A pre-made salted duck egg, salted duck eggs and a rapid pickling method

Abstract

This invention belongs to the field of egg product preparation technology, specifically relating to a pre-prepared salted duck egg, salted duck eggs, and a rapid pickling method. The rapid pickling method for salted duck eggs includes: (1) pre-treating duck eggs by immersing them in an organic acid solution; (2) immersing the pre-treated duck eggs in a pickling solution and pickling them using a vacuum pulsation method to obtain the pre-prepared salted duck egg; wherein, the vacuum pulsation method is: the vacuum degree of the pickling system is periodically alternating between high vacuum degree and low vacuum degree, the high vacuum degree is not higher than -0.08MPa, and the low vacuum degree is not lower than -0.05MPa. This invention, through vacuum pulsation technology combined with organic acid pre-treatment, achieves an oil yield of 66.5% in salted duck egg yolks and a salt content of 7.8% in egg whites within 20 days, and enriches DHA to 1434.2mg / kg and EPA to 78.0mg / kg, realizing a synergistic effect of shortening the pickling cycle and improving product quality.

Description

Technical Field

[0001] This invention belongs to the field of egg product preparation technology, specifically relating to a pre-prepared salted duck egg, salted duck eggs, and a rapid pickling method. Background Technology

[0002] Salted duck eggs are a popular traditional Chinese flavored egg product, whose flavor primarily comes from the slow denaturation of proteins caused by salt penetration and the release of oil from the yolk. Traditional pickling methods mainly include wood ash, mud wrapping, and high-concentration brine soaking. However, traditional processes have many drawbacks: the pickling period is long, as salt penetrates the egg through free diffusion under normal pressure, a slow process that typically takes 40-45 days to reach maturity; the quality is uneven and the oil yield is low, often resulting in overly salty egg whites while the yolk has not yet developed its characteristic "sandy" texture and oiliness, and the yolk oil yield is a key indicator of salted duck egg quality, which traditional methods struggle to disrupt in a short time to release the oil from the yolk emulsion system; the flavor is unsatisfactory, as the traditional pickling environment is limited and not conducive to the formation of flavor compounds such as esters and aldehydes, leading to a flat product flavor; furthermore, if hygiene is not properly controlled during the long pickling process, the eggs are susceptible to microbial contamination, causing spoilage.

[0003] To address the shortcomings of traditional processes, existing technologies attempt to accelerate salt penetration through methods such as heating, ultrasonic assistance, or high-pressure treatment. Heating-based pickling accelerates molecular motion by increasing ambient temperature, shortening the pickling period to 15 days; however, high temperatures can lead to excessive protein denaturation, resulting in a "hard center" in the yolk. Ultrasonic-assisted pickling utilizes the cavitation effect of ultrasound to disrupt the eggshell structure and promote salt penetration; however, ultrasonic treatment alone has limited penetration into deeper tissues, and prolonged ultrasound can cause the egg liquid temperature to become too high, affecting quality. High-pressure pickling alters the permeability of the eggshell and membrane using pressures of 100-300 MPa; however, high-pressure equipment is expensive and requires strict operating conditions, hindering industrial-scale implementation. While these improved technologies shorten the pickling period to some extent, they still suffer from limited penetration efficiency, difficulty in quality control, and high equipment costs.

[0004] Vacuum pulsation technology is a technique that periodically changes environmental pressure by alternating between high and low vacuum levels to promote mass transfer. It has been applied in fields such as fruit and vegetable preservation and meat curing. Its core principle lies in the high vacuum stage, which causes the gas inside the material to expand and release, creating negative pressure that allows the external solution to penetrate the micropores of the material. Then, a rapid transition to low vacuum causes a sudden pressure increase, driving the external solution to penetrate the material more quickly, forming a "pulsating" penetration. However, the application of vacuum pulsation technology in the curing of salted duck eggs has not been reported, especially lacking a dedicated process design tailored to the eggshell structure and yolk oil extraction mechanism of salted duck eggs. Therefore, developing a rapid curing method for salted duck eggs that can significantly shorten the curing cycle while improving yolk oil yield and flavor quality is a pressing technical problem to be solved in this field. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide a pre-prepared salted duck egg, salted duck eggs, and a rapid pickling method.

