Method for processing egg yolk and use of protease enzyme hydrolysate in the preparation of salted egg yolk

Abstract

The application relates to the food field and discloses a method for processing egg yolk and application of a protease enzyme hydrolysate in preparation of salted egg yolk. The method comprises the following steps: mixing egg yolk after enzymolysis and a protease enzyme hydrolysate; wherein the protease enzyme hydrolysate is a soybean protein isolate enzyme hydrolysate and / or an egg yolk granule protein enzyme hydrolysate. The method has higher oxidation degree of salted egg yolk fat, better salted egg yolk flavor, higher fat leakage rate and better formability.

Description

Technical Field

[0001] This invention relates to the food industry, specifically to a method for processing egg yolks and the application of protease hydrolysates in the preparation of salted egg yolks. Background Technology

[0002] Salted egg yolks are loose, sandy, and oily, with a unique flavor and delicious taste. They are rich in lecithin and unsaturated fatty acids, making them highly nutritious and suitable for direct consumption. Currently, salted egg yolks are mainly processed using traditional methods, which involve removing the shell and egg white from mature salted eggs. However, this method has significant drawbacks. First, after the eggs are matured, the salt content in the egg white is too high, resulting in poor flavor and making it unsuitable for consumption. Furthermore, desalting the egg white is extremely costly, leading to significant waste. Second, traditional production processes often involve poor hygiene, long production cycles, and difficulty in controlling the quality of salted eggs through standardized methods.

[0003] Given the shortcomings of traditional methods, Du Bing et al. employed a combined wet curing and ultra-high pressure technique. This technique not only promotes salt penetration into the egg and shortens the curing cycle, but also facilitates yolk formation, resulting in eggs with good chewiness, stickiness, and adhesion. However, because only brine was used for curing, the yolks became waterlogged. Therefore, how to improve the waterlogging problem of salted egg yolks during curing has attracted widespread attention from researchers. Fan Jinsong et al. added 0.25-2% calcium chloride, zinc chloride, or ferric citrate to the brine curing solution and found that the waterlogging problem of the yolks was significantly improved during the curing process. This may be because the addition of metal salts increases the osmotic pressure of the curing solution, causing water to escape from the inside of the yolk.

[0004] Dry curing is also a method for processing salted egg yolks and shortening the production cycle. Zhao Xujun et al. found that at 40℃, after evenly coating the egg yolks with wet salt and placing them in a specially made yolk pit for curing, mature salted egg yolks could be obtained within 20 hours. Salted egg yolks produced using this method have a high oil yield; however, the product is saltier and has a flatter shape. Salt particles easily adhere to the surface of the yolk, resulting in an unattractive product shape. Furthermore, the preparation of the salt pit requires a large amount of salt, and the yolks are prone to cracking during processing. To address the shortcomings of the above methods, Chen Jie et al. found that using a semi-permeable membrane during the curing of salted egg yolks effectively solves the problems of large amounts of salt adsorbing onto the yolk surface and the yolks being too salty. Simultaneously, using a stamping method to form the yolk pits ensures that the yolks maintain their original shape during curing and after molding. Because raw egg yolks are easily broken and difficult to shape, methods such as semi-permeable membrane dry curing, cold denaturation dry curing, mold-forming dry curing, and heat denaturation dry curing can effectively protect the integrity and original shape of the egg yolk. However, the texture of the egg yolk changes significantly during the process of curing it alone. Wang Zhengteng's research found that egg yolks cured alone exhibit a certain degree of gelatinization. Based on this, he conducted in-depth research on the gelatinization process and yolk granulation in salted eggs, pointing out that the texture of the egg yolk is significantly related to low-density lipoprotein, and that the gelatinization and granulation of the egg yolk are mainly affected by the salt penetration rate and salt content. Zhang Shaopu used ultraviolet light to irradiate egg yolks before transferring them to a permeable membrane or container for curing, finding that ultraviolet light can promote the conversion of some cholesterol in the egg yolk into vitamins. However, this method has problems such as slow yolk maturation and poor sensory quality of the product.

