Zinc tannate coated feed additive as well as preparation method and application thereof

Abstract

The invention provides a zinc tannate coated feed additive as well as a preparation method and application thereof, and belongs to the technical field of livestock feed breeding. The preparation method comprises the following steps: crushing a tannic acid-containing plant raw material, uniformly mixing the crushed tannic acid-containing plant raw material with a zinc-containing compound to obtain a plant-zinc-containing compound mixture, adding the plant-zinc-containing compound mixture into a double-screw extruder, mixing, shearing and compressing to obtain puffed plant zinc tannate, crushing the puffed plant zinc tannate, and performing extrusion molding to obtain the plant zinc tannate. Fluidizing and granulating, spraying lac coating liquid, and drying to obtain the zinc tannate coated feed additive. The plant containing tannic acid is used as a raw material, the tedious process of extracting tannic acid is omitted, the coordination reaction of tannic acid and zinc oxide in the plant is accelerated by utilizing a twin-screw extrusion process, targeted release of zinc tannate is realized by adding the shellac coating liquid, the bioavailability is improved, the whole preparation process is environment-friendly, and the preparation method is suitable for industrial production. The method is suitable for large-scale production and commercial utilization.

Description

Technical Field

[0001] The present invention belongs to the technical field of livestock feed breeding, and particularly relates to a zinc tannate coated feed additive, a preparation method thereof and an application thereof. Background Art

[0002] After piglets are weaned, various factors can cause diarrhea in piglets and even a large number of deaths. In the actual feeding process, the stress response of piglets is mainly alleviated by adding antibiotics or high-dose ZnO. However, long-term addition of antibiotics to pig feed will cause bacteria to gradually adapt and develop drug resistance, resulting in a decrease in the effectiveness of antibiotics, and the residual antibiotics may be transmitted to humans through the food chain. Long-term intake of animal-derived foods containing antibiotic residues will have an adverse impact on human health. Excessive addition of zinc will cause its large accumulation in animals, which is not only transmitted to consumers through meat, but also increases the zinc emissions in animal feces, causing pollution to soil, water sources, etc., and affecting soil quality and ecological balance. Therefore, in the context of the development of antibiotic substitution and zinc reduction, finding safe and green alternative products has become a research hotspot in the livestock field.

[0003] Tannic acid derived from natural plants has functions such as anti-stress and improving animal immunity. As an organic zinc compound, zinc tannate not only has the biological activity of tannic acid but also has the nutritional function of zinc, with higher bioavailability and stability, and has potential application value in feed additives. Traditional preparation methods of zinc tannate usually have problems such as complex processes, low bioavailability, long reaction times, and the introduction of organic solvents. For example, the patent with the publication number CN 109820098A discloses an organic zinc feed additive, its preparation method, and its antibacterial activity application. This organic zinc feed additive is an organic zinc feed additive. The preparation process is to mix a tannic acid solution and an inorganic zinc solution evenly, adjust the pH value to 6 with a dilute alkali solution, react to form a milky white precipitate, separate the obtained white precipitate, wash and dry it. The tannic acid solution used therein is extracted and prepared from gallnuts as raw materials. Before preparing the organic zinc feed additive, a separate extraction step of the tannic acid solution is required, which undoubtedly increases the complexity of the process. Moreover, the tannic acid molecule contains multiple active groups such as phenolic hydroxyl groups. During the extraction process, it is easily affected by external environmental factors such as temperature, pH value, and light, and is prone to oxidation, polymerization, and other reactions, resulting in the destruction of its own structure, reducing the purity and stability of tannic acid. The obtained tannic acid solution needs to be stored in the dark, otherwise, it will accelerate oxidation, reduce activity, and reduce bioavailability. The patent with the publication number CN 117143166A discloses a synthesis method of zinc tannate. This method first prepares a tannic acid alcohol solution and an acidic zinc solution, then mixes the two and reacts to prepare a mixture containing zinc tannate, and then prepares the zinc tannate finished product through vacuum distillation, freeze crystallization, centrifugal separation, dissolution, and spray drying. At the same time, the crystallization mother liquor obtained by vacuum separation and the alcohol solution obtained by the primary vacuum distillation can be recycled, improving the utilization rate of the alcohol solution, reducing costs and environmental impacts. However, in this preparation method of zinc tannate, there are problems such as long reaction time and the introduction of organic solvents.

