Chemistry Reference
In-Depth Information
Figure II.2.
Lactose solubility curves. DL: dulce de leche. Adapted from Fox and McSweeney
(1998).
and sucrose in the system, the aqueous phase of DL would be supersaturated
with lactose, with a concentration ca. 1.94 times higher than saturation
solubility. This concentration of lactose places the aqueous phase of DL in
the intermediate equilibrium zone, defined by the solubility curves of lactose
(Figure II.2). In this case, lactose crystallization may be inducted by seeding
with lactose crystals; however, spontaneous crystallization hardly ever occurs
or it is very slow (Holsinger, 1997).
In DL, the anomeric forms of lactose mutarotate to an equilibrium:
>
The equilibrium ratio of
:
-lactose is 1.68. If the total (typical) concen-
tration of lactose (
+
) in DL is 9.9%, w/w, the concentration of
-lactose in
DL would be 3.7%, w/w, while that of
-lactose would be 6.2%, w/w.
On the other hand, taking into account the final solubility of lactose
(i.e., 18 g/L), 15 g of lactose (i.e., 33-18 g) would be available for crystallization
from 100 g of the aqueous phase of DL; this is equivalent to 4.5 g of lactose
per 100 g DL. With these considerations, 5.4 g of lactose would eventually
