Method for preparing salted egg yolk powder by using differential frequency microwave curing method

Abstract

The invention belongs to the technical field of food preparation, and particularly relates to a method for preparing salted egg yolk powder by using a differential frequency microwave curing method, and the preparation method comprises the following steps: S1, pretreating egg yolk to obtain an egg yolk liquid; s2, preparing the salted egg yolk liquid; s3, preparing egg yolk pickling liquid; s4, performing high-speed centrifugal treatment and high-frequency microwave curing on the egg yolk pickling liquid by using a centrifugal machine to obtain oiled egg yolk particles; s5, performing rotary granulation on the oiled egg yolk particles; and S6, performing low-frequency microwave drying and superfine grinding. The salted egg yolk powder which is good in flavor, sufficient in nutrition and stable and excellent in quality can be obtained and can be widely applied to the fields of leisure food seasoning, catering seasoning and the like.

Description

Technical Field

[0001] This invention belongs to the field of food preparation technology, specifically relating to a method for preparing salted egg yolk powder using differential frequency microwave cooking. Background Technology

[0002] As the food industry upgrades towards functionality and convenience, salted egg yolk powder enjoys a continuously rising market demand due to its unique flavor and wide range of applications (covering baking, seasonings, and ready-to-cook meals). Currently, the mainstream preparation process in the industry is "raw material pretreatment - pickling - solid-liquid separation - maturation - drying - pulverization," relying heavily on off-shell pickling technology to extract egg yolk oil and form flavor. Subsequent steps such as centrifugation, microwave heating, and granulation are simply linked together as basic processing steps without creating a synergistic optimization effect. Existing processes can only meet basic production needs, lacking systematic design in core dimensions such as oil extraction efficiency, quality stability, production efficiency, and environmental safety. This results in products being concentrated in the low-to-mid-end market; high-end products still rely on imports due to poor flavor uniformity, low nutrient retention, and insufficient safety. The industry urgently needs technological breakthroughs to fill the gap in the high-end market.

[0003] The core pain points of the existing process lie in the insufficient coordination between the shell pickling technology itself and its supporting processes, specifically manifested in five major defects:

[0004] First, the pickling method is too simple, relying solely on the addition of salt and the slow action of endogenous lipase in egg yolks. This results in an oil yield of less than 40%, a pickling cycle of more than 24 hours, and a high risk of microorganisms such as Bacillus spores growing in the high temperature and humidity environment, leading to a high risk of exceeding the total bacterial count. Secondly, the centrifugation process has limitations. It is only used as a simple solid-liquid separation method and cannot break the stable structure of "protein micelles encapsulating oil droplets" in the egg yolk. This results in uneven oil droplet dispersion, which directly affects the sufficiency of oil extraction and the uniformity of oil distribution in the subsequent cooking process. Third, the cooking and drying technology is crude, often using high-temperature steaming or single-power microwave heating, which easily leads to fat oxidation (excessive POV peroxide value) and excessive protein denaturation (hard texture). Microwave drying is also prone to the phenomenon of "surface crusting and difficulty in removing internal moisture", resulting in poor product moisture uniformity. Fourth, there is a lack of overall process form control, and no systematic regulation of particle size and moisture content has been formed. Particles are prone to sticking together during the granulation stage, resulting in low drying efficiency (drying time for a single batch exceeds 30 minutes), uneven particle size of the pulverized product, and a solubility rate of less than 80%. Fifth, resource utilization efficiency is low, with the utilization rate of by-products such as centrifugation supernatant, eggshells, and egg membranes being less than 30%. This not only wastes resources but also increases environmental protection pressure, contradicting the trend of green production in the food industry. These shortcomings are interconnected and restrictive at each level, seriously affecting the production efficiency, product quality, and industrial upgrading process of salted egg yolk powder. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing salted egg yolk powder using differential frequency microwave cooking, which can produce salted egg yolk powder with excellent flavor, high nutritional value, and stable quality, and can be widely used in the fields of snack food seasoning and catering seasoning.

[0006] The specific technical solution adopted by this invention is as follows: A method for preparing salted egg yolk powder using differential frequency microwave cooking, the preparation method comprising the following steps: S1: Pre-treat the egg yolks to obtain egg yolk liquid; S1 includes the following steps: S11: Select fresh eggs that are free from damage, mold, and odor, with a yolk index ≥ 0.40 and Haugh unit ≥ 72, and remove unqualified eggs with broken shells, broken yolks, or spoilage. S12: Rinse qualified eggs under running water at 35-40℃ for 3-5 minutes, then immerse them in a sodium hypochlorite solution with a concentration of 50-100mg / L for 2-3 minutes. After rinsing with sterile distilled water to remove residual disinfectant, drain the surface water in a sterile environment. S13: Separate egg yolks and egg whites using aseptic manual separation method or automatic egg liquid separator; S14: Transfer the separated egg yolk liquid into a sterile mixing jar, and use a paddle mixer to mix at low speed. Set the mixing speed to 60-100 r / min and the mixing time to 8-12 minutes to obtain egg yolk liquid.

[0007] S2: Preparation of salted egg yolk liquid; S2 includes the following steps: S21: Select standard refined salt and edible alcohol; S22: According to the mass fraction of egg yolk liquid, first add 2-5% edible salt to the egg yolk liquid obtained in S1, turn on the mixer, the speed is 100-150r / min, stir for 5-8 minutes until the salt is completely dissolved, then slowly add 20-30% edible alcohol, and continue stirring for 10-15 minutes. During the stirring process, control the temperature inside the mixing bowl to 20-25℃. S23: After stirring, the mixture is homogenized once by passing it through a colloid mill with a grinding gap of 0.05-0.1mm and a rotation speed of 3000-5000r / min to obtain egg yolk slurry.

[0008] S3: Preparation of egg yolk curdling solution; S3 includes the following steps: S31: Use a sterile stainless steel pickling jar with a sealed lid. Before pickling, sterilize it with high-pressure steam at 121℃ for 20 minutes and cool it to room temperature before use. S32: Transfer the egg yolk liquid obtained in S2 into a sterile pickling tank, seal it, and place it in a constant temperature incubator. Control the pickling temperature at 30-45℃ and the pickling time at 16-24 hours. S33: During the marinating process, turn on the mixer every 4-6 hours and stir at low speed for 3-5 minutes, with a speed of 60-80 r / min; S34: The criteria for judging the end point of pickling are: the egg yolk liquid is uniformly milky yellow, with a small amount of oil on the surface, and the viscosity is 30-50% higher than before pickling.

