A low-salt salted egg pickling solution and a method for pickling low-salt salted eggs

Abstract

The application discloses a low-salt salted duck egg pickling solution and a method for pickling low-salt salted duck eggs, and belongs to the technical field of food processing. Each 100 parts by weight of water contains the following components by weight: 16-18 parts of salt, 0.2-2 parts of composite phosphate, 0-5 parts of baijiu, 0.1-1 parts of spice powder, 1-5 parts of sucrose, and 0.5-4 parts of sugar alcohol; the composite phosphate comprises sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate in a weight ratio of (1-3):(1-3):(1-3). The pickling solution can realize low-salt concentration pickling to obtain high-quality low-salt salted duck eggs, and significantly shortens the pickling period; the salted duck egg yolk of the obtained high-quality low-salt salted duck egg has the texture of loose sand, orange yellow color, high oil yield, low salt content, and after vacuum packaging storage for three months, the egg yolk is free of black circles and mud.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of food processing, more particularly, to a low-salt salted egg pickling liquid and a method for pickling low-salt salted eggs. BACKGROUND

[0002] Salted egg is a traditional egg product in China and is popular worldwide. In the traditional process, duck eggs without cleaning are directly pickled to avoid bad eggs during pickling. In order to inhibit microorganisms in the liquid, the salt content in the pickling liquid is high, and the salt content in egg white and yolk is greatly different. In addition, the influence of microorganisms makes the salted egg yolk prone to black ring and fading during storage. The production cycle of salted eggs produced by the traditional pickling process is long, the salt content of salted egg white is high and is often discarded, and the salted egg yolk is widely used due to its unique taste and rich nutrition, and is often used as an important raw material for making moon cakes, zongzi, egg yolk pastries and the like. Moreover, the salted egg yolk produced by the traditional pickling process is prone to quality instability such as black ring and fading after vacuum packaging sterilization and storage, which seriously affects the market value of salted eggs. Therefore, the excessive salt content of salted eggs and the unstable storage quality are problems that need to be solved in the industry.

[0003] Currently, the most common methods for reducing salt content on the market are mainly three kinds: directly reducing the amount of salt, compounding salt with certain substances, and improving processing technology. The first method can greatly reduce the salinity, but it will seriously reduce the flavor of the food; the second method is widely used in salt-reduced foods, among which KCl is a common and effective metal substitute salt; the intake of this salt will not cause functional hazards to the human body, and the taste of food is within the acceptable range of consumers, but the metallic taste and bitterness brought by KCl will affect its eating effect. In addition, reducing salt will affect the texture characteristics, physicochemical properties and storage properties of food. Therefore, how to reduce the salinity without affecting the sensory quality of food is an important difficulty faced by the food industry. The third method will increase the processing cost, and the effect of reducing salt is limited. For example, Chinese patent CN110269203A first uses a low-concentration salt solution to soak, then uses a pickling solution to soak for 12-72h, wherein the solid composition of the pickling solution is composed of sodium salt, potassium salt, magnesium chloride, calcium chloride and ferric citrate, and the salt content of the mature salted egg yolk is 1.22±0.32%; Chinese patent CN112385793A first cleans and disinfects duck eggs, and uses a segmented pickling method to obtain clean salted egg shells, moderate saltiness, high oil yield of egg yolk, no black circle and hard core, and the salt content of egg white and egg yolk is less than 4%; Chinese patent CN108634228A uses ultrasonic power and frequency of 350w and 20khz every 6 days to treat the pickling solution (mass fraction of 20%), and then uses a low-concentration pickling solution (mass fraction of 3%) for pickling. After pickling, the salt content of egg white is 5.07%, and the oil yield of egg yolk is 58.61%. However, this method is expensive, the operation process is complicated, the equipment maintenance cost is high, and it is actually less used in factories. SUMMARY

[0004] In view of the deficiencies of the prior art, one of the purposes of the present application is to provide a pickling solution for pickling low-salt salted eggs and a pickling method thereof, to solve the problems of excessive salt content, unstable storage quality, complex operation process and high production cost of salted eggs in the prior art.

[0005] The above purpose of the present application is achieved by the following technical solutions:

[0006] The present application provides a low-salt salted egg pickling solution, which contains the following components in an amount of 100 parts by weight of water: 16-18 parts of salt, 0.2-1.5 parts of composite phosphate, 0.1-5 parts of liquor, 0.1-1 parts of spice powder, 1-5 parts of sucrose, and 0.1-4 parts of sorbitol; the composite phosphate includes sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate in a weight ratio of (1-3):(1-3):(1-3).

[0007] Based on the technical scheme of the present application, the following beneficial effects are achieved:

[0008] (1) The pickling solution of the present application can realize low-salt concentration pickling to obtain high-quality low-salt salted duck eggs, and significantly shorten the pickling period (25-30 days). The salted duck eggs obtained have a high-quality salted yolk with a loose sand texture (hardness of about 500), an orange-yellow color, a high oil yield (higher than 60%), a low salt content (the salt content of egg white is about 4%, the salt content of yolk is about 1%, and the salt content of whole egg is about 2.5%), and no black ring and no mud after vacuum packaging storage for three months.

