Preparation method of purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules

Abstract

The present invention discloses a method for preparing purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules, which comprises the following steps: washing purple sweet potatoes, homogenizing them with water, filtering to obtain a slurry, standing and centrifuging the slurry to obtain a supernatant; mixing the supernatant with an aqueous solution of polysaccharide, adjusting the pH value to 2.5-7, and reacting to obtain a complex coacervate; centrifuging the complex coacervate to obtain a precipitate, and freeze-drying the precipitate to obtain purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules. By adding a charged polysaccharide to the purple sweet potato starch processing waste liquid (supernatant) and complex coacervating purple sweet potato protein and anthocyanin with opposite charges, purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules can be obtained, which can significantly improve the edible recovery rate of purple sweet potato protein and anthocyanin, and the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules have good antioxidant capacity. This method has the advantages of high efficiency, convenience, green safety and direct edibility.

Description

Technical Field

[0001] The present invention relates to the technical field of food, and particularly relates to a method for preparing purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules. Background Art

[0002] About 10% of protein is contained in the dry matter of purple sweet potato tubers. The purple sweet potato protein contains 18 kinds of amino acids, and the amino acid composition pattern conforms to the WHO / FAO recommended standard. The content of essential amino acids is higher than that of most other plant proteins, and the biological value is high. In addition, purple sweet potato tubers are also rich in anthocyanins. Anthocyanins are a kind of natural polyphenolic compounds, which are easily soluble in water and have many health benefits, such as scavenging free radicals, inhibiting inflammation and tumors, inhibiting lipid oxidation, preventing metabolic disorders and protecting eyesight. At present in industry, purple sweet potato roots are mainly used for wet processing of starch. However, this process consumes a large amount of water, and the purple sweet potato protein and polyphenols in the wastewater cannot be utilized. Moreover, if discharged without treatment, it may cause serious water pollution problems. Summary of the Invention

[0003] The main object of the present invention is to propose a method for preparing purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules, aiming to simply and effectively jointly recover the protein and polyphenols in the purple sweet potato starch processing wastewater, so as to obtain a purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsule with antioxidant function.

[0004] To achieve the above object, the present invention proposes a method for preparing purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules, comprising the following steps:

[0005] S10. Wash the purple sweet potatoes, add water to make a slurry, filter to obtain a slurry, and after standing and centrifuging the slurry, obtain a supernatant;

[0006] S20. Mix the supernatant with an aqueous solution of polysaccharide, adjust the pH value to 2.5 - 7, and react to obtain a coacervate;

[0007] S30. Centrifuge the coacervate to obtain a precipitate, and freeze-dry the precipitate to obtain purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules.

[0008] Optionally, in step S20, the polysaccharide includes at least one of chitosan, pectin, and carrageenan.

[0009] Optionally, in step S20, the polysaccharide includes chitosan, and the molecular weight of the chitosan is 30 - 300 kDa.

[0010] Optionally, in step S20, the polysaccharide includes chitosan, and the volume ratio of the supernatant to the aqueous solution of polysaccharide at 1 mg / mL is 1:1 - 90:1.

[0011] Optionally, in step S20, adjust the pH value to 4-7.

[0012] Optionally, in step S20, the polysaccharide includes pectin, and the volume ratio of the supernatant to the aqueous solution of the polysaccharide at 1 mg / mL is 1:1 to 100:1.

[0013] Optionally, in step S20, adjust the pH value to 2.5-4.5.

[0014] Optionally, in step S20, the polysaccharide includes carrageenan, and the volume ratio of the supernatant to the aqueous solution of the polysaccharide at 1 mg / mL is 1:1 to 100:1.

[0015] Optionally, in step S20, adjust the pH value to 2.5-5.5.

[0016] In the technical solution provided by the present invention, a charged polysaccharide is added to the purple sweet potato starch processing waste liquid (supernatant), and purple sweet potato protein and anthocyanin are coacervated by opposite charges to obtain purple sweet potato protein / anthocyanin / polysaccharide purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules, which can significantly improve the edible recovery rate of purple sweet potato protein and anthocyanin, and the purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules have good antioxidant capacity. Compared with other methods for treating high-protein waste liquid, this method has the advantages of high efficiency, convenience, green safety, and the purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules can be directly edible. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other relevant drawings can also be obtained based on these drawings.

