried out using known means such as filters or centrifuges.

[0023] In the method of this disclosure, the molecular weight of the extracted keratin is not particularly limited. For example, the molecular weight of the keratin extracted by the method of this disclosure is preferably 20 kDa to 100 kDa, and more preferably 40 kDa to 60 kDa. The molecular weight of keratin is determined by SDS-PAGE (SDS-polyamide gel electrophoresis). The molecular weight of keratin may be adjusted by the concentration of each component in the aqueous solution used in the extraction process, the extraction time, etc.

[0024] <Method for manufacturing keratin molded products> One embodiment of this disclosure is, The process involves extracting keratin using the keratin extraction method described above in this disclosure, A method for producing a keratin molded product, comprising the step of molding the keratin.

[0025] In the method of molding keratin according to the present disclosure, the method is not particularly limited. For example, a keratin molded product of the desired shape can be obtained by pouring a liquid containing extracted keratin (extract) into a mold or frame having a desired shape and removing the liquid component. If the keratin molded product is in the form of a film, its thickness is not particularly limited. To ensure sufficient mechanical strength and economic efficiency, the thickness of the film-like keratin molded product is preferably 0.01 mm to 0.10 mm, and more preferably 0.03 mm to 0.06 mm.

[0026] The keratin used in molding keratin molded products may be in a dried state after post-extraction processing. In this case, liquid components such as water may be added to the dried keratin before manufacturing the keratin molded products.

[0027] The keratin used in the method of this disclosure may be mixed with or not mixed with an additive. Additives that can be mixed with keratin include plasticizers, crosslinking agents, inorganic substances, excipients, and stabilizers. From the viewpoint of suppressing the influence on the physical and chemical behavior of keratin molded products, it is preferable that keratin is not mixed with additives, or that the amount of additives mixed with keratin is less than 10% by mass, less than 5% by mass, or less than 1% by mass of the total keratin molded product. From the viewpoint of suppressing the influence on the physical and chemical behavior of keratin molded products, it is preferable that keratin molded products do not contain additives.

[0028] From the standpoint of properties suitable for use as a biological model, it is preferable that keratin molded products contain moisture. The moisture content of keratin molded products is not particularly limited and can be selected according to the application of the keratin molded product. For example, a keratin molded product may consist of keratin and water. In this case, the keratin content may be 85% by mass or more of the total keratin molded product (the water content may be less than 15% by mass). Alternatively, the keratin content may be 95% by mass or less of the total keratin molded product (the water content may be greater than 5% by mass).

[0029] <Keratin molded product> One embodiment of this disclosure is, This is a keratin molded product containing keratin, in which a yield point is observed in the stress-strain curve obtained by performing a tensile test as specified in JIS K7127:1999 under conditions of 25°C and 60% relative humidity. In the keratin molded articles of this disclosure, the tensile test specified in JIS K7127:1999 is performed under the conditions described in the examples.

[0030] From the viewpoint of properties suitable for use as a biological model, the above yield point is preferably observed in the region where the strain is 4% or more, preferably in the region where the strain is 4.5% or more, and more preferably in the region where the strain is 5% or more. The strain mentioned above is the percentage (%) of the value obtained by dividing the elongation ΔL of the specimen by the original length L of the specimen (ΔL / L) in a stress-strain curve obtained with stress on the vertical axis and strain on the horizontal axis.

[0031] From the viewpoint of properties suitable for use as a biological model, the above yield point is preferably observed in the region where the strain is 8% or less, more preferably in the region where the strain is 7% or less, and more preferably in the region where the strain is 6% or less.

[0032] From the standpoint of properties suitable for use as a biological model, it is preferable that the keratin molded product of this disclosure has a fracture elongation of 5% or more, as measured by performing a tensile test as specified in JIS K7127:1999 under conditions of 25°C and 60% relative humidity. The above fracture elongation is the percentage (%) of the value obtained by dividing the elongation ΔL at the time of fracture of the test specimen in a tensile test by the original length L of the test specimen (ΔL / L).

[0033] From the viewpoint of properties suitable for use as a biological model, the above-mentioned elongation at break is preferably 5.5% or more, more preferably 6% or more, and even more preferably 6.5% or more.

[0034] From the viewpoint of properties suitable for use as a biological model and mechanical strength, the above-mentioned elongation at break is preferably 10% or less, more preferably 9% or less, and even more preferably 8% or less.

[0035] From the viewpoint of properties suitable for use as a biological model, the keratin molded product of this disclosure preferably has a breaking strength of 10 MPa or more, more preferably 12 MPa or more, and even more preferably 13 MPa or more, as measured by a tensile test performed in accordance with JIS K7127:1999 under conditions of 25°C and 60% relative humidity.

[0036] From the viewpoint of properties suitable for use as a biological model, the above-mentioned breaking strength is preferably 20 MPa or less, more preferably 18 MPa or less, and even more preferably 16 MPa or less.