[0005] In addition, researchers have also explored dried salted egg yolks and salted egg yolk flavoring bases. Chen Lihong et al. found that by mixing salt, disodium hydrogen phosphate, sodium alginate, and other additives in a certain ratio to prepare a pickling solution, and then soaking duck egg yolks in the pickling solution at 5-35℃ for 24-72 hours, removing them and baking them at 40-50℃ for 4 hours, adding preservatives, and then vacuum packaging them, dried salted egg yolk products can be obtained. This method can effectively reduce the preparation time of salted egg yolks. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems existing in the prior art and to provide a method for processing egg yolks and the application of protease hydrolysate in the preparation of egg yolks.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for processing egg yolks, the method comprising: mixing egg yolks with enzymatic hydrolysate; wherein the enzymatic hydrolysate is soybean isolated enzymatic hydrolysate and / or egg yolk particle enzymatic hydrolysate.

[0008] A second aspect of the present invention provides an egg yolk processed by the method described above.

[0009] A third aspect of the present invention provides the application of the above-mentioned protease hydrolysate in the preparation of salted egg yolks.

[0010] The fourth aspect of this invention provides the application of the above-mentioned protease hydrolysate in promoting lipid oxidation.

[0011] Through the above technical solutions, the egg yolks prepared by the method of the present invention have a higher degree of lipid oxidation, higher fat permeability, a superior salted egg yolk flavor, and better shapeability. In the production process of the present invention, only the egg yolks are used for pickling; the egg whites can be used for other purposes, avoiding waste and reducing enterprise losses. The present invention allows for precise control of the amount of edible salt used in the production of salted egg yolks, avoiding the consumption of large amounts of edible salt and reducing the enterprise's salt input. The process method of the present invention enables rapid preparation of salted egg yolks, greatly shortening the production cycle and significantly improving enterprise production efficiency. Detailed Implementation

[0012] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0013] The first aspect of the present invention provides a method for processing egg yolks, the method comprising: enzymatically hydrolyzing the egg yolks and mixing them with a protease hydrolysate; wherein the protease hydrolysate is a soybean protease hydrolysate isolated from soybeans and / or an egg yolk particle protease hydrolysate.

[0014] In this invention, in order to achieve a higher degree of lipid oxidation, a richer salted egg yolk flavor, and better formability in the egg yolk, the weight ratio of the egg yolk to the protease hydrolysate is 10:0.1-1, which can be 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, or any two of the above values ​​within a range.

[0015] Preferably, the mixing method is to stir and then seal. More preferably, the mixing conditions include: a temperature of 25-40°C, which can be any two of the values ​​formed by 25°C, 30°C, 35°C, 40°C or above, and a time of 0.5-3 hours, which can be any two of the values ​​formed by 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours or above, and a time of ...3 hours, 0.5 hours, and a time of 0.5 hours, 1 hour, 1.5 hours, 2 hours, 3 hours, and a time

[0016] Preferably, the egg yolk is a bird's egg yolk, more preferably a chicken egg yolk and / or a duck egg yolk, and even more preferably a fresh chicken egg.

[0017] Preferably, the soybean protein isolate hydrolysate is a product obtained by hydrolyzing soybean protein isolate with proteases. Preferably, the egg yolk granule hydrolysate is a product obtained by hydrolyzing egg yolk granule protein with proteases. Preferably, the egg yolk is bird egg yolk, more preferably chicken egg yolk and / or duck egg yolk. Even more preferably, the egg yolk is fresh egg yolk. The egg yolk and the yolk may be the same or different.

[0018] In this invention, the method for preparing the egg yolk granule protein includes: centrifuging the egg yolk, wherein the centrifugal force is 8000-12000g, which can be any two values ​​within the range of 8000g, 8500g, 9000g, 9500g, 10000g, 10500g, 11000g, 11500g, 12000g or more; more preferably, the centrifugation conditions include a temperature of 5-15℃, which can be any two values ​​within the range of 5℃, 7℃, 9℃, 11℃, 13℃, 15℃ or more, and a time of 30-60min, which can be any two values ​​within the range of 30min, 35min, 40min, 45min, 50min, 55min, 60min or more. The resulting precipitate is egg yolk granule protein.

