Method for visually separating and pickling salted egg yolk and application

Abstract

The invention discloses a method for visually separating and pickling salted egg yolk and application, and relates to the technical field of salted egg yolk processing technologies. The preparation method comprises the following steps: adjusting the pH value of initial yolk liquid by using a pH / freeze thawing-salt treatment-segmented heat treatment three-stage combined process, performing freezing-unfreezing treatment, and then performing preliminary gelation treatment through thermal induction; and adding salt ions for cross-linking, and then carrying out segmented heat treatment to finally prepare the salted egg yolk product which is good in oil yield and sand production effect compared with an unfreeze-thaw treatment process. The separation and pickling method of the salted egg yolk solves the problem of resource waste of egg white. The salted yolk sauce prepared from the salted egg yolk product is stable in color and luster, free of grease separation, good in flavor and taste and rich in nutritional value. The technological method provided by the invention is convenient to operate, easy to standardize and control, capable of remarkably shortening the production cycle, independent of expensive equipment and high-energy input, low in cost and easy to implement, and has a better industrial application prospect in the aspect of high-value application of the salted egg yolk.

Description

Technical Field

[0001] The invention relates to the technical field of salted egg yolk processing technology, and in particular to a method for visually separating and pickling salted egg yolks and an application thereof. Background Art

[0002] Egg yolk is rich in protein, lecithin, vitamin A, vitamin D, vitamin B12, as well as various nutrients such as iron and zinc, and has a high nutritional value. At present, the main consumption mode of eggs in my country is still fresh eggs, but the overall deep processing rate of poultry eggs is low. Salted egg yolk is widely used in the food industry because of its unique flavor. The use of egg yolk liquid to separate and pickle salted egg yolk, as well as the development of salted egg yolk and related products, can solve the weak aspects of my country's egg industry. However, the pickling process of salted egg yolk is a necessary operating unit in the processing of salted egg yolk products. The pickling process involves the denaturation and aggregation of egg yolk protein, the release and precipitation of oil, etc., which are closely related to the quality of the product. How to obtain salted egg yolk with loose sand and oil is a difficult problem that this field focuses on.

[0003] The traditional salted egg yolk curing process relies heavily on the osmotic pressure of a salty environment. Salt gradually migrates through the eggshell membrane and egg white into the yolk, causing the hydrophobic, hydrophilic, and lipophilic groups within the yolk to dissociate and recombine under the action of salt ions, continuously removing water and ultimately creating the unique, fluffy, and smooth texture of the salted egg yolk. For example, patent application CN107348393A discloses a traditional process for curing duck eggs in their shells to produce salted egg yolks. However, this process suffers from a long curing period (25-30 days) and the waste of the egg white due to the high salt content.

[0004] Rapid curing involves separating fresh egg yolks from egg whites, preserving the intact yolk membrane and yolk structure before curing. This includes dry curing (e.g., patent application CN112617136A and authorized patent CN113995099B), wet curing (e.g., patent applications CN110916112A and CN104473225A), and reconstitution (e.g., authorized patent CN102132896B and patent application CN109259117A). As an in vitro curing technique, rapid curing offers advantages such as a short cycle time, ease of preparation, and the ability to reuse the egg white.

[0005] Improvements to existing rapid curing methods often utilize auxiliary methods to accelerate curing. Commonly used auxiliary methods include ultrasonic technology, microwaves, temperature changes (increasing / cooling), pressure regulation, and the use of curing agents, allowing salted egg yolks to mature quickly. For example, patent CN111329003B utilizes ultrasound to promote the penetration of the curing liquid; patent CN108651955A utilizes microwaves to promote the texture and flavor development of salted egg yolks; patent CN115500480A (heating) and patent CN103141867B (freezing) utilize egg yolk coagulation and shaping methods to produce stable salted eggs; patent CN103610109A utilizes composite brine with reduced pressure and counterpressure to cure salted egg yolks; and patent CN117158552A utilizes ethanol to denature egg yolk powder. However, these various auxiliary methods often require dedicated equipment and high energy input, resulting in high production costs and making them unsuitable for industrial production. Existing in vitro curing technologies also face challenges such as poor uniformity (dry method) or waterlogging (wet method).

[0006] While traditional salted egg yolk flavors remain popular, consumer demand for innovative flavors is also growing. Salted egg yolk sauce, an emerging condiment, is gaining acceptance and popularity due to its oily, gritty texture and unique flavor profile. It is often used as a key flavor enhancer in common dishes such as fruit and vegetable salads, mixed noodles, baked shrimp, and fried chicken. Processing salted egg yolk into salted egg yolk sauce can broaden its market application and address the existing salted egg yolk sauce's monotonous flavor, rough texture, and greasiness.

[0007] Therefore, how to develop a deep processing technology for salted egg yolks that has obvious oil and sand removal effects and is fast and efficient in production has become the key to the production of salted egg yolk products. Summary of the Invention

[0008] The present invention provides a method and application for visually separating salted egg yolks. Through a three-step process consisting of pH / freeze-thaw control, salting, and staged heat treatment, the method produces step-by-step heat-induced salted egg yolk gelled particles that release oil from the sand. These particles exhibit a wide range of particle sizes and excellent oil and sand release characteristics, meeting the production needs of various salted egg yolk products. The technical solution of the present invention is detailed below.

