Chemistry Reference
In-Depth Information
120
0.8
Extrapolated
GAB Isotherm
100
80
Time-dependent
crystallization
0.6
60
Glass Transition Region
(Temperature-dependent
critical storage parameters)
40
20
0.4
0
T
g
Critical water activity
-20
0.2
-40
Critical water content
-60
-80
0
0
10
20
30
40
WATER CONTENT (g/100g dry solids)
Figure 2.2.
Water plasticization and glass transition temperatures of lactose at various water
contents. Depression of the glass transition temperature, T
g
, with water content was predicted by
the Gordon-Taylor equation (1). The critical water content and water activity correspond to
plasticization, depressing T
g
to room temperature. Higher water levels result in stickiness, caking,
increased browning rates and time-dependent lactose crystallization. Data from Haque and Roos
(2004).
transition of lactose (Roos and Karel, 1991a; Slade and Levine, 1991; Jouppila
et al., 1997; Hartel, 2001).
The objective of this review is to highlight properties of non-crystalline
lactose and its impact on dairy product characteristics at low water contents
and in the frozen state. The non-crystalline state of lactose is often a non-
equilibrium state showing time-dependent characteristics which may be
observed, for example, from changes in flow properties and time-dependent
lactose crystallization.
2.1.
State Diagram of Lactose
A state diagram may be considered as a 'map' which describes conditions at
which non-crystalline systems appear as solid glasses or as super-cooled
liquids at various water contents and temperatures. State diagrams describe
water plasticization behaviour of hydrophilic amorphous solids and the
concentration dependence of the glass transition of solutes taking into
account ice formation (solvent crystallization)
and its effect on solute
