Chufa-cottonseed probiotic compound nutritional powder and preparation method thereof

Abstract

The present application belongs to the technical field of functional solid food and coarse grain deep processing, and discloses a kind of chufa flaxseed prebiotic compound nutrition powder and preparation method thereof, including low-temperature supermicro chufa powder, low-temperature curing flaxseed powder, soybean lecithin and fructo-oligosaccharide, first chufa low-temperature drying and grading are made into coated chufa micro powder and main chufa micro powder, then flaxseed is sequentially subjected to controlled humidification activation, negative pressure decyanation, radio frequency assisted short curing, low-temperature vacuum drying and nitrogen protection crushing, low-temperature dry coating is carried out on flaxseed powder using coated chufa micro powder and soybean lecithin, then prebiotic dispersion premix powder is added for nitrogen airtight gradient mixing and pulse vacuum nitrogen filling packaging, the present application can reduce cyanogenic glycoside and oxidase activity, reduce unsaturated lipid oxidation, improve bitterness, grassiness, mixing uniformity, brewing dispersibility and storage stability.

Description

Technical Field

[0001] This invention belongs to the field of functional solid food and deep processing technology of grains, and particularly relates to a compound nutritional powder of tiger nuts and flax seeds with prebiotics and its preparation method. Background Technology

[0002] Tiger nuts contain oleic acid, phytosterols, dietary fiber, and plant protein, and have a nutty aroma and a mild taste. Flaxseed contains alpha-linolenic acid, lignans, plant protein, and dietary fiber. Making a compound nutritional powder from these two raw materials can achieve complementarity in lipid composition, dietary fiber, and plant active ingredients. Therefore, it is necessary to establish a compound processing method that takes into account the safe handling of flaxseed, the preservation of heat-sensitive nutrients, flavor improvement, powder dispersion, and storage stability.

[0003] Problems existing in the current technology: (1) Flaxseed contains cyanogenic glycosides, and endogenous lipases and lipoxygenases can promote the oxidation of unsaturated lipids. Conventional roasting mainly relies on long-term high-temperature treatment to achieve detoxification and enzyme inactivation, which can easily cause α-linolenic acid oxidation and lignan loss. Low-temperature treatment is difficult to simultaneously reduce cyanogenic glycosides and inactivate oxidases, making it difficult to balance safe flaxseed treatment, oxidation control and heat-sensitive nutrient retention.

[0004] (2) Existing compound grain powders usually put tiger nut powder, flaxseed powder and low amount of auxiliary materials into the mixing equipment at one time. They lack the surface coating structure of flaxseed particles and the gradient compounding process of powders with different particle sizes. Flaxseed unsaturated lipids will still come into direct contact with oxygen and are prone to bitter taste, grassy taste, component segregation, local clumping, reconstitution and spoilage. It is difficult to improve palatability, mixing uniformity and shelf stability at the same time. Summary of the Invention

[0005] To address the problems of flaxseed powder having a distinct bitter and grassy taste, residual cyanogenic glycosides, easy oxidation of unsaturated fatty acids caused by endogenous lipases and lipoxygenases, loss of α-linolenic acid and lignans due to conventional high-temperature cooking, and powder segregation, oxidation rancidity, separation during reconstitution, and clumping during storage when tiger nut powder and flaxseed powder are directly mixed, this invention provides a tiger nut and flaxseed prebiotic compound nutritional powder and its preparation method.

[0006] This invention first provides a compound nutritional powder of tiger nuts and flax seeds with prebiotics, which is made from the following raw materials in parts by weight: 55-70 parts of low-temperature ultrafine tiger nut powder, 30-45 parts of low-temperature cooked flaxseed powder, 0.1-0.3 parts of soybean lecithin and 0.5-1.5 parts of fructooligosaccharides.

[0007] This invention utilizes the starch, dietary fiber, plant protein, and oleic acid-rich lipid components in tiger nut powder to complement the α-linolenic acid, lignans, plant protein, and dietary fiber in flaxseed powder, and utilizes the nutty aroma and mild taste of tiger nut to reduce the bitterness and grassy taste of flaxseed powder.

[0008] In some implementations, the low-temperature ultrafine tiger nut powder includes coated tiger nut powder and main tiger nut powder. The median particle size of the coated tiger nut powder is 18-28 μm, and the median particle size of the main tiger nut powder is 50-75 μm. The coated tiger nut powder accounts for 10%-18% of the total mass of the low-temperature ultrafine tiger nut powder.

[0009] In some implementations, the median particle size of the low-temperature cooked flaxseed powder is 75–110 μm, and the ratio of the median particle size of the coated tiger nut powder to the median particle size of the low-temperature cooked flaxseed powder is 0.18–0.35, so that the coated tiger nut powder can adhere to the outer surface of the low-temperature cooked flaxseed powder particles.

[0010] In some implementations, coated tiger nut powder and soybean lecithin form lecithin tiger nut coated powder. The lecithin tiger nut coated powder is then coated onto the outer surface of low-temperature cooked flaxseed powder particles using a low-temperature dry coating method, forming tiger nut coated flaxseed composite particles.

[0011] In some implementation schemes, the tiger nut coating coverage of the flaxseed composite particles is not less than 85%. The coated tiger nut micro powder forms a physical isolation structure on the outer surface of the flaxseed powder particles, reducing the contact area between the unsaturated lipids of flaxseed and oxygen, and improving the wetting and dispersing properties of the composite particles by utilizing the interfacial structure formed by tiger nut powder and soybean lecithin.

[0012] In some implementations, low-temperature matured flaxseed powder is obtained by sequentially undergoing controlled humidification activation, negative pressure decyanation, radio frequency assisted short-time maturation, low-temperature vacuum drying, and nitrogen-protected pulverization.

[0013] In some implementation schemes, the moisture content of flaxseed after controlled humidification is 14%–17%, and the humidified flaxseed is activated in a nitrogen atmosphere at 44–48°C for 25–40 min, using appropriate amounts of moisture and temperature to promote the controlled conversion of cyanogenic glycosides in flaxseed tissue.

[0014] In some implementation schemes, the activated flaxseed is subjected to negative pressure decyanation under an absolute pressure of 18–28 kPa and a temperature of 58–65°C, while nitrogen gas is introduced at a flow rate of 0.3–0.6 L / min per kilogram of flaxseed for a treatment time of 15–25 min, so that the volatile cyanide-containing components generated during the conversion are discharged with the negative pressure airflow.

