Homogeneous preparation of osa-starch and use thereof

Abstract

The application provides a homogeneous preparation method of OSA-starch and application thereof, and the method comprises the following steps: dissolving starch in an alkali-urea solution, stirring and then freezing treatment; then thawing at room temperature to obtain a uniform and transparent starch solution, adjusting the pH to 8.0-9.0; adding 1-3% of OSA to the starch solution with the dry starch mass as a reference, reacting for 5-7 hours at room temperature under magnetic stirring, and keeping the pH at 8.0-9.0 during the reaction; then adjusting the pH of the solution to 6.0-7.0, ending the reaction, and obtaining an OSA starch solution; adding anhydrous ethanol to the OSA starch solution for alcohol precipitation, centrifuging to obtain a precipitate, washing the precipitate with an ethanol solution, and drying to obtain OSA-starch. The homogeneous preparation method improves the modification efficiency without damaging the structure of the starch, and the OSA-starch prepared by the method has better emulsifying performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of biomaterial preparation, and particularly relates to a homogeneous preparation method of OSA-starch and application thereof. BACKGROUND

[0002] Natural starch, as a key energy storage molecule in plants, occupies an important position in the industrial field due to its rich source and safe edible characteristics, and is widely used in food, medicine, papermaking and other industries. However, natural starch itself has many inherent defects, such as limited solubility in water, poor processing tolerance, poor storage stability and insufficient functionality, which greatly limit its efficient application in industrial production. In order to break through these limitations, researchers have modified natural starch through physical, chemical and enzymatic methods. Among them, the esterification technology in chemical modification derived OSA-starch (OSA-starch) has become one of the modified starches with great application potential.

[0003] OSA-starch is a representative of starch esterification modification. The hydroxyl groups of starch react with the carboxyl groups of OSA to introduce hydrophobic octenyl side chains to the starch molecular chain, giving starch amphiphilicity. This property makes it as a key ingredient of emulsifiers, stabilizers, thickeners and encapsulants, etc., which exhibits excellent performance in the food, pharmaceutical and cosmetic industries. At present, the annual consumption of OSA-starch in China has exceeded one million tons, and its development prospect is very broad.

[0004] At present, the synthesis of OSA-starch in industry generally adopts the traditional heterogeneous method. Specifically, the starch granules are suspended in weak alkaline water (pH at 8.5), and OSA is added dropwise to mix with starch for esterification reaction. However, this method has obvious drawbacks: there are a large number of hydrogen bonds in the starch molecules, and the solubility in water is extremely low, resulting in a non-homogeneous substitution reaction. The reaction mainly occurs on the surface of the starch granules. This non-homogeneous reaction not only leads to low reaction efficiency, but also causes uneven distribution of substitution groups in the starch molecules, which seriously affects the product quality and performance.

[0005] To solve the above problems, domestic and foreign researchers try to pretreat starch before esterification reaction. Enzymatic method refers to using different enzymes to enzymatically hydrolyze starch, for example, using alpha-amylase to induce the formation of pores in the interior of starch granules, or using pullulanase to perform debranching treatment on starch before adding OSA reagent to perform esterification reaction. Although this method can increase the reaction area of starch and OSA to some extent, it can damage the inherent structure of starch, reduce the degree of substitution of the product, and has low product recovery rate. Ionic solvent method refers to dissolving starch in a pure ionic liquid system and then performing esterification reaction. Although this method can improve the solubility of starch and the reaction efficiency, the modification conditions are harsh (temperature is higher than 70 DEG C and modification time is long), which causes the structure of starch granules to be damaged and the original functional properties to be lost. In summary, the existing pretreatment methods are difficult to significantly improve the degree of substitution and reaction efficiency of OSA-starch without damaging the structure of starch granules, and therefore an innovative homogeneous preparation method is needed to break through the bottleneck of the existing technology and realize the efficient and high-quality production of OSA-starch. SUMMARY

[0006] To solve the problems of low reaction efficiency and uneven distribution of substitution groups caused by the heterogeneous reaction of OSA-starch in the preparation process, and the technical problem of damaging the structure of starch by the existing pretreatment method, the purpose of the present application is to provide a homogeneous preparation method of OSA-starch and its application. By opening the structure of starch under alkaline conditions and using urea to compete for hydrogen bonds under low temperature conditions, the starch is completely dissolved to form a uniform solution, and then esterification modification is performed using OSA, so that the esterification modification is performed in a homogeneous system. On the one hand, the modification efficiency is improved without damaging the structure of starch, and on the other hand, the OSA-starch prepared by this method has better emulsifying performance.

