Etherification-esterification composite starch emulsifier and preparation method thereof

Abstract

The invention discloses an etherified-esterified composite starch emulsifier and a preparation method thereof. The etherification-esterification composite starch emulsifier is prepared by the following steps: adding an alkalizer accounting for 10-30% of the mass of a starch dry basis into starch, uniformly mixing, and placing in a drying oven at 30-50 DEG C for 0.5-2 hours to obtain a mixture; adding sodium chloroacetate into the mixture, uniformly mixing, and standing for 0.5-3 hours; adding fatty acid, uniformly mixing, and standing for 12-48 hours to obtain a reaction material; loading the reaction material into a ball milling tank of a stirring ball mill, adding a ball milling medium with the diameter of 4-8mm, stirring and reacting at 35-65 DEG C for 10-120 minutes, and separating the ball milling medium after the reaction is finished to obtain a reaction product; and soaking the reaction product with 70-95% ethanol to obtain the product. The etherification substitution degree of the etherification-esterification composite starch emulsifier reaches 0.3495 or above, the substitution degree can reach 0.00865 or above, the reaction efficiency reaches 32%, the emulsifying property reaches 92% or above, the emulsifying stability reaches 85% or above, and the emulsifying property is excellent.

Description

Technical Field

[0001] The invention relates to an emulsifier, in particular to an etherified-esterified composite starch emulsifier and a preparation method thereof. Background Art

[0002] Emulsifier is a surfactant with a special molecular structure of lipophilic and hydrophilic groups. It can disperse water-insoluble materials in water to form a uniform stable emulsion, ensure the performance, uniformity and long-term stability of the materials, and has incomparable advantages in emulsification, solubilization, thickening, dispersion and flocculation. It is widely used in food, papermaking, daily chemical industry, textile and other industries. However, traditional emulsifiers are generally prepared using petrochemical raw materials. In recent years, due to the shortage of natural oil resources, the continuous rise in oil prices and the depletion of resources, it is necessary to seek new sources of raw materials for emulsifiers. At the same time, since the production of emulsifiers will cause environmental pollution, it is harmful to the human body. Therefore, the development and utilization of natural polymer emulsifiers with natural renewable resources as raw materials, non-toxic and harmless, good biodegradability, high performance and low cost has become a hot topic of research.

[0003] Starch is a natural polymer compound with a polyhydroxyl hydrophilic structure that is widely available. Introducing lipophilic groups into starch macromolecules to improve the hydrophobicity of starch can make it have better dispersibility, thickening, solubilization, emulsification, film-forming and other properties, and it can be biodegraded, safe and environmentally friendly. Starch-based emulsifiers are usually modified starches obtained by esterification of starch, and hydrophobicity is imparted to starch products by hydroxyl substitution. Commonly used esterifying agents include octenyl succinic anhydride, hydroxycinnamic acid and acetic anhydride. Octenyl succinic acid starch ester is an esterification reaction between starch and octenyl succinic anhydride (octenyl succinic anhydride, OSA), and some hydrophobic groups are introduced to make starch hydrophilic and lipophilic. It is a highly safe emulsifying thickener and is widely used in food, pharmaceuticals, cosmetics and other fields. However, octenyl succinic anhydride, as a raw material for the production of octenyl succinic acid starch ester, mainly relies on imports, and the production process is complicated, the product substitution degree is low, and the production cost is high, which cannot meet the needs. In order to improve the reaction efficiency and obtain cost-effective starch emulsifiers, researchers focus on improving the preparation method or researching new starch emulsifiers. Invention patent application CN20221042890.3 "A method for preparing an octenyl succinate starch-based emulsifier with high emulsification performance" prepares octenyl succinate rice starch ester by stripping the peripheral lipids of rice starch. Octenyl succinic anhydride is easier to diffuse into the starch molecular chain for substitution reaction, the degree of substitution is increased, and the emulsification performance is increased. Invention patent application CN20171082648.3 "A new type of starch-based emulsifier" uses β-limit dextrin as the skeleton and octenyl succinic acid as the substituent group to prepare octenyl succinate β-limit dextrin. Octenyl succinate β-limit dextrin has good emulsification, high water solubility, good freeze-thaw stability, high reaction efficiency and other beneficial effects. Invention patent application CN20231054304.8 "A probiotic butyric acid-based emulsifier and its preparation method and application" uses butyric anhydride to react with the hydroxyl groups on starch molecules to prepare butyrate starch-based emulsifiers, and through short-chain fatty acid modification, the starch obtains properties similar to those of long-chain fatty acid-modified starches such as OSA. However, the emulsification ability and emulsification stability of single modified starch-based emulsifiers need to be improved and still cannot meet market demand.