[0009] A first aspect of the present invention provides a method for visually separating pickled salted egg yolks, comprising the following steps:

[0010] The pH value of the initial egg yolk liquid was adjusted to the isoelectric point of the egg yolk protein, frozen at -18--20°C for 3.5-4.5 hours, and thawed at 0-4°C for 8-12 hours to obtain the thawed egg yolk liquid;

[0011] The thawed egg yolk liquid is first heat-treated at 73-77° C. for 13-17 minutes, and after cooling, 1-2% of NaCl by weight of the thawed egg yolk liquid is added, stirred, and marinated at room temperature to obtain a salted egg yolk gel;

[0012] The salted egg yolk gel is subjected to a second heat treatment at 160-180° C. for 8-10 min, crushed, and subjected to a third heat treatment at 130-150° C. for 8-10 min to obtain a salted egg yolk product.

[0013] Optionally, the source of the initial egg yolk liquid selected in the above method includes but is not limited to chicken eggs, duck eggs, goose eggs or other poultry or non-poultry fresh eggs or separated pure egg yolk products.

[0014] Optionally, the pH value of the initial egg yolk solution can be adjusted using 0.2 M citric acid solution.

[0015] pH primarily influences the selective aggregation of yolk particles. By shifting the initial yolk solution's pH to the isoelectric points of the various proteins in the yolk, the yolk proteins can interact with the surrounding lipids and aggregate, significantly promoting the aggregation of yolk particles. This not only significantly shortens the curing time compared to the nearly one month required for traditional salted egg curing, but also allows the yolk proteins and lipids to jointly support the yolk's oily, sandy texture.

[0016] Furthermore, the freeze-thaw method is to freeze at -20°C for 4 h and thaw at 4°C for 10 h.

[0017] Furthermore, the egg yolk liquid is subjected to a first heat treatment at 75° C. for 15 min.

[0018] Furthermore, during the first heat treatment, stirring is performed at 150-200 r / min for 1-2 min every 3-5 min.

[0019] Furthermore, the amount of NaCl added is 1.5% of the mass of the egg yolk liquid.

[0020] Furthermore, after adding the NaCl, stirring is carried out at 250-300 r / min for 2-3 min.

[0021] Furthermore, the pickling time at room temperature is 22-26 h.

[0022] Furthermore, the salted egg yolk gel is heat-treated for a second time at 180° C. for 10 min, crushed, and heat-treated for a third time at 150° C. for 10 min.

[0023] Alternatively, the crushing process can be performed using a food grinder, and the crushing method can be selected as 400 r / min crushing for 2 minutes.

[0024] The second aspect of the present invention further provides an application of a salted egg yolk product prepared by any one of the above methods, specifically for preparing salted egg yolk sauce.

[0025] The third aspect of the present invention further provides a method for preparing salted egg yolk sauce, which is prepared from the salted egg yolk product prepared by any of the above methods.

[0026] The preparation method of the salted egg yolk sauce provided by the present invention is divided into two preparation processes of original salted egg yolk sauce and spicy salted egg yolk sauce.

[0027] Furthermore, when preparing the original salted egg yolk sauce, the salted egg yolk product and vegetable oil are mixed, white sugar is added, and the mixture is homogenized to obtain the salted egg yolk sauce;

[0028] Optionally, the vegetable oil may be a raw material of oil commonly used in food, such as a single variety of oil such as sunflower oil, corn germ oil, soybean oil, sesame oil, etc., or a blended oil obtained by mixing multiple varieties of the above oils.

[0029] Optionally, when preparing original salted egg yolk sauce, the mass of the added vegetable oil is 40-60% of the salted egg yolk product.

[0030] Optionally, when preparing original salted egg yolk sauce, the mass of added white sugar is 0.5-3% of the salted egg yolk product.

[0031] By adopting the preparation method of the present invention, an original salted egg yolk sauce with uniform sauce body (particle size ≤ 50 μm), golden color (L*=41.32, b*=47.56), and balanced salty and fragrant flavor is finally prepared.

[0032] Furthermore, when preparing spicy salted egg yolk sauce, vegetable oil and chili oil are mixed, flavor enhancers, auxiliary materials and spices are added and pre-mixed (for example, mixing at 500-700 rpm for 3-4 minutes), and the salted egg yolk product is added and homogenized to obtain spicy salted egg yolk sauce.

[0033] Optionally, compared to the original salted egg yolk sauce, the spicy salted egg yolk sauce can replace 15-50% of the vegetable oil with chili oil.

[0034] Optionally, the flavor enhancer can be selected from commonly used flavor enhancers in food, such as white sugar, MSG, chicken essence, oyster sauce, soy sauce, etc.

[0035] Optionally, the added amount of the flavor enhancer can be 0.8-1.2% of the mass of the salted egg yolk product.

[0036] Optionally, the mass of the auxiliary material added is 1-9% of the salted egg yolk product, and the specific amount added can be selected to be 5% of the salted egg yolk product.

[0037] Optionally, the auxiliary materials are one or more of sesame, tangerine peel, hawthorn, etc.

[0038] For example, specifically, when sesame, tangerine peel, and hawthorn are selected at the same time, the mass ratio can be (5-8):(1-4):1, and the specific mass ratio can be 5:4:1, 6:3:1, 7:2:1, and 8:1:1.

