Egg white protein-based slow-release colloidal sulfur microcapsule and low-cost green preparation method thereof

Abstract

The invention relates to an egg white protein-based slow-release colloidal sulfur microcapsule and a low-cost green preparation method thereof, and belongs to the technical field of functional cosmetic raw materials. The core of the invention is that commercially available egg white protein powder and sodium thiosulfate pentahydrate are utilized, the egg white protein powder forms a three-dimensional network structure through synchronous denaturation under an acidic condition, colloidal sulfur particles generated in situ are uniformly wrapped and fixed in the three-dimensional network structure, and then the microcapsule is constructed. The average particle size of the microcapsule is 200-400nm, the sulfur loading capacity is as high as 60-80wt%, the absolute value of Zeta potential is more than or equal to 30mV, the stability is excellent, and the agglomeration rate is less than or equal to 5% after the microcapsule is stored at room temperature for 6 months. The whole preparation process is carried out under mild conditions, no organic solvent, chemical cross-linking agent or complex equipment is needed, the cost is low, and the process is green and easy to amplify. The obtained product is good in biocompatibility and low in irritation, has a long-acting slow-release characteristic, is particularly suitable for oil-control, anti-acne and sensitive skin care cosmetics, and has remarkable practical value and market prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cosmetic functional raw material preparation, in particular to an egg white protein-based sustained-release colloidal sulfur microcapsule and a low-cost green preparation method thereof. BACKGROUND

[0002] Colloidal sulfur has a large specific surface area and high chemical activity, and has shown significant application potential in the fields of medicine, daily chemicals, agriculture, etc. In the medical field, it can be used as an antibacterial ingredient for the prevention and treatment of skin infections. In the daily chemical field, it can help improve the balance of the bacterial flora of oily skin. In the agricultural field, it can be used as a low-toxicity fungicide to prevent and control crop fungal diseases. Compared with traditional bulk sulfur or sulfur powder, it is more easily absorbed and utilized by organisms, and has higher efficiency, becoming a functional ingredient of interest in multiple fields.

[0003] However, the existing colloidal sulfur preparation technology has three major core pain points, which seriously limits its large-scale application and performance: (1) Poor carrier dispersibility: The colloidal sulfur particles prepared by traditional in-situ generation method (such as acidified sodium thiosulfate method) are prone to agglomeration. In order to improve the dispersibility, additional materials such as gum arabic and xanthan gum are used for post-processing wrapping. This post-processing process is complex and difficult to ensure uniform dispersion of colloidal sulfur particles in the carrier, ultimately leading to unstable product performance; (2) Contradiction between irritation and cost: In order to reduce the irritation of colloidal sulfur, some technologies choose carriers with good biocompatibility (such as collagen), but the cost of such raw materials is extremely high, making it difficult to meet the cost requirements of large-scale production; if low-cost carriers are chosen, the irritation problem of colloidal sulfur cannot be effectively solved, forming a dilemma of "low irritation" and "low cost" that cannot be reconciled; (3) Insufficient process synergy: The commonly used carriers (such as gelatin and sodium alginate) and the "in-situ generation + freeze-drying" process have poor compatibility. On the one hand, some carriers cannot be wrapped synchronously during the in-situ generation of colloidal sulfur, and additional wrapping steps are required; on the other hand, even if the wrapping is completed, the structure of the carrier is easily damaged during the subsequent freeze-drying process, leading to secondary agglomeration of colloidal sulfur particles and unable to guarantee the long-term stability of the product.

[0004] Through retrieval, existing patents (such as CN105742587B, CN11854821B) mainly focus on synthetic polymers, traditional plant gums or high-priced biocompatible carriers. Their technical solutions do not solve the above-mentioned "poor dispersibility, contradiction between irritation and cost, and insufficient process compatibility" problems. Therefore, a more optimal technical solution is needed to break through the existing bottlenecks and meet the high-performance and low-cost requirements of colloidal sulfur products in the fields of medicine, daily chemicals, etc. SUMMARY

[0005] The application provides an egg white protein-based sustained-release colloidal sulfur microcapsule and a low-cost green preparation method thereof, which integrates in-situ generation of sulfur particles and wrapping of egg white protein by using the synchronous denaturation-wrapping characteristics of egg white protein under acidic conditions, and realizes preparation of high-dispersion, low-irritation and long-acting and stable colloidal sulfur microcapsules by combining with freeze drying. The application aims to solve the problems of existing colloidal sulfur, such as easy agglomeration, poor stability during storage and application, and insufficient biocompatibility to easily cause irritation, and the problems of high cost and dependence on complex equipment or chemical reagents for preparation. The colloidal sulfur is modified by egg white protein wrapping to improve the core performance, simplify the process, reduce the cost, and meet the application requirements in the fields of medicine, daily chemicals, agriculture and the like.

