Sericin-containing powder and method for producing same

Abstract

To provide sericin-containing powder containing sericin of a high molecular weight, and excellent in solubility of the contained-sericin, and its manufacturing method.SOLUTION: Sericin-containing powder that contains sericin for which at least one band is detected in a range corresponding to a molecular weight of 150 kDa or more by a SDS-PAGE method, and the solubility of the contained sericin in water at a temperature of 80°C is 0.45 g / 100 g or more of aqueous solution.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a sericin-containing powder and a method for producing the same. More specifically, the present invention relates to a sericin-containing powder that contains high-molecular-weight sericin and has excellent solubility of the sericin contained therein, and a method for producing the same. [Background technology]

[0002] The cocoon threads spun by silkworms and other insects are primarily composed of two proteins: sericin and fibroin. Of these, fibroin is the protein that makes up the cocoon fibers, and sericin is the protein that coats the outer layer of the fibers formed by fibroin and is involved in adhesion.

[0003] The sericin contained in cocoons is solubilized when the cocoons are boiled in alkaline hot water to extract fibroin during the silk thread degumming process. Therefore, sericin is usually obtained from the wastewater of this degumming process, but its molecular weight has been reduced by hydrolysis.

[0004] On the other hand, it is known that sericin containing higher molecular weight than low molecular weight sericin exhibits superior tyrosinase inhibitory activity (Reference 1), collagenase inhibitory activity (Reference 2), and elastase inhibitory activity (Reference 3).

[0005] Another known method for obtaining high molecular weight sericin is to extract it with an aqueous urea solution at a temperature above 100°C and then separate the sericin from the extract using molecular sieve chromatography (Reference 4). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-40905 [Patent Document 2] Japanese Patent Application Publication No. 2020-132539 [Patent Document 3] Japanese Patent Publication No. 2020-132540 [Patent Document 4] Japanese Patent Application Publication No. 11-92564 Summary of the Invention [Problem to be solved by the invention]

[0007] However, high-molecular-weight sericin generally has poor solubility, making it difficult to incorporate into cosmetic formulations, especially when it is in powder form. Furthermore, even when high-molecular-weight sericin is obtained in aqueous solution, it gels over time, making it difficult to obtain in a stable state or to incorporate into cosmetic formulations. The present invention has been made in light of the above-mentioned circumstances, and its object is to provide a sericin-containing powder that contains high-molecular-weight sericin and has good solubility of the sericin contained therein, and a method for producing the same. [Means for solving the problem]

[0008] The gist of the present invention is as follows. [1] A powder containing sericin in which at least one band is detected in the range corresponding to a molecular weight of 150 kDa or more by SDS-PAGE, and the solubility of the sericin in water at 80°C is 0.45 g / 100 g of aqueous solution or more. [2] The sericin-containing powder according to [1], which contains at least one selected from an anionic surfactant and urea. [3] The sericin-containing powder according to [1] or [2], wherein the anionic surfactant is at least one selected from alkyl sulfates, alkenyl sulfates, alkyl ether sulfates, alkenyl ether sulfates, polyoxyalkylene alkyl ether sulfates, polyoxyalkylene alkenyl ether sulfates, alkyl sulfonates, alkyl ether sulfonates, and N-acylamino acid salts. [4] The sericin-containing powder according to [3], wherein at least one selected from the group consisting of alkyl sulfates, alkenyl sulfates, alkyl ether sulfates, alkenyl ether sulfates, polyoxyalkylene alkyl ether sulfates, and polyoxyalkylene alkenyl ether sulfates is a compound represented by formula (1), and the N-acylamino acid salt is a compound represented by formula (2). [ka] (In the formula, R 1 represents an alkylene group having 1 to 3 carbon atoms, and R 2 represents an alkyl or alkenyl group having 8 to 20 carbon atoms; n represents an integer of 0 or more; X + indicates a monovalent cation. R 3 represents an alkyl group having 8 to 20 carbon atoms, and R 4 represents an alkyl group having 1 to 3 carbon atoms; m represents an integer of 0 to 3; Y + indicates a monovalent cation.) [5] A method for producing a powder containing sericin, which comprises mixing a sericin extract obtained by contacting cocoons with water with at least one selected from an anionic surfactant and urea, and drying the resulting mixture. [6] A method for producing a sericin extract by contacting cocoons with water in the presence of an anionic surfactant. [7] A method for producing a sericin-containing powder by drying a sericin extract obtained by contacting cocoons with water in the presence of urea, or the sericin extract described in [6]. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a sericin-containing powder that contains high-molecular-weight sericin but exhibits good solubility (particularly in water), and a method for producing the same. Because the sericin contained in the sericin-containing powder of the present invention exhibits good solubility, it is highly suitable for incorporation into cosmetic formulations and is easy to handle. Furthermore, while storing sericin in solution can lead to hydrolysis of the sericin during storage, or, particularly in the case of sericin with a high molecular weight, undesirable gelation, the sericin of the present invention is in powder form, resulting in high storage stability. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a photograph showing the results of SDS-PAGE for the sericins obtained in Examples 1 to 9 and Comparative Example 1. [Figure 2] FIG. 2 is a photograph showing the results of SDS-PAGE for the sericins obtained in Examples 10 to 17 and Comparative Example 1. [Figure 3] FIG. 3 is a photograph showing the results of SDS-PAGE for the sericin obtained in Example 20. [Figure 4] FIG. 4 is a photograph showing the results of SDS-PAGE for the sericins obtained in Examples 22 to 27. [Figure 5] FIG. 5 is a photograph showing the results of SDS-PAGE for the sericin obtained in Example 28. [Figure 6] FIG. 6 is a photograph showing the results of SDS-PAGE for the sericins obtained in Examples 29 and 30. [Figure 7] FIG. 7 is a photograph showing the results of SDS-PAGE for the sericin obtained in Example 31. [Figure 8] FIG. 8 is a photograph showing the results of SDS-PAGE for the sericins obtained in Examples 32 to 35. [Figure 9] FIG. 9 is a photograph showing the results of SDS-PAGE for the sericins obtained in Examples 36 to 39 and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] (sericin-containing powder) The sericin contained in the sericin-containing powder of the present invention is one that produces clear bands in SDS-polyacrylamide gel electrophoresis (PAGE), rather than bands that are not visible or smeared. Specifically, at least one band is detected in the range corresponding to a molecular weight of 150 kDa or higher. The band may be detected in the range corresponding to a molecular weight of 150 kDa or higher, preferably in the range corresponding to a molecular weight of 160 kDa or higher, and more preferably in the range corresponding to a molecular weight of 180 kDa or higher. The number of bands detected in this range may be one or more, and there is no upper limit. However, the number of bands detected in this range is preferably one to five, and more preferably two to five. A sericin-containing powder containing sericin that produces a clear band near 250 kDa by SDS-PAGE is particularly preferred. A sericin-containing powder containing sericin that produces a clear band near 315 kDa by SDS-PAGE is also preferred. If the powder contains sericin in which these bands are detected, the sericin contained therein has not been reduced in molecular weight and exhibits the properties specific to high-molecular-weight sericin. The molecular weights corresponding to the bands detected in SDS-PAGE were determined by the marker proteins (e.g., Precision Plus Protein TM The molecular weight of the sericin contained in the sericin-containing powder of the present invention can be determined by comparing it with the bands of molecular weight fractions of a two-color standard (e.g., BIO-RAD, Product No. 1610374). The composition ratio of the bands can be calculated from the density of the bands. However, the composition of the sericin contained in the sericin-containing powder of the present invention is not particularly limited as long as it has a high molecular weight such that at least one band is detected in the range corresponding to a molecular weight of 150 kDa or more.

