Total Protein Methods and Their Potential Utility to Reduce the Risk of Food Protein Adulteration

Amino acid analysis is used to determine the amino acid content of amino acid-, peptide- and protein-containing samples. With minor exceptions, proteins are long linear polymers of amino acids connected to each other via peptide bonds. The first step of amino acid analysis involves hydrolyzing these peptide bonds. The liberated amino acids are then separated, detected, and quantified. The method was first developed by Moore, Stein and coworkers in the 1950s using HCl acid hydrolysis, and, despite considerable effort by many workers, the basic methodology remains relatively unchanged. This unit provides an overview and strategic planning for amino acid analysis, discussing a range of methodologies and issues. In addition, several common methods used for analysis of L-amino acids are described in detail, including: HCl acid hydrolysis, performic acid oxidation for methionine and cysteine analysis, base hydrolysis for tryptophan analysis, analysis of free amino acids, and analysis of reactive lysine.

A quantitative assay method for protein is described which is based on the color change occurring in Coomassie Brilliant Blue G-250 when it binds to protein. This modification of two similar procedures further increases the sensitivity, simplicity, and stability of the protein-dye binding assay over those of other commonly used assays for protein.