[0019] In this invention, the preparation method of the protease hydrolysate is a conventional method in the art of hydrolyzing protein raw materials with proteases. Preferably, the preparation method of the soybean protein isolate or egg yolk granule protein hydrolysate includes: in the presence of water, hydrolyzing soybean protein isolate or egg yolk granule protein with proteases and then inactivating the enzyme.

[0020] In this invention, to achieve better hydrolysis and obtain protease hydrolysates with higher lipid oxidation levels, higher fat permeability, higher salted egg yolk flavor, and better formability during egg yolk preparation, preferably, the content of soy protein isolate in the hydrolysis system is 2-10% by weight, which can be any two values ​​forming a range or value within the range of 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, or more. More preferably, the content of egg yolk granule protein in the hydrolysis system is 5-12% by weight, which can be any two values ​​forming a range or value within the range of 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, or more.

[0021] In this invention, to achieve better hydrolysis and obtain protease hydrolysates with higher lipid oxidation levels, higher fat permeability, higher salted egg yolk flavor, and better formability during egg yolk preparation, preferably, the total enzyme activity of the protease relative to 1g of the soy protein isolate is 1-240U. More preferably, the total enzyme activity of the protease relative to 1g of the egg yolk granule protein is 3-720U. Further preferably, the hydrolysis conditions include: a temperature of 35-65℃, which can be any two of the following values: 35℃, 40℃, 45℃, 50℃, 55℃, 60℃, 65℃, or higher; and a time of 0.5-1.5h, which can be any two of the following values: 0.5h, 0.7h, 0.9h, 1.1h, 1.3h, 1.5h, or higher.

[0022] In this invention, when preparing soy protein isolate hydrolysate, heating can be performed before hydrolyzing the soy protein isolate. The heating conditions include: a temperature of 90-100℃, which can be any two of the following values: 90℃, 92℃, 94℃, 96℃, 98℃, 100℃ or higher; and a time of 5-15 min, which can be any two of the following values: 5 min, 7 min, 9 min, 11 min, 13 min, 15 min or higher.

[0023] In this invention, when preparing soybean protein hydrolysate isolate, the enzyme-inactivating product can also be dried. The drying method is not limited, as long as the moisture in the enzyme-inactivating product is removed, and low-temperature drying is preferred.

[0024] In this invention, the enzyme inactivation method is a common method in the art, which will not affect the lipid oxidation of egg yolk, the flavor of salted egg yolk, the fat leakage rate and the formability. Preferably, it is heating. The heating method includes: a temperature of 90-100℃, which can be any two values ​​of 90℃, 92℃, 94℃, 96℃, 98℃, 100℃ or above, or values ​​within the range; and a time of 5-15min, which can be any two values ​​of 5min, 7min, 9min, 11min, 13min, 15min or above, or values ​​within the range.

[0025] In this invention, to achieve a higher fat leakage rate, a lower degree of lipid oxidation, a richer salted egg yolk flavor, and better formability in the egg yolk, the enzymatic hydrolysis method includes: subjecting the egg yolk to a first contact with a protease. Preferably, the total enzyme activity of the protease is 3-720 U relative to 1g of the egg yolk.

[0026] In this invention, the optimal hydrolysis temperature of the protease is generally 35-50℃. The inventors of this invention have discovered that when the temperature is 55-70℃, the egg yolk can achieve a higher degree of lipid oxidation, a higher salted egg yolk flavor and fat leakage rate, and better formability. Therefore, the conditions for the first contact include a temperature of 55-70℃, which can be any two values ​​from 55℃, 56℃, 57℃, 58℃, 59℃, 60℃, 61℃, 62℃, 63℃, 64℃, 65℃, 66℃, 67℃, 68℃, 69℃, 70℃ or higher, preferably 55-60℃; and a time of 2-6 hours, which can be any two values ​​from 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours, 6 hours or higher.