[0009] S4: The egg yolk curing liquid is subjected to high-speed centrifugation and high-frequency microwave cooking to obtain oily egg yolk particles. S4 includes the following: A horizontal spiral sedimentation centrifuge was selected, and the inner cavity of the equipment was aseptically cleaned and disinfected before centrifugation. Pump the filtered egg yolk curing liquid into a centrifuge, set the centrifugation speed to 4000-5000 r / min, and the centrifugation time to 15-20 minutes. During the centrifugation process, control the feed temperature to 25-30℃ to obtain salted duck egg yolk oil.

[0010] The high-frequency microwave curing includes the following steps: S41: Add 15-30% of the solid weight of the egg yolk to the obtained egg yolk liquid, add salted duck egg yolk oil, transfer to a sterile homogenizing tank, and use a high-shear homogenizer at a speed of 10000-15000 r / min for 8-12 minutes. S42: A continuous high-frequency microwave curing device is selected. The device cavity is sterilized. The homogenized mixture is evenly spread on the microwave transmission belt with a thickness of 5-8 mm. The transmission speed is controlled so that the heating time is 2-5 minutes to obtain oily egg yolk particles.

[0011] S5: Rotary granulation of the oily egg yolk particles; S5 includes the following steps: S51: Select a rotary drum granulator to transfer the cooked egg yolk granules from S4 into the granulator drum. Set the drum speed to 30-50 r / min and the drum tilt angle to 3-5°. At the same time, introduce sterile hot air at 30-40℃ with a wind speed of 0.5-1m / s. S52: The granulated particles are screened by a vibrating screen with sieve apertures of 0.2cm and 0.4cm. Uniform particles of 0.2-0.4cm are collected. Oversized particles on the sieve are returned to the granulator for regranulation, and undersized particles on the sieve are recycled as waste. S53: The screened particles must meet the following requirements: particle size variation coefficient ≤ 10%, and bulk density 0.6-0.8 g / cm³.

[0012] S6: Perform low-frequency microwave drying and ultra-fine pulverization.

[0013] A box-type low-frequency microwave dryer was selected, equipped with an online temperature and humidity monitoring system. The egg yolk particles obtained from S5 were evenly spread on a drying tray and placed in the microwave dryer. The drying temperature was set to 45-55℃. Microwave power is adjusted in segments: the first 0-10 minutes is for rapid dehydration; the second 10-25 minutes is for heat preservation and drying, with a total drying time of 15-25 minutes. The criteria for determining the drying endpoint are: particle moisture content ≤5%, moisture uniformity ≤0.5%, particles maintain their intact shape, and there is no cracking or pulverization.

[0014] The ultrafine pulverization process specifically employs the following methods: An airflow-type ultrafine pulverizer is selected, with a pulverizing pressure of 0.6-0.8 MPa and a pulverizing chamber temperature of ≤30℃. The equipment is sterilized and cleaned before pulverizing. The crushed salted egg yolk powder is screened through a 300-mesh sterile sieve to remove a small amount of coarse particles that are not completely crushed. The screened powder is then transferred to a sterile mixer and mixed at 60-80 r / min for 5-10 minutes. Finally, it is vacuum-packed in sterile aluminum foil bags and stored in a cool, dry place.

[0015] The technical effects achieved by this invention are as follows: This invention discloses a method for preparing salted egg yolk powder using differential frequency microwave curing. It innovatively proposes a "salt-alcohol synergistic curing + dynamic parameter linkage" mode. Based on the osmotic kinetic equation, it precisely proportions 2-5% edible salt and 20-30% food-grade alcohol. It utilizes the osmotic pressure of salt to loosen micelles and the antibacterial and viscosity-reducing effects of alcohol to simultaneously solve the three major pain points of "difficult oil extraction, long cycle, and high risk of contamination". This shortens the curing cycle by 15-20% and increases the oil yield to over 55%.

[0016] This invention discloses a method for preparing salted egg yolk powder using differential frequency microwave cooking. By innovating the centrifugation process and designing precise centrifugation parameters of 4000-5000 r / min based on the principles of colloid mechanics, the method targets and destroys the micelle structure and promotes oil droplet aggregation (increasing the particle size from 1-5 μm to 20-50 μm). Combined with precise control of the water content of 45-55%, it adapts to high-shear homogenization to form a homogeneous oil-solid system, thus fundamentally solving the problem of uneven oil extraction.

[0017] The present invention discloses a method for preparing salted egg yolk powder using differential frequency microwave cooking. By using "differential frequency segmented microwave processing" technology, the cooking stage uses low-frequency microwaves to achieve deep and uniform heating (temperature deviation ≤2℃), and the drying stage uses high-frequency microwaves + segmented power adjustment to balance cooking effect and nutrient retention. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the salted egg yolk liquid after cooking according to the present invention; Figure 2 This is the color difference analysis diagram of the present invention; Figure 3 This is a schematic diagram showing the PCA results of the present invention. Detailed Implementation

[0019] To make the objectives and advantages of this invention clearer, the invention will be specifically described below with reference to embodiments. It should be understood that the following text is merely used to describe one or more specific embodiments of the invention and does not strictly limit the scope of protection specifically claimed by the invention.

[0020] Example 1: like Figure 1 As shown, a method for preparing salted egg yolk powder using differential frequency microwave cooking includes the following steps: S1: Pre-treat the egg yolks to obtain egg yolk liquid; S1 includes the following steps: S11: Select fresh eggs that are free from damage, mold, and odor, with a yolk index (yolk height / yolk diameter) ≥0.40 and Haugh units ≥72, and remove unqualified eggs with broken shells, broken yolks, or spoilage. S12: Rinse qualified eggs under running water at 35-40℃ for 3-5 minutes to remove stains from the eggshell surface. Then immerse them in a sodium hypochlorite solution with a concentration of 50-100mg / L for 2-3 minutes for disinfection. After removal, rinse with sterile distilled water to remove residual disinfectant. Place them in a sterile environment to drain the surface moisture (draining time 15-20 minutes, ambient temperature 20-25℃, relative humidity 50-60%). S13: Use aseptic manual separation method or automatic egg liquid separator to separate egg yolk and egg white; separation efficiency ≥50 eggs / minute, egg yolk breakage rate ≤1%, avoid eggshell fragments from being mixed in during operation, and ensure that the egg yolk membrane is intact and undamaged; collect the separated egg white separately for later use, and transfer the egg yolk to the next step of processing immediately; S14: Transfer the separated egg yolk liquid into a sterile mixing jar and use a paddle mixer to mix at low speed (60-100 rpm) for 8-12 minutes to obtain the egg yolk liquid. Avoid generating air bubbles during mixing to break up any remaining egg white flocculent material, ensuring the fat, protein, and other components of the egg yolk are evenly dispersed, resulting in a homogeneous egg yolk liquid without obvious particles.

