Protein feed prepared by solid state fermentation using potato pulp and its preparation method

Abstract

The application discloses a kind of protein feed using potato residue solid fermentation and a preparation method thereof.Mainly with potato residue as main raw material, aspergillus niger, Candida tropicalis, Candida lipolytica and Saccharomyces cerevisiae are used as collaborative fermentation strains to carry out aerobic-anaerobic fermentation, and through single factor test and orthogonal test, the production process of solid fermentation bacterial protein feed using potato residue as raw material is studied.The bacterial protein feed process is produced by adopting composite strain solid fermentation, which can significantly increase the crude protein content and true protein content in fermentation product, improve the nutritional value, improve animal growth performance, and increase the shelf life and stability of protein feed, and also provides a new mode for non-grain type feed resources, especially potato residue waste resource utilization, effectively alleviates the plight of conventional feed resource shortage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of feed, in particular to a protein feed prepared by solid-state fermentation of potato residue and a preparation method thereof. BACKGROUND

[0002] Potato residue solid-state fermentation is a method that uses potato residue as a substrate to produce protein feed through microbial fermentation under suitable conditions. This method can convert agricultural by-products (such as potato residue) into high-protein, high-nutrition value feed, improving resource utilization efficiency and reducing environmental pollution.

[0003] In the process of preparing protein feed by potato residue solid-state fermentation, commonly used microorganisms include Aspergillus niger, Candida tropicalis, Candida lipolytica, and Saccharomyces cerevisiae. These microorganisms convert carbohydrates, proteins, and other substances in potato residue into organic acids, amino acids, enzymes, and other nutrients through metabolic action, thereby improving the nutritional value and bioavailability of protein feed.

[0004] Other methods for preparing protein feed also exist in the prior art, such as liquid-state fermentation, microbial fermentation, and chemical methods. Liquid-state fermentation methods usually use liquid culture medium to produce protein feed through microbial fermentation under suitable conditions. Commonly used microorganisms in microbial fermentation methods include bacteria, fungi, and yeast. Chemical methods synthesize protein feed through chemical reactions, common methods include hydrolysis, enzymatic hydrolysis, and amino acid synthesis.

[0005] Compared with other methods, potato residue solid-state fermentation for preparing protein feed has the following advantages: potato residue is a by-product of potato processing, and through solid-state fermentation, this resource can be effectively utilized, reducing waste. Potato residue is a renewable resource, and compared with other raw materials, it has better sustainability and environmental friendliness. Through solid-state fermentation, microorganisms can convert the protein in potato residue into a higher content and more easily digestible form, improving the nutritional value of protein feed. Compared with other methods, solid-state fermentation has a simple process flow and low cost, suitable for small-scale production.

[0006] However, it is crucial to further improve the true protein and crude protein content of protein feed and increase the storage stability of protein feed.

[0007] CN103540536B discloses a kind of protein-producing microbial inoculant, including the following mass fraction of each component: adsorbent 1000 parts, Trichoderma viride fermentation liquor and yeast strain fermentation liquor 60~100 parts;Wherein, the adsorbent is by the following mass fraction of each component: bran 700~900 parts, corn straw 100~300 parts, sucrose 15~30 parts, corn flour 25~50 parts;Trichoderma viride fermentation liquor and yeast strain fermentation liquor mass ratio is 1~3:1.The application makes full use of waste resources, low production cost, reduces environmental pollution, solves the problem of adsorbent raw material needed for producing microbial inoculant, and is harmless to human and livestock;Preparation method is simple and easy to operate;The protein-producing microbial inoculant of the application is used to produce protein feed with potato residue, which not only retains active ingredients but also avoids waste residue and waste liquid pollution, improves the protein content and nutritional value of potato residue.However, the protein feed prepared by the application has limited effect on increasing the content of true protein and crude protein in protein feed, and the storage stability of the prepared protein feed is poor. SUMMARY

[0008] In view of the low content of true protein and crude protein in protein feed and poor storage stability in the prior art, the technical problem to be solved by the application is to provide a method for preparing protein feed with high content of true protein and crude protein and good storage stability by solid-state fermentation of potato residue.