[0012] The sericin contained in the sericin-containing powder of the present invention has excellent solubility. Specifically, "excellent solubility" preferably means high solubility in water, and more preferably, for example, the solubility of the sericin contained in the sericin-containing powder in water at 80°C is 0.45 g / 100 g of aqueous solution or more. The solubility of the sericin contained in the sericin-containing powder can be determined by the following method. Sericin-containing powder was added to pure water to achieve a sericin concentration of 1% by mass, and dissolved at 80°C for 30 minutes. After dissolution, the solution was centrifuged at an acceleration of 9,500 × g for 5 minutes, and the supernatant was collected. The sericin concentration in the resulting aqueous solution was calculated using the Bradford method or absorbance at 280 nm. The mass of dissolved sericin was determined from the calculated sericin concentration. The sericin concentration was calculated from absorbance by creating a calibration curve. The dissolution rate was then calculated using the following formula from the mass of dissolved sericin and the mass of sericin initially added, and the solubility was then calculated using this dissolution rate. Dissolution rate of sericin (wt%) = (mass of dissolved sericin / mass of added sericin) x 100 Solubility of sericin (g / 100g of aqueous solution) = 100 (g) × 1 (wt%) × solubility of sericin (wt%)

[0013] The solubility of sericin contained in the sericin-containing powder in water at 80°C may be 0.45 g / 100 g of aqueous solution or more, preferably 0.50 g / 100 g of aqueous solution or more, more preferably 0.60 g / 100 g of aqueous solution or more, and even more preferably 0.70 g / 100 g of aqueous solution or more. The solubility of sericin contained in the sericin-containing powder may be the upper limit of the measurement method (1.00 g / 100 g of aqueous solution). The sericin contained in the sericin-containing powder has such a solubility, which makes it easy to incorporate it into cosmetic formulations and the like.

[0014] The sericin-containing powder preferably has excellent solubility, particularly high solubility in water. For example, the sericin-containing powder preferably has a solubility in water at 80°C of 0.50 g / 100 g of aqueous solution or more. The solubility of the sericin-containing powder can be determined by the following method. Sericin-containing powder was added to pure water to a concentration of 1% by mass and dissolved at 80°C for 30 minutes. After dissolution, the mixture was centrifuged at an acceleration of 9,500 x g for 5 minutes, the supernatant was collected, and the resulting aqueous solution was heated and dried to obtain a solids concentration, which was used as the concentration of the sericin-containing powder. The mass of the dissolved sericin-containing powder was then calculated from the concentration of the sericin-containing powder. The dissolution rate was then calculated using the following formula from the mass of the dissolved sericin-containing powder and the mass of the sericin-containing powder initially added, and the solubility was calculated using this dissolution rate. Dissolution rate of sericin-containing powder (wt%) = (mass of dissolved sericin-containing powder / mass of added sericin-containing powder) x 100 Solubility of sericin-containing powder (g / 100g of aqueous solution) = 100(g) x 1(wt%) x solubility of sericin-containing powder (wt%)

[0015] The solubility of the sericin-containing powder in water at 80°C is preferably 0.55 g / 100 g of aqueous solution or more, more preferably 0.60 g / 100 g of aqueous solution or more, and even more preferably 0.70 g / 100 g of aqueous solution or more. The solubility of the sericin-containing powder may be the upper limit of the measurement method (1.00 g / 100 g of aqueous solution).

[0016] The sericin-containing powder of the present invention is preferably a powder containing at least one selected from an anionic surfactant and urea.

[0017] The anionic surfactant is not particularly limited, and examples thereof include sulfate-based anionic surfactants such as alkyl sulfates, alkenyl sulfates, alkyl ether sulfates, alkenyl ether sulfates, alkylaryl ether sulfates, polyoxyalkylene alkyl ether sulfates, and polyoxyalkylene alkenyl ether sulfates; sulfonic acid-based anionic surfactants such as alkyl sulfonates, α-olefin sulfonates, alkyl ether sulfonates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl diphenyl ether disulfonates, alkyl glycidyl ether sulfonates, α-sulfofatty acid ester salts, acyl isethionates, alkyl sulfosuccinates, alkyl sulfoacetates, and N-acylmethyl taurines; carboxylic acid-based anionic surfactants such as polycarboxylates, aliphatic carboxylates, alkyl ether carboxylates, alkenyl succinates, N-acylamino acid salts, amide ether carboxylates, and acyl lactates; and phosphoric acid-based anionic surfactants such as alkyl phosphates, polyoxyalkylene alkyl ether phosphates, and alkylaryl ether phosphates. As the anionic surfactant, sulfate-based anionic surfactants, sulfonic acid-based anionic surfactants, and carboxylic acid-based anionic surfactants are preferred, with alkyl sulfates, alkenyl sulfates, alkyl ether sulfates, alkenyl ether sulfates, polyoxyalkylene alkyl ether sulfates, polyoxyalkylene alkenyl ether sulfates, alkyl sulfonates, alkyl ether sulfonates, and N-acylamino acid salts being more preferred, and alkyl sulfates, alkenyl sulfates, alkyl ether sulfates, alkenyl ether sulfates, polyoxyalkylene alkyl ether sulfates, polyoxyalkylene alkenyl ether sulfates, and N-acylamino acid salts being even more preferred. The "salt" mentioned above includes alkali metal salts such as lithium salt, sodium salt, potassium salt, etc.; alkaline earth metal salts such as magnesium salt, calcium salt, etc.; amine salts; ammonium salts, etc., with alkali metal salts and ammonium salts being preferred.

[0018] When the sericin-containing powder contains an anionic surfactant, the anionic surfactant may be one type only or two or more types, and there is no particular upper limit, but five types or less are preferred, and three types or less are more preferred.

