A method for preparing millet powder by coupling low-oxygen drum drying and complex enzymolysis

Abstract

The application discloses a method for preparing millet powder by low-oxygen drum drying coupled with composite enzymolysis, and belongs to the technical field of grain food processing. In the method, a composite antioxidant composition composed of tea polyphenol and rosemary extract and sodium citrate are added to the millet slurry after crushing in the slurry adjusting stage; then, medium-temperature alpha-amylase, neutral protease and cellulase are added for enzymolysis; the obtained material after the enzymolysis is subjected to drum drying under nitrogen protection, the oxygen volume concentration in the drying zone is controlled to be less than or equal to 3% during the process, and then the millet powder is prepared through low-temperature crushing. The application can inhibit the fat oxidation in the millet powder processing process by compounding plant source antioxidants and adopting the nitrogen low-oxygen protection drum drying process, and can effectively reduce the peroxide value and acid value of the millet powder.

Description

Technical Field

[0001] This invention relates to the field of grain deep processing and food quality control technology, and in particular to a method for preparing millet flour by low-oxygen drum drying coupled with compound enzymatic hydrolysis. Background Technology

[0002] Millet is rich in unsaturated fatty acids, dietary fiber and various vitamins, and has important nutritional and health value. Drum drying has become the mainstream technology for the large-scale production of millet flour due to its high efficiency and low cost. However, the traditional drum drying process has two major defects: (1) High temperature oxidation - the drying temperature is usually 120~160℃, oxygen is fully in contact, and the lipid auto-oxidation chain reaction is violent, resulting in the peroxide value (POV) of millet flour generally being higher than 0.25 g / 100g, acid value (KOH) >5 mg / g, and a serious rancid taste after 23 months of storage at room temperature, with a shelf life of less than 6 months; (2) Flavor deterioration - high temperature easily produces burnt or raw fishy taste, lacking pleasant roasted aroma, and companies often add synthetic flavorings to cover it up, which cannot meet the trend of clean labeling.

[0003] To address the aforementioned issues, those skilled in the art have been seeking solutions. For example, CN119679084A discloses a method for enhancing the film-forming properties of enzymatically hydrolyzed grain foods produced by drum drying, but it does not solve the problem of oxygen contact in the high-temperature zone of continuous drum drying; CN107125558A discloses a pre-enzymatic hydrolysis-extrusion puffing processing technology to improve the water solubility index of whole grain meal powder, but it does not involve inert gas protection for synergistic antioxidant effects. Therefore, there is an urgent need for a method to block the oxidation chain reaction at its source and simultaneously generate natural baked flavor precursors to achieve a leap in quality. Summary of the Invention

[0004] To address the problems of easy oxidation and burnt taste in millet flour due to high-temperature drying in existing technologies, the purpose of this invention is to provide a method for preparing millet flour using low-oxygen drum drying coupled with compound enzymatic hydrolysis, which significantly reduces the peroxide value of millet flour while improving sensory scores.

[0005] Technical solution In a first aspect, this application provides a method for preparing millet flour using low-oxygen drum drying coupled with enzymatic hydrolysis, comprising the following steps: (1) Slurry preparation: Add a compound antioxidant composition and sodium citrate to the pulverized millet slurry. The compound antioxidant composition contains tea polyphenols and rosemary extract. The amount of the compound antioxidant composition added is 0.02% to 0.12% of the dry weight of millet in the millet slurry. The amount of sodium citrate added is 0.01% to 0.08% of the dry weight of millet in the millet slurry. After thorough mixing, reactant 1 is obtained. (2) Enzymatic hydrolysis: medium-temperature α-amylase, neutral protease and cellulase are added to reactant 1, and the pH is adjusted to 6.0-6.8 using a citric acid-sodium citrate system. Reactant 2 is obtained by enzymatic hydrolysis at 50-60℃. Enzymatic hydrolysis produces reducing sugars, short peptides and amino acids, which provide flavor precursors for the subsequent Maillard reaction and reduce the viscosity of the liquid. At the same time, bound lipids are released, which facilitates the contact of subsequent antioxidants. (3) Drum drying: Reactant 2 is dried in a drum under nitrogen protection. The surface temperature of the drum is 120~150℃, and nitrogen is introduced to keep the oxygen concentration in the drying zone ≤3% until the moisture content is ≤5.0%. (4) Grinding: Millet flour is obtained by low-temperature grinding; The dry basis mass of millet refers to the mass of millet solids in the millet slurry after the water has been removed.