[0009] In order to achieve the above-mentioned application purposes, the application adopts the following technical solutions:

[0010] A method for preparing protein feed by solid-state fermentation of potato residue is as follows:

[0011] Mix potato residue and wheat bran to obtain a mixture, then add ammonium sulfate and water, inoculate fermentation strain after mixing uniformly, and ferment and culture at 30~35℃ for 24~96h to obtain protein feed.

[0012] Preferably, the method for preparing protein feed by solid-state fermentation of potato residue is as follows:

[0013] Mix potato residue and wheat bran to obtain a mixture, then add ammonium sulfate and water, inoculate fermentation strain after mixing uniformly, and ferment and culture at 30~35℃ for 24~96h, dry at 40~60℃, crush, pass through 50~200 mesh sieve to obtain protein powder; mix the protein powder with a protective agent, stir at 100~300 rpm for 1~3h to obtain protein feed.

[0014] Preferably, the potato residue and wheat bran are mixed in a mass ratio of 80~90:10~20 to obtain the mixture.

[0015] Preferably, the mass of the added ammonium sulfate and water is 1-3% and 65-70% of the mass of the mixture, respectively.

[0016] Preferably, the fermentation strain is one or a mixture of more than one of Aspergillus niger, Candida tropicalis, Candida lipolytica and Saccharomyces cerevisiae.

[0017] Preferably, the inoculation amount of each of the fermentation strains is 0.5-2% of the mass of the mixture.

[0018] Preferably, the mass ratio of the protein powder to the protective agent is 80-120: 1-5.

[0019] The protective agent is prepared as follows, by weight:

[0020] S1, 250-300 parts of isofraxidin is added to 1800-2200 parts of N, N-dimethylformamide, then 180-220 parts of 2-bromoethylamine hydrobromide and 250-300 parts of anhydrous potassium carbonate are added, and the mixture is stirred at 100-500 rpm in an oil heating bath at 100-120℃ for 1-5 h, filtered and purified, and the reaction medium is removed by concentration under reduced pressure, and the salt is removed with anhydrous ethanol, and the product is recrystallized with water twice, and dried at 50-70℃ under vacuum to obtain the functional agent;

[0021] S2, 4-6 parts of chitosan is added to 40-60 parts of isopropyl alcohol, and the mixture is stirred at 100-300 rpm at room temperature for 20-40 min, then 10-15 parts of 4-6 mol / L sodium hydroxide aqueous solution is added, and the mixture is stirred at 100-300 rpm for 30-60 min, then 20-40 parts of chloroacetic acid is added, and the mixture is heated to 50-70℃, and the mixture is stirred at 100-300 rpm at this temperature for 1-5 h, and the mixture is filtered, washed with methanol, and dried in an oven at 50-70℃ to obtain the pretreatment agent; the pretreatment agent is mixed with 10-30 parts of the functional agent prepared in step S1 to obtain the protective agent.

[0022] The fermentation substrate of the present application is obtained by mixing potato pulp and wheat bran at a mass ratio of 85:15. The potato pulp and wheat bran serve as substrates in the solid-state fermentation process, providing carbon sources and nutrients for the growth and metabolism of the fermentation strains to produce protein. According to the given ratio, when the potato pulp and wheat bran are mixed at a mass ratio of 85:15, the resulting protein feed contains the highest possible content. The possible reason for this is that potato pulp has a relatively high nitrogen content. Potato pulp generally contains high levels of protein and nitrogen compounds, which are important nutrients for microbial growth and protein synthesis. Therefore, during the fermentation process, potato pulp provides an abundant source of nitrogen, promoting the growth and protein synthesis of the strains. The carbon-nitrogen ratio of potato pulp is suitable, and the carbon-nitrogen ratio is one of the important parameters in the fermentation process. An appropriate carbon-nitrogen ratio can provide a suitable nutrient balance, promoting the growth and metabolism of microorganisms. In the present application, the high nitrogen content of potato pulp may result in a suitable carbon-nitrogen ratio, enabling microorganisms to better utilize the substrate for growth and protein synthesis. Wheat bran provides appropriate cellulose and other nutrients. Wheat bran is rich in cellulose and other organic matter, providing additional carbon sources and nutrients for microorganisms. These substances can increase the availability of the substrate and help the metabolic activity and protein synthesis of the fermentation strains. In summary, mixing potato pulp and wheat bran at a mass ratio of 85:15 can provide a suitable carbon-nitrogen ratio and abundant nutrients, promoting the growth and protein synthesis of the fermentation strains, thereby obtaining protein feed with a higher content.