[0004] Sodium carboxymethyl starch-stearate starch ester is prepared by liquid phase method with carboxymethyl starch as raw material, stearic acid as esterifying agent and lipase as catalyst. Its rheological properties are better than carboxymethyl corn starch and stearic acid corn starch ester. Compared with carboxymethyl starch, the solubility of carboxymethyl starch after esterification becomes smaller, the emulsification and emulsification stability are improved, the surface tension is reduced, the coagulation property is reduced, and the freeze-thaw stability is reduced. Invention patent application CN20161081798.0 "A starch-based natural polymer emulsifier for rabbit hair and hair oil and its preparation method" uses carboxymethyl starch as raw material and stearic acid as esterifying agent. The starch-based natural polymer emulsifier carboxymethyl starch-stearate starch ester is prepared by etherification and transesterification reaction in a liquid phase system. The emulsifier has strong emulsifying properties for each component in the formula of hair oil, and can be used as a natural polymer system emulsifier based on rabbit hair and hair oil, with good development prospects. However, it has not yet been widely used as an emulsifier. The main reason is that the preparation of composite modified starch is mostly carried out by liquid phase method, which has a complicated process, low yield, unstable product quality, and cannot form industrial production. Summary of the invention

[0005] The purpose of the present invention is to provide an etherified-esterified composite starch emulsifier with green preparation process, simple operation, low cost and good emulsification, which can effectively improve the emulsification effect and solve the problem of complex production process and unstable quality of starch emulsifier.

[0006] To achieve the purpose of the present invention, the following technical solution is provided: an etherified-esterified composite starch emulsifier, which is a carboxymethyl-fatty acid starch ester composite modified starch, is prepared by the following steps:

[0007] (1) adding 10% to 30% of the dry weight of starch to an alkalizer into starch, mixing well, and placing in an oven at 30 to 50° C. for 0.5 to 2 hours to obtain a mixture;

[0008] (2) adding sodium chloroacetate to the mixture, with the molar ratio of starch to sodium chloroacetate being 1:0.5-1.5, mixing well, and leaving for 0.5-3 hours;

[0009] (3) adding fatty acid dissolved in 5 to 20 mL of anhydrous ethanol, wherein the fatty acid accounts for 1% to 8% of the dry weight of starch, mixing evenly, and standing for 12 to 48 hours to obtain a reaction mass;

[0010] (4) the reaction material is loaded into a reaction tank of a stirring ball mill, and a ball milling medium with a diameter of 4 to 8 mm is added at a material-ball volume ratio of 1:8 to 12, and the reaction is stirred at 20 to 70° C. for 10 to 120 minutes, with the stirring blade rotating at a speed of 380 to 580 rpm. After the reaction is completed, the ball milling medium is separated to obtain a reaction product;

[0011] (5) Soak the reaction product in 60% to 95% ethanol for 0.5 to 5 hours, filter, wash, dry at 35 to 70° C. for 12 to 72 hours, grind into powder, and pass through a 80 to 200 mesh sieve to obtain the product.

[0012] In the step (1), the alkalizing agent used is solid sodium hydroxide or potassium hydroxide. In the step (3), the fatty acid is stearic acid.

[0013] As an embodiment of the present invention, in the step (1), the mass fraction of the alkalizing agent is 20%.

[0014] In the step (2), the molar ratio of starch to sodium chloroacetate is 1:1.

[0015] In the step (3), the mass fraction of fatty acid is 4%.

