A method for annealing modification of a low glycemic index normal corn starch

Abstract

The application discloses an annealing modification method of low-glycemic-index normal corn starch, and belongs to the technical field of deep processing of grains. After the normal corn starch is conditioned, annealing is carried out in a constant-humidity environment at 40-75 DEG C for 5-30 minutes, so that linear amylase is orderly rearranged along the surface of residual microcrystals to form high-melting-point RS3 resistant starch with a melting temperature of greater than or equal to 120 DEG C; then, fluidized bed rapid cooling is adopted to lock the crystal lattice below 25 DEG C, and low-temperature drying is carried out. The application is a pure physical zero-addition process, the obtained product has a GI value of less than or equal to 60, a resistant starch content of greater than or equal to 8%, and a RS3 melting temperature of greater than or equal to 120 DEG C, and is suitable for meal replacement powder, functional food raw materials and degradable packaging materials.

Description

Technical Field

[0001] This invention belongs to the field of deep grain processing technology, specifically relating to a purely physical annealing modification method for ordinary corn starch. Background Technology

[0002] Corn starch is one of the world's largest-produced starches, widely used in food, feed, and industrial sectors. Ordinary corn starch contains 20%-30% amylose and typically has a GI value between 70 and 80, classifying it as a high-GI food. The applicant's prior art discloses a method for maximizing annealing crystallization of high-amylose corn starch, but it does not optimize parameters for ordinary corn starch with a moderate amylose content. Ordinary corn starch and high-amylose corn starch differ in amylose content, particle structure, and gelatinization characteristics, requiring a specifically optimized annealing process. Summary of the Invention Purpose of the invention

[0003] The purpose of this invention is to provide an annealing modification method for ordinary corn starch, which achieves efficient generation of RS3 within a mild temperature window, with a product GI value ≤60, resistant starch content ≥8%, and a melting temperature of RS3 resistant starch ≥120℃. Technical solution The present invention includes the following steps: (1) conditioning ordinary corn starch to a moisture content of 15%-40%; (2) annealing in a constant humidity environment of 40-75℃ and 80%-95% for 5-30 minutes; (3) rapidly cooling to below 25℃ in 90 seconds using a fluidized bed to lock the crystal lattice; (4) drying at a low temperature not exceeding 50℃. Core Mechanism During annealing, the conditioned starch absorbs water and swells at an appropriate temperature. Amylose molecules dissolve from the starch granules and rearrange themselves in an orderly manner using residual natural microcrystals as seed crystals, forming high-melting-point RS3-type resistant starch. Excessive temperature leads to microcrystal melting and collapse, loss of heterogeneous nucleation, and a decrease in RS3 formation; conversely, insufficient amylose dissolution results in inadequate RS3 formation. Only when the annealing temperature, time, and moisture content are within a suitable range can high-melting-point RS3-type resistant starch with a melting temperature ≥120℃ be formed. Beneficial effects (1) A special annealing scheme for ordinary corn starch is proposed for the first time, with a GI value ≤60 and a resistant starch content ≥8%. (2) Annealing time is 5-30 minutes, which is suitable for industrial continuous production. (3) Pure physical process with zero additives. Detailed Implementation