[0023] During storage, protein feed can decompose into some volatile nitrogen-containing small molecules. In addition, during storage, the fat in protein feed can undergo oxidative rancidity. Lipid oxidation products can covalently bond with proteins, undergo free radical reactions and carbamino reactions. In addition, after oxidation of the lipids in protein feed, interactions between proteins and lipids occur. Secondary products produced by fat oxidation react with amino acid side chains, generating some small molecules of ammonia nitrogen, resulting in a decrease in true protein content. In addition, due to the action of enzymes and microorganisms, proteins are broken down to produce ammonia and amine alkaline nitrogen-containing substances. These substances are volatile, and the higher their content, the more amino acids are destroyed, especially methionine and tyrosine. The temperature and humidity in summer are suitable for the growth and reproduction of microorganisms. Rapid growth of microorganisms leads to a significant decrease in protein content.

[0024] The present application is under alkaline conditions, chitosan reacts with chloroacetic acid, the hydroxyl and amino are substituted by carboxymethyl, a pretreatment is synthesized, the addition of the pretreatment can increase the storage flexibility of the feed and the stability of the nutritional ingredients. The pretreatment can play the role of coating as a natural preservative, and the coating can prevent the components in the feed from coming out. In addition, the pretreatment contains lysozyme and amino polysaccharide groups that inhibit microbial growth, and the pretreatment has the effect of inhibiting bacterial growth, which is the same as the effect of chitosan on inhibiting the growth of bacteria and mold. The antibacterial performance of the pretreatment is better than that of chitosan. This is because the value of the degree of substitution of carboxymethyl in the pretreatment is higher than that of chitosan without carboxymethyl, which is the reason for the increase in antibacterial activity. One of the mechanisms that may occur in food preservation is that the pretreatment molecules have the ability to interact with the compounds on the surface of bacterial cells and are then absorbed to form a barrier that inhibits cell transport channels, causing cells to lack the substances required for growth and leading to cell death. In addition to meeting the microbial standards, chitosan and its derivatives are also chemically harmless.

[0025] The three-dimensional structure of isoliquiritigenin has a coplanar conformation with strong intramolecular hydrogen bonds, resulting in poor water solubility. The introduction of an ethylamine functional group into isoliquiritigenin changes the coplanar conformation of isoliquiritigenin and increases the dispersibility of isoliquiritigenin due to the increase in hydrophilic amino groups, making it possible to apply isoliquiritigenin to feed. Due to the poor dispersibility of isoliquiritigenin, its antibacterial effect is greatly limited. When used, its antibacterial activity is not utilized, and by improving the dispersibility of isoliquiritigenin, the antibacterial effect of isoliquiritigenin in the medium is greatly improved, and the functional agent obtained can inhibit the formation of microbial biogenic amines and achieve antibacterial effect. The main cause of the deterioration of protein feed is microbial deterioration and oxidation. Due to the effect of 2-bromoethylamine hydrobromide, the functional agent effectively inhibits the oxidation of lipids in the feed, and it has free radical scavenging ability, which can delay the lipid oxidation of the treated sample. Therefore, the functional agent has excellent preservative effect, which is not only related to its antibacterial effect, but also related to its good oxidation activity. It can effectively prolong the shelf life of the feed and reduce the occurrence of foodborne diseases.

[0026] In the present application, the functions of the functional agent and the pretreatment can be comprehensively exerted through their synergistic effect, reducing the degradation of protein, preventing oxidation and microbial contamination, and improving the storage stability of protein feed. This can prolong the shelf life of protein feed and improve its quality and utilization effect.

[0027] Compared with the prior art, the present application has the following beneficial effects:

[0028] 1) The present application takes potato residue as the main raw material, uses Aspergillus niger, Candida tropicalis, Candida lipolytica and Saccharomyces cerevisiae as collaborative fermentation strains for aerobic-anaerobic solid state fermentation, takes true protein growth rate as the evaluation index, studies the best production process of solid state fermentation of bacterial protein feed with potato residue as raw material through single factor test and orthogonal test design, and improves the contents of true protein and crude protein.

