Salted egg yolk pickling liquid based on controllable oxidation system and rapid pickling method

Abstract

The invention discloses a salted egg yolk pickling liquid based on a controllable oxidation system and a rapid pickling method, and belongs to the field of food processing. The pickling liquid disclosed by the invention is prepared by adding 8 to 15 weight percent of sodium chloride, 0.05 to 0.2 weight percent of food-grade hydrogen peroxide, 0.001 to 0.004 weight percent of ascorbic acid and 0.0001 to 0.0004 weight percent of ferric chloride into egg white and uniformly mixing. The egg white-hydrogen peroxide-iron ion Fenton system constructed by the invention can accelerate protein cross-linking and lipid migration in the egg yolk membrane, so that gelatinization and oil production of the egg yolk can be completed within a short time, rapid pickling is realized, and the color, flavor and texture characteristics of the salted egg yolk are enhanced at the same time.

Description

Technical Field

[0001] The present invention belongs to the field of food processing. Specifically, it relates to a salted egg yolk pickling solution and a pickling method, and particularly to a salted egg yolk pickling solution based on a controllable oxidation system (egg white - hydrogen peroxide - ferrous ion Fenton system) and a method for quickly pickling salted egg yolks. Background Art

[0002] Due to its unique flavor, delicate gel texture, and moderate oil - releasing characteristics, salted egg yolks are widely used in the food industry, such as mooncakes, pastries, flavored foods, and the catering industry. Traditional pickling methods usually use salt pickling or alkali solution soaking. Through long - term salt penetration and protein denaturation, the egg yolks gradually gel and form good oil - releasing characteristics. However, traditional pickling methods have problems such as long pickling cycles (usually 20 - 40 days), difficult quality control during the pickling process, and unstable oil release, which limit the production efficiency and quality stability of salted egg yolks. Therefore, developing an efficient and controllable rapid pickling technology is of great significance for improving the industrial production of salted egg yolk products.

[0003] In recent years, it has been found that oxidation plays a key role in the gelation and oil - releasing processes of egg yolks. Egg white is rich in easily oxidizable proteins such as ovalbumin, ovotransferrin, and lysozyme, which are prone to generating reactive oxygen species (ROS) during the pickling process, such as superoxide anion radical (O 2 -·), hydroxyl radical (·OH), and hydrogen peroxide (H 2 O 2 ). These free radicals can induce protein molecule cross - linking through oxidation, promote the reconstruction of low - density lipoprotein (LDL) and high - density lipoprotein (HDL) in the egg yolk, and thus accelerate the gelation process of the egg yolk. At the same time, moderate free radical oxidation can promote the migration of egg yolk lipids, optimize the oil - releasing characteristics, and enhance the taste and flavor. However, excessive oxidation may lead to abnormal protein aggregation and lipid oxidation deterioration, thereby affecting the texture and flavor of the egg yolk. Therefore, how to utilize oxidation to promote egg yolk gelation while avoiding quality degradation caused by excessive oxidation is the key issue in optimizing the salted egg yolk pickling process.

[0004] The inventor of the present invention has long been committed to the research of salted egg yolk products, and on June 21, 2024, a method for quickly pickling salted egg yolks was disclosed (patent publication number CN118216651A). The method includes the following steps: (1) Select fresh poultry eggs, wash and dry them, break the eggs and separate the egg whites, and roll the egg yolks on clean filter paper to remove the excess egg white on the surface of the egg yolks; (2) Cool the egg yolk pickling container in an environment of 3-5°C for 0.2-0.5 h in advance; (3) Take the egg yolks separated in step (1), pierce the egg yolk membranes, and collect the egg yolk liquid in the pickling container cooled in step (2); (4) Stir and mix the collected egg yolk liquid in an environment of 3-5°C for 0.1-0.3 h; (5) Add 0.5-2 wt% sodium chloride, 0.05-0.1 wt% food additive hydrogen peroxide, 0.001-0.002 wt% ascorbic acid, and 0.0001-0.0002 wt% ferric chloride to the mixed egg yolk liquid, and stir for 0.5-1 h in an environment of 3-5°C to make it uniform; (6) Place the egg yolk liquid obtained in step (5) in an environment of 20-40°C and pickle for 3-5 days to obtain a salted egg yolk pickled product that can be used as a flavoring. Although this patented technology discloses the technology of mixing sodium chloride, hydrogen peroxide, and iron ions as the pickling solution, its pickling object is the broken-membrane egg yolk liquid that is easy to penetrate and pickle; when pickling whole egg yolks, technicians need to solve problems such as how to maintain the integrity of the egg yolk membrane and the egg yolk structure during the pickling process, and how to overcome permeability regulation. Through retrieving domestic and foreign literature, there is currently no prior art to solve these technical problems. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a method for quickly pickling salted egg yolks based on a controllable oxidation system. By constructing a controllable free radical oxidation environment, it promotes the cross-linking of egg yolk proteins and lipid migration, accelerates the gelation and oil production of egg yolks, and realizes the acquisition of high-quality salted egg yolks in a short time. This method can significantly shorten the pickling cycle, improve production efficiency, and at the same time optimize the texture, flavor, and stability of salted egg yolks, and is suitable for industrial production.

