A starch annealing modification method based on ultrasonic assistance

Abstract

The application discloses a starch annealing modification method based on ultrasonic assistance, and belongs to the technical field of starch modification. After the starch-containing raw material is conditioned to a moisture content of 20%-35%, ultrasonic treatment is synchronously applied at an annealing temperature window of 50-65 DEG C, a frequency of 20-80 kHz and a power density of 0.5-5 W / mL for 8-20 minutes, the cavitation effect and microjet action of the ultrasonic waves are utilized to accelerate the ordered rearrangement of amylose molecules along the surface of residual natural starch microcrystals, and RS3 type resistant starch is generated; then, cooling, setting and low-temperature drying are carried out. Compared with conventional isothermal annealing, the annealing time can be shortened by 20%-40% through ultrasonic assistance, or the RS3 generation efficiency can be improved under the same time. The application is a pure physical zero-addition process, is suitable for low-protein or gluten-free starch raw materials such as rice starch, corn starch and potato starch, the resistant starch content of the obtained product is greater than or equal to 7%, the GI value is less than or equal to 65, and the RS3 melting temperature is greater than or equal to 120 DEG C. The application provides an efficient annealing path with high industrialization prospect.

Description

Technical Field

[0001] This invention belongs to the field of starch modification technology, specifically relating to a purely physical modification method that uses ultrasonic energy to accelerate the starch annealing process, applicable to starch-containing raw materials with low protein or no gluten. Background Technology Starch annealing is a purely physical modification technique that induces the ordered rearrangement of starch molecules by controlling temperature, moisture, and time. The applicant's prior core process has reduced the traditional annealing time of 12-72 hours to 8-20 minutes, achieving industrial-scale production. However, driven by industrial demands for higher efficiency and lower energy consumption, further shortening the annealing time or improving the RS3 generation efficiency remains a goal pursued in this field. Ultrasonic technology has been widely used in food processing. The cavitation effect generated when ultrasound acts on a liquid medium—including the formation, growth, and violent collapse of microbubbles—can produce localized high temperatures and pressures and powerful microjets at the microscale. These effects can theoretically accelerate the conformational adjustment and ordered arrangement of macromolecules. Existing research has shown that ultrasonic treatment can promote starch retrogradation and the formation of resistant starch. However, current technology has not yet proposed simultaneously coupling ultrasound with isothermal annealing to utilize the ultrasonic cavitation effect to accelerate the ordered rearrangement of amylose molecules along the residual microcrystal surface during annealing. This invention proposes for the first time a synergistic process of "ultrasonic-assisted annealing": ultrasonic waves with controllable parameters are applied during annealing, and the mechanical stirring and local energy input generated by cavitation microjets are used to accelerate the movement and orderly attachment of amylose molecular chains, thereby completing the construction of RS3 lattice of the same quality in a shorter time, or obtaining a higher RS3 generation efficiency in the same time. Summary of the Invention Purpose of the invention The purpose of this invention is to provide an ultrasonic-assisted starch annealing method, which utilizes the cavitation effect to accelerate the orderly rearrangement of starch molecules by simultaneously applying ultrasonic treatment during the annealing process, thereby significantly improving the annealing efficiency and achieving the efficient generation of RS3 resistant starch. Technical solution This invention adopts a synergistic technical approach of "ultrasonic heating + isothermal annealing", and includes the following steps: (1) Conditioning: Add water to low-protein or gluten-free starchy raw materials to condition to a moisture content of 20%-35%. (2) Ultrasonic assisted annealing: In a constant humidity environment with a relative humidity of 80%-95%, maintain at 50-65℃ for 8-20 minutes, while applying ultrasonic treatment with a frequency of 20-80kHz and a power density of 0.5-5W / mL. The cavitation effect of ultrasound generates a large number of microbubbles in the material. The microjets generated when the bubbles collapse can accelerate the conformational adjustment of the amylose molecular chains and their orderly attachment along the microcrystal surface. At the same time, the local energy input helps to overcome the energy barrier of molecular chain motion. (3) Cooling and shaping: Cool the material to below 35°C. (4) Low temperature drying: Dry at no more than 60℃ to safe moisture content. In step b, the selection of ultrasonic frequency and power density needs to be carefully balanced: if the frequency is too high, the cavitation effect will be weakened; if the frequency