A method for electrospinning starch by direct enzymatic hydrolysis

Abstract

The present invention relates to an electrospinning method for directly enzymatically hydrolyzing starch. The method uses ungelatinized common starch as the raw material, first undergoes a simple pretreatment, then performs enzymatic hydrolysis. The enzymatically hydrolyzed starch is washed, dried, and then dissolved in a solvent to obtain a spinning solution, which is then electrospun to produce starch fibers. The method is simple and low-cost. By performing a simple pretreatment and enzymatic hydrolysis on the ungelatinized starch, dissolving it in a solvent and performing electrospinning, the resulting starch micro-nanofibers exhibit a non-beaded fiber morphology and a uniform fiber diameter distribution, with an average fiber diameter ranging from 100 to 300 nm. These fibers can be widely used in drug delivery, wound dressings, adsorbent materials, flexible wearable materials, and other fields.

Description

Technical Field

[0001] The present invention relates to starch modification and its application field, and in particular to an electrostatic spinning method for directly enzymatically hydrolyzing starch. Background Art

[0002] Starch is a polysaccharide composed of glucose molecules, primarily consisting of amylose and amylopectin. Sources include corn starch, wheat starch, potato starch, and sweet potato starch. The ratio of amylose to amylopectin varies depending on the source, with amylose generally comprising 20% ​​to 30% of the total starch content. Starch is highly biodegradable and environmentally friendly due to its plant-based origin, making it a valuable research topic.

[0003] Ordinary starch has poor water solubility and a high number of branched chains, which significantly limits its suitability for electrospinning. Therefore, physical, chemical, enzymatic, and combined modification methods are often used to alter the starch's molecular structure or physicochemical properties. Enzymatic starch hydrolysis offers advantages such as high efficiency, safety, and high specificity. However, its preparation is time-consuming (International Journal of Biological Macromolecules, 2019, 140:350–357). Furthermore, the enzymatically hydrolyzed starch suffers from low yields and a reduced molecular weight. The resulting spinning solution, formed when mixed with water, has a low viscosity, making spinning difficult. Furthermore, since the spinning solution is water-based, it is sensitive to humidity during electrospinning. Excessive humidity can hinder water evaporation during electrospinning, resulting in the formation of beaded fibers. The patent application publication number CN 113882024A, "Method for preparing starch nanofibers by electrospinning," fully gelatinizes the relatively expensive high-amylose starch and then debranches it enzymatically to obtain a high-amylose debranching solution (with water as the only solvent). The debranching solution is sheared and homogenized to form a spinning solution to produce starch nanofibers.

[0004] In summary, the preparation of enzymatically hydrolyzed common starch in existing technologies is time-consuming, and the molecular weight of the starch is also reduced. The viscosity of the spinning solution formed when mixed with water is low, and the fibers are sensitive to humidity during the spinning process, resulting in spinning difficulties. The present invention performs a simple pretreatment on low-cost ungelatinized common starch, then performs enzymatic hydrolysis. The enzymatically hydrolyzed starch is washed, dried, and then dissolved in a solvent to obtain a spinning solution for electrospinning, thereby obtaining starch micro-nanofibers with uniform fiber distribution and a diameter of 100 to 300 nm. Summary of the Invention

[0005] The present invention provides an electrostatic spinning method for directly enzymatically hydrolyzing starch, comprising the steps of: subjecting ungelatinized common starch to a simple pretreatment, then enzymatically hydrolyzing the starch; washing and drying the enzymatically hydrolyzed starch, and then dissolving the enzymatically hydrolyzed starch in a solvent to obtain a spinning solution for spinning, thereby obtaining starch micro-nanofibers with uniform fiber distribution and a diameter of 100 to 300 nm.

[0006] In order to achieve the purpose of the present invention, the present invention adopts the following technical solutions:

[0007] A method for electrospinning directly enzymatically hydrolyzed starch, wherein the directly enzymatically hydrolyzed starch is prepared from the following components in parts by weight:

[0008] 100 parts starch milk

[0009] 0.001~0.1 parts of enzyme

[0010] The starch milk is prepared from the following components in parts by weight:

[0011] 100 parts starch

[0012] 500~3000 parts of buffer solution

[0013] The spinning solution in the electrospinning method is prepared from the following components in parts by weight:

[0014] 100 parts of direct enzymatic starch

[0015] 500-2000 parts of solvent

[0016] The present invention provides an electrospinning method for directly enzymatically hydrolyzing starch, comprising the following steps:

[0017] 1) The specific steps of preparing starch milk are as follows: 500 to 2000 parts of deionized water and a buffer system are mixed to prepare a solution with a pH of 4 to 7.5, and then the solution is uniformly mixed with 100 parts of starch to obtain starch milk;

[0018] 2) 100 parts of the starch milk obtained in step 1) are heat-treated at 55-70° C. or ultrasonically treated at room temperature, 100 parts of the pre-treated starch milk and 0.001-0.1 parts of enzyme are added to a reaction apparatus, and enzymatic hydrolysis is carried out at 35-50° C. and a speed of 100 r / min-1000 r / min for 0.5-10 h, followed by suction filtration, and the enzymatically hydrolyzed starch is washed with 500 parts of deionized water, dried, and then ground to obtain directly enzymatically hydrolyzed starch;

[0019] 3) dissolving 100 parts of the directly enzymatically hydrolyzed starch obtained in step 2) in 500 to 2000 parts of a solvent until the starch is uniformly dispersed to obtain a spinning solution.