[0027] In this invention, to achieve a higher fat leakage rate, a lower degree of lipid oxidation, a richer salted egg yolk flavor, and better formability in the egg yolk, the protease is a neutral protease and / or a flavor protease. The protease used in the egg yolk mixture and the protease used in preparing the protease hydrolysate can be the same or different.

[0028] In this invention, the neutral protease is generally derived from Bacillus subtilis, thermolytic proteolytic Bacillus, Aspergillus terrestris, and actinomycetes.

[0029] In this invention, the flavor enzyme is a complex flavor protease produced by fermentation of Aspergillus oryzae strain, followed by purification and compounding, which can alter the flavor of food during processing.

[0030] In this invention, the neutral protease activity is defined as the amount of enzyme required to produce 1 μg of casein per minute under conditions of pH 7.5 and temperature 40°C, which is one enzyme activity unit.

[0031] In this invention, the enzyme activity of the flavor protease is defined as the amount of enzyme required to produce 1 μg of casein per minute under conditions of pH 7.5 and temperature 37°C, which is one enzyme activity unit.

[0032] In this invention, in order to obtain mature salted egg yolks, the method further includes: subjecting the mixed product to heat treatment; the heat treatment conditions include: a temperature of 90-130°C and a time of 10-20 min.

[0033] In this invention, the heat treatment is a commonly used heating method in the art, such as steaming, baking, or microwave heating. It should be noted that when using conventional methods to process egg yolks, microwave heating produces salted egg yolks with better results than steaming or baking. However, when using the method of this application to process egg yolks, steaming or baking can achieve the same effect as microwave heating, reducing the use of equipment and facilitating industrial production.

[0034] In this invention, if the goal is to prepare salted egg yolks, the method further includes: the mixed product undergoing a second contact with salt before heat treatment.

[0035] In this invention, in order to make the egg yolks have a better flavor after pickling, the weight ratio of the egg yolks to salt is 100:1-3, which can be any two values ​​of 100:1, 100:1.5, 100:2, 100:2.5, 100:3 or the values ​​within the range.

[0036] A second aspect of the present invention provides an egg yolk processed by the method described above.

[0037] A third aspect of the present invention provides the application of the above-mentioned protease hydrolysate in the preparation of salted egg yolks.

[0038] The fourth aspect of the present invention provides the application of the above-mentioned proteolytic hydrolysate in promoting lipid oxidation.

[0039] The present invention will be described in detail below through examples. In the following examples, the neutral protease is sourced from Shanghai Yuanye Biotechnology Co., Ltd., product number: S10013. ， The enzyme activity is 100 U / g;

[0040] Flavor protease source: Shanghai Yuanye Biotechnology Co., Ltd., product number: S10153, enzyme activity is 3000U / g;

[0041] Alkaline protease source: Shanghai Yuanye Biotechnology Co., Ltd., product number: S10154, enzyme activity is 200U / g;

[0042] Trypsin source: Sigma-Aldrich, USA, product number: P7545, enzyme activity: 8×USP;

[0043] Preparation method of soy protein isolate: Add deionized water to soybean meal to a material-to-liquid ratio of 1:15, adjust the pH to 8, stir in a water bath for 90 min, filter with gauze, centrifuge the filtrate at 4000 r / min for 20 min, take the supernatant and adjust the pH to 4.5, let stand for 30 min, centrifuge at 1000 r / min for 5 min, repeat 3 times, pour off the excess liquid, leaving the protein precipitate, wash the soy protein isolate (SPI) 3 times with deionized water, adjust the pH to neutral, freeze dry under vacuum, and set aside for later use to obtain soy protein isolate.

[0044] Egg yolk granule protein: Separate and collect the egg yolks, mix them thoroughly, add an equal weight of deionized water to the egg yolks and stir for 20 minutes until homogeneous. Centrifuge at 10000g at 10℃ for 45 minutes. Retain the precipitated egg yolk granule protein.

