Chemistry Reference
In-Depth Information
completion of crystallization takes longer; slow mutarotation results in a
small amount of
-lactose being transformed into
-lactose for further
crystallization.
In practice, concentrate (lactose solution, SCM or whey) is cooled
rapidly to 308C in a flash cooler connected to the evaporator after which
the concentrate is seeded with fine lactose and allowed to cool rather slowly
(1-38C/h) to about 208C in the tank. This allows mutarotation and crystal-
lization to proceed at reasonable rates. Throughout the crystallization pro-
cess, it is very important to agitate the concentrate in the crystallization tank
vigorously and continuously, in order to transport supersaturated solution to
the surface of the crystals. Agitation also prevents the viscosity of the thixo-
tropic suspension from becoming too high, which would reduce the rate of
diffusion and mutarotation, and the distribution of seeds. In a study on SCM,
Kruk et al. (1974) showed that the percentage of lactose crystals greater than
30 mm increases with an increase in viscosity, resulting in sandiness.
The optimum seeding temperature for SCM is 25-308C because the
concentration of lactose in solution (prior to crystallization) is in the ''inter-
mediate region'' (Figure I.2). The percentage of total lactose in this product
Figure I.2.
The solubility of
- and
-lactose, the final solubility of lactose (line 1), and
supersaturation by a factor of 1.6 and 2.1, respectively (modified from Walstra & Jenness, 1984).
