Emulsifiers and oil-in-water emulsions

Abstract

This invention provides novel emulsifiers and oil-in-water emulsions using nanofibers. [Solution] The emulsifier according to the embodiment contains fibroin nanofibers. The oil-in-water emulsion according to the embodiment comprises an oil phase as a dispersed phase containing an oily component, and an aqueous phase as a dispersion medium containing water and fibroin nanofibers, wherein at least a portion of the fibroin nanofibers is adsorbed in the oil phase.

Description

Technical Field

[0001] The present invention relates to emulsifiers and oil-in-water emulsions.

Background Art

[0002] In various fields such as foods, cosmetics, pharmaceuticals, and paints, emulsifiers are used to obtain emulsions. An emulsifier is a chemical that stabilizes an emulsion by reducing the interfacial tension between oil and water, and various emulsifiers have been proposed.

[0003] Patent Document 1 discloses an emulsifying composition containing a polyhydric alcohol, an aqueous medium, biomass nanofibers, and an oil-soluble substance, and discloses that the biomass nanofibers are excellent in emulsifying ability, and specific examples thereof include cellulose nanofibers and silk nanofibers.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, Patent Document 1 describes that biomass nanofibers such as silk nanofibers can be used as emulsifiers. However, only the dispersion stability in an oil-in-water (O / W) emulsion containing a large amount of polyhydric alcohol has been evaluated, and fibroin nanofibers have not been disclosed.

[0006] Patent Document 2 discloses an additive for cosmetic compositions consisting of protein fibers containing an artificial structural protein, stating that the artificial structural protein is modified fibroin, and that the protein fibers are incorporated into an oil-in-water cosmetic composition. However, the protein fibers do not possess emulsifying properties, and fibroin nanofibers are not disclosed.

[0007] The present invention aims to provide novel emulsifiers and oil-in-water emulsions using nanofibers. [Means for solving the problem]

[0008] While diligently investigating the new possibilities of nanofibers, the inventors discovered that fibroin nanofibers possess emulsifying properties.

[0009] The present invention includes embodiments shown below. [1] An emulsifier containing fibroin nanofibers. [2] The emulsifier according to [1], wherein the number-average fiber diameter of the fibroin nanofibers is 10 nm or more and 500 nm or less. [3] The emulsifier according to [1] or [2], wherein the number average fiber length of the fibroin nanofibers is 5 μm or more and 150 μm or less.

[0010] [4] An oil-in-water emulsion comprising an oil phase as a dispersed phase containing an oily component, and an aqueous phase as a dispersion medium containing water and fibroin nanofibers, wherein at least a portion of the fibroin nanofibers is adsorbed in the oil phase. [5] The oil-in-water emulsion according to [4], wherein the content of the fibroin nanofibers is 0.1% by mass or more and 10% by mass or less based on 100% by mass of the aqueous phase. [6] The oil-in-water emulsion according to [4] or [5], wherein the volume ratio of the oil phase to the aqueous phase is 1 / 99 to 70 / 30. [Effects of the Invention]

[0011] According to embodiments of the present invention, novel emulsifiers and oil-in-water emulsions can be provided. [Brief explanation of the drawing]

[0012] [Figure 1] Fluorescence microscope image of an emulsion according to one embodiment. [Modes for carrying out the invention]

[0013] The emulsifier according to this embodiment contains fibroin nanofibers. Fibroin nanofibers are obtained by micronizing fibroin, a fibrous protein that is the main component of silk, to the nanoscale.

[0014] The number-average fiber diameter of the fibroin nanofibers is preferably 10 to 500 nm, more preferably 10 to 250 nm, more preferably 15 to 100 nm, and even more preferably 20 to 50 nm.

[0015] The number-average fiber length of the fibroin nanofibers is preferably 5 to 150 μm, more preferably 15 to 100 μm, more preferably 20 to 70 μm, and even more preferably 30 to 50 μm.

[0016] The average aspect ratio of fibroin nanofibers is not particularly limited and may be, for example, 50-5000, 100-3000, 500-2500, or 1000-2000.