[0015] In some implementations, the flaxseeds after negative pressure decyanation are subjected to short-term ripening using a radio frequency device with a frequency of 27.12MHz, so that the core temperature of the flaxseeds reaches 78-82°C and is maintained for 90-150s. The radio frequency volume heating rapidly reduces the activity of lipase and lipoxygenase, while shortening the time that α-linolenic acid is in a high-temperature environment.

[0016] In some implementations, the flaxseeds that have undergone radio frequency-assisted short-term ripening are vacuum dried at a temperature of 42–48°C and an absolute pressure of 20–30 kPa until the moisture content is no more than 5%, and then pulverized under nitrogen protection to obtain low-temperature ripened flaxseed powder.

[0017] In some implementation schemes, the preparation process of low-temperature ultrafine tiger nut powder includes tiger nut cleaning, low-temperature drying, nitrogen-protected pulverization and dual-scale classification. The low-temperature drying temperature is 40-45°C, and the moisture content of the dried tiger nut is 6%-6.5%.

[0018] In some implementation schemes, soybean lecithin is first premixed with coated tiger nut powder to obtain lecithin tiger nut coated powder. Then, the lecithin tiger nut coated powder is added to low-temperature cooked flaxseed powder for low-temperature dry coating. The coating speed is 500-750 r / min, the coating time is 8-12 min, and the powder temperature is below 40℃ during the coating process.

[0019] In some implementation schemes, fructooligosaccharides are first mixed with 8% to 12% of the total mass of the main tiger nut powder to form a prebiotic dispersion premix. Then, the prebiotic dispersion premix, tiger nut-coated flaxseed composite particles, and the remaining main tiger nut powder are mixed in a gradient.

[0020] In some implementations, gradient mixing is carried out in a nitrogen-sealed environment, with the oxygen volume fraction in the mixing equipment being less than 1%, and the powder temperature being less than 40°C during the mixing process. This reduces the local enrichment of fructooligosaccharides and soybean lecithin by premixing with low amounts of components and gradually increasing the mixing quality.

[0021] In some implementation schemes, the coefficient of variation of the fructooligosaccharide content in the gradient-mixed compound nutritional powder is no higher than 3%, so that fructooligosaccharides, soybean lecithin, tiger nut powder and flaxseed powder are uniformly distributed at different sampling locations.

[0022] In some implementations, the mixed compound nutritional powder is packaged using a pulsed vacuum nitrogen filling method after being sieved through a 100-mesh screen and inspected for foreign matter, with the residual oxygen volume fraction inside the packaging being less than 1%.

[0023] In some implementations, the tiger nut and flaxseed prebiotic compound nutritional powder is made from 65 parts of low-temperature ultrafine tiger nut powder, 35 parts of low-temperature cooked flaxseed powder, 0.2 parts of soybean lecithin, and 1.0 part of fructooligosaccharides.

[0024] Furthermore, this invention provides a method for preparing a compound nutritional powder of tiger nuts and flax seeds with prebiotics, comprising the following steps: Step S1: Clean and wash the tiger nuts, and dry them at a low temperature of 40-45℃ until the moisture content is 6%-6.5%.

[0025] In step S2, the tiger nuts dried at low temperature are subjected to two-stage pulverization and particle size classification under nitrogen protection to obtain coated tiger nut micro powder with a median particle size of 18-28 μm and bulk tiger nut micro powder with a median particle size of 50-75 μm.

[0026] Step S3 involves cleaning and humidifying the flaxseeds to achieve a moisture content of 14%–17%, followed by activation at 44–48°C for 25–40 minutes in a nitrogen atmosphere.

[0027] Step S4: Place the activated flaxseed in a negative pressure treatment device with an absolute pressure of 18-28 kPa and a temperature of 58-65°C, and simultaneously introduce nitrogen gas at a flow rate of 0.3-0.6 L / min per kilogram of flaxseed for negative pressure decyanation treatment for 15-25 minutes.

[0028] Step S5: The flax seeds after negative pressure decyanation are sent into a radio frequency device with a frequency of 27.12MHz for short-term ripening, so that the core temperature of the flax seeds reaches 78-82℃ and is maintained for 90-150s.

[0029] Step S6: The flaxseeds that have been short-term matured are vacuum dried at a temperature of 42-48℃ and an absolute pressure of 20-30kPa until the moisture content is no more than 5%, and then pulverized under nitrogen protection until the median particle size is 75-110μm to obtain low-temperature matured flaxseed powder.

[0030] Step S7: Add soybean lecithin to coated tiger nut powder for premixing to obtain lecithin-coated tiger nut powder.

[0031] Step S8: Add the lecithin tiger nut coating powder to the low-temperature cooked flaxseed powder, and perform low-temperature dry coating at 500-750 r / min for 8-12 minutes under nitrogen-sealed conditions to make the powder temperature below 40℃, thereby obtaining tiger nut coated flaxseed composite particles.

[0032] Step S9: Mix fructooligosaccharides with 8% to 12% of the total mass of the main-grade tiger nut powder to obtain a prebiotic dispersion premix powder.

[0033] Step S10: The tiger nuts coated with flaxseed composite particles, prebiotic dispersion premix powder and the remaining main tiger nut micro powder are sequentially added to a closed mixing device and gradient mixed in a nitrogen environment with an oxygen volume fraction of less than 1%. The powder temperature is below 40°C during the mixing process.

[0034] Step S11: Samples are taken from different locations of the mixing equipment to detect the content of fructooligosaccharides. When the coefficient of variation of the fructooligosaccharide content is not higher than 3%, the mixing is stopped to obtain compound nutritional powder.

[0035] Step S12: The compound nutritional powder is sieved through a 100-mesh sieve, and foreign matter mixed in during the production process is removed by magnetic separation and foreign matter detection.

[0036] Step S13: The sieved compound nutritional powder is sealed and packaged using a pulsed vacuum nitrogen filling method to ensure that the residual oxygen volume fraction inside the package is less than 1%, thus obtaining tiger nut and flaxseed prebiotic compound nutritional powder.

[0037] The beneficial effects of this invention are as follows: (1) By controlling the activation of humidification and the removal of volatile cyanide components from flaxseed through negative pressure nitrogen decyanation, the controlled conversion of cyanogenic glycosides in flaxseed is promoted. Then, radio frequency volume heating is used to perform short-term ripening of flaxseed. This reduces the activity of lipase and lipoxygenase while shortening the heating time of α-linolenic acid and lignans, thus solving the problem that conventional high-temperature roasting cannot simultaneously ensure the safe treatment of flaxseed, enzyme inactivation and heat-sensitive nutrient retention.

