Egg duck feed additive for relieving hard center of salted yolk and preparation method thereof

Abstract

The present application relates to the technical field of feed additive production, and particularly discloses an egg duck feed additive for relieving hard yolk of salted egg and a preparation method thereof, which comprises antioxidant components, flora regulating components, osmotic regulating components, protein structure stabilizing components, lipid emulsification regulating components and carriers. The egg duck feed additive provided by the present application effectively solves the problem of hard yolk of salted egg caused by anti-nutritional factors in high-miscellaneous-cornmeal daily ration through the synergistic effect of multiple components such as clostridium butyricum, gradient osmotic sugar, lecithin, casein phosphopeptide, coated phytase and coated tea polyphenol.

Description

Technical Field

[0001] This invention relates to the field of feed additive production technology, specifically to a feed additive for laying ducks used to alleviate the hard center of salted egg yolks and its preparation method. Background Technology

[0002] In large-scale duck farming, especially in southern regions where corn and soybean meal resources are scarce, farms typically use diets high in mixed meal (with rapeseed meal, cottonseed meal, sorghum meal, etc. added at ≥30%) to reduce feed costs. However, mixed meals contain anti-nutritional factors such as phytic acid and gossypol, which can easily affect the oxidative balance of ducks, leading to increased oxidation of egg yolk protein and lipids, thereby increasing the hardness of salted egg yolks and reducing the oiliness and sandiness of the yolks. Therefore, how to reduce the hardness of salted egg yolks is the technical problem that this invention aims to solve. Summary of the Invention

[0003] The purpose of this invention is to provide a feed additive for ducks that alleviates the hard center of salted egg yolks and its preparation method, so as to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A feed additive for laying ducks to alleviate the hard center of salted egg yolks and its preparation method, wherein the feed additive includes antioxidant components, microbial community regulating components, osmotic regulating components, protein structure stabilizing components, lipid emulsification regulating components, and a carrier.

[0006] As a further aspect of the present invention: the antioxidant component is selected from tea polyphenols and their coated formulations.

[0007] As a further aspect of the present invention, the microbial regulation component is selected from Bacillus subtilis, Clostridium butyricum, and combinations thereof.

[0008] As a further aspect of the present invention: the osmotic adjustment component is selected from sorbitol, trehalose, and combinations thereof.

[0009] As a further aspect of the present invention: the protein structure stabilizing component is selected from casein phosphopeptide (CPP) and coated tea polyphenols.

[0010] As a further aspect of the present invention, the lipid emulsification regulating component is lecithin.

[0011] As a further aspect of the present invention: the carrier is a conventional feed-grade powder, used to uniformly disperse the various functional components.

[0012] The present invention also provides a method for preparing the aforementioned feed additive for salted egg yolks used to alleviate hardness in egg yolks, the preparation method comprising:

[0013] Step S1: Weigh, pulverize, and preliminarily mix all functional components and carriers according to the formula;

[0014] Step S2: Mix all components thoroughly;

[0015] Step S3: Dry the uniformly mixed components at low temperature;

[0016] Step S4: Crush and sieve the components after low-temperature drying.

[0017] Compared with the prior art, the beneficial effects of the present invention are: the duck feed additive provided by the present invention effectively solves the problem of hard center of salted egg yolk caused by anti-nutritional factors in high-mixed meal diets through the synergistic effect of multiple components such as Clostridium butyricum, gradient osmotic sugar (sorbitol + trehalose), lecithin, casein phosphopeptide, coated phytase and coated tea polyphenols.

[0018] Among them, the coated phytase degrades phytic acid and other anti-nutritional factors, improving the absorption of egg yolk protein and lipids; Clostridium butyricum improves the intestinal flora and barrier function; gradient osmotic sugar and lecithin regulate the water distribution and lipid emulsification of egg yolk; casein phosphopeptides stabilize the protein structure, and the coated tea polyphenols provide long-lasting antioxidant protection, thereby reducing the hardening rate and hardening weight, and maintaining the egg yolk oxidation index within the ideal range; even under rapid pickling conditions (15-20 days), this additive can still ensure that the egg yolk produces oil and sand evenly and the hardening rate is significantly reduced. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention.

