1. Physical and chemical properties ▲. True lysine is white or light brown small particles or powder. ▲. True lysine is tasteless or slightly heterosexual, and the smell of fake lysine is not correct, and some are aromatic. 2, quality indicators Table 1. Quality Grade of Feed Grade L-Lysine Hydrochloride (NY39-1987) Index Name Index Content (based on C6H14?HCl dry basis) ≥98.5 Specific optical rotation [α]20 D +18.0°+21.5° Drying Weight loss 1.0 Burning residue 0.3 Ammonium salt (calculated as NH4+) 0.04 Heavy metal (in terms of Pb) 0.003 Arsenic (as As) 0.0002 3, the main detection indicators and testing methods ▲. Sensory detection method: pure lysine additive is white or light brown small particles or powder, tasteless or slightly specific odor, put acidity in the mouth, no sputum sensation; false lysine smell is not correct, with impurities Some sensations, some have aroma. ▲. Simple detection method: There are always fake and inferior lysines in the market circulation, and there are various forms of fake, such as starch, stone powder, gypsum powder, etc., or such substances in lysine. Therefore, in the absence of an automatic amino acid analyzer, how to quickly identify the true and false lysine is necessary, and now introduce several methods to quickly identify the true and false lysine: ▲. Solubility test: Lysine is easily soluble in water and insoluble in ethanol and ether. Weigh 1 g of lysine sample into a beaker, add about 50 ml of distilled water, and gently stir. The true lysine is completely dissolved, and the solution is clear without precipitate. If the solution is incomplete, the solution is cloudy or has a precipitate residue, it is a counterfeit or adulterated lysine. The beaker is placed on an electric furnace and heated. If the solution is thickened into a paste, the sample is a pseudo-lysine which is pretending to be a starchy substance or doped with a starchy substance. ▲. Burning method: Take 1g of lysine sample into the porcelain crucible and burn it on the electric furnace. When the real lysine is burning, it will emit the unpleasant smell similar to that when burning feathers. The acid generally does not have such an odor, or the odor is light. When it is burned to smokeless, it is transferred to a high-temperature furnace and burned at 550 ° C for 2-3 hours. The burning residue of true lysine should be below 0.3%, and almost no residue is visible to the naked eye. If there are more residues, it is pseudo-methionine, and it can be further identified according to the relevant method. 4, determine the key points and precautions ▲. Qualitative identification of L-lysine hydrochloride: The addition of silver nitrate solution to the aqueous solution of L-lysine hydrochloride sample should produce a white precipitate which is insoluble in dilute nitric acid and soluble in ammonia. ▲. (1:9) nitric acid solution preparation: 1 part by volume of concentrated nitric acid mixed with 9 parts by volume of distilled water. ▲. (1:2) ammonia water preparation: 1 part volume of concentrated ammonia water plus 2 parts of distilled water. ▲. Identification method: 1 g of the sample was weighed and dissolved in distilled water, and a 0.1 M nitric acid solution was added to produce a white precipitate. The precipitate was added with a (1:9) nitric acid solution, and the precipitate was not dissolved; the precipitate was taken up and dissolved by adding an excess of (1:2) ammonia water. ▲. It can identify the authenticity of lysine according to nitrogen content and estimate the content of lysine. The structure of lysine contains nitrogen. The determination of crude protein in the conventional test method is used to determine the nitrogen content. The amount of lysine is estimated based on the amount of nitrogen or the presence or absence of lysine. The specific method is the same as the method for measuring crude protein. Weigh a certain amount of sample, digest, distill, receive, hydrochloric acid titration to obtain the amount of standard hydrochloric acid consumption, and then calculate the nitrogen content of the lysine according to the following formula. N(%)=100×(V-V0)C×0.014×V1/(W×V2) where: the content of nitrogen in the sample of N, %; the volume of standard hydrochloric acid consumed when V titration of the sample, ml; V0 - the volume of standard hydrochloric acid consumed in the blank measurement, ml; the concentration of C-standard hydrochloric acid, mol / L; 0.014 a constant, each 1 ml of 1M hydrochloric acid equivalent to 0.014g of nitrogen; V1 - digestive solution diluted total volume, ml; V2 - The volume used for the elimination of chemical distillation, ml; W weighs, g; lysine has a molecular weight of 146, contains two nitrogen elements, and the theoretical nitrogen content is 2 × 14 ÷ 182.65 × 100% = 15.3%, This theoretical value is multiplied by the purity indicated on the trademark to give the amount of nitrogen that should be achieved. Compared with the actual determination of nitrogen content, the nitrogen content is normal in a nitrogen-containing unit, indicating that it is genuine; if the measured value is lower or higher than the theoretical value, the two nitrogen-containing units are hypocritical. Most of the pseudo-low-lysine in the market consists of borax, talcum powder, flour and appropriate amount of MSG. These substances contain almost no nitrogen or a small amount of nitrogen, so they can be identified by nitrogen measurement. The amino acid content in the sample can be estimated based on the measured nitrogen content of the sample divided by the theoretical value of the corresponding amino acid nitrogen. Namely: lysine%=N%÷15.3% ▲. This method is not applicable if the doping causes the dummy to add non-protein nitrogen to the lysine, such as urea or carbonic acid. However, these non-protein nitrogens are incorporated into lysine and are easily judged by sensory recognition. Because of the strong irritating odor or ammonia smell added to the urea and carbonic acid, the taste is bitter.
Method for detecting feed additive lysine