Sericin composition having excellent stability

Abstract

To provide a sericin composition having excellent stability.SOLUTION: Provided is a sericin composition having: a weight-average molecular weight of 3,000 to 45,000; a z-average molecular weight of 6,000 to 65,000; 70 to 100 wt.% of sericin having a molecular weight of 45,000 or less; 0 to less than 15 wt.% of sericin having a molecular weight of 50,000 or more; and an amino acid composition having a serine content of 30 to 40%, wherein the sericin composition has excellent characteristics in color, odor, and other physical properties, with little change over time.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a sericin composition having excellent stability, and more specifically, to a sericin composition which is favorable in color, odor and other physical properties and which is unlikely to change over time. [Background technology]

[0002] Silk thread is mainly composed of two types of proteins: highly crystalline fibroin and non-crystalline sericin. When sericin is removed from silk thread, the fiber mainly made of fibroin becomes silk thread. Meanwhile, sericin has been attracting attention recently due to its various physiological activities, and its use in various applications has been proposed.

[0003] Since sericin in silkworm cocoon filaments is a water-insoluble high molecular weight protein, sericin is generally extracted by hydrolysis using soap or alkali treatment, enzyme treatment, boiling treatment, etc., and then dissolving it in water. When extracting sericin, consideration has traditionally been given to its molecular weight from the standpoint of its uses, properties, etc.

[0004] For example, Japanese Patent Application Laid-Open No. 2005-272690 (Patent Document 1) describes that in order to form a porous body using sericin, the average molecular weight of sericin is required to be 30,000 to 400,000.The publication specifically discloses that the extraction is performed by boiling, and that the heat treatment is performed for 30 minutes at 105°C using an autoclave (paragraph 0042).

[0005] Furthermore, Japanese Patent Application Laid-Open No. 2001-039999 (Patent Document 2) describes that highly pure sericin of 50,000 to 300,000 can be obtained by circulating high-temperature water at 90 to 130°C for 10 to 180 minutes, and discloses specific extraction conditions as follows (paragraph 0036): using a high-pressure package dyeing machine, a liquid flow of 30 liters / kg / min, and a temperature of 110°C for 120 minutes.

[0006] In addition, Japanese Patent Laid-Open No. 11-131318 (Patent Document 3) describes that sericin having a molecular weight of 100,000 or more can be obtained by treating with high-temperature water at 100°C to 140°C, and specifically describes treatment in a high-pressure steam treatment device at 120°C for 30 minutes (paragraph 0028) or treatment in distilled water at 120°C for 60 minutes (paragraph 0030). In addition, Japanese Patent Laid-Open No. 2005-171218 (Patent Document 4) discloses conditions for extracting sericin, such as boiling in an autoclave at a temperature of 110 to 120°C and a pressure not exceeding 14 pounds per square inch for 25 to 30 minutes (paragraph 0005, where 14 pounds per square inch is approximately 0.1 MPa).

[0007] For example, when sericin is used as a cosmetic ingredient because of its moisturizing and antioxidant properties, it is required that its color and odor do not affect the overall composition, and that these properties do not change over time. It is also important that sericin does not produce sediment or other deposits over time.

[0008] As a proposal for improving the stability of sericin, for example, JP 2008-094723 A (Patent Document 5) proposes a method of encapsulating water-soluble silk protein in liposomes to suppress browning over time. The molecular weight of sericin disclosed in this document is 3,000 to 200,000, and extraction is performed using alkali. In addition, JP 2006-232787 A (Patent Document 6) discloses a technology of suppressing browning over time by adding a water-soluble reducing agent to a water-soluble silk protein aqueous composition containing sericin with a molecular weight of 3,000 to 200,000. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2005-272690 A [Patent Document 2] JP 2001-039999 A [Patent Document 3] Japanese Patent Application Publication No. 11-131318 [Patent Document 4] JP 2005-171218 A [Patent Document 5] JP 2008-094723 A [Patent Document 6] JP 2006-232787 A Summary of the Invention [Problem to be solved by the invention]

[0010] The present inventors have now discovered that a sericin composition with excellent stability can be obtained by controlling the molecular weight of the sericin contained therein and by controlling the amino acid composition. They have also discovered that such a sericin composition with excellent stability can be efficiently obtained by precisely controlling the extraction conditions from cocoons. The present invention is based on these discoveries.