[0029] 2) The solid state fermentation process of the present application can significantly increase the contents of crude protein and true protein in the fermentation product, improve the nutritional value, improve the growth performance of animals, and increase the shelf life and stability of the protein feed, and also provides a new mode for the utilization of non-grain type feed resources, especially potato residue waste resources, effectively alleviates the difficulties of insufficient conventional feed resources, and meets the demand of the livestock and poultry breeding industry for protein feed.

[0030] 3) The protein feed prepared by the present application can improve the storage stability of the protein feed by adding a protective agent. The synergistic effect of the functional agent and the pretreatment can inhibit the degradation of protein, prevent oxidation reaction and microbial contamination, prolong the shelf life of the protein feed, and reduce the quality loss.

[0031] 4) The preparation method of the present application is relatively simple, which can prepare the protein feed through mixing, fermentation, drying and mixing steps, which is helpful to reduce the production cost and improve the production efficiency. DETAILED DESCRIPTION

[0032] Main material sources:

[0033] Potato residue: Linqu County Huamao Feed Co., Ltd.

[0034] Wheat bran: Shandong Koda Biological Technology Co., Ltd., particle size: 200 meshes, grade: first-class.

[0035] Aspergillus niger: Latin name: Aspergillus niger, CGMCC: 3.15663.

[0036] Candida tropicalis: Latin name: Candida tropicalis, CGMCC: 2.3967.

[0037] Candida lipolytica: Latin name: Candida lipolytica, CGMCC: 2.1379.

[0038] Saccharomyces cerevisiae: Latin name: Saccharomyces cerevisiae, ATCC: 9763.

[0039] Chitosan: Henan Jijia Chemical Product Co., Ltd., product number: J-037.

[0040] Example 1

[0041] A preparation method of a protein feed using potato residue solid-state fermentation is as follows:

[0042] Potato residue and wheat bran are mixed in a mass ratio of 85:15 to obtain a mixture, then 2% of ammonium sulfate and 68% of water by mass of the mixture are added, and after being mixed uniformly, a fermentation strain is inoculated, the fermentation strain is a mixture of Aspergillus niger, Candida tropicalis, Candida lipolytica and Saccharomyces cerevisiae, the inoculation amount of each strain in the fermentation strain is 1% by mass of the mixture, and fermentation culture is carried out at 32℃ for 72h to obtain the protein feed.

[0043] Example 2

[0044] A preparation method of a protein feed using potato residue solid-state fermentation is as follows:

[0045] Potato residue and wheat bran are mixed in a mass ratio of 90:10 to obtain a mixture, then 2% of ammonium sulfate and 68% of water by mass of the mixture are added, and after being mixed uniformly, a fermentation strain is inoculated, the fermentation strain is a mixture of Aspergillus niger, Candida tropicalis, Candida lipolytica and Saccharomyces cerevisiae, the inoculation amount of each strain in the fermentation strain is 1% by mass of the mixture, and fermentation culture is carried out at 32℃ for 72h to obtain the protein feed.

[0046] Example 3

[0047] A preparation method of a protein feed using potato residue solid-state fermentation is as follows:

[0048] Potato residue and wheat bran are mixed in a mass ratio of 80:20 to obtain a mixture, then 2% of ammonium sulfate and 68% of water by mass of the mixture are added, and after being mixed uniformly, a fermentation strain is inoculated, the fermentation strain is a mixture of Aspergillus niger, Candida tropicalis, Candida lipolytica and Saccharomyces cerevisiae, the inoculation amount of each strain in the fermentation strain is 1% by mass of the mixture, and fermentation culture is carried out at 32℃ for 72h to obtain the protein feed.

[0049] Example 4

[0050] A preparation method of a protein feed using potato residue solid-state fermentation is as follows:

[0051] Mix potato residue and wheat bran with a mass ratio of 85:15 to obtain a mixture, then add 2% of the mass of the mixture of ammonium sulfate and 68% of water, mix uniformly, inoculate the fermentation strain, the fermentation strain is a mixture of Aspergillus niger, Candida tropicalis, Candida lipolytica and Saccharomyces cerevisiae, the inoculation amount of each strain in the fermentation strain is 1% of the mass of the mixture, ferment and culture at 32℃ for 72h, dry at 50℃, crush, pass through a 100 mesh sieve, and obtain protein powder; mix 100g of the protein powder with 3g of the protective agent, stir at 200rpm for 2h, and obtain the protein feed.