[0004] Therefore, the present invention proposes a zinc tannate-coated feed additive, its preparation method, and its application. Summary of the Invention

[0005] Aiming at the problems of the existing zinc tannate as a feed additive, such as cumbersome preparation process, insufficient synergy, and low bioavailability, the present invention proposes a zinc tannate-coated feed additive, its preparation method, and its application. It directly uses plants such as gallnuts with high tannic acid content as the source of tannic acid, chemically combines with zinc oxide through an extrusion expansion technology, and uses shellac resin with pH responsiveness for coating and granulation to prepare a feed additive with targeted release ability.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention:

[0008] A preparation method of zinc tannate-coated feed additive, comprising the following steps:

[0009] Crush the plant containing tannic acid and mix it evenly with the zinc compound to obtain a plant-zinc compound mixture;

[0010] Add the plant-zinc compound mixture into a twin-screw extruder, and after stirring, shearing, and compression extrusion, obtain expanded plant zinc tannate;

[0011] After crushing the expanded plant zinc tannate, fluidize granulate and spray shellac coating solution, and after drying, obtain the zinc tannate-coated feed additive.

[0012] Further, the plant raw material containing tannic acid is selected from galls, and the zinc compound is selected from zinc oxide.

[0013] Further, the mass ratio of tannic acid content in the plant raw material containing tannic acid to the zinc compound is 10:1.

[0014] Further, adjust the moisture content of the plant-zinc compound mixture to 10-50% and then add it to the twin-screw extruder, preferably adjust the moisture content to 30%.

[0015] Further, the temperatures of the 1st zone, 2nd zone, and 3rd zone of the twin-screw extruder sleeve are all 110°C, and the temperatures of the 4th zone, 5th zone, and 6th zone are independently selected from 130-170°C, preferably 160°C.

[0016] Further, the rotation speed of the twin-screw extruder is 40-200 r / min, preferably 120 r / min.

[0017] Further, crush the expanded plant zinc tannate to a mesh number of 5-80 meshes.

[0018] Further, the shellac coating solution is obtained by dissolving shellac resin in ethanol, adding glycerol after dissolution, and mixing. The dosage ratio of the shellac resin, ethanol, and glycerol is 25 g:100 mL:1 g, and the mass concentration of the ethanol is 95%. The present invention uses the shellac coating solution to perform enteric coating on the gall expanded material, which has the functions of airtightness, moisture resistance, and shielding of astringent taste, and the formed coating is acid-resistant, thereby reducing the dissolution and release of the additive functional component zinc tannate in the stomach; after the zinc tannate additive enters the duodenum, under the action of bile, etc., the additive coating swells and disintegrates, and the zinc tannate in the additive can be quickly dissolved and act on the intestinal mucosa, improving the bioavailability of zinc tannate.

[0019] Furthermore, when spraying the shellac coating solution, the air flow temperature is 45 °C, the spraying flow rate is 100 kg / h, and the spraying time is 2 h.

[0020] In natural cells, plant tannic acid often forms a weakly bound state with polysaccharides, proteins, etc. and is dispersed and fixed in plant cells. After the cell structure is destroyed under the action of a twin-screw high shear, tannic acid is released from the complex, the steric hindrance of its phenolic hydroxyl group is reduced, and the active sites are more fully exposed. When plant raw materials such as gallnuts are crushed and mixed with zinc-containing compounds such as zinc oxide, the hydrophilic groups (such as hydroxyl groups and carboxyl groups) in their cell walls can wrap ZnO particles through hydrogen bonding to form a nanoscale dispersion system, avoiding the agglomeration of pure zinc oxide powder. In addition, polyphenol derivatives (such as gallic acid, catechin, etc.) and organic acids (such as malic acid, succinic acid) contained in plant raw materials can be used as auxiliary ligands or acidic environment regulators. The hydroxyl groups of polyphenol derivatives can form a "ligand network" with tannic acid, and assist in stabilizing the coordination complex through hydrogen bonding or π-π stacking, reducing the agglomeration or precipitation of Zn 2+ , and dietary fibers such as cellulose and hemicellulose in plants form a porous structure during the puffing process, acting as a natural carrier to adsorb Zn 2+ , enabling tannic acid and Zn 2+ to form a "confined reaction environment" in the micropores, shortening the mass transfer distance, increasing the local reaction concentration, expanding the contact area between tannic acid and Zn 2+ , and significantly increasing the contact probability with Zn 2+ . The fibers in plant raw materials form a porous structure after puffing, providing a network carrier for subsequent fluidized granulation, making the particles of the coordination product (puffed zinc tannate) have higher strength and being more likely to form a uniform coating when spraying the shellac coating, indirectly protecting the stability of the coordination bond during storage and processing.

[0021] The second technical solution of the present invention:

[0022] A zinc tannate-coated feed additive prepared by the above method.

