Chemistry Reference
In-Depth Information
IV. Significance of Lactose in Milk Powders
P.M. Kelly
The expression ''milk powders'' is generally understood to embrace common
commodity-traded dairy products such as skim milk powder, whole milk
powder and whey powder, as well as an ever-increasing range of dried
ingredients derived from milk, such as demineralized whey powders, delac-
tosed whey powders, whey protein concentrate (WPC), milk protein concen-
trates (MPC) and permeate powders. In addition, fat-filled variations of
many of these ingredients are produced. Lactose in isolated form is harvested
by crystallization from either whey or permeate and dried after washing into
forms suitable for food use (edible-grade lactose) or further purified for
pharmaceutical applications as a drug-carrying excipient during tablet or
capsule production (see Chapter 4).
Lactose occurs in an amorphous state in skim and whole milk powders -
the rapid rate of concentration and spray drying does not allow sufficient time
for lactose to crystallize. Hence, it is ''trapped'' in a relatively unstable glassy
state which for the most part does not affect the free-flowing nature of spray-
dried milk products provided that appropriate environmental and packing
conditions are adhered to. Otherwise, because of the hygroscopic nature of
lactose in the amorphous state, such powders will absorb moisture and set in
train a series of physical changes that will ultimately impair product quality.
Occasionally, problems may arise at an earlier stage during drying when
''stickiness'' is evident as powder particles adhere to the side walls of the
drying chamber. Generally, the manufacture of whole and skim milk powders
is not a problem in terms of significant powder deposit formation for lactose
concentrations in the range 35-48%, w/w. However, the extensive range of
spray-dried dairy ingredients now being manufactured from milk frequently
P. Kelly
Moorepark Food Research Centre, Fermoy, Co. Cork, Teagasc, Ireland.
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