[0006] In order to achieve the above technical purpose, the inventor of the present invention conducted a large number of experimental studies and unremitting explorations, and finally prepared a salted egg yolk pickling solution composed of an egg white - hydrogen peroxide - ferric ion Fenton system, thereby precisely controlling the degree of oxidation, promoting the oxidative cross-linking of egg yolk proteins, enhancing the gel network structure, and accelerating lipid migration to improve the oil production rate.

[0007] Specifically, the object of the present invention is achieved as follows: A salted egg yolk pickling solution based on a controllable oxidation system, characterized in that the pickling solution is prepared by mixing 8-15 wt% sodium chloride, 0.05-0.2 wt% food-grade hydrogen peroxide, 0.001-0.004 wt% ascorbic acid, and 0.0001-0.0004 wt% iron chloride into egg white.

[0008] It should be noted that the addition percentages of sodium chloride, food-grade hydrogen peroxide, ascorbic acid, and iron chloride are based on the mass of the egg white, that is, the addition amounts of the above components account for the mass percentage of the egg white as follows: sodium chloride 8-15 wt%, food-grade hydrogen peroxide 0.05-0.2 wt%, ascorbic acid 0.001-0.004 wt%, and iron chloride 0.0001-0.0004 wt%.

[0009] Further preferably, for the salted egg yolk pickling solution based on the controllable oxidation system as described above, sodium chloride is first added to the egg white, and the mixture is stirred until the sodium chloride is completely dissolved, and then food-grade hydrogen peroxide, ascorbic acid, and iron chloride are added.

[0010] Further preferably, for the salted egg yolk pickling solution based on the controllable oxidation system as described above, after adding food-grade hydrogen peroxide, ascorbic acid, and iron chloride, it is stirred at a speed of 500-2000 rpm for 0.5-1 h in an environment of 3-5 °C.

[0011] In addition, the present invention also provides a method for quickly pickling salted egg yolks based on a controllable oxidation system, characterized in that the method comprises the following steps:

[0012] (1) Select fresh poultry eggs, wash and dry them, break the eggs and separate the egg whites, and roll the egg yolks on a clean filter paper to remove the excess egg white on the surface of the egg yolks;

[0013] (2) Cool the pickling container in an environment of 3-5 °C for 0.2-0.5 h in advance;

[0014] (3) Place the egg yolks obtained in step (1) into the pickling container cooled in step (2), and store them at 3-5 °C for standby;

[0015] (4) Take the egg white separated in step (1), add 8-15 wt% sodium chloride, and stir the mixture until the sodium chloride is completely dissolved;

[0016] (5) Add 0.05-0.2 wt% hydrogen peroxide, 0.001-0.004 wt% ascorbic acid, and 0.0001-0.0004 wt% iron chloride to the sodium chloride egg white solution obtained in step (4), and stir at a speed of 500-2000 rpm for 0.5-1 h in an environment of 3-5 °C to mix evenly to obtain a pickling solution;

[0017] (6) Add the pickling solution obtained in step (5) to the pickling container filled with egg yolks in step (3), and pickle for 1 - 3 days at 20 - 40°C;

[0018] (7) Take out the egg yolks, remove the excess pickling solution on the surface, and obtain the pickled salted egg yolk products.

[0019] It should be noted that the method for pickling salted egg yolks of the present invention is not only applicable to duck eggs, but also applicable to other poultry eggs. The obtained salted egg yolk products can be used as fillings in industrial production. Therefore, as described above, for the method of quickly pickling salted egg yolks based on a controllable oxidation system, the poultry eggs can be selected from at least one of the following: chicken eggs, duck eggs, quail eggs. Additionally, in step (6) of the above method for quickly pickling salted egg yolks based on a controllable oxidation system, the pickling temperature is preferably 25 - 30°C; the addition amount of the pickling solution is 20 - 50 mL per egg yolk.

[0020] Compared with the prior art, the pickling solution and pickling method for salted egg yolks provided by the present invention have the following advantages and progressiveness:

[0021] (1) The present invention controls the pickling speed of egg yolks and the stability and permeability of the egg yolk membrane by optimizing the pickling solution formula. First, the proteins and amino acids (such as cysteine, glutamic acid, etc.) in egg white have active hydrogens or electrons that are vulnerable to oxidation. The side chains or peptide chains of these amino acids may react with hydroxyl radicals to form more free radicals, further promoting the oxidation reaction. Second, the free radicals in egg white may also interact with the lipids in the egg yolk, promoting lipid migration, accelerating the oil - out process, and greatly shortening the pickling time. Additionally, free radicals may cause partial oxidation and structural changes in the egg yolk membrane, resulting in enhanced membrane permeability, accelerating the penetration of the pickling solution, and enabling the egg yolk to be pickled more quickly. Therefore, using egg white as the pickling agent matrix, with an appropriate concentration of sodium chloride and a low - concentration oxidant, a moderate Fenton reaction system is formed to promote the slow penetration of the pickling solution without overly damaging the egg yolk membrane. The intensity of the oxidation reaction is adjusted by the concentration of the oxidant, reaction time, and temperature, so that the egg yolk membrane maintains a certain strength during pickling, preventing embrittlement of the membrane structure due to over - oxidation.

