Determination of protein and amino acids

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Edited at 2024-11-25 19:48:07

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Determination of protein and amino acids

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Determination of protein and amino acids

Overview

protein composition

Proteins are complex nitrogen-containing organic compounds, which are composed of more than 20 amino acids combined in a certain way through amide bonds and have complex spatial structures. The main elements it contains are C, H, O, N, S, P, and there are also some trace elements Fe, Zn, 1, Cu, and Mn. The N content is an important symbol that distinguishes proteins from other organic compounds.

amino acids

Protein is a polymer compound composed of amino acids. There are mainly 20 types of amino acids that make up protein.

The significance of protein determination

Protein is one of the important nitrogen sources necessary in the microbial fermentation process. The protein content in fermentation raw materials has a great influence on the quality of fermentation products.

Protein determination method

Determine protein content using the common characteristics of proteins, namely nitrogen content, peptide bonds and refractive index;

Protein content is measured using specific amino acid residues, acidic and basic groups, and aromatic groups in proteins.

biuret method

Method Characteristics and Application Scope This method has low sensitivity, but is simple and fast to operate. Therefore, this method is commonly used to determine protein content in the field of biochemistry.

Operation method: The protein sample measured using Kjeldahl method is the standard curve.

Double indicator formaldehyde titration method

principle

Amino acids have acidic -COOH and basic -NH2. They interact to make the amino acids neutral internal salts. When a formaldehyde solution is added, the -NH2 group combines with the formaldehyde, causing it to lose its alkalinity. In this way, COOH can be titrated with a strong base standard solution and the total amount of amino acids can be determined indirectly.

Method characteristics and applications

This method is simple, fast and convenient, and the analysis results are similar to the ammonia nitrite volumetric method.

This method is commonly used in the fermentation industry to measure changes in amino acid content in fermentation broth to understand the amount and utilization of nitrogen sources that can be utilized by microorganisms, and as one of the indicators for controlling fermentation production.

If there are other substances in the solution that can react with formaldehyde, the results will often be high.

Evaporator accessories

Demister

Condenser and vacuum unit

Result calculation

Kjeldahl method

Digest the protein, measure its total N content, and then convert it into protein content.

Principle: Food is heated and digested with sulfuric acid, copper sulfate, and potassium sulfate to decompose protein, and the decomposed ammonia combines with sulfuric acid to form ammonium sulfate. Then alkaline distillation makes the ammonia free, absorbs it with boric acid, and titrates it with a sulfuric acid or hydrochloric acid standard titration solution. The protein content is obtained by multiplying the acid consumption by the conversion factor.

Titration: absorb with 4% boric acid and titrate with hydrochloric acid standard solution. Use a mixed indicator as indicator (methyl red-bromomethylphenol green mixed indicator). The national standard uses methylene blue and methyl red.

Scope of application: This method can be applied to the determination of protein content in various foods

Result calculation

W=[c(V2-V1)x0.014xF]/mx100

The role of potassium sulfate

Adding potassium sulfate can increase the boiling point of the solution and speed up the decomposition of organic matter.

Copper sulfate CuSO4

catalyst

Can indicate the arrival of the end point of digestion;

Used as an indicator for alkaline reactions during alkali distillation.