[0023] The third technical solution of the present invention:

[0024] An application of the zinc tannate-coated feed additive in preparing animal feed.

[0025] Exemplarily, a method for preparing a zinc tannate-coated feed additive using gallnuts and zinc oxide as examples includes the following steps:

[0026] (1) Crush the gallnuts, pass them through a standard test sieve with 60 meshes after crushing with a pulverizer, then measure the tannic acid content in the gallnuts, prepare materials according to the mass ratio of tannic acid to zinc oxide of 10:1, mix evenly to obtain a gallnut-zinc oxide mixture, and shade it to avoid direct sunlight, then it can be "sent to the storage bin for temporary storage";

[0027] (2) Adjust the gallnut-zinc oxide mixture to a moisture content of 10-50%, and then put it into a twin-screw extruder. Set the rotation speed of the twin-screw extruder to 40-200 r / min. The temperatures of zones 1, 2, and 3 of the twin-screw extruder barrel are all 110 °C, and the temperatures of zones 4, 5, and 6 are independently selected from 130-170 °C. After mixing, shearing, and compression extrusion, expanded zinc gallotannate is obtained.

[0028] (3) Dissolve 25 g of shellac in 100 mL of 95% ethanol. After dissolution, add 1 g of glycerol to obtain a shellac coating solution.

[0029] (4) Crush the prepared expanded zinc gallotannate to a mesh size of 5-80 meshes, put it into a fluidized granulator and fluidize it. Spray the prepared shellac coating solution into the upper part of the fluidized granulator. The air flow temperature is 45 °C, the flow rate is 100 kg / h, the spraying time is 2 h, and after drying and film forming, discharge to obtain a zinc gallotannate-coated feed additive.

[0030] In the above preparation process, the coordination principle of tannic acid and zinc oxide (ZnO) is shown in Figure 1 , specifically, the tannic acid contained in gallnuts is a macromolecular organic compound containing multiple phenolic hydroxyl groups. The oxygen atom in the phenolic hydroxyl group has a lone pair of electrons and can participate in coordination. By controlling the water content, temperature, and rotation speed of the twin-screw extrusion temperature, partial dissociation of zinc oxide (ZnO) occurs to generate Zn 2+ and O 2- . Then, the oxygen atom of the phenolic hydroxyl group in the tannic acid molecule will provide its lone pair of electrons to the zinc ions dissociated from zinc oxide. Zinc ions have empty orbitals and can accept the lone pair of electrons of the oxygen atom of the phenolic hydroxyl group, thus forming a coordination bond. Since tannic acid contains multiple phenolic hydroxyl groups, multiple phenolic hydroxyl groups can coordinate with multiple zinc ions, or one zinc ion can coordinate with the phenolic hydroxyl groups in multiple tannic acid molecules, ultimately forming a complex coordination structure. At the same time, during the reaction, the hydrogen atom on the phenolic hydroxyl group combines with the oxygen ions dissociated from zinc oxide to form water, promoting the progress of the coordination reaction.

[0031] In the present invention, plants containing tannins (such as gallnuts, etc.) are used to replace tannic acid. In addition to solving the problem of the complex tannic acid extraction process, its core advantage lies in utilizing the natural structural complexity, coexisting component synergy, and physical compatibility of plant tannins, and realizing an integrated process of "in-situ release - efficient contact - multi-stage coordination" through the crushing - shearing - expansion effect of the twin-screw process. Compared with pure tannic acid, the plant raw material not only retains the multi-hydroxyl coordination ability of tannins, but also significantly improves the efficiency of the coordination reaction, the stability of the product, and the process economy through the auxiliary dissociation of natural components, carrier dispersion, and mechanochemical strengthening. At the same time, the loss of activity during the separation of pure tannins is avoided, which is a coordination reaction promotion strategy with both functionality and practicality.

[0032] Compared with the prior art, the present invention has the following advantages and technical effects:

[0033] (1) The present invention uses plants containing tannic acid as raw materials, eliminating the cumbersome process of extracting tannic acid. By using a twin-screw extrusion process, under the action of shear and compression, the coordination reaction between tannic acid and zinc oxide in the plant is accelerated. The addition of a shellac coating solution with pH responsiveness provides enteric coating, realizing the targeted release of zinc tannate and improving bioavailability. The shellac coating process can further protect the coordination complex, enabling it to remain stable in a feed processing environment (such as granulation) with humidity, shear, and collision, avoiding premature release or degradation of the active ingredients.