[0006] To achieve the above objectives, the present invention can adopt the following technical solutions: The present invention provides a rapid pickling method for a pre-prepared salted duck egg product. The rapid pickling method includes: (1) immersing the duck egg in an organic acid solution for pretreatment; (2) immersing the pretreated duck egg in a pickling solution and pickling it using a vacuum pulsation method to obtain the pre-prepared salted duck egg product; wherein, the vacuum pulsation method is: the vacuum degree of the pickling system is periodically alternating between a high vacuum degree and a low vacuum degree, the high vacuum degree is not higher than -0.09MPa, and the low vacuum degree is not lower than -0.04MPa.

[0007] Preferably, in the above-mentioned rapid marinating method, the high vacuum degree is -0.09MPa to -0.08MPa, and the low vacuum degree is -0.05MPa to -0.04MPa.

[0008] Preferably, in the above-mentioned rapid marinating method, the periodic alternation includes: maintaining a high vacuum for 5 to 15 minutes and maintaining a low vacuum for 6 to 10 hours.

[0009] Preferably, in the above-mentioned rapid marinating method, the alternation interval between high vacuum and low vacuum is ≤30 seconds.

[0010] Preferably, in the above-mentioned rapid pickling method, the organic acid solution is a lactic acid solution with a mass fraction of 8% to 12%; and / or the pickling solution is a salt solution with a mass fraction of 18% to 22%.

[0011] More preferably, in the above-mentioned rapid pickling method, the salt solution also contains 0.5% to 1.5% of a spice extract by weight of the salt.

[0012] More preferably, in the above-mentioned rapid marinating method, the spice extract is one or more water extracts or alcohol extracts of star anise, Sichuan pepper, and cinnamon.

[0013] Preferably, in the above-mentioned rapid pickling method, the pretreatment time is 15 to 30 minutes; and / or the pickling temperature is 25°C to 35°C; and / or the total pickling time is 10 to 20 days.

[0014] Another aspect of the present invention provides a pre-processed salted duck egg, which is obtained by pickling using the rapid pickling method of the present invention.

[0015] In another aspect, the present invention provides a salted duck egg, which is obtained by cooking the aforementioned salted duck egg pre-process.

[0016] The beneficial effects of this invention include at least the following: by combining vacuum pulsation technology with organic acid pretreatment, this invention can achieve an oil yield of 66.5% in salted duck egg yolks and a salt content of 7.8% in egg whites within 20 days, and enrich DHA to 1434.15 mg / kg and EPA to 78.03 mg / kg, thus achieving a synergistic effect of shortening the pickling cycle and improving product quality. Attached Figure Description

[0017] Figure 1 Images of egg yolks under different pickling conditions; Figure 2 Heatmaps showing the differences in flavor compounds in egg yolks under different curing conditions. Detailed Implementation

[0018] The embodiments described are provided to better illustrate the present invention, but are not intended to limit the scope of the invention to the embodiments described. Therefore, non-essential improvements and adjustments made to the embodiments by those skilled in the art based on the above description are still within the scope of protection of the present invention.

[0019] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. Singular expressions include plural expressions unless they have a distinct meaning in the context. As used herein, it should be understood that terms such as “comprising,” “having,” “including,” are intended to indicate the presence of features, numbers, operations, components, parts, elements, materials, or combinations thereof. The terminology of the invention is disclosed in the specification and is not intended to exclude the possibility that one or more other features, numbers, operations, components, parts, elements, materials, or combinations thereof may be present or added. As used herein, “ / ” may be interpreted as “and” or “or,” depending on the context.

[0020] In a first aspect, embodiments of the present invention provide a rapid pickling method for a pre-prepared salted duck egg product. The rapid pickling method includes: (1) immersing the duck egg in an organic acid solution for pretreatment; (2) immersing the pretreated duck egg in a pickling solution and pickling it using a vacuum pulsation method to obtain the pre-prepared salted duck egg product; wherein, the vacuum pulsation method is: the vacuum degree of the pickling system is periodically alternating between a high vacuum degree and a low vacuum degree, the high vacuum degree being no higher than -0.09 MPa and the low vacuum degree being no lower than -0.04 MPa.

[0021] It should be noted that this invention uses fresh duck eggs as raw material. After cleaning and grading, the eggs are placed in a specially prepared pickling solution and pickled using a vacuum pulsation method. By controlling the vacuum level and performing periodic pulsations, the negative pressure environment increases the permeability of the eggshell and shell membrane, as well as the osmotic pressure difference between the inside and outside, accelerating the migration of salt into the egg and the release of lipids from the yolk. This method significantly shortens the pickling period. After 20 days of pickling, the yolk oil yield is significantly higher than that of traditional atmospheric pressure pickling, and the egg white salt content is moderate. At the same time, the vacuum environment promotes the accumulation of umami amino acids, polyunsaturated fatty acids, and the formation of volatile flavor substances such as aldehydes and esters, giving the salted duck eggs a unique and mellow flavor. This invention has a simple and efficient process, effectively solving the problems of long pickling time, low oil yield, and monotonous flavor in traditional salted duck eggs.