[0021] S2: Preparation of salted egg yolk liquid; S2 includes the following steps: S21: Select standard refined salt and edible alcohol; the edible salt shall be refined salt that meets the GB 2721-2015 standard for edible salt (sodium chloride content ≥99.1%, moisture ≤0.3%), and the edible alcohol shall be food-grade ethanol that meets the GB 31640-2016 standard for edible alcohol (alcohol content ≥95%, fusel oil ≤0.2g / L).

[0022] S22: Based on the mass fraction of egg yolk liquid, first add 2-5% edible salt to the egg yolk liquid obtained in S1. Turn on the stirrer at 100-150 r / min and stir for 5-8 minutes until the salt is completely dissolved. Then slowly add 20-30% edible alcohol and continue stirring for 10-15 minutes. During the stirring process, control the temperature inside the stirring container at 20-25℃ to prevent alcohol evaporation. The 2-5% salt concentration is based on the principle of osmotic pressure balance. This concentration can maintain the osmotic pressure difference across the egg yolk membrane at 0.3-0.5 MPa, which promotes fat precipitation and avoids excessive protein denaturation. The 20-30% alcohol volume fraction can inhibit the growth of putrefactive bacteria (such as Bacillus subtilis) and reduce the viscosity of the egg yolk liquid (viscosity decreases by 25-30%), thereby improving the efficiency of subsequent centrifugation. When the salt concentration is <2%, the osmotic pressure is insufficient, and the fat precipitation rate is less than 40%; when the salt concentration is >5%, the product is too salty, and excessive protein denaturation leads to a rough texture; when the alcohol concentration is <20%, the antibacterial effect is insufficient, and microorganisms are prone to grow during the pickling process.

[0023] S23: After stirring, homogenize the mixture once using a colloid mill with a grinding gap of 0.05-0.1mm and a rotation speed of 3000-5000r / min to ensure that the salt, alcohol and egg yolk liquid are fully integrated without any local high concentration, and to obtain a smooth and fluid egg yolk paste.

[0024] S3: Preparation of egg yolk curdling solution; S3 includes the following steps: S31: Use a sterile stainless steel pickling jar with a sealed lid. Before pickling, sterilize it with high-pressure steam at 121℃ for 20 minutes and cool it to room temperature before use. S32: Transfer the egg yolk liquid obtained in S2 into a sterile pickling tank, seal it, and place it in a constant temperature incubator. Control the pickling temperature at 30-45℃ and the pickling time at 16-24 hours. Adjust according to salt concentration: 20-24 hours for 2-3% salt mass fraction, and 16-20 hours for 3-5% salt mass fraction. 30-45℃ is the optimal temperature range for endogenous lipase in egg yolk (enzyme activity reaches 120-150 U / g), which can accelerate the hydrolysis of triglycerides into fatty acids and promote fat precipitation. The pickling time is negatively correlated with salt concentration, based on the osmotic pressure kinetic equation (osmotic rate is positively correlated with salt concentration). The osmotic rate is fast at high salt concentrations, which can shorten the pickling time and avoid excessive fat oxidation. When the temperature is below 30℃, lipase activity is insufficient (<80 U / g), and the fat extraction rate is less than 50%; when the temperature is above 45℃, protein thermal denaturation is aggravated, and the product has a hard texture; if the marinating time is too short (<16 hours), penetration is insufficient, and fat extraction is incomplete; if the time is too long (>24 hours), the fat oxidation value (POV) exceeds the standard (>0.2 g / 100g), affecting product safety.

[0025] S33: During the marinating process, turn on the mixer at low speed for 3-5 minutes every 4-6 hours, with a speed of 60-80r / min, to promote the penetration of salt and alcohol into the egg yolk and accelerate the precipitation of fat in the egg yolk; S34: The criteria for judging the end point of pickling are: the egg yolk liquid is uniformly milky yellow, with a small amount of oil on the surface, and the viscosity is 30-50% higher than before pickling.

[0026] S4: The egg yolk curing liquid is subjected to high-speed centrifugation and high-frequency microwave cooking to obtain oily egg yolk particles. S4 includes the following: A horizontal spiral sedimentation centrifuge with a separation factor ≥3000g and a throughput ≥50L / h was selected. Before centrifugation, the inner cavity of the equipment was sterilely cleaned and disinfected, and wiped with 75% alcohol and then dried. The filtered egg yolk curing liquid is pumped into a centrifuge, and the centrifugation speed is set to 4000-5000 r / min (corresponding to a centrifugal force of 2500-3200 g) for 15-20 minutes. During centrifugation, the feed temperature is controlled at 25-30℃ to obtain salted duck egg yolk oil. The fat in the egg yolk is encapsulated in protein micelles (composed of lipoproteins, phospholipids, etc.) in the form of oil droplets, forming a stable colloidal dispersion system. According to the principles of colloid mechanics, the centrifugal force corresponding to 4000-5000 r / min can precisely break the spatial structure of these micelles. Through mechanical shearing force, the hydrogen bonds and hydrophobic interactions between the micelles are destroyed, causing the encapsulated oil droplets to be released and aggregate, creating conditions for the oil precipitation during subsequent microwave heating and curing. At the same time, this centrifugal force can avoid excessive damage to the protein network (centrifugal force >3200g will cause protein molecular chains to break, which will instead adsorb oil droplets and hinder aggregation).

[0027] High-frequency microwave curing includes the following steps: S41: Add 15-30% (by weight of solid egg yolk) of salted duck egg yolk oil to the obtained egg yolk liquid, transfer to a sterile homogenizing tank, and homogenize for 8-12 minutes using a high-shear homogenizer at 10000-15000 r / min to fully integrate the oil and solid egg yolk, forming a homogeneous oil-solid mixture. The particle size of the homogenized mixture should be ≤50 μm. The 15-30% oil addition is based on the oil absorption rate curve of the solid egg yolk (up to 35%). This ratio ensures sufficient wetting of the solids, enhancing the oily texture of the matured product. If the oil addition is <15%, the product will have a dry texture; if the addition is >30%, excessive oil will make granulation difficult. S42: Select a continuous high-frequency microwave curing device (power 5-10 kW). The device cavity is sterilized. Spread the homogenized mixture evenly on the microwave transmission belt with a thickness of 5-8 mm. Control the transmission speed to make the heating time 2-5 minutes. Adjust according to the thickness of the spread: heat for 2-3 minutes when the thickness is 5-6 mm, and heat for 3-5 minutes when the thickness is 6-8 mm to obtain oily egg yolk particles.

