Low-temperature superfine grinding and quality maintaining system suitable for glutinous rice flour

Abstract

The invention discloses a low-temperature superfine grinding and quality maintaining process for glutinous rice flour. The process comprises the following steps: pretreatment: cleaning a glutinous rice raw material, atomizing, humidifying and tempering, and pre-cooling after wetting; environment construction: an inert gas circulation environment is constructed in a closed crushing system, the temperature of circulation gas in the system is controlled to be within a first low-temperature interval, and the oxygen concentration is controlled to be below a safety threshold value; graded crushing: feeding the treated raw materials into a crushing system, utilizing low-temperature circulating gas as a conveying medium, enabling the glutinous rice raw materials to sequentially pass through a plurality of crushing areas with gradually-decreased grinding gaps in the airflow direction to be subjected to graded crushing, and taking away heat generated by grinding by utilizing the low-temperature circulating gas; and separating fine powder. The system is high in integration level, the ultrafine glutinous rice flour is uniform and fine in particle size and controllable in broken starch rate through a low-temperature inert gas loop and graded crushing design, the gelatinization characteristic and the gel characteristic of the ultrafine glutinous rice flour are closer to those of raw materials, and the application range is wider.

Description

Technical Field

[0001] This invention relates to the field of ultrafine grinding technology, and in particular to a low-temperature ultrafine grinding and quality preservation system suitable for glutinous rice flour. Background Technology

[0002] Glutinous rice flour is a crucial ingredient in traditional foods such as glutinous rice balls and pastries, and its quality directly affects the taste and appearance of the final product. With the development of the food industry, the application of glutinous rice flour in mooncake skins and cosmetic bases has placed higher demands on its fineness, whiteness, freeze-thaw stability, thickening properties, and other functionalities. Currently, ultrafine grinding technology is generally used for production. This technology can significantly reduce particle size and increase specific surface area, theoretically improving the processing performance and functionality of glutinous rice flour.

[0003] However, traditional airflow milling or mechanical impact milling has serious drawbacks when processing glutinous rice: the enormous mechanical energy generated during milling is converted into heat, causing a rapid increase in temperature within the milling chamber. Glutinous rice starch granules are extremely sensitive to heat; high temperatures easily lead to partial pregelatinization, manifested as an abnormally high percentage of damaged starch, decreased whiteness, and a lower initial gelatinization temperature. Simultaneously, high temperatures may cause denaturation of small amounts of protein and lipid oxidation in the glutinous rice, not only damaging its natural raw starch aroma and white appearance but also altering its rheological properties. This results in abnormal water absorption and reduced structural support when making high-end pastries or frozen dough. These quality deteriorations severely limit the application of ultrafine glutinous rice flour in the high-end food sector. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies, such as heat accumulation during ultrafine grinding, which leads to pregelatinization of powder particles and alteration of the rheological properties of glutinous rice powder. Therefore, this invention proposes a low-temperature ultrafine grinding and quality preservation system suitable for glutinous rice powder.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A low-temperature ultrafine grinding and quality preservation process for glutinous rice flour includes the following steps:

[0007] S1. Pre-treatment: Clean the glutinous rice raw material and perform atomized humidification and conditioning. After moistening, pre-cooling treatment is performed.

[0008] S2. Environment Construction: Construct an inert gas circulation environment in a closed pulverizing system, control the temperature of the circulating gas in the system in the first low temperature range, and control the oxygen concentration below the safety threshold.

[0009] S3, Grading and Grinding: The raw materials treated by S1 are sent into the grinding system constructed by S2. Low-temperature circulating gas is used as the conveying medium to make the glutinous rice raw materials pass through multiple grinding zones with decreasing grinding gaps in sequence along the airflow direction for grading and grinding. The low-temperature circulating gas is used to remove the heat generated by grinding.

[0010] S4. Separating fine powder: The pulverized gas-solid mixture is classified by particle size to separate ultrafine glutinous rice powder that meets the particle size requirements, and then collected by gas-solid separation.

[0011] Preferably, in step S1, the humidification and conditioning adjusts the moisture content of the glutinous rice raw material to 13% to 15%.

