ABSTRACT
Proteins have many functions in the organism and constitute a key compound for the survival of animals and humans. Proteins are naturally constituted by 20 “standard” amino acids, which act as basic components of the polymeric structure (listed in Tables 15.1 and 15.2), although they also contain other derived from these. These “nonstandard” amino acids found in proteins (and also in natural peptides) are formed by posttranslational modication during protein synthesis and are essential for the function or regulation of that protein. Some of them are listed in Table 15.3. Once proteins are ingested, amino acids are released by enzymatic
digestion and absorbed into the body. So, protein quality strongly depends on its amino acid content and digestibility (Swaisgood and Catignani, 1991). Amino acids participate in many biochemical pathways for growth, maintenance, and metabolic activity of cells and organs and its requirements vary, depending on the stage of life. However, the quality of proteins may be affected by processing and storage (Reig and Toldrá, 1998, Friedman, 1996). Thus, the knowledge of the amino acid prole and the limiting amino acids in a protein is very important not only to check the quality of that protein but also to improve the nutritional quality by supplementation with the required amino acids.
