CHEMISTRY OF MILK.

New Zealand Herald, Volume LXI, Issue 18888, 22 December 1924, Page 16

CHEMISTRY OF MILK.

VALUE OF CONSTITUENTS.

The chemical composition" of milk, v broadly speaking, "is proteid, fat (hydrocarbon), mineral matter, and water. Of these constituents the largest is l.the water, . consisting, as it does, of about 87 per cent, of the milk., It is because of this, large proportion that milk, in its ordinary state, is regarded as a dilute and bulky form Dried, condensed, and evaporated milk, is milk from which the wafer has wholly, or in part, been driven off. The heating of mi!k for this purpose results in certain che-mic*. and bio-chemical ..'changes which, will be considered in due course. t The next largest, constituent is .lact<v,e (milk-sugar) amounting to from 4 or 5 per ceatjvand which represents the carqohy.dratfc Although it is a sugar, it is very different from the "more familiar sucrose (cane-sugar), more especially in its comparative freedom' from sweetness. In an article of diet so freely used as a food as milk, this is a distinct advantage, as it prevents tho taste of milk palling too readily upon the palate. Yet another difference of importance is the difficulty with which it is fermented, thus making milk of great value in the dietary •of • patients suffering fiom fermentative dilation of the stomach. On the other hand, unfortunately, it in very easily decomposed by certain micro-organisms, with the resultant production of lactic acid, and souring of the milk. This condition sometimes occurs in the intestine,, and it is authoritatively agreed that many cases of infantile summer diarrhoea are so occasioned. It is a fine white- powder in its pure form, slightly soluble in cold water, and possesses valuable medicinal qualities. ■ The commercial production of milk-sugar is an important side-issue of the dairying industry. The fat of milk, is the most complex constituent, consisting, as it does, of a large number of lesser components, chiefly the glycerides and tri-glycerides of certain fa'ttv acids, which largely determine the, peculiar flavour of milk. In normal milk the fat exists in the form of a very fine emulsion. The fat-globules in this emulsion are extraordinarily small, and it has been calculated that in a particle of milk, not larger than a pin's head, there are as manv as 1,500,000 separate globules. For. this reason milk-fat is very easily digested. The fat-globules are of a lesser specific gravity than the serum in which they are suspended, and when, therefore, milk is allowed to stand they tend to float to the surface, which tendency is, of course, made use of in the preparation of cream.' This condition may be destroyed by phvsical means, such as passing the milk through a homogenising machine, which, by pulverisation, reduces still further the size ol the globules until they cease to be seniiible to gravitational influence, and no' " cream-riso" can take place.