[0017] The number-average fiber diameter, number-average fiber length, and average aspect ratio can be measured as follows:

[0018] That is, an aqueous dispersion of fibroin nanofibers with a solid content ratio of 0.05 to 0.1% by mass is prepared, and the aqueous dispersion is cast onto glass to obtain a sample for observation with a scanning electron microscope (SEM). The sample for observation may be vapor-deposited using, for example, gold, platinum, osmium, etc. Then, observation is performed by an electron microscope image at any one of magnifications of 5000 times, 10000 times, or 50000 times according to the size of the constituent fibers. At that time, an axis with an arbitrary image width in the vertical and horizontal directions is assumed in the obtained image, and the sample and observation conditions (magnification, etc.) are adjusted so that 20 or more fibers intersect with respect to that axis. After obtaining an observation image satisfying this condition, two random axes in the vertical and horizontal directions per image are drawn on this image, and the fiber diameters of the fibers intersecting with the axis are visually read. In this way, at least three non-overlapping images of the surface portion are taken with an electron microscope, and the values of the fiber diameters of the fibers intersecting with the two axes are read respectively (therefore, at least 20 × 2 × 3 = 120 pieces of fiber diameter information are obtained). The arithmetic mean of the fiber diameters obtained in this way is defined as the number average fiber diameter.

[0019] Also, the number average fiber length of the fibroin nanofibers is calculated from the same observation image. Specifically, the length from the start point to the end point of the fiber (fiber length) is visually read for at least 10 fibers. For branched fibers, the length of the longest part of the fiber is defined as the fiber length. The arithmetic mean of the fiber lengths obtained in this way is calculated and defined as the number average fiber length. Using these values, the average aspect ratio is calculated according to the following formula. Average aspect ratio = number average fiber length (nm) / number average fiber diameter (nm)

[0020] The fibroin nanofibers preferably have a silk II-type crystal structure (β-sheet structure), which is the crystal structure of natural fibroin fibers. Having the silk II-type crystal structure can be confirmed by measuring the spectrum in the infrared wavelength band using a Fourier transform infrared spectrometer (FTIR). Specifically, in the FTIR spectrum, a peak corresponding to the stretch mode of the bond between the C atom and the O atom is at 1623 cm -1Observed near a peak corresponding to the angular vibration of the bond between N atom and H atom at 1505 cm -1 Whether it is observed near can be confirmed by comparing with natural fibroin fibers.

[0021] The method for preparing fibroin nanofibers is not particularly limited. For example, sericin can be removed by heating cocoon or its pulverized product under alkaline conditions (scouring step), and fibroin nanofibers can be obtained by subjecting the obtained scoured cocoon (fibrous fibroin) to physical fiber drawing treatment.

[0022] The scouring step (sericin removal step) is not particularly limited. For example, it can be carried out by putting cocoon or its pulverized product into an alkaline aqueous solution with a pH of 9 to 12 and heating it at a temperature of 80 to 100 ° C under normal pressure for about 1 to 3 hours. As the alkaline aqueous solution, for example, an alkaline aqueous solution containing at least one selected from carbonates, alkali metal hydroxides, and phosphates as a solute may be used. Examples of carbonates include alkali metal carbonates such as sodium carbonate, sodium hydrogen carbonate, and potassium carbonate. Examples of alkali metal hydroxides include sodium hydroxide and potassium hydroxide. Examples of phosphates include alkali metal phosphates such as sodium phosphate (e.g., sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate), potassium phosphate (e.g., potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate), sodium pyrophosphate, potassium pyrophosphate, and sodium metaphosphate. After the scouring step, the obtained fibrous fibroin may be washed with hot water until the pH becomes neutral.

[0023] The method for physical fiber drawing treatment of fibrous fibroin is not particularly limited. For example, it can be carried out by treating an aqueous dispersion of fibrous fibroin using a homomixer, high-pressure homogenizer, ultrasonic disperser, beater, disk-type refiner, conical-type refiner, double-disk-type refiner, grinder, etc. under high-speed rotation, and an aqueous dispersion of fibroin nanofibers can be obtained.

[0024] The concentration of the fibroin aqueous dispersion during the material fiber treatment is not particularly limited; for example, it may be 0.1 to 10% by mass or 0.5 to 5% by mass. Furthermore, after the material fiber treatment, the fibroin nanofiber aqueous dispersion may be concentrated using an evaporator.

[0025] An emulsifier according to one embodiment is a liquid emulsifier containing a fibroin nanofiber aqueous dispersion obtained as described above. The fibroin nanofiber aqueous dispersion is a dispersion of fibroin nanofibers in water. The emulsifier according to this embodiment may also be a powdered emulsifier obtained by drying the fibroin nanofiber aqueous dispersion, but in the case of a powdered emulsifier, it is necessary to redisperse it in water during emulsion preparation, so a liquid emulsifier that does not require such redispersion is more preferable.