[0006] In order to achieve the above-mentioned purpose, the application adopts the following specific scheme: In a first aspect, the application provides an egg white protein-based sustained-release colloidal sulfur microcapsule, which is a complex structure formed by synchronous occurrence of the denaturation process of egg white protein and the in-situ generation process of colloidal sulfur. In the denaturation process, the egg white protein forms a three-dimensional network structure and wraps and fixes the simultaneously generated colloidal sulfur particles. The average particle size of the obtained colloidal sulfur microcapsule is 200-400 nm, and the sulfur loading is 60wt%-80wt%.

[0007] Further, the absolute value of the Zeta potential of the obtained colloidal sulfur microcapsule in a pure water dispersion at 25 DEG C and pH 7.0 is greater than or equal to 30 mV, and the agglomeration rate is less than or equal to 5% after storage at room temperature for 6 months.

[0008] Further, the egg white protein powder is a food-grade egg white protein powder prepared by a spray drying process, and the protein content is greater than or equal to 80wt%.

[0009] In a second aspect, the application provides a low-cost preparation method of the above-mentioned low-cost egg white protein-based sustained-release colloidal sulfur microcapsule, which comprises the following steps: (1) Preparation of an egg white protein solution: egg white protein powder is taken and dissolved in an acetic acid-sodium acetate buffer solution with pH 4.0-4.8, and stirred uniformly at 25-30 DEG C to obtain an egg white protein solution with a mass concentration of 5%-10%; (2) In-situ generation-synchronous denaturation wrapping: sodium thiosulfate pentahydrate is added to the egg white protein solution obtained in step (1), and stirred to completely dissolve the sodium thiosulfate pentahydrate; then hydrochloric acid is slowly added to adjust the pH of the system to 2.2-2.8, the temperature of the system is increased to 45-60 DEG C, and the system is kept at constant temperature for 10-30 min, so that the colloidal sulfur is generated in-situ and wrapped by the three-dimensional network structure formed by the denaturation of the egg white protein, and a complex colloid is formed; (3) Freeze-drying shaping: after the composite colloidal obtained in step (2) is separated and washed, the solid is first pre-frozen at-50℃ to-70℃ for 2 to 4 hours, and then the pre-frozen solid is dried under the conditions of a vacuum degree of 0.12 to 0.18 mbar and a sublimation temperature of-12℃ to-8℃ for 10 to 20 hours, and finally a porous sponge-like egg white protein-based slow-release colloidal sulfur microcapsule is obtained.

[0010] Further, in step (2), the sodium thiosulfate pentahydrate is added according to a mass ratio of egg white protein powder to sodium thiosulfate pentahydrate of 1:(2.5-8).

[0011] Further, in step (2), the hydrochloric acid solution with a concentration of 0.5 mol / L is slowly added at a rate of 0.5-1 mL / min, so as to control the pH value of the system.

[0012] The preparation process of the application comprises the following principles: (1) In-situ generation and synchronous wrapping: under acidic conditions (pH 2.2-2.8), sodium thiosulfate pentahydrate reacts with hydrochloric acid to generate colloidal sulfur (in-situ generation process); at the same time, the acidic environment can trigger the denaturation of egg white protein, and the denatured egg white protein molecules rearrange to form a three-dimensional network structure, which can immediately wrap the small particle size colloidal sulfur particles generated inside the network structure, avoid the agglomeration of colloidal sulfur particles due to high surface energy, and realize the synergistic effect of "generation and wrapping".

