A method for measuring viscosity of pregelatinized starch

Abstract

The invention relates to a method for measuring the viscosity of pregelatinized starch. The method adopts a temperature of 125-135 DEG C and a drying time of 1-1.5 hours. The relative moisture content of the pregelatinized starch is increased by 2%, and the problem of low rotational viscosity measurement under the same mass caused by the increase of relative mass can be avoided. The method adopts anhydrous ethanol as a dispersant, so that the pregelatinized starch will not clump after adding water. Due to the mutual solubility of ethanol and water, a certain amount of anhydrous ethanol is added as a dispersant to disperse the sample and then add decarbonated distilled water to completely avoid the caking phenomenon. At the same time, the decarbonated distilled water can avoid the problem caused by water acidity. The method has good repeatability and high accuracy.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical analysis methods, and particularly relates to a method for measuring the viscosity of pregelatinized starch. Background Art

[0002] Pregelatinized starch is made from natural starch and modified. Compared with ordinary starch, it has the characteristics of fast dissolution and stable thermal viscosity, and is widely used in many industries such as medicine, food, cosmetics, feed, metal casting, textile, papermaking, etc. When used as a binder in the metallurgical industry, its performance indicators are usually characterized by measuring viscosity, swelling and solubility.

[0003] However, there is no method specifically for measuring the rotational viscosity of pregelatinized starch at this stage. When measuring, each laboratory usually refers to the GB / T 22427.7-2008 "Determination of Starch Viscosity" standard. However, when it is actually applied to pregelatinized starch, it is found that when the sample is directly weighed and dissolved in water, the amount of solid solution agglomerates will vary greatly each time, resulting in large viscosity measurement data. The viscosity measured each time is different, and the repeatability is poor.

[0004] In view of the above reasons, the present invention is proposed. Summary of the invention

[0005] In order to solve the technical problem that the viscosity of pregelatinized starch measured each time is different and the repeatability is poor in the prior art, the present invention provides a method for measuring the viscosity of pregelatinized starch. The method of the present invention can avoid the problem that the viscosity measurement of the rotation meter is low due to the inability to keep the pregelatinized starch constant after drying at 110°C. The method of the present invention has good repeatability and stable viscosity measurement.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for measuring the viscosity of pregelatinized starch, the method comprising the following steps:

[0008] (1) Sample preparation: Grind or ball-mill the pregelatinized starch, and sieve to obtain a sample;

[0009] (2) Drying: Dry the sample to constant weight, cool it to room temperature, obtain dry pregelatinized starch, and store it in a dry and sealed container for future use;

[0010] (3) Dissolving: Weigh the reserved pregelatinized starch, record the mass as m, place it in anhydrous ethanol, disperse it evenly, add carbon dioxide-free distilled water to the pre-dissolved theoretical volume V, heat and stir, add carbon dioxide-free distilled water to the pre-dissolved theoretical volume V, continue stirring for 1-3 minutes, and obtain a pregelatinized starch solution;

[0011] (4) adding the pregelatinized starch solution to a rotational viscometer, measuring the viscosity, and recording the rotational viscometer reading α;

[0012] (5) Calculation of viscosity of pregelatinized starch

[0013] Where, α is the reading of the rotational viscometer, mPa.s;

[0014] m——actual weighed amount of pregelatinized starch for use, g;

[0015] V——pre-dissolution theoretical volume, mL;

[0016] ω——Percentage of solids in pregelatinized starch.

[0017] Furthermore, the product in step (1) is sieved through a standard sieve of 110 to 130 meshes.

[0018] Furthermore, in step (2), the drying temperature is 125-135° C., and the drying time is 1-1.5 h.

[0019] When conventional 110° C. drying is adopted, the mass of pregelatinized starch continues to decrease during the constant weight process and the constant weight cannot be maintained. However, the constant weight effect can be achieved by adopting the drying temperature and time of the present invention, and the real moisture content is measured. The relative moisture content increases by 2%, which can avoid the problem of low rotational viscosity measurement under the same mass caused by the increase in relative mass.

[0020] Furthermore, the volume of anhydrous ethanol in step (3) is 1 / 20 to 1 / 10 of the theoretical volume of the pre-dissolution.

[0021] The theoretical pre-dissolution volume in the present invention is determined based on the percentage of solids in the pre-gelatinized starch. For example, if the rotational viscosity of pre-gelatinized starch with a solid content of 5% needs to be measured, the viscometer used needs to have a volume of at least 300 mL for measurement. The pre-dissolution volume can be any volume ≥ 300 mL, that is, Vхω = theoretical sample weight. Since the pre-gelatinized starch has a relatively large hygroscopicity, the actual weighing needs to be fast and accurate, and it should be approximately close to the theoretical mass. Just record the accurate value.