[0018] Figure 1 It is a protein recovery rate distribution diagram of the preparation method of purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules in Examples 1 to 12 of the present invention;

[0019] Figure 2 It is an anthocyanin recovery rate distribution diagram of the preparation method of purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules in Examples 1 to 12 of the present invention;

[0020] Figure 3 It is a microscope diagram of purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules obtained in Examples 1, 4, 13, 14, 7, and 10 of the present invention;

[0021] Figure 4It is the DPPH free radical scavenging rate distribution diagram of the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules obtained in Example 1, Example 4, Example 13, Example 14, Example 7 and Example 10 of the present invention;

[0022] Figure 5 It is the ABTS· free radical scavenging rate distribution diagram of the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules obtained in Example 1, Example 4, Example 13, Example 14, Example 7 and Example 10 of the present invention.

[0023] The realization, functional characteristics and advantages of the object of the present invention will be further described in conjunction with the embodiments with reference to the accompanying drawings. Detailed implementation manners

[0024] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified in the manufacturer are all conventional products that can be obtained through commercial purchase.

[0025] It should be noted that those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified in the manufacturer are all conventional products that can be obtained through commercial purchase. In addition, the meaning of "and / or" appearing throughout the text includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, or solution B, or the solution where A and B are satisfied at the same time. In addition, the technical solutions between the embodiments can be combined with each other, but it must be based on the fact that those skilled in the art can achieve it. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0026] The dry matter of purple sweet potato tubers contains about 10% protein. Purple sweet potato protein contains 18 kinds of amino acids, and the amino acid composition pattern conforms to the WHO / FAO recommended standard. The content of essential amino acids is higher than that of most other plant proteins, and the biological value is high. In addition, purple sweet potato tubers are also rich in anthocyanins. Anthocyanins are a kind of natural polyphenolic compounds, which are easily soluble in water and have many health benefits, such as scavenging free radicals, inhibiting inflammation and tumors, inhibiting lipid oxidation, preventing metabolic disorders and protecting eyesight. Currently in industry, purple sweet potato roots are mainly used for wet processing of starch. However, this process consumes a large amount of water, and the purple sweet potato protein and polyphenols in the wastewater cannot be utilized. Moreover, if discharged without treatment, it may cause serious water pollution problems.

[0027] In view of this, a preparation method of purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules proposed by the present invention aims to simply and effectively jointly recover proteins and polyphenols (i.e., anthocyanins) in purple sweet potato starch processing wastewater, so as to obtain purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules with antioxidant function.

[0028] The preparation method of purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules proposed in the embodiment of the present invention includes the following steps:

[0029] S10. Wash the purple sweet potatoes, add water to make a homogeneous slurry, filter to obtain a slurry, and after standing and centrifuging the slurry, obtain a supernatant;

[0030] S20. Mix the supernatant with an aqueous solution of polysaccharide, adjust the pH value to 2.5 - 7, and react to obtain a coacervate;

[0031] S30. Centrifuge the coacervate to obtain a precipitate, and freeze-dry the precipitate to obtain purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules.

[0032] In the technical solution provided by the present invention, a charged polysaccharide is added to the purple sweet potato starch processing waste liquid (the supernatant obtained in step S10), and purple sweet potato proteins and anthocyanins are coacervated through opposite charges to obtain purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules, which can significantly improve the edible recovery rate of purple sweet potato proteins and anthocyanins, and the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules have good antioxidant capacity. Compared with other methods for treating high-protein waste liquid, this method has the advantages of high efficiency, convenience, green safety, and the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules can be directly edible.

[0033] In step S10, the present invention does not limit the ratio of the purple sweet potatoes to water. In the embodiment of the present invention, the mass ratio of purple sweet potatoes to water is 1:10.

[0034] The present invention does not limit the types of polysaccharides, as long as they are polysaccharides, they are within the protection scope of the present invention. Preferably, in step S20, the polysaccharide includes at least one of chitosan, pectin, and carrageenan.

