Dairy Chemistry And Biochemistry

LACTOSE 37

110 -

100 -

h

90-

* :

• E 80-

E

?L

2

3

.-

‘ 70-

60

0 1 2 3 4 5

Powder moisture (%)

Figure 2.13 Influence of moisture content on the temperature of powder in a spray dryer (t,),

dryer outlet temperature (to) and sticking temperature (fJ The minimum product tempera-

tured required to avoid problems with sticking is at TPC with the corresponding dryer outlet

temperature TOC. (Modified from Hynd, 1980.)

for crystallization is 26-36°C. Pulverized @-lactose, or preferably lactose

‘glass’, is used as seed. Continuous vacuum cooling, combined with seeding,

gives the best product.

Ice-cream. Crystallization of lactose in ice-cream causes a sandy texture. In
freshly hardened ice-cream, the equilibrium mixture of a- and p-lactose is in
the ‘glass’ state and is stable as long as the temperature remains low and
constant. During the freezing of ice-cream, the lactose solution passes
through the labile zone so rapidly and at such a low temperature that
limited lactose crystallization occurs.
If ice-cream is warmed or the temperature fluctuates, some ice will melt,
and an infinite variety of lactose concentrations will emerge, some of which
will be in the labile zone where spontaneous crystallization occurs while
others will be in the metastable zone where crystallization can occur if
suitable nuclei, e.g. lactose crystals, are present. At the low temperature,
crystallization pressure is low and extensive crystallization usually does not
occur. However, the nuclei formed act as seed for further crystallization