[0022] When pregelatinized starch is directly added with water, heated and stirred to dissolve, some samples will always clump together, which cannot be removed after a long period of heating and stirring. In addition, the size and number of clumps are inconsistent each time. This will cause the mass fraction of the actual solid content to be inconsistent with the theory, resulting in large differences in parallel measurement results, incomparability of results from different laboratories, and poor repeatability.

[0023] The anhydrous ethanol in the present invention is used as a dispersant, so that the pregelatinized starch will not clump after adding water. Due to the mutual solubility of ethanol and water, the agglomeration phenomenon is completely avoided by adding a certain amount of anhydrous ethanol as a dispersant to disperse the sample and then adding decarbonated distilled water. At the same time, decarbonated distilled water can avoid problems caused by water acidity.

[0024] Furthermore, in step (3), the temperature of heating and stirring is 85 to 95° C., and the time is 20 to 40 minutes.

[0025] Since a small amount of ethanol or water will evaporate after heating and stirring, it is necessary to add carbon dioxide-free distilled water to the pre-dissolved theoretical volume.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The method of the present invention adopts a temperature of 125-135° C. and a drying time of 1-1.5 h, and the relative moisture content of the pregelatinized starch increases by 2%, which can avoid the problem of low rotational viscosity measurement under the same mass due to the increase in relative mass;

[0028] (2) The method of the present invention uses anhydrous ethanol as a dispersant, which can prevent the pregelatinized starch from agglomerating after adding water. Due to the miscibility of ethanol and water, the agglomeration phenomenon is completely avoided by adding a certain amount of anhydrous ethanol as a dispersant to disperse the sample and then adding decarbonated distilled water. At the same time, decarbonated distilled water can avoid problems caused by water acidity. The method of the present invention has good repeatability and high accuracy. DETAILED DESCRIPTION

[0029] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0030] Example 1

[0031] A method for measuring the viscosity of pregelatinized starch in this embodiment comprises the following steps:

[0032] (1) Sample preparation: Grind the pregelatinized starch and pass it through a 110-mesh standard sieve to obtain a sample;

[0033] (2) Drying: Dry the sample in an electric air drying oven to constant weight at a temperature of 125° C. for 1.5 h, cool to room temperature, and obtain dry pregelatinized starch, which is then placed in a dry and sealed container for later use;

[0034] (3) Dissolution: Weigh the pregelatinized starch for use, record the mass as m, and place it in anhydrous ethanol, the volume of which is 1 / 20 of the theoretical volume of the pre-dissolution. After uniform dispersion, add distilled water without carbon dioxide to the theoretical volume of the pre-dissolution V. After stirring for 40 min at a temperature of 85° C., add distilled water without carbon dioxide to the theoretical volume of the pre-dissolution V, and continue stirring for 1 min to obtain a pregelatinized starch solution.

[0035] (4) adding the pregelatinized starch solution to a rotational viscometer, measuring the viscosity, and recording the rotational viscometer reading α;

[0036] (5) Calculation of viscosity of pregelatinized starch

[0037] Where, α is the reading of the rotational viscometer, mPa.s;

[0038] m——actual weighed amount of pregelatinized starch for use, g;

[0039] V——pre-dissolution theoretical volume, mL;

[0040] ω——Percentage of solids in pregelatinized starch.

[0041] Example 2

[0042] A method for measuring the viscosity of pregelatinized starch in this embodiment comprises the following steps:

[0043] (1) Sample preparation: ball-mill the pregelatinized starch and pass it through a 120-mesh standard sieve to obtain a sample;

[0044] (2) Drying: Dry the sample in an electric air drying oven to constant weight at a temperature of 130° C. for 1.25 h, cool to room temperature, and obtain dry pregelatinized starch, which is then placed in a dry and sealed container for later use;

[0045] (3) Dissolution: Weigh the reserved pregelatinized starch, record the mass as m, put it in anhydrous ethanol, the volume of anhydrous ethanol is 1 / 12.5 of the theoretical volume of predissolution, and after uniform dispersion, add carbon dioxide-free distilled water to the theoretical volume of predissolution V. After stirring for 30 min at a temperature of 90° C., add carbon dioxide-free distilled water to the theoretical volume of predissolution V, and continue stirring for 2 min to obtain a pregelatinized starch solution;

[0046] (4) adding the pregelatinized starch solution to a rotational viscometer, measuring the viscosity, and recording the rotational viscometer reading α;

[0047] (5) Calculation of viscosity of pregelatinized starch

[0048] Where, α is the reading of the rotational viscometer, mPa.s;

[0049] m——actual weighed amount of pregelatinized starch for use, g;

[0050] V——pre-dissolution theoretical volume, mL;

[0051] ω——Percentage of solids in pregelatinized starch.