[0035] Polysaccharide complex coacervation protein utilizes the electrostatic self-assembly physical phase separation that occurs when proteins and polysaccharides carry opposite charges, and it is an efficient, environmentally friendly, and green extraction method. Chitosan is a commonly used linear polysaccharide obtained by deacetylating chitin. It is the only cationic polysaccharide found in nature that carries a positive charge. It has various physiological functions such as biodegradability, biocompatibility, non-toxicity, and antibacterial properties, and is widely used in food. Pectin is a component of plant cell walls and is a natural polymer. Due to its excellent gel properties and emulsification stability, it is widely used in the food, pharmaceutical, and daily necessities industries. Carrageenan is a type of natural polysaccharide extracted from red algae seaweeds. According to the different forms of combined sulfate esters, it can be divided into κ-type, ι-type, and λ-type carrageenan. The above types of carrageenan are all within the scope of protection of the present invention. In the embodiments of the present invention, polysaccharides with several typical charged groups are selected, including chitosan, pectin, and carrageenan. Through the method of physical complex coacervation, purple sweet potato proteins and anthocyanins are jointly extracted in one step, establishing a new method for efficiently co-extracting proteins and anthocyanins with low cost, good effect, and simple operation, and obtaining a microcapsule product with antioxidant functional characteristics.

[0036] In the first embodiment of the present invention, the polysaccharide includes chitosan. Preferably, in step S20, the polysaccharide includes chitosan, and the molecular weight of the chitosan is 30 - 300 kDa, such as 30 kDa, 50 kDa, 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, etc. Within the above range, chitosan is more likely to bind to proteins. More preferably, the molecular weight of the chitosan is 30 kDa. In this way, the recovery rate of the coacervated protein from purple sweet potato starch processing waste liquid can reach 94.35%, the recovery rate of anthocyanins can reach 86.76%, the DPPH radical scavenging rate of the formed microcapsules can reach 35.77%, and the ABTS radical scavenging rate can reach 61.31%. The recovery rate is high and the obtained microcapsules have good antioxidant effects.

[0037] Preferably, in step S20, the polysaccharide includes chitosan, and the volume ratio of the supernatant to the aqueous solution of the polysaccharide at 1 mg / mL is 1:1 - 90:1, such as 1:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, etc. Within the above range, adding a small amount of charged polysaccharide to coacervate purple sweet potato proteins and anthocyanins through opposite charges can obtain purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules, which can significantly improve the edible recovery rate of purple sweet potato proteins and anthocyanins, and the purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules have good antioxidant ability.

[0038] Preferably, in step S20, the pH value is adjusted to 4-7. For example, it can be 4, 5, 6, 7, etc. Within the above pH value range, the polysaccharide can fully react and combine with the protein and anthocyanin.

[0039] In the second embodiment of the present invention, the polysaccharide includes pectin. Preferably, in step S20, the polysaccharide includes pectin. The volume ratio of the supernatant to the aqueous solution of 1 mg / mL polysaccharide is 1:1-100:1. For example, 1:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, etc. Within the above range, a small amount of charged polysaccharide is added to coacervate purple sweet potato protein and anthocyanin through opposite charge, and purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules are obtained, which can significantly improve the edible recovery rate of purple sweet potato protein and anthocyanin, and the purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules have good antioxidant capacity.

[0040] Preferably, in step S20, the pH value is adjusted to 2.5-4.5. For example, it can be 2.5, 3, 3.5, 4, 4.5, etc. Within the above pH value range, the polysaccharide can fully react and combine with the protein and anthocyanin.

[0041] In the third embodiment of the present invention, the polysaccharide includes carrageenan. Preferably, in step S20, the polysaccharide includes carrageenan. The volume ratio of the supernatant to the aqueous solution of 1 mg / mL polysaccharide is 1:1-100:1. For example, 1:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, etc. Within the above range, a small amount of charged polysaccharide is added to coacervate purple sweet potato protein and anthocyanin through opposite charge, and purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules are obtained, which can significantly improve the edible recovery rate of purple sweet potato protein and anthocyanin, and the purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules have good antioxidant capacity.

[0042] Preferably, in step S20, the pH value is adjusted to 2.5-5.5. For example, it can be 2.5, 3, 3.5, 4, 4.5, 5, 5.5, etc. Within the above pH value range, the polysaccharide can fully react and combine with the protein and anthocyanin.

