PREPARATION METHOD OF CITRIC ACID MODIFIED STARCH WITH DIGESTION-RESISTANT PROPERTY

Abstract

The method employs citric acid as the modifier, combines the citric acid with starch, achieves the good modification effect of starch at high temperature, and improves the digestion-resistant property of starch. Citric acid itself is nontoxic, the process conditions are mild and the treatment methods are relatively safe, which shows very high practical values. In the method, starch and citric acid are cross-linked by using the infrared treatment technology, and the dry heating treatment is used to promote the modifier citric acid into starch, thereby achieving significant and stable modification effects, and high modification efficiency.

Claims

1. A method for preparing modified starch with a high degree of substitution, comprising the following steps: (1) preparing a citric acid aqueous solution; (2) adding starch into the citric acid aqueous solution for a reaction for a period of time to get a mixture of the citric acid and the starch; (3) placing the mixture of the citric acid and the starch obtained from step (2) under a condition of infrared radiation for a reaction for a period of time to get modified starch with a high degree of substitution; wherein an intensity of the infrared radiation in step (3) is 250° C.; a reaction time of the infrared radiation is 5 min to 7 min; the infrared radiation is mid-infrared radiation, with a wavelength ranging from 3.2 μm to 7.6 μm.

2. (canceled)

3. (canceled)

4. The method according to claim 1, wherein in step (1), a mass concentration of citric acid in the citric acid aqueous solution is 20% to 70%.

5. The method according to claim 1, wherein in step (2), a mass ratio of starch dry matter to the citric acid is 1:5 to 5:1.

5. The method according to claim 1, wherein after step (2) of obtaining the mixture of the citric acid and the starch, the method further comprises the steps of drying the mixture of citric acid and starch, then crushing and sieving, and collecting sieved powder.

7. The method according to claim 1, wherein after step (3) of placing the mixture of the citric acid and the starch obtained from step (2) under the condition of the infrared radiation for the reaction for the period of time, the method further comprises a step of dry heating reactants;

8. The method according to claim 7, wherein after dry heating the reactants, the method further comprises a step of removing extra unreacted citric acid from the reactants.

9. The method according to claim 8, wherein after removing the extra unreacted citric acid, the method further comprises the steps of drying and crushing the reactants.

10. The method according to claim 1, wherein the starch is located from cereal starch.

11. The method according to claim 7, wherein the dry heating is conducted at 50° C. to 150° C. for 0.5 h to 5 h.

12. The method according to claim 11, wherein after dry heating the reactants, the method further comprises a step of removing extra unreacted citric acid from the reactants.

Description

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] The present disclosure will be further illustrated below in combination with the following embodiments. The following are only preferable embodiments of the present disclosure but do not limit the present disclosure in any other forms. The above disclosures can be changed into equivalent embodiments with the same variations by these skilled in the art. Any simple modifications or equivalent changes made to the following embodiments according to the substantial technology of the present disclosure without deviating from the content of the present disclosure all fall within the protection scope of the present disclosure.

[0029] Embodiment 1. Preparation of Citric Acid Modified Starch

[0030] 20 g of citric acid was dissolved in 20 mL of distilled water, and stirred until citric acid was dissolved completely. 10 mol/L of NaOH solution was added to adjust pH to 3.0 to 4.0. 20 g of glutinous rice starch was added under continuous stirring and statically reacts for 16 h. The mixture of citric acid and starch was dried in a low-temperature drying oven to a moisture content of 8%, and the drying temperature was kept at 50° C. After drying, the mixture was taken out and crushed, then sieved over a 100-mesh sieve to collect the sieved starch powder. The collected starch powder was placed in the mid-infrared equipment at infrared radiation temperatures of 175° C., 200° C., 225° C., 250° C., and 275° C. respectively, within an infrared radiation range of 3.2 μm to 7.5 μm, so that they were reacted fully at high temperatures for 5 min. The reactants were taken out and placed into a constant temperature oven at 130° C. for dry heating for 2 h, then washed with water to remove extra citric acid that had not been reacted with starch. After washing with water, the starch samples were dried in a low-temperature drying oven at 50° C. to a moisture content lower than 14%. The dried samples were taken out and crushed to rapidly obtain the citric acid modified starch with a digestion-resistant property.

[0031] Embodiment 2, Detection on the Properties of Citric Acid Modified Starch prepared in Embodiment

[0032] The starch that has been treated by infrared radiation at five different temperatures in Embodiment 1 was determined for the degree of substitution by means of acid-base titration. The degree of substitution refers to the moles of active hydroxyl groups, substituted by ester groups, on each D-glucose unit of starch, the degree of substitution can reflect the denaturation degree of starch. The results were shown in Table 1 below, wherein the degree of substitution increased obviously at the infrared radiation temperature of 250° C., while the degree of substitution showed a downward trend correspondingly at the infrared radiation temperature of more than 250° C. Hence, at the infrared radiation temperature conditions ranging from 200° C.; to 250° C., the degree of substitution of the starch was at a high level, which indicates the suitable temperature range of infrared radiation was from 200° C. to 250° C.

TABLE-US-00001 TABLE 1 Degree of substitution of the starch before and after treatment in Embodiment 1 Temperature of infrared Degree of radiantion/° C. substitution Initial 0   175  0.072 200  0.091 225  0.125 250  0.141 275  0.107

[0033] Embodiment 3. Preparation of Citric Acid Modified Starch

[0034] 20 g of citric acid was dissolved in 20 mL of distilled water, and stirred until citric acid was dissolved completely. 10 mol/L of NaOH solution was added to adjust pH to 3.0 to 4.0, 20 g of cereal starch was added under continuous stirring and statically reacts for 16 h. The mixture of citric acid and starch was dried in a low-temperature drying oven to a moisture content of 8%, and the drying temperature was kept at 50° C. After drying, the mixture was taken out and crushed, then sieved over a 100-mesh sieve to collect the sieved starch powder. The collected starch powder was placed in the infrared equipment at an infrared radiation temperature of 250° C., and then fully reacts at the high temperature for 1 min, 3 min, 5 min, 7 min, and 9 min respectively. The reactants were taken out and placed into a constant temperature oven at 130° C. for dry heating for 2 h, then washed with water to remove extra citric acid that had not been reacted with starch. After washing with water, the starch samples were dried in a low-temperature drying oven at 50° C. to a moisture content lower than 14%. The dried samples were taken out and crushed to rapidly obtain the citric acid modified starch with a digestion-resistant property.

[0035] Embodiment 4. Detection on the Properties of the Citric Acid Modified Starch Prepared in Embodiment 3

[0036] The starch that has been treated by infrared radiation for five different times in Embodiment 3 was determined for the degree of substitution. The determination results on the degree of substitution were shown in Table 2 below, wherein when the starch was treated at an infrared radiation temperature of 250° C. for 7 min, the degree of substitution increased obviously; when it was treated for 5 min to 7 min, the degree of substitution was at a high level. Therefore, the suitable time range of infrared radiation was from 5 min to 7 min.

TABLE-US-00002 TABLE 2 Degree of substitution of the starch before and after treatment in Embodiment 3 Temperature of infrared Degree of radiantion/° C. substitution Initial 0   1  0.037 3  0.080 5  0.141 7  0.156 9  0.124