Dairy Ingredients for Food Processing

Whey-based Ingredients 183

point the protein content of the retentate is

about 60% to 65% of the dry matter. In order

to obtain a retentate with a higher percentage

of protein (up to 85%), water is added to con-

centrate the protein. The pressures used in this

process are relatively low: 2 to 6 bar. UF

membranes are typically purchased by the

nominal molecular cut - off provided by the

suppliers. However, the actual retention for a

membrane depends on the fouling layer on the

membrane which is controlled by the operat-

ing conditions (temperature and pressure),

feed stream (composition and processing his-

tory), and membrane design. A diagram of a

spiral - wound UF membrane unit is shown in

Figure 8.4. Figure 8.5 is a photograph of a

spiral wound membrane processing unit.

Nanofi ltration ( NF )

The membrane used in nanofi ltration allows

the preferential permeation of monovalent

salts (e.g., sodium, potassium, and chloride)

and retains divalent salts (e.g., calcium)

and lactose. The separation mechanism

involves both diffusion through the mem-

brane material (as in reverse osmosis) and

convective pore fl ow (as in ultrafi ltration).

Furthermore, separation of complex mixtures

foods. Another objective is to fractionate and
isolate components of higher value. In the
dairy industry a falling fi lm evaporator and a
spray dryer are commonly used for bulk
reduction and ingredient preservation.
Fractionation and isolation of whey proteins
is achieved either by membrane fi ltration,
through size selective permeability, or by ion
exchange, through charge attraction to a
porous surface.

Ultrafi ltration ( UF )

Ultrafi ltration is a pressure - driven, cross - fl ow
fi ltration process that concentrates whey pro-
teins through polymeric membranes. The
feed stream fl ows tangentially to the mem-
brane which acts as a barrier to the permeabil-
ity of selected molecules. In ultrafi ltration
the membrane has a pore size between 0.001
and 0.05 μ m; proteins and fats are retained,
whereas water, salts, sugars, and peptides
may permeate through the membrane (Figure
8.3 ). The process yields two streams: a reten-
tate with the concentrated protein solution
and a permeate that is rich in lactose and salts.
It is possible to produce a retentate of 22%
to 25% solids before the viscosity of this
stream impairs the separation process. At this

Figure 8.3. Relative size of whey components and membrane pore sizes. Reproduced by permission of Fonterra
Co - operative Ltd.

MF

UF

Casein

NF or RO

Whey

Protein

Milk Fat Globule

(~50% diameter)

Micelle