[0011] Therefore, an object of the present invention is to provide a sericin composition having excellent stability. [Means for solving the problem]

[0012] The sericin composition according to the present invention is The weight average molecular weight is 3,000 to 45,000, The z-average molecular weight is 6,000 to 65,000; Sericin having a molecular weight of 45,000 or less accounts for 70 to 100% by weight, and sericin having a molecular weight of 50,000 or more accounts for 0 to less than 15% by weight, It is characterized by having an amino acid composition with a serine content of 30 to 40%.

[0013] The method for producing a sericin composition according to the present invention further comprises the steps of: extracting sericin from the cocoons into an aqueous medium; The extraction is carried out under a pressure of 0.14 to 0.31 MPa and satisfies any one of the following conditions (1) to (3): (1) When the pressure is 0.14 MPa or more and less than 0.21 MPa, the temperature of the aqueous medium is set to 110 to less than 120°C, and extraction is performed for 360 to 600 minutes. (2) When the pressure is 0.21 MPa or more and less than 0.27 MPa, the temperature of the aqueous medium is set to 122 to less than 130°C, and extraction is performed for 120 to 600 minutes. (3) When the pressure is 0.27 MPa or more and 0.31 MPa or less, the temperature of the aqueous medium is set to 130 to 135°C, and extraction is performed for 60 to 600 minutes. Effect of the Invention

[0014] According to the present invention, a sericin composition having excellent stability is provided. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] definition As used herein, the term "sericin composition" means a mixture of sericins having a wide distribution of molecular weight and amino acid composition, but does not exclude sericin having a single or very narrow range of molecular weight and amino acid composition.

[0016] In addition, in this specification, when a numerical range is described with an upper limit and a lower limit, the lower limit and the upper limit are included in the numerical range, unless otherwise specified.

[0017] Sericin composition according to the present invention The sericin composition according to the present invention is characterized in that it has an amino acid composition having a weight-average molecular weight of 3,000 to 45,000, a z-average molecular weight of 6,000 to 65,000, with 70 to 100% by weight of sericin having a molecular weight of 45,000 or less and 0 to less than 15% by weight of sericin having a molecular weight of 50,000 or more, and a serine content of 30 to 40%.

[0018] The sericin composition of the present invention which satisfies the above requirements has good color, odor and other physical properties and is less susceptible to changes over time.

[0019] Weight average molecular weight and z-average molecular weight The weight-average molecular weight of sericin contained in the sericin composition according to the present invention is in the range of 3,000 to 45,000, with a preferred lower limit of 10,000 and a preferred upper limit of 30,000.The z-average molecular weight is in the range of 6,000 to 65,000, with a preferred lower limit of 15,000 and a preferred upper limit of 50,000.

[0020] In the present invention, the molecular weight is measured by liquid chromatography (GPC).

[0021] Sericin Content The sericin composition according to the present invention contains 70-100% by weight of sericin having a molecular weight of 45,000 or less, and 0-15% by weight of sericin having a molecular weight of 50,000 or more. According to a preferred embodiment of the present invention, the lower limit of the content of sericin having a molecular weight of 45,000 or less is 95% by weight, more preferably 99% by weight. The content of sericin having a molecular weight of 50,000 or more is preferably as small as possible.

[0022] Serine Content The sericin composition according to the present invention has an amino acid composition with a serine content of 30-40%, with a preferred lower limit of 32% and a preferred upper limit of 38%. According to a further preferred embodiment of the present invention, the sericin composition according to the present invention has an amino acid composition with a glycine content of preferably 13-20%, more preferably 14.5-18.5%. According to another further preferred embodiment of the present invention, the sericin composition according to the present invention has an amino acid composition with an alanine content of preferably 3-6%, more preferably 3.5-5.5%.