[0013] (2) Stability improvement: on the one hand, the three-dimensional network structure of egg white protein provides a stable "protective shell" for colloidal sulfur particles, reduces direct contact between particles, and reduces the risk of agglomeration; on the other hand, the freeze-drying process preserves the porous structure of the microcapsule, which not only reduces the oxidation loss of colloidal sulfur during storage (loss rate is only 2.5% after 30 days of accelerated aging at 40℃), but also prolongs the release time of colloidal sulfur (half-life period is 50h) through the "slow-release effect" of the pores.

[0014] (3) Low irritation: egg white protein is a natural protein, there is no risk of chemical reagent residue, and its molecular structure has good biocompatibility with human skin, and the rabbit ear skin irritation test shows that the erythema index is reduced by 15% compared with colloidal sulfur wrapped with collagen, which can effectively reduce the irritation of colloidal sulfur to the skin and is suitable for sensitive skin care products.

[0015] The innovation of the application lies in: (1) Raw material and coating mechanism innovation: breaking through the traditional modification mode of colloidal sulfur which relies on chemical reagents, natural egg white protein is selected as the coating material, and the specific interaction between protein and colloidal sulfur is used to realize the wrapping, which not only improves the biocompatibility and reduces the irritation, but also avoids the risk of chemical residue, which meets the safety needs of the medical and daily chemical fields.

[0016] (2) Structure and performance collaborative innovation: By egg white protein wrapping to build a complex system, inhibit the agglomeration of colloidal sulfur particles from the structure level, significantly improve its storage and application stability, while retaining the activity of colloidal sulfur, solve the "activity retention" and "stability improvement" difficult to balance the pain points.

[0017] (3) Preparation process innovation: Abandon the existing process of high pressure, high temperature equipment or complex reagent, using mild reaction conditions and simple operation process, while ensuring product performance, reduce production energy consumption and cost, more easily realize large-scale production, break the industrialization bottleneck.

[0018] Beneficial effects Compared with the existing colloidal sulfur preparation technology, the present application realizes the advantages in many aspects through the three-dimensional coordination of "material-process-performance", as follows: (1) Dispersion breakthrough: Selecting commercially available egg white protein powder (no need for purification), its three-dimensional network structure formed under acidic conditions can uniformly fix the in-situ generated colloidal sulfur particles, and the finished product microcapsule particle size is concentrated in 200-400 nm (laser particle size instrument detection). After rehydration, the dispersion uniformity is improved by more than 50% compared with traditional gum arabic wrapping process, and there is no obvious agglomeration phenomenon, which solves the core pain point of poor dispersion of traditional colloidal sulfur.

[0019] (2) Low irritation and low cost balance: Egg white protein is a natural source material, non-allergic, and no chemical residue risk, rabbit ear skin irritation test shows that its erythema index is reduced by 15% compared with colloidal sulfur wrapped with collagen protein, which effectively reduces skin irritation; At the same time, the raw material cost of egg white protein is only 1 / 4 of that of collagen protein, which perfectly balances the "low irritation" and "low cost" demand, and is suitable for large-scale production.

[0020] (3) Stability and release optimization: Using-50℃~-70℃ pre-freezing and vacuum freeze-drying process, the porous structure of microcapsule is retained, which can significantly reduce the oxidation loss of colloidal sulfur during storage. After 30 days of accelerated aging at 40℃, the sulfur content loss rate is only 2.5% (while the loss rate of traditional spray drying process is as high as 18%); In vitro release experiment shows that the release half-life of sulfur in microcapsule is 50h, which is significantly longer than that of ordinary colloidal sulfur (12h), which can realize long-acting acne and oil control effect, and meet the demand of skin care products for long-acting functional ingredients.

[0021] (3) Strong process compatibility: The whole preparation process does not need organic solvent, chemical crosslinking agent or special equipment such as high pressure and high temperature, and the existing cosmetic raw material production line can be adapted after simple adjustment, the industrialization threshold is low, and it is easy to realize large-scale production, which breaks the industrialization bottleneck of existing colloidal sulfur preparation technology.

[0022] (4) wide application range: the obtained microcapsules have sulfur loading of 60-80wt%, the agglomeration rate is less than or equal to 5% after 6 months of storage at room temperature, and the microcapsules have good biocompatibility and low irritation, and can be widely applied in acne-removing, oil-controlling cosmetics and sensitive skin care products, and also have potential application value in the fields of medicine (skin infection prevention and treatment) and agriculture (low-toxicity fungicide), and have strong practicability and broad market promotion prospect. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A structure diagram of the prepared colloidal sulfur microcapsules.