[0006] In some embodiments, the mass ratio of tea polyphenols to rosemary extract is (1~3):1, the mass content of catechins in the tea polyphenols is ≥50%, and the mass content of caryopsisic acid in the rosemary extract is ≥20%.

[0007] In some implementations, the process further includes step (5) mixing: mixing the millet flour obtained after low-temperature pulverization with flavor-regulating microcapsules, wherein the core material of the flavor-regulating microcapsules contains millet flavor, γ-aminobutyric acid and natural vitamin E, and the amount added is 0.3%~1.2% of the mass of the millet flour, and the sensory score of the mixed millet flour is ≥8.5 points (out of 10).

[0008] In some embodiments, the wall material of the flavor microcapsules is sodium octenyl succinate starch and maltodextrin, prepared by spray drying, with an encapsulation rate of ≥85%.

[0009] In some preferred embodiments, the mass ratio of sodium octenyl succinate starch to maltodextrin is 1:1.5, and the mass ratio of millet flavor, γ-aminobutyric acid and natural vitamin E is 5:2:1. The process is spray drying with an inlet air temperature of 180°C, an outlet air temperature of 85°C, and an encapsulation rate of ≥85%.

[0010] In some embodiments, the amount of the mesophilic α-amylase added is 0.01~0.06% of the dry weight of millet in the millet slurry, the amount of the neutral protease added is 0.05~0.15% of the dry weight of millet in the millet slurry, and the amount of the cellulase added is 0.02~0.1% of the dry weight of millet in the millet slurry.

[0011] In some implementations, the drum dryer is equipped with nitrogen purging devices in the feeding zone, drying zone, and discharge port to maintain the oxygen concentration in the feeding zone, drying zone, and discharge port at ≤3%.

[0012] In some implementations, the concentration of the millet slurry in step (1) is 15~28°Bx, wherein the millet is pulverized to a fineness of 60~110 mesh.

[0013] In some implementation schemes, in step (3), an integral sealing cover and an online oxygen concentration analyzer are provided in the feeding area, drying area and discharge port. The nitrogen flow rate is adjusted to 10~50 L / min according to the value of the oxygen concentration analyzer, and a slight positive pressure of 50~150 Pa is maintained inside the integral sealing cover.

[0014] In some preferred embodiments, the drum dryer is a single-drum dryer, which is surrounded by an integral sealed protective cover that completely covers the drum body. The protective cover maintains a slight positive pressure of 50-150 Pa and is equipped with three nitrogen purging zones: a nitrogen nozzle and a first oxygen sensor in the feeding zone, a nitrogen ring multi-point injection and a second oxygen sensor in the drying zone, and a nitrogen curtain and a third oxygen sensor in the discharging zone. A PID controller automatically adjusts the nitrogen flow rate to 10-50 L / min based on the oxygen concentration in the drying zone to ensure that the oxygen concentration is ≤3%.

[0015] In some implementations, the temperature is kept ≤30℃ during the low-temperature pulverization process described in step (4), and the fineness of the millet flour is 60~100 mesh.

[0016] In some implementations, the preparation method of the millet slurry in step (1) is as follows: (A) Soaking the rice: After removing impurities, soak the millet in clean water for 2-4 hours at a water temperature of 20-35℃ to allow the rice grains to fully absorb water and soften, thereby improving the uniformity of grinding and enzymatic hydrolysis.

[0017] (B) Milling: After soaking, the millet is wet-milled using a colloid mill. The amount of water added is adjusted, and the milling fineness is 60~110 mesh to obtain millet pulp with a solid content of 20~30%.

[0018] In some implementations, step (4) further includes fluidized bed cooling, wherein the millet flour after low-temperature pulverization is immediately cooled to ≤25°C in a fluidized bed with an ambient humidity of ≤45%.

[0019] In some implementation schemes, the material transport from enzymatic hydrolysis to mixing with flavor-regulating microcapsules is carried out in a relatively closed or continuously nitrogen-filled environment to prevent oxidation and moisture absorption in the intermediate stages.

[0020] Secondly, this application also provides a millet flour prepared by the above method, wherein the millet flour has a peroxide value ≤0.07 g / 100g, an acid value (KOH) ≤2.8 mg / g, and a sensory score ≥8.5 points.

[0021] Thirdly, this application also provides the application of millet flour prepared by the above method in the field of food processing.