[0016] In the step (4), the ball milling medium is zirconium oxide or aluminum oxide ceramic balls.

[0017] Preferably, in step (4), the diameter of the ball milling medium is 6 mm; the ball volume ratio is 1:8; the stirring reaction temperature is 50° C.; the reaction time is 60 min; and the stirring paddle speed is 380 rpm.

[0018] Preferably, in step (5), the ethanol soaking time is 3 hours; the powder is dried at 35-65°C for 12-72 hours, preferably at 50°C for 48 hours; and the powder particle size is 80-200 mesh, preferably 120 mesh.

[0019] Another object of the present invention is to provide a method for preparing the etherified-esterified composite starch emulsifier.

[0020] Specifically, the preparation method of the etherified-esterified composite starch emulsifier comprises the following steps:

[0021] (1) adding 10% to 30% of the dry weight of starch to an alkalizer into starch, mixing well, and placing in an oven at 30 to 50° C. for 0.5 to 2 hours to obtain a mixture;

[0022] (2) adding sodium chloroacetate to the mixture, with the molar ratio of starch to sodium chloroacetate being 1:0.5-1.5, mixing well, and leaving for 0.5-3 hours;

[0023] (3) adding fatty acid dissolved in 5 to 20 mL of anhydrous ethanol, wherein the fatty acid accounts for 1% to 8% of the dry weight of starch, mixing evenly, and standing for 12 to 48 hours to obtain a reaction mass;

[0024] (4) the reaction material is loaded into a reaction tank of a stirring ball mill, and a ball milling medium with a diameter of 4 to 8 mm is added at a material-ball volume ratio of 1:8 to 12, and the reaction is stirred at 20 to 70° C. for 10 to 120 minutes, with the stirring blade rotating at a speed of 380 to 580 rpm. After the reaction is completed, the ball milling medium is separated to obtain a reaction product;

[0025] (5) Soak the reaction product in 60% to 95% ethanol for 0.5 to 5 hours, filter, wash, dry at 35 to 70° C. for 12 to 72 hours, grind into powder, and pass through a 80 to 120 mesh sieve to obtain the product.

[0026] In the step (1), the alkalizing agent is sodium hydroxide or potassium hydroxide; in the step (3), the fatty acid is lauric acid, myristic acid, palmitic acid or stearic acid.

[0027] In the step (1), the mass fraction of the alkalizer used is 20%; in the step (2), the molar ratio of starch to sodium chloroacetate is 1:1; in the step (3), the mass fraction of fatty acid is 4%.

[0028] In the step (4), the ball milling medium is zirconium oxide or aluminum oxide ceramic balls; the diameter of the ball milling medium is 6 mm; the ball volume ratio is 1:8; the stirring reaction temperature is 50° C.; the stirring reaction time is 60 min; and the stirring paddle speed is 380 rpm.

[0029] In the step (5), the ethanol concentration is 90%, and the soaking time is 3 hours; the 90% ethanol is washed until it is neutral and the solution does not contain chloride ions, and then dried at 35-65° C. for 12-72 hours; the powder particle size is 80-200 mesh.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention uses starch, sodium chloroacetate, fatty acid raw materials, sodium hydroxide as an alkalizer and a catalyst, and obtains an etherified-esterified composite starch emulsifier through a mechanical grinding and dry one-step process. The obtained etherified-esterified composite starch emulsifier is in powder form, and a certain proportion of oil and water are added to mix and homogenize, and the emulsification reaches more than 92%, and the emulsification stability reaches more than 85%.

[0032] 2. The present invention uses a one-step dry reaction method to prepare starch emulsifiers, and can prepare starch emulsifiers under mild conditions, effectively solving the shortcomings of wet modified starch production, such as long process, multi-step reaction, multiple equipment, low reaction efficiency of main chemical reagents, long reaction time, low yield, generation of a large amount of difficult-to-treat sewage, starch agglomeration or caking phenomenon in dry production, poor reaction uniformity, unstable product quality, etc.