[0023] In the present invention, the analysis of amino acid composition is carried out by a post-column derivatization-fluorescence detection method using liquid chromatography. That is, after separating amino acids in a column, a derivatization fluorescent reagent is delivered and mixed to react, and the amino acids are introduced into a detector to qualitatively and quantitatively analyze the amino acids.

[0024] Properties of sericin composition and its uses The sericin composition according to the present invention has various physiological activities possessed by sericin, such as moisturizing properties, antioxidant activity, cell protective activity, and protein protective activity, and further has advantageous properties such as being good in color, odor, and other physical properties, and being unlikely to change over time after production. Due to these properties, the sericin composition according to the present invention is preferably used as a main component in applications such as cosmetics, foods, fiber processing agents, and pharmaceuticals. Furthermore, because of the cell activation effect, cryoprotection effect, antibody stabilization effect, enzyme stabilization effect, blocking effect, chelating effect, surfactant effect, coating effect, and function as an excipient, the sericin composition according to the present invention is also preferably used as an additive for cosmetics, foods, fiber processing agents, and pharmaceuticals.

[0025] The color of the sericin composition according to the present invention is amber or yellowish brown, and the color change over time is small, and the color change rate is preferably in the range of 1.0 to 1.8. In the present invention, the "color change rate" means the rate of change in absorbance at 400 nm before and after storing a sericin composition having a pH range of 4.5 to 7.2 at 50°C for 30 days. Therefore, the color change rate of the sericin composition according to the present invention preferably does not exceed 1.8 at any pH value between 4.5 and 7.2. The sericin composition having a pH range of 4.5 to 7.2 means either a composition having a pH in the above range without adjustment, or a composition having a pH in the above range after adjusting the pH with an acid or alkali.

[0026] In addition, sericin obtained by, for example, alkaline extraction may have unpleasant odors, insect odors, sulfur odors, and scouring odors that are characteristic of protein hydrolysates, but the sericin composition of the present invention does not have such odors or, if any, they are very slight.The sericin composition of the present invention is also advantageous in that the odor does not change much over time.

[0027] Furthermore, the sericin composition according to the present invention has the property of producing little precipitates such as sediment, and the turbidity change rate is in the range of 0.8 to 1.5. In the present invention, the "turbidity change rate" means the rate of change in absorbance at 600 nm before and after storing a sericin composition having a pH range of 4.5 to 7.2 at 50°C for 30 days. Therefore, the sericin composition according to the present invention preferably has a turbidity change rate in the range of 0.8 to 1.5 regardless of the pH value of the sericin composition from 4.5 to 7.2. The sericin composition having a pH range of 4.5 to 7.2 means either a composition having a pH in the range without adjustment, or a composition having a pH in the range after adjusting the pH with an acid or alkali.

[0028] The sericin composition of the present invention may be dried in a conventional manner and provided as a solid or powder. The sericin composition of the present invention is in the form of a powder, and when it is subsequently dissolved in water, its pH does not become alkaline. As a result, it has the advantage of being usable in a weakly acidic state without pH adjustment. For example, when it is incorporated into cosmetics, it can enhance turbidity stability without being affected by the pH of the cosmetics. Furthermore, when the sericin composition of the present invention is applied to the skin, it can be applied to the skin without pH adjustment, and by maintaining the weak acidity of the skin, it is possible to achieve enhanced barrier function, maintenance of lipid balance, and the like.

[0029] Method for producing sericin composition: Extraction conditions According to a preferred embodiment of the present invention, the sericin composition of the present invention is preferably produced by the following method. That is, the method for producing the sericin composition of the present invention comprises a step of extracting sericin from cocoons into an aqueous medium, the extraction being carried out under a pressure of 0.14 to 0.31 MPa, and satisfying any one of the following conditions (1) to (3): (1) When the pressure is 0.14 MPa or more and less than 0.21 MPa, the temperature of the aqueous medium is set to 110 to less than 120°C, and extraction is performed for 360 to 600 minutes. (2) When the pressure is 0.21 MPa or more and less than 0.27 MPa, the temperature of the aqueous medium is set to 122 to less than 130°C, and extraction is performed for 120 to 600 minutes. (3) When the pressure is 0.27 MPa or more and 0.31 MPa or less, the temperature of the aqueous medium is set to 130 to 135°C, and extraction is performed for 60 to 600 minutes.

