Reconstituted skim milk of 10% w/v total solids was prepared
from low heat skim milk powder (Fonterra Cooperative Group,
New Zealand) and purified water. The milks were allowed to stir
for at least 6 h to fully equilibrate. A small amount (0.02% w/v) of
sodium azide was added as a preservative. The milks were adjusted
to pH in the range from pH 6.5 to 7.1 with 1 M HCl or 1 M NaOH.
The pH-adjusted milks were allowed to equilibrate for 1 h before
final minor pH readjustments.