[0019] The at least one selected from the alkyl sulfates, alkenyl sulfates, alkyl ether sulfates, alkenyl ether sulfates, polyoxyalkylene alkyl ether sulfates, and polyoxyalkylene alkenyl ether sulfates is preferably a compound represented by the following formula (1):

[0020] [ka] (In the formula, R 1 represents an alkylene group having 1 to 3 carbon atoms, and R 2 represents an alkyl or alkenyl group having 8 to 20 carbon atoms; n represents an integer of 0 or more; X + indicates a monovalent cation.)

[0021] R 1 Examples of the alkylene group having 1 to 3 carbon atoms represented by the formula (I) include a methylene group, an ethanediyl group, and a propanediyl group, and the methylene group, an ethane-1,2-diyl group, and a propane-1,3-diyl group are preferred, and the ethane-1,2-diyl group is more preferred. When n is an integer of 2 or more, a plurality of R 1 may be the same or different, and are preferably the same.

[0022] R 2The alkyl group having 8 to 20 carbon atoms represented by the formula (I) may be either linear or branched, and examples thereof include an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a (2-methyl)heptyl group, a (2-ethyl)heptyl group, a (3-ethyl)heptyl group, a (1-hexyl)heptyl group, a (2-methyl)octyl group, a (2-ethyl)octyl group, a (1-heptyl)octyl group, a (2-ethyl)nonyl group, and a (1-octyl)nonyl group. 2 The alkyl group having 8 to 20 carbon atoms represented by R is preferably a linear alkyl group. 2 The alkyl group represented by the formula (I) preferably has 8 to 15 carbon atoms, and more preferably 10 to 13 carbon atoms.

[0023] R 2 The alkenyl group having 8 to 20 carbon atoms represented by the formula (I) may be either linear or branched, and examples thereof include an octenyl group, a nonenyl group, a decenyl group, an undecenyl group, a dodecenyl group, a tridecenyl group, a tetradecenyl group, a pentadecenyl group, a hexadecenyl group, a heptadecenyl group, an octadecenyl group, a nonadecenyl group, an icosenyl group, a 1,1-dimethyl-2-octenyl group, a 1-ethyl-2-octenyl group, and a 1,2-dimethyl-1-octenyl group. 2 The alkenyl group having 8 to 20 carbon atoms represented by the formula (I) is preferably a linear alkenyl group. 2 The alkenyl group represented by the formula (I) preferably has 8 to 16 carbon atoms, and more preferably 10 to 14 carbon atoms.

[0024] The integer of 0 or more represented by n is preferably an integer of 0 to 50, more preferably an integer of 0 to 25, even more preferably an integer of 0 to 15, even more preferably an integer of 0 to 10, and even more preferably 0.

[0025] X +Examples of the monovalent cation represented by the formula (I) include alkali metal ions such as lithium ion, sodium ion, potassium ion, and cesium ion; alkaline earth metal ions such as magnesium ion and calcium ion; and ammonium ion (NH 4+ ), primary ammonium ions, secondary ammonium ions, tertiary ammonium ions, quaternary ammonium ions, and other onium ions. X + The monovalent cation represented by the formula (I) is preferably an alkali metal ion or an onium ion, and more preferably an alkali metal ion or an ammonium ion (NH 4+ ), triethanolammonium ion is more preferred, sodium ion, ammonium ion (NH 4+ ) is more preferred.

[0026] Examples of the compound represented by formula (1) include sodium lauryl sulfate, sodium myristyl sulfate, sodium laureth sulfate, and ammonium lauryl sulfate.

[0027] The N-acylamino acid salt is preferably a compound represented by the following formula (2).

[0028] [ka] (In the formula, R 3 represents an alkyl group having 8 to 20 carbon atoms, and R 4 represents an alkyl group having 1 to 3 carbon atoms; m represents an integer of 0 to 3; Y + indicates a monovalent cation.)

[0029] R 3The alkyl group having 8 to 20 carbon atoms represented by the formula (I) may be either linear or branched, and examples thereof include an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a (2-methyl)heptyl group, a (2-ethyl)heptyl group, a (3-ethyl)heptyl group, a (1-hexyl)heptyl group, a (2-methyl)octyl group, a (2-ethyl)octyl group, a (1-heptyl)octyl group, a (2-ethyl)nonyl group, and a (1-octyl)nonyl group. 3 The alkyl group having 8 to 20 carbon atoms represented by R is preferably a linear alkyl group. 3 The alkyl group represented by the formula (I) preferably has 8 to 16 carbon atoms, and more preferably 10 to 14 carbon atoms.

[0030] R 4 The alkyl group having 1 to 3 carbon atoms represented by the formula (R) may be either linear or branched, and examples thereof include a methyl group, an ethyl group, a propyl group, and an isopropyl group. 4 The alkyl group having 1 to 3 carbon atoms represented by R is preferably a linear alkyl group. 4 The alkyl group represented by the formula (I) preferably has 1 to 2 carbon atoms, and more preferably 1 carbon atom.

[0031] As the integer of 0 to 3 represented by m, an integer of 0 to 2 is preferred, and 1 is more preferred.

[0032] Y + Examples of the monovalent cation represented by the formula (I) include alkali metal ions such as lithium ion, sodium ion, potassium ion, and cesium ion; alkaline earth metal ions such as magnesium ion and calcium ion; and ammonium ion (NH 4+ ), primary ammonium ions, secondary ammonium ions, tertiary ammonium ions, quaternary ammonium ions, and other onium ions. +The monovalent cation represented by the formula (I) is preferably an alkali metal ion or an onium ion, and more preferably an alkali metal ion or an ammonium ion (NH 4+ ), triethanolammonium ion is more preferred, ions of alkali metals are even more preferred, and sodium ion is even more preferred.

[0033] Examples of the compound represented by formula (2) include caproylmethyl β-alanine sodium, lauroylmethyl β-alanine sodium, and myristoylmethyl β-alanine sodium.

[0034] From the viewpoint of improving the solubility of the sericin-containing powder, the content of the anionic surfactant and / or urea in the sericin-containing powder is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and is preferably 90% by mass or less, more preferably 70% by mass or less, even more preferably 50% by mass or less, based on the total amount of the sericin-containing powder. When the sericin-containing powder contains two or more kinds selected from anionic surfactants and urea, it is preferable that the total content of these is within the above-mentioned range.