[0026] When the emulsifier is a liquid emulsifier containing a fibroin nanofiber aqueous dispersion, the concentration of fibroin nanofibers is not particularly limited, but is preferably 0.1 to 30% by mass, and more preferably 0.1 to 20% by mass.

[0027] In the case of a liquid emulsifier, the fibroin nanofiber aqueous dispersion contains water as the dispersion medium. However, the dispersion medium may consist of water alone, or it may contain water-soluble organic solvents such as ethanol, isopropyl alcohol, methanol, or other lower alcohols, to the extent that the effect is not impaired. When an organic solvent is included, the amount of water in 100% by mass of the dispersion medium is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The dispersion medium may also be an aqueous solution containing an acid, alkali, or their salts, as long as the effect is not impaired.

[0028] The emulsifier may consist solely of fibroin nanofibers. In the case of a liquid emulsifier, the emulsifier may consist solely of fibroin nanofibers and a dispersion medium. The emulsifier may also contain various water-soluble components such as polyhydric alcohols like propylene glycol and butylene glycol, sugars like monosaccharides and oligosaccharides, inorganic salts like NaCl, KCl, CaCl2, MgCl2, (NH4)2SO4, and Na2CO3, organic salts, preservatives, pH adjusters, and other additives.

[0029] The ratio of fibroin nanofibers to the total solid content of the emulsifier is not particularly limited, but the amount of fibroin nanofibers per 100% by mass of total solid content is preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and may also be 100% by mass.

[0030] Emulsifiers containing fibroin nanofibers have emulsifying ability for oily components and can be used to prepare oil-in-water (O / W) emulsions. An oil-in-water emulsion is a liquid obtained by emulsifying oily components using an emulsifier containing fibroin nanofibers, and is also called an emulsion. In this process, the fibroin nanofibers adsorb to the oil phase, that is, they adsorb to cover the surface of the oil droplets, thereby stabilizing the emulsified state of the oil-in-water emulsion. Therefore, the oil-in-water emulsion according to this embodiment comprises an oil phase as a dispersed phase containing oily components, and an aqueous phase as a dispersion medium containing water and fibroin nanofibers, with at least a portion of the fibroin nanofibers adsorbed to the oil phase.

[0031] Fibroin nanofibers possess emulsifying ability for various oily components, maintaining this emulsifying ability across a wide pH range and regardless of the presence or absence of salts, enabling the production of stable oil-in-water emulsions.

[0032] As oily components, various oily components (oils and / or waxes) used in fields such as food, cosmetics, pharmaceuticals, and paints can be used. Examples include hydrocarbon oils, higher alcohols, higher fatty acids, ester oils, silicone oils, vegetable oils, animal oils, and waxes. These can be used alone or in combination of two or more. In one embodiment, hydrophobic compounds that are liquid at room temperature (25°C) are preferred as oily components.

[0033] Examples of hydrocarbon oils include linear alkanes with 8 to 30 carbon atoms, α-olefin oligomers, squalane, squalene, limonene, ceresin, pristane, microcrystalline wax, liquid paraffin, petrolatum, and mineral oil.

[0034] Examples of higher alcohols include isostearyl alcohol, oleyl alcohol, octyldodecanol, chymyl alcohol, cholesterol, sitosterol, stearyl alcohol, cetanol, cetostearyl alcohol, cerakyl alcohol, decyltetradecanol, batyl alcohol, phytosterol, hexyldecanol, behenyl alcohol, lauryl alcohol, lanolin alcohol, hydrogenated lanolin alcohol, and octanol, all of which have 8 to 30 carbon atoms.

[0035] Examples of higher fatty acids include arachidonic acid, isostearic acid, undecylenic acid, oleic acid, stearic acid, palmitic acid, behenic acid, myristic acid, lauric acid, lanolinic acid, hard lanolinic acid, soft lanolinic acid, linoleic acid, and linolenic acid.