[0028] S5: Rotary granulation of the oily egg yolk particles; S5 includes the following steps: S51: Select a rotary drum granulator (drum diameter 500-800mm, length 1000-1500mm), transfer the cooked egg yolk granules from S4 into the granulator drum, set the drum speed to 30-50 r / min, the drum tilt angle to 3-5°, and simultaneously introduce sterile hot air at 30-40℃ with a wind speed of 0.5-1m / s. During the granulation process, the granule formation speed is controlled by adjusting the drum speed and tilt angle. S52: The granulated particles are screened by a vibrating screen with sieve apertures of 0.2cm and 0.4cm. Uniform particles of 0.2-0.4cm are collected. Oversized particles on the sieve are returned to the granulator for regranulation, and undersized particles on the sieve are recycled as waste. S53: The screened particles must meet the following requirements: particle size variation coefficient ≤10%, bulk density 0.6-0.8 g / cm³, good spreadability, and no obvious agglomeration.

[0029] S6: Perform low-frequency microwave drying and ultra-fine pulverization.

[0030] Select a box-type low-frequency microwave dryer (power 3-6 kW), equipped with an online temperature and humidity monitoring system. Spread the egg yolk particles obtained from S5 evenly on the drying tray (layer thickness 1-2cm, avoid particle overlap), place it in the microwave dryer, and set the drying temperature to 45-55℃. Microwave power is adjusted in segments: the first 0-10 minutes, power 5-6kW, for rapid dehydration; the second 10-25 minutes, power 3-4kW, for heat preservation and drying, with a total drying time of 15-25 minutes. During the drying process, the material temperature and humidity are recorded every 5 minutes to ensure that the material temperature does not exceed 60℃ (to avoid fat oxidation and loss of heat-sensitive nutrients). The drying endpoint is judged as follows: the moisture content of the particles is ≤5% (tested according to GB 5009.3-2016 "National Food Safety Standard Determination of Moisture in Food"), the moisture uniformity is ≤0.5%, and the particles maintain their intact shape without cracking or pulverization.

[0031] The ultrafine pulverization process specifically employs the following methods: An airflow-type ultrafine pulverizer is selected, with a pulverizing pressure of 0.6-0.8 MPa and a pulverizing chamber temperature of ≤30℃. The equipment is sterilized and cleaned before pulverizing. Ultrafine pulverization is achieved through particle collision. The pulverizing chamber temperature of ≤30℃ can avoid fat oxidation caused by frictional heat during pulverization (the oxidation rate doubles for every 10℃ increase in temperature). The pulverized salted egg yolk powder is screened through a 300-mesh sterile sieve to remove a small amount of coarse particles that are not completely pulverized. The screened powder is then transferred to a sterile mixer and mixed at 60-80 r / min for 5-10 minutes to ensure uniform particle size and generate a high-speed airflow (speed ≥300m / s). Finally, the powder is vacuum-packed in sterile aluminum foil bags (vacuum degree ≤-0.09MPa). After packaging, the product is stored in a cool, dry place (temperature ≤25℃, relative humidity ≤60%).

[0032] Example 2: Sensory evaluation The test used salted egg yolks prepared by S4 high-frequency microwave heating and curing as a base material before drying. The total score and evaluation of each indicator were divided into four levels: excellent, good, average, and poor, with different scores assigned to each. This allowed evaluators to conduct a more objective sensory assessment of the food. 80% of the score for each indicator is the boundary between excellent and good, 60% is the boundary between good and average, and a score below 40% is considered poor. Based on the content of the salted egg yolk scoring indicators and consultations with investigators, and referring to descriptions of various sensory evaluation standards, a salted egg yolk evaluation grading table that better reflects the results of this experiment was created (see table below).

[0033] Table 1 Sensory Evaluation Grading Standards for Salted Egg Yolk Powder

[0034] Example 3: Color difference measurement The properties of the dried salted egg yolk powder were tested. An UltraScan spectrophotometer was used to measure the salted egg yolk samples after heating. Approximately 5 g of each sample was placed in a resealable bag. The colorimeter was first calibrated using a black and white board (0=black, 100=white), and then calibrated using a blank resealable bag. Results were recorded using L... Indicates brightness, a Indicates red (+) and green (-) values, b Indicates yellow (+) and blue (-) values. Each sample was measured three times, and the average value was taken.

[0035] Electronic nose analysis The test examined the properties of the dried egg yolk powder. Sample pretreatment: Weigh 2 g of sample into a 15 ml headspace vial, seal the vial, and proceed with the analysis. Each sample was tested in triplicate. Detection conditions: Two chromatographic columns of different polarities, DB-5 and DB-1701 (10 m ~ 0.18 mm), were used, along with two FID detectors. A single injection was performed, and both columns were analyzed simultaneously. Headspace extraction temperature was 60°C; trapping well temperature was 50°C. Detection setup: The headspace vials containing the samples were placed in the sample tray according to the determination sequence. A blank sample was placed before and after all the samples being analyzed, and then the samples were analyzed according to the procedure.

[0036] Temperament measurement The properties of the salted egg yolk powder obtained after drying were tested. A 2 g sample of salted egg yolk was placed in a 20 ml headspace vial, and physiological saline was added to bring the volume to 5 g. Then, 10 μl of internal standard (cyclohexanone aqueous solution, 100 mg / L) was added. The sample was incubated at 60 °C for 30 min, and shaken at 500 rpm.

[0037] Gas chromatography conditions: DB-WAX capillary column (30 m × 0.25 mm × 0.25 μm, J&W Technologies, USA); Temperature program: 40°C for 4 min, ramped to 90°C at 5°C / min, then ramped to 230°C at 10°C / min and held for 6 min; Vaporization chamber temperature: 250°C; Carrier gas: He, flow rate: 0.80 mL / min; Splitless injection; Mass spectrometry conditions: EI ionization source, electron energy 70 eV, filament emission current 200 μA, ion source temperature 200°C, interface temperature 250°C, detector voltage 350 V, mass scan range 33–450 m / z.