[0007] The purpose of the present application is achieved by the following technical solutions:

[0008] The first aspect of the present application provides a homogeneous preparation method of OSA-starch, comprising the following steps:

[0009] (1) Dissolve starch in an alkali-urea solution, stir and then freeze treat; then thaw at room temperature to obtain a uniform and transparent starch solution, and adjust the pH to 8.0-9.0;

[0010] (2) Add 1-3% of OSA to the starch solution based on the mass of dry starch, react for 5-7 hours at room temperature under magnetic stirring, and maintain the pH at 8.0-9.0 during the reaction; then adjust the pH of the solution to 6.0-7.0 to end the reaction, and obtain an OSA starch solution;

[0011] (3) Add anhydrous ethanol to the OSA starch solution for alcohol precipitation, centrifuge to obtain a precipitate, wash the precipitate with a 75% ethanol solution, and dry to obtain OSA-starch.

[0012] Further, in step (1), the starch is waxy corn starch.

[0013] Further, in step (1), the alkali-urea solution is KOH or NaOH / urea aqueous solution, wherein the concentration of KOH or NaOH is 0.1-1.0 mol / L, and the concentration of urea is 0.1-1.0 mol / L.

[0014] Further, in step (1), the freezing treatment is performed at -20℃ for 12-36 hours.

[0015] Further, in step (3), the volume ratio of the OSA starch solution to anhydrous ethanol is 1:5-10.

[0016] Further, in step (3), the centrifugation is performed at 3000-5000g for 5-15 min.

[0017] Further, in step (3), the precipitate is washed with 75% ethanol solution for 2-5 times.

[0018] Further, in step (3), the drying treatment is performed at 40-50℃ for 36-48 hours.

[0019] The second aspect of the present application provides an OSA-starch prepared by the preparation method of the first aspect.

[0020] The third aspect of the present application provides an application of the preparation method of the first aspect in improving the modification efficiency of starch and the emulsification performance of OSA-starch.

[0021] The present application has the following beneficial effects compared with the prior art:

[0022] 1. Realizing the dissolution of starch and homogeneous modification: through the freeze-thaw treatment of alkali-urea solution, the starch can be completely dissolved in the alkali-urea solution, and the solution is clear and transparent. Compared with the condition of dispersing starch in alkali-urea solution at low temperature or room temperature reported in the literature, the freeze-thaw treatment effectively increases the solubility of starch, solves the problem of low solubility of starch in water phase, and creates conditions for homogeneous esterification reaction.

[0023] 2. Improving the modification efficiency: the homogeneous reaction significantly improves the degree of substitution of OSA-starch. Taking waxy corn starch (Waxy) as an example, the degree of substitution of OSA-starch prepared by homogeneous reaction is significantly higher than that of non-homogeneous reaction product, and the modification efficiency is improved by 30%. This shows that the reaction of starch in the dissolved state with OSA is more sufficient, and solves the problem of low reaction efficiency of traditional non-homogeneous method.

[0024] 3. Optimizing the emulsifying properties of OSA-starch: OSA-starch prepared by homogeneous reaction has better emulsifying properties. The lower the interfacial tension of the emulsifier, the stronger the emulsifying properties. For example, the interfacial tension of OSA-starch prepared by homogeneous reaction of waxy corn starch (Waxy) is significantly lower than that of the product of heterogeneous reaction. At the same time, the emulsifying properties of OSA-starch can be adjusted by adjusting the amount of OSA added. With the increase of the amount of OSA added, the interfacial tension of the product decreases and the emulsifying properties increase.

[0025] 4. Improve emulsion stability: OSA-starch prepared by homogeneous reaction has better emulsion stability. The emulsion prepared by OSA-starch of waxy corn starch prepared by heterogeneous reaction has the highest TSI value and the worst stability; the emulsion prepared by OSA-starch prepared by homogeneous reaction has the best stability and the smallest change in particle size during storage, and has the best storage stability. In addition, the stability and storage stability of the emulsion prepared by the product of homogeneous modification will increase with the increase of the amount of OSA added.