[0037] The keratin molded articles of this disclosure can be manufactured, for example, using keratin obtained by the keratin extraction method of this disclosure described above.

[0038] The shape of the keratin molded product of this disclosure is not particularly limited and can be selected according to the intended use of the keratin molded product. For example, the keratin molded product may be in the form of a film (keratin film). If the keratin molded product is in film form, its thickness is not particularly limited and can be selected from a range such as 0.5 mm to 2 mm.

[0039] The keratin molded product of this disclosure may or may not contain additives. Additives contained in keratin molded products include plasticizers, crosslinking agents, inorganic substances, excipients, and stabilizers. From the viewpoint of suppressing the influence on the physical and chemical behavior of keratin molded products, it is preferable that keratin is not mixed with additives, or that the amount of additives mixed with keratin is less than 10% by mass, less than 5% by mass, or less than 1% by mass of the total keratin molded product. From the viewpoint of suppressing the influence on the physical and chemical behavior of keratin molded products, it is preferable that keratin molded products do not contain additives.

[0040] From the standpoint of properties suitable for use as a biological model, it is preferable that keratin molded products contain moisture. The moisture content of keratin molded products is not particularly limited and can be selected according to the application of the keratin molded product. For example, a keratin molded product may consist of keratin and water. In this case, the keratin content may be 85% by mass or more of the total keratin molded product (the water content may be less than 15% by mass). Alternatively, the keratin content may be 95% by mass or less of the total keratin molded product (the water content may be greater than 5% by mass).

[0041] The uses of the keratin molded products of this disclosure are not particularly limited. For example, the keratin molded products of this disclosure may be used as biological models, particularly hair models.

[0042] <Biological Model> One embodiment of this disclosure is, This is a biological model that includes the keratin molded product described above. There are no particular restrictions on the type of biological model used; hair models, nail models, and skin models are examples of biological models. Among these, hair models are preferred. Hair models can be used, for example, to test or evaluate chemicals used on hair, such as shampoos, conditioners, hair styling products, hair dyes, and hair growth products. The shape of a biological model may differ from the shape of the object that the biological model is intended to reproduce. For example, the shape of a hair model may differ from that of actual hair (e.g., it may be film-like). [Examples]

[0043] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited thereto unless it exceeds the spirit of the disclosure.

[0044] <Example 1> 300 g of urea, 198 g of thiourea, 140 g of an aqueous solution of tris(3-hydroxypropyl)phosphine (concentration: 36.5-38.4% by mass, trade name: Hishikorin P540, Nippon Chemical Industries, Ltd.), and 3.09 g of tris(hydroxymethyl)aminomethane hydrochloride were mixed with 300 mL of deionized water to dissolve these components. Deionized water was further added to this aqueous solution to make up the total volume to 1 L. Furthermore, the pH of the aqueous solution was adjusted to 8.5 using a 1N hydrochloric acid aqueous solution to obtain an aqueous solution containing a reducing agent.

[0045] 11.0 g of 100% wool (product name: Canadian 3S, Hamanaka Co., Ltd.) was added to 200 mL of an aqueous solution containing a reducing agent as a raw material for keratin. Subsequently, a keratin extraction treatment was carried out by stirring the aqueous solution at a temperature of 23°C for 72 hours. After the extraction treatment, the residue was removed from the aqueous solution by centrifugation (17000 rpm, 30 minutes, 20°C). Furthermore, the aqueous solution was dialyzed using a dialysis tube (Visking tube, MWCO 3500 Da) and deionized water, and the precipitated insoluble matter was removed by centrifugation (17000 rpm, 30 minutes, 20°C) to obtain a reduced keratin aqueous solution containing keratin extracted from the keratin raw material.

[0046] A reduced keratin aqueous solution, with a keratin content of 5 mg / cm³ after drying. 2 The area will be 56 cm². 2 The mixture was poured into a silicone mold and allowed to dry in an environment of 25°C and 50% relative humidity to obtain a film-like keratin molded product (hereinafter also referred to as keratin film).

[0047] <Example 2> A keratin film was prepared in the same manner as in Example 1, except that the extraction conditions were set to 23°C for 24 hours.

[0048] <Example 3> A keratin film was prepared in the same manner as in Example 1, except that the extraction conditions were set to 23°C for 5 hours.

[0049] <Comparative Example 1> A keratin film was prepared in the same manner as in Example 1, except that the extraction conditions were set to 50°C for 72 hours.

[0050] <Comparative Example 2> A keratin film was prepared in the same manner as in Example 1, except that the extraction conditions were changed to 50°C for 24 hours.

[0051] <Comparative Example 3> A keratin film was prepared in the same manner as in Example 1, except that the extraction conditions were set to 50°C for 5 hours.