[0033] 3. The present invention optimizes the process parameters so that the degree of substitution of starch etherification reaction reaches above 0.3495, the degree of substitution of esterification reaction reaches above 0.008652, the total reaction efficiency reaches above 32%, the emulsification of the prepared starch emulsifier reaches above 92%, and the emulsification stability reaches above 85%.

[0034] 4. The preparation method provided by the present invention is simple and green, has low production cost and good product performance, and can realize industrial-scale production of emulsifiers and promote their use in textiles, daily chemicals, pharmaceuticals, and food. DETAILED DESCRIPTION

[0035] Methods for determining emulsification and emulsion stability:

[0036] Accurately weigh 1g of starch sample, place it in a 100mL beaker, add 25mL of distilled water, gelatinize in a boiling water bath for 20min, take it out and cool it to room temperature at room temperature, add 25mL of edible blending oil, use a handheld high-speed disperser to shear at 10000r / min for 1min at room temperature, after obtaining the emulsion, draw the emulsion from the bottom and move it into a 10ml centrifuge tube, centrifuge it at 3000r / min for 15min, and record the height of the emulsion layer and the total height of the liquid in the centrifuge tube. Let the centrifuge tube stand for 24h, centrifuge it at 3000r / min for 15min, and record the height of the emulsion layer and the total height of the liquid in the centrifuge tube after centrifugation. Calculate the emulsification and emulsion stability of starch according to the following formula.

[0037]

[0038] In the formula: EA is emulsification; ES is emulsion stability.

[0039] Embodiment 1

[0040] (1) adding 18% sodium hydroxide by weight of the dry basis of starch to the starch, mixing well, and placing in an oven at 50° C. for 1 hour to obtain a mixture;

[0041] (2) adding sodium chloroacetate to the mixture, with the molar ratio of starch to sodium chloroacetate being 1:1.25, mixing well, and leaving for 2 hours;

[0042] (3) adding stearic acid dissolved in 10 mL of anhydrous ethanol, wherein the mass fraction of stearic acid in the starch dry basis is 5%, mixing well, and standing for 24 hours to obtain a reaction mass;

[0043] (4) The reaction material is loaded into a reaction tank of a stirring ball mill, and a ball milling medium with a diameter of 6 mm is added at a material-ball volume ratio of 1:10, and the reaction is stirred at 50° C. for 60 minutes, with the stirring blade speed of 380 rpm. After the reaction is completed, the ball milling medium is separated to obtain a reaction product;

[0044] (5) Soak the reaction product in 80% ethanol for 3 hours, filter, wash, dry at 50° C. for 48 hours, grind into powder, and pass through a 120-mesh sieve to obtain the product.

[0045] The degree of substitution of the etherification reaction of the prepared etherified-esterified composite starch emulsifier is 0.3495, the degree of substitution of the esterification reaction is 0.008652, the total reaction efficiency is 32.34%, the emulsification reaches 92%, and the emulsion stability reaches 85%.

[0046] Embodiment 2

[0047] (1) adding 20% ​​sodium hydroxide by weight of the dry basis of starch to the starch, mixing well, and placing in an oven at 50° C. for 1 hour to obtain a mixture;

[0048] (2) adding sodium chloroacetate to the mixture, with the molar ratio of starch to sodium chloroacetate being 1:1, mixing well, and leaving for 3 hours;

[0049] (3) adding stearic acid dissolved in 10 mL of anhydrous ethanol, wherein the mass fraction of stearic acid in the starch dry basis is 4%, mixing well, and standing for 24 hours to obtain a reaction mass;

[0050] (4) The reaction material is loaded into a reaction tank of a stirring ball mill, and a ball milling medium with a diameter of 6 mm is added at a material-ball volume ratio of 1:8, and the reaction is stirred at 50° C. for 60 minutes, with the stirring blade speed of 380 rpm. After the reaction is completed, the ball milling medium is separated to obtain a reaction product;

[0051] (5) Soak the reaction product in 90% ethanol for 5 hours, filter, wash, dry at 40° C. for 72 hours, grind into powder, and pass through a 100-mesh sieve to obtain the product.

[0052] The degree of substitution of the etherification reaction of the prepared etherified-esterified composite starch emulsifier is 0.4533, the degree of substitution of the esterification reaction is 0.01185, the total reaction efficiency is 35%, the emulsification reaches 95%, and the emulsion stability reaches 90%.