[0043] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments and the accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0044] Example 1

[0045] (1) Wash the purple sweet potatoes, add water and homogenize them. The mass ratio of purple sweet potato tubers to water is 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0046] (2) Prepare a chitosan solution with a concentration of 1 mg / mL and a molecular weight of 30 kDa. Mix the starch extraction waste liquid and the chitosan solution in a volume ratio of 85:1. Adjust the pH value of the chitosan mixed solution to 4.0 with 1 mol / L NaOH and HCl. Stir evenly at room temperature for 10 min to obtain a composite condensate.

[0047] (3) Centrifuge the formed composite condensate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin complex coacervation microcapsules.

[0048] Example 2

[0049] (1) Wash the purple sweet potatoes, add water and homogenize them. The mass ratio of purple sweet potato tubers to water is 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0050] (2) Prepare a chitosan solution with a concentration of 1 mg / mL and a molecular weight of 30 kDa. Mix the starch extraction waste liquid and the chitosan solution in a volume ratio of 20:1. Adjust the pH value of the chitosan mixed solution to 5.5 with 1 mol / L NaOH and HCl. Stir evenly at room temperature for 10 min to obtain a composite condensate.

[0051] (3) Centrifuge the formed composite condensate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin complex coacervation microcapsules.

[0052] Example 3

[0053] (1) Wash the purple sweet potatoes, add water and homogenize them. The mass ratio of purple sweet potato tubers to water is 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0054] (2) Prepare a chitosan solution with a concentration of 1 mg / mL and a molecular weight of 30 kDa. Mix the starch extraction waste liquid and the chitosan solution in a volume ratio of 6:1. Adjust the pH value of the chitosan mixed solution to 7.0 with 1 mol / L NaOH and HCl. Stir evenly at room temperature for 10 min to obtain a composite condensate.

[0055] (3) Centrifuge the formed coacervate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin complex coacervation microcapsules.

[0056] Example 4

[0057] (1) Wash the purple sweet potatoes, add water and homogenize them. The mass ratio of purple sweet potato tubers to water is 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0058] (2) Prepare a chitosan solution with a concentration of 1 mg / mL and a molecular weight of 300 kDa. Mix the starch extraction waste liquid and the chitosan solution in a volume ratio of 90:1. Adjust the pH value of the chitosan mixed solution to 4.0 with 1 mol / L NaOH and HCl, and stir evenly at room temperature for 10 min to obtain a coacervate.

[0059] (3) Centrifuge the formed coacervate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin complex coacervation microcapsules.

[0060] Example 5

[0061] (1) Wash the purple sweet potatoes, add water and homogenize them. The mass ratio of purple sweet potato tubers to water is 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0062] (2) Prepare a chitosan solution with a concentration of 1 mg / mL and a molecular weight of 300 kDa. Mix the starch extraction waste liquid and the chitosan solution in a volume ratio of 20:1. Adjust the pH value of the chitosan mixed solution to 6.5 with 1 mol / L NaOH and HCl, and stir evenly at room temperature for 10 min to obtain a coacervate.

[0063] (3) Centrifuge the formed coacervate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin complex coacervation microcapsules.

[0064] Example 6

[0065] (1) Wash the purple sweet potatoes, add water and homogenize them. The mass ratio of purple sweet potato tubers to water is 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0066] (2) Prepare a chitosan solution with a concentration of 1 mg / mL and a molecular weight of 300 kDa. Mix the starch extraction waste liquid and the chitosan solution in a volume ratio of 1:1. Adjust the pH value of the chitosan mixed solution to 7.0 with 1 mol / L NaOH and HCl, and stir evenly at room temperature for 10 min to obtain a composite condensate.

[0067] (3) Centrifuge the formed composite condensate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin complex coacervation microcapsules.

[0068] Example 7

[0069] (1) Wash the purple sweet potatoes and homogenize them with water. The mass ratio of purple sweet potato tubers to water is 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the purple sweet potato starch extraction waste liquid.

[0070] (2) Prepare a pectin solution with a concentration of 1 mg / mL. Mix the starch extraction waste liquid and the pectin solution in a volume ratio of 100:1. Adjust the pH value of the pectin mixed solution to 2.5 with 1 mol / L NaOH and HCl, and stir magnetically for 10 min to obtain a composite condensate.