[0035] The content of anionic surfactant and / or urea in the sericin-containing powder can be determined by recovering the supernatant of the extract, calculating the sericin concentration in the resulting aqueous solution using the Bradford method or absorbance at 280 nm, and then subtracting this sericin concentration from the solids concentration obtained by heat-drying the resulting aqueous solution. Alternatively, the target compound (anionic surfactant or urea) can be separated from the sericin-containing powder using well-known analytical methods such as gas chromatography or liquid chromatography, and a calibration curve can be prepared using a standard substance. Alternatively, urea can be derivatized by a known method and then analyzed by chromatography.

[0036] The sericin content in the sericin-containing powder of the present invention is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, even more preferably 50% by mass or more, and even more preferably 60% by mass or more, from the viewpoint of the solubility of the sericin-containing powder, and is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less, from the viewpoint of the solubility of the sericin-containing powder. The sericin-containing powder of the present invention may contain other components in addition to sericin, anionic surfactants, and urea, as long as the high molecular weight sericin and the good solubility of the sericin contained therein are not impaired. However, the content of such other components is preferably 30% by mass or less, more preferably 10% by mass or less, of the total amount of the sericin-containing powder, and it is particularly preferable that the sericin-containing powder does not contain such other components.

[0037] (Method of manufacturing sericin-containing powder) Conventionally, sericin has been obtained by hydrolyzing and eluting cocoons, cocoon filaments, and raw silk from the cocoons using hydrolysis methods such as acid hydrolysis, alkaline hydrolysis, and enzymatic degradation. However, the sericin-containing powder of the present invention can be obtained, for example, by extracting sericin from cocoons, cocoon filaments, raw silk, etc. without using the above-mentioned hydrolysis methods and drying the extract. Therefore, the sericin-containing powder of the present invention contains unhydrolyzed sericin. Furthermore, the sericin-containing powder of the present invention may contain sericin hydrolyzed during the extraction process, as long as it contains high-molecular-weight sericin (sericin that exhibits a band in the range corresponding to a molecular weight of 150 kDa or more by SDS-PAGE). The sericin-containing powder of the present invention may also contain fibroin.

[0038] The cocoons, cocoon filaments, and raw silk may be produced by any silkworm, including wild silkworms of the Bombycidae family, such as the mulberry silkworm and the mulberry silkworm; wild silkworms of the Saturniidae family, such as the tsar silkworm, the tussah silkworm, and the tasar silkworm; or by insects such as honeybees, hornets, spiders, and caddisflies. The origin of the silkworms is also not particularly limited. Silkworms may be natural or may be those that have undergone mutation, breeding, or genetic engineering. For example, silkworms with poor fibroin production ability may be used because they tend to be able to efficiently extract high-molecular-weight sericin. Specifically, silkworms with reduced fibroin production ability due to mutation or breeding (e.g., Sericin Hope (sericin C), sericin N, Nd silkworm, Nd-s silkworm, MNS300, MCS300, etc.) may be used.

[0039] Silkworm cocoons are structures created by silkworm larvae secreting silk proteins from their silk glands during pupation, and are obtained by separating the pupae from the cocoons. Raw silk is obtained by combining several cocoon threads (silk fibers) extracted from the cocoons to form a thread.

[0040] In producing the sericin-containing powder, the cocoons may be used as they are, or may be processed by cutting, crushing, drying, or the like.

[0041] Examples of methods for producing the sericin-containing powder of the present invention include the following production method A and production method B.

[0042] ((Manufacturing method A)) Production method A is a method in which a sericin extract obtained by contacting cocoons (which may be the above-mentioned cocoon filaments or raw silk) with water is mixed with at least one selected from an anionic surfactant and urea, and the resulting mixture is dried.

[0043] In Production Method A, an organic solvent other than water may be used as an extraction solvent when extracting sericin. Examples of the organic solvent include lower alcohols having four or fewer carbon atoms, such as methanol, ethanol, and isopropanol; glycols, such as propylene glycol and diethylene glycol; and aprotic solvents, such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and N-methylmorpholine-N-oxide. A single extraction solvent may be used, or two or more may be mixed. Water alone is preferred as the extraction solvent.

[0044] In order to extract high-molecular-weight sericin, it is preferable to add an inorganic salt to the extraction solvent. The inorganic salt is not particularly limited, and examples thereof include salts of alkali metals and alkaline earth metals (alkali metal halides are particularly preferred), such as lithium bromide, potassium bromide, calcium bromide, lithium chloride, potassium chloride, calcium chloride, lithium thiocyanate, and potassium thiocyanate. One type may be used alone, or two or more types may be mixed together.

[0045] Examples of the extracting solvent containing an inorganic salt include an aqueous solution of lithium bromide, an aqueous solution of potassium bromide, an aqueous solution of lithium chloride, an aqueous solution of potassium chloride, an aqueous solution of lithium thiocyanate, an aqueous solution of potassium thiocyanate, an aqueous solution of calcium chloride, a calcium chloride / ethanol solution, a strong electrolyzed water, a calcium nitrate / methanol solution, etc., and one kind may be used alone or two or more kinds may be mixed and used. As the extracting solvent containing an inorganic salt, an aqueous solution of lithium bromide is preferred.

[0046] When the extracting solvent such as water contains an inorganic salt, the concentration of the inorganic salt is not particularly limited and can be appropriately set as long as it can efficiently extract sericin and sericin is not or is difficult to hydrolyze. For example, -1 More than 4 molL is preferable. -1 More preferably, 5 molL -1 More preferably, 6 molL -1 More preferably, 7 molL-1 More than 8 molL is more preferable. -1 More preferably, 20 molL -1 Less than 15 molL is preferred -1 The following is more preferred:

[0047] The amount of extraction solvent used in production method A can be set as appropriate, but is preferably 10 to 60 times, and more preferably 15 to 50 times, the mass ratio of the cocoons, for example.

[0048] The extraction temperature in production method A may be, for example, 100°C or lower, but from the viewpoint of suppressing hydrolysis, it is preferably 50°C or lower, more preferably 40°C or lower, and from the viewpoint of extraction efficiency, it is preferably 0°C or higher.

[0049] The extraction time in production method A can be set appropriately depending on the amount of raw materials used and the equipment used for extraction, but is, for example, preferably 48 hours or less, more preferably 24 hours or less, even more preferably 12 hours or less, even more preferably 6 hours or less, and from the viewpoint of extraction efficiency, preferably 0.5 hours or more.

[0050] In production method A, the sericin extract obtained by contacting the cocoons with an extraction solvent such as water may be subjected to one or more processes selected from the group consisting of filtration, centrifugation, purification, concentration, ultrafiltration, dialysis, and fractionation according to known methods, with centrifugation and / or dialysis being preferred. If necessary, the processes may be performed under normal or reduced pressure. These processes can remove insoluble matter, such as inorganic salts used during extraction. For example, when an aqueous lithium bromide solution is used for extraction, it is preferable to remove the lithium bromide by dialysis or other treatments. It is also preferable to adjust the liquid pH by adding, for example, Gly-NaOH (pH about 9) to the obtained extract.