[0020] 4) The spinning solution obtained in step 3) is subjected to an electrospinning process to prepare starch micro-nanofibers.

[0021] Preferably, the starch is any one of wheat starch, corn starch, potato starch, glutinous rice starch and glutinous corn starch.

[0022] Preferably, the buffer is prepared by mixing any one of a citric acid-sodium citrate buffer system, an acetic acid-sodium acetate buffer system and an imidazole-hydrochloric acid buffer system with deionized water.

[0023] Preferably, the enzyme is any one or more of α-amylase, β-amylase, γ-amylase, isoamylase, cellulase and hemicellulase.

[0024] Preferably, the solvent is any one or more of dimethyl sulfoxide, formic acid and diacetic acid.

[0025] Compared with the prior art, the electrospinning method of directly enzymatically hydrolyzing starch according to the present invention has the following advantages and significant progress:

[0026] (1) The present invention can avoid the reduction of the molecular weight of the enzymatically hydrolyzed starch after gelatinization by directly enzymatically hydrolyzing the starch, thereby making the spinning solution have better viscosity and the fiber is easy to form. (2) The present invention can increase the enzymatic hydrolysis rate of the starch milk by performing a simple pretreatment on the starch milk and then adding the enzyme, and has a good enzymatic hydrolysis effect within 0.5h to 10h. (3) The present invention can avoid the adverse effects of environmental humidity on fiber formation during the electrospinning process by dissolving the directly enzymatically hydrolyzed starch in a relatively volatile solvent to prepare the spinning solution. (4) The present invention adopts the electrospinning process to prepare starch-based micro-nano fibers with an average diameter of 100 to 300nm, which can be widely used in the fields of drug release, wound dressings, adsorption materials, flexible wearable materials, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 , Scanning electron microscope image of electrospun starch fiber in Example 1.

[0028] Figure 2 , fiber diameter distribution diagram of electrospun starch fibers in Example 1.

[0029] Figure 3 , Scanning electron microscope image of electrospun starch fiber in Example 2.

[0030] Figure 4 , fiber diameter distribution diagram of electrospun starch fibers in Example 2.

[0031] Figure 5 , Scanning electron microscope image of electrospun starch fiber in Example 3.

[0032] Figure 6 , fiber diameter distribution diagram of electrospun starch fibers in Example 3. DETAILED DESCRIPTION

[0033] The present invention will be described in detail with reference to the following examples. However, it should be understood that the following examples are merely illustrative of the embodiments of the present invention and are not intended to limit the scope of the present invention.

[0034] The relevant test methods in the embodiments are described as follows:

[0035] The electrospun samples were gold-sprayed and vacuum-dried, and the surface morphology of the electrospun samples was observed using a scanning electron microscope. The test voltage was 3 kV and the magnification was 5000 times. The fiber diameter distribution of the electrospun scans was calculated using Image J software. 5 to 10 images were taken for each sample, and 50 to 100 points were taken for each image.

[0036] Example 1:

[0037] The electrospinning method of direct enzymatic starch hydrolysis comprises the following steps:

[0038] 1) Preparation of starch milk: 700 parts of deionized water and acetic acid-sodium acetate were mixed to prepare a solution with a pH of 4.5, and then the solution was uniformly mixed with 100 parts of corn starch to obtain starch milk.

[0039] 2) Preparation of directly enzymatically hydrolyzed starch: 100 parts of the starch milk prepared in step 1) were heat-treated at 65° C., 100 parts of the pre-treated starch milk and 0.003 parts of α-amylase were added to a reaction apparatus, and enzymatic hydrolysis was carried out at 40° C. and 500 r / min for 6 hours. The enzymatically hydrolyzed starch was then filtered, washed with 500 parts of deionized water, dried, and then ground to obtain directly enzymatically hydrolyzed starch having a linear content of 60.1% and a yield of 75.3%.

[0040] 3) Preparation of spinning solution: 600 parts of formic acid solvent were added to 100 parts of directly enzymatically hydrolyzed starch prepared in step 2) until the starch was evenly dispersed to obtain a spinning solution.

[0041] 4) Preparation of starch fiber by electrospinning: The spinning solution prepared in step 3) was spun at a voltage of 15 kV, wherein the propulsion speed of the spinning solution was 0.7 ml / h, the needle distance was 10 cm, the needle gauge was 24 G, the speed of the winding drum was 600 r / min, and the spinning time was 8 h to obtain starch fiber ( Figure 1 ), with an average diameter ranging from 200 to 350 nm ( Figure 2 ).