[0022] In some implementations, a millet deep-processed product uses millet powder prepared using the method of this application as the main ingredient or auxiliary ingredient.

[0023] In some implementations, the millet deep-processed products include ready-to-eat millet flour, baking premix powder, and ready-to-eat cereal powder.

[0024] The tea polyphenols in this application possess both free radical scavenging and transition metal ion chelating abilities, exhibiting strong antioxidant capacity. They inhibit both aqueous protein and lipid oxidation, and also demonstrate clear inhibitory effects on common pathogenic and putrefactive bacteria such as Staphylococcus aureus, Listeria monocytogenes, and lactic acid bacteria. They are a rare dual-function component among natural antioxidants, offering both antioxidant and auxiliary antibacterial properties. The core active components of rosemary extract are caryopsisic acid, caryopsisol, and rosmarinic acid, belonging to the fat-soluble diterpenoid phenol class. These are among the most thermally stable natural antioxidants. They exhibit a dual function of highly efficient free radical scavenging and metal ion chelation. During heating, some caryopsisic acid can be converted to caryopsisol, retaining its antioxidant activity, thus demonstrating excellent long-term stability.

[0025] The millet flour production method disclosed in this application involves a process flow of slurry preparation (antioxidant compound), enzymatic hydrolysis (compound enzyme), drum drying (nitrogen protection), low-temperature pulverization, fluidized bed cooling, and flavor microcapsule mixing. Through the synergistic effect of "free radical blocking, Maillard precursor, anaerobic drying, and flavor stabilization", it achieves a lipid oxidation inhibition rate of ≥68% and imparts a roasted flavor in a targeted manner.

[0026] Beneficial effects: (1) The method for producing millet flour disclosed in this invention uses a composite antioxidant composition extracted from pure plants, combined with a nitrogen-protected drum drying process, which can effectively inhibit fat oxidation during the production process. The resulting millet flour has a peroxide value (POV) ≤ 0.07 g / 100g, which is ≥ 68% lower than that of the traditional process. The acid value (KOH) is ≤ 2.8 mg / g. After 12 months of accelerated storage test (38℃, 75% RH), the POV is still ≤ 0.12 g / 100g, the shelf life is significantly extended, and the oxidation induction period of 0~12 months is extended by more than 3 times. (2) The millet flour produced by the method of this invention actively regulates the flavor: enzymatic hydrolysis, drum drying and Maillard reaction generate natural roasted aroma compounds such as pyrazines and furanones. Combined with flavor microcapsules, the sensory score reaches 8.5~9.5 / 10 points, with no off-odor. (3) The production method of this invention is closely connected, suitable for continuous industrial production, the product has good resolubility, and a wide range of applications. Attached Figure Description

[0027] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a process flow diagram of an embodiment of this application; Figure 2 This is a layout diagram of the overall sealed protective cover, nitrogen purging nozzle, oxygen sensor, and closed-loop control circuit for a single-drum dryer.

[0028] In the diagram: 1. Overall sealed protective cover; 2. Feeding area nozzle; 3. First oxygen sensor; 4. Annular multi-point injection in the drying area; 5. Second oxygen sensor; 6. Nitrogen curtain in the discharge area; 7. Third oxygen sensor; 8. PID controller; 9. Airtight end cap. Detailed Implementation

[0029] To further understand the inventiveness and technical advancements of this invention, the invention will now be described in more detail with reference to the accompanying drawings and embodiments. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the components relevant to the invention.

[0030] This application provides a method for preparing millet flour using low-oxygen drum drying coupled with enzymatic hydrolysis, comprising the following steps: (1) Slurry preparation: Add the compound antioxidant composition and sodium citrate to the crushed millet slurry in sequence. The amount of the compound antioxidant composition added is 0.02%~0.12% of the dry weight of millet in the millet slurry, and the amount of sodium citrate added is 0.01%~0.08% of the dry weight of millet in the millet slurry. The compound antioxidant composition contains tea polyphenols and rosemary extract. After thorough mixing, reactant 1 is obtained. (2) Enzymatic hydrolysis: Add medium-temperature α-amylase, protease and cellulase to reactant 1, and enzymatically hydrolyze at 50~60℃ and pH 6.0~6.8 to obtain reactant 2; (3) Drum drying: Reactant 2 is dried in a drum under nitrogen protection. The surface temperature of the drum is 120~150℃, and nitrogen is introduced to keep the oxygen concentration in the drying zone ≤3%. (4) Grinding: Millet flour is obtained by grinding at low temperature.

