A method for heat-moisture treatment of high amylose starch under 15-20% low moisture conditions

Abstract

This invention discloses a method for hydrothermal treatment of high amylose under low moisture conditions of 15%-20%, belonging to the field of starch deep processing technology. The method includes: adjusting high amylose corn starch (amylose content ≥55%) with water to a moisture content of 15%-20%, feeding it into a jacketed stainless steel autoclave, and hydrothermally treating it for 5-12 minutes in a closed saturated steam environment at 95-110℃ with a self-generated pressure of 0.1-0.4 MPa based on the material's moisture content. After treatment, the material is rapidly cooled to below 25℃ using a fluidized bed with cold air at -5 to 0℃ within 90 seconds to lock the RS3 lattice structure. This method achieves internal structural reorganization of starch granules under limited moisture conditions within the 15%-20% lower moisture content range through hydrothermal treatment, resulting in RS3 resistant starch content ≥12% (determined according to AOAC 2002.02 standard method) and RS3 melting temperature ≥120℃ (determined by differential scanning calorimetry). This method locks the boundaries of the wet heat treatment parameters for the pure physical modification process in the low moisture range of 15%-20%.

Description

Technical Field

[0001] This invention belongs to the field of starch deep processing technology, specifically relating to a method for wet heat treatment of high amylose starch under conditions of 15%-20% lower than conventional moisture content. This method locks in the peripheral parameters of the core related patent by extending the lower boundary of moisture content to 15% and locking in the low moisture range through wet heat treatment, thus blocking the room for competitors to maneuver in the gray area of ​​low moisture content. Background Technology Humid heat treatment (HMT) is a common method for the physical modification of starch, typically carried out under low moisture (10%-35%) and high temperature (95-120℃) conditions. The core annealing patent protects annealing processes within the 20%-35% moisture range. Competitors might attempt to prepare RS3-type resistant starch using HMT in the 15%-20% moisture range (slightly below 20%), claiming non-infringement on the grounds that "the moisture content or treatment method is not within the scope of the annealing patent." Therefore, it is essential to apply for this patent to lock in the HMT route within the 15%-20% low moisture range. Existing literature in this field has investigated the effects of hydrothermal treatment on the RS content of starch under different moisture conditions. For example, some studies have used ordinary corn starch as raw material and observed an increase in RS content under hydrothermal treatment conditions of 15% and 20% moisture. However, the raw material used in these existing studies is ordinary corn starch (amylose content of about 25%-30%), which is fundamentally different in raw material characteristics from the high amylose corn starch (amylose content ≥55%) used in this invention. Due to its higher amylose content, high amylose exhibits significantly different molecular chain movement and recombination behavior during hydrothermal treatment compared to ordinary starch—the higher the amylose content, the easier it is for the molecular chains to achieve orderly recombination through thermal motion under limited moisture conditions, generating a higher content of RS3-type resistant starch. Furthermore, existing studies have not provided a quantitative indicator of RS3 content ≥12%, nor have they disclosed the parameter combination of a specific narrow temperature window range of 95-110℃ and a short treatment time of 5-12 minutes, and even less have they disclosed the thermal stability indicator of RS3 melting temperature ≥120℃. The key to hydrothermal treatment under low moisture conditions of 15%-20% lies in the precise control of the temperature window. The temperature needs to be controlled within a narrow window of 95-110℃—below 95℃, the kinetic energy of molecular chain movement is insufficient to achieve sufficient recombination under limited moisture conditions, and above 110℃, starch granules begin to over-gelatinize and degrade. By precisely controlling the treatment temperature and sealing time, the orderly recombination of the internal structure of starch granules can be achieved under limited moisture conditions, generating RS3-type resistant starch. Summary of the Invention Purpose of the invention A method for hydrothermal treatment of high amylose under low moisture conditions of 15%-20% is provided, which locks in the hydrothermal treatment route at the lower boundary of moisture content by precisely controlling the narrow window of temperature and time. Technical solution High-amylose corn starch (amylose content ≥55%) was adjusted with water to a moisture content of 15%-20%, and then fed into a jacketed stainless steel autoclave. It was subjected to hydrothermal treatment for 5-12 minutes in a closed, saturated steam environment at 95-110℃, relying on the material's own moisture pressure of 0.1-0.4 MPa. After treatment, the material was rapidly cooled to below 25℃ within 90 seconds using cold air at -5 to 0℃ to lock the RS3 crystal structure, and then dried at a low temperature not exceeding 50℃ until the moisture content was ≤13%. The resulting RS3-type resistant starch content was ≥12% (determined according to AOAC 2002.02 standard method), and the RS3 melting temperature was ≥120℃ (determined by differential scanning calorimetry). The protection range of this method is defined by four parameters: moisture content controlled at 15%-20%, wet heat treatment temperature controlled at 95-110℃, treatment time controlled at 5-12 minutes, and amylose content in the starch raw material controlled at ≥55%. If the moisture content is below 15% or above 20%, the treatment temperature is below 95℃ or above 110℃, the treatment time is less than 5 minutes or more than 12 minutes, or the amylose content is below 55%, the RS3 content and / or RS3 melting temperature will not meet the standards of ≥12% and ≥120℃, respectively. Core Mechanism The parameter linkage mechanism of low-moisture hydrothermal treatment is based on the coupling relationship between moisture, temperature, and time. Under low moisture conditions of 15%-20%, the moisture inside starch granules, which serves as the medium for molecular chain migration, is limited, and the movement of molecular chains is restricted by the local moisture environment. Increasing the temperature to 95-110℃ can significantly enhance the thermal kinetic energy of the molecular chains, enabling them to overcome intermolecular forces even under limited moisture conditions, achieving ordered recombination of amorphous chain segments and the perfection of microcrystals. The closed high-pressure autoclave environment ensures that moisture is not lost during the treatment process, and the material's self-generated moisture pressure of 0.1-0.4 MPa forms a saturated water vapor environment, maintaining the limited moisture environment inside the granules. The treatment time needs to be controlled within 5-12 minutes—too short a time will result in insufficient chain segment rearrangement, while too long a time will cause the granules to begin degrading in the high-temperature closed environment. The coupling relationship