[0038] (2) By dividing the low-temperature ultrafine tiger nut powder into coated tiger nut powder and main tiger nut powder, the small-particle-size coated tiger nut powder and soybean lecithin form an adhesion layer on the outer surface of flaxseed powder particles, reducing the direct contact between unsaturated lipids and oxygen in flaxseed, and using the nutty aroma of tiger nut to reduce the bitterness and grassy taste of flaxseed, the problem of the two raw materials being unable to effectively inhibit flaxseed oxidation and undesirable flavor when directly mixed is solved.

[0039] (3) By premixing prebiotic dispersion, nitrogen-sealed gradient mixing and pulsed vacuum nitrogen-filled packaging, low-dosage fructooligosaccharides and soybean lecithin are evenly dispersed, and oxygen exposure during powder mixing and storage is reduced, thereby simultaneously improving the mixing uniformity, reconstitution dispersion and storage stability of compound nutrient powder, and solving the problems of local enrichment, powder segregation and storage oxidation that easily occur when mixing powders of multiple particle sizes and densities at one time. Attached Figure Description

[0040] The accompanying drawings are provided to further understand the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the invention and do not constitute a limitation thereof.

[0041] Figure 1This is a flowchart illustrating the preparation process of the tiger nut and flaxseed prebiotic compound nutritional powder of the present invention. Figure 2 This is a schematic diagram illustrating the formation process and structure of the tiger nut-coated flaxseed composite particles of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0043] In the embodiments provided in this specification, operations not specified with particular technical conditions are carried out in accordance with conventional technical conditions in the food processing field, and raw materials and equipment not specified with manufacturers are all food-grade raw materials and conventional equipment purchased through formal channels.

[0044] The tiger nuts used in the following examples are mature, plump, mold-free, and insect-free dried tiger nuts. The moisture content of the tiger nuts is not higher than 10%, the acid value is not higher than 2 mg / g, and the peroxide value is not higher than 5 mmol / kg.

[0045] The flaxseeds used in the following examples are mature, plump, mold-free, and odorless food processing flaxseeds. The proportion of linolenic acid in the total fatty acids of flaxseeds is not less than 48%, and the moisture content of the flaxseed raw materials is not higher than 9%. Before entering the compounding process, the flaxseeds undergo controlled humidification activation, negative pressure decyanation, radio frequency assisted short-time ripening, low-temperature vacuum drying, and nitrogen low-temperature pulverization.

[0046] The soybean lecithin in the following examples is food-grade soybean lecithin in powder form, with a phospholipid mass fraction of not less than 95%; the fructooligosaccharide is food-grade fructooligosaccharide powder, with a fructooligosaccharide mass fraction of not less than 95%; and the nitrogen used in production is food-grade nitrogen with a purity of not less than 99.99%.

[0047] In the following examples, tiger nuts, flaxseed, soybean lecithin, and fructooligosaccharides were all processed on a production line isolated from gluten-containing raw materials. The production equipment underwent cleaning and allergen cross-contact checks before feeding materials, and the gluten content of the finished product was controlled below 20 mg / kg.

[0048] The present invention provides a compound nutritional powder of tiger nut and flaxseed prebiotics, comprising 55-70 parts by weight of low-temperature ultrafine tiger nut powder, 30-45 parts by weight of low-temperature cooked flaxseed powder, 0.1-0.3 parts by weight of soybean lecithin and 0.5-1.5 parts by weight of fructooligosaccharides.

[0049] Low-temperature ultrafine tiger nut powder is obtained by low-temperature drying of tiger nut and low-temperature classification and pulverization under nitrogen. Low-temperature ultrafine tiger nut powder includes coated tiger nut powder and main tiger nut powder. The median particle size of the coated tiger nut powder is smaller than that of the low-temperature cooked flaxseed powder, while the median particle size of the main tiger nut powder is close to that of the low-temperature cooked flaxseed powder.

[0050] Tiger nut powder, soybean lecithin, and low-temperature cooked flaxseed powder are coated in a nitrogen environment using a low-temperature dry coating process. This allows the coated tiger nut powder to form on the outside of the low-temperature cooked flaxseed powder particles with the help of soybean lecithin, resulting in tiger nut coated flaxseed composite particles. Then, fructooligosaccharides are premixed with a portion of the main tiger nut powder in a gradient to obtain a prebiotic dispersion premix powder.

[0051] The tiger nuts coated flaxseed compound particles, prebiotic dispersed premix powder, and the remaining main tiger nut micro powder are sequentially mixed in a nitrogen-sealed gradient. This allows the easily oxidized flaxseed powder particles to form an external physical barrier layer with the smaller tiger nut micro powder. At the same time, the nutty aroma of tiger nuts is used to reduce the concentrated release of the grassy and bitter taste of flaxseed.

[0052] The low-temperature cooked flaxseed powder used in this embodiment is not obtained by high-temperature long-term roasting. Instead, controlled humidification is first used to allow limited contact between the endogenous β-glucosidase and cyanogenic glycosides in flaxseed. Then, negative pressure and nitrogen sweeping are used to remove the volatile cyanogenic components formed. Subsequently, radio frequency-assisted short-time cooking is used to inactivate flaxseed lipase and lipoxygenase, thereby achieving the simultaneous reduction of cyanogenic glycosides, inactivation of oxidases, and retention of linolenic acid.

[0053] To evaluate the effects of controlled humidification activation and negative pressure decyanation on flaxseed, the reduction rate of cyanogenic glycosides was introduced and calculated according to Formula 1.

[0054] Formula 1:

[0055] In Formula 1, The rate of reduction of cyanogenic glycosides; To determine the cyanogenic glycoside content in flaxseed raw materials before treatment; The content of cyanogenic glycosides in flaxseed after negative pressure decyanation and short-term maturation.

[0056] This implementation method reduces the cyanogenic glycoside rate. The cyanide content is controlled to be no less than 80%, and the cyanide residue in the treated flaxseed powder is tested to ensure that the cyanide residue meets the safety requirements for the corresponding food raw materials.

[0057] In order to ensure that the coated tiger nut powder can be distributed on the outside of the low-temperature cooked flaxseed powder particles, a particle size matching coefficient is introduced and calculated according to Formula 2.

[0058] Formula 2:

[0059] In Formula 2, This refers to the particle size matching coefficient. The median particle size of the coated tiger nut powder; The median particle size of the low-temperature cooked flaxseed powder is given.

[0060] This embodiment uses the particle size matching coefficient The particle size distribution should be controlled between 0.18 and 0.35. When the particle size distribution coefficient is below 0.18, the coated tiger nut powder is too fine and easily forms dust agglomerates. When the particle size distribution coefficient is above 0.35, the coated tiger nut powder is difficult to form a continuous distribution on the outside of the low-temperature cooked flaxseed powder particles.