[0009] (2) The chelation of phosphate can effectively inhibit the generation of black ring of salted yolk. The chelation refers to that the oxygen atoms in the phosphate molecules are coordinated with metal ions through coordination bonds to form very stable complexes. The phosphate can chelate with the multivalent metal ions released in food to form stable water-soluble complexes, and the chelation can effectively prevent the discoloration of food caused by metal, thereby playing a color protection role. In addition, the phosphate has a strong penetration effect. A small amount of complex phosphate added can make the pickling solution reach a high ionic strength, effectively enhance the flux density of salt mass transfer into the egg, promote the penetration of each pickling agent into the egg, accelerate the pickling, and shorten the pickling period. The addition of phosphate can easily form a more ordered and smaller pore size inside the protein gel, forming a dense protein gel network, thereby facilitating the excretion of oil wrapped in lipoprotein, increasing the oil yield of yolk, and with the increase of oil yield, the yolk texture is looser.

[0010] (3) The addition of sucrose can further increase the ionic strength of the complex phosphate-sodium chloride system, further increase the ionic strength of the pickling environment, and promote the pickling process.

[0011] On the basis of the above scheme, the present application can also be improved as follows:

[0012] Preferably, 4-5 parts of sucrose are contained in 100 parts of water.

[0013] Preferably, 16 parts of salt are contained in 100 parts of water.

[0014] Preferably, 4-5 parts of white wine are contained in 100 parts of water. 25 flavor substances are detected in the salted yolk added with white wine, which are alcohols, aldehydes, alkenes, ketones, esters, aromatic compounds and hydrocarbon compounds, among which the proportion of alcohol substances is 18.55%, and the proportion of ester substances is 75.65%. White wine helps to improve the flavor of salted yolk.

[0015] Preferably, 0.4-0.6 parts of spice powder are contained in 100 parts of water.

[0016] Preferably, 0.9-1.5 parts of the compound phosphate is contained in 100 parts of water. At the adding amount, the low-salt salted egg has high quality and low pickling cost.

[0017] Preferably, the weight ratio of sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate in the compound phosphate is 1:1:1. At the ratio, the low-salt salted egg has optimal quality, short pickling period, low egg white salt content, high egg yolk oil out rate, long vacuum packaging storage time and no black ring.

[0018] Another object of the present application is to provide a method for pickling low-salt salted egg by using the pickling liquid, comprising the following steps:

[0019] S1, configuring a pickling liquid;

[0020] S2, soaking and pickling the cleaned duck egg in the pickling liquid for 26-30 days, and passing ozone every 3-12 days during the pickling process, and each time for 10-90 min.

[0021] In the traditional process, the pickling period is usually about 40 days, and the salted egg yolk is prone to black ring and desolventizing during storage, and the egg white salt content is high and not suitable for eating. Based on the method for pickling low-salt salted egg of the present application, the pickling period is about 28 days, which is significantly shortened. During the pickling process, the pickling liquid is sterilized by ozone treatment multiple times, which can significantly reduce the bacterial colony during the pickling process and ensure the quality of the salted duck egg during the pickling process. The pickling liquid system composed of salt, water and pickling aids (compound phosphate, sucrose, etc.) accelerates the pickling process, and obtains low-salt salted egg with low egg white salt content, high egg yolk oil out rate, salted egg yolk with soft texture, and orange yellow egg yolk color, and after vacuum packaging storage for three months, the egg yolk has no black ring and no mud; in addition, since the salt content of the pickled salted egg white and salted egg yolk is low, the destruction of the egg yolk gel during storage is small, and the oxidation of the protein is low, so that the salted egg yolk can better maintain the state of soft and orange yellow.

[0022] On the basis of the above scheme, the present application can also be improved as follows:

[0023] Preferably, in S2, ozone is passed every 5-9 days, and each time for 20-40 min. Under the treatment condition, the pickling liquid can always maintain a very low bacterial concentration during the pickling period.

[0024] Preferably, in step S2, the duck egg is soaked in 6-10% citric acid solution for 0.3-1.5 hours before being pickled, then taken out, washed and dried. The eggshell is mainly composed of calcium carbonate. After the eggshell is soaked in citric acid, calcium reacts with citric acid, the outer membrane of the eggshell falls off, the eggshell becomes thin, and the pore size of the eggshell is increased, so that the entry of salt and the entry and exit of water are accelerated, thereby accelerating the pickling speed, and the pickling period of the salted egg can be effectively shortened. The salt content of the pickling solution of the application is low. If citric acid soaking is not used, the osmotic pressure of the eggshell will be small, which will seriously affect the penetration rate, resulting in a long pickling time or an increase in the hard core rate. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 The cross-sectional view of the low-salt salted duck egg pickled by example 1 (A) and comparative examples 2-7 (B-H);

[0026] Figure 2 The intuitive diagram of the salted egg yolk during pickling;

[0027] Figure 3 The changes of the salt content (A), water content (B) and oil yield (C) of the salted egg during pickling;

[0028] Figure 4 The changes of the hardness (A) and elasticity (B) of the salted egg yolk during pickling;

[0029] Figure 5 The cross-sectional view of the salted egg yolk of the low-salt salted duck egg pickled by the application after vacuum storage for 3 months;

[0030] Figure 6 The appearance diagram of the salted duck egg yolk of the salted duck egg of comparative example 2 after vacuum storage for 3 months;

[0031] Figure 7 The conductivity-time change diagram under different sucrose addition amounts (A), different composite phosphate addition amounts (B) and different systems (C). DETAILED DESCRIPTION

[0032] The technical solutions of the application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the application, not all. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor belong to the protection scope of the application.