between moisture, temperature, and time can be quantitatively described as follows: for every 2 percentage point decrease in moisture content (within the range of 15%-20%), to maintain an RS3 content ≥12%, the hydrothermal treatment temperature needs to be increased by approximately 3-5℃, or the treatment time needs to be extended by approximately 1-2 minutes. For example, under 20% moisture conditions, a treatment temperature of approximately 95-100℃ and a treatment time of approximately 5-8 minutes can achieve an RS3 ≥12%; under 18% moisture conditions, a treatment temperature of approximately 100-105℃ and a treatment time of approximately 8-10 minutes can achieve the same RS3 level; and under 15% moisture conditions, a treatment temperature of approximately 105-110℃ and a treatment time of approximately 10-12 minutes can achieve the same RS3 level. This quantitative parameter linkage is the core technical characteristic of low-moisture hydrothermal treatment processes. This method achieves an RS3 content ≥12% and a melting point ≥120℃ under low moisture conditions of 15%-20%, producing unexpected technical effects—achieving the same RS3 content level as conventional HMT processes while maintaining a processing temperature 10℃ lower than conventional HMT and a processing time shortened to 1 / 3 of conventional HMT. Comparative Example 6 (same raw materials treated under conventional HMT conditions of 110℃ / 30 minutes / 25% moisture) had an RS3 content of approximately 14.0%, while Example 1 of this patent (100℃ / 10 minutes / 18% moisture) had an RS3 content of approximately 13.0%—achieving essentially the same RS3 content while reducing the processing temperature by 10℃ and shortening the processing time to 1 / 3 of conventional HMT (from 30 minutes to 10 minutes). This "low temperature, short processing time, no quality reduction" technical effect is something that those skilled in the art could not anticipate from conventional HMT processes. Detailed Implementation Example 1 (100℃ low moisture humid heat treatment) High-amylose corn starch (amylose content approximately 58%) was added to adjust the moisture content to approximately 18%, and then placed in a jacketed stainless steel autoclave. It was subjected to hydrothermal treatment for 10 minutes in a closed, saturated steam environment at 100°C, relying on the material's own moisture pressure of approximately 0.2 MPa. After treatment, the material was rapidly cooled to below 25°C within 90 seconds using a fluidized bed with -5°C cold air to lock the RS3 lattice structure, and then dried at 45°C to approximately 12% moisture content. Three batches were tested (n=3): RS3 content 13.0%±0.5% (≥12%, determined according to AOAC 2002.02 standard method), RS3 melting temperature 123±2°C (≥120°C, determined by DSC, heating rate 10°C / min, nitrogen atmosphere, sample amount 3-5 mg, temperature range 30-180°C, recording the peak temperature of the endothermic peak). Example 2 (105℃ low moisture humid heat treatment + high linear chain ≥70%) High-amylose corn starch (amylose content approximately 72%) with a moisture content of 17% was subjected to hydrothermal treatment for 8 minutes in a closed saturated steam environment at 105℃ and an autogenous pressure of approximately 0.25MPa. The RS3 content was 16.2%±0.8% (≥15%), and the RS3 melting temperature was 127±1℃ (≥122℃). Comparative Example 1 (Moisture content 12% - RS3 not up to standard) Using the same raw materials as in Example 1, with a moisture content of 12% (<15%), a processing temperature of 100°C, and a processing time of 10 minutes, the RS3 content was 8.5% ± 0.5% (<12%). The moisture content was too low, indicating a severe deficiency of the molecular recombination medium. Comparative Example 2 (Moisture content 25% - falls within the typical HMT range) The same raw materials as in Example 1 were used, with a moisture content of 25% (>20%) and a processing temperature of 100°C. The RS3 content was 13.2% ± 0.5% (compliant, but falling within the protection range of conventional damp heat treatment processes). Comparative Example 3 (processing temperature 85℃ - RS3 not up to standard) Using the same raw materials as in Example 1, the treatment temperature was 85°C (<95°C) for 15 minutes. The RS3 content was 9.0% ± 0.5% (<12%). Too low a temperature resulted in insufficient molecular recombination. Comparative Example 4 (processing temperature 120℃ - RS3 not up to standard) Using the same raw materials as in Example 1, the treatment temperature was 120°C (>110°C) for 8 minutes. The RS3 content was 8.5% ± 0.5% (<12%). Excessive temperature led to excessive degradation of the starch granules. Comparative Example 5 (linear chain content 27% - RS3 not up to standard) Ordinary corn starch (among others, approximately 27% linear content, <55%) was used, with a moisture content of 18%, and the treatment temperature was 100℃ for 10 minutes. The RS3 content was 7.0% ± 0.5% (<12%). Comparative Example 6 (Conventional HMT process window – 110℃ / 30 minutes / 25% moisture) Using the same high amylose corn starch as in Example 1, a conventional wet heat treatment process window was employed: 25% moisture content, wet heat treatment at 110°C for 30 minutes. The RS3 content was 14.0% ± 0.5%, and the RS3 melting temperature was 128 ± 2°C. The RS3 content (14.0%) in this comparative example is not significantly different from that in Example 1 (13.0%), but the treatment temperature (110°C) is 10°C higher than that in Example 1 (100°C), and the treatment time (30 minutes) is three times that of Example 1 (10 minutes). This demonstrates that the low-moisture, low-temperature, short-time wet heat treatment process of this patent, while maintaining a essentially unchanged RS3 content, reduces the treatment temperature by 10°C and shortens the treatment time to one-third of that of conventional HMT—this "low-temperature, short-time, no-quality reduction" technical effect is something that those skilled in the art cannot anticipate from conventional HMT processes. Comparative Example 7 (Processing time 4 minutes - RS3 not up to standard) Using the same raw materials as in Example 1, the treatment temperature was 100°C, and the treatment time was 4 minutes (<5 minutes). The RS3 content was 9.2% ± 0.5% (<12%). The treatment time was too short, resulting in insufficient molecular chain rearrangement. Industrial applications This method locks in the boundaries of the hydrothermal treatment parameters for purely physically modified RS3 resistant starch within the low moisture range of 15%-20%. The moisture content is controlled at 15%-20%, the treatment temperature at 95-110℃, the treatment time at 5-12 minutes, and the amylose content in the starch raw material is controlled at ≥55%. These four parameter windows together constitute the protection range of this method. This method, together with the conventional 20%-35% moisture annealing method, the 35%-40% medium moisture hydrothermal treatment method proposed in another application, and the 40%-45% high moisture annealing method, forms a complete protection loop in terms of moisture content—15%-20% (this method, hydrothermal treatment) → 20%-35% (conventional annealing) → 35%-40% (medium moisture hydrothermal treatment) → 40%-45% (high moisture annealing), covering the entire moisture range without any blind spots. The resulting RS3 resistant starch is suitable for low-GI foods, pharmaceutical excipients, industrial raw materials, or pet food.