[0031] In some embodiments, the mass ratio of tea polyphenols to rosemary extract is (1-3):1, the mass content of catechins in the tea polyphenols is ≥50%, and the mass content of sarsaparilla acid in the rosemary extract is ≥20%.

[0032] In some embodiments, the method further includes step (5) mixing: mixing the millet powder obtained after low-temperature pulverization with flavor-regulating microcapsules, wherein the core material of the flavor-regulating microcapsules contains millet flavor, γ-aminobutyric acid and natural vitamin E, and the amount added is 0.3%~1.2% of the mass of millet powder, and the sensory score of the mixed millet powder is ≥8.5 points.

[0033] In some embodiments, the method for producing millet powder in this application is as follows: Figure 1 As shown, the details are as follows: (1) Mixing the pulp (1.1) Soaking rice: Select high-quality millet (such as Qinzhou Yellow or Jingu No. 21), remove impurities and soak in clean water for 2-4 hours at a water temperature of 20-35℃ to allow the rice grains to fully absorb water and soften, thereby improving the uniformity of grinding and enzymatic hydrolysis.

[0034] (1.2) Grinding: After soaking, the millet is wet-ground using a colloid mill. The amount of water added is adjusted, and the fineness of the milling is 60-110 mesh to obtain millet pulp with a solid content of 20-30%.

[0035] (1.3) Slurry preparation: Adjust the slurry concentration to 15–28°Bx, add a composite antioxidant composition at a ratio of 0.02%–0.12% based on the dry weight of millet, and add sodium citrate at a ratio of 0.01%–0.08%; the composite antioxidant composition is prepared by mixing tea polyphenols and rosemary extract at a mass ratio of (1–3):1; mix evenly to chelate metal ions and scavenge free radicals. The catechin content in the tea polyphenols is ≥50%, and the carrageenan content in the rosemary extract is ≥20%; (2) Enzymatic hydrolysis: Based on the dry weight of millet, add medium-temperature α-amylase BAN480L (enzyme 480 KNU / g) to the slurry at a ratio of 0.01-0.06%, neutral protease (enzyme activity 50,000 U / g) at a ratio of 0.05-0.15%, and cellulase at a ratio of 0.02-0.1%. Maintain the pH at 6.0-6.8 using a citric acid / sodium citrate buffer system, and hydrolyze at 50-60℃ for 40-90 min. Enzymatic hydrolysis produces reducing sugars, short peptides, and amino acids, providing flavor precursors for the subsequent Maillard reaction and reducing the viscosity of the slurry. At the same time, it releases bound lipids, which facilitates the contact of subsequent antioxidants. (3) Drum drying (nitrogen protection): A single drum dryer is used, with the drum surface temperature controlled at 120-150℃, the rotation speed at 2-6 r / min, and the material film thickness at 0.2-0.5 mm. Nitrogen purging devices and oxygen concentration sensors are installed in the feeding zone, drying zone, and discharge port to maintain the oxygen volume concentration in the drying zone at ≤3% and dry to ≤5.0% moisture content. The nitrogen flow rate (10-50 L / min) is automatically adjusted according to the oxygen concentration, and airtight end caps are provided to prevent air backflow.

[0036] (4) Crushing (4.1) Crushing: The dried flakes are immediately transferred to a low-temperature crusher and crushed while maintaining a temperature of ≤30℃. They are then passed through a 60-100 mesh sieve to prevent the crushing process from generating heat and accelerating oxidation.

[0037] (4.2) Cooling: After crushing, the material enters the fluidized bed cooler and is cooled down to below 25°C by purified cold air at a temperature of ≤20°C. The relative humidity of the environment is ≤45%.

[0038] (5) Mixing: The cooled millet flour and flavor-regulating microcapsules are added to a V-type mixer at a mass ratio of 1:(0.3%~1.2%) and mixed evenly. After mixing, the mixture is packaged with nitrogen and the residual oxygen content of the package is ≤3%. The flavor microcapsules are prepared by using sodium octenyl succinate starch and maltodextrin (mass ratio 1:1.5) as wall materials and millet flavor, γ-aminobutyric acid and natural vitamin E (mass ratio 5:2:1) as core materials. The process is spray drying (inlet air temperature 180℃, outlet air temperature 85℃) and the encapsulation rate is ≥85%.