[0022] In some specific examples, the high vacuum degree in the above-mentioned rapid marinating method is -0.09MPa to -0.08MPa, and the low vacuum degree is -0.05MPa to -0.04MPa.

[0023] It should be noted that controlling the high vacuum degree at -0.09MPa to -0.08MPa and the low vacuum degree at -0.05MPa to -0.04MPa can create a stable and sufficient pressure difference without breaking the eggshell, allowing the salt to penetrate into the egg quickly and evenly. At the same time, it avoids excessive pressure fluctuations that could damage the egg liquid structure, thus ensuring uniform pickling and stable product quality.

[0024] In some specific examples, the periodic alternation in the above-mentioned rapid marinating method includes: maintaining a high vacuum for 5 to 15 minutes and maintaining a low vacuum for 6 to 10 hours.

[0025] It should be noted that maintaining a high vacuum for 5 to 15 minutes can quickly expel gas from the egg and open the eggshell membrane channels; maintaining a low vacuum for 6 to 10 hours allows salt to fully diffuse and penetrate during the pressure equilibrium stage. The combination of these two processes can achieve "pulsed mass transfer," significantly improving salt penetration efficiency and the speed of yolk oil extraction, while ensuring that the salt content of the egg white is moderate.

[0026] In some specific examples, the interval between alternating high and low vacuum levels in the above-mentioned rapid marinating method is ≤30 seconds.

[0027] It should be noted that rapid switching of vacuum levels can maintain the continuity of pressure difference and avoid a decrease in the penetration driving force due to slow switching. This ensures that salt can continuously and efficiently enter the egg, further improving the pickling speed and ensuring the yolk oil yield and flavor substance accumulation.

[0028] In some specific examples, in the above-mentioned rapid pickling method, the organic acid solution is a lactic acid solution with a mass fraction of 8% to 12%; and / or the pickling solution is a salt solution with a mass fraction of 18% to 22%.

[0029] It should be noted that 8% to 12% lactic acid solution can gently expand the micropores of the eggshell, improve permeability, and not damage the eggshell structure; 18% to 22% salt solution is a mature and stable pickling concentration, which can ensure sufficient osmotic pressure and prevent the protein from being too salty due to excessive salt concentration, so that the final salted duck egg has a moderate saltiness and excellent taste.

[0030] In some specific examples, the above-mentioned rapid pickling method also includes 0.5% to 1.5% of spice extract by weight of salt in the salt solution.

[0031] It should be noted that adding 0.5% to 1.5% of spice extract can slowly release flavor substances during the pickling process, reacting with lipids and amino acids in the egg to promote the formation of flavor substances such as aldehydes and esters, making the salted duck egg more mellow and fragrant, thus solving the problem of the monotonous flavor of traditional salted duck eggs.

[0032] In some specific examples, the spice extracts in the above-mentioned rapid marinating method are one or more water extracts or alcohol extracts of star anise, Sichuan pepper, and cinnamon.

[0033] It should be noted that the water or alcohol extracts of star anise, Sichuan pepper, and cinnamon are highly safe and have a pure flavor. They can penetrate into the egg more easily under vacuum pulsation conditions, and work synergistically with the egg yolk lipids to form a rich and complex aroma, thus enhancing the overall flavor and quality of the salted duck egg.

[0034] Preferably, in the above-mentioned rapid pickling method, the pretreatment time is 15 to 30 minutes; and / or the pickling temperature is 25°C to 35°C; and / or the total pickling time is 10 to 20 days.

[0035] It should be noted that a 15-30 minute pretreatment can fully open the micropores of the eggshell; a pickling temperature of 25-35℃ can accelerate molecular movement and salt diffusion, while avoiding protein denaturation caused by high temperature; and a pickling cycle of 10-20 days is much shorter than the traditional process of more than 40 days, and can achieve high oil yield, moderate salt content and excellent flavor in 20 days.

[0036] Secondly, embodiments of the present invention provide a pre-processed salted duck egg, which is obtained by pickling using the rapid pickling method of the present invention.