[0039] Optionally, the spices may be one or more of common spices such as cumin, white pepper, black pepper, perilla, licorice, cinnamon, star anise, angelica dahurica, cloves, bay leaves, tsaoko, and fennel, and the amounts of each may be adjusted arbitrarily (for example, each spice may be added in equal amounts).

[0040] Furthermore, the homogenization method is 2800-3200 r / min homogenization for 1-2 min.

[0041] Furthermore, in the preparation method of the salted egg yolk sauce of the present invention, an antioxidant may be added to inhibit lipid oxidation in the salted egg yolk sauce.

[0042] Alternatively, the antioxidant may be a naturally derived antioxidant or an artificially synthesized antioxidant.

[0043] Natural antioxidants can be selected from, for example, ascorbic acid (vitamin C), β-carotene, tocopherol, tea polyphenols, anthocyanins, rosemary extract, etc.

[0044] Specifically, the antioxidant can be obtained by compounding ascorbic acid and β-carotene. Based on the total mass of the salted egg yolk sauce, the ascorbic acid can be 0.5±0.05 g / kg, and the β-carotene can be 0.4±0.04 g / kg.

[0045] The salted egg yolk sauce prepared by the above method is sterilized and filled to obtain a finished product. The sterilization method can be high temperature (120°C) short time sterilization (10 minutes).

[0046] A fourth aspect of the present invention provides a salted egg yolk sauce prepared by the above-mentioned preparation method.

[0047] Compared with the prior art, the present invention is beneficial in that:

[0048] 1. The present invention utilizes a three-stage combined process of "pH / freeze-thaw-salt-stage heat treatment" to induce egg yolk protein granulation and gelation, thereby forming a step-by-step heat-induced salted egg yolk to produce a salted egg yolk product, and develops a method for preparing flavored salted egg yolk sauce.

[0049] This method differs from existing traditional whole-egg curing methods and some modified auxiliary curing methods. The present invention shifts the pH of the egg yolk liquid and then freeze-thaws it, utilizing the isoelectric point of the yolk particles for initial aggregation and freeze-induced larger-scale aggregation. The present invention also utilizes a staged heat treatment for gelation to produce the final salted egg yolk product, making it more efficient than traditional whole-egg curing (curing time is shortened to 4 days). Separate curing also helps prevent uneven quality, hard cores, and waterlogged salted egg yolks.

[0050] 2. The method for separating and pickling salted egg yolks provided by the present invention solves the resource waste of egg white and has better application prospects in the high-value application and production of salted egg yolks.

[0051] 3. The salted egg yolk sauce finally prepared by the present invention has stable color, no oil precipitation, good flavor and taste, and rich nutritional value.

[0052] 4. The process methods provided by the present invention are easy to operate, do not rely on expensive equipment and high energy input, are low in cost, easy to implement, and suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 : Particle size distribution of egg yolk emulsion gel prepared at different pH values in Example 1.

[0054] Figure 2 : Optical microscopic distribution diagram of egg yolk emulsion gel prepared at different pH values in Example 1.

[0055] Figure 3 : Rheological diagram of egg yolk emulsion gel prepared at different pH values in Example 1.

[0056] Figure 4 Comparison of particle size distribution of egg yolk emulsion gels subjected to different freeze-thaw times. (Left) The group undergoing freeze-thaw treatment followed by pH adjustment. (Right) The group undergoing pH adjustment followed by freeze-thaw treatment. C1 represents a single freeze-thaw treatment; C2 represents a double freeze-thaw treatment.

[0057] Figure 5 : Optical microscopic and macroscopic images of egg yolk emulsion gels using different freezing-thawing times.

[0058] Figure 6 : Comparison of stability index graphs of egg yolk emulsion gels using different freeze-thaw times. TSI stands for Turbiscan stability index.

[0059] Figure 7: Comparison of the appearance of the step-by-step heat-induced salted egg yolk particle gel prepared by the present invention and the control groups C1-FP-0 (pH 6) and C1-PF-0 (pH 4.5) that were not subjected to freeze-thaw treatment.

[0060] Figure 8 : Scanning electron microscopy comparison of the step-by-step thermally induced salted egg yolk particle gel prepared by the present invention and the control groups C1-FP-0 (pH 6) and C1-PF-0 (pH 4.5) that were not subjected to freeze-thaw treatment.

[0061] Figure 9 : Comparison of sanding rates of step-by-step heat-induced salted egg yolk particle gels prepared using different freezing-thawing times and sequences.

[0062] Figure 10 Comparison of oil yields of step-by-step thermally induced salted egg yolk granule gels prepared using different freeze-thaw times and sequences. Oil yields of the FP group (left) and the PF group (right).

[0063] Figure 11 : Comparison of laser confocal micrographs of the stepwise thermally induced salted egg yolk particle gel prepared by the present invention with those of the control groups C1-FP-0 (pH 6) and C1-PF-0 (pH 4.5) that were not subjected to freeze-thaw treatment.

[0064] Figure 12 Appearance of flavored salted egg yolk sauce made using step-by-step thermal induction of salted egg yolk particle gel. Original salted egg yolk sauce (left) and spicy salted egg yolk sauce (right).