[0033] The specific solutions provided by the application are as follows:

[0034] The low-salt salted duck egg pickling liquid according to the embodiment of the application contains the following components in the weight percentage of 100 parts of water: 16-18 parts of salt, 0.2-1.5 parts of composite phosphate, 0-5 parts of Chinese liquor, 0-1 part of spice powder, 1-5 parts of sucrose, and 0-4 parts of sugar alcohol; the composite phosphate includes sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate in a weight ratio of (1-3):(1-3):(1-3). The pickling liquid can realize low-salt concentration pickling to obtain high-quality low-salt salted duck eggs, significantly shorten the pickling period (25-30 days), and obtain high-quality low-salt salted duck eggs with the salted yolk having a loose sandy texture, orange yellow color, high oil yield (higher than 60%), and low salt content (the salt content of egg white is about 4%, the salt content of yolk is about 1%, and the salt content of whole egg is about 2.5%), and the yolk has no black ring and no mud after vacuum packaging storage for three months. The chelation of the phosphate can effectively inhibit the generation of the black ring of the salted yolk. The phosphate can form a soluble complex with metal cations (iron ions) in the solution to prevent the iron ions from being oxidized into ferrous ions, thereby inhibiting the generation of ferrous sulfide and the black ring of the salted yolk. In addition, the phosphate has a strong penetration effect. On the one hand, the composite phosphate has a strong metal ion chelation capacity, can chelate a large amount of salt ions, reduces the combination of salt ions (Na + ) and water, carries the salt ions to penetrate into the egg, for example, the sodium hexametaphosphate contains 6 phosphate groups, each phosphate ion is connected to the adjacent phosphate ion by sharing oxygen atoms to form a chemical bond, thereby forming a ring structure. The ring structure gives the sodium hexametaphosphate unique charge and chelation performance. A small amount of composite phosphate can make the pickling liquid have a high ionic strength, effectively enhance the mass transfer flux density of salt into the egg, promote the penetration of each pickling agent into the egg, accelerate pickling, and shorten the pickling period. On the other hand, the composite phosphate can penetrate into the egg yolk protein molecules and polymerize with the protein in the egg liquid to improve the potential difference of the electric potential of the protein charge, promote the penetration of salt ions (pickling agent), and the polymerization of the composite phosphate and the protein can make the protein deviate from the isoelectric point, so that the proteins repel each other and generate more space between the proteins, thereby facilitating the penetration of the (salt) pickling agent. In addition, the addition of phosphate can make the protein gel form more ordered and smaller pore size inside, thereby forming a dense protein gel network, facilitating the oil in the lipoprotein to seep out, and improving the oil yield of the yolk. With the increase of the oil yield, the yolk texture is looser and sandier. The addition of sucrose can further increase the ionic strength of the composite phosphate-sodium chloride system, further improve the ionic strength of the pickling environment, and promote the pickling process.

[0035] Preferably, 4-5 parts of sucrose are contained in 100 parts of water.

[0036] Preferably, 16 parts of salt are contained in 100 parts of water.

[0037] Preferably, 4-5 parts of baijiu are contained in 100 parts of water. 25 flavor substances are detected in the salted egg yolk added with baijiu, which are alcohol, aldehyde, alkene, ketone, ester, aromatic and hydrocarbon compounds, wherein the alcohol accounts for 18.55%, and the ester accounts for 75.65%, and the baijiu helps to improve the flavor of the salted egg yolk.

[0038] Preferably, 0.4-0.6 parts of spice powder are contained in 100 parts of water. The taste is more rich.

[0039] Preferably, 0.9-1.5 parts of composite phosphate are contained in 100 parts of water. Under the addition amount, the low-salt salted egg has high quality and low pickling cost.

[0040] Based on the low-salt salted egg pickling liquid of the embodiment of the application, the weight ratio of sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate in the composite phosphate is 1:1:1. Under the ratio, the quality of the low-salt salted egg is best, the pickling period is short, the egg white salt content is low, the egg yolk oil yield is high, the vacuum packaging storage time is long and there is no black circle.

[0041] The application also provides a method for pickling low-salt salted eggs by using the above pickling liquid, comprising the following steps:

[0042] S1, configuring a pickling liquid;

[0043] S2, soaking and pickling the cleaned duck eggs in the pickling liquid for 26-30 days, and passing ozone every 3-12 days during the pickling process, and each time for 10-90 min.

[0044] In the traditional process, the pickling period is usually about 40 days, and the salted egg yolk is prone to black circle and fading during storage, and the egg white salt content is high and not suitable for eating. Based on the method for pickling low-salt salted eggs of the application, the pickling period is about 28 days, and the time is significantly shortened. Among them, the ozone treatment during the pickling process can significantly reduce the bacterial colony during the pickling process, and guarantee the quality of the salted duck egg during the pickling process. The pickling liquid system composed of salt, water and pickling aids (composite phosphate, sucrose, etc.) can accelerate the pickling process, and obtain low-salt salted eggs with low egg white salt content, high egg yolk oil yield, soft texture of salted egg yolk, and orange yellow egg yolk color, and after vacuum packaging storage for three months, the egg yolk has no black circle and no mud.