[0052] The preparation method of the protective agent is as follows:

[0053] S1, add 270g of isoquercitrin to 2000g of N,N-dimethylformamide, then add 200g of 2-bromoethylamine hydrobromide and 280g of anhydrous potassium carbonate, stir at 300rpm in an oil heating bath at 115℃ for 3h, filter and purify, remove the reaction medium under reduced pressure, desalt with anhydrous ethanol, recrystallize with water twice, and dry at 60℃ under vacuum to obtain the functional agent;

[0054] S2, add 5g of chitosan to 50g of isopropyl alcohol, stir at 200rpm at room temperature for 30min, then add 13g of 5mol / L sodium hydroxide aqueous solution, stir at 200rpm for 45min, add 30g of chloroacetic acid, heat to 60℃, stir at 200rpm at this temperature for 3h, filter, wash with methanol, and dry in an oven at 60℃ to obtain the pretreatment agent; mix the pretreatment agent with 20g of the functional agent prepared in step S1 to obtain the protective agent.

[0055] Comparative Example 1

[0056] A preparation method of a protein feed using potato residue for solid-state fermentation is basically the same as that in Embodiment 4, and the only difference is that the protective agent is a pretreatment agent.

[0057] The preparation method of the protective agent is as follows:

[0058] Add 5g of chitosan to 50g of isopropyl alcohol, stir at 200rpm at room temperature for 30min, then add 13g of 5mol / L sodium hydroxide aqueous solution, stir at 200rpm for 45min, add 30g of chloroacetic acid, heat to 60℃, stir at 200rpm at this temperature for 3h, filter, wash with methanol, and dry in an oven at 60℃ to obtain the pretreatment agent.

[0059] Comparative Example 2

[0060] A preparation method of a protein feed using potato residue for solid-state fermentation is basically the same as that in Embodiment 4, and the only difference is that the protective agent is a functional agent.

[0061] The preparation method of the functional agent is as follows:

[0062] 270 g of isoquine is added to 2000 g of N,N-dimethylformamide, then 200 g of 2-bromoethylamine hydrobromide and 280 g of anhydrous potassium carbonate are added, and refluxed at 115°C in an oil heating bath at 300 rpm for 3 h, filtered and purified, the reaction medium is removed by concentration under reduced pressure, desalted with anhydrous ethanol, and recrystallized with water twice, and dried at 60°C under vacuum to obtain the functional agent.

[0063] Comparative Example 3

[0064] A method for preparing a protein feed using potato pulp solid-state fermentation is basically the same as that of Example 4, the only difference being that the protective agent is a mixture of 20 g of isoquine and 5 g of chitosan.

[0065] Test Example 1

[0066] Protein content test

[0067] True protein determination method

[0068] The true protein in the sample is precipitated by the salting-out effect of copper sulfate under alkaline conditions. 1 g of the protein feed prepared by the present application is placed in a 300 mL beaker, 100 mL of distilled water is added, and after boiling in a water bath for 30 min, 30 mL of 2.5 wt% sodium hydroxide solution and 10 wt% copper sulfate solution are added respectively, stirred uniformly, micro-boiled, and placed for 2 h, and then filtered. The filtered sample is placed in a digestion tube, 0.3 g of copper sulfate and 4 g of potassium sulfate, 10 mL of 98 wt% concentrated sulfuric acid are added, the digestion tube rack is placed on a graphite digestion furnace, and a waste cover is covered. The digestion process selects curve heating, and the heating program is set as: 190°C for 25 min, 320°C for 20 min, and 430°C for 60 min. After digestion is completed, cool to room temperature, and then determine by K9860 automatic Kjeldahl nitrogen determination instrument.

[0069] Crude protein determination method

[0070] 1 g of the protein feed prepared by the present application is weighed into a digestion tube, 0.3 g of copper sulfate and 4 g of potassium sulfate, 10 mL of 98 wt% concentrated sulfuric acid are added, the digestion tube rack is placed on a graphite digestion furnace, and a waste cover is covered. The digestion process selects curve heating, and the heating program is set as: 190°C for 25 min, 320°C for 20 min, and 430°C for 60 min. After digestion is completed, cool to room temperature, and then determine by K9860 automatic Kjeldahl nitrogen determination instrument.