[0012] The pre-cooling process cools the raw materials to 0°C to 10°C.

[0013] Preferably, in step S2, the inert gas is nitrogen;

[0014] The first low-temperature range is controlled between -10℃ and 0℃;

[0015] The safe threshold for the oxygen concentration is 300 ppm.

[0016] More preferably, in step S3, the temperature of the pulverizing zone is controlled below 20°C under the action of low-temperature circulating gas.

[0017] Preferably, in step S4, the target fineness of the ultrafine glutinous rice flour particles is D90≤15μm;

[0018] Alternatively, the target fineness of the ultrafine glutinous rice flour particles is D90≤10μm.

[0019] More preferably, the prepared ultrafine glutinous rice flour has a particle size distribution D90≤15μm, whiteness≥92.0%, an increase rate of damaged starch content ≤15% compared to the raw material, and a starch gelatinization characteristic change rate of less than 10% compared to the raw material.

[0020] A low-temperature ultrafine grinding and quality preservation system for glutinous rice flour includes:

[0021] The graded crushing host has multiple crushing zones with decreasing grinding gaps arranged sequentially along the material feeding direction, and the outer shell of the crushing zone is provided with a cooling jacket.

[0022] The cooling circulation loop is a closed loop constructed by the gas circulation pipeline. The classifying and crushing host is connected in series in the cooling circulation loop. The loop is equipped with a temperature control medium unit for providing inert gas and a circulating fan for driving the airflow.

[0023] The pretreatment unit is located at the feed end of the grading and crushing host and is used for wetting and pre-cooling the glutinous rice raw materials.

[0024] The grading and collection device is installed at the discharge end of the grading and crushing host. It is used to classify and screen the powder, separate and collect the powder that meets the requirements, and return the coarse powder that does not meet the requirements to the grading and crushing host for further crushing through the circulation loop.

[0025] More preferably, the grinding zone is selected from grinding discs or grinding rings, and at least two stages are provided. The first stage is set as a coarse crushing zone with a gap of 100-500μm; the final stage is an ultrafine grinding zone with a gap adjusted to 10-50μm.

[0026] More preferably, the temperature control medium unit includes a liquid nitrogen vaporizer and a temperature control module for monitoring and adjusting the temperature of the circulating gas.

[0027] More preferably, the collection device is a cyclone collector or a pulse bag filter.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. In this invention, the design of low-temperature nitrogen circulation loop and graded crushing makes crushing as gentle as possible, reducing heat generation and controlling the crushing environment temperature at an extremely low level. This fundamentally eliminates starch pregelatinization and protein denaturation caused by mechanical heat, preserving the natural raw starch characteristics and functional activity of glutinous rice flour. The temperature control and oxygen-free protection of the low-temperature inert gas loop also avoids heat accumulation in the system, realizes the recycling of cold source, and reduces operating costs.

[0030] 2. In this invention, the inert gas is used to protect the entire pulverizing process, thus isolating oxygen and preventing lipid oxidation and enzymatic browning of the ultrafine powder. This preserves the high whiteness, excellent color, and flavor of the product. For colored rice such as black glutinous rice, it can also preserve the heat-sensitive active ingredients to the greatest extent and prevent nutrient loss.

[0031] 3. In this invention, the pretreatment conditioning through wetting and pre-cooling, combined with a low-temperature environment, allows the glutinous rice to enter a cold and brittle state, making it more prone to brittle fracture rather than plastic deformation. This not only reduces the energy consumption of grinding, but also solves the problem of incomplete grinding of difficult-to-grind components, resulting in a narrower particle size distribution and a more uniform and delicate texture in the finished product.

[0032] This invention features a high degree of system integration. Through a low-temperature inert gas circuit and a graded pulverization design, the ultrafine glutinous rice flour has a uniform and delicate particle size, and the rate of broken starch is controllable. Its gelatinization and gelation properties are also closer to those of the raw material, making it applicable to a wider range of applications. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0034] A low-temperature ultrafine grinding and quality preservation process for glutinous rice flour includes the following steps:

[0035] S1. Pre-treatment: Clean the glutinous rice raw material and perform atomized humidification conditioning to adjust the moisture content of the glutinous rice raw material to 13% to 15%. After wetting, cool the raw material to 0℃ to 10℃ for pre-cooling.