[0030] The cocoons used in the production method according to the present invention are preferably in a state in which a part of the cocoon has been cut open and the pupa has been removed. The cocoon from which the pupa has been removed may be cut and used.

[0031] Examples of the aqueous medium include hydrophilic solvents such as water and physiological saline, and among these, distilled water is preferably used. According to a preferred embodiment, the aqueous medium is used in an amount (mass ratio) of 5 to 100 times the amount of the cocoons, more preferably 5 to 30 times the amount (mass ratio). EXAMPLES

[0032] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0033] In the following Examples and Comparative Examples, the weight average molecular weight and z-average molecular weight were measured as follows.

[0034] Weight average molecular weight and z-average molecular weight The molecular weight was measured using a high performance liquid chromatograph LC-20A GPC system (Shimadzu Corporation). The weight average molecular weight and z-average molecular weight were calculated using GPC data analysis software LabSolutions (Shimadzu Corporation). The area values ​​corresponding to the detected peaks and each molecular weight were corrected using Gel Filtration Calibration Kit LM (Global Life Science Technologies Japan, Inc.). The calculation formula is as follows:

number

[0035] Molecular weight distribution and content of sericin The content (%) of sericin having a molecular weight of 45,000 or less and the content (%) of sericin having a molecular weight of 50,000 or more were calculated from the area ratio for each molecular weight of sericin separated by the high performance liquid chromatography.

[0036] Serine Content The amino acid composition was measured by post-column derivatization-fluorescence detection using an ultra-high performance liquid chromatograph Prominence amino acid analysis system (Shimadzu Corporation). The amino acid composition was calculated using the amino acid analysis software LabSolutions (Shimadzu Corporation).

[0037] Example 1 Pupae were removed from cocoons of domesticated silkworms (Bombyx mori), washed three times with distilled water, and dried to obtain cut cocoons. Hereinafter, these cut cocoons are referred to as "washed and dried cocoons." 100 g of washed and dried cocoons were immersed in 2,000 g of distilled water, and sericin was extracted under conditions of 0.17 MPa, 115°C, and extraction time of 480 minutes. The obtained extract was filtered through a filter membrane with a pore size of 0.2 μm to obtain a purified liquid. The pH of the obtained purified liquid was 6.7. The purified liquid was then freeze-dried to obtain sericin powder. The powder was adjusted to 1.0 mass% with distilled water to obtain a sericin aqueous solution with a pH of 4.9. The weight-average molecular weight of this sericin was 19,000, and the z-average molecular weight was 36,000. Sericin with a molecular weight of 45,000 or less accounted for 92.4% by weight, and sericin with a molecular weight of 50,000 or more accounted for only 5.7% by weight. The serine content was 33.3%, the glycine content was 17.1%, and the alanine content was 4.8%.

[0038] Example 2 A purified liquid and sericin powder were obtained in the same manner as in Example 1, except that the conditions for sericin extraction were 0.23 MPa, 125°C under pressure and heating, and extraction time was 120 minutes. The pH of the purified liquid obtained was 6.7. The pH of the sericin aqueous solution obtained by adjusting the sericin powder to 1.0 mass% with distilled water was 4.9, and the weight-average molecular weight of the obtained sericin was 27,000 and the z-average molecular weight was 46,000. Sericin with a molecular weight of 45,000 or less accounted for 82.4% by weight, and sericin with a molecular weight of 50,000 or more accounted for only 14.1% by weight. The serine content was 32.0%, the glycine content was 18.4%, and the alanine content was 4.8%.

[0039] Example 3 A purified liquid and sericin powder were obtained in the same manner as in Example 2, except that the extraction time of the sericin extraction conditions was 240 minutes. The pH of the purified liquid obtained was 6.7. The pH of the sericin aqueous solution obtained by adjusting the sericin powder to 1.0 mass% with distilled water was 5.0, and the weight-average molecular weight of the obtained sericin was 17,000 and the z-average molecular weight was 32,000. Sericin with a molecular weight of 45,000 or less accounted for 94.2 weight%, and sericin with a molecular weight of 50,000 or more was only 4.1 weight%. The serine content was 37.0%, the glycine content was 17.0%, and the alanine content was 4.3%.