[0051] The concentration of sericin in the extract can be appropriately set depending on the extraction conditions, but is preferably 0.0001 to 50% by mass, and more preferably 0.001 to 20% by mass, for example.

[0052] Examples of the anionic surfactant in production method A include the same examples as those of the anionic surfactants described above, and preferred embodiments thereof are also the same. Alkyl sulfates, alkenyl sulfates, alkyl ether sulfates, alkenyl ether sulfates, polyoxyalkylene alkyl ether sulfates, and polyoxyalkylene alkenyl ether sulfates are more preferred, and the compounds represented by the above formula (1) are particularly preferred.

[0053] The amount of anionic surfactant used can be appropriately determined depending on the type used. However, from the viewpoint of improving the solubility of sericin contained in the resulting sericin-containing powder, it is preferable to add an amount such that the concentration when mixed with the extract is 0.05 to 5.0% by mass. The concentration when mixed with the extract is more preferably 0.10 to 4.0% by mass, and even more preferably 0.15 to 3.5% by mass. When two or more types of anionic surfactants are used, it is preferable that the total amount of the surfactants be within the concentration range when mixed with the extract.

[0054] The amount of anionic surfactant used is preferably 0.05 to 5.0 times, more preferably 0.10 to 4.0 times, and even more preferably 0.15 to 3.5 times, the mass ratio of sericin in the extract, from the viewpoint of improving the solubility of sericin in the resulting sericin-containing powder. When two or more kinds of anionic surfactants are used, the total amount thereof is preferably within the above mass ratio range.

[0055] The amount of urea used is, for example, 0.01 to 2.0 mol L when mixed with the extract, from the viewpoint of improving the solubility of sericin contained in the resulting sericin-containing powder. -1 It is preferable to add an amount so that the concentration when mixed with the extract is 0.03 to 1.5 mol / L. -1 More preferably, 0.05 to 1.2 molL -1 is more preferably 0.08 to 1.0 molL -1is even more preferred.

[0056] Furthermore, from the viewpoint of improving the solubility of sericin contained in the resulting sericin-containing powder, the amount of urea used is preferably, for example, 0.1 to 10 times by mass relative to the amount of sericin in the extract, more preferably 0.2 to 8.0 times, even more preferably 0.3 to 6.0 times, and even more preferably 0.4 to 5.0 times.

[0057] The method for mixing the sericin extract with at least one selected from an anionic surfactant and urea is not particularly limited, and any method that ensures sufficient mixing of the two can be selected as appropriate. For example, the mixture may be mixed by stirring using a known mixing device.

[0058] In the production method A, the sericin-containing powder is obtained by mixing a sericin extract with at least one selected from an anionic surfactant and urea, and then drying the mixture.

[0059] The method for drying the mixture obtained by mixing the sericin extract with at least one selected from an anionic surfactant and urea is not particularly limited, but examples include freeze-drying, reduced-pressure (vacuum or low vacuum) drying, and spray-drying, with freeze-drying and spray-drying being preferred, and freeze-drying being more preferred. All of these drying methods can be performed using known drying equipment, and drying conditions such as drying temperature and drying time can be appropriately set depending on the drying method.

[0060] ((Manufacturing method B)) Production method B is a method in which a sericin extract is obtained by contacting cocoons (which may be the above-mentioned cocoon filaments or raw silk) with water in the presence of at least one selected from an anionic surfactant and urea, and then drying the sericin extract.

[0061] Examples of the anionic surfactant in production method B include the same examples as the anionic surfactants described above, and the preferred embodiments are also the same. The compounds represented by the above formula (1) and the compounds represented by the above formula (2) are particularly preferred.

[0062] The amount of anionic surfactant used can be appropriately determined depending on the type of surfactant used. From the viewpoint of improving the solubility of sericin contained in the resulting sericin-containing powder and extracting efficiency, an amount that results in a concentration of 0.10 to 8.0% by mass when mixed with the extraction solvent is preferred. The concentration when mixed with the extraction solvent is more preferably 0.20 to 5.0% by mass, even more preferably 0.23 to 4.0% by mass, and even more preferably 0.25 to 3.5% by mass. When two or more anionic surfactants are used, the total amount of the surfactants is preferably within the concentration range when mixed with the extraction solution.

[0063] From the viewpoints of improving the solubility of sericin contained in the resulting sericin-containing powder and improving extraction efficiency, the amount of anionic surfactant used is preferably 0.01 to 3.5 times, more preferably 0.05 to 3.0 times, even more preferably 0.10 to 2.5 times, and even more preferably 0.13 to 2.0 times by mass relative to the amount of cocoons (or cocoon filaments or raw silk) used for extraction. When two or more types of anionic surfactants are used, the total amount thereof is preferably within the above-mentioned mass ratio range.

[0064] A method for producing a sericin extract by contacting cocoons with water in the presence of an anionic surfactant allows for the extraction of high-molecular-weight sericin, and the sericin extract obtained by this method can be used to produce a sericin-containing powder that contains high-molecular-weight sericin and has excellent solubility for the sericin contained therein.

[0065] The amount of urea used is, for example, 0.10 to 10 mol L when mixed with the extraction solvent, from the viewpoint of improving the solubility of sericin contained in the resulting sericin-containing powder and extracting efficiency.-1 It is preferable to add an amount so that the concentration when mixed with the extract is 0.20 to 8.0 mol / L. -1 More preferably, 0.30 to 6.0 molL -1 is more preferably 0.40 to 5.0 molL -1 is even more preferred.

[0066] Furthermore, from the viewpoint of improving the solubility of sericin contained in the resulting sericin-containing powder and of the extraction efficiency, the amount of urea used is preferably 0.1 to 12 times, more preferably 0.2 to 10 times, even more preferably 0.3 to 8.0 times, and even more preferably 0.4 to 6.0 times by mass relative to the amount of cocoons (or cocoon filaments or raw silk) used for extraction.

[0067] In production method B, when the cocoons are contacted with water in the presence of an anionic surfactant and / or urea, i.e., when sericin is extracted, an organic solvent other than water may be used as an extraction solvent. Examples of the organic solvent include lower alcohols such as methanol, ethanol, and isopropanol; glycols such as propylene glycol and diethylene glycol; and aprotic solvents such as dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and N-methylmorpholine-N-oxide. A single extraction solvent may be used, or two or more may be mixed. Water alone is preferred as the extraction solvent.

[0068] The amount of extraction solvent used in production method B can be set as appropriate, but is preferably 10 to 150 times, and more preferably 15 to 130 times, the mass ratio of the cocoons, for example.