[0034] (2) The preparation process of the present invention not only improves the bioavailability of zinc and the stability of the feed additive, but also eliminates the anti-nutritional side effects of tannic acid, realizing the efficient utilization and targeted release of functional ingredients, and having significant advantages in improving animal nutrition absorption and feed quality. The entire preparation process is environmentally friendly and produces no waste, being suitable for large-scale production and commercial utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0036] Figure 1 is the coordination principle of tannic acid and ZnO during the preparation of zinc tannate-coated feed additive using Chinese gallnut and zinc oxide as examples;

[0037] Figure 2 is a schematic diagram of the processing and application of preparing zinc tannate-coated feed additive using Chinese gallnut and zinc oxide as examples in the embodiments of the present invention;

[0038] Figure 3 is the FTIR diagram of zinc oxide, gallnut tannic acid (i.e., raw material Chinese gallnut), and expanded zinc gallnut tannate in Example 14;

[0039] Figure 4 is the SEM diagram of the expanded zinc gallnut tannate prepared in Example 14;

[0040] Figure 5 is the SEM diagram of the zinc tannate-coated feed additive prepared in Example 14. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0042] It should be understood that the terms used in the present invention are only for describing particular embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0043] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0044] Without departing from the scope or spirit of the present invention, various modifications and variations can be made to the specific embodiments of the present invention specification, which are obvious to those skilled in the art. Other embodiments obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are merely exemplary.

[0045] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0046] The embodiments of the present invention provide a preparation method of a zinc tannate-coated feed additive, comprising the following steps:

[0047] Crush the plant containing tannic acid and mix it evenly with the zinc compound to obtain a plant-zinc compound mixture;

[0048] Add the plant-zinc compound mixture into a twin-screw extruder, and obtain expanded plant zinc tannate after shearing, mixing, and compressing;

[0049] After crushing the expanded plant zinc tannate, fluidized granulation is carried out and a shellac coating solution is sprayed, and the zinc tannate-coated feed additive is obtained after drying.

[0050] In the preferred embodiment of the present invention, the plant raw material containing tannic acid is gallnut, but is not limited to gallnut, and also includes plants such as tara, acorn cup, and larch containing tannic acid. The zinc compound is zinc oxide and can also be zinc chloride.

[0051] In a preferred embodiment of the present invention, the mass ratio of tannic acid content in the plant raw material containing tannic acid to the zinc-containing compound is 10:1. The method for measuring the tannic acid content in the plant raw material containing tannic acid adopts the conventional method in the technical field. Exemplarily, in the embodiment of the present invention, the ultraviolet spectrophotometer method is used to measure the absorbance value of the plant raw material containing tannic acid at 276 nm. Taking the absorbance value as the abscissa and the concentration as the ordinate, a standard curve is fitted, and then the absorbance of the sample is measured and substituted into the standard curve to calculate the content.

[0052] In a preferred embodiment of the present invention, the moisture content of the plant-zinc-containing compound mixture is adjusted to 10-50% and then added to the twin-screw extruder, preferably adjusted to 30%.

[0053] In a preferred embodiment of the present invention, the temperatures of the 1st zone, 2nd zone and 3rd zone of the twin-screw extruder sleeve are all 110 °C, and the temperatures of the 4th zone, 5th zone and 6th zone are independently selected from 130-170 °C, preferably 160 °C.

[0054] The high-temperature environment (110-170 °C) of the twin-screw extruder increases the molecular kinetic energy of tannic acid and zinc oxide, the proportion of molecules exceeding the reaction activation energy rises, the effective collision frequency increases, accelerating the dissociation of ZnO and the deprotonation of phenolic hydroxyl groups of tannic acid, and promoting the formation of coordination bonds; the high temperature makes the moisture or polar components in the material (such as natural solvents in plant raw materials) form a liquid-phase environment, accelerating the 2+ dissolution and diffusion of Zn; and the shearing action of the screw in the twin-screw extruder breaks the cell wall in the gallnut, releasing the aggregated tannic acid in the cells and increasing the contact opportunity with Zn 2+ or ZnO; secondly, the high temperature promotes the hydrolysis of cell wall polysaccharides (cellulose, hemicellulose) in plant raw materials (such as gallnuts), serving as the backbone carrier for the subsequent expanded material.

[0055] In a preferred embodiment of the present invention, the rotation speed of the twin-screw extruder is 40-200 r / min, preferably 120 r / min.

[0056] The high shear force of the twin-screw (rotation speed of 40-200 r / min) crushes the plant raw material particles, increases the contact area between the plant raw material and zinc oxide, shortens the mass transfer distance, and enables tannic acid and ZnO to be fully mixed at the micro-nano particle or even molecular level; in addition, the shear force slides and rubs inside the material, continuously updating the two-phase interface, reducing the local concentration gradient, avoiding the accumulation of reactants, and ensuring the uniform progress of the coordination reaction in the whole material. The high shear force also triggers mechanochemical action, changing the surface defects of ZnO or the polarity of tannic acid molecular bonds through stress induction, reducing the reaction activation energy, and further accelerating the coordination reaction.