[0065] Figure 13 : Detailed photo of the spicy salted egg yolk sauce made using step-by-step thermal induction of salted egg yolk particle gel. DETAILED DESCRIPTION

[0066] The technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0067] In some embodiments provided by the present invention, the method for visually separating pickled salted egg yolks is provided, and the specific steps are as follows:

[0068] The pH value of the initial egg yolk liquid was adjusted to the isoelectric point of the egg yolk protein, frozen at -18--20°C for 3.5-4.5 hours, and thawed at 0-4°C for 8-12 hours to obtain the thawed egg yolk liquid;

[0069] The thawed egg yolk liquid is first heat-treated at 73-77° C. for 13-17 minutes, and after cooling, 1-2% of NaCl by weight of the thawed egg yolk liquid is added, stirred, and marinated at room temperature to obtain a salted egg yolk gel;

[0070] The salted egg yolk gel is subjected to a second heat treatment at 160-180° C. for 8-10 min, crushed, and subjected to a third heat treatment at 130-150° C. for 8-10 min to obtain a salted egg yolk product.

[0071] Optionally, the source of the initial egg yolk liquid includes but is not limited to chicken eggs, duck eggs, goose eggs or other poultry or non-poultry fresh eggs or separated pure egg yolk products.

[0072] Optionally, the freeze-thaw method is to freeze at -20°C for 4 h and thaw at 4°C for 10 h.

[0073] Optionally, the egg yolk liquid is first heat-treated at 75° C. for 15 min.

[0074] Optionally, during the first heat treatment, stirring is performed at 150-200 r / min for 1-2 min every 3-5 min.

[0075] Optionally, the amount of NaCl added is 1.5% of the mass of the egg yolk liquid.

[0076] Optionally, after adding the NaCl, stirring is carried out at 250-300 r / min for 2-3 min.

[0077] Optionally, the marinating time at room temperature is 22-26 hours.

[0078] Optionally, the salted egg yolk gel is heat-treated for a second time at 180° C. for 10 min, crushed, and heat-treated for a third time at 150° C. for 10 min.

[0079] The salted egg yolk product prepared by the method can be further prepared into salted egg yolk sauce with original flavor and spicy flavor.

[0080] Specifically, the preparation method of the original salted egg yolk sauce is: mix the salted egg yolk product with vegetable oil evenly, add white sugar, and homogenize until the original salted egg yolk sauce with uniform sauce body, golden color and balanced salty and fragrant flavor is obtained.

[0081] When preparing the original salted egg yolk sauce, the vegetable oil used may be selected from but not limited to sunflower oil, corn germ oil, soybean oil, sesame oil, or a blended oil obtained by mixing the above oils.

[0082] Optionally, when preparing the original salted egg yolk sauce, the mass of the added vegetable oil is 40%-60% of the salted egg yolk product, for example 40%, 45%, 50%, 55%, 60%, etc.

[0083] Optionally, the mass of the added white granulated sugar is 0.5-3% of the salted egg yolk product, for example, 0.5%, 1%, 2%, 3%, etc.

[0084] Specifically, the preparation method of the spicy salted egg yolk sauce is as follows: the salted egg yolk product, vegetable oil and chili oil are mixed, the flavor enhancer, auxiliary materials and spices are pre-mixed (for example, mixing at 500-700 rpm for 3-4 minutes), the salted egg yolk product is added and homogenized to prepare the spicy salted egg yolk sauce.

[0085] Alternatively, the total mass of vegetable oil and chili oil can be compared to the ratio in original salted egg yolk sauce. Compared to original salted egg yolk sauce, spicy salted egg yolk sauce replaces some of the vegetable oil with chili oil. The replacement ratio can be 15-50%. For example, the mass ratio of chili oil to vegetable oil can be 1:5, 1:4 (i.e., a 20% replacement ratio), 1:3, 1:2, or 1:1.

[0086] Optionally, the flavor enhancer can be selected from commonly used flavor enhancers in food, such as white sugar, MSG, chicken essence, oyster sauce, soy sauce, etc.

[0087] Optionally, the added amount of the flavor enhancer can be 0.8-1.2% of the mass of the salted egg yolk product.

[0088] Optionally, the auxiliary materials include but are not limited to one or more of sesame, tangerine peel, hawthorn, etc.

[0089] Specifically, when sesame, tangerine peel and hawthorn are selected at the same time, the mass ratio can be (5-8):(1-4):1, and the specific mass ratio can be 5:4:1, 6:3:1, 7:2:1 or 8:1:1.

[0090] The mass of the auxiliary materials added is 1-9% of the salted egg yolk product, and the specific amount added can be selected to be 5% of the salted egg yolk product.

[0091] Optionally, the spices may be one or more of common spices such as cumin, white pepper, black pepper, perilla, licorice, cinnamon, star anise, angelica dahurica, cloves, bay leaves, tsaoko, and fennel. The amounts of each spice used may be adjusted as needed (e.g., equal amounts of each spice may be added).

[0092] Optionally, when preparing original and spicy salted egg yolk sauces, the homogenization method is 2800-3200 r / min for 1-2 min.

[0093] Optionally, antioxidants may be added to the original and spicy flavored salted egg yolk sauces to prevent lipid oxidative rancidity and affect sensory quality.

[0094] The antioxidant may be a naturally derived antioxidant or a synthetic antioxidant. Natural antioxidants include, but are not limited to, ascorbic acid (vitamin C), β-carotene, tocopherol, tea polyphenols, anthocyanidins, rosemary extract, and the like.