[0045] Further, in S2, ozone is passed every 5-9 days, and each time for 20-40 min. Under the treatment condition, the pickling liquid can always maintain a very low bacterial concentration during the pickling period.

[0046] Further, in step S2, the duck eggs are soaked in a 6% to 10% citric acid solution for 0.3 to 1.5 hours before being pickled. After the eggshells are soaked in the citric acid solution, the pore size of the eggshells is increased, which can accelerate the pickling of the salted eggs.

[0047] In the following examples and comparative examples, the spice powder can be commercially available thirteen spices.

[0048] Example 1

[0049] The present example provides a method for pickling low-salt salted eggs, comprising the following steps:

[0050] (1) Take 100 fresh duck eggs, wash the surface with clean water first, and then dry.

[0051] (2) Soak the duck eggs in a 10% citric acid solution for 50 minutes, then take them out, wash them, and dry them. Then completely immerse the duck eggs in baijiu, and then put them into a pickling barrel.

[0052] (3) Mix 800g of salt, 75g of composite phosphate (wherein the weight ratio of sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate is 1:1:1), 30g of spice powder, 250g of sucrose, 50g of sorbitol and 10kg of water in the pickling barrel.

[0053] (4) Press the duck eggs with bamboo splints on the surface to make them all immersed in the brine for pickling for 28 days, wherein ozone is introduced into the pickling liquid for 30 minutes on the 8th day, the 15th day and the 22nd day during the pickling process, a total of 3 times of ozone treatment.

[0054] Example 2

[0055] The present example provides a method for pickling low-salt salted eggs, comprising the following steps:

[0056] (1) Take 100 fresh duck eggs, wash the surface with clean water first, and then dry.

[0057] (2) Soak the duck eggs in a 10% citric acid solution for 50 minutes, then take them out, wash them, and dry them.

[0058] (3) Mix 850g of salt, 60g of composite phosphate (wherein the weight ratio of sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate is 1:1:1), 25g of spice powder, 250g of sucrose, 40g of sorbitol, 250g of baijiu and 10kg of water in the pickling barrel.

[0059] (4) Press the duck eggs with bamboo splints on the surface to make them all immersed in the brine for pickling for 28 days, wherein ozone is introduced into the pickling liquid for 30 minutes on the 8th day, the 15th day and the 22nd day during the pickling process, a total of 3 times of ozone treatment.

[0060] Example 3

[0061] The present example provides a method for pickling low-salt salted eggs, comprising the following steps:

[0062] (1) Take 100 fresh duck eggs, first wash the surface with clean water, and then dry.

[0063] (2) First soak the duck eggs in a 10% citric acid solution for 50 minutes, then take them out, wash and dry.

[0064] (3) Mix 850g of salt, 45g of composite phosphate (sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate in a weight ratio of 1:1:1), 20g of spice powder, 200g of sucrose, 25g of sorbitol, 250g of white wine and 10kg of water in a pickling barrel.

[0065] (4) Press the duck eggs with bamboo splints on the surface to make them all soak in the brine for 28 days, and during the pickling process, introduce ozone into the pickling solution for 30 minutes on the 8th day, the 15th day and the 22nd day, respectively, for a total of 3 times of ozone treatment.

[0066] Comparative Example 1

[0067] The method of this comparative example is basically the same as that of Example 1, except that no sucrose is added.

[0068] Comparative Example 2

[0069] The method of this comparative example is basically the same as that of Example 1, except that no composite phosphate is added.

[0070] Comparative Example 3 (traditional pickling method)

[0071] The method of this comparative example is basically the same as that of Example 1, except that in step (3), only salt is added, and the amount of salt added is 1000g; in step (1), no clean water is used for washing, and in step (4), no ozone is introduced during the pickling process.

[0072] Comparative Example 4

[0073] The method of this comparative example is basically the same as that of Example 1, except that in step (1), after the duck eggs are dried, a 0.2% sodium hypochlorite solution is prepared and soaked for 30 minutes, then taken out, washed with clean water and dried; in step (3), only salt is added, and the amount of salt added is 900g; in step (4), no ozone is introduced during the pickling process.

[0074] Comparative Example 5

[0075] The method of this comparative example is basically the same as that of Example 1, except that in step (1), the duck eggs are dried under UV light for 30 min; in step (3), only salt is added, and the amount of salt added is 900 g; and in step (4), no ozone is introduced during the pickling process.

[0076] Comparative Example 6

[0077] The method of this comparative example is basically the same as that of Example 1, except that in step (3), only salt is added, and the amount of salt added is 900 g; and in step (4), ozone is introduced only once on the 8th day during the pickling process.

[0078] Comparative Example 7

[0079] The method of this comparative example is basically the same as that of Example 1, except that in step (3), only salt is added, and the amount of salt added is 900 g; and in step (4), ozone is introduced only once on the 8th day and once on the 15th day during the pickling process.

[0080] Comparative Example 8

[0081] The method of this comparative example is basically the same as that of Example 1, except that in step (3), only salt is added, and the amount of salt added is 900 g; and in step (4), ozone is introduced only once on the 8th day, once on the 15th day, and once on the 22nd day during the pickling process.

[0082] Comparative Example 9

[0083] The method of this comparative example is basically the same as that of Example 1, except that in step (3), only salt is added, and the amount of salt added is 900 g; and in step (4), no ozone is introduced during the pickling process.