[0069] The extraction temperature in production method B may be, for example, 150°C or lower. From the viewpoint of extracting high molecular weight sericin, it is preferably 130°C or lower, more preferably 120°C or lower, and even more preferably 110°C or lower. From the viewpoint of extraction efficiency, it is preferably 30°C or higher, more preferably 50°C or higher, and even more preferably 80°C or higher.

[0070] The extraction time in Production Method B can be set appropriately depending on the amount of raw materials used and the equipment used for extraction, but from the viewpoint of extracting high-molecular-weight sericin, it is preferably 10 hours or less, more preferably 5 hours or less, even more preferably 4 hours or less, and even more preferably 3 hours or less, and from the viewpoint of extraction efficiency, it is preferably 0.1 hours or more. During extraction, the mixture of cocoons and water containing anionic surfactant and / or urea may be mixed by stirring using a known mixing device.

[0071] The extraction rate of sericin in production method B is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 27% by mass or more, and the upper limit is not particularly limited and may be 100% by mass or 95% by mass or less. The extraction rate of sericin can be determined by the following method. First, the sericin concentration in the sericin extract is calculated using the Bradford method or absorbance at 280 nm, and the mass of sericin obtained by extraction is determined from the calculated sericin concentration. The sericin concentration is calculated from absorbance by creating a calibration curve. The extraction rate is then calculated using the following formula from the mass of sericin obtained by extraction and the mass of the cocoons (or cocoon filaments or raw silk) used to extract the sericin. Extraction rate (wt%) = (mass of sericin obtained by extraction / mass of cocoons used to extract sericin) x 100

[0072] The sericin extract obtained by Production Method B may be subjected to one or more treatments selected from the group consisting of filtration, centrifugation, and concentration according to known methods before drying. Preferably, insoluble matter is removed from the extract by filtration and / or centrifugation. If necessary, the treatments may be performed under normal pressure or reduced pressure.

[0073] In the production method B, the sericin-containing powder is obtained by drying the sericin extract.

[0074] The method for drying the sericin extract is not particularly limited, but examples include freeze-drying, reduced-pressure (vacuum or low vacuum) drying, and spray-drying. Freeze-drying and spray-drying are preferred, with freeze-drying being more preferred. All of these drying methods can be performed using known drying equipment, and drying conditions such as drying temperature and drying time can be appropriately set depending on the drying method.

[0075] The sericin-containing powder obtained by the above-described production method contains high-molecular-weight sericin and exhibits excellent solubility of the sericin contained therein. Because the sericin contained in the sericin-containing powder exhibits excellent solubility, it is easily incorpo- rated into cosmetic formulations and is easy to handle. Furthermore, because the powder contains high-molecular-weight sericin, it is less susceptible to instability, such as gelation of the solution or hydrolysis of the sericin, compared with a solution. [Example]

[0076] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is possible to carry out the invention by making appropriate modifications within the scope of the above and below-described aims, and all such modifications are included in the technical scope of the present invention.

[0077] The measurements in the examples and comparative examples were carried out by the following methods. (1) Sericin extraction rate The sericin concentration in the sericin extract was calculated using the Bradford method or absorbance at 280 nm, and the mass of sericin obtained by extraction was calculated from the calculated sericin concentration. The sericin concentration was calculated from absorbance by creating a calibration curve. The extraction rate was calculated using the following formula from the mass of sericin obtained by extraction and the mass of the Sericin Hope cocoons used to extract the sericin. Extraction rate (wt%) = (mass of sericin obtained by extraction / mass of Sericin Hope cocoons used to extract sericin) x 100 (2) Molecular weight of sericin Measurement was performed by SDS-PAGE. The gels used were Multigel II Mini Gradient Gel 2-15% 17-well (Cosmo Bio Co., Ltd.) or 4-15% Mini Protein TGX Stain-Free Gel (BIO-RAD). The molecular weight markers were Precision Plus Protein TM Two-color standard (BIO-RAD, product number 1610374), Multicolor Protein Ladder (10-350kPa) (Nippon Gene), or HiMark TM Unstained (Invitrogen) was used. As a result of the measurement, sericin in which at least one band was detected in the range corresponding to a molecular weight of 150 kDa or more was evaluated as ○, and sericin in which no band was detected in the range corresponding to a molecular weight of 150 kDa or more was evaluated as ×. (3) Solubility of sericin Sericin-containing powder was added to pure water to a sericin concentration of 1% by mass, and dissolved at 80°C for 30 minutes. After dissolution, the solution was centrifuged at 9,500 × g for 5 minutes, and the supernatant was collected. The sericin concentration in the resulting aqueous solution was calculated using the Bradford method or absorbance at 280 nm. The mass of dissolved sericin was determined from the calculated sericin concentration. The sericin concentration was calculated from absorbance by creating a calibration curve. The dissolution rate was calculated from the mass of dissolved sericin and the mass of sericin initially added using the following formula, and the solubility was determined. Dissolution rate of sericin (wt%) = (mass of dissolved sericin / mass of added sericin) x 100 Solubility of sericin (g / 100g of aqueous solution) = 100 (g) × 1 (wt%) × solubility of sericin (wt%)

[0078] Example 1 A flask was charged with 1 g of sericin "Hope" cocoons obtained from a selectively bred silkworm and 20 mL of 8 M LiBr (Fujifilm Wako Pure Chemical Corporation) solution and stirred at 35°C for 5 hours. The resulting solution was transferred to a centrifuge tube, washed with 5 mL of Gly-NaOH buffer (pH 9), and combined with the centrifuge tube. The mixture was centrifuged at 9,500 × g for 5 minutes at 4°C and then poured into a dialysis membrane (Spectra / Por 4) to initiate dialysis. The external solution was initially replaced with ion-exchanged water, with the external solution replaced after 2.5 and 5.5 hours. The external solution was then replaced with 0.1 mM carbonate buffer the following morning, evening, and morning of the following day. After a total of 48 hours, dialysis was stopped, the solution transferred to a centrifuge tube, and centrifuged at 9,500 × g for 1 hour at 4°C. The supernatant was collected, and the resulting aqueous solution was dried by heating. The solid content was taken as the sericin concentration, which was 1.0% by mass. Sodium lauryl sulfate (Emal OS, product name, manufactured by Kao Corporation) was added to the aqueous solution containing sericin at a concentration of 1.0% by mass so that the concentration after addition was 0.15% by mass, and the mixture was freeze-dried to obtain a sericin-containing powder. The molecular weight and solubility of the sericin contained in the obtained sericin-containing powder were measured. The measurement results are shown in Table 1. The molecular weight of sericin was measured using the aqueous solution recovered after dissolution and centrifugation in the solubility measurement. The results of SDS-PAGE are shown in Figure 1. The gel used was a Multigel II Mini Gradient Gel 2-15% 17-well (manufactured by Cosmo Bio Co., Ltd.). Lane 1 in Figure 1 indicates a molecular weight marker (Precision Plus Protein TM Two-color standard (manufactured by BIO-RAD; product number 1610374), lane 3 shows the results of Example 1.

