Essential Amino Acids

Authored by: María-Concepción Aristoy , Fidel Toldrá

Handbook of Analysis of Edible Animal By-Products

Print publication date:  April  2011
Online publication date:  April  2011

Print ISBN: 9781439803608
eBook ISBN: 9780203731529
Adobe ISBN:


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A large proportion of the total animal live weight is made up of by-products that are biologically edible. Thus, organs, fatty tissues, bones, and blood, represent 39% of the live weight of cattle, 30% of the live weight of pigs, and 35% of the live weight of lambs. 1 Edible meat by-products are recognized as a source of high-quality nutrients like essential amino acids and among them organ meat proteins have higher biological value than other edible by-products (lard, blood, etc.) being rich in protein content (by 20%) with a balanced essential amino acids profile similar to that of muscle proteins. As an example, taking the essential amino acid contents of chicken muscle proteins as 100, corresponding values were 105 for liver, 100 for heart, and 92 for gizzard. 2 Owing to their large content of these amino acids organ proteins are almost 100% digestible. Exceptions are those organs rich in connective tissue, mainly collagen, that have their composition especially rich in hydroxyproline, proline, hydroxylysine, and glycine, being low in tyrosine and devoid of tryptophane. 3 This is the case with tripe, stomach, lungs, chitterlings and other by-products like comb, tongue, ears, snouts or feet. It is clear that it is economically advantageous to make profit of these products, and, for this purpose, the nutritive quality must be demonstrated by adequate analytical techniques. Furthermore, the importance of essential amino acids in nutrition and health makes their analysis of high relevance.

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