Essential Amino Acids

Authored by: María-Concepción Aristoy , Fidel Toldrá

Handbook of Muscle Foods Analysis

Print publication date:  November  2008
Online publication date:  November  2008

Print ISBN: 9781420045291
eBook ISBN: 9781420045307
Adobe ISBN:


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An essential or indispensable amino acid cannot be synthesized de novo by an organism and therefore must be supplied in the diet. This is the case with the amino acids valine, leucine, isoleucine, phenylalanine, tryptophan, threonine, methionine, lysine, and histidine, which are generally regarded as essential for humans (Table 22.1). The importance of essential amino acids in nutrition and health makes their analysis of high relevance. The quality of a given protein depends on the balance among individual amino acids and is limited by the content of some of them, which are essential amino acids, also known as “limiting amino acids.” A limiting amino acid is the essential amino acid found in the smallest amount in a foodstuff. This is the case with lysine in cereals, and methionine or cysteine in legumes and milk or whey from bovines. The quality of a protein may be evaluated through different methods, including the amino acid score, the biological value, the net protein utilization, the protein digestibility corrected amino acid score, or the protein efficiency rate (PER). 1 For instance, PER values below 1.5 indicate a low quality protein, between 1.5 and 2.0 an intermediate quality, and above 2.0 a good quality. Meat proteins have calculated PER values higher than 2.7, indicating a high quality, and are considered as high biological value because they contain large amounts of all essential amino acids. 2,3 Nevertheless, not all meat proteins have the same nutritive value. This is the case with the connective tissue proteins collagen and elastine, which are rich in proline, glycine, and hydroxyproline but poor in tryptophan and sulfur-containing amino acids, and are thus of low biological value. Their presence in meat or meat products decreases those products’ value.

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