[0084] Comparative Example 10

[0085] The method of this comparative example is basically the same as that of Example 1, except that in step (4), no ozone is introduced during the pickling process.

[0086] Comparative Example 11

[0087] The method of this comparative example is basically the same as that of Example 1, except that in step (1), the duck eggs are washed clean and then irradiated with UV light for 30 min, and in step (4), no ozone is introduced during the pickling process.

[0088] Test Example

[0089] I. Physico-chemical property test of salted eggs

[0090] The salt content of yolk, the salt content of albumen, the oil out rate of yolk, the hardness of yolk, and the black ring rate of vacuum storage for 3 months of the salted duck eggs in Examples 1-3 and Comparative Examples 1-11 were tested, and the results are shown in Table 1.

[0091] Table 1 Physicochemical properties of salted duck eggs

[0092]

[0093]

[0094] II. Appearance of salted duck eggs

[0095] (1) The appearance of the salted duck eggs in Example 1, Comparative Example 1 and Comparative Example 2 after curing was observed. Most of the salted duck eggs in Comparative Example 1 after curing had a rotten egg phenomenon, while there was no rotten egg phenomenon in Example 1 and Comparative Example 2. The salted duck eggs in Example 1 and Comparative Example 2 after cooking were cut open for observation, and the results are shown as A and B in Figure 1 , respectively. As can be seen from Figure 1 , the albumen of the salted duck eggs with added phosphates was delicate, the tissue structure was complete, and the color was slightly white. The yolk structure was complete, the color was orange-red, there was no black ring, and the hard core area of the yolk was small. The albumen of the salted duck eggs without added phosphates was dark in color, the tissue structure was damaged, the yolk structure was incomplete and had a black ring, and the hard core area of the yolk was large. The quality of the salted duck eggs with added phosphates was higher than that of the salted duck eggs without added phosphates. The cross-sectional views of the salted duck eggs in Comparative Examples 3-8 after cooking are shown as C-H in Figure 1 , respectively. The albumen of the non-washed group (traditional curing method) was dark in color, the yolk was soft and rotten, and was not shaped. By comparing Comparative Examples 4-7, it can be found that the quality of the salted duck eggs obtained by using ozone sterilization technology is better than that of the salted duck eggs obtained by using sodium hypochlorite soaking and ultraviolet irradiation sterilization technology. By comparing Comparative Examples 6-8, it can be found that as the degree of sterilization of the eggshell surface increases, the color of the yolk gradually becomes orange-red, and the hard core area of the yolk becomes smaller. Among them, the albumen of the salted duck eggs in the three ozone groups is delicate and white, the yolk is shaped, and the yolk is soft and delicate.

[0096] By comparing Example 1, Comparative Example 2 and Comparative Example 11, it can be found that the use of ozone sterilization technology in combination with composite phosphates can obtain low-salt salted duck eggs with low albumen salt content, high yolk oil out rate, soft yolk texture, and orange-yellow yolk color. After vacuum packaging and storage for three months, the yolk has no black ring and no muddiness.

[0097] (2) The appearance of the yolk and albumen of the salted duck eggs in Example 1 during the curing process was observed, and the results are shown in Figure 2 , respectively. Figure 2It can be seen that during the pickling process, the high viscosity egg white gradually becomes watery, the outer part of the yolk gradually becomes gelatinous, and the yolk changes from orange to orange-red and from spherical to elliptical, and finally the texture becomes gelatinous. After 28 days of pickling, the egg white of the salted duck egg is delicate, the yolk is orange-red, and there is a hard core in the middle.

[0098] III. Changes in the physicochemical properties of salted eggs during pickling

[0099] 1. Salt content determination

[0100] During the pickling process of Example 1, the salt content of the yolk and albumen of the salted duck egg was determined, and the specific steps were as follows:

[0101] (1) On the 0th day, 7th day, 14th day, 21st day, and 28th day of pickling, 3g (accurate to 0.001g) of cooked salted duck egg sample was taken in a 100mL beaker, and 50mL of distilled water (DW) was added, followed by homogenization with a homogenizer at 5000r / min for 1min to form a uniform emulsion; then a precipitating agent composed of 4mL potassium ferrocyanide solution and 4mL zinc acetate solution was added, and the mixture was shaken thoroughly after the addition of the precipitating agent, and was allowed to stand at room temperature for 30min;

[0102] (2) The contents of the beaker were transferred to a 250mL volumetric flask and diluted with DW, then the solution was filtered and the filtrate was collected, and 10mL of the filtrate was taken in a conical flask;

[0103] (3) 30mL of water and 1mL of potassium chromate solution (5%) were added to the conical flask and shaken uniformly; titrate with 0.1mol / L silver nitrate solution until red yellow color (maintain 1min without fading), record the volume of silver nitrate standard titration solution consumed V1).

[0104] (4) 10mL of DW was taken in a conical flask as a blank control, 30mL of water and 1mL of potassium chromate (5%) were added to the conical flask and shaken uniformly; titrate with 0.1mol / L silver nitrate until red yellow color (maintain 1min without fading), record the volume of silver nitrate standard titration solution consumed (V2).

[0105] (5) The calculation formula of salt content is as follows:

[0106]

[0107] In the formula: C is the concentration of silver nitrate, K is the dilution coefficient, which is 25; m is the mass of the sample; V1 and V2 are the volumes of silver nitrate standard titrant consumed by 10mL of filtrate and 10mL of DW, respectively.