[0061] To evaluate the coating degree of the low-temperature cooked flaxseed powder particles, the exposed area of ​​flaxseed before and after coating was obtained by microscopic images and segmentation of the characteristic spectral regions of flaxseed, and the coating coverage rate of tiger nuts was calculated according to Formula 3.

[0062] Formula 3:

[0063] In Formula 3, The coverage rate of tiger nuts; The exposed area of ​​flaxseed powder particles in the detection area before low-temperature dry coating; This represents the exposed area of ​​flaxseed powder particles in samples of the same mass after low-temperature dry coating.

[0064] This embodiment measures the coverage rate of the tiger nuts. The coverage rate should be controlled to be no less than 85%. When the coverage rate of tiger nuts is less than 85%, nitrogen protection should be maintained and an additional low-temperature dry coating process should be applied for 2 to 4 minutes.

[0065] To evaluate the spatial uniformity of low-temperature cooked flaxseed powder in the finished product, the flaxseed lignan content was used as a tracer index, and the coefficient of variation of compound uniformity was calculated according to Formula 4.

[0066] Formula 4:

[0067] In Formula 4, The coefficient of variation for blend uniformity; The standard deviation of linseed lignan content at multiple sampling locations; This represents the average linolean content of flaxseed from multiple sampling locations.

[0068] This implementation method will use the coefficient of variation of compound uniformity. The control value should not exceed 3%. When the coefficient of variation of the uniformity of the compound exceeds 3%, add low-speed mixing for 3 minutes in a nitrogen environment and retest.

[0069] The preparation method of the tiger nut and flaxseed prebiotic compound nutritional powder provided in this embodiment specifically includes the following steps.

[0070] Step S1, tiger nut cleaning and low-temperature drying: Take tiger nut raw materials, remove shriveled, broken, sand and magnetic impurities by air separation, vibration screening and magnetic separation, wash twice with running drinking water, drain the surface water and then carry out circulating dehumidification drying at 40℃~45℃ until the moisture content of tiger nut is reduced to 6.0%~6.5%.

[0071] Step S2, dual-scale low-temperature pulverization of tiger nuts: The dried tiger nuts are fed into a nitrogen-protected low-temperature pulverization device. The temperature of the pulverization chamber is controlled below 30°C. The pulverized tiger nut powder is classified by airflow to form coated tiger nut micro powder and main tiger nut micro powder. The median particle size of the coated tiger nut micro powder is 18μm~28μm, and the median particle size of the main tiger nut micro powder is 50μm~75μm. The coated tiger nut micro powder accounts for 10%~18% of the total mass of the low-temperature ultrafine tiger nut powder.

[0072] Step S3, Flaxseed Cleaning and Controlled Humidification Activation: Take flaxseed raw material, remove impurities by air separation, screening and magnetic separation, place the flaxseed in a sealed humidification drum, adjust the flaxseed moisture content to 14% to 17% by atomized purified water, and maintain it in a nitrogen environment and at 44℃ to 48℃ for 25 min to 40 min, so that the endogenous β-glucosidase in flaxseed can have limited contact with cyanogenic glycosides.

[0073] Step S4, negative pressure decyanation of flaxseed: The flaxseed that has completed controlled humidification and activation is fed into the negative pressure decyanation equipment. The absolute pressure of the equipment is controlled at 18 kPa to 28 kPa, and the material temperature is controlled at 58℃ to 65℃. At the same time, nitrogen gas is introduced at a flow rate of 0.3 L / min to 0.6 L / min per kilogram of flaxseed. The treatment lasts for 15 min to 25 min, so that the volatile cyanide-containing components formed by the hydrolysis of cyanogenic glycosides are discharged with water vapor and nitrogen gas.

[0074] Step S5, Radio Frequency Assisted Short-Time Curing: The flaxseeds after negative pressure decyanation are fed into a radio frequency curing device with a radio frequency of 27.12MHz and an electrode spacing of 100mm to 140mm. The core temperature of the flaxseeds is raised to 78℃ to 82℃ and maintained for 90s to 150s, so that the activities of flaxseed lipase and lipoxygenase are reduced to less than 10% of the pre-treatment levels. Subsequently, the temperature of the flaxseeds is reduced to below 30℃ in a nitrogen atmosphere.

[0075] Step S6, Low-temperature vacuum drying and pulverization of flaxseed: The mature flaxseed is dried under an absolute pressure of 20 kPa to 30 kPa and a temperature of 42°C to 48°C until the moisture content is no more than 5%. Then, it is pulverized at low temperature in a nitrogen environment. During the pulverization process, the material temperature is no more than 30°C, and low-temperature mature flaxseed powder with a median particle size of 75 μm to 110 μm is obtained.

[0076] Step S7, Particle size matching and soybean lecithin pre-dispersion: The median particle size of coated tiger nut powder and low-temperature cooked flaxseed powder was detected, and the particle size matching coefficient was calculated according to Formula 2. The airflow classification parameters were adjusted according to the particle size matching coefficient, and then the coated tiger nut powder and soybean lecithin were added to a nitrogen-sealed premixer and premixed at 20 r / min to 30 r / min for 5 min to 8 min to obtain lecithin-coated tiger nut powder.

[0077] Step S8, Low-temperature dry coating: Add the low-temperature matured flaxseed powder to the dry coating equipment, introduce nitrogen to reduce the oxygen volume fraction in the equipment to below 1%, then add lecithin tiger nut coating powder, and process at 500r / min~750r / min for 8min~12min. During the coating process, the powder temperature is controlled below 40℃ to obtain tiger nut coated flaxseed composite particles.

[0078] Step S9, Preparation of prebiotic dispersion premix: Take 8% to 12% of the total mass of the main tiger nut micro powder from the main tiger nut micro powder, add the separated main tiger nut micro powder and fructooligosaccharide to a three-dimensional premixer, and mix at 15 r / min to 25 r / min for 8 min to 10 min in a nitrogen environment to obtain prebiotic dispersion premix.

[0079] Step S10, nitrogen-sealed gradient mixing: Add the remaining main body tiger nut micro powder and tiger nut-coated flaxseed composite particles to a three-dimensional motion mixer and premix at 12r / min to 18r / min for 8 minutes. Then add the prebiotic dispersion premixed powder in two batches, mixing for 5 minutes after each batch is added. After all the powder is added, continue mixing for 10 minutes. The oxygen volume fraction in the mixing chamber is controlled to be below 1%, and the actual temperature of the powder is controlled to be below 40℃.