[0022] (2) The egg white - hydrogen peroxide - iron ion Fenton system constructed in the present invention can accelerate the protein cross - linking and lipid migration within the egg yolk membrane, enabling the egg yolk to complete gelation and oil separation in a shorter time, achieving rapid pickling. At the same time, it enhances the color, flavor, and texture characteristics of the salted egg yolk. The oil separation rate (59.49 ± 1.61%) of the pickling method of the present invention is significantly higher than that of the egg yolk liquid pickling method (40.36 ± 2.63%), and the significant mark is "****" (p < 0.0001), indicating that the difference between the two is extremely significant. This extremely significant difference in the oil separation rate enables the present invention to obtain unexpected technical effects compared with the prior art (Patent CN118216651A). The higher oil separation rate of the pickling method of the present invention means that the texture of the egg yolk is finer and the sense of oiliness is stronger, which will surely bring a better sensory experience in food processing (such as salted egg yolk mooncakes, seasonings).

[0023] (3) The present invention controls the penetration rate by temperature and time. A staged pickling strategy is adopted, that is, in the early stage of pickling, namely the preparation stage, a lower temperature is used to slow down the structural change of the membrane, and at the same time, the pickling time is optimized to ensure that the salt and oxidant can uniformly penetrate the egg yolk without causing local over - oxidation or texture change.

[0024] (4) The method of the present invention can not only significantly shorten the pickling time, improve production efficiency, but also maintain the quality stability of the salted egg yolk. It can be widely applied to the industrial production of salted egg yolks, providing an efficient, stable, and standardized pickling scheme for food processing enterprises. Description of the Drawings

[0025] Figure 1 : Comparison of the oil separation rate of salted egg yolks under different pickling agents (%);

[0026] Figure 2 : Comparison of the scanning electron microscopy of salted egg yolks under different pickling agents;

[0027] Figure 3 : Comparison of the hydrogen proton imaging of salted egg yolks under different pickling agents;

[0028] Figure 4 : Comparison of the CDA content of salted egg yolks under different pickling agents;

[0029] Figure 5 : Comparison of the carbonyl group (nmol / mg) of salted egg yolks under different pickling agents;

[0030] Figure 6 : Comparison of the free sulfhydryl groups of salted egg yolks under different pickling agents;

[0031] Figure 7 : Comparison of the secondary structure of salted egg yolks under different pickling agents;

[0032] Figure 8 : Comparison of the solubility of salted egg yolks treated with different pickling agents;

[0033] Figure 9 : Comparison of the turbidity of salted egg yolks treated with different pickling agents;

[0034] Figure 10 : Comparison of the results of the electronic nose of salted egg yolks under different treatments;

[0035] Figure 11 : Comparison of the oil yield rates between pickling with egg yolk liquid and the present method;

[0036] Figure 12 : Salted egg yolk samples pickled with sodium chloride + Fenton system. Specific implementation manners

[0037] The technical solutions and technical effects of the present invention are further described below in conjunction with the embodiments and the drawings. However, it should be understood that the described embodiments are merely exemplary and do not constitute any limitation to the protection scope of the present invention. Those skilled in the art should also understand that without departing from the spirit of the present invention, modifications or substitutions can be made to the details and forms of the technical solutions, but these modifications or substitutions all fall within the protection scope of the present invention. In addition, for those steps or conditions of specific technical operations not specified in the embodiments, they are all carried out according to the general techniques or conditions described in the literature in this field or according to the product specifications; for the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchases.

[0038] Example 1: Pickling of salted egg yolks based on the egg white - hydrogen peroxide - ferric ion Fenton system

[0039] (1) Select fresh eggs produced within 24 hours, wash and dry them, break the eggshells and separate the egg whites, and roll the egg yolks on clean filter paper to remove the excess egg white on the surface of the egg yolks;

[0040] (2) Cool the aluminum boxes used for pickling the egg yolks in advance at 4°C for 0.5 h;

[0041] (3) Take the egg yolks obtained in step (1), gently place them in the pre-cooled aluminum boxes, and store them at 4°C for standby;

[0042] (4) Mix the egg white separated in step (1) with 10 wt% sodium chloride and stir evenly until the sodium chloride is completely dissolved;

[0043] (5) Add 0.05 wt% hydrogen peroxide, 0.004 wt% ascorbic acid and 0.0004 wt% ferric chloride to the egg white solution obtained in step (4), and stir at a speed of 1000 rpm for 0.5 h in an environment of 4°C to obtain a pickling solution;

[0044] (6) Take the pickling solution obtained in step (5), add it to the aluminum box containing egg yolks in step (3), about 30 mL of pickling solution for each egg yolk, place it in an environment of 25 °C, and pickle for 2 days (such as Figure 12 );

[0045] (7) After the pickling is completed, take out the egg yolks from the aluminum box, remove the excess egg white pickling solution on the surface, and obtain the complete salted egg yolk pickled product.

