UHT milk contains multiple forms of αS1-casein that undergo degradative changes during storage

► αS1-Casein in UHT milk was examined by 2-D electrophoresis and mass spectrometry. ► Genetic and phosphorylation variants were characterised. ► A novel form arising from alternative splicing was identified. ► Deamidation and loss of the N-terminal dipeptide occurred during storage.