[0080] Step S11, Mixing uniformity detection and feedback adjustment: Select three sampling points from the upper, middle and lower parts of the three-dimensional motion mixer respectively, detect the linolean content of each sampling point, calculate the coefficient of variation of compound uniformity according to Formula 4, and when the coefficient of variation of compound uniformity is higher than 3%, add low-speed mixing for 3 minutes, and sample and test again.

[0081] Step S12, sieving and metal foreign object control: The compound nutrient powder with the required mixing uniformity is passed through a 100-mesh vibrating screen under the protection of a nitrogen hood to remove hygroscopic and agglomerated particles. Then, it is passed through a magnetic grid with a surface magnetic induction intensity of 8000Gs to 12000Gs and a metal detection device.

[0082] Step S13, pulse vacuum nitrogen-filled packaging: The compound nutritional powder is placed in a clean packaging environment with a temperature of 20℃~25℃ and a relative humidity of no more than 35%. It is packaged in aluminum foil composite barrier packaging bags. The pressure inside the packaging bag is reduced to the gauge pressure of -0.05MPa~-0.07MPa. Then, food-grade nitrogen is introduced to restore it to normal pressure. The vacuum and nitrogen filling process is repeated twice before heat sealing, so that the residual oxygen volume fraction inside the packaging is no more than 1%.

[0083] Step S14, Finished Product Testing and Storage: Test the finished product for moisture content, water activity, linolenic acid content, lignan content, cyanogenic glycoside reduction rate, tiger nut coating coverage, compound uniformity coefficient of variation, peroxide value, reconstitution dispersion rate, gluten content, and microbial indicators. Qualified products should be stored in a light-protected environment at a temperature not exceeding 25°C.

[0084] Example 1: This example provides a compound nutritional powder of tiger nuts and flax seeds with prebiotics, including 65kg of low-temperature ultrafine tiger nut powder, 35kg of low-temperature cooked flax seed powder, 0.2kg of soybean lecithin and 1kg of fructooligosaccharides.

[0085] In step S1, tiger nuts are dried at 43°C until the moisture content is 6.2%. In step S2, the dried tiger nuts are pulverized at low temperature and subjected to air classification to obtain coated tiger nut powder with a median particle size of 23 μm and main tiger nut powder with a median particle size of 62 μm. The coated tiger nut powder weighs 10 kg and the main tiger nut powder weighs 55 kg.

[0086] In step S3, the moisture content of flaxseed is adjusted to 15.5% and maintained at 46°C under nitrogen atmosphere for 32 minutes. In step S4, the absolute pressure of the negative pressure decyanation equipment is controlled at 22 kPa, the material temperature is controlled at 62°C, and the nitrogen flow rate is controlled at 0.45 L / min per kilogram of flaxseed for 20 minutes.

[0087] In step S5, the core temperature of flaxseed was raised to 80°C using 27.12MHz radio frequency and held for 120s. The activity of flaxseed lipase and lipoxygenase was detected to be reduced to 6.8% and 7.5% of the pre-treatment levels, respectively.

[0088] In step S6, the mature flaxseed is dried at 45°C and 25 kPa absolute pressure until the moisture content is 4.6%, and then pulverized in a nitrogen environment to obtain low-temperature mature flaxseed powder with a median particle size of 92 μm and a particle size matching coefficient λLambda_d of 0.25.

[0089] In step S7, 10 kg of coated tiger nuts powder and 0.2 kg of soybean lecithin are premixed in a nitrogen environment at 25 r / min for 6 min. In step S8, 35 kg of low-temperature cooked flaxseed powder is added and treated at 650 r / min for 10 min under an oxygen volume fraction of 0.7% to 0.9%, with the highest powder temperature being 37.6℃.

[0090] In this embodiment, the tiger nut coating coverage rate K_B of the tiger nut coated flaxseed composite particles is 90.8%. In step S9, 5.5 kg of tiger nut micro powder is separated from 55 kg of main-grade tiger nut powder and mixed with 1 kg of fructooligosaccharide to prepare prebiotic dispersion premix powder.

[0091] In step S10, the remaining 49.5 kg of tiger nut micro powder and tiger nut coated flaxseed compound particles are premixed for 8 minutes, and then prebiotic dispersion premixed powder is added in two batches to finally obtain tiger nut flaxseed prebiotic compound nutritional powder with a compound uniformity variation coefficient CV_L of 1.9%.

[0092] The compound nutritional powder prepared in this embodiment is light brown in color, with the aroma of tiger nuts and a slight roasted flaxseed aroma. It does not have a distinct bitter taste, grassy taste, or rancid oily taste, and the residual oxygen volume fraction in the packaging is 0.58%.

[0093] Example 2: This example provides a high tiger nut content tiger nut and flaxseed prebiotic compound nutritional powder, including 70kg of low-temperature ultrafine tiger nut powder, 30kg of low-temperature cooked flaxseed powder, 0.1kg of soybean lecithin and 0.5kg of fructooligosaccharides.

[0094] The preparation method of this embodiment is the same as that of Embodiment 1, except that the coated tiger nut powder accounts for 12% of the total mass of the low-temperature ultrafine tiger nut powder, the median particle size of the low-temperature cooked flaxseed powder is 98 μm, the particle size matching coefficient is 0.24, and the low-temperature dry coating time is 9 min.

[0095] In this embodiment, the amount of low-temperature ultrafine tiger nut powder added is increased, resulting in a more pronounced tiger nut aroma in the compound nutritional powder, further reducing the grassy and bitter taste of flaxseed, while maintaining the nutritional supplementation effect of linolenic acid and lignans from flaxseed.

[0096] Example 3: This example provides a high-flaxseed-content tiger nut and flaxseed prebiotic compound nutritional powder, including 55kg of low-temperature ultrafine tiger nut powder, 45kg of low-temperature cooked flaxseed powder, 0.3kg of soybean lecithin and 1.5kg of fructooligosaccharides.

[0097] The preparation method of this embodiment is the same as that of Embodiment 1. The difference is that the coated tiger nuts micro powder accounts for 18% of the total mass of the low-temperature ultrafine tiger nuts powder, the low-temperature dry coating time is 12 min, the rotation speed of the dry coating equipment is 700 r / min, and the tiger nut coating coverage rate is 91.6% after the low-temperature dry coating is completed.

[0098] In this embodiment, the amount of low-temperature cooked flaxseed powder added is increased, and the amount of coated tiger nut powder, soybean lecithin and fructooligosaccharides added are increased accordingly, so that a higher proportion of flaxseed powder can still maintain uniform dispersion and low surface exposure.