[0039] In some embodiments, the single-drum dryer is surrounded by an integrally sealed protective cover 1, as shown in the attached figure. Figure 2 As shown, the sealing protective cover is preferably made of 304 stainless steel, 2mm thick, and completely covers the outside of the roller body and the airtight end caps 9 at both ends. The protective cover maintains a slight positive pressure of 50-150Pa and is equipped with three nitrogen purging zones: the feeding zone nozzle 2 and the first oxygen sensor 3, the drying zone annular multi-point injection 4 and the second oxygen sensor 5 (main controller), and the discharge zone nitrogen curtain 6 and the third oxygen sensor 7. The nitrogen flow rate is automatically adjusted by the PID controller 8 according to the oxygen concentration in the drying zone, from 10 to 50 L / min, to ensure that the oxygen concentration is ≤3%.

[0040] The working principle of the PID controller 8 is as follows: (1) The O2 concentration in the set drying zone is ≤ 3%; (2) Use the first oxygen sensor 3, the second oxygen sensor 5, and the third oxygen sensor 7 to monitor the oxygen concentration in the feeding area, drying area, and discharge area in real time; transmit the monitoring data to the PID controller for data analysis: if the oxygen concentration is higher than the threshold, issue an instruction to the nitrogen output device in the corresponding area to increase the nitrogen flow rate; if the oxygen concentration is lower than the threshold, reduce the flow rate to save energy and reduce consumption.

[0041] In some embodiments, the sealing cover 1 is provided with a viewing window and an inspection door to facilitate inspection of the roller surface and material condition, maintenance of the scraper, and cleaning of the roller. The bottom of the sealing cover 1 is provided with a regulating valve and a micro-pressure transformer, which are connected to a PID controller 8. When the micro-pressure transmitter detects low pressure, the PID controller sends a command to the regulating valve to automatically replenish nitrogen, ensuring a tight seal.

[0042] In a preferred embodiment, the roller specifications are: Φ1250×4200 mm, and the protective cover dimensions are: width 1600×height 1800×length 4500 mm; the micro-positive pressure inside the protective cover is 50~150Pa, and it is equipped with a micro-pressure transmitter (PIC-103) and a nitrogen replenishment pipeline.

[0043] In a preferred embodiment, an oxygen concentration over-limit interlock is also provided: if the O2 concentration in the drying zone is >4%, an audible and visual alarm is triggered and the nitrogen flow rate is automatically increased; if the O2 concentration is >5%, the heating is stopped and purging is maintained; nitrogen main pipe under-pressure protection: if the pressure is <0.3MPa, an alarm is triggered and the backup gas source is switched.

[0044] The sealing protective cover and its intelligent control system of this application have obvious advantages: (1) significantly reduce nitrogen consumption and save 20% to 30% of nitrogen; (2) eliminate the interference of crosswinds on oxygen concentration; (3) isolate high-temperature rotating parts and improve personnel safety protection; (4) facilitate centralized collection of waste gas; (5) even if the airtight end cap 9 ages and leaks slightly, the secondary sealing of the protective cover can still maintain the inert atmosphere in the dry area.

[0045] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0046] Example 1 Take 5 kg of high-quality Qinshui yellow millet and soak it at 30℃ for 3 hours; grind it into a colloid mill to 80 mesh; adjust the slurry concentration to 26°Bx; based on the dry weight of the millet, add 0.08% of a compound antioxidant composition (0.053% tea polyphenols, 0.027% rosemary extract) and 0.05% sodium citrate, and mix well; add 0.03% α-amylase, 0.1% neutral protease, and 0.05% cellulase; add a citric acid / sodium citrate buffer system to adjust the pH of the liquid to 6.3; and enzymatically hydrolyze at 55℃. The reactants were dried in a drum at 135°C for 60 minutes under nitrogen protection (oxygen concentration measured at 2.1%). The moisture content was 4.8% after drying. The mixture was then pulverized at low temperature and passed through an 80-mesh sieve. It was immediately cooled in a fluidized bed to 22°C to obtain millet flour. Flavor microcapsules (prepared according to the method described in the specific implementation, with core materials of millet flavor, γ-aminobutyric acid, and natural vitamin E in a mass ratio of 5:2:1) were added at a ratio of 0.8% by weight of the millet flour and mixed for 20 minutes. The final product had a peroxide value of 0.04 g / 100 g, an acid value of 2.3 mg / g, and a sensory score of 9.2. It exhibited a rich roasted millet aroma and no oxidative odor.

