A low-glycemic physical modification process specific to waxy rice

Abstract

This invention discloses a low-glycemic index physical modification process specifically for glutinous rice, belonging to the field of grain deep processing technology. The process involves pre-cooking glutinous rice in a moist heat until the gelatinization degree reaches 35%-55%, then immediately annealing it in a constant humidity environment at 60-63℃ for 12-15 minutes. This causes partial retrogradation and orderly rearrangement of the gelatinized amylopectin molecules, forming a resistant starch structure and lowering the glycemic index. Subsequently, the rice is forcibly and rapidly cooled to a core temperature ≤25℃, and then dried at a low temperature not exceeding 50℃ until the moisture content reaches 11%-13%, followed by sealed packaging. This invention specifically optimizes the characteristics of glutinous rice, which is almost entirely composed of amylopectin and has a soft and sticky texture. The resulting product has a GI value ≤65, a resistant starch content ≥5%, and a resistant starch retention rate ≥65% after secondary cooking. The cooked rice has a soft, sticky, and elastic texture, making it suitable as a daily staple food for people controlling their blood sugar, as well as for glutinous rice products such as zongzi (sticky rice dumplings) and nian gao (New Year's cake).

Description

Technical Field

[0001] This invention belongs to the field of deep grain processing technology, specifically involving a pure physical annealing modification method for glutinous rice varieties, which is used to reduce the glycemic index while retaining the soft, sticky and elastic texture of glutinous rice. Background Technology Glutinous rice is a widely consumed rice variety in China and Southeast Asia. Its starch composition differs fundamentally from that of indica and japonica rice: glutinous rice starch contains over 98% amylopectin and very little amylose (usually less than 2%), resulting in soft, sticky grains that become extremely sticky after cooking. Traditional glutinous rice typically has a glycemic index (GI) between 80 and 90, classifying it as a high-GI food. The applicant's prior art discloses a general method for semi-gelatinization annealing of rice, but it does not include specific parameter optimization tailored to the characteristics of glutinous rice varieties. Since glutinous rice contains almost no amylose, traditional annealing strategies based on the ordered rearrangement of amylose to form RS3-type resistant starch have limited effectiveness. Lowering the GI value of glutinous rice relies on partial retrogradation of amylopectin—that is, during annealing, the highly branched amylopectin molecules undergo localized ordered rearrangement to form an resistant structure. The temperature window required for this process is completely different from the amylose rearrangement window for indica and japonica rice. If the annealing parameters for indica or japonica rice are directly applied, glutinous rice will become over-gelatinized, lose its viscoelasticity, and fail to effectively lower its GI value. Therefore, glutinous rice requires a specially optimized annealing process. Summary of the Invention Purpose of the invention The purpose of this invention is to provide an annealing modification method specifically for glutinous rice varieties, which effectively reduces the GI value while retaining the soft, sticky and elastic texture of glutinous rice by optimizing the matching of temperature and time. Technical solution The present invention includes the following steps: (1) pre-cooking glutinous rice with wet heat until the gelatinization degree is 35%-55%; (2) annealing in a constant humidity environment of 60-63℃ and 80%-95% for 12-15 minutes. This temperature window is suitable for the high branched starch content and soft glutinous grain structure of glutinous rice and is lower than the annealing temperature window of indica rice and japonica rice; (3) forced rapid cooling to the center temperature of the rice body ≤25℃; (4) drying at a low temperature not exceeding 50℃; (5) sealing and packaging. Core Mechanism The amylopectin molecules in glutinous rice are highly branched, forming an extremely viscous system after gelatinization. During annealing, the linear branches of amylopectin undergo localized orderly rearrangement under appropriate temperature conditions, forming an indigestible structure and thus lowering the glycemic index (GI). The 60-63℃ window is significantly lower than the 62-65℃ window for indica rice and the 65-68℃ window for japonica rice. This is because the branched structure of amylopectin has lower thermal stability and is prone to excessive swelling and disintegration at higher temperatures. Excessively high temperatures (>63℃) lead to excessive gelatinization and loss of viscoelasticity in glutinous rice; excessively low temperatures (<60℃) result in insufficient chain mobility of amylopectin molecules and reduced retrogradation efficiency. The annealing time of 12-15 minutes is longer than that for indica and japonica rice to compensate for the slower retrogradation rate of amylopectin at lower temperatures. The drying temperature is controlled below 50℃ (lower than the 55℃ for indica and japonica rice) to protect the indigestible structure already formed in the soft and glutinous texture of glutinous rice from being destroyed by high temperatures. Beneficial effects (1) A special annealing solution for glutinous rice was proposed for the first time, reducing the GI value to below 65. (2) The resistant starch retention rate after the second steaming of the product is ≥65%, and the rice has a soft, sticky and elastic texture. (3) The annealing time is 12-15 minutes, which is suitable for continuous industrial production. (4) Purely physical with zero additives. Detailed Implementation Example 1 (Antifying Glutinous Rice) Take 1000 kg of Grade 1 glutinous rice and pre-cook it with normal pressure steam until the gelatinization degree reaches 45%. Transfer the pre-cooked glutinous rice to a constant temperature and humidity annealing equipment and anneal at 61℃ and 85% humidity for 13 minutes. After annealing, cool it with 12℃ cold water spray combined with side blowing for 75 seconds until the core temperature of the rice reaches 23℃. Then, dry it at 45℃ for 3 hours until the moisture content reaches 12.0%, and vacuum seal it for packaging. The resulting product showed a significantly lower GI value and a significantly higher resistant starch content. After secondary steaming, the rice was soft, sticky, and elastic, with a texture not significantly different from untreated glutinous rice. Comparative Example 1 (annealing temperature exceeding 63℃) The annealing temperature in Example 1 was changed to 65°C, while the other conditions remained unchanged. The resulting product was excessively gelatinized, lost its viscoelasticity after secondary cooking, and the rice had a mushy texture. This proves that temperatures exceeding 63℃ cause excessive swelling and disintegration of the amylopectin in glutinous rice, damaging its structural integrity. Comparative Example 2 (annealing temperature below 60℃) The annealing temperature in Example 1 was changed to 57°C, while the other conditions remained unchanged. The resulting product had low resistant starch content, a high GI value, and insufficient retrogradation efficiency. This demonstrates that below 60℃, the molecular chain mobility of amylopectin is insufficient, leading to a significant decrease in retrogradation efficiency. Comparative Example 3 (annealing time too short) The annealing time of Example 1 was shortened to 9 minutes, while the other conditions remained unchanged. The resulting product had a resistant starch retention rate of less than 65% after secondary cooking and a high GI value. This indicates that insufficient annealing time led to incomplete retrogradation of amylopectin. Comparative Example 4 (annealing time too long) The annealing time of Example 1 was extended to 18 minutes, while the other conditions remained unchanged. The resulting rice, after being steamed twice, had a harder texture and decreased viscosity and elasticity. This indicates that excessive annealing time led to excessive retrogradation of amylopectin, resulting in a deterioration in texture. Detection methods The degree of gelatinization was determined by enzymatic hydrolysis, the GI value was determined by the ISO 26642:2010 standard method, and the resistant starch content was determined by the AOAC 2002.02 standard method. Industrial applications This invention can be implemented on existing continuous pre-cooking-annealing-cooling-drying production lines. The core equipment includes a steam pre-cooking machine, a closed continuous annealing tower with a temperature control accuracy of ±0.5℃ across the entire range, a cold water spray quenching system, and a low-temperature airflow drying device.