[0020] Figure 1 This is an electron microscope image of Comparative Example 1.

[0021] Figure 2 This is an electron microscope image of Example 7. Detailed Implementation

[0022] To make the technical problems, solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0023] Unless otherwise specified, all methods used in this invention are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products.

[0024] Example 1:

[0025] In this embodiment of the invention, a feed additive for laying ducks to alleviate the hard center of salted egg yolks and its preparation method are provided. The feed additive comprises the following components per ton of complete feed:

[0026] Soy isoflavones: 10g (10mg / kg); This is a basic antioxidant component, specifically feed grade, purity ≥98%, powder form;

[0027] Vitamin E: 60g (60mg / kg); This is a basic antioxidant, specifically feed grade, α-tocopherol ≥96%, powder form;

[0028] Coated phytase: 80g (800U / kg, corresponding to 10000U / g coated phytase); This is an anti-meal factor component for oilseed meals, specifically feed grade, with enzyme activity ≥10000U / g, and the coating material is gum arabic and maltodextrin, with high temperature resistance ≥80℃;

[0029] Bacillus subtilis: 30g; (3×10 9 CFU / kg, corresponding to 1×10 11 (CFU / g microbial agent); This is a microbial regulator, specifically feed grade, with a live bacteria count ≥1×10⁻⁶. 11 CFU / g, powder, free from bacterial contamination;

[0030] Sorbitol: 2000g; This is an osmotic regulator, specifically food grade, purity ≥99%, powder, easily soluble in water;

[0031] Tea polyphenols: 80g (80mg / kg), these are antioxidants, specifically feed grade, tea polyphenol content ≥90%, powder form, odorless;

[0032] Corn cob powder, used to supplement feed additives to 10000g, is the carrier. The specific model is feed grade, 80 mesh, moisture ≤10%, and free of impurities.

[0033] Its preparation method is as follows:

[0034] Step S1: Raw material pretreatment (25 min):

[0035] Accurately weigh all components according to the formula (electronic balance error ≤ 0.02g) and place them in a clean stainless steel container; grind soy isoflavones, vitamin E, Bacillus subtilis, sorbitol, tea polyphenols, and corn cob powder through an 80-mesh sieve for 3 minutes (speed 2000r / min), and sieve to remove impurities; add coated phytase directly to the above-ground components without grinding (commercially available products are already 80-mesh powder), and mix evenly.

[0036] Step S2: Mix (35 min):

[0037] Place all pretreated components into a high-speed mixer, set the speed to 2500 r / min, and mix for 35 min.

[0038] Step S3: Low-temperature drying (2 hours):

[0039] Preheat the constant temperature drying oven to 55℃, spread the mixed material evenly on the tray (thickness ≤2cm); put it in the drying oven and dry at 55℃ for 2 hours, turning it over every 30 minutes to ensure even drying; after drying, take it out and let it cool naturally to room temperature (25℃).

[0040] Step S4: Crushing and sieving (10 min):

[0041] After cooling, crush the material through an 80-mesh sieve for 3 minutes (2000 r / min), and remove any incompletely crushed particles by sieving. Then, bag and label the material and store it in a cool, dry place (15-25℃, away from light and moisture).

[0042] It is worth mentioning that the feed can be a high-mixed meal diet (per ton), including: 250kg corn, 150kg rapeseed meal, 100kg cottonseed meal, 100kg corn DDGS, 150kg soybean meal, 60kg limestone powder, 15kg dicalcium phosphate, 3kg salt, 12kg soybean oil, 1kg additives, and the remainder is supplemented with rice bran to make up to 1000kg (total mixed meal addition 35%).