[0040] Example 4 A purified liquid and sericin powder were obtained in the same manner as in Example 1, except that the conditions for sericin extraction were 0.30 MPa, 134°C under pressure and heating, and extraction time was 60 minutes. The pH of the purified liquid obtained was 6.7. The pH of the sericin aqueous solution obtained by adjusting the sericin powder to 1.0 mass% with distilled water was 5.0, and the weight-average molecular weight of the obtained sericin was 26,000 and the z-average molecular weight was 46,000. Sericin with a weight-average molecular weight of 45,000 or less accounted for 79.2% by weight, and sericin with a weight-average molecular weight of 50,000 or more accounted for only 13.7% by weight. The serine content was 34.9%, the glycine content was 17.0%, and the alanine content was 3.9%.

[0041] Example 5 A purified liquid and sericin powder were obtained in the same manner as in Example 4, except that the extraction time of the sericin extraction conditions was 120 minutes. The pH of the purified liquid obtained was 6.7. The pH of the sericin aqueous solution obtained by adjusting the sericin powder to 1.0 mass% with distilled water was 4.9, and the weight-average molecular weight of the obtained sericin was 16,000 and the z-average molecular weight was 34,000. Sericin with a molecular weight of 45,000 or less accounted for 94.3 weight%, and sericin with a molecular weight of 50,000 or more was only 4.4 weight%. The serine content was 32.5%, the glycine content was 16.8%, and the alanine content was 4.7%.

[0042] Example 6 A purified liquid and sericin powder were obtained in the same manner as in Example 1, except that the conditions for sericin extraction were 0.17 MPa, 115°C under pressure and heating, and extraction time was 360 minutes. The pH of the purified liquid obtained was 6.7. The pH of the sericin aqueous solution obtained by adjusting the sericin powder to 1.0 mass% with distilled water was 5.1, and the weight-average molecular weight of the obtained sericin was 25,000 and the z-average molecular weight was 50,000. Sericin with a molecular weight of 45,000 or less accounted for 86.1 weight%, and sericin with a molecular weight of 50,000 or more accounted for only 11.1 weight%. The serine content was 32.5%, the glycine content was 17.8%, and the alanine content was 4.5%.

[0043] Comparative Example 1 A purified liquid and sericin powder were obtained in the same manner as in Example 1, except that the conditions for sericin extraction were 0.15 MPa, 112°C under pressure and heating, and extraction time was 240 minutes. The pH of the purified liquid obtained was 6.8. The pH of the sericin aqueous solution obtained by adjusting the sericin powder to 1.0 mass% with distilled water was 4.9, and the weight-average molecular weight of the obtained sericin was 38,000 and the z-average molecular weight was 54,000. Sericin with a molecular weight of 45,000 or less accounted for 73.0 weight%, and sericin with a molecular weight of 50,000 or more accounted for 22.8 weight%. The serine content was 32.0%, the glycine content was 18.7%, and the alanine content was 5.0%.

[0044] Comparative Example 2 A purified liquid and sericin powder were obtained in the same manner as in Example 1, except that the conditions for sericin extraction were 0.21 MPa, 121°C under pressure and heating, and extraction time was 120 minutes. The pH of the purified liquid obtained was 6.8. The pH of the sericin aqueous solution obtained by adjusting the sericin powder to 1.0 mass% with distilled water was 5.0, and the weight-average molecular weight of the obtained sericin was 37,000 and the z-average molecular weight was 54,000. Sericin with a molecular weight of 45,000 or less accounted for 73.9% by weight, and sericin with a molecular weight of 50,000 or more accounted for 21.7% by weight. The serine content was 33.0%, the glycine content was 18.0%, and the alanine content was 4.0%.

