What are the determination methods of protein and amino acids? Ask god for help

Hello, Landlord: The most basic method for the determination of protein is the determination of nitrogen, that is, the total nitrogen in the sample is determined first, and then the content of protein in the sample is calculated from the total nitrogen. Kjeldahl method is the most commonly used method to determine the content of protein. Kjeldahl method is one of the most accurate and simple methods to determine total organic nitrogen, which is widely used at home and abroad. In addition, double contraction pulse method, dye binding method and phenol reagent method are also commonly used to determine the content of protein. Because this method is simple and fast, it is often used for quality control analysis of production units. Protein and the determination of amino acids protein are the material basis of life and an important part of organism cells and tissues. All living things contain different types of protein. Maintain the acid-base balance and water balance of human body; Transmission of genetic information; The metabolism and transportation of substances are related to protein. People and animals can only obtain protein and its decomposition products from food to form their own protein, so protein is an important nutrient for human body and an important nutritional index in food. Protein is a complex nitrogen-containing organic compound with large molecular weight, which is composed of 20 amino acids bound by amide bonds in a certain way and has a certain spatial structure. Different protein has different proportions and ways of amino acid composition, so different protein has different nitrogen content. Protein can be hydrolyzed by enzyme, acid or alkali, and the final product is amino acid. Amino acids are the most basic substances that make up protein. Among the amino acids that make up protein, eight amino acids, such as leucine, isoleucine, lysine, phenylalanine, methionine, threonine, tryptophan and valine, cannot be synthesized in human body, so they are called essential amino acids. They have extremely important physiological functions for the human body, often leading to diseases due to lack in the body, or enhancing metabolism through supplementation. Therefore, the separation, identification and quantification of protein and amino acids in food and its raw materials are of great significance. Protein's determination protein's determination is the most basic nitrogen determination method, that is, the total nitrogen in the sample is determined first, and then the content of protein in the sample is calculated from the total nitrogen. Kjeldahl method is the most commonly used method to determine the content of protein. Kjeldahl method is one of the most accurate and simple methods to determine total organic nitrogen, which is widely used at home and abroad. In addition, double contraction pulse method, dye binding method and phenol reagent method are also commonly used to determine the content of protein. Because this method is simple and fast, it is often used for quality control analysis of production units. This method is suitable for the determination of protein in various foods. 1. Principle protein is decomposed by heating food with sulfuric acid and catalyst, and the decomposed ammonia is combined with sulfuric acid to produce ammonium sulfate. Then ammonia is liberated by alkali distillation, absorbed by excess boric acid, titrated with standard solution of sulfuric acid or hydrochloric acid, and the protein content is obtained by multiplying the consumption of acid by the conversion coefficient. The reaction process is divided into three stages and expressed by the following reaction formula. ① Digest 2nh2 (CH2) 2cooh4-13H2SO4-(NH. )2s 04+6 C02+ 12s 0 =+ 16h 20(NH4)2s 04+2na()h-2 NH3 ten+2h 20+。 Na2s042nh3+4h3803-, (NH4)2 B207+5H20 ③ Titrate (NH4) 2b207+2hcl+5h20-nh4c1+4h38032. Instrument ① Digester. (2) Kjeldahl nitrogen distillation unit. 3. The reagents used in the reagents are all prepared with distilled water and do not contain ammonia. The reagent is analytically pure. ①CuS04 .②K2SO .③ Concentrated H2SO 4. ④2% hydrogen wave solution. ⑤ Mixed indicator: When using, mix 1 part O. 1% methyl red ethanol solution and 5 parts O. 1% bromocresol green ethanol solution. When in use, 2 parts of O. 1% methyl red ethanol solution and 0. 1% methylene blue ethanol solution can also be mixed for use. ⑥ Saturated sodium hydroxide: Add 500 g sodium hydroxide into 500 mL water, stir and dissolve it, cool it for several days, and use it after clarification. ⑦ 0.0 1tooli。 1' or 0.05tool is called HCl standard solution (calibrated with anhydrous sodium carbonate before use). 4. Operation step ① Sample digestion: accurately weigh 0.2-2.0g solid sample or 2-5g semi-solid sample or suck 5-20ml liquid sample. Release 500 nautical miles. Add 0.2g copper sulfate, 3 g potassium sulfate and 20 mL concentrated HzSOa into a dry Kjeldahl flask, put a small funnel in the Kjeldahl bottle mouth, and use 45. Angle brace on asbestos net with small holes. (For more detailed consultation, please refer to www.rmhot.com, National Standard Material Network) Use an electric stove to heat it with a small fire. After the contents are completely carbonized and the foam stops, increase the fire to keep the liquid in the bottle slightly boiling, and continue to slightly heat for 30 min until the liquid becomes blue-green and transparent. Cool, carefully add 20 mL of water, then cool to room temperature, transfer to 100 mL volumetric flask, wash the flask lotion with a little water, put it into the volumetric flask, add water to the scale, and mix well for later use. Except for not adding samples, take the same amount of copper sulfate, potassium sulfate and sulfuric acid as the treated samples, and do reagent blank digestion in the same way. (2) Add the water in the steam generator bottle to about 2/3, add a few drops of methyl red indicator and a few milliliters of sulfuric acid to keep the water acidic, add a few glass beads to prevent boiling, and heat the water in the steam generator bottle to boil. (3) Add 10 ml of 2% boric acid solution and l drops of mixed indicator into the receiving bottle, insert the lower end of the condenser tube under the liquid surface, and suck lO mI. The sample digestion diluent flows into the reaction chamber from the small glass, and the small beaker flows into the reaction chamber with 10 mL water, and the rod glass stopper of the small glass is plugged. Pour 3 ~ 10 ml saturated sodium hydroxide solution into a small glass, lift the glass stopper to make it slowly flow into the reaction chamber, immediately cover the glass stopper, and add water to the small glass to prevent air leakage. Tighten the screw clamp and start distillation. Steam is introduced into the reaction chamber, so that ammonia enters the receiving bottle through the condensing tube, and distillation is carried out for 2-5 minutes. Then move the receiver bottle to make the lower end of the condenser tube leave the liquid level, then wash the outer side of the lower end of the cold suspect tube with a small amount of neutral water, then distill the receiver bottle 1 min, and titrate the end point with 0.0 1 mol until it is gray or blue-purple. Call 0.05mol 1 HCl standard solution. Simultaneously absorb 10 mI_, and operate the reagent blank digestive juice according to ③. 5. Count 6. Description ① Dry samples are weighed with weighing paper and digested with paper, and blank tubes are also digested with weighing paper. ② Samples with high sugar content and high oil content are easy to overflow when digested and heated slowly. ③ Whether ammonia is distilled completely can be judged by detecting whether the distillate is alkaline with pH test paper. (4) Before the experiment, all joints of the distillation device must be carefully checked to ensure no air leakage. Rubber hoses and plugs used should be soaked in sodium hydroxide (10%) and boiled for 10 minutes, then washed with water, boiled with water and then washed with water. ⑤ Add the sample carefully to avoid polluting the bottle mouth and bottleneck of Kjeldahl method.