[0095] In the following specific embodiment, the method for visually separating pickled salted egg yolks is as follows:

[0096] S1. Take the initial egg yolk liquid of fresh eggs, adjust the pH value of the initial egg yolk liquid to the isoelectric point (pH = 4.5 ± 0.5) with 0.2 M citric acid solution, stir evenly, freeze at -20°C for 4 h, and then thaw at 4°C for 10 h to obtain the thawed egg yolk liquid.

[0097] S2. The thawed egg yolk liquid is subjected to the first heat treatment at 75°C for 15 min.

[0098] During the first heat treatment, stirring was performed at a low speed (150 r / min) for 1 min every 3 min.

[0099] After the first heat treatment, the mixture was cooled to room temperature, and NaCl was added at a concentration of 1.5% (g / g) of the thawed egg yolk liquid. The mixture was stirred at a low speed (250 r / min) for 2 min to obtain salted egg yolk gel.

[0100] S3. Preheat the oven and heat-treat the salted egg yolk gel at 180°C for 10 min for the second time by baking; then crush it with a food grinder (400 r / min) for 2 min; and heat-treat it for the third time at 150°C for 10 min to finally prepare the salted egg yolk product.

[0101] In the following specific embodiment, the method for preparing original salted egg yolk sauce using salted egg yolk products is as follows:

[0102] P1. Mix the salted egg yolk product and vegetable oil (such as soybean oil) in a mass ratio of 2:1, add 3% of the mass of the salted egg yolk product in white sugar, and stir evenly.

[0103] P2. Homogenize the mixture using a colloid mill at 2800 r / min for 1 min to obtain a uniform sauce (particle size ≤ 50 μm), golden color (L*=41.32, b*=47.56), and a balanced salty and savory flavor.

[0104] In the following specific embodiment, the method for preparing original salted egg yolk sauce using salted egg yolk products is as follows:

[0105] Q1. Mix the salted egg yolk product, vegetable oil (such as soybean oil), and chili oil in a mass ratio of 2:1:0.2, add 1% of the salted egg yolk product mass of flavor enhancer, 5% of auxiliary materials, and 1% of spices, and stir evenly.

[0106] Among them, the auxiliary materials are sesame, tangerine peel and hawthorn with a mass ratio of 6:3:1;

[0107] Q2. Homogenize the mixture using a colloid mill at 2800 r / min for 1 min, and obtain a spicy salted egg yolk sauce with a sensory score of 39.65 points (out of 50).

[0108] Example 1: Effects of different pH values on the particle size, micromorphology, and rheological properties of egg yolk emulsion gels

[0109] In the preparation method of the salted egg yolk product provided in this embodiment, the pH value of the initial egg yolk liquid is adjusted to 4, 4.5, 5, and 5.5 respectively using 0.2 M citric acid solution, and the initial egg yolk liquid without adjusting the pH value (pH = 6.0) is used as the control group. Deionized water (1:1) is used for dispersion. (1) The particle size distribution of each sample emulsion is measured; (2) The morphology of each sample dispersed in water under rapid oscillation is observed using a 100x oil immersion lens; (3) The rheological properties of each sample are evaluated. The frequency sweep frequency range is 0.1 to 10 Hz to evaluate the storage modulus (G') and loss modulus (G") . The apparent viscosity shear rate range is 0.1 to 100 s -1 The whole process was carried out at 25°C.

[0110] The results are as follows Figure 1 and Figure 2 As shown in the figure. From the particle size results, the particle size of the initial egg yolk liquid after pH adjustment increases as the pH gradually decreases. When the pH is adjusted to 4.5, it is closest to the isoelectric point of the egg yolk particles. At this time, the egg yolk particles aggregate, causing the particle size to reach the maximum value. Further decreasing the pH, the egg yolk particles disaggregate from the aggregated state, and the particle size decreases again. This may be due to the Ca in the calcium phosphate bridge of the egg yolk particles. 2+ The yolk particles are dissociated, causing them to disaggregate under extremely acidic conditions. At a pH of 6, the egg yolk emulsion gel appears as a uniformly dispersed fluid. As the pH gradually shifts toward 4, aggregated particles gradually become visible. At a pH of 4.5, the sample particles aggregate into uniform, fine aggregates, and the microscopic results are consistent with the conclusions drawn from the particle size. However, as the pH continues to decrease to 4, the previously aggregated egg yolk particles redisperse and no longer aggregate.

[0111] The results are as follows Figure 3As shown in the figure, G′ and G″ increase with decreasing pH. At the same frequency, G″ is slightly larger than G′, indicating that viscosity is the main rheological property of egg yolk emulsion gel. The apparent viscosity of egg yolk emulsion gel is in the low shear rate range (0.1-10s -1 ) and decreased rapidly at high shear rates (10 s -1 ), the rheological properties of the egg yolk emulsion gel exhibit shear-thinning behavior, characteristic of a pseudoplastic fluid. As the pH approaches the isoelectric point of the egg yolk particles, the shear-thinning behavior weakens. Specifically, this is manifested by the aggregation of egg yolk particles, which enhances protein-protein interactions, alters its rheological properties, and increases the apparent viscosity of the egg yolk emulsion gel.

[0112] Therefore, adjusting the pH value of the initial egg yolk liquid to about 4.5 is the most suitable processing condition, which facilitates the subsequent rapid and efficient preparation of salted egg yolk products.