[0071] (3) Centrifuge the formed composite condensate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin complex coacervation microcapsules.

[0072] Example 8

[0073] (1) Wash the purple sweet potatoes and homogenize them with water. The mass ratio of purple sweet potato tubers to water is 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the purple sweet potato starch extraction waste liquid.

[0074] (2) Prepare a pectin solution with a concentration of 1 mg / mL. Mix the starch extraction waste liquid and the pectin solution in a volume ratio of 20:1. Adjust the pH value of the pectin mixed solution to 4.0 with 1 mol / L NaOH and HCl, and stir magnetically for 10 min to obtain a composite condensate.

[0075] (3) Centrifuge the formed composite condensate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin complex coacervation microcapsules.

[0076] Example 9

[0077] (1) Wash the purple sweet potatoes, add water and homogenize them. The mass ratio of purple sweet potato tubers to water is 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0078] (2) Prepare a pectin solution with a concentration of 1 mg / mL. Mix the starch extraction waste liquid and the pectin solution in a volume ratio of 1:1. Adjust the pH value of the pectin mixed solution to 4.5 with 1 mol / L NaOH and HCl, and stir magnetically for 10 min to obtain a composite condensate.

[0079] (3) Centrifuge the formed composite condensate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the complex coacervation microcapsules of polysaccharide / purple sweet potato protein / anthocyanin.

[0080] Example 10

[0081] (1) Wash the purple sweet potatoes, add water and homogenize them. The mass ratio of purple sweet potato tubers to water is 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0082] (2) Prepare a λ-carrageenan solution with a concentration of 1 mg / mL. Mix the starch extraction waste liquid and the λ-carrageenan solution in a volume ratio of 100:1. Adjust the pH value of the pectin mixed solution to 2.5 with 1 mol / L NaOH and HCl, and stir magnetically for 10 min to obtain a composite condensate.

[0083] (3) Centrifuge the formed composite condensate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the complex coacervation microcapsules of polysaccharide / purple sweet potato protein / anthocyanin.

[0084] Example 11

[0085] (1) Wash the purple sweet potatoes, add water and homogenize them. The mass ratio of purple sweet potato tubers to water is 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0086] (2) Prepare a λ-carrageenan solution with a concentration of 1 mg / mL. Mix the starch extraction waste liquid and the λ-carrageenan solution in a volume ratio of 10:1. Adjust the pH value of the pectin mixed solution to 4.0 with 1 mol / L NaOH and HCl, and stir magnetically for 10 min to obtain a composite condensate.

[0087] (3) Centrifuge the formed coacervate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin coacervate microcapsules.

[0088] Example 12

[0089] (1) Wash the purple sweet potatoes, add water to make a slurry, with the mass ratio of purple sweet potato tubers to water being 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0090] (2) Prepare a λ-carrageenan solution with a concentration of 1 mg / mL. Mix the starch extraction waste liquid and the λ-carrageenan solution in a volume ratio of 1:1. Adjust the pH value of the pectin mixture solution to 4.0 with 1 mol / L NaOH and HCl, and stir magnetically for 10 min to obtain a coacervate.

[0091] (3) Centrifuge the formed coacervate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin coacervate microcapsules.

[0092] Example 13

[0093] (1) Wash the purple sweet potatoes, add water to make a slurry, with the mass ratio of purple sweet potato tubers to water being 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0094] (2) Prepare a chitosan solution with a concentration of 1 mg / mL and a molecular weight of 100 kDa. Mix the starch extraction waste liquid and the chitosan solution in a volume ratio of 85:1. Adjust the pH value of the chitosan mixture solution to 4.0 with 1 mol / L NaOH and HCl, and stir evenly at room temperature for 10 min to obtain a coacervate.

[0095] (3) Centrifuge the formed coacervate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin coacervate microcapsules.

[0096] Example 14

[0097] (1) Wash the purple sweet potatoes, add water to make a slurry, with the mass ratio of purple sweet potato tubers to water being 1:10. Filter through a 200-mesh filter cloth. After the slurry stands for 12 h, the precipitate is purple sweet potato starch. Centrifuge at 6000 rpm for 20 min and collect the supernatant, which is the waste liquid for purple sweet potato starch extraction.