[0052] <Mechanical testing of keratin film> Mechanical testing of keratin film was performed in accordance with JIS K7127:1999 (ISO 527-3:1995). Specifically, dumbbell-shaped test specimens (Dumbbell No. 5) were prepared from keratin film using a film cutting device (Zwick), and tensile tests were performed. A texture analyzer (TA.XTplus, Stable Micro System) was used for the tensile tests, and the test speed was set to 20 mm / min. From the stress-strain curve obtained from the tensile tests, the elongation at fracture (%) and the load at fracture (N) were calculated using the cross-sectional area (mm²) of the test specimen. 2 The breaking strength (MPa) obtained by dividing by ) was measured. Mechanical tests were conducted in a constant temperature and humidity chamber (TBE-6H20W2P2CL, manufactured by Espec) under two conditions: Condition 1 (25°C, 60% relative humidity) and Condition 2 (25°C, 40% relative humidity).

[0053] An example of a stress-strain curve obtained from a tensile test conducted under Condition 1 is shown in Figure 1. The results of the tensile test conducted under Condition 1 (sample size N=3) are shown in Table 1, Figure 2, and Figure 3.

[0054] [Table 1]

[0055] An example of a stress-strain curve obtained from a tensile test conducted under Condition 2 is shown in Figure 4. The results of the tensile test conducted under Condition 2 (sample size N=3) are shown in Table 2, Figure 5, and Figure 6.

[0056] [Table 2]

[0057] As shown in Tables 1 and 2, the keratin films of Examples 1 to 3, in which the keratin extraction treatment was carried out at 23°C, tended to have higher values ​​for elongation at break and tensile strength (especially elongation at break) compared to the keratin films of Comparative Examples 1 to 3, in which the keratin extraction treatment was carried out at 50°C. This result suggests that keratin molded products obtained using keratin extracted by the method of this disclosure have properties suitable for use as a biological model, particularly a hair model.

[0058] Furthermore, while the keratin films of Examples 1-3 showed similar values ​​for elongation at break and tensile strength regardless of the extraction time, the keratin films of Comparative Examples 1-3 tended to decrease in elongation at break and tensile strength as the extraction time increased. This result suggests that the keratin extracted by the method of this disclosure maintains a good state because the degradation of keratin molecular chains during the extraction process is suppressed. To verify this hypothesis, polyacrylamide electrophoresis was performed to compare the molecular weight of keratin contained in the reduced keratin aqueous solutions obtained in Examples 1-3 and Comparative Examples 1-3. As a result, the molecular weight of keratin contained in the reduced keratin aqueous solutions obtained in Examples 1-3 tended to be larger than that of keratin contained in the reduced keratin aqueous solutions obtained in Comparative Examples 1-3.

[0059] As shown in Figure 1, the keratin films of Examples 1-3 showed yield points in the stress-strain curves obtained from tests conducted under condition 1 (25°C, 60% relative humidity). In other words, the keratin films of Examples 1-3 exhibited flexibility under the temperature and humidity conditions used in in vivo testing. This result suggests that the keratin molded products of this disclosure have properties suitable for use as biological models, particularly hair models.

Claims

1. The process includes a step of extracting keratin from a keratin-containing raw material in an aqueous solution containing a reducing agent, A method for extracting keratin, wherein the temperature of the aqueous solution is 20°C to 35°C.

2. The method for extracting keratin according to claim 1, wherein the reducing agent comprises an organophosphorus compound.

3. A step of extracting keratin by the keratin extraction method described in claim 1 or claim 2, A method for producing a keratin molded product, comprising the step of molding the keratin.

4. The method for producing a keratin molded article according to claim 3, wherein the keratin molded article consists of keratin and water, and the keratin content is 85% by mass or more.

5. A keratin molded product containing keratin, wherein a yield point is observed in the stress-strain curve obtained by performing a tensile test according to JIS K7127:1999 under conditions of 25°C and 60% relative humidity.

6. The keratin molded product according to claim 5, wherein the yield point is observed in the region where the strain in the stress-strain curve is 4% or more.

7. The keratin molded article according to claim 5 or claim 6, wherein the elongation at break measured by performing a tensile test as specified in JIS K7127:1999 under conditions of 25°C and 60% relative humidity is 5% or more.

8. The keratin molded article according to claim 5 or claim 6, wherein the breaking strength measured by performing a tensile test as specified in JIS K7127:1999 under conditions of 25°C and 60% relative humidity is 10 MPa or more.

9. The keratin molded product according to claim 5 or claim 6, wherein the keratin molded product consists of keratin and water, and the keratin content is 85% by mass or more.

10. A keratin molded product according to claim 5 or claim 6, which is in the form of a film.

11. A biological model comprising a keratin molded product according to claim 5 or claim 6.

12. A living model according to claim 10, which is a hair model.

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