[0053] Embodiment 3

[0054] (1) adding 22% sodium hydroxide by weight of the dry basis of starch to the starch, mixing well, and placing in an oven at 40° C. for 2 hours to obtain a mixture;

[0055] (2) adding sodium chloroacetate to the mixture, with the molar ratio of starch to sodium chloroacetate being 1:0.75, mixing well, and leaving for 2 hours;

[0056] (3) adding stearic acid dissolved in 15 mL of anhydrous ethanol, wherein the mass fraction of stearic acid in the starch dry basis is 3%, mixing evenly, and standing for 24 hours to obtain a reaction mass;

[0057] (4) the reaction material is loaded into a reaction tank of a stirring ball mill, and a ball milling medium with a diameter of 6 mm is added at a material-ball volume ratio of 1:9, and the reaction is stirred at 60° C. for 90 minutes, with the stirring blade speed of 380 rpm. After the reaction is completed, the ball milling medium is separated to obtain a reaction product;

[0058] (5) Soak the reaction product in 85% ethanol for 4 hours, filter, wash, dry at 50° C. for 48 hours, grind into powder, and pass through a 120-mesh sieve to obtain the product.

[0059] The degree of substitution of the etherification reaction of the prepared etherified-esterified composite starch emulsifier is 0.3682, the degree of substitution of the esterification reaction is 0.009347, the total reaction efficiency is 46.3%, the emulsification reaches 94%, and the emulsion stability reaches 89%.

[0060] Embodiment 4

[0061] (1) adding 24% sodium hydroxide by weight of the dry basis of starch to the starch, mixing well, and placing in an oven at 50° C. for 2 hours to obtain a mixture;

[0062] (2) adding sodium chloroacetate to the mixture, with the molar ratio of starch to sodium chloroacetate being 1:0.5, mixing well, and leaving for 2 hours;

[0063] (3) adding stearic acid dissolved in 10 mL of anhydrous ethanol, wherein the mass fraction of stearic acid in the starch dry basis is 4%, mixing well, and standing for 24 hours to obtain a reaction mass;

[0064] (4) The reaction material is loaded into a reaction tank of a stirring ball mill, and a ball milling medium with a diameter of 6 mm is added at a material-ball volume ratio of 1:8, and the reaction is stirred at 60° C. for 120 minutes, with the stirring blade speed of 380 rpm. After the reaction is completed, the ball milling medium is separated to obtain a reaction product;

[0065] (5) Soak the reaction product in 75% ethanol for 5 hours, filter, wash, dry at 40° C. for 72 hours, grind into powder, and pass through a 100-mesh sieve to obtain the product.

[0066] The degree of substitution of the etherification reaction of the prepared etherified-esterified composite starch emulsifier is 0.3522, the degree of substitution of the esterification reaction is 0.008842, the total reaction efficiency is 33.1%, the emulsification reaches 93%, and the emulsion stability reaches 87%.

[0067] Embodiment 5

[0068] (1) adding 30% sodium hydroxide by weight of the dry basis of starch to the starch, mixing well, and placing in an oven at 50° C. for 2 hours to obtain a mixture;

[0069] (2) adding sodium chloroacetate to the mixture, with the molar ratio of starch to sodium chloroacetate being 1:1.5, mixing well, and leaving for 2 hours;

[0070] (3) adding stearic acid dissolved in 20 mL of anhydrous ethanol, wherein the mass fraction of stearic acid in the starch dry basis is 6%, mixing well, and standing for 48 hours to obtain a reaction mass;

[0071] (4) the reaction material is loaded into a reaction tank of a stirring ball mill, and a ball milling medium with a diameter of 6 mm is added at a material-ball volume ratio of 1:8, and the reaction is stirred at 40° C. for 90 minutes, with the stirring blade speed of 380 rpm. After the reaction is completed, the ball milling medium is separated to obtain a reaction product;

[0072] (5) Soak the reaction product in 90% ethanol for 3 hours, filter, wash, dry at 50° C. for 48 hours, grind into powder, and pass through a 120-mesh sieve to obtain the product.