[0071] Each group is determined three times, and the average value of the results is taken, and the test results are shown in Table 1.

[0072] Table 1 Protein content test results

[0073]

[0074]

[0075] Test Example 2

[0076] Storage stability test

[0077] The protein feed prepared according to the present application was stored in a woven bag under natural conditions with ventilation and light protection for 1 year. Then, the true protein and crude protein contents were determined using the test method of Test Example 1, and each sample was tested 3 times to obtain an average value. The test results are shown in Table 2.

[0078] Table 2 Storage stability test results

[0079]

[0080] As can be seen from the test data in Tables 1 and 2, the protein feed prepared according to Examples 1 and 4 and Comparative Examples 1 to 3 of the present application has the highest protein content. The possible reason is that the fermentation substrate of the present application is obtained by mixing potato pulp and wheat bran at a mass ratio of 85:15. The potato pulp and wheat bran serve as the substrate in this solid-state fermentation process, providing carbon and nutrient sources for the growth and metabolism of the fermentation strain to produce protein. According to the given ratio, when the potato pulp and wheat bran are mixed at a mass ratio of 85:15, the protein feed obtained has the highest protein content. The possible reason is that the nitrogen content of potato pulp is relatively high. Potato pulp generally contains a high amount of protein and nitrogen compounds, which are important nutrient sources for microbial growth and protein synthesis. Therefore, during the fermentation process, the potato pulp provides a rich source of nitrogen, promoting the growth of the strain and protein synthesis. The carbon-nitrogen ratio of potato pulp is suitable, and the carbon-nitrogen ratio is one of the important parameters in the fermentation process. An appropriate carbon-nitrogen ratio can provide a suitable nutrient balance, promoting the growth and metabolism of microorganisms. In the present application, the high nitrogen content of potato pulp may result in a suitable carbon-nitrogen ratio, allowing microorganisms to better utilize the substrate for growth and protein synthesis. Wheat bran provides appropriate cellulose and other nutrients. Wheat bran is rich in cellulose and other organic matter, providing additional carbon sources and nutrients for microorganisms. These substances can increase the availability of the substrate and help the metabolic activity and protein synthesis of the fermentation strain. In summary, mixing potato pulp and wheat bran at a mass ratio of 85:15 can provide a suitable carbon-nitrogen ratio and abundant nutrients, promoting the growth and protein synthesis of the fermentation strain, thereby obtaining protein feed with a higher content.

[0081] The protein feed is decomposed into some volatile nitrogen-containing small molecules during storage, and the fat in the protein feed is oxidized and rancid during storage, and the lipid oxidation products are combined with the protein by covalent bond, and free radical reaction and carbonyl amine reaction occur. In addition, after the lipid in the protein feed is oxidized, the interaction between protein and lipid occurs, the secondary products produced by fat oxidation react with the side chain of amino acid to generate some ammonia nitrogen small molecules, so that the content of true protein decreases. In addition, due to the action of enzymes and microorganisms, the protein is decomposed to produce ammonia and amine and other alkaline nitrogen-containing substances, and such substances are volatile, and the higher the content is, the more the destruction of amino acids is, especially methionine and tyrosine. The temperature and humidity in summer are suitable for the growth and reproduction of microorganisms, and the rapid growth of microorganisms leads to a sharp decrease in protein content.

[0082] The true protein and crude protein contents of the protein feed prepared in Example 4 and Comparative Examples 1-3 of the present application decrease the least after storage, and the possible reason is that in the present application, under alkaline conditions, chitosan reacts with chloroacetic acid, the hydroxyl and amino groups are substituted with carboxymethyl, and a pretreatment product is synthesized. The addition of the pretreatment product can increase the storage elasticity and stability of the nutritional ingredients of the feed. The pretreatment product can play a role of coating film as a natural preservative, and this coating layer can prevent the components in the feed from coming out. In addition, the pretreatment product contains lysozyme and amino polysaccharide groups that inhibit the growth of microorganisms, and the pretreatment product has the function of inhibiting the growth of bacteria, which is the same as the function of chitosan in inhibiting the growth of bacteria and mold. The antibacterial performance of the pretreatment product is better than that of chitosan. This is because the degree of substitution of carboxymethyl in the pretreatment product is higher than that of chitosan without carboxymethyl, which is the reason for the increase in antibacterial activity. One of the mechanisms that may occur in food preservation is that the pretreatment product molecules have the ability to interact with the compounds on the surface of bacterial cells, and then are absorbed to form a barrier that inhibits the transport channel of the cells, so that the cells lack the substances required for growth, leading to cell death. In addition to meeting the microbial standards, chitosan and its derivatives are also harmless in chemistry.