[0043] Example 2:

[0044] Unlike Example 1, the feed additive, calculated per ton of complete feed for laying ducks, also includes: 1000g of lecithin, which is a lipid emulsification regulating component, specifically feed grade, with a purity ≥95%, in powder form, and easy to mix with feed; correspondingly, the amount of corn cob powder used is reduced, so that the total amount of feed additive is still 10000g.

[0045] The preparation method is as follows:

[0046] In the raw material pretreatment stage of step S1, the weighed components also include the lecithin.

[0047] Example 3:

[0048] Unlike Example 2, the feed additive, calculated per ton of complete feed for laying ducks, replaces Bacillus subtilis with Clostridium butyricum, while maintaining the same dosage. Specifically, the dosage of Clostridium butyricum is 30g (3×10⁻⁶). 9 CFU / kg, corresponding to 1×10 11 (CFU / g microbial agent), its function is to repair the intestinal barrier and provide energy components. The specific model is feed grade, with a live bacteria count ≥1×10⁻⁶. 11CFU / g, resistant to stomach acid and bile salts, in powder form.

[0049] The preparation method is as follows:

[0050] In the raw material pretreatment stage of step S1, the weighing components replace Bacillus subtilis with Clostridium butyricum. Clostridium butyricum is easily inactivated, so the temperature is controlled below 25°C during pulverization to avoid high temperature damage to live bacteria.

[0051] Example 4:

[0052] Unlike Example 3, the feed additive, calculated per ton of complete feed for laying ducks, replaces sorbitol with sorbitol and trehalose, while maintaining the total amount. Specifically, it includes:

[0053] Sorbitol: 1000g; This is a gradient osmosis regulating ingredient (surface layer), specifically food grade, purity ≥99%, powder form;

[0054] Trehalose: 1000g; This is a gradient osmotic adjustment ingredient (internal), specifically food grade, purity ≥99%, powder form, easily soluble in water;

[0055] The preparation method is as follows:

[0056] In the raw material pretreatment stage of step S1, the components are weighed to replace sorbitol with sorbitol and trehalose.

[0057] Example 5:

[0058] Unlike Example 4, the feed additive, calculated per ton of complete feed for laying ducks, increases casein phosphopeptide (CPP) based on Example 3. Correspondingly, the amount of corn cob powder used is updated to ensure the total amount of feed additive is 10,000g; specifically:

[0059] Casein phosphopeptide (CPP): 50g (50mg / kg). This is a protein structure stabilizing component. The specific model is feed grade, with a purity of ≥90%. It is in powder form, easy to mix with feed, and odorless.

[0060] The preparation method is as follows:

[0061] In the raw material pretreatment stage of step S1, the weighed components also include casein phosphopeptides (CPP).

[0062] Example 6:

[0063] Unlike Example 5, the feed additive, calculated per ton of complete feed for laying ducks, replaces tea polyphenols with coated tea polyphenols, while maintaining the same total amount, specifically as follows:

[0064] Coated tea polyphenols: 80g (50mg / kg), which are protein structure stabilizing components. The specific type is feed grade, with a purity of ≥90%, and is in powder form. The coating material is gum arabic and maltodextrin, and it is heat resistant to ≥80℃.

[0065] The preparation method is as follows:

[0066] In the raw material pretreatment stage of step S1, the weighing components replace tea polyphenols with coated tea polyphenols.

[0067] Example 7:

[0068] Unlike Example 6, the feed additive is calculated per ton of complete feed for laying ducks. Based on Example 6, soy isoflavones and vitamin E are removed, and the amount of corn cob powder is increased accordingly to ensure that the total amount of feed additive is 10,000g.

[0069] Preparation method:

[0070] For step S1, the update is as follows:

[0071] Accurately weigh all components according to the formula (remove soy isoflavones and vitamin E, and increase the amount of corn cob powder), with an electronic balance error ≤0.02g; pulverize Clostridium butyricum, sorbitol, trehalose, lecithin, CPP, and corn cob powder using an 80-mesh sieve for 3 minutes (2000 r / min), and sieve to remove impurities; coated phytase and coated tea polyphenols do not need to be pulverized, and can be directly added to the pulverized components above and mixed evenly; control the temperature below 25℃ when pulverizing Clostridium butyricum, and mix quickly after pulverizing CPP to avoid moisture absorption.