[0052] Example 3

[0053] A method for measuring the viscosity of pregelatinized starch in this embodiment comprises the following steps:

[0054] (1) Sample preparation: Grind the pregelatinized starch and pass it through a 130-mesh standard sieve to obtain a sample;

[0055] (2) Drying: Dry the sample in an electric air drying oven to constant weight at a temperature of 135° C. for 1 h, cool to room temperature, and obtain dry pregelatinized starch, which is then placed in a dry and sealed container for later use;

[0056] (3) Dissolution: Weigh the pregelatinized starch for use, record the mass as m, and place it in anhydrous ethanol, the volume of which is 1 / 10 of the theoretical volume of the pre-dissolution. After uniform dispersion, add distilled water without carbon dioxide to the theoretical volume of the pre-dissolution V. After stirring for 20 min at a temperature of 95° C., add distilled water without carbon dioxide to the theoretical volume of the pre-dissolution V, and continue stirring for 3 min to obtain a pregelatinized starch solution.

[0057] (4) adding the pregelatinized starch solution to a rotational viscometer, measuring the viscosity, and recording the rotational viscometer reading α;

[0058] (5) Calculation of viscosity of pregelatinized starch

[0059] Where, α is the reading of the rotational viscometer, mPa.s;

[0060] m——actual weighed amount of pregelatinized starch for use, g;

[0061] V——pre-dissolution theoretical volume, mL;

[0062] ω——Percentage of solids in pregelatinized starch.

[0063] Test Example 1

[0064] The accuracy of the viscosity of pregelatinized starch measured by the method of Example 2 was verified, wherein m=12.5037 g, ω was 5%, 8% and 10% respectively, the theoretical predissolution volume V=250 ml, and the viscosity of pregelatinized starch with three different ω was tested, and each group of data was tested six times, the test temperature was 25°C, and repeatability tests were performed to verify the analytical precision of the method of the present invention. The results are shown in Table 1 below.

[0065] The viscosity of pregelatinized starch is calculated as follows:

[0066]

[0067] The silicone oil standard material (No.: 202103201132, standard value 19.8±0.396mPa.s, t=25°C) of Zhangzhou Nanjixingchen Electronic Instrument Co., Ltd. was used for verification, and the actual measured value was 19.68mPa.s, which is within the allowable range of the standard value, proving that the rotational viscometer equipment is intact.

[0068] Table 1

[0069]

[0070] It can be seen from Table 1 that the relative standard deviation of the method of the present invention is ≤1%, and the analytical precision and repeatability are good.

[0071] The inventors have also conducted the above tests on other embodiments, and the results are basically the same. Due to limited space, they are not listed one by one.

[0072] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for measuring the viscosity of pregelatinized starch, characterized in that: The measuring method comprises the following steps: (1) Sample preparation: Grind or ball-mill the pregelatinized starch, and sieve to obtain a sample; (2) Drying: Dry the sample to constant weight, cool it to room temperature, obtain dry pregelatinized starch, and store it in a dry and sealed container for future use; wherein: The drying temperature is 125~135℃, and the drying time is 1~1.5h; (3) Dissolution: Weigh the reserved pregelatinized starch, record the mass as m, place it in anhydrous ethanol, disperse it evenly, add carbon dioxide-free distilled water to the pre-dissolution theoretical volume V, heat and stir, add carbon dioxide-free distilled water to the pre-dissolution theoretical volume V, continue stirring for 1-3 minutes, and obtain a pregelatinized starch solution; wherein: The volume of anhydrous ethanol is 1 / 20~1 / 10 of the theoretical volume of pre-dissolution; (4) adding the pregelatinized starch solution into a rotational viscometer, measuring the viscosity, and recording the rotational viscometer reading α; (5) Calculation of viscosity of pregelatinized starch ; Where, α is the reading of the rotational viscometer, mPa.s; m——actual weighed amount of pregelatinized starch for use, g; V——pre-dissolution theoretical volume, mL; ω——Percentage of solids in pregelatinized starch.

2. The method for measuring the viscosity of pregelatinized starch according to claim 1, characterized in that: In step (1), the product is sieved through a standard sieve of 110-130 mesh.

3. The method for measuring the viscosity of pregelatinized starch according to claim 1, characterized in that: The heating and stirring in step (3) is performed at a temperature of 85 to 95° C. and for a time of 20 to 40 minutes.

Images