[0073] The etherification reaction substitution degree of the prepared etherified-esterified composite starch emulsifier is 0.3502, the esterification reaction substitution degree is 0.01323, the total reaction efficiency is 33%, the emulsification reaches 95.2%, and the emulsion stability reaches 90%.

[0074] Embodiment 6

[0075] (1) adding 20% ​​of the dry weight of starch to the alkali to mix well, and placing in an oven at 50° C. for 1 hour to obtain a mixture;

[0076] (2) adding sodium chloroacetate to the mixture, with the molar ratio of starch to sodium chloroacetate being 1:1, mixing well, and leaving for 2 hours;

[0077] (3) adding stearic acid dissolved in 10 mL of anhydrous ethanol, wherein the mass fraction of stearic acid in the starch dry basis is 4%, mixing well, and standing for 24 hours to obtain a reaction mass;

[0078] (4) the reaction material is loaded into a reaction tank of a stirring ball mill, and a zirconia medium with a diameter of 6 mm is added at a material ball volume ratio of 1:8, and the reaction is stirred at 50° C. for 60 minutes, with the stirring blade speed of 380 rpm. After the reaction is completed, the grinding ball medium is separated to obtain a reaction product;

[0079] (5) Soak the reaction product in 80% by volume ethanol for 3 hours, filter, wash, dry at 50° C. for 48 hours, grind into powder, and pass through a 120-mesh sieve to obtain the product.

[0080] The degree of substitution of the etherification reaction of the prepared etherified-esterified composite starch emulsifier is 0.4623, the degree of substitution of the esterification reaction is 0.01337, the total reaction efficiency is 46.8%, the emulsification reaches 96%, and the emulsion stability reaches 92%.

[0081] Comparative Example

[0082] 3g of stearic acid was crushed, passed through a 120-mesh sieve, and then added to 100g (dry basis) of methyl starch that passed through a 120-mesh sieve, the degree of substitution of carboxymethyl starch being 0.2081, and then lipase (enzyme activity 5000u / g, added in an amount of 0.5g) was added, and heated in a 45°C water bath with stirring at a stirring rate of 120r / min; distilled water was added while stirring to control the moisture content of the system to 7%; after reacting for 1h, desiccant color-changing silica gel was added, and stirring was continued for 11h to terminate the reaction; after the reaction was completed, the enzyme activity was inactivated in a boiling water bath for 20min, and then washed with industrial alcohol until no precipitation reaction occurred with the silver nitrate solution; the alcohol was dried in a 5°C oven, and finally the desiccant was removed by filtration to obtain the product carboxymethyl starch stearate.

[0083] The degree of substitution of stearic acid groups of the prepared carboxymethyl starch stearate reached 0.01841, the emulsification reached 56.6%, and the emulsion stability reached 65.2%.

Claims

1. An etherified-esterified composite starch emulsifier, characterized in that: Prepared by the following steps: (1) adding 10% to 30% of the dry weight of starch to an alkalizer into starch, mixing well, and placing in an oven at 30 to 50° C. for 0.5 to 2 hours to obtain a mixture; (2) adding sodium chloroacetate to the mixture, with the molar ratio of starch to sodium chloroacetate being 1:0.5-1.5, mixing well, and leaving for 0.5-3 hours; (3) adding fatty acid dissolved in 5 to 20 mL of anhydrous ethanol, wherein the fatty acid accounts for 1% to 8% of the dry weight of starch, mixing evenly, and standing for 12 to 48 hours to obtain a reaction mass; (4) the reaction material is loaded into a reaction tank of a stirring ball mill, and a ball milling medium with a diameter of 4 to 8 mm is added at a material-ball volume ratio of 1:8 to 12, and the reaction is stirred at 20 to 70° C. for 10 to 120 minutes, with the stirring blade rotating at a speed of 380 to 580 rpm. After the reaction is completed, the ball milling medium is separated to obtain a reaction product; (5) Soak the reaction product in 60% to 95% ethanol for 0.5 to 5 hours, filter, wash, dry at 35 to 70° C. for 12 to 72 hours, grind into powder, and pass through a 80 to 120 mesh sieve to obtain the product.

