Chemistry Reference
In-Depth Information
than 1 mm and are not uniform in size. In the case of fluidized bed drying of
milk powder, the ideal size of crystals for optimum drying is, in fact, much
larger (200-250 mm). For this reason, it becomes important for processors to
know what is the correct amount of seed to use to control crystal size, or to
know what crystal size to expect in the product, given a certain size of the seed
used. For instance, if crystals in the seed used are 3 mm, 0.20% (w/w) lactose
should be added in order to limit crystal growth to
<
10 mm(seebelow).
When the concentration of lactose in the product, its solubility and the
specific gravity of its crystals are known, the number and size of lactose
crystals in the final product can be estimated using simple mathematical
calculations. Empirical equations derived from these calculations are useful
for quick determination of the number and final size of lactose crystals in
SCM. Similar equations can be derived for any other food product when the
concentration of lactose (in excess of its solubility) is known.
Lactose crystal size
ð
mm
Þ
in SCM
ð
after growth
Þ
¼
0
:
4106
size of seed
ð
mm
Þ
% seeding
0
:
33333
Maximum number of crystals
=
mm
3
in SCM
¼ð
5
:
84
10
9
% seed
Þ=
specific gravity of lactose crystals
ð
size of
seed in mm
3
Þ
or
¼
3
:
78
10
9
% seed
=ð
size of seed in mm
3
Þ;
since the specific gravity of lactose crystals is 1
:
545
Example: Using the equations given above, 280, 051 crystals with dimensions
of 9.8 mmpermm
3
are expected when the seed used is 3 mm and 0.20% is added.
Final lactose size
¼
9
:
8 mm
¼
0
:
410613
3
ð
0
:
20%
Þ
0
:
33333
Maximum number of crystals
¼
3
:
78
10
9
0
:
20%
=
3
3
¼
280
;
051
=
mm
3
These empirical equations are based on three parameters:
1) The solubility of lactose in SCM (15 g/100 g water; Hunziker, 1946)
2) Specific gravity of
-lactose (1.545)
3) Volume of
-lactose crystals found in SCM
1
/
6
p d
3
where
diameter
d
is
the
longest
axis
of
the
crystal
divided
by
1.33
(Hunziker,1946)