[0038] Example 4: (1) Egg yolk pretreatment Eggs meeting the freshness standards of GB 2748-2016 "Hygienic Standard for Fresh Eggs" were selected, requiring intact shells without damage or mold, no off-odors, a yolk index (yolk height / yolk diameter) ≥0.40, and a Haugh unit ≥72. Qualified eggs were rinsed under running water at 35℃ for 3-5 minutes to remove surface dirt. They were then disinfected by immersing in a 50 mg / L sodium hypochlorite solution for 2-3 minutes. After removal, residual disinfectant was rinsed with sterile distilled water, and the eggs were allowed to drain under sterile conditions (draining time 20 minutes, ambient temperature 25℃, relative humidity 55%). An automatic egg white separator (separation efficiency ≥50 eggs / minute, yolk membrane damage rate ≤1%) was used for separation. The separated egg whites were collected separately for later use, while the yolks were transferred to a sterile mixing tank and stirred at low speed (80 rpm) for 10 minutes using a paddle mixer to obtain the yolk liquid.

[0039] (2) Salted egg yolk marinating The edible salt used is refined salt that meets the GB 2721-2015 standard for edible salt (sodium chloride content ≥99.1%, moisture ≤0.3%); the edible alcohol used is food-grade ethanol that meets the GB 31640-2016 standard for edible alcohol (alcohol content ≥95%, fusel oil ≤0.2g / L). Based on the mass fraction of egg yolk liquid, first add 2% edible salt to the egg yolk liquid obtained in step (1), turn on the stirrer (speed 100 r / min) and stir for 8 minutes until the salt is completely dissolved; then slowly add 20% edible alcohol and continue stirring for 15 minutes. During the stirring process, control the temperature inside the stirring tank to 25℃ to avoid alcohol evaporation; after stirring, homogenize the mixture once by passing it through a colloid mill (grinding gap 0.1 mm, speed 4000 r / min).

[0040] (3) Marinate with egg yolk liquid Use a sterile stainless steel pickling tank with a sealed lid. Before pickling, sterilize the tank with high-pressure steam at 121℃ for 20 minutes. After cooling to room temperature, transfer the egg yolk liquid obtained in step (2) into the sterile pickling tank, seal it, and place it in a constant temperature incubator. Control the pickling temperature at 45℃ and the pickling time at 24 hours. Pickling process control: During the pickling period, turn on the mixer at low speed for 5 minutes (80 r / min) every 5 hours to promote the penetration of salt and alcohol into the egg yolk and accelerate the precipitation of fat in the egg yolk; the criteria for judging the end of pickling is: the egg yolk liquid is uniformly milky yellow, with a small amount of oil on the surface, and the viscosity is 30% higher than before pickling.

[0041] (4) High-speed centrifugation and high-frequency microwave curing A horizontal spiral sedimentation centrifuge (separation factor ≥3000g, throughput ≥50L / h) was selected. Before centrifugation, the inner cavity of the equipment was aseptically cleaned and disinfected (wiped with 75% alcohol and then dried). The egg yolk marinade was pumped into the centrifuge, and the centrifugation speed was set to 5000 r / min (corresponding to a centrifugal force of 2500-3200g), with a centrifugation time of 15 minutes. The feed temperature was controlled at 25℃ during centrifugation. Add 20% of the solid weight of the egg yolk to the obtained egg yolk liquid, then add salted duck egg yolk oil. Transfer the mixture to a sterile homogenizing tank and homogenize for 12 minutes using a high-shear homogenizer (10,000 r / min) to fully integrate the oil and egg yolk solids, forming a homogeneous oil-solid mixture. The particle size of the homogenized mixture is ≤50 μm. The salted duck egg yolk oil is made from food-grade products that meet the SB / T 10294-1998 standard for edible vegetable oils, with a purity of ≥99%, an acid value of ≤1.5mg KOH / g, and a peroxide value of ≤0.15g / 100g. A continuous high-frequency microwave cooking device (power 9 kW) was selected, and the device cavity was sterilized. The homogenized mixture was evenly spread on the microwave transmission belt (spreading thickness 6 mm), and the transmission speed was controlled so that the heating time was 3 minutes to obtain a cooked egg yolk mixture. (5) Rotary granulation A rotary drum granulator (600 mm in diameter and 1200 mm in length) was selected. The inner wall of the equipment was coated with polytetrafluoroethylene to prevent material adhesion. The cooked egg yolk mixture from step (4) was transferred into the drum of the granulator. The drum speed was set to 40 r / min, and sterile hot air at 40°C (wind speed 0.5 m / s) was introduced at the same time. The granulated particles were screened by a vibrating screen (0.2 cm and 0.4 cm sieve holes) to collect uniform particles of 0.2-0.4 cm. The particles that were too large on the screen were returned to the granulator for regranulation, and the particles that were too small on the screen were recycled as waste. (6) Low-frequency microwave drying and ultrafine grinding A box-type high-frequency microwave dryer was selected, and the equipment is equipped with an online temperature and humidity monitoring system. Spread the egg yolk particles obtained in step (5) evenly on the drying tray (layer thickness 2 cm, avoid particle overlap), and put it into the microwave dryer; set the drying temperature to 55℃, and adjust the microwave power in segments: power 5 kW in the early stage (0-10 minutes) for rapid dehydration; power 3 kW in the later stage (10-25 minutes) for heat preservation and drying, with a total drying time of 25 minutes; During the drying process, the material temperature and humidity are recorded every 5 minutes to ensure that the material temperature does not exceed 60℃ (to avoid fat oxidation and loss of heat-sensitive nutrients). The drying endpoint is judged as follows: the particle moisture content is ≤5% (tested according to GB 5009.3-2016 "National Food Safety Standard Determination of Moisture in Food"), the moisture uniformity is ≤0.5%, and the particles maintain their intact shape without cracking or pulverization. The dried egg yolk granules were fed into a grinder, with a grinding pressure of 0.8 MPa and a classifying wheel speed of 15,000 r / min. The particle size of the ground powder was controlled to be ≤100μm (measured by a laser particle size analyzer, D90≤100μm). The ground salted egg yolk powder was then sieved through a 300-mesh sterile sieve to remove a small amount of incompletely ground coarse particles. The sieved powder was then transferred to a sterile mixer (speed 80 r / min) and mixed for 8 minutes to ensure uniform particle size. Finally, the powder was vacuum-packed in sterile aluminum foil bags (vacuum degree ≤-0.09MPa) and stored in a cool, dry place (temperature ≤25℃, relative humidity ≤60%).