[0024] Figure 2 A scanning electron microscope picture of the colloidal sulfur microcapsules prepared in Example 2 of the present application.

[0025] Figure 3 A scanning electron microscope picture of the product prepared in Comparative Example 1 of the present application.

[0026] Figure 4 An elemental analysis picture of the colloidal sulfur microcapsules prepared in Example 1 of the present application.

[0027] Figure 5 An elemental analysis picture of the product prepared in Comparative Example 1 of the present application.

[0028] Figure 6 An infrared spectrum of the colloidal sulfur microcapsules prepared in Example 1 of the present application and Comparative Example 1.

[0029] Figure 7 A dispersion picture of the colloidal sulfur microcapsules prepared in Examples 1-3 of the present application. DETAILED DESCRIPTION

[0030] The technical solutions of the present application will be described clearly and completely in combination with specific embodiments, and obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0031] In one aspect, the present application provides an egg white protein-based sustained-release colloidal sulfur microcapsule, please refer to Figure 1, including wall material (egg white protein denatured to form a three-dimensional network structure under acidic conditions) and core material (colloidal sulfur particles generated in situ and uniformly fixed in the three-dimensional network structure). Specifically, the microcapsules are complex structures formed by the denaturation process of egg white protein and the in-situ generation process of colloidal sulfur occurring simultaneously; wherein the egg white protein forms a three-dimensional network structure during the deformation process and coats and fixes the simultaneously generated colloidal sulfur particles; the average particle size of the obtained colloidal sulfur microcapsules is 200-400 nm, the sulfur loading is 60wt%-80wt%, the absolute value of Zeta potential in a 25℃, pH 7.0 pure water dispersion is ≥30mV, and the agglomeration rate is ≤5% after 6 months of room temperature storage.

[0032] Among them, the egg white protein powder is directly used as a commercially available egg white protein powder (spray-dried food grade, protein content ≥80wt%), without further purification.

[0033] On the other hand, the present application provides a low-cost preparation method of egg white protein-based slow-release colloidal sulfur microcapsules, which will be described in detail below.

[0034] Step (1), preparation of egg white protein solution Take commercially available egg white protein powder and dissolve it in a pH 4.0-4.8 acetic acid-sodium acetate buffer, stir at a speed of 300-500 rpm at 25-30℃ for 20-30 min to obtain an egg white protein solution with a mass concentration of 5%-10%.

[0035] The role of this step is: first, the mild temperature of 25-30℃ and the stirring speed of 300-500 rpm can avoid premature denaturation and clumping of the protein due to high temperature, while ensuring that the egg white protein is completely dissolved in the acetic acid-sodium acetate buffer to form a uniform protein solution, laying a uniform system foundation for subsequent synchronous encapsulation of colloidal sulfur. Second, the mass concentration of the egg white protein solution is limited to 5%-10%, which is very critical, as it is the basis for ensuring the formation of a three-dimensional network structure and uniform fixation of colloidal sulfur. If the concentration is too low, the number of protein molecules is insufficient, and it is difficult to form a complete and effective three-dimensional network encapsulation structure to fix the colloidal sulfur particles; if the concentration is too high, the solution will become viscous, leading to system clumping and affecting the subsequent reaction. Third, the pH of the acetic acid-sodium acetate buffer is 4.0-4.8, which can maintain the initial pH of the system stable, avoid premature denaturation of the protein due to environmental pH fluctuations, and provide a smooth pH adjustment basis for subsequent pH adjustment to the denaturation critical point of egg white protein by adding hydrochloric acid.