[0036] S2. Environment Construction: Construct an inert gas circulation environment in a closed pulverizing system. Nitrogen is selected as the inert gas. The temperature of the circulating gas in the system is controlled in the first low temperature range of -10℃ to 0℃, and the oxygen concentration is controlled below the safety threshold. The safety threshold is set to 500 ppm, preferably below 300 ppm.

[0037] S3, Grading and Grinding: The raw materials treated by S1 are sent into the grinding system constructed by S2. Low-temperature circulating gas is used as the conveying medium, so that the glutinous rice raw materials pass through multiple grinding zones with decreasing grinding gaps in sequence along the airflow direction for grading and grinding. The low-temperature circulating gas is used to remove the heat generated by grinding, and the temperature of the grinding zone is controlled below 20 ℃.

[0038] S4. Separation of fine powder: The pulverized gas-solid mixture is subjected to particle size classification to separate ultrafine glutinous rice powder that meets the particle size requirements. The target fineness is set to D90≤15μm; preferably D90≤10μm. Gas-solid separation and collection are then performed.

[0039] The prepared ultrafine glutinous rice flour has a particle size distribution D90≤10μm, whiteness≥92.0%, increased rate of damaged starch content ≤15% compared to raw material, and starch gelatinization characteristics change rate less than 10% compared to raw material.

[0040] A low-temperature ultrafine grinding and quality preservation system for glutinous rice flour includes:

[0041] The graded pulverizing host has multiple pulverizing zones with decreasing grinding gaps arranged sequentially along the material feeding direction. Each pulverizing zone is externally equipped with a cooling jacket, which uses water cooling in conjunction with low-temperature gas for auxiliary cooling. The pulverizing zones are constructed using grinding discs or grinding rings, preferably turbine grinding discs or concentric grinding rings. At least two stages are included: the first stage is a coarse crushing zone with a gap of 100–500 μm; the final stage is an ultrafine pulverizing zone with a gap adjusted to 10–50 μm. Multiple fine crushing zones can be incorporated between the two stages.

[0042] The cooling circulation loop is a closed loop constructed by the gas circulation pipeline. The staged pulverizer is connected in series in the cooling circulation loop. The loop is equipped with a temperature control medium unit for providing inert gas and a circulation fan for driving the airflow. The temperature control medium unit includes a liquid nitrogen vaporizer and a PID temperature control module for monitoring and adjusting the temperature of the circulating gas.

[0043] The pretreatment unit is located at the feed end of the grading and crushing host and is used for wetting and pre-cooling the glutinous rice raw materials.

[0044] A grading and collection device is installed at the discharge end of the grading and crushing main unit. It is used to grade and screen the powder, separating and collecting powders that meet the requirements, while coarse powders that do not meet the requirements are returned to the grading and crushing main unit via a circulation loop for further crushing. The collection device uses a cyclone collector and a pulse bag filter.

[0045] Based on the above processing technology, the following embodiments were designed: Embodiment 1

[0046] Processing long-grain glutinous rice using the process and system of the present invention

[0047] The system configuration in this embodiment mainly consists of a pretreatment unit, a cooling circulation loop, a grading and pulverizing host, and a grading and collection device.

[0048] The pretreatment unit, located at the feed end of the grading and pulverizing main unit, is equipped with a raw material cleaning screen, a magnetic separator, an ultrasonic atomizing humidifier, a mixer, and a pre-cooling chamber. It is used to remove stones and impurities from long-grain glutinous rice raw materials through magnetic separation. The moisture content is adjusted to 14.5% through atomization humidification and mixing. The raw materials are pre-cooled to 5°C by introducing 5°C cold air into the pre-cooling chamber, reducing the initial heat load for subsequent low-temperature pulverization.

[0049] Cooling circulation loop: A closed-loop loop constructed from nitrogen circulation pipelines, with the staged pulverizer connected in series within this loop. The loop includes a circulating fan to drive the airflow, a liquid nitrogen vaporizer to provide cryogenic inert gas, and a PID temperature control module. The PID module monitors the circulating gas temperature in real time and controls the amount of liquid nitrogen vaporized, providing the system with cryogenic nitrogen at -5℃±2℃, while simultaneously establishing an inert environment with an oxygen concentration below 200ppm.