[0099] Example 4: This example provides a high-instance dispersible tiger nut and flaxseed prebiotic compound nutritional powder, including 60kg of low-temperature ultrafine tiger nut powder, 40kg of low-temperature cooked flaxseed powder, 0.3kg of soybean lecithin and 1.5kg of fructooligosaccharides.

[0100] The preparation method of this embodiment is the same as that of Embodiment 1, except that the median particle size of the main tiger nut micro powder is 55 μm. 12% of the main tiger nut micro powder is separated and mixed with fructooligosaccharides to make a prebiotic dispersion premix powder, and the final gradient mixing time is extended to 12 min.

[0101] This embodiment reduces the particle size of the main-grade tiger nut powder and increases the proportion of prebiotic dispersion premix powder, so that the powder is quickly wetted after contact with water, reducing the undispersed clumps formed by the local adhesion of oligofructose.

[0102] Example 5: This example provides a nut-flavor-enhanced tiger nut and flaxseed prebiotic compound nutritional powder, including 68kg of low-temperature ultrafine tiger nut powder, 32kg of low-temperature cooked flaxseed powder, 0.2kg of soybean lecithin and 1kg of fructooligosaccharides.

[0103] The preparation method of this embodiment is the same as that of Embodiment 1, except that the coated tiger nuts micro powder accounts for 15% of the total mass of the low-temperature ultrafine tiger nuts powder, the low-temperature dry coating time is 11 min, and the final tiger nut coating coverage rate is 92.3%.

[0104] This embodiment increases the coverage of tiger nut powder on the surface of flaxseed powder particles by increasing the proportion of coated tiger nut micro powder, so that the nutty aroma of tiger nut is released before the grassy aroma of flaxseed during the preparation process, and the resulting compound nutritional powder has a milder complex nutty aroma.

[0105] The raw material ratios and key structural parameters of each embodiment are shown in Table 1.

[0106] Table 1. Raw material ratios and key structural parameters for each embodiment:

[0107] Regarding the adjustment of parameters for controlled humidification and activation of flaxseed: The moisture content of flaxseed after humidification was controlled at 14%–17%, the activation temperature was controlled at 44℃–48℃, and the activation time was controlled at 25 min–40 min. When the moisture content was below 14%, the contact between the endogenous β-glucosidase and cyanogenic glycosides in flaxseed was insufficient. When the moisture content was above 17% and the activation time exceeded 40 min, the activity of flaxseed lipase was enhanced, increasing the risk of flaxseed oil oxidation.

[0108] Regarding the adjustment of parameters for negative pressure cyanide removal from flaxseed: The absolute pressure of the negative pressure cyanide removal equipment is controlled at 18 kPa to 28 kPa, the material temperature is controlled at 58℃ to 65℃, the processing time is controlled at 15 min to 25 min, and the nitrogen flow rate is controlled at 0.3 L / min to 0.6 L / min per kilogram of flaxseed. When the absolute pressure is higher than 28 kPa, the removal rate of volatile cyanide-containing components decreases, and when the material temperature is higher than 65℃, the oxidation rate of oil on the surface of flaxseed increases.

[0109] Regarding the adjustment of radio frequency assisted short-time curing parameters: The radio frequency is controlled at 27.12MHz, the core temperature of flaxseed is controlled at 78℃~82℃, and the holding time is controlled at 90s~150s. Radio frequency volume heating makes the internal and external parts of flaxseed heat up simultaneously and shortens the high temperature holding time. When the core temperature is below 78℃, the inactivation degree of lipase and lipoxygenase is insufficient. When the core temperature is above 82℃ and the holding time exceeds 150s, the loss of linolenic acid oxidation and the bitterness of roasting increase.

[0110] Regarding the adjustment of parameters for dual-scale tiger nut powder: The median particle size of the coated tiger nut powder is controlled at 18μm to 28μm, the median particle size of the main tiger nut powder is controlled at 50μm to 75μm, and the median particle size of the low-temperature cooked flaxseed powder is controlled at 75μm to 110μm. The particle size matching coefficient is controlled at 0.18 to 0.35. The smaller particle size of the coated tiger nut powder covers the larger particle size of the flaxseed powder particles, and the main tiger nut powder is used to maintain the overall flowability of the compound nutrient powder.

[0111] Regarding the adjustment of parameters for low-temperature dry coating: The oxygen volume fraction in the dry coating equipment is controlled to be below 1%, the equipment speed is controlled to be 500 r / min to 750 r / min, the processing time is controlled to be 8 min to 12 min, and the powder temperature is controlled to be below 40℃. When the equipment speed is below 500 r / min, the coated tiger nut micro powder is difficult to fully spread on the surface of flaxseed powder particles. When the equipment speed is above 750 r / min, the powder friction temperature increases and the degree of flaxseed particle breakage increases.

[0112] Regarding the adjustment of nitrogen closed gradient mixing parameters: The speed of the three-dimensional motion mixer is controlled at 12r / min to 18r / min, the oxygen volume fraction in the mixing chamber is controlled at less than 1%, the actual temperature of the powder is controlled at less than 40℃, the prebiotic dispersion premixed powder is added in two batches, and each batch is mixed for 5 minutes. Gradient mixing can reduce the local aggregation of low-added fructooligosaccharides in high-fat powder.

[0113] Comparative Example 1: This comparative example uses the raw material ratio of Example 1. The flaxseeds are not subjected to controlled humidification activation, negative pressure decyanation and radio frequency assisted short-time ripening. They are directly pulverized in the air to the same particle size as in Example 1. The rest of the preparation method is the same as in Example 1.

[0114] In this comparative example, the reduction in flaxseed cyanogenic glycosides was insufficient, lipase and lipoxygenase remained highly active, and the peroxide value and volatile oxidation product content increased rapidly during product storage.

[0115] Comparative Example 2: This comparative example uses the same raw material ratio as in Example 1. Flaxseeds are roasted at 130°C for 20 minutes and then pulverized to obtain flaxseed powder. The rest of the preparation method is the same as in Example 1.

[0116] This comparative ratio can reduce the activity of cyanogenic glycosides and oxidases, but prolonged high-temperature roasting causes a decrease in the retention rate of linolenic acid and lignans, and at the same time produces a more obvious burnt and bitter taste.

[0117] Comparative Example 3: This comparative example uses the same raw material ratio and flaxseed ripening method as in Example 1. It does not perform dual-scale particle size classification of tiger nuts, nor does it perform low-temperature dry coating. It directly mixes tiger nuts with a particle size of 200 mesh with low-temperature ripened flaxseed powder. The rest of the preparation method is the same as in Example 1.