[0036] Step (2), in-situ generation-synchronous denaturation encapsulation To the egg white protein solution obtained in step (1), sodium thiosulfate pentahydrate is added (mass ratio of egg white protein powder to sodium thiosulfate pentahydrate anhydride is 1: (2.5-8)), stirring at 300-500 rpm for 10-15 min to ensure complete dissolution of sodium thiosulfate pentahydrate; then 0.5 mol / L hydrochloric acid solution is slowly added at a rate of 0.5-1 mL / min, and the pH of the system is controlled to 2.2-2.8; the temperature of the system is raised to 45-60°C, and the reaction is carried out at this temperature for 10-30 min to generate "egg white protein-sulfur" composite colloids. In this process, the reticular structure formed by denaturation of egg white protein can "lock" the in-situ generated colloidal sulfur particles, effectively preventing particle agglomeration.

[0037] The purpose of this step is: first, stirring at 300-500 rpm for 10-15 min can ensure complete dissolution of sodium thiosulfate pentahydrate and thorough mixing with the egg white protein solution, avoiding local over-concentration of sodium thiosulfate pentahydrate, which in turn leads to uneven generation rate of colloidal sulfur when reacting with hydrochloric acid in the subsequent step. Second, slowly adding hydrochloric acid at a rate of 0.5-1 mL / min can accurately control the amount of hydrochloric acid added, allowing the pH of the system to be smoothly reduced to 2.2-2.8. This pH is both a suitable condition for the reaction of sodium thiosulfate pentahydrate with hydrochloric acid to generate colloidal sulfur and a critical point for denaturation of egg white protein, which can trigger the re-folding of egg white protein molecules to form a three-dimensional reticular structure, achieving the simultaneous effect of "colloidal sulfur generation being immediately encapsulated by protein". This effectively inhibits the agglomeration of colloidal sulfur from the source. Third, constant temperature reaction enhances the encapsulation effect and the stability of colloidal sulfur: constant temperature conditions of 45-60°C can accelerate the denaturation of egg white protein to form a stable reticular structure, ensuring that colloidal sulfur particles are firmly "locked" inside the structure; at the same time, this temperature can promote the complete reaction of sodium thiosulfate pentahydrate with hydrochloric acid, reducing the residual unreacted raw materials and improving the purity and stability of colloidal sulfur. A reaction time of 10-30 min can balance the reaction efficiency and product quality, avoiding incomplete reaction due to too short a reaction time or excessive protein structure contraction affecting subsequent dispersibility due to too long a reaction time.

[0038] Step (3), freeze-drying and shaping The egg white protein-sulfur composite colloids obtained in step (2) are separated and washed, and the solid is then placed in an environment of -50°C to -70°C for pre-freezing for 2-4 h (low-temperature rapid freezing can maximize the preservation of the porous structure of egg white protein, laying a foundation for subsequent sustained-release performance); then the pre-frozen solid is transferred to a freeze-drying machine and dried under the conditions of vacuum degree 0.12-0.18 mbar and sublimation temperature -12°C to -8°C for 10-20 h, finally obtaining porous sponge-like egg white protein-based sustained-release colloidal sulfur microcapsule powder.

[0039] The step has the following effects: firstly, low-temperature rapid pre-freezing at-50℃ to-70℃ can freeze the water in the solid to form fine ice crystals, avoiding the destruction of the network structure of egg white protein caused by slow ice crystal growth; meanwhile, rapid freezing can fix the position of colloidal sulfur particles in the protein structure, preventing migration and agglomeration of the colloidal sulfur particles in the subsequent drying process due to water loss. Secondly, vacuum freeze-drying removes water, achieving product shaping and long-term storage: high vacuum degree of 0.12 to 0.18 mbar and sublimation temperature of-12℃ to-8℃ can remove the frozen water in the form of sublimation, avoiding the collapse of the protein structure and the loss of colloidal sulfur caused by the presence of liquid water; drying for 10 to 20 hours can ensure complete removal of water, obtaining dry porous sponge-like powder, which not only facilitates product storage (reducing deterioration caused by water), but also provides a channel for subsequent rehydration dispersion and slow-release of the colloidal sulfur. Thirdly, the porous structure formed during freeze-drying can enable water to quickly enter the interior of the microcapsule when it is rehydrated, achieving rapid dispersion; meanwhile, the porous structure can slow down the release rate of colloidal sulfur, prolonging the release half-life (up to 50 hours), achieving long-term acne and oil control effects, and reducing the contact between colloidal sulfur and the external environment, thereby reducing oxidation loss during storage.

[0040] The technical solutions of the present application will be further described below in combination with specific examples.

