Lysinoalanine is a dipeptide formed from lysine and alanine, one of the cross-linked peptides generated in food proteins during thermal processing, especially under alkaline conditions. Heat and alkali drive β-elimination of cystine or serine residues followed by addition of lysine’s epsilon-amino group, creating the unnatural cross-link. It can serve as a chemical indicator of milk quality after thermal processing: elevated levels signal excessive heat treatment, which also reduces protein digestibility and the nutritional availability of lysine itself. Processors minimise its formation by controlling pH, temperature and holding time, and quantify it by HPLC or amino-acid analysis when validating milder process schedules.