[0037] It should be noted that the salted duck egg pre-processed product has a uniform salt distribution, and the yolk has fully demulsified and released lipids, possessing high oil yield potential. At the same time, it has accumulated rich umami amino acids, polyunsaturated fatty acids, and volatile flavor substances. High-quality salted duck eggs can be obtained simply by boiling.

[0038] Thirdly, embodiments of the present invention provide a salted duck egg, which is obtained by cooking the aforementioned salted duck egg pre-process.

[0039] It should be noted that the salted duck eggs made from this pre-made product have a high oil yield and good sandiness in the yolks, and the egg whites have a moderate saltiness, rich flavor, and are rich in polyunsaturated fatty acids such as DHA and EPA. The quality is significantly better than traditional atmospheric pressure pickled products. At the same time, the pickling cycle is greatly shortened, making it suitable for industrial production.

[0040] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below.

[0041] Preparation Example Example 1 (1) Selection, cleaning and decontamination of fresh duck eggs: Use an egg candling device to remove eggs with broken yolks, black spots and broken eggs. Select fresh duck eggs without cracks, wash the surface dirt with clean water and drain the water for later use.

[0042] (2) Sterilization: After washing, the duck eggs are soaked in high-proof liquor for 10 minutes to kill most of the microorganisms.

[0043] (3) Organic acid pretreatment: The sterilized duck eggs are immersed in a 10% lactic acid solution for 20 minutes to enlarge the micropores of the eggshell without damaging the integrity of the eggshell.

[0044] (4) Preparation of pickling solution: Prepare a 20% salt solution by mass, and add 1% spice extract by mass. The spice extract is an alcoholic extract of nutmeg, clove, and ginger. The specific preparation method is as follows: Mix and crush nutmeg, clove, and ginger in a mass ratio of 1:1:2, add 5 times their total mass of 75% ethanol solution, reflux extract at 60 °C for 2 hours, filter, concentrate under reduced pressure to recover ethanol until there is no ethanol odor, and obtain the solution. Boil to sterilize and cool to room temperature to use as the base pickling solution.

[0045] (5) Vacuum pulse pickling: The pretreated duck eggs are immersed in the pickling solution and placed in a vacuum pickling tank. The liquid level of the pickling solution after the duck eggs are immersed is controlled at 50% to 70% of the height of the pickling tank. During the pickling process, the system is first evacuated to -0.09MPa and maintained for 10 minutes. Then, the pressure is rapidly reduced to -0.04MPa within 15 seconds and maintained for 8 hours. This process is repeated for pickling. The pickling time is 20 days and the pickling temperature is controlled at 30℃.

[0046] (6) Cleaning and cooking: After the salted duck eggs are pickled, wash off the surface salt with clean water, put them into drinking water that has been filtered to remove impurities, bring to a boil, continue cooking for 15 minutes after the water boils, and then cool to obtain the product.

[0047] Example 2 Example 2 is basically the same as Example 1, except that the pickling time in step (5) is different, while the other steps and parameters are the same as in Example 1; wherein, the pickling time in Example 2 is 10 days.

[0048] Example 3 Example 3 is basically the same as Example 1, except that the mass fraction of lactic acid is different in step (3), while the other steps and parameters are the same as in Example 1; wherein, the mass fraction of lactic acid in Example 3 is 8%.

[0049] Example 4 Example 4 is basically the same as Example 1, except that the mass fraction of lactic acid is different in step (3), while the other steps and parameters are the same as in Example 1; wherein, the mass fraction of lactic acid in Example 4 is 12%.

[0050] Example 5 Example 5 is basically the same as Example 1, except that the vacuum negative pressure range in step (5) is different, while the other steps and parameters are the same as in Example 1; wherein, the high vacuum degree of Example 5 is -0.08MPa and the low vacuum degree is -0.05MPa.

[0051] Example 6 Example 6 is basically the same as Example 1, except that the vacuum negative pressure range in step (5) is different, while the other steps and parameters are the same as in Example 1; wherein, the high vacuum degree of Example 6 is -0.09MPa and the low vacuum degree is -0.05MPa.

[0052] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that in step (5) of Comparative Example 1, it is sealed and pickled for 20 days under normal pressure (i.e. 0 MPa) without vacuum pulsation operation. Other steps and parameters are the same as in Example 1.

[0053] Comparative Example 2 Comparative Example 2 is basically the same as Example 1, except that in step (5) of Comparative Example 1, it is sealed and pickled at normal pressure (i.e. 0 MPa) for 10 days without vacuum pulsation operation. Other steps and parameters are the same as in Example 1.