[0045] Comparative Example 3 100 g of the washed and dried cocoons obtained in Example 1 were immersed in 2,000 g of a 0.2% by weight aqueous sodium hydroxide solution, and sericin was extracted under conditions of 0.10 MPa, 95°C, and pressure heating for 60 minutes. The obtained extract was filtered and purified using a filter membrane with a pore size of 0.2 μm to obtain a purified liquid. The obtained purified liquid had a pH of 11.5. The purified liquid was then freeze-dried to obtain a sericin powder. The powder was adjusted to 1.0% by weight with distilled water to obtain a sericin aqueous solution with a pH of 11.3. The weight-average molecular weight of this sericin was 10,000, and the z-average molecular weight was 45,000. Sericin with a molecular weight of 45,000 or less accounted for 95.7% by weight, and sericin with a molecular weight of 50,000 or more accounted for 0.5% by weight. The serine content was 27.8%, the glycine content was 20.5%, and the alanine content was 5.8%.

[0046] The extraction conditions, pH of the purified liquid, and the pH, molecular weight, and amino acid composition of the 1.0 mass% aqueous solution in which the sericin powder obtained by freeze-drying the purified liquid was redissolved in water in Examples 1 to 6 and Comparative Examples 1 to 3 are summarized in Table 1 below. [Table 1]

[0047] Evaluation of stability of sericin aqueous solution (part 1) The sericin compositions obtained in Example 5 and Comparative Example 3 were dissolved in 0.7% by mass phenoxyethanol water to prepare 5% by mass sericin aqueous solutions. The aqueous solutions were then adjusted to pH 4.0, pH 4.5, pH 4.9, pH 6.5, pH 7.5, pH 8.5, and pH 9.0 with sodium hydroxide aqueous solution or hydrochloric acid, and filtered through a filter membrane with a pore size of 0.2 μm to obtain evaluation samples. The evaluation samples were left in a thermostatic chamber at 50° C., and the color, turbidity, and odor of the samples were evaluated after 0 days, 30 days, 60 days, and 90 days.

[0048] (a) Color tone The color tone was measured at an absorbance of 400 nm, and the rate of change was calculated using the following formula. The closer the rate of change is to 1.0, the more stable the product is over time. Rate of change = absorbance after storage / absorbance after 0 days

[0049] (b) Turbidity The turbidity was measured at an absorbance of 600 nm, and the rate of change was calculated using the following formula. The closer the rate of change is to 1.0, the more stable it is over time. Rate of change = absorbance after storage / absorbance after 0 days

[0050] (c) Odor The odor immediately after preparation and the change in odor over time were evaluated by a panel of five people using the following sensory evaluation method.

[0051] Odor immediately after preparation The less unpleasant odors, insect odors, sulfur odors, and scouring odors that are specific to sericin protein hydrolysates, the better the product. Evaluation was made on a three-point scale of good (2 points), neutral (1 point), and poor (0 point), and the average score was calculated from the scores of five panelists. An average score of 0.5 points or more is considered to be good. (Evaluation Criteria) ○ (1.5 points or above): Good. △ (0.5 points or more and less than 1.5 points): Fairly good. × (less than 0.5 points): Poor.

[0052] Changes in odor over time Compared to the control (stored at 5℃), the samples were rated on a three-point scale: no change (2 points), slight change (1 point), and change (0 point), and the average score was calculated from the scores of the five panelists. A mean score of 1.5 points or higher indicates excellent stability over time. (Evaluation Criteria) ○ (1.5 points or more): No change over time. △ (0.5 points or more and less than 1.5 points): Some change over time. × (less than 0.5 points): Changes occurred over time.

[0053] The results are shown in Table 2 below. [Table 2]

[0054] The sericin aqueous solution of Example 5 had a good odor, with the unpleasant odor, insect odor, sulfur odor, and scouring odor specific to protein hydrolysates reduced. Furthermore, even when stored at 50°C for 30 days at pH 4.5 to pH 7.5, no changes in color tone, turbidity, or odor were observed, and the solution was stable over time. Even when stored at 50°C for 90 days, the solution was stable over time. However, when the pH was less than 4.5, the turbidity stability was poor. On the other hand, even when the pH was more than 7.5, no changes in color tone, turbidity, or odor were observed, and the solution was stable over time.