[0045] Sensory evaluation method for salted egg yolk flavor base: A sensory evaluation team of 10 evaluators, including 3 women and 3 men, aged 21-27, was formed. All team members had undergone sensory training, and a consensus was reached on the definition and properties of salted egg yolk flavor, focusing on its primary characteristic. The sensory evaluation was based on a 100-point scale, with scores awarded based on four aspects: color (20 points), shape (25 points), flavor (30 points), and texture (25 points). Detailed sensory evaluation criteria are shown in Table 1. The sensory evaluation experiment was repeated twice.

[0046] Table 1

[0047]

[0048] Method for determining thiobarbituric acid value: Weigh a certain amount of sample and mix it thoroughly with TCA-TBA-HCl solution (containing 15% g / mL trichloroacetic acid, 0.375% g / mL thiobarbituric acid, and 0.25 mol / L hydrochloric acid) at a ratio of 2:1 (v / v), using deionized water as a blank control. Homogenize at 5000 rpm for 2 min using a homogenizer to ensure thorough mixing. Heat in a boiling water bath for 15 min, then remove and allow to cool naturally. Centrifuge at 3000g and 15℃ for 10 min in a low-temperature centrifuge, and collect the supernatant for determination. Measure the absorbance of the sample solution at 532 nm using a UV-Vis spectrophotometer. Calculate the TBARS value based on the standard curve of malondialdehyde (MDA), a decomposition product of tetraethoxypropane. The result is expressed as μmol MDA / mg egg yolk.

[0049] Fat leakage rate test method: The fat leakage rate is defined as the ratio of free fat content to total fat content. Take 5g of salted egg yolk flavor base sample into a centrifuge tube, add 25mL of deionized water, and homogenize at 5000rpm for 30s until completely mixed. After mixing, centrifuge at 11200×g, 20℃ for 30min. Retain the supernatant, and add 25mL of n-hexane:isopropanol (3:2, v / v) mixture to the supernatant. Place the mixture in a separatory funnel and allow it to separate into layers. Collect the solvent layer, and heat the collected liquid in an 82℃ water bath until the liquid no longer decreases. Then, dry it in a 105℃ oven to constant weight and weigh the remaining residue, which is the free fat content. Take 3g of salted egg yolk sample into a centrifuge tube, and add 35mL of n-hexane:isopropanol (3:2 v / v) mixture. Homogenize the mixture at 5000 rpm for 30 seconds until completely homogenized. Filter the mixture with filter paper and collect the filtrate. Heat the filtrate in an 82°C water bath until it no longer decreases in volume. Then, place it in a 105°C oven and dry it to constant weight. Weigh the remaining residue; this is the total fat content.

[0050] Headspace solid-phase microextraction and gas chromatography-mass spectrometry (testing of volatile flavor compounds in salted egg yolk flavor): Take 10g of salted egg yolk base sample and place it in a headspace extraction bottle. Add 2μL of internal standard 2-methyl-3-heptanone (0.816μg / μL) and quickly seal the sample. Pre-equilibrate the sample at 70℃ for 10 min. Then, insert the aged extraction head into the extraction bottle, with the extraction head 0.5cm–1cm away from the sample, and perform headspace adsorption for 30 min to extract volatile components. After extraction, immediately insert the extraction head into the GC-MS inlet and desorb at 250℃ for 5 min. Chromatographic conditions: A DB-WAX capillary column (30m × 250μm × 0.25μm) was used; the column oven was initially heated to 40℃ and held for 4 min, then increased to 90℃ at a rate of 5℃ / min, and then increased to 230℃ at a rate of 10℃ / min and held for 6 min; helium was used as the carrier gas at a flow rate of 1.0 mL / min; the injection port and interface temperatures were both 250℃, and splitless injection was used. Mass spectrometry conditions: An EI source with an electron energy of 70 eV was used; the quadrupole temperature was 150℃; the ion source temperature was 230℃; and full scan mode was used for signal acquisition.

[0051] Analysis method for the textural properties of salted egg yolk (measured using a Brookfield CTX texture analyzer): After the egg yolk flavor base is prepared, 5g of sample (accurate to 0.001) is accurately weighed and placed in a mold to form a cylinder with a diameter of 10mm and a height of 20mm for measurement. All samples are measured in parallel 5 times. The experiment uses texture profile analysis (TPA, also known as two chewing tests). Measurement parameters: pre-test speed 5.0mm / s; test speed 2.0mm / s; post-test speed 5.0mm / s; compression ratio 50%; trigger point load 5g; probe model TA36 cylindrical probe, diameter 36mm.