[0072] Comparative Example 1:

[0073] In this embodiment of the invention, a feed additive for laying ducks to alleviate the hard center of salted egg yolks and its preparation method are provided. The feed additive comprises the following components per ton of complete feed:

[0074] Corn cob powder, used to supplement feed additives to 10000g, is the carrier. The specific model is feed grade, 80 mesh, moisture ≤10%, and free of impurities.

[0075] It is worth mentioning that the feed can be a high-mixed meal diet (per ton), including: 250kg corn, 150kg rapeseed meal, 100kg cottonseed meal, 100kg corn DDGS, 150kg soybean meal, 60kg limestone powder, 15kg dicalcium phosphate, 3kg salt, 12kg soybean oil, 1kg additives, and the remainder is supplemented with rice bran to make up to 1000kg (total mixed meal addition 35%).

[0076] Comparative Example 2:

[0077] Unlike Comparative Example 1, the feed additive, calculated per ton of complete feed, further includes:

[0078] Vitamin E: 70g (70mg / kg); This is a basic antioxidant, specifically feed grade, α-tocopherol ≥96%, powder form;

[0079] Preparation method:

[0080] Accurately weigh vitamin E (feed grade, α-tocopherol ≥96%, powder) and corn cob powder. Premix vitamin E with a small amount of corn cob powder for 5 minutes, then add the remaining carrier and mix at 1500 r / min for 15 minutes to ensure uniformity.

[0081] Comparative Example 3:

[0082] Unlike Comparative Example 1, the feed additive, per ton of complete feed, also includes: conventional antioxidant (BHT): 70g.

[0083] Preparation method:

[0084] Accurately weigh BHT (feed grade, powder) and corn cob powder. Premix BHT with a small amount of corn cob powder for 5 minutes, then add the remaining carrier and mix at 1500 rpm for 15 minutes to ensure uniformity and avoid excessively high local concentrations of BHT.

[0085] Comparative Example 4:

[0086] Unlike Comparative Example 1, the feed additive, calculated per ton of complete feed, further includes:

[0087] Soy isoflavones: 10g (10mg / kg); This is a basic antioxidant component, specifically feed grade, purity ≥98%, powder form;

[0088] Vitamin E: 60g (60mg / kg); This is a basic antioxidant, specifically feed grade, α-tocopherol ≥96%, powder form;

[0089] Preparation method:

[0090] Accurately weigh soy isoflavones (feed grade, purity ≥90%, powder), vitamin E (feed grade, α-tocopherol ≥96%, powder), and corn cob powder (feed grade, 80 mesh, moisture ≤10%). First, premix the soy isoflavones and vitamin E with a small amount of corn cob powder for 8 minutes to fully dilute them and avoid uneven concentration in some areas. Then add the remaining carrier and mix in a mixer at 1500r / min for 15 minutes to ensure that all components are evenly mixed.

[0091] Experimental procedure:

[0092] I. Experimental Materials and Equipment:

[0093] 1. Experimental animals: 330 19-week-old Muscovy ducks with uniform weight (average weight 1.5±0.1kg), healthy and disease-free, were randomly divided into 11 groups of 30 ducks each.

[0094] 2. Experimental Feeds: The high-mixed meal diets were combined with Examples 1 to 7, and with Comparative Examples 1 to 4. Each high-mixed meal diet (per ton) included: 250 kg corn, 150 kg rapeseed meal, 100 kg cottonseed meal, 100 kg corn DDGS, 150 kg soybean meal, 60 kg limestone powder, 15 kg dicalcium phosphate, 3 kg salt, 12 kg soybean oil, and 1 kg additives. The remainder was supplemented with rice bran to bring the total to 1000 kg (total mixed meal addition 35%).

