CASEIN
Introduction
Casein is a derivative of skimmed milk and is used as a
raw material for thermoplastic materials formerly used
for products such as insulators, handles, buttons,
artificial fibres and bristles. It is also used in adhesives,
glues and micro-biological media, nerve tonic, for
priming artists' canvasses as well as being used to fortify
flour, bread and cereals. Casein is a protein present in
skimmed (non-fat) milk which can be obtained by
precipitation.
The composition of milk (%):
Water
Fat
Protein*
Lactose
Ash
Total solids
Cow
88.0
3.8
3.3
4.8
0.7
12.8
Mare
89.0
1.6
2.7
6.1
0.5
10.9
Goat
88.0
4.1
3.4
4.7
0.8
13.0
Casein can be obtained using by one of the following methods:
• By allowing the milk to sour. The lactic acid produced precipitates the casein – known as
lactic casein.
• By the addition of either dilute sulphuric or hydrochloric acid - the precipitate is known
as acid casein.
• By the addition of rennet which contains the enzyme rennin which results in the
precipitation of rennet casein which is much less soluble than the other two types (and
the solutions are less stable). Rennet casein is used in the plastics industry.
Casein is able to swell, although does not dissolve appreciably in water except when an alkali is
also present. Casein will therefore dissolve in a suspension of calcium hydroxide. However, when a
film of this solution is exposed to air, the casein gradually becomes insoluble owing to the
conversion of the calcium to calcium carbonate. This reaction is useful in the coatings industry,
and is the basis of oil-free distempers which contain casein, whiting and lime together with borax
or trisodium phosphate. It is supplied in powder form, which is mixed with water for use. The
casein is rendered soluble by the alkali, and then forms the binder. In the dry film the casein
gradually becomes insoluble, producing a hard coating.
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