Chemistry Reference
In-Depth Information
Durham et al. (2007) claim to produce USP lactose directly from whey
permeates by using ion exchange, nanofiltration, chromatography, evapora-
tion and crystallisation, without the need for a second crystallisation step,
with a yield approaching 95%.
Pharmaceutical-grade lactose is generally sold by mesh size, the differ-
ent products being milled to different degrees, possibly in conjunction with air
or sieve classification. As well as the traditional
-lactose monohydrate, two
other forms are sold to the pharmaceutical industry, i.e. anhydrous lactose (
-
lactose) and spray-dried lactose.
4.3.1.
Anhydrous Lactose
This has the same heavy metal, microbial and colour specifications as
USP-grade
-lactose monohydrate. Anhydrous lactose is usually made by
roller drying, a solution of USP-grade lactose at a temperature greater than
938C which produces a flaked-type product consisting of very fine crystals of
-lactose caked together. The flaked cake is then milled to the required size
distribution (Whittier, 1944).
4.3.2.
Spray-Dried Lactose
Fine pharmaceutical-grade
-lactose monohydrate crystals are par-
tially dissolved in clean water and the slurry is then spray dried. This produces
a product that has crystals of monohydrate lactose joined together by amor-
phous lactose into roughly spherical agglomerates. Because most of the
amorphous lactose is in the centre of the agglomerates, the resultant powder
is free flowing without becoming too sticky (Darcy and Buckton, 1998). The
amount of amorphous lactose present can be controlled by adjusting the
temperature of the water or lactose solution in which the
-lactose monohy-
drate crystals are suspended.
4.4.
Uses of Lactose
Lactose has many uses in the food and pharmaceutical industries. Affert-
sholt-Allen (2007) gave a breakdown of the uses of lactose in Europe and in
the USA as shown in Figures 4.6 and 4.7.
In the food industry, its uses are based on its relative sweetness and as a
source of energy. It is less sweet than sucrose, with up to 3.3 times the
concentration of lactose being required to give the same level of sweetness
as sucrose (Parrish et al., 1981). This means that more lactose can be used
without making the product too sweet. Lactose maintains the crystallised