[0052] Example 1

[0053] (1) A 4% by weight soy protein isolate solution was magnetically stirred for 1 hour until completely dissolved. The dissolved SPI solution was heated in a water bath at 95°C for 10 minutes. After the SPI solution cooled to room temperature, neutral protease (pH 7, 50°C) with an E / S ratio of 3% was added, and enzymatic hydrolysis was performed in a water bath for 1 hour. After hydrolysis, the enzyme was inactivated by water bath at 95°C for 10 minutes. After cooling to room temperature, the solution was freeze-dried at low temperature to obtain a freeze-dried powder of soy protein isolate hydrolysate.

[0054] (2) Take fresh duck eggs, wash them, break them open, and separate the yolks using a separator without damaging the yolk membrane. Place the yolks on absorbent paper and roll them slowly to remove the egg white adhering to the membrane. Collect the yolks and stir well to obtain 10g of yolk (1.575g of egg white). Add 0.04725g each of neutral protease and flavor protease to the yolks according to the E / S ratio of 3%, and stir well. Seal the container with plastic wrap and enzymatically hydrolyze in a 60℃ water bath for 2 hours. After that, remove the container and add 0.2g of freeze-dried soybean protease hydrolysate and stir well (temperature 35℃, time 1 hour). Add 0.2g of edible salt to the yolk hydrolysate and stir well. Steam the yolk hydrolysate in a steamer with the lid and opening for 15 minutes at 100℃, stirring constantly during steaming. After steaming, remove the container, seal it with plastic wrap, and refrigerate overnight at 4℃. The finished product is then obtained.

[0055] E: weight of the protease (in g), S: weight of the protein (in g).

[0056] Example 2

[0057] (1) A 4% by weight soy protein isolate solution was magnetically stirred for 1 hour until completely dissolved. The dissolved SPI solution was heated in a water bath at 95°C for 10 minutes. After the SPI solution cooled to room temperature, neutral protease (pH 7, 50°C) with an E / S ratio of 3% was added, and enzymatic hydrolysis was performed in a water bath for 1 hour. After hydrolysis, the enzyme was inactivated by water bath at 95°C for 10 minutes. After cooling to room temperature, the solution was freeze-dried at low temperature to obtain a freeze-dried powder of soy protein isolate hydrolysate.

[0058] (2) Take fresh duck eggs, wash them, break them open, and separate the yolks using a separator without damaging the yolk membrane. Place the yolks on absorbent paper and roll them slowly to remove the egg white adhering to the membrane. Collect the yolks and stir well to obtain 10g of yolk (1.575g of egg white). Add 0.04725g each of neutral protease and flavor protease to the yolks according to the E / S ratio of 3%, and stir well. Seal the container with plastic wrap and enzymatically hydrolyze in a 60℃ water bath for 2 hours. After that, remove the container and add 0.8g of freeze-dried soybean protease hydrolysate and stir well (temperature 30℃, time 2 hours). Add 0.2g of edible salt to the yolk hydrolysate and stir well. Steam the yolk hydrolysate in a steamer with the lid and opening for 20 minutes at 95℃, stirring constantly during steaming. After steaming, remove the container, seal it with plastic wrap, and refrigerate overnight at 4℃. The finished product is then obtained.

[0059] E: weight of the protease (in g), S: weight of the protein (in g).

[0060] Example 3

[0061] The method is the same as in Example 1, except that the neutral protease in step (1) is replaced with a flavor protease (pH 7, 50°C).

[0062] Example 4

[0063] The method is the same as in Example 1, except that the soybean isolate protein hydrolysate is replaced with egg yolk particle protein hydrolysate.