[0046] Comparative Example 1: Conventional pickling of salted egg yolks

[0047] (1) Select fresh eggs produced within 24 hours, wash and dry them, break the eggshells and separate the egg whites, roll the egg yolks on a clean filter paper to remove the excess protein on the surface of the egg yolks;

[0048] (2) Cool the aluminum box for pickling egg yolks in advance at 4 °C for 0.5 h;

[0049] (3) Take the egg yolks obtained in step (1), gently place them in the pre-cooled aluminum box, and store them at 4 °C for standby;

[0050] (4) Mix the egg white separated in step (1) with 10 wt% sodium chloride and stir evenly until the sodium chloride is completely dissolved, and use this as the pickling solution;

[0051] (5) Take the pickling solution obtained in step (4), add it to the aluminum box containing egg yolks in step (3), about 30 mL of pickling solution for each egg yolk, place it in an environment of 25 °C, and pickle for 2 days;

[0052] (6) After the pickling is completed, take out the egg yolks from the aluminum box, remove the excess egg white pickling solution on the surface, and obtain the complete salted egg yolk pickled product.

[0053] Example 2: Determination of the oil yield of salted egg yolks

[0054] Taking the egg yolks before and after pickling in Example 1 and Comparative Example 1 as the research objects, the oil yield was measured, and the measurement method was as follows: Free fat content: Weigh about 3 g of the sample, add 25 mL of distilled water, homogenize with a homogenizer (8000 - 10000 r / min) for about 30 s, centrifuge at 7500 r / min for 30 min with a high-speed centrifuge, and transfer the salted egg yolk liquid to a separatory funnel. Add 25 mL of organic solvent (V n-hexane:V isopropanol = 3:2) to the separatory funnel for extraction, and collect the upper layer liquid into a beaker with the corresponding number. First, volatilize most of the solvent in a 55 °C water bath, and then dry it to constant weight in a 105 °C oven. Total fat content: Take another about 1.5 g of the sample, add 20 mL of organic solvent (V n-hexane:V isopropanol = 3:2), homogenize at 8000 - 10000 r / min for about 1 min, filter with filter paper, volatilize most of the solvent in a 55 °C water bath, dry it in a 105 °C oven, and weigh it after cooling in a desiccator. After calculation, the percentage of total fat content is obtained, and the oil yield (%) = free fat content / total fat content.

[0055] Salted egg yolks are very popular among the public because of their unique flavor, delicate gel texture and moderate oil output characteristics. The oil yield of salted egg yolks was obtained ([ Figure 1 ). Before pickling, the oil seepage rates of the two treatments were relatively low. After pickling, the oil seepage rates increased significantly, and the seepage rate of the NaCl + Fenton reaction group was much higher than that of the NaCl group. The oil yields were 59.49 ± 1.61% and 34.23 ± 0% respectively, which was nearly 9 times higher than before pickling. The Fenton reaction significantly promoted oil seepage. The Fenton reaction generates hydroxyl radicals (·OH), which are highly reactive free radicals that can damage lipids, proteins and other macromolecules in the egg yolk. The chemical process of the Fenton reaction is: H 2 O 2 + Fe2+ → Fe3+ + ·OH + OH-. These free radicals can cause the oxidative decomposition of fatty acid chains and increase the external seepage of oil. The free radicals attack the double bonds in fatty acids, causing them to undergo oxidation reactions, destroying the fat molecular structure and resulting in the release of oil. The oxidation reaction also causes changes in the proteins in the egg yolk, which may loosen their structure and further promote the release of oil from cells or cell membranes.

[0056] Example 3: Scanning electron microscopy detection of salted egg yolks

[0057] Taking the egg yolks before and after pickling in Example 1 and Comparative Example 1 as the research objects, the microscopic morphology of the samples was detected and analyzed.

[0058] The SEM image of the NaCl-treated sample before pickling shows a relatively tight structure, relatively regular surface particles, and a relatively complete microstructure of the egg yolk ([ Figure 2)。The lipids may be in a relatively stable state. After salting, the surface becomes relatively loose, and obvious holes and cracks appear on the surface, indicating that some changes may have occurred in the structure of the egg yolk. These changes may be due to protein denaturation and lipid exudation caused by NaCl treatment. Before the NaCl+Fenton reaction treatment, the image is similar to that of NaCl treatment alone, the surface is still relatively tight, and there is no obvious structural damage. After salting, the holes and cracks are more obvious and larger, indicating that the Fenton reaction plays a stronger oxidation role during salting. Oxidative free radicals, such as hydroxyl radicals, may damage the integrity of the egg yolk, resulting in more oil exudation.

[0059] Example 4: Detection of hydrogen protons in salted egg yolks

[0060] Taking the egg yolks before and after salting in Example 1 and Comparative Example 1 as the research objects, the hydrogen proton distribution of the samples was detected and analyzed.

