Application of epigallocatechin gallate in relieving formation of hard core of salted egg yolk and improving quality of salted egg yolk

Abstract

The invention discloses application of epigallocatechin gallate in relieving formation of a hard core of salted egg yolk and improving the quality of the salted egg yolk, belongs to the field of food agriculture, and particularly discloses pickling liquid and pickling mud added with the epigallocatechin gallate and application of the pickling liquid and the pickling mud in poultry egg pickling. The epigallocatechin gallate is used as a food-borne antioxidant, and the epigallocatechin gallate is added into the pickling material to relieve the formation of the hard core of the salted egg yolk so as to improve the quality of the salted egg yolk. The salted egg pickling material is simple and easy to obtain, the hard heart rate and the hard heart mass ratio of the salted egg yolk are reduced and the hardness and the sandy property of the salted egg yolk are improved by adding the epigallocatechin gallate into the salty water or salty mud pickling material, and the invention aims to disclose a new application of the epigallocatechin gallate in salting the salted egg.

Description

Technical Field

[0001] The present invention relates to the technical field of food and agriculture, and more specifically, to an application of catechins in alleviating the formation of hard cores in salted egg yolks and improving the quality of salted egg yolks. Background Art

[0002] As the world's largest country in duck egg farming and duck egg product consumption, about 40% of the total duck egg consumption in China is salted eggs, which are mainly used for direct consumption or as raw materials for processing mooncakes, bread, etc. With the booming development of the baking industry, the market for salted duck eggs as raw materials has broad development prospects. However, at present, the problem of hard cores in duck egg yolk products during the pickling process is relatively common. In some parts of Guangdong, the hard core rate of salted egg yolks is even as high as over 65%. This not only affects the taste of salted egg yolk products but also restricts the development of salted duck egg enterprises to a certain extent. Therefore, developing food-derived functional additives to reduce the hard core rate of salted egg yolks and using them reasonably during the pickling of salted eggs has important application value for improving the quality of salted egg yolks. Summary of the Invention

[0003] In view of this, in order to overcome the shortcomings and deficiencies of the prior art, the primary object of the present invention is to provide an application of a tea polyphenol bioactive component - epigallocatechin gallate (EGCG) in alleviating the formation of hard cores in salted egg yolks and improving the quality of salted egg yolks.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] The present invention first clarifies the application of epigallocatechin gallate in alleviating the formation of hard cores in salted egg yolks and improving the quality of salted egg yolks.

[0006] Further, the epigallocatechin gallate is applied to the preparation of pickling solutions or pickling muds for poultry eggs.

[0007] Preferably, the poultry eggs are duck eggs, chicken eggs or goose eggs.

[0008] The present invention also provides a pickling solution for poultry eggs added with the epigallocatechin gallate. The salt content in the pickling solution is 15 wt% - 25 wt%, and the content of epigallocatechin gallate is 400 - 600 mg / L, more preferably 400 mg / L.

[0009] The present invention also provides a pickling mud for poultry eggs added with the epigallocatechin gallate. In the pickling mud, the mass ratio of plant ash: water: salt is 5:4:1, and the content of epigallocatechin gallate is 400 - 800 mg / L.

[0010] The present invention also provides an application of the pickling solution for poultry eggs in alleviating the formation of hard cores in salted egg yolks and improving the quality of salted egg yolks.

[0011] The present invention also provides the application of the above-mentioned pickled egg mud in alleviating the formation of hard cores in salted egg yolks and improving the quality of salted egg yolks.

[0012] The pickling time of the pickling solution or pickled mud for poultry eggs is 20 to 40 days.

[0013] As can be seen from the above technical solutions, compared with the prior art, the present invention has the following advantages and effects:

[0014] By adding epigallocatechin gallate (EGCG), an antioxidant, to the salted egg pickling material, the present invention reduces the cross-linked state of protein aggregation changes during the pickling process of salted eggs, increases the soluble protein content in the salted egg yolk, reduces the intermolecular force of the salted egg yolk protein, reduces the hardness of the salted egg yolk, thereby reducing the formation probability and the hard core mass ratio of hard cores during the pickling process of poultry eggs and improving the sandy texture of the salted egg yolk, which has important significance for solving the problems of high hard core rate and poor quality of salted egg yolks faced by current salted egg processing enterprises. Specific embodiments

[0015] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0016] Experimental example 1

[0017] Comparison and screening of antioxidants:

[0018] During the research process, through the preliminary screening of the in vitro antioxidant capacity of antioxidants, three antioxidants were obtained: rosemary extract, sage extract, and EGCG.