[0064] Step (1) Preparation of egg yolk granule enzymatic hydrolysate: Add deionized water to the egg yolk granule protein until the initial weight of the yolk is reached, and stir the egg yolk granule protein until completely reconstituted (protein content is 8% by weight). Add neutral protease (pH 7, 50℃) with E / S = 3% to the reconstituted solution, and perform enzymatic hydrolysis in a water bath for 1 hour. After hydrolysis, inactivate the enzyme by incubating in a 95℃ water bath for 10 minutes. After cooling to room temperature, store in a 4℃ refrigerator for later use to obtain egg yolk granule enzymatic hydrolysate. E: weight of protease (unit: g), S: weight of protein (unit: g).

[0065] Example 5

[0066] The method of Example 4 was followed, except that the neutral protease was replaced with a flavor protease (pH 7, 50°C) when preparing the egg yolk granule hydrolysate.

[0067] Example 6

[0068] The method is the same as in Example 1, except that the 60°C water bath in step (2) is changed to a 40°C water bath.

[0069] Example 7

[0070] The method is the same as in Example 1, except that the 60°C water bath in step (2) is changed to a 50°C water bath.

[0071] Example 8

[0072] The method is the same as in Example 1, except that the 60°C water bath in step (2) is changed to a 70°C water bath.

[0073] Example 9

[0074] The method is the same as in Example 1, except that the neutral protease and flavor protease in step (2) are replaced with alkaline protease (pH 10, 50°C).

[0075] Example 10

[0076] The method is the same as in Example 1, except that the neutral protease and flavor protease in step (2) are replaced with trypsin (pH 8, 37°C).

[0077] Comparative Example 1

[0078] The method is the same as in Example 1, except that soybean protein hydrolysate is not added and water is used instead.

[0079] Comparative Example 2

[0080] The method is the same as in Example 1, except that neutral protease and flavor protease are not added in step (2).

[0081] Test case

[0082] (1) The sensory evaluation of salted egg yolk flavor, TBARS value and fat leakage rate obtained by the examples and comparative examples are shown in Table 1. The TBARS value can assess the lipid oxidation in the egg yolk. The higher the degree of lipid oxidation and the higher the fat leakage rate, the richer the salted egg yolk flavor.

[0083] Table 1

[0084]

[0085]

[0086] In Examples 1-5, the salted egg yolks obtained by enzymatic hydrolysis of egg yolks at 60°C, with the addition of soybean protein hydrolysate and egg yolk particle hydrolysate respectively, exhibited significantly higher lipid oxidation and fat leakage rates than Comparative Examples 1 and 2, and possessed a rich salted egg yolk flavor. The salted egg yolks obtained by enzymatic hydrolysis at 60°C showed higher lipid oxidation, fat leakage rates, and sensory evaluation results than those obtained at 40°C, 50°C, and 70°C (Examples 6-8). However, for the salted egg yolks obtained by adding soybean protein / egg yolk particle hydrolysate obtained from alkaline protease or trypsin hydrolysis (Examples 9 and 10), although the lipid oxidation and fat leakage rates were higher, the sensory scores were lower.

[0087] (2) The concentrations of volatile compounds in salted egg yolks obtained in the examples and comparative examples (in ng / g) are shown in Table 2.

[0088] Table 2

[0089]

[0090]

[0091] Hexanal, benzaldehyde, and 2-n-pentylfuran are three components that significantly contribute to the flavor of salted egg yolks. High concentrations of hexanal impart a vanilla-like aroma, while benzaldehyde offers both nutty and fruity notes. It is also a key flavor compound in salted egg yolks, but excessively high concentrations result in lower sensory scores. 2-n-pentylfuran, a product of linoleic acid oxidation, is a crucial flavor component in egg products. In Examples 1-5, the salted egg yolks prepared by enzymatic hydrolysis at 60°C, with the addition of soybean protein hydrolysate and egg yolk particle protein hydrolysate, showed significantly higher levels of hexanal, benzaldehyde, and 2-n-pentylfuran compared to Comparative Examples 1 and 2. The concentrations of key flavor compounds in the salted egg yolks obtained by enzymatic hydrolysis at 60°C were also higher than those obtained at 40°C, 50°C, and 70°C (Examples 6-8). However, for salted egg yolks containing soy protein / egg yolk granule hydrolysates obtained by adding alkaline protease or trypsin hydrolysate (Examples 9 and 10), the high concentration of hexanal resulted in a low sensory score for the salted egg yolks.