[0079] Examples 2 to 9 A sericin-containing powder was obtained in the same manner as in Example 1, except that the amount of sodium lauryl sulfate added was changed so that the concentration in the aqueous solution after addition was as shown in Table 1. The molecular weight and solubility of the sericin contained in the obtained sericin-containing powder were measured, and the results are shown in Table 1. The molecular weight of sericin was measured using the aqueous solution recovered after dissolution and centrifugation in the solubility measurement. The results of SDS-PAGE are shown in Figure 1. The gel used was a Multigel II Mini Gradient Gel 2-15% 17-well (manufactured by Cosmo Bio Co., Ltd.). Lane 1 in Figure 1 is a molecular weight marker (Precision Plus Protein TM Two-color standard; manufactured by BIO-RAD; product number 1610374), lane 4 shows the results of Example 2, lane 5 shows the results of Example 3, lane 6 shows the results of Example 4, lane 7 shows the results of Example 5, lane 8 shows the results of Example 6, lane 9 shows the results of Example 7, lane 10 shows the results of Example 8, and lane 11 shows the results of Example 9.

[0080] (Examples 10 to 13) A sericin-containing powder was obtained in the same manner as in Example 1, except that the compound added was changed from sodium lauryl sulfate to polyoxyethylene (2) lauryl ether sodium sulfate (manufactured by Kao Corporation, trade name: Emeral E-27C), and the amount added was changed so that the concentration in the aqueous solution after addition was as shown in Table 1. The results of the molecular weight and solubility of the sericin contained in the obtained sericin-containing powder, measured, are shown in Table 1. The molecular weight of sericin was measured using the aqueous solution recovered after dissolution and centrifugation in the solubility measurement. The results of SDS-PAGE are shown in Figure 2. The gel used was a Multigel II Mini Gradient Gel 2-15% 17-well (manufactured by Cosmo Bio Co., Ltd.). Lane 1 in Figure 2 is a molecular weight marker (Precision Plus Protein TM Two-color standard; manufactured by BIO-RAD; product number 1610374), lane 3 shows the results of Example 10, lane 4 shows the results of Example 11, lane 5 shows the results of Example 12, and lane 6 shows the results of Example 13.

[0081] (Examples 14 to 17) A sericin-containing powder was obtained in the same manner as in Example 1, except that the compound added was changed from sodium lauryl sulfate to ammonium lauryl sulfate (manufactured by Kao Corporation, trade name: Emeral AD-25R), and the amount added was changed so that the concentration in the aqueous solution after addition was as shown in Table 1. The molecular weight and solubility of the sericin contained in the obtained sericin-containing powder were measured, and the results are shown in Table 1. The molecular weight of sericin was measured using the aqueous solution recovered after dissolution and centrifugation in the solubility measurement. The results of SDS-PAGE are shown in Figure 2. The gel used was a Multigel II Mini Gradient Gel 2-15% 17-well (manufactured by Cosmo Bio Co., Ltd.). Lane 1 in Figure 2 is a molecular weight marker (Precision Plus Protein TM Two-color standard; manufactured by BIO-RAD; product number 1610374), lane 7 shows the results of Example 14, lane 8 shows the results of Example 15, lane 9 shows the results of Example 16, and lane 10 shows the results of Example 17.

[0082] (Examples 18 to 21) A sericin-containing powder was obtained in the same manner as in Example 1, except that the compound added was changed from sodium lauryl sulfate to urea, and the amount added was changed so that the concentration in the aqueous solution after addition was as shown in Table 1. The molecular weight and solubility of the sericin contained in the obtained sericin-containing powder were measured, and the results are shown in Table 1. The molecular weight of sericin was measured using the aqueous solution recovered after dissolution and centrifugation in the solubility measurement. The results of SDS-PAGE are shown in Figure 3. The gel used was a Multigel II Mini Gradient Gel 2-15% 17-well (manufactured by Cosmo Bio Co., Ltd.). Lane 1 in Figure 3 is a molecular weight marker (Precision Plus Protein TM Two-color standard (BIO-RAD; product number 1610374), lane 3 shows the results of Example 20. Lane 2 in Figure 3 shows the results of SDS-PAGE using the supernatant after centrifugation of the dialysate in Example 1.

[0083] (Comparative Example 1) A sericin-containing powder was obtained in the same manner as in Example 1, except that sodium lauryl sulfate was not added. The molecular weight and solubility of the sericin contained in the obtained sericin-containing powder were measured, and the results are shown in Table 1. The molecular weight of sericin was measured using the aqueous solution recovered after dissolution and centrifugation in the solubility measurement. The results of SDS-PAGE are shown in Figures 1 and 2. The gel used was Multigel II Mini Gradient Gel 2-15% 17 well (manufactured by Cosmo Bio Co., Ltd.). Lane 2 in Figure 1 and lane 2 in Figure 2 show the results of Comparative Example 1.

[0084] Example 22 Sericin Hope cocoons obtained from silkworms produced through breeding were added to a test tube with a 0.25% by mass aqueous solution of sodium lauryl sulfate (Emal OS, product name, manufactured by Kao Corporation) so that the concentration of sericin Hope cocoons added was 1% by mass, and sericin was extracted at 95°C for 30 minutes. After extraction, insoluble matter was removed by centrifugation, and the sericin extraction rate was calculated from the sericin concentration in the supernatant. The molecular weight of sericin was also measured using the supernatant. The measurement results are shown in Table 2 below. The results of SDS-PAGE are shown in Figure 4. The gel used was a Multigel II Mini Gradient Gel 2-15% 17-well (manufactured by Cosmo Bio Co., Ltd.). Lane 1 in Figure 4 is a molecular weight marker (Precision Plus Protein TM Two-color standard (manufactured by BIO-RAD; product number 1610374), lane 2 shows the results of Example 22. The supernatant was then freeze-dried to obtain a powder containing sericin. The solubility of the sericin contained in the powder was measured. The measurement results are shown in Table 3.