[0041] Example 1 (60wt% sulfur loading) (I) Preparation of raw materials Commercially available egg white protein powder (food grade, protein content ≥80%): 1.00 g; Sodium thiosulfate pentahydrate (Na2S2O3•5H2O, analytical pure): 2.48 g; Acetic acid-sodium acetate buffer (0.2 mol / L, pH 4.5): 10 mL; 0.5 mol / L hydrochloric acid solution (for dropwise addition): about 1.2 mL.

[0042] (II) Preparation steps (1) In a 25 mL beaker, 1.00 g of egg white protein powder was dissolved in 10 mL of acetic acid-sodium acetate buffer to prepare a 10wt% protein solution; the solution was magnetically stirred at 25℃ and 300 rpm for 20 min to ensure complete dissolution of the protein; (2) 2.48 g of sodium thiosulfate pentahydrate was added to the protein solution, and the stirring was continued until the sodium thiosulfate pentahydrate was completely dissolved; 0.5 mol / L hydrochloric acid solution was added dropwise at a rate of 0.5 mL / min until the pH of the system dropped to 2.2±0.1 (the actual dropwise addition amount was about 1.1 mL); the beaker was placed in a constant-temperature water bath and heated to 45℃, and the solution was kept at this temperature for 30 min, obtaining a light yellow compound colloid; (3) The light yellow composite colloid was separated and washed, and the solid was pre-frozen at -70°C for 2h; then it was transferred into a freeze dryer, dried at a vacuum degree of 0.12-0.18mbar and a sublimation temperature of -12°C to -8°C for 10h to obtain a light yellow loose egg white protein-based slow-release colloidal sulfur microcapsule powder.

[0043] (III) Product performance Yield: about 1.05g of microcapsules; Sulfur loading (determined by elemental analysis): 61.3wt%; Particle size (determined by dynamic light scattering): D50 of 315nm; Zeta potential: -40mV (absolute value ≥ 30mV); Dispersion: completely dispersed in 10s; Stability: 2.5% (≤5%) of agglomeration rate after 4 weeks of accelerated aging at 45°C.

[0044] Example 2 (70wt% sulfur loading) (I) Preparation of raw materials Commercial egg white protein powder (food grade, protein content ≥80%): 0.70g; Sodium thiosulfate pentahydrate (Na2S2O3•5H2O, analytical pure): 3.10g; Acetic acid-sodium acetate buffer (0.2mol / L, pH4.5): 10mL; 0.5mol / L hydrochloric acid solution (for dropwise addition): about 1.4mL.

[0045] (II) Preparation steps (1) In a 25mL beaker, 0.70g of egg white protein powder was dissolved in 10mL of acetic acid-sodium acetate buffer, and the solution was magnetically stirred at 27°C and 400rpm for 25min to ensure complete dissolution of the protein; (2) 3.10g of sodium thiosulfate pentahydrate was added to the protein solution, and the stirring was continued until the sodium thiosulfate pentahydrate was completely dissolved; 0.5mol / L hydrochloric acid solution was added dropwise at a rate of 0.8mL / min until the pH of the system dropped to 2.5±0.1 (the actual dropwise addition amount was about 1.3mL); the beaker was placed in a constant temperature water bath and heated to 55°C for 25min, and a light yellow composite colloid was obtained; (3) The light yellow composite colloid was separated and washed, and the solid was pre-frozen at -70°C for 3h; then it was transferred into a freeze dryer, dried at a vacuum degree of 0.12-0.18mbar and a sublimation temperature of -12°C to -8°C for 15h to obtain a light yellow loose egg white protein-based slow-release colloidal sulfur microcapsule powder.

[0046] (III) Product performance Yield: about 1.12 g of microcapsules; Sulfur loading (determined by elemental analysis): 70.1 wt%; Particle size (determined by dynamic light scattering): D50 of 330 nm and PDI of 0.15; Zeta potential: -38 mV (absolute value ≥ 30 mV); Dispersion: completely dispersed in 15 s after rehydration; Stability: 3.2% (≤ 5%, meeting the requirements of cosmetic raw materials) after 4 weeks of accelerated aging at 45°C.