[0061] The hydrogen proton imaging images show the changes in the hydrogen proton distribution of salted egg yolks treated with NaCl and NaCl+Fenton reaction ( Figure 3 ). This technique is mainly used to observe the distribution of water and lipids because hydrogen protons mainly come from water and fat. Before the NaCl treatment, the brightness is low and the red area is small, indicating that the hydrogen proton signal is relatively weak and the mobility of water and lipids is low. After salting, the brightness increases slightly and the red area expands slightly, indicating that water redistributes during salting, which may lead to an increase in some hydrogen proton signals. Due to the presence of NaCl, proteins may denature, resulting in a change in the water-binding ability and a slight increase in the hydrogen proton signal. Before the NaCl+Fenton reaction treatment, the brightness is higher and the red area is more obvious than that of the NaCl group, indicating that after the Fenton reaction treatment, the state of water and lipids has changed. It may be due to the oxidation effect that causes partial release of lipids, resulting in an increase in the hydrogen proton signal. After salting, the brightness change is not significant, but the red area becomes more concentrated, which may indicate that the Fenton reaction further promotes the distribution and release of oil during salting, resulting in a more concentrated local hydrogen proton signal. Due to the oxidation effect, the Fenton reaction may cause damage to the protein-lipid structure, resulting in lipid exudation and aggregation in some areas, forming a stronger signal.

[0062] Example 5: Determination of CDA content in salted egg yolks

[0063] Taking the egg yolks before and after salting in Example 1 and Comparative Example 1 as the research objects, the CDA content of the samples was determined and analyzed.

[0064] The CDA value before the NaCl treatment is relatively low, about 4.88±0.60% ( Figure 4) This indicates that before pickling, the NaCl treatment has little effect on the formation of conjugated dienoic acids, probably because the increase in salt content has not significantly changed the structure of fatty acids. After pickling, the CDA value of the NaCl group increased significantly, approaching 23.01 ± 1.76%. The pickling process may cause changes in fatty acids. NaCl promotes the release of oil and the structural change of lipids, thus forming more conjugated dienoic acids. The CDA value before pickling with the NaCl + Fenton reaction was significantly higher than that of the NaCl group, about 11.05 ± 3.32%. The Fenton reaction promotes the oxidation of fatty acids by generating oxidative free radicals (such as hydroxyl radicals), resulting in the formation of more conjugated dienoic acids. The CDA value after pickling increased significantly to 40.15 ± 5.35%. The Fenton reaction significantly promoted the formation of conjugated dienoic acids during pickling. The oxidation destroyed the structure of fatty acids, forming more conjugated dienoic acids. The Fenton reaction can promote the formation of conjugated dienoic acids even before pickling. There was a significant difference between the NaCl group and the NaCl + Fenton group after pickling, indicating that the Fenton reaction significantly promoted the formation of conjugated dienoic acids after pickling.

[0065] Example 6: Determination of the carbonyl content of salted egg yolks

[0066] Taking the egg yolks before and after pickling in Example 1 and Comparative Example 1 as the research objects, the carbonyl content of the samples was measured and analyzed.

[0067] The change in carbonyl content is usually used to measure oxidative damage. The carbonyl content before pickling with the NaCl treatment was relatively low, about 1.68 ± 0.22 nmol / mg( Figure 5) This indicates that before pickling, the treatment with NaCl has little effect on the oxidation of egg yolks, and the change in carbonyl content is small. After pickling, the carbonyl content increases and approaches 4.49 ± 0.44 nmol / mg. During pickling, NaCl may promote the oxidation reaction by changing the structures of proteins and lipids, resulting in the generation of more carbonyls. The carbonyl content before pickling with the NaCl + Fenton reaction is slightly higher than that of the NaCl group, approximately 2.34 ± 0.34 nmol / mg. Before the Fenton reaction, the generation of oxidative free radicals has already affected the oxidation of egg yolks, leading to a slight increase in the carbonyl content. After pickling, the carbonyl content increases significantly, reaching 5.23 ± 0.13 nmol / mg. The oxidation effect of the Fenton reaction significantly exacerbates the oxidative damage in egg yolks, especially after pickling, where the carbonyl content increases significantly. This shows that the Fenton reaction promotes lipid oxidation by generating free radicals, resulting in the formation of more carbonyls. The Fenton reaction significantly exacerbates the oxidative damage during pickling, leading to a substantial increase in the carbonyl content. The Fenton reaction promotes the oxidation of lipids by generating more free radicals through oxidation, thereby leading to the formation of more carbonyls. The Fenton reaction significantly promotes the oxidation reaction, causing more severe oxidative damage to the lipids and proteins in egg yolks and generating a large amount of carbonyls.

[0068] Example 7: Determination of the Free Sulfhydryl Content of Salted Egg Yolks

[0069] Using the egg yolks before and after pickling in Example 1 and Comparative Example 1 as the research objects, the free sulfhydryl content of the samples was determined.

