07-01.01 Measurement of Acid-Stable Amino Acids
Acid-stable amino acids are those that quantitatively survive protein hydrolysis with 6N HCl under high vacuum. This method determines such amino acid contents in pure proteins, protein isolates, protein concentrates, protein-containing foods with fat contents less than 10%, and defatted protein-containing foods. Amino acids measured include: proline (PRO), glycine (GLY), alanine (ALA), valine (VAL), isoleucine (ILE), leucine (LEU), tyrosine (TYR), phenylalanine (PHE), lysine (LYS), histidine (HIS), arginine (ARG), and ammonia (AMM).
07-11.01 Measurement of Sulfur Amino Acids
To determine cysteic acid and methionine sulfone content by ion-exchange chromatography in grains, flours, meals, foods, and feeds. This method is not applicable to foods and feeds supplemented with free methionine or cysteine. Initially, protein is oxidized with performic acid to form cysteic acid and methionine sulfone; then it is hydrolyzed with 6N HCl.
07-20.01 Measurement of Tryptophan—Alkaline Hydrolysis
To measure tryptophan content in food products and feedstuffs by high-performance liquid chromatography (HPLC). Initially, protein is hydrolyzed under vacuum with 4.2N NaOH