Low glycemic index colored rice flour special powder and its characteristics

Abstract

The application discloses a low-glycemic-index colored rice special powder, and belongs to the technical field of food. The colored rice special powder is prepared from red rice or purple rice through a pure physical annealing process, and meets the following characteristics: a GI value of less than or equal to 65, a RS3 type resistant starch content of more than or equal to 7%, a RS3 type resistant starch melting temperature of more than or equal to 120 DEG C, an anthocyanin retention rate of more than or equal to 80%, a dietary fiber content of more than or equal to 4%, and an ingredient table containing only the colored rice powder. The low-GI colored rice special powder of the application retains the unique natural color of red rice and purple rice, the antioxidant activity of anthocyanin and the whole grain dietary fiber, significantly reduces the glycemic index, and is suitable for making sugar-controlled staple food, meal replacement powder, baking premix powder and other products.

Description

Technical Field

[0001] This invention belongs to the field of food technology, specifically relating to a special powder product for colored rice that is produced by a pure physical annealing process, has a low glycemic index, retains the natural color of colored rice, anthocyanin antioxidant activity, and whole grain dietary fiber. Background Technology Red rice and purple rice are two traditional varieties of colored rice, naturally red or purple due to their high anthocyanin content in their bran. Anthocyanins are the core health component of red and purple rice, offering antioxidant and anti-inflammatory benefits. As whole grains, red and purple rice retain their intact bran and germ, resulting in a much higher dietary fiber content than refined white rice, promoting gut health and increasing satiety. Traditional red and purple rice flour typically has a glycemic index (GI) between 65 and 75, classifying them as medium-to-high GI foods. For consumers who need to control post-meal blood sugar, colored rice products are a nutritious and healthy option for their daily staple foods, but there is still room for further reduction in their GI value. Anthocyanins in red and purple rice have poor thermal stability, beginning to degrade significantly above 50-60℃. Traditional methods for reducing the glycemic index (GI) of colored rice flour involve high-temperature pre-cooking or extrusion puffing. While these methods can partially reduce the GI, the high temperatures cause significant anthocyanin degradation, resulting in the product's color fading from red or purple to grayish-brown. Anthocyanin retention is typically less than 30%, and antioxidant activity is lost. Currently, the market lacks a specialized colored rice flour product that can reduce the GI, retain the natural color and anthocyanin activity of colored rice, preserve whole-grain dietary fiber, and has a clean ingredient list. Red rice and purple rice are highly similar in anthocyanin content, bran structure, and starch characteristics—both contain anthocyanins, have dense brans that hinder water penetration, and endosperm starch content and structure similar to ordinary rice. Therefore, the same mild annealing process and quality indicator system can be applied. The applicant's earlier patent application disclosed a method for physical modification of black rice to retain the bran and a method for low-GI modification of wild rice, which, through mild annealing, generates RS3-type resistant starch while retaining anthocyanins in the bran, thus lowering the GI value. This invention applies this method uniformly to both red and purple rice—the colored rice is pre-cooked in moist heat and then drained before being treated within a mild annealing window, causing the amylose to rearrange in an orderly manner to generate RS3-type resistant starch, lowering the GI value. Simultaneously, the annealing and drying temperatures are controlled below the safe window for rapid anthocyanin degradation, resulting in the retention of a large amount of anthocyanins and intact dietary fiber. This invention defines for the first time a colored rice flour product that simultaneously meets the characteristics of low GI, high anthocyanin retention rate, and high dietary fiber, and fully defines its quality through six quantitative indicators: GI value, RS3 content, RS3 melting temperature, anthocyanin retention rate, dietary fiber content, and ingredient list. Summary of the Invention Purpose of the invention This