[0036] Examples of ester oils include fatty acid esters such as lanolin acetate, isocetyl isostearate, cholesteryl isostearate, octyldodecyl erucate, cetyl ethylhexanoate, cetostearyl ethylhexanoate, octyldodecyl oleate, decyl oleate, hexyldecyl dimethyloctanoate, isocetyl stearate, cholesteryl stearate, butyl stearate, isopropyl palmitate, isotridecyl myristate, isopropyl myristate, octyldodecyl myristate, myristyl myristate, hexyl laurate, isopropyl lanolinate, cholesteryl lanolinate, and methyl decanoate; hydroxy acid esters such as cetyl lactate, myristyl lactate, cholesterol hydroxystearate, and diisostearyl malate; triglycerides such as glyceryl trimyristate and caprylic / capric triglyceride; and methoxycinnamate esters such as ethylhexyl methoxycinnamate.

[0037] Examples of silicone oils include dimethyl silicone oil, methylphenyl silicone oil, methyl hydrogen silicone oil, or modified silicone oils thereof.

[0038] Examples of vegetable oils include avocado oil, almond oil, olive oil, kukui nut oil, grapeseed oil, sesame oil, wheat germ oil, rice germ oil, rice bran oil, safflower oil, shea butter, soybean oil, tea oil (tea seed oil, tea seed oil), evening primrose oil, camellia oil, corn germ oil, rapeseed oil, peach kernel oil, Job's tears oil, palm oil, palm kernel oil, castor oil, hydrogenated castor oil, sunflower oil, hazelnut oil, macadamia nut oil, meadowhome oil, cottonseed oil, Japanese wax, coconut oil, peanut oil, and rosehip oil.

[0039] Examples of animal fats include fish oil, beef tallow, turtle oil, mink oil, and egg yolk oil.

[0040] Examples of waxes include carnauba wax, whale wax, shellac, jojoba oil, beeswax, bleached beeswax, montan wax, lanolin, lanolin derivatives, reduced lanolin, hard lanolin, and adsorbed refined lanolin.

[0041] The oil phase may consist solely of oily components, or it may contain additives as optional components along with the oily components. The oil phase is preferably composed substantially of oily components, but is not particularly limited. However, it is preferable that the amount of oily components is 80% by mass or more, more preferably 90% by mass or more, and may even be 100% by mass, relative to 100% by mass of the oil phase.

[0042] The aqueous phase contains water and fibroin nanofibers. Of these, at least a portion of the fibroin nanofibers is adsorbed onto the oil phase (oily components) at the interface with the oil phase, thereby exhibiting emulsifying ability for the oily components. The fibroin nanofibers may all be adsorbed onto the oil phase, but usually a portion is adsorbed onto the oil phase for emulsification, and the remainder is dispersed in the aqueous phase.

[0043] In oil-in-water emulsions, the fibroin nanofiber content is preferably 0.1 to 10% by mass relative to 100% by mass of the aqueous phase. That is, the concentration of fibroin nanofibers in the aqueous phase (including adsorbed material at the interface with the oil phase) is preferably 0.1 to 10% by mass, more preferably 0.3 to 8% by mass, and even more preferably 0.4 to 5% by mass.

[0044] The aqueous phase may contain water and fibroin nanofibers, as well as various water-soluble components such as water-soluble organic solvents, polyhydric alcohols, sugars, inorganic salts, and organic salts, and additives such as preservatives and pH adjusters, which can be added to the emulsifier. The water content in the aqueous phase is not particularly limited, but is preferably 80% by mass or more, and more preferably 90% by mass or more, relative to 100% by mass of the aqueous phase.

[0045] In an oil-in-water emulsion, the volume ratio of the oil phase to the aqueous phase (oil phase / aqueous phase) is preferably 1 / 99 to 70 / 30, and more preferably 5 / 95 to 50 / 50.

[0046] The content of oily components in the oil-in-water emulsion is not particularly limited and may be, for example, 0.5 to 70% by mass, 1 to 60% by mass, or 5 to 50% by mass. The content of fibroin nanofibers in the oil-in-water emulsion is not particularly limited and may be, for example, 0.05 to 5% by mass or 0.1 to 2% by mass.

[0047] The method for preparing oil-in-water emulsions is not particularly limited and can be prepared according to conventional methods. For example, it can be prepared by mixing an aqueous dispersion of fibroin nanofibers with an oily component, adding dilution water as needed, and stirring using a disperser such as an ultrasonic homogenizer.