[0098] (2) Prepare a chitosan solution with a concentration of 1 mg / mL and a molecular weight of 150 kDa. Mix the starch extraction waste liquid and the chitosan solution in a volume ratio of 85:1. Adjust the pH value of the chitosan mixed solution to 4.0 with 1 mol / L NaOH and HCl, and stir the reaction evenly at room temperature for 10 min to obtain a composite condensate.

[0099] (3) Centrifuge the formed composite condensate at 6000 rpm for 20 min, retain the precipitate, and freeze-dry it to obtain the polysaccharide / purple sweet potato protein / anthocyanin complex coacervation microcapsules.

[0100] For the preparation methods of the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules in Examples 1 to 12, the protein and anthocyanin recovery rates were measured respectively to obtain Figure 1 and Figure 2 , and the test method is as follows:

[0101] Centrifuge the formed complex coacervate at 6000 g for 20 min, take the supernatant and measure the protein concentration and anthocyanin concentration therein.

[0102] A. Determination of the recovery rate of purple sweet potato protein

[0103]

[0104] B. Determination of protein concentration

[0105] The protein concentration was determined by the Coomassie brilliant blue method. Take 5 μL of the protein sample and add it to 250 μL of the Coomassie brilliant blue G250 solution, react at room temperature for 10 min, and use an enzyme-linked immunosorbent assay reader to read the absorbance at 595 nm. Make a standard curve with bovine serum albumin at different concentrations: y = 0.6779x + 0.5552 (R 2 = 0.9987).

[0106] C. Determination of anthocyanin content

[0107] The anthocyanin content was determined by the pH differential method. Take 0.5 mL of the sample to be measured and dilute it to 10 mL with potassium chloride buffer solution with a pH value of 1.0 and sodium acetate buffer solution with a pH value of 4.5 respectively. Use a UV-visible spectrophotometer to measure the absorbance at 530 nm and 700 nm respectively. The total anthocyanin content in the sample is expressed in milliequivalents of cyanidin-3-O-glucoside (CGE) according to the formula:

[0108]

[0109] In the formula: c is the anthocyanin content (mg / g); A is the absorbance of the sample; V is the total volume of the sample to be measured (mL); n is the dilution factor; Mw is the molecular weight of CGE (449.4 g / mol); ε is the molar extinction coefficient of CGE (29600 L / cm*mol); d is the width of the cuvette (1 cm); m is the sample mass (g). Where A = (A 530 - A 700 ) pH1.0 -(A 530 - A 700 ) pH4.5 .

[0110] From Figure 1 and Figure 2 , it can be seen that in the preparation method of the purple sweet potato protein / anthocyanin / polysaccharide complex coacervate microcapsules in the embodiments of the present invention, the recovery rates of protein and anthocyanin in the supernatant are both relatively high, and the simple and effective combined recovery of protein and polyphenols in purple sweet potato starch processing wastewater can be achieved.

[0111] Add the purple sweet potato protein / anthocyanin / polysaccharide complex coacervate microcapsules obtained in Example 1 (chitosan molecular weight 30 kDa), Example 4 (chitosan molecular weight 300 kDa), Example 13 (chitosan molecular weight 100 kDa), Example 14 (chitosan molecular weight 150 kDa), Example 7 (pectin), and Example 10 (carrageenan) into water, ultrasonicate for 10 min, take the supernatant, and observe the structure of the microcapsules under an electron microscope with a 20x objective lens to obtain Figure 3 , and it can be seen that microcapsules are significantly formed.

[0112] Perform antioxidant capacity determination on the purple sweet potato protein / anthocyanin / polysaccharide complex coacervate microcapsules obtained in Example 1 (chitosan molecular weight 30 kDa), Example 4 (chitosan molecular weight 300 kDa), Example 13 (chitosan molecular weight 100 kDa), Example 14 (chitosan molecular weight 150 kDa), Example 7 (pectin), and Example 10 (carrageenan) to obtain Figure 4 and Figure 5 , and the determination method is as follows:

[0113] (1) Determination of DPPH (1,1-diphenyl-2-trinitrophenylhydrazine) radical scavenging ability

[0114] 5 mg of microcapsule powder was added to 1 mL of ultrapure water and ground thoroughly. 4 mL of ethanol was added for ultrasonic extraction of anthocyanins, and then centrifuged at 6000 rpm for 10 min to obtain the supernatant. 1.18 mg of DPPH solid was dissolved in 30 mL of 95% ethanol (or absolute ethanol, methanol), ultrasonicated for 5 min and shaken well to make the upper and lower parts uniform. Take 1 mL of the DPPH solution prepared in the above step, dilute it with 0.5 mL of 95% ethanol (or absolute ethanol, methanol) so that the absorbance at 517 nm is between 0.8 and 1.0.