[0095] 3. Marinating materials: food-grade salt, distilled water, transparent plastic film, egg crates (uniform size);

[0096] 4. Testing equipment and reagent kits:

[0097] Basic equipment: electronic balance (accuracy 0.001g), UV-Vis spectrophotometer (UV-1601), scanning electron microscope (S-3700N), digital micrometer, egg analyzer (ORKA), high-speed centrifuge (≥3500rpm), constant temperature water bath, mortar and pestle, tissue homogenizer, vortex mixer, 1mL glass cuvette, 96-well plate;

[0098] The test kits include: Malondialdehyde (MDA) test kit, Protein Carbonyl Test Kit (Bohu Biotechnology, catalog number BH-961160), and Free Thiol Test Kit (Bohu Biotechnology, catalog number BH-961175). These are all commercially available standard test kits that can be directly adapted to the detection of 5 core indicators. The Protein Carbonyl Test Kit uses the 2,4-dinitrophenylhydrazine (DNPH) colorimetric method, and the Free Thiol Test Kit uses the Ellman method (DTNB colorimetric method). The detection accuracy meets the experimental requirements.

[0099] II. Feeding and pickling process:

[0100] 1. Feeding trial (4 months):

[0101] The ducks were raised in a double-layered, tiered single-cage system (cage size 40×40×60cm galvanized wire cage). Each group was kept in the same environment (temperature 20-25℃, humidity 60-70%), with free access to feed and water. The duck house was cleaned daily and disinfected once a week.

[0102] Record the feed intake and egg production for each group and each repetition daily, and weigh the laying ducks once a week to ensure no abnormal deaths during the experiment (if any deaths occur, replace them with laying ducks of the same weight in a timely manner and record the cause).

[0103] After 4 months of feeding, the feeding trial was ended, and duck eggs from each group were collected for rapid pickling and indicator testing.

[0104] 2. Routine pickling test (40 days):

[0105] Forty fresh duck eggs were collected from each group (440 in total). The eggs were inspected by the MOBA egg product machine and selected as qualified duck eggs (no damage, no deformity, and uniform size).

[0106] Prepare the pickling solution, place qualified duck eggs into the pickling solution, with the liquid level 2cm above the duck eggs, seal with transparent plastic film, and pickle at room temperature (25℃) for 40 days. During this period, observe the pickling process daily to prevent damage and mold.

[0107] 3. Rapid pickling test (18 days):

[0108] Forty fresh duck eggs were collected from each group (440 in total). The eggs were inspected by the MOBA egg product machine and selected as qualified duck eggs (no damage, no deformity, and uniform size).

[0109] Prepare the pickling solution, place qualified duck eggs into the pickling solution, with the liquid level 2cm above the duck eggs, seal with transparent plastic film, and pickle at room temperature (25℃) for 18 days. During this period, observe the pickling process daily to prevent damage and mold.

[0110] III. Testing Process:

[0111] 1. In the routine pickling experiment, 10 salted duck eggs were selected from each group of duck eggs, and the hard core rate (%), hard core weight (g), malondialdehyde (nmol / g), protein carbonyl (nmol / mg prot) and free thiol (μmol / g) were measured. The average value of the data for each group was taken as the final result of that group of duck eggs.

[0112] 2. In the rapid pickling experiment, 10 salted duck eggs were selected from each group of duck eggs, and the hard core rate (%), hard core weight (g), malondialdehyde (nmol / g), protein carbonyl (nmol / mg prot) and free thiol (μmol / g) were measured. The average value of the data for each group was taken as the final result of that group of duck eggs.

[0113] The test methods for each parameter mentioned above are as follows:

[0114] Hardness rate: Place the salted egg yolks in an oven (KS-410) and bake at 145℃ for 15 minutes. After cooling at room temperature for 15 minutes, gently crush the yolks and observe the inside of the yolks: if there are hard lumps, it is a hard core; if there are no hard lumps and the yolks are crushed, it is not a hard core; Hardness rate (%) = (number of hard core yolks / total number of yolks tested) × 100%.