[0047] In this embodiment, the catechin content in the tea polyphenols is 53%, and the carrageenan content in the rosemary extract is 22%. The wall material of the flavor microcapsules is a mixture of sodium octenyl succinate starch and maltodextrin in a mass ratio of 1:1.5, with an encapsulation rate of 88%.

[0048] Example 2 The difference from Example 1 is that flavor microcapsules were not incorporated; otherwise, it is the same as Example 1. The final product has a peroxide value of 0.05 g / 100 g, an acid value of 2.5 mg / g, a sensory score of 8.6, and no oxidative odor.

[0049] Example 3 Take 5 kg of high-quality Qinzhou yellow millet and soak it at 20℃ for 4 hours; grind it into a colloid mill to 60 mesh; adjust the slurry concentration to 28°Bx, and add 0.12% of a compound antioxidant composition (0.09% tea polyphenols, 0.03% rosemary extract) and 0.08% sodium citrate based on the dry weight of the millet, and mix evenly; add 0.06% α-amylase, 0.15% neutral protease, and 0.1% cellulase, and enzymatically hydrolyze at 60℃ for 40 min; dry in a drum at 150℃ and 6 r / min under nitrogen protection (actual oxygen concentration 2.3%), and the moisture content is 4.7% after completion; pulverize at low temperature to 60 mesh; cool in a fluidized bed to 22℃; finally, add flavor microcapsules made according to the method described in the specific embodiment at 0.3% of the weight of millet flour, with the core material being millet flavor, γ-aminobutyric acid, and natural vitamin E (mass ratio: 5:2:1), and mix for 20 min. The final product has a peroxide value of 0.04g / 100g, an acid value of 2.3mg / g, and a sensory score of 9.4. It exhibits a rich roasted millet aroma and has no oxidative off-odors.

[0050] In this embodiment, the catechin content in the tea polyphenols is 53%, and the carrageenan content in the rosemary extract is 22%. The wall material of the flavor microcapsules is a mixture of sodium octenyl succinate starch and maltodextrin in a mass ratio of 1:1.5, with an encapsulation rate of 88%.

[0051] Example 4 Take 5 kg of high-quality Qinzhou yellow millet and soak it at 35℃ for 2 hours; grind it into a colloid mill to 100 mesh; adjust the slurry concentration to 15°Bx, and add 0.02% of a compound antioxidant composition (0.01% tea polyphenols, 0.01% rosemary extract) and 0.01% sodium citrate based on the dry weight of the millet, and mix evenly; add 0.01% α-amylase, 0.05% neutral protease, and 0.02% cellulase, and enzymatically hydrolyze at 50℃ for 90 min; dry in a drum at 120℃ and 2 r / min under nitrogen protection (actual oxygen concentration 2.7%), and the moisture content is 4.8% after completion; pulverize at low temperature to 100 mesh; cool in a fluidized bed to 22℃ to obtain millet flour; add flavor microcapsules (made according to the method described in the specific embodiment, the core material is millet flavor, γ-aminobutyric acid, and natural vitamin E, with a mass ratio of 5:2:1) at a ratio of 1.2% of the millet flour and mix for 20 min. The final product has a peroxide value of 0.07g / 100g, an acid value of 2.8mg / g, and a sensory score of 8.8. It exhibits a rich roasted millet aroma and has no oxidative off-odors.

[0052] In this embodiment, the catechin content in the tea polyphenols is 53%, and the carrageenan content in the rosemary extract is 22%. The wall material of the flavor microcapsules is a mixture of sodium octenyl succinate starch and maltodextrin in a mass ratio of 1:1.5, with an encapsulation rate of 88%.

[0053] Example 5 The composite antioxidant composition was added to the slurry at a ratio of 0.05% of the dry weight of millet. The enzymatic hydrolysis time was 50 min, the drum temperature was 130℃, the rotation speed was 6 r / min, and the nitrogen protection oxygen concentration was 2.8%. Other conditions were the same as in Example 1. The resulting millet flour had a peroxide value of 0.06 g / 100 g, an acid value of 2.7 mg / g, and a sensory score of 8.9, indicating excellent oxidation inhibition.

[0054] Example 6 Nitrogen protection was applied, and the measured oxygen concentration was 1.2%, with the rest consistent with Example 1.

