Study on Preparation Technology of Compound Amino Acid Chelated Zinc for Feed

Abstract The feed amino acid was obtained by hydrolysis of sulfuric acid to obtain complex amino acids, and reacted with zinc sulfate to prepare complex amino acid chelated zinc as a new generation feed additive. The effects of different factors on the synthesis of complex amino acid chelated zinc were studied by means of pH titration curve. It was confirmed that at a pH of 7.1, when the total amount of free amino acids and zinc were 2:1, the chelation rate could reach 92% or more.

Keywords compound amino acid; chelation; zinc

CLC number S816.34

The research and development of metal trace element amino acid chelate has been in China for more than 10 years. Amino acid chelate is better absorbed and metabolized than other general inorganic salt trace elements. It is generally reported that its main advantages are: 1 Promote the production of various enzymes, enhance the immunity and anti-stress ability of animal organisms. 2 Trace elements enter the blood circulation by amino acid absorption pathway, and the absorption rate is high. 3 can alleviate the antagonistic competition between minerals, and all kinds of trace elements are absorbed more thoroughly by livestock and poultry. 4 amino acid chelate is easier to dissolve than inorganic salts, and has high solubility [1]. Zinc is one of the essential trace elements in animals. As a third-generation feed additive, the application of amino acid zinc in aquatic products and livestock and poultry farming has achieved remarkable results. The production of amino acid chelate salts is also becoming more mature. The use of a single amino acid to chelate with trace elements can achieve good results, but in the application of aquaculture, the cost is higher. A small number of manufacturers in China have applied different protein sources to prepare complex amino acids, such as feather meal, blood meal and animal internal organs. These materials have high cost, some have high decomposition requirements, and some have serious environmental pollution. ideal. In this paper, soybean meal was used as the amino acid source, and the composite amino acid was obtained by acid hydrolysis method. Then the complex amino acid and the inorganic zinc were chelated under appropriate conditions to obtain the complex amino acid chelated zinc product. The method is simple, non-polluting and low in cost, and is an ideal method.

1 Materials and methods

1.1 Test materials

Cardamom (feed grade, CP 43%), zinc sulfate monohydrate (feed grade, 98%), sulfuric acid (analytical grade, 98%), lime slurry (commercially available), sodium hydroxide (analytical grade), acetone (analytical grade) ).

1.2 Test equipment

Atomic absorption spectrophotometer (SP2900), precision acidity meter PHS-3C, suction filter, centrifugal sedimentation machine.

1.3 Test methods

1.3.1 Soybean hydrolysis

Hydrolysis process:

Soybean meal crushed through 16 mesh sieve → sulfuric acid hydrolysis → suction filtration → lime slurry neutralization → suction filtration → complex amino acid solution

For the feed grade soybean meal (degreased), the crude protein content was determined first, and after pulverization, it was hydrolyzed with 4 mol/l sulfuric acid according to a certain ratio of solid to liquid. The mixture was hydrolyzed at a certain temperature for a certain period of time to determine the free amino acid content.

1.3.2 Chelation reaction

Chelation process:

Compound amino acid solution→Detecting free amino acid amount→Adding zinc sulfate→Adjusting pH value→Insulation chelation→Concentration drying→Crushing and moisture preservation

After detecting the free amino acid content of the compound amino acid solution, the zinc sulfate is added at a certain coordination ratio to adjust to the optimum chelation pH value, and after the sequestration for a certain period of time, the material liquid is concentrated and dried.

1.4 Detection method

1.4.1 Determination of crude protein

Kjeldahl method.

1.4.2 Determination of free amino acids

Improve the formaldehyde method [2,3].

1.4.3 Determination of chelation rate

1.4.3.1 Principle

Since the solubility of the complex amino acid chelated zinc in an organic solvent such as acetone is extremely small, the free zinc is soluble in the acetone solution [4]. Using this property, acetone was used to precipitate the amino acid chelated zinc, the precipitate was filtered off, and the soluble zinc in the filtrate was determined.

1.4.3.2 Method

0.1 g of the sample was weighed, dissolved in 10 ml of distilled water, dissolved completely, and concentrated by heating and evaporated to a solution volume of about 5 ml. Transfer to a 50 ml volumetric flask with acetone to volume. Filtration with a quantitative slow filter paper, and aspirating the filtrate to dilute a certain number of times to detect the zinc content.

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2 Results and discussion

2.1 Determination of process parameters of soybean meal hydrolysis

There are many reports on the hydrolysis of soybean meal, which are more mature, and the condition parameters are basically the same. In this paper, 4mol/l sulfuric acid is used as the hydrolyzate. For the convenience of control, atmospheric pressure and boiling reflux are used [5]. The soybean meal was crushed through a 16 mesh sieve. The ratio of soybean meal to sulfuric acid solution is 1g/2.5ml.

