A method of heat-moisture treatment of high amylose starch at 35-40% moisture

Abstract

This invention discloses a method for hydrothermal treatment of high amylose starch under 35%-40% moisture conditions, 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 35%-40%, feeding it into a jacketed stainless steel autoclave, and hydrothermally treating it for 8-15 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 medium moisture conditions within the 35%-40% moisture range through hydrothermal treatment, resulting in RS3-type resistant starch with a content ≥12% (determined according to AOAC 2002.02 standard method) and an RS3 melting temperature ≥120℃ (determined by differential scanning calorimetry). This method completes the intermediate range of moisture content from low moisture (15%-20%) to high moisture (40%-45%), locking the parameter boundaries of pure physical modification processes in the 35%-40% moisture range.

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 35%-40% moisture conditions. This method is patented with external parameter locking, specifically filling in the 35%-40% intermediate range between low moisture (15%-20%) and high moisture (40%-45%) in the moisture content dimension, forming a complete protective closed loop covering the entire moisture range without any dead angles. Background Technology The core annealing patent for purely physically modified RS3 resistant starch protects annealing processes in the 20%-35% moisture range. A separate patent application for low-moisture hydrothermal treatment protects the 15%-20% moisture range, and another separate patent application for high-moisture annealing protects the 40%-45% moisture range. However, the 35%-40% moisture range lies in the transition zone between annealing and hydrothermal treatment—this moisture content is below the lower limit of the academic definition of annealing (40%), but above the upper limit of conventional low-moisture hydrothermal treatment (usually ≤35%), creating a gray area. Competitors could exploit this gap by using hydrothermal treatment in the 35%-40% moisture range to prepare RS3 resistant starch, thereby circumventing the protection scope of existing patents. Therefore, this patent application is necessary to lock in the hydrothermal treatment route in the 35%-40% moisture range. Under humid heat treatment with a moisture content of 35%-40%, the moisture environment of starch granules falls between the "limited moisture" of low moisture and the "excess moisture" of high moisture. Compared to the low moisture conditions of 15%-20%, 35%-40% moisture provides a more sufficient medium for molecular chain migration, resulting in stronger mobility of amylose molecular chains and enabling them to complete ordered recombination in a relatively short time. However, compared to the high moisture annealing conditions of 40%-45%, 35%-40% moisture is still within the limited moisture range, requiring high-temperature treatment in a closed environment to drive molecular chain rearrangement, rather than relying on sufficient swelling in excess moisture. It is worth noting that the parameter window of the low moisture HMT patent (15%-20% moisture) cannot be simply extended to the 35%-40% moisture range—because the different moisture environments lead to fundamentally different molecular chain migration behaviors, requiring the establishment of an independent parameter window. Summary of the Invention Purpose of the invention A method for wet heat treatment of high amylose starch under 35%-40% moisture conditions is provided. The wet heat treatment route locks the parameter boundary of the medium moisture range and fills the intermediate gap in the moisture content dimension. Technical solution High-amylose corn starch (amylose content ≥55%) was adjusted with water to a moisture content of 35%-40%, and then fed into a jacketed stainless steel autoclave. It was subjected to hydrothermal treatment for 8-15 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 35%-40%, wet heat treatment temperature controlled at 95-110℃, treatment time controlled at 8-15 minutes, and amylose content in the starch raw material controlled at ≥55%. Under conditions where moisture content is below 35% or above 40%, treatment temperature is below 95℃ or above 110℃, treatment time is less than 8 minutes or more than 15 minutes, and 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 medium-moisture humidification is based on the coupling relationship between moisture, temperature, and time. Under medium-moisture conditions of 35%-40%, the moisture medium inside starch granules is more abundant than under low-moisture conditions (15%-20%), allowing for greater freedom of movement of molecular chains. However, the moisture content is still insufficient to fully swell the granules. Increasing the temperature to 95-110℃ enhances the thermal kinetic energy of the molecular chains. In a closed autoclave environment, the material's self-generated moisture pressure (0.1-0.4 MPa) creates a saturated steam environment, driving the molecular chains to complete orderly recombination within a limited but relatively abundant moisture medium. The processing time needs to be controlled within 8-15 minutes—5-12 minutes is longer for low-moisture HMT (due to higher moisture content, requiring more time for complete molecular chain recombination), but shorter for high-moisture annealing (20-30 minutes) (due to higher driving efficiency at higher temperatures). The coupling relationship between moisture, temperature, and time can be quantitatively described as follows: for every 2 percentage point increase in moisture content (within the range of 35%-40%), to maintain an RS3 content ≥12%, the wet heat treatment temperature needs to be reduced by approximately 2-3℃, or the treatment time needs to be extended by approximately 1-2 minutes. For example, under 35% moisture conditions, a treatment temperature of approximately 105-110℃ and a treatment time of approximately 8-10 minutes can achieve an RS3 ≥12%; under 38% moisture conditions, a treatment temperature of approximately 100-105℃ and a treatment