invention provides a special colored rice flour product that is produced through a purely physical annealing process, has a low glycemic index, retains the natural color of colored rice, anthocyanin antioxidant activity, and whole grain dietary fiber, and its quality is fully defined by six quantitative indicators. Technical solution This product uses red or purple rice as raw material. The colored rice is pre-cooked in a moist heat until the gelatinization degree reaches 30%-45%, and the moisture content is adjusted to 22%-28% by controlling the water content. It is then placed in a constant temperature and humidity equipment and annealed for 12-20 minutes in a mild, humid environment of 50-58℃ and 80%-95% relative humidity. During annealing, the amylose molecules rearrange themselves orderly along the surface of the residual microcrystals to form high-melting-point RS3-type resistant starch, reducing the product's GI value. The annealing temperature is strictly controlled below 58℃—this is the safe upper limit for the rapid degradation of anthocyanins; exceeding this temperature will result in significant anthocyanin degradation. After annealing, the rice is rapidly cooled to below 25℃ within 90 seconds using a fluidized bed to lock in the RS3 lattice structure and terminate the thermal degradation reaction of anthocyanins. It is then dried at a low temperature not exceeding 45℃ until the moisture content is below 13% to prevent secondary degradation of anthocyanins during drying. After drying, the colored rice is ground to the required fineness to obtain low-GI colored rice powder. The resulting product simultaneously meets the following requirements: GI value ≤ 65, RS3 resistant starch content ≥ 7%, RS3 resistant starch melting temperature ≥ 120℃, anthocyanin retention rate ≥ 80%, dietary fiber content ≥ 4%, and the ingredient list contains only the aforementioned colored rice flour. Core Mechanism Anthocyanins are the core health component of red and purple rice, and also the source of their natural color. Anthocyanins are heat-sensitive, beginning to degrade significantly above 50-60℃. Annealing temperatures are strictly controlled within a mild window of 50-58℃—58℃ is the safe upper limit for rapid anthocyanin degradation; exceeding this temperature will result in substantial degradation of anthocyanins, causing the product color to fade from red or purple to grayish-brown. 50℃ is the lower limit for amylose molecules to have sufficient thermal mobility to dissolve from the granules and rearrange in an orderly manner. Within this mild window of 50-58℃, amylose has ample time to complete the orderly rearrangement to form RS3, and anthocyanins are largely retained due to the temperature being far below their rapid degradation threshold, with a retention rate ≥80%. Drying temperatures are strictly controlled below 45℃ because anthocyanins are more thermally unstable in low-moisture environments. Rapid cooling locks in crystals and simultaneously terminates the thermal degradation reaction of anthocyanins, preventing continuous degradation caused by residual heat. A dietary fiber content of ≥4% quantifies the natural advantage of colored rice as a whole grain—this is 4-8 times that of refined white rice (approximately 0.5%-1%). The formation of RS3 resistant starch lowers the GI value, and its high melting temperature (≥120℃) ensures the stable maintenance of low GI characteristics during subsequent cooking. The three-stage treatment of pre-cooking, annealing, and low-temperature drying enables colored rice to retain its natural color and anthocyanin activity while achieving the dual goals of low GI and preservation of whole-grain nutrition. Beneficial effects (1) A complete quality index system for low-GI colored rice flour products was defined for the first time—ensuring low-GI characteristics through GI value and RS3 content, ensuring processing stability through RS3 melting temperature, ensuring antioxidant health benefits and natural color through anthocyanin retention rate, ensuring whole-grain nutrition through dietary fiber content, and ensuring clean label characteristics through ingredient list. (2) One patent covers two colored rice categories: red rice and purple rice. (3) Mild annealing treatment simultaneously achieves the triple effects of reducing GI, retaining anthocyanins and retaining dietary fiber, with efficient and synergistic process. (4) Purely physical with zero additives, the ingredient list contains only the aforementioned colored rice flour, meeting clean label requirements. Detailed Implementation Example 1: Red