[0026] 5. Enhance the solubility of OSA-starch: OSA-starch prepared by homogeneous reaction has good solubility and can be dissolved at room temperature without gelatinization, obtaining a clear and transparent solution; OSA-starch prepared by heterogeneous reaction cannot be dissolved in water at room temperature and needs to go through a gelatinization step to be dissolved.

[0027] 6. Precise control of OSA-starch properties: Under the condition of homogeneous reaction, the degree of esterification, emulsifying properties and emulsion stability of OSA-starch can be controlled by adjusting the amount of OSA added, which provides the possibility of precise control of product properties and meets the needs of different application scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0028] The application will be further described below in conjunction with the drawings and examples:

[0029] Figure 1 The solubility of different treated starches in Test Example 1 is shown;

[0030] Figure 2 The degree of substitution of OSA-starch obtained by homogeneous / heterogeneous reaction of different chain branch ratio (straight chain / branched chain ratio) starch in Test Example 2 is shown;

[0031] Figure 3 The interfacial tension of OSA-starch obtained by homogeneous / heterogeneous reaction of different chain branch ratio starch in Test Example 2 is shown;

[0032] Figure 4 The emulsion stability of OSA-starch prepared by homogeneous / heterogeneous reaction of different chain branch ratio starch in Test Example 3 is shown; A\B are both emulsion TSI values, B is the comparison result at 24h; C: average particle size of emulsion;

[0033] Figure 5 The solubility of the OSA waxy corn starch prepared by homogeneous / non-homogeneous preparation of Test Example 3 is shown;

[0034] Figure 6 The interfacial tension of the OSA waxy corn starch prepared by homogeneous / non-homogeneous preparation of Test Example 3 before and after gelatinization is shown;

[0035] Figure 7 The emulsion stability of the OSA waxy corn starch prepared by homogeneous / non-homogeneous preparation of Test Example 3 before and after gelatinization is shown; wherein, A\B are the emulsion TSI values, B is the comparison result at 24h; C: the average particle size of the emulsion;

[0036] Figure 8 The effect of the OSA addition amount described in Test Example 3 on the degree of substitution of the OSA waxy corn starch prepared by homogeneous preparation is shown;

[0037] Figure 9 The effect of the OSA addition amount described in Test Example 3 on the interfacial tension of the OSA waxy corn starch prepared by homogeneous preparation is shown;

[0038] Figure 10 The effect of the OSA addition amount described in Test Example 3 on the emulsion stability of the OSA waxy corn starch prepared by homogeneous preparation is shown; wherein, A\B are the emulsion TSI values, B is the comparison result at 24h; C: the average particle size of the emulsion. DETAILED DESCRIPTION

[0039] The specific embodiments and technical solutions of the present application are further described in detail below in combination with the drawings and specific examples. It should be clear that those skilled in the art can refer to the content herein and appropriately improve the process parameters to achieve. It should be particularly pointed out that all similar substitutions and changes are obvious to those skilled in the art, and they are considered to be included in the present application. The method and application of the present application have been described by the preferred embodiments, and the relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

[0040] The present application is described by specific examples, but the present application is not limited thereto.

[0041] In the following examples, some of the raw materials involved are:

[0042] The high-branched waxy corn starch (Waxy) produced by Cargill Biochemical Co., Ltd. has a branch chain ratio of 99%, the medium-branched corn starch (HA50) has a branch chain ratio of 50%, and the low-branched corn starch (HA70) has a branch chain ratio of 30%.

[0043] In the following examples, some of the detection methods involved are:

[0044] ①Degree of substitution determination: The degree of substitution (DS) was determined by Bruker NMR spectrometer. 10 mg of sample and 1 mL of DMSO-d6 were accurately weighed into a 5 mm NMR tube and dissolved at 80 °C with 200 r / min overnight. 100 μL of deuterated trifluoroacetic acid was added before testing. The sample was tested at room temperature with 128 scans. The degree of substitution of the sample can be calculated by the integration of the methyl proton peak of OSA and the anomeric proton peaks of the α-1,4 and α-1,6 glycosidic bonds of the starch molecule.