[0054] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that the organic acid pretreatment in step (3) is omitted, and the sterilized duck eggs are directly immersed in the pickling solution for vacuum pulsating pickling in step (5). Other steps and parameters are the same as in Example 1.

[0055] Comparative Example 4 Comparative Example 4 is basically the same as Example 1, except that in step (5), a continuous constant negative pressure is used for pickling: after the system is evacuated to -0.09MPa, the negative pressure is maintained for 20 days without pulsating pressure change process. Other steps and parameters are the same as in Example 1.

[0056] Comparative Example 5 (1) Selection, cleaning and decontamination of fresh duck eggs: Use an egg candling device to remove eggs with broken yolks, black spots and broken eggs. Select fresh duck eggs without cracks, wash the surface dirt with clean water and drain the water for later use.

[0057] (2) Cleaning and cooking: Put the cleaned fresh duck eggs into the filtered drinking water, bring to a boil, continue cooking for 15 minutes after boiling, and then cool to obtain the product.

[0058] Related tests (1) Determination of oil yield from egg yolk After grinding the egg yolks evenly, take 3g and add 35mL of n-hexane-isopropanol (3:2) reagent. Homogenize at room temperature for 5min, filter into a beaker, and concentrate the filtrate by evaporation in a 100℃ water bath. Then dry in a 105℃ oven to constant weight. The difference in weight of the beaker before and after drying is the total lipid content (M1). Take another 3g of evenly ground egg yolks and add 35mL of distilled water to homogenize. Centrifuge at 4000rpm for 20min, collect the supernatant, add 30mL of n-hexane-isopropanol (3:2) reagent to dissolve the suspension, shake well, and let stand for 5min to separate the layers. Transfer the upper lipid layer to a beaker, concentrate by evaporation in a boiling water bath, and dry in a 105℃ oven to constant weight. The difference in weight of the beaker before and after drying is the free lipid content (M2). Egg yolk oil yield = 100% × M2 / M1.

[0059] The oil yield of salted duck eggs prepared in the examples and comparative cases was tested according to the above test methods. Actual images of the egg yolks under different pickling conditions are shown below. Figure 1 As shown in Table 1, the results of the egg yolk oil yield test are as follows.

[0060] Table 1. Yolk oil yield of salted duck eggs prepared in the examples / comparative examples.

[0061] Table 1 shows that the egg yolk oil yield of Example 1 of the present invention was 66.5±1.2%, which was significantly higher than that of Comparative Example 1 (59.2±1.2%), which was cured under normal pressure for 20 days, and Comparative Example 2 (42.1±1.5%), which was cured under normal pressure for 10 days. P <0.05). Among them, Example 4 (12% lactic acid pretreatment) had the highest oil yield, reaching 67.1±1.4%, which was not significantly different from Example 1, but significantly higher than Example 3 (8% lactic acid pretreatment, 63.2±1.5%). This indicates that appropriately increasing the concentration of organic acids can more effectively soften and expand the microporous structure of the eggshell surface, thereby accelerating the rate of salt penetration into the egg under the action of vacuum pulsating pressure, promoting the removal of water and release of lipids from the yolk.

[0062] Furthermore, the oil yields of Comparative Example 3 (52.1 ± 1.8%) without organic acid pretreatment and Comparative Example 4 (48.5 ± 1.5%) using continuous constant negative pressure were significantly lower than those of Example 1. This indicates a significant synergistic effect between "mild organic acid etching pretreatment" and "vacuum pulsed pressure-switching mass transfer". In contrast, the single constant negative pressure (Comparative Example 4) resulted in poor convective mass transfer of the pickling solution in the micropores of the egg due to the lack of "pumping mass transfer effect" formed by periodic pressure changes, leading to a significant decrease in salt penetration and lipid release efficiency.

[0063] (2) Determination of protein salt content The salt content of egg white was determined by silver nitrate titration: A suitable amount of egg white, weighed as m, was homogenized with an appropriate volume of pure water (V1). Potassium chromate was added as a titration indicator. The titration was completed with a standard silver nitrate solution (concentration C) until a brick-red precipitate appeared, which was the titration endpoint. The volume of silver nitrate standard solution consumed, V2, was recorded. Therefore, the salt content of the egg white = 100% × M × C × V2 / (m × V1). Where M is the molar mass of sodium chloride, taken as 58.44 g / mol, used to convert the number of moles consumed in the titration into the mass of sodium chloride.

[0064] The salt content of the egg whites prepared in the examples and comparative examples was tested according to the above test methods, and the test results are shown in Table 2.

