When a food is processed or stored, amino acids can react with a number of chemical entities to produce new compounds that are often nutritionally unavailable to the consumer. Lysine is an important indispensable amino acid, and describing the lysine content of a food or feedstuff provides useful information about nutritional value. Chemical assays have thus been developed to allow determination of unaltered or reactive lysine. The in vitro procedures include three chemical procedures: the furosine procedure, the reactive lysine procedure and KOH solubility.