[0108] The potassium ferrocyanide solution is prepared by adding 10.6 g of potassium ferrocyanide into water to make up to 100 mL; the zinc acetate solution is prepared by adding 22 g of zinc acetate into 3 mL of glacial acetic acid, and then making up to 100 mL; the potassium chromate solution is a 5% mass fraction potassium chromate aqueous solution; and the silver nitrate solution is a 0.1 mol / L silver nitrate aqueous solution.

[0109] 2. Moisture content determination

[0110] The moisture content of the egg yolk is determined during the pickling process of Example 1, and the specific steps are as follows:

[0111] On the 0th day, the 7th day, the 14th day, the 21st day and the 28th day of pickling, 3 g of the sample is accurately taken into an aluminum box, and the moisture is dried at 105°C for 12 h to a constant weight. The total mass of the aluminum box and the sample after drying is recorded as W3. The calculation formula of the moisture content is as follows:

[0112]

[0113] In the formula, W1, W2 and W3 respectively represent the mass of the sample before drying, the mass of the aluminum box before drying and the total mass of the aluminum box and the sample after drying.

[0114] 3. Oil exudation determination

[0115] The oil exudation of the egg yolk is determined during the pickling process of Example 1, and the specific steps are as follows:

[0116] (1) The free lipid content is determined, and the specific steps are as follows: On the 0th day, the 7th day, the 14th day, the 21st day and the 28th day of pickling, 3 g of the salted egg yolk is taken, and 25 mL of DW is added. The mixture is homogenized at 5000 r / min for 1 min in a homogenizer. 25 mL of a mixture of n-hexane and isopropyl alcohol (the volume ratio of the two is 3:2) is added to the homogenate. Then it is transferred into a separatory funnel, and is allowed to stand to separate into layers to obtain the upper oil phase. The oil phase is poured into a beaker and is placed in a 55°C evaporator to evaporate most of the organic solution. Finally, the remaining oil phase is poured into a weighing dish and is placed in a 105°C oven to dry to a constant weight (the difference between the two weighing results is less than 0.2 mg). According to the mass of the weighing dish before drying m1, the mass of the weighing dish and the oil phase after drying m2 and the mass of the salted egg yolk M1, the percentage content of free lipid is calculated, and the formula is as follows:

[0117]

[0118] (2) The total lipid content was determined as follows: 1.5g of salted egg yolk was mixed with 20mL of a mixture of hexane and isopropanol (volume ratio 3:2). The mixture was homogenized at 5000r / min for 1min. The homogenate was then filtered. The filtrate was poured into a beaker and evaporated at 55℃ to remove most of the organic solution. Finally, the remaining oil phase was poured into a weighing dish and dried at 105℃ until constant weight (the difference between the two weighings was less than 0.2mg). The percentage of total lipids was calculated based on the mass m3 of the weighing dish before drying, the mass m4 of the weighing dish and oil phase after drying, and the mass M2 of the salted egg yolk. The formula is as follows:

[0119]

[0120] (3) Calculate the oil yield based on the percentage content of free fatty acids and the total fat content:

[0121]

[0122] During the pickling process, the salt content of the egg yolk and egg white changes as follows: Figure 3 As shown in Figure A, the water content of the egg yolk is as follows: Figure 3 As shown in Figure B, the oil yield of the egg yolk is as follows: Figure 3 As shown in C. From Figure 3 It can be seen that throughout the pickling process, the water content of the egg yolk gradually decreases while the salt content increases. After 28 days of pickling, the salt content of the yolk is 1.07%, the salt content of the egg white is 4.03%, the water content of the yolk is 29.27%, and the oil yield is 64.55%. During pickling, salt penetrates the pores on the surface of the duck egg, entering the yolk from the egg white. The salt content in both the egg white and yolk gradually increases, accompanied by yolk dehydration. Water permeates from the inside of the yolk into the egg white and finally to the outside of the eggshell. As the salt content in the yolk increases, the oil yield also increases. The osmosis of salt disrupts the aggregation state of low-density lipoprotein (LDL). The lipids, initially tightly bound and uniformly distributed with proteins, gradually become free and aggregate, causing the egg oil to precipitate from the lipoproteins.

[0123] 4. Determination of textural properties

[0124] In Example 1, total texture analysis (TPA) was performed on the egg yolks during the pickling process. The TPA was measured using a texture analyzer, and the specific steps are as follows:

[0125] The salted egg yolk was separated from the egg white and analyzed using a texture analyzer in TPA mode. The TPA operating parameters were as follows: pre-test speed 5.0 mm / s, test speed 1.0 mm / s, post-test speed 5.0 mm / s, compression ratio 20%, recovery time 5 s, trigger point load 5 g, and probe P / 36R cylindrical shape (25.4 mm). Texture data (hardness and springiness) were collected, and data calculations were performed using computer software.

[0126] Texture analysis results are as follows Figure 4 As shown, by Figure 4 It was observed that the hardness of the egg yolk gradually increased with prolonged pickling time. After 28 days of pickling, the hardness of the egg yolk was 573.46g. The hardness of the egg yolk was significantly correlated with the aggregation state of the proteins. Salt diffused into the egg yolk, causing the protein structure to collapse and aggregate (small protein molecules aggregated to form large protein molecules). The significant dehydration of the egg yolk further intensified this aggregation behavior, resulting in a loose and sandy texture in the egg yolk gel. With prolonged pickling time, the elasticity of the egg yolk decreased, contrary to the trend of hardness change. This was attributed to the destruction of the lipoprotein structure. As the egg yolk protein structure (secondary and tertiary structures) collapsed, lipids, initially tightly bound and uniformly distributed with proteins, gradually became free and aggregated. Egg yolk oil was extracted from the lipoproteins, resulting in a loose and sandy texture in the pickled egg yolk, making it a high-quality, low-salt salted egg.