[0048] The emulsifier according to this embodiment can be used to prepare oil-in-water emulsions in a wide range of applications, such as food and cosmetics. Here, food includes beverages. For example, a food according to one embodiment contains the oil-in-water emulsion and therefore contains an oily component, fibroin nanofibers, and water, with at least a portion of the fibroin nanofibers adsorbed onto the oily component. Similarly, a cosmetic according to one embodiment contains the oil-in-water emulsion and therefore contains an oily component, fibroin nanofibers, and water, with at least a portion of the fibroin nanofibers adsorbed onto the oily component. These food and cosmetic products may contain other components in addition to the oil-in-water emulsion, depending on their respective applications.

[0049] In detail, for example, an oil-in-water emulsion may be prepared by using the above-mentioned fibroin nanofiber aqueous dispersion as an emulsifier to emulsify oily components, and food or cosmetics may be prepared using this oil-in-water emulsion. Alternatively, food or cosmetics may be prepared by mixing the oil-in-water emulsion with other components and drying the mixture by heating or other means.

[0050] Specific examples of food products according to one embodiment include lactic acid bacteria beverages, yogurt, acidic milk beverages, sports drinks, ion drinks for infants, functional drinks, jelly drinks, calorie-consuming drinks, dessert drinks, baby food, jams, dressings, mayonnaise, ketchup, Worcestershire sauce, barbecue sauce, yakiniku sauce, various edible sauces, soups, jelly-like seasonings, and the like.

[0051] Specific examples of cosmetics according to one embodiment include lotions, emulsions, creams, foundations, eyeshadows, sunscreens, shampoos, rinses, hair conditioners, rinse-in shampoos, hair styling products, hair treatments, hair dyes, hair growth products, hair tonics, and the like. [Examples]

[0052] The present invention will be described in more detail below with reference to examples, but it is not limited to these.

[0053] [Manufacturing Example 1: Preparation of fibroin nanofibers] 100g of coarsely ground cocoons (manufactured by Nagasuna Cocoon Co., Ltd.) were added to 1L of distilled water and ground for 3 minutes using a mixer (Osaka Chemical Co., Ltd., Hi-Power Blender MX-1200XT / XTS), after which the water was removed by suction filtration. The ground cocoons were added to 1L of 0.9% by mass sodium carbonate aqueous solution and heated at 90°C for 1 hour. After that, the mixture was washed with hot water until the pH became neutral to obtain refined cocoons. Pure water was added to this to obtain a 1% by mass fibrous aqueous dispersion. The fibrous aqueous dispersion was processed four times at 1500 rpm using a millstone-type grinder (Masuko Sangyo Co., Ltd., Masukoroider MKCA6-3). The aqueous dispersion after processing was concentrated using an evaporator to obtain a 10% by mass fibroin nanofiber aqueous dispersion.

[0054] The pH of the obtained fibroin nanofiber aqueous dispersion was 7.0. Furthermore, when the spectrum in the infrared wavelength band was measured using a Fourier transform infrared spectrophotometer (FTIR) for the fibroin nanofibers, the FTIR spectrum showed a value of 1623 cm⁻¹. -1 and 1505cm -1 A peak was observed at a specific location in the spectrum, which is characteristic of the β-sheet structure found in natural fibroin crystals, indicating that the β-sheet structure is maintained.

[0055] [Manufacturing Example 2: Preparation of fibroin nanofibers] 100g of coarsely ground cocoons (manufactured by Nagasuna Cocoon Co., Ltd.) were added to 1L of distilled water and ground for 3 minutes using a mixer (Osaka Chemical Co., Ltd., Hi-Power Blender MX-1200XT / XTS), after which the water was removed by suction filtration. The ground cocoons were added to 1L of 0.9% by mass sodium carbonate aqueous solution and heated at 90°C for 1 hour. After that, the mixture was washed with hot water until the pH became neutral to obtain refined cocoons. Pure water was added to this to obtain a 1% by mass fibrous aqueous dispersion. The fibrous aqueous dispersion was processed twice at 1500 rpm using a millstone-type grinder (Masuko Sangyo Co., Ltd., Masukoroider MKCA6-3). The aqueous dispersion after processing was concentrated using an evaporator to obtain a 10% by mass fibroin nanofiber aqueous dispersion.