[0113] Example 2: Effects of freeze-thaw treatment sequence and treatment time on the physicochemical properties of egg yolk emulsion gel

[0114] After determining the optimal pH shift point (4.5), this example further investigated the effects of the freeze-thaw sequence and duration on the particle size, microscopic and macroscopic properties, and rheological properties of the egg yolk emulsion gel to determine the optimal process conditions for preparing the salted egg yolk product. The groups are shown in Table 1 below.

[0115] Table 1 Group classification table

[0116] In Table 1 above, the "FP" group represents a freeze-thaw treatment followed by adjustment of pH to 4.5, while the "PF" group represents a freeze-thaw treatment followed by adjustment of pH to 4.5.

[0117] "FP" group:

[0118] (1) Cycle 2 (C1). After freezing at -20°C for 0, 2, 4, and 6 h, the samples were transferred to a 4°C refrigerator for 10 h of thawing. After thawing, the pH was adjusted to 4.5 at 25°C. The control group, C1-FP-0 (pH 6), was not frozen and thawed.

[0119] (2) Cycle 2 (C2). After freezing at -20°C for 0, 2, 4, and 6 h, the samples were transferred to a 4°C refrigerator for 10 h, then frozen at -20°C for 0, 2, 4, and 6 h, and thawed at 4°C for 10 h. After thawing, the pH was adjusted to 4.5 at room temperature at 25°C.

[0120] PF group:

[0121] (1) Cycle 1 (C1). The egg yolk solution was first adjusted to pH 4.5 at 25°C; then frozen at -20°C for 0, 2, 4, and 6 hours, and then thawed in a 4°C refrigerator for 10 hours. The control group, C1-PF-0 (pH 4.5), was not frozen or thawed.

[0122] (2) Cycle 1 (C2). First, adjust the pH of the egg yolk solution to 4.5 at 25°C, then freeze it at -20°C for 0, 2, 4, and 6 h, and then transfer it to a 4°C refrigerator to thaw for 10 h; then freeze it at -20°C for 0, 2, 4, and 6 h, and then transfer it to a 4°C refrigerator to thaw for 10 h; this is recorded as Cycle 2 (C2).

[0123] In this example, the particle size distribution, microscopic, and macroscopic properties of each group of salted egg yolk products were measured using the same methods as in Example 1. The stability of each group of salted egg yolk products was also measured. A pulsed near-infrared light source (wavelength 850 nm) was used to periodically scan the samples from top to bottom. The scans were performed over a 12-hour period with 3-minute intervals. The backscattered light intensity was collected using this device and analyzed for stability index.

[0124] like Figure 4 As shown in the figure, particle size measurements show that within the FP group, C1-FP-0 (control group) has the smallest particle size. With increasing freeze-thaw time, the particle size of the groups treated with a single freeze-thaw treatment gradually increases. Freeze-thaw causes LDL in the egg yolk to break down, releasing lipids and causing protein-protein aggregation. Adjusting the pH to 4.5 further agglomerates already aggregated egg yolk particles. After a second cycle (Cycle 1 (C2)) lasting more than 2 hours, the particle size of the egg yolk emulsion gel significantly decreases. Excessive freeze-thaw time significantly disrupts the integrity of the egg yolk particles, leaving only a portion of them able to aggregate further.

[0125] like Figure 4 As shown, in the PF group, the particle size distribution of C1-PF-0 shifted to a wider range than that of C1-FP-0, and the particle size of the egg yolk emulsion gel subjected to a second freeze-thaw cycle (Cycle 1 (C2)) showed a significant shift. When the pH was adjusted to 4.5, the egg yolk particles aggregated. Subsequent freeze-thaw cycles disrupted some of the initial aggregation, leading to further aggregation of the majority of the yolk particles. In the C1-PF-4 group, the peak area in the 1-100 μm range was the largest, indicating that the most yolk aggregates were formed at this time. The particle size of the PF group subjected to a second freeze-thaw cycle also showed an initial increase followed by a decrease.

[0126] like Figure 5Morphological observations showed that after a single freeze-thaw cycle, the FP and PF groups showed the highest oil accumulation at 4 h. The C1-FP-4 group formed random droplets, while the C1-PF-4 group formed more uniform droplets. Overall, the egg yolk emulsion gel particles in the PF group were more compact than those in the FP group. The control group, which did not undergo freeze-thaw treatment, did not experience significant oil droplet growth. After a second freeze-thaw cycle (Cycle 1 (C2)) for 6 h, the egg yolk emulsion gel in the PF group exhibited slight fluidity, while the FP group showed no fluidity.

[0127] like Figure 6 As shown in the stability index (TSI), the TSI gradually increases with increasing freeze-thaw time, indicating that the freeze-thaw process affects the overall stability of the system. Furthermore, the secondary freeze-thaw treatment (Cycle 1 (C2)) increases the instability and aggregation of the system, leading to faster particle movement and a tendency towards instability. The TSI of the PF group was lower than that of the FP group. The yolk particles in the PF group, through pH adjustment, simultaneously aggregated in situ within the emulsion gel system, forming spherical aggregates of approximately the same size. Subsequently, different freeze-thaw times resulted in differences in particle size. However, the FP group initially formed irregular aggregates, resulting in a wider particle size distribution. The PF group exhibited a more coordinated stabilization effect than the FP group, forming more uniformly sized yolk aggregates, ultimately resulting in ideal, loose, granular salted egg yolk aggregates.

