Dairy Ingredients in Dairy Food Processing 427products is a chemical reaction that leads to
rancid off fl avors that are described as card-
board, painty, and fi shy. The oxidation reac-
tions that occur also oxidize sensitive
vitamins such as vitamins C and A and ribo-
fl avin, causing them to lose their biological
activity. Flavoring ingredients also can be
destroyed.
Protecting the powder from light, reduc-
ing oxygen, removing minerals that initiate
oxidation, and adding antioxidants improve
the shelf life of powders. Reducing the
oxygen in the headspace by fl ushing with
nitrogen is a common way to improve shelf
life. Flushing accomplishes nothing, however,
if the package does not have good oxygen
barrier properties or if the seal is not com-
plete. Metal cans exclude oxygen and mois-
ture quite well. Flexible fi lms based on
metallized polyester/low density polyethyl-
ene laminates, and metalized paperboard
or paper packages also minimize oxygen
transmission (Brown and Williams, 2003 ).
Moisture transfer that leads to rehydration of
the powder can cause caking and effects easy
reconstitution of powders. Humidity fl uctua-
tions can cause particles to cake, or stick
together. Lactose in milk powder commonly
cakes because it is can absorb moisture,
cause powders to stick together, and then
recrystallize (Barbosa - C á rnovas, 2005 ).
Anti - caking agents can be added to prevent
the bridging between particles, as can mois-
ture barrier packages. Metal cans provide an
effective barrier, as do fi lms containing poly-
propylene and ethylene vinyl alcohol (EvOH)
(Risch, 2009 ).
Packaging system also can directly
increase or decrease fl avors and off - fl avors in
the product. Flavors can migrate from the
package to the product, which is generally
undesirable. Plasticizers and solvents from
the package can migrate into the product
and affect the fl avor and safety. Styrene,
benzene, PCBs, and, most recently, bisphe-
nols have been found to migrate into food
from packages, and in the case of styrene, can(agglomeration) can be applied to make the
product more easily dispersible in water.
Powdered mixes can be created by blending
dry ingredients together. Although this
method requires much less capital investment
and maintenance, it is diffi cult to incorporate
fats and oils, no fi nal pasteurization is pos-
sible, there is no ability to agglomerate, and
the different powder densities can lead to
segregation of ingredients (Montagne et al.,
2009 ). Even in mixes that are blended and
spray dried, dry blending often occurs to mix
in emulsifi ers such as lecithin, and vitamin
and mineral premixes. A ribbon blender is
used to achieve the most homogeneous dis-
tribution of the dry components. The fi ll
level, blade type, and blade speed all affect
the ability of the mixer to achieve a homoge-
neous mix (Muzzio et al., 2008 ).
Storage and Conveying
Once mixes are completed, it is very impor-
tant that the powders are handled properly to
minimize the reduction in particle size (cre-
ation of fi nes) and the segregation of ingre-
dients based on variations in particle size.
Fines can be caused by abrasion of the
agglomerates due to the particles rubbing
against each other or the equipment.
Segregation is due to variations in particle
size and density, storage bin design, and air
transfers, which can “ classify ” the ingredi-
ents by their size. Segregation problems can
be minimized if the ingredient size ratios are
not greater than 3 : 1 (Barbosa - C á novas et al.,
2005 ).
Packaging
Packaging for powders is designed to mini-
mize oxygen and moisture transfer to the
product, and the design depends on the sen-
sitivity of the product. The fat content, deli-
cacy of the fl avor, and the inclusion of
sensitive vitamins are usually the main con-
siderations. Oxidation of the fat in powdered