[0004] Example 1 (Preferred Annealing) Take ordinary corn starch (amylose content 27%), add water to adjust to 28%, and adjust the temperature to 48℃. Feed the adjusted material into a constant temperature and humidity annealing equipment and anneal at 63℃ and 85% humidity for 12 minutes. Immediately after annealing, feed it into a fluidized bed and rapidly cool the powder temperature from 63℃ to 23℃ within 90 seconds using -3℃ cold air. Dry at 45℃ until the moisture content is 12.0%, and sieve to obtain the product. The resulting product had a significantly lower GI value, an RS3 melting temperature of 126℃, and a resistant starch content of 8.5%. Comparative Example 1 (annealing temperature exceeds the upper limit) The annealing temperature in Example 1 was changed to 78°C (exceeding the upper limit of 75°C), while the other conditions remained unchanged. The resulting product exhibited extensive microcrystal melting, and the amount of RS3 generated decreased significantly, with the RS3 melting temperature being <120℃. This demonstrates that excessively high temperatures lead to the loss of heterogeneous nucleation. Comparative Example 2 (annealing temperature below the lower limit) The annealing temperature in Example 1 was changed to 35°C (below the lower limit of 40°C), while the other conditions remained unchanged. The resulting product showed insufficient amylose dissolution, extremely low RS3 formation efficiency, and an RS3 melting temperature <120℃. This demonstrates that effective RS3 cannot be formed at excessively low temperatures. Comparative Example 3 (annealing time too short) The annealing time of Example 1 was shortened to 3 minutes (below the lower limit of 5 minutes), while the other conditions remained unchanged. The resulting product, RS3, was not fully formed, and its melting temperature was <120℃. This indicates that the time was too short and lattice repair was insufficient. Comparative Example 4 (annealing time too long) The annealing time of Example 1 was extended to 40 minutes (exceeding the 30-minute limit), while the other conditions remained unchanged. The resulting product exhibits excessive crystallization, resulting in a hard texture after rehydration and a significant increase in energy consumption. Detection methods Amylose content was determined by iodine colorimetry, resistant starch content by AOAC 2002.02, GI value by ISO26642:2010, and RS3 melting temperature by differential scanning calorimetry. Industrial applications It can be implemented on existing continuous tempering-annealing-cooling-drying production lines. The core equipment includes a biaxial differential atomizing continuous tempering tank, a closed mesh belt continuous annealing tower with a temperature control accuracy of ±0.5℃ across the entire range, a fluidized bed quenching system, and a low-temperature airflow drying device.

Claims

1. A method for annealing and modifying ordinary corn starch with a low glycemic index, characterized in that, Includes the following steps: a. Conditioning: Add water to ordinary corn starch and condition it to a moisture content of 15%-40%, while controlling the temperature at 40-55℃, so that the starch absorbs water and swells; b. Isothermal annealing: The conditioned material is kept in a constant humidity environment with a relative humidity of 80%-95% for 5-30 minutes within a temperature window of 40-75℃, so that the amylose can be orderly attached and rearranged along the surface of the residual microcrystals to form high melting point RS3 type resistant starch with a melting temperature ≥120℃. c. Rapid cooling and crystal locking: The annealed material is rapidly cooled to below 25°C within 90 seconds using a fluidized bed to lock the high melting point RS3 crystal structure; d. Low-temperature drying: Dry the cooled material at a temperature not exceeding 50°C until the moisture content is below 13%.

2. The method according to claim 1, characterized in that, The amylose content of the ordinary corn starch in step a is 20%-30%, preferably 25%-28%; the moisture content of the conditioning is preferably 25%-30%, and the conditioning temperature is preferably 45-50℃.

3. The method according to claim 1, characterized in that, The annealing temperature in step b is preferably 60-65℃, more preferably 62-64℃; the annealing time is preferably 10-14 minutes, more preferably 11-13 minutes.

4. The method according to claim 1, characterized in that, The fluidized bed quenching in step c uses cold air from -5°C to 0°C to cool the material from the annealing temperature to below 25°C within 90 seconds.

5. The method according to claim 1, characterized in that, The annealing process in step b is carried out in an environment with a relative humidity of 82%-88%.

6. A low glycemic index common corn starch, characterized in that, The starch is prepared by the method according to any one of claims 1-5, and the starch simultaneously satisfies the following conditions: GI value ≤ 60, RS3 resistant starch content ≥ 8%, RS3 resistant starch melting temperature ≥ 120℃, and the ingredient list contains only corn starch.

7. The application of the starch according to claim 6 in the preparation of sugar-controlled foods, meal replacement powders, functional food ingredients, and biodegradable packaging materials.