[0070] Free sulfhydryl is an important functional group in proteins and is usually closely related to the oxidation and structural changes of proteins. The free sulfhydryl content before pickling with NaCl treatment is approximately 8.91 ± 0.42 μmol / g protein. This indicates that before pickling, the NaCl treatment has no significant effect on the sulfhydryl groups in egg yolks. After pickling, the free sulfhydryl content decreases significantly, approximately 2.97 ± 0.28 μmol / g protein( Figure 6) During the pickling process, NaCl may change the protein structure, leading to the oxidation of free sulfhydryl groups or their combination with salt, thus reducing the content of free sulfhydryl groups. The content of free sulfhydryl groups before pickling with the NaCl+Fenton reaction was relatively high, about 10.68±0.12 μmol / g protein. The oxidative free radicals generated by the Fenton reaction had already had a certain impact on the protein structure of egg yolks before pickling, resulting in a slightly higher content of free sulfhydryl groups. After pickling, the content of free sulfhydryl groups in the NaCl+Fenton group decreased significantly, approaching 0.65±0.02 μmol / g protein. The Fenton reaction caused the loss of free sulfhydryl groups in proteins through oxidation, and the content of free sulfhydryl groups after pickling was significantly lower than that in the NaCl group. The Fenton reaction significantly exacerbated the loss of free sulfhydryl groups, especially after pickling. Due to the generation of oxidative free radicals, a large amount of sulfhydryl groups in proteins were oxidized, resulting in a substantial decrease in the content of free sulfhydryl groups. The Fenton reaction caused strong oxidative damage to proteins through oxidation, significantly affecting the content of free sulfhydryl groups and possibly changing the function and structure of proteins.

[0071] Example 8: Determination of the secondary structure composition of the protein in salted egg yolks

[0072] Taking the egg yolks before and after pickling in Example 1 and Comparative Example 1 as the research objects, the secondary structure composition of the samples was determined.

[0073] Changes in the secondary structure of proteins usually reflect the conformational stability, degree of denaturation, and oxidative damage of proteins ( Figure 7)。The secondary structure composition of salted egg yolk proteins under different treatments was compared in terms of the changes in protein secondary structures (α-helix, β-sheet, β-turn, and random coil) before and after pickling under NaCl treatment and NaCl+Fenton reaction treatment. Before pickling under NaCl treatment, α-helix and β-sheet were the main structures, and the protein structure was relatively stable. The proportion of β-sheet was approximately 40%-50%, which was the main component of the protein, indicating its strong stability in the egg yolk matrix. The proportion of α-helix was also relatively high, indicating that the protein was in a relatively regular conformation. After pickling, the change in the protein secondary structure was small, indicating that the NaCl treatment had little effect on the protein conformation. The proportions of α-helix and β-sheet remained basically the same, indicating that the overall stability of the protein was good during NaCl pickling. Before pickling under NaCl+Fenton reaction treatment, the protein structure had been affected to a certain extent, with a decrease in β-sheet and an increase in β-turn and random coil. The oxidative effect of the Fenton reaction damaged the protein secondary structure, causing the protein structure to start to loosen. After pickling, β-sheet decreased significantly, the content of α-helix decreased, and random coil increased significantly. Severe conformational damage occurred to the protein, possibly due to the free radicals of the Fenton reaction causing protein oxidation, resulting in protein deconstruction and aggregation. The protein changed from a regular secondary structure (α-helix, β-sheet) to random coil, indicating a decrease in its stability, which may lead to a decrease in protein solubility and even the formation of protein aggregates. The NaCl treatment had little effect on the protein secondary structure, and the protein structure remained relatively stable after pickling. The NaCl+Fenton reaction significantly damaged the protein secondary structure, reduced α-helix and β-sheet, and increased random coil, indicating that protein oxidative denaturation occurred. The Fenton reaction caused the protein to change from an ordered structure (α-helix, β-sheet) to a disordered structure (random coil), reflecting an increase in oxidative damage and a decrease in protein functionality.

[0074] Example 9: Determination of Protein Solubility of Salted Egg Yolk

[0075] Taking the egg yolks before and after pickling in Example 1 and Comparative Example 1 as the research objects, the protein solubility of the samples was determined.

[0076] Figure 8For the change in protein solubility before and after marinating. Protein solubility is a key indicator to measure the structural integrity and functional properties of proteins, and is usually affected by factors such as protein oxidation, denaturation, aggregation, etc. The protein solubility before marinating with NaCl treatment was 95.92 ± 2.17%, indicating that the protein had high solubility and relatively intact structure before marinating. After marinating, the protein solubility in the NaCl group decreased significantly to about 75.72 ± 1.16%, indicating that partial denaturation or aggregation of proteins occurred during marinating, resulting in decreased solubility. NaCl marinating may promote protein-salt interaction, leading to conformational changes in some proteins and thus decreasing their solubility. The protein solubility before marinating with NaCl + Fenton reaction treatment was similar to that of the NaCl group, close to 96.48 ± 1.91%, indicating that the solubility of proteins was not significantly affected before the Fenton reaction treatment. The protein solubility after marinating was about 80.14 ± 1.06%, slightly higher than that of the NaCl group, but still much lower than the level before marinating. The oxidation effect of the Fenton reaction may damage the secondary and tertiary structures of proteins, resulting in cross-linking and aggregation of some proteins. At the same time, the generated oxidation products may enhance the hydrophilicity of proteins, resulting in slightly higher solubility than the NaCl group. The oxidation effect of the NaCl + Fenton group may partially disrupt the hydrophobic interaction of proteins, making proteins more soluble, so the solubility is slightly higher than that of the NaCl group. The decrease in protein solubility caused by NaCl treatment may be due to the structural changes, aggregation and salting-out of proteins, making proteins less soluble. The Fenton reaction promoted the oxidation of proteins, but the oxidation effect may disrupt some hydrophobic interactions, making the protein solubility slightly higher than that of the NaCl group.

