Concentrated Fluid Milk Ingredients 137UHT Processed Milk Concentrates
Muir (1984) conducted a detailed study on
the effect of concentration on the rheology
and heat stability of UHT - sterilized milk con-
centrates. It is well known that the higher the
volume concentration ratio of milk by mem-
brane technology, the denser the packing of
fat globules and proteins. However, depend-
ing on the concentration process (RO, NF,
UF) used, the lactose and salts may be con-
centrated (Hinrichs, 2000 ). The viscosity of
milk increases with concentration, whereas
its heat stability decreases. A concentration
limit of 31% TS for making UHT concen-
trates from whole milk was suggested by
Muir (1992) because at concentrations higher
than 31% TS, the heat stability is dramati-
cally reduced and gelling is dramatically
accelerated. Gelling of UF milk concentratesUF. NF also has been commercially used to
produce lactose concentrate from permeate
resulting from UF of skim milk. Use of NF
in such applications removes most of the
monovalent minerals from the UF permeate
of milk, resulting in total solids of 20% to
22% in the NF retentate.
The lactose concentrate may be pro-
cessed into animal feed. It may further be
purifi ed into pharmaceutical grade lactose or
hydrolyzed into glucose and galactose using
β - galactosidase (lactase) and used in confec-
tionery. Lactose is one - third as sweet as
sucrose; therefore, three times more lactose
must be used to give identical sweetness of
sucrose, making it impractical to use lactose
as a sweetener in foods. However, lactose
may be used as a bulking agent. In baking
and confectionery industries, lactose is used
to produce a brown color and caramelized
fl avor. Because lactose is a reducing sugar, it
reacts with ε - amino acids of proteins to cause
browning to Maillard reaction, resulting in a
caramel fl avor.
RO is a concentration process in which
99% to 100% of the milk solids are concen-
trated in the retentate, whereas the RO per-
meate is essentially water. RO membranes
have a molecular weight cut off of 50 to 100
Daltons. Use of RO to increase the concen-
tration of solids of whole milk is fi nding
increased acceptance in the dairy industry
because the RO process does not change the
fl avor of whole milk like traditional evapora-
tion process does. The major attraction for
the dairy industry to energy savings. In the
RO process, water is removed without change
of phase or having to use extremes of tem-
perature as in traditional evaporation or
freeze concentration. Furthermore, the milk
is exposed to minimum heat during concen-
tration, which avoids protein denaturation,
development of a cooked fl avor, and the heat -
damaging effects on the constituents of milk.
The RO concentrates can be reconstituted
back into fresh fl uid milks by adding water
from a dispenser (Figure 5.1 ).
Figure 5.1. A dispensing machine for reconstituting
RO concentrate into fl uid milk.