Claims

1. A method for hydrothermal treatment of high amylose under low moisture conditions of 15%-20%, characterized in that, Includes the following steps: a. Conditioning: Add water to high amylose corn starch (amylose content ≥55%) and condition to a moisture content of 15%-20%; b. Moist heat treatment: The conditioned material is sent into a jacketed stainless steel autoclave and moist heat treated for 5-12 minutes in a closed saturated steam environment at 95-110℃ and 0.1-0.4MPa, which relies on the self-generated pressure of the material's moisture. This allows the internal structure of the starch granules to be reorganized under limited moisture conditions, generating RS3 type resistant starch. c. Rapid cooling and crystal locking: The processed material is rapidly cooled to below 25°C within 90 seconds using a fluidized bed with cold air at -5 to 0°C to lock the RS3 crystal structure. d. Drying: Dry the rapidly cooled material at a temperature not exceeding 50°C until the moisture content is ≤13%; The obtained RS3 resistant starch content is ≥12% (determined according to AOAC 2002.02 standard method), and the melting temperature of RS3 resistant starch is ≥120℃ (determined by differential scanning calorimetry, heating rate 10℃ / min, nitrogen atmosphere, sample amount 3-5mg, temperature range 30-180℃, and the peak temperature of the endothermic peak is recorded).

2. The method according to claim 1, characterized in that, The wet heat treatment temperature in step b is 100-105℃, the treatment time is 8-10 minutes, and the resulting RS3 type resistant starch has a melting temperature ≥122℃.

3. The method according to claim 1, characterized in that, The high amylose corn starch in step a has an amylose content of ≥70% and a moisture content of 17%-19%; the wet heat treatment time in step b is 5-8 minutes, and the resulting RS3 resistant starch content is ≥15%.

4. The application of RS3 resistant starch prepared according to claim 1 in low-GI foods, pharmaceutical excipients, industrial raw materials or pet foods.