is too low, the cavitation bubbles will be too large, which may cause local damage to starch particles. If the power density is too low, the cavitation effect will not be sufficient to significantly accelerate molecular rearrangement; if the power density is too high, the material may overheat, causing uncontrollable gelatinization or microcrystalline melting. Core Mechanism The core mechanism of ultrasonic-assisted annealing lies in the micromechanical effect of cavitation and local energy input. At the annealing temperature (50-65℃) and in a constant humidity environment, the moisture in the material acts as the ultrasonic propagation medium. The microjets generated by ultrasonic cavitation impact starch granules at speeds up to hundreds of meters per second, providing additional kinetic energy to the amylose molecular chains at the microscale. This additional kinetic energy input is equivalent to "local heating"—providing a stronger driving force for conformational adjustment of starch segments at the molecular level without increasing the macroscopic annealing temperature. Simultaneously, the mechanical stirring effect of the microjets helps the amylose molecules to arrange themselves in an orderly manner on the surface of the residual microcrystals, reducing steric hindrance for lattice rearrangement. It is important to note that ultrasonic-assisted annealing is fundamentally different from simply increasing the annealing temperature. Increasing the macroscopic temperature leads to the melting and collapse of residual microcrystals, while the energy input of ultrasound is microscopic and localized, keeping the macroscopic temperature within a safe window of 50-65℃, thus preserving the natural microcrystals intact. This synergistic effect of "microscopic energy enhancement and macroscopic crystal preservation" is the theoretical basis for the superiority of ultrasonic-assisted annealing over traditional isothermal annealing. Beneficial effects (1) Efficiency improvement: Ultrasonic assistance can shorten the annealing time by 20%-40%, or improve the RS3 generation efficiency in the same amount of time. (2) Pure physical zero additives: Ultrasonic waves are physical energy inputs and do not introduce any chemical reagents. The ingredient list only contains the raw materials themselves. (3) Selective enhancement: Ultrasonic energy acts on the liquid-solid interface, which has a selective enhancement effect on the orderly adhesion of linear starch on the surface of residual microcrystals. (4) Broad prospects for industrialization: Ultrasonic equipment has been widely used in the food industry, with low technical transformation threshold and clear path to large-scale scale-up. Detailed Implementation Example 1 (Rice flour, ultrasonic-assisted annealing) Take 1000g of rice flour (approximately 7% protein), add water to adjust to 28%, and maintain a temperature of 48℃. Place the adjusted material in a constant temperature and humidity ultrasonic reactor and anneal at 65℃ and 85% humidity for 12 minutes, simultaneously applying ultrasonic treatment at 40kHz and a power density of 2W / mL using an intermittent pulse mode (ultrasonic on-time accounts for 60% of the total treatment time). After annealing, rapidly cool to 23℃ with a fluidized bed of -3℃ cold air for 90 seconds. Subsequently, dry at 45℃ until the moisture content reaches 12.0%, then pulverize and sieve to obtain the product. Testing revealed a resistant starch content of 8.5%, a GI value of 61, and an RS3 melting temperature of 124℃. Compared to annealing under the same conditions without ultrasonic assistance (12 minutes, 65℃, 85% RH, resistant starch content 7.2%), the RS3 formation efficiency was improved by approximately 18%. Scanning electron microscopy revealed fine cavitation microjets on the surface of the product particles, a unique morphological feature of ultrasonic treatment. Example 2 (Corn starch, ultrasonic-assisted annealing) Take 1000g of corn starch, add water to adjust to 25%, and heat at 48℃. Anneal at 62℃ and 85% humidity for 14 minutes, while simultaneously applying ultrasonic treatment at 60kHz power density of 1.5W / mL in pulse mode (ultrasonic on 50%). After annealing, cool slowly to 33℃. Dry at 42℃ until the moisture content is 12.5%. Test results show that the resistant starch content is 7.8%, the GI value is 64, and the RS3 melting temperature is 122℃. Example 3 (Potato starch, ultrasonic-assisted annealing) Take 1000g of potato starch, add water to adjust to 28%, and heat at 48℃. Anneal at 63℃ and 85% humidity for 10 minutes, simultaneously applying ultrasonic treatment at 40kHz power density 2.5W / mL in pulse mode (ultrasonic on 70%). After annealing, rapidly cool in a fluidized bed to 23℃. Dry at 48℃ until the moisture content is 12.8%. Test results show that the resistant starch content is 7.5%, the GI value is 64, and the RS3 melting temperature is 121℃. Comparative Example 1 (annealing under the same conditions without ultrasonic assistance) Turn off the ultrasonic wave in Example 1, while keeping the other conditions unchanged (annealing at 65°C and 85% humidity for 12 minutes). Testing revealed a resistant starch content of 7.2% and an RS3 melting temperature of 120°C. Compared to Example 1, the RS3 formation efficiency was significantly