[0083] The three-dimensional structure of isofraxidin has a coplanar conformation with strong intramolecular hydrogen bonds, resulting in poor water solubility. The introduction of an ethylamine functional group into isofraxidin changes the coplanar conformation of isofraxidin, and the hydrophilic amino group increases the dispersibility of isofraxidin, making it possible to apply isofraxidin to feed. Due to the poor dispersibility of isofraxidin, its antibacterial effect is greatly limited. When in use, its antibacterial activity is not utilized. By improving the dispersibility of isofraxidin, the antibacterial effect of isofraxidin in the medium is greatly improved, and the functional agent obtained can inhibit the formation of microbial biogenic amines to achieve antibacterial effect. The main cause of deterioration of protein feed is microbial deterioration and oxidation. Due to the effect of 2-bromoethylamine hydrobromide, the functional agent effectively inhibits the oxidation of lipids in feed, and has free radical scavenging ability, which can delay the lipid oxidation of the treated sample. Therefore, the functional agent has excellent preservative effect, which is not only related to its antibacterial effect, but also related to its good oxidation activity. It can effectively prolong the shelf life of feed and reduce the occurrence of foodborne diseases.

Claims

1. A method for preparing protein feed using solid-state fermentation of potato residue, characterized in that, The steps are as follows: Potato residue and wheat bran are mixed to obtain a mixture. Ammonium sulfate and water are then added and mixed evenly. The mixture is then inoculated with a fermentation strain and fermented at 30-35℃ for 24-96 hours. After drying at 40-60℃, the mixture is pulverized and passed through a 50-200 mesh sieve to obtain protein powder. The protein powder is then mixed with a protective agent and stirred at 100-300 rpm for 1-3 hours to obtain protein feed. The potato residue and wheat bran were mixed at a mass ratio of 85:15 to obtain a mixture; The protective agent is prepared as follows, in parts by weight: S1. Add 250-300 parts of isofraffinate to 1800-2200 parts of N,N-dimethylformamide, then add 180-220 parts of 2-bromoethylamine hydrobromide and 250-300 parts of anhydrous potassium carbonate. Stir and reflux at 100-500 rpm for 1-5 hours in an oil heating bath at 100-120℃. Filter and purify, concentrate under reduced pressure to remove the reaction medium, desalt with anhydrous ethanol, recrystallize twice with water, and dry under vacuum at 50-70℃ to obtain the functional agent. S2. Add 4-6 parts of chitosan to 40-60 parts of isopropanol, stir at 100-300 rpm at room temperature for 20-40 min, then add 10-15 parts of 4-6 mol / L sodium hydroxide aqueous solution, stir at 100-300 rpm for 30-60 min, add 20-40 parts of chloroacetic acid, then heat to 50-70℃, stir at 100-300 rpm at this temperature for 1-5 h, filter, wash with methanol, and dry in an oven at 50-70℃ to obtain the pretreated material; mix the pretreated material with 10-30 parts of the functional agent prepared in step S1 to obtain the protective agent; The mass ratio of the protein powder to the protective agent is 80~120:1~5.

2. The method for preparing protein feed using solid-state fermentation of potato residue as described in claim 1, characterized in that, The added ammonium sulfate and water account for 1-3% and 65-70% of the mixture mass, respectively.

3. The method for preparing protein feed using solid-state fermentation of potato residue as described in claim 1, characterized in that, The fermentation strain is one or more of Aspergillus niger, Candida tropicalis, Candida lipolytica, and brewer's yeast.

4. The method for preparing protein feed using solid-state fermentation of potato residue as described in claim 3, characterized in that, The inoculation amount of each strain in the fermentation strain is 0.5 to 2% of the mass of the mixture.

5. A protein feed utilizing solid-state fermentation of potato residue, characterized in that, It is prepared by the method described in any one of claims 1 to 4.

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