136 Chapter 5
3 × concentration, 66% to 67% of lactose
passes into permeate, and 33% to 34% is
retained in the UF milk concentrate.
UF milk concentrates have been used to
increase the protein content of fl uid milks
(Quinones et al., 1997 ), and it has been found
that an increase of 0.9% in true protein content
of fl uid milk resulted in detection of perceiv-
able sensory attributes. Addition of fresh UF
milk concentrate to fl uid milks for increasing
protein content improves the fl avor and mouth
feel of fl uid milks naturally, compared to
adding NFDM. Addition of NFDM or con-
densed milk (CM) to fl uid milks for increas-
ing protein content results in a cooked fl avor
and increases sweetness from excess lactose
in NFDM or CM. NFDM also requires addi-
tional equipment for mixing with fl uid milks.
Addition of UF milk concentrate to ice cream
mix may reduce sandiness (caused by lactose
crystallization) during ice cream storage.
Diafi ltration (DF) is used to remove
lactose from UF milk. During DF, water is
added to the milk or to the UF milk to wash
out lactose, minerals, and other small mole-
cules that can pass through the membranes.
The combination of UF and DF is used to
produce concentrated milk that is high in
protein and fat, and low in lactose and salts.
The use of UF concentrates in the manufac-
ture of SCM eliminates the sandiness defect
(Sepraalverez et al., 1979) because of the low
lactose content of the condensed milk.
NF is often considered loose RO. NF
membranes concentrate multivalent salts to a
higher degree than monovalent salts in milk.
The molecular weight cut off of NF mem-
branes is less than 1,000 Daltons. The main
application of NF in the dairy industry is for
concentration and demineralization of whey
along with other fi ltration processes.
However, NF has been used for skim milk
modifi cation (Nguyen, 1996 ). Hinrichs
(2000) compared the heat stability of milk
concentrates made with UF, RO, and NF, and
reported that NF concentrates were interme-
diate in the heat stability, between RO andand serum - protein - rich permeate. The casein -
rich concentrate can be used in fortifying
cheese milk during cheese making or for
making milk beverages or micellar casein.
The serum - protein - rich permeate stream can
be concentrated by RO to make milk bever-
ages that do not contain caseins. The whey
protein beverages resulting from MF and RO
processing can have protein contents similar
to those found in milk. Such beverages are
suitable for individuals who are allergic to
caseins. A combination of MF and UF would
be needed if reduced - lactose whey - protein
fresh milk beverages are to made.
UF is a membrane process in which pro-
teins and fat in whole milk are concentrated.
UF membranes in the dairy industry are rated
by a molecular weight cut off, the maximum
molecular weight of the substance that will
pass into the permeate stream. UF mem-
branes are usually smaller than 0.1 microns.
MF and especially UF membranes retain all
the fat and practically all the protein in milk.
The retention coeffi cients of the non - protein
nitrogen compounds are generally 20% to
40%, and higher for the high concentration
factors (Grandison and Glover, 1997 ). Urea
and amino acids are mainly lost through the
membrane. Retention of lactose during UF
may be up to 10%. The minerals and other
ions retained during the membrane process-
ing of milk by UF are those that are attached
to the proteins, such as calcium, magnesium,
phosphate, and citrate, whereas others pass
into the permeate. Likewise, the fat - soluble
and protein - bound vitamins are retained
completely.
UF processes are used commercially to
modify the proportion of lactose in milk and
milk products. The concentrated milk prod-
ucts produced due to UF or MF have resulted
in lactose - modifi ed ice creams, milk powders,
yogurts, and a series of fl uid milks and dairy
beverages. The addition of UF concentrate of
milk changes the physical and chemical
properties of all the dairy products to which
it is added. During UF processing of milk to