lower without ultrasonic assistance during the same annealing time. This indirectly verifies that ultrasound significantly accelerates RS3 formation. Comparative Example 2 (ultrasound power density too low) The ultrasonic power density of Example 1 was reduced to 0.3 W / mL, while the other conditions remained unchanged. Testing revealed that the resistant starch content was 7.3%, which was not significantly different from the control group without ultrasound (7.2%). This demonstrates that when the power density is below 0.5 W / mL, the cavitation effect is insufficient to significantly accelerate starch molecule rearrangement. Comparative Example 3 (Excessive ultrasonic power density leading to localized overheating) The ultrasonic power density of Example 1 was increased to 6 W / mL, while the other conditions remained unchanged. Testing revealed a resistant starch content of 5.8% and a GI value of 67. Scanning electron microscopy revealed cracks and pores on the surface of some starch granules, indicating that excessively high ultrasonic power density caused localized overheating and physical damage to the starch granules, thus deteriorating the conditions for RS3 formation. Comparative Example 4 (annealing temperature below the lower limit of the window) The annealing temperature of Example 1 was changed to 48°C, the annealing time was extended to 18 minutes, and the other conditions remained unchanged. Testing revealed a resistant starch content of 5.5% and a GI value of 68. This demonstrates that even with ultrasonic assistance, the overall mobility of starch molecular chains remains insufficient at annealing temperatures below 50°C, resulting in inadequate driving force for lattice repair. Comparative Example 5 (Ultrasonic frequency out of range) The ultrasonic frequency in Example 1 was changed to 100kHz, while all other conditions remained the same. Testing revealed that the resistant starch content was 7.0%, with no significant difference compared to the control group without ultrasound. This demonstrates that at frequencies exceeding 80kHz, the cavitation bubble volume is too small, and the collapse energy is insufficient to generate an effective microjets acceleration effect. Detection methods Resistant starch content: AOAC 2002.02 standard method was used. GI value: based on the ISO 26642:2010 standard method. RS3 melting temperature: Differential scanning calorimetry (DSC) was used, with a heating rate of 10℃ / min, nitrogen atmosphere, and a temperature range of 10-180℃. Particle morphology: Observed using scanning electron microscopy (SEM) at an accelerating voltage of 5-10kV and a magnification of 1000-5000x. X-ray diffraction: An X-ray diffractometer (XRD) was used with a Cu target. The scanning range was 2θ = 5°-40°, and the scanning speed was 2° / min. The crystallinity was calculated using the peak separation method. Degree of gelatinization: Calculated using differential scanning calorimetry (DSC) based on the change in starch gelatinization enthalpy. Industrial applications The method of this invention can be implemented on existing continuous grain processing production lines. The core modification lies in integrating an ultrasonic transducer array inside the annealing tower. The transducers can be arranged in sections along the material conveying direction of the annealing tower, with each section having its power and frequency independently controlled, ensuring that the material receives uniform ultrasonic treatment throughout its continuous passage through the annealing tower. The ultrasonic power supply and control system can be integrated into the production line's central control system, enabling one-button start / stop and automatic parameter adjustment. Ultrasonic equipment has been widely used in the food industry (such as ultrasonic-assisted extraction, ultrasonic emulsification, and ultrasonic cleaning). The technology is highly mature and there are many equipment suppliers. The main challenge in scaling up is the design of sound field uniformity in large reactors and the optimization of energy efficiency during long-term operation. However, these problems have mature solutions at the engineering level. Summary of Ultrasonic Parameter Boundary Verification Determination of resistant starch content under ultrasonic conditions, raw material annealing time 40kHz, 2W / mL, 60% pulse (Example 1): Rice flour 8.5% after 12 minutes, acceptable (optimal efficiency). 60kHz, 1.5W / mL, 50% pulse (Example 2) Corn starch 7.8% after 14 minutes - Pass 40kHz, 2.5W / mL, pulse 70% (Example 3) Potato starch 7.5% after 10 minutes, qualified. No ultrasound (Comparative Example 1): Rice flour, 12 minutes, 7.2%, acceptable (low efficiency). 0.3 W / mL (Comparative Example 2) Rice flour 7.3% after 12 minutes - Unacceptable (no significant increase) 6 W / mL (Comparative Example 3) Rice flour 5.8% after 12 minutes - Unacceptable (overheat damage) 100kHz (Comparative Example 5) Rice flour 12 minutes 7.0% Failure (no significant improvement) The table above clearly demonstrates that an ultrasonic frequency of 20-80kHz, a power density of 0.5-5W / mL, combined with annealing at 50-65℃ and a processing time of 8-20 minutes, are the necessary parameter windows for achieving the enhanced effect of ultrasonic-assisted annealing.