[0019] The suppliers of rosemary extract, sage extract, and EGCG used in the examples are Guangdong Kangda Biotechnology, Chenguang Biotechnology, and Professional Phytochemical Raw Material Enterprise Store respectively.

[0020] Before conducting the relevant experiments of the present invention, the in vitro antioxidant capacities of the above three antioxidants were compared. The results are shown in Table 1, and it was found that the antioxidant capacities of the three were: EGCG > sage extract > rosemary extract.

[0021] Table 1 Comparison of in vitro antioxidant capacities of rosemary extract, sage extract, and EGCG

[0022] Rosemary extract Sage extract EGCG P value Antioxidant capacity <![CDATA[0.75±0.05 b > <![CDATA[0.79±0.03 b > 0.88±0.01a 0.005

[0023] The following studies the role of the preferred EGCG in the process of salted egg pickling through specific implementation cases.

[0024] Example 1

[0025] 480 fresh duck eggs from ducks fed with corn-soybean meal diet were collected and divided into 2 groups, with 180 duck eggs in each group. The duck eggs in the control group were pickled with brine with a NaCl mass concentration of 20%, and the table salt (NaCl) was commercially available; the duck eggs in the experimental group were pickled in 20% brine pickling solution added with 400 mg / L EGCG.

[0026] The process of salted egg pickling is as follows: According to the ratio of the mass of duck eggs in each group to the mass of water of 1:1, the corresponding volume of pure water was measured, and table salt with a concentration of 20 wt% or 400 mg / L EGCG was weighed into the pure water, stirred until the table salt and EGCG were completely dissolved, the weighed duck eggs were added, and the duck eggs were pressed into the pickling solution with a lid, and pickled at room temperature of 25°C for 30 days.

[0027] After the pickling was completed, the salted eggs in each group were cooked and ripened by high-temperature steam heating for 20 min, and then divided into 6 replicates, with 40 eggs in each replicate. 30 cooked salted egg yolks were taken from each replicate to measure the hard heart rate and the ratio of hard heart mass. 4 salted egg yolks were selected from each replicate to measure the texture properties, oil yield and sandiness. 3 salted egg yolks were selected from each replicate to measure the soluble protein, protein carbonyl, free sulfhydryl and disulfide bond contents and intermolecular forces respectively.

[0028] Hard heart rate and ratio of hard heart mass: After weighing the cooked egg yolk samples, gently rub the egg yolk by hand to separate the loose part on the outside, and the remaining egg yolk part was recorded as the egg yolk hard heart. The ratio of the number of egg yolks with hard hearts to the total number of egg yolks was the hard heart rate. The ratio of the hard heart mass m2 to the total mass m1 of the egg yolk was the ratio of hard heart mass. The calculation formula is as follows:

[0029]

[0030] Texture properties: Cut salted egg yolks with a size of 1 cm × 1 cm × 1 cm, and use a texture analyzer (TMS-Pro, USA) to measure their hardness, elasticity, cohesiveness, gumminess, chewiness, adhesiveness.

[0031] Oil yield: Take 8 qualitative filter papers with a diameter of 7 cm, overlap them, dry them at 105°C, and weigh (M 0 ). Place the egg yolk in a dry small beaker, gently stir and mix the egg yolk with a glass rod or a small spoon, take about 2.5 g, place the egg yolk on the 8-layer dried filter paper, and gently press it into a small thin cake shape with a small spoon, and weigh (M 1) Move the bottom 4 layers of filter paper on top of the egg yolk. Place the filter paper with the egg yolk on a clean flat plate. Place a 1 kg lock-shaped weight on the surface of the filter paper at the position of the egg yolk and place it in an incubator at 35 °C for 2 h. Take out the filter paper and the egg yolk, remove the egg yolk residue completely, dry the oil-containing filter paper to a constant weight, and weigh (M 2 ) Calculate the oil yield. The formula is:

[0032]

[0033] Sandiness: Weigh the salted egg yolk and record it as m 1 , put it into a beaker, add 150 mL of petroleum ether to the beaker, and stir (2 - 3 revolutions per minute, 10 min). Take a 20-mesh standard sieve and weigh it (m 2 ), filter the substances in the beaker with the standard sieve, and wash the unfiltered samples on the sieve with petroleum ether multiple times. Dry the standard sieve in an oven at 105 °C to a constant weight, weigh it after drying, and record it as m 3 .

