Microfiltration (MF) of milk with a ceramic membrane (0·1
μm mean pore
diam.) for the separation of casein micelles from soluble proteins was
studied.
Experiments were performed at constant flux density (J=65 or
75 l h−1 m−2) and
wall shear stress (τw=100 or 110 Pa) with milks containing
particles and solutes
with different sizes and charges, produced by physicochemical change (heat
and
mechanical treatment, pH, ionic strength, addition of ions). Membrane separation
performance was limited by the build up of a cake with characteristics
that depended
on the size of particles and soluble proteins. Best performance (higher
permeability
and whey protein transmission) was obtained with milk containing fat on
the one
hand and calcium phosphate on the other. An optimal value of the particle
size was
found, close to 0·5–3·0 μm; above this separation
performance decreased. In
addition, the present study confirmed that the transfer of charged solutes
is the
consequence of both size and ionic exclusion. Better performance was achieved
with
higher ionic strength (1 M).