The phosphorylated and dephosphorylated caseins were analyzed by PDQuest software and N-terminal sequencing, and the results are summarized in Table 4.1. Spots A–H of the phosphorylated casein fraction are β-caseins with molecular masses (Mr) ranging from 31.15 to 33.80 kDa and pIs ranging from 4.60 to 4.90. Spots I–N are α_S1-caseins with lower molecular weights with respect to the β-caseins, ranging from 27.40 to 31.20 kDa and more basic pI values, ranging from 4.90 to 5.40 (Fig. 4.1a and Table 4.1). Spots A1 and B1 observed in the dephosphorylated casein fraction (Fig. 4.1b and Table 4.1) are two β-caseins with very similar molecular masses (33.50 and 32.87 kDa, respectively) but different pI values (5.70 and 5.90, respectively). Spots C1 and I1 are two β-caseins but with slightly lower molecular masses while spots E1, F1, G1, and H1 are α_S1-caseins with different pI and molecular mass values. Under our experimental conditions, we have not observed α _S2– and κ-caseins, which might be present in trace amounts in donkey’s milk, as reported by other authors (Bertino et al. 2010).