[0055] Example 7 Nitrogen protection was applied, and the measured oxygen concentration was 2.8%, with the rest consistent with Example 1.

[0056] Example 8 Nitrogen protection was applied, and the measured oxygen concentration was 3%, with the rest consistent with Example 1.

[0057] Example 9 Nitrogen protection was applied, and the measured oxygen concentration was 5%, with the rest consistent with Example 1.

[0058] Example 10 (Industrial Scale-up Verification) Using a feed rate of 200 kg, the pilot-scale process was carried out in complete accordance with the parameters of Example 1. Three batches were produced in succession, with an average POV of 0.054±0.008 g / 100 g and an acid value of 2.6±0.2 mg / g, indicating that the process has excellent reproducibility.

[0059] Comparative Example 1 (No antioxidants / No enzymatic hydrolysis / No nitrogen) No antioxidants were added, no enzymatic hydrolysis was performed, and the millet flour was dried in a drum without nitrogen protection at a temperature of 150°C. All other parameters were the same as in Example 1. The resulting millet flour had a peroxide value of 0.29 g / 100 g, an acid value of 6.8 mg / g, a noticeable rancid odor, and a sensory score of 5.1.

[0060] Comparative Example 2 (without enzymatic digestion only) The remaining conditions were the same as in Example 1, but the enzymatic hydrolysis step was omitted. The peroxide value was 0.09 g / 100 g, the acid value was 3.2 mg / g, the flavor was bland and lacked roasted aroma, and the sensory score was 7.0. This indicates that enzymatic hydrolysis significantly enhanced the Maillard reaction precursor and improved the mouthfeel.

[0061] Comparative Example 3 (without nitrogen protection only) The rest was the same as in Example 1, except that the drum dryer was not purged with nitrogen (oxygen concentration 21%). The peroxide value was 0.14 g / 100 g, the acid value was 3.9 mg / g, a slight oxidized odor was observed, and the sensory score was 7.5. This verifies the indispensability of nitrogen protection.

[0062] The millet powder obtained in Example 1 was subjected to an accelerated storage stability test.

[0063] Experimental conditions: The millet flour was stored at 38℃ and 75% humidity for 12 months. POV value, acid value, and flavor sensory score were tested every three months. Specific data are detailed in Table 1. It can be seen that the millet flour prepared in Example 1 of this application still has a POV ≤0.12 g / 100g after 12 months of accelerated storage, and also exhibits good acid value and flavor sensory score. The shelf life is significantly extended, and the oxidation induction period from 0 to 12 months is extended by more than 3 times.

[0064] Samples from Comparative Example 1 and Example 1 were stored at room temperature (25°C) and 38°C with 75% relative humidity, respectively, and the peroxide value (POV) was measured periodically. The results showed that the shelf life of Comparative Example 1 at room temperature was approximately 2-3 months (with a POV of 0.12 g / 100g as the deterioration endpoint); after 12 months of accelerated storage at 38°C and 75% RH, the POV of Example 1 was still ≤0.12 g / 100g, and the deterioration endpoint was not reached, indicating that Example 1 remained stable under accelerated conditions.

[0065] The rate constant of lipid oxidation conforms to the Arrhenius equation k = A・exp (−Ea / RT) with temperature, and the shelf life is approximately inversely proportional to the rate constant. Taking the typical activation energy of lipid oxidation, Ea, as 60~80 kJ / mol, the acceleration factor at 38℃ relative to 25℃ is approximately 2.7~3.9, meaning that one month of storage at 38℃ is roughly equivalent to 2.7~3.9 months of storage at 25℃. Extrapolating from this, the shelf life of Example 1 at room temperature is approximately 33~46 months, more than 10 times longer than that of Comparative Example 1 (2~3 months at room temperature); and the oxidation induction period of Example 1 is approximately 3~5 times longer than that of Comparative Example 1. In summary, the shelf life of Example 1 at room temperature is ≥3 times longer than that of Comparative Example 1, demonstrating a significant improvement in antioxidant stability.

[0066] Comparing Comparative Example 1 with Example 1, the POV of the millet flour obtained in Comparative Example 1 was 0.29 g / 100 g, while the POV of the millet flour obtained in Example 1 was 0.04 g / 100 g. The lipid oxidation inhibition rate was calculated to be (0.29 - 0.04) / 0.29 × 100% ≈ 86.2%. Therefore, compared with the traditional process, the lipid oxidation inhibition rate of the millet flour prepared in this application is ≥68%.

