This dataset contains proteomic data generated to investigate the presence of β-casein variants A1 and A2 in raw cow milk. Milk protein extracts were fluorescently labeled and separated using a combined DIGE and OFFGEL fractionation strategy. OFFGEL fractions were subsequently analyzed by SDS-PAGE and visualized with a CCD-based imaging system. Selected bands were subjected to LC-MS/MS analysis for protein identification and confirmation of β-casein variants. The dataset includes raw spectra and search results to support reproducibility.