[0057] In a preferred embodiment of the present invention, the expanded zinc phytotannate is pulverized to a mesh size of 5 - 80 meshes.

[0058] In a preferred embodiment of the present invention, the shellac coating solution is obtained by dissolving shellac resin in ethanol, adding glycerol after dissolution, and mixing them. The dosage ratio of shellac resin, ethanol, and glycerol is 25 g∶100 mL∶1 g, and the mass concentration of ethanol is 95%.

[0059] In a preferred embodiment of the present invention, when spraying the shellac coating solution, the air flow temperature is 45°C, the spraying flow rate is 100 kg / h, and the spraying time is 2 h.

[0060] The embodiment of the present invention also provides a zinc tannate-coated feed additive prepared by the above method.

[0061] Exemplarily, a method for preparing a zinc tannate-coated feed additive using gallnuts and zinc oxide as examples includes the following steps:

[0062] (1) Crush the gallnuts, pulverize them with a pulverizer and then pass through a 60-mesh standard test sieve. After that, measure the tannic acid content in the gallnuts, prepare the materials according to the mass ratio of tannic acid to zinc oxide of 10∶1, mix them evenly to obtain a gallnut-zinc oxide mixture, and store it in an intermediate bin.

[0063] (2) Adjust the moisture content of the gallnut-zinc oxide mixture to 10 - 50%, and then put it into a twin-screw extruder. Set the rotation speed of the twin-screw extruder to 40 - 200 r / min. The temperatures of zones 1, 2, and 3 of the twin-screw extruder barrel are all 110°C, and the temperatures of zones 4, 5, and 6 are independently selected from 130 - 170°C. After stirring and extrusion, expanded gallnut zinc tannate is obtained.

[0064] (3) Dissolve 25 g of shellac in 100 mL of 95% ethanol, and add 1 g of glycerol after dissolution to obtain a shellac coating solution.

[0065] (4) Pulverize the prepared expanded gallnut zinc tannate to a mesh size of 5 - 80 meshes, put it into a fluidized granulator and make it fluidized. Spray the prepared shellac coating solution into the upper part of the fluidized granulator. The air flow temperature is 45°C, the flow rate is 100 kg / h, the spraying time is 2 h, and after drying and film-forming, discharge the product to obtain a zinc tannate-coated feed additive.

[0066] The zinc tannate-coated feed additive prepared in the embodiment of the present invention can be used to prepare piglet feed.

[0067] The processing and application schematic diagram of preparing a zinc tannate-coated feed additive using gallnuts and zinc oxide as examples in the embodiment of the present invention is shown in Figure 2 .

[0068] In the embodiments of the present invention, the gallnuts used were purchased from Wufeng Chicheng Biotechnology Co., Ltd., and zinc oxide, glycerol, and shellac were all obtained by commercial purchase. Among them, the shellac was purchased from Anning Daike Fine Chemical Co., Ltd.

[0069] The technical solution of the present invention will be further described below through embodiments.

[0070] Example 1

[0071] (1) The gallnuts were crushed, pulverized with a pulverizer, and then passed through a standard test sieve with 60 meshes. After that, the tannic acid content in the gallnuts was measured, and the materials were prepared according to the mass ratio of tannic acid to zinc oxide of 10:1. After mixing evenly, a gallnut-zinc oxide mixture was obtained and stored in the dark.

[0072] (2) The moisture content of the gallnut-zinc oxide mixture was adjusted to 30%, and then it was put into a twin-screw extruder. The rotation speed of the twin-screw extruder was set at 80 r / min, and the temperatures of the 1st, 2nd, and 3rd zones of the twin-screw extruder barrel were all 110 °C, and the temperatures of the 4th, 5th, and 6th zones were all 140 °C. After stirring and extrusion, expanded zinc gallnut tannate was obtained. After the coordination of tannic acid and zinc oxide, a product that is not easily soluble in water was formed. The index results are shown in Table 1.

[0073] Example 2

[0074] Same as Example 1, the only difference is that the moisture content of the gallnut-zinc oxide mixture was adjusted to 10%. The index results are shown in Table 1.

[0075] Example 3

[0076] Same as Example 1, the only difference is that the moisture content of the gallnut-zinc oxide mixture was adjusted to 20%. The index results are shown in Table 1.