[0127] IV. Storage Performance Testing

[0128] The salted duck eggs pickled in Example 1 were vacuum-packed, then autoclaved (121°C, 15 min), and finally vacuum-stored at room temperature for 3 months. The cross-sectional view of the salted egg yolks after 3 months is shown below. Figure 5 As shown; the salted duck eggs from Comparative Example 2 were vacuum-sealed for 3 months. After 3 months, the surface of the salted egg yolks resembled... Figure 6 As shown. By Figure 5 It can be seen that after vacuum storage for 3 months, the egg yolks in Example 1 with added phosphate were orange-yellow, and the egg white was clean and delicate. No black rings or dissolution were found at the interface between the two. The salted eggs in Comparative Example 2 without added phosphate showed black-green substances on the surface of the egg yolks. The quality of the eggs under vacuum packaging and room temperature storage deteriorated significantly and black rings appeared. The egg yolk structure was loose and the texture was soft and collapsed. This indicates that the addition of phosphate can effectively inhibit the spoilage and deterioration of low-salt salted duck eggs and the appearance of black rings. Moreover, the black ring rate of the egg yolks in Example 1 was 0%, which was significantly lower than the black ring rate (46.47%) of the eggs stored for three months under the traditional pickling process in Comparative Example 3. This shows that the ozone technology of the present invention combined with pickling aids can reduce salt content, improve the black ring situation of egg yolks, and maintain the original good quality of salted egg yolks.

[0129] V. Colony Analysis under Different Sterilization Methods

[0130] The total number of colonies in the pickling process of Example 1, Comparative Examples 3-7 was analyzed. The total number of colonies in the pickling liquid was determined according to the method of GB 4789.2-2016, and the specific steps were as follows:

[0131] Take 25 mL sample in 225 mL physiological saline, mix thoroughly, make 1:10 sample homogenate, dilute into 1:100, 1:1000 concentration gradient in turn. Take 1 mL sample homogenate in a sterile culture dish, two parallel samples for each dilution, and 1 mL of blank diluent as control. Pour 15 mL of medium into the culture dish and mix evenly. Place horizontally until the medium solidifies, then turn over the plate, and incubate at 36±1℃ for 48±2h. If the sample may contain colonies that grow on the surface of the agar medium, a thin layer of plate counting agar medium can be overlaid on the surface of the solidified agar medium. After solidification, turn over the plate and incubate. If only one dilution plate has colonies within the appropriate counting range, calculate the average number of colonies on the two plates, then multiply the average by the corresponding dilution factor to get the total number of colonies per g(mL) of sample. If two consecutive dilution plates have colonies within the appropriate counting range, the total number of colonies is calculated as follows:

[0132]

[0133] where n is the number of colonies in the sample; ∑C is the sum of the number of colonies on the plates (including plates with colonies within the appropriate range); n1 is the number of plates at the first dilution (low dilution factor); n2 is the number of plates at the second dilution (low dilution factor); d is the dilution factor (first dilution).

[0134] Table 2 Analysis of total number of colonies in pickling liquid under different bacteria reduction methods (unit: cfu / mL)

[0135]

[0136] The duck egg surface will have a thin film, which is a natural protective layer, help prevent bacteria, contaminants and moisture into the egg, so as to maintain the relative stability of the internal state, if the cleaning, duck eggs in the pickling process is easy to bad, the traditional process in order to avoid the pickling process in the presence of bad eggs, more using the duck egg without cleaning directly for pickling, in order to inhibit the liquid in the microorganism, must use high concentration of salt, salt content distribution in the egg (salt content of salted egg white is far greater than salted egg yolk) plus the influence of pickling and storage environment (temperature, microorganism, etc.) of influence, which makes the salted egg yolk in the storage process is easy to appear black circle and fade the phenomenon. As can be seen from table 2, the total number of colonies of pickling liquid after sterilization treatment is significantly less than that of high salt without cleaning group, fresh duck egg surface will be stained with feathers, blood stains, feces and other contaminants, according to statistics, the total number of colonies on the surface of each duck egg is about 10 7 -10 9 CFU, easy to form a layer of bacterial membrane on the surface of the eggshell, the membrane will form a barrier to salmonella and other spoilage bacteria, resulting in these spoilage bacteria still can survive in the pickling process. The results show that the use of sterilization treatment can indeed reduce the total number of colonies in the pickling liquid, further, the sterilization effect of ozone group becomes significant with the increase of ozone treatment times, among which the sterilization effect of example 1 after three times of ozone treatment and pickling liquid immersion is the highest, which can effectively kill the microorganism in the pickling liquid, such as Figure 1 As shown in A of figure 6, the salted egg yolk treated by three times of ozone has orange red color, no hard core, soft texture and clean white egg white.