[0055] The sericin aqueous solution of Comparative Example 3 had an unpleasant odor (sulfur odor, insect odor) immediately after preparation, and was poor in odor. In addition, the color stability was poor at pH 4.5 to pH 7.5. The turbidity stability was stable at pH 7.5, but poor at pH 4.5 to 6.5.

[0056] Evaluation of stability of sericin aqueous solution (part 2) The sericins of Examples 1 to 6 and Comparative Examples 1 to 3 were dissolved in purified water to prepare 1% by mass aqueous sericin solutions. The aqueous solutions were adjusted to pH 6.7 to 7.2 with aqueous sodium hydroxide solution or hydrochloric acid. Phenoxyethanol was then added to a final concentration of 0.3% by mass, mixed, and filtered through a membrane filter with a pore size of 0.2 μm to obtain samples for evaluation. The samples for evaluation were left to stand in a thermostatic chamber at 50° C. The color, turbidity, and odor of the samples after 0 days and 30 days were evaluated according to the same criteria as in the evaluation of the stability of the aqueous sericin solution (part 1).

[0057] To evaluate fluidity, the "gelling" property was tested as follows. Each evaluation sample was left to stand in a low-temperature cabinet at 5°C for 24 hours and evaluated according to the following evaluation criteria. A score of △ or higher was considered satisfactory. (Evaluation Criteria) ◯: No gelation. Δ: Slight gelation occurs within the range where the material has fluidity, but no aggregates are formed. ×: Gelled (no fluidity).

[0058] The results are shown in Table 3 below. [Table 3]

[0059] The sericin aqueous solutions of Examples 1 to 6 had a good odor, with the unpleasant odor, insect odor, sulfur odor, and scouring odor specific to sericin protein hydrolysates being reduced, and were stable over time with no change in color, turbidity, or odor observed even after storage at 50°C for 30 days.

[0060] The sericin aqueous solutions of Comparative Examples 1 and 2 contained more than 20% by weight of sericin having a molecular weight of 50,000 or more, and had an unpleasant odor (insect odor) immediately after preparation, and were poor in odor. The sericin aqueous solution of Comparative Example 3 had an unpleasant odor (sulfur odor, insect odor, etc.) immediately after preparation, and was poor in odor. The turbidity stability was also poor.

Claims

1. The weight average molecular weight is 3,000 to 45,000, The z-average molecular weight is 6,000 to 65,000; Sericin having a molecular weight of 45,000 or less accounts for 70 to 100% by weight, and sericin having a molecular weight of 50,000 or more accounts for 0 to less than 15% by weight, A sericin composition having an amino acid composition with a serine content of 30 to 40%.

2. 2. The sericin composition according to claim 1, having a weight average molecular weight of 10,000 to 30,000 and a z-average molecular weight of 15,000 to 50,000.

3. 3. The sericin composition according to claim 1, wherein the color change rate is 1.0 to 1.

8.

4. 3. The sericin composition according to claim 1, wherein the turbidity change rate is 0.8 to 1.

5.

5. A cosmetic, food, textile processing agent, or pharmaceutical, comprising the sericin composition according to claim 1 or 2.

6. A method for producing the sericin composition according to claim 1, comprising the steps of: extracting sericin from the cocoons into an aqueous medium; The method is characterized in that the extraction is carried out under a pressure of 0.14 to 0.31 MPa and satisfies any one of the following conditions (1) to (3): (1) When the pressure is 0.14 MPa or more and less than 0.21 MPa, the temperature of the aqueous medium is set to 110 to less than 120° C., and extraction is performed for 360 to 600 minutes. (2) When the pressure is 0.21 MPa or more and less than 0.27 MPa, the temperature of the aqueous medium is set to 122 to less than 130° C., and extraction is performed for 120 to 600 minutes. (3) When the pressure is 0.27 MPa or more and 0.31 MPa or less, the temperature of the aqueous medium is set to 130 to 135° C., and extraction is performed for 60 to 600 minutes.

7. The method according to claim 6, wherein the aqueous medium is water.

8. A sericin composition obtained by the method according to claim 6 or 7.

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