(MH+)a HPLC fractionb Amino acid sequence Peptided Biotinylated residue 1738.98 1 KYNVPQLEIVPK αs1-CN (118-129) Q123 1610.89 2 YNVPQLEIVPK αs1-CN (119-129) Q23 2508.30 3 IHPFAQAQSLVYPFTGPIPN β-CN (64-83) Q71 3775.11 4 SLPQNILPLTQTPVVVPPFLQPEIMGVPK β-CN (84-112) Q87, Q94 5956.73 5 IHPFAQAQSLVYPFTGPIPNSLPQNILPLTQTPVVVPPFLQPEIMGVPK β-CN (64-112) Q71, Q87, Q94

Table 1: aMH+ values observed by MALDI-TOF MS in reflectron mode, but fraction 5 in linear mode bThe numbered peaks in Figure 2 (panel a) were singly collected and submitted for nano ESI-MS/MS cAmino acid sequence determined by MS/MS experiment. Biotinylated Q-residues are indicated in bold dNumbers indicate the amino acid residues at the extremities of each peptide refers to as1-CN (P04653) and b-CN (P11839)