[0067] Table 1: Accelerated Storage Stability

[0068] Examples 6-9 are comparative verifications of different oxygen concentrations during drum drying, and the specific data are detailed in Table 2. It can be seen that the oxygen concentration during drum drying has a significant impact on the POV value, acid value, and roasted flavor intensity of millet flour; the lower the oxygen concentration, the better the antioxidant performance.

[0069] Test conditions: drum temperature 135℃, rotation speed 5r / min, other parameters same as in Example 1; POV determined according to GB 5009.227, acid value determined according to GB 5009.229, and roasted flavor intensity evaluated by a 10-person professional panel (1-10 points, 10 points being the highest). Table 2: Effect of different nitrogen protective oxygen concentrations on peroxide value

[0070] 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 method for preparing millet flour using low-oxygen drum drying coupled with enzymatic hydrolysis, characterized in that, Includes the following steps: (1) Slurry preparation: Add a compound antioxidant composition and sodium citrate to the crushed millet slurry in sequence. The compound antioxidant composition contains tea polyphenols and rosemary extract. The amount of the compound antioxidant composition added is 0.02%~0.12% of the dry weight of millet in the millet slurry. The amount of sodium citrate added is 0.01%~0.08% of the dry weight of millet in the millet slurry. After thorough mixing, reactant 1 is obtained. (2) Enzymatic hydrolysis: Add medium-temperature α-amylase, neutral protease and cellulase to reactant 1, adjust the pH to 6.0-6.8 with citric acid-sodium citrate system, and enzymatically hydrolyze for 40-90 min at 50-60℃ to obtain reactant 2; (3) Drum drying: Reactant 2 is dried in a drum under nitrogen protection. The surface temperature of the drum is 120~150℃, and nitrogen is introduced to keep the oxygen concentration in the drying zone ≤3% until the moisture content is ≤5.0%. (4) Grinding: Millet flour is obtained by grinding at low temperature.

2. The method for preparing millet flour by low-oxygen drum drying coupled with enzymatic hydrolysis according to claim 1, characterized in that, The mass ratio of tea polyphenols to rosemary extract is (1~3):1, the mass content of catechins in the tea polyphenols is ≥50%, and the mass content of carrageenan in the rosemary extract is ≥20%.

3. The method for preparing millet flour by oxygen drum drying coupled with enzymatic hydrolysis according to claim 1, characterized in that, It also includes step (5) mixing: mixing the millet powder obtained in step (4) with flavor-regulating microcapsules, wherein the core material of the flavor-regulating microcapsules contains millet flavor, γ-aminobutyric acid and natural vitamin E, and the amount added is 0.3% to 1.2% of the mass of millet powder.

4. The method for preparing millet flour by low-oxygen drum drying coupled with enzymatic hydrolysis according to claim 3, characterized in that, The wall material of the flavor microcapsules is sodium octenyl succinate starch and maltodextrin, and the microcapsule encapsulation rate is ≥85%.

5. The method for preparing millet flour by low-oxygen drum drying coupled with enzymatic hydrolysis according to claim 1, characterized in that, The amount of the mesophilic α-amylase added is 0.01~0.06% of the dry weight of millet in the millet slurry, the amount of the neutral protease added is 0.05~0.15% of the dry weight of millet in the millet slurry, and the amount of the cellulase added is 0.02~0.1% of the dry weight of millet in the millet slurry.

6. The method for preparing millet flour by low-oxygen drum drying coupled with enzymatic hydrolysis according to claim 1, characterized in that, The drum dryer is equipped with nitrogen purging devices in the feeding zone, drying zone, and discharge port to maintain the oxygen concentration in the feeding zone, drying zone, and discharge port at ≤3%.

7. The method for preparing millet flour by low-oxygen drum drying coupled with enzymatic hydrolysis according to claim 1, characterized in that, The concentration of the millet slurry in step (1) is 15~28°Bx, wherein the fineness of the millet is 60~110 mesh.

8. The method for preparing millet flour by low-oxygen drum drying coupled with enzymatic hydrolysis according to claim 1, characterized in that, In step (4), the temperature is kept ≤30℃ during the low-temperature pulverization process, and the fineness of the millet powder is 60~100 mesh.

9. A type of millet flour, characterized in that, It is produced by the method described in any one of claims 1-8.

10. An application of millet flour as described in claim 9 in the food processing field.

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