[0065] Table 2. Salt content of the salted duck eggs prepared in the examples / comparative examples.

[0066] Table 2 shows that the protein salt content of Example 1 was 7.8±0.3%, significantly higher than that of Comparative Example 1 (6.5±0.2%) under normal pressure for the same period. The protein salt content of Example 2 (cured for 10 days) reached 5.2±0.2%, significantly exceeding that of Comparative Example 2 (cured under normal pressure for 10 days) (4.1±0.3%). The experimental data indicate that vacuum pulse curing, through the periodic alternation of high and low vacuum, reconstructs a dynamic pressure gradient inside and outside the eggshell, forcibly driving high-concentration brine to permeate into the egg through the pores of the eggshell. Examples 5 and 6, due to reduced high vacuum or narrowed pressure range, showed a slower salt permeation rate compared to Example 1, but were still significantly better than the normal pressure group. Comparative Example 3, lacking the gentle loosening effect of lactic acid on the calcium carbonate matrix of the eggshell, suffered from hindered salt permeation, resulting in a protein salt content of only 5.5±0.4%, further confirming the technological advancement of this invention in salt control and rapid curing.

[0067] (3) Determination of protein conductivity Accurately weigh 2g of cooked protein, add 30mL of double-distilled water, homogenize at 7000rpm for 1min using a high-speed disperser, then thoroughly break down the protein particles with an ultrasonic homogenizer until the solution is clear and free of suspended matter. After standing at room temperature for 1h, the conductivity of the solution is measured using a conductivity meter (Leici DDS-11A, Shanghai). Before the measurement, the conductivity meter probe is calibrated with a 1408μs / cm standard solution.

[0068] The protein conductivity of the salted duck eggs prepared in the examples and comparative examples was tested according to the above test methods. The test results are shown in Table 3. The results show that the conductivity measurement results are consistent with the trend of salt content changes, further verifying the effect of salt penetration. The highest conductivity was observed in Examples 4 and 1, reaching 12.65±0.95 ms / cm and 12.25±0.87 ms / cm, respectively, indicating that the concentration of free sodium and chloride ions in their proteins was the highest and the electrolyte distribution was uniform. The conductivity of Comparative Example 3 (acid-free treatment) and Comparative Example 4 (constant negative pressure) was significantly lower than that of Example 1 ( P The value <0.05 indicates that, in the absence of pulsating pressure differentials and micropore channel expansion, salt has difficulty penetrating the eggshell membrane and yolk membrane barrier, resulting in a low ion concentration within the egg white. This data further confirms that the rapid pickling method in this invention can significantly improve the rate of material transfer within the egg product.

[0069] Table 3. Protein conductivity of salted duck eggs prepared in the examples / comparative examples

[0070] (4) Analysis of volatile flavor compounds in egg yolk Headspace solid-phase microextraction (HS-SPME) combined with gas chromatography-mass spectrometry (GC-MS) was used for analysis. Volatile components were enriched using a divinylbenzene / carbon molecular sieve / polydimethylsiloxane (DVB / CAR / PDMS) fiber (50 / 30 μm; Supelco, USA). Before use, the fiber was inserted into the GC inlet and activated at 250 °C. The headspace solid-phase microextraction procedure was as follows: 5 g of fresh egg yolk was placed in a 20 mL screw-cap glass vial and incubated at 50 °C for 50 min to enrich volatile components, followed by desorption directly into the GC inlet.

[0071] Chromatographic conditions: An Agilent 7890A / 5975C series gas chromatograph (Agilent Technologies) with a flame ionization detector (FID) was used, employing a DB-WAX capillary column (30m × 0.25mm inner diameter, 0.25μm film thickness, Agilent Technologies). The fiber was injected into the injection port, and desorption was performed at 250℃ in splitless mode for 5 min. The injection port temperature was 250℃, and the mass spectrometer detector temperature was 260℃. The carrier gas was high-purity helium with a purity ≥99.999% and a pressure of 7.07 Psi. The temperature program was as follows: initial temperature 40℃, held for 2 min, increased to 230℃ at a rate of 5℃ / min, and held at 230℃ for 10 min. Mass spectrometry used an electron impact ionization source with an ionization voltage of 70 eV, an ionization source temperature of 250℃, a scan range of 30-500 m / z, and a scan time of 0.69 s. Qualitative analysis of volatile components was completed by comparing the mass spectra with standard spectra in the NIST mass spectrometry library; the relative percentage content of each volatile component was calculated using the area normalization method, and the log2FoldChange value was calculated by comparing it with the control group.