2. The etherified-esterified composite starch emulsifier according to claim 1, characterized in that: In the step (1), the alkalizing agent is sodium hydroxide or potassium hydroxide.

3. The etherified-esterified composite starch emulsifier according to claim 1, characterized in that: In the step (3), the fatty acid is lauric acid, myristic acid, palmitic acid or stearic acid.

4. The etherified-esterified composite starch emulsifier according to claim 1, characterized in that: In the step (1), the mass fraction of the alkalizer used is 20%; in the step (2), the molar ratio of starch to sodium chloroacetate is 1:1; in the step (3), the mass fraction of fatty acid is 4%.

5. The etherified-esterified composite starch emulsifier according to claim 1, characterized in that: In the step (4), the ball milling medium is zirconium oxide or aluminum oxide ceramic balls; the diameter of the ball milling medium is 6 mm; the ball volume ratio is 1:8; the stirring reaction temperature is 50° C.; the stirring reaction time is 60 min; and the stirring paddle speed is 380 rpm.

6. The etherified-esterified composite starch emulsifier according to claim 1, characterized in that: In the step (5), the ethanol concentration is 90%, and the soaking time is 3 hours; the 90% ethanol is washed until it is neutral and the solution does not contain chloride ions, and then dried at 35-65° C. for 12-72 hours; the powder particle size is 80-200 mesh.

7. A method for preparing an etherified-esterified composite starch emulsifier, characterized in that: The following steps are involved: (1) adding 10% to 30% of the dry weight of starch to an alkalizer into starch, mixing well, and placing in an oven at 30 to 50° C. for 0.5 to 2 hours to obtain a mixture; (2) adding sodium chloroacetate to the mixture, with the molar ratio of starch to sodium chloroacetate being 1:0.5-1.5, mixing well, and leaving for 0.5-3 hours; (3) adding fatty acid dissolved in 5 to 20 mL of anhydrous ethanol, wherein the fatty acid accounts for 1% to 8% of the dry weight of starch, mixing evenly, and standing for 12 to 48 hours to obtain a reaction mass; (4) the reaction material is loaded into a reaction tank of a stirring ball mill, and a ball milling medium with a diameter of 4 to 8 mm is added at a material-ball volume ratio of 1:8 to 12, and the reaction is stirred at 20 to 70° C. for 10 to 120 minutes, with the stirring blade rotating at a speed of 380 to 580 rpm. After the reaction is completed, the ball milling medium is separated to obtain a reaction product; (5) Soak the reaction product in 60% to 95% ethanol for 0.5 to 5 hours, filter, wash, dry at 35 to 70° C. for 12 to 72 hours, grind into powder, and pass through a 80 to 120 mesh sieve to obtain the product.

8. The method for preparing the etherified-esterified composite starch emulsifier according to claim 7, characterized in that: In the step (1), the alkalizing agent is sodium hydroxide or potassium hydroxide; in the step (3), the fatty acid is lauric acid, myristic acid, palmitic acid or stearic acid.

9. The method for preparing the etherified-esterified composite starch emulsifier according to claim 7, characterized in that: In the step (1), the mass fraction of the alkalizer used is 20%; in the step (2), the molar ratio of starch to sodium chloroacetate is 1:1; in the step (3), the mass fraction of fatty acid is 4%.

10. The method for preparing the etherified-esterified composite starch emulsifier according to claim 7, characterized in that: In the step (4), the ball milling medium is zirconium oxide or aluminum oxide ceramic balls; the diameter of the ball milling medium is 6 mm; the ball volume ratio is 1:8; the stirring reaction temperature is 50° C.; the stirring reaction time is 60 min; and the stirring paddle speed is 380 rpm; In the step (5), the ethanol concentration is 90%, and the soaking time is 3 hours; the 90% ethanol is washed until it is neutral and the solution does not contain chloride ions, and then dried at 35-65° C. for 12-72 hours; the powder particle size is 80-200 mesh.

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