Claims

1. A low glycemic index cereal powder or starch, characterized in that, It is prepared by the following method: a. Conditioning: Add water to low-protein or gluten-free starchy raw materials and condition to a moisture content of 20%-35%; b. Ultrasonic assisted annealing: The conditioned material is kept in a constant humidity environment with a relative humidity of 80%-95% for 8-20 minutes within a temperature window of 50-65℃, while ultrasonic treatment with a frequency of 20-80kHz and a power density of 0.5-5W / mL is applied. The ultrasonic cavitation effect and micro-jet action are used to accelerate the orderly rearrangement of amylose molecules along the surface of residual natural starch microcrystals to generate RS3 type resistant starch. c. Cooling and shaping: Cool the annealed material to below 35°C; d. Low-temperature drying: Dry the cooled material at a temperature not exceeding 60°C until the moisture content is below 13%; The cereal flour or starch simultaneously meets the following requirements: resistant starch content ≥7% (determined according to AOAC 2002.02 standard method), RS3 type resistant starch melting temperature ≥120℃ (determined by differential scanning calorimetry), and GI value ≤65.

2. The low glycemic index cereal powder or starch according to claim 1, characterized in that, The low-protein or gluten-free starch-containing raw material mentioned in step a is selected from any one or more of rice flour, corn starch, potato starch, sweet potato starch, tapioca starch, buckwheat flour, millet flour, sorghum flour, oat starch, pea starch, and mung bean starch; the protein content of the raw material is ≤10%, and it does not contain gluten protein; the physical form of the raw material is powder or granules.

3. The low glycemic index cereal powder or starch according to claim 1, characterized in that, The ultrasonic frequency in step b is 40-60kHz, the power density is 1-3W / mL, the annealing temperature is 60-65℃, and the annealing time is 10-14 minutes.

4. The low glycemic index cereal powder or starch according to claim 3, characterized in that, When the raw material is rice flour, the annealing temperature is 63-65℃, the annealing time is 10-12 minutes, and the ultrasonic power density is 2-3W / mL; when the raw material is corn starch, the annealing temperature is 60-63℃, the annealing time is 12-14 minutes, and the ultrasonic power density is 1-2W / mL.

5. The low glycemic index cereal powder or starch according to claim 1, characterized in that, The ultrasonic wave applied in step b is intermittent pulsed ultrasonic wave, and the ultrasonic wave is turned on for 40%-80% of the total processing time to avoid overheating of the material.

6. The low glycemic index cereal powder or starch according to claim 1, characterized in that, The cooling and shaping mentioned in step c is selected from any one of gradient slow cooling, cold water spray cooling or fluidized bed rapid cooling; the fluidized bed rapid cooling uses cold air from -5℃ to 0℃ to cool the material from the annealing temperature to below 25℃ within 90 seconds.

7. The low glycemic index cereal powder or starch according to claim 1, characterized in that, After the ultrasonic-assisted annealing described in step b is completed, the crystallinity of the material is significantly improved compared with that before treatment, and the intensity of the X-ray diffraction characteristic peak of RS3 type resistant starch is improved compared with the annealing under the same conditions without ultrasonic assistance.

8. The low glycemic index cereal powder or starch according to any one of claims 1-7, characterized in that, The surface of the grain powder or starch particles exhibits a microscopic surface morphology that differs from that of pure heat-annealed products due to the impact of ultrasonic cavitation microjets.

9. The use of the low glycemic index cereal powder or starch according to any one of claims 1-8 in the preparation of low GI foods, pharmaceutical excipients, pet food, aquatic feed or biodegradable packaging materials.