Dairy Chemistry And Biochemistry

LACTOSE

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2.1

• 1

Figure 2.6 Initial solubility of a-lactose and b-lactose, final solubility at equilibrium (line l),

and supersaturation by a factor 1.6 and 2.1 (r-lactose excluding water of crystallization).

(Modified from Walstra and Jenness, 1984.)

Spontaneous crystallization can occur in the labile area without the

addition of seeding material.

The rate of nucleation is slow at low levels of supersaturation and in

highly supersaturated solutions owing to the high viscosity of the solution.

The stability of a lactose 'glass' is due to the low probability of nuclei

forming at very high concentrations.

Once a sufficient number of nuclei have formed, crystal growth occurs at

rate influenced by:

degree of supersaturation;

surface area available for deposition;

viscosity ;

agitation;

temperature;

mutarotation, which is slow at low temperatures.

?-Hydrate. cc-Lactose crystallizes as a monohydrate containing 5% water
of crystallization and can be prepared by concentrating aqueous lactose
solutions to supersaturation and allowing crystallization to occur below