[0050] The graded crushing host uses turbine grinding discs as the crushing zone. Multiple turbine grinding discs are connected in series in the cooling circulation loop. Three crushing zones are set in sequence along the material feeding direction: the first stage is set as the coarse crushing zone with a grinding gap of 300 μm; the second stage is the fine crushing zone with a gap of 100 μm; and the final stage is the ultrafine crushing zone with a gap adjusted to 30 μm.

[0051] Auxiliary cooling: The outer shell of the grinding zone is wrapped with a cooling jacket, and 5°C cooling water is introduced into the jacket for water cooling, which, together with the low-temperature nitrogen gas inside, provides double cooling from the inside and outside, ensuring that the side wall temperature of the final grinding zone is below 15°C.

[0052] Grading and screening device: A turbine classifier is used, located at the discharge end of the grading and pulverizing main unit. The cutting particle size D97 is set to 12μm to separate out the ultrafine powder that meets the requirements. The coarse powder that does not meet the requirements is returned to the feed inlet of the grading and pulverizing main unit for re-pulverization under the action of airflow.

[0053] Collection device: The collection device consists of a cyclone collector and a pulse bag filter connected in series at the discharge end of the turbine classifier. It efficiently collects the finished product under low-temperature nitrogen protection to prevent moisture absorption and condensation.

[0054] The above system is used to perform ultrafine grinding of glutinous rice according to the following process steps:

[0055] Step 1: Select long-grain glutinous rice as raw material, and after screening such as stone removal and magnetic separation, use an ultrasonic atomizing device to atomize and moisten it, then stir it evenly, adjust the moisture content to 14.5%, and then send it to the pre-cooling chamber to cool to 5℃.

[0056] Step 2: Start the cooling circulation system loop and continuously introduce vaporized low-temperature nitrogen into the closed system. With the help of the PID module for temperature regulation, control the temperature of the circulating nitrogen entering the classifying and pulverizing host to be controlled at -5℃±2℃. Wash the gas for 15 minutes, empty the air in the system, and detect that the oxygen concentration in the system has dropped to below 200 ppm to establish a low-temperature oxygen-free environment.

[0057] Step 3: The pre-cooled and conditioned glutinous rice raw material is sent into the graded grinding host along with low-temperature nitrogen gas. It goes through coarse crushing, fine crushing and ultra-fine grinding in sequence. During this process, the low-temperature nitrogen gas is combined with external water cooling to ensure that the temperature of the side wall of the grinding zone is always below 15 ℃, so as to prevent the ultra-fine powder from gelatinizing.

[0058] Step 4: The pulverized gas-solid mixture enters the turbine classifier for screening. Ultrafine powder with a particle size of less than 12μm enters the cyclone collector and pulse bag dust collector for collection. Coarse powder with a particle size of more than 12μm is thrown out under centrifugal force and flows back to the feed port of the classifying and pulverizing host for further pulverization with the nitrogen circulation loop.

[0059] After running the above steps continuously for four hours, samples were taken for testing. The resulting ultrafine glutinous rice flour had a D90 of 9.5 μm and a D50 of 4.2 μm, with a narrow and uniform particle size distribution, a whiteness of 93.5, and no browning. Using a rapid viscosity analyzer (RVA), the peak viscosity was measured, and compared to the uncrushed raw glutinous rice flour, the change rate was only 3.2%, indicating that the starch properties remained intact.

[0060] Example 2

[0061] This embodiment is basically the same as Embodiment 1, except that the key process parameters are adjusted to produce glutinous rice flour with a finer particle size.

[0062] The specific differences in process parameters are as follows:

[0063] In step two, the temperature of the circulating nitrogen entering the classifying and pulverizing host is controlled at -10℃±2℃.

[0064] In step four, adjust the speed of the classifying wheel of the turbine classifier and set the cutting particle size to D97 as 8μm.