Rice Powder Red rice was pre-cooked with steam at normal pressure until gelatinization reached 38%, and then the moisture content was reduced to 25%. It was then placed in a constant temperature and humidity equipment and gently annealed for 15 minutes at 54℃ and 85% humidity. During annealing, amylose molecules rearranged orderly along the surface of residual microcrystals to form RS3-type resistant starch, while anthocyanins were largely retained due to the temperature being far below the rapid degradation threshold. After annealing, the rice was rapidly cooled to below 25℃ within 90 seconds using a fluidized bed with -5℃ cold air to lock in the RS3 lattice structure and terminate the thermal degradation of anthocyanins. It was then dried at 42℃ until the moisture content was approximately 12%, and ground to a fineness of approximately 100 mesh to obtain low-GI red rice flour. The resulting product had a GI value of 61, an RS3-type resistant starch content of 7.8%, an RS3 melting temperature of 122℃, an anthocyanin retention rate of 86%, and a dietary fiber content of 4.5%. The ingredient list contained only red rice flour. The product was naturally reddish-brown, and after steaming or cooking, it had a soft and glutinous texture, showing no significant difference from untreated red rice. Example 2: Purple Rice Flour Purple rice was processed using the same conditions as in Example 1. The resulting product had a GI value of 60, an RS3 resistant starch content of 8.1%, an RS3 melting temperature of 123°C, an anthocyanin retention rate of 88%, and a dietary fiber content of 4.8%. The ingredient list contained only purple rice flour. The product was naturally purple and maintained its normal color after steaming or cooking. Comparative Example 1 (Traditional high-temperature pre-cooking treatment, resulting in significant degradation of anthocyanins) Red rice was pre-cooked using traditional high-temperature methods at 100℃ for 20 minutes. The GI value was 58, and the anthocyanin retention rate was only 25% (<80%). The product color faded from red to grayish-brown, and the dietary fiber content was 4.3% (meeting the standard). This demonstrates that while traditional high-temperature pre-cooking can lower the GI value, it severely damages anthocyanins, causing the product to lose its antioxidant activity and natural color. Comparative Example 2 (no annealing treatment, GI value not up to standard) Red rice was pre-cooked in a moist heat and then directly dried and ground without annealing. The resulting product had a GI value of 70 (>65), an RS3 resistant starch content of 2.5% (<7%), an anthocyanin retention rate of 82% (meeting the standard), and a dietary fiber content of 4.6% (meeting the standard). This demonstrates that pre-cooking alone cannot effectively reduce the GI value, and annealing is a necessary step for generating RS3 resistant starch. Industrial applications This product is suitable for the production of sugar-controlled staple foods, meal replacement powders, baking premixes, and other similar products. The product's GI value, RS3 content, RS3 melting temperature, anthocyanin retention rate, dietary fiber content, and ingredient list must be included in the product's factory inspection standards. The ingredient list contains only the aforementioned colored rice flour and complies with clean label requirements.

Claims

1. A low glycemic index colored rice flour, characterized in that, The colored rice flour meets the following characteristics: GI value ≤ 65, RS3 resistant starch content ≥ 7%, RS3 resistant starch melting temperature ≥ 120℃, anthocyanin retention rate ≥ 80%, dietary fiber content ≥ 4%, and the ingredient list contains only the colored rice flour.

2. The low glycemic index colored rice flour according to claim 1, characterized in that, The colored rice flour is derived from red rice or purple rice.

3. The low glycemic index colored rice flour according to claim 1, characterized in that, The anthocyanin retention rate was determined using the anthocyanin content of untreated colored rice as a baseline, and was measured by pH differential method or high performance liquid chromatography.

4. The low glycemic index colored rice flour according to claim 1, characterized in that, The GI value is ≤60, the RS3 resistant starch content is ≥8%, the anthocyanin retention rate is ≥90%, and the dietary fiber content is ≥5%.

5. The application of the low glycemic index colored rice flour according to any one of claims 1-4 in the preparation of sugar-controlled staple foods, meal replacement powders, and baking premixes.