[0118] In this comparative example, the surface exposure of flaxseed powder particles was relatively high, the masking effect of tiger nut aroma on the grassy aroma of flaxseed was reduced, and the area of ​​flaxseed lipids in direct contact with residual oxygen in the packaging was increased.

[0119] Comparative Example 4: This comparative example uses the same raw material ratio, flaxseed ripening method, and low-temperature dry coating method as in Example 1. Nitrogen protection is not used; the crushing, coating, mixing, and packaging are completed in an air environment. The remaining operations are the same as in Example 1.

[0120] The residual oxygen volume fraction in the packaging of this comparative example was 7.2%. Flaxseed powder is continuously exposed to air during the grinding, coating and mixing process, which increases the initial peroxide value and the oxidation rate during storage.

[0121] Comparative Example 5: This comparative example uses the same raw material ratio and nitrogen protection conditions as in Example 1. Prebiotic dispersion premixed powder is not prepared. Low-temperature ultrafine tiger pea powder, low-temperature cooked flaxseed powder, soybean lecithin and oligofructose are added into a three-dimensional motion mixer at one time. The rest of the operation is the same as in Example 1.

[0122] In this comparative example, fructooligosaccharides and soybean lecithin were locally enriched, the coefficient of variation of compound uniformity increased, and local clumps and oil floated to the surface when the powder was prepared.

[0123] Experimental Example 1: In this experimental example, the compound nutritional powders prepared in Examples 1 to 5 and Comparative Examples 1 to 5 were tested for cyanogenic glycoside reduction rate, residual oxidase activity, linolenic acid retention rate, lignan retention rate, tiger nut coating coverage, peroxide value, and sensory status. Three batches were prepared independently for each group, and the average value was taken.

[0124] The reduction rate of cyanogenic glycosides was calculated according to Formula 1. The residual activities of lipase and lipoxygenase were determined based on the ratio of enzyme activity after treatment to enzyme activity before treatment. The retention rates of linolenic acid and lignans were determined based on the content of the corresponding components after moisture and quality correction before and after treatment.

[0125] Sensory evaluation was conducted by fifteen trained evaluators. Bitterness and grassy taste were rated on a scale of 0 to 10, with 0 indicating that the corresponding taste was not perceived and 10 indicating that the corresponding taste was extremely strong.

[0126] The test results are shown in Table 2.

[0127] Table 2 Initial performance test results of compound nutritional powder:

[0128] As shown in Table 2, the reduction rate of cyanogenic glycosides in Examples 1 to 5 was 86.9%–88.2%, the residual activity of oxidase was 6.8%–7.8%, the retention rate of linolenic acid was 92.7%–94.1%, and the retention rate of lignans was 93.9%–94.8%. This indicates that controlled humidification activation, negative pressure decyanation, and radio frequency assisted short-term ripening can reduce the loss of linolenic acid and lignans while reducing the activity of cyanogenic glycosides and oxidases in flaxseed.

[0129] Comparative Example 1, which did not undergo flaxseed decyanation and maturation treatment, showed a reduction rate of only 9.6% in cyanogenic glycosides and a residual oxidase activity of 91.5%, indicating that directly grinding raw flaxseed makes it difficult to balance food safety and lipid storage stability.

[0130] Comparative Example 2 was roasted at 130℃ for a long time, and the retention rate of linolenic acid decreased to 74.3% and the retention rate of lignans decreased to 78.6%, and a distinct burnt and bitter taste was produced, indicating that radio frequency assisted short-time roasting improves the retention of heat-sensitive nutrients by shortening the high-temperature residence time.

[0131] Comparative Example 3, which did not undergo dual-scale particle size classification and low-temperature dry coating, had a tiger nut coating coverage of only 31.4%, and its bitterness score increased to 4.1 points. This indicates that using small-particle-size tiger nut micro powder to coat flaxseed powder particles can reduce the surface exposure of flaxseed and the concentrated release of bitterness.

[0132] In Comparative Example 4, after nitrogen protection was removed, the peroxide value increased to 5.1 mmol / kg and the linolenic acid retention rate decreased, indicating that continuous oxygen exposure during the grinding, coating and mixing stages of flaxseed accelerates the oxidation of unsaturated fatty acids.

[0133] Comparative Example 5, which did not prepare a premixed premix of prebiotics, showed lower uniformity of compounding and reconstitution state than Example 1, indicating that the premixed system formed by fructooligosaccharides with some of the main tiger nut micropowder can reduce the local aggregation of low-added prebiotics.

[0134] Experimental Example 2: This experimental example evaluates the reconstitution performance of Examples 1 to 5 and Comparative Examples 1 to 5. 20g of compound nutritional powder was weighed and added to 200mL of drinking water at 40℃. The mixture was stirred at 300r / min for 30s and allowed to stand for 5min before testing for undispersed agglomerates, bottom sedimentation, and surface oil.

[0135] The reconstitution dispersion rate was determined as a percentage of the difference between the initial mass of the compound nutrient powder and the dry mass of the undispersed agglomerates relative to the initial mass of the compound nutrient powder. The test results are shown in Table 3.

[0136] Table 3. Results of the mixing and reconstitution performance tests of compound nutritional powder:

[0137] As shown in Table 3, the coefficient of variation of compound uniformity in Examples 1 to 5 is 1.6% to 2.3%, the reconstitution dispersion rate is 95.1% to 98.0%, and the bottom settling rate is not higher than 2.0%. This indicates that dual-scale tiger nut micro powder, low-temperature dry coating, prebiotic dispersion premixing, and nitrogen closed gradient mixing can jointly improve the mixing uniformity and reconstitution dispersion of the powder.

[0138] Experimental Example 3: This experiment conducted a 12-month room temperature storage test on Examples 1 to 5 and Comparative Examples 1 to 5. Each group of products was placed in a light-proof environment with a temperature of 25°C and a relative humidity of 60%. The linolenic acid retention rate, peroxide value, hexanal content, powder agglomeration rate, and sensory status were tested every 3 months.

[0139] The powder agglomeration rate was determined by the percentage of agglomerated powder that could not pass through a 20-mesh sieve after storage, relative to the total mass of the sample. The results of the 12-month storage test are shown in Table 4.

[0140] Table 4. Stability test results of compound nutritional powder after 12 months of storage:

[0141] As shown in Table 4, the relative retention rate of linolenic acid after 12 months of storage in Examples 1 to 5 was 86.8% to 89.4%, the peroxide value was 4.3 mmol / kg to 5.2 mmol / kg, and the powder agglomeration rate was no higher than 2.6%. This indicates that low-temperature maturation, tiger nut micro powder coating, nitrogen-sealed processing, and pulsed vacuum nitrogen-filled packaging can jointly reduce the oxidation of unsaturated fatty acids in flaxseed and the agglomeration of powder.