[0065] After running the above steps continuously for four hours, samples were taken for testing. The resulting ultrafine glutinous rice flour had a D90 of 6.8 μm, a D50 of 3.1 μm, uniform particle size distribution, a whiteness of 92.8, and no browning. Using a rapid viscosity analyzer (RVA), the peak viscosity increased by 4.5% compared to the uncrushed raw glutinous rice flour, indicating that the starch properties remained intact and the increase in damaged starch content was controlled within 10%.

[0066] Example 3

[0067] The system and process in this embodiment are basically the same as those in Embodiment 1. The difference is that the raw material used in this embodiment is black glutinous rice, and the processing requirement is to maintain the anthocyanin activity in the raw material.

[0068] The specific differences in process parameters are as follows:

[0069] In step two, the temperature of the circulating nitrogen entering the classifying and pulverizing host is controlled at 0℃±1℃.

[0070] After running the above steps continuously for four hours, samples were taken for testing. The resulting ultrafine glutinous rice flour had a D90 of 10.5 μm and a D50 of 4.8 μm, with a uniform particle size distribution. The powder was purplish-black in color, with a uniform luster and no dull, burnt appearance. High-performance liquid chromatography (HPLC) analysis showed that the retention rate of anthocyanins (calculated as cyanidin-3-glucoside) in the finished product was 95.2%.

[0071] Comparative Example 1

[0072] This comparative example uses the same long-grain glutinous rice as in Example 1, except that no conditioning pretreatment is performed, and it is pulverized to a similar fineness (D90=9.8μm) using a conventional airflow mill.

[0073] The grinding process was monitored. After 30 minutes of operation, the airflow temperature in the grinding chamber and outlet rapidly increased to over 65 ℃, and the equipment casing became noticeably hotter as the operating time increased. Samples were taken four hours after grinding. The finished product had a particle size D90 of 10.0 μm, a powder whiteness of 86.2, and a slightly yellow tint. RVA testing showed that its peak viscosity decreased by 18.7% compared to the raw material, and the content of damaged starch increased significantly. The product had a slight cooked powder odor.

[0074] Comparative Example 2

[0075] This comparative example uses the same black glutinous rice as in Example 3, except that no conditioning pretreatment is performed, and it is pulverized to a similar fineness (D90=10.5 μm) using a conventional airflow mill.

[0076] The pulverization process was monitored. During operation, the outlet airflow temperature was maintained between 62℃ and 65℃, and significant heat accumulation was observed in the system. Samples were taken for testing four hours after pulverization. The finished product particle size D90 was 10.8 μm, the powder color was grayish-purple with tiny white spots, and HPLC analysis showed that the anthocyanin retention rate was 81.2%.

[0077] Based on the experimental data from the above embodiments and comparative examples, it is evident that the present invention demonstrates significant improvements in suppressing thermal damage, preventing oxidative degradation, and improving grinding uniformity. Compared to the two comparative examples, the lack of low-temperature inert gas protection resulted in severe heat buildup in the equipment during grinding, leading to severe mechanical gelatinization of the powder and a significant decrease in peak viscosity. The present invention, through dual temperature control of low-temperature inert gas circulation and external water cooling, effectively removes heat, controlling viscosity change to below 3.2%. For the ultrafine glutinous rice powder with a particle size D90 of 6.8 μm prepared in Example 2, this can also be controlled to below 4.5%, ensuring the natural raw powder characteristics and reprocessing potential of the ultrafine glutinous rice powder, such as for high-end snow skin mooncakes and cosmetic base materials. Regarding the retention of active ingredients, for black glutinous rice raw materials, the anthocyanin retention rate reaches as high as 95.2%. In terms of grinding uniformity, the low-temperature cold brittleness effect solves the problem of difficult grinding of black glutinous rice seed coat fibers, which leads to uneven grinding and white spots, significantly improving the sensory quality and commercial value of black glutinous rice ultrafine powder particles. This invention, through the synergistic design of raw material conditioning, low-temperature inert gas circuit and multi-stage pulverization, ensures the temperature control capability of the pulverization system, guarantees the processing quality of ultrafine powder in heat-sensitive grains, and breaks through technical limitations.