[0034]

[0035] Soluble protein: Take 1 g of egg yolk sample, add 50 mL of 0.05 mol / L Tris-HCl buffer solution (pH 6.5), mix well, homogenize at high speed at 5000 r / min for 2 min, centrifuge at high speed at 10000 r / min for 20 min, take the supernatant, and determine the soluble protein content of the salted egg yolk according to the operation instructions of the Bradford protein concentration assay kit (P0006, Beyotime Biotechnology, Shanghai).

[0036] Free sulfhydryl groups: The free sulfhydryl group content of the salted egg yolk is detected according to the operation instructions of the free sulfhydryl group detection kit (S0138S, Nanjing Jiancheng Bioengineering Institute, Nanjing).

[0037] Protein carbonyl groups: The protein carbonyl group content of the salted egg yolk is detected according to the DTNB method operation instructions of the protein carbonyl group content assay kit (A087-1-2, Beyotime Biotechnology, Shanghai).

[0038] Intermolecular forces: The content of chemical bonds was identified based on the solubility of the gel sample in different chemical bond modifiers. After grinding the salted egg yolk powder, 4 portions of 1.0 g samples were weighed and mixed well with 4 kinds of protein denaturing solvents, namely A (0.6 mol / L NaCl), B (0.6 mol / L NaCl + 1.5 mol / L urea), C (0.6 mol / L NaCl + 8 mol / L urea), and D (0.6 mol / L NaCl + 8 mol / L urea + 0.5 mol / L β-mercaptoethanol). Then, they were homogenized at a high speed of 6000 r / min for 30 s, and after centrifuging at 4000 r / min for 20 min, the supernatant was taken. The protein content was determined by the Coomassie brilliant blue method. The protein content in solvent A, the difference in protein content between solvents A and B, the difference in protein content between solvents B and C, and the difference in protein content between solvents C and D represent the content of ionic bonds, hydrogen bonds, hydrophobic interactions, and disulfide bonds, respectively. The test results are shown in Tables 2, 3, 4, 5, and 6 as follows:

[0039] Table 2 Effect of EGCG addition level in pickling solution on the occurrence of hard cores in salted egg yolks

[0040]

[0041]

[0042] Table 3 Effect of EGCG addition level in pickling solution on the texture properties of salted egg yolks

[0043] Index Control group Experimental group P value Hardness (N) <![CDATA[8.61±0.25 * > 7.61±0.27 0.009 Elasticity (mm) 1.04±0.07 0.98±0.05 0.490 Adhesion (N·mm) <![CDATA[0.213±0.010 * > 0.169±0.005 <0.001 Cohesiveness 0.216±0.008 0.216±0.005 0.966 Gumminess (N) 1.93±0.13 1.63±0.08 0.061 Chewiness (mj) <![CDATA[2.41±0.36 * > 1.79±0.19 0.129

[0044] Table 4 Effect of EGCG addition level in pickling solution on the oil yield and sandiness of salted egg yolks

[0045] Index Control group Experimental group P value Oil yield rate (%) 13.65±0.79 13.99±0.79 0.772 Sandy property (%) 90.23±1.86 <![CDATA[94.79±0.58 * > 0.041

[0046] Table 5 Effect of EGCG addition level in pickling solution on the content of soluble proteins, protein carbonyls, free sulfhydryls, and disulfide bonds in salted egg yolks

[0047] Index Control group Experimental group P value Soluble protein (mg / mL) 1.00±0.05 <![CDATA[1.31±0.02 * > <0.001 Protein carbonyl (mg / mL) 8.16±0.78 6.44±0.52 0.075 Free sulfhydryl (μmol / mg) 0.21±0.02 0.19±0.01 0.329

[0048] Table 6 Effect of EGCG addition level in pickling solution on the intermolecular forces in salted egg yolks

[0049]

[0050]

[0051] The results showed that the mass ratio of hard cores in the test group with 400 mg / L EGCG added to the pickling solution was significantly lower than that in the control group without EGCG added to the pickling solution (P<0.01), and the mass ratio of hard cores decreased by 25.2%. Compared with the control group, there was a tendency for the test group to reduce the hard core rate, adhesiveness, and protein carbonyl content of salted egg yolks (0.05<P<0.10), among which the hard core rate decreased by 31.5%. The hardness, adhesiveness, hydrogen bonds, and disulfide bonds of the salted egg yolks in the test group were all significantly lower than those in the control group (P<0.01), while the sandiness, soluble protein, and ionic bond content were all significantly higher than those in the control group (P<0.05).