[0115] Core weight: Separate the hardened yolks with tweezers and weigh the hardened yolks using an electronic balance (accuracy 0.001g). Record the weight of the hardened yolk for each hardened yolk separately and calculate the average core weight (g) for each group.

[0116] Malondialdehyde (MDA, nmol / g) detection: The thiobarbituric acid (TBA) colorimetric method and a commercially available MDA detection kit were used. Ten cured salted duck eggs were taken for each group. 0.5g of the sample was added to physiological saline and homogenized in an ice bath. The supernatant was collected by centrifugation. The corresponding reagent and TBA reagent were added. After reaction in a 95℃ water bath, the mixture was cooled and centrifuged. The absorbance was measured at a wavelength of 532nm. The MDA content per gram of egg yolk was calculated by combining the standard curve and conversion formula.

[0117] Protein carbonyl (nmol / mg prot) detection: UV colorimetry and Bohu Biotechnology's corresponding reagent kit were used. Sample preparation was the same as for MDA detection. At the same time, the protein concentration in the supernatant was measured and adjusted to an appropriate range. After adding the corresponding reagent and reacting in the dark, the sample was centrifuged, washed, and dissolved. The absorbance was measured at a wavelength of 370 nm. The protein carbonyl content was calculated by combining the absorbance difference and the protein concentration. Note that the operation should be carried out in the dark and the precipitate should be washed thoroughly.

[0118] Detection of free thiol (μmol / g): The Ellman method (DTNB colorimetric method) and the corresponding kit from Bohu Biotechnology were used. Sample preparation was the same as for MDA detection. The supernatant was diluted to an appropriate concentration. After adding the reagent and reacting for 10 min, the absorbance was measured at a wavelength of 412 nm. The free thiol content per gram of egg yolk was calculated by combining the GSH standard curve and conversion formula. The reagent was stored in the dark and the reaction time was controlled to ensure that the dilution factor was appropriate for the detection range.

[0119] The above testing procedures are all standard testing procedures and will not be described in detail here.

[0120] Experimental data:

[0121] The data from the conventional pickling experiment (40 days) are shown in Table 1:

[0122] Table 1

[0123] Comparative Example 1 28.72 1.27 212.10 7.92 24.7 Comparative Example 2 26.05 1.16 197.60 7.02 23.4 Comparative Example 3 24.63 1.11 186.30 6.85 22.9 Comparative Example 4 22.18 1.01 174.80 6.32 21.7 Example 1 20.62 0.96 167.90 6.05 21.0 Example 2 18.74 0.91 159.80 5.82 20.6 Example 3 17.35 0.86 151.90 5.55 19.7 Example 4 15.67 0.83 144.90 5.28 19.3 Example 5 14.38 0.79 137.80 4.98 18.6 Example 6 12.91 0.75 133.10 4.76 18.1 Example 7 11.83 0.74 129.20 4.58 17.6

[0124] The data from the rapid pickling experiment (18 days) are shown in Table 2:

[0125] Table 2

[0126] Comparative Example 1 43.10 1.82 262.30 9.05 28.8 Comparative Example 2 38.20 1.67 239.80 8.10 26.9 Comparative Example 3 35.40 1.52 221.40 7.75 25.6 Comparative Example 4 20.05 0.98 172.59 6.13 21.4 Example 1 26.70 1.12 184.60 6.55 22.5 Example 2 24.05 1.01 177.90 6.18 21.9 Example 3 21.95 0.96 171.10 5.95 21.1 Example 4 18.75 0.87 159.60 5.65 20.6 Example 5 15.60 0.83 147.90 5.25 19.4 Example 6 13.35 0.79 139.50 4.92 18.4 Example 7 11.00 0.75 129.81 4.57 17.3

