Free amino acids refer to unbound amino acids present in biological tissues, foods, and spices, distinct from those incorporated into proteins or peptides. They play key roles in flavor development (e.g., umami from glutamic acid), nutrition, and metabolism. Properties vary widely among the 20 standard amino acids; for example, solubility in water ranges from highly soluble (glycine) to moderately soluble (tyrosine). They are generally non-toxic and many are GRAS for food use. Comprehensive data requires specifying individual compounds such as L-glutamic acid or L-lysine.