[0078] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A low-temperature ultrafine grinding and quality preservation process for glutinous rice flour, characterized in that, Includes the following steps: S1. Pre-treatment: Clean the glutinous rice raw material and perform atomized humidification and conditioning. After moistening, pre-cooling treatment is performed. S2. Environment Construction: Construct an inert gas circulation environment in a closed pulverizing system, control the temperature of the circulating gas in the system in the first low temperature range, and control the oxygen concentration below the safety threshold. S3, Grading and Grinding: The raw materials treated by S1 are sent into the grinding system constructed by S2. Low-temperature circulating gas is used as the conveying medium to make the glutinous rice raw materials pass through multiple grinding zones with decreasing grinding gaps in sequence along the airflow direction for grading and grinding. The low-temperature circulating gas is used to remove the heat generated by grinding. S4. Separating fine powder: The pulverized gas-solid mixture is classified by particle size to separate ultrafine glutinous rice powder that meets the particle size requirements, and then collected by gas-solid separation.

2. The low-temperature ultrafine grinding and quality preservation process for glutinous rice flour according to claim 1, characterized in that, In step S1, the humidification and conditioning process adjusts the moisture content of the glutinous rice raw material to 13% to 15%. The pre-cooling process cools the raw materials to 0°C to 10°C.

3. The low-temperature ultrafine grinding and quality preservation process for glutinous rice flour according to claim 1, characterized in that, In step S2, the inert gas is nitrogen; The first low-temperature range is controlled between -10℃ and 0℃; The safe threshold for the oxygen concentration is 300 ppm.

4. The low-temperature ultrafine grinding and quality preservation process for glutinous rice flour according to claim 3, characterized in that, In step S3, the temperature of the pulverizing zone is controlled below 20°C under the action of low-temperature circulating gas.

5. The low-temperature ultrafine grinding and quality preservation process for glutinous rice flour according to claim 1, characterized in that, In step S4, the target fineness of the ultrafine glutinous rice flour particles is D90≤15μm; Alternatively, the target fineness of the ultrafine glutinous rice flour particles is D90≤10μm.

6. The low-temperature ultrafine grinding and quality preservation process for glutinous rice flour according to any one of claims 1-5, characterized in that, The prepared ultrafine glutinous rice flour has a particle size distribution D90≤15μm, whiteness≥92.0%, increased rate of damaged starch content ≤15% compared to raw material, and starch gelatinization characteristics change rate less than 10% compared to raw material.

7. A low-temperature ultrafine grinding and quality preservation system for glutinous rice flour used in implementing the process described in any one of claims 1-6, characterized in that, include: The graded crushing host has multiple crushing zones with decreasing grinding gaps arranged sequentially along the material feeding direction, and the outer shell of the crushing zone is provided with a cooling jacket. The cooling circulation loop is a closed loop constructed by the gas circulation pipeline. The classifying and crushing host is connected in series in the cooling circulation loop. The loop is equipped with a temperature control medium unit for providing inert gas and a circulating fan for driving the airflow. The pretreatment unit is located at the feed end of the grading and crushing host and is used for wetting and pre-cooling the glutinous rice raw materials. The grading and collection device is installed at the discharge end of the grading and crushing host. It is used to classify and screen the powder, separate and collect the powder that meets the requirements, and return the coarse powder that does not meet the requirements to the grading and crushing host for further crushing through the circulation loop.

8. The low-temperature ultrafine grinding and quality preservation system for glutinous rice flour according to claim 7, characterized in that, The grinding zone is selected from grinding discs or grinding rings, and at least two stages are set. The first stage is set as a coarse crushing zone with a gap of 100-500μm; the final stage is an ultrafine grinding zone with a gap adjusted to 10-50μm.

9. The low-temperature ultrafine grinding and quality preservation system for glutinous rice flour according to claim 7, characterized in that, The temperature control medium unit includes a liquid nitrogen vaporizer and a temperature control module, which are used to monitor and adjust the temperature of the circulating gas.

10. The low-temperature ultrafine grinding and quality preservation system for glutinous rice flour according to claim 7, characterized in that, The collection device is a cyclone collector and a pulse bag filter.