[0042] Example 2:

[0043] The electrospinning method of direct enzymatic starch hydrolysis comprises the following steps:

[0044] 1) Preparation of starch milk: 1500 parts of deionized water and citric acid-sodium citrate were mixed to prepare a solution with a pH of 6, and then the solution was uniformly mixed with 100 parts of wheat starch to obtain starch milk.

[0045] 2) Preparation of directly enzymatically hydrolyzed starch: 100 parts of the starch milk prepared in step 1) were heat-treated at 60° C., 100 parts of the pretreated starch milk and 0.005 parts of isoamylase were added to a reaction apparatus, and enzymatic hydrolysis was carried out at 50° C. and 300 r / min for 2 hours. The starch was then filtered and washed with 500 parts of deionized water, dried, and then ground to obtain directly enzymatically hydrolyzed starch having a linear content of 70.0% and a yield of 84.1%.

[0046] 3) Preparation of spinning solution: 1000 parts of dimethyl sulfoxide solvent were added to 100 parts of directly enzymatically hydrolyzed starch prepared in step 2) until the starch was evenly dispersed to obtain a spinning solution.

[0047] 4) Preparation of starch fiber by electrospinning: The spinning solution prepared in step 3) was spun at a voltage of 20 kV, wherein the spinning solution propulsion speed was 1 ml / h, the needle distance was 8 cm, the needle gauge was 22G, the spinning drum speed was 400 r / min, and the spinning time was 6 h to obtain starch fiber ( Figure 3 ), with an average diameter ranging from 100 to 300 nm ( Figure 4 ).

[0048] Example 3:

[0049] The electrospinning method of direct enzymatic starch hydrolysis comprises the following steps:

[0050] 1) Preparation of starch milk: 2500 parts of deionized water and imidazole-hydrochloric acid were mixed to prepare a solution with a pH of 7.5, and then the solution was evenly mixed with 100 parts of glutinous rice starch to obtain starch milk.

[0051] 2) Preparation of directly enzymatically hydrolyzed starch: 100 parts of the starch milk prepared in step 1) were ultrasonically treated at room temperature, and 100 parts of the pre-treated starch milk were added to a reaction apparatus together with 0.008 parts of β-amylase and isoamylase. The mixture was enzymatically hydrolyzed at 35° C. and 800 r / min for 8 hours, and then filtered. The enzymatically hydrolyzed starch was washed with 500 parts of deionized water, dried, and then ground to obtain directly enzymatically hydrolyzed starch with a linear chain content of 67.3% and a yield of 73.2%.

[0052] 3) Preparation of spinning solution: 1500 parts of diacetic acid as solvent were added to 100 parts of directly enzymatically hydrolyzed starch prepared in step 2) until the starch was evenly dispersed to obtain a spinning solution.

[0053] 4) Preparation of starch fiber by electrospinning: The spinning solution prepared in step 3) was spun at a voltage of 20 kV, wherein the propulsion speed of the spinning solution was 1.5 ml / h, the needle distance was 12 cm, the needle gauge was 26 G, the speed of the winding drum was 800 r / min, and the spinning time was 5 h to obtain starch fiber ( Figure 5 ), with an average diameter ranging from 100 to 300 nm ( Figure 6 ).

Claims

1. An electrospinning method for direct enzymatic starch hydrolysis, characterized in that: The method comprises the following steps: 1) Mixing 500-2000 parts of deionized water with a buffer system to prepare a solution with a pH of 4-7.5, and then uniformly mixing with 100 parts of starch to obtain a starch emulsion; 2) ultrasonically treating 100 parts of the starch milk obtained in step 1) at room temperature, adding 100 parts of the pre-treated starch milk and 0.001-0.1 parts of enzyme to a reaction apparatus, performing enzymatic hydrolysis at 35-50°C and 100 r / min-1000 r / min for 0.5-10 hours, then filtering, washing the enzymatically hydrolyzed starch with 500 parts of deionized water, drying, and then grinding to obtain directly enzymatically hydrolyzed starch; 3) dissolving 100 parts of the directly enzymatically hydrolyzed starch obtained in step 2) in 500-2000 parts of a solvent until the starch is uniformly dispersed to obtain a spinning solution; 4) preparing starch micro-nanofibers by electrospinning the spinning solution obtained in step 3); The enzyme is any one or more of α-amylase, β-amylase, γ-amylase, and isoamylase; The solvent is any one or more of dimethyl sulfoxide, formic acid and diacetic acid; The starch is any one of wheat starch, corn starch, potato starch, glutinous rice starch and glutinous corn starch.

2. The method according to claim 1, characterized in that The buffer solution is prepared by mixing any one of a citric acid-sodium citrate buffer system, an acetic acid-sodium acetate buffer system and an imidazole-hydrochloric acid buffer system with deionized water.

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