[0128] Therefore, the most suitable processing conditions for the subsequent preparation of salted egg yolk products were to adjust the pH of the egg yolk emulsion gel to 4.5, freeze it at -20°C for 4 h, and then thaw it at 4°C for 10 h.

[0129] Based on the experiments in Examples 1 and 2, it was determined that adjusting the pH of the egg yolk emulsion gel to 4.5, freezing it at -20°C for 4 hours, and then thawing it at 4°C for 10 hours were the most suitable processing conditions for the subsequent preparation of salted egg yolk products. During this process, the egg yolk proteins aggregated, and the protein aggregates were dispersed in the continuous phase of free lipids, forming a granular gel with a uniform particle size distribution. The salted egg yolk granular gel exhibited significant oil and sand removal performance.

[0130] Example 3: Verification of the gel aggregation effect of salted egg yolk particles in salted egg yolk products

[0131] 1. Preparation of test samples

[0132] (1) Wash the eggs and separate the yolks to obtain the initial yolk solution, which was then adjusted to pH 4.5 using 0.2 M citric acid solution. All experimental groups were set up as shown in Table 1. C1-FP-0 (pH 6) and C1-PF-0 (pH 4.5) in Table 1 of Example 1 were used as the control groups for freeze-thaw treatment.

[0133] (2) Preparation of salted egg yolk gel: The thawed egg yolk liquid of each group that had undergone freeze-thaw treatment was subjected to the first heat treatment by heating in a 75°C water bath for 15 min.

[0134] During the first heat treatment, stirring was performed at a low speed (150 r / min) for 1 min every 3 min to ensure a uniform gelation state.

[0135] After the first heat treatment, the mixture was cooled to room temperature and then 1.5% of the mass of the thawed egg yolk liquid was added with NaCl and stirred at a low speed (250 r / min) for 2 min.

[0136] (3) Preparation of salted egg yolk products: The oven was preheated, and the salted egg yolk gel of each group was placed at room temperature (25 °C) for 24 h to initiate salting. The salted egg yolk gel was then heat treated twice: the second heat treatment was performed at 180 °C for 10 min, the egg yolk was removed, and ground and crushed with a food grinder (400 r / min) for 2 min, and then the third heat treatment was performed (heated at 150 °C for 10 min) to obtain the final salted egg yolk product.

[0137] 2. Test results

[0138] Appearance as shown Figure 7 As shown, the salted egg yolk product formed in the control group, C1-FP-0, was large and uneven, while the salted egg yolk product formed in the PF group had a more uniform structure than the FP group. From the outside inward, the rate of ice crystal formation in the salted egg yolk product decreased, resulting in a harder gel structure on the outside and a more fragile gel structure on the inside. After adjusting the pH to the isoelectric point and subjecting the product to the same degree of heat induction, the resulting salted egg yolk product was less uniform. The experimental group, after a 4-hour freeze-thaw treatment, achieved the most ideal texture, exhibiting coarse particles. The salted egg yolk product in the C1-PF-4 group had looser particles than the C1-FP-4 group, closer to the ideal texture of salted egg yolk.

[0139] Scanning electron micrographs Figure 8As shown in the figure, the distance between smaller aggregates within the salted egg yolk network is further shortened after the double heat treatment, resulting in a densely packed structure of spherical aggregates with increased particle size. This suggests that the double heat treatment enhances the protein cross-linking density and directionality, driving the aggregates toward a dense spherical structure. Overall, the PF group forms a looser distribution and more extensive spherical aggregate packing network than the FP group, which is attributed to the initial aggregation of egg yolk particles at the isoelectric point (pH 4.5).

[0140] The salted egg yolk product formed in the control group exhibited a dense, unevenly sized gel structure after heating, indicating that the yolk particles, previously dispersed within the uniform salted egg yolk gel, aggregated under high temperature, forming large gel masses. In contrast, the experimental example maintained a well-defined distribution of microparticles after heat treatment. Therefore, the salted egg yolk product prepared in the present invention exhibited better oil and sand removal, as well as granulation, than the control group.

[0141] like Figure 9 As shown, the PF group had a higher sand-producing rate than the FP group. The C1-FP-4 group (82%) and the C1-PF-4 group (84.67%) exhibited the strongest sand-producing characteristics, indicating that a 4-hour freeze-thaw treatment is the optimal time for developing a sandy texture. In the experimental group obtained by freezing for 4 hours, the formation of small spherical aggregates and the dissociation of large aggregates reached a state of equilibrium. The formation of larger spherical aggregates was still reversible, resulting in the formation of medium-sized spherical aggregates. After thawing, the C1-FP-6 group absorbed energy only to open the outer connections of larger aggregates, and small aggregates gradually adhered to the surface, resulting in a denser gel.

[0142] like Figure 10 As shown, there was no significant difference in total lipid content between the FP and PF groups, indicating that freeze-thaw and pH adjustment had no effect on total oil content. However, the free lipid content in the PF group was significantly higher than that in the FP group, with the oil yield of the C1-PF-4 group (93.18%) exceeding that of the C1-FP-4 group (85.98%). Large aggregates formed in the C1-FP-6 group, which had a prolonged single-freeze period, and in the C2-FP-4 and C2-FP-6 groups, which had undergone repeated freeze-thaw cycles for extended periods. Some lipids within these aggregates were unable to be released, resulting in lower oil yields. With 24 hours of salting, further water removal occurred, and the spherical aggregates of the yolk particles partially contracted, resulting in a looser packing. The gradually seeping oil continuously filled the spaces between the spheres, promoting the ideal loose, sandy, and oily texture.