[0072] The volatile flavor compounds of salted duck egg yolks prepared in the above-described test methods were tested in the examples and comparative examples. Comparative Example 5 was used as a control. The test results are as follows: Figure 2As shown, GC-MS analysis revealed that Example 1 was significantly superior to the comparative group in terms of flavor composition and content: the relative content of esters (such as 2-ethylhexyl dihydrogen ester, isobutyl 2-hydroxybenzoate, etc.) was much higher than that of Comparative Example 3 (acid-free treatment), Comparative Example 4 (constant negative pressure), etc. The synergistic effect of vacuum pulsed pressure pickling and organic acid pretreatment not only promoted the esterification reaction of free fatty acids and alcohols in egg yolk, but also protected easily oxidized esters in a vacuum-oxygen-deficient environment, giving the product a rich and complex fruity aroma; hydrocarbons and Aromatic hydrocarbons (such as cyclopentene and 4,4'-dimethylbiphenyl) were significantly more enriched in Example 1 than in the comparative group. This is due to the mild degradation and rearrangement of lipids, which can reduce the muddy taste and enhance the fullness of the flavor. Aldehydes (such as 2,4-dimethylbenzaldehyde and hexylcinnamaldehyde), phenols (such as 2,4,6-tri-tert-butylphenol) and heterocyclic compounds (such as benzothiazole) were present in moderate amounts in Example 1 and no excessive oxidized halogen aldehydes were detected. This ensured the aroma of fat and nuts, while also giving it a unique roasted aroma and a sandy, salty taste. Compared to Comparative Example 3 (acid-free pretreatment) and Comparative Example 4 (constant negative pressure), the abundance of most flavor compounds in Example 1 far exceeded that of the comparative examples, confirming the synergistic effect of vacuum pulsed pressure variation and organic acid pretreatment: organic acids weaken the eggshell and eggshell membrane structure, vacuum pulsed pump-type mass transfer accelerates salt penetration and flavor precursor release, and at the same time, instantaneous negative pressure degassing locks in aroma and controls oxidation, ultimately making the salted egg yolk fat aroma, fruit aroma and complex roasted aroma of Example 1 far superior to those of traditional processes.

[0073] In addition, the flavor characteristics of the salted duck eggs prepared in the examples and comparative examples were tested. The specific evaluation method was as follows: an evaluation team composed of 10 people (5 men and 5 women) who had received professional sensory evaluation training conducted blind tests on the cooked salted duck eggs in a standard tasting room. The evaluators were required to provide a comprehensive description from the dimensions of saltiness, yolk texture, and aroma (alcoholic aroma, ester aroma, fruity aroma, etc.). The results are shown in Table 4 below.

[0074] Table 4 Flavor characteristics of salted duck eggs prepared in the examples / comparative examples

[0075] (5) Determination of free fatty acids in egg yolk Lipid extraction was performed using a solvent extraction-methyl esterification derivatization method combined with gas chromatography-mass spectrometry (GC-MS). 0.5 g of egg yolk powder was weighed into a 20 mL stoppered test tube, and 5 mL of a chloroform-methanol mixture (2:1 volume) was added for lipid extraction. After sonication for 20 min, the lower organic phase was collected by centrifugation and dried under nitrogen to obtain total lipids. 2 mL of 1% sulfuric acid-methanol solution was added to the lipids, and the mixture was refluxed in an 80 °C water bath for 60 min for methyl esterification. After cooling to room temperature, 2 mL of n-hexane and 1 mL of distilled water were added, and the mixture was vigorously shaken to extract fatty acid methyl esters (FAMEs). After standing and separating the layers, the upper n-hexane phase was collected and filtered through a 0.22 μm organic filter membrane for analysis.

[0076] Chromatographic conditions: An Agilent 7890A / 5975C series gas chromatograph (Agilent Technologies) with a flame ionization detector (FID) and a DB-WAX capillary column (30m × 0.25mm inner diameter, 0.25μm film thickness, Agilent Technologies) was used. The injection volume was 1μL, the split ratio was 10:1, the injection port temperature was 250℃, and the mass spectrometer detector temperature was 260℃. High-purity helium was used as the carrier gas at a constant flow rate of 1.0mL / min. The initial temperature was 100℃ and held for 1 min; then increased to 180℃ at 10℃ / min and held for 5 min; then increased to 240℃ at 3℃ / min and held for 15 min. An electron impact ionization (EI) source was used with an ionization voltage of 70 eV, an ion source temperature of 230℃, a quadrupole temperature of 150℃, a scan range of 35m / z–550m / z, and a solvent delay time of 3 min. The acquired mass spectra were compared with the retention times of the NIST mass spectral library and a mixed standard of 37 fatty acid methyl esters (Sigma-Aldrich) to complete the qualitative analysis of fatty acids.

