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MILK FAT. CASEIN. 647
fat-globules at least cannot contain these two proteins alone. They
must contain another protein, and it is still a question whether besides this
they also contain casein and lactalbumin.
The milk-fat which is obtained under the name of butter consists
mainly of olcin and palmitin. Besides these it contains, as triglycerides,
myristic acid, stearic acid, small amounts of lauric acid, arachidic acid,
and dioxystearic acid,, besides butyric acid and caproic acid, traces of
caprylic acid and capric acid. Riegel claims that triglycerides of vola-
tile fatty acids do not occur, but rather mixed triglycerides of volatile
and non-volatile fatty acids. Milk-fat also contains small quantities
of phosphatides (lecithin), and cholesterin and a yellow coloring-matter.
The quantity of volatile fatty acids in butter is, according to Duclaux,
on an average about 70 p.m., of which 37-51 p.m. is butyric acid and
30-33 p. m. is caproic acid. The non-volatile fat consists of iV-& olein
and the remainder is principally palmitin. The composition of butter
is not constant, but varies considerably under different circumstances. 1
The question whether the small fat-globules have a different composition
from the large ones is still disputed.
The milk-plasma, or that fluid in which the fat-globules are suspended,
contains several different proteins, the statements as to the number and
nature of which are somewhat at variance. The three following, casein,
lactalbumin, and lactoglobulin, have been most closely studied and are
well characterized. The milk-plasma contains at least two carbohy-
drates, of which the one, lactose, is of great importance. It also contains
extractive bodies, traces of urea, creatine, creatinine, orotic acid, hypoxan-
thine (?), cholesterin, citric acid (Soxhlet and Henkel 2
), and lastly also
mineral bodies and gases.
Casein. This protein substance, which thus far has been detected
positively only in milk, belongs to the nucleoalbumins, and differs from
the albuminates chiefly by its content of phosphorus and by its behavior,
with the rennet enzyme. Casein from cow’s milk has about the follow-
ing composition: C 53.0, H 7.0, N 15.7, S 0.8, P 0.85, and O 22.65 per
cent. Its specific rotation is, according to Hoppe-Seyler, rather variable;
in neutral solution it is (a) D =—80°; its faintly alkaline solution has a
stronger rotation, namely, — 97.8 to —111.8°, in a solution of N/10-N/5
’Riegel, Maly’s Jahresber., 34; Duclaux, Compt. Rend., 104. Various statement,
as to the composition of milk-fat can be found in Koefoed, Bull. d. l’Acad. Roys
Danoise, 1891, and Wanklyn, Chemical News, 63; Browne, Chem. Centralbl., 1899,
2, 883. In regard to the elementary composition of milk-fat see Fleischmann and
Warmbold, Zeitschr., f. Biol., 50.
2
Cited from Soldner, Die Salze der Milch, etc., Landwirthsch. Versuchsstation,
35, Separatabzug, 18.
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