[0045] ②Emulsion stability analysis: The Turbiscan stability analyzer was used to determine the stability of the oil-in-water emulsion. The prepared emulsion was poured into the measuring bottle, and the near-infrared light source (λair=880 nm) was vertically scanned from the bottom to the top of the measuring bottle, and the backscattered light reflected by the sample was detected. The backscattered light value is related to the particle size and concentration of the emulsion droplets. The particle size of the emulsion droplets increases, the concentration decreases, and the backscattered light value decreases; vice versa. Therefore, by comparing the change of the backscattered light value of the measured sample with time, it can be observed whether the emulsion droplets float, flocculate or coalesce during the determination. The test procedure is as follows: scan every 10 min, for 24 h. The backscattering light map and TSI index are obtained by software.

[0046] ③Measurement of interfacial tension (IFT): The dynamic interfacial tension change of OSA-starch was measured by pendant drop method at room temperature using an optical contact angle measuring instrument, and the recording time was 3000 s. The data were analyzed by Dataphysics.

[0047] Example 1

[0048] The present embodiment provides a homogeneous preparation method of OSA-starch, comprising the following steps:

[0049] (1) Dissolve 3% (w / w) starch in KOH / urea aqueous solution (KOH 0.5 mol / L, urea concentration 0.5 mol / L), stir and freeze at-20 °C for 24 hours; then thaw at room temperature to obtain a uniform and transparent starch solution, and adjust the pH to 8.5.

[0050] Among them, the starches are HA70, HA50 and waxy corn starch Waxy, respectively.

[0051] (2) Based on the mass of dry starch, 3% of OSA was added to the starch solution under magnetic stirring at room temperature for 6 hours, and the pH was maintained at 8.5 during the reaction; then the pH of the solution was adjusted to 6.5 to end the reaction, and an OSA-starch solution was obtained.

[0052] (3) Alcohol precipitation was performed by adding anhydrous ethanol (1:8, V / V) into the OSA-starch solution, and the precipitate was obtained by centrifugation at 4000g for 10 min. The precipitate was washed with 75% ethanol solution for three times, and dried in an oven at 45°C for 48h to obtain homogeneous-Waxy, homogeneous-HA70 and homogeneous-HA50 OSA-starches, respectively.

[0053] Comparative Example 1

[0054] The present example provides a heterogeneous preparation method of OSA-starch, comprising the following steps:

[0055] (1) 3% (w / w) waxy corn starch Waxy was suspended in distilled water under magnetic stirring, and the pH was adjusted to 8.5.

[0056] (2) 3% OSA was added into the starch solution under magnetic stirring based on the mass of dry starch, and the reaction was carried out for 6 hours while maintaining the pH at 8.5. Then the pH of the solution was adjusted to 6.5 to end the reaction.

[0057] (3) The precipitate was obtained by centrifugation at 4000g for 10 min, and the product was washed with distilled water and 75% ethanol for three times, respectively, and dried in an oven at 45°C for 48h to obtain OSA-starch (heterogeneous-Waxy).

[0058] Test Example 1

[0059] The present test example investigates the effect of different treatments and different solutions on the solubility of starch, specifically:

[0060] (1) 3% (w / w) starch was dissolved in 0.5mol / L KOH-0.5mol / L urea solution, and after stirring, it was frozen at -20°C for 24 hours.

[0061] (2) 3% (w / w) starch was dissolved in 0.5mol / L KOH-0.5mol / L urea solution, and after stirring, it was refrigerated at -4°C for 24 hours.

[0062] (3) 3% (w / w) starch was dissolved in 3mol / L KOH-0.5mol / L urea solution, and after stirring at room temperature for 24 hours.

[0063] (4) 3% (w / w) starch was dissolved in 3mol / L KOH solution, and after stirring at room temperature for 24 hours.

