Dairy Ingredients for Food Processing

Concentrated Fluid Milk Ingredients 135

and water (0.3 nm), respectively. Fat glob-

ules are retained by all types of membranes

currently used in milk processing, whereas

water is retained by none. Casein micelles

with a molecular size of 25 to 130 nm are

retained by the membranes of MF, UF, NF,

and RO.

Membrane processing of milk results in a

concentrated or fractionated milk stream that

has been obtained with little or no heating.

Processing milk by membrane technology is

ecologically friendly and gives high - quality

products with improved taste and shelf life

compared to the original milk. Use of mem-

brane technology allows modifi cations of

milk in such a way that the protein:lactose or

protein : fat ratio can be adjusted very easily

in the concentrated milks.

MF is used to separate and concentrate

large molecular size casein proteins of skim

milk. The size of MF membranes ranges

from 0.1 to 1 microns. Two streams of liquid

milk beverages are obtained as a result of

MF, one rich in casein proteins and another

rich in whey proteins. Skim milk can be frac-

tionated by MF into a casein - rich concentrate

greater than 1,000 Daltons. It is effectively
used to concentrate proteins (casein micelles),
fat, and bacteria from milk. The concen-
trated product has a composition markedly
different from evaporated skim milk and
therefore different properties (Table 5.5 ).
The UF milk has reduced Maillard brown-
ing during heating due to reduced lactose
content; it is more heat stable at identical
protein content and has higher viscosity at
identical TS content than milk concentrated
by evaporation.
Membrane processes are based on cross
fl ow or tangential fl ow fi ltration technolo-
gies for continuous fl ows of liquid streams
such as milk. MF, UF, and NF concentrate
and fractionate milk components, whereas
RO is a concentration process (Table 5.6 ).
MF and UF processes concentrate on the
basis of a sieving process; the molecules that
are too large to pass though the pore are
rejected and exist in the concentrate stream
while the smaller molecules that pass the
pore size of the membranes end in permeate
stream. The largest and smallest molecules
in milk are fat globules (2,000 to 10,000 nm)

Table 5.6. Composition of different skim milk concentrates of membrane technology.

Skim milk (1 × ) Skim milk – RO

concentrate (3 × )

Skim milk – UF

concentrate (3 × )

Skim milk – MF

concentrate (4 × )

% Protein 3.2 – 3.3 9.6 – 9.9 9.6 – 9.9 12.0 – 13.0

% Lactose 4.8 – 5.0 14.4 – 15.0 4.8 – 4.9 1.1 – 1.2

% Fat 0.08 – 0.10 0.24 – 0.30 0.24 – 0.30 0.3 – 0.4

% Minerals 0.70 – 0.72 2.10 – 2.16 1.2 – 1.3 1.8 – 2.0

% Solids - not - fat 8.70 – 9.0 26.0 – 27.0 15.6 – 16.6 15.0 – 16.0

% Total solids 8.78 – 9.1 26.3 – 27.3 15.80 – 16.80 15.3 – 16.4

× = Concentration factor.

Table 5.5. Mean composition of protein, fat, ash, and lactose in

UF skim milk at various concentration factors.

Concentration factor of UF skim milk

1.5 × 2 × 2.5 × 3 × 3.5 × 4 ×

% Protein 4.48 5.97 7.47 8.96 10.45 11.94

% Fat 5.51 7.34 9.18 11.01 18.85 14.68

% Ash 0.95 1.18 1.40 1.63 1.86 2.09

% Lactose 4.59 4.41 4.23 4.04 3.86 3.68