[0143] Figure 11The protein-lipid distribution of the stepwise heat-induced salted egg yolk particle gels at different freeze-thaw times is shown. Large protein aggregates are observed in the control group, C1-FP-0. CLSM observations show that the C1-PF-4 group exhibits more numerous and dispersed oil droplet aggregates than the C1-FP-4 group, resulting in more uniform particle size aggregation, consistent with the oil yield measurements. The C1-PF-4 group forms a stacking structure closer to that of salted egg yolk microspherical gel aggregates.

[0144] Example 4: Evaluation of salted egg yolk sauce made using salted egg yolk products

[0145] 1. Preparation of original salted egg yolk sauce

[0146] The original salted egg yolk sauce recipe used in this example is: 100 g of salted egg yolk product, 50 g of mature soybean salad oil, and 3 g of flavor enhancer (white sugar).

[0147] 2. Preparation of spicy salted egg yolk sauce

[0148] The recipe of the spicy salted egg yolk sauce used in this example is as follows: 100 g of salted egg yolk product, 50 g of mature soybean salad oil and chili oil (mass ratio 4:1), 1 g of flavor enhancer (white sugar), 5 g of auxiliary materials (mass ratio of sesame, tangerine peel and hawthorn is 6:3:1), and 1 g of spices (mass ratio of cumin: white pepper: perilla: cinnamon: fennel: bay leaf is 1:1:1:1:1:1).

[0149] After stirring evenly, sterilize at 120℃ for 10 min and fill aseptically to obtain the finished product. Figure 12 As shown, the product details are as follows Figure 13 The sensory evaluation reference standards of salted egg yolk sauce are shown in Table 2. After high-temperature sterilization, the flavored salted egg yolk sauce did not experience oil precipitation and stratification, and the product still maintained a uniform and easy-flowing appearance.

[0150] Table 2 Sensory evaluation reference standards for salted egg yolk sauce

[0151]

[0152] The above specific embodiments describe the implementation of the present invention in detail, but the present invention is not limited to the specific details of the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

Claims

1. A method for visually separating pickled salted egg yolks, characterized in that: The following steps are involved: The pH value of the initial egg yolk liquid was adjusted to the isoelectric point of the egg yolk protein, frozen at -18--20°C for 3.5-4.5 hours, and thawed at 0-4°C for 8-12 hours to obtain the thawed egg yolk liquid; The thawed egg yolk liquid is first heat-treated at 73-77° C. for 13-17 minutes, and after cooling, 1-2% of NaCl by weight of the thawed egg yolk liquid is added, stirred, and marinated at room temperature to obtain a salted egg yolk gel; The salted egg yolk gel is subjected to a second heat treatment at 160-180° C. for 8-10 min, crushed, and subjected to a third heat treatment at 130-150° C. for 8-10 min to obtain a salted egg yolk product.

2. The method for visually separating pickled salted egg yolks according to claim 1, wherein The freeze-thaw method is to freeze at -20°C for 4 h and thaw at 4°C for 10 h.

3. The method for visually separating pickled salted egg yolks according to claim 1, wherein The egg yolk liquid was first heat treated at 75°C for 15 min.

4. The method for visually separating pickled salted egg yolks according to claim 1, wherein During the first heat treatment, stirring is performed at 150-200 r / min for 1-2 min every 3-5 min.

5. The method for visually separating pickled salted egg yolks according to claim 1, wherein The amount of NaCl added is 1.5% of the mass of the egg yolk liquid.

6. The method for visually separating pickled salted egg yolks according to claim 1, wherein After adding the NaCl, the mixture was stirred at 250-300 r / min for 2-3 min.

7. The method for visually separating pickled salted egg yolks according to claim 1, characterized in that: The marinating time at room temperature is 22-26 hours.

8. The method for visually separating pickled salted egg yolks according to claim 1, wherein: The salted egg yolk gel was heat-treated for a second time at 180° C. for 10 min, crushed, and heat-treated for a third time at 150° C. for 10 min.

9. An application of a salted egg yolk product prepared by the method according to any one of claims 1 to 8, characterized in that: Used to prepare salted egg yolk sauce.

10. A method for preparing salted egg yolk sauce, characterized in that: The salted egg yolk product is prepared by the method according to any one of claims 1 to 8.

11. The method for preparing salted egg yolk sauce according to claim 10, characterized in that: Mixing the salted egg yolk product and vegetable oil, adding white sugar, and homogenizing to obtain salted egg yolk sauce; Alternatively, vegetable oil and chili oil are mixed, flavor enhancers, auxiliary materials and spices are pre-mixed, and the salted egg yolk product is added and homogenized to obtain salted egg yolk sauce.

12. The method for preparing salted egg yolk sauce according to claim 11, characterized in that: The homogenization method is 2800-3200 r / min homogenization for 1-2 min.

13. Salted egg yolk sauce prepared by the preparation method according to any one of claims 10 to 12.

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