[0077] Example 4

[0078] Same as Example 1, the only difference is that the moisture content of the gallnut-zinc oxide mixture was adjusted to 40%. The index results are shown in Table 1.

[0079] Example 5

[0080] Same as Example 1, the only difference is that the moisture content of the gallnut-zinc oxide mixture was adjusted to 50%. The index results are shown in Table 1.

[0081] Table 1 Indexes of expanded zinc gallnut tannate prepared with different moisture contents in Examples 1-5

[0082]

[0083] Example 6

[0084] (1) Break the gallnuts, crush them with a pulverizer, and then pass through a 60-mesh standard test sieve. After that, measure the tannic acid content in the gallnuts, prepare materials according to the mass ratio of tannic acid to zinc oxide of 10:1, mix evenly to obtain a gallnut-zinc oxide mixture, and store it away from light;

[0085] (2) Adjust the moisture content of the gallnut-zinc oxide mixture to 30%, and then put it into a twin-screw extruder. Set the rotation speed of the twin-screw extruder to 40 r / min, and the temperatures of zones 1, 2, and 3 of the twin-screw extruder barrel are all 110 °C, and the temperatures of zones 4, 5, and 6 are all 140 °C. After stirring and extrusion, expanded gallnut zinc tannate is obtained, and the index results are shown in Table 2.

[0086] Example 7

[0087] Same as Example 6, the only difference is that the rotation speed of the twin-screw extruder is set to 120 r / min, and the index results are shown in Table 2.

[0088] Example 8

[0089] Same as Example 6, the only difference is that the rotation speed of the twin-screw extruder is set to 160 r / min, and the index results are shown in Table 2.

[0090] Example 9

[0091] Same as Example 6, the only difference is that the rotation speed of the twin-screw extruder is set to 200 r / min, and the index results are shown in Table 2.

[0092] Table 2 Indexes of expanded gallnut zinc tannate prepared at different rotation speeds

[0093]

[0094] Example 10

[0095] (1) Break the gallnuts, crush them with a pulverizer, and then pass through a 60-mesh standard test sieve. After that, measure the tannic acid content in the gallnuts, prepare materials according to the mass ratio of tannic acid to zinc oxide of 10:1, mix evenly to obtain a gallnut-zinc oxide mixture, and store it away from light;

[0096] (2) Adjust the moisture content of the gallnut-zinc oxide mixture to 30%, and then put it into a twin-screw extruder. Set the rotation speed of the twin-screw extruder to 120 r / min, and the temperatures of zones 1, 2, and 3 of the twin-screw extruder barrel are all 110 °C, and the temperatures of zones 4, 5, and 6 are all 150 °C. After stirring and extrusion, expanded gallnut zinc tannate is obtained, and the index results are shown in Table 3.

[0097] Example 11

[0098] Same as Example 10, with the only difference being that the temperatures in zones 4, 5, and 6 are all 160 °C, and the index results are shown in Table 3.

[0099] Example 12

[0100] Same as Example 10, with the only difference being that the temperatures in zones 4, 5, and 6 are all 170 °C, and the index results are shown in Table 3.

[0101] Example 13

[0102] Same as Example 10, with the only difference being that the temperatures in zones 4, 5, and 6 are all 180 °C, and the index results are shown in Table 3.

[0103] Table 3 Indexes of zinc gallotannate expanded materials prepared at different temperatures

[0104]

[0105] Performance test

[0106] A high degree of expansion means that more porous structures are formed inside the particles, the specific surface area increases significantly, which can accelerate the dissolution and release of zinc gallotannate in the animal intestine, improve the bioavailability of zinc gallotannate. The pores, as the material transport channels, can regulate the slow-release rate of zinc gallotannate, avoid premature release in the acidic environment of the stomach, ensure its gradual release in the alkaline environment of the intestine, and improve the targeting. Combining Tables 1 - 3, it can be seen that during the preparation of expanded zinc gallotannate, when the moisture content of the gallnut-zinc oxide mixture is 30%, the screw speed is 120 r / min, and the sleeve temperatures in zones 4, 5, and 6 are 160 °C, the degree of expansion of the expanded zinc gallotannate is the best, and the pore distribution is uniform. Based on the above optimal conditions, a zinc gallotannate-coated feed additive is prepared.