Claims

1. A low-glycemic index physical modification process specifically for glutinous rice, characterized in that, Includes the following steps: a. Pre-cooking in a moist heat: Pre-cook glutinous rice in a moist heat environment until the starch gelatinization degree is 35%-55%; b. Isothermal annealing: The pre-cooked glutinous rice is kept in a constant humidity environment with a relative humidity of 80%-95% for 12-15 minutes within a temperature window of 60-63℃. The temperature window is suitable for the high amylopectin content and soft glutinous grain structure of glutinous rice, and is lower than the annealing temperature window of indica rice and japonica rice. This allows the gelatinized amylopectin molecules to partially regenerate and rearrange in an orderly manner to form a resistant starch structure. c. Forced rapid cooling: Cool the annealed glutinous rice to a core temperature of ≤25℃ within 50-120 seconds to terminate the gelatinization reaction; d. Low-temperature drying: Dry the cooled glutinous rice at a temperature not exceeding 50℃ until the moisture content is 11%-13%; e. Sealed packaging: The dried glutinous rice is sealed in packaging.

2. The method according to claim 1, characterized in that, The gelatinization degree of the wet heat precooking in step a is preferably 40%-50%.

3. The method according to claim 1, characterized in that, The annealing temperature in step b is 61-62℃, and the annealing time is 13-14 minutes.

4. The method according to claim 1, characterized in that, The forced rapid cooling described in step c uses cold water spray or cold air blast cooling, with a cooling time of 60-90 seconds and a cooling medium temperature ≤25℃.

5. The method according to claim 1, characterized in that, The drying temperature in step d is 40-45℃, and the total drying time is 2.5-3.5 hours.

6. A pre-cooked rice with a low glycemic index resistant starch specific to glutinous rice, characterized in that, The rice prepared by the method described in any one of claims 1-5 simultaneously satisfies the following conditions: GI value ≤ 65, resistant starch content ≥ 5%, resistant starch retention rate ≥ 65% after secondary cooking, and the rice has a soft, sticky, and elastic texture.

7. The rice according to claim 6, characterized in that, The rice has a GI value ≤ 62 and a resistant starch retention rate ≥ 70% after secondary cooking.

8. The application of the rice described in claim 6 or 7 in the preparation of sugar-controlled staple foods, zongzi (sticky rice dumplings), nian gao (New Year cake), tangyuan (glutinous rice balls), and glutinous rice pastries.