Chemistry Reference
In-Depth Information
7
1
6
0
5
-1
4
-2
-3
2
-4
1
-5
-30
-20
-10
0
10
20
30
Temperature (°C)
Figure 11.23.
Pectin methyl esterase activity in 20% sucrose solutions. Symbols: experimental
values of the initial rate from (Terefe and Hendrickx, 2002) (corrected for the variations in
concentration in frozen solutions). Solid line: k values predicted from the viscosity of the
freeze-concentrated phase calculated from the state diagram (Champion et al., 2004).
11.6.
Rehydration of Powders
The rate and extent at which a powder can be redispersed in water is an
essential quality attribute of milk powder as well as of milk components used
as ingredients in the food industry; this process is commonly considered as
comprising several steps: wetting, sinking, dispersion and dissolution (Ennis
et al., 1998). These steps were characterized for native phosphocaseinate by a
combination of viscosity and particle size measurements (Figure 11.24)
(Gaiani et al., 2006). The behaviour of dairy powders during these successive
steps is dependent on composition, processing parameters before and during
drying, storage conditions, pH and mineral composition of the dispersion
medium. We will review here only the effects of processing and storage events
that are water dependent.
Wettability and sinkability are influenced mainly by collapse, caking
and crystallization of lactose. The strong decrease in the dispersibility of skim
milk powder after 6 months' storage was attributed to the collapse of particle
structure. The decrease in the particle surface area results in a lower contact