[0047] Example 3 (80 wt% sulfur loading) (I) Preparation of raw materials Commercial egg white protein powder (food grade, protein content ≥ 80%): 0.50 g; Sodium thiosulfate pentahydrate (Na2S2O3•5H2O, analytical pure): 4.00 g (theoretical sulfur production amount about 0.505 g); Acetic acid-sodium acetate buffer (0.2 mol / L, pH 4.5): 10 mL; 0.5 mol / L hydrochloric acid solution (for dropwise addition): about 1.6 mL.

[0048] (II) Preparation steps (1) In a 25 mL beaker, 0.50 g of egg white protein powder was dissolved in 10 mL of acetic acid-sodium acetate buffer, and the solution was magnetically stirred at 30°C and 500 rpm for 30 min to ensure complete dissolution of the protein; (2) 4.00 g of sodium thiosulfate pentahydrate was added to the protein solution, and the stirring was continued until the sodium thiosulfate pentahydrate was completely dissolved. 0.5 mol / L hydrochloric acid solution was added at a rate of 1 mL / min until the pH of the system dropped to 2.8±0.1 (actual addition amount about 1.5 mL). The beaker was placed in a constant temperature water bath and heated to 60°C for 30 min to obtain a light yellow composite colloid; (3) The light yellow composite colloid was separated, washed, and then the solid was placed in a pre-freezing condition at -50°C for 4 h. Then it was transferred into a freeze dryer and dried at a vacuum degree of 0.12~0.18 mbar and a sublimation temperature of -12°C~-8°C for 20 h to obtain a light yellow egg white protein-based slow-release colloidal sulfur microcapsule powder.

[0049] (III) Product performance Yield: about 1.25 g of microcapsules; Sulfur loading (determined by elemental analysis): 80.3 wt%; Particle size (determined by dynamic light scattering): D50 of 350 nm and PDI of 0.18; Zeta potential: -36 mV (absolute value ≥ 30 mV); Dispersibility: completely dispersed in 25 s after rehydration; Stability: 4.1% (≤ 5%, meeting the requirements of cosmetic raw materials) after accelerated aging at 45°C for 4 weeks.

[0050] Comparative Example 1 (0 wt% loading rate) (I) Preparation of raw materials Commercial egg white protein powder (food grade, protein content ≥ 80%): 0.50 g; Acetic acid-sodium acetate buffer solution (0.2 mol / L, pH 4.5): 10 mL; 0.5 mol / L hydrochloric acid solution (for dropwise addition): about 1.4 mL.

[0051] (II) Preparation steps (1) In a 25 mL beaker, 0.70 g of egg white protein powder was dissolved in 10 mL of acetic acid-sodium acetate buffer solution, and the solution was magnetically stirred at 27°C and 400 rpm for 25 min to ensure complete dissolution of the protein; (2) 0.5 mol / L hydrochloric acid solution was added to the protein solution at a rate of 0.8 mL / min until the pH of the system dropped to 2.5±0.1 (the actual amount added was about 1.2 mL); the beaker was placed in a constant temperature water bath and heated to 55°C for 25 min, resulting in a light white composite colloid; (3) The above light white composite colloid was centrifuged and washed, and then pre-frozen at -70°C for 3 h; then it was transferred to a freeze dryer and dried at a vacuum degree of 0.12~0.18 mbar and a sublimation temperature of -12°C~-8°C for 15 h, resulting in a light white loose egg white protein powder.

[0052] The following Figures 2 to 7 were analyzed. As can be seen from Figure 2 and Figure 3 , the microcapsules prepared in Example 2 have a porous sponge-like morphology. As can be seen from Figure 4 and Figure 5 , the S element content of Example 1 is 61.3 wt%, while Comparative Example 1 only detects a small amount of S element (3.6 wt%), directly proving that colloidal sulfur is successfully loaded into the microcapsules and a high sulfur loading is achieved. As can be seen from Figure 6 , by comparing the curves of Example 1 and Comparative Example 2, it can be found that the characteristic absorption peak of egg white protein in Example 1 has obviously shifted or changed in shape, which proves that a specific chemical interaction has occurred between the functional groups of egg white protein and colloidal sulfur particles, forming a "coordinated absorption peak", which chemically verifies that the present application forms a stable complex through "synchronous denaturation-wrapping".Figure 7 It can be seen that the microcapsules of examples 1-3 are uniformly dispersed in water without obvious agglomeration, further proving the excellent dispersibility and stability of the products.