[0052] To sum up, adding 400 mg / L EGCG to the pickling solution can reduce the cross-linked state of protein aggregation changes and the hardness of salted egg yolks during the pickling process of salted eggs, effectively alleviate the formation of hard cores in salted egg yolks, and improve the sandiness of salted egg yolks.

[0053] Example 2

[0054] 480 fresh duck eggs fed with corn-soybean meal-based diets were collected and divided into 2 groups, with 180 duck eggs in each group. The duck eggs in the control group were pickled with brine with a NaCl mass concentration of 20%, and the table salt (NaCl) was commercially available; the duck eggs in the test group were pickled with 600 mg / L EGCG added to the 20% brine pickling solution. The test duck eggs were pickled for 30 days at a room temperature of 25°C. After pickling, each group of salted eggs was cooked and ripened by high-temperature steam heating for 20 min and then divided into 6 replicates, with 40 eggs in each replicate.

[0055] The occurrence of hard cores, texture characteristics, oil yield, and sandiness indexes and methods for detecting salted egg yolks during the pickling process of salted eggs were the same as those in Example 1.

[0056] The test results are shown in Tables 7-9. The mass ratio, hardness, and adhesiveness of hard cores in the salted egg yolks of the test group with 600 mg / L EGCG added to the pickling solution were all significantly lower than those in the control group without EGCG added to the pickling solution (P<0.05), and the mass ratio, hardness, and adhesiveness of hard cores decreased by 26.4%, 15.9%, and 16.0% respectively. Compared with the control group, there was a tendency for the test group to reduce the hard core rate and cohesiveness of salted egg yolks (0.05<P<0.10), among which the hard core rate decreased by 24.5%. The sandiness of the salted egg yolks in the test group was significantly higher than that in the control group (P<0.05).

[0057] Table 7 Effects of EGCG addition level in pickling solution on the occurrence of hard cores in salted egg yolks

[0058] Index Control group Experimental group P value Hard core mass ratio (%) <![CDATA[9.15±0.61 * > 6.73±0.13 0.010 Hard core rate (%) 31.65±3.07 23.90±2.34 0.072

[0059] Table 8 Effects of EGCG addition level in pickling solution on the texture characteristics of salted egg yolks

[0060] Index Control group Experimental group P value Hardness (N) <![CDATA[8.61±0.25 * > 7.24±0.23 <0.001 Elasticity (mm) 1.04±0.07 1.16±0.07 0.224 Adhesion (N·mm) <![CDATA[0.213±0.010 * > 0.179±0.008 0.009 Cohesiveness 0.216±0.008 0.238±0.008 0.053 Gumminess (N) 1.93±0.13 1.86±0.12 0.717 Chewiness (mj) 2.41±0.36 2.46±0.27 0.906

[0061] Table 9 Effects of EGCG addition level in pickling solution on oil yield and sandiness of salted egg yolks

[0062] Index Control group Experimental group P value Oil yield rate (%) 13.65±0.80 15.44±1.38 0.289 Sandy property (%) 90.23±1.86 95.92±1.07 0.044

[0063] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same or similar parts among the embodiments, reference can be made to each other. The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but rather will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Application of epigallocatechin gallate in alleviating the formation of hard core of salted egg yolk and improving the quality of salted egg yolk.

2. The use according to claim 1, characterized in that: The epigallocatechin gallate is used in the preparation of poultry egg pickling liquid or pickling mud.

3. The use according to claim 2, characterized in that: The poultry eggs are duck eggs, chicken eggs or goose eggs.

4. The egg pickling liquid according to claim 2, characterized in that: The salt content in the pickling liquid is 15wt-25wt%, and the epigallocatechin gallate content is 400-600mg / L.

5. The poultry egg pickled mud according to claim 2, characterized in that: The mass ratio of wood ash: water: salt in the pickling mud is 5:4:1, and the content of epigallocatechin gallate is 400-800 mg / L.

6. Use of the poultry egg pickling liquid according to claim 4 in alleviating the formation of hard core of salted egg yolk and improving the quality of salted egg yolk.

7. Use of the poultry egg pickled mud according to claim 5 in alleviating the formation of hard core of salted egg yolk and improving the quality of salted egg yolk.

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