[0115] A0 value: Take 1.0 mL of DPPH solution into a cuvette, add 1 mL of the corresponding organic solvent, dilute and mix, and measure the absorbance A0 value at 517 nm (A0 must be between 0.8 and 1.0).

[0116] A value: Add 1 mL of sample solution, then add 1.0 mL of DPPH solution, and mix to make the total volume of the reaction solution 2 mL. Measure the absorbance A value at 517 nm.

[0117] DPPH free radical scavenging rate (%) = (A0 - A / A0) × 100%

[0118] (2) Determination of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt) free radical scavenging ability

[0119] Take 4 mL of ABTS stock solution (7.4 mmol / L) and 4 mL of potassium persulfate stock solution (2.45 mmol / L), mix them, and place them at room temperature in the dark for 12 h. Dilute the mixture 10 - 20 times with absolute ethanol until the absorbance at 734 nm is 0.70 ± 0.02. This solution is the ABTS· free radical working solution. 5 mg of microcapsule powder was added to 1 mL of ultrapure water and ground thoroughly. 4 mL of ethanol was added for ultrasonic extraction of anthocyanins, and then centrifuged at 6000 rpm for 10 min to obtain the supernatant.

[0120] ABTS· free radical scavenging rate (%) = (A0 - A / A0) × 100%

[0121] A0 value: Take 1.0 mL of ABTS· free radical solution into a cuvette, add 1 mL of the corresponding organic solvent, dilute and mix, and measure the absorbance A0 value at 734 nm.

[0122] A value: Add 1 mL of sample solution, then add 1.0 mL of ABTS· free radical, and mix to make the total volume of the reaction solution 2 mL. Measure the absorbance A value at 734 nm.

[0123] From Figure 3 and Figure 4It can be seen that the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules obtained by using chitosan with different molecular weights, as well as pectin and carrageenan, all exhibit excellent DPPH free radical and ABTS· free radical scavenging abilities. It can be seen that the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules prepared in the examples of the present invention have antioxidant functional characteristics.

[0124] In summary, the preparation method of the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules proposed by the present invention can effectively recycle the protein and anthocyanin in the purple sweet potato starch processing waste liquid (supernatant) to prepare purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules, and the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules have good antioxidant ability. Compared with other methods for treating high-protein waste liquid, this method has the advantages of high efficiency, convenience, green safety, and the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules can be directly edible.

[0125] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. All equivalent structural transformations made by using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A preparation method of purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsules, characterized in that, Comprising the following steps: S10. Wash the purple sweet potatoes, homogenize them with water, filter to obtain a slurry, let the slurry stand and centrifuge to obtain a supernatant; S20. Mix the supernatant with an aqueous solution of polysaccharide, adjust the pH value to 2.5 - 7, and react to obtain a coacervate; S30. Centrifuge the coacervate to obtain a precipitate, and freeze-dry the precipitate to obtain purple sweet potato protein / anthocyanin / polysaccharide coacervate microcapsules; In step S20, the polysaccharide is chitosan, and the volume ratio of the supernatant to the aqueous solution of 1 mg / mL polysaccharide is 1:1 - 90:1, and the pH value is adjusted to 4 - 7; or, the polysaccharide is pectin, and the volume ratio of the supernatant to the aqueous solution of 1 mg / mL polysaccharide is 1:1 - 100:1, and the pH value is adjusted to 2.5 - 4.5; or, the polysaccharide is carrageenan, and the volume ratio of the supernatant to the aqueous solution of 1 mg / mL polysaccharide is 1:1 - 100:1; the pH value is adjusted to 2.5 - 5.

5.

2. The preparation method of the purple sweet potato protein / anthocyanin / polysaccharide complex coacervation microcapsule according to claim 1, characterized in that, In step S20, the polysaccharide is chitosan, and the molecular weight of the chitosan is 30 - 300 kDa.

Images