[0077] The free fatty acids in the yolks of salted duck eggs prepared according to the above test methods in the examples and comparative examples are shown in Table 5.

[0078] Table 5. Free fatty acid composition of salted duck egg yolks prepared in the examples / comparative examples.

[0079] In addition, for ease of comparison, the information on free fatty acids in egg yolks is summarized in Table 6.

[0080] Table 6. Summary of polyunsaturated fatty acids in the yolks of salted duck eggs prepared in the examples / comparative examples.

[0081] As shown in Tables 5 and 6 above, the release levels of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) in Examples 1 and 4 were significantly higher than those in the atmospheric pressure pickling group (Comparative Examples 1 and 2) and the fresh egg group (Comparative Example 5). P(<0.05) Particularly regarding polyunsaturated fatty acids with important physiological activities, Example 1 showed a DHA content of 1434.2 ± 52.2 mg / kg and an EPA content of 78.0 ± 12.2 mg / kg, significantly higher than Comparative Example 1 (DHA: 1201.7 mg / kg, EPA: 62.6 mg / kg). The underlying mechanism of this phenomenon lies in the alternating shear force generated during the vacuum pulsating pressure process, which effectively disrupts the network-like encapsulation structure of high-density lipoprotein and low-density lipoprotein in the egg yolk, promoting the conversion of bound lipids to free lipids. Simultaneously, pickling under vacuum and oxygen-deficient conditions greatly prevents the oxidative rancidity of highly unsaturated fatty acids such as DHA and EPA during the pickling process, thereby maximizing the preservation and enrichment of these nutrients.

[0082] Conversely, the PUFA release in Comparative Example 3 (acid-free treatment) and Comparative Example 4 (constant negative pressure) was significantly reduced, indicating that without the synergistic effect of the specific vacuum pulsed pressure variation process and organic acid pretreatment of this invention, the lipid demulsification and fatty acid release effects inside the egg yolk are greatly reduced. This invention not only shortens the pickling cycle but also endows salted duck eggs with extremely high nutritional value.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A rapid pickling method for pre-prepared salted duck eggs, characterized in that, Quick marinating methods include: (1) Pre-treatment by immersing duck eggs in an organic acid solution; (2) The pretreated duck eggs are immersed in the pickling solution and pickled using a vacuum pulsation method to obtain salted duck egg pre-products; The vacuum pulsation method involves periodically alternating the vacuum level of the pickling system between high and low vacuum levels, with the high vacuum level not exceeding -0.08 MPa and the low vacuum level not falling below -0.05 MPa.

2. The rapid marinating method according to claim 1, characterized in that, The high vacuum level is -0.09MPa to -0.08MPa, and the low vacuum level is -0.05MPa to -0.04MPa.

3. The rapid marinating method according to claim 1 or 2, characterized in that, The periodic alternation includes: maintaining a high vacuum for 5 to 15 minutes and maintaining a low vacuum for 6 to 10 hours.

4. The rapid marinating method according to claim 1 or 2, characterized in that, The interval between high vacuum and low vacuum is ≤30 seconds.

5. The rapid marinating method according to claim 1 or 2, characterized in that, The organic acid solution is a lactic acid solution with a mass fraction of 8%–12%; and / or The pickling solution is a salt solution with a mass fraction of 18% to 22%.

6. The rapid marinating method according to claim 5, characterized in that, The salt solution also contains 0.5% to 1.5% spice extract by weight of salt.

7. The rapid marinating method according to claim 6, characterized in that, The spice extract is an aqueous or alcoholic extract of one or more of star anise, Sichuan pepper, and cinnamon.

8. The rapid marinating method according to any one of claims 1 to 7, characterized in that, Pretreatment time is 15–30 minutes; and / or The pickling temperature is 25℃~35℃; and / or The total marinating time is 10 to 20 days.

9. A pre-made salted duck egg product, characterized in that, Obtained by pickling using the rapid pickling method described in any one of claims 1 to 8.

10. Salted duck egg, characterized in that, It is obtained by cooking the salted duck egg pre-process as described in claim 9.

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