[Loss of nutritional value of proteins in meat products caused by thermal processing]

In certain cases, the proteins in meat products may be damaged during thermal processing to such an extent that their nutritional value is reduced. This might be caused above all by a loss in the availability of the essential and semi-essential amino-acids. Cooking of the meat produces no marked change in the availability of the amino acids. More marked changes are observed at temperatures needed for sterilization. The availability of cystine is in most cases affected by the length and temperature of sterilization, which is due to a reduction of its digestibility and to its degradation. The extent of the cystine degradation follows from the difference from the average reduction of the availability of the other amino acids. Since the sulphur-containing amino acids in meat proteins are limiting ones, this loss results in a reduction of the nutritional value of the proteins. Apart from cystine, lysine may also become less available if greater amounts of polysaccharides are present. The reduction of the availability can be so marked that lysine may be considered to be a limiting amino acid. In these cases, lysine is essential for the nutritional value of the proteins in such products.