Amino Acids

Production route explains most of the differences. L-Arginine, L-Leucine, L-Alanine, L-Glutamic Acid and Gamma-Aminobutyric Acid are made by fermentation, which yields a single L form. Glycine and DL-Methionine are made by chemical synthesis, and methionine is sold as the racemic mixture because both forms are usable, whereas glycine has no chiral centre at all. L-Cystine is still largely recovered by hydrolysing keratin.

The practical axes are grade, chirality and physical form. Feed, food and pharmaceutical grades of the same amino acid differ in assay window, heavy metals and residue testing, and price follows the grade rather than the molecule. Solubility, particle size and taste then decide use, since glycine is sweet and works as a masking agent, while glutamic acid is the acid form of the familiar savoury salt and behaves quite differently in water from that salt.