[0085] (Examples 23 to 31) A sericin-containing powder was obtained in the same manner as in Example 22, except that the concentration of sericin Hope cocoons added, the concentration of the sodium lauryl sulfate aqueous solution, the sericin extraction conditions (extraction temperature, extraction time), and the drying method were changed as shown in Table 2. The results of measuring the sericin extraction rate, sericin molecular weight, and sericin solubility for each example are shown in Table 3. The results of SDS-PAGE are shown in Figures 4 to 7. For the gel, Multigel II Mini Gradient Gel 2-15% 17-well (Cosmo Bio Co., Ltd.) was used in Examples 23 to 27, and 4-15% Mini Protein TGX Stain-Free Gel (BIO-RAD) was used in Examples 28 to 31. Lane 1 in Figure 4 is a molecular weight marker (Precision Plus Protein TM Two-color standard; manufactured by BIO-RAD; product number 1610374), lane 3 is the result of Example 24, lane 4 is the result of Example 26, lane 5 is the result of Example 23, lane 6 is the result of Example 25, and lane 7 is the result of Example 27. In Figure 5, lane 1 is a molecular weight marker (Multicolor Protein Ladder (10-350 kPa); manufactured by Nippon Gene), and lane 2 is the result of Example 28. In Figure 6, lane 1 is a molecular weight marker (Multicolor Protein Ladder (10-350 kPa); manufactured by Nippon Gene), lane 2 is the result of Example 29, and lane 3 is the result of Example 30. In Figure 7, lane 1 is a molecular weight marker (HiMark TM Lane 1 shows the results for Example 31, and lane 3 shows the molecular weight marker (Multicolor Protein Ladder (10-350 kPa); Nippon Gene).

[0086] Examples 32 to 35 A sericin-containing powder was obtained in the same manner as in Example 22, except that the sodium lauryl sulfate aqueous solution was changed to a sodium lauroylmethyl-β-alanine aqueous solution (i.e., the compound added was changed from sodium lauryl sulfate to sodium lauroylmethyl-β-alanine), and the concentration of sericin Hope cocoons added, the concentration of the sodium lauroylmethyl-β-alanine aqueous solution, and the sericin extraction conditions (extraction time) were changed as shown in Table 2. The results of measuring the sericin extraction rate, molecular weight, and solubility of sericin in each example are shown in Table 3. The results of SDS-PAGE are shown in Figure 8. The gel used was a Multigel II Mini Gradient Gel 2-15% 17-well (Cosmo Bio Co., Ltd.). Lane 1 in Figure 8 is a molecular weight marker (Precision Plus Protein TM Two-color standard (manufactured by BIO-RAD; product number 1610374), lane 3 shows the results of Example 32, lane 4 shows the results of Example 33, lane 5 shows the results of Example 34, and lane 6 shows the results of Example 35. Note that lane 2 in Figure 8 shows the results of SDS-PAGE performed using the supernatant after centrifugation of the dialysate in Example 1.

[0087] (Examples 36 to 39) A sericin-containing powder was obtained in the same manner as in Example 22, except that the sodium lauryl sulfate aqueous solution was changed to a urea aqueous solution (i.e., the compound added was changed from sodium lauryl sulfate to urea), and the concentration of sericin Hope cocoons added, the concentration of the urea aqueous solution, and the sericin extraction conditions (extraction time) were changed as shown in Table 2. Table 3 shows the results of measuring the sericin extraction rate, sericin molecular weight, and sericin solubility in each example. Figure 9 also shows the results of SDS-PAGE. The gel used was a Multigel II Mini Gradient Gel 2-15% 17-well (Cosmo Bio Co., Ltd.). Lane 1 in Figure 9 is a molecular weight marker (Precision Plus Protein TM Two-color standard; manufactured by BIO-RAD; product number 1610374), lane 3 shows the results of Example 36, lane 4 shows the results of Example 37, lane 5 shows the results of Example 38, and lane 6 shows the results of Example 39.

[0088] (Comparative Examples 2 and 3) A sericin-containing powder was obtained in the same manner as in Example 22, except that the sodium lauryl sulfate aqueous solution was replaced with pure water, and the concentration of sericin Hope cocoons added and the sericin extraction conditions (extraction temperature, extraction time) were changed as shown in Table 2. Table 3 shows the results of measuring the sericin extraction rate, sericin molecular weight, and sericin solubility in each comparative example. Figure 9 shows the results of SDS-PAGE. The gel used was a Multigel II Mini Gradient Gel 2-15% 17-well (manufactured by Cosmo Bio Co., Ltd.). Lane 1 in Figure 9 shows the molecular weight marker (Precision Plus Protein TM Two-color standard (manufactured by BIO-RAD; product number 1610374), lane 2 shows the results of Comparative Example 2.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Table 3]

Claims

1. The sericin-containing powder contains sericin, which exhibits at least one band detected by SDS-PAGE in a range corresponding to a molecular weight of 150 kDa or more, and has a solubility of 0.45 g / 100 g of aqueous solution in water at a temperature of 80°C, obtained by dissolving the sericin in the water. The powder also contains at least one member selected from the group consisting of sodium lauryl sulfate, polyoxyethylene (2) lauryl ether sodium sulfate, ammonium lauryl sulfate, sodium lauroyl methyl β-alanine, and urea, and the total content of the sodium lauryl sulfate, the polyoxyethylene (2) lauryl ether sodium sulfate, the ammonium lauryl sulfate, the sodium lauroyl methyl β-alanine, and the urea is 10% by mass or more and 90% by mass or less of the total amount of the sericin-containing powder.

2. A method for producing a sericin-containing powder comprising at least one selected from the group consisting of sodium lauryl sulfate, polyoxyethylene (2) lauryl ether sodium sulfate, ammonium lauryl sulfate, lauroyl methyl β-alanine sodium, and urea, the method comprising the steps of: mixing a sericin extract obtained by contacting cocoons with water with at least one selected from the group consisting of sodium lauryl sulfate, polyoxyethylene (2) lauryl ether sodium sulfate, ammonium lauryl sulfate, lauroyl methyl β-alanine sodium, and urea; and drying the resulting mixture. The method comprises the steps of:

3. A method for producing a sericin-containing powder comprising at least one member selected from the group consisting of sodium lauryl sulfate, polyoxyethylene (2) lauryl ether sodium sulfate, ammonium lauryl sulfate, lauroyl methyl β-alanine Na, and urea, the method comprising drying a sericin extract obtained by contacting cocoons with water in the presence of at least one member selected from the group consisting of sodium lauryl sulfate, polyoxyethylene (2) lauryl ether sodium sulfate, ammonium lauryl sulfate, lauroyl methyl β-alanine Na, and urea, wherein the total content of the group consisting of sodium lauryl sulfate, polyoxyethylene (2) lauryl ether sodium sulfate, ammonium lauryl sulfate, lauroyl methyl β-alanine Na, and urea is 10% by mass or more and 90% by mass or less of the total amount of the sericin-containing powder.

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