[0042] Comparative Example 1: The only difference from Example 1 is that no alcohol is added in step (2), while the other parameters and conditions are the same as in Example 1.

[0043] Comparative Example 2: The only difference from Example 1 is that the high-speed centrifugation step (4) is deleted, while the other parameters and conditions are the same as in Example 1.

[0044] Comparative Example 3: The only difference from Example 1 is that step (4) of adding 20% ​​salted duck egg yolk oil is deleted, while other parameters and conditions are the same as in Example 1.

[0045] Comparative Example 4: The only difference from Example 1 is that step (4) “selecting a continuous high-frequency microwave curing device (power 9 kW)” is changed to “selecting a continuous high-frequency microwave curing device (power 5 kW)”, while the other parameters and conditions are the same as in Example 1.

[0046] Comparison of experimental test results between Example 1 and Comparative Examples 1-4: (1) Oil yield Example 4 > Comparative Example 4 > Comparative Example 1 > Comparative Example 2 > Comparative Example 3

[0047] like Figure 1As shown, the oil yield of salted egg yolks after pickling shows a trend of Example 4 > Comparative Example 4 > Comparative Example 1 > Comparative Example 2 > Comparative Example 3, fully demonstrating the core necessity of the key steps in the examples for improving the oil yield. Essentially, it involves breaking down the core barrier to oil seepage from the egg yolk through the synergistic effect of multiple steps. From Figure 2 The state of the cooked egg yolk liquid also shows that the oil yield of Example 4 is significantly higher than that of other samples, with a high oil separation rate and a perfect water-in-oil state. The difference in oil yield is due to the different degrees of damage to the egg yolk membrane structure, the demulsification efficiency of the emulsion system, and the different oil exudation dynamics. The optimized parameters and composite induction strategy used in Example 4 form a systematic advantage.

[0048] Comparative Example 4, due to its low microwave cooking power, could only slightly damage the yolk membrane structure and could not provide sufficient channels for oil exudation. Therefore, its oil yield was lower than that of Example 4 but higher than that of other control groups that did not use the core induction steps. Comparative Example 1 did not add alcohol, thus lacking the induction effect of alcohol in reducing the surface tension of oil and promoting the release of oil from the protein matrix, resulting in a significant decrease in oil yield. Comparative Example 2 did not undergo high-speed centrifugation, so it was impossible to accelerate the demulsification of the emulsion system inside the yolk through mechanical force. The binding state between oil and protein was difficult to dissociate quickly, resulting in a significant reduction in oil yield efficiency. Comparative Example 3 did not add egg yolk oil for emulsification induction, thus lacking the affinity induction effect of similar oils and being unable to further break the binding between oil and the internal components of the yolk, resulting in the lowest oil yield. In contrast, Example 4 demonstrates that its optimized microwave cooking power effectively disrupts the yolk membrane barrier, the addition of alcohol induces oil exudation through chemical means, high-speed centrifugation provides the mechanical power for demulsification, and the emulsification of egg yolk oil enhances oil release. These multiple steps work together to construct an efficient oil exudation pathway, which is the core reason why its oil yield is significantly higher than that of the control groups. This fully proves that the synergistic application of the key steps in the example is a necessary condition for improving the oil yield of salted egg yolks after pickling, and none of them can be omitted.

[0049] (2) Color difference like Figure 2 As shown, in color difference analysis (especially analysis based on the CIELAB color space), L a b These are three core parameters used to quantitatively describe the visual perception characteristics of color. They correspond to different dimensions of lightness and hue / saturation. Among them, L... Indicates the lightness or darkness of a color, reflecting the human eye's perception of whether a color is bright or dark; a This indicates the degree of color shift in the red-green direction, reflecting the hue tendency of the color; the larger the positive value, the more saturated the red. This indicates the degree of color shift in the yellow-blue direction, also reflecting the hue tendency of the color; the larger the positive value, the more saturated the yellow. During the ripening process of salted egg yolk slurry, oil release and Maillard reactions cause color changes. Theoretically, samples with higher oil release and better flavor will show decreased brightness, decreased yellowness, and increased redness. The results show a significant inverse trend in the color difference data of salted egg yolks after separation from the shell: redness values ​​are Example 4 > Comparative Example 1 > Comparative Example 2 > Comparative Example 3 > Comparative Example 4, while yellowness values ​​are Example 4 < Comparative Example 1 < Comparative Example 2 < Comparative Example 3 < Comparative Example 4. This trend is deeply correlated with the change in oil release rate, directly confirming the necessity of increasing oil release rate in the key steps of the examples. The core of the color difference stems from the regulatory effect of the degree of yolk membrane damage and emulsification / demulsification efficiency on oil exudation and pigment status: high or low redness values ​​are positively correlated with the enrichment of pigments such as carotenoids after oil exudation and the degree of Maillard reaction; high yellowness values ​​indicate insufficient oil exudation, with pigments encapsulated by the protein matrix or not effectively transformed. Comparative Example 4, due to its low microwave cooking power, only slightly damaged the yolk membrane, failing to provide sufficient channels for oil exudation. As a result, the oil and pigment were difficult to separate, leading to the lowest redness value and the highest yellowness value, corresponding to the worst oil extraction efficiency. Comparative Example 3, lacking egg yolk oil emulsification induction, could not break the bond between the oil and yolk components through the affinity of similar oils, resulting in insufficient demulsification, hindered oil exudation, and a lower redness value compared to the previous group while the yellowness value increased. Comparative Example 2 lacked a high-speed centrifugation step, lacking mechanical force to accelerate the dissociation of the emulsion system, resulting in low oil release efficiency, insufficient pigment enrichment and conversion, and a further decrease in redness value. Comparative Example 1, without added alcohol, lacked the chemical induction effect of reducing oil surface tension, resulting in a lower oil extraction effect than Example 4, with a slightly lower redness value and a slightly higher yellowness value. Example 4 constructs an efficient oil extraction pathway by optimizing the synergistic effects of microwave cooking, alcohol addition, high-speed centrifugation, and egg yolk oil emulsification induction. This allows the oil to fully seep out, driving pigment enrichment and transformation, ultimately resulting in high redness and low yellowness. This fully demonstrates that the synergistic application of key steps is a necessary condition for improving the oil extraction rate. The absence of any step will lead to a decrease in oil extraction efficiency, which in turn will cause a reverse deterioration in the color difference index.

