Chemistry Reference
In-Depth Information
which is secreted by cells in the brush border of the small intestine. The young of
most mammalian species secrete an adequate level of
-gal but as the animal
ages, the secretion of
-gal declines and eventually becomes inadequate to
hydrolyse ingested lactose which enters the large intestine, into which it draws
water, causing diarrhoea, and is metabolized by bacteria with the production of
gas which causes cramps and flatulence. In humans, this may occur at 8-10 years
of age. These problems cause many individuals to exclude milk from the diet.
The problems may be avoided by pre-hydrolysing the lactose using exogenous
-galactosidase (see Chapters 3 and 5) or removing it by membrane technology
(Chapter 3). The frequency and intensity oflactoseintolerance/malabsorption
varies widely among populations from
100% in south-east Asia to
5% in
north-west Europe (Paige and Davis, 1985; Mustapha et al., 1997; Chapter 6).
1.2.3.
Production and Utilization of Lactose
Previously, whey, from cheese or casein production, was considered a
waste material which was fed to farm animals, irrigated on land or disposed
into sewers. Economic and environmental considerations now dictate that
whey be used more efficiently. The principal product lines produced from
whey are various whey powders, whey protein products produced mainly by
membrane technology and lactose and its derivatives. Membrane technology
is being used increasingly to concentrate and fractionate milk; the resulting
permeate has a number of applications, including the production of lactose.
Lactose is prepared commercially by crystallization from concentrated
whey or ultrafiltrate. The crystals are usually recovered by centrifugation; this
process is essentially similar to that used for sucrose or other sugars. About
400,000 tonnes of crystalline lactose are produced annually (compared to
10
8
tonnes of sucrose p.a.). Developments and trends in the production and utiliza-
tion of lactose are discussed by de Boer and Dijksterhuis (1998) and in Chapter 4.
Owing to its relatively low sweetness and low solubility, the applications
of lactose are much more limited than sucrose or glucose. Its principal
application is in the production of ''humanized'' infant formulae based on
cows' milk (human milk contains
7% lactose in comparison with
4.6% in
bovine milk). The lactose used may be a crystalline product or demineralized
whey (for physiological reasons, it is necessary to reduce the concentration of
inorganic salts in bovine whey).
Lactose has a number of low-volume, special applications in the food
industry, e.g. as a free-flowing or agglomerating agent, to accentuate/enhance
the flavour of some foods, to improve the functionality of shortenings, and as
a diluent for pigments, flavours or enzymes. It is widely used in the tabletting
of drugs in the pharmaceutical industry where low hygroscopicity is a critical
property (see Chapter 4).