The hydrolysis time is the most important parameter in atmospheric hydrolysis. In this paper, the optimum hydrolysis time is judged by the hydrolysis time-alkali consumption curve, as shown in Figure 1.

A small amount of hydrolyzate was taken at different times, and the supernatant was clarified by a centrifuge to quantitatively absorb a certain volume, and titrated with a sodium hydroxide solution of the same concentration by reference to a formaldehyde method.

It can be seen from Fig. 1 that after the hydrolysis time exceeds 12 h, the curve is flat and the total amount of free amino acids has become stable. Therefore, it can be determined that the hydrolysis time is slightly more than 12 h.

2.2 Determination of chelation parameters

2.2.1 Important parameters affecting the chelation of complex amino acids with zinc

The pH value, molar ratio, chelation time and chelation temperature of the medium are all important parameters affecting the chelation of the complex amino acid with zinc. The pH of the medium has the greatest influence on the chelation reaction. When the pH is too large, the hydroxyl group easily forms a zinc hydroxide precipitate with zinc ions. When the pH is too small, H+ will replace the metal ion with the power supply group to reduce the chelation rate. Therefore, precise control of pH is critical for chelation reactions. This paper describes the chelation reaction of zinc ions with complex amino acids by pH titration curve, as shown in Figure 2.

In Fig. 2, the AA curve is a titration of a complex amino acid liquid curve with a sodium hydroxide solution of about 0.1 mol/l, and the AA+Zn curve is a curve of a complex amino acid solution obtained by titrating zinc sulfate with the same concentration of sodium hydroxide solution. Curve C is the difference curve of the above two curves.

It can be seen from Fig. 2 that when the pH value is about 4.5 on the AA+Zn line, the C curve starts to rise rapidly, indicating that H+ begins to appear in the system. This is consistent with the theory that amino acids are chelated with metal ions, ie, chelation of one molecule of amino acid with one molecule of zinc releases two molecules of H+. With the continuous addition of lye, the difference curve of AA+Zn line at pH 6.3~7.1 shows a flat line, indicating that the added alkali is fully neutralized by H+, resulting in no change in pH. pH = 7.1 can be considered as the completion point of the reaction, therefore, the optimum pH for the determination of chelation is 7.1.

2.2.2 Effect of molar ratio on chelation rate

The molar ratio refers to the molar ratio of free amino acids to zinc ions in the solution. The high molar ratio is beneficial to the complete chelation of zinc ions, but the zinc concentration in the product is low and the utilization rate of amino acids is not high. This is detrimental to reducing the cost of the product. If the molar ratio is too low, the chelation is incomplete and the product quality is low.

In this paper, the chelate test was carried out with the same total amount of free amino acids in a molar ratio of 1:1, 2:1, 3:1, 4:1, and the results are shown in Table 1.

The test results show that when the molar ratio is above 2:1, the zinc ion can be completely chelated with the complex amino acid, so the determined molar ratio is 2:1.

2.2.3 Effect of chelation temperature on chelation rate

The temperature at which the complex amino acid chelate with the metal ion is reported differently. This may be related to the different sources of complex amino acids. In this paper, the chelation is carried out at a temperature of 10 ° C, 30 ° C, 60 ° C, and 100 ° C in a ratio of 2:1, and the test data are shown in Table 2.

The test results show that the temperature has little effect on the chelation reaction. Better chelation at room temperature.

2.2.4 Effect of chelation time on chelation rate

The chelation reaction is a rapid reaction, as long as the zinc salt is completely dissolved, the chelation reaction is almost complete [6]. The chelation reaction is characterized by the production of H+ in the solution, so the progress of the chelation reaction will inevitably lead to a decrease in the pH of the solution. In this paper, the solution adjusted to pH=7.10 was observed with a precision acidity meter. The observation records are shown in Table 3.

As can be seen from Table 3, the chelation reaction is rapid, which is consistent with the literature reports.

3 Conclusion

3.1 Study the synthesis conditions of the compound amino acid chelated zinc, and determine the maturity parameters are molar ratio of 2:1, pH value of 7.1, temperature to room temperature, and its chelation rate can reach more than 92%. The test methods presented in this paper have certain reference value for the study of chelation of other metal ions with complex amino acids.

3.2 Based on the test, the production process is initially determined as follows:

Soybean meal → crushing → hydrolysis → neutralization → filtration → measuring amino acid → adding zinc salt → adjusting pH → chelation → concentration drying → crushing and mixing → finished packaging

The laboratory sample of the complex amino acid chelated zinc prepared according to the parameters determined herein has been tested to contain 32% crude protein and 9% total zinc, which can meet the production requirements of feed additives. It has certain reference value for industrial production.