[0127] The data from Examples 1 to 7 described above are explained below:

[0128] Before explaining the data from Examples 1 to 7, let's first describe the four comparative examples. Comparative Example 1 used only corn cob powder as a carrier and contained no functional regulatory components. Under the condition of a high-meal diet, anti-nutritional factors such as phytic acid and gossypol were not degraded, lipid metabolism in the laying ducks was hindered, and the binding of protein and minerals in the yolk was enhanced, resulting in a dense and uneven structure. At the same time, the lack of antioxidant protection led to a significant increase in lipid and protein oxidation levels (high MDA and carbonyl levels), ultimately resulting in the highest hard core rate and hard core weight. Under rapid curing conditions, due to the lack of osmotic regulation, salt entered too quickly and unevenly, further exacerbating the imbalance of the internal structure of the yolk. Therefore, this group served as the baseline control and had the worst overall quality. Comparative Example 2 added vitamin E to Comparative Example 1. It mainly scavenged free radicals through the lipid-soluble antioxidant effect, reducing lipid oxidation levels and lowering MDA and carbonyl indicators. However, because the problems of anti-nutritional factors and yolk structure were not resolved, the protein-mineral binding remained unchanged. The yolk hardening rate remained high despite a slight decrease in protein structure and uneven lipid deposition. Comparative Example 4, building upon Comparative Example 2, employed a complex antioxidant system of soy isoflavones and vitamin E. Through the synergistic effect of fat-soluble and estrogen-like antioxidants, it significantly reduced oxidative damage levels, further decreasing MDA and carbonyl groups. It also promoted yolk lipid metabolism to some extent, resulting in a significantly better hardening rate than the aforementioned comparative examples. However, since it did not involve the degradation and osmotic regulation of anti-nutritional factors, its improvement was still considered "oxidative optimization," and a significant hardening problem remained under rapid curing conditions. Comparative Example 3 used the synthetic antioxidant BHT, which has a stronger antioxidant efficiency than vitamin E. Therefore, it was superior to Comparative Example 2 in reducing MDA. However, its effect was still limited to lipid oxidation inhibition, without improving protein structure, mineral binding, or nutrient absorption, resulting in an uneven yolk structure. Furthermore, BHT does not participate in physiological metabolic regulation, thus its improvement on the hardening rate was limited.

[0129] Building upon the above, Example 1 introduces coated phytase to achieve the targeted release and degradation of anti-nutritional factors, effectively breaking the binding of phytic acid with minerals and proteins. This improves nutrient utilization and the yolk formation environment from the source, resulting in a more porous and uniform protein structure. This improvement directly addresses the core issue of high-meal-content diets, significantly reducing heart rate and oxidative indicators. Example 2 adds lecithin to Example 1, promoting lipid absorption and transport through emulsification. This results in a more uniform distribution of fat in the yolk, preventing localized lipid enrichment or deficiency, thereby further improving the yolk microstructure. This mechanism further reduces heart rate and also indirectly inhibits MDA (due to improved lipid stability). This is because lipid structure regulation and anti-nutritional factor degradation work synergistically. Example 3 replaced Bacillus subtilis with Clostridium butyricum, which enhanced intestinal barrier function by producing butyric acid, improved nutrient absorption efficiency, and reduced inflammatory response, making lipid and protein metabolism more stable. This change belongs to the gut-metabolic axis regulation, further enhancing the adaptability of high-meal-content diets, making the yolk formation process more stable, and both hardness rate and oxidation index continued to decrease. Example 4, based on Example 3, replaced sorbitol alone with a combination of "sorbitol + trehalose" to form a gradient osmotic regulation system, which changed the rapid mutation of salt and water migration during pickling to a gradual balance, thereby avoiding uneven water distribution inside the yolk. This process not only reduced the hardness rate under high-meal-content diet conditions, but also improved the performance of rapid pickling, with a significant decrease in hardness rate in rapid pickling scenarios.