time of approximately 10-12 minutes can achieve the same RS3 level; and under 40% moisture conditions, a treatment temperature of approximately 95-100℃ and a treatment time of approximately 12-15 minutes can achieve the same RS3 level. This quantitative parameter linkage is the core technical characteristic of the medium-moisture wet heat treatment process. This method achieves an RS3 content ≥12% and a melting point ≥120℃ under medium moisture conditions of 35%-40%, producing an unexpected technical effect—the parameter window of the low moisture HMT patent (15%-20% moisture) cannot be simply extended to the 35%-40% moisture range. Comparative Example 8 (processing material with 35% moisture using the low moisture HMT patent conditions at 100℃ / 10 minutes) showed an RS3 content of only 10.5%, proving that the parameter combination of the low moisture HMT window cannot achieve RS3 ≥12% in the 35%-40% moisture range—those skilled in the art would not have anticipated from the low moisture HMT patent that an independent parameter window (extending the processing time to 8-15 minutes) was needed to achieve RS3 compliance under medium moisture conditions. This patent completes this independent technical solution, and there is a fundamental difference in parameter window between it and the low moisture HMT patent (15%-20% moisture) and the high moisture annealing patent (40%-45% moisture). Detailed Implementation Example 1 (Moisture-heat treatment at 100°C) High-amylose corn starch (amylose content approximately 58%) was added to adjust the moisture content to approximately 38%, and then placed in a jacketed stainless steel autoclave. It was subjected to hydrothermal treatment for 12 minutes in a closed, saturated steam environment at 100°C, relying on the material's own moisture pressure of approximately 0.3 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 13.5%±0.5% (≥12%, determined according to AOAC 2002.02 standard method), RS3 melting temperature 124±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 (moisture-heat treatment at 105°C + high linear chain content ≥70%) High-amylose corn starch (amylose content approximately 72%) with a moisture content of 36% was subjected to hydrothermal treatment for 10 minutes in a closed saturated steam environment at 105℃ and an autogenous pressure of approximately 0.35MPa. The RS3 content was 16.8%±0.8% (≥15%), and the RS3 melting temperature was 128±1℃ (≥122℃). Comparative Example 1 (Moisture content 32% - falls within the range of conventional annealing or low moisture HMT) Using the same raw materials as in Example 1, with a moisture content of 32% (<35%), and a processing temperature of 100°C. RS3 content was 13.2% ± 0.5% (compliant, but falling within the protection range of conventional 20%-35% annealing or alternatively 15%-20% low moisture HMT). Comparative Example 2 (Moisture content 42% - falls within the high moisture annealing range) The same raw materials as in Example 1 were used, with a moisture content of 42% (>40%) and a processing temperature of 100°C. The RS3 content was 13.0% ± 0.5% (meets the standard, but falls within the protection range of 40%-45% high moisture annealing in another case). 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 8.8% ± 0.5% (<12%). 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 10 minutes. The RS3 content was 8.2% ± 0.5% (<12%). 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 38%, and the treatment temperature was 100℃ for 12 minutes. The RS3 content was 7.5% ± 0.5% (<12%). Comparative Example 6 (Processing time 7 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 7 minutes (<8 minutes). The RS3 content was 9.5% ± 0.5% (<12%). The treatment time was insufficient under medium moisture conditions, resulting in inadequate molecular chain rearrangement. Comparative Example 7 (Processing time 17 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 17 minutes (>15 minutes). The RS3 content was 9.0% ± 0.5% (<12%). Excessive treatment time caused the particles to begin degrading in the high-temperature, enclosed environment. Comparative Example 8 (Low Moisture HMT Window × Moisture 35% - Not up to standard) Using the same raw materials as in Example 1, with a moisture content of 35%, and employing the process conditions (100°C / 10 minutes) of a separate low-moisture HMT patent, the RS3 content was 10.5% ± 0.5% (< 12%). This demonstrates that the parameter window of the low-moisture HMT patent cannot be simply extended to the 35%-40% moisture range—those skilled in the art would not have anticipated from the low-moisture HMT patent that a separate parameter window (extending the processing time to 8-15 minutes) would be needed to achieve RS3 compliance under medium moisture conditions. Industrial applications This method locks in the boundaries of the hydrothermal treatment parameters for purely physically modified RS3 resistant starch within the 35%-40% moisture range. The moisture content is controlled at 35%-40%, the treatment temperature at 95-110℃, the treatment time at 8-15 minutes, and the amylose content in the starch raw material at ≥55%. These four parameter windows together constitute the protection scope of this method. This method, together with the 15%-20% low moisture hydrothermal treatment method, the conventional 20%-35% moisture annealing method, and the 40%-45% high moisture annealing method in another application, forms a complete protection loop in terms of moisture content: 15%-20% (low moisture hydrothermal treatment) → 20%-35% (conventional annealing) → 35%-40% (this method, 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 35%-40% moisture conditions, 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 35%-40%; b. Moist heat treatment: The conditioned material is sent into a jacketed stainless steel autoclave and moist heat treated for 8-15 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 medium 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 10-12 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 36%-38%; the wet heat treatment time in step b is 8-10 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.