[0053] In summary, according to examples 1-3 and comparative example 1, the method of the present application successfully prepares colloidal sulfur microcapsules with sulfur loading of 60-80wt% and average particle size of 200-400nm by precisely controlling the mass ratio of egg white protein to sodium thiosulfate (1:2.5-8) and the reaction pH (2.2-2.8). All example products exhibit excellent dispersibility (Zeta potential absolute value ≥ 30mV) and storage stability (agglomeration rate < 5% after 4 weeks of accelerated aging at 45℃), fully verifying the reliability of the process and the stability of product performance.

[0054] The present application innovatively utilizes the simultaneous denaturation characteristics of egg white protein under specific acidic conditions, combining the "in-situ generation" of colloidal sulfur with the "three-dimensional network wrapping" of protein, and solving the technical bottleneck of easy agglomeration and poor stability of colloidal sulfur from the source. This process abandons organic solvents and chemical cross-linking agents, and is mild, green and environmentally friendly throughout. It directly uses low-cost commercial egg white protein powder, reducing the raw material cost to about 1 / 4 of the traditional collagen carrier. The prepared microcapsules have high sulfur loading, low irritation and long-acting slow-release function, perfectly meeting the comprehensive requirements of high-end cosmetics for efficacy, safety and stability, and have significant industrialization advantages and market competitiveness.

Claims

1. An egg white protein-based slow release colloidal sulfur microcapsule characterized in that, The microcapsule is a complex structure formed by simultaneously occurring denaturation process of egg white protein and in-situ generation process of colloidal sulfur; In the denaturation process, the egg white protein forms a three-dimensional network structure and coats and fixes the simultaneously generated colloidal sulfur particles; The average particle size of the obtained colloidal sulfur microcapsule is 200-400 nm, and the sulfur loading is 60wt%-80wt%.

2. The microcapsule according to claim 1, wherein The absolute value of Zeta potential of the colloidal sulfur microcapsule in a dispersion in pure water at 25℃ and pH 7.0 is ≥30mV, and the agglomeration rate is ≤5% after 6 months of room temperature storage.

3. The microcapsule of claim 1, wherein The egg white protein powder is a food-grade egg white protein powder prepared by a spray drying process, and the protein content is ≥80wt%.

4. A low cost method of preparing egg white protein based slow release colloidal sulfur microcapsules as claimed in any one of claims 1-3, characterized in that, The method comprises the following steps: (1) preparing an egg white protein solution: taking egg white protein powder, dissolving it in an acetic acid-sodium acetate buffer solution with a pH of 4.0-4.8, and stirring uniformly at 25-30℃ to obtain an egg white protein solution with a mass concentration of 5%-10%; (2) in-situ generation-synchronous denaturation coating: adding sodium thiosulfate pentahydrate to the egg white protein solution obtained in step (1) and stirring to completely dissolve the sodium thiosulfate pentahydrate; then slowly adding hydrochloric acid to adjust the pH of the system to 2.2-2.8, and then increasing the temperature of the system to 45-60℃, and keeping the temperature constant for 10-30min, so that colloidal sulfur is generated in-situ and coated by the three-dimensional network structure formed by the denaturation of egg white protein, forming a complex colloid; (3) freeze-drying shaping: separating and washing the complex colloid obtained in step (2), and then placing the solid in an environment of-50℃ to-70℃ for pre-freezing for 2-4h, and then drying the pre-frozen solid under the conditions of a vacuum degree of 0.12-0.18mbar and a sublimation temperature of-12℃ to-8℃ for 10-20h, to finally obtain porous sponge-like egg white protein-based slow-release colloidal sulfur microcapsules.

5. The method of claim 4, wherein, In step (2), the sodium thiosulfate pentahydrate is added according to a mass ratio of egg white protein powder to sodium thiosulfate pentahydrate of 1:(2.5-8).

6. The method of claim 4, wherein, In step (2), a 0.5-1mL / min rate of slow drop of a hydrochloric acid solution with a concentration of 0.5mol / L is used to control the pH value of the system.

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