[0130] Example 5 adds casein phosphopeptide (CPP) to Example 4. By binding with minerals, it stabilizes the protein structure and prevents excessive aggregation of the protein during curing, keeping the yolk loose and sandy. This further reduces the protein carbonyl level, resulting in a significant decrease in core weight, as protein structural stability is another key factor affecting core formation. Example 6 replaces tea polyphenols with coated tea polyphenols to prevent premature release in the duck, instead releasing them gradually after yolk formation and during curing, thus delaying the antioxidant effect. This ensures a high degree of match between antioxidant protection and the curing process, significantly reducing MDA and carbonyl levels under rapid curing conditions, resulting in a stepwise decrease in core weight. Example 7 removes soy isoflavones and vitamin E from Example 6. Although this reduces traditional antioxidant components, the overall effect is not only not reduced but reaches its optimal level (lowest core weight and lowest oxidation index) due to the improved structural regulation, nutrient release, and time control processes. This result indicates that the mechanism of action of this invention does not depend on the superposition of antioxidants but on a synergistic process.

[0131] It should be noted that, regarding Examples 7 and 6, Example 6 adds soy isoflavones and vitamin E, both of which are strong antioxidants. The total amount of antioxidants is relatively high (soy isoflavones + vitamin E + coated tea polyphenols), which may lead to antagonism between high concentrations of fat-soluble antioxidants or the formation of byproducts. In addition, soy isoflavones and vitamin E are mainly fat-soluble antioxidants. In egg yolks, high concentrations of fat-soluble antioxidants may alter lipoprotein structure or micro-water-lipid distribution, and slightly affect water migration or osmotic gradient under baking or pickling conditions. After removing these two items in Example 7, the gradient osmotic regulation (sorbitol + trehalose) and the protein stabilizer CPP can play a more effective role, the moisture and protein structure of the egg yolk remain more uniform, and the hardness rate decreases.

[0132] In summary, Example 7 is the optimal example.

[0133] It is worth mentioning that, Figure 1 and Figure 2 Electron micrographs of Example 7 and Comparative Example 1 are shown, providing a more intuitive demonstration of the advancements of Example 7 at the microscopic level.

[0134] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A feed additive for laying ducks to alleviate the hard center of salted egg yolks, characterized in that, The feed additives include antioxidants, gut microbiota regulators, osmotic regulators, protein structure stabilizers, lipid emulsification regulators, and carriers.

2. The duck feed additive for relieving the hard center of salted egg yolks according to claim 1, and its preparation method, characterized in that, The antioxidant components are selected from tea polyphenols and their coated formulations.

3. The duck feed additive for relieving the hard center of salted egg yolks according to claim 1, and its preparation method, characterized in that, The microbial community regulating components are selected from Bacillus subtilis, Clostridium butyricum, and combinations thereof.

4. The duck feed additive for relieving the hard center of salted egg yolks according to claim 1, and its preparation method, characterized in that, The osmotic conditioning ingredients are selected from sorbitol, trehalose, and combinations thereof.

5. The duck feed additive for relieving the hard center of salted egg yolks according to claim 1, and its preparation method, characterized in that, The protein structure stabilizing components are selected from casein phosphopeptides (CPP) and coated tea polyphenols.

6. The duck feed additive for relieving the hard center of salted egg yolks according to claim 1, and its preparation method, characterized in that, The lipid emulsification regulating component is lecithin.

7. The duck feed additive for relieving the hard center of salted egg yolks according to claim 1, and its preparation method, characterized in that, The carrier is a conventional feed-grade powder used to uniformly disperse the various functional components.

8. A method for preparing a duck feed additive for alleviating the hard center of salted egg yolks as described in any one of claims 1 to 7, characterized in that, The preparation method includes: Step S1: Weigh, pulverize, and preliminarily mix all functional components and carriers according to the formula; Step S2: Mix all components thoroughly; Step S3: Dry the uniformly mixed components at low temperature; Step S4: Crush and sieve the components after low-temperature drying.

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