[0142] This invention provides a compound nutritional powder of tiger flaxseed prebiotics and its preparation method. The method involves controlled humidification to activate the endogenous β-glucosidase in flaxseed to participate in the conversion of cyanogenic glycosides. Then, negative pressure and nitrogen sweeping are used to remove volatile cyanogenic components. Radio frequency-assisted short-term ripening is used to deactivate lipase and lipoxygenase, thereby avoiding the problem of high cyanogenic glycoside and oxidase activity in raw flaxseed. At the same time, it reduces the loss of linolenic acid and lignans caused by high temperature and long-term roasting.

[0143] This invention obtains coated tiger nut micro powder and main tiger nut micro powder of different particle sizes through nitrogen low-temperature graded pulverization. The coated tiger nut micro powder and soybean lecithin are used to perform low-temperature dry coating on low-temperature cooked flaxseed powder. Then, the main tiger nut micro powder is used to carry oligofructose and perform gradient mixing. This allows the nutty aroma of tiger nut, the physical barrier structure of the powder, and the uniform dispersion structure of prebiotics to jointly improve the bitter taste, grassy taste, easy oxidation, and separation problems of flaxseed when brewed.

[0144] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Any adjustments and equivalent substitutions made by those skilled in the art to the raw material ratio, flaxseed decyanation parameters, radio frequency curing parameters, powder particle size, coating parameters, mixing sequence and packaging parameters without departing from the technical concept of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A compound nutritional powder containing tiger nuts and flax seeds with prebiotics, characterized in that, It is made from the following raw materials in parts by weight: 55-70 parts of low-temperature ultrafine tiger nut powder, 30-45 parts of low-temperature cooked flaxseed powder, 0.1-0.3 parts of soybean lecithin, and 0.5-1.5 parts of fructooligosaccharides. The low-temperature ultrafine tiger nut powder includes coated tiger nut powder and main tiger nut powder. The coated tiger nut powder and the soybean lecithin form lecithin tiger nut coated powder. The lecithin tiger nut coated powder is attached to the outer surface of the low-temperature cooked flaxseed powder particles to form tiger nut coated flaxseed composite particles.

2. The tiger nut and flaxseed prebiotic compound nutritional powder according to claim 1, characterized in that, The median particle size of the coated tiger nut powder is 18–28 μm, the median particle size of the bulk tiger nut powder is 50–75 μm, the median particle size of the low-temperature cooked flaxseed powder is 75–110 μm, and the coated tiger nut powder accounts for 10%–18% of the total mass of the low-temperature ultrafine tiger nut powder.

3. The tiger nut and flaxseed prebiotic compound nutritional powder according to any one of claims 1 to 2, characterized in that, The low-temperature cooked flaxseed powder is obtained by sequentially undergoing controlled humidification activation, negative pressure decyanation, radio frequency assisted short-time cooking, low-temperature vacuum drying, and nitrogen-protected pulverization. The moisture content of the low-temperature cooked flaxseed powder is not higher than 5%, and the tiger nut coating coverage of the tiger nut coated flaxseed composite particles is not less than 85%.

4. The tiger nut and flaxseed prebiotic compound nutritional powder according to any one of claims 1 to 3, characterized in that, It is made from the following ingredients in parts by weight: 65 parts of low-temperature ultrafine tiger pea powder, 35 parts of low-temperature cooked flaxseed powder, 0.2 parts of soybean lecithin and 1.0 part of fructooligosaccharides. The ingredients of the compound nutritional powder do not contain sucrose, artificial flavors, artificial colors and preservatives.

5. A method for preparing the tiger nut and flaxseed prebiotic compound nutritional powder according to any one of claims 1 to 4, characterized in that, Includes the following steps: Step S1: The tiger nuts are cleaned, washed and dried at low temperature, and then subjected to two-stage pulverization and particle size classification under nitrogen protection to obtain coated tiger nut powder and main tiger nut powder. Step S2 involves controlled humidification activation and negative pressure decyanation of flaxseed, followed by radio frequency assisted short-time ripening, low-temperature vacuum drying, and nitrogen-protected pulverization to obtain low-temperature ripened flaxseed powder. Step S3: Premix soybean lecithin with the coated tiger nut powder to obtain lecithin-coated tiger nut powder; Step S4: Add the lecithin tiger nut coating powder to the low-temperature cooked flaxseed powder for low-temperature dry coating to obtain tiger nut coated flaxseed composite particles. Step S5: Mix the fructooligosaccharides with a portion of the main-grade tiger nut powder to obtain a prebiotic dispersion premix powder; Step S6: The tiger nuts coated with flaxseed composite particles, the prebiotic dispersion premix powder, and the remaining main tiger nut micro powder are subjected to gradient mixing in a nitrogen-sealed environment. Step S7: The mixed powder is sequentially sieved, foreign matter detected, and pulsed vacuum nitrogen-filled packaging to obtain tiger nut and flaxseed prebiotic compound nutritional powder.

6. The preparation method according to claim 5, characterized in that, In step S2, the flaxseeds are moistened to a moisture content of 14%–17%, activated in a nitrogen atmosphere at 44–48°C for 25–40 min, and then placed in a negative pressure treatment device with an absolute pressure of 18–28 kPa and a temperature of 58–65°C, while nitrogen is introduced at a flow rate of 0.3–0.6 L / min per kilogram of flaxseeds for 15–25 min.

7. The preparation method according to any one of claims 5 to 6, characterized in that, In step S2, radio frequency assisted short-time ripening is carried out using radio frequency equipment with a frequency of 27.12MHz to bring the core temperature of flaxseed to 78-82℃ and maintain it for 90-150s. After ripening, the flaxseed is vacuum dried at a temperature of 42-48℃ and an absolute pressure of 20-30kPa until the moisture content is no higher than 5%.

8. The preparation method according to any one of claims 5 to 7, characterized in that, In step S4, the low-temperature dry coating is carried out under nitrogen-sealed conditions at 500-750 r / min for 8-12 min, and the powder temperature is below 40℃ during the coating process. In step S5, the main-grade tiger nut micro powder participating in the prebiotic dispersion premix accounts for 8%-12% of the total mass of the main-grade tiger nut micro powder. In step S6, the oxygen volume fraction is less than 1% and the powder temperature is below 40℃. After the packaging is completed in step S7, the residual oxygen volume fraction inside the packaging is less than 1%.

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