[0050] (3) Sensory rating Flavor: It has a balanced saltiness, a rich oily aroma, and no unpleasant odors; Appearance: The egg yolk powder is orange-yellow both inside and out, with a uniform internal and external structure, an oily feel, and no voids; Hardness: The egg yolk has a relatively soft texture and uniform hardness; Sandy texture: The egg yolk has a distinct sandy texture with clearly defined grains.

[0051] Table 2 Sensory Rating Table

[0052] The sensory evaluation results of the salted egg yolks after being separated from the shell showed a trend of Example 4 > Comparative Example 4 > Comparative Example 1 > Comparative Example 2 > Comparative Example 3. Among them, the values ​​of core evaluation indicators such as flavor, hardness, and looseness fluctuated synchronously with the group changes, which fully confirmed the necessity of the key steps of the examples in improving the sensory characteristics of salted egg yolks. Its essence is to optimize the internal structure of the egg yolk and the generation of flavor substances through multi-step synergistic optimization. The differences in sensory characteristics stem from the regulatory effects of key steps on yolk membrane disruption, emulsification and demulsification efficiency, and flavor compound enrichment: Comparative Example 4, due to its low microwave cooking power, only slightly damaged the yolk membrane, resulting in insufficient oil exudation. This not only led to insufficient formation of flavor compounds (such as sulfur-containing compounds and heterocyclic compounds) but also resulted in a hard yolk texture and a lack of looseness, thus its sensory score was lower than that of Example 4. Comparative Example 1, lacking the addition of alcohol, missed the effect of alcohol in reducing the surface tension of oil and promoting the release of flavor compounds, resulting in insufficient yolk flavor intensity. Its sensory performance was weaker than Example 4 but better than the groups that lacked the key steps. Comparative Example 2, lacking high-speed centrifugation, lacked the mechanical force to accelerate the dissociation of the emulsion system. The oil and protein were tightly bound, resulting in a sticky yolk texture and poor looseness. At the same time, the release of flavor compounds was hindered, further reducing the sensory score. Comparative Example 3, lacking the addition of egg yolk oil to induce emulsification, could not enhance the demulsification effect through the affinity of similar oils. It had the least oil exudation, the weakest flavor, and a hard texture without looseness, ultimately resulting in the lowest sensory score. Example 4, through the synergistic effect of optimizing microwave cooking power, adding alcohol, high-speed centrifugation, and inducing emulsification of egg yolk oil, ensured both appropriate disruption and sufficient demulsification of the yolk membrane, allowing for ample oil exudation and enrichment of flavor compounds, and precisely controlled the yolk's firmness and sandiness, achieving optimal sensory indicators. This result fully demonstrates that the synergistic application of key steps in the example is a necessary condition for improving the sensory characteristics of salted egg yolks; the absence of any step will lead to a significant deterioration in sensory quality.

[0053] (4) Electronic nose like Figure 3As shown, the PCA results revealed significant differences in the distribution of the salted egg yolk samples from Example 4, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 within the two-dimensional space defined by PC1 (47.3% contribution rate) and PC2 (20.1% contribution rate). Example 4 (black) was concentrated in the negative PC1 region (left side), clearly separated from other samples; Comparative Example 1 (red) and Comparative Example 3 (green) were located in the positive PC1 region (right side), but were further distinguished by PC2, with Comparative Example 3 leaning more towards the positive PC2 direction (above). The distribution of Comparative Example 4 (blue) lay between that of Comparative Example 1 and Comparative Example 3, partially overlapping with both, but with an independent center position, suggesting that its characteristics may lie between these two groups. The gray, red, green, and blue ellipses (95% confidence intervals) represent the degree of variation within each group. Example 4 has the smallest dispersion, while the comparative example has a wider distribution range, indicating that there is a certain degree of heterogeneity within the group. This shows that the examples and the comparative examples have significant differences in flavor. Each step in the patent claim specification has an important coupling relationship in forming a better salted egg yolk flavor, and none of them can be omitted.

[0054] (5) Volatile compound test Table 3. Major volatile compounds in Example 4

[0055] Currently, studies have demonstrated that various aldehydes, such as hexanal, nonanal, benzaldehyde, trans-2-octenal, 3-methylbutanal, 3-methylthiopropanal, and trans, trans-2,4-decadienal, are key volatile flavor compounds in egg yolk oil and powder. 1-Octen-3-one is one of the main sources of aroma in egg yolk powder. Alcohols include benzyl alcohol. Aromatic compounds detected in salted egg yolks mainly include phenol, indole, xylene, and m-xylene. Since most compounds containing benzene rings have aroma and low flavor thresholds, they significantly contribute to the flavor of cooked egg yolks. 2,5-Dimethylpyrazine (roasted nut flavor) and 5-methyl-2-ethylpyrazine (fruity aroma) have been identified as key volatile flavor compounds in egg yolk powder.

[0056] After processing the samples according to the examples, the gas chromatography-mass spectrometry (GC-MS) data were processed, and the average content and standard deviation of the main volatile flavor compounds were calculated and recorded. Volatile compounds with relatively high abundance included 2-pentyl-furan, hexanal, nonanal, 2-methylcyclopentanone, benzaldehyde, (E)-2-octenal, and (E)-2-heptenal. The volatile compound spectrum of the deshelled salted egg yolk powder showed a high degree of similarity to that of natural salted duck egg yolk, with a high overlap of core flavor compounds. 2-pentyl-furan is the signature aroma component of salted duck egg yolk, generated by the oxidative cracking of unsaturated fatty acids in the yolk, giving the product a unique nutty and oily aroma. It has the highest abundance in the salted egg yolk powder, matching the core flavor characteristics of natural egg yolk. Saturated fatty aldehydes such as hexanal and nonanal, as well as unsaturated fatty aldehydes such as (E)-2-heptenal and (E)-2-octenal, are also key components shared by both. These substances originate from lipid oxidation and contribute to the oily flavor and slight roasted aroma of the egg yolk powder. 2-Methylcyclopentanone and benzaldehyde impart a faint ketone aroma and a subtle fragrance to the powder products, which are consistent with the flavor profile of natural salted duck egg yolks, and can be used as high-quality substitutes for natural salted duck egg yolks.

