344
Vitamin A Study of Ghee
A or some closely related substances. β carotene and its partial oxidation
products, which still possess an intact β ionone ring, can react with antimony
trichloride to form the blue colour ; since these compounds have only an
indirect and indefinite value as sources of vitamin A, it remains to be shown
whether the chromogenic substances are related to the vitamin itself or to
some of its precursors.
Spectroscopic data have been of help in clarifying this point. The vitamin
A of cod liver oil and its concentrates in alcoholic solution give an absorption
band with a maximum at 328 m µ. The same band has been observed for
butterfat, but it has been found that this band disappears after the ghee has
been heated for a long period [Robinson, 1937 ; Lester Smith and Robinson,
1937]. Also vitamin A interacts with antimony trichloride in chloroform
solution to give a blue colour which has two absorption bands, one at 617 m µ
and the other at 583 m µ. Previous workers have shown that the 617 m µ
band belongs to vitamin A because its intensity can be correlated with the
intensity of the 328 m µ band and also to growth effects in rats [Morton and
Heilbron, 1928 ; Duliere, Morton, and Drummond, 1929 ; Coward, Dyer, and
Morton, 1932]. Of the carotenes, α carotene gives a blue colour with its
absorption band at 542 m µ and β carotene at 590 m µ.
In the present work, it has been found that the unsaponifiable matter of
ghee gives a blue colour with antimony trichloride which has an absorption
band with maximum at 615 m µ and a second band extending from 565-585
m µ with its maximum at 575 m µ. These two bands evidently correspond to
the two absorption bands of the vitamin A from cod liver oil and its concen
trates. The bands are always transient and last only for about 20 seconds.
After treatment of the ghee with hydrogen, it was found that the 615 m µ
band was considerably intensified and lasted longer than the second band. The
second band 565-580 m µ was fainter compared with the 615 m µ band and dis
appeared earlier than the 615 m µ band. (The original vitamin values of the
ghee were blue value 37.4 and yellow value 1.1 units per gm. of butterfat).
There was no evidence of the 590 m µ band or of the 542 m µ band in the absorp
tion spectrum, to show the existence in appreciable amounts of the two caro
tene-antimony trichloride addition compounds. There is thus little evidence
that the oxidised carotenes are affected in any way by hydrogen treatment.
Also there is no evidence from the absorption spectra that xanthophylls
influence the formation of the blue colour.
In order to ascertain whether similar changes occurred by treating ghee
with hydrogen in presence of a platinum catalyst, the blue colour formed
by unsaponifiable matter was spectroscopically examined. The two bands
(615 m µ and 565.580 m µ ) were evident but no new bands were visible. The
intensity of the latter band was found to be greater than that of the former.
The change observed in the intensity of the bands therefore was the reverse
of the changes occurring when the hydrogenation was carried out without
catalyst. The bands also were found to last longer than in the previous cases.
Photometric measurements of the intensity of the absorption bands were not
determined and hence it could not be deduced whether treatment with hydro
gen in the presence of catalyst affected the absolute intensity of the 615 m µ
band as well, although by visible observation, it was noted that the 565-580 m µ
band was comparatively more intense than the 615 m µ band.