[0056] [Manufacturing Example 3: Preparation of fibroin nanofibers] 100g of coarsely ground cocoons (manufactured by Nagasuna Cocoon Co., Ltd.) were added to 1L of distilled water and ground for 3 minutes using a mixer (manufactured by Osaka Chemical Co., Ltd., Hi-Power Blender MX-1200XT / XTS), after which the water was removed by suction filtration. The ground cocoons were added to 1L of 0.9% by mass sodium carbonate aqueous solution and heated at 90°C for 1 hour. After that, the mixture was washed with hot water until the pH became neutral to obtain refined cocoons. Pure water was added to this to obtain a 1% by mass fibrous aqueous dispersion. The fibrous aqueous dispersion was processed 6 times at 1200 rpm using a millstone-type grinder (manufactured by Masuko Sangyo Co., Ltd., Masukoroider MKCA6-3). The aqueous dispersion after processing was concentrated using an evaporator to obtain a 10% by mass fibroin nanofiber aqueous dispersion.

[0057] [Manufacturing Example 4: Preparation of fibroin microfibers] 100g of coarsely ground cocoons (manufactured by Nagasuna Cocoon Co., Ltd.) were added to 1L of distilled water and ground for 3 minutes using a mixer (Osaka Chemical Co., Ltd., Hi-Power Blender MX-1200XT / XTS), after which the water was removed by suction filtration. The ground cocoons were added to 1L of 0.9% by mass sodium carbonate aqueous solution and heated at 90°C for 1 hour. After that, the mixture was washed with hot water until the pH became neutral to obtain refined cocoons. Pure water was added to this to obtain a 10% by mass fibroin microfiber aqueous dispersion. The pH of the obtained fibroin microfiber aqueous dispersion was 7.0.

[0058] [Manufacturing Example 5: Preparation of Silk Nanofibers] 100 g of silk cocoon powder was added to 1 L of an aqueous solution adjusted to pH 11.0 with a mixture of sodium carbonate and sodium bicarbonate. The solution was then treated 10 times using a water jet treatment device (Starburst, manufactured by Sugino Machine Co., Ltd.) at 245 MPa and 700 m / s. The resulting aqueous dispersion of silk nanofibers had a pH of 11.0.

[0059] The number-average fiber diameter, number-average fiber length, and average aspect ratio were measured for the aqueous dispersions obtained in Production Examples 1-5. The measurement method is as follows. The results are shown in Table 1 below.

[0060] A scanning electron microscope (SEM) (JEOL, JSM-7500F) was used for the measurements. The samples were observed after deposition with osmium, and the number-average fiber diameter was calculated according to the method described above. Similarly, the number-average fiber length was calculated from the observed images according to the method described above. Then, using these number-average fiber diameter and number-average fiber length values, the average aspect ratio was calculated according to the formula described above.

[0061] [Table 1]

[0062] [Example 1] Using the fibroin nanofiber aqueous dispersion prepared in Production Example 1 as an emulsifier, pure water was added to the aqueous dispersion to adjust the solid content concentration to 0.1% by mass. A 0.1M aqueous sodium hydroxide solution or 0.1M hydrochloric acid was then added to prepare aqueous dispersions with pH levels of 7.0, 2.0, or 10.0. Furthermore, the aqueous dispersion with a pH of 7.0 was divided into two portions, and sodium chloride was added to one of them to obtain a NaCl-added fibroin nanofiber aqueous dispersion with a salt concentration of 0.1 mol / L.

[0063] To the four types of fibroin nanofiber aqueous dispersions obtained in this manner, n-hexadecane or n-octanol was added as the oil to be emulsified, in a volume ratio of oil to aqueous dispersion (= oil phase / aqueous phase) of 10 / 90. This was then processed six times using an ultrasonic homogenizer (Sonics & Materials, Inc., VCX-500) at 750kW, 20Hz, 90% output, with 10 seconds of irradiation / 10 seconds of pause, to prepare an oil-in-water emulsion.

[0064] Furthermore, to a fibroin nanofiber aqueous dispersion with a pH of 7.0 and no sodium chloride added, ethylhexyl methoxycinnamate, dimethyl silicone oil, or olive oil was added as the oil to be emulsified, in a volume ratio of oil to aqueous dispersion (= oil phase / aqueous phase) of 10 / 90. This was then processed six times using an ultrasonic homogenizer (Sonics & Materials, Inc., VCX-500) at 750kW, 20Hz, 90% output, with 10 seconds irradiation / 10 seconds pause, to prepare an oil-in-water emulsion.

[0065] For each emulsion, the emulsifying power of fibroin nanofibers, which act as an emulsifier, was evaluated under the following conditions. A: A uniform emulsion can be obtained. B: Some oil separation and aggregates are observed. C: Emulsion cannot be obtained.