[0064] As Figure 1As shown, in a 0.5 mol / L KOH-0.5 mol / L urea solution, starch dissolved after freeze-thaw treatment, resulting in a clear and transparent solution. However, in a starch solution stirred at -4℃, only partial dissolution occurred, and the solution remained only partially clear with no obvious large particles. This indicates that freeze-thaw treatment effectively increases the solubility of starch in a 0.5 mol / L KOH-0.5 mol / L urea solution, achieving homogeneous dissolution. When the KOH concentration is increased, starch dissolves at room temperature with stirring, meaning that low temperature is not a necessary condition for dissolving starch at high KOH concentrations, and the addition of urea at this concentration has little effect on dissolution. However, high KOH concentrations may lead to starch degradation. Therefore, a low-concentration alkali-urea solution was used to completely dissolve starch through freeze-thaw treatment.

[0065] Test Example 2:

[0066] This test case examined the degree of substitution and surface tension of OSA-starch prepared by different methods in Example 1 and Comparative Example 1.

[0067] like Figure 2 As shown, for waxy corn starch (Waxy), the degree of substitution of OSA-starch prepared by homogeneous reaction is significantly higher than that of heterogeneous reaction product, indicating that starch reacts more readily with OSA in the dissolved state, significantly improving the modification efficiency (by 30%). Furthermore, during homogeneous modification, the branching ratio of starch does not affect the degree of substitution of OSA-starch; there are no significant differences in the degree of substitution among homogeneous-Waxy, homogeneous-HA50, and homogeneous-HA70.

[0068] Interfacial tension reflects the emulsifying ability of an emulsifier; the lower the interfacial tension, the stronger the emulsifying performance. This test example measured the surface tension of OSA-starch prepared by different methods in Example 1 and Comparative Example 1.

[0069] like Figure 3 As shown, for waxy corn starch, the interfacial tension of homogeneously prepared OSA starch is significantly lower than that of heterogeneous reaction products, indicating that the OSA starch prepared by homogeneous reaction has better emulsifying properties. Furthermore, the ratio of linear to branched chains in starch affects emulsifying properties, with OSA starch prepared from waxy corn starch exhibiting the best emulsifying performance.

[0070] Test Example 3:

[0071] This test example uses OSA-starch prepared by different methods in Example 1 and Comparative Example 1 to prepare oil-in-water emulsions and determine their stability. TSI is the instability index; the lower the TSI, the better the stability.

[0072] The method for preparing the oil-in-water emulsion is as follows:

[0073] Dissolve 1% (w / w) OSA-starch in ultrapure water and stir magnetically until dissolved. Separate a portion of the sample for gelatinization treatment (heat at 80°C for 30 minutes) to obtain gelatinized and non-gelatinized OSA-starch solutions.

[0074] Gelatinized and non-gelatinized OSA starch solutions were mixed with soybean oil at a volume ratio of 10:1 and then sonicated under the following conditions: 35% amplitude for 2 minutes (3 seconds on, 7 seconds off) to obtain an oil-in-water emulsion.

[0075] Depend on Figure 4 It was found that the emulsion prepared from heterogeneously generated OSA-starch had the highest TSI value and the worst stability, while the emulsion prepared from homogeneously generated waxy corn starch had the lowest TSI value and the best stability. Further investigation into their storage stability revealed that the emulsion prepared from homogeneously generated waxy corn starch exhibited the smallest particle size change during storage, demonstrating the best storage stability. In contrast, the emulsion prepared from heterogeneously generated OSA-starch showed a significant increase in particle size after seven days of storage, indicating droplet aggregation or coalescence and poor stability.

[0076] Figure 5 The solubility of OSA waxy corn starch prepared homogeneously and heterogeneously is shown. The heterogeneously prepared OSA-starch is insoluble at room temperature and precipitates, requiring gelatinization to dissolve. Therefore, gelatinization is a necessary condition for the dissolution of heterogeneously prepared OSA-starch and its effective emulsifying properties. However, the OSA starch prepared by homogeneous reaction exhibits good solubility and dissolves without gelatinization, yielding a clear and transparent solution.

[0077] The interfacial tension of OSA starch was determined by gelatinizing it. Figure 6 The results showed that for heterogeneously prepared OSA starch, gelatinization significantly reduced its interfacial tension and increased its emulsifying properties. However, regardless of gelatinization, the interfacial tension of heterogeneously prepared OSA starch was greater than that of homogeneously prepared OSA starch, indicating that its emulsifying properties were significantly lower. For homogeneously prepared OSA starch, there was no significant change in interfacial tension before and after gelatinization, suggesting that homogeneously prepared OSA starch can exhibit good emulsifying properties without gelatinization.