[0057] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A method for preparing salted egg yolk powder using differential frequency microwave cooking, characterized in that: The preparation method includes the following steps: S1: Pre-treat the egg yolks to obtain egg yolk liquid; S2: Preparation of salted egg yolk liquid; S3: Preparation of egg yolk curdling solution; S4: The egg yolk curing liquid is subjected to high-speed centrifugation and high-frequency microwave cooking to obtain oily egg yolk particles. S5: Rotary granulation of the oily egg yolk particles; S6: Perform low-frequency microwave drying and ultra-fine pulverization.

2. The method for preparing salted egg yolk powder using differential frequency microwave cooking according to claim 1, characterized in that: S1 includes the following steps: S11: Select fresh eggs that are free from damage, mold, and odor, with a yolk index ≥ 0.40 and Haugh unit ≥ 72, and remove unqualified eggs with broken shells, broken yolks, or spoilage. S12: Rinse qualified eggs under running water at 35-40℃ for 3-5 minutes, then immerse them in a sodium hypochlorite solution with a concentration of 50-100mg / L for 2-3 minutes. After rinsing with sterile distilled water to remove residual disinfectant, drain the surface water in a sterile environment. S13: Separate egg yolks and egg whites using aseptic manual separation method or automatic egg liquid separator; S14: Transfer the separated egg yolk liquid into a sterile mixing jar, and use a paddle mixer to mix at low speed. Set the mixing speed to 60-100 r / min and the mixing time to 8-12 minutes to obtain egg yolk liquid.

3. The method for preparing salted egg yolk powder using differential frequency microwave cooking according to claim 1, characterized in that: S2 includes the following steps: S21: Select standard refined salt and edible alcohol; S22: According to the mass fraction of egg yolk liquid, first add 2-5% edible salt to the egg yolk liquid obtained in S1, turn on the mixer, the speed is 100-150r / min, stir for 5-8 minutes until the salt is completely dissolved, then slowly add 20-30% edible alcohol, and continue stirring for 10-15 minutes. During the stirring process, control the temperature inside the mixing bowl to 20-25℃. S23: After stirring, the mixture is homogenized once by passing it through a colloid mill with a grinding gap of 0.05-0.1 mm and a rotation speed of 3000-5000 r / min to obtain egg yolk slurry.

4. The method for preparing salted egg yolk powder using differential frequency microwave cooking according to claim 1, characterized in that: S3 includes the following steps: S31: Use a sterile stainless steel pickling jar with a sealed lid. Before pickling, sterilize it with high-pressure steam at 121℃ for 20 minutes and cool it to room temperature before use. S32: Transfer the egg yolk liquid obtained in S2 into a sterile pickling tank, seal it, and place it in a constant temperature incubator. Control the pickling temperature at 30-45℃ and the pickling time at 16-24 hours. S33: During the marinating process, turn on the mixer every 4-6 hours and stir at low speed for 3-5 minutes, with a speed of 60-80 r / min; S34: The criteria for judging the end point of pickling are: the egg yolk liquid is uniformly milky yellow, with a small amount of oil on the surface, and the viscosity is 30-50% higher than before pickling.

5. The method for preparing salted egg yolk powder using differential frequency microwave cooking according to claim 1, characterized in that: S4 includes the following: A horizontal spiral sedimentation centrifuge was selected, and the inner cavity of the equipment was aseptically cleaned and disinfected before centrifugation. Pump the filtered egg yolk curing liquid into a centrifuge, set the centrifugation speed to 4000-5000 r / min, and the centrifugation time to 15-20 minutes. During the centrifugation process, control the feed temperature to 25-30℃ to obtain salted duck egg yolk oil.

6. The method for preparing salted egg yolk powder using differential frequency microwave cooking according to claim 4, characterized in that: In step S4, the high-frequency microwave curing includes the following steps: S41: Add 15-30% of the solid weight of the egg yolk to the obtained egg yolk liquid, add salted duck egg yolk oil, transfer to a sterile homogenizing tank, and use a high-shear homogenizer at a speed of 10000-15000 r / min for 8-12 minutes. S42: A continuous high-frequency microwave curing device is selected. The device cavity is sterilized. The homogenized mixture is evenly spread on the microwave transmission belt with a thickness of 5-8 mm. The transmission speed is controlled so that the heating time is 2-5 minutes to obtain oily egg yolk particles.

7. The method for preparing salted egg yolk powder using differential frequency microwave cooking according to claim 1, characterized in that: S5 includes the following steps: S51: Select a rotary drum granulator to transfer the cooked egg yolk granules from S4 into the granulator drum. Set the drum speed to 30-50 r / min and the drum tilt angle to 3-5°. At the same time, introduce sterile hot air at 30-40℃ with a wind speed of 0.5-1m / s. S52: The granulated particles are screened by a vibrating screen with sieve apertures of 0.2cm and 0.4cm. Uniform particles of 0.2-0.4cm are collected. Oversized particles on the sieve are returned to the granulator for regranulation, and undersized particles on the sieve are recycled as waste. S53: The screened particles must meet the following requirements: particle size variation coefficient ≤ 10%, and bulk density 0.6-0.8 g / cm³.

8. The method for preparing salted egg yolk powder using differential frequency microwave cooking according to claim 1, characterized in that: In step S6, the low-frequency microwave drying specifically employs the following methods: A box-type low-frequency microwave dryer was selected, equipped with an online temperature and humidity monitoring system. The egg yolk particles obtained from S5 were evenly spread on a drying tray and placed in the microwave dryer. The drying temperature was set to 45-55℃. Microwave power is adjusted in segments: the first 0-10 minutes is for rapid dehydration; the second 10-25 minutes is for heat preservation and drying, with a total drying time of 15-25 minutes. The criteria for determining the drying endpoint are: particle moisture content ≤5%, moisture uniformity ≤0.5%, particles maintain their intact shape, and there is no cracking or pulverization.

9. The method for preparing salted egg yolk powder using differential frequency microwave cooking according to claim 1, characterized in that: In step S6, the ultrafine pulverization specifically employs the following methods: An airflow-type ultrafine pulverizer is selected, with a pulverizing pressure of 0.6-0.8 MPa and a pulverizing chamber temperature of ≤30℃. The equipment is sterilized and cleaned before pulverizing. The crushed salted egg yolk powder is screened through a 300-mesh sterile sieve to remove a small amount of coarse particles that are not completely crushed. The screened powder is then transferred to a sterile mixer and mixed at 60-80 r / min for 5-10 minutes. Finally, it is vacuum-packed in sterile aluminum foil bags and stored in a cool, dry place.

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