[0107] Example 14

[0108] A preparation method of a zinc gallotannate-coated feed additive, comprising the following steps:

[0109] (1) Crush the gallnuts, pulverize them with a pulverizer and then pass through a standard test sieve with 60 meshes. After that, measure the tannic acid content in the gallnuts, prepare the materials according to the mass ratio of tannic acid to zinc oxide of 10:1, mix them evenly to obtain a gallnut-zinc oxide mixture, and store it away from light;

[0110] (2) Adjust the moisture content of the gallnut-zinc oxide mixture to 30%, and then put it into a twin-screw extruder. Set the rotation speed of the twin-screw extruder to 120 r / min, and the temperatures in zones 1, 2, and 3 of the twin-screw extruder sleeve are all 110 °C, and the temperatures in zones 4, 5, and 6 are all 160 °C. After stirring and extrusion, expanded zinc gallotannate is obtained (FTIR diagrams of zinc oxide, gallotannic acid (i.e., the raw material gallnuts), and expanded zinc gallotannate are shown in Figure 3, the SEM image of expanded zinc gallotannate is shown in Figure 4 );

[0111] (3) Dissolve shellac in ethanol with a concentration of 95 wt%, and add glycerol after dissolution to obtain a shellac coating solution. The dosage ratio of shellac resin, ethanol, and glycerol is 25 g∶100 mL∶1 g;

[0112] (4) Grind the prepared expanded zinc gallotannate to 8 mesh, put it into a fluidized granulator and make it fluidized. Spray the prepared shellac coating solution into the upper part of the fluidized granulator. The air flow temperature is 45 °C, the flow rate is 100 kg / h, the spraying time is 2 h, and discharge after drying to form a film, obtaining a zinc gallotannate-coated feed additive (SEM image is shown in Figure 5 ).

[0113] From Figure 3 it can be seen that the vibration of the Zn-O bond is at 559 cm -1 . The stretching vibration of -OH of gallotannic acid shows a broad peak in the range of 3500 - 3200 cm -1 , which may be related to intermolecular hydrogen bonds. The stretching vibration of C=O is at 1718 cm -1 , and the characteristic peaks of the benzene ring are 1612, 1530, and 1448 cm -1 respectively. After coordination of zinc oxide with gallotannic acid, the characteristic absorption peaks of gallotannic acid shift. For example, the C=O peak shifts from 1718 cm -1 to a lower wavenumber of 1703 cm -1 nearby, because the change in electron cloud density leads to a decrease in bond energy, which further supports the coordination effect.

[0114] From Figure 4 and Figure 5 it can be seen that the expanded product, expanded zinc gallotannate, has a loose and porous structure, which is beneficial to the release of zinc gallotannate. After the expanded particles are coated with shellac resin, a film is formed on the surface, forming a relatively smooth surface.

[0115] Comparative Example 1

[0116] (1) Crush galls, grind them with a pulverizer and pass through a standard test sieve with 60 meshes. Then measure the tannic acid content in the galls, prepare materials according to the mass ratio of tannic acid to zinc oxide of 10∶1, mix them evenly to obtain a gall - zinc oxide mixture, and store it in the dark;

[0117] (2) Dissolve shellac in ethanol with a concentration of 95 wt%, and add glycerol after dissolution to obtain a shellac coating solution. The dosage ratio of shellac resin, ethanol, and glycerol is 25 g∶100 mL∶1 g;

[0118] (3) The prepared gallnut-zinc oxide mixture was mixed and pulverized to 8 mesh, put into a fluidized granulator to make it fluidized, and the prepared shellac coating solution was sprayed into the fluidized granulator from the upper part. The air flow temperature was 45 °C, the flow rate was 100 kg / h, the spraying time was 2 h, and after drying and film forming, the material was discharged to obtain zinc tannate-coated feed additive.

[0119] Performance test

[0120] The zinc tannate-coated feed additives prepared in Example 14 and Comparative Example 1 were respectively added to the piglet diet at an addition amount of 1%, and two other control groups were set up, using equal masses of gallnut and zinc oxide to replace the zinc tannate-coated feed additive and adding them to the piglet diet. The specific composition of the piglet diet was a corn-soybean meal type diet, and the specific components are shown in Table 4:

[0121] Table 4 Composition and nutritional level of corn-soybean meal type diet

[0122] Raw material Proportion / % Raw material Proportion / % Corn 65 Table salt 0.3 Soybean meal 22 Lysine 0.15 Bran 5 Methionine 0.05 Limestone powder 1.2 Premix 1.5 Calcium hydrogen phosphate 0.8 Soybean oil 4

[0123] The above-obtained piglet diet was used as feed to feed piglets, and the specific method was as follows:

[0124] Other parameters such as feeding amount, feeding time, feeding frequency, management during the feeding period, number of days of piglets, and initial weight of piglets need to be supplemented.