[0137] Six, explore the reason of adding amount of pickling aid phosphate and sucrose to shorten the pickling time

[0138] (1) a series of mass concentration of 16% salt water, add sucrose, the mass concentration of sucrose in the mixed solution after adding sucrose is 0%, 1%, 2%, 3%, 4%, 5%, remove the yolk and egg white to get empty eggshell, put DW water into the empty eggshell, clamp and fix the empty eggshell and immerse the outer surface into each mixed solution, then insert the conductivity meter into the DW water in the empty eggshell and measure the conductivity in 10 hours. Conductivity is an index of the ability of solution to conduct current, which can reflect the permeability of eggshell and eggshell membrane. The greater the ion concentration, the greater the conductivity. Sucrose solution has very low conductivity. The addition of sucrose can increase the conductivity of salt water. The results are shown in A of figure 7. As can be seen from the figure, with the addition of sucrose, the conductivity of salt water increases gradually with the addition of sucrose. Considering that further increase of sucrose will reduce the amount of salt molecules entering the inside of the eggshell, 5% sucrose is selected as the optimal concentration for salted egg pickling. Figure 7

[0139] ​(2) Configuration of a series of 16% salt water, adding composite phosphate, the mass concentration of composite phosphate in the mixed solution after adding composite phosphate is 0 (control group), 0.3%, 0.6%, 0.9%, 1.2%, 1.5%, respectively, and the conductivity of each mixed solution is measured by conductivity meter. Figure 7 As shown in B in the figure, with the addition of a small amount of composite phosphate, the conductivity of salt water increases significantly. The metal ion chelating ability of composite phosphate is strong, which can reduce the combination of metal ions and water. For example, the six phosphate groups in sodium hexametaphosphate are in a ring structure, and the metal ion chelating ability is strong, which reduces the combination of metal ions (Na+) and water. Only a small amount of composite phosphate needs to be added to make the pickling solution reach a high ionic strength. The metal ion chelating ability of composite phosphate is strong, which reduces the combination of metal ions and water, increases the ionic strength of the pickling solution, and makes the pickling solution have a high conductivity, so that salt molecules can easily and quickly penetrate into the salted egg, accelerate pickling, and shorten the pickling period. Combined with the oil-out effect of salted egg yolk, the mass concentration of 1.5% of the composite phosphate is selected as the optimal concentration for salted egg pickling.

[0140] (4) Four 16% salt water solutions were prepared respectively, the first one was used as a blank control (16% salt); the second one was added with sucrose to make the mass concentration of sucrose in the mixed solution 5% (16% salt + 5% sucrose); the third one was added with composite phosphate to make the mass concentration of composite phosphate in the mixed solution 1.5% (16% salt + 1.5% composite phosphate); the fourth one was added with sucrose and composite phosphate (5% sucrose + 16% salt + 1.5% composite phosphate), so that the mass concentration of sucrose in the mixed solution was 5% and the concentration of composite phosphate was 1.5%, and the conductivity of the four solutions was measured by conductivity meter; the results are shown in C in the figure. Figure 7 As shown in C in the figure, after the eggshell was placed in the solution for 10h, the conductivity inside the eggshell in the sucrose-salt-composite phosphate, salt-sucrose, salt-composite phosphate and salt systems was 70.05uS / cm, 57.5uS / cm, 45.2uS / cm and 18.9uS / cm, respectively. The ion concentration in the sucrose-salt-composite phosphate system was the highest, which indicated that the combination of sucrose and phosphate can increase the ion concentration in the pickling solution, increase the osmotic pressure, and enhance the mass transfer flux density of salt into the egg, promote the penetration of salt into the egg, accelerate pickling, shorten the pickling period, and obtain high-quality low-salt salted duck eggs.

[0141] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for pickling low-salt salted eggs with a pickling solution, characterized by, The pickling liquid comprises the following components in the weight parts per 100 parts of water: 16-18 parts of salt, 0.9-1.5 parts of composite phosphate, 0.1-5 parts of white wine, 0.1-1 part of spice powder, 4-5 parts of sucrose, and 0.1-4 parts of sorbitol; the composite phosphate comprises sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate in a weight ratio of (1-3):(1-3):(1-3); The method comprises the following steps: S1, configuring a pickling liquid; S2, soaking the cleaned duck eggs in the pickling liquid for pickling for 26-30 days, and passing ozone every 3-12 days during the pickling process, each time for 10-90 min.

2. The method for pickling low-salt salted eggs with pickling solution according to claim 1, characterized in that, 16 parts of salt per 100 parts of water.

3. The method for pickling low-salt salted eggs with pickling solution according to claim 1, characterized in that, 4-5 parts of white wine per 100 parts of water.

4. The method for pickling low-salt salted eggs with pickling solution according to claim 1, characterized in that, 0.4-0.6 parts of spice powder per 100 parts of water.

5. The method for pickling low-salt salted eggs with pickling solution according to claim 1, characterized in that, The weight ratio of sodium pyrophosphate, sodium tripolyphosphate and sodium hexametaphosphate in the composite phosphate is 1:1:

1.

6. The method for pickling low-salt salted eggs with pickling solution according to claim 1, characterized in that, In S2, ozone is passed every 6-8 days, each time for 20-40 min.

7. The method for pickling low-salt salted eggs with pickling solution according to claim 1, characterized in that, In step S2, before pickling, the duck eggs are first soaked in a 6%-10% citric acid solution for 0.3-1.5 h, then taken out, washed and dried.

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