**2.2. Source of caseins**

Whole caseins were prepared by isoelectric precipitation of the individual skimmed milk samples obtained from a Jersey cow and French-Alpine goats. The precipitate was dissolved by the addition of NaOH to yield a solution of pH 7.0. The casein was re-precipitated, washed, and then re-suspended. The sodium caseinate was subsequently cooled to 4°C and centrifuged at 100,000 × g for 30 min to remove residual fat using a Beckman Optima XL-A (Beckman Instruments Inc., Palo Alto, CA, USA) analytical ultracentrifuge. Finally, the suspension was dialyzed against cold deionized water at 4°C for 72 h with three changes and then lyophilized. The integrity of the samples was confirmed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) and the percentages of the various component caseins estimated by densitometry as previously described [22]. The casein composition of the samples is as follows: αs2-casein (bovine casein 12.1%; caprine αs1-I-casein 9.2%; caprine αs1-II-casein 5.3%), αs1-casein (type I): (bovine casein 0%; caprine αs1-I-casein 4.0%; caprine αs1-II-casein 0%); αs1 casein (type II): (bovine casein 39.5%; caprine αs1-I-casein 21.1%; caprine αs1-II-casein 25.6%); β-casein: (bovine casein 37.2%; caprine αs1-I-casein 51.6%; caprine αs1-II-casein 60.6%); and κ-casein: (bovine casein 11.2%; caprine αs1-I-casein 13.8%; caprine αs1-II-casein 9.6%) [20].