[0066] [Examples 2-11] Except for changing the type of emulsifier, the concentration of fibroin nanofibers in the fibroin nanofiber aqueous dispersion used for emulsification (fiber concentration in the aqueous phase), and the volume ratio of the oil phase / aqueous phase as shown in Tables 2 and 3, an oil-in-water emulsion was prepared in the same manner as in Example 1, and the emulsifying power was evaluated.

[0067] [Comparative Examples 1-3] Except for changing the type of emulsifier as shown in Table 3, an oil-in-water emulsion was prepared in the same manner as in Example 2, and its emulsifying power was evaluated.

[0068] In Table 3, "CNF" in Comparative Example 3 refers to cellulose nanofiber (Reocrysta I-2SX, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0069] [Table 2]

[0070] [Table 3]

[0071] The results are shown in Tables 2 and 3. In Comparative Example 1, which used fibroin microfibers as an emulsifier, the emulsifying power was inferior regardless of pH. This is thought to be because the microfibers have a large fiber diameter and therefore could not adsorb to the oil droplets.

[0072] In Comparative Example 2, which used silk nanofibers as an emulsifier, the emulsifying power was excellent under alkaline conditions with a pH of 10.0, but poor under acidic conditions with a pH of 2.0. In Comparative Example 3, which used cellulose nanofibers as an emulsifier, the emulsifying power was excellent under neutral to alkaline conditions for low-polarity hexadecane, but poor under acidic conditions, and poor for high-polarity octanol regardless of pH. In Comparative Example 3, the emulsifying power was also excellent for olive oil, but poor for ethylhexyl methoxycinnamate and dimethyl silicone oil.

[0073] In contrast, Examples 1-11, which used fibroin nanofibers as an emulsifier, demonstrated emulsifying power not only for the low-polarity hexadecane but also for the highly-polarity octanol, regardless of pH or the presence or absence of salt. Examples 1-11 also demonstrated emulsifying power for ethylhexyl methoxycinnamate, dimethyl silicone oil, and olive oil.

[0074] [Observation of dispersion state using a microscope] In Example 2, n-octanol was used as the oil to be emulsified, and an oil-in-water emulsion was emulsified in a fibroin nanofiber aqueous dispersion adjusted to pH 7.0 and salt concentration 0.0 mol / L. This emulsion was then observed using a fluorescence microscope.

[0075] In detail, a droplet of oil-in-water emulsion was placed on a clean glass slide, and one drop of chalcoflorine white stain (Sigma-Aldrich, Calcofluor White M2R, 1 g / L; Evans blue 0.5 g / L) and one drop of 10% by mass KOH (50 mL of distilled water with KOH (Wako Pure Chemical Industries, Fujifilm Special Grade) added) were added. A coverslip was then placed over the sample and left for 1 minute. After that, the sample was observed using a fluorescence microscope (Raymar Corporation, inverted biological microscope SXJ-5800TPHL and reflected fluorescence unit SXJ FC2).

[0076] The observed image is shown in Figure 1, where a layer of blue-stained fibroin nanofibers is formed around the oil phase, enveloping it and confirming that the fibroin nanofibers are adsorbed onto the oil phase.

[0077] Furthermore, the various numerical ranges described in this specification can be any combination of their upper and lower limits, and all such combinations are described herein as preferred numerical ranges. Also, the description of a numerical range as "X~Y" means X or greater and Y or less.

[0078] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, and modifications are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

Claims

1. An emulsifier containing fibroin nanofibers.

2. The emulsifier according to claim 1, wherein the number-average fiber diameter of the fibroin nanofibers is 10 nm or more and 500 nm or less.

3. The emulsifier according to claim 1 or 2, wherein the number-average fiber length of the fibroin nanofibers is 5 μm or more and 150 μm or less.

4. An oil-in-water emulsion comprising an oil phase as a dispersed phase containing an oily component, and an aqueous phase as a dispersion medium containing water and fibroin nanofibers, wherein at least a portion of the fibroin nanofibers is adsorbed in the oil phase.

5. The oil-in-water emulsion according to claim 4, wherein the content of the fibroin nanofibers is 0.1% by mass or more and 10% by mass or less based on 100% by mass of the aqueous phase.

6. The oil-in-water emulsion according to claim 4 or 5, wherein the volume ratio of the oil phase to the aqueous phase is 1 / 99 to 70 / 30.

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