[0125] After feeding for 21 days, growth performance, stress and immune performance, intestinal health performance, oxidation and residue performance were tested, among which:

[0126] Feed conversion ratio (FCR) = total feed consumption / total animal weight gain;

[0127] Diarrhea rate (%) = number of diarrhea pigs in each treatment / total number of pigs in each treatment test × 100;

[0128] Serum cortisol was tested by enzyme-linked immunosorbent assay and quantified by colorimetric reaction of enzyme-catalyzed reaction;

[0129] Immunoglobulin IgG was tested by enzyme-linked immunosorbent assay. The enzyme-labeled antibody was used to bind to IgG, and the concentration was quantified by colorimetric reaction;

[0130] The ratio of villus height to crypt depth was tested by HE staining method. The tissue samples of duodenum, jejunum and ileum were made into tissue sections and observed under an optical microscope. The villus height and crypt depth of the selected field of view were measured, and the villus-crypt ratio (villus height / crypt depth) was calculated;

[0131] The number of lactic acid bacteria was counted by colony counting method. The lactic acid bacteria were separated by culture medium, and the number of viable bacteria was counted by colony forming units; Serum MDA was tested by enzyme-linked immunosorbent assay. The specific antibody against MDA was used, and the concentration of serum MDA was detected by competitive method;

[0132] The zinc residue in feces was directly determined for the zinc ion content by an inductively coupled plasma mass spectrometer.

[0133] The test results of various performances are shown in Table 5.

[0134] Table 5 Test Results of Various Performances of Each Group

[0135]

[0136] Note: ↑ indicates that the higher the value, the better; ↓ indicates that the lower the value, the better.

[0137] As can be seen from Table 5, after adding the zinc tannate coated feed additive of the present invention, the anti-diarrhea effect is significantly improved. Compared with the control group (galla chinensis), it is increased by 65%. Compared with the control group (zinc oxide), it is increased by 55.79%. Compared with the simple mixture of galla chinensis and zinc oxide directly used, it is increased by 52.81%. It shows that the method of the present invention accelerates the coordination reaction between tannic acid and zinc oxide in galla chinensis, achieving the improvement of the biological utilization of zinc and the stability of the feed additive. In addition, the zinc tannate coated feed additive of the present invention also has an intestinal protection effect and improves the intestinal morphology through the sustained release characteristics, which is superior to the single component of the control group. Finally, the zinc tannate coated feed additive of the present invention has an environmental protection and safety effect, with the zinc residue reduced and the environmental pollution decreased.

[0138] The above is only the preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A preparation method of zinc tannate-coated feed additive, characterized in that, It includes the following steps: Crush the plant raw material containing tannic acid and mix it evenly with the zinc compound to obtain a plant-zinc compound mixture; Add the plant-zinc compound mixture into a twin-screw extruder, and obtain expanded zinc tannate after mixing, shearing, and compression extrusion; After crushing the expanded zinc tannate, fluidize and granulate it, spray the shellac coating solution, and obtain the coated zinc tannate feed additive after drying.

2. The preparation method of the zinc tannate-coated feed additive according to claim 1, characterized in that, The plant raw material containing tannic acid is selected from Chinese gallnuts; the zinc compound is selected from zinc oxide.

3. The preparation method of the zinc tannate-coated feed additive according to claim 1, characterized in that The mass ratio of tannic acid content in the plant raw material containing tannic acid to the zinc compound is 10∶1.

4. The preparation method of the zinc tannate-coated feed additive according to claim 1, characterized in that, The water content of the plant-zinc compound mixture is 10-50%.

5. The preparation method of the zinc tannate-coated feed additive according to claim 1, characterized in that, The temperatures of zones 1, 2, and 3 of the twin-screw extruder sleeve are all 110°C, and the temperatures of zones 4, 5, and 6 are independently selected from 130-170°C.

6. The preparation method of the zinc tannate-coated feed additive according to claim 5, characterized in that, The rotation speed of the twin-screw extruder is 40-200 r / min.

7. The preparation method of the zinc tannate-coated feed additive according to claim 1, characterized in that, The shellac coating solution is obtained by dissolving shellac resin in ethanol, adding glycerol after dissolution, and mixing, wherein the dosage ratio of shellac resin, ethanol, and glycerol is 25 g∶100 mL∶1 g.

8. The method for zinc tannate-coated feed additive according to claim 1, characterized in that, When spraying the shellac coating solution, the air flow temperature is 45°C, the spraying flow rate is 100 kg / h, and the spraying time is 2 h.

9. A coated zinc tannate feed additive prepared by the preparation method according to any one of claims 1-8.

10. Use of the coated zinc tannate feed additive according to claim 9 in the preparation of animal feed.

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