[0077] Example 10: Turbidity Measurement of Salted Egg Yolks

[0078] Taking the egg yolks before and after marinating in Example 1 and Comparative Example 1 as the research objects, turbidity measurement was carried out on the samples.

[0079] Turbidity is an important indicator to measure protein aggregation, precipitation and particle dispersion state, and is usually closely related to protein denaturation, decreased solubility and oxidation ( Figure 9)。The turbidity value before pickling with NaCl treatment was relatively low, about 1.02±0.01 FTU, indicating that before pickling, the solubility of proteins was relatively high, the dispersion of protein particles was relatively good, and thus the turbidity was relatively low. After pickling, the turbidity value of the NaCl group increased significantly, about 4.47±0.05 FTU. During the pickling process, proteins may undergo salting out, denaturation, and decreased solubility, resulting in protein aggregation and the formation of large particles, which increases the turbidity of the solution. This change may be due to NaCl promoting the structural change of proteins, causing them to aggregate and form precipitates, thereby increasing the turbidity. The turbidity before pickling with NaCl+Fenton reaction was slightly higher than that of the NaCl group, about 1.43±0.08 FTU, indicating that the oxidative effect of the Fenton reaction had already begun to damage the protein structure, causing some proteins to form small aggregates, thus slightly increasing the turbidity. The turbidity value after pickling increased significantly to 5.21±0.10 FTU, which was higher than that of the NaCl group, indicating that the oxidative effect of the Fenton reaction significantly exacerbated protein aggregation. The oxidative free radicals generated by the Fenton reaction may damage the secondary and tertiary structures of proteins, leading to protein cross-linking, aggregation, and even precipitation, thereby resulting in a significant increase in turbidity. The NaCl treatment increased the turbidity of proteins, probably because during the pickling process, the solubility of proteins decreased and salting out occurred, leading to protein aggregation and the formation of particles, making the solution turbid. The NaCl+Fenton treatment significantly exacerbated the increase in turbidity. The oxidative effect of the Fenton reaction may damage the protein structure, causing protein aggregation, cross-linking, and precipitation, forming more large particles and significantly increasing the turbidity.

[0080] Example 11: Electronic nose determination of salted egg yolks

[0081] Taking the egg yolks before and after pickling in Example 1 and Comparative Example 1 as the research objects, the samples were measured for odor using an electronic nose.

[0082] Testing different samples using an electronic nose, the results are shown in Figure 10, the electronic nose sensor codes and their representative substances are as follows: W1C - aromatic compounds, W5S - nitrogen oxides, W3C - ammonia, aromatic molecules, W6S - hydrides, W5C - olefins, aromatics, polar molecules, W1S - alkanes, W1W - sulfur compounds, W2S - alcohols, some aromatic compounds, W2W - aromatic compounds, organic compounds of sulfur. The odor characteristics under four different conditions are shown by a radar chart. Each different curve represents the difference in odor perception before and after pickling with NaCl treatment and NaCl + Fenton reaction treatment. Analyze the influence of different pickling treatments on the odor characteristics of egg yolks. From the radar chart, the sensor data corresponding to the four different treatments (before NaCl pickling, after NaCl pickling, before NaCl + Fenton reaction pickling, after NaCl + Fenton reaction pickling) show the changes in different odor components. Sensors W1C, W3C, and W5S before NaCl pickling show higher values, meaning that the samples before pickling may contain more aromatic compounds (such as benzene, toluene), ammonia, aromatic molecules, and nitrogen oxides. These components may come from the natural components of the egg yolk itself, or be due to a small range of oxidation or release of odor substances caused by NaCl treatment. Sensors W1S, W2S, and W3S after NaCl pickling show even higher values, especially in alkanes and aromatic compounds. This indicates that after pickling, the influence of NaCl may promote the formation of some oxidation or charred products, or the increase in the concentration of these chemical substances, resulting in changes in odor. The values of W1C and W5S before NaCl + Fenton reaction pickling are higher, suggesting that aromatic compounds and nitrogen oxides still dominate, possibly due to the slight oxidation reaction caused by the Fenton reaction. The free radicals of the Fenton reaction may increase the concentration of these substances. After NaCl + Fenton reaction pickling, sensors W1S and W2S show obvious changes, especially in alkanes and aromatic compounds, indicating that the oxidation effect of the Fenton reaction significantly exacerbates the oxidation of lipids and proteins, generating more oxidation products (such as charred products, aromatic hydrocarbons, etc.). These oxidation products may come from the lipid and protein components in the egg yolk, resulting in significant changes in odor characteristics.

[0083] The influence of NaCl treatment on odor components is relatively mild, but after pickling, it may promote the increase of aromatic compounds and charred products, which may be due to the influence of NaCl on the structure change and water migration of the egg yolk. The influence of NaCl + Fenton reaction (before and after pickling) is more significant, especially after pickling. The Fenton reaction significantly promotes the formation of oxidation products and charred products, and these products may increase the odor intensity and complexity of the sample. The Fenton reaction further changes the chemical structure of lipids and proteins in the egg yolk by generating oxidation free radicals, resulting in an increase in new odor components (such as aromatic compounds and charred odors).