[0092] (3) The textural properties of the salted egg yolks obtained in the examples and comparative examples are shown in Table 3.

[0093] Table 3

[0094]

[0095]

[0096] Texture properties reflect the mouthfeel of salted egg yolk samples. The hardness, chewiness, and viscosity of salted egg yolks need to be moderate, neither too high nor too low. In Examples 1-5, the egg yolks were enzymatically hydrolyzed at 60°C, and the salted egg yolk products prepared by adding soybean protein hydrolysate and egg yolk particle protein hydrolysate, respectively, had significantly lower hardness and chewiness than Comparative Example 2 (sample with unhydrolyzed egg yolks). Enzymatic hydrolysis of egg yolks at 70°C (Example 7) causes the egg yolks to coagulate into a gel, significantly increasing their hardness and chewiness while decreasing their viscosity, resulting in a poorer mouthfeel compared to Example 1.

Claims

1. A method for processing egg yolks, characterized in that, The method includes: hydrolyzing egg yolks and then mixing them with protein hydrolysates; The protease hydrolysate is soybean isolated protease hydrolysate and / or egg yolk granule protease hydrolysate; The method for enzymatic hydrolysis of egg yolk includes: making a first contact between the egg yolk and a protease; The conditions for the first contact include: a temperature of 55-60℃ and a time of 0.5-6h; The protease is a neutral protease and / or a flavor protease; The weight ratio of egg yolk to protein hydrolysate is 10:0.1-1; The total enzyme activity of the protease is 3-720 U relative to 1 g of the egg yolk.

2. The method according to claim 1, wherein, The mixing conditions include: a temperature of 25-40℃ and a time of 0.5-3h; And / or, the yolk is a bird's yolk.

3. The method according to claim 2, wherein, The egg yolk is a chicken egg yolk and / or a duck egg yolk.

4. The method according to claim 2 or 3, wherein, The egg yolk is a fresh egg yolk.

5. The method according to claim 1, wherein, The soybean protein isolate hydrolysate is the product obtained by hydrolyzing soybean protein isolate with proteases. And / or, the egg yolk granule protease hydrolysate is a product obtained by protease hydrolysis of egg yolk granule protein.

6. The method according to claim 5, wherein, The yolk in question is bird yolk.

7. The method according to claim 5, wherein, The egg yolk is chicken egg yolk and / or duck egg yolk.

8. The method according to any one of claims 5-7, wherein, The egg yolk is fresh.

9. The method according to claim 5, wherein, The method for preparing the soybean protein isolate or egg yolk protein isolate includes: in the presence of water, the soybean protein isolate or egg yolk protein is hydrolyzed with a protease and then inactivated.

10. The method according to claim 9, wherein, In the hydrolysis system, the content of the soy protein isolate is 2-10% by weight. And / or, in the hydrolysis system, the content of the egg yolk granule protein is 5-12% by weight; And / or, relative to 1g of the soy protein isolate, the total enzyme activity of the protease is 1-240U; And / or, relative to 1g of the egg yolk granule protein, the total enzyme activity of the protease is 3-720U; And / or, the hydrolysis conditions include: a temperature of 35-65°C and a time of 0.5-1.5 h.

11. The method according to claim 1 or 2, wherein, The method further includes: subjecting the mixed product to heat treatment.

12. The method according to claim 11, wherein, The heat treatment conditions include: a temperature of 90-100℃ and a time of 10-20 min; And / or, the method further includes: subjecting the mixture to a second contact with salt prior to heat treatment.

13. The method according to claim 12, wherein, The weight ratio of egg yolk to salt is 100:1-3.

14. Egg yolks treated by the method according to any one of claims 1-13.

15. The application of the method for processing egg yolks according to any one of claims 1-13 in the preparation of salted egg yolks.

16. The use of the method for treating egg yolk according to any one of claims 1-13 in promoting the oxidation of egg yolk lipids.

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