[0078] Emulsions were prepared using gelatinized and non-gelatinized OSA starch, and their stability was determined. The results are as follows: Figure 7As shown, the stability of the emulsion is consistent with the emulsification performance trend, and the OSA starch prepared by homogeneous phase has the best emulsification performance, and the emulsion prepared by non-gelatinized OSA starch has the best stability. By exploring the storage stability, it can be found that the emulsion prepared by non-gelatinized OSA starch prepared by homogeneous phase has the smallest particle size change during storage and the best storage stability; in addition, the emulsion prepared by gelatinized OSA starch prepared by heterogeneous phase has good storage stability. However, the emulsion prepared by non-gelatinized OSA starch prepared by homogeneous phase has the smallest particle size and the highest emulsification efficiency.

[0079] The degree of substitution of OSA-starch under different OSA addition amounts is as follows: Figure 8 As shown, the degree of substitution of OSA starch prepared by homogeneous phase increases with the increase of OSA addition amount, indicating that the degree of esterification of OSA starch can be adjusted by adjusting the addition amount of OSA.

[0080] The interfacial tension of OSA-starch under different OSA addition amounts is as follows: Figure 9 As shown, the interfacial tension of OSA starch prepared by homogeneous phase decreases with the increase of OSA addition amount, indicating that the emulsification performance of OSA starch can be adjusted by adjusting the addition amount of OSA.

[0081] The emulsion stability of OSA-starch under different OSA addition amounts is as follows: Figure 10 As shown, the emulsion stability and storage stability of OSA starch prepared by homogeneous phase increase with the increase of OSA addition amount, indicating that the stability of the emulsion prepared by OSA starch can be adjusted by adjusting the addition amount of OSA.

[0082] Finally, it should be noted that the above is only used to illustrate the technical solutions of the present application and is not limited. Although the present application has been described in detail with reference to the preferred arrangement, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A homogeneous preparation method for OSA-starch, characterized in that, The preparation method includes the following steps: (1) Dissolve starch in an alkali-urea solution, stir and freeze; then thaw at room temperature to obtain a uniform and transparent starch solution, and adjust the pH to 8.0~9.0; The alkali-urea solution is a KOH or NaOH / urea aqueous solution, wherein the concentration of KOH or NaOH is 0.1~1.0 mol / L and the concentration of urea is 0.1~1.0 mol / L; (2) Based on the mass of dry starch, add 1-3% OSA dropwise to the starch solution and react at room temperature for 5-7 hours under magnetic stirring, maintaining the pH at 8.0-9.0 during the reaction; then adjust the pH of the solution to 6.0-7.0 and stop the reaction to obtain OSA starch solution. (3) Add anhydrous ethanol to the OSA starch solution for alcohol precipitation, centrifuge to obtain the precipitate, wash the precipitate with ethanol solution, and dry to obtain OSA-starch.

2. The homogeneous preparation method of OSA-starch according to claim 1, characterized in that, In step (1), the starch is waxy corn starch.

3. The homogeneous preparation method of OSA-starch according to claim 1, characterized in that, In step (1), the freezing conditions include freezing at -20 ℃ for 12 to 36 hours.

4. The homogeneous preparation method of OSA-starch according to claim 1, characterized in that, In step (3), the volume ratio of OSA starch solution to anhydrous ethanol is 1:5~10.

5. The homogeneous preparation method of OSA-starch according to claim 1, characterized in that, In step (3), the centrifugation conditions include: 3000~5000 g, centrifugation for 5~15 min.

6. The homogeneous preparation method of OSA-starch according to claim 1, characterized in that, In step (3), the precipitate is washed 2 to 5 times with 75% ethanol solution.

7. The homogeneous preparation method of OSA-starch according to claim 1, characterized in that, In step (3), the drying conditions include drying in an oven at 40~50 ℃ for 36~48 hours.

8. An OSA-starch prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the preparation method according to any one of claims 1 to 7 in improving starch modification efficiency and enhancing the emulsifying properties of OSA-starch.

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