[0084] Example 12: Comparison of Oil Yield between Egg Yolk Liquid Marinating Method and Membrane-Containing Egg Yolk Marinating Method

[0085] Taking the egg yolks before and after marinating in Example 1 of Patent CN118216651A (egg yolk liquid marinating method) and Example 1 of the present invention (membrane-containing egg yolk marinating method) as the research objects, the oil yield of the samples was measured.

[0086] Figure 11 The comparison of the oil yield before and after marinating by the egg yolk liquid marinating method and the method of the present invention (membrane-containing egg yolk marinating method) is shown. The oil yield is an important indicator to measure the lipid release ability of egg yolks, directly affecting the taste, flavor and quality of egg yolks. The oil yields of the egg yolk liquid marinating and the method of the present invention before marinating are relatively low, and there is no significant difference between them (marked as "ns"). This indicates that before marinating, most of the lipids in the egg yolk are still inside the egg yolk particles (lipoprotein complexes) and are not significantly released. After marinating, the oil yield of the egg yolk liquid marinating increases significantly (40.36±2.63%), indicating that marinating promotes the change of the egg yolk particle structure, making it easier for lipids to be released. In addition, The oil yield (59.49 ± 1.61%) of the marinating method (including marinating with membrane-containing egg yolks) of the present invention is significantly higher than that of the marinating method with egg yolk liquid, and the significance marker is "****" (p < 0.0001), indicating that the difference between the two is extremely significant. This extremely significant difference in oil yield enables the present invention to achieve unexpected technical effects compared with the prior art (Patent CN118216651A). Figure 11

[0087] From ​ the test results, it can be seen that the membrane-containing egg yolk marinating method of the present invention can release more fat than the egg yolk liquid marinating method of Patent CN118216651A. During the marinating process of the membrane-containing egg yolk, the slow penetration of the egg yolk membrane structure and the Fenton reaction may cause the rearrangement of the proteins inside the egg yolk, resulting in the easier decomposition of the lipoprotein complex, thus increasing the oil yield. The increase in the oil yield may mean a richer egg yolk flavor because the release of oil helps the diffusion of fat-soluble flavor substances. Therefore, the higher oil yield of the method of the present invention means that the texture of the egg yolk is finer and the sense of oiliness is stronger, which will surely bring a better sensory experience in food processing (such as salted egg yolk mooncakes, seasonings).

Claims

1. A salted egg yolk pickling liquid based on a controlled oxidation system, characterized in that: The pickling liquid is prepared by adding 8-15wt% sodium chloride, 0.05-0.2wt% food-grade hydrogen peroxide, 0.001-0.004wt% ascorbic acid and 0.0001-0.0004wt% ferric chloride into egg white and then mixing the mixture evenly.

2. The salted egg yolk pickling liquid based on the controlled oxidation system according to claim 1, characterized in that: The pickling liquid is prepared by first adding sodium chloride into egg white, mixing and stirring until the sodium chloride is completely dissolved, and then adding food-grade hydrogen peroxide, ascorbic acid and ferric chloride.

3. The salted egg yolk pickling liquid based on the controlled oxidation system according to claim 2, characterized in that: After adding food grade hydrogen peroxide, ascorbic acid and ferric chloride, stir at 500-2000 rpm for 0.5-1 h at 3-5°C.

4. A method for quickly pickling salted egg yolks based on a controlled oxidation system, characterized in that: The method comprises the following steps: (1) Select fresh poultry eggs, wash and dry them, break the eggs to separate the egg white, and roll the egg yolk on a clean filter paper to remove excess protein on the surface of the egg yolk; (2) Cool the pickling container in an environment of 3-5°C for 0.2-0.5h in advance; (3) placing the egg yolk obtained in step (1) in the pickling container cooled in step (2) and storing at 3-5° C. for later use; (4) taking the egg white separated in step (1), adding 8-15 wt % sodium chloride, and mixing and stirring until the sodium chloride is completely dissolved; (5) adding 0.05-0.2 wt % hydrogen peroxide, 0.001-0.004 wt % ascorbic acid and 0.0001-0.0004 wt % ferric chloride to the sodium chloride egg white solution obtained in step (4), stirring at 500-2000 rpm for 0.5-1 h at 3-5° C. to obtain a pickling solution; (6) adding the pickling liquid obtained in step (5) into the pickling container containing the egg yolk in step (3), and pickling at 20-40° C. for 1-3 days; (7) taking out the egg yolk and removing the excess pickling liquid on the surface to obtain a salted egg yolk pickled product.

5. The method for quickly pickling salted egg yolks based on a controlled oxidation system according to claim 4, characterized in that: The poultry eggs are selected from at least one of the following: chicken eggs, duck eggs, and quail eggs.

6. The method for quickly pickling salted egg yolks based on a controlled oxidation system according to claim 4, characterized in that: The pickling temperature in step (6) is preferably 25-30°C.

7. The method for quickly pickling salted egg yolks based on a controlled oxidation system according to claim 4, characterized in that: In step (6), the amount of pickling liquid added is 20-50 mL per egg yolk.

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